The Effect of Tramadol Versus Sufentanil on Controlling Postoperative Pain for Men Who Smoke and Do Not Smoke: A Randomized Clinical Trial.

BACKGROUND: Smoking behavior alters the analgesic threshold, which challenges postoperative pain management for patients who smoke. OBJECTIVES: We aimed to assess the analgesic efficacy of tramadol versus sufentanil in relieving postoperative pain for patients who do and do not smoke who underwent a partial hepatectomy. STUDY DESIGN: Double-blinded randomized controlled trial. SETTING: Eastern Hepatobiliary Surgery Hospital, Shanghai, China. METHODS: All patients in this study were men. A total of 66 patients who smoke were randomly assigned to receive tramadol or sufentanil (n = 33 each). In addition, a total of 66 patients who do not smoke were randomly assigned to receive tramadol or sufentanil (n = 33 each). The primary outcome was the consumption of additional analgesics within the first 48 hours to control postoperative pain. Secondary outcomes included the postoperative pain level, the frequency of postoperative nausea and vomiting, the sedation score, and the frequency of fever within 48 hours postsurgery. RESULTS: A significant interaction between "analgesic strategy" and "smoking history" was detected on the consumption of additional analgesics. In those who smoke, the requests for additional doses of analgesics were significantly less in those receiving tramadol than those receiving sufentanil; such a difference was not observed in those who do not smoke. The postoperative pain level was not significantly different between the tramadol group and the sufentanil group within patients who smoke within 48 hours postsurgery. The incidence of treatment-related adverse events was not significantly different between the tramadol group and the sufentanil group within both those who do and do not smoke. LIMITATIONS: Only men patients were included. Also, the superior analgesic effect and the incidence of adverse events of tramadol in patients who smoke were only assessed within the first 48 hours postsurgery. CONCLUSIONS: Our data suggest that tramadol has a better analgesic effect than sufentanil in relieving postoperative pain in patients who smoke.

MicroRNA-330 Directs Downregulation of the GABABR2 in the Pathogenesis of Pancreatic Cancer Pain.

Pancreatic cancer is one of the most aggressive and deadly malignancies with a very poor prognosis. Pancreatic cancer-induced visceral pain is very common and is generally presented among the initial symptoms in patients; such pain is strongly associated with poor quality of life, impaired functional activity, and decreased survival. However, the principal neurobiological mechanisms of pain caused by pancreatic cancer have not been fully elucidated. Accumulating studies have shown that miRNAs play a major role in chronic pain by suppressing key molecules involved in nociception. In the present study, we report that microRNA (miR)-330 is highly expressed in the spinal dorsal horn (SDH) of nude mice with pancreatic cancer pain. Mimicking pancreatic carcinoma-induced SDH miR-330 upregulation by microinjection of miR-330 mimic into the SDH significantly induced abdominal mechanical allodynia in normal nude mice. Additionally, we found that the expression of GABABR2 was significantly decreased in the SDH of nude mice with pancreatic cancer pain and was regulated directly by miR-330 both in vitro and in vivo. Furthermore, inhibition of miR-330 rescued the expression of GABABR2 and alleviated pancreatic carcinoma-induced abdominal pain hypersensitivity in nude mice with pancreatic carcinoma. These results show that miR-330 participates in the genesis of pancreatic carcinoma-induced pain hypersensitivity by inhibiting GABABR2 expression in the SDH and might be a potential therapeutic target for pancreatic cancer pain.

Wrist-ankle acupuncture attenuates cancer-induced bone pain by regulating descending pain-modulating system in a rat model.

