Indiplon Is Hydrolyzed by Arylacetamide Deacetylase in Human Liver

Abstract

Human arylacetamide deacetylase (AADAC) catalyzes the hydrolysis of some clinically used drugs, but the information available on its substrates is limited. To increase our knowledge of the AADAC substrates, we examined whether AADAC catalyzes the hydrolysis of indiplon, which was initially developed as a hypnotic sedative drug. It has been reported that approximately 30-40% of the administered indiplon was hydrolyzed to deacetylindiplon in humans, but the enzyme responsible for this hydrolysis had not been identified. We detected high levels of indiplon hydrolase activity in human liver microsomes (HLMs), but the levels found in human liver cytosol and plasma were scarcely detectable. Recombinant AADAC showed a high level of indiplon hydrolase activity, whereas recombinant carboxylesterase 1 (CES1) and 2 (CES2) showed marginal activity. The indiplon hydrolase activity of HLM was potently inhibited by vinblastine, a potent inhibitor of AADAC and CES2, but it was not inhibited by digitonin and telmisartan, inhibitors of CES1 and CES2, respectively. In a panel of 24 individual HLM samples, the indiplon hydrolase activities were significantly correlated with the hydrolase activities of flutamide, phenacetin, and rifampicin, which are known AADAC substrates. An HLM sample with a homozygous AADAC*3 allele, which was previously found to exhibit decreased enzyme activity, showed the lowest indiplon hydrolase activity among the 24 tested samples. Collectively, we found that human AADAC is responsible for the hydrolysis of indiplon. Thus, we can add indiplon to the list of human AADAC substrates.

Arylacetamide Deacetylase is Responsible for Activation of Prasugrel in Human and Dog

“…To estimate the contribution of AADAC, CES1, and CES2 to prasugrel hydrolase activity in HIMs and HLMs, RAF values for each esterase in HIMs and HLMs were calculated (Table 2). We previously demonstrated that indiplon, fenofibrate, and procaine were specifically hydrolyzed by AADAC, CES1, and CES2, respectively (Shimizu et al, 2014a;Fukami et al, 2015). Therefore, we selected these compounds as the specific substrates of each esterase.…”

“…Indiplon, Phenacetin, Fenofibrate, and Procaine Hydrolase Activity. Indiplon, phenacetin, fenofibrate, and procaine hydrolase activities were measured according to previous studies (Watanabe et al, 2010;Shimizu et al, 2014a;Fukami et al, 2015). Their substrate concentrations were 1 mM, 5 mM, 25 mM, and 5 mM, respectively.…”

“…The formed prasugrel thiolactone was quantified by HPLC analysis based on the decreased amount of prasugrel, according to a method described in a previous study for indiplon hydrolysis (Shimizu et al, 2014a). Briefly, prasugrel at concentrations of 1 and 10 mM was incubated with HLMs (0.1 mg/ml).…”

“…To date, it has been shown that human AADAC catalyzes the hydrolysis of flutamide, phenacetin, rifamycins, and indiplon (Watanabe et al, 2009(Watanabe et al, , 2010Nakajima et al, 2011;Shimizu et al, 2014a). Recent studies have uncovered that human AADAC prefers compounds containing a quite small acyl moiety (e.g., Fukami et al, 2015).…”

Comparison of substrate specificity among human arylacetamide deacetylase and carboxylesterases

“…We have demonstrated that AADAC is responsible for the hydrolysis of several drugs, such as flutamide (Watanabe et al, 2009), phenacetin (Watanabe et al, 2010), rifamycins (rifampicin, rifabutin, and rifapentine) (Nakajima et al, 2011), and indiplon (Shimizu et al, 2014). AADAC is primarily expressed in the liver and gastrointestinal tract (Watanabe et al, 2009), where it is localized to the endoplasmic reticulum membrane (Frick et al, 2004).…”