Induction of cytochrome CYPIA1 and formation of toxic metabolites of benzo[a]pyrene by rat aorta: a possible role in atherogenesis.

Abstract

Cigarette smoking is a leading risk factor for atherosclerosis. Endothelial ijur may be the initial event in this process. The carcinogenic metabolites of the polycyclic aromatic hydrocarbons found in cigarette smoke tars could cause this injury. We tested this model by examining the effect of 3-methyicholanthrene adminisration on aortic polycyclic aromatic hydrocarbon metabolism. Immunoblotting with a monoclonal antibody (mAb 1-7-1) specific for cytochromes CYPIA1 and CYPIA2 showed that aortic microsomes from treated, but not from control, animals contained CYPIA1; the CYPIA1 was primarily in the endothelium. Aortic microsomes from induced animals metabolized benzo[alpyrene (BaP) to the 7R,8S,9,10-tetrahydrotetrol-, 7,8-dhydrodiol-, 1,6 quinone-, 3,6 quinone-, 6,12 quinone-, 3-hydroxy-, and 9-hydroxy-BaP. mAb 1-7-1 inhibited the formation of the tetrahydrotetrol, the dihydrodiol-BaP, and the 3-hydroxy-BaP but did not inhibit the quinones or the 9-hydroxy-BaP. Arachidonic acid did not affect metabolism. These data suggest that the aortas of induced animals metabolize the BaP in cigarette smoke to carcinogenic and toxic products and that this metabolism may initiate vessel injury and lead to the accelerated atherosclerosis seen in cigarette smokers.Atherosclerotic vascular disease is the leading cause of death in developed nations. This process may be initiated by endothelial injury, which leads to the formation of a nidus for mononuclear cellular infiltration, cholesterol deposition, and platelet aggregation (1). Cardio-and cerebral vascular events are more frequent in individuals with hypertension, hyperlipidemia, and diabetes mellitus and in smokers. There has been some question of whether the increased incidence of vascular events seen in smokers is due to increased atherosclerosis or to alterations in other systems, such as the coagulation pathways. Although the latter may be important, the preponderance of evidence suggests that smokers have a significant increase in the incidence and degree of atherosclerosis in both the coronary and peripheral arteries (2).It is unclear which of the toxic products in the smokecarbon monoxide (3), nicotine (4), or the tars-are responsible for this acceleration. The tars, which include the polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (BaP), are possible candidates (5). Although BaP is not toxic, it is metabolically activated to highly toxic, mutagenic, and carcinogenic products-such as various epoxides and quinones. These toxic metabolites, if formed in the vessel wall, could initiate atherosclerosis by injuring the endothelial and muscle cells. If such is the case, then the arterial wall should catalyze their formation because it is unlikely that they could be transported to the peripheral vessels from the liver or lungs. Previous workers have found that a specific cytochrome P450, CYPIA1, catalyzes this metabolism in other organs (6, 7). In smooth muscle cells of young animals CYPIA1 is a constitutive form (8), but in older animals it is found in many or...

The tar fraction of cigarette smoke does not promote arteriosclerotic plaque development.

“…Evidence for activation of cytochrome P450 enzymes, which is necessary for the metabolism of the PAH carcinogens, has been reported in the vascular system following in vivo and in vitro exposures to carcinogens that are present in cigarette tar (22,31,32,50). However, the concentrations of individual PAH carcinogens, e.g., B(a)P or 3-methylcholanthrene, needed to activate P450 enzymes in vascular smooth muscle or endothelial cells are orders of magnitude higher (17,22,31) than the concentrations of these and related compounds in cigarette smoke (13). Thus, there is little direct evidence of a role for environmentally relevant levels of tar fraction compounds in the development of arteriosclerosisis.…”

“…When the PAH carcinogens are delivered to artery wall cells at high concentrations, the carcinogens can be activated metabolically by cytochrome P450 enzymes in the artery wall (17,22,31,32,48).…”

“…Surgeon General over 30 years ago (30). It is widely assumed that tar fraction components of cigarette smoke-especially the PAH carcinogens (e.g., B(a)P) and nitrosamines (e.g., NNK)-are primarily responsible for these profound health effects (14,17,18,(20)(21)(22)(31)(32)(33)(34)(35)(36)(37) (10,11,23,38). There are two characteristics of this animal model of arteriosclerosis that make it particularly valuable for studies of the type described here.…”

“…Polynuclear aromatic hydrocarbon (PAH) carcinogens, e.g., benzo(a)pyrene [B(a)P], and nitrosamines in the tar fraction are considered primarily responsible for the effects of CS on lung cancer and heart disease. Indeed, these and related compounds are effective at inducing or promoting these diseases experimentally, but only when administered at levels many times (often orders of magnitude) higher than the levels at which they are found in mainstream smoke or in ETS (14)(15)(16)(17)(18)(19)(20)(21)(22).…”

Methoxyestradiols Mediate Estradiol-Induced Antimitogenesis in Human Aortic SMCs

“…VSMCs produce cytochrome P450 (CYP450) enzymes that metabolize estradiol to 2-and 4-hydroxyestradiol 9 and catechol-O-methyltransferase (COMT) that converts 2-and 4-hydroxyestradiol to 2-and 4-methoxyestradiol. 10 However, the hypothesis that conversion of estradiol to hydroxyestradiols and methoxyestradiols occurs in human VSMCs and mediates the antigrowth effects of locally applied estradiol is not well tested.…”