Dietary vitamin E supplementation lowers blood pressure in spontaneously hypertensive rats

Association of gamma-tocopherol serum concentrations and blood pressure among adults in the United States: a cross-sectional study

Background

hypertension is one of the major preventable risk factors for numerous diseases. The role of vitamin E in blood pressure (BP) has been controversial. We aimed to investigate the relationship between gamma-tocopherol serum concentration (GTSC) and BP.

Methods

Data from 15,687 US adults from the National Health and Nutrition Examination Survey (NHANES) were analyzed. The correlations of GTSC with systolic BP (SBP), diastolic BP (DBP), and prevalence of hypertension were investigated by multivariate logistic regression models, generalized summation models, and fitted smoothing curves. Subgroup analyses were performed to investigate possible effect modifiers between them.

Results

With each natural log increase in GTSC, SBP, and DBP increased by 1.28 mmHg (β 1.28, 95% CI 0.71-1.84) and 1.15 mmHg (β 1.15, 95% CI 0.72-1.57), respectively, both P for trend < 0.001; the prevalence of hypertension increased by 12% (OR 1.12, 95% CI 1.03-1.22), P for trend 0.008. In subgroup analysis, in drinkers, with each natural log increase in GTSC, SBP, and DBP increased by 1.77 mmHg (β 1.77,95% CI 1.13-2.41) and 1.37 mmHg (β 1.37,95% CI 0.9-1.85), respectively, whereas they were not correlated in non-drinkers.

Conclusion

GTSC was linearly and positively associated with SBP, DBP, and the prevalence of hypertension, and alcohol consumption may modify the relationship of GTSC with SBP and DBP.

Oxidative Stress, Antioxidants and Hypertension

As a major cause of morbidity and mortality globally, hypertension remains a serious threat to global public health. Despite the availability of many antihypertensive medications, several hypertensive individuals are resistant to standard treatments, and are unable to control their blood pressure. Regulation of the renin-angiotensin-aldosterone system (RAAS) controlling blood pressure, activation of the immune system triggering inflammation and production of reactive oxygen species, leading to oxidative stress and redox-sensitive signaling, have been implicated in the pathogenesis of hypertension. Thus, besides standard antihypertensive medications, which lower arterial pressure, antioxidant medications were tested to improve antihypertensive treatment. We review and discuss the role of oxidative stress in the pathophysiology of hypertension and the potential use of antioxidants in the management of hypertension and its associated organ damage.

The Ameliorative Effects of a Tocotrienol-Rich Fraction on the AGE-RAGE Axis and Hypertension in High-Fat-Diet-Fed Rats with Metabolic Syndrome

The clinical value of tocotrienols is increasingly appreciated because of the unique therapeutic effects that are not shared by tocopherols. However, their effect on metabolic syndrome is not well-established. This study aimed to investigate the effects of a tocotrienol-rich fraction (TRF) from palm oil in high-fat-diet-treated rats. Male, post-weaning Sprague Dawley rats were provided high-fat (60% kcal) diet for eight weeks followed by a TRF (60 mg/kg) treatment for another four weeks. Physical, metabolic, and histological changes were compared to those on control and high-fat diets respectively. High-fat feeding for eight weeks induced all hallmarks of metabolic syndrome. The TRF reversed systolic and diastolic hypertension, hypercholesterolemia, hepatic steatosis, impaired antioxidant defense, and myeloperoxidase hyperactivity triggered by the high-fat diet. It also conferred an inhibitory effect on protein glycation to reduce glycated hemoglobin A1c and advanced glycation end products (AGE). This was accompanied by the suppression of the receptor for advanced glycation end product (RAGE) expression in the liver. The treatment effects on visceral adiposity, glycemic control, triglyceride level, as well as peroxisome proliferator-activated receptor α and γ expression were negligible. To conclude, treatment with a TRF exhibited protective effects on the cardiovascular and liver health in addition to the amelioration of plasma redox imbalance and AGE-RAGE activation. Further investigation as a therapy for metabolic syndrome is therefore worthwhile.

