Treatment with analgesics after mouse sciatic nerve injury does not alter expression of wound healing-associated genes

The comparative effects of estrogen and tacrolimus on crushed sciatic nerve regeneration in male mice: functional and histopathological evaluation

Some pharmacological agents can be effective for peripheral nerve injuries treatments. Present study was aimed to apply different agents and to compare the nerve regenerative effects following crushed sciatic nerve injuries. Twenty-four adult male mice were conducted in this study. Standard unilateral left side sciatic nerve crush was performed with 2.00 mm width mosquito hemostat forceps. The mice were randomly divided into four groups with the same numbers in each group which received subcutaneously, estrogen (group I), tacrolimus (group II), the combination of estrogen and tacrolimus (group III), and saline 0.90%. Functional recovery, histopathology, and immunohistochemistry (IHC) were performed on days 14^th and 28^th. Walking track analysis on day 14^th showed no significant difference between experimental groups, however, they showed significant difference compared to the control group. At the same time, experimental groups showed similar results of inflammatory cell infiltration, axonal edema, and count with significant differences compared to control group. At the end of the study, group I and III showed a significant difference in functional recovery between group II and control. After fourth week significant histopathological difference of axonal count was observed in group III. On day 28^th, only IHC assessment in group III showed more glial fibrillary acidic protein (GFAP) expression compared to the same group on day 14^th. This study revealed subcutaneous administration of combined estrogen and tacrolimus could be effective with acceptable results in nerve regeneration.

Vitamin C regulates Schwann cell myelination by promoting DNA demethylation of pro-myelinating genes

Ascorbic acid (vitamin C) is critical for Schwann cells to myelinate peripheral nerve axons during development and remyelination after injury. However, its exact mechanism remains elusive. Vitamin C is a dietary nutrient that was recently discovered to promote active DNA demethylation. Schwann cell myelination is characterized by global DNA demethylation in vivo and may therefore be regulated by vitamin C. We found that vitamin C induces a massive transcriptomic shift (n = 3,848 genes) in primary cultured Schwann cells while simultaneously producing a global increase in genomic 5-hydroxymethylcytosine (5hmC), a DNA demethylation intermediate which regulates transcription. Vitamin C up-regulates 10 pro-myelinating genes which exhibit elevated 5hmC content in both the promoter and gene body regions of these loci following treatment. Using a mouse model of human vitamin C metabolism, we found that maternal dietary vitamin C deficiency causes peripheral nerve hypomyelination throughout early development in resulting offspring. Additionally, dietary vitamin C intake regulates the expression of myelin-related proteins such as periaxin (PRX) and myelin basic protein (MBP) during development and remyelination after injury in mice. Taken together, these results suggest that vitamin C cooperatively promotes myelination through 1) increased DNA demethylation and transcription of pro-myelinating genes, and 2) its known role in stabilizing collagen helices to form the basal lamina that is necessary for myelination.

A mechanistic approach to HPLC analysis, antinociceptive, anti-inflammatory and postoperative analgesic activities of panch phoron in mice

Background

Panch phoron is a mixture of five spices containing an equal proportion of Foeniculum vulgare (fennel), Trigonella foenum-graecum Linn (fenugreek), Nigella sativa (black cumin), Cuminum cyminum (cumin) and Brassica nigra (black mustard). The mixture is commonly used in Bangladeshi cuisine and possesses many pharmacological effects. In this study, we evaluated the antinociceptive and anti-inflammatory activities of aqueous panch phoron extract (PPE) in vivo, its possible mechanism of action and phytochemical analysis by High-Performance Liquid Chromatography (HPLC). We also investigated the effect of PPE on postoperative pain in mice.

Methods

HPLC was carried out using LC-20A Modular HPLC system to identify the bioactive compounds present in PPE. Five groups of Swiss albino male mice (n = 6 per group) were orally treated with 10 ml/kg of distilled water or 10 mg/kg of sodium diclofenac or three doses of PPE (100 mg/kg, 300 mg/kg, 500 mg/kg). In vivo assessment was carried out by the writhing test, tail-flick test, formalin test, and carrageenan induced paw edema test. The opioid antagonist, naloxone was used in the acetic acid test to evaluate the involvement of opioid receptors. To assess the effect of PPE in postoperative pain, mice that underwent sciatic nerve surgery were measured for the paw withdrawal latency in a hot water bath.

Results

In HPLC analysis, different types of phenolic compounds and flavonoids, including catechin hydrate, para-coumaric acid, vanillic acid, and syringic acid were detected. Treatment with PPE exhibited dose-dependent antinociceptive and anti-inflammatory activities in pain models (p < 0.05). Furthermore, naloxone did not reverse the effect of PPE in the writhing test. Mice that underwent sciatic nerve surgery showed that the paw withdrawal latency increased gradually over 7 days.

Conclusions

Our results demonstrate that PPE has significant antinociceptive and anti-inflammatory activities and can provide significant postoperative analgesia.

