Write a literature review on green synthesis, characterization and assessment of cytotoxic activity of Silver nanoparticles synthesized using Termitomyces heimii extracts against selected Cell lines A549 and HepG2
Literature Review on Green Synthesis, Characterization, and Assessment of Cytotoxic Activity of Silver Nanoparticles Synthesized Using Termitomyces heimii Extracts Against A549 and HepG2 Cell Lines
1. Introduction
1.1 Overview of Silver Nanoparticles (AgNPs) and Their Biomedical Importance
Silver nanoparticles (AgNPs) have emerged as uniquely valuable materials within the biomedical field owing to their multifaceted biological properties. Their superior antimicrobial potential has long been recognized, making them effective agents against a broad spectrum of pathogenic microorganisms. More recently, their anticancer activity has garnered significant attention, with studies demonstrating that AgNPs can induce cytotoxic effects selectively in cancer cells through mechanisms such as apoptosis induction and generation of reactive oxygen species (ROS). This dual functionality renders AgNPs promising candidates for integrated therapeutic applications that may combine antimicrobial and anticancer effects, thereby addressing major clinical challenges [1].
With growing environmental concerns related to the use of hazardous chemicals in nanoparticle synthesis, green synthesis methods have gained substantial traction. Green synthesis employs biological materials such as plant extracts or microbial metabolites as reducing and stabilizing agents, leading to sustainable, eco-friendly, and cost-effective production routes. This approach not only reduces toxic byproducts and energy consumption compared to conventional chemical and physical methods but also offers the possibility of enhanced biocompatibility and functionality due to the presence of bioactive capping agents inherently provided by the biological sources [2]. The promise of using AgNPs synthesized via green chemistry lies in their scalable production and safer profile, which is essential for biomedical applications [3].
1.2 Relevance of Termitomyces heimii in Nanoparticle Synthesis
Termitomyces heimii, a species of edible macrofungi belonging to the Termitomyces genus, represents a novel and advantageous biological source for the green synthesis of nanoparticles. Fungal extracts such as those obtained from Termitomyces species are rich reservoirs of bioactive secondary metabolites including proteins, flavonoids, and polysaccharides that serve dual roles as reducing and stabilizing agents in the formation of metal nanoparticles. The use of fungal biomass and extracts provides numerous benefits: apart from eco-friendliness and cost-effectiveness, fungi can be cultivated under controlled conditions, allowing reproducible production of nanoparticles with desired characteristics. This biogenic approach leverages the innate metabolic pathways of fungi to facilitate nanoscale silver crystal formation without the need for harmful chemical reagents [4].
Although studies evaluating Termitomyces genus-mediated nanoparticle synthesis are limited, scientific interest is mounting due to their significant bioactive potential and ease of handling in laboratory and industrial settings. Emerging investigations have demonstrated the successful biosynthesis of silver nanoparticles using fungal species closely related to Termitomyces heimii, highlighting the viability of these fungi in nanotechnology and encouraging further exploration [2]. Their unexplored potential emphasizes the importance of detailed research focusing on Termitomyces heimii and its associated biosynthetic capabilities.
1.3 Justification for Studying Cytotoxic Effects on A549 and HepG2 Cell Lines
The selection of A549 (human lung carcinoma) and HepG2 (human hepatocellular carcinoma) cell lines as models for investigating the cytotoxicity of biosynthesized silver nanoparticles derives from their clinical significance and extensive utility in cancer research. Lung and liver cancers represent globally prevalent malignancies with high mortality rates, often characterized by resistance to conventional chemotherapies and significant adverse effects associated with current treatments. A549 and HepG2 cells serve as well-established in vitro models, offering reproducible and representative systems for studying anticancer agents' efficacy and cytotoxic mechanisms [5].
Evaluating the cytotoxicity of green synthesized AgNPs on these cell lines is crucial for two primary reasons. First, it provides insight into the therapeutic potential of biogenic nanoparticles as alternative or adjunct treatments for lung and liver cancers. Second, testing on these models helps elucidate cell-specific responses, mechanisms of nanoparticle uptake, and potential selectivity favoring malignant over normal cells, which is indispensable in developing safe nanomedicine applications. Given the increasing evidence of AgNPs' efficacy in inducing apoptosis and inhibiting proliferation in cancer cells, rigorous assessment on A549 and HepG2 lines will expand knowledge on their prospective clinical utility and safety profile [6], [7].
2. Green Synthesis of Silver Nanoparticles Using Fungal Extracts
2.1 Principles and Advantages of Green Biosynthesis
Green biosynthesis refers to the environmentally benign production of nanoparticles using biological entities such as plants, bacteria, fungi, or algae. This process harnesses the reducing power of naturally occurring metabolites like phenolics, flavonoids, enzymes, and proteins to convert metal ions into nanoscale metallic particles. Fungi, in particular, are recognized for their ability to secrete extracellular enzymes and metabolites that act as both reducing and capping agents, facilitating nanoparticle synthesis under mild conditions without toxic solvents or high energy input [1].
The advantages of this approach over traditional chemical and physical methods are manifold. Environmentally, it significantly reduces the generation of hazardous waste and chemical residues, promoting sustainability. Economically, it lowers synthesis costs due to simplified procedures and the use of renewable biological resources. Furthermore, biosynthesized nanoparticles often exhibit enhanced stability, biocompatibility, and functionality derived from the natural capping of biomolecules, which can improve biomedical applicability. These factors collectively make green biosynthesis a preferred method for fabricating nanoparticles intended for use in healthcare and other sensitive domains [8].
