Arginase inhibitor reduces fungal dissemination in murine pulmonary cryptococcosis by promoting anti-cryptococcal immunity

Elevation of arginase enzyme activity in the lung contributes to the pathogenesis of various chronic inflammatory diseases and infections. Inhibition of arginase expression and activity is able to alleviate those effects. Here, we investigated the immunomodulatory effect of arginase inhibitor in C. neoformans infection. In the pulmonary cryptococcosis model that was shown to recapitulate human infection, we found arginase expression was excessively induced in the lung during the late stage of infection. To inhibit the activity of arginase, we administered a specific arginase inhibitor, nor-NOHA, during C. neoformans infection. Inhibition of arginase reduced eosinophil infiltration and level of IL-13 secretion in the lungs. Whole lung transcriptome RNA-sequencing analysis revealed that treatment with nor-NOHA resulted in shifting the Th2-type gene expression patterns induced by C. neoformans infection to the Th1-type immune profile, with higher expression of cytokines Ifng, Il6, Tnfa, Csf3, chemokines Cxcl9 and Cxcl10 and transcription factor Stat1. More importantly, mice treated with arginase inhibitor had more infiltrating brain leukocytes and enhanced gene expression of Th1-associated cytokines and chemokines that are known to be essential for protection against C. neoformans infection. Inhibition of arginase dramatically attenuated spleen and brain infection, with improved survival. Taken together, these studies demonstrated that inhibiting arginase activity induced by C. neoformans infection can modulate host immune response by enhancing protective type-1 immune response during C. neoformans infection. The inhibition of arginase activity could be an immunomodulatory target to enhance protective anti-cryptococcal immune responses.

PD-1 inhibition with retifanlimab and/or arginase inhibition with INCB001158 in Japanese patients with solid tumors: A phase I study

BACKGROUND

Retifanlimab is a humanized monoclonal antibody targeting programmed death protein-1, and INCB001158 is an oral arginase inhibitor. This phase Ib study investigated retifanlimab, INCB001158, and their combination in Japanese patients with advanced solid tumors.

METHODS

Patients received retifanlimab (500 mg every 4 weeks [Q4W] i.v.) or escalating doses of INCB001158 (75 or 100 mg twice daily [BID]) monotherapy in Part 1 and combination of retifanlimab (500 mg Q4W) and INCB001158 (100 mg BID) in Part 2. Primary endpoints were safety, tolerability, dose-limiting toxicities (DLTs), and determination of recommended phase II doses in Japanese patients.

RESULTS

Eighteen patients (retifanlimab or INCB001158 monotherapy and combination; n = 6 each) were enrolled at 2 sites in Japan. There were no DLTs, fatal adverse events (AEs), or discontinuations due to AEs. Rash (all grade 1) was the most common treatment-emergent AE with retifanlimab (n = 6). Treatment-related AEs were reported with retifanlimab (n = 4) or INCB001158 (n = 2) monotherapy and with combination (n = 4); an immune-related AE (thyroid disorder, grade 2) was reported with combination. Two responses were observed with retifanlimab monotherapy (1 complete, 1 partial) and 1 stable disease (SD), for an overall response rate of 33.3% (95% confidence interval [CI], 4.3-77.7) and disease control rate (DCR) of 50% (95% CI, 11.8-88.2). Three patients had SD with INCB001158 monotherapy (DCR 50%; 95% CI, 11.8-88.2). No responses or SD were observed with combination therapy.

CONCLUSION

Retifanlimab, INCB001158, and their combination had acceptable safety profiles. Promising retifanlimab antitumor activity warrants further investigation in Japanese patients.

Benzimidazole Derivatives as New and Selective Inhibitors of Arginase from Leishmania mexicana with Biological Activity against Promastigotes and Amastigotes

Leishmaniasis is a disease caused by parasites of the Leishmania genus that affects 98 countries worldwide, 2 million of new cases occur each year and more than 350 million people are at risk. The use of the actual treatments is limited due to toxicity concerns and the apparition of resistance strains. Therefore, there is an urgent necessity to find new drugs for the treatment of this disease. In this context, enzymes from the polyamine biosynthesis pathway, such as arginase, have been considered a good target. In the present work, a chemical library of benzimidazole derivatives was studied performing computational, enzyme kinetics, biological activity, and cytotoxic effect characterization, as well as in silico ADME-Tox predictions, to find new inhibitors for arginase from Leishmania mexicana (LmARG). The results show that the two most potent inhibitors (compounds 1 and 2) have an I₅₀ values of 52 μM and 82 μM, respectively. Moreover, assays with human arginase 1 (HsARG) show that both compounds are selective for LmARG. According to molecular dynamics simulation studies these inhibitors interact with important residues for enzyme catalysis. Biological activity assays demonstrate that both compounds have activity against promastigote and amastigote, and low cytotoxic effect in murine macrophages. Finally, in silico prediction of their ADME-Tox properties suggest that these inhibitors support the characteristics to be considered drug candidates. Altogether, the results reported in our study suggest that the benzimidazole derivatives are an excellent starting point for design new drugs against leishmanisis.

Severe COVID-19 Is Characterized by an Impaired Type I Interferon Response and Elevated Levels of Arginase Producing Granulocytic Myeloid Derived Suppressor Cells

COVID-19 ranges from asymptomatic in 35% of cases to severe in 20% of patients. Differences in the type and degree of inflammation appear to determine the severity of the disease. Recent reports show an increase in circulating monocytic-myeloid-derived suppressor cells (M-MDSC) in severe COVID 19 that deplete arginine but are not associated with respiratory complications. Our data shows that differences in the type, function and transcriptome of granulocytic-MDSC (G-MDSC) may in part explain the severity COVID-19, in particular the association with pulmonary complications. Large infiltrates by Arginase 1+ G-MDSC (Arg+G-MDSC), expressing NOX-1 and NOX-2 (important for production of reactive oxygen species) were found in the lungs of patients who died from COVID-19 complications. Increased circulating Arg+G-MDSC depleted arginine, which impaired T cell receptor and endothelial cell function. Transcriptomic signatures of G-MDSC from patients with different stages of COVID-19, revealed that asymptomatic patients had increased expression of pathways and genes associated with type I interferon (IFN), while patients with severe COVID-19 had increased expression of genes associated with arginase production, and granulocyte degranulation and function. These results suggest that asymptomatic patients develop a protective type I IFN response, while patients with severe COVID-19 have an increased inflammatory response that depletes arginine, impairs T cell and endothelial cell function, and causes extensive pulmonary damage. Therefore, inhibition of arginase-1 and/or replenishment of arginine may be important in preventing/treating severe COVID-19.

Mammalian Arginase Inhibitory Activity of Methanolic Extracts and Isolated Compounds from Cyperus Species

Polyphenolic enriched extracts from two species of Cyperus, Cyperus glomeratus and Cyperus thunbergii, possess mammalian arginase inhibitory capacities, with the percentage inhibition ranging from 80% to 95% at 100 µg/mL and 40% to 64% at 10 µg/mL. Phytochemical investigation of these species led to the isolation and identification of two new natural stilbene oligomers named thunbergin A-B (1–2), together with three other stilbenes, trans-resveratrol (3), trans-scirpusin A (4), trans-cyperusphenol A (6), and two flavonoids, aureusidin (5) and luteolin (7), which were isolated for the first time from C.thunbergii and C. glomeratus. Structures were established on the basis of the spectroscopic data from MS and NMR experiments. The arginase inhibitory activity of compounds 1–7 was evaluated through an in vitro arginase inhibitory assay using purified liver bovine arginase. As a result, five compounds (1, 4–7) showed significant inhibition of arginase, with IC₅₀ values between 17.6 and 60.6 µM, in the range of those of the natural arginase inhibitor piceatannol (12.6 µM). In addition, methanolic extract from Cyperus thunbergii exhibited an endothelium and NO-dependent vasorelaxant effect on thoracic aortic rings from rats and improved endothelial dysfunction in an adjuvant-induced arthritis rat model.

Cinnamides Target Leishmania amazonensis Arginase Selectively

Caffeic acid and related natural compounds were previously described as Leishmania amazonensis arginase (L-ARG) inhibitors, and against the whole parasite in vitro. In this study, we tested cinnamides that were previously synthesized to target human arginase. The compound caffeic acid phenethyl amide (CAPA), a weak inhibitor of human arginase (IC₅₀ = 60.3 ± 7.8 μM) was found to have 9-fold more potency against L-ARG (IC₅₀ = 6.9 ± 0.7 μM). The other compounds that did not inhibit human arginase were characterized as L-ARG, showing an IC₅₀ between 1.3–17.8 μM, and where the most active was compound 15 (IC₅₀ = 1.3 ± 0.1 μM). All compounds were also tested against L. amazonensis promastigotes, and only the compound CAPA showed an inhibitory activity (IC₅₀ = 80 μM). In addition, in an attempt to gain an insight into the mechanism of competitive L-ARG inhibitors, and their selectivity over mammalian enzymes, we performed an extensive computational investigation, to provide the basis for the selective inhibition of L-ARG for this series of compounds. In conclusion, our results indicated that the compounds based on cinnamoyl or 3,4-hydroxy cinnamoyl moiety could be a promising starting point for the design of potential antileishmanial drugs based on selective L-ARG inhibitors.

