Mitochondrial expression of arginase II in male and female rat inner medullary collecting ducts

The Ginsenoside Rg1 Rescues Mitochondrial Disorders in Aristolochic Acid-Induced Nephropathic Mice

Chronic exposure to aristolochic acid (AA) leads to renal interstitial fibrosis and nephropathy. In this study, we aimed to investigate the renoprotective effects of Panax ginseng extract (GE) and ginsenoside saponin (GS) on AA-induced nephropathy (AAN) in mice. Eighty female C3H/He mice were randomly divided into eight groups, including normal; AA (3 μg/mL for 56 days); AA with GE (125, 250, or 500 mg/kg/d for 14 days); and AA with important GE ingredients, Rg₁, Rb₁, or Rd (5 mg/kg/d for 14 days). Compared with the AA group, renal injuries were significantly decreased in the GE (250 mg/kg/d), Rb₁, and Rg₁ treatment groups. Rg₁ exhibited the best renoprotection among all GS-treated groups. There were 24 peaks significantly altered among normal, AA, and AA + Rg₁ groups, and four mitochondrial proteins were identified, including acyl-CoA synthetase medium-chain family member 2, upregulated during skeletal muscle growth 5 (Usmg5), mitochondrial aconitase 2 (ACO2), and cytochrome c oxidase subunit Va preprotein (COX5a). We demonstrated for the first time that the AAN mechanism and renoprotective effects of Rg₁ are associated with expression of mitochondrial proteins, especially ACO2, Usmg5, and COX5a.

Selective inhibition of arginase-2 in endothelial cells but not proximal tubules reduces renal fibrosis

Fibrosis is the final common pathway in the pathophysiology of most forms of chronic kidney disease (CKD). As treatment of renal fibrosis still remains largely supportive, a refined understanding of the cellular and molecular mechanisms of kidney fibrosis and the development of novel compounds are urgently needed. Whether arginases play a role in the development of fibrosis in CKD is unclear. We hypothesized that endothelial arginase-2 (Arg2) promotes the development of kidney fibrosis induced by unilateral ureteral obstruction (UUO). Arg2 expression and arginase activity significantly increased following renal fibrosis. Pharmacologic blockade or genetic deficiency of Arg2 conferred kidney protection following renal fibrosis, as reflected by a reduction in kidney interstitial fibrosis and fibrotic markers. Selective deletion of Arg2 in endothelial cells (Tie2Cre/Arg2fl/fl) reduced the level of fibrosis after UUO. In contrast, selective deletion of Arg2 specifically in proximal tubular cells (Ggt1Cre/Arg2fl/fl) failed to reduce renal fibrosis after UUO. Furthermore, arginase inhibition restored kidney nitric oxide (NO) levels, oxidative stress, and mitochondrial function following UUO. These findings indicate that endothelial Arg2 plays a major role in renal fibrosis via its action on NO and mitochondrial function. Blocking Arg2 activity or expression could be a novel therapeutic approach for prevention of CKD.

Mitochondria as a Source and a Target for Uremic Toxins

Elucidation of molecular and cellular mechanisms of the uremic syndrome is a very challenging task. More than 130 substances are now considered to be "uremic toxins" and represent a very diverse group of molecules. The toxicity of these molecules affects many cellular processes, and expectably, some of them are able to disrupt mitochondrial functioning. However, mitochondria can be the source of uremic toxins as well, as the mitochondrion can be the site of complete synthesis of the toxin, whereas in some scenarios only some enzymes of the pathway of toxin synthesis are localized here. In this review, we discuss the role of mitochondria as both the target and source of pathological processes and toxic compounds during uremia. Our analysis revealed about 30 toxins closely related to mitochondria. Moreover, since mitochondria are key regulators of cellular redox homeostasis, their functioning might directly affect the production of uremic toxins, especially those that are products of oxidation or peroxidation of cellular components, such as aldehydes, advanced glycation end-products, advanced lipoxidation end-products, and reactive carbonyl species. Additionally, as a number of metabolic products can be degraded in the mitochondria, mitochondrial dysfunction would therefore be expected to cause accumulation of such toxins in the organism. Alternatively, many uremic toxins (both made with the participation of mitochondria, and originated from other sources including exogenous) are damaging to mitochondrial components, especially respiratory complexes. As a result, a positive feedback loop emerges, leading to the amplification of the accumulation of uremic solutes. Therefore, uremia leads to the appearance of mitochondria-damaging compounds, and consecutive mitochondrial damage causes a further rise of uremic toxins, whose synthesis is associated with mitochondria. All this makes mitochondrion an important player in the pathogenesis of uremia and draws attention to the possibility of reducing the pathological consequences of uremia by protecting mitochondria and reducing their role in the production of uremic toxins.

