Introduction
In recent years, invasive fungal infections have emerged as a significant public health threat, particularly among immunocompromised individuals such as those with HIV/AIDS, uncontrolled diabetes, hematological diseases, or those undergoing chemotherapy. Commonly encountered pathogens include Aspergillus, Coccidioides, Mucorales, and Candida auris, which can lead to life-threatening infections. Despite the availability of traditional antifungal treatments, the prevalence of these infections continues to rise, partly due to the fungi’s ability to develop resistance mechanisms against existing therapies. In response to this challenge, the development of nanoformulations, including metallic and polymer-based nanoparticles, has gained attention. These formulations aim to enhance the efficacy of conventional antifungals while minimizing adverse side effects. Strategies such as the use of coating materials, green chemistry-synthesized complexes, and polymer coupling have been employed to create new therapeutic options for treating aspergillosis and Candida infections. However, treatment options for coccidioidomycosis and mucormycosis remain limited, with most advancements still in the early stages.
Fungi, which are diverse eukaryotic organisms, thrive in various ecological niches and are capable of causing infections in humans. Although the majority of fungi are opportunistic pathogens that primarily affect individuals with weakened immune systems, a few species pose a serious threat to healthy individuals. The ability of these fungi to tolerate body temperature, grow rapidly, invade tissues, and evade the host immune system contributes to their pathogenicity. Despite the availability of both traditional and modern antifungal drugs, mycotic infections continue to rise, often due to fungal resistance to existing treatments. This scenario emphasizes the need for alternative therapeutic strategies, such as the development of drug delivery systems based on nanomaterials or nanoparticles. Nanoparticles, made from lipids, polymers, or metals, offer several advantages over traditional drugs, including reduced side effects, improved specificity to infection sites, and increased stability, solubility, and efficacy. These characteristics make nanoparticles a promising approach for combating fungal infections and overcoming resistance mechanisms, thus improving antifungal therapy and offering hope for more effective treatments in the future.
Overview of the Fungal Disease
In recent years, the incidence of invasive filamentous fungal infections has significantly increased, particularly among immunosuppressed individuals, such as those with HIV/AIDS, uncontrolled diabetes, hematological diseases, or those undergoing chemotherapy. Common pathogens like Aspergillus, Coccidioides, Mucorales, and Candida auris pose a serious public health threat. These fungi can cause severe, life-threatening infections. This review highlights the potential of nanomaterials, including both metallic and polymeric nanoparticles, as innovative strategies for treating prevalent invasive fungal infections. Additionally, the geographical distribution and epidemiological data of these fungi are summarized in the accompanying table.
Aspergillosis:
Aspergillus species, particularly Aspergillus flavus and Aspergillus fumigatus, are common molds that can produce mycotoxins, leading to various health issues such as allergies, liver toxicity, and cancer. These molds are widely found in hospital environments, causing significant patient complications. Aspergillus fumigatus, a saprotrophic fungus, spreads via airborne conidia, and can lead to lung infections, chronic pulmonary aspergillosis, or invasive pulmonary aspergillosis, particularly in immunocompromised individuals. Aspergillus is also a common cause of fungal keratitis, making it a significant life-threatening pathogen.
Coccidioidomycosis:
Coccidioidomycosis, also known as valley fever, is caused by the fungi Coccidioides immitis and Coccidioides posadasii, primarily found in the soil of certain regions in the Western Hemisphere. It is transmitted through respiratory inhalation of airborne spores. Although most infected individuals do not develop symptoms, some may experience fever, fatigue, cough, chest pain, and pneumonia. In immunocompromised individuals, the infection can disseminate to organs such as the spleen, liver, brain, and bone, leading to severe complications that require medical intervention.
Mucormycosis:
Mucormycosis is a life-threatening fungal infection caused by species of the Mucorales order, with Rhizopus and Mucor being the most common agents. These fungi are typically acquired through inhalation, ingestion, or direct skin inoculation, especially in individuals with conditions like uncontrolled diabetes, cancer, or organ transplantation. Mucormycosis can present in several forms, including rhinoorbital/cerebral, pulmonary, and cutaneous infections. The rise of COVID-19 has introduced new risk factors, with increasing cases of mucormycosis reported in COVID-19 patients, particularly in immunocompromised individuals.
