PARP inhibition attenuates neuroinflammation and oxidative stress in chronic constriction injury induced peripheral neuropathy

NAMPT/NAD+/PARP1 Pathway Regulates CFA-Induced Inflammatory Pain via NF-κB Signaling in Rodents

Emerging evidence has implicated nicotinamide adenine dinucleotide (NAD+) metabolism in various inflammatory diseases. In the study, the role of NAD+ metabolism in Complete Freund's Adjuvant (CFA)-evoked inflammatory pain and the underlying mechanisms are investigated. The study demonstrated that CFA induced upregulation of nicotinamide phosphoribosyltransferase (NAMPT) in dorsal root ganglia (DRG) without significant changes in the spinal cord. Inhibition of NAMPT expression by intrathecal injection of NAMPT siRNA alleviated CFA-induced pain-like behavior, decreased NAD+ contents in DRG, and lowered poly-(ADP-ribose) polymerase 1 (PARP1) activity levels. These effects are all reversed by the supplement of nicotinamide mononucleotide (NMN). Inhibition of PARP1 expression by intrathecal injection of PARP1 siRNA alleviated CFA-induced pain-like behavior, while elevated NAD+ levels of DRG. The analgesic effect of inhibiting NAMPT/NAD+/PARP1 axis can be attributed to the downregulation of the NF-κB/IL-1β inflammatory pathway. Double immunofluorescence staining showed that the expression of NAMPT/NAD+/PARP1 axis is restricted to DRG neurons. In conclusion, PARP1 activation in response to CFA stimulation, fueled by NAMPT-derived NAD+, mediates CFA-induced inflammatory pain through NF-κB/IL-1β inflammatory pathway.

Autophagy as an Anti-senescent in Aging Neurocytes

Neuron homeostasis is crucial for the organism, and its maintenance is multifactorial, including autophagy. The turnover of aberrant intracellular components is a fundamental pathogenetic mechanism for cell aging. Autophagy is involved in the acceleration of the neurocyte aging process and the modification of cell longevity. Neurocyte aging is a process of loss of cell identity through cellular and subcellular changes that include molecular loss of epigenetics, transcriptomic, proteomic, and autophagy dysfunction. Autophagy dysfunction is the hallmark of neurocyte aging. Cell aging is the credential feature of neurodegenerative diseases. Pathophysiologically, aged neurocytes are characterized by dysregulated autophagy and subsequently neurocyte metabolic stress, resulting in accelerated neurocyte aging. In particular, chaperone- mediated autophagy perturbation results in upregulated expression of aging and apoptosis genes. Aged neurocytes are also characterized by the down-regulation of autophagy-related genes, such as ATG5-ATG12, LC3-II / LC3-I ratio, Beclin-1, and p62. Slowing aging through autophagy targeting is sufficient to improve prognosis in neurodegenerative diseases. Three primary anti-senescent molecules are involved in the aging process: mTOR, AMPK, and Sirtuins. Autophagy therapeutic effects can be applied to reverse and slow aging. This article discusses current advances in the role of autophagy in neurocyte homeostasis, aging, and potential therapeutic strategies to reduce aging and increase cell longevity.

Evaluated periodontal tissues and oxidative stress in rats with neuropathic pain-like behavior

BACKGROUND

Oxidative stress has a critical effect on both persistent pain states and periodontal disease. Voltage-gated sodium NaV1.7 (SCN9A), and transient receptor potential ankyrin 1 (TRPA1) are pain genes. The goal of this study was to investigate oxidative stress markers, periodontal status, SCN9A, and TRPA1 channel expression in periodontal tissues of rats with paclitaxel-induced neuropathic pain-like behavior (NPLB).

METHODS AND RESULTS

Totally 16 male Sprague Dawley rats were used: control (n = 8) and paclitaxel-induced pain (PTX) (n = 8). The alveolar bone loss and 8-hydroxy-2-deoxyguanosine (8-OHdG) levels were analyzed histometrically and immunohistochemically. Gingival superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities (spectrophotometric assay) were measured. The relative TRPA1 and SCN9A genes expression levels were evaluated using quantitative real-time PCR (qPCR) in the tissues of gingiva and brain. The PTX group had significantly higher alveolar bone loss and 8-OHdG compared to the control. The PTX group had significantly lower gingival SOD, GPx and CAT activity than the control groups. The PTX group had significantly higher relative gene expression of SCN9A (p = 0.0002) and TRPA1 (p = 0.0002) than the control in gingival tissues. Increased nociceptive susceptibility may affect the increase in oxidative stress and periodontal destruction.

CONCLUSIONS

Chronic pain conditions may increase TRPA1 and SCN9A gene expression in the periodontium. The data of the current study may help develop novel approaches both to maintain periodontal health and alleviate pain in patients suffering from orofacial pain.

Poly (ADP-ribose) polymerase 1 and neurodegenerative diseases: Past, present, and future

Poly (ADP-ribose) polymerase 1 (PARP1) is a first responder that recognizes DNA damage and facilitates its repair. Neurodegenerative diseases, characterized by progressive neuron loss driven by various risk factors, including DNA damage, have increasingly shed light on the pivotal involvement of PARP1. During the early phases of neurodegenerative diseases, PARP1 experiences controlled activation to swiftly address mild DNA damage, thereby contributing to maintain brain homeostasis. However, in late stages, exacerbated PARP1 activation precipitated by severe DNA damage exacerbates the disease condition. Consequently, inhibition of PARP1 overactivation emerges as a promising therapeutic approach for neurodegenerative diseases. In this review, we comprehensively synthesize and explore the multifaceted role of PARP1 in neurodegenerative diseases, with a particular emphasis on its over-activation in the aggregation of misfolded proteins, dysfunction of the autophagy-lysosome pathway, mitochondrial dysfunction, neuroinflammation, and blood-brain barrier (BBB) injury. Additionally, we encapsulate the therapeutic applications and limitations intrinsic of PARP1 inhibitors, mainly including limited specificity, intricate pathway dynamics, constrained clinical translation, and the heterogeneity of patient cohorts. We also explore and discuss the potential synergistic implementation of these inhibitors alongside other agents targeting DNA damage cascades within neurodegenerative diseases. Simultaneously, we propose several recommendations for the utilization of PARP1 inhibitors within the realm of neurodegenerative disorders, encompassing factors like the disease-specific roles of PARP1, combinatorial therapeutic strategies, and personalized medical interventions. Lastly, the encompassing review presents a forward-looking perspective along with strategic recommendations that could guide future research endeavors in this field.

Poly (ADP-Ribose) polymerase 1 and parthanatos in neurological diseases: From pathogenesis to therapeutic opportunities

Poly (ADP-ribose) polymerase-1 (PARP-1) is the most extensively studied member of the PARP superfamily, with its primary function being the facilitation of DNA damage repair processes. Parthanatos is a type of regulated cell death cascade initiated by PARP-1 hyperactivation, which involves multiple subroutines, including the accumulation of ADP-ribose polymers (PAR), binding of PAR and apoptosis-inducing factor (AIF), release of AIF from the mitochondria, the translocation of the AIF/macrophage migration inhibitory factor (MIF) complex, and massive MIF-mediated DNA fragmentation. Over the past few decades, the role of PARP-1 in central nervous system health and disease has received increasing attention. In this review, we discuss the biological functions of PARP-1 in neural cell proliferation and differentiation, memory formation, brain ageing, and epigenetic regulation. We then elaborate on the involvement of PARP-1 and PARP-1-dependant parthanatos in various neuropathological processes, such as oxidative stress, neuroinflammation, mitochondrial dysfunction, excitotoxicity, autophagy damage, and endoplasmic reticulum (ER) stress. Additional highlight contains PARP-1's implications in the initiation, progression, and therapeutic opportunities for different neurological illnesses, including neurodegenerative diseases, stroke, autism spectrum disorder (ASD), multiple sclerosis (MS), epilepsy, and neuropathic pain (NP). Finally, emerging insights into the repurposing of PARP inhibitors for the management of neurological diseases are provided. This review aims to summarize the exciting advancements in the critical role of PARP-1 in neurological disorders, which may open new avenues for therapeutic options targeting PARP-1 or parthanatos.

