Molecular Mechanisms involved in Toxicity of Cleistanthus Collinus

Abstract

In vitro exposure of rat renal homogenate to C. collinus aqueous extract resulted in a significant decrease in total ATPase activity compared to the control. Since acid - base balance in the kidney is maintained by pumps localized on the renal brush border and basolateral membranes, experiments were then carried out on fractionated renal BBM and BLM. A concentration dependence study on the BBM and BLM revealed that treatment with C. collinus aqueous extract resulted in higher inhibition in the BBM when compared to the BLM, suggesting that most of the inhibitable activity is localized in the BBM. Further characterization of the ATPase activity inhibited by C. collinus revealed similarity to that inhibited by NEM, suggesting that the V-ATPase could be a putative target for C. collinus inhibition, since NEM has been shown to be a specific inhibitor of V- ATPases. Comparative studies also indicated that ATPase activity seemed to be more sensitive to C. collinus inhibition when compared to proton pumping activity. In conclusion, initial observations suggested that exposure to C. collinus aqueous extract resulted in the significant inhibition of ATPase activity in the rat kidney. Further characterization suggested that the inhibitable ATPase activity was localized predominantly in the renal brush border membrane, where the vacuolar H* ATPase is abundantly present. This fact, coupled with the inhibition of ATPase activity to a similar extent with NEM, which has been shown earlier to affect V-ATPase, suggested the identity of the C. collinus inhibitable activity to be V-ATPase on the renal brush border membrane, which had the functional consequence of compromising proton transport as well. Hence, these results of our study suggest that the renal V-ATPase is a putative target involved in the clinical symptoms after Cleistanthus collinus poisoning and strategies to bypass this inhibition or development of targeted antidotes may help in better medical management of patients with Cleistanthus collinus poisoning.