From gum inflammation to oral cancers: pyroptosis as the molecular torchbearer in periodontitis-driven carcinogenesis

Abstract

Periodontitis, a chronic inflammatory disease caused by bacterial infections in dental plaque, results in an environment rich in oxidative stress and pro-inflammatory cytokines, both of which contribute to oral cancers development. One critical mediator of inflammation in periodontitis is pyroptosis, a form of programmed cell death linked to inflammatory processes. Gasdermin D (GSDMD) is a key player in pyroptosis, where its cleavage forms membrane pores, leading to cell rupture and the release of pro-inflammatory cytokines like IL-1β and IL-18 creating an environment that favors cancer cell survival and proliferation. In periodontitis, pyroptosis is closely associated with the activation of inflammasomes, particularly NLRP3, in response to oral bacteria, which in turn leads to the release of cytokines that exacerbate inflammation. Furthermore, the tissue breakdown caused by pyroptosis releases damage-associated molecular patterns (DAMPs), which can activate oncogenic signaling in neighboring epithelial cells, further promoting oral cancers development. So, inhibiting pyroptotic mediators like GSDMD or NLRP3 inflammasomes can reduce inflammation in periodontitis and slow oral cancer progression. Interestingly, inducing pyroptosis in cancer cells or infected tissues may offer a potential therapeutic approach. These findings underscore the critical link between periodontitis, pyroptosis, and oral cancer, suggesting that targeting these pathways may offer therapeutic potential for preventing or treating both diseases. This review aims to elucidate the role of pyroptosis in periodontitis, their impacts on oral cancers, and the potential therapeutic strategies to modulate this inflammatory cell death.

Introduction

Periodontitis is a chronic inflammatory disease that impacts the tissues surrounding and supporting the teeth. It is initiated by an infection with pathogenic microorganisms, primarily bacteria present in dental plaque. When plaque is not adequately removed, it hardens into tartar, providing a favorable environment for bacterial colonization. These bacteria trigger an immune response and inflammation in the gums, resulting in tissue damage [1–3]. Recent studies suggest that periodontitis and oral cancers share common risk factors, including chronic inflammation and oxidative stress, which may create a permissive environment for tumor development [4–6]. This interplay necessitates a deeper understanding of the molecular mechanisms underlying periodontitis and its systemic effects. Oral cancers, particularly oral squamous cell carcinoma (OSCC), have been associated with chronic inflammatory conditions like periodontitis.

While OSCC is the main focus, some evidence suggests that chronic inflammation and inflammatory pathways like pyroptosis could also influence the progression of rarer oral cancers such as verrucous carcinoma, salivary gland tumors, and mucosal melanoma [7–9].

The persistent inflammation and immune dysregulation in periodontitis can contribute to a microenvironment that fosters carcinogenesis [10–12]. Pyroptosis, as an inflammatory form of programmed cell death, may further exacerbate this process by amplifying pro-inflammatory cytokines such as IL-1β and IL-18, which are known to promote tumor progression and immune evasion [13, 14]. Additionally, the breakdown of periodontal tissue due to pyroptosis releases damage-associated molecular patterns (DAMPs), which can activate oncogenic signaling pathways in adjacent oral epithelial cells [14–16].

Pyroptosis, a form of programmed cell death characterized by inflammatory responses, has been the subject of extensive research since its initial discovery in the late 1980s [17]. Over the years, scientists have made significant strides in understanding the mechanisms and players involved in pyroptosis. Early observations pointed to the role of anthrax lethal toxin [17] and caspase-1 in macrophage cell death [18–20], and the activation of IL-1β [21–23]. The distinction between pyroptosis and apoptosis, a non-inflammatory form of cell death, was established in 2001, and the concept of the inflammasome shed light on the activation of inflammatory caspases [24]. Gasdermin D (GSDMD), as a critical mediator of pyroptosis, cleavage leading to formation of membrane pores and cell membrane rupture [25]. Recent studies have unveiled additional factors influencing pyroptosis, such as caspase-3/7 [26], ESCRT machinery [27], fumarate [28], chemotherapeutic agents [29, 30], caspase-8 [31], granzyme B [32], and granzyme A [33].

In the context of periodontitis, pyroptosis is closely associated with the extensive inflammation observed in the disease. Activation of inflammasomes, particularly the NLRP3 inflammasome, occurs in response to oral bacteria and host immune interactions, initiating pyroptotic processes. These pathways exacerbate inflammation, disrupt the balance between bone formation and resorption, and promote periodontal tissue destruction, including the loss of alveolar bone [34–40]. Given the overlapping mechanisms between periodontitis and oral cancers, the inflammatory cascade triggered by pyroptosis could potentially play a role in the tumor microenvironment of oral cancers. Chronic inflammation, combined with dysregulated cell death, may contribute to cancer initiation and progression. Understanding these shared pathways could uncover novel therapeutic targets to mitigate the effects of both conditions. This review aims to explore the role of pyroptosis in periodontitis, its implications for oral cancers, and the potential for therapeutic interventions to modulate this inflammatory form of cell death.

Periodontitis and oral cancers

Emerging evidence highlights a strong correlation between periodontal infections and an elevated risk of various cancers, with specific oral pathogens playing a key role. For example, Aggregatibacter actinomycetemcomitans has been linked to gastric precancerous lesions, including chronic atrophic gastritis and intestinal metaplasia, suggesting its involvement in gastric cancer development [41]. Similarly, Fusobacterium nucleatum and Bacteroides have been implicated in colorectal cancer and other conditions, with F. nucleatum being a notable component of the oral microbiome in colorectal cancer patients. In esophageal cancer, pathogens such as Treponema denticola, Streptococcus mitis, and Streptococcus anginosus are frequently observed [42], while P. gingivalis is found in oral samples of esophageal, colorectal, and pancreatic cancer patients. However, the exact mechanisms behind these associations require further investigation [43–46].

Research also indicates that periodontal diseases, including periodontitis-associated bone loss, may act as risk factors for oral cancer. Periodontitis-related bone loss can play a role in the development and worsening of oral cancer by creating long-term inflammation, changing the balance of bacteria in the mouth, and affecting the environment around tumors. Inflammatory substances like IL-6 and TNF-α encourage abnormal cell growth and the formation of new blood vessels that feed tumors. Harmful bacteria such as Porphyromonas gingivalis and Fusobacterium nucleatum have also been linked to more aggressive cancer behavior. Additionally, as bone breaks down, it releases growth factors that can help cancer cells grow. People with periodontitis often face higher risks of advanced cancer and lower survival rates. From diagnosis to treatment, changes caused by gum disease can make care more complicated. Taking care of your gums and teeth may not only support oral health but also improve outcomes for those at risk of oral cancer [47]. Advanced periodontitis may increase susceptibility to malignancy due to local inflammation and tissue destruction. Notably, certain streptococcal species, such as Streptococcus intermedius and S. mitis, have been detected in cervical lymph nodes of oral cancer patients [48–50], indicating a possible role in tumor development. Moreover, Helicobacter pylori, a bacterium commonly linked to gastrointestinal disorders such as gastritis and peptic ulcers, has also been associated with periodontitis and oral cancer, highlighting the intricate connection between oral health and systemic conditions. Its presence in the oral cavity underscores the role of oral pathogens not only in local inflammatory responses but also in broader systemic effects, potentially contributing to the progression of chronic diseases and malignancies beyond the oral cavity [51].

The role of the oral microbiome in cancer involves more than just bacterial pathogens. Yeasts like Candida metabolize alcohol into acetaldehyde, a carcinogen linked to head and neck cancers. Additionally, certain bacteria in periodontitis convert nitrates into nitrites or produce acetaldehyde, both of which are carcinogenic. The combined effects of microbial activity, along with tobacco and alcohol use, amplify the risk of cancer. These factors promote chronic inflammation, oxidative stress, and DNA damage in periodontal tissues, creating a favorable environment for cancer progression. This highlights the critical role of oral health in cancer prevention [52, 53].

P. Gingivalis in oral cancer

P. gingivalis, a major pathogen in periodontal diseases, plays a critical role in the development of oral cancer through various molecular and cellular mechanisms [54, 55]. It invades oral epithelial cells by targeting the transcription factor GRHL2, which is crucial for maintaining the integrity of the epithelial barrier. Indeed, by disrupting the expression of tight junction proteins, P. gingivalis compromises the barrier function, leading to increased inflammation and tissue destruction in periodontal tissues [56].