Functional Nutrition as Integrated Intervention for In- and Outpatient with Schizophrenia

Schizophrenia is a chronic and progressive disorder characterized by cognitive, emotional, and behavioral abnormalities associated with neuronal development and synaptic plasticity alterations. Genetic and epigenetic abnormalities in cortical parvalbumin-positive GABAergic interneurons and consequent alterations in glutamate-mediated excitatory neurotransmission during early neurodevelopment underlie schizophrenia manifestation and progression. Also, epigenetic alterations during pregnancy or early phases of postnatal life are associated with schizophrenia vulnerability and inflammatory processes, which are at the basis of brain pathology and a higher risk of comorbidities, including cardiovascular diseases and metabolic syndrome. In addition, schizophrenia patients adopt an unhealthy lifestyle and poor nutrition, leading to premature death. Here, I explored the role of functional nutrition as an integrated intervention for the long-term management of patients with schizophrenia. Several natural bioactive compounds in plant-based whole foods, including flavonoids, phytonutrients, vitamins, fatty acids, and minerals, modulate brain functioning by targeting neuroinflammation and improving cognitive decline. Although further clinical studies are needed, a functional diet rich in natural bioactive compounds might be effective in synergism with standard treatments to improve schizophrenia symptoms and reduce the risk of comorbidities.

NAD+ metabolism in peripheral neuropathic pain

Nicotinamide adenine dinucleotide (NAD⁺) is an omnipresent metabolite that participates in redox reactions. Multiple NAD⁺-consuming enzymes are implicated in numerous biological processes, including transcription, signaling, and cell survival. Multiple pieces of evidence have demonstrated that NAD⁺-consuming enzymes, including poly(ADP-ribose) polymerases (PARPs), sirtuins (SIRTs), and sterile alpha and TIR motif-containing 1 (SARM1), play major roles in peripheral neuropathic pain of various etiologies. These NAD⁺ consumers primarily participate in peripheral neuropathic pain via mechanisms such as mitochondrial dysfunction, oxidative stress, and inflammation. Furthermore, NAD⁺ synthase and nicotinamide phosphoribosyltransferase (NAMPT) have recently been found to contribute to the regulation of pain. Here, we review the evidence indicating the involvement of NAD⁺ metabolism in the pathological mechanisms of peripheral neuropathic pain. Advanced understanding of the molecular and cellular mechanisms associated with NAD⁺ in peripheral neuropathic pain will facilitate the development of novel treatment options for diverse types of peripheral neuropathic pain.

Neuroprotective Effect of Natural Compounds in Paclitaxel-Induced Chronic Inflammatory Pain

The current study explored the effects of natural compounds, berbamine, bergapten, and carveol on paclitaxel-associated neuroinflammatory pain. Berbamine, an alkaloid obtained from BerberisamurensisRuprhas been previously researched for anticancer and anti-inflammatory potential. Bergapten is 5-methoxsalenpsoralen previously investigated in cancer, vitiligo, and psoriasis. Carveol obtained from caraway is a component of essential oil. The neuropathic pain model was induced by administering 2 mg/kg of paclitaxel (PTX) every other day for a week. After the final PTX injection, a behavioral analysis was conducted, and subsequently, tissue was collected for molecular analysis. Berbamine, bergapten, and carveol treatment attenuated thermal hypersensitivity, improved latency of falling, normalized the changes in body weight, and increased the threshold for pain sensation. The drugs increased the protective glutathione (GSH) and glutathione S-transferase (GST) levels in the sciatic nerve and spinal cord while lowering inducible nitric oxide synthase (iNOS) and lipid peroxidase (LPO). Hematoxylin and eosin (H and E) and immunohistochemistry (IHC) examinations confirmed that the medication reversed the abnormal alterations. The aforementioned natural substances inhibited cyclooxygenase-2 (COX-2), tumor necrosis factor-alpha (TNF-α), and nuclear factor kappa B (NF-κb) overexpression, as evidenced by enzyme-linked immunosorbant assay (ELISA) and Western blot and hence provide neuroprotection in chronic constriction damage.

Gastrodin promotes the regeneration of peripheral nerves by regulating miR-497/BDNF axis

Background

Gastrodin (GAS), is a kind of phenolic compound extracted from the traditional Chinese herbal medicine Gastrodia elata Blume (GEB). This study was aimed at probing into the protective effect of GAS on peripheral nerve injury (PNI) and the underlying mechanism.

Methods

A rat model with PNI was established, followed by intraperitoneal injection of GAS (20 mg/kg/day). Sciatic nerve function index (SFI) was used to analyze the function of sciatic nerve. The amplitude and latency of compound muscle action potential (CMAP) were examined by electrophysiology. Schwann cells (SCs) were isolated from fetal rats and treated with GAS 200 μg/mL, and H₂O₂-induced model of oxidative stress injury was established. EdU and Transwell assays were adopted to detect the viability and migration of SCs. Dual-luciferase reporter gene assays were applied to verify the binding site between miR-497 and brain-derived neurotrophic factor (BDNF) 3’UTR. MiR-497 expression was probed by quantitative real-time polymerase chain reaction (qRT-PCR). BDNF, neurofilament-200 (NF-200) and myelin basic protein (MBP) expression levels were detected by Western blotting. Malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, glutathione content (GSH) and catalase (CAT) activity in SCs were also measured.

Results

GAS treatment could significantly increase the SFI and amplitude of CMAP, shorten the refractory period, and ameliorate muscle atrophy of the rats with PNI. GAS treatment could markedly restrain miR-497 expression and increase the expression levels of BDNF, NF-200 and MBP in SCs. BDNF was confirmed as the target of miR-497 and BDNF overexpression could reverse the impacts of miR-497 overexpression on the proliferation, migration, and oxidative stress response of SCs.

Conclusions

GAS promotes the recovery of PNI via modulating miR-497 / BDNF axis and inhibiting oxidative stress.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03483-z.

FeTMPyP a peroxynitrite decomposition catalyst ameliorated functional and behavioral deficits in chronic constriction injury induced neuropathic pain in rats

Neuropathic pain is a maladaptive pain phenotype that results from injury or damage to the somatosensory nervous system and is proposed to be linked to a cascade of events including excitotoxicity, oxidative stress, mitochondrial dysfunction, neuroinflammation and apoptosis. Oxidative/nitrosative stress is a critical link between neuroinflammation and neurodegeneration through poly (ADP) ribose polymerase (PARP) overactivation. Hence, the present study investigated the antioxidant and anti-inflammatory effects of peroxynitrite decomposition catalyst; FeTMPyP in chronic constriction injury (CCI) of sciatic nerve-induced neuropathy in rats. CCI of the sciatic nerve manifested significant deficits in behavioral, biochemical, functional parameters and was markedly reversed by administration of FeTMPyP. After 14 days of CCI induction, oxidative/nitrosative stress and inflammatory markers such as iNOS, NF-kB, TNF-α and IL-6 were elevated in sciatic nerves of CCI rats along with depleted levels of ATP and elevated levels of poly (ADP) ribose (PAR) in both sciatic nerves in ipsilateral (L4-L5) dorsal root ganglions (DRG's), suggesting over activation of PARP. Additionally, CCI resulted in aberrations in mitochondrial function as evident by decreased Mn-SOD levels and respiratory complex activities with increased mitochondrial fission protein DRP-1. These changes were reversed by treatment with FeTMPyP (1 & 3 mg/kg, p.o.). Findings of this study suggest that FeTMPyP, by virtue of its antioxidant properties, reduced both PARP over-activation and subsequent neuroinflammation resulted in protection against CCI-induced functional, behavioral and biochemical deficits.

