Ischemic reperfusion causes lipid peroxidation and fiber degeneration

Role of Oxygen and Its Radicals in Peripheral Nerve Regeneration: From Hypoxia to Physoxia to Hyperoxia

Oxygen is compulsory for mitochondrial function and energy supply, but it has numerous more nuanced roles. The different roles of oxygen in peripheral nerve regeneration range from energy supply, inflammation, phagocytosis, and oxidative cell destruction in the context of reperfusion injury to crucial redox signaling cascades that are necessary for effective axonal outgrowth. A fine balance between reactive oxygen species production and antioxidant activity draws the line between physiological and pathological nerve regeneration. There is compelling evidence that redox signaling mediated by the Nox family of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases plays an important role in peripheral nerve regeneration. Further research is needed to better characterize the role of Nox in physiological and pathological circumstances, but the available data suggest that the modulation of Nox activity fosters great therapeutic potential. One of the promising approaches to enhance nerve regeneration by modulating the redox environment is hyperbaric oxygen therapy. In this review, we highlight the influence of various oxygenation states, i.e., hypoxia, physoxia, and hyperoxia, on peripheral nerve repair and regeneration. We summarize the currently available data and knowledge on the effectiveness of using hyperbaric oxygen therapy to treat nerve injuries and discuss future directions.

Therapeutic effects of masitinib on abnormal mechanoreception in a mouse model of tourniquet-induced extremity ischemia-reperfusion

Tourniquets are widely used to stop extremity hemorrhage, but their use and subsequent release can result in nerve damage and degeneration, leading to neurological deficits. Increasing evidence has suggested a pivotal role of inflammation in nerve damage and abnormal mechanoreception. In this study, we investigated the therapeutic effects of masitinib (Mas), an anti-neuroinflammatory drug, on the mechanoreception of sensory neurons in a mouse model of tourniquet-induced hind paw ischemia-reperfusion (tourniquet/IR). C57BL/6 mice were subjected to 3 h of ischemia by placing a rubber band at the ankle joint and evaluated for subsequent reperfusion injury on day 1, 3, 7, 14, and 28 based on the experiments. Treatment with Mas (28 mg/kg/day, i.p.) began on the day of IR induction and lasted for 1, 3, 7, 14, or 28 days. Tourniquet/IR caused sensory nerve denervation in the skin of paw pads and abolished the hind paw mechanoreception to mechanical stimulation during the first 3 days of reperfusion. Sensory nerves gradually reinnervated in the skin of paw pads and allodynia began to appear on day 7. The maximum reaction occurred on day 14 and was maintained throughout the study period. Treatment with Mas mitigated nerve damage and improved hind paw mechanoreception to mechanical stimulation by decreasing the production of reactive oxygen species (ROS) during the early stages of tourniquet/IR. Mas also alleviated allodynia and decreased inflammatory cytokines (IL-1β and TNFα) in the skin of paw pads from days 7-28. Our data suggest that treatment with Mas significantly ameliorated paw numbness and allodynia in mouse hind paw tourniquet/IR.

Can MitoTEMPO protect rat sciatic nerve against ischemia-reperfusion injury?

Abdominal ischemia-reperfusion (I/R) is known to cause both structural and functional damage to sciatic nerve which is related to the oxidative stress. We investigated the protective effects of mitochondria-targeted antioxidant (2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl) triphenylphosphonium chloride (MitoTEMPO) on ischemia-reperfusion-induced nerve damage by using the conduction velocity distribution (CVD) calculations from in vitro compound nerve action potential (CNAP) recordings from rat sciatic nerve. Adult male Wistar albino rats were divided into three groups. The IR and IR + MT groups had aortic cross-clamping for 1 h followed by 2 h reperfusion, while SHAM group had the same procedure without cross-clamping. IR + MT group received 0.7 mg/kg/day MitoTEMPO injection for 28 days before I/R, while other groups received vehicle alone. Ischemia-reperfusion resulted in a significant decrease (p < .05) in maximum depolarizations (mV), areas (mV.ms), and maximum and minimum upstroke velocities (mV/ms) of CNAPs, while injection of MitoTEMPO showed a complete protective effect on these impairments. The histograms for CVD showed that I/R blocked the contribution of fast-conducting fibers (> 60 m/s). MitoTEMPO prevented that blockage and caused a shift in the CVD. Functional nerve damage caused by I/R can be prevented by MitoTEMPO, which can enter mitochondria, the main source of reactive oxygen species (ROS).

