Histamine H2-receptor antagonism improves conduit artery endothelial function and reduces plasma aldosterone level without lowering arterial blood pressure in angiotensin II-hypertensive mice.

Aldosterone through the mineralocorticoid receptor MR has detrimental effects on cardiovascular disease. It reduces the bioavailability of nitric oxide and impairs endothelium-dependent vasodilatation. In resistance arteries, aldosterone impairs the sensitivity of vascular smooth muscle cells to nitric oxide by promoting the local secretion of histamine which activates H2 receptors. The present experiments tested in vivo and ex vivo the hypothesis that systemic H2-receptor antagonism reduces arterial blood pressure and improves vasodilatation in angiotensin II-induced chronic hypertension. Hypertension was induced by intravenous infusion of angiotensin II (60 ng kg-1 min-1) in conscious, unrestrained mice infused concomitantly with the H2-receptor antagonist ranitidine (27.8 µg kg-1 min-1) or vehicle for 24 days. Heart rate and arterial blood pressure were recorded by indwelling arterial catheter. Resistance (mesenteric) and conductance (aortae) arteries were harvested for perfusion myography and isometric tension recordings by wire myography, respectively. Plasma was analyzed for aldosterone concentration. ANGII infusion resulted in elevated arterial blood pressure and while in vivo treatment with ranitidine reduced plasma aldosterone concentration, it did not reduce blood pressure. Ranitidine improved ex vivo endothelial function (acetylcholine 10-9 to 10-6 mol L-1) in mesenteric resistance arteries. This was abolished by ex vivo treatment with aldosterone (10-9 mol L-1, 1 h). In aortic segments, in vivo ranitidine treatment impaired relaxation. Activation of histamine H2 receptors promotes aldosterone secretion, does not affect arterial blood pressure, and protects endothelial function in conduit arteries but promotes endothelial dysfunction in resistance arteries during angiotensin II-mediated hypertension. Aldosterone contributes little to angiotensin II-induced hypertension in mice.

TNFα induces endothelial dysfunction in rheumatoid arthritis via LOX-1 and arginase 2: reversal by monoclonal TNFα antibodies.

AIMS: Rheumatoid arthritis (RA) is a chronic inflammatory disease affecting joints and blood vessels. Despite low levels of low-density lipoprotein cholesterol (LDL-C), RA patients exhibit endothelial dysfunction and are at increased risk of death from cardiovascular complications, but the molecular mechanism of action is unknown. We aimed in the present study to identify the molecular mechanism of endothelial dysfunction in a mouse model of RA and in patients with RA. METHODS AND RESULTS: Endothelium-dependent relaxations to acetylcholine were reduced in aortae of two tumour necrosis factor alpha (TNFα) transgenic mouse lines with either mild (Tg3647) or severe (Tg197) forms of RA in a time- and severity-dependent fashion as assessed by organ chamber myograph. In Tg197, TNFα plasma levels were associated with severe endothelial dysfunction. LOX-1 receptor was markedly up-regulated leading to increased vascular oxLDL uptake and NFκB-mediated enhanced Arg2 expression via direct binding to its promoter resulting in reduced NO bioavailability and vascular cGMP levels as shown by ELISA and chromatin immunoprecipitation. Anti-TNFα treatment with infliximab normalized endothelial function together with LOX-1 and Arg2 serum levels in mice. In RA patients, soluble LOX-1 serum levels were also markedly increased and closely related to serum levels of C-reactive protein. Similarly, ARG2 serum levels were increased. Similarly, anti-TNFα treatment restored LOX-1 and ARG2 serum levels in RA patients. CONCLUSIONS: Increased TNFα levels not only contribute to RA, but also to endothelial dysfunction by increasing vascular oxLDL content and activation of the LOX-1/NFκB/Arg2 pathway leading to reduced NO bioavailability and decreased cGMP levels. Anti-TNFα treatment improved both articular symptoms and endothelial function by reducing LOX-1, vascular oxLDL, and Arg2 levels.

