Effects of statins on myocardial and coronary artery response to ischemia-reperfusion

This study tested the hypotheses that (i) lipophilic statins (atorvastatin and simvastatin) impair ventricular recovery from myocardial ischemia-reperfusion, owing to their greater myocyte permeability, compared with a hydrophilic statin (pravastatin), and (ii) statins enhance endothelium-dependent vasodilation of isolated coronary arteries from the ischemic region. Farm pigs consumed chow supplemented with atorvastatin (2.5 mg.kg(-1).d(-1); n=6), pravastatin (10 (n=3) or 20 (n=2) mg.kg(-1).d(-1)), simvastatin (5 mg.kg(-1).d(-1); n=6), or no statin (control; n=6) for 3 weeks. Animals were anesthetized and instrumented to measure regional (% segment shortening) and global (dP/dt max) left ventricular (LV) function during coronary artery occlusion (10 min) and reperfusion (30 min). Coronary resistance (i.d. = 119 +/- 3 microm) and conductance (i.d. = 487 +/- 11 microm) arteries were isolated from the ischemic region to measure receptor-dependent (acetylcholine (ACh)) and -independent (KCl) vasoconstriction, and endothelium-dependent (bradykinin (BK)) and -independent (sodium nitroprusside (SNP)) vasodilation. At 30 min reperfusion, neither percent recovery of regional ventricular function (atorvastatin, 24% +/- 15%; pravastatin, 36% +/- 13%; simvastatin, 29% +/- 13%; control, 36% +/- 13%) nor percent recovery of global LV cardiac function differed among groups. However, BK-induced vasorelaxation of coronary conductance vessels was greater (P<0.05) in statins versus controls, and ACh-induced vasoconstriction was less in simvastatin-treated animals, suggesting the potential for enhanced coronary arterial blood flow to the jeopardized region. In conclusion, our data suggest that ischemia-induced myocardial stunning is similar among pigs treated for 3 weeks with atorvastatin, pravastatin, or simvastatin, even though statin treatment appears to augment endothelium-dependent vasodilation of conductance, but not resistance, vessels subjected to ischemia-reperfusion.     

Shear stress-induced vasodilation in porcine coronary conduit arteries is independent of nitric oxide release

The present study was performed to determine the importance of nitric oxide in eliciting epicardial coronary artery dilation during sustained increases in shear stress in the absence of pulsatile flow. Isolated first-order porcine epicardial coronary conduit arteries (approximately 500 microm) were preconstricted (U-46619) and subjected to steady-state changes in flow in vitro. Nonpulsatile flow (shear stress range from 0 to approximately 100 dyn/cm2) produced a graded dilation of epicardial arteries. Inhibiting nitric oxide synthase with 10(-5) M N(omega)-nitro-L-arginine methyl ester (L-NAME) blocked bradykinin-induced vasodilation but did not affect the flow-diameter relation or the maximum change in diameter from static conditions (67 +/- 10 microm in control vs. 71 +/- 8 microm after L-NAME, P = not significant). The addition of indomethacin (10(-5) M) had no effect on flow-mediated vasodilation. Depolarizing vascular smooth muscle with KCl (60 mM) or removing the endothelium blocked bradykinin vasodilation and completely abolished flow-mediated responses. The K+ channel blocker tetraethylammonium chloride (TEA; 10(-4)M) attenuated flow-mediated vasodilation (maximum diameter change was 110 +/- 18 microm under control conditions vs. 58 +/- 10 microm after TEA, P < 0.001). These data indicate that epicardial coronary arteries dilate to steady-state changes in nonpulsatile flow via a mechanism that is independent of nitric oxide production. The ability to completely block this with KCl and attenuate it with TEA supports the hypothesis that epicardial coronary arteries dilate to steady levels of shear stress through hyperpolarization of vascular smooth muscle. This may be secondary to the release of an endothelium-dependent hyperpolarizing factor.     