The bacterium activates key inflammatory pathways, including NF-κB and mitogen-activated protein kinase (MAPK), which trigger the release of pro-inflammatory cytokines, such as interleukin-6 (IL-6). Elevated IL-6 levels can activate tumorigenic pathways, including the STAT1 transcription factor, contributing to cancer development [57–59]. In addition, P. gingivalis induces the production of matrix metalloproteinase 9 (MMP-9), which is involved in breaking down the extracellular matrix and facilitating cancer cell invasion and metastasis, particularly in OSCC [60, 61].

Another critical mechanism involves the induction of epithelial-mesenchymal transition (EMT), a process that promotes cell mobility, invasiveness, and resistance to apoptosis. P. gingivalis modulates the activity of glycogen synthase kinase 3β (GSK3β), a key regulator of EMT, which contributes to the transition of epithelial cells to a more mesenchymal, invasive phenotype. This process further increases the potential for cancer cells to spread [62–64].

Additionally, P. gingivalis influences systemic inflammation by elevating C-reactive protein (CRP) levels, which can contribute to the development of epithelial cancers. CRP helps the immune system recognize and eliminate P. gingivalis, but chronic elevation of CRP is associated with an increased risk of cancers like ovarian, breast, and colorectal cancers. This suggests a potential role for P. gingivalis in not only oral cancer but also systemic cancer progression [65–68].

P. gingivalis also manipulates several cellular signaling pathways, including the JAK/STAT and PI3K/Akt pathways. The bacterium phosphorylates JAK1 and STAT3 proteins [69], leading to the overexpression of anti-apoptotic genes, thereby inhibiting apoptosis. Moreover, P. gingivalis activates the PI3K/Akt pathway, which promotes cell survival and inhibits cell death by inactivating tumor suppressors such as PTEN and increasing anti-apoptotic proteins like Bad [70, 71].

P. gingivalis employs various virulence factors to interact with host cells, with gingipains—cysteine proteases—playing a central role. Gingipains bind to and activate protease-activated receptors (PARs), specifically PAR2 and PAR4, which are G-protein-coupled receptors expressed on epithelial cells, fibroblasts, and immune cells. This interaction initiates complex intracellular signaling cascades that drive inflammation and tissue destruction [60, 72–75].

One major pathway activated by gingipain-PAR interactions involves the extracellular signal-regulated kinase (ERK1/2) and p38 MAPK signaling pathways. These pathways orchestrate critical cellular responses, including survival, migration, and inflammation. Downstream of ERK1/2 and p38 MAPK activation, key targets such as the transcription factor Ets1 and the molecular chaperone heat shock protein 27 (HSP27) are phosphorylated. Ets1 regulates genes involved in ECM remodeling, angiogenesis, and cell invasion, while HSP27 facilitates cytoskeletal rearrangements and stress responses that promote cell migration [60, 72–75]. Activation of these signaling pathways culminates in the increased production and secretion of MMP-9, a proteolytic enzyme that degrades ECM components such as collagen and elastin. This degradation disrupts the structural integrity of tissues, enabling not only the local invasion of P. gingivalis but also creating a microenvironment conducive to cancer cell migration and metastasis. MMP-9, in particular, is a critical mediator of ECM breakdown, facilitating tumor invasion into surrounding tissues and contributing to the aggressive behavior of cancer cells [60, 72–75].

Additionally, the chronic inflammatory milieu induced by P. gingivalis exacerbates this process. Persistent activation of PARs and their downstream pathways maintains ECM degradation, angiogenesis, and immune modulation, all of which are hallmarks of cancer progression. This interplay between P. gingivalis virulence factors and host signaling pathways underscores the pathogen’s potential role in promoting systemic diseases, including cancer, linking periodontitis to broader health complications [60, 72–75].

Role of cytokines in periodontitis

Inflammation in periodontitis is mediated by various factors, including cytokines. Studies mostly focused on two specific cytokines, IL-1β and IL-18, and their roles in the development and progression of periodontitis (Table 1).

Table 1.

A summary of the role of IL-1β and IL-18 in periodontitis [76–87]

Cytokine	Roles in Periodontitis	Cell Types Involved
IL-1β	• Upregulating collagenolytic enzymes and MMPs • Upregulating RANKL expression • Promoting osteoclast genesis and inflammatory bone loss • Promoting inflammatory cell infiltration toward alveolar bone, aggravating alveolar bone loss • Stimulating various cell types to synthesize and secrete inflammatory factors such as IL-8, TNF-α, IL-6, CCL20, CXCL10, IL-2, IL-23, IFN-γ, IL-13, TNF-α, PGE2 • Upregulating apoptotic signaling pathways, autophagy, and oxidative stress, contributing to tissue damage	Macrophages, dendritic cells, gingival fibroblasts (GFs), periodontal ligament cells (PDLCs), osteoblasts, chondrocytes, retinal microvascular endothelial cells, fibroblast-like synoviocytes, human periodontal ligament stem cells (HPDLSCs), human periodontal ligament fibroblasts (HPDLFs), human gingival fibroblasts (HGFs), periodontal ligament stem cells (PDLSCs).
IL-18	• Promoting proinflammatory cytokine production in periodontal ligament cells, including IFN-γ, IL-2, and TNF-α • Promoting the secretion of MMPs in HPDLFs by activating NF-kB signaling	Periodontal ligament cells (PDLCs), and periodontal ligament fibroblasts (HPDLFs).

IL-1β is recognized as a pivotal factor in the tissue damage observed in periodontitis [88]. It is generated by various cell types within the periodontium, including gingival fibroblasts, macrophages, osteoblasts, periodontal ligament cells, and dendritic cells. Research studies have demonstrated that individuals with periodontitis and gingivitis exhibit notably elevated levels of IL-1β in their saliva compared to individuals with healthy periodontal conditions [79–81]. Elevated levels of IL-1β have been linked to the degradation of the extracellular matrix and bone resorption in periodontal tissues [89]. IL-1β directly upregulates collagenolytic enzymes and matrix metalloproteinases (MMPs), which are responsible for breaking down the structural components of the tissues. This process leads to the destruction of connective tissues and the loss of bone in the affected area [90–92].

Moreover, IL-1β promotes the expression of receptor activator for NF-kB ligand (RANKL), a molecule involved in the formation and activation of osteoclasts, the cells responsible for bone resorption. By upregulating RANKL expression, IL-1β enhances osteoclast genesis and contributes to the inflammatory bone loss seen in periodontitis [93–95]. In addition to its direct effects on tissue destruction, IL-1β also triggers the release of other inflammatory factors from various cell types. These include IL-8, TNF-α, IL-6 [96–98], C-C motif chemokine ligand (CCL) 20, and C-X-C motif chemokine ligand (CXCL) 10 [99–101]. These factors further amplify the inflammatory response, attract inflammatory cells to the site of infection, and contribute to the overall inflammation and tissue damage in periodontitis.

IL-1β, although primarily recognized for its pro-inflammatory and tissue-destructive roles, exhibits a dual impact on the osteogenic potential of periodontal ligament stem cells (PDLSCs). At low doses, IL-1β has been found to stimulate osteogenesis in PDLSCs by activating the BMP/Smad pathway, which plays a crucial role in bone formation. Conversely, higher doses of IL-1β have been shown to inhibit osteogenesis by activating the NF-κB and MAPK signaling pathways. However, the precise influence of IL-1β on osteogenesis within the context of pyroptosis-mediated periodontitis, which represents a severe inflammatory condition, necessitates further comprehensive investigation [102]. Furthermore, IL-1β has been implicated in other processes that contribute to tissue damage independently of inflammation. It upregulates apoptotic signaling pathways [76–78], autophagy [103], and oxidative stress [104, 105], all of which can contribute to the destruction of periodontal tissues. These additional pathways further highlight the multifaceted role of IL-1β in periodontitis pathogenesis.

