Effect of the Norepinephrine Transporter (NET) Inhibition on μ-Opioid Receptor (MOR)-Induced Anti-nociception in a Bone Cancer Pain Model

Multiple effectiveness aspects of tapentadol for moderate-severe cancer-pain treatment: an observational prospective study

Background

Previous studies have shown the efficacy of tapentadol (TP) for chronic cancer pain. We evaluated multiple effectiveness aspects of TP prolonged release on moderate–severe cancer-related pain, neuropathic pain (NeP), patient satisfaction, and quality of life.

Methods

An observational prospective study was conducted on 80 cancer patients. Opioid-naïve patients received a starting dose of prolonged-release TP 50 mg twice daily, and opioid-experienced patients were switched to TP, not to exceed 500 mg/day. Treatment response was evaluated at 3, 6, 30–40, and 60–70 days through response rate, numeric rating-scale scoring, survival analysis (time to event for response), pain-intensity difference, TP escalation-index percentage, and effects on NeP. The drug-sparing effect on concomitant therapies was evaluated.

Results

Seventy of 80 patients (88%) were responders to treatment (95% CI 78%–94%). Compared to T₀, pain-intensity reductions were statistically significant for all intervals (P<0.01), with better results at T₃/T₄. NeP was significantly reduced at T₄ (P<0.01). The probability of response was low at the initial stages and increased during the study. Pain-intensity differences decreased during the study, though without significance. Two patients (2.5%) left the study for TP-induced side effects. A significant improvement in quality of life was observed after 30–40 days (P<0.01). The majority of patients were “satisfied”, “very satisfied”, or “extremely satisfied” (T₃–T₄).

Conclusion

TP was effective in terms of drug-sparing effect, response rate, TP escalation-index percentage, and NeP management. By comparing data from the survival analysis with the response rate and time to response (numeric rating scale from T₀ to T₄), we found that although TP induced a quick response, a longer period of therapy and higher doses were needed to improve the positive result.

Activation of the P2X7 receptor in midbrain periaqueductal gray participates in the analgesic effect of tramadol in bone cancer pain rats

Background

Cancer pain is a well-known serious complication in metastatic or terminal cancer patients. Current pain management remains unsatisfactory. The activation of spinal and supraspinal P2X₇ receptors plays a crucial role in the induction and maintenance mechanisms of various kinds of acute or chronic pain. The midbrain periaqueductal gray is a vital supraspinal site of the endogenous descending pain-modulating system. Tramadol is a synthetic, centrally acting analgesic agent that exhibits considerable efficacy in clinically relieving pain. The purpose of this study was to determine whether the activation of P2X₇ receptor in the ventrolateral region of the periaqueductal gray (vlPAG) participates in the analgesic mechanisms of tramadol on bone cancer pain in rats. The bone cancer pain rat model was established by intratibial cell inoculation of SHZ-88 mammary gland carcinoma cells. The analgesic effects of different doses of tramadol (10, 20, and 40 mg/kg) were assessed by measuring the mechanical withdrawal threshold and thermal withdrawal latency values in rats by using an electronic von Frey anesthesiometer and radiant heat stimulation, respectively. Alterations in the number of P2X₇ receptor-positive cells and P2X₇ protein levels in vlPAG were separately detected by using immunohistochemistry and Western blot assay. The effect of intra-vlPAG injection of A-740003 (100 nmol), a selective competitive P2X₇ receptor antagonist, on the analgesic effect of tramadol was also observed.

Results

The expression of P2X₇ receptor in the vlPAG on bone cancer pain rats was mildly elevated, and the tramadol (10, 20, and 40 mg/kg) dose dependently relieved pain-related behaviors in bone cancer pain rats and further upregulated the expression of P2X₇ receptor in the vlPAG. The intra-vlPAG injection of A-740003 pretreatment partly but significantly antagonized the analgesic effect of tramadol on bone cancer pain rats.

Conclusions

The injection of tramadol can dose dependently elicit analgesic effect on bone cancer pain rats by promoting the expression of the P2X₇ receptor in vlPAG.

Assessment of the antinociceptive and ulcerogenic activity of the tapentadol-diclofenac combination in rodents

Preclinical Research & Development The objective of the present study was to evaluate the tapentadol-diclofenac combination in three dose-ratios in the mouse acetic acid-induced visceral pain and their ulcerogenic activity on the stomachal mucous. Dose-response curves were generated for tapentadol, diclofenac, and their combination in the acetic acid-induced writhing test in mice. Moreover, the stomachs of animals were surgically removal and gastrointestinal ulcerogenic action of the combination was assessed. The isobolographic analysis, interaction index, and ANOVA were used to analyze the data. The isobolographic analysis and interaction index showed a similar antinociceptive activity for the three combinations of the analgesic mixture. Moreover, tapentadol and the proportions 1:1 or 3:1 of the analgesic combination caused a mild gastrointestinal damage. These data indicate that the systemic co-administration of tapentadol and diclofenac produced a synergistic interaction in the acetic acid-induced visceral pain test with an acceptable gastric damage profile in mice.

The Antinociceptive Effect of a Tapentadol-Ketorolac Combination in a Mouse Model of Trigeminal Pain is Mediated by Opioid Receptors and ATP-Sensitive K+ Channels

Preclinical Research The aim of the present study was to evaluate the antinoceptive interaction between the opioid analgesic, tapentadol, and the NSAID, ketorolac, in the mouse orofacial formalin test. Tapentadol or ketorolac were administered ip 15 min before orofacial formalin injection. The effect of the individual drugs was used to calculate their ED₅₀ values and different proportions (tapentadol-ketorolac in 1:1, 3:1, and 1:3) were assayed in the orofacial test using isobolographic analysis and interaction index to evaluate the interaction between the drugs. The combination showed antinociceptive synergistic and additive effects in the first and second phase of the orofacial formalin test. Naloxone and glibenclamide were used to evaluate the possible mechanisms of action and both partially reversed the antinociception produced by the tapentadol-ketorolac combination. These data suggest that the mixture of tapentadol and ketorolac produces additive or synergistic interactions via opioid receptors and ATP-sensitive K⁺ channels in the orofacial formalin-induced nociception model in mice. Drug Dev Res 78 : 63-70, 2017. © 2016 Wiley Periodicals, Inc.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).