In Vitro Metabolism and Pharmacokinetic Studies on Methylone

Abstract

Abuse of the stimulant designer drug methylone (methylenedioxymethcathinone) has been documented in most parts of the world. As with many of the new designer drugs that continuously appear in the illicit drug market, little is known about the pharmacokinetics of methylone. Using in vitro studies, CYP2D6 was determined to be the primary enzyme that metabolizes methylone, with minor contributions from CYP1A2, CYP2B6, and CYP2C19. The major metabolite was identified as dihydroxymethcathinone, and the minor metabolites were N-hydroxy-methylone, nor-methylone, and dihydromethylone. Measuring the formation of the major metabolite, biphasic Michaelis-Menten kinetic parameters were determined: V max,1 = 0.046 6 0.005 (S.E.) nmol/min/mg protein, K m,1 = 19.0 6 4.2 mM, V max,2 = 0.22 6 0.04 nmol/min/mg protein, and K m,2 = 1953 6 761 mM; the low-capacity and high-affinity contribution was assigned to the activity of CYP2D6. Additionally, a time-dependent loss of CYP2D6 activity was observed when the enzyme was preincubated with methylone, reaching a maximum rate of inactivation at high methylone concentrations, indicating that methylone is a mechanism-based inhibitor of CYP2D6. The inactivation parameters were determined to be K I = 15.1 6 3.4 (S.E.) mM and k inact = 0.075 6 0.005 minute 21.

Pharmacokinetic Profiles and Pharmacodynamic Effects for Methylone and Its Metabolites in Rats

“…The data in Figure 3 clearly demonstrate that plasma concentrations of methylone and MDC increase more than expected based on the doses administered, providing an indication of non-linear accumulation for these analytes in plasma. Methylone inhibits human CYP2D6 in vitro (Dinger et al, 2016;Pedersen et al, 2013), and the present non-linear increases in plasma methylone and MDC seem to agree with this observation. It should be mentioned that non-linear kinetics resulting from inhibition of CYP2D1 (ie, the rat isoform of CYP2D6 responsible for methylone O-demethylenation) should result in appreciable decreases in the formation of HHMC and HMMC (see Concheiro et al, 2014).…”

“…These investigators showed that methylone is metabolized in a manner akin to MDMA involving two major pathways ( Figure 1): (1) O-demethylenation to form ( ± )-3,4-dihydroxy-N-methylcathinone (HHMC) followed by O-methylation to form ( ± )-4-hydroxy-3-methoxy-N-methylcathinone (HMMC) and (2) N-demethylation to produce ( ± )-3,4-methylenedioxycathinone (MDC) (Kamata et al, 2006). Methylone is primarily biotransformed by cytochrome p450 2D6 (CYP2D6) in humans, the same isoform responsible for metabolism of MDMA (Pedersen et al, 2013). Lopez-Arnau et al (2013) evaluated methylone PK and pharmacodynamic effects in rats and found that methylone exhibits rapid kinetics, with peak blood concentrations occurring 30 min after oral administration, and readily crosses the blood-brain barrier (Lopez-Arnau et al, 2013).…”

The Psychostimulant Khat (Catha edulis) Inhibits CYP2D6 Enzyme Activity in Humans

“…13 Likewise, other in vitro studies have shown that synthetic cathinones are CYP2D6 substrates and inhibitors. 14 The increasing daily use of khat in East Africa and Arabia is a major concern for public health. 6,15 There is evidence that herbdrug interactions represent a potential risk to patients taking conventional medicines, resulting in serious clinical consequences.…”

“Legal Highs” – An Emerging Epidemic of Novel Psychoactive Substances

“…Six phase I metabolites of mephedrone were detected in rat urine and seven in human urine (Meyer, Wilhelm, et al, 2010). Cytochrome P450 2D6 (CYP2D6) is the main enzyme responsible for the in vitro phase I metabolism of mephedrone and methylone (Pedersen, Petersen, & Linnet, 2013;Pedersen, Reitzel, Johansen, & Linnet, 2013); CYP2D6, CYP2C19, and COMT are involved in metabolism of MDPV (Meyer, Du, Schuster, & Maurer, 2010;Strano-Rossi, Cadwallader, de la Torre, & Botrè, 2010); CYP1A2, CY3A4, and CYP2D6 catalyze dealkylation and hydroxylation of BZP and TFMPP (Antia, Lee, Kydd, Tingle, & Russell, 2009;. Phase I metabolites are eliminated with urine as glucuronide conjugates and sulfate conjugates.…”