Endothelin-1 modulates angiotensin II in the development of hypertension in fructose-fed rats

Health position paper and redox perspectives - Disease burden by transportation noise

Transportation noise is a ubiquitous urban exposure. In 2018, the World Health Organization concluded that chronic exposure to road traffic noise is a risk factor for ischemic heart disease. In contrast, they concluded that the quality of evidence for a link to other diseases was very low to moderate. Since then, several studies on the impact of noise on various diseases have been published. Also, studies investigating the mechanistic pathways underlying noise-induced health effects are emerging. We review the current evidence regarding effects of noise on health and the related disease-mechanisms. Several high-quality cohort studies consistently found road traffic noise to be associated with a higher risk of ischemic heart disease, heart failure, diabetes, and all-cause mortality. Furthermore, recent studies have indicated that road traffic and railway noise may increase the risk of diseases not commonly investigated in an environmental noise context, including breast cancer, dementia, and tinnitus. The harmful effects of noise are related to activation of a physiological stress response and nighttime sleep disturbance. Oxidative stress and inflammation downstream of stress hormone signaling and dysregulated circadian rhythms are identified as major disease-relevant pathomechanistic drivers. We discuss the role of reactive oxygen species and present results from antioxidant interventions. Lastly, we provide an overview of oxidative stress markers and adverse redox processes reported for noise-exposed animals and humans. This position paper summarizes all available epidemiological, clinical, and preclinical evidence of transportation noise as an important environmental risk factor for public health and discusses its implications on the population level.

Camel milk protein hydrosylate alleviates hepatic steatosis and hypertension in high fructose-fed rats

CONTEXT

Camel milk is used in traditional medicine to treat diabetes mellitus hypertension and other metabolic disorders.

OBJECTIVE

This study evaluated the antisteatotic and antihypertensive effects of camel milk protein hydrolysate (CMH) in high fructose (HF)-fed rats and compared it with the effects afforded by the intact camel milk protein extract (ICM).

MATERIALS AND METHODS

Adult male Wistar rats were divided into 6 groups (n = 8 each) as 1) control, 2) ICM (1000 mg/kg), 3) CMH (1000 mg/kg), 4) HF (15% in drinking water), 5) HF (15%) + ICM (1000 mg/kg), and 6) HF (15%) + CMH (1000 mg/kg). All treatments were given orally for 21 weeks, daily.

RESULTS

Both ICM and CMH reduced fasting glucose and insulin levels, serum and hepatic levels of cholesterol and triglycerides, and serum levels of ALT and AST, angiotensin II, ACE, endothelin-1, and uric acid in HF-fed rats. In addition, both ICM and CMH reduced hepatic fat deposition in the hepatocytes and reduced hepatocyte damage. This was associated with an increase in the hepatic activity of AMPK, higher PPARα mRNA, reduced expression of fructokinase C, SREBP1, SREBP2, fatty acid synthase, and HMG-CoA-reductase. Both treatments lowered systolic and diastolic blood pressure. However, the effects of CMH on all these parameters were greater as compared to ICM.

DISCUSSION AND CONCLUSIONS

The findings of this study encourage the use of CMH in a large-scale population and clinical studies to treat metabolic steatosis and hypertension.

The Sweet and Salty Dietary Face of Hypertension and Cardiovascular Disease in Lebanon

According to the World Health Organization (WHO), an estimated 1.28 billion adults aged 30–79 years worldwide have hypertension; and every year, hypertension takes 7.6 million lives. High intakes of salt and sugar (mainly fructose from added sugars) have been linked to the etiology of hypertension, and this may be particularly true for countries undergoing the nutrition transition, such as Lebanon. Salt-induced hypertension and fructose-induced hypertension are manifested in different mechanisms, including Inflammation, aldosterone-mineralocorticoid receptor pathway, aldosterone independent mineralocorticoid receptor pathway, renin-angiotensin system (RAS), sympathetic nervous system (SNS) activity, and genetic mechanisms. This review describes the evolution of hypertension and cardiovascular diseases (CVDs) in Lebanon and aims to elucidate potential mechanisms where salt and fructose work together to induce hypertension. These mechanisms increase salt absorption, decrease salt excretion, induce endogenous fructose production, activate fructose-insulin-salt interaction, and trigger oxidative stress, thus leading to hypertension. The review also provides an up-to-date appraisal of current intake levels of salt and fructose in Lebanon and their main food contributors. It identifies ongoing salt and sugar intake reduction strategies in Lebanon while acknowledging the country’s limited scope of regulation and legislation. Finally, the review concludes with proposed public health strategies and suggestions for future research, which can reduce the intake levels of salt and fructose levels and contribute to curbing the CVD epidemic in the country.

Redox Switches in Noise-Induced Cardiovascular and Neuronal Dysregulation

Environmental exposures represent a significant health hazard, which cumulatively may be responsible for up to 2/3 of all chronic non-communicable disease and associated mortality (Global Burden of Disease Study and The Lancet Commission on Pollution and Health), which has given rise to a new concept of the exposome: the sum of environmental factors in every individual’s experience. Noise is part of the exposome and is increasingly being investigated as a health risk factor impacting neurological, cardiometabolic, endocrine, and immune health. Beyond the well-characterized effects of high-intensity noise on cochlear damage, noise is relatively well-studied in the cardiovascular field, where evidence is emerging from both human and translational experiments that noise from traffic-related sources could represent a risk factor for hypertension, ischemic heart disease, diabetes, and atherosclerosis. In the present review, we comprehensively discuss the current state of knowledge in the field of noise research. We give a brief survey of the literature documenting experiments in noise exposure in both humans and animals with a focus on cardiovascular disease. We also discuss the mechanisms that have been uncovered in recent years that describe how exposure to noise affects physiological homeostasis, leading to aberrant redox signaling resulting in metabolic and immune consequences, both of which have considerable impact on cardiovascular health. Additionally, we discuss the molecular pathways of redox involvement in the stress responses to noise and how they manifest in disruptions of the circadian rhythm, inflammatory signaling, gut microbiome composition, epigenetic landscape and vessel function.

