Drug metabolic enzyme genotype-phenotype discrepancy: High phenoconversion rate in patients treated with antidepressants.

Cytochromes from the P450 family (CYP) play a central role in the primary metabolism of frequently prescribed antidepressants, potentially affecting their efficacy and tolerance. There are however important differences in the drug metabolic capacities of each individual resulting from a combination of intrinsic and environmental factors. This variability can present an important risk for patients and increases the difficulty of drug prescription in clinical practice. Pharmacogenetic studies have uncovered a number of alleles defining the intrinsic metabolizer status, however, additional factors affecting cytochrome activity can modify this activity and result in a phenoconversion. The present study investigates the discrepancy between the genetically predicted and actually measured activities for the six most important liver cytochromes (CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6 and CYP3A4) in a cohort of patients under antidepressant treatment, previously shown to have a high proportion of patients with low metabolizing activities. We now performed the genetic characterization of this cohort to determine the extent of the genetic versus environmental contribution in these decreased activities. For all enzyme tested, we observed an important rate of phenoconversion, affecting between 33 % and 65 % of the patients, as well as a significant (p < 1E-06) global reduction in the effective but not predicted activities of CYP2D6, CYP2C9 and CYP2C19 compared to the general population. Our results highlight the advantages of phenotyping versus genotyping as well as the increased risk of treatment failure or adverse effect occurrence in a polymedicated population.

Coadministration of ticagrelor and ritonavir: Toward prospective dose adjustment to maintain an optimal platelet inhibition using the PBPK approach.

Ticagrelor is a potent antiplatelet drug metabolized by cytochrome (CYP)3A. It is contraindicated in patients with human immunodeficiency virus (HIV) because of the expected CYP3A inhibition by most protease inhibitors, such as ritonavir and an increased bleeding risk. In this study, a physiologically based pharmacokinetic (PBPK) model was created for ticagrelor and its active metabolite (AM). Based on the simulated interaction between ticagrelor 180 mg and ritonavir 100 mg, a lower dose of ticagrelor was calculated to obtain, when coadministered with ritonavir, the same pharmacokinetic (PK) and platelet inhibition as ticagrelor administered alone. A clinical study was thereafter conducted in healthy volunteers. Observed PK profiles of ticagrelor and its AM were successfully predicted with the model. Platelet inhibition was nearly complete in both sessions despite administration of a fourfold lower dose of ticagrelor in the second session. This PBPK model could be prospectively used to broaden the usage of ticagrelor in patients with ritonavir-treated HIV regardless of the CYP3A inhibition.

Geneva cocktail for cytochrome p450 and P-glycoprotein activity assessment using dried blood spots.

The suitability of the capillary dried blood spot (DBS) sampling method was assessed for simultaneous phenotyping of cytochrome P450 (CYP) enzymes and P-glycoprotein (P-gp) using a cocktail approach. Ten volunteers received an oral cocktail capsule containing low doses of the probes bupropion (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), dextromethorphan (CYP2D6), midazolam (CYP3A), and fexofenadine (P-gp) with coffee/Coke (CYP1A2) on four occasions. They received the cocktail alone (session 1), and with the CYP inhibitors fluvoxamine and voriconazole (session 2) and quinidine (session 3). In session 4, subjects received the cocktail after a 7-day pretreatment with the inducer rifampicin. The concentrations of probes/metabolites were determined in DBS and plasma using a single liquid chromatography-tandem mass spectrometry method. The pharmacokinetic profiles of the drugs were comparable in DBS and plasma. Important modulation of CYP and P-gp activities was observed in the presence of inhibitors and the inducer. Minimally invasive one- and three-point (at 2, 3, and 6 h) DBS-sampling methods were found to reliably reflect CYP and P-gp activities at each session.

Applications of CYP450 testing in the clinical setting.

