Inhalation of carbon monoxide does not accelerate arteriosclerosis in cockerels

The emerging role of outdoor and indoor air pollution in cardiovascular disease

Outdoor and indoor air pollution poses a significant cardiovascular risk, and has been associated with atherosclerosis, the main underlying pathology in many cardiovascular diseases. Although, it is well known that exposure to air pollution causes pulmonary disease, recent studies have shown that cardiovascular health consequences of air pollution generally equal or exceed those due to pulmonary diseases. The objective of this article is to evaluate the current evidence on the emerging role of environmental air pollutions in cardiovascular disease, with specific focus on the types of air pollutants and mechanisms of air pollution-induced cardiotoxicity. Published literature on pollution was systematically reviewed and cited in this article. It is hoped that this review will provide a better understanding of the harmful cardiovascular effects induced by air pollution exposure. This will help to bring a better understanding on the possible preventive health measures and will also serve regulatory agencies and researchers. In addition, elucidating the biological mechanisms underlying the link between air pollution and cardiovascular disease is an essential target in developing novel pharmacological strategies aimed at decreasing adverse effects of air pollution on cardiovascular system.

Chronic carbon monoxide exposure is associated with the increases in carotid intima-media thickness and C-reactive protein level

Being the most common cause of death from poisoning worldwide, cardiovascular manifestations of acute carbon monoxide (CO) poisoning have been subject of various studies but current evidence about effects of chronic CO exposure on atherosclerosis is limited which is very common. We aimed to investigate association of chronic CO exposure with atherosclerosis by measuring carotid intima-media thickness (CIMT) and high-sensitivity C-reactive protein (hs-CRP). Forty healthy male non-smoker indoor barbecue workers (mean age; 33.0 +/- 9.0 years) working in different restaurants for at least three years and 48 age-matched healthy men (mean age; 34.3 +/- 6.6 years) enrolled in the study. Clinical characteristics of indoor barbecue workers and control group were comparable in terms of body mass index, blood pressure, and lipid profile. However, carboxyhemoglobin (COHb) (6.4 +/- 1.5% vs. 2.0 +/- 1.1%), hs-CRP (2.7 +/- 2.0 mg/L vs. 1.1 +/- 0.8 mg/L) and CIMT (1.1 +/- 0.3 mm vs. 0.9 +/- 0.1 mm) were higher in indoor barbecue workers (p < 0.001 for each). In Pearson correlation analysis, CIMT was correlated with COHb concentration (r = 0.635, p < 0.001) and hs-CRP level (r = 0.466, p < 0.001). Among indoor barbecue workers, the years worked (years exposed to CO) are correlated with COHb, hs-CRP and CIMT. In multivariate analysis, COHb concentration is the only independent predictor of CIMT (beta = 0.571, p < 0.001). The increased CIMT and hs-CRP in indoor barbecue workers suggest that chronic CO exposure may increase the risk of atherosclerotic cardiovascular events.

Chronic inhalation of carbon monoxide: effects on the respiratory and cardiovascular system at doses corresponding to tobacco smoking

Carbon monoxide (CO) is a dangerous poison in high concentrations, but the long-term effects of low doses of CO, as in the gaseous component of tobacco smoke, are not well known. The aims of our study were to evaluate the long-term effects of inhaled CO on the respiratory and cardiovascular system at doses corresponding to tobacco smoking and its effect on tumourigenesis and pulmonary neuroendocrine (NE) cells. Female Wistar rats were exposed to either CO (200 ppm) for 20 h/day (n=51) or air (n=26) for 72 weeks. Carboxyhaemoglobin was 14.7+/-0.3% in CO exposed animals and 0.3+/-0.1% in controls. In the lungs, no signs of pathology similar to that associated with cigarette smoking were observed, and no differences in number of pulmonary NE cells were observed between the groups. Chronic CO inhalation induced a 20% weight increase of the right ventricle (p=0.001) and a 14% weight increase of the left ventricle and interventricular septum (p<0.001). Histological examination of the myocardium did not reveal any signs of scarring. In the aorta and femoral artery, no signs of atherosclerosis were observed in CO exposed rats. No exposure related carcinogenic effects were observed. Spontaneous tumours were identified in 29% of CO exposed animals and in 28% of the controls. Our results suggest that low dose CO exposure is probably not responsible for the respiratory pathology associated with tobacco smoking. The effects on the cardiovascular system seem to involve myocardial hypertrophy, but not atherogenesis.

