Gene transfer of endothelial nitric oxide synthase improves relaxation of carotid arteries from diabetic rabbits

The impact of environmental and dietary exposure on gestational diabetes mellitus: a comprehensive review emphasizing the role of oxidative stress

Gestational diabetes mellitus (GDM) is a common pregnancy complication closely associated with maternal oxidative and antioxidant imbalance, known as oxidative stress. Environmental and dietary exposure plays an important role in inducing oxidative stress during pregnancy. This review aims to provide an in-depth analysis of the role of oxidative stress induced by environmental and dietary exposure in GDM while incorporating current research frontiers. Environmental pollution, smoking, excessive nutrition, and unhealthy eating habits such as a high-fat diet and vitamin deficiency, may contribute to the generation and accumulation of reactive oxygen species (ROS), leading to oxidative stress. Within the pathway of oxidative stress in GDM, the production and clearance mechanisms of ROS play a pivotal role. Relevant studies have demonstrated that ROS production is closely linked to insulin resistance, adipose tissue accumulation, inflammation, and other pathological processes. Antioxidant substances like vitamins C and E or glutathione can mitigate oxidative stress damage on pregnant women and fetuses by scavenging ROS. Currently, there remain several cutting-edge issues regarding the involvement of the oxidative stress pathway in GDM pathogenesis as well as its relationship with environmental and dietary factors, for instance: how to reduce maternal oxidative stress levels through dietary adjustments or lifestyle modifications; how antioxidant substances can be utilized for intervention treatment; and accurate assessment methods for maternal oxidative stress status along with its association with GDM risk. In conclusion, environmental and dietary factors exert significant influence on GDM pathogenesis while highlighting increasing attention toward understanding the role played by the oxidative stress pathway within this context. In-depth research endeavors within this field are anticipated to offer novel insights into prevention strategies as well as therapeutic approaches for GDM.

Soluble epoxide hydrolase inhibition reverses cognitive dysfunction in a mouse model of metabolic syndrome by modulating inflammation

Midlife metabolic syndrome (MetS) is associated with cognitive impairment in late life. The mechanism of delayed MetS-related cognitive dysfunction (MetSCD) is not clear, but it has been linked to systemic inflammation and chronic cerebral microangiopathy. Currently there is no treatment for late life MetSCD other than early risk factor modification. We investigated the effect of soluble epoxide hydrolase (sEH) inhibitor 4-[[trans-4-[[(tricyclo[3.3.1.13,7]dec-1-ylamino)carbonyl]amino]cyclohexyl]oxy]-benzoic acid (t-AUCB) on cognitive performance, cerebral blood flow (CBF), and central and peripheral inflammation in the high-fat diet (HFD) model of MetS in mice. At 6 weeks of age, male mice were randomly assigned to receive either HFD or standard chow (STD) for 6 months. Mice received either t-AUCB or vehicle for 4 weeks. Cognitive performance was evaluated, followed by CBF measurement using magnetic resonance imaging (MRI). At the end of the study, blood was collected for measurement of eicosanoids and inflammatory cytokines. The brains were then analyzed by immunohistochemistry for glial activation markers. The HFD caused a significant impairment in novel object recognition. Treatment with t-AUCB increased plasma levels of 14,15-EET, prevented this cognitive impairment and modified hippocampal glial activation and plasma cytokine levels, without affecting CBF in mice on HFD. In conclusion, sEH inhibition for four weeks prevents cognitive deficits in mice on chronic HFD by modulating inflammatory processes without affecting CBF.

Oxidative phosphorylation promotes vascular calcification in chronic kidney disease

Metabolism has been reported to associate with the progression of vascular diseases. However, how vascular calcification in chronic kidney disease (CKD) is regulated by metabolic status remains poorly understood. Using a model of 5/6 nephrectomy, we demonstrated that the aortic tissues of CKD mice had a preference for using oxidative phosphorylation (OXPHOS). Both high phosphate and human uremic serum-stimulated vascular smooth muscle cells (VSMCs) had enhanced mitochondrial respiration capacity, while the glycolysis level was not significantly different. Besides, 2-deoxy-d-glucose (2-DG) exacerbated vascular calcification by upregulating OXPHOS. The activity of cytochrome c oxidase (COX) was higher in the aortic tissue of CKD mice than those of sham-operated mice. Moreover, the expression levels of COX15 were higher in CKD patients with aortic arch calcification (AAC) than those without AAC, and the AAC scores were correlated with the expression level of COX15. Suppressing COX sufficiently attenuated vascular calcification. Our findings verify the relationship between OXPHOS and calcification, and may provide potential therapeutic approaches for vascular calcification in CKD.

Hypertrophic preconditioning attenuates myocardial ischemia/reperfusion injury through the deacetylation of isocitrate dehydrogenase 2

To test the hypothesis that transient nonischemic stimulation of hypertrophy would render the heart resistant to subsequent ischemic stress, short-term transverse aortic constriction (TAC) was performed in mice and then withdrawn for several days by aortic debanding, followed by subsequent myocardial exposure to ischemia/reperfusion (I/R). Following I/R injury, the myocardial infarct size and apoptosis were markedly reduced, and contractile function was significantly improved in the TAC preconditioning group compared with the control group. Mechanistically, hypertrophic preconditioning remarkably alleviated I/R-induced oxidative stress, as evidenced by the increased reduced nicotinamide adenine dinucleotide phosphate (NADPH)/nicotinamide adenine dinucleotide phosphate (NADP) ratio, increase in the reduced glutathione (GSH)/oxidized glutathione (GSSH) ratio, and reduced mitochondrial reactive oxygen species (ROS) production. Moreover, TAC preconditioning inhibited caspase-3 activation and mitigated the mitochondrial impairment by deacetylating isocitrate dehydrogenase 2 (IDH2) via a sirtuin 3 (SIRT3)-dependent mechanism. In addition, the expression of a genetic deacetylation mimetic IDH2 mutant (IDH2 K413R) in cardiomyocytes, which increased IDH2 enzymatic activity and decreased mitochondrial ROS production, and ameliorated I/R injury, whereas the expression of a genetic acetylation mimetic (IDH2 K413Q) in cardiomyocytes abolished these protective effects of hypertrophic preconditioning. Furthermore, both the activity and expression of the SIRT3 protein were markedly increased in preconditioned mice exposed to I/R. Treatment with an adenovirus encoding SIRT3 partially emulated the actions of hypertrophic preconditioning, whereas genetic ablation of SIRT3 in mice blocked the cardioprotective effects of hypertrophic preconditioning. The present study identifies hypertrophic preconditioning as a novel endogenous self-defensive and cardioprotective strategy for cardiac I/R injury that induces IDH2 deacetylation through a SIRT3-dependent mechanism. A therapeutic strategy targeting IDH2 may be a promising treatment for cardiac ischemic injury.

Hypertrophic preconditioning cardioprotection after myocardial ischaemia/reperfusion injury involves ALDH2-dependent metabolism modulation

Brief episodes of ischaemia and reperfusion render the heart resistant to subsequent prolonged ischaemic insult, termed ischaemic preconditioning. Here, we hypothesized that transient non-ischaemic stress by hypertrophic stimulation would induce endogenous cardioprotective signalling and enhance cardiac resistance to subsequent ischaemic damage. Transient transverse aortic constriction (TAC) or Ang-Ⅱ treatment was performed for 3-7 days in male mice and then withdrawn for several days by either aortic debanding or discontinuing Ang-Ⅱ treatment, followed by subsequent exposure to regional myocardial ischaemia by in situ coronary artery ligation. Following ischaemia/reperfusion (I/R) injury, myocardial infarct size and apoptosis were markedly reduced and contractile function was significantly improved in the TAC preconditioning group compared with that in the control group. Similar results were observed in mice receiving Ang-Ⅱ infusion. Mechanistically, TAC preconditioning enhanced ALDH2 activity, promoted AMPK activation and improved mitochondrial energy metabolism by increasing myocardial OXPHOS complex expression, elevating the mitochondrial ATP content and improving viable myocardium glucose uptake. Moreover, TAC preconditioning significantly mitigated I/R-induced myocardial iNOS/gp91^phox activation, inhibited endoplasmic reticulum stress and ameliorated mitochondrial impairment. Using a pharmacological approach to inhibit AMPK signalling in the presence or absence of preconditioning, we demonstrated AMPK-dependent protective mechanisms of TAC preconditioning against I/R injury. Furthermore, treatment with adenovirus-encoded ALDH2 partially emulated the actions of hypertrophic preconditioning, as evidenced by improved mitochondrial metabolism, inhibited oxidative stress-induced mitochondrial damage and attenuated cell death through an AMPK-dependent mechanism, whereas genetic ablation of ALDH2 abrogated the aforementioned actions of TAC preconditioning. The present study demonstrates that preconditioning with hypertrophic stress protects the heart from I/R injury via mechanisms that improve mitochondrial metabolism, reduce oxidative/nitrative stress and inhibit apoptosis. ALDH2 is obligatorily required for the development of cardiac hypertrophic preconditioning and acts as the mediator of this process.

