Free radicals in diabetic endothelial cell dysfunction

Effects of endurance training on tissue glutathione homeostasis and lipid peroxidation in streptozotocin-induced diabetic rats

The aims of our study were to assess whether endurance training strengthens glutathione-dependent antioxidant defenses and decreases oxidative stress in experimental diabetes. Streptozotocin-induced diabetic rats were divided into trained and untrained groups, which were further divided into resting and acute exercise groups. Endurance training consisted of treadmill running for 8 weeks. For acute exhaustive exercise, graded treadmill running was conducted until exhaustion. Eight weeks' treadmill training increased the endurance, favorably decreased lipid peroxidation as measured by thiobarbituric acid reactive substances but not conjugated dienes levels in kidney and vastus lateralis muscle and upregulated glutathione peroxidase in red gastrocnemius muscle. However, it adversely decreased total glutathione level and glutathione peroxidase activity in kidney. Acute exhaustive exercise up-regulated glutathione peroxidase activity in liver. Endurance training did not prevent the increase in thiobarbituric acid reactive substances level in liver due to acute exhaustive exercise. Activities of glutathione disulfide reductase and glutathione S-transferase were not affected. Even though endurance training appeared to upregulate glutathione dependent antioxidant defense in skeletal muscle and to decrease lipid peroxidation in kidney and vastus lateralis muscle as measured by TBARS, our results suggests that beneficial effects of 8 weeks of endurance training are limited in this rat model of uncontrolled diabetes mellitus.

Effects of diabetes mellitus and acute hypertension on plasma nitric oxide and endothelin concentrations in rats

AIM

To examine the plasma nitrate/nitrite (NOx-two end products of the nitric oxide metabolism) and endothelin (ET) concentrations, and response to acute adrenaline induced hypertension in diabetic rats.

MATERIALS AND METHODS

Four groups of 4-month-old rats were used: control rats (C, n=10) rats received adrenaline (A, 40 microg/kg i.v., n=10), rats received streptozotocin (S, 50 mg/kg i.v., n=8), and rats received STZ and adrenaline (SA, n=9). The experiments were performed 4 weeks after the STZ administration. Plasma NOx, ET, glucose, and mean arterial blood pressure (MAP) were measured.

RESULTS

Plasma ET concentrations were significantly increased in diabetic rats (S and SA) in comparison with the controls and adrenaline-only administered rats. NOx concentrations in diabetic groups (S and SA) were significantly decreased in comparison with the controls. Acute adrenaline induced hypertension in diabetes leads to a significant decrease of NOx concentrations in comparison with the controls, adrenaline-only administered and STZ-only administered rats. There was no difference between the MAP in diabetic and control rats. Adrenaline injection caused a significant increase of MAP in A and SA groups. Plasma glucose concentrations in diabetic rats (S and SA) were significantly increased in comparison with the nondiabetic groups (C and A). There was a weak but significant correlation between the NOx and ET concentrations in the controls, which probably reveal the balance between these vasoactive factors. In A, S, and SA groups, no significant correlation between the NOx/ET was found.

CONCLUSION

An impairment of the NOx and ET formation could be involved in the pathogenesis of diabetes mellitus and especially acute hypertension and diabetes. A lack of correlation between the NOx and ET probably indicated that in diabetes and acute hypertension, a primary mechanism of compensatory nitric oxide might be lost.

Sequential morphological and permeability changes in the rete capillaries during hyperglycaemia

With the rete model of the eel swimbladder, we have studied the appearance and development of a microangiopathy during a 2-year period of hyperglycaemia. Hyperglycaemia was induced in the eel by chronic exposure to cold water. At 3-5 months, basement membrane thickness was twice the normal value and increased only slightly thereafter. Diffusion coefficients of permeability were measured in counter-current perfusion experiments for a variety of tracers that are believed to use different pathways of transcapillary transport. The permeability to sucrose was the first to significantly increase, at 6-8 months, followed by that of albumin, insulin, and inulin, at 9-11 months and that of sodium, at 18-24 months. The permeability to water and antipyrine remained stable throughout the study. The results indicate that in the rete model, chronic hyperglycaemia induces a rapid thickening of the capillary basement membrane and selective permeability increments in the various paths of transcapillary transport.

Diabetes-induced changes in responsiveness of rat bladder and vas deferens to peptides in vitro: susceptibility to reversal by insulin

Changes in responsiveness of the vas deferens and urinary bladder to bradykinin (BK) receptor agonists (Tyr8-BK and des-Arg9-BK), substance P (SP), and endothelin-1 (ET-1) were assessed 8 weeks after streptozotocin (STZ)-induced diabetes. Preparations from control or STZ-treated (60 mg/kg i.p.) male rats were tested for contractile and neurogenic twitch potentiating (TP, in VD only) effects of all four agonists (1 nM to 0.3 or 3 microM). In diabetic VD, contractile effects of Tyr8-BK, des-Arg9-BK, and SP were enhanced, but ET-1 effects were unchanged. In contrast, TP by des-Arg9-BK was unaffected, that by Tyr8-BK was decreased, and those by SP and ET-1 were increased. In diabetic UB, only contractions to des-Arg9-BK and SP were enhanced. Following insulin replacement (human, 1-3 U/day s.c.), starting 1 week after STZ, TP induced by Tyr8-BK and des-Arg9-BK in VD were further inhibited, but all other changes in both preparations were reversed at least partially. Insulin treatment of nondiabetic rats, however, also affected VD (but not UB) responsiveness, such that contractions to Tyr8-BK and TP by ET-1 were increased, but TP by Tyr8-BK was decreased. Thus, STZ-induced type I diabetes causes important alterations in responsiveness of non-vascular smooth muscle tissues of the rat to BK, SP, and ET-1. Long term insulin replacement, at doses normalising glycaemia, effectively reversed most changes in VD or UB responsiveness, but it is unclear if this is truly due to blocking of STZ-induced changes, since the treatment also affected responsiveness of nondiabetic tissues.

Hypertension in L-NAME-treated diabetic rats depends on an intact sympathetic nervous system

We demonstrated previously that induction of diabetes in rats that were treated chronically with the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) causes a severe, progressive increase in mean arterial pressure. This study tested the role of the sympathetic nervous system in that response. Rats were instrumented with chronic artery and vein catheters and assigned randomly to four diabetic groups pretreated with vehicle (D), L-NAME (D+L), the alpha(1)- and beta-adrenergic receptor antagonists terazosin and propranolol (D+B), or L-NAME, terazosin, and propranolol (D+LB). After baseline measurements were taken, rats were pretreated; 6 days later, streptozotocin was administered and 3 wk of diabetes ensued. D+L rats had a marked, progressive increase in arterial pressure that by day 20 was approximately 60 mmHg greater than in D rats. The pressor response to L-NAME was significantly attenuated in diabetic rats cotreated with adrenergic blockers. During week 1 of diabetes, plasma renin activity (PRA) increased and then returned to control levels in D rats. PRA increased progressively in D+L rats, and chronic adrenergic receptor blockade restored the biphasic renin response in D+LB rats. These results suggest that the sympathetic nervous system may be involved in the hypertensive response to onset of diabetes in L-NAME-treated rats, possibly through control of renin secretion.

Multiple mechanisms of early hyperglycaemic injury of the rat intestinal microcirculation

1. Hyperglycaemia in the vast majority of humans with diabetes mellitus is the end result of profound insulin resistance secondary to obesity. For patients in treatment, hyperglycaemia is usually not sustained but, rather, occurs intermittently. In in vivo studies of the rat intestinal microcirculation, endothelial impairment occurs within 30 min at D-glucose concentrations > or = 300 mg/dL. Endothelial-dependent dilation to acetylcholine and constriction to noradrenaline is impaired. Vasodilation to exogenous nitric oxide (NO) remains normal. 2. When initiated before hyperglycaemia, suppression of oxygen radicals by both scavenging and pretreatment with cyclo-oxygenase blockade to prevent oxygen radical formation minimized endothelial impairments during hyperglycaemia. Neither treatment was effective in restoring endothelial function once it was damaged by hyperglycaemia. 3. A mechanism that may initiate the arachidonic acid- oxygen radical process is activation of specific isoforms of protein kinase C (PKC). De novo formation of diacylglycerol during hyperglycaemia activates PKC. Blockade of the beta II PKC isoform with LY-333531 prior to hyperglycaemia protected NO formation within the arteriolar wall, as judged with NO-sensitive microelectrodes. Furthermore, once suppression of endothelial dilation was present in untreated animals, PKC blockade could substantially restore endothelial-dependent dilation. 4. These results indicate that acute hyperglycaemia is far from benign and, in the rat, causes rapid endothelial impairment. Both oxygen radical scavenging and cyclo-oxygenase blockade prior to bouts of hyperglycaemia minimize endothelial impairment with limited side effects. Blockade of specific PKC isozymes protects endothelial function both as a pre- or post-treatment during moderately severe hyperglycaemia.