Natriuretic peptides relax human intrarenal arteries through natriuretic peptide receptor type-A recapitulated by soluble guanylyl cyclase agonists.

AIM: Natriuretic peptides, BNP and ANP increase renal blood flow in experimental animals. The signalling pathway in human kidney vasculature is unknown. It was hypothesized that BNP and ANP cause endothelium-independent relaxation of human intrarenal arteries by vascular natriuretic peptide receptor-A, but not -B and -C, which is mimicked by agonists of soluble guanylyl cyclase sGC. METHODS: Human (n = 54, diameter: 665 ± 29 µm 95% CI) and control murine intrarenal arteries (n = 83, diameter 300 ± 6 µm 95% CI) were dissected and used for force recording by four-channel wire myography. Arterial segments were pre-contracted, then subjected to increasing concentrations of BNP, ANP, phosphodiesterase 5-inhibitor sildenafil, sGC-activator BAY 60-2770 and -stimulator BAY 41-2272. Endothelial nitric oxide synthase (eNOS) dependence was examined by use of L-NAME and eNOS knockout respectively. Molecular targets (NPR A-C, sGC, phosphodiesterase-5 and neprilysin) were mapped by PCR, immunohistochemistry and RNAscope. RESULTS: BNP, ANP, sildenafil, sGC-activation and -stimulation caused concentration-dependent relaxation of human and murine intrarenal arteries. BNP responses were independent of eNOS and were not potentiated by low concentration of phosphodiesterase-5-inhibitor, sGC-stimulator or NPR-C blocker. PCR showed NPR-A and C, phosphodiesterase-5, neprilysin and sGC mRNA in renal arteries. NPR-A mRNA and protein was observed in vascular smooth muscle and endothelial cells in arteries, podocytes, Bowmans capsule and vasa recta. NPR-C was observed in tubules, glomeruli and vasculature. CONCLUSION: Activation of transmembrane NPR-A and soluble guanylyl cyclase relax human preglomerular arteries similarly to phosphodiestase-5 inhibition. The human renal arterial bed relaxes in response to cGMP pathway.

Major histocompatibility complexes are up-regulated in glomerular endothelial cells via activation of c-Jun N-terminal kinase in 5/6 nephrectomy mice.

BACKGROUND AND PURPOSE: This study aims to explore the mechanism underlying the up-regulation of major histocompatibility complex (MHC) proteins in glomerular endothelial cells in 5/6 nephrectomy mice. EXPERIMENTAL APPROACH: C57/BL6 mice were randomly allocated to sham-operated (2K) and 5/6 nephrectomy (5/6Nx) groups. Mouse splenic lymphocytes, from either syngeneic or allogeneic background, were injected into 5/6Nx mice after total body irradiation. Human glomerular endothelial cells (HGECs) were cultured for experiments in vitro. Western blots, PCR, immunohistochemical and fluorescent staining were used, along with assays of tissue cytokines, lymphocyte migration and renal function. KEY RESULTS: Four weeks after nephrectomy, expression of both mRNA and protein of MHC II, CD80, and CD86 were increased in 5/6Nx glomerular endothelial cells. After total body irradiation, 5/6Nx mice injected with lymphocytes from Balb/c mice, but not those from C57/BL6 mice, exhibited increased creatinine levels, indicating that allograft lymphocyte transfer impaired renal function. In HGECs, the protein levels of MHC and MHC Class II transactivator (CIITA) were increased by stimulation with TNF-α or IFN-γ, which promoted human lymphocytes movement. These increases were reduced by JNK inhibitors. In the 5/6Nx mice, JNK inhibition down-regulated MHC II protein in glomerular endothelial cells, suggesting that JNK signalling participates in the regulation of MHC II protein. CONCLUSION AND IMPLICATIONS: Chronic inflammation in mice subjected to nephrectomy induces the up-regulation of MHC molecules in glomerular endothelial cells. This up-regulation is reduced by inhibition of JNK signalling.