HMG-CoA reductase inhibitors reduce adhesion of human monocytes to endothelial cells.

HMG-CoA reductase inhibitors (statins) are believed to reduce coronary heart disease by mechanisms in addition to their well-known cholesterol-lowering effect. We studied the effect of these drugs on monocyte cell adhesion to endothelium. Pretreatment of monocytic cells (U937, THP-1, human CD14(+) monocytes) with 0.01-10 microM concentrations of atorvastatin, cerivastatin, or simvastatin significantly reduced cell adhesion to endothelium. In contrast, pretreatment of endothelium with statins did not affect adhesion of monocytes. Adhesion of monocytes to vascular cell adhesion molecule-1-coated dishes was reduced by these drugs. Cerivastatin also reduced PMA induction of NF-kappaB. Since monocyte adhesion to endothelium is an early event in atherogenesis, treatment with statins in prevention of coronary heart disease may have additional salutary effects to lowering of plasma LDL cholesterol. Our results indicate that the reduction of monocyte adhesion by HMG-CoA reductase inhibitors may be considered as a class effect.     

Differential effects of different statins on endothelin-1 gene expression and endothelial NOS phosphorylation in porcine aortic endothelial cells

It has been reported that 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase inhibitors (statins) produce a variety of cardiovascular protective effects independent of their ability to lower total and low-density lipoprotein cholesterol. Recent studies have also reported that statins produce pleiotropic effects through improved endothelial function, enhanced fibrinolysis, and antithrombotic actions. In the present study, we examined the effects of pitavastatin, pravastatin, atorvastatin, and cerivastatin on endothelin (ET)-1 production in cultured porcine aortic endothelial cells (PAECs). Treatment with cerivastatin but not pitavastatin, pravastatin, or atorvastatin decreased basal and TNF-alpha-stimulated ET-1 release from PAECs in a dose-dependent manner (1-10 microM). Northern blot analysis showed that cerivastatin markedly suppressed prepro ET-1 mRNA expression in both conditions. In addition, these inhibitory effects of cerivastatin on ET-1 release and prepro ET-1 mRNA expression were completely abolished by simultaneous treatment with 200 microM mevalonate. Furthermore, cerivastatin did not have any effects on endothelial nitric oxide synthase (eNOS) protein levels, but induced eNOS phosphorylation at Ser1177. From these findings, it is most likely that cerivastatin suppresses ET-1 production, possibly through an increase in eNOS activity and the subsequent nitric oxide production in PAECs. These findings also suggest that cerivastatin may have beneficial effects on ET-1-related diseases.     

Association between risk of myopathy and cholesterol-lowering effect: a comparison of all statins

In the present study, we examined the mechanisms underlying the cytotoxicity of pitavastatin, a new statin, and we compared the in vitro potencies of muscle cytotoxicity using a prototypic embryonal rhabdomyosarcoma cell line (RD cells), a typical side effect of statins and compared the cholesterol-lowering effects of statins using Hep G2 hepatoma cells. Pitavastatin reduced the number of viable cells and caused caspase-9 and -3/7 activation in a time- and concentration-dependent manner. The comparison of cytotoxities of statins showed that statins significantly reduced cell viability and markedly enhanced activity of caspase-3/7 in concentration-dependent manner. On the other hand, the effects of hydrophilic statins, pravastatin, rosuvastatin were very weak. The rank order of cytotoxicity was cerivastatin > simvastatin acid> fluvastatin > atorvastatin > lovastatin acid > pitavastatin > rosuvastatin, pravastatin. Statin-induced cytotoxicity is associated with these partition coefficients. On the other hand, the cholesterol-lowering effect of statins did not correlate with these partition coefficients and cytotoxicity. Thus, it is necessary to consider the association between risk of myopathy and cholesterol-lowering effect of a statin for precise use of statins.     

