Enhancing therapy with nano-based delivery systems: exploring the bioactive properties and effects of apigenin

Abstract

Apigenin, a potent natural flavonoid, has emerged as a key therapeutic agent due to its multifaceted medicinal properties in combating various diseases. However, apigenin's clinical utility is greatly limited by its poor water solubility, low bioavailability and stability issues. To address these challenges, this review paper explores the innovative field of nanotechnology-based delivery systems, which have shown significant promise in improving the delivery and effectiveness of apigenin. This paper also explores the synergistic potential of co-delivering apigenin with conventional therapeutic agents. Despite the advantageous properties of these nanoformulations, critical challenges such as scalable production, regulatory approvals and comprehensive long-term safety assessments remain key hurdles in their clinical adoption which must be addressed for commercialization of apigenin-based formulations.

Plain Language Summary

Apigenin is a natural substance found in plants that might help treat illnesses like cancer, diabetes, heart problems and brain disorders. But it doesn't work very well because it doesn't dissolve in water, is hard for the body to use and isn't very stable. To fix this, scientists are putting apigenin inside tiny carriers called nanocarriers. These tiny carriers help apigenin dissolve better, be absorbed by the body more easily and work better.

There are different kinds of nanocarriers, like tiny fat bubbles, tiny solid particles and tiny gels. These can be made to target specific parts of the body, which helps reduce side effects. Apigenin can also be mixed with other medicines in these carriers to work even better.

However, there are big challenges in making these treatments widely available, like making enough of them, getting permission from health authorities and making sure they are safe for a long time. This review talks about the latest progress and future possibilities in using nanotechnology to deliver apigenin, aiming to make it better for treating diseases.

Tweetable Abstract

Unlocking Apigenin full potential: Nanotechnology steps in to overcome delivery challenges, enhancing its effectiveness for clinical use. #Apigenin #NanotechHealth #Nanomedicine

Plain language summary

Highlights.

Potential of herbal bioactives

• Includes a wide range of chemical classes such as polyphenols, alkaloids, terpenoids and flavonoids.

• Known for their antioxidant, anti-inflammatory, antimicrobial, anticancer and neuroprotective properties.

• Flavonoids help reduce oxidative stress and inflammation, potentially managing heart disease and cancer.

Potential of Apigenin

• Apigenin, a flavonoid, has significant therapeutic potential due to its antioxidant, anticancer and anti-inflammatory properties.

• It helps reduce the risk of cardiovascular diseases and treats neurodegenerative disorders.

Physicochemical properties of Apigenin

• Classified under Class II of the Biopharmaceutical Classification System.

• Partition coefficient: 2.87; water solubility: 1.35 μg/ml at 25°C.

• Molecular weight: 270.24 g/mol; melting point: 347.5°C.

Constraints in delivery of Apigenin

• Limited therapeutic efficacy due to poor bioavailability, low solubility, reduced stability and interactions with other medications.

Nanocarriers for delivery of Apigenin

• Utilized nanocarriers include liposomes, solid lipid nanoparticles, polymeric nanoparticles, nanogels and more.

• Nanocarriers improve aqueous solubility, bioavailability, stability, controlled drug release and targeting.

• Specific targeting enabled by functionalizing nanoparticle surfaces with ligands and polymers.

Co-delivery of Apigenin with other drugs

• Co-delivery offers synergistic effects, enhanced therapeutic outcomes and minimized toxic effects.

• Apigenin co-delivered with other drugs shows better therapeutic potential.

1. Introduction

Herbal bioactives, also recognized as phytochemicals or plant secondary metabolites, have recently gained significant attention for their potential health benefits and therapeutic properties [1]. These natural compounds, derived from various parts of plants such as roots, leaves, fruits and stems, have been used for centuries in traditional medicine worldwide. Encompassing a broad spectrum of chemical classes, including polyphenols, alkaloids, terpenoids, flavonoids, etc., many of these compounds are renowned for their antioxidant, anti-inflammatory, antimicrobial, anticancer and neuroprotective properties. They effectively interact with various biological targets, modulating signalling pathways and metabolic processes, thus playing a crucial role in preventing and managing chronic diseases [2]. Among them, flavonoids are naturally occurring compounds found in various fruits, vegetables and beverages like tea and red wine, have garnered particular interest for their health-promoting benefits, especially in the prevention and treatment of diseases. Flavonoids have been recognized for their antioxidant properties that can help reduce inflammation and oxidative stress, thereby contributing to the management of conditions such as heart disease and cancer [3]. Research suggests that the consumption of flavonoid-rich foods may support overall health and play a role in disease prevention and management.

This paper focuses on the bioactive plant flavonoid, apigenin, a member of the flavone subclass. Apigenin is distinguished for its enhanced therapeutic potential attributed to its various bioactive properties: antioxidant, anticancer, anti-inflammatory, antibacterial, antiviral, antidiabetic and antidepressive. It also plays a significant role in reducing the risk of cardiovascular diseases, treating neurodegenerative disorders, such as Alzheimer's disease and improve bone health [4]. However, the therapeutic efficacy of apigenin is limited due to its poor bioavailability, low solubility, reduced stability and interactions with other medications. There is ongoing research to to optimize delivery systems and dosages to maximize its therapeutic impact. Nanocarrier-based delivery systems have emerged as a promising approach to enhance the bioavailability and therapeutic efficacy of various bioactive compounds, including apigenin [5]. This study aims to thoroughly review the literature, focusing on the role of apigenin and its nano-formulations in treating and preventing various diseases.

2. Therapeutic potential of Apigenin

2.1. Antioxidant Activity

Apigenin functions as an antioxidant, effectively neutralizing singlet oxygen and peroxyl radicals. When the body absorbs oxygen, it can rapidly react with anions, producing various free radicals, including hydroxyl (OH•), superoxide (O2•−), nitric oxide (NO•), nitrogen dioxide (NO2•), peroxyl (ROO•) and lipid peroxyl (LOO•). The excessive presence of these free radicals and oxidants leads to oxidative stress (OS), a detrimental process that can cause cellular damage and disrupt normal body functions [6]. Prolonged exposure to oxidative stress can accelerate the aging process and contribute to the development of chronic diseases. Oxidants such as hydrogen peroxide, nitrates, metal ions and glutamic acid are known to cause cellular dysfunction and contribute to various diseases [7].

There has been extensive research on the beneficial effects of apigenin in combating diseases caused by OS-induced progression, including cancer, neurodegenerative disorders, cardiovascular diseases, liver injuries and diabetes mellitus. In both in vitro and in vivo studies, apigenin has been consistently shown to improve cell viability and decrease tissue damage by boosting resistance to oxidative stress inducers [8]. Apigenin's protective effects are primarily due to its ability to neutralize endogenous reactive oxygen species (ROS) and reduce malondialdehyde (MDA) levels.

2.2. Anti-inflammatory activity

Recent in vivo and in vitro studies have highlighted the anti-inflammatory properties of apigenin. In an in vitro study, apigenin reduced the injury response in LPS-stimulated RAW 264.7 macrophage cells by lowering nitric oxide (NO) levels [9]. Apigenin lowered the levels of pro-inflammatory cytokines TNF-α, IL-18 and IL-6 during this process. Additionally, it downregulated the expression of enzymes such as COX-2 and iNOS and lowered the production of intracellular ROS.

An in vivo study with mouse leukocytes showed that apigenin could inhibit the LPS-induced intracellular cell adhesion molecules (ICAMs), monocyte inflammatory protein (MIP-1α) and monocyte chemotactic protein (MCP-1α), thereby eliciting an anti-inflammatory response. Apigenin's impact on specific transcription factors and kinases, such as extracellular signal-regulated kinases (ERK), NF-κB and mitogen-activated protein kinase (MAPK), is believed to be responsible for the downregulation of these pro-inflammatory factors [10].