The NO-donor MPC-1011 stimulates angiogenesis and arteriogenesis and improves hindlimb ischemia via a cGMP-dependent pathway involving VEGF and SDF-1α.

BACKGROUND AND AIMS: Peripheral arterial disease (PAD) is an important cause of morbidity and mortality with little effective medical treatment currently available. Nitric oxide (NO) is crucially involved in organ perfusion, tissue protection and angiogenesis. METHODS: We hypothesized that a novel NO-donor, MPC-1011, might elicit vasodilation, angiogenesis and arteriogenesis and in turn improve limb perfusion, in a hindlimb ischemia model. Hindlimb ischemia was induced by femoral artery ligation in Sprague-Dawley rats, which were randomized to receive either placebo, MPC-1011, cilostazol or both, up to 28 days. Limb blood flow was assessed by laser Doppler imaging. RESULTS: After femoral artery occlusion, limb perfusion in rats receiving MPC-1011 alone or in combination with cilostazol was increased throughout the treatment regimen. Capillary density and the number of arterioles was increased only with MPC-1011. MPC-1011 improved vascular remodeling by increasing luminal diameter in the ischemic limb. Moreover, MPC-1011 stimulated the release of proangiogenic cytokines, including VEGF, SDF1α and increased tissue cGMP levels, reduced platelet activation and aggregation, potentiated proliferation and migration of endothelial cells which was blunted in the presence of soluble guanylyl cyclase inhibitor LY83583. In MPC-1011-treated rats, Lin-/CD31+/CXCR4+ cells were increased by 92.0% and Lin-/VEGFR2+/CXCR4+ cells by 76.8% as compared to placebo. CONCLUSIONS: Here we show that the NO donor, MPC-1011, is a specific promoter of angiogenesis and arteriogenesis in a hindlimb ischemia model in an NO-cGMP-VEGF- dependent manner. This sets the basis to evaluate and confirm the efficacy of such therapy in a clinical setting in patients with PAD and impaired limb perfusion.

Adipocyte fatty acid-binding protein exacerbates cerebral ischaemia injury by disrupting the blood-brain barrier.

AIMS: Adipocyte fatty acid-binding protein (A-FABP) is an adipokine implicating in various metabolic diseases. Elevated circulating levels of A-FABP correlate positively with poor prognosis in ischaemic stroke (IS) patients. No information is available concerning the role of A-FABP in the pathogenesis of IS. Experiments were designed to determine whether or not A-FABP mediates blood-brain barrier (BBB) disruption, and if so, to explore the molecular mechanisms underlying this deleterious effects. METHODS AND RESULTS: Circulating A-FABP and its cerebral expression were increased in mice after middle cerebral artery occlusion. Genetic deletion and pharmacological inhibition of A-FABP alleviated cerebral ischaemia injury with reduced infarction volume, cerebral oedema, neurological deficits, and neuronal apoptosis; BBB disruption was attenuated and accompanied by reduced degradation of tight junction proteins and induction of matrix metalloproteinases-9 (MMP-9). In patients with acute IS, elevated circulating A-FABP levels positively correlated with those of MMP-9 and cerebral infarct volume. Mechanistically, ischaemia-induced elevation of A-FABP selectively in peripheral blood monocyte-derived macrophages and cerebral resident microglia promoted MMP-9 transactivation by potentiating JNK/c-Jun signalling, enhancing degradation of tight junction proteins and BBB leakage. The detrimental effects of A-FABP were prevented by pharmacological inhibition of MMP-9. CONCLUSION: A-FABP is a key mediator of cerebral ischaemia injury promoting MMP-9-mediated BBB disruption. Inhibition of A-FABP is a potential strategy to improve IS outcome.

Deficiency of T-type voltage-gated calcium channels results in attenuated weight gain and improved endothelium-dependent dilatation of resistance vessels induced by a high-fat diet in mice.