Effect of estrogen on endothelial dysfunction in postmenopausal women with diabetes

BACKGROUND

Treatment with estrogen causes increased release of nitric oxide and this appears to be an important mechanism involved in the cardioprotective effect of estrogen. Previous studies have clearly shown that estrogen has an acute vasodilatory effect. Recently, abnormality of flow mediated endothelial dilation, which is defined as an endothelial dysfunction, has been proposed as an early manifestation of atherogenesis. However, its effect in type 2 diabetes is unknown. Stimulus-provoked endothelium dependent dilatation, using high-resolution external vascular ultrasound, is a useful method in the measurement of endothelial function. The main advantages of this method are that it is completely non-invasive, accurate and reproducible. This classical method for the measurement of endothelial dysfunction, utilizing non-invasive, high-resolution ultrasonography, has some limitations especially in terms of reproducibility. To improve the accuracy and reproducibility of this method, measurements made for this study involved the use of an additional attachment. This device was an ultrasound probe that was attached to the arm of patient. In addition, this study evaluated not only a change in diameter in terms of flow mediated vasodilation, but also initial and peak response times during this test. The aims of this study are: (1) to evaluate the flow mediated peak vasoreactivity (FMD), the lag time from base line to initiation of vasodilation (IRT) and the peak response of endothelial dependent vasodilation in a control group and in young diabetic patients; and (2) to evaluate the effect of estrogen treatment on flow mediated vasodilation in postmenopausal women with diabetes.

METHOD

Measurements were taken for flow mediated vasodilation (endothelial dependent vasodilation: FMD), endothelial independent vasodilation (EID) and lag time from base line to initial reaction of FMD. The aforementioned non-invasive method and attachment were used. Subjects for the experiment were 12 young people with diabetes (six male and six female, mean age 26.3) and 12 age-matched healthy controls (six male and six female, mean age 25.6). In addition, measurements were taken for FMD, EID and lag time in the brachial artery before and after estrogen supplementation (Premarin 0.625 mg for 7 days). Subjects for the experiment were 16 normal postmenopausal women and 18 age-matched postmenopausal women with type 2 diabetes.

RESULT

There is no significant difference in BMI (body mass index), mean age, or blood pressure between the control group and the young diabetic group. There were no differences in age, total and LDL cholesterol levels or body mass index between the groups of postmenopausal women (P<0.05). However, the HDL cholesterol level was found to be significantly lower in postmenopausal women with diabetes than in normal postmenopausal women (respectively, a mean+/-SD; 38.95+/-11.96 mg/dl vs. 52.20+/-9.55 mg/dl, P<0.05). The FMD of young diabetic patients is slightly lower than that of age-matched young healthy controls (healthy control: 8.9+/-2.7%, young diabetic patients: 6.3+/-2.1%, P<0.05). There was no difference in endothelial independent vasodilation between the control group and the young diabetic group. The IRT of FMD was significantly shorter in the healthy control group than in the young diabetic group (healthy control: 20.4+/-2.8 s, diabetic group: 29.5+/-5.4 s, P<0.0001). In contrast, the IRT of EID was no different between the two groups. The IRT of FMD showed a significant negative correlation with FMD (r=-0.61, P<0.01) and a significant negative correlation with high-density lipoprotein (HDL) cholesterol (r=-0.68, P<0.0001). The basal endothelium dependent vascular reactivity was significantly decreased in postmenopausal women with diabetes compared with normal postmenopausal women (8.0+/-3.9 vs. 13.7+/-6.2%, P<0.05). Estrogen supplementation increased endothelium dependent vasodilation not only in postmenopausal women with diabetes (from 8.0+/-3.9 to 15.1+/-4.0%, P<0.05) but also in normal postmenopausal women (from 13.7+/-6.2 to 20.1+/-4.7%, P<0.05). In contrast, the responses to sublingual nitroglycerin were comparable between postmenopausal women with diabetes (from 21.1+/-6.0 to 22.1+/-4.1%, P>0.05) and normal postmenopausal women (from 25.8+/-7.8 to 25.2+/-4.5%, P>0.05), both before and after estrogen supplementation.

CONCLUSION

These findings indicate that in addition to the percentage change in FMD, lag time from base line to initial response time (IRT) of FMD is a good indicator for evaluation of endothelial dysfunction. Also, this new parameter may be a more sensitive parameter for differentiation between the diseased state and the normal state of the endothelium than percentage changes in FMD. In terms of postmenopausal women, endothelial dysfunction was prominent in women with diabetes and was significantly improved by estrogen but not reversed. These results suggest that other factors in addition to estrogen deficiency play a role in endothelial dysfunction in postmenopausal women with diabetes mellitus.

Gender differences and antioxidant treatment affect aortic reactivity in short-term diabetic rats

Diabetes is associated with gender-specific macrovascular complications arising from increased oxidant stress in the vascular wall. In this study, male and female rats were treated with two structurally unrelated drugs sharing antioxidant properties, lercanidipine and Leucoselect (both 3 mg/kg/day), for 1 week starting 1 day after streptozotocin-diabetes induction. Concentration-response curves to L-nitroarginine methylester (L-NAME), superoxide dismutase and acetylcholine in aortic rings showed significantly greater nitric oxide-mediated relaxation in female compared with male non-diabetic rats. Diabetes increased contractility to noradrenaline and L-NAME in both genders, whereas relaxation to acetylcholine and iloprost were significantly attenuated in females only. Treatment with lercanidipine and Leucoselect restored, at least in part, responses to noradrenaline, acetylcholine and iloprost without affecting those to L-NAME and sodium nitroprusside. Unexpectedly, both drugs impaired superoxide dismutase response in female tissues. In conclusion, female rat aorta is markedly exposed to short-term diabetic vascular injury, which may be prevented by antioxidant treatment.

Oxidative stress and renal dysfunction in salt-sensitive hypertension

Hypertension is a risk factor for the development of end-stage renal disease. The mechanisms underlying hypertensive nephropathy are poorly understood. There is evidence, however, that in hypertension there is an accumulation of partially reduced oxygen and its derivatives, known collectively as reactive oxygen species, which may contribute to progressive renal dysfunction. In the present study, we assess the contribution of oxidative stress in the development of salt-dependent hypertensive nephrosclerosis. Going beyond previous end point studies, which inferred renal function either indirectly or only qualitatively, we have determined oxidative stress concurrently with direct and quantitative measurements of renal function (via inulin and p-aminohippuric acid clearances). Moreover, in this time-dependent study, the measurements have been taken under low- as well as high-salt diets. As was expected from previous studies, in the Dahl salt-sensitive rat, a high-salt diet (8% NaCl) resulted in the development of hypertension, in a decreased glomerular filtration rate, and in a decreased renal plasma flow as compared with the normotensive control, the Dahl salt-resistant rat. In addition, however, we found clear evidence for the accumulation of reactive oxygen species in renal tissue homogenates of Dahl salt-sensitive rats on the high-salt diet. Our time-dependent protocol also indicated that renal oxidative stress follows, in time, the development of hypertension. We also found that after 2 weeks of increased salt loading, Dahl salt-sensitive rats excreted less cyclic guanosine monophosphate and NO(x) than Dahl salt-resistant rats on the same diet. It is known that urinary cyclic guanosine monophosphate and NO(x) represent the activity and stable derivatives of renal NO., respectively, and that they closely correlate with renal vascular resistance. Therefore, our results suggest that, in the Dahl salt-sensitive rat, increased oxidative stress is associated with salt-dependent hypertensive nephrosclerosis and that decreased NO. bioavailability may represent a common factor responsible for the vascular and glomerular dysfunction.

Prostaglandin H synthase and vascular function

Prostaglandin H synthase (PGHS) is a rate-limiting enzyme in the production of prostaglandins and thromboxane, which are important regulators of vascular function. Under normal physiological conditions, PGHS-dependent vasodilators (such as prostacyclin) modulate vascular tone. However, PGHS-dependent vasoconstriction (mediated by thromboxane and/or its immediate precursor, PGH(2)) predominates in some vascular pathologies (eg, systemic hypertension, diabetes, cerebral ischemia, and aging). This review will discuss the role of PGHS-dependent modulation of vascular function in a number of vascular beds (systemic, pulmonary, cerebral, and uterine) with an emphasis on vascular pathophysiology. Moreover, the specific contributions of the different isoforms (PGHS-1 and PGHS-2) are discussed. Understanding the role of PGHS in vascular function is of particular importance because they are the targets of the commonly used nonsteroidal antiinflammatory drugs (NSAIDs), which include aspirin and ibuprofen. Importantly, with the advent of specific PGHS-2 inhibitors for treatment of conditions such as chronic inflammatory disease, it is an opportune time to review the data regarding PGHS-dependent modulation of vascular function.

