Role of COX-2 in the bioactivation of methylenedianiline and in its proliferative effects in vascular smooth muscle cells

Role of the human N-acetyltransferase 2 genetic polymorphism in metabolism and genotoxicity of 4, 4'-methylenedianiline

4, 4'-Methylenedianiline (MDA) is used extensively as a curing agent in the production of elastomers and is classified as reasonably anticipated to be a human carcinogen based on sufficient evidence in animal experiments. Human N-acetyltransferase 1 (NAT1) and 2 (NAT2) catalyze the N-acetylation of aromatic amines and NAT2 is subjected to a common genetic polymorphism in human populations separating individuals into rapid, intermediate, and slow acetylator phenotypes. Although MDA is known to undergo N-acetylation to mono- and di-acetyl metabolites, very little is known regarding whether this metabolism is subject to the NAT2 genetic polymorphism. We investigated the N-acetylation of MDA by recombinant human NAT1, NAT2, genetic variants of NAT2, and cryoplateable human hepatocytes obtained from rapid, intermediate and slow acetylators. MDA N-acetylation was catalyzed by both recombinant human NAT1 and NAT2 exhibiting a fivefold higher affinity for human NAT2. N-acetylation of MDA was acetylator genotype dependent as evidenced via its N-acetylation by recombinant human NAT2 genetic variants or by cryoplateable human hepatocytes. MDA N-acetylation to the mono-acetyl or di-acetyl-MDA was highest in rapid, lower in intermediate, and lowest in slow acetylator human hepatocytes. MDA-induced DNA damage in the human hepatocytes was dose-dependent and also acetylator genotype dependent with highest levels of DNA damage in rapid, lower in intermediate, and lowest in slow acetylator human hepatocytes under the same MDA exposure level. In summary, the N-acetylation of MDA by recombinant human NAT2 and cryopreserved human hepatocytes support an important role for the NAT2 genetic polymorphism in modifying MDA metabolism and genotoxicity and potentially carcinogenic risk.

4,4'-Methylenedianiline Alters Serotonergic Transport in a Novel, Sex-Specific Model of Pulmonary Arterial Hypertension in Rats

Pulmonary arterial hypertension (PAH) is a cardiovascular disorder characterized by elevated pulmonary artery pressure as a result of arterial wall thickening. Patients are 3-4 times more likely to be women than men. This gender discrepancy demonstrates a need for an animal model with similar sex differences. 4,4'-Methylenedianiline (DAPM) is an aromatic amine used industrially in the synthesis of polyurethanes. Chronic, intermittent treatment of male and female rats with DAPM resulted in medial hyperplasia of pulmonary arterioles, exclusively in females, coupled to increases in pulmonary arterial pressures. Significant increases in plasma levels of endothelin-1 (ET-1) and serotonin, but decreases in nitrite [Formula: see text], were observed in females treated with DAPM. A decrease was observed in the serum ratio of the estrogen metabolites 2-hydroxyestradiol (2-OHE1)/16α-hydroxyestrogen (16α-OHE1). In females, ET-1,[Formula: see text] , and 2-OHE1/16α-OHE1 were significantly correlated with peak pressure gradient, an indirect measure of pulmonary arterial pressure. Expression of the serotonin transport protein (SERT) was significantly higher in the arteries of DAPM-treated females. In vitro, DAPM induced human pulmonary vascular smooth muscle cell proliferation and serotonin uptake, both of which were inhibited by treatment with the estrogen receptor antagonist ICI 182,780 or the selective serotonin reuptake inhibitor fluoxetine. DAPM also induced the release of serotonin from human pulmonary endothelial cells in culture, which is blocked by ICI 182,780. Taken together, this suggests that DAPM-mediated dysregulation of serotonin transport is estrogen-receptor dependent. Thus, DAPM-induced PAH pathology may be a new tool to clarify the sex selectivity of PAH disease pathogenesis.

A comparative study of the structure and vibrational spectra of diphenylmethane, the carcinogen 4,4'-methylenedianiline and 4,4'-methylenebis(N,N-dimethylaniline)

The structural stability of 4,4'-methylenedianiline (MDA), 4,4'-methylenebis(N,N-dimethylaniline) (MBDMA) and their parent diphenylmethane (DPM) was investigated by the DFT-B3LYP and ab initio MP2 calculations with the 6-311G(**) basis set. From the calculations the three diphenylmethanes were predicted to exist predominantly in a non-planar structure with a near C2 molecular symmetry in agreement with X-ray studies. The CCCC angles in DPM and the two dianilines were calculated to be nearly equal of about 60° as compared to X-ray angles of 17° and 67° for MDA. The NH2 inversion barriers in MDA was estimated to be about 1-5 kcal/mol. On comparison of the Raman spectra of the three compounds, the line intensity and position of the characteristic ring breathing mode were shown to be sensitive to the amino substitution. The vibrational wavenumbers of the optimized structures of the two dianilines were computed at the DFT-B3LYP level of theory. Tentative vibrational assignments were made on the basis of combined DFT and experimental FT-IR and FT-Raman data of MDA and MBDMA.