title: 13-cis-retinoic acid is an endogenous compound in human serum.
abstract: The occurrence of 13-cis-retinoic acid as an endogenous component in human serum has been confirmed by cochromatography with standards in both normal-phase and reverse-phase high-performance liquid chromatographic (HPLC) system, by the lambda max of its UV spectrum recorded simultaneously with the HPLC run, and by chromatography of its methyl derivative. The method using solid-phase extraction followed by a gradient reverse-phase HPLC procedure with an internal standard and sensitive UV detector, provides an efficient and sensitive technique for the separation and quantification of serum 13-cis- and all-trans-retinoic acid. Serum levels of 13-cis- and all-trans-retinoic acid in 26 fasting volunteers ranged from 1.0 to 2.2 ng/ml (mean +/- SEM = 1.4 +/- 0.3 ng/ml) and from 1.1 to 1.9 ng/ml (mean +/- SEM = 1.4 +/- 0.2 ng/ml), respectively. The levels determined by a liquid-liquid double-phase extraction method were 90% higher in both 13-cis- and all- trans-retinoic acid than those from a solid-phase extraction. Human small intestine can isomerize all-trans-retinoic acid. 13-cis-Retinoic acid is the predominant cis isomer after incubation of intestinal mucosa homogenates with all-trans-retinoic acid. Moreover, the concentration of retinoic acid in serum is related to diet in that the level of total retinoic acid was 36% higher (n = 10) 2 h after a nonstandard breakfast than in fasting subjects.
authors.affiliation: USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111.
authors.forename: G W
authors.initials: GW
authors.lastname: Tang
authors.forename: R M
authors.initials: RM
authors.lastname: Russell
mesh_terms: D000328:Adult; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism; D007536:Isomerism; D015474:Isotretinoin / Q000097:blood* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D013056:Spectrophotometry, Ultraviolet
chemical_list: D015474:Isotretinoin