Ciliary alterations in hamster respiratory tract epithelium after exposure to carcinogens and cigarette smoke

Animal models of smoke inhalation injury and related acute and chronic lung diseases

Smoke inhalation injury leads to various acute and chronic lung diseases and thus is the dominant cause of fire-related fatalities. In a search for an effective treatment and validation of therapies different classes of animal models have been developed, which include both small and large animals. These models have advanced our understanding of the mechanism of smoke inhalation injury, enabling a better understanding of pathogenesis and pathophysiology and development of new therapies. However, none of the animal models fully mirrors human lungs and their pathologies. All animal models have their limitations in replicating complex clinical conditions associated with smoke inhalation injury in humans. Therefore, for a correct interpretation of the results and to avoid bias, a precise understanding of similarities and differences of lungs between different animal species and humans is critical. We have reviewed and presented comprehensive comparison of different animal models and their clinical relevance. We presented an overview of methods utilized to induce smoke inhalation injuries, airway micro-/macrostructure, advantages and disadvantages of the most commonly used small and large animal models.

Animal models in carotenoids research and lung cancer prevention

Numerous epidemiological studies have consistently demonstrated that individuals who eat more fruits and vegetables (which are rich in carotenoids) and who have higher serum β-carotene levels have a lower risk of cancer, especially lung cancer. However, two human intervention trials conducted in Finland and in the United States have reported contrasting results with high doses of β-carotene supplementation increasing the risk of lung cancer among smokers. The failure of these trials to demonstrate actual efficacy has resulted in the initiation of animal studies to reproduce the findings of these two studies and to elucidate the mechanisms responsible for the harmful or protective effects of carotenoids in lung carcinogenesis. Although these studies have been limited by a lack of animal models that appropriately represent human lung cancer induced by cigarette smoke, ferrets and A/J mice are currently the most widely used models for these types of studies. There are several proposed mechanisms for the protective effects of carotenoids on cigarette smoke-induced lung carcinogenesis, and these include antioxidant/prooxidant effects, modulation of retinoic acid signaling pathway and metabolism, induction of cytochrome P450, and molecular signaling involved in cell proliferation and/or apoptosis. The technical challenges associated with animal models include strain-specific and diet-specific effects, differences in the absorption and distribution of carotenoids, and differences in the interactions of carotenoids with other antioxidants. Despite the problems associated with extrapolating from animal models to humans, the understanding and development of various animal models may provide useful information regarding the protective effects of carotenoids against lung carcinogenesis.

Alcohol, vitamin A, and beta-carotene: adverse interactions, including hepatotoxicity and carcinogenicity

Isozymes of alcohol and other dehydrogenases convert ethanol and retinol to their corresponding aldehydes in vitro. In addition, new pathways of retinol metabolism have been described in hepatic microsomes that involve, in part, cytochrome P450s, which can also metabolize various drugs. In view of these overlapping metabolic pathways, it is not surprising that multiple interactions between retinol, ethanol, and other drugs occur. Accordingly, prolonged use of alcohol, drugs, or both, results not only in decreased dietary intake of retinoids and carotenoids, but also accelerates the breakdown of retinol through cross-induction of degradative enzymes. There is also competition between ethanol and retinoic acid precursors. Depletion ensues, with associated hepatic and extrahepatic pathology, including carcinogenesis and contribution to fetal defects. Correction of deficiency through vitamin A supplementation has been advocated. It is, however, complicated by the intrinsic hepatotoxicity of retinol, which is potentiated by concomitant alcohol consumption. By contrast, beta-carotene, a precursor of vitamin A, was considered innocuous until recently, when it was found to also interact with ethanol, which interferes with its conversion to retinol. Furthermore, the combination of beta-carotene with ethanol results in hepatotoxicity. Moreover, in smokers who also consume alcohol, beta-carotene supplementation promotes pulmonary cancer and, possibly, cardiovascular complications. Experimentally, beta-carotene toxicity was exacerbated when administered as part of beadlets. Thus ethanol, while promoting a deficiency of vitamin A also enhances its toxicity as well as that of beta-carotene. This narrowing of the therapeutic window for retinol and beta-carotene must be taken into account when formulating treatments aimed at correcting vitamin A deficiency, especially in drinking populations.

