Weiyan Li

Pentoxifylline attenuates the development of hyperalgesia in a rat model of neuropathic pain.

Pentoxifylline, a non-specific cytokine inhibitor, has shown to be beneficial in inflammatory pain in both experimental and clinical studies. The present study demonstrates for the first time, to our knowledge, the antihyperalgesic effect of pentoxifylline in the neuropathic pain using L5 spinal nerve transection rat model. In a preventive paradigm, pentoxifylline (12.5, 25, 50, or 100mg/kg intraperitoneally) was administered systemically daily, beginning 1h prior to nerve transection. Pentoxifylline (50, or 100mg/kgi.p.) produced significant decrease in the mechanical and thermal hyperalgesia. However, pentoxifylline (100mg/kgi.p.) did not influence the paw pressure thresholds and paw withdrawal latency in sham-operated rats. In order to understand the possible antinocicieptive effect of pentoxifylline in neuropathic pain, we examined the level of TNFalpha, IL-1beta, IL-6 and IL-10 protein in the contralateral brain on day 7 post-transection. Pentoxifylline administration resulted in a dose-dependent reduction of the production of proinflammatory cytokines like TNFalpha, IL-1beta and IL-6, and enhancement of IL-10. Furthermore, we investigated the activity of nuclear factor kappa B (NF-kappaB) in the contralateral brain on days 7 after surgery. In accordance with the change of proinflammatory cytokines, Pentoxifylline (50 or 100mg/kg) significantly inhibited the activation of NF-kappaB in the brain. This research supports a growing body of literature emphasizing the importance of neuroinflammation and neuroimmune activation in the development of neuropathic pain states, and the potential preventive value of pentoxifylline in the treatment of neuropathic pain.

Intrathecal administration of clonidine attenuates spinal neuroimmune activation in a rat model of neuropathic pain with existing hyperalgesia

Central neuroimmune activation contributes to the initiation and maintenance of neuropathic pain after nerve injury. The current study was aimed to examine the modulation of neuroimmune activation in the spinal cord by the alpha(2) adrenoceptor agonist, clonidine, in a rat model of neuropathic pain induced by partial sciatic nerve ligation (PSNL). Animals were randomly assigned into 6 groups: sham-operation with 20 microg clonidine or saline; and PSNL with clonidine (5, 10, and 20 microg) or saline. Fourteen days post-operation, various doses of clonidine or saline were injected intrathecally. The paw pressure threshold and paw withdrawal latencies were measured before and at 30, 60, 90, and 120 min after the injection of clonidine. Glial activation markers such as macrophage antigen complex-1 (mac-1) and glial fibrillary acidic protein (GFAP), interleukin (IL)-1beta and IL-6, nuclear factor-kappa B (NF-kappaB) activation, and p-p38 mitogen-activated protein kinase (MAPK) activation in the lumbar spinal cord were determined as well. Administration of clonidine resulted in a dose-dependent attenuation in PSNL-induced mechanical and thermal hyperalgesia. Furthermore, clonidine could markedly inhibit neuroimmune activation characterized by glial activation, production of cytokines, NF-kappaB activation as well as p38 activation. The antihyperalgesic effect of intrathecal clonidine in rats receiving PSNL might partly attribute to the inhibition of neuroimmune activation associated with the maintenance of neuropathic pain.

Suppression of spinal connexin 43 expression attenuates mechanical hypersensitivity in rats after an L5 spinal nerve injury.

