The molecular mechanism of traditional Chinese medicine in the treatment of oropharyngeal candidiasis (OPC)

Abstract

Background

Oropharyngeal candidiasis (OPC) is a prevalent fungal infection primarily caused by Candida species, notably Candida albicans, posing significant health challenges. Traditional Chinese medicine (TCM) has gained attention due to its multifaceted pharmacological properties and lower incidence of adverse effects compared to conventional treatments.

Objective

This article aims to explore the application of TCM in OPC therapy and elucidate the potential molecular mechanisms underlying its efficacy.

Design

A comprehensive analysis of relevant studies and research findings was conducted to investigate the bioactive components of TCM and their mechanisms of action.

Results

The analysis reveals that TCM exerts beneficial effects through inhibition of fungal growth, regulation of immune responses, and enhancement of oral microecological balance.

Conclusions

TCM offers a holistic approach to managing OPC, leveraging its multifaceted mechanisms to address this common yet troublesome infection effectively.

Introduction

Oropharyngeal candidiasis (OPC), also known as ‘thrush’, is a typical oral mucosal damaging disease caused by the infection of the oral mucosa by Candida albicans [1]. In recent years, the widespread use of antibiotics and immunosuppressants in clinical practice has led to dysbiosis or reduced immunity, resulting in an increasing number of people suffering from fungal infections in the viscera, skin, and mucous membranes, with a corresponding rise in the incidence of OPC. This disease can occur in any part of the oral cavity, such as the lips, tongue, cheeks, soft palate, and hard palate, and patients often experience discomfort such as dry mouth, stickiness, pain, loss of taste, and burning sensations in the mouth, negatively impacting their normal lives.

Current antifungal therapy for OPC primarily relies on azoles (e.g. fluconazole) and polyenes (e.g. amphotericin B) [2]. While fluconazole is widely used due to its oral bioavailability and relatively favourable safety profile, its fungistatic nature and extensive use have contributed to the emergence of resistant Candida strains, leading to treatment failures and recurrent infections [3]. Amphotericin B, a fungicidal agent derived from natural sources, remains effective but is limited by its toxicity, intravenous administration requirement, and high cost, restricting its use especially in resource-limited settings [4]. Additionally, side effects such as nephrotoxicity and infusion-related reactions pose significant concerns with amphotericin B therapy [5]. The increasing incidence of antifungal resistance and adverse drug reactions underscores the urgent need for novel therapeutic strategies that are both effective and safer for long-term use in vulnerable populations [6].

Traditional Chinese medicine (TCM), with its rich history and complex herbal formulations, offers a promising complementary approach to OPC treatment. The multifaceted nature of herbal medicines, containing diverse bioactive constituents, allows for multi-target antifungal effects and immunomodulation, which may enhance efficacy and reduce the likelihood of resistance development [7]. Several studies have demonstrated potent antifungal activities of herbal extracts and isolated compounds against Candida species, including fluconazole-resistant strains, through mechanisms such as ergosterol binding disruption, inhibition of biofilm formation, and attenuation of virulence factors [8]. For example, phytolaccagenin from Phytolacca tetramera berries exhibits synergistic effects with conventional antifungals, enabling dose reductions and mitigating toxicity while effectively inhibiting Candida biofilms [9]. Similarly, natural peptides like blapstin derived from medicinal insects show selective antifungal activity with minimal cytotoxicity, representing novel antifungal candidates with potential clinical applications [10].

Beyond direct antifungal effects, TCM components may also modulate host immune responses and reduce inflammatory damage associated with candidalysin and other fungal virulence factors [11]. This immunomodulatory capacity could alleviate symptoms and prevent excessive tissue injury, addressing a critical aspect of OPC pathogenesis that conventional antifungals do not target. Additionally, some herbal extracts possess antioxidant properties that can counteract oxidative stress induced by fungal infections, further contributing to mucosal healing and symptom relief [12]. Importantly, the complex phytochemical profiles of TCM preparations may reduce the risk of adverse effects commonly observed with single-agent antifungals, providing a safer therapeutic profile for long-term management of OPC in immunocompromised patients [11].

In summary, OPC remains a challenging infection due to the limitations of current antifungal drugs, including resistance development and toxicity. Traditional Chinese medicine, with its multi-component and multi-target characteristics, offers distinct advantages by combining antifungal efficacy with reduced side effects and potential immunomodulatory benefits. This review aims to systematically summarise recent advances in the use of TCM for OPC treatment, focusing on its therapeutic advantages and underlying mechanisms for side effect mitigation. By integrating evidence from pharmacological studies and clinical observations, we seek to provide a theoretical foundation to support the rational clinical application of TCM in managing OPC, ultimately improving patient outcomes and quality of life.

Oral pharyngeal candidiasis caused by C. albicans

Biological characteristics of C. albicans

C. albicans is an opportunistic pathogenic fungus that mainly colonises on mucosal surfaces such as those of the oral cavity, digestive tract and vagina. C. albicans exhibits polymorphism and can manifest as either yeast form or hyphal form. In the yeast form, it is non-toxic to the host; however, when it transforms into the hyphal form, it becomes toxic [13]. The pathogenicity of C. albicans is dependent on multiple virulence factors, including its adhesion and invasion of oral mucosal epithelial cells, morphological transformation of hyphae, formation of biofilms and quorum sensing [14]. C. albicans can secrete adhesins to promote cell binding, hydrolases can enhance its invasive ability, the transformation of C. albicans from yeast form to hyphal form can also enhance its invasive ability. In addition, the formation of biofilms increases its drug resistance [15].

