Effect of chronic treatment with vitamin E on endothelial dysfunction in a type I in vivo diabetes mellitus model and in vitro

Impact of Lifestyles (Diet and Exercise) on Vascular Health: Oxidative Stress and Endothelial Function

Healthy lifestyle and diet are associated with significant reduction in risk of obesity, type 2 diabetes, and cardiovascular diseases. Oxidative stress and the imbalance between prooxidants and antioxidants are linked to cardiovascular and metabolic diseases. Changes in antioxidant capacity of the body may lead to oxidative stress and vascular dysfunction. Diet is an important source of antioxidants, while exercise offers many health benefits as well. Recent findings have evidenced that diet and physical factors are correlated to oxidative stress. Diet and physical factors have debatable roles in modulating oxidative stress and effects on the endothelium. Since endothelium and oxidative stress play critical roles in cardiovascular and metabolic diseases, dietary and physical factors could have significant implications on prevention of the diseases. This review is aimed at summarizing the current knowledge on the impact of diet manipulation and physical factors on endothelium and oxidative stress, focusing on cardiovascular and metabolic diseases. We discuss the friend-and-foe role of dietary modification (including different diet styles, calorie restriction, and nutrient supplementation) on endothelium and oxidative stress, as well as the potential benefits and concerns of physical activity and exercise on endothelium and oxidative stress. A fine balance between oxidative stress and antioxidants is important for normal functions in the cells and interfering with this balance may lead to unfavorable effects. Further studies are needed to identify the best diet composition and exercise intensity.

Roles of vitamins in stem cells

Stem cells can differentiate to diverse cell types in our body, and they hold great promises in both basic research and clinical therapies. For specific stem cell types, distinctive nutritional and signaling components are required to maintain the proliferation capacity and differentiation potential in cell culture. Various vitamins play essential roles in stem cell culture to modulate cell survival, proliferation and differentiation. Besides their common nutritional functions, specific vitamins are recently shown to modulate signal transduction and epigenetics. In this article, we will first review classical vitamin functions in both somatic and stem cell cultures. We will then focus on how stem cells could be modulated by vitamins beyond their nutritional roles. We believe that a better understanding of vitamin functions will significantly benefit stem cell research, and help realize their potentials in regenerative medicine.

Endothelium-dependent responses in the microcirculation observed in vivo

Endothelium-dependent responses were first demonstrated 40 years ago in the aorta. Since then, extensive research has been conducted in vitro using conductance vessels and materials derived from them. However, the microcirculation controls blood flow to vital organs and has been the focus of in vivo studies of endothelium-dependent dilation beginning immediately after the first in vitro report. Initial in vivo studies employed a light/dye technique for selectively damaging the endothelium to unequivocally prove, in vivo, the existence of endothelium-dependent dilation and in the microvasculature. Endothelium-dependent constriction was similarly proven. Endothelium-dependent agonists include acetylcholine (ACh), bradykinin, arachidonic acid, calcium ionophore A-23187, calcitonin gene-related peptide (CGRP), serotonin, histamine and endothelin-1. Normal and disease states have been studied. Endothelial nitric oxide synthase, cyclooxygenase and cytochrome P450 have been shown to generate the mediators of the responses. Some of the key enzyme systems generate reactive oxygen species (ROS) like superoxide which may prevent EDR. However, one ROS, namely H₂ O₂ , is one of a number of hyperpolarizing factors that cause dilation initiated by endothelium. Depending upon microvascular bed, a single agonist may use different pathways to elicit an endothelium-dependent response. Interpretation of studies using inhibitors of eNOS is complicated by the fact that these inhibitors may also inhibit ATP-sensitive potassium channels. Other in vivo observations of brain arterioles failed to establish nitric oxide as the mediator of responses elicited by CGRP or by ACh and suggest that a nitrosothiol may be a better fit for the latter.

