Celecoxib reduces hyperalgesia and tactile allodynia in diabetic rats

Celecoxib ameliorates diabetic neuropathy by decreasing apoptosis and oxidative stress in dorsal root ganglion neurons via the miR-155/COX-2 axis

Celecoxib (CXB) is the only clinical cyclooxygenase-2 (COX-2) inhibitor. Oral administration of CXB in experimental diabetic mice effectively relieved the symptoms of diabetic neuropathy (DN); however, the molecular mechanism remains unclear. The present study aimed to investigate the potential molecular mechanisms of CXB in the treatment of DN. An in vitro cellular model of DN was produced by stimulating dorsal root ganglion (DRG) neurons with high glucose. Cell viability and apoptosis were assessed by Cell Counting Kit-8 assays and flow cytometry, respectively. Reactive oxygen species (ROS) kits, ELISA kits and western blotting were used to determine oxidative cellular damage. The expression level of microRNA (miR)-155 was analyzed by reverse transcription-quantitative PCR. The starBase database and dual-luciferase assays were performed to predict and determine the interaction between miR-155 and COX-2. Protein expression of neurotrophic factors, oxidative stress-related proteins and COX-2 were analyzed by western blotting. Incubation with high glucose led to a decrease in DRG neuron cell viability, facilitated apoptosis, downregulated NGF and BDNF expression, increased ROS and MDA generation and decreased SOD activity. Treatment with CXB significantly protected DRG neurons against high glucose-evoked damage. CXB promoted the expression of miR-155 and COX-2 was revealed to be a direct target of miR-155. Inhibition of COX-2 enhanced the protective effect of CXB on DRG neurons and that treatment with an miR-155 inhibitor partially rescued this effect. The present study demonstrated the involvement of the miR-155/COX-2 axis in the protective effect of CXB against high glucose-induced DN.

Synergistic antiallodynic and antihyperalgesic interaction between L-DOPA and celecoxib in parkinsonian rats is mediated by NO-cGMP-ATP-sensitive K+ channel

Pain is a usual and troublesome non-motor symptom of Parkinson's disease, with a prevalence of 29-82%. Therefore, it's vital to find pharmacological treatments for managing PD-associated pain symptoms, to improve patients' quality of life. For this reason, we tested the possible synergy between L-DOPA and celecoxib in decreasing allodynia and hyperalgesia induced by unilateral lesioning with 6-OHDA into the SNpc in rats. We also tested whether the antiallodynic and antihyperalgesic effect induced by combination of L-DOPA and celecoxib is mediated by the NO-cGMP-ATP-sensitive K⁺ channel pathway. Tactile allodynia and mechanical hyperalgesia were evaluated using von Frey filament. Isobolographic analyses were employed to define the nature of the drug interaction using a fixed dose ratio (0.5: 0.5). We found that acute and sub-acute (10-day) treatment with a single dose of L-DOPA (3-25 mg/kg, i. p.) or celecoxib (2.5-20 mg/kg, i. p.) induced a dose-dependent antiallodynic and antihyperalgesic effect in parkinsonian rats. Isobolographic analysis revealed that the ED₅₀ values obtained by L-DOPA + celecoxib combination was significantly less than calculated additive values, indicating that co-administration of L-DOPA with celecoxib produces synergistic interactions in its antiallodynic and antihyperalgesic effect in animals with nigrostriatal lesions. Moreover, the antiallodynic and antihyperalgesic effects induced by L-DOPA + celecoxib combination were blocked by intrathecal pre-treatment with L-NAME, ODQ, and glibenclamide. Taken together, the data suggest that L-DOPA + celecoxib combination produces an antiallodynic and antihyperalgesic synergistic interaction at the systemic level, and these effects are mediated, at the central level, through activation of the NO-cGMP-ATP-sensitive K⁺ channel pathway.

Catecholaminergic and opioidergic system mediated effects of reboxetine on diabetic neuropathic pain

RATIONALE

Current data indicate that the noradrenergic system plays a critical role in neuropathic pain treatment. Notably, drugs that directly affect this system may have curative potential in neuropathy-associated pain.

OBJECTIVES

The aim of this study was to evaluate the potential therapeutic efficacy of reboxetine, a potent and selective noradrenaline reuptake inhibitor, on hyperalgesia and allodynia responses in rats with experimental diabetes. Furthermore, mechanistic studies were performed to elucidate the possible mode of actions.

METHODS

Experimental diabetes was induced by a single dose of streptozotocin. Mechanical hyperalgesia, mechanical allodynia, thermal hyperalgesia, and thermal allodynia responses in diabetic rats were evaluated by Randall-Selitto, dynamic plantar, Hargreaves, and warm plate tests, respectively.

