Oxidative stress and lipids in diabetes: a role in endothelium vasodilator dysfunction?

Timing Matters: Effects of Early and Late Estrogen Replacement Therapy on Glucose Metabolism and Vascular Reactivity in Ovariectomized Aged Wistar Rats

Cardiovascular disease incidence increases after menopause due to the loss of estrogen cardioprotective effects. However, there are conflicting data regarding the timing of estrogen therapy (ERT) and its effect on vascular dysfunction associated with impaired glucose metabolism. The aim of this work was to evaluate the effect of early and late ERT on blood glucose/insulin balance and vascular reactivity in aged ovariectomized Wistar rats. Eighteen-month-old female Wistar rats were randomized as follows: (1) sham, (2) 10-week postovariectomy (10 w), (3) 10 w postovariectomy+early estradiol therapy (10 w-early E2), (4) 20-week postovariectomy (20 w), and (5) 20-week postovariectomy+late estradiol therapy (20 w-late E2). Early E2 was administered 3 days after ovariectomy and late therapy after 10 weeks, in both groups. 17β-Estradiol (E2) was administered daily for 10 weeks (5 μg/kg/day). Concentration-response curves to angiotensin II, KCl, and acetylcholine (ACh) were performed. Heart rate (HR), diastolic and systolic blood pressure (DBP and SBP), glucose, insulin, HOMA-IR, and nitric oxide (NO) levels were determined. Higher glucose levels were found in all groups compared to the sham group, except the 20 w-late E2 group. Insulin was increased in all ovariectomized groups compared to sham. The HOMA-IR index showed insulin resistance in all ovariectomized groups, except for the 10 w-early E2 group. The 10 w-early E2 group increased NO levels vs. the 10 w group. After 10 w postovariectomy, the vascular response to KCl and Ach increases, despite early E2 administration. Early and late E2 treatment decreased vascular reactivity to Ang II. At 20-week postovariectomy, DBP increased, even with E2 administration, while SBP and HR remained unchanged. The effects of E2 therapy on blood glucose/insulin balance and vascular reactivity depend on the timing of therapy. Early ERT may provide some protective effects on insulin resistance and vascular function, whereas late ERT may not have the same benefits.

Natural Alkaloids and Diabetes Mellitus: A Review

BACKGROUND

The use of herbal therapies for treatment and management of diabetes mellitus and complications associated with this chronic condition is increasing. Plants contain a bounty of phytochemicals that have been proven to be protective by reducing the risk of various ailments and diseases, including alkaloids. Moreover, alkaloids are known to be among the oldest natural products used by humans for highlighting drugs that play crucial roles as therapeutic agents. The reason for this expanding interest and uses of alkaloids as a part of plant natural compounds-based treatments is that a significant proportion of diabetic patients do not respond very well to conventional therapeutic medication. Furthermore, other explanations to this fact are the cost of medication, side-effects, accessibility, and availability of health facilities and drugs and the inefficiency of these medicines in certain cases.

OBJECTIVE

In this study we aimed to review the literature on the valuable effects of herbs and plants and their isolated alkaloids compounds as medication for management of diabetes, a prevalent risk factor for several other disorders and illnesses.

METHODS

In the current review, PubMed, ScienceDirect, Springer and google scholar databases were used and the criterion for inclusion was based on the following keywords and phrases: diabetes, hyperglycemia, complications of diabetes, alkaloids, antidiabetic alkaloids, hypoglycemic alkaloids, alkaloids and complications of diabetes mellitus, mechanisms of action and alkaloids.

RESULTS

In the current review, we demonstrate that alkaloids in the form of extracts and isolated molecules obtained from a large variety of species demonstrated their efficiency for improving raises in blood glucose either in animal models via experimental studies or in human subjects via clinical trials. Medicinal species as chillies (Capsicum annuum), turmeric (Curcuma longa), barberry (Berberis vulgaris) and cress (Lepidium sativum) are among the most common and therapeutic plants used for controlling diabetes that were the subject of several experimental and clinical investigations. Whereas, isolated alkaloids such as berberine, capsaicin and trigonelline have received more interest in this field. Interestingly, the therapeutic impact of alkaloids against blood glucose pathogenesis is mediated through a variety of signaling cascades and pathways, via inhibiting or stimulating diversity of systems such as inhibition of α-glucosidase enzyme, blockade of PTP- 1B, deactivation of DPP-IV, increasing insulin sensitivity and modulating the oxidative stress.

CONCLUSION

Based on the findings of the present review, alkaloids could be used as preventive and curative agents in the case of endocrine disorders, particularly diabetes and could play a promoting function for the discovery of new antidiabetic agents.

Launaea taraxacifolia leaf partitions ameliorate alloxan-induced pathophysiological complications via antioxidant mechanisms in diabetic rats

Launaea taraxacifolia (Wild.) Amin ex. Jeffery belongs to family Asteracaea. The plant is used for treatment of diseases and eaten as vegetable in Nigeria. This study investigated the ameliorative potentials of L. taraxacifolia leaf partitions in alloxan induced diabetic complications. Male Albino rats were divided into eleven groups of five rats each. Diabetes was induced following intraperitoneal administration of 150 mg/kg alloxan monohydrate and was treated with 200 and 300 mg/kg of each partitioned fractions. Hyperglycemia was reversed in all treated rats within seven days of treatments. Rats treated with the partitions showed significant increase in hematological parameters compared with diabetic control. N-hexane fraction had the best overall effect against oxidative stress particularly on heart and pancreas reduced glutathione (GSH), superoxide dismutase (SOD) and kidney glutathione S-transferase (GST) activities. The various degrees of degeneration observed in the kidney, liver, pancreas and heart of the untreated diabetic rats were milder in rats treated with partitions. The results therefore revealed the ameliorative potentials of the partitioned fractions of L. taraxacifolia leaf extract against diabetes mellitus complications via activation of the antioxidant enzymes.

