title: 1β,25-Dihydroxyvitamin D3: A new vitamin D metabolite in human serum.
abstract: The measurement of 1α,25(OH)2D3in human serum poses a true challenge as concentrations are very low and structurally similar metabolites can interfere.
  
  
  
  During optimization of our in-house LC-MSMS method for serum 1α,25(OH)2D3a previously co-eluting isobaric interference was separated. The isobar was identified as 1β,25(OH)2D3by comparing retention time and fragmentation spectra to standards (other isobaric dihydroxylated vitamin D3analogs). 1β,25(OH)2D3showed specific cluster formation (water), not present in 1α,25(OH)2D3. 1β,25(OH)2D3was measured in serum of apparently healthy human volunteers (n=20), patients with high serum 25-hydroxyvitamin D [25(OH)D] concentrations (>50ng/mL) (n=33 among which 4 with very high levels (>150ng/mL)) and patients with kidney failure (n=68; 39 stage 1-3, 29 stage 4-5). Pearson's r was calculated for correlations and Mann-Whitney statistic to compare group medians.
  
  
  
  Median serum 1β,25(OH)2D3was 11pg/mL in apparently healthy volunteers and increased to 20pg/mL for serum 25(OH)D concentrations above 80ng/mL (n=22) (p<0.0001). 1β,25(OH)2D3concentrations were significantly correlated to serum 25(OH)D concentrations (r=0.85) for the combined results from healthy volunteers and patient sera (n=53) (p<0.0001). For patients with kidney failure, median serum 1β,25(OH)2D3was 7pg/mL and not different from the median level in healthy volunteers (p=0.06). The median concentration did not vary with different stages.
  
  
  
  We present evidence for the widespread presence of 1β,25(OH)2D3, a new vitamin D metabolite, in human serum. The level increases with rising serum 25(OH)D concentrations and is particularly high in patients with very high 25(OH)D levels. We previously demonstrated that 1β,25(OH)2D3is a poor genomic agonist but a potent non-genomic antagonist of 1α,25(OH)2D3.The clinical implications of the presence of this analog therefore require further exploration.
authors.affiliation: Department of Laboratory Medicine, University Hospitals Leuven, 3000 Leuven, Belgium; Department of Cardiovascular Sciences, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Steven
authors.initials: S
authors.lastname: Pauwels
authors.affiliation: Department of Laboratory Medicine, University Hospitals Leuven, 3000 Leuven, Belgium.
authors.forename: Ivo
authors.initials: I
authors.lastname: Jans
authors.affiliation: Department of Laboratory Medicine, University Hospitals Leuven, 3000 Leuven, Belgium; Laboratory of Clinical and Experimental Endocrinology, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Jaak
authors.initials: J
authors.lastname: Billen
authors.affiliation: Endocrine Laboratory, Department of Clinical Chemistry, VU University medical center, Amsterdam, the Netherlands.
authors.forename: Annemieke
authors.initials: A
authors.lastname: Heijboer
authors.affiliation: Laboratory of Clinical and Experimental Endocrinology, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Annemieke
authors.initials: A
authors.lastname: Verstuyf
authors.affiliation: Laboratory of Clinical and Experimental Endocrinology, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Geert
authors.initials: G
authors.lastname: Carmeliet
authors.affiliation: Laboratory of Clinical and Experimental Endocrinology, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Chantal
authors.initials: C
authors.lastname: Mathieu
authors.affiliation: Department of Fundamental Chemistry, University of A Coruña, A Coruña, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Maestro
authors.affiliation: Department of Cellular and Molecular Medicine, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Etienne
authors.initials: E
authors.lastname: Waelkens
authors.affiliation: Department of Immunology and Microbiology, Laboratory of Nephrology, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: Evenepoel
authors.affiliation: Laboratory of Clinical and Experimental Endocrinology, KU Leuven, 3000 Leuven, Belgium. Electronic address: roger.bouillon@kuleuven.be.
authors.forename: Roger
authors.initials: R
authors.lastname: Bouillon
authors.affiliation: Department of Laboratory Medicine, University Hospitals Leuven, 3000 Leuven, Belgium; Laboratory of Clinical and Experimental Endocrinology, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Dirk
authors.initials: D
authors.lastname: Vanderschueren
authors.affiliation: Department of Laboratory Medicine, University Hospitals Leuven, 3000 Leuven, Belgium; Department of Cardiovascular Sciences, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: Vermeersch
mesh_terms: D000328:Adult; D002117:Calcitriol / Q000097:blood* / Q000378:metabolism; D002853:Chromatography, Liquid / Q000379:methods; D006801:Humans; D057230:Limit of Detection; D008875:Middle Aged; D053719:Tandem Mass Spectrometry / Q000379:methods*; D014815:Vitamins / Q000097:blood* / Q000378:metabolism; D055815:Young Adult
chemical_list: D014815:Vitamins; D002117:Calcitriol
keywords: 1,25-dihydroxyvitamin D; Liquid chromatography; Mass Spectrometry; Metabolism; Vitamin D