Time course of asymmetric dimethylarginine (ADMA) and oxidative stress in fructose-hypertensive rats: A model related to metabolic syndrome

Interplay between efferocytosis and atherosclerosis

In an adult human, billions of cells die and turn over daily. During this process, many apoptotic cells are produced and subsequently cleared by phagocytes - a process termed efferocytosis, which plays a critical role in tissue homeostasis. Efferocytosis is an important mechanism in the control of inflammatory processes. Efficient efferocytosis inhibits accumulation of apoptotic cells/debris and maintains homeostasis before the onset of necrosis (secondary necrosis), which promotes inflammation or injury. During efferocytosis, mitochondrial fission and the oxidative stress process are linked through reactive oxygen species production and oxidative stress control. Autophagy plays an important role in inhibiting inflammation and apoptosis, and in promoting efferocytosis by activated inflammatory cells, particularly neutrophils and macrophages. Autophagy in neutrophils is activated by phagocytosis of pathogens or activation of pattern recognition receptors. Autophagy is essential for major neutrophil functions, including degranulation, reactive oxygen species production, oxidative stress and release of neutrophil extracellular cytokines. Failed efferocytosis is a key mechanism driving the development and progression of chronic inflammatory diseases, including atherosclerosis, cardiometabolic pathology, neurodegenerative disease and cancer. Impairment of efferocytosis in apoptotic macrophages is a determinant of atherosclerosis severity and the vulnerability of plaques to rupture. Recent results suggest that inhibition of efferocytosis in the protection of the myocardium results in reduced infiltration of reparatory macrophages into the tissue, in association with oxidative stress reduction. Activated macrophages play a central role in the development and resolution of inflammation. The resolution of inflammation through efferocytosis is an endogenous process that protects host tissues from prolonged or excessive inflammation. Accordingly, therapeutic strategies that ameliorate efferocytosis control would be predicted to dampen inflammation and improve resolution. Thus, therapies targeting efferocytosis will provide a new means of treating and preventing cardiovascular and metabolic diseases involving the chronic inflammatory state.

N-acetyl cysteine can blunt metabolic and cardiovascular effects via down-regulation of cardiotrophin-1 in rat model of fructose-induced metabolic syndrome

In this study, we investigated the ability of N-acetyl cysteine (NAC) to alleviate the metabolic disorders in fructose-induced metabolic syndrome (MS) in male rats and to examine its protective effect on aortic and cardiac tissues via its influence on cardiotrophin-1 (CT-1) expression. NAC (20 mg/kg b.w./day) was administered to fructose induced MS animals for 12 weeks. Chronic fructose consumption (20% w/v) increased body weight gain, relative heart weight, systolic blood pressure (SBP), diastolic blood pressure (DBP), insulin resistance (IR), and associated with metabolic alterations. Histological and immunohistochemical examination revealed aortic stiffness and myocardial degeneration and fibrosis together with increased CT-1 expression. Treatment with NAC improved IR, SBP, DBP, and mitigated dyslipidaemia and oxidative stress. Additionally, NAC down-regulated CT-1 expression in the heart and aorta. These findings demonstrated the protective effect of NAC against aortic and myocardial degeneration and fibrosis through down-regulation of CT-1 in fructose induced MS animal model.

The investigation of antioxidant and anti-inflammatory potentials of apitherapeutic agents on heart tissues in nitric oxide synthase inhibited rats via Nω-nitro-L-arginine methyl ester

BACKGROUND

High blood pressure effects heart and vessels. Development of pathogenesis is the result of oxidative stress. We aimed to investigate the antioxidant effects of propolis, caffeic acid phenethyl ester (CAPE), and pollen on the hearts of rats which chronic nitric oxide synthase (NOS) inhibited through Nω-nitro-L-arginine methyl ester (L-NAME). Paraoxonase 1 (PON1), total antioxidant status (TAS), total oxidant status (TOS), oxidative stress index (OSI), asymmetric dimethylarginine (ADMA), and nuclear factor-κB (NF-κB) were analyzed on the heart.

MATERIAL AND METHODS

Sprague-Dawley rats were divided five groups of seven rats in every group; Group I: Control, Group II: L-NAME, Group III: L-NAME+propolis, Group IV: L-NAME+CAPE and Group V: L-NAME+pollen. L-NAME become dissolved in regular saline (0.9% NaCl w/v). The ethanolic extract of propolis (200 mg/kg/days, gavage), pollen (100 mg/kg/days, by gavage), CAPE (50 µM/kg/days, intraperitoneally), and the NOS inhibitor L-NAME (40 mg/kg, intraperitoneally) had been administered.

RESULTS

Blood pressure (BP) of rats treated with propolis, CAP,E and pollen statistically significant decreased. Decreasing in BP of the rats of pollen group was more than CAPE and propolis groups (P < .05). PON1 and TAS levels decreased in L-NAME-treated groups (P < .05), but ranges have been better in propolis, CAPE and pollen groups. TOS, ADMA and NF-κB levels increased (P < .05) in L-NAME group; however, these parameters were lower (P < .05) in propolis and CAPE groups (P < .05).

