Acanthamoeba Infection Research Articles

Applications of medicinal chemistry for drug discovery against Acanthamoeba infections.

Acanthamoeba is a genus of free-living amoebae, pervasively found in the environment. Most of its pathogenic species are the causative agent of sight-threatening Acanthamoeba keratitis and fatal granulomatous amoebic encephalitis. Despite the advancements in the field of chemotherapy, treating Acanthamoeba infections is still challenging due to incomplete knowledge of the complicated pathophysiology. In case of infection, the treatment regimen for the patients is often ineffective due to delayed diagnosis, poor specificity, and side-effects. Besides the resistance of Acanthamoeba cysts to most of the drugs, the recurrence of infection further complicates the recovery. Thus, it is necessary to develop an effective treatment which can eradicate these rare, but serious infections. Based on various computational and in vitro studies, it has been established that the synthetic scaffolds such as heterocyclic compounds may act as potential drug leads for the development of antiamoebic drugs. In this review, we report different classes of synthetic compounds especially heterocyclic compounds which have shown promising results against Acanthamoeba. Moreover, the antiamoebic activities of synthetic compounds with their possible mode of actions against Acanthamoeba, have been summarized and discussed in this review.

Antimicrobial effect of auranofin against Acanthamoeba spp.

Acanthamoebae are opportunistic pathogens that cause serious infections, including Acanthamoeba keratitis, a sight-threatening disease affecting mainly contact lens wearers, and granulomatous amoebic encephalitis, an infection of the central nervous system that occurs mostly in immunocompromised individuals. Although these infections are rare, they are a challenge for healthcare providers. In the last decade, the search for and implementation of novel treatment approaches against these parasites and the infections they cause have intensified, but current options are still unsatisfactory. The aim of this study was to investigate the in vitro activity of the gold-based compound auranofin against Acanthamoeba spp. The study showed that auranofin has potent antimicrobial activity against Acanthamoeba spp., with an IC50 ranging from 2.9 to 3.48 µM, and thus may be useful in the prevention and control of Acanthamoeba infections.

Generation of Infectious Mimivirus Virions Through Inoculation of Viral DNA Within Acanthamoeba castellanii Shows Involvement of Five Proteins, Essentially Uncharacterized.

One of the most curious findings associated with the discovery of Acanthamoeba polyphaga mimivirus (APMV) was the presence of many proteins and RNAs within the virion. Although some hypotheses on their role in Acanthamoeba infection have been put forward, none have been validated. In this study, we directly transfected mimivirus DNA with or without additional proteinase K treatment to extracted DNA into Acanthamoeba castellanii. In this way, it was possible to generate infectious APMV virions, but only without extra proteinase K treatment of extracted DNA. The virus genomes before and after transfection were identical. We searched for the remaining DNA-associated proteins that were digested by proteinase K and could visualize at least five putative proteins. Matrix-assisted laser desorption/ionization time-of-flight and liquid chromatography–mass spectrometry comparison with protein databases allowed the identification of four hypothetical proteins—L442, L724, L829, and R387—and putative GMC-type oxidoreductase R135. We believe that L442 plays a major role in this protein–DNA interaction. In the future, expression in vectors and then diffraction of X-rays by protein crystals could help reveal the exact structure of this protein and its precise role.

Peranan Free Living Amoeba - Achantamoeba sebagai patogen penyebab kelainan pada otak dan mata

The free-living amoeba (FLA) group of protozoa that can be found in various types of conditions in nature, one of which is the genus Acanthamoeba. Although, the number of infections caused by this protozoan is low, the diagnosis was still difficult to confirm and therefore there were a higher mortality, especially those associated with encephalitis. This review presents some information about the biology, pathogenesis, clinical symptoms caused by Acanthamoeba in humans, as well as diagnostic and therapeutic methods. Acanthamoeba infection in humans can cause disorders such as granulomatous amoebic encephalitis (GAE), acanthamoeba keratitis and cutaneous acanthamoeba. In addition, this parasite can also act as a vector of pathogens.

