Arginase II Promotes Macrophage Inflammatory Responses Through Mitochondrial Reactive Oxygen Species, Contributing to Insulin Resistance and Atherogenesis

Arginine as host directed therapy in tuberculosis: insights from modulating arginine metabolism by supplementation and arginase inhibition

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a global health challenge. Arginine metabolism is central to immune responses, regulating nitric oxide (NO) production via inducible NO synthase (Nos2) and competing pathways mediated by arginases (Arg1 and Arg2). This study examines the impact of arginine supplementation and arginase inhibition during the acute phase of Mtb infection in mouse lungs, focusing on immune function, lung pathology, and mitochondrial function. Arginine supplementation enhanced Nos2 expression, promoted mitophagy, and supported angiogenesis and/or tissue repair by upregulating Vegfa. These mechanisms synergized to balance pro-inflammatory responses with tissue repair, improving immune defense while mitigating lung damage. In contrast, arginase inhibition disrupted Vegfa-mediated immune homeostasis, and impaired mitophagy, leading to exacerbated lung pathology. These findings underscore the complementary roles of Nos2 and arginase-mediated pathways in maintaining immune equilibrium during Mtb infection. Our results highlight arginine supplementation as a promising host-directed therapy for TB, capable of enhancing protective immunity and facilitating tissue repair. Conversely, caution is warranted for strategies targeting arginase due to potential adverse effects on inflammation resolution and mitochondrial quality control. Future studies should explore the long-term efficacy of arginine-based therapies and their integration with existing antibiotic regimens for optimal TB management.

Supplementary Information

The online version contains supplementary material available at 10.1186/s44280-025-00070-6.

Arginase-II promotes melanoma and lung cancer cell growth by regulating Sirt3-mtROS axis

Background

Aberrant mitochondrial metabolism is a key source of massive mitochondrial reactive oxygen species (mtROS) in tumour cells. Arginase-II (Arg-II), a widely expressed mitochondrial metabolic enzyme, has recently been shown to enhance mtROS production and melanoma progression. However, how Arg-II enhances mtROS and whether mtROS is involved in stimulation of cancer cell proliferation and migration remain unclear.

Methods and results

Here, we show that ablation of arg-ii suppresses cell growth, migration, nuclear deformation, and DNA damage in melanoma cells. Vice versa, overexpression of arg-ii in melanoma cells promotes melanoma cell growth and migration accompanied by enhanced nuclear deformation and DNA damage. Ablation or overexpression of arg-ii reduces or enhances mtROS, respectively, accounting for the effects of Arg-II on melanoma growth, migration, and DNA damage. Further data demonstrate that Arg-II enhances mtROS through decreasing Sirtuin 3 (Sirt3) levels. Silencing sirt3 promotes melanoma growth, migration, nuclear deformation, and DNA damage through enhancing mtROS. In supporting of these findings, overexpression of sirt3 prevented Arg-II-induced mtROS production with concomitant prevention of Arg-II-induced cell growth, migration, nuclear deformation and DNA damage. Furthermore, we show that upregulation of Arg-II under hypoxia induces nuclear deformation and DNA damage through suppressing Sirt3. Similar results are obtained in A549 human lung carcinoma cells. In addition, analysis of publicly accessible datasets reveals that elevated arg-ii mRNA levels in human tumor samples including skin cutaneous melanoma and lung cancers associate with poorer prognosis.

Conclusion

Altogether, our findings demonstrate a critical role of Arg-II-Sirt3-mtROS cascade in promoting melanoma growth, migration, nuclear deformation, and DNA damage linking to melanoma progression and malignancy, which could be therapeutic targets for cancers such as melanoma and lung carcinoma.

Arginine metabolism in myeloid cells in health and disease

Metabolic flexibility is key for the function of myeloid cells. Arginine metabolism is integral to the regulation of myeloid cell responses. Nitric oxide (NO) production from arginine is vital for the antimicrobial and pro-inflammatory responses. Conversely, the arginase 1 (ARG1)-dependent switch between the branch of NO production and polyamine synthesis downregulates inflammation and promotes recovery of tissue homeostasis. Creatine metabolism is key for energy supply and proline metabolism is required for collagen synthesis. Myeloid ARG1 also regulates extracellular arginine availability and T cell responses in parasitic diseases and cancer. Cancer, surgery, sepsis and persistent inflammation in chronic inflammatory diseases, such as neuroinflammatory diseases or arthritis, are associated with dysregulation of arginine metabolism in myeloid cells. Here, we review current knowledge on arginine metabolism in different myeloid cell types, such as macrophages, neutrophils, microglia, osteoclasts, tumor-associated macrophages (TAMs), tumor-associated neutrophils (TANs) and myeloid-derived suppressor cells (MDSCs). A deeper understanding of the function of arginine metabolism in myeloid cells will improve our knowledge on the pathology of several diseases and may set the platform for novel therapeutic applications.

Linarin Identified as a Bioactive Compound of Lycii Cortex Ameliorates Insulin Resistance and Inflammation Through the c-FOS/ARG2 Signaling Axis

Insulin resistance (IR) is a central pathophysiological process underlying numerous chronic metabolic disorders, including type 2 diabetes and obesity. Lycii Cortex, a widely used traditional Chinese herb, has demonstrated potential benefits in preventing and managing diabetes and IR. Whereas, the specific bioactive compounds responsible for these protective effects and their underlying mechanisms of action remain elusive. This study aimed to identify the bioactive components within Lycii Cortex that contribute to its anti-diabetic effects and to elucidate the molecular mechanisms underlying its beneficial actions on insulin resistance. Network pharmacology and molecular docking analyses were employed to identify the potential active compounds in Lycii Cortex and their corresponding target proteins. An in vitro model of IR was established using palmitic acid (PA)-treated HepG2 cells. Cell viability was assessed using the CCK-8 assay, while glucose uptake was evaluated by 2-NBDG staining and extracellular glucose measurement. To validate the in vitro findings, an in vivo model of obesity-induced IR was established using high-fat diet (HFD)-fed mice. The network pharmacology analysis preliminarily identified 13 candidate chemicals and 10 hub LyC and IR-related genes (LIRRGs). Molecular docking analysis demonstrates that Linarin as the potential active component exhibits the greatest potential to target c-FOS for preventing obesity-induced IR. Enrichment analysis suggested that Linarin-targeted pathways are correlated with inflammation. In vitro experimental validation demonstrated that Linarin was capable of protecting against PA-induced IR in HepG2 cells evidenced by improving glucose uptake ability and reducing extracellular glucose content. Additionally, we found that Linarin ablated PA-induced increase in the expression of c-FOS and inflammatory cytokines. Furthermore, in PA-treated cells, silencing c-FOS markedly improved glucose consumption, and reduced inflammation and Arginase 2 (ARG2) expression. Similarly, as exposure to PA, silencing ARG2 also ameliorated glucose uptake and inflammation, while not affecting c-FOS expression. In vivo experiments further showed that Linarin administration remarkably improved glucose tolerance and insulin sensitivity, and reduced the fat mass and body weight in HFD-induced obese mice. In this study, Linarin has been identified as the bioactive compound of Lycii Cortex to ameliorate obesity-related IR and inflammation through the c-FOS/ARG2 signaling cascade. These findings underscore the therapeutic potential of Linarin and provide valuable insights into developing novel intervention strategies for type 2 diabetes therapy.

Arginase-II gene deficiency reduces skeletal muscle aging in mice

Age-associated sarcopenia decreases mobility and is promoted by cell senescence, inflammation, and fibrosis. The mitochondrial enzyme arginase-II (Arg-II) plays a causal role in aging and age-associated diseases. Therefore, we aim to explore the role of Arg-II in age-associated decline of physical activity and skeletal muscle aging in a mouse model. Young (4-6 months) and old (20-24 months) wild-type (wt) mice and mice deficient in arg-ii (arg-ii-/-) of both sexes are investigated. We demonstrate a decreased physical performance of old wt mice, which is partially prevented in arg-ii-/- animals, particularly in males. The improved phenotype of arg-ii-/- mice in aging is associated with reduced sarcopenia, cellular senescence, inflammation, and fibrosis, whereas age-associated decline of microvascular endothelial cell density, satellite cell numbers, and muscle fiber types in skeletal muscle is prevented in arg-ii-/- mice. Finally, we demonstrate an increased arg-ii gene expression level in aging skeletal muscle and found Arg-II protein expression in endothelial cells and fibroblasts, but not in skeletal muscle fibers, macrophages, and satellite cells. Our results suggest that increased Arg-II in non-skeletal muscle cells promotes age-associated sarcopenia, particularly in male mice.

Opportunities and Challenges of Arginase Inhibitors in Cancer: A Medicinal Chemistry Perspective

The overexpression of two arginase (ARG) isoforms, ARG1 and ARG2, contributes to the onset of numerous disorders, including cardiovascular and immune-mediated diseases, as well as tumors. To elucidate the specific roles of ARG1 and ARG2 without interfering with their physiological functions, it is crucial to develop effective ARG inhibitors that target only one isoform, while maintaining low toxicity and an adequate pharmacokinetic profile. In this context, we present a comprehensive overview of the different generations of ARG inhibitors. Given the general lack of selectivity in most existing inhibitors, we analyzed the structural features and plasticity of the ARG1 and ARG2 binding sites to explore the potential for designing inhibitors with novel binding patterns. We also review ongoing preclinical and clinical studies on selected inhibitors, highlighting both progress and challenges in developing potent, selective ARG inhibitors. Furthermore, we discuss medicinal chemistry strategies that may accelerate the discovery of selective ARG inhibitors.