CONCLUSIONS

Vasorelaxant properties and free radical scavenging actions of propolis, CAPE, and pollen may reduce the oxidative stress and blood pressure in the rats chronic NOS inhibited through L-NAME.

Orally administered octacosanol improves some features of high fructose-induced metabolic syndrome in rats

We examined whether orally administered octacosanol, a long-chain aliphatic saturated alcohol, improves the features of high fructose-induced metabolic syndrome in rats. Five-week-old rats were fed a high fructose diet containing 60% fructose for 3 weeks. Then, the high fructose fed rats received a daily single oral administration of octacosanol (10 or 100 mg/kg body weight) with high fructose feeding for one week. Three- or four-week high fructose feeding increased insulin resistance, serum insulin, triglyceride, total cholesterol, free fatty acids, uric acid, and lipid peroxide concentrations, and hepatic triglyceride and cholesterol contents significantly and decreased serum high-density lipoprotein cholesterol and adiponectin concentrations significantly but did not affect blood pressure and hepatic lipid peroxide and reduced glutathione contents. Four-week high fructose feeding decreased hepatic ascorbic acid content significantly. Oral administration of octacosanol (10 or 50 mg/kg body weight) to high fructose-fed rats for the last 1-week fructose diet feeding attenuated these changes except serum insulin level and insulin resistance significantly and increased hepatic reduced glutathione content significantly. The higher dose of Oct decreased hepatic lipid peroxide content significantly. These results indicate that orally administered octacosanol improves dyslipidemia, hyperuricemia, hypoadiponectinemia, and oxidative stress associated with the features of high fructose-induced metabolic syndrome rats.

Homocysteine and Asymmetrical Dimethylarginine in Diabetic Rats Treated with Docosahexaenoic Acid-Loaded Zinc Oxide Nanoparticles

Hyperglycemia, the hallmark of diabetes mellitus, is considered one of the endothelial dysfunction risk factors, the main reason of vascular complication. In this study, we aimed to evaluate homocysteine (Hcy) and asymmetrical dimethylarginine (ADMA) levels in diabetic rats and the possibility to attenuate the elevation of these two parameters by supplementation of docosahexaenoic acid (DHA) alone or loaded zinc oxide nanoparticles (ZnONPs) to improve endothelial dysfunction in streptozotocin (STZ)-induced diabetic rats. Forty male albino rats weighing 180-200 g were classified as control, diabetic, diabetic treated with DHA, and diabetic treated with DHA-loaded zinc oxide nanoparticles (DHA/ZnONPs) groups. Fasting blood glucose, insulin, ADMA, Hcy, and nitric oxide (NO) were estimated. Fatty acids (linoleic acid (LA), arachidonic acid (AA), DHA, α-linolenic acid (ALA), and oleic acid (OA)) were also evaluated by reversed phase HPLC using a UV detector. The results showed that fasting blood sugar, insulin resistance, LA, AA, OA, ADMA, and Hcy increased significantly in diabetic rats compared with control while fasting insulin, DHA, ALA, and NO decreased significantly in diabetic rats. In both treated groups, fasting blood sugar, insulin resistance, LA, AA, OA, ADMA, and Hcy significantly decreased as compared with the diabetic group while fasting insulin, DHA, ALA, and NO were significantly increased. In conclusion, DHA and DHA/ZnONP supplementation protect against diabetic complications and improve endothelial dysfunction as well as hyperhomocysteinemia in diabetes. DHA/ZnONP-treated group appeared more efficient than DHA alone.

Impact of Alpha-Lipoic Acid Chronic Discontinuous Treatment in Cardiometabolic Disorders and Oxidative Stress Induced by Fructose Intake in Rats

Insulin resistance (IR) and cardiometabolic disorders are the main consequences of today’s alimentary behavior. This study evaluates the effects of a chronic-discontinuous treatment with alpha-lipoic acid (AL), an antioxidant substance that improves glycemic control associated with diabetes mellitus, on metabolic disorders and plasma oxidative stress induced by fructose intake, in rats. Sprague-Dawley rats (48 animals) were randomized into two series (n = 24): rats fed with standard chow or with standard chow supplemented with 60% fructose. In each of the two series, for 2 weeks/month over 12 weeks, a group of rats (n = 12) was intraperitoneally injected with NaCl 0.9%, and a second group (n = 12) received AL 50 mg/kg/day. Body weight, glycemia, and systolic blood pressure were monitored throughout the study. After 12 weeks, IR, plasma lipoproteins, uric acid, transaminase activities, and oxidative stress markers were assessed. The high fructose-enriched diet induced cardiometabolic disorders (hypertension, hyperglycemia, IR and dyslipidemia), an increase in uric acid concentration, transaminase activities and C-reactive protein level. This diet also enhanced plasma products of lipid and protein oxidation, homocysteine level, and decreased GSH/GSSG ratio. In this field, there is evidence to indicate that oxidative stress plays an important role in the etiology of diabetic complications. AL discontinuous treatment prevents the metabolic disorders induced by fructose intake, reduced plasma lipid and protein oxidation-products, and restored the GHS/GSSG ratio. Our study proves a promising potential of the chronic-discontinuous treatment of AL and highlights the pleiotropic effects of this antioxidant substance in metabolic disorders such as diabetes.

