Biocompatibility of hydroxylated metabolites of BISGMA and BFDGE.

Unpolymerized dental monomers can leach out into the oral biophase and are bioavailable for metabolism. We hypothesize that metabolites would be less toxic than parent monomers. We first identified the formation of metabolites from bisphenol F diglycidyl ether (BFDGE) and Bisphenol A glycidyl methacrylate (BISGMA) after their exposure to liver S9 fractions. Then, the metabolites and parent compounds were subjected to in vitro cytotoxicity, mutagenicity, and estrogenicity studies. Bisphenol A bis(2,3-dihydroxypropyl) ether and bisphenol F bis(2,3-dihydroxypropyl) ether were the hydroxylated metabolites of BISGMA and BFDGE, respectively. Cytotoxicity against L929 cells showed that the metabolites were significantly (p < 0.05) less cytotoxic than the parent monomers. Only BFDGE was mutagenic in the Ames assay with strain TA100 of Salmonella typhimurium. Parent and metabolite compounds did not stimulate estrogen-dependent MCF-7 cell proliferation above solvent controls. These results indicated that the hydroxylated metabolites were non-mutagenic, non-estrogenic, and less cytotoxic than their parent monomers.

Aromatic dental monomers affect the activity of cholesterol esterase.

The dental restorative monomer, BISGMA (2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane), and bisphenol A diglycidyl ether (BADGE) increase the velocity of the reaction catalyzed by pancreatic cholesterol esterase (CEase, bovine). The metabolite of these monomers, bisphenol A bis(2,3-dihydroxypropyl) ether, and a common plasticizer, di-2-ethylhexyl phthalate (DEHP), also increase the velocity of CEase-catalyzed ester hydrolysis. BISGMA at concentrations of 1.5-8.0 microM increases the velocity to 126-169% of its value in the absence of BISGMA. Increasing BISGMA above 8 microM caused no further increase in velocity. BADGE at 7-25 microM increases the velocity to 112-205% of its value without BADGE. The metabolite of BISGMA and BADGE at concentrations of 2.0-7.1 microM increases the velocity to 103-113% of its value without metabolite. DEHP at concentrations of 0.52-4.3 microM increases the velocity to 108-187% of its value without DEHP. On the other hand, bisphenol A dimethacrylate is a competitive inhibitor of CEase, with a K(i) of 3.1 microM.

The stability of methacrylate biomaterials when enzyme challenged: kinetic and systematic evaluations.

This study addressed whether methacrylate monomers and polymers used in dentistry might degrade from enzymolysis by acetylcholinesterase (ACHE), cholesterol esterase (CHE), porcine liver esterase (PRLE), and a pancreatic lipase (PNL). Short (hour) and long-term (day) exposures were performed. Product ratios were used to determine surface hydrolysis of the polymeric materials. Enzyme kinetics were studied for the monomers when challenged by ACHE, CHE, and PRLE. In the case of PRLE, the V(max) for the dimethacrylate substrates varied slightly, but amounted to as much as 10% of that of p-nitrophenylacetate. The K(m) for triethylene glycol dimethacrylate (TEGDMA) was 197 microM for ACHE and 1107 microM for CHE. The V(max) was 2.7 nmol/min for ACHE and 3.5 nmol/min for CHE. TEGDMA was converted by CHE at 2% the rate of cholesteryl oleate. Long-term incubations of monomers with CHE and ACHE produced degrees of hydrolysis that evidenced structure dependency in the ability of the enzymes to effect hydrolysis. Particularly resistant were aromativ derivatives and those with branching in methacrylate linkages. Overall, the study confirms the ability of physiologically important esterases to catalyze the hydrolysis of biomaterial methacrylates.

Metabolism of terfenadine associated with CYP3A(4) activity in human hepatic microsomes.

Terfenadine (Seldane) undergoes extensive metabolism to form azacyclonol and terfenadine alcohol. Terfenadine alcohol is subsequently metabolized to azacyclonol and terfenadine acid. Although testosterone 6 beta-hydroxylation [CYP3A(4)] has been shown to be the principal enzyme involved in the first step in terfenadine's biotransformation (formation of azacyclonol and terfenadine alcohol), the enzymes catalyzing the subsequent metabolic steps in the conversion of terfenadine alcohol to azacyclonol and terfenadine acid have not been identified. The purpose of these studies was to determine the role of cytochrome P450 isoforms in the biotransformation of terfenadine and terfenadine alcohol. To this end, both terfenadine and its alcohol were incubated with 10 individual human liver microsomal samples that have been characterized for major isozyme activities. The metabolites and parent drugs were quantified by HPLC. The formation of azacyclonol and terfenadine alcohol from terfenadine is confirmed to be catalyzed predominantly by CYP3A(4) isozyme, and the ratio of the rate of terfenadine alcohol formation to that of azacyclonol is 3:1. Involvement of the CYP3A(4) in terfenadine metabolism was further confirmed by the following studies: a) inhibition of terfenadine alcohol formation by ketoconazole and troleandomycin, two specific inhibitors of CYP3A(4), and b) time course of terfenadine alcohol formation by cloned human CYP3A(4). When terfenadine alcohol was used as substrate, both the terfenadine acid and azacyclonol formation were also catalyzed by CYP3A(4) isozyme. However, the rate of formation of the terfenadine acid metabolite is almost 9 times faster than that of azacyclonol. The net ratio of terfenadine acid to azacyclonol is 2:1.

Quantitative determination of 21-hydroxy-deflazacort in human plasma using gradient semi-microbore liquid chromatography.

A sensitive and selective liquid chromatographic procedure to quantitate the deflazacort metabolite 21-hydroxy-deflazacort (DF-21OH) in human plasma was developed and validated. DF-21OH and fludrocortisone acetate (internal standard, IS) were isolated from human plasma (2 mL) by solid-phase extraction onto C-18 cartridges. Potential interferences were selectively removed and analytes were eluted with ethyl acetate. Following evaporation, the residue was reconstituted for HPLC analysis. Separation was achieved by gradient elution using a 5 microns YMC Basic column (2.0 x 100 mm) with mobile phases consisting of 20% methanol and 50% acetonitrile in 50 mM phosphate buffer (pH 3) at a temperature of 50 degrees C. Flow rate was maintained at 0.3 mL/min., and analytes were quantified spectrophotometrically at 246 nm. The assay was validated over the range 1.0 to 500 ng/mL DF-21OH. Calibration curves were prepared using a weighted (1/concentration) nonlinear quadratic regression algorithm. Peak-height ratios were proportional to the amount of DF-21OH added to plasma. Assay precision (%RSD) ranged from 4.2 to 11%, with a corresponding assay accuracy (% relative error) of +/- 2.8%. Absolute recovery of DF-21OH from plasma was 78-86% over the concentration range. The minimum quantitation limit was 1.0 ng/mL.