In vitro anti-Acanthamoeba activity of flavonoid glycosides isolated from Delphinium gracile, D. staphisagria, Consolida oliveriana and Aconitum napellus.

Acanthamoeba spp. are widely distributed in the environment and cause serious infections in humans. Treatment of Acanthamoeba infections is very challenging and not always effective which requires the development of more efficient drugs against Acanthamoeba spp. The purpose of the present study was to test medicinal plants that may be useful in the treatment of Acanthamoeba spp. Here we evaluated the trophozoital and cysticidal activity of 13 flavonoid glycosides isolated from Delphinium gracile, D. staphisagria, Consolida oliveriana and from Aconitum napellus subsp. Lusitanicum against the amoeba Acanthamoeba castellanii. AlamarBlue Assay Reagent® was used to determine the activity against trophozoites of A. castellanii, and cytotoxic using Vero cells. Cysticidal activity was assessed on treated cysts by light microscopy using a Neubauer chamber to quantify cysts and trophozoites. Flavonoids 1, 2, 3 and 4 showed higher trophozoital activity and selectivity indexes than the reference drug chlorhexidine digluconate. In addition, flavonoid 2 showed 100% cysticidal activity at a concentration of 50 μm, lower than those of the reference drug and flavonoid 3 (100 μm). These results suggest that flavonoids 2 and 3 might be used for the development of novel therapeutic approaches against Acanthamoeba infections after satisfactory in vivo evaluations.

Potential anti-Acanthamoeba and anti-adhesion activities of Annona muricata and Combretum trifoliatum extracts and their synergistic effects in combination with chlorhexidine against Acanthamoeba triangularis trophozoites and cysts

Plants with medicinal properties have been used in the treatment of several infectious diseases, including Acanthamoeba infections. The medicinal properties of Cambodian plant extracts; Annona muricata and Combretum trifoliatum were investigated against Acanthamoeba triangularis. A total of 39 plant extracts were evaluated and, as a result, 22 extracts showed positive anti-Acanthamoeba activity. Of the 22 extracts, 9 and 4 extracts showed anti-Acanthamoeba activity against trophozoites and cysts of A. triangularis, respectively. The minimum inhibitory concentration of A. muricata and C. trifoliatum extracts against trophozoites and cysts was 500 and 1,000 μg/mL, respectively. The combination of A. muricata at 1/4×MIC with chlorhexidine at 1/8×MIC demonstrated a synergistic effect against trophozoites, but partial synergy against cysts. A 40% reduction in trophozoites and 60% of cysts adhered to the plastic surface treated with both extracts at 1/2×MIC were noted comparing to the control (P < 0.05). Furthermore, a reduction of 80% and 90% of trophozoites adhered to the surface was observed after pre-treatment with A. muricata and C. trifoliatum extracts, respectively. A 90% of cysts adhered to the surface was decreased with pre-treatment of A. muricata at 1/2×MIC (P < 0.05). A 75% of trophozoites and cysts from Acanthamoeba adhered to the surface were removed after treatment with both extracts at 4×MIC (P < 0.05). In the model of contact lens, 1 log cells/mL of trophozoites and cysts was significantly decreased post-treatment with both extracts compared to the control. Trophozoites showed strong loss of acanthopodia and thorn-like projection pseudopodia, while cysts demonstrated retraction and folded appearance treated with both extracts when observed by SEM, which suggests the potential benefits of the medicinal plants A. muricata and C. trifoliatum as an option treatment against Acanthamoeba infections.