Effects of carotid baroreceptor stimulation on aortic remodeling in obese rats

BACKGROUND AND AIM

Our previous study found carotid baroreceptor stimulation (CBS) reduces body weight and white adipose tissue (WAT) weight, restores abnormal secretion of adipocytokines and inflammation factors, decreases systolic blood pressure (SBP) by inhibiting activation of sympathetic nervous system (SNS) and renin-angiotensin system (RAS) in obese rats. In this study, we explore effects of CBS on aortic remodeling in obese rats.

METHODS AND RESULTS

Rats were fed high-fat diet (HFD) for 16 weeks to induce obesity and underwent either CBS device implantation and stimulation or sham operation at 8 weeks. BP and body weight were measured weekly. RAS activity of WAT, histological, biochemical and functional profiles of aortas were detected after 16 weeks. CBS effectively decreased BP in obese rats, downregulated mRNA expression of angiotensinogen (AGT) and renin in WAT, concentrations of AGT, renin, angiotensin II (Ang II), protein levels of Ang II receptor 1 (AT1R) and Ang II receptor 2 (AT2R) in WAT were declined. CBS inhibited reactive oxygen species (ROS) generation, inflammatory response and endoplasmic reticulum (ER) stress in aortas of obese rats, restrained vascular wall thickening and vascular smooth muscle cells (VSMCs) phenotypic switching, increased nitric oxide (NO) synthesis, promoted endothelium-dependent vasodilatation by decreasing protein expression of AT1R and leptin receptor (LepR), increasing protein expression of adiponectin receptor 1 (AdipoR1) in aortic VSMCs.

CONCLUSION

CBS reduced BP and reversed aortic remodeling in obese rats, the underlying mechanism might be related to the suppressed SNS activity, restored adipocytokine secretion and restrained RAS activity of WAT.

Molecular mechanisms underlying fructose-induced cardiovascular disease: exercise, metabolic pathways and microRNAs

NEW FINDINGS

What is the central question of this study? What are the mechanisms underlying the cardiac protective effect of aerobic training in the progression of a high fructose-induced cardiometabolic disease in Wistar rats? What is the main finding and its importance? At the onset of cardiovascular disease, aerobic training activates the p-p70S6K, ERK and IRβ-PI3K-AKT pathways, without changing the miR-126 and miR-195 levels, thereby providing evidence that aerobic training modulates the insulin signalling pathway. These data contribute to the understanding of the molecular cardiac changes that are associated with physiological left ventricular hypertrophy during the development of a cardiovascular disease.

ABSTRACT

During the onset of cardiovascular disease (CVD), disturbances in myocardial vascularization, cell proliferation and protein expression are observed. Aerobic training prevents CVD, but the underlying mechanisms behind left ventricle (LV) hypertrophy are not fully elucidated. The aim of this study was to investigate the mechanisms by which aerobic training protects the heart from LV hypertrophy during the onset of fructose-induced cardiometabolic disease. Male Wistar rats were allocated to four groups (n = 8/group): control sedentary (C), control training (CT), fructose sedentary (F) and fructose training (FT). The C and CT groups received drinking water, and the F and FT groups received d-fructose (10% in water). After 2 weeks, the CT and FT rats were assigned to a treadmill training protocol at moderate intensity for 8 weeks (60 min/day, 4 days/week). After 10 weeks, LV morphological remodelling, cardiomyocyte apoptosis, microRNAs and the insulin signalling pathway were investigated. The F group had systemic cardiometabolic alterations, which were normalised by aerobic training. The LV weight increased in the FT group, myocardium vascularisation decreased in the F group, and the cardiomyocyte area increased in the CT, F and FT groups. Regarding protein expression, total insulin receptor β-subunit (IRβ) decreased in the F group; phospho (p)-IRβ and phosphoinositide 3-kinase (PI3K) increased in the FT group; total-AKT and p-AKT increased in all of the groups; p-p70S6 kinase (p70S6K) protein was higher in the CT group; and p-extracellular signal-regulated kinase (ERK) increased in the CT and FT groups. MiR-126, miR-195 and cardiomyocyte apoptosis did not differ among the groups. Aerobic training activates p-p70S6K and p-ERK, and during the onset of a CVD, it can activate the IRβ-PI3K-AKT pathway.

A Flounder Fish Peptide Shows Anti-Hypertensive Effects by Suppressing the Renin-Angiotensin-Aldosterone System and Endothelin-1

BACKGROUND

Many fishes have been known for their good nutritional effects especially in the cardiovascular aspect. Some specific fish peptides have anti-hypertensive effects.

OBJECTIVE

In the present study, we hypothesized that the hexapeptide (MEVFVP) from flounder fish muscle can be a potent antihypertensive peptide, therefore, decided to perform this experiment.

METHODS

The peptide MEVFVP from flounder fish muscle (40 mg/kg) and vehicle were administered per os to spontaneously hypertensive rats (SHRs) (SHR-M and SHR-C, respectively). Additionally, plasma MEVFVP was measured serially before and after its oral administration to Sprague Dawley rats.

RESULTS

Blood pressures (BPs), especially systolic BP, in SHR rats were decreased around 3-6 hours after MEVFVP administration. Compared with SHR-C rats, endothelin-1 (ET-1) mRNA expression in multiple tissues, and plasma levels of ET-1, angiotensin II, and aldosterone were lower in SHR-M rats, whereas the phosphorylation of AMP-activated protein kinase (AMPK) was increased in the kidney of SHR-M rats. The administered peptide was not detected in rat plasma, while ex vivo incubation of the peptide in rat plasma caused its rapid degradation within minutes.

CONCLUSION

Our results show that the MEVFVP has an antihypertensive effect by regulating renin-angiotensin-aldosterone system, ET-1 and AMPK despite its limited bioavailability.

