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PubMedDate not supplied

Conversion of a qualitative screening test to a quantitative measurement of urinary cystine and homocystine.

Qualitative urinary screening procedures were converted to quantitative methods for urinary cystine and homocystine based on the reactions between these amino acids and cyanide-nitroprusside reagents. Cystine and homocystine are quantified by the measurement of absorbances at 521 and 524 nm, respectively. Cyanide-nitroprusside reacts with both cystine and homocystine. However, in the presence of silver nitrate, only homocystine reacts to produce a magenta color. Following the cyanide-nitroprusside reaction, absorbance must be read within three minutes for cystine and immediately for homocystine. The stability of the absorption spectra has no apparent effect on these quantitative assays. Amino acid concentrations are expressed as ratios to creatinine, which tends to eliminate false negative results in dilute urine specimens. The normal urine value for cystine and homocystine combined is 66.8 +/- 52 (n = 50) mg per g creatinine. The normal value for homocystine alone is 29.9 +/- 16.8 (n = 24) mg per g creatinine. The simplicity of these procedures allows these quantitative methods to be used as screening tests for cystinuria and homocystinuria.

Amino Acids↗
PubMed1990

Disruption of thymidylate synthesis and glycine-serine interconversion by L-methionine and L-homocystine in Raji cells.

Excessive concentrations of L-methionine inhibited the folate-dependent de novo synthesis of thymidylic acid (TMP) in Raji cells, demonstrating the usefulness of this cell line for the study of methionine-folate antagonism. The effect was also produced by L-homocystine but not by other amino acids including D-methionine and L-ethionine, suggesting that this effect is exerted by a common intermediate of methionine and homocystine metabolism. L-Methionine, L-homocysteine, S-adenosylmethionine (SAM), and S-adenosylhomocysteine (SAH) are not inhibitors of thymidylate synthase activity. On the other hand the capacity of the cells to incorporate serine 3-carbon and glycine 2-carbon into DNA is impaired by the presence of L-methionine or L-homocystine. Studies with cell-free extracts demonstrated that the glycine cleavage enzyme is inhibited by 45% by L-methionine, L-homocysteine, SAM or SAH. Serine hydroxymethylase on the other hand was slightly stimulated by these sulfur-containing compounds and this stimulation was shown to occur in the intact cell as well. These findings suggest that when levels of L-methionine metabolites are elevated, there is an increase in the use of glycine to maintain the intracellular concentration of serine, which is required for homocysteine detoxification by conversion to cystathionine. The reduction in TMP synthesis caused by excess L-methionine or L-homocystine may result from increased utilization of one-carbon units for serine synthesis.

Amino Acids↗
PubMed1976

Homocystine-induced arteriosclerosis. The role of endothelial cell injury and platelet response in its genesis.

The atherogenic mechanism of homocystinemia has been defined by measuring endothelial cell loss and regeneration, platelet consumption, and intimal lesion formation in a primate model. Three groups of baboons were studied: (a) 8 control animals; (b) 15 animals after 3 mo of continuous homocystinemia; and (c) 11 animals after 3 mo of combined homocystinemia and oral treatment with dipyridamole. Experimental homocystinemia caused patchy endothelial desquamation comprising about 10% of the aortic surface despite a 25-fold increase in endothelial cell regeneration. Neither endothelial cell loss nor regeneration was changed significantly by dipyridamole. Homocystine-induced vascular deendothelialization produced a threefold increase in platelet consumption that was interrupted by dipyridamole inhibition of platelet function. All homocystinemic animals developed typical arteriosclerotic or preatherosclerotic intimal lesions composed of proliferating smooth muscle cells averaging 10-15 cell layers surrounded by large amounts of collagen, elastic fibers, glycosaminoglycans, and sometimes lipid. Intimal lesion formation was prevented by dipyridamole therapy. We conclude that homocystine-induced endothelial cell injury resulted in arteriosclerosis through platelet-mediated intimal proliferation of smooth muscle cells that can be prevented by drug-induced platelet dysfunction.