Arginase inhibition by (-)-Epicatechin reverses endothelial cell aging

Endothelial dysfunction (EnD) occurs with aging and endothelial nitric oxide (NO) production by NO synthase (NOS) can be impaired. Low NO levels have been linked to increased arginase (Ar) activity as Ar competes with NOS for L-arginine. The inhibition of Ar activity can reverse EnD and (-)-epicatechin (Epi) inhibits myocardial Ar activity. In this study, through in silico modeling we demonstrate that Epi interacts with Ar similarly to its inhibitor Norvaline (Norv). Using in vitro and in vivo models of aging, we examined Epi and Norv-inhibition of Ar activity and its endothelium-protective effects. Bovine coronary artery endothelial cells (BCAEC) were treated with Norv (10 μM), Epi (1 μM) or the combination (Epi + Norv) for 48 h. Ar activity increased in aged BCAEC, with decreased NO generation. Treatment decreased Ar activity to levels seen in young cells. Epi and Epi + Norv decreased nitrosylated Ar levels by ~25% in aged cells with lower oxidative stress (~25%) (dihydroethidium) levels. In aged cells, Epi and Epi + Norv restored the eNOS monomer/dimer ratio, protein expression levels and NO production to those of young cells. Furthermore, using 18 month old rats 15 days of treatment with either Epi (1 mg/kg), Norv (10 mg/kg) or combo, decreased hypertension and improved aorta vasorelaxation to acetylcholine, blood NO levels and tetra/dihydribiopterin ratios in cultured rat aortic endothelial cells. In conclusion, results provide evidence that inhibiting Ar with Epi reverses aged-related loss of eNOS function and improves vascular function through the modulation of Ar and eNOS protein levels and activity.

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.

Boronic acid-based arginase inhibitors in cancer immunotherapy

Arginase is an enzyme that converts l-arginine to l-ornithine and urea in the urea cycle. There are two isoforms of arginase in mammals: ARG-1 and ARG-2. l-Arginine level changes occur in patients with various types of affliction. An overexpression of arginase leads to the depletion of arginine and then to inhibition of the growth of T and NK cells, and in effect to the tumor escape of the immune response. Based on those observations, an inhibition of arginase is proposed as a method to improve anti-tumor immune responses (via an activation and proliferation of T and NK cells). Boronic acid derivatives as arginase inhibitors are leading, potential therapeutic agents for the treatment of several diseases. All these compounds are derived from the original 2-(S)-amino-6-boronohexanoic acid (ABH), the first boronic acid arginase inhibitor proposed by Christianson et al. This article focuses on the review of such sub-class of arginase inhibitors and highlights their SAR and PK properties. It covers molecules published until early 2020, including patent applications.

High cholesterol diet promotes dysfunction of arginase and cholinergic enzymatic system in rats: ameliorative role of caffeic and chlorogenic acids

BACKGROUND

Dietary phenolic compounds intake have been reported to have an inverse relationship to the prevalence of hypercholesterolemia. The objective of this study is to determine the effect of caffeic acid (CFA) and chlorogenic acid (CGA) on rats fed with high cholesterol diet (HCD).

METHODS

Experimental animals were fed with high cholesterol diet (HCD) for a period of 21 days while simvastatin (0.2 mg/kg BWT), CFA and CGA (10 and 15 mg/kg BWT) were administered daily.

RESULTS

Activity of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and arginase were significantly (P<0.05) higher in the rats fed with HCD alone. Also, level of malondiadehyde equivalent compounds (MDA) was significantly (P<0.05) elevated in hypercholesterolemic rats. Nevertheless, treatment with simvastatin, CFA and CGA normalized altered AChE, BChE and arginase activities as well as improved antioxidant status in hypercholesterolemic rats.

CONCLUSION

CFA and CGA could offer protective role in hypercholeseterolemic rats via their antioxidant potentials as well as restoring altered activity of acetylcholinesterase, butrylcholinesterase and arginase. Based on our findings chlorogenic acid exhibits better attribute.

Vasorelaxant effects of Crataegus pentagyna: Links with arginase inhibition and phenolic profile

ETHNOPHARMACOLOGICAL RELEVANCE

Crataegus leaves, flowers and fruits have been traditionally used to improve blood circulation, numerous preclinical and clinical studies supporting the cardiovascular benefits of Crataegus preparations. In this respect, there is very limited data on Crataegus pentagyna; in addition, the chemical profile of this species is still incompletely elucidated.

AIM OF THE STUDY

The objective of this study was to examine the cardiovascular benefits of Crataegus pentagyna Waldst. et Kit. ex Willd. (small-flowered black hawthorn, Rosaceae) extracts (leaf, flower and fruit ethyl acetate extracts) and the underlying mechanisms. We hypothesized that C. pentagyna extracts might exert vasodilatory effects and inhibit arginase activity due, in large part, to their polyphenolic constituents.

MATERIALS AND METHODS

C. pentagyna extracts induced-relaxation and the mechanisms involved were studied ex vivo in isolated aortic rings from Sprague-Dawley rats. The inhibitory effects on bovine liver arginase I were assessed by an in vitro assay. Metabolite profiling of C. pentagyna extracts was performed and the most endothelium- and nitric oxide synthase-dependent; flower extract additionally reduced Ca²⁺ entry and, to a lesser extent, Ca²⁺ release from the sarcoplasmic reticulum. C. pentagyna proved to be an important source of arginase inhibitors with potential benefits in endothelial dysfunction that remains to be explored.

The potential therapeutic effect of NG-hydroxy-nor-L-arginine in 7,12-dimethylbenz(a)anthracene-induced breast cancer in rats

Advances in our understanding of the metabolism and molecular functions of arginine and their alterations in cancer have led to resurgence in the interest of targeting arginine catabolism as an anticancer strategy. Therefore, arginase inhibitors have been proposed as a way to treat cancer. In this study, the anti-tumor potential of the arginase inhibition by N^G-hydroxy-nor-L-arginine (nor-NOHA) (3 mg/kg/day, i.p.), administered for 5 weeks (parallel tumors development, every 3th day) against 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinogenesis in rats has been investigated. Treatment by nor-NOHA has obvious inhibition effects on development of carcinogenesis in rats was shown. That was seen in downregulation of rats' tumors size and number, mortality rate, in stopped alteration of tissue histopathology, in decrease of polyamines, NO and MDA (malondialdeide) concentrations (in blood). Results have shown arginase and NO-synthase can cooperate to restrain quantities of polyamines and NO for cancer progression. The results obtained can serve as a base to use this model for determination of productive, noncytotoxic antitumor and immune modulating concentration of anticancer agents. Perspectives of targeting arginase and NOS in cancer management can ground application in clinical medicine.

Targeting the arginine metabolic brake enhances immunotherapy for leukaemia

Therapeutic approaches which aim to target Acute Myeloid Leukaemia through enhancement of patients' immune responses have demonstrated limited efficacy to date, despite encouraging preclinical data. Examination of AML patients treated with azacitidine (AZA) and vorinostat (VOR) in a Phase II trial, demonstrated an increase in the expression of Cancer-Testis Antigens (MAGE, RAGE, LAGE, SSX2 and TRAG3) on blasts and that these can be recognised by circulating antigen-specific T cells. Although the T cells have the potential to be activated by these unmasked antigens, the low arginine microenvironment created by AML blast Arginase II activity acts a metabolic brake leading to T cell exhaustion. T cells exhibit impaired proliferation, reduced IFN-γ release and PD-1 up-regulation in response to antigen stimulation under low arginine conditions. Inhibition of arginine metabolism enhanced the proliferation and cytotoxicity of anti-NY-ESO T cells against AZA/VOR treated AML blasts, and can boost anti-CD33 Chimeric Antigen Receptor-T cell cytotoxicity. Therefore, measurement of plasma arginine concentrations in combination with therapeutic targeting of arginase activity in AML blasts could be a key adjunct to immunotherapy.

Phenylhydrazides as inhibitors of Leishmania amazonensis arginase and antileishmanial activity

Searching for new substances with antileishmanial activity, we synthesized and evaluated a series of α,α-difluorohydrazide and α,α-difluoramides against Leishmania amazonensis arginase (LaArg). Four α,α-difluorohydrazide derivatives showed activity against LaArg with K_i in the range of 1.3-26 μM. The study of the kinetics of LaArg inhibition showed that these substances might act via different inhibitory mechanisms or even by a combination of these. The compounds were tested against L. amazonensis promastigotes and the best result was obtained to the compound 4 (EC₅₀ of 12.7 ± 0.3 μM). In addition, in order to obtain further insight into the binding mode of such compounds, molecular docking studies were performed to obtain additional validation of experimental results. Considering these results, it is possible to conclude that α,α-difluorohydrazide derivatives are a promising scaffold in the development of new substances against the etiological agent of leishmaniasis by targeting LaArg.

