Effects of alpha-lipoic acid on endothelial function in aged diabetic and high-fat fed rats

Mechanosensory entities and functionality of endothelial cells

The endothelial cells of the blood circulation are exposed to hemodynamic forces, such as cyclic strain, hydrostatic forces, and shear stress caused by the blood fluid's frictional force. Endothelial cells perceive mechanical forces via mechanosensors and thus elicit physiological reactions such as alterations in vessel width. The mechanosensors considered comprise ion channels, structures linked to the plasma membrane, cytoskeletal spectrin scaffold, mechanoreceptors, and junctional proteins. This review focuses on endothelial mechanosensors and how they alter the vascular functions of endothelial cells. The current state of knowledge on the dysregulation of endothelial mechanosensitivity in disease is briefly presented. The interplay in mechanical perception between endothelial cells and vascular smooth muscle cells is briefly outlined. Finally, future research avenues are highlighted, which are necessary to overcome existing limitations.

Effects of alfa lipoic acid and coenzyme Q10 treatment on AFB1-induced oxidative, inflammatory, and DNA damages in rats

Food contamination with Aflatoxin B1 (AFB1) is a worldwide concern that adversely affects animal and human health. The study aimed to evaluate the protective effect of alpha lipoic acid (ALA) and/or co-enzyme Q10 (CQ10) against the harmful effects of AFB1 on the liver and kidneys. Fifty-six mature male Wistar Albino rats (180-200 g) were divided into seven groups, each with eight rats: (1) saline was given as a control, (2) ALA (100 mg/kg bw/day) was given by stomach gavage for fifteen days, and (3) CQ10 (10 mg/kg bw/day) was given by stomach gavage for fifteen days. Group (4) orally given AFB1 (2.5 mg/kg bw) on days 12th and 14th, (5) received AFB1 and ALA, (6) received AFB1 and CQ10, and (7) received AFB1, ALA, and CQ10, as previously described in the ALA, CQ10, and AFB1 groups. After the exposure to AFB1, a significant increase in liver markers (AST, ALT, ALP, and LDH) and renal function tests (BUN and creatinine) was observed compared with the control. ALA and/or CQ10 significantly reduced enzymes of liver and renal functions, as compared with AFB1. AFB1 exposure threw off the balance between oxidants and antioxidants. Still, ALA and/or CQ10 made oxidative stress (MDA, NO, and 8-OHdG) much lower and antioxidant activities (GSH, GSH-Px, SOD, and CAT) much higher. When we used the two together, the activities matched the control levels. Interestingly, this study shows that ALA and CQ10 significantly lowered IL-1β, IL-6, and TNF-α levels compared to the control values when used together after AFB1 exposure caused robust inflammation. Some CQ10 treatment parameters significantly outperformed those of ALA. ALA and CQ10 together worked better than either one alone to protect against AFB1-induced toxicity in the hepatic and renal parenchyma in terms of reducing inflammation, preventing DNA damage, and fighting free radicals.

Roles of mitochondrial dynamics and mitophagy in diabetic myocardial microvascular injury

Myocardial microvessels are composed of a monolayer of endothelial cells, which play a crucial role in maintaining vascular barrier function, luminal latency, vascular tone, and myocardial perfusion. Endothelial dysfunction is a key factor in the development of cardiac microvascular injury and diabetic cardiomyopathy. In addition to their role in glucose oxidation and energy metabolism, mitochondria also participate in non-metabolic processes such as apoptosis, intracellular ion handling, and redox balancing. Mitochondrial dynamics and mitophagy are responsible for regulating the quality and quantity of mitochondria in response to hyperglycemia. However, these endogenous homeostatic mechanisms can both preserve and/or disrupt non-metabolic mitochondrial functions during diabetic endothelial damage and cardiac microvascular injury. This review provides an overview of the molecular features and regulatory mechanisms of mitochondrial dynamics and mitophagy. Furthermore, we summarize findings from various investigations that suggest abnormal mitochondrial dynamics and defective mitophagy contribute to the development of diabetic endothelial dysfunction and myocardial microvascular injury. Finally, we discuss different therapeutic strategies aimed at improving endothelial homeostasis and cardiac microvascular function through the enhancement of mitochondrial dynamics and mitophagy.

Methods to evaluate vascular function: a crucial approach towards predictive, preventive, and personalised medicine

Endothelium, the gatekeeper of our blood vessels, is highly heterogeneous and a crucial physical barrier with the ability to produce vasoactive and protective mediators under physiological conditions. It regulates vascular tone, haemostasis, vascular inflammation, remodelling, and angiogenesis. Several cardio-, reno-, and cerebrovascular diseases begin with the dysfunction of endothelial cells, and more recently, COVID-19 was also associated with endothelial disease highlighting the need to monitor its function towards prevention and reduction of vascular dysfunction. Endothelial cells are an important therapeutic target in predictive, preventive, and personalised (3P) medicine with upmost importance in vascular diseases. The development of novel non-invasive techniques to access endothelial dysfunction for use in combination with existing clinical imaging modalities provides a feasible opportunity to reduce the burden of vascular disease.

This review summarises recent advances in the principles of endothelial function measurements. This article presents an overview of invasive and non-invasive techniques to determine vascular function and their major advantages and disadvantages. In addition, the article describes mechanisms underlying the regulation of vascular function and dysfunction and potential new biomarkers of endothelial damage. Recognising these biomarkers is fundamental towards a shift from reactive to 3P medicine in the vascular field. Identifying vascular dysfunction earlier with non-invasive or minimally invasive techniques adds value to predictive diagnostics and targeted prevention (primary, secondary, tertiary care). In addition, vascular dysfunction is a potential target for treatments tailored to the person.

Effects of alpha lipoic acid on metabolic syndrome: A comprehensive review

Metabolic syndrome (MetS) is a multifactorial disease with medical conditions such as hypertension, diabetes, obesity, dyslipidemia, and insulin resistance. Alpha-lipoic acid (α-LA) possesses various pharmacological effects, including antidiabetic, antiobesity, hypotensive, and hypolipidemia actions. It exhibits reactive oxygen species scavenger properties against oxidation and age-related inflammation and refines MetS components. Also, α-LA activates the 5' adenosine monophosphate-activated protein kinase and inhibits the NFκb. It can decrease cholesterol biosynthesis, fatty acid β-oxidation, and vascular stiffness. α-LA decreases lipogenesis, cholesterol biosynthesis, low-density lipoprotein and very low-density lipoprotein levels, and atherosclerosis. Moreover, α-LA increases insulin secretion, glucose transport, and insulin sensitivity. These changes occur via PI3K/Akt activation. On the other hand, α-LA treats central obesity by increasing adiponectin levels and mitochondrial biogenesis and can reduce food intake mainly by SIRT1 stimulation. In this review, the most relevant articles have been discussed to determine the effects of α-LA on different components of MetS with a special focus on different molecular mechanisms behind these effects. This review exhibits the potential properties of α-LA in managing MetS; however, high-quality studies are needed to confirm the clinical efficacy of α-LA.

