Methamphetamine toxicity: Thermal degradation, CYP450-mediated metabolic activation and cytotoxic epoxide formation.
Date of Graduation
Methamphetamine hydrochloride and other drugs of abuse undergo thermal degradation upon smoking. Pyrolytic degradation products of cocaine, phencyclidine and methamphetamine laced on tobacco have been identified in simulated smoking experiments. However, thermal degradation products of methamphetamine hydrochloride alone are not known. Differential scanning calorimetry was used to simulate smoking conditions and to thermally degrade methamphetamine hydrochloride. trans-1-Phenyl-1-propene was one of the major thermal degradation products identified. In pooled human liver microsomes, trans-1-phenyl-1-propene was converted to trans-1-phenylpropylene oxide ( trans-2-methyl-3-phenyloxirane) and cinnamyl alcohol (3-phenyl-2-propen-1-ol). Epoxide formation in pooled human liver microsomes showed an apparent K m of 110 Â± 16 Î¼M and Vmax of 165 Â± 10 pmol/min/mg protein. Apparent Km (118 Â± 18 Î¼M) and Vmax (334 Â± 22 pmol/min/mg protein) values were also estimated for cinnamyl alcohol formation. Incubations of trans-1-phenyl-1-propene with microsomes in the presence of iosform-specific P450 enzyme inhibitors suggested the involvement of CYP3A4, CYP2D6, CYP1A2, and CYP2E1 isoforms in these biotransformations. Studies with recombinant enzymes confirmed that trans-1-phenyl-1-propene is a good substrate for CYP1A2 catalyzed epoxide formation, and CYP2E1 is the primary enzyme involved in the cinnamyl alcohol pathway. To evaluate the potential cytotoxicity of the epoxide metabolite, studies conducted with cultured C6 glial cells demonstrated that 1-phenylpropylene oxide is cytotoxic in a concentration dependent manner based on cell degeneration and death. trans-1-Phenylpropylene oxide was metabolized further by conjugation with glutathione in a reaction catalyzed by human liver cytosolic enzymes to form 1-phenylpropylene oxide-glutathione adduct. The epoxide also reacted with a dodecamer oligonucleotide to from adducts. Such adducts formed from 1-phenylpropylene oxide and other common cellular nucleophiles can be potential biomarkers of smoked methamphetamine hydrochloride.
Sanga, Madhu, "Methamphetamine toxicity: Thermal degradation, CYP450-mediated metabolic activation and cytotoxic epoxide formation." (2004). Graduate Theses, Dissertations, and Problem Reports. 9709.