Probucol attenuates NF-κB/NLRP3 signalling and augments Nrf-2 mediated antioxidant defence in nerve injury induced neuropathic pain

Neuroinflammation is one of the most significant pathological drivers following nerve injury which along with immune cell activation, oxidative stress and other associated molecular mechanisms contribute to development of neuropathic pain characterized by hyperalgesia and allodynia. In the current study we have investigated the pharmacological effect of probucol (prb) using chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain (NP) model in rats. CCI of sciatic nerve resulted in marked decrease in pain threshold along with perturbations in anti-oxidant defence, enhanced inflammatory mediators and abnormal foot posture. Administration of prb at the doses of 8 and 16 mg/kg, p.o. for 14 days significantly attenuated the behavioural, biochemical and functional deficits following CCI of sciatic nerve. To further explore the molecular mechanisms of prb, we assessed the post treatment levels of inflammatory and oxidative stress markers like NLRP3 inflammasome, NF-κB and associated proinflammatory molecules such as IL-1 β, TNF-α & IL-6 along with Nrf-2 and HO-1. Our findings demonstrated that CCI induced changes in levels of these markers were dose dependently reversed by administration of prb. Of note, at molecular level the elevated expression of transcription factors such as NF-κB which is crucial for Nlrp3 activation and diminished levels of Nrf-2 were manifested following CCI induction, these changes were markedly reversed with 14 days treatment of prb at both the doses. Our findings highlighted the dual pharmacological effect of prb, anti-inflammatory and anti-oxidant via modulation of NF-κB/NLRP3 signalling and Nrf-2 pathway in attenuation of CCI of sciatic nerve induced NP.

Calotropis procera (leaves) supplementation exerts curative effects on promoting functional recovery in a mouse model of peripheral nerve injury

Peripheral nerve injuries are among those complicated medical conditions, which are still waiting for their highly effective first-line therapies. In this study, the role of Calotropis procera crude leaves was evaluated at different doses for their effectiveness in improving functional recovery following sciatic nerve injury-induced in the mouse model. Thirty-two healthy albino mice were divided into four groups as Normal chow group (control, n = 8) and C. procera chow groups (50 mg/kg (n = 8), 100 mg/kg (n = 8) and 200 mg/kg (n = 8)). Behavioral analyses were performed to assess and compare improved functional recovery along with skeletal muscle mass measurement in all groups. Serum samples were analyzed for oxidative stress markers. Results showed that C. procera leaves at dose-dependent manner showed statistically prominent (p < .05) increase in sensorimotor functions reclamation as confirmed by behavioral analyses along with muscle mass restoration and prominent decline in TOS and momentous increase in TAC along with the augmented activity of antioxidative enzymes.

Effect of m-Trifluoromethyl-diphenyl diselenide on the Pain-Depression Dyad Induced by Reserpine: Insights on Oxidative Stress, Apoptotic, and Glucocorticoid Receptor Modulation

Chronic pain and depression often coexist sharing common pathological mechanisms, and available analgesics and antidepressants have demonstrated limited clinical efficacy. Evidence has demonstrated that neuronal oxidative stress, apoptosis, and also glucocorticoid receptor dysregulation facilitate the occurrence and development of both chronic pain and depression. This study evaluated the effect of the organoselenium compound m-trifluoromethyl-diphenyl diselenide [(m-CF₃-PhSe)₂] in the pain-depression comorbidity induced by reserpine. Mice were treated with reserpine 0.5 mg/kg for 3 days (intraperitoneal, once a day), and in the next 2 days, they were treated with (m-CF₃-PhSe)₂ 10 mg/kg (intragastric, once a day). Thirty minutes after the last administration of (m-CF₃-PhSe)₂, mice were subjected to the behavioral testing. (m-CF₃-PhSe)₂ treatment reverted the reserpine-increased thermal hyperalgesia and depressive-like behavior observed in the hot-plate test and forced swimming test, respectively. Reserpine provoked a decrease of crossings and rearings in the open-field test, while (m-CF₃-PhSe)₂ presented a tendency to normalize these parameters. Reserpine and/or (m-CF₃-PhSe)₂ treatments did not alter the locomotor activity of mice observed in the rota-rod test. These effects could be related to modulation of oxidative stress, apoptotic pathway, and glucocorticoid receptors, once (m-CF₃-PhSe)₂ normalized thiobarbituric acid reactive substances and 4-hydroxynonenal modified protein levels, markers of lipoperoxidation, poly(ADP-ribose) polymerase cleaved/total ratio, and glucocorticoid receptor levels increased by reserpine in the hippocampus. Considering that pain-depression dyad is a complex state of difficult treatment, this organoselenium compound could raise as an interesting alternative to treat pain-depression condition.

Effects of varying degrees of ligation in a neuropathic pain model induced by chronic constriction injury

AIM

Ligature tightness of chronic constriction injury (CCI) model remains inconsistent and controversial, presenting barriers for researchers.

METHODS

We summarized the different ligation criteria in literature and attempted to clarify their effects. To assess constriction under different criteria, we calculated the radial strain (ε_R) of ligated nerves from digital photographs. The mechanical withdrawal thresholds (MWT), thermal withdrawal latency (TWL) and sciatic functional index (SFI) were observed in rats of different groups to assess the state of model. Changes of myelin sheath were detected by pathological staining and immunohistochemistry.

RESULTS

The median ε_R values in the Loose, Medium and Tight groups were 13.6%, 15.2% and 21.7%, respectively. Ligated groups had lower MWT than Sham group and the TWL of rats in the Loose approached to rats with sham operation, while that of the Tight group was higher than Medium group 14 days after surgery. Medium and Tight groups showed more abnormal in SFI, compared with the other two groups 14 days. Pathological staining revealed demyelination in three CCI groups, especially in the sciatic nerves. Myelin protein zero levels decreased in the sciatic nerves as the degree of constriction increased, but myelin basic protein of the Medium group was lowest abundant in the spinal cords of all rats.

CONCLUSIONS

Our study demonstrated that the surrounding muscles briefly twitched when the diameter of the sciatic nerves was constricted by approximately 14-15%, which may provide a reference for other researchers for establishing CCI models.

