Free radical production in endothelial cells as a pathogenetic factor for vascular dysfunction in the insulin resistance state

Sodium-glucose cotransporter 2 inhibitors represent a paradigm shift in the prevention of heart failure in type 2 diabetes patients

Recent major clinical trials of the use of sodium-glucose cotransporter 2 (SGLT2) inhibitors in patients with type 2 diabetes have shown that they reduce three-point major adverse cardiovascular events, cardiovascular death, hospitalization for heart failure (HF) and a composite renal outcome. These beneficial effects of SGLT2 inhibitors are also evident in type 2 diabetes patients with a previous history of atherosclerotic cardiovascular disease or advanced renal disease. HF is a major determinant of the prognosis of diabetes patients. Although HF with low ejection fraction can be effectively treated with antihypertensive drugs, these treatments do not reduce mortality in HF patients with preserved ejection fraction (HFpEF). HFpEF is clinically characterized by left ventricular diastolic dysfunction, perivascular fibrosis and stiffness of cardiomyocytes, defined as "cardiomyopathy". Therefore, HFpEF is considered to be an entirely separate entity to HF with low ejection fraction. Recent studies have suggested that HFpEF might be treatable using SGLT2 inhibitors, which ameliorate visceral adiposity, insulin resistance, hyperglycemia, hyperlipidemia, volume overload, hypertension and cardiac inflammation. In the final part of the present review, we discuss the biochemical and molecular mechanisms of the effects of SGLT2 inhibitors in type 2 diabetes patients with HFpEF. These involve amelioration of the low nitric oxide production and oxidative stress, a reduction in cardiac inflammatory cytokine signaling, inhibition of Ca2+ overload, and an improvement in cardiac energy metabolism as a result of ketone body production. Investigations of the beneficial effects of SGLT2 inhibitors on cardiorenal outcomes, including hospitalization for HF, are now being carried out in preclinical and clinical studies.

Argan Oil as an Effective Nutri-Therapeutic Agent in Metabolic Syndrome: A Preclinical Study

The present study aims at examining the effects of argan oil on the three main cardiovascular risk factors associated with metabolic syndrome (hypertension, insulin resistance and obesity) and on one of its main complications, neuropathic pain. Male Sprague-Dawley rats had free access to a drinking solution containing 10% d-glucose or tap water for 12 weeks. The effect of argan oil was compared to that of corn oil given daily by gavage during 12 weeks in glucose-fed rats. Glucose-fed rats showed increases in systolic blood pressure, epididymal fat, plasma levels of triglycerides, leptin, glucose and insulin, insulin resistance, tactile and cold allodynia in association with a rise in superoxide anion production and NADPH oxidase activity in the thoracic aorta, epididymal fat and gastrocnemius muscle. Glucose-fed rats also showed rises in B₁ receptor protein expression in aorta and gastrocnemius muscle. Argan oil prevented or significantly reduced all those anomalies with an induction in plasma adiponectin levels. In contrast, the same treatment with corn oil had a positive impact only on triglycerides, leptin, adiponectin and insulin resistance. These data are the first to suggest that argan oil is an effective nutri-therapeutic agent to prevent the cardiovascular risk factors and complications associated with metabolic syndrome.

Metabolic Syndrome as a Multifaceted Risk Factor for Oxidative Stress

SIGNIFICANCE

Metabolic syndrome (MetS) is associated with a greater risk of diabetes and cardiovascular diseases. It is estimated that this multifactorial condition affects 20%-30% of the world's population. A detailed understanding of MetS mechanisms is crucial for the development of effective prevention strategies and adequate intervention tools that could curb its increasing prevalence and limit its comorbidities, particularly in younger age groups. With advances in basic redox biology, oxidative stress (OxS) involvement in the complex pathophysiology of MetS has become widely accepted. Nevertheless, its clear association with and causative effects on MetS require further elucidation. Recent Advances: Although a better understanding of the causes, risks, and effects of MetS is essential, studies suggest that oxidant/antioxidant imbalance is a key contributor to this condition. OxS is now understood to be a major underlying mechanism for mitochondrial dysfunction, ectopic lipid accumulation, and gut microbiota impairment.

CRITICAL ISSUES

Further studies, particularly in the field of translational research, are clearly required to understand and control the production of reactive oxygen species (ROS) levels, especially in the mitochondria, since the various therapeutic trials conducted to date have not targeted this major ROS-generating system, aimed to delay MetS onset, or prevent its progression.

FUTURE DIRECTIONS

Multiple relevant markers need to be identified to clarify the role of ROS in the etiology of MetS. Future clinical trials should provide important proof of concept for the effectiveness of antioxidants as useful therapeutic approaches to simultaneously counteract mitochondrial OxS, alleviate MetS symptoms, and prevent complications. Antioxid. Redox Signal. 26, 445-461.

A single oral dose of fructose induces some features of metabolic syndrome in rats: role of oxidative stress

BACKGROUND AND AIMS

To determine if a single oral dose of fructose to rats reproduces some features of metabolic syndrome observed after chronic administration and if so, to investigate its mechanisms.

METHODS AND RESULTS

Systolic blood pressure was measured in rats before and after oral administration of fructose, and in animals pretreated with lipoic acid, methyldopa, losartan or streptozotocin. In other rats, glucose, insulin, uric acid, and insulin sensitivity index, were determined before and after fructose or lipoic acid plus fructose. Glutathione was measured in liver before and after fructose administration. In aortic rings from other rats, incubation with mannitol, fructose, or fructose plus lipoic acid was evaluated on the relaxation by acetylcholine. Fructose produced a moderate increase in blood pressure, which was prevented by lipoic acid or streptozotocin. Methyldopa and losartan decreased the pressor response minimally. Fructose increased oxidized glutathione, plasma glucose, insulin and uric acid, and diminished the insulin sensitivity index, and the reduced glutathione. Lipoic acid prevented hyperglycemia and hyperuricemia, and improved the insulin sensitivity index. Finally, endothelial dysfunction was prevented by lipoic acid.

CONCLUSION

A single dose of fructose reproduces some of the features of metabolic syndrome, most changes were caused by oxidative stress and insulin resistance.

