Hydrogen peroxide induces contraction and raises [Ca2+]i in canine cerebral arterial smooth muscle: participation of cellular signaling pathways

Involvement of Reactive Oxygen Species in Angiotensin II-Induced Vasoconstriction

In recent years it has been shown that angiotensin II (Ang II) stimulates formation of reactive oxygen species (ROS), presumably by activation of NAD(P)H oxidase. This ROS formation has been primarily associated with cellular growth regulation by Ang II. The objective of the present study was to investigate whether these ROS contribute to Ang II-induced vasoconstriction. Experiments were performed in isolated rat thoracic aorta. Concentration response curves were constructed for Ang II in the absence and presence of the NAD(P)H oxidase inhibitor DPI, and ROS scavengers catalase and EUK-8. Inhibition of NAD(P)H oxidase as well as scavenging of ROS, decreased the contractile response to Ang II. Administration of NADPH, a substrate for NAD(P)H oxidase, produced vasoconstriction that proved to be sensitive for DPI, catalase, and EUK-8. Exposure of the vessels to exogenous ROS, induced by electrolysis of the organ bath medium, also resulted in a contractile response that was decreased by ROS scavenging. The results suggest that ROS play a role in Ang II-induced vasoconstriction via the activation of NAD(P)H oxidase.

Hydrogen peroxide induces apoptosis in cerebral vascular smooth muscle cells: possible relation to neurodegenerative diseases and strokes

Recently, reactive oxygen species (ROS) have been suggested as important mediators of brain damage in a number of disease states, including traumatic brain injury, neurodegenerative diseases and strokes. Apoptosis has been suggested to play an important role in neurodegenerative diseases, traumatic brain injury and strokes. The aim of this study was to determine whether or not cerebral vascular smooth muscle cells (CVSMCs) undergo apoptosis following treatment with hydrogen peroxide (H2O2). Herein, we demonstrate, for the first time, that H2O2 can induce apoptosis in a concentration-dependent manner in primary cultured CVSMCs, as measured by several morphological and biochemical criteria. H2O2-induced apoptosis may be initiated by stimulating Ca2+-dependent endonuclease activity. The present new data suggest that apoptosis in cerebral VSMCs, induced by ROS, such as H2O2, could play important roles in neruodegenerative processes, traumatic brain injury and strokes.

Catalase prevents elevation of [Ca(2+)](i) induced by alcohol in cultured canine cerebral vascular smooth muscle cells: Possible relationship to alcohol-induced stroke and brain pathology

Several studies have suggested that alcohol-induced brain injury is associated with generation of reactive oxygen species (ROS). The recent findings, that antioxidants (Vitamin E and pyrrolidine dithiocarbamate (PDTC)) prevent intracellular Ca(2+) ([Ca(2+)](i)) overload in cerebral vascular smooth muscle cells, induced by alcohol, demonstrate indirectly that ROS formation is related to cerebral vascular injury. The present experiments were designed to test the hypothesis that catalase, an hydrogen peroxide (H(2)O(2)) scavenging enzyme, can prevent or ameliorate alcohol-induced elevation of [Ca(2+)](i). Preincubation of cultured canine cerebral vascular smooth muscle cells with catalase (20-1000 units/ml) didn't produce any apparent changes from controls in resting levels of [Ca(2+)](i) after 1-3 days. Exposure of the cerebral vascular cells to culture media containing 10-100mM ethanol resulted in significant rises in [Ca(2+)](i) (p<0.01). Although exposure of these cells to a low concentration of catalase (20 units/ml) failed to prevent the increased level of [Ca(2+)](i) induced by ethanol, concomitant addition of higher concentrations of catalase (100-1000 units/ml) and ethanol (10-100mM) inhibited or ameliorated the rises of [Ca(2+)](i) induced by ethanol either at 24h or at 3 days, in a concentration-dependent manner. Catalase, in the range of 100-200 units/ml, inhibited approximately 50% of the [Ca(2+)](i) increases caused by ethanol in the first 24h. Catalase at a concentration of 1000 units/ml inhibited completely excessive [Ca(2+)](i) accumulation. The present results when viewed in light of other recently published data suggest that H(2)O(2) generation may be one of the earliest events triggered by alcohol in alcohol-induced brain-vascular damage, neurobehavioral actions and stroke.

