Vascular dysfunction in retinopathy-an emerging role for arginase

The Role of Salivary Vascular Endothelial Growth Factor A, Cytokines, and Amino Acids in Immunomodulation and Angiogenesis in Breast Cancer

In this work, we focused on the analysis of VEGF content in saliva and its relationship with pro-inflammatory cytokines and amino acids involved in immunomodulation and angiogenesis in breast cancer. The study included 230 breast cancer patients, 92 patients with benign breast disease, and 59 healthy controls. Before treatment, saliva samples were obtained from all participants, and the content of VEGF and cytokines in saliva was determined by an enzyme-linked immunosorbent assay, as well as the content of amino acids by high-performance liquid chromatography. It was found that VEGF was positively correlated with the level of pro-inflammatory cytokines IL-1β (r = 0.6367), IL-6 (r = 0.3813), IL-8 (r = 0.4370), and IL-18 (r = 0.4184). Weak correlations were shown for MCP-1 (r = 0.2663) and TNF-α (r = 0.2817). For the first time, we demonstrated changes in the concentration of VEGF and related cytokines in saliva in different molecular biological subtypes of breast cancer depending on the stage of the disease, differentiation, proliferation, and metastasis to the lymph nodes. A correlation was established between the expression of VEGF and the content of aspartic acid (r = -0.3050), citrulline (r = -0.2914), and tryptophan (r = 0.3382) in saliva. It has been suggested that aspartic acid and citrulline influence the expression of VEGF via the synthesis of the signaling molecule NO, and then tryptophan ensures tolerance of the immune system to tumor cells.

Metabolic effects of L-citrulline in type 2 diabetes

The prevalence of type 2 diabetes (T2D) is increasing worldwide. Decreased nitric oxide (NO) bioavailability is involved in the pathophysiology of T2D and its complications. L-citrulline (Cit), a precursor of NO production, has been suggested as a novel therapeutic agent for T2D. Available data from human and animal studies indicate that Cit supplementation in T2D increases circulating levels of Cit and L-arginine while decreasing circulating glucose and free fatty acids and improving dyslipidemia. The underlying mechanisms for these beneficial effects of Cit include increased insulin secretion from the pancreatic β cells, increased glucose uptake by the skeletal muscle, as well as increased lipolysis and β-oxidation, and decreased glyceroneogenesis in the adipose tissue. Thus, Cit has antihyperglycemic, antidyslipidemic, and antioxidant effects and has the potential to be used as a new therapeutic agent in the management of T2D. This review summarizes available literature from human and animal studies to explore the effects of Cit on metabolic parameters in T2D. It also discusses the possible mechanisms underlying Cit-induced improved metabolic parameters in T2D.

Metabolomic comparison followed by cross-validation of enzyme-linked immunosorbent assay to reveal potential biomarkers of diabetic retinopathy in Chinese with type 2 diabetes

PURPOSE

To identify the biomarkers in the critical period of development in diabetic retinopathy (DR) in Chinese with type 2 diabetes using targeted and untargeted metabolomics, and to explore the feasibility of their clinical application.

METHODS

This case-control study described the differential metabolites between 83 Chinese type 2 diabetes mellitus (T2DM) samples with disease duration ≥ 10 years and 27 controls matched cases. Targeted metabolomics using high-resolution mass spectrometry with liquid chromatography was performed on plasma samples of subjects. The results were compared to our previous untargeted metabolomics study and ELISA was performed to validate the mutual differential metabolites of targeted and untargeted metabolomics on plasma. Multiple linear regression analyses were performed to adjust for the significance of different metabolites between groups.

RESULT

Mean age of the subjects was 66.3 years and mean T2DM duration was 16.5 years. By cross-validating with results from previous untargeted metabolomic assays, we found that L-Citrulline (Cit), indoleacetic acid (IAA), 1-methylhistidine (1-MH), phosphatidylcholines (PCs), hexanoylcarnitine, chenodeoxycholic acid (CDCA) and eicosapentaenoic acid (EPA) were the most distinctive metabolites biomarkers to distinguish the severity of DR for two different metabolomic approaches in our study. We mainly found that samples in the DR stage showed lower serum level of Cit and higher serum level of IAA compared with samples in the T2DM stage, while during the progression of diabetic retinopathy, the serum levels of CDCA and EPA in PDR stage were significantly lower than NPDR stage. Among them, 4 differential key metabolites including Cit, IAA, CDCA and EPA were confirmed with ELISA.

CONCLUSION

This is the first study to compare the results of targeted and untargeted metabolomics via liquid chromatography-mass spectrometry to find the serum biomarkers which could reflect the metabolic variations among different stages of DR in Chinese. The progression of DR in Chinese at different critical stages was related to the serum levels of specific differential metabolites, of which there is a significant correlation between DR progression and increased IAA and decreased Cit, hexanoylcarnitine, CDCA, and EPA. However, larger studies are needed to confirm our results. Based on this study, it could be inferred that the accuracy of targeted metabolomics for metabolite expression in serum is to some extent higher than that of untargeted metabolomics.