Activation of spinal astrocytes may contribute to neuropathic pain. Adjacent astrocytes can make direct communication through gap junctions formed by connexin 43 (Cx43) in the central nervous system. Yet, the role of spinal astroglial gap junctions in neuropathic pain is not fully understood. Since Cx43 is the connexin isoform expressed preferentially in astrocytes in the spinal cord, we used a small interfering RNA (siRNA) approach to examine whether suppression of spinal Cx43 expression inhibits mechanical hypersensitivity in rats after an L5 spinal nerve ligation (SNL). SNL rats were administered intrathecal Cx43 siRNA (3μg/15μl, twice/day) or an equal amount of mismatch siRNA (control) on days 14-17 post-SNL. Cx43 siRNA, but not mismatch siRNA, alleviated mechanical hypersensitivity in SNL rats. Furthermore, Western blot analysis showed that the pain inhibition induced by Cx43 siRNA correlated with downregulation of Cx43 expression, but not that of Cx36 (the neuronal gap junction protein) or glial fibrillary acidic protein (GFAP, a marker for reactive astrocytes) in the spinal cord of SNL rats. Western blot analysis and immunohistochemistry also showed that SNL increased GFAP expression, but decreased Cx43 expression, in spinal cord. Our results provide direct evidence that selective suppression of spinal Cx43 after nerve injury alleviates neuropathic mechanical hypersensitivity. These findings suggest that in the spinal cord, the enhanced function of astroglial gap junctions, especially those formed by Cx43, may be important to neuropathic pain in SNL rats.

Effects of clonidine on bilateral pain behaviors and inflammatory response in rats under the state of neuropathic pain

This study was conducted to investigate the effects of clonidine on bilateral pain behaviors and inflammatory responses in neuropathic pain induced by partial sciatic nerve ligation (PSNL), and to better understand whether the antinociception of clonidine was related to α(2)-adrenoceptor mechanisms. Rats were divided randomly into five groups: sham-operation with saline, i.p.; PSNL with clonidine (0.2mg/kg) or saline, i.p.; PSNL with yohimbine (2mg/kg) followed by clonidine (0.2mg/kg), i.p.; and PSNL with naloxone (0.3mg/kg) followed by clonidine (0.2mg/kg), i.p. On post-operative days 1, 3, 7, 14, and 21, both ipsilateral and contralateral pain behaviors were measured. In rats receiving antagonists, bilateral behavioral changes were measured on day 14. Bilateral paw pressure threshold and paw withdrawal latencies were measured, and the extent of glial activation was dertermined by measuring macrophage antigen complex-1 (Mac-1) and glial fibrillary acidic protein (GFAP). Additionally, the levels of tumor necrosis factor α (TNF-α) and interleukin (IL)-6 were determined. PSNL induced bilateral behavioral hyperalgesia, with the ipsilateral level displaying a higher extent of behavior changes than the contralateral side. In addition, the glial activation markers and cytokine production were augmented bilaterally. Clonidine caused significant attenuation of bilateral mechanical allodynia and thermal hyperalgesia, accompanied by inhibition of glial activation and the expression of cytokines. The effects of clonidine were blocked by the α(2)-adrenoceptor antagonist yohimbine and partially reversed by the μ-opioid receptor antagonist naloxone. These data suggest that the bilateral antinoceptive effects of clonidine might mediate through immunomodulation by acting on α(2)-adrenoceptor in rats undergoing neuropathic pain.

Intrathecal carbenoxolone inhibits neuropathic pain and spinal wide-dynamic range neuronal activity in rats after an L5 spinal nerve injury.

Spinal glial gap junctions may play an important role in dorsal horn neuronal sensitization and neuropathic pain. In rats after an L5 spinal nerve ligation (SNL), we examined the effects of intrathecal injection of carbenoxolone (CBX), a gap junction decoupler, on neuropathic pain manifestations and on wide-dynamic range (WDR) neuronal activity in vivo. Intrathecal injection of CBX dose-dependently (0.1-50 μg, 10 μl) inhibited mechanical hypersensitivity in rats at 2-3 weeks post-SNL. However, the same doses of glycyrrhizic acid (an analogue of CBX that does not affect gap junctions) and mefloquine hydrochloride (a selective neuronal gap junction decoupler) were ineffective. Intrathecal CBX (5μg) also attenuated heat hypersensitivity in SNL rats. Further, rats did not develop tachyphylaxis to CBX-induced inhibition of mechanical hypersensitivity after repetitive drug treatments (25 μg/day) during days 14-16 post-SNL. Electrophysiological study in SNL rats showed that spinal topical application of CBX (100 μg, 50 μl), which mimics intrathecal drug administration, attenuated WDR neuronal responses to mechanical stimuli and to repetitive intracutaneous electrical stimuli (0.5 Hz) that induce windup, a short-form of activity-dependent neuronal sensitization. The current findings suggest that the inhibition of neuropathic pain manifestations by intrathecal injection of CBX in SNL rats may involve an inhibition of glial gap junctions and an attenuation of WDR neuronal activity in the dorsal horn.