Mechanisms underlying the hydrogen peroxide-induced, endothelium-independent relaxation of the norepinephrine-contraction in guinea-pig aorta

The mechanisms underlying the hydrogen peroxide-induced relaxation of the norepinephrine-contraction were studied by measuring isometric force, myosin light chain (MLC(20)) phosphorylation and cyclic GMP in endothelium-denuded muscle from the guinea-pig aorta. Norepinephrine (5.2+/-1.3 microM) produced a phasic, followed by a tonic contraction. Hydrogen peroxide (10 and 100 microM), glyceryl trinitrate (30 and 300 nM) and 8-bromo cyclic GMP (30 and 100 microM) did not change the basal tone, but reduced the norepinephrine-induced contraction. Phosphorylation of MLC(20) (percentage of phosphorylated to total MLC(20)) was increased 1 min (5.9+/-1.0% vs. 35.9+/-4.9%) and, to a lesser extent, 20 min (3.7+/-1.7% vs. 13.9+/-1.6%) after the addition of norepinephrine. Hydrogen peroxide (100 microM) did not modify basal MLC(20) phosphorylation, but reduced the increase in MLC(20) phosphorylation induced by 1-min exposure to norepinephrine (20.9+/-4.1%). Its effect was abolished by catalase. When the tissue was incubated for 20 min with norepinephrine in the presence of hydrogen peroxide, norepinephrine-induced MLC(20) phosphorylation was not changed (13.6+/-1.5%), as compared to that in the absence of hydrogen peroxide. Hydrogen peroxide relaxed norepinephrine-stimulated aortas in a concentration-dependent fashion with EC(50) values of 5.9+/-0.2 microM. The relaxation was inhibited by soluble guanylate cyclase inhibitors and increased by an inhibitor of cyclic GMP-selective phosphodiesterase. In aorta precontracted with norepinephrine, hydrogen peroxide (100 microM) relaxed the tissue by 89+/-11% and almost doubled tissue concentrations of cyclic GMP, whereas sodium nitroprusside (1 microM) relaxed the tissue by 100% and increased cyclic GMP concentrations 30-fold. It is suggested that the inhibitory effects of hydrogen peroxide on the norepinephrine-induced phasic and sustained contractions are explained by a decrease in MLC(20) phosphorylation and by an alteration in MLC(20) phosphorylation-independent mechanisms, respectively. The effects of hydrogen peroxide were in part mediated by cyclic GMP.

Inhibitor of nuclear factor-Kappa B activation attenuates venular constriction, leukocyte rolling-adhesion and microvessel rupture induced by ethanol in intact rat brain microcirculation: relation to ethanol-induced brain injury

The present study was designed to test the hypothesis that acute, local administration of a specific inhibitor of nuclear factor-Kappa B activation (which prevents rapid proteolysis of IKB-alpha) will attenuate cerebral (cortical) venular constrictions, leukocyte-endothelial wall interactions and postcapillary damage induced by medium to high concentrations of ethanol in the intact rat brain. Perivascular or i.p. administration of ethanol (100, 250 mg/dl) to the intact rat brain resulted in concentration-dependent venular vasospasm, rolling and adherence of leukocytes to venular walls and rupture of postcapillary venules with focal hemorrhages. Superfusion of the in-situ brain with N(alpha)-L-tosyl-L-phenylalanine chloromethyl ketone (TPCK), a specific inhibitor of IKB-alpha proteolysis, attenuated greatly the spasmogenic, leukocyte rolling-endothelial cell adhesion and postcapillary hemorrhages induced by ethanol. These new data suggest that inhibition of alcohol-inducible degradation of IKB-alpha by TPKC can prevent much of the adverse microvascular actions of ethanol in the intact rat brain. Moreover, these new in-situ results suggest that activation of nuclear factor-Kappa B seems to play a major modulatory role in the adverse cerebral vascular actions of concentrations of alcohol found in the blood of alcohol-intoxicated subjects and human stroke victims.

