Nicotine Attenuates Morphological Deficits in a Contusion Model of Spinal Cord Injury

Protective Effect of Natural Products against Huntington's Disease: An Overview of Scientific Evidence and Understanding Their Mechanism of Action

Huntington's disease (HD), a neurodegenerative disease, normally starts in the prime of adult life, followed by a gradual occurrence of characteristic psychiatric disturbances and cognitive and motor dysfunction. To the best of our knowledge, there is no treatment available to completely mitigate the progression of HD. Among various therapeutic approaches, exhaustive literature reports have confirmed the medicinal benefits of natural products in HD experimental models. Building on this information, this review presents a brief overview of the neuroprotective mechanism(s) of natural products against in vitro/in vivo models of HD. Relevant studies were identified from several scientific databases, including PubMed, ScienceDirect, Scopus, and Google Scholar. After screening through literature from 2005 to the present, a total of 14 medicinal plant species and 30 naturally isolated compounds investigated against HD based on either in vitro or in vivo models were included in the present review. Behavioral outcomes in the HD in vivo model showed that natural compounds significantly attenuated 3-nitropropionic acid (3-NP) induced memory loss and motor incoordination. The biochemical alteration has been markedly alleviated with reduced lipid peroxidation, increased endogenous enzymatic antioxidants, reduced acetylcholinesterase activity, and increased mitochondrial energy production. Interestingly, following treatment with certain natural products, 3-NP-induced damage in the striatum was ameliorated, as seen histologically. Overall, natural products afforded varying degrees of neuroprotection in preclinical studies of HD via antioxidant and anti-inflammatory properties, preservation of mitochondrial function, inhibition of apoptosis, and induction of autophagy.

Overexpression of HIPK2 attenuates spinal cord injury in rats by modulating apoptosis, oxidative stress, and inflammation

HIPK2 is considered to be a tumor suppressor. It also has been implicated in several functions such as apoptosis and inflammation that are linked to spinal cord injury (SCI). However, whether HIPK2 ameliorates the neurological pain of SCI remains unclear. Here, we investigated the effects of HIPK2 on neurological function, oxidative stress, levels of inflammatory cytokines and expression of Bcl-2/Bax in an SCI model. Firstly, we evaluated the therapeutic effects of HIPK2 on neurological pain in the SCI rat using the Basso, Beattie and Bresnahan scores and H & E staining. Overexpression of HIPK2 significantly elevated the levels of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF), and reduced the mRNA expression of Nogo-A and RhoA in SCI rats. Furthermore, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assays showed that overexpression of HIPK2 significantly reduced the number of apoptotic cells. Overexpression of HIPK2 also decreased expression of Bax and Caspase-3 and elevated expression of Bcl-2 in the SCI model, indicating that HIPK2 exhibited its protective activity by inhibiting SCI-induced apoptosis. Then, we measured the serum concentrations of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-PX). We also determined the mRNA and protein levels of nuclear factor-κB p65 unit, tumor necrosis factor-α (TNF-α), and interleukin (IL)-1β. HIPK2 overexpression reduced oxidative stress and the levels of inflammatory cytokines compared with SCI control animals. Additionally, acetylation of HIPK2 was reduced in SCI rats. Overexpression of HIPK2 could enhance autophagy by elevating the expression of Beclin-1 and LC3-II while autophagy is regarded as a beneficial regulator to improve spinal cord injury. Together, overexpression of HIPK2 improved contusive SCI induced pain by modulating oxidative stress, Bcl‑2 and Bax signaling, and inflammation, and also regulating autophagy.

Neuroprotective mechanisms of rutin for spinal cord injury through anti-oxidation and anti-inflammation and inhibition of p38 mitogen activated protein kinase pathway

Rutin has anti-inflammatory, antioxidant, anti-viral, anti-tumor and immune regulatory effects. However, the neuroprotective effects of rutin in spinal cord injury are unknown. The p38 mitogen activated protein kinase (p38 MAPK) pathway is the most important member of the MAPK family that controls inflammation. We assumed that the mechanism of rutin in the repair of spinal cord injury is associated with the inhibition of p38 MAPK pathway. Allen's method was used to establish a rat model of spinal cord injury. The rat model was intraperitoneally injected with rutin (30 mg/kg) for 3 days. After treatment with rutin, Basso, Beattie and Bresnahan locomotor function scores increased. Water content, tumor necrosis factor alpha, interleukin 1 beta, and interleukin 6 levels, p38 MAPK protein expression and caspase-3 and -9 activities in T_8–9 spinal cord decreased. Oxidative stress related markers superoxide dismutase and glutathione peroxidase levels increased in peripheral blood. Rutin exerts neuroprotective effect through anti-oxidation, anti-inflammation, anti-apoptosis and inhibition of p38 MAPK pathway.

