Abnormal biopterin metabolism is a major cause of impaired endothelium-dependent relaxation through nitric oxide/O2- imbalance in insulin-resistant rat aorta

Nanoparticle-mediated delivery of tetrahydrobiopterin restores endothelial function in diabetic rats

Endothelial dysfunction, underlying the vascular complications of diabetes and other cardiovascular disorders, may result from uncoupling of endothelial nitric oxide synthase (eNOS) activity due to decreased levels of tetrahydrobiopterin (BH4), a critical co-factor for eNOS. Some clinical trials attempting to deliver exogenous BH4 as a potential therapeutic strategy in vascular disease states have failed due to oxidation of BH4 in the circulation. We sought to develop a means of protecting BH4 from oxidation while delivering it to dysfunctional endothelial cells. Polymeric and solid lipid nanoparticles (NPs) loaded with BH4 were delivered by injection or oral gavage, respectively, to streptozotocin-induced diabetic rats. BH4 was measured in coronary endothelial cells and endothelium-dependent vascular reactivity was assessed in vascular rings. Lymphatic uptake of orally delivered lipid NPs was verified by sampling mesenteric lymph. BH4-loaded polymeric NPs maintained nitric oxide production by cultured endothelial cells under conditions of oxidative stress. BH4-loaded NPs, delivered via injection or ingestion, increased coronary endothelial BH4 concentration and improved endothelium-dependent vasorelaxation in diabetic rats. Pharmacodynamics assessment indicated peak concentration of solid lipid NPs in the systemic bloodstream 6 hours after ingestion, with disappearance noted by 48 hours. These studies support the feasibility of utilizing NPs to deliver BH4 to dysfunctional endothelial cells to increase nitric oxide bioavailability. BH4-loaded NPs could provide an innovative tool to restore redox balance in blood vessels and modulate eNOS-mediated vascular function to reverse or retard vascular disease in diabetes.

Onosma hispidum L. extract reverses hyperlipidemia, hypertension, and associated vascular dysfunction in rats

Onosma hispidum.L (O. hispidum) belongs to the family Boregineacea. A preliminary study and its medicinal use suggested its role in the management of hyperlipidemia. The present study aimed to assess the effect of methanolic root extract of O. hispidum in hyperlipidemia and associated vascular dysfunction. Oral administration of O. hispidum crude extract (Oh. Cr) to tyloxopol and high fat diet-induced hyperlipidemic Sprague-Dawley rats for 10 and 28 days significantly reduced total triglycerides and cholesterol (p < 0.001), compared to hyperlipidemic rats. Oh. Cr 250 mg/kg orally treated rats significantly (p < 0.001) reduced both the total body weight and atherogenic index in tylaxopol and HFD rats. In HMG-CoA assay, the inhibition of the enzyme was significant in Oh.Cr (250 mg/kg) treated group. Histopathological studies indicated that the group treated with Oh.Cr 250 mg/kg/day showed regular morphology of aortic intima, media and adventitia, and improved the endothelial damage. To investigate the vascular dysfunction, isolated rat aorta rings from all groups were pre-contracted with 1 µM phenylephrine (PE), and the effect of acetylcholine (Ach) was monitored. In the aorta isolated from Oh.Cr (50 mg/kg) treated group, Ach completely relaxed the PE-induced contraction with EC50 value of 0.05 µg/mL 0.015 (0.01-0.2) compared to the hyperlipidemic control group (<30% relaxation). In atorvastatin (10 mg/kg) treated rat aorta, Ach showed 50% relaxation. The Oh.Cr extract also reduced (105.92 ± 1.14 to 66.63 ± 0.85 mmHg) mean arterial pressure in hyperlipidemic hypertensive rats. These findings suggest that extract of O. hispidum is an effective remedy for hypercholesterolemia, and hypertriglyceridemia, which acts through inhibition of HMG-CoA and improving vascular dysfunction.

Metabolic reprogramming, oxidative stress, and pulmonary hypertension

Mitochondria are highly dynamic organelles essential for cell metabolism, growth, and function. It is becoming increasingly clear that endothelial cell dysfunction significantly contributes to the pathogenesis and vascular remodeling of various lung diseases, including pulmonary arterial hypertension (PAH), and that mitochondria are at the center of this dysfunction. The more we uncover the role mitochondria play in pulmonary vascular disease, the more apparent it becomes that multiple pathways are involved. To achieve effective treatments, we must understand how these pathways are dysregulated to be able to intervene therapeutically. We know that nitric oxide signaling, glucose metabolism, fatty acid oxidation, and the TCA cycle are abnormal in PAH, along with alterations in the mitochondrial membrane potential, proliferation, and apoptosis. However, these pathways are incompletely characterized in PAH, especially in endothelial cells, highlighting the urgent need for further research. This review summarizes what is currently known about how mitochondrial metabolism facilitates a metabolic shift in endothelial cells that induces vascular remodeling during PAH.

Renal Tubular Handling of Glucose and Fructose in Health and Disease

The proximal tubule of the kidney is programmed to reabsorb all filtered glucose and fructose. Glucose is taken up by apical sodium-glucose cotransporters SGLT2 and SGLT1 whereas SGLT5 and potentially SGLT4 and GLUT5 have been implicated in apical fructose uptake. The glucose taken up by the proximal tubule is typically not metabolized but leaves via the basolateral facilitative glucose transporter GLUT2 and is returned to the systemic circulation or used as an energy source by distal tubular segments after basolateral uptake via GLUT1. The proximal tubule generates new glucose in metabolic acidosis and the postabsorptive phase, and fructose serves as an important substrate. In fact, under physiological conditions and intake, fructose taken up by proximal tubules is primarily utilized for gluconeogenesis. In the diabetic kidney, glucose is retained and gluconeogenesis enhanced, the latter in part driven by fructose. This is maladaptive as it sustains hyperglycemia. Moreover, renal glucose retention is coupled to sodium retention through SGLT2 and SGLT1, which induces secondary deleterious effects. SGLT2 inhibitors are new anti-hyperglycemic drugs that can protect the kidneys and heart from failing independent of kidney function and diabetes. Dietary excess of fructose also induces tubular injury. This can be magnified by kidney formation of fructose under pathological conditions. Fructose metabolism is linked to urate formation, which partially accounts for fructose-induced tubular injury, inflammation, and hemodynamic alterations. Fructose metabolism favors glycolysis over mitochondrial respiration as urate suppresses aconitase in the tricarboxylic acid cycle, and has been linked to potentially detrimental aerobic glycolysis (Warburg effect). © 2022 American Physiological Society. Compr Physiol 12:2995-3044, 2022.

Endogenous fructose is correlated with urinary albumin creatinine ratios and uric acid in type 2 diabetes mellitus

AIM

To detect the expression levels of fasting serum fructose and ketohexokinase (KHK) in patients with type 2 diabetes mellitus (T2DM) at different stages of urinary albumin creatinine ratios (UACR) and serum uric acid (sUA).

METHODS

339 T2DM patients and 107 normal volunteers were divided into the normal uric acid (275 cases) and high uric acid group (171 cases) according to uric acid levels. T2DM patients were divided into the normal albuminuria group (118 cases, UACR < 30 mg/g), microalbuminuria group (112 cases, UACR 30-300 mg/g) and large amount of albuminuria group (109 cases, UACR > 300 mg/g). Levels of fasting serum fructose and KHK were detected and statistical analysis was carried out.

RESULTS

Fasting serum fructose and KHK levels increased with the increase of UACR and sUA (P < 0.05). Correlation analysis showed that fasting serum fructose and KHK levels were positively correlated with UACR and sUA (P < 0.05). Ridge regression analysis showed that fasting serum fructose and KHK were also correlated with urinary albumin and uric acid (P < 0.05).

CONCLUSION

Fasting serum fructose and KHK in endogenous fructose are associated with serum uric acid and urinary albumin levels in patients with T2DM. Trial number: ChiCTR2000039870.