Reactive oxygen species mediate arachidonic acid-induced dilation in porcine coronary microvessels

Reactive oxygen species (ROS) have been proposed to mediate vasodilation in the microcirculation. We investigated the role of ROS in arachidonic acid (AA)-induced coronary microvascular dilation. Porcine epicardial coronary arterioles (110 +/- 4 microm diameter) were mounted onto pipettes in oxygenated Krebs buffer. Vessels were incubated with vehicle or 1 mM Tiron (a nonselective ROS scavenger), 250 U/ml polyethylene-glycolated (PEG)-superoxide dismutase (SOD; an O2- scavenger), 250 U/ml PEG-catalase (a H2O2 scavenger), or the cyclooxygenase (COX) inhibitors indomethacin (10 microM) or diclofenac (10 microM) for 30 min. After endothelin constriction (30-60% of resting diameter), cumulative concentrations of AA (10(-10)-10(-5)M) were added and internal diameters measured by video microscopy. AA (10-7 M) produced 37 +/- 6% dilation, which was eliminated by the administration of indomethacin (4 +/- 7%, P < 0.05) or diclofenac (-8 +/- 8%, P < 0.05), as well as by Tiron (-4 +/- 5%, P < 0.05), PEG-SOD (-10 +/- 6%, P < 0.05), or PEG-catalase (1 +/- 4%, P < 0.05). Incubation of small coronary arteries with [3H]AA resulted in the formation of prostaglandins, which was blocked by indomethacin. In separate studies in microvessels, AA induced concentration-dependent increases in fluorescence of the oxidant-sensitive probe dichlorodihydrofluorescein diacetate, which was inhibited by pretreatment with indomethacin or by SOD + catalase. We conclude that in porcine coronary microvessels, COX-derived ROS contribute to AA-induced vasodilation.     

Relaxant effects of pravastatin, atorvastatin and cerivastatin on isolated rat aortic rings

Increasing evidence suggests that statins may have pleiotropic effects on vascular wall independent of their cholesterol lowering properties. In the present study, we investigated the acute vascular effects of pravastatin, atorvastatin and cerivastatin on rat isolated aortic rings. Statins effectively and comparably relaxed the aortic rings precontracted submaximally with noradrenaline, in a concentration-dependent manner, in which a high potency was observed with cerivastatin. Endothelium removal or incubation of the aortic rings with nitric oxide synthase inhibitor L-NOARG (10(-4) M) and/or cyclooxygenase inhibitor indomethacin (10(-5) M) significantly attenuated the acute vasorelaxation induced by either of statin. Additionally, different from the other two statins, a significant reduction was observed in response to cerivastatin in the presence of KATP channel inhibitor, glibenclamide (10(-5) M) and Na+- K+ ATPase inhibitor, ouabain (10(-4) M). Furthermore, pretreatment of the rings with the cholesterol precursor mevalonate (10(-3) M) significantly inhibited the endothelium-mediated relaxant effects of the statins. Our findings suggest that statins could acutely modulate vascular tone importantly by endothelium-dependent and mevalonate-related pathways.     

Simvastatin upregulates coronary vascular endothelial nitric oxide production in conscious dogs

