Nicotine Downregulates the Compensatory Angiotensin-Converting Enzyme 2/Angiotensin Type 2 Receptor of the Renin-Angiotensin System

Smoking is a major risk factor for the development of cardiovascular and pulmonary diseases. The importance of the renin-angiotensin system in the development of cardiovascular and pulmonary disease is well established. Angiotensin-II, by means of its type 1 receptor (angiotensin type 1 receptor, AT R), promotes increased sympathetic activity, salt and water reabsorption, vasoconstriction, inflammation, and aldosterone and vasopressin release, contributing to tissue fibrosis, endothelium dysfunction, and hypertension. Angiotensin-converting enzyme 2 cleaves angiotensin-II into the vasodilator peptide, angiotensin-(1-7), hence playing a pivotal role in the angiotensin-converting enzyme 2/angiotensin-(1-7) compensatory axis of the renin-angiotensin system. Angiotensin type 2 receptor (AT R), another receptor for angiotensin-II, opposes the deleterious effects of AT R activation, and angiotensin-converting enzyme 2-formed angiotensin-(1-7) has been shown to activate AT R. The goal of the present study was to examine how nicotine, the addictive component of cigarette smoke, alters the homeostasis of the renin-angiotensin system. Quantitative real-time polymerase chain reaction was performed to examine the expression of the components of the renin-angiotensin system after cigarette smoke exposure or direct nicotine inhalation. Radio telemetry was used for continuous blood pressure recording in conscious, unrestrained mice. Our study showed that cigarette smoke or direct nicotine inhalation inhibits the expression of angiotensin-converting enzyme 2/AT R in multiple organs and cell types. In the lung, cigarette smoke (6 cigarettes/d, 12 wk) inhibited the expression of both angiotensin-converting enzyme 2 and AT R. In cardiac fibroblasts, nicotine exposure resulted in near complete suppression of angiotensin-converting enzyme 2 and AT R. In the brain, nicotine vapor inhalation inhibited angiotensin-converting enzyme 2 expression in the hypothalamus, a region involved in central regulation of cardiopulmonary function. In addition, cultured Neuro2A cells exposed to nicotine showed a dose-dependent reduction of enzymatic activity of angiotensin-converting enzyme 2. Functionally, mice exposed to nicotine vapor (12 h/d, 4 wk) exhibited significantly increased mean arterial blood pressure, which was more pronounced during the night active cycle (mean ± SE, 124 ± 0.6 mm Hg in nicotine vapor-exposed mice vs. 107 ± 0.4 mm Hg in air control mice; P