Benzazepinone Nav1.7 blockers: potential treatments for neuropathic pain

A series of benzazepinones were synthesized and evaluated as hNa(v)1.7 sodium channel blockers. Several compounds from this series displayed good oral bioavailability and exposure and were efficacious in a rat model of neuropathic pain.

Peripheral benzodiazepine receptor-induced myocardial protection is mediated by inhibition of mitochondrial membrane permeabilization

Opening of the permeability transition pore (PTP) is a key event in ischemia-reperfusion injury and several ligands of the peripheral benzodiazepine receptor (PBR), a mitochondrial outer membrane protein possibly associated with PTP, have been demonstrated as potent cardioprotective agents. Here, we investigated the mechanisms by which the specific PBR ligand 4'-chlorodiazepam (CDZ) protected the myocardium against ischemia-reperfusion. In either global or regional models of myocardial ischemia-reperfusion in rats, CDZ reduced infarct size in a dose-dependent manner (e.g., 11 +/- 1% of the area at risk at 10 mg/kg versus 31 +/- 3% in control; p < 0.05) and to a similar extent as ischemic or diazoxide-induced preconditioning. CDZ (10 mg/kg) reduced apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling staining), restored mitochondrial recovery, improved oxidative phosphorylation parameters, and reduced mitochondrial membrane permeabilization with inhibition of cytochrome c and apoptosis-inducing factor releases. CDZ increased the resistance of mitochondria to Ca2+-induced PTP opening. All these cardioprotective effects of CDZ were associated with an improved stabilization of the association of Bcl-2 with the mitochondrial membrane and inhibition of the association of a cytosolic fragment of Bax, occurring during ischemia-reperfusion, with the outer mitochondrial membrane. In addition, the PTP opener atractyloside (20 microM) and the Bcl-2 inhibitor ethyl-2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (HA14-1) (20 microM) abrogated CDZ-induced reduction of infarct size. These results demonstrate that PBR occupancy by CDZ renders the heart more resistant to ischemia-reperfusion injury by limiting mitochondrial membrane permeabilization. This is due to a reorganization of the balance between pro- and antiapoptotic proteins of the Bcl-2 family proteins at the level of mitochondrial membranes.

Fludarabine-mediated suppression of the excision repair enzyme ERCC1 contributes to the cytotoxic synergy with the DNA minor groove crosslinking agent SJG-136 (NSC 694501) in chronic lymphocytic leukaemia cells

In this study, we set out to establish whether fludarabine could enhance the DNA interstrand crosslinking capacity of SJG-136 in primary human chronic lymphocytic leukaemia (CLL) cells and thereby offer a rationale for its clinical use in combination with SJG-136. SJG-136 rapidly induced DNA crosslinking in primary CLL cells which was concentration-dependent. Further, the level of crosslinking correlated with sensitivity to SJG-136-induced apoptosis (P=0.001) and higher levels of crosslinking were induced by the combination of SJG-136 and fludarabine (P=0.002). All of the samples tested (n=40) demonstrated synergy between SJG-136 and fludarabine (mean combination index (CI)=0.54±0.2) and this was even retained in samples derived from patients with fludarabine resistance (mean CI=0.62±0.3). Transcription of the excision repair enzyme, ERCC1, was consistently increased (20/20) in response to SJG-136 (P<0.0001). In contrast, fludarabine suppressed ERCC1 transcription (P=0.04) and inhibited SJG-136-induced ERCC1 transcription when used in combination (P=0.001). Importantly, the ability of fludarabine to suppress ERCC1 transcription correlated with the degree of synergy observed between SJG-136 and fludarabine (r²=0.28; P=0.017) offering a mechanistic rationale for the synergistic interaction. The data presented here provides a clear indication that this combination of drugs may have clinical utility as salvage therapy in drug-resistant CLL.