Endogenous Fructose Metabolism Could Explain the Warburg Effect and the Protection of SGLT2 Inhibitors in Chronic Kidney Disease

Chronic low-grade inflammation underlies the pathogenesis of non-communicable diseases, including chronic kidney diseases (CKD). Inflammation is a biologically active process accompanied with biochemical changes involving energy, amino acid, lipid and nucleotides. Recently, glycolysis has been observed to be increased in several inflammatory disorders, including several types of kidney disease. However, the factors initiating glycolysis remains unclear. Added sugars containing fructose are present in nearly 70 percent of processed foods and have been implicated in the etiology of many non-communicable diseases. In the kidney, fructose is transported into the proximal tubules via several transporters to mediate pathophysiological processes. Fructose can be generated in the kidney during glucose reabsorption (such as in diabetes) as well as from intra-renal hypoxia that occurs in CKD. Fructose metabolism also provides biosynthetic precursors for inflammation by switching the intracellular metabolic profile from mitochondrial oxidative phosphorylation to glycolysis despite the availability of oxygen, which is similar to the Warburg effect in cancer. Importantly, uric acid, a byproduct of fructose metabolism, likely plays a key role in favoring glycolysis by stimulating inflammation and suppressing aconitase in the tricarboxylic acid cycle. A consequent accumulation of glycolytic intermediates connects to the production of biosynthetic precursors, proteins, lipids, and nucleic acids, to meet the increased energy demand for the local inflammation. Here, we discuss the possibility of fructose and uric acid may mediate a metabolic switch toward glycolysis in CKD. We also suggest that sodium-glucose cotransporter 2 (SGLT2) inhibitors may slow the progression of CKD by reducing intrarenal glucose, and subsequently fructose levels.

Sterile inflammation in the pathogenesis of maturation failure of arteriovenous fistula

Chronic kidney disease is a widespread terminal illness that afflicts millions of people across the world. Hemodialysis is the predominant therapeutic management strategy for kidney failure and involves the external filtration of metabolic waste within the circulation. This process requires an arteriovenous fistula (AVF) for vascular access. However, AVF maturation failures are significant obstacles in establishing long-term vascular access for hemodialysis. Appropriate stimulation, activation, and proliferation of smooth muscle cells, proper endothelial cell orientation, adequate structural changes in the ECM, and the release of anti-inflammatory markers are associated with maturation. AVFs often fail to mature due to inadequate tissue repair and remodeling, leading to neointimal hyperplasia lesions. The transdifferentiation of myofibroblasts and sterile inflammation are possibly involved in AVF maturation failures; however, limited data is available in this regard. The present article critically reviews the interplay of various damage-associated molecular patterns (DAMPs) and the downstream sterile inflammatory signaling with a focus on the NLRP3 inflammasome. Improved knowledge concerning AVF maturation pathways can be unveiled by investigating the novel DAMPs and the mediators of sterile inflammation in vascular remodeling that would open improved therapeutic opportunities in the management of AVF maturation failures and its associated complications.

Sodium-glucose cotransporter 2 inhibitors represent a paradigm shift in the prevention of heart failure in type 2 diabetes patients

Recent major clinical trials of the use of sodium-glucose cotransporter 2 (SGLT2) inhibitors in patients with type 2 diabetes have shown that they reduce three-point major adverse cardiovascular events, cardiovascular death, hospitalization for heart failure (HF) and a composite renal outcome. These beneficial effects of SGLT2 inhibitors are also evident in type 2 diabetes patients with a previous history of atherosclerotic cardiovascular disease or advanced renal disease. HF is a major determinant of the prognosis of diabetes patients. Although HF with low ejection fraction can be effectively treated with antihypertensive drugs, these treatments do not reduce mortality in HF patients with preserved ejection fraction (HFpEF). HFpEF is clinically characterized by left ventricular diastolic dysfunction, perivascular fibrosis and stiffness of cardiomyocytes, defined as "cardiomyopathy". Therefore, HFpEF is considered to be an entirely separate entity to HF with low ejection fraction. Recent studies have suggested that HFpEF might be treatable using SGLT2 inhibitors, which ameliorate visceral adiposity, insulin resistance, hyperglycemia, hyperlipidemia, volume overload, hypertension and cardiac inflammation. In the final part of the present review, we discuss the biochemical and molecular mechanisms of the effects of SGLT2 inhibitors in type 2 diabetes patients with HFpEF. These involve amelioration of the low nitric oxide production and oxidative stress, a reduction in cardiac inflammatory cytokine signaling, inhibition of Ca2+ overload, and an improvement in cardiac energy metabolism as a result of ketone body production. Investigations of the beneficial effects of SGLT2 inhibitors on cardiorenal outcomes, including hospitalization for HF, are now being carried out in preclinical and clinical studies.

Functional implications of vascular endothelium in regulation of endothelial nitric oxide synthesis to control blood pressure and cardiac functions

The endothelium is the innermost vascular lining performing significant roles all over the human body while maintaining the blood pressure at physiological levels. Malfunction of endothelium is thus recognized as a biomarker linked with many vascular diseases including but not limited to atherosclerosis, hypertension and thrombosis. Alternatively, prevention of endothelial malfunctioning or regulating the functions of its associated physiological partners like endothelial nitric oxide synthase can prevent the associated vascular disorders which account for the highest death toll worldwide. While many anti-hypertensive drugs are available commercially, a comprehensive description of the key physiological roles of the endothelium and its regulation by endothelial nitric oxide synthase or vice versa is the need of the hour to understand its contribution in vascular homeostasis. This, in turn, will help in designing new therapeutics targeting endothelial nitric oxide synthase or its interacting partners present in the cellular pool. This review describes the central role of vascular endothelium in the regulation of endothelial nitric oxide synthase while outlining the emerging drug targets present in the vasculature with potential to treat vascular disorders including hypertension.

Screening of the active fractions from the Coreopsis tinctoria Nutt. Flower on diabetic endothelial protection and determination of the underlying mechanism

ETHNOPHARMACOLOGICAL RELEVANCE

The Coreopsis tinctoria Nutt. flower (CTF) has been used traditionally in China for treating hypertension and diabetes as well as reducing body weight and blood fat. However, the vascular protection effect of the CTF has not been studied to date.

AIM OF THE STUDY

This study aimed to screen and identify bioactive fractions from the CTF with a diabetic endothelial protection effect and to clarify the underlying mechanism.

MATERIALS AND METHODS

The vascular protection effect of Fraction A was studied in high-fat diet and streptozocin-induced diabetic models. The endothelial protection effect of Fraction A-2 was further studied in an in vitro vascular endothelial dysfunction model induced by high glucose. In a high glucose-induced human umbilical vein endothelial cell (HUVEC) model, Fractions A-2-2 and A-2-3 were screened, and their detailed mechanisms of endothelial protection were studied. Liquid chromatography mass spectrometry (LC-MS) was used to identify the main components in Fractions A-2-2 and A-2-3.

RESULTS

Fraction A treatment significantly improved the endothelium-dependent vasodilation of the mesenteric artery induced by acetylcholine in diabetic rats. The maximum relaxation was 79.82 ± 2.45% in the control group, 64.36 ± 9.81% in the model group, and 91.87 ± 7.38% in the Fraction A treatment group (P < 0.01). Fraction A treatment also decreased rat tail pressure compared with the model group at the 12th week. The systolic blood pressure was 152.7 5 ± 16.99 mmHg in the control group, 188.50 ± 5.94 mmHg in the model group, and 172.60 ± 14.31 mmHg in the Fraction A treatment group (P < 0.05). The mean blood pressure was 128.50 ± 13.79 mmHg in the control group, 157.00 ± 6.06 mmHg in the model group, and 144.80 ± 11.97 mmHg in the Fraction A treatment group (P < 0.05). In an in vitro vascular endothelium-dependent vasodilation dysfunction model induced by high glucose, Fraction A-2 improved the vasodilation of the mesenteric artery. The maximum relaxation was 82.15 ± 16.24% in the control group, 73.29 ± 14.25% in the model group, and 79.62 ± 13.89% in the Fraction A-2 treatment group (P < 0.05). In a high glucose-induced HUVEC model, Fraction A-2-2 and Fraction A-2-3 upregulated the expression of IRS-1, Akt, and eNOS and increased the levels of p-IRS-1^Ser307, p-Akt ^Ser473, and p-eNOS^Ser1177 and also decreased the expression of NOX4, TNF-α, IL-6, sVCAM, sICAM, and NF-κB (P < 0.01). With the intervention of AG490 and LY294002, the above effects of Fraction A-2-2 and Fraction A-2-3 were inhibited (P < 0.01). LC-MS data showed that in Fraction A-2-2 and Fraction A-2-3, there were 10 main components: flavanocorepsin; polyphenolic; flavanomarein; isochlorogenic acid A; dicaffeoylquinic acid; coreopsin; marein; coreopsin; luteolin-7-O-glucoside; and 3',5,5',7-tetrahydroxyflavanone-O-hexoside.

