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PubMed2004

Distribution and properties of arginase in the salivary glands of four species of laboratory mammals.

Important progress in arginine metabolism includes the discovery of widespread expression of two isoforms of arginase, arginase I and II, not only in hepatic cells but also in non-hepatic cells, and the formation of nitric oxide, a widely distributed signal-transducing molecule, from arginine by nitric oxide synthase. Possible physiological roles of arginase may therefore include regulation of nitric oxide synthesis through arginine availability for nitric oxide synthase. In this paper, arginase was investigated in the submandibular, sublingual, and parotid glands of rat, mouse, guinea pig, and rabbit. From their arginase contents, the salivary glands of these species were divided into two groups. Variable levels of arginase activity were detected in the salivary glands of mouse and rat. However, salivary glands of rabbit and guinea pig had almost no arginase activity. The presence of nitric oxide synthase has been reported in all the salivary glands used in this study. Therefore, one of the important findings was the presence of species specificity in the co-localization of arginase and nitric oxide synthase in the salivary glands of the four species. The highest specific activity of arginase was found in mouse parotid gland. In rat, considerable arginase activity was detected in all three glands, at 3.6-7.3% of that in rat liver. In rat submandibular gland, arginase was detected in both cytosolic and particulate fractions. In addition, arginase was detected in isolated acinar cells, but not in duct cells. Experiments on the intracellular distribution and the effects of the arginase inhibitors ornithine and N(omega)-hydroxy-L-arginine (NOHA), suggested the presence of both arginase I and arginase II in rat submandibular gland.

Animals↗

PubMed2005

Evolutionary conservation of alternative activation of macrophages: structural and functional characterization of arginase 1 and 2 in carp (Cyprinus carpio L.).

Classically activated macrophages (caMF) play an important role in type-I immune responses and alternatively activated macrophages (aaMF) function in type-II immune responses. While the classical activation of fish macrophages has been well described, the existence of aaMF has not yet been described for teleosts. Arginase is the characteristic enzyme in aaMF and two isoforms have been described for mammals. To study the presence of aaMF in a primitive vertebrate species we cloned arginase 1 and 2 cDNA of common carp. Carp arginase 1 is a 340 aa protein with 63% aa sequence identity to human arginase 1. Carp arginase 2 is a 347 aa protein with 63% aa sequence identity to human arginase 2. Three highly homologous arginase 2 genes were found, each showing only single non-synonymous substitutions. Basal arginase 1 expression is mainly found in carp mid kidney. In contrast, arginase 2 was expressed in all organs examined with the highest basal gene expression in liver. Cultured carp head kidney-derived macrophages were used to study aaMF in vitro. Carp macrophages showed significant arginase activity which could be induced by dibutyryl cyclic adenosine mono phosphate (cAMP) and specifically inhibited by NG-hydroxy-L-arginine (NOHA). At the gene level, arginase 2 gene expression was upregulated by cAMP stimulation, while arginase 1 gene expression was not influenced. LPS stimulation did not alter the arginase 1 or 2 expression, inducible nitric oxide synthase (iNOS) expression was, however, upregulated. This expression of iNOS was used as a measure of classical activation of carp macrophages. Thus, in contrast to mammals, fish arginase 2 and not arginase 1 is differentially regulated and likely involved in the alternative activation of fish macrophages. Our data suggest there may be an evolutionary conservation of the presence of aaMF down to teleost fish.

Amino Acid Sequence↗

PubMed2000

The involvement of tyrosine kinases, cyclic AMP/protein kinase A, and p38 mitogen-activated protein kinase in IL-13-mediated arginase I induction in macrophages: its implications in IL-13-inhibited nitric oxide production.