Suppression of Myeloid Cell Arginase Activity leads to Therapeutic Response in a NSCLC Mouse Model by Activating Anti-Tumor Immunity

BACKGROUND

Tumor orchestrated metabolic changes in the microenvironment limit generation of anti-tumor immune responses. Availability of arginine, a semi-essential amino acid, is critical for lymphocyte proliferation and function. Levels of arginine are regulated by the enzymes arginase 1,2 and nitric oxide synthase (NOS). However, the role of arginase activity in lung tumor maintenance has not been investigated in clinically relevant orthotopic tumor models.

METHODS

RNA sequencing (RNA-seq) of sorted cell populations from mouse lung adenocarcinomas derived from immunocompetent genetically engineered mouse models (GEMM)s was performed. To complement mouse studies, a patient tissue microarray consisting of 150 lung adenocarcinomas, 103 squamous tumors, and 54 matched normal tissue were stained for arginase, CD3, and CD66b by multiplex immunohistochemistry. Efficacy of a novel arginase inhibitor compound 9 in reversing arginase mediated T cell suppression was determined in splenocyte ex vivo assays. Additionally, the anti-tumor activity of this compound was determined in vitro and in an autochthonous immunocompetent KrasG12D GEMM of lung adenocarcinoma model.

RESULTS

Analysis of RNA-seq of sorted myeloid cells suggested that arginase expression is elevated in myeloid cells in the tumor as compared to the normal lung tissue. Accordingly, in the patient samples arginase 1 expression was mainly localized in the granulocytic myeloid cells and significantly elevated in both lung adenocarcinoma and squamous tumors as compared to the controls. Our ex vivo analysis demonstrated that myeloid derived suppressor cell (MDSC)s cause T cell suppression by arginine depletion, and suppression of arginase activity by a novel ARG1/2 inhibitor, compound 9, led to restoration of T cell function by increasing arginine. Treatment of KrasG12D GEMM of lung cancer model with compound 9 led to a significant tumor regression associated with increased T cell numbers and function, while it had no activity across several murine and human non-small cell (NSCLC) lung cancer lines in vitro.

CONCLUSIONS

We show that arginase expression is elevated in mouse and patient lung tumors. In a KRASG12D GEMM arginase inhibition diminished growth of established tumors. Our data suggest arginase as an immunomodulatory target that should further be investigated in lung tumors with high arginase activity.

Can Arginase Inhibitors Be the Answer to Therapeutic Challenges in Alzheimer's Disease?

While the extensive hunt for therapeutics combating Alzheimer's disease (AD) has fallen short of delivering effective treatments, breakthroughs towards understanding the disease mechanisms and identifying areas for future research have nevertheless been enabled. The majority of clinical trials with β- and γ-secretase modulators have been suspended from additional studies or terminated due to toxicity issues and health concerns. The lack of progress in developing innovative AD therapies has also prompted a resurgence of interest in more traditional symptomatic treatments with cholinesterase inhibitors and N-methyl-D-aspartate receptor antagonists, as well as in the research of immune response modulators. Recently, evidence has emerged showing that inhibitors of arginine metabolism and in particular blockers of arginase, an enzyme that catalyzes the breakdown of L-arginine, could present an effective therapeutic candidate for halting the progression of AD and boosting cognition and memory. In this commentary, we present a brief overview of reports on arginase inhibitors in AD mouse models and discuss emerging advantages and areas for careful consideration on the road to clinical translation.

Targeting arginase and nitric oxide metabolism in chronic airway diseases and their co-morbidities

In the airways, arginase and NOS compete for the common substrate l-arginine. In chronic airway diseases, such as asthma and COPD, elevated arginase expression contributes to airway contractility, hyperresponsiveness, inflammation and remodeling. The disrupted l-arginine homeostasis, through changes in arginase and NOS expression and activity, does not only play a central role in the development of various airways diseases such as asthma or COPD. It possibly also affects l-arginine homeostasis throughout the body contributing to the emergence of co-morbidities. This review focusses on the role of arginase, NOS and ADMA in co-morbidities of asthma and COPD and speculates on their possible connection.

Effectiveness of arginase inhibitors against experimentally induced stroke

Stroke is a lethal disease, but it disables more than it kills. Stroke is the second leading cause of death and the most frequent cause of permanent disability in adults worldwide, with 90% of survivors having residual deficits. The pathophysiology of stroke is complex and involves a strong inflammatory response associated with oxidative stress and activation of several proteolytic enzymes. The current study was designed to investigate the effect of arginase inhibitors (L-citruline and L-ornithine) against ischemic stroke induced in rats by middle cerebral artery occlusion (MCAO). MCAO resulted in alteration in rat behavior, brain infarct, and edema associated with disruption of the blood-brain barrier (BBB). This was mediated through overexpression of arginase I and II, inducible NOS (iNOS), malondialdehyde (MDA), advanced glycation end products (AGEs), TNF-α, and IL-1β and downregulation of endothelial nitric oxide synthase (eNOS). Treatment with L-citruline and L-ornithine and the standard neuroprotective drug cerebrolysin ameliorated all the deleterious effects of stroke. These results indicate the possible use of arginase inhibitors in the treatment of stroke after suitable clinical trials are done.

Phenolic Compounds as Arginase Inhibitors: New Insights Regarding Endothelial Dysfunction Treatment

Endothelial dysfunction is characterised by the low bioavailability of nitric oxide with a relevant negative impact on the nitric oxide/cGMP pathway. The loss of nitric oxide/cGMP signaling may be caused by an increased arginase activity. Plant-derived substances, especially polyphenols, are compounds that have the potential to inhibit arginase activity and they may represent an attractive therapeutic option to combat clinical outcomes related to endothelial dysfunction. An extensive review was carried out using all available data published in English in the Pubmed database, and without restriction regarding the year of publication. Despite the increased number of new substances that have been tested as arginase inhibitors, it is rare to find a compound that satisfies all the toxicological criteria to be used in the development of a new drug. On the other hand, recent data have shown that substances from plants have great potential to be applied as arginase inhibitors, most of which are polyphenols. Of the relevant mechanisms in this process, the inhibition of arginase by natural products seems to act against endothelial dysfunction by reestablishing the vascular function and elevating nitric oxide levels (by increasing the amounts of substrate (L-arginine, and endothelial nitric oxide synthase activation and stabilisation) as well as decreasing the generation of reactive species (formed by uncoupledendothelial nitric oxide synthase). This review summarises several topics regarding arginase inhibition by natural substances as well as indicating this pathway as an emergent strategy to elevate nitric oxide levels in disorders involving endothelial dysfunction. In addition, some aspects regarding structural activity and future perspectives are discussed.

Pharmacokinetics and Pharmacodynamics of Promising Arginase Inhibitors

Up-regulation of arginase activity in several chronic disease conditions, including cancer and hypertension, may suggest new targets for treatment. Recently, the number of new arginase inhibitors with promising therapeutic effects for asthma, cancer, hypertension, diabetes mellitus, and erectile dysfunction has shown a remarkable increase. Arginase inhibitors may be chemical substances, such as boron-based amino acid derivatives, α-difluoromethylornithine (DMFO), and Nω-hydroxy-nor-L-arginine (nor-NOHA) or, of plant origin such as sauchinone, salvianolic acid B (SAB), piceatannol-3-O-β-D-glucopyranoside (PG) and obacunone. Despite their promising therapeutic potential, little is known about pharmacokinetics and pharmacodynamics of some of these agents. Several studies were conducted in different animal species and in vitro systems and reported significant differences in pharmacokinetics and pharmacodynamics of arginase inhibitors. Therefore, extra caution should be considered before extrapolating these studies to human. Physicochemical and pharmacokinetic profiles of some effective arginase inhibitors make it challenging to formulate stable and effective formulation. In this article, existing literature on the pharmacokinetics and pharmacodynamics of arginase inhibitors were reviewed and compared together with emphasis on possible drug interactions and solutions to overcome pharmacokinetics challenges and shortage of arginase inhibitors in clinical practice.

Cytokine Signaling Protein 3 Deficiency in Myeloid Cells Promotes Retinal Degeneration and Angiogenesis through Arginase-1 Up-Regulation in Experimental Autoimmune Uveoretinitis

The suppressor of cytokine signaling protein 3 (SOCS3) critically controls immune cell activation, although its role in macrophage polarization and function remains controversial. Using experimental autoimmune uveoretinitis (EAU) as a model, we show that inflammation-mediated retinal degeneration is exaggerated and retinal angiogenesis is accelerated in mice with SOCS3 deficiency in myeloid cells (LysM^Cre/+SOCS3^fl/fl). At the acute stage of EAU, the population of infiltrating neutrophils was increased and the population of macrophages decreased in LysM^Cre/+SOCS3^fl/fl mice compared with that in wild-type (WT) mice. Real-time RT-PCR showed that the expression of tumor necrosis factor-α, IL-1β, interferon-γ, granulocyte-macrophage colony-stimulating factor, and arginase-1 was significantly higher in the LysM^Cre/+SOCS3^fl/fl EAU retina in contrast to the WT EAU retina. The percentage of arginase-1⁺ infiltrating cells was significantly higher in the LysM^Cre/+SOCS3^fl/fl EAU retina than that in the WT EAU retina. In addition, bone marrow-derived macrophages and neutrophils from the LysM^Cre/+SOCS3^fl/fl mice express significantly higher levels of chemokine (C-C motif) ligand 2 and arginase-1 compared with those from WT mice. Inhibition of arginase using an l-arginine analog amino-2-borono-6-hexanoic suppressed inflammation-induced retinal angiogenesis without affecting the severity of inflammation. Our results suggest that SOCS3 critically controls the phenotype and function of macrophages and neutrophils under inflammatory conditions and loss of SOCS3 promotes the angiogenic phenotype of the cells through up-regulation of arginase-1.

