Atherogenesis in the White Carneau pigeon. Further studies of the role of carbon monoxide and dietary cholesterol

Carbon monoxide levels experienced by heavy smokers impair aerobic capacity and cardiac contractility and induce pathological hypertrophy

Cigarette smoke contains hundreds of potentially toxic compounds and is an important risk factor for cardiovascular disease. However, the key components responsible for endothelial and myocardial dysfunction have not been fully identified. The objective of the present study was to determine the cardiovascular effects of long-term inhalation of carbon monoxide (CO) administrated to give concentrations in the blood similar to those observed in heavy smokers. Female rats were exposed to either CO or air (control group) (n = 12). The CO group was exposed to 200 ppm CO (100 h/wk) for 18 mo. Rats exposed to CO had 24% lower maximal oxygen uptake, longer (145 vs. 123 microm) and wider (47 vs. 25 microm) cardiomyocytes, reduced cardiomyocyte fractional shortening (12 vs. 7%), and 26% longer time to 50% re-lengthening than controls. In addition, cardiomyocytes from CO-exposed rats had 48% lower intracellular calcium (Ca2 +) amplitude, 22% longer time to Ca2 + decay, 34% lower capacity of sarcoplasmic reticulum Ca2 +-ATPase (SERCA2a), and 37% less t-tubule area compared to controls. Phosphorylation levels of phospholamban at Ser16 and Thr17 were significantly reduced in the CO group, whereas total concentration of phospholamban and SERCA2a were unchanged. Cardiac atrial natriuretic peptide, vascular endothelial growth factor, cyclic guanosine monophosphate, calcineurin, calmodulin, pERK, and pS6 increased, whereas pAkt and pCaMKII delta remained unchanged by CO. Endothelial function and systemic blood pressure were not affected by CO exposure. Long-term CO exposure reduces aerobe capacity and contractile function and leads to pathological hypertrophy. Impaired Ca2 + handling and increased growth factor signaling seem to be responsible for these pathological changes.

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.

Coronary vessel alterations following chronic carbon monoxide exposure in the adult rat

Adult male rats were exposed to 500 ppm CO continuously for 30 days, while litter-mate controls remained in room air (AIR). Heart weight-to-body weight ratio and hematocrit were increased significantly. Right ventricle (RV) free wall thickness was increased significantly as was right to left heart diameter and average heart diameter. Cross-sectional areas of the left ventricle (LV) free wall, interventricular septum (S) and RV midway between the apex and base were increased significantly. Morphometric analysis of the CO-exposed and AIR hearts revealed no significant differences in the number of small (27-114 microns) or larger (> 114 microns) blood vessels in any region; however, there was a trend towards an increased number of the smaller vessels, both arterioles and venules, in the CO-exposed rats. The larger arteries in the S and RV were significantly larger in the CO-exposed rats. There was a significant overall effect of CO on larger artery diameter across all heart regions, consistent with the appearance of heart radiographs taken. There were no differences in the diameter of the small vessels in any region of the heart between the CO-exposed and AIR rats. The vessel cross-sectional area of the larger vessels tended to be increased in all regions of the heart. The cross-sectional area of the large arteries in the LV was increased significantly. Arterial wall thickness was decreased significantly in RV and there was a significant overall effect of CO in decreasing wall thickness and the ratio of wall thickness-to-vessel luminal diameter in these vessels. No vascular pathology was observed. The results of this study suggest changes in coronary vessel architecture during chronic CO-induced cardiac hypertrophy and are consistent with earlier hemodynamic and morphometric studies of CO-exposed hearts.

Chronic carbon monoxide exposure in young rats alters coronary vessel growth

The goal of this study was to determine whether chronic monoxide exposure in the developing heart produces long-lasting coronary vasculature alterations. One-day-old male rat pups were exposed to 500 ppm CO continuously for 30 d, while littermate controls remained in room air (AIR). At 61 and 110 d of age hearts were removed, perfusion fixed, x-rayed, and processed for analysis of coronary vessel architecture. Body weight (BW) and heart weight (HW) increased with age; the ratio of HW/BW decreased. There were no differences in HW and ventricular dimensions at either age due to prior CO exposure. Morphometric analysis of the fixed hearts from CO-exposed and AIR rats revealed no significant individual group differences in the number of small (27-114 microns) or larger (> 114 microns) vessels in any heart region. The septum (S) in CO rats was an exception: There were more small veins at 61 d of age and more larger veins at 110 d of age. There was a significant increase in the number of small arteries at both ages in the CO rats across all heart regions, and in the smaller veins at 61 d of age. The large vessels in the S at 61 d of age had a significantly greater diameter in CO compared to AIR rats. This was also true for the large arteries in the S and right ventricle (RV) of the 110-d-old rats. Taking all heart regions together, the large arteries in CO rats were larger than in AIR rats. Previous CO exposure significantly increased large artery and total cross-sectional area in the S and RV at 61 d of age, and in RV at 110 d of age. Total cross-sectional area of veins in the S was also increased. Taking all heart regions together, CO significantly increased small artery cross-sectional area at 61 d of age, and small, large, and total artery cross-sectional area at 110 d of age. With one exception (small veins, 110 d of age), there was no effect of CO on vein cross-sectional area. These changes resulted in the percentage of total cross-sectional area contributed by the larger vessels being increased. Pathological examination showed nothing abnormal. The results suggest profound and persistent changes in coronary vessel architecture following chronic neonatal CO exposure.

