CYX-5, a G-protein biassed MOP receptor agonist, DOP receptor antagonist and KOP receptor agonist, evokes constipation but not respiratory depression relative to morphine in rats.

BACKGROUND: Strong opioid analgesics such as morphine alleviate moderate to severe acute nociceptive pain (e.g. post-surgical or post-trauma pain) as well as chronic cancer pain. However, they evoke many adverse effects and so there is an unmet need for opioid analgesics with improved tolerability. Recently, a prominent hypothesis has been that opioid-related adverse effects are mediated by ß-arrestin2 recruitment at the µ-opioid (MOP) receptor and this stimulated research on discovery of G-protein biassed opioid analgesics. In other efforts, opioids with MOP agonist and δ-opioid (DOP) receptor antagonist profiles are promising for reducing side effects c.f. morphine. Herein, we report on the in vivo pharmacology of a novel opioid peptide (CYX-5) that is a G-protein biassed MOP receptor agonist, DOP receptor antagonist and kappa opioid (KOP) receptor agonist. METHODS: Male Sprague-Dawley received intracerebroventricular bolus doses of CYX-5 (3, 10, 20 nmol), morphine (100 nmol) or vehicle, and antinociception (tail flick) was assessed relative to constipation (charcoal meal and castor oil-induced diarrhoea tests) and respiratory depression (whole body plethysmography). RESULTS: CYX-5 evoked naloxone-sensitive, moderate antinociception, at the highest dose tested. Although CYX-5 did not inhibit gastrointestinal motility, it reduced stool output markedly in the castor oil-induced diarrhoea test. In contrast to morphine that evoked respiratory depression, CYX-5 increased tidal volume, thereby stimulating respiration. CONCLUSION: Despite its lack of recruitment of ß-arrestin2 at MOP, DOP and KOP receptors, CYX-5 evoked constipation, implicating a mechanism other than ß-arrestin2 recruitment at MOP, DOP and KOP receptors, mediating constipation evoked by CYX-5 and potentially other opioid ligands.

Assessment of the anti-allodynic efficacy of a glycine transporter 2 inhibitor relative to pregabalin and duloxetine in a rat model of prostate cancer-induced bone pain.

BACKGROUND: The pathobiology of prostate cancer-induced bone pain (PCIBP) is underpinned by both inflammatory and neuropathic components. Here, we used a rat model of PCIBP to assess the analgesic efficacy of a glycine transporter 2 (GlyT2) inhibitor (N-(6-((1,3-dihydroxypropan-2-yl)amino)-2-(dimethylamino)pyridin-3-yl)-3,5-dimethoxy-4-(4-(trifluoromethyl)phenoxy) benzamide) relative to two clinically available adjuvant drugs that are recommended for the relief of neuropathic pain, viz, pregabalin and duloxetine. METHODS: PCIBP was induced in male Wistar Han rats following intra-tibial injection (ITI) of rat prostate cancer (AT3B) cells into the left tibia. Sham-rats received an ITI of heat-killed AT3B cells. PCIBP rats with fully developed mechanical allodynia in the ipsilateral hindpaws as assessed using von Frey filaments, received single oral (p.o.) bolus doses of the GlyT2 inhibitor (3-30 mg/kg), pregabalin (3-100 mg/kg), duloxetine (3-100 mg/kg), or vehicle. Baseline paw withdrawal thresholds (PWTs) were determined in the ipsilateral (injured side) and contralateral hindpaws immediately prior to dosing and at scheduled times for 3 h post dosing in individual animals. RESULTS: Single oral bolus doses of the GlyT2 inhibitor (3-30 mg/kg) evoked partial pain relief at the doses tested in the ipsilateral hindpaws of PCIBP rats without any discernible behavioural side effects. By contrast, single oral bolus doses of pregabalin at 10-100 mg/kg evoked dose-dependent and complete alleviation of mechanical allodynia. By comparison, single oral bolus doses of duloxetine at doses up to 100 mg/kg lacked efficacy. CONCLUSION: Oral administration of this GlyT2 inhibitor evoked partial pain relief in PCIBP rats and did not evoke central nervous system side effects in contrast to GlyT2 inhibitors reported by others.

Countering opioid-induced respiratory depression by non-opioids that are respiratory stimulants.

