Abstract
Clinical studies have shown that cigarette smoking is a dose-dependent and independent risk factor for acute pancreatitis. Cigarette smoke contains nicotine which can be converted to the potent receptor ligand and toxin, NNK [4-(methylnitrosamino)-1-(3-pyridyI)-1-butanone]. Previously, we have shown that NNK induces premature activation of pancreatic zymogens in rats, an initiating event in pancreatitis, and this activation is prevented by pharmacologic inhibition of nicotinic acetylcholine receptors (nAChR). In this study, we determined whether NNK mediates pancreatitis through the alpha 7 isoform of nAChR using alpha 7nAChR knockout mice. PCR analysis confirmed expression of non-neuronal alpha 7nAChR in C57BL/6 (WT) mouse and human acinar cells. NNK treatment stimulated trypsinogen activation in acini from WT but not alpha 7nAChR(-/-) mice. NNK also stimulated trypsinogen activation in human acini. To further confirm these findings, WT and alpha 7nAChR(-/-) mice were treated with NNK in vivo and markers of pancreatitis were measured. As observed in acini NNK treatment induced trypsinogen activation in WT but not alpha 7nAChR(-/-) mice. NNK also induced other markers of pancreatitis including pancreatic edema, vacuolization and pyknotic nuclei in WT but not alpha 7nAChR(-/-) animals. NNK treatment led to increased neutrophil infiltration, a marker of inflammation, in WT mice and to a significantly lesser extent in alpha 7nAChR(-/-) mice. We also examined downstream targets of alpha 7nAChR activation and found that calcium and PKC activation are involved down stream of NNK stimulation of alpha 7nAChR. In this study we used genetic deletion of the alpha 7nAChR to confirm our previous inhibitor studies that demonstrated NNK stimulates pancreatitis by activating this receptor. Lastly, we demonstrate that NNK can also stimulate zymogen activation in human acinar cells and thus may play a role in human disease.