title: Metabolism of human insulin after subcutaneous administration: A possible means to uncover insulin misuse.
abstract: The misuse of insulin for performance enhancement in sport or as toxic agent has frequently been reported in the past. In contrast to synthetic insulin analogues, the administration of recombinant human insulin is hardly recognized by mass spectrometry. The present study was designed to uncover the misuse of recombinant human insulin for doping control purposes as well as for forensic applications. It is hypothesized that an altered metabolite profile of circulating insulin prevails after subcutaneous administration due to exposure of insulin to epidermal proteases. In vitro experiments with skin tissue lysates (S9 fraction and microsomes), different biological fluids (urine, serum, plasma) and recombinant human insulin were performed and the deriving metabolites were characterized by liquid chromatography coupled to high resolution mass spectrometry (HRMS). Afterwards, authentic blood samples of patients suffering from diabetes mellitus and a control group of healthy humans were analysed. Therefore, a method using protein precipitation, ultrafiltration and antibody-coated magnetic beads for purification with subsequent separation by nano-scale liquid chromatography coupled a Q Exactive mass spectrometer was applied. Several metabolites of insulin with C-terminally truncated sequences of the B-chain (and A-chain in minor extent) were identified within this study. Here, the DesB30 human insulin represents the major metabolite in all experiments. This metabolite is frequently found in urine samples due to degradation processes and, thus, disqualifies this matrix for the intended purposes. In contrast, blood samples do commonly not contain DesB30 insulin, which was corroborated by data obtained from the control group. In post-administration blood samples, minute but distinct amounts (approx. 50 pg mL(-1)) of DesB30 insulin were found and suggest the use of this analyte as potential marker for subcutaneous human insulin administration, supporting the attempts to uncover illicit recombinant human insulin administrations.
authors.affiliation: Center for Preventive Doping Research and Institute of Biochemistry, German Sport University Cologne, Am Sportpark Müngersdorf 6, 50933, Cologne, Germany. Electronic address: a.thomas@biochem.dshs-koeln.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Thomas
authors.affiliation: Department II of Internal Medicine and Center for Molecular Medicine Cologne, University of Cologne, Cologne, Germany; Department of Geriatric Medicine, St. Marien-Hospital, Cologne, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Brinkkötter
authors.affiliation: Center for Preventive Doping Research and Institute of Biochemistry, German Sport University Cologne, Am Sportpark Müngersdorf 6, 50933, Cologne, Germany.
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Schänzer
authors.affiliation: Center for Preventive Doping Research and Institute of Biochemistry, German Sport University Cologne, Am Sportpark Müngersdorf 6, 50933, Cologne, Germany.
authors.forename: Mario
authors.initials: M
authors.lastname: Thevis
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006801:Humans; D007279:Injections, Subcutaneous; D007328:Insulin / Q000008:administration & dosage* / Q000097:blood / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D008875:Middle Aged; D015813:Substance Abuse Detection
chemical_list: D007328:Insulin
keywords: Peptide metabolism; Skin tissue microsomes; Sport drug testing