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Amino Acids: The Forum for Amino Acid, Peptide and Protein Research (v.18, #3)

Indicators of l-arginine metabolism and cardiovascular risk factors A cross-sectional study in healthy middle-aged men by J. Penttinen; S. Pennanen; J. Liesivuori (pp. 199-206).

This study examines the relationship between traditional risk factors of coronary artery disease and indicators involved in the metabolism of l-arginine (plasma and urine l-arginine, plasma l-citrulline, serum creatinine and urine orotic acid). Our study population consisted of 40 healthy male volunteers aged between 35 and 55 years. We found an inverse association between serum creatinine and blood pressure, between plasma l-citrulline and blood pressure, as well as between urine l-arginine and blood pressure. We also found a positive association between plasma LDL-cholesterol and urine l-arginine and a negative correlation between plasma l-arginine and LDL-cholesterol. Orotic acid measured from urine was not associated with any of the indicators of l-arginine metabolism. Our results indicate that l-arginine metabolism is of profound significance for cardiovascular health. However, our study does not answer questions relating to causality. Further studies are needed to clarify the causal relationship between cardiovascular risk factors, especially elevated blood pressure and high LDL-cholesterol, and indicators of l-arginine metabolism.

Keywords: Keywords: Amino acids – Atherosclerosis –l-Arginine – Creatinine – Citrulline

Anaerobic accumulation of amino acids in rice roots: role of the glutamine synthetase/glutamate synthase cycle by R. Reggiani; M. Nebuloni; M. Mattana; I. Brambilla (pp. 207-217).

Accumulation of amino acids was studied in rice roots of 3-day-old seedlings subjected for 48 h to anaerobic conditions. Alanine and Gaba were the main amino acids accumulated under anoxia. Their synthesis was strongly inhibited by MSX and AZA, inhibitors of glutamine synthetase and glutamate synthase. These activities increased after 8 h of anaerobic treatment and, by immunoprecipitation of ³⁵S-labeled proteins, it was shown that glutamine synthetase and ferredoxin-dependent glutamate synthase were synthesized during the treatment. These findings indicate that the glutamine synthetase/glutamate synthase cycle play an important role in anaerobic amino acid accumulation.

Keywords: Keywords: Amino acids – Anoxia – Glutamate synthase – Glutamine synthetase – Rice – Root

The peptides of α-aminosuberic acid I New intermediates for synthetic studies by E. Wünsch; H. Stocker; P. Maloň; V. Gut; V. Čeřovská; M. Žertová; D. D. Laffan (pp. 219-227).

The paper describes the synthesis of α-aminosuberic acid derivatives suitable for the synthesis of peptides. These include Z-, Boc- and Fmoc-protection on the α-amino group, benzyl ester, Boc-hydrazide and Z-hydrazide as well as the free carboxylic function in the side chain, and methyl ester, benzyl ester or free α-carboxylic group. Their use is demonstrated on the synthesis of the respective derivatives of Asu-Val-Leu. The enzyme catalyzed reaction was succesfully used both as a route to L-Asu from the D,L-compound as well as for the direct synthesis of the optically active tripeptide derivative from the Z-D,L-Asu-OH.

Keywords: Keywords:α-Aminosuberic acid – Enzymatic resolution – Peptide synthesis – Synthetic intermediates

Inducible nitric oxide synthase activity in colon biopsies from inflammatory areas: correlation with inflammation intensity in patients with ulcerative colitis but not with Crohn's disease by G. Guihot; R. Guimbaud; V. Bertrand; B. Narcy-Lambare; D. Couturier; P. H. Duée; S. Chaussade; F. Blachier (pp. 229-237).