Mammalian target of rapamycin inhibition attenuates myocardial ischaemia-reperfusion injury in hypertrophic heart

Pathological cardiac hypertrophy aggravated myocardial infarction and is causally related to autophagy dysfunction and increased oxidative stress. Rapamycin is an inhibitor of serine/threonine kinase mammalian target of rapamycin (mTOR) involved in the regulation of autophagy as well as oxidative/nitrative stress. Here, we demonstrated that rapamycin ameliorates myocardial ischaemia reperfusion injury by rescuing the defective cytoprotective mechanisms in hypertrophic heart. Our results showed that chronic rapamycin treatment markedly reduced the phosphorylated mTOR and ribosomal protein S6 expression, but not Akt in both normal and aortic-banded mice. Moreover, chronic rapamycin treatment significantly mitigated TAC-induced autophagy dysfunction demonstrated by prompted Beclin-1 activation, elevated LC3-II/LC3-I ratio and increased autophagosome abundance. Most importantly, we found that MI/R-induced myocardial injury was markedly reduced by rapamycin treatment manifested by the inhibition of myocardial apoptosis, the reduction of myocardial infarct size and the improvement of cardiac function in hypertrophic heart. Mechanically, rapamycin reduced the MI/R-induced iNOS/gp91phox protein expression and decreased the generation of NO and superoxide, as well as the cytotoxic peroxynitrite. Moreover, rapamycin significantly mitigated MI/R-induced endoplasmic reticulum stress and mitochondrial impairment demonstrated by reduced Caspase-12 activity, inhibited CHOP activation, decreased cytoplasmic Cyto-C release and preserved intact mitochondria. In addition, inhibition of mTOR also enhanced the phosphorylated ERK and eNOS, and inactivated GSK3β, a pivotal downstream target of Akt and ERK signallings. Taken together, these results suggest that mTOR signalling protects against MI/R injury through autophagy induction and ERK-mediated antioxidative and anti-nitrative stress in mice with hypertrophic myocardium.

Perivascular macrophages mediate the neurovascular and cognitive dysfunction associated with hypertension

Hypertension is a leading risk factor for dementia, but the mechanisms underlying its damaging effects on the brain are poorly understood. Due to a lack of energy reserves, the brain relies on continuous delivery of blood flow to its active regions in accordance with their dynamic metabolic needs. Hypertension disrupts these vital regulatory mechanisms, leading to the neuronal dysfunction and damage underlying cognitive impairment. Elucidating the cellular bases of these impairments is essential for developing new therapies. Perivascular macrophages (PVMs) represent a distinct population of resident brain macrophages that serves key homeostatic roles but also has the potential to generate large amounts of reactive oxygen species (ROS). Here, we report that PVMs are critical in driving the alterations in neurovascular regulation and attendant cognitive impairment in mouse models of hypertension. This effect was mediated by an increase in blood-brain barrier permeability that allowed angiotensin II to enter the perivascular space and activate angiotensin type 1 receptors in PVMs, leading to production of ROS through the superoxide-producing enzyme NOX2. These findings unveil a pathogenic role of PVMs in the neurovascular and cognitive dysfunction associated with hypertension and identify these cells as a putative therapeutic target for diseases associated with cerebrovascular oxidative stress.

Improvement of vascular function by magnetic nanoparticle-assisted circumferential gene transfer into the native endothelium

Gene therapy is a promising approach for chronic disorders that require continuous treatment such as cardiovascular disease. Overexpression of vasoprotective genes has generated encouraging results in animal models, but not in clinical trials. One major problem in humans is the delivery of sufficient amounts of genetic vectors to the endothelium which is impeded by blood flow, whereas prolonged stop-flow conditions impose the risk of ischemia. In the current study we have therefore developed a strategy for the efficient circumferential lentiviral gene transfer in the native endothelium under constant flow conditions. For that purpose we perfused vessels that were exposed to specially designed magnetic fields with complexes of lentivirus and magnetic nanoparticles thereby enabling overexpression of therapeutic genes such as endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF). This treatment enhanced NO and VEGF production in the transduced endothelium and resulted in a reduction of vascular tone and increased angiogenesis. Thus, the combination of MNPs with magnetic fields is an innovative strategy for site-specific and efficient vascular gene therapy.

Gene Therapy for the Extension of Vein Graft Patency: A Review

The mainstay of treatment for long-segment small-vessel chronic occlusive disease not amenable to endovascular intervention remains surgical bypass grafting using autologous vein. The procedure is largely successful and the immediate operative results almost always favorable. However, the lifespan of a given vein graft is highly variable, and less than 50% will remain primarily patent after 5 years. The slow process of graft malfunction is a result of the vein's chronic maladaptive response to the systemic arterial environment, its primary component being the uncontrolled proliferation of vascular smooth muscle cells (SMCs). It has recently been suggested that this response might be attenuated through pre-implantation genetic modification of the vein, so-called gene therapy for the extension of vein graft patency. Gene therapy seems particularly well suited for the prevention or postponement of vein graft failure since: (1) the stimulation of SMC proliferation appears to largely be an early and transient process, matching the kinetics of current gene transfer technology; (2) most veins are relatively normal and free of disease at the time of bypass allowing for effective gene transfer using a variety of systems; and (3) the target tissue is directly accessible during operation because manipulation and irrigation of the vein is part of the normal workflow of the surgical procedure. This review briefly summarizes the current knowledge of the incidence and basic mechanisms of vein graft failure, the vector systems and molecular targets that have been proposed as possible pre-treatments, the results of experimental genetic modification of vein grafts, and the few available clinical studies of gene therapy for vascular proliferative disorders.

Myocardin restores erectile function in diabetic rats: phenotypic modulation of corpus cavernosum smooth muscle cells

This study aimed to investigate whether gene transfer of myocardin to the penis of diabetic rats can modulate corpus cavernosum smooth muscle (CCSM) cells phenotype and restore erectile function. Five normal control rats, and 22 diabetic rats were randomly divided into four groups: rats transfected with adCMV-myocardin (N = 6), treated with empty vector (N = 6), injected with medium (N = 5), and sham-operated rats (N = 5). The erectile response was measured 7 days after transfection. The percent of smooth muscle and the expressions of SMα-actin, smooth muscle myosin heavy chain (SMMHC), calponin were evaluated. The increases in intracorporal pressure(ICP)/mean arterial pressure and total ICP in response to nerve stimulation in the adCMV-myocardin treated rats were significantly greater than those in the empty vector (P < 0.001 and P < 0.001), medium only (P < 0.001 and P < 0.001), and sham-operated rats (P < 0.001 and P < 0.001). The suppressed expressions of SMα-actin, SMMHC and calponin were completely restored, and the amount of smooth muscle in diabetic rats were not restored after treatment. It is concluded that myocardin ameliorated erectile responses in diabetic rats mainly via promoting phenotypic modulation of CCSM cells from a proliferative to a contractile state.