Reversibility of endothelial dysfunction in diabetes: role of polyphenols

The endothelium, a thin single sheet of endothelial cells, is a metabolically active layer that coats the inner surface of blood vessels and acts as an interface between the circulating blood and the vessel wall. The endothelium through the secretion of vasodilators and vasoconstrictors serves as a critical mediator of vascular homeostasis. During the development of the vascular system, it regulates cellular adhesion and vessel wall inflammation in addition to maintaining vasculogenesis and angiogenesis. A shift in the functions of the endothelium towards vasoconstriction, proinflammatory and prothrombic states characterise improper functioning of these cells, leading to endothelial dysfunction (ED), implicated in the pathogenesis of many diseases including diabetes. Major mechanisms of ED include the down-regulation of endothelial nitric oxide synthase levels, differential expression of vascular endothelial growth factor, endoplasmic reticulum stress, inflammatory pathways and oxidative stress. ED tends to be the initial event in macrovascular complications such as coronary artery disease, peripheral arterial disease, stroke and microvascular complications such as nephropathy, neuropathy and retinopathy. Numerous strategies have been developed to protect endothelial cells against various stimuli, of which the role of polyphenolic compounds in modulating the differentially regulated pathways and thus maintaining vascular homeostasis has been proven to be beneficial. This review addresses the factors stimulating ED in diabetes and the molecular mechanisms of natural polyphenol antioxidants in maintaining vascular homeostasis.

α-Tocopherol Improves Microcirculatory Dysfunction on Fructose Fed Hamsters

Fructose, an everyday component of western diet associated to chronic hyperglycemia and enhanced free radical production, impairs endothelial function and supplementation with antioxidants might improve it. In this study we investigated if vitamin E could reverse the microvascular damage elicited by fructose. Male Syrian golden hamsters drank either 10% fructose solution (F) or filtered water (C), combined with three concentrations of vitamin E in their chows [zero, normal (VE) or 5X (5XVE)] during 60 days. Microvascular reactivity in response to topical application of acetylcholine (Ach; endothelium-dependent vasodilator) or sodium nitroprusside (SNP; endothelium-independent vasodilator) and macromolecular permeability increase induced by either 30 min ischemia followed by reperfusion (I/R) or topical application of histamine (5 μM) were assessed using the cheek pouch preparation. Compared to controls (drinking filtered water), fructose-drinking animals showed decreased vasodilatation to acetylcholine in all concentrations tested (-56.2% for 10^-9M, -53.9% for 10^-7M and -43.7% for 10^-5M). On the other hand, vitamin E supplementation resulted in increased responses for both water and fructose drinking groups (177.4% for F vs. F/5XVE and 241.6% for C vs. C/5XVE for 10^-5M Ach). Endothelial-independent vasodilatation explored by topical application of SNP was restored and even enhanced with the supplementation of 5X vitamin E in both groups (80.1% for F vs. F/5XVE; 144.2% for C vs. C/5XVE; 3.4% of difference for C/5XVE vs. F/5XVE on 10^-5M SNP). The number of leaky sites after I/R and histamine stimuli in vitamin E supplemented animals decreased (-25.1% and -15.3% for F vs. F/5XVE; and -21.7% and -16% of leaky sites comparing C vs. C/5XVE, respectively for I/R and histamine stimuli) pointing to tightening of the endothelial barrier for macromolecular permeability. Our results strongly suggest that vitamin E could improve the endothelial function and permeability barrier and also reverse impairments elicited by sugar overload.

Dietary fish oil improves endothelial function and lowers blood pressure via suppression of sphingolipid-mediated contractions in spontaneously hypertensive rats

OBJECTIVE

Long-chain n-3 polyunsaturated fatty acids from oily fish reduce blood pressure (BP) in hypertension. Previously, we demonstrated that hypertension is associated with marked alterations in sphingolipid biology and elevated ceramide-induced vasoconstriction. Here we investigated in spontaneously hypertensive rats (SHRs) whether fish oil improves endothelial function including reduced vascular contraction induced via the sphingolipid cascade, resulting in reduced BP.

METHODS

Twelve-week-old SHRs were fed a control or fish oil-enriched diet during 12 weeks, and BP was recorded. Plasma sphingolipid levels were quantified by mass spectrometry and the response of isolated carotid arteries towards different stimuli was measured. Furthermore, erythrocyte membrane fatty acid composition, thromboxane A2 formation and cytokine secretion in ex-vivo lipopolysaccharide-stimulated thoracic aorta segments were determined.

