In vitro biotransformation of 3-methylmethcathinone (3-MMC) through incubation with human liver microsomes and cytosol and application to in vivo samples

Synthetic cathinones are the second largest group of new psychoactive substances (NPS) monitored by the European Monitoring Centre for Drugs and Drug Addiction. Although 3-methylmethcathinone (3-MMC, C11H15NO) is legally banned in many countries, it is readily available for purchase online and on the street. Due to the scarcity of information regarding the pharmacokinetic and toxicological profile of 3-MMC, understanding its biotransformation pathways is crucial in determining its potential toxicity in humans and in the development of analytical methods for screening of human matrices. To gain more insight, Phase I and Phase II in vitro biotransformation of 3-MMC was investigated using human liver microsomes and human liver cytosol. Suspect and non-target screening approaches were employed to identify metabolites. To confirm in vitro results in an in vivo setting, human matrices (i.e., plasma, urine, saliva and hair) positive for 3-MMC (n=31) were screened. In total three biotransformation products were identified in vitro: C11H15NO2 (a hydroxylated derivate), C11H17NO (a keto-reduced derivate) and C10H13NO (an N-desmethyl derivate). All three were confirmed as human metabolites in respectively 16%, 52% and 42% of the analysed human samples. In total, 61% of the analysed samples were positive for at least one of the three metabolites. Interestingly, three urine samples were positive for all three metabolites. The presence of 3-MMC in saliva and hair indicates its potential applicability in specific settings, e.g., roadside testing or chronic consumption analysis. To our knowledge, C11H17NO was not detected before in vivo. Although some of these metabolites have been previously suggested in vitro or in a single post mortem case report, a wide in vivo confirmation including the screening of four different human matrices was performed for the first time. These metabolites could serve as potential human biomarkers to monitor human 3-MMC consumption effectively.