2.3. Anticancer activity

Apigenin is recognized for its strong inhibitory effects on the growth of various human cancer cells, including those from colon, bladder, breast, skin, prostate and liver cancers, indicating its potential for broad applications in both the prevention and treatment of cancer [11]. Apigenin's anti-cancer effects can be attributed to multiple mechanisms, such as inhibiting the NF-B pathway, deactivating of various kinases and controlling the proteasomal degradation of HER-2/neu proteins [12]. Research has shown that apigenin specifically inhibits protein kinase CK2, leading to higher cell death rates in CK2α-high acute myeloid leukemia cells compared with CK2α-low cells. Furthermore, apigenin induces cell cycle arrest and triggers apoptosis in cancer cells.

Ferroptosis, identified by Dixon et al. in 2012, is a form of cell death marked by glutathione depletion and the buildup of lipid peroxides [13]. This process includes increased endoplasmic reticulum stress, inhibition of the cystine/glutamate antiporter and activation of MAPK and mitochondrial voltage-dependent anion channels. Recent research indicates a complex relationship between ferroptosis and cancer, offering a novel approach to cancer treatment. Therefore, clinical trials are crucial to evaluate the effectiveness of ferroptosis-inducing drugs in cancer therapy. Notably, multiple studies have demonstrated that apigenin can trigger ferroptosis in cancer cells, resulting in their death. For instance, Adham et al. reported that treating the NCI-H929 multiple myeloma cell line with apigenin resulted in ferroptosis, autophagy, apoptosis and cell cycle arrest [1]. Remarkably, the cytotoxic effect of apigenin was entirely counteracted by the ferroptosis inhibitor ferrostatin-1.

In addition to its anti-cancer properties, apigenin also demonstrates anti-allergic properties, regulates blood lipids, helps in the prevention of cardiovascular diseases and serves as a natural pigment in the food industry [14].

2.4. Antibacterial & antiviral activities

Studies have demonstrated that apigenin can inhibit the growth of various bacterial strains, including both Gram-positive and Gram-negative bacteria. Its antibacterial mechanisms include disrupting the bacterial cell membrane, inhibiting nucleic acid synthesis and interfering with essential bacterial enzymes [15]. For instance, apigenin has been shown to effectively inhibit the growth of Staphylococcus aureus and Escherichia coli by inducing oxidative stress within the bacterial cells, leading to cell damage and death [16]. Additionally, its anti-inflammatory properties enhance its effectiveness by modulating the host's immune response to bacterial infection. Apigenin also has been found to inhibit several viruses, including enterovirus 71 (EV71), herpes simplex virus HSV-1 and HSV-2, hepatitis C virus, influenza virus, hand, foot and mouth disease virus and African swine fever virus (ASFV), but not coxsackievirus A16 (CAV16). EV71, a major cause of hand, foot and mouth disease (HFMD), is part of the Enterovirus genus within the Picornaviridae family. Research revealed that apigenin inhibited both the replication of EV71 in vitro and its cytopathogenic effects [17]. The inhibited processes included the production of viral polyproteins, EV71-induced cell death, the formation of intracellular reactive oxygen species (ROS) and the upregulation of cytokines. Apigenin might interfere with the function of the viral internal ribosome entry site (IRES) and prevent the activation of c-Jun N-terminal kinase (JNK), which is essential for viral replication in the presence of EV71.

3. Physicochemical properties of Apigenin

Apigenin, a bioactive plant flavonoid (4′,5,7-trihydroxyflavone), belongs to the flavone subclass. Rich natural sources of apigenin include dried flowers of chamomile, parsley, celery, thyme, oregano, olives, onions, kumquats, cherries, oranges, broccoli, tomatoes, barley, carrots and legumes [18]. Apigenin is a member of the Apium genus and family of plants. As a naturally occurring flavonoid, apigenin is recognized for its wide range of physicochemical properties. This yellow crystalline compound, with a molecular formula of C₁₅H₁₀O₅ and a molecular weight of approximately 270.24 g/mol, is sparingly soluble in water but shows better solubility in organic solvents like ethanol and dimethyl sulfoxide (DMSO). Apigenin has poor aqueous solubility of 2.35 μg/ml and high partition coefficient (log P) of 2.87. The effective permeability (P_eff) for 100 μg/ml solution of apigenin was found 0.713*10^-4 ± 0.063, 0.396*10^-4 ± 0.04, 0.302*10^-4 ± 0.02 and 0.302*10^-4 ± 0.02 cm/s in duodenum, jejunum, ileum and colon respectively which demonstrated that apigenin can be absorbed through entire intestine. The absorptive apparent permeability (P_app) was calculated as 4.5*10^-5 cm/s utilizing Caco-2 cells which advocated the proficient permeability for apigenin. Hence, the poor aqueous solubility and high permeability makes the apigenin fall under class II of Biopharmaceutics Classification System (BCS) [19]. Apigenin is characterized by its low melting point, around 347°C, making it suitable for various laboratory applications. Its UV-Vis absorption spectrum, displaying peaks around 269 and 334 nm, is crucial for detection and quantification [4]. The basic carbon skeleton of APG consists of a flavan nucleus, which has a flavanol structure (C6-C3-C6) with 15 carbons grouped in two aromatic rings (named as rings A and B) and linked by a heterocyclic ring C (a 3-carbon bridge). The molecule also features three hydroxyl groups located at positions 5 and 7 on the chromone (C6-C3 ring system) and 4′ on ring B, plus an oxo group at position 4 on the chromone system, as illustrated in Figure 1 [20].

Figure 1.

Molecular structure of apigenin, highlighting its functional groups and aromatic rings.

In the human body, flavonoids such as apigenin undergo extensive metabolism, leading to various conjugates like sulphates, methylates, and/or glucuronides entering the bloodstream. These compounds' increased permeability and reduced water solubility allow them to easily cross the host organism's plasma membrane. However, the lipophilic nature of apigenin makes it susceptible to degradation in the acidic environment of the digestive tract, restricting its potential use in pharmaceuticals and functional foods. These physicochemical properties, coupled with its antioxidant and anti-inflammatory attributes, make apigenin a valuable compound for both research and potential therapeutic applications [21]. Furthermore, the advent of nanotechnology has facilitated the development of targeted drug delivery systems, specifically focusing on tumor-specific tissues.

4. Challenges with Apigenin

Apigenin's classification within the BCS is challenging due to its low aqueous solubility, which significantly impacts its bioavailability and stability. Its relatively low aqueous solubility, place it in Class II (low solubility, high permeability). Studies have shown that apigenin is poorly soluble in both fat and water, with solubility levels of 2.35 μg/ml in water and 0.001–1.63 mg/ml in non-polar solvents [22]. Although it is generally considered highly permeable, this limited solubility can impede its dissolution in the gastrointestinal tract, potentially affecting its bioavailability. This low solubility can result in limited bioavailability, as the compound may not effectively enter the bloodstream to exert its therapeutic effects.

Additionally, apigenin can undergo rapid metabolism in the liver (first-pass metabolism effect), which further reduces its bioavailability [23]. Moreover, its extensive first-pass metabolism significantly diminishes the amount of apigenin reaching systemic circulation. The bioavailability of apigenin can vary depending on several factors, such as its source, formulation and mode of administration [24]. Studies have reported that apigenin has relatively low oral bioavailability due to its limited solubility and potential degradation in the GI tract [25]. Apigenin's effectiveness as a bioactive substance is influenced by several factors, including its molecular structure, digestibility, presence in the food matrix, bioaccessibility and the availability of transporters and metabolizing enzymes [26].

