Activation of the stem cell-derived tyrosine kinase/RON receptor tyrosine kinase by macrophage-stimulating protein results in the induction of arginase activity in murine peritoneal macrophages.
(57/943)
Regulation of macrophage activities in response to inflammatory stimuli must be finely tuned to promote an effective immune response while, at the same time, preventing damage to the host. Our lab and others have previously shown that macrophage-stimulating protein (MSP), through activation of its receptor RON, negatively regulates NO production in response to IFN-gamma and LPS by inhibiting the expression of inducible NO synthase (iNOS). Furthermore, activated macrophages from mice harboring targeted mutations in RON produce increased levels of NO both in vitro and in vivo, rendering them more susceptible to LPS-induced endotoxic shock. In this study, we demonstrate that stimulation of murine peritoneal macrophages with MSP results in the RON-dependent up-regulation of arginase, an enzyme associated with alternative activation that competes with iNOS for the substrate L-arginine, the products of which are involved in cell proliferation and matrix synthesis. Expression of other genes associated with alternative activation, including scavenger receptor A and IL-1R antagonist, is also up-regulated in MSP-stimulated murine macrophages. Stimulation of cells with IFN-gamma and LPS blocks the ability of MSP to induce arginase activity. However, pretreatment of cells with MSP results in the up-regulation of arginase and inhibits their ability to produce NO in response to IFN-gamma and LPS, even in the presence of excess substrate, suggesting that the inhibition of NO by MSP occurs primarily through its ability to regulate iNOS expression. (+info)
Nitrogen metabolism and excretion in the mangrove killifish Rivulus marmoratus II. Significant ammonia volatilization in a teleost during air-exposure.
(58/943)
The mangrove killifish Rivulus marmoratus can tolerate prolonged periods of air-exposure (>1 month). During these periods of emersion, we hypothesized that R. marmoratus would convert potentially toxic ammonia into urea and free amino acids (FAAs). In air-exposed fish, both ammonia (J(Amm)) and urea (J(Urea)) excretion continued at approximately 57 % and 39 %, respectively, of submerged rates. Remarkably, approximately 42 % of the total ammonia excreted during air-exposure was through NH(3) volatilization. Ammonia did not accumulate in whole-body tissues of air-exposed fish, but levels of both urea and some FAAs (primarily alanine and glutamine) were up to twofold higher after 10 days. The activities of the ornithine-urea cycle enzymes carbamoyl phosphate synthetase III and ornithine transcarbamylase increased (by approximately 30 % and 36 %, respectively) in whole-body tissues of air-exposed fish, while levels of arginase remained unchanged. The activities of enzymes involved in amino acid and oxidative metabolism were not significantly different between control and air-exposed fish. Partitioning of the anterior and posterior ends of immersed fish revealed that just over half (57 %) of the total nitrogen (ammonia+urea) was excreted through the anterior end of the fish, presumably via the branchial tissues, while emersed fish increased excretion via the posterior end (kidney+skin). R. marmoratus do not undergo a shift towards ureotelism during air-exposure. Rather, we propose that R. marmoratus are able to survive on land for extended periods without significant ammonia accumulation because they continuously release ammonia, partially by NH(3) volatilization. (+info)
Interpretation of the kinetics of consecutive enzyme-catalyzed reactions. Studies on the arginase-urease system.
(59/943)
Physiocochemical properties of beef liver arginase are reported, particular attention being given to its state of aggregation in the concentration range encountered in enzymic assays. It is shown that a species of molecular weight 114,000 is the operational kinetic unit. Evidence is also provided that arginase does not associate heterogeneously with urease, and therefore, in the absence of macromolecular interactions, the arginase-urease couple provides a suitable experimental system to test the applicability of theory previously developed to guide the interpretation of coupled assay results. Application of the theory led to values of the Michaelis constant and maximal velocity describing the first reaction in the sequence, catalyzed by arginase, which agreed within experimental error with the corresponding values obtained by studying the arginase-catalyzed reaction alone. Comment is also made on the product inhibition of arginase by ornithine, which must be considered in the comparison of experimental results describing the time course of a coupled assay with theoretical solutions obtained by numerical integration. (+info)
Arginase in glomerulonephritis.
(60/943)
l-Arginine is converted to nitric oxide and citrulline by the enzyme nitric oxide synthase (NOS). Its in vivo inhibition has led to the revelation of a multitude of diverse, often conflicting functions in the inflammatory melee. l-Arginine is also converted to ornithine and urea by the enzyme arginase as a part of the hepatic urea cycle. However, a more holistic interpretation of the two pathways and the associated metabolism (summarized in Fig. 1) has led to its reassessment as a pathologically significant enzyme. This is reflected by the continued increase over the past five years of the number of publications discussing both nitric oxide and arginase. The strong association between inflammation and high arginase and NOS activity is epitomized by immune complex-induced glomerulonephritis and other glomerulonephritides. Arginase is encoded by two recently discovered genes (Arginase I and Arginase II). There is now substantial evidence for an interaction between both arginase isoforms and all three NOS isoforms in pathological situations. This review considers the relationship between Arginases I and II and the inflammation-associated isoform of NOS called NOS II. In particular, it consolidates the current understanding of arginase and associated metabolic pathways, and highlights some of the issues that are often overlooked in such studies. (+info)
Arginine catabolism in lactating porcine mammary tissue.
