Chen-Huei Leo - Academia.edu (original) (raw)

Papers by Chen-Huei Leo

American Journal of Physiology - Heart and Circulatory Physiology, 2015

The vascular effects of exogenous relaxin treatment are well established, and include decreased m... more The vascular effects of exogenous relaxin treatment are well established, and include decreased myogenic reactivity and enhanced relaxation responses to vasodilators in small resistance arteries. These vascular responses are reduced in older animals, suggesting that relaxin is less effective in mediating arterial function with aging. This study investigated the role of endogenous relaxin in the aorta and the possibility that vascular dysfunction occurs more rapidly with aging in relaxin-deficient (Rln-/-) mice. We compared vascular function and underlying vasodilatory pathways in the aorta of male wild type (Rln+/+) and Rln-/- mice at 4 and 16 months of age using wire myography. Superoxide production, but not nitrotyrosine or NADPH oxidase expression, was significantly increased in the aorta of young Rln-/- mice, whereas endothelial nitric oxide (NO) synthase and basal NO availability were both significantly decreased compared to Rln+/+ mice. In the presence of the cyclooxygenase inhibitor, indomethacin, sensitivity to acetylcholine was significantly decreased in young Rln-/- mice, demonstrating altered NO-mediated relaxation that was normalized in the presence of a membrane-permeable superoxide dismutase or ROS scavenger. These vascular phenotypes were not exacerbated in old Rln-/- mice and in most cases, did not differ significantly from old Rln+/+ mice. Despite the vascular phenotypes in Rln-/- mice, endothelium-dependent and -independent vasodilation were not adversely affected. Our data show a role for endogenous relaxin in reducing superoxide production and maintaining NO availability in the aorta, but also demonstrate that relaxin deficiency does not compromise vascular function in this artery or exacerbate endothelial dysfunction associated with aging.

Pharmacological research : the official journal of the Italian Pharmacological Society, 2012

The aim of the study was to investigate whether diabetes-induced oxidant stress affects the contr... more The aim of the study was to investigate whether diabetes-induced oxidant stress affects the contribution of nitroxyl (HNO) to endothelium-dependent relaxation in the rat aorta. Organ bath techniques were employed to determine vascular function of rat aorta. Pharmacological tools (3mM l-cysteine, 5mM 4-aminopyridine (4-AP), 200μM carboxy-PTIO and 100μM hydroxocobalamin, HXC) were used to distinguish between NO and HNO-mediated relaxation. Superoxide anion levels were determined by lucigenin-enhanced chemiluminescence. In the diabetic aorta, where there is increased superoxide anion production, responses to the endothelium-dependent relaxant ACh were not affected when the contribution of NO to relaxation was abolished by either HXC or carboxy-PTIO, indicating a preserved HNO-mediated relaxation. Conversely, when the contribution of HNO was inhibited with l-cysteine or 4-AP, the sensitivity and maximum relaxation to ACh was significantly decreased, suggesting that the contribution of N...

The peptide hormone relaxin has striking effects on the vascular system. Specifically, endogenous... more The peptide hormone relaxin has striking effects on the vascular system. Specifically, endogenous relaxin treatment reduces myogenic reactivity through nitric oxide (NO)-mediated vasorelaxation and increases arterial compliance in small resistance arteries. However, less is known about the vascular roles of endogenous relaxin, particularly in males. Therefore, we used male wild-type (Rln +/+ ) and relaxin knockout (Rln 2/2 ) mice to test the hypothesis that passive wall properties and vascular reactivity in mesenteric arteries would be compromised in Rln 2/2 mice. Passive compliance was determined in arteries (n = 8-9) mounted on a pressure myograph and in Ca 2+ -free Krebs containing 2 mM EGTA. Passive volume compliance was significantly (P = 0.01) decreased in the mesenteric arteries of Rln 2/2 mice. Vascular reactivity was assessed using wire myography. In mesenteric arteries (n = 5) of Rln 2/2 mice, there was a significant (P,0.03) increase in sensitivity to the vasoconstrictors phenylephrine and thromboxane-mimetic U41669. This enhanced responsiveness to vasoconstrictors was abolished by endothelial denudation, and attributed to impaired NO and prostanoid pathways in Rln 2/2 mice. Sensitivity to the endothelial agonist acetylcholine was significantly (n = 7-9, P#0.03) decreased, and this was abolished in the presence of the cyclooxygenase inhibitor, indomethacin (2 mM). This indicates that prostanoid vasoconstrictor pathways were upregulated in the mesenteric arteries of Rln 2/2 mice. In summary, we demonstrate endothelial dysfunction and impaired arterial wall remodeling in male mice deficient in relaxin. Thus, our results highlight a role for endogenous relaxin in the maintenance of normal mesenteric artery structure and function in males.