Nitric oxide synthase (NOS) activities are responsible for the enzymatic conversion of L-arginine into NO and L-citrulline. Relatively low amounts of NO are produced in intestinal epithelial cells or are released from nerve endings. The effects of NO production are related to the maintenance of epithelial integrity and permeability. A pathological role of an increased NO production has been suggested to play a role in models of experimental colitis. In humans, NOS activity in colon mucosa from patients with ulcerative colitis is clearly increased when compared with the activity of the control group. In contrast, an increase of NOS activity in the colon mucosa from patients with Crohn's disease remains controversial. In the present work, we have measured NOS activity in colon biopsies originating from the control group (n = 16), from patients with ulcerative colitis (n = 23) and Crohn's disease (n = 17) using the radiochemical method of the conversion of L-[guanido-¹⁴C] arginine into radioactive L-citrulline. In the control group, NOS activity was mainly of the inducible type (88% of total NOS activity) since it was characterised by its insensibility to the absence of calcium in the assay medium. In colon biopsies originating from patients with ulcerative colitis, inducible NOS activity was increased 3 fold (p < 0.005) and in patients with Crohn's disease, inducible NOS activity was increased 5 fold (p < 0.005). Correlations between NOS activity in colon biopsies and the intensity parameters of the disease i.e. Truelove index, endoscopic score and histo-logical parameters were evidenced in patients with ulcerative colitis. In contrast, in patients with Crohn's disease, the high inducible NOS activity was not correlated with any intensity parameters of the disease. From these data, we concluded that although inducible NOS activity was increased several fold in colon biopsies originating from patients with both ulcerative colitis and Crohn's disease, a correlation between this activity and the severity of bowel inflammation was not found in either cases.

Keywords: Keywords: Amino acids – Nitric oxide synthase – Colon biopsies – Ulcerative colitis – Crohn's disease

The effects of thiopentone on free intracellular amino acids in polymorphonuclear leucocytes by J. Mühling; V. Knülle; M. Fuchs; M. G. Dehne; S. Weiss; G. Hempelmann (pp. 239-249).

Previous studies have shown the inhibitory effects of thiopentone on polymorphonuclear leucocyte (PML) function. However, major biochemical mechanisms which have been involved are still unknown. The aim of this study was therefore to investigate thiopentone's effects on intracellular amino acid metabolism in PML using both advanced PML separation – and HPLC techniques, especially developed for this purpose and precisely validated in our institute. Overall, our study indicates important dose-dependent alterations of free intracellular amino acid metabolism following thiopentone treatment and draw attention to the biochemical mechanisms which may be involved in both thiopentone-induced modulation in PML function and cellular immunocompetence.

Keywords: Keywords: Amino acids – Leucocytes – Thiopentone – Intracellular amino acids – High-performance liquid chromatography – Amino acid metabolism

Chemical and toxicological studies of products resulting from sorbic acid and methylamine interaction in food conditions by C. Ferrand; F. Marc; P. Fritsch; P. Cassand; G. de Saint Blanquat (pp. 251-263).

Sorbic acid has a system of conjugated double bonds which makes it able to undergo nucleophilic addition reactions with certain functions. The interactions between sorbic acid and an amine present in the endogenous constituents of food were quantified. We demonstrated the formation of new products and studied the underlying mechanisms using ethyl sorbate and various amines. HPLC, GC, GC-SM and NMR analyses of the reaction mixes enabled the isolation and identification of the products. The addition reactions led, at 20°C, to linear monoadducts and, at 50°C, to cyclic derivatives resulting from double addition. Mutagenesis studies, involving Ames test and genotoxicity studies with HeLa cells and on plasmid DNA, in cyclic interaction products, showed that none of the products studied presented neither mutagenic nor genotoxic activities.

Keywords: Keywords: Amino acids – Sorbic acid – Methylamine – Interaction products – 3-D-test – Ames test

Consequences of renal mass reduction on amino acid and biogenic amine levels in nephrectomized mice by M. Al Banchaabouchi; B. Marescau; R. D'Hooge; S. Engelborghs; P. P. De Deyn (pp. 265-277).

Amino acid and biogenic amine changes were investigated in nephrectomized mice ten days postsurgery. Uremic mice exhibited changes in amino acid concentrations in plasma, urine and brain. Particularly plasma methionine, citrulline and arginine levels were significantly enhanced in nephrectomized mice compared to controls whereas serine was decreased. Urinary excretion of methionine, citrulline and alanine was higher in nephrectomized mice compared to controls whereas many amino acids were increased in brain of nephrectomized mice. Brain and urinary amino acid changes were more pronounced in the 75% than in the 50% nephrectomized mice. Brain norepinephrine and dopamine and its metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were significantly increased whereas serotonin was decreased comparing the 75% nephrectomized mice to the sham-operated mice. This study demonstrates that at very early stages of renal insufficiency, specific amino acid and biogenic amine changes occur in plasma, urine and brain. These alterations might depend qualitatively and quantitatively on the degree of functional renal mass reduction.

