Recent developments in nematode steroid biochemistry.

Current knowledge of steroid nutrition, metabolism, and function in free-living, plant-parasitic and animal-parasitic nematodes is reviewed, with emphasis upon recent investigation of Caenorhabditis elegans. A number of 4-desmethylsterols with a trans-A/B ring configuration can satisfy the steroid nutritional requirement in C. elegans, but sterols with a cis-A/B ring configuration or trans-A/B sterols with a 4-methyl group cannot. C. elegans removes methyl or ethyl substituents at C-24 of the plant sterols sitosterol, campesterol, stigmasterol, stigmastanol, and 24-methylene-cholesterol to produce various sterols with structures partially dependent upon that of the dietary sterol. Additional metabolic steps in C. elegans include reduction of Delta(2)(2)- and Delta-bonds, C-7 dehydrogenation, isomerization of a Delta-bond to a Delta(1)-bond, and 4alpha-methylation. An azasteroid and several long-chain alkyl amines interfere with the dealkylation pathway in C. elegans by inhibiting the Delta(2)-sterol reductase; these compounds also inhibit growth and reproduction in various plant-parasitic and animal-parasitic nematodes. A possible hormonal role for various steroids identified in nematodes is discussed.