Efficacy of bretazenil against cortical epileptic afterdischarges increases during early ontogeny in rats

The effect of a benzodiazepine partial agonist bretazenil on cortical epileptic afterdischarges was studied in 12-, 18- or 25-day-old rat pups with implanted electrodes. Afterdischarges were induced by low-frequency stimulation of sensorimotor area four times in each animal and bretazenil (0.1; 1; 5; 10; or 25 mg/kg) and/or solvent were administered intraperitoneally between the first and second stimulation. Bretazenil was able to decrease the duration of afterdischarges as well as intensity of clonic seizures accompanying these afterdischarges in all age groups in a dose-dependent manner. The efficacy of bretazenil was age-dependent: the most marked effect on duration of afterdischarges was observed in 25-day-old rats. It is in sharp contrast with our earlier data for full agonists clonazepam and midazolam demonstrating the strongest action in the youngest group.

Implication of glucocorticoid in anti-inflammatory effects of Ro5-4864 in mouse pleurisy induced by carrageenan

Mouse pleurisy induced by carrageenan is used to determine the mechanism of anti-inflammatory action of 7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2-H-1,4-benzodiazepin-2 (Ro5-4864). Pre-treatment with Ro5-4864 inhibits different inflammatory parameters, such as neutrophil influx, MPO activity and NO levels in the early phase (4 h), as well as mononuclear cells and ADA activity in the late phase (48 h) of pleurisy. dl-Aminoglutethimide, inhibitor of steroidal synthesis, reverted the effect of Ro5-4864 on these different inflammatory parameters. Our results suggest that anti-inflammatory action of Ro5-4864 may be partly due to its capacity to inhibit leukocyte migration, as well as leukocyte activation and formation of NO by a mechanism dependent on glucocorticoids.

Influence of P-glycoprotein expression on in vitro cytotoxicity and in vivo antitumour activity of the novel pyrrolobenzodiazepine dimer SJG-136

SJG-136 is a novel pyrrolobenzodiazepine dimer analogue that acts as a minor-groove interstrand DNA cross-linking agent. The present study investigated the impact of ABCB1 (mdr-1) expression on the activity of SJG-136 using both in vitro and in vivo systems. SJG-136 was highly potent in the colon cancer cell lines HCT-116, HT-29 and SW620 (IC50 0.1-0.3 nM). However, HCT-8 and HCT-15 cells expressing significant levels of mdr-1 were less sensitive (IC50 2.3 and 3.7 nM, respectively) using a SRB assay. The cytotoxicity was increased in HCT-15 and A2780(AD) in presence of 5 microg/ml verapamil. Mdr-1 mRNA expression was determined by qRT-PCR and correlated to SJG-136 IC50s (r2=0.86, P=0.0001). Isogenic 3T3 cells expressing mdr-1 cDNA (3T3 pHamdr-1) were less sensitive to SJG-136 than the parental 3T3 cells (IC50 208 and 6.3 nM, respectively). Finally, SJG-136 (120 microg/kg/d dx5) was highly active against A2780 xenografts (SGD=275) but not A2780(AD) xenografts (SGD=67).

Ro5-4864, a peripheral benzodiazepine receptor ligand, reduces reactive gliosis and protects hippocampal hilar neurons from kainic acid excitotoxicity

The peripheral-type benzodiazepine receptor (PBR) is a critical component of the mitochondrial permeability transition pore, which is involved in the regulation of cell survival. Different forms of brain injury result in induction of the expression of the PBR in the areas of neurodegeneration, mainly in reactive glial cells. The consequences of induction of PBR expression after brain injury are unknown. To test whether PBR may be involved in the regulation of neuronal survival after injury, we have assessed the effect of two PBR ligands, Ro5-4864 and PK11195, on neuronal loss induced by kainic acid in the hippocampus. Systemic administration of kainic acid to male rats resulted in the induction of a reactive phenotype in astrocytes and microglia and in a significant loss of hilar neurons in the dentate gyrus. Administration of Ro5-4864, before the injection of kainic acid, decreased reactive gliosis in the hilus and prevented hilar neuronal loss. In contrast, PK11195 was unable to reduce reactive gliosis and did not protect hilar neurons from kainic acid. These findings suggest that the PBR is involved in control of neuronal survival and gliosis after brain injury and identify this molecule as a potential target for neuroprotective interventions.

Anxioselective anxiolytics: can less be more?

