Mechanisms of hydroxyl radical-induced contraction of rat aorta

The Endothelium and COVID-19: An Increasingly Clear Link Brief Title: Endotheliopathy in COVID-19

The endothelium has a fundamental role in the cardiovascular complications of coronavirus disease 2019 (COVID-19). Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) particularly affects endothelial cells. The virus binds to the angiotensin-converting enzyme 2 (ACE-2) receptor (present on type 2 alveolar cells, bronchial epithelial cells, and endothelial cells), and induces a cytokine storm. The cytokines tumor necrosis factor alpha, interleukin-1 beta, and interleukin-6 have particular effects on endothelial cells-leading to endothelial dysfunction, endothelial cell death, changes in tight junctions, and vascular hyperpermeability. Under normal conditions, apoptotic endothelial cells are removed into the bloodstream. During COVID-19, however, endothelial cells are detached more rapidly, and do not regenerate as effectively as usual. The loss of the endothelium on the luminal surface abolishes all of the vascular responses mediated by the endothelium and nitric oxide production in particular, which results in greater contractility. Moreover, circulating endothelial cells infected with SARS-CoV-2 act as vectors for viral dissemination by forming clusters that migrate into the circulation and reach distant organs. The cell clusters and the endothelial dysfunction might contribute to the various thromboembolic pathologies observed in COVID-19 by inducing the formation of intravascular microthrombi, as well as by triggering disseminated intravascular coagulation. Here, we review the contributions of endotheliopathy and endothelial-cell-derived extracellular vesicles to the pathogenesis of COVID-19, and discuss therapeutic strategies that target the endothelium in patients with COVID-19.

Uremic Toxins and Vascular Dysfunction

Vascular dysfunction is an essential element found in many cardiovascular pathologies and in pathologies that have a cardiovascular impact such as chronic kidney disease (CKD). Alteration of vasomotricity is due to an imbalance between the production of relaxing and contracting factors. In addition to becoming a determining factor in pathophysiological alterations, vascular dysfunction constitutes the first step in the development of atherosclerosis plaques or vascular calcifications. In patients with CKD, alteration of vasomotricity tends to emerge as being a new, less conventional, risk factor. CKD is characterized by the accumulation of uremic toxins (UTs) such as phosphate, para-cresyl sulfate, indoxyl sulfate, and FGF23 and, consequently, the deleterious role of UTs on vascular dysfunction has been explored. This accumulation of UTs is associated with systemic alterations including inflammation, oxidative stress, and the decrease of nitric oxide production. The present review proposes to summarize our current knowledge of the mechanisms by which UTs induce vascular dysfunction.

PPAR-α agonists acutely inhibit Ca2+-independent PLA2 to reduce H2O2-induced contractions in aortae of spontaneously hypertensive rats

Hypertension is associated with endothelial dysfunction, which favors the release of endothelium-derived contracting factors, including vasoconstrictor prostanoids and reactive oxygen species. Peroxisome proliferator-activated receptor-α (PPAR-α) agonists, clinically used as lipid-lowering drugs, possess antioxidant properties and exert beneficial effects in the vascular system. The present study aimed to identify the mechanism(s) underlying the acute effects of the PPAR-α agonists Wy14643 and fenofibate on endothelium-dependent contractions, in particular those related to oxidative stress, in the aorta of the spontaneously hypertensive rat (SHR). Aortic rings with and without endothelium of male SHRs and normotensive Wistar-Kyoto rats were suspended in organ chambers for isometric tension measurements and homogenized for enzyme activity assays. Contractions to acetylcholine in quiescent SHR aortae with endothelium were reduced by tiron (superoxide anion scavenger), diethyldithiocarbamic acid (superoxide dismutase inhibitor), and acute treatment with either Wy14643 or fenofibrate. Similarly to contractions evoked by acetylcholine, H₂O₂-induced increases in tension in SHR aortae involved, in succession, phospholipase A₂ (PLA₂), cyclooxygenase, and thromboxane-prostanoid receptors. Wy14643 or fenofibrate, by decreasing the activity of endothelial Ca²⁺-independent PLA₂, attenuated the contractions to H₂O₂. In conclusion, the increased oxidative stress in the SHR aorta (mainly increased production of H₂O₂ and its partially reduced product, hydroxyl radical) contributed to acetylcholine-induced, endothelium-dependent contractions; PPAR-α agonists likely inhibit the H₂O₂-mediated contractions by inhibiting endothelial Ca²⁺-independent PLA₂. The present study highlights the prospective therapeutic effects of PPAR-α agonists in improving endothelial function in hypertension and other vascular implications due to oxidative stress. NEW & NOTEWORTHY Peroxisome proliferator-activated receptor-α agonists, which are used clinically as lipid-lowering drugs, acutely reduce H₂O₂-induced contractions in aortae of hypertensive rats by inhibiting the activity of endothelial Ca²⁺-independent phospholipase A₂. These vascular effects of peroxisome proliferator-activated receptor-α agonists suggest that they may help to prevent vascular complications under pathological conditions associated with oxidative stress.