Modifications in GPR21 and GPR82 genes expression as a consequence of metabolic syndrome etiology

Metabolic syndrome (MS) has been related with alterations in expression levels of orphan G protein coupled receptors (GPCRs) such as GPR21 and GPR82, which could be involved in some of the elements that characterizes the metabolic syndrome. The aim of this work was to evaluate changes in GPR21 and GPR82 receptors expression in two models of metabolic syndrome: one genetic (Zucker rats), and the other based on a diet (70% fructose for 9 weeks). GPR21 and GPR82 gene expressions were evaluated in brain, heart, aorta, liver and kidney by RT-qPCR. Rats with a high fructose diet, as well as obese Zucker rats, showed initial stages of pancreatic damage and alterations in some biochemical parameters related to the model consistent with the classification of MS. GPR21 and GPR82 receptors expressed in all tissues. The expression of GPR21 decreased in heart, aorta and kidney, but in liver the expression was different: decreased in diet model and increased in genetic model. In contrast, GPR82 expression depended of tissue and metabolic syndrome model. The results highlight the possible role of GPR21 and GPR82 receptors in the development MS. We conclude that the expression of GPR21 and GPR82 in different tissues is related with MS and depend of the origin of the syndrome, so they could be a therapeutic target for that syndrome.

Oxidative stress and inflammation contribute to traffic noise-induced vascular and cerebral dysfunction via uncoupling of nitric oxide synthases

Environmental pollution and non-chemical stressors such as mental stress or traffic noise exposure are increasingly accepted as health risk factors with substantial contribution to chronic noncommunicable diseases (e.g. cardiovascular, metabolic and mental). Whereas the mechanisms of air pollution-mediated adverse health effects are well characterized, the mechanisms of traffic noise exposure are not completely understood, despite convincing clinical and epidemiological evidence for a significant contribution of environmental noise to overall mortality and disability. The initial mechanism of noise-induced cardiovascular, metabolic and mental disease is well defined by the „noise reaction model“ and consists of neuronal activation involving the hypothalamic-pituitary-adrenal (HPA) axis as well as the sympathetic nervous system, followed by a classical stress response via cortisol and catecholamines. Stress pathways are initiated by noise-induced annoyance and sleep deprivation/fragmentation. This review highlights the down-stream pathophysiology of noise-induced mental stress, which is based on an induction of inflammation and oxidative stress. We highlight the sources of reactive oxygen species (ROS) involved and the known targets for noise-induced oxidative damage. Part of the review emphasizes noise-triggered uncoupling/dysregulation of endothelial and neuronal nitric oxide synthase (eNOS and nNOS) and its central role for vascular dysfunction.

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Exposure to (traffic) noise causes non-auditory (indirect) cardiovascular and cerebral health harms via neuronal activation.

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Noise activates the HPA axis and sympathetic nervous system increasing levels of stress hormones, vasoconstrictors and ROS.

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Noise induces inflammation and stimulates several ROS sources leading to cerebral and cardiovascular oxidative damage.

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Noise leads to eNOS and nNOS uncoupling contributing to cardiometabolic disease and cognitive impairment.

High-fructose corn syrup-sweetened soft drink consumption increases vascular resistance in the kidneys at rest and during sympathetic activation

We first tested the hypothesis that consuming a high-fructose corn syrup (HFCS)-sweetened soft drink augments kidney vasoconstriction to sympathetic stimulation compared with water (study 1). In a second study, we examined the mechanisms underlying these observations (study 2). In study 1, 13 healthy adults completed a cold pressor test, a sympathoexcitatory maneuver, before (preconsumption) and 30 min after drinking 500 mL of decarbonated HFCS-sweetened soft drink or water (postconsumption). In study 2, venous blood samples were obtained in 12 healthy adults before and 30 min after consumption of 500 mL water or soft drinks matched for caffeine content and taste, which were either artificially sweetened (Diet trial), sucrose-sweetened (Sucrose trial), or sweetened with HFCS (HFCS trial). In both study 1 and study 2, vascular resistance was calculated as mean arterial pressure divided by blood velocity, which was measured via Doppler ultrasound in renal and segmental arteries. In study 1, HFCS consumption increased vascular resistance in the segmental artery at rest (by 0.5 ± 0.6 mmHg·cm^-1·s^-1, P = 0.01) and during the cold pressor test (average change: 0.5 ± 1.0 mmHg·cm^-1·s^-1, main effect: P = 0.05). In study 2, segmental artery vascular resistance increased in the HFCS trial (by 0.8 ± 0.7 mmHg·cm^-1·s^-1, P = 0.02) but not in the other trials. Increases in serum uric acid were greater in the HFCS trial (0.3 ± 0.4 mg/dL, P ≤ 0.04) compared with the Water and Diet trials, and serum copeptin increased in the HFCS trial (by 0.8 ± 1.0 pmol/L, P = 0.06). These findings indicate that HFCS acutely increases vascular resistance in the kidneys, independent of caffeine content and beverage osmolality, which likely occurs via simultaneous elevations in circulating uric acid and vasopressin.

Gut dysbiosis contributes to high fructose-induced salt-sensitive hypertension in Sprague-Dawley rats

OBJECTIVES

Although it is known that high fructose intake causes salt-sensitive hypertension, the underlying mechanism remains unclear. The aim of this study was to determine whether chronic intake of high fructose coupled with salt (HFS) might alter the structure of the gut microbiota, which contributes to elevated blood pressure.

METHODS

For 8 wk, Sprague-Dawley rats were given 20% fructose in drinking water and 4% sodium chloride in their diet to induce hypertension. A non-absorbable antibiotic vancomycin was used to modify gut microbiota. The 16 S rRNA sequencing for fecal samples was assessed and blood pressure was recorded. Enzyme-linked immunosorbent assay and quantitative polymerase chain reaction were used to examine the renin-angiotensin system in serum, urine, and the kidney.

RESULTS

Compared with the control group, HFS feeding resulted in gut dysbiosis by altering the diversity and richness of gut microbiota and decreased the ratio of Firmicutes to Bacteroidetes. Vancomycin reshaped dramatically the HFS-induced dysbiosis. And vancomycin (van) attenuated HFS-increased blood pressure (HFS: 121.3 ± 2.8 mm Hg; HFS-van: 111.1 ± 1.7 mm Hg) and heart rate (HFS: 360.5 ± 9.0 bpm; HFS-van: 318.7 ± 5.6 bpm) as well as the content of angiotensinogen, renin, and angiotensin II in the urine and the angiotensinogen mRNA level in renal cortical tissues. However, HFS-increased triacylglycerol, renin, and angiotensin II in serum were not decreased by vancomycin.

