Effect of vitamin B6 on Ieucine-induced

Disturbances in the tryptophan-niacin pathway seen in endemic pellagra among sorghum eaters have been ascribed to high dietary intake of leucine. Vitamin B, plays an important role in several steps of this pathway. Therefore, studies on possible metabolic interrelations between excess dietary leucine and vitamin B, were undertaken in normal healthy human subjects. The results indicated that vitamin B, could successfully counteract the effects of leucine on quinolinic acid excretion in urine, and on in vitro nicotinamide nucleotide synthesis by erythrocytes, and also could correct the abnormalities of 5-hydroxytryptamine metabolism induced by excess leucine. These observations suggest that vitamin B, nutritional status may have a contributory role in the pathogenesis of endemic pellagra. Am. J. C/in. Nuir. 29: 177-181, 1976. The occurrence of endemic pellagra among sorghum eaters has been reported from some parts of India, and the results of several studies have demonstrated that the high amount of the essential amino acid-leucine-present in sorghum is etiologically related. Administration of leucine to normal human volunteers has been found to increase the urinary excretion of quinolinic acid (1), to inhibit the capacity of erythrocytes to synthesize NAD in vitro (2), and to depress the activity of quinolinate phosphoribosyl transferase-a key enzyme in NAD synthesis in rats (3). It has recently been reported that pyridoxine deficiency in man leads to increased excretion of quinolinic acid, in addition to increased xanthurenic acid, and that these changes are corrected by the administration of pyridoxine (4). In women taking steroidal oral contraceptives, which are known to lead to pyridoxine deficiency, as well as in a subject given deoxypyridoxinewhich is a pyridoxine antagonist-increased excretion of quinolinic acid in urine has been reported (5). A number of enzymes in the tryptophanniacinribonucleotide pathway are vitamin B6-dependent, and disturbances in this pathway are a feature of pyridoxine deficiency. Although pellagra is a disease arising from deficiency of nicotinic acid, it is not unusual to see signs of associated deficiency of other vitamins of the B complex group. Studies on possible metabolic interrelationships between excess dietary leucine and pyridoxine were, therefore, undertaken to determine whether pyridoxine nutritional status had a contributory role in the pathogenesis of endemic pellagra among sorghum eaters. Materials and methods Six apparently normal and healthy male volunteers, ages between 25 and 35 years, were investigated in a metabolic ward. The subjects were stabilized on a standard diet for a period of 7 days. The standard diet provided about 2500 calories and 45 g of protein daily, all the protein being derived from vegetable sources. The diet was calculated to contain 1.5 to 1.8 mg of vitamin B, and 3.5 to 4.0 g of leucine. After the period of stabilization on a standard diet, two 24-hr urine samples were collected. The subjects were then given S g of leucine/day for a period of 10 days and urine samples were collected again. Leucine was administered orally in the form of a suspension in water with glucose syrup as a sweetening agent in a single dose, after breakfast. Leucine was withdrawn for the next 10-day period and after collection of the urine samples during the last 2 days. 5 g of leucine were given daily together with 50 mg pyridoxine orally for the next 10 days and final urine samples were collected for 2 days. Pyridoxine was administered twice daily in tablet form, the first dose being given 2 to 3 hr after ‘From the National Institute of Nutrition, Indian Council of Medical Research, Jamai-Osmania, Hyderabad-500007, India. 2 Senior Research Officer. Assistant Research Officer. ‘Director. by on O cber 0, 2010 w w w .an.org D ow nladed fom 178 KRISHNASWAMY ET AL. * P < 0.01 using paired t test. All values are mean ± SE. leucine administration. Quinolinic acid and nicotinic acid in urine were determined by microbiological assay (6). A similar experimental design was followed for studies on 5-hydroxytryptamine (5-HT) metabolism. Five grams of leucine were given to volunteers for either 5 days or 10 days and platelet 5-HT and 5-hydroxyindoleacetic acid (S-HIAA) in urine were estimated initially, after giving leucine for either S or 10 days, after withdrawing leucine, and finally, after giving leucine together with pyridoxine. Blood was drawn under fasting conditions for 5-HT estimation and platelet S-HT was determined. Platelet 5-HT was determined by the method of Weissbach (7): S-HIAA in urine was estimated by the method of Korf and Valkenburgh-Sikkema (8). Six normal subjects were taken up for studying levels of preformed nucleotides and the in vitro synthesis of nicotinamide nucleotides by erythrocytes. Fasting blood was analyzed initially for the nucleotides and after leucine administration (10 g/day) for a period of 10 days. After this period, the subjects were continued on 10 g of leucine/day, but in addition received pyridoxine, 50 mg/day by the parenteral route, for the next 10 days: at the end of this period blood was again drawn for nucleotide estimation. Erythrocytes were separated and prepared as described by Leder and Handler (9). Total nicotinamide nucleotides were estimated fluorometrically by the method of Levitas et al. (10). The in vitro synthesis of nucleotides from nicotinic acid was studied by the method of Preiss and Handler (II).