Stimulated tyrosine phosphorylation of phosphatidylinositol 3-kinase causes acidic pH-induced contraction in spontaneously hypertensive rat aorta

Acidic pH induced a contraction (APIC) in isolated aortas from spontaneously hypertensive (SHR) and Wistar Kyoto rats, but failed to produce any response in age-matched Wistar rat aorta. This study was conducted to test the hypothesis that tyrosine phosphorylation of proteins is a molecular mechanism underlying the APIC. Tyrosine kinase inhibitors, genistein and tyrphostin 23 inhibited the APIC in a concentration-dependent manner. APIC was inhibited by phosphatidylinositol 3-kinase (PI3-kinase) inhibitors, LY-294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride] and wortmannin. Consistent with the results from tension measurement experiments, Western blot analysis showed that acidic pH induced an appreciable increment of tyrosine phosphorylation of 85-kDa protein (p85) in SHR aorta, which was completely inhibited by tyrphostin 23, whereas in Wistar rat aorta, the protein tyrosine phosphorylation was not observed. Further investigations using immunoprecipitation followed by Western blotting confirmed an increase in the tyrosine phosphorylation of p85. Analysis by SDS-polyacrylamide gel electrophoresis followed by silver staining of the gel revealed that amounts of multiple proteins with molecular sizes of 120, 130, 210, and 225 kDa were increased at acidic pH, which were immunoprecipitated with anti-phosphotyrosine antibody. Western blotting using a specific anti-PI3-kinase antibody identified the p85 as the regulatory subunit of PI3-kinase, whereas 120-, 130-, and 225-kDa proteins were identified by mass spectrometry as pro-alpha2 (I) collagen, collagen alpha1 (I) chain, and fibernectin I, respectively. As assayed by Western blotting using anti-myosin light chain (MLC) antibody, acidic pH induced a stimulation of MLC phosphorylation, and the stimulated MLC phosphorylation was abolished by tyrphostin 23 and LY-294002. These results suggest that acidic pH induces an increase in tyrosine phosphorylation of PI3-kinase, resulting in the MLC phosphorylation-dependent contraction of SHR aorta.

Ethanol induces rapid lipid peroxidation and activation of nuclear factor-kappa B in cerebral vascular smooth muscle: relation to alcohol-induced brain injury in rats

The present study was designed to test the hypothesis that acute administration of alcohol (ethanol) to primary cultured cerebral vascular smooth muscle cells will cause lipid peroxidation, inhibition of IkappaB phosphorylation, and inhibition of nuclear transcription factor-kappa B (NF-kappaB). Ethanol (10, 25, 100 mM) resulted in concentration-dependent rises in malondialdehyde in as little as 30-45 min after exposure to the alcohol, rising to levels 2.5-10x normal after 18-24 h. Using EMSA assays and specific antibodies, ethanol caused three DNA-binding proteins (p50, p65, c-Rel) to rise in nuclear extracts in a concentration-dependent manner. Using a rabbit antibody, IkappaB phosphorylation (and degradation) was stimulated by ethanol (in a concentration-dependent manner) and inhibited by a low concentration of the NF-kappaB inhibitor, pyrrolidine dithiocarbamate. These new biochemical and molecular data indicate that ethanol, even in physiologic concentrations, can elicit rapid lipid peroxidation and activation of NF-kappaB in cerebral vascular muscle cells. The present results when viewed in light of other recently published data suggest that ethanol-induced lipid peroxidation and activation of nuclear transcription factors probably play important roles in alcohol-induced brain-vascular damage, neurobehavioral actions and stroke.

Mechanism of vascular smooth muscle cells activation by hydrogen peroxide: role of phospholipase C gamma

BACKGROUND

Hydrogen peroxide (H2O2) formation is a critical factor in processes involving ischaemia/ reperfusion. However, the precise mechanism by which reactive oxygen species (ROS) induce vascular damage are insufficiently known. Specifically, activation of phospholipase C gamma (PLCgamma) is a probable candidate pathway involved in vascular smooth muscle cells (VSMC) activation by H2O2.

METHODS

The activation of human venous VSMC was measured as cytosolic free calcium mobilization, shape change and protein phosphorylation, focusing on the role of tyrosine phosphorylation-activated PLCgamma.