Nitric oxide induces hypoxia ischemic injury in the neonatal brain via the disruption of neuronal iron metabolism

We have recently shown that increased hydrogen peroxide (H₂O₂) generation is involved in hypoxia–ischemia (HI)-mediated neonatal brain injury. H₂O₂ can react with free iron to form the hydroxyl radical, through Fenton Chemistry. Thus, the objective of this study was to determine if there was a role for the hydroxyl radical in neonatal HI brain injury and to elucidate the underlying mechanisms. Our data demonstrate that HI increases the deposition of free iron and hydroxyl radical formation, in both P7 hippocampal slice cultures exposed to oxygen–glucose deprivation (OGD), and the neonatal rat exposed to HI. Both these processes were found to be nitric oxide (NO) dependent. Further analysis demonstrated that the NO-dependent increase in iron deposition was mediated through increased transferrin receptor expression and a decrease in ferritin expression. This was correlated with a reduction in aconitase activity. Both NO inhibition and iron scavenging, using deferoxamine administration, reduced hydroxyl radical levels and neuronal cell death. In conclusion, our results suggest that increased NO generation leads to neuronal cell death during neonatal HI, at least in part, by altering iron homeostasis and hydroxyl radical generation.

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HI increases the deposition of free iron and hydroxyl radical formation in the neonatal brain.

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Both these processes are NO dependent.

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Increased iron deposition is mediated via increased TfR and decreased ferritin expression.

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These processes are involved in the neuronal cell death associated with neonatal HI.

Preserving mitochondrial function prevents the proteasomal degradation of GTP cyclohydrolase I

The development of pulmonary hypertension is a common accompaniment of congenital heart disease (CHD) with increased pulmonary blood flow. Our recent evidence suggests that asymmetric dimethylarginine (ADMA)-induced mitochondrial dysfunction causes endothelial nitric oxide synthase (eNOS) uncoupling secondary to a proteasome-dependent degradation of GTP cyclohydrolase I (GCH1) that results in a decrease in the NOS cofactor tetrahydrobiopterin (BH(4)). Decreases in NO signaling are thought to be an early hallmark of endothelial dysfunction. As l-carnitine plays an important role in maintaining mitochondrial function, in this study we examined the protective mechanisms and the therapeutic potential of l-carnitine on NO signaling in pulmonary arterial endothelial cells and in a lamb model of CHD and increased pulmonary blood flow (Shunt). Acetyl-l-carnitine attenuated the ADMA-mediated proteasomal degradation of GCH1. This preservation was associated with a decrease in the association of GCH1 with Hsp70 and the C-terminus of Hsp70-interacting protein (CHIP) and a decrease in its ubiquitination. This in turn prevented the decrease in BH(4) levels induced by ADMA and preserved NO signaling. Treatment of Shunt lambs with l-carnitine also reduced GCH1/CHIP interactions, attenuated the ubiquitination and degradation of GCH1, and increased BH(4) levels compared to vehicle-treated Shunt lambs. The increases in BH(4) were associated with decreased NOS uncoupling and enhanced NO generation. Thus, we conclude that L-carnitine may have a therapeutic potential in the treatment of pulmonary hypertension in children with CHD with increased pulmonary blood flow.

Multiple antioxidants and L-arginine modulate inflammation and dyslipidemia in chronic renal failure rats

The kidney is an important source of L-arginine, the endogenous precursor of nitric oxide (NO). Surgical problems requiring extensive renal mass reduction (RMR) decrease renal NO production, leading to multiple hemodynamic and homeostatic disorders manifested by hypertension, oxidative stress, and increased inflammatory cytokines. Using the RMR model of chronic renal failure (CRF), we assessed the effects of twelve weeks' administration of L-arginine and/or a mixture of antioxidants (L-carnitine, catechin, vitamins E and C) on plasma cytokines, soluble intercellular adhesion molecule-1 (sICAM-1), nitrate and nitrites (NO(2)/NO(3)), lipid profile, blood pressure, and renal function. CRF rats showed increased plasma IL-1 alpha, IL1-beta, IL-6, TNF-alpha, and sICAM-1 levels and decreased anti-inflammatory cytokines IL-4 and 10 levels, hypertension, and dyslipidemia. L-arginine treatment improved kidney functions, decreased systolic blood pressure, and decreased inflammatory cytokines levels. Antioxidants administration decreased inflammatory cytokines and sICAM-1 levels and increased IL-4 levels. Combined use of both L-arginine and the antioxidant mixture were very effective in their tendency to recover normal values of kidney functions, plasma cytokines, sICAM-1, blood pressure, NO(2)/NO(3), cholesterol, and triglycerides concentrations. Indeed, the effects of L-arginine and the antioxidants on the reduction of proinflammatory cytokines may open new perspectives in the treatment of uremia.

Asymmetric dimethylarginine inhibits HSP90 activity in pulmonary arterial endothelial cells: role of mitochondrial dysfunction

Increased asymmetric dimethylarginine (ADMA) levels have been implicated in the pathogenesis of a number of conditions affecting the cardiovascular system. However, the mechanism(s) by which ADMA exerts its effect has not been adequately elucidated. Thus the purpose of this study was to determine the effect of increased ADMA on nitric oxide (NO) signaling and to begin to elucidate the mechanism by which ADMA acts. Our initial data demonstrated that ADMA increased NO synthase (NOS) uncoupling in both recombinant human endothelial NO synthase (eNOS) and pulmonary arterial endothelial cells (PAEC). Furthermore, we found that this endothelial NOS (eNOS) uncoupling increased 3-nitrotyrosine levels preferentially in the mitochondria of PAEC due to a redistribution of eNOS from the plasma membrane to the mitochondria. This increase in nitration in the mitochondria was found to induce mitochondrial dysfunction as determined by increased mitochondrial-derived reactive oxygen species and decreased generation of ATP. Finally, we found that the decrease in ATP resulted in a reduction in the chaperone activity of HSP90 resulting in a decrease in its interaction with eNOS. In conclusion increased levels of ADMA causes mitochondrial dysfunction and a loss of heat shock protein-90 chaperone activity secondary to an uncoupling of eNOS. Mitochondrial dysfunction may be an understudied component of the endothelial dysfunction associated with various cardiovascular disease states.