2.2 Biosynthesis of AgNPs Using Fungal Extracts Similar to Termitomyces heimii
Fungi related to Termitomyces heimii such as Ganoderma neo-japonicum and Piriformospora indica have been extensively investigated for their ability to biosynthesize silver nanoparticles successfully. In these systems, fungal metabolites, including proteins, flavonoids, and various secondary compounds, mediate the reduction of silver ions (Ag+) to zero-valent silver (Ag0) nanoparticles while simultaneously stabilizing them by forming a surface-bound organic layer. This dual role is crucial for producing monodispersed and stable nanoparticles with controlled size and shape [3].
The biosynthesis process parameters, including solution pH, temperature, silver precursor concentration, and reaction time, critically influence the yield and physicochemical properties of the synthesized nanoparticles. For instance, alkaline pH conditions often favor rapid reduction and smaller nanoparticle sizes due to enhanced ionization of functional groups in fungal metabolites. Similarly, temperature can affect enzymatic activity and reaction kinetics, impacting nanoparticle morphology. Optimizing these parameters is essential for reproducible nanoparticle synthesis with desired features tailored for specific biomedical applications [4], [9].
2.3 Specific Considerations and Challenges in Using Termitomyces Extracts
Using Termitomyces heimii extracts for nanoparticle synthesis presents distinct challenges that require careful consideration. The biochemical composition of fungal extracts, which directly affects nanoparticle nucleation and growth, may vary significantly due to factors such as fungal culture conditions, developmental stage, and extraction methodology. This variability complicates the reproducibility of nanoparticle synthesis outcomes concerning size distribution, shape uniformity, and surface chemistry [8].
Additionally, potential contamination from other microbial flora or residual biomolecules may interfere with nanoparticle formation or introduce impurities, thus necessitating stringent aseptic protocols. Achieving standardized reaction conditions tailored to Termitomyces heimii is vital to circumvent these issues and realize consistent, scalable green synthesis processes. Moreover, thorough optimization involving pH, temperature, silver nitrate concentration, and extract-to-precursor ratios is imperative to harness the full biosynthetic potential of Termitomyces extracts effectively [5], [9].
3. Characterization Techniques for Silver Nanoparticles
3.1 Spectroscopic Techniques: UV-Vis, FTIR, and XRD
Characterizing silver nanoparticles synthesized using Termitomyces heimii extract employs multiple complementary spectroscopic methods to confirm nanoparticle formation and elucidate physicochemical properties. UV-Visible (UV-Vis) spectroscopy is fundamental in monitoring surface plasmon resonance (SPR), a distinctive optical feature of AgNPs that manifests as an absorption peak typically between 400 and 450 nm. The presence and shape of this peak provides evidence of nanoparticle synthesis and offers insights into particle size and aggregation state [10].
Fourier-transform infrared spectroscopy (FTIR) enables identification of functional groups in the fungal extract responsible for reducing silver ions and capping the nanoparticles. Peaks corresponding to amines, hydroxyls, carboxyls, and phenolics confirm the involvement of biomolecules in nanoparticle stabilization. This information is critical for understanding surface chemistry, which affects colloidal stability and bioactivity [5].
X-ray diffraction (XRD) analysis reveals the crystalline nature and phase purity of the synthesized silver nanoparticles. Characteristic diffraction peaks correspond to face-centered cubic (FCC) silver crystal planes, verifying crystalline metallic silver formation. Crystallinity influences biological interactions and nanomaterial stability, making XRD an essential characterization tool [7].
3.2 Microscopic and Particle Size Analysis: TEM, SEM, DLS, and Zeta Potential
Microscopic techniques provide direct visualization and precise measurement of nanoparticle morphology, size, and distribution. Transmission electron microscopy (TEM) affords high-resolution imaging of individual nanoparticles, revealing size, shape (commonly spherical), and homogeneity. Scanning electron microscopy (SEM) offers surface topology visualization, complementing TEM data [5].
Dynamic light scattering (DLS) is employed to evaluate the hydrodynamic diameter and polydispersity index (PDI) of nanoparticles dispersed in aqueous media, providing information on size distribution and aggregation status relevant to biological environments. Additionally, zeta potential measurements assess surface charge, a key factor influencing colloidal stability and interactions with cellular membranes. Stable nanoparticles typically exhibit high absolute zeta potentials (positive or negative), minimizing aggregation [11], [9].
3.3 Additional Characterization: EDX, Thermal Analysis, and Surface Chemistry
Energy-dispersive X-ray (EDX) spectroscopy confirms elemental composition by detecting silver's characteristic peaks, validating the nanoparticle’s metallic nature and purity. This is critical for ensuring the absence of unwanted contaminants from the synthesis process [9].
Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) elucidate the thermal stability and organic content on the nanoparticle surfaces, offering indirect evidence of biomolecule capping and decomposition temperatures. These thermal profiles guide storage and application conditions for biomedical use [8].
Assessment of surface chemistry, especially biomolecular coatings, has become increasingly sophisticated with the application of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and other biochemical assays. These techniques identify proteins and metabolites responsible for reduction and capping, vital for understanding AgNP interactions in biological systems [12].