Strong opioid analgesics are the mainstay of therapy for the relief of moderate to severe acute nociceptive pain that may occur post-operatively or following major trauma, as well as for the management of chronic cancer-related pain. Opioid-related adverse effects include nausea and vomiting, sedation, respiratory depression, constipation, tolerance, and addiction/abuse liability. Of these, respiratory depression is of the most concern to clinicians owing to the potential for fatal consequences. In the broader community, opioid overdose due to either prescription or illicit opioids or co-administration with central nervous system depressants may evoke respiratory depression. To address this problem, there is ongoing interest in the identification of non-opioid respiratory stimulants to reverse opioid-induced respiratory depression but without reversing opioid analgesia. Promising compound classes evaluated to date include those that act on a diverse array of receptors including 5-hydroxytryptamine, D 1-dopamine, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-D-aspartate (NMDA) receptor antagonists, and nicotinic acetylcholine as well as phosphodiesterase inhibitors and molecules that act on potassium channels on oxygen-sensing cells in the carotid body. The aim of this article is to review recent advances in the development potential of these compounds for countering opioid-induced respiratory depression.

Intracerebroventricular administration of CYX-6, a potent µ-opioid receptor agonist, a δ- and κ-opioid receptor antagonist and a biased ligand at µ, δ & κ-opioid receptors, evokes antinociception with minimal constipation and respiratory depression in rats in contrast to morphine.

Mu opioid receptor (MOPr) agonists are thought to produce analgesia via modulation of G-protein-coupled intracellular signalling pathways whereas the ß-arrestin2 pathway is proposed to mediate opioid-related adverse effects. Here, we report the antinociception, constipation and respiratory depressant profile of CYX-6, a potent MOPr agonist that is also a delta and a kappa opioid receptor (DOPr/KOPr) antagonist and that lacks ß-arrestin2 recruitment at each of the MOPr, DOPr and the KOPr. In anaesthetised male Sprague Dawley rats, an intracerebroventricular (i.c.v.) guide cannula was stereotaxically implanted. After 5-7 days post-surgical recovery, rats received a single i.c.v. bolus dose of CYX-6 (3-30 nmol), morphine (100 nmol) or vehicle. Antinociception was assessed using the warm water tail flick test (52.5 ± 0.5 °C). Constipation was assessed using the charcoal meal gut motility test and the castor oil-induced diarrhoea test. Respiratory depression was measured by whole-body plethysmography in awake, freely moving animals, upon exposure to a hypercapnic gas mixture (8% CO2, 21% O2 and 71% N2). The intrinsic pharmacology of CYX-6 given by the i.c.v. route in rats showed that it produced dose-dependent antinociception. It also produced respiratory stimulation rather than depression and it had a minimal effect on intestinal motility in contrast to the positive control, morphine. CYX-6 is an endomorphin-2 analogue that dissociates antinociception from constipation and respiratory depression in rats. Our findings provide useful insight to inform the discovery and development of novel opioid analgesics with a superior tolerability profile compared with morphine.

Progress in understanding mechanisms of opioid-induced gastrointestinal adverse effects and respiratory depression.

Opioids evoke analgesia through activation of opioid receptors (predominantly the µ opioid receptor) in the central nervous system. Opioid receptors are abundant in multiple regions of the central nervous system and the peripheral nervous system including enteric neurons. Opioid-related adverse effects such as constipation, nausea, and vomiting pose challenges for compliance and continuation of the therapy for chronic pain management. In the post-operative setting opioid-induced depression of respiration can be fatal. These critical limitations warrant a better understanding of their underpinning cellular and molecular mechanisms to inform the design of novel opioid analgesic molecules that are devoid of these unwanted side-effects. Research efforts on opioid receptor signalling in the past decade suggest that differential signalling pathways and downstream molecules preferentially mediate distinct pharmacological effects. Additionally, interaction among opioid receptors and, between opioid receptor and non-opioid receptors to form signalling complexes shows that opioid-induced receptor signalling is potentially more complicated than previously thought. This complexity provides an opportunity to identify and probe relationships between selective signalling pathway specificity and in vivo production of opioid-related adverse effects. In this review, we focus on current knowledge of the mechanisms thought to transduce opioid-induced gastrointestinal adverse effects (constipation, nausea, vomiting) and respiratory depression.