Defective nitric oxide production and functional renal reserve in patients with type 2 diabetes who have microalbuminuria of African and Asian compared with white origin

Diabetic nephropathy is a leading cause of end-stage renal failure. Its incidence is higher and is increasing in persons of Indo-Asian and African-Caribbean (African-Asian) compared with those of white origin. Nitric oxide deficiency is associated with progressive renal disease. It was hypothesized that differences in the capacity to increase glomerular filtration (functional renal reserve) would exist between these racial groups in relation to nitric oxide availability. Patients with type 2 diabetes of African-Asian (n = 9) and white (n = 9) origin with microalbuminuria were studied under euglycemic conditions. Glomerular filtration, renal plasma flow, and clearance of the stable metabolites of nitric oxide, nitrite, and nitrate were measured before and after a renal vasodilatory stimulus of a mixed amino acid intravenous infusion. There were no significant differences in age, duration of diabetes, and baseline glomerular filtration (57.1 [14.1] versus 55.8 [10.1] yr; P = 0.82, 14.5 [10.2] versus 9.1 [7.0] yr; P = 0.19 and 125.9 [30.9] versus 127.2 [44.6] ml/min per 1.73 m(2); P = 0.94) between the African-Asian and white groups. Functional renal reserve, change in renal plasma flow, and percentage change in nitrate and nitrite clearance was significantly higher in the white compared with the African-Asian group (21.9 [45.7] versus -2.5 [28.2] ml/min per 1.73 m(2); P = 0.043, 155.8 [205.9] versus -90.1 [146.0]; P = 0.03 ml/min per 1.73 m(2) and 26.7 [85.1] versus -44.7 [16.9] %; P = 0.013, respectively). The differences in functional reserve were not confounded after adjustment for diabetes duration (P = 0.034). The data suggest that these patients with type 2 diabetes of African and Asian origin lose functional renal reserve earlier in the evolution of nephropathy than whites. The differences appear to be due to defective nitric oxide production or bioavailability and might explain some of the propensity to develop end-stage renal disease.

Nitric oxide and free stable nitroxyl radicals in the mechanism of biological action of the spin-labeled compounds

A comparison of more important physical, chemical and biological properties of the nitric oxide (NO) and free stable nitroxyl radicals (nitroxides) on the base of their structural similarity is made in the article. The active moiety in the nitroxide molecule represents a sterically hindered nitric oxide. The mechanisms of biological action of the nitroxides and especially of their derivatives with antitumor agents from the groups of nitrogen mustards, nitrosoureas, aziridines and triazenes (spin-labeled compounds) is explained through the biological activities of sterically hindered NO. Similarly to NO, nitroxides also can react with superoxide anion radical (O(2)(-)), they possess superoxide dismutase (SOD) mimetic action. While the interaction of NO with O(2)(-)yields very toxic peroxynitrite (ONOO(-)), its formation is strongly limited in the presence of a nitroxide. It is known that the nitrosourea antitumor drugs, like lomustine (CCNU) and carmustine (BCNU), showed high general toxicity, one of the reasons for that probability is the formation of NO, and subsequently of ONOO(-), during their metabolism. The biological investigations of the nitroxides showed their considerably lower general toxicity that could be explained with the SOD-mimetic action of the nitroxide present in their molecule.

Dietary polyunsaturated fatty acid and antioxidant modulation of vascular dysfunction in the spontaneously hypertensive rat

Two currently available edible oils-olive and canola-and two oil blends of plant origin having different n-3/n-6 polyunsaturated fatty acid (PUFA) ratios were evaluated for their ability to modify vascular dysfunction in the spontaneously hypertensive rat (SHR). Synthetic diets supplemented with test oils (5% w/w) were fed for 12 weeks, and segments of thoracic aorta used to assess vascular function. Vessels from the SHR displayed a spontaneous constrictor response after the inhibition of endothelial cell nitric oxide (NO) with N(omega)-nitro-L-arginine (NOLA). Dietary alpha -linoleate enrichment led to a reduction (P<0.05) in this abnormality with a dietary n-3/n-6 PUFA ratio of 1.0 (blend-1) yielding the best outcome. Relaxation to acetylcholine (ACh) was unaffected by dietary lipid supplementation. NOLA treated rings also displayed contractions to ACh that were abolished by indomethacin, thromboxane antagonists SQ29548, picotamide and flavonoids kaempferol and quercetin. In contrast, alpha-tocopherol, rutin and the lipoxygenase inhibitor esculetin resulted in only partial (30-55%) inhibition, and were ineffective against the NOLA-induced contraction suggesting the operation of different biochemical mechanisms in mediating the spontaneous and Ach-induced contractions. Results implicate plant-based oils and antioxidants as potential modulators of vascular function.

Effect of alpha-lipoic acid on the progression of endothelial cell damage and albuminuria in patients with diabetes mellitus: an exploratory study

Oxidative stress plays a central role in the pathogenesis and progression of late microangiopathic complications (diabetic nephropathy) in diabetes mellitus. Previous studies suggested that treatment of diabetic patients with the antioxidant alpha-lipoic acid reduce oxidative stress and urinary albumin excretion. In this prospective, open and non-randomized study, the effect of alpha-lipoic acid on the progression of endothelial cell damage and the course of diabetic nephropathy, as assessed by measurement of plasma thrombomodulin and urinary albumin concentration (UAC), was evaluated in 84 patients with diabetes mellitus over 18 months. Forty-nine patients (34 with Type 1 diabetes, 15 with Type 2 diabetes) had no antioxidant treatment and served as a control group. Thirty-five patients (20 with Type 1 diabetes, 15 with Type 2 diabetes) were treated with 600 mg alpha-lipoic acid per day. Only patients with an urinary albumin concentration <200 mg/l were included into the study. After 18 months of follow up, the plasma thrombomodulin level increased from 35.9+/-9.5 to 39.7+/-9.9 ng/ml (P<0.05) in the control group. In the alpha-lipoic acid treated group the plasma thrombomodulin level decreased from 37.5+/-16.2 to 30.9+/-14.5 ng/ml (P<0.01). The UAC increased in patients without alpha-lipoic acid treatment from 21.2+/-29.5 to 36.9+/-60.6 ng/l (P<0.05), but was unchanged with alpha-lipoic acid. It is postulated that the significant decrease in plasma thrombomodulin and failure of UAC to increase observed in the alpha-lipoic acid treated group is due to antioxidative effects of alpha-lipoic acid, and if so that oxidative stress plays a central role in the pathogenesis of diabetic nephropathy. Furthermore, progression of the disease might be inhibited by antioxidant drugs. A placebo-controlled study is needed.

The role of oxidative stress in the onset and progression of diabetes and its complications: a summary of a Congress Series sponsored by UNESCO-MCBN, the American Diabetes Association and the German Diabetes Society

This review summarises the results and discussions of an UNESCO-MCBN supported symposium on oxidative stress and its role in the onset and progression of diabetes. There is convincing experimental and clinical evidence that the generation of reactive oxygen species (ROI) is increased in both types of diabetes and that the onset of diabetes is closely associated with oxidative stress. Nevertheless there is controversy about which markers of oxidative stress are most reliable and suitable for clinical practice. There are various mechanisms that contribute to the formation of ROI. It is generally accepted that vascular cells and especially the endothelium become one major source of ROI. An important role of oxidative stress for the development of vascular and neurological complications is suggested by experimental and clinical studies. The precise mechanisms by which oxidative stress may accelerate the development of complications in diabetes are only partly known. There is however evidence for a role of protein kinase C, advanced glycation end products (AGE) and activation of transcription factors such as NF kappa B, but the exact signalling pathways and the interactions with ROI remain a matter of discussion. Additionally, results of very recent studies suggest a role for ROI in the development of insulin resistance. ROI interfere with insulin signalling at various levels and are able to inhibit the translocation of GLUT4 in the plasma membrane. Evidence for a protective effect of antioxidants has been presented in experimental studies, but conclusive evidence from patient studies is missing. Large-scale clinical trials such as the DCCT Study or the UKPDS Study are needed to evaluate the long-term effects of antioxidants in diabetic patients and their potential to reduce the medical and socio-economic burden of diabetes and its complications.

