Early Inflammatory Responses in Experimental Cardiac Hypertrophy and Fibrosis: Effects of 11β-Hydroxysteroid Dehydrogenase Inactivation

TLDR

Mineralocorticoid receptors in epithelial tissues are protected from glucocorticoid activation by 11β‑hydroxysteroid dehydrogenase type 2, whereas in non‑epithelial tissues such as cardiomyocytes and vascular smooth muscle cells the enzyme is low or absent, leaving glucocorticoids to act as MR antagonists; the basis for this tissue selectivity remains unclear. The study aimed to test whether blocking 11βHSD in vascular smooth muscle cells would allow glucocorticoids to activate MR and trigger inflammatory responses similar to mineralocorticoid/salt administration. Uninephrectomized rats were given 0.9 % NaCl and either a single subcutaneous dose of deoxycorticosterone or daily carbenoxolone in the drinking water to inhibit 11βHSD. Both deoxycorticosterone and carbenoxolone raised blood pressure, heart and kidney weight, and induced COX‑2, macrophage infiltration, and osteopontin expression, effects that were blocked by the MR antagonist eplerenone, indicating that local glucocorticoid excess can mimic mineralocorticoid excess and drive coronary vascular inflammation under high‑salt conditions.

Abstract

In epithelial tissues such as kidney, mineralocorticoid receptors (MR) are protected against glucocorticoid occupancy by the enzyme 11β-hydroxysteroid dehydrogenase (11βHSD) type 2. If the enzyme is congenitally inactive, or blocked by carbenoxolone, physiologic glucocorticoids act as MR agonists in such tissues. In most nonepithelial tissues, including cardiomyocytes, 11βHSD2 is expressed at minimal levels; in these tissues physiologic glucocorticoids act as MR antagonists, with the basis for this tissue selectivity currently unknown. Vascular smooth muscle cells (VSMC) express MR and 11βHSD1/2, with 11βHSD1 reported to show uncharacteristic oxidase activity, so that VSMC thus constitute a potential physiologic aldosterone target tissue. Because mineralocorticoid/salt administration triggers marked inflammatory responses in coronary vasculature, we reasoned that VSMC (like epithelial) MR may be activated by glucocorticoids if the protective enzyme is blocked. We thus gave uninephrectomized rats 0.9% NaCl solution to drink, and deoxycorticosterone (DOC, as a single 20 mg sc dose) or carbenoxolone (CBX, 2.5 mg/d in the drinking solution). Both DOC and CBX increased systolic blood pressure, heart, and kidney weight, and expression of cyclooxygenase 2, ED-1-positive macrophages, and osteopontin, with effects of both DOC and CBX blocked by the selective MR antagonist eplerenone. These findings suggest that local glucocorticoid excess, reflecting lower VSMC 11βHSD1/2 activity may mimic systemic mineralocorticoid excess, and play a direct etiologic role in coronary vascular inflammatory responses under circumstances of a high salt intake.