Antinociceptive and neuropharmacological activities of methanol extract of Phoenix sylvestris fruit pulp.

Fruits of Phoenix sylvestris Roxb. (Arecaceae) are used to treat back pain, toothache, headache, arthritis, nervous debility and as sedative. The aim of this study was to evaluate the antinociceptive and neuropharmacological activities of methanol extract of P. sylvestris fruit pulp (MEPS). The antinociceptive activity of MEPS was evaluated by heat-induced (hot plate, tail immersion test) and chemical-induced pain models (acetic acid-induced writhing, formalin-induced nociception, glutamate-induced nociception and paw edema test). The effect of MEPS on central nervous system (CNS) was studied using hole cross test, open field test, sodium thiopental-induced sleeping time and elevated plus maze test. MEPS showed strong, significant and dose-dependent antinociceptive activity in all heat-induced and chemical-induced pain models at all experimental doses. Involvement of opioid receptor mediated analgesia was evident from the reversal of analgesic effect by naloxone. MEPS also showed reduced locomotor activity in both hole cross and open field tests. The increase in sleeping time in sodium thiopental-induced sleeping test and anxiolytic activity in elevated plus maze test were also significant. So, it is evident that MEPS possesses strong central and peripheral antinociceptive activity as well as CNS depressant, sedative and anxiolytic activity. The results justify the ethnomedicinal use of P. sylvestris fruit in different painful conditions and CNS disorders.

Evaluation of Antinociceptive Activity of Ethanol Extract of Leaves of Adenanthera pavonina.

Adenanthera pavonina is a deciduous tree commonly used in the traditional medicine to treat inflammation and rheumatism. The aim of this study was to evaluate the antinociceptive activity of ethanol extract of leaves of A. pavonina (EEAP). EEAP was investigated using various nociceptive models induced thermally or chemically in mice including hot plate and tail immersion test, acetic acid-induced writhing, and glutamate- and formalin-induced licking tests at the doses of 50, 100, and 200 mg/kg body weight (p.o.). In addition, to assess the possible mechanisms, involvement of opioid system was verified using naloxone (2 mg/kg) and cyclic guanosine monophosphate (cGMP) signaling pathway by methylene blue (MB; 20 mg/kg). The results have demonstrated that EEAP produced a significant and dose-dependent increment in the hot plate latency and tail withdrawal time. It also reduced the number of abdominal constrictions and paw lickings induced by acetic acid and glutamate respectively. EEAP inhibited the nociceptive responses in both phases of formalin test. Besides, the reversal effects of naloxone indicated the association of opioid receptors on the exertion of EEAP action centrally. Moreover, the enhancement of writhing inhibitory activity by MB suggests the possible involvement of cGMP pathway in EEAP-mediated antinociception. These results prove the antinociceptive activity of the leaves of A. pavonina and support the traditional use of this plant.

Antinociceptive effect of methanol extract of leaves of Persicaria hydropiper in mice.

BACKGROUND: Persicaria hydropiper (Linn.) Delarbre is a common plant of Polygonaceae family commonly called Bishkatali in Bangladesh. Leaves of the plant are traditionally used in the treatment of rheumatic pain, gout, and skin diseases such as ringworms, scabies, boils, abscesses, carbuncles, bites of snakes, dogs or insects. This study evaluated the antinociceptive effect of the methanol extract of P. hydropiper leaves (MEPH). METHODS: The antinociceptive activity of MEPH was investigated using heat-induced (hot-plate and tail-immersion test) and chemical-induced (acetic acid, formalin, glutamic acid, cinnamaldehyde) nociception models in mice at 25, 50, and 75 mg/kg doses. Involvement of opioid system, cyclic guanosine monophosphate (cGMP) pathway, and ATP-sensitive K(+) channel pathway were also tested using naloxone, methylene blue and glibenclamide respectively. RESULTS: MEPH showed antinociceptive activity in both heat- and chemical induced pain models. In both hot plate and tail immersion tests MEPH significantly increases the latency to the thermal stimuli. In acetic acid-induced writhing test the extract inhibited the number of abdominal writhing. Likewise, MEPH produced significant dose-dependent inhibition of paw licking in both neurogenic and inflammatory pain induced by intraplantar injection of formalin. Besides, MEPH also significantly inhibited the glutamate-induced pain and cinnamaldehyde-induced pain in mice. It was also clear that pretreatment with naloxone significantly reversed the antinociception produced by MEPH in hot plate and tail immersion test suggesting the involvement of opioid system in its effect. In addition, administration of methylene blue, a non specific inhibitor of NO/guanylyl cyclase, enhanced MEPH induced antinociception while glibenclamide, an ATP-sensitive K(+) channel antagonist, could not reverse antinociceptive activity induced by MEPH. CONCLUSION: Based on the results of the current study it can be said that MEPH possesses significant antinociceptive activity which acts in both peripheral and central mechanisms.

