Second Hand Cigarette Smoke Exposure Impairs the Vasodilator Response to Apelin in Rat Coronary Arteries

Passive exposure to second hand smoke is a risk factor for cardiovascular disorders, including coronary artery disease. Mechanisms underlying adverse effects of cigarette smoke on coronary arteries are poorly understood. Apelin is an endogenous ligand for APJ receptors, which are highly expressed throughout the cardiovascular system, including coronary arteries. APJ receptors signal via G‐protein‐dependent and ‐independent pathways, including activation of G‐protein‐coupled‐receptor kinase 2 (GRK2). We previously reported that apelin causes relaxation of coronary arteries via the release of endothelium‐derived nitric oxide (NO) (J Pharmacol Exp Ther 366:265–273, 2018), but little is known about regulation of coronary vasomotor tone by apelin under pathological conditions. Here, we tested the hypothesis that apelin‐induced relaxation is impaired in coronary arteries exposed to cigarette smoke extract (CSE), an established model of second hand smoke exposure. In cultured rat coronary endothelial cells exposed to CSE for 4 hrs, immunoblot analysis demonstrated increased expression of GRK2, which is known to inhibit eNOS activity and NO production in endothelial cells. Rat isolated coronary arterial rings were suspended in myographs in the absence (vehicle control) and presence of CSE for 4 hrs. In rings contracted with 5‐HT (10 −7 M), apelin (10 −9 ‐10 −6 M) caused relaxation of control coronary arteries (pD 2 =7.41 ± 0.28; E max = 50 ± 6% relaxation), but had no effect in rings exposed to CSE. By contrast, treatment with CSE had no effect on endothelium‐dependent relaxations to CMF‐019 (10 −9 ‐10 −5 M), an APJ receptor biased agonist that acts selectively through the G‐protein‐dependent pathway with little effect on GRK2. Endothelium‐dependent relaxation to acetylcholine (ACh) (10 −9 ‐10 −6 M) was similar in control and CSE‐treated arteries; however, in the presence of apelin (10 −7 M), the response to ACh was markedly impaired in arteries exposed to CSE (pD 2 =7.13 ± 0.22 vs 6.57 ± 0.05, and E max = 93 ± 4 vs 76 ± 5% relaxation, in the absence and presence of apelin, respectively; n=5; p<0.05). ACh‐induced relaxation was unaffected by CMF‐019 (10 −7 M) in either control or CSE‐treated coronary arteries. Moreover, apelin (10 −7 M) had no effect on relaxation to the NO‐donor, DEA NONOate (10 −9 ‐10 −4 M), in either control or CSE‐treated arteries. Taken together, the data indicate that apelin failed to cause relaxation in coronary arteries exposed to CSE, likely due to impaired production or release of NO from endothelial cells rather than interfering with the action of NO on coronary smooth muscle cells. Following exposure of coronary arteries to CSE, apelin instead actively inhibited relaxation to another endothelium‐dependent vasodilator; i.e. ACh. That the effects of the G‐protein biased agonist, CMF‐019, did not differ in control and CSE‐treated coronary arteries is consistent with a role for GRK2 activation in the altered response to apelin in CSE‐treated arteries. APJ receptor signaling via the GRK2 pathway may contribute to both the loss of relaxation to apelin itself as well as the ability of apelin to inhibit endothelium‐dependent relaxation to ACh in CSE‐treated coronary arteries. Support or Funding Information Supported by NHLBI (HL124338)