title: Quantitation of retinaldehyde in small biological samples using ultrahigh-performance liquid chromatography tandem mass spectrometry.
abstract: We report an ultrahigh-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method to quantify all-trans-retinal in biological samples of limited size (15-35mg), which is especially advantageous for use with adipose. To facilitate recovery, retinal and the internal standard 3,4-didehydroretinal were derivatized in situ into their O-ethyloximes. UHPLC resolution combined with high sensitivity and specificity of MS/MS allowed quantification of retinal-O-ethyloximes with a 5-fmol lower limit of detection and a linear range from 5fmol to 1pmol. This assay revealed that extraocular concentrations of retinal range from approximately 2 to 40pmol/g in multiple tissues-the same range as all-trans-retinoic acid. All-trans-retinoic acid has high affinity (kd⩽0.4nM) for its nuclear receptors (RARα, -β, and -γ), whereas retinal has low (if any) affinity for these receptors, making it unlikely that these retinal concentrations would activate RAR. We also show that the copious amount of vitamin A used in chow diets increases retinal in adipose depots 2- to 5-fold relative to levels in adipose of mice fed a vitamin A-sufficient diet, as recommended for laboratory rodents. This assay also is proficient for quantifying conversion of retinol into retinal in vitro and, therefore, provides an efficient method to study metabolism of retinol in vivo and in vitro.
authors.affiliation: Graduate Program in Metabolic Biology, Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Jinshan
authors.initials: J
authors.lastname: Wang
authors.affiliation: Graduate Program in Metabolic Biology, Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Hong Sik
authors.initials: HS
authors.lastname: Yoo
authors.affiliation: Graduate Program in Metabolic Biology, Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Kristin M
authors.initials: KM
authors.lastname: Obrochta
authors.affiliation: Graduate Program in Metabolic Biology, Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Priscilla
authors.initials: P
authors.lastname: Huang
authors.affiliation: Graduate Program in Metabolic Biology, Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720, USA. Electronic address: jna@berkeley.edu.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Napoli
mesh_terms: D053000:Analytic Sample Preparation Methods; D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010091:Oximes / Q000737:chemistry; D012172:Retinaldehyde / Q000032:analysis* / Q000097:blood / Q000737:chemistry; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D010091:Oximes; D012172:Retinaldehyde
keywords: Liquid chromatography; Mass spectrometry; Retinal; Retinaldehyde; Retinoic acid; Retinol