Anti-Acanthamoeba synergistic effect of chlorhexidine and Garcinia mangostana extract or \u03b1-mangostin against Acanthamoeba triangularis trophozoite and cyst forms

Acanthamoeba spp. can cause amoebic keratitis (AK). Chlorhexidine is effective for AK treatment as monotherapy, but with a relative failure on drug bioavailability in the deep corneal stroma. The combination of chlorhexidine and propamidine isethionate is recommended in the current AK treatment. However, the effectiveness of treatment depends on the parasite and virulence strains. This study aims to determine the potential of Garcinia mangostana pericarp extract and α-mangostin against Acanthamoeba triangularis, as well as the combination with chlorhexidine in the treatment of Acanthamoeba infection. The minimal inhibitory concentrations (MICs) of the extract and α-mangostin were assessed in trophozoites with 0.25 and 0.5 mg/mL, for cysts with 4 and 1 mg/mL, respectively. The MIC of the extract and α-mangostin inhibited the growth of A. triangularis trophozoites and cysts for up to 72 h. The extract and α-mangostin combined with chlorhexidine demonstrated good synergism, resulting in a reduction of 1/4–1/16 of the MIC. The SEM results showed that Acanthamoeba cells treated with a single drug and its combination caused damage to the cell membrane and irregular cell shapes. A good combination displayed by the extract or α-mangostin and chlorhexidine, described for the first time. Therefore, this approach is promising as an alternative method for the management of Acanthamoeba infection in the future.

Evaluation of Anti-amoebic Activity of Spring Leaf Extract of Artemisia Aucheri on Acanthamoeba (T4 strain) In vitro

Background: Acanthamoeba belongs to the free-living amoebae genus that causes a widespread infection with different severities in humans and animals. Treatment of these opportunistic protozoan infections is still not safe or effective. The aim of the present study was to evaluate the effect of spring extract of Artemisia aucheri on Acanthamoeba in vitro. Method: Trophozoites and cysts of Acanthamoeba were cultured on non-nutrient agar plates containing bacteria Escherichia coli. Macrophage cells were cultured in RPMI-1640 medium. : Different concentrations of spring extracts of A. aucheri were added to cultivated parasites and macrophages and additionally calculated to determine the 50% inhibitory concentration (IC50) for parasites and 50% cytotoxic concentration (CC50) for macrophages. Then, the viability of parasites were evaluated using counting assay. MTT assay was carried out on macrophage cells based on growth inhibition. Furthermore, in order to determine the possible induction of apoptosis in cysts of Acanthamoeba, flow cytometry method was employed using annexin staining. Results: The effect of A. aucheri on trophozoites and cysts of Acanthamoeba was effective and had a reverse relationship with its concentration. The IC50 value of spring extract on trophozoites and cysts of the parasite was estimated to be 200 and 333 μg/ml at 24 h, respectively. According to the results of flow cytometry, the spring A. aucheri extract caused about 20% apoptosis. Conclusion: Regarding the above results, it can be concluded that spring A. aucheri extract was effective against trophozoite and cyst forms of Acanthamoeba in vitro. Therefore, this plant could be an appropriate herbal drug candidate for the treatment of Acanthamoeba infections.

A Rare Case Of Acanthamoeba Endophthalmitis Following Cataract Surgery

Acanthamoeba are ubiquitous microorganisms and are considered opportunistic pathogens in humans. Acanthamoeba infection involving the vitreous, retina or choroid is uncommon and is mostly seen following corneal infections or corneal transplant surgeries. (1,2) We present a rare case of post-operative endophthalmitis due to Acanthamoeba in a 30-year old gentleman who underwent cataract surgery in his left eye. The initial routine microscopy and culture reports were negative for bacteria and fungus, and inspite of empirical treatment for endophthamitis, the patient’s ocular condition worsened. Following multiple vitrectomy surgery and repeated negative culture as well as polymerase chain reaction (PCR) for bacteria, virus and fungi, PCR for Acanthamoeba species was reported positive. On starting the patient on intravitreal and topical voriconazole along with oral ketoconazole the patient’s eye condition improved with moderate recovery of visual acuity. To the best of our knowledge, this is the first case reported of Acanthamoeba endophthalmitis following cataract surgery.