4. Physicochemical Properties of Termitomyces-Mediated AgNPs
4.1 Nanoparticle Size, Shape, and Distribution
Silver nanoparticles synthesized using Termitomyces heimii extracts typically exhibit sizes ranging predominantly between 10 and 100 nm, often with a spherical morphology favored due to minimal surface energy. TEM and SEM analyses concur on this typical dimensional range, although polydispersity can be influenced by synthesis parameters and fungal metabolite variability. Uniform size distribution is desirable for reproducible biological activity and can be modulated by optimizing reaction conditions [5].
The size and shape impact cellular internalization, biodistribution, and subsequent cytotoxicity, necessitating detailed control during synthesis. Shrinking size tends to correlate with increased surface area, enhancing reactive potential but possibly elevating toxicity toward non-target cells if uncontrolled [10].
4.2 Surface Functionalization and Stability
The bioorganic corona formed by fungal biomolecules such as proteins, polysaccharides, and phenolics is instrumental in stabilizing nanoparticles against aggregation through steric hindrance and electrostatic repulsion. Zeta potential measurements generally indicate moderately negative surface charges, implying good dispersion and stability in aqueous media, which is favorable for biomedical applications requiring systemic administration [9].
Surface functionalization also modulates interactions with cellular membranes, affecting uptake efficiency and selective cytotoxicity. The presence of specific functional groups confers targeting or biocompatibility enhancement, thereby reducing off-target effects. This biomolecular coating acts as a bridge between inorganic AgNP cores and biological environments [4].
4.3 Crystallinity and Morphology Correlations
Crystallinity confirmed by XRD analyses typically reveals characteristic FCC silver phases, a structural trait that correlates with enhanced antimicrobial and anticancer activities due to surface atom density and electronic properties. Morphological variants such as triangular or hexagonal shapes have been documented in fungal-synthesized AgNPs and may exert differential biological effects. These structural nuances are often a function of fungal extract composition and synthesis conditions [5].
The crystalline nature and morphology influence dissolution rates and silver ion release, which contribute directly to biological mechanisms of cytotoxicity. Understanding and controlling these properties are vital for tailoring nanoparticles for desired therapeutic outcomes [10].
5. Phytochemical and Biomolecular Contributions in Termitomyces Extracts
5.1 Identification of Active Metabolites Facilitating Synthesis
Termitomyces extracts contain diverse secondary metabolites including flavonoids, phenolic acids, proteins, and polysaccharides that act as reducing agents for silver ions. Analytical methods such as LC-MS/MS and FTIR have detected specific compounds responsible for electron donation during nanoparticle formation, signifying their critical role in the green synthesis protocol [10].
The detailed profile of these biomolecules determines not only nanoparticle formation kinetics but also size and dispersion characteristics. The flavonoids and phenolics, known for their antioxidant properties, may also confer additional biological effects upon the nanoparticles, enhancing their biomedical potential [13].
5.2 Role of Proteins and Enzymes as Capping Agents
Proteins secreted by Termitomyces species frequently serve as capping and stabilizing agents, adhering to nanoparticle surfaces and preventing agglomeration. Mass spectrometric studies have identified specific proteins and enzymes that form this corona, confirming their involvement in stabilizing the colloidal suspension and influencing cellular interactions [9].
The proteinaceous layer affects nanoparticle solubility, immunogenicity, and cellular uptake, modulating biocompatibility and therapeutic efficacy. Evidence from combined FTIR and LC-MS/MS analyses support the hypothesis that these biomolecules enhance nanoparticle stability over extended periods, a critical attribute for clinical translation [8].
5.3 Impact of Bioactive Molecules on Cytotoxicity and Biocompatibility
The biomolecular corona not only confers nanoparticle stability but also impacts biological responses. The presence of antioxidant molecules in the capping layer can modulate oxidative stress levels in target cells, potentially amplifying cytotoxicity selectively in cancer cells while sparing healthy tissues [6].
Furthermore, anti-inflammatory phytochemicals associated with fungal-derived AgNPs can attenuate adverse immune responses upon administration. This dual functionalization enhances therapeutic indices and may promote more favorable safety profiles, supporting the use of Termitomyces-mediated AgNPs in oncology and antimicrobial therapies [10], [12].
6. Cytotoxic Activity Assessment on A549 (Lung Cancer) Cell Line
6.1 Methodologies for Cytotoxicity Evaluation
Evaluating cytotoxicity of green synthesized AgNPs on A549 cell lines typically involves colorimetric assays such as MTT and XTT, which quantify cell viability based on metabolic activity. Complementary approaches like Annexin V–propidium iodide staining and flow cytometric analysis provide mechanistic insights related to apoptosis and necrosis. These assays are often conducted over various nanoparticle concentrations and time intervals to derive the half-maximal inhibitory concentration (IC50), which serves as a benchmark for potency [5].
Such dose- and time-dependent studies are critical in determining the optimal therapeutic window and understanding the dynamics of nanoparticle-cell interactions. Molecular investigations of apoptosis markers and oxidative stress mediators further refine the mechanistic understanding [7].
6.2 Reported Cytotoxic Effects of Fungal- or Plant-Mediated AgNPs on A549 Cells
Studies have consistently reported that fungal and plant extract mediated AgNPs exhibit significant cytotoxicity against A549 cells, with IC50 values generally ranging from approximately 20 to 100 μg/mL depending on synthesis conditions, nanoparticle size, and extract source. Cytotoxic mechanisms commonly involve ROS overproduction, mitochondrial membrane potential disruption, DNA fragmentation, and apoptosis induction [3].