In macrophages, L-arginine can be used by NO synthase and arginase to form NO and urea, respectively. Therefore, activation of arginase may be an effective mechanism for regulating NO production in macrophages through substrate competition. Here, we examined whether IL-13 up-regulates arginase and thus reduces NO production from LPS-activated macrophages. The signaling molecules involved in IL-13-induced arginase activation were also determined. Results showed that IL-13 increased arginase activity through de novo synthesis of the arginase I mRNA and protein. The activation of arginase was preceded by a transient increase in intracellular cAMP, tyrosine kinase phosphorylation, and p38 mitogen-activated protein kinase (MAPK) activation. Exogenous cAMP also increased arginase activity and enhanced the effect of IL-13 on arginase induction. The induction of arginase was abolished by a protein kinase A (PKA) inhibitor, KT5720, and was down-regulated by tyrosine kinase inhibitors and a p38 MAPK inhibitor, SB203580. However, inhibition of p38 MAPK had no effect on either the IL-13-increased intracellular cAMP or the exogenous cAMP-induced arginase activation, suggesting that p38 MAPK signaling is parallel to the cAMP/PKA pathway. Furthermore, the induction of arginase was insensitive to the protein kinase C and p44/p42 MAPK kinase inhibitors. Finally, IL-13 significantly inhibited NO production from LPS-activated macrophages, and this effect was reversed by an arginase inhibitor, L-norvaline. Together, these data demonstrate for the first time that IL-13 down-regulates NO production through arginase induction via cAMP/PKA, tyrosine kinase, and p38 MAPK signalings and underline the importance of arginase in the immunosuppressive activity of IL-13 in activated macrophages.

Animals↗

PubMed1999

Th1/Th2-regulated expression of arginase isoforms in murine macrophages and dendritic cells.

Activated murine macrophages metabolize arginine by two alternative pathways involving the enzymes inducible NO synthase (iNOS) or arginase. The balance between the two enzymes is competitively regulated by Th1 and Th2 T helper cells via their secreted cytokines: Th1 cells induce iNOS, whereas Th2 cells induce arginase. Whereas the role of macrophages expressing iNOS as inflammatory cells is well established, the functional competence of macrophages expressing arginase remains a matter of speculation. Two isoforms of mammalian arginases exist, hepatic arginase I and extrahepatic arginase II. We investigated the regulation of arginase isoforms in murine bone marrow-derived macrophages (BMMPhi) in the context of Th1 and Th2 stimulation. Surprisingly, in the presence of either Th2 cytokines or Th2 cells, we observe a specific induction of the hepatic isoform arginase I in BMMPhi. Induction of arginase I was shown on the mRNA and protein levels and obeyed the recently demonstrated synergism among the Th2 cytokines IL-4 and IL-10. Arginase II was detectable in unstimulated BMMPhi and was not significantly modulated by Th1 or Th2 stimulation. Similar to murine BMMPhi, murine bone marrow-derived dendritic cells, as well as a dendritic cell line, up-regulated arginase I expression and arginase activity upon Th2 stimulation, whereas arginase II was never detected. In addition to revealing the unexpected expression of arginase I in the macrophage/monocyte lineage, these results uncover a further intriguing parallelism between iNOS and arginase: both have a constitutive and an inducible isoform, the latter regulated by the Th1/Th2 balance.

Animals↗

PubMed2000

Beta adrenoceptor regulation of macrophage arginase activity.

BACKGROUND: Arginase, which metabolizes L-arginine within the urea cycle, is essential for production of polyamines and affects production of nitric oxide by depletion of L-arginine, the common substrate for both arginase and nitric oxide synthase. Having shown that trauma increases splenic macrophage arginase activity, we seek to define the mechanisms for this. RAW macrophage arginase activity and expression are increased by 8-bromo-cAMP in vitro. We hypothesize that since catecholamines increase cAMP, trauma-induced splenic arginase activity may be mediated by post-injury catecholamine release. METHODS: RAW 264.7 macrophage arginase activity was measured in vitro in response to 4 catecholamines with or without propranolol or lipopolysaccharide (LPS). C57BL/6 mice underwent laparotomy as a model of moderate trauma after propranolol treatment, with and without intraperitoneal Escherichia coli LPS administration as a simulated pro-inflammatory stimulus. RESULTS: Macrophage arginase activity increased in vitro in response to catecholamines or LPS (P < .05). Propranolol pretreatment blocked macrophage arginase activity induced by epinephrine (10 mumol/L) in vitro (P < .05). Trauma or LPS alone increased splenic arginase activity in vivo (P < .05). Propranolol did not alter LPS-induced splenic arginase activity but did significantly reduce trauma-induced splenic arginase activity (P < .05). CONCLUSIONS: Catecholamines alone increase macrophage arginase activity through beta-adrenoceptor activation. Increased splenic arginase activity induced by moderate trauma is decreased by beta-adrenoceptor blockade, suggesting that trauma-induced arginase activity is partly mediated by endogenous catecholamines.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2001

Elevated arginase I expression in rat aortic smooth muscle cells increases cell proliferation.