CONCLUSION

The present results demonstrated that gut dysbiosis develops after chronic fructose plus salt intake and contributes to the increase of blood pressure and the activation of the intrarenal renin-angiotensin system. Therefore, targeting gut microbiota provides a helpful therapy method to improve HFS-induced hypertension.

Effects of a novel isoflavonoid from the stem bark of Alstonia scholaris against fructose-induced experimental cataract

OBJECTIVE

The present study investigated the anticataract activity of a novel isoflavonoid, isolated from stem bark of Alstonia scholaris, against fructose-induced experimental cataract.

METHODS

The bioactivity of fractions extracted from A. scholaris, an isolated isoflavonoid (ASII) was screened using in vitro (goat lens) and in vivo (albino rats) experimental cataract models. For the in vivo evaluation, albino rats (12-15 weeks old) were divided into five groups (n = 6). Group I (normal) received 0.3% carboxymethyl cellulose solution (10 mL/[kg·d], p.o.). Group II (control) received 10% (w/v) fructose solution in their drinking water. Groups III-V received ASII at three different doses, 0.1, 1.0 and 10 mg/(kg·d), concurrently with 10% (w/v) fructose solution. Treatment was given daily for 8 consecutive weeks. During the protocol, systolic blood pressure, diastolic blood pressure, blood glucose level and lenticular opacity were monitored at 2-week intervals. Pathophysiological markers (catalase, superoxide dismutase, glutathione peroxidase, reduced glutathione and malondialdehyde) in eye lenses were examined at the end of the 8-week treatment period.

RESULTS

The results of in vitro study showed that A. scholaris extract and the active fraction (A₃) reduced the lenticular opacity as compared to toxic control group. The in vivo study showed that 8-week administration of ASII (0.1, 1.0 and 10 mg/[kg·d], p.o.) led to significant reduction in blood pressure and blood glucose level and retarded the initiation and evolution of cataractogenesis, compared to the fructose-induced cataract model control. Additionally, ASII treatment led to significant improvement in lens antioxidants (catalase, superoxide dismutase, glutathione peroxidase and reduced glutathione) and decreased lens malondialdehyde, compared to the control group (group II).

CONCLUSION

Results revealed that administration of ASII played a crucial role in the reduction of cataract formation in diabetic and hypertensive models.

Intra-Renal Angiotensin Levels Are Increased in High-Fructose Fed Rats in the Extracorporeal Renal Perfusion Model

Overconsumption of fructose leads to metabolic syndrome as a result of hypertension, insulin resistance, and hyperlipidemia. In this study, the renal function of animals submitted to high fructose intake was analyzed from weaning to adulthood using in vivo and ex vivo methods, being compared with a normal control group. We investigated in ex vivo model of the role of the renin Angiotensin system (RAS) in the kidney. The use of perfused kidney from animals submitted to 8-week fructose treatment showed that high fructose intake caused metabolic and cardiovascular alterations that were consistent with other studies. Moreover, the isolated perfused kidneys obtained from rats under high fructose diet showed a 33% increase in renal perfusion pressure throughout the experimental period due to increased renal vascular resistance and a progressive fall in the glomerular filtration rate, which reached a maximum of 64% decrease. Analysis of RAS peptides in the high fructose group showed a threefold increase in the renal concentrations of angiotensin I (Ang I) and a twofold increase in angiotensin II (Ang II) levels, whereas no change in angiotensin 1-7 (Ang 1-7) was observed when compared with the control animals. We did not detect changes in angiotensin converting enzyme (ACE) activity in renal tissues, but there is a tendency to decrease. These observations suggest that there are alternative ways of producing Ang II in this model. Chymase the enzyme responsible for Ang II formation direct from Ang I was increased in renal tissues in the fructose group, confirming the alternative pathway for the formation of this peptide. Neprilysin (NEP) the Ang 1-7 forming showed a significant decrease in activity in the fructose vs. control group, and a tendency of reduction in ACE2 activity. Thus, these results suggest that the Ang 1-7 vasodilator peptide formation is impaired in this model contributing with the increase of blood pressure. In summary, rats fed high fructose affect renal RAS, which may contribute to several deleterious effects of fructose on the kidneys and consequently an increase in blood pressure.

Bilateral renal cryodenervation decreases arterial pressure and improves insulin sensitivity in fructose-fed Sprague-Dawley rats

Consumption of food high in fructose is prevalent in modern diets. One week of moderately high fructose intake combined with high salt diet has been shown to increase blood pressure and failed to suppress plasma renin activity (PRA). We tested the hypothesis that the hypertension and high PRA are consequences of elevated renal sympathetic nerve activity (RSNA). In protocol 1, we assessed RSNA by telemetry in conscious Sprague-Dawley rats given 20% fructose or 20% glucose in drinking water on a 0.4% NaCl diet (NS) for 1 wk and then transitioned to a 4% NaCl diet (HS). After an additional week, mean arterial pressure (MAP) and RSNA increased significantly in fructose-fed but not glucose-fed HS rats. In protocol 2, fructose (Fruc)- or glucose (Glu)-fed rats on NS or HS diet for 3 wk underwent sham denervation (shamDNX) or bilateral renal denervation using cryoablation (cryoDNX). MAP was higher in Fruc-HS rats compared with Glu-NS, Glu-HS, or Fruc-NS rats and decreased after cryoDNX ( P < 0.01). MAP did not change in Fruc-HS shamDNX rats. Renal norepinephrine content decreased by 85% in cryoDNX ( P < 0.01 vs. shamDNX). PRA significantly decreased after cryoDNX in both Fruc-NS and Fruc-HS rats. Nonfasting blood glucose levels were similar among the four groups. Glucose-to-insulin ratio significantly increased in Fruc-HS cryoDNX rats, consistent with greater insulin sensitivity. Taken together, these studies show that renal sympathoexcitation is, at least in part, responsible for salt-dependent increases in MAP, increased PRA, and decreased insulin sensitivity in rats fed a moderately high fructose diet for as little as 3 wk.