Brown fat lipoatrophy and increased visceral adiposity through a concerted adipocytokines overexpression induces vascular insulin resistance and dysfunction

In this study, we analyzed the role played by concerted expression of adipocytokines associated with brown fat lipoatrophy and increased visceral adiposity on triggering vascular insulin resistance and dysfunction in brown adipose tissue (BAT) insulin receptor knockout (BATIRKO) mice. In addition, we assessed whether vascular insulin resistance may aggravate vascular damage. The 52-wk-old, but not 33-wk-old, BATIRKO mice had a significant decrease of BAT mass associated with a significant increase of visceral white adipose tissue (WAT) mass, without changes in body weight. Brown fat lipoatrophy and increased visceral adiposity enhanced the concerted expression of adipocytokines (TNF-α, leptin, and plasminogen activator inhibitor 1) and nuclear factor-κB binding activity in BAT and visceral WAT, mainly in the gonadal depot, and aorta. Although those mice showed insulin sensitivity in the liver and skeletal muscle, insulin signaling in WAT (gonadal depot) and aorta was markedly impaired. Treatment with anti-TNF-α antibody impaired the inflammatory activity in visceral adipose tissue, attenuated insulin resistance in WAT and aorta and induced glucose tolerance. Finally, 52-wk-old BATIRKO mice showed vascular dysfunction, macrophage infiltration, oxidative stress, and a significant increase of gene markers of endothelial activation and inflammation, the latter effect being totally reverted by anti-TNF-α antibody treatment. Our results suggest that brown fat lipoatrophy and increased visceral adiposity through the concerted overexpression of cytoadipokines induces nuclear factor-κB-mediated inflammatory signaling, vascular insulin resistance, and vascular dysfunction. Inhibition of inflammatory activity by anti-TNF-α antibody treatment attenuates vascular insulin resistance and impairs gene expression of vascular dysfunction markers.

Tackling endothelial dysfunction by modulating NOS uncoupling: new insights into its pathogenesis and therapeutic possibilities

Endothelial nitric oxide synthase (eNOS) serves as a critical enzyme in maintaining vascular pressure by producing nitric oxide (NO); hence, it has a crucial role in the regulation of endothelial function. The bioavailability of eNOS-derived NO is crucial for this function and might be affected at multiple levels. Uncoupling of eNOS, with subsequently less NO and more superoxide generation, is one of the major underlying causes of endothelial dysfunction found in atherosclerosis, diabetes, hypertension, cigarette smoking, hyperhomocysteinemia, and ischemia/reperfusion injury. Therefore, modulating eNOS uncoupling by stabilizing eNOS activity, enhancing its substrate, cofactors, and transcription, and reversing uncoupled eNOS are attractive therapeutic approaches to improve endothelial function. This review provides an extensive overview of the important role of eNOS uncoupling in the pathogenesis of endothelial dysfunction and the potential therapeutic interventions to modulate eNOS for tackling endothelial dysfunction.

Essential role of caveolin-3 in adiponectin signalsome formation and adiponectin cardioprotection

OBJECTIVE

Adiponectin (APN) system malfunction is causatively related to increased cardiovascular morbidity/mortality in diabetic patients. The aim of the current study was to investigate molecular mechanisms responsible for APN transmembrane signaling and cardioprotection.

METHODS AND RESULTS

Compared with wild-type mice, caveolin-3 knockout (Cav-3KO) mice exhibited modestly increased myocardial ischemia/reperfusion injury (increased infarct size, apoptosis, and poorer cardiac function recovery; P<0.05). Although the expression level of key APN signaling molecules was normal in Cav-3KO, the cardioprotective effects of APN observed in wild-type were either markedly reduced or completely lost in Cav-3KO. Molecular and cellular experiments revealed that APN receptor 1 (AdipoR1) colocalized with Cav-3, forming AdipoR1/Cav-3 complex via specific Cav-3 scaffolding domain binding motifs. AdipoR1/Cav-3 interaction was required for APN-initiated AMP-activated protein kinase (AMPK)-dependent and AMPK-independent intracellular cardioprotective signalings. More importantly, APPL1 and adenylate cyclase, 2 immediately downstream molecules required for AMPK-dependent and AMPK-independent signaling, respectively, formed a protein complex with AdipoR1 in a Cav-3 dependent fashion. Finally, pharmacological activation of both AMPK plus protein kinase A significantly reduced myocardial infarct size and improved cardiac function in Cav-3KO animals.

CONCLUSIONS

Taken together, these results demonstrated for the first time that Cav-3 plays an essential role in APN transmembrane signaling and APN anti-ischemic/cardioprotective actions.

Expression of cytoskeleton and energetic metabolism-related proteins at human abdominal aortic aneurysm sites

OBJECTIVE

The purpose of this study was to evaluate the expression of proteins related to cytoskeleton and energetic metabolism at abdominal aortic aneurysm (AAA) sites using proteomics. Several remodeling-related mechanisms have been associated with AAA formation but less is known about the expression of proteins associated with cytoskeleton and energetic metabolism in AAAs.

METHODS

AAA samples (6.73 ± 0.40 cm size) were obtained from 13 patients during elective aneurysm repair. Control abdominal aortic samples were obtained from 12 organ donors. Proteins were analyzed using two-dimensional electrophoresis and mass spectrometry.

RESULTS

The expression of filamin was increased in the AAA site compared to control abdominal aortic samples while microfibril-associated glycoprotein-4 isotype 1, annexin A5 isotype 1, and annexin A2 were reduced compared with control abdominal aortic samples. Reduction in expression level of energetic metabolism-associated proteins such as triosephosphate isomerase, glyceraldehyde 3-phosphate dehydrogenase, and cytosolic aldehyde dehydrogenase was also observed in AAAs compared to controls. Reduction of triosephosphate isomerase expression was also observed by Western blot, which was accompanied by diminished triosephosphate isomerase activity. At the AAA site, pyruvate dehydrogenase expression was reduced and the content of both lactate and pyruvate was increased with respect to controls without changes in lactate dehydrogenase activity.

CONCLUSIONS

The present results suggest that an anaerobic metabolic state may be favored further to reduce the expression of cytoskeleton-related proteins. The better knowledge of molecular mechanism involved in AAAs may favor development of new clinical strategies.

Reactive oxygen species-induced impairment of endothelium-dependent relaxations in rat aortic rings: protection by methanolic extracts of Phoebe grandis

Generation of reactive oxygen species plays a pivotal role in the development of cardiovascular diseases. The present study describes the effects of the methanolic extract of Phoebe grandis (MPG) stem bark on reactive oxygen species-induced endothelial dysfunction in vitro. Endothelium-dependent (acetylcholine, ACh) and -independent relaxation (sodium nitroprusside, SNP) was investigated from isolated rat aorta of Sprague-Dawley (SD) in the presence of the β-NADH (enzymatic superoxide inducer) and MPG extract. Superoxide anion production in aortic vessels was measured by lucigen chemiluminesence. Thirty minutes incubation of the rat aorta in vitro with β-NADH increased superoxide radical production and significantly inhibited ACh-induced relaxations. Pretreatment with MPG (0.5, 5 and 50 μg/mL) restored the ACh-induced relaxations (R_max: 92.29% ± 2.93, 91.02% ± 4.54 and 88.31 ± 2.36, respectively) in the presence of β-NADH. MPG was ineffective in reversing the impaired ACh-induced relaxations caused by pyrogallol, a non-enzymatic superoxide generator. Superoxide dismutase (a superoxide scavenger), however, reversed the impaired ACh relaxations induced by both β-NADH and pyrogallol. MPG also markedly inhibited the β-NADH-induced generation of the superoxide radicals. Furthermore, MPG scavenging peroxyl radicals generated by tBuOOH (10⁻⁴ M).These results indicate that MPG may improve the endothelium dependent relaxations to ACh through its scavenging activity as well as by inhibiting the NADH/NADPH oxidase induced generation of superoxide anions.

Curcumin supplementation could improve diabetes-induced endothelial dysfunction associated with decreased vascular superoxide production and PKC inhibition

Background

Curcumin, an Asian spice and food-coloring agent, is known for its anti-oxidant properties. We propose that curcumin can improve diabetes-induced endothelial dysfunction through superoxide reduction.

Methods

Diabetes (DM) was induced in rats by streptozotocin (STZ). Daily curcumin oral feeding was started six weeks after the STZ injection. Twelve weeks after STZ injection, mesenteric arteriolar responses were recorded in real time using intravital fluorescence videomicroscopy. Superoxide and vascular protein kinase C (PKC-βII) were examined by hydroethidine and immunofluorescence, respectively.