250 Fatal Disseminated Acanthamoeba Infection in a Kidney Transplant Recipient

250 Fatal Disseminated Acanthamoeba Infection in a Kidney Transplant Recipient

Should Veterinary Practitioners Be Concerned about Acanthamoeba Keratitis?

When presented with an animal exhibiting signs of keratitis (inflammation of the cornea), such as impaired vision, mucoid discharges, redness, swelling, and corneal oedema, most veterinarians would think of bacteria, viruses, or fungi as the potential causative agent(s). However, evidence has arisen in recent years of a possible connection between the protozoan Acanthamoeba and keratitis in animals. Acanthamoeba infection is underdiagnosed, but potentially common, in animals. In view of the paucity of evidence regarding Acanthamoeba keratitis (AK) in animals, this review has been written to increase awareness of veterinary professionals of the potential threat associated with AK and to stimulate more studies into the extent of occurrence and clinical impact of AK in animals.

A Systematic Review of Intracellular Microorganisms within Acanthamoeba to Understand Potential Impact for Infection.

Acanthamoeba, an opportunistic pathogen is known to cause an infection of the cornea, central nervous system, and skin. Acanthamoeba feeds different microorganisms, including potentially pathogenic prokaryotes; some of microbes have developed ways of surviving intracellularly and this may mean that Acanthamoeba acts as incubator of important pathogens. A systematic review of the literature was performed in order to capture a comprehensive picture of the variety of microbial species identified within Acanthamoeba following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Forty-three studies met the inclusion criteria, 26 studies (60.5%) examined environmental samples, eight (18.6%) studies examined clinical specimens, and another nine (20.9%) studies analysed both types of samples. Polymerase chain reaction (PCR) followed by gene sequencing was the most common technique used to identify the intracellular microorganisms. Important pathogenic bacteria, such as E. coli, Mycobacterium spp. and P. aeruginosa, were observed in clinical isolates of Acanthamoeba, whereas Legionella, adenovirus, mimivirus, and unidentified bacteria (Candidatus) were often identified in environmental Acanthamoeba. Increasing resistance of Acanthamoeba associated intracellular pathogens to antimicrobials is an increased risk to public health. Molecular-based future studies are needed in order to assess the microbiome residing in Acanthamoeba, as a research on the hypotheses that intracellular microbes can affect the pathogenicity of Acanthamoeba infections.

Immunopathogenicity of Acanthamoeba spp. in the Brain and Lungs.

Free-living amoebas, including Acanthamoeba spp., are widely distributed in soil, water, and air. They are capable of causing granulomatous amebic encephalitis, Acanthamoeba pneumonia, Acanthamoeba keratitis, and disseminated acanthamoebiasis. Despite low occurrence worldwide, the mortality rate of Acanthamoeba spp. infections is very high, especially in immunosuppressed hosts. Acanthamoeba infections are a medical problem, owing to limited improvement in diagnostics and treatment, which is associated with incomplete knowledge of pathophysiology, pathogenesis, and the host immune response against Acanthamoeba spp. infection. The aim of this review is to present the biochemical and molecular mechanisms of Acanthamoeba spp.–host interactions, including the expression of Toll-like receptors, mechanisms of an immune response, the activity of metalloproteinases, the secretion of antioxidant enzymes, and the expression and activity of cyclooxygenases. We show the relationship between Acanthamoeba spp. and the host at the cellular level and host defense reactions that lead to changes in the selected host’s organs.