The deletion of T-type Cav3.1 channels may reduce high-fat diet (HFD)-induced weight gain, which correlates positively with obesity and endothelial dysfunction. Therefore, experiments were designed to study the involvement of T-type Cav3.1 channels in HFD-induced endothelial dysfunction in mice. Wildtype (WT) and Cav3.1-/- mice were fed either a normal diet (ND) or an HFD for 8 weeks. Body composition was assessed, and thoracic aortae and mesenteric arteries were harvested for myography to assess endothelium-dependent responses. Changes in intracellular calcium were measured by fluorescence imaging, and behavior was assessed with the open-field test. Cav3.1-/- mice had attenuated HFD-induced weight gain and lower total fat mass compared with WT mice. Cav3.1-/- mice on an HFD had reduced plasma cholesterol levels compared with WT mice on the same diet. Increased feeding efficiency, independent of food intake, was observed in WT mice on an HFD compared with an ND, but no difference in feeding efficiency between diets was observed for Cav3.1-/- mice. Nitric oxide-dependent dilatation was increased in mesenteric arteries of Cav3.1-/- mice compared with WT mice on an HFD, with no difference observed in aortae. No differences in mouse locomotor activity were observed between the experimental groups. Mice on an HFD lacking T-type channels have reduced weight gain, lower total cholesterol levels, and increased dilatation of resistance vessels compared with WT mice on an HFD, suggesting that Cav3.1 deletion protects against endothelial dysfunction in resistance vessels but not in large conduit vessels.

Cardiomyocyte-Specific JunD Overexpression Increases Infarct Size following Ischemia/Reperfusion Cardiac Injury by Downregulating Sirt3.

Ischemia/reperfusion (I/R) injury in acute myocardial infarction activates several deleterious molecular mechanisms. The transcription factor JunD regulates pathways involved in oxidative stress as well as in cellular proliferation, differentiation, and death. The present study investigated the potential role of JunD as a modulator of myocardial injury pathways in a mouse model of cardiac I/R injury. Infarct size, systemic and local inflammation, and production of reactive oxygen species, as well as cytosolic and mitochondrial apoptotic pathways were investigated in adult males after myocardial I/R. In wild-type (WT) mice, 30 minutes after ischemia and up to 24 hours following reperfusion, cardiac JunD messenger ribonucleic acid expression was reduced while JunB increased. Cardiac-specific JunD overexpressing mice (JunDTg/0 ) displayed larger infarcts compared with WT. However, postischemic inflammatory or oxidative responses did not differ. JunD overexpression reduced Sirt3 transcription by binding to its promoter, thus leading to mitochondrial dysfunction, myocardial cell death, and increased infarct size. On the other hand, JunD silencing reduced, while Sirt3 silencing increased infarct size. In human myocardial autopsy specimens, JunD-positive areas within the infarcted left ventricle staining corresponded to undetectable Sirt3 areas in consecutive sections of the same heart. Cardiac-specific JunD overexpression increases myocardial infarct size following I/R. These effects are mediated via Sirt3 transcriptional repression, mitochondrial swelling, and increased apoptosis, suggesting that JunD is a key regulator of myocardial I/R injury. The present data set the stage for further investigation of the potential role of Sirt3 activation as a novel target for the treatment of acute myocardial infarction.

Piezo Ion Channels in Cardiovascular Mechanobiology.

Mechanotransduction has a key role in vascular development, physiology, and disease states. Piezo1 is a mechanosensitive (MS) nonselective cationic channel that occurs in endothelial and vascular smooth muscle cells. It is activated by shear stress associated with increases in local blood flow, as well as by cell membrane stretch upon elevation of blood pressure. Here, we briefly review the pharmacological modulators of Piezo and discuss current understanding of the role of Piezo1 in vascular mechanobiology and associated clinical disorders, such as atherosclerosis and hypertension. Ultimately, we believe that this research will help identify novel therapeutic strategies for the treatment of vascular diseases.