Effects of the Intake of Sesame Seeds (Sesamum indicum L.) and Derivatives on Oxidative Stress: A Systematic Review

This study is aimed at assessing the scientific evidence on the effect of the intake of sesame seeds and derivatives on oxidative stress of individuals with systemic hypertension, dyslipidemia, and type 2 diabetes mellitus. A systematic review was conducted in seven databases (Lilacs, PubMed, ISI Web of Knowledge, Cochrane Library, Scopus, Trip Database, and Scielo) from September 2013 to January 2014. Clinical trials on the intake of sesame seeds and derivatives assessing the outcomes related to oxidative stress were retrieved. The risk of bias in the results of the studies selected was assessed according to the criteria of the Cochrane Handbook for Systematic Reviews of Interventions. This review included seven clinical trials showing that the intake of sesame resulted in the increase in enzymatic and nonenzymatic antioxidants, as well as in a reduction in oxidative stress markers. This was mainly observed with the use of sesame oil for hypertensive individuals during 2 months and black sesame meal capsules for prehypertensive individuals during four weeks. Most studies involved a small number of participants, sample size being considered a limiting factor for this review. In addition, a significant heterogeneity was observed in the type of population studied and the type of sesame and derivatives used, as well as their amount. The follow-up time was considered a limiting factor, because it varied in the different studies. The high risk of randomization and blinding biases found in the studies assessed determines lower scientific evidence of the results. Despite the limitations and biases identified in this systematic review, sesame showed relevant effects on oxidative stress, suggesting it could increase the antioxidant capacity.

Dietary Vitamin E Supplementation Attenuates Hypertension in Dahl Salt-Sensitive Rats

There is strong evidence that excess dietary salt (NaCl) is a major factor contributing to the development of hypertension. Salt-sensitive humans and rats develop hypertension even on a normal-salt diet. Salt sensitivity is associated with glucose intolerance and insulin resistance in both humans and animal models, including Dahl salt-sensitive (DSS) rats. In insulin resistance, impaired glucose metabolism leads to elevated endogenous aldehydes that bind sulfhydryl groups of membrane proteins, altering calcium channels, and increasing cytosolic free calcium ([Ca2+] i) and blood pressure. Vitamin E lowers tissue aldehyde conjugates, cytosolic [Ca2+] i, and blood pressure in spontaneously hypertensive rats and fructose-induced hypertensive Wistar Kyoto rats, models of insulin resistance. This study investigated the effect of a normal-salt diet on tissue aldehyde conjugates, cytosolic [Ca2+] i, and blood pressure in DSS rats and the effect of vitamin E supplementation on blood pressure and associated biochemical changes in these animals. Seven-week-old DSS rats were divided into 3 groups of 6 animals each and treated for 6 weeks with diets as follows: low-salt (0.4% NaCl); normal-salt (0.7% NaCl) and normal salt (0.7% NaCl) plus vitamin E (34 mg/kg feed). At completion, animals in the normal-salt group had significantly elevated systolic blood pressure, cytosolic [Ca2+] i, and tissue aldehyde conjugates compared with the low-salt group. They also showed smooth muscle cell hyperplasia in small arteries and arterioles of the kidney. Dietary vitamin E supplementation significantly attenuated the increase in systolic blood pressure and associated biochemical and histopathologic changes.

The effect of multivitamin-multimineral supplementation on the health status of inbred Wistar and spontaneously hypertensive rat strains