Luteolin Improves Perivascular Adipose Tissue Profile and Vascular Dysfunction in Goto-Kakizaki Rats

We investigated the effects of luteolin on metabolism, vascular reactivity, and perivascular adipose tissue (PVAT) in nonobese type 2 diabetes mellitus animal model, Goto-Kakizaki (GK) rats. Methods: Wistar and GK rats were divided in two groups: (1) control groups treated with vehicle; (2) groups treated with luteolin (10 mg/kg/day, for 2 months). Several metabolic parameters such as adiposity index, lipid profile, fasting glucose levels, glucose and insulin tolerance tests were determined. Endothelial function and contraction studies were performed in aortas with (PVAT+) or without (PVAT−) periaortic adipose tissue. We also studied vascular oxidative stress, glycation and assessed CRP, CCL2, and nitrotyrosine levels in PVAT. Results: Endothelial function was impaired in diabetic GK rats (47% (GK − PVAT) and 65% (GK + PVAT) inhibition of maximal endothelial dependent relaxation) and significantly improved by luteolin treatment (29% (GK − PVAT) and 22% (GK + PVAT) inhibition of maximal endothelial dependent relaxation, p < 0.01). Vascular oxidative stress and advanced glycation end-products’ levels were increased in aortic rings (~2-fold, p < 0.05) of diabetic rats and significantly improved by luteolin treatment (to levels not significantly different from controls). Periaortic adipose tissue anti-contractile action was significantly rescued with luteolin administration (p < 0.001). In addition, luteolin treatment significantly recovered proinflammatory and pro-oxidant PVAT phenotype, and improved systemic and metabolic parameters in GK rats. Conclusions: Luteolin ameliorates endothelial dysfunction in type 2 diabetes and exhibits therapeutic potential for the treatment of vascular complications associated with type 2 diabetes.

The Role of Epidermal Growth Factor Receptor Family of Receptor Tyrosine Kinases in Mediating Diabetes-Induced Cardiovascular Complications

Diabetes mellitus is a major debilitating disease whose global incidence is progressively increasing with currently over 463 million adult sufferers and this figure will likely reach over 700 million by the year 2045. It is the complications of diabetes such as cardiovascular, renal, neuronal and ocular dysfunction that lead to increased patient morbidity and mortality. Of these, cardiovascular complications that can result in stroke and cardiomyopathies are 2- to 5-fold more likely in diabetes but the underlying mechanisms involved in their development are not fully understood. Emerging research suggests that members of the Epidermal Growth Factor Receptor (EGFR/ErbB/HER) family of tyrosine kinases can have a dual role in that they are beneficially required for normal development and physiological functioning of the cardiovascular system (CVS) as well as in salvage pathways following acute cardiac ischemia/reperfusion injury but their chronic dysregulation may also be intricately involved in mediating diabetes-induced cardiovascular pathologies. Here we review the evidence for EGFR/ErbB/HER receptors in mediating these dual roles in the CVS and also discuss their potential interplay with the Renin-Angiotensin-Aldosterone System heptapeptide, Angiotensin-(1-7), as well the arachidonic acid metabolite, 20-HETE (20-hydroxy-5, 8, 11, 14-eicosatetraenoic acid). A greater understanding of the multi-faceted roles of EGFR/ErbB/HER family of tyrosine kinases and their interplay with other key modulators of cardiovascular function could facilitate the development of novel therapeutic strategies for treating diabetes-induced cardiovascular complications.

An Overview of NO Signaling Pathways in Aging

Nitric Oxide (NO) is a potent signaling molecule involved in the regulation of various cellular mechanisms and pathways under normal and pathological conditions. NO production, its effects, and its efficacy, are extremely sensitive to aging-related changes in the cells. Herein, we review the mechanisms of NO signaling in the cardiovascular system, central nervous system (CNS), reproduction system, as well as its effects on skin, kidneys, thyroid, muscles, and on the immune system during aging. The aging-related decline in NO levels and bioavailability is also discussed in this review. The decreased NO production by endothelial nitric oxide synthase (eNOS) was revealed in the aged cardiovascular system. In the CNS, the decline of the neuronal (n)NOS production of NO was related to the impairment of memory, sleep, and cognition. NO played an important role in the aging of oocytes and aged-induced erectile dysfunction. Aging downregulated NO signaling pathways in endothelial cells resulting in skin, kidney, thyroid, and muscle disorders. Putative therapeutic agents (natural/synthetic) affecting NO signaling mechanisms in the aging process are discussed in the present study. In summary, all of the studies reviewed demonstrate that NO plays a crucial role in the cellular aging processes.

The effect of Alpha-lipoic acid supplementation on endothelial function: A systematic review and meta-analysis

There is evidence that alpha-lipoic acid (ALA) supplementation plays an important role in preventing cardiovascular diseases. However, its effect, specifically, on endothelial function (EF) is unclear. Therefore, this systematic review and meta-analysis aimed to evaluate the effects of ALA supplementation on EF. Databases including PubMed/Medline, Scopus, and ISI Web of Science were searched to identify eligible publications from inception up to April 2020. Randomized controlled trials assessing the effect of ALA supplementation on flow-mediated dilation (FMD) levels in adults were included. The pooled results were obtained using the random-effects model and are expressed as weighted mean differences (WMD) with 95% confidence intervals (CI). Five studies including six effect sizes and 300 participants were included. ALA supplementation significantly increased FMD levels by 2.36% (95% CI: 1.21-3.51; p < .001), compared with the control. Subgroup analyses suggested that the effects of ALA on FMD could be changed by age and health status of the participants. Dose-response analysis also showed that ALA dosage had a significant non-linear effect on FMD levels. The results showed that ALA supplementation appears to improve the EF. However, the role of ALA supplementation in improving other biomarkers of EF requires further research.

Pulmonary and vascular effects of acute ozone exposure in diabetic rats fed an atherogenic diet

Air pollutants may increase risk for cardiopulmonary disease, particularly in susceptible populations with metabolic stressors such as diabetes and unhealthy diet. We investigated effects of inhaled ozone exposure and high-cholesterol diet (HCD) in healthy Wistar and Wistar-derived Goto-Kakizaki (GK) rats, a non-obese model of type 2 diabetes. Male rats (4-week old) were fed normal diet (ND) or HCD for 12 weeks and then exposed to filtered air or 1.0 ppm ozone (6 h/day) for 1 or 2 days. We examined pulmonary, vascular, hematology, and inflammatory responses after each exposure plus an 18-h recovery period. In both strains, ozone induced acute bronchiolar epithelial necrosis and inflammation on histopathology and pulmonary protein leakage and neutrophilia; the protein leakage was more rapid and persistent in GK compared to Wistar rats. Ozone also decreased lymphocytes after day 1 in both strains consuming ND (~50%), while HCD increased circulating leukocytes. Ozone increased plasma thrombin/antithrombin complexes and platelet disaggregation in Wistar rats on HCD and exacerbated diet effects on serum IFN-γ, IL-6, KC-GRO, IL-13, and TNF-α, which were higher with HCD (Wistar>GK). Ex vivo aortic contractility to phenylephrine was lower in GK versus Wistar rats at baseline(~30%); ozone enhanced this effect in Wistar rats on ND. GK rats on HCD had higher aortic e-NOS and tPA expression compared to Wistar rats. Ozone increased e-NOS in GK rats on ND (~3-fold) and Wistar rats on HCD (~2-fold). These findings demonstrate ways in which underlying diabetes and HCD may exacerbate pulmonary, systemic, and vascular effects of inhaled pollutants.

Omentin: A novel therapeutic approach for the treatment of endothelial dysfunction in type 2 diabetes

BACKGROUND

Perivascular adipose tissue (PVAT) locally influences the functioning of blood vessels and promotes vascular complications associated with diabetes and obesity. The aim of this work was to study the impact of omentin-1 on endothelial function and PVAT in a non-obese type 2 diabetes mellitus animal model, Goto-Kakizaki (GK) rats with or without high fat diet.