Redox Functions of Heme Oxygenase-1 and Biliverdin Reductase in Diabetes

In patients with diabetes, the hyperglycemia-driven excess generation of reactive oxygen species (ROS) induces oxidative stress (OS) in a variety of tissues. OS is closely associated with chronic inflammation and has a key role in the pathogenesis of vascular complications. The enzymes that generate ROS and gasotransmitters are redox regulated and are implicated in cellular signaling. As a result of cellular metabolism, cells produce significant amounts of carbon monoxide (CO), mainly from heme degradation catalyzed by heme oxygenases (HOs). These reactions also generate biliverdin, bilirubin (BR), and iron. The conversion of biliverdin to BR is catalyzed by biliverdin reductase-A (BVR-A). In this review, we focus on the importance of the HO-1/CO system and BVR in the pathophysiology and therapy of inflammation associated with diabetes.

Effects of propolis, caffeic acid phenethyl ester, and pollen on renal injury in hypertensive rat: An experimental and theoretical approach

The objective of this study was to evaluate the antioxidant effects of propolis, caffeic acid phenethyl ester (CAPE; active compound in propolis), and pollen on biochemical oxidative stress biomarkers in rat kidney tissue inhibited by N^ω -nitro-L-arginine methyl ester (L-NAME). The biomarkers evaluated were paraoxonase (PON1), oxidative stress index (OSI), total antioxidant status (TAS), total oxidant status (TOS), asymmetric dimethylarginine (ADMA), and nuclear factor kappa B (NF-κB). TAS levels and PON1 activity were significantly decreased in kidney tissue samples in the L-NAME-treated group (P < 0.05). The levels of TAS and PONI were higher in the L-NAME plus propolis, CAPE, and pollen groups compared with the L-NAME-treated group. TOS, ADMA, and NF-κB levels were significantly increased in the kidney tissue samples of the L-NAME-treated group (P < 0.05). However, these parameters were significantly lower in the L-NAME plus propolis, CAPE, and pollen groups (P < 0.05) compared with rats administered L-NAME alone (P < 0.05). Furthermore, the binding energy of CAPE within catalytic domain of glutathione reductase (GR) enzyme as well as its inhibitory mechanism was determined using molecular modeling approaches. In conclusion, experimental and theoretical data suggested that oxidative alterations occurring in the kidney tissue of chronic hypertensive rats may be prevented via active compound of propolis, CAPE administration.

Lack of Reactive Oxygen Species Deteriorates Blood Pressure Regulation in Acute Stress

This study investigated the contribution of reactive oxygen species (ROS) to blood pressure regulation in conscious adult male Wistar rats exposed to acute stress. Role of ROS was investigated in rats with temporally impaired principal blood pressure regulation systems using ganglionic blocker pentolinium (P, 5 mg/kg), angiotensin converting enzyme inhibitor captopril (C, 10 mg/kg), nitric oxide synthase inhibitor L-NAME (L, 30 mg/kg) and superoxide dismutase mimeticum tempol (T, 25 mg/kg). Mean arterial pressure (MAP) was measured by the carotid artery catheter and inhibitors were administered intravenously. MAP was disturbed by a 3-s air jet, which increased MAP by 35.2±3.0 % vs. basal MAP after the first exposure. Air jet increased MAP in captopril- and tempol-treated rats similarly as observed in saline-treated rats. In pentolinium-treated rats stress significantly decreased MAP vs. pre-stress value. In L-NAME-treated rats stress failed to affect MAP significantly. Treatment of rats with P+L+C resulted in stress-induced MAP decrease by 17.3±1.3 % vs. pre-stress value and settling time (20.1±4.2 s). In P+L+C+T-treated rats stress led to maximal MAP decrease by 26.4±2.2 % (p<0.005 vs. P+L+C) and prolongation of settling time to 32.6±3.3 s (p<0.05 vs. P+L+C). Area under the MAP curve was significantly smaller in P+L+C-treated rats compared to P+L+C+T-treated ones (167±43 vs. 433±69 a.u., p<0.008). In conclusion, in rats with temporally impaired blood pressure regulation, the lack of ROS resulted in greater stress-induced MAP alterations and prolongation of time required to reach new post-stress steady state.