ARG2 knockdown promotes G0/G1 cell cycle arrest and mitochondrial dysfunction in adenomyosis via regulation NF-κB and Wnt/Β-catenin signaling cascades

BACKGROUND

Adenomyosis is a common gynecological disease, characterized by overgrowth of endometrial glands and stroma in the myometrium, however its exact pathophysiology still remains uncertain. Emerging evidence has demonstrated the elevated level of arginase 2 (ARG2) in endometriosis and adenomyosis. This study aimed to determine whether ARG2 involved in mitochondrial function and epithelial to mesenchymal transition (EMT) in adenomyosis and its potential underlying mechanisms.

MATERIALS AND METHODS

RNA interference was used to inhibit ARG2 gene, and then Cell Counting Kit (CCK-8) assay and flow cytometery were performed to detect the cell proliferation capacity, cell cycle, and apoptosis progression, respectively. The mouse adenomyosis model was established and RT-PCR, Western blot analysis, mitochondrial membrane potential (Δψm) detection and mPTP opening evaluation were conducted.

RESULTS

Silencing ARG2 effectively down-regulated its expression at the mRNA and protein levels in endometrial cells, leading to decreased enzyme activity and inhibition of cell viability. Additionally, ARG2 knockdown induced G0/G1 cell cycle arrest, promoted apoptosis, and modulated the expression of cell cycle- and apoptosis-related regulators. Notably, the interference with ARG2 induces apoptosis by mitochondrial dysfunction, ROS production, ATP depletion, decreasing the Bcl-2/Bax ratio, releasing Cytochrome c, and increasing the expression of Caspase-9/-3 and PARP. In vivo study in a mouse model of adenomyosis demonstrated also elevated levels of ARG2 and EMT markers, while siARG2 treatment reversed EMT and modulated inflammatory cytokines. Furthermore, ARG2 knockdown was found to modulate the NF-κB and Wnt/β-catenin signaling pathways in mouse adenomyosis.

CONCLUSION

Consequently, ARG2 silencing could induce apoptosis through a mitochondria-dependent pathway mediated by ROS, and G0/G1 cell cycle arrest via suppressing NF-κB and Wnt/β-catenin signaling pathways in Ishikawa cells. These findings collectively suggest that ARG2 plays a crucial role in the pathogenesis of adenomyosis and may serve as a potential target for therapeutic intervention.

Unraveling molecular mechanistic disparities in pathogenic visceral Leishmania resistance between reptiles and mammals through comparative transcriptomic analyses

Leishmaniasis is one of the most important neglected tropical parasitic diseases, manifesting various clinical forms depending on the parasite species and the genetic background of the host. In order to elucidate the underlying mechanisms of reptilian defense against pathogenic Leishmania species and to delineate the global gene expression profile alterations during host-pathogen interaction, we established experimental animal and cell models using both heterothermic lizards (Phrynocephalus przewalskii) and homothermic mammals (BALB/c mice) infected with pathogenic Leishmania infantum (high virulence HCZ strain) and Leishmania donovani (low virulence 801 strain). Overall, the lizards didn't show any obvious clinical symptoms or immune responses in vivo. Using RNA-seq methodology, differentially expressed genes identified in the HCZ and 801-comparison groups of P. przewalskii were primarily associated with arginine biosynthesis, the MAPK signaling pathway and the PI3K-Akt signaling pathway. In contrast, higher parasite loads, exacerbated hepatic inflammatory lesions and enhanced immune responses were observed in BALB/c mice, with DEGs predominantly associated with immunological diseases, innate and adaptive immune responses. By integrating transcriptional data from reptile and mammalian hosts, we elucidated the pivotal role of amino acid metabolism and lipid metabolism in parasite control. In contrast to findings from animal experiments, Leishmania parasites effectively infected peritoneal macrophages of lizards in vitro, demonstrating a high infection rate. Furthermore, we used RT-qPCR to detect changes in cytokine expression in macrophages and found that Th1-type cytokines were significantly upregulated in lizards, facilitating the clearance of the HCZ strain 24 hours post-infection. Conversely, cytokine expression was generally suppressed in BALB/c mice, allowing immune evasion by the parasites.

Pathophysiology of Arginases in Cancer and Efforts in Their Pharmacological Inhibition

Arginases are key enzymes that hydrolyze L-arginine to urea and L-ornithine in the urea cycle. The two arginase isoforms, arginase 1 (ARG1) and arginase 2 (ARG2), regulate the proliferation of cancer cells, migration, and apoptosis; affect immunosuppression; and promote the synthesis of polyamines, leading to the development of cancer. Arginases also compete with nitric oxide synthase (NOS) for L-arginine, and their participation has also been confirmed in cardiovascular diseases, stroke, and inflammation. Due to the fact that arginases play a crucial role in the development of various types of diseases, finding an appropriate candidate to inhibit the activity of these enzymes would be beneficial for the therapy of many human diseases. In this review, based on numerous experimental, preclinical, and clinical studies, we provide a comprehensive overview of the biological and physiological functions of ARG1 and ARG2, their molecular mechanisms of action, and affected metabolic pathways. We summarize the recent clinical trials' advances in targeting arginases and describe potential future drugs.

Targeting amino acid-metabolizing enzymes for cancer immunotherapy

Despite the immune system's role in the detection and eradication of abnormal cells, cancer cells often evade elimination by exploitation of various immune escape mechanisms. Among these mechanisms is the ability of cancer cells to upregulate amino acid-metabolizing enzymes, or to induce these enzymes in tumor-infiltrating immunosuppressive cells. Amino acids are fundamental cellular nutrients required for a variety of physiological processes, and their inadequacy can severely impact immune cell function. Amino acid-derived metabolites can additionally dampen the anti-tumor immune response by means of their immunosuppressive activities, whilst some can also promote tumor growth directly. Based on their evident role in tumor immune escape, the amino acid-metabolizing enzymes glutaminase 1 (GLS1), arginase 1 (ARG1), inducible nitric oxide synthase (iNOS), indoleamine 2,3-dioxygenase 1 (IDO1), tryptophan 2,3-dioxygenase (TDO) and interleukin 4 induced 1 (IL4I1) each serve as a promising target for immunotherapeutic intervention. This review summarizes and discusses the involvement of these enzymes in cancer, their effect on the anti-tumor immune response and the recent progress made in the preclinical and clinical evaluation of inhibitors targeting these enzymes.

Aging Increases Hypoxia-Induced Endothelial Permeability and Blood-Brain Barrier Dysfunction by Upregulating Arginase-II

Increased endothelial permeability plays an important role in blood-brain barrier (BBB) dysfunction and is implicated in neuronal injury in many diseased conditions. BBB disruption is primarily determined by dysfunction of endothelial cell-cell junctions. Deprivation of oxygen supply or hypoxia, a common feature of a variety of human diseases, is a major risk factor for BBB disruption. The molecular regulatory mechanisms of hypoxia-induced BBB dysfunction remain incompletely understood. The mitochondrial enzyme, arginase type II (Arg-II), has been shown to promote endothelial dysfunction. However, its role in hypoxia-induced BBB dysfunction has not been explored. In the C57BL/6J mouse model, hypoxia (8% O2, 24 hours) augments vascular Arg-II in the hippocampus, decreases cell-cell junction protein levels of Zonula occludens-1 (ZO-1), occludin, and CD31 in endothelial cells, increases BBB leakage in the brain in old mice (20 to 24 months) but not in young animals (3 to 6 months). These effects of hypoxia in aging are suppressed in arg-ii-/- mice. Moreover, the age-associated vulnerability of endothelial integrity to hypoxia is demonstrated in senescent human brain microvascular endothelial cell (hCMEC/D3) culture model. Further results in the cell culture model show that hypoxia augments Arg-II, decreases ZO-1 and occludin levels, and increases endothelial permeability, which is prevented by arg-ii gene silencing or by inhibition of mitochondrial reactive oxygen species (mtROS) production. Our study demonstrates an essential role of Arg-II in increased endothelial permeability and BBB dysfunction by promoting mtROS generation, resulting in decreased endothelial cell-cell junction protein levels under hypoxic conditions particularly in aging.

Construction and evaluation of endometriosis diagnostic prediction model and immune infiltration based on efferocytosis-related genes

Background: Endometriosis (EM) is a long-lasting inflammatory disease that is difficult to treat and prevent. Existing research indicates the significance of immune infiltration in the progression of EM. Efferocytosis has an important immunomodulatory function. However, research on the identification and clinical significance of efferocytosis-related genes (EFRGs) in EM is sparse. Methods: The EFRDEGs (differentially expressed efferocytosis-related genes) linked to datasets associated with endometriosis were thoroughly examined utilizing the Gene Expression Omnibus (GEO) and GeneCards databases. The construction of the protein-protein interaction (PPI) and transcription factor (TF) regulatory network of EFRDEGs ensued. Subsequently, machine learning techniques including Univariate logistic regression, LASSO, and SVM classification were applied to filter and pinpoint diagnostic biomarkers. To establish and assess the diagnostic model, ROC analysis, multivariate regression analysis, nomogram, and calibration curve were employed. The CIBERSORT algorithm and single-cell RNA sequencing (scRNA-seq) were employed to explore immune cell infiltration, while the Comparative Toxicogenomics Database (CTD) was utilized for the identification of potential therapeutic drugs for endometriosis. Finally, immunohistochemistry (IHC) and reverse transcription quantitative polymerase chain reaction (RT-qPCR) were utilized to quantify the expression levels of biomarkers in clinical samples of endometriosis. Results: Our findings revealed 13 EFRDEGs associated with EM, and the LASSO and SVM regression model identified six hub genes (ARG2, GAS6, C3, PROS1, CLU, and FGL2). Among these, ARG2, GAS6, and C3 were confirmed as diagnostic biomarkers through multivariate logistic regression analysis. The ROC curve analysis of GSE37837 (AUC = 0.627) and GSE6374 (AUC = 0.635), along with calibration and DCA curve assessments, demonstrated that the nomogram built on these three biomarkers exhibited a commendable predictive capacity for the disease. Notably, the ratio of nine immune cell types exhibited significant differences between eutopic and ectopic endometrial samples, with scRNA-seq highlighting M0 Macrophages, Fibroblasts, and CD8 Tex cells as the cell populations undergoing the most substantial changes in the three biomarkers. Additionally, our study predicted seven potential medications for EM. Finally, the expression levels of the three biomarkers in clinical samples were validated through RT-qPCR and IHC, consistently aligning with the results obtained from the public database. Conclusion: we identified three biomarkers and constructed a diagnostic model for EM in this study, these findings provide valuable insights for subsequent mechanistic research and clinical applications in the field of endometriosis.

