ToxSci Advance Access published online on April 27, 2005
Toxicological Sciences, doi:10.1093/toxsci/kfi179
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1 Research and Development Department, R. J. Reynolds Tobacco Co., Winston-Salem, NC 27102
* To whom correspondence should be addressed. Cigarettes that burn tobacco produce a complex mixture of chemicals, including mutagens and carcinogens. Cigarettes that primarily heat tobacco produce smoke with marked reductions in the amount of mutagens and carcinogens and demonstrate reduced mutagenicity and carcinogenicity in a battery of toxicological assays. Chemically-induced oxidative stress, DNA damage, and inflammation may alter cell cycle regulation, and are important biological events in the carcinogenic process. The objective of this study was to characterize and compare the effects of smoke condensates from cigarettes that burn or primarily heat tobacco on gene expression in NHBE cells using quantitative RT/PCR and to evaluate the effects on cell cycling using flow cytometry. Cigarette smoke condensates (CSCs) were prepared from Kentucky 1R4F cigarettes (a tobacco-burning product designed to represent the average full-flavor, low "tar" cigarette in the US market) and Eclipse (a cigarette that primarily heats tobacco) using FTC machine smoking conditions. CSC from 1R4F cigarettes induced statistically-significant increases in the mRNA levels of genes responsive to DNA damage (GADD45) and involved in cell cycle regulation (p21;WAF1/CIP1), compared to CSC from Eclipse cigarettes. Additionally, genes coding for cyclooxygenase-2 (COX-2) and interleukin 8 (IL-8), which are associated with oxidative stress and inflammation, respectively, were increased statistically-significantly more by CSC from 1R4F than Eclipse. Furthermore, a dose-dependent increase in IL-8 protein secretion into cell culture media was stimulated by 1R4F exposure while minimal IL-8 protein was secreted following Eclipse treatment. The biological relevance of the differential effect on gene expression was reflected in differential cell cycle regulation, as cells exposed to 1R4F CSC exhibited more significant S- and G2-phase accumulation than cells exposed to Eclipse CSC. These data indicate that the simplified smoke chemistry of the tobacco-heating Eclipse cigarette yields statistically-significant reductions in the expression of key genes involved in DNA damage, oxidative stress, inflammatory response, and cell cycle regulation in normal human bronchial epithelial cells compared to a representative tobacco-burning cigarette.
Received February 16, 2005
Accepted April 18, 2005
Immunotoxiocology
Gene expression in normal human bronchial epithelial (NHBE) cells following in vitro exposure to cigarette smoke condensate
Wanda R. Fields, E-mail: fieldsw{at}rjrt.com
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