Effect of infliximab and tocilizumab on fructose-induced hyperinsulinemia and hypertension in rats

Fructose administration can induce hypertension, insulin resistance and hypertriglyceridemia. Here, we investigated the possible protective effect of infliximab (IFX), a tumor necrosis factor alpha (TNF-α) inhibitor, or tocilizumab (TOC), an interleukin-6 (IL6) inhibitor, on fructose-induced increase in blood pressure, insulin resistance and hyperlipidemia in rats. The animals were fed a 60% fructose diet in the absence or presence of IFX (5 mg/kg, i.p., once weekly) or TOC (8 mg/kg, i.p., once every two weeks). Fructose significantly increased blood pressure, heart rate and homeostatic model assessment of insulin resistance (HOMA-IR). Fructose also significantly raised the concentrations of fasting plasma insulin, triglycerides, total cholesterol, uric acid, tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), malondialdhyde (MDA) and nitric oxide. Fructose also significantly decreased plasma superoxide dismutase (SOD) and catalase activities. In addition, fructose significantly increased aortic endothelin and nitric oxide concentrations. Both IFX and TOC attenuated the fructose-induced increase in blood pressure, insulin resistance, and the concentrations of uric acid, MDA and IL-6. TOC significantly reduced fructose-induced increase in triglycerides and cholesterol. In addition, IFX increased plasma SOD and catalase activities. Our results showed that both IFX and TOC were partially successful in reversing fructose - induced changes.

Fructose-rich diet differently affects angiotensin II receptor content in the nucleus and a plasma membrane fraction of visceral adipose tissue

The adipose tissue renin-angiotensin system (RAS) is proposed to be a pathophysiological link between adipose tissue dysregulation and metabolic disorders induced by a fructose-rich diet (FRD). RAS can act intracellularly. We hypothesized that adipocyte nuclear membranes possess angiotensin receptor types 1 and 2 (AT1R and AT2R), which couple to nuclear signaling pathways and regulate oxidative gene expression under FRD conditions. We analyzed the effect of consumption of 10% fructose solution for 9 weeks on biochemical parameters, adipocyte morphology, and expression of AT1R, AT2R, AT1R-associated protein (ATRAP), NADPH oxidase 4 (NOX4), matrix metalloproteinase-9 (MMP-9), and manganese superoxide dismutase (MnSOD) in adipose tissue of Wistar rats. We detected AT1R and AT2R in the nuclear fraction. FRD reduced the level of angiotensin receptors in the nucleus, while increased AT1R and decreased AT2R levels were observed in the plasma membrane. FRD increased the ATRAP mRNA level and decreased MnSOD mRNA and protein levels. No significant differences were observed for MMP-9 and NOX4 mRNA levels. These findings coincided with hyperleptinemia, elevated blood pressure and triglycerides, and unchanged visceral adipose tissue mass and morphology in FRD rats. Besides providing evidence for nuclear localization of angiotensin receptors in visceral adipose tissue, this study demonstrates the different effects of FRD on AT1R expression in different cellular compartments. Elevated blood pressure and decreased antioxidant capacity in visceral fat of fructose-fed rats were accompanied by an increased AT1R level in the plasma membrane, while upregulation of ATRAP and a decrease of nuclear membrane AT1R suggest an increased capacity for attenuation of excessive AT1R signaling and visceral adiposity.

Asiatic acid attenuates renin-angiotensin system activation and improves vascular function in high-carbohydrate, high-fat diet fed rats

Background

In the rat model of high carbohydrate, high fat (HCHF) diet-induced metabolic syndrome (MS), previous studies have found that asiatic acid has an antihypertensive effect. In this study, we investigated effects of asiatic acid on vascular structure, vascular function and renin-angiotensin system (RAS) in HCHF diet-induced MS rats.

Methods

Male Sprague–Dawley rats were divided into three treatment groups for the 15 week study: a control group fed a normal diet, a MS group fed HCHF diet plus 15 % fructose in their drinking water for 15 weeks, and an asiatic acid treated group that received a HCHF diet plus fructose for 15 weeks and also received orally administered asiatic acid (20 mg/kg BW/day) for the final 3 weeks. Vascular structure and function were investigated. AT₁ receptor expression in aortic tissues and eNOS protein expression in the mesenteric arteries were detected. The levels of serum angiotensin (Ang) II, angiotensin converting enzyme (ACE) and plasma norepinephrine (NE) were measured. The differences among treatment groups were analyzed by one-way analysis of variance (ANOVA) followed by post-hoc Bonferroni tests.

Results

At the end of the study, all rats fed a HCHF diet exhibited signs of MS including, hypertension, dyslipidemia and insulin resistance. Vascular remodeling in large and small arteries, overexpression of AT₁ receptor, and high levels of serum Ang II and ACE were also observed in MS group (p < 0.05). Contractile responses to sympathetic nerve stimulation were enhanced relating to high plasma NE level in MS rats (p < 0.05). The response to exogenous NE was not changed in the mesenteric bed. Vasorelaxation responses to acetylcholine were blunted in thoracic aorta and mesenteric beds, which is consistent with downregulation of eNOS expression in MS rats (p < 0.05). Restoration of metabolic alterations, hemodynamic changes, RAS and sympathetic overactivity, increased plasma NE, endothelium dysfunction, and downregulation of eNOS expression was observed in the asiatic acid treated group (p < 0.05). However, asiatic acid failed to alleviate vascular remodeling in MS rats.

Conclusion

Our findings suggest that the observed antihypertensive effect of asiatic acid in MS rats might be related to its ability to alleviate RAS overactivity and improve vascular function with restoration of sympathetic overactivity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1100-6) contains supplementary material, which is available to authorized users.

Antihypertensive effects of fargesin in vitro and in vivo via attenuating oxidative stress and promoting nitric oxide release

Fargesin, a bioactive neolignan isolated from magnolia plants, is widely used in the treatment of managing rhinitis, inflammation, histamine, sinusitis, and headache. To provide more biological information about fargesin, we investigated the effects of fargesin on rat aortic rings and 2-kidney, 1-clip (2K1C) hypertensive rats. In vitro, fargesin caused concentration-dependent vasorelaxation in rat isolated aortic rings induced by KCl and norepinephrine. The effect was weakened by endothelium denudation and nitric oxide (NO) synthesis inhibition. In vivo, the evolution of systolic blood pressure (SBP) was followed by weekly measurements. Angiotensin II (Ang II) and endothelin (ET) levels, NO and nitric oxide synthase (NOS), and plasma and liver oxidative stress markers were determined at the end of the experimental period. After 5 weeks of fargesin treatment, we found that fargesin treatment reduced SBP, cardiac hypertrophy, and Ang II and ET levels of hypertensive rats. Increased NOS activity and NO level were observed in fargesin-treated rats. Normalisation of plasma MDA concentrations and improvement of the antioxidant defence system in plasma and liver accompanied the antihypertensive effect of fargesin. Taken together, these results provided substantial evidences that fargesin has antihypertensive effect in 2K1C hypertensive rats via inhibiting oxidative stress and promoting NO release.