Generation of superoxide anion impairs histamine-induced increases in macromolecular efflux

The first goal of this study was to determine the effect of generation of superoxide anion using pyrogallol on histamine-induced increases in macromolecular efflux. We used intravital microscopy and fluorescein isothiocyanate-dextran (FITC-dextran; MW 70K) to examine macromolecular extravazation from postcapillary venules in the hamster cheek pouch in response to histamine before and following topical application of vehicle or pyrogallol. Extravazation of macromolecules was quantitated by counting venular leaky sites. Histamine elicited reproducible increases in venular leaky sites before and during infusion of vehicle. In contrast, topical application of pyrogallol (0.5 mM) abolished histamine-induced increases in formation of venular leaky sites. Our second goal was to examine whether pyrogallol-induced inhibition of venular leaky site formation could be reversed by superoxide dismutase. Application of superoxide dismutase (300 U/ml) to the cheek pouch in the presence of pyrogallol restored histamine-induced increases in venular leaky sites. Thus, the generation of superoxide anion alters histamine-induced increases in macromolecular efflux. These results support the concept that disease states that produce oxidative stress may impair agonist-induced increases in microvascular permeability via inactivation of nitric oxide.

Ascorbate restores endothelium-dependent vasodilation impaired by acute hyperglycemia in humans

BACKGROUND

Endothelium-dependent vasodilation is impaired in patients with insulin-dependent and non-insulin-dependent diabetes mellitus and restored by vitamin C administration, implicating a causative role for oxidant stress. Hyperglycemia per se attenuates endothelium-dependent vasodilation in healthy subjects. Accordingly, this study investigated whether impaired endothelium-dependent vasodilation caused by hyperglycemia in nondiabetic humans is restored by administration of the antioxidant vitamin C.

METHODS AND RESULTS

Endothelium-dependent vasodilation was measured by incremental brachial artery administration of methacholine chloride (0.3 to 10 microg/min) during euglycemia, after 6 hours of hyperglycemia (300 mg/dL) created by dextrose (50%) intra-arterial infusion, and with coadministration of vitamin C (24 mg/min) during hyperglycemia. Endothelium-dependent vasodilation was significantly diminished by hyperglycemia (P:=0.02 by ANOVA) and restored by vitamin C (P:=0.04). In contrast, endothelium-dependent vasodilation was not affected by equimolar infusions of mannitol, with and without vitamin C coinfusion (P:=NS). Endothelium-independent vasodilation was measured by incremental infusion of verapamil chloride (10 to 300 microg/min) without and with coadministration of N:(G)-monomethyl-L-arginine (L-NMMA). In the absence of L-NMMA, endothelium-independent vasodilation was not significantly altered during hyperglycemia (P:=NS) but was augmented by vitamin C (P:=0.04). The coadministration of L-NMMA eliminated the vitamin C-related augmentation in verapamil-mediated vasodilation.

CONCLUSIONS

Vitamin C administration restores endothelium-dependent vasodilation impaired by acute hyperglycemia in healthy humans in vivo. These findings suggest that hyperglycemia may contribute in part to impaired vascular function through production of superoxide anion.

Reactive oxygen species, apoptosis and alte1red NGF-induced signaling in PC12 pheochromocytoma cells cultured in elevated glucose: AnIn Vitro cellular model for diabetic neuropathy

Diabetic neuropathies, affecting the autonomic, sensory, and motor peripheral nervous system, are among the most frequent complications of diabetes. The symptoms of diabetic polyneuropathies are multi-faceted; the etiology and the underlying mechanisms are as yet unclear. Clinical studies established a significant correlation between the control of the patients' blood glucose level and the severity of the damage to the peripheral nervous system. Recent in vitro studies suggest that elevated glucose levels induced dysfunction and apoptosis in cultured cells of neuronal origin, possibly through the formation of reactive oxygen species (ROS). Based on these results, we hypothesized that elevated glucose levels impair neuronal survival and function via ROS dependent intracellular signaling pathways. In order to test this hypothesis, we cultured neural crest-derived PC12 pheochromocytoma cells under euglycemic (5 mM) and hyperglycemic (25 mM) conditions. Continuous exposure of undifferentiated PC12 cells for up to 72 h to elevated glucose induced the enhanced generation of ROS, as assessed from the increase in the cell-associated fluorescence of the ROS-sensitive fluorogenic indicator, 2,7-dichlorodihydrofluorescein diacetate. In cells cultured in high glucose, both basal and secretagogue-stimulated catecholamine release were enhanced. Furthermore, high glucose, reduced (by ca. 30%) the rate of cell proliferation and enhanced the occurrence of apoptosis, as assessed by DNA fragmentation, TUNEL assay and the activation of an apoptosis-specific protease, caspase CCP32. Elevated glucose levels significantly attenuated nerve growth factor (NGF)-induced neurite extension, as quantitated by computer-aided image analysis. Culturing PC12 cells in high glucose resulted in alterations in basal and NGF-stimulated mitogen-activated protein kinase (MAPK) signaling pathways, specifically in a switch from the neuronal survival/differentiation-associated MAPK ERK to that of apoptosis/stress-associated MAPK p38 and JNK. Based on our results we present a model in which the prolonged, excess formation of ROS represents a common mechanism for hyperglycemia-induced damage to neuronal cells. We propose that this simple in vitro system might serve as an appropriate model for evaluating some of the effects of elevated glucose on cultured cells of neuronal origin.

Role of PKC and TGF-beta receptor in glucose-induced proliferation of smooth muscle cells

The role of protein kinase C (PKC) and transforming growth factor (TGF)-beta in the proliferation of vascular smooth muscle cells (SMCs) under a high glucose condition was investigated. [3H]-thymidine incorporation under 20 mM glucose was significantly accelerated compared with that under 5.5 mM glucose, and this increase was inhibited by an anti-TGF-beta antibody or a PKC-beta specific inhibitor, LY333531. The amount of active and total TGF-beta1 in the conditioned media did not differ between 5.5 and 20 mM glucose. However, the expression of TGF-beta receptor type II under 20 mM glucose was significantly increased, but that of the TGF-beta receptor type I was not. This increased expression of the TGF-beta receptor type II was prevented by LY333531. These observations suggest that the increased expression of the TGF-beta receptor type II via PKC-beta plays an important role in the accelerated proliferation of SMCs under a high glucose condition, leading to the development of diabetic macroangiopathy.

Endothelial dysfunction and salt-sensitive hypertension in spontaneously diabetic Goto-Kakizaki rats

Endothelial dysfunction is associated with hypertension, hypercholesterolemia, and heart failure. We tested the hypothesis that spontaneously diabetic Goto-Kakizaki (GK) rats, a model for type 2 diabetes, exhibit endothelial dysfunction. Rats also received a high-sodium diet (6% NaCl [wt/wt]) and chronic angiotensin type 1 (AT(1)) receptor blockade (10 mg/kg PO valsartan for 8 weeks). Compared with age-matched nondiabetic Wistar control rats, GK rats had higher blood glucose levels (9.3+/-0.5 versus 6.9+/-0.2 mmol/L for control rats), 2.7-fold higher serum insulin levels, and impaired glucose tolerance (all P<0.05). Telemetry-measured mean blood pressure was 15 mm Hg higher in GK rats (P<0.01) compared with control rats, whereas heart rates were not different. Heart weight- and kidney weight-to-body weight ratios were higher in GK rats (P<0.05), and 24-hour albuminuria was increased 50%. Endothelium-mediated relaxation of noradrenaline-precontracted mesenteric arterial rings by acetylcholine was impaired compared with the control condition (P<0.05), whereas the sodium nitroprusside-induced relaxation was similar. Preincubation of the arterial rings with the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester and the cyclooxygenase inhibitor diclofenac inhibited relaxations to acetylcholine almost completely in GK rats but not in Wistar rats, suggesting that endothelial dysfunction can be in part attributed to reduced relaxation via arterial K(+) channels. Perivascular monocyte/macrophage infiltration and intercellular adhesion molecule-1 overexpression were observed in GK rat kidneys. A high-sodium diet increased blood pressure by 24 mm Hg and 24-hour albuminuria by 350%, induced cardiac hypertrophy, impaired endothelium-dependent relaxation further, and aggravated inflammation (all P<0.05). The serum level of 8-isoprostaglandin F(2alpha), a vasoconstrictor and antinatriuretic arachidonic acid metabolite produced by oxidative stress, was increased 400% in GK rats on a high-sodium diet. Valsartan decreased blood pressure in rats fed a low-sodium diet and prevented the inflammatory response. In rats fed a high-sodium diet, valsartan did not decrease blood pressure or improve endothelial dysfunction but protected against albuminuria, inflammation, and oxidative stress. As measured by quantitative autoradiography, AT(1) receptor expression in the medulla was decreased in GK compared with Wistar rats, whereas cortical AT(1) receptor expression, medullary and cortical angiotensin type 2 (AT(2)) receptor expressions, and adrenal ACE and neutral endopeptidase expressions were unchanged. A high-sodium diet did not influence renal AT(1), AT(2), ACE, or neutral endopeptidase expressions. In valsartan-treated GK rats, the cortical and medullary AT(1) receptor expressions were decreased in the presence and absence of a high-sodium diet. A high-sodium diet increased plasma brain natriuretic peptide concentrations in presence and absence of valsartan treatment. We conclude that hypertension in GK rats is salt sensitive and associated with endothelial dysfunction and perivascular inflammation. AT(1) receptor blockade ameliorates inflammation during a low-sodium diet and partially protects against salt-induced vascular damage by blood pressure-independent mechanisms.

