From rats to man: a perspective on dietary L-arginine supplementation in human renal disease.
(17/1042)
Experimental studies have shown both therapeutic and detrimental consequences of modifying dietary L-arginine intake in renal diseases which likely reflect the complexity of L-arginine metabolism. L-Arginine intake is semi-essential and provides substrate for a number of L-arginine metabolites involved in renal pathology. Dietary L-arginine restriction has been identified as a key mediator of the beneficial effects of low protein diets on human renal fibrosis. Supplementing dietary L-arginine in renal diseases with increased iNOS expression appears to be detrimental and thus, may be harmful in immune-mediated human kidney disorders. Increasing L-arginine intake is beneficial in experimental models of hypertensive renal disease. Based upon available data, we believe additional questions must be answered experimentally, not only to prevent an adverse outcome in humans, but to enhance our chances of human trials which will result in substantially better amelioration of disease than currently available. (+info)
An enhancer element located downstream of the major glutamate dehydrogenase gene of Bacillus subtilis.
(18/1042)
The rocG gene of Bacillus subtilis, encoding a catabolic glutamate dehydrogenase, is transcribed by SigL (sigma(54))-containing RNA polymerase and requires for its expression RocR, a member of the NtrC/NifA family of proteins that bind to enhancer-like elements, called upstream activating sequences (UAS). Unlike the case for other sigma(54)-dependent genes, rocG has no UAS; instead, its expression depends on a sequence located 1.5 kilobases downstream of the rocG promoter, beyond the end of the rocG coding region. The same sequence also serves as the UAS for the downstream rocABC operon and can activate rocG if moved upstream of its promoter. Furthermore, the activating sequence can be moved as far as 15 kilobases downstream of the rocG promoter and still retain partial activity. (+info)
Aberrations of ammonia metabolism in ornithine carbamoyltransferase-deficient spf-ash mice and their prevention by treatment with urea cycle intermediate amino acids and an ornithine aminotransferase inactivator.
(19/1042)
Sparse fur with abnormal skin and hair (spf-ash) mice are deficient in ornithine carbamoyltransferase (OCT) activity, but their OCT protein is kinetically normal. We administered ammonium chloride to spf-ash mice, in order to analyze ammonia metabolism and to find a rationale for the therapy of OCT deficiency. Ammonia concentration in the liver of spf-ash mice increased to a level much higher than in the control. Ammonium chloride injection caused an increase in ornithine (Orn) 5 min after injection and an increase in the sum of Orn, citrulline (Cit) and arginine (Arg) for at least 15 min in the liver of control mice, but no increase in Orn, Cit and Arg in the liver of spf-ash mice. Treatment of spf-ash mice with Arg 5-20 min prior to the injection of ammonium chloride kept the hepatic ammonia concentration at a level comparable to that without the load. A significant reciprocal relationship between ammonia and Orn concentrations in the liver of spf-ash mice 5 min after an ammonium chloride load with or without Arg strongly suggests that ammonia disposal is dependent on the supply of Orn. In spf-ash mice loaded with tryptone as a nitrogen source, Arg supplementation showed a dramatic decrease in urinary orotic acid excretion in a dose-dependent manner. Similar effects were observed with Cit and Orn at the same dose, and a long-lasting effect with an ornithine aminotransferase inactivator, 5-(fluoromethyl)ornithine, at a much lower dose. The rate of urea formation in liver perfused with ammonium chloride was lower in spf-ash mice than in controls, but with the addition of Orn to the medium it increased to a similar level in control and spf-ash mice. These results indicate that OCT is not saturated with Orn in vivo under physiological conditions and that the administration or enrichment of the urea cycle intermediate amino acids enhances the OCT reaction so that the ammonia metabolism of OCT-deficient spf-ash mice is at least partially normalized. (+info)
Cartilage protection by nitric oxide synthase inhibitors after intraarticular injection of interleukin-1beta in rats.