MATERIAL AND METHODS

Diabetic GK rats were divided into four groups: 1) control group; 2) group treated with omentin-1; 3) group of GK rats fed a high fat diet (GKHFD) and 4) group of GKHFD treated with omentin-1. Several in vivo parameters such as adiposity and Lee indexes, lipid profile, fasting glucose levels, glucose and insulin tolerance tests were determined. At the vascular level, endothelial dependent and independent relaxation and contraction studies were performed in aortic rings in the absence (PVAT-) or in the presence (PVAT+) of thoracic PVAT. We also evaluated vascular oxidative stress and determined the pro-inflammatory status of PVAT.

RESULTS

Endothelium-dependent relaxation to acetylcholine, assessed by wire myography, was impaired in GK and GKHFD rats and improved by the omentin-1 treatment. In addition, vascular superoxide production was increased in the vascular wall of diabetic rats, accompanied by reduced nitric oxide bioavailability and significantly improved by omentin treatment. PVAT anti-contractile action found under physiological conditions was lost in type 2 diabetes, and partially recovered with omentin-1 administration. In addition, omentin-1 treatment significantly improved proinflammatory and pro-oxidant PVAT phenotype (decreasing C-reactive protein and nitrotyrosine levels). Furthermore, it was observed an improvement in various systemic and metabolic biochemical parameters of diabetic animals treated for one month with omentin.

CONCLUSIONS

Omentin-1 ameliorates endothelial dysfunction in type 2 diabetes and presents therapeutic potential for the treatment of vascular complications associated with type 2 diabetes.

Increased inflammation, oxidative stress and a reduction in antioxidant defense enzymes in perivascular adipose tissue contribute to vascular dysfunction in type 2 diabetes

BACKGROUND

Perivascular adipose tissue (PVAT) surrounds most large blood vessels and plays an important role in vascular homeostasis. The present study was conducted to investigate the contribution of PVAT to vascular dysfunction in a rat model of type 2 diabetes.

MATERIAL AND METHODS

Several in vivo parameters such as lipid profile (total cholesterol and triglyceride systemic levels), fasting glucose levels, glucose tolerance and insulin sensitivity (through glucose and insulin tolerance tests, respectively) were determined in Goto-Kakizaki (GK) diabetic rats and compared with control Wistar rats. At the vascular level, endothelial dependent and independent relaxation and contraction studies were performed in aortic rings in the absence (PVAT-) or in the presence (PVAT+) of thoracic PVAT. We also evaluated vascular oxidative stress and performed western blots, PCR and immunohistochemistry analysis of cytokines and various enzymes in PVAT.

RESULTS

Endothelium-dependent relaxation to acetylcholine, assessed by wire myography, was impaired in GK rats and improved by the antioxidant TEMPOL and by the TLR4 inhibitor, CLI-095 suggesting an increase in oxidative stress and inflammation. In addition, vascular superoxide and peroxynitrite production was increased in the vascular wall of diabetic rats, accompanied by reduced nitric oxide bioavailability. The presence of PVAT had an anticontractile effect in response to phenylephrine in Wistar rats that was lost in GK rats. Western blot and immunohistochemistry analysis revealed that PVAT phenotype shifts, under diabetic conditions, towards a proinflammatory (with increment in CRP, CCL2, CD36), pro-oxidant (increased levels of aldose reductase, and reduced levels of antioxidant deference enzymes) and vasoconstriction state.

CONCLUSION

Our data suggest that this rat model of type 2 diabetes is associated with perivascular adipose dysfunction that contributes to oxidative stress, inflammation and endothelial dysfunction.

Lipoic acid antagonizes paraquat-induced vascular endothelial dysfunction by suppressing mitochondrial reactive oxidative stress

Paraquat (PQ) is a widely used herbicide in the agricultural field. The lack of an effective antidote is the significant cause of high mortality in PQ poisoning. Here, we investigate the antagonistic effects of alpha lipoic acid (α-LA), a naturally existing antioxidant, on PQ toxicity in human microvascular endothelial cells (HMEC-1). All the doses of 250, 500 and 1000 μM α-LA significantly inhibited 1000 μM PQ-induced cytotoxicity in HMEC-1 cells. α-LA pretreatment remarkably diminished the damage to cell migration ability, recovered the declined levels of the vasodilator factor nitric oxide (NO), elevated the expression level of endothelial nitric oxide synthases (eNOS), and inhibited the upregulated expression of vasoconstrictor factor endothelin-1 (ET-1). Moreover, α-LA pretreatment inhibited reactive oxygen species (ROS) generation, suppressed the damage to the mitochondrial membrane potential (ΔΨ _m) and mitigated the inhibition of adenosine triphosphate (ATP) production in HMEC-1 cells. These results suggested that α-LA could alleviate PQ-induced endothelial dysfunction by suppressing oxidative stress. In summary, our present study provides novel insight into the protective effects and pharmacological potential of α-LA against PQ toxicity in microvascular endothelial cells.

The effect of alpha-lipoic acid on expression of VCAM-1 in type 2 diabetic rat

Macrovascular diabetes complications are generally caused by a process called atherosclerosis. Evidences suggest that to initiate atherosclerosis, oxidated low-density lipoprotein (oxLDL) has to promote the expression of adhesion molecule. Several studies have evidenced the relevance of oxidative stress and atherosclerosis. However, the protective effect of alpha-lipoic acid (ALA) at atherosclerosis still needs to be explored. This study is aimed at investigating the concentration of plasma oxLDL and the expression of adhesion molecule of type 2 diabetes mellitus (DM) using rat model. Eighteen male rats were segregated into three groups labeled as control group, DM group and DM+ALA group. Type 2 diabetes was induced by intraperitoneal injection of streptozotocin (50 mg/kg) followed by nicotinamide (110 mg/kg). ALA was administered at a dose of 60 mg/kg body weight/day throughout the feeding period of 3 weeks. Plasma oxLDL concentration was measured by enzyme-linked immunosorbent assays and expression of vascular cell adhesion molecule-1 (VCAM-1) was measured by immunohistochemistry. Expression of abdominal aortic adhesion molecule was assessed by calculation with Adobe Photoshop CS3. Analysis of variance test was used to compare the concentration of plasma oxLDL and expression of adhesion molecule. A P-value of 0.05 was considered statistically significant. Plasma oxLDL was lower in diabetic rat+ALA compared with the diabetic rat. Percentage of area VCAM-1 in DM+ALA group was lower than DM group. There were no significant differences between groups in intensity of VCAM-1. In conclusion, ALA showed protective effects against early atherosclerosis in diabetic rats.

Alpha-lipoic acid (ALA) supplementation effect on glycemic and inflammatory biomarkers: A Systematic Review and meta- analysis

BACKGROUND & AIMS

Several randomized clinical trials (RCTs) have investigated the effect of Alpha - Lipoic Acid (ALA) supplementation on metabolic parameters, with conflicting results. Therefore, the present study assessed the effect of ALA on some glycemic and inflammatory parameters.

METHODS

A comprehensive literature search was conducted up from inception to July 2018 on PubMed, Scopus, Cochrane databases, Google Scholar, ProQuest, Web of Science, and Embase. From among eligible trials, 41 articles were selected for the meta-analysis. Two reviewers independently assessed the risk of bias and extracted data from the included studies. Meta-analyses using the random-effects model were performed to analyze the data.