Derivatisation of metronidazole enhances cytotoxic effect against Acanthamoeba genotype T4 isolates and leads to cytomorphological changes in trophozoites

Amoebae of the genus Acanthamoeba are worldwide distributed causative agents of serious human infections such as granulomatous amoebic encephalitis (GAE) and Acanthamoeba keratitis (AK). To date, treatment of these infections is non-uniform and frequently unsuccessful. Recently, the phosphonium salts were studied for their high levels of antimicrobial activity. This work was aimed to investigate the cytotoxic effect of metronidazole and two phosphonium salts (PS1, PS2) on two clinical Acanthamoeba isolates. The isolates showed distinctly higher susceptibility to both phosphonium salts than to metronidazole. The highest susceptibility was noted to PS1 after 48 h of incubation. Metronidazole derivate PS2 showed higher susceptibility than metronidazole. The values of EC50 of PS2 were approximately twenty times lower than EC50 of metronidazole for Acanthamoeba lugdunensis strain and sixteen times lower for Acanthamoeba quina strain after 48 h. Although the therapeutic effect of metronidazole in Acanthamoeba infections is usually insufficient, its derivatisation can result in a significantly higher amoebicidal effect. Cytomorphological changes of trophozoites after exposure to tested compounds included rounding up of the cells, damage of membrane integrity, presence of pathological protrusions, elongation of the cells or pseudocyst-like stages. Obtained results indicate possible therapeutic potential of studied phosphonium salts.

COMMERCIAL EYE DROPS TRIGGERS NECROTIC EFFECT IN Acanthamoeba sp.

Eye infection due to microbial infection is hard to treat and painful. Two types of eye drops that are commonly used to relieve eye pain offered by pharmacists have been tested in this study namely solution A (containing tetrahydrozoline hydrochloride) and solution B (containing gentamicin and dexamethasone). The efficacy and the activities of these eye drops were tested on Acanthamoeba sp. (a clinical isolate from an Acanthamoeba keratitis patient) to study the cytotoxicity effects of the solutions on the Acanthamoeba. The Acanthamoeba were exposed to solution A and B for 24 hr and cell viability was assessed using MTT assays, morphological changes using the light microscope and through acridine orange and propidium iodide (AO/PI) staining for cytoplasmic biochemical activities. The IC50 value for Acanthamoeba cell viability was 45.1% and 20.3% for solutions A and B respectively. Morphological observation shows the inhibition of acanthapodia formation on the surface of the cells. Solution A and B-treated Acanthamoeba appeared in the red color of the cytoplasm upon staining with AO/PI indicating a necrotic mode of cell death. This is due to loss of membrane integrity of Acanthamoeba cell membrane after exposed to solution A and B at their IC50 value. It is shown that solutions A and B can cause cell death in trophozoite of Acanthamoeba cells at moderate IC50 value. Unfortunately, the necrosis mode of cell death is not a preferable type of cell death for treating Acanthamoeba infection. Therefore, it can be concluded that solutions A and B are not suitable to treat eye infected with Acanthamoeba sp. as it does not promise absolute healing as the solution concentration needed is quite high and the cell death mechanism is necrosis.

In vitro amoebicidal effect of Aloe vera ethanol extract and honey against Acanthamoeba spp. cysts.