The nutraceutical industry has proliferated in recent years, with the most popular form of supplementation being the multivitamin-multimineral (MVMM) supplement. In the animal health sector, supplement use has also expanded. The objective of this study was to determine the effects of MVMM supplementation, beneficial or otherwise, on the general health status of the spontaneously hypertensive rat (SHR) strain, an animal model used in hypertension research. A commercially prepared MVMM supplement was given tri-weekly via oral dosing for 8 weeks to two groups of seven adult female SHR and Wistar rats. Their corresponding control groups were dosed with deionised water only. Systolic and diastolic blood pressure, fasting blood glucose, growth rate and food and water intake were measured weekly. At the end of 8 weeks, the animals were euthanased and a full blood profile, urine sodium to potassium ratio, blood urea nitrogen levels and total plasma cholesterol was measured for all groups. The results indicated that growth rate was higher for the SHR supplemented group. Supplementation also decreased diastolic blood pressure in both Wistar and SHR groups and increased red blood cell count and decreased total cholesterol in the SHR group. No adverse effects on the general health status of the animals were observed. MVMM supplementation may therefore be useful in aiding growth and delaying the onset of hypertension and its effects. It may also assist in the longevity of the breeding stock of SHR rats.

Ascorbic acid reduces gentamicin-induced nephrotoxicity in rats through the control of reactive oxygen species

BACKGROUND & AIM

Oxidative stress has been implicated in the pathophysiology of many forms of acute renal failure. The aim was examine the effect of vitamin C on oxidative stress and its relationship with nitric oxide on gentamicin-induced nephrotoxicity in rats.

METHODS

We utilized 32 Wistar rats allocated in four groups of eight animals each: control (CTL), vitamin C (VIT C), gentamicin (GENTA), and GENTA + VIT C; all groups were treated during seven days.

RESULTS

Serum urea and creatinine, serum and renal tissue malondialdehyde, blood superoxide anion and hydrogen peroxide in GENTA were increased vs CTL and vs VIT C, and decreased in GENTA + VIT C vs GENTA (all P < 0.05). Serum nitric oxide increased in GENTA vs CTL and vs VIT C, and reduced in GENTA + VIT C vs GENTA (P < 0.001). Urinary nitric oxide was reduced in GENTA vs CTL and vs VIT C and increased in GENTA + VIT C vs GENTA (P < 0.001). Severe degeneration of proximal tubules was present in GENTA, but only mild lesions were observed in GENTA + VIT C.

CONCLUSION

This study suggests that VIT C is a valuable tool to protect against GENTA-induced nephrotoxicity, by reducing reactive oxygen species and increasing the nitric oxide.

The antihypertensive effect of arginine

Hypertension is a leading cause of morbidity and mortality worldwide. Individuals with hypertension are at increased risk of stroke, heart disease and kidney failure. Although the etiology of essential hypertension has a genetic component, lifestyle factors such as diet play an important role. Reducing dietary salt is effective in lowering blood pressure in salt-sensitive individuals. Insulin resistance and altered glucose metabolism are common features of hypertension in humans and animal models, with or without salt sensitivity. Altered glucose metabolism leads to increased formation of advanced glycation end products. Insulin resistance is also linked to oxidative stress, and alterations in the nitric oxide pathway and renin angiotensin system. A diet rich in protein containing the semiessential amino acid, arginine, and arginine treatment, lowers blood pressure in humans and in animal models. This may be due to the ability of arginine to improve insulin resistance, decrease advanced glycation end products formation, increase nitric oxide, and decrease levels of angiotensin II and oxidative stress, with improved endothelial cell function and decreased peripheral vascular resistance. The Dietary Approaches to Stop Hypertension (DASH) study demonstrated that the DASH diet, rich in vegetables, fruits and low-fat dairy products; low in fat; and including whole grains, poultry, fish and nuts, lowered blood pressures even more than a typical North American diet with similar reduced sodium content. The DASH diet is rich in protein; the blood pressure-lowering effect of the DASH diet may be due to its higher arginine-containing protein, higher antioxidants and low salt content.

