The calcium ionophore A23187 induces endothelium-dependent contractions in femoral arteries from rats with streptozotocin-induced diabetes

Maternal exposure to glyphosate-based herbicide causes vascular dysfunction in offspring female rats

This study analyzed how glyphosate exposure in the gestational period affects vascular function in their female offspring and whether oxidative stress is involved in this effect. To this, pregnant Wistar rats were exposed through drinking water to 0.2% of a glyphosate commercial formulation, and we analyzed the response to acetylcholine and phenylephrine in the aorta from offspring of Glyphosate-based herbicide (O-GBH) and controls (O-CON) rats at six months of age. Relaxation to acetylcholine was reduced in O-GBH than in O-CON. Acute Indomethacin and Apocynin increased relaxation to acetylcholine in O-GBH. The aorta from O-GBH was hyperactive to phenylephrine; the preincubation with N-nitro-L-arginine methyl ester (L-NAME) increased contraction to phenylephrine more in O-CON than O-GBH. TEMPOL similarly reduced phenylephrine response, and L-NAME prevented this effect. The TBARS and GSH levels were increased in O-GBH than in O-CON. Results reinforce the concept that oxidative stress during the perinatal period contributes to the development of vascular changes in adulthood. Results also reveal that oxidative stress parameters altered, and the current levels considered safe for exposure to Glyphosate deserve further investigation, especially in the female gender.

Coronary "Microvascular Dysfunction": Evolving Understanding of Pathophysiology, Clinical Implications, and Potential Therapeutics

Until recently, it has been generally held that stable angina pectoris (SAP) primarily reflects the presence of epicardial coronary artery stenoses due to atheromatous plaque(s), while acute myocardial infarction (AMI) results from thrombus formation on ruptured plaques. This concept is now challenged, especially by results of the ORBITA and ISCHEMIA trials, which showed that angioplasty/stenting does not substantially relieve SAP symptoms or prevent AMI or death in such patients. These disappointing outcomes serve to redirect attention towards anomalies of small coronary physiology. Recent studies suggest that coronary microvasculature is often both structurally and physiologically abnormal irrespective of the presence or absence of large coronary artery stenoses. Structural remodelling of the coronary microvasculature appears to be induced primarily by inflammation initiated by mast cell, platelet, and neutrophil activation, leading to erosion of the endothelial glycocalyx. This leads to the disruption of laminar flow and the facilitation of endothelial platelet interaction. Glycocalyx shedding has been implicated in the pathophysiology of coronary artery spasm, cardiovascular ageing, AMI, and viral vasculitis. Physiological dysfunction is closely linked to structural remodelling and occurs in most patients with myocardial ischemia, irrespective of the presence or absence of large-vessel stenoses. Dysfunction includes the impairment of platelet and vascular responsiveness to autocidal coronary vasodilators, such as nitric oxide, prostacyclin, and hydrogen sulphide, and predisposes both to coronary vasoconstriction and to a propensity for microthrombus formation. These findings emphasise the need for new directions in medical therapeutics for patients with SAP, as well as a wide range of other cardiovascular disorders.

Targeting endothelial dysfunction and inflammation

Vascular endothelium maintains vascular homeostasis through liberating a spectrum of vasoactive molecules, both protective and harmful regulators of vascular tone, structural remodeling, inflammation and atherogenesis. An intricate balance between endothelium-derived relaxing factors (nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor) and endothelium-derived contracting factors (superoxide anion, endothelin-1 and constrictive prostaglandins) tightly regulates vascular function. Disruption of such balance signifies endothelial dysfunction, a critical contributor in aging and chronic cardiometabolic disorders, such as obesity, diabetes, hypertension, dyslipidemia and atherosclerotic vascular diseases. Among many proposed cellular and molecular mechanisms causing endothelial dysfunction, oxidative stress and inflammation are often the pivotal players and they are naturally considered as useful targets for intervention in patients with cardiovascular and metabolic diseases. In this article, we provide a recent update on the therapeutic values of pharmacological agents, such as cyclooxygenase-2 inhibitors, renin-angiotensin-system inhibitors, bone morphogenic protein 4 inhibitors, peroxisome proliferator-activated receptor δ agonists, and glucagon-like peptide 1-elevating drugs, and the physiological factors, particularly hemodynamic forces, that improve endothelial function by targeting endothelial oxidative stress and inflammation.

Kv7 Channels in Cyclic-Nucleotide Dependent Relaxation of Rat Intra-Pulmonary Artery

Pulmonary hypertension is treated with drugs that stimulate cGMP or cAMP signalling. Both nucleotides can activate Kv7 channels, leading to smooth muscle hyperpolarisation, reduced Ca²⁺ influx and relaxation. Kv7 activation by cGMP contributes to the pulmonary vasodilator action of nitric oxide, but its contribution when dilation is evoked by the atrial natriuretic peptide (ANP) sensitive guanylate cyclase, or cAMP, is unknown. Small vessel myography was used to investigate the ability of Kv7 channel blockers to interfere with pulmonary artery relaxation when cyclic nucleotide pathways were stimulated in different ways. The pan-Kv7 blockers, linopirdine and XE991, caused substantial inhibition of relaxation evoked by NO donors and ANP, as well as endothelium-dependent dilators, the guanylate cyclase stimulator, riociguat, and the phosphodiesterase-5 inhibitor, sildenafil. Maximum relaxation was reduced without a change in sensitivity. The blockers had relatively little effect on cAMP-mediated relaxation evoked by forskolin, isoprenaline or treprostinil. The Kv7.1-selective blocker, HMR1556, had no effect on cGMP or cAMP-dependent relaxation. Western blot analysis demonstrated the presence of Kv7.1 and Kv7.4 proteins, while selective activators of Kv7.1 and Kv7.4 homomeric channels, but not Kv7.5, caused pulmonary artery relaxation. It is concluded that Kv7.4 channels contribute to endothelium-dependent dilation and the effects of drugs that act by stimulating cGMP, but not cAMP, signalling.

Vitamin D deficiency attenuates endothelial function by reducing antioxidant activity and vascular eNOS expression in the rat microcirculation

This study examined the effects of vitamin D deficiency on vascular function and tissue oxidative status in the microcirculation; and whether or not these effects can be ameliorated with calcitriol, the active vitamin D metabolite. Three groups (n = 10 each) of male Sprague Dawley rats were fed for 10 weeks with control diet (CR), vitamin D-deficient diet without (DR), or with oral calcitriol supplementation (0.15 μg/kg) for the last four weeks (DSR). After 10 weeks, rats were sacrificed; mesenteric arterial rings were studied using wire myograph. Oxidative stress biomarkers malondialdehyde (MDA) levels and superoxide dismutase (SOD) activity were measured in the mesenteric arterial tissue. Vascular protein expression of endothelial nitric oxide synthase (eNOS) was determined by Western blotting. Acetylcholine-induced endothelium-dependent relaxation of DR was lower than CR. eNOS expression and SOD activity were lower in mesenteric arterial tissue of DR compared to CR. Calcitriol supplementation to DSR did not ameliorate the above parameters; in fact, augmented endothelium-dependent contraction was observed. Serum calcium was higher in DSR compared to CR and DR. In conclusion, vitamin D deficiency impaired microvascular vasodilation, associated with eNOS downregulation and reduced antioxidant activity. Calcitriol supplementation to vitamin D-deficient rats at the dosage used augmented endothelium-dependent contraction, possibly due to hypercalcaemia.