Transmembrane member 16A participates in hydrogen peroxide-induced apoptosis by facilitating mitochondria-dependent pathway in vascular smooth muscle cells

BACKGROUND AND PURPOSE

Transmembrane member 16A (TMEM16A), an intrinsic constituent of the Ca2+ -activated Cl- channel, is involved in vascular smooth muscle cell (VSMC) proliferation and hypertension-induced cerebrovascular remodelling. However, the functional significance of TMEM16A for apoptosis in basilar artery smooth muscle cells (BASMCs) remains elusive. Here, we investigated whether and how TMEM16A contributes to apoptosis in BASMCs.

EXPERIMENTAL APPROACH

Cell viability assay, flow cytometry, Western blot, mitochondrial membrane potential assay, immunogold labelling and co-immunoprecipitation (co-IP) were performed.

KEY RESULTS

Hydrogen peroxide (H2 O2 ) induced BASMC apoptosis through a mitochondria-dependent pathway, including by increasing the apoptosis rate, down-regulating the ratio of Bcl-2/Bax and potentiating the loss of the mitochondrial membrane potential and release of cytochrome c from the mitochondria to the cytoplasm. These effects were all reversed by the silencing of TMEM16A and were further potentiated by the overexpression of TMEM16A. Endogenous TMEM16A was detected in the mitochondrial fraction. Co-IP revealed an interaction between TMEM16A and cyclophilin D, a component of the mitochondrial permeability transition pore (mPTP). This interaction was up-regulated by H2 O2 but restricted by cyclosporin A, an inhibitor of cyclophilin D. TMEM16A increased mPTP opening, resulting in the activation of caspase-9 and caspase-3. The results obtained with cultured BASMCs from TMEM16A smooth muscle-specific knock-in mice were consistent with those from rat BASMCs.

CONCLUSIONS AND IMPLICATIONS

These results suggest that TMEM16A participates in H2 O2 -induced apoptosis via modulation of mitochondrial membrane permeability in VSMCs. This study establishes TMEM16A as a target for therapy of several remodelling-related diseases.

Long-term dietary restriction up-regulates activity and expression of renal arginase II in aging mice

Arginase II is a mitochondrial enzyme that catalyses the hydrolysis of L-arginine into urea and ornithine. It is present in other extra-hepatic tissues that lack urea cycle. Therefore, it is plausible that arginase II has a physiological role other than urea cycle which includes polyamine, proline, glutamate synthesis and regulation of nitric oxide production. The high expression of arginase II in kidney, among extrahepatic tissues, might have an important role associated with kidney functions. The present study is aimed to determine the age-associated alteration in the activity and expression of arginase II in the kidney of mice of different ages. The effect of dietary restriction to modulate the agedependent changes of arginase II was also studied. Results showed that renal arginase II activity declines significantly with the progression of age (p less than 0.01 and p less than 0.001 in 6- and 18-month-old mice, respectively as compared to 2-month old mice) and is due to the reduction in its protein as well as the mRNA level (p less than 0.001 in both 6- and 18-month-old mice as compared to 2-month-old mice). Long-term dietary restriction for three months has significantly up-regulated arginase II activity and expression level in both 2- and 18-month-old mice (p less than 0.01 and p less than 0.001, respectively as compared to AL group). These findings clearly indicate that the reducing level of arginase II during aging might have an impact on the declining renal functions. This age-dependent down-regulation of arginase II in the kidney can be attenuated by dietary restriction which may help in the maintenance of such functions.

Probiotic supplementation promotes a reduction in T-cell activation, an increase in Th17 frequencies, and a recovery of intestinal epithelium integrity and mitochondrial morphology in ART-treated HIV-1-positive patients

INTRODUCTION

HIV infection is characterized by a persistent immune activation associated to a compromised gut barrier immunity and alterations in the profile of the fecal flora linked with the progression of inflammatory symptoms. The effects of high concentration multistrain probiotic (Vivomixx®, Viale del Policlinico 155, Rome, Italy in EU; Visbiome®, Dupont, Madison, Wisconsin in USA) on several aspects of intestinal immunity in ART-experienced HIV-1 patients was evaluated.

