Methadone Metabolism by Early Gestational Age Placentas

ABSTRACT

The objective of this study was to identify the enzyme that metabolizes methadone in preterm placentas. Microsomal fractions were obtained from preterm (17 to 34 weeks) placentas (36 total; 12 per each gestational age group) and their activity in metabolizing methadone to 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) was determined. The enzyme catalyzing the reaction was identified by using chemical inhibitors selective for various cytochrome P450 isozymes and monoclonal antibodies raised against them. The metabolism of methadone by microsomes revealed saturation kinetics. Methadone was N-demethylated to EDDP by aromatase. The affinity of methadone to aromatase (apparent K _m) did not change with gestation, but the activity of the enzyme (V _max) increased and varied widely between individual placentas. Aromatase/CYP19 is the placental enzyme metabolizing methadone during pregnancy. The variability in enzyme activity among individuals should be reflected by the concentration of methadone in the fetal circulation and might be one of the factors affecting the incidence and intensity of neonatal abstinence syndrome.

Pregnancy - methadone maintenance programs - human placental aromatase/CYP19

REFERENCES

• 1 Allen M H. Detoxification considerations in the medical management of substance abuse in pregnancy.  Bull NY Acad Med. 1991;  67 270-276
• 2 Warner E A, Kosten T R, O'Connor P G. Pharmacotherapy for opioid and cocaine abuse.  Med Clin North Am. 1997;  81 909-925
• 3 Drozdick III J, Berghella V, Hill M, Kaltenbach K. Methadone trough levels in pregnancy.  Am J Obstet Gynecol. 2002;  187 1184-1188
• 4 Doberczak T M, Kandall S R, Friedmann P. Relationship between maternal methadone dosage, maternal-neonatal methadone levels, and neonatal withdrawal.  Obstet Gynecol. 1993;  81 936-940
• 5 Dashe J S, Sheffield J S, Olscher D A, Todd S J, Jackson G L, Wendell Jr G D. Relationship between maternal methadone dosage and neonatal withdrawal.  Obstet Gynecol. 2002;  100 1244-1249
• 6 Rosen T S, Pippenger C E. Disposition of methadone and its relationship to severity of withdrawal in the newborn.  Addict Dis. 1975;  2 169-178
• 7 Kandall S R, Albin S, Gartner L M, Lee K, Eidelman A, Lowinson J. The narcotic-dependent mother: fetal and neonatal consequences.  Early Hum Dev. 1977;  1 159-169
• 8 Mack G, Thomas D, Giles W, Buchanan N. Methadone levels and neonatal withdrawal.  J Paediatr Child Health. 1991;  27 96-100
• 9 Berghella V, Lim P J, Hill M K, Cherpes J, Chennat J, Kaltenbach K. Maternal methadone dose and neonatal withdrawal.  Am J Obstet Gynecol. 2003;  189 312-317
• 10 Doberczak T M, Kandall S R, Wilets I. Neonatal opiate abstinence syndrome in term and preterm infants.  J Pediatr. 1991;  118 933-937
• 11 Frederiksen M C. Physiologic changes in pregnancy and their effect on drug disposition.  Semin Perinatol. 2001;  25 120-123
• 12 Loebstein R, Koren G. Clinical relevance of therapeutic drug monitoring during pregnancy.  Ther Drug Monit. 2002;  24 15-22
• 13 Juchau M R. Drug biotransformation in the placenta.  Pharmacol Ther. 1980;  8 501-524
• 14 Pasanen M, Pelkonen O. The expression and environmental regulation of P450 enzymes in human placenta.  Crit Rev Toxicol. 1994;  24 211-229
• 15 Pasanen M, Hukkanen J, Pelkonen O et al.. Expression of xenobiotic-metabolizing cytochrome P450 forms in human full-term placenta.  Biochem Pharmacol. 1996;  51 403-411
• 16 Nanovskaya T N, Deshmukh S V, Nekhayeva I A, Zharikova O L, Hankins G DV, Ahmed M S. Methadone metabolism by human placenta.  Biochem Pharmacol. 2004;  68 583-591
• 17 Moody D E, Alburges M E, Parker R J, Collins J M, Strong J M. The involvement of cytochrome P450 3A4 in the demethylation of L-α-acetylmethadol (LAAM), norLAAM, and methadone.  Drug Metab Dispos. 1997;  25 1347-1353
• 18 Foster D J, Somogyi A A, Bochner F. Methadone N-demethylation in human liver microsomes: lack of stereoselectivity and involvement of CYP3A4.  Br J Clin Pharmacol. 1999;  47 403-412
• 19 Iribarne C, Berthou F, Baird S et al.. Involvement of cytochrome P450 3A4 enzyme in the N-demethylation of methadone in human liver microsomes.  Chem Res Toxicol. 1996;  9 365-373
• 20 Ferrari A, Coccia C PR, Bertolini A, Sternieri E. Methadone-metabolism, pharmacokinetics, and interactions.  Pharmacol Res. 2004;  50 551-559
• 21 Gerber J G, Rhodes R J, Gal J. Stereoselective metabolism of methadone N-demethylation by cytochrome P4502B6 and 2C19.  Chirality. 2004;  16 36-44
• 22 Oda Y, Kharasch E D. Metabolism of methadone and levo-alpha-acetylmethadol (LAAM) by human intestinal cytochrome P450 3A4 (CYP3A4): potential contribution of intestinal metabolism to presystemic clearance and bioactivation.  J Pharmacol Exp Ther. 2001;  298 1021-1032
• 23 Beckett A H, Taylor J F, Casy A F, Hassan M MA. The biotransformation of methadone in man: synthesis and identification of a major metabolite.  J Pharm Pharmacol. 1968;  20 754-762
• 24 Pohland A, Boaz H E, Sullivan H R. Synthesis and identification of metabolites resulting from the biotransformation of dl-methadone in man and in the rat.  J Med Chem. 1971;  14 194-197
• 25 Billings R E, Booher R, Smits S, Pohland A, McMahon R E. Metabolism of acetylmethadol: a sensitive assay for noracetylmethadol and the identification of a new active metabolite.  J Med Chem. 1973;  16 305-306
• 26 Hakkola J, Raunio H, Purkunen R et al.. Detection of cytochrome P450 gene expression in human placenta in first trimester of pregnancy.  Biochem Pharmacol. 1996;  52 379-383
• 27 Hakkola J, Pasanen M, Hukkanen J et al.. Expression of xenobiotic-metabolizing cytochrome P450 forms in human full-term placenta.  Biochem Pharmacol. 1996;  51 403-411
• 28 Kitawaki J, Yoshida N, Osawa Y. An enzyme-linked immunosorbent assay for quantitation of aromatase cytochrome P-450.  Endocrinology. 1989;  124 1417-1423
• 29 Stresser D M, Turner S D, McNamara J et al.. A high-throughput screen to identify inhibitors of aromatase (CYP19).  Anal Biochem. 2000;  284 427-430
• 30 Kitawaki J, Inoue S, Tamura T et al.. Increasing aromatase cytochrome P-450 level in human placenta during pregnancy: studied by immunohistochemistry and enzyme-linked immunosorbent assay.  Endocrinology. 1992;  130 2751-2757
• 31 Deshmukh S V, Nanovskaya T N, Ahmed M S. Aromatase is the major enzyme metabolizing buprenorphine in human placenta.  J Pharmacol Exp Ther. 2003;  306 1099-1105
• 32 Ayub M, Levell M J. Structure-activity relationships of the inhibition of human placental aromatase by imidazole drugs including ketoconazole.  J Steroid Biochem. 1988;  31 65-72