Analysis of hypoxanthine and lactic acid levels in vitreous humor for the estimation of post-mortem interval (PMI) using LC–MS/MS

Hypoxanthine (Hx) is produced during terminal stages of purine catabolism in humans. The concentrations of Hx and l-lactic acid in vitreous humor highly correlate with post-mortem interval (PMI). In this study, we measured the concentrations of Hx and l-lactic acid in uncontrolled authentic vitreous humor from cadavers, and investigated the correlation between these molecules and PMI. A liquid chromatography–tandem mass spectrometry (LC–MS/MS) was used for the quantitative analysis of Hx and l-lactic acid in vitreous humor. These concentrations were also corrected by four seasons such as spring, summer, autumn, and winter and temperatures on the day of death such as −10 to 5 °C, 6–15 °C, 16–25 °C, and 26–32 °C that may affect the biomarker concentrations. Vitreous humors were collected from cadavers with known time of death at the National Forensic Service (NFS), Republic of Korea. The correlation between the concentrations of Hx and l-lactic acid in vitreous humors and PMI was evaluated using 79 corpses (53 males and 26 females), with sampling time ranging from 13 to 103 h after death. The average daily ambient temperature at the time of death of each sample was investigated to calibrate the correlation with PMI. Following correction of the concentrations of Hx and l-lactic acid with temperature, the correlation of Hx and l-lactic acid with PMI increased from 0.53 to 0.59 for Hx and 0.38 to 0.42 for l-lactic acid. The highest correlation of Hx and l-lactic acid concentrations with PMI was observed in the winter season, with an R2 value of 0.80 and 0.71 for Hx and l-lactic acid, respectively. The correlation of Hx and l-lactic acid with PMI was corrected by ambient temperature for each season, resulting in an increase in the R2 value to 0.88 for Hx and 0.72 for l-lactic acid. The best correlation was observed when the temperature was corrected after dividing by season.