Assessment of Vascular Tone Responsiveness using Isolated Mesenteric Arteries with a Focus on Modulation by Perivascular Adipose Tissues.

Altered vascular tone responsiveness to pathophysiological stimuli contributes to the development of a wide range of cardiovascular and metabolic diseases. Endothelial dysfunction represents a major culprit for the reduced vasodilatation and enhanced vasoconstriction of arteries. Adipose (fat) tissues surrounding the arteries play important roles in the regulation of endothelium-dependent relaxation and/or contraction of the vascular smooth muscle cells. The cross-talks between the endothelium and perivascular adipose tissues can be assessed ex vivo using mounted blood vessels by a wire myography system. However, optimal settings should be established for arteries derived from animals of different species, ages, genetic backgrounds and/or pathophysiological conditions.

Acute activation of endothelial AMPK surprisingly inhibits endothelium-dependent hyperpolarization-like relaxations in rat mesenteric arteries.

BACKGROUND AND PURPOSE: Endothelium-dependent hyperpolarizations (EDHs) contribute to the regulation of peripheral resistance. They are initiated through opening of endothelial calcium-activated potassium channels (KCa ); the potassium ions released then diffuse to the underlying smooth muscle cells, causing hyperpolarization and thus relaxation. The present study aimed to examine whether or not AMPK modulates EDH-like relaxations in rat mesenteric arteries. EXPERIMENTAL APPROACH: Arterial rings were isolated for isometric tension recording. AMPK activity and protein level were measured by ELISA and western blotting respectively. KEY RESULTS: The AMPK activator, AICAR, reduced ACh-induced EDH-like relaxations and increased AMPK activity in preparations with endothelium; these responses were prevented by compound C, an AMPK inhibitor. AICAR inhibited relaxations induced by SKA-31 (opener of endothelial KCa ) but did not affect potassium-induced, hyperpolarization-attributable relaxations or increase AMPK activity in preparations without endothelium. A769662, another AMPK activator, not only caused a similar inhibition of relaxations to ACh and SKA-31 in preparations with endothelium but also inhibited hyperpolarization-attributable relaxations and augmented AMPK activity in rings without endothelium. Protein levels of total AMPKα, AMPKα1, or AMPKß1/2 were comparable between preparations with and without endothelium. CONCLUSIONS AND IMPLICATIONS: Activation of endothelial AMPK, by either AICAR or A769662, acutely inhibits EDH-like relaxations of rat mesenteric arteries. Furthermore, A769662 inhibits signalling downstream of smooth muscle hyperpolarization. In view of the major blunting effect of AMPK activation on EDH-like relaxations, caution should be applied when administering therapeutic agents that activate AMPK in patients with endothelial dysfunction characterized by reduced production and/or bioavailability of NO.

The acute blood pressure-lowering effect of amiloride is independent of endothelial ENaC and eNOS in humans and mice.

AIMS: The epithelial sodium channel (ENaC) is expressed in cultured endothelial cells and inhibitory coupling to eNOS activity has been proposed. The present study tested the hypothesis that ENaC blockers increase systemic NO-products and lower blood pressure in patients and mice, depending on eNOS. METHODS: NO-products and cGMP were measured in diabetes patient urine and plasma samples before and after amiloride treatment (20-40 mg for two days, plasma n = 22, urine n = 12 and 5-10 mg for eight weeks, plasma n = 52, urine n = 55). Indwelling catheters were implanted in the femoral artery and vein in mice for continuous arterial blood pressure and heart rate recordings and infusion. RESULTS: Treatment with amiloride for two days increased plasma and urine NO-products, while plasma cGMP decreased and urinary cGMP was unchanged in patient samples. Eight weeks of treatment with amiloride did not alter NO-products and cGMP. In mice, amiloride boli of 5, 50, and 500 µg/kg lowered heart rate and arterial blood pressure significantly and acutely. Benzamil had no effect on pressure and raised heart rate. In hypertensive eNOS-/- and L-NAME-treated mice, amiloride lowered blood pressure significantly. L-NAME infusion significantly decreased NO-products in plasma; amiloride and eNOS-deletion had no effect. An acetylcholine bolus resulted in acute blood pressure drop that was attenuated in eNOS-/- and L-NAME mice. ENaC subunit expressions were not detected consistently in human and mouse arteries and endothelial cells. CONCLUSION: Amiloride has an acute hypotensive action not dependent on ENaC and eNOS and likely related to the heart.

