Biochemical reversal of proton pump inhibition in vivo

Abstract

Background: There is a surpmmgly rapid rate ol recovery of acid secretion afier short or long term treatment with PPIs except tar pantoprazole This has been ascribed to glutathionedependent reve~at at the inhibitory PPI-disulfide linkage in the luminal vestibule of the proton pump at cysteme 813 or also cysteme 321 tar lansnprazole. The pantoprazole-cysteine 822 linkage is irtaccessible to glutathione making it truly irreversible (Gastroenterology 123, 1588-97, 2002). These experiments wen: performed in vitro on the H,K ATPase isolated t~-om PP1 inhibited rats and their relevance to the situation in the intact srorr~lch needed to be established. Aims: To compare the stability, of PPI binding to the gaslric H,K ATPase in viva after stinmlation o{ acid secretion in rats Methods: Rats were injected ~ t h ~*C omeprazole or ~'% pantoprazole after stimulation of acid secretion and the decay of radioactw W bound to the H,R ATPase followed as a function of time after administratinn Quantitative data reflecting stability of the PPI-pump complex were obtained using Western immune;blots of gradient-gel separated ATPase and determining specific radioactivity of the i00 kDa band. Results: The rate at loss of bound omeprazo/e {~om the pump in viva was faster than expected from the 54 hr halblito of the protein whereas the rate of loss of panroprazole corresponded to the expected turnover of the ATPase Conclusions: The results demonstrate that ~he PPl-cTsteine 813 bond tanned by omeprazole is accessible to glntafhione in viva and that reversal of inhihinon by this mechanism plays a role in the rate of recovery of acid .secretion or ATPase activity (tl/2 = 20h and 15 h) in this specms and probably also in man In contrast the binding of pantoprazole to cysteine 822 is not reversed it! viva as predicted from the ex viva enzy'me analyzed in vitro. These data predict a longer duration of inhibition of acid secretion with pantoprazole treatment as compared to omeprazole.