BACKGROUND: Cancer-induced bone pain (CIBP) presents a multiple-mechanism of chronic pain involving both inflammatory and neuropathic pain, and its pathogenesis is closely related to endogenous descending system of pain control. However, the action mechanism underlying the effects of wrist-ankle acupuncture (WAA) versus electroacupuncture (EA) on CIBP remains unknown. METHODS: Thirty-two Wistar rats were divided into sham, CIBP, EA-treated and WAA-treated groups. CIBP was induced in rats of the latter three groups. Time courses of weight and mechanical hyperalgesia threshold (MHT) were evaluated. After 6 days of EA or WAA treatment, the expressions of 5-hydroxytryotamine type 3A receptor (5-HT3AR) and µ-opioid receptor (MOR) in rostral ventromedial medulla (RVM) and/or spinal cord, as well as the levels of 5-HT, ß-endorphin, endomorphin-1 and endomorphin-2 in RVM and spinal cord, were detected. RESULTS: Injection of cancer cells caused decreased MHT, which was attenuated by EA or WAA (P < 0.05). WAA had a quicker analgesic effect than EA (P < 0.05). No significant difference of MOR in RVM was found among the four groups. EA or WAA counteracted the cancer-driven upregulation of 5-HT3AR and downregulation of MOR in spinal cord (P < 0.05), and upregulation of 5-HT and downregulation of endomorphin-1 in both RVM and spinal cord (P < 0.05). ß-endorphin and endomorphin-2 in RVM and spinal cord decreased in CIBP group compared with sham group (P < 0.05), but EA or WAA showed no significant effect on them, although a tendency of increasing effect was observed. CONCLUSION: WAA, similar to EA, alleviated mechanical hyperalgesia in CIBP rats by suppressing the expressions of 5-HT and 5-HT3AR, and increasing the expressions of MOR and endomorphin-1 in RVM-spinal cord pathway of the descending pain-modulating system. However, WAA produced a quicker analgesic effect than EA, the mechanisms of which need further investigation.

Intravenous Dexmedetomidine Combined with Ultrasound-Guided Rectus Sheath Block for Open Gastrectomy: a Prospective Randomized Trial.

PURPOSE: To compare the incidences of positive hemodynamic response (HR > 100 beats min-1 or SBP > 160 mmHg) during abdominal exploration and moderate pain after surgery, when using dexmedetomidine infusion and rectus sheath block. METHODS: One hundred patients undergoing open gastrectomy were randomized to receive rectus sheath block with ropivacaine (Group B, n = 25), initial loading dose of 0.6 µg kg-1 dexmedetomidine, followed by a continuous infusion of 0.2 µg kg-1 h-1 throughout surgery (Group D, n = 25), both rectus sheath block and dexmedetomidine (Group BD, n = 25), or neither rectus sheath block nor dexmedetomidine (Group C, n = 25). General anesthesia techniques were standardized. HR, SBP, and positive hemodynamic response at peritoneum incision (TPI), 5 min (TAE-5), 10 min (TAE-10), and 15 min (TAE-15) after the start of abdominal exploration, and incidences of moderate postoperative pain were recorded. RESULTS: Positive hemodynamic responses during abdominal exploration were more common in Groups B (82%) and C (74%) than in Groups D (14%) and BD (9%) (all P = 0.000). HR and SBP were lower in Groups D and BD, compared with those in Groups C and B (all P < 0.05). Compared with TPI, HR and SBP increased significantly in Groups B and C during abdominal exploration (all P < 0.05), but not in Group BD (except HR at TAE-15). The incidences of moderate pain in Groups B and BD were noticeably lower than in Groups C and D at 1 h, 2 h, and 6 h after surgery (all P < 0.0083). CONCLUSION: Dexmedetomidine infusion combined with rectus sheath block provided more hemodynamic stability during abdominal exploration and better analgesia after surgery.

Inhibition of Mast Cell Degranulation Relieves Visceral Hypersensitivity Induced by Pancreatic Carcinoma in Mice.

