Comparison of 6-Methylnicotine (6MN), a “No Nicotine, No Tobacco” Constituent, with Nicotine in Murine Mesenteric Artery: Mechanisms of Vasorelaxation

The nicotine analog, 6-methylnicotine (6MN), is used in "nicotine and tobacco-free" products to skirt tobacco regulatory legislation. However, nothing is known about the cardiovascular actions of 6MN. As 6MN is structurally similar to nicotine, and nicotine is a known vasoactive agent, we compared the direct vasoactive effects of nicotine (base and salt forms) with 6MN in isolated murine aorta and superior mesenteric artery (SMA). Because 6MN is present in Spree Bar, we also tested Spree Bar e-liquid for vasoactivity. In phenylephrine (PE)-precontracted SMA but not in aorta, 6MN induced a sensitive, concentration-, endothelial-, NO-, guanylyl cyclase, and CGRP receptor-dependent relaxation (EC ₅₀ : 0.9±0.4 µM, n=5) that was 3x more potent than S-nicotine (EC ₅₀ , salt: 2.3±0.3 µM, n=13; EC ₅₀ , base: 2.7±0.1 µM, n=4; P<0.05 vs 6MN) yet less potent than ACh (EC ₅₀ : 0.1±0.03 µM, n=3; P<0.05). In PE-precontracted SMA, both 6MN- and nicotine-induced relaxations were significantly blocked by: endothelial disruption; L-NAME; in SMA of eNOS-null mice; by mecamylamine; by α4β2-antagonist dihydro-β-erythroidine (DHBE); and, by the CGRP receptor antagonist SB-268262. It was unaffected by a-bungarotoxin or in SMA of α7-nicotinic receptor-null mice. Importantly, Spree Bar e-liquid induced a similarly potent vasorelaxation in SMA as pure 6MN as confirmed by LC-MS/MS quantification of 6MN levels in Spree Bar e-liquids. Endothelial-localized α4 receptors were confirmed by immunofluorescence. Thus, 6MN and nicotine activate an endothelial-, CGRP receptor antagonist-, mecamylamine-, and DHBE-sensitive and likely α4 subtype nAChR in the SMA. These findings reveal that 6MN is more potent than nicotine (base or salt) in SMA. Further research is required to assess how 6MN’s potent vasoaction in vitro may influence systemic hemodynamics such as enhanced blood flow, hypotension, and dizziness in vivo (as in nicotine poisoning).