Intraarticular Morphine Analgesia in Chronic Pain Patients with Osteoarthritis

Optimization and analytical behavior of a morphine electrochemical sensor in environmental and biological samples based on graphite rod electrode using graphene/Co3O4 nanocomposite

In this research, a new sensor based on graphene/Co₃O₄ (Gr/Co₃O₄) nanocomposite was employed for electrochemically determination of morphine (MOR). The modifier was synthesized with a simple hydrothermal technique and well characterized using X-ray difraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) tools. The modified graphite rod electrode (GRE) was revealed a high electrochemical catalytic activity for the MOR oxidation and employed for the electroanalysis of trace MOR concentration by means of differential pulse voltammetry (DPV) technique. At the optimum experimental factors, the resulting sensor offered a good response for MOR in the concentration range of 0.5-100.0 μM with a detection limit of 80 nM. In addition, the modified electrode demonstrated an acceptable selectivity, stability and reproducibility. This assay was also provided a valid platform for the detection of MOR in environmental and biological samples with acceptable recoveries and RSD in the range of 97.2-102.8% and 1.7-3.4%, respectively. Taking to the simplicity, low cost and short analysis time, this approach is suggested for clinical, environmental and forensic testing of MOR.

Exercise reverses pain-related weight asymmetry and differentially modulates trabecular bone microarchitecture in a rat model of osteoarthritis

There is great interest in developing and utilizing non-pharmacological/non-invasive forms of therapy for osteoarthritis (OA) pain including exercise and other physical fitness regimens.

AIMS

The present experiments determined the effects of prior wheel running on OA-induced weight asymmetry and trabecular bone microarchitecture.

MAIN METHODS

Wheel running included 7 or 21days of prior voluntary access to wheels followed by OA induction, followed by 21days post-OA access to wheels. OA was induced with monosodium iodoacetate (MIA), and weight asymmetry was measured using a hind limb weight bearing apparatus. Bone microarchitecture was characterized using ex vivo μCT.

KEY FINDINGS

Relative to saline controls, MIA (3.2mg/25μl) produced significant weight asymmetry measured on post-days (PDs) 3, 7, 14, 21 in sedentary rats. Seven days of prior running failed to alter MIA-induced weight asymmetry. In contrast, 21days of prior running resulted in complete reversal of MIA-induced weight asymmetry on all days tested. As a comparator, the opioid agonist morphine (3.2-10mg/kg) dose-dependently reversed weight asymmetry on PDs 3, 7, 14, but was ineffective in later-stage (PD 21) OA. In runners, Cohen's d (effect sizes) for OA vs. controls indicated large increases in bone volume fraction, trabecular number, trabecular thickness, and connective density in lateral compartment, and large decreases in the same parameters in medial compartment. In contrast, effect sizes were small to moderate for sedentary OA vs.

CONTROLS

SIGNIFICANCE

Results indicate that voluntary exercise may protect against OA pain, the effect varies as a function of prior exercise duration, and is associated with distinct trabecular bone modifications.

Scientific Evaluation of Pharmacological Treatment of Osteoarthritis in the Canon of Medicine

Osteoarthritis is the most common articular disease worldwide. Nonetheless, common osteoarthritis treatments are either not effective or associated with side effects. Now the materials derived from plants have found a relevant place in drug discovery. Until the mid-18th century, osteoarthritis in all medical schools worldwide had been managed as general arthritis. Avicenna, the famous scholar of Iranian traditional medicine has provided a long list of herbs that have been used traditionally to treat arthritis. To gain this worthy list, we searched his most famous medical masterpiece: Canon of Medicine. Some of these materials are investigated and employed by modern medicine. However, it is difficult to ignore that still more of these naturally occurring materials could be of use in modern medicine not only to prevent osteoarthritis progression but also osteoarthritis management as natural anti-inflammatory drugs.

Peripherally applied opioids for postoperative pain: evidence of an analgesic effect? A systematic review and meta-analysis

BACKGROUND

Opioids applied peripherally at the site of surgery may produce postoperative analgesia with few side effects. We performed this systematic review to evaluate the analgesic effect of peripherally applied opioids for acute postoperative pain.

METHODS

We searched PubMed (1966 to June 2013), Embase (1980 to June 2013), and the Cochrane Central Register of Controlled Trials (The Cochrane Library 2013, Issue 6). Randomized controlled trials investigating the postoperative analgesic effect of peripherally applied opioids vs. systemic opioids or placebo, measured by pain intensity scores, consumption of supplemental analgesics and time to first analgesic were included. Trials with sample sizes of fewer than 10 patients per treatment group or trials with opioids administered intra-articularly or as peripheral nerve blocks were excluded.

RESULTS

Data from 26 studies, including 1531 patients and 13 different surgical interventions were included. Clinical heterogeneity of the studies was substantial. Meta-analysis indicated statistically significant, but not clinically relevant, reductions in VAS score at 6-8 h (mean difference -4 mm, 95% CI: -6 to -2) and 12 h postoperatively (mean difference -5 mm, 95% CI: -7 to -3) for peripherally applied opioids vs. placebo and statistically significant increased time to first analgesic (mean difference 153 min, 95% CI: 41-265). When preoperative inflammation was reported (five studies), peripherally applied opioids significantly improved postoperative analgesia.

CONCLUSION

Evidence of a clinically relevant analgesic effect of peripherally applied opioids for acute postoperative pain is lacking. The analgesic effect of peripherally applied opioids may depend on the presence of preoperative inflammation.

Local analgesic effect of tramadol is not mediated by opioid receptors in early postoperative pain in rats

BACKGROUND AND OBJECTIVES

Tramadol is known as a central acting analgesic drug, used for the treatment of moderate to severe pain. Local analgesic effect has been demonstrated, in part due to local anesthetic-like effect, but other mechanisms remain unclear. The role of peripheral opioid receptors in the local analgesic effect is not known. In this study, we examined role of peripheral opioid receptors in the local analgesic effect of tramadol in the plantar incision model.

METHODS

Young male Wistar rats were divided into seven groups: control, intraplantar tramadol, intravenous tramadol, intravenous naloxone-intraplantar tramadol, intraplantar naloxone-intraplantar tramadol, intravenous naloxone-intravenous tramadol, and intravenous naloxone. After receiving the assigned drugs (tramadol 5mg, naloxone 200 μg or 0.9% NaCl), rats were submitted to plantar incision, and withdrawal thresholds after mechanical stimuli with von Frey filaments were assessed at baseline, 10, 15, 30, 45 and 60 min after incision.