Furthermore, the stability of apigenin is significantly compromised in the presence of iron (Fe) and copper (Cu), especially when exposed to temperatures of 37°C [27]. This decline in stability is quite pronounced and further research indicates that apigenin's biological activity, which includes apoptosis induction, generation of intracellular ROS, DNA damage and growth inhibiting, is significantly reduced following heat treatments at temperatures of 37°C and 100°C, or with the addition of Fe/Cu. The most substantial decrease in apigenin's biological activity is observed after exposure to high temperatures, particularly those exceeding 100°C. To address these challenges, researchers have been exploring the application of nanotechnology-based delivery systems, such as nanoparticles, liposomes, polymeric micelles and carbon nanotubes to enhance apigenin's solubility and protect it from metabolism, thereby potentially improving its therapeutic efficacy.

5. Nanotechnology-based drug delivery systems

The majority of herbal bioactives faces challenges in realizing their pharmacological potential due to limited aqueous solubility, low permeability, rapid metabolism and poor absorption in the gastrointestinal tract. These limitations have significantly hindered the clinical utility of herbal bioactives. As a result, there is an urgent need to explore innovative technologies or delivery systems to enhance the aqueous solubility and permeability which ensure the improved bioavailability of these compounds [28].

Nanotechnology-based delivery systems have emerged as a promising solution to improve the bioavailability and therapeutic efficacy of various bioactive compounds, including apigenin. Research studies has shown that nanocarriers are an effective and widely adopted strategy to for increasing the dissolution rate and permeability of various drugs owing to their nano size [29]. Nanocarriers, including liposomes, micelles, nanoparticles and nanogels, offer a versatile platform for encapsulating apigenin, protecting it from degradation and improving its solubility and permeability resulting in improved bioavailability [30]. These nanocarriers are designed to release apigenin in a controlled manner, ensuring prolonged medicinal benefits. Furthermore, their small size enables them to overcome various biological barriers, allowing for efficient drug delivery to target tissues.

The use of nanocarrier-based delivery systems for apigenin flavonoids presents several advantages [31,32]. First, they increase the aqueous solubility as well as permeability of apigenin, ensuring improved absorption and bioavailability upon administration. Second, they protect apigenin from degradation due to light, heat, or enzymatic processes, thereby preserving its therapeutic efficacy. Third, nanocarriers can be functionalized with ligands or antibodies, enabling targeted delivery to specific cells or tissues, minimizing off-target effects and reducing systemic toxicity. Additionally, these nanocarrier systems can be tailored for different routes of administration, such as oral, intravenous, or topical, increasing the flexibility and versatility of apigenin delivery (Figure 2).

Figure 2.

Advantages of nanocarriers for delivery of apigenin into the body.

Overall, the nanocarrier-based delivery systems for apigenin hold significant potential in revolutionizing the field of drug delivery, ensuring the effective and targeted delivery of this potent natural compound for diverse therapeutic applications. Nanomedicine platforms such as nanoparticles, liposomes and micelles are critical in overcoming apigenin intrinsic problems, which include poor aqueous solubility and quick degradation. These delivery systems not only shield apigenin from enzymatic breakdown and premature metabolism, but also allow for targeted administration to specific tissues or cells. For example, nanoparticle-based formulations can take advantage of tumors increased permeability and retention (EPR) effect, boosting apigenin accumulation at the target site while limiting systemic toxicity. By encapsulating apigenin in nanocarriers, the pharmacokinetic properties of the apigenin can be finely adjusted. This includes increasing circulation time, improving cellular absorption and fostering sustained release kinetics. Such alterations are critical for sustaining therapeutic concentrations of apigenin over time, maximizing its efficacy in chronic diseases. One of the primary benefits of nanomedicine is the ability to establish controlled release kinetics of apigenin. This capability enables exact control of medication release rates, which can be customized to match certain biological rhythms or illness development patterns. Controlled release formulations not only increase therapeutic efficacy but also improve patient compliance by reducing the frequency of dose. Furthermore, nanotechnology allows for the simultaneous administration of apigenin and other therapeutic agents, such as chemotherapeutic medicines or immunomodulators. This synergistic approach can improve therapeutic outcomes by addressing various pathways involved in disease progression or overcoming medication resistance mechanisms. The capacity to build multifunctional nanocarriers capable of transporting various payloads emphasizes the versatility and potential of apigenin nanomedicines in personalized medicine methods. While preclinical investigations have yielded encouraging results, bringing apigenin nanomedicines into clinical practice requires addressing crucial issues such as scalability, repeatability and safety. Furthermore, streamlining manufacturing processes and maintaining regulatory compliance are critical elements in clinical translation. To effectively progress apigenin nanomedicines from bench to bedside, researchers, doctors and the pharmaceutical industry must work together.

5.1. Liposomes

Liposomes have emerged as a promising drug delivery system for herbal bioactives such as apigenin, due to their wide range of beneficial properties. These properties include their ability to encapsulate high doses of drugs, the ability to carry both hydrophilic and hydrophobic drugs, extended drug circulation time in the body, biodegradability, compatibility with biological systems, enhanced durability, minimal side effects, precise control over drug release, improved drug solubility, targeted drug delivery to specific cells, ease of production and adaptability [33]. Moreover, the liposomes can be coated using polyethylene glycol (PEG) to extend the circulation half-life while reducing clearance [34]. The significance of liposomes to deliver apigenin is evident by various researches in which delivery and therapeutic efficiency of apigenin was improved in the treatment of various indications. For example, Xin Jin et al. combined two potent chemotherapeutic agents—liposomal apigenin and tyroservatide— for the treatment of lung cancer. They concluded that apigenin could be delivered more effectively to tumor cells both in vitro and in vivo when combined with tocopherol derivative-containing D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) liposomes. Importantly, in vivo data demonstrated that tyroservatide and apigenin TPGS liposomes had inhibitory effects on tumor growth in mice carrying A549 cells [35]. Stealth liposomes were fabricated by Shetti et al. to improve the delivery and therapeutic efficiency of apigenin in cancer. The optimized formulation exhibited reduced particle size, greatest entrapment efficiency and increased drug release at 2 days. The result outcomes of in vivo testing predicted enhanced bioavailability and improved anticancer activity of apigenin in form of stealth liposomes than free solution. In addition, the apigenin in stealth liposomes exhibited prolonged exposure time than free solution of apigenin [36].

The findings of apigenin loaded liposomes predicted improved bioavailability, stability, enhanced cellular uptake and decreased adverse effects resulting in improved therapeutic efficiency in various diseases. In addition, apigenin loaded liposomes can be targeted to cancerous site using conjugation with various ligands like folic acid, hyaluronic acid, aptamers etc. which binds to overexpressed receptors present at the surface of cancer cells [37]. The results of preclinical studies are in favour of liposomes to deliver apigenin but clinical studies are required for their applicability in the treatment of various diseases.

Transferosomes are a second group of liposomes, characterized by their improved membrane flexibility, ultra-deformability and soft nature. The flexible nature of transferosomes enables deformation of them resulting in enhanced skin permeation of entrapped molecules [38]. They consist edge activator or penetration enhancers like span, tween and sodium deoxycholate in their composition which provide deformation of their structure [39]. Transferosomes can be combined with phytochemicals to improve the bioavailability and site-specific delivery of these compounds through the skin [40]. As an example, Jangdey and his colleagues explored the effectiveness of apigenin-loaded transferosomes in treating skin cancer. These transferosomes were prepared using Tween 80 and phosphatidylcholine via a rotary evaporation sonication method. The optimized transferosomes exhibited particle size, drug loading and encapsulation efficiency of 35.41 nm, 8.042% and 84.28% respectively. The in vitro drug release for optimized transferosomes was 61.20% in 24 h while 10–15% apigenin was released in first 2 h predicting the sustained release pattern of the transferosomes. The optimized formulation demonstrated a flux of 6.68 ± 0.46 μg/cm²/h and a drug retention percentage of 0.79 ± 0.05, both higher than the parameters observed for the apigenin suspension and marketed product. The study revealed that apigenin permeation from optimized transferosomes through mouse skin was significantly higher than from both an apigenin suspension and a commercial product [41]. Transferosomes can be effectively fabricated to enhance the delivery and therapeutic efficacy of various drugs including herbal bioactives to treat skin problems including cancer.

