Medicinal and Pharmaceutical Chemistry Commons^™

Uplc-Ms/Ms Analysis Of The Michaelis-Menten Kinetics Of Cyp3a-Mediated Midazolam 1′- And 4-Hydroxylation In Rat Brain Microsomes, Devaraj Venkatapura Chandrashekar, Barent Dubois, Reza Mehvar

Pharmacy Faculty Articles and Research

Midazolam (MDZ) is a short-acting benzodiazepine with rapid onset of action, which is metabolized by CYP3A isoenzymes to two hydroxylated metabolites, 1′-hydroxymidazolam and 4-hydroxymidazolam. The drug is also commonly used as a marker of CYP3A activity in the liver microsomes. However, the kinetics of CYP3A-mediated hydroxylation of MDZ in the brain, which contains much lower CYP content than the liver, have not been reported. In this study, UPLC-MS/MS and metabolic incubation methods were developed and validated for simultaneous measurement of low concentrations of both hydroxylated metabolites of MDZ in brain microsomes. Different concentrations of MDZ (1–500 µM) were incubated with …

Kinetics Of Dextromethorphan-O-Demethylase Activity And Distribution Of Cyp2d In Four Commonly-Used Subcellular Fractions Of Rat Brain, Barent N. Dubois, Farideh Amirrad, Reza Mehvar

Pharmacy Faculty Articles and Research

The purpose of this study was to compare the enzymatic kinetics and distribution of cytochrome P450 2D (CYP2D) among different rat brain subcellular fractions.

Rat brains were used to prepare total membrane, crude mitochondrial, purified mitochondrial, and microsomal fractions, in addition to total homogenate. Michaelis–Menten kinetics of the brain CYP2D activity was estimated based on the conversion of dextromethorphan (DXM) to dextrorphan using UPLC-MS/MS. Protein levels of CYP2D and subcellular markers were determined by Western blot.

Microsomal CYP2D exhibited high affinity and low capacity, compared with the mitochondrial CYP2D that had a much lower (∼50-fold) affinity but a higher (∼six-fold) …

Uplc-Ms/Ms Analysis Of Dextromethorphan-O-Demethylation Kinetics In Rat Brain Microsomes, Barent N. Dubois, Reza Mehvar

Pharmacy Faculty Articles and Research

Formation of dextrorphan (DXT) from dextromethorphan (DXM) has been widely used to assess cytochrome P450 2D (CYP2D) activity. Additionally, the kinetics of CYP2D activity have been well characterized in the liver microsomes. However, studies in brain microsomes are limited due to the lower microsomal content and abundance of CYP2D in the brain relative to the liver. In the present study, we developed a micro-scale enzymatic incubation method, coupled with a sensitive UPLC-MS/MS assay for the quantitation of the rate of DXT formation from DXM in brain microsomes. Rat brain microsomes were incubated with different concentrations of DXM for various times. …