Olive (Olea europaea L.) leaf extract attenuates early diabetic neuropathic pain through prevention of high glucose-induced apoptosis: in vitro and in vivo studies

Aim of study

Since the leaves of olive have been recommended in the literature as a remedy for the treatment of diabetes and they also contain antioxidant agents, we decided to investigate the possible effects of olive leaf extract (OLE) on in vitro and in vivo models of diabetic pain neuropathy.

Materials and methods

The high glucose-induced cell damage in naive and NGF-treated Pheochromocytoma (PC12) cells and streptozotocin-induced diabetic rats were used. Tail-flick test was used to access nociceptive threshold. Cell viability was determined by MTT assay. Biochemical markers of neural apoptosis were evaluated using immunoblotting.

Results

We found that elevation of glucose (4 times of normal) sequentially increases functional cell damage and caspase-3 activation in NGF-treated PC12 cells. Incubation of cells with OLE (200, 400 and 600 μg/ml) decreased cell damage. Furthermore, the diabetic rats developed neuropathic pain which was evident from decreased tail-flick latency (thermal hyperalgesia). Activated caspase 3 and Bax/Bcl2 ratio were significantly increased in spinal cord of diabetic animals. OLE treatment (300 and 500 mg/kg per day) ameliorated hyperalgesia, inhibited caspase 3 activation and decreased Bax/Bcl2 ratio. Furthermore, OLE exhibited potent DPPH free radical scavenging capacity.

Conclusion

The results suggest that olive leaf extract inhibits high glucose-induced neural damage and suppresses diabetes-induced thermal hyperalgesia. The mechanisms of these effects may be due, at least in part, to reduce neuronal apoptosis and suggest therapeutic potential of olive leaf extract in attenuation of diabetic neuropathic pain.     

小剂量氯胺酮抑制瑞芬太尼麻醉后痛敏反应的临床研究

目的研究小别量氯胺酮对瑞芬太尼麻醉术后痛敏反应的抑制作用,为临床合理应用瑞芬太尼提供理论依据。方法选择ASA Ⅰ-Ⅱ级妇科行腹腔镜检和宫腹腔镜检手术患者90例,随机分为对照组（C）、瑞芬太尼组（R组）、小剂量氯胺酮组（K组）,每组30例。3组均采用静吸复合麻醉,除Ⅰ组外另二组用瑞芬太尼诱导与维持,手术近结束缝合皮肤时K组静脉给予氯胺酮0．5mg／kg,C组和R组暂不给药,术毕送恢复室,当患者出现中等程度疼痛时给予曲马多2mg／kg。记录3组患者拔除气管导管后的口述疼痛评分（VRS）,再次要求镇痛的时间和拔管后24h内的不良反应。结果1）C组的VRS评分低于R组,差异显著（P〈0．05）;2）K组的VRS评分明显低于C组和R组,差异显著（P〈0．05）;3）所有组无一例要求再次镇痛;4）3组间麻醉后不良反应无统计学差异（P〉0．05）。结论大剂量瑞芬太尼麻醉可引起术后早期痛觉超敏;小剂量氯胺酮对瑞芬太尼麻醉术后痛觉超敏有明显的抑制作用。     

Bradykinin receptor antagonists and cyclooxygenase inhibitors in vincristine-and streptozotocin-induced hyperalgesia

Pain that accompanies neuropathy is difficult to treat. Analgesics administered as monotherapies possess low activities in relieving this kind of pain.The effect of the simultaneous administration of indomethacin (a preferential inhibitor of cyclooxygenase-1; COX-1) or celecoxib (a relatively selective inhibitor of cyclooxygenase-2; COX-2), with selective antagonists of bradykinin₂ (B₂) bradykinin1 (B₁) receptors (HOE 140 or des-Arg¹⁰-HOE 140) on the eleviation of diabetic and toxic neuropathic pain was investigated.Pretreatment with indomethacin (0.1 mg/kg, sc) increased the antihyperalgesic activity of low daily doses of HOE 140 or des-Arg¹⁰HOE 140 (70 nmol/kg, ip) in a diabetic (streptozotocin(STZ)-induced) neuropathy/hyperalgesia experimental model. Premedication with celecoxib before HOE 140 or des-Arg¹⁰HOE 140 administration resulted in a gradual reduction of STZ hyperalgesia. Furthermore, on days 23–24, almost complete abolishment of STZ hyperalgesia was observed. After cessation of drug administration, hyperalgesia quickly returned to the baseline threshold.The results of this study suggest that inhibitors of cyclooxygenases can increase the antihyperalgesic activity of selective antagonists of B₂ and B₁ receptors in diabetic and toxic neuropathic pain models. These observations may be clinically relevant.     

