Stimulation of either cholecystokinin receptor subtype reduces while antagonists potentiate or sensitize a morphine-induced excitatory response.

Cholecystokinin peptides (CCK) have been shown to antagonize many opioid-mediated effects. The present study was undertaken to determine whether peripheral injections of cholecystokinin sulphated octapeptide (CCK8), cholecystokinin tetrapeptide (CCK4), the CCK(1) (lorglumide) and the CCK(2) (PD-135,158 and LY-225910) receptor antagonists can influence a classic morphine excitatory effect, i.e. the display of Straub tail reaction in mice (STR). A total of 570 female Balb/C mice were tested. Experiment 1 was undertaken to determine whether i.p. injections of CCK8 or CCK4 can influence STR. Each animal was treated with i.p. injections of saline or CCK8 (10 and 20 nmol/kg) or CCK4 (20 and 40 nmol/kg). After 30 min all animals received an i.p. injection of morphine hydrochloride (10.0 mg/kg). The highest doses of both CCK8 (35% STR) and CCK4 (40% STR) significantly reduced STR as compared to saline (85% STR) treated mice (Fisher test; P < 0.01). In experiment 2 each animal was treated with ip injections of saline or 1.0 mg/kg lorglumide or PD-135,158 fifteen minutes before an injection of morphine at doses ranging from 1.0 to 50.0 mg/kg. In experiment 3 animals were treated with injections of saline, 0.1 or 10.0 mg/kg lorglumide or LY-225910 before an injection of a fixed MC dose (2.0 mg/kg). Both lorglumide and PD-135,158 induced a significant shift to the left in the morphine dose-response curves as well as a significant decrease in ED50 of the STR. ED50 for lorglumide was significantly lower than ED50 for PD-135,158. Both doses of lorglumide and the highest dose of LY-225910 significantly increased the percent of animals displaying STR. Experiment 4 was undertaken to determine whether repeated peripheral injections of morphine or the morphine-potentiating agents CCK(1) (lorglumide) and the CCK(2) (LY-225910) receptor antagonists can induce morphine sensitization. Each animal was treated with 5 daily i.p. injections of saline (control group), 1.5 mg/Kg morphine hydrochloride (group morphine), and 1.0 mg/Kg lorglumide (group LOR) or LY-225910 (group LY). One, two, three and four weeks after the last treatment day, all animals were challenged with one i.p. injection of morphine (1.5 mg/Kg). The morphine, LOR groups and group LY showed a significant increase in percentage of animals displaying STR. These data demonstrate that the blockade of endogenous CCK actions leads to morphine sensitization probably through both CCK receptors. The present data are consistent with the antagonistic effects of CCK and opioids in the control of morphine-induced STR. In addition, these results suggest that both CCK receptors are involved in the modulatory effects of CCK on this morphine effect.     

Modulation of acute morphine tolerance by corticotropin-releasing factor and dynorphin A in the mouse spinal cord.

Previously, we have demonstrated that intrathecally (i.t.) administered corticotropin-releasing factor (CRF) in mice produces stimulus-specific antinociception and modulation of morphine-induced antinociception by mechanisms involving spinal kappa opioid receptors. Recently, we also have found that CRF releases immunoreactive dynorphin A, a putative endogenous kappa opioid receptor agonist, from superfused mice spinal cords in vitro. Dynorphin A administered intracerebroventricularlly (i.c.v.) to mice has been shown to modulate the expression of morphine tolerance. In the present study, the possible modulatory effects of i.t. administered CRF as well as dynorphin A on morphine tolerance were studied in an acute tolerance model. Subcutaneous administration of 100 mg/kg of morphine sulfate (MS) to mice caused an acute tolerance to morphine-induced antinociception. The antinociceptive ED50 of MS was increased from 4.4 mg/kg (naive mice) to 17.9 mg/kg (4 hours after the injection of 100 mg/kg MS). To study the modulatory effects of spinally administered CRF and dynorphin A on the expression of morphine tolerance, CRF and dynorphin A were injected i.t. at 15 min and 5 min, respectively, before testing the tolerant mice by the tail-flick assay. The antinociceptive ED50 of MS in tolerant mice was decreased to 8.8 mg/kg and 7.1 mg/kg, respectively, after i.t. administration of CRF (0.1 nmol) and dynorphin A (0.2 nmol). In contrast, 0.5 nmol of alpha-helical CRF (9-41), a CRF antagonist and 0.4 nmol of norbinaltorphimine, a highly selective kappa opioid receptor antagonist, when administered i.t. at 15 min before the tail-flick test in tolerant mice, increased the antinociceptive ED50 of MS to 56.6 mg/kg and 88.8 mg/kg, respectively. These data confirmed the modulatory effect of dynorphin A on morphine tolerance and suggested that CRF, which releases dynorphin A in several central nervous system regions, also plays a modulatory role in the expression of morphine tolerance.     

