In vitro efflux of lactic acid by schistosomes cultured in varying concentrations of glucose: potential toxicity of accumulated lactic acid

Abstract

While residing in the mammalian bloodstream, adult schistosomes consume large quantities of glucose and metabolize it to lactic acid. The accumulating load of this end product in the parasite tissue lowers the cellular pH, hence the need for a system to flux it out to avoid compromising metabolic processes. In the present study, we assayed the rate of secretion of lactic acid into the culture medium by adult worms and schistosomula. When cultured in RPMI-1640 medium containing 2 mM glucose, the rate of lactic acid secretion was 0.022 mmol/mg dry wt/h and the secretion increased to 0.043 mmol/mg dry wt/h when they were cultured in medium containing 10 mM glucose. Continuous culture of the parasite resulted in accumulation of lactic acid in the media to about 10 mM whereupon further increase was markedly slower. The media pH in such extended cultures had dropped from an initial 7.4 to about 6.7. In separate experiments, schistosomula were found to be sensitive to >10 mM lactic acid in medium. These results suggest that drugs that inhibit transport of lactic acid may have therapeutic potential against schistosomes.

Keywords: schistosomes, metabolism, glucose, lactic acid

Journal of Tropical Microbiology and Biotechnology Vol. 2(1) 2006: 31−36