Transient Decrease in Circulatory Testosterone and Homocysteine Precedes the Development of Metabolic Syndrome Features in Fructose-Fed Sprague Dawley Rats

Background. Increased fructose consumption is linked to the development of metabolic syndrome (MS). Here we investigated the time course of development of MS features in high-fructose-fed Sprague Dawley rats along with circulatory testosterone and homocysteine levels. Methods. Rats were divided into control and experimental groups and fed with diets containing 54.5% starch and fructose, respectively, for 4, 12, and 24 weeks. Plasma testosterone and homocysteine levels were measured along with insulin, glucose, and lipids. Body composition, insulin resistance, and hepatic lipids were measured. Results. Increase in hepatic triglyceride content was first observed in metabolic disturbance followed by hypertriglyceridemia and systemic insulin resistance in fructose-fed rats. Hepatic lipids were increased in time-dependent manner by fructose-feeding starting from 4 weeks, but circulatory triglyceride levels were increased after 12 weeks. Fasting insulin and Homeostatis Model Assessment of Insulin Resistance (HOMA-IR) were increased after 12 weeks of fructose-feeding. Decreased visceral adiposity, circulatory testosterone, and homocysteine levels were observed after 4 weeks of fructose-feeding, which were normalized at 12 and 24 weeks. Conclusions. We conclude that transient decrease in circulatory testosterone and homocysteine levels and increased hepatic triglyceride content are the earliest metabolic disturbances that preceded hypertriglyceridemia and insulin resistance in fructose-fed SD rats.

Omeprazole impairs vascular redox biology and causes xanthine oxidoreductase-mediated endothelial dysfunction

Proton pump inhibitors (PPIs) are widely used drugs that may increase the cardiovascular risk by mechanisms not entirely known. While PPIs increase asymmetric dimethylarginine (ADMA) levels and inhibit nitric oxide production, it is unknown whether impaired vascular redox biology resulting of increased xanthine oxidoreductase (XOR) activity mediates PPIs-induced endothelial dysfunction (ED). We examined whether increased XOR activity impairs vascular redox biology and causes ED in rats treated with omeprazole. We also examined whether omeprazole aggravates the ED found in hypertension. Treatment with omeprazole reduced endothelium-dependent aortic responses to acetylcholine without causing hypertension. However, omeprazole did not aggravate two-kidney, one-clip (2K1C) hypertension, nor hypertension-induced ED. Omeprazole and 2K1C increased vascular oxidative stress as assessed with dihydroethidium (DHE), which reacts with superoxide, and by the lucigenin chemiluminescence assay. The selective XOR inhibitor febuxostat blunted both effects induced by omeprazole. Treatment with omeprazole increased plasma ADMA concentrations, XOR activity and systemic markers of oxidative stress. Incubation of aortic rings with ADMA increased XOR activity, DHE fluorescence and lucigenin chemiluminescence signals, and febuxostat blunted these effects. Providing functional evidence that omeprazole causes ED by XOR-mediated mechanisms, we found that febuxostat blunted the ED caused by omeprazole treatment. This study shows that treatment with omeprazole impairs the vascular redox biology by XOR-mediated mechanisms leading to ED. While omeprazole did not further impair hypertension-induced ED, further studies in less severe animal models are warranted. Our findings may have major relevance, particularly to patients with cardiovascular diseases taking PPIs.

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Proton pump inhibitors are widely used and increase the cardiovascular risk by unknown mechanisms.

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Omeprazole increased vascular oxidative stress and caused endothelial dysfunction (ED).

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Those effects were dependent on the prooxidant enzyme xanthine oxidoreductase (XOR).

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XOR inhibition by the selective XOR inhibitor febuxostat blunted both effects induced by omeprazole.

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Omeprazole impairs the vascular redox biology by XOR-mediated mechanisms leading to ED.

Immunoreactivity of glucose transporter 8 is localized in the epithelial cells of the choroid plexus and in ependymal cells

High fructose intake is known to be associated with increased plasma triglyceride concentration, impaired glucose tolerance, insulin resistance, and high blood pressure. In addition, excess fructose intake is also thought to be a risk factor for dementia. Previous immunohistochemical studies have shown the presence of glucose transporter 5 (GLUT5), a major transporter of fructose, in the epithelial cells of the choroid plexus and ependymal cells in the brains of humans, rats, and mice, while GLUT2, a minor transporter of fructose, was localized in the ependymal cells of rat brain. In this study, immunoreactivity for the fructose transporter GLUT8 was observed in the cytoplasm of the epithelial cells in the choroid plexus and in the ependymal cells of the brains of humans and mice. These structures were not immunoreactive for GLUT7, GLUT11, and GLUT12. Our findings support the hypothesis of the transport of intravascular fructose through the epithelial cells of the choroid plexus and the ependymal cells.

Asymmetric Dimethylarginine Limits the Efficacy of Simvastatin Activating Endothelial Nitric Oxide Synthase

Background

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of endothelial nitric oxide synthase (eNOS), is considered a risk factor for the pathogenesis of cardiovascular diseases. Simvastatin, a lipid‐lowering drug with other pleiotropic effects, has been widely used for treatment of cardiovascular diseases. However, little is known about the effect and underlying molecular mechanisms of ADMA on the effectiveness of simvastatin in the vascular system.

