Anita Ćosić

The role of cyclo-oxygenase-1 in high-salt diet-induced microvascular dysfunction in humans.

Recent studies have shown that some of the deleterious effects of a high‐salt (HS) diet are independent of elevated blood pressure and are associated with impaired endothelial function. Increased generation of cyclo‐oxygenase (COX‐1 and COX‐2)‐derived vasoconstrictor factors and endothelial activation may contribute to impaired vascular relaxation during HS loading. The present study aimed to assess the regulation of microvascular reactivity and to clarify the role of COX‐1 and COX‐2 in normotensive subjects on a short‐term HS diet. The present study demonstrates the important role of COX‐1 derived vasoconstrictor metabolites in regulation of microvascular blood flow during a HS diet. These results help to explain how even short‐term HS diets may impact upon microvascular reactivity without changes in blood pressure and suggest that a vasoconstrictor metabolite of COX‐1 could play a role in this impaired tissue blood flow.

Hyperbaric oxygenation modulates vascular reactivity to angiotensin-(1-7) in diabetic rats: potential role of epoxyeicosatrienoic acids.

Previously, a facilitating effect of hyperbaric oxygenation (HBO2) on aortic ring responses to angiotensin-(1-7) in healthy rats was reported, with epoxyeicosatrienoic acids (EETs) possibly playing an important role. The aim of this study was to assess whether HBO2 exerts similar effects in diabetic rats and to further explore the role of specific cytochrome P450 (CYP) enzymes in changes induced by HBO2. Aortic relaxation to angiotensin-(1-7) was significantly higher in HBO2 diabetic rats compared to control diabetic rats, while HBO2 had no effect on angiotensin II contraction. N-methylsulphonyl-6-(2-propargyloxyphenyl/hexanamide inhibited the facilitation of angiotensin-(1-7) responses in HBO2 rats, suggesting an important role of EETs in this modulation. mRNA expression of CYP2J3 and protein expression of CYP2C11 were significantly upregulated in HBO2 diabetic rats, whereas CYP4A1, CYP4A2 and CYP4A3 mRNA and CYP2J3 protein expression was similar between groups. Mean arterial pressure, ferric reducing ability of plasma and Thiobarbituric Acid Reactive Substances levels and serum angiotensin-(1-7) concentrations were not significantly changed.

Attenuated flow-induced dilatation of middle cerebral arteries is related to increased vascular oxidative stress in rats on a short-term high salt diet.

Recent studies have shown that high salt (HS) intake leads to endothelial dysfunction and impaired vascular reactivity in different vascular beds in both animal and human models, due to increased oxidative stress. The objective of this study was to assess vascular response to flow‐induced dilatation (FID) and to elucidate the role of vascular oxidative stress/antioxidative capacity in middle cerebral arteries (MCAs) of HS‐fed rats in vitro. The novelty of this study is in demonstrating impaired flow‐induced dilatation of MCAs and down‐regulation of vascular antioxidant genes with HS intake, leading to increased levels of oxidative stress in blood vessels and peripheral lymph organs, which together contribute to impaired FID. In addition, results show increased oxidative stress in leukocytes of peripheral lymph organs, suggesting the occurrence of inflammatory processes due to HS intake. Recirculation of leukocytes might additionally increase vascular oxidative stress in vivo.

Effects of AT1 receptor blockade on plasma thromboxane A2 (TXA2) level and skin microcirculation in young healthy women on low salt diet.

Objective: To determine the effect of AT1 receptor antagonism on skin microcirculation and plasma level of thromboxane A2 (TXA2). Methods: Healthy women (n=20) maintained 7 days low salt (LS) diet (intake <40 mmol Na/day) without (LS) or together with 50 mg/per day of losartan (a selective AT1 receptor inhibitor) (LS diet+losartan group). Laser Doppler flowmetry (LDF) measurements of changes in post occlusive hyperemic blood flow, plasma concentration of stable TXA2 metabolite thromboxane B2 (TXB2) and plasma renin activity (PRA) aldosterone concentration, electrolytes (Na+, K+), as well as blood pressure and heart rate were determined before and after study protocols. Results: PRA and aldosterone increased significantly after 7 days of both LS diet and LS diet+losartan. LS diet or LS diet+losartan administrations had no significant effect on post-occlusion hyperemia While there was no change in TXB2 after LS diet TXB2 significantly increased after one week of LS+losartan compared to control levels (cTXB2 pg/mL control 101±80 vs. LS diet+losartan 190±116, p<0.05). Conclusion: These data suggest that inhibition of AT1 receptors could lead to activation of AT2 receptors, which maintain hyperemia, despite the increased level of vasoconstrictor TXA2. These findings also suggest an important role of crosstalk between renin-angiotensin system (RAS) and arachidonic acid metabolites in the regulation of microcirculation under physiological conditions.