Journal of Cardiovascular Pharmacology, 2014

As flavonols are present in fruits and vegetables they are consumed in considerable amounts in th... more As flavonols are present in fruits and vegetables they are consumed in considerable amounts in the diet. There is growing evidence that the well-recognised antioxidant, anti-inflammatory and vasorelaxant actions of flavonols may, at least in part, result from modulation of biochemical signaling pathways and kinases. It is well established that diabetes is associated with increased cardiovascular morbidity and mortality. Despite clinical management of blood glucose levels, diabetes often results in cardiovascular disease. There is good evidence that endothelial dysfunction contributes significantly to the progression of diabetic cardiovascular diseases. This review describes the biological actions of flavonols that may ameliorate adverse cardiovascular events in diabetes. We discuss evidence that flavonols may be developed as novel pharmacological agents to prevent diabetes-induced vascular dysfunction.

The FASEB Journal, 2014

Relaxin is a potent vasodilator of small resistance arteries and modifies arterial compliance in ... more Relaxin is a potent vasodilator of small resistance arteries and modifies arterial compliance in some systemic vascular beds, yet receptors for relaxin, such as RXFP1, have only been localized to vascular smooth muscle. This study first aimed to localize RXFP1 in rat arteries and veins from different organ beds and determine whether receptors are present in endothelial cells. We then tested the hypothesis that region-specific vascular effects of relaxin may be influenced by the cellular localization of RXFP1 within different blood vessels. The aorta, vena cava, mesenteric artery, and vein had significantly higher (P<0.05) RXFP1 immunostaining in endothelial cells compared with vascular smooth muscle, whereas the femoral artery and vein and small pulmonary arteries had higher (P<0.01) RXFP1 immunostaining in the vascular smooth muscle. Male rats were treated subcutaneously with recombinant human relaxin-2 (serelaxin; 4 g/h) for 5 d; vasodilation and compliance in mesenteric and femoral arteries and veins were compared with placebo controls. Serelaxin significantly (P‫)40.0؍‬ reduced wall stiffness and increased volume compliance in mesenteric arteries but not in the other vessels examined. This was associated with changes in geometrical properties, and not compositional changes in the extracellular matrix. Serelaxin treatment had no effect on acetylcholine-mediated relaxation but significantly (P< 0.001) enhanced bradykinin (BK)-mediated relaxation in mesenteric arteries, involving enhanced nitric oxide but not endothelium-derived hyperpolarization or vasodilatory prostanoids. In conclusion, there is differential distribution of RXFP1 on endothelial and smooth muscle across the vasculature. In rats, mesenteric arteries exhibit the greatest functional response to chronic serelaxin treatment.-Jelinic, M., Leo, C-H., Post Uiterweer, E. P., Sandow, S. L., Gooi, J. H., Wlodek, M. E., Conrad, K. P., Parkington, H., Tare, M., Parry, L. J. Localization of relaxin receptors in arteries and veins, and regionspecific increases in compliance and bradykinin-mediated relaxation after in vivo serelaxin treatment. FASEB J. 28, 000 -000 (2014). www.fasebj.org