Magnesium ions and opioid agonists in vincristine-induced neuropathy

Neuropathic pain is difficult to treat. Classic analgesics (i.e., opioid receptor agonists) usually possess low activity. Therefore other agents such as antidepressants, anticonvulsants, and corticosteroids are used. It is commonly known that NMDA antagonists increase analgesic activity of opioids. Unfortunately, clinical use of NMDA antagonists is limited because of the relatively frequent occurrence of adverse effects e.g., memory impairment, psychomimetic effects, ataxia and motor in-coordination. Magnesium ions (Mg²⁺) are NMDA receptor blockers in physiological conditions. Therefore, in this study the effect of opioid receptor agonists and the influence of Mg²⁺ on the action of opioid agonists in vincristine-induced hyperalgesia were examined. Opioid agonists such as morphine (5 mg/kg, ip), and fentanyl (0.0625 mg/kg, ip), as well as the partial agonist buprenorphine (0.075 mg/kg, ip) administered alone on 5 consecutives days did not modify the hyperalgesia in vincristine rats. In contrast, pretreatment with a low dose of magnesium sulfate (30 mg/kg, ip) resulted in a progressive increase of the analgesic action of all three investigated opioids. After discontinuation of drug administration, the effect persisted for several days.     

辣椒素受体拮抗剂治疗避水应激引起内脏痛觉过敏作用

目的研究避水应激引起内脏痛觉敏感性的变化及特异性辣椒素受体(VR1)拮抗剂辣椒平与非特异性VR1拮抗剂钌红对避水应激引起内脏痛觉过敏的治疗作用。方法将6周龄雄性Wistar大鼠54只分为无应激对照组(Neg组,n=18)、生理盐水对照组(NS组,n=12)、辣椒平治疗组(CZP组,n=12)、钌红治疗组(RR组,n=12),Neg组又分为三个小组,分别为直肠内注入生理盐水组、直肠内注入辣椒素组、直肠扩张组,NS组、CZP组和RR组只分为直肠内注入辣椒素组和直肠扩张组两小组,每小组均为6只动物。给予避水应激,每天1h连续10d。第11天Neg组与NS组腹腔注射溶媒,CZP组腹腔注射辣椒平,RR组腹腔注射钌红,30min后每小组6只动物直肠内注入生理盐水或辣椒素,进行疼痛评分,或给予结直肠扩张(CRD)刺激,进行腹直肌肌电记录。结果避水应激引起动物对直肠注射辣椒素敏感性增加,腹腔注射辣椒平与钌红均能抑制注射辣椒素引起的疼痛反应;避水应激也引起动物CRD刺激后腹直肌肌电活动增加,腹腔注射辣椒平与钌红均能降低肌电活动的增加幅度,而钌红则完全抑制肌电活动的增加。结论辣椒素受体拮抗剂可抑制避水应激引起的内脏痛觉过敏,辣椒...     

Representation of UV-B-induced thermal and mechanical hyperalgesia in the human brain: a functional MRI study

Surrogate models of pain and hyperalgesia allow the investigation of underlying mechanisms in healthy volunteers. Here, we investigated brain activation patterns during mechanical and heat hyperalgesia in an inflammatory human pain model using functional magnetic resonance imaging. Heat and mechanical hyperalgesia were induced on the right forearm by UV-B application in 14 healthy subjects. All four conditions (nonsensitized heat and nonsensitized mechanical pain, sensitized heat and sensitized mechanical pain) were perceptually matched. A 2 x 2 factorial analysis was performed. Areas with main effect of sensitization were insula, anterior cingulate cortex (ACC), prefrontal cortices (PFC), parietal association cortices (PA), thalamus, and basal ganglia. A main effect of modality with more activation during heat hyperalgesia was found in primary somatosensory cortex (S1), ACC, PFC, and PA. A main effect of modality with more activation during mechanical hyperalgesia was found in secondary somatosensory cortices, posterior insula, and contralateral inferior frontal cortex (IFC). An interaction of sensitization and modality was found bilaterally in IFC. Areas with similar effects of sensitization in both stimulus modalities were ACC, bilateral anterior insula and bilateral IFC. We conclude that different types of hyperalgesia in a human surrogate model of inflammatory pain produce different brain activation patterns. This is partly due to a differential processing of thermal and mechanical pain and an interaction of sensitization and modality in the caudal portion of the IFC. Finally, the data provide evidence for the existence of a common "sensitization network" consisting of ACC, bilateral anterior insula, and parts of the IFC.     