Metabolomics of various samples advancing biomarker discovery and pathogenesis elucidation for diabetic retinopathy

Diabetic retinopathy (DR) is a universal microvascular complication of diabetes mellitus (DM), which is the main reason for global sight damage/loss in middle-aged and/or older people. Current clinical analyses, like hemoglobin A1c, possess some importance as prognostic indicators for DR severity, but no effective circulating biomarkers are used for DR in the clinic currently, and studies on the latent pathophysiology remain lacking. Recent developments in omics, especially metabolomics, continue to disclose novel potential biomarkers in several fields, including but not limited to DR. Therefore, based on the overview of metabolomics, we reviewed progress in analytical technology of metabolomics, the prominent roles and the current status of biomarkers in DR, and the update of potential biomarkers in various DR-related samples via metabolomics, including tear as well as vitreous humor, aqueous humor, retina, plasma, serum, cerebrospinal fluid, urine, and feces. In this review, we underscored the in-depth analysis and elucidation of the common biomarkers in different biological samples based on integrated results, namely, alanine, lactate, and glutamine. Alanine may participate in and regulate glucose metabolism through stimulating N-methyl-D-aspartate receptors and subsequently suppressing insulin secretion, which is the potential pathogenesis of DR. Abnormal lactate could cause extensive oxidative stress and neuroinflammation, eventually leading to retinal hypoxia and metabolic dysfunction; on the other hand, high-level lactate may damage the structure and function of the retinal endothelial cell barrier via the G protein-coupled receptor 81. Abnormal glutamine indicates a disturbance of glutamate recycling, which may affect the activation of Müller cells and proliferation via the PPP1CA-YAP-GS-Gln-mTORC1 pathway.

β-Aminoisobutyric acid supplementation attenuated salt-sensitive hypertension in Dahl salt-sensitive rats through prevention of insufficient fumarase

The human Dietary Approaches to Stop Hypertension-Sodium Trial has shown that β-aminoisobutyric acid (BAIBA) may prevent the development of salt-sensitive hypertension (SSHT). However, the specific antihypertensive mechanism remains unclear in the renal tissues of salt-sensitive (SS) rats. In this study, BAIBA (100 mg/kg/day) significantly attenuated SSHT via increased nitric oxide (NO) content in the renal medulla, and it induced a significant increase in NO synthesis substrates (L-arginine and malic acid) in the renal medulla. BAIBA enhanced the activity levels of total NO synthase (NOS), inducible NOS, and constitutive NOS. BAIBA resulted in increased fumarase activity and decreased fumaric acid content in the renal medulla. The high-salt diet (HSD) decreased fumarase expression in the renal cortex, and BAIBA increased fumarase expression in the renal medulla and renal cortex. Furthermore, in the renal medulla, BAIBA increased the levels of ATP, ADP, AMP, and ADP/ATP ratio, thus further activating AMPK phosphorylation. BAIBA prevented the decrease in renal medullary antioxidative defenses induced by the HSD. In conclusion, BAIBA's antihypertensive effect was underlined by the phosphorylation of AMPK, the prevention of fumarase's activity reduction caused by the HSD, and the enhancement of NO content, which in concert attenuated SSHT in SS rats.

Therapeutic effect of ursolic acid on fetal development in pregnant rats with gestational diabetes mellitus via AGEs-RAGE signaling pathway

To investigate the effect of ursolic acid on the fetal development of gestational diabetes mellitus (GDM) caused by streptozotocin (STZ) and explore the potential mechanism for it. For the current experimental research, SD rats (pregnant animal) were used. STZ has been used to cause the diabetes mellitus in pregnant rats. Rats with evolved GDM were randomly divided and ursolic acid was given to pregnant rats in the experimental period up to 19 days in a dose-dependent manner. Blood samples and fetal rats of all group rats were collected at 19 days (pregnant rats), fetal rats and placental rats were weighted and the blood glucose, plasma insulin, C-peptide, and lipid parameters of pregnant women were estimated prior to delivery. Advanced serum glycation end-products (AGEs) were estimated at regular intervals in the heart and brain of pregnant rats. Monocyte Chemoattractant Protein-1 (MCP-1), NADPH oxidase 2 (Nox2), Role of advanced glycation end product (RAGE), Vascular endothelial growth factor (VEGF), p65, and vascular cell adhesion molecule 1 (VCAM-1) mRNA expression were estimated in the placenta. STZ-induced GDM pregnant rats showed significantly decreased placental weight and weight of fetal rats and dose-dependent ursolic acid treatment (p < .001) improved placental weight and weight of fetal rats at dose-dependent levels. After the ursolic acid treatment, serum blood glucose and lipid level were improved especially fasting blood glucose (FBG), high density lipoprotein (HDL), hepatic glycogen, fasting insulin (FINS), and serum insulin level and reached near to the normal control group rats. The antioxidant level of pancreas and liver were significantly (p < .001) reduced by the dose-dependent treatment of ursolic acid. Treatment with Ursolic acid moderately but not significantly decreases the risk of fetal development defects relative to the GDM group. The potential effect on fetal development in Pregnant Rats with Gestational Diabetes Mellitus via AGEs-RAGE signaling pathway was shown by Ursolic acid. PRACTICAL APPLICATIONS: As we know that the gestational diabetes mellitus increases worldwide day by day. In the current experimental study, we try to examine the gestational diabetic effect of ursolic acid. The finding of the current study showed the gestational diabetic protective effect in the female rats via AGEs-RAGE signaling pathway. The result showed the antioxidant, anti-inflammatory, and biochemical parameters. On the basis of the result, we can say that the ursolic acid can be the protective drug for treatment of gestational diabetes mellitus.

