Systemic administration of a β2-adrenergic receptor agonist reduces mechanical allodynia and suppresses the immune response to surgery in a rat model of persistent post-incisional hypersensitivity

Beta 2 adrenergic receptor (β2 AR) activation in the central and peripheral nervous system has been implicated in nociceptive processing in acute and chronic pain settings with anti-inflammatory and anti-allodynic effects of β2-AR mimetics reported in several pain states. In the current study, we examined the therapeutic efficacy of the β2-AR agonist clenbuterol in a rat model of persistent postsurgical hypersensitivity induced by disruption of descending noradrenergic signaling in rats with plantar incision. We used growth curve modeling of ipsilateral mechanical paw withdrawal thresholds following incision to examine effects of treatment on postoperative trajectories. Depletion of spinal noradrenergic neurons delayed recovery of hypersensitivity following incision evident as a flattened slope compared to non-depleted rats (-1.8 g/day with 95% CI -2.4 to -1.085, p < 0.0001). Chronic administration of clenbuterol reduced mechanical hypersensitivity evident as a greater initial intercept in noradrenergic depleted (6.2 g with 95% CI 1.6 to 10.8, p = 0.013) and non-depleted rats (5.4 g with 95% CI 1.2 to 9.6, p = 0.018) with plantar incision compared to vehicle treated rats. Despite a persistent reduction in mechanical hypersensitivity, clenbuterol did not alter the slope of recovery when modeled over several days (p = 0.053) or five weeks in depleted rats (p = 0.64). Systemic clenbuterol suppressed the enhanced microglial activation in depleted rats and reduced the density of macrophage at the site of incision. Direct spinal infusion of clenbuterol failed to reduce mechanical hypersensitivity in depleted rats with incision suggesting that beneficial effects of β2-AR stimulation in this model are largely peripherally mediated. Lastly, we examined β2-AR distribution in the spinal cord and skin using in-situ hybridization and IHC. These data add to our understanding of the role of β2-ARs in the nervous system on hypersensitivity after surgical incision and extend previously observed anti-inflammatory actions of β2-AR agonists to models of surgical injury.

Mechanism of Incisional Pain: Novel Finding on Long Noncoding RNA XIST/miR-340-5p/RAB1A Axis

The objective of this study is to investigate the effect of long noncoding RNA (lncRNA) XIST on postoperative pain and inflammation of plantar incision pain (PIP) in rats and its underlying mechanisms. PIP rat models were established by plantar incision. Rats in the sham group were subjected to povidone-iodine scrubbing, and no incision was made. To explore the role of XIST/ miR-340-5p/RAB1A in postoperative pain and inflammation, PIP rats were separately or simultaneously injected with lentivirus containing sh-NC, sh-XIST, mimic NC, miR-340-5p mimic, inhibitor NC, miR-340-5p inhibitor, pcDNA3.1, or pcDNA3.1-RAB1A through an intrathecal catheter. The paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) values of rats in each group were assessed to evaluate the pain behavior. RT-qPCR and Western blot were utilized to determine the levels of XIST, miR-340-5p, RAB1A, and NF-κB pathway-related proteins (p-IκBα, IκBα, p-p65, and p65). The concentrations of inflammatory cytokines (TNF-α, IL-1β, and IL-6) in rat spinal dorsal horn tissues were inspected by ELISA. H and E staining was applied to observe the pathological changes of neurons in the spinal dorsal horn, TUNEL staining to detect neuronal apoptosis, and immunohistochemistry to measure RAB1A level. Plantar incision surgery caused decreased PWT and PWL values, enhanced levels of XIST, RAB1A, and inflammatory cytokines, along with an increased proportion of apoptotic neurons. The pain sensitivity and inflammation of rats were motivated after plantar incision surgery. Intrathecal injection of sh-XIST or miR-340-5p mimic ameliorated the pain and inflammation of PIP rats, while silencing of miR-340-5p or overexpression of RAB1A partly reversed the effect of sh-XIST on PIP rats. XIST targeted miR-340-5p and miR-340-5p negatively regulated RAB1A. The XIST/ miR-340-5p/RAB1A axis activated the NF-κB signaling pathway. LncRNA XIST aggravates inflammatory response and postoperative pain of PIP rats by activating the NF-κB pathway via the miR-340-5p/RAB1A axis.