The regulatory role of eosinophils in adipose tissue depends on autophagy

Introduction

Obesity is a metabolic condition that elevates the risk of all-cause mortality. Brown and beige adipose tissues, known for their thermogenic properties, offer potential therapeutic targets for combating obesity. Recent reports highlight the role of immune cells, including eosinophils, in adipose tissue homeostasis, while the underlying mechanisms are poorly understood.

Methods

To study the role of autophagy in eosinophils in this process, we used a genetic mouse model lacking autophagy-associated protein 5 (Atg5), specifically within the eosinophil lineage (Atg5 eoΔ).

Results

The absence of Atg5 in eosinophils led to increased body weight, impaired glucose metabolism, and alterations in the cellular architecture of adipose tissue. Our findings indicate that Atg5 modulates the functional activity of eosinophils within adipose tissue rather than their abundance. Moreover, RNA-seq analysis revealed upregulation of arginase 2 (Arg2) in Atg5-knockout eosinophils. Increased Arg2 activity was shown to suppress adipocyte beiging. Furthermore, we observed enrichment of the purine pathway in the absence of Atg5 in eosinophils, leading to a pro-inflammatory shift in macrophages and a further reduction in beiging.

Discussion

The data shed light on the importance of autophagy in eosinophils and its impact on adipose tissue homeostasis by suppressing Arg2 expression and limiting inflammation in adipose tissue.

CTRP6 promotes the macrophage inflammatory response, and its deficiency attenuates LPS-induced inflammation

Macrophages play critical roles in inflammation and tissue homeostasis, and their functions are regulated by various autocrine, paracrine, and endocrine factors. We have previously shown that CTRP6, a secreted protein of the C1q family, targets both adipocytes and macrophages to promote obesity-linked inflammation. However, the gene programs and signaling pathways directly regulated by CTRP6 in macrophages remain unknown. Here, we combine transcriptomic and phosphoproteomic analyses to show that CTRP6 activates inflammatory gene programs and signaling pathways in mouse bone marrow-derived macrophages (BMDMs). Treatment of BMDMs with CTRP6 upregulated proinflammatory, and suppressed the antiinflammatory, gene expression. We also showed that CTRP6 activates p44/42-MAPK, p38-MAPK, and NF-κB signaling pathways to promote inflammatory cytokine secretion from BMDMs, and that pharmacologic inhibition of these signaling pathways markedly attenuated the effects of CTRP6. Pretreatment of BMDMs with CTRP6 also sensitized and potentiated the BMDMs response to lipopolysaccharide (LPS)-induced inflammatory signaling and cytokine secretion. Consistent with the metabolic phenotype of proinflammatory macrophages, CTRP6 treatment induced a shift toward aerobic glycolysis and lactate production, reduced oxidative metabolism, and elevated mitochondrial reactive oxygen species production in BMDMs. Importantly, in accordance with our in vitro findings, BMDMs from CTRP6-deficient mice were less inflammatory at baseline and showed a marked suppression of LPS-induced inflammatory gene expression and cytokine secretion. Finally, loss of CTRP6 in mice also dampened LPS-induced inflammation and hypothermia. Collectively, our findings suggest that CTRP6 regulates and primes the macrophage response to inflammatory stimuli and thus may have a role in modulating tissue inflammatory tone in different physiological and disease contexts.

A review of nitric oxide and oxidative stress in typical ovulatory women and in the pathogenesis of ovulatory dysfunction in PCOS

Polycystic ovary syndrome (PCOS) is a heterogeneous functional endocrine disorder associated with a low-grade, chronic inflammatory state. Patients with PCOS present an increased risk of metabolic comorbidities and often menstrual dysregulation and infertility due to anovulation and/or poor oocyte quality. Multiple mechanisms including oxidative stress and low-grade inflammation are believed to be responsible for oocyte deterioration; however, the influence of nitric oxide (NO) insufficiency in oocyte quality and ovulatory dysfunction in PCOS is still a matter for debate. Higher production of superoxide (O2•-) mediated DNA damage and impaired antioxidant defense have been implicated as contributory factors for the development of PCOS, with reported alteration in superoxide dismutase (SOD) function, an imbalanced zinc/copper ratio, and increased catalase activity. These events may result in decreased hydrogen peroxide (H2O2) accumulation with increased lipid peroxidation events. A decrease in NO, potentially due to increased activity of NO synthase (NOS) inhibitors such as asymmetric dimethylarginine (ADMA), and imbalance in the distribution of reactive oxygen species (ROS), such as decreased H2O2 and increased O2•-, may offset the physiological processes surrounding follicular development, oocyte maturation, and ovulation contributing to the reproductive dysfunction in patients with PCOS. Thus, this proposal aims to evaluate the specific roles of NO, oxidative stress, ROS, and enzymatic and nonenzymatic elements in the pathogenesis of PCOS ovarian dysfunction, including oligo- anovulation and oocyte quality, with the intent to inspire better application of therapeutic options. The authors believe more consideration into the specific roles of oxidative stress, ROS, and enzymatic and nonenzymatic elements may allow for a more thorough understanding of PCOS. Future efforts elaborating on the role of NO in the preoptic nucleus to determine its influence on GnRH firing and follicle-stimulating hormone/Luteinizing hormone (FSH/LH) production with ovulation would be of benefit in PCOS. Consequently, treatment with an ADMA inhibitor or NO donor may prove beneficial to PCOS patients experiencing reproductive dysfunction and infertility.

Pyrrolidine dithiocarbamate in combination with L-N-monomethyl arginine alleviates Staphylococcus aureus infection via regulation of CXCL8/CXCR1 axis in peritoneal macrophages in vitro

The CXCL8/CXCR1 axis in conjoint with the free radicals and anti-oxidants dictates the severity of inflammation caused by the bacteria, Staphylococcus aureus. S.aureus mediated inflammatory processes is regulated by NF-κB and its product, iNOS. The objective of this study was to examine the effects of inhibition of NF-κB and iNOS on CXCL8/CXCR1, alteration in M1/M2 polarization of macrophages and associated inflammatory responses during S.aureus infection in vitro. For this, the murine peritoneal macrophages were pretreated with NF-κB inhibitor, Pyrrolidine dithiocarbamate (PDTC) and iNOS inhibitor, L-N-monomethyl arginine (LNMMA), either alone or in combination, followed by time-dependent S.aureus infection. The chemotactic migrations of macrophages were determined by the agarose spot assay. The iNOS, NF-κB and CXCR1 protein expressions were evaluated. The ROS level (superoxide, H2O2, NO) and antioxidant activities (SOD, CAT, GSH, arginase) were measured. The intra-macrophage phagoctyic activity had been analyzed by confocal microscopy. S.aureus activated macrophages showed increased iNOS expression that symbolizes M1 characterization of macrophages. The results suggest that the combination treatment of LNMMA + PDTC was effective in diminution of CXCL8 production and CXCR1 expression through downregulation of NF-κB and iNOS signaling pathway. Consequently, there was decrement in macrophage migration, reduced ROS generation, elevated antioxidant enzyme activity as well as bacterial phagocytosis at 90 min post bacterial infection. The increased arginase activity further proves the switch from pro-inflammatory M1 to anti-inflammatory M2 polarization of macrophages. Concludingly, the combination of PDTC + LNMMA could resolve S.aureus mediated inflammation through mitigation of CXCL8/CXCR1 pathway switching from M1 to M2 polarization.

Arginase 2 Promotes Cisplatin-Induced Acute Kidney Injury by the Inflammatory Response of Macrophages

Acute kidney injury (AKI) is a complex clinical syndrome with a rapid decrease in renal function caused by several different etiologies, including sepsis, ischemia, and the administration of nephrotoxic drugs. Tubular arginase 2 (ARG2), an arginine-metabolic enzyme, is a potential therapeutic target for AKI, but it has not been confirmed under various AKI conditions. The aim of this study was to investigate ARG2 as a therapeutic target for cisplatin-induced AKI. Cisplatin-treated mice with a genetic deficiency in Arg2 had significant amelioration of renal dysfunction, characterized by decreased acute tubular damage and apoptosis. In contrast, cisplatin-induced tubular toxicity was not ameliorated in proximal tubule cells derived from Arg2-deficient mice. Immunohistochemical analysis demonstrated the increased infiltration of ARG2-positive macrophages in kidneys damaged by cisplatin. Importantly, cisplatin-treated Arg2 knockout mice exhibited a significant reduction in kidney inflammation, characterized by the decreased infiltration of inflammatory macrophages and reduced gene expression of interleukin (IL)-6 and IL-1β. The secretion of IL-6 and IL-1β induced by lipopolysaccharides was decreased in bone marrow-derived macrophages isolated from Arg2-deficient mice. Furthermore, the lipopolysaccharide-induced elevation of mitochondrial membrane potential and production of reactive oxygen species were reduced in bone marrow-derived macrophages lacking Arg2. These findings indicate that ARG2 promotes the inflammatory responses of macrophages through mitochondrial reactive oxygen species, resulting in the exacerbation of AKI. Therefore, targeting ARG2 in macrophages may constitute a promising therapeutic approach for AKI.

