The effect of chelation therapy on the amino aciduria and peptiduria of Wilson's disease.

1. There is an excess urinary output of free amino acids and of urinary peptides in most cases of untreated Wilson's disease. Studies of 11 patients have shown that both these abnormalities are greatly improved by two years of standard chelation therapy. 2. The reduction in excretion of both free amino acids and peptides is purely quantitative, there being no significant change in the percentage composition of amino acids, either free or combined, in relation to their total urinary output. 3. Arguments are advanced that the peptiduria of the disease is usually due to a proximal renal tubular reabsorption defect, but in rare cases it may be due to excess bone breakdown or even to a combination of bone and renal tubular disease in the same patient.

Peptiduria in experimental Fanconi syndrome in rats.

1. The plasma concentrations and urinary output of proline and hydroxyproline contained in peptides were measured in normal rats and in rats with Fanconi syndrome produced by injection of sodium maleate. All animals received a prior injection of 10 mg of the dipeptide L-prolyl-L-hydroxy-proline to increase plasma and urinary peptide content. There was a significant increase of urinary output of the two imino acids contained in peptides and a fall in their plasma concentrations. 2. It is concluded that increased output of peptides derived from collagen degradation in the experimental Fanconi syndrome in rats is at least in part due to diminished tubular reabsorption of these compounds from the glomerular filtrate. The results are claimed to be relevant to the increased output of urinary peptides in the Fanconi syndrome in man.

Peptide excretion in experimental Fanconi syndrome in the rat.

A study has been made of urinary peptide output in rats before and after production of a Fanconi syndrome induced by a single injection of sodium maleate. There was an unequivocal increase of urinary peptides on the first and second days after the injection, without any detectable change in the concentration of plasma peptides. 2. Similar results were obtained in osteolathyritic rats in which skeletal lesions had been produced by ingestion of beta-aminopropionitrile. 3. The fractional amino acid content of urinary peptides after maleate and beta-aminopropionitrile is shown to be significantly different from that in control animals. 4. Evidence is presented that the increased output of peptides is mainly due to increased renal clearance similar to that previously described for amino acids, glucose and several electrolytes in this type of experimental Fanconi syndrome.

Peptiduria in the Fanconi syndrome.

Peptide excretion has been studied in 20 cases of Wilson's disease and in maleate-induced Fanconi syndrome in the rat, ligand-exchange column chromatography being used to separate peptides from free amino acids. There is a statistically significant increase in urinary peptides in both types of the Fanconi syndrome. In both man and the rat, a large fraction of the excreted peptides has been shown to contain hydroxyproline, and therefore to be derived from collagen degradation. In both groups there is a close correlation between the output of hydroxyproline and that of total peptide-bound amino acids. Arguments are advanced that the peptiduria is due to increased urinary clearance of plasma peptides rather than to a metabolic cause. Peptides excreted in patients with the Fanconi syndrome are shown to have a different proportionate amino acid composition to those in urine specimens from normal controls. The mean size of urinary peptides derived from collagen must be at least five or six amino acids per peptide chain. Maleate-induced Fanconi syndrome in the rat is thought to be a close analogue of the syndrome in man, and further results obtained in the animal model may well be directly applicable to human disease.

Urinary excretion of peptides and of hydroxyproline in Wilson's disease.

1. A study has been made of peptide excretion in twenty cases of Wilson's disease, ligand-exchange column chromatography being used to separate peptides from free amino acids. Previous reports of excess of peptide output in the disease were confirmed and the excess was shown to be highly significant statistically. 2. A considerable fraction of the excess of peptide output was shown to consist of hydroxyproline-containing peptides derived from collagen degradation. 3. The method of rank correlation showed that the difference both in free amino acid and peptide-bound amino acid output in cases of Wilson's disease and in control subjects was mainly quantitative; the pattern of amino acid excretion was qualitatively similar in both groups. 4. Evidence is presented that the increase copper output in the urine in the disease is not secondary to peptiduria.

Depression of jejunal dipeptide transport by pyridoxine deficiency in the rat.