Alcohol-induced stress in painful alcoholic neuropathy

Chronic alcohol consumption induces a painful small-fiber peripheral neuropathy, the severity of which increases during alcohol withdrawal. Chronic alcohol consumption also produces a sustained increase in stress hormones, epinephrine and corticosterone, that is exacerbated during alcohol withdrawal. We report that adrenal medullectomy and administration of a glucocorticoid receptor antagonist, mifepristone (RU 38486), both prevented and reversed a model of painful peripheral neuropathy in alcohol binge-drinking rats. Chronic administration of stress levels of epinephrine to rats that had undergone adrenal medullectomy and were being fed the alcohol diet reconstituted this phenotype. Intrathecal administration of oligodeoxynucleotides antisense to the β₂-adrenergic- or glucocorticoid-receptor also prevented and reversed the pro-nociceptive effects of ethanol. Our results suggest a convergence of the effects of mediators of the hypothalamic-pituitary- and sympathoadrenal-stress axes on sensory neurons in the induction and maintenance of alcohol-induced painful peripheral neuropathy.     

Analysis of nociception, sex and peripheral nerve innervation in the TMEV animal model of multiple sclerosis

Although pain was previously not considered an important element of multiple sclerosis (MS), recent evidence indicates that over 50% of MS patients suffer from chronic pain. In the present study, we utilized the Theiler's murine encephalomyelitis virus (TMEV) model of MS to examine whether changes in nociception occur during disease progression and to investigate whether sex influences the development of nociception or disease-associated neurological symptoms. Using the rotarod assay, TMEV infected male mice displayed increased neurological deficits when compared to TMEV infected female mice, which mimics what is observed in human MS. While both male and female TMEV infected mice exhibited thermal hyperalgesia and mechanical allodynia, female mice developed mechanical allodynia at a faster rate and displayed significantly more mechanical allodynia than male mice. Since neuropathic symptoms have been described in MS patients, we quantified sensory nerve fibers in the epidermis of TMEV-infected and non-infected mice to determine if there were alterations in epidermal nerve density. There was a significantly higher density of PGP9.5 and CGRP-immunoreactive axons in the epidermis of TMEV-infected mice versus controls. Collectively these results indicate that the TMEV model is well suited to study the mechanisms of MS-induced nociception and suggest that alterations in peripheral nerve innervation may contribute to MS pain.     

Effect of insulin and its combination with resveratrol or curcumin in attenuation of diabetic neuropathic pain: participation of nitric oxide and TNF-alpha

Diabetic neuropathic pain, an important microvascular complication in diabetes mellitus, is recognized as one of the most difficult types of pain to treat. The underlying mechanisms of painful symptoms may be closely associated with hyperglycaemia but a lack of the understanding of its proper aetiology, inadequate relief, development of tolerance and potential toxicity of classical antinociceptives warrant the investigation of newer agents to relieve this pain. The aim of the present study was to explore the antinociceptive effect of insulin and its combinations with resveratrol and curcumin in attenuating diabetic neuropathic pain. The study also aimed to examine the effect of these combinations on tumour necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) levels in streptozotocin (STZ) induced diabetic mice. Four weeks after a single intraperitoneal injection of streptozotocin (200 mg/kg), mice were tested in the tail immersion and hot-plate assays. Diabetic mice exhibited significant hyperalgesia along with increased plasma glucose and decreased body weights compared with control mice. Chronic treatment with insulin (10 IU/kg/day, s.c.) and its combinations with antioxidants (resveratrol 20 mg/kg or curcumin 60 mg/kg, p.o.) for 4 weeks starting from the 4th week of STZ injection significantly attenuated thermal hyperalgesia and the hot-plate latencies. There was a significant inhibition of TNF-alpha and NO levels when these drugs were given in combination compared with their effects per se. These results indicate an antinociceptive activity of resveratrol and curcumin and point towards the beneficial effect of these combinations with insulin in attenuating diabetic neuropathic pain, possibly through the participation of NO and TNF-alpha.     

Opiate-induced hypernociception and chemokine receptors

Opiates, such as morphine, are typically employed to alleviate acute or chronic pain states. However, there are a myriad of side effects including constipation, nausea, respiratory depression, cough suppression, vomiting, sedation, addiction and tolerance. It has also been reported experimentally and clinically that exposure to opiate can elicit paradoxical pain (opiate-induced tactile hyperalgesia; OIH) in regions of the body unrelated to the initial pain complaint. Several mechanisms have been suggested to be responsible for OIH such as sensitization of peripheral nociceptors, enhanced production/release of glutamate and neuropeptides in the spinal cord, protein kinase C γ-induced signaling, and/or enhanced descending facilitation of nociceptive pathways from the rostral ventromedial medulla; however signaling pathways known to lead to directly to OIH remain undiscovered. Recent publications from our laboratory and others have discovered a potentially important link to OIH that involves the chemokine (chemotactic cytokine), stromal-derived factor 1 (SDF1 also known as CXCL12) and its cognate receptor CXCR4.