Role of methylglyoxal in essential hypertension

Altered glucose metabolism due to insulin resistance is a common feature of essential hypertension in humans and in animal models. Elevated endogenous aldehydes in genetic (spontaneously hypertensive rats) and acquired (fructose-induced hypertensive rats) models of essential hypertension may be due to increased production of the reactive aldehyde methylglyoxal, resulting from altered glucose metabolism. Excess methylglyoxal binds sulfhydryl groups of membrane proteins, altering calcium channels and increasing cytosolic free Ca(2+) and blood pressure. It has been demonstrated that methylglyoxal, when given in drinking water to Wistar-Kyoto rats, leads to an increase in kidney aldehyde conjugates, cytosolic free Ca(2+) concentration, decreased serum nitric oxide, renal vascular hyperplasia and hypertension. N-acetylcysteine (NAC) in the diet of these animals prevented hypertension and associated biochemical and morphological changes. NAC normalizes blood pressure by directly binding to excess methylglyoxal, thus normalizing Ca(2+) channels, cytosolic Ca(2+) and nitric oxide. NAC also leads to increased levels of tissue glutathione, a storage form of cysteine. Glutathione acts as a cofactor in the enzymatic catabolism of methylglyoxal. Cysteine and other antioxidants, such as vitamins B(6), C and E, and lipoic acid, prevented hypertension and associated biochemical and morphological changes in both genetic and acquired rat models of hypertension. The antihypertensive effect of dietary antioxidants may be due to an increase in tissue cysteine and glutathione, which improves glucose metabolism and decreases tissue methylglyoxal. A diet rich in these antioxidants may be effective in preventing and controlling hypertension in humans.

Structural features and bioactivities of the chitosan

Fourier transform infrared (FT-IR) spectroscopic studies (3500-600 cm(-1)) showed some different bands of chitosan. The absorption at 3439 cm(-1) is stretching vibration of -OH and -NH(2) bonds, indicating the association of the hydrogen-bond between them. The bands at 1659, 1599 and 1321 cm(-1) are attributable to the peaks of stretching vibrations of amide I (ν((C=O))), II (δ((N-H))), and the peak of stretching and bending vibrations of III (ν((C-N))) (δ((N-H))). The chitosan showed strong free radical scavenging activities. Pretreatment with chitosan significantly prevented the decrease of antioxidant enzymes activities and the increase of p-JNK at 3 h after renal ischemia and reduced renal tubular epithelial cell apoptosis.

Sesame oil exhibits synergistic effect with anti-diabetic medication in patients with type 2 diabetes mellitus

BACKGROUND & AIMS

Recently, studies have reported that sesame oil lowered blood pressure and improved antioxidant status in hypertensive and diabetic-hypertensive patients. The aim of this study was to evaluate the effectiveness of sesame oil with anti-diabetic (glibenclamide) medication as combination therapy in mild-to moderate diabetic patients.

METHODS

This open label study included sixty type 2 diabetes mellitus patients divided into 3 groups, receiving sesame oil (n = 18), 5 mg/day (single dose) of glibenclamide (n = 20), or their combination (n = 22). The patients were supplied with sesame oil [BNB Sesame oil(TM)] except glibenclamide group, and instructed to use approximately 35 g of oil/day/person for cooking, or salad preparation for 60 days. 12 h-fasting venous blood samples were collected at baseline (0 day) and after 60 days of the experiment for various biochemical analysis.

RESULTS

As compared with sesame oil and glibenclamide alone, combination therapy showed an improved anti-hyperglycemic effect with 36% reduction of glucose (P < 0.001 vs before treatment, P < 0.01 vs sesame oil monotherapy, P < 0.05 vs glibenclamide monotherapy) and 43% reduction of HbA(1c) (P < 0.001 vs before treatment, P < 0.01 vs sesame oil monotherapy, P < 0.05 vs glibenclamide monotherapy) at the end point. Significant reductions in the plasma TC, LDL-C and TG levels were noted in sesame oil (20%, 33.8% and 14% respectively vs before treatment) or combination therapies (22%, 38% and 15% respectively vs before treatment). Plasma HDL-C was significantly improved in sesame oil (15.7% vs before treatment) or combination therapies (17% before treatment). Significant (P < 0.001) improvement was observed in the activities of enzymatic and non-enzymatic antioxidants in patients treated with sesame oil and its combination with glibenclamide.

CONCLUSIONS

Sesame oil exhibited synergistic effect with glibenclamide and can provide a safe and effective option for the drug combination that may be very useful in clinical practice for the effective improvement of hyperglycemia.