ACUTE ETHANOL EXPOSURE DECREASES THE ANALGESIC POTENCY OF MORPHINE IN MICE

Chronic (7 days), forced ethanol drinking can decrease the analgesic potency of opioid agonists in mice. In the present study, the effect of short-term ethanol treatment was examined using forced ethanol access and ethanol injection protocols. Mice were given forced access to 1, 3 or 7% (v/v) ethanol for 24 hr and then tested for s.c. morphine analgesia using the tailflick assay. Controls had access to water. Another group of mice was injected i.p. with 2.5 g/kg ethanol or water 4 times over a 21 hr period and tested 3 hr after the final injection for morphine analgesia. Other mice were injected once i.p. with 1, 2 or 3 g/kg ethanol or water and tested 24 hr later using the tailflick. In the forced access study, ethanol dose-dependently decreased morphine's analgesic potency with the highest dose (7%) producing a 1.6-fold shift in the ED₅₀. This decrease in morphine potency was similar to that found in a related study using 7% ethanol for 7 days (1.8-fold shift). Repeated ethanol injections significantly reduced the analgesic potency of morphine (1.9-fold shift), whereas, a single injection of 1, 2 or 3 g/kg ethanol did not alter the potency of morphine. Control studies indicated that neither 24 hr water nor food deprivation affected morphine potency. Overall, these data show that sustained exposure to ethanol over a 24 hr period will dose-dependently decrease morphine's analgesic potency. © 1998 Elsevier Science Inc.     

The role of T-type calcium channels in morphine analgesia,development of antinociceptive tolerance and dependence to morphine,and morphine abstinence syndrome

Involvement of T-type voltage dependent Ca2+ channels (VDCCs) on morphine antinociception, in the development of tolerance and dependence to morphine, and naloxone-precipitated abstinence syndrome in morphine dependent mice was examined by using mibefradil, a T-type VDCCs blocker. Mice were rendered tolerant and dependent on morphine by subcutaneous (s.c.) implantation of a morphine pellet containing 75 mg of morphine base for 72 hr. The tail-flick test was used to assess the nociceptive threshold. Coadministration of acute mibefradil (10 mg/kg, i.p.) with morphine enhanced the antinociceptive effects of acute morphine. Repeated mibefradil administration (10 mg/kg, i.p., just before, 24 and 48 hr after morphine pellet implantation) completely blocked the development of tolerance to the antinociceptive effect of morphine and even by this effect reached supersensitivity to morphine. However, repeated mibefradil treatment did not alter the development of dependence to morphine assessed by the A(50) values of naloxone (s.c.) required to precipitate withdrawal jumping 72 hr after morphine pellet. But, acute mibefradil (10, 30, and 50 mg/kg, i.p.) dose dependently decreased the expression of morphine abstinence syndrome when given directly 30 min prior to naloxone (0,05 mg/kg, s.c.) 72 hr after morphine pellet. These results indicate a critical role of T-type VDCCs in morphine antinociception, the development of tolerance to the antinociceptive effects of morphine and in morphine abstinence syndrome.     

