title: Plasma LDL cholesterol has no impact on P-glycoprotein (MDR1/ABCB1) activity in human peripheral blood mononuclear cells.
abstract: Several studies have demonstrated that the adenosine triphosphate-binding cassette transporter P-glycoprotein (P-gp) is at least partly located in cholesterol- and sphingolipid-enriched parts of the plasma membrane called "lipid rafts" and that modification of cellular cholesterol content has an impact on the activity of P-gp in vitro and ex vivo. Cholesterol modulation in vitro does not closely reflect the in vivo situation. The aim of our study was therefore to investigate whether differences in individual plasma low-density lipoprotein (LDL) cholesterol levels in humans have an impact on cholesterol content in peripheral blood mononuclear cells (PBMCs) and thereby on individual activity of P-gp. PBMCs of 20 ambulatory patients with elevated LDL cholesterol (173.9 +/- 22.4 mg/dl; range 151.0-234.4 mg/dl) and 28 controls (125.2 +/- 16.9 mg/dl; range 74.6-149.6 mg/dl) were isolated. Cellular cholesterol was measured by an enzymatic fluorimetric assay, efflux activity of P-gp in PBMCs was determined by a flow cytometric method (rhodamine123 efflux), and messenger ribonucleic acid expression was quantified by reverse transcriptase real-time polymerase chain reaction (RT-PCR). There was no difference in cellular cholesterol or P-gp activity between the two groups suggesting that high plasma LDL cholesterol concentration as observed in dyslipidemic patients does not correlate with cellular cholesterol content or P-gp activity in PBMCs. There was, however, a significant negative relationship between age and P-gp efflux activity indicating that P-gp activity in PBMCs decreases with advancing age. These results need further confirmation because investigation of age dependency of P-gp activity was not the primary aim of the study.
authors.affiliation: Department of Internal Medicine VI, Clinical Pharmacology and Pharmacoepidemiology, University of Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany.
authors.forename: Caroline Henrike
authors.initials: CH
authors.lastname: Storch
authors.forename: Hans-Dieter
authors.initials: HD
authors.lastname: Klimm
authors.forename: Tilman
authors.initials: T
authors.lastname: Heinrich
authors.forename: Walter Emil
authors.initials: WE
authors.lastname: Haefeli
authors.forename: Johanna
authors.initials: J
authors.lastname: Weiss
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000097:blood* / Q000235:genetics; D000367:Age Factors; D000368:Aged; D008078:Cholesterol, LDL / Q000097:blood*; D005260:Female; D005434:Flow Cytometry; D005456:Fluorescent Dyes; D005838:Genotype; D006801:Humans; D006949:Hyperlipidemias / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D011110:Polymorphism, Genetic; D012333:RNA, Messenger / Q000097:blood; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020112:Rhodamine 123; D013050:Spectrometry, Fluorescence
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D008078:Cholesterol, LDL; D005456:Fluorescent Dyes; D012333:RNA, Messenger; D020112:Rhodamine 123