Nicotine promotes development of bile duct ligation-induced liver fibrosis by increasing expression of nicotinic acetylcholine receptors in rats

Aim of the study: Liver fibrosis and cigarette smoking seem to be directly linked. Nicotine, as an agonist of nicotinic acetylcholine receptors (nAChRs), induces many downstream signaling pathways. The pathways through which nicotine affects the process of liver fibrosis have not been clarified. The present study aimed to investigate the nicotine-induced effects on fibrosis progression in cholestatic rats. Material and methods: First, the Wistar rats were subjected to sham or bile duct ligation (BDL) surgery. The rats were treated with low and high doses of nicotine (1 or 10 mg/kg) for three weeks. They were monitored for their body weights before and 21 days after BDL. Also, spleens were weighed to calculate the spleen/body weight ratio. Ductular proliferation and fibrosis were evaluated using hematoxylin and eosin (H&E) as well as Masson's trichrome staining. The mRNA expression of alpha 4nAChR, alpha 7nAChR, and fibrosis gene alpha-smooth muscle actin (alpha-SMA) was measured by real-time PCR. Results: The findings showed that nicotine promotes the development of BDL-induced liver fibrosis. The ratio of spleen/body weight was significantly affected by nicotine exposure. H&E and Masson's trichrome staining showed that the level of liver fibrosis was higher in the cholestatic BDL groups, and this effect was significantly augmented in the nicotine-treated rats. Also, alpha 4nAChR, alpha 7nAChR, and alpha-SMA expression was observed in the BDL rats and increased following nicotine treatment. Conclusions: The activation of nAChR triggers biliary proliferation and liver fibrosis. Studying the intracellular mechanism of nicotine and alteration in the expression of nicotinic receptors following nicotine exposure can be useful both in diagnosing nicotine-related diseases and finding new treatment strategies.