Effect of methamphetamine on the development of acute morphine tolerance and dependence in mice

The effect of methamphetamine on morphine analgesia (tail-flick assay) was studied in non-tolerant mice and in mice made acutely tolerant to morphine following a single injection of 100 mg/kg morphine. The analgesic potency of morphine was increased in non-tolerant and tolerant mice to the same extent by 3.2 mg/kg methamphetamine (3.3 and 4.4 fold increases, respectively). In contrast, the ED50's for morphine analgesia and naloxone-precipitated jumping in mice pretreated with either 100 mg/kg morphine or both morphine and 3.2 mg/kg methamphetamine were not significantly different, indicating that methamphetamine had no effect on the development of acute morphine tolerance and dependence. Although methamphetamine had no effect on the development of acute tolerance to morphine, 4-day pretreatment with methamphetamine produced cross-tolerance to morphine analgesia. However, cross-tolerance to morphine was not accompanied by enchanced sensitivity to naloxone.     

Modification of Morphine-induced Hyperlocomotion and Antinociception in Mice by Clorgyline,a Monoamine Oxidase-A Inhibitor

We evaluated the effects of pretreatment with clorgyline, an irreversible monoamine oxidase (MAO)-A inhibitor, on morphine-induced hyperlocomotion and antinociception. A single administration of morphine (30 mg/kg, i.p.) to male ICR mice induced a hyperlocomotion. ANOVA analysis revealed the statistical significance of the morphine effect on horizontal locomotion and of the clorgyline pretreatment × morphine interaction effect, but not of the effect of clorgyline pretreatment. The initial (5 min after challenge) phase of morphine actions vs. saline challenge appeared as if morphine had a strong inhibitory effect on locomotor activity in combination with different doses of clorgyline. The mice administered with morphine in combination of clorgyline (1 and 10 mg/kg) did not show any stereotypic behaviors. Clorgyline at a dose of 0.1 mg/kg but not other doses tested significantly potentiated morphine-induced antinociception evaluated by tail flick but not hot plate test. During the measurements of locomotor activity and antinociception, clorgyline at doses of 1 and 10 mg/kg significantly inhibited monoamine metabolism through MAO. These results suggest that clorgyline showed an inhibitory effect on morphine-induced hyperlocomotion, but not antinociception, through MAO inhibition. There is not a possibility that clorgyline pretreatment enhanced morphine action on motor activity, resulting in the abnormal behavior from hyperlocomotion to stereotypic movements.     

Antinociceptive properties of the methanolic extract and two triterpenes isolated from Epidendrum Mosenii stems (Orchidaceae)

The antinociceptive effect of the methanolic extract (ME) and two triterpenes isolated from E. mosenii (Orchidaceae) has been investigated in chemical and thermal models of nociception in mice. The ME of E. mosenii (0.3-30 mg kg(-1), i.p. or 50-400 mg kg(-1), p.o.) produced dose-related, significant and long-lasting (4 to 6 h) inhibition of acetic acid-induced abdominal constriction, with ID50 values of 3.9 and 137.0 mg kg(-1), respectively. Pholidotin and 24-methylenecycloartenol isolated from E. mosenii (0.1-3.0 mg kg(-1), i.p.) also produced marked and dose-related inhibition of acetic acid-induced pain, with ID50 values of 0.9 and 1.1 mg kg(-1). However, these compounds and the ME were about 3- to 13-fold more potent at the level of ID50 than diclofenac when assessed in acetic acid-induced abdominal constriction. The ME of E. mosenii in the same range of doses produced dose-related inhibition of both phases of formalin-induced licking, with mean ID50 values for the first and the second phases of 0.9, 122.0 mg kg(-1) and 0.7, 258.0 mg kg(-1), respectively by i.p. or p.o. routes. In addition, the ME (0.3-30 mg kg(-1), i.p., or 50-400 mg kg(-1), p.o.) also caused dose-related inhibition of capsaicin-induced neurogenic pain with mean ID50 values of 5.2 and 130.0 mg kg(-1), respectively. Treatment of animals with naloxone (5 mg kg(-1), i.p.) completely reversed the antinociceptive effect caused by morphine (5 mg kg(-1), s.c.) and that caused by ME of E. mosenii (1 mg kg(-1), i.p.) when assessed against either phase of the formalin-induced pain. Furthermore, when assessed in the hot-plate test, ME (100 mg kg(-1), i.p.) and morphine (10 mg kg(-1), s.c.) caused significant increase in response latency. However, ME given daily for to 7 consecutive days did not develop tolerance to itself nor did it induce cross-tolerance to morphine. Taken together these data demonstrate that the ME of E. mosenii elicited pronounced antinociception, when assessed by i.p. or p.o. routes, against several models of pain. Its actions involve, at least in part, an interaction with opioid system, seeming no to be related with a non-specific peripheral or central depressant actions. Finally, the active principle(s) responsible for the antinociceptive action of E. mosenii is likely related to the presence of the triterpenes.     