α1 -Adrenoceptor activation of PKC-ε causes heterologous desensitization of thromboxane receptors in the aorta of spontaneously hypertensive rats

BACKGROUND AND PURPOSE

In the aorta of adult spontaneously hypertensive (SHR), but not in that of normotensive Wistar-Kyoto (WKY), rats, previous exposure to phenylephrine inhibits subsequent contractions to PGE2 . The present experiments were designed to examine the mechanism(s) underlying this inhibition.

EXPERIMENTAL APPROACH

Isometric tension was measured in isolated rings of SHR and WKY aortae. Gene expression and protein presence were measured by quantitative real-time PCR and Western blotting respectively.

KEY RESULTS

In aorta of 18 weeks SHR, but not age-matched WKY, pre-exposure to phenylephrine inhibited subsequent contractions to PGE2 that were mediated by thromboxane prostanoid (TP) receptors. This inhibition was not observed in preparations of pre-hypertensive 5-week-old SHR, and was significantly larger in those of 36- than 18-week-old SHR. Pre-exposure to the PKC activator, phorbol 12,13-dibutyrate, also inhibited subsequent contractions to PGE2 in SHR aortae. The selective inhibitor of PKC-ε, ε-V1-2, abolished the desensitization caused by pre-exposure to phenylephrine. Two molecular PKC bands were detected and their relative intensities differed in 36-week-old WKY and SHR vascular smooth muscle. The mRNA expressions of PKC-α, PKC-ε, PK-N2 and PKC-ζ and of G protein-coupled kinase (GRK)-2, GRK4 and β-arrestin2 were higher in SHR than WKY aortae.

CONCLUSIONS AND IMPLICATIONS

These experiments suggest that in the SHR but not the WKY aorta, α1 -adrenoceptor activation desensitizes TP receptors through activation of PKC-ε. This heterologous desensitization is a consequence of the chronic exposure to high arterial pressure.

Enhanced vascular PI3K/Akt-NOX signaling underlies the peripheral NMDAR-mediated pressor response in conscious rats

The molecular mechanisms for peripheral N-methyl-D-aspartate receptor (NMDAR)-mediated vascular oxidative stress and pressor response are not known. We conducted integrative (in vivo) and ex vivo biochemical studies to test the hypothesis that reactive oxygen species (ROS)-dependent calcium influx, triggered by the activation of vascular kinases, underlies the NMDAR-mediated pressor response. Pharmacological inhibition of phosphoinositide 3-kinase (PI3K)/Akt (wortmannin, 15 μg/kg), protein kinase C (chelerythrine: 5 mg/kg, intravenous), Ca²⁺ influx (nifedipine, 0.35 or 0.75 mg/kg), or NADPH oxidase (NOX: apocynin, 5 mg/kg) attenuated the peripheral NMDAR-mediated pressor response in conscious male Sprague-Dawley rats. NMDAR activation enhanced the phosphorylation of Akt, ERK1, JNK and p38 (Western blot), and NOX activity in vascular tissues collected during the pressor response caused by NMDA infusion (180 μg·kg⁻¹·min⁻¹, 30 minutes). Furthermore, ex vivo studies showed that wortmannin, chelerythrine, or apocynin abrogated the NMDAR-mediated vascular nitric oxide (NO) and ROS generation and NOX activation in the vasculature. These findings implicate vascular PI3K/Akt-protein kinase C signaling in the peripheral NMDAR-mediated increases in vascular NO and NOX activation (ROS), which ultimately lead to calcium influx and pressor response in conscious rats.