RESULTS

Plantar incision led to marked mechanical hyperalgesia during the whole period of observation in the control group, no mechanical hyperalgesia were observed in intraplantar tramadol group, intraplantar naloxone-intraplantar tramadol group and intravenous naloxone-intraplantar tramadol. In the intravenous tramadol group a late increase in withdrawal thresholds (after 45 min) was observed, the intravenous naloxone-intravenous tramadol group and intravenous naloxone remained hyperalgesic during the whole period.

CONCLUSIONS

Tramadol presented an early local analgesic effect decreasing mechanical hyperalgesia induced by plantar incision. This analgesic effect was not mediated by peripheral opioid receptors.

The effects of morphine and methylnaltrexone on gastrointestinal pain in healthy male participants

BACKGROUND

Opioid antagonists are increasingly used to abolish the gastrointestinal side effects of opioids. However, they can potentially interfere with local analgesia exerted via opioid receptors in the gut. Thus, in the current study we aimed to explore the effect of rectal morphine before and after blocking opioid receptors outside the central nervous system with methylnaltrexone (MNTX).

METHODS

In this randomized, placebo controlled, cross-over study 15 healthy male participants received the following drugs at three separate sessions: (i) placebo, (ii) 30 mg morphine administered per rectum, or (iii) 12 mg MNTX given subcutaneously before 30 mg rectal morphine. At baseline and after drug administration peripheral and central effects of the drugs were assessed by experimental pain to the skin, muscle, rectum and pupillometry.

KEY RESULTS

Compared to placebo there was no local effect of morphine on mechanical rectal distension. In contrast, an increase in tolerated volume was seen following MNTX/morphine administration (p < 0.001), starting 7 min after dosing. Both morphine and MNTX/morphine had a central effect manifested as an increase in mechanical muscle pressure thresholds (both p < 0.001) and a decrease in pupil diameter (both p < 0.001). These effects occurred 30 min after dosing.

CONCLUSIONS & INFERENCES

No peripheral analgesic effect of morphine was found. Methodological shortcomings may have contributed to the lack of peripheral analgesia and thus, a peripheral morphine effect on rectal pain cannot be excluded. On the other hand, the combination of MNTX and morphine exerted a local effect on rectal distensions and seems to improve analgesia.

[Local analgesic effect of tramadol is not mediated by opioid receptors in early postoperative pain in rats]

BACKGROUND AND OBJECTIVES

Tramadol is known as a central acting analgesic drug, used for the treatment of moderate to severe pain. Local analgesic effect has been demonstrated, in part due to local anesthetic-like effect, but other mechanisms remain unclear. The role of peripheral opioid receptors in the local analgesic effect is not known. In this study, we examined role of peripheral opioid receptors in the local analgesic effect of tramadol in the plantar incision model.

METHODS

Young male Wistar rats were divided into seven groups: control, intraplantar tramadol, intravenous tramadol, intravenous naloxone-intraplantar tramadol, intraplantar naloxone-intraplantar tramadol, intravenous naloxone-intravenous tramadol, and intravenous naloxone. After receiving the assigned drugs (tramadol 5mg, naloxone 200μg or 0.9% NaCl), rats were submitted to plantar incision, and withdrawal thresholds after mechanical stimuli with von Frey filaments were assessed at baseline, 10, 15, 30, 45 and 60min after incision.

RESULTS

Plantar incision led to marked mechanical hyperalgesia during the whole period of observation in the control group, no mechanical hyperalgesia were observed in intraplantar tramadol group, intraplantar naloxone-intraplantar tramadol group and intravenous naloxone-intraplantar tramadol. In the intravenous tramadol group a late increase in withdrawal thresholds (after 45min) was observed, the intravenous naloxone-intravenous tramadol group and intravenous naloxone remained hyperalgesic during the whole period.

CONCLUSIONS

Tramadol presented an early local analgesic effect decreasing mechanical hyperalgesia induced by plantar incision. This analgesic effect was not mediated by peripheral opioid receptors.

Ultrasonographic evaluation in symptomatic knee osteoarthritis: clinical and radiological correlation

AIM

To explore the relationship among clinical, radiological and ultrasonographical findings in knee osteoarthritis (OA).

METHOD

Sixty-one patients (122 knees) with knee OA were enrolled. Patients' knees were classified into two groups according to symptom severity. Group I consisted of 61 more symptomatic knees and Group II comprised 61 less symptomatic knees. Subjects were clinically assessed for pain and functional status by using a visual analog scale and the Western Ontario and McMaster Universities Arthritis Index (WOMAC), respectively. Knee radiographs were evaluated by using the Kellgren-Lawrence (K-L) grading system. All knees were also evaluated ultrasonographically for meniscal bulging, distal femoral cartilage thickness, cartilage grading and also for the presence of effusion, Baker's cyst and so on.

RESULTS

Baker's cyst and joint effusion were observed more in Group I when compared with Group II. Positive correlations were found between meniscal bulging and all WOMAC scores (all P < 0.05). K-L grades of the patients were also positively correlated with WOMAC scores (all P < 0.05). Meniscal bulging measurements and K-L grades were positively correlated (P < 0.001). There was a negative correlation between cartilage grades and cartilage thickness measurements (all P < 0.001).

CONCLUSIONS

We found that joint space narrowing seemed to be associated with meniscal bulging. Moreover, increased meniscal bulging and presence of Baker's cyst/joint effusion were associated with worse pain or poorer function.

Nebulized lidocaine alone or combined with fentanyl as a premedication to general anesthesia in spontaneously breathing pediatric patients undergoing rigid bronchoscopy

INTRODUCTION

Pediatric bronchoscopy is an intensely stimulating procedure that requires a deep level of anesthesia to prevent hemodynamic overstimulation and straining. Topical anesthesia of the airway may be a beneficial component of the anesthetic technique to achieve adequate depth without residual sedation. Experimental evidence suggests that in addition to its central effects, locally applied opioids elicit potent analgesic effects.

METHODS

Forty-five patients aged 1-6 years scheduled for rigid bronchoscopy for foreign body removal were selected and subjected preoperatively to a nebulizer setting according to its components patients were divided into three groups. Group A: Nebulized solution contains 4 mg·kg(-1) lidocaine 1%. Group B: Nebulized solution contains 4 mg·kg(-1) lidocaine 1% plus 2 μg·kg(-1) fentanyl. Group C: Nebulized solution contains 0.9% normal saline. Anesthesia was induced with 8% sevoflurane in 100% oxygen and maintained with continuous infusion of propofol 200 μg·kg(-1). Increments of 500 μg·kg(-1) propofol were given to the patient in case of straining or coughing. Patients were followed for the hemodynamics, the intraoperative difficulties, postoperative sedation score, time to full wakefulness and the postoperative complications.