Arginase, which exists as the isoforms arginase I and II, catalyzes the hydrolysis of arginine to ornithine and urea. Ornithine is the principal precursor for production of polyamines, which are required for cell proliferation. Rat aortic smooth muscle cells (RASMC) contain constitutive arginase I, and arginase inhibitors cause inhibition of cell proliferation. The objective of this study was to determine whether the elevated expression of arginase I in RASMC causes increased cell proliferation. RASMC were stably transfected with either rat arginase I cDNA or a beta-galactosidase control expression plasmid. Western blots and arginase enzymatic assays revealed high-level expression of cytosolic arginase I in arginase I-transfected RASMC. Moreover, this observation was associated with the increased production of urea and polyamines and higher rates of RASMC proliferation. The two selective inhibitors of arginase, N(G)-hydroxy-l-arginine and S-(2-boronoethyl)-l-cysteine, inhibited arginase and decreased the production of urea and polyamines in arginase I-transfected RASMC, all of which were associated with the inhibition of cell proliferation. This study demonstrates that elevated arginase I expression increases RASMC proliferation by mechanisms involving increased production of polyamines. These observations suggest that arginase I plays a potentially important role in controlling RASMC proliferation.

Animals↗

PubMed1997

Coinduction of nitric-oxide synthase and arginase I in cultured rat peritoneal macrophages and rat tissues in vivo by lipopolysaccharide.

Nitric oxide is synthesized by nitric-oxide synthase from arginine, a common substrate of arginase. Rat peritoneal macrophages were cultured in the presence of bacterial lipopolysaccharide (LPS), and expression of the inducible isoform of nitric-oxide synthase (iNOS) and liver-type arginase (arginase I) was analyzed. mRNAs for iNOS and arginase I were induced by LPS in a dose-dependent manner. iNOS mRNA appeared 2 h after LPS treatment and increased to a near maximum at 8-12 h. On the other hand, arginase I mRNA that was undetectable prior to the treatment began to increase after 4 h with a lag time and reached a maximum at 12 h. Immunoblot analysis showed that iNOS and arginase I proteins were also induced. mRNA for arginase II, an arginase isozyme, was not detected in the LPS-activated peritoneal cells. mRNA for CCAAT/enhancer-binding protein beta (C/EBPbeta), a transactivator of the arginase I gene, was also induced, and the induction was more rapid than that of arginase I mRNA. Changes in iNOS and arginase I mRNAs were also examined in LPS-injected rats in vivo. iNOS mRNA increased rapidly in the lung and spleen, reached a maximum 2-6 h after the LPS treatment, and decreased thereafter. Arginase I mRNA was induced markedly and more slowly in both tissues, reaching a maximum in 12 h. Thus, arginase I appears to have an important role in down-regulating nitric oxide synthesis in murine macrophages by decreasing the availability of arginine, and the induction of arginase I is mediated by C/EBPbeta.

Animals↗

PubMed2006

Involvement of arginase in regulating myometrial contractions during gestation in the rat.

This study was designed to investigate the role of arginase in regulating myometrial contractions during gestation in the rat. Arginase activity in the myometrium was significantly decreased during the 7th-21st day of gestation, with the lowest value on the 14th day. However, the enzyme activity became significantly higher at term gestation (22nd day) than that in the non-pregnant myometrium. Arginase I protein was undetectable in the non-pregnant myometrium, at 7th and 14th day of gestation and after delivery. A slight positive signal for arginase I was detectable at 21st day of gestation. However, the protein was clearly up-regulated at term gestation (22nd day), although arginase II protein was down-regulated during gestation, with the lowest value on the 14th day. Gestational changes in arginase activity negatively correlated with those in cyclic GMP production, whereas the changes positively correlated with those in endogenous nitric oxide synthase (NOS) inhibitors and endothelin-1 (ET-1) contents. Myometrial arginase activity was inhibited by N(G)-hydroxy-L-arginine as an intermediate of NO production from L-arginine in a concentration-dependent manner. Both basal and stimulated guanylyl cyclase activities were enhanced at mid- and reduced at term gestation and after delivery, thereby partly increasing cyclic GMP production at mid- and partly decreasing the nucleotide production at term gestation and after delivery. These results suggest that the decreased arginase activity at mid-gestation possibly results from the down-regulation of arginase II protein. Whereas, the enhanced overall arginase activity at term gestation seems to be because of the induced functional arginase I in concert with the attenuated arginase II expression. The enhanced arginase activity at term gestation would be implicated in increasing myometrial contractions mediated by the increased ET-1. The increased peptide production at term gestation is possibly because of the reduced cyclic GMP production resulting from enhanced arginase activity, accumulated endogenous NOS inhibitors and attenuated guanylyl cyclase activity.

