Diminished phenylketonuria in phenylpyruvic oligophrenia after administration of L-glutamine, L-glutamate or L-asparagine

Single amino acid supplementation in aminoacidopathies: a systematic review

Aminoacidopathies are a group of rare and diverse disorders, caused by the deficiency of an enzyme or transporter involved in amino acid metabolism. For most aminoacidopathies, dietary management is the mainstay of treatment. Such treatment includes severe natural protein restriction, combined with protein substitution with all amino acids except the amino acids prior to the metabolic block and enriched with the amino acid that has become essential by the enzymatic defect. For some aminoacidopathies, supplementation of one or two amino acids, that have not become essential by the enzymatic defect, has been suggested. This so-called single amino acid supplementation can serve different treatment objectives, but evidence is limited. The aim of the present article is to provide a systematic review on the reasons for applications of single amino acid supplementation in aminoacidopathies treated with natural protein restriction and synthetic amino acid mixtures.

Chronic hyperphenylalaninemia produces cerebral hyperglycinemia in immature rats

The amino acid content of three tissues was measured in 10-day-old rats made hyperphenylalaninemic from age 3 to 10 days by daily injection of phenylalanine plus alpha-methylphenylalanine to inhibit phenylalanine hydroxylase (PAH). At 12 h after the last injection, the concentrations of alanine, valine, methionine, isoleucine, and leucine in the cerebral hemispheres were depressed by 25-50%, whereas that of glycine was elevated 2.3-fold. In the spinal cord, the levels of phosphoserine, methionine, and leucine were decreased by 40-50%, and those of serine and threonine increased by 50%. Tyrosine and phenylalanine concentrations were high in all tissues, 2-3 and 15-30 times normal, respectively; of the amino acids investigated, they were the only ones changed in the liver. Cerebral hyperglycinemia was also produced by chronic treatment with phenylalanine plus p-chlorophenylalanine to inhibit PAH, but not by acute (12 h) hyperphenylalaninemia. An increase in cerebral phosphoserine phosphatase activity was greater in rats treated with phenylalanine plus PAH inhibitor than with inhibitor alone. The content of brain glycine normally declines with age from birth to 15 days; this decrease was prevented by chronic hyperphenylalaninemia. Attempts to reduce the cerebral glycine content of the hyperphenylalaninemic rats were unsuccessful. However, one of the therapeutic protocols, methionine loading, may be useful because it increased the methionine and decreased the phenylalanine contents in the brain.

The kinetics of intramolecular distribution of 15N in uric acid after administration of (15N) glycine. A reappraisal of the significance of preferential labeling of N-(3+9) of uric acid in primary gout

THE CONCEPT OF AN ABNORMALITY OF GLUTAMINE METABOLISM IN PRIMARY GOUT WAS FIRST PROPOSED ON THE BASIS OF ISOTOPE DATA: when [(15)N]glycine was administered to gouty subjects, there was disproportionately great enrichment of N-(3 + 9) of uric acid, which derive from the amide-N of glutamine. An unduly high concentration of (15)N in glutamine was postulated, and attributed to a hypothetical defect in catabolism of glutamine. Excess glutamine was proposed as the driving force of uric acid overproduction. WE HAVE REEXAMINED THIS PROPOSITION IN FOUR GOUTY SUBJECTS: one mild overproducer of uric acid with "idiopathic gout," one marked overproducer with high-grade but "partial" hypoxanthine-guanine phosphoribosyl-transferase deficiency, and two extraordinary overproducers with superactive phosphoribosylpyrophosphate synthetases. In the last three, the driving force of excessive purine biosynthesis is a known surplus of alpha-5-phosphoribosyl-1-pyrophosphate. Disproportionately high labeling of N-(3 + 9) was present in all four gouty subjects, most marked in the most flamboyant overproducers. The precursor glucine pool was sampled by periodic administration of benzoic acid and isolation of urinary hippuric acid. Similarly, the precursor glutamine pool was sampled by periodic administration of phenylacetic acid and isolation of the amide-N of urinary phenylacetylglutamine. The time course of (15)N enrichment of hippurate differed from that of the amide-N of glutamine. Whereas initial enrichment values of hippurate were very high, those of glutamine-amide-N were low, increasing to a maximum at about 3 h, and then declining less rapidly than those of hippurate. However, enrichment values of hippurate and of phenacetyl glutamine were normal in all of the gouty subjects studied. Thus, preferential enrichment of N-(3 + 9) in gouty overproducers given [(15)N]glycine does not necessarily reflect a specific abnormality of glutamine metabolism, but rather appears to be a kinetic phenomenon associated with accelerated purine biosynthesis per se.In addition, greater enrichment of N-9 than of N-3 on days 1 and 2 provided suggestive evidence for a second pathway for synthesis of the initial precursor of purine biosynthesis, phosphoribosylamine, perhaps utilizing ammonia rather than the amide-N of glutamine as nitrogen donor. In this limited study, the activity of this potential second pathway did not appear to be selectively increased in gout.

Plasma and urinary amino acids in primary gout, with special reference to glutamine

Measurement of the plasma free amino acids by column chromatography (AutoAnalyzer) in 32 patients with primary gout showed statistically significant increases or decreases in several components when compared with the spectrum in 18 control subjects, but the absolute amounts involved were small and the mean total plasma amino acid concentrations in both groups were the same. In the urine all major amino acid components, notably glutamine, serine, threonine, and leucine, were lower in our gouty than in our nongouty subjects, as were also the corresponding renal clearance ratios. These deficits could be reproduced by restricting dietary protein, so appear to be due largely to the some-what reduced mean dietary protein intake of our gouty subjects. However, the low renal clearance of glutamine, the most striking and consistent of the deficits in urinary amino acids noted, could not be accounted for by dietary or other relevant factors, and is interpreted as indicating increased tubular reabsorption of glutamine in primary gout. This interpretation was supported by the results of glutamine loading. The possible compensatory relationship of the abnormality in renal handling of glutamine to the deficiency in renal production of ammonia previously reported is discussed.