Abstract Body (Do not enter title and authors here): Background: The presence of synthetic nicotine analogs in "tobacco-free" products, such as 6-methylnicotine (6MN) in SPREE BAR (aka Metatine™), presents regulatory and public health challenges. Although SPREE BAR is already in the marketplace, little is known about its potential cardiovascular toxicity.
Hypothesis: Because 6MN is structurally similar to nicotine (it has a single added methyl group at 6-position of the pyridine ring), we hypothesized that S-6MN would have similar vascular effects as S-nicotine.
Methods: To test our hypothesis, we compared the direct vasoactive effects of S-6MN with S-nicotine in isolated murine blood vessels including aorta and superior mesenteric artery (SMA). Because S-6MN is found in SPREE BAR, we also tested for direct vasoactivity of SPREE BAR Blue Razz Ice E-liquid.
Results: S-6MN induced a concentration-and NO-dependent relaxation (EC₅₀: 0.9±0.4 µM, n=5) in phenylephrine (PE)-precontracted SMA that was more potent than that of nicotine (EC₅₀: 2.7±0.1 µM, n=4; P<0.05, t-test) and sensitive to LNAME. Similarly, either a 5- or 60-min incubation of aorta with S-6MN (300 mM) induced endothelial dysfunction (ED) -- measured as an impaired acetylcholine (ACh)-induced relaxation. For example, the Control ACh relaxation was -86.3±3.4% (n=4) whereas incubation with 300 mM S-6MN diminished ACh relaxation (-69.2±5.6%, n=4; p<0.05 vs Control) and S-nicotine did not alter ACh relaxation (-77.9±2.2%, n=4) indicating that, in both blood vessels, S-6MN was more potent than S-nicotine. Neither S-6MN nor S-nicotine had any effect on the relaxation induced by an NO donor (i.e., sodium nitroprusside). Surprisingly, direct addition of SPREE BAR E-liquid to isolated aorta resulted in significantly and profoundly impaired contractility of either phenylephrine or high potassium – an effect that was slowly reversible with repeated washout. This effect was not observed with either S-6MN or S-nicotine indicating another component is present in SPREE BAR Blue Razz Ice E-liquid that has a profound inhibitory action in blood vessels.
Conclusions: These findings reveal that S-6MN, a nicotine analog, has more potent vasoactivity than S-nicotine. As S-6MN induced ED in vitro, it potentially could elevate cardiovascular disease risk in users of products containing 6MN. These data stress the need for immediate FDA regulatory oversight of new and emerging non-nicotine containing products.