The effect of surgical complications on long-term prognosis following oesophagectomy

INTRODUCTION

Complications are frequent after oesophagectomy, and there is evidence these adversely impact long-term prognosis. However, the effect of multiple complications, and the absolute magnitude of effect on survival is unclear. This study aimed to examine these effects in a single high-volume UK unit.

METHODS

Patients undergoing oesophagectomy for cancer and who survived to 90 days post-oesophagectomy were analysed. Complications were graded according to the Clavien-Dindo (CD) classification and the Comprehensive Complication Index (CCI). The effect and magnitude of effect of complications on survival were assessed using multivariable cox regression and the risk-adjusted population attributable fraction.

RESULTS

In total, 380 patients were included. Complications occurred in 251 (66.1%). Suffering ≥3 complications (HR 1.89, 95%CI 1.13-3.16, p = 0.015) or an unplanned escalation in care (HR 2.22, 95%CI 1.43-3.45, p < 0.001) significantly reduced survival whereas pulmonary complications and anastomotic leak did not. Patients with a CCI>30 had worse overall survival (HR 1.91, 95%CI 1.32-2.76, p < 0.001) and CCI>30 due to multiple minor complications gave a worse prognosis compared to CCI>30 due to major complications (HR 2.44, 95%CI 1.14-5.20, p = 0.022). An estimated 9.1% (95%CI 3.4-14.4%) of deaths at 5 years were attributable to a CCI>30.

CONCLUSION

Long-term survival following oesophagectomy for cancer is significantly affected by complications and the cumulative effect of multiple complications. Interestingly, multiple minor complications had a worse effect on survival than major complications. The absolute magnitude of effect is substantial: minimising all types of postoperative complications could have significant benefit to overall outcomes.

O7: APPARENT PATHOLOGICAL COMPLETE RESPONSE TO NEOADJUVANT THERAPY LEADS TO SELECTION OF TREATMENT RESISTANT CANCER STEM CELLS IN OESOPHAGEAL ADENOCARCINOMA

Introduction

In oesophageal adenocarcinoma with an apparent pathological complete response (pCR) to neoadjuvant therapy (NAT) there remains debate as to whether oesophagectomy is required. Single Cell RNA sequencing (scRNAseq) enables identification and characterisation of cell populations at higher resolution than diagnostic techniques.

Method

ScRNAseq was used to determine transcriptomic profiles of cell populations in 24 OAC tumours and 13 matched normal samples. Five were also analysed using bulk RNA sequencing and high-precision mass spectrometry proteomics. Immunohistochemistry (IHC) was used to validate pCR. Paired scRNAseq analysis of pre-and post-treatment specimens from three further patients was used to compare transcriptomic profiles before and after NAT. Cancer cells (CCs) were assigned a cancer stem cell (CSC) score curated from published gene sets.

Result

We analysed a total of 22,738 single cells forming 29 different cell phenotypes. In two samples with apparent pCR, IHC staining, bulk RNA sequencing and proteomics of post-treatment samples failed to identify CCs. ScRNAseq, conversely, revealed persistent CCs (12/978 and 45/774). Transcriptomic analysis identified upregulation of stem cell markers and high CSC scores in these cells.

Conclusion

We have shown that CCs persist beneath the lower detection limit of standard approaches in apparent pCR. These cells express marker genes and expression programs consistent with CSCs. CSCs are a critical subpopulation that drive tumour initiation, growth, invasion, metastasis and resistance to therapy. These gene expression programs are not enriched in non-responders and straight to surgery samples. Oesophagus sparing treatment algorithms in pCR may subject patients to unnecessary risk of progression.

Take-home message

Cancer cells remain within tumours after apparent complete pathological response. These cells express stem cell markers associated with resistance to therapy and cancer progression.

Multicentre cohort study to define and validate pathological assessment of response to neoadjuvant therapy in oesophagogastric adenocarcinoma

BACKGROUND

This multicentre cohort study sought to define a robust pathological indicator of clinically meaningful response to neoadjuvant chemotherapy in oesophageal adenocarcinoma.

METHODS

A questionnaire was distributed to 11 UK upper gastrointestinal cancer centres to determine the use of assessment of response to neoadjuvant chemotherapy. Records of consecutive patients undergoing oesophagogastric resection at seven centres between January 2000 and December 2013 were reviewed. Pathological response to neoadjuvant chemotherapy was assessed using the Mandard Tumour Regression Grade (TRG) and lymph node downstaging.

RESULTS

TRG (8 of 11 centres) was the most widely used system to assess response to neoadjuvant chemotherapy, but there was discordance on how it was used in practice. Of 1392 patients, 1293 had TRG assessment; data were available for clinical and pathological nodal status (cN and pN) in 981 patients, and TRG, cN and pN in 885. There was a significant difference in survival between responders (TRG 1-2; median overall survival (OS) not reached) and non-responders (TRG 3-5; median OS 2·22 (95 per cent c.i. 1·94 to 2·51) years; P < 0·001); the hazard ratio was 2·46 (95 per cent c.i. 1·22 to 4·95; P = 0·012). Among local non-responders, the presence of lymph node downstaging was associated with significantly improved OS compared with that of patients without lymph node downstaging (median OS not reached versus 1·92 (1·68 to 2·16) years; P < 0·001).

CONCLUSION

A clinically meaningful local response to neoadjuvant chemotherapy was restricted to the small minority of patients (14·8 per cent) with TRG 1-2. Among local non-responders, a subset of patients (21·3 per cent) derived benefit from neoadjuvant chemotherapy by lymph node downstaging and their survival mirrored that of local responders.

The Development, Application and Analysis of an Enhanced Recovery Programme for Major Oesophagogastric Resection

BACKGROUND

Enhanced recovery programmes improve outcomes in surgery, but their implementation after upper gastrointestinal resection has been limited. The aim of this study was to compare short-term outcomes for patients undergoing oesophagogastric surgery in an enhanced recovery programme (EROS).

METHODS

EROS was developed after a multidisciplinary meeting by multiple rounds of revision. EROS was applied to all patients undergoing major upper GI resection at a university teaching hospital in the UK from 20/9/13, with data reviewed at 18/09/15. EROS was assessed to identify predictors for compliance.

RESULTS

One hundred six patients underwent major upper GI resection including 81 oesophagectomies, 24 gastrectomies and 1 colonic interposition graft. Major complications (Clavien Dindo ≥3) occurred in 12 patients with 1 in-hospital death. Thirty-five patients (44%) were discharged on target day 8 of the EROS programme. Age and complications were independently associated with missing this discharge target.

CONCLUSION

Enhanced recovery is feasible and safe after major upper gastrointestinal surgery.

Population-based cohort study of variation in the use of emergency cholecystectomy for benign gallbladder diseases

Background

The aims of this prospective population-based cohort study were to identify the patient and hospital characteristics associated with emergency cholecystectomy, and the influences of these in determining variations between hospitals.

Methods

Data were collected for consecutive patients undergoing cholecystectomy in acute UK and Irish hospitals between 1 March and 1 May 2014. Potential explanatory variables influencing the performance of emergency cholecystectomy were analysed by means of multilevel, multivariable logistic regression modelling using a two-level hierarchical structure with patients (level 1) nested within hospitals (level 2).