Interindividual variability in drug response is a major clinical problem. Polymedication and genetic polymorphisms modulating drug-metabolising enzyme activities (cytochromes P450, CYP) are identified sources of variability in drug responses. We present here the relevant data on the clinical impact of the major CYP polymorphisms (CYP2D6, CYP2C19 and CYP2C9) on drug therapy where genotyping and phenotyping may be considered, and the guidelines developed when available. CYP2D6 is responsible for the oxidative metabolism of up to 25% of commonly prescribed drugs such as antidepressants, antipsychotics, opioids, antiarrythmics and tamoxifen. The ultrarapid metaboliser (UM) phenotype is recognised as a cause of therapeutic inefficacy of antidepressant, whereas an increased risk of toxicity has been reported in poor metabolisers (PMs) with several psychotropics (desipramine, venlafaxine, amitriptyline, haloperidol). CYP2D6 polymorphism influences the analgesic response to prodrug opioids (codeine, tramadol and oxycodone). In PMs for CYP2D6, reduced analgesic effects have been observed, whereas in UMs cases of life-threatening toxicity have been reported with tramadol and codeine. CYP2D6 PM phenotype has been associated with an increased risk of toxicity of metoprolol, timolol, carvedilol and propafenone. Although conflicting results have been reported regarding the association between CYP2D6 genotype and tamoxifen effects, CYP2D6 genotyping may be useful in selecting adjuvant hormonal therapy in postmenopausal women. CYP2C19 is responsible for metabolising clopidogrel, proton pump inhibitors (PPIs) and some antidepressants. Carriers of CYP2C19 variant alleles exhibit a reduced capacity to produce the active metabolite of clopidogrel, and are at increased risk of adverse cardiovascular events. For PPIs, it has been shown that the mean intragastric pH values and the Helicobacter pylori eradication rates were higher in carriers of CYP2C19 variant alleles. CYP2C19 is involved in the metabolism of several antidepressants. As a result of an increased risk of adverse effects in CYP2C19 PMs, dose reductions are recommended for some agents (imipramine, sertraline). CYP2C9 is responsible for metabolising vitamin K antagonists (VKAs), non-steroidal anti-inflammatory drugs (NSAIDs), sulfonylureas, angiotensin II receptor antagonists and phenytoin. For VKAs, CYP2C9 polymorphism has been associated with lower doses, longer time to reach treatment stability and higher frequencies of supratherapeutic international normalised ratios (INRs). Prescribing algorithms are available in order to adapt dosing to genotype. Although the existing data are controversial, some studies have suggested an increased risk of NSAID-associated gastrointestinal bleeding in carriers of CYP2C9 variant alleles. A relationship between CYP2C9 polymorphisms and the pharmacokinetics of sulfonylureas and angiotensin II receptor antagonists has also been observed. The clinical impact in terms of hypoglycaemia and blood pressure was, however, modest. Finally, homozygous and heterozygous carriers of CYP2C9 variant alleles require lower doses of phenytoin to reach therapeutic plasma concentrations, and are at increased risk of toxicity. New diagnostic techniques made safer and easier should allow quicker diagnosis of metabolic variations. Genotyping and phenotyping may therefore be considered where dosing guidelines according to CYP genotype have been published, and help identify the right molecule for the right patient.

Identification and weighting of the most critical "real-life" drug-drug interactions with acenocoumarol in a tertiary care hospital.

PURPOSE: The objective of this study was to identify the most clinically relevant drug-drug interactions (DDIs) at risk of affecting acenocoumarol safety in our tertiary care university hospital, a 2,000 bed institution. METHODS: We identified DDIs occurring with acenocoumarol by combining two different sources of information: a 1-year retrospective analysis of acenocoumarol prescriptions and comedications from our Computerized Physician Order Entry (CPOE) system (n = 2,439 hospitalizations) and a retrospective study of clinical pharmacology consultations involving acenocoumarol over the past 14 years (1994-2007) (n = 407). We classified these DDIs using an original risk-analysis method. A criticality index was calculated for each associated drug by multiplying three scores based on mechanism of interaction, involvement in a supratherapeutic international normalized ratio (INR) (≥ 6) and involvement in a severe bleeding. RESULTS: One hundred and twenty-six DDIs were identified and weighted. Twenty-eight drugs had a criticality index ≥ 20 and were therefore considered at high risk for interacting with acenocoumarol by increasing its effect: 75% of these drugs involved a pharmacokinetic mechanism and 14 % a pharmacodynamic mechanism. An unknown mechanism of interaction was involved in 11 % of drugs. CONCLUSION: Twenty-eight specific drugs were identified as being at high risk for interacting with acenocoumarol in our hospital using an original risk-analysis method. Most analyzed drugs interact with acenocoumarol via a pharmacokinetic mechanism. Actions such as the implementation of alerts in our CPOE system should be specifically developed for these drugs.