Third group of liposomes, Ethosomes (ETs) are another vesicular carriers which facilitate the improved bioavailability of the drugs through skin due to the presence of high concentrations of ethanol, along with phosphatidylcholine and water [42]. The combination of phosphatidylcholines and ethanol in ETs facilitates the opening of pores in the stratum corneum, resulting in increased skin permeation properties [43].They are known for their extended stability, enhanced softness, improved solubility of lipophilic drugs and transport of drugs through the deeper layers of the skin resulting in improving drug availability [44]. Shen et al. conducted research on the potential of apigenin-loaded ETs in treating UVB-induced skin inflammation. The ETs were developed using Lipoid S75 as the phospholipid and a combination of ethanol and propylene glycol as the alcohol component, employing sonication. The optimized apigenin loaded ETs had reduced vesicle size and high zeta potential of 67.09 ± 4.10 nm and 19.30 ± 0.89 mv respectively. The formulation had high entrapment efficiency from 91.22 ± 6.38 %. The study found that the optimized ETs showed 0.176 ± 0.010 μg/cm² skin deposition on in vivo study at 2 h and 0.188 ± 0.051 μg/cm² skin deposition on in vitro study at 12 h which was higher than liposomes and deformable liposomes. The study's findings on the effects on UVB-induced skin inflammation showed the highest inhibition of COX-2 levels, which were induced by UVB exposure, in the group treated with optimized ETs [45]. In another study, transethosomal gel of apigenin was formulated by Adnan et al. to enhance its delivery and therapeutic efficacy in the treatment of skin cancer. Transethosomes were prepared using span 80 by the thin hydration technique. The optimized formulation exhibited vesicle size of 108.75 ± 2.31 nm along with entrapment efficiency of 78.75 ± 3.14 %. The formulation released 92.25 ± 3.5 % apigenin which was only 53.40 ± 3.10 % for conventional gel on in vitro testing. The findings of ex vivo studies revealed 86.20 ± 3.60 % permeation of apigenin from transethosomal gel while it was only 51.20 ± 3.20 % for conventional gel after 24 h. Furthermore, optimized formulation showed improved reduction in viability of HaCat cells than conventional gel along with without affecting the normal cells. Based on the findings of these studies, ethosomes based formulations would be a better approach to deliver various herbal bioactives for various skin disorders including skin cancer [46].

Another latest group of liposomes, Bilosomes (BILs) are an innovative, nano-sized variant of liposomes, incorporating bile salts alongside lipids and non-ionic surfactants in their composition. The inclusion of bile salts enhances their stability, protecting the encapsulated molecules from the harsh gastric environment [47]. In BILs, bile salts function as both solubilizing and permeation-enhancing agents, thereby improving the absorption of the entrapped drugs [48]. As compared with other delivery systems, BILs provided superior intestinal permeation. BILs have been utilized for delivering various phytochemicals, including apigenin, piperine, lycopene and epigallocatechin-3-gallate, in the treatment of different diseases [49]. The potential of BILs to deliver apigenin was studied by Zafar along with his colleagues in which BILs of apigenin were prepared using cholesterol, span-80 and sodium deoxycholate through the thin-film hydration method followed by ultrasonication in the treatment of type-II diabetes mellitus. The optimized formulation of apigenin-loaded BILs (APG-BIL) demonstrated 4.49 and 4.67-times greater permeation and area under the curve (AUC) compared with free apigenin. This increased effectiveness could be attributed to the nano size of APG-BIL and the avoidance of hepatic metabolism. APG-BIL showed enhanced hypoglycemic activity, as evidenced by a reduction in blood glucose levels up to 12 hours after administration, while free apigenin only reduced blood glucose levels for up to 4 hours [50]. In another study, apigenin loaded BILs were prepared followed by coating with chitosan to improve permeation and therapeutic efficiency of apigenin. Chitosan coated BILs of apigenin exhibited higher permeation through egg membrane and increased antibacterial activity than apigenin loaded BILs and pure liquid apigenin which could be due to presence of positive charge on chitosan enabling the BILs to interact with membrane having negative charge. The chitosan coated apigenin loaded BILs exhibited 1.94-fold and 2.26-fold reduced IC50 value than pure apigenin against A549 lung cell lines and MCF7 breast cancer cell lines respectively [51]. The results of these studies provide valuable insights into the potential of BILs to enhance the delivery and therapeutic efficiency of apigenin in various diseases. Additionally, these findings suggest that BILs could be effectively used to deliver other herbal bioactives that face similar biopharmaceutical challenges.

5.2. Solid lipid nanoparticles & nanostructured lipid carriers

Lipid nanoparticles (SLNs and NLCs) have attracted significant attention from researchers for efficacious delivery of various drugs including herbal bioactives due to several notable attributes, including enhanced drug solubility, minimal adverse effects and improved drug bioavailability, the ability to encapsulate both hydrophilic and hydrophobic drugs, increased stability, specificity and the potential for large-scale production [52]. Distinguishing features of SLNs include their biodegradability and biocompatibility, making them a safer alternative to other nanocarriers like polymeric nanoparticles. Additionally, their small size (less than 400 nm), ease of functionalization, chemical and mechanical integrity and the ability to improve the distribution of lipophilic phytochemicals, make SLNs highly advantageous [53].

SLNs were fabricated by Gilani et al. for enhancing the delivery and therapeutic efficacy of apigenin in the treatment of arthritis. Glyceryl monostearate, d -α-Tocopheryl polyethylene glycol 1000 succinate were utilized to fabricate the SLNs of apigenin by sonication technique. The prepared SLNs were coated with chitosan and found to have particle size and zeta potential of 185.4 nm and 0.45 + 26.7 mV respectively. Chitosan coated SLNs of apigenin demonstrated biphasic drug release in which quick release elicited in 2 h followed by sustained release up to 12 h. Plain SLNs of apigenin provided 73.32 ± 2.6% release of apigenin whereas chitosan coated SLNs of apigenin provided 61.81 ± 3.4% release which could be due to hindrance in the desorption and diffusion of apigenin by the chitosan. The permeation flux of apigenin dispersion, SLNs of apigenin and chitosan coated SLNs of apigenin was 11.24 ± 1.1, 20.34 ± 2.3 and 29.36 ± 1.9 μg/cm2/h respectively. The high permeation flux of chitosan coated SLNs could be due to the presence of chitosan which aids in opening of the tight junctions and also enables the paracellular absorption of the apigenin via intestine. The findings of anti-arthritic activity demonstrated noteworthy reduction in IL-1β and TNF-α levels (130.04 ± 10.51 and 61.73 ± 6.83) by chitosan coated SLNs of apigenin than arthritic group having IL-1β and TNF-α levels of 193.2 ± 16.27 and 138.19 ± 12.19 and group treated with apigenin dispersion (157.26 ± 12.66 and 102.83 ± 8.04). The improved therapeutic efficacy of chitosan coated SLNs of apigenin could be attributed to the nanometric size, increased solubility of apigenin in surfactant and the presence of chitosan on the surface of SLNs [54]. These findings have suggested that SLNs can be utilized as effective carrier for various herbal bioactives to improve their therapeutic potential in the treatment of various diseases. However, SLNs have certain drawbacks that need to be addressed, such as inadequate drug loading capacity, drug ejection, an increased risk of polymorphic transitions and unpredictable agglomeration [28].

