title: Unbound free fatty acid profiles in human plasma and the unexpected absence of unbound palmitoleate.
abstract: We determined for the first time the profiles of the nine most abundant unbound FFAs (FFAus) in human plasma. Profiles were determined for a standard reference plasma of pooled healthy adults for which the Lipid MAPSMAPS Consortium had determined the total FFA profiles. Measurements were performed by using 20 different acrylodan-labeled fatty acid binding protein mutants (probes), which have complementary specificities for the nine FFAs that comprise more than 96% of long-chain plasma FFA. The acrylodan fluorescence emission for each probe changes upon binding a FFAu. The plasma concentrations of each of the nine FFAus were determined by combining the measured fluorescence ratios of the 20 probes. The total molar FFAu concentration accounted for <10-5of the total FFA concentration, and the mole fractions of the FFAu profiles were substantially different than the total FFA profiles. Myristic acid, for example, comprises 22% of the unbound versus 2.8% of the total. The most surprising difference is our finding of zero unboundcis-9-palmitoleic acid (POA), whereas the total POA was 7.2%. An unidentified plasma component appears to specifically prevent the release of POA. FFAus are the physiologically active FFAs, and plasma FFAu profiles may provide novel information about human health.
authors.affiliation: Membrane Sciences, San Diego, CA 92121.
authors.forename: Andrew H
authors.identifier: 0000-0001-6207-6148
authors.initials: AH
authors.lastname: Huber
authors.affiliation: Membrane Sciences, San Diego, CA 92121 akleinfeld@membranesci.com.
authors.forename: Alan M
authors.identifier: 0000-0003-1313-4369
authors.initials: AM
authors.lastname: Kleinfeld
mesh_terms: D015081:2-Naphthylamine / Q000031:analogs & derivatives / Q000737:chemistry; D050556:Fatty Acid-Binding Proteins / Q000097:blood* / Q000737:chemistry / Q000235:genetics; D005229:Fatty Acids, Monounsaturated / Q000097:blood*; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D005453:Fluorescence; D064368:Healthy Volunteers; D006801:Humans; D050356:Lipid Metabolism; D019814:Myristic Acid / Q000097:blood
chemical_list: D050556:Fatty Acid-Binding Proteins; D005229:Fatty Acids, Monounsaturated; D005230:Fatty Acids, Nonesterified; D019814:Myristic Acid; C008757:palmitoleic acid; C038518:acrylodan; D015081:2-Naphthylamine
keywords: albumin binding; fatty acid binding proteins; fluorescence; lipidomics; metabolism; physical biochemistry; quantitation