Administration of chlorogenic acid alleviates spinal cord injury via TLR4/NF‑κB and p38 signaling pathway anti‑inflammatory activity

Chlorogenic acid, as a secondary metabolite of plants, exhibits a variety of effects including free radical scavenging, antiseptic, anti‑inflammatory and anti‑viral, in addition to its ability to reduce blood glucose, protect the liver and act as an anti‑hyperlipidemic agent and cholagogue. The present study demonstrated that administration of chlorogenic acid alleviated spinal cord injury (SCI) via anti‑inflammatory activity mediated by nuclear factor (NF)‑κB and p38 signaling pathways. Wistar rats were used to structure a SCI model rat to explore the effects of administration of chlorogenic acid on SCI. The Basso, Beattie and Bresnahan test was executed for assessment of neuronal functional recovery and then spinal cord tissue wet/dry weight ratio was recorded. The present study demonstrated that chlorogenic acid increased SCI‑inhibition of BBB scores and decreased SCI‑induction of spinal cord wet/dry weight ratio in rats. In addition, chlorogenic acid suppressed SCI‑induced inflammatory activity, inducible nitric oxide synthase activity and cyclooxygenase‑2 protein expression in the SCI rat. Furthermore, chlorogenic acid suppressed Toll like receptor (TLR)‑4/myeloid differentiation primary response 88 (MyD88)/NF‑κB/IκB signaling pathways and downregulated p38 mitogen activated protein kinase protein expression in SCI rats. The findings suggest that administration of chlorogenic acid alleviates SCI via anti‑inflammatory activity mediated by TLR4/MyD88/NF‑κB and p38 signaling pathways.

Wogonoside alleviates inflammation induced by traumatic spinal cord injury by suppressing NF-κB and NLRP3 inflammasome activation

Wogonoside possesses anti-oxidative, anti-inflammatory, anti-allergy and anti-tumor properties. The aim of the present study was to evaluate whether wogonoside alleviates spinal cord injury (SCI)-induced inflammation via nuclear factor (NF)-κB and nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome activation. Sprague-Dawley rats were positioned in the jaws of a calibrated aneurysm clip with a closing pressure of 55 g. The jaws were placed on the dorsal and ventral surfaces of the spinal cord and left in place for 1 min. SCI rats were treated with 12, 25 and 50 mg/kg wogonoside. Following this, the locomotor function was assessed using the Basso Beattie Bresnahan scale. The water content of the spinal cord was measured, tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-6 levels were assessed and western blot analysis was performed to evaluate the expressions of NF-κB and NLRP3. Wogonoside was demonstrated to significantly ameliorate the SCI-induced reduction in Basso Beattie Bresnahan score (P<0.01) and significantly reduce the water content of the spinal cord in rats with SCI-induced inflammation (P<0.01). Results also indicated that treatment with wogonoside significantly reduced the levels of IL-1β, TNF-α and IL-6 in rats with SCI-induced inflammation (P<0.01), potentially via the phosphorylation of NF-κB inhibitor α. Furthermore, treatment with wogonoside inhibited the expressions of toll-like receptor 4, NLRP3 and caspase-1 protein in SCI model rats (P<0.01). In conclusion, the results of the present study suggest that wogonoside alleviates SCI-induced inflammation by suppressing NF-κB and NLRP3 inflammasome activation.

Synaptic modulation of excitatory synaptic transmission by nicotinic acetylcholine receptors in spinal ventral horn neurons

Nicotinic acetylcholine receptors (nAChRs) are distributed widely in the central nervous system and play important roles in higher brain functions, including learning, memory, and recognition. However, functions of the cholinergic system in spinal motoneurons remain poorly understood. In this study, we investigated the actions of presynaptic and postsynaptic nAChRs in spinal ventral horn neurons by performing whole-cell patch-clamp recordings on lumbar slices from male rats. The application of nicotine or acetylcholine generated slow inward currents and increased the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs). Slow inward currents by acetylcholine or nicotine were not inhibited by tetrodotoxin (TTX) or glutamate receptor antagonists. In the presence of TTX, the frequency and amplitude of miniature excitatory postsynaptic currents (mEPSCs) were also increased by acetylcholine or nicotine. A selective α4β2 nicotinic receptor antagonist, dihydro-β-erythroidine hydrobromide (DhβE), significantly decreased nicotine-induced inward currents without affecting the enhancement of sEPSCs and mEPSCs. In addition, a selective α7 nicotinic receptor antagonist, methyllycaconitine, did not affect either nicotine-induced inward currents or the enhancement of sEPSCs and mEPSCs. These results suggest that α4β2 AChRs are localized at postsynaptic sites in the spinal ventral horn, non-α4β2 and non-α7 nAChRs are located presynaptically, and nAChRs enhance excitatory synaptic transmission in the spinal ventral horn.