Endothelium-dependent contraction: The non-classical action of endothelial prostacyclin, its underlying mechanisms, and implications

Although commonly thought to produce prostacyclin (prostaglandin I₂ ; PGI₂ ) that evokes vasodilatation and protects vessels from the development of diseases, the endothelial cyclooxygenase (COX)-mediated metabolism has also been found to release substance(s) called endothelium-derived contracting factor(s) (EDCF) that causes endothelium-dependent contraction and implicates in endothelial dysfunction of disease conditions. Various mechanisms have been proposed for the process; however, the major endothelial COX metabolite PGI₂ , which has been classically considered to activate the I prostanoid receptor (IP) that mediates vasodilatation and opposes the effects of thromboxane (Tx) A₂ produced by COX in platelets, emerges as a major EDCF in health and disease conditions. Our recent studies from genetically altered mice further suggest that vasomotor reactions to PGI₂ are collectively modulated by IP, the vasoconstrictor Tx-prostanoid receptor (TP; the prototype receptor of TxA₂ ) and E prostanoid receptor-3 (EP3; a vasoconstrictor receptor of PGE₂ ) although with differences in potency and efficacy; a contraction to PGI₂ reflects activities of TP and/or EP3 outweighing that of the concurrently activated IP. Here, we discuss the history of endothelium-dependent contraction, evidences that support the above hypothesis, proposed mechanisms for the varied reactions to endothelial PGI₂ synthesis as well as the relation of its dilator activity to the effect of another NO-independent vasodilator mechanism, the endothelium-derived hyperpolarizing factor. Also, we address the possible pathological and therapeutic implications as well as questions remaining to be resolved or limitations of our above findings obtained from genetically altered mouse models.

Calcitriol Supplementation Ameliorates Microvascular Endothelial Dysfunction in Vitamin D-Deficient Diabetic Rats by Upregulating the Vascular eNOS Protein Expression and Reducing Oxidative Stress

Diabetes mellitus contributes to macro- and microvascular complications, leading to adverse cardiovascular events. This study examined the effects of vitamin D deficiency on the vascular function and tissue oxidative status in the microcirculation of diabetic rats and to determine whether these effects can be reversed with calcitriol (active vitamin D metabolite) supplementation. Streptozotocin-induced diabetic rats were fed for 10 weeks with control diet (DC) or vitamin D-deficient diet without (DD) or with oral calcitriol supplementation (0.15 μg/kg) in the last four weeks (DDS) (10 rats each group). A nondiabetic rat group that received control diet was also included (NR). After 10 weeks, rats were sacrificed; mesenteric arterial rings with and without endothelium were studied using wire myograph. Western blotting of the mesenteric arterial tissue was performed to determine the protein expression of endothelial nitric oxide synthase (eNOS) enzyme. Antioxidant enzyme superoxide dismutase (SOD) activity and oxidative stress marker malondialdehyde (MDA) levels in the mesenteric arterial tissue were also measured. The DC group had significantly lower acetylcholine-induced relaxation and augmented endothelium-dependent contraction, with reduced eNOS expression, compared to NR rats. In mesenteric arteries of DD, acetylcholine-induced endothelium-dependent and sodium nitroprusside-induced endothelium-independent relaxations were lower than those in DC. Calcitriol supplementation in DDS restored endothelium-dependent relaxation. Mesenteric artery endothelium-dependent contraction of DD was greater than DC; it was not affected by calcitriol supplementation. The eNOS protein expression and SOD activity were significantly lower while MDA levels were greater in DD compared to DC; these effects were not observed in DDS that received calcitriol supplementation. In conclusion, vitamin D deficiency causes eNOS downregulation and oxidative stress, thereby impairing the vascular function and posing an additional risk for microvascular complications in diabetes. Calcitriol supplementation to diabetics with vitamin D deficiency could potentially be useful in the management of or as an adjunct to diabetes-related cardiovascular complications.

Model for type 2 diabetes exhibits changes in vascular function and structure due to vascular oxidative stress and inflammation

We used a type 2 diabetes rat model produced by a high fat diet (HFD) followed by low dose streptozotocin (STZ) to study diabetic vasculopathy. Animals were evaluated for early vascular structural changes, endothelial function, inflammation, lipid profile and oxidative stress. We used 20 male Sprague-Dawley rats divided equally into control and diabetic groups. Diabetic rats were fed an HFD for 4 weeks, injected intraperitoneally with STZ, then sacrificed at week 15. Aortic endothelial nitric oxide synthase (eNOS), aortic superoxide dismutase (SOD), endothelial-dependent and independent relaxation and contraction, intima-media thickness (IMT), malondialdehyde (MDA) and tumor necrosis factor-alpha (TNF-α) were measured. Histopathological characteristics also were assessed. Diabetic rats exhibited higher fasting blood glucose (FBG), low density lipoprotein, total cholesterol and triglycerides compared to the control group. Aortic endothelium-dependent relaxation due to acetylcholine (ACh) was lower, while aortic endothelium-dependent contraction due to calcium ionophore and endothelium-independent contraction due to phenylephrine (PE) were higher for the diabetic group. eNOS expression was lower in the diabetic group compared to controls. IMT and MDA levels were increased, while SOD activity was decreased in the diabetic group compared to controls. TNF-α was higher in the diabetic group than for controls. Our type 2 diabetes model exhibited endothelial dysfunction associated with early vascular structural changes, dyslipidemia, increased vascular oxidative stress, and inflammation. Therefore, the model is suitable for studying diabetic atherosclerosis.

Clinacanthus nutans Leaves Extract Reverts Endothelial Dysfunction in Type 2 Diabetes Rats by Improving Protein Expression of eNOS

Diabetes mellitus is associated with endothelial dysfunction; it causes progressive vascular damage resulting from an impaired endothelium-dependent vasorelaxation. In the diabetes state, presence of hyperglycemia and insulin resistance predisposes to endothelial dysfunction. Clinacanthus nutans, widely used as a traditional medicine for diabetes is reported to have hypoglycemic, hypolipidemic, antioxidant, and anti-inflammatory properties. However, the possibility of C. nutans affecting the vascular endothelial function in diabetes remains unclear. This study was aimed at evaluating the effects of C. nutans methanolic leaves extract (CNME) on endothelial function in a type 2 diabetes (T2DM) rat model. Sixty male Sprague-Dawley rats were divided into five groups (n = 12 per group): nondiabetic control, nondiabetic treated with four weeks of CNME (500 mg/kg/daily), untreated diabetic rats, diabetic treated with metformin (300 mg/kg/daily), and diabetic treated with CNME (500 mg/kg/daily). T2DM was induced by a single intraperitoneal injection of low-dose streptozotocin (STZ) to rats fed with high-fat diet (HFD). Endothelial-dependent and endothelial-independent relaxations and contractions of the thoracic aorta were determined using the organ bath. Aortic endothelial nitric oxide synthase (eNOS) expression was determined using Western blotting. Endothelial-dependent relaxation was reduced in diabetic rats. Both diabetic groups treated with CNME or metformin significantly improved the impairment in endothelium-dependent vasorelaxation; this was associated with increased expression of aortic eNOS protein. CNME- and metformin-treated groups also reduced aortic endothelium-dependent and aortic endothelium-independent contractions in diabetics. Both of these diabetic-treated groups also reduced blood glucose levels and increased body weight compared to the untreated diabetic group. In conclusion, C. nutans improves endothelial-dependent vasodilatation and reduces endothelial-dependent contraction, thus ameliorating endothelial dysfunction in diabetic rats. This may occur due to its effect on increasing eNOS protein expression.

Contributions of Rho-kinase and AMP-related kinase signaling pathways to responses mediated by endothelium-derived contracting factors in diabetic rat aorta

Diabetes-induced endothelial damage leads to vascular dysfunction. The current study investigated the effects of short-term (4-week) streptozotocin (STZ)-induced diabetes on responses mediated by endothelium-derived contracting factors (EDCFs) as well as possible contributions of Rho-kinase and AMP-activated kinase (AMPK) signaling pathways. The effects of STZ-diabetes on vascular function were examined in isolated thoracic aorta preparations of 30-week-old rats (n = 27). The diabetes-associated changes in vascular function were studied with calcium ionophore A23187, acetylcholine, Rho-kinase inhibitor Y27632 ((R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide dihydrochloride), and AMPK activator AICAR (5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside). The phosphorylation of acetyl-CoA carboxylase, AMPK, and phospholamban and the protein levels of sarcoplasmic/endoplasmic Ca2+-ATPase 2 (SERCA2) and Rho-associated protein kinase (ROCKII) were measured in aortic preparations. Although the acetylcholine-mediated relaxation responses were preserved in 4-week STZ-induced diabetes, the increased activation of the Rho-kinase pathway was demonstrated via twofold enhancement in A23187-mediated contractile responses and significantly augmented protein levels of ROCKII. The AICAR-activated AMPK-mediated relaxation response was also augmented ∼4-fold in diabetic rats, without any alteration in phospholamban phosphorylation; further, this relaxation response suppressed A23187-mediated contraction in both groups. Diabetic rats showed an increase in AICAR-induced AMPK-mediated vasorelaxation and a 2.5-fold elevation of phosphorylated AMPK levels. These results indicate a possible compensation between hyperglycemia-induced endothelium-dependent hypercontractility and AMPK-mediated vasorelaxation in diabetes.