Endothelial SIRT1 prevents age-induced impairment of vasodilator responses by enhancing the expression and activity of soluble guanylyl cyclase in smooth muscle cells.

AIMS: Aged arteries are characterized by attenuated vasodilator and enhanced vasoconstrictor responses, which contribute to the development of diseases such as arterial hypertension, atherosclerosis, and heart failure. SIRT1 is a longevity regulator exerting protective functions against vascular ageing, although the underlying mechanisms remain largely unknown. This study was designed to elucidate the signalling pathways involved in endothelial SIRT1-mediated vasodilator responses in the arteries of young and old mice. In particular, the contributions of nitric oxide (NO), endothelial NO synthase (eNOS), cyclooxygenase (COX), and/or soluble guanylyl cyclase (sGC) were examined. METHODS AND RESULTS: Wild type (WT) or eNOS knockout (eKO) mice were cross-bred with those overexpressing human SIRT1 selectively in the vascular endothelium (EC-SIRT1). Arteries were collected from the four groups of mice (WT, EC-SIRT1, eKO, and eKO-SIRT1) to measure isometric relaxations/contractions in response to various pharmacological agents. Reduction of NO bioavailability, hyper-activation of COX signalling, and down-regulation of sGC collectively contributed to the decreased vasodilator and increased vasoconstrictor responses in arteries of old WT mice. Overexpression of endothelial SIRT1 did not block the reduction in NO bioavailability but attenuated the hyper-activation of COX-2, thus protecting mice from age-induced vasoconstrictor responses in arteries of EC-SIRT1 mice. Deficiency of eNOS did not affect endothelial SIRT1-mediated anti-contractile activities in arteries of eKO-SIRT1 mice. Mechanistic studies revealed that overexpression of endothelial SIRT1 enhanced Notch signalling to up-regulate sGCß1 in smooth muscle cells. Increased expression and activity of sGC prevented age-induced hyper-activation of COX-2 as well as the conversion of endothelium-dependent relaxations to contractions in arteries of EC-SIRT1 mice. CONCLUSION: Age-induced down-regulation of sGC and up-regulation of COX-2 in arteries are at least partly attributable to the loss-of-endothelial SIRT1 function. Enhancing the endothelial expression and function of SIRT1 prevents early vascular ageing and maintains vasodilator responses, thus representing promising drug targets for cardiovascular diseases.

Periarterial fat from two human vascular beds is not a source of aldosterone to promote vasoconstriction.

Mouse adipocytes have been reported to release aldosterone and reduce endothelium-dependent relaxation. It is unknown whether perivascular adipose tissue (PVAT) releases aldosterone in humans. The present experiments were designed to test the hypothesis that human PVAT releases aldosterone and induces endothelial dysfunction. Vascular reactivity was assessed in human internal mammary and renal segmental arteries obtained at surgery. The arteries were prepared with/without PVAT, and changes in isometric tension were measured in response to the vasoconstrictor thromboxane prostanoid receptor agonist U46619 and the endothelium-dependent vasodilator acetylcholine. The effects of exogenous aldosterone and of mineralocorticoid receptor (MR) antagonist eplerenone were determined. Aldosterone concentrations were measured by ELISA in conditioned media incubated with human adipose tissue with/without angiotensin II stimulation. Presence of aldosterone synthase and MR mRNA was examined in perirenal, abdominal, and mammary PVAT by PCR. U46619 -induced tension and acetylcholine-induced relaxation were unaffected by exogenous and endogenous aldosterone (addition of aldosterone and MR blocker) in mammary and renal segmental arteries, both in the presence and absence of PVAT. Aldosterone release from incubated perivascular fat was not detectable. Aldosterone synthase expression was not consistently observed in human adipose tissues in contrast to that of MR. Thus, exogenous aldosterone does not affect vascular reactivity and endothelial function in ex vivo human arterial segments, and the tested human adipose tissues have no capacity to synthesize/release aldosterone. In perspective, physiologically relevant effects of aldosterone on vascular function in humans are caused by systemic aldosterone originating from the adrenal gland.

