Diabetes-induced vascular dysfunction involves arginase I

Arginase 2 deficiency reduces hyperoxia-mediated retinal neurodegeneration through the regulation of polyamine metabolism

Hyperoxia treatment has been known to induce neuronal and glial death in the developing central nervous system. Retinopathy of prematurity (ROP) is a devastating disease in premature infants and a major cause of childhood vision impairment. Studies indicate that, in addition to vascular injury, retinal neurons are also affected in ROP. Using an oxygen-induced retinopathy (OIR) mouse model for ROP, we have previously shown that deletion of the arginase 2 (A2) significantly reduced neuro-glial injury and improved retinal function. In the current study, we investigated the mechanism of A2 deficiency-mediated neuroprotection in the OIR retina. Hyperoxia treatment has been known to induce neuronal death in neonates. During the hyperoxia phase of OIR, a significant increase in the number of apoptotic cells was observed in the wild-type (WT) OIR retina compared with A2-deficient OIR. Mass spectrometric analysis showed alterations in polyamine metabolism in WT OIR retina. Further, increased expression level of spermine oxidase was observed in WT OIR retina, suggesting increased oxidation of polyamines in OIR retina. These changes were minimal in A2-deficient OIR retina. Treatment using the polyamine oxidase inhibitor, N, N'-bis (2, 3-butadienyl)-1, 4-butanediamine dihydrochloride, significantly improved neuronal survival during OIR treatment. Our data suggest that retinal arginase is involved in the hyperoxia-induced neuronal degeneration in the OIR model, through the regulation of polyamine metabolism.

Role for high-glucose-induced protein O-GlcNAcylation in stimulating cardiac fibroblast collagen synthesis

Excess enzyme-mediated protein O-GlcNAcylation is known to occur with diabetes mellitus. A characteristic of diabetic cardiomyopathy is the development of myocardial fibrosis. The role that enhanced protein O-GlcNAcylation plays in modulating the phenotype of cardiac fibroblasts (CF) is unknown. To address this issue, rat CF were cultured in normal glucose (NG; 5 mM glucose) or high-glucose (HG; 25 mM) media for 48 h. Results demonstrate that CF cultured in HG have higher levels (~50%) of overall protein O-GlcNAcylation vs. NG cells. Key regulators of collagen synthesis such as transforming-growth factor-β1 (TGF-β1), SMADs 2/3, and SMAD 7 protein levels, including those of arginase I and II, were altered, leading to increases in collagen levels. The nuclear transcription factor Sp1 and arginase II evidence excess O-GlcNAcylation in HG cells. Expression in CF of an adenovirus coding for the enzyme N-acetylglucosaminidase, which removes O-GlcNAc moieties from proteins, decreased Sp1 and arginase II O-GlcNAcylation and restored HG-induced perturbations in CF back to NG levels. These findings may have important pathophysiological implications for the development of diabetes-induced cardiac fibrosis.

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

RATIONALE

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSION

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

Requirement of NOX2 expression in both retina and bone marrow for diabetes-induced retinal vascular injury

Objective

Diabetic retinopathy, a major cause of blindness, is characterized by increased expression of vascular endothelial growth factor (VEGF), leukocyte attachment to the vessel walls and increased vascular permeability. Previous work has shown that reactive oxygen species (ROS) produced by the superoxide generating enzyme NOX2/NADPH oxidase play a crucial role in the vascular pathology. The aim of this work was to identify the cellular sources of the damaging NOX2 activity by studies using bone marrow chimera mice.

Methods

Bone marrow cells were collected from the femurs and tibias of wild type and NOX2 deficient (NOX2^-/-) donor mice and injected intravenously into lethally irradiated NOX2^-/- and wild type recipients. Following recovery from radiation, mice were rendered diabetic by streptozotocin injections. The following groups of bone marrow chimeras were studied: non-diabetic WT→WT, diabetic WT→WT, diabetic WT→NOX2^-/-, diabetic NOX2^-/-→WT. After 4 weeks of diabetes, early signs of retinopathy were examined by measuring ROS, expression of VEGF and ICAM-1, leukocyte attachment to the vessel wall and vascular permeability.

Results

The retinas of the diabetic WT→WT chimeras showed significant increases in ROS as compared with the non-diabetic chimeras. These diabetes-induced alterations were correlated with increases in expression of VEGF and ICAM-1, leukocyte adhesion and vascular permeability. Each of these diabetes-induced alterations were significantly attenuated in the diabetic WT→NOX2^-/- and NOX2^-/-→WT chimera groups (p<0.05).