Protective influence of vitamin E on the antioxidant defence system in the whole blood and liver of normal and alloxan-induced diabetic rats

The effect of oral administration of vitamin E for twenty-eight consecutive days on blood glucose, reduced glutathione levels, antioxidant enzymes (superoxide dismutase and catalase activities), and levels of malondialdehyde (as an index of free radical-mediated lipid peroxidation) was observed in the whole blood and liver of normal and alloxan-induced diabetic rats. It was found that oral administration of vitamin E significantly (p<0.05) lowered the blood glucose level and increased the body weight of the diabetic rats. The activities of superoxide dismutase and levels of reduced glutathione increased significantly (p<0.05) while the level of lipid peroxidation decreased.

Diabetes-associated macrovasculopathy: pathophysiology and pathogenesis

The complications associated with diabetic vasculopathy are commonly grouped into two categories: microvascular and macrovascular complications. In diabetes, macrovascular disease is the commonest cause of mortality and morbidity and is responsible for high incidence of vascular diseases such as stroke, myocardial infarction and peripheral vascular diseases. Macrovascular diseases are traditionally thought of as due to underlying obstructive atherosclerotic diseases affecting major arteries. Pathological changes of major blood vessels leading to functional and structural abnormalities in diabetic vessels include endothelial dysfunction, reduced vascular compliance and atherosclerosis. Besides, advanced glycation end product formation interacts with specific receptors that lead to overexpression of a range of cytokines. Haemodynamic pathways are activated in diabetes and are possibly amplified by concomitant systemic hypertension. Apart from these, hyperglycaemia, non-enzymatic glycosylation, lipid modulation, alteration of vasculature and growth factors activation contribute to development of diabetic vasculopathy. This review focuses on pathophysiology and pathogenesis of diabetes-associated macrovasculopathy.

Ferritin and ferritin isoforms II: protection against uncontrolled cellular proliferation, oxidative damage and inflammatory processes

Ferritin is a major iron storage protein involved in the regulation of iron availability. Each ferritin molecule comprises 24 subunits. Various combinations of H-subunits and L-subunits make up the 24-subunit protein structure and these ferritin isoforms differ in their H-subunit to L-subunit ratio, as well as in their metabolic properties. Ferritin is an acute-phase protein and its expression is up-regulated in conditions such as uncontrolled cellular proliferation, in any condition marked by excessive production of toxic oxygen radicals, and by infectious and inflammatory processes. Under such conditions ferritin up-regulation is predominantly stimulated by increased reactive oxygen radical production and by cytokines. The major function of ferritin in these conditions is to reduce the bio-availability of iron in order to stem uncontrolled cellular proliferation and excessive production of reactive oxygen radicals. Ferritin is not, however, indiscriminately up-regulated in these conditions as a marked shift towards a predominance in H-subunit rich ferritins occurs. Preliminary indications are that, while the L-subunit primarily fulfils the conventional iron storage role, the H-subunit functions primarily as rapid regulator of iron availability, and perhaps indirectly as regulator of other cellular processes. It is suggested that the optimum differential expression of the two subunits differ for different cells and under different conditions and that the expression of appropriate isoferritins offers protection against uncontrolled cellular proliferation, oxidative stress and against side effects of infectious and inflammatory conditions.

Maternal food restriction in the second half of pregnancy affects vascular function but not blood pressure of rat female offspring

Food restriction during pregnancy in rats induces intrauterine growth retardation with consequences persisting into adulthood. In the present study we have investigated the hypothesis that malnutrition in pregnant rats may lead to altered cardiovascular function in adult female offspring. Perinatal growth retardation was induced by a 50 % reduction of normal dietary intake in rats during the second half of pregnancy. Systolic and diastolic blood pressure values and heart rate were recorded in conscious female offspring (100 d old) using a femoral artery probe. No significant differences in heart rate, or in systolic and diastolic blood pressures were recorded between control offspring and offspring of nutritionally deprived rats. In order to ascertain whether cardiovascular variables in the offspring were influenced by lactation, subgroups of offspring from food-restricted dams were fostered with lactating dams fed on a normal diet. Blood pressure and heart rate were also found to be normal in these offspring. The rise in blood pressure associated with NO inhibition was similar in all groups. Isolated resistance artery function was assessed in vitro in offspring (100–120 d old) of a second group of semi-starved dams. Small mesenteric arteries from these animals showed reduced endothelium-dependent relaxation (to acetylcholine and bradykinin), but enhanced sensitivity to exogenous NO (sodium nitroprusside). We conclude that food restriction during the second half of pregnancy and/or lactation does not induce hypertension in adult offspring, but may effect subtle changes in vascular function.

Postprandial hyperglycaemia and vascular damage--the benefits of acarbose

Traditional risk factors do not fully explain the increased risk of cardiovascular disease (CVD) in diabetes. Epidemiology shows that hyperglycaemia is a continuous CVD risk factor and that two-hour postprandial glucose levels are more strongly associated with CVD than fasting glucose. Good glycaemic control is proven to reduce the risk of microvascular complications, but equivalent evidence for CVD risk reduction is lacking. However, in the Study to Prevent Non-Insulin Dependent Diabetes Mellitus (STOP-NIDDM), acarbose reduced the risk of diabetes in those with impaired glucose tolerance by 36% (p=0.0017) and the risk of any cardiovascular event by 49% (p=0.0326) versus placebo. Furthermore, a meta-analysis of trials of acarbose in patients with type 2 diabetes suggests a significant reduction of CVD events. This review examines evidence that postprandial hyperglycaemia plays a major role in vascular damage, particularly through non-traditional risk factors such as oxidative stress and subclinical inflammation, and how acarbose may prevent this damage.