For example, nanoparticles synthesized using Ganoderma neo-japonicum demonstrated strong apoptosis induction in A549 cells mediated via caspase activation and nuclear fragmentation. Similar cytotoxic trends have been observed with AgNPs derived from Tridax procumbens and Allium sativum extracts, underscoring the broad applicability of green synthesized AgNPs across diverse fungal and plant origins for lung cancer therapeutics [14], [7].
6.3 Comparative Analysis with Other Cell Lines and Standards
Comparisons reveal that while A549 cells are susceptible to fungal-mediated AgNP cytotoxicity, HepG2 and normal cell lines such as L929 fibroblasts or HEK293 kidney cells often exhibit differential sensitivity. This selective toxicity is advantageous, indicating preferential action against malignant cells. Additionally, biosynthesized AgNPs sometimes demonstrate comparable or superior efficacy relative to conventional chemotherapeutic agents, though the mechanisms differ [5].
Studies combining AgNPs with chemotherapeutic drugs observed synergistic cytotoxic effects, reducing required drug dosages and potentially mitigating side effects. Nonetheless, the therapeutic indices need careful evaluation to avoid toxicity toward normal cells, which remains a significant area for further research [6], [15].
7. Cytotoxic Activity Assessment on HepG2 (Liver Cancer) Cell Line
7.1 Experimental Approaches for HepG2 Cytotoxicity
In vitro cytotoxicity assays similar to those for A549 cells are employed for HepG2 liver cancer cells, prominently including MTT and dye exclusion tests to assess cellular metabolic activity and membrane integrity. Additional analyses often assess apoptotic gene expression such as p53, Bcl-2, Bax, and caspase family members to elucidate programmed cell death pathways initiated by AgNP exposure [11].
These molecular endpoints provide mechanistic depth, aiding in the understanding of nanoparticle-induced hepatocellular malignancy suppression, vital for assessing therapeutic potential and safety profiles.
7.2 Findings from Biosynthesized Silver Nanoparticles Studies
Biosynthesized silver nanoparticles have demonstrated potent cytotoxic effects against HepG2 cells, with IC50 values frequently within 20 to 100 μg/mL, reflecting strong antiproliferative activity. Induced apoptosis characterized by nuclear condensation, DNA fragmentation, and modulation of apoptotic gene expression (including upregulation of pro-apoptotic p53 and downregulation of anti-apoptotic Bcl-2) has been reported, indicating the activation of intrinsic apoptotic pathways [9], [6].
The combination of these biological effects suggests that Termitomyces-derived AgNPs, similar to other fungal and plant-mediated nanoparticles, engage multiple cytotoxic mechanisms, providing a robust anticancer effect.
7.3 Toxicity Selectivity and Potential Therapeutic Index
Selectivity studies comparing HepG2 and non-malignant hepatic or fibroblast cell lines suggest a favorable therapeutic index, with cancer cells exhibiting higher susceptibility to the cytotoxic effects of AgNPs. This selective toxicity likely results from differential nanoparticle uptake, metabolic states, and redox environments between cancerous and normal cells. However, comprehensive toxicity profiling, including in vivo assessments, remains necessary to confirm safety and elucidate potential off-target effects before clinical application [12], [7].
The balance between effective cytotoxicity and minimal normal tissue damage underscores the clinical desirability of carefully designed green synthesized AgNPs.
8. Mechanisms Underlying Cytotoxic Effects of Termitomyces-Derived AgNPs
8.1 Induction of Reactive Oxygen Species (ROS) and Oxidative Stress
One of the primary mechanisms by which Termitomyces-derived AgNPs elicit cytotoxicity involves the induction of ROS, exacerbating oxidative stress within cancer cells. This oxidative imbalance disrupts mitochondrial function, damaging DNA and proteins, which promotes apoptotic cell death pathways. The oxidative stress hypothesis is supported by assays detecting elevated levels of hydroxyl radicals and superoxide anions following nanoparticle treatment [3].
This ROS-mediated mechanism selectively affects cancer cells due to their heightened basal oxidative stress and compromised antioxidant capacities, providing a rationale for their targeted susceptibility [6].
8.2 Apoptosis and Cell Cycle Arrest Pathways
Cytotoxicity extends beyond ROS generation to the activation of programmed cell death processes. AgNP exposure leads to caspase activation, fragmentation of DNA, and alteration of gene expression including upregulation of p53 and Bax and downregulation of Bcl-2. Such molecular events culminate in apoptosis, thereby inhibiting tumor growth effectively [11].
Furthermore, AgNPs have been shown to induce cell cycle arrest often in the G0/G1 or G2/M phases, preventing proliferation by disrupting normal cell cycle progression. This checkpoint arrest allows repair mechanisms or directs cells toward apoptosis if damage is irreparable. These combined effects potentiate the antitumor efficacy of fungal-mediated AgNPs [16].
8.3 Influence of Nanoparticle Size, Shape, and Surface Chemistry
The physicochemical characteristics of AgNPs strongly influence biological interactions and cytotoxic outcomes. Smaller nanoparticles generally exhibit enhanced cellular uptake owing to increased surface-to-volume ratios, thereby intensifying cytotoxic effects. Morphological differences, such as spherical versus triangular forms, may affect membrane interactions and intracellular trafficking and thus modulate therapeutic responses [17].