RESULTS

Based on the Cochrane risk of bias tool, 19 articles had a good quality, 16 trials had a poor quality and 6 trials had a fair quality. The results demonstrated the significant effect of ALA on Fasting Blood Sugar (FBS) (weighted mean difference (WMD)) = -6.57, 95% confidence interval (CI: -11.91 to -1.23, P = 0.016), Hemoglobin A1c (HbA1c) (WMD = -0.35, 95% CI: -0.55 to -0.15, P = 0.004), Tumor Necrosis Factor Alpha (TNF-α) (WMD = -1.57, 95% CI: -2.29 to -0.85, P < 0.05), Interleukin 6 levels (IL-6) (WMD = -1.15, 95% CI: -1.58 to -0.72, P < 0.001), and C-reactive protein (CRP) (WMD = -0.31, 95% CI: -0.47 to -0.16, P > 0.001). No effect was detected for ALA on insulin and the homeostatic model assessment of insulin resistance (HOMA-IR).

CONCLUSIONS

These findings suggest that ALA is a viable supplement to improve some of the glycemic and inflammatory biomarkers.

Vascular Oxidative Stress: Impact and Therapeutic Approaches

Oxidative stress has been defined as an imbalance between oxidants and antioxidants and more recently as a disruption of redox signaling and control. It is generally accepted that oxidative stress can lead to cell and tissue injury having a fundamental role in vascular dysfunction. Physiologically, reactive oxygen species (ROS) control vascular function by modulating various redox-sensitive signaling pathways. In vascular disorders, oxidative stress instigates endothelial dysfunction and inflammation, affecting several cells in the vascular wall. Vascular ROS are derived from multiple sources herein discussed, which are prime targets for therapeutic development. This review focuses on oxidative stress in vascular physiopathology and highlights different strategies to inhibit ROS production.

RBPs Play Important Roles in Vascular Endothelial Dysfunction Under Diabetic Conditions

Diabetes is one of the major health care problems worldwide leading to huge suffering and burden to patients and society. Diabetes is also considered as a cardiovascular disorder because of the correlation between diabetes and an increased incidence of cardiovascular disease. Vascular endothelial cell dysfunction is a major mediator of diabetic vascular complications. It has been established that diabetes contributes to significant alteration of the gene expression profile of vascular endothelial cells. Post-transcriptional regulation by RNA binding proteins (RBPs) plays an important role in the alteration of gene expression profile under diabetic conditions. The review focuses on the roles and mechanisms of critical RBPs toward diabetic vascular endothelial dysfunction. Deeper understanding of the post- transcriptional regulation by RBPs could lead to new therapeutic strategies against diabetic manifestation in the future.

Lipoic Acid Prevents High-Fat Diet-Induced Hepatic Steatosis in Goto Kakizaki Rats by Reducing Oxidative Stress Through Nrf2 Activation

Prevention of hepatic fat accumulation may be an important approach for liver diseases due to the increased relevance of hepatic steatosis in this field. This study was conducted to investigate the effects of the antioxidant α-lipoic acid (α-LA) on hepatic steatosis, hepatocellular function, and oxidative stress in a model of type 2 diabetes fed with a high fat diet (HFD). Goto-Kakizaki rats were randomly divided into four groups. The first group received only a standard rat diet (control GK) including groups 2 (HFD), 3 (vehicle group), and 4 (α-LA group), which were given HFD, ad libitum during three months. Wistar rats are the non-diabetic control group. Carbohydrate and lipid metabolism, liver function, plasma and liver tissue malondialdehyde (MDA), liver GSH, tumor necrosis factor-α (TNF-α) and nuclear factor E2 (erythroid-derived 2)-related factor-2 (Nrf2) levels were assessed in the different groups. Liver function was assessed using quantitative hepatobiliary scintigraphy, serum aspartate, and alanine aminotransferases (AST, ALT), alkaline phosphatase, gamma-glutamyltranspeptidase, and bilirubin levels. Histopathologically steatosis and fibrosis were evaluated. Type 2 diabetic animals fed with HFD showed a marked hepatic steatosis and a diminished hepatic extraction fraction and both were fully prevented with α-LA. Plasma and liver tissue MDA and hepatic TNF-α levels were significantly higher in the HFD group when compared with the control group and significantly lower in the α-LA group. Systemic and hepatic cholesterol, triglycerides, and serum uric acid levels were higher in hyperlipidemic GK rats and fully prevented with α-LA. In addition, nuclear Nrf2 activity was significantly diminished in GK rats and significantly augmented after α-LA treatment. In conclusion, α-LA strikingly ameliorates steatosis in this animal model of diabetes fed with HFD by decrementing the inflammatory marker TNF-α and reducing oxidative stress. α-LA might be considered a useful therapeutic tool to prevent hepatic steatosis by incrementing antioxidant defense systems through Nrf2 and consequently decreasing oxidative stress and inflammation in type 2 diabetes.

Endothelial function and dysfunction: Impact of metformin

Cardiovascular and metabolic diseases remain the leading cause of morbidity and mortality worldwide. Endothelial dysfunction is a key player in the initiation and progression of cardiovascular and metabolic diseases. Current evidence suggests that the anti-diabetic drug metformin improves insulin resistance and protects against endothelial dysfunction in the vasculature. Hereby, we provide a timely review on the protective effects and molecular mechanisms of metformin in preventing endothelial dysfunction and cardiovascular and metabolic diseases.

The Hepato-protective Effects of Portulaca oleracea L. extract: Review

BACKGROUND

Portulaca oleracea L. (Purslane) has been used in traditional medicine against hepatic injury, although its actual efficacy has not been fully understood. The present study aimed to critically review the recent literature data from 1990 to 2017 regarding the hepato-protective effects of Portulaca oleracea L. and its underlying mechanisms.

METHODS

Online literature resources were checked using different search engines such as Medline, PubMed, Iran Medex, Scopus, and Google Scholar to identify articles, editorials, and reviews about antidotal effects of Portulaca oleracea L. against hepatotoxic agents.

RESULTS

Few studies have indicated that Portulaca oleracea L. shows protective effects against hepatotoxic agents. However, due to lack of information in humans, more studies are needed to confirm the efficacy of Portulaca oleracea L. as a hepato-protective agent.

CONCLUSION

The study found that Portulaca oleracea L. may be effective on hepatotoxicity by modulating oxidative stress and inflammation.

Role of carnitine and its derivatives in the development and management of type 2 diabetes

Type 2 diabetes is a highly prevalent chronic metabolic disorder characterized by hyperglycemia and associated with several complications such as retinopathy, hyperlipidemia and polyneuropathy. The dysregulated fatty acid metabolism along with tissue lipid accumulation is generally assumed to be associated in the development of insulin resistance and T2D. Moreover, several studies suggest a central role for oxidative stress in the pathogenesis of the disease. Since L-carnitine (LC) has an indispensable role in lipid metabolism via its involvement in the β-oxidation of long-chain fatty acids and it has antioxidant properties as well, carnitine supplementation may prove to be an effective tool in the management of the clinical course of T2D. In this review we summarize the results from animal and clinical studies demonstrating the effects of supplementation with LC or LC derivatives (acetyl-LC, propionyl-LC) on various metabolic and clinical parameters associated with T2D.