L-Citrulline Supplementation Increases Plasma Nitric Oxide Levels and Reduces Arginase Activity in Patients With Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is becoming a major contributor to cardiovascular disease. One of the early signs of T2DM associated cardiovascular events is the development of vascular dysfunction. This dysfunction has been implicated in increasing the morbidity and mortality of T2DM patients. One of the important characteristics of vascular dysfunction is the impaired ability of endothelial cells to produce nitric oxide (NO). Additionally, decreases in the availability of NO is also a major contributor of this pathology. NO is produced by the activity of endothelial NO synthase (eNOS) on its substrate, L-arginine. Reduced availability of L-arginine to eNOS has been implicated in vascular dysfunction in diabetes. Arginase, which metabolizes L-arginine to urea and ornithine, competes directly with NOS for L-arginine. Hence, increases in arginase activity can decrease arginine levels, reducing its availability to eNOS and decreasing NO production. Diabetes has been linked to elevated arginase and associated vascular endothelial dysfunction. We aimed to determine levels of plasma NO and arginase activity in (T2DM) patients and the effects of L-citrulline supplementation, a natural arginase inhibitor, on inhibiting arginase activity in these patients. Levels of arginase correlated with HbA1c levels in diabetic patients. Twenty-five patients received L-citrulline supplements (2000 mg/day) for 1 month. Arginase activity decreased by 21% in T2DM patients after taking L-citrulline supplements. Additionally, plasma NO levels increased by 38%. There was a modest improvement on H1Ac levels in these patients, though not statistically significant. The effect of L-citrulline on arginase activity was also studied in bovine aortic endothelial cells (BAECs) grown in high glucose (HG) conditions. HG (25 mM, 72 h) caused a 2-fold increase in arginase activity in BAECs and decreased NO production by 30%. L-citrulline (2.5 mM) completely prevented the increase in arginase activity and restored NO production levels. These data indicate that L-citrulline can have therapeutic benefits in diabetic patients through increasing NO levels and thus maintaining vascular function possibly through an arginase inhibition related pathway.

Acrolein: A Potential Mediator of Oxidative Damage in Diabetic Retinopathy

Diabetic retinopathy (DR) is the leading cause of vision loss among working-age adults. Extensive evidences have documented that oxidative stress mediates a critical role in the pathogenesis of DR. Acrolein, a product of polyamines oxidation and lipid peroxidation, has been demonstrated to be involved in the pathogenesis of various human diseases. Acrolein’s harmful effects are mediated through multiple mechanisms, including DNA damage, inflammation, ROS formation, protein adduction, membrane disruption, endoplasmic reticulum stress, and mitochondrial dysfunction. Recent investigations have reported the involvement of acrolein in the pathogenesis of DR. These studies have shown a detrimental effect of acrolein on the retinal neurovascular unit under diabetic conditions. The current review summarizes the existing literature on the sources of acrolein, the impact of acrolein in the generation of oxidative damage in the diabetic retina, and the mechanisms of acrolein action in the pathogenesis of DR. The possible therapeutic interventions such as the use of polyamine oxidase inhibitors, agents with antioxidant properties, and acrolein scavengers to reduce acrolein toxicity are also discussed.

Mechanisms of Diabetes-Induced Endothelial Cell Senescence: Role of Arginase 1

We have recently found that diabetes-induced premature senescence of retinal endothelial cells is accompanied by NOX2-NADPH oxidase-induced increases in the ureohydrolase enzyme arginase 1 (A1). Here, we used genetic strategies to determine the specific involvement of A1 in diabetes-induced endothelial cell senescence. We used A1 knockout mice and wild type mice that were rendered diabetic with streptozotocin and retinal endothelial cells (ECs) exposed to high glucose or transduced with adenovirus to overexpress A1 for these experiments. ABH [2(S)-Amino-6-boronohexanoic acid] was used to inhibit arginase activity. We used Western blotting, immunolabeling, quantitative PCR, and senescence associated β-galactosidase (SA β-Gal) activity to evaluate senescence. Analyses of retinal tissue extracts from diabetic mice showed significant increases in mRNA expression of the senescence-related proteins p16^INK4a, p21, and p53 when compared with non-diabetic mice. SA β-Gal activity and p16^INK4a immunoreactivity were also increased in retinal vessels from diabetic mice. A1 gene deletion or pharmacological inhibition protected against the induction of premature senescence. A1 overexpression or high glucose treatment increased SA β-Gal activity in cultured ECs. These results demonstrate that A1 is critically involved in diabetes-induced senescence of retinal ECs. Inhibition of arginase activity may therefore be an effective therapeutic strategy to alleviate diabetic retinopathy by preventing premature senescence.

