Peripheral and central activation of nitric oxide-cyclic GMP pathway by sildenafil

Antinociceptive Effect of Lodenafil Carbonate in Rodent Models of Inflammatory Pain and Spinal Nerve Ligation-Induced Neuropathic Pain

Introduction

New therapeutic alternatives for pain relief include the use of phosphodiesterase-5 (PDE5) inhibitors, which could prevent the transmission of painful stimuli by neuron hyperpolarization via nitric oxide (NO)/cyclic 3',5'-guanosine monophosphate (cGMP) pathway. The present work investigated the antinociceptive activity of a new PDE5 inhibitor, lodenafil carbonate, in inflammatory and neuropathic pain models.

Methods and Results

Although no effect was detected on neurogenic phase of formalin test in mice, oral administration of lodenafil carbonate dose-dependently reduced reactivity in the inflammatory phase (200.6 ± 39.1 to 81.9 ± 18.8 s at 10 μmol/kg, p= 0.0172) and this effect was totally blocked by NO synthase inhibitor, L-Nω-nitroarginine methyl ester (L-NAME). Lodenafil carbonate (10 μmol/kg p.o.) significantly reduced nociceptive response as demonstrated by increased paw withdrawal latency to thermal stimulus (from 6.8 ± 0.7 to 10.6 ± 1.3 s, p= 0.0006) and paw withdrawal threshold to compressive force (from 188.0 ± 14.0 to 252.5 ± 5.3 g, p<0.0001) in carrageenan-induced paw inflammation model. In a spinal nerve ligation-induced neuropathic pain, oral lodenafil carbonate (10 μmol/kg) also reversed thermal hyperalgesia and mechanical allodynia by increasing paw withdrawal latency from 17.9 ± 1.5 to 22.8 ± 1.9 s (p= 0.0062) and paw withdrawal threshold from 26.0 ± 2.8 to 41.4 ± 2.9 g (p= 0.0196). These effects were reinforced by the reduced GFAP (3.4 ± 0.5 to 1.4 ± 0.3%, p= 0.0253) and TNF-alpha (1.1 ± 0.1 to 0.4 ± 0.1%, p= 0.0111) stained area densities as detected by immunofluorescence in ipsilateral dorsal horns.

Conclusion

Lodenafil carbonate demonstrates important analgesic activity by promoting presynaptic hyperpolarization and preventing neuroplastic changes, which may perpetuate chronic pain, thus representing a potential treatment for neuropathic pain.

Nitric oxide: Antidepressant mechanisms and inflammation

Millions of individuals worldwide suffers from mood disorders, especially major depressive disorder (MDD), which has a high rate of disease burden in society. Although targeting the biogenic amines including serotonin, and norepinephrine have provided invaluable links with the pharmacological treatment of MDD over the last four decades, a growing body of evidence suggest that other biologic systems could contribute to the pathophysiology and treatment of MDD. In this chapter, we highlight the potential role of nitric oxide (NO) signaling in the pathophysiology and thereby treatment of MDD. This has been investigated over the last four decades by showing that (i) levels of NO are altered in patients with major depression; (ii) modulators of NO signaling exert antidepressant effects in patients with MDD or in the animal studies; (iii) NO signaling could be targeted by a variety of antidepressants in animal models of depression; and (iv) NO signaling can potentially modulate the inflammatory pathways that underlie the pathophysiology of MDD. These findings, which hypothesize an NO involvement in MDD, can provide a new insight into novel therapeutic approaches for patients with MDD in the future.