In response to the limitations of SLNs, Nanostructured Lipid Carriers (NLCs) have been developed as advanced drug carriers, demonstrating proven efficacy in the treatment of various diseases like cancer. The versatility of NLCs as drug carriers arises from their unique features, including enhanced drug encapsulation capacity, extended chemical and physical stability of the encapsulated drug, enhanced bioavailability, along with the potential for surface modifications and targeted delivery [55]. Lipophilic bioactive compounds are more soluble in liquid lipid matrices compared with solid lipid matrices [56]. As a result, increasing the amount of liquid lipids leads to higher drug loading, better encapsulation efficiency and the creation of lattice defects. NLCs provide benefits in pharmacokinetics, stability and bioactive substance adhesion due to their exceptional stability, high encapsulation efficiency and substantial drug-loading capacity. NLCs incorporate both liquid and solid lipids in their structure, creating imperfections in the lipid matrix. These imperfections are essential for preventing drug leakage during long-term storage, thereby enhancing drug loading. The coexistence of both liquid and solid lipids in NLCs allows for a greater drug capacity compared with using either solid or liquid lipids alone [57].

Wang et al. demonstrated the efficiency of NLCs to deliver apigenin in the treatment of non-small-cell lung cancer (NSCLC). The NLCs of apigenin were prepared using glyceryl triacetate, glyceryl monostearate and poloxamer 188 by melt sonication technique. The NLCs had particle size, drug loading and entrapment efficiency of 50 nm, 4.22 ± 0.13% and 88.22 ± 1.61% respectively. The results of in vitro drug dissolution displayed quick release of 28.38 ± 0.61% in initial 4 h followed by sustained release of 47.73 ± 1.17% apigenin in 24 h. The rate of haemolysis for both apigenin loaded NLCs and plain NLCs was observed less than 5% which reveals the safety of NLCs. Additionally, apigenin loaded NLCs demonstrated a higher capacity than plain apigenin to impede NCI-H1299 cell growth, migration and invasion [58]. Hyaluronic acid conjugated NLCs (HA-APG-NLCs) were prepared by Mahmoudi et al. to improve the delivery and therapeutic efficacy of apigenin in NSCLC. The optimized formulation exhibited particle size and entrapment efficiency of 89 nm and 70% respectively. Cell viability results demonstrated 1.5-fold reduced IC50 value for HA-APG-NLCs than APG-NLCs which could be due to the increased intracellular deposition of apigenin by binding of hyaluronic acid with Nrf2 overexpressed at the surface of cancer cells and nanometric size of the NLCs particles. Furthermore, real-time PCR analysis of gene expression revealed that treatment of A549 cells with HA-APG-NLCs led to a substantial drop in Nrf2, MRP2, HO-1 and Bcl-2, as well as an increase in Bid mRNA levels in comparison to the other groups [59]. Research by Ding et al. on the production and in vitro testing of apigenin-loaded NLCs, revealed that the optimal size for these particles was 46.1 nm [60]. These apigenin-NLCs demonstrated a sustained in vitro release pattern, as opposed to free apigenin, and exhibited higher tissue penetration and bioavailability than unformulated drug extracts. Due to its lipophilic nature, apigenin benefits from the lipid core of NLCs, which aids its transmembrane and chylomicron transport. Furthermore, the adhesion of NLCs to the gastrointestinal wall enhances apigenin's bioavailability by prolonging its contact with intestinal epithelial cells. These findings highlight the effectiveness of NLCs as carriers for apigenin.

5.3. Polymeric micelles

Polymeric micelles (PMs) offer several key advantages, such as improved drug solubility in aqueous environments, excellent biocompatibility, enhanced permeability, loading of hydrophilic and hydrophobic drugs, consistent drug release profile and reduced toxicity [61,62]. While typically smaller in size than liposomes, ranging from 10 to 80 nm, micelles have a shorter circulation period but excel in tumor targeting due to the Enhanced Permeability and Retention (EPR) effect [63].

The efficacy of PMs to improve the solubility and bioavailability of apigenin was evaluated by Zhai et al. in their study. PMs were prepared using Solutol HS 15 and Pluronic P123 by a thin-film dispersion technique. The prepared PMs had average size, zeta potential and PDI of 16.9 nm, -5.87 mV and 0.046 respectively. The size less than 200 nm may decrease reticuloendothelial system (RES) uptake and effectively enable passive tumor targeting through enhanced EPR effects. The formulation exhibited burst release in initial 1 h followed by sustained release of apigenin. The inhibition rates of apigenin loaded PMs on HepG2 and MCF-7 were greater than those of apigenin DMSO solution. This could be attributed to the improved uptake of apigenin-loaded micelles by the cells, as well as the enhanced solubility of the poorly soluble apigenin in micelle solution. Apigenin loaded PMs and apigenin DMSO solution had IC50 value of 5.57 μg/ml and 20.19 μg/ml toward HepG2 cell lines and these value against MCF-7 cell lines were 3.75 μg/ml and 16.62 μg/ml respectively [64]. The selectivity and efficacy of PMs are further increased by the addition of various functional groups [65]. For instance, Munyendo et al. demonstrated that the loading of apigenin in TPGS modified mixed micelles exhibit improved stability for 90 days and 2.4-times greater absorption through intestine than pure apigenin dispersion. The results of in vivo studies assessed cancer inhibition of 72.9% for TPGS modified mixed micelles and 19.5% for apigenin phospholipid complex on oral dose to tumor bearing mice [66]. These findings have provided a clue to deliver efficiently herbal bioactives in the treatment of various dreadful diseases like cancer in future.

5.4. Polymeric nanoparticles

Polymeric nanoparticles (PNPs) are distinguished by several key features, such as reduced size, an enhanced surface-to-volume ratio, biocompatibility, biodegradability, drug release in controlled and sustained manner and the ease of modifying their surface and structure [67,68]. PNPs can be made using various natural (such as chitosan, albumin, cellulose, gelatin and collagen) and synthetic (including poly(lactide-co-glycolide) [PLGA], thiolated polymethacrylic acid and polylactic acid [PLA]) polymers. Among these, PLGA is a widely accepted polymer for developing PNPs for phytochemical delivery [69].

Coating PNPs with polyethylene glycol (PEG) enhances drug circulation and prevents drug interaction with blood proteins. This PEG coating leads to increased drug half-lives in the blood and improved stability [70].

They have been extensively used for delivering phytochemicals [28] which can be shown in a research conducted by Ganguly et al. In this research, galactose (GAL) conjugated apigenin loaded PLGA NPs (GAL-APG-PLGA NPs) were developed to achieve target ability of apigenin in liver cancer. GAL-APG-PLGA NPs had significantly higher cellular uptake of apigenin compared with free apigenin and plain apigenin nanoparticles, resulting in markedly increased cytotoxic and apoptotic effects in HepG2 cells. It could be possible due to binding of GAL with the overexpressed receptors asialoglycoproteins in liver cancer. APG-GAL-NPs demonstrated a more pronounced protective effect against liver cancer in rats, as evidenced by a reduction in nodule development, the downregulation of matrix metalloproteinases (MMP-2 and MMP-9) and the induction of apoptosis in the liver [71]. Ramkrishna Sen conducted a study using PLGA NPs loaded with apigenin and meso-2,3-dimercaptosuccinic acid (DMSA) for treating melanoma lung metastasis. The study found that treating B16F10 cells with DMSA-APG-NPs resulted in a significant depolarization of mitochondrial transmembrane potential and increased caspase activity, compared with cells treated with APG-NPs alone. These findings suggest that DMSA-conjugated APG-NPs, when administered orally, exhibit improved bioavailability and enhanced anti-tumor and anti-metastatic properties [72]. In another study, Dutta et al. studied the potential of aptamers functionalized apigenin loaded NPs (Apt-ANPs) to alleviate colorectal cancer. The pharmacokinetic results demonstrated enhanced concentration of apigenin in plasma and colon from Apt-ANPs than pure apigenin and plain NPs of apigenin. The presence of greater amount of apigenin in plasma and colon from Apt-ANPs could be due to interaction of aptamers with overexpressed Epithelial Cell Adhesion Molecule in the colorectal cancer [73].

