Resistance to
antimony is a major cause of failure to
therapy in a large proportion of
visceral leishmaniasis cases. Methods to distinguish resistant and sensitive parasite are urgently needed as the standard in vitro intracellular drug susceptibility assays are cumbersome and time consuming. Differential expression profiling studies have led to the identification of several
antimony resistance-associated genes; however, their efficacy as a potential
biomarker for monitoring
antimony resistance remains imprecise. We analysed the expression of eight genes [
antimony metabolism-associated genes - multidrug resistance
protein A (MRPA), γ-
glutamylcysteine synthetase (γ-GCS) and aquaporin-1 (AQP1) - and genes identified by
proteome/transcriptome profiling—heat
shock protein 83,
mitogen-activated protein kinase 1 and
histones H1, H2A and H4) in
antimony-resistant (n=10) and
antimony-sensitive (n=4) clinical isolates of Leishmania donovani by quantitative real-time PCR, in comparison with a lab-generated resistant and a standard sensitive isolate. We observed a significant differential expression of MRPA,
histone H1 (p<0.01), γ-GCS, HSP83 (p<0.005) and
histone H2A and H4 (p<0.0001) in a group of
sodium antimony gluconate-resistant isolates compared to sensitive isolates. Preferential AQP1 expression was observed in all the sensitive isolates (p<0.0001). Overall, expression profile in field isolates for all the genes studied showed altered expression in majority of isolates, while in some, the expression was static. All the isolates showed a mosaic of expression pattern of the genes analysed indicating constellation of genes contributes towards the drug susceptibility of parasite. As none of the genes exhibit an absolute correlation with phenotype, targeted expression analysis of a set of genes should be considered as
biomarker for distinguishing the
antimony-resistant and
antimony-sensitive parasite.