Leptin's activity on the hydroxyl radical: a possible link to the oxidative stress-related endothelial vasodilation in patients with obstructive sleep apnea

PURPOSE

Obstructive sleep apnea (OSA) is associated with increased cardiovascular morbidity, whereas the underlying mechanism is still eluding, the thought participants are chronic intermittent hypoxia with consequent increase in the reactive oxygen species, leading to endothelial cell damage and dysfunction in these patients. As the hydroxyl radical (·OH) mediates the vascular smooth muscle relaxation, identification of its scavengers might reveal sentinel markers of decreased vascular responsiveness and worse long-term comorbid outcome. We therefore assessed leptin's scavenger effect on (∙)OH using the electronic paramagnetic resonance (EPR) method.

METHODS

The (∙)OH was generated by the Fenton reaction in the presence of spin-trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DMPO) with various concentrations of leptin (0.25, 2.5, and 25 μg/ml) and without leptin. EPR spectrometer settings were: modulation frequency, 100 kHz; X band microwave frequency, 9.5 GHz; microwave power, 20 mW (milliwatts); modulation amplitude, 1.0 G (gauss); time constant, 160 s; scan time, 200 s; and receiver gain, 1 × l0(5). EPR signal intensity between 3,440 and 3,540 G of measurements taken in at least three separate experiments was reported. Mannitol, a known (∙)OH scavenger, at 100 mM significantly decreased the DMPO-OH adduct formation and was used as the active-control agent.

RESULTS

Leptin added to aqueous solutions at all concentrations was associated with a statistically significant decrease in EPR signal compared with controls due to its scavenging activity towards the ·OH.

CONCLUSIONS

Leptin could be further investigated as a sentinel biomarker of decreased vascular responsiveness and future risk of atherosclerotic disease in obese OSA patients.

Interplay of endothelial and inducible nitric oxide synthases modulates the vascular response to ischaemia-reperfusion in the rabbit lung

AIM

Lung ischaemia-reperfusion induces nitric oxide synthesis and reactive nitrogen species, decreasing nitric oxide bioavailability. We hypothesized that in the ventilated lung, this process begins during ischaemia and intensifies with reperfusion, contributing to ischaemia-reperfusion-induced pulmonary vasoconstriction. The aim was to determine whether ischaemia-reperfusion alters inducible and endothelial nitric oxide synthase expression/activity, reactive nitrogen species generation, and nitric oxide bioavailability, potentially affecting pulmonary perfusion.

METHODS

Ischaemia-reperfusion was induced for various times in anesthetized rabbits with ventilated lungs by reversibly occluding the right pulmonary artery and initiating reperfusion. Nitric oxide synthase activity/expression and phosphorylation, reactive nitrogen species generation and total nitrate/nitrite were determined in lung tissue.

RESULTS

Inducible nitric oxide synthase expression and activity, and reactive nitrogen species formation coincided with increased pulmonary vascular resistance during reperfusion and increased with ischaemia duration, further increasing after 2-h reperfusion. Total nitrate/nitrite also increased with ischaemia but decreased after 2-h reperfusion. Pre-treatment with an inducible nitric oxide synthase inhibitor (1400W; Cayman Chemical Company, Ann Arbor, MI, USA) attenuated inducible nitric oxide synthase activity, reactive nitrogen species generation and pulmonary vascular resistance, but did not affect total nitrate/nitrite. Endothelial nitric oxide synthase expression was unchanged by ischaemia-reperfusion; however, its phosphorylation on serine 1177 and dephosphorylation on threonine 495 was uncoupled, suggesting decreased endothelial nitric oxide synthase activity. 1400W prevented uncoupling of endothelial nitric oxide synthase phosphorylation, maintaining its activity during reperfusion.