RESULTS

Reboxetine treatment (8 and 16 mg/kg for 2 weeks) demonstrated an effect comparable to that of the reference drug, pregabalin, improving the hyperalgesic and allodynic responses secondary to diabetes mellitus. Pretreatment with phentolamine, metoprolol, SR 59230A, and atropine did not alter the abovementioned effects of reboxetine; however, the administration of α-methyl-para-tyrosine methyl ester, propranolol, ICI-118,551, SCH-23390, sulpiride, and naltrindole significantly inhibited these effects. Moreover, reboxetine did not induce a significant difference in the rat plasma glucose levels.

CONCLUSIONS

Our findings indicate that the antihyperalgesic and antiallodynic effects of reboxetine are mediated by the catecholaminergic system; β₂-adrenoceptors; D₁-, D₂/D₃-dopaminergic receptors; and δ-opioid receptors. The results suggest that this analgesic effect of reboxetine, besides its neutral profile on glycemic control, may be advantageous in the pharmacotherapy of diabetic neuropathy-induced pain.

Hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2) ion channels drive pain in mouse models of diabetic neuropathy

Diabetic patients frequently suffer from continuous pain that is poorly treated by currently available analgesics. We used mouse models of type 1 and type 2 diabetes to investigate a possible role for the hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2) ion channels as drivers of diabetic pain. Blocking or genetically deleting HCN2 channels in small nociceptive neurons suppressed diabetes-associated mechanical allodynia and prevented neuronal activation of second-order neurons in the spinal cord in mice. In addition, we found that intracellular cyclic adenosine monophosphate (cAMP), a positive HCN2 modulator, is increased in somatosensory neurons in an animal model of painful diabetes. We propose that the increased intracellular cAMP drives diabetes-associated pain by facilitating HCN2 activation and consequently promoting repetitive firing in primary nociceptive nerve fibers. Our results suggest that HCN2 may be an analgesic target in the treatment of painful diabetic neuropathy.

Chemical characterization and pharmacological assessment of polysaccharide free, standardized cashew gum extract (Anacardium occidentale L.)

ETHNOPHARMACOLOGICAL RELEVANCE

The cashew gum (Anacardium occidentale L.) is used in traditional Brazilian medicine in the treatment of inflammatory conditions, asthma, diabetes, and gastrointestinal disturbances.

AIM OF THE STUDY

In the present study, we aimed at forming a chemical characterization and investigation of the antinociceptive and anti-inflammatory activities of the aqueous extract of cashew gum without the presence of polysaccharides in its composition (CGE).

MATERIALS AND METHODS

The CGE was obtained after the precipitation and removal of polysaccharides through the use of acetone. After, the acetone was removed by rotaevaporation, and the concentrated extract was lyophilized. The chemical characterization of CGE was performed by liquid chromatography mass spectrometry (LC-MS) and tandem mass spectrometry (MS/MS) analyses. Mice were used for the evaluation of the antinociceptive and anti-inflammatory activities. CGE was analyzed via the Irwin test, acetic acid-induced writhing test, formalin-induced pain test, and carrageenan-induced paw edema test. The motor activity or probable sedation was verified through the chimney, open-field, and sodium pentobarbital-induced sleep tests. We investigated if the analgesic and anti-inflammatory effects of CGE depend of reduction in PGE₂ levels, were performed the carrageenan or PGE₂-induced hyperalgesia tests.

RESULTS

The chemical characterization of CGE showed the presence of anacardic acids as the predominant phytoconstituents. The treatment with CGE (75, 150, and 300mg/kg, p.o.) inhibited the number of writhing in a dose-dependent manner. With an intermediate dose, CGE did not cause motor impairment with the chimney test or alterations in either the open-field or sodium pentobarbital-induced sleep. In the formalin-induced pain test, CGE (150mg/kg, p.o.) produced an antinociceptive effect only in the first phase of the test, suggesting anti-inflammatory activity. With the same dosage, CGE also reduced the carrageenan-induced paw edema at all hours of the test, confirming its anti-inflammatory effect. Furthermore, CGE (150mg/kg, p.o.) presented an antihyperalgic effect at all hours of the carrageenan-induced hyperalgesia test. However, this dose of CGE was not able to reduce the hyperalgesia induced by PGE₂, suggesting that the anti-inflammatory effect of this extract depends on the reduction in the PGE₂ levels.

CONCLUSION

The anacardic acids are the predominant phytoconstituents identified in the CGE. The action mechanisms of CGE suggest the reduction in the PGE₂ levels. These findings support the use of cashew gum in popular medicine and demonstrate that part of its antinociceptive and anti-inflammatory effects should also be attributed to the presence of anacardic acids in its composition, independent of the presence of polysaccharides.

