A novel finding of nalbuphine-6-glucuronide, an active opiate metabolite, possessing potent antinociceptive effects: Synthesis and biological evaluation

Nalbuphine-6-glucuronide is a potent analgesic with superior safety profiles by altering binding affinity and selectivity for mu-/kappa-opioid receptors

Although nalbuphine, a semi-synthetic analgesic compound, is less potent than morphine in terms of alleviating severe pain, our recent findings have revealed that nalbuphine-6-glucuronide (N6G), one of the glucuronide metabolites of nalbuphine, promotes a significantly more robust analgesic effect than its parent drug. Nevertheless, despite these promising observations, the precise mechanisms underlying the analgesic effects of nalbuphine glucuronides have yet to be determined. In this study, we aim to elucidate the mechanisms associated with the analgesic effects of nalbuphine glucuronides. Pharmacokinetic and pharmacodynamic studies were conducted to investigate the relationship between the central and peripheral compartments of nalbuphine and its derivatives. The analgesic responses of these compounds were evaluated based on multiple behavioral tests involving thermal and mechanical stimuli. Radioligand binding assays were also performed to determine the binding affinity and selectivity of these compounds for different opioid receptors. The results of these tests consistently confirmed that the heightened analgesic effects of N6G are mediated through its enhanced binding affinity for both mu- and kappa-opioid receptors, even comparable to those of morphine. Notably, N6G exhibited fewer side effects and did not induce sudden death, thereby highlighting its superior safety profile. Additionally, pharmacokinetic studies indicated that N6G could cross the blood-brain barrier when administered peripherally, offering pain relief. Overall, N6G provides great analgesic efficacy and enhanced safety. These findings highlight the potential value of nalbuphine glucuronides, particularly N6G, as promising candidates for the development of novel analgesic drugs.

A systematic review on the kappa opioid receptor and its ligands: New directions for the treatment of pain, anxiety, depression, and drug abuse

Kappa opioid receptor (KOR) is a member of the opioid receptor system, the G protein-coupled receptors that are expressed throughout the peripheral and central nervous systems and play crucial roles in the modulation of antinociception and a variety of behavioral states like anxiety, depression, and drug abuse. KOR agonists are known to produce potent analgesic effects and have been used clinically for the treatment of pain, while KOR antagonists have shown efficacy in the treatment of anxiety and depression. This review summarizes the history, design strategy, discovery, and development of KOR ligands. KOR agonists are classified as non-biased, G protein-biased, and β-arrestin recruitment-biased, according to their degrees of bias. The mechanisms and associated effects of the G protein signaling pathway and β-arrestin recruitment signaling pathway are also discussed. Meanwhile, KOR antagonists are classified as long-acting and short-acting, based on their half-lives. In addition, we have special sections for mixed KOR agonists and selective peripheral KOR agonists. The mechanisms of action and pharmacokinetic, pharmacodynamic, and behavioral studies for each of these categories are also discussed in this review.

Preemptive Nalbuphine Attenuates Remifentanil-Induced Postoperative Hyperalgesia After Laparoscopic Cholecystectomy: A Prospective Randomized Double-Blind Clinical Trial

Background

Remifentanil-induced hyperalgesia (RIH) is a paradoxical phenomenon that may increase sensitivity to painful stimuli. Nalbuphine, which is both a μ-receptor antagonist and κ-receptor agonist, may affect RIH. The aim of this study was to evaluate the effects of nalbuphine on RIH during laparoscopic cholecystectomy.

Methods

A total of 96 patients were divided into the following four groups: 0.4 μg/kg/min of remifentanil with 0.2 mg/kg of nalbuphine (HRNA), 0.4 μg/kg/min of remifentanil with saline (HRSA), 0.1 μg/kg/min of remifentanil with 0.2 mg/kg of nalbuphine (LRNA), and 0.1 μg/kg/min of remifentanil with saline (LRSA). The pain thresholds of postoperative mechanical hyperalgesia were measured with von Frey filaments. Pain intensity and analgesic consumption were recorded up to 48 h after surgery.

Results

Pain thresholds on the inner forearm decreased in the HRSA group compared with the HRNA (P = 0.0167), LRNA (P = 0.0027), and LRSA (P = 0.0318) groups at 24 h after surgery. Pain thresholds on the peri-incisional area decreased in the HRSA group compared with HRNA, LRNA, and LRSA (all P < 0.0001) groups at 24 h after surgery. Patients in the HRNA group showed lower numeric rating scale scores at 1 h (P = 0.0159), 3 h (P = 0.0118), 6 h (P = 0.0213), and 12 h (P = 0.0118) than those in the HRSA group. Postoperative requirement for sufentanil was greater in the HRSA group than the HRNA group during the first 3 h (P = 0.0321) and second 3 h (P = 0.0040). Postoperative sufentanil consumption was also greater in the LRSA group than in the LRNA group during the first 3 h (P = 0.0321) and second 3 h (P = 0.0416).

Conclusion

Preemptive nalbuphine can ameliorate postoperative hyperalgesia induced by high-dose remifentanil in patients undergoing laparoscopic cholecystectomy.