CONCLUSION

Ischaemia-reperfusion up-regulates inducible nitric oxide synthesis and/activity, which coincides with reduced endothelial nitric oxide synthase activity as suggested by its uncoupling and may contribute to ischaemia-reperfusion-induced pulmonary vasoconstriction.

Acute antioxidant supplementation and skeletal muscle vascular conductance in aged rats: role of exercise and fiber type

Age-related increases in oxidative stress contribute to impaired skeletal muscle vascular control. However, recent evidence indicates that antioxidant treatment with tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl) attenuates flow-mediated vasodilation in isolated arterioles from the highly oxidative soleus muscle of aged rats. Whether antioxidant treatment with tempol evokes similar responses in vivo at rest and during exercise in senescent individuals and whether this effect varies based on muscle fiber type composition are unknown. We tested the hypothesis that redox modulation via acute systemic tempol administration decreases vascular conductance (VC) primarily in oxidative hindlimb locomotor muscles at rest and during submaximal whole body exercise (treadmill running at 20 m/min, 5% grade) in aged rats. Eighteen old (25–26 mo) male Fischer 344 x Brown Norway rats were assigned to either rest ( n = 8) or exercise ( n = 10) groups. Regional VC was determined via radiolabeled microspheres before and after intra-arterial administration of tempol (302 μmol/kg). Tempol decreased mean arterial pressure significantly by 9% at rest and 16% during exercise. At rest, similar VC in 26 out of 28 individual hindlimb muscles or muscle parts following tempol administration compared with control resulted in unchanged total hindlimb muscle VC (control: 0.18 ± 0.02; tempol: 0.17 ± 0.05 ml·min−1·100 g−1·mmHg−1; P > 0.05). During exercise, all individual hindlimb muscles or muscle parts irrespective of fiber type composition exhibited either an increase or no change in VC with tempol (i.e., ↑11 and ↔17 muscles or muscle parts), such that total hindlimb VC increased by 25% (control: 0.93 ± 0.04; tempol: 1.15 ± 0.09 ml·min−1·100 g−1·mmHg−1; P ≤ 0.05). These results demonstrate that acute systemic administration of the antioxidant tempol significantly impacts the control of regional vascular tone in vivo presumably via redox modulation and improves skeletal muscle vasodilation independently of fiber type composition during submaximal whole body exercise in aged rats.

Luteolin reduces high glucose-mediated impairment of endothelium-dependent relaxation in rat aorta by reducing oxidative stress

While luteolin, a flavone rich in many plants, has some cardiovascular activity, it is not clear whether luteolin has beneficial effects on the vascular endothelial impairment in hyperglycemia/high glucose. Here, we reveal the protective effect of luteolin on endothelium-dependent relaxation in isolated rat aortic rings exposed to high glucose. The thoracic aorta of male Sprague-Dawley rats was rapidly dissected out and the effect of luteolin on the tension of aortic rings pretreated with high glucose (44mM) for 4h was measured in an organ bath system. The levels of nitric oxide (NO), hydroxy radical (OH(-)) and reactive oxygen species (ROS), and the activity of superoxide dismutase (SOD) and nitric oxide synthase (NOS) were measured in aortas. The vasorelaxation after treatment with luteolin for 8 weeks in aortic rings from diabetic rats was also determined. We found that exposure to high glucose decreased acetylcholine-induced endothelium-dependent relaxation. However, high mannitol had no effect on vasorelaxation. Luteolin evoked a concentration-dependent relaxation in aortic rings previously contracted by phenylephrine, and the pD(2) value was 5.24+/-0.04. The EC(50) of luteolin markedly attenuated the inhibition of relaxation induced by high glucose, which was significantly weakened by pretreatment with l-NAME (0.1mM), but not by indomethacin (0.01mM). Luteolin significantly inhibited the increase of ROS level and OH(-) formation, and the decrease of NO level, NOS and SOD activity caused by high glucose. The improving effect of luteolin on endothelium-dependent vasorelaxation in diabetic rat aortic rings was reversed by pretreatment with l-NAME or methylene blue. The results indicate that the decrease of endothelium-dependent relaxation in rat aortic rings exposed to high glucose is markedly attenuated by luteolin, which may be mediated by reducing oxidative stress and enhancing activity in the NOS-NO pathway.