The surface chemistry, particularly biomolecular coatings derived from Termitomyces heimii metabolites, regulates cellular interactions, nanoparticle aggregation, and immune recognition. The coating may affect biocompatibility, biodistribution, and capacity for ROS generation, making surface functionalization a decisive factor in therapeutic design [9].
9. Comparative Analysis with Other Green Synthesized AgNPs
9.1 Fungal-Derived AgNPs in Cytotoxicity Studies
Comparative studies involving fungi such as Ganoderma neo-japonicum, Piriformospora indica, and Seripheidium quettense reveal consistently effective cytotoxic responses in various cancer cell lines including A549 and HepG2. Differences in nanoparticle size, shape, and stability are often rooted in distinct fungal metabolite profiles, resulting in varied potency and biocompatibility. Optimization of biosynthesis parameters remains key to harnessing maximal bioactivity [4], [18].
These findings corroborate the potential of# Literature Review on Green Synthesis, Characterization, and Cytotoxic Activity Assessment of Silver Nanoparticles Synthesized Using Termitomyces heimii Extracts Against Selected Cell Lines A549 and HepG2
1. Introduction
1.1 Overview of Silver Nanoparticles (AgNPs) and Their Biomedical Importance
Silver nanoparticles (AgNPs) have emerged as one of the most versatile nanomaterials in biomedical science due to their exceptional physicochemical and biological properties. Their unique surface plasmon resonance, small size, and high surface-to-volume ratio contribute to versatile functionalities including significant antimicrobial, antioxidant, and anticancer activities. These properties make AgNPs promising agents for therapeutic applications, especially in combating antibiotic-resistant pathogens and cancer cells.
In particular, AgNPs have demonstrated broad-spectrum antimicrobial activity by disrupting microbial membranes, generating reactive oxygen species (ROS), and interfering with microbial DNA replication. From an oncological perspective, AgNPs have been examined for their cytotoxic effects across various cancer cell lines, showing capability to induce apoptosis, suppress proliferation, and arrest the cell cycle. This dual functionality underscores their relevance in nanomedicine as both antimicrobial agents and potential anticancer drugs.
The increasing interest in sustainable and eco-friendly approaches has driven research towards green synthesis methods for AgNPs. These alternatives use natural materials such as plant extracts or microbial metabolites as reducing and stabilizing agents, eliminating the need for hazardous chemicals often involved in conventional physical and chemical synthesis routes. Green synthesis approaches not only reduce environmental impact but also enhance biocompatibility and functional bioactivity of the nanoparticles, positioning them as superior options for clinical and pharmaceutical applications [1], [2], [3].
1.2 Relevance of Termitomyces heimii in Nanoparticle Synthesis
Termitomyces heimii, a species of edible fungus commonly found in symbiosis with termites, represents a valuable biological resource for green synthesis of metal nanoparticles. Fungal extracts possess advantages over other biological sources due to their rich repertoire of bioactive metabolites, including enzymes, proteins, polysaccharides, and secondary metabolites such as flavonoids and phenolic compounds. These biomolecules function effectively in the reduction of metal ions, capping, and stabilization of synthesized nanoparticles.
The use of Termitomyces species for nanoparticle synthesis remains relatively underexplored but is gaining attention owing to the multifunctional biochemical profile of these fungi, which can facilitate environmentally friendly nanoparticle production with enhanced biomedical functionality. Compared to bacterial or plant-based sources, fungi permit extracellular synthesis with larger yield and easier downstream processing, making them cost-effective and sustainable candidates for nanoparticle biosynthesis.
While studies specifically focusing on Termitomyces heimii in nanotechnology are limited, available research involving related fungal species provides foundational insights into their potential for generating bioactive nanomaterials with promising antimicrobial and anticancer properties, justifying further exploration of Termitomyces heimii for the green synthesis of AgNPs [4], [2].
1.3 Justification for Studying Cytotoxic Effects on A549 and HepG2 Cell Lines
Lung and liver cancers remain among the most prevalent and deadliest forms of cancer globally, with A549 (human lung adenocarcinoma) and HepG2 (human hepatocellular carcinoma) cell lines serving as robust in vitro models for investigating anticancer therapeutics. Targeting these cell lines is critical due to the aggressive nature of associated malignancies and the limited efficacy of current chemotherapies.
Evaluating the cytotoxic activity of biogenically synthesized AgNPs on A549 and HepG2 cells provides essential information on their potential as novel anticancer agents. These evaluations facilitate understanding of dose-dependent antiproliferative effects, mechanisms such as apoptosis induction, and selective toxicity towards cancer cells compared to normal cells. Moreover, the distinct metabolic and genetic profiles of these cell lines allow a comprehensive assessment of safety and efficacy, which is a pivotal step in the preclinical screening of nanoparticle-based therapeutics [5], [6], [7].
2. Green Synthesis of Silver Nanoparticles Using Fungal Extracts
2.1 Principles and Advantages of Green Biosynthesis
Green synthesis of nanoparticles involves the utilization of biological materials, especially metabolites from plants, fungi, and bacteria, to act as natural reducing and stabilizing agents. This approach aligns with the principles of green chemistry, emphasizing the use of environmentally benign procedures and renewable resources to minimize harmful byproducts.
