Role of caveolin-1 in chronic postsurgical pain in rats.

Chronic postsurgical pain (CPSP) has a high incidence, but the underlying mechanisms remain elusive. Previous studies have indicated that caveolin-1 (Cav-1) plays a notable role in pain modulation. To study the role of Cav-1 in CPSP in the present study, a rat model of skin/muscle incision and retraction (SMIR) was established. Under anesthesia, skin and superficial muscle of the medial thigh were incised and a small pair of retractors inserted. It was revealed that SMIR increased the expression of Cav-1 in the dorsal root ganglion (DRG) and the injured tissue around the incision. Furthermore, the infiltration of endothelial cells and macrophages in the injured tissue around the incision increased constantly, and the vascular permeability increased due to the destruction of the vascular endothelial barrier function around the injured tissue. Cav-1 was mainly expressed by CD68-positive macrophages and CD34-positive endothelial cells in the injured tissues around the incision, while it was also primarily localized in the medium and large neurofilament 200-positive neurons and a small number of calcitonin gene-related peptide- and isolectin B4-positive small and medium-sized neurons in the DRG. The results demonstrated that the sustained high expression levels of Cav-1 in the injured tissue around the incision could lead to the dysfunction of the vascular endothelial barrier and, thus, could induce the inflammatory response through the lipoprotein transport of endothelial cells, thereby resulting in peripheral sensitization. In addition, the sustained high expression levels of Cav-1 in the DRG could sensitize large-sized neurons and change the transmission mode of noxious stimuli. The findings of the present study indicated that a Cav-1-mediated process could participate in neuronal transmission pathways associated with pain modulation.

Role of p120 Catenin in Epac1-Induced Chronic Postsurgical Pain in Rats.

Chronic postsurgical pain (CPSP) is a chronic pain state that is difficult to be treated clinically. A series of complicated changes have been produced from nociceptive stimulation to the occurrence and development of postsurgical pain. Many mechanisms remain unclear. In order to study the role of intercellular gap junctions in inducing inflammatory microenvironment at the beginning of nociceptor after operation, the model of skin/muscle incision and retraction (SMIR) was established. We observed the changes of the expression of exchange proteins directly activated by cAMP-1 (Epac1) and p120 catenin (p120), the quantities of macrophages and endothelial cells, vascular endothelial permeability, and mechanical withdrawal threshold (MWT). It was found that macrophages and endothelial cells were functionally coupled through Epac1-p120. Adhesive linkage disorder remodeled the chronic, inflammatory, and eutrophic microenvironment at the beginning of nociceptor after operation through macrophages, endothelial cells, and endothelial paracellular pathways. It might be an early event and a key step in peripheral sensitization of CPSP. The expression of p120 in muscle tissue around the incision might become a prognostic marker for the conversion of acute postsurgical pain into CPSP. Targeted intervention of Epac1-p120 might be a clinical strategy for inhibiting the conversion of acute postsurgical pain into CPSP.

Peripheral KATP activation inhibits pain sensitization induced by skin/muscle incision and retraction via the nuclear factor-κB/c-Jun N-terminal kinase signaling pathway.

The aim of the current study was to assess the effect of pinacidil activation of ATP­sensitive potassium (KATP) channels prior to skin/muscle incision and retraction (SMIR) surgery on peripheral and central sensitization, and investigate molecular interferential targets for preventive analgesia. Male Sprague-Dawley rats were randomly assigned to one of the following five groups: Control, incision (sham surgery), incision plus retraction (SMIR) group, SMIR plus pinacidil (pinacidil) group and the SMIR plus pyrrolidine dithiocarbamate (PDTC) group. The rats in the pinacidil and PDTC groups were intraperitoneally injected with pinacidil or PDTC, respectively, prior to the SMIR procedure. The mechanical withdrawal threshold (MWT) was determined. Western blotting was performed to detect the alterations in the subunits of the KATP channels, Kir6.1 and SUR2, levels of nuclear factor­κB (NF­κB) in the tissue around the incision and c­Jun N­terminal kinase (JNK) in the spinal cord. There was a significant increase observed in the levels of NF­κB and JNK following SMIR surgery compared with the control group, and a significant reduction in MWT and the levels of Kir6.1 and SUR2. Additionally, intraperitoneal administration of pinacidil inhibited the reduction in MWT, and Kir6.1 and SUR2 levels. SMIR was observed to result in increases in the levels of NF­κB and JNK. In addition, in the PDTC group, the alterations in MWT, NF­κB, JNK, Kir6.1 and SUR2 resulting from SMIR were blocked. The results of the current study suggest that the deteriorations in the microenvironment resulting from the SMIR procedure can induce peripheral and central sensitization, and that the activation of peripheral KATP by pinacidil prior to SMIR is able to inhibit peripheral and central sensitization via the NF­κB/JNK signaling pathway, thus resulting in preventive analgesia.