RESULTS

The fish oil diet reduced the mean arterial BP (P < 0.001) and improved endothelial function, as indicated by a substantially increased relaxation potential towards ex-vivo methacholine exposure of the carotid arteries (P < 0.001). The long-chain n-3 polyunsaturated fatty acid diet resulted in altered levels of specific (glucosyl)ceramide subspecies (P < 0.05), reduced membrane arachidonic acid content (P < 0.001) and decreased thromboxane concentrations in plasma (P < 0.01). Concomitantly, the fish oil diet largely reduced ceramide-induced contractions (P < 0.01), which are predominantly mediated by thromboxane. Furthermore, thromboxane A2 and interleukin-10 were reduced in supernatants of lipopolysaccharide-stimulated thoracic aorta of SHRs fed the fish oil diet while RANTES (regulated on activation, normal T-cell expressed and secreted) was enhanced. This may contribute to reduced vasoconstriction in vivo.

CONCLUSIONS

Dietary fish oil lowers BP in SHRs and improves endothelial function in association with suppression of sphingolipid-dependent vascular contraction.

Physiological mechanisms of vascular response induced by shear stress and effect of exercise in systemic and placental circulation

Physiological vascular function regulation is essential for cardiovascular health and depends on adequate control of molecular mechanisms triggered by endothelial cells in response to mechanical and chemical stimuli induced by blood flow. Endothelial dysfunction is one of the main risk factors of cardiovascular pathology, where the imbalance between the synthesis of vasodilator and vasoconstrictor molecules is common in the development of vascular disorders in systemic and placental circulation. In the placenta, an organ without autonomic innervations, the local control of vascular tone is critical for maintenance of fetal growth and mechanisms that underlie shear stress response induced by blood flow are essential during pregnancy. In this field, shear stress induced by moderate exercise is one of the most important mechanisms to improve vascular function through nitric oxide synthesis and stimulation of mechanical response of endothelial cells triggered by ion channels, caveolae, endothelial NO synthase, and vascular endothelial growth factor, among others. The demand for oxygen and nutrients by tissues and organs, especially in placentation and pregnancy, determines blood flow parameters, and physiological adaptations of vascular beds for covering metabolic requirements. In this regard, moderate exercise versus sedentarism shows potential benefits for improving vascular function associated with the enhancement of molecular mechanisms induced by shear stress. In this review, we collect evidence about molecular bases of physiological response to shear stress in order to highlight the relevance of moderate exercise-training for vascular health in adult and fetal life.

Erythritol is a sweet antioxidant

OBJECTIVE

Hyperglycemia, oxidative stress, and the onset and progression of diabetic complications are strongly linked. Reduction of oxidative stress could be of utmost importance in the long-term treatment of diabetic patients. The chronic nature of the disease calls for a mode of antioxidant intake that can be sustained easily, e.g., by the diet. Erythritol, a simple polyol, could be such a compound. It is orally available, well tolerated, and its chemical structure resembles that of mannitol, a well-known hydroxyl radical (HO*) scavenger.

METHODS

We studied the antioxidant properties of erythritol in vitro and subsequently determined its antioxidant activity and its vasoprotective effect in the streptozotocin diabetic rat.

RESULTS

Erythritol was shown to be an excellent HO* radical scavenger and an inhibitor of 2,2'-azobis-2-amidinopropane dihydrochloride-induced hemolysis but inert toward superoxide radicals. High-performance liquid chromatographic and electron spin resonance spectroscopy studies showed that the reaction of erythritol with hydroxyl radicals resulted in the formation of erythrose and erythrulose by abstraction of a carbon-bound hydrogen atom. In the streptozotocin diabetic rat, erythritol displayed an endothelium-protective effect and, in accordance with the in vitro experiments, erythrose was found in the urine of erythritol-consuming rats.

CONCLUSION

Erythritol acts as an antioxidant in vivo and may help protect against hyperglycemia-induced vascular damage.