A comprehensive review on regulatory effects of crocin on ischemia/reperfusion injury in multiple organs

Ischemia-reperfusion (I/R) injury affects o₂-dependent organs including liver, kidneys, heart, brain, and intestine. I/R injury is described as the cellular injury in an organ caused by ischemia and then further aggravated during the reperfusion due to intracellular alterations. It is a process that happens in clinical settings such as organ transplantation, reperfusion after thrombolytic therapy, and coronary angioplasty. Crocus sativus L. known as saffron used in folk medicine for its beneficial effects. It contains multiple bioactive compounds including the crocin, crocetin, picrocrocin, and safranal. Crocin, a water-soluble carotenoid has antitumor, radical scavenging, anti hyperlipidemia and memory improving effects. Moreover, crocin has antioxidant, and protective effects on I/R models in rats at various organs such as heart, brain, kidney, stomach, liver, and kidney as described in detail in this review.

Ischemia-Reperfusion Injury of Sciatic Nerve in Rats: Protective Role of Combination of Vitamin C with E and Tissue Plasminogen Activator

An ischemia/reperfusion injury of rat's sciatic nerve was experimentally developed. In this model, we measured the in vivo production of superoxide radical, as a marker of oxidative stress and the occludin expression as an indicator of blood-nerve barrier function and we examined potential protective innervations against these abnormalities. Right sciatic nerves of the animals underwent 3 h of ischemia followed by 7 days of reperfusion and were divided into three groups: ischemic, pretreated with vitamin C in conjunction with vitamin E and treated with tissue plasminogen activator. Compared to measurements from left sciatic nerves used as sham, the ischemic group showed significantly increased superoxide radical and reduced expression of occludin in western blot and immunohistochemistry. No such differences were detected between sham and nerves in the vitamin or tissue plasminogen activator groups. It is suggested that the experimental ischemia/reperfusion model was suitable for studying the relationship between oxidative state and blood-nerve barrier. The reversion of abnormalities by the applied neuroprotective agents might prove to be a clinically important finding in view of the implication of vascular supply derangement in various neuropathies in humans.

Inhibition of the NMDA receptor protects the rat sciatic nerve against ischemia/reperfusion injury

Inhibition of the N-methyl-D-aspartate (NMDA) receptor by MK-801 reduces ischemia/reperfusion (I/R) injury in the central nervous system. However, few previous studies have evaluated the neuroprotective effects of MK-801 against peripheral I/R injury. The present study aimed to investigate the protective effects of MK-801 pretreatment against I/R injury in the rat sciatic nerve (SN). Sprague-Dawley rats were subjected to a sham surgery (n=8) or to a 5-h ischemic insult by femoral artery clamping (I/R and I/R+MK-801 groups; n=48 per group). I/R+MK-801 rats were intraperitoneally injected with MK-801 (0.5 ml or 1 mg/kg) at 15 min prior to reperfusion. The rats were sacrificed at 0, 6, 12, 24, 72 h, or 7 days following reperfusion. Plasma malondialdehyde (MDA) and nitric oxide (NO) concentrations, and SN inducible NO synthase (iNOS) protein expression levels, were measured using colorimetry. In addition, the protein expression levels of tumor necrosis factor-α (TNF-α) were measured using immunohistochemistry, and histological analyses of the rat SN were conducted using light and electron microscopy. Alterations in the mRNA expression levels of TNF-α and TNF-α converting enzyme (TACE) in the rat SN were detected using reverse transcription-quantitative polymerase chain reaction. In the I/R group, plasma concentrations of NO (175.3±4.2 µmol/l) and MDA (16.2±1.9 mmol/l), and the levels of iNOS (2.5±0.3) in the SN, peaked at 24 h post-reperfusion. At 24 h, pretreatment with MK-801 significantly reduced plasma NO (107.3±3.6 µmol/l) and MDA (11.8±1.6 mmol/l), and SN iNOS (1.65±0.2) levels (all P<0.01). The mRNA expression levels of TNF-α and TACE in the SN were significantly reduced in the I/R+MK-801 group, as compared with the I/R group (P<0.05). Furthermore, MK-801 pretreatment was shown to have alleviated histological signs of I/R injury, including immune cell infiltration and axon demyelination. The results of the present study suggested that pretreatment with MK-801 may alleviate I/R injury of the SN by inhibiting the activation of TNF-α and reducing the levels of iNOS in the SN.