Fenofibrate improves vascular endothelial function and contractility in diabetic mice

Fenofibrate, a peroxisome proliferator-activated receptors α (PPARα) agonist, reduces vascular complications of diabetic patients but its protective mechanisms are not fully understood. Here we tested the hypothesis that fenofibrate improves vascular endothelial dysfunction by balancing endothelium-dependent relaxation and contractility of the aorta in diabetes mellitus (DM). In streptozotocin-induced diabetic mice, eight weeks of fenofibrate treatment (100 mg/Kg/d) improved endothelium dependent relaxation in the macro- and microvessels, increased nitric oxide (NO) levels, reduced renal damage markers and effects of the vasoconstrictor prostaglandin. Levels of superoxide dismutase and catalase were both reduced and hydrogen peroxide was increased in vehicle-treated DM, but these changes were reversed by fenofibrate treatment. Vasodilation of the aorta after fenofibrate treatment was reversed by PPARα or AMPKα inhibitors. Western blots showed that fenofibrate treatment elevated PPARα expression, induced liver kinase B1 (LKB1) translocation from the nucleus to the cytoplasm and activated AMP-activated protein kinase-α (AMPKα), thus activating endothelial NO synthase (eNOS). Also, fenofibrate treatment decreased NF-κB p65 and cyclooxygenase 2 proteins in aortas. Finally, incubation with indomethacin in vitro improved aortic contractility in diabetic mice. Overall, our results show that fenofibrate treatment in diabetic mice normalizes endothelial function by balancing vascular reactivity via increasing NO production and suppressing the vasoconstrictor prostaglandin, suggesting mechanism of action of fenofibrate in mediating diabetic vascular complications.

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Fenofibrate improves diabetic endothelial function is via PPAR/LKB1/AMPK/eNOS signal.

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Fenofibrate reduces diabetic endothelial contractility is via NF-κB/COX-2 pathway.

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Diabetes-associated oxidative stress is attenuated by fenofibrate treatment.

The toxic effects of monosodium glutamate (MSG) - The involvement of nitric oxide, prostanoids and potassium channels in the reactivity of thoracic arteries in MSG-obese rats

We investigated the potential effects of monosodium glutamate (MSG)-induced obesity with regards to nitric oxide and prostanoid production, as well as potassium channel function, in rat thoracic arteries. Newborn male Wistar rats were injected intraperitoneally with typically reported MSG (4.0 mg/g) once daily for 4 consecutive days. At 90 days postnatal, the rats were sacrificed and the thoracic aortas were evaluated for vascular responses and for prostanoid production. Nitric oxide was studied with calcium ionophore (A23187), acetylcholine (ACh) and sodium nitroprusside (SNP). The release of prostanoids was measured under basal and ACh-stimulated conditions, and the vasomotor effect of exogenous thromboxane A₂ mimetic, U46619 was assessed. Potassium channel activities were analyzed using an NS1619 opener for BK_Ca channels and pinacidil for K_ATP channels. Arteries from MSG-obese rats exhibited a reduced maximal contraction to potassium chloride and hyper-responsiveness to U46619, suggesting that MSG also alters the responsiveness of vascular smooth muscles. The endothelium-dependent relaxation to ACh and A23817 was attenuated, suggesting low nitric oxide bioavailability. The hypersensitivity of arteries to an exogenous nitric oxide donor, SNP, occurred. The secondary contraction to A23817 was augmented, suggesting increased activation of the prostanoid receptor. The prostanoid release was increased in both basal- and acetylcholine-stimulated rings. In addition, down-regulation of K_ATP and BK_Ca channels influenced hyperpolarizing mechanisms. Our findings suggest that increased prostanoid production and hypersensitivity to thromboxane A₂ together with down-regulation of potassium channels and low nitric oxide bioavailability may contribute to the increase in blood pressure found in adult MSG-obese male rats.

Role of thromboxane A2 signaling in endothelium-dependent contractions of arteries

Thromboxane A₂ (TxA₂) plays a very important role in various cardiovascular diseases through its action on platelet aggregation, vasoconstriction, and proliferation. The present article focuses on the role of TxA₂ signaling in endothelium-dependent contractions of arteries. Arachidonic acid (AA) is metabolized by cyclooxygenase (COX) to form the unstable prostaglandin H₂ which is further converted into TxA₂. After being produced by thromboxane synthase (TxAS), TxA₂ ultimately stimulates TxA₂/prostanoid (TP) receptor to induce vasoconstriction. The calcium ionophore A23187, the prostanoid precursor AA, or the muscarinic receptor agonist acetylcholine (ACh) can evoke endothelium-dependent contractions associated with TxA₂. The endothelium-dependent contractions shown in hypertension, diabetes, atherogenesis, and other cardiovascular diseases have been significantly reduced by antagonism of COX, TxAS, or TP receptor. So inhibition of the bioavailability and/or effect of TxA₂ may be promising therapeutic targets to prevent these diseases. Especially some bioactive compounds isolated from medicinal plants will provide new pharmacological approaches to promote vascular health.

Macro- and microvascular endothelial dysfunction in diabetes

Endothelial cells, as well as their major products nitric oxide (NO) and prostacyclin, play a key role in the regulation of vascular homeostasis. Diabetes mellitus is an important risk factor for cardiovascular disease. Diabetes-induced endothelial dysfunction is a critical and initiating factor in the genesis of diabetic vascular complications. The present review focuses on both large blood vessels and the microvasculature. The endothelial dysfunction in diabetic macrovascular complications is characterized by reduced NO bioavailability, poorly compensated for by increased production of prostacyclin and/or endothelium-dependent hyperpolarizations, and increased production or action of endothelium-derived vasoconstrictors. The endothelial dysfunction of microvascular complications is primarily characterized by decreased release of NO, enhanced oxidative stress, increased production of inflammatory factors, abnormal angiogenesis, and impaired endothelial repair. In addition, non-coding RNAs (microRNAs) have emerged as participating in numerous cellular processes. Thus, this reviews pays special attention to microRNAs and their modulatory role in diabetes-induced vascular dysfunction. Some therapeutic strategies for preventing and restoring diabetic endothelial dysfunction are also highlighted.

Estrogen Activates AMP-Activated Protein Kinase in Human Endothelial Cells via ERβ/Ca(2+)/Calmodulin-Dependent Protein Kinase Kinase β Pathway

Our previous studies suggested that Estrogen inhibits cytokine-induced expression of VCAM-1 and ICAM-1 in cultured human endothelial cells via AMP-activated protein kinase (AMPK) activation. Here, we sought to delineate the mechanisms underlying estrogen activation of AMPK. AMPK can be considered a 'fuel gauge' of cellular energy status in response to metabolic stress. It is controlled by upstream kinases such as Ca(2+)/calmodulin-dependent protein kinase kinase β (CaMKKβ) or LKB1. The present study of human endothelial cells demonstrates that AMPK is activated by estradiol (E2) through a Ca(2+)-dependent mechanism involving the estrogen receptor-β (ERβ) activation. Inhibition of CaMKK with STO-609, a specific inhibitor of CaMKKα and CaMKKβ, attenuated E2-induced AMPK activation, suggesting that CaMKKβ was the responsible AMPK kinase. Conversely, down-regulation of LKB1 did not affect E2-induced AMPK activation. E2 stimulation caused phosphorylation of acetyl coenzyme A carboxylase (ACC) and endothelial nitric oxide synthase (eNOS), two main targets of AMPK. Inhibition or down-regulation of CaMKKβ eliminated phosphorylation of ACC and eNOS in response to E2. Together, our data highlight the role of Ca(2+) as a regulator of AMPK activation in response to E2 stimulation. We demonstrate that E2 activates AMPK via an ERβ/Ca(2+)/CaMKKβ-dependent pathway in endothelial cells.