Statin drugs can upregulate endothelial nitric oxide (NO) synthase (eNOS) in isolated endothelial cells independent of lipid-lowering effects. We investigated the effect of short-term simvastatin administration on coronary vascular eNOS and NO production in conscious dogs and canine tissues. Mongrel dogs were instrumented under general anesthesia to measure coronary blood flow (CBF). Simvastatin (20 mg. kg(-1). day(-1)) was administered orally for 2 wk; afterward, resting CBF was found to be higher compared with control (P < 0.05) and veratrine- (activator of reflex cholinergic NO-dependent coronary vasodilation) and ACh-mediated coronary vasodilation were enhanced (P < 0.05). Response to endothelium-independent vasodilators, adenosine and nitroglycerin, was not potentiated. After simvastatin administration, plasma nitrate and nitrite (NO(x)) levels increased from 5.22 +/- 1.2 to 7. 79 +/- 1.3 microM (P < 0.05); baseline and agonist-stimulated NO production in isolated coronary microvessels were augmented (P < 0.05); resting in vivo myocardial oxygen consumption (MVO(2)) decreased from 6.8 +/- 0.6 to 5.9 +/- 0.4 ml/min (P < 0.05); NO-dependent regulation of MVO(2) in response to NO agonists was augmented in isolated myocardial segments (P < 0.05); and eNOS protein increased 29% and eNOS mRNA decreased 50% in aortas and coronary vascular endothelium. Short-term administration of simvastatin in dogs increases coronary endothelial NO production to enhance NO-dependent coronary vasodilation and NO-mediated regulation of MVO(2).     

Metabolism of adrenic acid to vasodilatory 1alpha,1beta-dihomo-epoxyeicosatrienoic acids by bovine coronary arteries

Adrenic acid (docosatetraenoic acid), an abundant fatty acid in the vasculature, is produced by a two-carbon chain elongation of arachidonic acid. Despite its abundance and similarity to arachidonic acid, little is known about its role in the regulation of vascular tone. Gas chromatography/mass spectrometric analysis of bovine coronary artery and endothelial cell lysates revealed arachidonic acid concentrations of 2.06 +/- 0.01 and 6.18 +/- 0.60 microg/mg protein and adrenic acid concentrations of 0.29 +/- 0.01 and 1.56 +/- 0.16 microg/mg protein, respectively. In bovine coronary arterial rings preconstricted with the thromboxane mimetic U-46619, adrenic acid (10(-9)-10(-5) M) induced concentration-related relaxations (maximal relaxation = 83 +/- 4%) that were similar to arachidonic acid relaxations. Adrenic acid relaxations were blocked by endothelium removal and the K(+) channel inhibitor, iberiotoxin (100 nM), and inhibited by the cyclooxygenase inhibitor, indomethacin (10 microM, maximal relaxation = 53 +/- 4%), and the cytochrome P-450 inhibitor, miconazole (10 microM, maximal relaxation = 52 +/- 5%). Reverse-phase HPLC and liquid chromatography/mass spectrometry isolated and identified numerous adrenic acid metabolites from coronary arteries including dihomo (DH)-epoxyeicosatrienoic acids (EETs) and DH-prostaglandins. DH-EET [16,17-, 13,14-, 10,11-, and 7,8- (10(-9)-10(-5) M)] induced similar concentration-related relaxations (maximal relaxations averaged 83 +/- 3%). Adrenic acid (10(-6) M) and DH-16,17-EET (10(-6) M) hyperpolarized coronary arterial smooth muscle. DH-16,17-EET (10(-8)-10(-6) M) activated iberiotoxin-sensitive, whole cell K(+) currents of isolated smooth muscle cells. Thus, in bovine coronary arteries, adrenic acid causes endothelium-dependent relaxations that are mediated by cyclooxygenase and cytochrome P-450 metabolites. The adrenic acid metabolite, DH-16,17-EET, activates smooth muscle K(+) channels to cause hyperpolarization and relaxation. Our results suggest a role of adrenic acid metabolites, specifically, DH-EETs as endothelium-derived hyperpolarizing factors in the coronary circulation.     