Different dose-dependent effects of ebselen in sciatic nerve ischemia-reperfusion injury in rats

Ebselen is an organoselenium compound which has strong antioxidant and anti-inflammatory effects. We investigated the neuroprotective role of ebselen pretreatment in rats with experimental sciatic nerve ischemia-reperfusion (I/R) injury. Adult male Sprague Dawley rats were divided into four groups (N = 7 in each group). Before sciatic nerve I/R was induced, ebselen was injected intraperitoneally at doses of 15 and 30 mg/kg. After a 2 h ischemia and a 3 h reperfusion period, sciatic nerve tissues were excised. Tissue levels of malondialdehyde (MDA) and nitric oxide (NO), and activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) were measured. Sciatic nerve tissues were also examined histopathologically. The 15 mg/kg dose of ebselen reduced sciatic nerve damage and apoptosis (p<0.01), levels of MDA, NO, and inducible nitric oxide synthase (iNOS) positive cells (p<0.01, p<0.05, respectively), and increased SOD, GPx, and CAT activities (p<0.001, p<0.01, p<0.05, respectively) compared with the I/R group that did not receive ebselen. Conversely, the 30 mg/kg dose of ebselen increased sciatic nerve damage, apoptosis, iNOS positive cells (p<0.01, p<0.05, p<0.001) and MDA and NO levels (p<0.05, p<0.01) and decreased SOD, GPx, and CAT activities (p<0.05) compared with the sham group. The results of this study suggest that ebselen may cause different effects depending on the dose employed. Ebselen may be protective against sciatic nerve I/R injury via antioxidant and antiapoptotic activities at a 15 mg/kg dose, conversely higher doses may cause detrimental effects.

Impact of aortic cross-clamping time on peripheral nerves: experimental model

PURPOSE

The present study investigated the correlation between extend aortic cross-clamping time and peripheral nerve injury on rats.

METHODS

24 male, Sprague Dawley rats were divided into 3 groups; (a) control group: abdomen was directly closed after reached aorta, and followed by 72 hours, (b) short-term ischaemia-reperfusion group: peripheral nerve ischemia was induced in rats by supraceliac aortic occlusion for 20 min followed by 72 h of reperfusion, (c) long-term ischaemia-reperfusion group: peripheral nerve ischemia was induced for 30 min followed by 72 h of reperfusion. Preoperative and postoperative, electromyography (EMG) recordings were done. End of 72 h, the sciatic nerves were harvested from each animal for histopathological and biochemical analysis.

RESULTS

The mean compound muscle action potential (CMAP) amplitude of long-term ischaemia-reperfusion group was statically significant reduced when compared to the control group (p <0.01). However, the mean distal latency value of long-term ischaemia-reperfusion group was statically significant increased (p <0.01). On the other hand, there were statically significant differences between the results of malondialdehyde, edema and ischemia fiber degeneration grades on control and long-term ischaemia-reperfusion group (p <0.001).

CONCLUSION

This study demonstrated that the extending cross clamping time directly harms the peripheral nerve of rats.

Effects of α-MSH on ischemia/reperfusion injury in the rat sciatic nerve

Background:

Ischemia/reperfusion (I/R) causes the production of toxic free radicals and leads to pathological changes in nerve tissue. We investigated the effect of alpha-melanocyte stimulating hormone (α-MSH) in a rat model for sciatic nerve I/R and discuss the possible cytoprotective and antioxidant mechanism of α-MSH against ischemic fiber degeneration.