Chrysin suppressed inflammatory responses and the inducible nitric oxide synthase pathway after spinal cord injury in rats

Chrysin (CH), a natural plant flavonoid, has shown a variety of beneficial effects. Our present study was conducted to evaluate the therapeutic potential of CH three days after spinal cord injury (SCI) in rats and to probe the underlying neuroprotective mechanisms. SCI was induced using the modified weight-drop method in Wistar rats. Then, they were treated with saline or CH by doses of 30 and 100 mg/kg for 26 days. Neuronal function was assessed with the Basso Beattle Bresnahan locomotor rating scale (BBB). The water content of spinal cord was determined after traumatic SCI. The NF-κB p65 unit, TNF-α, IL-1β and IL-6 in serums, as well as the apoptotic marker, caspase-3, of spinal cord tissues were measured using commercial kits. The protein level and activity of inducible nitric oxide synthase (iNOS) were detected by western blot and a commercial kit, respectively. NO (nitric oxide) production was evaluated by the determination of nitrite concentration. The rats with SCI showed marked reductions in BBB scores, coupled with increases in the water content of spinal cord, the NF-κB p65 unit, TNF-α, IL-1β, IL-6, iNOS, NO production and caspase-3. However, a CH supplement dramatically promoted the recovery of neuronal function and suppressed the inflammatory factors, as well as the iNOS pathway in rats with SCI. Our findings disclose that CH improved neural function after SCI in rats, which might be linked with suppressing inflammation and the iNOS pathway.

The functional and neuroprotective actions of Neu2000, a dual-acting pharmacological agent, in the treatment of acute spinal cord injury

The goal of the present study was to examine the neuroprotective and functional significance of targeting both N-methyl-D-aspartate (NMDA) receptor-mediated excitotoxicity and oxidative stress using a dual-acting compound, Neu2000, in rat model of moderate spinal cord injury (SCI). An initial set of experiments was conducted in uninjured rats to study the pharmacokinetic profile of Neu2000 following intraperitoneal and intravenous administration. A second experiment measured free radical production in mitochondria isolated from sham or injured spinal cords of animals receiving vehicle or Neu2000 treatment. A third set of animals was divided into three treatment groups consisting of vehicle treatment, a single dose of Neu2000 (50 mg/kg) administered at 10 min following injury, or a repeated treatment paradigm consisting of a single bolus of Neu2000 at 10 min following injury (50 mg/kg) plus a maintenance dose (25 mg/kg) administered every 24 h for an additional 6 days. Animals were tested once a week for a period of 6 weeks for evidence of locomotor recovery in an open field and kinematic analysis of fine motor control using the DigiGait Image Analysis System. At the end of the testing period, spinal cord reconstruction was performed to obtain nonbiased stereological measures of tissue sparing. The results of this study demonstrate that Neu2000 treatment significantly reduced the production of mitochondrial free radicals and improved locomotor outcomes that were associated with a significant increase in the volume of spared spinal cord tissue.

Acetylcholinesterase inhibitors may improve myelin integrity

Recent clinical trials have revealed that cholinergic treatments are efficacious in a wide spectrum of neuropsychiatric disorders that span the entire human lifespan and include disorders without cholinergic deficits. Furthermore, some clinical and epidemiological data suggest that cholinergic treatments have disease modifying/preventive effects. It is proposed that these observations can be usefully understood in a myelin-centered model of the human brain. The model proposes that the human brain's extensive myelination is the central evolutionary change that defines our uniqueness as a species and our unique vulnerability to highly prevalent neuropsychiatric disorders. Within the framework of this model the clinical, biochemical, and epidemiologic data can be reinterpreted to suggest that nonsynaptic effects of cholinergic treatments on the process of myelination and myelin repair contributes to their mechanism of action and especially to their disease modifying/preventive effects. The ability to test the model in human populations with safe and noninvasive imaging technologies makes it possible to undertake novel clinical trial efforts directed at primary prevention of some of the most prevalent and devastating of human disorders.

Application of nicotine enantiomers, derivatives and analogues in therapy of neurodegenerative disorders

This review gives a brief overview over the major aspects of application of the nicotine alkaloid and its close derivatives in the therapy of some neurodegenerative disorders and diseases (e.g. Alzheimer's disease, Parkinson's disease, Tourette's syndrome, schizophrenia etc.). The issues concerning methods of nicotine analysis and isolation, and some molecular aspects of nicotine pharmacology are included. The natural and synthetic analogues of nicotine that are considered for medical practice are also mentioned. The molecular properties of two naturally occurring nicotine enantiomers are compared--the less-common but less-toxic (R)-nicotine is suggested as a natural compound that may find its place in pharmaceutical practice.