The effects of CYP2D6 and CYP3A activities on the pharmacokinetics of immediate release oxycodone.

BACKGROUND AND PURPOSE: There is high interindividual variability in the activity of drug-metabolizing enzymes catalysing the oxidation of oxycodone [cytochrome P450 (CYP) 2D6 and 3A], due to genetic polymorphisms and/or drug-drug interactions. The effects of CYP2D6 and/or CYP3A activity modulation on the pharmacokinetics of oxycodone remains poorly explored. EXPERIMENTAL APPROACH: A randomized crossover double-blind placebo-controlled study was performed with 10 healthy volunteers genotyped for CYP2D6 [six extensive (EM), two deficient (PM/IM) and two ultrarapid metabolizers (UM)]. The volunteers randomly received on five different occasions: oxycodone 0.2 mg x kg(-1) and placebo; oxycodone and quinidine (CYP2D6 inhibitor); oxycodone and ketoconazole (CYP3A inhibitor); oxycodone and quinidine+ketoconazole; placebo. Blood samples for plasma concentrations of oxycodone and metabolites (oxymorphone, noroxycodone and noroxymorphone) were collected for 24 h after dosing. Phenotyping for CYP2D6 (with dextromethorphan) and CYP3A (with midazolam) were assessed at each session. KEY RESULTS: CYP2D6 activity was correlated with oxymorphone and noroxymorphone AUCs and C(max) (-0.71 < Spearman correlation coefficient rhos < -0.92). Oxymorphone C(max) was 62% and 75% lower in PM than EM and UM. Noroxymorphone C(max) reduction was even more pronounced (90%). In UM, oxymorphone and noroxymorphone concentrations increased whereas noroxycodone exposure was halved. Blocking CYP2D6 (with quinidine) reduced oxymorphone and noroxymorphone C(max) by 40% and 80%, and increased noroxycodone AUC(infinity) by 70%. Blocking CYP3A4 (with ketoconazole) tripled oxymorphone AUC(infinity) and reduced noroxycodone and noroxymorphone AUCs by 80%. Shunting to CYP2D6 pathway was observed after CYP3A4 inhibition. CONCLUSIONS AND IMPLICATIONS: Drug-drug interactions via CYP2D6 and CYP3A affected oxycodone pharmacokinetics and its magnitude depended on CYP2D6 genotype.

Genetic polymorphisms and drug interactions modulating CYP2D6 and CYP3A activities have a major effect on oxycodone analgesic efficacy and safety.

BACKGROUND AND PURPOSE: The major drug-metabolizing enzymes for the oxidation of oxycodone are CYP2D6 and CYP3A. A high interindividual variability in the activity of these enzymes because of genetic polymorphisms and/or drug-drug interactions is well established. The possible role of an active metabolite in the pharmacodynamics of oxycodone has been questioned and the importance of CYP3A-mediated effects on the pharmacokinetics and pharmacodynamics of oxycodone has been poorly explored. EXPERIMENTAL APPROACH: We conducted a randomized crossover (five arms) double-blind placebo-controlled study in 10 healthy volunteers genotyped for CYP2D6. Oral oxycodone (0.2 mg x kg(-1)) was given alone or after inhibition of CYP2D6 (with quinidine) and/or of CYP3A (with ketoconazole). Experimental pain (cold pressor test, electrical stimulation, thermode), pupil size, psychomotor effects and toxicity were assessed. KEY RESULTS: CYP2D6 activity was correlated with oxycodone experimental pain assessment. CYP2D6 ultra-rapid metabolizers experienced increased pharmacodynamic effects, whereas cold pressor test and pupil size were unchanged in CYP2D6 poor metabolizers, relative to extensive metabolizers. CYP2D6 blockade reduced subjective pain threshold (SPT) for oxycodone by 30% and the response was similar to placebo. CYP3A4 blockade had a major effect on all pharmacodynamic assessments and SPT increased by 15%. Oxymorphone C(max) was correlated with SPT assessment (rho(S)= 0.7) and the only independent positive predictor of SPT. Side-effects were observed after CYP3A4 blockade and/or in CYP2D6 ultra-rapid metabolizers. CONCLUSIONS AND IMPLICATIONS: The modulation of CYP2D6 and CYP3A activities had clear effects on oxycodone pharmacodynamics and these effects were dependent on CYP2D6 genetic polymorphism.