The effects of phentolamine on fructose-fed rats

Metabolic syndrome (MS) is a combination of medical disorders that increase the risk of developing cardiovascular disease and diabetes. MS is associated with obesity, increased blood pressure, hyperlipidemia, and hyperglycemia. This study was designed to investigate the pharmacological profile of phentolamine, a nonselective α adrenergic receptor antagonist, in the prevention of increased blood pressure in fructose-fed rats. Phentolamine prevented the fructose-induced increase in systolic blood pressure without affecting insulin sensitivity and major metabolic parameters. The levels of plasma noradrenaline and angiotensin II, 2 proposed contributors to the development of fructose-induced elevated blood pressure, were examined. Neither noradrenaline nor angiotensin II levels were affected by phentolamine treatment. Since overproduction of nitric oxide has been shown to lead to an elevation in peroxynitrite, the role of oxidative stress, a proposed mechanism of fructose-induced elevated blood pressure and insulin resistance, was examined by measuring plasma levels of total nitrate/nitrite. Plasma nitrate/nitrite was significantly elevated in all fructose-fed animals, regardless of treatment with phentolamine. Another proposed contributor toward fructose-induced MS is an elevation in uric acid levels. In this experiment, plasma levels of uric acid were found to be increased by dietary fructose and were unaffected by phentolamine treatment.

Apocynin improves endothelial function and prevents the development of hypertension in fructose fed rat

Background and Objectives:

Exaggerated production of superoxide and inactivation of nitric oxide have been implicated in pathogenesis of hypertension. NAD(P)H oxidase is one of the major source of reactive oxygen species in vasculature. In the present study, we aimed to determine the effect of chronic administration of Apocynin an NAD(P)H oxidase inhibitor on endothelial function and hypertension in fructose-fed rat.

Materials and Methods:

Endothelial function, vascular superoxide, and nitric oxide production/bioavailability in aortas from fructose-fed rats and age-matched controls treated with or without apocynin were assessed using isometric tension studies in organ chambers. Systolic blood pressure was measured by the tail cuff method.

Results:

In fructose-fed rats, acetylcholine-induced relaxation was impaired, vascular superoxide production was increased, and nitric oxide bioavailability was decreased along with an increase in systolic blood pressure compared to controls. Apocynin treatment prevented the increased generation of superoxide, decreased nitric oxide bioavailability, impaired acetylcholine-induced relaxation, and elevation of systolic blood pressure.

Conclusion:

Chronic administration of apocynin improves the endothelial function by reducing oxidative stress, improving NO bioavailability, and prevents the development hypertension in fructose-fed rat.

Clinical science review article: understanding the implications of diabetes on the vascular system

Patients with diabetes comprise an extremely complex subset of patients for the vascular surgeon. Often, they have numerous comorbidities that can further complicate matters. The diabetic environment is highly complex and the interplay of various diseases makes this an extremely challenging condition to manage. Knowing the mechanisms by which diabetes inflicts adverse microscopic changes in the vasculature allows the clinician to anticipate problems and minimize the heightened risks observed in diabetic patients undergoing surgery. In this review, we will illustrate how diabetes affects the vasculature and how the molecular and cellular derangements that occur in diabetic environments lead to these pathophysiologic consequences.

Resistance to acute NO-mimetic and EDHF-mimetic effects of leptin in the metabolic syndrome

AIMS

We examined mechanisms leading to the impairment of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF)-dependent vasorelaxation in response to acutely administered leptin in rats with the metabolic syndrome.

MAIN METHODS

Effects of leptin on blood pressure and NO and cGMP in the aortic wall were studied in four groups of rats: (1) lean control, (2) obese, fed "cafeteria diet" for 3months (hyperleptinemia and hyperinsulinemia), (3) hyperleptinemia induced by administration of exogenous leptin for 8days, and (4) fructose-fed, receiving 20% fructose in the drinking water for 8weeks (hyperinsulinemia with slightly elevated leptin).

KEY FINDINGS

Stimulatory effect of leptin on NO and cGMP production in the aortic wall was impaired in obese and hyperleptinemic groups but not in the fructose group. In contrast, EDHF-mimetic effect of leptin was impaired in obese and fructose-fed but not in the hyperleptinemic group. Leptin increased tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) in the aortic wall, and this effect was impaired in obese and fructose-fed animals. The EDHF-mimetic effect of leptin was abolished by phosphoinositide 3-kinase inhibitor, wortmannin, whereas its effect on NO was not. In addition, IRS-1 phosphorylation at Ser(307) and Ser(612) was enhanced in obese and fructose-fed but not in hyperleptinemic rats.

SIGNIFICANCE

These results indicate that: (1) long-term hyperleptinemia induces resistance to acute vascular NO-mimetic effect of leptin in obesity/metabolic syndrome, (2) leptin stimulates EDHF in IRS-1 and PI3K-dependent manner, and this effect is impaired in obesity due to excessive serine phosphorylation of IRS-1.

The fructose-fed rat: a review on the mechanisms of fructose-induced insulin resistance and hypertension

The metabolic syndrome is an important public health concern that predisposes individuals to the development of cardiovascular disease and/or Type 2 diabetes. The fructose-fed rat is an animal model of acquired systolic hypertension that displays numerous features of the metabolic syndrome. This animal model is used to study the relationship between insulin resistance/compensatory hyperinsulinemia and the development of hypertension. Several mechanisms have been proposed to mediate the link between insulin resistance and hypertension. In this review, we have addressed the role of sympathetic nervous system overactivation, increased production of vasoconstrictors, such as endothelin-1 and angiotensin II, and prostanoids in the development of hypertension in fructose-fed rats. The roles of nitric oxide, impaired endothelium-dependent relaxation and sex hormones in the pathogenesis of the fructose-fed induced hypertensive rats have also been highlighted. More recently, increased formation of reactive oxygen species and elevated levels of uric acid have been reported to contribute to fructose-induced hypertension.

Positive and negative regulation of insulin signaling by reactive oxygen and nitrogen species

Regulated production of reactive oxygen species (ROS)/reactive nitrogen species (RNS) adequately balanced by antioxidant systems is a prerequisite for the participation of these active substances in physiological processes, including insulin action. Yet, increasing evidence implicates ROS and RNS as negative regulators of insulin signaling, rendering them putative mediators in the development of insulin resistance, a common endocrine abnormality that accompanies obesity and is a risk factor of type 2 diabetes. This review deals with this dual, seemingly contradictory, function of ROS and RNS in regulating insulin action: the major processes for ROS and RNS generation and detoxification are presented, and a critical review of the evidence that they participate in the positive and negative regulation of insulin action is provided. The cellular and molecular mechanisms by which ROS and RNS are thought to participate in normal insulin action and in the induction of insulin resistance are then described. Finally, we explore the potential usefulness and the challenges in modulating the oxidant-antioxidant balance as a potentially promising, but currently disappointing, means of improving insulin action in insulin resistance-associated conditions, leading causes of human morbidity and mortality of our era.