An ultrastructural study of primary cilia, abnormal cilia and ciliary knobs from the ciliated cells of the guinea-pig trachea

Single primary cilia are found in developing as well as mature ciliated cells of guinea-pig tracheal epithelium. A few biciliated cells were observed, and in a rare case one cell had developed four such processes. Primary cilia are characterized by a 9 + 0 microtubular arrangement near the base, while a transition to an 8 + 1 pattern occurs at a slightly more distal position. Spokes are lacking, and dynein arms are absent or incompletely developed. The function, if any, of primary cilia remains unknown. In the population of the motile 9 + 2 cilia atypical forms are very rare, i.e. less than 0.1%. Of the various abnormalities cilia with supernumary microtubules are most common. Only one atypical basal body was observed. Although some of the aberrant forms undoubtedly are non-motile, their very low number suggests that they have no practical influence on the muco-ciliary clearance. Local extrusions of the ciliary membrane, here named ciliary knobs, are believed to be fixation artefacts. It is suggested that they represent circumscribed regions of the ciliary membrane which are sensitive to changes in the environmental osmotic pressure.

Deposition and clearance of labeled cigarette smoke particles in rat respiratory and digestive tract

In this investigation 160 8-wk-old Sprague-Dawley rats inhaled smoke from 14C-labeled cigarettes in a Hamburg II smoking machine. The research cigarettes were labeled with [16,17-14C]dotriacontane. Eighty of the rats were acclimatized to smoke from nonlabeled research cigarettes for 21 d before inhaling labeled cigarette smoke. The investigation was divided into four experiments. In experiment I all rats were killed immediately after exposure to the 14C-labeled smoke from 30 cigarettes (10 muCi per cigarette) and the organs of the respiratory and digestive tracts were measured for 14C activity. These animals showed high activity in the apex nasi, fundus nasi, and larynx. The highest activity was found in the lobus dexter caudalis and the lobus sinister of the lung. The lungs contained four-fifths of the condensate inhaled into the respiratory tract. In experiment II three animals were killed immediately after smoking, three after 6 h, and four after 24 h. No activity was found after 6 h in apex, fundus nasi, larynx, and trachea. The lungs showed no clearance at all. The activity in the digestive tract was highest in the stomach and the esophagus immediately after cessation of smoking. These values decreased rapidly after 6 h. In experiment III the animals were killed after 7, 21, and 42 d. Clearance from the upper respiratory tract was fast, whereas clearance from the lungs was slow. Clearance from all lung lobes was faster in the nonacclimatized animals. In experiment IV the rats inhaled the smoke from 14C-labeled cigarettes (2 muCi per cigarette) on 5 successive days. The animals were killed 7, 14, and 21 d after the last smoke inhalation. Clearance from the lungs was slower in acclimatized and non-acclimatized animals than in experiment III.

Cigarette smoke induced pathology of the rat respiratory tract: a comparison of the effects of the particulate and vapour phases

Changes in the rat respiratory tract produced by a 12-week exposure to the particulate or vapour phases of cigarette smoke are described and compared with the changes produced by combined exposure to both phases. The most extensive changge in the upper respiratory tract was a pronounced squamous metaplasia of the laryngeal epithelium, along with extensive deciliation and squame cell production. In the lung, smoke exposure produced marked increase in the numbers of bronchial goblet cells and intra-alveolar brown-gold macrophages. None of the above changes could be directly attributed to exposure to vapour phase alone, and in many cases the lesions produced by whole smoke and by carbon filtered smoke were directly comparable. For lesions to occur in some ciliated areas of the tract both phases of the smoke were required.

Pulmonary tumorigenesis in Syrian golden hamsters after intratracheal instillations with automobile exhaust condensate

Syrian golden hamsters were intratracheally instilled once every two weeks for life with automobile exhaust condensate (AEC) at two dose levels. The condensate was prepared from the most common German passenger car driven in the Europa-Test cycle (simulated city driving) and contained 340 microgram/g benzo(a)pyrene (B(a)P). Despite the very low total dose of B(a)P received, all animals of both dosage groups developed multiple pulmonary adenomas. Electron microscopy revealed these tumors to resemble B(a)P induced pulmonary adenomas in their ultrastructure. Numerous condensate-laden macrophages in tumor and peripheral lung tissues indicated that little of the instilled condensate had been removed from the airways through mucociliary action.