Methods:

Experiments were performed using 42 adult male Wistar rats. Rats were divided into six experimental groups: control group, ischemia group, I/R groups, and α-MSH treated groups. Ischemia was produced by clamping of the femoral vessels. Immediately after ischemia that lasted 3 h, 75 μg/kg of α-MSH was administered subcutaneously before reperfusion and the tissue malondialdehyde (MDA) level was evaluated as an indicator of lipid peroxidation in groups with different reperfusion periods.

Results:

The reperfusion injury did not begin in the first hour of reperfusion after 3 h of ischemia, and MDA levels increased on the first day of reperfusion. During the first day, blood MDA levels were decreased in the α-MSH group compared to the control group. The tissue from animals pre-treated with α-MSH showed fewer morphological alterations. Myelin breakdown was significantly diminished after treatment with α-MSH, and the ultrastructural features of axons showed remarkable improvement. Two-way analysis of variance was used for comparing three or more groups. When a significant difference existed, the post-hoc multiple-comparison test was applied to demonstrate the differences.

Conclusions:

The results confirm that pre-treatment with α-MSH after ischemia protected the peripheral nerves against I/R injury.

Ameliorative potential of montelukast on ischemia-reperfusion injury induced vasculitic neuropathic pain in rat

AIMS

Ischemia-reperfusion (I/R) event in vascular and nervous system has been documented to rising ischemic and vasculitic neuropathic pain, clinically resembles the complex regional pain syndrome (CRPS). The present study evaluated the effect of montelukast, a cysteinyl leukotriene receptor (Cys-LTC(4) and Cys-LTD(4)) antagonist on ischemia -reperfusion (I/R) induced vasculitic neuropathic pain in rats.

MAIN METHODS

Behavioral parameters were assessed at different time intervals (i.e. 0, 1, 7, 14 and 21st day) and biochemical analysis in sciatic nerve tissue samples were also performed along with histopathological studies.

KEY FINDINGS

Behavioral pain assessment has shown increase in paw and tail withdrawal threshold in montelukast treated groups against thermal and mechanical stimuli as compared to I/R control group. We observed a decrease in the total calcium, thiobarbituric acid reactive substance (TBARS) and myeloperoxidase (MPO) activity levels, whereas there is rise in reduced glutathione level in montelukast treated groups as compared to I/R control group. However, significant behavioral and biochemical results were observed only in medium and high dose of treated groups which were comparable to normal control group. Moreover, histopathological study has revealed the reduction of I/R induced neuronal edema and axonal degeneration due to montelukast.

SIGNIFICANCE

Montelukast has ameliorated I/R induced vasculitic neuropathic pain, these effects may be due to inhibition of lipid peroxidation, reduction of oxidative stress, release of inflammatory mediators and neuroprotective actions. Hence, it could be used as a novel therapeutic agent for the management of vasculitic inflammation related neuropathic pain.

Effect of thymoquinone, a constituent of Nigella sativa L., on ischemia-reperfusion in rat skeletal muscle

Thymoquinone have been shown to decrease ischemia-reperfusion injury (IRI) in some tissues such as gastric mucosa and brain. In this study, the effect of thymoquinone was evaluated on an animal model of IRI in the rat hind limb. Hind limb ischemia was induced by clamping the common femoral artery and vein. After 2 h ischemia, the clamp on the femoral vessels was taken off and the animal underwent 1 h reperfusion. Muscle injuries were evaluated by recording the electromyographic (EMG) potentials and performing some biochemical analysis including thiobarbituric acid reactive substances (TBARS), total sulfhydryl (SH) groups, and antioxidant capacity of muscle using ferric reducing ability of plasma (FRAP) assay. Ischemia was induced using free-flap surgery in skeletal muscle. Thymoquinone (20, 40 and 80 mg/kg) and normal saline (10 ml/kg) were administered intraperitoneally 1 h prior to reperfusion. The average peak-to-peak amplitude during ischemic reperfusion was significantly increased in thymoquinone groups in comparison with the control group. Following thymoquinone administration, the total SH contents and antioxidant capacity were elevated in muscle flap. The malondialdehyde (MDA) level was declined significantly in test groups. It is concluded that thymoquinone have some protective effects against the muscle tissue injury caused by lower limb ischemia-reperfusion.