Animals↗

PubMed2001

Arginase I expression and activity in human mononuclear cells after injury.

OBJECTIVE: To determine the effect of trauma on arginase, an arginine-metabolizing enzyme, in cells of the immune system in humans. SUMMARY BACKGROUND DATA: Arginase, classically considered an enzyme exclusive to the liver, is now known to exist in cells of the immune system. Arginase expression is induced in these cells by cytokines interleukin (IL) 4, IL-10, and transforming growth factor beta, corresponding to a T-helper 2 cytokine profile. In contrast, nitric oxide synthase expression is induced by IL-1, tumor necrosis factor, and gamma interferon, a T-helper 1 cytokine profile. Trauma is associated with a decrease in the production of nitric oxide metabolites and a state of immunosuppression characterized by an increase in the production of IL-4, IL-10, and transforming growth factor beta. This study tests the hypothesis that trauma increases arginase activity and expression in cells of the immune system. METHODS: Seventeen severely traumatized patients were prospectively followed up in the intensive care unit for 7 days. Twenty volunteers served as controls. Peripheral mononuclear cells were isolated and assayed for arginase activity and expression, and plasma was collected for evaluation of levels of arginine, citrulline, ornithine, nitrogen oxides, and IL-10. RESULTS: Markedly increased mononuclear cell arginase activity was observed early after trauma and persisted throughout the intensive care unit stay. Increased arginase activity corresponded with increased arginase I expression. Increased arginase activity coincided with decreased plasma arginine concentration. Plasma arginine and citrulline levels were decreased throughout the study period. Ornithine levels decreased early after injury but recovered by postinjury day 3. Increased arginase activity correlated with the severity of trauma, early alterations in lactate level, and increased levels of circulating IL-10. Increased arginase activity was associated with an increase in length of stay. Plasma nitric oxide metabolites were decreased during this same period. CONCLUSIONS: Markedly altered arginase expression and activity in cells of the human immune system after trauma have not been reported previously. Increased mononuclear cell arginase may partially explain the benefit of arginine supplementation for trauma patients. Arginase, rather than nitric oxide synthase, appears to be the dominant route for arginine metabolism in immune cells after trauma.

Adult↗

PubMed2004

Arginase pathway in human endothelial cells in pathophysiological conditions.

Objective. - Arginase is a nitric oxide synthase-alternative pathway for l-arginine breakdown leading to biosynthesis of urea and l-ornithine. Arginase pathway is inducible by inflammatory molecules-such as cytokines and bacterial endotoxin-in macrophages and smooth muscle cells. The presence of an arginase pathway in human endothelial cells and its possible modulation by inflammation are unknown. Methods. - We have: (i) characterised arginase pathway in terms of activity, isoform type and gene expression in a primary human umbilical vein endothelial cells (HUVEC) line; (ii) evaluated arginase functional role in cell proliferation with the aid of l-norvaline, an arginase inhibitor and (iii) determined the effects of tumour necrosis factor-alpha and endotoxin on arginase pathway. Results. - HUVEC showed a baseline arginase activity and expression of both arginase isoforms (arginase I and II (A-I and A-II, respectively)) which resulted in l-norvaline-inhibitable cellular polyamine synthesis. The baseline arginase activity is important for HUVEC proliferation as cell cycle analysis and nuclear factor Ki-67 immunostaining revealed. Following incubation with inflammatory molecules, arginase activity increased but HUVEC cell cycling decreased. Conclusions. - A-I and A-II are constitutively expressed in HUVEC where they take part to the regulation of cell cycling. Although arginase activity is positively modulated by inflammatory molecules, it is insufficient to counteract the overall cell cycling inhibiting effects of inflammation.