Losartan improved respiratory function and coenzyme Q content in brain mitochondria of young spontaneously hypertensive rats

Increased production of free radicals and impairment of mitochondrial function are important factors in the pathogenesis of hypertension. This study examined the impact of hypertension on mitochondrial respiratory chain function, coenzyme Q(9) (CoQ(9)), coenzyme Q(10) (CoQ(10)), and alpha-tocopherol content in brain mitochondria, and the effect of blockade of angiotensin II type 1 receptors (AT1R) in the prehypertensive period on these parameters. In addition, blood pressure, heart and brain weight to body weight ratios, and the geometry of the basilar artery supplying the brain were evaluated. In the 9th week blood pressure and heart weight/body weight ratio were significantly increased and brain weight/body weight ratio was significantly decreased in spontaneously hypertensive rats (SHR) when compared to Wistar rats (WR). The cross-sectional area of the basilar artery was increased in SHR. Glutamate-supported respiration, the rate of ATP production, and concentrations of CoQ(9), CoQ(10), and alpha-tocopherol were decreased in SHR. The succinate-supported function and cytochrome oxidase activity were not changed. The treatment of SHR with losartan (20 mg/kg/day) from 4th to 9th week of age exerted preventive effect against hypertension, heart and arterial wall hypertrophy, and brain weight/body weight decline. After the therapy, the rate of ATP production and the concentration of CoQ increased in comparison to untreated SHR. The impairment of energy production and decreased level of lipid-soluble antioxidants in brain mitochondria as well as structural alterations in the basilar artery may contribute to increased vulnerability of brain tissue in hypertension. Long-term treatment with AT1R blockers may prevent brain dysfunction in hypertension.

Is the anti-hypertensive effect of dietary supplements via aldehydes reduction evidence based? A systematic review

Growing evidence indicates that insulin resistance and oxidative stress are involved in the pathogenesis of essential hypertension. In insulin-resistant states, like obesity and type 2 diabetes, altered glucose metabolism may lead to increased formation of methylglyoxal and other ketoaldehydes. Animal studies have shown that increased levels of endogenous aldehydes may lead to hypertension and oxidative stress. In animal models, the administration of vitamin C, vitamin B6 or alpha-lipoic acid reduced tissue levels of aldehydes, prevented oxidative stress, and lowered blood pressure. The purpose of this review article is to critically evaluate the available evidence for the role of dietary supplements in hypertension treatment.

Oxidative stress in prehypertension: rationale for antioxidant clinical trials

Prehypertension has been recently described as an independent category of blood pressure. Mounting evidence suggests that blood pressure in the prehypertensive range is associated with an increased risk of developing hypertension and cardiovascular disease. Several reports have assigned a critical role for oxidative stress in these disease processes. This review focuses on the clinical and experimental studies done in prehypertension and hypertension within the context of oxidative stress. This article also provides insights into why diverse therapeutic interventions, which have in common the ability to reduce oxidative stress, can impede or delay the onset of hypertension in prehypertension subjects.

Protective effect of L-propionylcarnitine in chronic cyclosporine-a induced nephrotoxicity

Cyclosporine (CyA) is an immunosuppressive agent used after solid organ transplantation, but its clinical use is limited by side effects, the most important of which is nephrotoxicity. In a previous work we demonstrated that L-propionylcarnitine (L-PC), a propionyl ester of L-carnitine, is able to prevent CyA-induced acute nephrotoxicity reducing lipid peroxidation in the isolated and perfused rat kidney. CyA administration was associated with a dose dependent increase in renovascular resistance prevented by a pretreatment with L-PC. The aim of the present study was to confirm L-PC protective effect, previously described in vitro, in an in vivo rat model. Chronic nephrotoxicity study was carried out for 28 days. L-PC was administered (i.p. 25 mg/kg b.w.) since the first day, while CyA treatment was performed for the last 21 days (by oral administration 25 mg/kg b.w.). We demonstrate that L-PC was able to significantly lower blood pressure in CyA treated animals and to prevent CyA induced decrease in creatinine clearance. Moreover renal tissue analysis revealed that L-PC was able to reduce lipid hydroperoxide content and morphological abnormalities associated to chronic CyA administration. In conclusion our study demonstrated for the first time in vivo that L-PC protects against functional and tissue damage associated to chronic CyA administration.