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.

Aging impairs flow-induced dilation in coronary arterioles: role of NO and H(2)O(2)

Aging contributes significantly to the development of cardiovascular disease and is associated with elevated production of reactive oxygen species (ROS). The beneficial effects of nitric oxide (NO)-mediated vasodilation are quickly abolished in the presence of ROS, and this effect may be augmented with aging. We previously demonstrated an age-induced impairment of flow-induced dilation in rat coronary arterioles. Therefore, the purpose of this study was to determine the effects of O(2)(-) scavenging, as well as removal of H(2)O(2), the byproduct of O(2)(-) scavenging, on flow-mediated dilation in coronary resistance arterioles of young (4 mo) and old (24 mo) male Fischer 344 rats. Flow increased NO and H(2)O(2) production as evidenced by enhanced diaminofluorescein and dichlorodihydrofluorescein fluorescence, respectively, whereas aging reduced flow-induced NO and H(2)O(2) production. Endothelium-dependent vasodilation was evaluated by increasing intraluminal flow (5-60 nl/s) before and after treatment with the superoxide dismutase mimetic Tempol (100 muM), the H(2)O(2) scavenger catalase (100 U/ml), or Tempol plus catalase. Catalase reduced flow-induced dilation in both groups, whereas Tempol and Tempol plus catalase diminished vasodilation in young but not old rats. Tempol plus deferoxamine (100 muM), an inhibitor of hydroxyl radical formation, reversed Tempol-mediated impairment of flow-induced vasodilation in young rats and improved flow-induced vasodilation in old rats compared with control. Immunoblot analysis revealed increases in endogenous superoxide dismutase, catalase, and nitrotyrosine protein levels with aging. Collectively, these data indicate that NO- and H(2)O(2)-mediated flow-induced signaling decline with age in coronary arterioles and that elevated hydroxyl radical formation contributes to the age-related impairment of flow-induced vasodilation.

Sustained contraction and endothelial dysfunction induced by reactive oxygen species in porcine coronary artery

A combination of purine and xanthine oxidase (XOD) dose-dependently elicited sustained contraction of porcine coronary arterial rings and resulted in increased concentrations of superoxide anions and hydrogen peroxide. These contractile responses appeared, with a delay, after the application of purine and XOD, used as a reactive oxygen species (ROS)-generating system. Coronary arteries precontracted with prostaglandin F(2alpha) failed to relax in response to substance P after exposing the arterial preparation to this ROS-generating system. The contractile response of the coronary artery to the ROS-generating system was almost completely inhibited by catalase (130 U/ml), and was partially inhibited by superoxide dismutase (60 U/ml), or mannitol (30 mM). A voltage-dependent L-type Ca(2+) channel antagonist, nicardipine, had no effect on contraction. Dysfunction of endothelial cells was completely prevented by catalase, but not by superoxide dismutase or mannitol. These results suggest that superoxide anions, hydrogen peroxide and hydroxyl radicals might be involved in eliciting sustained, delayed-onset coronary artery contraction, which is not related to L-type Ca(2+) channels. They also suggest that hydrogen peroxide might play a major role in endothelial dysfunction of the porcine coronary artery.

Regional heterogeneity of functional changes in conduit arteries after high-fat diet

OBJECTIVE

To determine effects of dietary fat content on vascular responses in different conduit arteries in mice.

METHODS AND PROCEDURES

Vascular responses to reactive oxygen species (ROS)/hydroxyl radical (.OH), acetylcholine (ACh), endothelin-1 (ET-1), and angiotensin II (Ang II) were determined in carotid and femoral arteries of C57BL/6J mice fed with diets varying in fat content (low fat (LF), 12.3%; high fat (HF), 41%; and very high fat (VHF), 58% (kcal from fat)) for 15 weeks, beginning at 4 weeks of age.

