Role of the NO-cGMP pathway in the systemic antinociceptive effect of clonidine in rats and mice

The Involvement of l-Arginine-Nitric Oxide-cGMP-ATP-Sensitive K+ Channel Pathway in Antinociception of BBHC, a Novel Diarylpentanoid Analogue, in Mice Model

The present study focuses on the possible involvement of l-arginine-nitric oxide-cGMP-ATP-sensitive K⁺ channel pathway in the antinociceptive activity of a novel diarylpentanoid analogue, 2-benzoyl-6-(3-bromo-4-hydroxybenzylidene)cyclohexen-1-ol (BBHC) via a chemical nociceptive model in mice. The antinociceptive action of BBHC (1 mg/kg, i.p.) was attenuated by the intraperitoneal pre-treatment of l-arginine (a nitric oxide synthase precursor) and glibenclamide (an ATP-sensitive K⁺ channel blocker) in acetic acid-induced abdominal constriction tests. Interestingly, BBHC’s antinociception was significantly enhanced by the i.p. pre-treatment of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a selective inhibitor of soluble guanylyl cyclase (p < 0.05). Altogether, these findings suggest that the systemic administration of BBHC is able to establish a significant antinociceptive effect in a mice model of chemically induced pain. BBHC’s antinociception is shown to be mediated by the involvement of l-arginine-nitric oxide-cGMP-ATP-sensitive K⁺ channel pathway, without any potential sedative or muscle relaxant concerns.

The anti-nociceptive activity of naringenin passes through L-arginine/NO/cGMP/KATP channel pathway and opioid receptors

As a promising flavonoid, naringenin has shown potential anti-inflammatory and antioxidant properties mainly in inflammatory pain models by oral administration. Therefore, we investigated the antinociceptive activity of this compound by intraperitoneally (i.p.) administration, as well as, associated mechanism of action considering the involvement of L-arginine/nitric oxide (NO)/cyclic GMP (cGMP)/potassium channel (KATP) pathway and opioid receptors. The antinociceptive effect of naringenin was evaluated in male NMRI mice using formalin test at early and late phases. To assess the involvement of L-arginine/NO/cGMP/KATP pathway and opioid receptors, mice were pretreated i.p. with L-arginine (NO precursor), S-nitroso-N-acetylpenicillamine (SNAP, NO donor), N(gamma)-nitro-L-arginine methyl ester (L-NAME, inhibitor of nitric oxide synthase), sildenafil (inhibitor of phosphodiesterase enzyme), glibenclamide (KATP channel blocker) and naloxone (an opioid receptor antagonist), respectively 20 min before administration of the most effective dose of naringenin. Naringenin showed a dose-dependent antinociceptive effect at both early and late phases of the formalin test. The dose of 100 mg/kg of naringenin was identified as the most effective dose and selected for further experiments. Our mechanistic evaluations showed that L-arginine, SNAP and sildenafil could enhance the antinociceptive effects of naringenin, revealing the critical role of NO and cGMP during its antinociceptive effect. On the other hand, glibenclamide and naloxone could mitigate the antinociceptive potential of naringenin at both phases of formalin test, which confirmed the associated role of KATP channels and opioid receptors. In conclusion, naringenin could be a promising antinociceptive agent acting through opioid receptors and L-arginine/NO/cGMP/KATP channel pathway.

The antinociceptive mechanisms of melatonin: role of L-arginine/nitric oxide/cyclic GMP/KATP channel signaling pathway

Pain is one of the most common medical challenges, reducing life quality. Despite the progression in pain management, it has remained a clinical challenge, which raises the need for investigating novel antinociceptive drugs with correspondence signaling pathways. Besides, the precise antinociceptive mechanisms of melatonin are not revealed. Accordingly, owing to the critical role of L-arginine/nitric oxide (NO)/cyclic GMP (cGMP)/KATP in the antinociceptive responses of various analgesics, the role of this signaling pathway is evaluated in the antinociceptive effects of melatonin. Male NMRI mice were intraperitoneally pretreated with the injection of L-arginine (NO precursor, 100 mg/kg), N(gamma)-nitro-L-arginine methyl ester [L-NAME, NO synthase (NOS) inhibitor, 30 mg/kg], S-nitroso-N-acetylpenicillamine (SNAP, NO donor, 1 mg/kg), sildenafil (phosphodiesterase inhibitor, 0.5 mg/kg), and glibenclamide (KATP channel blocker, 10 mg/kg) alone and before the administration of the most effective dose of melatonin amongst the intraperitoneal doses of 50, 100, and 150 mg/kg. The formalin test (2%, 25 µL, intra-plantarly) was done following the melatonin administration, then the nociceptive responses of mice were evaluated during the early phase for 5 min and the late phase for 15 min. The results showed that 100 mg/kg dose of melatonin carried out the most antinociceptive effects. While the antinociceptive effect of melatonin was increased by L-arginine, SNAP, and sildenafil, it was significantly reduced by L-NAME and glibenclamide in both phases of the formalin test, with no relation to the sedative effects of melatonin evaluated by the inclined plane test. In conclusion, the antinociceptive effect of melatonin is mediated through the L-arginine/NO/cGMP/KATP pathway.