Reduced Dietary Selenium Impairs Vascular Function by Increasing Oxidative Stress in Sprague-Dawley Rat Aortas

This study aimed to determine whether low dietary Se content affects the function and mechanisms mediating the vascular relaxation of rat aortas, and to test the role of oxidative stress in observed differences. Male Sprague Dawley (SD) rats were maintained for 10 weeks on low Se (low-Se group; N = 20) or normal Se content (norm-Se group; N = 20) rat chow. Dose responses to acetylcholine (ACh; 10−9–10−5M) and the response to reduced pO2 were tested in noradrenaline-precontracted aortic rings in the absence/presence of the nitric oxide synthase (NOS) inhibitor nitro-l-arginine methyl ester (l-NAME), the cyclooxygenase 1 and 2 (COX-1, 2) inhibitor Indomethacin, and the antioxidative agent Tempol in tissue bath. mRNA expression of glutathione peroxidase 1 (GPx1), catalase (CAT), and Cu/Zn superoxide dismutase (SOD) was measured in rat aortas. Oxidative stress (Thiobarbituric Acid Reactive Substances; TBARS), antioxidative plasma capacity (ferric reducing ability of plasma assay; FRAP), and protein levels of GPx1 were measured in plasma and serum samples, respectively. Reduced ACh-induced relaxation (AChIR) (dominantly mediated by NO) in the low-Se group compared to the norm-Se group was restored by Tempol administration. Hypoxia-induced relaxation (HIR) (dominantly mediated by COX-1, 2), TBARS, and FRAP as well as GPx1 serum concentrations were similar between the groups. mRNA GPx1 expression in rat aortas was significantly decreased in the low-Se compared to the norm-Se group. These data suggest that low dietary Se content increases the local oxidative stress level, which subsequently affects the NO-mediated vascular response.

Hyperbaric oxygenation and 20- hydroxyeicosatetreanoic acid inhibition reduce stroke volume in female diabetic Sprague–Dawley rats

What is the central question of this study? Is there a beneficial effect and what are the mechanisms of acute and multiple hyperbaric oxygenation (HBO2) exposures on the outcome of cerebral tissue injury induced by a transient middle cerebral artery occlusion model in diabetic female rats? Are 20‐hydroxyeicosatetreanoic acid and epoxyeicosatrienoic acids involved? What is the main finding and its importance? Equal reduction of cortical and total infarct size in rats treated with HBO2 and HET0016 (20‐hydroxyeicosatetreanoic acid production inhibitor) and significant mRNA upregulation of epoxyeicosatrienoic acid‐producing enzymes (Cyp2J3 and Cyp2C11) in treated groups suggest that HBO2 and HET0016 are highly effective stroke treatments and that cytochrome P450 metabolites are involved in this therapeutic effect.

Anti-Inflammatory Effects of Hyperbaric Oxygenation during DSS-Induced Colitis in BALB/c Mice Include Changes in Gene Expression of HIF-1α, Proinflammatory Cytokines, and Antioxidative Enzymes

Reactive oxygen species (ROS) and nitrogen species have an indispensable role in regulating cell signalling pathways, including transcriptional control via hypoxia inducible factor-1α (HIF-1α). Hyperbaric oxygenation treatment (HBO2) increases tissue oxygen content and leads to enhanced ROS production. In the present study DSS-induced colitis has been employed in BALB/c mice as an experimental model of gut mucosa inflammation to investigate the effects of HBO2 on HIF-1α, antioxidative enzyme, and proinflammatory cytokine genes during the colonic inflammation. Here we report that HBO2 significantly reduces severity of DSS-induced colitis, as evidenced by the clinical features, histological assessment, impaired immune cell expansion and mobilization, and reversal of IL-1β, IL-2, and IL-6 gene expression. Gene expression and antioxidative enzyme activity were changed by the HBO2 and the inflammatory microenvironment in the gut mucosa. Strong correlation of HIF-1α mRNA level to GPx1, SOD1, and IL-6 mRNA expression suggests involvement of HIF-1α in transcriptional regulation of these genes during colonic inflammation and HBO2. This is further confirmed by a strong correlation of HIF-1α with known target genes VEGF and PGK1. Results demonstrate that HBO2 has an anti-inflammatory effect in DSS-induced colitis in mice, and this effect is at least partly dependent on expression of HIF-1α and antioxidative genes.