CONCLUSION

The protective effect of the CTF on diabetic endothelial dysfunction may be due to its effect on the JAK2/IRS-1/PI3K/Akt/eNOS pathway and the related oxidative stress and inflammation. The results strongly suggested that Fraction A-2-2 and Fraction A-2-3 were the active fractions from the CTF, and the CTF might be a potential option for the prevention of vascular complications in diabetes.

Effects of Nigella sativa on endothelial dysfunction in diabetes mellitus: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Endothelial dysfunction is involved in lesion generation by the promotion of both early and late mechanism(s) of atherosclerosis such as adhesion molecules up-regulation, increased chemokine secretion and leukocyte adherence, increased cell permeability, enhanced low-density lipoprotein oxidation, cytokine elaboration, platelet activation and vascular smooth muscle cell migration, and proliferation. Nigella sativa is from the Ranunculaceae family which is used in some countries for various medicinal purposes. Nigella sativa seed has been widely used in traditional medicine for the treatment of diabetes.

AIM OF THE REVIEW

This review article summarized the therapeutic effects of Nigella sativa on endothelial dysfunction.

METHODS

Databases such as PubMed, Web of Science, Google Scholar, Scopus, and Iran Medex were considered. The search terms were " Nigella sativa " or "endothelium" and " Diabetes"," endothelial dysfunction ", " Thymoquinone " and " anti-inflammatory effect ".

RESULTS

The current review shows that Nigella sativa and Thymoquinone have a protective effect on endothelial dysfunction induced by diabetes. This is done by several mechanisms such as reduction of inflammatory and apoptotic markers, improving hyperglycemia, hyperlipidemia and antioxidant function, inhibiting platelet aggregation, and regulating eNOS, VCAM-1 and LOX-1 genes expression that involve in the endothelial dysfunction. Thymoquinone also reduces expression and secretion of some cytokines such as MCP-1, interleukin-1β, TNF-α, NF-κB, and Cox-2 that result in anti-inflammation effect.

CONCLUSION

Thymoquinone, the main phenolic terpene found in Nigella sativa, has several important properties such as antidiabetic, anti-inflammatory, and antioxidant activity. Therefore, Nigella sativa can improve endothelial dysfunction.

Fructose Production and Metabolism in the Kidney

Understanding fructose metabolism might provide insights to renal pathophysiology. To support systemic glucose concentration, the proximal tubular cells reabsorb fructose as a substrate for gluconeogenesis. However, in instances when fructose intake is excessive, fructose metabolism is costly, resulting in energy depletion, uric acid generation, inflammation, and fibrosis in the kidney. A recent scientific advance is the discovery that fructose can be endogenously produced from glucose under pathologic conditions, not only in kidney diseases, but also in diabetes, in cardiac hypertrophy, and with dehydration. Why humans have such a deleterious mechanism to produce fructose is unknown, but it may relate to an evolutionary benefit in the past. In this article, we aim to illuminate the roles of fructose as it relates to gluconeogenesis and fructoneogenesis in the kidney.

L-sepiapterin restores SLE serum-induced markers of endothelial function in endothelial cells

OBJECTIVE

SLE serves as an independent risk factor` for endothelial dysfunction (ED) not explained by Framingham risk factors. We sought to understand the development of SLE-induced ED on a cellular level in order to develop strategies aimed at reversing cellular abnormalities. This study assessed the impact of SLE patient serum on endothelial nitric oxide synthase (eNOS), nitric oxide (NO) production and functional changes in the cell.

METHODS

Human umbilical vein endothelial cells (HUVECs) cultured in serum of either SLE (n=25) or healthy patients (n=14) or endothelial basal medium 2 (EBM-2) culture media supplemented with fetal bovine serum with or without L-sepiapterin were used for our studies. We applied the fluorescent probe DAF-FM diacetate for intracellular NO detection using flow cytometry. Total RNA isolates were analysed using reverse transcription PCR for eNOS mRNA expression. Oxygen consumption rate was determined using seahorse analysis. Neutrophil adhesion and migration were determined using a calcein AM microscopy assay.

RESULTS

The mRNA expression of eNOS was increased in SLE cultured HUVECs compared with healthy control (p<0.05). The SLE eNOS mRNA level correlated with SLE patient age (p=0.008); however, this trend was not observed with healthy patients. SLE serum reduced NO production in HUVECs compared with EBM-2 cultured cells (p<0.05). Co-treatment of endothelial cells with L-sepiapterin preserved HUVEC capacity to produce NO in SLE conditions (p<0.01). SLE serum enhanced neutrophil migration (p<0.01) but not neutrophil adhesion compared with healthy controls. The bioenergetic health index was not different.

CONCLUSIONS

SLE likely causes disruption of endothelial cell eNOS function and NO modulated pathways.

Sources of Vascular Nitric Oxide and Reactive Oxygen Species and Their Regulation

Nitric oxide (NO) is a small free radical with critical signaling roles in physiology and pathophysiology. The generation of sufficient NO levels to regulate the resistance of the blood vessels and hence the maintenance of adequate blood flow is critical to the healthy performance of the vasculature. A novel paradigm indicates that classical NO synthesis by dedicated NO synthases is supplemented by nitrite reduction pathways under hypoxia. At the same time, reactive oxygen species (ROS), which include superoxide and hydrogen peroxide, are produced in the vascular system for signaling purposes, as effectors of the immune response, or as byproducts of cellular metabolism. NO and ROS can be generated by distinct enzymes or by the same enzyme through alternate reduction and oxidation processes. The latter oxidoreductase systems include NO synthases, molybdopterin enzymes, and hemoglobins, which can form superoxide by reduction of molecular oxygen or NO by reduction of inorganic nitrite. Enzymatic uncoupling, changes in oxygen tension, and the concentration of coenzymes and reductants can modulate the NO/ROS production from these oxidoreductases and determine the redox balance in health and disease. The dysregulation of the mechanisms involved in the generation of NO and ROS is an important cause of cardiovascular disease and target for therapy. In this review we will present the biology of NO and ROS in the cardiovascular system, with special emphasis on their routes of formation and regulation, as well as the therapeutic challenges and opportunities for the management of NO and ROS in cardiovascular disease.

Argirein alleviates vascular endothelial insulin resistance through suppressing the activation of Nox4-dependent O2- production in diabetic rats

BACKGROUND

Insulin resistance in endothelial cells contributes to the development of cardiovascular disease in type 2 diabetes mellitus (T2DM). Therefore, there are great potential clinical implications in developing pharmacological interventions targeting endothelial insulin resistance. Our previous studies indicated that argirein which was developed by combining rhein with L-arginine by a hydrogen bond, could substantially relieved stress related exacerbation of cardiac failure and alleviated cardiac dysfunction in T2DM, which was associated with suppressing NADPH oxidase activity. However, it is unclear whether argirein treatment attenuates the vascular lesion and dysfunction in T2DM and its underlying mechanisms.

METHODS AND RESULTS

The rat aortic endothelial cells (RAECs) were used to treat with palmitic acid (PA), a most common saturated free fatty acid, which could induce insulin resistance. It was showed that argirein increased glucose uptake and glucose transporter-4 (Glut4) expression and reversed the phosphorylation of IRS-1-ser307 and AKT-ser473, consequently resulting in the increase of the production of eNOS and NO in PA-induced RAECs. We further found that argirein blocked the Nox4-dependent superoxide (O₂^-.) generation, which regulated glucose metabolism in RAECs during PA stimulation. In vitro, argirein increased the release of endothelial NO to relieve the vasodilatory response to acetylcholine and insulin, and restored the expression of Nox4 and pIRS-1-ser307 in the aorta endothelium of high-fat diet (HFD)-fed rats following an injection of streptozocin (STZ).

CONCLUSION

These results suggested that argirein could improve endothelial insulin resistance which was attributed to inhibiting Nox4-dependent redox signaling in RAECs. These studies thus revealed the novel effect of argirein to prevent the vascular complication in T2DM.

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.