5.5. Hybrid nanoparticles

Hybrid nanoparticles offer a range of beneficial characteristics such as higher stability, increased drug loading, improved biocompatibility, controlled drug release, extended half-lives, increased therapeutic activity and reduced adverse effects [74]. They consist of a core made of polymers and an outer shell composed of lipid bilayers. Their unique structure allows for both passive and active drug targeting through functionalization with various ligands, such as folic acid, aptamers and mannose. Additionally, these nanoparticles can be designed to be stimuli-responsive, releasing drugs in a precise manner at specific sites. They avoid the burst release of drugs and uptake by the reticuloendothelial system (RES), which are common issues with other nanocarriers [75]. Hybrid nanoparticles have been used to encapsulate a variety of drugs, including phytochemicals [76] which can be well explained in a study by Kazmi et al. in which polymer-lipid hybrid nanoparticles containing apigenin (APG-LHPNPs) exhibited improved cytotoxicity than free apigenin against MCF-7 and MDA-MB-231 breast cancer cells as evident by IC50 values. The IC50 value for APG-LHPNPs against MCF-7 and MDA-MB-231 cells was observed 21.86 ± 2.53 μM and 30.47 ± 2.87 μM respectively which was 39.45 ± 3.37 μM and 56.27 ± 4.07 μM for plain apigenin. The improved cytotoxicity of APG-LHPNPs can be attributed to tiny particle size which offers a greater surface area for exposure to the cancer cells and controlled release of apigenin from hybrid nanoparticle matrix. In addition, APG-LHPNPs showed no toxicity against MCF-10A and 3T3 normal cells, indicating the safety profile of these nanoparticles [77]. In another study, Zafar et al. fabricated hybrid polymeric nanoparticles (APG-HPNPs) to improve the anticancer and antimicrobial activity of apigenin. The optimized APG-HPNPs had size, zeta potential and entrapment efficiency of 192.6 ± 4.2 nm, 69.35 ± 1.1% and +36.54 mV respectively along with sustained release of 61.5 ± 2.5% in 24 h. The optimized formulation demonstrated increased permeation of 220.2 ± 16.6 μg/cm² than free apigenin (60.6 ± 4.6 μg/cm²) in 6 h. The optimized formulation displayed reduced cell viability of 18.55 ± 2.76% than pure apigenin (42.11 ± 3.21%) in 48 h. In addition, optimized formulation demonstrated improved antibacterial activity than pure apigenin against B. subtilis and S. typhimurium [78]. These findings provide a new avenue for the efficacious delivery of herbal bioactives in the treatment of various diseases.

5.6. Dendrimers

A dendrimer is a nanoscale, multi-branched, star-shaped polymeric structure, akin to a tree, consisting of interior branches, a central core and various functional groups on its outer surface [79]. The external branches of dendrimers facilitate the co-delivery of multiple drugs, making them highly effective as drug carriers, particularly in cancer treatment. They are recognized for their low polydispersity index, controlled molecular weight and enhanced biocompatibility. The functional groups dendrimers' surface enables the encapsulation of different drug, which can be specifically tailored for targeting specific cancerous sites. Additionally, dendrimers enhance drug solubility in aqueous environments, improve drug stability, increase drug bioavailability, reduce adverse effects, allow for higher drug dosages and enhance overall drug effectiveness, while providing controlled and sustained drug release [80].

Dendrimers have also demonstrated successful applications in the treatment, immunotherapy and radio-immunotherapy of various types of tumor, including melanoma and squamous skin carcinoma [81]. Furthermore, they have been used in the diagnostic imaging of cancer cells, particularly in magnetic resonance imaging (MRI). Notably, gadolinium-conjugated dendrimers have enabled precise targeting and comprehensive imaging of tumors, thereby enhancing their selectivity in these applications [82]. Apigenin encapsulated G3 and G4 phosphorylated poly(amide-amine) (PAMAM) dendrimers were fabricated by Zhau et al. to elicit improved antibacterial activity toward dentine as well as remineralization of dentine. The findings demonstrated efficient release of apigenin from both G3 and G4 phosphorylated PAMAM dendrimers to cause improved antibacterial activity toward dentine. In addition, mineralization in stimulated saliva substantially blocked dentine tubules. Apigenin loaded G4 PAMAM dendrimers exhibited more remineralization of dentine than G3 PAMAM dendrimers owing to presence of more peripheral phosphate groups in G4 PAMAM dendrimers. The result outcomes of cell viability performed on L929 cells demonstrated that both G3 and G4 PAMAM dendrimers have high cell viability when the concentration is less than 3000 μg/ml. This study suggested a new treatment modality for the alleviation of dentine problems in future which are increasing at constant pace across the world [83].

5.7. Nanoemulsions

Nanoemulsions (NEs) provide several advantages, including enhanced drug solubilization, improved permeability, faster onset of action, reduced fluctuations in the volume of the gastrointestinal tract (GIT), extended shelf life, toxicological safety, encapsulation of both hydrophilic and lipophilic drugs and the potential for large-scale manufacturing [84,85]. NEs can be targeted to specific sites within the body by conjugation with molecules like antibodies [86]. Various phytochemicals, such as apigenin, piperine, emodin, quercetin, catechin and carotene, have been successfully delivered using NEs [87].

For example, nanoemulsions were fabricated by Chou et al. to improve the topical delivery of apigenin in treating skin inflammation. The NEs were produced using black soldier fly larvae (BSFL) oil, avocado (AV) oil, hyaluronic acid and d-α-tocopheryl polyethylene glycol succinate (TPGS) as polymers, employing a homogenization process followed by ultrasonication. It was observed that TPGS-conjugated NEs containing BSFL oil and AV oil showed greater stability and enhanced the antioxidant activity of apigenin. It could be due to the reduction of size of droplets by the addition of TPGS [88]. Jangdey et al. fabricated apigenin loaded nanoemulsion gel having tamarind gum as emulsifier and carbopol as gelling agent to alleviate the UV tempted skin cancer. The prepared nanoemulsion gel had good physical stability along with reduced size and great encapsulation efficiency. Confocal laser scanning microscopy (CLSM) studies displayed enhanced permeation of apigenin through skin from nanoemulsion gel than pure apigenin. In addition, nanoemulsion gel exhibited improved cytotoxicity against A341 cells while reduced toxicity for HaCaT cells. As compared with commercial formulation, the apigenin nanoemulsion gel formulation had superior penetrability throughout goat skin. Thus, the nanoemulsion based formulations for apigenin may prove productive for treating the skin cancer in future [89].

5.8. Metallic nanoparticles

Seeing the advantageous characteristics of various metals like gold, platinum, selenium and silver on health, they have been employed to develop nanoparticles termed as metallic nanoparticles [90]. Researchers are increasingly interested in metallic nanoparticles due to their low toxicity, reduced immunogenicity, biocompatibility and enhanced cellular absorption. They facilitate targeted drug delivery, improve bioavailability and solubility, reduce toxicity and enhance drug action in targeted tissues [91]. They protect therapeutic agents from degradation and enable precise delivery to specific tissues [92]. They are characterized by their large surface-to-volume ratio and the ability to modify their charge, hydrophilicity and functionality through surface chemistries. Their surfaces can be decorated with polymers to improve stability, drug loading and cellular uptake [93].

