No abstract

Rat aortic endothelial cells were found to contain both constitutive and lipopolysaccharide (LPS)-inducible arginase activity. Studies were performed to determine whether induction of nitric oxide synthase (NOS) by LPS and cytokines is accompanied by sufficient arginase induction to render arginine concentrations rate limiting for high-output NO production. Unactivated cells contained abundant arginase activity accompanied by continuous urea formation. LPS induced the formation of both inducible NOS (iNOS) and arginase, and this was accompanied by increased production of NO, citrulline, and urea. Immunoprecipitation experiments revealed the constitutive presence of arginase-I in both unactivated and LPS-activated cells and arginase-II induction by LPS. Arginase-I and iNOS were verified by reverse transcriptase-polymerase chain reaction. Induction of large amounts of iNOS by LPS plus several cytokines resulted in large quantities of NO, citrulline, and NG-hydroxy-L-arginine (NOHA), but urea production was markedly diminished. Decreased urea production was attributed to increased formation of NOHA, the precursor to NO and citrulline and a potent inhibitor of arginase-I activity with an inhibitory constant of 10-12 microM. Inhibition of iNOS activity by NG-methyl-L-arginine decreased NO and NOHA production and increased urea production. This study reveals for the first time that substantial arginase activity is present constitutively in rat aortic endothelial cells, a different isoform of arginase is induced by LPS, and intracellular arginase activity can be markedly inhibited during cytokine induction of iNOS because of NOHA formation. The inhibition of arginase activity that occurs by NOHA during marked iNOS induction may be a mechanism to ensure sufficient arginine availability for high-output production of NO.

Helicobacter pylori infection induces innate immune responses in macrophages, contributing to mucosal inflammation and damage. Macrophage apoptosis is important in the pathogenesis of mucosal infections but has not been studied with H. pylori. NO derived from inducible NO synthase (iNOS) can activate macrophage apoptosis. Arginase competes with iNOS by converting l-arginine to l-ornithine. Since we reported that H. pylori induces iNOS in macrophages, we now determined whether this bacterium induces arginase and the effect of this activation on apoptosis. NF-κB-dependent induction of arginase II, but not arginase I, was observed in RAW 264.7 macrophages cocultured with H. pylori. The time course of apoptosis matched those of both arginase and iNOS activities. Surprisingly, apoptosis was blocked by the arginase inhibitors Nω-hydroxy-l-arginine or Nω-hydroxy-nor-l-arginine, but not by the iNOS inhibitor N-iminoethyl-l-lysine. These findings were confirmed in peritoneal macrophages from iNOS-deficient mice and were not dependent on bacterial-macrophage contact. Ornithine decarboxylase (ODC), which metabolizes l-ornithine to polyamines, was also induced in H. pylori-stimulated macrophages. Apoptosis was abolished by inhibition of ODC and was restored by the polyamines spermidine and spermine. We also demonstrate that arginase II expression is up-regulated in both murine and human H. pylori gastritis tissues, indicating the likely in vivo relevance of our findings. Therefore, we describe arginase- and ODC-dependent macrophage apoptosis, which implicates polyamines in the pathophysiology of H. pylori infection.

Inherited urea cycle disorders comprise eight disorders (UCD), each caused by a deficiency of one of the protein that is essential for ureagenesis. We report on a cross sectional investigation to determine clinical and laboratory characteristics of patients with UCD in the United States. The data used for the analysis was collected at the time of enrollment of individuals with inherited UCD into a longitudinal observation study. The study has been conducted by the Urea Cycle Disorders Consortium (UCDC) within the Rare Diseases Clinical Research Network (RDCRN) funded by the National Institutes of Health. One hundred eighty three patients were enrolled into the study. Ornithine transcarbamylase (OTC) deficiency was the most frequent disorder (55%), followed by argininosuccinic aciduria (17%) and citrullinemia (11%). 79% of the participants were white (16% Latinos), and 6% were African American. Intellectual and developmental disabilities were reported in 39% with learning disabilities (35%) and half had abnormal neurological examination. 63% were on a protein restricted diet, 37% were on Na-phenylbutyrate and 5% were on Na-benzoate. 45% of OTC deficient patients were on L-citrulline, while most patients with citrullinemia (58%) and argininosuccinic (79%) were on L-arginine. Plasma levels of branched-chain amino acids were reduced in patients treated with ammonia scavenger drugs. Plasma glutamine levels were higher in proximal UCD disorders and in the neonatal type disease. The RDCRN allows comprehensive analyses of rare inherited UCD, their frequencies and current medical practices.