The Sulforaphane and pyridoxamine supplementation normalize endothelial dysfunction associated with type 2 diabetes

In this study we investigate pyridoxamine (PM) and/or sulforaphane (SFN) as therapeutic interventions to determine whether activators of NFE2-related factor 2 (Nrf2) can be used in addition with inhibitors of advanced glycation end products (AGE) formation to attenuate oxidative stress and improve endothelial dysfunction in type 2 diabetes. Goto-kakizaki (GK) rats, an animal model of non-obese type 2 diabetes, were treated with or without PM and/or SFN during 8 weeks and compared with age-matched Wistar rats. At the end of the treatment, nitric oxide (NO)-dependent and independent vasorelaxation in isolated aorta and mesenteric arteries were evaluated. Metabolic profile, NO bioavailability and vascular oxidative stress, AGE and Nrf2 levels were also assessed. Diabetic GK rats presented significantly lower levels of Nrf2 and concomitantly exhibited higher levels of oxidative stress and endothelial dysfunction. PM and SFN as monotherapy were capable of significantly improving endothelial dysfunction in aorta and mesenteric arteries decreasing vascular oxidative damage, AGE and HbA1c levels. Furthermore, SFN + PM proved more effective reducing systemic free fatty acids levels, normalizing endothelial function, NO bioavailability and glycation in GK rats. Activators of Nrf2 can be used therapeutically in association with inhibitors of AGE and cross-linking formation to normalize endothelial dysfunction in type 2 diabetes.

THE MECHANISM OF ALPHA LIPOIC ACID ON REDUCING THE MDA LEVEL AND MCP-1 EXPRESSION IN ENDOTHELIAL DYSFUNCTION OF HYPERCHOLESTEROLEMIA RAT (Rattus norvegicus) MODEL

Endothelial dysfunction is an initial condition of atherosclerosis and other vascular diseases where one of the risk factors is hypercholesterolemia. Blood cholesterol levels is associated with an increase in the production of reactive oxygen species (ROS). The increasing of ROS production can cause increased oxidative stress which in turn resulting in endothelial dysfunction. Alpha lipoic acid (ALA) is one of the antioxidant compound that has been developed and studied. In this study we found that the use of ALA in Rattus norvegicus rats signifficantly lower the total cholesterol levels at dose 60 mg/kgBW (p=0.020). ALA also inhibit the expression of Monocyte Chemoattractant Protein-1 (MCP-1) at dose 60 mg/kgBW (p=0.044) and reduces the formation of Malondialdehyde (MDA) at dose 120 mg/kgBW (p=0.009), which is the initial stage of the atherogenic development and prognosis of events, thus, ALA can reduce the risk of further damage to the endothelium.

Adiponectin improves endothelial function in mesenteric arteries of rats fed a high-fat diet: role of perivascular adipose tissue

BACKGROUND AND PURPOSE

Adiponectin, the most abundant peptide secreted by adipocytes, is involved in the regulation of energy metabolism and vascular physiology. Here, we have investigated the effects of exogenous administration of adiponectin on metabolism, vascular reactivity and perivascular adipose tissue (PVAT) of mesenteric arteries in Wistar rats fed a high-fat diet.

EXPERIMENTAL APPROACH

The effects of adiponectin on NO-dependent and independent vasorelaxation were investigated in isolated mesenteric arteries from 12-month-old male Wistar rats (W12m) fed a high-fat diet (HFD) for 4 months and compared with those from age-matched rats given a control diet. Adiponectin ((96 μg·day^-1 ) was administered by continuous infusion with a minipump, implanted subcutaneously, for 28 days.

KEY RESULTS

Chronic adiponectin treatment reduced body weight, total cholesterol, free fatty acids, fasting glucose and area under the curve of intraperitoneal glucose tolerance test, compared with HFD rats. It also normalized NO-dependent vasorelaxation increasing endothelial NO synthase (eNOS) phosphorylation in mesenteric arteries of HFD rats. In PVAT from aged (W12m) and HFD rats there was increased expression of chemokines and pro-inflammatory adipokines, the latter being important contributors to endothelial dysfunction. Infusion of adiponectin reduced these changes.

CONCLUSIONS AND IMPLICATIONS

Adiponectin normalized endothelial cell function by a mechanism that involved increased eNOS phoshorylation and decreased PVAT inflammation. Detailed characterization of the adiponectin signalling pathway in the vasculature and perivascular fat is likely to provide novel approaches to the management of atherosclerosis and metabolic disease.

LINKED ARTICLES

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue - Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc.

Chronic treatment of (R)-α-lipoic acid reduces blood glucose and lipid levels in high-fat diet and low-dose streptozotocin-induced metabolic syndrome and type 2 diabetes in Sprague-Dawley rats

(R)‐ α ‐lipoic acid (ALA), an essential cofactor in mitochondrial respiration and a potential antioxidant, possesses a wide array of metabolic benefits including anti‐obesity, glucose lowering, insulin‐sensitizing, and lipid‐lowering effects. In this study, the curative effects of ALA (100 mg/kg) on a spectrum of conditions related to metabolic syndrome and type 2 diabetes (T2D) were investigated in a high‐fat diet (HFD)‐fed and low‐dose streptozotocin (STZ)‐induced rat model of metabolic syndrome and T2D. The marked rise in the levels of glucose, triglycerides, total‐cholesterol, LDL‐cholesterol, and VLDL‐cholesterol in the blood of HFD‐fed and low‐dose STZ‐injected rats were significantly reduced by ALA treatment. Furthermore, ALA treatment significantly increased the serum HDL‐cholesterol levels and tended to inhibit diabetes‐induced weight reduction. Mathematical computational analysis revealed that ALA also significantly improved insulin sensitivity and reduced the risk of atherosclerotic lesions and coronary atherogenesis. This study provides scientific evidence to substantiate the use of ALA to mitigate the glucose and lipid abnormality in metabolic syndrome and T2D.

Methylglyoxal in Metabolic Disorders: Facts, Myths, and Promises

Glucose and fructose metabolism originates the highly reactive byproduct methylglyoxal (MG), which is a strong precursor of advanced glycation end products (AGE). The MG has been implicated in classical diabetic complications such as retinopathy, nephropathy, and neuropathy, but has also been recently associated with cardiovascular diseases and central nervous system disorders such as cerebrovascular diseases and dementia. Recent studies even suggested its involvement in insulin resistance and beta-cell dysfunction, contributing to the early development of type 2 diabetes and creating a vicious circle between glycation and hyperglycemia. Despite several drugs and natural compounds have been identified in the last years in order to scavenge MG and inhibit AGE formation, we are still far from having an effective strategy to prevent MG-induced mechanisms. This review summarizes the endogenous and exogenous sources of MG, also addressing the current controversy about the importance of exogenous MG sources. The mechanisms by which MG changes cell behavior and its involvement in type 2 diabetes development and complications and the pathophysiological implication are also summarized. Particular emphasis will be given to pathophysiological relevance of studies using higher MG doses, which may have produced biased results. Finally, we also overview the current knowledge about detoxification strategies, including modulation of endogenous enzymatic systems and exogenous compounds able to inhibit MG effects on biological systems.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Diosgenin reorganises hyperglycaemia and distorted tissue lipid profile in high-fat diet-streptozotocin-induced diabetic rats

BACKGROUND

Diabetes is often connected with significant morbidity, mortality and also has a pivotal role in the development of cardiovascular diseases. Diet intervention, particularly naturaceutical antioxidants have anti-diabetic potential and avert oxidative damage linked with diabetic pathogenesis. The present study investigated the effects of diosgenin, a saponin from fenugreek, on the changes in lipid profile in plasma, liver, heart and brain in high-fat diet-streptozotocin (HFD-STZ)-induced diabetic rats. Diosgenin was administered to HFD-STZ induced diabetic rats by orally at 60 mg kg(-1) body weight for 30 days to assess its effects on body weight gain, glucose, insulin, insulin resistance and cholesterol, triglycerides, free fatty acids and phospholipids in plasma, liver, heart and brain.

