Cannabinoid Stability in Postmortem Brain Samples Stored at Different Temperatures

Drug stability is an important concern of forensic toxicological testing, particularly postmortem (PM) samples that may be stored for an extensive period of time before analysis. In PM toxicology, the complex assessment of analyte stability in biological matrices can profoundly impact the interpretation of toxicological results and the outcome of forensic casework. The aim of this work is to assess the stability of ∆9-tetrahydrocannabinol (THC), cannabidiol, 11-hydroxy-THC (11-OH-THC), 11-nor-9-carboxy-∆9-THC (THCCOOH) and 11-nor-∆9-THC-9-carboxylic acid glucuronide (THCCOOH-glucuronide) in brain stored at three different temperatures (4°C, -20°C and -70°C) up to over 12 months (390 days) in order to establish the best storage condition for preventing potential drug degradation during the storage period. Brain is suitable and useful for xenobiotic concentrations and is a valuable specimen in the interpretation of PM toxicological results. In our study, pooled brain specimens were spiked at low and high concentrations to evaluate the change in concentration over time. Stable compounds were quantified within ±20% of the target concentration (the mean concentration resulting from the initial analysis). According to stability criteria, our preliminary findings revealed that all the cannabinoids studied are stable in frozen brain samples (-20°C and -70°C) for over 12 months: all the analytes' concentrations remained unaffected during storage over time, with the analytical variation staying within ±20%. On the contrary, under refrigeration conditions (4°C), 11-OH-THC, THCCOOH and THCCOOH-glucuronide were instable. Authentic brain samples, collected from eight cases during the autopsy, were analyzed, and the stability was evaluated. This study provided new data on cannabinoid stability in brain. The stability of the brain samples, both in spiked samples and in authentic caseworks, highlights the importance of the brain as a valid testing matrix when retesting is required after a long period of time or when laboratories are faced with backlog.