Keywords: Keywords: Amino acids – Biogenic amines – Renal insufficiency – Mice

Identification of the site of glucocorticoid action on neutral amino acid transport in superficial nephrons of rat kidney by M. Schwertfeger; M. Roskos; C. Fleck (pp. 279-288).

Glucocorticoid hormones enhance the reabsorptive capacity of filtered amino acids in rat kidney, as it was shown in previous in vivo clearance experiments. In the present study, the site of glucocorticoid action on neutral amino acid transport in superficial nephrons of rat kidney was investigated using in vivo micropuncture technique. Adult female Wistar rats were treated with dexamethasone (DEX), and fractional excretion of L-glutamine (L-Gln) and L-leucine (L-Leu) were determined and related to inulin after microinfusion into different nephron segments. DEX reduced fractional excretion of both neutral amino acids as a sign of enhanced reabsorptive capacity. The site of main DEX action on L-Leu reabsorption has been localized in the proximal straight tubule. However, in the case of L-Gln, the inhibition of γ-glutamyltranspeptidase (γ-GT) by administration of acivicin indicated the importance of this brush border enzyme in reduced L-Gln excretion. DEX enhanced γ-GT activity by tubular acidification. It can be presumed a DEX-inducible transport system for neutral amino acids mainly localized in proximal straight tubules of rat kidney.

Keywords: Keywords: Amino acid transport – Kidney – Glucocorticoid hormone – Glutamine – Leucine – Micropuncture – Gamma-glutamyltranspeptidase – Rat

Impaired glucose tolerance (IGT) is not associated with disturbed homocysteine metabolism by A. Pixa; J. Pietzsch; U. Julius; M. Menschikowski; M. Hanefeld (pp. 289-298).

Elevated plasma total homocysteine (tHcy) has been suggested to be an additional risk factor for cardiovascular disease in subjects with impaired glucose tolerance (IGT) and Type 2 diabetes (T2D). In order to investigate whether an insulin resistant/chronic hyperinsulinemic situation in male diabetic and prediabetic subjects directly influences the tHcy metabolism, fasting tHcy and post-methionine load tHcy plasma levels (PML-tHcy) were determined in 15 men with IGT, 13 men with newly dia-gnosed T2D, and 16 normoglycemic controls (NGT). Fasting tHcy (IGT, 13.1 ± 4.6; T2D, 12.8 ± 4.0; NGT, 10.7 ± 4.4 μmol/L) and PML-tHcy (IGT, 46.5 ± 17.39; T2D, 41.1 ± 6.8; NGT, 38.0 ± 9.7 μmol/L) showed no differences between the groups. Fasting tHcy and PML-tHcy correlated with fasting proinsulin (r = 0.395, p < 0.05; r = 0.386, p< 0.05) and creatinine (r = 0.489, p < 0.01; r = 0.339, p < 0.05), resp. Multiple regression analysis showed only a relationship between fasting tHcy and creatinine. No relationships have been found between fasting tHcy and PML-tHcy, resp., and indicators of an insulin resistant state, e.g., insulin and proinsulin, as well as serum cobalamin and folate concentrations. In conclusion, our data suggest that the degree of glucose intolerance has no direct impact on the metabolism of homocysteine. However, tHcy levels tend to be elevated with the development of nephropathy, indicating an association between tHcy and renal function in these subjects.

Keywords: Keywords: Amino acids – Impaired glucose tolerance – Type 2 diabetes – Homocysteine – Renal function

Excitatory amino acid stimulation of the survival of rat cerebellar granule cells in culture is associated with an increase in SMN, the spinal muscular atrophy disease gene product by C. Andreassi; A. L. Patrizi; C. Brahe; M. L. Eboli (pp. 299-304).

Excitatory amino acids which promote the survival of cerebellar granule cells in culture, also promote the expression of the survival of motor neuron (SMN) protein. Immunolocalization studies using SMN monoclonal antibody showed that SMN is decreased in cultures grown in low K⁺ or chemically defined medium with respect to cultures grown in high K⁺ medium and that an increase of SMN can be induced by treatment of low K⁺ cultures with glutamate or N-methyl-D-aspartate.

Keywords: Keywords: Amino acids – Cerebellar granule cell – Excitatory amino acid – Trophic factor – Survival of motor neuron protein – Spinal muscular atrophy

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Amino Acids: The Forum for Amino Acid, Peptide and Protein Research (v.18, #3)

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Amino Acids: The Forum for Amino Acid, Peptide and Protein Research (v.18, #3)