RESULTS

The exposure of VSMC to exogenous H2O2 caused a rapid increase in cytosolic free calcium concentration ([Ca2+]i), and induced a significant VSMC shape change. Both effects were dependent on a tyrosine kinase-mediated mechanism, as determined by the blockade of short-term treatment of VSMC with the protein tyrosine kinase inhibitor, genistein. Giving further support to the putative role of phospholipase C (PLC)-dependent pathways, the [Ca2+]i and VSMC shape change response were equally inhibited by the specific PLC blocker, 1-(6-((17-beta-methoxyestra-1,3,5(10)trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122). In addition, U73122 had a protective effect against the deleterious action (24 h) of H2O2 on non-confluent VSMC. As a further clarification of the specific pathway involved, the exposure to H2O2 significantly stimulated the tyrosine phosphorylation of PLCgamma with a concentration- and time-profile similar to that of [Ca(2+)](i) mobilization.

CONCLUSIONS

The present study reveals that H(2)O(2) activates PLCgamma on VSMC through tyrosine phosphorylation and that this activation has a major role in rapid [Ca(2+)](i) mobilization, shape-changing actions and damage by H(2)O(2) in this type of cells. These findings have direct implications for understanding the mechanisms of the vascular actions of H(2)O(2) and may help to design pharmacologically protective strategies.

Phosphatidylinositol 3-kinase inhibitor failed to reduce cerebral vasospasm in dog model of experimental subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Phosphatidylinositol 3-kinase (PI3-kinase) is involved in smooth muscle contraction induced by growth factors and/or G protein-coupled receptor agonists. To evaluate the role of PI3-kinase in the pathogenesis of delayed vasospasm, we applied 2 PI3-kinase inhibitors to an established canine double-hemorrhage model of experimental subarachnoid hemorrhage.

METHODS

Twenty-four dogs underwent double blood injections via the cisterna magna on days 0 and 2. The dogs were killed on day 7. Dogs were treated with either vehicle (dimethyl sulfoxide), wortmannin, or LY294002 once per day on day 2 through day 6. Angiography was performed before blood injection and before the dogs were killed. The basilar arteries were collected for morphology, Western blot analysis, and PI3-kinase activity.

RESULTS

The residual diameter of the basilar arteries in the dimethyl sulfoxide treatment group, which was compared with day 0 angiogram, decreased markedly on day 7 (the percentage of the residual diameter was 47.8+/-0.8%). Wortmannin and LY294002 did not significantly change residual diameter on day 7. Both PI3-kinase inhibitors abolished PI3-kinase activity compared with the vehicle treatment group. However, both PI3-kinase inhibitors failed to significantly attenuate PI3-kinase protein expression (Western blot) (P>0.05, ANOVA).

CONCLUSIONS

Delayed treatment, which was to mimic the clinical situation, with PI3-kinase inhibitors failed to reverse vasospasm. PI3-kinase may not play an important role in the delayed vasospasm. The possible effect of PI3-kinase inhibitors in the early stage of vasospasm was not investigated in the present study.

Are endothelium-derived hyperpolarizing and contracting factors isoprostanes?

The endothelium releases many vasoactive substances, including prostacyclin, nitric oxide and endothelin, in addition to several other factors about which little is known. The latter are referred to as 'endothelium-derived hyperpolarizing factors' (EDHFs) and 'endothelium-derived contracting factors' (EDCFs). Although there is much debate about the identities of EDHFs and EDCFs, a prevailing hypothesis is that they are cyclooxygenase-independent metabolites of arachidonic acid and many researchers associate them with free radicals. These properties are shared with isoprostanes. In this article, I compare the properties of EDHFs and EDCFs with those of the isoprostanes and propose novel experiments that might identify isoprostanes as candidate molecules for EDHFs and EDCFs.