Evaluation of antinociceptive effect of methanolic extract of leaves of Crataeva nurvala Buch.-Ham.

BACKGROUND: Crataeva nurvala Buch.-Ham. (Family: Capparidaceae) is widely used as anti-inflammatory, contraceptive, laxative, lithotropic, febrifuge and as tonic in traditional medicine. This study evaluated the antinociceptive effect of the methanolic extract of the leaves of Crataeva nurvala (MECN). METHODS: The antinociceptive activity was investigated using heat-induced (hot-plate and tail-immersion test) and chemical-induced (acetic acid, formalin and glutamic acid) nociception models in mice at different doses (50, 100, and 200 mg/kg, p.o.) of MECN. Morphine sulphate (5 mg/kg, i.p.) and diclofenac sodium (10 mg/kg, i. p.) were used as reference analgesic drugs. RESULTS: MECN produced significant dose-dependent antinociception when assessed using hot plate test, tail immersion test and acetic acid-induced abdominal writhing test (65.55%). Likewise, MECN at similar doses produced significant dose-dependent inhibition in both neurogenic (50.82%) and inflammatory pain (73.53%) induced by intraplantar injection of formalin (2.5% formalin, 20 µl/paw). Besides, MECN also significantly inhibited the glutamate-induced (10 µM/paw) pain in mice (74.68%). It was demonstrated that pretreatment with naloxone (2 mg/kg, i.p.) significantly reversed antinociception produced by MECN in hot plate and tail immersion test suggesting the involvement of opioid receptor. In addition, administration of glibenclamide (10 mg/kg, i.p.), an ATP-sensitive K+ channel antagonist could not reverse antinociceptive activity induced by MECN. CONCLUSION: The results suggest that MECN possesses antinociceptive activity involving inhibition of opioid system as well as the glutamatergic system supporting its traditional uses.

Evaluation of antinociceptive activity of hydromethanol extract of Cyperus rotundus in mice.

BACKGROUND: Cyperus rotundus Linn. (Cyperaceae) is used to treat inflammation, pain, fever, wounds, boils and blisters in folk medicine. This study evaluated the antinociceptive effect of the hydromethanol extract of whole plant of C. rotundus (HMCR). METHODS: The antinociceptive activity of HMCR was investigated in thermal-induced (hot plate and tail immersion) and chemical-induced (formalin) nociception models in mice at three different doses (50, 100 and 200 mg/kg; p.o.). Morphine sulphate (5 mg/kg, i.p.) and diclofenac sodium (10 mg/kg, i.p.) were used as reference analgesic agents. RESULTS: In the hot-plate and tail-immersion tests HMCR significantly increased the latency period to the thermal stimuli at all the tested doses (50, 100 and 200 mg/kg) (p < 0.05). The significant increase in latency is clear from the observations at 60 and 90 min. In formalin-induced paw licking test oral administration of HMCR at 100 and 200 mg/kg doses decreased the licking of paw in early phase. All the tested doses (50, 100 and 200 mg/kg) significantly decreased the licking of paw in late phase of the test (p < 0.001). The dose 200 mg/kg was most effective showing maximum percentage of inhibition of licking in both early (61.60%) and late phase (87.41%). CONCLUSION: These results indicate the antinociceptive effect of C. rotundus and suggest that this effect is mediated by both peripheral and central mechanisms. These results support the traditional use of this plant in different painful conditions.

Antinociceptive effect of ethanol extract of leaves of Lannea coromandelica.