Long-term estradiol treatment improves VIP-mediated vasodilation in atherosclerotic proximal coronary arteries

The aim of the present study was to evaluate the impact of long-term estrogen replacement therapy (ERT) on the vasodilatory effect of the two peptides vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) in atherosclerotic coronary and cerebral arteries.Female ovariectomized homozygous Watanabe heritable hyperlipidemic rabbits were randomized to 16 weeks treatment with 17beta-estradiol or placebo. The diet was semisynthetic, thereby avoiding the influence of phytoestrogens. Artery ring segments were mounted for isometric tension recordings in myographs. Following precontraction, the dose-response relationships for VIP and PACAP were evaluated.Treatment with 17beta-estradiol significantly improved the maximum VIP-mediated vasodilation (E(max), percentage of precontraction) in proximal coronary arteries (45.8+/-9.6% vs. 24.1+/-3.7%, p<0.05). In the same artery segment, 17beta-estradiol induced a significant decrease in the relative ratio between the repeated contractile response to potassium 30 and 120 mM (100+/-7% vs. 132+/-11%, p<0.05). For distal coronary arteries, there was a tendency to similar changes, but no statistical differences for the potassium or VIP responses in cerebral or distal coronary arteries were found between the two groups. 17beta-estradiol induced no changes in the PACAP-mediated vasodilation.These results suggest that long-term treatment with 17beta-estradiol improves the VIP-mediated but not the PACAP-mediated vasodilation in atherosclerotic proximal coronary arteries.     

A Survey of the FDA's AERS Database Regarding Muscle and Tendon Adverse Events Linked to the Statin Drug Class

Background

Cholesterol management drugs known as statins are widely used and often well tolerated; however, a variety of muscle-related side effects can arise. These adverse events (AEs) can have serious impact, and form a significant barrier to therapy adherence. Surveillance of post-marketing AEs is of vital importance to understand real-world AEs and reporting differences between individual statin drugs. We conducted a review of post-approval muscle and tendon AE reports in association with statin use, to assess differences within the drug class.

Methods

We analyzed all case reports from the FDA AE Reporting System (AERS) database linking muscle-related AEs to statin use (07/01/2005–03/31/2011). Drugs examined were: atorvastatin, simvastatin, lovastatin, pravastatin, rosuvastatin, and fluvastatin.

Results

Relative risk rates for rosuvastatin were consistently higher than other statins. Atorvastatin and simvastatin showed intermediate risks, while pravastatin and lovastatin appeared to have the lowest risk rates. Relative risk of muscle-related AEs, therefore, approximately tracked with per milligram LDL-lowering potency, with fluvastatin an apparent exception. Incorporating all muscle categories, rates for atorvastatin, simvastatin, pravastatin, and lovastatin were, respectively, 55%, 26%, 17%, and 7.5% as high, as rosuvastatin, approximately tracking per milligram potency (Rosuvastatin>Atorvastatin>Simvastatin>Pravastatin≈Lovastatin) and comporting with findings of other studies. Relative potency, therefore, appears to be a fundamental predictor of muscle-related AE risk, with fluvastatin, the least potent statin, an apparent exception (risk 74% vs rosuvastatin).

Interpretation

AE reporting rates differed strikingly for drugs within the statin class, with relative reporting aligning substantially with potency. The data presented in this report offer important reference points for the selection of statins for cholesterol management in general and, especially, for the rechallenge of patients who have experienced muscle-related AEs (for whom agents of lower expected potency should be preferred).     

Tonic regulation of vascular tone by nitric oxide and chloride ions in rat isolated small coronary arteries

We have investigated the involvement of Cl(-) in regulating vascular tone in rat isolated coronary arteries mounted on a small vessel myograph. Mechanical removal of the endothelium or inhibition of nitric oxide (NO) synthase with N(omega)-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) led to contraction of rat coronary arteries, and these contractions were sensitive to nicardipine (10(-6) M). This suggests that release of NO tonically inhibits a contractile mechanism that involves voltage-dependent Ca(2+) channels. In arteries contracted with L-NAME, switching the bathing solution to physiological saline solution with a reduced Cl(-) concentration potentiated the contraction. DIDS (5 x 10(-6)-3 x 10(-4) M) caused relaxation of L-NAME-induced tension (IC(50) = 55 +/- 10 microM), providing evidence for a role of Cl(-). SITS (10(-5)-5 x 10(-4) M) did not affect L-NAME-induced tension, suggesting that DIDS is not acting by inhibition of anion exchange. Mechanical removal of the endothelium led to contraction of arteries, which was sensitive to DIDS (IC(50) = 50 +/- 8 microM) and was not affected by SITS. This study suggests that, in rat coronary arteries, NO tonically suppresses a contractile mechanism that involves a Cl(-) conductance.     