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.

Vitamin D Metabolism and the Implications for Atherosclerosis

Vitamin D levels and metabolism may play a role in the pathogenesis and treatment of atherosclerosis and subsequent cardiovascular health. Herein, we discuss both normal and disordered vitamin D metabolism as it pertains to atherosclerosis, and we review major clinical trials regarding vitamin D levels and effects of supplementation. Although there are no official recommendations for vitamin D as it applies to atherosclerosis, it is clear that these two entities are linked. Further study of the complex association between vitamin D and atherosclerosis, as well as the effects of supplementation, are recommended.

The endothelial cyclooxygenase pathway: Insights from mouse arteries

To date, cyclooxygenase-2 (COX-2) is commonly believed to be the major mediator of endothelial prostacyclin (prostaglandin I2; PGI2) synthesis that balances the effect of thromboxane (Tx) A2 synthesis mediated by the other COX isoform, COX-1 in platelets. Accordingly, selective inhibition of COX-2 is considered to cause vasoconstriction, platelet aggregation, and hence increase the incidence of cardiovascular events. This idea has been claimed to be substantiated by experiments on mouse models, some of which are deficient in one of the two COX isoforms. However, results from our studies and those of others using similar mouse models suggest that COX-1 is the major functional isoform in vascular endothelium. Also, although PGI2 is recognized as a potent vasodilator, in some arteries endothelial COX activation causes vasoconstrictor response. This has again been recognized by studies, especially those performed on mouse arteries, to result largely from endothelial PGI2 synthesis. Therefore, evidence that supports a role for COX-1 as the major mediator of PGI2 synthesis in mouse vascular endothelium, reasons for the inconsistency, and results that elucidate underlying mechanisms for divergent vasomotor reactions to endothelial COX activation will be discussed in this review. In addition, we address the possible pathological implications and limitations of findings obtained from studies performed on mouse arteries.

Serelaxin (recombinant human relaxin-2) prevents high glucose-induced endothelial dysfunction by ameliorating prostacyclin production in the mouse aorta

Diabetes-induced endothelial dysfunction is a critical initiating factor in the development of cardiovascular complications. Treatment with relaxin improves tumour necrosis factor α-induced endothelial dysfunction by enhancing endothelial nitric oxide synthase (eNOS) activity and restoring superoxide dismutase 1 protein in rat aortic rings ex vivo. It is, therefore, possible that relaxin treatment could alleviate endothelial dysfunction in diabetes. This study aimed to test the hypothesis that serelaxin (recombinant human relaxin-2) prevents high glucose-induced vascular dysfunction in the mouse aorta. Abdominal aortae were isolated from C57BL/6 male mice and incubated in M199 media for 3days with either normal glucose (5.5mM) or high glucose (30mM), and co-incubated with placebo (20mM sodium acetate) or 10nM serelaxin at 37°C in 5% CO2. Vascular function was analysed using wire-myography. High glucose significantly reduced the sensitivity to the endothelium-dependent agonist, acetylcholine (ACh) (pEC50; normal glucose=7.66±0.10 vs high glucose=7.29±0.10, n=11-12, P<0.05) and the contraction induced by NOS inhibitor, L-NAME (200μM) (normal glucose=59.9±8.3% vs high glucose=38.7±4.3%, n=6, P<0.05), but had no effect on the endothelium-independent agonist, sodium nitroprusside (SNP)-mediated relaxation. Treatment with serelaxin restored endothelial function (pEC50; 7.83±0.11, n=11) but not NO availability. The presence of the cyclooxygenase (COX) inhibitor, indomethacin (1μM) (pEC50; control=7.29±0.10 vs indo=7.74±0.18, n=6-12, P<0.05) and a superoxide dismutase mimetic, tempol (10μM) (pEC50; control=7.29±0.10 vs tempol=7.82±0.05, n=6-12, P<0.01) significantly improved sensitivity to ACh in high glucose treated aortae, but had no effect in serelaxin treated aortae. This suggests that high glucose incubation alters the superoxide and COX-sensitive pathway, which was normalized by co-incubation with serelaxin. Neither high glucose incubation nor serelaxin treatment had an effect on cyclooxygenase 1 and 2 (Ptgs1, Ptgs2), prostacyclin synthase (PTGIS) and receptor (Ptgir) as well as thromboxane A2 receptor (Tbxa2r) mRNA expression. Importantly, production of prostacyclin was significantly (P<0.05) attenuated in high glucose treated aortae, which was prevented by serelaxin treatment. Our data show that serelaxin treatment for 3 days restores high glucose-induced endothelial dysfunction by ameliorating vasodilator prostacyclin production and possibly through the reduction of superoxide in the mouse aorta.

Constrictor prostanoids and uridine adenosine tetraphosphate: vascular mediators and therapeutic targets in hypertension and diabetes

Vascular dysfunction plays a pivotal role in the development of systemic complications associated with arterial hypertension and diabetes. The endothelium, or more specifically, various factors derived from endothelial cells tightly regulate vascular function, including vascular tone. In physiological conditions, there is a balance between endothelium-derived factors, that is, relaxing factors (endothelium-derived relaxing factors; EDRFs) and contracting factors (endothelium-derived contracting factors; EDCFs), which mediate vascular homeostasis. However, in disease states, such as diabetes and arterial hypertension, there is an imbalance between EDRF and EDCF, with a reduction of EDRF signalling and an increase of EDCF signalling. Among EDCFs, COX-derived vasoconstrictor prostanoids play an important role in the development of vascular dysfunction associated with hypertension and diabetes. Moreover, uridine adenosine tetraphosphate (Up4 A), identified as an EDCF in 2005, also modulates vascular function. However, the role of Up4 A in hypertension- and diabetes-associated vascular dysfunction is unclear. In the present review, we focused on experimental and clinical evidence that implicate these two EDCFs (vasoconstrictor prostanoids and Up4 A) in vascular dysfunction associated with hypertension and diabetes.

Recombinant interleukin-1β dilates steelhead trout coronary microvessels: effect of temperature and role of the endothelium, nitric oxide and prostaglandins

Interleukin (IL)-1β is associated with hypotension and cardiovascular collapse in mammals during heat stroke, and the mRNA expression of this pro-inflammatory cytokine increases dramatically in the blood of Atlantic cod (Gadus morhua) at high temperatures. These data suggest that release of IL-1β at high temperatures negatively impacts fish cardiovascular function and could be a primary determinant of upper thermal tolerance in this taxa. Thus, we measured the concentration-dependent response of isolated steelhead trout (Oncorhynchus mykiss) coronary microvessels (<150 μm in diameter) to recombinant (r) IL-1β at two temperatures (10 and 20°C). Recombinant IL-1β induced a concentration-dependent vasodilation with vessel diameter increasing by approximately 8 and 30% at 10(-8) and 10(-7) mol l(-1), respectively. However, this effect was not temperature dependent. Both vessel denudation and cyclooxygenase blockade (by indomethacin), but not the nitric oxide (NO) antagonist L-NIO, inhibited the vasodilator effect of rIL-1β. In contrast, the concentration-dependent dilation caused by the endothelium-dependent calcium ionophore A23187 was completely abolished by L-NIO and indomethacin, suggesting that both NO and prostaglandin signaling mechanisms exist in the trout coronary microvasculature. These data: (1) are the first to demonstrate a functional link between the immune and cardiovascular systems in fishes; (2) suggest that IL-1β release at high temperatures may reduce systemic vascular resistance, and thus, the capacity of fish to maintain blood pressure; and (3) provide evidence that both NO and prostaglandins play a role in regulating coronary vascular tone, and thus, blood flow.