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.

Netrin-1 is a novel regulator of vascular endothelial function in diabetes

BACKGROUND

Netrin-1, a secreted laminin-like protein identified as an axon guidance molecule, has been shown to be of critical importance in the cardiovascular system. Recent studies have revealed pro-angiogenic, anti-apoptotic and anti-inflammatory properties of netrin-1 as well as cardioprotective actions against myocardial injury in diabetic mice.

AIM

To examine the role of netrin-1 in diabetes-and high glucose (HG)-induced vascular endothelial dysfunction (VED) using netrin-1 transgenic mice (Tg3) and cultured bovine aortic endothelial cells (BAEC).

MAIN OUTCOME

Overexpression of netrin-1 prevented diabetes-induced VED in aorta from diabetic mice and netrin-1 treatment attenuated HG-induced impairment of nitric oxide synthase (NOS) function in BAECs.

METHODS AND RESULTS

Experiments were performed in Tg3 and littermate control (WT) mice rendered diabetic with streptozotocin (STZ) and in BAECs treated with HG (25 mmol/L). Levels of netrin-1 and its receptor DCC, markers of inflammation and apoptosis and vascular function were assessed in aortas from diabetic and non-diabetic Tg3 and WT mice. Vascular netrin-1 in WT mice was reduced under diabetic conditions. Aortas from non-diabetic Tg3 and WT mice showed similar maximum endothelium-dependent relaxation (MEDR) (83% and 87%, respectively). MEDR was markedly impaired in aorta from diabetic WT mice (51%). This effect was significantly blunted in Tg3 diabetic aortas (70%). Improved vascular relaxation in Tg3 diabetic mice was associated with increased levels of phospho-ERK1/2 and reduced levels of oxidant stress, NFκB, COX-2, p16INK4A, cleaved caspase-3 and p16 and p53 mRNA. Netrin-1 treatment prevented the HG-induced decrease in NO production and elevation of oxidative stress and apoptosis in BAECs.

CONCLUSIONS

Diabetes decreases aortic levels of netrin-1. However, overexpression of netrin-1 attenuates diabetes-induced VED and limits the reduction of NO levels, while increasing expression of p-ERK1/2, and suppressing oxidative stress and inflammatory and apoptotic processes. Enhancement of netrin-1 function may be a useful therapeutic means for preventing vascular dysfunction in diabetes.

The microRNA-7-mediated reduction in EPAC-1 contributes to vascular endothelial permeability and eNOS uncoupling in murine experimental retinopathy

AIMS

To investigate the consequences of oxidative stress and hypoxia on EPAC-1 expression during retinopathy.

METHODS

Oxygen-induced retinopathy was induced in mice and EPAC-1 expression investigated by immunofluorescence. In silico analyses were used to identify a link between EPAC-1 expression and microRNA-7-5p in endothelial cells and confirmed by western blot analyses on cells expressing microRNA-7-5p. In vitro, endothelial cells were either incubated at 2% oxygen or transfected with microRNA-7-5p, and the effects of these treatments on EPAC-1 expression, endothelial hyperpermeability and NO production were assessed. In the Ins2Akita mouse model, levels of EPAC-1 expression as well as microRNA-7-5p were assessed by qPCR. Endothelial nitric oxide synthase was assessed by immunoblotting in the Ins2Akita model.

RESULTS

Hypoxia induces the expression of microRNA-7-5p that translationally inhibits the expression of EPAC-1 in endothelial cells, resulting in hyperpermeability and the loss of eNOS activity. Activation of EPAC-1 by the cAMP analogue 8-pCPT-2'-O-Me-cAMP reduced the sensitivity of EPAC-1 to oxidative stress and restored the endothelial permeability to baseline levels. Additionally, 8-pCPT-2'-O-Me-cAMP rescued eNOS activity and NO production. In mouse models of retinopathy, i.e., oxygen-induced retinopathy and the spontaneous diabetic heterozygous Ins2^Akita mice, EPAC-1 levels are decreased which is associated with an increase in microRNA-7-5p expression and reduced eNOS activity.

CONCLUSION/INTERPRETATION

In retinopathy, EPAC-1 expression is decreased in a microRNA-7-mediated manner, contributing to endothelial dysfunction. Pharmacological activation of remnant EPAC-1 rescues endothelial function. Collectively, these data indicate that EPAC-1 resembles an efficacious and druggable target molecule for the amelioration of (diabetic) retinopathy.

Effects of the Hydroalcoholic Extract of Zingiber officinale on Arginase I Activity and Expression in the Retina of Streptozotocin-Induced Diabetic Rats

BACKGROUND

Emerging evidence suggests that an increased arginase activity is involved in vascular dysfunction in experimental animals. Zingiber officinale Roscoe, commonly known as ginger, has been widely used in the traditional medicine for treatment of diabetes.