Animals↗
PubMed1976

Effect of induced elevated plasma levels of homocystine and methionine in rats on collagen and elastin structures.

Young growing rats were intraperitoneally injected with mixtures of homocystine and methionine for several weeks. The growth of the animals was inhibited. After 3 weeks 25% of the rats died and isolation of tail tendon collagen and aorta elastin showed that these proteins were deficient in chemical cross-links. Seventy-five % of the rats survived further injections for another 3 weeks and isolated collagen and elastin were found to be normal in cross-linking. The variability in susceptibility of these rats to homocystine-methionine treatment is discussed in relationship to human homocystinuria. It is speculated that the variability is due to variability in in vivo homocysteine levels.

Animals↗
PubMed1987

Urinary homocystine levels in a newborn infant with cystathionine synthase deficiency.

A boy with homocystinuria due to cystathionine synthase deficiency was found to have hypermethioninaemia by neonatal blood screening, but was not diagnosed as homocystinuric until 3 months of age because urinary homocystine was not detected by the cyanide-nitroprusside test or on two examinations with a sensitive amino acid autoanalyser. These findings indicate that tests for urinary homocystine should be made repeatedly with an amino acid autoanalyser in newborn infants with hypermethioninaemia until the enzyme defect is identified.

Cystathionine beta-Synthase↗
PubMedDate not supplied

Effect of methionine replacement by homocystine in cultures containing both malignant rat breast carcinosarcoma (Walker-256) cells and normal adult rat liver fibroblasts.

When malignant W-256 rat breast carcinosarcoma cells are mixed with an equal number of normal adult rat liver fibroblasts and allowed to grow in a medium containing sufficient L-methionine and an excess of vitamin B12 and of folic acid, the malignant cells outgrow the normal cells, and within 2 weeks the tissue culture flasks contain only neoplastic cells. However, when ample DL-homocystine or homocysteine replaces methionine in the medium containing the same amount of vitamin B12 and folic acid, and seeded with the same type and number of malignant and normal cells, the malignant cells die and the normal cells thrive. Substantiating this conclusion are the results of injections into rats of comparable numbers of cells from each group after 3 weeks of growth in tissue culture. Fatal malignancies are produced by the homocystein-cultivated cells.

Animals↗
PubMed1968

Activation of Hageman factor by L-homocystine.

L-Homocystine activates Hageman factor, as demonstrated by its capacity to initiate clotting and to induce the evolution of plasma kinins. Perhaps, strategically located deposits of this amino acid are responsible for the unusual frequency of thrombosis in patients with homocystinuria.

Adsorption↗
PubMed1979

Sulphr containing amino acids in chronic renal failure with particular reference to homocystine and cysteine-homocysteine mixed disulphide.

We measured plasma sulphur amino acids in twenty-two patients with chronic renal failure and compared the findings with those obtained in twenty-two normal subjects. In fasting blood (08.00 hours) cysteine-homocysteine mixed disulphide was significantly increased in the renal patients, mean values (+/- SD) being 8.2 +/- 3.4 and 3.1 +/- 1.0 mumol/l respectively (P less than 0.001). The increase was positively correlated with reduced renal function, as assessed by serum creatinine (r = 0.62; P less than 0.01). Homocystine was detected in nineteen patients, the mean concentration (+/- SD) being 1.7 +/- 0.6 mumol/l; it was not found in any normal subject. Methionine levels were not different but there were significant increases in cystine (P less than 0.001) and taurine (P less than 0.05) in the patients. Similar values for these amino acids were found in a second blood sample drawn at 16.00 hours. Changes in the other neutral and acidic amino acids measured were in agreement with those reported in chronic azotaemia. We concluded that plasma levels of all the principal sulphur amino acids except methionine are elevated in chronic renal failure emphasizing the importance of the kidney in sulphur excretion. Prolonged accumulation of homocysteine and cysteine-homocysteine mixed disulphide may be relevant to the development of accelerated vascular disease in patients with chronic renal failure by producing endothelial damage.

Amino Acids, Sulfur↗