Results

The dilatory response to acetylcholine (ACh) significantly decreased in DM arterioles as compared to control arterioles. There was no difference among groups when sodium nitroprusside (SNP) was used. ACh responses were significantly improved by both low and high doses (30 and 300 mg/kg, respectively) of curcumin supplementation. An oxygen radical-sensitive fluorescent probe, hydroethidine, was used to detect intracellular superoxide anion (O₂^●-) production. O₂^●- production was markedly increased in DM arterioles, but it was significantly reduced by supplementation of either low or high doses of curcumin. In addition, with a high dose of curcumin, diabetes-induced vascular PKC-βII expression was diminished.

Conclusion

Therefore, it is suggested that curcumin supplementation could improve diabetes-induced endothelial dysfunction significantly in relation to its potential to decrease superoxide production and PKC inhibition.

Short-term type 1 diabetes alters the mechanism of endothelium-dependent relaxation in the rat carotid artery

The aim of the present study was to examine the effect of an early stage of streptozotocin-induced diabetes on the mechanism(s) of endothelium-dependent relaxation. Diabetes was induced by a single injection of streptozotocin (48 mg/kg iv), and the ACh-induced relaxation of rat carotid arteries was examined 6 wk later. A diabetes-induced increase in superoxide levels, determined by L-012-induced chemiluminescence, from carotid arteries was associated with endothelial nitric oxide (NO) synthase (eNOS) uncoupling and increased catalytic subunit of NADPH oxidase expression. The sensitivity and maximum response to ACh were similar in normal and diabetic rats despite a decrease in NO release detected by 4-amino-5-methylamino-2′,7′-difluorofluorescein. In normal rats, N-nitro-l-arginine (100 μM) plus 1 H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (10 μM), to inhibit NOS and soluble guanylate cyclase (sGC), respectively, abolished ACh-induced relaxation, whereas in diabetic rats, the maximum relaxation to ACh was attenuated (maximum relaxation: 25 ± 5%), but not abolished, by that treatment. The remaining ACh-induced relaxation was abolished by NO scavengers, cupric chloride (to degrade nitrosothiols), or blockers of endothelial K+ channels. Western blot analysis of the carotid arteries indicated that diabetes significantly increased the expression of eNOS but decreased the proportion of eNOS expressed as the dimer. These findings demonstrate that in early diabetes, ACh-induced relaxation is maintained but is resistant to NOS inhibition. In early diabetes, nitrosothiol-mediated opening of K+ channels may act in conjunction with NO stimulation of sGC to maintain endothelium-dependent relaxation despite the increase in vascular superoxide levels.

Deferasirox removes cardiac iron and attenuates oxidative stress in the iron-overloaded gerbil

Iron-induced cardiovascular disease is the leading cause of death in iron-overloaded patients. Deferasirox is a novel, once daily oral iron chelator that was recently approved for the treatment of transfusional iron overload. Here, we investigate whether deferasirox is capable of removing cardiac iron and improving iron-induced pathogenesis of the heart using the iron overload gerbil model. Animals were randomly divided into three groups: control, iron overload, and iron overload + deferasirox treatment. Iron-dextran was given 100 mg/kg per 5 days i.p for 10 weeks. Deferasirox treatment was taken post iron loading and was given at 100 mg/kg/day p.o for 1 or 3 months. Cardiac iron concentration was determined by inductively coupled plasma atomic emission spectroscopy. Compared with the untreated group, deferasirox treatment for 1 and 3 months decreased cardiac iron concentration 17.1% (P = 0.159) and 23.5% (P < 0.05), respectively. These treatment-associated reductions in cardiac iron were paralleled by decreases in tissue ferritin expression of 20% and 38% at 1 and 3 months, respectively (P < 0.05). Using oxyblot analysis and hydroethidine fluorescence, we showed that deferasirox significantly reduces cardiac protein oxidation and superoxide abundance by 36 and 47.1%, respectively (P < 0.05). Iron-induced increase in oxidative stress was also associated with increased phosphorylation of ERK-, p38-, and JNK-mitogen-activated protein kinase (MAPK). Interestingly, deferasirox treatment significantly diminished the phosphorylation of all three MAPK subfamilies. These results suggest that deferasirox may confer a cardioprotective effect against iron induced injury.

A pivotal role of endothelial-specific NF-kappaB signaling in the pathogenesis of septic shock and septic vascular dysfunction

Although the role of NF-kappaB in the pathogenesis of sepsis and septic shock has been extensively studied, little is known about the causative contribution of endothelial-intrinsic NF-kappaB to these pathological processes. In this study, we used transgenic (TG) mice (on FVB genetic background) that conditionally overexpress the NF-kappaB inhibitor, mutant I-kappaBalpha, selectively on endothelium and their transgene-negative littermates (wild type (WT)) to define the causative role of endothelial-specific NF-kappaB signaling in septic shock and septic vascular dysfunction. In WT mice, LPS challenge caused systemic hypotension, a significantly blunted vasoconstrictor response to norepinephrine, and an impaired endothelium-dependent vasodilator response to acetylcholine, concomitant with a markedly increased aortic inducible NO synthase expression, significantly elevated plasma and aortic levels of nitrite/nitrate, increased aortic TNF-alpha expression, and decreased aortic endothelial NO synthase (eNOS) expression. In TG mice whose endothelial NF-kappaB was selectively blocked, LPS caused significantly less hypotension and no impairments in vasoconstrictor and endothelium-dependent vasodilator responses, associated with significantly reduced aortic inducible NO synthase expression, decreased plasma and aortic levels of nitrite/nitrate, reduced aortic TNF-alpha expression, and increased aortic eNOS expression. TNF-alpha knockout mice prevented LPS-induced eNOS down-regulation. WT mice subjected to cecal ligation and puncture showed significant systemic hypotension, which was prevented in TG mice. Our data show that selective blockade of endothelial-intrinsic NF-kappaB pathway is sufficient to abrogate the cascades of molecular events that lead to septic shock and septic vascular dysfunction, demonstrating a pivotal role of endothelial-specific NF-kappaB signaling in the pathogenesis of septic shock and septic vascular dysfunction.

INO-4885 [5,10,15,20-tetra[N-(benzyl-4'-carboxylate)-2-pyridinium]-21H,23H-porphine iron(III) chloride], a peroxynitrite decomposition catalyst, protects the heart against reperfusion injury in mice

Oxidative/nitrative stress caused by peroxynitrite, the reaction product of superoxide (O2(.-)) and nitric oxide (NO), is the primary cause of myocardial ischemia/reperfusion injury. The present study determined whether INO-4885 [5,10,15,20-tetra[N-(benzyl-4'-carboxylate)-2-pyridinium]-21H,23H-porphine iron(III) chloride], a new peroxynitrite decomposition catalyst, may provide cellular protection and protect heart from myocardial ischemia/reperfusion injury. Adult male mice were subjected to 30 min of ischemia and 3 or 24 h of reperfusion. Mice were randomized to receive vehicle, INO-4885 without catalytic moiety, or INO-4885 (3-300 microg/kg i.p.) 10 min before reperfusion. Infarct size, apoptosis, nitrotyrosine content, NO/O2(.-) production, and inducible nitric-oxide synthase (iNOS)/NADPH oxidase expression were determined. INO-4885 treatment reduced ischemia/reperfusion-induced protein nitration and caspase 3 activation in a dose-dependent fashion in the range of 3 to 100 microg/kg. However, doses exceeding 100 microg/kg produced nonspecific effects and attenuated its protective ability. At the optimal dose (30 microg/kg), INO-4885 significantly reduced infarct size (p < 0.01), decreased apoptosis (p < 0.01), and reduced tissue nitrotyrosine content (p < 0.01). As expected, INO-4885 had no effect on ischemia/reperfusion-induced iNOS expression and NO overproduction. To our surprise, this compound significantly reduced superoxide production and partially blocked NADPH oxidase overexpression in the ischemic/reperfused cardiac tissue. Additional experiments demonstrated that INO-4885 provided better cardioprotection than N-(3-(aminomethyl)benzyl)acetamidine (1400W, a selective iNOS inhibitor), apocynin (an NADPH oxidase inhibitor), or Tiron (a cell-permeable superoxide scavenger). Taken together, our data demonstrated that INO-4885 is a cardioprotective molecule that attenuates myocardial reperfusion injury by facilitating peroxynitrite decomposition and inhibiting NADPH oxidase-derived O2(.-) production.