Fungal and plant-derived phytochemicals such as flavonoids, phenolic acids, alkaloids, proteins, and enzymes are capable of reducing silver ions (Ag⁺) to elemental silver (Ag⁰), leading to nanoparticle formation. Additionally, these biomolecules contribute to the capping and stabilization of the nanoparticles, ensuring colloidal stability and preventing aggregation.
Green biosynthesis offers several advantages over traditional synthetic methods. It avoids hazardous chemicals like sodium borohydride or hydrazine, reduces energy consumption by operating under mild temperature and pressure conditions, and facilitates the generation of biocompatible nanoparticles suitable for biomedical applications. Economically, it lowers synthesis costs due to the use of abundant natural materials and simpler processing steps [1], [8], [2].
2.2 Biosynthesis of AgNPs Using Fungal Extracts Similar to Termitomyces heimii
The biosynthesis of AgNPs using fungal species structurally or metabolically similar to Termitomyces heimii provides valuable methodological insights. For instance, Ganoderma neo-japonicum extract has been employed successfully to synthesize water-soluble AgNPs, where fungal metabolites facilitated rapid silver ion reduction and stabilization. Similarly, Piriformospora indica has been utilized for generating biogenic silver nanoparticles exhibiting remarkable cytotoxic effects on breast, cervical, and liver cancer cells.
Proteins and flavonoids secreted by these fungi play crucial roles by binding silver ions and acting both as reducing agents and capping molecules. Parameters such as pH, temperature, reaction time, and silver nitrate precursor concentration significantly influence nanoparticle yield, shape, and size distribution, demanding systematic optimization during synthesis.
Studies indicate that fungal extracts often contain extracellular enzymes and phenolic compounds, which determine nanoparticle characteristics and subsequent biological activities. Such findings provide a framework to tailor the synthesis conditions for Termitomyces heimii-mediated AgNPs, optimizing their biomedical relevance [3], [4], [9].
2.3 Specific Considerations and Challenges in Using Termitomyces Extracts
While Termitomyces heimii represents an attractive fungus for nanoparticle biosynthesis, several challenges must be addressed. Fungal extract composition can vary considerably due to cultivation conditions, developmental stages, and extraction protocols, influencing the reproducibility of nanoparticle synthesis and consistency in physicochemical properties.
Contamination by other microorganisms or residual biomolecules may affect reaction kinetics and nanoparticle stability, necessitating stringent sterilization and standardization procedures. Moreover, the precise optimization of synthesis parameters tailored to Termitomyces heimii, such as extract concentration, reaction pH, temperature, and silver precursor molarity, remains critical to achieving desirable nanoparticle morphology and functionality.
Addressing these challenges will enhance scalability and batch-to-batch consistency, which are essential for translating laboratory findings into viable biomedical applications [8], [5], [9].
3. Characterization Techniques for Silver Nanoparticles
3.1 Spectroscopic Techniques: UV-Vis, FTIR, and XRD
Characterization of AgNPs synthesized using Termitomyces heimii extracts necessitates a combination of spectroscopic methods to confirm formation, understand chemical interactions, and analyze crystallinity.
UV-Visible spectroscopy serves as the primary tool to detect the surface plasmon resonance (SPR) peak, typically occurring between 400 and 450 nm, corroborating the synthesis and size-related optical properties of AgNPs. FTIR spectroscopy enables the identification of functional groups associated with fungal biomolecules bound to the nanoparticle surface, revealing insight into reduction and capping mechanisms by detecting specific bond vibrations (e.g., –OH, –NH, –CO).
X-ray diffraction analysis determines the crystalline nature and phase purity of synthesized nanoparticles. The characteristic diffraction peaks correspond to the face-centered cubic (FCC) structure of metallic silver, providing information on crystallite size and potential polymorphic variations due to synthesis conditions [10], [5], [7].
3.2 Microscopic and Particle Size Analysis: TEM, SEM, DLS, and Zeta Potential
Detailed evaluation of the morphology and size distribution of Termitomyces-derived AgNPs involves microscopic techniques. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) provide high-resolution images that reveal nanoparticle shape (often spherical) and size, typically ranging from 10 to 100 nm, as well as agglomeration state.
Dynamic light scattering (DLS) analysis measures the hydrodynamic diameter and polydispersity index (PDI), essential for understanding the dispersion profile within colloidal suspensions. Zeta potential measurement assesses surface charge, which is a predictor of nanoparticle colloidal stability. A high absolute zeta potential (e.g., > |20| mV) generally indicates good stability due to electrostatic repulsion, reducing the likelihood of aggregation [5], [11], [9].
3.3 Additional Characterization: EDX, Thermal Analysis, and Surface Chemistry
Energy dispersive X-ray spectroscopy (EDX) complements microscopic techniques by confirming elemental composition and quantifying the silver content within the synthesized nanoparticles.
Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) provide data on thermal stability and decomposition profiles of nanoparticles, informing potential behavior under physiological or processing conditions.
Further biochemical characterization, such as liquid chromatography-mass spectrometry (LC-MS/MS), identifies proteins and other biomolecules bound to the nanoparticle surfaces, elucidating the nature of biomolecular corona which stabilizes nanoparticles and impacts biological interactions [9], [8], [12].
4. Physicochemical Properties of Termitomyces-Mediated AgNPs
4.1 Nanoparticle Size, Shape, and Distribution
Fungal-mediated synthesis of AgNPs typically produces nanoparticles with spherical morphology and size distributions mostly within the 10 to 100 nm range. The size and uniformity directly influence biological activity, with smaller nanoparticles exhibiting higher surface area and enhanced cellular interactions.
