Meredith J. Luttrell

NAD(P)H oxidase-derived reactive oxygen species contribute to age-related impairments of endothelium-dependent dilation in rat soleus feed arteries

We tested the hypothesis that age-related endothelial dysfunction in rat soleus muscle feed arteries (SFA) is mediated in part by NAD(P)H oxidase-derived reactive oxygen species (ROS). SFA from young (4 mo) and old (24 mo) Fischer 344 rats were isolated and cannulated for examination of vasodilator responses to flow and acetylcholine (ACh) in the absence or presence of a superoxide anion (O(2)(-)) scavenger (Tempol; 100 μM) or an NAD(P)H oxidase inhibitor (apocynin; 100 μM). In the absence of inhibitors, flow- and ACh-induced dilations were attenuated in SFA from old rats compared with young rats. Tempol and apocynin improved flow- and ACh-induced dilation in SFA from old rats. In SFA from young rats, Tempol and apocynin had no effect on flow-induced dilation, and apocynin attenuated ACh-induced dilation. To determine the role of hydrogen peroxide (H(2)O(2)), dilator responses were assessed in the absence and presence of catalase (100 U/ml) or PEG-catalase (200 U/ml). Neither H(2)O(2) scavenger altered flow-induced dilation, whereas both H(2)O(2) scavengers blunted ACh-induced dilation in SFA from young rats. In old SFA, catalase improved flow-induced dilation whereas PEG-catalase improved ACh-induced dilation. Compared with young SFA, in response to exogenous H(2)O(2) and NADPH, old rats exhibited blunted dilation and constriction, respectively. Immunoblot analysis revealed that the NAD(P)H oxidase subunit gp91phox protein content was greater in old SFA compared with young. These results suggest that NAD(P)H oxidase-derived reactive oxygen species contribute to impaired endothelium-dependent dilation in old SFA.

Mineralocorticoid receptors modulate vascular endothelial function in human obesity

Obesity increases linearly with age and is associated with impaired vascular endothelial function and increased risk of cardiovascular disease. MRs (mineralocorticoid receptors) contribute to impaired vascular endothelial function in cardiovascular disease; however, their role in uncomplicated human obesity is unknown. Because plasma aldosterone levels are elevated in obesity and adipocytes may be a source of aldosterone, we hypothesized that MRs modulate vascular endothelial function in older adults in an adiposity-dependent manner. To test this hypothesis, we administered MR blockade (eplerenone; 100 mg/day) for 1 month in a balanced randomized double-blind placebo-controlled cross-over study to 22 older adults (ten men, 55-79 years) varying widely in adiposity [BMI (body mass index): 20-45 kg/m²], but who were free from overt cardiovascular disease. We evaluated vascular endothelial function [brachial artery FMD (flow-mediated dilation)] via ultrasonography) and oxidative stress (plasma F2-isoprostanes and vascular endothelial cell protein expression of nitrotyrosine and NADPH oxidase p47phox) during placebo and MR blockade. In the whole group, oxidative stress (P>0.05) and FMD did not change with MR blockade (6.39 ± 0.67 compared with 6.23 ± 0.73%; P=0.7). However, individual improvements in FMD in response to eplerenone were associated with higher total body fat (BMI: r=0.45, P=0.02; and dual-energy X-ray absorptiometry-derived percentage body fat: r=0.50, P=0.009) and abdominal fat (total: r=0.61, P=0.005; visceral: r=0.67, P=0.002; and subcutaneous: r=0.48, P=0.03). In addition, greater improvements in FMD with eplerenone were related to higher baseline fasting glucose (r=0.53, P=0.01). MRs influence vascular endothelial function in an adiposity-dependent manner in healthy older adults.

Vascular smooth muscle responsiveness to nitric oxide is reduced in healthy adults with increased adiposity