Novel (S)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acids: peroxisome proliferator-activated receptor γ selective agonists with protein-tyrosine phosphatase 1B inhibition

A novel series of 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid derivatives were synthesized and (S)-2-[(2E,4E)-hexadienoyl]-7-(2-{5-methyl-2-[(1E)-5-methylhexen-1-yl]oxazol-4-yl}ethoxy)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (14i) was identified as a potent human peroxisome proliferator-activated receptor γ (PPARγ) selective agonist (EC(50)=0.03 μM) and human protein-tyrosine phosphatase 1B (PTP-1B) inhibitor (IC(50)=1.18 μM). C(max) after oral administration of 14i at 10mg/kg was 2.2 μg/ml (4.5 μM) in male SD rats. Repeated administration of 14i and rosiglitazone for 14 days dose-dependently decreased plasma glucose levels, ED(50)=4.3 and 23 mg/kg/day, respectively, in male KK-A(y) mice. In female SD rats, repeated administration of 14i at 12.5-100mg/kg/day for 28 days had no effect on the hematocrit value (Ht) and red blood cell count (RBC), while rosiglitazone significantly decreased them from 25mg/kg/day. In conclusion, 14i showed about a fivefold stronger hypoglycemic effect and fourfold or more weaker hemodilution effect than rosiglitazone, indicating that 14i is 20-fold or more safer than rosiglitazone. Compound 14i is a promising candidate for an efficacious and safe anti-diabetic drug targeting PPARγ and PTP-1B.     

Evaluation of the antinociceptive action caused by ether fraction and a triterpene isolated from resin of Protium kleinii.

This study investigates the antinociception caused by i.p. and p.o. administration of ether fraction and the triterpene identified as urs-12-ene-3beta-16beta-diol, known as Brein, isolated from Protium kleinii in several models of nociception in mice. The systemic administration of ether fraction (0.3 to 10 mg/kg, i.p. or 3 to 60 mg/kg, p.o.) caused a dose-related antinociception when assessed against acetic acid-induced writhing, with mean ID50 values of 1.2 and 16.4 mg/kg, respectively. The ether fraction (5 to 60 mg/kg, i.p. or 30 to 300 mg/kg, p.o.) also produced dose-related inhibition of both phases of formalin induced licking. The mean ID50s values for the early phase were > 60.0 and 62.1 mg/kg, while for the late phase they were 15.4 and 60.0 mg/kg, respectively, given by i.p. and p.o. routes. The ether fraction (3 to 30 mg/kg, i.p. or 10 to 100 mg/kg, p.o.) produced significant inhibition of the neurogenic nociception caused by topical injection of capsaicin, with mean ID50 values of 6.2 and 16.0 mg/kg, respectively. Given orally (1 to 30 mg/kg) the ether fraction produced graded and pronounced inhibition of glutamate-induced hyperalgesia in mice with a mean ID50 value of 15.2 mg/kg. In contrast, the ether fraction failed to produce antinociception when assessed in the thermal model of pain, the tail flick and hot plate tests. The antinociception caused by the ether fraction, in contrast to that of morphine, was not reversed by naloxone when assessed in the formalin-induced licking. The ether fraction did not affect motor coordination or the core body temperature in mices. The triterpene Brein isolated from P. kleinii, given by i.p. route (10 to 100 mg/kg) produced dose-related inhibition of both phases of formalin induced-licking, with mean ID50s values of 15.3 and 20.6 for the early and the late phases, respectively. These data show that the active principle(s) present in the ether fraction from the resin of P. kleinii elicited pronounced antinociception when assessed by i.p. or p.o routes, against both inflammatory and neurogenic nociception. Such effects seem, at least in part, to be related to the presence of the triterpene Brein in the extract. The mechanisms responsible for the antinociceptive action are at this moment not completely understood, but the involvement of the opioid pathway seems unlikely.     

