In Vitro Amoebicidal Activity of Titanium Dioxide/UV-A Combination AgainstAcanthamoeba

Applications of photodynamic therapy in keratitis

Keratitis is corneal inflammatory disease which may be caused by several reason such as an injury, allergy, as well as a microbial infection. Besides these, overexposure to ultraviolet light and unhygienic practice of contact lenses are also associated with keratitis. Based on the cause of keratitis, different lines of treatments are recommended. Photodynamic therapy is a promising approach that utilizes light activated compounds to instigate either killing or healing mechanism to treat various diseases including both communicable and non-communicable diseases. This review focuses on clinically-important patent applications and the recent literature for the use of photodynamic therapy against keratitis.

Therapeutic contact lenses for the treatment of corneal and ocular surface diseases: advances in extended and targeted drug delivery

The eye is one of the most important organs in the human body providing critical information on the environment. Many corneal diseases can lead to vision loss affecting the lives of people around the world. Ophthalmic drug delivery has always been a major challenge in the medical sciences. Since traditional methods are less efficient (∼ 5%) at delivering drugs to ocular tissues, contact lenses have generated growing interest in ocular drug delivery due to their potential to enhance drug bioavailability in ocular tissues. The main techniques used to achieve sustained release are discussed in this review, including soaking in drug solutions, incorporating drug into multilayered contact lenses, use of vitamin E barriers, molecular imprinting, nanoparticles, micelles and liposomes. The most clinically relevant results on different eye pathologies are presented. In addition, this review summarizes the benefits of contact lenses over eye drops, strategies for incorporating drugs into lenses to achieve sustained release, results of in vitro and in vivo studies, and the recent advances in the commercialization of therapeutic contact lenses for allergic conjunctivitis.

Modular nanotheranostic agents for protistan parasitic diseases: Magic bullets with tracers

Protistan parasitic infections contribute significantly to morbidity and mortality, causing more than 2 billion human infections annually. However, current treatments are often limited; due to ineffective drugs and drug resistance, thus better options are urgently required. In the present context, theranostics agents are those that offer simultaneous detection, diagnosis and even treatment of protistan parasitic diseases. "Nanotheranostics" is the term used to describe such agents, that are around 100 nm or less in size. Anti-parasitic activity of nanoparticles (NPs) has been reported, and many have useful intrinsic imaging properties, but it is perhaps their multifunctional nature that offers the greatest potential. NPs may be used as adapters onto which various subunits with different functions may be attached. These subunits may facilitate targeting parasites, coupled with toxins to eradicate parasites, and probe subunits for detection of particles and/or parasites. The modular nature of nano-platforms promises a "mix and match" approach for the construction of tailored agents by using combinations of these subunits against different protistan parasites. Even though many of the subunits have shown promise alone, these have not yet been put together convincingly enough to form working theranostics against protistan parasites. Although the clinical application of nanotheranostics to protistan parasitic infections in humans requires more research, we conclude that they offer not just a realisation of Paul Ehrlich's long imagined "magic bullet" concept, but potentially are magic bullets combined with tracer bullets.

The Activity of Polyhomoarginine against Acanthamoeba castellanii

Arginine-rich peptides can have broad-spectrum anti-bacterial and anti-fungal activities. Polyhomoarginine consists of highly cationic residues which can act on the negatively charged microbial cell membranes. Acanthamoeba is a free-living protozoan known to cause a rare corneal infection which is difficult to diagnose and treat. This study evaluated the activity of the polyhomoarginines against Acanthamoeba castellanii. Acanthamoeba amoebicidal, amoebistatic, encystation and excystment assays were performed using protocols described in the literature. The activity of polyhomoarginines (PHAs) of different lengths (10 to 400 residues) was measured against the trophozoites and cysts of Acanthamoeba castellanii ATCC30868 in concentrations ranging from 0.93 μM to 15 μM. Data were represented as mean ± SE and analysed using one-way ANOVA. Overall, PHAs demonstrated good anti-acanthamoeba activity against both trophozoites and cysts. PHA 30 reduced the number of viable trophozoites by 99%, inhibited the formation of cysts by 96% and the emergence of trophozoites from cysts by 67% at 3.75 μM. PHA 10 was similarly active, but at a slightly higher concentration of 15 μM, reducing the numbers of viable trophozoites by 98%, inhibiting cyst formation by 84% and preventing the emergence of trophozoites from cysts by 99%. At their greatest anti-amoeba concentrations, PHA 10 gave only 8% haemolysis at 15 μM while PHA 30 gave <40 % haemolysis at 3.75 μM. Polyhomoarginine 10 showed excellent anti-amoebic activity against both forms of Acanthamoeba castellanii and was non-toxic at its most active concentrations. This implies that polyhomoarginines can be developed into a potential therapeutic agent for Acanthamoeba keratitis. However, there is a need to carry out further pre-clinical and then in vivo experiments in the AK animal model.

