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Metabolism of 14C-labeled tryptophan and 3-hydroxyanthranilic acid were administered to early hepatoma patients to evaluate the conversion of these precursors to niacin metabolites and to assess the effect of dietary supplementation with vitamin B-6, riboflavin, thiamin and vitamin C on the extent of conversion. Expired labeled carbon dioxide and urinary excretion of picolinic acid (PA), quinolinic acid (QA), nicotinic acid (NA), N1-methylnicotinamide (N1MeNAm) and N1-methyl-2-pyridone-5-carboxamide (MPCA) were measured by carrier isolations. There were no consistent statistical differences in these conversions before and after vitamin supplementation, suggesting that the patients' nutrition was adequate and that none of the vitamins were rate-limiting under these conditions.

The cerebral uptake of 11C-nicotinic acid (11C-NAC) and 11C-nicotinamide (11C-NAM) was quantified by the use of PET. Based on the amount of activity injected, the PET images showed a low cerebral uptake of 11C-NAC, while 11C-NAM was clearly visualized in the cortical areas. This discrepancy was found to be the result of the binding of 11C-NAC to the red blood cells by a factor of 5 to 20 above that for 11C-NAM. 11C-NAM was better extracted by the cerebrum than 11C-NAC, as shown by the mean values of the cortical tissue/plasma ratio of 1.9 for 11C-NAC and 5 for 11C-NAM at 30 min. post-injection. An analysis of Patlak-Gjedde plot curves revealed a metabolic compartment for 11C-NAC and 11C-NAM with similar values of about 0.02 l/min for the accumulation constant K3. This was indicative of a slower transport rate for 11C-NAC. A significant finding of the study was the increasing ratio of activity concentrations in red blood cells versus the concentrations in plasma (over time). There were no significant differences between the data from normal volunteers and patients with Huntington's or Alzheimer's disease.

Labeled enantiomers of tryptophan, kynurenine, and hydroxykynurenine were given to five patients with scleroderma. Blood samples were drawn periodically over a 24-hr period. When the D-isomers were given, peak blood levels of radioactivity did not appear until 8 hr, whereas with the natural L-isomers peak levels were reached in 2 hr Considerable radioactivity was found firmly bound to the precipitated plasma proteins from both the L- and D-isomers. Incubation studies confirmed the binding of the D-isomers to the serum proteins. These experiments show that the use of pure labeled L-isomers is required, when studying the metabolism of amino acids in man, and that compounds other than L-tryptophan are bound to serum proteins in significant quantities.

South African Bantu patients with a scurvy-type skin, which developed after a prolonged, iron-induced hemosiderosis, were studied with ascorbic acid-1-C14 and the 2 gm tryptophan load test. The metabolism of the two compounds was found to be abnormal in these patients. The data suggested that ascorbic acid was rapidly (iron accelerated) metabolized to monodehydroascorbate, a compound that rapidly reacts with tissue DPNH to form DPN. This mechanism could reduce tissue levels of DPNH such that the feed-back control of tryptophan pyrolase enzyme was depressed. The change in control level of the pyrrolase enzyme permitted large quantities of tryptophan to be converted into the kynurenine pathway products, and a smaller quantity for the serotonin pathway. This mechanism could contribute to the abnormal tryptophan metabolism found in chronic pellagrins with dementia.

Six South African White miners were studied with the 2-g L-tryptophan load test and tracer doses of L-tryptophan-7a-14C, L-kynurenine-keto-14C and hydroxy-L-kynurenine-keto-14C. The breath 14CO2 and 14 urinary metabolities were measured. When they were compared with a previous study of American women with scleroderma, similar 14CO2 and tryptophan metabolite excretion patterns were observed in the data from the miners. The labelled quinolinic acid excretion was more significantly elevated in the South African miners' urine than in the urine of the American women. The data from both studies suggest that some patients with scleroderma have an altered step in the tryptophan metabolic pathway after hydroxy-anthranilic acid. What relationship exists between the induction of pulmonary silicosis and the subsequent development of scleroderma, requires additional human studies.

The object of this study was to determine the effect of large oral doses of L-leucine, vitamin B1, vitamin B2, vitamin B6 or vitamin C, given over a period of days, on the plasma free amino acid levels and protein nutrition index values of South African Blacks on a maize diet. In addition, single loads of L-tryptophan or L-kynurenine were given before and after the above regimen of L-leucine or vitamin to determine the effect of tryptophan or kynurenine with and without the influence of these factors on the plasma free amino acid levels and protein nutrition index values. Vitamin C therapy or a single dose of L-tryptophan increased the total plasma free amino acid levels. L-leucine therapy or a single loading dose of L-tryptophan increased the protein nutrition index. Single loading doses of L-kynurenine decreased the protein nutrition index. The levels of non-essential amino acids in the plasma of Blacks were much higher than those of Whites, and consequently the protein nutrition index values were much lower.

Erthrocytes from African blacks with primary hepatoma were incubated with physiological amounts (1.64 microM) of nicotinamide-14C (NM-14C) and it was found that these erythrocytes could synthesize NAD from NM. After 3-hr incubation with NM-14C, a large percentage of the 14C was found in NMN, nicotinamide riboside (NR) and NAD, but was undetectable in nicotinic acid nucleotides (NAMN and NAAD). This suggested that the NAD synthesized from NM was not through the Preiss-Handler pathway. After 6-plus hr incubation, the 14C found in NAMN and NAAD suggested the NAD synthesized was being broken down and reutilized through Preiss-Handler pathway for synthesis of NAD. This reutilization pathway was confirmed by incubating nicotinic acid-14C (NA-14C) with erythrocytes. Apparently the metabolites from the breakdown of NAD were deaminated. The metabolism of NM-14C was slower than NA-14C. However, after 24 hr incubation with NM-14C, 72.26% of 14C was found in NAD. A high percentage of 14C in NR at the initial incubation and a later drop suggested that NR was another intermediate in the pathway.

Nonproliferating cells of Chromobacterium violaceum incubated with glycine, methionine, and succinate as substrates accumulated beta-cyanoalanine in the culture fluid. Tracer experiments showed that carbons-2, -3, and -4 of beta-cyanoalanine are derived from the 2-carbon of glycine. When methionine-methyl-(14)C, succinate-1,4-(14)C, or succinate-2,3-(14)C was used as substrate, beta-cyanoalanine did not become labeled. If K(14)CN and serine were used as substrates, the cyano group of beta-cyanoalanine was labeled. Radioactive beta-cyanoalanine, labeled in the 3-carbon, was formed when glycine and H(14)CHO were used as substrates. (14)C-formic acid did not replace formaldehyde. Asparagine also accumulated in the incubated mixture and was found to be labeled in the amide carbon. Incubation of cells with beta-cyanoalanine-4-(14)C produced labeled aspartic acid in cell hydrolysates.