Chronic administration of clomipramine inhibits morphine hot plate analgesia

Clomipramine, chronically administered in mice, for 3 days, inhibits partially but significantly morphine analgesia in the hot plate test, when used at dose of 10 mg/kg/day, i.p.; 2.5 and 5 mg/kg/day were ineffective. Neither higher doses (20 and 40 mg/kg/day) nor longer duration of pretreatment (8 and 16 days) modified the intensity of this inhibition. Reduction in morphine analgesia was obtained after a 24h delay between the last injection of clomipramine and that of morphine (30 min before testing), while clomipramine did not induce any antinociceptive effect and clomipramine and desmethylclomipramine plasma and brain levels were low or undetectable. These results provide new evidence for the interaction between clomipramine and the endogenous opiate system. A pharmacokinetic interaction between clomipramine and morphine was excluded; involvement of change in opiate and 5 HT2 receptors by chronic administration of clomipramine is discussed.     

Comparison of naloxonazine and beta-funaltrexamine antagonism of mu 1 and mu 2 opioid actions.

beta-Funaltrexamine (beta-FNA) irreversibly blocks morphine analgesia, lethality and its inhibition of gastrointestinal transit, confirming that these actions involve mu receptors. In dose-response studies, beta-FNA antagonized all the actions with similar potencies (ID50 values of 12.1, 11.3 and 12.3 mg/kg, respectively). beta-FNA also reduced intra-cerebroventricular and intrathecal DAMGO analgesia equally well (ID50 values of 6.09 and 7.7 mg/kg, respectively). Naloxanazine blocked systemic morphine analgesia (ID50 value 9.5 mg/kg) and supraspinal DAMGO analgesia (ID50 value 6.1 mg/kg) as potently as beta-FNA. However, against spinal DAMGO analgesia, morphine's inhibition of gastro-intestinal transit or lethality, naloxonazine (ID50 values 38.8, 40.7 and 40.9 mg/kg, respectively) was significantly less active than beta-FNA (p less than 0.05). beta-FNA remains a valuable tool in the classification of mu opioid actions. Within the mu category, actions can be defined as either mu 1 (naloxonazine-sensitive) or mu 2 (naloxonazine-insensitive).     

Role of benzodiazepine-GABAA receptor complex in attenuation of U-50,488H-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin in mice

In the present study, the role of benzodiazepine-GABAA receptor complex in the attenuation of U-50,488H (U50), a selective kappa opioid agonist-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin (GTS) was investigated using the mice tail-flick test. The intraperitoneal (i.p.) treatment of GTS (100 and 200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently attenuated the U50 (40 mg/kg, i.p.)-induced analgesia. GTS (0.001-10 microg/ml) did not alter binding of [3H]naloxone to mice whole brain membrane. The attenuation effect of GTS (100 mg/ kg) and diazepam (0.5 mg/kg) on U50-induced analgesia was blocked by flumazenil (0.1 mg/kg, i.p.), a benzodiazepine receptor antagonist, and picrotoxin (1 mg/kg, i.p.), a GABAA-gated chloride channel blocker. However, bicuculline (1 mg/kg, i.p.), a GABAA receptor antagonist blocked the attenuation effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on U50-induced analgesia. Chronic treatment (day 4-day 6) of GTS (50-200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently inhibited the tolerance to U50-induced analgesia. Flumazenil (0.1 mg/kg) and picrotoxin (1 mg/kg) on chronic treatment blocked the inhibitory effect of GTS (100 mg/kg) and diazepam (0.5 mg/kg) on tolerance to U50-induced analgesia. On the other hand, chronic treatment of bicuculline (1 mg/kg) blocked the inhibitory effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on tolerance to U50-induced analgesia. In conclusion, the findings suggest that GTS attenuates U50-induced analgesia and inhibits tolerance to its analgesia and this action involves benzodiazepine receptors and GABAA-gated chloride channels.     