RESULTS

In precontracted rings of carotid and femoral artery, ROS/.OH-induced a rapid, transient vasodilation. In the carotid, but not in femoral artery, ROS/.OH-induced dilation increased with increasing dietary fat intake (P < 0.05 vs. LF diet), while contractile responses to ROS/.OH remained unaffected. In femoral arteries, ROS/.OH-induced contractions were reversed into relaxations after both HF and VHF diet (P < 0.05 vs. LF diet). Both ET-1 and Ang II induced strong contractions in the femoral artery that were unaffected by dietary fat intake. In contrast, in the carotid artery Ang II-induced contraction was attenuated after HF and VHF diets (P < 0.005 vs. LF diet), whereas ET-1-induced vasoconstriction was significantly increased (P < 0.05 VHF vs. LF and HF). Treatment with VHF diet enhanced ACh-mediated endothelium-dependent relaxation only in the femoral artery (P < 0.05 vs. HF).

DISCUSSION

These findings demonstrate that dietary fat content has regional and distinct effects on vascular function in different vascular beds. The data also suggest the possibility that in selected conduit arteries ROS-dependent vasodilator mechanisms become activated in response to increased dietary fat intake.

Endothelin stimulates vascular hydroxyl radical formation: effect of obesity

Reactive oxygen species (ROS) and endothelin-1 (ET-1) contribute to vascular pathophysiology in obesity. In this context, whether ET-1 modulates hydroxyl radical (•OH) formation and the function of ROS/•OH in obesity is not known. In the present study, formation and function of ROS, including •OH, were investigated in the aorta of lean and leptin-deficient obese ob/ob mice. Hydroxyl radical formation was detected ex vivo using terephthalic acid in intact aortic rings and the involvement of ROS in ET-1-mediated vasoreactivity was analyzed using the antioxidant EPC-K1, a combination of α-tocopherol and ascorbic acid. Generation of either •OH, •O2−, and H2O2was strongly inhibited by EPC-K1 (all P < 0.05). In obese mice, basal vascular •OH formation and ROS activity were reduced by 3-fold and 5-fold, respectively ( P < 0.05 vs. lean). ET-1 markedly enhanced •OH formation in lean (6-fold, P < 0.05 vs. untreated) but not in obese mice. Obesity increased ET-1-induced contractions ( P < 0.05 vs. lean), and ROS scavenging further enhanced the response ( P < 0.05 vs. untreated). Exogenous ROS, including •OH caused stronger vasodilation in obese animals ( P < 0.05 vs. lean), whereas endothelium-dependent relaxation was similar between lean and obese animals. In conclusion, we present a sensitive method allowing ex vivo measurement of vascular •OH generation and provide evidence that ET-1 regulates vascular •OH formation. The data indicate that in obesity, vascular formation of ROS, including •OH is lower, whereas the sensitivity to ROS is increased, suggesting a novel and important role of ROS, including •OH in the regulation of vascular tone in disease status associated with increased body weight.

Differential inhibition by oxygen radicals of vasoactive amines-induced contractions in the porcine coronary artery

Reactive oxygen species (ROS) play an important role in normal metabolic and signaling processes. Excess ROS, however, can cause severe cardiovascular damage. Thus, the present study was designed to examine effects of H(2)O(2) and xanthine plus xanthin oxidase (X/XO) on the serotonin (5HT), histamine (His) and acetylcholine (ACh)-induced contractions of porcine coronary arteries. In addition, to explore the site of ROS formation and species of it, the inhibitory effects of edaravone and EDTA were also tested. 5HT- and His-induced contractions were suppressed by H(2)O(2) and X/XO treatment. However, these suppressions of ACh-induced contraction by H(2)O(2) treatment was relatively weak and X/XO treatment caused no suppression on ACh-induced contraction. In the presence of edaravone which is thought to be a scavenger for .OH, significant decrease of inhibition of 5HT- and His-induced contractions was observed when coronary artery strips were treated with X/XO, but not H(2)O(2). On the other hand, inhibitory effects by EDTA treatments were also observed in X/XO treatments. These results suggest that 1) ROSs produced by additions of H(2)O(2) or X/XO are considered to be responsible for several physiological functions of coronary artery contractions, 2) the site of ROS produced by X/XO system, probably .OH, was outside the cell, but the inhibitory action of H(2)O(2), was inside the cell, and 3) a low susceptibility of ACh-induced contraction to H(2)O(2) and X/XO may indicates the signal transduction pathway(s) of ACh-induced contraction is different from those of 5HT and His.