Conclusion

NOX2-generated ROS produced by both bone marrow-derived cells and resident retinal cells contribute importantly to retinal vascular injury in the diabetic retina. Targeting NOX2 in bone marrow and/or retinal cells may represent a novel therapeutic strategy for the treatment/prevention of vascular injury in the diabetic retina.

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.

Akita spontaneously type 1 diabetic mice exhibit elevated vascular arginase and impaired vascular endothelial and nitrergic function

BACKGROUND

Elevated arginase (Arg) activity is reported to be involved in diabetes-induced vascular endothelial dysfunction. It can reduce L-arginine availability to nitric oxide (NO) synthase (NOS) and NO production. Akita mice, a genetic non-obese type 1 diabetes model, recapitulate human diabetes. We determined the role of Arg in a time-course of diabetes-associated endothelial dysfunction in aorta and corpora cavernosa (CC) from Akita mice.

METHODS AND RESULTS

Endothelium-dependent relaxation, Arg and NOS activity, and protein expression levels of Arg and constitutive NOS were assessed in aortas and CC from Akita and non-diabetic wild type (WT) mice at 4, 12 and 24 wks of age. Systolic blood pressure (SBP) was assessed by tail cuff. In aorta and CC, Akita mice exhibited a progressive impairment of vascular endothelial and nitrergic function increased Arg activity and expression (Arg1 in aorta and both Arg1 and Arg2 in CC) compared with that of age-matched WT mice. Treatment of aorta and CC from Akita mice with an Arg inhibitor (BEC or ABH) reduced diabetes-induced elevation of Arg activity and restored endothelial and nitrergic function. Reduced levels of phospho-eNOS at Ser(1177) (in aorta and CC) and nNOS expression (in CC) were observed in Akita mice at 12 and 24 wks. Akita mice also had decreased NOS activity in aorta and CC at 12 and 24 wks that was restored by BEC treatment. Further, Akita mice exhibited moderately increased SBP at 24 wks and increased sensitivity to PE-induced contractions in aorta and sympathetic nerve stimulation in CC at 12 and 24 wks.

CONCLUSIONS

Over 24 wks of diabetes in Akita mice, both aortic and cavernosal tissues exhibited increased Arg activity/expression, contributing to impaired endothelial and nitrergic function and reduced NO production. Our findings demonstrate involvement of Arg activity in diabetes-induced impairment of vascular function in Akita mouse.

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.

The subcellular compartmentalization of arginine metabolizing enzymes and their role in endothelial dysfunction

The endothelial production of nitric oxide (NO) mediates endothelium-dependent vasorelaxation and restrains vascular inflammation, smooth muscle cell proliferation, and platelet aggregation. Impaired production of NO is a hallmark of endothelial dysfunction and promotes the development of cardiovascular disease. In endothelial cells, NO is generated by endothelial nitric oxide synthase (eNOS) through the conversion of its substrate, l-arginine to l-citrulline. Reduced access to l-arginine has been proposed as a major mechanism underlying reduced eNOS activity and NO production in cardiovascular disease. The arginases (Arg1 and Arg2) metabolize l-arginine to generate l-ornithine and urea and increased expression of arginase has been proposed as a mechanism of reduced eNOS activity secondary to the depletion of l-arginine. Indeed, supplemental l-arginine and suppression of arginase activity has been shown to improve endothelium-dependent relaxation and ameliorate cardiovascular disease. However, this simple relationship is complicated by observations that l-arginine concentrations in endothelial cells remain sufficiently high to support NO synthesis. Accordingly, the subcellular compartmentalization of intracellular l-arginine into poorly interchangeable pools has been proposed to allow for the local depletion of pools or pockets of l-arginine. In agreement with this, there is considerable evidence supporting the importance of the subcellular localization of l-arginine metabolizing enzymes. In endothelial cells in vitro and in vivo, eNOS is found in discrete intracellular locations and the capacity to generate NO is heavily influenced by its localization inside the cell. Arg1 and Arg2 also reside in different subcellular environments and are thought to differentially influence endothelial function. The plasma membrane solute transporter, CAT-1 and the arginine recycling enzyme, arginosuccinate lyase, co-localize with eNOS and facilitate NO release. Herein, we highlight the importance of the subcellular location of eNOS and arginine transporting and metabolizing enzymes to NO release and cardiovascular disease.