Inhibition of NLRP3 Inflammasome Prevents LPS-Induced Inflammatory Hyperalgesia in Mice: Contribution of NF-κB, Caspase-1/11, ASC, NOX, and NOS Isoforms

The nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3), an intracellular signaling molecule that senses many environmental- and pathogen/host-derived factors, has been implicated in the pathogenesis of several diseases associated with inflammation. It has been suggested that NLRP3 inflammasome inhibitors may have a therapeutic potential in the treatment of NLRP3-related inflammatory diseases. The aim of this study was to determine whether inhibition of NLRP3 inflammasome prevents inflammatory hyperalgesia induced by lipopolysaccharide (LPS) in mice as well as changes in expression/activity of nuclear factor κB (NF-κB), caspase-1/11, nicotinamide adenine dinucleotide phosphate oxidase (NOX), and endothelial/neuronal/inducible nitric oxide synthase (eNOS/nNOS/iNOS) that may regulate NLRP3/apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC)/pro-caspase-1 inflammasome formation and activity by using a selective NLRP3 inflammasome inhibitor, MCC950. Male mice received saline (10 ml/kg; i.p.), LPS (10 mg/kg; i.p.), and/or MCC950 (3 mg/kg; i.p.). Reaction time to thermal stimuli within 1 min was evaluated after 6 h. The mice were killed and the brains, hearts, and lungs were collected for measurement of NF-κB, caspase-1, caspase-11, NLRP3, ASC, NOX subunits (gp91^phox; NOX2), and p47^phox; NOXO2), nitrotyrosine, eNOS, nNOS, iNOS, and β-actin protein expression, NOS activity, and interleukin (IL)-1β levels. LPS-induced hyperalgesia was associated with a decrease in eNOS, nNOS, and iNOS protein expression and activity as well as an increase in expression of NF-κB p65, caspase-1 p20, caspase-11 p20, NLRP3, ASC, gp91^phox, p47^phox, and nitrotyrosine proteins in addition to elevated IL-1β levels. The LPS-induced changes were prevented by MCC950. The results suggest that inhibition of NLRP3/ASC/pro-caspase-1 inflammasome formation and activity prevents inflammatory hyperalgesia induced by LPS in mice as well as changes in NF-κB, caspase-11, NOX2, NOXO2, and eNOS/nNOS/iNOS expression/activity.

Antinociceptive effect of methanol extract of Dalbergia sissoo leaves in mice

BACKGROUND

Dalbergia sissoo DC. (Family: Fabaceae) is a medium to large deciduous tree, is locally called "shishu" in Bangladesh. It is used to treat sore throats, dysentery, syphilis, bronchitis, inflammations, infections, hernia, skin diseases, and gonorrhea. This study evaluated the antinociceptive effect of the methanol extract of D. sissoo leaves (MEDS) in mice.

METHODS

The extract was assessed for antinociceptive activity using chemical and heat induced pain models such as hot plate, tail immersion, acetic acid-induced writhing, formalin, glutamate, and cinnamaldehyde test models in mice at the doses of 100, 200, and 400 mg/kg (p.o.) respectively. Morphine sulphate (5 mg/kg, i.p.) and diclofenac sodium (10 mg/kg, i.p.) were used as reference analgesic drugs. To confirm the possible involvement of opioid receptor in the central antinociceptive effect of MEDS, naloxone was used to antagonize the effect.

RESULTS

MEDS demonstrated potent and dose-dependent antinociceptive activity in all the chemical and heat induced mice models (p < 0.001). The findings of this study indicate that the involvement of both peripheral and central antinociceptive mechanisms. The use of naloxone verified the association of opioid receptors in the central antinociceptive effect.

CONCLUSIONS

This study indicated the peripheral and central antinociceptive activity of the leaves of D. sissoo. These results support the traditional use of this plant in different painful conditions.