Antioxidants prevent depletion of [Mg2+]i induced by alcohol in cultured canine cerebral vascular smooth muscle cells: possible relationship to alcohol-induced stroke

Low serum concentrations of Mg(2+) ions have been reported, recently, in patients with coronary disease, atherosclerosis, and stroke as well as in patients with cerebral hemorrhage. The aim of the present study was to determine whether potent antioxidants [alpha-tocopherol and pyrrolidine dithiocarbamate (PDTC)] can prevent or ameliorate intracellular Mg(2+) ([Mg(2+)](i)) depletion associated with cerebral vascular injury induced by alcohol. Exposure of cultured canine cerebral vascular smooth muscle cells to alcohol (10-100 mM) for 24 h induced marked depletion in [Mg(2+)](i) (i.e., approximately 30-65%, depending upon alcohol concentration). Treatment of the cultured cells with either PDTC (0.1 microM) or alpha-tocopherol (15 microM) for 24 h, alone, failed to interfere with basal [Mg(2+)](i) levels. However, preincubation of the cells with either alpha-tocopherol or PDTC for 24 h completely inhibited the depletion of [Mg(2+)](i) induced by exposure to 10-100 mM ethanol. These results indicate that alpha-tocopherol and PDTC prevent decreases in [Mg(2+)](i) produced by ethanol. Moreover, these new results suggest that such protective effects of alpha-tocopherol and PDTC on cerebral vascular cells might be useful therapeutic tools in prevention and amelioration of cerebral vascular injury and stroke in alcoholics.

Antioxidants prevent ethanol-induced contractions of canine cerebral vascular smooth muscle: relation to alcohol-induced brain injury

The present study was designed to test the hypothesis that alpha-tocopherol (Vit. E) and pyrrolidine dithiocarbamate (PDTC) might exert direct effects on alcohol-induced contractions of canine basilar cerebral arteries. After precontraction of arterial ring segments with ethanol, PDTC (10(-8)-10(-6) M) and Vit. E (10(-6)-10(-4) M) induced concentration-dependent relaxations of cerebral arteries, compared to untreated controls. The effective concentrations producing approximately 50% of the maximal relaxation responses (EC(50) values) were about 2.48+/-0.09 x 10(-7) M for PDTC, and 1.87+/-0.10 x 10(-5) mM for Vit. E, respectively. Preincubation of these arterial rings with EC(50)'s of PDTC or Vit. E for 40 min attenuate markedly the contractions produced by alcohol, at concentrations of 1-400 mM. However, both PDTC and Vit.E do not relax equi-potent precontractions induced by either KCl or prostaglandin F(2alpha) (PGF(2alpha)) or inhibit their contractions. These data suggest that alcohol-induced contractions of cerebral arteries are mediated via excitation-contraction coupling pathways different from those used by KCl or receptor-mediated agonists such as PGF(2alpha). The present results, when viewed in light of other recently published data, suggest that antioxidants may prove useful in the amelioration and treatment of alcohol-induced brain damage and strokes.

Oxidative stress and vascular smooth muscle cell function in liver disease

Reactive oxygen species and reactive nitroxy species are now being recognized as regulatory molecules in signaling pathways influencing contractile and noncontractile functions of healthy vascular smooth muscle cells. In liver disease, oxidative stress is a systemic phenomenon, whose extent correlates with the severity of disease. A role for oxidative stress in the development of the hyperdynamic circulation in portal hypertension has been proposed. Evaluation of the limited available data indicates that it is premature to conclude that oxidative stress per se impacts on vascular smooth muscle cell function in liver disease.

Mechanisms of hydrogen peroxide-induced relaxation in rabbit mesenteric small artery

The effects of hydrogen peroxide were studied on isolated rabbit mesenteric small artery; rabbit superior mesenteric artery and mouse aorta were also studied as reference tissues. For mesenteric small artery, hydrogen peroxide (1 to 100 microM) relaxed a norepinephrine-stimulated artery in a concentration-dependent manner. The relaxation was not significantly affected by removal of the endothelium and was less pronounced in arteries contracted with high-KCl solution plus norepinephrine than in those contracted with norepinephrine alone. The relaxation response to hydrogen peroxide was increased by isobutylmethylxanthine and zaprinast, inhibited by diclofenac, methylene blue and dithiothreitol and unaffected by atropine, tetraethylammonium, superoxide dismutase, deferoxamine, dimethyl sulfoxide or the Rp stereoisomer of adenosine cyclic monophosphothioate. Hydrogen peroxide shifted concentration-contractile response curves for norepinephrine to the right and downwards. Norepinephrine and caffeine elicited a transient, phasic contraction of the mesenteric small artery exposed for 0.5, 1 and 2 min to a Ca2+-free solution. Hydrogen peroxide inhibited the norepinephrine-induced contraction, and to a lesser extent the caffeine-induced contraction, and verapamil did not alter the contraction to norepinephrine. These pharmacological properties of hydrogen peroxide were similar to those of 8-bromo cGMP; 8-bromo cGMP inhibited more potently the norepinephrine-induced than the KCl-induced contraction and the contraction elicited by norepinephrine in Ca2+-free solution. The present results suggest that hydrogen peroxide induces endothelium-independent relaxation of the rabbit mesenteric small artery precontracted with norepinephrine. The effects of hydrogen peroxide may be at least in part mediated by cGMP and cyclooxygenase products in the vascular smooth muscles now used.

