Zrinka Mihaljević

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.

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.

Acute Hyperbaric Oxygenation, Contrary to Intermittent Hyperbaric Oxygenation, Adversely Affects Vasorelaxation in Healthy Sprague-Dawley Rats due to Increased Oxidative Stress

The present study was aimed at assessing endothelium-dependent vasorelaxation, at measuring superoxide production in the aorta and femoral artery, and at determining antioxidative enzyme expression and activity in aortas of male Sprague-Dawley rats (N = 135), randomized to an A-HBO2 group exposed to a single hyperbaric oxygenation session (120′ of 100% O2 at 2.0 bars), a 24H-HBO2 group (single session, examined 24 h after exposure), a 4D-HBO2 group (4 consecutive days of single sessions), and a CTRL group (untreated group). Vasorelaxation of aortic rings in response to acetylcholine (AChIR) and to reduced pO2 (HIR) was tested in vitro in the absence/presence of NOS inhibitor L-NAME and superoxide scavenger TEMPOL. eNOS, iNOS, antioxidative enzyme, and NADPH oxidase mRNA expression was assessed by qPCR. Serum oxidative stress markers and enzyme activity were assessed by spectrometry, and superoxide production was determined by DHE fluorescence. Impaired AChIR and HIR in the A-HBO2 group were restored by TEMPOL. L-NAME inhibited AChIR in all groups. Serum oxidative stress and superoxide production were increased in the A-HBO2 group compared to all other groups. The mRNA expression of iNOS was decreased in the A-HBO2 and 24H-HBO2 groups while SOD1 and 3 and NADPH oxidase were increased in the 4D-HBO2 group. The expression and activity of catalase and glutathione peroxidase were increased in the 4D-HBO2 group as well. AChIR was NO dependent. Acute HBO2 transiently impaired vasorelaxation due to increased oxidative stress. Vasorelaxation was restored and oxidative stress was normalized 24 h after the treatment.

High salt intake shifts the mechanisms of flow-induced dilation in the middle cerebral arteries of Sprague-Dawley rats

The goal of the present study was to examine the effect of 1 wk of high salt (HS) intake and the role of oxidative stress in changing the mechanisms of flow-induced dilation (FID) in isolated pressurized middle cerebral arteries of male Sprague-Dawley rats ( n = 15-16 rats/group). Reduced FID in the HS group was restored by intake of the superoxide scavenger tempol (HS + tempol in vivo group). The nitric oxide (NO) synthase inhibitor Nω-nitro-l-arginine methyl ester, cyclooxygenase inhibitor indomethacin, and selective inhibitor of microsomal cytochrome P-450 epoxidase activity N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide significantly reduced FID in the low salt diet-fed group, whereas FID in the HS group was mediated by NO only. Cyclooxygenase-2 mRNA (but not protein) expression was decreased in the HS and HS + tempol in vivo groups. Hypoxia-inducible factor-1α and VEGF protein levels were increased in the HS group but decreased in the HS + tempol in vivo group. Assessment by direct fluorescence of middle cerebral arteries under flow revealed significantly reduced vascular NO levels and increased superoxide/reactive oxygen species levels in the HS group. These results suggest that HS intake impairs FID and changes FID mechanisms to entirely NO dependent, in contrast to the low-salt diet-fed group, where FID is NO, prostanoid, and epoxyeicosatrienoic acid dependent. These changes were accompanied by increased lipid peroxidation products in the plasma of HS diet-fed rats, increased vascular superoxide/reactive oxygen species levels, and decreased NO levels, together with increased expression of hypoxia-inducible factor-1α and VEGF. NEW & NOTEWORTHY High-salt (HS) diet changes the mechanisms of flow-induced dilation in rat middle cerebral arteries from a combination of nitric oxide-, prostanoid-, and epoxyeicosatrienoic acid-dependent mechanisms to, albeit reduced, a solely nitric oxide-dependent dilation. In vivo reactive oxygen species scavenging restores flow-induced dilation in HS diet-fed rats and ameliorates HS-induced increases in the transcription factor hypoxia-inducible factor-1α and expression of its downstream target genes.