RESULTS

The hemodynamic parameters were much more stable in the fentanyl group relative to the other two groups. Also, the incidence of intraoperative difficulties was less significantly evident among patients in the fentanyl group (As regards cough P(1) = 0.003, P(2) = 0.0001, As regards the need to manual ventilation P(1) = 0.037, P(2) = 0.001, As regards Propofol increments P(1) = 0.001, P(2) = 0.001 where P(1) refers to the fentanyl group relative to the lidocaine group, and P(2) refers to fentanyl group relative to the placebo group). The postoperative sedation score was significantly higher, and the time to full wakefulness was significantly prolonged among patients in the fentanyl group relative to the other groups (P = 0.0001).

CONCLUSION

It is concluded that preoperative nebulized fentanyl reduces the hemodynamic response to bronchoscopy and decreases the intraoperative coughing in response to surgical manipulation without significant side effects except prolonged time to full wakefulness of patients.

Targeting inflammation and wound healing by opioids

Opioid receptors are expressed on peripheral sensory nerve endings, cutaneous cells, and immune cells; and local application of opioids is used for the treatment of inflammatory pain in arthritis, burns, skin grafts, and chronic wounds. However, peripherally active opioids can also directly modulate the inflammatory process and wound healing. Here, we discuss the underlying mechanisms of opioid action and the conceivable therapeutic approaches for opioid treatment, as investigated in experimental and clinical studies. A large number of in vitro experiments and animal model investigations have produced evidence that peripherally active opioids can reduce plasma extravasation, vasodilation, proinflammatory neuropeptides, immune mediators, and tissue destruction. In contrast to currently available anti-inflammatory agents, opioids have not demonstrated organ toxicity, thus making them interesting candidates for drug development. Few clinical studies have tapped into this potential to date.

Heterogeneity of chronic pain

Chronic pain is a widespread public health issue that has many effects on physical, emotional and cognitive functions. An estimated 10-55% of all adults are thought to have chronic pain. Chronic pain is a multifactorial condition, caused by the complex interplay of nociceptive, neuropathic or mixed pathogenic mechanisms. Chronic pain is associated with specific and non-specific medical conditions such as cancer, HIV/AIDS, rheumatoid arthritis, fibromyalgia, osteoarthritis, low back pain or spinal stenosis and is broadly categorized as cancer pain and non-cancer pain. Evaluation of chronic pain requires a clear understanding of the nature of the pain and its underlying pathophysiology. Adequate assessment of pain, using validated tools, is an essential prerequisite of successful pain management. Unidimensional scales are useful for the measurement of pain intensity, while multidimensional scales measure both pain intensity and the extent to which pain interferes with life activity and emotional functioning. Patients should be reassessed and followed up in order to monitor progress and measure improvements in pain.

Topical morphine gel in the treatment of painful leg ulcers, a double-blind, placebo-controlled clinical trial: a pilot study

Chronic painful wounds, a major health problem, have a detrimental impact on the quality of life due to associated pain. Some clinical reports have suggested that local administration of morphine could be beneficial. The aim of this study was to evaluate the analgesic effect of topically applied morphine on chronic painful leg ulcers. Twenty-one patients were randomly assigned to receive either morphine or placebo in a randomised, placebo-controlled, crossover pilot study. Each patient was treated four times in total. Pain was measured by the visual analogue score (VAS) before application of gel, directly after and after 2, 6, 12 and 24 hours. Although an overall, clinically relevant, reduction of pain was observed upon treatment with morphine, the difference was not statistically significant. Morphine reduced pain scores more than placebo on treatment occasions 1 and 2. The difference was statistically significant only 2 hours after dressing on the first treatment occasion. Thus, our study did not demonstrate a consistent and globally significant difference in nociception in patients treated with morphine. However, the relatively small number of patients included in our study and other methodological limitations makes it difficult for us to draw general conclusions regarding efficacy of topically applied morphine as an effective treatment for some painful ulcers. Further studies are warranted to evaluate the value of topically applied morphine in the treatment of patients with chronic painful leg ulcers.

Intra-articular opioid analgesia is effective in reducing pain and inflammation in an equine LPS induced synovitis model

REASONS FOR PERFORMING STUDY

Intra-articular administration of morphine as a local analgesic and anti-inflammatory drug is widely used in human medicine. In equids, little is known about its clinical analgesic and anti-inflammatory efficacy.

OBJECTIVES

To use an inflammatory orthopaedic pain model to investigate the analgesic and anti-inflammatory effects of intra-articularly administered morphine as a new treatment modality in horses with acute arthritis.

METHODS

In a crossover study design, synovitis was induced in the left or right talocrural joint by means of intra-articular injection of 0.5 ng lipopolyssacharide (LPS). The effect of 120 mg morphine, intra-articularly administered at 1 h after induction of synovitis, was evaluated using both physiological and behavioural pain variables. Synovial fluid was sampled at 0, 4, 8, 28 and 52 h after induction of synovitis and analysed for total protein concentration, leucocyte count and for prostaglandin E(2), bradykinin and substance P concentrations by ELISA. Ranges of motion of metatarsophalangeal and talocrural joints were measured as kinematic variables with the horses walking and trotting on a treadmill under sound and lame conditions. Clinical lameness scores and several behavioural variables related to the perception of pain were obtained.

RESULTS

LPS injection caused marked transient synovitis, resulting in increased concentrations of inflammatory synovial fluid markers, clinical lameness, joint effusion and several behavioural changes, such as increased time spent recumbent, decreased limb loading at rest and decreased time spent eating silage. Intra-articular morphine resulted in a significant decrease in synovial white blood cell count, prostaglandin E(2) and bradykinin levels and improvement in clinical lameness, kinematic and behavioural parameters, compared to placebo treatment.

CONCLUSIONS

Intra-articular morphine offers potent analgesic and anti-inflammatory effects in horses suffering from acute synovitis.

POTENTIAL RELEVANCE

Local administration of opioids may be useful for horses with acute inflammatory joint pain and offers possibilities for multimodal analgesic therapies without opioid-related systemic side effects.