Journal of Neuroendocrinology, 2014

Type 1 and 2 diabetes are associated with dysfunction in multiple hormone systems, as well as inc... more Type 1 and 2 diabetes are associated with dysfunction in multiple hormone systems, as well as increased sympathetic nerve activity, which may contribute to the development of diabetic complications. In other pathologies, such as myocardial infarction, increased sympathetic drive is associated with neuroinflammation and microglial activation in the hypothalamic paraventricular nucleus (PVN), a brain region that regulates sympathetic drive and multiple endocrine responses. In the present study, we used immunohistochemistry to study microglial and neuronal activation in the PVN and related brain regions in streptozotocin (STZ)-induced diabetic rats. As expected, STZ treatment was associated with elevated blood glucose within 1 week. STZ injections also caused neuronal activation in the PVN and superoptic nucleus (SON) but not in the nucleus tractus solitarius (NTS), which was evident by 6 weeks. STZ-treated rats showed increased plasma osmolarity, which would be expected to activate PVN and SON neurones. There was no apparent increase in histochemical markers of microglial activation, including phospho-p38, phospho-extracellular signal regulated kinase, P2X4 receptor or interleukin 1-β even at 10 weeks after STZ-treatment. However, we did see a significant increase in the percentage of microglia with an activated morphology in the PVN, SON and NTS, although not in surrounding hypothalamic, brainstem or cortical regions. These morphological changes included a significant reduction in microglial process length and were evident by 8 weeks but not 6 weeks. The delayed onset of microglial changes compared to neuronal activation in the PVN and SON suggests the over-excitation of neurones as a mechanism of microglial activation. This delayed microglial activation may, in turn, contribute to the endocrine dysregulation and the elevated sympathetic nerve activity reported in STZ-treated rats.

Heart, Lung and Circulation, 2013

European Journal of Pharmacology, 2011

Diabetes is known to cause an overproduction of reactive oxygen species (ROS), contributing to th... more Diabetes is known to cause an overproduction of reactive oxygen species (ROS), contributing to the impairment of endothelium-dependent relaxation in microvasculature, however it is not clear whether antioxidants are able to reverse microvascular endothelial dysfunction. The aim of this study is to investigate whether the synthetic flavonol 3′,4′-dihydroxyflavonol (DiOHF) could reduce the levels of reactive oxygen species (ROS) and improve endothelium-dependent relaxation in mesenteric arteries from both type 1 and type 2 diabetic rats. Endothelial function of third order mesenteric arteries from type 1 and type 2 diabetic rats was assessed using wire-myography. Superoxide levels in the mesenteric arteries were measured by L-012induced chemiluminescence. Mesenteric arteries from type 1 and type 2 diabetic rats had elevated levels of superoxide production compared to control, which was accompanied by impaired responses to the endothelium-dependent relaxant, acetylcholine (ACh). The acute presence of DiOHF ex vivo significantly reduced the superoxide levels in the diabetic mesenteric arteries and restored endothelial function. The antioxidant activity of DiOHF is comparable to superoxide dismutase mimetics (tempol and MnTMPyP), which also significantly reduced the superoxide levels and improved endothelial function in diabetic arteries. Therefore, the synthetic flavonol DiOHF could effectively reduce oxidant stress and restore microvascular endothelium-dependent relaxation in diabetic rats.

British Journal of Pharmacology, 2011

To investigate whether diabetes affects either or both nitric oxide (NO)-mediated and endothelium... more To investigate whether diabetes affects either or both nitric oxide (NO)-mediated and endothelium-derived hyperpolarizing factor (EDHF)-type relaxation in endothelium-dependent relaxation of mesenteric arteries from streptozotocin-induced diabetic rats. Wire myography was employed to examine endothelial function of mesenteric arteries. Superoxide levels were measured by L-012 and lucigenin-enhanced chemiluminescence. Western blotting was used to quantify protein expression levels. Superoxide levels were significantly increased in diabetic mesenteric arteries compared with normal arteries. Diabetes significantly reduced the sensitivity to the endothelium-dependent relaxant, acetylcholine (ACh) in mesenteric arteries. When the contribution of NO to relaxation was abolished by N-nitro-L-arginine (L-NNA) + a soluble guanylate cyclase inhibitor (ODQ), the sensitivity to ACh was significantly decreased in the diabetic arteries compared with normal arteries, indicating an impaired EDHF-type relaxation despite increased expression of intermediate- and small-conductance calcium-activated potassium channels. Conversely, when the contribution of EDHF was inhibited with TRAM-34 + apamin + iberiotoxin, maximum relaxations to ACh were significantly decreased in diabetic compared with normal arteries, suggesting that the contribution of NO was also impaired by diabetes. Basal levels of NO release, indicated by contraction to L-NNA, were also significantly decreased in diabetic arteries. Western blot analysis demonstrated that diabetic arteries had an increased expression of Nox2, decreased pSer⁴⁷³ Akt and a reduced proportion of endothelial NO synthase (eNOS) expressed as a dimer, indicating uncoupling. The contribution of both NO and EDHF-type relaxations was impaired in diabetes and was caused by increased oxidative stress, decreased pSer⁴⁷³ Akt and/or eNOS uncoupling.

