Endothelial-dependent relaxation of α-pinene and two metabolites, myrtenol and verbenol, in isolated murine blood vessels

Epidemiological evidence shows that residential proximity to greenspaces is associated with lower risk of all-cause and cardiovascular mortality; however, the mechanism(s) underlying this link remains unclear. Plants emit biogenic volatile organic compounds such as alpha-pinene that could elicit beneficial cardiovascular effects. To explore the role of alpha-pinene more directly, we studied the metabolism and the vascular effects of alpha-pinene. We found that exposure of mice to alpha-pinene (1 ppm, 6 h) generated two phase I oxidation metabolites, cis- and trans-verbenol [(1R,2R,5R)-verbenol and (1 R,2S,5R)-verbenol)] and myrtenol [(1S,5R)-(+)-myrtenol] that were identified in urine by GC-MS. Precontracted naive murine male and female aorta and superior mesenteric artery (SMA) were relaxed robustly (60% tension reduction) by increasing concentrations of alpha-pinene, myrtenol, and verbenol to 0.3 mM, whereas 1 mM alpha-pinene was vasotoxic. The SMA was six times more sensitive than the aorta to alpha-pinene. Both myrtenol and verbenol were equally potent and efficacious as parent alpha-pinene in male and female SMA. The sensitive portion of the alpha-pinene-, myrtenol-, and verbenol-induced relaxations in male SMA was mediated by 1) endothelium, 2) eNOS-derived NO, and 3) guanylyl cyclase (GC) activity. Moreover, alpha-pinene activated the transient receptor potential ankyrin-1 (TRPA1) channel whereas the metabolites did not. Endothelial-derived NO regulates blood flow, blood pressure, and thrombosis, and it is plausible that inhaled (and ingested) alpha-pinene (or its metabolites) augments NO release to mediate the cardiovascular benefits of exposure to greenness.