Pathologic role of nitrergic neurotransmission in mood disorders

Mood disorders are chronic, recurrent mental diseases that affect millions of individuals worldwide. Although over the past 40 years the biogenic amine models have provided meaningful links with the clinical phenomena of, and the pharmacological treatments currently employed in, mood disorders, there is still a need to examine the contribution of other systems to the neurobiology and treatment of mood disorders. This article reviews the current literature describing the potential role of nitric oxide (NO) signaling in the pathophysiology and thereby the treatment of mood disorders. The hypothesis has arisen from several observations including (i) altered NO levels in patients with mood disorders; (ii) antidepressant effects of NO signaling blockers in both clinical and pre-clinical studies; (iii) interaction between conventional antidepressants/mood stabilizers and NO signaling modulators in several biochemical and behavioral studies; (iv) biochemical and physiological evidence of interaction between monoaminergic (serotonin, noradrenaline, and dopamine) system and NO signaling; (v) interaction between neurotrophic factors and NO signaling in mood regulation and neuroprotection; and finally (vi) a crucial role for NO signaling in the inflammatory processes involved in pathophysiology of mood disorders. These accumulating lines of evidence have provided a new insight into novel approaches for the treatment of mood disorders.

Central neural alterations predominate in an insect model of nociceptive sensitization

Many organisms respond to noxious stimuli with defensive maneuvers. This is noted in the hornworm, Manduca sexta, as a defensive strike response. After tissue damage, organisms typically display sensitized responses to both noxious or normally innocuous stimuli. To further understand this phenomenon, we used novel in situ and in vitro preparations based on paired extracellular nerve recordings and videography to identify central and peripheral nerves responsible for nociception and sensitization of the defensive behavior in M. sexta. In addition, we used the in vivo defensive strike response threshold assayed with von Frey filaments to examine the roles that N-methyl-D-aspartate receptor (NMDAR) and hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels play in this nociceptive sensitization using the inhibitors MK-801 and AP5 (NMDAR), and ivabradine and ZD7288 (HCN). Using our new preparations, we found that afferent activity evoked by noxious pinch in these preparations was conveyed to central ganglia by axons in the anterior- and lateral-dorsal nerve branches, and that sensitization induced by tissue damage was mediated centrally. Furthermore, sensitization was blocked by all inhibitors tested except the inactive isomer L-AP5, and reversed by ivabradine both in vivo and in vitro. Our findings suggest that M. sexta's sensitization occurs through central signal amplification. Due to the relatively natural sensitization method and conserved molecular actions, we suggest that M. sexta may be a valuable model for studying the electrophysiological properties of nociceptive sensitization and potentially related conditions such as allodynia and hyperalgesia in a comparative setting that offers unique experimental advantages. J. Comp. Neurol. 525:1176-1191, 2017. © 2016 Wiley Periodicals, Inc.

Involvement of NMDA receptors and L-arginine/nitric oxide/cyclic guanosine monophosphate pathway in the antidepressant-like effects of topiramate in mice forced swimming test

Topiramate (TPM) is an agent primarily used in the treatment of epilepsy. Using mice model of forced swimming test (FST) the current study was basically aimed to investigate the influence of TPM on depression by inhibiting NMDA receptor and nitric oxide-cGMP production. When TPM was administered in a dose of 20 and 30 mg/kg by i.p. route it reduced the immobility time during FST. However this effect of TPM (30 mg/kg, i.p.) in the FST was abolished when the mice were pretreated either with NMDA (75 mg/kg, i.p.), or l-arginine (750 mg/kg, i.p. NO precursor), or sildenafil (5mg/kg, i.p. Phosphodiesterase 5 inhibitor). The immobility time in the FST was reduced after administration of L-NAME (10mg/kg, i.p, a non-specific NOS inhibitor), 7-nitoinidazol (30 mg/kg, i.p. a nNOS inhibitor) or MK-801 (0.05 mg/kg, i.p, a NMDA receptor antagonist) in combination with a subeffective dose of TPM (10mg/kg, i.p.) as compared with single use of either drug. Co-administrated of lower doses of MK-801 (0.01 mg/kg) or L-NAME (1mg/kg) failed to effect immobility time. However, simultaneous administration of these two agents in the same doses with subeffective dose of TPM (10mg/kg, i.p.), reduced the immobility time during FST. None of these drugs were found to have a profound effect on the locomotor activity per se during the open field test. Taken together, our data demonstrates that TPM exhibit antidepressant-like effect which is accomplished either due to inhibition of NMDA receptors or NO-cGMP production.