Possible involvement of mu1-opioid receptors in the fentanyl- or morphine-induced antinociception at supraspinal and spinal sites

Fentanyl has been shown to be a potent analgesic with a lower propensity to produce tolerance and physical dependence in the clinical setting. The present study was designed to investigate the mechanisms of fentanyl- or morphine-induced antinociception at both supraspinal and spinal sites. In the mouse tail-flick test, the antinociceptive effects induced by both fentanyl and morphine were blocked by either the mu1-opioid receptor antagonist naloxonazine or the mu1/mu2-opioid receptor antagonist beta-funaltrexamine (beta-FNA) after s.c., i.c.v. or i.t. injection. In contrast, both fentanyl and morphine given i.c.v. or i.t. failed to produce antinociception in mu1-deficient CXBK mice. These findings indicate that like morphine, the antinociception induced by fentanyl may be mediated predominantly through mu1-opioid receptors at both supraspinal and spinal sites in mice. We also determined the ED50 values for s.c.-, i.c.v.- and i.t.-administered fentanyl- or morphine-induced antinociception in mice. The ED50 values for s.c.-, i.c.v.- and i.t.-administered fentanyl-induced antinociception were 73.7, 18.5 and 1.2-fold lower than that of morphine, respectively. The present data clearly suggest the usefulness of peripheral treatment with fentanyl for the control of pain.     

The effect of an endogenous compound 1-methyl-1,2,3,4,-tetrahydroisoquinoline on morphine-induced analgesia, dependence and neurochemical changes in dopamine metabolism in rat brain structures.

1,2,3,4-Tetrahydroisoquinolines, among them the most interesting neuroprotective substance, an inhibitor of MAO, 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), are endogenous compounds present in the central nervous system of mammals and humans. In this study, we investigated the effect of 1MeTIQ on morphine-induced analgesia, tolerance and abstinence syndrome as well as its effect on morphine-induced changes in dopamine metabolism in rat brain structures (nucleus accumbens, striatum, substantia nigra) using HPLC methodology. The experiments were carried out on male Wistar rats. Morphine analgesia was measured in the "hot-plate" test. To induce tolerance, morphine was given chronically (20 mg/kg i.p.) alone or following 1MeTIQ (50 mg/kg i.p.) injection. The development of dependence was assessed in the naloxone (2 mg/kg i.p.) precipitation test, after 10 days of morphine administration. The behavioral studies have shown that an endogenous compound, 1MeTIQ produced strong potentiation of morphine analgesia, prevented the development of morphine tolerance and inhibited expression of morphine abstinence syndrome in morphine-dependent rats. In neurochemical studies, we have demonstrated that 1MeTIQ antagonized morphine-induced changes in dopamine metabolism observed in rat brain structures. The main finding of this study was demonstration for the first time of an anti-abuse effect of an endogenous compound, 1MeTIQ, and its efficiency in counteracting morphine-induced addiction in the way useful from clinical point of view. The obtained results suggested a possibility of clinical application of 1MeTIQ in morphine addiction.     

Chimeric peptide of Met-enkephalin and FMRFa induces antinociception and attenuates development of tolerance to morphine antinociception.