HNF4 alpha and the Ca-channel TRPC1 are novel disease candidate genes in diabetic nephropathy

OBJECTIVE

The nuclear receptor hepatic nuclear factor 4 alpha (HNF 4 alpha) is a master regulatory protein and an essential player in the control of a wide range of metabolic processes. Dysfunction of HNF 4 alpha is associated with metabolic disorders including diabetes. We were particularly interested in investigating molecular causes associated with diabetic nephropathy.

RESEARCH DESIGN AND METHODS

Novel disease candidate genes were identified by the chromatin immunoprecipitation-cloning assay and by sequencing of immunoprecipitated DNA. Expression of candidate genes was analyzed in kidney and liver of Zucker diabetic fatty (ZDF) and of streptozotocin (STZ)-administered rats and after siRNA-mediated silencing of HNF 4 alpha.

RESULTS

We identified the calcium-permeable nonselective transient receptor potential cation channel, subfamily C, member 1 (TRPC1) as a novel HNF 4 alpha gene target. Strikingly, TRPC1 is localized on human chromosome 3q22-24, i.e., a region considered to be a hotspot for diabetic nephropathy. We observed a significant reduction of TRPC1 gene expression in kidney and liver of diabetic ZDF and of STZ-administered rats as a result of HNF 4 alpha dysfunction. We found HNF 4 alpha and TRPC1 protein expression to be repressed in kidneys of diabetic patients diagnosed with nodular glomerulosceloris as evidenced by immunohistochemistry. Finally, siRNA-mediated functional knock down of HNF 4 alpha repressed TRPC1 gene expression in cell culture experiments.

CONCLUSIONS

Taken collectively, results obtained from animal studies could be translated to human diabetic nephropathy; there is evidence for a common regulation of HNF 4 alpha and TRPC1 in human and rat kidney pathologies. We propose dysregulation of HNF 4 alpha and TRPC1 as a possible molecular rationale in diabetic nephropathy.

Endothelial dysfunction in diabetes mellitus

Diabetes mellitus is associated with an increased risk of cardiovascular disease, even in the presence of intensive glycemic control. Substantial clinical and experimental evidence suggest that both diabetes and insulin resistance cause a combination of endothelial dysfunctions, which may diminish the anti-atherogenic role of the vascular endothelium. Both insulin resistance and endothelial dysfunction appear to precede the development of overt hyperglycemia in patients with type 2 diabetes. Therefore, in patients with diabetes or insulin resistance, endothelial dysfunction may be a critical early target for preventing atherosclerosis and cardiovascular disease. Microalbuminuria is now considered to be an atherosclerotic risk factor and predicts future cardiovascular disease risk in diabetic patients, in elderly patients, as well as in the general population. It has been implicated as an independent risk factor for cardiovascular disease and premature cardiovascular mortality for patients with type 1 and type 2 diabetes mellitus, as well as for patients with essential hypertension. A complete biochemical understanding of the mechanisms by which hyperglycemia causes vascular functional and structural changes associated with the diabetic milieu still eludes us. In recent years, the numerous biochemical and metabolic pathways postulated to have a causal role in the pathogenesis of diabetic vascular disease have been distilled into several unifying hypotheses. The role of chronic hyperglycemia in the development of diabetic microvascular complications and in neuropathy has been clearly established. However, the biochemical or cellular links between elevated blood glucose levels, and the vascular lesions remain incompletely understood. A number of trials have demonstrated that statins therapy as well as angiotensin converting enzyme inhibitors is associated with improvements in endothelial function in diabetes. Although antioxidants provide short-term improvement of endothelial function in humans, all studies of the effectiveness of preventive antioxidant therapy have been disappointing. Control of hyperglycemia thus remains the best way to improve endothelial function and to prevent atherosclerosis and other cardiovascular complications of diabetes. In the present review we provide the up to date details on this subject.

Sub-chronic nicotine exposure induces intercellular communication failure and differential down-regulation of connexins in cultured human endothelial cells

BACKGROUND

Tobacco abuse is still among the most important cardiovascular risk factors in modern society. We investigated whether sub-chronic nicotine exposure can induce endothelial dysfunction and communication failure.

