title: The algal hepatoxoxin okadaic acid is a substrate for human cytochromes CYP3A4 and CYP3A5.
abstract: The hepatotoxin okadaic acid (OA) was incubated with nine human recombinant cytochrome P450s (1A1, 1A2, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4 and 3A5). Both CYP3A4 and CYP3A5 converted OA to a mixture of the same four metabolites, but incubation with CYP3A4 resulted in higher levels of conversion. Michaelis-Menten parameters, K(m) (73.4 microM) and V(max) (7.23 nmol of metabolitesnmol(-1)min(-1)) for CYP3A4 were calculated by analyzing double-reciprocal plots. LC-MS(n) analysis and chemical interconversion indicate that metabolites 2 and 3 are the 11S-hydroxy and 11R-hydroxy okadaic acid respectively, while metabolite 4 is 11-oxo okadaic acid. LC-MS(n) analysis of metabolite 1 shows a molecular ion which corresponds to an addition of 16 amu to OA, also suggesting hydroxylation, but the specific site has not been identified. The same four metabolites were produced upon incubation of okadaic acid with pooled human liver microsomes. This transformation could be completely inhibited with ketokonazole, and inhibitor of the CYP3A family of enzymes. The metabolites were determined to be only slightly less potent inhibitors of serine threonine protein phosphatase 2A (PP2A) when compared to OA. As PP2A is the principle molecular target for OA, these oxidative transformations may not effectively detoxify OA.
authors.affiliation: Department of Chemistry and Biochemistry, Florida International University, 11200 SW 8th St., Miami, FL 33199, USA.
authors.forename: Fujiang
authors.initials: F
authors.lastname: Guo
authors.forename: Tianying
authors.initials: T
authors.lastname: An
authors.forename: Kathleen S
authors.initials: KS
authors.lastname: Rein
mesh_terms: D001711:Biotransformation; D056486:Chemical and Drug Induced Liver Injury / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism*; D065692:Cytochrome P-450 CYP3A Inhibitors; D004791:Enzyme Inhibitors / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000201:enzymology; D019319:Okadaic Acid / Q000378:metabolism* / Q000494:pharmacology; D010084:Oxidation-Reduction; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors; D011994:Recombinant Proteins / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D015262:Xenobiotics / Q000378:metabolism
chemical_list: D065692:Cytochrome P-450 CYP3A Inhibitors; D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D015262:Xenobiotics; D019319:Okadaic Acid; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D054648:Protein Phosphatase 2
references.citation: Toxicon. 2008 Jun 15;51(8):1338-44
references.pmid: 18538364
references.citation: Mutat Res. 1996 Dec 12;361(2-3):133-41
references.pmid: 8980699
references.citation: Rapid Commun Mass Spectrom. 2008 Apr;22(8):1127-36
references.pmid: 18335462
references.citation: Hum Exp Toxicol. 1999 May;18(5):345-50
references.pmid: 10372758
references.citation: Chirality. 2004 Feb;16(2):79-85
references.pmid: 14712470
references.citation: Drug Metab Dispos. 2002 Apr;30(4):438-45
references.pmid: 11901098
references.citation: Toxicon. 2002 Jan;40(1):33-42
references.pmid: 11602276
references.citation: Toxicon. 2007 Sep 15;50(4):470-8
references.pmid: 17540428
references.citation: Mutat Res. 1993 Oct;289(2):275-80
references.pmid: 7690896
references.citation: J Pharmacol Exp Ther. 2003 Apr;305(1):315-22
references.pmid: 12649384
references.citation: FEBS Lett. 2004 Jan 16;557(1-3):1-8
references.pmid: 14741332
references.citation: J Chromatogr B Biomed Appl. 1996 Jun 7;681(2):227-32
references.pmid: 8811431
references.citation: Nat Toxins. 1994;2(5):293-301
references.pmid: 7866665
references.citation: Eur J Biochem. 2004 Oct;271(19):3962-9
references.pmid: 15373842
references.citation: Environ Toxicol. 2005 Feb;20(1):1-17
references.pmid: 15712332
references.citation: Mutagenesis. 2003 May;18(3):293-8
references.pmid: 12714697
references.citation: Toxicon. 1999 Aug;37(8):1109-21
references.pmid: 10400295
references.citation: Cell. 2006 Oct 20;127(2):341-53
references.pmid: 17055435
references.citation: Toxicon. 1996 Jul;34(7):743-52
references.pmid: 8843575
references.citation: Toxicon. 2002 Feb;40(2):159-65
references.pmid: 11689237
references.citation: J Pharmacol Exp Ther. 1997 Nov;283(2):434-42
references.pmid: 9353355
references.citation: Chem Res Toxicol. 1990 Nov-Dec;3(6):566-73
references.pmid: 2103328
references.citation: Adv Cancer Res. 1993;61:143-94
references.pmid: 8394044
references.citation: Toxicon. 1992 Dec;30(12):1621-30
references.pmid: 1488771
references.citation: Nature. 1989 Jan 5;337(6202):78-81
references.pmid: 2562908
references.citation: Curr Med Chem. 2002 Nov;9(22):1939-80
references.pmid: 12369865
references.citation: J Mass Spectrom. 2008 Aug;43(8):1140-7
references.pmid: 18383308
references.citation: Toxicon. 2003 Jan;41(1):93-7
references.pmid: 12467666
references.citation: Environ Toxicol. 2004 Apr;19(2):123-8
references.pmid: 15037998