Acanthamoeba Keratitis: an update on amebicidal and cysticidal drug screening methodologies and potential treatment with azole drugs

Introduction: Acanthamoeba encompasses several species of free-living ameba encountered commonly throughout the environment. Unfortunately, these species of ameba can cause opportunistic infections that result in Acanthamoeba keratitis, granulomatous amebic encephalitis, and occasionally systemic infection.Areas covered: This review discusses relevant literature found through PubMed and Google scholar published as of January 2021. The review summarizes current common Acanthamoeba keratitis treatments, drug discovery methodologies available for screening potential anti-Acanthamoeba compounds, and the anti-Acanthamoeba activity of various azole antifungal agents.Expert opinion: While several biguanide and diamidine antimicrobial agents are available to clinicians to effectively treat Acanthamoeba keratitis, no singular treatment can effectively treat every Acanthamoeba keratitis case.Efforts to identify new anti-Acanthamoeba agents include trophozoite cell viability assays, which are amenable to high-throughput screening. Cysticidal assays remain largely manual and would benefit from further automation development. Additionally, the existing literature on the effectiveness of various azole antifungal agents for treating Acanthamoeba keratitis is incomplete or contradictory, suggesting the need for a systematic review of all azoles against different pathogenic Acanthamoeba strains.

Antimicrobial nanomedicine for ocular bacterial and fungal infection

Ocular infection induced by bacteria and fungi is a major cause of visual impairment and blindness. Topical administration of antibiotics remains the first-line treatment, as effective eradication of pathogens is the core of the anti-infection strategy. Whereas, eye drops lack efficiency and have relatively low bioavailability. Intraocular injection may cause concurrent ocular damage and secondary infection. In addition, antibiotic-based management can be limited by the low sensitivity to multidrug-resistant bacteria. Nanomedicine is proposed as a prospective, effective, and noninvasive platform to mediate ocular delivery and combat pathogen or even resistant strains. Nanomedicine can not only carry antimicrobial agents to fight against pathogens but also directly active microbicidal capability, killing pathogens. More importantly, by modification, nanomedicine can achieve enhanced residence time and release time on the cornea, and easy penetration through corneal tissues into anterior and posterior segments of the eye, thus improving the therapeutic effect for ocular infection. In this review, several categories of antimicrobial nanomedicine are systematically discussed, where the efficiency and possibility of further embellishment and improvement to adapt to clinical use are also investigated. All in all, novel antimicrobial nanomedicine provides potent and prospective ways to manage severe and refractory ocular infections.

Anti-amoebic potential of azole scaffolds and nanoparticles against pathogenic Acanthamoeba

Acanthamoeba spp. are free living amoeba (FLA) which are widely distributed in nature. They are opportunistic parasites and can cause severe infections to the eye, skin and central nervous system. The advances in drug discovery and modifications in the chemotherapeutic agents have shown little improvement in morbidity and mortality rates associated with Acanthamoeba infections. The mechanism-based process of drug discovery depends on the molecular drug targets present in the signaling pathways in the genome. Synthetic libraries provide a platform for broad spectrum of activities due to their desired structural modifications. Azoles, originally a class of synthetic anti-fungal drugs, disrupt the fungal cell membrane by inhibiting the biosynthesis of ergosterol through the inhibition of cytochrome P450 dependent 14α-lanosterol, a key step of the sterol pathway. Acanthamoeba and fungi share the presence of similar sterol intermediate, as ergosterol is also the major end-product in the sterol biosynthesis in Acanthamoeba. Sterols present in the eukaryotic cell membrane are one of the most essential lipids and exhibit important structural and signaling functions. Therefore, in this review we highlight the importance of specific targeting of ergosterol present in Acanthamoebic membrane by azole compounds for amoebicidal activity. Previously, azoles have also been repurposed to report antimicrobial, antiparasitic and antibacterial properties. Moreover, by loading the azoles into nanoparticles through advanced techniques in nanotechnology, such as physical encapsulation, adsorption, or chemical conjugation, the pharmacokinetics and therapeutic index of the drugs can be significantly improved. The current review proposes an important strategy to target Acanthamoeba using synthetic libraries of azoles and their conjugated nanoparticles for the first time.

Nanoparticles based therapeutic efficacy against Acanthamoeba: Updates and future prospect

Acanthamoeba sp. is a free living amoeba that causes severe, painful and fatal infections, viz. Acanthamoeba keratitis and granulomatous amoebic encephalitis among humans. Antimicrobial chemotherapy used against Acanthamoeba is toxic to human cells and show side effects as well. Infections due to Acanthamoeba also pose challenges towards currently used antimicrobial treatment including resistance and transformation of trophozoites to resistant cyst forms that can lead to recurrence of infection. Therapeutic agents targeting central nervous system infections caused by Acanthamoeba should be able to cross blood-brain barrier. Nanoparticles based drug delivery put forth an effective therapeutic method to overcome the limitations of currently used antimicrobial chemotherapy. In recent years, various researchers investigated the effectiveness of nanoparticles conjugated drug and/or naturally occurring plant compounds against both trophozoites and cyst form of Acanthamoeba. In the current review, a reasonable effort has been made to provide a comprehensive overview of various nanoparticles tested for their efficacy against Acanthamoeba. This review summarizes the noteworthy details of research performed to elucidate the effect of nanoparticles conjugated drugs against Acanthamoeba.