Methods and Results

We conducted a prospective cohort study to enroll 648 consecutive patients with coronary artery disease for a follow‐up period of 8 years. In patients with plasma ADMA level ≥0.49 μmol/L (a cut‐off value from receiver operating characteristic curve), statin treatment had no significant effect on cardiovascular events. We also conducted randomized, controlled studies using in vitro and in vivo models. In endothelial cells, treatment with ADMA (≥0.5 μmol/L) impaired simvastatin‐induced nitric oxide (NO) production, endothelial NO synthase (eNOS) phosphorylation, and angiogenesis. In parallel, ADMA markedly increased the activity of NADPH oxidase (NOX) and production of reactive oxygen species (ROS). The detrimental effects of ADMA on simvastatin‐induced NO production and angiogenesis were abolished by the antioxidant, N‐acetylcysteine, NOX inhibitor, or apocynin or overexpression of dimethylarginine dimethylaminohydrolase 2 (DDAH‐2). Moreover, in vivo, ADMA administration reduced Matrigel plug angiogenesis in wild‐type mice and decreased simvastatin‐induced eNOS phosphorylation in aortas of apolipoprotein E–deficient mice, but not endothelial DDAH‐2‐overexpressed aortas.

Conclusions

We conclude that ADMA may trigger NOX‐ROS signaling, which leads to restricting the simvastatin‐conferred protection of eNOS activation, NO production, and angiogenesis as well as the clinical outcome of cardiovascular events.

Glucose transporter 5 (GLUT5)-like immunoreactivity is localized in subsets of neurons and glia in the rat brain

This study aimed at examining the distribution of glucose transporter 5 (GLUT5), which preferentially transports fructose, in the rat brain by immunohistochemistry and Western blotting. Small immunoreactive puncta (less than 0.7μm) were sparsely distributed all over the brain, some of which appeared to be associated with microglial processes detected by an anti-ionized calcium-binding adapter molecule 1 (Iba-1) monoclonal antibody. In addition, some of these immunoreactive puncta seemed to be associated with tanycyte processes that were labeled with anti-glial fibrillary acidic protein (GFAP) monoclonal antibody. Ependymal cells were also found to be immunopositive for GLUT5. Furthermore, several noticeable GLUT5 immunoreactive profiles were observed. GLUT5 immunoreactive neurons, confirmed by double staining with neuronal nuclei (NeuN), were seen in the entopeduncular nucleus and lateral hypothalamus. Cerebellar Purkinje cells were immunopositve for GLUT5. Dense accumulation of immunoreactive puncta, some of which were neuronal elements (confirmed by immunoelectron microscopy), were observed in the optic tract and their terminal fields, namely, superior colliculus, pretectum, nucleus of the optic tract, and medial terminal nucleus of the optic tract. In addition to the associated areas of the visual system, the vestibular and cochlear nuclei also contained dense GLUT5 immunoreactive puncta. Western blot analysis of the cerebellum indicated that the antibody used recognized the 33.5 and 37.0kDa bands that were also contained in jejunum and kidney extracts. Thus, these results suggest that GLUT5 may transport fructose in subsets of the glia and neurons for an energy source of these cells.

Asymmetric dimethylarginine in somatically healthy schizophrenia patients treated with atypical antipsychotics: a case-control study

BACKGROUND

Schizophrenia is associated with increased cardiovascular morbidity and mortality. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of the nitric oxide synthase, and the L-arginine:ADMA ratio are markers of endothelial dysfunction that predict mortality and adverse outcome in a range of cardiovascular disorders. Increased ADMA levels may also lead to increased oxidative stress. We hypothesized that ADMA and the L-arginine:ADMA ratio are increased in somatically healthy schizophrenia patients treated with atypical antipsychotics (AAP), and that the ADMA and the L-arginine: ADMA ratio are positively correlated to measures of oxidative stress.

METHODS

We included 40 schizophrenia patients treated with AAP, but without somatic disease or drug abuse, and 40 healthy controls. Plasma concentrations of ADMA and L-arginine were determined by high-performance liquid chromatography. Data were related to markers of systemic oxidative stress on DNA, RNA and lipids, as well as measures of medication load, duration of disease and current symptomatology.

RESULTS

Plasma ADMA and the L-arginine:ADMA ratio did not differ between schizophrenia patients and controls. Furthermore, ADMA and the L-arginine:ADMA ratio showed no correlations with oxidative stress markers, medication load, or Positive and Negative Syndrome Scale scores.

CONCLUSIONS

Schizophrenia and treatment with AAP was not associated with increased levels of plasma ADMA or the L-arginine:ADMA ratio. Furthermore, plasma levels of ADMA were not associated with levels of systemic oxidative stress in vivo.