Candidiasis (Candida auris):
Candida auris, an emerging pathogenic species, has raised significant concerns due to its high resistance to antifungals and its ability to spread rapidly. It is a serious opportunistic pathogen, particularly for immunocompromised patients, and can cause various infections including cutaneous, oropharyngeal, candidemia, and systemic infections. Candida auris exhibits resistance to common antifungals such as fluconazole, amphotericin B, and echinocandins, likely due to the overuse of existing treatments. Its ability to survive on environmental surfaces and resist disinfectants further complicates treatment, making the development of new nanoparticle-based antifungals crucial in combating infections caused by this species.
The Current Treatment
The antifungal agents currently available for treating systemic fungal infections are amphotericin B and liposomal preparations (lipid complexes and liposomes) of amphotericin B; azoles, specially triazoles: fluconazole, itraconazole, voriconazole, posaconazole, and isavuconazole; and echinocandins. Table 2 presents the recommendations for the treatment of fungal infections caused by filamentous fungi.
Table 2. Recommendations for the treatment of fungal infections caused by filamentous fungi and Candida auris.
Aspergillosis:
Aspergillosis is treated with three main classes of antifungal agents: polyenes, azoles, and echinocandins. Voriconazole is the first-line treatment, followed by liposomal amphotericin B. Other options include itraconazole, posaconazole, and echinocandins, particularly for patients intolerant to primary therapies. Azole-resistant Aspergillus species are emerging, and mortality from infections caused by these resistant strains has risen. Combination therapies involving amphotericin B and voriconazole or posaconazole have shown effectiveness against these infections.
Coccidioidomycosis:
The choice of antifungal treatment for coccidioidomycosis depends on infection severity and patient condition. Oral azoles like fluconazole are commonly used, but adverse effects such as hepatotoxicity and cardiac issues can occur. Overuse of fluconazole has led to resistance. In severe cases, amphotericin B is used, but it has dose-related toxicities, prompting the development of liposomal formulations to improve safety and efficacy.
Mucormycosis:
Treating mucormycosis is complex and requires early diagnosis and multiple strategies, including surgery and antifungal therapy. Amphotericin B is the primary treatment, with lipid formulations offering better therapeutic outcomes. However, nephrotoxicity and side effects are significant concerns. Other antifungals like posaconazole and isavuconazole may be used as alternatives, but updated treatment guidelines are needed for more effective management.
Candidiasis (Candida auris):
C. auris infections are challenging due to intrinsic resistance to multiple antifungal drugs, including fluconazole. Echinocandins are the recommended first-line therapy, as most isolates are susceptible to this class. While resistant to azoles, some strains of C. auris have shown susceptibility to isavuconazole, making it an option for treatment, though resistance remains a major concern.
Nanotechnology in Antifungal Therapy
Nanoparticles (NPs) are particles with sizes ranging from 1 to 100 nm and come in various shapes, such as spherical, cylindrical, or spiral. These materials have gained attention in the scientific community for their potential therapeutic and diagnostic applications, including drug delivery and detection of biological and chemical agents. NPs offer several benefits, including low toxicity, the ability to overcome biological barriers, and improved solubility and stability when conjugated with hydrophobic or hydrophilic drugs and macromolecules.
NPs are classified into three types: organic, inorganic, and carbon nanoparticles. Organic NPs, such as liposomes and dendrimers, are biodegradable and not toxic, making them ideal for biomedical applications like drug delivery. Inorganic NPs include metallic particles derived from metals like gold, silver, and zinc, as well as metal oxide nanoparticles such as titanium oxide and zinc oxide. Carbon nanoparticles include fullerenes, graphene, and carbon nanotubes, each with unique properties that make them valuable in various applications.
