No abstract

Prasugrel, a thienopyridine anti-platelet agent, is pharmacologically activated by hydrolysis and hydroxylation. It is efficiently hydrolyzed in the intestine after oral administration, and the enzyme responsible for the hydrolysis in humans was demonstrated to be carboxylesterase (CES)2. Prasugrel hydrolase activity is detected in dog intestines, where CES enzymes are absent; therefore, this prompted us to investigate the involvement of an enzyme(s) other than CES. Human arylacetamide deacetylase (AADAC) is highly expressed in the small intestine, catalyzing the hydrolysis of several clinical drugs containing small acyl moieties. In the present study, we investigated whether AADAC catalyzes prasugrel hydrolysis. Recombinant human AADAC was shown to catalyze prasugrel hydrolysis with a CL int value of 50.0 6 1.2 ml/min/mg protein with a similar K m value to human intestinal and liver microsomes, whereas the CL int values of human CES1 and CES2 were 4.6 6 0.1 and 6.6 6 0.3 ml/min/mg protein, respectively. Inhibition studies using various chemical inhibitors and the relative activity factor approach suggested that the contribution of AADAC to prasugrel hydrolysis in human intestine is comparable to that of CES2. In dog intestine, the expression of AADAC, but not CES1 and CES2, was confirmed by measuring the marker hydrolase activities of each human esterase. The similar K m values and inhibition profiles between recombinant dog AADAC and small intestinal microsomes suggest that AADAC is a major enzyme responsible for prasugrel hydrolysis in dog intestine. Collectively, we found that AADAC largely contributes to prasugrel hydrolysis in both human and dog intestine.

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.

No abstract

Diltiazem, a calcium channel blocker, is mainly metabolized via demethylation or deacetylation in humans. Diltiazem demethylation is catalyzed by cytochrome P450 2D6 and 3A4. Although it was previously reported that the area under the curve ratio of deacetyldiltiazem to diltiazem after oral dosing with diltiazem in rats was sevenfold higher than in humans, the molecular mechanisms underlying this species difference remain to be clarified. In the present study, we compared the diltiazem deacetylase activity in liver, intestinal, renal, and pulmonary microsome preparations of human and experimental animal tissues to identify the specific deacetylase enzyme(s) involved in deacetylation. Diltiazem deacetylase activity was detected in rat liver and small intestine microsome preparations, but not in those from human, monkey, dog, and mouse tissues. Further purification of rat liver microsome (RLM) proteins identified four carboxylesterase (Ces) enzymes (Ces1d, Ces1e, Ces1f, and Ces2a) as potential candidate deacetylases. On the basis of their tissue distribution, the Ces2a enzyme was considered to be the enzyme that was responsible for diltiazem deacetylation. Furthermore, recombinant rat Ces2a expressed in Sf21 cells displayed efficient diltiazem deacetylase activity with similar Km values as RLM. In addition, the inhibitory characteristics of various chemical inhibitors were similar between recombinant rat Ces2a and RLM. In conclusion, we determined that only rat tissues were able to catalyze diltiazem deacetylation. The characterization of Ces enzymes in animal species, as undertaken in this study, will prove useful to predict the species-specific pharmacokinetics differences between the in vivo models used for drug development.