Biochemical and histological effects of intermittent carbon monoxide exposure in cynomolgus monkeys (Macaca fascicularis) in relation to atherosclerosis

Exposure to automotive pollution increases plasma susceptibility to oxidation

Low-density lipoprotein oxidation is implicated in the development of atherosclerosis. Plasma susceptibility to oxidation may be used as a marker of low-density lipoprotein oxidation and thus predict atherosclerotic risk. In this study the authors investigated the relationship between plasma susceptibility to oxidation and exposure to automotive pollution in a group of automobile mechanics (n = 16) exposed to high levels of automotive pollution, vs. matched controls (n = 13). The authors induced plasma oxidation by a free radical initiator and they determined susceptibility to oxidation by (1) change in absorbance at 234 nm, (2) lag time to conjugated diene formation, and (3) linear slope of the oxidation curve. Mechanics had significantly higher values (mean +/- standard error) for change in absorbance (1.60 +/- 0.05 vs. 1.36 +/- 0.05; p < .002), and slope (1.6 x 10(-3) +/- 0.1 x 10(-3) vs. 1.3 x 10(-3) +/- 0.1 x 10(-3); p < .001), compared with controls. These results indicate that regular exposure to automotive pollutants increases plasma susceptibility to oxidation and may, in the long-term, increase the risk of developing atherosclerosis.

Acute exposure to carbon monoxide does not affect plasma lipids, lipoproteins, and apolipoproteins

STUDY OBJECTIVES

To examine the effects of acute exposure to carbon monoxide and hypoxia on plasma lipids, lipoproteins, and apolipoproteins.

DESIGN

Random-order assignment to blinded, inhaled exposures of carbon monoxide and hypoxia.

SETTING

Research laboratory of ambulatory subjects.

SUBJECTS

10 elderly, male nonsmokers with chronic stable angina.

INTERVENTION

Random-order two-hour inhaled exposure to clean air at sea level, carbon monoxide at sea level, carbon monoxide at high altitude, and clean air at high altitude.

MEASUREMENTS

Fasting plasma lipids, lipoproteins, and apolipoproteins before and after exposures.

RESULTS

No differences were noted between fasting plasma lipid, lipoprotein, or apolipoprotein levels before and after exposures.

CONCLUSION

Acute exposure to carbon monoxide and high altitude does not affect fasting plasma lipid, lipoprotein, or apolipoprotein levels.

The atherogenic potential of carbon monoxide

This paper reviews the available evidence concerning the atherogenic potential of carbon monoxide. The evidence comes from two different types of studies--epidemiology studies on populations of humans chronically exposed to carbon monoxide, and animal studies conducted under conditions of controlled exposure to carbon monoxide. Data from both epidemiology and animal studies suggest that carbon monoxide is not atherogenic. Therefore, the increased levels of atherosclerosis associated with smoking as reported in epidemiology studies of human smokers probably cannot be attributed to CO exposure.

The influence of passive smoking on the cardiovascular system

Cardiovascular effects of tobacco smoke have been studied in passive smokers far less extensively than in active smokers. Under real-life conditions, passive smokers inhale approximately 0.02 to 0.01 of the amount of particulate matter taken up by active smokers. Their nicotine concentration in serum is within a range that is barely distinguishable from the background level. The increase in carboxyhemoglobin rarely exceeds 1%. In healthy subjects heavily exposed to tobacco smoke, no or only slightly acute effects on the cardiovascular system are found. Whether or not passive smoking is likely to aggravate symptoms in patients with advanced coronary heart disease has not yet been unequivocally established and requires further investigation. From a few studies on occupational groups exposed to carbon monoxide (CO) and from experiments with animals chronically treated with CO or nicotine, the conclusion can be drawn that neither CO nor nicotine is likely to play a role in the development and progression of coronary heart disease in those concentrations normally found in passive smokers.

Effect of carbon monoxide on atherogenesis in normal pigs and pigs with von Willebrand's disease

The extent of coronary and aortic atherosclerosis was examined in pigs following balloon-catheter injury of coronary arteries and subsequent feeding of an atherogenic diet for 4 months. The pigs were either exposed intermittently to 100 ppm carbon monoxide or to ambient air alone. Three types of pigs were used: normals, homozygotes for von Willebrand's disease (bleeders), and heterozygotes (carriers). The 3 types of pigs developed coronary artery intimal lesions of similar thickness. Aortic lesions, quantified as percent of aortic surface involved with sudanophilia and raised fibrous plaques, were slightly less extensive in bleeder pigs than in normals. Carbon monoxide exposure did not increase the thickness of coronary artery intimal lesions, nor did it increase the percent of aortic surface involved with sudanophilia or raised fibrous lesions. These results suggest that exposure to low levels of carbon monoxide does not perceptibly enhance atherogenesis induced by hypercholesterolemia. None of 14 bleeder pigs showed evidence of myocardial infarction, despite significant coronary artery narrowing. Of the 24 normal and carrier pigs, 5 showed myocardial infarction. Four of these 5 pigs were exposed to carbon monoxide, while 1 was not exposed. These findings suggest that exposure to low levels of carbon monoxide may increase the incidence of myocardial infarction and that the absence of von Willebrand factor may be protective.