Results

Data were collected on 4744 cholecystectomies from 165 hospitals. Increasing age, lower ASA fitness grade, biliary colic, the need for further imaging (magnetic retrograde cholangiopancreatography), endoscopic interventions (endoscopic retrograde cholangiopancreatography) and admission to a non-biliary centre significantly reduced the likelihood of an emergency cholecystectomy being performed. The multilevel model was used to calculate the probability of receiving an emergency cholecystectomy for a woman aged 40 years or over with an ASA grade of I or II and a BMI of at least 25·0 kg/m2, who presented with acute cholecystitis with an ultrasound scan showing a thick-walled gallbladder and a normal common bile duct. The mean predicted probability of receiving an emergency cholecystectomy was 0·52 (95 per cent c.i. 0·45 to 0·57). The predicted probabilities ranged from 0·02 to 0·95 across the 165 hospitals, demonstrating significant variation between hospitals.

Conclusion

Patients with similar characteristics presenting to different hospitals with acute gallbladder pathology do not receive comparable care.

Systematic review and meta-analysis of immunohistochemical prognostic biomarkers in resected oesophageal adenocarcinoma

BACKGROUND

Oesophageal adenocarcinoma (OAC) is one of the fastest rising malignancies with continued poor prognosis. Many studies have proposed novel biomarkers but, to date, no immunohistochemical markers of survival after oesophageal resection have entered clinical practice. Here, we systematically review and meta-analyse the published literature, to identify potential biomarkers.

METHODS

Relevant articles were identified via Ovid medline 1946-2013. For inclusion, studies had to conform to REporting recommendations for tumor MARKer (REMARK) prognostic study criteria. The primary end-point was a pooled hazard ratio (HR) and variance, summarising the effect of marker expression on prognosis.

RESULTS

A total of 3059 articles were identified. After exclusion of irrelevant titles and abstracts, 214 articles were reviewed in full. Nine molecules had been examined in more than one study (CD3, CD8, COX-2, EGFR, HER2, Ki67, LgR5, p53 and VEGF) and were meta-analysed. Markers with largest survival effects were COX-2 (HR=2.47, confidence interval (CI)=1.15-3.79), CD3 (HR=0.51, 95% CI=0.32-0.70), CD8 (HR=0.55, CI=0.31-0.80) and EGFR (HR=1.65, 95% CI=1.14-2.16).

DISCUSSION

Current methods have not delivered clinically useful molecular prognostic biomarkers in OAC. We have highlighted the paucity of good-quality robust studies in this field. A genome-to-protein approach would be better suited for the development and subsequent validation of biomarkers. Large collaborative projects with standardised methodology will be required to generate clinically useful biomarkers.

Thoracoabdominal herniation--but not as you know it

Thoracoabdominal hernias are uncommon following blunt trauma. If diaphragmatic rupture does occur, the abdominal viscera can herniate into the thorax through the diaphragm. We report a rare case of thoracoabdominal herniation in which the bowel herniated through the lateral abdominal wall, migrating cranially and entering the thorax through an intercostal defect. This case highlights the need for early and definitive surgical repair.

A prospective comparison of totally minimally invasive versus open Ivor Lewis esophagectomy

The majority of esophagectomies in Western parts of the world are performed by a transthoracic approach reflecting the prevalence of adenocarcinoma of the lower esophagus or esophagogastric junction. Minimally invasive esophagectomy (MIE) has been reported in a variety of formats, but there are no series that directly compare totally minimally invasive thoracolaparoscopic 2 stage esophagectomy (MIE-2) with open Ivor Lewis (IVL). A prospective single-center cohort study of patients undergoing elective MIE-2 or IVL between January 2005 and November 2010 was performed. Short-term clinicopathologic outcomes were recorded using validated systems. One hundred and six patients (median age 66, range 36-85, 88 M : 18 F) underwent two-stage esophagectomy (53 MIE-2 and 53 IVL). Patient demographics (age, sex, body mass index, American Society of Anesthesiologists grade, tumor characteristics, neoadjuvant chemotherapy, and TNM stage) were comparable between the two groups. Outcomes for MIE-2 and IVL were comparable for anastomotic leak rates (5 [9%] vs. 2 [4%], P= 0.241), resection margin clearance (R0) (43 [81%] vs. 38 [72%], P= 0.253), median lymph node yield (19 vs. 18, P= 0.584), and median length of stay (12 [range 7-91] vs. 12 [range 7-101] days), respectively. Blood loss was significantly less for MIE-2 compared with IVL (median 300 [range 0-1250] mL vs. 400 [range 0-3000] mL, respectively, P= 0.021). MIE-2 in this series of selected patients supports its efficacy, when performed by an experienced minimally invasive surgical team. A well-designed multicenter trial addressing clinical effectiveness is now required.

Impact of integrated PET/CT in the staging of oesophageal cancer: a UK population-based cohort study

AIM

To document the impact of integrated positron-emission tomography and computed tomography (PET/CT) on the management of a cohort of UK patients undergoing PET/CT as part of their staging investigations for potentially curable oesophageal cancer.

MATERIALS AND METHODS

A multicentre, prospective study of newly diagnosed patients with oesophageal cancer undergoing PET/CT was set up across five cancer networks covering a total population of 6.6 million. Data were prospectively collected for cases diagnosed between 1 November 2006 and 31 October 2007.

RESULTS

One hundred and ninety-one patients underwent PET/CT, with 31 (16%) positive for possible metastatic disease. Amongst the 31 positive examinations, 18 (9.4%) were confirmed to have metastatic disease, and 13 (6.5%) patients had no subsequent evidence of metastatic disease, although in three (1.6%) of these a second previously unsuspected pathology was diagnosed. Two patients had false-negative PET/CT and were found to have metastatic disease. The results of the PET/CT examination down-staged 10 (5%) patients thought to have coeliac/M1a node involvement on CT. Fifteen of 110 (13%) patients with stage 3 or 4 disease at CT and endoscopic ultrasound (EUS) had confirmed metastatic disease at PET/CT, compared with none of 18 with stage 2b, three of 52 (6%) with stage 2a, and none of 10 with stage 1 disease.

CONCLUSION

This study confirms the role of PET/CT in a multicentre UK setting in the management of patients with potentially curable carcinoma of the oesophagus, improving the accuracy of pre-treatment staging compared with CT and EUS alone. Early tumours infrequently show evidence of metastasis on PET/CT, although further data are required to confidently determine the stage of tumours where PET/CT has no additional value.

Specific blockade of morphine- and cocaine-induced reinforcing effects in conditioned place preference by nitrous oxide in mice

Nitrous oxide (N(2)O), a pharmacological active gas and an antagonist of N-methyl-D-aspartic acid receptors, has been reported to be effective in the treatment of alcohol and tobacco withdrawal syndrome. However, the neurobiological bases of N(2)O effects are unknown. The aim of the present studies was to examine the effect of N(2)O on acquisition and expression of morphine- (10 mg/kg; s.c.) and cocaine- (20 mg/kg; i.p.) induced conditioned place preference (CPP) in mice. Unbiased place conditioning method was used. Mice were exposed to N(2)O during the conditioning phase (acquisition of CPP) or during postconditioning phase (expression of CPP). The same protocol was used to evaluate the impact of N(2)O on locomotor activity, two-trial recognition task (memory), spontaneous alternation, sucrose consumption (anhedonic state), forced swim (depressive state) and elevated O-maze tests (anxiety state). In all these tests, mice were treated with morphine (10 mg/kg, s.c.) the first day, the following day mice were given saline. This sequence alternated during the next 4 days. Control animals received saline every day. The behavior of animals was evaluated on day 8. N(2)O did not induce CPP but impaired the acquisition of morphine-induced CPP and blocked the expression of cocaine- and morphine-induced CPP. The effects of the gas were long lasting and persist 4 days following the exposure. Moreover no behavioral modifications in tests usually used to investigated emotional state as compared with control mice were observed in animals exposed to N(2)O, ruling out an effect of this gas on attention, anxiety, depression, locomotion and anhedonia. These studies raise the possibility that N(2)O could have a clinical benefit in the management of morphine and cocaine addiction.

