Background: The prevalence of metabolic syndrome is especially high in older adults. Metabolic syndrome is associated with impaired vascular endothelial function, insulin resistance, and increased risk for cardiovascular disease but the underlying mechanisms are not fully elucidated. Plasma aldosterone is independently associated with metabolic syndrome and is linked to endothelial dysfunction and insulin resistance. Thus, we hypothesized that mineralocorticoid receptor (MR) blockade would improve flow-mediated dilation and insulin resistance in older adults with metabolic syndrome.
Methods: To test this hypothesis, we conducted a balanced, randomized, double-blind, placebo-controlled, crossover study using selective MR blockade (eplerenone; 100 mg/day) for 1 month with 1 month washout in older adults with metabolic syndrome (62.6 ± 3.2 yrs; mean ± standard error). We evaluated brachial artery flow-mediated dilation (ultrasonography), oxidative stress (oxidized low-density lipoproteins and F2-isoprostanes) and insulin resistance (homeostatic model assessment).
Results: In response to MR blockade, flow-mediated dilation (5.37 ± 0.85 vs. 5.98 ± 1.29%; placebo vs. eplerenone; P = 0.4), oxidized low-density lipoproteins (51.6 ± 11.5 vs. 56.1 ± 10.9 U/L; P = 0.6), and F2-isoprostanes (0.07 ± 0.02 vs. 0.06 ± 0.01 pg/mL; P = 0.3) did not improve. Insulin resistance also did not change following MR blockade (1.04 ± 0.26 vs. 1.38 ± 0.50; P = 0.6). However, MR blockade resulted in a large reduction (10 mmHg) in systolic blood pressure (140 ± 6 vs. 130 ± 6 mmHg; P = 0.02), with no significant change in diastolic blood pressure (81 ± 3 vs. 75 ± 2 mmHg; P = 0.2).
Conclusions: Our data do not support a contributing role for MRs in endothelial dysfunction and insulin resistance in older adults with metabolic syndrome. However, our findings suggest MR activation is an important contributor to systolic hypertension in this patient group.