Carbazeran citrate

Characterization of aldehyde oxidase enzyme activity in cryopreserved human hepatocytes.[Pubmed:22031625]

Drug Metab Dispos. 2012 Feb;40(2):267-75.

Substrates of aldehyde oxidase (AO), for which human clinical pharmacokinetics are reported, were selected and evaluated in pooled mixed-gender cryopreserved human hepatocytes in an effort to quantitatively characterize AO activity. Estimated hepatic clearance (Cl(h)) for BIBX1382, carbazeran, O(6)-benzylguanine, zaleplon, and XK-469 using cryopreserved hepatocytes was 18, 17, 12, <4.3, and <4.3 ml . min(-)(1) . kg(-)(1), respectively. The observed metabolic clearance in cryopreserved hepatocytes was confirmed to be a result of AO-mediated metabolism via two approaches. Metabolite identification after incubations in the presence of H(2)(1)(8)O confirmed that the predominant oxidative metabolite was generated by AO, as expected isotope patterns in mass spectra were observed after analysis by high-resolution mass spectrometry. Second, clearance values were efficiently attenuated upon coincubation with hydralazine, an inhibitor of AO. The low exposure after oral doses of BIBX1382 and carbazeran ( approximately 5% F) would have been fairly well predicted using simple hepatic extraction (f(h)) values derived from cryopreserved hepatocytes. In addition, the estimated hepatic clearance value for O(6)-benzylguanine was within approximately 80% of the observed total clearance in humans after intravenous administration (15 ml . min(-)(1) . kg(-)(1)), indicating a reasonable level of quantitative activity from this in vitro system. However, a 3.5-fold underprediction of total clearance was observed for zaleplon, despite the 5-oxo metabolite being clearly observed. These data taken together suggest that the use of cryopreserved hepatocytes may be a practical approach for assessing AO-mediated metabolism in discovery and potentially useful for predicting hepatic clearance of AO substrates.

Chronotropic and inotropic actions of amrinone, carbazeran and isobutylmethyl xanthine: role of phosphodiesterase inhibition.[Pubmed:2478244]

Br J Pharmacol. 1989 Sep;98(1):291-301.

1. The chronotropic and inotropic effects of amrinone, carbazeran and 3-isobutyl-1-methyl xanthine (IBMX) were examined in isolated preparations of papillary muscle and right atria from rabbit heart. The effects of the drugs on cardiac phosphodiesterase and cyclic nucleotide content were also examined. 2. Amrinone (2.4 x 10(-4)M-2 x 10(-3) M), carbazeran (9.1 x 10(-6) M-1.2 x 10(-3) M), and IBMX (1.8 x 10(-5) M-4.5 x 10(-4) M) produced concentration-dependent positive inotropic responses of papillary muscle preparations, the rank order of potency being carbazeran = IBMX greater than amrinone. Sub-threshold positive inotropic concentrations of all three compounds potentiated the positive inotropic effects of isoprenaline; leftward shifts in the concentration-effect curves were 5 fold (IBMX), 11 fold (amrinone) and 46 fold (carbazeran). 3. Amrinone and IBMX produced concentration-dependent positive chronotropic responses in isolated right atria and showed a similar rate selectivity to isoprenaline, but carbazeran elicited a decrease in beating frequency. None of these drugs potentiated the positive chronotropic effects of isoprenaline. 4. Concentrations of amrinone, carbazeran and IBMX that produced similar positive inotropic responses were associated with different increases in papillary muscle cyclic AMP and cyclic GMP concentrations. 5. All three compounds inhibited right atrial and ventricular phosphodiesterase, with amrinone being the least potent. There was, however, a marked difference between the IC50 and EC50 values for phosphodiesterase inhibition and positive inotropy. In contrast the positive chronotropic effects of amrinone and IBMX were observed in the same concentration ranges that produced phosphodiestrease inhibition. 6. The results indicate that amrinone possesses a similar rate/force selectivity to isoprenaline and IBMX. In contrast, carbazeran exerts both positive inotropic and negative chronotropic effects. Phosphodiesterase inhibition and elevation of intracellular cyclic AMP concentration may be involved, at least in part, in the cardiac effects of these drugs.