Cancer pain induced by pancreatic carcinoma is one of the most common symptoms and is difficult to endure, especially in the advanced stage. Evidence suggests that mast cells are recruited and degranulate in enteric disease-related visceral hypersensitivity. However, whether mast cells promote the visceral pain induced by pancreatic carcinoma remains unclear. Here, using toluidine blue staining and western blotting, we observed that mast cells were dramatically recruited to tissues surrounding pancreatic carcinoma, but not inside the carcinoma in patients with severe visceral pain. The levels of mast cell degranulation products, including tryptase, histamine, and nerve growth factor, were significantly increased in pericarcinoma tissues relative to their levels in normal controls, as evidenced by enzyme-linked immunosorbent assay. We determined that systemic administration of mast cell secretagogue compound 48/80 exacerbated pancreatic carcinoma-induced visceral hypersensitivity in a male BALB/c nude mouse model as assessed by measuring the hunching behavior scores and mechanical withdrawal response frequency evoked by von Frey stimulation. In contrast, the mast cell stabilizer ketotifen dose-dependently alleviated pancreatic cancer pain. In addition, we observed incomplete development of abdominal mechanical hyperalgesia and hunching behavior in mast cell-deficient mice with pancreatic carcinoma. However, ketotifen did not further attenuate visceral hypersensitivity in mast cell-deficient mice with carcinoma. Finally, we confirmed that intraplantar injection of pericarcinoma supernatants from BALB/c nude mice but not mast cell-deficient mice caused acute somatic nociception. In conclusion, our findings suggest that mast cells contribute to pancreatic carcinoma-induced visceral hypersensitivity through enrichment and degranulation in pericarcinoma tissues. The inhibition of mast cell degranulation may be a potential strategy for the therapeutic treatment of pancreatic carcinoma-induced chronic visceral pain.

Trypsin-protease activated receptor-2 signaling contributes to pancreatic cancer pain.

Pain treatment is a critical aspect of pancreatic cancer patient clinical care. This study investigated the role of trypsin-protease activated receptor-2 (PAR-2) in pancreatic cancer pain. Pancreatic tissue samples were collected from pancreatic cancer (n=22) and control patients (n=22). Immunofluorescence analyses confirmed colocalization of PAR-2 and neuronal markers in pancreatic cancer tissues. Trypsin levels and protease activities were higher in pancreatic cancer tissue specimens than in the controls. Supernatants from cultured human pancreatic cancer tissues (PC supernatants) induced substance P and calcitonin gene-related peptide release in dorsal root ganglia (DRG) neurons, and FS-NH2, a selective PAR-2 antagonist, inhibited this effect. A BALB/c nude mouse orthotopic tumor model was used to confirm the role of PAR-2 signaling in pancreatic cancer visceral pain, and male Sprague-Dawley rats were used to assess ambulatory pain. FS-NH2 treatment decreased hunch scores, mechanical hyperalgesia, and visceromotor reflex responses in tumor-bearing mice. In rats, subcutaneous injection of PC supernatant induced pain behavior, which was alleviated by treatment with FS-NH2 or FUT-175, a broad-spectrum serine protease inhibitor. Our findings suggest that trypsin-PAR-2 signaling contributes to pancreatic cancer pain in vivo. Treatment strategies targeting PAR-2 or its downstream signaling molecules might effectively relieve pancreatic cancer pain.

DNMT3a contributes to the development and maintenance of bone cancer pain by silencing Kv1.2 expression in spinal cord dorsal horn.

Abstract: Metastatic bone tumor-induced changes in gene transcription and translation in pain-related regions of the nervous system may participate in the development and maintenance of bone cancer pain. Epigenetic modifications including DNA methylation regulate gene transcription. Here, we report that intrathecal injection of decitabine, a DNA methyltransferase (DNMT) inhibitor, dose dependently attenuated the development and maintenance of bone cancer pain induced by injecting prostate cancer cells into the tibia. The level of the de novo DNMT3a, but not DNMT3b, time dependently increased in the ipsilateral L4/5 dorsal horn (not L4/5 dorsal root ganglion) after prostate cancer cells injection. Blocking this increase through microinjection of recombinant adeno-associated virus 5 (AAV5) expressing Dnmt3a shRNA into dorsal horn rescued prostate cancer cells-induced downregulation of dorsal horn Kv1.2 expression and impaired prostate cancer cells-induced pain hypersensitivity. In turn, mimicking this increase through microinjection of AAV5 expressing full-length Dnmt3a into dorsal horn reduced dorsal horn Kv1.2 expression and produced pain hypersensitivity in the absence of prostate cancer cells injection. Administration of neither decitabine nor virus affected locomotor function and acute responses to mechanical, thermal, or cold stimuli. Given that Dnmt3a mRNA is co-expressed with Kcna2 mRNA (encoding Kv1.2) in individual dorsal horn neurons, our findings suggest that increased dorsal horn DNMT3a contributes to bone cancer pain through silencing dorsal horn Kv1.2 expression. DNMT3a may represent a potential new target for cancer pain management.