Blockade of morphine-induced behavioral sensitization by a combination of amisulpride and RB101, comparison with classical opioid maintenance treatments

BACKGROUND AND PURPOSE

Maintenance treatments with methadone or buprenorphine are more or less efficient procedures for helping heroin addicts to stop or reduce drug abuse. Another approach to treat opiate dependence could be to target the endogenous opioid system by enhancing the effects of enkephalins by protecting them from enzymic degradation by the dual peptidase inhibitor RB101.

EXPERIMENTAL APPROACH

As chronic treatment with the dopamine D2 antagonist amisulpride facilitates RB101-induced behavioral effects, we chose in this study to treat mice previously sensitized to the hyperlocomotor effects induced by morphine with a combination of amisulpride and RB101.

KEY RESULTS

Expression of morphine-induced locomotor sensitization was abolished after combined treatment with amisulpride (20 mg x kg(-1), i.p.) and RB101 (80 mg x kg(-1), i.p.), whereas these drugs were not effective when used alone. We then compared these results with the effects of amisulpride combined with buprenorphine (0.1 mg x kg(-1), i.p.) or methadone (2.5 mg x kg(-1), i.p.) upon morphine-induced behavioral sensitization. Whereas the combination of amisulpride and buprenorphine partially blocked the expression of morphine sensitization, amisulpride+methadone was not effective in this paradigm.

CONCLUSIONS AND IMPLICATIONS

The combination of amisulpride+RB101 appears to be very efficient in blocking the expression of morphine-induced behavioral sensitization. This could reflect a reinstatement of a balance between the function of the dopamine and opioid systems and could represent a new approach in maintenance treatments for opiate addiction.

Physiological control of emotion-related behaviors by endogenous enkephalins involves essentially the delta opioid receptors

The endogenous pentapeptide enkephalins bind to the mu and delta opioid receptors, with a slightly higher affinity for the latter. It remains a controversy regarding the respective physiological role of mu and delta opioid receptors in the control of emotion and motivation. One of the difficulties to investigate this problem is the low tonic extracellular release of enkephalins in various brain structures. To overcome this problem the synaptic levels of these pentapeptides were enhanced by inhibition of enzymes involved in their catabolism with the selective inhibitor H3N-CH(CH2-CH2-S-CH3)-CH2-S-S-CH2-CH(CH2phi)-CONH-CH(CH2phi)-COOCH2phi (RB101). This compound was shown to increase the extracellular levels and lifetime of endogenous enkephalins. Similar responses were obtained in wild-type and mu opioid receptor knockout mice following RB 101 administration in behavioral tests measuring locomotor activity, anxiety (elevated O-maze), and motivation (forced swim test and conditioned suppression of motility). In contrast, RB 101 led to antinociceptive responses only in wild-type animals using hot plate and tail immersion tests. These results clearly demonstrate the critical role of delta opioid receptors activated by the endogenous opioid peptides, in the physiological control of emotion- and motivation-related behaviors. In contrast, antinociceptive modulation, at least with respect to thermal nociceptive stimuli, involves enkephalin-activated mu opioid receptors. These findings could open new perspectives in the treatment of mood disorders using either inhibitors of enkephalin catabolism or delta opioid agonists.

Facilitation of enkephalins-induced delta-opioid behavioral responses by chronic amisulpride treatment

The endogenous opioid system is known to have a great influence on the dopaminergic system. Conversely, blockade of the dopaminergic system in D2 receptor knock-out mice triggers an increase in enkephalin supporting the important physiological relationship between both systems. Therefore, the aim of this study was to investigate whether or not chronic treatment with the specific D2 antagonist amisulpride (20mg/kg, i.p., twice daily for 5 days) could lead to a facilitation of behavioral effects of enkephalins, protected from their enzymatic degradation by the dual inhibitor N-[(R,S)-2-benzyl-3[(S)(2-amino-4-methylthio)butyl dithio]-1-oxopropyl]-l-phenylalanine benzyl ester (RB101) (5mg/kg, i.v.) in mice. RB101 induced an increase in locomotor activity, antidepressant-like effects in the forced swim test, and antinociceptive effects in the hot-plate test. Chronic treatment with amisulpride potentiated the action of RB101 and this effect seemed to be restricted to behavioral responses induced by opioids acting on delta-opioid receptors (locomotor activity and forced swim test). This was confirmed by the use of the selective delta-opioid receptor agonist, (+)-4-[alpha-R*)-alpha-((2S*,5R*)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80; 2.5mg/kg, i.p.), and antagonist, naltrindole (5mg/kg, i.p.). Considering the involvement of delta-opioid receptors in mood regulation, the interaction between amisulpride and RB101 could lead to a new therapeutic approach in the treatment of some mood disorders.

[Plusridisciplinary approaches to understand the neutoxic effects of Ecstasy]

Recreational use of the illicit drug ecstasy (MDMA) has increased dramatically in recent years. Although generally regarded as relatively safe, several studies have suggested a toxic effect on brain neurons in animals and possibly in humans. Others have demonstrated that the neurotoxic effects of MDMA on 5-HT neurons may be reversible, while the effects of MDMA on memory function may be long-lasting. To clearly evaluated the risks of repeated MDMA use, it is crucial to characterize its targets. Moreover, in animal, the direct injection of MDMA into the brain does not reproduce neurotoxic effects observed after peripheral administration. This fact suggests a possible implication of MDMA metabolites in the development of neurotoxicity, which should be identified. These metabolites may play a role in the long term psychological effects of MDMA. To be able to answer all, or at least most of the questions on the risks induced by repeated use of MDMA, a wide range of disciplines should be used, chemistry, genomic, proteomic and pharmacology.

Mixed-inhibitor-prodrug as a new approach toward systemically active inhibitors of enkephalin-degrading enzymes

In order to evaluate the possible advantages of potentiating the effects of the endogenous enkephalins, to obtain analgesia without the serious drawbacks of morphine, it was essential to design systemically active compounds which inhibit the two metabolizing enzymes, aminopeptidase N (APN) and neutral endopeptidase 24.11 (NEP). A new concept combining the idea of "prodrug" and "mixed inhibitor" was therefore developed. Given the high efficiency of beta-mercaptoalkylamines as APN inhibitors and of N-(mercaptoacyl) amino acids as NEP inhibitors, compounds associating these molecules through disulfide or thioester bonds, which are known to increase lipophilicity and to favor passage across the blood-brain barrier, have been synthesized. An HPLC study indicated that the disulfide bridge was resistant to serum enzymes but was cleaved by brain membrane homogenates, suggesting that the active inhibitors were released in the central nervous system. The validity of the approach was verified by the efficient antinociceptive responses obtained in the hot plate test in mice after iv administration of disulfide-containing inhibitors (ED50s of from 4 to 26 mg/kg on the jump latency time). The analgesic potencies of the "mixed inhibitor-prodrug" RB 101 [H2NCH(CH2CH2SCH3)CH2SSCH2CH(CH2Ph)CONHCH( CH2Ph)COOCH2Ph] after iv administration were three times greater than those of a similar combined dose of its two constitutive moieties. The separation of the two diastereoisomers constituting RB 101 showed that the analgesia has a stereochemical dependence, the (S,S,S)-isomer being more active than the (S,R,S)-isomer. Furthermore, in the tail flick test in the rat, RB 101 gave 38% analgesia at a dose of 80 mg/kg. Due to its high efficiency and its longer pharmacological effect, RB 101 was selected for a complete study of its analgesic properties.

