Han-Kyul Kim

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.

Novel all-extremity high-intensity interval training improves aerobic fitness, cardiac function and insulin resistance in healthy older adults

Aging is associated with decreased aerobic fitness and cardiac remodeling leading to increased risk for cardiovascular disease. High-intensity interval training (HIIT) on the treadmill has been reported to be more effective in ameliorating these risk factors compared with moderate-intensity continuous training (MICT) in patients with cardiometabolic disease. In older adults, however, weight-bearing activities are frequently limited due to musculoskeletal and balance problems. The purpose of this study was to examine the feasibility and safety of non-weight-bearing all-extremity HIIT in older adults. In addition, we tested the hypothesis that all-extremity HIIT will be more effective in improving aerobic fitness, cardiac function, and metabolic risk factors compared with all-extremity MICT. Fifty-one healthy sedentary older adults (age: 65±1years) were randomized to HIIT (n=17), MICT (n=18) or non-exercise control (CONT; n=16). HIIT (4×4min 90% of peak heart rate; HRpeak) and isocaloric MICT (70% of HRpeak) were performed on a non-weight-bearing all-extremity ergometer, 4×/week for 8weeks under supervision. All-extremity HIIT was feasible in older adults and resulted in no adverse events. Aerobic fitness (peak oxygen consumption; VO2peak) and ejection fraction (echocardiography) improved by 11% (P<0.0001) and 4% (P=0.001), respectively in HIIT, while no changes were observed in MICT and CONT (P≥0.1). Greater improvements in ejection fraction were associated with greater improvements in VO2peak (r=0.57; P<0.0001). Insulin resistance (homeostatic model assessment) decreased only in HIIT by 26% (P=0.016). Diastolic function, body composition, glucose and lipids were unaffected (P≥0.1). In conclusion, all-extremity HIIT is feasible and safe in older adults. HIIT, but not MICT, improved aerobic fitness, ejection fraction, and insulin resistance.

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.

Sex impacts the flow-mediated dilation response to acute aerobic exercise in older adults

ABSTRACT There is growing evidence of sex differences in the chronic effect of aerobic exercise on endothelial function (flow‐mediated dilation; FMD) in older adults, but whether there are sex differences also in the acute effect of aerobic exercise on FMD in older adults is unknown. The purpose of this study was to test the hypothesis that sex modulates the FMD response to acute aerobic exercise in older adults. Thirteen older men and fifteen postmenopausal women (67 ± 1 vs. 65 ± 2 years, means ± SE, P = 0.6), non‐smokers, free of major clinical disease, participated in this randomized crossover study. Brachial artery FMD was measured: 1) prior to exercise; 2) 20 min after a single bout of high‐intensity interval training (HIIT; 40 min; 4 × 4 intervals 90% peak heart rate (HRpeak)), moderate‐intensity continuous training (MICT; 47 min 70% HRpeak) and low‐intensity continuous training (LICT; 47 min 50% HRpeak) on treadmill; and 3) following 60‐min recovery from exercise. In older men, FMD was attenuated by 45% following HIIT (5.95 ± 0.85 vs. 3.27 ± 0.52%, P = 0.003) and by 37% following MICT (5.97 ± 0.87 vs. 3.73 ± 0.47%, P = 0.03; P = 0.9 for FMD response to HIIT vs. MICT) and was normalized following 60‐min recovery (P = 0.99). In postmenopausal women, FMD did not significantly change in response to HIIT (4.93 ± 0.55 vs. 6.31 ± 0.57%, P = 0.14) and MICT (5.32 ± 0.62 vs. 5.60 ± 0.68%, P = 0.99). In response to LICT, FMD did not change in postmenopausal women nor older men (5.21 ± 0.64 vs. 6.02 ± 0.73%, P = 0.7 and 5.70 ± 0.80 vs. 5.55 ± 0.67%, P = 0.99). In conclusion, sex and exercise intensity influence the FMD response to acute aerobic exercise in older adults. HighlightsSex impacts flow‐mediated dilation (FMD) response to acute aerobic exercise in aging.In older men, FMD was attenuated after a bout of high‐intensity interval training.FMD was also attenuated after a bout of moderate‐intensity continuous training.However, FMD was unchanged after a bout of low‐intensity continuous training.In postmenopausal (PM) women, FMD did not change following acute aerobic exercise.

