Oxidative and reductive metabolism of 9-cis-retinoic acid in the rat. Identification of 13,14-dihydro-9-cis-retinoic acid and its taurine conjugate.
9-cis-Retinoic acid (9-cis-RA), a hormone that binds and activates all known retinoid receptor subtypes, is structurally similar to all-trans-retinoic acid and may share common metabolic fates. Both oral and intravenous doses of 9-cis-RA to rats led to hydroxylation and ketone formation at carbon-4. 9-Cis-RA also isomerized in vivo to 13-cis-retinoic acid, 9-cis, 13-cis-retinoic acid, and all-trans-retinoic acid. After administration of [11-3H]9-cis-RA, the proportion of plasma radioactivity that was volatile increased over time, which suggested that beta-oxidative chain-shortening of 9-cis-RA might occur. An equimolar mixture of [1-13C2H3]9-cis-RA and 9-cis-RA was administered to rats for stable-isotope-labeled metabolite production. A chromatographic peak that had a lambdamax = 290 nm vs. 348 nm for the parent compound, had a retention time similar to the parent, and yielded a 1:1 positive-ion isotope cluster at m/z 303/307 in its mass spectrum. NMR analysis revealed 9-cis and 13,14-dihydro configurations, indicating that 9-cis-RA can be metabolized in rat by reduction to 13,14-dihydro-9-cis-RA. An earlier-eluting HPLC peak that exhibited a lambdamax at 290 nm, and a negative-ion-MS isotope cluster at m/z 408/412 was observed during separations of rat liver extracts. LC/MS/MS analysis revealed product ions for this peak diagnostic for carboxylic acid taurine conjugates. In rats, reduction of 9-cis-RA to 13,14-dihydro-9-cis-RA may represent an initial step leading to beta-oxidation, although available data demonstrate it is conjugated with taurine to form a novel metabolite.
Shirley
M A
MA
Department of Drug Safety, Ligand Pharmaceuticals, Inc., San Diego, CA 92121, USA.
Bennani
Y L
YL
Boehm
M F
MF
Breau
A P
AP
Pathirana
C
C
Ulm
E H
EH
D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D005260:Female; D006801:Humans; D007641:Keratolytic Agents / Q000097:blood / Q000737:chemistry / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000378:metabolism; D008297:Male; D010084:Oxidation-Reduction; D051381:Rats; D017207:Rats, Sprague-Dawley; D014212:Tretinoin / Q000031:analogs & derivatives / Q000097:blood / Q000737:chemistry / Q000378:metabolism*
D007641:Keratolytic Agents; D014212:Tretinoin