Benzodiazepines remain widely used for the treatment of anxiety disorders despite a side-effect profile that includes sedation, myorelaxation, amnesia, and ataxia, and the potential for abuse. gamma-Aminobutyric acid(A) (GABA(A)) receptor partial agonists, subtype-selective agents, and compounds combining both of these features are being developed in an attempt to achieve benzodiazepine-like efficacy without these potentially limiting side effects. This article reviews the nonclinical and clinical studies of "anxioselective" anxiolytics that target GABA(A) receptors and discusses potential mechanisms subserving an anxioselective profile.

Therapeutic effects of PKC activators in Alzheimer's disease transgenic mice

Alzheimer's disease (AD) characteristically presents with early memory loss. Regulation of K(+) channels, calcium homeostasis, and protein kinase C (PKC) activation are molecular events that have been implicated during associative memory which are also altered or defective in AD. PKC is also involved in the processing of the amyloid precursor protein (APP), a central element in AD pathophysiology. In previous studies, we demonstrated that benzolactam (BL), a novel PKC activator, reversed K(+) channels defects and enhanced secretion of APP alpha in AD cells. In this study we present data showing that another PKC activator, bryostatin 1, at subnanomolar concentrations dramatically enhances the secretion of the alpha-secretase product sAPP alpha in fibroblasts from AD patients. We also show that BL significantly increased the amount of sAPP alpha and reduced A beta 40 in the brains of APP[V717I] transgenic mice. In a more recently developed AD double-transgenic mouse, bryostatin was effective in reducing both brain A beta 40 and A beta 42. In addition, bryostatin ameliorated the rate of premature death and improved behavioral outcomes. Collectively, these data corroborate PKC and its activation as a potentially important means of ameliorating AD pathophysiology and perhaps cognitive impairment, thus offering a promising target for drug development. Because bryostatin 1 is devoid of tumor-promoting activity and is undergoing numerous clinical studies for cancer treatment in humans, it might be readily tested in patients as a potential therapeutic agent for Alzheimer's disease.

Ligands of the peripheral benzodiazepine receptor have therapeutic effects in pneumopathies in vivo

In this study, we documented the effects of different peripheral benzodiazepine receptor (PBR) ligands: PK 11195, Ro5-4864 and the newly described SSR 180575 on the development of pulmonary inflammation in vivo. To this aim, we used MRL/lpr mice that develop pathological signs similar to the human lupus erythematosus (LE) signs. We found that a chronic treatment (at 3 mg/kg per i.p. for 30 days) with PBR ligands had a significant beneficial therapeutic action and decreased the inflammatory pulmonary responses and alveolitis onset. When analyzing PBR expression in inflamed tissues, we observed that in addition to the infiltrated leukocytes, PBR was expressed in the bronchial epithelium, and especially we evidenced for the first time that PBR in expressed in Clara cells. Interestingly, we observed that PBR expression in those cells was reduced when MRL/lpr mice developed the pathology and restored upon PBR ligand treatment. These original findings support a role of PBR in pulmonary inflammatory process and suggest new therapeutic applications in auto immune disorders for specific potent PBR ligands.

Comparison of two PBR ligands with classical antiinflammatory drugs in LPS-induced arthritis in rats

The antinociceptive and anti-edematogenic effects of peripheral benzodiazepine receptor (PBR) ligands, Ro5-4864 (7-chloro-5- (4-chlorophenyl)-1,3-dihydro-1-methyl-2-H-1,4-benzodiazepine-2) and PK11195 (1-(2-chlorophenyl)-N-methyl-N(1-methylpropyl)-3-isoquinoline carboxamide), were studied in an experimental model of carrageenan/LPS -induced arthritis in rats. These effects were compared with those of indomethacin and dexamethasone. Both pre and post-treatments with PK11195 were found to be anti-edematogenic and antinociceptive. The lower dose (0.01 mg/kg) exhibited the higher anti-edematogenic effect. On the other hand, the higher dose (0.5 mg/kg) produced antinociception, but with a decreased anti-edematogenic effect. Ro5-4864 produced a negligible antinociception and anti-edematogenic effect as pretreatment, but a pro-edematogenic effect when given as post-treatment. Dexamethasone and indomethacin presented parallel and dose-dependent antinociceptive and anti-edematogenic effects. In conclusion, PK11195 can effectively diminish arthritic nociception and edema elicited by LPS, but probably by mechanisms different from those of dexamethasone or indomethacin. RO5-4864 seemed to have opposite effect on this model.