Obesity-induced vascular dysfunction and arterial stiffening requires endothelial cell arginase 1

AIMS

Elevation of arginase activity has been linked to vascular dysfunction in diabetes and hypertension by a mechanism involving decreased nitric oxide (NO) bioavailability due to L-arginine depletion. Excessive arginase activity also can drive L-arginine metabolism towards the production of ornithine, polyamines, and proline, promoting proliferation of vascular smooth muscle cells and collagen formation, leading to perivascular fibrosis. We hypothesized that there is a specific involvement of arginase 1 expression within the vascular endothelial cells in this pathology.

METHODS AND RESULTS

To test this proposition, we used models of type 2 diabetes and metabolic syndrome. Studies were performed using wild type (WT), endothelial-specific arginase 1 knockout (EC-A1-/-) and littermate controls(A1con) mice fed high fat-high sucrose (HFHS) or normal diet (ND) for 6 months and isolated vessels exposed to palmitate-high glucose (PA/HG) media. Some WT mice or isolated vessels were treated with an arginase inhibitor, ABH [2-(S)-amino-6-boronohexanoic acid. In WT mice, the HFHS diet promoted increases in body weight, fasting blood glucose, and post-prandial insulin levels along with arterial stiffening and fibrosis, elevated blood pressure, decreased plasma levels of L-arginine, and elevated L-ornithine. The HFHS diet or PA/HG treatment also induced increases in vascular arginase activity along with oxidative stress, reduced vascular NO levels, and impaired endothelial-dependent vasorelaxation. All of these effects except obesity and hypercholesterolemia were prevented or significantly reduced by endothelial-specific deletion of arginase 1 or ABH treatment.

CONCLUSION

Vascular dysfunctions in diet-induced obesity are prevented by deletion of arginase 1 in vascular endothelial cells or arginase inhibition. These findings indicate that upregulation of arginase 1 expression/activity in vascular endothelial cells has an integral role in diet-induced cardiovascular dysfunction and metabolic syndrome.

Cyperaceae Species Are Potential Sources of Natural Mammalian Arginase Inhibitors with Positive Effects on Vascular Function

The inhibition of arginase is of substantial interest for the treatment of various diseases of public health interest including cardiovascular diseases. Using an ex vivo experiment on rat aortic rings and an in vitro assay with liver bovine purified arginase, it was demonstrated that several polyphenolic extracts from Cyperus and Carex species possess vasorelaxant properties and mammalian arginase inhibitory capacities. Phytochemical studies performed on these species led to the identification of eight compounds, including monomers, dimers, trimers, and tetramers of resveratrol. The potential of these stilbenes as inhibitors of mammalian arginase was assessed. Five compounds, scirpusin B (5), ε-viniferin (4), cyperusphenol B (6), carexinol A (7), and the new compound virgatanol (1), showed significant inhibition of arginase, with percentage inhibition ranging from 70% to 95% at 100 μg/mL and IC₅₀ values between 12.2 and 182.1 μM, confirming that these stilbenes may be useful for the development of new pharmaceutical products.

In vitro inhibition of phosphodiesterase-5 and arginase activities from rat penile tissue by two Nigerian herbs (Hunteria umbellata and Anogeissus leiocarpus)

BACKGROUND

Anogeissus leiocarpus and Hunteria umbellata have been reportedly used in traditional medicine for the management of erectile dysfunction (ED). However, the scientific basis for their use has not been well established. Therefore, this study was designed to investigate the inhibitory effects of water extractable phytochemicals of H. umbellata and A. leiocarpus on phosphodiesterase-5 (PDE-5) and arginase as well as pro-oxidants induced lipid peroxidation in rat penile tissue.

METHODS

The effects of the extracts on important enzymes (PDE-5 and arginase) linked with ED and pro-oxidants (Fe2+ and sodium nitroprusside) induced lipid peroxidation were investigated. Also, radicals scavenging and metal chelating abilities were determined. In addition, phenolic contents were determined and characterized using HPLC.

RESULTS

The results showed that both extracts inhibited PDE-5 and arginase activities in a dose-dependent manner. Inhibitory property of A. leiocarpus (IC50 - 174.19 μg/mL) was significantly better (p<0.05) than that of H. umbellata (IC50 - 537.72 μg/mL) in PDE-5 assay. The extracts were potent inhibitors of arginase than PDE-5, and these extracts were equally potent in inhibiting arginase. Furthermore, Fe2+ and sodium nitroprusside caused a significant increase in malondialdehyde content; however, both extracts reduced malondialdehyde level in concentration-dependent manner. It is noteworthy that both extracts scavenged radicals (OH* and ABTS*) and chelated Fe2+. HPLC analysis revealed abundance of rutin, chlorogenic acid, gallic acid, caffeic acid, and quercetin, among others.

CONCLUSIONS

The ability of the extracts to inhibit PDE-5, arginase and pro-oxidant induced lipid peroxidation, and chelate metal might suggest their folkloric use for the management of ED.

Inhibition of Rho kinase protects from ischaemia-reperfusion injury via regulation of arginase activity and nitric oxide synthase in type 1 diabetes

AIM

RhoA/Rho-associated kinase and arginase are implicated in vascular complications in diabetes. This study investigated whether RhoA/Rho-associated kinase and arginase inhibition protect from myocardial ischaemia-reperfusion injury in type 1 diabetes and the mechanisms behind these effects.

METHODS

Rats with streptozotocin-induced type 1 diabetes and non-diabetic rats were subjected to 30 min myocardial ischaemia and 2 h reperfusion after being randomized to treatment with (1) saline, (2) RhoA/Rho-associated kinase inhibitor hydroxyfasudil, (3) nitric oxide synthase inhibitor N^G-monomethyl-l-arginine monoacetate followed by hydroxyfasudil, (4) arginase inhibitor N-omega-hydroxy-nor-l-arginine, (5) N^G-monomethyl-l-arginine monoacetate followed by N-omega-hydroxy-nor-l-arginine or (6) N^G-monomethyl-l-arginine monoacetate given intravenous before ischaemia.

RESULTS

Myocardial arginase activity, arginase 2 expression and RhoA/Rho-associated kinase activity were increased in type 1 diabetes ( p < 0.05). RhoA/Rho-associated kinase inhibition and arginase inhibition significantly reduced infarct size in diabetic and non-diabetic rats ( p < 0.001). The cardioprotective effects of hydroxyfasudil and N-omega-hydroxy-nor-l-arginine in diabetes were abolished by nitric oxide synthase inhibition. RhoA/Rho-associated kinase inhibition attenuated myocardial arginase activity in diabetic rats via a nitric oxide synthase-dependent mechanism.

CONCLUSION

Inhibition of either RhoA/Rho-associated kinase or arginase protects from ischaemia-reperfusion injury in rats with type 1 diabetes via a nitric oxide synthase-dependent pathway. These results suggest that inhibition of RhoA/Rho-associated kinase and arginase constitutes a potential therapeutic strategy to protect the diabetic heart against ischaemia-reperfusion injury.

Investigation of Mammal Arginase Inhibitory Properties of Natural Ubiquitous Polyphenols by Using an Optimized Colorimetric Microplate Assay

Polyphenols are plant secondary metabolites which possess many positive effects on human health. Although these beneficial effects could be mediated through an increase in nitric oxide synthase activity, little is known regarding the inhibitory effect of polyphenols on mammal arginase, an enzyme which competes with nitric oxide synthase for their common substrate, L-arginine. The aim of the present study was to determine the potential of a series of polyphenols as mammalian arginase inhibitors and to identify some structure-activity relationships. For this purpose, we first developed a simple and cost-effective in vitro colorimetric microplate method using commercially-available mammal bovine liver arginase (b-ARG 1). Among the ten tested polyphenolic compounds [chlorogenic acid, piceatannol, resveratrol, (-)-epicatechin, taxifolin, quercetin, fisetin, caffeic acid, quinic acid, and kaempferol], cholorogenic acid and piceatannol exhibited the highest inhibitory activities (IC₅₀ = 10.6 and 12.1 µM, respectively) but were however less active as (S)-(2-Boronoethyl)-L-cysteine (IC₅₀ = 3.3 µM), used as reference compound. Enzyme kinetic studies showed that both chlorogenic acid and piceatannol are competitive arginase inhibitors. Structural data identified the importance of the caffeoyl (3,4-dihydroxycinnamoyl)-part and of the catechol function in the inhibitory activity of the tested compounds. These results identified chlorogenic acid and piceatannol as two potential core structures for the design of new arginase inhibitors.