Vitamin D and atherosclerosis

PURPOSE OF REVIEW

To provide an overview of the association between vitamin D deficiency and atherosclerosis.

RECENT FINDINGS

Vitamin D exerts protective effects on atherosclerosis through multiple mechanisms. It has been shown to protect against endothelial dysfunction, vascular smooth muscle cell proliferation and migration, and modulation of the immune system, as well as the inflammatory response. In addition, vitamin D has been shown to have systemic effects on insulin resistance, dyslipidemia, and hypertension.

SUMMARY

Vitamin D deficiency is widely prevalent in the United States and worldwide. Although deficiency of this fat-soluble vitamin is usually associated with musculoskeletal disorder, it is associated with a wide range of disease processes that include multiple organ systems. Recently, there has been mounting evidence linking vitamin D deficiency to cardiovascular disease and atherosclerosis.

Uncoupling protein-2 mediates DPP-4 inhibitor-induced restoration of endothelial function in hypertension through reducing oxidative stress

AIMS

Although uncoupling protein 2 (UCP2) negatively regulates intracellular reactive oxygen species (ROS) production and protects vascular function, its participation in vascular benefits of drugs used to treat cardiometabolic diseases is largely unknown. This study investigated whether UCP2 and associated oxidative stress reduction contribute to the improvement of endothelial function by a dipeptidyl peptidase-4 inhibitor, sitagliptin, in hypertension.

RESULTS

Pharmacological inhibition of cyclooxygenase-2 (COX-2) but not COX-1 prevented endothelial dysfunction, and ROS scavengers reduced COX-2 mRNA and protein expression in spontaneously hypertensive rats (SHR) renal arteries. Angiotensin II (Ang II) evoked endothelium-dependent contractions (EDCs) in C57BL/6 and UCP2 knockout (UCP2KO) mouse aortae. Chronic sitagliptin administration attenuated EDCs in SHR arteries and Ang II-infused C57BL/6 mouse aortae and eliminated ROS overproduction in SHR arteries, which were reversed by glucagon-like peptide 1 receptor (GLP-1R) antagonist exendin 9-39, AMP-activated protein kinase (AMPK)α inhibitor compound C, and UCP2 inhibitor genipin. By contrast, sitagliptin unaffected EDCs in Ang II-infused UCP2KO mice. Sitagliptin increased AMPKα phosphorylation, upregulated UCP2, and downregulated COX-2 expression in arteries from SHR and Ang II-infused C57BL/6 mice. Importantly, exendin 9-39, compound C, and genipin reversed the inhibitory effect of GLP-1R agonist exendin-4 on Ang II-stimulated mitochondrial ROS rises in SHR endothelial cells. Moreover, exendin-4 improved the endothelial function of renal arteries from SHR and hypertensive patients.

INNOVATION

We elucidate for the first time that UCP2 serves as an important signal molecule in endothelial protection conferred by GLP-1-related agents. UCP2 could be a useful target in treating hypertension-related vascular events.

CONCLUSIONS

UCP2 inhibits oxidative stress and downregulates COX-2 expression through GLP-1/GLP-1R/AMPKα cascade.

Vasoconstrictor role of cyclooxygenase-1-mediated prostacyclin synthesis in non-insulin-dependent diabetic mice induced by high-fat diet and streptozotocin

This study tested the hypothesis that in diabetic arteries, cyclooxygenase (COX)-1 mediates endothelial prostacyclin (PGI2) synthesis, which evokes vasoconstrictor activity under the pathological condition. Non-insulin-dependent diabetes was induced to C57BL/6 mice and those with COX-1 deficiency (COX-1−/− mice) using a high-fat diet in combination with streptozotocin injection. In vitro analyses were performed 3 mo after. Results showed that in diabetic aortas, the endothelial muscarinic receptor agonist ACh evoked an endothelium-dependent production of the PGI2 metabolite 6-keto-PGF1α, which was abolished in COX-1−/− mice. Meanwhile, COX-1 deficiency or COX-1 inhibition prevented vasoconstrictor activity in diabetic abdominal aortas, resulting in enhanced relaxation evoked by ACh. In a similar manner, COX-1 deficiency increased the relaxation evoked by ACh in nitric oxide synthase-inhibited diabetic renal arteries. Also, in diabetic abdominal aortas and/or renal arteries, both PGI2 and the COX substrate arachidonic acid evoked contractions similar to those of nondiabetic mice. However, the contraction to arachidonic acid, but not that to PGI2, was abolished in vessels from COX-1−/− mice. Moreover, we found that 3 mo after streptozotocin injection, systemic blood pressure increased in diabetic C57BL/6 mice but not in diabetic COX-1−/− mice. These results explicitly demonstrate that in the given arteries from non-insulin-dependent diabetic mice, COX-1 remains a major contributor to the endothelial PGI2 synthesis that evokes vasoconstrictor activity under the pathological condition. Also, our data suggest that COX-1 deficiency prevents or attenuates diabetic hypertension in mice, although this could be related to the loss of COX-1-mediated activities derived from both vascular and nonvascular tissues.

Increased calcium influx triggers and accelerates cortical spreading depression in vivo in male adult rats

Cortical spreading depression (CSD) is a depolarization wave associated with neurological disorders such as migraine, cerebral ischemia and traumatic brain injury. The mechanism of action of this phenomenon still remains unclear. Although it is suggested that extracellular K(+) accumulation contributes to CSD, other ions may play a relevant role in the mechanism of propagation of the wave. In this context, we hypothesize that Ca(2+) may play an important function in the wave propagation. Our results demonstrate that enhancing Ca(2+) influx into the cells by topical cortical application of the ionophore A23187 (10 μM, 50 μM and 100 μM solutions) increases the velocity of CSD propagation in a dose-dependent manner, and a much higher dose of this compound (2 mM) triggers CSD. In conclusion, increased Ca(2+) influx can be a key element in the induction mechanism of the CSD, and should be assessed in further experimental strategies targeting brain disorders related to CSD.

Chronic supplementation of paeonol combined with danshensu for the improvement of vascular reactivity in the cerebral basilar artery of diabetic rats

One of the leading causes of death in the world is cerebrovascular disease. Numerous Chinese traditional medicines, such as Cortex Moutan (root bark of Paeonia suffruticosa Andrew) and Radix Salviae miltiorrhizae (root and rhizome of Salvia miltiorrhiza Bunge), protect against cerebrovascular diseases and exhibit anti-atherosclerotic effects. Traditional medicines have been routinely used for a long time in China. In addition, these two herbs are prescribed together in clinical practice. Therefore, the pharmacodynamic interactions between the active constituents of these two herbs, which are paeonol (Pae) and danshensu (DSS), should be particularly studied. The study of Pae and DSS can provide substantial foundations in understanding their mechanisms and empirical evidence to support clinical practice. This study investigated the effects and possible mechanisms of the pharmacodynamic interaction between Pae and DSS on cerebrovascular malfunctioning in diabetes. Experimental diabetes was induced in rats, which was then treated with Pae, DSS, and Pae + DSS for eight weeks. Afterward, cerebral arteries from all groups were isolated and equilibrated in an organ bath with Krebs buffer and ring tension. Effects of Pae, DSS, and Pae + DSS were observed on vessel relaxation with or without endothelium as well as on the basal tonus of vessels from normal and diabetic rats. Indexes about oxidative stress were also determined. We report that the cerebral arteries from diabetic rats show decreased vascular reactivity to acetylcholine (ACh) which was corrected in Pae, DSS, and Pae + DSS treated groups. Furthermore, phenylephrine (PE)-induced contraction response decreased in the treated groups. Phenylephrine and CaCl(2)-induced vasoconstrictions are partially inhibited in the three treated groups under Ca2+-free medium. Pre-incubated with tetraethylammonium, a non-selective K+ channel blocker, the antagonized relaxation responses increased in DSS and Pae + DSS treated diabetic groups compared with those in diabetic and Pae-treated diabetic groups. In addition, superoxide dismutase activity and thiobarbituric acid reactive substances content significantly changed in the presence of Pae + DSS. We therefore conclude that both Pae and DSS treatments prevent diabetes-induced vascular damage. Furthermore, Pae + DSS prove to be the most efficient treatment regimen. The combination of Pae and DSS produce significant protective effects through the reduction of oxidative stress and through intracellular Ca2+ regulatory mechanisms.