Vascular smooth muscle responsiveness to nitric oxide, as assessed by nitroglycerin-induced dilation (NID), is impaired in clinical cardiovascular disease, but its relation to adiposity is unknown. We determined the relation of NID to total and abdominal adiposity in healthy adults varying widely in adiposity. In 224 men and women [age, 18-79 years; body mass index (BMI), 16.4-42.2 kg/m(2)], we measured NID (brachial artery dilation to 0.4 mg sublingual nitroglycerin), total body adiposity [BMI and percent body fat (percent BF via dual-energy X-ray absorptiometry)], and indexes of abdominal adiposity [waist circumference (WC) and waist-to-hip ratio (WHR)]. In a subgroup (n = 74), we also measured total abdominal fat (TAF), abdominal visceral fat (AVF), and subcutaneous fat (ASF) using computed tomography. Based on multiple linear regression, NID was negatively related to BMI [part correlation coefficient (r(part)) = -0.19, P = 0.004] and abdominal adiposity (WC, r(part) = -0.22; WHR, r(part) = -0.19; TAF, r(part) = -0.36; AVF, r(part) = -0.36; and ASF, r(part) = -0.30; all P ≤ 0.009) independent of sex, but only tended to be related to total percent BF (r(part) = -0.12, P = 0.07). In a subgroup of subjects with the highest compared with the lowest amount of AVF, NID was 35% lower (P = 0.003). Accounting for systolic blood pressure, HDL cholesterol, glucose, insulin resistance, adiponectin, and brachial artery diameter reduced or abolished some of the relations between NID and adiposity. In conclusion, NID is or tends to be negatively associated with measures of total adiposity (BMI and percent BF, respectively) but is consistently and more strongly negatively associated with abdominal adiposity. Adiposity may influence NID in part via other cardiovascular risk factors.

Role of mineralocorticoid receptors in arterial stiffness in human aging

Arterial stiffness, an independent predictor of cardiovascular disease, is increased in aging, but the underlying mechanisms are not completely understood. Mineralocorticoid receptors (MR) may contribute to oxidative stress and arterial stiffness in healthy older adults. To test the hypothesis that short-term MR blockade may reduce oxidative stress and improve arterial stiffness, we conducted a randomized, double blind, crossover study using the selective MR blocker Eplerenone or placebo in 23 older adults (age, 64±1 years; mean±SE) free from overt cardiovascular and other clinical disease (e.g, diabetes, renal and liver disease). In response to MR blockade, brachial and carotid blood pressure decreased (P≤0.01). However, MR blockade had no effect on oxidative stress (oxidized LDL, 61.2±6.8 vs. 62.4±7.4 U/L, P=0.9; placebo vs. Eplerenone) and arterial stiffness (aortic pulse wave velocity (PWV), 9.17±1.19 vs. 8.92±1.19 m/s, P=0.5; leg PWV, 13.45±0.45 vs. 12.81±0.47 m/s, P=0.3; arm PWV, 11.43±0.62 vs. 11.73±0.68 m/s, P=0.7; carotid artery compliance, 0.150±0.013 vs. 0.149±0.014 mm(2)/mmHg, P=0.8; distensibility, 23.1±1.8 vs. 23.3±1.7 10(-3)/kPa, P=0.8; β stiffness index, 3.5±0.3 vs. 3.6±0.3, P=0.6; and augmentation index, 16.0±2.2 vs. 15.6±2.8%, P=0.8). These results provide the first evidence that MR do not appear to contribute to oxidative stress in human aging and that short-term MR blockade does not result in reduced oxidative stress and improved arterial stiffness.

Higher levels of adiponectin in vascular endothelial cells are associated with greater brachial artery flow-mediated dilation in older adults.

Adiponectin, an adipocyte-derived protein, exerts anti-atherosclerotic effects on the vascular endothelium. Recently adiponectin protein has been reported in murine vascular endothelial cells, however, whether adiponectin is present in human vascular endothelial cells remains unexplored. We sought to examine 1) adiponectin protein in vascular endothelial cells collected from older adults free of overt cardiovascular disease; 2) the relation between endothelial cell adiponectin and in vivo vascular endothelial function; and 3) the relation between endothelial cell adiponectin, circulating (plasma) adiponectin and related factors. We measured vascular endothelial function (brachial artery flow-mediated dilation using ultrasonography), vascular endothelial cell adiponectin (biopsy coupled with quantitative immunofluorescence) and circulating adiponectin (Mercodia, ELISA) in older, sedentary, non-smoking, men and women (55-79 years). We found that higher endothelial cell adiponectin was related with greater flow-mediated dilation (r = 0.43, P < 0.05) and greater flow-mediated dilation normalized for shear stress (r = 0.56, P < 0.01), but was not related with vascular smooth muscle responsiveness to nitric oxide (r = 0.04, P = 0.9). Vascular endothelial cell adiponectin was not related with circulating adiponectin (r = -0.14, P = 0.6). Endothelial cell and circulating adiponectin were differentially associated with adiposity, metabolic and other factors, but both were inversely associated with renal function (r = 0.44 to 0.62, P ≤ 0.04). In conclusion, higher endothelial cell adiponectin levels are associated with higher vascular endothelial function, independent of circulating adiponectin levels in older adults.

The Intriguing Role of Histamine in Exercise Responses

In humans, histamine is a molecular transducer of physical activity responses, and antihistamines modify more than 25% of the genes responding to exercise. Although the upstream signal that results in release of histamine within exercising skeletal muscle remains to be identified, it is likely a fundamental exercise response and not an allergic reaction.