Inhibition by L-arginine and spermidine of hemoglobin glycation and lipid peroxidation in rats with induced diabetes

The effect of L-arginine and spermidine on hemoglobin glycation and lipid peroxidation in serum of normal and diabetic rats was studied. Five groups of 40 rats were studied during 20 days and compared with a control group (Group I) that consisted of normal rats (N = 6) not treated with L-arginine or spermidine. Group II, diabetic rats (alloxan 120 mg/kg, i.p. at the day 0 and alloxan 60 mg/kg, i.p. at the day 10) were considered as diabetic control. Group III, diabetic rats treated with 10 mM L-arginine (i.p.). Group IV, diabetic rats treated with 10 microM spermidine (i.p.). Group V, normal rats treated with 10 mM L-arginine (i.p.). Group VI, normal rats treated with 10 microM spermidine (i.p.). The rats of each group were divided in subgroups of four each. Rats were anesthetized and blood was taken from aorta to determine glucose, triglycerides (TGs), total cholesterol (TC), low- and high-density lipoproteins (LDL and HDL), glycated hemoglobin (HbA(1C)), and thiobarbituric acid-reactive substances (TBARS). We observed that the alloxan concentrations used in this study reproduced the clinical manifestations of disease including hyperglycemia (from 116 +/- 7 mg/dl to 435 +/- 80 mg/dl) in 96 hours. As a consequence the levels of TGs, TC, LDL, TBARS, and HbA(1C) were increased, whereas HDL diminished. HbA(1C) concentration was significantly correlated with the concentration of TBARS. The L-arginine and spermidine injection tended to normalize the glycemia from 24 hours, similarly, hyperlipidemia, TBARS, and HbA(1C). From these results, we conclude that l-arginine and spermidine exerted an inhibitory effect of hemoglobin glycation and lipid peroxidation in vivo, which may be relevant in preventing diabetic complications.

Amla (Emblica officinalis Gaertn.) Extracts Reduce Oxidative Stress in Streptozotocin-Induced Diabetic Rats

The antioxidant properties of amla extracts and their effects on the oxidative stress in streptozotocin-induced diabetes were examined in rats. Amla in the form of either the commercial enzymatic extract SunAmla (Taiyo Kagaku Co. Ltd., Yokkaichi, Japan) (20 or 40 mg/kg of body weight/day) or a polyphenol-rich fraction of ethyl acetate extract (10 or 20 mg/kg of body weight/day) was given orally for 20 days to the streptozotocin-induced diabetic rats. Amla extracts showed strong free radical scavenging activity. Amla also showed strong inhibition of the production of advanced glycosylated end products. The oral administration of amla extracts to the diabetic rats slightly improved body weight gain and also significantly alleviated various oxidative stress indices of the serum of the diabetic rats. The elevated serum levels of 5-hydroxymethylfurfural, which is a glycosylated protein that is an indicator of oxidative stress, were significantly reduced dose-dependently in the diabetic rats fed amla. Similarly, the serum level of creatinine, yet another oxidative stress parameter, was also reduced. Furthermore, thiobarbituric acid-reactive substances levels were significantly reduced with amla, indicating a reduction in lipid peroxidation. In addition, the decreased albumin levels in the diabetic rats were significantly improved with amla. Amla also significantly improved the serum adiponectin levels. These results form the scientific basis supporting the efficacy of amla for relieving the oxidative stress and improving glucose metabolism in diabetes.

Effect of α-tocopherol on the metabolic control and oxidative stress in female type 2 diabetics

In this study we evaluate the effects of alpha-tocopherol on the metabolic control and oxidative stress in female patients with type 2 diabetes mellitus. Thirty-four female type 2 diabetics 40-70 years old up to 14 years with diabetes, under medical treatment, were randomly divided in two groups. One group received placebo (Control group, n = 21) and the other received alpha-tocopherol (800 IU/day, n = 13) during 6 weeks. Blood samples were collected at the beginning and at the end of the study to measure malondialdehyde production, glycated hemoglobin, selenium dependent-glutathione peroxidase, Cu,Zn-superoxide dismutase in erythrocytes and total antioxidant status, glucose, lipid and lipoproteins in serum. Erythrocyte malondialdehyde decreased and serum-total antioxidant status increased after alpha-tocopherol treatment (P < 0.0001). However, an unexpected increase on cholesterol levels and a reduced erythrocyte-Cu,Zn-superoxide dismutase activity was observed after alpha-tocopherol treatment. alpha-Tocopherol administration did not affect glucose, glycated hemoglobin, triacylglycerides, lipoprotein levels and serum malondialdehyde. A minor oxidative stress was observed in female type 2 diabetic patients after alpha-tocopherol treatment inferred from the reduced levels of erythrocyte malondialdehyde and the increased values of total antioxidant status. On the other hand, no beneficial changes were observed on glycemic control or lipid metabolism.

Tempol therapy attenuates medial smooth muscle cell apoptosis and neointima formation after balloon catheter injury in carotid artery of diabetic rats

Accumulating data support the hypothesis that reactive oxygen species (ROS) play a critical role in the vascular complications observed in diabetes. However, the mechanisms of ROS-mediated vascular complications in diabetes are not clear. We tested the hypothesis that ROS-mediated increase in proapoptotic factor Bax expression leads to medial smooth muscle cell (SMC) apoptosis that is associated with neointima formation. We used a fructose-rich diet for 4 wk to model Type 2 diabetes in rats. SOD mimetic membrane-permeable 4-hydroxy-2,2,6,6,-tetramethylpiperidine-1-oxyl (Tempol, 1 mM) was administered in drinking water to scavenge superoxide starting 1 day before surgery and continued during the duration of the experiment. Vascular injury resulted in a significant increase in medial SMC apoptosis that was associated with neointima formation. The number of medial SMC positive for Bax immunostaining significantly increased in injured arteries compared with uninjured arteries. Superoxide scavenging by Tempol treatment inhibited both the Bax-positive index as well as the apoptotic index of medial SMC in response to vascular injury. Tempol treatment inhibited apoptotic loss of medial SMC, thus increasing their density in the injured arteries. These alterations in the media were associated with a marked decrease in neointima formation in injured arteries. We conclude that Bax expression may play an important role in vascular SMC apoptosis and, finally, that this regulatory mechanism is redox sensitive.