Moving on to IL-18, it belongs to the IL-1 family of cytokines and has been extensively studied in various infections. Polymorphism of the IL-18 gene has been associated with periodontitis, suggesting a potential genetic predisposition to the disease [106]. Studies have shown that IL-18 stimulation can induce the production of proinflammatory cytokines, including IFN-γ, IL-2, and TNF-α, in periodontal ligament cells [107]. When infected with the periodontal pathogen Porphyromonas gingivalis, blocking IL-18 has been found to inhibit the release of cytokines, chemokines, and MMPs, such as IL-1β, IL-6, IL-8, and MMP-1/8/9. This inhibition leads to reduced recruitment of inflammatory cells into periodontal tissues and less alveolar bone resorption [108]. Moreover, IL-18 has been reported to promote the secretion of MMPs in human periodontal ligament fibroblasts (HPDLFs) by activating NF-κB signaling. MMPs are enzymes that degrade the extracellular matrix and play a role in tissue remodeling and destruction. Therefore, IL-18 contributes to tissue damage in periodontitis by enhancing the production of these matrix-degrading enzymes [109].

Pyroptosis and its mechanisms

Pyroptosis is a form of programmed cell death linked to inflammatory processes. The activation of pyroptosis is mediated by protein complexes called inflammasomes. Inflammasomes, multiprotein complexes responsible for activating pyroptosis, function as signaling platforms that activate caspase-1. The extensively studied inflammasomes comprise NOD-like receptors (NLRs) or AIM2-like receptors (ALRs), apoptosis-associated speck-like (ASC) protein containing a caspase recruitment domain, and pro-caspase-1 [34]. NLRs, such as NLRP1, NLRP3, NLRP6, and NLRC4, serve as sensors for various intracellular molecules, detecting pathogen-associated and damage-associated molecular patterns [34, 110, 111]. AIM2, an ALR, identifies cytosolic double-stranded DNA [112, 113], while ASC acts as an adapter protein, facilitating inflammasome complex assembly by interacting with NLRs or ALRs [114, 115]. Pro-caspase-1 is recruited to the assembled inflammasome, where it undergoes dimerization and activation. This process leads to the cleavage of substrates, including GSDMD, resulting in the formation of pores in the cell membrane and subsequent cell lysis and pyroptotic cell death. Inflammasomes play a pivotal role in the immune response by detecting infections and cellular damage, triggering an inflammatory response through pyroptosis [34, 116, 117].

The canonical pathway of inflammasome activation involves the recognition of microbial components or endogenous danger signals by pattern recognition receptors (PRRs) like Toll-like receptors (TLRs) and NLRs, which detect PAMPs or DAMPs. This recognition initiates a signaling cascade that upregulates inflammasome components [118, 119]. Among the NLR family, NLRP3 is the most extensively studied inflammasome sensor and can be activated by various stimuli, including microbial products, crystals, and cellular stress signals [120]. Other NLR family members like NLRP1, NLRP6, and NLRC4 can also form inflammasomes [121]. NLR proteins commonly exhibit a characteristic structure comprising a central nucleotide-binding and oligomerization domain (NACHT or NBD), a C-terminal leucine-rich repeat (LRR) domain responsible for detecting ligands, and an N-terminal effector domain. In the case of NLRP proteins, the effector domain is represented by a pyrin domain (PYD), whereas NLRC proteins feature a caspase recruitment domain (CARD) as their effector domain [122–125].

In the canonical pathway, the intricate process of assembling the inflammasome complex hinges on the interplay between the PYD or CARD domains of NLR proteins and the CARD domain of the adapter protein ASC. This assembly event gives rise to the formation of the inflammasome complex, which serves as a scaffold for the recruitment and activation of pro-caspase-1. Once the inflammasome complex is established, pro-caspase-1 molecules draw close to one another, leading to their dimerization and subsequent activation through autoproteolytic cleavage. The resultant activated caspase-1, also known as interleukin-1β-converting enzyme (ICE), carries out the cleavage of precursor forms of pro-inflammatory cytokines, namely IL-1β and IL-18 [126–128]. The enzymatic cleavage of pro-IL-1β and pro-IL-18 yields their mature forms, which are subsequently liberated from the cell and serve as initiators of inflammatory responses [129]. Moreover, upon activation, caspase-1 can cleave GSDMD, leading to the generation of N-terminal fragments that assemble into pores on the cellular membrane. These pores disrupt osmotic equilibrium, causing cellular swelling, and ultimately culminate in cellular lysis, which is a hallmark feature of pyroptotic cell death [130, 131].

The noncanonical pathway of inflammasome activation presents an alternative mechanism that operates autonomously from NLRs and instead relies on the direct activation of caspase-11 in mice or caspase-4 and caspase-5 in humans. This pathway is specifically initiated by the recognition of cytosolic lipopolysaccharide (LPS) originating from Gram-negative bacteria [132]. In the noncanonical pathway of inflammasome activation, the direct recognition of cytosolic LPS by caspase-11 in mice (or caspase-4 and caspase-5 in humans) plays a pivotal role. Upon binding to LPS, these caspases undergo a conformational change that results in their activation. Once activated, caspase-11 (or caspase-4 and caspase-5) orchestrates a cascade of proteolytic events, culminating in the activation of caspase-1. Similar to the canonical pathway, the activated caspase-11 (or caspase-4 and caspase-5) executes the cleavage and activation of GSDMD. Consequently, the N-terminal fragments of GSDMD self-assemble to form pores in the cellular membrane. This pore-formation event induces cell lysis and facilitates the release of pro-inflammatory cytokines, notably IL-1β and IL-18, which serve as key initiators of the ensuing inflammatory response (Fig. 1) [133–137]. The recruitment and activation of immune cells such as neutrophils, macrophages, and dendritic cells are critical outcomes of pyroptosis. IL-1β promotes the expression of adhesion molecules on endothelial cells, enhancing the migration of leukocytes to the site of infection or injury [138]. These immune cells then engage in phagocytosis, clearing extracellular pathogens and cellular debris, and producing additional inflammatory mediators that sustain and amplify the immune response. This process is essential for controlling infections and initiating tissue repair [139].

Fig. 1.

Canonical and non-canonical pathways triggering pyroptosis. In the canonical pathway, a diverse array of stimuli induces the activation of inflammasomes, with NLRP3 being a prominent player. This activation event leads to the assembly of the inflammasome complex, the activation of caspase-1, and subsequent cleavage of pro-inflammatory cytokines and GSDMD. Notably, NF-κB can also stimulate the production of pro-inflammatory cytokines such as IL-1β and IL-18. The cleaved GSDMD then forms pores in the cell membrane, resulting in cell lysis and the release of pro-inflammatory molecules. On the other hand, the non-canonical pathway is specifically triggered by the detection of cytosolic LPS by caspase-11 (or caspase-4/5 in humans). Once activated, caspase-11 cleaves GSDMD, leading to pore formation and cell lysis. While the canonical pathway relies mainly on inflammasome activation, the non-canonical pathway involves a direct sensing of LPS. These pathways represent distinct mechanisms by which cells undergo pyroptosis, contributing to the inflammatory response and immune defense against pathogens. It is worth noting that these pathways can be interconnected and involve other inflammasomes and caspases, underscoring the complexity of pyroptosis

Moreover, pyroptosis plays a significant role in the activation and modulation of the adaptive immune response. The inflammatory milieu created by pyroptosis enhances the maturation and antigen-presenting capabilities of dendritic cells and other antigen-presenting cells [140, 141]. These cells process pathogen-derived antigens and present them to T cells, facilitating the activation of specific adaptive immune responses. This interaction between innate and adaptive immunity ensures a comprehensive and effective immune defense, capable of not only responding to immediate threats but also providing long-term immunity [141, 142].

However, the potent inflammatory response induced by pyroptosis can have detrimental effects if not properly regulated [47, 143]. In chronic inflammatory conditions such as periodontitis, the persistent activation of pyroptosis can lead to continuous tissue damage [144]. Periodontal pathogens like Porphyromonas gingivalis can trigger repeated cycles of pyroptosis in gingival cells, releasing IL-1β and IL-18 and perpetuating inflammation [145, 146]. This chronic inflammation results in the breakdown of periodontal tissues and bone, characteristic of advanced periodontitis [38, 147, 148].

Unlike the canonical pathway, the noncanonical pathway does not involve the assembly of a large protein complex like the inflammasome. Instead, it relies on the direct recognition of cytosolic LPS by caspase-11 (or caspase-4 and caspase-5), followed by the activation of caspase-1 through a cascade of proteolytic events. This pathway provides an additional mechanism for the immune system to respond to Gram-negative bacterial infections and trigger inflammation [133– [137, 149].