(61/943)
In vivo studies have shown that the uptake of plasma arginine by the lactating porcine mammary gland greatly exceeds the output of arginine in milk, but little is known about the metabolic fate of arginine in this organ. The objective of this study was to quantify arginine catabolism via arginase and nitric oxide synthase pathways in the mammary tissue of sows on d 28 of lactation. Mammary tissue slices (approximately 60 mg) were incubated at 37 degrees C for 1 h in 2 mL of Krebs bicarbonate buffer containing 0.5 or 2 mM L-[U-14C]arginine, and arginine metabolites were measured using HPLC and radiochemical techniques. Rates of arginine utilization were similar to rates of urea production. Proline, ornithine, urea, glutamate, glutamine, CO2 and polyamines (putrescine + spermidine + spermine) were formed from arginine, accounting for 46, 31, 17, 2.3, 1.5, 0.22, and 0.30%, respectively, of the metabolized arginine carbons. Relatively small amounts of arginine were utilized for nitric oxide and citrulline synthesis, with citrulline accounting for 2% of the metabolized arginine carbons. Production of all arginine metabolites increased with increasing extracellular arginine concentrations from 0.5 to 2 mM, indicating a high capacity for arginine degradation. Consistent with the metabolic findings, the activities of arginases, ornithine aminotransferase, and pyrroline-5-carboxylate reductase were high, whereas those of pyrroline-5-carboxylate dehydrogenase, ornithine decarboxylase, and nitric oxide synthases were relatively low, and there was no proline oxidase, ornithine carbamoyltransferase or pyrroline-5-carboxylase synthase activity in the mammary tissue. Our results demonstrate for the first time that proline, ornithine, and urea were the major products of arginine catabolism via the arginase pathway in lactating porcine mammary tissue and provide a biochemical basis to explain a relative enrichment of proline but a relative deficiency of arginine in sow's milk. (+info)
The quantity of nitric oxide released by macrophages regulates Chlamydia-induced disease.
(62/943)
Intracellular bacteria of the genus Chlamydia cause numerous typically chronic diseases, frequently with debilitating sequelae. Genetic determinants of disease susceptibility after infection with Chlamydia bacteria are unknown. C57BL/6 mice develop severe pneumonia and poor immunity against Chlamydia after moderate respiratory infection whereas BALB/c mice are protected from disease and develop vigorous Th1 immunity. Here we show that infected C57BL/6 macrophages release more NO synthesized by NO synthase 2 (NOS2) than BALB/c macrophages and have lower mRNA concentrations of arginase II, a competitor of NOS2 for the common substrate, l-arginine. Reduction, but not elimination, of NO production by incomplete inhibition of NOS2 abolishes susceptibility of C57BL/6 mice to Chlamydia-induced disease. Thus, the quantity of NO released by infected macrophages is the effector mechanism that regulates between pathogenic and protective responses to chlamydial infection, and genes controlling NO production determine susceptibility to chlamydial disease. (+info)
Helicobacter pylori induces macrophage apoptosis by activation of arginase II.
(63/943)
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-kappa B-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 N(omega)-hydroxy-L-arginine or N(omega)-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. (+info)
Arginine catabolism, liver extracts and cancer.
(64/943)
Although it is self evident that cells will not grow in amino acid deficient medium, an observation less well appreciated is that malignant cells are particularly vulnerable to such deprivation, which can lead to their rapid demise. Indeed, the more flagrantly malignant the phenotype (anaplastic the tumor), the more susceptible the cells seem to be to deprivation. While some attempts to employ this strategy in cancer treatment have been made, the difference between normal and malignant cells should be more fully exploited as a means of selectively eliminating tumor cell populations. To be successful, information on differences between the normal and the deranged cell cycle engine and checkpoints, especially how these are affected by deprivation, is of crucial importance. Since it is only recently that the controls at restriction points have been elucidated, it is little surprise that earlier attempts to control tumor cell growth by limiting the availability of an essential amino acid have met with limited success. Studies have been sporadic and isolated, often with little more than anecdotal descriptions as far as clinical work was concerned. This review concentrates on what has been accomplished primarily in vitro and since about 1950 with regard to arginine catabolism, while recognising that other essential amino acids have also been the focus of attention by some investigators. Treatments have included medium and plasma manipulation, dietary control, enzymatic degradation, and the use of liver extracts. On some occasions, substitution of amino acid analogues has been explored. It is argued that current knowledge, combined with past experience, calls for a much closer examination of the full potential of amino acid (and specifically arginine) deprivation as a means of controlling tumor growth, with greater attention to protocols that might be used to treat human cancers. (+info)