Antiamoebic activity of plant-based natural products and their conjugated silver nanoparticles against Acanthamoeba castellanii (ATCC 50492)

Areeba Anwar,Elaine Lim Siew Ting,Noor Ul Ain,Ayaz Anwar,Muhammad Raza Shah,Ruqaiyyah Siddiqui,Shaheen Faizi,Naveed Ahmed Khan

doi:10.1186/s13568-020-0960-9

Abstract

Acanthamoeba spp. are the causative agent of Acanthamoeba keratitis and granulomatous amoebic encephalitis (GAE). The current options to treat Acanthamoeba infections have limited success. Silver nanoparticles show antimicrobial effects and enhance the efficacy of their payload at the specific biological targets. Natural folk plants have been widely used for treating diseases as the phytochemicals from several plants have been shown to exhibit amoebicidal effects. Herein, we used natural products of plant or commercial sources including quercetin (QT), kolavenic acid (PGEA) isolated from plant extracts of Polyalthia longifolia var pendula and crude plant methanolic extract of Caesalpinia pulcherrima (CPFLM) as antiacanthamoebic agents. Furthermore, these plant-based materials were conjugated with silver nanoparticles (AgNPs) to determine the effects of the natural compounds and their nanoconjugates against a clinical isolate of A. castellanii from a keratitis patient (ATCC 50492) belonging to the T4 genotype. The compounds were conjugated with AgNPs and characterized by using ultraviolet visible spectrophotometry and atomic force microscopy. Quercetin coated silver nanoparticles (QT-AgNPs) showed characteristic surface plasmon resonance band at 443 nm and the average size distribution was found to be around 45 nm. The natural compounds alone and their nanoconjugates were tested for the viability of amoebae, encystation and excystation activity against A. castellanii. The natural compounds showed significant growth inhibition of A. castellanii while QT-AgNPs specifically exhibited enhanced antiamoebic effects as well as interrupted the encystation and excystation activity of the amoebae. Interestingly, these compounds and nanoconjugates did not exhibit in vitro cytotoxic effects against human cells. Plant-based compounds and extracts could be an interesting strategy in development of alternative therapeutics against Acanthamoeba infections.

Highlights

Acanthamoeba is ubiquitously found in nature (Martinez and Visvesvara 1997)
Quercetin-AgNPs (QT-AgNPs) gave a characteristic surface plasmon resonance band at 443 nm as a representative example of QT, PGEA and CPFLM exhibited significant amoebicidal effects while silver nanoparticles conjugation enhanced their antiamoebic activity Amoebicidal assay was performed to observe the effects of the natural products and their nanoconjugates on the viability of A. castellanii. 10 μM QT, PGEA and CPFLM significantly reduced the number of A. castellanii from 5 × 105 to 2.3 × 105, 2.18 × 105 and 8.12 × 104 respectively (Fig. 3)
Several drugs have been developed to treat amoeba i.e. chlorhexidine, amphotericin B, pentamidine etc. (Niyyati et al 2016), there are several difficulties faced by the treatment introduced including toxicity of the drugs towards human cells, limited penetration through the blood brain barrier, and the morphological transformation of the trophozoites into cysts which are more tough to kill (Khan 2006)

Summary

Introduction

Acanthamoeba is ubiquitously found in nature (Martinez and Visvesvara 1997). The life cycle of Acanthamoeba consists of an active stage called trophozoites, and a dormant cyst stage (Marciano-Cabral and Cabral 2003).Acanthamoeba converts to cysts when the environment is not optimal for survival (Khan 2006). Acanthamoeba is ubiquitously found in nature (Martinez and Visvesvara 1997). The life cycle of Acanthamoeba consists of an active stage called trophozoites, and a dormant cyst stage (Marciano-Cabral and Cabral 2003). Acanthamoeba converts to cysts when the environment is not optimal for survival (Khan 2006). Cysts are very resistant in order to survive under harsh conditions. Acanthamoeba is resistant to chlorine, biocides and antibiotics (De Jonckheere and Van de Voorde 1976; Lloyd et al 2001; Turner et al 2000). The cysts may survive under low temperature ranging from 0 to 2 °C (Brown and Cursons 1977)

Methods

Results

Conclusion