Nitric oxide suppresses L-type calcium currents in basilar artery smooth muscle cells in rabbits

OBJECTIVES

Nitric oxide (NO) is well known to be a vasodilator, and NO donor compounds are currently used for treating vasospasm following subarachnoid hemorrhage. However, the action mechanism of cerebral vascular relaxation is not yet clear. L-type calcium channels have been determined to play an essential role in smooth muscle contraction. To investigate the role of L-type calcium channels in NO-induced relaxation of basilar smooth muscle cells, we examined the effect of the NO donor, sodium nitroprusside (SNP) on calcium (Ca2+) currents using smooth muscle cells isolated from a rabbit basilar artery.

METHOD

The smooth muscle cells were isolated from rabbit basilar artery by enzyme treatment. To identify L-type Ca2+ currents, we used cesium chloride, a potassium channel blocker and Bay K8644, an activator of L-type Ca2+ channel.

RESULTS

The L-type calcium currents (91±13.0 pA; n = 11) were significantly reduced by SNP (32±5 pA; n = 11; P<0.05). 1H-[1,2,4] Oxadiazolo [4,3-a] quinoxalin-1-one, a 3',5'-cyclic guanosine monophosphate inhibitor, blocked the effect of SNP on L-type Ca2+ currents, and similar results were obtained after the application of 7-nitroindazole, a specific NO synthase inhibitor. Furthermore, inward currents were enhanced by Bay K8644 (170±22 pA; n = 5) and were suppressed by SNP (54±13 pA; n = 5; P<0.05).

DISCUSSION

These results demonstrate that NO suppresses the L-type Ca2+ currents in rabbit basilar smooth muscle cells, and suggest that L-type Ca2+ channels may play a pivotal role in NO-induced vascular relaxation.

NO/cGMP production is important for the endogenous peripheral control of hyperalgesia during inflammation

Various studies have demonstrated the role of the nitric oxide (NO)/cGMP pathway in pain processing. Our group has also shown that this system participates in opioid-induced antinociception during peripheral inflammation. We have previously observed that inflammation mobilizes an endogenous opioidergic system to control hyperalgesia. Here, we investigated whether the NO/cGMP pathway underlies peripheral endogenous nociception control during inflammation. In this study, a pharmacological approach was used in conjunction with the rat paw pressure test to assess the effects of intraplantar NO synthase inhibitor NG-Nitro-l-arginine (NOArg), guanylyl cyclase inhibitor methylene blue (MB), phosphodiesterase-5 inhibitor zaprinast (ZP), or NO precursor l-arginine injection on carrageenan-induced hyperalgesia, which mimics an inflammatory process, or by prostaglandin E(2) (PGE(2)), which directly sensitizes nociceptors. Intraplantar carrageenan (62.5, 125, 250 or 500μg) or PGE(2) (0.1, 0.5 or 2μg) administration produced hyperalgesia, which manifested as a reduction in the rat nociceptive threshold to mechanical stimuli. NOArg (25, 50 or 100μg/paw) and MB (125, 250 or 500μg/paw) induced significant and dose-dependent reductions in the nociceptive threshold of carrageenan-induced (125μg/paw) hyperalgesia, but not PGE(2)-induced (0.5μg/paw) hyperalgesia. This was a local effect because it did not produce any modifications in the contralateral paw. Both Zaprinast (100, 200 or 400μg/paw) and l-arginine (100, 200 or 400μg/paw) significantly counteracted carrageenan-induced hyperalgesia (250μg/paw), yielding an increase in the nociceptive threshold compared with the control. Zaprinast (200μg/paw) or l-arginine (400μg/paw) did not produce an antinociceptive effect in the contralateral paw, indicating local action. In addition, at the same dose that was able to modify carrageenan-induced hyperalgesia, neither zaprinast nor l-arginine modified PGE(2) (2μg) injection-induced hyperalgesia of the rat paw. Taken together, these results indicate that the l-arginine/NO/cGMP pathway functions as an endogenous modulator of peripheral inflammatory hyperalgesia.

