Sterols in nematodes

The present difficulty in routine culture of parasitic nematodes through their entire life cycles away from their plant or animal hosts has severely hindered investigations of their biochemistry and physiolo. Consequently, most studies of sterol nutrition and metabolism in nematodes have necessarily involved the... 

Lack of De Novo Sterol Biosynthesis in Nematodes. The dietary requirement tor sterol results from the lack ofde novo sterol biosynthesis in nematodes. Species In which radiolabeled acetate or mevalonate are not converted to radiolabeled sterol Include T. aceti (14, 15), Caenorhabditls (15) and the animal parasites AscarTs (l6), Dirof aria immitis (17), and Brugia pahangi (17). On occasion, radiolabeled sterols Identified by thin-layer cRromatography have been detected from nematodes incubated with radiolabeled acetate in the lone case in which such compounds were further characterized by gas-liquid chromatography, the radiolabeled components possessed retention times much earlier than cholesterol (16). 

One should expect sterols to function similarly In nematodes and other animals consequently, sterols should be Integral structural... 

Potential research topics. Because of their steroidal structure, the brassinosteroids offer many potential avenues for research both in phytochemistry and zoochemistry. If, for example, the presence of the brassinosteroids is relatively ubiquitous in plants, is it then possible that they play a role in host parasite relationships It is of note that many plant parasitic and intestinal nematodes must obtain their cholesterol precursors from their respective hosts (18), a paradigm of the former being the plant gall inducing nematode Ditylenchus dipsaci and of the latter the somewhat large intestinal nematode Ascaris lumbricoides. Certain phytopathogenic fungi also have a sterol requirement for completion of their life cycle (19), as do certain insects (20). 

Because of the previously described problems in culture of parasitic nematodes, investigation of sterol metabolism in these organisms has been largely limited to comparison of the sterol compositions of host and parasite. For example, lathosterol and cholesterol were the major sterols of N. carpocapsae DD-136 propagated in wax moth larvae, organisms that contained cholesterol as their principal sterol. Radiolabeled cholesterol injected into host larvae was recovered as radiolabeled lathosterol and cholesterol in the nematode (19). 

We have recently discovered similar but not identical pathways in T. aceti and P. redivivus (Chitwood et al., unpublished). Cysts of Heterodera zeae did not contain 4-methyl sterols (27), but possibly other life stages of H. zeae or other parasitic nematodes may contain 4-methylsteroTs. 

Effects of Inhibitors on sterol metabolic pathways in C. elegans. The most specific effects on nematodes of Ue azasteroids, amines and amides have been obtained through our Investigations of . 

Phytosterols are of particular importance to insects, nematodes, and certain crustaceans, because they cannot synthesize cholesterol de novo. These organisms degrade dietary C28 and C29-phytosterols to C2 -sterols (usually cholesterol) or obtain C27-sterols directly from other organisms (Ikek-awa, 1983). These steroidal products are then used in the synthesis of biologically active sterols that the organisms require. There is evidence that dealkylation of phytosterols proceeds as indicated in (Fig. 23.14) (Harrison, 1985 Ikek-awa, 1983). 

Chitwood DJ, Lusby WR, Salt TA (1987) Sterol metabolism in the nematodes Panagrellus redivivuSy Turbatrix aceti and Caenorhabditis elegans. Comp Biochem Physiol 86B 103-107 Clarke AG, Smith JN (1975) Glutathione S-aryltransferase as a model for the glutathione S-transferases. In Coulston F, Korte F (eds) Environmental quality and safety, Suppl 3. Thieme, Stuttgart, pp 346-350... 

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