Carvacrol abates NLRP3 inflammasome activation by augmenting Keap1/Nrf-2/p62 directed autophagy and mitochondrial quality control in neuropathic pain

Objectives: We aimed to evaluate the effect of carvacrol (CRC), a phenolic monoterpene with high nutritional value on NLRP3 activation against chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain (NP) in rats and in lipopolysacharide (LPS) induced neuroinflammation in neuro2a (N2A) cells. Methods: NP was induced in male SD rats by performing CCI and CRC (30 and 60 mg/kg, p.o) was administered for 14 days. Behavioural and functional parameters were evaluated using standard procedures. Various molecular experimentations were conducted to evaluate the efficacy of CRC against CCI induced neuropathy and in LPS (1 μg/ml) primed and ATP (5 μM) treated N2A cells.Results: CCI resulted in marked development of hyperalgesia and allodynia. Further, CCI rats, LPS and ATP treated N2A cells showed enhanced expression of NLRP3, ASC, Caspase-1 and IL-1β. In addition, CCI rats exhibited diminished levels of Nrf-2 with an increase in Keap1 expression. Also, CCI animals manifested with compromised mitochondrial function along with decreased autophagy markers and enhanced p62 levels when compared to sham rats. However, CRC administration significantly ameliorated these changes suggesting NLRP3 inhibition by CRC may be attributed to activation of autophagy via Keap1/Nrf-2/p62 forward feedback loop and augmentation of mitochondrial quality control. Intriguingly, pretreatment of CRC (50 and 100 μM) to LPS and ATP treated N2A cells resulted in decreased colocalization of NLRP3 and ASC.Discussion: These findings revealed the neuroprotective potential of CRC against CCI induced NP and delineate the critical role of autophagy and mitochondrial quality control in NLRP3 regulation.

Inhibition of PARP activity improves therapeutic effect of ARPE-19 transplantation in RCS rats through decreasing photoreceptor death

Photoreceptor (PR) dysfunction or death is the key pathological change in retinal degeneration (RD). The death of PRs might be due to a primary change in PRs themselves or secondary to the dysfunction of the retinal pigment epithelium (RPE). Poly(ADP-ribose) polymerase (PARP) was reported to be involved in primary PR death, but whether it plays a role in PR death secondary to RPE dysfunction has not been determined. To clarify this question and develop a new therapeutic approach, we studied the changes in PAR/PARP in the RCS rat, a RD model, and tested the effect of PARP intervention when given alone or in combination with RPE cell transplantation. The results showed that poly(ADP-ribosyl)ation of proteins was increased in PRs undergoing secondary death in RCS rats, and this result was confirmed by the observation of similar changes in sodium iodate (SI)-induced secondary RD in SD rats. The increase in PAR/PARP was highly associated with increased apoptotic PRs and decreased visual function, as represented by lowered b-wave amplitudes on electroretinogram (ERG). Then, as we expected, when the RCS rats were treated with subretinal injection of the PARP inhibitor PJ34, the RD process was delayed. Furthermore, when PJ34 was given simultaneously with subretinal ARPE-19 cell transplantation, the therapeutic effects were significantly improved and lasted longer than those of ARPE-19 or PJ34 treatment alone. These results provide a potential new approach for treating RD.

[Effects of different materials for partial sciatic nerve ligation on glial cell activation in rat models of chronic constriction injury]

OBJECTIVE

To compare the effects of different materials for partial sciatic nerve ligation on glial cell activation in the spinal cord in a rat model of chronic constriction injury (CCI).

METHODS

SD rats were randomly divided into the sham group (n=15), silk suture CCI group (n=15) and chromic catgut CCI group (n=14). The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) of the rats were detected at 3, 7, 11 and 15 days after the operation. The changes in the sciatic nerve, the activation of spinal cord glial cells and the expression of inflammatory factors were observed using Western blotting and RT-PCR.

RESULTS

At 3 to 15 days after the surgery, MWT and TWL of the rats were significantly lower in silk suture group and chromic catgut group than in the control group (P &lt; 0.05), and was significantly lower in chromic catgut group than in the silk suture group (P &lt; 0.05) at 3 days after the surgery. The results of sciatic nerve myelin staining showed that the sciatic nerve was damaged and demyelinated in both the ligation groups. The expressions of CD11b, GFAP, IL-1β and TNF-α in the two ligation groups were similar and all significantly higher than those in the control group (P &lt; 0.05). IL-6 mRNA level was significantly higher in chromic catgut group than in the silk suture group (P &lt; 0.05).

CONCLUSIONS

The CCI models established by partial sciatic nerve ligation with silk suture and chromic catgut all show glial activation, and the inflammatory response is stronger in chromic catgut group.

NLRP3 inflammasome mediates 2,5-hexanedione-induced neurotoxicity through regulation of macrophage infiltration in rats

Currently, whether nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome activation contributes to neuropathy induced by 2,5-Hexanedione (HD), the toxic metabolite of n-hexane, remains unknown. In this study, we found that HD intoxication elevated NLRP3 expression, caspase-1 activation and interleukin-1β production in sciatic nerve of rats, indicating activation of NLRP3 inflammasome. The increased cleavage of gasdermin D (GSDMD) protein, an important mediator of pyroptosis, and axon degeneration were also observed in sciatic nerves of HD-intoxicated rats. Interestingly, glybenclamide, a widely used inhibitor of NLRP3 inflammasome, significantly reduced NLRP3 inflammasome activation, which was associated with decreased GSDMD cleavage and axon degeneration as well as improved motor performance of HD-intoxicated rats. Subsequently, we found that inhibition of NLRP3 inflammasome by glybenclamide attenuated macrophage infiltration, activation and M1 polarization in sciatic nerves of HD-intoxicated rats. Furthermore, decreased malondialdehyde (MDA) contents and increased glutathione (GSH) level and total anti-oxidative capacity were also observed in sciatic nerves of rats treated with combined glybenclamide and HD compared with HD alone group. Altogether, our findings suggest that NLRP3 inflammasome activation contributes to HD-induced neurotoxicity by enhancing macrophage infiltration and activation as well as oxidative stress, providing a novel mechanism of neuropathy induced by this neurotoxicant.

PARP-1-regulated TNF-α expression in the dorsal root ganglia and spinal dorsal horn contributes to the pathogenesis of neuropathic pain in rats

Emerging evidence has implicated poly-(ADP-ribose) polymerase 1 (PARP-1), a transcriptional coregulator, in a variety of inflammatory diseases. In the current study, the role of PARP-1 in neuropathic pain and the underlying mechanisms were investigated. Neuropathic pain was determined by assessing the paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) following lumbar 5 spinal nerve ligation (SNL) in male rates. Western blotting, qRT-PCR, immunohistochemistry, chromatin immunoprecipitation (ChIP), and Co-IP assays were performed to elucidate the mechanisms. The results showed that SNL resulted in a significant increase in the expression and activation of PARP-1 in the ipsilateral L4/5 dorsal root ganglia (DRG) and spinal dorsal horn, which occurred on day one, reached peak on day 7, and persisted more than 2 weeks after surgery. Double immunofluorescence staining revealed that PARP-1 was expressed exclusively in DRG A-type and C-type neurons. In the spinal cord, PARP-1 mainly colocalized with the neuronal marker NeuN and the astrocytic marker GFAP specifically in the superficial lamina. Prior intrathecal (i.t.) injection of PJ-34, a PARPs inhibitor, or Tiq-A, a specific PARP-1 inhibitor, dose-dependently prevented the reductions in PWT and PWL following SNL. Established neuropathic pain-like hypersensitivity was also attenuated with i.t. injection of PJ-34 and Tiq-A starting on day 7 following SNL, a timepoint at which neuropathic pain was fully established. SNL-induced mechanical allodynia and thermal hyperalgesia were also alleviated by i.t. injection of PARP-1 siRNA following a reduction in PARP-1 expression in the dorsal horn. Moreover, the SNL-induced increases in TNF-α protein and mRNA in the dorsal horn and DRG were dramatically suppressed by i.t. injection of Tiq-A or PARP-1 siRNA. The i.t. lipopolysaccharide (LPS)-induced increase in the production of TNF-α in the dorsal horn was also inhibited by prior to i.t. injection of PARP-1 siRNA. Results of ChIP assay showed that SNL-induced PARP-1 activation promoted the binding of NF-κB p65 with the TNF-α promoter in the dorsal horn and that PARP-1 inhibition reduced this binding and suppressed TNF-α expression. Co-IP assay revealed that SNL caused a significant increase in the level of histone H1 poly(ADP)-ribosylation. Together, these results indicate that PARP-1-regulated TNF-α expression in the DRG and spinal dorsal horn following SNL contributes to the development and maintenance of neuropathic pain. Targeting PARP-1 might be a promising therapeutic strategy for the treatment of the chronic pain.

