Choline deprivation induces hyperhomocysteinemia in rats fed low methionine diets

To clarify the relationship between dietary choline level and plasma homocysteine concentration, the effects of choline deprivation on plasma homocysteine concentration and related variables were investigated in rats fed a standard (25%) casein (25C) diet or standard soybean protein (25S) diet. Using the 25S diet, the time-dependent effect of choline deprivation and the comparative effects of three kinds of lipotropes were also investigated. Feeding rats with the choline-deprived 25S diet for 10 d significantly increased plasma total homocysteine concentration to a level 2.68-times higher than that of the control group, whereas choline deprivation had no effect in rats fed the 25C diet. Increases in hepatic S-adenosylhomocysteine and homocysteine concentrations, decreases in hepatic betaine concentration and the activity of cystathionine beta-synthase, but not betaine-homocysteine S-methyltransferase, and fatty liver also occurred in rats fed the choline-deprived 25S diet. Plasma homocysteine concentration increased when rats were fed the choline-deprived 25S diet for only 3 d, and the increase persisted up to 20 d. The hyperhomocysteinemia induced by choline deprivation was effectively suppressed by betaine or methionine supplementation. Choline deprivation caused hyperhomocysteinemia also in rats fed a choline-deprived low (10%) casein diet. The results indicate that choline deprivation can easily induce prominent hyperhomocysteinemia when rats are fed relatively low methionine diets such as a standard soybean protein diet and low casein diet, possibly through the suppression of homocysteine removal by both remethylation and cystathionine formation. This hyperhomocysteinemia might be a useful model for investigating the role of betaine in the regulation of plasma homocysteine concentration.