Development and validation of a chemical hydrolysis method for dextromethorphan and dextrophan determination in urine samples: application to the assessment of CYP2D6 activity in fibromyalgia patients.

Dextromethorphan (DEM) is a widely used probe drug for human cytochrome P450 2D6 isozyme activity assessment by measuring the ratio between DEM and its N-demethylated metabolite dextrorphan (DOR). DOR is excreted in urine mainly conjugated to glucuronic acid. Prior to quantification, DOR must be deconjugated to avoid variability caused by the polymorphic glucuronosyltransferase enzyme. A chemical hydrolysis method was optimized using a chemometric approach. Three factors (acid concentration, hydrolysis time and temperature) were selected and simultaneously varied to study their effect on conjugated DOR hydrolysis. Hydrolysis conditions that maximize DOR release without significant degradation of both DEM and DOR were chosen and results were compared to those obtained by enzymatic method using beta-glucuronidase. An HPLC method with fluorescence detection was developed for the simultaneous quantitation of DEM, DOR and levallorphan, used as an internal standard. Separation was performed on a phenyl analytical column (150 mmx4.6 mm i.d., 5 microm) with a mobile phase consisting of 18% acetonitrile and 50 mM phosphoric acid (pH 3). The overall analytical procedure was validated and showed good performances in terms of selectivity, linearity, sensitivity, precision and accuracy. Finally, this assay was used to determine DEM/DOR molar ratios in fibromyalgia patients for the purpose of determining phenotype status for the CYP2D6.

Systemic allergic reaction and diffuse bone pain after exposure to a preparation of betamethasone.

Allergic reactions to corticosteroids are unexpected as they seem to contradict their pharmacodynamic action. Nevertheless, they are not infrequent, with an estimated incidence of up to 4% for cutaneous reactions. Systemic reactions are rarely reported, but their incidence might be underestimated. We report here an unusual allergic reaction to betamethasone presenting with diffuse bone pain, erythema, and bronchoconstriction, which was confirmed by a positive rechallenge in a double-blind procedure. This is the first case report of a systemic reaction to betamethasone confirmed by a positive rechallenge. An impurity in betamethasone diproprionate cannot be excluded. As this substance is frequently used in rheumatologic soft-tissue injections, it is important to recognize this potentially life-threatening side effect.

Neurophysiologic evidence for a central sensitization in patients with fibromyalgia.

OBJECTIVE: To determine whether abnormalities of peripheral and central nociceptive sensory input processing exist outside areas of spontaneous pain in patients with fibromyalgia (FM) as compared with controls, by using quantitative sensory testing (QST) and a neurophysiologic paradigm independent from subjective reports. METHODS: A total of 164 outpatients with FM who were attending a self-management program were invited to participate in the study. Data for 85 patients were available and were compared with those for 40 non-FM controls matched for age and sex. QST was performed using thermal, mechanical, and electrical stimuli at locations of nonspontaneous pain. Pain assessment was 2-fold and included use of subjective scales and the spinal nociceptive flexion reflex (NFR), a specific physiologic correlate for the objective evaluation of central nociceptive pathways. Questionnaires regarding quality of life and the impact of FM were available. RESULTS: Participants were mainly middle-aged women, with a mean disease duration of 8 years. Between-group differences were significant for neurophysiologic, clinical, and quality of life measures. In patients with FM, peripheral QST showed significantly altered cold and heat pain thresholds, and tolerance to cold pain was radically reduced. The median NFR threshold in patients with FM (22.7 mA [range 17.5-31.7]) was significantly decreased compared with that in controls (33 mA [range 28.1-41]). A cutoff value of <27.6 mA for NFR provided sensitivity of 73% and specificity of 80% for detecting central allodynia in the setting of FM. CONCLUSION: Our results strongly, although indirectly, point to a state of central hyperexcitability of the nociceptive system in patients with FM. The NFR can be used to assess central allodynia in FM. It may also help discriminate patients who may benefit from use of centrally acting analgesics.