Unbalanced Redox With Autophagy in Cardiovascular Disease

Precise redox balance is essential for the optimum health and physiological function of the human body. Furthermore, an unbalanced redox state is widely believed to be part of numerous diseases, ultimately resulting in death. In this review, we discuss the relationship between redox balance and cardiovascular disease (CVD). In various animal models, excessive oxidative stress has been associated with increased atherosclerotic plaque formation, which is linked to the inflammation status of several cell types. However, various antioxidants can defend against reactive oxidative stress, which is associated with an increased risk of CVD and mortality. The different cardiovascular effects of these antioxidants are presumably due to alterations in the multiple pathways that have been mechanistically linked to accelerated atherosclerotic plaque formation, macrophage activation, and endothelial dysfunction in animal models of CVD, as well as in in vitro cell culture systems. Autophagy is a regulated cell survival mechanism that removes dysfunctional or damaged cellular organelles and recycles the nutrients for the generation of energy. Furthermore, in response to atherogenic stress, such as the generation of reactive oxygen species, oxidized lipids, and inflammatory signaling between cells, autophagy protects against plaque formation. In this review, we characterize the broad spectrum of oxidative stress that influences CVD, summarize the role of autophagy in the content of redox balance-associated pathways in atherosclerosis, and discuss potential therapeutic approaches to target CVD by stimulating autophagy.

Antioxidant-rich Terminalia catappa fruit exerts antihypertensive effect via modulation of angiotensin-1-converting enzyme activity and H2S/NO/cGMP signaling pathway in Wistar rats

INTRODUCTION

The present study aimed at investigating the effect of Terminalia catappa fruits on blood pressure, NO/cGMP signalling pathway, angiotensin-1-converting enzyme and arginase activity, and oxidative stress biomarkers in L-NAME-induced hypertensive rats.

MATERIALS AND METHODS

Forty-two Wistar rats were divided into seven groups. Hypertension was induced via oral administration of 40 mg/kg of L-NAME for 21 days. Thereafter, the hypertensive rats were treated with Terminalia catappa fruit-supplemented diet and sildenafil citrate for 21 days. The blood pressure was measured and cardiac homogenate was prepared for biochemical analyses.

RESULTS

The results showed that L-NAME caused a significant (p < 0.05) increase in systolic and diastolic blood pressure, and heart rate as well as ACE, arginase and PDE-5 activity, with a simultaneous decrease in NO and H₂S levels as well as increased oxidative stress biomarkers. However, treatment with Terminalia catappa fruits-supplemented diets and sildenafil citrate lowered blood pressure and modulated ACE, arginase, and PDE-5 activity, improved NO and H₂S levels, as well as antioxidant status.

CONCLUSION

Findings presented in this study provide useful information on the antihypertensive property of Terminalia catappa fruits, alongside some possible mechanisms. Hence, Terminalia catappa fruits could be considered a dietary regimen and functional food in alleviating hypertension.

ETNPPL impairs autophagy through regulation of the ARG2-ROS signaling axis, contributing to palmitic acid-induced hepatic insulin resistance

Excessive free fatty acids (FFAs) accumulation is a leading risk factor for the pathogenesis of insulin resistance (IR) in metabolic tissues, including the liver. Ethanolamine-phosphate phospho-lyase (ETNPPL), a newly identified metabolic enzyme, catalyzes phosphoethanolamine (PEA) to ammonia, inorganic phosphate, and acetaldehyde and is highly expressed in hepatic tissue. Whether it plays a role in regulating FFA-induced IR in hepatocytes has yet to be understood. In this study, we established an in vitro palmitic acid (PA)-induced IR model in human HepG2 cells and mouse AML12 cells with chronic treatment of PA. Next, we overexpressed ETNPPL by using lentivirus-mediated ectopic to investigate the effects of ETNPPL per se on IR without PA stimulation. We show that ETNPPL expression is significantly elevated in PA-induced IR and that silencing ETNPPL ameliorates this IR in hepatocytes. Inversely, overexpressing ETNPPL under normal conditions without PA promotes IR, reactive oxygen species generation, and ARG2 activation in both HepG2 and AML12 cells. Moreover, ETNPPL depletion markedly down-regulates ARG2 expression in hepatocytes. Besides, silencing ARG2 prevents ETNPPL-induced ROS accumulation and inhibition of autophagic flux and IR in hepatocytes. Finally, we found that phytopharmaceutical disruption of ETNPPL by quercetin ameliorates PA-induced IR in hepatocytes. Our study discloses that ETNPPL inhibiting autophagic flux mediates insulin resistance triggered by PA in hepatocytes via ARG2/ROS signaling cascade. Our findings provide novel insights into elucidating the pathogenesis of obesity-associated hepatic IR, suggesting that targeting ETNPPL might represent a potential approach for T2DM therapy.

Impact of l-citrulline on nitric oxide signaling and arginase activity in hypoxic human pulmonary artery endothelial cells

Impaired nitric oxide (NO) signaling contributes to the development of pulmonary hypertension (PH). The l-arginine precursor, l-citrulline, improves NO signaling and has therapeutic potential in PH. However, there is evidence that l-citrulline might increase arginase activity, which in turn, has been shown to contribute to PH. Our major purpose was to determine if l-citrulline increases arginase activity in hypoxic human pulmonary artery endothelial cells (PAECs). In addition, to avoid potential adverse effects from high dose l-citrulline monotherapy, we evaluated whether the effect on NO signaling is greater using co-treatment with l-citrulline and another agent that improves NO signaling, folic acid, than either alone. Arginase activity was measured in human PAECs cultured under hypoxic conditions in the presence of l-citrulline (0-1 mM). NO production and endothelial nitric oxide synthase (eNOS) coupling, as assessed by eNOS dimer-to-monomer ratios, were measured in PAECs treated with l-citrulline and/or folic acid (0.2 μM). Arginase activity increased in hypoxic PAECs treated with 1 mM but not with either 0.05 or 0.1 mM l-citrulline. Co-treatment with folic acid and 0.1 mM l-citrulline increased NO production and eNOS dimer-to-monomer ratios more than treatment with either alone. The potential to increase arginase activity suggests that there might be plasma l-citrulline concentrations that should not be exceeded when using l-citrulline to treat PH. Rather than progressively increasing the dose of l-citrulline as a monotherapy, co-therapy with l-citrulline and folic acid merits consideration, due to the possibility of achieving efficacy at lower doses and minimizing side effects.

ROS-responsive magnesium-containing microspheres for antioxidative treatment of intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is a degenerative disease characterized by lower-back pain, causing disability globally. Antioxidant therapy is currently considered one of the most promising strategies for IVDD treatment, given the crucial role of reactive oxygen species (ROS) in IVDD pathogenesis. Herein, a ROS-responsive magnesium-containing microsphere (Mg@PLPE MS) was constructed for the antioxidative treatment of IVDD. The Mg@PLPE MS has a core-shell structure comprising poly(lactic-co-glycolic acid) (PLGA) and ROS-responsive polymer poly(PBT-co-EGDM) as the shell and a magnesium microparticle as the core. The poly(PBT-co-EGDM) can be destroyed by H₂O₂ through the H₂O₂-triggered hydrophobic-to-hydrophilic transition, subsequently promoting an Mg-water reaction to produce H₂. Thus, Mg@PLPE MS provides a valuable platform for H₂O₂ elimination and controlled H₂ release. The generated H₂ scavenge for ROS by reacting with noxious •OH. Notably, the Mg@PLPE MS exerted significant antioxidative and anti-inflammatory effects in a disc degeneration rat model and alleviated extracellular matrix degradation and disc cells apoptosis, thereby underlining its efficacy in IVDD treatment. The Mg@PLPE MS also exhibited robust biocompatibility and negligible toxicity, presenting the promise for the antioxidative treatment of IVDD in vivo. STATEMENT OF SIGNIFICANCE: Antioxidant therapy is currently considered one of the most promising strategies for intervertebral disc degeneration (IVDD) treatment, given the crucial role of reactive oxygen species (ROS) in IVDD pathogenesis. Here, ROS-responsive magnesium-containing microspheres (Mg@PLPE MSs) were constructed to alleviate IVDD through controlled release of hydrogen gas. The Mg@PLPE MSs can effectively scavenge overproduced ROS by simultaneously reacting with H₂O₂ and •OH, thus creating a suitable microenvironment for inhibition of ECM degradation. As a result, Mg@PLPE MSs treated IVDD rats exhibit minimal nucleus pulposus decrease, less extracellular matrix degradation, minimal radial fissure of fibrous rings, and higher disc height index. Therefore, the as-prepared Mg@PLPE MSs may shed a new light on clinical treatment of IVDD.

