THE EFFECT OF LEAD TOXICITY ON THE ATPase ACTIVITIES OF CALCIUM-PUMP AND P-GLYCOPROTEIN IN SOME ISOLATES OF PLASMODIUM FALCIPARUM

Abstract

The technique of ion exchange chromatography was used to isolate free Plasmodium falciparum used in the study and other techniques such as spectrophotometry, centrifugation, electrophoresis and densitometric scanning were employed in monitoring the biochemical parameters involved in the study. Basal ATPase activities of Ca²⁺-ATPase and P-glycoprotein of 15 local isolates and two strains of known drug susceptibility profiles (D6-chloroquine sensitive and W2-chloroquine resistant of P. falciparum were studied. Activities of 5 isolates (NCP1, NCP5, NCP14. W2 and D6) were partially characterized. Lead acetate at various concentrations (0-40μg/ml) was used to simulate the effect of lead toxicity on Ca²⁺ -ATPase and P-glycoprotein ATPase activities of Strains W2 and D6 of P. falciparum. The choice drug for malaria (chloroquine) at concentrations of (0-4.0μg/ml) was used to study the effect of chloroquine on the basal activities of the two transport proteins in strains D6 and W2, NL56 and UNC. The modulatory effect of lead toxicity on the action of chloroquine on the ATPase activities of the two proteins was studied by combining the effective inhibitory concentration of lead (10μg/ml) with effective inhibitory concentration of Chloroquine (2.6μg/ml) on chlorogiaine resistant strain W2 of P. falciparum. All the 17 isolates of P.falciparum studied exhibited significant Ca2+ -ATPase and P-glycoprotein ATPase activities. The Ca²⁺ -ATPase and P-glycoprotein activity potentials in chloroquine resistant strain (W2) are, respectively, about 5 fold higher than in chloroquine sensitive strain (D6). The local isolates expressed ATPase activities within the extremes of the activities expressed by W2 and D6. The results also suggest possible association between functional expression of Ca²⁺-ATPase and acquisition of chloroquine resistance. However, there seems to be no relationship between ATPase activity of P- glycoprotein and acquisition of chloroquine resistance by P.falciparum. The study also revealed that toxic concentrations of lead modulate Ca²⁺ -ATPase activity of P. falciparum. Toxic concentrations of lead (>20μg/ml) on chloroquine sensitive strain (D6) can alter its ATPase activity which will enable it to behave as that in chloroquine resistant strain (W2). Chloroquine inhibited Ca²⁺ -ATPase and P- glycoprotein ATPase activities in all the isolates of P. falciparum studied. The 50% inhibitory concentration (IC50) was found to be 2.6μg/ml) for the two proteins. However, combinations of effective concentrations of lead (10μg/ml) and chloroquine (2.6μg/ml) reversed the individual effects of lead and chloroquine respectively on the two transport proteins. These results indicate that the presence of lead along with chloroquine could reverse the effect of the action of the drug on the target cell. In conclusion, the study revealed that lead ions can interact with transport proteins in biological systems to modulate their activities in general, and specifically lead can effect change in biochemical response to chloroquine by CQ sensitive strain of P. falciparum to behave as chloroquine resistant strain. Lead concentrations can also interact with drugs in the environment of disease agents or cells to reverse the probable therapeutic effect of such drugs. These findings are significant in knowing more about the characteristics of drug resistant malaria parasites among populations exposed to malaria and environmental lead.