Alkyl-carbon chain length of two distinct compounds and derivatives are key determinants of their anti-Acanthamoeba activities

Abstract

the opportunistic pathogen, Acanthamoeba castellanii is the causative agent for the sight threatening infection Acanthamoeba keratitis (AK). it is commonly associated with contact lens wearers, and prevalence is increasing at an alarming rate due to an inadequate preventive strategy to protect the lens from this protist. This problem is compounded by the lack of an effective acanthamoebocide, particularly with cysticidal activity in the contact lens solutions. We have used cytotoxicity assays and a variety of biophysical approaches to show that two molecules with tails made of alkyl carbon, alkylphosphocholines (APCs) and quaternary ammonium compounds (QACs) had significant chain-length dependent efficacy against A. castellanii trophozoites, the latter producing death via permeabilization, and DNA complexing. QACs were more effective than APCs and had activity against cysts. Conversely, the QAC with 12 alkyl carbon chain, was non toxic, its presence increased A. castellanii trophozoites biomass and delayed encystation by 96 h. Interestingly, it was unable to induce excystation and increased trophozoite sensitivity to APC16. These results present a mono-and multi-inhibitor management strategy effective against trophozoites and cysts that may be useful for formulating into contact lense cleaning solutions and reducing AK incidence. Acanthamoeba are free-living protists, existing as active trophozoites and non-replicative cysts characterised by double cellulose cell walls 1. They have opportunistic tendencies and can cause the diseases, Acanthamoeba keratitis (AK), cutaneous acanthamoebiasis (CA) and granulomatous amoebic encephalitis (GAE) 2,3. Whilst CA and GAE are lethal but rare and affect the skin and CNS, respectively, the non-lethal AK causes severe infection in the cornea, threatening sight loss and causing emotional and psychological trauma, described as life-changing in patients 4. Trophozoites to cysts interconversion and vice versa (encystation and excystation) is induced by external environmental cues 5,6 and poses significant challenges for curative treatment particularly causing AK resurgences and relapses 7. AK cases are increasing and prevalence is high amongst contact lens users 8,9. Cases of AK within the UK have risen drastically within the last 20 years and continue to do so 10. The reason for this upsurge in incidence rates does not appear to be as a result of increased lens wearers but is as of yet unknown, likely the result of multiple factors 10. Spatial geographic differences are common with 15 times more cases reported in the UK than the USA 11,12 , and 8 times more in Scotland than England 13. These differences are strongly linked with water supply, quality and usage 12. Indeed, the incidence of AK in contact lens users is believed to be due to rinsing of contact lenses with domestic tap water 14. Further, the lack of anti-acanthamoebocides in cleaning solutions is another issue. Despite the presence of preservative compounds such as polyhexamethylene biguanide used in existing solutions,...

Structure and Antiparasitic Activity Relationship of Alkylphosphocholine Analogues against Leishmania donovani

“…The significant activity of APC12 against Sb-and Milt-resistant parasites, suggests that it can be used for treatment of leishmaniasis caused by these parasites in clinics. This observed phenomenon from the APC series in this study is pathogen-specific, as a parallel study using the same compounds against the parasitic protist, Acanthamoeba, showed that APC16 was the most active [21]. Studies from elsewhere have also produced mixed results.…”

“…Studies from elsewhere have also produced mixed results. For example, short-and long-chain APCs were most effective in reducing tumour development and against fungal infections, respectively [21][22][23][24][25]. The reason for this is speculative and possibly depends on the pathogen's membrane infrastructure, where membranes with fatty acids with long chains are easily disrupted with complementary APCs.…”

Applications of medicinal chemistry for drug discovery against Acanthamoeba infections

“…During the last two decades the AK disease has been increased especially in United Kingdom due to the extensive use of contact lens. 88,119 A large number of compounds and drugs have been used for the treatment of AK, but most of them are reported ineffective against cyst forms of Acanthamoeba castellanii. Therefore, Mooney et al, 88 assessed the biological activities of APCs and QACs against Acanthamoeba castellanii.…”

Drug Discovery against Acanthamoeba Infections: Present Knowledge and Unmet Needs

“…To develop a holistic approach to control AK certain measures should be included to augment pharmacotherapy, for example, by reducing incidence of eye infection by including new compounds with proven efficacies against trophozoites and cysts in cleaning solutions of contact lenses. In this regard, a recent study [83] showed that quaternary ammonium compounds (QACs) are more potent than APCs and had cysticidal activity against matured cysts at IC 50s 19.00 ± 0.03 µg/mL and 15.00 ± 0.06 µg/mL for QAC16, and QAC18, respectively. QAC with 12 alkyl carbon chain (QAC12) increased the biomass of trophozoites, delayed encystation by 96 h, but failed to trigger excystation.…”