Oxidative metabolism of carbazeranin vitroby liver cytosol of baboon and man

Abstract

The metabolism of carbazeran has been investigated in vitro using liver cytosol from dog, baboon and man. Carbazeran was not metabolized in cytosol prepared from dog liver but was rapidly metabolized to a single product in baboon- and human-liver cytosol. The product was identified as 4-hydroxy carbazeran. The enzyme responsible for the 4-hydroxylation of carbazeran in vitro was shown by the use of inhibitors to be liver aldehyde oxidase. Species differences in the metabolism of carbazeran in vitro correlate well with studies in vivo; these showed that following an oral dose to man and baboon, the compound was almost completely cleared via pre-systemic 4-hydroxylation, whereas in the dog, this metabolic route appeared unimportant.

Aldehyde Oxidase Activity in Fresh Human Skin

“…3). Together with reaction specificities of carbazeran 4-hydroxylation (Kaye et al, 1985) and zoniporide 2-hydroxylation , potent inhibition by hydralazine offers additional evidence for cutaneous activity of AO.…”

“…Although AO has long been known to oxidize nitrogen-containing heterocycles (Knox, 1946;Stanulovi c and Chaykin, 1971;Stubley et al, 1979), its importance to drug metabolism first emerged in the case of carbazeran, a phosphodiesterase-2 inhibitor discontinued due to low oral bioavailability and short half-life in humans (Kaye et al, 1984(Kaye et al, , 1985. Based on analysis of chemical structure, a recent review suggested that a large number of drugs on the market (;13%) or candidate drugs (almost 45% of drugs in development) could be AO substrates (Pryde et al, 2010).…”

“…To investigate the activity of AO in the human skin, two reactions selectively catalyzed by AO were studied: carbazeran 4-hydroxylation (Kaye et al, 1984(Kaye et al, , 1985 and zoniporide 2-hydroxylation (Dalvie et al, , 2012 (Fig. 1).…”

“…Although AO drug metabolism is relevant for pharmacotherapy, many researchers failed to predict high in vivo AO metabolic clearance based on in vitro results, leading to notable drug failures, such as carbazeran (Kaye et al, 1984), BIBX1382 (Dittrich et al, 2002), zoniporide , RO1 (Zhang et al, 2011), SGX523 (Diamond et al, 2010), and FK3453 (Akabane et al, 2011). Difficulties in predicting AO clearance probably arise from several confounding factors: 1) cytosolic enzyme localization (Kaye et al, 1985); 2) apparent enzyme instability in the in vitro assay systems (Duley et al, 1985;Al-Salmy, 2001;Hutzler et al, 2014); 3) large interindividual (Hutzler et al, 2014) and interspecies differences ; and 4) potential contribution of extrahepatic tissues, most notably kidneys (Nishimura and Naito, 2006) and respiratory tissues (Moriwaki et al, 2001). Thus, further research is needed to better understand and characterize AO drug metabolism, especially its tissue localization, suitable in vitro experimental systems, and methods that would aid in vitro-in vivo extrapolation.…”

“…Enzyme activities of two specific AO substrates (Fig. 1), carbazeran (Kaye et al, 1984(Kaye et al, , 1985 and zoniporide , were tested in healthy skin from 13 donors, also shedding light on interindividual variability. Results reveal, for the first time, that human skin possesses significant AO activity, with reaction rates comparable to those of other more established cutaneous elimination routes, for example, glucuronidation, sulfation, and N-acetylation.…”