Endothelium-dependent vasodilation induced by Hancornia speciosa in rat superior mesenteric artery

The vasodilator effect of the ethanolic extract of leaves from Hancornia speciosa Gomes (HSE) was evaluated in superior mesenteric artery rings. HSE produced a concentration-dependent vasodilation (IC50 = 10.8 +/- 4.0 microg/mL) in arterial rings pre-contracted with phenylephrine, which was completely abolished in endothelium-denuded vessels. Endothelium-dependent vasodilation induced by HSE was strongly reduced by L-NAME (100 microM), a nitric oxide (NO) synthase inhibitor, but neither by atropine, a muscarinic receptor antagonist (1 microM), nor by indomethacin (10 microM), a cyclooxygenase inhibitor. In rings pre-contracted with 80 mM KCl, the vasodilator effect of HSE was shifted to the right and was completely abolished in the presence of L-NAME (100 microM). Similar effects were obtained in mesenteric rings pre-contracted with phenylephrine in the presence of KCl 25 mM alone or in addition to 100 microM L-NAME. In addition, BaCl2 (1 mM) dramatically reduced the vasodilation induced by HSE. Together, these findings led us to conclude that HSE induces an endothelium-dependent vasodilation in rat mesenteric artery, by a mechanism dependent on NO, on the activation of potassium channels and endothelium-derived hyperpolarizing factor release. Rutin, identified as a major peak in the HPLC fingerprint obtained for HSE, might contribute for the observed vasodilator effect, since it was able to induce an endothelium-dependent vasodilation in rat superior mesenteric arteries.     

Chronic nitric oxide synthase inhibition blunts endothelium-dependent function of conduit coronary arteries, not arterioles

Current literature suggests that chronic nitric oxide synthase (NOS) inhibition has differential effects on endothelium-dependent dilation (EDD) of conduit arteries vs. arterioles. Therefore, we hypothesized that chronic inhibition of NOS would impair EDD of porcine left anterior descending (LAD) coronary arteries but not coronary arterioles. Thirty-nine female Yucatan miniature swine were included in the study. Animals drank either tap water or water with N(G)-nitro-L-arginine methyl ester (L-NAME; 100 mg/l), resulting in control and chronic NOS inhibition (CNI) groups, respectively. Treatment was continued for 1-3 mo (8.3 +/- 0.6 mg x kg(-1) x day(-1)). In vitro EDD of coronary LADs and arterioles was assessed via responses to ADP (LADs only) and bradykinin (BK), and endothelium-independent function was assessed via responses to sodium nitroprusside (SNP). Chronic NOS inhibition diminished coronary artery EDD to ADP and BK. Incubating LAD rings with L-NAME decreased relaxation responses of LADs from control pigs but not from CNI pigs such that between-group differences were abolished. Neither indomethacin (Indo) nor sulfaphenazole incubation significantly affected relaxation responses of LAD rings to ADP or BK. Coronary arteries from CNI pigs showed enhanced relaxation responses to SNP. In contrast to coronary arteries, coronary arterioles from CNI pigs demonstrated preserved EDD to BK and no increase in dilation responses to SNP. L-NAME, Indo, and L-NAME + Indo incubation did not result in significant between-group differences in arteriole dilation responses to BK. These results suggest that although chronic NOS inhibition diminishes EDD of LAD rings, most likely via a NOS-dependent mechanism, it does not affect EDD of coronary arterioles.     

Inhibition of LOX-1 by statins may relate to upregulation of eNOS.