Endothelial Cell Metabolism

Endothelial cells (ECs) are more than inert blood vessel lining material. Instead, they are active players in the formation of new blood vessels (angiogenesis) both in health and (life-threatening) diseases. Recently, a new concept arose by which EC metabolism drives angiogenesis in parallel to well-established angiogenic growth factors (e.g., vascular endothelial growth factor). 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3-driven glycolysis generates energy to sustain competitive behavior of the ECs at the tip of a growing vessel sprout, whereas carnitine palmitoyltransferase 1a-controlled fatty acid oxidation regulates nucleotide synthesis and proliferation of ECs in the stalk of the sprout. To maintain vascular homeostasis, ECs rely on an intricate metabolic wiring characterized by intracellular compartmentalization, use metabolites for epigenetic regulation of EC subtype differentiation, crosstalk through metabolite release with other cell types, and exhibit EC subtype-specific metabolic traits. Importantly, maladaptation of EC metabolism contributes to vascular disorders, through EC dysfunction or excess angiogenesis, and presents new opportunities for anti-angiogenic strategies. Here we provide a comprehensive overview of established as well as newly uncovered aspects of EC metabolism.

Computational analysis of interactions of oxidative stress and tetrahydrobiopterin reveals instability in eNOS coupling

In cardiovascular and neurovascular diseases, an increase in oxidative stress and endothelial dysfunction has been reported. There is a reduction in tetrahydrobiopterin (BH4), which is a cofactor for the endothelial nitric oxide synthase (eNOS), resulting in eNOS uncoupling. Studies of the enhancement of BH4 availability have reported mixed results for improvement in endothelial dysfunction. Our understanding of the complex interactions of eNOS uncoupling, oxidative stress and BH4 availability is not complete and a quantitative understanding of these interactions is required. In the present study, we developed a computational model for eNOS uncoupling that considers the temporal changes in biopterin ratio in the oxidative stress conditions. Using the model, we studied the effects of cellular oxidative stress (Qsupcell) representing the non-eNOS based oxidative stress sources and BH4 synthesis (QBH4) on eNOS NO production and biopterin ratio (BH4/total biopterins (TBP)). Model results showed that oxidative stress levels from 0.01 to 1nM·s-1 did not affect eNOS NO production and eNOS remained in coupled state. When the Qsupcell increased above 1nM·s-1, the eNOS coupling and NO production transitioned to an oscillatory state. Oxidative stress levels dynamically changed the biopterin ratio. When Qsupcell increased from 1 to 100nM·s-1, the endothelial cell NO production, TBP levels and biopterin ratio reduced significantly from 26.5 to 2nM·s-1, 3.75 to 0.002μM and 0.99 to 0.25, respectively. For an increase in BH4 synthesis, the improvement in NO production rate and BH4 levels were dependent on the extent of cellular oxidative stress. However, a 10-fold increase in QBH4 at higher oxidative stresses did not restore the NO-production rate and the biopterin ratio. Our mechanistic analysis reveals that a combination of enhancing tetrahydrobiopterin level with a reduction in cellular oxidative stress may result in significant improvement in endothelial dysfunction.

Relationship between cardiovascular risk factors and hemorheology assessed by microchannel method in patients with type 2 diabetes mellitus

Aim

In addition to atherosclerosis, impairment of blood rheology is an important factor in cardiovascular events. The present study attempted to clarify the relationship between hemorheology and cardiovascular risk factors in patients with type 2 diabetes mellitus assessed by a microchannel method.

Methods

We enrolled 294 patients with type 2 diabetes mellitus (109 males and 185 females; mean age, 69 ± 11 years) with no history of cardiovascular events. Hemorheology was evaluated with a microchannel array flow analyzer, and the relationship between whole-blood passage time (WBPT) and various clinical parameters was examined.

Results

WBPT was significantly correlated with advanced glycation end-product (AGE) levels at the skin (r = 0.49, p < 0.001), serum reactive oxygen metabolite concentrations (oxidative stress markers) (r = 0.25, p < 0.001), the cardio-ankle vascular index (CAVI, arterial function marker) (r = 0.32, p < 0.001), and a number of classical cardiovascular risk factors in an individual (r = 0.45, p < 0.001). Multiple regression analysis revealed that these factors were selected as independent variables for WBPT as a subordinate factor.

Conclusion

Hemorheology is significantly associated with novel cardiovascular risk factors, such as AGEs, in vivo oxidative stress, and CAVI, and clustering of classical cardiovascular risk factors in patients with type 2 diabetes mellitus.

Sex-gender-related therapeutic approaches for cardiovascular complications associated with diabetes

Diabetes is a chronic disease associated with micro- and macrovascular complications and is a well-established risk factor for cardiovascular disease. Cardiovascular complications associated with diabetes are among the most important causes of death in diabetic patients. Interestingly, several sex-gender differences have been reported to significantly impact in the pathophysiology of diabetes. In particular, sex-gender differences have been reported to affect diabetes epidemiology, risk factors, as well as cardiovascular complications associated with diabetes. This suggests that different therapeutic approaches are needed for managing diabetes-associated cardiovascular complications in men and women. In this review, we will discuss about the sex-gender differences that are known to impact on diabetes, mainly focusing on the cardiovascular complications associated with the disease. We will then discuss the therapeutic approaches for managing diabetes-associated cardiovascular complications and how differences in sex-gender can influence the existing therapeutic approaches.

Tetrahydrobiopterin rescues impaired responses of cerebral resistance arterioles during type 1 diabetes

Our goal was to test the hypothesis that administration of tetrahydrobiopterin (BH4) would improve impaired endothelial nitric oxide synthase-dependent dilation of cerebral arterioles during type 1 diabetes. In addition, we examined the influence of BH4 on levels of superoxide in brain tissue. In vivo diameter of cerebral arterioles in nondiabetic and diabetic rats was measured in response to endothelial nitric oxide synthase-dependent agonists (acetylcholine and adenosine 5'-diphosphate) and an endothelial nitric oxide synthase-independent agonist (nitroglycerine) before and during application of BH4 (1.0 µM). We also measured levels of superoxide from cortex tissue in nondiabetic and diabetic rats under basal states and during BH4 Acetylcholine and adenosine 5'-diphosphate dilated cerebral arterioles in nondiabetic rats, but this vasodilation was significantly impaired in diabetic rats. In contrast, nitroglycerine produced similar vasodilation in nondiabetic and diabetic rats. Application of BH4 did not enhance vasodilation in nondiabetic rats but improved impaired cerebral vasodilation in diabetic rats. Basal superoxide levels were increased in cortex tissue from diabetic rats, and BH4 reduced these levels to that found in nondiabetic rats. Thus, BH4 is an important mediator of endothelial nitric oxide synthase-dependent responses of cerebral arterioles in diabetes and may have therapeutic potential for the treatment of cerebral vascular disease.

Factors Associated with High-sensitivity Cardiac Troponin T in Patients with Type 2 Diabetes Mellitus

BACKGROUND

The blood concentration of high-sensitivity cardiac troponin T (hs-cTnT) is an established, useful biomarker for evaluating the pathogenesis of heart failure and predicting cardiovascular events. The aim of this study was to evaluate factors that are potentially associated with elevated blood hs-cTnT in patients with type 2 diabetes mellitus.

PATIENTS AND METHODS

Patients with type 2 diabetes mellitus (N=280, 111 men and 169 women; mean ± SD age: 71±9 years) with no history of cardiovascular events were enrolled. Relationships between hs-cTnT level and various clinical parameters were examined.

RESULTS

Hs-cTnT was detected in 244 (87.1%) patients. There were no significant relationships between hs-cTnT and fasting blood glucose levels or insulin resistance. hs-cTnT was significantly correlated with advanced glycation end-product levels at the skin (r=0.23, p<0.001), blood concentrations of brain natriuretic peptide (r=0.23, p<0.001), reactive oxygen metabolites as markers of oxidative stress (r=0.28, p<0.001), and the augmentation index at the radial artery as marker of arterial reflection (r=0.31, p<0.001). Furthermore, multiple regression analysis revealed that these factors were also selected as independent variables, with hs-cTnT as a subordinate factor.

CONCLUSION

These results indicate that novel cardiovascular risk factors including advanced glycation end-products, in vivo oxidative stress, and high arterial reflection are closely associated with high concentrations of blood hs-cTnT in patients with type 2 diabetes mellitus.