The mechanisms underlying fructose-induced hypertension: a review

We are currently in the midst of an epidemic of metabolic disorders, which may, in part, be explained by excess fructose intake. This theory is supported by epidemiological observations as well as experimental studies in animals and humans. Rising consumption of fructose has been matched with growing rates of hypertension, leading to concern from public health experts. At this stage, the mechanisms underlying fructose-induced hypertension have not been fully characterized and the bulk of our knowledge is derived from animal models. Animal studies have shown that high-fructose diets up-regulate sodium and chloride transporters, resulting in a state of salt overload that increases blood pressure. Excess fructose has also been found to activate vasoconstrictors, inactivate vasodilators, and over-stimulate the sympathetic nervous system. Further work is required to determine the relevance of these findings to humans and to establish the level at which dietary fructose increases the risk of developing hypertension

Experimental gestational diabetes mellitus induces blunted vasoconstriction and functional changes in the rat aorta

Diabetic conditions increase vascular reactivity to angiotensin II in several studies but there are scarce reports on cardiovascular effects of hypercaloric diet (HD) induced gestational diabetes mellitus (GDM), so the objective of this work was to determine the effects of HD induced GDM on vascular responses. Angiotensin II as well as phenylephrine induced vascular contraction was tested in isolated aorta rings with and without endothelium from rats fed for 7 weeks (4 before and 3 weeks during pregnancy) with standard (SD) or hypercaloric (HD) diet. Also, protein expression of AT₁R, AT₂R, COX-1, COX-2, NOS-1, and NOS-3 and plasma glucose, insulin, and angiotensin II levels were measured. GDM impaired vasoconstrictor response (P < 0.05 versus SD) in intact (e+) but not in endothelium-free (e−) vessels. Losartan reduced GDM but not SD e− vasoconstriction (P < 0.01 versus SD). AT₁R, AT₂R, and COX-1 and COX-2 protein expression were significantly increased in GDM vessels (P < 0.05 versus SD). Results suggest an increased participation of endothelium vasodilator mediators, probably prostaglandins, as well as of AT₂ vasodilator receptors as a compensatory mechanism for vasoconstrictor changes generated by experimental GDM. Considering the short term of rat pregnancy findings can reflect early stage GDM adaptations.

Effect of Cydonia oblonga Mill. leaf extracts or captopril on blood pressure and related biomarkers in renal hypertensive rats

ETHNOPHARMACOLOGICAL RELEVANCE

Cydonia oblonga Mill. (COM) is used in traditional Uyghur medicine to treat or prevent cardiovascular disease. In a previous study COM leaf extracts were found to be active in renal hypertensive rats (RHR). The present study tests the dose-dependence of the effect of ethanol leaf extracts on hypertension and on biomarkers associated with blood pressure control, such as angiotensin-II (AII), plasma renin activity (PRA), apelin-12 (A), endothelin (ET) and nitric oxide (NO), compared to captopril.

METHODS

Two-kidney one-clip (2K1C) Goldblatt model rats were divided randomly into six groups: sham, model, captopril 25 mg/kg, COM leaf extract 80, 160 and 320 mg/kg (n=10 each). Drugs were administered orally daily for eight weeks. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured before treatment and every 2 weeks. Blood and kidney samples were collected after the last treatment to measure AII, PRA, A, ET and NO.

RESULTS

RHR had increased blood pressure, AII, A, PRA, ET and decreased NO. Treatment with captopril reduced blood pressure, AII, A, PRA, and ET, though not quite to normal values. COM leaf extracts significantly and dose-dependently reduced blood pressure, AII, A, RA and ET, whereas NO was increased. The highest dose of COM had the same effects as captopril.

CONCLUSION

The effects of COM extracts on blood pressure and biomarkers were dose-dependent and at the highest dose similar to those of captopril. This suggests an action of COM on the renin-angiotensin system, which could explain its antihypertensive effect.

Selective alpha(1)-adrenoceptor blockade prevents fructose-induced hypertension

The purpose of this study was to investigate the effect of chronic treatment with prazosin, a selective α1-adrenoceptor antagonist, on the development of hypertension in fructose-fed rats (FFR). High-fructose feeding and treatment with prazosin (1 mg/kg/day via drinking water) were initiated simultaneously in male Wistar rats. Systolic blood pressure, fasted plasma parameters, insulin sensitivity, plasma norepinephrine (NE), uric acid, and angiotensin II (Ang II) were determined following 9 weeks of treatment. FFR exhibited insulin resistance, hyperinsulinemia, hypertriglyceridemia, and hypertension, as well as elevations in plasma NE and Ang II levels. Treatment with prazosin prevented the rise in blood pressure without affecting insulin levels, insulin sensitivity, uric acid, or Ang II levels, while normalizing plasma NE levels in FFR. These data suggest that over-activation of the sympathetic nervous system, specifically α1-adrenoceptors, contributes to the development of fructose-induced hypertension, however, this over-activation does not appear to an initial, precipitating event in FFR.

The effects of phentolamine on fructose-fed rats

Metabolic syndrome (MS) is a combination of medical disorders that increase the risk of developing cardiovascular disease and diabetes. MS is associated with obesity, increased blood pressure, hyperlipidemia, and hyperglycemia. This study was designed to investigate the pharmacological profile of phentolamine, a nonselective α adrenergic receptor antagonist, in the prevention of increased blood pressure in fructose-fed rats. Phentolamine prevented the fructose-induced increase in systolic blood pressure without affecting insulin sensitivity and major metabolic parameters. The levels of plasma noradrenaline and angiotensin II, 2 proposed contributors to the development of fructose-induced elevated blood pressure, were examined. Neither noradrenaline nor angiotensin II levels were affected by phentolamine treatment. Since overproduction of nitric oxide has been shown to lead to an elevation in peroxynitrite, the role of oxidative stress, a proposed mechanism of fructose-induced elevated blood pressure and insulin resistance, was examined by measuring plasma levels of total nitrate/nitrite. Plasma nitrate/nitrite was significantly elevated in all fructose-fed animals, regardless of treatment with phentolamine. Another proposed contributor toward fructose-induced MS is an elevation in uric acid levels. In this experiment, plasma levels of uric acid were found to be increased by dietary fructose and were unaffected by phentolamine treatment.