Effect of Epac1 on pERK and VEGF Activation in Postoperative Persistent Pain in Rats.

The function of guanine nucleotide exchange protein conversion factor (Epac1) in regenerating nerves, stimulating insulin release, controlling vascular pressure, and controlling other metabolic activities has been recognized; however, few studies have addressed the potential role of Epac1 in controlling chronic postoperative pain. Using a rat model of skin/muscle incision and retraction (SMIR), our study tested the hypothesis that increased Epac1 signaling is a factor in postoperative chronic pain. Rats were randomly divided into normal, sham operation, SMIR, SMIR + Epac1 siRNA (Epac1 inhibitor), and normal + 8-pCPT (Epac1 agonist) groups. The mechanical withdrawal threshold (MWT) was used as an index of pain sensitivity. Epac1 expression in the incision-site muscle, DRG, and spinal cord was assessed using western blotting and immunofluorescence. The effects of Epac1 agonists and Epac1 siRNA on MWT and phosphorylated extracellular signal-regulated kinase (pERK), vascular endothelial growth factor (VEGF), protein release in the spinal cord, and DRG levels were also studied. SMIR increased Epac1 expression in the incision-site muscle, spinal cord, and DRG, and decreased MWT. 8-pCPT induced the development of hypersensitivity and increased pERK and VEGF expression in normal rats, whereas siRNA decreased the expression of pERK and VEGF. This study suggests that activation of the Epac1 signal might induce local postoperative recovery process, which could be an important mechanism by which to control postoperative chronic pain. Our data suggest that therapy targeted at decreasing Epac1 levels provides promise for the prevention and treatment of chronic postoperative pain.

[A study on cytokine levels and nitric oxide content in rabbit aqueous humor after lens extraction and intraocular lens implantation].

OBJECTIVE: To investigate the relationship among inflammatory reaction and cytokine levels, nitric oxide (NO) content in aqueous humor after intraocular lens implantation. METHODS: Eighteen New Zealand rabbits were divided randomly into 3 groups (each 6 rabbits): (1) control group, (2) extracapsular cataract extraction group (ECCE) and (3) ECCE and posterior chamber intraocular lens implantation group (ECCE + IOL). The inflammation of all experimental rabbit eyes were observed by a zoom-photo slit-lamp microscope 0, 1, 3, 7, 14, 30 days postoperatively, including corneal edema and anterior chamber exudation. Meanwhile, aqueous humor was drawn for white blood cell (WBC) count and classification, as well as for NO(2)(-)/NO(3)(-) and cytokine assays, including interleukin-2 (IL-2), tumor necrosis factor-alpha (TNF-alpha). Statistics were taken by SPSS software. RESULTS: (1) The anterior chamber exudation was the most serious and monocyte/macrophage in aqueous humor were the highest in ECCE + IOL group in postoperative 7 - 14 days. (2) The levels of IL-2, TNF-alpha and the content of NO(2)(-)/NO(3)(-) in aqueous humor of ECCE + IOL group were higher than that in ECCE group and control group in the postoperative 1 - 14 days respectively, and they increased to their peak values at the postoperative 3 - 7 days and decreased gradually after postoperative two weeks. (3) The change regularity of IL-2, TNF-alpha, NO(2)(-)/NO(3)(-) and inflammatory reaction in each group were basically similar, i.e. the more serious the reaction, the higher the levels of the contents. CONCLUSION: The intraocular inflammation after intraocular lens implantation is closely related to the changes of cytokine levels and NO content in aqueous humor.