Endothelial dysfunction in adiponectin deficiency and its mechanisms involved

Endothelial dysfunction is the earliest pathologic alteration in diabetic vascular injury and plays a critical role in the development of atherosclerosis. Plasma levels of adiponectin (APN), a novel vasculoprotective adipocytokine, are significantly reduced in diabetic patients, but its relationship with endothelial dysfunction remains unclear. The present study aims to determine whether APN deficiency may cause endothelial dysfunction and to investigate the involved mechanisms. Vascular rings were made from the aortic vessels of wild type (WT) or APN knockout (APN(-/-)) mice. Endothelial function, total NO production, eNOS expression/phosphorylation, superoxide production, and peroxynitrite formation were determined. ACh and acidified NaNO2 (endothelial dependent and independent vasodilators, respectively) caused similar concentration-dependent vasorelaxation in WT vascular rings. APN(-/-) rings had a normal response to acidified NaNO2, but a markedly reduced response to ACh (>50% reduction vs. WT, P<0.01). Both superoxide and peroxynitrite production were increased in APN(-/-) vessels (P<0.01 vs. WT). Pretreatment with superoxide scavenger Tiron significantly, but incompletely restored vascular vasodilatory response to ACh. In APN(-/-) vessels, eNOS expression was normal, but NO production and eNOS phosphorylation was significantly reduced (P<0.01 vs. WT). Treatment of APN(-/-) mice in vivo with the globular domain of adiponectin reduced aortic superoxide production, increased eNOS phosphorylation, and normalized vasodilatory response to ACh. Increased NO inactivation combined with decreased basal NO production contributes to endothelial dysfunction development when there is a paucity of APN production. Interventions directed towards increasing plasma APN levels may improve endothelial function, and reduce cardiovascular complications suffered by diabetic patients.

L-Arginine prevents metabolic effects of high glucose in diabetic mice

We tested the hypothesis that activation of the polyol pathway and protein kinase C (PKC) during diabetes is due to loss of NO. Our results show that after 4 weeks of streptozotocin-induced diabetes, treatment with L-arginine restored NO levels and prevented tissue accumulation of sorbitol in mice, which was accompanied by an increase in glutathiolation of aldose reductase. L-Arginine treatment decreased superoxide generation in the aorta, total PKC activity and PKC-beta(II) phosphorylation in the heart, and the plasma levels of triglycerides and soluble ICAM. These data suggest that increasing NO bioavailability by L-arginine corrects the major biochemical abnormalities of diabetes.

Aging influences multiple indices of oxidative stress in the heart of the Fischer 344/NNia x Brown Norway/BiNia rat

We report the influence of aging on multiple markers of oxidative-nitrosative stress in the heart of adult (6-month), aged (30-month) and very aged (36-month) Fischer 344/NNiaHSd x Brown Norway/BiNia (F344/NXBN) rats. Compared to adult (6-month) hearts, indices of oxidative (superoxide anion [O2*-], 4-hydroxy-2-nonenal [4-HNE]) and nitrosative (protein nitrotyrosylation) stress were 34.1 +/- 28.1%, 186 +/- 28.1% and 94 +/- 5.8% higher, respectively, in 36-month hearts and these findings were highly correlated with increases in left ventricular wall thickness (r > 0.669; r > 0.710 and P < 0.01, respectively). Regression analysis showed that increases in cardiac oxidative-nitrosative stress with aging were significantly correlated with changes in the expression and/or regulation of proteins involved in transcriptional (NF-kappaB) activities, signaling (mitogen-activated protein kinases along with Src), apoptotic (Bcl-2, Traf-2), and cellular stress (HSPs). These results suggest that the aging F344/NXBN heart may be highly suited for unraveling the molecular events that lead to age-associated alterations in cardiac oxidative stress.

Enalapril improves impairment of SERCA-derived relaxation and enhancement of tyrosine nitration in diabetic rat aorta

We investigated the involvement of angiotensin II and vascular smooth muscle sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) function in the impaired NO-induced relaxation seen in established streptozotocin-induced diabetes. Plasma angiotensin II levels, which were elevated in untreated diabetic rats (vs age-matched controls), were improved by treatment with the angiotensin-converting enzyme inhibitor enalapril. Systolic blood pressure was significantly decreased in chronic enalapril-treated diabetics (vs the other two groups). Intact aortae from diabetic rats and chronic angiotensin II-infused control rats, but not those from diabetic rats treated with enalapril, showed impaired endothelium-dependent relaxations to acetylcholine (vs controls). The relaxation induced by Angeli's Salt (a NO donor) was significantly impaired in endothelium-denuded aortae from diabetic rats (vs controls) but it was normalised by enalapril treatment. After preincubation with the irreversible SERCA inhibitor, thapsigargin, the relaxation induced by Angeli's Salt was significantly impaired in endothelium-denuded aortae from the controls, but not from the diabetics, and there was no significant difference between the thapsigargin-treated groups. Nitrotyrosine, an indirect marker of peroxynitrite, was markedly increased in aortic smooth muscle from diabetic rats, while chronic enalapril administration reduced this increase. These results suggest that in streptozotocin-induced diabetic rats, excessive angiotensin II production may lead to the generation of peroxynitrite and that this may in turn trigger a dysfunction of vascular smooth muscle SERCA. Enalapril improved the diabetes-related impairments.

Postprandial endothelial dysfunction: role of glucose, lipids and insulin

Endothelium plays a key role in the regulation of vascular tone and development of atherosclerosis. Endothelial function is impaired early in patients with risk factors and endothelial dysfunction is a strong and independent predictor of cardiovascular events. Because in normal subjects blood concentrations of glucose, lipids and insulin are increased after each meals, and postprandial changes last a long time after the meals, these changes might be of importance in the process of atherosclerosis initiation and development. Experimental and human studies have shown that a transient increase of blood concentrations of glucose, triglycerides and fatty acids, and insulin are able to depress endothelium-dependent vasodilation in healthy subjects and that hyperglycemia, hypertriglyceridemia and hyperinsulinemia are generator of reactive oxygen species at the origin of a cascade of pathophysiological events resulting in the activation of nuclear factor-kappaB. Nuclear factor-kappaB is an ubiquitous transcription factor controlling the expression of numerous genes and is involved in immunity, inflammation, regulation of cell proliferation and growth and apoptosis. These mechanisms may be involved in the development of atherosclerosis in normal subjects when food intake is chronically modified towards glucids and lipids with cumulative effects both on depression of endothelium dependent dilation and oxidative stress.

Thioredoxin reduces post-ischemic myocardial apoptosis by reducing oxidative/nitrative stress

BACKGROUND AND PURPOSE

Thioredoxin (Trx) is an oxidoreductase that prevents free radical-induced cell death in cultured cells. Here we assessed the mechanism(s) underlying the cardioprotective effects of Trx in vivo.

EXPERIMENTAL APPROACH

The effects of myocardial ischemia (30 min) and reperfusion were measured in mice, with assays of myocardial apoptosis, superoxide production, NOx and nitrotyrosine content, and myocardial infarct size. Recombinant human Trx (rhTrx, 0.7-20 mg kg(-1), i.p.) was given 10 min before reperfusion.

KEY RESULTS

Treatment with 2 mg kg(-1) rhTrx significantly decreased myocardial apoptosis and reduced infarct size (P<0.01). Nitrotyrosine content of cardiomyocytes was markedly reduced in rhTrx-treated animals (P<0.01). To further identify the mechanisms by which rhTrx may exert its anti-nitrative effect, iNOS expression and production of NOx and superoxide were determined. Treatment with rhTrx had no significant effect on iNOS expression or NOx content in the ischemic/reperfused heart. However, it markedly upregulated mSOD and reduced tissue superoxide content. To further establish a causative link between the anti- peroxynitrite effect and the cardioprotective effect of rhTrx, cultured adult cardiomyocytes were incubated with SIN-1, a peroxynitrite donor, (50 microM for 3 h) resulting in a nitrotyrosine content comparable to that seen in the ischemic/reperfused heart and causing significant cardiomyocyte apoptosis (P<0.01). Treatment with rhTrx markedly decreased SIN-1 induced apoptosis (P<0.01).

CONCLUSIONS AND IMPLICATIONS

These results demonstrate that Trx is a novel anti-apoptotic and cardioprotective molecule that exerts its cardioprotective effects by reducing ischemia/reperfusion-induced oxidative/nitrative stress.