Flow- and acetylcholine-induced dilatation in small arteries from rats with renovascular hypertension — effect of tempol treatment

We investigated whether renovascular hypertension alters vasodilatation mediated by nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) and the influence of the superoxide dismutase mimetic tempol on vasodilatation. One-kidney one-clip hypertensive Sprague-Dawley rats, treated with either vehicle or tempol (from weeks 5 to 10 after placement of the clip), and uninephrectomized control rats were investigated. In renal hypertensive rats systolic blood pressure increased to 171+/-6 mmHg (n=10), while in tempol-treated rats systolic blood pressure remained normal (139+/-7 mmHg, n=5). In isolated pressurized mesenteric small arteries NO-mediated dilatation was obtained by increasing flow rate and EDHF-mediated dilatation by acetylcholine. In arteries from hypertensive rats, flow-induced dilatation was blunted, as compared to normotensive and tempol-treated rats, while acetylcholine-induced dilatation remained normal. Measured by dihydroethidium staining there was an increased amount of superoxide in arteries from vehicle-treated rats, but not from tempol-treated rats. Expression by immunoblotting of endothelial NO synthase and the NAD(P)H oxidase subunit p47phox remained unaffected by high blood pressure and tempol treatment. Simultaneous measurements of NO-concentration and relaxation were performed in isolated coronary arteries from the same animals. As compared to vehicle-treated rats, both acetylcholine-induced relaxation and NO-concentration increased in arteries from tempol-treated animals, while only the relaxation was improved by the NO donor, S-nitroso-N-acetylpenicillamine (SNAP). In conclusion renovascular hypertension selectively inhibits flow-induced NO-mediated vasodilatation, while EDHF-type vasodilatation remains unaffected, suggesting that high blood pressure leads to increased generation of superoxide contributing to decreased NO bioavailability. Furthermore, the abnormal endothelium function can be corrected by tempol treatment, but this seems to involve mechanisms partly independent of NO.

Role of PKC in the novel synergistic action of urotensin II and angiotensin II and in urotensin II-induced vasoconstriction

The intracellular signaling of human urotensin II (hU-II) and its interaction with other vasoconstrictors such as ANG II are poorly understood. In endothelium-denuded rat aorta, coadministration of hU-II (1 nM) and ANG II (2 nM) exerted a significant contractile effect that was associated with increased protein kinase C (PKC) activity and phosphorylation of PKC-alpha/betaII and myosin light chain, whereas either hU-II or ANG II administered alone at these concentrations had no statistically significant effect. This synergistic effect was abrogated by the PKC inhibitor chelerythrine (10 and 30 microM), the selective PKC-alpha/betaII inhibitor Gö-6976 (0.1 and 1 microM), the hU-II receptor ligand urantide (30 nM and 1 microM), or the ANG II antagonist losartan (1 microM). Moreover, in endothelium-intact rat aorta, the synergistic effect of hU-II and ANG II was not exerted any longer, and this synergistic effect was unmasked by pretreatment of the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester. hU-II (10 nM) alone caused a long-lasting increase in phospho-PKC-theta, phospho-myosin light chain, and PKC activity, which was associated with long-lasting vasoconstriction. These changes were prevented by chelerythrine. Methoxyverapamil-thapsigargin treatment reduced the hU-II-induced vasoconstriction by approximately 50%. The methoxyverapamil-thapsigargin-resistant component of hU-II-induced vasoconstriction was dose-dependently inhibited by chelerythrine. In conclusion, hU-II induces a novel PKC-dependent synergistic action with ANG II in inducing vasoconstriction. PKC-alpha/betaII is probably the PKC isoform involved in this synergistic action. Nitric oxide produced in the endothelium probably masks this synergistic action. The long-lasting vasoconstriction induced by hU-II alone is PKC dependent and associated with PKC-theta phosphorylation.

