title: α-Klotho is unstable in human urine.
abstract: α-Klotho is an interesting new biomarker in kidney and cardiovascular disease. As α-Klotho is primarily expressed in renal epithelial tissue, various papers have reported α-Klotho concentrations in urine. As these studies did not address the reliability of urinary α-Klotho measurements and as urine is known to be a complex milieu, we investigated the stability of α-Klotho in both fresh catheter and fresh voided urine. α-Klotho was measured in these fresh urine samples and in the same samples under several other conditions. Storage of fresh catheter urine for 3 h at 37 °C, comparable to storage in the bladder, led to a 82% decrease in α-Klotho concentrations. Compared with fresh voided urine, α-Klotho concentrations decreased on an average of 45 and 82% after storage at -80 °C and -20 °C, respectively. An additional freeze-thaw cycle further decreased α-Klotho concentrations. The addition of a protease inhibitor or 0.1% albumin partly prevented degradation in fresh voided urine. Thus, α-Klotho is highly unstable in urine. Future studies showing results of urinary α-Klotho should mention conservation conditions and prove the reliability of the α-Klotho measurements.
authors.affiliation: Department of Nephrology, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Aaltje Y
authors.initials: AY
authors.lastname: Adema
authors.affiliation: Department of Nephrology, VU University Medical Center, Amsterdam, The Netherlands.|Institute for Cardiovascular Research VU (ICaR-VU), VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Marc G
authors.initials: MG
authors.lastname: Vervloet
authors.affiliation: Department of Clinical Chemistry, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Marinus A
authors.initials: MA
authors.lastname: Blankenstein
authors.affiliation: Department of Clinical Chemistry, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Annemieke C
authors.initials: AC
authors.lastname: Heijboer