Arteriolar nitric oxide concentration is decreased during hyperglycemia-induced betaII PKC activation

betaII protein kinase C (betaPKC) is activated during acute and chronic hyperglycemia and may alter endothelial cell function. We determined whether blockade of betaPKC protected in vivo endothelial formation of NO, as measured with NO-sensitive microelectrodes in the rat intestinal vasculature. NaCl hyperosmolarity, a specific endothelial stimulus to increase NO formation, caused approximately 20% arteriolar vasodilation and approximately 30% increase in NO concentration ([NO]). After topical 300 mg/dl hyperglycemia for 45 min, both responses were all but abolished. In comparison, pretreatment with LY-333531, a specific betaPKC inhibitor, maintained vasodilation and [NO] responses to NaCl hyperosmolarity after hyperglycemia. The betaPKC inhibitor alone had no significant effects on resting diameter or [NO] or their responses to NaCl hyperosmolarity. In separate rats, after topical hyperglycemia had suppressed dilation to ACh, LY-333531 restored approximately 70% of the dilatory response. These data demonstrated that activation of betaPKC during acute hyperglycemia depressed in vivo endothelial formation of NO at rest and during stimulation. This abnormality can be minimized by inhibition of betaPKC before hyperglycemia and can be substantially reversed by PKC inhibition after hyperglycemia-induced abnormalities have occurred.

Superoxide anions and endothelial cell proliferation in normoglycemia and hyperglycemia

-Oxygen free radicals are believed to play a key role in cellular proliferation, and increased concentrations of these molecules have been implicated in the pathogenesis of endothelial dysfunction in diabetes mellitus. Our aim was to study the role of superoxide anions in endothelial cell proliferation under conditions of normoglycemia and hyperglycemia. Human aortic endothelial cells (HAECs) and human umbilical vein endothelial cells (HUVECs) exposed to adenoviral vectors encoding CuZnSOD (AdCuZnSOD), ss-galactosidase (Adssgal), or diluent (control) were cultured in normal glucose (NG, 5.5 mmol/L) or high glucose (HG, 28 mmol/L) medium. Cell proliferation was compared by use of [(3)H]thymidine incorporation and cell count in transduced and control cells in the setting of NG and HG. Transgene expression was detected in transduced cells by X-gal staining and by Western analysis and SOD activity assay in AdCuZnSOD-transduced cells. Superoxide production was significantly (P:<0.05) decreased in AdCuZnSOD-transduced cells cultured in both NG and HG medium. In NG, AdCuZnSOD-transduced endothelial cells had decreased proliferation compared with control cells. After 48 hours in HG, superoxide levels were increased and DNA synthesis was decreased (P:<0.05) in control and Adssgal-transduced but were not affected in AdCuZnSOD-transduced cells. In addition, after 7 days in HG, cell counts were reduced (P:<0.05) in control (73+/-2.5%) and Adssgal-transduced (75+/-3.4%) but not in AdCuZnSOD-transduced cells (89+/-3.4%). These results suggest that either a deficiency or an excess of superoxide anions inhibits endothelial cell proliferation, and the inhibitory effect of increased superoxide due to hyperglycemia can be reversed by CuZnSOD overexpression.

Effects of blood pressure and glucose on endothelial function

Hypertension and diabetes mellitus are associated with accelerated atherosclerosis and an increased prevalence of cardiovascular disease. Loss of the modulatory role of the endothelium can be considered the link between these conditions and cardiovascular disease. Substantial evidence suggests that vasodilation mediated by endothelium-derived nitric oxide (NO) is impaired in animal models and in patients with hypertension and diabetes mellitus. NO is a principal factor involved in the anti-atherosclerotic properties of the endothelium. Therefore, the pathogenesis of hypertensive and diabetic vascular disease may involve a reduced bioavailability of endothelium-derived NO. Inactivation of NO by reactive oxygen species is an important common mechanism by which endothelial dysfunction may occur. This review summarizes experimental and clinical evidence for impaired NO-mediated vasodilation in the presence of high blood pressure and hyperglycemia. A better understanding of the mechanisms leading to endothelial dysfunction may unmask new preventive strategies to reduce cardiovascular morbidity and mortality in these conditions.

The effect of bradykinin on the oxidative state of rats with acute hyperglycaemia

Many clinical and experimental studies have established the beneficial effect of kinins in hypertension, heart failure and ischaemia-reperfusion syndrome, but little attention has been given to the role of kinins in hyperglycaemic conditions. The purpose of the present study was to determine the influence of bradykinin on the levels of glucose, insulin, malondialdehyde and hydrogen peroxide, as well as antioxidative enzyme activity in rats with streptozotocin (STZ)-induced acute hyperglycaemia. In STZ-induced hyperglycaemic rats the levels of glucose, hydrogen peroxide and malondialdehyde were increased by 256% (from 6.0+/-0.3 to 21.4+/-1.3 mmol/l, P<0.001), 33% (from 1.9+/-0.1 to 5.6+/-0.3 mmol H(2)O(2)/ml, P<0.001) and 19% (from 3.7+/-0.3 to 4.9+/-0.2 nmol/l, P<0.001) respectively. The activity of superoxide dismutase, catalase and glutathione peroxidase and the level of insulin were decreased by 46% (from 1367+/-73 to 737+/-59 U/g Hb, P<0.001), 36% (from 2.3+/-0.3 to 1.4+/-0.1 U Bergmayera/g Hb, P<0.001), 31% (from 236+/-19 to 163+/-24 U/g Hb, P<0.001) and 91% (from 47.5+/-1.7 to 2.4+/-0.5 mU/l, P<0.001) respectively in rats treated with streptozotocin. The administration of bradykinin caused the decrease in glucose, hydrogen peroxide and malondi-aldehyde levels by 38% (from 21.4+/-1.3 to 13.3+/-1.0 mmol/l, P<0.001), 37% (from 5.6+/-0.3 to 4.3+/-0.2 mmol H2O2/ml, P<0.001), 39% (from 4.9+/-0.2 to 3.0+/-0.2 nmol/l, P<0.001) respectively and the increase in insulin level and superoxide dismutase, catalase and glutathione peroxidase activity by 62% (from 2.4+/-0.5 to 4.0+/-0.4 mU/l, P<0.001), 23% (from 736.8+/-58.5 to 906.7+/-47.8 U/g Hb, P<0.001), 23% (from 1.4+/-0.1 to 1.9+/-0.1 U Bergmayera/g Hb, P<0.01) and 19% (from 163.1+/-23.6 to 202.3+/-11.7 U/g Hb, P<0.001) respectively in rats with hyperglycaemia. Thus, bradykinin is able to reduce oxidative stress in hyperglycaemic conditions.

Potassium channel function in vascular disease

Potassium ion (K(+)) channel activity is a major regulator of vascular muscle cell membrane potential (E(m)) and is therefore an important determinant of vascular tone. There is growing evidence that the function of several types of vascular K(+) channels is altered during major cardiovascular diseases, such as chronic hypertension, diabetes, and atherosclerosis. Vasoconstriction and the compromised ability of an artery to dilate are likely consequences of defective K(+) channel function in blood vessels during these disease states. In some instances, increased K(+) channel function may help to compensate for increased vascular tone. Endothelial cell dysfunction is commonly associated with cardiovascular disease, and altered activity of nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factor could also contribute to changes in resting K(+) channel activity, E(m), and K(+) channel-mediated vasodilatation. Our current knowledge of the effects of disease on vascular K(+) channel function almost exclusively relies on interpretation of data obtained by using pharmacological modulators of K(+) channels. As further progress is made in the development of more selective drugs and through molecular approaches such as gene targeting technology in mice, specific K(+) channel abnormalities and their causes in particular diseases should be more readily identified, providing novel directions for vascular therapy.

Impairment of endothelial nitric oxide production by acute glucose overload

We examined the effects of acute glucose overload (pretreatment for 3 h with 23 mM D-glucose) on the cellular productivity of nitric oxide (NO) in bovine aortic endothelial cells (BAEC). We had previously reported (Kimura C, Oike M, and Ito Y. Circ Res, 82: 677-685, 1998) that glucose overload impairs Ca(2+) mobilization due to an accumulation of superoxide anions (O(2)(-)) in BAEC. In control cells, ATP induced an increase in NO production, assessed by diaminofluorescein 2 (DAF-2), an NO-sensitive fluorescent dye, mainly due to Ca(2+) entry. In contrast, ATP-induced increase in DAF-2 fluorescence was impaired by glucose overload, which was restored by superoxide dismutase, but not by catalase or deferoxamine. Furthermore, pyrogallol, an O(2)(-) donor, also attenuated ATP-induced increase in DAF-2 fluorescence. In contrast, a nonspecific intracellular Ca(2+) concentration increase induced by the Ca(2+) ionophore A-23187, which depletes the intracellular store sites, elevated DAF-2 fluorescence in both control and high D-glucose-treated cells in Ca(2+)-free solution. These results indicate that glucose overload impairs NO production by the O(2)(-)-mediated attenuation of Ca(2+) entry.