Inhalation of carbon monoxide does not accelerate arteriosclerosis in cockerels

The effects of chronic exposure to moderate levels of carbon monoxide (CO) upon the augmentation of arteriosclerotic plaque development were investigated in a series of in vivo studies. Cockerels were exposed to carefully regulated CO levels in dynamic exposure chambers. The plaque volume percentage in the aortic walls of experimental and control animals was determined by point-counting. Chronic CO inhalation, at levels up to 200 ppm, did not stimulate arteriosclerotic plaque development (at 200 ppm CO, carboxyhemoglobin (COHb) levels 10 min after exposures ended were 11-12%). When administered concomitantly with cholesterol feeding, CO did not augment plaque development. When administered after either carcinogen-associated or diet-promoted plaque size increases had occurred, CO elicited no further plaque size increases. Thus, in this animal model, daily exposures to moderately high CO levels were without discernable effect upon arteriosclerotic plaque development, although high COHb levels were attained.

Ingestion of chlorinated water has no effect upon indicators of cardiovascular disease in pigeons

Cardiovascular disease (CVD) accounts for nearly half the deaths, yearly, in the United States. The arterio(athero)sclerotic plaque is the principal lesion of CVD. The White Carneau (WC) pigeon is an animal model that has been employed extensively for studying CVD. Cholesterol (CHOL) feeding aggravates atherosclerosis in WC pigeons greater than 2 years old. In 1986, two reports appeared from a single laboratory claiming a direct effect of drinking chlorinated (Cl) water upon lipid levels and plaque development in young (less than 1 year) WC pigeons. These are the only reports of such direct effects, to date. Three months' exposure to 2 ppm or 15 ppm Cl in the drinking water, resulted in increased circulating CHOL levels in young male WC pigeons fed a normocholesterolemic (NC) diet in which Ca2+ levels were reduced. In addition, at both Cl concentrations there was a significant increase in plaque size, compared to controls. Pigeons in the 2 ppm group also exhibited elevated low density lipoprotein (LDL) levels after 3 months on the NC diet. These findings, if extrapolated to man, could have considerable public health consequences, since nearly 200 million people in the United States drink Cl water. We have carried out a similar set of studies but with strikingly different results. We used the same suppliers of pigeons and feed as did the authors of the 1986 reports and followed their approach where possible. Six month-old male WC pigeons drank water with 2 ppm or 15 ppm Cl (pH 8.5) and ate a NC diet with Ca2+ reduced to 80% of normal. At both 1 and 3 months, body weight, CHOL, triglyceride and LDL levels were unaffected by drinking Cl water. There was also no effect of Cl water on plaque size after 3 months. Thus, we found no evidence that drinking chlorinated water has any effect upon circulating lipid levels or upon the development of arteriosclerotic plaques, in this animal model.

Exacerbation of coronary artery disease by occupational carbon monoxide exposure: a report to two fatalities and a review of the literature

The recent deaths of two workers with coronary artery disease (CAD) following exposure to carbon monoxide (CO) at work reinforced our appreciation of the hazard of this exposure to individuals with preexisting heart disease. Carbon monoxide acts to precipitate ischemia by reducing oxygen delivery to the myocardium. Animal and in vitro experiments suggest that CO may accelerate the development of atherosclerosis, particularly if exposure is in association with other risk factors. Thus, persons with known CAD who are exposed to CO at work are at risk for both the acceleration of the course of the underlying disease and for precipitation of acute ischemia or infarction following excessive exposure. Particular attention should be given to control of CO exposures in light of this hazard. For various reasons, preplacement evaluations or other job selection procedures do not adequately address his hazard. In view of the high prevalence of CAD in the U.S. and the high frequency of workplace exposure to CO, particular attention should be given to control of CO exposure through industrial hygiene measures.

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.

Failure of chronic cigarette smoke exposure to alter plasma lipoproteins of stumptailed macaques (Macaca arctoides)

Twenty-one 8-14 kg adult male stumptailed macaques, Macaca arctoides, were fed a standard laboratory diet and divided into 3 groups. The high-dose group and low-dose group were exposed to cigarette smoke at the human equivalent of 3 packs and 1 pack per day, respectively, 7 days per week, for 3-5 years. Eight animals served as cage an sham controls. Peak blood carboxyhemoglobin (COHb) levels measured immediately after smoking showed levels of 0.5+/- 0.1%, 3.6+/-1.0%, and 5.7+/-2.8% for sham controls, low, and high dose smokers, respectively. Hemoglobin and hematocrit values were 2-7% higher (N.S. to P less than 0.05) for smoking groups, presumably as a consequence of chronically elevated COHb levels. No significant differences were seen in total plasma cholesterol and lipoprotein cholesterol concentration measured at four intervals over period of one year. We conclude from these data that, while fed a low fat diet, chronic cigarette smoke inhalation fails to alter plasma lipoprotein levels in this animal model.