A randomised, double blind, placebo controlled crossover study of the cholecystokinin 2 antagonist L-365,260 as an adjunct to strong opioids in chronic human neuropathic pain

The aim of this study was to establish if the cholecystokinin (CCK) 2 antagonist L-365,260 augments the analgesic effect of morphine in human subjects with chronic neuropathic pain. This is a randomised, double blind, placebo controlled study of 40 adult subjects taking morphine for neuropathic pain. Each received placebo, L-365,260 30 mg and L-365,260 120 mg in three divided doses daily separated by a washout period in random order. Pain, activity, sedation, sleep and side effects were recorded along with 12 lead ECGs, renal and liver function tests and full blood pictures. L-365,260 failed to augment the analgesic effect of morphine at any of the dose levels used. Side effects were minor. There were no changes in ECGs and biochemical indices were unaltered with its use. The CCK 2 antagonist L-365,260 does not augment the analgesic effect of morphine in subjects with chronic neuropathic pain. L-365,260 was well tolerated and side effects from its use were minor.

A phase 1 study of the cholecystokinin (CCK) B antagonist L-365,260 in human subjects taking morphine for intractable non-cancer pain

To investigate the safety and tolerability of L-365,260 in human subjects taking morphine for intractable pain. An open label study of nine adult subjects. Two doses of L-365,260 were administered to all subjects separated by a 4 h interval (three received 10 mg, three 30 mg and three 60 mg). Haemodynamic and respiratory variables were recorded from immediately prior to first drug administration to T + 600 min. In addition, continuous electrocardiogram (ECG) monitoring and serial 12 lead ECGs were recorded along with pain and side effect measurements. No major side effects were observed. L-365,260 was well tolerated. No abnormalities in blood pressure, heart rate, respiratory rate or ECG measurements were recorded. Minor side effects were observed. L-365,260 can be safely administered at the doses investigated to human subjects receiving morphine for intractable pain.

Group III mGlu receptor agonists potentiate the anticonvulsant effect of AMPA and NMDA receptor block

We report the anticonvulsant action in DBA/2 mice of two mGlu Group III receptor agonists: (R,S)-4-phosphonophenylglycine, (R,S)-PPG, a compound with moderate mGlu8 selectivity, and of (1S,3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid, ACPT-1, a selective agonist for mGlu4alpha receptors. Both compounds, given intracerebroventricularly at doses which did not show marked anticonvulsant activity, produced a consistent shift to the left of the dose-response curves (i.e. enhanced the anticonvulsant properties) of 1-(4'-aminophenyl)-3,5-dihydro-7,8-dimethoxy-4H-2,3-benzodiazepin-4-one hydrochloride, CFM-2, a noncompetitive AMPA receptor antagonist, and 3-((+/-)-2-carboxypiperazin-4-yl)-1-phosphonic acid, CPPene, a competitive NMDA receptor antagonist, in DBA/2 mice. In addition, (R,S)-PPG and ACPT-1 administered intracerebroventricularly prolonged the time course of the anticonvulsant properties of CFM-2 (33 micromol/kg, i.p.) and CPPene (3.3 micromol/kg, i.p.) administered intraperitoneally. We conclude that modest reduction of synaptic glutamate release by activation of Group III metabotropic receptors potentiates the anticonvulsant effect of AMPA and NMDA receptor blockade.

Non-nucleoside HIV-1 reverse transcriptase (RT) inhibitors: past, present, and future perspectives

Along with nucleoside reverse transcriptase inhibitors (NRTIs) and protease inhibitors (PIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs) have gained a definitive and important place in the treatment of HIV-1 infections, and are in rapid development. These compounds can be grouped into two classes: the first generation NNRTIs, mainly discovered by random screening, and the second generation NNRTIs, developed as a result of comprehensive strategies involving molecular modelling, rationale-based drug synthesis, biological and pharmacokinetic evaluations. The recent boom of NNRTIs is mainly due to their antiviral potency, high specificity and low toxicity. The rapid emergence of drug-resistant HIV-1 strains induced by the first generation drugs is a disadvantage bypassed, in part, by the broad spectrum second generation NNRTIs. Starting from the first generation, this review will focus on the second generation NNRTIs dealing with the recent and most interesting published results, highlighting the guidelines for the development of a third generation of NNRTIs.

