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

Abstract

The present study extends the current scope of rat inhalation studies on surrogates of environmental tobacco smoke. The 12-mo inhalation period enabled an investigation of the potential progression or occurrence of new morphologic effects from subchronic to chronic inhalation. In addition, pulmonary inflammation and oxidative DNA damage were investigated. Female Wistar rats were whole-body exposed to room-aged cigarette sidestream smoke (RASS) generated from the reference cigarette 1R4F at 6 and 12 mug total particulate matter/L for 12 h/day, 5 days/wk, for 12 mo. To enable an evaluation of the exposure mode, another group of rats was exposed head-only to 12 mug 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 nicotine, were additionally taken up by routes other than inhalation. Independent from the exposure mode, blood carboxyhemoglobin and the hemoglobin adduct of 4-aminobiphenyl were used as biomarkers for the RASS concentration and dose, respectively. Histopathological changes were minimal to moderate reservecell hyperplasia and slight squamous metaplasia of the respiratory epithelium, as well as minimal reserve-cell hyperplasia and atrophy of the olfactory epithelium in the anterior nasal cavity; slight eosinophilic globules in sustentacular cells of the olfactory epithelium in the anterior and posterior nasal cavity; pronounced squamous metaplasia and hyperplasia in the larynx at the base of the epiglottis; and slight reserve-cell hyperplasia in the bronchial respiratory epithelium. Most of the changes were adaptive and similar in type and degree to those seen in previous subchronic RASS inhalation studies. A flow cytometric analysis of bronchoalveolar lavage cells, that is, alveolar macrophages, lymphocytes, and polymorphonuclear leukocytes, did not show signs of pulmonary inflammation after 6 or 12 mo of inhalation. As a measure for oxidative DNA modifications, 8-hydroxydeoxyguanosine was determined in the lungs and nasal epithelia. No change was seen for this parameter at either time point in the lungs. There was a slight but not consistent increase in the nasal respiratory and olfactory epithelia as well as in urinary 8-hydroxydeoxyguanosine excretion. In summary, there was little indication for progression or occurrence of new effects from 3 or 6 mo to 12 mo of RASS inhalation. There were also no signs of inflammation or oxidative DNA modification in the lungs. Chronic head-only exposure to RASS was shown to be technically feasible and is generally considered preferable for smoke inhalation studies over whole-body exposure to avoid artificial changes in smoke composition and the noninhalative uptake of smoke constituents.