OBJECTIVES

This study aimed at investigating the effects of the hydroalcoholic extract of Z. officinale on arginase I activity and expression in the retina of streptozotocin (STZ)-induced diabetic rats.

METHODS

In this experimental study, 16 male Wistar rats weighing 200 - 250 g were assessed. Diabetes was induced via a single intraperitoneal injection of STZ (60 mg/kg body weight). The rats were randomly allocated into four experimental groups. Untreated healthy and diabetic controls received 1.5 mL/kg distilled water. Treated diabetic rats received 200, and 400 mg/kg of the Z. officinale extract dissolved in distilled water (1.5 mL/kg). Body weight, blood glucose and insulin concentration were measured by standard methods. The arginase I activity and expression were determined by spectrophotometric and western blot analysis, respectively.

RESULTS

Our results showed that blood glucose concentration was significantly decreased in diabetic rats treated with the extract compared to untreated diabetic controls (P < 0.01). Treatment with 400 mg/kg of the extract reduced arginase I activity and expression (P < 0.05). A significant elevation in body weight was observed in diabetic rats treated with the extract. Serum insulin was significantly increased in diabetic rats treated with 400 mg/kg of the extract compared to diabetic controls (P < 0.05).

CONCLUSIONS

Our results suggest that the Z. officinale hydroalcoholic extract may potentially be a promising therapeutic option for treating diabetes-induced vascular disorders, possibly through reducing arginase I activity and expression in the retina.

Arginase as a Critical Prooxidant Mediator in the Binomial Endothelial Dysfunction-Atherosclerosis

Arginase is a metalloenzyme which hydrolyzes L-arginine to L-ornithine and urea. Since its discovery, in the early 1900s, this enzyme has gained increasing attention, as literature reports have progressively pointed to its critical participation in regulating nitric oxide bioavailability. Indeed, accumulating evidence in the following years would picture arginase as a key player in vascular health. Recent studies have highlighted the arginase regulatory role in the progression of atherosclerosis, the latter an essentially prooxidant state. Apart from the fact that arginase has been proven to impair different metabolic pathways, and also as a consequence of this, the repercussions of the actions of such enzyme go further than first thought. In fact, such metalloenzyme exhibits direct implications in multiple cardiometabolic diseases, among which are hypertension, type 2 diabetes, and hypercholesterolemia. Considering the epidemiological repercussions of these clinical conditions, arginase is currently seen under the spotlights of the search for developing specific inhibitors, in order to mitigate its deleterious effects. That said, the present review focuses on the role of arginase in endothelial function and its participation in the establishment of atherosclerotic lesions, discussing the main regulatory mechanisms of the enzyme, also highlighting the potential development of pharmacological strategies in related cardiovascular diseases.

CD200R signaling inhibits pro-angiogenic gene expression by macrophages and suppresses choroidal neovascularization

Macrophages are rapidly conditioned by cognate and soluble signals to acquire phenotypes that deliver specific functions during inflammation, wound healing and angiogenesis. Whether inhibitory CD200R signaling regulates pro-angiogenic macrophage phenotypes with the potential to suppress ocular neovascularization is unknown. CD200R-deficient bone marrow derived macrophages (BMMΦ) were used to demonstrate that macrophages lacking this inhibitory receptor exhibit enhanced levels of Vegfa, Arg-1 and Il-1β when stimulated with PGE₂ or RPE-conditioned (PGE₂-enriched) media. Endothelial tube formation in HUVECs was increased when co-cultured with PGE₂-conditioned CD200R^−/− BMMΦ, and laser-induced choroidal neovascularization was enhanced in CD200R-deficient mice. In corroboration, signaling through CD200R results in the down-regulation of BMMΦ angiogenic and pro-inflammatory phenotypes. Translational potential of this pathway was investigated in the laser-induced model of choroidal neovascularization. Local delivery of a CD200R agonist mAb to target myeloid infiltrate alters macrophage phenotype and inhibits pro-angiogenic gene expression, which suppresses pathological angiogenesis and CNV development.