RESULTS

The levels of body weight, glucose, insulin, insulin resistance, cholesterol, triglycerides, free fatty acids, phospholipids, VLDL-C and LDL-C were increased significantly (P < 0.05) whereas HDL-C level decreased in the HFD/STZ diabetic rats. Administration of diosgenin to HFD-STZ diabetic rats caused a decrease in body weight gain, blood glucose, insulin, insulin resistance and also it modulated lipid profile in plasma and tissues.

CONCLUSION

The traditional plant fenugreek and its constituents mediate its anti-diabetic potential through mitigating hyperglycaemic status, altering insulin resistance by alleviating metabolic dysregulation of lipid profile in both plasma and tissues.

Ginkgolide B increases hydrogen sulfide and protects against endothelial dysfunction in diabetic rats

Aim

To evaluate the effect of ginkgolide B treatment on vascular endothelial function in diabetic rats.

Methods

The study included four groups with 15 male Sprague-Dawley rats: control group; control group treated with ginkgolide B; diabetic group; and diabetic treated with ginkgolide B. The activity of superoxide dismutase (SOD), malondialdehyde content, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, and glutathione peroxidase 1 (GPX1) protein expression were determined in aortic tissues. Vasoconstriction to phenylephrine (PHE) and vasorelaxation to acetylcholine (Ach) and sodium nitroprusside (SNP) were assessed in aortic rings. Nitric oxide (NO) and hydrogen sulfide (H₂S) were measured, as well as cystathionine γ lyase (CSE) and cystathionine β synthetase (CBS) protein expression, and endothelial nitric oxide synthase (eNOS) activity.

Results

Diabetes significantly impaired PHE-induced vasoconstriction and Ach-induced vasorelaxation (P < 0.001), reduced NO bioavailability and H₂S production (P < 0.001), SOD activity, and GPX1 protein expression (P < 0.001), and increased malondialdehyde content and NADPH oxidase subunits, and CSE and CBS protein expression (P < 0.001). Ginkgolide B treatment improved PHE vasoconstriction and Ach vasorelaxation (P < 0.001), restored SOD (P = 0.005) and eNOS (P < 0.001) activities, H₂S production (P = 0.044) and decreased malondialdehyde content (P = 0.014). Vasorelaxation to SNP was not significantly different in control and diabetic rats with or without ginkgolide B treatment. Besides, ginkgolide B increased GPX1 protein expression and reduced NADPH oxidase subunits, CBS and CSE protein expression.

Conclusion

Ginkgolide B alleviates endothelial dysfunction by reducing oxidative stress and elevating NO bioavailability and H₂S production in diabetic rats.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.

The protective effect of lipoic acid on selected cardiovascular diseases caused by age-related oxidative stress

Oxidative stress is considered to be the primary cause of many cardiovascular diseases, including endothelial dysfunction in atherosclerosis and ischemic heart disease, hypertension, and heart failure. Oxidative stress increases during the aging process, resulting in either increased reactive oxygen species (ROS) production or decreased antioxidant defense. The increase in the incidence of cardiovascular disease is directly related to age. Aging is also associated with oxidative stress, which in turn leads to accelerated cellular senescence and organ dysfunction. Antioxidants may help lower the incidence of some pathologies of cardiovascular diseases and have antiaging properties. Lipoic acid (LA) is a natural antioxidant which is believed to have a beneficial effect on oxidative stress parameters in relation to diseases of the cardiovascular system.

Alpha-lipoic acid activates eNOS through activation of PI3-kinase/Akt signaling pathway

BACKGROUND

Lipoic acid (LA) exerts therapeutic effects on cardiovascular diseases. However, the mechanisms underlying these therapeutic effects remain elusive. Endothelial nitric oxide synthase (eNOS) plays a critical role in cardiovascular homeostasis. LA was shown to potently activate PI3-kinase/Akt pathway, and the latter is critical in the regulation of eNOS activity. In the present study, we test the hypothesis that LA improves endothelial function through PI3-kinase/Akt-mediated eNOS activation.

METHODS AND RESULTS

Western blot analysis showed that LA time- and dose-dependently induced phosphorylation of Akt and eNOS in human umbilical vein endothelial cells (HUVECs). Both PI3-kinase and Akt inhibitors abolished LA-induced eNOS phosphorylation, indicating that LA induces eNOS phosphorylation through the PI3-kinase/Akt pathway. This increase in eNOS phosphorylation was paralleled by an increase in NO release by HUVECs, supporting its relevance in eNOS activity regulation. Myograph analysis revealed that LA relaxed phenylephrine-induced contraction. Endothelium removal and NOS inhibition by L-NAME abolished this vasodilator action of LA, and Akt but not AMPK inhibition significantly reduced the vasodilator action of LA, indicating that it is mediated by PI3-kinase/Akt pathway-dependent activation of eNOS. Consistent with in vitro results, intraperitoneal injection with LA significantly increased plasma nitrite and nitrate levels in C57Bl/6j mice.

CONCLUSIONS

LA activates eNOS through a PI3-kinase/Akt signaling pathway-dependent mechanism, offering a potential molecular basis for the therapeutic effects of LA on cardiovascular diseases.

Catechin averts experimental diabetes mellitus-induced vascular endothelial structural and functional abnormalities

Diabetes mellitus is associated with an induction of vascular endothelial dysfunction (VED), an initial event that could lead to the pathogenesis of atherosclerosis and hypertension. Previous studies showed that catechin, a key component of green tea, possesses vascular beneficial effects. We investigated the effect of catechin hydrate in diabetes mellitus-induced experimental vascular endothelial abnormalities (VEA). Streptozotocin (50 mg/kg, i.p., once) administration to rats produced diabetes mellitus, which subsequently induced VEA in 8 weeks by markedly attenuating acetylcholine-induced endothelium-dependent relaxation in the isolated aortic ring preparation, decreasing aortic and serum nitrite/nitrate concentrations and impairing aortic endothelial integrity. These abnormalities in diabetic rats were accompanied with elevated aortic superoxide anion generation and serum lipid peroxidation in addition to hyperglycemia. Catechin hydrate treatment (50 mg/kg/day p.o., 3 weeks) markedly prevented diabetes mellitus-induced VEA and vascular oxidative stress. Intriguingly, in vitro incubation of L-NAME (100 μM), an inhibitor of nitric oxide synthase, or Wortmannin (100 nM), a selective inhibitor of phosphatidylinositol 3-kinase (PI3K), markedly prevented catechin hydrate-induced improvement in acetylcholine-provoked endothelium-dependent relaxation in the diabetic rat aorta. Moreover, catechin hydrate treatment considerably reduced the elevated level of serum glucose in diabetic rats. In conclusion, catechin hydrate treatment prevents diabetes mellitus-induced VED through the activation of endothelial PI3K signal and subsequent activation of eNOS and generation of nitric oxide. In addition, reduction in high glucose, vascular oxidative stress, and lipid peroxidation might additionally contribute to catechin hydrate-associated prevention of diabetic VEA.