Centrally acting drug moxonidine decreases reactive oxygen species via inactivation of the phosphoinositide-3 kinase signaling in the rostral ventrolateral medulla in hypertensive rats

OBJECTIVE

Centrally acting antihypertensive action of moxonidine is a result of activation of Imidazoline-1 receptor (I1R) in the rostral ventrolateral medulla (RVLM). Hypertension shows an increase in reactive oxygen species (ROS) in the RVLM. The present objective was to determine the phosphoinositide-3 kinase (PI3K) signaling pathway involved in the effect of moxonidine on ROS generation in the RVLM of spontaneously hypertensive rat (SHR).

METHODS

Wistar-Kyoto rats and SHR received intracisternal infusion (2 weeks) of tested agents which were subjected to subsequent experiments. In-situ ROS in the RVLM was evaluated by the oxidative fluorescence dye. Western blot and PCR analysis were performed to detect the expression levels of PI3K signaling pathway. Lentivirus was injected bilaterally into the RVLM for silencing PI3K signaling.

RESULTS

ROS production in the RVLM was dose-dependently reduced in SHRs treated with infusion of moxonidine (20 nmol/day), which was prevented by the I1R antagonist efaroxan but not by the α2-adrenoceptor antagonist yohimbine. Moxonidine pretreatment significantly blunted cardiovascular sensitivity to injection of tempol (5 nmol) or angiotensin II (10 pmol) into the RVLM in SHR. Expression levels of PI3K/Akt, nuclear factor kappa-B (NFκB), NADPHase (NOX4), and angiotensin type I receptor (AT1R) in the RVLM were markedly decreased in SHR treated with moxonidine. Infection of lentivirus containing PI3K shRNA in the RVLM effectively prevented effects of moxonidine on cardiovascular activity and expression levels of Akt, NFκB, NOX4, and AT1R.

CONCLUSION

The centrally antihypertensive drug moxonidine decreases ROS production in the RVLM through inactivation of the PI3K/Akt signaling pathway in hypertension.

Pharmacological mechanisms involved in the antinociceptive effects of dexmedetomidine in mice

Dexmedetomidine (DEX) is a α₂ -adrenoceptor (α₂ -AR) agonist used as an anesthetic adjuvant and as sedative in critical care settings. Typically, α₂ -AR agonists release nitric oxide (NO) and subsequently activate NO-GMPc pathway and have been implicated with antinociception. In this study, we investigate the pharmacological mechanisms involved in the antinociceptive effects of DEX, using an acetic acid-induced writhing assay in mice. Saline or DEX (1, 2, 5, or 10 μg/kg) was intravenously injected 5 min before ip administration of acetic acid and the resulting abdominal constrictions were then counted for 10 min. To investigate the possible mechanisms related to antinociceptive effect of DEX (10 μg/kg), the animals were also pretreated with one of the following drugs: 7-nitroindazole (7-NI; 30 mg/kg ip); 1H-[1,2,4] oxadiazole [4,3-a] quinoxaline-1-one (ODQ; 2.5 mg/kg, ip); yohimbine (YOH; 1 mg/kg, ip); atropine (ATRO; 2 mg/kg, ip); glibenclamide (GLIB; 1 mg/kg, i.p.) and naloxone (NAL; 0.2 mg/kg, ip). A rotarod and open-field performance test were performed with DEX at 10 μg/kg dose. DEX demonstrated its potent antinociceptive effect in a dose-dependent manner. The pretreatment with 7-NI, ODQ, GLIB, ATRO, and YOH significantly reduced the antinociceptive affects of DEX. However, NAL showed no effecting DEX-induced antinociception. The rotarod and open-field tests confirmed there is no detectable sedation or even significant motor impairment with DEX at 10 μg/kg dose. Our results suggest that the α₂ -AR and NO-GMPc pathways play important roles in the systemic antinociceptive effect of DEX in a murine model of inflammatory pain. Furthermore, the antinociceptive effect exerted by DEX appears to be dependent on KATP channels, independent of opioid receptor activity.