The causes and pathogenesis of oropharyngeal candidiasis

Oral pharyngeal candidiasis (OPC) is mainly caused by C. albicans, which is triggered by the virulence factors of C. albicans and its interaction with oral epithelial cells [16]. When the balance of the internal environment of the body is disrupted, the immune function is impaired, providing favourable conditions for the excessive growth of C. albicans [17] (Figure 1). The factors that trigger infection include nutritional deficiency, decreased saliva function, smoking, wearing dentures, and organ transplantation, which promote the virulence factors and adaptability of C. albicans [18].

Figure 1.

Mechanism of OPC pathogenesis. Under the immunodeficiency caused by factors such as nutritional deficiency, decreased salivary function, smoking, and organ transplantation, C. albicans adheres to the epithelial cells of oral mucosa through adhesion factors ALS3 and Hwp1 and establishes colonisation in the oral cavity. When C. albicans transforms from yeast form to hyphal form, the hyphae have stronger invasive ability. Hyphal form of C. albicans can secrete candidalysin, damage epithelial cells and secrete inflammatory factors; the expressed hyphae-degrading enzymes degrade intercellular junction proteins to cause cell detachment; it can also secrete aspartic proteinase to damage immune function and eventually lead to the occurrence of oropharyngeal candidiasis.

During the early stage of infection, to maintain colonisation in the oropharynx, C. albicans must adhere to the epithelial cells of the oral mucosa. Through the adhesion factors ALS3 and Hwp1, it binds to the epithelial cells of the oral mucosa and then colonises in the oral cavity while avoiding being destroyed by host antimicrobial factors, this laid the foundation for the subsequent infection process [19]. The core reason for the occurrence of OPC is the morphological transformation of C. albicans [20]. When C. albicans transforms from yeast form to hyphal form, the hyphae have stronger invasive ability and the ability to evade host immune attack, such as avoiding phagocytosis by macrophages [21]. In addition to the active penetration process driven by C. albicans, another supplementary mechanism for C. albicans to invade host cells is endocytosis, which is an immune evasion mechanism induced by infectious fungi but driven by host cells. Inside the cell, C. albicans can take advantage of the intracellular environment to multiply while avoiding direct recognition and elimination by the host's immune system. C. albicans can secrete a variety of enzymes, such as hydrolase, phospholipase, etc., which can degrade oral mucosal tissue, leading to epithelial cell shedding and inflammatory reaction [22]. The Candida yeasts with hyphal morphology (form) can penetrate the epithelial layer of the mucosa and enter the deeper tissues, thereby causing more severe infections. Recent studies have found that the epithelial damage induced by hyphae is mainly mediated by the secretion of a cell-dissolving peptide toxin called candidal toxin, which is a toxin released by Candida and encoded by the hyphal-specific gene ECE1 [23]. It can be cleaved by the Kex2 protease into eight peptides, of which only one can penetrate the epithelial cell membrane, induce epithelial cell damage and stimulate the secretion of cytokines. The hyphae-expressed lysis enzymes can penetrate the epithelial cell barrier through the paracellular pathway or by degrading intercellular junction proteins, enabling the organism to penetrate the epithelial cells [24]. Among the extracellular secreted enzymes closely related to the virulence of C. albicans, secreted aspartic proteinases (SAPs) can participate in host tissue invasion and nutrient acquisition. SAPs can also evade host defence by degrading molecules of the host immune system, including antibodies and antimicrobial peptides [25] (Figure 1).

The role of the immune system in Candida infections

In OPC, when C. albicans enters the oral cavity and attempts to adhere to the epithelial cells of the oral cavity, the immune system prevents the further spread of C. albicans by recognising and eliminating it., the immune system begins to function. The interaction between C. albicans and the host immune system plays a crucial role in infection [26]. For healthy individuals, their immune systems usually can effectively identify and eliminate C. albicans, thereby avoiding the occurrence of diseases. For those with weakened immunity, such as patients undergoing organ transplantation or those on long-term antibiotic therapy often face a higher risk of infection due to a weakened immune state, their defence against C. albicans is weakened, making them prone to infections [27]. The immune system combats Candida infection through the coordinated action of innate immunity and adaptive immunity. Innate immunity provides rapid but non-specific protection, while adaptive immunity offers lasting and specific protection [28]. The two work together to jointly maintain the health of the body and the stability of the immune system.

Innate immunity

During OPC occurrence, the local defence capability of the host's oral cavity is often weakened, allowing fungi to invade and damage oral epithelial cells. The collective is first invaded and then initiates an innate immune response, which occurs during the first systemic C. albicans infection, non-specifically recognising and phagocytosing the pathogenic microorganisms for clearance. The primary step in the host's innate immune response is the effective recognition of the receptors for invading pathogens, which are involved in the recognition and successful activation of epithelial cells, neutrophils, macrophages, dendritic cells, and NK cells against C. albicans.