Aspergillosis and Nanotechnology
Nanotechnology is being explored as a promising strategy to combat Aspergillosis, a fungal infection. Nanomaterials, with their high surface area, can interact effectively with microorganisms, offering potential antimicrobial properties. The use of different nanomaterials, including metallic and polymeric nanoparticles, is being researched to enhance the effectiveness of treatments against Aspergillus infections.
Metal Nanoparticles
Metal nanoparticles, such as silver (Ag), gold (Au), and zinc oxide (ZnO), are being studied as potential antimicrobial agents. These nanoparticles show promise in inhibiting the growth of various fungi, including Aspergillus species. Studies have shown that combinations of metal nanoparticles, like Ag and ZnO, can enhance antifungal activity, with some formulations exhibiting results comparable to traditional antifungal treatments, such as amphotericin B (AmB). Additionally, these nanoparticles have shown minimal toxicity to human cells at certain concentrations, making them a viable option for antifungal treatments.
Organic Materials-Based Nanoparticles
The synthesis method of nanoparticles plays a crucial role in determining their antimicrobial properties. Organic materials-based nanoparticles, such as those made from silver and stabilized with organic molecules like citric or maleic acid, exhibit varying antifungal activities. Smaller, rounder nanoparticles tend to show better antimicrobial effects due to their increased surface area and higher release of silver ions. Additionally, nanoparticles can be combined with polymers to create composites that offer enhanced antifungal properties, especially when exposed to light or ultraviolet radiation, which generates reactive oxygen species (ROS) that damage fungal cell membranes.
Nanocomposites, such as those made from polyurethane or polyvinyl alcohol (PVA) combined with silver or titanium oxide nanoparticles, have been shown to improve antifungal activities by increasing ROS production and disrupting fungal cell membranes. These nanocomposites are effective against Aspergillus species and could provide a new approach to combating fungal infections.
Plant Extracts-Based Nanoparticles
Use of Plant Extracts for Nanoparticle Synthesis
Plant extracts are commonly studied as reducing or capping agents for synthesizing nanoparticles due to their low cost and minimal environmental toxicity. For instance, Jaffri et al. [103] used a leaf extract of Prunus cerasifera to synthesize ZnO nanoparticles (NPs) and tested their antifungal activity against drug-resistant Aspergillus strains. The synthesized ZnO NPs showed significant inhibition of growth, with larger inhibition zones than Amphotericin B (AmB) against resistant strains. This antifungal effect is attributed to the generation of reactive oxygen species (ROS) and oxidative stress.
Khan et al. [104] also synthesized ZnO NPs using Trianthema portulacastrum extract. The NPs inhibited the growth of A. niger, A. flavus, and A. fumigatus by 45%, 41%, and 51%, respectively, without causing toxic effects on human cells. Additionally, Lateef et al. [105, 106] synthesized silver nanoparticles (AgNPs) from paper wasp nest extract and Petiveria alliacea leaf extract, both showing antifungal activity against Aspergillus strains. AgNPs from both sources caused significant inhibition, with the wasp nest extract showing a stronger thrombolytic and anticoagulant activity.
Prokaryotic/Eukaryotic Culture-Based Nanoparticle Synthesis
Prokaryotic and eukaryotic cell cultures are also utilized for the green synthesis of nanoparticles. For example, El Sayed et al. [107] used Fusarium solani culture to synthesize metal NPs (Ag, Cu, ZnO) and tested their antifungal activity against Aspergillus species. The results indicated varying levels of inhibition with ZnO NPs showing the most potent effect. This effect is attributed to cell membrane damage and ROS generation.
In another study, Hashem et al. [109] used Penicillium expansum to synthesize selenium nanoparticles (Se NPs), which exhibited antifungal activity against A. fumigatus and A. niger. However, these Se NPs had relatively higher MIC values compared to other NPs. Similarly, Khan et al. [110] synthesized AgNPs from Bacillus sp. culture, which showed strong antifungal activity against A. niger, but high cytotoxicity limited their use in clinical applications. Ojo et al. [111] synthesized both monometallic and bimetallic NPs from Bacillus safensis culture, with the bimetallic Ag-Au NPs showing superior antifungal efficacy.