Uric acid and fructose: potential biological mechanisms

Excessive fructose consumption is associated with the development of metabolic syndrome and type II diabetes. Both conditions are well-known risk factors for cardiovascular and renal diseases. Uric acid synthesis is linked biochemically to fructose metabolism, thus the widespread consumption of this monosaccharide has been related to steady increasing levels of serum uric acid during the past few decades. Recent evidence has suggested that uric acid may act as a cardiorenal toxin. In this regard, experimental studies have suggested that the primary noxious effect of uric acid occurs inside the cell and is likely the stimulation of oxidative stress. More studies to disclose the harmful mechanisms associated with increasing intracellular uric acid levels after a fructose load are warranted.

High dietary fructose intake: Sweet or bitter life?

Epidemiological data show that the consumption of added sugars as ingredients in processed or prepared foods and caloric beverages has dramatically increased. Fructose and fructose-based sweeteners are the most commonly added sugars and high-fructose corn syrup (HFCS-55: 55% fructose, 42% glucose and 3% higher saccharides) accounts for over 40% of all added caloric sweeteners. Concerns regarding the health risk of added sugar follow the demonstration that the consumption of foods and beverages high in sugars is associated with an increased prevalence of obesity, insulin resistance, dyslipidemia and, more recently, ischemic heart and kidney diseases. The molecular mechanism(s) underlying the detrimental effects of sugar are not completely understood and their elucidation is critical to provide new insights on the health risk of fructose-based sweeteners. A better understanding of the key role of fructose overconsumption in the development of metabolic disorders may contribute to planning new strategies for preventing deleterious dietary behaviors from becoming established and, thus, curbing the rise in the number of insulin-resistant, obese and diabetic populations worldwide.

Effects of insulin resistance and testosterone on the participation of cyclooxygenase isoforms in vascular reactivity

Testosterone plays an important role in mediating hypertension and altered vascular reactivity associated with insulin resistance. In addition to other pathways, testosterone-dependent changes in aortic cyclooxygenase (COX-2) mRNA levels affect blood pressure following insulin resistance. However their effects on vascular tone are unclear. We studied the changes in contraction response to phenylephrine (PE) in the aorta and superior mesenteric artery (SMA) from intact and gonadectomized fructose-fed rats. Constriction response to PE was studied in tissues incubated with the COX-1 and COX-2-selective antagonists, SC-560 and NS-398, respectively, and indomethacin, in addition to assessing its role in endothelium-dependent relaxation. Finally changes in COX-2 protein expression and plasma thromboxane A2 (TXA2), a downstream vasoconstrictor metabolite of COX-2, were measured. In fructose-fed rats, castration prevented the increase in blood pressure but not insulin resistance. The involvement of COX-2 in mediating the alpha-adrenergic vasoconstriction was higher in intact rat aorta compared to COX-1, which was prevented by castration. However, in the SMA, COX-2 participation was dependent on testosterone alone. Fructose-induced attenuation of endothelial relaxation was restored by indomethacin, which suggests a pro-vasoconstrictor role for COX. Both diet and testosterone did not alter vascular COX-2 expression thus suggesting the involvement of downstream testosterone-dependent pathways. This is supported by increased plasma TXA2 in the castrated rats compared to intact rats. Isoform-specific actions of COX are tissue-selective in states of insulin resistance and involve potential testosterone-dependent downstream targets. Further studies are needed to investigate the role of androgens and insulin resistance in vascular arachidonic acid metabolism.

Endothelin, hypertension and chronic kidney disease: new insights

PURPOSE OF REVIEW

Endothelin is important in the development of cardiorenal disease. This review discusses recent developments in understanding endothelin's role in hypertension and chronic kidney disease (CKD).

RECENT FINDINGS

Endothelin-1 production is increased in hypertension and CKD. Endothelin-1 stimulates vasoconstriction, inflammation and fibrosis, thereby promoting hypertension, atherosclerosis and CKD. These effects are closely linked to angiotensin II and reactive oxygen species. In preclinical studies, endothelin receptor antagonists were effective in treating hypertension (particularly with endothelial dysfunction) and CKD. In preclinical studies, endothelin A-selective, as opposed to combined endothelin A and B, receptor blockers have generally been more efficacious. Few clinical trials have been conducted in hypertension and/or kidney disease, partly due to concerns over side effects of testicular toxicity and fluid retention. Endothelin blockade reduces blood pressure in patients with resistant hypertension, with additional beneficial metabolic effects. Endothelin antagonism improves proteinuria in CKD (diabetic or not), particularly in patients taking inhibitors of angiotensin II action.

SUMMARY

Endothelin is a promising target in the treatment of resistant hypertension and CKD, with additional potential benefits on atherosclerosis and the metabolic syndrome. The nature and mechanisms of drug side effects require elucidation before the potential of this new class of drugs can be fully realized.

GPCR agonist-induced transactivation of the EGFR upregulates MLC II expression and promotes hypertension in insulin-resistant rats

AIMS

The presence of metabolic abnormalities such as insulin resistance and elevated levels of various vasoconstrictor G-protein-coupled receptor (GPCR) agonists contributes to the development of hypertension. Recent studies have suggested a link between disease progression and activation of growth factor receptor signalling pathways such as the epidermal growth factor receptor (EGFR) by matrix metalloproteinases (MMPs). We hypothesized that excessive stimulation of GPCRs such as alpha(1)-adrenergic receptors activates MMP-dependent EGFR transactivation and contributes to the development of hypertension by promoting increased synthesis of contractile proteins in vascular smooth muscle (VSM).

