Antipruritic Effect of Nalbuphine, a Kappa Opioid Receptor Agonist, in Mice: A Pan Antipruritic

Abstract

Antipruritic effects of kappa opioid receptor (KOR) agonists have been shown in rodent models of acute and chronic scratching (itchlike behavior). Three KOR agonists, nalfurafine, difelikefalin, and nalbuphine, are in clinical studies for antipruritic effects in chronic itch of systemic and skin diseases. Nalfurafine (in Japan) and difelikefalin (in the USA) were approved to be used in the treatment of chronic itch in hemodialysis patients. The FDA-approved nalbuphine has been used in clinic for over 40 years, and it is the only narcotic agonist that is not scheduled. We aimed to study (a) antiscratch activity of nalbuphine against TAT-HIV-1 protein (controls HIV transcription)-, deoxycholic acid (DCA, bile acid)-, and chloroquine (CQ)-induced scratching in a mouse model of acute itch; and (b) whether the effect of nalbuphine is produced via KORs. First, dose-responses were developed for pruritogens. Mice were pretreated with nalbuphine (0.3-10 mg/kg) and then a submaximal dose of pruritogens were administered and the number of scratching bouts was counted. To study if the antiscratch effect of nalbuphine is produced via KOR, we used KOR knock out mice and pharmacologic inhibition of KORs using nor-binaltorphimine, a KOR antagonist. For this aim, we used CQ as a pruritogen. We found that: (a) TAT-HIV-1 protein elicits scratching in a dose-dependent manner; (b) nalbuphine inhibits scratching induced by TAT-HIV-1, DCA, and CQ dose-dependently; and (c) nalbuphine inhibits scratching induced by CQ through KORs. In conclusion, nalbuphine inhibits scratching elicited by multiple pruritogens.

Keywords: TAT-HIV; chloroquine; cholestasis; deoxycholic acid; kappa opioid receptor agonist; mice; nalbuphine; pruritis; scratching.

Figure 1

Chemical structures of nalfurafine, difelikefalin, and nalbuphine.

Figure 2

Subcutaneous behind the neck injection of TAT-HIV-1 induces scratching in a dose-dependent manner. (a) Mice were administered saline (s.c., flank area) and then 30 min later they were injected with either saline or TAT-HIV-1 (0.1–1 mg/kg, behind the neck). One min following injections, the number of scratching bouts was counted for 30 min. Both TAT-HIV-1 at 0.3 and 1 mg/kg elicited scratching significantly compared to saline (one-way ANOVA followed by Dunnett’s multiple comparison; *** p < 0.001, **** p < 0.0001; n = 6). Nalbuphine inhibits TAT-HIV-1-induced scratching in a dose-dependent manner; (b) Nalbuphine at 3 and 10 mg/kg doses inhibited scratching elicited by submaximal dose of TAT-HIV-1 (0.3 mg/kg) significantly compared to control (one-way ANOVA followed by Dunnett’s multiple comparison; * p < 0.05, ** p < 0.01; n = 6). Nalbuphine at 10 mg/kg also alleviated scratching induced by maximum dose of TAT-HIV-1 (1 mg/kg); (c) (unpaired Student’s t-test; **** p < 0.0001; n = 6). Swiss–Webster mice were used for these studies.

Figure 2

Subcutaneous behind the neck injection of TAT-HIV-1 induces scratching in a dose-dependent manner. (a) Mice were administered saline (s.c., flank area) and then 30 min later they were injected with either saline or TAT-HIV-1 (0.1–1 mg/kg, behind the neck). One min following injections, the number of scratching bouts was counted for 30 min. Both TAT-HIV-1 at 0.3 and 1 mg/kg elicited scratching significantly compared to saline (one-way ANOVA followed by Dunnett’s multiple comparison; *** p < 0.001, **** p < 0.0001; n = 6). Nalbuphine inhibits TAT-HIV-1-induced scratching in a dose-dependent manner; (b) Nalbuphine at 3 and 10 mg/kg doses inhibited scratching elicited by submaximal dose of TAT-HIV-1 (0.3 mg/kg) significantly compared to control (one-way ANOVA followed by Dunnett’s multiple comparison; * p < 0.05, ** p < 0.01; n = 6). Nalbuphine at 10 mg/kg also alleviated scratching induced by maximum dose of TAT-HIV-1 (1 mg/kg); (c) (unpaired Student’s t-test; **** p < 0.0001; n = 6). Swiss–Webster mice were used for these studies.