The gasdermin (GSDM) family consists of several members, with GSDMD being the most extensively studied. GSDMA, GSDMB, GSDMC, GSDME, and DFNB59 are other members that require further investigation [150]. GSDMD is involved in both the canonical and noncanonical pathways of inflammasome activation and is responsible for mediating pyroptosis [131, 151]. GSDME and GSDMC, although less studied, have also been implicated in pyroptosis [152, 153]. GSDME can be cleaved by caspase-3, generating an N-terminal fragment that promotes pyroptosis [154]. GSDMC, on the other hand, can be cleaved by caspase-8, particularly with TNFα treatment, resulting in the induction of pyroptosis [155]. In addition to caspases, other proteases are involved in the cleavage of GSDMs. Granzyme A can cleave GSDMB in lymphocytes, contributing to the activation of pyroptosis [33]. Granzyme B has been shown to directly cleave GSDME in tumor cells, promoting pyroptosis and tumor suppression. Neutrophil elastase (ELANE), a serine protease produced by neutrophils, cleaves the GSDMD at the N-terminal, leading to pyroptosis and influencing its biological effects [156]. Of note, while the roles of GSDMD, GSDME, GSDMC, and other GSDM family members in pyroptosis have been established to some extent, there is still a need for further research to fully understand their specific functions, cleavage mechanisms, and implications in various biological contexts, including periodontitis [33, 131, 142, 155, 156].

Pyroptosis in periodontitis based on evidence

The pathogenesis of periodontitis, a condition characterized by inflammation and tissue damage in the periodontium, has been linked to the occurrence of pyroptosis. Pyroptosis activates the inflammasome complex leading to the secretion of pro-inflammatory cytokines such as IL-1β. The release of IL-1β and other pro-inflammatory molecules contributes to tissue damage and the perpetuation of the inflammatory response in periodontal tissues [34, 157, 158].

As mentioned in the Sect. 2, periodontitis is primarily caused by the continuous presence of harmful microorganisms in the mouth, including bacteria, fungi, viruses, and mycoplasma. These microorganisms contribute to the development and progression of periodontitis by triggering an immune response and promoting inflammation [159–161]. One important component of the immune response is the recognition of specific patterns on the surface of microorganisms. TLR4 is a type of receptor known as a pattern recognition receptor, which is responsible for detecting these patterns, particularly LPS found on the surface of many bacteria [162]. TLR4 is found on various immune cells and plays a crucial role in initiating the immune response to microbial infections [163]. In the context of periodontitis, TLR4 has been extensively studied due to its involvement in the LPS-mediated pyroptosis pathway. When TLR4 recognizes LPS, it triggers a signaling pathway that leads to the activation of inflammatory responses, including the production and release of pro-inflammatory molecules [164] (Fig. 2).

Fig. 2.

Pyroptosis in periodontitis. In the context of periodontitis, a chronic inflammatory disease affecting the tissues surrounding the teeth, TLR4 has emerged as a focal point of research due to its pivotal role in the LPS-mediated pyroptosis pathway, a form of programmed cell death marked by inflammatory cell lysis. TLR4, present on various immune cells like macrophages, dendritic cells, and epithelial cells, functions primarily to detect and respond to specific molecular patterns associated with pathogens, particularly bacterial LPS found in gram-negative bacteria’s outer membrane. Upon encountering LPS in periodontal tissues, TLR4 initiates a signaling cascade within the cell, activating downstream pathways leading to inflammatory responses characterized by the production and release of pro-inflammatory molecules. This activation triggers intracellular signaling events involving adapter proteins like MyD88, culminating in the activation of transcription factors such as NF-κB, which promote the transcription of genes encoding cytokines like IL-1β, IL-6, and TNF-α, as well as chemokines that attract immune cells to the site of inflammation. Consequently, the released pro-inflammatory molecules and chemokines recruit and activate immune cells like neutrophils and monocytes, exacerbating the inflammatory response and contributing to the degradation of periodontal tissues. Overall, TLR4’s recognition of bacterial LPS and subsequent activation of inflammatory pathways are central to periodontitis’s pathogenesis, perpetuating chronic inflammation and tissue damage in affected individuals

Research studies, particularly those using mouse models with TLR4 knockout (TLR4-KO), where the TLR4 gene is modified to be non-functional, have provided valuable insights into the role of TLR4 in periodontitis and peri-implantitis induced by Porphyromonas gingivalis, a key pathogen associated with periodontal disease. These studies have shown that the absence of functional TLR4 results in reduced inflammatory responses and decreased bone loss associated with periodontitis. By utilizing TLR4-KO mouse models, researchers have demonstrated that TLR4 is involved in the activation of the pyroptosis pathway triggered by LPS from Porphyromonas gingivalis. This further highlights the significance of TLR4 in the inflammatory processes underlying periodontitis and peri-implantitis [165, 166].

In periodontitis, bacterial virulence factors such as lipopolysaccharide (LPS) from pathogens like Porphyromonas gingivalis activate inflammasomes, particularly the NLRP3 inflammasome, which in turn activates caspase-1 (canonical pathway) or caspases-4/5 (non-canonical pathway). These caspases cleave gasdermin D (GSDMD), whose N-terminal fragment forms pores in the cell membrane, leading to pyroptotic cell death and the release of pro-inflammatory cytokines such as interleukin-1β (IL-1β) and IL-18. This cytokine release creates a highly inflammatory microenvironment that not only exacerbates periodontal tissue destruction by promoting bone resorption via upregulation of RANKL but also sustains a chronic inflammatory state. The persistent inflammation driven by pyroptosis contributes to DNA damage, cellular proliferation, and immune evasion mechanisms that favor the transformation of oral epithelial cells, thus linking periodontitis to OSCC. Moreover, pyroptosis-induced cytokines and reactive oxygen species (ROS) promote an environment conducive to oncogenesis by activating signaling pathways such as NF-κB, which supports tumor growth and survival. Additionally, pyroptosis may modulate the tumor microenvironment by influencing immune cell infiltration and function, potentially aiding tumor progression or immune escape [82, 167].

Advancements in research have also revealed the crucial role of myeloid differentiation protein-2 (MD-2) in facilitating the binding of LPS to TLR4. MD-2 enhances the affinity of TLR4 for LPS, stabilizing the complex and initiating downstream signaling events [168]. This interaction sets in motion a cascade of intracellular events, beginning with the homotypic interaction between TLR4’s intracellular toll/interleukin-1 receptor (TIR) domain and adaptor molecules like myeloid differentiation factor 88 (MyD88) and TIR domain-containing adapter protein inducing IFN-Beta (TRIF) [169]. Subsequently, MyD88 associates with interleukin-1 receptor-associated kinase (IRAK) 1 and 2, leading to the assembly of tumor necrosis factor receptor-associated factor 6 (TRAF6) [169, 170]. This assembly triggers the phosphorylation and activation of IκB kinases α/β (IKKα/β) through the activation of transforming growth factor β-activated kinase 1 (TAK1). IKKα/β, in turn, phosphorylates IκB, leading to its degradation and subsequent release of NF-κB. The translocation of NF-κB into the nucleus ultimately results in the activation of genes involved in the inflammatory response [171, 172]. This cascade of events, initiated by the binding of LPS to TLR4 and involving MD-2, MyD88, TRIF, IRAK1/2, TRAF6, TAK1, IKKα/β, and NF-κB, plays a pivotal role in the regulation of immune responses and the induction of inflammatory mediators in various cellular contexts. This particular step described is crucial for the transcription of key inflammatory molecules, including NLRP3, pro-IL-1β, and pro-IL-18, and represents the priming step required for the subsequent activation of the NLRP3 inflammasome [169].

The activation of TLR4 and its downstream adaptors, such as MyD88 and TRIF, leads to the activation of various signaling pathways that contribute to cytokine production [173, 174]. In the TRIF-dependent pathway, molecules including TRAF3 and TRAF6 play a critical role in activating the mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways [175–177]. The activation of these signaling pathways, in conjunction with the transcriptional events mediated by TLR4, MyD88, and TRIF, collectively contribute to the synthesis and release of cytokines, including IL-1β and IL-18, which are crucial inflammatory mediators involved in the progression of various inflammatory diseases (Fig. 3) [169].

Fig. 3.

