Characterization of methadone as a β-arrestin-biased μ-opioid receptor agonist.
BACKGROUND
Methadone is a unique µ-opioid receptor agonist. Although several researchers have insisted that the pharmacological effects of methadone are mediated through the blockade of NMDA receptor, the underlying mechanism by which methadone exerts its distinct pharmacological effects compared to those of other µ-opioid receptor agonists is still controversial. In the present study, we further investigated the pharmacological profile of methadone compared to those of fentanyl and morphine as measured mainly by the discriminative stimulus effect and in vitro assays for NMDA receptor binding, µ-opioid receptor-internalization, and µ-opioid receptor-mediated β-arrestin recruitment.


RESULTS
We found that fentanyl substituted for the discriminative stimulus effects of methadone, whereas a relatively high dose of morphine was required to substitute for the discriminative stimulus effects of methadone in rats. Under these conditions, the non-competitive NMDA receptor antagonist MK-801 did not substitute for the discriminative stimulus effects of methadone. In association with its discriminative stimulus effect, methadone failed to displace the receptor binding of MK801 using mouse brain membrane. Methadone and fentanyl, but not morphine, induced potent µ-opioid receptor internalization accompanied by the strong recruitment of β-arrestin-2 in µ-opioid receptor-overexpressing cells.


CONCLUSIONS
These results suggest that methadone may, at least partly, produce its pharmacological effect as a β-arrestin-biased µ-opioid receptor agonist, similar to fentanyl, and NMDA receptor blockade is not the main contributor to the pharmacological profile of methadone.
Department of Pharmacology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Ebara, Shinagawa-ku, Tokyo, Japan.
Seira
S
Doi
Department of Pharmacology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Ebara, Shinagawa-ku, Tokyo, Japan.
Tomohisa
T
Mori
Department of Pharmacology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Ebara, Shinagawa-ku, Tokyo, Japan.
Naoki
N
Uzawa
Department of Pharmacology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Ebara, Shinagawa-ku, Tokyo, Japan.
Takamichi
T
Arima
Department of Pharmacology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Ebara, Shinagawa-ku, Tokyo, Japan.
Tomoyuki
T
Takahashi
Department of Pharmacology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Ebara, Shinagawa-ku, Tokyo, Japan.
Masashi
M
Uchida
Department of Pharmacology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Ebara, Shinagawa-ku, Tokyo, Japan.
Ayaka
A
Yawata
Department of Pharmacology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Ebara, Shinagawa-ku, Tokyo, Japan.
Michiko
M
Narita
Division of Cancer Pathophysiology, National Cancer Center Research Institute, Tokyo, Japan.
Yasuhito
Y
Uezono
Institute of Drug Addiction Research, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Tokyo, Japan.
Tsutomu
T
Suzuki
Department of Pharmacology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Ebara, Shinagawa-ku, Tokyo, Japan Life Science Tokyo Advanced Research Center (L-StaR), Hoshi University School of Pharmacy and Pharmaceutical Sciences, Tokyo, Japan narita@hoshi.ac.jp t-mori@hoshi.ac.jp.
Minoru
M
Narita
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects; D005283:Fentanyl / Q000494:pharmacology; D005772:Gastrointestinal Transit / Q000187:drug effects; D008297:Male; D008691:Methadone / Q000494:pharmacology*; D008813:Mice, Inbred ICR; D059225:Nociception / Q000187:drug effects; D011916:Rats, Inbred F344; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000819:agonists*; D000071557:beta-Arrestins / Q000378:metabolism*
D016194:Receptors, N-Methyl-D-Aspartate; D017450:Receptors, Opioid, mu; D000071557:beta-Arrestins; D016291:Dizocilpine Maleate; D008691:Methadone; D005283:Fentanyl
Methadone; NMDA receptor; internalization; µ-opioid receptor