Arginase as a mediator of diabetic retinopathy

We have shown previously that diabetes causes increases in retinal arginase activity that are associated with impairment of endothelial cell (EC)-dependent vasodilation and increased formation of the peroxynitrite biomarker nitrotyrosine. Arginase blockade normalizes vasodilation responses and reduces nitrotyrosine formation, suggesting that overactive arginase contributes to diabetic retinopathy by reducing NO and increasing oxidative stress. We tested this hypothesis by studies in streptozotocin-induced diabetic mice and high glucose (HG) treated retinal ECs. Our results show that arginase activity is increased in both diabetic retinas and HG-treated retinal ECs as compared with the controls. Western blot shows that both arginase isoforms are present in retinal vessels and ECs and arginase I is increased in the diabetic vessels and HG-treated retinal ECs. Nitrate/nitrite levels are significantly increased in diabetic retinas, indicating an increase in total NO products. However, levels of nitrite, an indicator of bioavailable NO, are reduced by diabetes. Imaging analysis of NO formation in retinal sections confirmed decreases in NO formation in diabetic retinas. The decrease in NO is accompanied by increased O2.− formation and increased leukocyte attachment in retinal vessels. Studies in knockout mice show that arginase gene deletion enhances NO formation, reduces O2.− and prevents leukostasis in the diabetic retinas. HG treatment of retinal ECs also reduces NO release, increases oxidative stress, increases ICAM-1, and induces EC death. Arginase inhibitor treatment reverses these effects. In conclusion, diabetes- and HG-induced signs of retinal vascular activation and injury are associated with increased arginase activity and expression, decreased bioavailable NO, and increased O2.− formation. Blockade of the arginase pathway prevents these alterations, suggesting a primary role of arginase in the pathophysiological process.

Insights into the arginine paradox: evidence against the importance of subcellular location of arginase and eNOS

Reduced production of nitric oxide (NO) is one of the first indications of endothelial dysfunction and precedes overt cardiovascular disease. Increased expression of Arginase has been proposed as a mechanism to account for diminished NO production. Arginases consume l-arginine, the substrate for endothelial nitric oxide synthase (eNOS), and l-arginine depletion is thought to competitively reduce eNOS-derived NO. However, this simple relationship is complicated by the paradox that l-arginine concentrations in endothelial cells remain sufficiently high to support NO synthesis. One mechanism proposed to explain this is compartmentalization of intracellular l-arginine into distinct, poorly interchangeable pools. In the current study, we investigated this concept by targeting eNOS and Arginase to different intracellular locations within COS-7 cells and also BAEC. We found that supplemental l-arginine and l-citrulline dose-dependently increased NO production in a manner independent of the intracellular location of eNOS. Cytosolic arginase I and mitochondrial arginase II reduced eNOS activity equally regardless of where in the cell eNOS was expressed. Similarly, targeting arginase I to disparate regions of the cell did not differentially modify eNOS activity. Arginase-dependent suppression of eNOS activity was reversed by pharmacological inhibitors and absent in a catalytically inactive mutant. Arginase did not directly interact with eNOS, and the metabolic products of arginase or downstream enzymes did not contribute to eNOS inhibition. Cells expressing arginase had significantly lower levels of intracellular l-arginine and higher levels of ornithine. These results suggest that arginases inhibit eNOS activity by depletion of substrate and that the compartmentalization of l-arginine does not play a major role.

Arginase promotes skeletal muscle arteriolar endothelial dysfunction in diabetic rats

Endothelial dysfunction is a characteristic feature in diabetes that contributes to the development of vascular disease. Recently, arginase has been implicated in triggering endothelial dysfunction in diabetic patients and animals by competing with endothelial nitric oxide synthase for substrate l-arginine. While most studies have focused on the coronary circulation and large conduit blood vessels, the role of arginase in mediating diabetic endothelial dysfunction in other vascular beds has not been fully investigated. In the present study, we determined whether arginase contributes to endothelial dysfunction in skeletal muscle arterioles of diabetic rats. Diabetes was induced in male Sprague Dawley rats by streptozotocin injection. Four weeks after streptozotocin administration, blood glucose, glycated hemoglobin, and vascular arginase activity were significantly increased. In addition, a significant increase in arginase I and II mRNA expression was detected in gracilis muscle arterioles of diabetic rats compared to age-matched, vehicle control animals. To examine endothelial function, first-order gracilis muscle arterioles were isolated, cannulated in a pressure myograph system, exposed to graded levels of luminal flow, and internal vessel diameter measured. Increases in luminal flow (0–50 μL/min) caused progressive vasodilation in arterioles isolated from control, normoglycemic animals. However, flow-induced vasodilation was absent in arterioles obtained from streptozotocin-treated rats. Acute in vitro pretreatment of blood vessels with the arginase inhibitors N^ω-hydroxy-nor-l-arginine or S-(2-boronoethyl)-l-cysteine restored flow-induced responses in arterioles from diabetic rats and abolished differences between diabetic and control animals. Similarly, acute in vitro pretreatment with l-arginine returned flow-mediated vasodilation in vessels from diabetic animals to that of control rats. In contrast, d-arginine failed to restore flow-induced dilation in arterioles isolated from diabetic animals. Administration of sodium nitroprusside resulted in a similar degree of dilation in arterioles isolated from control or diabetic rats. In conclusion, the present study identifies arginase as an essential mediator of skeletal muscle arteriolar endothelial dysfunction in diabetes. The ability of arginase to induce endothelial dysfunction in skeletal muscle arterioles may further compromise glucose utilization and facilitate the development of hypertension in diabetes.