Epinephrine is associated with both erectile dysfunction and lower urinary tract symptoms

OBJECTIVE

To determine whether patients with erectile dysfunction (ED) have a higher incidence of insulin resistance (IR) when compared with controls.

DESIGN

Prospective case-control study.

SETTING

Academic medical center.

PATIENT(S)

Twenty-nine nondiabetic men aged 18-66 years were enrolled. Of these, 28 completed the study: 17 had ED, and 11 did not.

INTERVENTION(S)

Validated ED questionnaires, examination, serum hormones evaluation, and oral glucose tolerance testing.

MAIN OUTCOME MEASURE(S)

Association of IR with ED.

RESULT(S)

The association between worsening degrees of both lower urinary tract symptoms (LUTS) and ED was reaffirmed, as was a potential correlation between the two-epinephrine. There was a negative association between serum levels of epinephrine and scores on the 5-item version of the International Index of Erectile Dysfunction for ED (Spearman correlation coefficient = -0.38). On the other hand, men with ED were not more likely to have IR compared with controls.

CONCLUSION(S)

Epinephrine may be the common link between ED and LUTS.

Comparative effects of N-acetyl-l-cysteine and ramipril on arterial hypertension, insulin resistance, and oxidative stress in chronically glucose-fed rats

Beneficial effects of an antioxidant (N-acetyl-l-cysteine, NAC) and an angiotensin I-converting enzyme (ACE) inhibitor (ramipril) were assessed in a rat model of insulin resistance induced by 10% glucose feeding for 20 weeks. Treatments with NAC (2 g/kg per day) and ramipril (1 mg/kg per day) were initiated at 16 weeks in the drinking fluid. Systolic blood pressure, plasma levels of insulin and glucose, and insulin resistance were significantly higher in rats treated with glucose for 20 weeks. This was associated with a higher production of superoxide anion and NADPH oxidase activity in aorta and liver and with a marked reduction in protein expression of skeletal muscle insulin receptor substrate-1 (IRS-1) in the gastrocnemius muscle. NAC prevented all these alterations. Although ramipril also reversed high blood pressure, it had a lesser effect on insulin resistance (including IRS-1) and blocked superoxide anion production only in aorta. Ramipril, in contrast to NAC, did not reduce NADPH oxidase activity in aorta and liver or plasma levels of 4-hydroxynonenal and malondialdehyde. Results suggest that the inhibition of the oxidative stress in hypertensive and insulin-resistant states contributes to the therapeutic effects of NAC and ramipril. Whereas NAC exerts effective antioxidant activity in multiple tissues, ramipril appears to preferentially target the vasculature.

Hypotensive and vasorelaxant effects of the procyanidin fraction from Guazuma ulmifolia bark in normotensive and hypertensive rats

THE AIM OF THE STUDY

was to investigate the in vivo and in vitro cardiovascular activity of a procyanidin fraction (PCF) obtained from acetone extract of Guazuma ulmifolia bark which has traditionally been used as an antihypertensive agent.

RESULTS

10 mg/kg PCF doses orally administered to sugar-fed hypertensive rats decreased both the systolic arterial pressure and the heart rate, whereas the same doses intravenously administered induced arterial hypotension which was attenuated by NG-nitro-L-arginine methylester (L-NAME 31 mg/kg) pretreatment. In these experiments we employed carbachol as a positive control test. The PCF reduced the contraction induced by norepinephrine (1x10(-7) M) in isolated aortic rings of normotensive (IC50=35.3+/-12.4 ng/mL) and sugar-fed hypertensive (IC50=101.3+/-57.2 ng/mL) rats. This relaxant activity was inhibited by either vascular endothelium removal or L-NAME (30 microM) pretreatment, while indomethacin (10 microM) or atropine (10 microM) had no effect. Preliminary analysis of the PCF by HPLC-DAD-MS and FAB+ mass spectrometry allowed the detection of the main components such as the complex of procyanidin oligomers consisting mainly of tetramers and trimers.

CONCLUSIONS

Guazuma ulmifolia bark possesses long-lasting antihypertensive and vasorelaxing properties linked to the endothelium related factors, where nitric oxide is involved.

Adverse effects of reactive oxygen species on vascular reactivity in insulin resistance

Insulin resistance (IR) has adverse effects on the reactivity of arteries and arterioles and promotes arterial hypertension and vascular occlusive diseases. Altered reactivity of resistance vessels occurs at both the endothelium and smooth-muscle levels. One major mechanism of vascular dysfunction with IR involves the augmented generation, availability, and/or actions of reactive oxygen species (ROS). Scavengers of ROS are able immediately to restore normal dilator responsiveness in arteries from IR animals. Other factors, such as increased importance of constrictor agents such as endothelin, also restrict normal dilator responses. The basis of ROS-mediated vascular dysfunction in IR may be secondary to underlying inflammatory processes throughout the arterial wall. Although ROS scavengers may be beneficial in the short term, prolonged treatments involving behavioral approaches, such as changes in diet, weight loss, and regular exercise, and pharmacological approaches, involving the use of insulin-sensitizing agents, inhibitors of the renin-angiotensin system, or administration of statins, appear to offer benefits against the detrimental vascular effects of IR. Nonetheless, the most effective approach appears to involve prevention of IR via adoption of a healthy lifestyle by young people.

