The Influrence Of Pentoxifylline On Neuropathic Pain And Its Related Cytokines

The influrence of pentoxifylline on neuropathic pain and its related cytokinesObjectiveNeuropathic pain is a complicated pain syndrome initiated by the injury or disease of peripheral and central nerve system. Recent researches found that the immune reaction may involved in the process of neuropathic pain. Immune system and nerve system interact via different transmitter, neuropeptide, cytikines and theirs ligands respectively, which cytokines play a key role. Although there are mounting studies about the role of cytokines in neuropathic pain, but the results are not coincident. There is the possibility that different cytokines may play different role in different type of pain. Moreover, the feature of the expression of cytokines may rely on the different animal model and the type and location of the tissue detected. Therefore, it is necessary to further evaluate the contribution of cytokines to neuropathic pain. Pentoxifylline is a methylxanthine purine derivative which was used to treat cerebrovascular disease and disease of peripheral blood vessel. In the late 90's, it was found that pentoxifylline can inhibit the release of cytokines dose-dependently in cultured cells in vitro. It is untill recently that pentoxifylline is found to be a metabolic inhibitor of glial cells. Pentoxifylline can pass the blood brain barrier easily, and can protect the neurons through multiple mechanisms. In some types of inflammatory pain model, the analegia effect of pentoxifylline were observed. Because of the different mechanism involved in inflammatory pain and neuropathic pain, that if pentoxifylline can also alleviate the neuropathic pain is still unknown.The objective of the present study was to determine whether preemptive systemic admisnistration of pentoxifylline could attenuate the pain behavior in a rat model of neuropathic pain induced by chronic construction injury of the sciatic nerve. On this basis, quantitive RT-PCR technic and ELISA method were used to detect the changes of m RNA and protein of TNFα,IL-1β,IL-6 in spinal cord dynamically, and to explore their meaningness in the initiation and maitainance of neuropathic pain. The influrence of pentoxifylline on them was observed at the same time.Part oneThe effects of pentoxifylline on neuropathic painMaterials and Methods1. Chronic constriction injury(CCI)model.1.1 Animals. Experiments were performed on adult, male Sprague- Dawley rats weighing 250±20g at the beginning of the experiments.1.2 Chronic constriction of sciatic nerve. The left common sciatic nerve of anesthetized rats was exposed, four silk ligatures were tied loosely proximal to the sciatic's trifurcation. Sham surgery was done by exposing the left sciatic nerve without ligation.2. Experimental paradigm.Rats were divided randomly into Sham group, CCI group and PTX group. Pentoxifylline(100mg/kg i.p.)was given before the sugery in PTX group. The same volume of saline was given in Sham group and CCI group. Hind paw thermal withdrawl latency(TWL)to thermal stimulus and mechanical withdrawl threshold(MWT)of mechanical stimulus were recorded before ligation or on 1, 3, 7, 11, 14, 21 day after ligation respectively(n=8).3. Data analysis and statistics. Data were expressed as mean±SEM. The results of MWT were analyzed by non-parameter test with Mann-Whitney test. The results of TWL were analyzed by analysis of variance(ANOVA)with Tukey's as th post hoc test. Values of P＜0.05 were considered as statistically significant.Results1. Effects of chronic constriction injury on the MWT and TWL of hind paws of ratsThere were no significant differences on the values of MWT and TWL before ligation between groups. Compared with Sham group, the MWT and TWL of rats in CCI group significantly decreased after ligation(P＜0.01 or P＜0.05) and continued to be decreased until 21 day after ligation.2. Effects of pentoxifylline on the MWT and TWL in CCI model.The MWT and TWL in PTX group were increased significantly compared with CCI group at different time course after the surgery with no significant differences among timepoints(P＜0.01 or P＜0.05).Part twoEffects of pentoxifylline on the pain-related cytokines in spinal cord of ratsMaterials and Methods1. CCI rats. The same as that in Part one.2. Experimental paradigm.90 rats were divided randomly into Sham group, CCI group and PTX group. These groups were further divided into 5 sub-group according to the different time survival (n=6). Rats were sacrificed at before, 1, 7, 14, 21 days after surgery respectively.3. ELISA was used to assess the protein contents of TNFα,IL-1β,IL-6 in spinal cord.4. FQ-RT-PCR was used to detect the m RNA expression of TNFα,IL-1β,IL-6 in spinal cord.5. Data analysis and statistics. Data were expressed as mean±SEM. The results were analyzed by analysis of variance(ANOVA). Values of P＜0.05 were considered as statistically significant.Results1. Effects of pentoxifylline on TNFαprotein and mRNA expression in spinal cord of rats.Compared with before surgery, TNFαprotein and mRNA expression increased significantly at 1, 7, 14 day after surgery in CCI group(P＜0.05), and higer than sham group(P＜0.05). However, it decreased significantly in PTX group compared with CCI group(P＜0.01). There was no diffirence among groups at 21 day after surgery(P＞0.05).2. Effects of pentoxifylline on IL-1βprotein and mRNA expression inspinal cord of rats.Compared with before surgery, IL-1βprotein expression and mRNA begin to increase at 1 day after surgery and maitained untill 14 day post-surgery(P＜0.01).IL-1βprotein and mRNA expression in PTX group decreased significantly compared with CCI group(P＜0.01 or P＜0.05). There was no diffirence among groups at 21 day after surgery.3. Effects of pentoxifylline on IL-6 protein and mRNA expression in spinal cord of rats. Compared with before surgery, IL-6 protein and mRNA expression begin to increase at 1 day after surgery and maitained untill 21 day post-surgery(P＜0.01 or P＜0.05). IL-1βprotein and mRNA expression in PTX group decreased significantly compared with that of CCI group(P＜0.05).Conclusions1. CCI model was set up successfully, thermal hyperalgesia and mechanical allodynia were observed.2. Preemptive systemic administration of pentoxifylline can be effectively inhibit the neuropathic pain in CCI model.3. Antinociceptive effects of pentoxifylline may be related to the decrease of proinflammatory cytokines TNFα,IL-1β,IL-6 in spinal cord.4. The time courses of expression of TNFα,IL-1β,IL-6 are different in spinal cord, which two former be more involved in the genesis and latter be more involved in the maintainance of neuropathic pain.