Cigarettes That Primarily Heat Tobacco Versus Cigarettes That Burn Tobacco

A Comparison Of The Effects Of Mainstream Smoke From A Cigarette That Primarily Heats Tobacco Versus A Cigarette That Burns Tobacco Using A Subchronic Nose-Only Inhalation Study Design

     This report compared the potential biologic activity of mainstream smoke from a cigarette that primarily heats tobacco (PHT; Eclipse) with that from mainstream smoke from a 1R4F reference cigarette, one that burns tobacco.  Male and female rats were studies in a subchronic, nose-only inhalation study design.  The authors monitored clinical signs, body and organ weights, clinical chemistry, hematology, carboxyhemoglobin, serum nicotine, plethysmography, gross pathology, and histopathology.  Animals were exposed to smoke for 1 h/day, 5 days/wk for 13 weeks; concentrations of 0, 0.16, 0.32, or 0.64 mg wet total particulate matter (WTPM) per liter of air were used.  The smoke was generated on modified AMESA  Mark III smoking machines (CH Technologies at http://www.toxics.com) which were operated using the US Federal Trade Commission standard of 2-second puff of 35 ml at a rate of one time per minute.  Identical concentrations of mainstream smoke WTPM were generated for both the PHT cigarettes and the reference cigarettes.

     PHT cigarettes generate heat by burning a carbon heat source located at the tip of the cigarette; this in turn heats the tobacco rod.  The first part of the rod contains glycerol, which is vaporized along with tobacco flavors.  The condensation of these vapors produces the mainstream smoke.  The smoke is then drawn through a cellulose acetate cigarette filter.  Since only a minute amount of tobacco is burned at initial ignition, the smoke generated contains significantly reduced concentrations of specific tobacco smoke components including benzo(a)pyrene, catechol, 4-aminobiphenyl, formaldehyde, free-radicals, and tobacco-specific nitrosamines as compared to the mainstream smoke generated from the reference 1R4F cigarette.  It follows that if these specific smoke components were responsible for toxicity, then the mainstream smoke generated from the PHT cigarettes would be expected to have less biologic activity.  In support of this, the scientific literature assessing DNA-adduct formation, in vitro genotoxicity studies, cell cytotoxicity via functional gap junction assessment, inflammatory potential (measurement of production of inflammatory factors), and dermal promotion assays support the hypothesis that PHT cigarettes have lower biological activity than cigarettes that burn tobacco.

     By this sub-chronic inhalation study, the authors demonstrated that when rats were exposed to equivalent concentrations of WTPM from either cigarette, less biological activity was observed in experimental animals exposed to PHT smoke.  Subsets of rats from each exposure group were maintained for an additional 13 weeks without smoke exposure.   Upon sacrifice, most of the effects noted at the end of the smoke exposure period had disappeared.  Those effects that remained were regressing toward a normal baseline.  This provides information and support on the apparent short-term reversibility of any changes that occurred in either smoke group.  The results of this study support the existing literature regarding the reduced biological activity of mainstream smoke generated from PHT cigarettes as compared to mainstream smoke generated from cigarettes that burn tobacco.

Source: Ayres, P.H., Hayes, J.R., Higuchi, M.A., Mosberg, A.T., and Sagartz, J.W.  2001. Subchronic Inhalation by Rats of Mainstream Smoke from a Cigarette that Primarily Heats Tobacco Compared to a Cigarette that Burns Tobacco. Inhalation Toxicology 13:149-186

By:      Arlene L. Weiss, MS, DABT

Contributing Editor