Advances with analgesics and NSAIDs for the treatment of spinal disorders.

One of the major developments with regard to chronic non-malignant pain in these last few years has been a better understanding of the mechanisms that act to maintain pain, while inferences about the pathophysiology have facilitated therapeutic decision-making. This chapter reviews the strength of evidence for the therapeutic effect of pharmacological symptomatic approaches using non-steroidal anti-inflammatory agents, opioids and co-analgesics in acute and chronic back pain with an emphasis on the results of randomized controlled trials as well as on the need for long-term comparative trials of drug efficacy, toxicity and compliance.

The tramadol option.

Tramadol is an option for the treatment of rheumatological pain. Its mode of action and safety profile distinguishes it from other opioids. Tramadol differs from other opioids by combining a weak opioid and a monoaminergic mode of action. It is effective in different types of moderate-to-severe pain, including neuropathic pain. Moreover, as the mode of action of tramadol does not overlap with that of NSAIDs, it is a useful agent to be combined with these drugs. Tramadol induces fewer opioid adverse reactions for a given level of analgesia compared with traditional opioids. Common adverse reactions of tramadol such as nausea and dizziness, which usually occur only at the beginning of therapy and attenuate over time, can be further minimized by up-titrating the drug over several days. Dose adjustment is only necessary in patients over 75 years of age, or in those with either hepatic or renal insufficiency. Tramadol should be avoided or used with caution in epileptics, or in individuals who are receiving seizure-threshold lowering drugs. Finally, tramadol has a low risk of abuse because it has only a weak opioid effect and its monoaminergic action could inhibit the development of dependence. The low abuse potential of tramadol has been demonstrated by postmarketing surveillance data.

Contribution of cytochrome P-4502D6 phenotype to the neuromodulatory effects of dextromethorphan.

Dextromethorphan (DEM)-mediated N-methyl-D-aspartate receptor blockade may result from an action of unchanged DEM or its active metabolite, dextrorphan (DOR). In humans, DEM is metabolized into DOR by the polymorphic enzyme CYP2D6. We therefore investigated the impact of quinidine (Qd), a selective inhibitor of CYP2D6, on DEM disposition and the contribution of CYP2D6 phenotype on DEM antinociceptive and neuromodulatory effects. Using a randomized, double-blind, crossover, placebo-controlled design, healthy volunteers (n = 7) received Qd (50 mg Qd sulfate orally) or a placebo and, 12 h later, either DEM (50 mg DEM hydrobromide orally) or a placebo. DEM and DOR pharmacodynamics were assessed for their antinociceptive and neuromodulatory effects. Antinociceptive effects were assessed over 4 h by subjective pain threshold and RIII nociceptive reflex (RIII) monitoring. Neuromodulatory effects were studied using the primary and secondary hyperalgesia induced by the topical application of capsaicin. Two of seven subjects were genotypic CYP2D6 PM. Pretreatment of EM by Qd suppressed DOR formation and increased the plasma level of DEM to the levels of poor metabolizers. In poor metabolizers, DEM induced a significant increase in objective (+45%) and subjective (+35%) pain thresholds. In extensive metabolizers, only a slight and short-lasting increase in the subjective threshold was observed, whereas no effect was seen on the objective threshold. DEM modulates secondary hyperalgesia compared with DOR. The CYP2D6 phenotype affects the disposition of DEM and the production of the active metabolite DOR. The impact of the CYP2D6 phenotype is of major importance for the spinal antinociceptive and neuromodulatory effects of DEM.

Contribution of monoaminergic modulation to the analgesic effect of tramadol.