Possible participation of nitric oxide/cyclic guanosine monophosphate/protein kinase C/ATP-sensitive K(+) channels pathway in the systemic antinociception of flavokawin B

The possible mechanisms of action in the antinociceptive activity induced by systemic administration (intraperitoneal, i.p.) of flavokawin B (FKB) were analysed using chemical models of nociception in mice. It was demonstrated that i.p. administration of FKB to the mice at 0.3, 1.0, 3.0 and 10 mg/kg produced significant dose-related reduction in the number of abdominal constrictions. The antinociception induced by FKB in the acetic acid test was significantly attenuated by i.p. pre-treatment of mice with L-arginine, the substrate for nitric oxide synthase or glibenclamide, the ATP-sensitive K(+) channel inhibitor, but was enhanced by methylene blue, the non-specific guanylyl cyclase inhibitor. FKB also produced dose-dependent inhibition of licking response caused by intraplantar injection of phorbol 12-myristate 13-acetate, a protein kinase C activator (PKC). Together, these data indicate that the NO/cyclic guanosine monophosphate/PKC/ATP-sensitive K(+) channel pathway possibly participated in the antinociceptive action induced by FKB.

Zerumbone-induced antinociception: involvement of the L-arginine-nitric oxide-cGMP -PKC-K+ ATP channel pathways

This study investigated the antinociceptive effects of zerumbone in chemical behavioural models of nociception in mice. Zerumbone given through intraperitoneal route (i.p.) produced dose-related antinociception when assessed on acetic acid-induced abdominal writhing test in mice. In addition, the i.p. administration of zerumbone exhibited significant inhibition of the neurogenic pain induced by intraplantar (i.pl.) injection of capsaicin and bradykinin. Likewise, zerumbone given by i.p. route reduced the nociception produced by i.pl. injection of glutamate and phorbol myristate acetate (PMA). The antinociception caused by zerumbone in the acetic acid test was significantly attenuated by i.p. pre-treatment of mice with l-arginine (nitric oxide precursor) and glibenclamide (ATP-sensitive K(+) channel inhibitor). However, the antinociception of zerumbone was enhanced by methylene blue (non-specific gyanylyl cyclase inhibitor). Together, these results indicate that zerumbone produces pronounced antinociception against chemical models of nociception in mice. It also strongly suggests that the l-arginine-nitric oxide-cGMP-PKC-K(+) ATP channel pathways, the TRPV1 and kinin B2 receptors play an important role in the zerumbone-induced antinociception.

Superoxide and Nitric Oxide Involvement in Enhancing of N-methyl-D-aspartate Receptor-Mediated Central Sensitization in the Chronic Post-ischemia Pain Model

BACKGROUND

Recent studies indicate that reactive oxygen species (ROS) are involved in persistent pain, including neuropathic and inflammatory pain. Since the data suggest that ROS are involved in central sensitization, the present study examines the levels of activated N-methyl-D-aspartate (NMDA) receptors in the dorsal horn after an exogenous supply of three antioxidants in rats with chronic post-ischemia pain (CPIP). This serves as an animal model of complex regional pain syndrome type-I induced by hindpaw ischemia/reperfusion injury.

METHODS

The application of tight-fitting O-rings for a period of three hours produced CPIP in male Sprague-Dawley rats. Allopurinol 4 mg/kg, allopurinol 40 mg/kg, superoxide dismutase (SOD) 4,000 U/kg, N-nitro-L-arginine methyl ester (L-NAME) 10 mg/kg and SOD 4,000 U/kg plus L-NAME 10 mg/kg were administered intraperitoneally just after O-ring application and on the first and second days after reperfusion. Mechanical allodynia was measured, and activation of the NMDA receptor subunit 1 (pNR1) of the lumbar spinal cord (L4-L6) was analyzed by the Western blot three days after reperfusion.

RESULTS

Allopurinol reduced mechanical allodynia and attenuated the enhancement of spinal pNR1 expression in CPIP rats. SOD and L-NAME also blocked spinal pNR1 in accordance with the reduced mechanical allodynia in rats with CPIP.

CONCLUSIONS

The present data suggest the contribution of superoxide, produced via xanthine oxidase, and the participation of superoxide and nitric oxide as a precursor of peroxynitrite in NMDA mediated central sensitization. Finally, the findings support a therapeutic potential for the manipulation of superoxide and nitric oxide in ischemia/reperfusion related pain conditions.