[Arginase inhibitor nor-NOHA induces apoptosis and inhibits invasion and migration of HepG2 cells]

Objective To investigate the cell inhibitory effect of arginase inhibitor nor-NOHA on HepG2 hepatocellular carcinoma cells and related mechanism. Methods CCK-8 assay was used to detect the cell proliferation and flow cytometry to detect the apoptosis of HepG2 cells treated with (0, 0.5, 1.0, 2.0, 3.0) ng/μL nor-NOHA. The protein levels of arginase 1 (Arg1), P53, matrix metalloproteinase-2 (MMP-2), E-cadherin (ECD) were determined by Western blotting. Real time quantitative PCR was employed to examine the changes in the mRNA level of inducible nitric oxide synthase (iNOS). Griess assay was used to measure the concentration of nitric oxide (NO) in HepG2 cells. Transwell^TM assay and wound-healing assay were performed to evaluate the changes of the cell invasion and migration ability, respectively. Results nor-NOHA inhibited the proliferation and induced the apoptosis of HepG2 cells. It also decreased the expression levels of Arg1 and MMP-2, increased the expression levels of P53 and ECD as well as the production of NO; in addition, nor-NOHA inhibited the invasion and migration of HepG2 cells. Conclusion Nor-NOHA can induce cell apoptosis and inhibit the ability of invasion and migration of HepG2 cells by inhibiting Arg1, which is related with the increase of iNOS expression and the high concentration of NO.

Arginase Inhibitor 2,3,5,4'-Tetrahydroxystilbene-2-O-β-D-Glucoside Activates Endothelial Nitric Oxide Synthase and Improves Vascular Function

Endothelial arginase constrains the activity of endothelial nitric oxide synthase by reducing nitric oxide bioavailability, which contributes to vascular diseases. During screening, we identified a novel compound from the rhizome of Polygonum multiflorum (Polygonaceae), 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside (THSG), which inhibited arginase activity. THSG exhibited noncompetitive inhibition of arginase II and inhibited both arginases I and II in a dose-dependent manner. THSG-dependent arginase inhibition reciprocally increased nitric oxide production and decreased reactive oxygen species generation in aortic endothelia. These effects were associated with increased dimerization of endothelial nitric oxide synthase without changes in the protein expression levels of arginase I, arginase II, or endothelial nitric oxide synthase. In vascular tension assays, when aortic vessels from wild-type mice are incubated with THSG, responses to the nitric oxide-dependent vasorelaxant acetylcholine were augmented, but responses to an nitric oxide donor, sodium nitroprusside, were not affected. On the other hand, phenylephrine-dependent vasoconstriction was significantly retarded in THSG-treated vessels. In a high-cholesterol diet-fed atherogenic model mice (ApoE^-/-), THSG improved endothelial function by enhancement of the nitric oxide-cGMP pathway. Taken together, these results suggest that THSG may exert vasoprotective effects through augmentation of nitric oxide signaling by inhibiting arginase. Therefore, THSG may be useful in the treatment of vascular diseases that are derived from endothelial dysfunction, such as atherosclerosis.

Stachytarpheta cayennensis extract inhibits promastigote and amastigote growth in Leishmania amazonensis via parasite arginase inhibition

ETHNOPHARMACOLOGY RELEVANCE

Stachytarpheta cayennensis is a plant that is traditionally used to treat tegumentary leishmaniasis and as an anti-inflammatory agent.

AIM OF THE STUDY

This study aimed to evaluate the action of S. cayennensis extracts on the Leishmania (Leishmania) amazonensis arginase enzyme.

MATERIALS AND METHODS

S. cayennensis was collected from the Brazilian Amazon region. Aqueous extracts were fractionated with n-butanol. The leishmanicidal effects of the n-butanolic fraction (BUF) were evaluated in L. (L.) amazonensis promastigotes and amastigotes. BUF was tested against recombinant arginase from both L. (L.) amazonensis and macrophage arginase. Promastigote cultures and infected macrophage cultures were supplemented with L-ornithine to verify arginase inhibition. NMR analysis was used to identify the major components of BUF.

RESULTS

BUF showed an EC₅₀ of 51 and 32µg/mL against promastigotes and amastigotes of L. (L.) amazonensis, respectively. BUF contains a mixture of verbascoside and isoverbascoside (7:3 ratio) and is a potent L. (L.) amazonensis arginase inhibitor (IC₅₀=1.2µg/mL), while macrophage arginase was weakly inhibited (IC₅₀>1000µg/mL). The inhibition of arginase by BUF in promastigotes and amastigotes could be demonstrated by culture media supplementation with L-ornithine, a product of the hydrolysis of L-arginine by arginase.

CONCLUSIONS

Leishmanicidal effects of the S. cayennensis BUF fraction on L. (L.) amazonensis are associated with selective parasite arginase inhibition.

Arginase Inhibition Improves Microvascular Endothelial Function in Patients With Type 2 Diabetes Mellitus

OBJECTIVES

The development of microvascular complications in diabetes is a complex process in which endothelial dysfunction is important. Emerging evidence suggests that arginase is a key mediator of endothelial dysfunction in type 2 diabetes mellitus by reciprocally regulating nitric oxide bioavailability. The aim of this prospective intervention study was to test the hypothesis that arginase activity is increased and that arginase inhibition improves microvascular endothelial function in patients with type 2 diabetes and microvascular dysfunction.

DESIGN

Microvascular endothelium-dependent and -independent dilatation was determined in patients with type 2 diabetes (n = 12) and healthy age-matched control subjects (n = 12) with laser Doppler flowmetry during iontophoretic application of acetylcholine and sodium nitroprusside, respectively, before and after administration of the arginase inhibitor N^ω-hydroxy-nor-L-arginine (120 min). Plasma ratios of amino acids involved in arginase and nitric oxide synthase activities were determined. The laser Doppler flowmetry data were the primary outcome variable.

RESULTS

Microvascular endothelium-dependent dilatation was impaired in subjects with type 2 diabetes (P < .05). After administration of N^ω-hydroxy-nor-L-arginine, microvascular endothelial function improved significantly in patients with type 2 diabetes to the level observed in healthy controls. Endothelium-independent vasodilatation did not change significantly. Subjects with type 2 diabetes had higher levels of ornithine and higher ratios of ornithine/citrulline and ornithine/arginine (P < .05), suggesting increased arginase activity.

CONCLUSION

Arginase inhibition improves microvascular endothelial function in patients with type 2 diabetes and microvascular dysfunction. Arginase inhibition may represent a novel therapeutic strategy to improve microvascular endothelial function in patients with type 2 diabetes.

Arginase Inhibition Restores Peroxynitrite-Induced Endothelial Dysfunction via L-Arginine-Dependent Endothelial Nitric Oxide Synthase Phosphorylation

PURPOSE

Peroxynitrite plays a critical role in vascular pathophysiology by increasing arginase activity and decreasing endothelial nitric oxide synthase (eNOS) activity. Therefore, the aims of this study were to investigate whether arginase inhibition and L-arginine supplement could restore peroxynitrite-induced endothelial dysfunction and determine the involved mechanism.

MATERIALS AND METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with SIN-1, a peroxynitrite generator, and arginase activity, nitrite/nitrate production, and expression levels of proteins were measured. eNOS activation was evaluated via Western blot and dimer blot analysis. We also tested nitric oxide (NO) and reactive oxygen species (ROS) production and performed a vascular tension assay.

RESULTS

SIN-1 treatment increased arginase activity in a time- and dose-dependent manner and reciprocally decreased nitrite/nitrate production that was prevented by peroxynitrite scavenger in HUVECs. Furthermore, SIN-1 induced an increase in the expression level of arginase I and II, though not in eNOS protein. The decreased eNOS phosphorylation at Ser1177 and the increased at Thr495 by SIN-1 were restored with arginase inhibitor and L-arginine. The changed eNOS phosphorylation was consistent in the stability of eNOS dimers. SIN-1 decreased NO production and increased ROS generation in the aortic endothelium, all of which was reversed by arginase inhibitor or L-arginine. N(G)-Nitro-L-arginine methyl ester (L-NAME) prevented SIN-1-induced ROS generation. In the vascular tension assay, SIN-1 enhanced vasoconstrictor responses to U46619 and attenuated vasorelaxant responses to acetylcholine that were reversed by arginase inhibition.

CONCLUSION

These findings may explain the beneficial effect of arginase inhibition and L-arginine supplement on endothelial dysfunction under redox imbalance-dependent pathophysiological conditions.

Arginase Inhibition Reverses Endothelial Dysfunction, Pulmonary Hypertension, and Vascular Stiffness in Transgenic Sickle Cell Mice

BACKGROUND

In sickle cell disease (SCD), hemolysis results in the release and activation of arginase, an enzyme that reciprocally regulates nitric oxide (NO) synthase activity and thus, NO production. Simply supplementing the common substrate L-arginine, however, fails to improve NO bioavailability. In this study, we tested the hypothesis that arginase inhibition would improve NO bioavailability and thereby attenuate systemic and pulmonary vascular endothelial dysfunction in transgenic mice with SCD.