Phenotypes of mice with invalidation of cholecystokinin (CCK(1) or CCK(2)) receptors

Cholecystokinin (CCK) is a peptide originally discovered in the gastrointestinal tract, but also found in high density in the mammalian brain. This peptide has been shown to be involved in numerous physiological functions such as feeding behavior, central respiratory control and cardiovascular tonus, vigilance states, memory processes, nociception, emotional and motivational responses. CCK interacts with nanomolar affinites with two different receptors designated CCK(1) and CCK(2). Primarily, the functional role of these binding sites in the brain and the periphery has been investigated thanks to the development of potent and selective CCK receptor antagonists and agonists. However, several studies have yielded conflicting data. Knockout mice provide unique opportunities to analyse diverse aspects of gene function in vivo. This review highlights recent progress in our understanding of the role of CCK(1) and CCK(2) receptors obtained by using mice with genetic invalidation of CCK(1) or CCK(2) receptors or natural CCK receptors mutants. The limits of this approach is discussed and some results were compared to those obtained by pharmacological blockade of CCK receptors by selective antagonists.

Long lasting antinociceptive properties of enkephalin degrading enzyme (NEP and APN) inhibitor prodrugs

Prodrugs of phosphinic dual inhibitors of the enkephalin degrading enzymes, neutral endopeptidase (NEP) and aminopeptidase N (APN), corresponding to the formula H(3)N(+)CH(R(1))P(O)(OR)CH(2)CH(CH(2)Bip)CONHCH(CH(3))COOCH(2)Ph, with R(1) = CH(3) or Ph and R being a benzyl ester, a S-acyl-2-thioethyl derivative, or an acyloxyalkyl group, were synthesized to improve the poor central bioavailability of their precursors. As expected, these compounds (50 mg/kg, iv or ip) induced long lasting ( approximately 2 h) antinociceptive responses in the hot plate test in mice with a ceiling effect varying between 25 and 42% of analgesia. A very rapid hydrolysis of the carboxylate ester contrasting with a slow deprotection of the phosphinate group (t(1/2) approximately 1 h) was observed in serum while 80% of free drug was obtained after 1 h incubation with brain membranes. These results account for the long duration of action observed with these prodrugs.

Facilitation of enkephalins catabolism inhibitor-induced antinociception by drugs classically used in pain management

The aim of this study was to investigate the facilitatory effects of subanalgesic or low doses of different drugs (acetylsalicylic acid, ibuprofen and morphine) on the antinociceptive responses induced by the endogenous opioid peptides, enkephalins, protected from their catabolism by the dual enkephalin-degrading enzymes inhibitor RB101. According to the analgesic profile of the three studied compounds different antinociceptive assays were used: the hot plate and formalin tests in mice, and the tail flick and paw pressure tests on inflamed paws in rats and polyarthritic rats. Facilitatory effects of subanalgesic doses of acetylsalicylic acid and ibuprofen on RB101-induced antinociceptive responses were observed in the early and late phases of the formalin test, respectively. In the hot plate, tail flick and paw pressure tests, the dose-dependent analgesic effects of RB101 were strongly potentiated by subanalgesic doses of morphine (0.5 mg/kg), while in these tests, acetylsalicylic acid and ibuprofen were unable to modify the RB101-induced antinociceptive responses. The synergism in antinociceptive effects observed with the combination of RB101 and morphine supported by isobolographic analysis, may have interesting clinical implications, considering both the lack of opiate drawbacks observed with RB101 and the high potentiation of its antinociceptive effects with very low doses of morphine.

Influence of psychiatric disorder on the controlling behaviour of mothers with 1-year-old infants. A study of women with maternal eating disorder, postnatal depression and a healthy comparison group

BACKGROUND

Certain styles of parental controlling behaviour influence child development. Work with mothers with eating disorders suggests that they may be particularly controlling of their infants.

AIMS

To examine the nature and specificity of maternal controlling behaviour in mothers with eating disorders compared with mothers who had experienced postnatal depression and a healthy comparison group.

METHOD

Mothers with eating disorders (n=34), postnatal depression (n=39) and a healthy comparison group (n=61) and their 12-month-old infants were observed during play and mealtimes, and blind ratings made of verbal and non-verbal control exerted by the mother.

RESULTS

Mothers in the eating disorder group used more verbal control, especially strong control. There were no differences between the groups on gentle verbal control and physical contact. Maternal dietary restraint was the one feature of eating disorder psychopathology associated with the use of verbal control. Marital criticism was also associated with the extent of verbal controlling behaviour.

CONCLUSIONS

Aspects of maternal control of infants were found to be specific to maternal eating disorder psychopathology.

First discrete autoradiographic distribution of aminopeptidase N in various structures of rat brain and spinal cord using the selective iodinated inhibitor [125I]RB 129

The selective and potent aminopeptidase N inhibitor [125I]RB 129 has been used for the radioautographic localization of this enzyme in rat brain, spinal cord and intestine. Brain microvessels and intestine brush-border cells were shown to present a high concentration of aminopeptidase N. Moreover, a labeling of various brain structures was observed. A very high level of binding occurred in the meninges, choroid plexus, pineal gland, paraventricular nucleus and pituitary gland. Moderate to high labeling was also observed in the cortex, caudate-putamen, subthalamic nucleus, central periaqueductal gray, thalamus, as well as in the dorsal and ventral horn of the spinal cord, which are known to contain a high concentration of enkephalins, opioid receptors and neutral endopeptidase. This co-localization confirms the physiological implication of aminopeptidase N in the inactivation of enkephalins accounting for the requirement of dual inhibition of neutral endopeptidase and aminopeptidase N to observe highly significant morphine-like effects induced by the protected endogenous opioid peptides. Aminopeptidase N was also visualized in moderate to high levels in other brain structures such as the hippocampus, nucleus accumbens, substantia nigra, hypothalamus (dorsomedial and ventromedial nuclei), raphe nucleus, pontine nucleus, inferior olive, and in high concentration in the granular layer of cerebellum. In summary, aminopeptidase N has been visualized for the first time in numerous brain areas using the selective inhibitor [125I]RB 129. This iodinated probe could allow the ex vivo and in vivo localization of aminopeptidase N in various tissues to be investigated and may also be used to evaluate quantitative changes in aminopeptidase N expression in pathological situations. Aminopeptidase N, which preferably removes NH2-terminal neutral amino acids from peptides, has probably a host of substrates. Nevertheless, a certain in vivo selectivity could be achieved by the presence of the enzyme in structures where the peptide effector and its receptors are also co-localized.