Fructose induces prothrombotic phenotype in human endothelial cells : A new role for "added sugar" in cardio-metabolic risk

Intake of large amounts of added sweeteners has been associated with the pathogenesis of cardiometabolic risk. Several studies have shown that fructose increases the cardiovascular risk by modulating endothelial dysfunction and promoting atherosclerosis. Recently, a potential role for fructose in cardiovascular thrombosis has been suggested but with controversial results. Tissue factor (TF) plays a pivotal role in the pathophysiology of cardiovascular thrombosis by triggering the formation of intracoronary thrombi following endothelial injury. This study investigates the effects of fructose, in a concentration range usually observed in the plasma of patients with increased cardiovascular risk, on TF in human umbilical endothelial cells (HUVECs). Cells were stimulated with increasing concentrations of fructose (0.25, 1 and 2.5 mM) and then processed to evaluate TF-mRNA levels by real-time PCR as well as TF expression/activity by FACS analysis and procoagulant activity. Finally, a potential molecular pathway involved in modulating this phenomenon was investigated. We demonstrate that fructose induces transcription of mRNA for TF. In addition, we show that this monosaccharide promotes surface expression of TF that is functionally active. Fructose effects on TF appear modulated by the oxygen free radicals through activation of the transcription factor NF-κB since superoxide dismutase and NF-κB inhibitors suppressed TF expression. Data of the present study, although in vitro, indicate that fructose, besides promoting atherosclerosis, induces a prothrombotic phenotype in HUVECs, thus indicating one the mechanism(s) by which this sweetener might increase cardiometabolic risk.

Asymmetric dimethylarginine (ADMA) elevation and arginase up-regulation contribute to endothelial dysfunction related to insulin resistance in rats and morbidly obese humans

KEY POINTS

The presence of insulin resistance (IR) is determinant for endothelial dysfunction associated with obesity. Although recent studies have implicated the involvement of mitochondrial superoxide and inflammation in the defective nitric oxide (NO)-mediated responses and subsequent endothelial dysfunction in IR, other mechanisms could compromise this pathway. In the present study, we assessed the role of asymmetric dimethylarginine (ADMA) and arginase with respect to IR-induced impairment of endothelium-dependent vasodilatation in human morbid obesity and in a non-obese rat model of IR. We show that both increased ADMA and up-regulated arginase are determinant factors in the alteration of the l-arginine/NO pathway associated with IR in both models and also that acute treatment of arteries with arginase inhibitor or with l-arginine significantly alleviate endothelial dysfunction. These results help to expand our knowledge regarding the mechanisms of endothelial dysfunction that are related to obesity and IR and establish potential therapeutic targets for intervention.

ABSTRACT

Insulin resistance (IR) is determinant for endothelial dysfunction in human obesity. Although we have previously reported the involvement of mitochondrial superoxide and inflammation, other mechanisms could compromise NO-mediated responses in IR. We evaluated the role of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) and arginase with respect to IR-induced impairment of l-arginine/NO-mediated vasodilatation in human morbid obesity and in a non-obese rat model of IR. Bradykinin-induced vasodilatation was evaluated in microarteries derived from insulin-resistant morbidly obese (IR-MO) and non-insulin-resistant MO (NIR-MO) subjects. Defective endothelial vasodilatation in IR-MO was improved by l-arginine supplementation. Increased levels of ADMA were detected in serum and adipose tissue from IR-MO. Serum ADMA positively correlated with IR score and negatively with pD2 for bradykinin. Gene expression determination by RT-PCR revealed not only the decreased expression of ADMA degrading enzyme dimethylarginine dimethylaminohydrolase (DDAH)1/2 in IR-MO microarteries, but also increased expression of arginase-2. Arginase inhibition improved endothelial vasodilatation in IR-MO. Analysis of endothelial vasodilatation in a non-obese IR model (fructose-fed rat) confirmed an elevation of circulating and aortic ADMA concentrations, as well as reduced DDAH aortic content and increased aortic arginase activity in IR. Improvement of endothelial vasodilatation in IR rats by l-arginine supplementation and arginase inhibition provided functional corroboration. These results demonstrate that increased ADMA and up-regulated arginase contribute to endothelial dysfunction as determined by the presence of IR in human obesity, most probably by compromising arginine availability. The results provide novel insights regarding the mechanisms of endothelial dysfunction related to obesity and IR and establish potential therapeutic targets for intervention.

Nitric Oxide Resistance Reduces Arteriovenous Fistula Maturation in Chronic Kidney Disease in Rats

Background

Autologous arteriovenous (AV) fistulas are the first choice for vascular access but have a high risk of non-maturation due to insufficient vessel adaptation, a process dependent on nitric oxide (NO)-signaling. Chronic kidney disease (CKD) is associated with oxidative stress that can disturb NO-signaling. Here, we evaluated the influence of CKD on AV fistula maturation and NO-signaling.

Methods

CKD was established in rats by a 5/6^th nephrectomy and after 6 weeks, an AV fistula was created between the carotid artery and jugular vein, which was followed up at 3 weeks with ultrasound and flow assessments. Vessel wall histology was assessed afterwards and vasoreactivity of carotid arteries was studied in a wire myograph. The soluble guanylate cyclase (sGC) activator BAY 60–2770 was administered daily to CKD animals for 3 weeks to enhance fistula maturation.

Results

CKD animals showed lower flow rates, smaller fistula diameters and increased oxidative stress levels in the vessel wall. Endothelium-dependent relaxation was comparable but vasorelaxation after sodium nitroprusside was diminished in CKD vessels, indicating NO resistance of the NO-receptor sGC. This was confirmed by stimulation with BAY 60–2770 resulting in increased vasorelaxation in CKD vessels. Oral administration of BAY 60–2770 to CKD animals induced larger fistula diameters, however; flow was not significantly different from vehicle-treated CKD animals.

Conclusions

CKD induces oxidative stress resulting in NO resistance that can hamper AV fistula maturation. sGC activators like BAY 60–2770 could offer therapeutic potential to increase AV fistula maturation.

Blunted flow-mediated responses and diminished nitric oxide synthase expression in lymphatic thoracic ducts of a rat model of metabolic syndrome

Shear-dependent inhibition of lymphatic thoracic duct (TD) contractility is principally mediated by nitric oxide (NO). Endothelial dysfunction and poor NO bioavailability are hallmarks of vasculature dysfunction in states of insulin resistance and metabolic syndrome (MetSyn). We tested the hypothesis that flow-dependent regulation of lymphatic contractility is impaired under conditions of MetSyn. We utilized a 7-wk high-fructose-fed male Sprague-Dawley rat model of MetSyn and determined the stretch- and flow-dependent contractile responses in an isobaric ex vivo TD preparation. TD diameters were tracked and contractile parameters were determined in response to different transmural pressures, imposed flow, exogenous NO stimulation by S-nitro-N-acetylpenicillamine (SNAP), and inhibition of NO synthase (NOS) by l-nitro-arginine methyl ester (l-NAME) and the reactive oxygen species (ROS) scavenging molecule 4-hydroxy-tempo (tempol). Expression of endothelial NO synthase (eNOS) in TD was determined using Western blot. Approximately 25% of the normal flow-mediated inhibition of contraction frequency was lost in TDs isolated from MetSyn rats despite a comparable SNAP response. Inhibition of NOS with l-NAME abolished the differences in the shear-dependent contraction frequency regulation between control and MetSyn TDs, whereas tempol did not restore the flow responses in MetSyn TDs. We found a significant reduction in eNOS expression in MetSyn TDs suggesting that diminished NO production is partially responsible for impaired flow response. Thus our data provide the first evidence that MetSyn conditions diminish eNOS expression in TD endothelium, thereby affecting the flow-mediated changes in TD lymphatic function.

Vascular nitric oxide: Beyond eNOS

As the first discovered gaseous signaling molecule, nitric oxide (NO) affects a number of cellular processes, including those involving vascular cells. This brief review summarizes the contribution of NO to the regulation of vascular tone and its sources in the blood vessel wall. NO regulates the degree of contraction of vascular smooth muscle cells mainly by stimulating soluble guanylyl cyclase (sGC) to produce cyclic guanosine monophosphate (cGMP), although cGMP-independent signaling [S-nitrosylation of target proteins, activation of sarco/endoplasmic reticulum calcium ATPase (SERCA) or production of cyclic inosine monophosphate (cIMP)] also can be involved. In the blood vessel wall, NO is produced mainly from l-arginine by the enzyme endothelial nitric oxide synthase (eNOS) but it can also be released non-enzymatically from S-nitrosothiols or from nitrate/nitrite. Dysfunction in the production and/or the bioavailability of NO characterizes endothelial dysfunction, which is associated with cardiovascular diseases such as hypertension and atherosclerosis.