Peripheral benzodiazepine receptor ligands reverse apoptosis resistance of cancer cells in vitro and in vivo

The mitochondrial peripheral benzodiazepine receptor (mPBR) is involved in a functional structure designated as the permeability transition pore, which controls apoptosis. Binding of Fas/APO-1/CD95 triggers a prototypic apoptosis-inducing pathway. Using four different human tumor cell lines (T-cell Jurkat, neuroblastoma SHEP, osteosarcoma 143N2, and glioblastoma SNB79 cell lines), all of which express CD95 and mPBR, we investigated the potential role of mPBR ligands in CD95-induced apoptosis. We show that, in vitro, the three mPBR ligands tested (RO5-4864, PK11195, and diazepam) enhanced apoptosis induced by anti-CD95 antibody in Jurkat cells, as demonstrated by mitochondrial transmembrane potential drop and DNA fragmentation. In contrast, RO5-4864, but not PK11195 or diazepam, enhanced anti-CD95 apoptosis in all other cell lines. These effects were obtained in Bcl-2-overexpressing SHEP cell lines, but not in Bcl-X(L) SHEP cell lines. Enhancement of anti-CD95 antibody-induced apoptosis by RO5-4864 was characterized by an increased mitochondrial release of cytochrome c and Smac/DIABLO proteins and an enhanced activation of caspases 9 and 3, suggesting a mitochondrion-dependent mechanism. Preincubation of cells with the different mPBR ligands or anti-CD95 did not affect the levels of expression of either mPBR or CD95. In vivo, we found that the RO5-4864 mPBR ligand significantly increased the growth inhibition induced by two chemotherapeutic agents, etoposide and ifosfamide, using two human small cell lung cancers xenografted into nude mice. Peripheral benzodiazepine receptor ligands may therefore act as chemosensitizing agents for the treatment of human neoplasms.

Enhanced anticonvulsant activity of neuroactive steroids in a rat model of catamenial epilepsy

PURPOSE

Perimenstrual catamenial epilepsy may in part be due to withdrawal of the endogenous progesterone-derived neurosteroid allopregnanolone that potentiates gamma-aminobutyric acidA (GABA(A)) receptor-mediated inhibition. Here we sought to determine whether the anticonvulsant potencies of neuroactive steroids, benzodiazepines, phenobarbital (PB), and valproate (VPA) are altered during the heightened seizure susceptibility accompanying neurosteroid withdrawal in a rat model of perimenstrual catamenial epilepsy.

METHODS

Test drugs were evaluated for their ability to alter the convulsant activity of pentylenetetrazol (PTZ) in young adult female rats, in pseudopregnant rats with prolonged exposure to high levels of progesterone (and its neurosteroid metabolites), and in pseudopregnant rats 24 h after acute withdrawal of neurosteroids by treatment with the 5alpha-reductase inhibitor finasteride. Test drugs were administered at doses equivalent to twice their ED50 values for protection against PTZ-induced clonic seizures in naive young adult female rats.

RESULTS

The anticonvulsant activity of allopregnanolone (5 mg/kg, s.c.), pregnanolone (5 mg/kg, s.c.), allotetrahydrodeoxycorticosterone (15 mg/kg, s.c.), and tetrahydrodeoxycorticosterone (10 mg/kg, s.c.) were enhanced by 34-127% after neurosteroid withdrawal. The anticonvulsant activity of PB (65 mg/kg, i.p.) was also enhanced by 24% in neurosteroid-withdrawn animals. In contrast, the anticonvulsant activity of diazepam (4 mg/kg, i.p.), bretazenil (0.106 mg/kg, i.p.), and VPA (560 mg/kg, i.p.) were reduced or unchanged in neurosteroid-withdrawn animals.