This study evaluated in vitro effect of different concentrations of Aloe vera (A. vera) ethanol extract and honey against Acanthamoeba spp. cysts in comparison with chlorhexidine (the drug of choice for treatment of Acanthamoeba infection) at different incubation periods. Four different concentrations of the tested agents were used, 100, 200, 400, and 600μg/ml for A. vera ethanol extract and 25, 50, 100, and 200μg/ml for honey. Isolated Acanthamoeba spp. cysts from keratitis patients were incubated with different concentrations of the tested agents as well as chlorhexidine 0.02% (drug control) for different incubation periods (24, 48, 72h). After each incubation period, the effect of A. vera extract and honey against Acanthamoeba cysts was assessed by counting the number of viable cysts, determining the inhibitory percentage and detecting the morphological alternations of treated cysts compared to non-treated and drug controls. Both A. vera ethanol extract and honey showed a concentration and time-dependent effect on the viability of Acanthamoeba cysts. In comparison with chlorhexidine (the drug control), A. vera ethanol extract possessed a potent cysticidal activity at all tested concentrations throughout different incubation periods, except for concentration 100μg/ml which recorded the lower inhibitory effect. With increasing the dose of A. vera ethanol extract to 200, 400, 600µg/ml, the recorded inhibitory percentages of Acanthamoeba cysts viability were 82.3%, 92.9% and 97.9% respectively, after 72h compared to 76.3% of chlorhexidine. Similarly, honey at concentrations of 50-100µg/ml gave higher inhibitory effect of 59% and 76.7%, respectively compared to chlorhexidine which showed an inhibitory percentage of 55.7% after 24h. Meanwhile, the lowest tested concentration of honey (25µg/ml) gave an inhibitory effect by 47.7-67% which was less than that of chlorhexidine throughout different incubation periods. With increasing the dose of honey to 200µg/ml, the inhibitory effect was 98.9% after 72h higher than that of chlorhexidine (76.9%). Using a scanning electron microscope, Acanthamoeba cysts treated by A. vera ethanol extract showed alternations in their shapes with flattening, collapsing, and laceration of their walls. Also, treated cysts by honey were highly distorted and difficult to identify because most of them were shrinkage and collapsed to a tiny size. On the other hand, chlorhexidine showed less structural and morphological changes of Acanthamoeba cysts. A. vera ethanol extract and honey had considerable cysticidal effects on Acanthamoeba cysts. They may give promising results for treatment of Acanthamoeba keratitis.

PLGA nanoparticles loaded with Gallic acid- a constituent of Leea indica against Acanthamoeba triangularis

Acanthamoeba, a genus that contains at least 24 species of free-living protozoa, is ubiquitous in nature. Successful treatment of Acanthamoeba infections is always very difficult and not always effective. More effective drugs must be developed, and medicinal plants may have a pivotal part in the future of drug discovery. Our research focused on investigating the in vitro anti- acanthamoebic potential of Leea indica and its constituent gallic acid in different concentrations. Water and butanol fractions exhibited significant amoebicidal activity against trophozoites and cysts. Gallic acid (100 µg/mL) revealed 83% inhibition of trophozoites and 69% inhibition of cysts. The butanol fraction induced apoptosis in trophozoites, which was observed using tunnel assay. The cytotoxicity of the fractions and gallic acid was investigated against MRC-5 and no adverse effects were observed. Gallic acid was successfully loaded within poly (D,L-lactide-co-glycolide) (PLGA) nanoparticles with 82.86% encapsulation efficiency, while gallic acid showed 98.24% in vitro release at 48 hours. Moreover, the gallic acid encapsulated in the PLGA nanoparticles exhibited 90% inhibition against trophozoites. In addition, gallic acid encapsulated nanoparticles showed reduced cytotoxicity towards MRC-5 compared to gallic acid, which evidenced that natural product nanoencapsulation in polymeric nanoparticles could play an important role in the delivery of natural products.

Antiamoebic activity of 3-aryl-6,7-dimethoxyquinazolin-4(3H)-one library against Acanthamoeba castellanii.

Acanthamoeba castellanii is a free-living amoeba which can cause a blinding keratitis and fatal granulomatous amoebic encephalitis. The treatment of Acanthamoeba infections is challenging due to formation of cyst. Quinazolinones are medicinally important scaffold against parasitic diseases. A library of nineteen new 3-aryl-6,7-dimethoxyquinazolin-4(3H)-one derivatives was synthesized to evaluate their antiamoebic activity against Acanthamoeba castellanii. One-pot synthesis of 3-aryl-6,7-dimethoxyquinazolin-4(3H)-ones (1-19) was achieved by reaction of 2-amino-4,5-dimethoxybenzoic acid, trimethoxymethane, and different substituted anilines. These compounds were purified and characterized by standard chromatographic and spectroscopic techniques. Antiacanthamoebic activity of these compounds was determined by amoebicidal, encystation, excystation and host cell cytopathogenicity in vitro assays at concentrations of 50 and 100μg/mL. The IC50 was found to be between 100 and 50μg/mL for all the compounds except compound 5 which did not exhibit amoebicidal effects at these concentrations. Furthermore, lactate dehydrogenase assay was also performed to evaluate the in vitro cytotoxicity of these compounds against human keratinocyte (HaCaT) cells. The results revealed that eighteen out of nineteen derivatives of quinazolinones significantly decreased the viability of A. castellanii. Furthermore, eighteen out of nineteen tested compounds inhibited the encystation and excystation, as well as significantly reduced the A. castellanii-mediated cytopathogenicity against human cells. Interestingly, while tested against human normal cell line HaCaT keratinocytes, all compounds did not exhibit any overt cytotoxicity. Furthermore, a detailed structure-activity relationship is also studied to optimize the most potent hit from these synthetic compounds. This report presents several potential lead compounds belonging to 3-aryl-6,7-dimethoxyquinazolin-4(3H)-one derivatives for drug discovery against infections caused by Acanthamoeba castellanii.