Ulinastatin Promotes Regeneration of Peripheral Nerves After Sciatic Nerve Injury by Targeting let-7 microRNAs and Enhancing NGF Expression

Background

Peripheral nerve injury is characterized as a common clinical problem. Ulinastatin (UTI) is a serine protease inhibitor with many biological activities including anti-inflammatory and antioxidant effects. Nonetheless, it is unknown whether UTI has a protective effect on peripheral nerve injury.

Methods

Thirty rats were divided into the sham operation group, the sciatic nerve injury group (injected with normal saline), and the UTI treatment group (80mg/kg/day for two consecutive weeks). Sciatic nerve function index (SFI) was used to assess the biological functions of the sciatic nerve, and compound muscle action potential (CMAP) was measured by electrophysiology. The expressions of let-7 miRNA members were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Nerve growth factor (NGF), nerve regeneration-related proteins GAP43 and NF200, and myelin formation-related proteins MAG and PMP22 expressions were explored by Western blot. After Schwann cells were transfected with let-7 mimics, pcDNA3.1-NGF, let-7 inhibitors, NGF siRNA and their corresponding controls, 5-ethynyl-2ʹ-deoxyuridine (EdU) assay, and Transwell assays were employed to investigate the proliferation and migration of Schwann cells. H₂O₂ was utilized to construct oxidative injury to cells, and the contents of MDA, SOD, GSH, and CAT were determined.

Results

UTI treatment remarkably increased SFI of the rats and CMAP of sciatic nerve, enhanced nerve regeneration, and myelin regeneration, and raised the production of GAP43, NF200, MAG, and PMP22. Furthermore, it was found that UTI markedly reduced let-7 miRNAs’ expressions and increased NGF expression after sciatic nerve injury. The dual-luciferase reporter assay validated that let-7 miRNAs targeted NGF, and functional experiments demonstrated that low expression of let-7 miRNAs and NGF overexpression contributed to Schwann cells’ proliferation and migration. Additionally, UTI treatment repressed the oxidative stress regulated by let-7/NGF axis.

Conclusion

UTI modulates the let-7/NGF axis to inhibit oxidative stress, promote nerve regeneration, and facilitate function recovery after peripheral nerve injury.

Strychnos nux-vomica L. seed preparation promotes functional recovery and attenuates oxidative stress in a mouse model of sciatic nerve crush injury

Background

Peripheral nerve injury is a debilitating condition that may lead to partial or complete motor, sensory and autonomic function loss and lacks effective therapy until date. Therefore, it is quite imperative to explore impending remedies for rapid and accurate functional retrieval following such conditions. Natural product-based intervention can prove effective to facilitate the process of functions regain.

Methods

Here, we investigated the effect of processed Strychnos nux-vomica seeds at a dose of 250 mg/kg body weight in a mouse model of induced Sciatic nerve lesion in promoting the recovery of the functions. A compression injury was induced in the Sciatic nerve of the right leg in the mice. Sensory function recovery was evaluated by hot-plate and formalin tests, whereas the motor function retrieval was assessed by measuring muscle grip strength, sciatic functional index, and muscle mass restoration. Oxidative stress and blood cell count were measured by biochemistry and haematological analyses.

Results

This study indicates that Strychnos nux-vomica seeds enhance the rate of recovery of both sensory and motor functions. It helps restore the muscle mass, attenuates total oxidant status and enhances the total anti-oxidant capacity of the biological system. Moreover, the treated animals manifested an enhanced glucose tolerance aptitude and augmented granulocyte and platelet counts. Improved oxidant control, enhanced glucose sensitivity and amended granulocyte and platelet counts are likely to contribute to the advantageous effects of Strychnos nux-vomica, and warrant further in-depth studies for deciphering possible mechanisms and identification of active constituent(s) responsible for these effects.

Conclusion

Strychnos nux-vomica seed offers functional recovery promoting effects following a mechanical injury to the Sciatic nerve and the possible reasons behind this effect can be reduced oxidative stress and improved glycaemic control. Further and detailed investigations can unravel this mystery.

Poly (ADP-Ribose) polymerase-1 (PARP-1) overactivity plays a pathogenic role in bile acids-induced nephrotoxicity in cholestatic rats

Cholestatic liver disease is a clinical complication with a wide range of etiologies. The liver is the primary organ influenced by cholestasis. Other organs, rather than the liver (e.g., kidneys), could also be affected by cholestatic liver disease. Cholestasis-induced renal injury is known as cholemic nephropathy (CN). Although the structural and functional alterations of the kidney in cholestasis have been well described, the cellular and molecular mechanisms of CN are not well understood. Some studies mentioned the role of oxidative stress and mitochondrial impairment in CN. Several cellular targets, including proteins, lipids, and DNA, could be affected by oxidative stress. Poly (ADP-Ribose) polymerase-1 (PARP-1) is an enzyme that its physiological activity plays a fundamental role in DNA repair. However, PARP-1 overexpression is associated with enhanced oxidative stress and cell death. The current study was designed to evaluate the role of PARP-1 activity in the pathogenesis of CN. Bile duct ligated (BDL) rats were treated with nicotinamide (NA) as a PARP-1 inhibitor. Kidney, urine, and plasma samples were collected at scheduled time intervals (3, 7, 14, and 28 days after BDL surgery). Serum and urine biomarkers of kidney injury, markers of oxidative stress and DNA damage, PARP-1 expression and activity in the kidney tissue, inflammatory response, renal fibrosis markers, and kidney histopathological alterations were assessed. Significant changes in the serum and urine biomarkers of kidney injury were evident in the BDL rats. Markers of oxidative stress were increased, and tissue ATP levels and antioxidant capacity were decreased in the kidney of cholestatic animals. A significant increase in PARP-1 expression and activity was evident in BDL rats (3, 7, 14, and 28 days after BDL). Moreover, inflammatory response (IL-1β and TNF-α expression; and myeloperoxidase activity), renal tissue histopathological alterations, and kidney fibrosis (α-SMA and TGF-β expression, as well as collagen deposition) were detected in cholestatic animals. It was found that the PARP-1 inhibitor, NA (50 and 100 mg/kg, i.p), significantly mitigated cholestasis-induced renal injury. The positive effects of NA were more significant at a lower dose and the early stage of CN. These data indicate a pathogenic role for PARP-1 overexpression in CN.

Therapeutic applications of PARP inhibitors in ovarian cancer

Ovarian cancer is the most lethal gynecologic malignancy with a high recurrence rate. Poly(ADP-ribose) polymerase inhibitors (PARPi) are one of the most active new therapies for treatment of ovarian cancer. These treatment modalities are based on the mechanisms of "synthetic lethal" and "PARP trapping", especially for patients with homologous recombination deficiencies, and they demonstrate a high survival advantage. However, resistance to PARPi is an emerging problem. Identifying potential biomarkers to monitor the resistance and developing drug combination strategies are effective ways to address PARPi resistance. This review introduces the mechanisms of anticancer activity of PARPi and the developmental history in clinical research. Moreover, this paper systematically analyzes the functions of PARP family proteins. Additionally, this work highlights the treatment prospects of the combination of immunotherapy and PARPi in ovarian cancer. Finally, we propose several novel technologies to overcome the limitations of current preclinical studies and utilize them to select potential targets for combined drug therapy and identify biomarkers of PARPi resistance in ovarian cancer.