Epithelial cells separate the host from the environment and are traditionally viewed as a physical barrier against infection; however, it is now recognised that epithelial structures also possess direct antimicrobial activity and respond to pathogen invasion through tissue-specific immunity [29]. Generally, invasive C. albicans first comes into contact with epithelial cells. The receptors on the surface of epithelial cells can recognise the adhesion molecules of Candida, thereby induce a strong antifungal response in epithelial cells by triggering the release of pro-inflammatory cytokines and chemokines: activated epithelial cells secrete antimicrobial peptides that directly kill the fungus and release pro-inflammatory cytokines to recruit neutrophils to the site of infection, where they can kill C. albicans and limit the extent of epithelial cell damage. These inflammatory factors can also chemotactically recruit innate immune cells to work alongside epithelial cells in clearing fungal infections. Epithelial cells also respond to the invasion of C. albicans by releasing a specific spectrum of cytokines, which can recruit, activate, and differentiate immune cells [30].

As frequent colonisers of the oral mucosa, the host immune response in the oral cavity tends to be more tolerant; specifically, saliva not only prevents Candida from adhering to epithelial cells but is also rich in anti-Candida peptides, which are considered part of the host's innate immunity [31]. Host defence peptides (HDPs) are one of the first lines of defence against microbial invasion. Epithelial cells release various types of HDPs, including β-defensins and antimicrobial peptides, which can kill or inhibit the growth of C. albicans [32]. Different HDPs have different mechanisms of action, targeting the fungal cell membrane and mitochondria. Studies have shown that even in the absence of immunosuppression, Mbd-1 deficient mice exhibit severe oral thrush (OPC), demonstrating the importance of epithelial cell-derived HDPs in host defence against OPC [33]. Immunocompetent mice are resistant to OPC, clearing the infection within 2−3 days after oral exposure to C. albicans. Mice lacking IL-17RA or IL-17RC are unable to upregulate oral epithelial HDPs during C. albicans infection, making them highly susceptible to OPC [34]. Among them, histatin (Hst) in saliva, which is the most potent antimicrobial peptide in saliva, can protect oral tissues from C. albicans invasion and has broad-spectrum antimicrobial activity [35]. Hst5, as one of the most effective antimicrobial peptides, is closely related to various oral infection-related diseases. Hst has the ability to protect oral epithelium from C. albicans infection [36]. When Hst5 adsorbs onto oral epithelium, the formation of C. albicans hyphae is inhibited, the formation of C. albicans biofilm is suppressed, and the further aggregation and growth of microbial communities are prevented, thereby reducing the invasive ability of C. albicans on oral epithelium [36]. In addition, the mechanism of action of Hst5 may also include destroying the cell membrane of C. albicans, inhibiting its respiratory function, interfering with the cell cycle [37].

Neutrophils, following closely behind epithelial cells, respond promptly to infection, neutrophils rapidly migrate to the site of infection. They ingest and destroy fungal particles through phagocytosis. The release of pro-inflammatory cytokines and chemokines leads to the recruitment of neutrophils, which are key cells in the oral mucosal immune response against Candida [38]. In addition to phagocytosis, neutrophils possess a wide array of other antifungal weapons. They secrete soluble mediators, such as HDPs, proteases, and pro-inflammatory cytokines, to further promote pathogen clearance. Macrophages, as key effector cells in controlling C. albicans, not only phagocytise and kill the yeast, preventing its transition to a toxic filamentous form, but also secrete cytokines such as IL-12, IL-6, and TNF-α, enhancing their phagocytic capacity against C. albicans. As antigen-presenting cells (APCs), macrophages may present processed Candida antigens to T cells in the late stage of infection, thereby initiating an adaptive immune response [39].

NK cells mainly exert their functions continuously during the infection process before the initiation of the adaptive immune response. NK cells can recognise and kill cells infected by Candida or abnormal cells. By releasing substances such as perforin and granzyme, NK cells directly destroy the target cells. NK cells can also secrete cytokines, such as IFN-γ, to enhance the activity of other immune cells [40].

Dendritic cells (DCs) serve as an important link between innate and adaptive immune responses, initiating adaptive T cell responses that provide immune protection against C. albicans. Their immature form is regulated by epithelial cells beneath the mucosal surface, where chemokines and antimicrobial peptides secreted during microbial infection are gathered at the site of infection. Once a certain number of DCs accumulate, their recognition of C. albicans occurs through the interaction between pattern recognition receptors (PRRs) expressed on the DC surface and pathogen-associated molecular patterns (PAMPs) present on the Candida cell wall. The recognition of PAMPs by PRRs activates signalling pathways within the DCs, ultimately leading to the induction of specific adaptive cellular immune responses [41].The recognition of PAMPs triggers phagocytic or antimicrobial responses against the target microbes. Helper T cells (Th) are activated in an antigen-specific manner to coordinate epithelial defences, enhance innate immune functions, activate antibody responses, and ultimately control fungal burden and resolve inflammation. Epithelial cells induce the secretion of several antimicrobial peptides that have direct killing effects on fungal cells, helping to control local colonisation. Epithelial cells secrete pro-inflammatory mediators, such as cytokines and chemokines, signalling neutrophils, macrophages, and dendritic cells to be recruited to the site of infection [42].

Adaptive immunity

Although neutrophils, macrophages, epithelial cells and NK cells mainly play roles in innate immunity, their activities also create conditions for the initiation of adaptive immunity. Especially dendritic cells, as the bridge connecting innate immunity and adaptive immunity, present C. albicans antigens to T cells, thereby initiating specific immune responses. After the innate immune system responds, the adaptive immune system requires some time to generate and select mature antigen-specific T cells and B lymphocytes, leading to a more specific but slower systemic immune response mediated by T or B lymphocytes.