Metronidazole conjugated magnetic nanoparticles loaded with amphotericin B exhibited potent effects against pathogenic Acanthamoeba castellanii belonging to the T4 genotype

Acanthamoeba castellanii can cause granulomatous amoebic encephalitis and Acanthamoeba keratitis. Currently, no single drug has been developed to effectively treat infections caused by Acanthamoeba. Recent studies have shown that drugs conjugated with nanoparticles exhibit potent in vitro antiamoebic activity against pathogenic free-living amoebae. In this study, we have developed a nano drug delivery system based on iron oxide nanoparticles conjugated with metronidazole which were further loaded with amphotericin B to produce enhanced antiamoebic effects against Acanthamoeba castellanii. The results showed that metronidazole-nanoparticles-amphotericin B (Met-MNPs-Amp) significantly inhibited the viability of these amoebae as compared to the respective controls including drugs and nanoparticles alone. Met-MNPs-Amp exhibited IC₅₀ at 50 μg/mL against both A. castellanii trophozoites and cysts. Furthermore, these nanoparticles did not affect the viability of rat and human cells and showed safe hemolytic activity. Hence, the results obtained in this study have potential utility in drug development against infections caused by Acanthamoeba castellanii. A combination of drugs can lead to successful prognosis against these largely neglected infections. Future studies will determine the value of conjugating molecules with diagnostic and therapeutic potential to provide theranostic approaches against these serious infections.

Isoniazid Conjugated Magnetic Nanoparticles Loaded with Amphotericin B as a Potent Antiamoebic Agent against Acanthamoeba castellanii

The pathogenic free-living amoeba, Acanthamoeba castellanii, is responsible for a rare but deadly central nervous system infection, granulomatous amoebic encephalitis and a blinding eye disease called Acanthamoeba keratitis. Currently, a combination of biguanides, amidine, azoles and antibiotics are used to manage these infections; however, the host cell cytotoxicity of these drugs remains a challenge. Furthermore, Acanthamoeba species are capable of transforming to the cyst form to resist chemotherapy. Herein, we have developed a nano drug delivery system based on iron oxide nanoparticles conjugated with isoniazid, which were further loaded with amphotericin B (ISO-NPs-AMP) to cause potent antiamoebic effects against Acanthamoeba castellanii. The IC₅₀ of isoniazid conjugated with magnetic nanoparticles and loaded with amphotericin B was found to be 45 μg/mL against Acanthamoeba castellanii trophozoites and 50 μg/mL against cysts. The results obtained in this study have promising implications in drug discovery as these nanomaterials exhibited high trophicidal and cysticidal effects, as well as limited cytotoxicity against rat and human cells.

Cobalt nanoparticles as novel nanotherapeutics against Acanthamoeba castellanii

Background

Species of Acanthamoeba are facultative pathogens which can cause sight threatening Acanthamoeba keratitis and a rare but deadly brain infection, granulomatous amoebic encephalitis. Due to conversion of Acanthamoeba trophozoites to resistant cyst stage, most drugs are found to be ineffective at preventing recurrence of infection. This study was designed to test the antiacanthamoebic effects of different cobalt nanoparticles (CoNPs) against trophozoites and cysts, as well as parasite-mediated host cell cytotoxicity.

Methods

Three different varieties of CoNPs were synthesized by utilizing hydrothermal and ultrasonication methods and were thoroughly characterized by X-ray diffraction and field emission scanning electron microscopy. Amoebicidal, encystation, excystation, and host cell cytopathogenicity assays were conducted to study the antiacanthamoebic effects of CoNPs.

Results

The results of the antimicrobial evaluation revealed that cobalt phosphate Co₃(PO₄)₂ hexagonal microflakes, and 100 nm large cobalt hydroxide (Co(OH)₂) nanoflakes showed potent amoebicidal activity at 100 and 10 µg/ml against Acanthamoeba castellanii as compared to granular cobalt oxide (Co₃O₄) of size 35–40 nm. Furthermore, encystation and excystation assays also showed consistent inhibition at 100 µg/ml. CoNPs also inhibited amoebae-mediated host cell cytotoxicity as determined by lactate dehydrogenase release without causing significant damage to human cells when treated alone.

Conclusions

To our knowledge, these findings determined, for the first time, the effects of composition, size and morphology of CoNPs against A. castellanii. Co₃(PO₄)₂ hexagonal microflakes showed the most promising antiamoebic effects as compared to Co(OH)₂ nanoflakes and granular Co₃O₄. The results reported in the present study hold potential for the development of antiamoebic nanomedicine.