Genetic variability of pain perception and treatment—clinical pharmacological implications

MgO and ZnO nanoparticles anti-nociceptive effect modulated by glutamate level and NMDA receptor expression in the hippocampus of stressed and non-stressed rats

The anti-nociceptive mechanisms of MgO and ZnO nanoparticles have not been thoroughly investigated; in this study, we evaluated the effects of anti-nociceptive dose of MgO and ZnO NPs on glutamate level and NMDA receptor subunits expression (NR1, NR2 and NR2B) in the rat whole hippocampus with and without acute restraint stress. Adult rats were divided into control, MgO and ZnO NPs 5 mg/kg, the stress of 90 min alone and with MgO or ZnO NPs 5 mg/kg groups. All components injected intraperitoneally and the nociceptive response was measured with hot plate apparatus 90 min after injections or stress induction. Magnesium, zinc, glutamate levels and NMDA receptor subunits expression were measured in the animal hippocampus. MgO NPs, ZnO NPs and acute stress induced anti-nociceptive effect. MgO NPs observably decreased glutamate and increased magnesium levels and NR2B subunit expression. ZnO NPs decreased glutamate level. Stress elevated endogenous magnesium and zinc levels and also the NR2B expression, but did not change glutamate level. MgO and ZnO NPs in the presence of stress increased the glutamate level and ZnO NPs increased the zinc and the NR2A expression. Stress decreased endogenous magnesium in the hippocampus. MgO and ZnO NPs could affect pain perception by changing glutamate level in the whole hippocampus tissue, while ion level changes followed by injection could probably affect the gene expression in the presence and the absence of stress. It seems that stress indirectly could adverse nanoparticles effects on glutamate level and increase zinc ion releasing from ZnO NPs by activating the gene expression without affecting pain perception.

Simultaneous pain intensity rating and quantification of ischemia throughout exercise and recovery in proximal versus distal arterial claudication

Data on simultaneous hemodynamic changes and pain rating estimation in arterial claudication while walking are lacking. This study was conducted to determine if a difference in transcutaneous oxygen pressure (tc pO2) exists between proximal and distal localization at pain appearance (PAINapp), maximal pain (PAINmax) and pain relief (PAINrel) in proximal or distal claudication and if a relationship exists between tc pO2 changes and pain intensity. We analyzed the pain rating (Visual Analog Scale (VAS)) to lower limb ischemia, measured with the decrease from rest of oxygen pressure (DROP) tc pO2 index during constant-load treadmill tests in patients with calf ( n = 41) or buttock ( n = 19) claudication. Calves versus buttocks results were analyzed with ANOVA tests. The R2 correlation coefficient between individual VAS versus DROP was calculated. Ischemia intensity versus pain rating changes were correlated. Significant ischemia was required for pain appearance, but pain disappeared despite the persistence of ischemia. We observed no statistical difference for DROP at PAINapp, PAINmax or PAINrel between proximal or distal claudication. A significant correlation between pain rating versus DROP was found: from PAINapp to PAINmax, R2 = 0.750 (calves) and 0.829 (buttocks), and from PAINmax to PAINrel, R2 = 0.608 (calves) and 0.560 (buttocks); p<0.05. Pain appeared after a significant decrease of hemodynamic parameters but disappeared while parameters were not normalized. No difference in pain rating was found in proximal versus distal claudication.

Short Report: TRPV1-polymorphism 1911 A>G alters capsaicin-induced sensory changes in healthy subjects

Background

C-fibers express transient receptor potential (TRP) channels. These high-voltage gated channels function as integrators of different physical stresses (e.g. heat, protons, ATP). Additionally channel activation can be induced by capsaicin. Topically applied, capsaicin elicits burning pain, heat and mechanical hyperalgesia and serves as a human surrogate model for pain. It was suggested that the TRPV1-variant rs8065080 (1911A>G) plays a pivotal role in patients with neuropathic pain syndromes. We investigated the effect of this TRPV1-SNP on thermal sensitivity and superficial skin perfusion in 25 healthy subjects.

Methods and findings

Nine subjects being homozygous TRPV1 wild type (AA), 8 heterozygous (AG) and 8 homozygous variant (GG) carriers were selected out of a pool of genotyped healthy individuals. Under physiological conditions (no capsaicin application), there was no statistical significant difference in thermal thresholds or skin perfusion between carriers of different TRPV1 1199A>G genotypes. However, intra-individual calculations (Δ% pre vs. post capsaicin) revealed (1) less warm-detection in AA/AG (-82.1%) compared to GG (-13.1%) and (2) a gain of heat pain sensitivity in AA/AG (+22.2%) compared to GG carriers (+15.6%) after adjustment for perfusion measurements ((1)p = 0.009, (2)p = 0.021).