The adaptive immune system includes B cells and T cells. B cells are crucial for antibody production, while T cells provide necessary support for mucosal host defence and innate immune responses. T cells exist in different subtypes. Among CD4 + T cells, Th1 and Th17 cells promote the phagocytic clearance of fungal cells by releasing inflammatory cytokines such as IFN-γ and IL-17A/F, and these T cell subsets are critical for protective antifungal immunity. On the other hand, Th2 cells inhibit the responses of Th1 and Th17, favoring the persistence of fungi and promoting allergic manifestations. Among these, Th17 cells are the predominant subset, while Th1 and Th2 cells are secondary subsets. The primary protective role of Th17 cells in antifungal immunity is accomplished through T cell and IL-17 signalling. T cells are a component of the host's adaptive immune response to C. albicans, capable of responding in an antigen-specific manner. The antigen-specific activation of T cells also depends on their interaction with DCs, and their activation is controlled by the dendritic cell population. After the yeast form of Candida is phagocytised by DCs, the DCs secrete cytokines such as IL-1, IL-6, and TNF-α to regulate the differentiation of CD4 + T cells into Th-1 cells, initiating the immune response; when the filamentous form of Candida is taken up by DCs, it activates Th-2, promoting the secretion of IL-4 and IL-10, inhibiting IL-5, and facilitating the growth and development of B lymphocytes and humoral immunity. After infection with C. albicans, CD4 + Th precursor cells differentiate into three effector T cell subtypes: Th1, Th2, and Th17, each producing different cytokines, leading to differences in Th cell type-specific effector mechanisms [43].

B cells play a major role in oral and OPC by generating specific antibodies. These antibodies can directly bind to the antigens on the surface of Candida, thereby preventing its adhesion and invasion of host cells. Firstly, during Candida infection, B cells differentiate into plasma cells and produce specific antibodies against Candida surface antigens, such as IgA, IgG, and IgM, etc. These antibodies can trigger humoral immune responses by preventing Candida adhesion, neutralising toxins, and promoting the phagocytic action of phagocytes, etc., exerting antifungal effects. After the initial infection with Candida, some B cells differentiate into memory B cells. These cells can rapidly proliferate and differentiate into plasma cells upon encountering the same pathogen again, thereby generating a large amount of specific antibodies more quickly and accelerating the process of pathogen clearance [44].

The direct inhibitory effect of traditional Chinese medicine on C. albicans

Traditional Chinese medicine has enriched the range of options for medical treatment and has opened new avenues for the treatment of C. albicans with its unique pharmacological mechanisms, such as regulating the body's balance, enhancing immunity, or directly inhibiting pathogens. There have been many new attempts and studies on the inhibitory mechanisms of drugs against C. albicans [8,45] (Table 1). Many antifungal drugs can hinder the formation of hyphae, keeping the cells in yeast form, thereby reducing the ability of C. albicans to invade the body and achieving an antibacterial effect, such as Coptis chinensis [46] and Sanquinine [47]; they can also reduce the resistance of C. albicans to drugs by affecting the synthesis of its cell wall and cell membrane, such as dihydroartemisinin and Houttuynia cordata; or exert antibacterial effects by inhibiting the formation of biofilms, such as tetrandrine [48]; or by regulating the body's immunity to exert its antibacterial effects, such as Kangfuxin Liquid.

Table 1.

The table lists traditional Chinese medicines that directly inhibit fungal growth through different mechanisms: those that inhibit hyphal formation include Coptis detoxification decoction and Sanguinarine; those that damage cell membranes include Dihydroartemisinin and Cao Huang Gui Xiang formula; those that damage cell walls include Paeonia lactiflora and Houttuynia cordata; those that affect biological membranes include Honokiol 、Magnolol 、Paeoniflorin and Tetrandrine; those that influence the oral and pharyngeal microecological balance include Sophora flavescens and Lonicera japonica; those that affect local Immune response include BWM-7, Paeonia lactiflora and Houttuynia cordata.

Action mechanism	Traditional Chinese medicine	Reference
Inhibit the formation of Candida albicans' hyphae	Coptis detoxification decoction	[46]
	Sanguinarine	[47]
	Cao Huang Gui Xiang formula	[49]
Destroy the cell wall of Candida albicans	Paeonia lactiflora	[50]
Affect the biofilm of Candida albicans	Honokiol	[51]
	Magnolol
	Paeoniflorin	[52]
Affect ecological balance	Sophora flavescens	[53]
	Lonicera japonica	[54]

The inhibition of C. albicans hyphal growth by traditional Chinese medicine

Traditional Chinese medicine (TCM) contains a comprehensive array of natural products with active components capable of regulating the pathogenicity of C. albicans. Various TCM extracts and compounds exhibit direct antifungal activity against C. albicans (Figure 2). The expression of virulence factors plays a crucial role during infection; thus, inhibiting the activity of these factors is one of the effective means for the prevention and treatment of Candida infections. Hyphal formation is a key component of the virulence factors of C. albicans [55].

Figure 2.

Different traditional Chinese medicines can directly inhibit the growth of fungi through various mechanisms: Sanguinarine can affect the formation of hyphae [47]; Dihydroartemisinin can damage the cell membrane of C. albicans; Paeoniflorin can damage the cell wall of C. albicans [50]; Tetrandrine can affect the biofilm of C. albicans [48]; Sophora flavescens can affect the microecological balance [53].