METHODS

A sub-study of a longitudinal pilot study was performed in HIV-1 patients who received the probiotic supplement twice a day for 6 months (T6). T-cell activation and CD4+ and CD8+ T-cell subsets expressing IFNγ (Th1, Tc1) or IL-17A (Th17, Tc17) were stained by cytoflorimetric analysis. Histological and immunohistochemical analyses were performed on intestinal biopsies while enterocytes apoptosis index was determined by TUNEL assay.

RESULTS

A reduction in the frequencies of CD4+ and CD8+ T-cell subsets, expressing CD38+ , HLA-DR+ , or both, and an increase in the percentage of Th17 cell subsets, especially those with central or effector memory phenotype, was recorded in the peripheral blood and in gut-associated lymphoid tissue (GALT) after probiotic intervention. Conversely, Tc1 and Tc17 levels remained substantially unchanged at T6, while Th1 cell subsets increase in the GALT. Probiotic supplementation was also associated to a recovery of the integrity of the gut epithelial barrier, a reduction of both intraepithelial lymphocytes density and enterocyte apoptosis and, an improvement of mitochondrial morphology sustained in part by a modulation of heat shock protein 60.

CONCLUSIONS

These findings highlight the potential beneficial effects of probiotic supplementation for the reconstitution of physical and immunological integrity of the mucosal intestinal barrier in ART-treated HIV-1-positive patients.

Arginase-2 mediates renal ischemia-reperfusion injury

Novel therapeutic interventions for preventing or attenuating kidney injury following ischemia-reperfusion injury (IRI) remain a focus of significant interest. Currently, there are no definitive therapeutic or preventive approaches available for ischemic acute kidney injury (AKI). Our objective is to determine 1) whether renal arginase activity or expression is increased in renal IRI, and 2) whether arginase plays a role in development of renal IRI. The impact of arginase activity and expression on renal damage was evaluated in male C57BL/6J (wild type) and arginase-2 (ARG2)-deficient (Arg2^-/- ) mice subjected to bilateral renal ischemia for 28 min, followed by reperfusion for 24 h. ARG2 expression and arginase activity significantly increased following renal IRI, paralleling the increase in kidney injury. Pharmacological blockade or genetic deficiency of Arg2 conferred kidney protection in renal IRI. Arg2^-/- mice had significantly attenuated kidney injury and lower plasma creatinine and blood urea nitrogen levels after renal IRI. Blocking arginases using S-(2-boronoethyl)-l-cysteine (BEC) 18 h before ischemia mimicked arginase deficiency by reducing kidney injury, histopathological changes and kidney injury marker-1 expression, renal apoptosis, kidney inflammatory cell recruitment and inflammatory cytokines, and kidney oxidative stress; increasing kidney nitric oxide (NO) production and endothelial NO synthase (eNOS) phosphorylation, kidney peroxisome proliferator-activated receptor-γ coactivator-1α expression, and mitochondrial ATP; and preserving kidney mitochondrial ultrastructure compared with vehicle-treated IRI mice. Importantly, BEC-treated eNOS-knockout mice failed to reduce blood urea nitrogen and creatinine following renal IRI. These findings indicate that ARG2 plays a major role in renal IRI, via an eNOS-dependent mechanism, and that blocking ARG2 activity or expression could be a novel therapeutic approach for prevention of AKI.

OxLDL triggers retrograde translocation of arginase2 in aortic endothelial cells via ROCK and mitochondrial processing peptidase

RATIONALE

Increased arginase activity contributes to endothelial dysfunction by competition for l-arginine substrate and reciprocal regulation of nitric oxide synthase (NOS). The rapid increase in arginase activity in human aortic endothelial cells exposed to oxidized low-density lipoprotein (OxLDL) is consistent with post-translational modification or subcellular trafficking.

OBJECTIVE

To test the hypotheses that OxLDL triggers reverse translocation of mitochondrial arginase 2 (Arg2) to cytosol and Arg2 activation, and that this process is dependent on mitochondrial processing peptidase, lectin-like OxLDL receptor-1 receptor, and rho kinase.