ETHNOPHARMACOLOGICAL RELEVANCE: Lannea coromandelica (Houtt.) Merr. is a plant locally called "Jiga", found all over Bangladesh. Leaf of the plant is traditionally used in the treatment of local swellings, pains of body, toothache etc. This study evaluated the antinociceptive effect of the ethanol extract of L. coromandelica leaves (EELC). MATERIALS AND METHODS: The antinociceptive activity of the extract (at the doses of 50, 100, and 200 mg/kg) was evaluated by using chemical- and heat-induced pain models such as acetic acid-induced writhing, hot plate, tail immersion, formalin, and glutamate test. To verify the possible involvement of opioid receptor in the central antinociceptive effect of EELC, naloxone was used to antagonize the effect. Besides, the involvements of ATP-sensitive K(+) channel and cGMP pathway were also justified by using glibenclemide and methylene blue. RESULTS: EELC demonstrated significant dose-dependent antinociceptive activity in the chemical- and heat-induced nociception in mice models (p<0.05). These findings imply the involvement of both peripheral and central antinociceptive mechanisms. The use of naloxone confirmed the association of opioid receptors in the central antinociceptive effect. EELC also showed the involvements of ATP-sensitive K(+) channel and cGMP pathway for antinociceptive activity. CONCLUSIONS: This study reported the antinociceptive activity of the leaf of L. coromandelica and rationalized the traditional use of the leaf in the treatment of different painful conditions.

Awareness regarding the importance of calcium and vitamin D among the undergraduate pharmacy students in Bangladesh.

BACKGROUND: Calcium and vitamin D are two important micronutrients required for maintaining proper bone health. Previous works intended to determine the status of these micronutrients in local population have reported that the people in Bangladesh are at high risk of calcium insufficiency and hypovitaminosis D related health complications. Lack of awareness and insufficient knowledge of the essentiality of these two nutrients are assumed to cause this problem in Bangladesh. The present study was designed and conducted to establish a basic understanding on the level of gap of knowledge and awareness among pharmacy students at undergraduate level in Bangladesh. FINDINGS: A total of 713 students of Bachelor of Pharmacy course participated in the study. The students were asked about basic idea related to calcium and vitamin D and the disorders due to their deficiency, name of common foods containing calcium and vitamin D, their perception regarding the essentiality of the said nutrients etc. It was found that most of the students were familiar with the importance of calcium (98.9%) and vitamin D (99.3%) in bone health. 82.2% students know about the term osteoporosis. Unfortunately, 10.7% and 18.8% students failed to mention at least one food that is rich in calcium and vitamin D, respectively. Most of the students got familiar about the nutrients from their teachers (48.9%) and textbooks (32.8%). CONCLUSION: Being a student of pharmacy, the students should have more comprehensive knowledge about calcium and vitamin D. The present study indicates that the pharmacy students have lack of knowledge about calcium and vitamin D and thus it can be clearly predicted that the condition of general people may be worse.

Antinociceptive activity of methanol extract of flowers of Impatiens balsamina.

ETHNOPHARMACOLOGICAL RELEVANCE: Impatiens balsamina Linn. (Balsaminaceae), an annual herb locally called "Dopati", is cultivated as an ornamental garden plant in Bangladesh. Flowers of the plant are used in folk medicine to treat lumbago, neuralgia, burns and scalds. AIM OF THE STUDY: This study evaluated the antinociceptive effect of the methanol extract of I. balsamina flowers (MIB). MATERIALS AND METHODS: The extract was evaluated for antinociceptive activity using chemical- and heat-induced pain models such as acetic acid-induced writhing, hot plate, tail immersion and formalin test. To verify the possible involvement of opioid receptor in the central antinociceptive effect of MIB, naloxone was used to antagonize the effect. The effect of MIB on central nervous system (CNS) was also studied using hole cross and open field tests. RESULTS: MIB demonstrated strong and dose-dependent antinociceptive activity in all the chemical- and heat-induced mice models (p<0.05). These findings imply the involvement of both peripheral and central antinociceptive mechanisms. The use of naloxone confirmed the association of opioid receptors in the central antinociceptive effect. MIB also showed significant central nervous system depressant effect (p<0.05). CONCLUSION: This study reported the peripheral and central antinociceptive activity of the flowers of I. balsamina and rationalized the traditional use of the flower in the treatment of different painful conditions.