1. In humans, the central analgesic effect of tramadol 100 mg orally is only partially reversed by the opioid antagonist naloxone (0.8 mg intravenously). As suggested by in vitro and animal data tramadol analgesia may thus result from an action on opioid as well as monoaminergic pathways. We therefore investigated the effect of alpha 2-adrenoceptor antagonism with yohimbine on tramadol analgesia. 2. Healthy volunteers (n = 10) received tramadol (100 mg orally), followed (+3 h) by yohimbine (0.1 mg kg-1 intravenously), and yohimbine + naloxone (0.8 mg intravenously) and their respective placebo according to a randomized, double-blind crossover, placebo (P) controlled design. Analgesia was assessed over 8 h by subjective pain threshold (pain intensity numerical scale--PINS) and objective pain threshold (RIII nociceptive reflex--RIII) monitoring. 3. Tramadol induced a significant increase in both pain thresholds. Peak analgesic effect was observed at 3.7 h (RIII + 39.6 +/- 3.9% and PINS 50.1 +/- s.e.mean 5%) and the analgesia lasted about 6 h. 4. Yohimbine significantly reversed the analgesic effects of tramadol for 2.8 h with a maximum decrease of 97 +/- 4% (RIII) and 67 +/- 12% (PINS), whereas the addition of naloxone abolished tramadol effects throughout the study period with a decrease of 90 +/- 6% (RIII) and 79 +/- 9% (PINS), P < 0.05). 5. Yohimbine alone did not significantly reduce pain thresholds. 6. alpha 2-Adrenoceptor antagonism reverses tramadol effects, thus pointing to the significant role of monoaminergic modulation and the synergy with opioid agonism in tramadol antinociception after a single oral dose.

Influence of the sympathetic nervous system in the development of abnormal pain-related behaviours in a rat model of neuropathic pain.

This study evaluated the effect of surgical sympathectomy on pain-related behaviours in a well established model of peripheral mononeuropathy produced by loose ligatures around the common sciatic nerve in the rat. Behavioural abnormalities include spontaneous abnormal position of the hindpaw after the nerve constriction, indicative of "spontaneous pain", and changes in responses to mechanical or thermal stimuli applied to this paw. These changes are usually maximal at week 2 after the surgery, stable until weeks 3-4, and disappear between weeks 8 and 12. To assess the role of the sympathetic nervous system in the development and persistence of these abnormalities, four groups of rats were behaviourally tested: (i) rats receiving a complete sham surgery, (ii) rats with a sciatic nerve constriction produced by loose ligatures around the common nerve trunk plus a sham sympathectomy, (iii) rats receiving a lumbar sympathectomy with a sham nerve ligature, and (iv) rats receiving a simultaneous surgical lumbar sympathectomy and a sciatic nerve constriction. The efficacy of the sympathectomy was assessed by the measure of the noradrenaline level in the sciatic nerve. Sympathectomy reduced selectively or even prevented the abnormal reaction to cold temperature and to heat (45 degrees C) in rats with a peripheral mononeuropathy. In contrast, the abnormal reaction to mechanical pressure was not influenced, and the behavioural abnormalities indicating spontaneous pain were still present. Sympathectomy alone resulted in a reduction of the vocalization threshold to pressure on both hindpaws, but also a short-lasting increased tolerance to cold immersion. This study confirms the selective role of the sympathetic nervous system in affecting the development and maintenance of some abnormal pain-related behaviours to thermal stimuli in rats with a moderate, but persistent, constriction of one sciatic nerve.

[Which analgesic dosage of paracetamol?]. / Quelle posologie antalgique du paracétamol?

The purpose of this study was to evaluate the dose-response of paracetamol and to assess its plasma concentration-effect relationship. According to a randomized, double-blind, and placebo controlled design healthy volunteers (n = 11) received 0.5, 1 and 2 g paracetamol (as propacetamol) intravenously (15 min). The extent of analgesic effect was measured over 8 hours by objective pain threshold (R-III) monitoring after selective transcutaneous electrical stimulation of the ipsilateral sural nerve. Maximal R-III threshold increase is at 2 hours after 0.5 g and 2.5 hours after 1 g and 2 g. The delayed peak effects, when compared to peak plasma concentrations, draw counter clockwise hysteresis. Duration of paracetamol antinociceptive effect increased concomitantly to dosage increment. Intravenous paracetamol exerts a dose-dependent central analgesia.

Selective opioid receptor agonists modulate mechanical allodynia in an animal model of neuropathic pain.