Fructose and uric acid in diabetic nephropathy

Clinical studies have reported associations between serum uric acid levels and the development of diabetic nephropathy, but the underlying mechanisms remain elusive. There is evidence from animal studies that blocking uric acid production protects the kidney from tubulointerstitial injury, which may suggest a causal role for uric acid in the development of diabetic tubular injury. In turn, when fructose, which is endogenously produced in diabetes via the polyol pathway, is metabolised, uric acid is generated from a side-chain reaction driven by ATP depletion and purine nucleotide turnover. For this reason, uric acid derived from endogenous fructose could cause tubulointerstitial injury in diabetes. Accordingly, our research group recently demonstrated that blocking fructose metabolism in a diabetic mouse model mitigated the development of tubulointerstitial injury by lowering tubular uric acid production. In this review we discuss the relationship between uric acid and fructose as a novel mechanism for the development of diabetic tubular injury.

Differential effect of amylin on endothelial-dependent vasodilation in mesenteric arteries from control and insulin resistant rats

Insulin resistance (IR) is frequently associated with endothelial dysfunction and has been proposed to play a major role in cardiovascular disease (CVD). On the other hand, amylin has long been related to IR. However the role of amylin in the vascular dysfunction associated to IR is not well addressed. Therefore, the aim of the study was to assess the effect of acute treatment with amylin on endothelium-dependent vasodilation of isolated mesenteric arteries from control (CR) and insulin resistant (IRR) rats and to evaluate the possible mechanisms involved. Five week-old male Wistar rats received 20% D-fructose dissolved in drinking water for 8 weeks and were compared with age-matched CR. Plasmatic levels of glucose, insulin and amylin were measured. Mesenteric microvessels were dissected and mounted in wire myographs to evaluate endothelium-dependent vasodilation to acetylcholine. IRR displayed a significant increase in plasmatic levels of glucose, insulin and amylin and reduced endothelium-dependent relaxation when compared to CR. Acute treatment of mesenteric arteries with r-amylin (40 pM) deteriorated endothelium-dependent responses in CR. Amylin-induced reduction of endothelial responses was unaffected by the H₂O₂ scavenger, catalase, but was prevented by the extracellular superoxide scavenger, superoxide dismutase (SOD) or the NADPH oxidase inhibitor (VAS2870). By opposite, amylin failed to further inhibit the impaired relaxation in mesenteric arteries of IRR. SOD, or VAS2870, but not catalase, ameliorated the impairment of endothelium-dependent relaxation in IRR. At concentrations present in insulin resistance conditions, amylin impairs endothelium-dependent vasodilation in mircrovessels from rats with preserved vascular function and low levels of endogenous amylin. In IRR with established endothelial dysfunction and elevated levels of amylin, additional exposure to this peptide has no effect on endothelial vasodilation. Increased superoxide generation through NADPH oxidase activity may be a common link involved in the endothelial dysfunction associated to insulin resistance and to amylin exposure in CR.

FM19G11 reverses endothelial dysfunction in rat and human arteries through stimulation of the PI3K/Akt/eNOS pathway, independently of mTOR/HIF-1α activation

BACKGROUND AND PURPOSE

FM19G11 up-regulates mammalian target of rapamycin (mTOR)/hypoxia inducible factor-1α (HIF-1α) and PI3K/Akt pathways, which are involved in endothelial function. We evaluated the effects of FM19G11 on defective endothelial vasodilatation in arteries from rats and humans and investigated the mechanisms involved.

EXPERIMENTAL APPROACH

Effects of chronic in vivo administration of FM19G11 on aortic endothelial vasodilatation were evaluated together with ex vivo treatment in aortic and mesenteric arteries from control and insulin-resistant rats (IRR). Its effects on vasodilator responses of penile arteries (HPRAs) and corpus cavernosum (HCC) from men with vasculogenic erectile dysfunction (ED) (model of human endothelial dysfunction) were also evaluated. Vascular expression of phosphorylated-endothelial NOS (p-eNOS), phosphorylated-Akt (p-Akt) and HIF-1α was determined by immunodetection and cGMP by elisa.

KEY RESULTS

Chronic administration of FM19G11 reversed the impaired endothelial vasodilatation in IRR. Ex vivo treatment with FM19G11 also significantly improved endothelium-dependent vasodilatation in aorta and mesenteric arteries from IRR. These effects were accompanied by the restoration of p-eNOS and cGMP levels in IRR aorta and were prevented by either NOS or PI3K inhibition. p-Akt and p-eNOS contents were increased by FM19G11 in aortic endothelium of IRR. FM19G11-induced restoration of endothelial vasodilatation was unaffected by mTOR/HIF-1α inhibitors. FM19G11 also restored endothelial vasodilatation in HPRA and HCC from ED patients.

CONCLUSIONS AND IMPLICATIONS

Stimulation of the PI3K/Akt/eNOS pathway by FM19G11 alleviates impaired NO-mediated endothelial vasodilatation in rat and human arteries independently of mTOR/HIF-1α activation. This pharmacological strategy could be beneficial for managing pathological conditions associated with endothelial dysfunction, such as ED.

The role of reactive oxygen species in microvascular remodeling

The microcirculation is a portion of the vascular circulatory system that consists of resistance arteries, arterioles, capillaries and venules. It is the place where gases and nutrients are exchanged between blood and tissues. In addition the microcirculation is the major contributor to blood flow resistance and consequently to regulation of blood pressure. Therefore, structural remodeling of this section of the vascular tree has profound implications on cardiovascular pathophysiology. This review is focused on the role that reactive oxygen species (ROS) play on changing the structural characteristics of vessels within the microcirculation. Particular attention is given to the resistance arteries and the functional pathways that are affected by ROS in these vessels and subsequently induce vascular remodeling. The primary sources of ROS in the microcirculation are identified and the effects of ROS on other microcirculatory remodeling phenomena such as rarefaction and collateralization are briefly reviewed.

Cardioprotective efficacy depends critically on pharmacological dose, duration of ischaemia, health status of animals and choice of anaesthetic regimen: a case study with folic acid

BACKGROUND

Acute, high-dose folic acid (FA) administration has recently been shown to possess unprecedented effective cardioprotection against ischaemia/reperfusion (I/R) injury. Here we explore the translation potential of FA as treatment modality for cardiac I/R.

METHODS

Dependency of FA protection on dose, ischaemia duration, and eNOS was examined in an isolated mouse heart I/R model, whereas dependency on animal health status and anaesthesia was examined in an in vivo rat model of regional cardiac I/R.

RESULTS

50 μM FA provided maximal reduction (by 95%) of I/R-induced cell death following 25 min ischaemia in isolated wild-type hearts, with protection associated with increased coupled eNOS protein. No protection was observed with 35 min I or in eNOS(-/-) hearts. Acute intravenous administration of FA during a 25 min ischaemic period reduced infarct size by 45% in in vivo pentobarbital-anaesthetised young, healthy rats. FA did not reduce infarct size in aged or pre-diabetic rats, although it did preserve hemodynamics in the pre-diabetic rats. Finally, using a clinically-relevant anaesthetic regimen of fentanyl-propofol anaesthesia, FA treatment was ineffective in young, aged and pre-diabetic animals.

CONCLUSIONS

The protective potential of an initially promising cardioprotective treatment of high dose FA against cardiac I/R infarction, is critically dependent on experimental conditions with relevance to the clinical condition. Our data indicates the necessity of expanded pre-clinical testing of cardioprotective interventions before embarking on clinical testing, in order to prevent too many "lost-in-translation" drugs and unnecessary clinical studies.

Ursodeoxycholic acid ameliorates fructose-induced metabolic syndrome in rats

The metabolic syndrome (MS) is characterized by insulin resistance, dyslipidemia and hypertension. It is associated with increased risk of cardiovascular diseases and type-2 diabetes. Consumption of fructose is linked to increased prevalence of MS. Ursodeoxycholic acid (UDCA) is a steroid bile acid with antioxidant, anti-inflammatory activities and has been shown to improve insulin resistance. The current study aims to investigate the effect of UDCA (150 mg/kg) on MS induced in rats by fructose administration (10%) in drinking water for 12 weeks. The effects of UDCA were compared to fenofibrate (100 mg/kg), an agonist of PPAR-α receptors. Treatment with UDCA or fenofibrate started from the 6^th week after fructose administration once daily. Fructose administration resulted in significant increase in body weight, elevations of blood glucose, serum insulin, cholesterol, triglycerides, advanced glycation end products (AGEs), uric acid levels, insulin resistance index and blood pressure compared to control rats. Moreover, fructose increased oxidative stress in aortic tissues indicated by significant increases of malondialdehyde (MDA), expression of iNOS and reduction of reduced glutathione (GSH) content. These disturbances were associated with decreased eNOS expression, increased infiltration of leukocytes and loss of aortic vascular elasticity. Treatment with UDCA successfully ameliorated the deleterious effects of fructose. The protective effect of UDCA could be attributed to its ability to decrease uric acid level, improve insulin resistance and diminish oxidative stress in vascular tissues. These results might support possible clinical application of UDCA in MS patients especially those present with liver diseases, taking into account its tolerability and safety. However, further investigations on human subjects are needed before the clinical application of UDCA for this indication.