Beneficial and detrimental effects of intensive glycaemic control, with emphasis on type 2 diabetes mellitus

Diabetes mellitus is a major health problem in the world. Several clinical trials have shown that some of the major complications of diabetes mellitus can be partially prevented or delayed by intensive glycaemic control. However, there are benefits and risks in aiming for near normal blood glucose levels. Intensive glycaemic control delays the onset and progression of retinopathy, nephropathy and neuropathy. Epidemiological and observational studies have shown that cardiovascular events may be correlated with the severity and duration of diabetes mellitus, but major randomised trials have only shown weak and nonsignificant benefits of intensive glycaemic management in decreasing event rates. A modest improvement in lipid profile results from blood glucose control although, in the majority of cases, not enough to reach current targets. Detrimental effects of intensive glycaemic control include bodyweight gain and hypoglycaemia. Controversial issues in the management of patients with diabetes mellitus include the unproven increase in cardiovascular morbidity from sulphonylureas and hyperinsulinaemia, and the still unknown long term effects of newer oral antihyperglycaemic agents alone or in combination with traditional therapies (such as sulphonylureas and metformin). It is important to individualise management in setting glycaemic goals. Control of cardiovascular risk factors through blood pressure and lipid control and treatment with aspirin (acetylsalicylic acid) and ACE inhibitors have consistently shown benefits in the prevention of both macro- and microvascular complications in patients with diabetes mellitus; these measures deserve priority.

Reactive oxygen species and acute renal failure

Acute renal failure is commonly due to acute tubular necrosis (ATN), the latter representing an acute, usually reversible loss of renal function incurred from ischemic or nephrotoxic insults occurring singly or in combination. Such insults instigate a number of processes-hemodynamic alterations, aberrant vascular responses, sublethal and lethal cell damage, inflammatory responses, and nephron obstruction-that initiate and maintain ATN. Eventually, reparative and regenerative processes facilitate the resolution of renal injury and the recovery of renal function. Focusing mainly on ischemic ATN, this article reviews evidence indicating that the inordinate or aberrant generation of reactive oxygen species (ROS) may contribute to the initiation and maintenance of ATN. This review also discusses the possibility that ROS may instigate adaptive as well as maladaptive responses in the kidney with ATN, and raises the possibility that ROS may participate in the recovery phase of ATN.

Role of vasoactive factors in the pathogenesis of early changes in diabetic retinopathy

Several interactive and mutually perpetuating abnormal biochemical pathways, such as protein kinase C (PKC) activation, augmented polyol pathway, and non-enzymatic glycation, may be activated as a result of sustained hyperglycemia in diabetes. These abnormal pathways may in turn influence several vasoactive factors, which are probably instrumental in the production of functional and morphological changes in the retina in diabetes. The vasoactive factors such as endothelins, nitric oxide, vascular endothelial growth factors, etc., are of importance in mediating functional and structural alterations in early diabetic retinopathy. Intricate and interactive regulatory mechanism(s) among these factors may control ultimate availability of these molecules to produce biologically significant effects. A better understanding of these factors and their interactions would aid the development of adjuvant therapies for the treatment of diabetic retinopathy.

Effects of ouabain on the pressor response to phenylephrine and on the sodium pump activity in diabetic rats

The diabetes mellitus insulin-dependent is usually associated with cardiovascular disorders and with changes in the activity of the Na(+),K(+)-ATPase. The effects of ouabain, a Na(+),K(+)-ATPase inhibitor, on the pressor response of 7-day streptozotocin-induced diabetes were investigated in anesthetized rats and on the vascular reactivity of the perfused rat tail vascular bed. Diabetes was characterized by hyperglycemia (86+/-7.8 vs. 471+/-18.5 mg/dl) without changes in arterial blood pressure. Blood pressure increased after the treatment with 18 microg/kg ouabain in controls but not in diabetic rats; acute hyperglycemia, in non-treated rats, did not change these effects. Control tail vascular beds showed increased maximal response to phenylephrine after treatment with 10 nM ouabain for 1 h; this response was abolished in streptozotocin-treated rats. These rats showed an increased sensitivity to phenylephrine without changing the maximal vasoconstrictor response when compared to control rats. The relaxation induced by acetylcholine was reduced in diabetic rats. The functional activity of the Na(+),K(+)-ATPase was inhibited in vascular beds from diabetic rats, when compared to control rats, and the inhibition of the Na(+),K(+)-ATPase with 10 nM ouabain was not effective in these rats. Results suggested that in 7-day diabetic rats, the increase of arterial blood pressure or the sensitization of the vascular bed produced by ouabain is lost as a consequence of the reduction of the functional activity of the Na(+), K(+)-ATPase probably as a result of insulin lack and a deficient endothelial nitric oxide activity.

Nitric oxide may be required to prevent hypertension at the onset of diabetes

Nitric oxide (NO) plays an important role in the regulation of vascular tone, and evidence suggests that endothelial-dependent relaxation, possibly mediated via NO, is impaired in diabetes. However, the role of the endothelium in arterial pressure control early in diabetes, before dysfunction develops, is not known. This was evaluated in the present study by comparing the responses to induction of diabetes in vehicle-treated rats (D, n = 7) vs. rats chronically treated with N(G)-nitro-L-arginine methyl ester (L-NAME; D+L, n = 8). A nondiabetic group also was treated with L-NAME (L, n = 7) to control for L-NAME effects over time, independent of diabetes. After baseline measurements, rats were given either vehicle or L-NAME (10 microg. kg(-1). min(-1) iv) infusion throughout the experiment. Six days later, streptozotocin (60 mg/kg iv) was administered, followed by a 3-wk diabetic study period. Induction of diabetes in the D+L rats caused a marked and progressive increase in mean arterial pressure throughout the diabetic period, averaging approximately 70 mmHg greater than in the D rats and approximately 20 mmHg greater than in the L rats. Glomerular filtration rate and renal plasma flow tended to increase during diabetes, but this trend was reversed in the D+L rats. In addition, plasma renin activity increased in the D and D+L rats during week 1 of diabetes but then returned to control in the D rats, while continuing to increase in the D+L rats. These results suggest that, in the early stages of diabetes, NO synthesis is important to prevent hypertension from developing, possibly through actions to maintain glomerular filtration and suppress renin secretion.

Blunted suppression of plasma renin activity in diabetes

We have documented, contrary to expectation, that the renin-angiotensin-aldosterone system (RAAS) is stimulated normally by restriction of sodium intake inpatients with Type 2 diabetes mellitus (DM) and hypertension. Conversely, plasma renin activity (PRA)is suppressed less than in normal subjects by a high-salt diet in these patients. Increasing plasma angiotensin II (Ang II) concentration through intravenous Ang II infusion also suppresses renin release, via the short feedback loop. In this study, we sought to ascertain whether the limited renin suppression in Type 2 diabetes mellitus via high-salt intake is a unique defect or part of a more generalised abnormality of PRA suppression. We studied 38 patients with Type 2 DM and hypertension, 158 hypertensive control patients, and 61 normotensive controls. All patients were studied while in metabolic balance on a 10 mEq sodium (Na) diet. The response to the Ang II infusion at 3 ng/kg/min for 45 minutes was measured. We found that PRA fell significantly in normal subjects, from 4.0 +/- 0.33 to 2.5 +/- 0.23 ngAngI/ml/hr (p=0.0056). In patients with essential hypertension, the Ang II infusion also led to a fall in PRA from 3.51 +/- 0.23 to 2.76 +/- 0.17 ng Angl/ml/hr(p=0.014). In patients with DM, despite a similar basal PRA (3.7 +/- 0.40 ng AngI/ml/hr), the infusion of Ang II did nor influence PRA significantly (3.43 +/- 0.42ng AngI/ml/hr; p > 0.77), though these patients had the most robust mean arterial pressure response. Our data are in complete accord with the concept of high intrarenal Ang II in DM and suggest lower systemic Ang II despite comparable PRA.

Haptoglobin reduces renal oxidative DNA and tissue damage during phenylhydrazine-induced hemolysis

BACKGROUND

Haptoglobin knockout (Hp-/-) mice are more sensitive to phenylhydrazine-induced hemolysis than Hp+/+ mice.

METHODS

Hemolysis was induced in Hp-/- and Hp+/+ mice using phenylhydrazine. Relative renal tissue damage and function were then assessed.