Effects of high-sucrose feeding on insulin resistance and hemodynamic responses to insulin in spontaneously hypertensive rats

This study was designed to investigate the effects of a sucrose diet on vascular and metabolic actions of insulin in spontaneously hypertensive rats (SHR). Male SHR were randomized to receive a sucrose or regular chow diet for 4 wk. Age-matched, chow-fed Wistar-Kyoto (WKY) rats were used as normotensive control. In a first series of experiments, the three groups of rats had pulsed Doppler flow probes and intravascular catheters implanted to determine blood pressure, heart rate, and blood flows. Insulin sensitivity was assessed during a euglycemic hyperinsulinemic clamp performed in conscious rats. In a second series of experiments, new groups of rats were used to examine glucose transport activity in isolated muscles and to determine endothelial nitric oxide synthase (eNOS) protein expression in muscles and endothelin content in vascular tissues. Sucrose feeding was shown to markedly enhance the pressor response to insulin and its hindquarter vasoconstrictor effect when compared with chow-fed SHR. A reduction in eNOS protein content in muscle, but no change in vascular endothelin-1 protein, was noted in sucrose-fed SHR when compared with WKY rats, but these changes were not different from those noted in chow-fed SHR. Similar reductions in insulin-stimulated glucose transport were observed in soleus muscles from both groups of SHR when compared with WKY rats. In extensor digitorum longus muscles, a significant reduction in insulin-stimulated glucose transport was only seen in sucrose-fed rats when compared with the other two groups. Environmental factors, that is, high intake of simple sugars, could possibly potentiate the genetic predisposition in SHR to endothelial dysfunction and insulin resistance.

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.

Contributions of the sympathetic nervous system, glutathione, body mass and gender to blood pressure increase with normal aging: influence of heredity

Body mass and sympathetic activity increase with aging and might underlie blood pressure (BP) elevation. Increased body mass index (BMI) may elevate BP by increasing sympathetic activity. Glutathione (GSH) can decrease BP, and declines with aging. We measured systolic (SBP) and diastolic BP, BMI, plasma (NE(pl)) and urine norepinephrine (NEu), and plasma GSH in n=204 twins across the age spectrum. BP correlated directly with BMI, NEpl, and NEu, but inversely with GSH. Age correlated with BP, BMI, NEpl, and NEu. BP, BMI, NEpl, and NEu were higher in older subjects than younger subjects, whereas GSH was lower with aging. In older subjects with high (above median) NEpl, SBP was 8 mmHg higher than in those of comparable age with low NE. In younger subjects with high GSH, BP was significantly lower than in younger subjects having low GSH. NEu was significantly reduced in young high-BMI subjects vs young low-BMI subjects. The heritability (h2) of NEpl, NEu, and GSH ranged from approximately 50 to approximately 70%, and these biochemical quantities were considerably more heritable than BP. We conclude that increases in sympathetic activity contribute to aging-induced SBP elevations, especially in older females. GSH reductions apparently participate in aging-induced BP elevations, most strongly in males. BMI increases contribute to BP elevations, particularly in younger subjects. BMI elevations apparently raise BP mainly by peripheral mechanisms, with generally little sympathetic activation. Substantial h(2) for plasma GSH, NE, and urine NE suggests that such traits may be useful 'intermediate phenotypes' in the search for genetic determinants of BP.

Impaired insulin-induced vasodilation in small coronary arteries of Zucker obese rats is mediated by reactive oxygen species

Insulin resistance (IR) and associated hyperinsulinemia are major risk factors for coronary artery disease. Mechanisms linking hyperinsulinemia to coronary vascular dysfunction in IR are unclear. We evaluated insulin-induced vasodilation in isolated small coronary arteries (SCA; approximately 225 microm) of Zucker obese (ZO) and control Zucker lean (ZL) rats. Vascular responses to insulin (0.1-100 ng/ml), ACh (10(-9)-10(-5) mol/l), and sodium nitroprusside (10(-8)-10(-4) mol/l) were assessed in SCA by measurement of intraluminal diameter using videomicroscopy. Insulin-induced dilation was decreased in ZO compared with ZL rats, whereas ACh and sodium nitroprusside elicited similar vasodilations. Pretreatment of arteries with SOD (200 U/ml), a scavenger of reactive oxygen species (ROS), restored the vasorelaxation response to insulin in ZO arteries, whereas ZL arteries were unaffected. Pretreatment of SCA with N-nitro-L-arginine methyl ester (100 micromol/l), an inhibitor of endothelial nitric oxide (NO) synthase (eNOS), elicited a vasoconstrictor response to insulin that was greater in ZO than in ZL rats. This vasoconstrictor response was reversed to vasodilation in ZO and ZL rats by cotreatment of the SCA with SOD or apocynin (10 micromol/l), a specific inhibitor of vascular NADPH oxidase. Lucigenin-enhanced chemiluminescence showed increased basal ROS levels as well as insulin (330 ng/ml)-stimulated production of ROS in ZO arteries that was sensitive to inhibition by apocynin. Western blot analysis revealed increased eNOS expression in ZO rats, whereas Mn SOD and Cu,Zn SOD expression were similar to ZL rats. Thus IR in ZO rats leads to decreased insulin-induced vasodilation, probably as a result of increased production of ROS by vascular NADPH oxidase, leading to decreased NO bioavailability, despite a compensatory increase in eNOS expression.

Involvement of oxidative stress and NADPH oxidase activation in the development of cardiovascular complications in a model of insulin resistance, the fructose-fed rat

Growing evidences suggest a role of oxidative stress in hypertension and cardiac hypertrophy. The fructose (60%)-fed rat represents a model of metabolic syndrome, associating insulin resistance and high blood pressure. In this model, hypertension, cardiac and vessels hypertrophy and markers of oxidative stress were determined. In addition, the production of reactive oxygen species (ROS) was evaluated at different times after the initiation of fructose-enriched diet in aorta, heart and polymorphonuclear cells. High fructose feeding was associated with an early (1-week) increase in ROS production by aorta, heart and circulatory polymorphonuclear cells, in association with enhanced markers of oxidative stress. Vascular and cardiac hypertrophy was also rapidly observed, while the rise in blood pressure was significant only after 3 weeks. In summary, our study suggests that the production of reactive oxygen species can be a key-event in the initiation and development of cardiovascular complications associated with insulin resistance.

