Response of rat lung to tobacco smoke condensate or fractions derived from it administered repeatedly by intratracheal instillation

Potential inhibitors of tobacco carcinogenesis

Tobacco smoking is causally associated with cancer of the lung, upper aerodigestive tract, pancreas, renal pelvis and urinary bladder. Tobacco chewers and especially snuff dippers face an increased risk for cancer of the oral cavity and pharynx. Although cessation of the tobacco habits is the only sure way to avoid an increased risk of tobacco-related cancers, certain modified products should be available to lower the incidence rates for cancer among those tobacco chewers and smokers who are unable to give up their tobacco habits. The modified cigarette has been the first approach toward the reduction of cancer risk. In the case of cancer of the lung, the long-term smoker of low-yield filter cigarettes has a risk reduction of 30-50% over that of the smoker of nonfilter cigarettes; however, the risk of filter cigarette smokers for cancer of the lung and cancer at other sites is still many times higher than that of the nonsmoker. A second modality is the application of natural or synthetic chemopreventive agents. Clinical studies with tobacco users have been primarily limited to the application of beta-carotene and retinoids. Although the data appear encouraging in respect to reducing early lesions in the oral cavity of tobacco chewers and smokers and in respect to second primaries in smokers, the benefits of beta-carotene and retinoids are gradually reversed upon withholding these micronutrients. It is understandable that activities in respect to chemopreventive agents in clinical trials on smokers are limited, since cessation of smoking alone leads within only a few years to a significant reduction of the cancer risk. Another reason for the limited interest in clinical trials on smokers may relate to the lack of laboratory data on the actual effects of chemopreventive agents in animals induced with tobacco-specific carcinogens. However, during the last few years, a number of natural or synthetic chemopreventive agents in animals induced with tobacco-specific carcinogens. However, during the last few years, a number of natural or synthetic chemopreventive agents have been tested in mice and rats which were treated with carcinogenic, tobacco-specific N-nitrosamines (TSNA). The results appear most encouraging in respect to lung tumor reduction. It is hoped that this type of research will gain in interest. Human data suggest that the fat content of the diet influences the cancer risk of smokers.(ABSTRACT TRUNCATED AT 400 WORDS)

Squamous lesions in lungs of rats exposed to tobacco-smoke-condensate fractions by repeated intratracheal instillation

Twice-weekly intratracheal instillations in rats of up to 24 mg of Fraction (R + P)G suspended in either infusine (I) or buffered saline/gelatine (BS/G) gave rise to foci of squamous metaplasia of alveolar epithelium (SqM) and squamous neoplasms (SqN). Fraction (R + P)G, which is a fraction of cigarette-smoke condensate almost as tumorigenic for mouse skin as the nearly 30 × larger mass of condensate from which it is derived, could be given in this way for up to 40 weeks without excessive mortality or any marked effect on the rate of body-weight gain. By contrast, similar treatment with Fraction N(QG), a fraction having very low tumorigenic activity for mouse skin, induced no SqN and barely any excess of SqM over that induced by either vehicle alone.The effects of Fraction (R + P)G on the incidence of SqM and SqN were both time and dose related, the effect on SqM incidence being already evident after 10 weeks of treatment. No SqN seen were unequivocally malignant, though, due to the design of the experiment, only 5 rats exposed to Fraction (R + P)G were observed more than 60 weeks after the start of the experiment.Other changes in the lung, including aggregates of alveolar macrophages laden with golden-brown pigment (GBM) and foci of cuboidal/columnar metaplasia of alveolar epithelium (CCM), were frequently seen in response to both fractions. Fraction (R + P)G administered in I was more effective in causing SqM and SqN than the same fraction administered in BS/G. The implications of the findings are discussed, particularly the possibility that the intratracheal/instillation technique might be useful as a rapid bioassay for comparing the tumorigenicity of different cigarette-smoke condensates.

Response of rat lung to inhaled tobacco smoke with or without prior exposure to 3,4-benzpyrene (BP) given by intratracheal instillation

SPF rats were exposed to the smoke from 10 cigarettes per week from the age of 10 weeks until they died. Survival, body weight, tumour incidence and histopathological appearances of the lungs were compared with those for untreated sham exposed rats. Two further groups were given a single dose of 3,4-benzyprene (BP) by intratracheal instillation. One of these was then exposed to the smoke of 10 cigarettes per week till death. Compared with untreated or sham exposed rats, exposure to smoke was associated with a significant reduction in incidence of mammary tumours. Exposure to smoke was associated with an increasing incidence of collections of macrophages laden with golden-brown pigment (GBM) and of areas of cuboidal or columnar metaplasia (CCM) or squamous metaplasia (Sq.M) of alveolar epithelium. In control rats there was virtually no GBM, a low incidence of CCM and Sq.M. Four out of 406 smoke exposed rats which came to post mortem had squamous neoplasms in the lungs, 3 having lesions of doubtful malignancy and one having a squamous carcinoma. In contrast, no squamous neoplasms were seen in 197 control rats. This difference was not statistically significant. The findings in rats given a single dose of BP were, in all the above respects, similar to those in untreated rats, except that one developed a squamous carcinoma of the lung. The effects of a single dose of BP followed by smoke exposure were in general similar to those of smoke exposure only. Three rats on this treatment regimen developed squamous cancers of the lung. None of the treatments increased the incidence of adenomata of the lungs. The results are discussed in relation to other studies of the effects of smoke exposure on rats and other species.

Response of rat lung to 3,4-benzpyrene administered by intratracheal instillation in infusine with or without carbon black

In a controlled experiment groups of SPF Wistar rats were give 18 once-fortnightly doses of 0-5, 1-0 or 2-0 mg 3,4-benzpyrene (BP) suspended in infusine (I) or in carbon black (CB) + I by intratracheal instillation. Of rats examined post mortem, 1/16 given I+CB only, 0/16 given I only, 15/51 given BP in I+CB and 24/48 given BP in I developed squamous neoplasms of the lung. The incidence of tumours was significantly related to dose of BP. At the 1 or 2 mg dose levels BP in I only was more productive of tumours than BP in I+CB. Other changes encountered included squamous metaplasia of alveolar and bronchiolar epithelium (Sq.M), but not of bronchial epithelium, and cuboidal and columnar metaplasia of alveolar epithelium in the vicinity of terminal bronchioles (CCM). Sq.M was associated with exposure to BP or I+CB. CCM was strongly associated with exposure to I+CB but only weakly with exposure to BP.