Oxidative stress at the vascular wall. Mechanistic and pharmacological aspects

During the process of energy production in aerobic respiration, vascular cells produce reactive oxygen species (ROS). A growing body of evidence indicates that oxidative stress refers to a condition in which cells are subjected to excessive levels of ROS. Overall vascular function is dependent upon a fine balance of oxidant and antioxidant mechanisms, which determine endothelial functions. Considerable experimental and clinical data indicate that intracellular oxidant milieu is also involved in several redox-sensitive cellular signaling pathways such as ion transport systems, protein phosphorylation, and gene expression and thus also plays important roles as modulator of vascular cell functions such as cell growth, apoptosis, migration, angiogenesis and cell adhesion. Overproduction of ROS under pathophysiologic conditions is integral in the development of cardiovascular diseases. This fact has raised an intensive search of new pharmacological approaches to improve vascular hemostasis and particularly those intended to decrease oxidative stress or augment the antioxidant defense mechanisms.

Effects of angiotensin II receptor antagonist on impaired endothelium-dependent and endothelium-independent relaxations in type II diabetic rats

BACKGROUND

Diabetes mellitus is an important risk factor for cardiovascular diseases, and vasodilator dysfunction may contribute to vascular complications in diabetes. We previously demonstrated that the angiotensin II receptor blocker (ARB) corrected the impaired endothelium-derived hyperpolarizing factor (EDHF)-mediated arterial hyperpolarization and relaxation associated with hypertension or aging, partially independently of blood pressure.

OBJECTIVE

To test whether EDHF-mediated, as well as endothelium-independent, relaxations would be altered in arteries from type II diabetic Goto-Kakizaki rats, and whether ARB would correct these alterations.

METHODS

Goto-Kakizaki rats were treated with either the ARB candesartan or a combination of hydralazine and hydrochlorothiazide for 8 weeks, beginning at 10 weeks of age. Membrane potentials and contractile responses were recorded from the isolated mesenteric arteries.

RESULTS

The two treatments lowered blood pressure comparably. Acetylcholine-induced, EDHF-mediated hyperpolarization and relaxation in mesenteric arteries were markedly impaired in untreated Goto-Kakizaki rats compared with age-matched Wistar rats, and neither ARB nor the combination therapy improved these responses. On the other hand, relaxations to endothelium-derived nitric oxide, assessed in rings precontracted with high potassium solution, were similar among the four groups. Relaxation to the nitric oxide donor sodium nitroprusside and that to levcromakalim, an ATP-sensitive K-channel opener, were also impaired in untreated Goto-Kakizaki rats, and the response to sodium nitroprusside was partially improved in treated Goto-Kakizaki rats.

CONCLUSIONS

These findings suggest that EDHF-mediated hyperpolarization and relaxation and endothelium-independent relaxations are both impaired in arteries of type II diabetic rats, and antihypertensive treatment with or without ARB partially corrects endothelium-independent relaxations to the nitric oxide donor but not EDHF-mediated responses.

Aging influences multiple incidices of oxidative stress in the aortic media of the Fischer 344/NNiaxBrown Norway/BiNia rat

Here, we determine the influence of aging on multiple markers of oxidative stress in the aorta of adult (6-month), aged (30-month) and very aged (36-month) Fischer 344/NNiaHSdxBrown Norway/BiNia (F344/NxBN) rats. Compared to adults, increases in as determined by oxidation of hydroethidine (HE) to ethidium (Et) were increased 79.7+/-7.0% in 36-month aortae and this finding was highly correlated with increases in medal thickness (r=0.773, p<0.01) and total protein nitration (r=0.706, p<0.01) but not Ki67, a marker for cell proliferation. Regression analysis showed that increases in aortic superoxide anion (O.-2) with aging were significantly correlated with changes in the expression and/or regulation of proteins involved in metabolic (AMPK-alpha), signaling (mitogen activated protein kinases (MAPKs) along with c-Src), apoptotic (Bax, Bcl-2, Traf-2) and transcriptional (NF-kappaB) activities. These results suggest that the aging F344/NxBN aorta may be highly suited for unraveling the molecular events that lead to age-associated alterations in aortic oxidative stress.

Superoxide anion production in the rat penis impairs erectile function in diabetes: influence of in vivo extracellular superoxide dismutase gene therapy

INTRODUCTION

Superoxide anion may contribute to erectile dysfunction (ED) in diabetes mellitus by reducing cavernosal nitric oxide (NO) bioavailability. The purpose of this study was to determine if gene transfer of extracellular superoxide dismutase (EC-SOD) can reduce superoxide anion formation and determine if this reactive oxygen species may contribute to diabetes-related ED in an experimental model of diabetes.

METHODS

Three groups of animals were utilized: (1) control; (2) streptozotocin (STZ)-diabetic rats [60 mg/kg intraperitoneally (ip)] intracavernosally injected with AdCMVbetagal (negative control); and (3) STZ-rats intracavernosally injected with AdCMVEC-SOD. Two months after ip injection of STZ, groups 2 and 3 were transfected with the adenoviruses and 2 days after transfection, all animals underwent cavernosal nerve stimulation (CNS) to assess erectile function. Confocal microscopy for superoxide anion and von Willebrand Factor (vWF) was performed in the STZ-diabetic rat. Superoxide anion production, total SOD activity, and cyclic guanosine monophosphate (cGMP) levels were measured in each experimental group of rats.

RESULTS

Confocal microscopy demonstrated superoxide in smooth muscle and endothelial cells of the STZ-rat cavernosum and colocalized with vWF in the endothelium. Higher superoxide anion levels and decreased cGMP levels were found in the penis of STZ-rats at a time when erectile function was reduced. Two days after administration of AdCMVEC-SOD, superoxide anion levels were significantly lower in the penis of STZ-rats. Total SOD activity and cavernosal cGMP was increased in the penis of EC-SOD-transfected rats. STZ-rats transfected with AdCMVEC-SOD had a peak intracavernosal pressure (ICP) and total ICP to CNS that was similar to control rats.

CONCLUSIONS

These data demonstrate that in vivo adenoviral gene transfer of EC-SOD can reduce corporal superoxide anion levels and raise cavernosal cGMP levels by increasing NO bioavailability thus restoring erectile function in the STZ-diabetic rat.

[Endothelial dysfunction in patients with diabetes: identification, pathogenesis and treatment]

Cardiovascular diseases are the leading cause of morbidity and mortality in people with diabetes. Vascular abnormalities can be observed long before atherosclerosis develops and in sites not usually prone to atherosclerosis. These vascular abnormalities are known to be due to endothelial dysfunctions, one of the most frequent of which is depressed endothelium-dependent dilation. In patients with diabetes, this is mainly linked to decreased bioavailability of nitric oxide. Although inactivation of tetrahydrobiopterin, a co-factor of NO-synthase, may depress nitric oxide production, the latter is more likely due to the inactivation of nitric oxide by superoxide anions: enhanced oxidative stress increases their production in people with diabetes. Moreover, hyperglycemia directly activates oxidative stress, which in turn depresses endothelium-dependent vasodilation. Glycemia and oxidative stress are positively correlated in people with diabetes. However, while depression of endothelium-dependent dilation may be a visible functional manifestation of oxidative stress, the oxidative stress itself is mainly responsible for the cascade of endothelial events that play a key role in development of vascular atherosclerosis and its complications. Especially important among these events are the activation of NF-kappaB and the oxidation of LDL-cholesterol. Although antioxidants provide short-term improvement of endothelial function in humans, all studies of the effectiveness of preventive antioxidant therapy have been disappointing. Control of hyperglycemia thus remains the best way to improve endothelial function and to prevent atherosclerosis and other cardiovascular complications of diabetes.