METHODS AND RESULTS

We tested this concept in experiments using insulin-resistant VSM cells (VSMCs) and fructose hypertensive rats (FHRs), a model of acquired systolic hypertension and insulin resistance. We found that insulin resistance and agonist stimulation increased the expression and activity of MMPs (MMP-2 and MMP-7), the EGFR, contractile proteins such as myosin light chain kinase and MLC II, and their transcriptional activators including P90 ribosomal kinase (P90RSK) and serum response factor, possibly via the activation of extracellular signal-regulated kinase (ERK1/2) in VSMCs. Further, in insulin-resistant VSMCs and arteries from FHRs, disruption of MMP-EGFR signalling either by a pharmacological or small interfering RNA approach normalized the increased expression and activity of contractile proteins and their transcriptional activators and prevented the development of hypertension in FHRs.

CONCLUSION

Our data suggest that the MMP-EGFR pathway could be a potential target in the treatment of hypertension in insulin resistance and/or hyperglycaemic conditions such as type 2 diabetes.

Endothelin-1 receptor blockade induces upregulation of renin-angiotensin-aldosterone system expression in terms of blood pressure regulation

Objective. To compare the level of expression of the renin-angiotensin-aldosterone system (RAAS) in mice with or without the endothelin-1 receptor antagonist bosentan and to examine the potential value in blood pressure regulation.

Materials and methods. Bosentan (10 mg/kg/d) and placebo were given to two groups of male C57BL/6 mice (n=5) from ages 6 to 12 weeks. The mRNAs of liver, kidney and lung were isolated for Northern blot analysis. A further 15 male C57BL/6 mice were divided into three groups (n=5): mice in group A were given the angiotensin II type 1 receptor blocker valsartan (10 mg/kg/d); mice in group B were given bosentan (10 mg/kg/d); and mice in group C were given both valsartan and bosentan (10 mg/ kg/d for each drug). All mice were administered the drugs from 6 to 12 weeks of age and had their systolic blood pressure (SBP) measured at the end of the drug treatments.

Results. Northern blot analysis demonstrated that the expression levels of angiotensinogen in liver (p=0.0126), renin in kidney (p=0.002), and angiotensin-converting enzyme in lung (p=0.0041) were upregulated in mice treated with bosentan. No difference in SBP was found among the groups before drug administration. Six weeks after monotherapy with valsartan, SBP was slightly lowered (126±2 vs. 122±3 mmHg, p=0.0381). Monotherapy with bosentan also had a small effect on SBP (126±2 vs. 122±3 mmHg, p=0.0381), whereas dual blockade with valsartan and bosentan significantly lowered SBP (127±3 vs. 103±3 mmHg, p<0.001). Conclusions. We conclude that RAAS components are upregulated under endothelin blockade. Dual blockade of the RAAS and endothelin system is beneficial for blood pressure control.

Combination of captopril and allopurinol retards fructose-induced metabolic syndrome

BACKGROUND

Both ACE inhibitors and allopurinol have been shown to partially prevent metabolic syndrome induced by fructose. We tested the hypothesis that combined therapy might be more effective at blocking the metabolic syndrome induced with fructose.

METHODS

Male Sprague-Dawley rats were fed a high fructose diet with or without allopurinol, captopril, or the combination for 20 weeks. A control group received a normal diet. All groups were pair-fed to assure equivalent caloric intake.

RESULTS

Despite reduced energy intake, the fructose-fed rats developed features of metabolic syndrome including elevated blood pressure, abdominal obesity, hypertriglyceridemia, hyperuricemia and hyperinsulinemia. While both allopurinol and captopril alone tended to reduce features of the metabolic syndrome, the combined therapy was synergistic, with significant reduction in blood pressure, less accumulation of abdominal fat, an improvement in the dyslipidemia and a complete prevention of insulin resistance.

CONCLUSION

A high fructose diet can induce metabolic syndrome even in the setting of caloric restriction. Captopril and allopurinol synergistically reduce features of the metabolic syndrome, especially hypertension, insulin resistance and dyslipidemia. Combination allopurinol and ACE inhibitor therapy might provide a superior means to prevent diabetes and cardiovascular disease.

The fructose-fed rat: a review on the mechanisms of fructose-induced insulin resistance and hypertension

The metabolic syndrome is an important public health concern that predisposes individuals to the development of cardiovascular disease and/or Type 2 diabetes. The fructose-fed rat is an animal model of acquired systolic hypertension that displays numerous features of the metabolic syndrome. This animal model is used to study the relationship between insulin resistance/compensatory hyperinsulinemia and the development of hypertension. Several mechanisms have been proposed to mediate the link between insulin resistance and hypertension. In this review, we have addressed the role of sympathetic nervous system overactivation, increased production of vasoconstrictors, such as endothelin-1 and angiotensin II, and prostanoids in the development of hypertension in fructose-fed rats. The roles of nitric oxide, impaired endothelium-dependent relaxation and sex hormones in the pathogenesis of the fructose-fed induced hypertensive rats have also been highlighted. More recently, increased formation of reactive oxygen species and elevated levels of uric acid have been reported to contribute to fructose-induced hypertension.

Chronic etanercept treatment prevents the development of hypertension in fructose-fed rats

The purpose of this study was to investigate the effect of chronic treatment with etanercept (a soluble recombinant fusion protein consisting of the extracellular ligand-binding domain of tumor necrosis factor receptor type 2) on the development of hypertension in fructose-fed rats (FFR). High fructose feeding and treatment with etanercept (0.3 mg/kg, three times per week) was initiated simultaneously in male Wistar rats. Systolic blood pressure, fasted plasma parameters, insulin sensitivity, vascular reactivity, plasma angiotensin II (Ang II), and norepinephrine were determined following 9 weeks of treatment. FFR exhibited insulin resistance, hyperinsulinemia, hypertriglyceridemia, endothelial dysfunction, and hypertension. Treatment with etanercept prevented the rise in blood pressure without affecting insulin levels, insulin sensitivity, triglycerides, or Ang II levels in FFR. Etanercept treatment improved acetylcholine-induced relaxation and normalized endothelial nitric oxide synthase expression in aortas from FFR. The results of this study suggest that treatment with etanercept prevented the development of hypertension by improving vascular function and restoring endothelial nitric oxide synthase expression in FFR.