A summary of the molecular events triggered by TLR4 upon binding LPS. MD-2 facilitates this interaction, initiating a cascade involving adaptors like MyD88 and TRIF. This cascade activates molecules like IRAKs and TRAF6, leading to NF-κB activation and subsequent transcription of inflammatory genes, including NLRP3, pro-IL-1β, and pro-IL-18. Downstream adaptors also activate MAPK and ERK1/2 pathways, contributing to cytokine production, crucial in various inflammatory diseases’ progression

While the mechanisms linking inflammasomes to pyroptosis and interferon release remain unclear, an alternative pathway mediated by TRIF, a TLR4 adaptor, activates IRF3/7, leading to type I interferon release. TRIF also activates the JAK/STAT pathway and upregulates pro-caspase-11, contributing to a noncanonical form of pyroptosis. Though not directly verified in periodontitis, pyroptosis has been observed in various cell types involved in the disease, suggesting its potential role in its development [178–180]. While the role of LPS and TLR4 in pyroptosis has been explored, these findings have not been specifically validated in periodontitis. However, pyroptosis has been observed in various periodontitis-related cell types, including gingival fibroblasts, macrophages, oral epithelial cells, periodontal ligament fibroblasts, periodontal ligament stem cells, and osteoblasts. These findings suggest that pyroptosis likely plays a role in the development and progression of periodontitis and subsequently, oral cancer development [181–187].

Apart from the aforementioned factors, the human gingival epithelium (HGE), the outermost protective layer of gum tissue, is crucial for defending against pathogens. However, bacteria like Streptococcus sanguinis and butyrate produced by oral anaerobic bacteria can compromise this barrier by triggering pyroptosis. Streptococcus sanguinis upregulates caspase-3/GSDME, while butyrate upregulates caspase-1. Thus, activation of these caspases leads to the breakdown of the gingival epithelial barrier [188, 189]. HGFs contribute to inflammation and tissue destruction in periodontitis. Activation of pyroptosis in HGFs has been observed in response to porphyromonas gingivalis and lipopolysaccharide (LPS), which induce inflammation and periodontal damage. These bacteria activate the NLRP3/NLRP6/caspase-1/GSDMD pathway, leading to pyroptosis in HGFs [190–192].

Additionally, evidence suggests that the noncanonical pyroptosis pathway, involving caspase-4 and GSDMD, can be activated in HGFs by the surface protein Tp92 from Treponema pallidum, the bacterium responsible for syphilis. Interaction of Tp92 with HGFs activates caspase-4, leading to GSDMD cleavage and pore formation in the cell membrane, resulting in pyroptotic cell death. These findings indicate that Tp92 may induce pyroptosis through the noncanonical pathway, potentially contributing to the inflammation and tissue damage seen in periodontitis associated with Treponema pallidum infection. Further research is needed to explore this pathway’s role in periodontitis and the immune response to Treponema pallidum [193].

Macrophages, immune cells implicated in the inflammatory response and periodontitis, exhibit two distinct phenotypes: M1 and M2. M1 macrophages, characterized by their pro-inflammatory nature, produce cytokines that contribute to tissue damage if overly activated. Conversely, M2 macrophages possess anti-inflammatory properties and aid in resolving inflammation [194]. The polarization of macrophages is influenced by various factors, including cytokines IL-4 and IL-13, which induce M2 polarization, and IFN-γ, TNF-α, or LPS, which induce M1 polarization, followed by the production of pro-inflammatory cytokines TNF-α, IL-1α, IL-1β, IL-6, IL-12, and IL-23. Interestingly, the signaling pathways involved in M1 polarization overlap with those associated with pyroptosis. M1 macrophages exhibit elevated caspase-1 expression, and inhibiting caspase-1 can impede M1 polarization. However, the intricate interplay between macrophage polarization and pyroptosis in the context of periodontitis remains inadequately understood. Further investigations, such as gene knockout studies, are necessary to unravel and elucidate this relationship [195–201] (Fig. 4).

Fig. 4.

Macrophages response to bacterial products in pyroptosis. When macrophages encounter bacterial products like LPS, they activate signaling pathways leading to inflammasome assembly and caspase-1 activation. This triggers cell swelling and pyroptosis, releasing pro-inflammatory cytokines and cellular contents. While aiding in pathogen clearance, this process can also contribute to tissue damage, especially in chronic conditions like periodontitis. Thus, bacterial products can activate NF-κB, promoting the expression of NLRP3 and pro-inflammatory cytokines, thus initiating pyroptosis, contributing to the immune response and tissue damage. Notably, macrophage response via pyroptosis is crucial for immune defense but may have detrimental effects in certain contexts. Further, pyroptosis in macrophages can promote inflammation and the pathogenesis of periodontitis

Numerous pathogens and factors have been identified as contributors to the induction of pyroptosis in macrophages, thereby playing a role in the development of periodontitis. These include Porphyromonas gingivalis, Mycoplasma salivarium, Treponema denticola surface protein Td92, E. faecalis, LPS, cyclic stretch, dental calculus, and outer membrane vesicles of Porphyromonas gingivalis. The occurrence of pyroptosis in macrophages can potentiate inflammation and contribute to the pathogenesis of periodontitis [202–206].

Recent advancements in the field have provided a deeper understanding of the regulation of pyroptosis, a form of programmed cell death. Studies have revealed that Ninjurin-1 facilitates the breakdown of the plasma membrane into smaller fragments following GSDMD-induced pyroptosis, thereby enhancing inflammation and pathogen clearance [207]. Additionally, recent research has uncovered a significant link between the Ragulator-Rag complex of the mTORC1 pathway and the pore-forming activity of GSDMD in macrophages. The mTORC1 pathway is a crucial regulator of cellular processes, while GSDMD is a key player in pyroptosis. Studies have demonstrated that the Ragulator-Rag complex, which controls mTORC1 activation in response to amino acid availability, is also essential for the activation of GSDMD in macrophages. The exact mechanisms underlying this connection are still being explored, but it is believed that the Ragulator-Rag complex may influence the intracellular trafficking or localization of GSDMD or its interactions with other proteins involved in the pyroptosis pathway [208].

The regulation of pyroptosis is influenced by posttranslational modifications of GSDMs. Notably, the ubiquitin ligase IpaH7.8 plays a role in this process by facilitating the ubiquitylation and degradation of GSDMD and GSDMB. This mechanism effectively hinders pyroptosis, thereby promoting the persistence of infection [209, 210]. Another posttranslational modification, known as succination, impacts pyroptosis regulation. Specifically, succination occurs at a specific site in GSDMD, leading to a reduction in its binding to caspase-1. Consequently, this impedes the processing and oligomerization of GSDMD, ultimately inhibiting pyroptosis-induced cell death [28]. Furthermore, the process of pyroptosis is also influenced by the palmitoylation of GSDME, which is facilitated by chemotherapy drugs. This specific chemical modification acts as a modulator, promoting pyroptosis and contributing to its induction [211].

Pyroptosis’s crosstalk with other forms of programmed cell death in periodontitis

The interplay between pyroptosis, apoptosis, and necroptosis underscores the intricate relationships among these programmed cell death pathways. Recent evidence challenges the traditional view of these processes as distinct, revealing connections and shared components between pyroptosis and apoptosis. Caspase-3, commonly associated with apoptosis, has emerged as a key mediator of pyroptosis, acting on the GSDME protein [30, 212]. Similarly, caspase-8, the initiator of extrinsic apoptosis, has been found to participate in pyroptosis, blurring the boundaries between these pathways [213, 214]. Bidirectional signaling exists between pyroptosis and apoptosis, with certain stimuli triggering both pathways simultaneously. However, the dominance of one pathway over the other often depends on protein expression levels, caspase activity, and the specific cell type involved.

In the context of periodontitis, pyroptosis and necroptosis play substantial roles, contributing to tissue damage and inflammatory responses. Periodontal pathogens such as Porphyromonas gingivalis and LPS can induce both pyroptosis and necroptosis, exacerbating the progression of the disease. Moreover, molecules implicated in necroptosis, including RIPK1, RIPK3, and MLKL, have been linked to the activation of pyroptosis during periodontitis. Unlike apoptosis, pyroptosis and necroptosis elicit robust immune responses, contributing to the pathology of periodontal disease. However, the intricate interactions among these pathways in periodontitis are still not well understood, highlighting the need for novel therapeutic approaches [215–219].

