Opioid peptide receptor studies. 12. Buprenorphine is a potent and selective ?/? antagonist in the [35S]-GTP-?-S functional binding assay

Abstract

We utilized the [(35)S]-GTP-gamma-S functional binding assay to determine the selectivity of opioid receptor agonists in guinea pig caudate membranes. The study focused on two opioid agonists used for treating opioid-dependent patients: methadone and buprenorphine. Selective antagonists were used to generate agonist-selective conditions: TIPP + nor-BNI to measure mu receptors, CTAP + nor-BNI to measure gamma receptors and TIPP + CTAP to measure kappa receptors. The assay was first validated with opioid agonists of known subtype specificity (DAMGO for mu, SNC80 for delta, and U69, 593 for kappa receptors). Methadone-stimulated [(35)S]-GTP-gamma-S binding was mu-specific and less potent and efficacious than etorphine (K(d) = 1,537 nM vs. K(d) = 7.8 nM). Buprenorphine failed to stimulate [(35)S]-GTP-gamma-S binding but inhibited agonist-stimulated [(35)S]-GTP-gamma-S binding. The antagonist-K(i) values (nM) of buprenorphine at mu, delta, and kappa receptors were 0.088 nM, 1.15 nM, and 0.072 nM, respectively. The antagonist-K(i) values (nM) of naloxone at mu, delta, and kappa receptors were 1.39 nM, 25.0 nM, and 11.4 nM, respectively. Autoradiographic studies showed that buprenorphine failed to stimulate [(35)S]-GTP-gamma-S binding in caudate-level rat brain sections but blocked DAMGO-stimulated [(35)S]-GTP-gamma-S binding. In cells expressing the cloned rat mu receptor, buprenorphine was a partial agonist and potent mu antagonist. Administration of buprenorphine to rats produced a long-lasting (>24 h) decrease in mu and kappa2 receptor binding and attenuated mu-stimulated [(35)S]-GTP-gamma-S binding. Viewed collectively, these data indicate that, in this assay system, buprenorphine is a potent mu and gamma receptor antagonist. The clinical implications remain to be elucidated. Synapse 34:83-94, 1999. Published 1999 Wiley-Liss, Inc.

Use of Irreversible Antagonists to Determine the Relative Efficacy of μ-Opioids in a Pigeon Drug Discrimination Procedure: Comparison of β-Funaltrexamine and Clocinnamox

“…35 S] GTP␥S binding, in vitro estimates of efficacy, has also been shown to be greater than that of morphine and methadone (Yu et al, 1997;Romero et al, 1999). The quantitative efficacy estimates for sufentanil and l-methadone were also higher than that for morphine and are in agreement with other reports indicating that in assays of antinociception, sufentanil is more resistant than morphine to irreversible antagonism, chronic opioid administration, and increases in nociceptive stimulus intensity (Mjanger and Yaksh, 1991;Dirig and Yaksh, 1995).…”

Buprenorphine Blocks ϵ- and μ-Opioid Receptor-Mediated Antinociception in the Mouse

“…Our results are consistent with the work done by Pick et al (1997) showing buprenorphine is unable to block the antinociceptive affects of 1 -opioid agonist U50,488H or ␦-opioid agonist DPDPE. Although other groups have shown -opioid (Leander, 1988;Pick et al, 1997;Romero et al, 1999) and ␦-opioid (Neilan et al, 1999) antagonistic effects with buprenorphine, we simply conclude that buprenorphine given i.c.v. at doses 0.1 to 1 g does not show any significant -or ␦-opioid antagonistic components with the respective agonists we administered.…”

“…35 S]GTP␥S binding assay (Romero et al, 1999). Buprenorphine also blocks the -opioid agonist U-50,488H-induced inhibition of abdominal stretching induced by intraperitoneal injection of acetic acid in mice (Leander, 1988).…”

Buprenorphine and Opioid Antagonism, Tolerance, and Naltrexone-Precipitated Withdrawal

“…Unlike methadone, however, buprenorphine is a relatively weak partial agonist and, under some conditions, the antagonist effects of buprenorphine predominate. For example, buprenorphine antagonizes [D-Ala2, NMe-Phe4,Gly-ol5]-enkephalin-stimulated [ 35 S]-GTP␥S binding in guinea pig caudate (Romero et al, 1999) and, in vivo, buprenorphine antagonizes the antinociceptive and ventilatory effects of morphine and other -opioid agonists (Walker et al, 1995;Liguori et al, 1996). Likewise, buprenorphine dose-dependently attenuates the physiological and subjective effects of hydromorphone in human studies (Bickel et al, 1988).…”