The role of arginase I in diabetes-induced retinal vascular dysfunction in mouse and rat models of diabetes

AIMS/HYPOTHESIS

A reduction in retinal blood flow occurs early in diabetes and is likely to be involved in the development of diabetic retinopathy. We hypothesise that activation of the arginase pathway could have a role in the vascular dysfunction of diabetic retinopathy.

METHODS

Experiments were performed using a mouse and rat model of streptozotocin (STZ)-induced diabetes for in vivo and ex vivo analysis of retinal vascular function. For in vivo studies, mice were infused with the endothelial-dependent vasodilator acetylcholine (ACh) or the endothelial-independent vasodilator sodium nitroprusside (SNP), and vasodilation was assessed using a fundus microscope. Ex vivo assays included pressurised vessel myography, western blotting and arginase activity measurements.

RESULTS

ACh-induced retinal vasodilation was markedly impaired in diabetic mice (40% of control values), whereas SNP-induced dilation was not altered. The diabetes-induced vascular dysfunction was markedly blunted in mice lacking one copy of the gene encoding arginase I and in mice treated with the arginase inhibitor 2(S)-amino-6-boronohexanoic acid. Ex vivo studies performed using pressure myography and central retinal arteries isolated from rats with STZ-induced diabetes showed a similar impairment of endothelial-dependent vasodilation that was partially blunted by pretreatment of the isolated vessels with another arginase inhibitor, (S)-2-boronoethyl-L-cysteine. The diabetes-induced vascular alterations were associated with significant increases in both arginase I protein levels and total arginase activity.

CONCLUSIONS/INTERPRETATION

These results indicate that, in the mouse and rat model, diabetes-induced increases in arginase I were involved in the diabetes-induced impairment of retinal blood flow by a mechanism involving vascular endothelial cell dysfunction.

Vitamin D is a regulator of endothelial nitric oxide synthase and arterial stiffness in mice

The vitamin D hormone 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3] is essential for the preservation of serum calcium and phosphate levels but may also be important for the regulation of cardiovascular function. Epidemiological data in humans have shown that vitamin D insufficiency is associated with hypertension, left ventricular hypertrophy, increased arterial stiffness, and endothelial dysfunction in normal subjects and in patients with chronic kidney disease and type 2 diabetes. However, the pathophysiological mechanisms underlying these associations remain largely unexplained. In this study, we aimed to decipher the mechanisms by which 1,25(OH)2D3 may regulate systemic vascular tone and cardiac function, using mice carrying a mutant, functionally inactive vitamin D receptor (VDR). To normalize calcium homeostasis in VDR mutant mice, we fed the mice lifelong with the so-called rescue diet enriched with calcium, phosphate, and lactose. Here, we report that VDR mutant mice are characterized by lower bioavailability of the vasodilator nitric oxide (NO) due to reduced expression of the key NO synthesizing enzyme, endothelial NO synthase, leading to endothelial dysfunction, increased arterial stiffness, increased aortic impedance, structural remodeling of the aorta, and impaired systolic and diastolic heart function at later ages, independent of changes in the renin-angiotensin system. We further demonstrate that 1,25(OH)2D3 is a direct transcriptional regulator of endothelial NO synthase. Our data demonstrate the importance of intact VDR signaling in the preservation of vascular function and may provide a mechanistic explanation for epidemiological data in humans showing that vitamin D insufficiency is associated with hypertension and endothelial dysfunction.

L-arginine, tetrahydrobiopterin, nitric oxide and diabetes

PURPOSE OF REVIEW

The endothelial isoform of nitric oxide synthase (eNOS) is constitutively expressed but dynamically regulated by a number of factors. Building our knowledge of this regulation is necessary to understand and modulate the bioavailability of nitric oxide, central to the cardiovascular complications of diabetes and other diseases. This review will focus on the eNOS substrate (L-arginine), its cofactor (tetrahydrobiopterin), and mechanisms related to the uncoupling of eNOS activity.

