Quantification of nitrogenous bases, DNA and Collagen type I for the estimation of the postmortem interval in bone remains

Estimating the postmortem interval (PMI) is an important goal in forensic medicine and continues to be one of the most difficult tasks of the forensic investigator. Few accurate methods exist to determine the time since death of skeletonized human remains due to the great number of intrinsic and external factors that may alter the normal course of postmortem change. The purpose of this research was to assess the usefulness of various biochemical parameters, such as nitrogenous bases (adenine, guanine, purines, cytosine, thymine, pyrimidines, hypoxanthine and xanthine), DNA and Collagen Type I peptides to estimate PMI. These parameters were analysed in cortical bone for the establishment of data in a total of 80 long bones of 80 corpses (50 males, 30 females) with a mean age of 68.31 years (S.D. = 18.021, range = 20-97). The bones were removed from the cement niches of a cemetery in Murcia (south-eastern Spain), where they had lain for between 5 and 47 years (mean time 23.83 years, S.D. = 10.85). Our results show a significant decrease in adenine (p = 0.0004), guanine (p = 0.0001), purines (p = 0.0001), cytosine (p = 0.0001), thymine (p = 0.0226), pyrimidines (p = 0.0002) and the number of peptides of Collagen type I (p = 0.0053) in those with a PMI ≥ 20 years. In a curvilinear regression analysis the results show that 30.6% of the variable PMI could be explained by guanine concentration, in bones with a PMI < 20 years, while in cases of a PMI ≥ 20 years, the variable that best explained membership of this group was adenine (38.0%). In the discriminant analysis applied to the all the variables as a function of PMI when two groups were established, 86.7% of the cases were correctly classified. These results show that the quantification of Collagen type I proteins and nitrogenous bases could be used as a complementary tool, together with other analyses, in the estimation of PMI.