Hyperoxic gassing with Tiron enhances bradykinin-induced endothelium-dependent and EDH-type relaxation through generation of hydrogen peroxide

Vasodilator reactive oxygen species ameliorate perturbed myocardial oxygen delivery in exercising swine with multiple comorbidities

Multiple common cardiovascular comorbidities produce coronary microvascular dysfunction. We previously observed in swine that a combination of diabetes mellitus (DM), high fat diet (HFD) and chronic kidney disease (CKD) induced systemic inflammation, increased oxidative stress and produced coronary endothelial dysfunction, altering control of coronary microvascular tone via loss of NO bioavailability, which was associated with an increase in circulating endothelin (ET). In the present study, we tested the hypotheses that (1) ROS scavenging and (2) ETA+B-receptor blockade improve myocardial oxygen delivery in the same female swine model. Healthy female swine on normal pig chow served as controls (Normal). Five months after induction of DM (streptozotocin, 3 × 50 mg kg-1 i.v.), hypercholesterolemia (HFD) and CKD (renal embolization), swine were chronically instrumented and studied at rest and during exercise. Sustained hyperglycemia, hypercholesterolemia and renal dysfunction were accompanied by systemic inflammation and oxidative stress. In vivo ROS scavenging (TEMPOL + MPG) reduced myocardial oxygen delivery in DM + HFD + CKD swine, suggestive of a vasodilator influence of endogenous ROS, while it had no effect in Normal swine. In vitro wire myography revealed a vasodilator role for hydrogen peroxide (H2O2) in isolated small coronary artery segments from DM + HFD + CKD, but not Normal swine. Increased catalase activity and ceramide production in left ventricular myocardial tissue of DM + HFD + CKD swine further suggest that increased H2O2 acts as vasodilator ROS in the coronary microvasculature. Despite elevated ET-1 plasma levels in DM + HFD + CKD swine, ETA+B blockade did not affect myocardial oxygen delivery in Normal or DM + HFD + CKD swine. In conclusion, loss of NO bioavailability due to 5 months exposure to multiple comorbidities is partially compensated by increased H2O2-mediated coronary vasodilation.

Myoendothelial feedback in mouse mesenteric resistance arteries is similar between the sexes, dependent on nitric oxide synthase, and independent of TPRV4

Myoendothelial feedback (MEF), the endothelium-dependent vasodilation following sympathetic vasoconstriction (mediated by smooth muscle to endothelium gap junction communication), has been well studied in resistance arteries of males, but not females. We hypothesized that MEF responses would be similar between the sexes, but different in the relative contribution of the underlying nitric oxide and hyperpolarization mechanisms, given that these mechanisms differ between the sexes in agonist-induced endothelium-dependent dilation. We measured MEF responses (diameter changes) of male and female first- to second-order mouse mesenteric arteries to phenylephrine (10 µM) over 30 min using isolated pressure myography ± blinded inhibition of nitric oxide synthase (NOS) using Nω-nitro-l-arginine methyl ester (l-NAME; 0.1-1.0 mM), hyperpolarization using 35 mM KCl, or transient receptor potential vanilloid 4 (TRPV4) channels using GSK219 (0.1-1.0 µM) or RN-1734 (30 µM). MEF was similar [%dilation (means ± SE): males = 26.7 ± 2.0 and females = 26.1 ± 1.9 at 15 min] and significantly inhibited by l-NAME (1.0 mM) at 15 min [%dilation (means ± SE): males = 8.2 ± 3.3, P < 0.01; females = 6.8 ± 1.9, P < 0.001] and over time (P < 0.01) in both sexes. l-NAME (0.1 mM) + 35 mM KCl nearly eliminated MEF in both sexes (P < 0.001-0.0001). Activation of TRPV4 with GSK101 (0.1-10 µM) induced similar dilation between the sexes. Inhibition of TRPV4, which is reportedly involved in the hyperpolarization mechanism, did not inhibit MEF in either sex. Similar expression of eNOS was found between the sexes with Western blot. Thus, MEF is prominent and similar in murine first- and second-order mesenteric resistance arteries of both sexes, and reliant primarily on NOS and secondarily on hyperpolarization, but not TRPV4.NEW & NOTEWORTHY We found that female mesenteric resistance arteries have similar postconstriction dilatory responses (i.e., myoendothelial feedback) to a sympathetic neurotransmitter analog as male arteries. Both sexes use nitric oxide synthase (NOS) and hyperpolarization, but not TRPV4, in this response. Moreover, the key protein involved in this pathway (eNOS) is similarly expressed in these arteries between the sexes. These similarities are surprising given that agonist-induced endothelium-dependent dilatory mechanisms differ in these arteries between the sexes.

Mechanisms mediating the vasodilatory effects of juglone in porcine isolated coronary artery

Juglone (5-hydroxy-1, 4-naphthoquinone), is a natural phenolic compound that has been shown to relax smooth muscle. Therefore the aim of this study was to determine the effect of juglone on vascular tone using porcine coronary artery (PCA). Segments of PCA, with or without endothelium, were mounted for isometric tension recording in isolated tissue baths and precontracted with the thromboxane A₂ analog U46619 or KCl. After pre-contraction, cumulative concentrations of juglone were added to the tissues, in the presence or absence of a variety of inhibitors on intracellular signaling pathways. Juglone (10^-9 to 10^-5 M) produced a concentration-dependent relaxation of the PCA which was reduced in endothelium-denuded vessels, as well as in vessels pre-treated with the nitric oxide synthase inhibitor L-NAME, indicating that at least part of the effect of juglone is mediated through an endothelium, NO-dependent mechanism. Juglone also inhibited contractions in response to influx of extracellular calcium and release of intracellular calcium, indicating that juglone may inhibit a common signaling pathway downstream of calcium. Contractions to the protein kinase C activator Phorbol 12-myristate 13-acetate were also reduced by juglone, suggesting that juglone might be acting through inhibition of protein kinase C. In summary, juglone produces a relaxation of the porcine coronary artery through activation of the nitric oxide pathway and inhibition of calcium-induced contractions.