Cigarette smoking, endothelial injury and cardiovascular disease

Despite the fact that the epidemiological evidence linking cigarette smoking with cardiovascular disease is overwhelming, the precise components of cigarette smoke responsible for this relationship and the mechanisms by which they exert their effect have not yet been elucidated. There are however, some promising pointers as a result of recent developments and this review concentrates on new evidence since earlier reviews of this topic. It is now known that the endothelium has a vastly more important role than was ever thought to be the case a decade ago. Its role in health and disease is increasingly understood, as is the relationship between endothelial injury and the development of atherosclerosis. There is considerable evidence that cigarette smoking can result in both morphological and biochemical disturbances to the endothelium both in vivo and in cell culture systems. Cigarette smoke is a complex mixture and only a few components have been extensively studied. Nicotine and carbon monoxide are much less damaging than is whole smoke. However the free radical components of cigarette smoke have been shown to cause damage in model systems. Further work will be necessary to consolidate the evidence base but the data reported in this review suggest that the free radical components of cigarette smoke may be responsible for the morphological and functional damage to endothelium that has been observed in model systems.

Inhalation of steady-state sidestream smoke from one cigarette promotes arteriosclerotic plaque development

BACKGROUND

A number of epidemiologic studies have suggested that every year environmental tobacco smoke (second-hand smoke) is responsible for tens of thousands of deaths, mostly from heart disease, in the United States. Environmental tobacco smoke is composed mainly (80% to 85%) of aged and diluted sidestream smoke. The remainder is exhaled mainstream smoke. Among the thousands of compounds that have been identified in environmental tobacco smoke are a number of carcinogens, including polynuclear aromatic hydrocarbon carcinogens, such as benzo(a)pyrene. We have demonstrated previously that a number of carcinogens, including benzo(a)pyrene, promote plaque development after injection into cockerels. There have been almost no studies showing a direct stimulatory effect of environmental tobacco smoke on plaque development. Recently we demonstrated that cockerels exposed to sidestream smoke for approximately 0.4% of their projected lifespan exhibited accelerated development of arteriosclerotic plaques. In that study, cockerels in specially designed inhalation chambers were exposed to the steady-state sidestream smoke from 5 cigarettes for 6 h/d for 16 weeks. This level of exposure is high but environmentally plausible. Statistically significant increases in plaque size were demonstrated in the smoke-exposed cockerels.

METHODS AND RESULTS

In the present study, exposure levels were decreased by a factor of 5. Thirty cockerels were exposed to the steady-state sidestream smoke from 1 cigarette for 6 hours per day for 16 weeks. The smoke was mixed with filtered air. Ten control cockerels were exposed to filtered air only. Levels of smoke surrogates, including carbon monoxide and total suspended particulates, were measured three times a day. Again, there was a statistically significant increase in plaque size in the smoke-exposed cockerels. To place these studies within a context of environmental relevance, levels of carbon monoxide were measured independently over 1 to 3 hours in four bars where there was heavy smoking. Measured carbon monoxide levels were as high or higher in the bars than they were in the exposure chambers during the 1-cigarette sidestream-smoke study.

CONCLUSIONS

Experimental exposure to secondhand smoke at levels equal to or even below those routinely encountered by people in smoke-filled environments is sufficient to promote arteriosclerotic plaque development.

Inhalation of sidestream cigarette smoke accelerates development of arteriosclerotic plaques

BACKGROUND

Environmental tobacco smoke has been blamed for approximately 40,000 excess deaths from heart disease annually in the United States. As yet, no pathophysiological process that could be responsible for these deaths has been identified. Environmental tobacco smoke is composed mainly of aged and diluted sidestream smoke but also contains 15% to 20% exhaled mainstream smoke. Carcinogens, including nitrosamines and polynuclear aromatic hydrocarbons, are present in mainstream smoke and sidestream smoke. Carcinogen levels in sidestream smoke, unlike those in mainstream smoke, are not reduced in filtered cigarettes. The US Environmental Protection Agency has designated environmental tobacco smoke as a human (class A) carcinogen. In cockerels, subtumorigenic doses of polynuclear aromatic hydrocarbons carcinogens accelerate aortic arteriosclerotic plaque development.

METHODS AND RESULTS

To determine whether sidestream smoke inhalation affects arteriosclerotic plaque development, we exposed cockerels to sidestream smoke (n = 30) or to filtered air (n = 12) in inhalation chambers for 6 hours per day, 5 days a week from 6 to 22 weeks of age (0.4% of projected lifespan). Chamber levels of carbon monoxide, total suspended particulates, and nicotine were measured regularly during the exposures. The abdominal aorta from each cockerel was cut into 10 segments, and the plaque index (mean plaque cross-sectional area [mm2]/mean luminal circumference [mm] x 100) was calculated for each segment. There were no differences in plaque incidence or distribution between sidestream smoke-exposed and control cockerels; however, plaque indexes were significantly greater for sidestream smoke-exposed than control cockerels in all segments.

CONCLUSIONS

Thus, relatively brief exposures to sidestream smoke early in life are sufficient to enhance arteriosclerotic plaque development.