LOX-1, a receptor for oxidized low-density lipoprotein (ox-LDL), plays a critical role in endothelial dysfunction and atherosclerosis; both of these conditions are associated with diminished expression of constitutive endothelial nitric oxide synthase (eNOS). Recent studies show that HMG CoA reductase inhibitors (statins) exert cardioprotective effect. We examined the role of LOX-1 in eNOS expression and modulation of this relationship by two different statins, simvastatin and atorvastatin in human coronary artery endothelial cells (HCAECs). Ox-LDL (40 microg/ml) upregulated the expression of LOX-1; simultaneously, there was a reduction in eNOS expression. Pretreatment of HCAECs with simvastatin or atorvastatin (1 and 10 microM) reduced ox-LDL-induced upregulation of LOX-1 and downregulation of eNOS (both P < 0.05). High concentration of statins (10 microM) was more potent than the low concentration (1 microM) (P < 0.05). Both statins also attenuated ox-LDL-mediated activation of MAP kinase. These observations indicate that statins attenuate the effect of ox-LDL on eNOS expression. Inhibitory effect on LOX-1 and subsequently MAP kinase activity provides a potential mechanism of beneficial effects of statins beyond lowering cholesterol.     

Human coronary arteriolar dilation to adrenomedullin: role of nitric oxide and K(+) channels

Adrenomedullin (ADM) is a vasodilator produced by vascular endothelium and smooth muscle cells. Although plasma ADM levels are increased in patients with hypertension, heart failure, and myocardial infarction, little information exists regarding the microvascular response to ADM in the human heart. In the present study we tested the hypothesis that ADM produces coronary arteriolar dilation in humans and examined the mechanism of this dilation. Human coronary arterioles were dissected and cannulated with micropipettes. Internal diameter was measured by video microscopy. In vessels constricted with ACh, the diameter response to cumulative doses of ADM (10(-12)-10(-7) M) was measured in the presence and absence of human ADM-(22-52), calcitonin gene-related peptide-(8-37), N(omega)-nitro-L-arginine methyl ester (L-NAME), indomethacin (Indo), (1)H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, SQ-22536, or KCl (60 mM). ADM dilated human coronary arterioles through specific ADM receptors (maximum dilation = 69 +/- 11%). L-NAME or N-monomethyl-L-arginine attenuated dilation to ADM (for L-NAME, maximum dilation = 66 +/- 7 vs. 41 +/- 13%, P < 0.05). Thus the mechanism of ADM-induced dilation involves generation of nitric oxide. However, neither (1)H-[1,2,4]oxadiazolo-[4, 3-a]quinoxalin-1-one, SQ-22536, nor Indo alone altered dilation to ADM. High concentrations of KCl blocked dilation to ADM. The magnitude of ADM dilation was reduced in subjects with hypertension. We propose that, in human coronary arterioles, ADM elicits vasodilation in part through production of nitric oxide and in part through activation of K(+) channels, with little contribution from adenylyl cyclase. The former dilator mechanism is independent of the more traditional pathway involving activation of soluble guanylate cyclase.     

Impaired capsaicin-induced relaxation of coronary arteries in a porcine model of the metabolic syndrome