Comparison of Nociceptive Effects of Buprenorphine, Firocoxib, and Meloxicam in a Plantar Incision Model in Sprague–Dawley Rats

Due to their reduced frequency of dosing and ease of availability, NSAIDs are generally preferred over opioids for rodent analgesia. We evaluated the efficacy of the highly COX2-selective NSAID firocoxib as compared with meloxicam and buprenorphine for reducing allodynia and hyperalgesia in rats in a plantar incision model of surgical pain. After a preliminary pharmacokinetic study using firocoxib, Sprague–Dawley rats (n = 12 per group, 6 of each sex) were divided into 6 groups: no surgery (anesthesia only), saline (surgery but no analgesia), buprenorphine (0.05 mg/kg SC every 8 h), meloxicam (2 mg/kg SC every 24 h), and 2 dosages of firocoxib (10 and 20 mg/kg SC every 24 h). The nociception assays were performed by using von Frey and Hargreaves methodology to test mechanical allodynia and thermal hyperalgesia. These assays were performed at 24 h before and at 20, 28, 44, and 52 h after start of surgery. None of the analgesics used in this study produced significantly different responses in allodynia or hyperalgesia from those of saline-treated rats. In the Hargreaves assay, female saline-treated rats experienced significantly greater hyperalgesia than did males. These findings add to a growing body of literature suggestingthat commonly used dosages of analgesics may not provide sufficient analgesia in rats experiencing incisional pain.

Direct Plantar Approach to Plantar Plate Repair and Associated Wound Complications

Category: Lesser Toes Introduction/Purpose: Lesser toe metatarsophalangeal joint instability, secondary to plantar plate tear, has been the focus of numerous recent publications, majority reporting on repair through a dorsal approach. A plantar approach has been described with the advantage of direct ligamentous repair or repair to bone, which follows conventional techniques employed throughout the body. Previous clinical studies have shown success in deformity correction and longevity of both approaches. The proponents of the dorsal approach advocate that indirect repair of the plantar plate avoids perceived risks of complications with a plantar incision, without evidence of superior outcomes. The purpose of this study was to investigate the safety and efficacy of direct plantar approach to plantar plate repairs by reporting the rate of specific complications in a large clinical series. Methods: This was an IRB approved retrospective study of 204 plantar plate repairs, in 185 patients, (194 lesser MTP, 10 hallux MTP) with average age of 56 and mean BMI of 28. Surgical technique involved repair with absorbable braided suture (88%) versus suture anchor (12%) with or without MTPJ pinning (80%). Mean follow up was 53 weeks (range 5-170). Patients were screened for associated risk factors including diabetes mellitus (8%), tobacco use (5%), neuropathy (1%) and additional concurrent procedures (96%). Complications were defined as superficial or deep infection, painful scar, and reoperation. Analysis was conducted by using Wilcoxon-Mann-Whitney test or Fisher’s exact tests for continuous and categorical variables, respectively. Risk factors were analyzed using univariate logistic analysis to produce odds ratios (OR) with 95% confidence interval (CI) and an inclusion criterion of a p-value > 0.2 for multivariate analysis as determined by Wald tests (significance at p<0.05 for final modeling). Results: Overall, there were 31 total complications (15%) demonstrated by 14 superficial infections (6.8%) and 17 painful scars (8.3%) along with three reoperations (1.4%). All reoperations were performed for deformity or instability, not scar revision. There were no deep infections. No increased odds of complications were found with suture anchor repair, MTPJ pinning, neuropathy, or diabetes. Patients that used tobacco had 7.5 (CI 1.66- 34.06) the odds of developing any wound complication compared with nonsmokers. Tobacco use was also found to significantly increase the odds for superficial infection by 9.8 (CI 2.08 - 46.15). There was no increase in painful scar or reoperation in tobacco users. This study did not find an increased complication rate with additional ipsilateral procedures performed at the time of surgery. Conclusion: To our knowledge, this is the largest study evaluating the direct plantar approach to plantar plate repair, as well as the evaluation of associated complications with the plantar incision. With low complication and minimal reoperation rates, the results of this study have demonstrated the clinical viability of plantar based incisions. Previous studies have demonstrated the success of plantar plate repair and correction of deformity with a direct approach. This case series further demonstrates the safety and efficacy of plantar based incisions, particularly for direct plantar plate repairs.