The effects of repetitive compression on nerve conduction and blood flow in the rabbit sciatic nerve

The objective of this study was to clarify the effect of repetitive compression on nerve physiology in an experimental rabbit model. We defined 80 mmHg as a compression force which caused temporary disturbance of nerve conduction and blood flow with a brief compression. The following compressions were applied for 30 minutes to rabbit sciatic nerves: continuous compression, low frequency release compression (1 second of release time every 30 seconds) and high frequency release compression (1 second of release time every 10 seconds). Compound nerve action potentials and nerve blood flow were evaluated from the start of compression until 30 minutes after release. Endoneurial microvascular permeability was evaluated with Evans Blue albumin. The repetitive compression groups showed delay in recovery of compound nerve action potentials and blood flow after release, with endoneurial oedema. These findings suggest that repetitive compression may increase the risk of breakdown of the blood nerve barrier.

The effect of 2,5-hexanedione on permeability of blood-nerve barrier in rats

To explore the effect of 2,5-hexanedione on permeability of blood-nerve barrier, adult Wistar rats were administered with 400 mg x kg(-1) x d(- 1) 2,5-hexanedione to establish animal model of 2,5-hexnedione neuropathy. Evans blue was injected through left femoral vein of the rats after the model had been established. The distribution of fluorescence in sciatic-tibial nerve was observed and assessed. For the transverse sections of sciatic-tibial nerves, the average fluorescence intensity of proximal section was stronger (p < .01) than those of intermediate and distal sections and the average fluorescence intensity of intermediate section was stronger (p < .01) than that of distal section in the intoxicated group. In the control, the weak fluorescence was shown, and average fluorescence intensity of distal section was stronger (p < .05) than that of proximal section. The average fluorescence intensity of proximal, intermediate and distal sections in the intoxicated group was stronger (p < .01) than those of the corresponding sections in the control. For the longitudinal sections of sciatic-tibial nerves, fluorescence was observed in both proximal and distal sections in the intoxicated group. The fluorescence intensity of distal section in the control was weak and almost no fluorescence was shown in the proximal section. The permeability of blood-nerve barrier could be increased by 2,5-hexanedione.

EFFECTS OF L-ARGININE AND NG-NITRO L-ARGININE METHYL ESTER ON LIPID PEROXIDE, SUPEROXIDE DISMUTASE AND NITRATE LEVELS AFTER EXPERIMENTAL SCIATIC NERVE ISCHEMIA-REPERFUSION IN RATS

Nitric oxide (NO) has been reported to function in both cytoprotective and cytotoxic tissue ischemia-reperfusion (I/R). In this study, we evaluated the effects of L-arginine, the substrate for NO, and NG-nitro L-arginine methyl ester (L-NAME), NO synthase (NOS) inhibitor on super oxide dismutase (SOD) enzyme activity, malondialdehyde (MDA), a marker of lipid peroxidation, nitrate levels, and histopathological structure in rat sciatic nerve 2 h after ischemia, followed by 3 h of reperfusion. Reperfusion resulted in a significant increase in lipid peroxidation level and a decrease in nitrate level of the sciatic nerve. The increased level of lipid peroxidation was partly reduced by NOS inhibition. The decrease in sciatic nerve SOD level, observed in group subjected to I/R, was prevented by inhibition of NOS by L-NAME. These results were supported by histological findings that in the L-arginine-treated group, degenerations of both myelin sheath and axon were observed, while in the L- NAME-treated group, no pathological changes were detected. Our results suggested that excessive NO formation accelerates lipid peroxidation, as well as axonal degeneration on the early reperfusion period of the sciatic nerve.

Impact of diabetic polyneuropathy and cardiovascular autonomic neuropathy on the excretion of urinary 8-epi-PGF2αand its metabolites (2, 3-dinor and 2, 3-dinor-5, 6-dihydro)