Isoquercitrin promotes peripheral nerve regeneration through inhibiting oxidative stress following sciatic crush injury in mice

Background

Oxidative stress has been recognized to play a crucial role in the pathogenesis of peripheral nerve injury. Isoquercitrin (quercetin-3-glucoside) is a flavonoid that exhibited many biological activities, including anti-oxidative effect. However, it is unclear whether isoquercitrin has protective effects on peripheral nerve injury.

Methods

Mice treated by isoquercitrin were used as a case group, and mice injected with saline was the control group. Sciatic behavioral function was assessed using SFI and CMAPs were measured by electrophysiology. Schwann cells proliferation and migration were tested using EdU staining and Transwell migration chambers respectively. The expression of oxidative stress related factors were detected by qRT-PCR and Western blotting.

Results

In present study, our results demonstrated that isoquercitrin (20 mg/kg/day) treatment achieved significantly higher SFI and higher amplitude of CMAP, promoted the nerve regeneration and remyelination, increased the production of GAP43, NF200, MAG and PMP22, alleviated target muscle atrophy and autophagy, and suppressed the expression of ATG7, PINK1 and Beclin1 in soleus muscles after sciatic nerve crush. In vitro studies found that isoquercitrin promoted the axonal regeneration of DRGs neurons, the proliferation and migration of Schwann cells, and the expression of proliferating cell nuclear antigen (PCNA) in Schwann cells. The administration of isoquercitrin at 40 and 320 µM showed a dose dependent, and high doses of isoquercitrin (160 and 320 µM) showed better performance in promoting axonal regeneration of DRGs neurons, and the proliferation and migration of Schwann cells than low dose of isoquercitrin (40 µM). Furthermore, isoquercitrin significantly inhibited oxidative stress through reducing the production of Nox4 and Duox1, and promoting the expression of Nrf2 and SOD2 in soleus muscles after sciatic nerve crush.

Conclusions

Isoquercitrin may promote motor functional recovery and nerve regeneration following peripheral nerve injury though inhibition of oxidative stress, which highlighted the therapeutic values of isoquercitrin as a neuroprotective drug for peripheral nerve repair applications.

Spinal Reactive Oxygen Species and Oxidative Damage Mediate Chronic Pain in Lame Dairy Cows

Simple Summary

Chronic inflammatory diseases could impact central nervous system homeostasis, being oxidative damage of the dorsal horn, a relevant mechanism mediating central sensitization. Chronic inflammatory lameness in dairy cows is a painful condition that affects animal welfare, affecting dairy production worldwide. This study reveals increased levels of reactive oxygen species, malondialdehyde, and carbonyl groups, indicating lipid and protein damage in the spinal cord of cows with chronic lameness. Moreover, antioxidant system activity was similar between lame and non-lame cows which suggests that antioxidant dysregulation was not the cause of oxidative damage, as has been proposed previously. Based on the fact that nociceptive pathways are strongly conserved between species, there is no reason to neglect that chronic pain in cows promotes Central Nervous System (CNS) alterations, such as oxidative damage. Moreover, lame cows develop central sensitization, as allodynia and hyperalgesia are centrally and not peripherally mediated. Our results support the current assumption that chronic pain is a central nervous system disease and lameness in dairy cows is far beyond an inflammation of the hoof.

Abstract

Lameness in dairy cows is a worldwide prevalent disease with a negative impact on animal welfare and herd economy. Oxidative damage and antioxidant system dysfunction are common features of many CNS diseases, including chronic pain. The aim of this study was to evaluate the levels of reactive oxygen species (ROS) and oxidative damage markers in the spinal cord of dairy cows with chronic inflammatory lameness. Locomotion score was performed in order to select cows with chronic lameness. Dorsal horn spinal cord samples were obtained post mortem from lumbar segments (L2–L5), and ROS, malondialdehyde (MDA), and carbonyl groups were measured along with the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and total antioxidant response (TAR). Lame cows had increased levels of ROS, MDA, and carbonyl groups, while no differences were observed between lame and non-lame cows in SOD, GPx, CAT, and TAR activity. We conclude that painful chronic inflammatory lameness in dairy cows is associated with an increase in ROS, MDA, and carbonyl groups. Nonetheless, an association between ROS generation and dysfunction of the antioxidant system, as previously proposed, could not be established.

Poly (ADP-Ribose) Polymerase Inhibition for Chemotherapy-Induced Peripheral Neuropathy: A Meta-Analysis of Placebo-Controlled Trials

Background: Chemotherapy-induced peripheral neuropathy is characterized by pain, numbness, and tingling in the hands and feet and by diminished quality of life. Multiple previous studies, mostly preclinical, suggest that poly (ADP-ribose) polymerase (PARP) inhibitors may help with these symptoms. Objective: To assess the relationship between PARP inhibition and prevention/palliation of peripheral neuropathy in a clinical setting. Design: Meta-analysis of placebo-controlled clinical trials with PARP inhibitors. Setting/Subjects: We conducted 9 literature searches that included PubMed and other sources to compile fully published placebo-controlled clinical trials that tested PARP inhibitors and that reported on peripheral neuropathy. Measurements: The relative risks for neuropathy of all grades based on PARP inhibition were calculated for each trial. Each trial was weighted by its respective sample size. A forest plot was constructed. Results: Five trials, inclusive of 843 patients, met this study's eligibility criteria. Four included a concomitant PARP inhibitor (either olaparib or veliparib) and paclitaxel, a neuropathy-causing chemotherapy agent; the remaining trial evaluated long-term monotherapy with olaparib. The pooled overall relative risk for the development of neuropathy with PARP inhibition was 1.06 (95% confidence interval: 1-1.4). Conclusions: PARP inhibition does not appear to reduce the risk of chemotherapy-induced peripheral neuropathy. Whether PARP inhibitors may palliate (rather than prevent) neuropathy remains an area in need of further investigation.

Rosmarinic Acid Mitigates Mitochondrial Dysfunction and Spinal Glial Activation in Oxaliplatin-induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting complication which develops as a consequence of treatment with chemotherapeutic agents like oxaliplatin and is a mainstay of therapy for colorectal cancer. Ever since CIPN was identified, understanding its exact pathomechanisms remains a clinical challenge. The role of mitochondrial dysfunction and glial cell activation has surfaced in the etiology of CIPN. Rosmarinic acid (RA), a known mitoprotectant exerts neuroprotection against the oxidative stress and neuroinflammation in various disease conditions. Hence, in the present study, we investigated the effect using rosmarinic acid (25 and 50 mg/kg, po) in the experimental model of oxaliplatin-induced peripheral neuropathy (OIPN) in rats. Results showed that RA significantly (p < 0.001) prevented the functional deficits, reversed oxaliplatin-induced mechanical allodynia and cold hyperalgesia in rats. It reduced the oxidative stress, improved the mitochondrial function, and prevented the oxaliplatin-induced loss of ATP levels. RA significantly (p < 0.01) inhibited the spinal glial cell activation and suppressed the expression of inflammatory markers. RA treatment also resulted in the activation of adenosine monophosphate-activated protein kinase (AMPK) in the peripheral nerves and dorsal root ganglion (DRG) which also might have contributed to its neuroprotective actions. In vitro screening also revealed that RA did not compromise the anti-cancer activity of oxaliplatin in colon cancer cells (HT-29). Taken together, the above results demonstrate the therapeutic activity of RA against the oxaliplatin-induced mitochondrial dysfunction and neuroinflammation and thus, suggest its potential for the management of OIPN. Graphical Abstract Schematic representation of neuroprotective mechanisms of rosmarinic acid via AMPK activation in oxaliplatin-evoked peripheral neuropathy.