METHODS AND RESULTS

OxLDL-triggered translocation of Arg2 from mitochondria to cytosol in human aortic endothelial cells and in murine aortic intima with a concomitant rise in arginase activity. All of these changes were abolished by inhibition of mitochondrial processing peptidase or by its siRNA-mediated knockdown. Rho kinase inhibition and the absence of the lectin-like OxLDL receptor-1 in knockout mice also ablated translocation. Aminoterminal sequencing of Arg2 revealed 2 candidate mitochondrial targeting sequences, and deletion of either of these confined Arg2 to the cytoplasm. Inhibitors of mitochondrial processing peptidase or lectin-like OxLDL receptor-1 knockout attenuated OxLDL-mediated decrements in endothelial-specific NO production and increases in superoxide generation. Finally, Arg2(-/-) mice bred on an ApoE(-/-) background showed reduced plaque load, reduced reactive oxygen species production, enhanced NO, and improved endothelial function when compared with ApoE(-/-) controls.

CONCLUSIONS

These data demonstrate dual distribution of Arg2, a protein with an unambiguous mitochondrial targeting sequence, in mammalian cells, and its reverse translocation to cytoplasm by alterations in the extracellular milieu. This novel molecular mechanism drives OxLDL-mediated arginase activation, endothelial NOS uncoupling, endothelial dysfunction, and atherogenesis.

l-Citrulline Protects from Kidney Damage in Type 1 Diabetic Mice

RATIONALE

Diabetic nephropathy (DN) is a major cause of end-stage renal disease, associated with endothelial dysfunction. Chronic supplementation of l-arginine (l-arg), the substrate for endothelial nitric oxide synthase (eNOS), failed to improve vascular function. l-Citrulline (l-cit) supplementation not only increases l-arg synthesis, but also inhibits cytosolic arginase I, a competitor of eNOS for the use of l-arg, in the vasculature.

AIMS

To investigate whether l-cit treatment reduces DN in streptozotocin (STZ)-induced type 1 diabetes (T1D) in mice and rats and to study its effects on arginase II (ArgII) function, the main renal isoform.

METHODS

STZ-C57BL6 mice received l-cit or vehicle supplemented in the drinking water. For comparative analysis, diabetic ArgII knock out mice and l-cit-treated STZ-rats were evaluated.

RESULTS

l-Citrulline exerted protective effects in kidneys of STZ-rats, and markedly reduced urinary albumin excretion, tubulo-interstitial fibrosis, and kidney hypertrophy, observed in untreated diabetic mice. Intriguingly, l-cit treatment was accompanied by a sustained elevation of tubular ArgII at 16 weeks and significantly enhanced plasma levels of the anti-inflammatory cytokine IL-10. Diabetic ArgII knock out mice showed greater blood urea nitrogen levels, hypertrophy, and dilated tubules than diabetic wild type (WT) mice. Despite a marked reduction in collagen deposition in ArgII knock out mice, their albuminuria was not significantly different from diabetic WT animals. l-Cit also restored nitric oxide/reactive oxygen species balance and barrier function in high glucose-treated monolayers of human glomerular endothelial cells. Moreover, l-cit also has the ability to establish an anti-inflammatory profile, characterized by increased IL-10 and reduced IL-1β and IL-12(p70) generation in the human proximal tubular cells.

CONCLUSION

l-Citrulline supplementation established an anti-inflammatory profile and significantly preserved the nephron function during T1D.

Arginase inhibition mediates renal tissue protection in diabetic nephropathy by a nitric oxide synthase 3-dependent mechanism

Recently we showed that pharmacological blockade or genetic deficiency of arginase-2 confers kidney protection in diabetic mouse models. Here we tested whether the protective effect of arginase inhibition is nitric oxide synthase-3 (eNOS)-dependent in diabetic nephropathy. Experiments were conducted in eNOS knockout and their wild type littermate mice using multiple low doses of vehicle or streptozotocin and treated with continuous subcutaneous infusion of vehicle or the arginase inhibitor S-(2-Boronoethyl)-L-cysteine by an osmotic pump. Inhibition of arginases for 6 weeks in diabetic wild type mice significantly attenuated albuminuria, the increase in plasma creatinine and blood urea nitrogen, histopathological changes, kidney fibronectin and TNF-α expression, kidney macrophage recruitment, and oxidative stress compared to vehicle-treated diabetic wild type mice. Arginase inhibition in diabetic eNOS knockout mice failed to affect any of these parameters but reduced kidney macrophage recruitment and kidney TNF-α expression compared to vehicle-treated diabetic eNOS knockout mice. Furthermore, diabetic wild type and eNOS knockout mice exhibited increased kidney arginase-2 protein, arginase activity and ornithine levels. Thus, arginase inhibition mediates renal tissue protection in diabetic nephropathy by an eNOS-dependent mechanism and has an eNOS-independent effect on kidney macrophage recruitment.