CONCLUSIONS

The anticonvulsant activity of neuroactive steroids is potentiated after neurosteroid withdrawal, supporting the use of such agents in the treatment of perimenstrual catamenial epilepsy.

Anti-depressant action of melatonin in chronic forced swimming-induced behavioral despair in mice, role of peripheral benzodiazepine receptor modulation

The possible antidepressant effect of physiological and pharmacological doses of melatonin was investigated in the Porsolt forced swimming-induced behavioral despair test. The duration of immobility period of BALB/c and C57BL/6J mice during a 6-min swim test was measured at noon (11:00-12:00 h), early dark (20:00-21:00 h) and at midnight (1:00-2:00 h), respectively. The circadian time cycle did not alter the duration of immobility in either strains of mice. Similarly, exogenously administered melatonin (10-1000 microg/kg congruent with 50 nM to 5 microM/mouse), a dose that could act on high affinity melatonin receptors, did not modify the duration of immobility period at any of the time intervals studied in either strains of the mice. This suggested that neither circadian variation influenced the duration of immobility period of BALB/c and C57BL/6J mice nor at physiological doses melatonin showed any anti-depressant action. Acute administration of higher doses of melatonin (2.5-10 mg/kg) failed to induce any anti-depressant activity in mice which were subjected to forced swimming test for the first time. However, daily administration of melatonin (2.5-10 mg/kg) prior to swimming test significantly reversed the increase in immobility period that was observed on chronic exposure to swimming test. This effect was comparable with the effect of GABA-benzodiazepine (BZ) receptor agonists. Similarly, like GABAergic drugs, acute administration of melatonin also showed anti-depressant activity in a mice which were exposed to chronic forced swimming test. The anti-depressant action of melatonin was sensitive to reversal by peripheral BZ receptor antagonist, PK11195. Whereas, flumazenil failed to reverse the anti-depressant action of melatonin, thereby suggesting that central BZ receptor were not involved in its action. In conclusion the study showed that at pharmacological doses melatonin has anti-depressant action in chronic forced swimming-induced despair behavior by an action involving peripheral BZ receptors.

Cholecystokinin-B/gastrin receptors enhance wound healing in the rat gastric mucosa

Although physiological functions of the CCK-B/gastrin receptor are well explored, little is known about its role during healing. Here, we evaluated the role of this receptor in the rat oxyntic mucosa following the introduction of a cryoulcer. In this model, we located and quantified CCK-B/gastrin receptors by reverse transcriptase PCR and receptor autoradiography. Rats with cryoulcers were treated with placebo, omeprazole, the CCK-B/gastrin receptor antagonist YF-476, omeprazole plus YF-476, gastrin-17, and gastrin 17 plus YF-476. During wound healing, CCK-B/gastrin receptors were specifically expressed and localized to the regenerative mucosal ulcer margin. This high expression was limited in time, and the pattern of expression of CCK-B/gastrin receptors correlated closely with the proliferative activity of the regenerative mucosa. Functionally, omeprazole and gastrin-17 caused profound hypergastrinemia, increased cell proliferation in the mucosal ulcer margin and accelerated the late ulcer healing phase. These effects were completely reversed by cotherapy with YF-476. These in vivo and vitro data suggest that CCK-B/gastrin receptors in regenerative rat gastric oxyntic mucosa enhance trophic effects during wound healing.

Supraspinal cholecystokinin may drive tonic descending facilitation mechanisms to maintain neuropathic pain in the rat