Neutrophils, crucial regulators in periodontitis, exhibit complex responses to pathogens, including the release of neutrophil extracellular traps (NETs) through a process known as NETosis [220]. While NETosis primarily serves as a host defense mechanism, it may also contribute to tissue damage in periodontitis. Interestingly, pathogens that induce NETosis have been reported to trigger pyroptosis in other cell types within periodontal tissues, illustrating the interconnected nature of these processes. Nevertheless, the factors determining whether neutrophils undergo NETosis, pyroptosis, or phagocytosis in response to specific triggers remain unclear, warranting further investigation [221–224].

Lastly, the concept of PANoptosis, a newly recognized proinflammatory programmed cell death pathway, sheds light on the convergence of pyroptosis, apoptosis, and necroptosis. The PANoptosome, composed of molecules from these pathways, functions as a sensor and executor during infection. Although its relevance to periodontitis has not been explored, understanding PANoptosis may provide insights into innovative treatment strategies for the disease [225, 226]. Overall, unraveling the complex interplay among pyroptosis, apoptosis, necroptosis, and other cell death pathways holds great promise for advancing our comprehension and management of periodontal disease [82, 227–229] (Table 2).

Table 2.

Pyroptosis’s crosstalk with other forms of programmed cell death in periodontitis [82, 227–229]

Crosstalk Type	Interaction Details
Pyroptosis and Apoptosis	• Caspase-3/GSDME acts as a switch between apoptosis and pyroptosis, with caspase-3 cleaving GSDME to induce pyroptosis. • Caspase-8 is involved in both extrinsic apoptosis and pyroptosis pathways, mediating pyroptosis during Yersinia infection and promoting GSDMC cleavage. • Granzyme A and B, known for their roles in apoptosis, can also cleave GSDMs, further linking apoptosis and pyroptosis.
Pyroptosis and Necroptosis	• Receptors for initiating necroptosis are implicated in pyroptosis pathways. • RIPK1, RIPK3, and MLKL are involved in both necroptosis and activation of NLRP3/caspase 1, suggesting their roles in activating pyroptosis during periodontitis.
Pyroptosis and NETosis	• Periodontal pathogens inducing NETosis have been shown to trigger pyroptosis in other cell types within periodontal tissues. • Neutrophil proteases and low caspase expression levels favor NETosis over pyroptosis in neutrophils responding to identical triggers.
Pyroptosis, Apoptosis, and Necroptosis	• Caspase-8 acts as a master regulator, influencing apoptosis, necroptosis, and pyroptosis pathways. • XIAP and cIAP1/2 inhibit apoptotic caspase activity, enhancing necroptosis and pyroptosis. • Loss of XIAP and cIAP1/2 enhances both apoptotic and necroptotic pathways. • RIPK1 limits RIPK3 and caspase-8-mediated cell death, with RIPK1 deficiency leading to uncontrolled cell death via caspase-8, RIPK3, or NLRP3/IL-1β activation.
PANoptosis	• PANoptosome consists of molecules from pyroptotic, apoptotic, and necroptotic pathways, acting as a sensor and executor during infection. • ZBP1 recruits RIPK3 and caspase-8 during viral infections, triggering PANoptosis. • Caspase-6 facilitates interactions between RIPK3 and ZBP1. • Different pathogens can trigger PANoptosis through both ZBP1-dependent and ZBP1-independent pathways, suggesting diverse PANoptosome components in response to specific microbes.

Signaling pathways in oral cancers via inflammation inducing pyroptosis and periodontitis

Chronic inflammation, a prolonged and persistent immune response, has been closely linked to cancer development through multiple mechanisms such as pyroptosis and periodontitis (Fig. 5) [230–232].

Fig. 5.

Chronic inflammation, driven by mechanisms like pyroptosis and periodontitis, plays a pivotal role in oral cancer progression. Inflammatory cytokines and mediators released during pyroptosis create a tumor-promoting microenvironment by enhancing immune evasion, genome instability, and resistance to cell death. Inflammation also stimulates angiogenesis, ensuring tumor growth by providing blood supply, and sustains proliferative signaling, driving uncontrolled cell division. Sustained proliferation involves MAPK and PI3K-AKT pathways. Growth suppression evasion links p53 inactivation. Apoptosis resistance involves Bcl-2 and caspases. Telomerase activation enables immortality. Angiogenesis is driven by VEGF. Invasion/metastasis involves EMT and MMPs. Genome instability arises from DDR (DNA damage response) defects. Inflammation activates NF-κB. Metabolic shifts include the Warburg effect. Immune evasion uses checkpoint inhibitors like PD-L1. These interconnected signals promote tumor development and progression in oral cancers

One significant pathway involved in this process is the MAPK/ERK signaling pathway, which regulates cell growth, survival, and differentiation [233]. Chronic inflammation activates this pathway, triggering a cascade of molecular events that lead to uncontrolled cell division and tumor growth. Dysregulation of the MAPK/ERK and JNK pathways is often observed in cancer, where their aberrant activity promotes tumor development, invasion, and resistance to cell death. Targeting these pathways has become a focus of cancer therapy, aiming to disrupt their signaling and inhibit tumor progression [234–238].

Another critical factor is the role of the Bcl-2 family of proteins, which regulate apoptosis, the programmed cell death essential for maintaining cellular homeostasis [239]. Chronic inflammation disrupts the balance between pro-apoptotic and anti-apoptotic proteins, tipping it toward cell survival. This evasion of apoptosis allows damaged cells to persist, accumulate genetic mutations, and potentially form tumors, highlighting the link between inflammation and cancer [240–242].

Pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6 further amplify these effects by sustaining chronic inflammation and promoting tumorigenic processes. TNF-α activates the NF-κB and AP-1 pathways, inducing genes that enhance cell survival, proliferation, and resistance to apoptosis. IL-1β stimulates the expression of adhesion molecules and MMPs, facilitating tissue invasion and remodeling. IL-6 drives cell cycle progression and reduces apoptotic sensitivity through the JAK/STAT signaling pathway [148, 243, 244].

Chemokines like CXCL5 and CXCL10 exacerbate these effects by recruiting immune cells to the site of inflammation. While immune cell infiltration is protective in acute responses, in chronic inflammation, it causes sustained tissue damage and remodeling. Chemokines also support angiogenesis, enhance cancer cell migration, and modulate the immune environment, aiding immune evasion by tumor cells [245–247].

Preclinical and clinical evidence

Bacterial LPS from pathogens like E. coli and P. gingivalis induce pyroptosis in periodontal cells, activating inflammasomes (NLRP3, caspase-1) and releasing inflammatory cytokines. This contributes to tissue damage and bone loss in periodontitis, highlighting pyroptosis as a potential therapeutic target (Table 3).

Table 3.

Preclinical and clinical insights into inflammasome activity in periodontal disease [248–261]

Study	Focus/Mechanism	Models Used	Key Findings
Bostanci & Belibasakis	Role of inflammasomes in periodontal disease; NLRP3 activity in gum tissues	Human samples	Elevated NLRP3, caspase-1, and IL-18 in periodontal epithelium; inflammasomes key in immune response
Zhang et al. (2021)	Pyroptosis mechanisms in PDLCs; role of GSK-3β	PDLCs treated with E. coli LPS	LPS activated NLRP3, GSDMD, cleaved caspase-1; GSK-3β inhibition blocked pyroptosis
Oka et al. (2021)	LPS effects on caspase-1/11, NF-κB, and Dec2 regulation	HGFs, PDLCs, mice	Dec2 knockout increased pyroptosis and IL-1β release, reduced NF-κB activity
Chen et al. (2021)	Role of MALAT1 in inflammation and pyroptosis	PDLCs treated with LPS	MALAT1 knockout enhanced viability, reduced inflammation; increased MALAT1 and HIF3A linked to reduced miR-769-5p
Liu et al. (2020)	Oxidative stress-mediated pyroptosis	Human osteoblast-like cells	ROS inhibition reduced NLRP3-mediated pyroptosis; NAC and MCC950 restored differentiation
Cheng et al. (2018)	LPS-induced pyroptosis and bone resorption	PDLCs, rat model	VX765 (caspase-1 inhibitor) reduced IL-1β, IL-6, IL-8 expression, and bone loss
Cecil et al. (2017)	OMVs from bacteria inducing inflammasome activation	Monocytes, macrophages	P. gingivalis OMVs triggered NLRP3 activation, IL-1β secretion; viable P. gingivalis did not activate NLRP3
Brown et al. (2015)	P. gingivalis infection’s impact on systemic inflammation and atherosclerosis	Mouse model	NLRP3 activation exacerbated periodontal lesions and atherosclerosis, particularly in females
Taxman et al. (2012)	P. gingivalis evasion of immune response through inflammasome suppression	Polymicrobial environment	Suppressed NLRP3 activation via adaptive mechanisms; evades immune surveillance

Researchers Bostanci and Belibasakis conducted an insightful study into the role of inflammasomes in periodontal disease, particularly comparing the gum tissues of patients with periodontal disease to those of healthy individuals. Their findings revealed significantly higher activity of inflammasomes in the gum tissues of patients with periodontal disease [261]. Using immunohistochemical analysis, they observed particularly elevated levels of NLRP3 in patients with chronic periodontitis and generalized aggressive periodontitis. This increase was most prominently seen in the periodontal epithelium layer, which is crucial for the immune response to periodontal pathogens [260].