METHODS AND RESULTS

Primary human umbilical vein endothelial cells (HUVEC) were cultured with or without 1 microM nicotine given for the entire cell culture passage until confluence (5+/-0.5 days). Cells were cultured on special Petri dishes consisting of two compartments which communicated only via a small cellular bridge. We determined the propagation of the NO signal after stimulation of compartment A with ATP by simultaneous spectrophotometric measurement of ATP and methemoglobin formation indicating NO release in compartment B. In HUVECs grown under nicotine we found significantly reduced NO formation in compartment B 5 min after ATP stimulation of compartment A. At that time, there was no ATP detectable in compartment B. The difference in NO-signal-propagation could be abolished with the gap junction blocker Na-propionate. Western blot and immunohistochemistry indicated significantly reduced levels of endothelial gap junction proteins Cx37 and Cx43, but not Cx40. Dye transfer experiments revealed reduced number of communicating cells in nicotine exposed cells indicating the functional relevance.

CONCLUSIONS

These results - for the first time - show that nicotine induces functional intercellular communication failure in endothelial cells probably resulting from down-regulated Cx37 and Cx43 expression.

Effect of quercetin on altered vascular reactivity in aortas isolated from streptozotocin-induced diabetic rats

The present work examined ex vivo the acute effect of quercetin on diabetic rat aortic ring reactivity in response to endothelium-dependent (acetylcholine, ACh) and endothelium-independent (sodium nitroprusside, SNP) relaxants, and to the alpha(1)-adrenergic agonist phenylephrine (PE). Responses were compared to those of aortic rings from age- and sex-matched euglycemic rats. Compared to euglycemic rat aortic rings, diabetic rings showed less relaxation in response to ACh and SNP, and greater contraction in response to PE. Pretreatment with quercetin (10microM, 20min) increased ACh-induced relaxation and decreased PE-induced contraction in diabetic, but did not affect euglycemic rat aortic ring responses. Following pretreatment with the nitric oxide synthase inhibitor Nomega-nitro-l-arginine methyl ester (l-NAME, 10microM), quercetin reduced PE-induced contractions in both aortic ring types, although l-NAME attenuated the reduction in the diabetic rings. Quercetin did not alter SNP vasodilatory effects in either ring type compared to their respective controls. These findings indicate that quercetin acutely improved vascular responsiveness in blood vessels from diabetic rats, and that these effects were mediated, at least in part, by enhanced endothelial nitric oxide bioavailability. These effects of quercetin suggest the possible beneficial effects of quercetin in vivo in experimental diabetes and possibly in other cardiovascular diseases.

Effect of vitamin E and C supplementation combined with oral antidiabetic therapy on the endothelial dysfunction in the neonatally streptozotocin injected diabetic rat

BACKGROUND

This study investigates the contribution of vitamin supplementation to the efficacy of oral antidiabetic therapy on the reversal of endothelial dysfunction in a model of type-2 diabetes in rat.

METHODS

Diabetes was induced by streptozotocin injection to neonatal rats which were breastfed for 4 weeks, then fed 6 weeks with normal food or food supplemented with 2% vitamin E and 4% vitamin C. Some diabetic rats were treated with gliclazide for 6 weeks. Endothelium-dependent and -independent relaxations to acetylcholine and sodium nitroprusside (SNP) were recorded in thoracic aortic rings. Plasma insulin, HbA(1c) and antioxidant vitamins (A, C and E); plasma and aortic malondialdehyde (MDA) levels were determined.

RESULTS

Induction of diabetes resulted in decreased body weight and increased blood glucose, plasma insulin and HbA(1c) levels compared to controls. Acetylcholine relaxation was impaired in diabetic aorta, while SNP relaxation remained unchanged. Aortic MDA level was significantly higher, while plasma vitamin levels were lower in diabetic rats. Diminished acetylcholine response, enhanced aortic MDA level and decreased plasma vitamin levels were all restored after gliclazide and/or vitamin therapy. However, vitamin supplementation in control rats significantly impaired acetylcholine relaxations and increased aortic MDA levels.