Rajendran et al. developed apigenin-encapsulated gold nanoparticles (APG-AuNPs) to evaluate their efficacy in epidermoid carcinoma cells, specifically A431 cells. The deprotonated OH group in apigenin facilitated the reduction of Au³⁺ ions, leading to the formation of AuNPs with increased stability. The study indicated that APG-AuNPs showed superior anticancer potential in both A431 and SiHa cells. Importantly, APG-AuNPs were found to be non-toxic to normal epidermoid cells, specifically HaCat cells [94]. Similarly, Ngernyuang et al. fabricated apigenin conjugated gold nanoparticles (APG-AuNPs) to provide improved efficacy of apigenin in Cholangiocarcinoma. APG-AuNPs decreased the proliferation, migration and in vitro tube formation of vascular endothelial cells and markedly inhibited the migration of KKU-M055 cells [95]. In another study, Sharifiaghdam et al. developed apigenin coated AuNPs to reduce cardiotoxicity by decreasing the apoptosis. APG-AuNPs prevented myocardial apoptosis by modifying Bax, caspase3 and Bcl-2 and reducing tissue damage brought on by doxorubicin [96]. Mohammadi et al. developed green synthesized silver nanoparticles (APG-AgNPs) which had antioxidant property up to 32 μg/ml and beyond this concentration, it showed pro-oxidant activity. These nanoparticles were safe up to concentration of 256 μg/ml in dermal fibroblast cells of human [97].

5.9. Nanogels

Nanogels are three-dimensional (3D) hydrophilic structures capable of absorbing significant amounts of water or physiological fluids. Their 3D structure allows for the encapsulation of both hydrophilic and hydrophobic drugs within their internal network, potentially protecting these drugs from degradation during storage or in blood circulation. Nanogels are characterized by biocompatibility, increased surface area, enhanced absorption, high loading capacity, ample internal space, controlled release and swelling, making them ideal for drug delivery [98]. Surface modifications can be made to nanogels to enhance their multifunctionality, targeting ability and circulation time [99].

Various herbal bioactives including apigenin has been delivered successfully using the nanogels which can be exemplified by a research in which Samadian et al. explored the potential of apigenin-entrapped nanogels in human chronic myeloid leukemia cells. These nanogels were developed using chitosan through an ultrasonication technique. The MTT assay results showed a higher IC50 value for the apigenin-entrapped nanogels compared with pure apigenin, indicating increased cytotoxicity due to the encapsulation of apigenin in the nanogel. The degree of apoptosis induced by the apigenin-loaded nanogel against K562 cell lines was greater than that caused by free apigenin, as demonstrated by flow cytometry studies at various time points [100]. The solubility and activity of apigenin was improved by Lestari et al. using nanohydrogel to enhance the antibacterial potential of apigenin. It was observed that primary amines in S-benzyl-L-cysteine (SBLC) modified nanogels had improved antibacterial activity than unmodified nanogels [101].

5.10. Silk fibroin nanostructures

Silk fibroin (SF)-based nanostructures are garnering interest for their unique properties, including high biocompatibility, biodegradability, regenerability, non-immunogenicity and structural adaptability. These nanostructures offer controlled drug release, reduced adverse effects and a decreased frequency of drug administration [102]. The amphiphilic nature of SF allows for the entrapment of both hydrophilic and lipophilic drugs through van der Waals interactions and hydrophobic interactions, respectively. Additionally, the surface of SF-based nanostructures can be functionalized with covalent bonding of drugs and attachment of ligands to enhance therapeutic efficiency [103]. Various small-sized drugs, such as anticancer drugs, gene drugs and growth factor drugs, have been successfully delivered using SF-based nanostructures.

For example, Qu et al. investigated the effectiveness of apigenin-entrapped SF (APG-SF) nanospheres in the treatment of breast cancer. The optimized APG-SF formulation exhibited particle size of 163.35 nm, zeta potential of -18.5 mV and loading of 6.20%. The efficacy of APG-SF was tested against MDA-MB-231 and 4T1 breast cancer cell lines, revealing that apigenin-loaded SF nanospheres exhibited superior cytotoxicity compared with free apigenin. The relative bioavailability of apigenin in the APG-SF formulation was 1.47-times higher than that of free apigenin. In addition, APG-SF was found safe owing to its biocompatible nature [104]. To the best of our knowledge, only this research study has been conducted to deliver the apigenin by silk fibroin nanostructures but these nanostructures provide an idea to enhance the delivery and therapeutic efficacy of apigenin in future.

5.11. Carbon nanopowders

Carbon nanopowders (CNPs) are one-dimensional carbon-based nanomaterials with a size less than 100 nm. Their intrinsic properties, including a large surface area, a flexible structure for efficient loading and interaction with cargo, increased stability, biocompatibility and the ability to selectively release drugs at specific locations due to their nanoneedle morphology, make CNPs a compelling choice for effective drug delivery [105]. CNPs have been widely used for targeted drug delivery, particularly in cancer treatment. The use of CNPs as carriers in solid dispersion (SD) formulations is expected to enhance drug solubility, as nanoparticles have proven effective in SD applications.

In his study, Ding et al. developed solid dispersions of apigenin loaded onto carbon nanopowders and demonstrated an improvement in bioavailability compared with pure apigenin, with no observed intestinal toxicity. Pharmacokinetic studies indicated that the relative bioavailability from the apigenin-loaded CNP SDs was about 1.83-times higher than that of pure apigenin and the physical mixture. Intestinal toxicity studies revealed no adverse effects, as evidenced by the unchanged mucosal structure and the presence of goblet cells across all groups [106].

The various nanocarriers employed for the effective delivery of apigenin (APG) are summarized in Supplementary Table S1.

6. Co-delivery of Apigenin with other drugs

Co-delivery, a term short for “combination delivery,” is a pharmaceutical or drug delivery strategy where two or more therapeutic agents, such as drugs, bioactive compounds, or nanoparticles, are administered simultaneously in a coordinated manner. The goal of co-delivery is to achieve synergistic or complementary effects, enhance therapeutic outcomes, minimize side effects, or tackle specific challenges associated with individual agents (Figure 3). The co-delivery of apigenin with other drugs has recently gained significant attention for its potential to create synergistic therapeutic effects.

Figure 3.

Advantages of combining nanocarriers with apigenin in therapeutic applications.

Apigenin has been extensively studied for its antioxidant, anti-inflammatory and anticancer properties. When co-delivered with conventional chemotherapeutic agents, apigenin has been shown to increase therapeutic efficacy while minimizing the drugs' adverse effects. For example, a study by Jones et al. (2019) explored the co-delivery of apigenin with curcumin and resveratrol, two other herbal compounds, focusing on neurodegenerative diseases. This combination of polyphenol compounds significantly decreased oxidative stress and neuroinflammation, suggesting a potential role in slowing the progression of Alzheimer's disease and other related conditions. The study employed a nanoemulsion-based delivery system to ensure effective drug dispersion and bioavailability. Additionally, research by Shukla and Gupta demonstrated that when apigenin was co-administered with doxorubicin, a widely used chemotherapy drug, it increased the drug's cytotoxicity against cancer cells, potentially allowing for lower doses of doxorubicin and reduced side effects [107]. Apigenin ability to modulate various cellular pathways, including those involved in drug resistance, positions it as a promising candidate for combination therapy in treating a variety of diseases, including cancer and cardiovascular disorders. This co-delivery approach opens up new possibilities for improving the efficacy of existing therapeutic regimens while minimizing the toxicity of conventional drugs.

Apigenin in combination with other drugs in the form of nanocarriers have been summarized in the Table 1.

Table 1.

Comprehensive overview of co-delivery of apigenin with other drugs in the nanoformulations, detailing nanocarrier types, particle sizes, co-delivered drug, targeted diseases and key findings.