Biological Time‐Dependent Difference in Effect of Peroxynitrite Demonstrated by the Mouse Hot Plate Pain Model

We previously demonstrated the rhythmic pattern of L-arginine/nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) cascade in nociceptive processes. The coupled production of excess NO and superoxide leads to the formation of an unstable intermediate peroxynitrite, which is primarily responsible for NO-mediated toxicity. In the present study, we evaluated the biological time-dependent effects of exogenously administered peroxynitrite on nociceptive processes and peroxynitrite-induced changes in the analgesic effect of morphine using the mouse hot-plate pain model. Experiments were performed at four different times of day (1, 7, 13, and 19 hours after lights on, i.e., HALO) in mice of both sexes synchronized to a 12 h:12 h light-dark cycle. Animals were injected intraperitoneally (i.p.) with saline or 10 mg/kg morphine 30 min before and 0.001 mg/kg peroxynitrite 30 sec before hot-plate testing, respectively. The analgesic effect of morphine exhibited significant biological time-dependent differences in the thermally-induced algesia; whereas, administration of peroxynitrite alone exhibited either significant algesic or analgesic effect, depending on the circadian time of its injection. Concomitant administration of peroxynitrite and morphine reduced morphine-induced analgesia at three of the four different study time points. In conclusion, peroxynitrite displayed nociceptive and antinociceptive when administered alone according to the circadian time of treatment, while it diminished analgesic activity when administered in combination with morphine at certain biological times.

Pre-emptive anti-hyperalgesic effect of electroacupuncture in carrageenan-induced inflammation: role of nitric oxide

Central sensitization theory has been defined as pivotal for understanding the excitability changes in central neurons following peripheral inflammation or neuropathic injury. Considerable evidence has demonstrated that activation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors and subsequent nitric oxide (NO) production are the key in these changes. Consequently, neuromodulator drugs have been developed during the last decades. The electroacupuncture (EA) that acts as biochemical modulator in the spinal horn cord would prevent these changes. The aim of this study was to determine the thermal anti-hyperalgesic effect of EA (10 Hz, 3 mA) and its combination with L-NAME as nitric oxide synthase (NOS) inhibitor in carrageenan-induced hyperalgesia in rats. Also, it investigated the changes in the plasmatic concentrations of NO metabolites. Moreover, the EA combination with sub-effective dose of ketamine as a NMDA antagonist was tested. The EA pre-treatment conducted in unsedated, unrestrained and conscious animals showed a thermal anti-hyperalgesic effect in correspondence with plasmatic increase of NO metabolites. The L-NAME (30 mg/kg) pre-administration decreased significantly the plasmatic concentrations of NO(2)(-)/NO(3)(-) and suppressed the anti-hyperalgesic effect of EA. The combination of EA with ketamine enhanced the anti-hyperalgesic effect. These data constitute the first report that suggested the participation, at least in part, of the L-arginine-NOS-NO-GMPc pathway activation in anti-hyperalgesic effect of EA in carrageenan-induced inflammation model.

The role of NO-cGMP pathway and potassium channels on the relaxation induced by clonidine in the rat mesenteric arterial bed

The mechanisms involved in the vasodilation action of clonidine have not yet been completely elucidated. We investigated the potential mechanisms that seem to be involved in the clonidine vasodilator effect using rat isolated mesenteric arterial bed (MAB). In precontracted MAB, clonidine (10-300 pmol) induced a dose-dependent relaxation, that was inhibited by endothelium removal (deoxycholic acid - 2.5 mM) and reduced by the alpha(2) adrenoceptor inhibitors yohimbine (1-3 microM) and rauwolscine (1 microM). The endothelium-dependent vasodilation induced by clonidine was reduced by the nitric oxide (NO) synthase inhibitor L-NAME (0.3 mM) and guanylyl cyclase inhibitor ODQ (10 microM) but was not affected by indomethacin (3-10 microM) alone. High K+ (25 mM) solution reduced the vasodilator effect of clonidine that was further attenuated by L-NAME. In the presence of high K+ plus L-NAME, the residual vasodilator effect of clonidine was further reduced by indomethacin (3 microM). The Ca(2+)-dependent K+ channel (K+(Ca2+)) inhibitors, charybdotoxin (ChTx; 0.1 microM) plus apamin (0.1 microM), also reduced the vasodilation induced by clonidine, however this response was not further reduced in the presence of L-NAME as observed with acetylcholine (10 pmol). In the presence of ATP-dependent K+ channel (K+(ATP)) blocker, glibenclamide (10 microM), the inhibitory effect of ChTx plus apamin plus L-NAME was increased. In contrast, the vasodilation induced by clonidine was not affected by voltage-dependent K+ channels (K(V)) blocker, 4-aminopyridine (4-AP, 1 mM). In conclusion, our results demonstrate that clonidine activates alpha(2)-adrenoceptors in rat MAB and that the endothelium-dependent vasodilation is mediated by activation of NO-cGMP pathway, hyperpolarization due to activation of K+(Ca) and K+(ATP) channels. Prostaglandins might participate in the vasodilator effect of clonidine when NO and EDHF mechanisms are blunted.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.