Regulation of obesity and insulin resistance by nitric oxide

Obesity is a risk factor for developing type 2 diabetes and cardiovascular disease and has quickly become a worldwide pandemic with few tangible and safe treatment options. Although it is generally accepted that the primary cause of obesity is energy imbalance, i.e., the calories consumed are greater than are utilized, understanding how caloric balance is regulated has proven a challenge. Many "distal" causes of obesity, such as the structural environment, occupation, and social influences, are exceedingly difficult to change or manipulate. Hence, molecular processes and pathways more proximal to the origins of obesity-those that directly regulate energy metabolism or caloric intake-seem to be more feasible targets for therapy. In particular, nitric oxide (NO) is emerging as a central regulator of energy metabolism and body composition. NO bioavailability is decreased in animal models of diet-induced obesity and in obese and insulin-resistant patients, and increasing NO output has remarkable effects on obesity and insulin resistance. This review discusses the role of NO in regulating adiposity and insulin sensitivity and places its modes of action into context with the known causes and consequences of metabolic disease.

Curcumin attenuates fructose-induced vascular dysfunction of isolated rat thoracic aorta rings

CONTEXT

Consumption of high fructose is associated with metabolic abnormalities, insulin resistance, and hypertension. It is not known whether this hypertensive effect of fructose is related to metabolic abnormalities or due to the direct effect of fructose on blood vessels.

OBJECTIVE

Here, we investigated the direct effect of fructose on rat isolated aorta and the possible protective effect of curcumin.

MATERIALS AND METHODS

The isolated rat thoracic aorta rings were used to measure the contractile responses to different concentrations of both phenylephrine and KCl, and the relaxant response to acetylcholine (Ach). The effect of curcumin (1 µM) alone or in combination with tempol (1 mM), a superoxide dismutase mimetic agent, and N-{[3(amino-methyl)-phenyl]-methyl} ethanimidamide dihydrochloride (1400 W), a specific inducible nitric oxide synthase (iNOS) inhibitor, (1 µM) on fructose-treated aorta was compared. The aortic rings were incubated with different treatments for 60 min before starting the experiment. Changes in the intracellular calcium in response to KCl and nitric oxide levels were also measured.

RESULTS AND DISCUSSION

Fructose strongly increased the contractile response of aortic rings to both phenylephrine and KCl (Emax was increased by 147.3% and 150.5%, respectively) but it did not affect the relaxant response to Ach. Curcumin significantly decreased the hyper responsiveness of arterial rings to both vasopressors (for phenylephrine, Emax decreased from 147.3% in fructose incubated aorta to 81%, and for KCl, Emax decreased from 150.5% in fructose-incubated aorta to 77.24% respectively). Curcumin also reduces the intracellular calcium level (85% reduction in intracellular calcium). A 1400 W was the only agent that potentiates the effect of curcumin.

CONCLUSION

Fructose has a direct deleterious effect on aortic vascular reactivity. Curcumin can partially protect against fructose-induced impairment in vascular contractility via an antioxidant effect and reduction of elevated intracellular calcium.

Oxidative stress and metabolic pathologies: from an adipocentric point of view

Oxidative stress plays a pathological role in the development of various diseases including diabetes, atherosclerosis, or cancer. Systemic oxidative stress results from an imbalance between oxidants derivatives production and antioxidants defenses. Reactive oxygen species (ROS) are generally considered to be detrimental for health. However, evidences have been provided that they can act as second messengers in adaptative responses to stress. Obesity represents a major risk factor for deleterious associated pathologies such as type 2 diabetes, liver, and coronary heart diseases. Many evidences regarding obesity-induced oxidative stress accumulated over the past few years based on established correlations of biomarkers or end-products of free-radical-mediated oxidative stress with body mass index. The hypothesis that oxidative stress plays a significant role in the development of metabolic disorders, especially insulin-resistance state, is supported by several studies where treatments reducing ROS production reverse metabolic alterations, notably through improvement of insulin sensitivity, hyperlipidemia, or hepatic steatosis. In this review, we will develop the mechanistic links between oxidative stress generated by adipose tissue in the context of obesity and its impact on metabolic complications development. We will also attempt to discuss potential therapeutic approaches targeting obesity-associated oxidative stress in order to prevent associated-metabolic 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.

Antiobesogenic role of endothelial nitric oxide synthase

The prevalence of obesity has increased remarkably in the past four decades. Because obesity can promote the development of type 2 diabetes and cardiovascular disease, understanding the mechanisms that engender weight gain and discovering safe antiobesity therapies are of critical importance. In particular, the gaseous signaling molecule, nitric oxide (NO), appears to be a central factor regulating adiposity and systemic metabolism. Obese and diabetic states are characterized by a deficit in bioavailable NO, with such decreases commonly attributed to downregulation of endothelial NO synthase (eNOS), loss of eNOS activity, or quenching of NO by its reaction with oxygen radicals. Gain-of-function studies, in which vascular-derived NO has been increased pharmacologically or genetically, reveal remarkable actions of NO on body composition and systemic metabolism. This review addresses the metabolic actions of eNOS and the potential therapeutic utility of harnessing its antiobesogenic effects.

Effects of atorvastatin, amlodipine, and their combination on vascular dysfunction in insulin-resistant rats

Deficiency of tetrahydrobiopterin (BH4) in the vascular tissue contributes to endothelial dysfunction through reduced eNOS activity and increased superoxide anion (O2(-)) generation in the insulin-resistant state. We investigated the effects of atorvastatin, a 3-hydroxyl-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitor; amlodipine, a calcium antagonist; and their combination on blood pressure, arterial relaxation and contraction, and vascular oxidative stress in aortas of high fructose-fed rats. Oral administration of atorvastatin for 8 weeks did not significantly lower blood pressure, but normalized angiotensin II-induced vasoconstriction and endothelial function in the fructose-fed rats. Atorvastatin treatment of fructose-fed rats increased vascular BH4 content, which was associated with an increase in endothelial NO synthase activity as well as a reduction in endothelial O2(-) production. On the other hand, administration of amlodipine did not affect the angiotensin II-induced vasoconstriction and endothelial function, but normalized the elevated blood pressure in the fructose-fed rats. The combined treatment did not show synergistic but additive beneficial effects. The present study suggests that combined therapy of HMG-CoA reductase inhibitors and calcium antagonists prevents functional vascular disorders in the insulin-resistant state, possibly resulting in the protection against or delay of development of hypertension, vascular dysfunction in diabetes, and thereafter atherosclerosis.

Tranilast alleviates endothelial dysfunctions and insulin resistance via preserving glutathione peroxidase 1 in rats fed a high-fat emulsion

We investigated the effects of treatment with tranilast on vascular and metabolic dysfunction induced by a high-fat emulsion intragastric administration. Wistar rats were randomized to receive water or high-fat emulsion with or without tranilast treatment (400 mg/kg per day) for 4 weeks. Insulin sensitivity was determined with a hyperinsulinemic-euglycemic clamp experiment and short insulin tolerance test. Vascular reactivity was evaluated using aortic rings in organ chambers. Glutathione peroxidase 1 (GPX1) expressions, eNOS phosphorylation and activity, MCP-1, H2O2 formation, and NO production were determined in vascular or soleus tissues. Tranilast treatment was found to prevent alterations in vascular reactivity and insulin sensitivity and to prevent increases in plasma glucose and insulin noted in the high-fat emulsion-treated rats. These were associated with increased antioxidant enzyme GPX1 expression, eNOS phosphorylation and activity, and NO production, but reductions in H2O2 accumulation. Moreover, tranilast preserved GPX1 expression in palmitic acid (PA)-treated endothelial cells with a consequent decreased ROS formation and increased eNOS phosphorylation and NO production. Therefore, oxidative stress induced by a relatively short-term high-fat diet could cause the early development of vascular and metabolic abnormalities in rats, and tranilast has a beneficial effect in vascular dysfunctions and insulin resistance via preserving GPX1 and alleviating oxidative stress.