This study evaluated the antinociceptive effects of systemically administered selective opioid agonists of mu (DAMGO), delta (BUBU) and kappa (U 69593) receptors on the vocalization threshold to paw pressure in a rat model of peripheral unilateral mononeuropathy produced by loose ligatures around the common sciatic nerve. DAMGO (0.5-2 mg/kg), BUBU (1.5-6 mg/kg) and U 69593 (0.75-3 mg/kg) injected intravenously (i.v.) produced a potent long-lasting antinociceptive effect on both hind paws. The effects on the lesioned paw were clearly and statistically more potent than for the non-lesioned paw. The selective antinociceptive effect of 2 mg/kg DAMGO, 3 mg/kg BUBU and 1.5 mg/kg U 69593 were completely prevented by prior administration of the appropriate antagonists: 0.1 mg/kg naloxone, 1 mg/kg naltrindole and 0.4 mg/kg MR 2266. The present data clearly show that an acute i.v. injection of these selective opioid agonists induces potent antinociceptive effects in a rat model of peripheral neuropathy. These data are discussed with regard to the classical view that there is opioid resistance in neuropathic pain.

The highly selective delta agonist BUBU induces an analgesic effect in normal and arthritic rat and this action is not affected by repeated administration of low doses of morphine.

The effect of various doses of the selective delta agonist BUBU (Tyr-D-Ser(O-t-butyl)-Gly-Phe-Leu-Thr(O-t-butyl) on the vocalization threshold to paw pressure were compared in normal and arthritic rats, a suitable clinical model of chronic pain. In both group of rats, the intravenous administration of BUBU (6, 9, 12 mg/kg in normal and 1.5, 3, 6 mg/kg in arthritic rats) led to significant antinociceptive effects. The same dose of BUBU (6 mg/kg i.v.) produced a much more potent antinociceptive effect in arthritic than in normal rats, and a dose as low as 1.5 mg/kg produced a significant analgesic effect in the arthritic animal, whereas at 3 mg/kg BUBU was ineffective in normal rats. The analgesic effects of BUBU (9 mg/kg in normal and 3 mg/kg in arthritic rats) were completely prevented by the selective delta antagonist naltrindole (1 mg/kg i.v. a dose devoid of analgesic potency per se), while they were not affected by the selective mu antagonist naloxone (0.05 mg/kg i.v.). In addition, 3 mg/kg i.v. of BUBU remained effective in morphine tolerant arthritic rats. These results suggest that delta opioid receptor activation can modulate the transmission of cutaneous mechanical nociceptive information in rats, especially in inflammatory pain conditions.

Opposite effects of axon damage on heat shock proteins (hsp 70) and ubiquitin contents in motor neurons of neuropathic rats.

Alteration in the motoneurone contents of heat shock protein (hsp 70) and ubiquitin were studied in rats which had been subject to loose ligation of one common sciatic nerve. This results in a unilateral peripheral neuropathy which peaks at 14 days following ligation and is characterized by transient degeneration of both myelinated and unmyelinated nerve fibres, abnormal motor behaviours (posture of the hind limb, walking patterns) and thermal and mechanical allodynia of the hind paw. Hsp 70 and ubiquitin are proteins involved in protein metabolism and their expression is regulated during cellular stress. The contralateral unlesioned side was used as control. Motoneurone staining for hsp 70 and ubiquitin were differentially altered at the peak of the neuropathy. Axon damage resulted in a decrease in hsp 70 labeling while ubiquitin staining increased. At the same time motoneurones undergoing axon damage overstained for the immediate early gene encoded protein c-JUN and for nerve growth factor receptor (rNGF). In contrast, no clear alteration was seen, at that time, in the intensity of labeling for calcitonin gene-related peptide (CGRP). This study demonstrates that peripheral neuropathy resulting from loose ligation of the common sciatic nerve not only produces sensory alterations as previously reported but also leads to pronounced alterations in motoneurone functioning that could partly explain the observed abnormal motor behaviours. Results are discussed in accordance with presumed roles for hsp 70 and ubiquitin in protein metabolism and in relationship with possible interaction with c-JUN and rNGF expressions.