The cholesterol levels increase in peripheral nerve tissue and post-mortem interval evaluation

Background. Previous studies evidenced as median nerve fibers underwent a marked demyelinization process, related to the time-since-death and associated to an evident increase in tissue cholesterol levels. Aims. The present research was aimed to correlate the increment in tissue cholesterol concentration (CHOL) with the post-mortem interval (PMI). Methods. Male and female Caucasian subjects (25-53 years old) without diagnosed neurological or metabolic diseases were chosen for the study. Two samples of median nerves were collected from the right and left wrist at intervals ranging from 30 minutes to two hours (t1 and t2). Fragments of approximately 1 cm were collected and analyzed by gas chromatographic/mass spectrometry (GC/MS), after chemical digestion in basic environment. CHOL quantification in median nerve was performed by means of a calibration curve in the range (9.25-150) ng/µL. The method was validated according to FDA guidelines. Data have been corrected with respect to the amount of nerve tissue analyzed and CHOL concentrations (in µg/mgtissue) were correlated to PMI (all samples were analyzed in triplicate and the mean values considered) and a statistical description of data performed. Results. An increment in cholesterol levels at t2 with respect to concentrations was detected at t1 recorded in all enrolled subjects. In order to eliminate inter-individual variations in cholesterol increment due to differences in collection times, concentrations were corrected with respect to dt (t2-t1=dt). Data elaboration was based on %ΔCHOL/dt, calculated as (CHOLt2-CHOLt1)/CHOLt2*100), within sampling time, dt = t2-t1. According to previous results, data confirmed the increment in post-mortem tissue cholesterol levels also in samples collected at a difference of 1-2 hrs. The percentages of cholesterol increment with respect to the mean PMI seemed to follow a linear relationship. Moreover, the phenomenon evolves in a similar way in both arms, thus allowing a better estimation of PMI with respect to data obtained considering a single arm. Conclusions. The possibility of withdrawal median nerve samples at both arms allows the reduction of inter-individual variations and a better estimation of time-since-death. Although it requires further confirmation via analyses of larger numbers of samples, the method proposed here can currently be applied to PMI determinations.