Nanoparticle-Based Drug Delivery Systems
Nanoparticle-based drug delivery systems offer a promising approach for enhancing the effectiveness of antifungal treatments. Roy et al. synthesized polyethylene glycol (PEG)-based nanocomposites encapsulating hexaconazole and found that the nanocomposite showed better antifungal activity against A. niger and A. fumigatus than the non-encapsulated formulation. Bhatta et al. explored the use of lecithin/chitosan nanoparticles (L/C NPs) for delivering natamycin against C. albicans and A. fumigatus, finding that L/C NPs showed comparable antifungal effects to commercial suspensions without ocular damage in in vivo testing.
Chhonker et al. used L/C NPs to deliver amphotericin B (AmB) and observed that the NPs showed similar antifungal activity against A. fumigatus compared to the commercial formulation. However, the NPs restricted drug release, suggesting a potential advantage in controlled release. Malhotra et al. encapsulated fluconazole analogs in O-alkylated dextran nanoparticles, which showed enhanced uptake and antifungal activity against A. fumigatus, requiring lower concentrations compared to free drugs.
Jung et al. encapsulated AmB in lipid nanoparticles (LNPs) and compared their antifungal activity against fluconazole-resistant A. fumigatus. The AmB-loaded LNPs showed higher in vivo survival rates in a mouse infection model than commercial formulations. Similarly, Van de Ven et al. [119] used AmB-loaded poly(D, L-lactide-co-glycolide) (PLGA) NPs, which showed significantly higher antifungal activity against A. fumigatus than other AmB formulations.
In another study, Shirkhani et al. used AmB-polymethacrylic acid (PMA) nanoparticles as a prophylactic treatment, achieving complete inhibition of fungal growth in a mouse model of invasive aspergillosis. Khames et al. developed solid lipid nanoparticles (SLNs) for natamycin delivery, which showed improved antifungal effects and a significant increase in the inhibition zone against A. fumigatus. Lakhani et al. synthesized AmB-loaded PEGylated nanostructures for improved ocular biodistribution and antifungal activity, demonstrating their potential for treating fungal infections effectively.
Coccidioidomycosis
Coccidioidomycosis, a fungal infection caused by Coccidioides species, has seen significant advancements in treatment due to nanobiotechnology. Nanotechnology has enabled the development of new drug formulations with optimized pharmacokinetic and pharmacodynamics properties, improving the efficacy and safety of treatments. Lipid-based formulations of amphotericin B (AmB), such as AmBisome (liposomal AmB) and Abelcet (AmB lipid complex), have been approved by the FDA for systemic fungal infections. These formulations address the toxicity issues associated with conventional amphotericin B by encapsulating the drug in lipid structures, which help reduce side effects while enhancing drug delivery to target areas.
Studies have demonstrated the effectiveness of these lipid formulations in treating coccidioidomycosis, including cases of disseminated and meningeal infections. AmBisome, in particular, has been shown to be a safe alternative, even for patients on steroid therapy, and it has fewer renal toxicity concerns compared to Abelcet. Research comparing the two formulations in treating coccidioidal meningitis in animal models found both were highly effective, but AmBisome showed less renal toxicity. Furthermore, lipid formulations allow for higher dosing, which could sterilize tissues and improve survival in animal models, offering a promising approach to treating severe coccidioidomycosis in humans.
Mucormycosis
Mucormycosis, caused by Mucorales fungi, has become increasingly difficult to treat due to the development of multi-drug resistance to antifungal agents such as amphotericin B, posaconazole, and isavuconazole. This resistance highlights the urgent need for new antifungal therapies. Recent developments in nano-based treatments, including nanoemulsions (NB-201), silver nanoparticles (AgNPs), and zirconium oxide nanoparticles (ZrO2NPs), show promise. While these therapies are still largely in the experimental stage, they offer potential alternatives to combat this deadly infection.