Coptis chinensis has antifungal effects against C. albicans and is a common TCM for treating OPC caused by Candida infections [56]. It appears most frequently in various prescriptions for treating OPC, and studies have shown that Coptis chinensis has a strong antifungal effect against C. albicans [56]. Coptis detoxification decoction is a well-known multi-herb formula in China, containing various bioactive secondary metabolites, primarily including alkaloids from Coptis chinensis and Phellodendron bark, flavonoids from Scutellaria baicalensis, and terpenes from Gardenia jasminoides [11]. The extract of Coptis chinensis can weaken its virulence and tissue invasion potential by intervening in the morphological transition process of C. albicans [46]. Observations under inverted microscopy, fluorescence microscopy, and scanning electron microscopy revealed that after the effective drug concentration of Coptis detoxification decoction acted on the biofilm, most observed morphologies were yeast cells, indicating its ability to inhibit hyphal formation [46]. Further qRT-PCR results showed that Coptis extract could downregulate the expression of hyphal-related genes such as HWP1, ALS3, SUN41, and UME6, maintaining the cells in the yeast form and making it difficult to transition to the hyphal form, thereby reducing the invasive ability of C. albicans [46].

Moreover, the transition between the yeast and hyphal forms involves multiple interconnected signalling pathways. The Cph1-mediated MAPK pathway and the Efg1-mediated cAMP/PKA pathway are the two most clearly defined signalling pathways in the morphological transition mechanism of C. albicans [57]. The cAMP/PKA pathway plays the most significant role. Its core component is Cyr1, the only adenylate cyclase that catalysers cAMP synthesis in C. albicans [57]. When cAMP levels increase, cAMP binds to the regulatory subunit Bcy1, releasing its inhibition and thereby activating the two catalytic subunits of PKA, Tpk1 and Tpk2 [57]. Both catalytic subunits act on the transcription factor Efg1, which binds to the promoters of hyphal-specific genes, upregulating their expression and inducing hyphal formation [57].

Sanguinarine (SAN) is a phenanthrene alkaloid with broad pharmacological activities, including antitumor, antibacterial, anti-inflammatory, and anti-angiogenic effects [58]. To investigate the effect of SAN on hyphal formation, C. albicans cells were incubated under hyphae-inducing conditions in various fungal culture media [59]. C. albicans formed hyphae in all fungal culture media, whereas hyphal formation was inhibited in all media supplemented with SAN, with all C. albicans cells remaining in the yeast form (Figure 2). RT-PCR results showed that after SAN treatment, the expression of ALS3, HWP1, ECE1, HGC1, and CYR1 – genes related to the cAMP/PKA pathway – was downregulated [59]. Because of this downregulation of cAMP/PKA pathway-related genes after SAN treatment, researchers conducted further experiments and found that adding cAMP could rescue the morphological defects caused by SAN, further demonstrating SAN's ability to downregulate endogenous cAMP levels [59].

The destruction of fungal cell membranes by traditional Chinese medicine

Cell membranes are crucial for various biological functions, with ergosterol as the main component. When fungi are subjected to certain harmful stimuli, the damage to their structure and function can lead to the leakage of intracellular substances and hinder physiological metabolism, ultimately resulting in cell death [60]. Research has found that dihydroartemisinin can inhibit fungal activity by disrupting the integrity of fungal cell membranes, while also reducing their invasiveness and virulence [61,62]. Further studies revealed that the inhibitory effect of dihydroartemisinin on C. albicans may be due to its ability to damage and deform the cell wall and cell membrane, causing cytoplasmic aggregation and damage or dissolution of organelles [63]. Dihydroartemisinin damages the fungal cell membrane and its integrity by reducing the precursor substances of ergosterol or blocking its synthesis pathway (Figure 2). The herbal formula of Cao Huang Gui Xiang has been empirically used to treat Candida infections [49]. To explore the antifungal mechanism of Cao Huang Gui Xiang, flow cytometry and microscopy analyses were conducted to examine its effects on cell membrane integrity [49]. The results indicated that Cao Huang Gui Xiang may impair membrane integrity, thereby exerting an inhibitory effect on fungi.

The destruction of fungal cell walls by traditional Chinese medicine

Fungal cell walls are mainly composed of polysaccharides and proteins, which help maintain the integrity of the fungal body, balance internal and external pressures, provide a surface for interaction with the host, and play an important role in fungal adhesion and biofilm formation [64]. Once the cell wall is damaged, its original barrier function is compromised, leading to significant changes in the permeability of fungal cells, which may subsequently cause the cell wall to rupture [65]. The cell wall contains glycoproteins and abundant carbohydrates, primarily glucans, mannans, and chitin [66]. Research has shown that after the application of peony ethanol extract to C. albicans, the integrity of the cell wall is compromised [50]. Further measurements revealed that the peony ethanol extract can reduce the activity of (1,3)-β-D-glucan synthase, inhibiting cell wall synthesis, resulting in abnormal cell wall structure and impaired function in C. albicans, thereby inhibiting its growth (Figure 2). Additionally, a perennial herb, Houttuynia cordata, contains sodium houttuyfonate, which is not only stable in nature but also has anti-inflammatory and detoxifying activities [67]. It can also induce the reconstruction of fungal cell walls by exposing β-1,3-glucan and chitin, thereby providing resistance against C. albicans [68].

The impact of traditional Chinese medicine on biofilms

Components of traditional Chinese medicine have been found to hinder the formation of Candida biofilms, which are crucial for antifungal treatment and immune evasion [69]. Among the important small molecules with therapeutic effects on candidiasis, honokiol and magnolol are key active components of magnolia, a traditional Chinese medicinal plant. Both honokiol and magnolol can inhibit the formation and adhesion of C. albicans biofilms [51]. Additionally, honokiol can damage the cell membrane of C. albicans, leading to the leakage of intracellular contents and swelling of the cell wall.