Role of pulmonary epithelial arginase-II in activation of fibroblasts and lung inflammaging

Elevated arginases including type-I (Arg-I) and type-II isoenzyme (Arg-II) are reported to play a role in aging, age-associated organ inflammaging, and fibrosis. A role of arginase in pulmonary aging and underlying mechanisms are not explored. Our present study shows increased Arg-II levels in aging lung of female mice, which is detected in bronchial ciliated epithelium, club cells, alveolar type 2 (AT2) pneumocytes, and fibroblasts (but not vascular endothelial and smooth muscle cells). Similar cellular localization of Arg-II is also observed in human lung biopsies. The age-associated increase in lung fibrosis and inflammatory cytokines, including IL-1β and TGF-β1 that are highly expressed in bronchial epithelium, AT2 cells, and fibroblasts, are ameliorated in arg-ii deficient (arg-ii^-/- ) mice. The effects of arg-ii^-/- on lung inflammaging are weaker in male as compared to female animals. Conditioned medium (CM) from human Arg-II-positive bronchial and alveolar epithelial cells, but not that from arg-ii^-/- cells, activates fibroblasts to produce various cytokines including TGF-β1 and collagen, which is abolished by IL-1β receptor antagonist or TGF-β type I receptor blocker. Conversely, TGF-β1 or IL-1β also increases Arg-II expression. In the mouse models, we confirmed the age-associated increase in IL-1β and TGF-β1 in epithelial cells and activation of fibroblasts, which is inhibited in arg-ii^-/- mice. Taken together, our study demonstrates a critical role of epithelial Arg-II in activation of pulmonary fibroblasts via paracrine release of IL-1β and TGF-β1, contributing to pulmonary inflammaging and fibrosis. The results provide a novel mechanistic insight in the role of Arg-II in pulmonary aging.

Role of Zerumbone, a Phytochemical Sesquiterpenoid from Zingiber zerumbet Smith, in Maintaining Macrophage Polarization and Redox Homeostasis

Macrophages and microglia are highly versatile cells that can be polarized into M1 and M2 phenotypes in response to diverse environmental stimuli, thus exhibiting different biological functions. In the central nervous system, activated resident macrophages and microglial cells trigger the production of proinflammatory mediators that contribute to neurodegenerative diseases and psychiatric disorders. Therefore, modulating the activation of macrophages and microglia by optimizing the inflammatory environment is beneficial for disease management. Several naturally occurring compounds have been reported to have anti-inflammatory and neuroprotective properties. Zerumbone is a phytochemical sesquiterpenoid and also a cyclic ketone isolated from Zingiber zerumbet Smith. In this study, we found that zerumbone effectively reduced the expression of lipocalin-2 in macrophages and microglial cell lines. Lipocalin-2, also known as neutrophil gelatinase-associated lipocalin (NGAL), has been characterized as an adipokine/cytokine implicated in inflammation. Moreover, supplement with zerumbone inhibited reactive oxygen species production. Phagocytic activity was decreased following the zerumbone supplement. In addition, the zerumbone supplement remarkably reduced the production of M1-polarization-associated chemokines CXC10 and CCL-2, as well as M1-polarization-associated cytokines interleukin (IL)-6, IL-1β, and tumor necrosis factor-α. Furthermore, the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 and the production of NO were attenuated in macrophages and microglial cells supplemented with zerumbone. Notably, we discovered that zerumbone effectively promoted the production of the endogenous antioxidants heme oxygenase-1, glutamate-cysteine ligase modifier subunit, glutamate-cysteine ligase catalytic subunit, and NAD(P)H quinone oxidoreductase-1 and remarkably enhanced IL-10, a marker of M2 macrophage polarization. Endogenous antioxidant production and M2 macrophage polarization were increased through activation of the AMPK/Akt and Akt/GSK3 signaling pathways. In summary, this study demonstrated the protective role of zerumbone in maintaining M1 and M2 polarization homeostasis by decreasing inflammatory responses and enhancing the production of endogenous antioxidants in both macrophages and microglia cells. This study suggests that zerumbone can be used as a potential therapeutic drug for the supplement of neuroinflammatory diseases.

Arginase 2 negatively regulates sorafenib-induced cell death by mediating ferroptosis in melanoma

Ferroptosis, a newly defined and iron-dependent cell death, morphologically and biochemically differs from other cell deaths. Melanoma is a serious type of skin cancer, and the poor efficacy of current therapies causes a major increase in mortality. Sorafenib, a multiple kinase inhibitor, has been evaluated in clinical phase trials of melanoma patients, which shows modest efficacy. Emerging evidence has demonstrated that arginase 2 (Arg2), type 2 of arginase, is elevated in various types of cancers including melanoma. To investigate the role and underlying mechanism of Arg2 in sorafenib-induced ferroptosis in melanoma, reverse transcriptase-quantitative polymerase chain reaction, western blot analysis, adenovirus and lentivirus transduction, and in vivo tumor homograft model experiments were conducted. In this study, we show that sorafenib treatment leads to melanoma cell death and a decrease in Arg2 at both the mRNA and protein levels. Knockdown of Arg2 increases lipid peroxidation, which contributes to ferroptosis, and decreases the phosphorylation of Akt. In contrast, overexpression of Arg2 rescues sorafenib-induced ferroptosis, which is prevented by an Akt inhibitor. In addition, genetic and pharmacological suppression of Arg2 is able to ameliorate the anticancer activity of sorafenib in melanoma cells in vitro and in tumor homograft models. We also show that Arg2 suppresses ferroptosis by activating the Akt/GPX4 signaling pathway, negatively regulating sorafenib-induced cell death in melanoma cells. Our study not only uncovers a novel mechanism of ferroptosis in melanoma but also provides a new strategy for the clinical applications of sorafenib in melanoma treatment.

Arginase: Biological and Therapeutic Implications in Diabetes Mellitus and Its Complications

Arginase is a ubiquitous enzyme in the urea cycle (UC) that hydrolyzes L-arginine to urea and L-ornithine. Two mammalian arginase isoforms, arginase1 (ARG1) and arginase2 (ARG2), play a vital role in the regulation of β-cell functions, insulin resistance (IR), and vascular complications via modulating L-arginine metabolism, nitric oxide (NO) production, and inflammatory responses as well as oxidative stress. Basic and clinical studies reveal that abnormal alterations of arginase expression and activity are strongly associated with the onset and development of diabetes mellitus (DM) and its complications. As a result, targeting arginase may be a novel and promising approach for DM treatment. An increasing number of arginase inhibitors, including chemical and natural inhibitors, have been developed and shown to protect against the development of DM and its complications. In this review, we discuss the fundamental features of arginase. Next, the regulatory roles and underlying mechanisms of arginase in the pathogenesis and progression of DM and its complications are explored. Furthermore, we review the development and discuss the challenges of arginase inhibitors in treating DM and its related pathologies.

Arginase: shedding light on the mechanisms and opportunities in cardiovascular diseases

Arginase, a binuclear manganese metalloenzyme in the urea, catalyzes the hydrolysis of L-arginine to urea and L-ornithine. Both isoforms, arginase 1 and arginase 2 perform significant roles in the regulation of cellular functions in cardiovascular system, such as senescence, apoptosis, proliferation, inflammation, and autophagy, via a variety of mechanisms, including regulating L-arginine metabolism and activating multiple signal pathways. Furthermore, abnormal arginase activity contributes to the initiation and progression of a variety of CVDs. Therefore, targeting arginase may be a novel and promising approach for CVDs treatment. In this review, we give a comprehensive overview of the physiological and biological roles of arginase in a variety of CVDs, revealing the underlying mechanisms of arginase mediating vascular and cardiac function, as well as shedding light on the novel and promising therapeutic approaches for CVDs therapy in individuals.

Virtual Screening for FDA-Approved Drugs That Selectively Inhibit Arginase Type 1 and 2

Arginases are often overexpressed in human diseases, and they are an important target for developing anti-aging and antineoplastic drugs. Arginase type 1 (ARG1) is a cytosolic enzyme, and arginase type 2 (ARG2) is a mitochondrial one. In this study, a dataset containing 2115-FDA-approved drug molecules is virtually screened for potential arginase binding using molecular docking against several ARG1 and ARG2 structures. The potential arginase ligands are classified into three categories: (1) Non-selective, (2) ARG1 selective, and (3) ARG2 selective. The evaluated potential arginase ligands are then compared with their clinical use. Remarkably, half of the top 30 potential drugs are used clinically to lower blood pressure and treat cancer, infection, kidney disease, and Parkinson’s disease thus partially validating our virtual screen. Most notable are the antihypertensive drugs candesartan, irbesartan, indapamide, and amiloride, the antiemetic rolapitant, the anti-angina ivabradine, and the antidiabetic metformin which have minimal side effects. The partial validation also favors the idea that the other half of the top 30 potential drugs could be used in therapeutic settings. The three categories greatly expand the selectivity of arginase inhibition.

Arginase: An emerging and promising therapeutic target for cancer treatment

Arginase is a key hydrolase in the urea cycle that hydrolyses L-arginine to urea and L-ornithine. Increasing number of studies in recent years demonstrate that two mammalian arginase isoforms, arginase 1 (ARG1) and arginase 2 (ARG2), were aberrantly upregulated in various types of cancers, and played crucial roles in the regulation of tumor growth and metastasis through various mechanisms such as regulating L-arginine metabolism, influencing tumor immune microenvironment, etc. Thus, arginase receives increasing focus as an attractive target for cancer therapy. In this review, we provide a comprehensive overview of the physiological and biological roles of arginase in a variety of cancers, and shed light on the underlying mechanisms of arginase mediating cancer cells growth and development, as well as summarize the recent clinical research advances of targeting arginase for cancer therapy.