Hyperoxia does not directly affect vascular tone in isolated arteries from mice

Hospitalized patients often receive oxygen supplementation, which can lead to a supraphysiological oxygen tension (hyperoxia). Hyperoxia can have hemodynamic effects, including an increase in systemic vascular resistance. This increase suggests hyperoxia-induced vasoconstriction, yet reported direct effects of hyperoxia on vessel tone have been inconsistent. Furthermore, hyperoxia-induced changes in vessel diameter have not been studied in mice, currently the most used mammal model of disease. In this study we set out to develop a pressure-myograph model using isolated vessels from mice for investigation of pathways involved in hyperoxic vasoconstriction. Isolated conduit and resistance arteries (femoral artery and gracilis arteriole, respectively) from C57BL/6 mice were exposed to normoxia (PO₂ of 80 mmHg) and three levels of hyperoxia (PO₂ of 215, 375 and 665 mmHg) in a no-flow pressure myograph setup. Under the different PO₂ levels, dose-response agonist induced endothelium-dependent vasodilation (acetylcholine, arachidonic acid), endothelium-independent vasodilation (s-nitroprusside), as well as vasoconstriction (norepinephrine, prostaglandin F2α) were examined. The investigated arteries did not respond to oxygen by a change in vascular tone. In the dose-response studies, maximal responses and EC50 values to any of the aforementioned agonists were not affected by hyperoxia either. We conclude that arteries and arterioles from healthy mice are not intrinsically sensitive to hyperoxic conditions. The present ex-vivo model is therefore not suitable for further research into mechanisms of hyperoxic vasoconstriction.

Reproductive toxicity provoked by titanium dioxide nanoparticles and the ameliorative role of Tiron in adult male rats

Titanium dioxide nanoparticles (TDN) are widely used in paints, plastics, ceramics, cosmetics, printing ink, rubber and paper. Tiron is a water soluble metal chelator and antioxidant. This study was designed to investigate the reproductive toxicity of TDN in male albino rats and the ameliorative role of Tiron to minimize such toxic effects. Eighty adult male albino rats were assigned into 4 equal groups, group 1: control; group 2: received TDN at 100 mg/kg/day orally for 8 weeks; group 3: received Tiron at 470 mg/kg/day intraperitoneally for 2 weeks (the last 2 weeks of the experimental period); group 4: received both TDN and Tiron by the same previously mentioned dose, route and duration. The results revealed that TDN provoked reproductive toxicity which was proved by the deteriorated spermogram picture, high incidence of micronucleated RBCs, elevated oxidative stress parameters and up regulation of Testin gene. Whereas, Tiron co-treatment ameliorated most of these toxic alterations. Our findings highlighted the protective role of tiron against TDN intoxication.

Internal Pudental Artery Dysfunction in Diabetes Mellitus Is Mediated by NOX1-Derived ROS-, Nrf2-, and Rho Kinase-Dependent Mechanisms

Oxidative stress plays an important role in diabetes mellitus (DM)-associated vascular injury. DM is an important risk factor for erectile dysfunction. Functional and structural changes in internal pudendal arteries (IPA) can lead to erectile dysfunction. We hypothesized that downregulation of nuclear factor E2-related factor 2 (Nrf2), consequent to increased nicotinamide adenine dinucleotide phosphate oxidase 1 (NOX1)-derived reactive oxygen species (ROS), impairs IPA function in DM. IPA and vascular smooth muscle cells from C57BL/6 (control) and NOX1 knockout mice were used. DM was induced by streptozotocin in C57BL/6 mice. Functional properties of IPA were assessed using a myograph, protein expression and peroxiredoxin oxidation by Western blot, RNA expression by polymerase chain reaction, carbonylation by oxyblot assay, ROS generation by lucigenin, nitrotyrosine, and amplex red, and Rho kinase activity and nuclear accumulation of Nrf2 by ELISA. IPA from diabetic mice displayed increased contractions to phenylephrine (control 138.5±9.5 versus DM 191.8±15.5). ROS scavenger, Nrf2 activator, NOX1 and Rho kinase inhibitors normalized vascular function. High glucose increased ROS generation in IPA vascular smooth muscle cell. This effect was abrogated by Nrf2 activation and not observed in NOX1 knockout vascular smooth muscle cell. High glucose also increased levels of nitrotyrosine, protein oxidation/carbonylation, and Rho kinase activity, but reduced Nrf2 activity and expression of Nrf2-regulated genes (catalase [25.6±0.05%], heme oxygenase-1 [21±0.1%], and

NAD(P)H

quinone oxidoreductase 1 [22±0.1%]) and hydrogen peroxide levels. These effects were not observed in vascular smooth muscle cell from NOX1 knockout mice. In these cells, high glucose increased hydrogen peroxide levels. In conclusion, Rho kinase activation, via NOX1-derived ROS and downregulation of Nrf2 system, impairs IPA function in DM. These data suggest that Nrf2 is vasoprotective in DM-associated erectile dysfunction.