Oxidant stress and constrictor reactivity impair cerebral artery dilation in obese Zucker rats

This study tested the hypothesis that evolution of the metabolic syndrome in obese Zucker rats (OZR) leads to impaired dilator reactivity of cerebral resistance arteries vs. responses determined in lean Zucker rats (LZR). Middle cerebral arteries (MCA) from 17-wk-old male LZR and OZR were isolated and cannulated with glass micropipettes. Vascular reactivity was assessed in response to challenge with ACh, sodium nitroprusside (SNP), reductions and elevations in Po2, 5-HT, and increased intralumenal pressure. Vessels were treated with the free radical scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (tempol) to assess the role of superoxide production in altering reactivity, and passive vascular wall mechanics was assessed in each vessel. Vascular superoxide production was assessed in isolated arteries using fluorescence microscopy. Vessel dilation to ACh and hypoxia was impaired in OZR vs. LZR, although responses to SNP were normal. Vessel constriction to 5-HT, elevated Po2, and elevated intralumenal pressure was enhanced in OZR vs. LZR. Fluorescence microscopy demonstrated an increased superoxide production in arteries of OZR vs. LZR, correctable by incubation with tempol. Although treatment of vessels from OZR with tempol improved dilation to ACh and hypoxia, constrictor responses to 5-HT, elevated Po2, and pressure were not altered by tempol treatment. Indexes of vessel wall mechanics were comparable between groups. These results suggest that vasodilator reactivity of MCA of OZR in response to endothelium-dependent dilator stimuli is impaired vs. LZR and that this may represent a reduced bioavailability of signaling molecules due to oxidant scavenging. However, oxidative stress-independent increases in myogenic tone and constrictor reactivity may contribute to blunted dilator responses of cerebral microvessels.

Red wine polyphenols alone or in association with ethanol prevent hypertension, cardiac hypertrophy, and production of reactive oxygen species in the insulin-resistant fructose-fed rat

The effects of a red wine polyphenolic extract (RWPE), ethanol, or both combined were evaluated in insulin resistant rats. Rats were fed for 6 weeks with fructose (60%)-enriched food and force-fed with (a) water only (F group), (b) aqueous solution of RWPE (100 mg/kg, FP group), (c) 10% (v/v) mixture of ethanol and water (FE group), or (d) solution containing the same amount of the RWPE and ethanol (FPE group). Animals fed a standard chow (C group) were used for comparison purpose. After 6 weeks, blood pressure was higher in F (130.0 x b1 1.7 mm Hg) than in C animals (109.6 x b1 0.9 mm Hg) and similar to the C group in all other fructose-fed treatment groups. Relative heart weight was higher in F (3.10 x b1 0.05) than in C (2.78 x b1 0.07) and significantly lower in FP (2.92 x b1 0.04) and FPE (2.87 x b1 0.08 mg/g) than in F animals. Left ventricle and aorta productions of reactive oxygen species (O2*-) were higher in F than in C groups and lowered by the RWPE but not by the ethanol treatment. Ethanol but not the RWPE treatment reduced the degree of insulin resistance in the fructose-fed rats. In summary, our study showed that polyphenols are able to prevent cardiac hypertrophy and production of reactive oxygen species in the insulin resistant fructose-fed rat.

Cerebrovascular dysfunction in Zucker obese rats is mediated by oxidative stress and protein kinase C

Insulin resistance (IR) impairs vascular function in the peripheral and coronary circulations, but its effects on cerebral arteries are virtually unexplored. We examined the vascular responses of the basilar artery (BA) and its side branches through a cranial window in Zucker lean (ZL) and IR Zucker obese (ZO) rats. Nitric oxide (NO) and K+ channel-mediated dilator responses, elicited by acetylcholine, iloprost, cromakalim, and elevated [K+], were greatly diminished in the ZO rats compared with ZL rats. In contrast, sodium nitroprusside induced similar relaxations in the two experimental groups. Expressions of the K+ channel pore-forming subunits were not affected by IR, while endothelial NO synthase was upregulated in the ZO arteries compared with ZL arteries. Protein kinase C (PKC) activity and production of superoxide anion were increased in the cerebral arteries of ZO rats, and pretreatment with superoxide dismutase restored all examined dilator responses. In contrast, application of PKC inhibitors improved only receptor-linked NO-mediated relaxation, but not K+ channel-dependent responses. Thus, IR induces in ZO rats cerebrovascular dysfunction, which is mediated by oxidative stress and partly by PKC activation. The revealed impairment of NO and K+ channel-dependent dilator responses may be responsible for the increased risk of cerebrovascular events and neurodegenerative disorders in IR.

Potassium Channel Dysfunction in Cerebral Arteries of Insulin-Resistant Rats Is Mediated by Reactive Oxygen Species

Background and Purpose— Insulin resistance (IR) increases the risk of stroke in humans. One possible underlying factor is cerebrovascular dysfunction resulting from altered K + channel function. Thus, the goal of this study was to examine K + channel–mediated relaxation in IR cerebral arteries.

Methods— Experiments were performed on pressurized isolated middle cerebral arteries (MCAs) from fructose-fed IR and control rats.

Results— Dilator responses to iloprost, which are BK Ca channel mediated, were reduced in the IR compared with control arteries (19±2% versus 33±2% at 10 −6 mol/L). Similarly, relaxation to the K ATP opener pinacidil was diminished in the IR MCAs (17±2%) compared with controls (38±2% at 10 −5 mol/L). IR also reduced the K ATP channel–dependent component in calcitonin gene-related peptide–induced dilation; however, the magnitude of the relaxation remained unchanged in IR because of a nonspecified K + channel–mediated compensatory mechanism. In contrast, K ir channel–mediated relaxation elicited by increases in extracellular [K + ] (4 to 12 mmol/L) was similar in the control and IR arteries. Blockade of the K ir and K v channels with Ba 2+ and 4-aminopyridine, respectively, constricted the MCAs in both experimental groups with no significant difference. Pretreatment of arteries with superoxide dismutase (200 U/mL) plus catalase (150 U/mL) restored the dilatory responses to iloprost and pinacidil in the IR arteries. Immunoblots showed that the expressions of the pore-forming subunits of the examined K + channels are not altered by IR.

Conclusions— IR induces a type-specific K + channel dysfunction mediated by reactive oxygen species. The alteration of K ATP and BK Ca channel–dependent vascular responses may be responsible for the increased risk of cerebrovascular events in IR.