Nintedanib ameliorates oxidized low-density lipoprotein -induced inflammation and cellular senescence in vascular endothelial cells

Atherosclerosis (AS) is a life-threatening cardiovascular disease and it has been reported that endothelial dysfunction is the initial inducer of AS. Recent reports suggest that inflammation and oxidative stress-induced cell senescence are main inducers of endothelial dysfunction. Nintedanib is an effective inhibitor of multityrosine kinase receptors developed for the treatment of fibrosis, which was recently reported to exert inhibitory effects against inflammation and oxidative stress. The present study plans to study the effect and mechanism of Nintedanib on endothelial dysfunction. We found that in oxidized low-density lipoprotein (ox-LDL)-treated human umbilical vein endothelial cells (HUVECs), the increased production of total cholesterol (TC), free cholesterol (FC), and pro-inflammatory cytokines were observed, reversed by 10 μM and 25 μM Nintedanib. The elevated reactive oxygen species (ROS) and malondialdehyde (MDA) levels, as well as the declined activity of glutathione peroxidase (GSH-Px) in ox-LDL-treated HUVECs, were significantly abolished by 10 μM and 25 μM Nintedanib. Increased proportion of senescence-associated β-galactosidase (SA-β-gal) positive staining cells, activated p53/p21 pathway, and promoted cell fraction in the G0/G1 phase were observed in ox-LDL-treated HUVECs, all of which were dramatically reversed by 10 μM and 25 μM Nintedanib. Lastly, the increased expression level of Arginase-II (Arg-II) in HUVECs by ox-LDL was repressed by Nintedanib. The protective effects of Nintedanib on ox-LDL- induced cellular senescence were pronouncedly blocked by the overexpression of Arg-II. Collectively, our data suggest that Nintedanib mitigates ox-LDL-induced inflammation and cellular senescence in vascular endothelial cells by downregulating Arg-II.

The Unitary Micro-Immunotherapy Medicine Interferon-γ (4 CH) Displays Similar Immunostimulatory and Immunomodulatory Effects than Those of Biologically Active Human Interferon-γ on Various Cell Types

As a cytokine, gamma-interferon (IFN-γ) is considered a key player in the fine-tuned orchestration of immune responses. The extreme cellular sensitivity to cytokines is attested by the fact that very few of these bioactive molecules per cell are enough to trigger cellular functions. These findings can, at least partially, explain how/why homeopathically-prepared cytokines, and especially micro-immunotherapy (MI) medicines, are able to drive cellular responses. We focused our fundamental research on a unitary MI preparation of IFN-γ, specifically employed at 4 CH, manufactured and impregnated onto sucrose-lactose pillules as all other MI medicines. We assessed the IFN-γ concentration in the medium after dilution of the IFN-γ (4 CH)-bearing pillules and we evaluated in vitro drug responses in a wide range of immune cells, and in endothelial cells. Our results showed that IFN-γ (4 CH) stimulated the proliferation, the activation and the phagocytic capabilities of primary immune cells, as well as modulated their cytokine-secretion and immunity-related markers’ expression in a trend that is quite comparable with the well-recognized biological effects induced by IFN-γ. Altogether, these data provide novel and additional evidences on MI medicines, and specifically when active substances are prepared at 4 CH, thus suggesting the need for more investigations.

Hypoxia Induces Renal Epithelial Injury and Activates Fibrotic Signaling Through Up-Regulation of Arginase-II

The ureohydrolase, type-II arginase (Arg-II), is a mitochondrial enzyme metabolizing L-arginine into urea and L-ornithine and is highly expressed in renal proximal tubular cells (PTC) and upregulated by renal ischemia. Recent studies reported contradictory results on the role of Arg-II in renal injury. The aim of our study is to investigate the function of Arg-II in renal epithelial cell damage under hypoxic conditions. Human renal epithelial cell line HK2 was cultured under hypoxic conditions for 12–48 h. Moreover, ex vivo experiments with isolated kidneys from wild-type (WT) and genetic Arg-II deficient mice (Arg-II^–/–) were conducted under normoxic and hypoxic conditions. The results show that hypoxia upregulates Arg-II expression in HK2 cells, which is inhibited by silencing both hypoxia-inducible factors (HIFs) HIF1α and HIF2α. Treatment of the cells with dimethyloxaloylglycine (DMOG) to stabilize HIFα also enhances Arg-II. Interestingly, hypoxia or DMOG upregulates transforming growth factor β1 (TGFβ1) levels and collagens Iα1, which is prevented by Arg-II silencing, while TGFβ1-induced collagen Iα1 expression is not affected by Arg-II silencing. Inhibition of mitochondrial complex-I by rotenone abolishes hypoxia-induced reactive oxygen species (mtROS) and TGFβ1 elevation in the cells. Ex vivo experiments show elevated Arg-II and TGFβ1 expression and the injury marker NGAL in the WT mouse kidneys under hypoxic conditions, which is prevented in the Arg-II^–/– mice. Taking together, the results demonstrate that hypoxia activates renal epithelial HIFs-Arg-II-mtROS-TGFβ1-cascade, participating in hypoxia-associated renal injury and fibrosis.

Innate Immune Response to Fasting and Refeeding in the Zebrafish Kidney

Animals acquire nutrients and energy through feeding to achieve a balance between growth and organismal health. When there is a change in nutrient acquisition, the state of growth changes and may also cause changes in the intrinsic immune system. Compensatory growth (CG), a specific growth phenomenon, involves the question of whether changes in growth can be accompanied by changes in innate immunity. The zebrafish (Danio rerio), a well-known fish model organism, can serve as a suitable model. In this study, the zebrafish underwent 3 weeks of fasting and refeeding for 3 to 7 day periods. It was found that CG could be achieved in zebrafish. Zebrafish susceptibility to Streptococcus agalactiae increased after starvation. In addition, the amount of melano-macrophage centers increased after fasting and the proportion of injured tubules increased after refeeding for 3 and 5 days, respectively. Furthermore, the kidneys of zebrafish suffering from starvation were under oxidative stress, and the activity of several antioxidant enzymes increased after starvation, including catalase, glutathione peroxidases and superoxide dismutase. Innate immune parameters were influenced by starvation. Additionally, the activity of alkaline phosphatase and lysozyme increased after starvation. The mRNA expression of immune-related genes like il-1β was elevated to a different extent after fasting with or without lipopolysaccharides (LPS) challenge. This study showed that the function of the innate immune system in zebrafish could be influenced by nutrition status.

Arginase Activity in Eisenia andrei Coelomocytes: Function in the Earthworm Innate Response

Arginase is the manganese metalloenzyme catalyzing the conversion of l-arginine to l-ornithine and urea. In vertebrates, arginase is involved in the immune response, tissue regeneration, and wound healing and is an important marker of alternative anti-inflammatory polarization of macrophages. In invertebrates, data concerning the role of arginase in these processes are very limited. Therefore, in the present study, we focused on the changes in arginase activity in the coelomocytes of Eisenia andrei. We studied the effects of lipopolysaccharide (LPS), hydrogen peroxide (H₂O₂), heavy metals ions (e.g., Mn²⁺), parasite infection, wound healing, and short-term fasting (5 days) on arginase activity. For the first time in earthworms, we described arginase activity in the coelomocytes and found that it can be up-regulated upon in vitro stimulation with LPS and H₂O₂ and in the presence of Mn²⁺ ions. Moreover, arginase activity was also up-regulated in animals in vivo infected with nematodes or experiencing segment amputation, but not in fasting earthworms. Furthermore, we confirmed that the activity of coelomocyte arginase can be suppressed by l-norvaline. Our studies strongly suggest that similarly to the vertebrates, also in the earthworms, coelomocyte arginase is an important element of the immune response and wound healing processes.

Parallel Multi-Omics in High-Risk Subjects for the Identification of Integrated Biomarker Signatures of Type 1 Diabetes

BACKGROUND

Biomarkers are crucial for detecting early type-1 diabetes (T1D) and preventing significant β-cell loss before the onset of clinical symptoms. Here, we present proof-of-concept studies to demonstrate the potential for identifying integrated biomarker signature(s) of T1D using parallel multi-omics.

METHODS

Blood from human subjects at high risk for T1D (and healthy controls; n = 4 + 4) was subjected to parallel unlabeled proteomics, metabolomics, lipidomics, and transcriptomics. The integrated dataset was analyzed using Ingenuity Pathway Analysis (IPA) software for disturbances in the at-risk subjects compared to controls.

RESULTS

The final quadra-omics dataset contained 2292 proteins, 328 miRNAs, 75 metabolites, and 41 lipids that were detected in all samples without exception. Disease/function enrichment analyses consistently indicated increased activation, proliferation, and migration of CD4 T-lymphocytes and macrophages. Integrated molecular network predictions highlighted central involvement and activation of NF-κB, TGF-β, VEGF, arachidonic acid, and arginase, and inhibition of miRNA Let-7a-5p. IPA-predicted candidate biomarkers were used to construct a putative integrated signature containing several miRNAs and metabolite/lipid features in the at-risk subjects.

CONCLUSIONS

Preliminary parallel quadra-omics provided a comprehensive picture of disturbances in high-risk T1D subjects and highlighted the potential for identifying associated integrated biomarker signatures. With further development and validation in larger cohorts, parallel multi-omics could ultimately facilitate the classification of T1D progressors from non-progressors.

