Dealkylation of various 14‐alkylsterols by the nematodeCaenorhabditis elegans

Abstract

Abstract The metabolism of 4 dietary 24‐alkylsterols was investigated in the free‐living nematode Caenorhabditis elegans . The major unesterified sterols of C. elegans in media supplemented with either campesterol, 22‐dihydrobrassicasterol or stigmasterol included cholesta‐5,7‐dienol, cholesterol, cholest‐7‐enol, and 4α‐methylcholest‐8(14)‐enol. Dietary stigmastanol yielded cholest‐7‐enol, cholestanol, cholest‐8(14)‐enol, and 4α‐methylcholest‐8(14)‐enol as major unesterified sterols. Esterified sterols comprised less than 22% of the total sterol. Removal of a C‐24 ethyl substituent of sterols was neither hindered by the presence of a Δ 22 ‐bond in the sterol side chain nor was it depedent on unsaturation in ring B of the steroid nucleus. C. elegans reduced a Δ 22 ‐bond during its metabolism of stigmasterol; it did not introduce a Δ 22 ‐bond during stigmastanol metabolism. C. elegans was capable of removing a C‐24 methyl substituent regardless of its stereochemical orientation. Metabolic processes involving the steroid ring system of cholesterol (C‐7 dehydrogenation, Δ 5 ‐bond, 4α‐methylation, Δ 8(14) ‐isomerization in C. elegans were not hindered by the presence of a 24‐methyl group; various 24‐methylsterol metabolites from campesterol were detected, mostly 24‐methylcholesta‐5,7‐dienol. In contrast, no 24‐ethylsterol metabolites from the dietary ethylsterols were found. More dietary 24‐methylsterol remained unmetabolized than did dietary 24‐ethylsterol. A 24α‐ethyl group and a 24β‐methyl group were dealkylated to a greater extent by C. elegans than was a 24α‐methyl group, perhaps reflecting the substrate specificity of the dealkylation enzyme system, or suggesting different enzymes altogether.

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