Post-mortem vitreous humour as potential specimen for detection of insulin analogues by LC-MS/MS

Differentiation of insulin analogues is required in forensic and clinical toxicology as well as in sports doping control. Immunoassay results provide only weak evidence for exogenous administration of insulin, as concentrations cannot be reliably interpreted and specific information on the insulin species remains unknown. In post-mortem blood, insulin degrades rapidly. In this study, improved methodology consisting of precipitation of proteins, immunoaffinity purification and liquid chromatography coupled to high resolution/high accuracy mass spectrometry were applied to post-mortem vitreous humour. Ten successive cases with a post-mortem interval from four to ten days were investigated for insulin analogues. The cause of death in these cases was connected with diabetes and its complications, as well as with chronic cardiovascular disease, alcoholism and cancer. In all cases, the manner of death was natural (disease). Insulin was positively detected in post-mortem vitreous humour in three cases out of ten by mass spectrometry. In two cases, the method revealed the long-acting insulin glargine (Lantus) metabolite M2 (DesB31-32 Lantus), and human insulin was detected in one case. The findings were in agreement with the documented history of insulin medication. No other obvious reason could be found for the failure of detecting insulins in the other cases than insulin degradation during the lengthy post-mortem interval. Vitreous humour is still a most prospective specimen for detection of insulin analogues post-mortem.