Adhesion is the first step in the formation of biofilms and the generation of pathogenicity by C. albicans, and its adhesion ability is positively correlated with cell surface hydrophobicity (GSH). For example, paeoniflorin exhibits inhibitory effects against C. albicans, and research shows that paeoniflorin can significantly inhibit cell adhesion function by affecting GSH [52]. Further studies have found that genes related to controlling cell surface hydrophobicity are associated with the cAMP pathway. These active components of traditional Chinese medicine can achieve their inhibitory function on C. albicans adhesion by suppressing the expression of some adhesion and specificity essential genes related to the cAMP pathway. Additionally, data from studies indicate that tetrandrine (TET) can inhibit biofilm formation by reducing adhesion and morphological transformation, rather than inhibiting the growth of C. albicans [48]. In-depth exploration of TET's mechanism of action on C. albicans biofilms reveals that TET not only reduces GSH but also inhibits the growth of C. albicans at high concentrations and suppresses the morphological transition from yeast to hyphae (Figure 2). Therefore, the anti-biofilm effect of TET seems to be attributed to its anti-adhesion and anti-morphological transformation activities. Furthermore, RT-PCR results show that after TET treatment, several important hyphal and adhesion-related genes are downregulated. We further discovered that many of the downregulated genes after TET treatment, including HWP1, ALS3, ECE1, and HGC1, are regulated by the Ras/cAMP pathway [70], and exogenous cAMP can restore the morphological transition of C. albicans under TET exposure conditions. These results suggest that TET may inhibit filamentous cell growth by downregulating the Ras/cAMP pathway.

The impact of traditional Chinese medicine on the ecological balance of the oral and pharyngeal microbiome

In the oral cavity, the microbiome not only participates in physiological processes such as digestion and metabolism but is also closely related to oral health. When the microbiome is imbalanced, such as excessive proliferation of C. albicans, it may trigger oral diseases like oropharyngeal candidiasis. Therefore, maintaining the homoeostasis of the microbiome and strengthening host defence mechanisms is an important strategy for preventing Candida-related infections and ensuring human health.

The active components in TCM can regulate the balance of the microbiome. By inhibiting the growth of harmful bacteria (such as C. albicans) and promoting the proliferation of beneficial bacteria, they restore the microecological balance in the oral cavity. Some components in TCM also have antifungal effects, which can directly inhibit the growth and reproduction of C. albicans. By inhibiting the growth of Candida, the amount of Candida in the oral cavity can be reduced, thereby alleviating the symptoms of oropharyngeal candidiasis. In addition, there is a close interaction between the microbiome and the host's immune system. Some components in TCM can regulate the function of the immune system and enhance the host's resistance to C. albicans. By regulating the immune response, TCM can enhance the host's clearance ability of Candida, thereby accelerating the recovery of the disease.

There is a very typical active ingredient of traditional Chinese medicine, namely berberine in Coptis chinensis [71]. Currently, various studies have shown that it plays a representative role in regulating the microbiome for the treatment of OPC. Firstly, berberine can directly combat C. albicans infection by destroying the cell membrane and cell wall and inhibiting virulence factors [72]. Berberine can also increase the proportion of probiotics in the oral cavity, promote the growth of beneficial bacteria such as salivary lysozyme, and reduce bacteria that have a synergistic effect with C. albicans, such as Staphylococcus aureus [73]. In addition, berberine can regulate immunity, such as enhancing the defence of oral epithelial cells and reducing inflammatory damage [74].

Apart from berberine, Sophora flavescens and its active ingredient matrine, as well as Lonicera japonica and its active ingredient chlorogenic acid, can treat OPC by regulating the ecological balance of the oral pharyngeal microbiome [53] (Figure 2). Matrine promotes microbial group remodelling, increases the proportion of Actinobacteria, reduces the number of Proteobacteria, and enhances the inhibitory effect of oral symbiotic bacteria Streptococcus sanguinis on C. albicans [53].Chlorogenic acid inhibits the farnesol-mediated quorum sensing system of C. albicans [54]. Farnesol, a quorum sensing molecule produced by C albicans, can block the transition from yeast to hyphal form, biofilm formation, and other virulence factors, thereby regulating fungal virulence expression [57]. It can also reduce the levels of IL-17 and IL-23, and alleviate the inflammatory response caused by C. albicans [75].

The regulatory effect of traditional Chinese medicine on immune response after C. albicans infection.

When infected with oral candidiasis (OPC), the body defends against C. albicans infection through both innate and adaptive immunity, and the efficacy of traditional Chinese medicine in treating OPC may stem from its ability to modulate the host's immune system. Inflammation is a significant aspect of the immune response to OPC, and herbal medicine typically possesses anti-inflammatory properties.

The enhancing effect of traditional Chinese medicine on local immune response

The phagocytic action of innate immune cells is one of the most effective barriers to prevent the proliferation and spread of microorganisms within the host. Macrophages and neutrophils are innate immune cells that play a key role in host defence by phagocytosing and destroying C. albicans cells.