Caffeine intake improves fructose-induced hypertension and insulin resistance by enhancing central insulin signaling

Recent clinical studies found that fructose intake leads to insulin resistance and hypertension. Fructose consumption promotes protein fructosylation and formation of superoxide. In a previous study, we revealed that inhibition of superoxide production in the nucleus tractus solitarii (NTS) reduces blood pressure. Caffeine displays significant antioxidant ability in protecting membranes against oxidative damage and can lower the risk of insulin resistance. However, the mechanism through which caffeine improves fructose-induced insulin resistance is unclear. The aim of this study was to investigate whether caffeine consumption can abolish superoxide generation to enhance insulin signaling in the NTS, thereby reducing blood pressure in rats with fructose-induced hypertension. Treatment with caffeine for 4 weeks decreased blood pressure, serum fasting glucose, insulin, homeostatic model assessment-insulin resistance, and triglyceride levels and increased the serum direct high-density lipoprotein level in fructose-fed rats but not in control rats. Caffeine treatment resulted in the recovery of fructose-induced decrease in nitric oxide production in the NTS. Immunoblotting and immunofluorescence analyses further showed that caffeine reduced the fructose-induced phosphorylation of insulin receptor substrate 1 (IRS1(S307)) and reversed Akt(S473) and neuronal nitric oxide synthase phosphorylation. Similarly, caffeine was able to improve insulin sensitivity and decrease insulin levels in the NTS evoked by fructose. Caffeine intake also reduced the production of superoxide and expression of receptor of advanced glycation end product in the NTS. These results suggest that caffeine may enhance insulin receptor substrate 1-phosphatidylinositol 3-kinase-Akt-neuronal nitric oxide synthase signaling to decrease blood pressure by abolishing superoxide production in the NTS.

Post-translational regulation of endothelial nitric oxide synthase in vascular endothelium

Nitric oxide (NO) is a short-lived gaseous signaling molecule. In blood vessels, it is synthesized in a dynamic fashion by endothelial nitric oxide synthase (eNOS) and influences vascular function via two distinct mechanisms, the activation of soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP)-dependent signaling and the S-nitrosylation of proteins with reactive thiols (S-nitrosylation). The regulation of eNOS activity and NO bioavailability is critical to maintain blood vessel function. The activity of eNOS and ability to generate NO is regulated at the transcriptional, posttranscriptional, and posttranslational levels. Post-translational modifications acutely impact eNOS activity and dysregulation of these mechanisms compromise eNOS activity and foster the development of cardiovascular diseases (CVDs). This review will intergrate past and current literature on the post-translational modifications of eNOS in both health and disease.

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.

Redox signaling in cardiovascular health and disease

Spatiotemporal regulation of the activity of a vast array of intracellular proteins and signaling pathways by reactive oxygen species (ROS) governs normal cardiovascular function. However, data from experimental and animal studies strongly support that dysregulated redox signaling, resulting from hyperactivation of various cellular oxidases or mitochondrial dysfunction, is integral to the pathogenesis and progression of cardiovascular disease (CVD). In this review, we address how redox signaling modulates the protein function, the various sources of increased oxidative stress in CVD, and the labyrinth of redox-sensitive molecular mechanisms involved in the development of atherosclerosis, hypertension, cardiac hypertrophy and heart failure, and ischemia-reperfusion injury. Advances in redox biology and pharmacology for inhibiting ROS production in specific cell types and subcellular organelles combined with the development of nanotechnology-based new in vivo imaging systems and targeted drug delivery mechanisms may enable fine-tuning of redox signaling for the treatment and prevention of CVD.

4-Hydroxy hexenal derived from docosahexaenoic acid protects endothelial cells via Nrf2 activation

Recent studies have proposed that n-3 polyunsaturated fatty acids (n-3 PUFAs) have direct antioxidant and anti-inflammatory effects in vascular tissue, explaining their cardioprotective effects. However, the molecular mechanisms are not yet fully understood. We tested whether n-3 PUFAs showed antioxidant activity through the activation of nuclear factor erythroid 2-related factor 2 (Nrf2), a master transcriptional factor for antioxidant genes. C57BL/6 or Nrf2^−/− mice were fed a fish-oil diet for 3 weeks. Fish-oil diet significantly increased the expression of heme oxygenase-1 (HO-1), and endothelium-dependent vasodilation in the aorta of C57BL/6 mice, but not in the Nrf2^−/− mice. Furthermore, we observed that 4-hydroxy hexenal (4-HHE), an end-product of n-3 PUFA peroxidation, was significantly increased in the aorta of C57BL/6 mice, accompanied by intra-aortic predominant increase in docosahexaenoic acid (DHA) rather than that in eicosapentaenoic acid (EPA). Human umbilical vein endothelial cells were incubated with DHA or EPA. We found that DHA, but not EPA, markedly increased intracellular 4-HHE, and nuclear expression and DNA binding of Nrf2. Both DHA and 4-HHE also increased the expressions of Nrf2 target genes including HO-1, and the siRNA of Nrf2 abolished these effects. Furthermore, DHA prevented oxidant-induced cellular damage or reactive oxygen species production, and these effects were disappeared by an HO-1 inhibitor or the siRNA of Nrf2. Thus, we found protective effects of DHA through Nrf2 activation in vascular tissue, accompanied by intra-vascular increases in 4-HHE, which may explain the mechanism of the cardioprotective effects of DHA.

Effects of tempol on endothelial and vascular dysfunctions and insulin resistance induced by a high-fat high-sucrose diet in the rat

We investigated the effects of treatment with tempol (an antioxidant) on vascular and metabolic dysfunction induced by a high-fat high-sucrose (HFHS) diet. Rats were randomized to receive an HFHS or chow diet with or without tempol treatment (1.5 mmol·(kg body mass)−1·day−1) for 4 weeks. Blood pressure, heart rate, and blood flow were measured in the rats by using intravascular catheters and Doppler flow probes. Insulin sensitivity and vascular responses to insulin were assessed during a euglycemic–hyperinsulinemic clamp. In-vitro studies were performed to evaluate vascular reactivity and endothelial and inducible nitric oxide synthase (eNOS; iNOS) expression in vascular and muscle tissues. Endothelin, nitrotyrosine, and NAD(P)H oxidase expressions were determined in vascular tissues, and glucose transport activity and glucose transporter 4 (GLUT4) expression were examined in muscles. Tempol treatment was found to prevent alterations in insulin sensitivity, glucose transport activity, GLUT4 expression, and vascular reactivity, and to prevent increases in plasma insulin, blood pressure, and heart rate noted in the untreated HFHS-fed rats. These were associated with increased levels of eNOS expression in vascular and muscle tissues, but reductions in nitrotyrosine, endothelin, NAD(P)H oxidase, and iNOS expressions. Therefore, oxidative stress induced by a relatively short-term HFHS diet could contribute to the early development of vascular and metabolic abnormalities in rats.

Effect of meditation on endothelial function in Black Americans with metabolic syndrome: a randomized trial

OBJECTIVES

Psychological stress may play a role in metabolic syndrome. A consequence of metabolic syndrome is endothelial dysfunction, which is also influenced by psychological stress. We sought to compare the effect of consciously resting meditation (CRM), a sound based meditation, with a control intervention of health education (HE) on endothelial function in the setting of metabolic syndrome.

METHODS

Sixty-eight black Americans with metabolic syndrome risk factors (age, 30-65 years) were randomized to either CRM (n = 33) or HE (n = 35); interventions were matched for frequency and duration of sessions and lasted 12 months. Endothelial function was assessed by brachial artery flow-mediated dilation at baseline and at 6 and 12 months. Arterial elasticity, metabolic risk factors, and psychosocial and behavioral variables were secondary end points.

RESULTS

Although flow-mediated dilation improved in the CRM group for 12 months, this increase was not significantly higher than that in the HE group (p = .51 for the interaction between group and time). Non-endothelium-dependent dilation and arterial elasticity did not change in either group. Most metabolic syndrome risk factors showed beneficial trends in the CRM group only. A risk factor score counting the number of metabolic syndrome components decreased in the CRM group only (p = .049 for the interaction between treatment group and time).

CONCLUSIONS

Among black Americans with metabolic syndrome risk factors, CRM, did not improve endothelial function significantly more than a control intervention of HE. CRM resulted in favorable trends in metabolic syndrome risk factors, which were examined as secondary outcomes.