Coping with Phantom Limb Pain

Phantom limb pain is a chronic neuropathic pain that develops in 45-85% of patients who undergo major amputations of the upper and lower extremities and appears predominantly during two time frames following an amputation: the first month and later about 1 year. Although in most patients the frequency and intensity of pain diminish over time, severe pain persists in about 5-10%. It has been proposed that factors in both the peripheral and central nervous systems play major roles in triggering the development and maintenance of pain associated with extremity amputations. Chronic pain is physically and mentally debilitating, affecting an individual's capacity for self-care, but also diminishing an individual's daily capacity for personal and economic independence. In addition, the pain may lead to depression and feelings of hopelessness. A National Center for Biotechnology Information study found that in the USA alone, the annual cost of dealing with neuropathic pain is more than $600 billion, with an estimated 20 million people in the USA suffering from this condition. Although the pain can be reduced by antiepileptic drugs and analgesics, they are frequently ineffective or their side effects preclude their use. The optimal approach for eliminating neuropathic pain and improving individuals' quality of life is the development of novel techniques that permanently prevent the development and maintenance of neuropathic pain, or that eliminate the pain once it has developed. What is still required is understanding when and where an effective novel technique must be applied, such as onto the nerve stump of the transected peripheral axons, dorsal root ganglion neurons, spinal cord, or cortex to induce the desired influences. This review, the second of two in this journal volume, examines the techniques that may be capable of reducing or eliminating chronic neuropathic pain once it has developed. Such an understanding will improve amputees' quality of life by blocking the mechanisms that trigger and/or maintain PLP and chronic neuropathic pain.

Anesthesia may alter mRNA expression of certain wound healing-associated genes in dermal wound environment of the rats

Some anesthetics including ketamine/xylazine and thiopental have been shown to alter the expression of genes related with inflammatory cytokines and chemokines in previous studies unassociated with wound healing, arising the question of whether commonly used anesthetics in wound healing models could interfere with the transcriptional responses of the genes associated with skin wound healing. The gene expression profile in wound biopsies of rats who received widely used anesthetics doses of intraperitoneal ketamine/xylazine (50 mg/kg and 10 mg/kg) or thiopental (50 mg/kg) in comparison with control rats was analyzed by monitoring the expression of genes effective on various phases of wound healing. The expression levels of 84 genes were determined on 3rd, 7th and 14th days of post-wounding using a qPCR array system. Of the genes either up or downregulated fivefolds or more, three (Egf, Col5a1 and Cxcl3) and two (Tgfa and Il2) genes were found to be the most responsive ones to ketamine/xylazine or thiopental anesthesia respectively in a period of 14 days after correction for multiple testing. However, up to 22 and 24 genes for ketamine/xylazine and thiopental were found to be differentially expressed in the same period without correction for multiple-comparisons testing (p < 0.05). In conclusion, our data suggest that ketamine/xylazine and thiopental may alter the transcriptional responses of some genes associated with wound healing in rats. We strongly suggest to consider the possible alteration effect of these anesthetics on gene expression in animal models of dermal wound healing.

The effect of Jun dimerization on neurite outgrowth and motif binding

Axon regeneration is a necessary step toward functional recovery after spinal cord injury. The AP-1 transcription factor c-Jun has long been known to play an important role in directing the transcriptional response of Dorsal Root Ganglion (DRG) neurons to peripheral axotomy that results in successful axon regeneration. Here we performed ChIPseq for Jun in mouse DRG neurons after a sciatic nerve crush or sham surgery in order to measure the changes in Jun's DNA binding in response to peripheral axotomy. We found that the majority of Jun's injury-responsive changes in DNA binding occur at putative enhancer elements, rather than proximal to transcription start sites. We also used a series of single polypeptide chain tandem transcription factors to test the effects of different Jun-containing dimers on neurite outgrowth in DRG, cortical and hippocampal neurons. These experiments demonstrated that dimers composed of Jun and Atf3 promoted neurite outgrowth in rat CNS neurons as well as mouse DRG neurons. Our work provides new insight into the mechanisms underlying Jun's role in axon regeneration.

Identification of miRNAs involved in DRG neurite outgrowth and their putative targets

Peripheral neurons regenerate their axons after injury. Transcriptional regulation by microRNAs (miRNAs) is one possible mechanism controlling regeneration. We profiled miRNA expression in mouse dorsal root ganglion neurons after a sciatic nerve crush, and identified 49 differentially expressed miRNAs. We evaluated the functional role of each miRNA using a phenotypic analysis approach. To predict the targets of the miRNAs we employed RNA-Sequencing and examined transcription at the isoform level. We identify thousands of differentially expressed isoforms and bioinformatically associate the miRNAs that modulate neurite growth with their putative target isoforms to outline a network of regulatory events underlying peripheral nerve regeneration. MiR-298, let-7a, and let-7f enhance neurite growth and target the majority of isoforms in the differentially expressed network.