Arginase in retinopathy

Ischemic retinopathies, such as diabetic retinopathy (DR), retinopathy of prematurity and retinal vein occlusion are a major cause of blindness in developed nations worldwide. Each of these conditions is associated with early neurovascular dysfunction. However, conventional therapies target clinically significant macula edema or neovascularization, which occur much later. Intra-ocular injections of anti-VEGF show promise in reducing retinal edema, but the effects are usually transient and the need for repeated injections increases the risk of intraocular infection. Laser photocoagulation can control pathological neovascularization, but may impair vision and in some patients the retinopathy continues to progress. Moreover, neither treatment targets early stage disease or promotes repair. This review examines the potential role of the ureahydrolase enzyme arginase as a therapeutic target for the treatment of ischemic retinopathy. Arginase metabolizes l-arginine to form proline, polyamines and glutamate. Excessive arginase activity reduces the l-arginine supply for nitric oxide synthase (NOS), causing it to become uncoupled and produce superoxide and less NO. Superoxide and NO react and form the toxic oxidant peroxynitrite. The catabolic products of polyamine oxidation and glutamate can induce more oxidative stress and DNA damage, both of which can cause cellular injury. Studies indicate that neurovascular injury during retinopathy is associated with increased arginase expression/activity, decreased NO, polyamine oxidation, formation of superoxide and peroxynitrite and dysfunction and injury of both vascular and neural cells. Furthermore, data indicate that the cytosolic isoform arginase I (AI) is involved in hyperglycemia-induced dysfunction and injury of vascular endothelial cells whereas the mitochondrial isoform arginase II (AII) is involved in neurovascular dysfunction and death following hyperoxia exposure. Thus, we postulate that activation of the arginase pathway causes neurovascular injury by uncoupling NOS and inducing polyamine oxidation and glutamate formation, thereby reducing NO and increasing oxidative stress, all of which contribute to the retinopathic process.

Vasomotor regulation of coronary microcirculation by oxidative stress: role of arginase

Overproduction of reactive oxygen species, i.e., oxidative stress, is associated with the activation of redox signaling pathways linking to inflammatory insults and cardiovascular diseases by impairing endothelial function and consequently blood flow dysregulation due to microvascular dysfunction. This review focuses on the regulation of vasomotor function in the coronary microcirculation by endothelial nitric oxide (NO) during oxidative stress and inflammation related to the activation of L-arginine consuming enzyme arginase. Superoxide produced in the vascular wall compromises vasomotor function by not only scavenging endothelium-derived NO but also inhibiting prostacyclin synthesis due to formation of peroxynitrite. The upregulation of arginase contributes to the deficiency of endothelial NO and microvascular dysfunction in various vascular diseases by initiating or following oxidative stress and inflammation. Hydrogen peroxide, a diffusible and stable oxidizing agent, exerts vasodilator function and plays important roles in the physiological regulation of coronary blood flow. In occlusive coronary ischemia, the release of hydrogen peroxide from the microvasculature helps to restore vasomotor function of coronary collateral microvessels with exercise training. However, excessive production and prolonged exposure of microvessels to hydrogen peroxide impairs NO-mediated endothelial function by reducing L-arginine availability through hydroxyl radical-dependent upregulation of arginase. The redox signaling can be a double-edged sword in the microcirculation, which helps tissue survival in one way by improving vasomotor regulation and elicits oxidative stress and tissue injury in the other way by causing vascular dysfunction. The impact of vascular arginase on the development of vasomotor dysfunction associated with angiotensin II receptor activation, hypertension, ischemia-reperfusion, hypercholesterolemia, and inflammatory insults is discussed.

Myeloid cells expressing VEGF and arginase-1 following uptake of damaged retinal pigment epithelium suggests potential mechanism that drives the onset of choroidal angiogenesis in mice

Whilst data recognise both myeloid cell accumulation during choroidal neovascularisation (CNV) as well as complement activation, none of the data has presented a clear explanation for the angiogenic drive that promotes pathological angiogenesis. One possibility that is a pre-eminent drive is a specific and early conditioning and activation of the myeloid cell infiltrate. Using a laser-induced CNV murine model, we have identified that disruption of retinal pigment epithelium (RPE) and Bruch's membrane resulted in an early recruitment of macrophages derived from monocytes and microglia, prior to angiogenesis and contemporaneous with lesional complement activation. Early recruited CD11b(+) cells expressed a definitive gene signature of selective inflammatory mediators particularly a pronounced Arg-1 expression. Accumulating macrophages from retina and peripheral blood were activated at the site of injury, displaying enhanced VEGF expression, and notably prior to exaggerated VEGF expression from RPE, or earliest stages of angiogenesis. All of these initial events, including distinct VEGF (+) Arg-1(+) myeloid cells, subsided when CNV was established and at the time RPE-VEGF expression was maximal. Depletion of inflammatory CCR2-positive monocytes confirmed origin of infiltrating monocyte Arg-1 expression, as following depletion Arg-1 signal was lost and CNV suppressed. Furthermore, our in vitro data supported a myeloid cell uptake of damaged RPE or its derivatives as a mechanism generating VEGF (+) Arg-1(+) phenotype in vivo. Our results reveal a potential early driver initiating angiogenesis via myeloid-derived VEGF drive following uptake of damaged RPE and deliver an explanation of why CNV develops during any of the stages of macular degeneration and can be explored further for therapeutic gain.

