12-MONTH INHALATION STUDY ON ROOM-AGED CIGARETTE SIDESTREAM SMOKE IN RATS

The present study extends the current scope of rat inhalation studies on surrogates of environmental tobacco smoke. The 12-mo inhalation per iod enabled an investigation of the potential progression or occurrenc e of new morphologic effects from subchronic to chronic inhalation. In addition, pulmonary inflammation and oxidative DNA damage were invest igated. Female Wistar rats were whole-body exposed to room-aged cigare tte sidestream smoke (RASS) generated from the reference cigarette 1R4 F at 6 and 72 mu g total particulate matter/L for 12 h/day, 5 days/wk, for 12 mo. To enable an evaluation of the exposure mode, another grou p of rats was exposed head-only to 12 mu g total particulate matter/L for 7 h/day. Whole-body exposure conditions per se resulted in changes of the RASS composition. An analysis of urinary nicotine metabolites showed that with whole-body exposure, RASS components, such as nicotin e, were additionally taken up by routes other than inhalation. Indepen dent from the exposure mode, blood carboxyhemoglobin and the hemoglobi n adduct of 4-aminobiphenyl were used as biomarkers for the RASS conce ntration and dose, respectively. Histopathological changes were minima l to moderate reserve-cell hyperplasia and slight squamous metaplasia of the respiratory epithelium, as well as minimal reserve-cell hyperpl asia and atrophy of the olfactory epithelium in the anterior nasal cav ity; slight eosinophilic globules in sustentacular cells of the olfact ory epithelium in the anterior and posterior nasal cavity; pronounced squamous metaplasia and hyperplasia in the larynx at the base of the e piglottis; and slight reserve-cell hyperplasia in the bronchial respir atory epithelium. Most of the changes were adaptive and similar in typ e and degree to those seen in previous subchronic RASS inhalation stud ies. A flow cytometric analysis of bronchoalveolar lavage cells, that is, alveolar macrophages, lymphocytes, and polymorphonuclear leukocyte s, did not show signs of pulmonary inflammation after 6 or 12 mo of in halation. As a measure for oxidative DNA modifications, 8-hydroxydeoxy -guanosine was determined in the lungs and nasal epithelia. No change was seen for this parameter at either rime point in the lungs. There w as a slight but not consistent increase in the nasal respiratory and o lfactory epithelia as well as in urinary 8-hydroxydeoxy-guanosine excr etion. In summary, there was little indication for progression or occu rrence of new effects from 3 or 6 mo to 12 mo of RASS inhalation. Ther e were also no signs of inflammation or oxidative DNA modification in the lungs. Chronic head-only exposure to RASS was shown to be technica lly feasible and is generally considered preferable for smoke inhalati on studies over whole-body exposure to avoid artificial changes in smo ke composition and the noninhalative uptake of smoke constituents.