Cellular and molecular actions of Methylene Blue in the nervous system

Methylene Blue (MB), following its introduction to biology in the 19th century by Ehrlich, has found uses in various areas of medicine and biology. At present, MB is the first line of treatment in methemoglobinemias, is used frequently in the treatment of ifosfamide-induced encephalopathy, and is routinely employed as a diagnostic tool in surgical procedures. Furthermore, recent studies suggest that MB has beneficial effects in Alzheimer's disease and memory improvement. Although the modulation of the cGMP pathway is considered the most significant effect of MB, mediating its pharmacological actions, recent studies indicate that it has multiple cellular and molecular targets. In the majority of cases, biological effects and clinical applications of MB are dictated by its unique physicochemical properties including its planar structure, redox chemistry, ionic charges, and light spectrum characteristics. In this review article, these physicochemical features and the actions of MB on multiple cellular and molecular targets are discussed with regard to their relevance to the nervous system.

Role of cGMP and cAMP in the hemodynamic response to intrathecal sildenafil administration

INTRODUCTION

Results from our laboratory have demonstrated that intracerebroventricular administration of sildenafil to conscious rats promoted a noticeable increase in both lumbar sympathetic activity and heart rate, with no change in the mean arterial pressure. The intracerebroventricular administration of sildenafil may have produced the hemodynamic effects by activating sympathetic preganglionic neurons in the supraspinal regions and spinal cord. It is well documented that sildenafil increases intracellular cGMP levels by inhibiting phosphodiesterase type 5 and increases cAMP levels by inhibiting other phosphodiesterases.

OBJECTIVE

To examine and compare, in conscious rats, the hemodynamic response following the intrathecal administration of sildenafil, 8-bromo-cGMP (an analog of cGMP), forskolin (an activator of adenylate cyclase), or dibutyryl-cAMP (an analog of cAMP) in order to elucidate the possible role of the sympathetic preganglionic neurons in the observed hemodynamic response.

RESULTS

The hemodynamic responses observed following intrathecal administration of the studied drugs demonstrated the following: 1) sildenafil increased the mean arterial pressure and heart rate in a dose-dependent manner, 2) increasing doses of 8-bromo-cGMP did not alter the mean arterial pressure and heart rate, 3) forskolin did not affect the mean arterial pressure but did increase the heart rate and 4) dibutyryl-cAMP increased the mean arterial pressure and heart rate, similar to the effect observed following the intrathecal injection of the highest dose of sildenafil.

CONCLUSION

Overall, the findings of the current study suggest that the cardiovascular response following the intrathecal administration of sildenafil to conscious rats involves the inhibition of phosphodiesterases other than phosphodiesterase type 5 that increase the cAMP level and the activation of sympathetic preganglionic neurons.

Roles of adenosine and serotonin receptors on the antinociception of sildenafil in the spinal cord of rats

PURPOSE

The phosphodiesterase 5 inhibitor sildenafil has antinociceptive effects, mediated by an increase in cGMP. This study examined the role of spinal adenosine and serotonin receptors played in the antinociceptive effects of intrathecal sildenafil.

MATERIALS AND METHODS

Intrathecal catheters were inserted into the subarachnoid space of Sprague-Dawley male rats as a drug delivery device. Pain was induced by injecting formalin into the plantar surface of rats and observing nociceptive behavior (flinching response) for 60 minutes. Then, the effects of intrathecal adenosine and serotonin receptor antagonists on the antinociceptive activity of intrathecal sildenafil were examined.

RESULTS

Intrathecal sildenafil suppressed the flinching response in a dose-dependent manner during phases 1 and 2 in the formalin test. Both CGS 15943 and dihydroergocristine decreased the antinociceptive effects of sildenafil during phases 1 and 2 in the formalin test.

CONCLUSION

Intrathecal sildenafil effectively attenuated the pain evoked by formalin injection. Both adenosine and serotonin receptors may be involved in the antinociceptive action of sildenafil at the spinal level.