Oxidative status interactome map: towards novel approaches in experiment planning, data analysis, diagnostics and therapy

Experimental evidence suggests an immense variety of processes associated with and aimed at producing reactive oxygen and/or nitrogen species. Clinical studies implicate an enormous range of pathologies associated with reactive oxygen/nitrogen species metabolism deregulation, particularly oxidative stress. Recent advances in biochemistry, proteomics and molecular biology/biophysics of cells suggest oxidative stress to be an endpoint of complex dysregulation events of conjugated pathways consolidated under the term, proposed here, "oxidative status". The oxidative status concept, in order to allow for novel diagnostic and therapeutic approaches, requires elaboration of a new logic system comprehending all the features, versatility and complexity of cellular pro- and antioxidative components of different nature. We have developed a curated and regularly updated interactive interactome map of human cellular-level oxidative status allowing for systematization of the related most up-to-date experimental data. A total of more than 600 papers were selected for the initial creation of the map. The map comprises more than 300 individual factors with respective interactions, all subdivided hierarchically for logical analysis purposes. The pilot application of the interactome map suggested several points for further development of oxidative status-based technologies.

Nitric oxide synthase derangements and hypertension in kidney disease

PURPOSE OF REVIEW

Nitric oxide deficiency occurs by multiple mechanisms and contributes to the pathogenesis of progression of chronic kidney disease (CKD) and its cardiovascular complications. This article concentrates on recent developments on the regulation of the endogenous nitric oxide synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA) in CKD and on the importance of the nitric oxide synthases in kidney disease progression, particularly in diabetic nephropathy.

RECENT FINDINGS

The increased plasma ADMA seen in renal disease is generally predictive of severity of CKD progression and cardiovascular risk. However, some assumptions about the control of ADMA have been challenged: the primacy of the kidney as a metabolic organ for plasma ADMA regulation has come under scrutiny and the relative importance of the two isoforms of the ADMA-metabolizing enzymes dimethylarginine dimethylaminohydrolases (DDAHs) is being re-evaluated. Alterations in NOS also contribute to CKD progression with the endothelial isoform playing a major role in diabetic nephropathy.

SUMMARY

Improving our understanding of ADMA regulation is important since pharmacologic targeting of DDAH is underway. The major role of endothelial NOS-derived nitric oxide in diabetic nephropathy should lead to novel therapies. The beneficial actions of dietary nitrate supplementation on blood pressure and kidney disease are of considerable clinical relevance.

Oxidative species increase arginase activity in endothelial cells through the RhoA/Rho kinase pathway

BACKGROUND AND PURPOSE

NO produced by endothelial NOS is needed for normal vascular function. During diabetes, aging and hypertension, elevated levels of arginase can compete with NOS for available l-arginine, reducing NO and increasing superoxide (O(2) (.-)) production via NOS uncoupling. Elevated O(2) (.-) combines with NO to form peroxynitrite (ONOO(-)), further reducing NO. Oxidative species increase arginase activity, but the mechanism(s) involved are not known. Our study determined the mechanism involved in peroxynitrite and hydrogen peroxide-induced enhancement in endothelial arginase activity. We hypothesized that oxidative species increase arginase activity through PKC-activated RhoA/Rho kinase (ROCK) pathway.

EXPERIMENTAL APPROACH

Arginase activity/expression was analysed in bovine aortic endothelial cells (BAEC) treated with an ONOO(-) generator (SIN-1) or H(2) O(2). Pretreatment with inhibitors of Rho kinase (Y-27632) or PKC (Gö6976) was used to investigate the mechanism involved in arginase activation.

KEY RESULTS

Exposure to SIN-1 (25 µM, 24 h) or H(2) O(2) (25 µM, 8 h) increased arginase I expression and arginase activity (35% and 50%, respectively), which was prevented by ROCK inhibitor, Y-27632, PKC inhibitor, Gö6976 or siRNA to p115-Rho GEF. There was an early activation of p115-Rho GEF (SIN-1, 2 h; H(2) O(2), 1 h) and Rho A (SIN-1, 4 h; H(2) O(2), 1 h) that was prevented by using the PKC inhibitor. Exposure to SIN-1 and H(2) O(2 ) also reduced NOS activity, which was blocked by pretreatment with p115-RhoGEF siRNA.

CONCLUSIONS AND IMPLICATIONS

Our data indicate that the oxidative species ONOO(-) and H(2) O(2) increase arginase activity/expression through PKC-mediated activation of RhoA/Rho kinase pathway.

Inflammation and diabetic retinal microvascular complications

Diabetic retinopathy (DR) is one of the most common complications of diabetes and is a leading cause of blindness in people of the working age in Western countries. A major pathology of DR is microvascular complications such as non-perfused vessels, microaneurysms, dot/blot hemorrhages, cotton-wool spots, venous beading, vascular loops, vascular leakage and neovascularization. Multiple mechanisms are involved in these alternations. This review will focus on the role of inflammation in diabetic retinal microvascular complications and discuss the potential therapies by targeting inflammation.