Measurement of methylglyoxal in rat tissues by electrospray ionization mass spectrometry and liquid chromatography

INTRODUCTION

Increased methylglyoxal formation due to insulin resistance has been implicated in the development of essential hypertension and in type-2 diabetic complications in animal models. Methylglyoxal is a highly reactive aldehyde, which binds sulfhydryl and amino groups of membrane proteins forming conjugates, advanced glycation end products (AGEs), which alter membrane function, leading to increased blood pressure and oxidative stress. We have shown elevated aldehyde conjugates in tissues of hypertensive rats which may be formed primarily from methylglyoxal. Our objective was to develop a specific method to measure methylglyoxal in rat tissues.

METHOD

This method involves preparation of plasma, blood and tissue homogenates, solid phase extraction of methylglyoxal, derivitization using o-phenylenediamine, further purification of derivatized products by solid phase extraction and quantification by electrospray ionization liquid chromatography mass spectrometry (ESI/LC/MS).

RESULTS

Methylglyoxal was highest in aorta followed by heart, liver, kidney and blood in that order in Sprague-Dawley rats. Levels of methylglyoxal in plasma were about an order of magnitude lower than that in tissues, but above the concentration used for the lowest calibration standard.

DISCUSSION

We have successfully developed an ESI/LC/MS method for quantification of methylglyoxal in rat tissues. The high selectivity of this method offers an advantage over other methods based on fluorescence. This method will allow the evaluation of methylglyoxal in essential hypertension and type-2 diabetes.

Alpha-tocopherol supplementation favorable effects on blood pressure, blood viscosity and cardiac remodeling of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) were separated into two groups (n = 6 per group) and, since 5 months old, received alpha-tocopherol (alpha-tocopherol acetate120 IU) or vehicle by daily gavage for 2 weeks. Blood viscosity, blood pressure (BP) and myocardial remodeling were analyzed. The SHRs treated with alpha-tocopherol showed a significant reduction of BP and a major reduction of blood viscosity in comparison with the control SHRs. The cardiac hypertrophy indices showed some differences when the two SHR groups were compared, the LV mass index was not different between the groups; however, the cardiomyocyte size was more than 20% smaller in SHRs treated with alpha-tocopherol than in control SHRs (P < .05). The intramyocardial vessels distribution was more than 45% greater in alpha-tocopherol-treated SHRs than in control rats, significantly improving the vessels-to-myocytes ratio in treated SHRs than in control SHRs (P < .05). In conclusion, present findings strongly suggest a beneficial effect of alpha-tocopherol supplementation to genetically hypertensive rats. This was observed by a reduction of both blood viscosity and BP, and a consequent cardiomyocyte hypertrophy in treated SHRs; an improvement of vessels-to-myocytes ratio in these rats was also observed.

Chronic N-acetylcysteine prevents fructose-induced insulin resistance and hypertension in rats

We examined if administration of an antioxidant compound protects against the development of insulin resistance and hypertension. Male rats were assigned randomly into four groups, and treated for 12 weeks with normal chow, normal chow plus N-acetylcysteine (1.5 g/day/kg), fructose (60% of diet), and fructose plus N-acetylcysteine. After 10 weeks, plasma triglyceride and 15-F2t-isoprostane, and insulin sensitivity were measured, and after 12 weeks, pressor response to methoxamine (15-60 microg/kg min) was assessed. Relative to normal chow-fed controls, the fructose-fed rats had increased blood pressure, plasma insulin, triglyceride and 15-F2t-isoprostane, and decreased insulin sensitivity; these changes were inhibited by N-acetylcysteine. Maximal pressor response to methoxamine was attenuated in the fructose-fed rats given N-acetylcysteine relative to the other three groups. Therefore, chronic treatment with N-acetylcysteine increases insulin sensitivity and prevents the blood pressure increase associated with fructose feeding in rats, the mechanism may involve the decrease of oxidative stress and alpha-adrenoceptor-mediated vasoconstriction.