Identification of Early RET+ Deep Dorsal Spinal Cord Interneurons in Gating Pain.

The gate control theory (GCT) of pain proposes that pain- and touch-sensing neurons antagonize each other through spinal cord dorsal horn (DH) gating neurons. However, the exact neural circuits underlying the GCT remain largely elusive. Here, we identified a new population of deep layer DH (dDH) inhibitory interneurons that express the receptor tyrosine kinase Ret neonatally. These early RET+ dDH neurons receive excitatory as well as polysynaptic inhibitory inputs from touch- and/or pain-sensing afferents. In addition, they negatively regulate DH pain and touch pathways through both pre- and postsynaptic inhibition. Finally, specific ablation of early RET+ dDH neurons increases basal and chronic pain, whereas their acute activation reduces basal pain perception and relieves inflammatory and neuropathic pain. Taken together, our findings uncover a novel spinal circuit that mediates crosstalk between touch and pain pathways and suggest that some early RET+ dDH neurons could function as pain "gating" neurons.

Effect of recombinant adenovirus coding for endomorphin-2 on neuropathic pain in rats.

OBJECTIVE: To construct a transgene expressing human endomorphin-2 by linking the signal peptide of mouse nerve growth factor (PN) to a human endomorphin-2 DNA sequence containing a short linker recognized by the protease FURIN and test the analgesic effect of endomorphin-2 on neuropathic pain. METHODS: The transgene was inserted into the cosmid pAxCAwt to generate PN-EM-2-pAxCAwt. The recombinant adenovirus Ad-PNEM2 was packaged and propagated in HEK293 cells. After the Ad-PNEM2-infected NIH3T3 cells had been cultured, protein expression was examined by immunofluorescence and ELISA. A CCI rat model was constructed and the Ad-PNEM2 was administered intrathecally. The rats' pain thresholds (PWL) were measured and the presence of endomorphin-2 in the cerebrospinal fluid was confirmed through ELISA. RESULTS: The Ad-PNEM2 expressed endomorphin-2 smoothly and abundantly in NIH3T3 cells at a significantly higher rate than the viral control (P<0.01) or blank control (P<0.01). The expressed endomorphin-2 was mainly observed in the cytoplasm. The concentration of endomorphin-2 in the cerebrospinal fluid increased 1 day after injection and peaked between 7 and 14 days after injection. After injection, PWL approached normal levels in the operated study group. No significant change was observed in the control groups. There was a significant correlation between PWL and endomorphin-2 level (r = 0.944, P<0.001). CONCLUSION: The constructed human endomorphin-2 transgene was expressed effectively, and endomorphin-2 expressed by the recombinant adenovirus altered the threshold to thermal stimulus and showed good analgesic effect.

Down-regulation of GAP-43 by inhibition of caspases-3 in a rat model of neuropathic pain.

BACKGROUND: Neuropathic pain remains a prevalent and persistent clinical problem due to incomplete understanding of its pathogenesis. OBJECTIVE: The present study aimed to investigate the role of caspase-3 in the neuropathic pain in rats with chronic constriction injury (CCI). METHODS: SD rats were randomly assigned four groups (n=18 per group): sham group, normal saline group (NS group), Z-DEVD-FMK group (DEVD group) and RNA interference group (siRNA group). Z-DEVD-FMK (1 U/30 µl), siRNA targeting caspase-3 (10 µg/30 µl) and NS of equal volume were intrathecally administered once daily for 5 days starting 1 day before surgery in the DEVD, siRNA and NS group, respectively. Thermal hyperalgesia was assessed at one day before and 1, 2, 4, 5, 6, 7 and 10 days after surgery. The mRNA and protein expressions of caspase-3 were measured by real time PCR and immunofluorescence assay. Apoptosis was detected by TUNEL staining. GAP-43 expression was measured by immunofluorescence and western blot assays. RESULTS: The right paw withdrawal latency (PWL) was decreased after CCI (P<0.05). TUNEL-positive neurons and the mRNA and protein expressions of caspase-3 in the spinal cord were increased significantly. After Z-DEVD-FMK or siRNA treatment, TUNEL-positive neurons were decreased, PWLs increased (P<0.05) and the mRNA and protein expressions of caspase-3 decreased. The expression of GAP-43, a sprouting related protein, was decreased in the DEVD and siRNA group as compared to NS group (P<0.05). Up-regulation of GAP-43 following CCI was decreased following caspase-3 inhibition. Following sciatic nerve ligation, the gene expression, translation and transcription are significantly changed in the neurons which finally results in neuron apoptosis. The neuron apoptosis induce the up-regulation of GAP-43 expression leading to hyperalgesia. CONCLUSION: Caspase-3 mediated neuron apoptosis is probably responsible for the neuropathic pain in CCI rats. Inhibition of caspase-3 may serve as a treatment of neuropathic pain.