Anti-inflammation effect of Exercise and Korean red ginseng in aging model rats with diet-induced atherosclerosis

BACKGROUND/OBJECTIVES

The aim of this study was to investigate the effects of exercise (EX) and Korean red ginseng (KRG) on inflammation mechanism in aging model rats with diet-induced atherosclerosis.

MATERIALS/METHODS

Forty-eight male Sprague-Dawley rats were divided into 6 groups: Young control (Y-C), Aging control (A-C), A-C with HFD (AHF), AHF with EX (AHF-EX), AHF-EX with KRG (AHF-EX+RG), and AHF with KRG (AHF-RG). Aging was induced by D-gal (100mg/kg) and atherosclerosis was induced by HFD (60% fat) for 9 weeks. The experimental rats were performed swimming (60 min/day, 5 days/week) and supplied KRG orally (dose of 200 mg/kg) for 8 weeks. All rat aorta samples were harvested for biochemical and immunohistochemical analyses.

REULTS

The EX and KRG supplementation significantly inhibited body weight and levels of TC, TG, LDL-C, and enhance of HDL-C compared with untreated AHF groups. AHF-EX, AHF-EX+RG, and AHF-RG group showed a decreased plasma CRP and increase plasma NO activities compared to AHF group. In addition, these groups revealed reduced 4-HNE, NF-kB, TNF-α, IL-6, COX-2, ICAM-1, VCAM-1 and enhanced eNOS expression in the aorta.

CONCLUSION

These results suggest that EX alone, KRG alone, and combined treatment of EX and KRG may be an effective anti-inflammatory therapeutic for the atherosclerosis, possibly acting via the decreased of CRP and pro-inflammation proteins and the increased NO and eNOS.

Low-molecular-weight fucoidan protects endothelial function and ameliorates basal hypertension in diabetic Goto-Kakizaki rats

Endothelial dysfunction, characterized by impairment of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) bioavailability, has been implicated in diabetic cardiovascular pathogenesis. In this study, low-molecular-weight fucoidan (LMWF), which has multiple biological activities including anti-inflammatory and anti-oxidative properties, was investigated for its protective effect against endothelial dysfunction in Goto-Kakizaki type 2 diabetic rats. LMWF (50, 100, or 200 mg/kg/day) or probucol (100 mg/kg/day) were given to diabetic rats for 12 weeks. Basal blood pressure, acetylcholine- or flow-mediated relaxation of mesenteric and paw arteries, endothelium-dependent dilation of aorta, eNOS phosphorylation, and NO production were measured using laser Doppler flowmetry, force myograph, hematoxylin and eosin staining, western blot analysis, and an NO assay. We found that LMWF robustly ameliorated the basal hypertension and impairment of endothelium-dependent relaxation in the aorta, as well as mesenteric and paw arteries in diabetic rats. In addition, the reduction in eNOS phosphorylation at Ser1177, eNOS expression, and NO production because of diabetes were partially reversed by LMWF treatment. However, probucol, a lipid-modifying drug with antioxidant properties, displayed only mild effects. Moreover, LMWF induced, in a dose-dependent manner, endothelium-dependent vasodilation and eNOS phosphorylation at Ser1177 in normal aorta, and also promoted Ser1177 phosphorylation and NO synthesis in primary cultured vasoendothelial cells. Thus, these data demonstrate for the first time that fucoidan protects vasoendothelial function and reduces basal blood pressure in type 2 diabetes rats via, at least in part, preservation of eNOS function. Fucoidan is therefore a potential candidate drug for protection of endothelium in diabetic cardiovascular complications.

Effects of atorvastatin and insulin in vascular dysfunction associated with type 2 diabetes

Atorvastatin and insulin have distinct mechanisms of action to improve endothelial function. Therefore, we hypothesized that atorvastatin and insulin therapies alone or in combination could have beneficial effects on endothelium-dependent vascular reactivity, oxidative stress, inflammation and metabolic parameters in Goto-Kakizaki (GK) rats, a model of type 2 diabetes fed with atherogenic diet (GKAD). In parallel with the development of diabetes and lipid profile, the generation of oxidative stress was determined by measurement of lipid peroxides and oxidized proteins and the presence of inflammation was evaluated by assessing C-reactive protein (CRP). Additionally, endothelial dependent and independent vascular sensitivity to acetylcholine and sodium nitroprusside were evaluated. GKAD showed increased carbonyl stress, inflammation, fasting glycemia, dyslipidemia and endothelial dysfunction when compared to control GK rats. Noteworthy, supplementation with insulin deteriorated endothelial dysfunction while atorvastatin induced an improvement. Atorvastatin and insulin therapies in combination improved metabolic parameters, CRP levels and insulin resistance indexes and ameliorated endothelial dysfunction in GKAD rats while they were unable to reduce urinary 8-isoprostranes and plasma carbonyl compounds. The therapeutic association of atorvastatin and insulin provided a better metabolic control with a reduction in endothelial dysfunction in GKAD rats by a mechanism that involves an improvement in systemic inflammation.

Fish oil blunted nicotine-induced vascular endothelial abnormalities possibly via activation of PPARγ-eNOS-NO signals

Nicotine exposure is associated with an induction of vascular endothelial dysfunction (VED), a hallmark of various cardiovascular disorders. The present study investigated the effect of fish oil in nicotine-induced experimental VED. VED was assessed by employing isolated aortic ring preparation, estimating aortic and serum nitrite/nitrate, aortic superoxide anion generation, and serum TBARS, and carrying out electron microscopic and histological studies of thoracic aorta. Nicotine (2 mg/kg/day, i.p., 4 weeks) administration produced VED in rats by attenuating acetylcholine-induced endothelium-dependent relaxation in the isolated aortic ring preparation, decreasing aortic and serum nitrite/nitrate concentration, impairing endothelial integrity, and inducing vascular oxidative stress. Treatment with fish oil (2 mL/kg/day p.o., 4 weeks) markedly prevented nicotine-induced endothelial functional and structural abnormalities and oxidative stress. However, administration of GW9662, a selective inhibitor of PPARγ, to a significant degree attenuated fish oil-associated anti-oxidant action and vascular endothelial functional and structural improvements. Intriguingly, in vitro incubation of L-NAME (100 μM), an inhibitor of nitric oxide synthase (NOS), markedly attenuated fish oil-induced improvement in endothelium-dependent relaxation in the aorta of nicotine-administered rats. Nicotine administration altered the lipid profile by increasing serum total cholesterol, which was significantly prevented by fish oil treatment. The vascular protective potential of fish oil in preventing nicotine-induced VED may pertain to its additional properties (besides its lipid-lowering effect) such as activation of PPARγ and subsequent possible activation of endothelial NOS and generation of nitric oxide, and consequent reduction in oxidative stress.