Antibodies, Antinuclear↗

PubMed2003

Utilization of lacrimal urea assay in the monitoring of hemodialysis: conditions, limitations and lacrimal arginase characterization.

The lacrimal urea content was found to be proportional to that of blood, which suggested its possible utilization in the monitoring of hemodialysis as a less invasive method. On the other hand, however, arginase activity was detected in tears, which may influence the urea content independently of blood urea concentration. The feasibility of using lacrimal urea measurement to replace blood urea measurement in the monitoring hemodialysis was also investigated. Blood and tear samples of 35 healthy persons and 43 renal patients undergoing hemodialysis were tested. Tear samples were collected on Schirmer paper strips. After elution the lacrimal urea content was measured by a colorimetric method. The determination of arginase activity was based on the release of urea and ornithine. The correlation between blood and lacrimal urea and arginase was studied by multivariate regression analysis. The lacrimal arginase isoenzyme pattern was investigated by native polyacrylamide gel electrophoresis and Western blotting. The effect of partially isoform-specific inhibitors was also studied. Blood urea levels in blood were significantly higher in the renal patients before dialysis than in the control patients (12.86 +/- 0.59 vs. 6.45 +/- 0.41 mM, p < 0.0001). Blood sera arginase activity was very low. Lacrimal arginase activity was significantly higher in tears than in sera (p < 0.0001 for each group). The tear/serum ratio of urea content was significantly different between controls and renal patients, particularly in postdialytic samples (1.89 +/- 0.07 vs. 3.49 +/- 0.31, p < 0.0001). The correlation between lacrimal and blood sera urea was best in controls (r = 0.89) and was better in predialytic (r = 0.75) than in postdialytic (r = 0.52) samples, depending on the level of arginase activity. In postdialytic samples a stronger correlation (r = 0.77) between tear urea and arginase was observed. Both arginase isoforms were detected in tears, but the extrahepatic (arginase II) isoenzyme was present in higher concentration. In conclusion, the determination of lacrimal urea level as a possible less invasive replacement for blood urea determination could only be utilized in the monitoring of hemodialysis if lacrimal arginase is also measured. Blood urea levels can be correctly determined by using equations, which take into account arginase activity. The accuracy of these equations was checked on a new patient population. Both arginase isoenzymes were observed in lacrimal samples.

Arginase↗

PubMed1997

Human type II arginase: sequence analysis and tissue-specific expression.

A full-length cDNA encoding type II arginase was isolated from a human kidney cDNA library and its sequence compared to those of vertebrate type I arginases as well as to arginases of bacteria, fungi and plants. The predicted sequence of human type II arginase is 58% identical to the sequence of human type I arginase but is 71% identical to the sequence of Xenopus type II arginase, suggesting that duplication of the arginase gene occurred before mammals and amphibians diverged. Seven residues known to be essential for activity were found to be conserved in all arginases. Type II arginase mRNA was detected in virtually all human and mouse RNA samples tested whereas type I arginase mRNA was found only in liver. At least five mRNA species hybridizing to type II arginase cDNA were found in the human RNA samples whereas only a single type II arginase mRNA species was found in the mouse. This raises the possibility that the multiple type II arginase mRNAs in humans arise from differential RNA processing or usage of alternative promoters.

Amino Acid Sequence↗

PubMed1999

Regulation of the genes for arginase isoforms and related enzymes in mouse macrophages by lipopolysaccharide.

Arginase exists in two isoforms, the hepatic (arginase I) and extrahepatic types (arginase II). Arginase I is markedly induced in rat peritoneal macrophages and rat tissues in vivo by bacterial lipopolysaccharide (LPS). In contrast, both arginase I and arginase II are induced in LPS-activated mouse peritoneal macrophages. In the present study, expression of arginase isoforms and related enzymes was studied in mouse tissues in vivo and in peritoneal macrophages with RNA blot and immunoblot analyses and enzyme assay. When mice were injected intraperitoneally with LPS, inducible nitric oxide synthase (iNOS) and arginase II were induced early in the lung and spleen. mRNAs for argininosuccinate synthase (AS) and ornithine decarboxylase (ODC) were also induced early. In comparison, arginase I was induced later in the lung. Early induction of iNOS, arginase II, AS, ODC, and cationic amino acid transporter 2 and late induction of arginase I were observed in LPS-activated peritoneal macrophages. These results indicate that the genes for the two arginase isoforms are regulated differentially. Possible roles of the arginase isoforms in the regulation of nitric oxide production and in polyamine synthesis are discussed.