Lipocalin-2 derived from adipose tissue mediates aldosterone-induced renal injury.

Lipocalin-2 is not only a sensitive biomarker, but it also contributes to the pathogenesis of renal injuries. The present study demonstrates that adipose tissue-derived lipocalin-2 plays a critical role in causing both chronic and acute renal injuries. Four-week treatment with aldosterone and high salt after uninephrectomy (ANS) significantly increased both circulating and urinary lipocalin-2, and it induced glomerular and tubular injuries in kidneys of WT mice. Despite increased renal expression of lcn2 and urinary excretion of lipocalin-2, mice with selective deletion of lcn2 alleles in adipose tissue (Adipo-LKO) are protected from ANS- or aldosterone-induced renal injuries. By contrast, selective deletion of lcn2 alleles in kidney did not prevent aldosterone- or ANS-induced renal injuries. Transplantation of fat pads from WT donors increased the sensitivity of mice with complete deletion of Lcn2 alleles (LKO) to aldosterone-induced renal injuries. Aldosterone promoted the urinary excretion of a human lipocalin-2 variant, R81E, in turn causing renal injuries in LKO mice. Chronic treatment with R81E triggered significant renal injuries in LKO, resembling those observed in WT mice following ANS challenge. Taken in conjunction, the present results demonstrate that lipocalin-2 derived from adipose tissue causes acute and chronic renal injuries, largely independent of local lcn2 expression in kidney.

Low but not high frequency of intermittent hypoxia suppresses endothelium-dependent, oxidative stress-mediated contractions in carotid arteries of obese mice.

Obstructive sleep apnea is characterized by intermittent hypoxia (IH) during sleep and predisposes to endothelial dysfunction. Obesity is a major risk factor for the occurrence of sleep apnea. The present study compared the functional impact of low- (IH10; 10 hypoxic events/h) and high-frequency (IH60; 60 hypoxic events/h) IH for 4 wk on endothelial function in male C57BL/6 mice with or without high-fat (HF) diet-induced obesity. Mean arterial blood pressure (tail cuff method) was increased in obese mice after IH60 exposure, i.e., HF + IH60 group. The serum levels of the oxidative stress marker malondialdehyde were augmented in lean IH60 and HF groups, with a further increase in HF + IH60 but a reduction in HF + IH10 mice compared with the HF group. Vascular responsiveness was assessed as changes in isometric tension in isolated arteries. Relaxations to the endothelium-dependent vasodilator acetylcholine were impaired in HF + IH60 aortae. Endothelium-dependent contractions (EDC; response to acetylcholine in the presence of the nitric oxide synthase inhibitor l-NAME) in carotid arteries were augmented in the HF group, but this HF-induced augmentation was suppressed by low-frequency IH exposure. The addition of apocynin (antioxidant) reduced EDC in HF and HF + IH60 groups but not in HF + IH10 group. In conclusion, these findings suggest that exposure of obese mice to mild IH exerts preconditioning-like suppression of endothelium-dependent and oxidative stress-mediated contractions. When IH severity increases, this suppression diminishes and endothelial dysfunction accelerates. NEW & NOTEWORTHY The present study demonstrates, for the first time, that low-frequency intermittent hypoxia may exert a preconditioning-like suppression of oxidative stress-induced endothelium-dependent contractions in mice with diet-induced obesity. This relative suppression was diminished as intermittent hypoxia became more severe, and a deleterious effect on endothelial function emerged.

