Inhibition by β‐Carotene of Upper Respiratory Tumorigenesis in Hamsters Receiving Diethylnitrosamine Followed by Cigarette Smoke Exposure

In recent intervention studies, β‐carotene failed to reduce or even increased the incidence of lung cancers in smokers. In the present investigation, the modifying effects of β‐Carotene at various doses on the development of upper respiratory tract tumors were investigated in Syrian hamsters treated with diethylnitrosamine (DEN) and cigarette smoke. A total of 120 male 5‐week‐old hamsters were divided into 4 groups, each consisting of 30 animals. After a sing le subcutaneous (s.c.) injection of 100 mg/kg DEN, hamsters in groups 1–4 were respectively administered diets supplemented with β‐carotene at doses of 0.5%, 0.05%, 0.005% or 0% during experimental weeks 1 to 13, and simultaneously exposed to cigarette smoke. The duration of cigarette smoke exposure was 9 min twice a day, 5 days a week. Because of a marked reduction of body weight in group 1, the highest dose of β‐carotene was changed to 0.25% after 10 days. In all groups, epithelial hyperplasias and/or papillomas were induced in the larynx and trachea. However, the incidence and multiplicity of papillomas in group 1 were significantly (P<0.05) lower than the group 4 values. Moreover, the β‐carotene treatments significantly (P<0.05 or 0.01) reduced both the incidence and multiplicity of hyperplasias in a dose‐dependent manner. The levels of retinol and β‐carotene in the serum, and the retinol level in the liver, were also elevated with dose dependence. Our results thus indicate that β‐carotene inhibits tumorigenesis, even at the high dose of 0.25%, under the present experimental conditions.