Can Poly (ADP-Ribose) Polymerase Inhibitors Palliate Paclitaxel-Induced Peripheral Neuropathy in Patients With Cancer?

Background:

Paclitaxel-treated patients can suffer from years of peripheral neuropathy with pain, numbness, and tingling. Promising preclinical data with poly (ADP-ribose) polymerase (PARP) inhibitors led us to explore this class of agents to palliate this neuropathy.

Methods:

We relied on a completed trial that tested the antineoplastic effects of veliparib (NCT01012817). Data from patients who had been enrolled on NCT01012817, who previously received paclitaxel, and who had completed a validated pain assessment instrument were evaluated for improvement in their pain scores.

Results:

All 34 eligible patients were women, and all had a metastatic gynecological malignancy. On a 10-point scale (higher numbers indicative of worse pain), the average baseline score was 3.6 (range: 0-7). Seven patients (21%; 95% confidence interval: 9%-38%) manifested a drop in pain score (1 score lower than baseline followed by at least one consecutive value also below baseline). Of note, no patients initiated other therapy for neuropathy while on NCT01012817.

Conclusion:

The PARP inhibitors merit further study for chemotherapy-induced peripheral neuropathy. For patients suffering from peripheral neuropathy, these putative palliative effects might prompt earlier consideration of a PARP inhibitor as part of cancer treatment.

Signatures of Altered Gene Expression in Dorsal Root Ganglia of a Fabry Disease Mouse Model

Fabry disease is an X-linked lysosomal storage disorder with involvement of the nervous system. Accumulation of glycosphingolipids within peripheral nerves and/or dorsal root ganglia results in pain due to small-fiber neuropathy, which affects the majority of patients already in early childhood. The α-galactosidase A deficient mouse proved to be an adequate model for Fabry disease, as it shares many symptoms including altered temperature sensitivity and pain perception. To characterize the signatures of gene expression that might underlie Fabry disease-associated sensory deficits and pain, we performed one-color based hybridization microarray expression profiling of DRG explants from adult α-galactosidase A deficient mice and age-matched wildtype controls. Protein-protein interaction (PPI) and pathway analyses were performed for differentially regulated mRNAs. We found 812 differentially expressed genes between adult α-galactosidase A deficient mice and age-matched wildtype controls, 506 of them being upregulated, and 306 being downregulated. Among the enriched pathways and processes, the disease-specific pathways “lysosome” and “ceramide metabolic process” were identified, enhancing reliability of the current analysis. Novel pathways that we identified include “G-protein coupled receptor signaling” and “retrograde transport” for the upregulated genes. From the analysis of downregulated genes, immune-related pathways, autoimmune, and infection pathways emerged. The current analysis is the first to present a differential gene expression profile of DRGs from α-galactosidase A deficient mice, thereby providing knowledge on possible mechanisms underlying neuropathic pain related symptoms in Fabry patients. Therefore, the presented data provide new insights into the development of the pain phenotype and might lead to new treatment strategies.

New approach for the treatment of neuropathic pain: Fibroblast growth factor 1 gene-transfected adipose-derived mesenchymal stem cells

BACKGROUND

Neuropathic pain triggered by peripheral nerve lesion is extremely difficult to manage with current approaches, hence the importance of exploring therapeutic alternatives.

METHODS

We have analysed adipose-derived mesenchymal stem cells (AD-MSCs) and fibroblast growth factor 1 gene-transfected adipose-derived mesenchymal stem cells (AD-MSCs ^FGF1 ) on chronic constriction injury (CCI). The mechanical and thermal hypersensitivity were assessed using the von Frey filament, radiant heat and acetone drop tests. Histopathological and apoptotic changes and the level of FGF1, GFAP and TNFα proteins were assessed in the lumbar portion (L4-L6). Moreover, AD-MSCs ^FGF1 were labelled with ^99m Tc -HMPAO and isolated organ counting were performed upon AD-MSCs ^FGF1 administration.

RESULTS

Administration of AD-MSCs ^FGF1 attenuated the CCI-induced mechanical and thermal hypersensitivity. Spinal structural alterations and apoptosis were decreased in the AD-MSCs ^FGF1 group. The injection of either phosphate-buffered saline or normal NIH3T3 fibroblasts could not attenuate the behavioural symptoms of neuropathic pain. Increased genetically engineered cells were counted in the injured sciatic nerve and the elevated levels of FGF1 were detected in the spinal tissue. Stem cell therapy lead to decrement the level of the CCI-induced TNF-α and GFAP expression.

CONCLUSION

The intravenous administration of AD-MSCs ^FGF1 could be considered as a potential remedy for the management of neuropathic pain.

SIGNIFICANCE

AD-MSCs ^FGF1 attenuated the CCI-induced mechanical and thermal hypersensitivity. Spinal structural alterations and apoptosis were significantly decreased in the AD-MSCs ^FGF1 group. Elevated levels of FGF1 were detected in the spinal tissue.

Melatonin prevents mitochondrial dysfunction and promotes neuroprotection by inducing autophagy during oxaliplatin-evoked peripheral neuropathy

Oxaliplatin, an organoplatinum compound, is used in the treatment of colorectal cancer, but its clinical use can be limited due to the development of peripheral neuropathy. Whilst mitochondrial dysfunction has been implicated as a major pathomechanism for oxaliplatin-induced neurotoxicity, the prevention of autophagy may also aggravate neuronal cell death. Melatonin, a well-known mitoprotectant and autophagy inducer, was used to examine its neuroprotective role in oxaliplatin-induced peripheral neuropathy (OIPN). Melatonin prevented the loss of mitochondrial membrane potential (Ψm) and promoted neuritogenesis in oxaliplatin-challenged neuro-2a cells. It did not interfere with the cytotoxic activity of oxaliplatin in human colon cancer cell line, HT-29. Melatonin treatment significantly alleviated oxaliplatin-induced pain behavior and neuropathic deficits in rats. It also ameliorated nitro-oxidative stress mediated by oxaliplatin, thus prevented nitrosylation of proteins and loss of antioxidant enzymes, and therefore, it improved mitochondrial electron transport chain function and maintained cellular bioenergetics by improving the ATP levels. The protective effects of melatonin were attributed to preventing oxaliplatin-induced neuronal apoptosis by increasing the autophagy pathway (via LC3A/3B) in peripheral nerves and dorsal root ganglion (DRG). Hence, it preserved the epidermal nerve fiber density in oxaliplatin-induced neuropathic rats. Taken together, we provide detailed molecular mechanisms for the neuroprotective effect of melatonin and suggest it has translational potential for oxaliplatin-induced neuropathy.