San Huang Decoction is composed of three traditional Chinese medicines: Huanglian, Huangqin, and Dahuang [76]. The compound San Huang Decoction is a clinical formula, and preliminary laboratory work based on the San Huang Decoction for clearing damp-heat removed Dahuang and added Huangbai, resulting in a compound San Huang Decoction with better anti-C. albicans effects [77]. The compound San Huang Decoction was extracted through ethanol reflux and concentrated under reduced pressure to obtain a paste. After re-dissolving in water, it was extracted with ethyl acetate and then subjected to silica gel column chromatography (petroleum ether: ethyl acetate as the elution system). The petroleum ether: ethyl acetate−3:1 layer (BWM-7) obtained showed the best antibacterial activity. In an experiment on the effect of BWM-7 on C. albicans, researchers found through macrophage phagocytosis experiments that BWM-7 can enhance the ability of macrophages to phagocytose C. albicans (Figure 3; Table 1). Western blot analysis detected the expression of inflammatory proteins NF-KB and INOS, and ELISA was used to measure the expression of inflammatory cytokines IL-2, IL-6, IL-12, and TNF-a. The experimental results indicated that after C. albicans infection, the expression levels of proteins and cytokines in macrophages significantly increased, while BWM-7 treatment reduced the inflammatory response caused by C. albicans infection in macrophages [77]. This suggests that BWM-7 not only inhibits the growth of C. albicans but also enhances the phagocytic ability of macrophages, and reduces the inflammatory response caused by C. albicans infection by regulating proteins and cytokines in macrophages, thereby achieving resistance to C. albicans and maintaining normal cellular status [77].

Figure 3.

Traditional Chinese medicine treats OPC by regulating local and systemic immunity. The herbal medicines that regulate local immunity include: BWM-7, which acts on macrophages by regulating proteins and cytokines, thereby enhancing the phagocytic ability of macrophages and reducing inflammatory responses; Genistein [78], which activate the HOG pathway through Hog1p phosphorylation and stimulate the production of the anti-inflammatory cytokine IL−10 in neutrophils, thus enhancing the body's phagocytic activity and reducing inflammation; and Huangqin, which enhances the killing activity of NK cells by activating corresponding lymphocytes. The herbal medicines that regulate systemic immunity include Kangfuxin Liquid, which increases the number of T cells to strengthen their function; it can also promote the opening of ion channels in macrophages, thereby enhancing the phagocytic action of macrophages and NK cells against pathogens; and it increases the number of neutrophils to reduce inflammatory responses.

Neutrophils are widely distributed and have the same phagocytic function as macrophages. Traditional Chinese medicine activates macrophages and neutrophils through multi-level signal transduction, enhancing their phagocytic efficacy and stimulating the release of antimicrobial peptides and cytokines, thereby triggering a series of antibacterial responses in the host. Various traditional Chinese medicines can act on immune cells, such as Zhimu, Mudanpi, and Huangqin, which can enhance the phagocytic action of neutrophils against C. albicans [78]. Among them, the Genistein can phosphorylate Hog1p in C. albicans [78], thereby activating the high osmolarity glycerol (HOG) pathway, stimulating the production of the anti-inflammatory cytokine IL-10, and enhancing the body's phagocytic activity. It can also effectively regulate the levels of anti-inflammatory cytokines, helping to balance the immune response and reduce tissue damage (Figure 3). Research has found that a natural compound antibacterial spray made from extracts of Huangqin, Tianma protein concentrate, along with extracts from Dendrobium and other herbs, has a significant inhibitory effect on C. albicans [11]. The rich active components in Huangqin can enhance both specific and non-specific immunity [79]. The main component of Huangqin that exerts an immune-enhancing effect is baicalin, which activates the immune system and acts on the systemic immune response [46]. According to related studies, Huangqin can enhance the killing activity of NK cells in the spleen by activating corresponding lymphocytes, thereby mobilising the specific immune system (Table 1; Figure 3).

The regulatory effect of traditional Chinese medicine on the systemic immune system

Traditional Chinese medicine formulations contain a rich variety of substances, leading to a wide range of pharmacological effects. They can simultaneously inhibit bacteria, fungi, and viruses, relieve pain, improve local microcirculation, and enhance the body's immunity, while also being less likely to produce drug resistance and having minimal adverse reactions, allowing for long-term use.

Kangfuxin Liquid, a pure traditional Chinese medicine formulation containing various active ingredients such as amino acids, animal fats, polyols, and proteins, has been shown in studies to significantly regulate the adaptive immune response of T cells and B cells, thereby enhancing the body's antifungal immune capacity [80]. The special polyols and antimicrobial peptides contained in it can modulate the immune function, improve the immune status of the body, promote the proliferation of mucosal capillaries, improve local blood circulation, facilitate the growth of new tissues and the regeneration of tissue cells, and accelerate the repair of wound tissues [80]. It can also increase the number of T cells and enhance their function; promote the opening of ion channels in macrophages, enhancing the phagocytic action of macrophages and NK cells against pathogens; increase the number of neutrophils, improve the chemotactic function of neutrophils, promote the reconstruction of wound tissues, reduce local inflammatory responses, and facilitate wound healing (Figure 3). Additionally, it can activate the immune function of nonspecific immune cells, secreting interleukins, leukotrienes, prostaglandins, and interferons, which can quickly counteract inflammation, promote the proliferation of capillaries in affected mucosa, improve microcirculation, accelerate the repair of injured tissues, and promote the generation of analgesic substances [80]. Kangfuxin Liquid contains glucosamine, which has anti-inflammatory properties and enhances the body's immune function by activating nonspecific immune cells and increasing the activity of macrophages, directly phagocytising pathogens [80]. Moreover, when macrophages are stimulated by polysaccharides from conditioned yeast, they release a large amount of oxygen free radicals, which can enter cells and kill microorganisms within them. The peptide epidermal growth factor and polyols in Kangfuxin Liquid activate the human immune system, enhance cellular immune function, increase the number of neutrophils in wound tissues, promote angiogenesis, improve microcirculation, and accelerate the repair of damaged tissues [80].