Rosuvastatin improves cerebrovascular function in Zucker obese rats by inhibiting NAD(P)H oxidase-dependent superoxide production

Insulin-resistance induces cerebrovascular dysfunction and increases the risk for stroke. We investigated whether rosuvastatin (RSV), a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, can reverse reduced cerebrovascular responsiveness in insulin-resistant rats. Dilator responses of the basilar artery (BA) were examined after 1-day or 4-wk RSV (2 mg.kg(-1).day(-1)) treatment in anesthetized 12-wk-old insulin-resistant Zucker obese (ZO) and lean (ZL) rats by using a cranial window preparation. Vehicle-treated ZO rats had significantly higher fasting insulin, total cholesterol (TC), and triglyceride (TG) levels compared with ZL rats. In addition, in the ZO rats, dilator responses of the BA to acetylcholine, iloprost, cromakalim, and potassium chloride were significantly reduced when compared with ZL rats. One-day RSV treatment improved dilator responses of the ZO BAs without altering lipid levels. Four-week RSV treatment lowered both TC and TG by 30% and also improved dilator responses of the ZO BAs, although without additional effects compared with the 1-day RSV treatment. NAD(P)H oxidase-dependent superoxide production was significantly higher in the cerebral arteries of vehicle-treated ZO rats compared with ZL rats, but both 1-day and 4-wk RSV treatments normalized elevated superoxide levels in the ZO arteries. These findings demonstrate that RSV improves cerebrovascular function in insulin-resistance independently from its lipid-lowering effect by the inhibition of NAD(P)H oxidase.

Mechanisms underlying endothelial dysfunction in diabetes mellitus: therapeutic implications

Hyperglycemia is the major causal factor in the development of endothelial dysfunction in patients with diabetes mellitus. Although the mechanisms underlying this phenomenon are likely to be multifactorial, recent in vivo and in vitro studies have indicated a crucial role of the diacylglycerol (DAG)-protein kinase C (PKC) pathway in mediating this phenomenon. PKC may have multiple adverse effects on vascular function, including the activation of superoxide-producing enzymes such as the nicotinamide adenine dinicleotide phosphate (NADPH) oxidase as well as increased expression of a dysfunctional, superoxide-producing, uncoupled endothelial nitric oxide synthase (NOS III). PKC-mediated superoxide production may inactivate nitric oxide (NO) derived from endothelial NOS III, but also may inhibit the activity and/or expression of the NO downstream target, the soluble guanylyl cyclase. Among the different isoforms of PKC, mainly the beta-isoforms have been shown to be activated. Recent studies with selective (isoform-specific) and non-selective PKC inhibitors show that they are able to beneficially influence glucose-induced endothelial dysfunction in experimental animal models as well as in patients, pointing to the therapeutic potential of these compounds in the prevention and treatment of vascular complications of diabetes.

Hypertension, stroke, and endothelium

Endothelial dysfunction, the complex, multifaceted, pathologic product of various vasculotoxic agents or injuries, is an intermediate attractant phenotype of cardiovascular diseases that usually has a long and unpredictable natural history. Furthermore, endothelial dysfunction may not only represent a vascular disease marker, but actually may play an important pathogenetic role that leads to the progression of the disease and the unfavorable outcomes. Among these vascular diseases, cerebrovascular accidents, particularly stroke, clearly represent a paradigmatic example of the potential role of dysfunctional endothelium. Elevated blood pressure has long been recognized as one of the most important risk factors for stroke; other factors, however, seem to play an important role. Indeed, epidemiologic evidence suggests that, in spite of an improved control of blood pressure, the secular trends of stroke in well-controlled populations are increasing. In this brief review, we analyze current evidence suggesting that endothelial dysfunction can play a role in the pathogenesis of ischemic stroke.

TGF-beta impairs renal autoregulation via generation of ROS

Impaired autoregulation in chronic kidney disease can result in elevation of glomerular capillary pressure and progressive glomerular damage; however, the factors linking chronic glomerular disorders to impaired autoregulation have not been identified. We tested the hypothesis that the cytokine most closely associated with progressive glomerular disease, transforming growth factor (TGF)-beta, may also attenuate autoregulation. Kidneys from normal rats were prepared for videomicroscopy, using the blood-perfused juxtamedullary nephron technique. Autoregulatory responses were measured under control conditions and during superfusion with TGF-beta1 (10 ng/ml). Control afferent arteriolar diameter averaged 18.4 +/- 1 microm and significantly decreased to 16.3 +/- 0.9 and 13.2 +/- 0.8 microm at perfusion pressures of 130 and 160 mmHg, respectively. In the presence of TGF-beta1, autoregulatory responses were completely blocked. In similar experiments performed using PDGF-BB (10 ng/ml) and HGF (25 ng/ml), the normal autoregulatory response was not affected. In vitro studies, using isolated preglomerular vascular smooth muscle cells, revealed that exposure to TGF-beta1 stimulated a rapid increase in reactive oxygen species (ROS) that was inhibited by NADPH oxidase inhibitors. In situ studies, with dihydroethidium staining, revealed a marked increase in renal vessel ROS production on exposure to TGF-beta1. Pretreatment of the juxtamedullary afferent arterioles with tempol, a ROS scavenger, or with apocynin, a NADPH oxidase inhibitor, prevented the impaired autoregulation induced by TGF-beta1. These data reveal a novel hemodynamic pathway by which TGF-beta could lead to progressive glomerular injury by impairing normal renal microvascular function.

Endothelial nitric oxide synthase gene transfer restores endothelium-dependent relaxations and attenuates lesion formation in carotid arteries in apolipoprotein E-deficient mice

Nitric oxide (NO) and monocyte chemoattractant protein-1 (MCP-1) exert partly opposing effects in vascular biology. NO plays pleiotropic vasoprotective roles including vasodilation and inhibition of platelet aggregation, smooth muscle cell proliferation, and endothelial monocyte adhesion, the last effect being mediated by MCP-1 downregulation. Early stages of arteriosclerosis are associated with reduced NO bioactivity and enhanced MCP-1 expression. We have evaluated adenovirus-mediated gene transfer of human endothelial NO synthase (eNOS) and of a N-terminal deletion (8ND) mutant of the MCP-1 gene that acts as a MCP-1 inhibitor in arteriosclerosis-prone, apolipoprotein E-deficient (ApoE(-/-)) mice. Endothelium-dependent relaxations were impaired in carotid arteries instilled with a noncoding adenoviral vector but were restored by eNOS gene transfer (p < 0.01). A perivascular collar was placed around the common carotid artery to accelerate lesion formation. eNOS gene transfer reduced lesion surface areas, intima/media ratios, and macrophage contents in the media at 5-week follow-up (p < 0.05). In contrast, 8ND-MCP-1 gene transfer did not prevent lesion formation. In conclusion, eNOS gene transfer restores endothelium-dependent vasodilation and inhibits lesion formation in ApoE(-/-) mouse carotids. Further studies are needed to assess whether vasoprotection is maintained at later disease stages and to evaluate the long-term efficacy of eNOS gene therapy for primary arteriosclerosis.

High glucose mediates pro-oxidant and antioxidant enzyme activities in coronary endothelial cells

AIM

Excess levels of free radicals such as nitric oxide (NO) and superoxide anion (O(2)(-)) are associated with the pathogenesis of endothelial cell dysfunction in diabetes mellitus. This study was designed to investigate the underlying causes of oxidative stress in coronary microvascular endothelial cells (CMECs) exposed to hyperglycaemia.

METHODS

CMECs were cultured under normal (5.5 mmol/l) or high glucose (22 mmol/l) concentrations for 7 days. The activity and expression (protein level) of endothelial NO synthase (eNOS), inducible NOS (iNOS), NAD(p)H oxidase and antioxidant enzymes, namely, superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) were investigated by specific activity assays and Western analyses, respectively, while the effects of hyperglycaemia on nitrite and O(2)(-) generation were investigated by Griess reaction and cytochrome C reduction assay, respectively.

RESULTS

Hyperglycaemia did not alter eNOS or iNOS protein expressions and overall nitrite generation, an index of NO production. However, it significantly reduced the levels of intracellular antioxidant glutathione by 50% (p < 0.05) and increased the protein expressions and activities of p22-phox, a membrane-bound component of pro-oxidant NAD(p)H oxidase and antioxidant enzymes (p < 0.05). Free radical scavengers, namely, Tiron and mercaptopropionylglycine (MPG) (0.1-1 micromol/l) reduced hyperglycaemia-induced antioxidant enzyme activity and increased glutathione and nitrite generation to the levels observed in CMEC cultured in normoglycaemic medium (p < 0.01). The differences in enzyme activity and expressions were independent of the increased osmolarity generated by high glucose levels as investigated by using equimolar concentrations of mannitol in parallel experiments.