Impact of chronic nicotine on sciatic nerve injury in the rat

Chronic nicotine exposure and the immune response to peripheral nerve injury has not been investigated thoroughly. Rats were exposed to chronic nicotine or saline followed by chronic constriction injury (CCI) of the sciatic nerve. Mechanical sensitivity was measured at various time points and the immune response was investigated at 21 days post-CCI. Chronic nicotine increased mechanical hypersensitivity, microglia activation, and the production of IL-1beta, but not the number of immune cells at the site of injury. These results suggest that chronic nicotine increases mechanical hypersensitivity following peripheral nerve injury through a mechanism that may involve an increased production and release of central and peripheral cytokines.

Quantification of Locomotor Recovery following Spinal Cord Contusion in Adult Rats

Injury to the spinal cord not only disrupts the functioning of spinal circuits at the site of the impact, but also limits sensorimotor function caudal to the level of the lesion. Ratings of gross locomotor skill are generally used to quantify locomotor recovery following spinal cord injury (SCI). The purpose of this study was to assess behavioral recovery following SCI with three tasks: (1) BBB ratings, (2) walking on a horizontal ladder, and (3) footprint analyses. Behavioral testing was conducted for 6 postoperative weeks, and then the spinal cords were processed for the amount of white matter spared. As expected, BBB ratings dramatically decreased and then improved during recovery. The number of hindlimb foot-faults on the horizontal ladder increased after injury and remained elevated during the recovery period. Footprint analyses revealed that sham-control rats used several different gaits to cross the runway. In contrast, the locomotor function of rats with a SCI was impaired throughout the postoperative period. Some locomotor parameters of the injured rats improved slightly (velocity, stride length, stride duration, stance duration), some did not change (interlimb coordination, swing duration, forelimb base of support, hindpaw angle), and others declined (hindlimb base of support) during the recovery period. Together, these results show that gross locomotor skill improved after SCI, while recovery of fine locomotor function was more limited. Multiple tests should be included in future experiments in order to assess gross and fine changes in sensorimotor function following SCI.

Neuroprotective effect of nicotine against 3-nitropropionic acid (3-NP)-induced experimental Huntington's disease in rats

Nicotinic acetylcholine receptors (nAChRs) are regarded as potential therapeutic targets to control various neurodegenerative diseases. Owing to the relevance of cholinergic neurotransmission in the pathogenesis of Huntington's disease (HD) this investigation was aimed to study the effect of nicotine, a nAChR agonist, on 3-nitropropionic acid (3-NP)-induced neurodegeneration in female Wistar rats. Systemic administration of 3-NP in rats serves as an important model of HD. The animals received subcutaneous injections of nicotine (0, 0.25, 0.50 and 1.00 mg/kg) daily for 7 days. 3-NP (25 mg/kg, i.p.) was administered daily 30 min after nicotine for the same duration. One additional group of rats served as control (vehicle only). On day 8, the animals were observed for neurobehavioral performance (motor activity, inclined plane test, grip strength test, paw test and beam balance). Immediately after behavioral studies, the animals were transcardially perfused with neutral buffered formalin (10%) and brains were fixed for histological studies. Lesions in the striatal dopaminergic neurons were assessed by immunohistochemical method using tyrosine hydroxylase (TH) immunostaining. Treatment of rats with nicotine significantly and dose-dependently attenuated 3-NP-induced behavioral deficits. Administration of 3-NP alone caused significant depletion of striatal dopamine (DA) and glutathione (GSH), which was significantly and dose-dependently attenuated by nicotine. Preservation of striatal dopaminergic neurons by nicotine was also confirmed by immunohistochemical studies. These results clearly showed neuroprotective effect of nicotine in experimental model of HD. The clinical relevance of these findings in HD patients remains unclear and warrants further studies.

Neuronal nicotinic receptors as targets for novel analgesics

The potential use of nicotinic acetylcholine receptor agonists has been the subject of a number of recent reviews. Despite the promises of better things to come, few new compounds have been identified that circumvent the issues hindering the widespread use of the previously described nicotinic analgesics, mainly a narrow therapeutic window between analgesic efficacy and toxicity, and a lack of knowledge of native nicotinic acetylcholine receptor expression. However, several recent developments have potentially opened new windows of opportunity in the use of nicotinic agents for analgesia. A small number of laboratories have reported that peripheral nerve injury alters the pharmacology of nicotinic receptors, resulting in a leftward shift of analgesic potency but not of toxicity. Another important development in the pathophysiology of neuropathic pain is the reliance of nerve injury-induced behavioural hypersensitivity on both peripheral and central neural immune interactions. Finally, the reported neuroprotective effects of nicotine following spinal cord injury may provide an opportunity for the development of selective nicotinic agonists that are capable of attenuating chronic pain. The current review will attempt to highlight these recent developments and outline key findings that demonstrate further opportunity for the development of nicotinic agonists as novel analgesics.