Delta9-tetrahydrocannabinol releases and facilitates the effects of endogenous enkephalins: reduction in morphine withdrawal syndrome without change in rewarding effect

Recent studies have suggested that cannabinoids might initiate the consumption of other highly addictive substances, such as opiates. In this work, we show that acute administration of Delta9-tetrahydrocannabinol in mice facilitates the antinociceptive and antidepressant-like responses elicited by the endogenous enkephalins protected from their degradation by RB 101, a complete inhibitor of enkephalin catabolism. This emphasizes the existence of a physiological interaction between endogenous opioid and cannabinoid systems. Accordingly, Delta9-tetrahydrocannabinol increased the release of Met-enkephalin-like material in the nucleus accumbens of awake and freely moving rats measured by microdialysis. In addition, this cannabinoid agonist displaced the in vivo [3H]diprenorphine binding to opioid receptors in total mouse brain. The repetitive pretreatment during 3 weeks of Delta9-tetrahydrocannabinol in mice treated chronically with morphine significantly reduces the naloxone-induced withdrawal syndrome. However, this repetitive administration of Delta9-tetrahydrocannabinol did not modify or even decrease the rewarding responses produced by morphine in the place preference paradigm. Taken together, these behavioural and biochemical results demonstrate the existence of a direct link between endogenous opioid and cannabinoid systems. However, chronic use of high doses of cannabinoids does not seem to potentiate the psychic dependence to opioids.

Overexpression of dynamin is induced by chronic stimulation of mu- but not delta-opioid receptors: relationships with mu-related morphine dependence

Several studies using selective opioid agonists or mice with a deletion of the mu-opioid receptor, have shown that morphine dependence is essentially due to chronic stimulation of mu- but not delta-opioid receptors. Because dependence is assumed to be related to persistent intracellular modifications, we have investigated modifications putatively induced by chronic activation of mu receptors with morphine or selective agonists in vitro in SH-SY5Y cells and in vivo in different strains of mice, including mice lacking the mu-opioid receptor gene. The results show a similar down-regulation and desensitization of mu and delta binding sites, whereas an overexpression of dynamin occurred only with mu agonists, strongly suggesting the relevance of this up-regulation with the opiate dependence. Moreover, translocation of overexpressed dynamin from intracellular pools to plasma membranes was observed in chronic morphine-treated rats. This recruitment could be critically involved in long-lasting changes such as alterations of axonal transport observed in opioid dependence.

Phosphinic derivatives as new dual enkephalin-degrading enzyme inhibitors: synthesis, biological properties, and antinociceptive activities

The development of dual inhibitors of the two zinc metallopeptidases, neprilysin (neutral endopeptidase) and aminopeptidase N involved in the inactivation of the opioid peptides, enkephalins, represents an attractive physiological approach in the search for new analgesics devoid of the major drawbacks of morphine. Phosphinic compounds, corresponding to the general formula H(3)N(+)-CH(R(1))-P(O)(OH)-CH(2)-CH(R(2))-CONH-CH(R(3))-COO(-), able to act as transition-state analogues and to fit the S(1), S(1)', and S(2)' subsites of both enzymes were designed. Selection of the R(1), R(2), and R(3) residues for optimal recognition of these enzymes led to the first dual competitive inhibitors with K(i) values in the nanomolar range for neprilysin and aminopeptidase N. These compounds induce potent analgesic responses after intracerebroventricular or intravenous administrations in mice (hot plate test), and several of them were shown to be, at least, 10 times more potent than the previously described dual inhibitors.

CCK-B receptor: chemistry, molecular biology, biochemistry and pharmacology

Cholecystokinin (CCK) is a peptide originally discovered in the gastrointestinal tract but also found in high density in the mammalian brain. The C-terminal sulphated octapeptide fragment of cholecystokinin (CCK8) constitutes one of the major neuropeptides in the brain; CCK8 has been shown to be involved in numerous physiological functions such as feeding behavior, central respiratory control and cardiovascular tonus, vigilance states, memory processes, nociception, emotional and motivational responses. CCK8 interacts with nanomolar affinities with two different receptors designated CCK-A and CCK-B. The functional role of CCK and its binding sites in the brain and periphery has been investigated thanks to the development of potent and selective CCK receptor antagonists and agonists. In this review, the strategies followed to design these probes, and their use to study the anatomy of CCK pathways, the neurochemical and pharmacological properties of this peptide and the clinical perspectives offered by manipulation of the CCK system will be reported. The physiological and pathological implication of CCK-B receptor will be confirmed in CCK-B receptor deficient mice obtained by gene targeting (Nagata el al., 1996. Proc. Natl. Acad. Sci. USA 93, 11825-11830). Moreover, CCK receptor gene structure, deletion and mutagenesis experiments, and signal transduction mechanisms will be discussed.

The cholecystokininB receptor is coupled to two effector pathways through pertussis toxin-sensitive and -insensitive G proteins

Previous binding studies have suggested the existence of two affinity states for type B cholecystokinin receptors (CCK(B)R), which could correspond to different coupling states of the receptor to G proteins. To test this hypothesis, we have further investigated signal transduction pathways coupled to rat CCK(B)R stably transfected in Chinese hamster ovary cells. We show that CCK(B)R are coupled to two distinct transduction pathways involving two different G proteins, a pertussis toxin-insensitive/phospholipase C pathway leading to the production of inositol phosphate and arachidonic acid, and a pertussis toxin-sensitive/phospholipase A2 pathway leading to the release of arachidonic acid. We further demonstrate that the relative degree of activation of each effector pathway by different specific CCK(B)R agonists is the same, and that a specific CCK(B)R antagonist, RB213, can differentially antagonize the two signal transduction pathways elicited by these agonists. Taken all together, these data could be explained by the recently proposed theory assuming that the receptor can exist in a three-state model in which two active conformations corresponding to the complex formed by the receptor with two different G proteins coexist. According to this model, agonists or antagonists could recognize preferentially either conformation of the activated receptor, leading to variable behavior in a system containing a single receptor type.

[Enkephalin catabolism inhibitors and antalgics of the future: from preclinical research to clinical trials]

It is now well accepted that the pain suppression effect of morphine is related to the interaction of this alkaloid with binding sites located in the central nervous system. The wide distribution of opioid receptors probably accounts for the multiplicity of pharmacological responses elicited by morphine administration, as in addition to its strong analgesic potency morphine induces side effects. Therefore, there is a critical need for new analgesics able to fulfil the gap existing between opioid analgesics and antalgics. These new analgesics could be of major interest in a number of severe pain syndromes. The discovery that the endogenous morphine-like peptides enkephalins are degraded by well-defined metabolic pathways represents a promising outlook for the development of new analgesics. The complete inhibitors of enkephalin catabolism produce their physiological effects by increasing the extracellular levels of endogenous opioid peptides released either tonically or following stimuli-evoked depolarization. Under these conditions, their effects will depend upon the magnitude and duration of the enkephalin release evoked by a particular stimulus, which probably varies in the different enkephalinergic pathways. It is expected that increasing the levels of endogenous opioid peptides would avoid serious drawbacks inasmuch as they appear related to a ubiquitous overstimulation of brain opioid receptors. Some mixed inhibitors of enkephalin degrading enzymes are now undergoing preclinical trials.

