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Division of Nutritional Sciences, School of Public Health, University of California, Los Angeles, CA 90024
Because of evidence linking methyl group deficiency and increased tumor formation in experimental animals, we explored other possible methods of producing a methyl group deficiency. Rats fed a low methionine diet lacking choline (MCD) were injected intraperitoneally daily for 3 wk with large doses of nicotinamide. Hepatic levels of lipids were elevated, S-adenosylmethionine (SAM) levels and the SAM:S-adenosylhomocysteine (SAH) ratio were decreased, and SAH level was not consistently changed. In livers of rats fed the MCD diet without folate (MCFD), lipids were also elevated and SAM reduced as compared to MCD-fed rats. In rats fed the MCD diet plus a methionine (Met) supplement (MCD + Met), hepatic SAM levels and the SAM:SAH ratio were higher and lipid levels lower than in MCD-fed rats, indicating that the MCD diet is marginally deficient in methyl donor groups. The injection of nicotinamide or the removal of folate from the MCD diet increased the severity of methyl donor deficiency, as shown by lower hepatic SAM levels and higher hepatic lipid levels. Hepatic glutathione levels were similar in MCD- and MCFD-fed rats and were lower than in rats fed the methionine-supplemented MCD diet or injected with nicotinamide.
KEY WORDS: nicotinamide S-adenosylmethionine S-adenosylhomocysteine glutathione cysteine methylation liver rat
1 Supported by National Institutes of Health Grant No. 1 P01-CA 42710-01 and DAAD (Academic Exchange Service)/NATO fellowship (Germany).
2 Presented in part at the 71st Annual Meeting of the Federation of American Societies for Experimental Biology, Washington, D.C., March, 1987 [Fed. Proc. 46: 572 (abs.)].
Manuscript received 5 December 1988. Revision accepted 1 May 1989.
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