In addition to NLRP3, other inflammasome-related proteins, such as caspase-1, caspase-4, and IL-18, were also found in greater quantities in inflamed gum tissues. Caspase-1 is vital for the activation of pro-inflammatory cytokines, while caspase-4 plays a role in non-canonical inflammasome activation. IL-18 is a pro-inflammatory cytokine involved in the body’s immune response, activated by caspase-1. These elevated levels indicate a robust inflammatory response in the periodontal tissues of affected individuals, underscoring the importance of inflammasomes in the pathogenesis of periodontal disease [254, 255, 262].

The pattern of increased inflammasome activity was consistent across both human studies and animal models. For instance, in a rat model exposed to LPS from P. gingivalis, an increase in caspase-11 was observed. Caspase-11 is crucial in the non-canonical inflammasome pathway and responds to intracellular LPS. This consistency across different models reinforces the role of inflammasomes in periodontal inflammation and disease [262].

A particularly notable finding was the effect of P. gingivalis on inflammasome activation. P. gingivalis is known to inhabit subgingival biofilms. The presence of this bacterium was shown to directly influence inflammasome activity. When P. gingivalis was removed from these biofilms, the levels of NLRP3 and IL-1β normalized. This suggests that P. gingivalis plays a direct role in upregulating inflammasome activity and contributing to the inflammatory state observed in periodontal disease [38, 263].

In addition, elevated levels of pyroptosis markers such as GSDMD, NLRP3, cleaved caspase-1, and IL-1β have been observed in these tissues. This process not only worsens periodontal disease but also affects the alveolar bone that supports teeth. For example, experiments with mice have shown that the absence of caspase-1, but not NLRP3, can reduce bone loss caused by the pathogen Aggregatibacter actinomycetemcomitans, highlighting caspase-1’s critical role in inflammation and subsequent bone damage [264].

Various studies have explored the mechanisms behind pyroptosis induced by bacterial components such as LPS. Zhang et al. (2021) found that E. coli LPS decreased cell viability and triggered the release of pro-inflammatory cytokines (IL-1β, IL-18, IL-6, TNF-α) in periodontal ligament cells (PDLCs) in a time- and dose-dependent manner. This activation involved the NLRP3 inflammasome, GSDMD, and cleaved caspase-1, alongside upregulation of glycogen synthase kinase-3β (GSK-3β). Thus, inhibiting GSK-3β blocked NLRP3-mediated pyroptosis, indicating its pivotal role in this inflammatory process [259].

In a complementary study, Oka et al. (2021) used P. gingivalis LPS to stimulate HGFs and PDLCs, as well as a mouse model of periodontitis. They found that LPS activated caspase-1, caspase-11, and NF-κB. Dec2 knockout mice showed increased pyroptosis and IL-1β release, coupled with reduced NF-κB phosphorylation and translocation, underscoring Dec2’s regulatory role in inflammation and pyroptosis [258].

Chen et al. (2021) investigated the role of metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) in PDLCs treated with P. gingivalis LPS in vitro. Their findings showed that MALAT1 knockout enhanced cell viability and inhibited both inflammation and pyroptosis. Periodontitis patients and LPS-treated PDLCs exhibited increased expression of MALAT1 and hypoxia-inducible factor 3 A (HIF3A), along with reduced miR-769-5p, suggesting a complex regulatory mechanism involving these molecules [257]. Moreover, Liu et al. (2020) studied E. coli LPS effects on human osteoblast-like cells in vitro and found that LPS induced NLRP3-mediated pyroptosis in a time- and dose-dependent manner. Inhibiting reactive oxygen species (ROS) with N-acetyl-L-cysteine (NAC) attenuated oxidative stress-mediated pyroptosis. Similarly, the NLRP3 inhibitor MCC950 mitigated pyroptosis and restored osteogenic differentiation-related protein expression, highlighting the role of oxidative stress in facilitating pyroptosis [256].

Cheng et al. (2018) evaluated the effects of LPS from E. coli and P. gingivalis on PDLCs in vitro and in a rat model of periodontitis. Using VX765, a caspase-1 inhibitor, they were able to reduce the expression of IL-1β, MCP-1, IL-6, and IL-8 in vitro and suppress bone loss in vivo, linking pyroptosis to bone resorption in acute apical periodontitis [255]. Another study explored the effects of LPS from E. coli and P. gingivalis on HGFs under normoxic and hypoxic conditions both in vitro and in a mouse model of periodontitis. They found that P. gingivalis LPS decreased NLRP3 and IL-1β under normoxic conditions, but hypoxia reversed these effects, promoting caspase-1 activation and IL-1β maturation. E. coli LPS, however, enhanced IL-1β maturation under both conditions, emphasizing the influence of oxygen levels on inflammasome activation and cytokine production [254].

Cecil et al. (2017) investigated how outer membrane vesicles (OMVs) from P. gingivalis, T. denticola, and T. forsythia interact with monocytes and macrophages. OMVs induced phagocytosis, NF-κB activation, IL-1β secretion, and cell death via NLRP3 activation. Notably, P. gingivalis OMVs dysregulated the immune response, while OMVs from T. denticola and T. forsythia promoted disease progression [253]. Fleetwood et al. (2017) found that OMVs from P. gingivalis activated caspase-1, produced IL-1β and IL-18, released lactate dehydrogenase (LDH), and indicated pyroptosis, while viable P. gingivalis did not activate NLRP3. This suggests that bacterial membrane components play a significant role in triggering inflammasome activation and subsequent inflammatory responses [252]. Furthermore, Lu et al. (2017) examined the combined effects of muramyl dipeptide (MDP) and LPS on PDLCs in vitro. Both agents promoted the expression of NLRP3 and caspase-1 and the secretion of IL-1β. When combined, these effects were synergistic or additive, emphasizing the complex interplay of bacterial components in modulating inflammasome activity [251].

Several studies presented delve into the intricate relationship between P. gingivalis and the host immune system. For instance, Brown et al. (2015) demonstrated in a mouse model that P. gingivalis infection significantly exacerbates periodontal lesions and atherosclerosis, particularly in females, with CD36/SR-B2-dependent pathways playing a crucial role in this process. Activation of the NLRP3 inflammasome by P. gingivalis was identified as a key mechanism leading to systemic release of pro-inflammatory cytokines and inducing pyroptosis, highlighting the bacterium’s ability to promote chronic inflammation and cardiovascular disease [250, 265].

In parallel, Taxman et al. (2012) elucidated how P. gingivalis strategically evades host immune responses by suppressing NLRP3 inflammasome activation through specific pathways. While lacking direct capability to activate the NLRP3 inflammasome, P. gingivalis can suppress its activation by various stimuli, including other bacteria and molecular patterns involved in endocytosis-mediated pathways. This unique mechanism of inflammasome repression sheds light on the bacterium’s adaptive strategies to evade immune surveillance, contributing to its persistence and pathogenicity in polymicrobial environments characteristic of periodontal disease [249] .

Furthermore, Domon et al. (2009) provided insights into the immunomodulatory effects of P. gingivalis LPS in human macrophages obtained from periodontitis patients. While the expression of unfolded protein response (UPR) related genes was upregulated in periodontitis lesions compared to gingivitis lesions, P. gingivalis LPS failed to induce this response, indicating a unique immunomodulatory profile distinct from other bacterial LPS. This suggests a nuanced mechanism by which P. gingivalis modulates host immune responses, potentially contributing to the chronic inflammation characteristic of periodontal disease [248].