Effects of gemfibrozil treatment on vascular reactivity of streptozotocin-diabetic rat aorta

The effects of gemfibrozil treatment on plasma lipids, lipid peroxides and vascular reactivity of aorta were investigated in diabetic rats. Rats were divided randomly into two groups: control and diabetic. Diabetes was induced by a single intraperitoneal injection of streptozotocin (45 mg kg(-1)). Twelve weeks after the induction of diabetes, some of the control and diabetic rats were started treatment with gemfibrozil (100 mg kg(-1) daily; gavage) for 2 weeks. Blood glucose, plasma triglyceride, cholesterol, low-density lipoprotein (LDL) cholesterol and thiobarbituric acid reactive substances (TBARS) levels were markedly increased and gemfibrozil treatment restored these parameters in diabetic rats. However high-density lipoprotein (HDL) cholesterol levels did not differ in all experimental groups. In diabetic rats, the endothelium-dependent relaxations to acetylcholine were decreased when compared with control rats. Gemfibrozil treatment restored the endothelium-dependent responses to acetylcholine in diabetic rats. The endothelium-independent relaxation responses to sodium nitroprusside were not altered in all groups. These findings suggest that gemfibrozil treatment has beneficial effects against cardiovascular and metabolic complications of diabetes via its hypolipidaemic and antioxidant properties.

Current concepts of cardiovascular diseases in diabetes mellitus

The incidence of diabetes has reached epidemic proportions across the world. In patients with diabetes, there is a two to four times increased risk of developing coronary artery disease (CAD). Diabetes seems to eliminate the protective benefits of hormones in women against CAD. Patients with type II diabetes also have hypertension, dyslipidemia, obesity, endothelial dysfunction and prothrombotic factors, called 'the metabolic syndrome'. Not only the incidence of CAD is higher in diabetes, the mortality of the diabetic patients after a cardiac event is significantly increased as compared to non-diabetics, including sudden death. Although in the past 35 years there has been a decline in the rate of death due to CAD in the general population, this has not been seen among patients with diabetes. Primary prevention can play an important role in decreasing the incidence of CAD in diabetic patients. Aggressive treatment of hyperlipidemia and hypertension is essential. Recent knowledge about the protective effects of aspirin, statins, angiotension converting enzyme inhibitors, and glitazones in the diabetic patients, if used appropriately will go a long way in primary and secondary prevention of CAD in patients with diabetes.

Cardiovascular function in acromegaly

Even with modern treatment, acromegaly is associated with a 2- to 3-fold increase in mortality, mainly from vascular disease, which is probably a result of the long exposure of tissues to excess GH before diagnosis and treatment. There is accumulating evidence that effective treatment to lower serum GH levels to less than 1-2 ng/ml (glucose suppressed or random, respectively) and normalize IGF-I improves long-term outcome and survival. In addition to recognized cardiovascular risk factors of hypertension, type 2 diabetes mellitus, and dyslipidemia, there is accumulating evidence of specific structural and functional changes in the heart in acromegaly. Along with endothelial dysfunction, these changes may contribute to the increased mortality in this disease. There are specific structural changes in the myocardium with increased myocyte size and interstitial fibrosis of both ventricles. Left ventricular hypertrophy is common even in young patients with short duration of disease. Some of these structural changes can be reversed by effective treatment. Functionally, the main consequence of these changes is impaired left ventricular diastolic function, particularly when exercising, such that exercise tolerance is reduced. Diastolic function improves with treatment, but the effect on exercise tolerance is more variable, and more longitudinal data are required to assess the benefits. What scant data there are on rhythm changes suggest an increase in complex ventricular arrhythmias, possibly as a result of the disordered left ventricular architecture. The functional consequences of these changes are unclear, but they may provide a useful early marker for the ventricular remodeling that occurs in the acromegalic heart. Endothelial dysfunction, especially flow-mediated dilatation, is an early marker of atherosclerosis, and limited data imply that this is impaired in active acromegaly and can be improved with treatment. Similarly, early arterial structural changes, such as thickened intima media layer, appear more common in acromegalics, and there are hints that this may diminish with effective treatment, although more studies are required for a definite conclusion on this topic. In conclusion, impaired cardiac and endothelial structure and function in acromegaly are risk factors for vascular mortality and should be regarded as legitimate therapeutic targets in the overall management of this condition.

Recent advances in the treatment of erectile dysfunction in patients with diabetes mellitus

OBJECTIVE

To present current information on the pathogenesis of and available therapeutic options for erectile dysfunction (ED) in patients with diabetes.

METHODS

We provide a detailed review of the following topics: (1) peripheral and central neurotransmitter pathways involved in the penile erectile process (for example, nitric oxide, acetylcholine, vasoactive intestinal polypeptide, and prostaglandin E(1)), (2) pathogenesis of ED in patients with diabetes (vascular insufficiency, endothelial dysfunction, and autonomic neuropathy), (3) currently available treatment options for ED and their advantages and disadvantages, (4) potential new avenues for future research, and (5) the possibility of preventive treatment.

RESULTS

Clearly a need exists for effective treatment options for ED in patients with diabetes. Because the development of ED in patients with diabetes is often caused by several interrelated mechanisms, including vascular disease, endothelial dysfunction, autonomic neuropathy, hormone imbalance, and certain medications, a thorough understanding of the various pathways involved in penile erection and their modulation in diabetes is essential for physicians to design an effective treatment plan. Interventions that modulate the erectile pathway at different points include therapies that enhance the erectile mechanism (amplification of the nitric oxide pathway), inhibit the detumescence mechanism, or affect the final common pathway by augmenting smooth muscle relaxation. Oral therapy, intracavernosal injections, transurethral pellets, combination therapy, and surgical procedures are available treatment strategies.