Conclusion

Presence of homozygous variant TRPV1 genotype (GG) demonstrated less capsaicin-induced warm hypoesthesia in warm-detection and less capsaicin-induced heat pain sensitivity suggesting an altered channel function. This demonstrates not only the functional influence of TRPV1 rs8065080 polymorphism itself; it further more underpins the relevance of genotyping-based approaches in both patients and surrogate models of neuropathic pain in healthy volunteers.

[Chronic pain care : Reality and entitlement]

From the point of view of healthcare policies, improvement in pain care has been required for years; however, there is a great discrepancy between the current need for pain care and the actual provision by healthcare services. This article seeks to demonstrate that while healthcare policies are one of the critical factors involved, a variety of conceptual, diagnostic and therapeutic causes should also be taken into account. Firstly, considering that pain care is primarily concerned with the suffering of pain by patients, the focus lies with their conscious experience in order to define the patients' understanding of pain. Additionally, in this article current biomedical and psychosocial comprehension concerning chronic pain will be illustrated and why it is necessary to broaden our horizons in order to do justice to patients with chronic pain.

Systematic review of enriched enrolment, randomised withdrawal trial designs in chronic pain: a new framework for design and reporting

Enriched enrolment, randomised withdrawal (EERW) pain trials select, before randomisation, patients who respond by demonstrating a predetermined degree of pain relief and acceptance of adverse events. There is uncertainty over the value of this design. We report a systematic review of EERW trials in chronic noncancer pain together with a critical appraisal of methods and potential biases in the methods used and recommendations for the design and reporting of future EERW trials. Electronic and other searches found 25 EERW trials published between 1995 and June 2014, involving 5669 patients in a randomised withdrawal phase comparing drug with placebo; 13 (median, 107 patients) had a randomised withdrawal phase of 6 weeks or less, and 12 (median, 334) lasted 12 to 26 weeks. Risks of bias included short duration, inadequate outcome definition, incomplete outcome data reporting, small size, and inadequate dose tapering on randomisation to placebo. Active treatment was usually better than placebo (22/25 trials). This review reduces the uncertainty around the value of EERW trials in pain. If properly designed, conducted, and reported, they are feasible and useful for making decisions about pain therapies. Shorter, small studies can be explanatory; longer, larger studies can inform practice. Current evidence is inadequate for valid comparisons in outcome between EERW and classical trials, although no gross differences were found. This systematic review provides a framework for assessing potential biases and the value of the EERW trials, and for the design of future studies by making recommendations for the conduct and reporting of EERW trials.

Lost but making progress--Where will new analgesic drugs come from?

There is a critical need for effective new pharmacotherapies for pain. The paucity of new drugs successfully reaching the clinic calls for a reassessment of current analgesic drug discovery approaches. Many points early in the discovery process present significant hurdles, making it critical to exploit advances in pain neurobiology to increase the probability of success. In this review, we highlight approaches that are being pursued vigorously by the pain community for drug discovery, including innovative preclinical pain models, insights from genetics, mechanistic phenotyping of pain patients, development of biomarkers, and emerging insights into chronic pain as a disorder of both the periphery and the brain. Collaborative efforts between pharmaceutical, academic, and public entities to advance research in these areas promise to de-risk potential targets, stimulate investment, and speed evaluation and development of better pain therapies.

Pharmacological treatment of pain: future trends and novel insights

The pharmacological treatment of chronic pain is generally hampered by a limited clinical outcome. Hence, there is a strong need for new therapeutic concepts considering the identification of novel targets and related drugs, but also optimization of established therapeutic regimes through individualization. In this issue, focused on "Pain," we discuss some of the recent new concepts in pain treatment, understanding of pain heterogeneity, and subsequent optimization of analgesic treatment, but also novel insights into interactions of nonopioids.

Exploratory study on association of single-nucleotide polymorphisms with hydromorphone analgesia in ED

OBJECTIVES

The objective of this study is to provide information on distribution of important single-nucleotide polymorphisms (SNPs) and evaluate their associations with clinical response to intravenous hydromorphone in emergency department.

METHODS

A prospective exploratory study was performed. A convenience sample of adult emergency department patients with acute pain deemed to require intravenous opioids received 1 mg of intravenous hydromorphone. Primary outcome was pain score (numeric rating scale, NRS) reduction between baseline and 30 minutes after medication administration. Secondary outcomes were pain relief, patient satisfaction with analgesia, desire for more analgesics, and side effects (nausea, vomiting, and pruritis). Single-nucleotide polymorphisms in OPRM1 gene (opioid receptor, A118G), ABCB1 gene (opioid transporter, C3435T), COMT gene (pain sensitivity, G1947A), and UGT2B7 gene (opioid metabolism, -G840A) were tested. We used Kruskal-Wallis test to compare the primary outcome and χ(2) test (or Fisher test) to compare the secondary outcomes among patients carrying different SNPs.