METHODS

We studied 5-month-old transgenic sickle cell (SC) mice and age matched wild-type (WT) controls. SC mice were treated with the arginase inhibitor, 2(S)-amino-6-boronohexanoic acid (ABH; approximately 400 μg/d) for 4 weeks or left untreated.

RESULTS

Vascular arginase activity was significantly higher at baseline in untreated SC mice compared to WT controls (SC versus WT, 346 ± 69.3 vs 69 ± 17.3 pmol urea/mg protein/minute; P = 0.0043; n = 4-5 animals per group). Treatment with ABH may significantly decrease arginase activity to levels near WT controls (SC + ABH 125.2 ± 17.3 pmol urea/mg protein/minute; P = 0.0213). Aortic strips from untreated SC mice showed decreased NO and increased reactive oxygen species (ROS) production (NO: fluorescence rate 0.76 ± 0.14 vs 1.34 ± 0.17 RFU/s; P = 0.0005 and ROS: fluorescence rate 3.96 ± 1.70 vs 1.63 ± 1.20 RFU/s, P = 0.0039; n = 3- animals per group). SC animals treated with ABH for 4 weeks demonstrated NO (fluorescence rate: 1.16 ± 0.16) and ROS (fluorescence rate: 2.02 ± 0.45) levels comparable with age-matched WT controls (n = 3- animals per group). The maximal endothelial-dependent vasorelaxation response to acetylcholine was impaired in aortic rings from SC mice compared with WT (57.7% ± 8.4% vs 80.3% ± 11.0%; P = 0.02; n = 6 animals per group). The endothelial-independent response was not different between groups. In SC mice, the right ventricular cardiac output index and end-systolic elastance were similar (4.60 ± 0.51 vs 2.9 ± 0.85 mL/min/100 g and 0.89 ± 0.48 vs 0.58 ± 0.11 mm Hg/μL), whereas the pulmonary vascular resistance index and right ventricular end-systolic pressure were greater (2.9 ± 0.28 vs 5.5 ± 2.0 mm Hg × min/μL/100 g and 18.9 ± 1.1 vs 23.1 ± 4.0 mm Hg; n = 8 animals per group). Pulse wave velocity (a measure of arterial stiffness) was greater in SC mice compared with WT (3.74 ± 0.54 vs 3.25 ± 0.21 m/s; n = 20 animals per group), arginase inhibition for 4 weeks significantly reduced the vascular SC phenotype to one similar to WT animals (P = 0.0009).

CONCLUSIONS

Arginase inhibition improves NO bioavailability and thereby attenuates systemic and pulmonary vascular endothelial dysfunction in transgenic mice with SCD. Therefore, arginase is a potential therapeutic target in the treatment of cardiovascular dysfunction in SCD.

Asymmetric dimethylarginine (ADMA) elevation and arginase up-regulation contribute to endothelial dysfunction related to insulin resistance in rats and morbidly obese humans

KEY POINTS

The presence of insulin resistance (IR) is determinant for endothelial dysfunction associated with obesity. Although recent studies have implicated the involvement of mitochondrial superoxide and inflammation in the defective nitric oxide (NO)-mediated responses and subsequent endothelial dysfunction in IR, other mechanisms could compromise this pathway. In the present study, we assessed the role of asymmetric dimethylarginine (ADMA) and arginase with respect to IR-induced impairment of endothelium-dependent vasodilatation in human morbid obesity and in a non-obese rat model of IR. We show that both increased ADMA and up-regulated arginase are determinant factors in the alteration of the l-arginine/NO pathway associated with IR in both models and also that acute treatment of arteries with arginase inhibitor or with l-arginine significantly alleviate endothelial dysfunction. These results help to expand our knowledge regarding the mechanisms of endothelial dysfunction that are related to obesity and IR and establish potential therapeutic targets for intervention.

ABSTRACT

Insulin resistance (IR) is determinant for endothelial dysfunction in human obesity. Although we have previously reported the involvement of mitochondrial superoxide and inflammation, other mechanisms could compromise NO-mediated responses in IR. We evaluated the role of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) and arginase with respect to IR-induced impairment of l-arginine/NO-mediated vasodilatation in human morbid obesity and in a non-obese rat model of IR. Bradykinin-induced vasodilatation was evaluated in microarteries derived from insulin-resistant morbidly obese (IR-MO) and non-insulin-resistant MO (NIR-MO) subjects. Defective endothelial vasodilatation in IR-MO was improved by l-arginine supplementation. Increased levels of ADMA were detected in serum and adipose tissue from IR-MO. Serum ADMA positively correlated with IR score and negatively with pD2 for bradykinin. Gene expression determination by RT-PCR revealed not only the decreased expression of ADMA degrading enzyme dimethylarginine dimethylaminohydrolase (DDAH)1/2 in IR-MO microarteries, but also increased expression of arginase-2. Arginase inhibition improved endothelial vasodilatation in IR-MO. Analysis of endothelial vasodilatation in a non-obese IR model (fructose-fed rat) confirmed an elevation of circulating and aortic ADMA concentrations, as well as reduced DDAH aortic content and increased aortic arginase activity in IR. Improvement of endothelial vasodilatation in IR rats by l-arginine supplementation and arginase inhibition provided functional corroboration. These results demonstrate that increased ADMA and up-regulated arginase contribute to endothelial dysfunction as determined by the presence of IR in human obesity, most probably by compromising arginine availability. The results provide novel insights regarding the mechanisms of endothelial dysfunction related to obesity and IR and establish potential therapeutic targets for intervention.

Verbascoside Inhibits Promastigote Growth and Arginase Activity of Leishmania amazonensis

Verbascoside (1) is a phenylethanoid glycoside that has antileishmanial activity against Leishmania infantum and Leishmania donovani. In this study, we verified the activity of 1 on Leishmania amazonensis and arginase inhibition. Compound 1 showed an EC50 of 19 μM against L. amazonensis promastigotes and is a competitive arginase inhibitor (Ki = 0.7 μM). Docking studies were performed to assess the interaction of 1 with arginase at the molecular level. Arginase is an enzyme of the polyamine biosynthesis pathway that is important to parasite infectivity, and the results of our study suggest that 1 could be useful to develop new approaches for treating leishmaniasis.

Arginase Flavonoid Anti-Leishmanial in Silico Inhibitors Flagged against Anti-Targets

Arginase, a drug target for the treatment of leishmaniasis, is involved in the biosynthesis of polyamines. Flavonoids are interesting natural compounds found in many foods and some of them may inhibit this enzyme. The MetIDB database containing 5667 compounds was screened using an EIIP/AQVN filter and 3D QSAR to find the most promising candidate compounds. In addition, these top hits were screened in silico versus human arginase and an anti-target battery consisting of cytochromes P450 2a6, 2c9, 3a4, sulfotransferase, and the pregnane-X-receptor in order to flag their possible interactions with these proteins involved in the metabolism of substances. The resulting compounds may have promise to be further developed for the treatment of leishmaniasis.

Arginase inhibitor attenuates pulmonary artery hypertension induced by hypoxia

Hypoxia-induced pulmonary arterial hypertension (HPAH) is a refractory disease characterized by increased proliferation of pulmonary vascular smooth cells and progressive pulmonary vascular remodeling. The level of nitric oxide (NO), a potential therapeutic vasodilator, is low in PAH patients. L-arginine can be converted to either beneficial NO by nitric oxide synthases or to harmful urea by arginase. In the present study, we aimed to investigate whether an arginase inhibitor, S-(2-boronoethyl)-L-cysteine ameliorates HPAH in vivo and vitro. In a HPAH mouse model, we assessed right ventricle systolic pressure (RVSP) by an invasive method, and found that RSVP was elevated under hypoxia, but was attenuated upon arginase inhibition. Human pulmonary artery smooth muscle cells (HPASMCs) were cultured under hypoxic conditions, and their proliferative capacity was determined by cell counting and flow cytometry. The levels of cyclin D1, p27, p-Akt, and p-ERK were detected by RT-PCR or Western blot analysis. Compared to hypoxia group, arginase inhibitor inhibited HPASMCs proliferation and reduced the levels of cyclin D1, p-Akt, p-ERK, while increasing p27 level. Moreover, in mouse models, compared to control group, hypoxia increased cyclin D1 expression but reduced p27 expression, while arginase inhibitor reversed the effects of hypoxia. Taken together, these results suggest that arginase plays an important role in increased proliferation of HPASMCs induced by hypoxia and it is a potential therapeutic target for the treatment of pulmonary hypertensive disorders.

Effect of Pneumoperitoneum on Oxidative Stress and Inflammation via the Arginase Pathway in Rats

PURPOSE

Oxidative stress during CO₂ pneumoperitoneum is reported to be associated with decreased bioactivity of nitric oxide (NO). However, the changes in endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and arginase during CO₂ pneumoperitoneum have not been elucidated.

MATERIALS AND METHODS

Thirty male Sprague-Dawley rats were randomized into three groups. After anesthesia induction, the abdominal cavities of the rats of groups intra-abdominal pressure (IAP)-10 and IAP-20 were insufflated with CO₂ at pressures of 10 mm Hg and 20 mm Hg, respectively, for 2 hours. The rats of group IAP-0 were not insufflated. After deflation, plasma NO was measured, while protein expression levels and activity of eNOS, iNOS, arginase (Arg) I, and Arg II were analyzed with aorta and lung tissue samples.