Effects of glutathione-depleting drug buthionine sulfoximine and aging on activity of endothelium-derived relaxing and contracting factors in carotid artery of Sprague-Dawley rats

The role of the antioxidant glutathione (GSH) in mediating endothelial (dys)function, and how that role may depend on age, is unclear. The main purpose of the current study was to investigate the effect of 10-day treatment with the GSH-depleting drug l-buthionine sulfoximine (BSO) on endothelium-derived relaxing factor and endothelium-derived contracting factor activities in the isolated common carotid artery (CCA) of Adult and Aging animals. CCA blood pressure and flow were unaffected by age or BSO. Endothelium-derived relaxing factor activity, examined in precontracted CCA as relaxation to cumulative acetylcholine (ACh), was largely nitric oxide synthase (NOS) mediated and was not different between Adult and Aging animals at lower ACh; however, at higher ACh, relaxation was blunted in Aging CCA, an effect abolished by cyclooxygenase (COX) inhibition but not by NOS inhibition nor by the reactive oxygen species (ROS) inhibitors 4-hydroxy-TEMPO or Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin,tetratosylate,hydroxide. Specific examination of endothelium-derived contracting factor activity in quiescent NOS-inhibited CCA established that higher ACh elicited a contractile response, ∼3.5-fold greater in Aging versus Adult CCA, which was abolished by COX-1-specific inhibition but unaffected by ROS inhibitors. Aging was unrelated to changes in liver or vascular tissue GSH or ROS content. BSO was effective in significantly decreasing GSH and increasing ROS content in both animal cohorts. However, NOS-mediated endothelium-derived relaxing factor activity was well preserved and age-related COX-mediated endothelium-derived contracting factor activity was unaffected in response to these BSO-induced perturbations, as were exogenous H2O2-stimulated NOS/non-NOS-mediated relaxation and COX-mediated contractile activities. These data suggest that, regardless of age, chronic partial depletion of GSH in vivo does not necessarily cause endothelium-dependent vasomotor dysfunction.

Endothelium-mediated control of vascular tone: COX-1 and COX-2 products

Endothelium-dependent contractions contribute to endothelial dysfunction in various animal models of aging, diabetes and cardiovascular diseases. In the spontaneously hypertensive rat, the archetypal model for endothelium-dependent contractions, the production of the endothelium-derived contractile factors (EDCF) involves an increase in endothelial intracellular calcium concentration, the production of reactive oxygen species, the predominant activation of cyclooxygenase-1 (COX-1) and to a lesser extent that of COX-2, the diffusion of EDCF towards the smooth muscle cells and the subsequent stimulation of their thromboxane A2-endoperoxide TP receptors. Endothelium-dependent contractions are also observed in various models of hypertension, aging and diabetes. They generally also involve the generation of COX-1- and/or COX-2-derived products and the activation of smooth muscle TP receptors. Depending on the model, thromboxane A(2), PGH(2), PGF(2α), PGE(2) and paradoxically PGI(2) can all act as EDCFs. In human, the production of COX-derived EDCF is a characteristic of the aging and diseased blood vessels, with essential hypertension causing an earlier onset and an acceleration of this endothelial dysfunction. As it has been observed in animal models, COX-1, COX-2 or both isoforms can contribute to these endothelial dysfunctions. Since in most cases, the activation of TP receptors is the common downstream effector, selective antagonists of this receptor should curtail endothelial dysfunction and be of therapeutic interest in the treatment of cardiovascular disorders.

Effects of terutroban, a thromboxane/prostaglandin endoperoxide receptor antagonist, on retinal vascularity in diabetic rats

BACKGROUND

The aim of the present study is to investigate the effectiveness of terutroban, a selective antagonist of the thromboxane/prostaglandin endoperoxide receptor, in preventing retinal ischaemia in a model of diabetes in rats.

METHODS

Experimental diabetes was induced with streptozotocin. Rats were distributed into five groups (n = 20): (1) non-diabetic rats, (2) rats with diabetes (DR) treated with vehicle, (3) DR treated with aspirin (2 mg/kg/day p.o.), (4) DR treated with terutroban (5 mg/kg/day p.o.), (5) DR treated with terutroban (30 mg/kg/day p.o.). The follow-up period was 3 months. The main assessment was the percentage of retinal surface covered with vessels permeable to peroxidase. Platelet aggregation, aortic prostacyclin and nitric oxide production, plasma levels of lipid peroxides (thiobarbituric-acid-reactive substances) and 3-nitrotyrosine and serum levels of IL-6 were evaluated.

RESULTS

Diabetes induced a reduction in retinal vascularity (76.9%), aortic prostacyclin (37.8%) and nitric oxide production (35.0%), and increased platelet aggregation, lipid peroxides, 3-nitrotyrosine. When compared with vehicle-treated DR, terutroban increased the percentage of retinal surface covered by PVPP (38% for terutroban-5 and 61% for terutroban-30), aortic prostacyclin (188% for terutroban-5 and 146% for terutroban-30) and nitric oxide production (320% for terutroban-5 and 390% for terutroban-30). Moreover, terutroban reduced platelet reactivity (27.8–95.1%, according to the inducer), lipid peroxides (60.7% for terutroban-5 and 50.0% for terutroban-30), 3-nitrotyrosine (43.8% for terutroban-5 and 36.8% for terutroban-30) and IL-6 concentration (18.0% for terutroban-30). The effect of terutroban in retinal, nitrosative and aortic parameters was significantly higher than that of aspirin.

CONCLUSIONS

Terutroban significantly protected retinal vascularity from ischaemia in experimental diabetes, and this result could be attributed not only to its antiplatelet/antithrombotic activities but also to its vascular properties.

Upregulation of heme oxygenase 1 by hemin impairs endothelium-dependent contractions in the aorta of the spontaneously hypertensive rat

Heme oxygenase converts heme to carbon monoxide, biliverdin (subsequently converted to bilirubin), and free iron. Pharmacological induction of heme oxygenase 1 has an antihypertensive effect in the spontaneously hypertensive rat. The present study investigated whether upregulation of heme oxygenase 1 by hemin reduces endothelial dysfunction in this animal. Thirty-six-week-old rats were divided into a hemin treatment (50 mg/kg, IP injection, once) and a control group. Aortas were isolated for the measurement of isometric tension, production of reactive oxygen species, and heme oxygenase activity, as well as gene and protein expressions. Hemin treatment augmented the expression and activity of heme oxygenase 1. This in vivo induction of heme oxygenase 1, but not in vitro incubation with the heme oxygenase products carbon monoxide or bilirubin, led to an improvement of endothelial function in that acetylcholine-induced relaxations were potentiated and acetylcholine- and calcium ionophore-induced contractions were attenuated. Free radical production was suppressed by hemin treatment, judging from the results of 2',7'-dichlorodihydrofluoresein diacetate staining, dihydroethidium staining, and lucigenin chemiluminescence, which was explained by the decreased expressions of NADPH oxidase 2 and cyclooxygenase 1. The production of prostacyclin was decreased by heme oxygenase 1 induction, which was explained by a lower expression of cyclooxygenase 1. Contractions to vasoconstrictor concentrations of prostacyclin and its mimetic iloprost were attenuated, suggesting that the responsiveness of thromboxane-prostanoid receptors to prostacyclin was decreased in hemin-treated rats. The suppressed production of free radicals and prostacyclin and the decrease of thromboxane-prostanoid receptors sensitivity concur to explain the impairment of endothelium-dependent contractions caused by heme oxygenase 1 induction by hemin.