Aminophosphinic inhibitors as transition state analogues of enkephalin-degrading enzymes: a class of central analgesics

Inhibition of aminopeptidase N and neutral endopeptidase-24.11, two zinc metallopeptidases involved in the inactivation of the opioid peptides enkephalins, produces potent physiological analgesic responses, without major side-effects, in all animal models of pain in which morphine is active. Dual inhibitors of both enzymes could fill the gap between opioid analgesics and antalgics. Until now, attempts to find a compound with high affinity both for neutral endopeptidase and aminopeptidase N have failed. We report here the design of dual competitive inhibitors of both enzymes with KI values in the nanomolar range. These have been obtained by selecting R1, R2, and R3 determinants in aminophosphinic-containing inhibitors: NH2---CH(R1)P(O)---(OH)CH2---CH(R2)CONH---CH(R3)COOH, for optimal recognition of the two enkephalin inactivating enzymes, whose active site peculiarities, determined by site-directed mutagenesis, have been taken into account. The best inhibitors were 10x more potent than described dual inhibitors in alleviating acute and inflammatory nociceptive stimuli in mice, thus providing a basis for the development of a family of analgesics devoid of opioid side effects.

Binding sites and transduction process of the cholecystokininB receptor: involvement of highly conserved aromatic residues of the transmembrane domains evidenced by site-directed mutagenesis

The functional significance of the extracellular amino-terminal region and of three highly conserved aromatic residues present in the fifth (TM-V) and sixth (TM-VI) transmembrane domains of the rat cholecystokinin (CCK)B receptor, transfected in Cos-7 cells, was investigated by site-directed mutagenesis. The amino-terminal region of the CCKB receptor seemed to be weakly involved in CCK binding in that the affinities of CCK8 and selective agonists and antagonists were not modified by truncation of this region. Substitution of Phe347 in TM-VI with alanine produced a mutant receptor that displays the same affinity and selectivity as the wild-type receptor for agonists, but a slightly increased affinity for the selective CCKB antagonist L-365,260. However, the addition of saturating CCK8 concentrations to cells expressing this mutant did not result in the production of inositol phosphates, demonstrating the critical role of Phe347 in CCKB receptor to G protein coupling. Substitution of Phe227 with alanine was without effect on the affinities of CCKB ligands and on phosphoinositide turnover but modified the affinity of the CCKA antagonist L-364,718. Residue Trp351 located within the CCKB receptor TM-VI is involved in the binding of CCK8 and CCK4 and of the CCK4-based antagonist PD-134,308, as illustrated by the decreased affinities of these ligands in W351A mutant. The lower affinity for CCK8 observed with this mutated CCKB receptor accounts for the higher EC50 value for phosphotidylinositol hydrolysis. This study suggests that at least part of the binding site for the agonist is located inside the transmembrane domain of the CCKB receptor, partially overlapping that of antagonists, and gives new insights into the regions involved in the transduction process.

Synthesis and biological properties of new constrained CCK-B antagonists: discrimination of two affinity states of the CCK-B receptor on transfected CHO cells

To improve our knowledge of the bioactive conformation of CCK-B antagonists, we have developed a new series of constrained dipeptoids whose synthesis and biochemical properties are reported here. These compounds, of general structure N alpha-[(2-adamantyloxy)carbonyl]-alpha-methyltryptophanyl-(4 -X)-proline, were designed by introducing a cyclization in the structure of the previously described CCK-B/peptoid antagonist RB 210, N-[N-[(2-adamantyloxy)carbonyl]-DL-alpha-methyltryptophanyl] -N-(2-phenylethyl)glycine (Blommaert et al. J. Med. Chem. 1993, 36, 2868-2877), by means of a five-membered ring. Structure-affinity relationship studies showed that an R configuration of Trp-C alpha and a cis configuration of the pyrrolidine substituents were favorable for receptor recognition. The most potent compounds of this new series had similar affinities for the CCK-B receptor as RB 210 and proved to be far more efficient in inhibiting inositol phosphate production in CHO cells stably transfected with rat brain CCK-B receptor, with IC50 values approaching those of the commonly used antagonists L-365,260 and PD-134,308. Moreover, binding studies performed using transfected CHO cells showed that two affinity states of the CCK-B receptor can be discriminated by some of these compounds which also have different biological profiles and are therefore highly interesting tools for the biochemical and pharmacological characterization of CCK-B receptor heterogeneity.

The role of dopaminergic systems in opioid receptor desensitization in nucleus accumbens and caudate putamen of rat after chronic morphine treatment

Morphine treatment of rats (60-70 mg/kg/day, 7 days) reduced delta opioid receptor-mediated inhibition of adenylyl cyclase activity in caudate putamen without any change in regulation by mu receptors. Earlier studies suggested that dopamine D1 and mu opioid receptors that regulate adenylyl cyclase are expressed preferentially by striato-nigral neurons, whereas adenosine A2a and delta1 opioid receptors are expressed preferentially by striato-pallidal neurons. Chronic morphine treatment also resulted in a reduction of dopamine D2 receptor-mediated inhibition of A2a receptor-stimulated adenylyl cyclase. Treatment with a D2 receptor antagonist (eticlopride; 1 mg/kg/day) for 7 days reduced D1 receptor stimulation of adenylyl cyclase. In contrast, chronic treatment with a D1 receptor antagonist R(+)-7-chloro-8-dihydroxy-3-methyl-1-phenyl-2,3,4, 5-tetrahydro-1H-3-benzazepine HCL (SCH 23390; 2.5 mg/kg/day) resulted in a reduction of delta1 and delta2 opioid inhibition of adenylyl cyclase, with no change in the inhibitory activity of a mu agonist. The inhibitory activity of the D2 agonist quinelorane against adenosine A2a-activated enzyme was also reduced by this treatment. Thus chronic D1 blockade, like chronic morphine treatment, appears to cause a selective impairment of the regulation of adenylyl cyclase in A2a receptor-expressing striato-pallidal neurons. D2 receptor activation appears to play an important role in the desensitization of delta receptors, because concurrent administration of the D2 antagonist eticlopride with morphine prevented the densitization of delta and D2 receptors. Similar results were obtained in nucleus accumbens, which suggests a role for D2 receptor desensitization in the adaptive response of this brain region to chronic morphine.

Contribution of endopeptidase 3.4.24.15 to central neurotensin inactivation

The tridecapeptide, neurotensin elicits naloxone-insensitive analgesia after its intracebroventricular administration in mice. We used this central pharmacological effect to assess the putative contribution of the endopeptidase 3.4.24.15 to central inactivation of the peptide. By means of combinatorial chemistry, we previously designed the first potent endopeptidase 3.4.24.15 inhibitor. This agent, Z-(L,D)Phe psi(PO2CH2)(L,D)Ala-Lys-Met (phosphodiepryl 21), is shown here to behave as a fully specific endopeptidase 3.4.24.15 inhibitor, as demonstrated by the absence of effect on a series of other exo- and endopeptidases belonging to various classes of proteolytic activities present in murine brain membranes. Furthermore, central administration of phosphodiepryl 21 drastically prolongs the forepaw licking latency of mice tested on the hot plate and injected with sub-maximally active doses of neurotensin. Altogether, our results demonstrated that, in addition to endopeptidase 3.4.24.16, endopeptidase 3.4.24.15 likely contributes to the physiological termination of the neurotensinergic message in murine brain.

