In vitro metabolic study on alkanes in hepatic microsomes from humans and rats
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Abstract
The purpose of this in vitro study was to measure the efficiency of rats and humans at linear, branched and naphthenic hydrocarbon metabolism. The biotransformation of three radiolabelled alkanes, namely 14C-heptadecane (n-alkane, 17 carbon atoms), 3H-pristane (branched-alkane, 19 carbon atoms) and 3H-dodecylcyclohexane (cyclo-alkane, 18 carbon atoms) was investigated using liver microsomes from three rat strains (Wistar, Sprague-Dawley and Fischer 344) and from three different pools of human donors (at least 10 donors in each case). In each case, both males and females were studied and three concentrations (20, 40 and 60 µM) were tested.
After incubation with microsomes, the hydrocarbon substrate and produced metabolites were extracted then separated and quantified by radio-HPLC. The hydroxylation rate was evaluated from the sum of the different metabolites.
On average, the hydroxylation rates of heptadecane incubated with male rat liver microsomes at the highest concentration tested (60 µM) varied from 78 ± 32 moles/hr/mg proteins in Sprague Dawley rats to 101 ± 20 pmoles/hr/mg proteins (total amount of metabolites formed) in Fischer 344 rats. For females, incubations carried out at the same concentration resulted in values varying from 76 ± 38 pmoles/hr/mg proteins (Fischer 344) to 148 ± 47 pmoles/hr/mg proteins (Sprague Dawley). In humans, the heptadecane hydroxylation rates determined for 60 µM incubations was 159 ± 46 pmoles/hr/mg proteins and 180 ± 10 pmoles/hr/mg proteins, for males and females, respectively.
No metabolism was detected when pristane or dodecylcyclohexane were incubated with human or rat hepatic microsomes (irrespective of the rat strain investigated).