Hyperbaric oxygenation and 20‐HETE inhibition reduce stroke volume in female diabetic Sprague–Dawley rats

What is the central question of this study? Is there a beneficial effect and what are the mechanisms of acute and multiple hyperbaric oxygenation (HBO2) exposures on the outcome of cerebral tissue injury induced by a transient middle cerebral artery occlusion model in diabetic female rats? Are 20‐hydroxyeicosatetreanoic acid and epoxyeicosatrienoic acids involved? What is the main finding and its importance? Equal reduction of cortical and total infarct size in rats treated with HBO2 and HET0016 (20‐hydroxyeicosatetreanoic acid production inhibitor) and significant mRNA upregulation of epoxyeicosatrienoic acid‐producing enzymes (Cyp2J3 and Cyp2C11) in treated groups suggest that HBO2 and HET0016 are highly effective stroke treatments and that cytochrome P450 metabolites are involved in this therapeutic effect.

The Metabolites of Arachidonic Acid in Microvascular Function

Arachidonic acid (AA) metabolites have an important role in mediating vascular reactivity to various stimuli, affecting tissue perfusion and tissue supply. In addition, they exert proinflammatory or anti‐inflammatory effects on vessels. AA is metabolized by cyclooxygenases (COX) 1 and 2 to prostaglandins (PGs) and thromboxane (TX), by lipooxygenase to leukotrienes; by cytochrome P450 (CYP450)‐hydroxylase to 20‐ hydroxyeicosatetraenoic acid (20‐HETE) and by CYP450‐epoxygenase to epoxyeicosa‐ trienoic acids (EETs). Increased vascular oxidative stress may induce non‐enzymatic production of isoprostanes from AA, which, together with vasoconstrictor metabolites of AA underlie endothelial damage and impaired vascular function. The balance among vasodilator and vasoconstrictor metabolites of AA may be disturbed in cardiometabolic diseases. (e.g. hypertension,obesity,diabetes) Dietary habits significantly affect the metabolism of AA, particularly excessive kitchen salt (NaCl) intake. Control of environmental risks factors, good maintenance of the occurring diseases and balanced nutrition with restricted salt intake can significantly improve the metabolism of AA and alleviate microvascular dysfunction and subsequent organ damage. Current research on pharmacological manipulation of certain components of the AA pathways (such as 20‐HETE production inhibition or prolongation of the life of epoxyeicoatrienoic acids(EETs) by inhibitors of soluble epoxide hydrolaze (sEH)promises effective therapy of cardiovascular and cerebrovascular diseases in the future.

Urodilatin reverses the detrimental influence of bradykinin in acute ischemic stroke

Occlusion of cerebral arteries leads to ischemic stroke accompanied by subsequent brain edema. Bradykinin (BK) is involved in the formation of cerebral edema, and natriuretic peptides (NPs) potentially have beneficial effects on brain edema formation via a still unknown mechanism. The aim of this study was clarifying the mechanisms of action of NPs on BK signaling, and their interactive effects after ischemic brain injury. We used a mouse model for stroke, the middle cerebral artery (MCA) occlusion. Brain lesion and edema were measured by microcomputerized tomography volumetric measurements. To determine the effects of NPs on the BK signaling pathway in the MCAs we measured changes in vessel diameter and membrane potentials in endothelial cells. To determine the effects of NPs on BK signaling pathway in isolated astrocytes and neurons, membrane potentials and intercellular Ca2+ concentrations were measured. Urodilatin inhibited and when applied together with BK, reduced the formation of the ischemic lesion via activation of G-Protein-Signaling Protein Type 4 at the cellular (atrocities, neurons) and blood vessel (endothelial cells and isolated MCA) level as well as in in vivo experiments. The results of this study show the existence of a natural antagonist of BK in the brain, and the possible use of NPs in the treatment of stroke.