Chronic N-Acetylcysteine Administration Prevents Development of Hypertension in N.OMEGA.-Nitro-L-Arginine Methyl Ester-Treated Rats: The Role of Reactive Oxygen Species

The aim of this study was to evaluate the production of superoxide anions as well as their role in the induction and/or maintenance of high blood pressure in rats with N(omega)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension. In the preventive study, we compared adult Wistar rats treated with L-NAME for 4 weeks with L-NAME-treated rats that were simultaneously given N-acetylcysteine (NAC) in their drinking water. Basal blood pressure, superoxide production, conjugated dienes concentration and NO synthase (NOS) activity were measured at the end of the experiment. Chronic NOS inhibition by L-NAME treatment increased blood pressure, enhanced superoxide production in the aorta and elevated the concentration of conjugated dienes in the heart and kidney. All these changes were prevented by simultaneous NAC administration, which augmented NOS activity in L-NAME-treated rats. In the therapeutic study, the effects of chronic NAC treatment were studied in rats with established hypertension which developed during 4 weeks of L-NAME administration. The blood pressure effects of chronic NAC treatment in established L-NAME hypertension were only moderate, although this treatment also restored NOS activity and lowered conjugated dienes in the heart and kidney. Since chronic NAC treatment had better preventive than therapeutic effects, it seems that reactive oxygen species play a more important role in the induction than in the maintenance of L-NAME hypertension.

Prevention of fructose-induced hypertension by dietary vitamins

Essential hypertension in humans may develop through a combination of genetic and environmental factors. Diet has long been under investigation as a potential effector of blood pressure. A diet high in sucrose or fructose can give rise to hyperlipidemia, insulin resistance and hypertension. Insulin resistance, glucose intolerance and oxidative stress are common features of hypertension. If glucose metabolism through the glycolytic pathway is impaired, as in insulin resistance, there will be a build-up of glyceraldehyde, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate with further metabolism to methylglyoxal, a highly reactive ketoaldehyde. Excess aldehydes can bind sulfhydryl groups of membrane proteins, altering membrane calcium channels, increasing cytosolic free calcium, peripheral vascular resistance and blood pressure. The presence of reactive aldehydes can also lead to oxidative stress. Dietary management through lower sucrose or fructose intake and increased consumption of vitamins improves glucose metabolism, lowers tissue aldehydes, increases anti-oxidant capacity and may also prevent hypertension.

Enhanced oxidative stress and impaired thioredoxin expression in spontaneously hypertensive rats

As oxidative stress plays a crucial role in the development and pathogenesis of hypertension, we analyzed the redox (reduction/oxidation) status in tissues from Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR), and stroke-prone SHR (SHRSP). Expressions of 8-hydroxy-2'-deoxyguanosine, a marker for oxidative stress-induced DNA damage, and protein carbonylation, a marker for oxidation status of proteins, were enhanced in aorta, heart, and kidney from SHR and SHRSP compared with WKY. The expression of redox regulating protein, thioredoxin (TRX), estimated by immunohistochemistry and western blot, and expression of TRX gene estimated by real-time RT-PCR were markedly suppressed in those tissues from SHR and SHRSP compared with WKY. Induction of TRX was impaired after angiotension II treatment in peripheral blood mononuclear cells isolated from SHR and SHRSP compared with those isolated from WKY. Although previous reports have shown that TRX is induced by a variety of oxidative stress in tissues, the present study shows the impaired induction of TRX in tissues from genetically hypertensive rats despite the relative increment of oxidative stress. Redox imbalance in essential organs may play a crucial role in the development and pathogenesis of hypertension.

