Browsing Pathways

Valproic acid (VPA) is metabolized almost entirely in the liver, via at least there routes: glucuronidation, beta oxidation in the mitochondria, and cytochrome P450 mediated oxidation. The glucuronidation of VPA is mediated by UGT1A3, UGT1A4, UGT1A6, UGT1A8, UGT1A9, UGT1A10, UGT2B7 and UGT2B15. The key CYP-mediated reaction of the VPA metabolic pathway is the generation of 4-ene-VPA by CYP2C9, CYP2A6 and CYP2B6. These three enzymes also catalyze the formation of 4-OH-VPA and 5-OH-VPA. Moreover, CYP2A6 mediates the oxidation of VPA to 3-OH-VPA. Inside the mitochondria, the first step of oxidation is the formation of (VPA-CoA) catalyzed by medium-chain acyl-CoA synthase, followed by the conversion to 2-ene-VPA-CoA through 2-methyl-branched chain acyl-CoA dehydrogenase (ACADSB). 2-ene-VPA-CoA is further converted to 3-hydroxyl-valproyl-VPA (3-OH-VPA-CoA) by an enoyl-CoA hydratase, crotonase (ECSH1) and then 3-OH-VPA-CoA is metabolized to 3-keto-valproyl-CoA (3-oxo-VPA-CoA) through the action of 2-methyl-3-hydroxybutyryl-CoA dehydrogenase. Another route of VPA metabolism in the mitochondria includes the conversion of 4-ene-VPA to 4-ene-VPA-CoA ester catalyzed by ACADSB, followed by a beta-oxidation to form 2,4-diene-VPA-CoA ester. The latter metabolite can furthermore be conjugated to glutathione to form thiol metabolites.

Venlafaxine (also named as Effexor or Elafax) is an antidepressant medication, which belongs to the class of serotonin-norepinephrine reuptake inhibitor (SNRI). Venlafaxine is well absorbed into the circulation system. Venlafaxine is also metabolized to N-desmethylvenlafaxine. The N-demethylation is catalyzed by CYP3A4 and CYP2C19. N-desmethylvenlafaxine is a weaker serotonin and norepinephrine reuptake inhibitor. Both O-desmethylvenlafaxine (as potent a serotonin-norepinephrine reuptake inhibitor) and N-desmethylvenlafaxine are further metabolized by CYP2C19, CYP2D6 and/or CYP3A4 to a minor metabolite N,O-didesmethylvenlafaxine that is further metabolized into N,N,O-tridesmethylvenlafaxine or excreted as N,O-didesmethylvenlafaxine gucuronide. Later on, O-desmethylvenlafaxine is exported without any change in chemical structure. Venlafaxine is exported via two transporters: Multidrug resistance protein 1 and ATP-binding cassette sub-family G member 2.