RECENT FINDINGS

The global arginine bioavailability ratio has been proposed as a biomarker reflective of L-arginine availability, arginase activity, and citrulline cycling, as all of these processes impact eNOS activity. The failure of oral supplementation of tetrahydrobiopterin to recouple eNOS has emphasized the importance of the tetrahydrobiopterin to dihydrobiopterin ratio. Identification of transporters for biopterin species as well as signals that regulate endogenous arginine production have provided insight for alternative strategies to raise endothelial tetrahydrobiopterin levels while reducing dihydrobiopterin and alter eNOS activity. Finally, new information about redox regulation of eNOS itself may point to ways of controlling oxidative stress in the vasculature.

SUMMARY

Restoring proper eNOS activity is key to ameliorating or preventing cardiovascular complications of diabetes. Continued investigation is needed to uncover new means for maintaining endothelial nitric oxide bioavailability.

Arginase Inhibition Improves Endothelial Function in Patients With Coronary Artery Disease and Type 2 Diabetes Mellitus

Background—

Endothelial dysfunction plays an important role in the early development of atherosclerosis and vascular complications in type 2 diabetes mellitus. Increased expression and activity of arginase, metabolizing the nitric oxide substrate l -arginine, may result in reduced production of nitric oxide and thereby endothelial dysfunction. We hypothesized that inhibition of arginase activity improves endothelial function in patients with coronary artery disease (CAD) and type 2 diabetes mellitus.

Methods and Results—

Three groups of subjects were included: 16 patients with CAD, 16 patients with CAD and type 2 diabetes mellitus (CAD+Diabetes), and 16 age-matched healthy control subjects. Forearm endothelium-dependent and endothelium-independent vasodilatation were assessed with venous occlusion plethysmography before and during intra-arterial infusion of the arginase inhibitor N ω -hydroxy-nor- l -arginine (nor-NOHA; 0.1 mg/min). Nor-NOHA was also coinfused with the nitric oxide synthase inhibitor ( N G -monomethyl L-arginine). The expression of arginase was determined in the internal mammary artery of patients undergoing bypass surgery. Nor-NOHA markedly increased endothelium-dependent vasodilatation (up to 2-fold) in patients with CAD+Diabetes and CAD ( P <0.001) but not in the control group. N G -monomethyl L-arginine completely inhibited the increase in endothelium-dependent vasodilatation induced by nor-NOHA. Endothelium-independent vasodilatation was slightly improved by nor-NOHA in the CAD+Diabetes group. Arginase I was expressed in vascular smooth muscle cells and endothelial cells, and arginase II was expressed in endothelial cells of patients with and without diabetes mellitus.

Conclusions—

Arginase inhibition markedly improves endothelial function in patients with CAD and type 2 diabetes mellitus suggesting that increased arginase activity is a key factor in the development of endothelial dysfunction.

Prevention of diabetes-induced arginase activation and vascular dysfunction by Rho kinase (ROCK) knockout

AIMS

We determined the role of the Rho kinase (ROCK) isoforms in diabetes-induced vascular endothelial dysfunction and enhancement of arginase activity and expression.

METHODS AND RESULTS

Studies were performed in aortic tissues from haplo-insufficient (H-I) ROCK1 and ROCK2 mice and wild-type (WT) mice rendered diabetic with streptozotocin and in bovine aortic endothelial cells (BAECs) treated with high glucose (HG, 25 mM). Protein expression of both ROCK isoforms was substantially elevated in aortas of WT mice after 8 weeks of diabetes and in BAECs after 48 h in HG. Impairment of endothelium-dependent vasorelaxation of aortas was observed in diabetic WT mice. However, there was no impairment in aortas of diabetic ROCK1 H-I mice and less impairment in aortas of diabetic ROCK2 H-I mice, compared with non-diabetic mice. These vascular effects were associated with the prevention of diabetes-induced decrease in nitric oxide (NO) production and a rise in arginase activity/expression. Acute treatment with the arginase inhibitor, BEC, improved endothelium-dependent vasorelaxation of aortas of both diabetic WT and ROCK2, but not of ROCK1 mice.

CONCLUSION

Partial deletion of either ROCK isoform, but to a greater extent ROCK1, attenuates diabetes-induced vascular endothelial dysfunction by preventing increased arginase activity and expression and reduction in NO production in type 1 diabetes. Limiting ROCK and arginase activity improves vascular function in diabetes.