Cigarette smoking is an established risk factor for cancer of the lung and the pancreas. Certain epidemiological studies indicate that the development of lung and pancreatic cancer in smokers is influenced by the type and amount of dietary polyunsaturated fatty acids (PUFA). A nicotine-derived nitrosamine, NNK, is known to induce lung and pancreatic cancers in rodents. Hoffmann et al. showed that compared to a low-corn oil diet (5.0%), a high-corn oil diet (23.5%) increased the potency of NNK to induce cancers of the pancreas and the lung in rats (Cancer Res., 53: 2758-2761, 1993). However, the biochemical and molecular mechanisms by which the type of dietary fat alters NNK-induced carcinogenesis remains unknown. Toward this end, we initiated a study to better understand the effect of the type of PUFA in NNK-induced lung cancer in rats at the protein level. Male F344 rats were divided into 4 groups and fed high fat diets containing either corn oil (CO) or fish oil (FO). Two groups also received 2 ppm of NNK in drinking water. The FO diet contained 17% fish oil and 3% corn oil, while the CO diet contained 20% corn oil. Rats were sacrificed at 3 month intervals and the lung and pancreatic tissues were excised and snap-frozen in liquid nitrogen. Whole lung tissue proteins were separated by two-dimensional liquid chromatography in which separation was based on isoelectric point (pI) in a first-dimension chromatofocusing step, followed by hydrophobicity in a reversed-phase step in the second dimension. Using a peak height threshold value of 0.001 in the second-dimension chromatograms we observed over 500 separate protein peaks in the pI range of 4.0 to 8.0. Overall two-dimensional protein fingerprints were very similar among samples. Comparison of two-dimensional proteome maps, however, showed that two proteins in the pI range of 5.4 to 5.7 were overexpressed in the lungs of rats fed CO as compared FO, while the remaining 35 proteins in this pI range did not change. These two overexpressed proteins were identified as apolipoprotein A-I (Apo-AI) and Clara cell 17-KDa protein (CC17) by MALDI-TOF-MS/MS analysis and confirmed by Western blot analyses. Additionally, NNK treatment further increased the expression of Apo-AI in rats fed CO, showing a three fold increase compared to those fed FO. NNK supplementation had no measurable effect on the expression of CC17 in both groups of rats fed either CO or FO. These findings are consistent with previous studies demonstrating that the elevated expression of Apo-AI in human serum and tissues is associated with the risk of breast and colonic adenocarcinoma progression. Supported by NCI grants PO1 CA70972 and CA76228.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]