CONCLUSION

Despite the availability of many treatment options for ED, early intervention and prevention (by such measures as improved glycemic control and general reduction of associated risk factors) should be emphasized because many of the diabetes-related complications leading to ED are irreversible.

Oxidative stress and functional deficit in diabetic cardiomyopathy

When the equilibrium between free-radical production and cellular antioxidant defences is disturbed in favour of more free radicals, it causes oxidative stress which can promote cellular injury. Oxidative stress has been suggested to play a role in the pathogenesis of diabetic cardiomyopathy. In streptozotocin-induced diabetes, there is a decrease in antioxidant enzyme activities and an increase in myocardial lipid peroxidation. Probucol, an antioxidant, was found to improve cardiac function which may have been due to an increase in myocardial antioxidant enzyme activities and a decrease in lipid peroxidation in the diabetic animals. Some of the beneficial effects of probucol may also be due to an improvement in plasma insulin levels and a decrease in the plasma glucose. The diabetic state is also associated with endothelial dysfunction, retinopathy, neuropathy and renopathy. Some of these secondary complications may also be mediated by oxidative stress. It is suggested that diabetic cardiomyopathy is associated with an antioxidant deficit and that antioxidant therapy may be useful in improving cardiac function in diabetes.

Aggressive lipid lowering does not improve endothelial function in type 2 diabetes: the Diabetes Atorvastatin Lipid Intervention (DALI) Study: a randomized, double-blind, placebo-controlled trial

OBJECTIVE

Endothelial dysfunction is considered an important early marker of atherosclerosis and cardiovascular risk and is currently used as a surrogate end point for cardiovascular risk in clinical trials. Type 2 diabetic patients show a characteristic dyslipidemia. Aggressive lipid lowering might be an effective method to improve endothelial function in these patients.

RESEARCH DESIGN AND METHODS

A randomized, double-blind, placebo-controlled trial was completed to study the effect of 30 weeks' administration of atorvastatin 10 mg and 80 mg on endothelial function, as assessed by B-mode ultrasound of the brachial artery, in 133 patients with type 2 diabetes without a history of cardiovascular disease.

RESULTS

Patients with diabetes and diabetic dyslipidemia had considerable endothelium-dependent and endothelium-independent dysfunction; mean flow-mediated vasodilation (SD) was 3.16% (3.56), and mean response on sublingual nitroglycerin was 6.58% (6.04). Despite substantial lowering of all atherogenic lipid parameters, no improvement of endothelium-dependent vasodilatation was found (P > 0.8).

CONCLUSIONS

We observed considerable baseline endothelium-dependent and endothelium-independent dysfunction in patients with diabetes and diabetic dyslipidemia without a history of cardiovascular disease. Aggressive lipid lowering by administration of atorvastatin, resulting in substantial improvement of the lipid profile, did not reverse endothelial dysfunction.

Oxidative stress parameters in type I, type II and insulin-treated type 2 diabetes mellitus; insulin treatment efficiency

BACKGROUND

Our aim was to evaluate oxidative stress parameters on three groups of diabetic patients, insulin-dependent diabetes mellitus (IDDM), non-insulin-dependent diabetes mellitus (NIDDM), and insulin-treated type 2 diabetes mellitus (ITDM2), with similar HbA1c value and to determine if insulin's impact on these parameters was the same for IDDM and ITDM2.

METHODS

This study has been conducted on 18 IDDM, 55 NIDDM, 27 ITDM2, compared to 12 healthy subjects. Plasmatic concentrations of thiobarbituric acid reactive substances (TBARS), fatty acids, total antioxidant status (TAS), alpha-tocopherol, and erythrocyte reduced glutathione (GSH) were measured as well as enzymatic activities of superoxide dismutase (SOD), and glutathione peroxidase/reductase.

RESULTS

Diabetic patients have significant increase of SOD activity, of TBARS concentration (concomitant with low levels of unsaturated fatty acids) and significant decrease of GSH and alpha-tocopherol. NIDDM have significantly lower levels of GSH and higher levels of TBARS compared to IDDM. ITDM2 values are intermediate between IDDM and NIDDM but are far from reaching those of IDDM.

CONCLUSION

Diabetic patients undergo an important oxidative stress that is nearly corrected for IDDM, but only partially improved for ITDM2, although length of insulin treatment and HbA1c values are similar, suggesting metabolic differences between the two types of diabetes.

Homocysteine and cardiovascular disease in diabetes mellitus

BACKGROUND

Patients with diabetes mellitus (DM) have 2- to 6-fold increase in the prevalence of cardiovascular disease (CVD) compared to non-DM subjects. Epidemiological data show that DM is synergic with other conventional risk factors. Total plasma homocysteine (tHcy) is an emerging CVD risk factor. We reviewed the literature to explore the relation between tHcy and CVD in patients with DM.

METHODS

We searched the MEDLINE database for articles on homocysteine, DM and CVD published from January 1991 to October 2000.

RESULTS

The mean plasma tHcy level is usually low or normal in DM patients, except when nephropathy is present. Levels in that case tend to be higher than in non-DM patients. An independent association with tHcy and CVD was shown in retrospective studies, for DM patients. Prospective studies showed an association between elevated tHcy and all cause mortality in DM patients. In general, the association between elevated levels of tHcy and the outcome was stronger than in non-DM individuals, for all types of study.

DISCUSSION

To date, there are no prospective work that specifically examined the relationship between levels of tHcy and the presence of CVD in the DM population. Nor are there studies to show that treating elevated tHcy results in a reduction of CVD events. Such studies are ongoing. Nevertheless, since hyperhomocysteinemia is potentially reversible with vitamin therapy, interaction of DM with high levels tHcy on the risk of CVD may have consequences with regard to management of primary and secondary prevention in DM patients who are at particularly high risk of CVD events.