Effect of a novel selective and potent phosphinic peptide inhibitor of endopeptidase 3.4.24.16 on neurotensin-induced analgesia and neuronal inactivation

1. We have examined a series of novel phosphinic peptides as putative potent and selective inhibitors of endopeptidase 3.4.24.16. 2. The most selective inhibitor, Pro-Phe-psi(PO2CH2)-Leu-Pro-NH2 displayed a Ki value of 12 nM towards endopeptidase 3.4.24.16 and was 5540 fold less potent on its related peptidase endopeptidase 3.4.24.15. Furthermore, this inhibitor was 12.5 less potent on angiotensin-converting enzyme and was unable to block endopeptidase 3.4.24.11, aminopeptidases B and M, dipeptidylaminopeptidase IV and proline endopeptidase. 3. The effect of Pro-Phe-psi(PO2CH2)-Leu-Pro-NH2, in vitro and in vivo, on neurotensin metabolism in the central nervous system was examined. 4. Pro-Phe-psi(PO2CHH2)-Leu-Pro-NH2 dose-dependently inhibited the formation of neurotensin 1-10 and concomittantly protected neurotensin from degradation by primary cultured neurones from mouse embryos. 5. Intracerebroventricular administration of Pro-Phe-psi(PO2CH2)-Leu-Pro-NH2 significantly potentiated the neurotensin-induced antinociception of mice in the hot plate test. 6. Altogether, our study has established Pro-Phe-psi(PO2CH2)-Leu-Pro-NH2 as a fully selective and highly potent inhibitor of endopeptidase 3.4.24.16 and demonstrates, for the first time, the contribution of this enzyme in the central metabolism of neurotensin.

Association of aminopeptidase N and endopeptidase 24.15 inhibitors potentiate behavioral effects mediated by nociceptin/orphanin FQ in mice

The behavioral effects induced by central administration in mice of the endogenous ORL1 (opioid receptor-like1) ligand, nociceptin/orphanin FQ, were investigated in the absence or presence of inhibitors of aminopeptidase N (bestatin) and endopeptidase 24.15 (Z-(L,D)Phe psi(PO2CH2)(L,D)Ala-Arg-Phe) recently shown to be involved in the metabolism of the heptadecapeptide in vitro. A severe reduction in motor activity induced by nociceptin/orphanin FQ was measured in two tests (spontaneous motor activity and open field). This pharmacological effect was shown to be potentiated by the association of bestatin and Z-(L,D)Phe psi(PO2CH2)(L,D)Ala-Arg-Phe, confirming in vivo the involvement of these peptidases in nociceptin/orphanin FQ inactivation. In our conditions, these inhibitors were devoid of intrinsic effects, suggesting a low tonic regulation by the heptadecapeptide of the measured behaviour.

Nociceptin/orphanin FQ metabolism: role of aminopeptidase and endopeptidase 24.15

The endogenous opioid receptor-like1 (ORL1) ligand, nociceptin/orphanin FQ (FGGFTGARKSARKLANQ), a heptadecapeptide structurally resembling dynorphin A, has recently been identified. The wide distribution of ORL1 mRNA and nociceptin/orphanin FQ precursor in the CNS, particularly in the limbic system regions and in several areas known to be involved in pain perception, suggests that nociceptin/orphanin FQ is potentially endowed with various central functions. In general, activation and/or inactivation of regulatory peptides occur through the action of cell surface peptidases. The physiological mechanisms under which nociceptin/orphanin FQ is metabolized should lead to a better understanding of its physiological functions. Mouse brain cortical slices were incubated in medium containing the heptadecapeptide in the presence or in the absence of peptidase inhibitors. The critical sites of enzymatic cleavage are Phe1-Gly2, Ala7-Arg8, Ala11-Arg12, and Arg12-Lys13 bonds. The major role played by metallopeptidases was confirmed by the complete protection of metabolism in the presence of EDTA. Aminopeptidase N and endopeptidase 24.15 are the two main enzymes involved in nociceptin/orphanin FQ metabolism, whereas endopeptidase 24.11 (involved in enkephalin [YGGFM(L)] catabolism) does not appear critically involved in nociceptin/orphanin FQ metabolism. The physiological relevance of aminopeptidase N and endopeptidase 24.15 in the heptadecapeptide metabolism remains to be determined.

Opposite role of delta 1- and delta 2-opioid receptors activated by endogenous or exogenous opioid agonists on the endogenous cholecystokinin system: further evidence for delta-opioid receptor heterogeneity

Using the mouse caudate-putamen, where delta-opioid receptor subtypes have been shown to regulate adenylyl cyclase activity, we show in this study that endogenous enkephalins inhibit enzyme activity through activation of delta 1- and delta 2-opioid receptors. Thus, naltriben or 7-benzylidenenaltrexone as well as the delta-selective antagonist naltrindole (mixed delta 1 and delta 2 antagonist) antagonized inhibition of adenylyl cyclase activity induced by methionine- or leucine-enkephalin, while the micro-antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) was without effect. Furthermore, we have previously shown that activation of delta-opioid receptors increases cholecystokinin release in the central nervous system, resulting in a potentiation of micro-opioid antinociceptive responses, and the respective role of delta 1- and delta 2-opioid receptors in this facilitatory effect has now been evaluated. Activation of delta 2-opioid receptors, either by endogenous enkephalins protected from catabolism by the complete enkephalin-degrading enzyme inhibitor N-((R,S)-2-benzyl-3((S)(2-amino-4-methyl-thio) butyldithio)-1-oxopropyl)-L-phenyl-alanine benzyl ester (RB 101), or by the delta 2-selective agonist Tyr-D-Ser(O-tert-butyl)-Gly-Phe-Leu-Thr(O-tert-butyl) (BUBU), potentiated micro-opioid antinociceptive responses in the hot-plate test in mice. This effect was antagonized by a selective cholecystokinin-A antagonist. Activation of delta 1-opioid receptors by endogenous opioid peptides decreased the micro-opioid responses. These results suggest that stimulation of delta 2-opioid receptors potentiates micro-opioid analgesia in the hot-plate test in mice through an increase in endogenous cholecystokinin release, while activation of delta 1-opioid receptors could decrease it. Thus, the pre-existing physiological balance between opioid and cholecystokinin systems seems to be modulated in opposite directions depending on whether delta 1- or delta 2-opioid receptors are selectively activated. This is the first demonstration that endogenous enkephalins, methionine- and leucine-enkephalin, are the natural ligands of delta-opioid receptor subtypes, and that delta 2-opioid receptor activation may facilitate the endogenous cholecystokinin-related modulation of micro-opioid analgesia, while the delta 1-opioid receptors may have an inhibitory role. These results could have important applications for the characterization of opioid delta 1 and delta 2 as subtypes or subsites and in pain alleviation.

Association of enkephalin catabolism inhibitors and CCK-B antagonists: a potential use in the management of pain and opioid addiction

The overlapping distribution of opioid and cholecystokinin (CCK) peptides and their receptors (mu and delta opioid receptors; CCK-A and CCK-B receptors) in the central nervous system have led to a large number of studies aimed at clarifying the functional relationships between these two neuropeptides. Most of the pharmacological studies devoted to the role of CCK and enkephalins have been focused on the control of pain. Recently the existence of regulatory mechanisms between both systems have been proposed, and the physiological antagonism between CCK and endogenous opioid systems has been definitely demonstrated by coadministration of CCK-B selective antagonists with RB 101, a systemically active inhibitor, which fully protects enkephalins from their degradation. Several studies have also been done to investigate the functional relationships between both systems in development of opioid side-effects and in behavioral responses. This article will review the experimental pharmacology of association of enkephalin-degrading enzyme inhibitors and CCK-B antagonists to demonstrate the interest of these molecules in the management of both pain and opioid addiction.