Resveratrol improves high-fructose-induced vascular dysfunction in rats

High levels of fructose in the diet results in metabolic abnormalities and vascular disorders. In this study, the effect of resveratrol (RES) on vascular relaxation and contraction responses was examined in the aorta of high-fructose (HFr)-fed rats. mRNA expressions of aortic sirtuin 1 (SIRT1), GLUT5, and aldolase B were also investigated. Rats were given fructose (30%) and (or) RES (50 mg·L−1) in their drinking water for 8 weeks. In the HFr-fed rats, plasma levels of arginine and the ratio of arginine:asymmetric dimethylarginine (ADMA) decreased, whereas leptin levels increased. Decreased relaxation and increased contractile responses were detected in aortic rings. However, the aortic expressions of SIRT1, GLUT5, and aldolase B remained unchanged. RES treatment restored HFr-induced vascular dysfunction without improvements in insulin resistance. Treatment of HFr-fed rats with RES increased plasma levels of arginine and the l-arginine:ADMA ratio, and decreased plasma levels of leptin. RES increased SIRT1 expression, but decreased the expression of GLUT5 and aldolase B in aortas from HFr-fed rats. These results suggest that RES contributes to the restoration of HFr-induced vascular dysfunction in rats, at least in part, by up-regulation of SIRT 1 and down-regulation of GLUT5 and aldolase B in the aorta. Moreover, RES may have a positive influence on vasculature by partly restoring the plasma arginine:ADMA ratio and leptin levels.

Melatonin prevents maternal fructose intake-induced programmed hypertension in the offspring: roles of nitric oxide and arachidonic acid metabolites

Fructose intake has increased globally and is linked to hypertension. Melatonin was reported to prevent hypertension development. In this study, we examined whether maternal high fructose (HF) intake causes programmed hypertension and whether melatonin therapy confers protection against the process, with a focus on the link to epigenetic changes in the kidney using next-generation RNA sequencing (NGS) technology. Pregnant Sprague-Dawley rats received regular chow or chow supplemented with HF (60% diet by weight) alone or with additional 0.01% melatonin in drinking water during the whole period of pregnancy and lactation. Male offspring were assigned to four groups: control, HF, control + melatonin (M), and HF + M. Maternal HF caused increases in blood pressure (BP) in the 12-wk-old offspring. Melatonin therapy blunted the HF-induced programmed hypertension and increased nitric oxide (NO) level in the kidney. The identified differential expressed gene (DEGs) that are related to regulation of BP included Ephx2, Col1a2, Gucy1a3, Npr3, Aqp2, Hba-a2, and Ptgs1. Of which, melatonin therapy inhibited expression and activity of soluble epoxide hydrolase (SEH, Ephx2 gene encoding protein). In addition, we found genes in arachidonic acid metabolism were potentially involved in the HF-induced programmed hypertension and were affected by melatonin therapy. Together, our data suggest that the beneficial effects of melatonin are attributed to its ability to increase NO level in the kidney, epigenetic regulation of genes related to BP control, and inhibition of SEH expression. The roles of DEGs by the NGS in long-term epigenetic changes in the adult offspring kidney require further clarification.

Diabetes, oxidative stress and therapeutic strategies

BACKGROUND

Diabetes has emerged as a major threat to health worldwide.

SCOPE OF REVIEW

The exact mechanisms underlying the disease are unknown; however, there is growing evidence that excess generation of reactive oxygen species (ROS), largely due to hyperglycemia, causes oxidative stress in a variety of tissues. Oxidative stress results from either an increase in free radical production, or a decrease in endogenous antioxidant defenses, or both. ROS and reactive nitrogen species (RNS) are products of cellular metabolism and are well recognized for their dual role as both deleterious and beneficial species. In type 2 diabetic patients, oxidative stress is closely associated with chronic inflammation. Multiple signaling pathways contribute to the adverse effects of glucotoxicity on cellular functions. There are many endogenous factors (antioxidants, vitamins, antioxidant enzymes, metal ion chelators) that can serve as endogenous modulators of the production and action of ROS. Clinical trials that investigated the effect of antioxidant vitamins on the progression of diabetic complications gave negative or inconclusive results. This lack of efficacy might also result from the fact that they were administered at a time when irreversible alterations in the redox status are already under way. Another strategy to modulate oxidative stress is to exploit the pleiotropic properties of drugs directed primarily at other targets and thus acting as indirect antioxidants.

MAJOR CONCLUSIONS

It appears important to develop new compounds that target key vascular ROS producing enzymes and mimic endogenous antioxidants.

GENERAL SIGNIFICANCE

This strategy might prove clinically relevant in preventing the development and/or retarding the progression of diabetes associated with vascular diseases.

Endothelial dysfunction in experimental models of arterial hypertension: cause or consequence?