Opioid receptors and opioid peptide-producing leukocytes in inflammatory pain--basic and therapeutic aspects

This review summarizes recent findings on neuro-immune mechanisms underlying opioid-mediated inhibition of pain. The focus is on events occurring in peripheral injured tissues that lead to the sensitization and excitation of primary afferent neurons, and on the modulation of such mechanisms by immune cell-derived opioid peptides. Primary afferent neurons are of particular interest from a therapeutic perspective because they are the initial generators of impulses relaying nociceptive information towards the spinal cord and the brain. Thus, if one finds ways to inhibit the sensitization and/or excitation of peripheral sensory neurons, subsequent central events such as wind-up, sensitization and plasticity may be prevented. This is in part achieved by endogenously released immune cell-derived opioid peptides within inflamed tissue. In addition, exogenous opioid receptor ligands that selectively modulate primary afferent function and do not cross the blood-brain barrier, avoid centrally mediated untoward side effects of conventional analgesics (e.g., opioids, anticonvulsants). This article discusses peripheral opioid receptors and their signaling pathways, opioid peptide-producing/secreting inflammatory cells and arising therapeutic perspectives.

Blockade of intra-articular adrenergic receptors increases analgesic demands for pain relief after knee surgery

Activation of opioid receptors on peripheral sensory nerve terminals by opioid peptides that are produced and released from immune cells can result in inhibition of inflammatory pain. This study tests the hypothesis that postoperative pain is attenuated endogenously through a local sympathetic neurotransmitter-activated release of opioids in patients undergoing knee surgery. We examined the expression of opioid peptides and adrenergic receptors in cells infiltrating inflamed synovial tissue and we hypothesized that intra-articular (i.a.) administration of the adrenergic receptor antagonist labetalol will increase postoperative analgesic consumption and/or pain intensity in these patients. In a double-blind, randomized manner, 75 patients undergoing therapeutic knee arthroscopy received i.a. placebo (20 ml saline) or labetalol (2.5 or 5 mg in 20 ml saline) at the end of surgery. Postoperative pain intensity was assessed by visual analog and verbal rating scales at rest and on exertion, and by the consumption of morphine via patient-controlled analgesia. Synovial biopsies were taken during the operation for double-immunofluorescence confocal microscopy studies. Alpha(1)- and beta(2)-adrenergic receptors were co-expressed in opioid peptide-containing cells. No significant difference was seen in pain scores, but patients receiving 2.5 mg labetalol requested significantly higher amounts of morphine. These findings are consistent with the notion that surgical stress induces sympathetically activated release of endogenous opioids from inflammatory cells and subsequent analgesia via activation of peripheral opioid receptors.

Morphine-induced early delays in wound closure: involvement of sensory neuropeptides and modification of neurokinin receptor expression

Dose-limiting side effects of centrally acting opioid drugs have led to the use of topical opioids to reduce the pain associated with chronic cutaneous wounds. However, previous studies indicate that topical morphine application impairs wound healing. This study was designed to elucidate the mechanisms by which morphine delays wound closure. Rats were depleted of sensory neuropeptides by treatment with capsaicin, and full-thickness 4-mm diameter wounds were excised from the intrascapular region. Wounds were treated topically twice daily with 5mM morphine sulfate, 1mM substance P, 1mM neurokinin A, or 5mM morphine combined with 1mM substance P or neurokinin A and wound areas assessed. During closure, wound tissue was taken 1, 3, 5, and 8 days post-wounding from control and morphine-treated rats and immunostained for neurokinin receptors and markers for macrophages, myofibroblasts, and vasculature. Results obtained from capsaicin-treated animals demonstrated a significant delay in the early stages of wound contraction that was reversed by neuropeptide application. Treatment of capsaicin-treated rats with topical morphine did not further delay wound closure, suggesting that topical opioids impair wound closure via the inhibition of peripheral neuropeptide release into the healing wound. Morphine application altered neurokinin-1 and neurokinin-2 receptor expression in inflammatory and parenchymal cells essential for wound healing in a cell-specific manner, demonstrating a direct effect of morphine on neurokinin receptor regulation within an array of cells involved in wound healing. These data provide evidence indicating a potentially detrimental effect of topical morphine application on the dynamic wound healing process.

Topical fentanyl in a randomized, double-blind study in patients with corneal damage

OBJECTIVES

Corneal damage causes severe pain. This study investigated whether peripheral opioid receptors are present in the human cornea and assessed the efficacy of topical fentanyl in patients with corneal erosion.

METHODS

Immunohistochemical staining experiments were performed to examine the presence of both mu and delta-receptors on peripheral nerve fibers within human corneal tissue. In a randomized, double-blind clinical trial dexpanthenol (n=20) or dexpanthenol plus 10 microg fentanyl (n=20) were topically applied every 4 hours to the eye of patients with a surgical intervention of corneal damage and subjective pain intensity was determined by a numerical rating scale.

RESULTS

Immunohistochemical staining identified peripheral nerve fibers in human cornea expressing both mu and delta-opioid receptors. In patients with corneal damage the ophthalmic intervention in local anesthesia decreased the subjective pain intensity significantly. At 4-hour intervals after the ophthalmic intervention, moderate pain intensity levels were not altered by the application of dexpanthenol with or without fentanyl. At 24 hours pain intensity dropped significantly, most likely owing to a natural decrease in pain, because the erosion was almost healed.

DISCUSSION

Both mu and delta-receptors are localized on nerve fibers within the cornea, which are accessible for topical opioid treatment. However, our formulation and dose of topical fentanyl in combination with dexpanthenol did not show any benefit in relieving pain from corneal erosion. Future studies are planned to determine the optimal protocol and dose of topical opioid treatment.

Opioids and sensory nerves

This chapter reviews the expression and regulation of opioid receptors in sensory neurons and the interactions of these receptors with endogenous and exogenous opioid ligands. Inflammation of peripheral tissues leads to increased synthesis and axonal transport of opioid receptors in dorsal root ganglion neurons. This results in opioid receptor upregulation and enhanced G protein coupling at peripheral sensory nerve terminals. These events are dependent on neuronal electrical activity, and on production of proinflammatory cytokines and nerve growth factor within the inflamed tissue. Together with the disruption of the perineurial barrier, these factors lead to an enhanced analgesic efficacy of peripherally active opioids. The major local source of endogenous opioid ligands (e.g. beta-endorphin) is leukocytes. These cells contain and upregulate signal-sequence-encoding messenger RNA of the beta-endorphin precursor proopiomelanocortin and the entire enzymatic machinery necessary for its processing into the functionally active peptide. Opioid-containing immune cells extravasate using adhesion molecules and chemokines to accumulate in inflamed tissues. Upon stressful stimuli or in response to releasing agents such as corticotropin-releasing factor, cytokines, chemokines, and catecholamines, leukocytes secrete opioids. Depending on the cell type, this release is contingent on extracellular Ca(2+) or on inositol triphosphate receptor triggered release of Ca(2+) from endoplasmic reticulum. Once secreted, opioid peptides activate peripheral opioid receptors and produce analgesia by inhibiting the excitability of sensory nerves and/or the release of proinflammatory neuropeptides. These effects occur without central untoward side effects such as depression of breathing, clouding of consciousness, or addiction. Future aims include the development of peripherally restricted opioid agonists, selective targeting of opioid-containing leukocytes to sites of painful injury, and the augmentation of peripheral opioid peptide and receptor synthesis.