Arginase-2 mediates diabetic renal injury

OBJECTIVE

To determine 1) whether renal arginase activity or expression is increased in diabetes and 2) whether arginase plays a role in development of diabetic nephropathy (DN).

RESEARCH DESIGN AND METHODS

The impact of arginase activity and expression on renal damage was evaluated in spontaneously diabetic Ins2(Akita) mice and in streptozotocin (STZ)-induced diabetic Dilute Brown Agouti (DBA) and arginase-2-deficient mice (Arg2(-/-)).

RESULTS

Pharmacological blockade or genetic deficiency of arginase-2 conferred kidney protection in Ins2(Akita) mice or STZ-induced diabetic renal injury. Blocking arginases using S-(2-boronoethyl)-L-cysteine for 9 weeks in Ins2(Akita) mice or 6 weeks in STZ-induced diabetic DBA mice significantly attenuated albuminuria, the increase in blood urea nitrogen, histopathological changes, and kidney macrophage recruitment compared with vehicle-treated Ins2(Akita) mice. Furthermore, kidney arginase-2 expression increased in Ins2(Akita) mice compared with control. In contrast, arginase-1 expression was undetectable in kidneys under normal or diabetes conditions. Arg2(-/-) mice mimicked arginase blockade by reducing albuminuria after 6 and 18 weeks of STZ-induced diabetes. In wild-type mice, kidney arginase activity increased significantly after 6 and 18 weeks of STZ-induced diabetes but remained very low in STZ-diabetic Arg2(-/-) mice. The increase in kidney arginase activity was associated with a reduction in renal medullary blood flow in wild-type mice after 6 weeks of STZ-induced diabetes, an effect significantly attenuated in diabetic Arg2(-/-) mice.

CONCLUSIONS

These findings indicate that arginase-2 plays a major role in induction of diabetic renal injury and that blocking arginase-2 activity or expression could be a novel therapeutic approach for treatment of DN.

Hypoxia-reduced nitric oxide synthase activity is partially explained by higher arginase-2 activity and cellular redistribution in human umbilical vein endothelium

Hypoxia relates with altered placental vasodilation, and in isolated endothelial cells, it reduces activity of the endothelial nitric oxide synthase (eNOS) and l-arginine transport. It has been reported that arginase-2 expression, an alternative pathway for l-arginine metabolism, is increased in adult endothelial cells exposed to hypoxia as well as in pre-eclamptic placentae. We studied in human umbilical vein endothelial cells (HUVEC) whether hypoxia-reduced NO synthesis results from increased arginase-mediated l-arginine metabolism and changes in subcellular localization of eNOS and arginase-2. In HUVEC exposed (24 h) to 5% (normoxia) or 2% (hypoxia) oxygen, l-arginine transport kinetics, arginase activity (urea assay), and NO synthase (NOS) activity (l-citrulline assay) were determined. Arginase-1, arginase-2 and eNOS expression were determined by RT-PCR and Western blot. Subcellular localization of arginase-2 and eNOS were studied using confocal microscopy and indirect immunofluorescence. Experiments were done in absence or presence of S-(2-boronoethyl)-l-cysteine-HCl (BEC, arginase inhibitor) or N(G)-nitro-l-arginine methyl ester (l-NAME). Hypoxia-induced reduction in eNOS activity was associated with a reduction in eNOS phosphorylation at Serine-1177 and increased phosphorylation at Threonine-495. This was paralleled with an induction in arginase-2 expression and activity, and decreased l-arginine transport. In hypoxia the arginase inhibition, restored NO synthesis and l-arginine transport, without changes in the eNOS post-translational modification status. Hypoxia increased arginase-2/eNOS colocalization, and eNOS redistribution to the cell periphery. Altogether these data reinforce the thought that eNOS cell location, post-translational modification and substrate availability are important mechanisms regulating eNOS activity. If these mechanisms occur in pregnancy diseases where feto-placental oxygen levels are reduced remains to be clarified.