Hypertension is a risk factor for other cardiovascular diseases and endothelial dysfunction was found in humans as well as in various commonly employed animal experimental models of arterial hypertension. Data from the literature indicate that, in general, endothelial dysfunction would not be the cause of experimental hypertension and may rather be secondary, that is, resulting from high blood pressure (BP). The initial mechanism of endothelial dysfunction itself may be associated with a lack of endothelium-derived relaxing factors (mainly nitric oxide) and/or accentuation of various endothelium-derived constricting factors. The involvement and role of endothelium-derived factors in the development of endothelial dysfunction in individual experimental models of hypertension may vary, depending on the triggering stimulus, strain, age, and vascular bed investigated. This brief review was focused on the participation of endothelial dysfunction, individual endothelium-derived factors, and their mechanisms of action in the development of high BP in the most frequently used rodent experimental models of arterial hypertension, including nitric oxide deficient models, spontaneous (pre)hypertension, stress-induced hypertension, and selected pharmacological and diet-induced models.

Endothelial dysfunction in experimental models of arterial hypertension: cause or consequence?

Hypertension is a risk factor for other cardiovascular diseases and endothelial dysfunction was found in humans as well as in various commonly employed animal experimental models of arterial hypertension. Data from the literature indicate that, in general, endothelial dysfunction would not be the cause of experimental hypertension and may rather be secondary, that is, resulting from high blood pressure (BP). The initial mechanism of endothelial dysfunction itself may be associated with a lack of endothelium-derived relaxing factors (mainly nitric oxide) and/or accentuation of various endothelium-derived constricting factors. The involvement and role of endothelium-derived factors in the development of endothelial dysfunction in individual experimental models of hypertension may vary, depending on the triggering stimulus, strain, age, and vascular bed investigated. This brief review was focused on the participation of endothelial dysfunction, individual endothelium-derived factors, and their mechanisms of action in the development of high BP in the most frequently used rodent experimental models of arterial hypertension, including nitric oxide deficient models, spontaneous (pre)hypertension, stress-induced hypertension, and selected pharmacological and diet-induced models.

Immunoreactivity of glucose transporter 5 is located in epithelial cells of the choroid plexus and ependymal cells

High fructose intake is associated with increased plasma triglyceride concentration, hepatic steatosis, impaired glucose tolerance, insulin resistance, and high blood pressure. In addition, increased fructose intake has recently been supposed to be a risk factor for dementia. However, direct effects of fructose on the brain function remain to be clarified. The localization of glucose transporter 5 (Glut5), a representative transporter of fructose, was immunohistochemically examined in the brains of humans, rats, and mice to clarify whether fructose was transported from the blood into the brain. Glut5 immunoreactivity was demonstrated to be located in the epithelial cells of the choroid plexus and the ependymal cells in the brains of humans and rats using commercial antibodies for Glut5. In addition, mRNA expression of mouse Glut5 was confirmed in the brains of mice. Immunohistochemical examination using a custom-made antibody against two regions of amino acid sequences of mouse Glut5 revealed that Glut5 immunoreactivity was also seen in the epithelial cells of the choroid plexus and the ependymal cells in the brains of mice. These findings show that Glut5 immunoreactivity is located in the epithelial cells of the choroid plexus and the ependymal cells, suggesting the possibility of the direct transportation of intravascular fructose into the brain parenchyma.

Asymmetric and symmetric dimethylarginine in adolescents with hyperuricemia

The purpose of this work was to investigate if in adolescents with hyperuricemia serum levels of asymmetric and symmetric dimethylarginine (ADMA, SDMA) are increased and if their levels correlate with serum uric acid (UA). Patients and Methods. The study group consisted of 58 hyperuricemic patients aged median 16.15 Q1–Q3 (14–17). The reference group contained 27 healthy individuals with normal serum UA level. ADMA and SDMA were measured by immunoenzymatic ELISA commercial kits and expressed in μmol/L. Serum UA was measured by the colorimetric method. Results. In hyperuricemic patients serum ADMA values did not differ between two estimated groups (P > 0.05); however, SDMA was significantly higher than in reference group (P < 0.01). Serum ADMA and SDMA correlated positively with UA (r = 0.34, P < 0.01) (r = 0.31, P < 0.01) and hs-CRP (r = 0.20, P < 0.05) (r = 0.36, P < 0.01), respectively. Conclusion. We demonstrated increased SDMA but not ADMA levels in adolescents with hyperuricemia and their correlation with serum uric acid levels. However, at the moment it is difficult to answer the question if it is just coexistence of these factors or any mechanism linking uric acid and methylated arginines really exists.

Direct and indirect antioxidant properties of α-lipoic acid and therapeutic potential

Diabetes has emerged as a major threat to worldwide health. The exact mechanisms underlying the disease are unknown; however, there is growing evidence that the excess generation of reactive oxygen species (ROS) associated with hyperglycemia, causes oxidative stress in a variety of tissues. In this context, various natural compounds with pleiotropic actions like α-lipoic acid (LA) are of interest, especially in metabolic diseases such as diabetes. LA, either as a dietary supplement or a therapeutic agent, modulates redox potential because of its ability to match the redox status between different subcellular compartments as well as extracellularly. Both the oxidized (disulfide) and reduced (di-thiol: dihydro-lipoic acid, DHLA) forms of LA show antioxidant properties. LA exerts antioxidant effects in biological systems through ROS quenching but also via an action on transition metal chelation. Dietary supplementation with LA has been successfully employed in a variety of in vivo models of disease associated with an imbalance of redox status: diabetes and cardiovascular diseases. The complex and intimate association between increased oxidative stress and increased inflammation in related disorders such as diabetes, makes it difficult to establish the temporal sequence of the relationship.