Acute Effect of Mineralocorticoid Receptor Antagonism on Vascular Function in Healthy Older Adults

Mineralocorticoid receptor (MR) activation by aldosterone may regulate vascular function in health or contribute to vascular dysfunction in cardiovascular disease. Whether the effects are beneficial or detrimental to vascular function appear to be dependent on the integrity of the vascular endothelium and whether the responses are short-term or chronic. Acute modulation of MR activation has resulted in conflicting outcomes on vascular function in young healthy adults. Little is known about the vascular role of aldosterone and MR activation in healthy human aging. The primary objective of this study was to examine whether acute inhibition of MR by the selective antagonist eplerenone, influences vascular function in healthy older adults. We performed a randomized, double-blind, placebo-controlled crossover study in 22 adults (61±1 years; mean±SE, 53-79 years) who were free from overt clinical cardiovascular disease. We measured brachial artery flow-mediated endothelium-dependent dilation and endothelium-independent dilation to sublingual nitroglycerin (0.4 mg) following eplerenone (100 mg/dose, 2 doses, 24h between doses) or placebo. In response to acute MR antagonism, flow-mediated dilation decreased by 19% (from 6.9±0.5 to 5.6±0.6%, P=0.02; placebo vs. eplerenone). Endothelial nitric oxide synthase (eNOS) activity also decreased following MR antagonism based on the ratio of phosphorylated eNOS(Ser1177) to total eNOS (1.53±0.08 vs. 1.29±0.06, P=0.02). Nitroglycerin-induced dilation and blood pressure were unaffected (nitroglycerin-induced dilation: 21.9±1.9 vs. 21.0±1.5%, P=0.5 and systolic/diastolic blood pressure: 135/77±4/2 vs. 134/77±4/2 mmHg, P≥0.6). In conclusion, acute MR antagonism impairs vascular endothelial function in healthy older adults without influencing vascular smooth muscle responsiveness to exogenous nitric oxide or blood pressure.

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.

All-extremity Exercise Training Improves Arterial Stiffness in Older Adults.

Large elastic arteries stiffen with age, which predisposes older adults to increased risk for cardiovascular disease. Aerobic exercise training is known to reduce the risk for cardiovascular disease, but the optimal exercise prescription for attenuating large elastic arterial stiffening in older adults is not known. Purpose The purpose of this randomized controlled trial was to compare the effect of all-extremity high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on aortic pulse wave velocity (PWV) and carotid artery compliance in older adults. Methods Forty-nine sedentary older adults (age = 64 ± 1 yr), free of overt major clinical disease, were randomized to HIIT (n = 17), MICT (n = 18), or nonexercise controls (CONT; n = 14). HIIT (4 × 4 min at 90% HRpeak interspersed with 3 × 3 min active recovery at 70% HRpeak) and isocaloric MICT (70% HRpeak) were performed on an all-extremity non–weight-bearing ergometer, 4 d·wk−1 for 8 wk under supervision. Aortic (carotid to femoral PWV [cfPWV]) and common carotid artery compliance were assessed at pre- and postintervention. Results cfPWV improved by 0.5 m·s−1 in MICT (P = 0.04) but did not significantly change in HIIT and CONT (P > 0.05). Carotid artery compliance improved by 0.03 mm2·mm Hg−1 in MICT (P = 0.001), but it remained unchanged in HIIT and CONT (P > 0.05). Improvements in arterial stiffness in response to MICT were not confounded by changes in aortic or brachial blood pressure, HR, body weight, total and abdominal adiposity, blood lipids, or aerobic fitness. Conclusion All-extremity MICT, but not HIIT, improved central arterial stiffness in previously sedentary older adults free of major clinical disease. Our findings have important implications for aerobic exercise prescription in older adults.