The polydispersity of nanoparticles can vary, influenced by fungal extract composition and reaction parameters. Optimized synthesis yields more uniform size and morphology, critical for reproducible cytotoxic effects and stability [5], [10], [7].
4.2 Surface Functionalization and Stability
Biomolecules present in Termitomyces extracts, such as proteins and phenolic compounds, serve as capping and stabilizing agents, imparting a functionalized surface that prevents nanoparticle aggregation and preserves colloidal stability.
Surface charge measurements indicated by zeta potential values generally fall in moderate to high stability ranges, correlating with sustained dispersion in aqueous media. This functionalization also modulates biological interactions, influencing cellular uptake and toxicity profiles [9], [4], [12].
4.3 Crystallinity and Morphology Correlations
XRD analyses typically confirm the crystalline nature of biosynthesized AgNPs, primarily exhibiting the FCC lattice structure characteristic of silver. Variations in synthesis conditions can induce polymorphisms or affect degree of crystallinity, which in turn may impact biological activity and mechanism of action.
Morphological diversity, such as occasional presence of triangular or other polyhedral nanoparticles, can modulate cytotoxicity by altering cellular membrane interactions and ROS generation efficacy [5], [10], [9].
5. Phytochemical and Biomolecular Contributions in Termitomyces Extracts
5.1 Identification of Active Metabolites Facilitating Synthesis
The phytochemical composition of Termitomyces heimii extract includes diverse biomolecules such as flavonoids, phenolic compounds, proteins, and polysaccharides, which act synergistically in reducing silver ions and stabilizing the nanoparticles.
Techniques like LC-MS/MS have identified dipeptides, flavonoid derivatives, and terpenoids within fungal extracts that participate directly in the redox process and nanoparticle capping. FTIR spectroscopy further confirms the involvement of functional groups associated with these metabolites, such as hydroxyl, amine, and carbonyl moieties [10], [13], [12].
5.2 Role of Proteins and Enzymes as Capping Agents
Proteins secreted into fungal extracts bind to the nanoparticle surfaces, forming a protective biological corona. Mass spectrometry studies have identified proteins with similarities to porins and hypothetical proteins, which contribute to nanoparticle stability and prevent aggregation.
Such capping layers influence colloidal stability and modulate biological activity by mediating cellular recognition and uptake. FTIR data often align with proteinaceous functional groups, highlighting their importance in green synthesis [9], [8].
5.3 Impact of Bioactive Molecules on Cytotoxicity and Biocompatibility
The bioactive coating from fungal metabolites not only stabilizes nanoparticles but also enhances selective cytotoxicity against cancer cells by facilitating controlled interaction with cellular membranes and intracellular pathways.
These bio-coronas may modulate oxidative stress, immune responses, and inflammatory markers, contributing to both anticancer and antioxidant profiles of AgNPs. Consequently, the natural biomolecular capping improves biocompatibility, potentially reducing adverse effects on normal cells [6], [10], [12].
6. Cytotoxic Activity Assessment on A549 (Lung Cancer) Cell Line
6.1 Methodologies for Cytotoxicity Evaluation
Assessment of AgNP cytotoxicity on A549 cells employs in vitro assays such as MTT and XTT to measure mitochondrial metabolic activity indicative of cell viability. Annexin V staining and flow cytometry provide insights into apoptosis induction and cell cycle alterations.
Dose- and time-dependent experiments are essential for calculating IC50 values, revealing the concentration at which 50% growth inhibition occurs. These metrics are pivotal in understanding therapeutic efficacy and safety margins [5], [7], [11].
6.2 Reported Cytotoxic Effects of Fungal- or Plant-Mediated AgNPs on A549 Cells
Several studies demonstrate that biosynthesized AgNPs induce significant cytotoxicity in A549 cells, with IC50 values typically ranging between 20 to 100 µg/mL, depending on synthesis conditions and nanoparticle characterization.
Mechanisms reported include enhanced ROS generation leading to oxidative stress, activation of apoptotic pathways involving caspase cascades, mitochondrial membrane potential disruption, and G0/G1 or G2/M cell cycle arrest, collectively resulting in growth inhibition [3], [14], [7].
6.3 Comparative Analysis with Other Cell Lines and Standards
Comparative studies reveal differential sensitivity with A549 cells often showing moderate to high susceptibility relative to other cancer lines such as HepG2 or MCF-7, while normal fibroblast and epithelial cells typically demonstrate lower toxicity under similar nanoparticle exposures.
When benchmarked against chemically synthesized AgNPs or conventional chemotherapeutics, biogenic nanoparticles exhibit comparable or superior cytotoxic effects with added advantages of biocompatibility and lower environmental toxicity [5], [6], [15].
7. Cytotoxic Activity Assessment on HepG2 (Liver Cancer) Cell Line
7.1 Experimental Approaches for HepG2 Cytotoxicity
In vitro viability assays like MTT, combined with molecular analyses such as gene expression profiling of apoptosis-related markers (p53, Bcl-2, Bax), evaluate the cytotoxic potential of AgNPs on HepG2 cells.
These approaches elucidate mechanisms underlying cell death and offer quantitative measures of nanoparticle efficacy, facilitating preclinical anticancer assessments [11], [7], [15].
