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.
References:
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;143:329-36.
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;42:303-14.
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;48:459-62..
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;114:1383-8.
10. Maeda Y, Okita W, Ichimura K. Increased nasal patency caused
by smoking and contraction of isolated human nasal mucosa. Rhinology
2004;42:63-7.
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;59:303-7.
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;111:1054-8.
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;65:575-9.
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;9:53-7.
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;50:161-8.
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