CONCLUSIONS

Apparently, a selective endothelial dysfunction accompanies the imbalance in oxidant/antioxidant status in the type-2 diabetes model of rat and gliclazide and/or vitamin supplementation improves the impairment in diabetic vasculature. However, vitamin supplementation triggers oxidative stress in normal aortic tissue, thereby, leads to endothelial dysfunction; indicating that nutritional extra-supplementation of antioxidant vitamins isn't advisable for normal subjects, although it's beneficial in disease status.

Antioxidants and endothelium protection

The endothelium is a complex organ system that controls the homeostasis of the vasculature by integrating signals between the vascular wall and the vessel lumen. Under physiological conditions, it maintains a normal vascular tone and blood fluidity by elaborating a variety of factors, such as nitric oxide, prostacyclin and endothelin. However, in pathological situations the endothelium can also modify its phenotype facilitating vasoconstriction, inflammation, and thrombotic events. These abnormal responses manifest in different clinical settings, such as hypercholesterolemia, hypertension, diabetes mellitus, and occur in the absence of any morphological change of the vessel. The etiology of these altered endothelial functions is multi-factorial, and the mechanisms underlying them are complex and not yet fully elucidated. Today, there is substantial evidence that many endothelial functions are sensitive to the presence of reactive oxygen species and subsequent oxidative stress. Here, I will review the increasing number of studies showing that exogenous antioxidants can modulate the endothelium-dependent vasodilation responses, the homeostatic endothelium-leukocyte interactions, the balance between pro- and anti-thrombotic properties, and the vascular apoptotic responses. Finally, the non-antioxidant activities of some antioxidant will also be described.

Dietary habits and nutritional biomarkers in Italian type 1 diabetes families: evidence of unhealthy diet and combined-vitamin-deficient intakes

OBJECTIVE

Nutritional status and lifestyle can have profound effects on health. To analyse behaviour patterns in population subgroups of public health importance, we compared lifestyle, dietary intake of energy and selected nutrients, and nutritional biomarkers of type 1 diabetes (T1DM) patients and nondiabetic first-degree relatives against control subjects with no family history of T1DM.

DESIGN

A cross-sectional study.

SETTING

Department of Internal Medicine, University of Pisa, Italy.

SUBJECTS

A total of 209 individuals including 38 type 1 patients, 76 relatives, and 95 healthy subjects.

INTERVENTIONS

We used the European Prospective Investigation of Cancer and Nutrition questionnaires to assess dietary intake and lifestyle. Anthropometric indices and nutritional biomarkers (such as plasma levels of albumin, iron, lipids, homocysteine, vitamin B9 and vitamin B12 as well as urinary outputs of nitrogen, sodium and potassium) were evaluated.

RESULTS

Emerging health issues: (1) In total, 45% of controls were overweight. Increasing age was associated with increasing body mass and decreasing activity in sport in front of an unchanged energy intake. (2) The distribution of energy sources was incorrect. The proportion of caloric intake derived from total fat and cholesterol did not match general guidelines. Total dietary fibre consumption was assessed to be adequate (25 g/day) in only 27% of all the participants. (3) Estimated daily intakes of water-soluble vitamin B9 and fat-soluble vitamin D and vitamin E were deficient in comparison with dietary reference intakes. (4) The prevalence of adoption and maintenance of healthful eating and physical activity habits was higher in women and T1DM patients (probably as a consequence of the medical educational intervention). On the contrary, supportiveness of the family in term of changing the undesirable behaviours at home seemed to fail.

CONCLUSIONS

This study provides first evidence indicating unhealthy dietary behaviours, which could even predispose to the development of diabetes and cardiovascular complications, in subjects living in Pisa. The combination of vitamin B9 and vitamin E deprivation could be deleterious for endothelial function, since these antioxidants have been implicated in the modulation of nitric oxide and eicosanoid signalling.

