Role of specific cytochrome P450 enzymes in the N-oxidation of the antiarrhythmic agent mexiletine.

1. Mexiletine is extensively metabolized in man by C- and N-oxidation and the aim of the present study was to characterize major cytochrome P450 enzyme(s) involved in the formation of N-hydroxymexiletine. 2. Incubations with genetically engineered microsomes indicated that the formation rate of N-hydroxymexiletine was highest in the presence of microsomes expressing high levels of either CYP1A2 or CYP2E1 and the formation of N-hydroxymexiletine by human liver microsomes was inhibited about 40% by antibodies directed against CYP1A1/1A2 or CYP2E1. Additional incubations demonstrated that formation of N-hydroxymexiletine was decreased 47 and 51% by furafylline, 40 microm and 120 microm, respectively, and decreased 55 and 67% by alpha-naphthoflavone, 1 microm and 3 microm, respectively (all p < 0.05 versus control). 3. The formation rate of N-hydroxymexiletine in human liver microsomes was highly correlated with CYP2B6 (RS-mexiletine, r = 0.7827; R-(-)-enantiomer, r = 0.7034; S-(+)-enantiomer, r = 0.7495), CYP2E1 (S-(+)-enantiomer, r = 0.7057) and CYP1A2 (RS-mexiletine, r = 0.5334; S-(+)-enantiomer, r = 0.6035). 4. In conclusion, we have demonstrated that CYP1A2 is a major human cytochrome P450 enzyme involved in the formation of N-hydroxymexiletine. However, other cytochrome P450 enzymes (CYP2E1 and CYP2B6) also appear to play a role in the N-oxidation of this drug.

alpha-Terpineol from hydration of crude sulfate turpentine oil.

Hydration of alpha-pinene under various conditions was studied and compared with the literature. Optimal reaction conditions have been established for the hydration of alpha-pinene and crude turpentine oil in the absence of catalyst and using a low volume of acetone. A detailed reaction product analysis is reported. The main hydration product, alpha-terpineol, was obtained at a yield of 67 wt % of the initial alpha-pinene by reacting with 15% aqueous sulfuric acid and an excess of acetone in an oil bath heated to 80-85 degrees C over the course of 4 h. A progressive transformation of alpha-terpineol to 4-(2-hydroxypropyl)-1-methylcyclohexanol (1,8-terpine) takes place as the hydration time exceeds 4 h. A crude turpentine oil sample was also hydrated under conditions similar to those of alpha-pinene. The alpha-terpineol yield was 77 wt % of the initial alpha-pinene in the crude turpentine oil. The chemical analysis of the crude turpentine oil before and after hydration was carried out, and the distribution of the products was discussed.

Production of monomeric phenols by thermochemical conversion of biomass: a review.

Biomass is a renewable and alternative source for the production of fuels and chemicals. This paper provides a brief survey of lignin precursors as well as thermogravimetric and pyrolysis studies of lignin with special reference to the production of phenols. Thermogravimetric analysis provides information on pyrolysis kinetics while thermogravimetry in combination with mass or infrared spectrometers allowed a rapid characterization of the vapours produced by thermal treatment. Pyrolysis enabled even greater insight into the thermal behaviour of lignin. Pyrolysis of single, dimeric and trimeric model lignin compounds can determine the thermal stability of the intermediate compounds formed and the origin of the pyrolysis products. A free radical mechanism has been suggested as a major route during the early lignin degradation stages followed by a combined free radical and concerted pathway at elevated temperatures. Pyrolysis of lignin in the presence of catalysts as additives was investigated. Significant differences in terms of yields of pyrolysis products and phenolic compounds were observed. The addition of salts resulted in a high weight loss at low temperature and yielded more char than untreated wood. Some metal catalysts such as transition metals and metal oxides such as Fe2O3 and Cu exhibited a better activity in terms of selectivity for the degradation of lignin.

The polyurethane foam covering the Même breast prosthesis: a biomedical breakthrough or a biomaterial tar baby?

Because controversy continues to surround the implantation of the polyurethane foam-covered Même breast prosthesis, in vitro experiments were conducted to determine: (1) whether the polyurethane foam contains extractable toluene diamine isomers (TDAs), and (2) whether the polyurethane foam releases TDAs on exposure to mild hydrolytic conditions. Results confirmed the presence of extractable TDAs and other impurities in the foam covering the unused Même prosthesis, and that the concentrations of these impurities could be significantly reduced by washing the foam in a regular detergent. This washing step was omitted from the manufacturer's production process. Furthermore, on exposure to mild alkalis, the foam exhibited significant degradation, rapid fragmentation, loss of mechanical strength and physical integrity, as well as the release of additional TDAs. Because of the potential long-term risks associated with the release of TDAs in vivo, continued clinical use of the Même prosthesis containing this particular type of foam appears questionable.