Peripheral mechanisms of pain and analgesia

This review summarizes recent findings on peripheral mechanisms underlying the generation and inhibition of pain. The focus is on events occurring in peripheral injured tissues that lead to the sensitization and excitation of primary afferent neurons, and on the modulation of such mechanisms. Primary afferent neurons are of particular interest from a therapeutic perspective because they are the initial generator of noxious impulses traveling towards relay stations in the spinal cord and the brain. Thus, if one finds ways to inhibit the sensitization and/or excitation of peripheral sensory neurons, subsequent central events such as wind-up, sensitization and plasticity may be prevented. Most importantly, if agents are found that selectively modulate primary afferent function and do not cross the blood-brain-barrier, centrally mediated untoward side effects of conventional analgesics (e.g. opioids, anticonvulsants) may be avoided. This article begins with the peripheral actions of opioids, turns to a discussion of the effects of adrenergic co-adjuvants, and then moves on to a discussion of pro-inflammatory mechanisms focusing on TRP channels and nerve growth factor, their signaling pathways and arising therapeutic perspectives.

Mechanical hyperalgesia is attenuated by local administration of octreotide in pristane-induced arthritis in Dark-Agouti rats

AIMS

The Dark-Agouti (DA) rat is very susceptible to pristane-induced arthritis (PIA) and represents a suitable model for rheumatoid arthritis. In the present study, we examined the pain sensitivity and the effect of local administration of octreotide (OCT) on mechanical hyperalgesia in PIA DA rats.

MAIN METHODS

Arthritis was induced by intradermal injection of pristane (300 microl). The mechanical withdrawal threshold (MWT) and heat withdrawal latency (HWL) were used to evaluate the pain sensitivity. In addition, we recorded the discharge firings in the tibial nerve sensory C-fibers innervating the inflamed toe joints of arthritic DA rats.

KEY FINDINGS

Two weeks after injection of pristane, all DA rats developed severe arthritis. This symptom was associated with a decreased MWT (78.50+/-5.68 mN before pristane injection, 19.50+/-6.27 mN on day 14 after pristane injection), indicating a mechanical hyperalgesia in PIA. In contrast, HWL was comparable before and after pristane injection (10.25+/-0.70 s before injection; 9.45+/-1.23 s on day 14 after injection). Local injection of OCT markedly increased MWT and relieved the hyperalgesia in PIA. In addition, OCT significantly decreased the discharge rate of afferent C units evoked by both non-noxious and noxious joint movements.

SIGNIFICANCE

Taken together, the results demonstrate that mechanical hyperalgesia, but not thermal hyperalgesia is associated with PIA and that the mechanical hyperalgesia and the discharge of afferent C units are attenuated by local administration of OCT. These observations provide evidence for a novel therapeutic strategy for pain control in rheumatoid arthritis.

Amelioration of pain and histopathologic joint abnormalities in the Col1-IL-1beta(XAT) mouse model of arthritis by intraarticular induction of mu-opioid receptor into the temporomandibular joint

OBJECTIVE

To evaluate opioid receptor function as a basis for novel antinociceptive therapy in arthritis.

METHODS

We induced human mu-opioid receptor (HuMOR) expression in arthritic joints of mice, using the feline immunodeficiency virus (FIV) vector, which is capable of stably transducing dividing, growth-arrested, and terminally differentiated cells. Male and female Col1-IL-1beta(XAT)-transgenic mice developed on a C57BL/6J background and wild-type littermates were studied.

RESULTS

A single injection of FIV(HuMOR) into the temporomandibular joints of Col1-IL-1beta(XAT)-transgenic mice 1 week prior to induction of arthritis prevented the development of orofacial pain and joint dysfunction, and reduced the degree of histopathologic abnormality in the joint. In addition, FIV(HuMOR) prevented the attendant sensitization of trigeminal sensory neurons and activation of astroglia in brainstem trigeminal sensory nuclei. These effects were mediated by the transduction of primary sensory neurons via transport of FIV vectors from peripheral nerve endings to sensory ganglia, as evidenced by HuMOR expression in neuronal cell bodies located in the trigeminal ganglia, as well as in their proximal and distal nerve branches located in the main sensory and subnucleus caudalis of the brainstem and joints, respectively. The presence of MOR ligands predominantly in the descending trigeminal nucleus suggested that the observed antinociception occurred at the subnucleus caudalis. Articular chondrocytes and meniscal tissue were also infected by FIV(HuMOR), which presumably exerted an antiinflammatory effect on cartilage.

CONCLUSION

Our results indicate that prophylactic therapy with MOR overexpression in joints can successfully prevent the development of pain, dysfunction, and histopathologic abnormalities in the joints in arthritis. These findings may provide a basis for the future development of spatiotemporally controlled antinociceptive and antiinflammatory therapy for arthritis.

Peripheral Suppression of Arthritic Pain by Intraarticular Fadolmidine, an α2-Adrenoceptor Agonist, in the Rat

BACKGROUND

Earlier results suggest that peripheral alpha(2)-adrenoceptors and opioid receptors may reduce arthritic pain. Fadolmidine is a highly selective alpha(2)-adrenoceptor agonist that has only limited central access after peripheral administration. We assessed the peripheral antinociceptive properties of fadolmidine and the potential contribution of peripheral opioid receptors to its antinociceptive effect in experimental monoarthritis.

METHODS

After induction of monoarthritis in the knee joints of rats, we determined the frequency of vocalization induced by repetitive movement of the knee joint. Fadolmidine and clonidine were administered intraarticularly ipsi- or contralateral to the inflamed joint. Reversal of the fadolmidine-induced effect was attempted with subcutaneous (s.c.) administration of atipamezole, an alpha(2)-adrenoceptor antagonist, and intraarticular administration of naloxone methiodide, an opioid receptor antagonist that does not penetrate the blood-brain barrier.

RESULTS

Fadolmidine produced a dose-dependent attenuation of the vocalization response to movement of the inflamed knee joint, and this effect was significantly stronger after ipsi- than contralateral drug administration. Clonidine also produced a dose-dependent attenuation of the vocalization response, but this effect was not significantly different after ipsi- versus contralateral drug administration. Fadolmidine-induced antinociception was reversed by s.c. administration of atipamezole. Furthermore, intraarticular administration of naloxone methiodide into the inflamed, but not the contralateral, joint reversed the antinociceptive effect of fadolmidine independent of whether fadolmidine was administered into the inflamed or contralateral joint.