(20/1042)
OBJECTIVE: To evaluate the effect of nitric oxide synthase (NOS) inhibitors on proteoglycan synthesis following intraarticular administration of interleukin-1beta (IL-1beta) in rats. METHODS: Recombinant human IL-1beta and NOS inhibitors with different selectivity for inducible NOS (N-monomethyl-L-arginine [L-NMA], N-iminoethyl-L-ornithine [L-NIO], and S-methylisothiourea [SMT]) were simultaneously administered in rats by a single intraarticular injection in each knee. L-NMA was also infused for 72 hours using an Alzet mini osmotic pump implanted into the peritoneal cavity 24 hours before IL-1beta challenge. NO production was determined as nitrate and nitrite, either in synovial fluid or ex vivo in supernatants of synovium and patellae. Proteoglycan synthesis was measured by ex vivo incorporation of 35SO4(2-) into patellar cartilage. RESULTS: IL-1beta induced a time-dependent increase in NO production in synovial fluid. Synovium and patellae released large amounts of nitrate and nitrite under ex vivo conditions, indicating that both tissues are effective sources of NO within the joint. This production of NO was accompanied by a delayed inhibition of proteoglycan synthesis. The intraarticular administration of L-NMA and L-NIO reduced NO release in synovial fluid and resulted in a partial recovery of proteoglycan synthesis. Under our experimental conditions, SMT failed to reduce NO synthesis and to restore proteoglycan synthesis. The protection of cartilage was improved by the systemic and sustained delivery of L-NMA. However, the complete inhibition of NO production in synovial fluid was not sufficient to fully restore cartilage anabolism. CONCLUSION: Our findings show that in rats: 1) NO may be an early mediator of the effect of IL-1beta on cartilage, 2) NO inhibition may have therapeutic relevance, although it is not sufficient to fully reverse the deleterious effects of IL-1beta, 3) among NOS inhibitors tested, only amino acid derivatives are effective, 4) protection can be achieved by local administration of NOS inhibitors, and 5) systemic and sustained delivery of the NOS inhibitor with the highest efficacy after intraarticular injection provides the most benefit. (+info)
Mechanisms of fluoroquinolone transport by human neutrophils.
(21/1042)
Neutrophils accumulate ciprofloxacin and other fluoroquinolones, a process that enhances the killing of intracellular pathogens and could facilitate the delivery of these agents to infection sites by migrating neutrophils. The mechanisms by which transport occurs have not been characterized. In the present study, quiescent neutrophils transported ciprofloxacin with an observed K(m) of 167 microgram/ml (501 microM) and a maximum velocity of 25.2 ng/min/10(6) cells. When neutrophils were stimulated with phorbol myristate acetate (PMA), a second component of ciprofloxacin transport was induced. This pathway had an apparent K(m) of 9.76 microgram/ml (29.3 microM) and a maximum velocity of 59.3 ng/min/10(6) cells. Transport by both pathways was Na(+) independent. Ciprofloxacin transport by quiescent cells was relatively insensitive to pH and N-ethylmaleimide but was competitively inhibited by adenine (K(i) = 1.55 mM). Papaverine, a benzylisoquinoline known to inhibit nucleobase transport, also inhibited ciprofloxacin transport by quiescent cells. In contrast, transport by PMA-stimulated cells was enhanced at pH 8.2, inhibited at pH 6.2, and blocked by N-ethylmaleimide. Cationic and neutral amino acids and cystine competitively inhibited ciprofloxacin transport by PMA-stimulated neutrophils (K(i) = 158 microM for ornithine) but had little effect on quiescent cells. PMA-activated transport was not inhibited when the Na(+) in the medium was replaced with K(+) or Li(+), and the pattern of inhibition by cationic and neutral amino acids was similar. In summary, neutrophils continuously transport ciprofloxacin via a transport pathway shared by adenine. Activation by PMA induces a separate, higher-affinity transport pathway shared by a broad scope of amino acids. Neutrophils utilize one or both of these mechanisms to transport other fluoroquinolones. (+info)
Ornithinicoccus hortensis gen. nov., sp. nov., a soil actinomycete which contains L-ornithine.
(22/1042)
Two Gram-positive coccoid, non-motile bacteria with L-ornithine as diagnostic diamino acid of the peptidoglycan and an interpeptide bridge of L-Orn<--Gly(1,2)<--D-Glu were isolated from a sample of garden soil. The major menaquinone is MK-8(H4). 13-methyl and 12-methyl tetradecanoic acids are the predominant fatty acids. The polar lipids are phosphatidylinositol, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylserine and two unknown phospholipids. Mycolic acids are absent. The DNA base composition is 72 mol% G + C. Recent comparative 16S rDNA studies revealed that strains HKI 0125T and HKI 0131 represent a novel lineage adjacent to the family Intrasporangiaceae of the order Actinomycetales but distinct from the previously described genera of this family. On the basis of the genotypic, chemotaxonomic, morphological and physiological characteristics of these two isolates it is proposed to classify HKI 0125T and HKI 0131 in a new genus and species for which the name Ornithinicoccus hortensis gen. nov., sp. nov. is proposed. The type strain is HKI 0125T (= DSM 12335T). (+info)
Biochemical and ultrastructural changes in rabbit sclera after treatment with 7-methylxanthine, theobromine, acetazolamide, or L-ornithine.
