Topical κ-opioid receptor agonist asimadoline improves dermatitis in a canine model of atopic dermatitis

This prospective, 4-week, placebo-controlled, cross-over study aimed to investigate the efficacy of 1% topical κ-opioid agonist, asimadoline, in a model of canine atopic dermatitis (AD). Fourteen beagles were challenged with house dust mites every 3-4 days for a total of 9 challenges. Severity of dermatitis was assessed, and pruritus was monitored using GoPro HERO cameras. Pruritus scoring was evaluated at 10 time periods; baseline, 4 h post allergen challenge and the last day of the study on Day 28. Scoring was done blindly by personnel using BORIS software. A global subjective score was also given using a visual analogue scale (VAS). A 4-week washout period occurred and dogs were crossed-over, the study was repeated, and the results were analysed using combined data. Gel was applied once daily on inguinal area (0.6 ml/dog). ANOVA showed significant effect of time (p < 0.0001) and group (p = 0.0001) on dermatitis scores. Overall, no statistically significant effect on pruritus was found due to a crossing of scores on Day 17. Overtime the placebo scores increased while the active ingredient showed decrease after first 3 weeks. It is concluded that this approach is promising in dogs with AD and longer studies with more frequent application may be beneficial.

Remifentanil functions in the adaptive protection of cardiac function following ischemia

The present study aimed to investigate the effects of remifentanil during adaptation followinsg myocardial ischemia, and its possible clinical applications. Remifentanil was used during the simulation of adaptation following ischemia, which was performed using a Langendorff heart perfusion system. A total of 75 rats were divided into five groups, and the coronary flow, cardiac output and the cardiac enzyme content in coronary effluent prior to ischemia and post-reperfusion were recorded. Electron microscopy was used to observe myocardial ultrastructure, and the volume of aortic and coronary effluent was also measured. The recovery of cardiac output upon reperfusion was significantly higher following remifentanil treatment (91%), as compared with the ischemic control group (78%; P<0.05). The coronary flow of the experimental group following reperfusion decreased by 4 ml/min compared with the control group not exposed to ischemia, whilst the coronary flow of the ischemic control group was reduced by 20-24 ml/min. Flameng scoring of the mitochondria demonstrated improved mitochondrial ultrastructure following remifentanil treatment (score, 1.25±0.31), as compared the ischemic control group (score, 3.14±0.17). Lactate dehydrogenase (LDH) levels in the remifentanil-treated group were significantly lower at 10 and 30 min post-reperfusion (15.3±7.1 and 10.2±6.8 U/l, respectively), as compared with the control group (29.7±8.3 and 20.6±6.8 U/l, respectively; P<0.05). The results of the present study suggested that the application of remifentanil following ischemia protected heart function via the opioid receptors by reducing myocardial enzyme release, and attenuating ischemia-induced changes to the myocardial cell and mitochondrial structure.

μ-Opioid receptor activation and noradrenaline transport inhibition by tapentadol in rat single locus coeruleus neurons

BACKGROUND AND PURPOSE

Tapentadol is a novel analgesic that combines moderate μ-opioid receptor agonism and noradrenaline reuptake inhibition in a single molecule. Both mechanisms of action are involved in producing analgesia; however, the potency and efficacy of tapentadol in individual neurons has not been characterized.

EXPERIMENTAL APPROACH

Whole-cell patch-clamp recordings of G-protein-coupled inwardly rectifying K(+) (KIR 3.x) currents were made from rat locus coeruleus neurons in brain slices to investigate the potency and relative efficacy of tapentadol and compare its intrinsic activity with other clinically used opioids.

KEY RESULTS

Tapentadol showed agonist activity at μ receptors and was approximately six times less potent than morphine with respect to KIR 3.x current modulation. The intrinsic activity of tapentadol was lower than [Met]enkephalin, morphine and oxycodone, but higher than buprenorphine and pentazocine. Tapentadol inhibited the noradrenaline transporter (NAT) with potency similar to that at μ receptors. The interaction between these two mechanisms of action was additive in individual LC neurons.

CONCLUSIONS AND IMPLICATIONS

Tapentadol displays similar potency for both µ receptor activation and NAT inhibition in functioning neurons. The intrinsic activity of tapentadol at the μ receptor lies between that of buprenorphine and oxycodone, potentially explaining the favourable profile of side effects, related to μ receptors.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.