Coping with endothelial superoxide: potential complementarity of arginine and high-dose folate

Superoxide overproduction is a prominent mediator of the endothelial dysfunction associated with a range of vascular disorders, acting in a number of complementary ways to inhibit effective endothelial nitric oxide (NO) activity. The ability of superoxide to quench NO is well known, but oxidants derived from superoxide also appear to inhibit dimethylarginine dimethylaminohydrolase (DDAH) and to oxidize tetrahydrobiopterin (THBP). The former effect boosts the level of methylated arginines that act as potent competitive inhibitors of NO synthase, whereas the latter effect decreases the ability of this enzyme to generate NO, while converting it to a form that readily generates superoxide. The adverse impact of DDAH deficiency on NO production can be offset with supplemental arginine. Although supplementation with THBP has the potential to compensate for the rapid oxidative destruction of this compound, and maintaining optimal vitamin C nutrition may protect or restore the endothelial THBP pool to a limited extent, the most practical way to optimize NO synthase activity in the context of THBP deficit may be administration of high-dose folic acid. The primary circulating metabolite of folate, 5-methyltetrahydrofolate (5MTHF), is structurally analogous to THBP, and appears to normalize the activity of NO synthase in THBP-depleted endothelial cells, either because it "pinch hits" for the absent THBP, or interacts allosterically with NO synthase in some other way to promote the proper function of this enzyme. This observation may rationalize recent clinical studies showing a favorable effect of oral folic acid (5-10 mg daily) on dysfunctional endothelium, independent of any concurrent modulation of homocysteine levels. A recent study reports that, whereas either arginine or THBP alone have only a modest impact on dysfunctional aortic endothelium derived from hypercholesterolemic mice, the combination of the two produces a complete normalization of endothelial function. In aggregate, these considerations suggest that joint administration of arginine and high-dose folate may represent a fruitful approach to preventing and treating vascular disorders - albeit the underlying overproduction of superoxide should also be addressed by ameliorating relevant vascular risk factors.

An elevation of triglycerides reflecting decreased triglyceride clearance may not be pathogenic – relevance to high-carbohydrate diets

The fact that carbohydrate-rich diets often increase plasma triglycerides has led some to question the wisdom of such diets. This increase is primarily attributable to a decrease in the efficiency of triglyceride clearance -- whereas the elevation of triglycerides observed in insulin-resistant subjects stems mainly from increased hepatic production of VLDL particles. There is growing reason to suspect that the increased coronary risk associated with elevated triglycerides in Western epidemiology reflects the fact that high triglycerides are a marker for insulin resistance syndrome, rather than any inherent pathogenic role of triglycerides per se. Thus, endothelial dysfunction is seen only in those hypertriglyceridemic subjects who are insulin resistant, and is absent in patients whose markedly elevated triglycerides reflect genetically defective lipoprotein lipase activity. Triglyceride levels are relatively high in certain Third World societies which are virtually immune to coronary disease so long as they persist in their traditional very-low-fat diets; in Ornish's celebrated study, a moderate rise in triglycerides coincided with a marked reduction in coronary events. Although the particle size of both LDL and HDL tends to decrease when triglyceride levels are high, it is questionable whether this effect has a major pathogenic impact. The one clear drawback of high-carbohydrate diets is a decrease in HDL particle number, resulting from decreased hepatic production of apoA-I; this effect is seen whether or not triglycerides increase. The very favorable effects of very-low-fat, whole food, quasi-vegan diets on LDL cholesterol, insulin sensitivity, and body weight appear to more than compensate for this decrease in HDL; it is notable that HDL levels tend to be quite low in Third World cultures at minimal risk for coronary disease. On the other hand, this decrease in HDL may be of more significance in the context of omnivore diets only moderately low in fat, as suggested by the fact that diets higher in unsaturated fats emerge as more protective in Western prospective epidemiology. The tendency of high-carbohydrate diets to boost triglycerides can be minimized by exercise training, supplemental fish oil, an emphasis on fiber-rich, low-glycemic-index whole foods, and the "spontaneous" weight loss often seen with ad libitum consumption of such diets -- measures which are highly recommendable whether or not triglycerides are a concern.

Effect of the NAD(P)H oxidase inhibitor, apocynin, on peripheral nerve perfusion and function in diabetic rats

Upregulation of vascular NAD(P)H oxidase has been considered an important source for elevated levels of reactive oxygen species that contribute to several cardiovascular disease states, including the vascular complications of diabetes mellitus. Previous studies have shown that treatment with antioxidants corrects impaired nerve function and blood flow in diabetic rats. The aim was to assess the degree of involvement of NAD(P)H oxidase in experimental diabetic neuropathy. To this end, after 6 weeks of untreated streptozotocin-diabetes, rats were treated for 2 weeks with the NAD(P)H oxidase, apocynin. Two high doses (15 and 100 mg/kg) were used to ensure that maximal effects were registered. Diabetes caused a 20% reduction in sciatic nerve motor conduction velocity, and a 14% deficit for sensory saphenous nerve. Apocynin treatment corrected these defects by 32% and 48%, respectively: there were no significant differences between the effects of the 2 doses. Sciatic nerve nutritive endoneurial perfusion was measured by hydrogen clearance microelectrode polarography. Blood flow and vascular conductance were 47% and 40% reduced by diabetes, respectively. Both doses of apocynin had similar effects, correcting the blood flow deficit by 31% and conductance by 47%. Thus, the data show that NAD(P)H oxidase contributes to the neurovascular deficits in diabetic rats. While only accounting for part of the elevated reactive oxygen species production in diabetes, this mechanism could provide a novel therapeutic candidate for further investigation in diabetic neuropathy and vasculopathy.

Relationship between carotid atherosclerosis and erythrocyte membrane cholesterol oxidation products in type 2 diabetic patients

Oxidative stress is well known to play a critical role in atherosclerosis. This study investigated an appropriate marker of in vivo oxidative stress and whether it could predict macroangiopathy in diabetes. The lipid composition of erythrocyte membranes was analyzed in 64 type 2 diabetic patients using gas chromatography-mass spectrometry (GC/MS). After 3,5,7-cholestatriene (a cholesterol oxidation product) was detected, the peak height ratio of 3,5,7-cholestatriene to cholesterol was calculated. Carotid artery intima-media thickness (IMT) was measured to evaluate atherosclerosis. The IMT was independently associated with 3,5,7-cholestatriene (P<0.0001), age (P=0.0001), and HbA1c (P=0.05) by stepwise multiple regression analysis (R2=0.416, P<0.0001). When the subjects were divided into groups with or without carotid atherosclerosis, the 3,5,7-cholestatriene level was significantly higher in 37 subjects with atherosclerosis than in 27 subjects without it (0.41+/-0.22 vs. 0.16+/-0.16%, P<0.0001). Among 38 subjects with no clinical manifestations of macroangiopathy and long-term good glycemic control, the 3,5,7-cholestatriene level was also significantly higher in the patients with carotid atherosclerosis than in those without it (0.40+/-0.20 vs. 0.18+/-0.12%, P=0.0003). These data suggest that the 3,5,7-cholestatriene level in erythrocyte membrane lipids may be a useful predictor of subclinical atherosclerosis.