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AIMS: To examine a possible effect of 7-methylxanthine, theobromine, acetazolamide, or L-ornithine on the ultrastructure and biochemical composition of rabbit sclera. METHODS: Groups of pigmented rabbits, six in each group, were dosed during 10 weeks with one of the substances under investigation, and one untreated group was the control. Samples of anterior and posterior sclera were taken for determination of hydroxyproline, hydroxylysine, proline, proteoglycans, uronic acids and dermatan sulphate, chondroitin sulphate, and hyaluronic acid. Sections were examined with electron microscopy, and the diameter of the individual collagen fibrils was measured. RESULTS: Treatment with theobromine produced a significant increase in the contents of hydroxylysine, hydroxyproline, and proline in both anterior and posterior sclera, while 7-methylxanthine increased the contents of hydroxyproline and proline selectively in posterior sclera. Acetazolamide, on the other hand, significantly decreased the contents of hydroxyproline and proline in samples from anterior sclera. Uronic acids in both anterior and posterior sclera were significantly reduced by treatment with 7-methylxanthine, and L-ornithine significantly reduced uronic acids in posterior sclera. An inverse correlation between contents of hydroxyproline and uronic acids was found. The mean diameter of collagen fibrils was significantly higher in the posterior sclera from rabbits treated with 7-methylxanthine or theobromine, and significantly lower in rabbits treated with acetazolamide or L-ornithine compared with controls. In the anterior sclera, fibril diameter was significantly reduced in all treatment groups compared with controls. A positive, significant correlation between fibril diameter and content of hydroxyproline and proline was found in posterior sclera. CONCLUSION: 7-Methylxanthine, a metabolite of caffeine, increases collagen concentration and the diameter of collagen fibrils in the posterior sclera, and may be useful for treatment or prevention of conditions associated with low level and/or inferior quality of scleral collagen, such as axial myopia, chronic open angle glaucoma, and possibly neovascular age related macular degeneration. The apparent loss of collagen induced by chronic treatment with acetazolamide should be taken into consideration as a potentially harmful side effect. These results may indicate that scleral biochemistry and ultrastructure are influenced by the retinal pigment epithelium. One possible explanation is that the scleral fibroblasts which produce the collagen are sensitive to changes in the physiological electric field created by the retinal pigment epithelium. (+info)
Amino acid nutrition and immune function in tumour-bearing rats: a comparison of glutamine-, arginine- and ornithine 2-oxoglutarate-supplemented diets.
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Dietary supplementation with glutamine (Gln), arginine (Arg) or ornithine 2-oxoglutarate (alpha-ketoglutarate; OKG) has attracted recent attention for the potential to improve anti-cancer immune function. However, since these compounds have not been compared systematically in an internally controlled study, their relative efficacy is difficult to estimate. Buffalo rats were fed on nutritionally complete semi-purified diets supplemented with Gln, Arg or OKG for 14 days after implantation of the Morris hepatoma 7777 (n>/=7 per diet). The control diet was made isonitrogenous and isoenergetic by addition of a mixture of non-essential amino acids. After 14 days, peritoneal macrophages and splenocytes were isolated to determine cell phenotypes, macrophage cytostatic activity and natural killer (NK) cell cytotoxicity, as well as nitric oxide (NO) and cytokine production. Diet had no effect on tumour weight (1.6+/-0.2 g; n=59). However, rats fed OKG had increased macrophage cytostatic activity and NK cell cytotoxicity (P<0.05). Although enhanced killing ability by NK cells was associated with higher splenocyte NO production (P<0.04), increased cytotoxicity was not inhibited by a specific inhibitor of inducible NO synthase. The proportion of interleukin-2-receptor-positive T cells after stimulation increased in rats fed OKG (P<0.05); however, cytokine production was not affected by diet. None of OKG, Gln or Arg altered tumour growth compared with a control mixture of non-essential amino acids. These results suggest no net advantage for anti-cancer immunity, but do not preclude benefits in immune responses to disease recurrence or metastasis, therapy or secondary infection. (+info)