Nonimmune Cells Contribute to Crosstalk between Immune Cells and Inflammatory Mediators in the Innate Response to Trypanosoma cruzi Infection

Chagas myocarditis, which is caused by infection with the intracellular parasite Trypanosoma cruzi, remains the major infectious heart disease worldwide. Innate recognition through toll-like receptors (TLRs) on immune cells has not only been revealed to be critical for defense against T. cruzi but has also been involved in triggering the pathology. Subsequent studies revealed that this parasite activates nucleotide-binding oligomerization domain- (NOD-)like receptors and several particular transcription factors in TLR-independent manner. In addition to professional immune cells, T. cruzi infects and resides in different parenchyma cells. The innate receptors in nonimmune target tissues could also have an impact on host response. Thus, the outcome of the myocarditis or the inflamed liver relies on an intricate network of inflammatory mediators and signals given by immune and nonimmune cells. In this paper, we discuss the evidence of innate immunity to the parasite developed by the host, with emphasis on the crosstalk between immune and nonimmune cell responses.

Endothelial arginase II and atherosclerosis

Atherosclerotic vascular disease is the leading cause of morbidity and mortality in developed countries. While it is a complex condition resulting from numerous genetic and environmental factors, it is well recognized that oxidized low-density lipoprotein produces pro-atherogenic effects in endothelial cells (ECs) by inducing the expression of adhesion molecules, stimulating EC apoptosis, inducing superoxide anion formation and impairing protective endothelial nitric oxide (NO) formation. Emerging evidence suggests that the enzyme arginase reciprocally regulates NO synthase and NO production by competing for the common substrate L-arginine. As oxidized LDL (OxLDL) results in arginase activation/upregulation, it appears to be an important contributor to endothelial dysfunction by a mechanism that involves substrate limitation for endothelial NO synthase (eNOS) and NO synthesis. Additionally, arginase enhances production of reactive oxygen species by eNOS. Arginase inhibition in hypercholesterolemic (ApoE^-/-) mice or arginase II deletion (ArgII^-/-) mice restores endothelial vasorelaxant function, reduces vascular stiffness and markedly reduces atherosclerotic plaque burden. Furthermore, arginase activation contributes to vascular changes including polyamine-dependent vascular smooth muscle cell proliferation and collagen synthesis. Collectively, arginase may play a key role in the prevention and treatment of atherosclerotic vascular disease.

Expression and function of arginine-producing and consuming-enzymes in the kidney

The kidney plays a key role in arginine metabolism. Arginine production is controlled by argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL) which metabolize citrulline and aspartate to arginine and fumarate whereas arginine consumption is dependent on arginine:glycine amidinotransferase (GAT), which mediates creatine and ornithine synthesis. Histological and biochemical techniques have been used to study the distribution and activity of these enzymes in anatomically dissected segments, in isolated fragments of tubules and in whole tissues. ASS and ASL mRNAs and proteins are expressed in the proximal tubule. Within this nephron segment, the proximal convoluted tubule has a higher arginine synthesis capacity than the proximal straight tubules. Furthermore, this arginine-synthesizing portion of the nephron matches perfectly with the site of citrulline reabsorption from the glomerular filtrate. The kidney itself can produce citrulline from methylated arginine, but this capacity is limited. Therefore, intestinal citrulline synthesis is required for renal arginine production. Although the proximal convoluted tubule also expresses a significant amount of GAT, only 10% of renal arginine synthesis is metabolized to guanidinoacetic acid, possibly because GAT has a mitochondrial localization. Kidney arginase (AII) is expressed in the cortical and outer medullary proximal straight tubules and does not degrade significant amounts of newly synthesized arginine. The data presented in this review identify the proximal convoluted tubule as the main site of endogenous arginine biosynthesis.