Three dipeptides (L-alanyl-L-alanine, beta-alanyl-L-histidine and L-prolylglycine), representative of distinctly different transport groups, and a dicarboxylic acid dipeptide (L-glutamyl-L-glutamic acid) showed a quantitatively equivalent decrease of absorption (mean difference, 12% disappearance 15 min-1 5 cm-1) from jejunal loops in vivo in pyridoxine deficient rats, compared with pyridoxine-repleted controls. Analysis of results for seven dipeptides, including three studied previously, indicated that pyridoxine deficiency caused a general or non-specific reduction in dipeptide transport, similar for all dipeptides. Decrease in dipeptide transport in vitamin deficiency ran parallel to, but was significantly less than, the decrease in amino acid transport, suggesting in theory involvement of pyridoxine in a common cellular efflux mechanism or, less likely, in the energetics of active transport.

Amino acid imbalance in cystinuria.

After oral ingestion of a free amino acid mixture by three cystinuric patients, plasma increments of lysine and arginine were lower and those of many other amino acids were significantly higher than those found in control subjects. Similar results were obtained in control subjects after amino acid imbalance had been artificially induced by the omission of cystine, lysine, and arginine from the amino acid mixture. Especially high increments of alanine and proline provided the best evidence of amino acid imbalance caused by a temporary lysine and, to a lesser extent, arginine and cystine deficit. No such amino acid imbalance was found to occur in the cystinuric patients after ingestion of whole protein, indicating that absorption of oligopeptides produced by protein digestion provided a balanced physiological serum amino acid increment. This is considered to explain the lack of any unequivocal nutritional deficit in cystinuric patients despite poor absorption of the essential free amino acid, lysine.

Intestinal absorption of an arginine-containing peptide in cystinuria.

Separate tolerance tests involving oral intake of the dipeptide, L-arginyl-L-aspartate, and of a corresponding free amino acid mixture, were carried out in a single type 2 cystinuric patient. Absorption of aspartate was within normal limits, whilst that of arginine was normal after the peptide but considerably reduced after the amino acid mixture. The results are compared with the increments of serum arginine found in eight normal subjects after the oral intake of the free amino acid mixture. Analyses of urinary pyrrolidine and of tetramethylenediamine in urine samples obtained after the two tolerance tests in the patient support the view that arginine absorption was subnormal after the amino acid mixture but within normal limits after the dipeptide.

Studies on intestinal absorption of amino acids and a dipeptide in a case of Hartnup disease.

A severely affected case of Hartnup disease is reported, where the patient responded rapidly to nicotinamide. This supports the view that all the clinical features, except reduced stature from general nutritional defect, are secondary to tryptophan and nicotinamide deficiency rather than to an unknown toxic factor. Severe malabsorption of both tryptophan and phenylalanine was demonstrated. The dipeptide carnosine was absorbed normally whereas when the two constituent amino acids, beta-alanine and L-histidine, were ingested, absorption of the former was normal but that of the latter was grossly defective. The suggestion is advanced that in cases of Hartnup disease protein nutrition is maintained by intestinal uptake of amino acids as oligopeptides rather than as free amino acids. By contrast, both modes of absorption are probably important in normal subjects. Radiology of the small intestine is abnormal in Hartnup disease when a large amount of protein is admixed with the barium meal.

Intestinal absorption of two dipeptides in Hartnup disease.

The results of oral tolerance tests of two dipeptides and of their constitutent amino acids are compared in normal subjects and in a case of Hartnup disease. In the control subjects the rate of absorption of phenylalanine from phenylalanyl-phenylalanine and of tryptophan from glycyl-tryptophan was slower than after the equivalent amount of the free amino acids. Absorption of the two essential amino acids (tryptophan and phenylalanine) in the patient was almost zero after administration in the free form, but was much greater after the dipeptide. Results of experiments on absorption and hydrolysis of the two peptides in the rat small intestine are also reported. It is suggested that whereas normal subjects absorb essential amino acids by a dual mechanism of mucosal uptake of free amino acids and oligopeptides, nutrition in Hartnup disease is largely dependent on uptake of oligopeptides containing the amino acids affected by the intestinal transport defect of the disease.

Intestinal absorption of carnosine and its constituent amino acids in man.

Serum concentrations of beta-alanine and l-histidine are compared in five normal adults after ingestion of the dipeptide carnosine (beta-alanyl-l-histidine) and after equivalent amounts of the constituent free amino acids. The results indicate that absorption is significantly more rapid after the ingestion of the amino acids than after the dipeptide. The use of the test in a case of Hartnup disease suggests that carnosine is taken up by intestinal cells as the dipeptide, but subsequent hydrolysis and delivery of the constituent amino acids to the portal blood is a slower process than transport of the free amino acids themselves.