CONCLUSIONS

In rats, intraarticular administration of fadolmidine provides a marked suppression of pain-related behavior in arthritis, due to a selective action on peripheral alpha(2)-adrenoceptors and opioid receptors.

Role of peripheral mu-opioid receptors in inflammatory orofacial muscle pain

The aims of this project were to investigate whether inflammation in the orofacial muscle alters mu opioid receptor (MOR) mRNA and protein expressions in trigeminal ganglia (TG), and to assess the contribution of peripheral MORs under acute and inflammatory muscle pain conditions. mRNA and protein levels for MOR were quantified by reverse-transcription-polymerase chain reaction (RT-PCR) and Western blot, respectively, from the TG of naïve rats, and compared with those from the rats treated with complete Freund's adjuvant (CFA) in the masseter. TG was found to express mRNA and protein for MOR, and CFA significantly up-regulated both MOR mRNA and protein by 3 days following the inflammation. The MOR protein up-regulation persisted to day 7 and returned to the baseline level by day 14. We then investigated whether peripheral application of a MOR agonist, D-Ala2, N-Me-Phe4, Gly5-ol-enkephalin acetate salt (DAMGO), attenuates masseter nociception induced by masseteric infusion of hypertonic saline (HS) in lightly anesthetized rats. DAMGO (1, 5, 10 microg) or vehicle was administered directly into the masseter 5-10 min prior to the HS infusion. The DAMGO effects were assessed on mean peak counts (MPC) and overall magnitude as calculated by the area under the curve (AUC) of the HS-evoked behavioral responses. Under this condition, only the highest dose of DAMGO (10 microg) significantly reduced MPC, which was prevented when H-D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP), a selective MOR antagonist, was co-administered. DAMGO pre-treatment in the contralateral masseter did not attenuate MPC. The same doses of DAMGO administered into CFA-inflamed rats, however, produced a greater attenuation of both MPC and AUC of HS-evoked nocifensive responses. These results demonstrated that activation of peripheral MOR provides greater anti-nociception in inflamed muscle, and that the enhanced MOR effect can be partly explained by significant up-regulation of MOR expression in TG.

Naloxone antagonizes the local antihyperalgesic effect of fentanyl in burnt skin of healthy humans

The aim of this study was to investigate local opioid effects in the inflamed skin of healthy human volunteers. To induce inflammation, the circular tip of a 10-mm-diameter probe was heated to 48 degrees C and applied for 120 seconds to a site on each forearm of 24 healthy participants. Thirty minutes later, 0.2 mL of normal saline was injected subcutaneously into 1 inflamed site, and the opioid antagonist naloxone hydrochloride (80 microg in 0.2 mL) was injected subcutaneously into the other inflamed site. Participants completed tests of pain sensitivity (heat pain thresholds, heat pain ratings, and mechanical pain ratings) before and after the injections. Fentanyl citrate (10 microg in 0.2 mL) was then injected into the pretreated sites, and pain sensitivity was measured again. The thermal injuries produced thermal and mechanical hyperalgesia that did not differ between the saline and naloxone sites. After the fentanyl injections, decreases in thermal and mechanical hyperalgesia were greater at the saline site than the naloxone site. These findings demonstrate that pretreatment with naloxone blocks local opioid effects produced by the subcutaneous injection of a low dose of fentanyl in the inflamed skin of healthy humans. Thus, peripheral opioid receptors could be a therapeutic target for painful cutaneous disorders.

PERSPECTIVE

This article demonstrates that activation of opioid receptors in the skin inhibits sensitivity to painful mechanical and thermal stimuli. Thus, local application of low-dose opioid medications could relieve painful skin disorders.

Revisión sistemática: ¿son eficaces los opiáceos mayores en el tratamiento del dolor osteomuscular?

BACKGROUND AND OBJECTIVE

To evaluate the efficacy of major opioids in the treatment of musculoskeletal pain.

MATERIAL AND METHOD

Systematic review. A sensitive search strategy was undertaken in MEDLINE and EMBASE up to April 2005. The Cochrane Library and the abstracts of the 2004-2005 meetings of the American College of Rheumatology were also hand searched. All randomized controlled trials of major opiods in patients with musculoskeletal pain were selected. An analytical review was performed and evidence tables produced. A meta-analysis was run when appropriate.

RESULTS

We obtained 427 references from the search, (27 duplicated from MEDLINE and EMBASE, 2 from the Cochrane Library, and 5 abstracts), of which 68 articles plus one meeting abstract were selected for detailed analysis. Of these, 23 finally met the inclusion criteria. Combined analysis of oral major opioids versus placebo showed significant improvement in pain relief in patients with osteoarthritis.

CONCLUSIONS

Specific major opioids can reduce pain in patients with chronic musculoskeletal disorders. The clinical trials report positive effects on pain and the meta-analysis confirms these effects.

Opioids

Opioids are the most effective and widely used drugs in the treatment of severe pain. They act through G protein-coupled receptors. Four families of endogenous ligands (opioid peptides) are known. The standard exogenous opioid analgesic is morphine. Opioid agonists can activate central and peripheral opioid receptors. Three classes of opioid receptors (mu, delta, kappa) have been identified. Multiple pathways ofopioid receptor signaling (e.g., G(i/o) coupling, cAMP inhibition, Ca++ channel inhibition) have been described. The differential regulation of effectors, preclinical pharmacology, clinical applications, and side effects will be reviewed in this chapter.

Anti-allodynic effects of peripheral delta opioid receptors in neuropathic pain

The analgesic effects of local administration of opioid agonists into peripheral tissues in alleviating pain have been well documented in both clinical and preclinical studies, although few studies have examined their effects in neuropathic pain. In this study, we investigated the anti-allodynic effects of peripherally acting delta opioid receptor (DOR) agonists in a rat model of neuropathic pain. Peripheral nerve injury (PNI) produced a time-dependent decrease in mechanical withdrawal thresholds that was attenuated by local administration into the hind paw of either morphine or the DOR agonist deltorphin II. Using Western blotting techniques, no change in DOR protein expression was detected in DRG ipsilateral to the site of injury compared to contralateral. However, an up-regulation of DOR protein was found in neuropathic DRG compared to sham, suggesting that there may be a bilateral increase in the expression of DOR following PNI. Results obtained from immunohistochemical studies confirmed up-regulation in small and large DRG neurons in neuropathic compared to sham animals. Additionally, there was an increase in DOR protein within the ipsilateral sciatic nerve of neuropathic animals compared to sham and contralateral neuropathic conditions indicating the occurrence of receptor trafficking to the site of injury. Taken together, our findings suggest that functional peripheral DORs are present in sensory neurons following PNI and validate the development of selective DOR agonists for alleviating neuropathic pain.