Repaglinide administration improves brachial reactivity in type 2 diabetic patients

OBJECTIVE

Several studies have demonstrated that endothelial dysfunction plays a central role in diabetic mortality and that the prooxidative effect of postprandial hyperglycemia may actively contribute to atherogenesis. Thus, we investigated the possible effect of short-acting (repaglinide) and long-acting (glibenclamide) insulin secretagogues on endothelial function in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

Sixteen type 2 diabetic patients undergoing diet treatment and with poor glucose control volunteered for the study. The study was designed as a 4-month, randomized, cross-over, parallel-group trial of repaglinide (1 mg twice a day) versus glibenclamide (5 mg twice a day). All patients underwent the following investigations: 1) anthropometrics determinations, 2) blood sampling for routine laboratory analyses and for assessment of oxidative stress indexes, and 3) a brachial reactivity test to evaluate the endothelial function through the study of arterial diameter and flow changes with and without intraarterial infusion of N(G)-monomethyl-l-arginine, an inhibitor of nitric oxide synthase and tetraethylammonium chloride (TEA), a Ca(2+)-activated K(+) (K(Ca)) channel blocker. All patients were randomly assigned to receive repaglinide or glibenclamide for a period of 4 weeks.

RESULTS

Repaglinide administration was associated with a significant reduction in 2-h plasma glucose levels (P < 0.001) and in plasma thiobarbituric acid-reactive substances (TBARS) concentrations (P < 0.001) and with a significant increase in plasma antioxidant power, assessed as Trolox equivalent antioxidant capacity (TEAC) (P < 0.001), effects not observed after glibenclamide administration. With regard to brachial reactivity parameters, repaglinide but not glibenclamide was associated with a significant improvement in brachial reactivity parameters (P < 0.003 for all parameters). In contrast, intra-arterial infusion of L-NMMA and TEA reduced the beneficial effect of repaglinide.

CONCLUSIONS

Repaglinide administration, through good control of postprandial glucose levels, improves brachial reactivity and declines oxidative stress indexes.

RSK4 and PAK5 Are Novel Candidate Genes in Diabetic Rat Kidney and Brain

The orphan hepatic nuclear factor (HNF) HNF4alpha is of pivotal importance for liver development and hepatocellular differentiation and plays an essential role in a regulatory circuitry to control a wide range of metabolic processes. It also targets genes in other organs, including pancreas, kidney, intestine, and colon; promotes expression of an epithelial phenotype; triggers de novo formation of functional tight junctions; and contributes to epithelial cell polarity. In particular, HNF4alpha dysfunction leads to metabolic disorders, including diabetes. We used the chromatin immunoprecipitation (ChIP) cloning procedure and a bioinformatic approach to search for candidate genes associated with impaired liver, pancreas, and kidney function. We identified two novel targets regulated by HNF4alpha, which participate in the control, at least in part, in cell-cycle regulation and are members of the mitogen-activated kinase pathway. In multiple ChIP assays, ribosomal S6 kinase 4 (RSK4) and p21-activated kinase 5 (PAK5) were confirmed, and in vitro binding of HNF4alpha was evidenced by electrophoretic mobility shift assays (EMSA) using oligonucleotides, which harbor novel binding sites. We also used EMSA to probe for binding sites in promoters of HNF1alpha, apolipoprotein B, alpha1-antitrypsin, and angiotensinogen. We further studied RSK4 and PAK5 kinase expression in streptozotocin-induced diabetic rat kidney and brain and observed significant repression of HNF4alpha, RSK4, and PAK5 as determined by quantitative real-time reverse transcriptase-polymerase chain reaction. RSK4 and PAK5 may provide a molecular rationale for late-stage complications in disease, and further studies are warranted to explore these targets for the treatment of diabetic nephro- and neuropathy, frequently seen in patients with HNF4alpha dysfunction.

Intake of alpha-tocopherol is limited among US adults

OBJECTIVE

To examine alpha-tocopherol intake and food sources of alpha-tocopherol in the US population relative to current Dietary Reference Intakes for vitamin E.

DESIGN

We analyzed food source and intake data from the 1994 to 1996 Continuing Survey of Food Intakes by Individuals (CSFII) with added values for alpha-tocopherol from the US Department of Agriculture National Nutrient Database for Standard Reference Release 15.

SUBJECTS

Data from 5,056 men and 4,703 women aged 20 years and older were obtained from the 1994 to 1996 CSFII.

STATISTICAL ANALYSES PERFORMED

The complex design and sampling weights of the CSFII survey were taken into account to calculate the mean alpha-tocopherol intake from diet, the SEM, and the percent of the Estimated Average Requirements (EARs) for alpha-tocopherol intake by age group and region.