Differences among mouse strains in the regulation by mu, delta 1 and delta 2 opioid receptors of striatal adenylyl cyclases activated by dopamine D1 or adenosine A2a receptors

It is well established that the intensity of the morphine-induced locomotor stimulatory response in rodents is genetically determined. We have evaluated the ability of mu (DAMGO). delta 1 (DPDPE) and delta 2 ([D-Ala2]deltorphin II; DT-II) selective opioid receptor agonists to inhibit receptor-activated adenylyl cyclase activity. Previous studies have shown that dopamine D1 receptors are preferentially expressed in striatonigral neurons, while adenosine A2a receptors are preferentially expressed in striatopallidal neurons. Our results indicate that in striatum of wild-type CD1 mice as in rat. mu-agonists inhibit D1-activated adenylyl cyclase, but were without inhibitory activity against A2a-activated adenylyl cyclase. In all tested mouse strains, the delta 1 selective agonist, DPDPE, inhibited the A2a-activated adenylyl cyclase but not the D1-activated enzyme. In contrast, the delta 2 agonist, DT-II, inhibited both D1 and A2a activated enzyme in all strains except DBA/2J, where DT-II did not inhibit D1-activated adenylyl cyclase. In C57BL/6J mice, which are highly sensitive to morphine-induced motor stimulation, mu agonists were potent inhibitors of A2a-activated adenylyl cyclase but did not inhibit the D1-activated enzyme, while mu opioids did not inhibit A2a-activated enzyme in DBA/2J mice which show little locomotor response to morphine. In CXBK mice, a strain with known deficiencies in mu-receptor expression, both forms of receptor-activated adenylyl cyclase were less sensitive than in CD1 mice to inhibition by DAMGO. The results suggest probable differences in the specific neural locations of opioid receptor subtypes in certain inbred strains of mice with varying sensitivities to the behavioral effects of morphine.

Differential desensitization of mu- and delta- opioid receptors in selected neural pathways following chronic morphine treatment

1. Morphine produces a plethora of pharmacological effects and its chronic administration induces several side-effects. The cellular mechanisms by which opiates induce these side-effects are not fully understood. Several studies suggest that regulation of adenylyl cyclase activity by opioids and other transmitters plays an important role in the control of neural function. 2. The aim of this study was to evaluate desensitization of mu- and delta- opioid receptors, defined as a reduced ability of opioid agonists to inhibit adenylyl cyclase activity, in four different brain structures known to be involved in opiate drug actions: caudate putamen, nucleus accumbens, thalamus and periaqueductal gray (PAG). Opiate regulation of adenylyl cyclase in these regions has been studied in control and morphine-dependent rats. 3. The chronic morphine treatment used in the present study (subcutaneous administration of 15.4 mg morphine/rat/day for 6 days via osmotic pump) induced significant physical dependence as indicated by naloxone-precipitated withdrawal symptoms. 4. Basal adenylyl cyclase in the four brain regions was not modified by this chronic morphine treatment. In the PAG and the thalamus, a desensitization of mu- and delta-opioid receptors was observed, characterized by a reduced ability of Tyr-D-Ala-Gly-(NMe)Phe-Gly-ol (DAMGO; mu), Tyr-D-Pen-Gly-Phe-D-Pen (DPDPE; delta) and [D-Ala2]-deltorphin-II (DT-II; delta) to inhibit adenylyl cyclase, activity following chronic morphine treatment. 5. The opioid receptor desensitization in PAG and thalamus appeared to be heterologous since the metabotropic glutamate receptor agonists, L-AP4 and glutamate, and the 5-hydroxytryptamine (5-HT)1A receptor agonist, R(+)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT), also showed reduced inhibition of adenylyl cyclase activity following chronic morphine treatment. 6. In the nucleus accumbens and the caudate putamen, desensitization of delta-opioid receptor-mediated inhibition without modification of mu-opioid receptor-mediated inhibition was observed. An indirect mechanism probably involving dopaminergic systems is proposed to explain the desensitization of delta-mediated responses and the lack of mu-opioid receptor desensitization after chronic morphine treatment in caudate putamen and nucleus accumbens. 7. These results suggest that adaptive responses occurring during chronic morphine administration are not identical in all opiate-sensitive neural populations.

Differential regulation of D1 dopamine receptor- and of A2a adenosine receptor-stimulated adenylyl cyclase by mu-, delta 1-, and delta 2-opioid agonists in rat caudate putamen

Inhibition and stimulation of adenylyl cyclase by opioid and D1 dopamine or A2a adenosine agonists, respectively, were characterized in the caudate putamen of rats. D1 dopamine receptors have been reported to be localized preferentially on striatonigral neurons and A2a adenosine receptors on striatopallidal neurons. The aim of the present study was to evaluate the effects of mu-[Tyr-D-Ala-Gly-(N-Me)Phe-Gly-ol (DAMGO)], delta 1-[Tyr-D-Pen-Gly-Phe-D-Pen (DPDPE)], and delta 2- ([D-Ala2]deltorphin-II [DT-II]) opioid agonists on the D1 dopamine receptor- and A2a adenosine receptor-stimulated adenylyl cyclase in membranes from rat caudate putamen. The results show that DAMGO, DPDPE, and DT-II inhibit forskolin-stimulated adenylyl cyclase [selectively antagonized by D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP; mu antagonist), 7-benzylidenenaltrexone (BNTX; delta 1 antagonist), and naltriben (NTB; delta 2 antagonist), respectively], but only mu- and delta 2-opioid agonists inhibit D1 dopamine-stimulated adenylyl cyclase (antagonized by CTOP and NTB, respectively). Furthermore, DT-II and DPDPE inhibit A2a adenosine-stimulated adenylyl cyclase (antagonized by NTB and BNTX, respectively), whereas DAMGO did not inhibit A2a adenosine-stimulated adenylyl cyclase activity. These results suggest that mu-, delta 1-, and delta 2-opioid receptors display differential localization and provide neurochemical evidence suggesting the differential location of the delta 1 and delta 2 subtypes. mu-Opioid receptors may be preferentially expressed by striatonigral neurons, delta 1-by striatopallidal neurons, and delta 2-by these two striatal efferent neuron populations.

Assessment of endogenous enkephalins efficacy in the hot plate test in mice: comparative study with morphine

The in vivo spare receptor population and the relative efficacies of morphine and the endogenous enkephalins to alleviate thermal nociceptive inputs were compared by using the mu irreversible antagonist beta-funaltrexamine (beta-FNA). Twenty-four hours after i.c.v. administration of beta-FNA at increasing concentrations (0.005-2.5 micrograms), parallel rightward shifts of both morphine and RB 101 (mixed enkephalin-degrading-enzyme inhibitor) dose-response curves, were observed, but the concentration of beta-FNA required to reduce the analgesic responses was about 10 times higher for RB 101 (0.1 microgram) than for morphine (0.01 microgram). The preferential involvement of mu receptors in the analgesic responses obtained after beta-FNA pretreatment, was supported by the inability of the delta-selective antagonist naltrindole to block these effects. In conclusion, it seems that to elicit the same antinociceptive responses, enkephalins could occupy a smaller proportion of mu opioid receptors than morphine, suggesting that the endogenous peptides have a higher efficacy.