RESULTS

One thousand four hundred thirty-eight patients were screened, and 163 patients were enrolled in the study. The mean age was 39 years. Sixty-three percent were female, 58% were Hispanic, and 67% had pain located in abdomen. The median pain NRS reduction at 30 minutes was 5 (interquartile range, 3-8). There was no difference in pain NRS reduction among patients carrying different SNPs. Secondary outcome analysis revealed statistically significant associations between patient satisfaction with treatment and OPRM1 and between nausea and UGT2B7.

CONCLUSIONS

This exploratory study did not show a significant difference in pain NRS reduction among patients carrying different SNPs. Patient satisfaction with analgesia and nausea were statistically significantly associated with OPRM1 and UGT2B7, respectively.

The use of opioids for treatment of cancer pain

INTRODUCTION

Pain is commonly experienced by patients with cancer, particularly those with advanced disease. Alleviating pain is an important goal of cancer treatment. Opioids are the cornerstone of the analgesic treatment.

AREAS COVERED

Pharmacology, characteristics, and use of opioids in clinical practice are presented.

EXPERT OPINION

Although the use of opioids is largely accepted as a fundamental step for controlling cancer pain, existing data supporting this statement are poor. All opioids provide analgesia and are effective in controlling cancer pain. New drugs have been developed and experience is accumulating among clinicians. Despite these drugs having different pharmacokinetic and chemical properties, there is no proof that one opioid is better than another one. Thus, the optimum benefit depends on the experience of the users. Clinicians should weight evidence, clinical experience, patient preferences, and treatment costs when choosing the optimal treatment for an individual patient with cancer pain. New opioids with specific receptor activities are under investigation.

A review of the studies using buprenorphine in cats

Pain management is a crucial component of feline medicine and surgery. This review critically evaluates studies using buprenorphine in cats and highlights the clinical application of the opioid in this species. The pharmacokinetic-pharmacodynamic (PK-PD) modeling of IV buprenorphine has been best described by a combined effect compartmental/receptor association-dissociation model with negative hysteresis. Therefore, plasma concentrations of the drug are not correlated with analgesia, and clinicians should not expect to observe pain relief immediately after drug administration. In addition, a ceiling effect has not been demonstrated after administration of clinical doses of buprenorphine in cats; dosages of up to 0.04 mg/kg have been reported. The route of administration influences the onset, duration, and magnitude of antinociception and analgesia when using this drug in cats. At clinical dosages, the SC route of administration does not appear to provide adequate antinociception and analgesia whereas the buccal route has produced inconsistent results. Intravenous or IM administration at a dosage of 0.02-0.04 mg/kg is the preferred for treatment of pain in the acute setting. A literature search found 14 clinical trials evaluating buprenorphine sedation, analgesia, or both in cats. There were 22 original research studies reporting the antinociceptive effects of buprenorphine by means of thermal threshold, mechanical threshold, or both, minimal alveolar concentration, or PK-PD. Individual variability in response to buprenorphine administration has been reported, indicating that buprenorphine may not provide sufficient analgesia in some cats. Pain assessment is important when evaluating the efficacy of buprenorphine and determining whether additional analgesic treatment is needed.

The costs and consequences of adequately managed chronic non-cancer pain and chronic neuropathic pain

BACKGROUND

Chronic pain is distressing for patients and a burden on healthcare systems and society. Recent research demonstrates different aspects of the negative impact of chronic pain and the positive impact of successful treatment, making an overview of the costs and consequences of chronic pain appropriate.

OBJECTIVE

To examine recent literature on chronic noncancer and neuropathic pain prevalence, impact on quality and quantity of life, societal and healthcare costs, and impact of successful therapy.

METHODS

Systematic reviews (1999 to February 2012) following PRISMA guidelines were conducted to identify studies reporting appropriate outcomes.

RESULTS

Chronic pain has a weighted average prevalence in adults of 20%; 7% have neuropathic pain, and 7% have severe pain. Chronic pain impeded activities of daily living, work and work efficiency, and reduced quality and quantity of life. Effective pain therapy (pain intensity reduction of at least 50%) resulted in consistent improvements in fatigue, sleep, depression, quality of life, and work.

CONCLUSION

Strenuous efforts should be put into obtaining good levels of pain relief for people in chronic pain, including the opportunity for multiple drug switching, using reliable, validated, and relatively easily applied patient-centered outcomes. Detailed, thoughtful and informed decision analytic policy modeling would help understand the key elements in organizational change or service reengineering to plan the optimum pain management strategy to maximize pain relief and its stream of benefits against budgetary and other constraints. This paper contains the information on which such models can be based.