Epigallocatechin gallate elicits contractions of the isolated aorta of the aged spontaneously hypertensive rat

The present study examined the effect of the green tea catechin epigallocatechin gallate (EGCG) on endothelium-dependent responses in the aorta of 36-week-old spontaneously hypertensive rats (SHR). Isometric tension was measured in isolated aortic rings. The release of prostanoid end products was determined using enzyme immunoassay kits and the intracellular reactive oxygen species (ROS) concentration using confocal microscopy. EGCG did not improve endothelium-dependent relaxations evoked by acetylcholine, except in the presence of indomethacin. EGCG did not inhibit endothelium-dependent contractions induced by acetylcholine or ATP. At 10(-6) M and higher concentrations, EGCG caused increases in tension in the SHR aorta. The EGCG-induced contractions were accompanied by an increased production of ROS. The amount of prostanoid end products was increased significantly by EGCG, indicating that their production followed the activation of cyclooxygenase (COX). These prostanoids in turn stimulated thromboxane-prostanoid (TP) receptors and caused contractions. EGCG induced significantly smaller contractions in aortae of normotensive Wistar-Kyoto rats (WKY), accompanied with a lower production of ROS and a lesser release of prostanoids. These observations suggest that EGCG-induced contractions occur more readily in blood vessels of hypertensive than normotensive animals. The present findings indicate that the increased oxidative stress in the ageing hypertensive animals contributes to the loss of the beneficial effects and the enhancement of the adverse effects of EGCG.

Weight and inflammation are the major determinants of vascular dysfunction in the aortae of db/db mice

The key roles that obesity, hyperglycemia, hyperlipidemia, inflammation, and oxidative stress play in the progression of diabetes vascular complications are well recognized; however, the relative contribution and importance of these individual factors remain uncertain. At 6, 10, or 14 weeks old, blood samples and thoracic aortae were collected from db/db mice and their non-diabetic controls. Plasma samples were analyzed for glucose, 8-isoprostane, CRP, triglycerides, LDL, and HDL as markers of glycemic status, oxidative stress, inflammation, and dyslipidemia, respectively. The responses of the aortic rings to high KCl, phenylephrine (PE), acetylcholine (ACh), and sodium nitroprusside were examined. Statistical methods were used to estimate the strength of the association between plasma variables and vascular functions. Systemic inflammation occurred in db/db mice at an earlier age than did hyperglycemia or oxidative stress. Aortae of db/db showed augmented contractions to PE which were positively correlated with weight, plasma glucose, 8-isoprostane, and CRP. Also, db/db mice showed impaired endothelium-dependent ACh vasorelaxation which was negatively correlated with weight, plasma glucose, and 8-isoprostane. Multivariate analysis and stepwise modeling show that CRP is the major determinant of the contractile responses, while weight and HDL are the major determinants of ACh-induced relaxation. Among the traditional risk factors of obesity, hyperglycemia, oxidative stress, inflammation, and dyslipidemia, our study reveals that weight and inflammation are the major determinants of vascular dysfunction in the aortae of db/db mice. Our findings partially resolve the complexity of diabetes vasculopathies and suggest targeting weight loss and inflammation for effective therapeutic approaches.

The thromboxane/endoperoxide receptor (TP): the common villain

The stimulation of thromboxane/endoperoxide receptors (TP) elicits diverse physiological/pathophysiological reactions, including platelet aggregation and contraction of vascular smooth muscle. Furthermore, the activation of endothelial TP promotes the expression of adhesion molecules and favors adhesion and infiltration of monocytes/macrophages. In various cardiovascular diseases, endothelial dysfunction is predominantly the result of the release of endothelium-derived contracting factors that counteract the vasodilator effect of nitric oxide produced by the endothelial nitric oxide synthase. Endothelium-dependent contractions involve the activation of cyclooxygenases, the production of reactive oxygen species along with that of endothelium-derived contracting factors, which diffuse toward the vascular smooth muscle cells and activate their TP. TP antagonists curtail the endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and reduce vascular inflammation. Therefore, TP antagonists, because of this triple activity, may have a unique potential for the treatment of cardiovascular disorders.

COX-mediated endothelium-dependent contractions: from the past to recent discoveries

Endothelial cells release various substances to control the tone of the underlying vascular smooth muscle. Nitric oxide (NO) is the best defined endothelium-derived relaxing factor (EDRF). Endothelial cells can also increase vascular tone by releasing endothelium-derived contracting factors (EDCF). The over-production of EDCF contributes to the endothelial dysfunctions which accompanies various vascular diseases. The present review summarizes and discusses the mechanisms leading to the release of EDCFs derived from the metabolism of arachidonic acid. This release can be triggered by agonists such as acetylcholine, adenosine nucleotides or by stretch. All these stimuli are able to induce calcium influx into the endothelial cells, an effect which can be mimicked by calcium ionophores. The augmentation in intracellular calcium ion concentration initiates the release of EDCF. Downstream processes include activation of phospholipase A(2) (PLA(2)), cyclooxygenases (COX) and the production of reactive oxygen species (ROS) and vasoconstrictor prostanoids (endoperoxides, prostacyclin, thromboxane A(2) and other prostaglandins) which subsequently diffuse to, and activate thromboxane-prostanoid (TP) receptors on the vascular smooth muscle cells leading to contraction.

Chronic treatment with vitamin D lowers arterial blood pressure and reduces endothelium-dependent contractions in the aorta of the spontaneously hypertensive rat

Vitamin D has cardiovascular protective effects besides regulating calcium homeostasis. To examine the chronic in vivo effect of a physiological dose of 1,25-dihydroxyvitamin D(3) on the occurrence of endothelium-dependent contractions, spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) were treated with the vitamin D derivative for 6 wk. The serum 1,25-dihydroxyvitamin D(3) level of both treated WKY and SHR was significantly higher than in untreated rats while the mean arterial blood pressure of the treated SHR was significantly lower than that of control SHR. Aortic rings with or without endothelium were studied in conventional organ chambers for isometric force measurement. Confocal microscopy was used to measure the cytosolic free calcium concentration (with the fluorescent dye fluo 4) and reactive oxygen species (ROS; with dichlorodihydrofluorescein diacetate). Reverse transcription PCR and Western blotting were used to determine the mRNA and protein expression level of cyclooxygenase-1 (COX-1), prostacyclin synthase, and thromboxane synthase. The endothelium-dependent concentration-contraction curves to both acetylcholine- and A-23187-induced contractions were shifted to the right in aortas from treated SHR but not from treated WKY. The chronic treatment normalized the relaxations of contracted preparations to acetylcholine. There were no significant differences in the increases in cytosolic free calcium concentration evoked by acetylcholine and A-23187 between control and treated groups. The endothelial ROS level was higher in SHR than WKY aortas and reduced by the chronic treatment. The gene and protein expression studies indicated that the overexpression of COX-1 observed in SHR aorta was reduced by the chronic treatment. These results demonstrate that chronic treatment with 1,25-dihydroxyvitamin D(3) modulates vascular tone and this modulation is accompanied by a lowered blood pressure, reduced expression of COX-1 mRNA and protein, and reduced ROS level in SHR. The reduction in endothelium-dependent contractions does not involve the surge in endothelial cytosolic calcium concentration that initiates the contractions.

Vasoconstrictor prostanoids

In cardiovascular diseases and during aging, endothelial dysfunction is due in part to the release of endothelium-derived contracting factors that counteract the vasodilator effect of the nitric oxide. Endothelium-dependent contractions involve the activation of endothelial cyclooxygenases and the release of various prostanoids, which activate thromboxane prostanoid (TP) receptors of the underlying vascular smooth muscle. The stimulation of TP receptors elicits not only the contraction and the proliferation of vascular smooth muscle cells but also diverse physiological/pathophysiological reactions, including platelet aggregation and activation of endothelial inflammatory responses. TP receptor antagonists curtail endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and prevent vascular inflammation.

