Identification of metabolites and potential biomarkers of kratom in urine

Mitragyna speciosa (kratom) is a drug that is increasingly used recreationally and "therapeutically", in the absence of medical supervision. The drug has been associated with a growing number of fatalities, and although its medicinal properties as an atypical opioid require further study, there are legitimate concerns regarding its unregulated use. Mitragynine is the most widely reported alkaloid within the plant, although more than forty other alkaloids have been identified. 7-Hydroxymitragynine is reported to have greater abuse liability due to its increased potency relative to mitragynine. In this report, biomarkers for mitragynine were investigated using liquid chromatography-quadrupole/time of flight mass spectrometry (LC-Q/TOF-MS). Speciociliatine and speciogynine were identified as alternative biomarkers, often exceeding the concentration of mitragynine in unhydrolyzed urine. 9-O-Demethylmitragynine and 7-hydroxymitragynine were identified in unhydrolyzed urine in 75% and 63% of the cases. Deconjugation of phase II metabolites using chemical hydrolysis was not suitable due to degradation of the Mitragyna alkaloids. Enzymatic hydrolysis was evaluated using three traditional glucuronidases, four sulfatases and four recombinant enzymes. Although enzymatic hydrolysis increased the concentration of 16-carboxymitragynine, it had nominal benefit for other metabolites. Deconjugation of urine was not necessary due to the abundance of parent drug (mitragynine), its diastereoisomers (speciociliatine and speciogynine) or metabolites (9-O-demethylmitragynine and 7-hydroxymitragynine).