title: Cyclooxygenase-2, malondialdehyde and pyrimidopurinone adducts of deoxyguanosine in human colon cells.
abstract: Cyclooxygenases (COX) catalyse the oxygenation of arachidonic acid to prostaglandin (PG) endoperoxides. Activity of one of the COX isoforms, COX-2, results in production of prostaglandin E(2) (PGE(2)) via the endoperoxide PGH(2). COX-2 has been implicated in the pathogenesis of colorectal cancer. Malondialdehyde (MDA) is a mutagen produced by spontaneous and enzymatic breakdown of PGH(2). MDA reacts with DNA to form adducts, predominantly the pyrimidopurinone adduct of deoxyguanosine (M(1)G). Here the hypothesis was tested that COX-2 activity in human colon cells results in formation of MDA and generation of M(1)G adducts. M(1)G was detected in basal cultures of human non-malignant colon epithelial (HCEC) and malignant SW48, SW480, HT29 and HCA-7 colon cells, at levels from 77 to 148 adducts/10(8) nucleotides. Only HCA-7 and HT29 cells expressed COX-2 protein. Levels of M(1)G correlated significantly (r = 0.98, P < 0.001) with those of intracellular MDA determined colorimetrically in the four malignant cell types, but neither parameter correlated with expression of COX-2 or PG biosynthesis. Induction of COX-2 expression by phorbol 12-myristate 13-acetate in HCEC cells increased PGE(2) production 20-fold and MDA concentration 3-fold. Selective inhibition of COX-2 activity in HCA-7 cells by NS-398 significantly inhibited PGE(2) production, but altered neither MDA nor M(1)G levels. Malondialdehyde treatment of HCEC cells resulted in a doubling of M(1)G levels. These results show for the first time in human colon cells that COX-2 activity is associated with formation of the endogenous mutagen, MDA. Moreover, they demonstrate the correlation between MDA concentration and M(1)G adduct levels in malignant cells.
authors.affiliation: Oncology Department and MRC Toxicology Unit, University of Leicester, Leicester LE1 9HN, UK. ras20@le.ac.uk
authors.forename: R A
authors.initials: RA
authors.lastname: Sharma
authors.forename: A
authors.initials: A
authors.lastname: Gescher
authors.forename: J P
authors.initials: JP
authors.lastname: Plastaras
authors.forename: C
authors.initials: C
authors.lastname: Leuratti
authors.forename: R
authors.initials: R
authors.lastname: Singh
authors.forename: B
authors.initials: B
authors.lastname: Gallacher-Horley
authors.forename: E
authors.initials: E
authors.lastname: Offord
authors.forename: L J
authors.initials: LJ
authors.lastname: Marnett
authors.forename: W P
authors.initials: WP
authors.lastname: Steward
authors.forename: S M
authors.initials: SM
authors.lastname: Plummer
mesh_terms: D003106:Colon / Q000378:metabolism*; D003110:Colonic Neoplasms / Q000378:metabolism; D051546:Cyclooxygenase 2; D004247:DNA / Q000378:metabolism; D018736:DNA Adducts / Q000096:biosynthesis*; D003849:Deoxyguanosine / Q000378:metabolism*; D015232:Dinoprostone / Q000096:biosynthesis / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D008315:Malondialdehyde / Q000378:metabolism*; D008565:Membrane Proteins; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D011687:Purines / Q000378:metabolism*; D011743:Pyrimidines / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D018736:DNA Adducts; D007527:Isoenzymes; D008565:Membrane Proteins; D011687:Purines; D011743:Pyrimidines; C107643:pyrimido(1,2-a)purin-10(3H)-one; D008315:Malondialdehyde; D004247:DNA; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D003849:Deoxyguanosine; D015232:Dinoprostone