Pathophysiological implications of insulin resistance on vascular endothelial function

BACKGROUND

Insulin resistance is a key component of the insulin resistance syndrome and is a crucially important metabolic abnormality in Type 2 diabetes. Insulin-resistant individuals are at significantly increased risk of cardiovascular disease, although the underlying mechanisms remain incompletely understood. The endothelium is thought to play a critical role in maintaining vascular homeostasis, a process dependent on the balance between the production of nitric oxide, superoxide and other vasoactive substances. Endothelial dysfunction has been demonstrated in insulin-resistant states in animals and humans and may represent an important early event in the development of atherosclerosis. Insulin resistance may be linked to endothelial dysfunction by a number of mechanisms, including disturbances of subcellular signalling pathways common to both insulin action and nitric oxide production. Other potential unifying links include the roles of oxidant stress, endothelin, the renin angiotensin system and the secretion of hormones and cytokines by adipose tissue. Lifestyle measures and drug therapies which improve insulin sensitivity and ameliorate endothelial dysfunction may be important in delaying the progression to overt cardiovascular disease in at risk individuals.

METHODS

We conducted a literature search using Medline, restricted to articles published in the English language between 1966 and the present, and reviewed bibliographies of relevant articles. An initial search strategy employing combinations of the MeSH terms: insulin resistance; endothelium, vascular; insulin; nitric oxide or hyperinsulinaemia produced over 300 references. Focused searches using keywords relevant to the molecular aspects of endothelial function and insulin signalling, and lifestyle or pharmacological interventions relevant to insulin resistance or endothelial function, produced over 300 further references. Abstracts of all references were screened before selecting those relevant to this review.

Alterations in KATP and KCa channel function in cerebral arteries of insulin-resistant rats

We examined whether insulin resistance alters the function of ATP-dependent and Ca(2+)-activated K(+) channels (K(ATP) and K(Ca) channels, respectively) in pressurized isolated middle cerebral arteries (MCAs) from fructose-fed insulin-resistant (IR) and control rats. Blockade of K(Ca) channels with tetraethylammonium chloride (TEA, 2.5 mM) or iberiotoxin (IBTX, 0.1 microM) increased the spontaneously developed tone in control MCAs by 10.5 +/- 1.3% (n = 10) and 13.3 +/- 2.3% (n = 6), respectively. In the IR arteries, TEA induced similar constrictions (8.0 +/- 1.1%, n = 10), but IBTX constricted the IR arteries by only 3.1 +/- 0.9% (n = 8; P < 0.01). Bradykinin (BK)-induced endothelium-mediated relaxation was reduced in IR MCAs. Maximum relaxation to BK (10(-6) M) was 42 +/- 4% in control (n = 9) and 19 +/- 2% in IR (n = 10; P < 0.01) arteries. Pretreatment with TEA, IBTX, or the K(ATP) channel blocker glibenclamide (10 microM) inhibited relaxation to BK in control MCAs but did not alter dilation in IR arteries. Relaxation to the K(ATP) channel opener cromakalim was also diminished in IR MCAs. Maximum relaxation to cromakalim (10(-5) M) was 48 +/- 3% in control (n = 6) and 19 +/- 2% in IR arteries (n = 6; P < 0.01). These findings demonstrate that insulin resistance alters the function of K(ATP) and K(Ca) channels in isolated MCAs and affects the control of resting vascular tone and the mediation of dilator stimuli.

Policosanol safely down-regulates HMG-CoA reductase - potential as a component of the Esselstyn regimen

Many of the wide-ranging health benefits conferred by statin therapy are mediated, not by reductions in LDL cholesterol, but rather by inhibition of isoprenylation reactions essential to the activation of Rho family GTPases; this may be the mechanism primarily responsible for the favorable impact of statins on risk for ischemic stroke, senile dementia, and fractures, as well as the anti-hypertensive and platelet-stabilizing actions of these drugs. Indeed, the extent of these benefits is such as to suggest that most adults would be wise to take statins; however, owing to the significant expense of statin therapy, as well as to the potential for dangerous side effects that mandates regular physician follow-up, this strategy appears impractical. However, policosanol, a mixture of long-chain aliphatic alcohols extractable from sugar cane wax, has shown cholesterol-lowering potency comparable to that of statins, and yet appears to be devoid of toxic risk. Recent evidence indicates that policosanol down-regulates cellular expression of HMG-CoA reductase, and thus has the potential to suppress isoprenylation reactions much like statins do. Consistent with this possibility, the results of certain clinical and animal studies demonstrate that policosanol has many effects analogous to those of statins that are not likely explained by reductions of LDL cholesterol. However, unlike statins, policosanol does not directly inhibit HMG-CoA reductase, and even in high concentrations it fails to down-regulate this enzyme by more than 50% - thus likely accounting for the safety of this nutraceutical. In light of the fact that policosanol is quite inexpensive and is becoming available as a non-prescription dietary supplement, it may represent a practical resource that could enable the general public to enjoy health benefits comparable to those conferred by statins. In a long-term clinical study enrolling patients with significant symptomatic coronary disease, Esselstyn has demonstrated that a low-fat, whole-food vegan diet, coupled with sufficient statin therapy to maintain serum cholesterol below 150 mg/dL, can stop the progression of coronary disease and virtually eliminate further risk for heart attack. A comparable regimen, in which policosanol is used in place of statins, may represent a practical strategy whereby nearly everyone willing to commit to health-protective eating can either prevent coronary disease, or prevent pre-existing coronary disease from progressing to a life-threatening event.

