Arsenic induced alteration in Mrp-1 like activity leads to zebrafish hepatocyte apoptosis: The cellular GSH connection.

Multidrug-resistance protein-1 facilitates the efflux of arsenic conjugated with reduced glutathione nonetheless; the relation between Mrp-1 ATPase activity and cellular GSH levels is contentious. To study this, Mrp-1-ATPase activity was measured in 5 μM arsenic trioxide exposed zebrafish hepatocytes (ZFH) and correlated with intracellular GSH levels. Alongside, mrp-1 gene expression as well as Mrp-1 protein level was also monitored. Diverse mode of Mrp-1 inhibition was reflected from differential level of Km and Vmax of Mrp-1 at different time points. 3 h post-arsenic treatment demonstrated non-competitive inhibition. At 6 h, there was significant increase in Km and ZFH death, suggesting reduced binding affinity of Mrp-1 for ATP. Increased caspase-9-cytochromeC-ATP levels (putative apoptosome), reinforced ZFH apoptosis. The increase in Vmax coupled with reduced substrate affinity of Mrp-1 suggests malfunctioning in arsenic- tolerance mechanisms. We posit the triggering glutathione level regulate arsenic tolerance in ZFH. Irreversible impairment of ATP binding to Mrp-1 culminates in arsenic-induced ZFH apoptosis.