Beyond Animal Research
By Jonathan Balcombe, Ph.D.
Animal Smoking Experiments: Part II
Scientists have known for decades that smoking can have devastating effects on human health. Yet researchers continue to conduct smoking experiments on animals. Do such experiments offer new insights?
In an earlier column (Part I), I discussed several recent animal smoking experiments that appear merely to confirm what is already known from human studies. To investigate further, I followed up on four of these animal studies (all published in 2004) using the National Institutes of Health’s online PubMed database.
Animal study 1: This study found that lung tumor rates tend to rise with increased smoke exposure in mice.1
Clinical precedent: Smoking’s infamous link to lung cancer first became scientifically evident from two landmark epidemiological studies published in 1950.2, 3 Since then, tens of thousands of studies have reinforced that link. A PubMed search of “smoking AND human AND lung tumors” on October 25 yielded 7,754 hits, of which some 340 papers have appeared in 2004 alone.
Animal study 2: This study found that rats exposed to both a known tobacco carcinogen and asbestos developed higher rates of lung cancer than rats exposed to just one pathogen. The authors acknowledge a “suspected synergism of smoking [and] asbestos carcinogenesis [in rats].”4
Clinical precedent: The relationship between tobacco smoke, asbestos, and cancer risk has been documented since the 1960s by a wide range of research, including a multitude of epidemiological studies and meta-analyses.5,6,7 There is even a term—the relative asbestos effect (RAE)—for the relative risk of lung cancer due to asbestos exposure in non-smokers and smokers.8
Animal study 3: Study of the nasal linings of rats chronically exposed to tobacco smoke suggests that smell loss [in humans] may be triggered by loss of olfactory sensory neurons.9
Clinical precedent: There are dozens of human clinical studies examining smoking’s effects on nasal/sinus health and function. Human studies can investigate both cellular and behavioral effects10,11,12,13 and they offer two additional advantages: the subjects can report their symptoms (e.g., ability to smell something), and the results are clearly applicable to the human condition.
Animal study 4: This study found that rats exposed to cigarette smoke had smaller kidneys.14
Clinical precedent: The effects of smoking on kidney morphology and function can be studied in living or deceased human patients. Not surprisingly, data pre-exist this study. For example, a recent study found that renal size increased with pack-years of smoking in middle-aged people.15
With a wealth of human clinical data on tobacco smoking and human health—and the common knowledge that smoking is harmful—these mundane animal studies do not benefit human health. Yet they continue to be approved, funded, and published.
1. Witschi H, Espiritu I, Uyeminami D, Suffia M, Pinkerton KE. Lung tumor response in strain A mice exposed to tobacco smoke: some dose-effect relationships. Inhal Toxicol. 2004;16:27-32.
2. Wynder DL, Graham EA. Tobacco smoking as a possible etiologic factor in bronchiogenic cancer. JAMA. 1950;143:329-336.
3. Doll R, Hill AB. Smoking and carcinoma of the lung (preliminary report). Brit Med J. 1950;117:39-48.
4. Loli P, Topinka J, Georgiadis P, Dusinska M, Hurbankova M, Kovacikova Z, Volkovova K, Wolff T, Oesterle D, Kyrtopoulos SA. Benzo[a]pyrene-enhanced mutagenesis by asbestos in the lung of lambda-lacI transgenic rats. Mutat Res. 2004;553:79-90.
5. Kurihara N, Wada O. Silicosis and smoking strongly increase lung cancer risk in silica-exposed workers. Ind Health. 2004;42:303-314.
6. Savastano L, Bonacci S, Saracino V, Longo M. [The association of lung cancer with asbestos and tobacco smoking (Article in Italian)]. Clin Ter. 2004;155:69-74.
7. Cai SX, Zhang CH, Zhang X, Morinaga K. Epidemiology of occupational asbestos-related diseases in China. Ind Health. 2001;39:75-83.
8. Berry G, Liddell FD. The interaction of asbestos and smoking in lung cancer: a modified measure of effect. Ann Occup Hyg. 2004;48:459-462.
9. Vent J, Robinson AM, Gentry-Nielsen MJ, Conley DB, Hallworth R, Leopold DA, Kern RC. Pathology of the olfactory epithelium: smoking and ethanol exposure. Laryngoscope. 2004;114:1383-1388.
10. Maeda Y, Okita W, Ichimura K. Increased nasal patency caused by smoking and contraction of isolated human nasal mucosa. Rhinology. 2004;42:63-67.
11. Vachier I, Vignola AM, Chiappara G, Bruno A, Meziane H, Godard P, Bousquet J, Chanez P. Inflammatory features of nasal mucosa in smokers with and without COPD. Thorax. 2004;59:303-307.
12. Sugiyama K, Matsuda T, Kondo H, Mitsuya S, Hashiba M, Murakami S, Baba S. Postoperative olfaction in chronic sinusitis: smokers versus nonsmokers. Ann Otol Rhinol Laryngol. 2002;111:1054-1058.
13. Rosenblatt MR, Olmstead RE, Iwamoto-Schaap PN, Jarvik ME. Olfactory thresholds for nicotine and menthol in smokers (abstinent and nonabstinent) and nonsmokers. Physiol Behav. 1998;65:575-579.
14. Dundar M, Kocak I, Culhaci N. Effects of long-term passive smoking on the diameter of glomeruli in rats: Histopathological evaluation. Nephrology (Carlton). 2004;9:53-57.
15. Paivansalo MJ, Merikanto J, Savolainen MJ, Lilja M, Rantala AO, Kauma H, Reunanen A, Kesaniemi YA, Suramo I. Effect of hypertension, diabetes and other cardiovascular risk factors on kidney size in middle-aged adults. Clin Nephrol. 1998;50:161-168.