Animals↗

PubMed2005

Inhibition of phosphodiesterase 4 amplifies cytokine-dependent induction of arginase in macrophages.

Arginase is greatly elevated in asthma and is thought to play a role in the pathophysiology of this disease. As inhibitors of phosphodiesterase 4 (PDE4), the predominant PDE in macrophages, elevate cAMP levels and reduce inflammation, they have been proposed for use in treatment of asthma and chronic obstructive pulmonary disease. As cAMP is an inducer of arginase, we tested the hypothesis that a PDE4 inhibitor would enhance macrophage arginase induction by key cytokines implicated in asthma and other pulmonary diseases. RAW 264.7 cells were stimulated with IL-4 or transforming growth factor (TGF)-beta, with and without the PDE4 inhibitor rolipram. IL-4 and TGF-beta increased arginase activity 16- and 5-fold, respectively. Rolipram alone had no effect but when combined with IL-4 and TGF-beta synergistically enhanced arginase activity by an additional 15- and 5-fold, respectively. The increases in arginase I protein and mRNA levels mirrored increases in arginase activity. Induction of arginase II mRNA was also enhanced by rolipram but to a much lesser extent than arginase I. Unlike its effect in RAW 264.7 cells, IL-4 alone did not increase arginase activity in human alveolar macrophages (AM) from healthy volunteers. However, combining IL-4 with agents to induce cAMP levels induced arginase activity in human AM significantly above the level obtained with cAMP-inducing agents alone. In conclusion, agents that elevate cAMP significantly enhance induction of arginase by cytokines. Therefore, consequences of increased arginase expression should be evaluated whenever PDE inhibitors are proposed for treatment of inflammatory disorders in which IL-4 and/or TGF-beta predominate.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1994

Thyroid hormone-dependent differential regulation of multiple arginase genes during amphibian metamorphosis.

We have cloned three nonhepatic arginase genes in Xenopus laevis. The deduced amino acid sequences of the three arginases are almost identical and share about 60% identity with mammalian as well as Xenopus liver arginase. Both the liver and nonhepatic arginase genes are activated early during embryogenesis. The liver arginase gene is strongly expressed in tadpole liver, but weakly in other tissues. In contrast, the nonhepatic arginase genes have the strongest expression in the tadpole tail. During metamorphosis, the liver and nonhepatic arginase genes show distinct regulation patterns. In the intestine, both types of arginase genes are activated during the remodeling period. In the tail, the liver arginase gene is activated during tail resorption, whereas the nonhepatic ones are highly expressed throughout all stages examined. Finally, in the hindlimb, the liver arginase is up-regulated slightly during development, whereas the nonhepatic ones have low levels of expression until the end of metamorphosis. During 3,5,3'-L-triiodothyronine (T3)-induced metamorphosis, the nonhepatic arginase genes are activated very quickly, whereas the liver arginase gene is a late T3 response gene. These differential regulation patterns during normal and T3-induced metamorphosis suggest potential functions for the arginases during tissue remodeling.

Amino Acid Sequence↗

PubMed2002

Induction of arginase II in livers of bile duct-ligated rats.