Role of tubular epithelial arginase-II in renal inflammaging

The aging kidney undergoes complex changes and is vulnerable to injury and development of chronic kidney disease (CKD) with preponderance affecting more women than men. Evidence has been presented that the type-II L-arginine:ureohydrolase, arginase-II (Arg-II) plays a role in the acceleration of aging. Arg-II is highly expressed in the kidney. However, the role of Arg-II in renal aging is not known. This study is to investigate whether Arg-II is involved in the kidney aging process dependently on sex. Arg-II level in the kidney of wild type (WT) mice is significantly elevated with aging, which is accompanied by an increase in expression of the inflammatory cytokines/chemokines, tissue macrophages, factors involved in fibrosis, and tubulointestitial fibrosis in both males and females. This renal aging phenotype is significantly suppressed in arg-II^−/− mice, mainly in the females in which Arg-II level is higher than in the males. Importantly, numerous factors such as IL-1β, MCP1, VCAM-1, and TGFβ1 are mainly localized in the proximal tubular S3 segment cells expressing Arg-II in the aging kidney. In human proximal tubular cells (HK-2), TNF-α enhances adhesion molecule expression dependently on Arg-II upregulation. Overexpression of Arg-II in the cells enhances TGFβ1 levels which is prevented by mitochondrial ROS inhibition. In summary, our study reveals that renal proximal tubular Arg-II plays an important role in the kidney aging process in females. Arg-II could be a promising therapeutic target for the treatment and prevention of aging-associated kidney diseases.

The Paired Siglecs in Brain Tumours Therapy: The Immunomodulatory Effect of Dexamethasone and Temozolomide in Human Glioma In Vitro Model

The paired sialic acid-binding immunoglobulin like lectins (Siglecs) are characterized by similar cellular distribution and ligand recognition but opposing signalling functions attributed to different intracellular sequences. Since sialic acid—Siglec axis are known to control immune homeostasis, the imbalance between activatory and inhibitory mechanisms of glycan-dependent immune control is considered to promote pathology. The role of sialylation in cancer is described, however, its importance in immune regulation in gliomas is not fully understood. The experimental and clinical observation suggest that dexamethasone (Dex) and temozolomide (TMZ), used in the glioma management, alter the immunity within the tumour microenvironment. Using glioma-microglia/monocytes transwell co-cultures, we investigated modulatory action of Dex/TMZ on paired Siglecs. Based on real-time PCR and flow cytometry, we found changes in SIGLEC genes and their products. These effects were accompanied by altered cytokine profile and immune cells phenotype switching measured by arginases expression. Additionally, the exposure to Dex or TMZ increased the binding of inhibitory Siglec-5 and Siglec-11 fusion proteins to glioma cells. Our study suggests that the therapy-induced modulation of the interplay between sialoglycans and paired Siglecs, dependently on patient’s phenotype, is of particular signification in the immune surveillance in the glioma management and may be useful in glioma patient’s therapy plan verification.

Detrimental Effects of Chronic L-Arginine Rich Food on Aging Kidney

The impaired L-arginine/nitric oxide pathway is a well-recognized mechanism for cardiovascular and renal diseases with aging. Therefore, supplementation of L-arginine is widely proposed to boost health or as adjunct therapy for the patients. However, clinical data, show adverse effects and even enhanced mortality in patients receiving long-term L-arginine supplementation. The effects of long-term L-arginine supplementation on kidney aging and the underlying mechanisms remain elusive. Moreover, high protein and high amino acid diet has been thought detrimental for kidney. We therefore investigated effects of chronic dietary L-arginine supplementation on kidney aging. In both young (4 months) and old (18-24 months) mice, animals either receive standard chow containing 0.65% L-arginine or diet supplemented with L-arginine to 2.46% for 16 weeks. Inflammation and fibrosis markers and albuminuria are then analyzed. Age-associated increases in tnf-α, il-1β, and il-6, vcam-1, icam-1, mcp1, inos, and macrophage infiltration, collagen expression, and S6K1 activation are observed, which is not favorably affected, but rather further enhanced, by L-arginine supplementation. Importantly, L-arginine supplementation further enhances age-associated albuminuria and mortality particularly in females, accompanied by elevated renal arginase-II (Arg-II) levels. The enhanced albuminuria by L-arginine supplementation in aging is not protected in Arg-II^-/- mice. In contrast, L-arginine supplementation increases ROS and decreases nitric oxide production in old mouse aortas, which is reduced in Arg-II^-/- mice. The results do not support benefits of long-term L-arginine supplementation. It rather accelerates functional decline of kidney and vasculature in aging. Thus, the long-term dietary L-arginine supplementation should be avoided particularly in elderly population.

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.

Atherosclerosis Linked to Aberrant Amino Acid Metabolism and Immunosuppressive Amino Acid Catabolizing Enzymes

Cardiovascular disease is the leading global health concern and responsible for more deaths worldwide than any other type of disorder. Atherosclerosis is a chronic inflammatory disease in the arterial wall, which underpins several types of cardiovascular disease. It has emerged that a strong relationship exists between alterations in amino acid (AA) metabolism and the development of atherosclerosis. Recent studies have reported positive correlations between levels of branched-chain amino acids (BCAAs) such as leucine, valine, and isoleucine in plasma and the occurrence of metabolic disturbances. Elevated serum levels of BCAAs indicate a high cardiometabolic risk. Thus, BCAAs may also impact atherosclerosis prevention and offer a novel therapeutic strategy for specific individuals at risk of coronary events. The metabolism of AAs, such as L-arginine, homoarginine, and L-tryptophan, is recognized as a critical regulator of vascular homeostasis. Dietary intake of homoarginine, taurine, and glycine can improve atherosclerosis by endothelium remodeling. Available data also suggest that the regulation of AA metabolism by indoleamine 2,3-dioxygenase (IDO) and arginases 1 and 2 are mediated through various immunological signals and that immunosuppressive AA metabolizing enzymes are promising therapeutic targets against atherosclerosis. Further clinical studies and basic studies that make use of animal models are required. Here we review recent data examining links between AA metabolism and the development of atherosclerosis.

Amino Acid Metabolism in Rheumatoid Arthritis: Friend or Foe?

In mammals, amino acid metabolism has evolved to act as a critical regulator of innate and adaptive immune responses. Rheumatoid arthritis (RA) is the most common form of inflammatory arthropathy sustained by autoimmune responses. We examine here the current knowledge of tryptophan and arginine metabolisms and the main immunoregulatory pathways in amino acid catabolism, in both RA patients and experimental models of arthritis. We found that l-tryptophan (Trp) metabolism and, in particular, the kynurenine pathway would exert protective effects in all experimental models and in some, but not all, RA patients, possibly due to single nucleotide polymorphisms in the gene coding for indoleamine 2,3-dioxygenase 1 (IDO1; the enzyme catalyzing the rate-limiting step of the kynurenine pathway). The function, i.e., either protective or pathogenetic, of the l-arginine (Arg) metabolism in RA was less clear. In fact, although immunoregulatory arginase 1 (ARG1) was highly induced at the synovial level in RA patients, its true functional role is still unknown, possibly because of few available preclinical data. Therefore, our analysis would indicate that amino acid metabolism represents a fruitful area of research for new drug targets for a more effective and safe therapy of RA and that further studies are demanding to pursue such an important objective.

Arginase-II promotes melanoma migration and adhesion through enhancing hydrogen peroxide production and STAT3 signaling

Elevated arginase type II (Arg-II) associates with higher grade tumors. Its function and underlying molecular mechanisms in melanoma remain elusive. In the present study, we observed a significantly higher frequency of Arg-II expression in melanoma of patients with metastasis than those without metastasis. Silencing Arg-II in two human melanoma cell lines slowed down the cell growth, while overexpression of native but not a catalytically inactive Arg-II promoted cell proliferation without affecting cell death. Treatment of cells with arginase inhibitor also reduced melanoma cell number, demonstrating that Arg-II promotes melanoma cell proliferation dependently of its enzymatic activity. However, results from silencing Arg-II or overexpressing native or the inactive Arg-II as well as treatment with arginase inhibitor showed that Arg-II promotes melanoma metastasis-related processes, such as melanoma cell migration and adhesion on endothelial cells, independently of its enzymatic activity. Moreover, the treatment of the cells with STAT3 inhibitor suppressed Arg-II-promoted melanoma cell migration and adhesion. Furthermore, catalase, but not superoxide dismutase, prevented STAT3 activation as well as increased melanoma cell migration and adhesion induced by overexpressing native or the inactive Arg-II. Taken together, our study uncovers both activity-dependent and independent mechanisms of Arg-II in promoting melanoma progression. While Arg-II enhances melanoma cell proliferation through polyamine dependently of its enzymatic activity, it promotes metastasis-related processes, that is, migration and adhesion onto endothelial cell, through mitochondrial H₂ O₂ -STAT3 pathway independently of the enzymatic activity. Suppressing Arg-II expression rather than inhibiting its enzymatic activity may, therefore, represent a novel strategy for the treatment of melanoma.

Inhibition of p38mapk Reduces Adipose Tissue Inflammation in Aging Mediated by Arginase-II

BACKGROUND

Adipose tissue inflammation occurs not only in obesity but also in aging and is mechanistically linked with age-associated diseases. Studies show that ablation of the l-arginine-metabolizing enzyme arginase-II (Arg-II) reduces adipose tissue inflammation and improves glucose tolerance in obesity. However, the role of Arg-II in aging adipose tissue inflammation is not clear.

