Amodiaquine Clearance and Its Metabolism toN-Desethylamodiaquine Is Mediated by CYP2C8: A New High Affinity and Turnover Enzyme-Specific Probe Substrate

Abstract

Amodiaquine (AQ) metabolism to N-desethylamodiaquine (DEAQ) is the principal route of disposition in humans. Using human liver microsomes and two sets of recombinant human cytochrome P450 isoforms (from lymphoblastoids and yeast) we performed studies to identify the CYP isoform(s) involved in the metabolism of AQ. CYP2C8 was the main hepatic isoform that cleared AQ and catalyzed the formation of DEAQ. The extrahepatic P450s, 1A1 and 1B1, also cleared AQ and catalyzed the formation of an unknown metabolite M2. The K m and V max values for AQ N-desethylation were 1.2 M and 2.6 pmol/ min/pmol of CYP2C8 for recombinant CYP2C8, and 2.4 M and 1462 pmol/min/mg of protein for human liver microsomes (HLMs), respectively. Relative contribution of CYP2C8 in the formation of DEAQ was estimated at 100% using the relative activity factor method. Correlation analyses between AQ metabolism and the activities of eight hepatic P450s were made on 10 different HLM samples. Both the formation of DEAQ and the clearance of AQ showed excellent correlations (r 2 ϭ 0.98 and 0.95) with 6␣-hydroxylation of paclitaxel, a marker substrate for CYP2C8. The inhibition of DEAQ formation by quercetin was competitive with K i values of 1.96 for CYP2C8 and 1.56 M for HLMs. Docking of AQ into the active site homology models of the CYP2C isoforms showed favorable interactions with CYP2C8, which supported the likelihood of an N-desethylation reaction. These data show that CYP2C8 is the main hepatic isoform responsible for the metabolism of AQ. The specificity, high affinity, and high turnover make AQ desethylation an excellent marker reaction for CYP2C8 activity.Amodiaquine (AQ) is a 4-aminoquinoline derivative that has been widely used for treatment of malaria over the past 50 years. It is intrinsically more active than the other 4-aminoquinoline, chloroquine, against Plasmodium falciparum parasites, which are moderately chloroquine resistant. The drug is therefore increasingly being considered as a replacement for chloroquine as a first line drug in Africa because of widespread chloroquine resistance. Because of major side effects, mainly agranulocytosis, observed during prophylactic use of the drug, AQ is now only recommended for treatment of malaria, for which no serious cases of toxicity have been reported (Laurent et al., 1993).Upon oral administration, AQ is rapidly absorbed and extensively metabolized such that very little of the parent drug is detected in the plasma. The main metabolite of AQ is N-desethylamodiaquine (DEAQ) with other minor metabolites being 2-hydroxyl-DEAQ and N-bisdesethylAQ (bis-DEAQ) (Churchill et al., 1985Mount et al., 1986). Whereas the formation of DEAQ is rapid, its elimination is very slow with a terminal half-life of over 100 h (Winstanley et al., 1987;Laurent et al., 1993). AQ and DEAQ both have antimalarial activity, but AQ is 3 times more active (Churchill et al., 1985). However, since AQ is rapidly cleared and the formed DEAQ attains high plasma concentrations for a long time, AQ is considered a prodrug,...

Development of a novel mouse model of amodiaquine-induced liver injury with a delayed onset

“…Although it is still used in some countries, AQ was withdrawn from the market because of severe idiosyncratic drug reactions (IDR) that included hepatotoxicity (Larrey et al, 1986;Neftel et al, 1986), agranulocytosis (Rouveix et al, 1989), and aplastic anemia (Hatton et al, 1986). The mechanism of AQ-induced adverse reactions is currently not well understood, but AQ is metabolized to N-desethylamodiaquine (DEAQ) by CYP2C8 (Li et al, 2002), and both AQ or DEAQ can be oxidized to a reactive quinoneimine, which reacts with proteins to form covalent adducts (Maggs et al, 1987(Maggs et al, , 1988.…”

Induction of Amodiaquine Metabolism by Rifampicin Following Concurrent Administration in Healthy Volunteers

“…It is known that ADQ exhibits interindividual variations in its pharmacokinetics. 33 This is especially true because genetic polymorphisms can characterize CYP2C8 in the metabolism of drugs and provide basis for pharmacokinetic variations in individuals as well as responses to drug actions. 34 There was occurrence of a pronounced increase in the metabolic ratio.…”

“…ADQ is almost entirely metabolized by the polymorphic cytochrome P450 (CYP) isoform 2C8 to the pharmacologically active desethylamodiaquine (DEAQ). 15 Expression of each CYP is influenced by a unique combination of mechanisms and factors, including genetic polymorphisms, induction by xenobiotics, regulation by cytokines hormones and during disease states, as well as sex, age and others. 16 Multiallelic genetic polymorphisms, which strongly depend on ethnicity, play a major role in the function of CYPs 2D6, 2C8, 2C9 and 2B6, and lead to distinct pharmacogenetic phenotypes, termed as poor, intermediate, extensive and ultra-rapid metabolizers.…”

Can pharmacogenomics improve malaria drug policy?

“…22 People with mutant genotypes of CYP2C8, CYP1A1 and CYP1B1 have been found to have immunogenic adverse reactions to amodiaquine. [23][24][25][26][27][28] Wide variations in the CYP2C8 genotype mean that individuals experience broad differences in the drug's efficacy and toxicity. Evidence suggests that decreased function of the CYP2C8 enzyme impairs metabolism of the drug and can form a toxic metabolite that causes hepatotoxicity and agranulocytosis.…”