Diabetes-induced vascular dysfunction involves arginase I

Arginase can cause vascular dysfunction by competing with nitric oxide synthase for l-arginine and by increasing cell proliferation and collagen formation, which promote vascular fibrosis/stiffening. We have shown that increased arginase expression/activity contribute to vascular endothelial cell (EC) dysfunction. Here, we examined the roles of the two arginase isoforms, arginase I and II (AI and AII, respectively), in this process. Experiments were performed using streptozotocin-induced diabetic mice: wild-type (WT) mice and knockout mice lacking the AII isoform alone (AI(+/+)AII(-/-)) or in combination with partial deletion of AI (AI(+/-)AII (-/-)). EC-dependent vasorelaxation of aortic rings and arterial fibrosis and stiffness were assessed in relation to arginase activity and expression. Diabetes reduced mean EC-dependent vasorelaxation markedly in diabetic WT and AI(+/+)AII(-/-) aortas (53% and 44% vs. controls, respectively) compared with a 27% decrease in AI(+/-)AII (-/-) vessels. Coronary fibrosis was also increased in diabetic WT and AI(+/+)AII(-/-) mice (1.9- and 1.7-fold vs. controls, respectively) but was not altered in AI(+/-)AII (-/-) diabetic mice. Carotid stiffness was increased by 142% in WT diabetic mice compared with 51% in AI(+/+)AII(-/-) mice and 19% in AI(+/-)AII (-/-) mice. In diabetic WT and AI(+/+)AII(-/-) mice, aortic arginase activity and AI expression were significantly increased compared with control mice, but neither parameter was altered in AI(+/-)AII (-/-) mice. In summary, AI(+/-)AII (-/-) mice exhibit better EC-dependent vasodilation and less vascular stiffness and coronary fibrosis compared with diabetic WT and AI(+/+)AII(-/-) mice. These data indicate a major involvement of AI in diabetes-induced vascular dysfunction.

Anti-inflammatory therapy for diabetic retinopathy

Diabetic retinopathy (DR) is one of the most common complications of diabetes. This devastating disease is a leading cause of blindness in people of working age in industrialized countries and affects the daily lives of millions of people. Despite tight glycemic control, blood pressure control and lipid-lowering therapy, the number of DR patients keeps growing and therapeutic approaches are limited. Moreover, there are significant limitations and side effects associated with the current therapies. Thus, there is a great need for development of new strategies for prevention and treatment of DR. Studies have shown that DR has prominent features of chronic, subclinical inflammation. This article focuses on the role of inflammation in DR and summarizes the progress of studies of anti-inflammatory strategies for DR.

Novel mechanisms of endothelial dysfunction in diabetes

Diabetes mellitus is a major risk factor for cardiovascular morbidity and mortality. This condition increases the risk of developing coronary, cerebrovascular, and peripheral arterial disease fourfold. Endothelial dysfunction is a major contributor to the pathogenesis of vascular disease in diabetes mellitus patients and has recently received increased attention. In this review article, some recent developments that could improve the knowledge of diabetes-induced endothelial dysfunction are discussed.

Role of advanced glycation end product receptors in the pathogenesis of diabetic retinopathy

PROBLEM

Advanced glycation end products (AGEs) and the interaction with their receptors (RAGE) play an important role in the pathogenesis of diabetic retinopathy (DR). Our study investigated whether serum soluble (s) RAGE (sRAGE) could serve as a prognostic tool for identifying the susceptibility to DR. Moreover, we examined the association between soluble forms of vascular cell adhesion molecules (sVCAM-1), nitric oxide (NO) and sRAGE levels in serum and the severity of DR.

METHODS

Circulating levels of sRAGE, sVCAM-1, and NO were examined in 37 type 2 diabetic patient and 20 age-matched healthy nondiabetic subjects using ELISA. The diabetic subjects were categorized as patients without retinopathy, patients with nonproliferative DR (NPDR), and patients with proliferative DR (PDR).

RESULTS

Serum sRAGE levels were significantly lower in patients with NPDR and PDR than in healthy controls and in those without retinopathy (1331.13 ± 126.13, 934.87 ± 66.27 vs. 1712.69 ± 167.3, 1833.1 ± 153.06 pg/ml, respectively, P<.05). Serum sVCAM-1 and NO were significantly higher in diabetic patients (1310.215 ± 54.712 vs. 616.55 ± 12.9 ng/ml and 96.432 ± 0.864 vs. 28.78 ± 5.88 μmol/l, respectively, P<.05) and were positively associated with the severity of DR.

CONCLUSIONS

The results indicate that sRAGE is an endogenous protection factor against the occurrence of accelerated DR.

Diabetic retinopathy, superoxide damage and antioxidants

Retinopathy, the leading cause of acquired blindness in young adults, is one of the most feared complications of diabetes, and hyperglycemia is considered as the major trigger for its development. The microvasculature of the retina is constantly bombarded by high glucose, and this insult results in many metabolic, structural and functional changes. Retinal mitochondria become dysfunctional, its DNA is damaged and proteins encoded by its DNA are decreased. The electron transport chain system becomes compromised, further producing superoxide and providing no relief to the retina from a continuous cycle of damage. Although the retina attempts to initiate repair mechanisms by inducing gene expressions of the repair enzymes, their mitochondrial accumulation remains deficient. Understanding the molecular mechanism of mitochondrial damage should help identify therapies to treat/retard this sight threatening complication of diabetes. Our hope is that if the retinal mitochondria are maintained healthy with adjunct therapies, the development and progression of diabetic retinopathy can be inhibited.