RESULTS

Hp-/- mice had higher basal levels of renal lipid peroxidation, as evidenced by levels of malonaldehyde and 4-hydroxy-2(E)-nonenal (MDA/HNE). After the administration of phenylhydrazine, levels of 8-hydroxyguanine (but not other products of oxidative DNA damage) were significantly elevated in the renal DNA. There was also increased induction of heme oxygenase-1. The more severe renal damage in Hp-/- mice was also evident in the delayed erythropoietin gene expression and poorer renal clearance of 3H-inulin. This reduction in glomerular filtration function in Hp+/+ and Hp-/- mice could be restored to baseline by vasodilators (prazosin or diazoxide), implicating renal vasoconstriction as a major mechanism of acute renal failure during induced hemolysis. Precipitation of hemoglobin in the kidney was not increased in Hp-/- mice.

CONCLUSIONS

Haptoglobin appears to play an important physiological role as an antioxidant, particularly during hemolysis.

Analysis of glutathionyl hemoglobin levels in diabetic patients by electrospray ionization liquid chromatography-mass spectrometry: effect of vitamin E administration

By using electrospray ionization liquid chromatography-mass spectrometry, we demonstrated that glutathionyl hemoglobin (Hb)beta-chain levels are markedly increased in the erythrocytes of diabetic patients as compared with healthy subjects. The administration of vitamin E to the diabetic patients for 8 weeks significantly decreased the levels of glutathionyl Hbbeta, whereas it did not affect the levels of HbA1c, glycated Hbbeta or glycated Hbalpha. Glutathionyl Hb levels can be used as a new clinical marker of oxidative stress.

Effects of simulated hyperglycemia, insulin, and glucagon on endothelial nitric oxide synthase expression

Diabetes is associated with endothelial dysfunction and increased risk of hypertension, cardiovascular disease, and renal complications. Earlier studies have revealed that hyperglycemia impairs nitric oxide (NO) production and diabetes causes endothelial dysfunction in humans and experimental animals. This study was designed to test the effects of altered concentrations of glucose, insulin, and glucagon, the principal variables in types I and II diabetes, on NO production and endothelial NO synthase (eNOS) expression in cultured human coronary endothelial cells. Cultured endothelial cells were incubated in the presence of glucose at either normal (5.6 mM) or high (25 mM) concentrations for 7 days. The rates of basal and bradykinin-stimulated NO production (nitrate + nitrite) and eNOS protein expression (Western blot) were then determined at the basal condition and in the presence of insulin (10(-8) and 10(-7) M), glucagon (10(-8) and 10(-7) M), or both. Incubation with a high-glucose concentration for 7 days significantly downregulated, whereas insulin significantly upregulated, basal and bradykinin-stimulated NO production and eNOS expression in cultured endothelial cells. The stimulatory action of insulin was mitigated by high-glucose concentration and abolished by cotreatment of cells with glucagon. Thus hyperglycemia, insulinopenia, and hyperglucagonemia, which frequently coexist in diabetes, can work in concert to suppress NO production by human coronary artery endothelial cells.

Activation of TxA2/PGH2 receptors and protein kinase C contribute to coronary dysfunction in superoxide treated rat hearts

We have previously shown that superoxide anion (O2-) stimulates the release of vasoconstrictor prostanoids and induces a prolonged rise in coronary perfusion pressure (CPP) that persists even after removal of O2-. In this study, we tested the hypothesis that the increased CPP is mediated by activation of TxA2/ PGH2 (TP) receptors and protein kinase C (PKC)-dependent mechanisms. In Langendorff perfused rat hearts, O2- was applied for 15 min and then washed out over a period of 20 min. Application of O2- increased the release of vasoconstrictive (TxA2 and PGF2alpha) and decreased vasodilating (PGI2 and PGE2) prostanoids. Although indomethacin (10 microM), a cyclooxygenase inhibitor, attenuated the rise in CPP during O2- perfusion, the increase was not completely blocked. OKY 046Na (10 microM), a thromboxane synthase inhibitor, had no effect on O2--induced increases in CPP, whereas ONO 3708 (10 microM), a TP receptor antagonist, suppressed this effect. PKC activity was also elevated by more than 50% by O2- perfusion. CPP typically increased throughout the O2- wash-out. This post-O2- vasoconstriction was not inhibited by indomethacin, nitroglycerin or nitrendipine. In contrast, ONO 3708 (10 microM) and two PKC inhibitors, staurosporine (10 nM) and calphostin C (100 nM), completely blocked the rise in CPP, and even elicited vasodilation. PDBu enhanced the post-O2- vasoconstriction. We conclude that O2--induced coronary vasoconstriction is initially mediated by TP receptors, but activation of PKC sustains the response.

Role of reactive oxygen species in bradykinin-induced mitogen-activated protein kinase and c-fos induction in vascular cells

Bradykinin stimulates proliferation of aortic vascular smooth muscle cells (VSMCs). We investigated the action of bradykinin on the phosphorylation state of the mitogen-activated protein kinases p42(mapk) and p44(mapk) in VSMCs and tested the hypothesis that reactive oxygen species (ROS) might be involved in the signal transduction pathway linking bradykinin activation of nuclear transcription factors to the phosphorylation of p42(mapk) and p44(mapk). Bradykinin (10(-8) mol/L) rapidly increased (4- to 5-fold) the phosphorylation of p42(mapk) and p44(mapk) in VSMCs. Preincubation of VSMCs with either N-acetyl-L-cysteine and/or alpha-lipoic acid significantly decreased bradykinin-induced cytosolic and nuclear phosphorylation of p42(mapk) and p44(mapk). In addition, the induction c-fos mRNA levels by bradykinin was completely abolished by N-acetyl-L-cysteine and alpha-lipoic acid. Using the cell-permeable fluorescent dye dichlorofluorescein diacetate, we determined that bradykinin (10(-8) mol/L) rapidly increased the generation of ROS in VSMCs. The NADPH oxidase inhibitor diphenylene iodonium (DPI) blocked bradykinin-induced c-fos mRNA expression and p42(mapk) and p44(mapk) activation, implicating NADPH oxidase as the source for the generation of ROS. These findings demonstrate that the phosphorylation of cytosolic and nuclear p42(mapk) and p44(mapk) and the expression of c-fos mRNA in VSMCs in response to bradykinin are mediated via the generation of ROS and implicate ROS as important mediators in the signal transduction pathway through which bradykinin promotes VSMC proliferation in states of vascular injury.

Evidence for a NADH/NADPH oxidase in human umbilical vein endothelial cells using electron spin resonance

A growing body of evidence has suggested that a membrane-bound NADH/NADPH oxidase is the predominant source of reactive oxygen species (ROS) in vascular cells. Prior studies have used indirect assessments of superoxide including lucigenin-enhanced chemiluminescence, cytochrome c, and fluorescent dye techniques. The present study was performed to determine if NADH/NADPH oxidase function could be detected human endothelial cells using electron spin resonance. Human umbilical vein endothelial cells (HUVEC) were homogenized and fractionated into cytosolic and membrane components. Cell fractions were incubated in buffer containing either NADH or NADPH (100 microM for each) and the spin trap 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO). EPR signals were obtained in a Bruker EMX spectrometer. Cytoplasmic fractions were devoid of activity. In contrast, incubation of membrane fractions with NADH produced a signal with a total peak intensity of 1,038 +/- 64, which was significantly greater than that observed with NADPH (540 +/- 101). The signal was completely inhibited by either manganese superoxide dismutase (MnSOD, 100 U/ml) or the flavoprotein inhibitor diphenylene iodinium (DPI, 100 microM). Rotenone (100 microM) did not significantly alter the signal intensity, (833 +/- 88). These data demonstrate direct evidence for a functional NADH/NADPH oxidase in human endothelial cells and show that electron spin resonance is a useful tool for study of this enzyme system.

Elevated sympathetic activity contributes to hypertension and salt sensitivity in diabetic obese Zucker rats

Zucker rats are a useful model in which to define the mechanisms that link obesity to diabetes and associated cardiovascular disease. The present study tests the hypothesis that diabetic obese (compared with nondiabetic lean) Zucker rats are hypertensive and display a further increase in arterial pressure when fed a high salt diet. Male, nondiabetic lean and diabetic obese Zucker rats were chronically instrumented with telemetry probes and fed a basal salt diet for 3 weeks followed by exposure to a high salt diet for 11 days. On the basal diet, obese (vs lean) rats had significantly higher arterial pressures ( approximately 13 mm Hg), and the high salt diet significantly elevated mean arterial pressure (MAP) in obese (but not lean) Zucker rats ( approximately 12 mm Hg). Blockade of the sympathetic nervous system with hexamethonium caused a significantly larger decrease in MAP in obese (vs lean) Zucker rats fed the basal diet (51 vs 33 mm Hg), but the high salt diet did not increase the hexamethonium-induced reduction in arterial pressure in obese rats. Acute blockade of angiotensin receptors with losartan resulted in similar decreases in MAP in both groups on either diet. Acetylcholine-induced vasodilatory capacity of the carotid artery was significantly less in the obese (vs lean) Zucker rats. Together these data indicate that increased sympathetic nervous system activity and decreased vascular reactivity may contribute to elevated arterial pressure in type 2 diabetic, obese Zucker rats, but the sympathetic nervous system does not appear to contribute to the dietary salt-sensitive hypertension in this model.