Advantages of traditional Chinese medicine in treating (OPC) compare to conventional drugs

Conventional antifungal treatments and their limitations

The conventional management of OPC predominantly involves antifungal agents such as fluconazole, itraconazole, and amphotericin B, which target fungal cell membranes or ergosterol biosynthesis pathways [2]. Fluconazole, a triazole antifungal, is widely used due to its oral bioavailability and efficacy; however, the emergence of drug-resistant Candida strains, particularly among non-albicans species like C. glabrata and C. krusei, poses significant clinical challenges [81]. Resistance mechanisms include alterations in ergosterol biosynthesis genes, efflux pump overexpression, and biofilm-associated tolerance, which reduce antifungal susceptibility [4]. Amphotericin B, though effective with a broad antifungal spectrum, is limited by poor solubility and notable nephrotoxicity, necessitating formulation improvements such as fast-dissolving films to enhance local delivery and reduce systemic side effects [82]. Itraconazole and other azoles also carry risks of hepatotoxicity and drug-drug interactions, complicating their use, especially in immunocompromised patients [5]. Long-term antifungal therapy may lead to recurrence and treatment failure, partly due to persistent biofilms and immune evasion by Candida [83]. Furthermore, systemic side effects such as gastrointestinal discomfort, hepatotoxicity, and nephrotoxicity adversely affect patient adherence [84]. The limited antifungal armamentarium, coupled with slow development of novel agents, underscores the need for alternative therapies.

Low toxicity and multi-target actions of TCM components

Traditional Chinese medicine (TCM) exhibits a distinctive advantage in treating OPC due to the inherently low toxicity of its herbal components and their multi-target mechanisms of action. Unlike single-compound pharmaceuticals, TCM formulations typically comprise complex mixtures of bioactive ingredients that act synergistically, thereby reducing the potential toxicity associated with any individual constituent. This synergistic effect not only enhances therapeutic efficacy but also mitigates adverse reactions commonly seen with conventional antifungal agents. For instance, studies have demonstrated that compounds such as berberine, a major alkaloid in Coptidis rhizoma, selectively inhibit Candida albicans by targeting the gC1qR-EGFR co-receptor pathway, which is critical for fungal invasion of oral epithelial cells, while sparing host cells from cytotoxicity [56]. This selective antifungal activity reduces collateral damage to host tissues, thereby lowering the risk of side effects. Furthermore, TCM components often modulate metabolic pathways in a mild and balanced manner, which lessens the burden on hepatic and renal systems responsible for drug metabolism and excretion [85]. This is exemplified by the use of herbal compounds that regulate immune responses and inflammatory cascades without triggering excessive systemic toxicity [86]. The multi-target nature of TCM also allows simultaneous modulation of fungal virulence factors, host immune defences, and tissue repair mechanisms, providing a comprehensive therapeutic approach that minimises the need for high-dose monotherapy and its associated toxicities. Overall, the low intrinsic toxicity of TCM constituents combined with their multi-faceted mechanisms contributes significantly to the reduced side effect profile observed in OPC treatment.

Conclusions

Traditional Chinese medicine (TCM) treatment of oral candidiasis (OPC) involves a multifaceted and holistic approach that targets not only the fungi responsible for the infection but also the host's immune responses. TCM has the remarkable ability to modulate both the stability of biofilms – complex communities of microorganisms – and the enzymatic activities of key biomolecules such as hydrolytic enzymes through a variety of intricate pathways. Additionally, TCM is particularly effective in treating infections induced by C. albicans, a common fungal pathogen, by inhibiting the activity of various virulence factors that contribute to its pathogenicity.

There exists a wide array of TCM modalities that exhibit antifungal activity, each with its own unique mechanisms of action reflecting the rich diversity of this ancient medical system. Both basic and clinical research have consistently demonstrated the impressive efficacy of these treatments, alongside a notably low propensity for inducing antifungal resistance; this underscores their significant value in modern therapeutic contexts. A thorough and systematic analysis of the antifungal mechanisms employed by TCM is necessary to accurately identify the key targets and pathways through which these treatments exert their beneficial effects. This understanding not only aids in optimising the application strategies of TCM in the management of fungal infections but also provides a robust theoretical foundation and scientific basis for effectively preventing and controlling such infections in clinical practice.

Moreover, a deeper exploration of the theoretical underpinnings of traditional Chinese medicine, along with its intricate mechanisms of action, are anticipated to foster the emergence of innovative antifungal treatment strategies. This exploration will enable healthcare practitioners to tailor more precise and individualised treatment plans for patients, thereby ushering in a new era of antifungal therapy that is both effective and aligned with the principles of holistic care.

Funding Statement

Tianming Wang is funded by National Natural Science Foundation of China (82374121). Wenfan Wei is funded by National Natural Science Foundation of China (32300020), and Natural Science Foundation of Anhui Province (2023AH050735). (Anhui Provincial Natural Science Foundation) (2023AH050735) (National Natural Foundation of China) (82374121) (1908085MH291)

Disclosure statement

No potential conflict of interest was reported by the author(s).