Additive antinociception between intrathecal sildenafil and morphine in the rat formalin test

The possible characteristics of spinal interaction between sildenafil (phosphodiesterase 5 inhibitor) and morphine on formalin-induced nociception in rats was examined. Then the role of the opioid receptor in the effect of sildenafil was further investigated. Catheters were inserted into the intrathecal space of male Sprague-Dawley rats. For induction of pain, 50 microL of 5% formalin solution was applied to the hind-paw. Isobolographic analysis was used for the evaluation of drug interaction between sildenafil and morphine. Furthermore, naloxone was intrathecally given to verify the involvement of the opioid receptor in the antinociception of sildenafil. Both sildenafil and morphine produced an antinociceptive effect during phase 1 and phase 2 in the formalin test. The isobolographic analysis revealed an additive interaction after intrathecal delivery of the sildenafil-morphine mixture in both phases. Intrathecal naloxone reversed the antinociception of sildenafil in both phases. These results suggest that sildenafil, morphine, and the mixture of the two drugs are effective against acute pain and facilitated pain state at the spinal level. Thus, the spinal combination of sildenafil with morphine may be useful in the management of the same state. Furthermore, the opioid receptor is contributable to the antinocieptive mechanism of sildenafil at the spinal level.

Possible involvement of L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling pathway in the antidepressant activity of berberine chloride

Berberine is an isoquinoline alkaloid isolated from Berberis aristata, a major herb widely used in Indian and Chinese systems of medicine. Berberine possessed a wide range of biological activity including antidiarrheal, antimicrobial, anti-inflammatory effects and some central nervous system activity as well. The present study was designed to explore the antidepressant activity and its possible mechanism of action. Further, the involvement of L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling pathway in the antidepressant action of berberine chloride was investigated. The antidepressant activity was assessed in forced-swim and tail-suspension tests. Total immobility period was recorded during a six-min test. Berberine (5-20 mg/kg, i.p.) produced a reduction in immobility period in both the tests. When berberine (5 mg/kg, i.p.) was co-administered with other antidepressant drugs, it enhanced the anti-immobility effect of subeffective doses of imipramine (2 mg/kg, i.p.), desipramine (5 mg/kg, i.p.), tranylcypromine (4 mg/kg, i.p.), fluoxetine (5 mg/kg, i.p.), venlafaxine (2 mg/kg, i.p.) or bupropion (10 mg/kg, i.p.) in forced-swim test. However, berberine did not modify the effects of mianserine (32 mg/kg, i.p.) or trazodone (2 mg/kg, i.p.), the two atypical antidepressant drugs. The neurochemical analysis revealed that berberine (5 mg/kg, i.p.) increased the levels of norepinephrine, serotonin or dopamine in the mouse whole brain. The antidepressant-like effect of berberine (5 mg/kg, i.p.) in forced-swim test was prevented by pretreatment with L-arginine (750 mg/kg, i.p.) [substrate for nitric oxide synthase (NOS)]. Pretreatment of mice with 7-nitroindazole (25 mg/kg, i.p.) [a specific neuronal nitric oxide synthase (nNOS) inhibitor] produced potentiation of the action of subeffective dose of berberine (2 mg/kg, i.p.). In addition, treatment of mice with methylene blue (10 mg/kg, i.p.) [direct inhibitor of both nitric oxide synthase (NOS) and soluble guanylate cyclase (sGC)] potentiated the effect of berberine (2 mg/kg, i.p.) in the forced-swim test. Furthermore, the reduction in the immobility period elicited by berberine (5 mg/kg, i.p.) was also inhibited by pretreatment with sildenafil (5 mg/kg, i.p.) [phosphodiesterase 5 inhibitor]. The various modulators and their combination with berberine did not produce any changes in locomotor activity. Our findings demonstrated that berberine exerted antidepressant-like effect in various behavioural paradigms of despair possibly by modulating brain biogenic amines (norepinephrine, serotonin or dopamine) and further, the antidepressant-like effect of berberine in the forced-swim test involved an interaction with the L-arginine-NO-cGMP pathway.