Figure 3

Nalbuphine inhibits DCA-induced scratching. DCA at 1, 3, and 10 mg/kg induces significant scratching compared to saline. (a) (one-way ANOVA followed by Dunnett’s multiple comparison; * p < 0.05, *** p < 0.001; n = 7–8). Pretreatment with nalbuphine 10 mg/kg significantly reduces the number of scratching bouts in 30 min; (b) (unpaired Student’s t-test; ** p < 0.01); n = 6). Swiss–Webster mice were used for these studies.

Figure 3

Nalbuphine inhibits DCA-induced scratching. DCA at 1, 3, and 10 mg/kg induces significant scratching compared to saline. (a) (one-way ANOVA followed by Dunnett’s multiple comparison; * p < 0.05, *** p < 0.001; n = 7–8). Pretreatment with nalbuphine 10 mg/kg significantly reduces the number of scratching bouts in 30 min; (b) (unpaired Student’s t-test; ** p < 0.01); n = 6). Swiss–Webster mice were used for these studies.

Figure 4

Nalbuphine significantly reduced CQ-induced scratching bouts in a dose-dependent manner. (a) Swiss–Webster mice were injected with either saline or nalbuphine (1, 3, or 10 mg/kg). Thirty min later, they were administered a submaximal dose (10 mg/kg, s.c., behind the neck) of CQ. Then, the number of scratching bouts was counted for 30 min. Nalbuphine did not decrease scratching in KOR KO mice; (b) Nalbuphine at 10 mg/kg did not have significant effect in C57BL/6J WT mice as in Swiss–Webster. Nalbuphine at 20 mg/kg significantly reduced scratching induced by CQ in WT mice, but not in KOR KO mice. Nalbuphine had no antiscratch effect in Swiss–Webster mice pretreated with nor-BNI; (c) Mice were administered with nor-BNI or saline 20 h before the nalbuphine injection. Then, mice received either saline or nalbuphine. Thirty min later, they were injected with CQ. Nalbuphine significantly reduced scratching in mice pretreated with saline the day before; however, no significant effect was observed in mice pretreated with nor-BNI. (one-way ANOVA followed by Dunnett’s multiple comparison; * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001; n = 7–8).

Figure 4

Nalbuphine significantly reduced CQ-induced scratching bouts in a dose-dependent manner. (a) Swiss–Webster mice were injected with either saline or nalbuphine (1, 3, or 10 mg/kg). Thirty min later, they were administered a submaximal dose (10 mg/kg, s.c., behind the neck) of CQ. Then, the number of scratching bouts was counted for 30 min. Nalbuphine did not decrease scratching in KOR KO mice; (b) Nalbuphine at 10 mg/kg did not have significant effect in C57BL/6J WT mice as in Swiss–Webster. Nalbuphine at 20 mg/kg significantly reduced scratching induced by CQ in WT mice, but not in KOR KO mice. Nalbuphine had no antiscratch effect in Swiss–Webster mice pretreated with nor-BNI; (c) Mice were administered with nor-BNI or saline 20 h before the nalbuphine injection. Then, mice received either saline or nalbuphine. Thirty min later, they were injected with CQ. Nalbuphine significantly reduced scratching in mice pretreated with saline the day before; however, no significant effect was observed in mice pretreated with nor-BNI. (one-way ANOVA followed by Dunnett’s multiple comparison; * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001; n = 7–8).