Plasma levels of endothelin, lipid peroxides and prostacyclin in diabetic patients with macroangiopathy

The prevalence of macroangiopathy is increased in diabetes mellitus. Endothelial cell injury is thought to be an early event leading to atherosclerosis which may be initiated by several factors. We have investigated the relationship between plasma endothelin, lipid peroxide (measured as thiobarbituric acid reacting species (TBARS)) and 6-keto-prostaglandin-F1A (6-keto-PG-F1A) in Type 2 diabetic patients with macroangiopathy. Fifty-three diabetic subjects with macroangiopathy were investigated, together with 50 diabetic and 50 control subjects without evidence of vascular disease. Both the endothelin and TBARS levels were significantly higher in diabetic patients with macroangiopathy (10.8 (8.0-14.4) pmol/l and 5.6 (3.2-9.7) micromol/l, respectively) compared with control subjects (7.6 (5.0-11.0) pmol/l and 4.5 (3.0-6.4) micromol/l, P<0.001) and with diabetic subjects without macroangiopathy (7.4 (4.9-11.2) pmol/l (P<0.001) and 4.9 (3.0-8.0) micromol/l (P<0.05)). 6-Keto-PG-F1A levels were significantly decreased in diabetic subjects with macroangiopathy 209 (123-355) pg/ml than in normal subjects 241 (137-425) pg/ml, (P<0.05) and diabetic subjects without macroangiopathy 224 (162-309) pg/ml, (P<0.05). Comparison of levels of endothelin with those of TBARS in macroangiopathy group, showed that endothelin is a more consistent marker of the atherogenic process (P<0.01). In conclusion, we have shown that there are abnormalities of endothelium-derived factors in diabetic patients with macroangiopathy, mainly in endothelin. Furthermore, in this group there was a positive correlation between endothelin and fasting insulin levels.

Effect of antioxidant treatment of streptozotocin-induced diabetic rats on endoneurial blood flow, motor nerve conduction velocity, and vascular reactivity of epineurial arterioles of the sciatic nerve

We have shown that diabetes-induced reduction in endoneurial blood flow (EBF) and impaired endothelium-dependent vascular relaxation precede slowing of motor nerve conduction velocity (MNCV) and decreased sciatic nerve Na(+)/K(+) ATPase activity. Furthermore, vascular dysfunction was accompanied by an accumulation of superoxide in arterioles that provide circulation to the sciatic nerve. In the present study, we examined the effect that treatment of streptozotocin-induced diabetic rats with antioxidants has on vascular and neural function. Diabetic rats were treated with 0.5% alpha-lipoic acid as a diet supplement or with hydroxyethyl starch deferoxamine (HES-DFO) by weekly intravenous injections at a dose of 75 mg/kg. The treatments significantly improved diabetes-induced decrease in EBF, acetylcholine-mediated vascular relaxation in arterioles that provide circulation to the region of the sciatic nerve, and MNCV. The treatments also reduced the production of superoxide by the aorta and superoxide and peroxynitrite by arterioles that provide circulation to the region of the sciatic nerve. Treating diabetic rats with alpha-lipoic acid prevented the diabetes-induced increase in thiobarbituric acid-reactive substances in serum and significantly improved lens glutathione levels. In contrast, treating diabetic rats with HES-DFO did not prevent diabetes-induced changes of either of these markers of oxidative stress. Diabetes-induced increase in sciatic nerve conjugated diene levels was not improved by treatment with either alpha-lipoic acid or HES-DFO. Treating diabetic rats with alpha-lipoic acid but not HES-DFO partially improved sciatic nerve Na(+)/K(+) ATPase activity and myo-inositol content. The increase in sciatic nerve sorbitol levels in diabetic rats was unchanged by either treatment. These studies suggest that diabetes-induced oxidative stress and the generation of superoxide may be partially responsible for the development of diabetic vascular and neural complications.

Diabetes and endothelial dysfunction: a clinical perspective

The main etiology for mortality and a great percent of morbidity in patients with diabetes mellitus is atherosclerosis. A hypothesis for the initial lesion of atherosclerosis is endothelial dysfunction, defined pragmatically as changes in the concentration of the chemical messengers produced by the endothelial cell and/or by blunting of the nitric oxide-dependent vasodilatory response to acetylcholine or hyperemia. Endothelial dysfunction has been documented in patients with diabetes and in individuals with insulin resistance or at high risk for developing type 2 diabetes. Factors associated with endothelial dysfunction in diabetes include activation of protein kinase C, overexpression of growth factors and/or cytokines, and oxidative stress. Several therapeutic interventions have been tested in clinical trials aimed at improving endothelial function in patients with diabetes. Insulin sensitizers may have a beneficial effect in the short term, but the virtual absence of trials with cardiovascular end-points preclude any definitive conclusion. Two trials offer optimism that treatment with ACE inhibitors may have a positive impact on the progression of atherosclerosis. Although widely used, the effect of hypolipidemic agents on endothelial function in diabetes is not clear. The role of antioxidant therapy is controversial. No data have been published regarding the effects of hormonal replacement therapy on endothelial dysfunction in postmenopausal women with type 2 diabetes.

The effect of dietary fat on malondialdehyde concentrations in Fischer 344 rats

The effects of dietary fat and age on the level of malondialdehyde (MDA), a product of lipid peroxidation, were investigated in cerebellum, kidney, and liver tissues of female Fischer 344 rats. Groups of rats were fed diets containing various levels of corn oil (3, 5, 10, 15, or 20%), starting at 57 days of age, for a duration of 2, 10, or 20 weeks. High fat diets are thought to promote tumor formation, diabetes, and cardiovascular diseases via induction of oxidation stress, and this can begin early in the lifespan. However, it was observed that rats chronically consuming 3 and 5% corn oil diets yielded significantly higher levels of MDA, as analyzed by high-performance liquid chromatography, compared with those fed higher fat diets. After 20 weeks of feeding, the concentration of MDA in each of the three organs studied showed no significant differences among rats consuming diets containing 10, 15, or 20% corn oil. The levels of MDA were highest in the cerebellum, followed by kidney, and lowest in liver. Over the 20-week feeding period, a decrease in MDA level in both cerebellum and liver was observed.