Activation of NQO-1 mediates the augmented contractions of isolated arteries due to biased activity of soluble guanylyl cyclase in their smooth muscle.

Earlier studies on isolated arteries demonstrated that the para-quinone thymoquinone, like acute hypoxia, induces augmentation of contractions, depending on biased activity of soluble guanylyl cyclase (sGC), generating inosine-3',5'-cyclic monophosphate (cyclic IMP) rather than guanosine-3',5'-cyclic monophosphate (cyclic GMP). NAD(P)H:quinone oxidoreductase 1 (NQO-1), the enzyme responsible for biotransformation of quinones into hydroquinones, was examined for its involvement in these endothelium-dependent augmentations, establishing a link between the metabolism of quinones by NQO-1 and biased sGC activity. Isolated arteries of Sprague-Dawley rats (aortae and mesenteric arteries) and farm pigs (coronary arteries) were studied for measurement of changes in tension and collected to measure NQO-1 activity or its protein level. ß-lapachone, an ortho-quinone and hence substrate of NQO-1, increased the activity of the enzyme and augmented contractions in arteries with endothelium. This augmentation was inhibited by endothelium removal and inhibitors of endothelial NO synthase (eNOS), sGC, or NQO-1; in preparations without endothelium or treated with an eNOS inhibitor, it was restored by the NO donor DETA NONOate and by ITP and cyclic IMP, revealing biased sGC activity as the underlying mechanism, as with thymoquinone. Hydroquinone, the end product of quinone metabolism by NQO-1, augmented contractions depending on sGC activation but in an endothelium-independent manner. In coronary arteries, repeated acute hypoxia caused similar augmentations as those to quinones that were inhibited by the NQO-1 inhibitor dicoumarol. Augmentations of contraction observed with different naturally occurring quinones and with acute hypoxia are initiated by quinone metabolism by NQO-1, in turn interfering with the NO/biased sGC pathway, suggesting a possibly detrimental role of this enzyme in ischemic cardiovascular disorders.

No Protective Effect of Constitutive Activation of AMPK in Endothelial Cells on Vascular Function in Aged Obese Mice but Augmented α1-Adrenergic Contractions in Renal Arteries Reversible by Weight Loss.

BACKGROUND: Aging, obesity, and diabetes favor vascular dysfunction. Endothelial activation of adenosine monophosphate-activated protein kinase (AMPK) has protective effects in diabetes. METHODS: Mice with constitutive endothelial activation of AMPK (CA-AMPK) were given a high fat diet to induce obesity or kept on standard chow as lean controls for up to 2 years. A subset of obese animals was changed to standard chow after 30 weeks of high fat feeding. En-dothelium-dependent and endothelium-independent responses were examined by isometric tension recording. RESULTS AND CONCLUSION: Endothelium-dependent nitric oxide (NO)- and apamin plus charybdotoxin-sensitive relaxations were preserved and similar between aortic or renal arterial preparations of lean and obese CA-AMPK mice and their wild-type littermates. Despite comparable release of vasoconstrictor prostanoids, cyclooxygenase-dependent contractions were enhanced during NO synthase inhibition in carotid arterial rings of obese CA-AMPK mice. Contractions to the α1-adrenoceptor agonist phenylephrine were augmented in renal arteries of obese animals, a genotype-independent phenomenon reversible by weight loss. These data indicate a higher α1-adrenergic reactivity in renal arteries of aged mice with obesity. The current results highlight the potential of weight loss to alleviate vascular dysfunction. However, endothelial activation of the AMPK pathway in obesity may not be sufficient to prevent vascular dysfunction without lifestyle changes.