Celecoxib Alleviates Memory Deficits by Downregulation of COX-2 Expression and Upregulation of the BDNF-TrkB Signaling Pathway in a Diabetic Rat Model

Previous studies conveyed that diabetes causes learning and memory deficits. Data also suggest that celecoxib exerts an anti-hyperalgesic, anti-allodynic, and a plethora of other beneficial effects in diabetic rats. However, whether celecoxib could alleviate memory deficit in diabetic rat is unknown. In the present study, we aimed to examine the potential of celecoxib to counter memory deficits in diabetes. Experimental diabetes was induced by streptozotocin (STZ, 60 mg/kg) in male SD rats. Rats were divided into three groups (n = 16/group): normal control group injected with normal saline, diabetes group injected with STZ, and diabetes + celecoxib group in which diabetic rats were administered with celecoxib by gavage in drinking water (10 mg/kg) for 10 days in terms of which memory performance in animals was measured, hippocampal tissue harvested, and long-term potentiation assessed. Western blotting and immunohistochemical staining were performed to determine cyclooxygenase 2 (COX-2) expression in hippocampus. The results showed that a rat model of STZ-induced diabetes was successfully established and that celecoxib treatment significantly improved the associated nephropathy and inflammation. Moreover, spatial memory and hippocampal long-term potentiation (LTP) were impaired in diabetic model (P < 0.05). Interestingly, our data revealed that oral application of celecoxib reversed the memory deficit and hippocampal LTP in the diabetic rats. To understand the underlying mechanisms, the expression of some important pathways involved in memory impairment was determined. We found that brain-derived neurotrophic factor (BDNF) and phosphorylated tropomyosin-related kinase (p-TrkB) were decreased in diabetic rats but were effectively reversed by celecoxib treatment. As evidenced by western blotting and immunohistochemical staining, the expression of COX-2 in hippocampus was significantly upregulated in diabetic rat (P < 0.05) but inhibited by celecoxib treatment. The present findings provide novel data that celecoxib reverses memory deficits via probable downregulation of hippocampal COX-2 expression and upregulation of the BDNF-TrkB signaling pathway in a diabetic rat.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 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, drug abuse and alcohol, 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.

Celecoxib alleviates oxaliplatin-induced hyperalgesia through inhibition of spinal ERK1/2 signaling

Numerous pieces of evidence have revealed that oxaliplatin (OXA) evokes mechanical and cold hypersensitivity. However, the mechanism underlying these bothersome side effects needs to be further investigated. It is well known that cyclooxygenase-2 (COX-2) and extracellular signal-regulated kinases (ERK1/2) signaling play crucial roles in several pain states. Our previous data showed that Akt2 in the dorsal root ganglion (DRG) participated in the regulation of OXA-induced neuropathic pain. But it is still unclear whether spinal ERK1/2 signaling is involved in the regulation of OXA-induced hyperalgesia, and the linkage between COX-2 and ERK1/2 signaling in mediating OXA-induced hyperalgesia also remains unclear. In this research, we investigated the possible mechanism of celecoxib, a COX-2 inhibitor, in OXA-induced neuropathic pain. Our results show that single dose of OXA (12 mg/kg) significantly attenuated both the tail withdrawal latency (TWL) and mechanical withdrawal threshold (MWT) at days 4 after the OXA treatment. Administration of celecoxib (30 mg/kg/day) for 4 and 6 days inhibited the decrease in TWL and MWT, and each was significantly higher than that of the OXA+vehicle group and was equivalent to that of the vehicles group. OXA increased the expression of cyclooxygenase-2 (COX-2) mRNA and phosphorylated extracellular signal-regulated kinase1/2 (pERK1/2) protein in the lumbar 4-5 (L4-5) spinal cord dorsal horn neurons. Administration of celecoxib for 7 days suppressed the increase in expression of COX-2 and pERK1/2 induced by OXA. Our findings suggested that COX-2 and ERK1/2 signaling in spinal cord contributed to the OXA-induced neuropathic pain.

HCN2 ion channels: basic science opens up possibilities for therapeutic intervention in neuropathic pain

Nociception — the ability to detect painful stimuli — is an invaluable sense that warns against present or imminent damage. In patients with chronic pain, however, this warning signal persists in the absence of any genuine threat and affects all aspects of everyday life. Neuropathic pain, a form of chronic pain caused by damage to sensory nerves themselves, is dishearteningly refractory to drugs that may work in other types of pain and is a major unmet medical need begging for novel analgesics. Hyperpolarisation-activated cyclic nucleotide (HCN)-modulated ion channels are best known for their fundamental pacemaker role in the heart; here, we review data demonstrating that the HCN2 isoform acts in an analogous way as a ‘pacemaker for pain’, in that its activity in nociceptive neurons is critical for the maintenance of electrical activity and for the sensation of chronic pain in pathological pain states. Pharmacological block or genetic deletion of HCN2 in sensory neurons provides robust pain relief in a variety of animal models of inflammatory and neuropathic pain, without any effect on normal sensation of acute pain. We discuss the implications of these findings for our understanding of neuropathic pain pathogenesis, and we outline possible future opportunities for the development of efficacious and safe pharmacotherapies in a range of chronic pain syndromes.