CONCLUSIONS

These results suggest that hyperglycaemia-induced oxidative stress may arise in CMEC as a result of enhanced pro-oxidant enzyme activity and diminished generation of antioxidant glutathione. By increasing the antioxidant enzyme capacity, CMEC may protect themselves against free radical-induced cell damage in diabetic conditions.

Antioxidant vitamins C and E ameliorate hyperglycaemia-induced oxidative stress in coronary endothelial cells

OBJECTIVE

Vitamins C and E have protective features in many disease states associated with enhanced oxidative stress. The aim of this study was to investigate whether vitamin(s) C and/or E modulate hyperglycaemia-induced oxidative stress by regulating enzymatic activities of prooxidant, i.e. NAD(P)H oxidase and/or antioxidant enzymes, namely endothelial nitric oxide synthase (eNOS), superoxide dismutase, catalase and glutathione peroxidase, using coronary microvascular endothelial cells (CMEC).

METHODS

CMEC were cultured under normal (5.5 mM) or high glucose (22 mM) concentrations for 7 days. The enzyme activities were determined by specific assays. The levels of O(2) (-) and nitrite were measured by cytochrome c reduction and Griess assays respectively.

RESULTS

Hyperglycaemia did not alter eNOS activity or overall nitrite generation, an index of NO production. However, it increased NAD(P)H oxidase and antioxidant enzyme activities (p < 0.05). Specific inhibitors of NAD(P)H oxidase, i.e. phenylarsine oxide (0.1-3 microm) and 4-(2-aminoethyl)benzenesulfonyl fluoride (5-100 microm) and vitamins C and E (0.1-1 microm) significantly reduced prooxidant and antioxidant enzyme activities in CMEC exposed to hyperglycaemia (p < 0.01). The differences in enzyme activities were independent of increases in osmolarity generated by high glucose levels as investigated by using equimolar concentrations of mannitol in parallel experiments.

CONCLUSIONS

Vitamins C and E may protect CMEC against hyperglycaemia-induced oxidative stress by concomitantly regulating prooxidant and antioxidant enzyme activities.

Effect of combination endothelial nitric oxide synthase gene therapy and sildenafil on erectile function in diabetic rats

Erectile dysfunction associated with diabetes mellitus is caused in part by disordered endothelial smooth muscle relaxation, neuropathy, and a decrease in cavernosal nitric oxide synthase (NOS) activity. The purpose of this study was to determine whether a combination of sildenafil and adenoviral gene transfer of endothelial NOS (eNOS) could enhance the erectile response in diabetic rats. Five groups of animals were utilized: (1) age-matched control rats, (2) streptozotocin (STZ)-induced diabetic rats (60 mg/kg i.p.), (3) STZ-rats + sildenafil (2 mg/kg i.v.), (4) STZ-rats transfected with AdCMVbetagal or AdCMVeNOS, and (5) STZ-rats transfected with AdCMVeNOS +sildenafil (2 mg/kg i.v.). At 2 months after i.p. injection of STZ, groups 4 and 5 were transfected with the adenoviruses and 1-2 days after transfection, all animals underwent cavernosal nerve stimulation (CNS) to assess erectile function. Cyclic 3',5'-guanosine monophosphate (cGMP) levels were assessed in the cavernosal tissue. STZ-diabetic rats had a significant decrease in erectile function as determined by the peak intracavernosal pressure (ICP) and total ICP (area under the erectile curve; AUC) after CNS when compared to control rats. STZ-diabetic rats+AdCMVeNOS had a peak ICP and AUC, which were similar to control animals. STZ-diabetic rats administered sildenafil demonstrated a significant increase in peak ICP at the 5 and 7.5 V settings, while the AUC was significantly increased at all voltage (V) settings. The increase in both ICP and AUC of STZ-diabetic rats transfected with AdCMVeNOS at all V settings was greater than STZ-diabetic rats transfected with AdCMVbetagal. STZ-diabetic rats transfected with AdCMVeNOS and administered sildenafil had a significant increase in total ICP that was greater than eNOS gene therapy alone. Cavernosal cGMP levels were significantly decreased in STZ-diabetic rats, but were increased after transfection with AdCMVeNOS to values greater than control animals. In conclusion, overexpression of eNOS and cGMP in combination with sildenafil significantly increased both the peak ICP and total ICP to CNS in the STZ-diabetic rat, which was similar to the response observed in control rats. Moreover, the total erectile response was greater in STZ-diabetic rats receiving eNOS gene therapy plus sildenafil than STZ-rats receiving sildenafil or eNOS gene therapy alone.

4-Hydroxy tempol-induced impairment of mitochondrial function and augmentation of glucose transport in vascular endothelial and smooth muscle cells

The water-soluble and cell permeable nitroxide derivative 4-hydroxy tempol (TPL) has been shown to reduce or ameliorate oxidative stress-induced dysfunction and damage in vascular endothelial cells. We studied the effects of TPL on glucose transport and metabolism in bovine aortic endothelial (VEC) and smooth muscle cells (VSMC) under normal and high glucose conditions. Normally, these cells operate an autoregulatory protective mechanism that limits the rate of glucose transport under hyperglycemic conditions by decreasing the cell content of their typical glucose transporter GLUT-1 mRNA and protein as well as its plasma membrane abundance. TPL augmented the rate of glucose transport both under normo- and hyperglycemic conditions by increasing GLUT-1 mRNA and protein content and its plasma membrane abundance in both types of cells, leading to an increased flux of glucose into the cells. These effects were found related to ROS-generating and oxidant activities of TPL and to a decreased rate of mitochondrial ATP production under both normo- and hyperglycemic conditions. Since impaired mitochondrial functions, and in particular decreased rate of ATP production, augment the expression of GLUT-1 protein and glucose transport and metabolism, we suggest that the stimulatory effects of TPL in vascular cells results from its unfavorable interactions in the mitochondrion. It is therefore suggested that effects of TPL in cells of cardiovascular system be evaluated in parallel to its adverse effects on glucose and energy metabolism.

Abeta-induced vascular oxidative stress and attenuation of functional hyperemia in mouse somatosensory cortex

We investigated the role of vascular oxidative stress in the mechanisms of the impairment in cerebrovascular regulation produced by the amyloid-beta peptide (Abeta). In particular, we sought to provide evidence of vascular oxidative stress in mice overexpressing the amyloid precursor protein (APP) and to determine whether the Abeta-induced attenuation in functional hyperemia is mediated by free radical overproduction. Oxidative/nitrosative stress was assessed by 3-nitrotyrosine immunoreactivity, while free radical production was determined in cerebral microvessels by hydroethidine microfluorography. To study functional hyperemia the somatosensory cortex was activated by whisker stimulation while local blood flow was monitored by laser-Doppler flowmetry. It was found that APP mice show signs of oxidative/nitrosative stress in pial and intracerebral blood vessels well before they develop oxidative stress in neurons and glia or amyloid plaques. Treatment of cerebral microvessels isolated from wild-type mice with Abeta (1 microM) increased free radical production as assessed by the hydroethidine technique. The Abeta-induced attenuation of the increase in somatosensory cortex blood flow produced by whisker stimulation was prevented by treatment with the free radical scavengers MnTBAP or tiron. These data provide evidence that in APP mice vascular oxidative stress precedes the development of parenchymal oxidative stress, and that Abeta-produced vascular reactive oxygen species are involved in the attendant attenuation in functional hyperemia. Thus, vascular oxidative stress is an early event in the course of the brain dysfunction produced by APP overexpression and Abeta, and, as such, could be the target of early therapeutic interventions based on antioxidants.

Nitric oxide, an iceberg in cardiovascular physiology:

The endothelium is now recognized not only as a physical barrier between blood and vascular wall, but also as an important and strategically located organ with multiple endocrine and paracrine functions. By releasing vasoactive substances, the endothelium acts as an inhibitory regulator of vascular contraction, leukocyte adhesion, vascular smooth muscle cell growth, and platelet aggregation. This review intends to demonstrate how much the picture of the biological functions of nitric oxide has changed in cardiovascular physiology, extending beyond its vessel-relaxing activity, as well as to highlight new insights into the factors affecting its bioavailability and regulation in relation with many cardiovascular diseases.