Recent studies implicate channels of the transient receptor potential vanilloid family (e.g., TRPV1) in regulating vascular tone; however, little is known about these channels in the coronary circulation. Furthermore, it is unclear whether metabolic syndrome alters the function and/or expression of TRPV1. We tested the hypothesis that TRPV1 mediates coronary vasodilation through endothelium-dependent mechanisms that are impaired by the metabolic syndrome. Studies were conducted on coronary arteries from lean and obese male Ossabaw miniature swine. In lean pigs, capsaicin, a TRPV1 agonist, relaxed arteries in a dose-dependent manner (EC50 = 116 +/- 41 nM). Capsaicin-induced relaxation was blocked by the TRPV1 antagonist capsazepine, endothelial denudation, inhibition of nitric oxide synthase, and K+ channel antagonists. Capsaicin-induced relaxation was impaired in rings from pigs with metabolic syndrome (91 +/- 4% vs. 51 +/- 10% relaxation at 100 microM). TRPV1 immunoreactivity was prominent in coronary endothelial cells. TRPV1 protein expression was decreased 40 +/- 11% in obese pigs. Capsaicin (100 microM) elicited divalent cation influx that was abolished in endothelial cells from obese pigs. These data indicate that TRPV1 channels are functionally expressed in the coronary circulation and mediate endothelium-dependent vasodilation through a mechanism involving nitric oxide and K+ channels. Impaired capsaicin-induced vasodilation in the metabolic syndrome is associated with decreased expression of TRPV1 and cation influx.     

Resveratrol for protection against statin toxicity in C2C12 and H9c2 cells

Statins are among the most commonly prescribed drugs for the treatment of high blood cholesterol. Myotoxicity of statins in certain individuals is often a severe side effect leading to withdrawal. Using C2C12 and H9c2 cells, both exhibiting characteristics of skeletal muscle cells, we addressed whether resveratrol (RSV) can prevent statin toxicity. Statins decreased cell viability in a dose and time‐dependent manner. Among the five statins tested, atorvastatin, simvastatin, lovastatin, pravastatin, and fluvastatin, simvastatin is the most toxic one. Simvastatin at 10 µM caused about 65% loss of metabolic activity as measured by 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assays in C2C12 cells or H9c2 cells. Inhibition of metabolic activity correlates with an increase in caspase activity. RSV was found to protect H9c2 cells from simvastatin‐induced activation of caspase‐3/7. However, such protection was not found in C2C12 cells. This cell type‐dependent effect of RSV adds to the complexity in muscle cell toxicity of statins.     

Effects of streptozotocin-induced diabetes on Kv channels in rat small coronary smooth muscle cells

Diabetes impairs endothelium dependent vasodilation, but the mechanism of endothelium independent dilation is not well understood. In the present study, we examined the effect of streptozotocin (STZ)-induced diabetes on the vasomotor of small coronary artery and the activity of voltage-dependent K+ channel of vascular smooth muscle cells in STZ rats [corrected] using the videomicroscopy and patch clamp method. STZ-induced diabetes appeared to [corrected] reduce the vasodilation induced by beta-adrenoceptor agonist, isoproterenol (10(-9)-10(-5) mol/l), and adenylyl cyclase activator forskolin (10(-9)-10(-5) mol/l) respectively (isoproterenol: 44.2 +/- 6.7% vs. 82.5 +/- 4.8%, and forskolin: 54.4 +/- 4.5% vs. 94.3 +/- 2.4%). 4-AP, a Kv channel blocker of VSMC, further decreased dilation to isoproterenol (44.2 +/- 6.7% vs. 10.2 +/- 3.5%) and forskolin (54.4 +/- 4.5% vs. 13.8 +/- 11.0%) significantly. Whole cell K+ current recording demonstrated that STZ-induced diabetes decreased isoproterenol and forskolin-induced K+ current (ISO: 55.6 +/- 7.8 pA/pF vs. 28.4 +/- 3.4 pA/pF, forskolin: 61.3 +/- 9.8 pA/pF vs. 32.4 +/- 3.4 pA/pF). 4-AP further reduced the decreased K+ current (ISO: 28.4 +/- 3.4 pA/pF vs. 14.3 +/- 2.1 pA/pF, forskolin: 32.4 +/- 3.4 pA/pF vs. 14.8 +/- 2.9 pA/pF). These results indicated that STZ-induced diabetes impaired cAMP mediated dilation of small coronary artery and suppressed the Kv channel activity of vascular smooth muscle cells. Kv channel of VSMC was shown to play a determinate role reducing dilation of small coronary artery in STZ rats.