Metformin-coated silver nanoparticles exhibit anti-acanthamoebic activities against both trophozoite and cyst stages

Acanthamoeba castellanii is an opportunistic protozoan responsible for serious human infections including Acanthamoeba keratitis and granulomatous amoebic encephalitis. Despite advances in antimicrobial therapy and supportive care, infections due to Acanthamoeba are a major public concern. Current methods of treatment are not fully effective against both the trophozoite and cyst forms of A. castellanii and are often associated with severe adverse effects, host cell cytotoxicity and recurrence of infection. Therefore, there is an urgent need to develop new therapeutic approaches for the treatment and management of Acanthamoebic infections. Repurposing of clinically approved drugs is a viable avenue for exploration and is particularly useful for neglected and rare diseases where there is limited interest by pharmaceutical companies. Nanotechnology-based drug delivery systems offer promising approaches in the biomedical field, particularly in diagnosis and drug delivery. Herein, we conjugated an antihyperglycemic drug, metformin with silver nanoparticles and assessed its anti-acanthamoebic properties. Characterization by ultraviolet–visible spectrophotometry and atomic force microscopy showed successful formation of metformin-coated silver nanoparticles. Amoebicidal and amoebistatic assays revealed that metformin-coated silver nanoparticles reduced the viability and inhibited the growth of A. castellanii significantly more than metformin and silver nanoparticles alone at both 5 and 10 μM after 24 h incubation. Metformin-coated silver nanoparticles also blocked encystation and inhibited the excystation in Acanthamoeba after 72 h incubation. Overall, the conjugation of metformin with silver nanoparticles was found to enhance its antiamoebic effects against A. castellanii. Furthermore, the pretreatment of A. castellanii with metformin and metformin-coated silver nanoparticles for 2 h also reduced the amoebae-mediated host cell cytotoxicity after 24 h incubation from 73% to 10% at 10 μM, indicating that the drug-conjugated silver nanoparticles confer protection to human cells. These findings suggest that metformin-coated silver nanoparticles hold promise in the improved treatment and management of Acanthamoeba infections.

Drug Discovery against Acanthamoeba Infections: Present Knowledge and Unmet Needs

Although major strides have been made in developing and testing various anti-acanthamoebic drugs, recurrent infections, inadequate treatment outcomes, health complications, and side effects associated with the use of currently available drugs necessitate the development of more effective and safe therapeutic regimens. For any new anti-acanthamoebic drugs to be more effective, they must have either superior potency and safety or at least comparable potency and an improved safety profile compared to the existing drugs. The development of the so-called ‘next-generation’ anti-acanthamoebic agents to address this challenge is an active area of research. Here, we review the current status of anti-acanthamoebic drugs and discuss recent progress in identifying novel pharmacological targets and new approaches, such as drug repurposing, development of small interfering RNA (siRNA)-based therapies and testing natural products and their derivatives. Some of the discussed approaches have the potential to change the therapeutic landscape of Acanthamoeba infections.