Insulin's stimulation of endothelial superoxide generation may reflect up-regulation of isoprenyl transferase activity that promotes rac translocation

Recent research demonstrates that statin drugs exert a number of favorable effects on endothelial function, independent of lipid modulation, that appear to be mediated by a partial inhibition of prenylation reactions. Statin-induced suppression of PKC-evoked superoxide production may be attributable to an inhibition of rac prenylation and thus translocation that impedes activation of the membrane-bound NAD(P)H oxidase. Conversely, it is now known that hyperinsulinemia up-regulates prenylation reactions by boosting the activities of isoprenyl transferases. In light of new evidence that hyperinsulinemia stimulates endothelial superoxide production via NAD(P)H oxidase, it is tempting to conclude that up-regulation of rac prenylation is at least partially responsible for this phenomenon. In patients afflicted with insulin resistance syndrome, this adverse impact of hyperinsulinemia may be exacerbated by an excessive free fatty acid flux that activates endothelial PKC - another stimulant of the NAD(P)H oxidase - while impeding insulin-mediated activation of nitric oxide synthase. The resulting imbalance of endothelial nitric oxide and superoxide production may be responsible for much of the excess vascular risk associated with this syndrome.

Impaired endothelium-mediated relaxation in isolated cerebral arteries from insulin-resistant rats

Insulin resistance (IR) impairs vascular responses in peripheral arteries. However, the effects of IR on cerebrovascular control mechanisms are completely unexplored. We examined the vascular function of isolated middle cerebral arteries (MCAs) from fructose-fed IR and control rats. Endothelium-dependent vasodilation elicited by bradykinin (BK) was reduced in IR compared with control MCAs. Maximal dilation to BK (10(-6) M) was 38 +/- 3% (n = 13) in control and 19 +/- 3% (n = 10) in IR arteries (P < 0.01). N(omega)-nitro-L-arginine methyl ester (L-NAME; 10 microM) decreased responses to BK in control arteries by approximately 65% and inhibited the already reduced responses completely in IR MCAs. Indomethacin (10 microM) reduced relaxation to BK in control MCAs by approximately 40% but was largely ineffective in IR arteries. Combined L-NAME and indomethacin treatments eliminated the BK-induced dilation in both groups. Similarly to BK, endothelium-mediated and mainly cyclooxygenase (COX)-dependent dilation to calcium ionophore A23187 was reduced in IR arteries compared with controls. In contrast, vascular relaxation to sodium nitroprusside was similar between the IR and control groups. These findings demonstrate that endothelium-dependent dilation in cerebral arteries is impaired in IR primarily because of a defect of the COX-mediated pathways. In contrast, nitric oxide-mediated dilation remains intact in IR arteries.

Prevention of hypertension, insulin resistance, and oxidative stress by alpha-lipoic acid

The aim of the present study was to investigate whether a dietary supplementation of alpha-lipoic acid could prevent blood pressure elevation, insulin resistance, and the increase in aorta superoxide anion production in a new experimental model of hypertension associated with insulin resistance. Sprague-Dawley rats were given 10% D-glucose in their drinking water combined either with a normal chow diet or with an alpha-lipoic acid-supplemented diet and were compared with control rats during 3 weeks. Oxidative stress was evaluated by measuring the aortic superoxide anion production using the lucigenin chemiluminescence method. Increases in blood pressure, insulin resistance, and aorta superoxide production observed in glucose-fed rats were prevented by the supplementation of the diet with lipoic acid. Positive correlations were found between aortic superoxide production and blood pressure, between insulin resistance and blood pressure, or between superoxide production and insulin resistance. Moreover, a decrease in the activity of plasma glutathione peroxidase observed in the glucose-fed rats was prevented by lipoic acid treatment. These findings demonstrate that high-glucose feeding rapidly induced hypertension and insulin resistance in association with the induction of a vascular oxidative stress. The antihypertensive action and the prevention of insulin resistance by lipoic acid appears to be associated to its antioxidative properties because it prevented the increase in oxidative stress, as reflected by the normalization of superoxide anion production in aorta and the prevention of the fall in the activity of glutathione peroxidase in the glucose-fed rats.

Lipid hydroperoxide and markers of renal disease susceptibility in African-Caribbean and Caucasian patients with Type 2 diabetes mellitus

AIMS

The reasons for the increased incidence of diabetic nephropathy in African-Caribbean compared with Caucasian subjects are poorly understood. Increased oxidative stress is linked to the development of endothelial dysfunction and histological abnormalities associated with diabetic renal disease. Therefore, it was assessed whether a marker of oxidative stress, lipid hydroperoxide (LOOH) and endothelial damage, von Willebrand factor (vWF) varied according to ethnic origin in the presence or absence of early diabetic nephropathy.

METHODS

Eighty-eight patients with Type 2 diabetes mellitus of African-Caribbean or Caucasian origin without a history of cardiovascular disease or clinical proteinuria were studied. Patients were classified as having microalbuminuria or normal albumin excretion. Fasting plasma vWF and LOOH were measured by an inhouse enzyme-linked immunoassay and ferrous oxidation with xylenol orange (FOX) assay, respectively. The relationship of LOOH to urinary albumin status, the metabolic disturbances of diabetes, blood pressure and ethnic origin were assessed using multivariate analysis.

RESULTS

Compared with Caucasian patients those of African-Caribbean origin had higher systolic blood pressure and HDL-cholesterol (157.8 +/- 17.0 vs. 147.8 +/- 24.4, P = 0.041 and 1.6 +/- 0.4 vs. 1.3 +/- 0.5, P = 0.018) but lower total triglycerides (1.3 +/- 0.8 vs. 1.9 +/- 1.1, P = 0.008). LOOH was significantly higher in the African-Caribbean patients compared with Caucasians (5.98 +/- 2.49 vs. 4.49 +/- 2.19, P = 0.006). vWF tended to be higher in microalbuminuric patients but showed no variation with ethnicity. In logistic regression analysis, LOOH was the only independent predictor of a raised albumin excretion rate (P = 0.008). In multiple regression analysis, African-Caribbean ethnicity (P = 0.020) HDL-cholesterol (P = 0.036), total triglycerides (P = 0.002) and a raised albumin excretion rate (P = 0.002) were independent predictors of LOOH.

CONCLUSIONS

In this group of Type 2 diabetic patients an increase in LOOH is associated with abnormal urinary albumin excretion. African-Caribbean origin was a determinant of LOOH independently of microalbuminuria. It is postulated that increased oxidative stress is of pathophysiological significance in accelerating the development of renal disease in African-Caribbean patients.