RESULTS

Plasma nitrite concentration and eNOS expression were significantly suppressed in groups IAP-10 and IAP-20 compared to IAP-0. While expression of iNOS and Arg I were comparable between the three groups, Arg II expression was significantly greater in group IAP-20 than in group IAP-0. Activity of eNOS was significantly lower in groups IAP-10 and IAP-20 than in group IAP-0, while iNOS activity was significantly greater in group IAP-20 than in groups IAP-0 and IAP-10. Arginase activity was significantly greater in group IAP-20 than in groups IAP-0 and IAP-10.

CONCLUSION

The activity of eNOS decreases during CO₂ pneumoperitoneum, while iNOS activity is significantly increased, a change that contributes to increased oxidative stress and inflammation. Moreover, arginase expression and activity is increased during CO₂ pneumoperitoneum, which seems to act inversely to the NO system.

Effects of Arginase Inhibition in Hypertensive Hyperthyroid Rats

BACKGROUND

This study analyzed the effects of chronic administration of N[omega]-hydroxy-nor-l-arginine (nor-NOHA), an inhibitor of arginase, on the hemodynamic, oxidative stress, morphologic, metabolic, and renal manifestations of hyperthyroidism in rats.

METHODS

Four groups of male Wistar rats were used: control, nor-NOHA-treated (10 mg/kg/day), thyroxine (T4)-treated (75 μg/rat/day), and thyroxine- plus nor-NOHA-treated rats. All treatments were maintained for 4 weeks. Body weight, tail systolic blood pressure (SBP), and heart rate (HR) were recorded weekly. Finally, morphologic, metabolic, plasma, and renal variables were measured. Arginase I and II protein abundance and arginase activity were measured in aorta, heart, and kidney.

RESULTS

The T4 group showed increased arginase I and II protein abundance, arginase activity, SBP, HR, plasma nitrates/nitrites (NOx), brainstem and urinary isoprostanes, proteinuria and cardiac and renal hypertrophy in comparison to control rats. In hyperthyroid rats, chronic nor-NOHA prevented the increase in SBP and HR and decreased proteinuria in association with an increase in plasma NOx and a decrease in brainstem and urinary isoprostanes. In normal rats, nor-NOHA treatment did not significantly change any hemodynamic, morphologic, or renal variables. Acute nor-NOHA administration did not affect renal or systemic hemodynamic variables in normal or T4-treated rats.

CONCLUSION

Hyperthyroidism in rats is associated with the increased expression and activity of arginase in aorta, heart, and kidney. Chronic arginase inhibition with nor-NOHA suppresses the characteristic hemodynamic manifestations of hyperthyroidism in association with a reduced oxidative stress. These results indicate an important role for arginase pathway alterations in the cardiovascular and renal abnormalities of hyperthyroidism.

FoxO4 promotes early inflammatory response upon myocardial infarction via endothelial Arg1

RATIONALE

Inflammation in post-myocardial infarction (MI) is necessary for myocyte repair and wound healing. Unfortunately, it is also a key component of subsequent heart failure pathology. Transcription factor forkhead box O4 (FoxO4) regulates a variety of biological processes, including inflammation. However, its role in MI remains unknown.

OBJECTIVE

To test the hypothesis that FoxO4 promotes early post-MI inflammation via endothelial arginase 1 (Arg1).

METHODS AND RESULTS

We induced MI in wild-type and FoxO4(-/-) mice. FoxO4(-/-) mice had a significantly higher post-MI survival, better cardiac function, and reduced infarct size. FoxO4(-/-) hearts had significantly fewer neutrophils, reduced expression of cytokines, and competitive nitric oxide synthase inhibitor Arg1. We generated conditional FoxO4 knockout mice with FoxO4 deleted in cardiac mycoytes or endothelial cells. FoxO4 endothelial cell-specific knockout mice showed significant post-MI improvement of cardiac function and reduction of neutrophil accumulation and cytokine expression, whereas FoxO4 cardiac mycoyte-specific knockout mice had no significant difference in cardiac function and post-MI inflammation from those of control littermates. FoxO4 binds the Foxo-binding site in the Arg1 promoter and activates Arg1 transcription. FoxO4 knockdown in human aortic endothelial cells upregulated nitric oxide on ischemia and suppressed monocyte adhesion that can be reversed by ectopic-expression of Arg1. Furthermore, chemical inhibition of Arg1 in wild-type mice had similar cardioprotection and reduced inflammation after MI as FoxO4 inactivation and administration of nitric oxide synthase inhibitor to FoxO4 KO mice reversed the beneficial effects of FoxO4 deletion on post-MI cardiac function.

CONCLUSIONS

FoxO4 activates Arg1 transcription in endothelial cells in response to MI, leading to downregulation of nitric oxide and upregulation of neutrophil infiltration to the infarct area.

Effect of polyamine metabolism inhibitors on Lewis lung carcinoma growth and metastasis

AIM

To study the influence of polyamine metabolism inhibitors on the growth, metastasis and ornithine decarboxylase (ODC) activity of Lewis lung carcinoma.

MATERIALS AND METHODS

Experiments were performed on female mice C57Bl/6 with Lewis lung carcinoma. Nω-hydroxy-nor-arginine (nor-NOHA) and α-difluoromethylornithine (DFMO) were used as arginase and ODC inhibitors, correspondently. Inhibition of tumor growth was calculated by comparison of tumor volume in the treated and control groups. The average number of metastases per animal in the group and the average volume of pulmonary metastases per animal in the group have been determined. Determination of ODC - the key enzyme of the polyamine synthesis - in the samples of experimental tumors was performed by method of Luqman S.

RESULTS

Administration of DFMO or it's combination with nor-NOHA resulted in the decrease of tumor growth rate, number and volume of lung metastases and was accompanied with reduced ODC activity in tumor tissue.

CONCLUSION

Modifiers of polyamine metabolism may be considered as promising targeted cancer therapy.

Arginase: an old enzyme with new tricks

Arginase has roots in early life-forms. It converts L-arginine to urea and ornithine. The former provides protection against NH3; the latter serves to stimulate cell growth and other physiological functions. Excessive arginase activity in mammals has been associated with cardiovascular and nervous system dysfunction and disease. Two relevant aspects of this elevated activity may be involved in these disease states. First, excessive arginase activity reduces the supply of L-arginine needed by nitric oxide (NO) synthase to produce NO. Second, excessive production of ornithine leads to vascular structural problems and neural toxicity. Recent research has identified inflammatory agents and reactive oxygen species (ROS) as drivers of this pathologic elevation of arginase activity and expression. We review the involvement of arginase in cardiovascular and nervous system dysfunction, and discuss potential therapeutic interventions targeting excess arginase.

Upregulation of arginase activity contributes to intracellular ROS production induced by high glucose in H9c2 cells

Arginase is upregulated in some tissues under diabetes states. Arginase can compete with nitroxide synthase (NOS) for the common substrate L-arginine and thus increases oxidative stress by NOS uncoupling. We want to analyze whether arginase is upregulated and contribute to oxidative stress in H9c2 cells during high glucose treatment. H9c2 cells were cultured in normal or high glucose DMEM. Arginase activity increased in parallel with increased cell death and oxidative stress. Arginase inhibitor N ω-hydroxy-nor-l-arginine (nor-NOHA) and NOS inhibitor N ω-nitro-l-arginine methyl ester (L-NAME) could reverse these effects. Despite of upregulated NOS activity, NO production was impaired which could be preserved by nor-NOHA, suggesting a decreased substrate availability of NOS due to increased arginase activity. L-arginine supplementation decreased superoxide production while it could not protect cells from death. Upregulated arginase activity in H9c2 treated with high glucose can cause NOS uncoupling and subsequently reactive oxygen species augmentation and cell death. These findings suggest that arginase will be a novel therapeutic target for treatment of diabetic cardiomyopathy.

Pomegranate juice polyphenols induce a phenotypic switch in macrophage polarization favoring a M2 anti-inflammatory state

It was documented that pomegranate has anti-inflammatory effects. In this study, we investigated a direct effect of pomegranate juice (PJ) and its polyphenols on macrophage inflammatory phenotype. In vitro, PJ and its major polyphenols dose-dependently attenuated macrophage response to M1 proinflammatory activation in J774.A1 macrophage-like cell line. This was evidenced by a significant decrease in TNFα and IL-6 secretion in response to stimulation by IFNγ and Lipopolysaccharide. In addition, PJ and punicalagin dose-dependently promoted the macrophages toward a M2 anti-inflammatory phenotype, as determined by a significant increase in the spontaneous secretion of IL-10. In mice, supplementation with dietary PJ substantially inhibited the M2 to M1 macrophage phenotypic shift associated with age, toward a favorable anti-inflammatory M2 phenotype. This effect was also reflected in the mice atherosclerotic plaques, as evaluated by the distinct expression of arginase isoforms. PJ consumption inhibited the increment of arginase II (Arg II, M1) mRNA expression during aging, and maintained the levels of Arg I (M2) expression similar to those in young mice aorta. This study demonstrates, for the first time, that pomegranate polyphenols directly suppress macrophage inflammatory responses and promote M1 to M2 switch in macrophage phenotype. Furthermore, this study indicates that PJ consumption may inhibit the progressive proinflammatory state in the aorta along atherosclerosis development with aging, due to a switch in macrophage phenotype from proinflammatory M1 to anti-inflammatory M2.