Involvement of L-arginine-nitric oxide-cyclic guanosine monophosphate pathway in the antidepressant-like effect of venlafaxine in mice

The involvement of L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling pathway in the antidepressant action of venlafaxine (dual serotonin and norepinephrine reuptake inhibitor) was investigated in mice. The antidepressant activity was assessed in forced swim test (FST) behavioral paradigm. Total immobility time was registered during the period of 6 min. Venlafaxine produced dose-dependent (4-16 mg/kg, i.p.) reduction in immobility period. The antidepressant-like effect of venlafaxine (8 mg/kg, i.p.) was prevented by pretreatment with l-arginine (750 mg/kg, i.p.) [substrate for nitric oxide synthase (NOS)]. Pretreatment of mice with 7-nitroindazole (7-NI) (25 mg/kg, i.p.) [a specific neuronal nitric oxide synthase (nNOS) inhibitor] produced potentiation of the action of subeffective dose of venlafaxine (2 mg/kg, i.p.). In addition, treatment of mice with methylene blue (10 mg/kg, i.p.) [direct inhibitor of both nitric oxide synthase (NOS) and soluble guanylate cyclase (sGC)] potentiated the effect of venlafaxine (2 mg/kg, i.p.) in the FST. Furthermore, the reduction in the immobility time elicited by venlafaxine (8 mg/kg, i.p.) was also inhibited by pretreatment with sildenafil (5 mg/kg, i.p.) [phosphodiesterase 5 inhibitor]. The various modulators used in the study did not produce any changes in locomotor activity per se. The results demonstrated that the antidepressant-like effect of venlafaxine in the FST involved an interaction with the L-arginine-NO-cGMP pathway.

Involvement of nitric oxide (NO) signaling pathway in the antidepressant action of bupropion, a dopamine reuptake inhibitor

The present study was undertaken to elucidate the alterations in various behavioral and neurochemical basis of antidepressant action of bupropion [(+/-)-alpha-t-butylamino-3-chloropropiophenone], a dopamine reuptake inhibitor and to elucidate the possible mechanism of its action. The involvement of L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling pathway in the antidepressant action of bupropion was investigated besides its actions on various brain transmitters like norepinephrine, dopamine and homovanillic acid. Bupropion (10, 15, 20 and 40 mg/kg., i.p.) dose dependently inhibited the immobility period in mice in both forced swim test and tail suspension test. ED(50) values of bupropion in reducing the immobility period was found to be 18.5 and 18 mg/kg i.p., in forced swim test and tail suspension test, respectively. Bupropion (10, 20 and 40 mg/kg., i.p.) reversed the reserpine-induced behavioral despair also. When different doses (10, 15, 20 and 40 mg/kg., i.p.) of bupropion were tested for locomotor activity, it (15, 20 and 40 mg/kg., i.p.) increased locomotor activity. At 20 and 40 mg/kg doses the drug showed hypothermia. The neurochemical analysis of brain samples revealed that bupropion dose dependently (10-40 mg/kg., i.p.) increased the brain contents of dopamine and homovanillic acid in the mouse whole brain. The levels of norepinephrine were also increased at 20 mg/kg dose. The antidepressant-like effect of bupropion (20 mg/kg., i.p.) was prevented by pretreatment with L-arginine (750 mg/kg., i.p.) [substrate for nitric oxide synthase (NOS)]. Pretreatment of mice with 7-nitroindazole (25 mg/kg., i.p.) [a specific neuronal nitric oxide synthase (nNOS) inhibitor] produced potentiation of the action of subeffective dose of bupropion (10 mg/kg i.p.). In addition, treatment of mice with methylene blue (10 mg/kg., i.p.) [direct inhibitor of both nitric oxide synthase (NOS) and soluble guanylate cyclase (sGC)] potentiated the effect of bupropion (10 mg/kg., i.p.) in the forced swim test. Furthermore, the reduction in the immobility period elicited by bupropion (20 mg/kg., i.p.) was also inhibited by pretreatment with sildenafil (5 mg/kg., i.p.) [phosphodiesterase 5 inhibitor]. The study indicated that bupropion possesses antidepressant activities in different animal models of depression through its dopaminergic and/or by modulating the L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling pathway.