Nanocarrier	Co-delivered drug	Particle size	Disease target	Key findings	Ref.
Liposomes	Tyroservatide	118.6 ± 8.1 nm	Lung cancer	Combination of apigenin liposomes with tyroservatide showed synergistic effect in inhibition of A549 lung cancer cell lines than apigenin liposomes and tyroservatide alone.	[108]
Liposomes	5-Fluorouracil (5-FU)	98.17 nm	Colorectal cancer	Liposomes loaded with APG and 5-FU exhibited improved cytotoxicity, increased anti-angiogenesis and higher tumor vasculature than liposomes having APG and 5-FU alone.	[109]
Chitosan NPs	DOX and cisplatin	100 nm	Hepatocellular carcinoma	Albumin-folic acid coated chitosan NPs (AP-CH-BSA-FANPs) in combination with DOX or cisplatin provided decreased IC50 value than AP-CH-BSA-FANPs) and free APG.	[37]
NLCs	Rosehip oil	<200 nm	Cancer	APG encapsulated NLCs exhibited improved cytotoxicity against A549, MCF-7 and MV4–11 cell lines without affecting MCF-10A healthy cells.	[110]
Liposomes	Small interfering RNA glycosylation end products (SiRAGE)		Ischemic heart disease	PEG modified liposomes having APG and SiRAGE prevented oxidative stress injury, downregulated RAGE expression and reduced cellular inflammatory factors release in H9C2 cells on in vitro studies. In addition, prevented arrhythmia and myocardial pathological injury, as well as reducing apoptosis and the area of necrotic myocardium in rats.	[111]

7. Patents related to Apigenin formulations

A comprehensive search for patents on apigenin formulations was carried out using several patent databases, such as the USPTO Patent search, Google Patents, WIPO IP Portal and Patent Lens and found only few patents for apigenin formulations along with their applicability. Typically, they cover a range of aspects, including the composition of these formulations, their preparation methods, the use of apigenin in specific therapeutic applications and its potential synergies with other compounds or drugs [112]. Initially, patent searching was done to identify the apigenin nanoformulation. Most inventions in this category primarily focused on improving stability, enhancing the solubility and increasing the bioavailability of apigenin. Recent patents published in the last years are summarized in Table 2.

Table 2.

List of patents of apigenin formulations.

S.no.	Patent number	Patent inventor(s)	Patent title
1.	EP2444061A1	Mitsuru Sugiyama, Shinya Kasamatsu	Apigenin-containing composition
2.	CN102631405A	Ouyang Wuqing, Sun Jianghong, Cao Tongbu	Compound apigenin nanoemulsion antihypertensive drug
3.	CN113069415A	Lu Shan, Zhou Lijing, Xu Renjie	Insoluble drug nanosuspension and preparation method thereof
4.	CN108487928B	Lu Yi Pang Min Wang Haiqiao Shi Shiliang Tian Zhaojun Ye Qing	A kind of compound apigenin nanoemulsion material and preparation method thereof that prevention and treatment water storage goaf coal spontaneous is under fire
5.	CN113956225A	Yan Tingxuan, Song Xingfang, Han Xinya, Wang Shuangshou, Bian Jinlei, Lu Xuming, Wu Binbin, Fang Weihong	Method for preparing apigenin nanoparticles by supercritical enhanced solution dispersion method
6.	CN110623159A	Huang Juan	Pig feed containing linseed oil and apigenin solid lipid nanoparticles and preparation method thereof
7.	CA2778441	Birbara, Philip J.	Hydrated microparticles of apigenin and/or luteolin with improved solubility
8.	WO 2022/170064 A1	Kelly Kimberly, Hung Jessica	Compositions and methods for targeted antifibrotic therapy in chronic pancreatitis

8. Conclusion

In summary, two promising directions in pharmaceutical research and personalized medicine are the use of nanocarriers for apigenin delivery and the co-delivery of apigenin with other drugs. Nanocarriers, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers and polymeric micelles, hold significant potential in overcoming the challenges of apigenin's solubility and bioavailability. Encapsulating apigenin in these systems can markedly enhance its bioavailability and therapeutic efficacy, particularly in treating conditions like cancer. Nevertheless, further refinements and safety evaluations are necessary for their clinical applications. On the other hand, co-delivery offers a synergistic approach, especially beneficial in cancer therapy, where combining multiple drugs can target different aspects of cancer cells, potentially reducing drug resistance and improving treatment outcomes. This strategy enhances the overall effectiveness of apigenin and co-administered drugs while minimizing side effects. Both approaches embody the innovative essence of pharmaceutical research and their translation into clinical practice will require further research and clinical trials. Ultimately, these strategies hold the promise of benefiting patients by providing more effective and targeted treatments in the realm of personalized medicine.

9. Future perspective

This review has highlighted the potential of nanocarriers in delivering apigenin for various diseases, underscoring the considerable advantages they offer, such as controlled and sustained drug release, a lower toxicity profile and reduced dosing frequency, all of which contribute to improved patient outcomes. However, certain nanocarriers, including nanocrystals, magnetic nanoparticles, nanosponges, nanofibers and niosomes, have yet to demonstrate their effectiveness in delivering apigenin. Additionally, the nanocarriers used for apigenin delivery must undergo thorough pharmacodynamic assessments to justify the use of nano-apigenin in treating various illnesses. Furthermore, key challenges such as regulatory approvals, the long-term safety potential and scaling up for large-scale production need to be addressed in future research to facilitate the transition of apigenin nanoformulations from laboratory research to commercial markets.

Funding Statement

The authors acknowledge Fundação para a Ciência e a Tecnologia (FCT), Portugal in the scope of the projects UIDB/04326/2020 (DOI:10.54499/UIDB/04326/2020), UIDP/04326/2020 (DOI:10.54499/UIDP/04326/2020) and LA/P/0101/2020 (DOI:10.54499/LA/P/0101/2020) of the Research Unit Center for Marine Sciences—CCMAR and UIDB/04565/2020 (DOI:10.54499/UIDB/04565/2020) and UIDP/04565/2020 (DOI:10.54499/UIDP/04565/2020) of the Research Unit Institute for Bioengineering and Biosciences—iBB and LA/P/0140/2020 (DOI:10.54499/LA/P/0140/2020) of the Associate Laboratory Institute for Health and Bioeconomy—i4HB.

Supplemental material

Supplemental data for this article can be accessed at https://doi.org/10.1080/20415990.2024.2386928

Author contributions

G Kumar: writing original draft; P Jain: writing-review and editing; T Virmani: conceptualization; A sharma: visualization; MS Akhtar: funding acquisition; SA Aldosari: supervision; MF Khan: writing – review & editing; SOD Duarte: writing original draft, writing review, validation; P Fonte: funding acquisition and supervision.

Financial disclosure

This work was funded by Fundação para a Ciência e a Tecnologia (FCT), Portugal in the scope of the projects UIDB/04326/2020 (DOI:10.54499/UIDB/04326/2020), UIDP/04326/2020 (DOI:10.54499/UIDP/04326/2020) and LA/P/0101/2020 (DOI:10.54499/LA/P/0101/2020) of the Research Unit Center for Marine Sciences—CCMAR and UIDB/04565/2020 (DOI:10.54499/UIDB/04565/2020) and UIDP/04565/2020 (DOI:10.54499/UIDP/04565/2020) of the Research Unit Institute for Bioengineering and Biosciences—iBB and LA/P/0140/2020 (DOI:10.54499/LA/P/0140/2020) of the Associate Laboratory Institute for Health and Bioeconomy—i4HB. Deanship of Research and Graduate Studies, King Khalid University, Grant number RGP2/317/45. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Competing interests disclosure

The authors have no competing interests or relevant affiliations with any organization or entity with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, stock ownership or options and expert testimony.

Writing disclosure

No writing assistance was utilized in the production of this manuscript.