OBJECTIVE

This study investigated the role of Arg-II in age-associated adipose tissue inflammation.

METHODS

Visceral adipose tissues of young (3-6 months) and old (20-24 months) wild-type (WT) and Arg-II-/- mice were investigated. Immunofluorescence confocal microscopy was performed for analysis of macrophage accumulation and cellular localization of arginase and cytokines; expression of arginase and cytokines was analyzed by qRT-PCR or immunoblotting or ELISA; activation of mitogen-activated protein kinases in adipose tissues was analyzed by immunoblotting; and arginase activity was measured by colorimetric determination of urea production.

RESULTS

In the old WT mice, there is more macrophage accumulation in the visceral adipose tissues than in Arg-II knockout animals. An age-associated increase in arginase activity and Arg-II expression in adipose tissues of WT mice is observed. Arg-II knockout enhances Arg-I expression and activity, but inhibits interleukin (IL)-6 expression and secretion and reduces active p38mapk in aging adipose tissue macrophages and stromal cells. Treatment of aging adipose tissues of WT mice with a specific p38mapk inhibitor SB203580 reduces IL-6 secretion.

CONCLUSIONS

Arg-II promotes IL-6 production in aging adipose tissues through p38mapk. The results suggest that targeting Arg-II or inhibiting p38mapk could be beneficial in reducing age-associated adipose tissue inflammation.

Myeloid Cell-Derived Arginase in Cancer Immune Response

Amino acid metabolism is a critical regulator of the immune response, and its modulating becomes a promising approach in various forms of immunotherapy. Insufficient concentrations of essential amino acids restrict T-cells activation and proliferation. However, only arginases, that degrade L-arginine, as well as enzymes that hydrolyze L-tryptophan are substantially increased in cancer. Two arginase isoforms, ARG1 and ARG2, have been found to be present in tumors and their increased activity usually correlates with more advanced disease and worse clinical prognosis. Nearly all types of myeloid cells were reported to produce arginases and the increased numbers of various populations of myeloid-derived suppressor cells and macrophages correlate with inferior clinical outcomes of cancer patients. Here, we describe the role of arginases produced by myeloid cells in regulating various populations of immune cells, discuss molecular mechanisms of immunoregulatory processes involving L-arginine metabolism and outline therapeutic approaches to mitigate the negative effects of arginases on antitumor immune response. Development of potent arginase inhibitors, with improved pharmacokinetic properties, may lead to the elaboration of novel therapeutic strategies based on targeting immunoregulatory pathways controlled by L-arginine degradation.

The Mechanism of Zinc Sulfate in Improving Fertility in Obese Rats Analyzed by Sperm Proteomic Analysis

This study investigates the mechanism underlying the improving effect of zinc on fertility in obese rats using proteomics. The effects of three different doses of ZnSO₄ on spermatogenesis and hormone levels were studied. Testicular spermatogenesis was observed by HE staining. Serum estrogen and testosterone levels were measured by chemiluminescent microparticle immunoassay. Sperm proteomic analysis was performed by liquid chromatography-mass spectrometry. The DAVID database was used to perform the GO enrichment analysis and KEGG pathway analysis of the differentially expressed genes, and the STRING online database was used to construct a PPI network. The sperm count, sperm motility, and testosterone hormones of the ZnSO₄-treated rats group were increased. ZnSO₄ improved testicular structure and spermatogenesis abnormalities caused by obesity. Proteomic analysis showed that there were 401 differentially expressed proteins in a total of 6 sperm samples from the ZnSO₄-treated group and the obesity groups. Differential proteins were input into the DAVID website. The 341 identified proteins were then classified according to their biological functions. The KEGG analysis showed that the enriched signal pathways included glycolysis/gluconeogenesis, carbon metabolism, citrate cycle, fatty acid metabolism, and pyruvate metabolism. Some proteins were shown to be associated with valine, leucine, and isoleucine degradation pathways. STRING analysis obtained 36 node proteins. Cytoscape analysis showed that these proteins mainly participated in nine networks including metabolic process, oxidation-reduction, aerobic respiration, RNA splicing, and glutathione conjugation. ZnSO₄ may improve the fertility of obese male rats by regulating protein expression related to metabolism, inflammation, and sperm maturation.

A Phenotypic and Genotypic Evaluation of Developmental Toxicity of Polyhexamethylene Guanidine Phosphate Using Zebrafish Embryo/Larvae

Polyhexamethylene guanidine-phosphate (PHMG-P), a guanidine-based cationic antimicrobial polymer, is an effective antimicrobial biocide, potent even at low concentrations. Due to its resilient bactericidal properties, it has been used extensively in consumer products. It was safely used until its use in humidifiers led to a catastrophic event in South Korea. Epidemiological studies have linked the use of PHMG-P as a humidifier disinfectant to pulmonary fibrosis. However, little is known about its harmful impacts other than pulmonary fibrosis. Thus, we applied a zebrafish embryo/larvae model to evaluate developmental and cardiotoxic effects and transcriptome changes using RNA-sequencing. Zebrafish embryos were exposed to 0.1, 0.2, 0.3, 0.4, 0.5, 1, and 2 mg/L of PHMG-P from 3 h to 96 h post fertilization. 2 mg/L of PHMG-P resulted in total mortality and an LC50 value at 96 h was determined at 1.18 mg/L. Significant developmental changes were not observed but the heart rate of zebrafish larvae was significantly altered. In transcriptome analysis, immune and inflammatory responses were significantly affected similarly to those in epidemiological studies. Our qPCR analysis (Itgb1b, TNC, Arg1, Arg2, IL-1β, Serpine-1, and Ptgs2b) also confirmed this following a 96 h exposure to 0.4 mg/L of PHMG-P. Based on our results, PHMG-P might induce lethal and cardiotoxic effects in zebrafish, and crucial transcriptome changes were linked to immune and inflammatory response.

Role of Arginase 2 as a potential pharmacological target for the creation of new drugs to correct cardiovascular diseases

Introduction: The review provides relevant information about arginase 2, the role of this enzyme in the formation of endothelial dysfunction and, as a consequence, the development of cardiovascular diseases.

History of the discovery of arginase and its functions: The discovery of arginase took place long before its active study as a substance that affects the formation of endothelial dysfunction.

Role of arginase 2 in the development of a number of cardiovascular diseases: The role of NO synthase and arginase 2 in the formation of oxidative stress is determined. The pathophysiological mechanisms of the development of a number of cardiovascular diseases, such as coronary heart disease, atherosclerosis, and aortic aneurysm, are described. The modern possibilities of treatment of endothelial dysfunction in the pathology of the cardiovascular system and the possibility of creation of new drugs are considered. An increase in the activity of arginase 2 was proven to occur in the case of the development of coronary heart disease (CHD), hypertension, type II diabetes mellitus, hypercholesterolemia, as well as in the process of aging. According to the WHO, coronary heart disease and apoplectic attack have topped the list of causes of death worldwide over the past 15 years.

Arginase 2 as a potential pharmacological target: The purpose of this literature review is to determine the possibilities of use of arginase 2 as a new target for the pharmacological correction of cardiovascular diseases.

Arginase Pathway in Acute Retina and Brain Injury: Therapeutic Opportunities and Unexplored Avenues

Ischemic retinopathies represent a major cause of visual impairment and blindness. They include diabetic retinopathy (DR), acute glaucoma, retinopathy of prematurity (ROP), and central (or branch) retinal artery occlusion (CRAO). These conditions share in common a period of ischemia or reduced blood supply to the retinal tissue that eventually leads to neuronal degeneration. Similarly, acute brain injury from ischemia or trauma leads to neurodegeneration and can have devastating consequences in patients with stroke or traumatic brain injury (TBI). In all of these conditions, current treatment strategies are limited by their lack of effectiveness, adverse effects or short time window for administration. Therefore, there is a great need to identify new therapies for acute central nervous system (CNS) injury. In this brief review article, we focus on the pathway of the arginase enzyme as a novel therapeutic target for acute CNS injury. We review the recent work on the role of arginase enzyme and its downstream components in neuroprotection in both retina and brain acute injury models. Delineating the similarities and differences between the role of arginase in the retina and brain neurodegeneration will allow for better understanding of the role of arginase in CNS disorders. This will also facilitate repurposing the arginase pathway as a new therapeutic target in both retina and brain diseases.

Is the Arginase Pathway a Novel Therapeutic Avenue for Diabetic Retinopathy?

Diabetic retinopathy (DR) is the leading cause of blindness in working age Americans. Clinicians diagnose DR based on its characteristic vascular pathology, which is evident upon clinical exam. However, extensive research has shown that diabetes causes significant neurovascular dysfunction prior to the development of clinically apparent vascular damage. While laser photocoagulation and/or anti-vascular endothelial growth factor (VEGF) therapies are often effective for limiting the late-stage vascular pathology, we still do not have an effective treatment to limit the neurovascular dysfunction or promote repair during the early stages of DR. This review addresses the role of arginase as a mediator of retinal neurovascular injury and therapeutic target for early stage DR. Arginase is the ureohydrolase enzyme that catalyzes the production of L-ornithine and urea from L-arginine. Arginase upregulation has been associated with inflammation, oxidative stress, and peripheral vascular dysfunction in models of both types of diabetes. The arginase enzyme has been identified as a therapeutic target in cardiovascular disease and central nervous system disease including stroke and ischemic retinopathies. Here, we discuss and review the literature on arginase-induced retinal neurovascular dysfunction in models of DR. We also speculate on the therapeutic potential of arginase in DR and its related underlying mechanisms.