title: A method for the quantification of 8-methoxypsoralen by mass spectrometry for offline extracorporeal photopheresis.
abstract: Extracorporeal photopheresis (ECP) is an efficient method to treat various autoimmune diseases, cutaneous T-cell lymphoma, and graft-versus-host disease. It is based on the ex vivo inactivation of lymphocytes by 8-methoxypsoralen (8-MOP)/UV light treatment. Despite the adhesive, lipophilic nature of 8-MOP, no quality control is established for the ECP procedure.
  
  
  
  We developed a sensitive high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) assay to monitor residual 8-MOP concentration after UVA irradiation in the whole blood supernatant after acetonitrile precipitation.
  
  
  
  The preanalytical stability of 8-MOP exceeded 7 days, allowing batch mode analysis. Linearity was determined with R2above 0.99. The 8-MOP concentrations decreased exponentially after UV exposure, with decay constants of 0.0259 in plasma and 0.0528 in saline. The recovery of 8-MOP in photopheresates was about 68%, indicating binding to DNA as well as to plastic structures. UVA induced no 8-MOP fragmentation, but caused self-adducts under extreme conditions (10-fold UV dosage).
  
  
  
  Detection of 8-MOP proved to be feasible and demonstrated that the doses were in the pharmaceutically active range.
authors.affiliation: Institute for Clinical Chemistry and Laboratory Medicine, Transfusion Medicine, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany. norbert.ahrens@ukr.de.
authors.forename: Viola
authors.initials: V
authors.lastname: Hähnel
authors.affiliation: Institute for Clinical Chemistry and Laboratory Medicine, Transfusion Medicine, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany. norbert.ahrens@ukr.de.
authors.forename: Frauke
authors.initials: F
authors.lastname: Dormann
authors.affiliation: Labor Friedle GmbH, von-Heyden-Str. 11, 93105 Tegernheim, Germany.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Nitsopoulos
authors.affiliation: Labor Friedle GmbH, von-Heyden-Str. 11, 93105 Tegernheim, Germany.
authors.forename: Albrecht
authors.initials: A
authors.lastname: Friedle
authors.affiliation: Institute for Clinical Chemistry and Laboratory Medicine, Transfusion Medicine, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany. norbert.ahrens@ukr.de.
authors.forename: Norbert
authors.identifier: 0000-0002-4680-2688
authors.initials: N
authors.lastname: Ahrens
mesh_terms: D000293:Adolescent; D000328:Adult; D001774:Blood Chemical Analysis / Q000379:methods*; D002648:Child; D002851:Chromatography, High Pressure Liquid; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D008297:Male; D008730:Methoxsalen / Q000032:analysis*; D008875:Middle Aged; D017893:Photopheresis; D017319:Photosensitizing Agents / Q000032:analysis*; D053719:Tandem Mass Spectrometry; D014466:Ultraviolet Rays; D055815:Young Adult
chemical_list: D017319:Photosensitizing Agents; D008730:Methoxsalen