RhoA-Rho kinase signaling mediates endothelium- and endoperoxide-dependent contractile activities characteristic of hypertensive vascular dysfunction

Hypertensive vasomotor dysfunction is defined by endothelium-dependent contractions involving prostaglandins and ROS. Since both thromboxane-prostanoid receptor (TPr) signaling and ROS activate RhoA-Rho kinase (ROCK) in vascular smooth muscle (VSM) preparations, we hypothesized that enhanced endothelium-dependent contraction in the common carotid artery (CCA) of spontaneously hypertensive rats (SHRs) is ROCK mediated. ACh-stimulated contractions were approximately twofold greater in SHRs versus normotensive Wistar-Kyoto (WKY) rats, abolished by endothelial denudation or cyclooxygenase (COX)-1 inhibition, and nearly eliminated by TPr blockade. RhoA but not ROCK-II protein expression was increased ( approximately 50%) in the SHR CCA. Inhibition of ROCK, but not protein kinase C, caused a dose-dependent reduction in endothelium-dependent contractions to ACh across strains, with the highest dose mirroring the effect of high-dose TPr antagonism. Conversely, ROCK inhibition caused dose-dependent and endothelium- and nitric oxide-independent relaxation in CCAs precontracted with the TPr agonist U-46619. Prostacyclin was the predominant prostaglandin produced by ACh-stimulated CCAs, with greater than twofold more prostacyclin released from SHR versus WKY rats, and its production was unaffected by ROCK inhibition. RhoA activation was approximately twofold higher in quiescent SHR CCAs compared with those from WKY rats and was significantly increased by ACh stimulation. Augmentation of chemical superoxide quenching with tiron or inhibition of the NADPH oxidase-derived superoxide-producing pathway with apocynin reduced ACh-stimulated contractile activity in SHR more than in WKY rats, whereas the SOD mimetic tempol amplified the response. Exposure of CCAs to exogenous H(2)O(2) caused contractions, similar to ACh stimulation, that were greater in SHR than in WKY rats, abolished by COX-1 inhibition, and highly attenuated by TPr blockade or ROCK inhibition. These results indicate that RhoA-ROCK may act as a molecular switch, transducing signals from endothelium-derived prostaglandin(s) and ROS, which are overproduced in SHR CCAs, to "turn on" VSM contractile pathways, thus mediating the enhanced endothelium- and endoperoxide-dependent vascular contractions characteristic of hypertension, among other cardiovascular disease states, such as diabetes and aging.

Endothelial dysfunction: a strategic target in the treatment of hypertension?

Endothelial dysfunction is a common feature of hypertension, and it results from the imbalanced release of endothelium-derived relaxing factors (EDRFs; in particular, nitric oxide) and endothelium-derived contracting factors (EDCFs; angiotensin II, endothelins, uridine adenosine tetraphosphate, and cyclooxygenase-derived EDCFs). Thus, drugs that increase EDRFs (using direct nitric oxide releasing compounds, tetrahydrobiopterin, or L-arginine supplementation) or decrease EDCF release or actions (using cyclooxygenase inhibitor or thromboxane A2/prostanoid receptor antagonists) would prevent the dysfunction. Many conventional antihypertensive drugs, including angiotensin-converting enzyme inhibitors, calcium channel blockers, and third-generation beta-blockers, possess the ability to reverse endothelial dysfunction. Their use is attractive, as they can address arterial blood pressure and vascular tone simultaneously. The severity of endothelial dysfunction correlates with the development of coronary artery disease and predicts future cardiovascular events. Thus, endothelial dysfunction needs to be considered as a strategic target in the treatment of hypertension.

Calcium-independent phospholipase A(2) plays a key role in the endothelium-dependent contractions to acetylcholine in the aorta of the spontaneously hypertensive rat

Phospholipase A(2) (PLA(2)), a regulatory enzyme found in most mammalian cells, catalyzes the breakdown of membrane phospholipids to arachidonic acid. There are two major cytosolic types of the enzyme, calcium-dependent (cPLA(2)) and calcium-independent (iPLA(2)) PLA(2). The present study investigated whether or not iPLA(2) plays a role in the endothelium-dependent contractions of the aorta of the spontaneously hypertensive rat and its normotensive counterpart, the Wistar-Kyoto rat. The presence of iPLA(2) in the endothelial cells was identified by using immunochemistry and immunoblotting. Aortic rings with and without the endothelium were suspended in organ chambers for isometric tension recording. The production of prostanoids was measured by using enzyme immunoassay kits. iPLA(2) was densely distributed in endothelial cells of the aorta of both strains. At 3 x 10(-6) M, the selective iPLA(2) inhibitor, bromoenol lactone (BEL), abrogated endothelium-dependent contractions induced by acetylcholine but not those evoked by the calcium ionophore A-23187. The effects of BEL were similar in the aortae of Wistar-Kyoto and spontaneously hypertensive rats. The nonselective PLA(2) inhibitor quinacrine abolished the contractions triggered by both acetylcholine and A-23187, whereas the store-operated calcium channel inhibitor SKF-96365 prevented only the acetylcholine-induced contraction. The acetylcholine- but not the A-23187-induced release of 6-keto prostaglandin F(1alpha) was inhibited by BEL. The release of thromboxane B(2) by either acetylcholine or A-23187 was not affected by BEL. In conclusion, iPLA(2) plays a substantial role in the generation of endothelium-derived contracting factor evoked by acetylcholine.

TP receptors and oxidative stress hand in hand from endothelial dysfunction to atherosclerosis

Thromboxane A(2) and the activation of TP receptors that it causes play an important role in platelet aggregation and therefore in thrombosis. However, TP receptors are also involved in the pathologies of the vascular wall including impaired endothelium-dependent vasodilation, increased oxidant generation, and increased expression of adhesion molecules. The beneficial effects of TP antagonists on the vascular wall attenuate these features of vascular disease. They are not shared by aspirin. In fact, TP antagonists are active in patients treated with aspirin, indicating that their potential beneficial effects are mediated by mechanisms different from the antithrombotic actions of aspirin. Our studies have demonstrated the vascular benefits of TP antagonists in experimental animals, particularly in models of diabetes mellitus, in which elevated levels of eicosanoids play a role not only in vascular pathologies but also in those of the kidney and other tissues. They suggest that TP blockade protects against fundamental and widespread tissular dysfunction associated with metabolic disease including hyperlipidemia and hyperglycemia. TP receptor antagonists represent a promising avenue for the prevention of vascular disease in part because of these pleiotropic actions that extend beyond their antithrombotic properties.

Prostaglandins in action indispensable roles of cyclooxygenase-1 and -2 in endothelium-dependent contractions

Endothelium regulates local vascular tone by means of releasing relaxing and contracting factors, of which the latter have been found to be elevated in vascular pathogenesis of hypertension, diabetes, hypercholesterolemia, and aging. Endothelium-derived contracting factors (EDCFs) are mainly metabolites of arachidonic acid generated by cyclooxygenase (COX), as vasodilatations in patients with hypertension, metabolic diseases, or advancing age are improved by acute treatment with COX inhibitor indomethacin. COX is presented in two isoforms, COX-1 and COX-2, with the former regarded as constitutive and the latter mainly expressed upon induction. Experiments with animal models of vascular dysfunctions, however, reveal that both isoforms have similar capacity to participate in endothelium-dependent contractions, with augmented expression and activity. COX-derived prostaglandin (PG) H(2), PGF(2α), PGE(2), prostacyclin (PGI(2)), and thromboxane A(2) (TxA(2)) are the proposed EDCFs that mediate endothelium-dependent contractions via the activation of thromboxane-prostanoid (TP) receptor in various vascular beds from different species. Although COX inhibition seems to be a possible strategy in combating COX-associated vascular complications, the incidence of adverse cardiovascular effects of Vioxx has greatly antagonized this concept. Further review of COX inhibitors is required, especially toward the selectivity of coxibs and whether it directly inhibits prostacyclin synthase activity. Meanwhile, TP receptor antagonism may emerge as a therapeutic alternative to reverse prostanoid-mediated vascular dysregulations.