Nitric oxide (NO) has been implicated in playing a role in liver cirrhosis, but the regulatory mechanisms are still unclear. As arginase shares a common substrate with NO synthase (NOS), the aim of this study was to investigate the expression of arginase I and II in cirrhotic liver. Liver cirrhosis was induced in rats by chronic bile duct ligation (BDL). Controls were sham-operated. Competitive polymerase chain reaction was performed to assay the expression of messenger RNA of arginase I and II. Protein expression was detected by immunohistochemistry and western-blotting. The level of arginine in plasma was lower in BDL rats, while the ornithine level in plasma was correspondingly higher (r= -0.96, P<0.0001). Arginase I messenger RNA was reduced significantly in BDL rats (3.34+/-0.32 vs. 1.32+/-0.21 x 10(4) attomole/microg of total RNA, sham vs. BDL, P<0.001), as well as arginase I protein. In contrast, arginase II mRNA was induced in the livers of BDL rats, with negligible expression in controls (0.35+/-0.11 vs. 3.64+/-0.54 attomole/microg of total RNA, sham vs. BDL, P<0.001). Arginase II protein was localized in some hepatocytes and hyperplastic bile ductular epithelial cells of cirrhotic livers but not in control livers. In conclusion, arginase II was induced in BDL livers, while the expression of arginase I was down-regulated. These data suggest that arginase I and II are regulated differently and may have different functions in the livers of BDL rats. Reduction of arginase I in BDL livers may be responsible for the lowering of arginine levels in the plasma, while induction of arginase II could be important in regulating NO synthesis as well as other important mechanisms involved in liver cirrhosis.

Animals↗

PubMed2001

A useful ELISA system for human liver-type arginase, and its utility in diagnosis of liver diseases.

OBJECTIVES: To develop a new ELISA system for liver-type arginase using monoclonal antibodies against the enzyme, and to verify the utility of the arginase in diagnosis of hepatic disorders. DESIGN AND METHODS: We have developed an enzyme-linked immunosorbent assay (ELISA), using two kinds of monoclonal antibodies (Mo6G3 and Mo9C5) for human liver-type arginase as the first and second antibodies respectively. We have also developed a new method to eliminate the influence of erythrocyte-derived arginase contamination in hemolytic samples. This ELISA was applied to specimens received from patients with acute and chronic hepatic disease and also patients who had undergone partial hepatectomy. RESULTS: This assay is sensitive and reproducible for the measurement of liver-type arginase in the sera of patients with liver dysfunction, and enabled us to detect enzyme concentrations as low as 27 pmol/L without any processing of the samples. The assay showed within-run coefficients of variation (CV) ranging from 1.9 to 4.1% and between-day CV from 3.6 to 5.1% for arginase concentrations varying from 57.1 to 1200 pmol/L. The recovery was 113% (mean) with a range of 96 to 129%. These antibodies reacted strongly with both recombinant and native liver-type arginases, while, to some extent, with erythrocyte-derived arginase. Correction for erythrocyte-derived arginase contamination in hemolytic samples was, however, easily made by assaying peroxidase-like activity of hemoglobin. From the view of a limited localization of arginase in the liver, the marked increase of the enzyme in serum reflects initiation of liver injury, while the rapid decrease reflects termination of the damage. Such quick normalization in circulating liver-type arginase indicated another merit of the enzyme in diagnosis of liver diseases. CONCLUSIONS: The changes in circulating liver-type arginase level could be helpful not only in the diagnosis of liver diseases but also subsequent treatment of the patients with liver damage.

Acute Disease↗

PubMedDate not supplied

Biochemical analysis of arginase and ornithine carbamoyltransferase in human vitreous humor.

BACKGROUND: The presence of arginase and ornithine carbamoyltransferase (OTC'ase) enzymes in human vitreous humor after death was investigated in this study. To the best of our knowledge, there is no prior report on the activity of arginase or ornithine carbamoyltransferase in human vitreous humor. METHODS: The presence of arginase and OTC'ase activities were examined in the human vitreous humor of 19 samples. Spectrophotometric methods were used to determine activities of arginase and OTC'ase. RESULTS: Arginase activity was detected in human vitreous humor, whereas OTC'ase activity was below the detection limit. Therefore, we focused on biochemical analysis of arginase in human vitreous humor. Kinetic properties of arginase activity in vitreous humor were optimized. In contrast to other arginases, optimal preincubation temperature and pH were 40 degrees C and 8.8, respectively. Km of vitreous arginase for L-arginine was 6 mM. Preincubation of the enzyme with Mn(2)+ ions caused a significant increase (33%) in arginase activity. CONCLUSIONS: The activity and presence of arginase as well as its kinetics in human vitreous are documented in this study. Biochemical functions and the importance of arginase in vitreous humor are not well understood. However, its presence may be explained by means of its involvement in polyamine biosynthesis as observed in the other extrahepatic tissues.

Adult↗