Metabolomics reveals that tumor xenografts induce liver dysfunction

Metabolomics, based on ultraperformance liquid chromatography coupled with electrospray ionization quadrupole mass spectrometry, was used to explore metabolic signatures of tumor growth in mice. Urine samples were collected from control mice and mice injected with squamous cell carcinoma (SCCVII) tumor cells. When tumors reached ∼2 cm, all mice were killed and blood and liver samples collected. The urine metabolites hexanoylglycine, nicotinamide 1-oxide, and 11β,20α-dihydroxy-3-oxopregn-4-en-21-oic acid were elevated in tumor-bearing mice, as was asymmetric dimethylarginine, a biomarker for oxidative stress. Interestingly, SCCVII tumor growth resulted in hepatomegaly, reduced albumin/globulin ratios, and elevated serum triglycerides, suggesting liver dysfunction. Alterations in liver metabolites between SCCVII-tumor-bearing and control mice confirmed the presence of liver injury. Hepatic mRNA analysis indicated that inflammatory cytokines, tumor necrosis factor α, and transforming growth factor β were enhanced in SCCVII-tumor-bearing mice, and the expression of cytochromes P450 was decreased in tumor-bearing mice. Further, genes involved in fatty acid oxidation were decreased, suggesting impaired fatty acid oxidation in SCCVII-tumor-bearing mice. Additionally, activated phospholipid metabolism and a disrupted tricarboxylic acid cycle were observed in SCCVII-tumor-bearing mice. These data suggest that tumor growth imposes a global inflammatory response that results in liver dysfunction and underscore the use of metabolomics to temporally examine these changes and potentially use metabolite changes to monitor tumor treatment response.

Adenosine A1-receptor deficiency diminishes afferent arteriolar and blood pressure responses during nitric oxide inhibition and angiotensin II treatment

Adenosine mediates tubuloglomerular feedback responses via activation of A1-receptors on the renal afferent arteriole. Increased preglomerular reactivity, due to reduced nitric oxide (NO) production or increased levels of ANG II and reactive oxygen species (ROS), has been linked to hypertension. Using A1-receptor knockout (A1−/−) and wild-type (A1+/+) mice we investigated the hypothesis that A1-receptors modulate arteriolar and blood pressure responses during NO synthase (NOS) inhibition or ANG II treatment. Blood pressure and renal afferent arteriolar responses were measured in nontreated mice and in mice with prolonged Nω-nitro-l-arginine methyl ester hydrochloride (l-NAME) or ANG II treatment. The hypertensive responses to l-NAME and ANG II were clearly attenuated in A1−/− mice. Arteriolar contractions to l-NAME (10−4 mol/l; 15 min) and cumulative ANG II application (10−12 to 10−6 mol/l) were lower in A1−/− mice. Simultaneous treatment with tempol (10−4 mol/l; 15 min) attenuated arteriolar responses in A1+/+ but not in A1−/− mice, suggesting differences in ROS formation. Chronic treatment with l-NAME or ANG II did not alter arteriolar responses in A1−/− mice, but enhanced maximal contractions in A1+/+ mice. In addition, chronic treatments were associated with higher plasma levels of dimethylarginines (asymmetrical and symmetrical) and oxidative stress marker malondialdehyde in A1+/+ mice, and gene expression analysis showed reduced upregulation of NOS-isoforms and greater upregulation of NADPH oxidases. In conclusion, adenosine A1-receptors enhance preglomerular responses during NO inhibition and ANG II treatment. Interruption of A1-receptor signaling blunts l-NAME and ANG II-induced hypertension and oxidative stress and is linked to reduced responsiveness of afferent arterioles.

The Relation between Fructose-Induced Metabolic Syndrome and Altered Renal Haemodynamic and Excretory Function in the Rat

This paper explores the possible relationships between dietary fructose and altered neurohumoral regulation of renal haemodynamic and excretory function in this model of metabolic syndrome. Fructose consumption induces hyperinsulinemia, hypertriglyceridaemia, insulin resistance, and hypertension. The pathogenesis of fructose-induced hypertension is dubious and involves numerous pathways acting both singly and together. In addition, hyperinsulinemia and hypertension contribute significantly to progressive renal disease in fructose-fed rats. Moreover, increased activity of the renin-angiotensin and sympathetic nervous systems leading to downregulation of receptors may be responsible for the blunted vascular sensitivity to angiotensin II and catecholamines, respectively. Various approaches have been suggested to prevent the development of fructose-induced hypertension and/or metabolic alteration. In this paper, we address the role played by the renin-angiotensin and sympathetic nervous systems in the haemodynamic alterations that occur due to prolonged consumption of fructose.