A synthetic chimeric peptide of Met-enkephalin and FMRFamide (YGGFMKKKFMRFa), based on MERF was synthesized. This peptide was tested for possible antinociceptive effects using the tail flick test in mice. The effect of the chimeric peptide on morphine antinociception and development of tolerance to the antinociceptive action of morphine was also investigated. The chimeric peptide produced significant, dose-dependent antinociception (40, 60 and 90 mg/kg) in the tail flick test. Pretreatment with naloxone (5 mg/kg, IP) significantly attenuated the antinociceptive effect induced by the chimeric peptide (90 mg/kg, IP), indicating involvement of an opioidergic mechanism. In combination experiments with morphine, the antinociceptive dose of the chimeric peptide (60 mg/kg, IP) potentiated morphine (7 mg/kg, IP) antinociception. A low dose of the chimeric peptide (10 mg/kg, IP), that did not produce significant antinociception on its own, also potentiated morphine antinociception. In the tolerance studies, male albino mice received twice daily injections of morphine (20 mg/kg, IP) followed by either saline (0.1 ml) or chimeric peptide (80 mg/kg, IP) for a period of 4 days. A control group received twice daily injections of saline (0.1 ml) for the same period. When tested on Day 5, tolerance to antinociceptive action of morphine (15 mg/kg, IP) was evidenced by decreased response in chronic morphine plus saline treated mice compared to control group. Concurrent administration of chimeric peptide (80 mg/kg, IP) with morphine significantly attenuated the development of tolerance to the antinociceptive action of morphine. The preliminary results of this study demonstrate that peripherally administered chimeric peptide can produce dose dependent, naloxone reversible, antinociception; potentiate morphine antinociception and attenuate morphine tolerance, indicating a possible role of these type of amphiactive sequences in antinociception and its modulation. These chimeric peptides may also prove to be useful tools for further ascertaining the role of FMRFa family of peptides in mechanisms leading to opiate tolerance and dependence.     

Effect of Bacopasides on acquisition and expression of morphine tolerance

Opioids are extensively used for the management of both chronic malignant and non malignant pains. One major serious limitation associated with chronic use of opioids is the development of tolerance to its analgesic effect. The effect of Bacopa monnieri, a renowned ayurvedic medicine for acquisition and expression of morphine tolerance in mice, was investigated. Bacopa monnieri, n-Butanol fraction was analyzed on High performance liquid chromatography (HPLC), for Bacopaside A major components i.e. Bacoside A₃, Bacopaside ll and Bacosaponin C. Antinociceptive effect of n-Butanol extract of Bacopa monnieri (n Bt-ext BM) (5, 10 and 15 mg/kg) was assessed on hot plate. Effect of different doses of n Bt-ext BM on morphine antinociception was also assessed. n Bt-ext BM was also screened for development of tolerance to antinociceptive effect of Bacopa monnieri by administering 15 mg/kg n Bt-ext BM for seven days. Tolerance to morphine analgesia was induced in mice by administering intraperitoneally (I.P.) 20 mg/kg morphine twice daily for five days. Acute and Chronic administration of 5, 10 and 15 mg/kg n Bt-ext BM significantly reduced both expression and development of tolerance to morphine analgesia in mice. Additionally, Bacopa monnieri was found to enhance antinociceptive effect of morphine in intolerant animals. However, no tolerance to Bacopa monnieri antinociceptive effect was observed in seven days treatment schedule. These findings indicate effectiveness of Bacopa monnieri for management of morphine tolerance.     

Discovery and stereoselective synthesis of the novel isochroman neurokinin-1 receptor antagonist 'CJ-17,493'

A novel central nervous system (CNS) selective neurokinin-1 (NK(1)) receptor antagonist, (2S,3S)-3-[(1R)-6-methoxy-1-methyl-1-trifluoromethylisochroman-7-yl]-methylamino-2-phenylpiperidine 'CJ-17,493' (compound (+)-1), was synthesized stereoselectively using a kinetic resolution by lipase-PS as a key step. Compound (+)-1 displayed high and selective affinity (K(i)=0.2 nM) for the human NK(1) receptor in IM-9 cells, potent activity in the [Sar(9), Met(O(2))(11)]SP-induced gerbil tapping model (ED(50)=0.04 mg/kg, s.c.) and in the ferret cisplatin (10mg/kg, i.p.)-induced anti-emetic activity model (vomiting: ED(90)=0.07 mg/kg, s.c.), all levels of activity comparable with those of CP-122,721. In addition, compound (+)-1 exhibited linear pharmacokinetics rather than the super dose-proportionality of CP-122,721 and this result provides a potential solution for the clinical issue observed with CP-122,721.     