Direct production of L-ornithine from casein by commercial digestive enzymes and in situ activated arginase

There is a great demand for L-ornithine, which is used as a dietary supplement, and in the pharmaceutical industry. In the present study, when milk casein was hydrolyzed at 37 degrees C by using commercial digestive enzymes, namely, Pancreatin F and Protease A, a significant accumulation of L-ornithine in the hydrolysate and the simultaneous disappearance of L-arginine was noted. In a radiometric assay, transient but distinct arginase activity, which was sufficiently high for L-ornithine production, was detected in the hydrolysate for a certain period during casein hydrolysis. On the basis of the results of the enzymatic analyses, arginase was thought to be proteolytically generated from an inactive precursor, which may generally be contained in Pancreatin F, and ultimately degraded by further proteolysis. This conversion process using the above-mentioned digestive enzymes is useful for the production of L-ornithine directly from protein sources that are abundant in nature.

Predicting metabolic biomarkers of human inborn errors of metabolism

Early diagnosis of inborn errors of metabolism is commonly performed through biofluid metabolomics, which detects specific metabolic biomarkers whose concentration is altered due to genomic mutations. The identification of new biomarkers is of major importance to biomedical research and is usually performed through data mining of metabolomic data. After the recent publication of the genome-scale network model of human metabolism, we present a novel computational approach for systematically predicting metabolic biomarkers in stochiometric metabolic models. Applying the method to predict biomarkers for disruptions of red-blood cell metabolism demonstrates a marked correlation with altered metabolic concentrations inferred through kinetic model simulations. Applying the method to the genome-scale human model reveals a set of 233 metabolites whose concentration is predicted to be either elevated or reduced as a result of 176 possible dysfunctional enzymes. The method's predictions are shown to significantly correlate with known disease biomarkers and to predict many novel potential biomarkers. Using this method to prioritize metabolite measurement experiments to identify new biomarkers can provide an order of a 10-fold increase in biomarker detection performance.

Arginase enzymes in isolated airways from normal and nitric oxide synthase 2-knockout mice exposed to ovalbumin

Arginase has been suggested to compete with nitric oxide synthase (NOS) for their common substrate, l-arginine. To study the mechanisms underlying this interaction, we compared arginase expression in isolated airways and the consequences of inhibiting arginase activity in vivo with NO production, lung inflammation, and lung function in both C57BL/6 and NOS2 knockout mice undergoing ovalbumin-induced airway inflammation, a mouse model of asthma. Arginases I and II were measured by western blot in isolated airways from sensitized C57BL/6 mice exposed to ovalbumin aerosol. Physiological and biochemical responses - inflammation, lung compliance, airway hyperreactivity, exhaled NO concentration, arginine concentration - were compared with the responses of NOS2 knockout mice. NOS2 knockout mice had increased total cells in lung lavage, decreased lung compliance, and increased airway hyperreactivity. Both arginase I and arginase II were constitutively expressed in the airways of normal C57BL/6 mice. Arginase I was up-regulated approximately 8-fold in the airways of C57BL/6 mice exposed to ovalbumin. Expression of both arginase isoforms were significantly upregulated in NOS2 knockout mice exposed to ovalbumin, with about 40- and 4-fold increases in arginases I and II, respectively. Arginine concentration in isolated airways was not significantly different in any of the groups studied. Inhibition of arginase by systemic treatment of C57BL/6 mice with a competitive inhibitor, Nomega-hydroxy-nor-l-arginine (nor-NOHA), significantly decreased the lung inflammatory response to ovalbumin in these animals. We conclude that NOS2 knockout mice are more sensitive to ovalbumin-induced airway inflammation and its sequelae than are C57BL/6 mice, as determined by increased total cells in lung lavage, decreased lung compliance, and increased airway hyperreactivity, and that these findings are strongly correlated with increased expression of both arginase isoforms in the airways of the NOS2 knockout mice exposed to ovalbumin.