Analgesic action of acetaminophen in symptomatic osteoarthritis of the knee

OBJECTIVES

The study was designed to investigate the analgesic effects and mechanisms of acetaminophen (paracetamol) in symptomatic osteoarthritis (OA) of the knee.

METHODS

Twenty patients with symptomatic OA were randomly allocated to two groups treated with either acetaminophen or rofecoxib for 3 months. Visits and measurements were scheduled upon entry (T0), at month 1 (T1) and at month 3 (T3). The intensity of joint pain was evaluated with a 100-mm visual analogue scale (VAS). The physical function of the affected knee was evaluated with a questionnaire comparable to the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC). Levels of serotonin, substance P (SP) and beta-endorphin (BEND) were determined with commercial enzyme-linked immunoassay kits. The expression of kappa opioid receptor (KOR) in peripheral mononuclear blood cells (PBMCs) was quantified by real-time PCR.

RESULTS

Both acetaminophen and rofecoxib relieved pain considerably but with different kinetics, and affected different biomarkers. Rofecoxib appeared to be more efficient, reducing pain intensity by 56% at T1 (P<0.01), whereas acetaminophen reduced it by only 29%. Physical function improved in both groups by T3. Correlated with the pain relief, acetaminophen significantly reduced plasma BEND levels, whereas rofecoxib did not do so. In both groups plasma SP levels were elevated compared with T0. A reduction in serum serotonin was detected in the rofecoxib group at T1 (P=0.004) but had recovered at T3. No changes in KOR mRNA in PBMCs were observed in either group.

CONCLUSIONS

There is a correlation between reduction in circulating BEND and OA pain relief in patients treated with acetaminophen.

[Potential applications and significance of peripheral opioid analgesia]

Recently, the local application of analgesic substances has attracted much interest and has become increasingly relevant in daily clinical practice. The lack of the well-known therapy-limiting central side effects of systemically administered opioids is a clear advantage of "peripheral opioid analgesia". Important prerequisites for the occurrence of peripheral analgesic effects of opioids are good accessibility of the painful site, presence of clinically relevant pain, signs of a local inflammation, exclusion of a fast systemic absorption, and adequately potent analgesic substances. This review gives an outline of recent experience with various clinical applications of "peripheral opioid analgesia".

Analgesic effect of intra-articular tramadol compared with morphine after arthroscopic knee surgery

PURPOSE

The aim of the study was to compare the analgesic effect of 5 mg intra-articular (IA) morphine with 50 mg IA tramadol.

TYPE OF STUDY

Prospective double-blind randomized trial.

METHODS

Seventy-five patients having elective arthroscopic surgery of the knee were randomized to receive IA tramadol 50 mg (tramadol group), IA morphine 5 mg (morphine group), or IA normal saline (control group), in equivalent volumes (20 mL). The tourniquet was released 10 minutes after analgesic administration. Verbal pain rating score between 0 and 10 (VRS), supplemental analgesic requirements, and incidence of side effects were recorded postoperatively.

RESULTS

Results are given as (median [5-95 percentiles]). The control group had a significantly shorter time to first analgesic request (25 min [15-55]) than morphine group, (34 min [15-158], P < .008) and the tramadol group, (33 min [17-728], P < .008). The patients in the control group complained of more severe pain (VRS 7 [4-10]) when they arrived at the postanesthesia care unit compared with the morphine group (VRS 1 [0-9], P = .002) and with the tramadol group (VRS 0 [0-9], P = .002). These treatment benefits were especially prominent in the patients who had meniscectomy or in the subgroup of patients with more than 6 months of preoperative pain. There was no statistical difference between the tramadol and morphine groups in the time to first analgesia, postoperative pain scores after arrival at the postanesthesia care unit, consumption of rescue analgesic, or side effects.

CONCLUSIONS

We conclude that 50 mg IA tramadol provides analgesia equivalent to 5 mg IA morphine.

LEVEL OF EVIDENCE

Level II, randomized controlled trial that shows no significant difference and lacks narrow confidence intervals.

Assessment of the effectiveness of peripheral administration of morphine with local articaine anaesthesia for surgery in inflamed oral and maxillofacial tissues

The controversy surrounding clinical trials of peripherally applied morphine with local anaesthetic and the attendant ambiguous results led to a study of our own clinical material. The aim of the study was to assess the effectiveness of peripheral administration of morphine with local articaine anaesthesia in inflamed oral and maxillofacial tissues. Sixty patients who qualified for the randomized, double-blinded study were randomly divided into two groups. Group 'LA' received a standard local anaesthetic solution (articaine plus epinephrine) while group 'LA-Mo' received the standard solution with an addition of 1 mg of morphine. Pain intensity was assessed using the Visual Analogue Scale, before and directly after surgery as well as at 1, 2, 6, 12, 24 and 48 h after completion of surgery. Furthermore, supplemental consumption of the prescribed analgesic was recorded. Despite a very similar average level of initial pain, there was a marked difference between the groups in the pain level during surgery. Moreover, during the next 12 h, there were significant differences observed in the level of pain between both groups. There was also considerable difference between both groups in the time of first analgesic intake and the total amount of analgesic. Our results show that modified local anaesthesia may be of benefit for the relief of operative and post-operative pain and may also help reduce analgesic intake after oral surgery.

Kappa and delta opioid receptors are expressed but down-regulated in fibroblast-like synoviocytes of patients with rheumatoid arthritis and osteoarthritis

OBJECTIVE

To investigate the expression and regulation of the kappa-opioid receptor (KOR) and the delta-opioid receptor (DOR) in fibroblast-like synoviocytes (FLS) from patients with osteoarthritis (OA) and rheumatoid arthritis (RA), and to explore the potential antiarthritic mechanisms of peripheral KORs.

METHODS

FLS isolated from synovial tissues of 6 OA patients, 8 RA patients, and 2 healthy individuals were exposed to the selective KOR agonist U69593, the selective DOR agonist SNC 80, and kappa-opioid dynorphin A in the presence or absence of the KOR antagonist nor-binaltorphimine, the DOR antagonist naltrindole, and the proinflammatory cytokines tumor necrosis factor alpha (TNFalpha) and interleukin-1beta (IL-1beta). The expression of KOR and DOR in OA and RA FLS was evaluated on the messenger RNA (mRNA) and protein levels with TaqMan real-time reverse transcriptase-polymerase chain reaction and immunofluorescence staining, respectively. KOR/DOR-mediated activation of ERK-1 and ERK-2 was investigated by Western blotting.