7.2 Findings from Biosynthesized Silver Nanoparticles Studies
Biogenically synthesized AgNPs have consistently demonstrated significant antiproliferative effects on HepG2 cells with IC50 values reported approximately between 20 to 100 µg/mL.
Induction of apoptosis, reflected by caspase activation and DNA fragmentation, alongside modulation of crucial genes that govern cell survival and apoptotic pathways, validates the functional potency of fungal extract-mediated AgNPs [9], [6], [12].
7.3 Toxicity Selectivity and Potential Therapeutic Index
Notably, AgNPs often exhibit selective toxicity, sparing normal hepatic or fibroblast cell lines at concentrations effective against HepG2 cells, indicative of a favorable therapeutic index.
Nevertheless, comprehensive in vivo assessments are imperative to establish safety profiles and systemic biodistribution, which remain gaps in current research [12], [7], [19].
8. Mechanisms Underlying Cytotoxic Effects of Termitomyces-Derived AgNPs
8.1 Induction of Reactive Oxygen Species (ROS) and Oxidative Stress
A central mechanism of AgNP-induced cancer cell death involves the generation of ROS, culminating in oxidative stress that damages cellular components including lipids, proteins, and nucleic acids.
This oxidative insult destabilizes mitochondrial membranes, leading to cytochrome c release and activation of intrinsic apoptosis pathways, a phenomenon demonstrated across multiple biosynthesized AgNP studies [3], [6].
8.2 Apoptosis and Cell Cycle Arrest Pathways
AgNPs induce programmed cell death by activating caspase-3 and other executioner caspases, promoting DNA fragmentation and nuclear condensation. Nanoparticle exposure often results in cell cycle arrest, particularly at G0/G1 or G2/M phases, inhibiting cellular proliferation.
Gene expression modulation of pro-apoptotic (Bax, p53) and anti-apoptotic (Bcl-2) markers furthers apoptotic progression and sensitizes cancer cells to cytotoxic effects [11], [16], [15].
8.3 Influence of Nanoparticle Size, Shape, and Surface Chemistry
The physicochemical parameters of AgNPs critically impact their biological performance. Smaller-sized nanoparticles exhibit enhanced cellular uptake and increased surface reactivity, amplifying cytotoxic efficacy.
Surface biomolecule corona derived from fungal extracts modulates interactions with cellular membranes, affects endocytosis rates, and influences intracellular fate, collectively determining cytotoxic outcomes [17], [9].
9. Comparative Analysis with Other Green Synthesized AgNPs
9.1 Fungal-Derived AgNPs in Cytotoxicity Studies
A comparison among AgNPs biosynthesized from various fungi such as Ganoderma neo-japonicum, Piriformospora indica, and Seripheidium quettense reveals consistent cytotoxic potency toward cancer cell lines.
Variability in particle size, shape distribution, and stabilization molecules across fungal species accounts for differences in efficacy and stability, underscoring the importance of optimizing fungal strain selection and synthesis parameters [4], [18], [9].
9.2 Plant-Based Biosynthesis and Cytotoxicity
Plant-derived AgNPs from species like Tridax procumbens, Rhizophora apiculata, and Moringa oleifera also display pronounced anticancer activity, often influenced by the mixture of phytochemicals intrinsic to the extracts.
Comparatively, fungal-derived AgNPs tend to produce more uniform nanoparticles with superior capping by proteins, potentially leading to enhanced biocompatibility when contrasted with plant-derived counterparts [20], [21], [6].
9.3 Nanoparticle Characteristic Influence on Biological Outcomes
Synthesizing conditions directly shape nanoparticle properties such as crystallinity, size, and surface biofunctionalization, all of which modulate biological interaction and therapeutic potential.
Studies indicate that precise control over these parameters can optimize cytotoxic effects while minimizing off-target toxicity, highlighting the need for standardized protocols and thorough characterization during green synthesis [5], [9], [22].
10. Conclusions and Future Perspectives
10.1 Summary of Current Evidence on Termitomyces-Mediated AgNPs
Green synthesis of silver nanoparticles using Termitomyces heimii extracts represents a sustainable and effective method to produce biocompatible AgNPs exhibiting promising cytotoxic activity against A549 and HepG2 cancer cell lines.
Characterization techniques confirm the formation of stable, predominantly spherical crystalline nanoparticles in the desirable size range, with fungal biomolecules playing dual roles in reduction and capping. Cytotoxicity studies indicate significant apoptosis induction and growth inhibition in lung and liver cancer models, supporting potential anticancer applications [4], [11].
10.2 Identified Research Gaps and Challenges
Despite encouraging in vitro findings, critical gaps remain including comprehensive molecular elucidation of cytotoxic mechanisms, long-term safety evaluations, in vivo efficacy, and toxicity studies.
Reproducibility challenges stemming from fungal extract variability and nanoparticle physicochemical heterogeneity underscore the need for rigorous standardization. Scale-up limitations and biocompatibility profiling also warrant attention to advance clinical translation [9], [12].
10.3 Recommendations for Future Research Directions
Future investigations should focus on in-depth molecular studies employing gene expression and proteomic profiling to unravel precise intracellular pathways affected by Termitomyces mediated AgNPs.
Functionalization approaches incorporating targeting moieties could enhance selectivity and therapeutic index while minimizing adverse effects. Establishing standardized, reproducible green synthesis protocols will facilitate consistent biological evaluations and potential industrial application [8], [22].