Study of the antinociceptive effect of tetrahydropapaveroline derivatives. Interaction with opioids

The antinociceptive effect of racemic tetrahydropapaveroline (THP), of its two R(+)- and S(−) enantiomers, of 1-2-dehydro-THP and of 1-carboxy-THP was assessed using different pain tests in mice. None of these drugs possessed a significant activity in the hot-plate and tail-flick tests. However, after i.p. injection, they reduced the number of abdominal writhes induced by phenylbenzoquinone, with ED₅₀ values of 51 ± 7, 73 ± 9 and 79 ± 7 mg/kg for the most potent compounds: 1,2-dehydro-THP, ±THP and -THP, respectively. This activity was not antagonized by naloxone (1 mg/Kg, S.c.). However combination of inactive doses of these three compounds (32 mg/Kg, I.p.) and of morphine (0.5 mg/Kg, S.c.) led to a significant antinociceptive effect (83 to 85 % of reduction of the number of writhes). This synergistic potentiation confirmed with the combination of ±THP (16 mg/Kg, I.p.) and morphine (0.5 mg/Kg, S.c.) was totally inhibited by naloxone (1 mg/Kg, S.c.). These results, although excluding a direct agonistic effect of THP derivatives on opiate receptors, suggest an indirect interaction of these drugs with the endogenous opioid system.     

Antinociceptive activity of a novel buprenorphine analogue

HS-599 is a didehydroderivative of buprenorphine that displays high affinity and good selectivity for mu-opioid receptors. We studied its antinociceptive properties after s.c. injection in mice with the tail-flick and hot-plate tests. In the tail-flick test HS-599 (AD50 = 0.2801 micromol/kg s.c.) behaved as a full agonist and was twice as potent as buprenorphine (AD50=0.4569 micromol/kg s.c.) and 50 times more potent than morphine (AD50 = 13.3012 micromol/kg s.c.). Whereas the mu-opioid receptor antagonists naloxone (1-10 mg/kg s.c.) and naltrexone (5-15 mg/kg s.c.) antagonized HS-599 induced analgesia, the delta-opioid receptor antagonist naltrindole (20 mg/kg s.c.) and the kappa-opioid receptor antagonist nor-binaltorphimine (20 mg/kg s.c.) did not. With the hot-plate test at 50 degrees C, HS-599 (AD50 = 0.0359 micromol/kg s.c.) was a full agonist about 130 times more potent than morphine (AD50 = 4.8553 micromol/kg s.c.). With a high intensity nociceptive stimulus (55 degrees C) HS-599 (AD50 = 1.0382 micromol/kg s.c.) remained 7 times more potent than morphine (AD50 = 7.0210 micromol/kg s.c.) but never exceeded the 55% of the maximum possible effect, behaving as a partial agonist able to antagonize morphine antinociception in a dose-dependent manner. HS-599 promises to be a potent and safe new analgesic, preferentially acting at spinal level.     

SAR of 2,6-diamino-3,5-difluoropyridinyl substituted heterocycles as novel p38MAP kinase inhibitors

2,6-Diamino-3,5-difluoropyridinyl substituted pyridinylimidazoles, -pyrroles, -oxazoles, -thiazoles and -triazoles have been identified as novel p38alpha inhibitors. Pyridinylimidazole 11 potently inhibited LPS-induced TNFalpha in mice, showed good efficacy in the established rat adjuvant (ED(50): 10 mg/kg po b.i.d.) and collagen induced arthritis (ED(50): 5 mg/kg po b.i.d.) with disease modifying properties based on histological analysis of the joints.