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.

Cholesterol-independent endothelial dysfunction in virgin and pregnant rats fed a diet high in saturated fat

1. Western diets high in saturated fat are associated with an increased incidence of cardiovascular diseases. In this study we have evaluated vascular endothelial function and oxidative stress in virgin rats fed a normal (VC) or high in saturated fat diet (VHF) (20 % lard and corn oil w/w) from weaning until adulthood, and throughout subsequent pregnancy (PC and PHF, respectively). 2. The saturated fat diet was associated with enhanced noradrenaline sensitivity in small mesenteric arteries from VHF rats (VHF vs. VC, P < 0.05) and blunted endothelium-dependent relaxation in VHF and PHF rats (VHF vs. VC, P < 0.001; PHF vs. PC, P < 0.05). Endothelial dysfunction was attributable to a reduced nitric oxide component of relaxation in VHF rats, and blunted prostacyclin and endothelium-derived hyperpolarizing factor components in PHF rats. 3. Other than plasma cholesterol, which was reduced in VHF and PHF rats, plasma lipids were normal. Fasting plasma insulin and glucose concentrations were raised in VHF rats (P < 0.05) and the plasma marker of oxidative stress, 8-iso PGF2alpha, was increased in PHF animals (P < 0.01). 4. These findings suggest that endothelial dysfunction induced by a saturated fat diet is cholesterol independent and likely to be of different mechanistic origin in virgin and pregnant rats.

In vivo effect of 8-epi-PGF2alpha on retinal circulation in diabetic and non-diabetic rats

Retinal hemodynamic responses to a F2-isoprostane, 8-epi-PGF2alpha, were quantitated in vivo in non-diabetic and diabetic rats using a video fluorescein angiography system. Vascular diameters and retinal mean circulation time were determined before and after 5 microl intra-vitreous injection of 8-epi-PGF2alpha (10(-5) to 10(-3) M), 10(-4) M 8-epi-PGF2alpha, + 10(-3) M SQ29,548 or 10(-3) M LCB2853 (two inhibitors of TXA2 receptor), 10(4) M 9beta-PGF2alpha, or the carrier in non-diabetic animals. Diabetic rats received either 8-epi-PGF2alpha 10(-4) M, or the carrier. Compared to control animals, diabetic rats presented in the basal state a venous vasodilation (P<0.01), without modification of retinal mean circulation time or blood flow. After intravitreous injection of 8-epi-PGF2alpha, a significant arterial vasoconstriction was observed in control but not in diabetic animals. This vasoconstriction was concomitant with increased retinal mean circulation time in control but not in diabetic rats, inducing an impaired reduction of blood flow. No vasoconstriction was observed after injection of either the carrier, 9beta-PGF2alpha or the isoprostane associated to the inhibitors of TXA2 receptors. This is the first direct observation that the isoprostane 8-iso-PGF2alpha is a potent vasoconstricting agent in the retina. It occurs at the arterial but not venous level, and is likely mediated through a TXA2-like receptor. Differences observed between control and diabetic animals suggest altered adaptative mechanisms toward vasoconstrictor substances (such as isoprostanes) in diabetic rats.

Comorbidity of hypertension and diabetes: the fosinopril versus amlodipine cardiovascular events trial (FACET)

Macrovascular disease is the major cause of mortality in persons with type 2 diabetes mellitus, and hypertension is an important factor contributing to this high prevalence. High blood pressure is about twice as common in persons with diabetes mellitus as in those without. Up to 75% of diabetes-related cardiovascular complications are attributed to hypertension. These observations are part of the rationale for recommendations for more aggressive lowering of blood pressure (to < 130/85 mm Hg) in persons with coexistent diabetes and hypertension. This may require therapy with a combination of antihypertensive agents. The Fosinopril versus Amlodipine Cardiovascular Events Trial (FACET), discussed herein, supports the case for combination therapy with an angiotensin-converting enzyme (ACE) inhibitor and a calcium antagonist in diabetic patients with hypertension.

Dyslipoproteinaemia and hyperoxidative stress in the pathogenesis of endothelial dysfunction in non-insulin dependent diabetes mellitus: an hypothesis

Endothelial dysfunction in non-insulin dependent (Type 2) diabetes mellitus (NIDDM) has implications for the pathogenesis of the two major complications, macrovascular disease and microangiopathy. Endothelial dysfunction is a consequence of a disturbance in the L-arginine/nitric oxide pathway. Its occurrence in NIDDM is well supported by both in vitro and in vivo studies. NIDDM results in diverse abnormalities in lipoprotein metabolism, the most significant being hypertriglyceridaemia which is associated with increased plasma concentrations of small dense LDL and low levels of HDL. Dysglycaemia results in hyperoxidative stress and increased formation of advanced-glycosylation endproducts, both of which enhance the oxidative modification of lipoprotein particles. Based on extensive in vitro studies and on human data, we generate the hypothesis that the development of endothelial dysfunction in NIDDM is a consequence of the effect of dyslipoproteinaemia, in particular increased circulatory concentrations of modified small dense LDL and of hyperoxidative stress on the formation, action and disposal of nitric oxide, by diverse molecular mechanisms; HDL is proposed to have a protective effect on these processes through its enzymic antioxidant properties. The hypothesis proposed is simple, testable and consistent with wide sources of evidence. The practical implications of the hypothesis and the existing opportunities for the prevention and reversal of endothelial dysfunction in NIDDM are also reviewed and discussed.