RESULTS

We detected functional KOR and DOR in normal FLS and observed a reduction of both receptors in OA and RA FLS, which was more distinct in RA FLS. U69593 enhanced KOR mRNA expression in both OA and RA FLS in a KOR antagonist-reversible manner. However, the dose required for maximal enhancement in RA FLS was 10 times higher than that required in OA FLS. TNFalpha and IL-1beta both suppressed the expression of DOR and KOR mRNA in both OA and RA FLS.

CONCLUSION

DOR and KOR are constitutively present in normal FLS and are suppressed under inflammatory conditions, such as RA and OA. Most interestingly, the KOR agonist U69593 may exert an antiarthritic effect via up-regulation of KOR in OA and RA FLS.

Peripheral opioid analgesia: Clinical applications

Peripheral opioid analgesia is undoubtedly of clinical relevance, especially considering that systemic opioid therapy often is hampered by central side effects. Despite some clinical studies that do not show peripheral opioid-mediated pain control, mostly because of methodologic shortcomings, studies evaluating inflammatory pain conditions show clear evidence and the number and the sites of applications are increasing. The intention of this paper is to give insight into the recent experience with the clinical applications of peripheral opioid analgesia.

Practical considerations in the assessment and treatment of pain in adults with physical disabilities

Adults aging with physical disabilities experience a variety of pain disorders that affect their functionality and QOL. It is important that clinicians caring for this population be knowledgeable about this common symptom and be able to perform a thorough history and physical examination. In addition, it is imperative to have a good working knowledge of the strengths and limitations of the treatments available.

Controlling Pain by Influencing Neurogenic Pathways

Neurogenic inflammation and ensuing pain can be modulated by inhibiting the function of primary afferent neurons. The best studied mechanism to accomplish such inhibition is the opioid system. Under inflammatory conditions, the anterograde axonal transport of opioid receptors from dorsal root ganglia toward the peripheral sensory nerve endings is augmented. The increased number of opioid receptors (among other mechanisms) leads to improved analgesic effects of exogenously administered ligands (eg, morphine) and of endogenous leukocyte-derived opioid peptides (eg, beta-endorphin). A current concept proposes that during inflammatory processes endogenous opioid peptides can be secreted from immunocytes, occupy peripheral opioid receptors on sensory nerve endings, and produce analgesia by inhibiting the excitability of these nerves or the release of proinflammatory neuropeptides. This article focuses on the role of peripheral opioid receptors in pain control and on novel pharmaceutical concepts for the treatment of patients who suffer from rheumatoid arthritis and other inflammatory pain.

Increased numbers of opioid expressing inflammatory cells do not affect intra-articular morphine analgesia

BACKGROUND

Both locally expressed beta-endorphin (END) and low doses of morphine relieve pain within inflamed knee joints. Here we examined whether enhanced inflammation and END expression within the synovial tissue of patients undergoing arthroscopic knee surgery might shift the analgesic dose-response curve of intra-articular (i.a.) morphine.

METHODS

Following IRB approval and informed consent, patients were randomly assigned to the following i.a. treatments at the end of surgery: group I (n=39), isotonic saline; group II (n=40), 1 mg morphine hydrochloride; group III (n=48), 2 mg morphine hydrochloride; group IV (n=39), 4 mg morphine hydrochloride. Postoperative pain intensity was assessed by the visual analogue scale (VAS), by the time to first analgesic request and by the supplemental piritramide consumption. Synovial specimens from each patient were stained for the presence of inflammatory cells and END and were discriminated into groups with low versus high numbers of these cells. Differences between groups were statistically analyzed by chi(2), anova and mancova where appropiate.

RESULTS

Patient characteristics and VAS scores did not differ between groups. Total postoperative piritramide consumption decreased and the time to first analgesic request increased significantly with increasing doses of i.a. morphine (P<0.05, anova and linear regression). These dose-response relationships were not different between patients with low versus high numbers of inflammatory and END-containing synovial cells (P>0.05, mancova).

CONCLUSIONS

The dose-response relationship of i.a. morphine analgesia is not shifted by enhanced inflammation and END expression within synovial tissue. Thus, the presence of END within inflamed synovial tissue does not seem to interfere with i.a. morphine analgesia.

The role of opioid analgesics in rheumatoid disease in the elderly population

Adequate pain therapy is an important aspect in the treatment of the elderly patient with rheumatoid disease. Problems with traditional NSAIDs include potentially serious gastrointestinal, cardiovascular and renal adverse effects, especially in the elderly. In addition, the selective cyclo-oxygenase-2 inhibitors have been associated with renal and cardiovascular adverse effects which may limit their use in the elderly with renal or cardiovascular disease. Opioids provide a treatment option for the management of pain in elderly patients with rheumatoid disease in whom pain control under standard management is poor; however, various therapeutic difficulties are encountered in the heterogeneous elderly population (increased risk of adverse effects, multimorbidity, and polypharmacy). Lower initial opioid dosage, prolonged dosage intervals and slower dosage titrations are advisable because of altered pharmacokinetics and pharmacodynamics. Kidney function should be tightly monitored and a timely use of laxatives is to be encouraged. Randomised clinical studies of opioids in musculoskeletal pain (e.g. osteoarthritis) have increasingly extended the scientific basis for their use. However, no randomised controlled clinical trials have examined the efficacy and the benefit/risk ratio of opioids in rheumatoid arthritis. Opioids also demonstrate an analgesic effect following local peripheral application. This opens the way to new therapeutic options in the future through the development of systemic peripherally selective opioids without CNS adverse effects.

Expression of functional mu-opioid receptors in human osteoarthritic cartilage and chondrocytes

There is evidence of effects of morphine on cell proliferation and intraarticular morphine produces analgesia and has an anti-inflammatory effect in chronic arthritis. The effects of opioids are mediated through the G-protein-coupled receptors affecting the cAMP pathway. We demonstrated that human osteoarthritic cartilage and cultured chondrocytes possess the mu-opioid receptor. The presence of the receptor was shown by immunodetection, polymerase chain reaction, and Western blotting. Stimulation of chondrocytes with beta-endorphin resulted in decreased phosphorylation of the transcription factor cAMP responsive element binding protein (CREB). The effect was reversed by naltrexone. The obtained results indicate that in human articular chondrocytes opioids affect, via the mu-opioid receptor, the transcription factor CREB which in turn can cause subsequent changes in gene expression.