RESULTS

Only 8.0% of men and 2.4% of women in the United States met the new EARs for vitamin E intake from foods alone. Regionally, only 5.8% of men and 2.1% of women in the South met these EARs, relative to 9.0% and 2.6%, respectively, in the Northeast. Top contributors of alpha-tocopherol for men and women included ready-to-eat cereal, sweet baked products, white bread, beef, oils, and salad dressing.

APPLICATIONS/CONCLUSIONS

The majority of men and women in the United States fail to meet the current recommendations for vitamin E intake. Many of the top contributors are not particularly high sources of alpha-tocopherol but are consumed frequently. Greater inclusion of sources such as nuts, seeds, and vitamin E-rich oils, could improve intake of alpha-tocopherol.

Effect of a beta 2-adrenoceptor stimulation on hyperglycemia-induced endothelial dysfunction

To investigate whether beta(2)-adrenoceptors exist on endothelial cells and whether a beta(2)-adrenoceptor stimulation might prevent the development of hyperglycemia-induced endothelial dysfunction, porcine aortic endothelial cells (PAECs) were cultured and chronically exposed to either 5 mM D-glucose ("normoglycemia") or 20 mM D-glucose ("hyperglycemia"), with or without 100 nM salbutamol in absence or presence of beta(2)-adrenoceptor antagonist ICI 118,551 [1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxyl]-3-[(1-methylethyl)-amino]-2-butanol] or beta(1)-antagonist metoprolol. For osmotic control, PAECs were exposed to 15 mM L-glucose. We measured nitric oxide release using the met-hemoglobin assay and assessed beta-adrenoceptor density and subtypes by radioligand binding. Furthermore, we determined intracellular NADH and NADPH using high-performance liquid chromatography. High D-glucose concentrations but not L-glucose led to significantly reduced basal and stimulated nitric oxide release. Chronic salbutamol treatment significantly antagonized the impairment of the nitric oxide response, which was inhibited by ICI 118,551 but not by metoprolol. The number of giant cells was significantly increased in hyperglycemia, which could be prevented by salbutamol. Binding of the radioligand (-)-[(125)I]iodocyanopindolol revealed a total beta-adrenoceptor density of 29.8 +/- 3.7 (normoglycemic) and 30.3 +/- 3.6 (hyperglycemic) fmol/mg protein. Displacement by ICI 118,551 revealed beta-adrenoceptor subtype distribution with 30.3 +/- 4.4 (normoglycemic) and 29.1 +/- 3.8% beta(2)-adrenoceptors. NADH production increased in hyperglycemia, which was completely prevented by salbutamol. We conclude that hyperglycemia in PAEC induces endothelial dysfunction with impaired nitric oxide release and that this can be prevented by beta(2)-adrenoceptor stimulation.

Probucol restores the defective leukocyte–endothelial interaction in experimental diabetes

Defective leukocyte-endothelial interactions have been observed in experimental type 1 diabetes. One of the mechanisms involved in the late complications of diabetes mellitus is the formation of free radicals species. Antioxidant treatment has been demonstrated to have beneficial effects on the complications observed in this pathology. Using intravital microscopy to visualize venules of the internal spermatic fascia, we demonstrated that the defective leukocyte-endothelial interactions in alloxan-induced diabetic rats could be corrected by probucol treatment. The defects were quantitated by the number of leukocytes rolling along the venular endothelium, sticking to the venular wall after topical application of zymosan-activated plasma (10%-0.1 ml) or leukotriene B4 (1 microM/0.1 ml) and migrated after the application of a local irritant stimulus (carrageenan, 100 microg/0.1 ml). Leukocyte counts, erythrocyte velocity and venular shear rate, unaltered in diabetic rats, were not modified by this treatment. Reactive oxygen species formation by endothelial cells increased in diabetic preparations, and the reduced expression of adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) and P-selectin in cross-sections of the whole testis of the animals, were both restored by the antioxidant agent. Therefore, antioxidant treatment improves leukocyte-endothelial interaction in diabetic rats at least in part by restoring the expression of adhesion molecules in venules of diabetic rats.