Small interference RNA targeting TLR4 gene effectively attenuates pulmonary inflammation in a rat model.

OBJECTIVE: The present study was to investigate the feasibility of adenovirus-mediated small interference RNA (siRNA) targeting Toll-like receptor 4 (TLR4) gene in ameliorating lipopolysaccharide- (LPS-) induced acute lung injury (ALI). METHODS: In vitro, alveolar macrophages (AMs) were treated with Ad-siTLR4 and Ad-EFGP, respectively, for 12 h, 24 h, and 48 h, and then with LPS (100 ng/mL) for 2 h, and the function and expression of TLR4 were evaluated. In vivo, rats received intratracheal injection of 300 µL of normal saline (control group), 300 µL of Ad-EGFP (Ad-EGFP group), or 300 µL of Ad-siTLR4 (Ad-siTLR4 group) and then were intravenously treated with LPS (50 mg/kg) to induce ALI. RESULTS: Ad-siTLR4 treatment significantly reduced TLR4 expression and production of proinflammatory cytokines following LPS treatment both in vitro and in vivo. Significant alleviation of tissue edema, microvascular protein leakage, and neutrophil infiltration was observed in the AdsiTLR4-treated animals. CONCLUSION: TLR4 plays a critical role in LPS-induced ALI, and transfection of Ad-siTLR4 can effectively downregulate TLR4 expression in vitro and in vivo, accompanied by alleviation of LPS-induced lung injury. These findings suggest that TLR4 may serve as a potential target in the treatment of ALI and RNA interfering targeting TLR4 expression represents a therapeutic strategy.

Suppression of acute morphine withdrawal syndrome by adenovirus-mediated ß-endorphin in rats.

BACKGROUND: Endogenous ß-endorphin (ß-EP) in the central nervous system (CNS) is decreased upon opioid addiction. The current study examined whether exogenous ß-EP, delivered using an adenoviral vector into the CNS could attenuate morphine withdrawal syndrome in rats. METHODS: The model of opioid-dependent rats was set up by receiving subcutaneous injection of morphine using an escalating regimen for 6days (5, 10, 20, 40, 50, 60mg/kg, three times/day). The adenovirus mediated ß-EP gene was constructed based on our previous work. The ilea of opioid-dependent rats were isolated and treated with the supernatant of Ad-NEP. The basic and naloxone-induced (4µm/l) contractions of dependent ilea were recorded. The Ad-NEP was injected into the left lateral ventricle of the addition rats. The expression of the ß-EP gene was verified by radioimmunoassay of the cerebrospinal fluid (CSF) and immunocytochemistry for ß-EP. Withdrawal syndrome was evaluated after intraperitoneal injection of naloxone. RESULTS: The contractions of dependent ilea were attenuated with supernatant containing ß-EP expressed by Ad-NEP. Injection of the Ad-NEP resulted in significant increases in ß-EP level in the CSF and ß-EP-positive neurons. Rats receiving adenovirus carrying the ß-EP gene had significantly less severe withdrawal symptoms upon naloxone challenge. CONCLUSIONS: Exogenous ß-EP mediated by adenovirus could attenuate withdrawal syndrome in morphine-dependent rats.

Intrathecal siRNA against Toll-like receptor 4 reduces nociception in a rat model of neuropathic pain.