Silver nanoparticles, in particular, have shown effectiveness against Mucorales with low toxicity to human cells, making them a promising antifungal option. Research indicates that silver nanoparticles, when encapsulated with β-cyclodextrin, can reduce the growth of Mucor ramosissimus, a common Mucorales pathogen. Similarly, zirconium oxide nanoparticles have demonstrated antifungal activity against several species of Mucor and Rhizopus, while the nanoemulsion NB-201, which contains benzalkonium chloride, has proven effective in inhibiting the growth of various Mucorales species. These new nanoformulations provide hope for safer and more effective treatments for mucormycosis.
Candidiasis (Candida auris)
Various nanoparticle-based antifungal therapies are being developed and evaluated as a promising strategy to combat Candida auris (C. auris) infections, particularly against the challenges posed by multi-drug resistance. These nanoscale particles offer a new generation of antifungals with the potential to overcome fungal infections effectively. Recent research highlights the efficacy of silver nanoparticles (AgNPs), which have demonstrated significant inhibitory activity against the growth and biofilm formation of C. auris. AgNPs disrupt the cell wall of C. auris, leading to alterations in its structure, and have also shown effectiveness on medical surfaces, including silicone elastomers and bandage fibers, in preventing biofilm formation.
In addition to AgNPs, trimetallic nanoparticles composed of silver, copper, and cobalt (Ag-Cu-Co) exhibit strong fungicidal properties against C. auris. These trimetallic nanoparticles cause a reduction in fungal growth, less cell viability, and damage to the mitochondrial membrane, inducing the release of apoptotic markers. Importantly, they show no toxicity in ongoing in vivo studies, making them promising candidates for the development of antifungal agents. Bismuth nanoparticles (BiNPs) have also shown powerful antimicrobial activity, though further studies are needed to fully assess their potential against C. auris. Additionally, nanoparticles generating nitric oxide (NO) have been found to effectively eliminate C. auris, suppressing both biofilm and planktonic growth, positioning them as excellent candidates in the fight against this multidrug-resistant fungus.
Conclusion
The rise in invasive fungal diseases, exacerbated by limited antifungal options and the development of drug resistance, has highlighted the inadequacy of current therapies. This underscores the urgent need for new therapeutic strategies. Nanotechnology has emerged as a promising tool in the search for more effective treatments for invasive fungal infections. The development of various nanoformulations is currently underway, offering improvements in efficacy while minimizing adverse effects associated with conventional antifungals. Nanomaterials, such as metallic nanoparticles, green chemistry-derived complexes, and polymer-based coatings, not only enhance treatment effectiveness but also improve patient quality of life by reducing side effects, particularly during prolonged therapy. This progress is summarized in Figure 1, which outlines both current pharmacological treatments and new antifungal strategies for diseases like aspergillosis, coccidioidomycosis, mucormycosis, and candidiasis caused by Candida auris.
Figure 1. Current pharmacological treatments and the new antifungal strategies for aspergillosis, coccidioidomycosis, mucormycosis, and candidiasis caused by Candida auris.
Efforts to develop new antifungal agents, as discussed in this review, are ongoing, but therapeutic options for coccidioidomycosis and mucormycosis remain limited or are still in the early stages of development. The COVID-19 pandemic has further emphasized the need to address the increasing prevalence of these fungal infections. Moving forward, the expansion of nanotechnology and continued research are crucial to advancing the development of novel therapeutic alternatives, ultimately contributing to the progress in treating these challenging infections.
Source: León-Buitimea A, Garza-Cervantes JA, Gallegos-Alvarado DY, Osorio-Concepción M, Morones-Ramírez JR. Nanomaterial-Based Antifungal Therapies to Combat Fungal Diseases Aspergillosis, Coccidioidomycosis, Mucormycosis, and Candidiasis. Pathogens. 2021 Oct 12;10(10):1303. doi: 10.3390/pathogens10101303. PMID: 34684252; PMCID: PMC8539376.