Rosuvastatin attenuated the existing morphine tolerance in rats with L5 spinal nerve transection through inhibiting activation of astrocytes and phosphorylation of ERK42/44.

Recent studies suggested that statins have anti-inflammatory effects beyond their lipid-lowering properties. In the present study, we sought to investigate whether rosuvastatin could alleviate morphine tolerance by attenuating the glia mediated neuroinflammation in the spinal cord. Using a rat model of L5 spinal nerve transection, on day 8 after surgery morphine (10 mg/kg) was injected subcutaneously twice daily for consecutive 10 days. On day 13, with the establishment of morphine tolerance, rosuvastatin (10 mg/kg) was given o.p. for 5 days. On day 18, lumbar spinal cord was collected immediately after last behavioral testing. The analgesic effect of morphine was determined as the percentage of maximal possible effect (%MPE) after a single morphine (4 mg/kg) injection via tail vein on day 8, 13, and 18. The MPE decreased significantly after administration of morphine to rats with neuropathy for 5 days. Rosuvastatin administration for 5 days could restore morphine antinociceptive effect significantly. Additionally, the activation of astrocytes, the phosphorylation of extracellular signal-regulated kinase 42/44 (ERK(42/44)) and the expressions of TNFα and IL-1β were inhibited significantly by rosuvastatin. Our data suggested that rosuvastatin was a promising choice to treat neuropathic pain in combination with morphine.

The Effect of Pentoxifylline on Existing Hypersensitivity in a Rat Model of Neuropathy

BACKGROUND:Using a rat L5 spinal nerve transection model we previously showed that pentoxifylline prevents hyperalgesia through antiinflammation in the prefrontal brain. In this study, we examined efficacy when applied after injury. METHODS:We examined the effect of pentoxifylline on existing mechanical allodynia, observing glial activation and proinflammatory cytokine expression in the lumbar spinal cord, when given 7 days after L5 spinal nerve transection. RESULTS:There was no effect from pentoxifylline on existing hypersensitivity, glial activation, and cytokine expression when applied after L5 spinal nerve transection. CONCLUSION:Pentoxifylline administered intraperitoneally on day 7 postsurgery failed to alleviate existing hypersensitivity, or reduce glial activation and cytokine expression.

Protective effects of Garcinol against neuropathic pain – Evidence from in vivo and in vitro studies

Neuroinflammatory processes have a vital role in the pathogenesis of neuropathic pain. Garcinol, harvested from Garcinia indica, is known to exert potent anti-inflammatory properties. Recent studies have indicated that Garcinol may inhibit activation of nuclear factor-κB (NF-κB) by inhibiting NF-κB/p65 acetylation. These findings prompted us to evaluate the protective effects of Garcinol in the lumbar fifth spinal nerve ligation (SNL)-induced rat model of neuropathic pain and Lipopolysaccharide(LPS)-stimulated primary cultured microglia. In the present study, we found that intrathecal administration of Garcinol significantly attenuated SNL-induced nociceptive behaviors. Garcinol suppressed microglial activation as well as the expression of interleukin (IL)-1β, IL-6, inducible nitric oxide synthase (iNOS)/nitric oxide (NO), and cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) in the spinal cord of SNL rats. It also reduced the nuclear translocation of NF-κB by decreasing acetyl-p65 protein expression. Similarly, in the in vitro study, Garcinol decreased the production of NO/iNOS, PGE2/COX-2, and proinflammatory cytokines in LPS-exposed microglia. Likewise, Garcinol inhibited the NF-κB signaling pathway by downregulating acetyl-p65 levels in LPS-challenged microglia. Our findings suggest that Garcinol may have protective effects against neuropathic pain that are associated with the inhibition of neuroinflammation in microglia. Therefore, Garcinol could be a promising agent in the treatment of neuropathic pain.