Complete or partial spinal section at T(8) has been shown to block tactile allodynia but not thermal hyperalgesia following L(5)/L(6) spinal nerve ligation (SNL), suggesting the supraspinal integration of allodynia in neuropathic pain. In the present study, the possibility of mediation of nerve injury-associated pain through tonic activity of descending nociceptive facilitation arising from the rostroventromedial medulla (RVM) was investigated. Specifically, the actions of brainstem cholecystokinin and the possible importance of sustained afferent input from injured nerve fibers were determined using pharmacological and physiological approaches in rats with SNL. Lidocaine given bilaterally into the RVM blocked tactile allodynia and thermal hyperalgesia in SNL rats and was inactive in sham-operated rats. Bilateral injection of L365,260 (CCK(B) receptor antagonist) into the RVM also reversed both tactile allodynia and thermal hyperalgesia. Microinjection of CCK-8 (s) into the RVM of naive rats produced a robust tactile allodynic effect and a more modest hyperalgesia. CCK immunoreactivity was not significantly different between SNL and sham-operated rats. The anti-nociceptive effect of morphine given into the ventrolateral periaqueductal gray region (PAG) was substantially reduced by SNL. The injection of L365,260 into the RVM or of bupivacaine at the site of nerve injury restored the potency and efficacy of PAG morphine in SNL rats. These results suggest that changes in supraspinal processing are likely to contribute to the observed poor efficacy of opioids in clinical states of neuropathic pain. These data also indicate that the activation of descending nociceptive facilitatory pathways is important in the maintenance of neuropathic pain, appears to be dependent on CCK release, and may be driven from sustained afferent input from injured nerves to brainstem sites. Collectively, these data support the hypothesis that abnormal tonic activity of descending facilitation mechanisms may underlie chronic pain from peripheral nerve injury.

Antiarrhythmic efficacy of selective blockade of the cardiac slowly activating delayed rectifier current, I(Ks), in canine models of malignant ischemic ventricular arrhythmia

BACKGROUND

To date, the lack of potent and selective inhibitors has hampered the physiological assessment of modulation of the cardiac slowly activating delayed rectifier current, I(Ks). The present study, using the I(Ks) blocker L-768,673, represents the first in vivo assessment of the cardiac electrophysiological and antiarrhythmic effects of selective I(Ks) blockade.

METHODS AND RESULTS

In an anesthetized canine model of recent (8.5+/-0.4 days) anterior myocardial infarction, 0.003 to 0.03 mg/kg L-768,673 IV significantly suppressed electrically induced ventricular tachyarrhythmias and reduced the incidence of lethal arrhythmias precipitated by acute, thrombotically induced posterolateral myocardial ischemia. Antiarrhythmic protection afforded by L-768,673 was accompanied by modest 7% to 10% increases in noninfarct zone ventricular effective refractory period, 3% to 5% increases in infarct zone ventricular effective refractory period, and 4% to 6% increases in QTc interval. In a conscious canine model of healed (3 to 4 weeks) anterior myocardial infarction, ventricular fibrillation was provoked by transient occlusion of the left circumflex coronary artery during submaximal exercise. Pretreatment with 0.03 mg/kg L-768,673 IV elicited a modest 7% increase in QTc, prevented ventricular fibrillation in 5 of 6 animals, and suppressed arrhythmias in 2 additional animals.

CONCLUSIONS

The present findings suggest that selective blockade of I(Ks) may be a potentially useful intervention for the prevention of malignant ischemic ventricular arrhythmias.

Combination treatment of hepatic encephalopathy due to thioacetamide-induced fulminant hepatic failure in the rat with benzodiazepine and opioid receptor antagonists

BACKGROUND/AIMS

Treatment of hepatic encephalopathy with drugs acting on the target organ of this syndrome, the brain, is unsatisfactory. Combination treatment with different neurotransmitter receptor antagonists may be a rational option to optimize treatment.

METHODS

The effects of various doses of the benzodiazepine receptor antagonist Ro 15-3505 and the opioid receptor antagonist naloxone, alone or in combination, were tested on hepatic encephalopathy in rats with thioacetamide-induced hepatic failure in an open-field activity meter. Comparison of single and combination treatment was also done using a neurological test battery. In addition, we compared survival of treatment-responder rats with treatment non-responders.

RESULTS

Naloxone dose dependently increased ambulatory activity and improved neurological score. Ro 15-3505 also improved ambulatory activity and neurological score; however, the improvement was less evident at higher doses. Combination treatment was not superior to single treatment. Survival was increased in treatment-responder rats.

CONCLUSIONS

The failure of combination treatment with Ro 15-3505 and naloxone to further improve hepatic encephalopathy may suggest that the two neurotransmitter systems are interrelated or that hepatic encephalopathy may not be further improved by drugs acting on the brain.