Role of oxidative stress in age-related reduction of NO-cGMP-mediated vascular relaxation in SHR

The incidence of hypertension increases during the late stages of aging; however, the vascular mechanisms involved are unclear. We investigated whether the late stages of aging are associated with impaired nitric oxide (NO)-mediated vascular relaxation and enhanced vascular contraction and whether oxidative stress plays a role in the age-related vascular changes. Aging (16 mo) male spontaneously hypertensive rats (SHR) nontreated or treated for 8 mo with the antioxidant tempol (1 mM in drinking water) or vitamin E (E; 5,000 IU/kg chow) and vitamin C (C; 100 mg. kg-1. day-1 in drinking water) and adult (12 wk) male SHR were used. After the arterial pressure was measured, aortic strips were isolated from the rats for measurement of isometric contraction. The arterial pressure and phenylephrine (Phe)-induced vascular contraction were enhanced, and the ACh-induced vascular relaxation and nitrite/nitrate production were reduced in aging compared with adult rats. In aging rats, the arterial pressure was nontreated (188 +/- 4), tempol-treated (161 +/- 6), and E + C-treated (187 +/- 1 mmHg). Phe (10-5 M) caused an increase in active stress in nontreated aging rats (14.3 +/- 1.0) that was significantly (P < 0.05) reduced in tempol-treated (9.0 +/- 0.7) and E + C-treated rats (9.8 +/- 0.6 x 104 N/m2). ACh produced a small relaxation of Phe contraction in nontreated aging rats that was enhanced (P < 0.05) in tempol- and E + C-treated rats. l-NAME (10-4 M), inhibitor of NO synthase, or ODQ (10-5 M), inhibitor of cGMP production in smooth muscle, inhibited ACh relaxation and enhanced Phe contraction in tempol- and E + C-treated but not the nontreated aging rats. ACh-induced vascular nitrite/nitrate production was not different in nontreated, tempol- and E + C-treated aging rats. Relaxation of Phe contraction with sodium nitroprusside, an exogenous NO donor, was smaller in aging than adult rats but was not different between nontreated, tempol- and E + C-treated aging rats. Thus, during the late stages of aging in SHR rats, an age-related inhibition of a vascular relaxation pathway involving not only NO production by endothelial cells but also the bioavailability of NO and the smooth muscle response to NO is partially reversed during chronic treatment with the antioxidants tempol and vitamins E and C. The data suggest a role for oxidative stress in the reduction of vascular relaxation and thereby the promotion of vascular contraction and hypertension during the late stages of aging.

Dietary vitamin E and C supplementation prevents fructose induced hypertension in rats

In fructose-induced hypertension in Wistar-Kyoto (WKY) rats, excess endogenous aldehydes bind sulfhydryl groups of membrane proteins, altering membrane Ca2+ channels and increasing cytosolic free calcium and blood pressure. The thiol compound N-acetyl cysteine prevents fructose-induced hypertension by binding excess endogenous aldehydes and normalizing membrane Ca2+ channels and cytosolic free calcium. The aim of the present study was to investigate whether dietary supplementation of vitamin E and vitamin C which are known to increase tissue glutathione, a storage form of cysteine, prevents this hypertension and its associated biochemical and histopathological changes. Starting at 7 weeks of age, animals were divided into four groups of six animals each and treated as follows: control group, normal diet and normal drinking water; fructose group, normal diet and 4% fructose in drinking water; fructose + vitamin E group, diet supplemented with vitamin E (34 mg/ kg feed) and 4% fructose in drinking water; fructose + vitamin C group, diet supplemented with vitamin C (1,000 mg/kg feed) and 4% fructose in drinking water. At 14 weeks, systolic blood pressure, platelet [Ca2+]i and kidney and aortic aldehyde conjugates were significantly higher in the fructose group. These animals also displayed smooth muscle cell hyperplasia in the small arteries and arterioles of the kidneys. Dietary vitamin E and C supplementation in fructose-treated WKY rats prevented the increase in systolic blood pressure by normalizing cytosolic [Ca2+]i and kidney and aortic aldehyde conjugates and preventing adverse renal vascular changes.