Effects of long-term administration of acetaminophen on the nutritional utilization of dietary protein

Nutritional regulation of homocysteine: effects of drugs

Homocysteine plays a critical regulation role at the intersection of two metabolic pathways: remethylation and transsulfuration. Both are nutritionally regulated per se, and this issue constitutes the main goal of the present short review. In addition, several factors (i.e., drugs) may change the nutritional modulation, altering the normal functioning of the methionine/methylation cycle. The metabolism of a substrate is closely linked to that of it cofactors: in the case of homocysteine, there are three vitamins acting as cofactors or coenzymes: B6, B12 and folate. Vitamin B6 is involved in the formation of cystathionine from homocysteine (transsulfuration pathway). It is also critical for the formation of 5,10-methylentetrahydrofolate from tetrahydrofolate (folic acid derivatives), and therefore is closely related to the metabolism of folate. The latter is in conjunction with vitamin B12 involved in the remethylation of homocysteine to methionine. This reaction is B12-dependent. Different animal and human studies have proved the existence of a relation between vitamin status and homocysteine. Other dietary components as methionine content, riboflavin, alcohol or coffee consumption are being investigated in relation to homocysteine concentration. Drugs may interfere with the utilization of nutrients. This fact may be of special importance for vitamins (i.e., folate). Administration of drugs in populations with adequate vitamin intake is not usually a problem, but the existence of risk groups (the elderly, adolescents, smokers, dieters, etc.) may lead to specific vitamin deficiencies which may lead to elevated homocysteine. The case of folate is analysed since this vitamin shows the most reported number of interactions with drugs.

High dietary folate supplementation affects gestational development and dietary protein utilization in rats

There is new evidence that good folate status may play a critical role in the prevention of neural tube defects and in the maintenance of adequate homocysteine levels, an amino acid recently identified as a risk factor for cardiovascular disease. This has led to different folate recommendations, all of them much higher than the present dietary recommendations. Folic acid is a water-soluble vitamin with a low potential toxicity. However, the possible consequences of long-term, high folate intakes are unknown. Therefore, the present study was undertaken to determine the effects of long-term, high dietary folate supplementation on gestational and nutritional markers in pregnant and virgin rats. Four groups of Wistar rats were classified on the basis of physiological status (virgin or pregnant) and the experimental diets administered (folic acid supplemented, 40 mg/kg diet; or control diet, 2 mg folic acid/kg diet). Rats were fed their respective diets for 3 wk. Two critical periods were used for metabolic balance studies (experimental d 1-5 and 17-21), which involved the determination of fat and protein digestibilities as well as metabolic protein utilization (MPU) and net protein utilization (NPU). Gestational development (number of live fetuses) was adequate in both diet groups regardless of folate supplementation. However, body weight and vertex-coccyx length in fetuses from supplemented dams were less than (P < 0.0001) in fetuses of control dams. Fat and nitrogen digestibilities were not affected by supplementation, but MPU and NPU coefficients were significantly lower (P < 0.05) in the folic acid-supplemented groups, irrespective of physiological status, compared to control rats. These new findings of macro-micronutrient interactions caused by high folate supplementation are discussed on the basis that the vitamin may act as a xenobiotic more than as a nutrient.