Carvedilol prevents functional deficits in peripheral nerve mitochondria of rats with oxaliplatin-evoked painful peripheral neuropathy

Oxaliplatin use as chemotherapeutic agent is frequently limited by cumulative neurotoxicity which may compromise quality of life. Reports relate this neurotoxic effect to oxidative stress and mitochondrial dysfunction in peripheral nerves and dorsal root ganglion (DRG). Carvedilol is an antihypertensive drug, has also been appreciated for its antioxidant and mitoprotective properties. Carvedilol co-treatment did not reduce the anti-tumor effects of oxaliplatin in human colon cancer cells (HT-29), but exhibited free radical scavenging activity against oxaliplatin-induced oxidative stress in neuronal cells (Neuro-2a). Hence, the present study was designed to investigate the effect of carvedilol in the experimental model of oxaliplatin-induced peripheral neuropathy (OIPN) in Sprague-Dawley rats. Oxaliplatin reduced the sensory nerve conduction velocity and produced the thermal and mechanical nociception. Carvedilol significantly (P<0.001) attenuated these functional and sensorimotor deficits. It also counteracted oxidative/nitrosative stress by reducing the levels of nitrotyrosine and improving the mitochondrial superoxide dismutase expression in both sciatic nerve and DRG tissues. It improved the mitochondrial function and prevented the oxaliplatin-induced alteration in mitochondrial membrane potential in sciatic nerve thus prevented loss of intra epidermal nerve fiber density in the foot pads. Together the results prompt the use of carvedilol along with chemotherapy with oxaliplatin to prevent the peripheral neuropathy.

Nrf2 and NF-κB modulation by Plumbagin attenuates functional, behavioural and biochemical deficits in rat model of neuropathic pain

BACKGROUND

Plumbagin is known to exhibit a broad range of biological activities including anti-cancer, antimicrobial and has been widely used traditionally. Nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) inhibitory and Nuclear factor (erythroid derived-2) like-2 (Nrf2) modulatory activities of Plumbagin have been reported already. In nerve injury model of neuropathy in rats, the role of NF-κB upregulation and declined antioxidant defence has been well recognized. So, we evaluated neuroprotective potential of Plumbagin in chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain in male Sprague-Dawley rats.

METHODS

Animals were tested for functional, behavioural and biochemical changes. Various markers associated with oxidative stress and inflammatory changes were assessed in the sciatic nerve and dorsal root ganglion (DRG) of the animals exposed to CCI mediated nerve injury.

RESULTS

CCI induced nerve injury led to long-lasting mechanical hyperalgesia, loss of hind limb function and abnormal pain sensation. Plumbagin treatment (10 and 20mg/kg, po) significantly and dose-dependently reversed mechanical hyperalgesia and other functional deficits. There was a marked increase in NF-κB and reduced Nrf2 levels in sciatic nerve and DRG following nerve injury. Plumbagin strengthened the antioxidant defence by improving Nrf2 levels and checked the neuroinflammation by decreasing NF-κB levels in sciatic nerve and DRG.

CONCLUSIONS

Together, these results suggested that Plumbagin alleviated CCI-induced neuropathic pain via antioxidant and anti-inflammatory mechanisms. Hence, the study suggests that Plumbagin may be useful for the management of trauma-induced neuropathic pain.

Combination strategy of PARP inhibitor with antioxidant prevent bioenergetic deficits and inflammatory changes in CCI-induced neuropathy

Neuropathic pain, a debilitating pain condition and the underlying pathogenic mechanisms are complex and interwoven amongst each other and still there is scant information available regarding therapies which promise to treat the condition. Evidence indicate that oxidative/nitrosative stress induced poly (ADP-ribose) polymerase (PARP) overactivation initiate neuroinflammation and bioenergetic crisis culminating into neurodegenerative changes following nerve injury. Hence, we investigated the therapeutic effect of combining an antioxidant, quercetin and a PARP inhibitor, 4-amino 1, 8-naphthalimide (4-ANI) on the hallmark deficits induced by chronic constriction injury (CCI) of sciatic nerve in rats. Quercetin (25 mg/kg, p.o.) and 4-ANI (3 mg/kg, p.o.) were administered either alone or in combination for 14 days to examine sciatic functional index, allodynia and hyperalgesia using walking track analysis, Von Frey, acetone spray and hot plate tests respectively. Malondialdehyde, nitrite and glutathione levels were estimated to detect oxidative/nitrosative stress; mitochondrial membrane potential and cytochrome c oxidase activity to assess mitochondrial function; NAD & ATP levels to examine the bioenergetic status and levels of inflammatory markers were evaluated in ipsilateral sciatic nerve. Quercetin and 4-ANI alone improved the pain behaviour and biochemical alterations but the combination therapy demonstrated an appreciable reversal of CCI-induced changes. Nitrotyrosine and Poly ADP-Ribose (PAR) immunopositivity was decreased and nuclear factor erythroid 2-related factor (Nrf-2) levels were increased significantly in micro-sections of the sciatic nerve and dorsal root ganglion (DRG) of treatment group. These results suggest that simultaneous inhibition of oxidative stress-PARP activation cascade may potentially be useful strategies for management of trauma induced neuropathic pain.

Morin Mitigates Chronic Constriction Injury (CCI)-Induced Peripheral Neuropathy by Inhibiting Oxidative Stress Induced PARP Over-Activation and Neuroinflammation

Neuropathic pain is initiated or caused due to the primary lesion or dysfunction in the nervous system and is proposed to be linked to a cascade of events including excitotoxicity, oxidative stress, neuroinflammation and apoptosis. Oxidative/nitrosative stress aggravates the neuroinflammation and neurodegeneration through poly (ADP) ribose polymerase (PARP) overactivation. Hence, the present study investigated the antioxidant and anti-inflammatory effects of the phytoconstituent; morin in chronic constriction injury (CCI) induced neuropathy. Neuropathic pain was induced by chronic constriction of the left sciatic nerve in rats, and the effect of morin (15 and 30 mg/kg, p.o.) was evaluated by measuring behavioural and biochemical changes. Mechanical, chemical and thermal stimuli confirmed the CCI-induced neuropathic pain and treatment with morin significantly improved these behavioural deficits and improved the sciatic functional index by the 14th day after CCI induction. After 14 days of CCI induction, oxidative/nitrosative stress and inflammatory markers were elevated in rat lumbar spinal cord. Oxidative stress induced PARP overactivation resulted in depleted levels of ATP and elevated levels of poly (ADP) ribose (PAR). Treatment with morin reduced the levels of nitrites, restored glutathione levels and abrogated the oxidant induced DNA damage. It also mitigated the increased levels of TNF-α and IL-6. Protein expression studies confirmed the PARP inhibition and anti-inflammatory activity of morin. Findings of this study suggest that morin, by virtue of its antioxidant properties, limited PARP overactivation and neuroinflammation and protected against CCI induced functional, behavioural and biochemical deficits.

Poly(ADP-ribose) polymerase inhibition reveals a potential mechanism to promote neuroprotection and treat neuropathic pain

Neuropathic pain is triggered by the lesions to peripheral nerves which alter their structure and function. Neuroprotective approaches that limit the pathological changes and improve the behavioral outcome have been well explained in different experimental models of neuropathy but translation of such strategies to clinics has been disappointing. Experimental evidences revealed the role of free radicals, especially peroxynitrite after the nerve injury. They provoke oxidative DNA damage and consequent over-activation of the poly(ADP-ribose) polymerase (PARP) upregulates pro-inflammatory pathways, causing bioenergetic crisis and neuronal death. Along with these changes, it causes mitochondrial dysfunction leading to neuronal apoptosis. In related preclinical studies agents that neutralize the free radicals and pharmacological inhibitors of PARP have shown benefits in treating experimental neuropathy. This article reviews the involvement of PARP over-activation in trauma induced neuropathy and therapeutic significance of PARP inhibitors in the experimental neuropathy and neuropathic pain.