Mechanisms of cerebral arterial relaxations to hydrogen peroxide

BACKGROUND AND PURPOSE

The role of hydrogen peroxide in the regulation of cerebral arterial tone is not completely understood. Previous studies have demonstrated that hydrogen peroxide causes vasodilation of small cerebral arteries. The present study was designed to determine the mechanisms responsible for relaxations of large cerebral arteries to hydrogen peroxide.

METHODS

Rings of canine middle cerebral arteries without endothelium were suspended for isometric force recording in modified Krebs-Ringer bicarbonate solution bubbled with 94% O(2)/6% CO(2) (37 degrees C, pH 7.4). Radioimmunoassay technique was used to determine the levels of cAMP and cGMP.

RESULTS

During contraction to UTP (3 x 10(-6) or 10(-5) mol/L), hydrogen peroxide (10(-6) to 10(-4) mol/L) caused concentration-dependent relaxations. Catalase (1200 U/mL) abolished the relaxations to hydrogen peroxide. Inhibition of cyclooxygenase by indomethacin (10(-5) mol/L) significantly reduced relaxations to hydrogen peroxide. In arteries contracted by KCl (20 mmol/L), the relaxations to hydrogen peroxide were significantly reduced. In the presence of a nonselective potassium channel inhibitor, BaCl(2) (10(-4) mol/L), a delayed rectifier potassium channel inhibitor, 4-aminopyridine (10(-3) mol/L), or a calcium-activated potassium channel inhibitor, charybdotoxin (3 x 10(-8) mol/L), the relaxations to hydrogen peroxide were also significantly reduced. An ATP-sensitive potassium channel inhibitor, glyburide (5 x 10(-6) mol/L), did not affect the relaxations to hydrogen peroxide. Hydrogen peroxide produced concentration-dependent increase in levels of cAMP. Indomethacin (10(-5) mol/L) inhibited the stimulatory effect of hydrogen peroxide on cAMP production. In contrast, hydrogen peroxide did not affect the levels of cGMP.

CONCLUSIONS

These results suggest that hydrogen peroxide may cause relaxations of large cerebral arteries in part by activation of arachidonic acid metabolism via cyclooxygenase pathway with subsequent increase in cAMP levels and activation of potassium channels.

Pyrrolidine dithiocarbamate prevents ethanol-induced elevation of [Ca2+]i in cultured canine cerebral vascular smooth muscle cells

Pyrrolidine dithiocarbamate (PDTC) has been shown to block nuclear transcription factor (NF-kappaB) activation induced by a wide range of stimuli in different cell lines. NF-kappaB is a common element of the promoter region of inflammatory cytokines which can be stimulated by ethanol. Recently, we have shown that PDTC can ameliorate cerebrovascular damage, brain cortical damage, leukocyte adhesion and rolling, and stroke induced by ethanol. We, therefore, tested the effects of preincubation with PDTC on alcohol-induced changes in intracellular free calcium ions ([Ca2+]i) in cultured canine cerebral smooth muscle cells. These vascular cells, chronically treated with ethanol (10-100 mM) for 24 and 72 h, exhibited concentration-dependent rises in [Ca2+]i. PDTC (0.1 microM) itself failed to influence resting levels of [Ca2+]i in these vascular muscle cells. PDTC (0.1 microM) pretreatment, however, inhibited completely the elevations in [Ca2+]i induced by chronic ethanol (10-100 mM). The present results suggest that ethanol-induced production of reactive oxygen species and elevation of [Ca2+]i in cultured canine cerebral vascular smooth muscle cells triggers induction of transcription factor NF-kappaB, which could play an important role in alcohol-induced brain damage and stroke.