Cigarette smoke increases intimal hyperplasia (IH) and homocysteine (Hcy) in a rat CEA model

Purpose: Evaluate cigarette smoke exposure on post CEA IH and define Hcy’s role in this effect. Introduction: HyperHcys and smoking are independent risks for CVD, however the relationship of these two factors with post CEA IH are unclear. We performed a CEA in rats exposed to cigarette smoke with the hypothesis that smoking would increase IH that may relate to an elevated plasma Hcy. Folic acid (FA) was used to test for the significance of Hcy elevation. Methods: All rats underwent an open CEA with direct removal of the intima and suture closure of the carotid. N = 13 rats received “smoke” exposure and N = 12 received “no smoke”. Smoke exposure was 8 cigarettes/day 2 weeks prior, and 2 weeks post CEA. The ‘no smoke’ and ‘smoked’ rats were given either control (N = 7, N = 6) or 25 ppm added FA (N = 6, N = 6), resulting in 4 groups of rats. Rats were sacrificed at 2 weeks post CEA; liver, urine, blood and carotid arteries samples were obtained. Endpoints were: IH (% luminal stenosis), plasma Hcy and 2 enzymes responsible for Hcy metabolism MTHFR and CBS, as well as urinary cotinine (a nicotine metabolite). Results: Smoke exposure increased IH vs. no-smoke controls by nearly 120% (57.8 ± 6.2 vs. 26.8 ± 5.4 %, p = 0.005). Smoke exposed rats had an increased plasma Hcy vs no smoke controls (8.3 ± 0.8 vs 5.7 ± 0.8 umol/L, p = 0.015). Regression analysis showed a positive correlation between IH and plasma Hcy (R = 0.41, p = 0.039). FA in the no smoke group produced no changes in IH or Hcy. Smoked rats given FA had decreased plasma Hcy from smoke group and similar to no smoke group. Along with reductions in Hcy, FA eliminated the increase in IH seen with smoke exposure (33.5 ± 6.2 vs. 57.8 ± 6.2 %, p = 0.003). CBS activity decreased in smoked rats by nearly 20% vs no smoke rats (474.2 ± 12.2 vs. 592.0 ± 30.1 u/mg, p = 0.004). FA supplementation in smoked rats increased CBS activity to control no smoke group levels. There were no changes in MTHFR activity among the groups. Smoked rats had increased urinary peak cotinine levels vs no smoke rats (1111.1 ± 302.7 vs. 39.7 ± 12.5, p = 0.04) which decreased with FA (p = 0.01). Conclusion: Smoking increases plasma Hcy and post-CEA IH. This suggests Hcy has an etiological role in the IH increase observed with smoking, since both were negated with FA.