Arginase 2 deficiency prevents oxidative stress and limits hyperoxia-induced retinal vascular degeneration

Background

Hyperoxia exposure of premature infants causes obliteration of the immature retinal microvessels, leading to a condition of proliferative vitreoretinal neovascularization termed retinopathy of prematurity (ROP). Previous work has demonstrated that the hyperoxia-induced vascular injury is mediated by dysfunction of endothelial nitric oxide synthase resulting in peroxynitrite formation. This study was undertaken to determine the involvement of the ureahydrolase enzyme arginase in this pathology.

Methods and Findings

Studies were performed using hyperoxia-treated bovine retinal endothelial cells (BRE) and mice with oxygen-induced retinopathy (OIR) as experimental models of ROP. Treatment with the specific arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) prevented hyperoxia-induced apoptosis of BRE cells and reduced vaso-obliteration in the OIR model. Furthermore, deletion of the arginase 2 gene protected against hyperoxia-induced vaso-obliteration, enhanced physiological vascular repair, and reduced retinal neovascularization in the OIR model. Additional deletion of one copy of arginase 1 did not improve the vascular pathology. Analyses of peroxynitrite by quantitation of its biomarker nitrotyrosine, superoxide by dihydroethidium imaging and NO formation by diaminofluoroscein imaging showed that the protective actions of arginase 2 deletion were associated with blockade of superoxide and peroxynitrite formation and normalization of NOS activity.

Conclusions

Our data demonstrate the involvement of arginase activity and arginase 2 expression in hyperoxia-induced vascular injury. Arginase 2 deletion prevents hyperoxia-induced retinal vascular injury by preventing NOS uncoupling resulting in decreased reactive oxygen species formation and increased nitric oxide bioavailability.

Effect of arginase inhibition on ischemia-reperfusion injury in patients with coronary artery disease with and without diabetes mellitus

BACKGROUND

Arginase competes with nitric oxide synthase for their common substrate L-arginine. Up-regulation of arginase in coronary artery disease (CAD) and diabetes mellitus may reduce nitric oxide bioavailability contributing to endothelial dysfunction and ischemia-reperfusion injury. Arginase inhibition reduces infarct size in animal models. Therefore the aim of the current study was to investigate if arginase inhibition protects from endothelial dysfunction induced by ischemia-reperfusion in patients with CAD with or without type 2 diabetes (

CLINICAL TRIAL REGISTRATION NUMBER

NCT02009527).

METHODS

Male patients with CAD (n = 12) or CAD + type 2 diabetes (n = 12), were included in this cross-over study with blinded evaluation. Endothelium-dependent vasodilatation was assessed by flow-mediated dilatation (FMD) of the radial artery before and after 20 min ischemia-reperfusion during intra-arterial infusion of the arginase inhibitor (Nω-hydroxy-nor-L-arginine, 0.1 mg/min) or saline.

RESULTS

The forearm ischemia-reperfusion was well tolerated. Endothelium-independent vasodilatation was assessed by sublingual nitroglycerin. Ischemia-reperfusion decreased FMD in patients with CAD from 12.7±5.2% to 7.9±4.0% during saline administration (P<0.05). Nω-hydroxy-nor-L-arginine administration prevented the decrease in FMD in the CAD group (10.3±4.3% at baseline vs. 11.5±3.6% at reperfusion). Ischemia-reperfusion did not significantly reduce FMD in patients with CAD + type 2 diabetes. However, FMD at reperfusion was higher following nor-NOHA than following saline administration in both groups (P<0.01). Endothelium-independent vasodilatation did not differ between the occasions.

CONCLUSIONS

Inhibition of arginase protects against endothelial dysfunction caused by ischemia-reperfusion in patients with CAD. Arginase inhibition may thereby be a promising therapeutic strategy in the treatment of ischemia-reperfusion injury.

Arginase inhibition ameliorates hepatic metabolic abnormalities in obese mice

OBJECTIVES

We examined whether arginase inhibition influences hepatic metabolic pathways and whole body adiposity in diet-induced obesity.

METHODS AND RESULTS

After obesity induction by a high fat diet (HFD), mice were fed either the HFD or the HFD with an arginase inhibitor, Nω-hydroxy-nor-L-arginine (nor-NOHA). Nor-NOHA significantly prevented HFD-induced increases in body, liver, and visceral fat tissue weight, and ameliorated abnormal lipid profiles. Furthermore, nor-NOHA treatment reduced lipid accumulation in oleic acid-induced hepatic steatosis in vitro. Arginase inhibition increased hepatic nitric oxide (NO) in HFD-fed mice and HepG2 cells, and reversed the elevated mRNA expression of hepatic genes in lipid metabolism. Expression of phosphorylated 5' AMPK-activated protein kinase α was increased by arginase inhibition in the mouse livers and HepG2 cells.

CONCLUSIONS

Arginase inhibition ameliorated obesity-induced hepatic lipid abnormalities and whole body adiposity, possibly as a result of increased hepatic NO production and subsequent activation of metabolic pathways involved in hepatic triglyceride metabolism and mitochondrial function.

Isolation of arginase inhibitors from the bioactivity-guided fractionation of Byrsonima coccolobifolia leaves and stems

Byrsonima coccolobifolia leaf and stem extracts were studied in the search for possible leishmanicidal compounds using arginase (ARG) from Leishmania amazonensis as a molecular target. Flavonoids 1b, 1e-1g, 2a, 2b, and 2d-2f showed significant inhibitory activity, with IC50 values ranging from 0.9 to 4.8 μM. The kinetics of the most active compounds were determined. Flavonoids 1e, 1f, 2a, 2b, and 2e were characterized as noncompetitive inhibitors of ARG with dissociation constants (Ki) ranging from 0.24 to 3.8 μM, demonstrating strong affinity. Structure-activity relationship studies revealed some similarities in the structural features of flavonoids related to ARG activity.

Inhibition of Leishmania (Leishmania) amazonensis and rat arginases by green tea EGCG, (+)-catechin and (-)-epicatechin: a comparative structural analysis of enzyme-inhibitor interactions

Epigallocatechin-3-gallate (EGCG), a dietary polyphenol (flavanol) from green tea, possesses leishmanicidal and antitrypanosomal activity. Mitochondrial damage was observed in Leishmania treated with EGCG, and it contributed to the lethal effect. However, the molecular target has not been defined. In this study, EGCG, (+)-catechin and (−)-epicatechin were tested against recombinant arginase from Leishmania amazonensis (ARG-L) and rat liver arginase (ARG-1). The compounds inhibit ARG-L and ARG-1 but are more active against the parasite enzyme. Enzyme kinetics reveal that EGCG is a mixed inhibitor of the ARG-L while (+)-catechin and (−)-epicatechin are competitive inhibitors. The most potent arginase inhibitor is (+)-catechin (IC₅₀ = 0.8 µM) followed by (−)-epicatechin (IC₅₀ = 1.8 µM), gallic acid (IC₅₀ = 2.2 µM) and EGCG (IC₅₀ = 3.8 µM). Docking analyses showed different modes of interaction of the compounds with the active sites of ARG-L and ARG-1. Due to the low IC₅₀ values obtained for ARG-L, flavanols can be used as a supplement for leishmaniasis treatment.

Arginase regulates red blood cell nitric oxide synthase and export of cardioprotective nitric oxide bioactivity

The theory that red blood cells (RBCs) generate and release nitric oxide (NO)-like bioactivity has gained considerable interest. However, it remains unclear whether it can be produced by endothelial NO synthase (eNOS), which is present in RBCs, and whether NO can escape scavenging by hemoglobin. The aim of this study was to test the hypothesis that arginase reciprocally controls NO formation in RBCs by competition with eNOS for their common substrate arginine and that RBC-derived NO is functionally active following arginase blockade. We show that rodent and human RBCs contain functional arginase 1 and that pharmacological inhibition of arginase increases export of eNOS-derived nitrogen oxides from RBCs under basal conditions. The functional importance was tested in an ex vivo model of myocardial ischemia-reperfusion injury. Inhibitors of arginase significantly improved postischemic functional recovery in rat hearts if administered in whole blood or with RBCs in plasma. By contrast, arginase inhibition did not improve postischemic recovery when administered with buffer solution or plasma alone. The protective effect of arginase inhibition was lost in the presence of a NOS inhibitor. Moreover, hearts from eNOS(-/-) mice were protected when the arginase inhibitor was given with blood from wild-type donors. In contrast, when hearts from wild-type mice were given blood from eNOS(-/-) mice, the arginase inhibitor failed to protect against ischemia-reperfusion. These results strongly support the notion that RBCs contain functional eNOS and release NO-like bioactivity. This process is under tight control by arginase 1 and is of functional importance during ischemia-reperfusion.