Hydrogen attenuates postoperative pain through Trx1/ASK1/MMP9 signaling pathway

Background: Postoperative pain is a serious clinical problem with a poorly understood mechanism and lack of effective treatment. Considering hydrogen (H 2 ) could reduce neuroinflammation, we hypothesizes that hydrogen may alleviate postoperative pain and investigate the mechanism. Methods: Mice were used to establish postoperative pain model via performing a plantar incision surgery. Mechanical allodynia was measured using the Von Frey test. Cell signaling was assayed using gelatin zymography, western blotting, immunohistochemistry and immunofluorescence staining. The animals or BV-2 cells were received with/without ASK1 and Trx1 inhibitor to investigate the effects of H 2 on microglia. Results: Plantar incision surgery significantly decreased the mechanical threshold, and increased MMP-9 activity and ASK1 phosphorylation in the spinal cord of mice. MMP-9 knockout and ASK1 inhibitor NQDI-1 attenuated postoperative pain. H 2 treatment increased Trx1 expression, decreased ASK1, p38 and JNK phosphorylation, MMP-9 activity, pro-IL-1β maturation and IBA-1 expression in the spinal cord of postoperative pain mice, and ameliorated postoperative pain. In vitro, H 2 increased Trx1 expression and reduced MMP-9 activity induced by LPS in BV-2 cells. Additionally, H 2 also reduced ASK1, p38 and JNK phosphorylation, and IBA-1 expression induced by LPS, which were abolished by Trx1 inhibitor PX12 in BV-2 cells. Conclusions: For the first time the results confirm that H 2 can work as a therapeutic agent for ameliorating postoperative pain through Trx1/ASK1/MMP9 signaling pathway. MMP-9 and ASK1 may be the targeting molecules to relieve postoperative pain.

Global transcriptome analysis of rat dorsal root ganglia to identify molecular pathways involved in incisional pain

To develop non-opioid therapies for postoperative incisional pain, we must understand its underlying molecular mechanisms. In this study, we assessed global gene expression changes in dorsal root ganglia neurons in a model of incisional pain to identify pertinent molecular pathways. Male, Sprague–Dawley rats underwent infiltration of 1% capsaicin or vehicle into the plantar hind paw (n = 6–9/group) 30 min before plantar incision. Twenty-four hours after incision or sham (control) surgery, lumbar L4–L6 dorsal root ganglias were collected from rats pretreated with vehicle or capsaicin. RNA was isolated and sequenced by next generation sequencing. The genes were then annotated to functional networks using a knowledge-based database, Ingenuity Pathway Analysis. In rats pretreated with vehicle, plantar incision caused robust hyperalgesia, up-regulated 36 genes and downregulated 90 genes in dorsal root ganglias one day after plantar incision. Capsaicin pretreatment attenuated pain behaviors, caused localized denervation of the dermis and epidermis, and prevented the incision-induced changes in 99 of 126 genes. The pathway analyses showed altered gene networks related to increased pro-inflammatory and decreased anti-inflammatory responses in dorsal root ganglias. Insulin-like growth factor signaling was identified as one of the major gene networks involved in the development of incisional pain. Expression of insulin-like growth factor -2 and IGFBP6 in dorsal root ganglia were independently validated with quantitative real-time polymerase chain reaction. We discovered a distinct subset of dorsal root ganglia genes and three key signaling pathways that are altered 24 h after plantar incision but are unchanged when incision was made after capsaicin infiltration in the skin. Further exploration of molecular mechanisms of incisional pain may yield novel therapeutic targets.