Pyroptosis as a novel therapeutic agent for oral cancer

Studies have documented elevated levels of pyroptosis in the affected periodontal tissues. Thus, researchers have sought to explore the therapeutic potential of pharmacological inhibitors targeting pyroptosis, leading to promising findings in impeding the progression of periodontitis. For instance, inhibitors of caspase-1, such as vx-765 and Z-YVAD-FMK, have demonstrated efficacy in suppressing bone loss and attenuating the expression of key inflammatory factors, including IL-1β, MCP-1, IL-6, and IL-8, in experimental models of periodontitis [186, 255]. Furthermore, inhibitors targeting caspase-4, Gasdermin D (GSDMD), Z-LEVD-FMK, and other molecules implicated in pyroptosis have exhibited promising anti-inflammatory effects in various cell types pertinent to periodontitis [183, 187].

Another notable inhibitor, MCC950, which targets the NLRP3 inflammasome, has shown the ability to restore the functionality of MG63 cells involved in osteogenesis [256]. Although MCC950 (also known as CRID3) has not yet advanced to late-stage clinical trials, its analogs and other NLRP3 inhibitors are being evaluated in early-phase clinical trials for inflammatory conditions including rheumatoid arthritis and type 2 diabetes (ClinicalTrials.gov identifiers: NCT04540120, NCT04281910). Patients treated with canakinumab for cardiovascular inflammation also showed a lower incidence of cancer, according to the CANTOS (Canakinumab Anti-Inflammatory Thrombosis Outcome Study) trial. These results indirectly support targeting pyroptosis as a preventive strategy in inflammation-associated malignancies, possibly including those originating from chronic periodontitis, since IL-1β is a significant activator of pyroptosis [266].

Recently developed small molecules such as NSA (necrosulfonamide) and Disulfiram have been shown to inhibit GSDMD pore formation, thereby blocking pyroptosis. Disulfiram, originally used for alcohol aversion therapy, has shown anticancer properties in preclinical models of head and neck cancers, and its repurposing for pyroptosis-related pathologies is under investigation (NCT04216744).

Furthermore, the therapeutic implications of targeting pyroptosis extend to the potential for combination therapy with existing treatment modalities. Pyroptosis-targeting agents can be synergistically combined with antibiotics or anti-inflammatory drugs to achieve enhanced treatment outcomes. For instance, antibiotics can target pathogenic bacteria within the periodontal biofilm, while pyroptosis modulation addresses the dysregulated host immune response. This combination therapy approach holds promise for improving treatment efficacy and reducing the risk of antimicrobial resistance, a growing concern in periodontal disease management [267–269].

In a combination therapy approach, antibiotics serve to directly target and reduce the pathogenic bacteria within the periodontal biofilm, which is a primary driver of periodontitis. These antibiotics help to eliminate the bacterial load and disrupt the biofilm, making it easier for the immune system to clear the infection [270]. However, antibiotics alone do not effectively address the dysregulated host immune response, which is where pyroptosis-targeting agents come into play [271, 272]. Thus, by modulating pyroptosis, these agents can reduce excessive inflammation and tissue damage caused by the immune response. This dual approach not only tackles the infection at its source but also mitigates the harmful effects of chronic inflammation.

On the other hand, lifestyle changes such as adopting a healthier diet, staying physically active, and quitting smoking have been found to impact pyroptosis-related pathways by influencing key molecular components—like the activation of the NLRP3 inflammasome, caspase-1 function, and the production of inflammatory cytokines such as IL-1β and IL-18. For example, diets rich in polyphenols and omega-3 fatty acids can help reduce oxidative stress and regulate redox-sensitive signaling pathways, including NF-κB, which play a role in inflammation. Probiotics and treatments aimed at balancing the oral microbiome may also help by restoring microbial balance, thereby reducing abnormal inflammasome activity and preventing excessive pyroptotic cell death. Even basic oral hygiene habits—like regular brushing, flossing, and using antiseptic mouthwash—can contribute by lowering bacterial levels and minimizing the presence of harmful virulence factors that trigger inflammation. Together, these preventive strategies, grounded in our growing understanding of pyroptosis, offer a promising way to tackle periodontitis early on and possibly lower the risk of more serious complications, including cancer [273, 274].

Conclusions and future directions

This review underscored the critical link between periodontitis, pyroptosis, and oral cancer, suggesting that targeting these inflammatory pathways may provide new therapeutic opportunities. Inhibiting pyroptotic mediators like GSDMD or NLRP3 inflammasomes could reduce inflammation and prevent tissue damage, potentially slowing the progression of oral cancer. Similarly, targeting pyroptosis-related cytokines such as IL-1β and IL-18 could diminish the inflammatory microenvironment that supports tumor growth. Furthermore, inducing controlled pyroptosis in cancer cells or infected tissues might offer a therapeutic approach to selectively eliminate malignant cells while stimulating immune responses that target tumors.

Large-scale, multicenter clinical cohort studies should be the main focus of future research in order to confirm the molecular connections between oral carcinogenesis, periodontitis, and pyroptosis. These studies will improve the generalizability of results by facilitating longitudinal patient tracking, consistent diagnostic criteria, and assessment of confounding factors across various populations. Furthermore, to create targeted treatments that alter pyroptosis pathways and evaluate their clinical effectiveness in lowering the risk of oral cancer in patients with periodontitis, translational research is required. Ethnic and environmental factors will become clearer when mechanistic investigations are expanded to include varied populations. In this area, the combination of bioinformatics and artificial intelligence (AI) has exciting prospects. Large clinical and omics datasets can be analyzed by AI to find new biomarkers, forecast patient risk, and enhance diagnostic precision by automatically analyzing tissue images. Comprehensive multi-omics data integration is made easier by bioinformatics tools, which also reveal intricate regulatory networks and novel treatment targets. By customizing prevention and treatment plans according to each patient’s unique molecular and clinical characteristics, these technologies work together to promote personalized medicine methods. In oral oncology driven by periodontitis, a focus on multicenter research in conjunction with AI and bioinformatics can expedite the conversion of genetic discoveries into better clinical outcomes. In this line, genetic differences in certain pyroptosis-related genes can play a major role in how likely someone is to develop periodontitis and how this condition might progress to oral cancer. For example, changes in genes like NLRP3, NLRC4, GSDMB, and AIM2 have been linked to varying cancer risks, including oral squamous cell carcinoma (OSCC), because they influence how the body’s immune system responds to inflammation and how effectively cells undergo pyroptosis—a form of programmed cell death. These genetic variations mean that people may react differently to gum inflammation, which can affect their chances of developing cancer in the mouth. With the rise of precision medicine, there is growing potential to use genetic and multi-omics information to personalize care. By combining genetic testing with clinical and molecular data, healthcare providers can better identify individuals at higher risk, anticipate how the disease might progress, and choose treatments that specifically target the pyroptosis pathways involved. This tailored approach not only helps with earlier detection and prevention but also allows for more customized treatment plans, ultimately aiming to improve outcomes for patients facing periodontitis-related oral cancer.

Abbreviations

OSCC

Oral squamous cell carcinoma

PAMPs

Pathogen-associated molecular patterns

DAMPs

Danger-associated molecular patterns

GSDM

Gasdermin

NLRs

NOD-like receptors

ALRs

AIM2-like receptors

ASC

Apoptosis-associated speck-like

TLR

Toll-like receptors

PRRs

Pattern recognition receptors

CARD

Caspase recruitment domain

NBD

Nucleotide-binding and oligomerization domain

LPS

lLipopolysaccharide

ELANE

Neutrophil elastase

MAPK

Mitogen-activated protein kinase

ERK1/2

Extracellular signal-regulated kinase 1/2

PDLSCs

Periodontal ligament stem cells

Author contributions

the core of the study came from Shahryar Irannejadrankouhi, and Mohsen Nabi Afjadi. Shabnam Ghasemzadeh, Farzad Fattah, Sahand Emrahoglu, Seyed Mahdi Madani, Seyedeh Tabasom Nejati, Ava OstovarRavari, Elham Oveili, Shahryar Irannejadrankouhi, and Mohsen Nabi Afjadi wrote the manuscript. Shahryar Irannejadrankouhi, and Mohsen Nabi Afjadi supervised the manuscript.

Funding

This study did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethical approval and consent to participate

This research was a review, and no participants took part, so there was no need for it.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.