BACKGROUND: Neuropathic pain is characterized by hyperalgesia, allodynia and spontaneous pain. It often occurs as a result of injury to peripheral nerves, dorsal root ganglions (DRG), spinal cord, or brain. Recent studies have suggested that Toll-like receptor 4 (TLR4) might play a role in neuropathic pain. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we investigated the role of TLR4 in a rat chronic constriction injury (CCI) model and explored the feasibility of treating neuropathic pain by inhibiting TLR4. Our results demonstrated that intrathecal siRNA-mediated suppression of TLR4 attenuated CCI-induced mechanical allodynia and thermal hyperalgesia through inhibiting the activation of NF-kappaB p65 and production of proinflammatory cytokines (e.g., TNF-alpha and IL-1 beta). CONCLUSIONS/SIGNIFICANCE: These findings suggest that suppression of TLR4 mediated by intrathecally administered siRNA may be a new strategy for the treatment of neuropathic pain.

Bilateral downregulation of Nav1.8 in dorsal root ganglia of rats with bone cancer pain induced by inoculation with Walker 256 breast tumor cells.

BACKGROUND: Rapid and effective treatment of cancer-induced bone pain remains a clinical challenge and patients with bone metastasis are more likely to experience severe pain. The voltage-gated sodium channel Nav1.8 plays a critical role in many aspects of nociceptor function. Therefore, we characterized a rat model of cancer pain and investigated the potential role of Nav1.8. METHODS: Adult female Wistar rats were used for the study. Cancer pain was induced by inoculation of Walker 256 breast carcinosarcoma cells into the tibia. After surgery, mechanical and thermal hyperalgesia and ambulation scores were evaluated to identify pain-related behavior. We used real-time RT-PCR to determine Nav1.8 mRNA expression in bilateral L4/L5 dorsal root ganglia (DRG) at 16-19 days after surgery. Western blotting and immunofluorescence were used to compare the expression and distribution of Nav1.8 in L4/L5 DRG between tumor-bearing and sham rats. Antisense oligodeoxynucleotides (ODNs) against Nav1.8 were administered intrathecally at 14-16 days after surgery to knock down Nav1.8 protein expression and changes in pain-related behavior were observed. RESULTS: Tumor-bearing rats exhibited mechanical hyperalgesia and ambulatory-evoked pain from day 7 after inoculation of Walker 256 cells. In the advanced stage of cancer pain (days 16-19 after surgery), normalized Nav1.8 mRNA levels assessed by real-time RT-PCR were significantly lower in ipsilateral L4/L5 DRG of tumor-bearing rats compared with the sham group. Western-blot showed that the total expression of Nav1.8 protein significantly decreased bilaterally in DRG of tumor-bearing rats. Furthermore, as revealed by immunofluorescence, only the expression of Nav1.8 protein in small neurons down regulated significantly in bilateral DRG of cancer pain rats. After administration of antisense ODNs against Nav1.8, Nav1.8 protein expression decreased significantly and tumor-bearing rats showed alleviated mechanical hyperalgesia and ambulatory-evoked pain. CONCLUSIONS: These findings suggest that Nav1.8 plays a role in the development and maintenance of bone cancer pain.

Acute PAR2 activation reduces alpha, beta-MeATP sensitive currents in rat dorsal root ganglion neurons.

It has been reported that proteinase-activated receptor 2 (PAR2) receptor activation enhances the animal's pain response and PAR2 coexpresses with P2X3 in dorsal root ganglion neurons. However, whether PAR2 activation has a direct impact on P2X3 currents is still not clear. In this study, we performed the patch-clamp experiments in cultured dorsal root ganglion neurons and found that when incubated with trypsin or the PAR2 agonist SL-NH2 for a short time (3 min), instead of increasing, P2X3 currents amplitude decreased significantly. Meanwhile, the opening of P2X3 ion channel accelerated. Protein kinase A inhibitor H89 could not reverse above phenomenon, but played a synergistic effect on the contrary. These results suggest that the enhanced pain response caused by PAR2 activation is not through direct increase of the P2X3 current amplitude, and the acceleration of P2X3 opening may participate in the enhanced pain response in a long-time view. Moreover, protein kinase A does not participate in the inhibition of P2X3 currents caused by PAR2 activation.