COX-2 Mediated Vascular Toxicity of Methylenedianiline

Louisiana State Univ Hsc Shreveport, Shreveport LA

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Abstract

DESCRIPTION (Taken from the Investigator's Abstract) Vascular medial hyperplasia is an important event in the etiologies of many cardiovascular diseases (CVD), including hypertension, atherosclerosis, and restenosis. CVD continues to kill more Americans each year than any other disease, and since 1984, more women are dying from CVD than men (AHA, 2000). The candidate's laboratory has recently discovered a previously unknown effect of exposure to the aromatic amine 4,4'-diaminodiphenylmethane (DAPM, 4,4'methylenedianiline): vascular medial hyperplasia in both the liver and lung following intermittent, low-dose exposure of rats, with greater effects in females than males. DAPM is a compound used in the production of polyurethanes, which are made into a plethora of products ranging from floor coverings to dialysis tubing and breast implants. This new discovery raises the possibility that other aromatic amines, ubiquitous compounds found in a variety of sources, including cigarette smoke, dyes, cured meats, and grilled food, may also have roles in the onset of CVD. In the candidate's preliminary studies, she has shown that treatment of vascular smooth muscle cells (VSMC) in culture with DAPM leads to VSMC proliferation. Relevant to this newly revealed toxicity, a recent report suggested that greater than 50% of DAPM metabolite bound to protein in the blood is likely formed through metabolism by extrahepatic peroxidase enzymes. Peroxidase enzymes metabolize aromatic amines like DAPM to their corresponding imines, which are highly reactive intermediates capable of binding covalently to DNA and protein. The candidate has shown that VSMC express the peroxidase enzyme cyclooxygenase-2 (COX-2), and that treatment of VSMC with DAPM results in increased peroxidase activity detected 12h after exposure. DAPM or its metabolites thus appear to upregulate the expression of COX-2. Finally, VSMC proliferation is attenuated when cells are simultaneously treated with N- acetylcysteine, a nonprotein thiol capable of reacting with electrophilic intermediates, thus preventing reactions of these intermediates with endogenous molecules and possibly preventing cell damage. These results suggest that VSMC are capable of metabolizing or bioactivating DAPM to toxic intermediates. Thus, the candidate will test the following hypotheses: 1) DAPM is metabolized to reactive intermediates by VSMC cyclooxygenase; 2) reactive metabolites of DAPM produced by COX further upregulate the expression of COX-2; and 3) this increase in expression of COX-2, and/or phospholipase A2 (PLA2), contributes to increases in rates of VSMC proliferation in response to DAPM.