Endothelial dysfunction - a major mediator of diabetic vascular disease

The vascular endothelium is a multifunctional organ and is critically involved in modulating vascular tone and structure. Endothelial cells produce a wide range of factors that also regulate cellular adhesion, thromboresistance, smooth muscle cell proliferation, and vessel wall inflammation. Thus, endothelial function is important for the homeostasis of the body and its dysfunction is associated with several pathophysiological conditions, including atherosclerosis, hypertension and diabetes. Patients with diabetes invariably show an impairment of endothelium-dependent vasodilation. Therefore, understanding and treating endothelial dysfunction is a major focus in the prevention of vascular complications associated with all forms of diabetes mellitus. The mechanisms of endothelial dysfunction in diabetes may point to new management strategies for the prevention of cardiovascular disease in diabetes. This review will focus on the mechanisms and therapeutics that specifically target endothelial dysfunction in the context of a diabetic setting. Mechanisms including altered glucose metabolism, impaired insulin signaling, low-grade inflammatory state, and increased reactive oxygen species generation will be discussed. The importance of developing new pharmacological approaches that upregulate endothelium-derived nitric oxide synthesis and target key vascular ROS-producing enzymes will be highlighted and new strategies that might prove clinically relevant in preventing the development and/or retarding the progression of diabetes associated vascular complications.

Coronary endothelial dysfunction and mitochondrial reactive oxygen species in type 2 diabetic mice

Endothelial cell (EC) dysfunction is implicated in cardiovascular diseases, including diabetes. The decrease in nitric oxide (NO) bioavailability is the hallmark of endothelial dysfunction, and it leads to attenuated vascular relaxation and atherosclerosis followed by a decrease in blood flow. In the heart, decreased coronary blood flow is responsible for insufficient oxygen supply to cardiomyocytes and, subsequently, increases the incidence of cardiac ischemia. In this study we investigate whether and how reactive oxygen species (ROS) in mitochondria contribute to coronary endothelial dysfunction in type 2 diabetic (T2D) mice. T2D was induced in mice by a high-fat diet combined with a single injection of low-dose streptozotocin. ACh-induced vascular relaxation was significantly attenuated in coronary arteries (CAs) from T2D mice compared with controls. The pharmacological approach reveals that NO-dependent, but not hyperpolarization- or prostacyclin-dependent, relaxation was decreased in CAs from T2D mice. Attenuated ACh-induced relaxation in CAs from T2D mice was restored toward control level by treatment with mitoTempol (a mitochondria-specific O2(-) scavenger). Coronary ECs isolated from T2D mice exhibited a significant increase in mitochondrial ROS concentration and decrease in SOD2 protein expression compared with coronary ECs isolated from control mice. Furthermore, protein ubiquitination of SOD2 was significantly increased in coronary ECs isolated from T2D mice. These results suggest that augmented SOD2 ubiquitination leads to the increase in mitochondrial ROS concentration in coronary ECs from T2D mice and attenuates coronary vascular relaxation in T2D mice.

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.

Methylglyoxal, obesity, and diabetes

Methylglyoxal (MG) is a highly reactive compound derived mainly from glucose and fructose metabolism. This metabolite has been implicated in diabetic complications as it is a strong AGE precursor. Furthermore, recent studies suggested a role for MG in insulin resistance and beta-cell dysfunction. Although several drugs have been developed in the recent years to scavenge MG and inhibit AGE formation, we are still far from having an effective strategy to prevent MG-induced mechanisms. This review summarizes the mechanisms of MG formation, detoxification, and action. Furthermore, we review the current knowledge about its implication on the pathophysiology and complications of obesity and diabetes.

A prescribed Chinese herbal medicine improves glucose profile and ameliorates oxidative stress in Goto-Kakisaki rats fed with high fat diet

Oxidative stress (OS) plays a role in hyperglycemia induced islet β cell dysfunction, however, studies on classic anti-oxidants didn’t show positive results in treating diabetes. We previously demonstrated that the prescribed Chinese herbal medicine preparation “Qing Huo Yi Hao” (QHYH) improved endothelial function in type 2 diabetic patients. QHYH protected endothelial cells from high glucose-induced damages by scavenging superoxide anion and reducing production of reactive oxygen species. Its active component protected C2C12 myotubes against palmitate-induced oxidative damage and mitochondrial dysfunction. In the present study, we investigated whether QHYH protected islet β cell function exacerbated by high fat diet (HFD) in hyperglycemic GK rats. 4-week-old male rats were randomly divided into high HFD feeding group (n = 20) and chow diet feeding group (n = 10). Each gram of HFD contained 4.8 kcal of energy, 52% of which from fat. Rats on HFD were further divided into 2 groups given either QHYH (3 ml/Kg/d) or saline through gastric tube. After intervention, serum glucose concentrations were monitored; IPGTTs were performed without anesthesia on 5 fasting rats randomly chosen from each group on week 4 and 16. Serum malondialdehyde (MDA) concentrations and activities of serum antioxidant enzymes were measured on week 4 and 16. Islet β cell mass and OS marker staining was done by immunohistochemistry on week 16. QHYH prevented the exacerbation of hyperglycemia in HFD feeding GK rats for 12 weeks. On week 16, it improved the exacerbated glucose tolerance and prevented the further loss of islet β cell mass induced by HFD. QHYH markedly decreased serum MDA concentration, increased serum catalase (CAT) and SOD activities on week 4. However, no differences of serum glucose concentration or OS were observed on week 16. We concluded that QHYH decreased hyperglycemia exacerbated by HFD in GK rats by improving β cell function partly via its antioxidant effect.

Alpha-lipoic acid protects against indomethacin-induced gastric oxidative toxicity by modulating antioxidant system

Gastroprotective effects of α-lipoic acid (ALA) against oxidative gastric damage induced by indomethacin (IND) have been investigated. All doses (50, 75, 100, 150, 200, and 300 mg/kg body weight) of ALA reduced the ulcer index with 88.2% to 96.1% inhibition ratio. In biochemical analyses of stomach tissues, ALA administration decreased the level of lipid peroxidation (LPO) and activities of myeloperoxidase (MPO) and catalase (CAT) in gastric tissues, which were increased after IND application. ALA also increased the level of glutathione (GSH) and activities of superoxide dismutase (SOD) and glutathione S-transferase (GST) that were decreased in gastric damaged stomach tissues. In conclusion, the gastroprotective effect of ALA could be attributed to its ameliorating effect on the antioxidant defense systems.

α-Lipoic acid reduced weight gain and improved the lipid profile in rats fed with high fat diet

The purpose of this study was to investigate the effects of α-lipoic acid on body weight and lipid profiles in Sprague-Dawley rats fed a high fat diet (HFD). After 4 weeks of feeding, rats on the HFD were divided into three groups by randomized block design; the first group received the high-fat-diet (n = 10), and the second group received the HFD administered with 0.25% α-lipoic acid (0.25LA), and the third group received the high-fat diet with 0.5% α-lipoic acid (0.5LA). The high fat diet with α-lipoic acid supplemented groups had significantly inhibited body weight gain, compared to that in the HFD group (P < 0.05). Organ weights of rats were also significantly reduced in liver, kidney, spleen, and visible fat tissues in rats supplemented with α-lipoic acid (P < 0.05). Significant differences in plasma lipid profiles, such as total lipids, total cholesterol, triglycerides, low-density lipoprotein, and high-density lipoprotein, were observed between the HFD and 0.5LA groups. The atherogenic index and the plasma high density lipoprotein-cholesterol/total cholesterol ratio improved significantly with α-lipoic acid supplementation in a dose-dependent manner (P < 0.05). Total hepatic cholesterol and total lipid concentration decreased significantly in high fat fed rats supplemented with α-lipoic acid in a dose-dependent manner (P < 0.05), whereas liver triglyceride content was not affected. In conclusion, α-lipoic acid supplementation had a positive effect on weight gain and plasma and liver lipid profiles in rats.