Intracellular-produced hydroxyl radical mediates H2O2-induced Ca2+ influx and cell death in rat beta-cell line RIN-5F

The melastatin-related transient receptor potential channel TRPM2 is a Ca(2+)-permeable channel that is activated by H(2)O(2), and the Ca(2+) influx through TRPM2 mediates cell death. However, the responsible oxidants for TRPM2 activation remain to be identified. In the present study, we investigated the involvement of hydroxyl radical on TRPM2 activation in TRPM2-expressing HEK293 cells and the rat beta-cell line RIN-5F. In both cell types, H(2)O(2) induced Ca(2+) influx in a concentration-dependent manner. However, the addition of hydroxyl radical, which was produced by mixing FeSO(4) and H(2)O(2), to the cells, did not increase intracellular Ca(2+) concentration. Interestingly, when H(2)O(2) was added to the cells under intracellular Fe(2+)-accumulated conditions, Ca(2+) influx was markedly enhanced compared to H(2)O(2) alone. In addition, the H(2)O(2)-induced Ca(2+) influx was reduced by hydroxyl radical scavengers and an iron chelator. Under intracellular Fe(2+)-accumulated conditions, H(2)O(2)-induced RIN-5F cell death through TRPM2 activation was also markedly enhanced. Hydroxyl radical scavengers and an iron chelator suppressed the RIN-5F cell death by H(2)O(2). These results strongly suggest that the intracellular hydroxyl radical plays a key role in the activation of TRPM2 during H(2)O(2) treatment, and TRPM2 activation mediated by hydroxyl radical is implicated in H(2)O(2)-induced cell death in the beta-cell line RIN-5F.

Hypersensitivity to hydroxyl radicals in rat basilar artery after subarachnoid hemorrhage

Vasospasm after subarachnoid hemorrhage (SAH) is a serious complication and we have been investigating the relationship between vasoconstrictors and vasospasm after SAH. The present study was designed to investigate the vasocontractile responses to reactive oxygen species in isolated rat basilar arteries from the control and experimental SAH rats. Contractile responses to hydroxyl radicals in basilar arteries from SAH rats were 3-6-fold higher than those in control rats. The present results clearly indicate that hypersensitivity to hydroxyl radicals may contribute to the vasospasm after SAH.

Cooling-induced contraction of the rat gastric fundus: mediation via transient receptor potential (TRP) cation channel TRPM8 receptor and Rho-kinase activation

1. Cooling has been shown to induce contractions of several smooth muscles in vitro. However, the mechanism involved in the response is not yet known. In the present study, we investigated the possible involvement of transient receptor potential (TRP) cation channel TRPM8 receptors and the Rho-kinase pathway in cooling-induced contraction of the rat fundus. 2. Cooling-induced contractions were inversely proportional to temperature. Contractions were significantly reduced (by 65.6 +/- 2.4%; P < 0.05) in a Ca2+-free (1 mmol/L EGTA) medium, but were not significantly inhibited by nifedipine (10(-6) mol/L). 3. Capsazepine (3 x 10(-6) and 3 x 10(-5) mol/L), a TRPM8 receptor antagonist, inhibited cooling-induced contraction of the rat gastric fundus. 4. The Rho-kinase inhibitor Y-27632 concentration-dependently inhibited cooling-induced contraction of the gastric fundus, producing approximately 90% inhibition at a concentration of 10(-5) mol/L. Contractions were also inhibited by genistein (3 x 10(-5) mol/L), a tyrosine kinase inhibitor, but not by GF 109203X (10(-7) mol/L), a protein kinase C inhibitor. 5. Using reverse transcription-polymerase chain reaction techniques, it was observed that the mRNA for the TRPM8 receptor and Rho-kinase were expressed in the rat gastric fundus. 6. These results would suggest that cooling-induced contraction of the rat fundus is mediated by activation of TRPM8 receptors via a mechanism involving activation of Rho-kinase.