AJP: Heart and Circulatory Physiology, 2010

The aim of the present study was to examine the effect of an early stage of streptozotocin-induce... more The aim of the present study was to examine the effect of an early stage of streptozotocin-induced diabetes on the mechanism(s) of endothelium-dependent relaxation. Diabetes was induced by a single injection of streptozotocin (48 mg/kg iv), and the ACh-induced relaxation of rat carotid arteries was examined 6 wk later. A diabetes-induced increase in superoxide levels, determined by L-012-induced chemiluminescence, from carotid arteries was associated with endothelial nitric oxide (NO) synthase (eNOS) uncoupling and increased catalytic subunit of NADPH oxidase expression. The sensitivity and maximum response to ACh were similar in normal and diabetic rats despite a decrease in NO release detected by 4-amino-5-methylamino-2&amp;#39;,7&amp;#39;-difluorofluorescein. In normal rats, N-nitro-l-arginine (100 microM) plus 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (10 microM), to inhibit NOS and soluble guanylate cyclase (sGC), respectively, abolished ACh-induced relaxation, whereas in diabetic rats, the maximum relaxation to ACh was attenuated (maximum relaxation: 25 + or - 5%), but not abolished, by that treatment. The remaining ACh-induced relaxation was abolished by NO scavengers, cupric chloride (to degrade nitrosothiols), or blockers of endothelial K(+) channels. Western blot analysis of the carotid arteries indicated that diabetes significantly increased the expression of eNOS but decreased the proportion of eNOS expressed as the dimer. These findings demonstrate that in early diabetes, ACh-induced relaxation is maintained but is resistant to NOS inhibition. In early diabetes, nitrosothiol-mediated opening of K(+) channels may act in conjunction with NO stimulation of sGC to maintain endothelium-dependent relaxation despite the increase in vascular superoxide levels.

AJP: Heart and Circulatory Physiology, 2013

29 30 Abbreviated title: Low running capacity and progressive cardiac remodeling 31 Word Count: 4... more 29 30 Abbreviated title: Low running capacity and progressive cardiac remodeling 31 Word Count: 4483 (excluding abstract, acknowledgments, figure captions and references) ABSTRACT 35 Rats selectively bred for low (LCR) or high (HCR) intrinsic running capacity simultaneously 36 present with contrasting risk factors for cardiovascular and metabolic disease. However, the 37 impact of these phenotypes on left ventricular (LV) morphology and microvascular function, 38 and their progression with aging, remains unresolved. We tested the hypothesis that the LCR 57 58 capacity runner (LCR); metabolic syndrome; resistance arteries 59 60 157 were mounted in standard organ baths and allowed to equilibrate for 60 min at a resting 158

PLoS ONE, 2011

Background: 3',4'-Dihydroxyflavonol (DiOHF) is an effective antioxidant that acutely preserves ni... more Background: 3',4'-Dihydroxyflavonol (DiOHF) is an effective antioxidant that acutely preserves nitric oxide (NO) activity in the presence of elevated reactive oxygen species (ROS). We hypothesized that DiOHF treatment (7 days, 1 mg/kg per day s.c.) would improve relaxation in mesenteric arteries from diabetic rats where endothelial dysfunction is associated with elevated oxidant stress.