Increased Glutathionyl Hemoglobin in Diabetes Mellitus and Hyperlipidemia Demonstrated by Liquid Chromatography/Electrospray Ionization-Mass Spectrometry

Background: Erythrocytes contain a large amount of glutathione (GSH), which protects cells from oxidative injury. The purpose of this study was to examine whether hemoglobin (Hb) is modified with glutathione by oxidation of the thiol groups in diabetes mellitus and hyperlipidemia, and to determine the oxygen affinity of glutathionyl Hb.

Methods: Hb samples obtained from patients with type 2 diabetes, patients with hyperlipidemia, and healthy subjects were analyzed by liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS). Glutathionyl Hb was synthesized in vitro by incubating Hb with GSH. The oxygen affinity of glutathionyl Hb was determined by measuring its oxygen dissociation curve.

Results: We first demonstrated that the concentration of glutathionyl Hbβ chains is markedly increased in the diabetic patients and hyperlipidemic patients compared with healthy subjects. The in vitro synthesis of glutathionyl Hb by incubation of Hb with GSH was enhanced by adding H2O2, a reactive oxygen species, into the incubation solution. The glutathionyl Hb prepared in vitro by incubating Hb with GSH showed a marked increase in oxygen affinity and a marked decrease in the Hill coefficient compared with Hb incubated without GSH.

Conclusions: Glutathionyl Hb may be useful as a clinical marker of oxidative stress. The increased concentrations of glutathionyl Hb with high oxygen affinity and low cooperativity in diabetes and hyperlipidemia may lead to reduced tissue oxygen delivery.

Acetyl salicylic acid improves somatosensory evoked potentials in streptozotocin-diabetic rats

The effects of acetyl salicyclic acid (ASA) on somatosensory evoked potentials (SEP) and neural levels of thiobarbituric acid reactive substances (TBARS), products of lipid peroxidation, were studied in streptozotocin-diabetic rats. ASA (100 mg/kg, in rat chow) was given to diabetic rats (n = 8) after the induction of diabetes for 16 weeks. ASA-treated normal control rats (n = 8), untreated diabetic rats (n = 8) and normal control rats (n = 8) were used for comparison. At the 8 weeks, SEP latency in diabetic group (15.4 +/- 0.5 ms) was significantly longer than that in normal control group (10.0 +/- 0.8 ms, P < 0.05). When compared to levels in diabetic control group, ASA shortened SEP latency significantly (12.7 +/- 0.1 ms; P < 0.05). This effect of ASA was significant in all three measurements from week 8 to 16 (P < 0.05 vs. diabetic control group). Neural TBARS level in diabetic control group (60.1 +/- 2.2 nmol/g) was significantly, higher than that in normal control group (28.5 +/- 3.6 nmol/g, P < 0.05). When compared to levels in diabetic control group, ASA depressed TBARS level significantly (41.5 +/- 12 nmol/g; P < 0.05). TBARS level in ASA-treated diabetic group (27.2 +/- 5.7 nmol/g) was comparable with that in normal control group (NS). These results suggest that ASA has beneficial effect on diabetic neuropathy and this effect may be related in part with prevention of lipid peroxidation.

The effects of chronic L-arginine treatment on vascular responsiveness of streptozotocin-diabetic rats

In this study, the protective effects of L-arginine treatment in vivo on vascular reactivity of streptozotocin (STZ)-induced 12-week-old diabetic rats were examined. Loss of weight, polydipsia, polyphagia, hyperglycemia, hypoinsulinemia, and elevated levels of plasma cholesterol and triglyceride were observed in diabetic rats. L-arginine treatment (1 mg/mL in drinking water) did not significantly affect these metabolic and biochemical abnormalities. Plasma malondialdehyde (MDA) levels in untreated diabetic rats were also significantly higher than untreated controls. However, L-arginine treatment prevented the increase in MDA level of plasma of diabetic rats. Contractile responses, but not sensitivity to noradrenaline (NA), were significantly increased in diabetic rats compared to controls. Treatment of diabetic rats with L-arginine completely prevented the increase in NA responses. Relaxation response to acetylcholine (ACh), but not to sodium nitroprusside (SNP), in diabetic aorta has been found to be significantly decreased as compared with controls. However, there were no significant differences in pD2 values of acetylcholine in either of the groups. L-arginine treatment increased the ACh responses to the control level. All effects of L-arginine on vascular reactivity were found to be specific for diabetic rats and not controls. These results suggest that functional abnormalities occurred in aorta from diabetic rat might at least in part result from L-arginine deficiency, and the lipid peroxidation-lowering effect of L-arginine may account for its protective effect on vascular reactivity of diabetic rats.

Regulation of uveal and retinal blood flow in STZ-diabetic and non-diabetic rats; involvement of nitric oxide

PURPOSE

In experimental and human diabetes mellitus evidence for an impaired function of the vascular endothelial cells has been found. The purpose of the present experiments was to measure uveal and retinal blood flow and vascular resistance at an early stage of experimental diabetes mellitus and to evaluate the effects of acetylcholine and L-arginine in control and L-NAME-pretreated animals.

METHOD

The radioactively labelled microsphere method was applied to normal Sprague-Dawley rats and rats with STZ-induced diabetes of three weeks duration.

RESULTS

In the present study, similar blood flow and vascular resistance were observed in the uvea of normal and STZ-diabetic rats. Evidence for a basal vasodilating NO-tone was found both in the uvea and in the retina of both groups. In the normal rats as well as in the diabetic animals, acetylcholine induced choroidal vasodilation. Local blood flow increased from 54 +/- 17 to 142 +/- 32 mg x min(-1) in normal rats and from 57 +/- 18 to 112 +/- 23 mg x min(-1) in diabetic rats (P < 0.05 respectively). No hemodynamic changes were observed in the anterior uvea, demonstrating a difference in reactivity between these vascular beds. In animals pretreated with the NO-synthase inhibitor L-NAME, acetylcholine did not significantly affect local blood flow in the choroid, suggesting NO as a mediator of the vasodilation.

CONCLUSION

The results indicate a normal action of NO in the ocular vascular beds at this stage of experimental diabetes mellitus in the rat.

An aldose reductase inhibitor prevents the glucose-induced increase in PDGF-beta receptor in cultured rat aortic smooth muscle cells

To examine the role of platelet-derived growth factor (PDGF) and the polyol pathway in the growth activity of smooth muscle cells (SMCs), [(3)H]-thymidine incorporation, [(125)I]-PDGF-BB binding and expression of PDGF-beta receptor protein were measured in rat aortic SMCs cultured with 5.5 or 20 mM glucose with or without anti-PDGF antibody or an aldose reductase inhibitor, epalrestat. SMCs cultured with 20 mM glucose demonstrated an accelerated thymidine incorporation compared with SMCs cultured with 5.5 mM glucose, which was prevented by anti-PDGF antibody. This acceleration of growth activity by 20 mM glucose was accompanied by an increase in PDGF-BB binding, which was due to the increased number of PDGF-beta receptors and the overexpression of PDGF-beta receptor protein. Epalrestat prevented all these abnormalities. These observations suggest that polyol pathway hyperactivity plays an important role in the proliferation of SMCs which may be mediated through the accelerated expression of PDGF-beta receptor protein.

Endothelial cell dysfunction and the pathogenesis of diabetic macroangiopathy

Type 2 diabetes mellitus (DM) represents a high risk condition for the development of atherosclerotic and thromboembolic macroangiopathy, which make major contributions to diabetic mortality and morbidity. While many cardiovascular risk factors are common to both atherosclerosis and Type 2 DM, the enhanced risk of diabetic macroangiopathy may be attributable to additional pro-atherogenic mediators associated with insulin resistance syndrome. Given the central pathogenic role of endotheliopathy in atherosclerosis, it is likely that this vascular monolayer is the ultimate target of injury in response to such mediators. Furthermore, a pro-oxidative, dysfunctional endothelium may actively contribute to the pro-atherogenic environment through an inappropriate regulation of vascular tone, permeability, coagulation, fibrinolysis, cell adhesion and proliferation. Such dysfunction may mediate hypertension, dyslipidaemia and altered haemostasis, in addition to aggravating in vivo insulin resistance.