Intrathecal injection of phosphodiesterase 4B-specific siRNA attenuates neuropathic pain in rats with L5 spinal nerve ligation

Phosphodiesterase 4 (PDE4) is an adenosine cyclic 3,5-monophosphate-specific degradative enzyme, which is closely associated with the inflammatory response. Among its four subtypes (A-D), it remains unclear which one exerts suppressive effects on inflammation and reduces neuropathic pain. The present study aimed to examine the modulation of neuroinflammation by PDE4 subtypes in the spinal cord of a rat model of L5 spinal nerve ligation (SNL)-induced neuropathic pain. The expression levels of PDE4A-D were measured in the lumbar spinal cords of naïve rats. The rats were then divided into seven groups: The sham group (sham surgery + saline), the saline group (SNL + saline), the vehicle group (SNL + Lipofectamine® RNAiMAX), the mismatch small interfering (si)RNA group (SNL + mismatch siRNA), the PDE4A-siRNA group (SNL + PDE4A-siRNA), the PDE4B-siRNA group (SNL + PDE4B-siRNA) and the PDE4D-siRNA group (SNL + PDE4D-siRNA). In order to determine behavioral changes, mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were recorded. The mRNA and protein expression levels of PDE4s were also detected. Furthermore, the association between behavioral changes and individual subtypes of PDE4 were studied following intrathecal administration of PDE4A, B and D-specific siRNA. The expression levels of protein kinases, including phosphorylated-extracellular signal-regulated kinases (p-ERK), and inflammatory cytokines were measured, in order to explore the underlying mechanisms. Subtypes A, B and D, but not C, were detected in the naïve rats. After SNL, both MWT and TWL were reduced. The mRNA and protein expression levels of PDE4A, B and D were significantly upregulated after 2, 4, 6 and 8 days of SNL. Subtype-specific siRNA significantly suppressed the elevated expression levels; however, only rats treated with PDE4B siRNA exhibited improved MWT and TWL. Further analysis of the PDE4B siRNA-treated rats demonstrated that 8 days after SNL, the intensity of p-ERK was reduced, the expression levels of CD11b and glial fibrillary acidic protein GFAP were reduced, as well as the expression levels of proinflammatory cytokines such as tumor necrosis factor-α, interleukin (IL)-1β and IL-6. These results suggested that selective inhibition of PDE4B may relieve neuropathic pain, potentially via the suppression of glial activation and the release of cytokines in the spinal cord.

The impact of intra-abdominal pressure on the stroke volume variation and plethysmographic variability index in patients undergoing laparoscopic cholecystectomy

The purpose of the present study was to evaluate the effect of increasing intra-abdominal pressure (IAP) on stroke volume variation (SVV) and plethysmographic variability index (PVI) in patients undergoing laparoscopic cholecystectomy. PVI examined by Masimo Radical 7 pulse oximeter and SVV determined using FloTrac/Vigileo were monitored simultaneously in forty-five patients undergoing laparoscopic cholecystectomy (LC). Mean arterial blood pressure (MAP), heart rate (HR), cardiac index (CI), perfusion index (PI), airway pressures (P), SVV, and PVI were also recorded at the following predetermined time: 5 min after endotracheal intubation (T1), 5 min after pneumoperitoneum at 5 mmHg (T2), 5 min after pneumoperitoneum at 10 mmHg (T3), 5 min after pneumoperitoneum at 15 mmHg (T4), and 5 min after the termination of pneumoperitoneum (T5). Forty-five patients with a total of 225 pairs of measurements were included in the analysis. Compared with the values at T1, both SVV and PVI showed significant progressive increases as the IAP was adjusted from 5 to 10, 15 mmHg at T2, T3, and T4, respectively. No significant difference was found when the pneumoperitoneum was terminated at T5. Further regressive analysis indicated strong relationships between SVV and IAP (r = 0.8118, p < 0.001), PVI and IAP(r = 0.8876, p < 0.001) respectively. Both PVI and SVV showed rapid and IAP correlative changes with increasing intra-abdominal pressure in patients undergoing laparoscopic cholecystectomy.