Mitochondrial arginase II constrains endothelial NOS-3 activity

Emerging evidence supports the idea that arginase, expressed in the vascular endothelial cells of humans and other species, modulates endothelial nitric oxide (NO) synthase-3 (NOS-3) activity by regulating intracellular L-arginine bioavailability. Arginase II is thought to be expressed in the mitochondria of a variety of nonendothelial cells, whereas arginase I is known to be confined to the cytosol of hepatic and other cells. The isoforms that regulate NOS-3 and their subcellular distribution, however, remain incompletely characterized. We therefore tested the hypothesis that arginase II is confined to the mitochondria and that mitochondrial arginase II reciprocally regulates vascular endothelial NO production. Western blot analysis, immunocytochemistry with MitoTracker, and immunoelectron microscopy confirmed that arginase II is confined predominantly but not exclusively to the mitochondria. Arginase activity was significantly decreased, whereas NO production was significantly increased in the aorta and isolated endothelial cells from arginase II knockout (ArgII(-/-)) mice compared with wild-type (WT) mice. The vasorelaxation response to acetylcholine (ACh) was markedly enhanced and the vasoconstrictor response to phenylephrine (PE) attenuated in ArgII(-/-) in pressurized mouse carotid arteries. Furthermore, inhibition of NOS-3 by N(G)-nitro-L-arginine methyl ester (L-NAME) impaired ACh response and restored the PE response to that observed in WT vessels. Vascular stiffness, as assessed by pulse wave velocity (PWV), was significantly decreased in ArgII(-/-) compared with WT mice. On the other hand, 14 days of oral L-NAME treatment significantly increased PWV in both WT and ArgII(-/-) mice, such that they were not significantly different from one another. These data suggest that arginase II is predominantly confined to the mitochondria and that this mitochondrial arginase II regulates NO production, vascular endothelial function, and vascular stiffness by modulating NOS-3 activity.

Spatial gene expression in the T-stage mouse metanephros

The E11.5 mouse metanephros is comprised of a T-stage ureteric epithelial tubule sub-divided into tip and trunk cells surrounded by metanephric mesenchyme (MM). Tip cells are induced to undergo branching morphogenesis by the MM. In contrast, signals within the mesenchyme surrounding the trunk prevent ectopic branching of this region. In order to identify novel genes involved in the molecular regulation of branching morphogenesis we compared the gene expression profiles of isolated tip, trunk and MM cells using Compugen mouse long oligo microarrays. We identified genes enriched in the tip epithelium, sim-1, Arg2, Tacstd1, Crlf-1 and BMP7; genes enriched in the trunk epithelium, Innp1, Itm2b, Mkrn1, SPARC, Emu2 and Gsta3 and genes spatially restricted to the mesenchyme surrounding the trunk, CSPG2 and CV-2, with overlapping and complimentary expression to BMP4, respectively. This study has identified genes spatially expressed in regions of the developing kidney involved in branching morphogenesis, nephrogenesis and the development of the collecting duct system, calyces, renal pelvis and ureter.

Arginase modulates myocardial contractility by a nitric oxide synthase 1-dependent mechanism

Cardiac myocytes contain two constitutive NO synthase (NOS) isoforms with distinct spatial locations, which allows for isoform-specific regulation. One regulatory mechanism for NOS is substrate (l-arginine) bioavailability. We tested the hypothesis that arginase (Arg), which metabolizes l-arginine, constrains NOS activity in the cardiac myocyte in an isoform-specific manner. Arg activity was detected in both rat heart homogenates and isolated myocytes. Although both Arg I and II mRNA and protein were present in whole heart, Arg II alone was found in isolated myocytes. Arg inhibition with S-(2-boronoethyl)-l-cysteine (BEC) augmented Ca(2+)-dependent NOS activity and NO production in myocytes, which did not depend on extracellular l-arginine. Arg II coimmunoprecipited with NOS1 but not NOS3. Isolation of myocyte mitochondrial fractions in combination with immuno-electron microscopy demonstrates that Arg II is confined primarily to the mitochondria. Because NOS1 positively modulates myocardial contractility, we determined whether Arg inhibition would increase basal myocardial contractility. Consistent with our hypothesis, Arg inhibition increased basal contractility in isolated myocytes by a NOS-dependent mechanism. Both the Arg inhibitors N-hydroxy-nor-l-arginine and BEC dose-dependently increased basal contractility in rat myocytes, which was inhibited by both nonspecific and NOS1-specific NOS inhibitors N(G)-nitro-l-arginine methyl ester and S-methyl-l-thiocitrulline, respectively. Also, BEC increased contractility in isolated myocytes from WT and NOS3 but not NOS1 knockout mice. We conclude that mitochondrial Arg II negatively regulates NOS1 activity, most likely by limiting substrate availability in its microdomain. These findings have implications for therapy in pathophysiologic states such as aging and heart failure in which myocardial NO signaling is disrupted.