The objective of this study was to establish if diabetes in the presence of polyneuropathy (PN) and/or cardiovascular autonomic neuropathy (CAN) is associated with alterations in the amounts of 8-epi-PGF2alpha (IP) and its metabolites including 2, 3-dinor-8-epi-PGF2alpha (dinor-IP) and 2, 3-dinor-5, 6 dihydro-8-epi-PGF2alpha (dinor-dihydro-IP) in urine. Mass spectrometric separation showed that excretion of IP was similar in the PN + /CAN- and PN+/CAN+ groups but higher than in the PN-/CAN- group (n = 103, 22 and 60, respectively; P < 0.05). By contrast, excretion of dinor-IP or dinor-dihydro-IP were similar in the PN-/CAN- and PN+/CAN- groups but higher than in PN+/CAN+ group. Correlations were obtained between IP and dinor-IP or dinor-dihydro-IP (r = 0.30; P < 0.001 and r = 0.31; P < 0.001, respectively). A significant association was also observed between dinor-IP and dinor-dihydro-IP (r = 0.48; P < 0.001). In conclusion, these biomarkers should prove useful in studies evaluating the impact of therapeutic drugs or antioxidant interventions aimed at delaying the onset of diabetic complications.

Rats with chronic post-ischemia pain exhibit an analgesic sensitivity profile similar to human patients with complex regional pain syndrome--type I

Chronic post-ischemia pain was induced in anesthetized rats by placing a tourniquet at the ankle joint for 3 h, and removing it to allow reperfusion. The effectiveness of standard analgesic drugs to attenuate mechanical allodynia was assessed 2 and 7 days after ischemia/reperfusion. Only high doses of morphine, dexamethasone and pregabalin partially reduced mechanical allodynia 2 days post-ischemia/reperfusion, while other treatments (ibuprofen, acetaminophen, amitriptyline) were not effective. Furthermore, only the highest dose of pregabalin reduced mechanical allodynia 7 days post-ischemia/reperfusion. These results are consistent with findings that complex region pain syndrome-I pain is refractory to most standard analgesic treatments.

Decreased peripheral nerve damage after ischemia-reperfusion injury in mice lacking TNF-alpha

We sought to explore the role of tumor necrosis factor-alpha (TNF-alpha) in the pathogenesis of peripheral nerve ischemia-reperfusion (IR) injury. We established an ischemia-reperfusion model in wild type (WT) and TNF-alpha knockout (KO) mice. Electrophysiology, behavioral score and morphological indices (edema and ischemic fiber degeneration [IFD]) were examined to determine the influence of TNF-alpha on peripheral nerve structure and function following ischemia followed by reperfusion. TNF-alpha and nuclear factor-kappa B (NF-kappaB) expression were evaluated using immunohistochemistry. TNF-alpha KO mice, compared to WT had, in sciatic nerve, marked improvement in nerve pathology. This is a region subject to moderate ischemia-reperfusion injury. There was also a significant improvement in electrophysiological and some behavioral indices. TNF-alpha and NF-kappaB expression were abundant in sciatic-tibial nerves of WT mice subjected to IR, but there was less, or complete lack of, expression in ischemic nerve of TNF-alpha KO mice. We conclude that TNF-alpha plays an essential role in the pathogenesis of peripheral nerve ischemia-reperfusion injury, possibly partly through the activation of NF-kappaB.

Crocus sativus L. (Saffron) extract and its active constituents (crocin and safranal) on ischemia-reperfusion in rat skeletal muscle

Saffron and its constituents have been shown to decrease ischemia-reperfusion (I/R) injury in kidney or brain tissues. In this study, the effects of saffron ethanolic extract and its constituents, crocin and safranal, were evaluated in skeletal muscle during I/R injury. Hind limb ischemia was induced using clamping the common femoral artery and vein. After 2 h ischemia, the clamp of the femoral vessels of animals was taken off and the animal underwent 1h reperfusion. Muscle injuries were evaluated by recording of the electromyographic (EMG) potentials and performing some biochemical analysis including thiobarbituric acid reactive substances (TBARS), total sulfhydryl (SH) groups and antioxidant capacity of muscle (using FRAP assay). The ethanolic extract of saffron (5, 20 and 80 mg kg(-1)), crocin (50, 200 and 400 mg kg(-1)), safranal (0.1, 0.25 and 0.5 ml kg(-1)) and normal saline (10 ml kg(-1)) were administered intraperitoneally 1 h prior reperfusion. The average peak-to-peak amplitude during I/R was significantly increased in extract, crocin and safranal groups in comparison with control-ischemic group. Following saffron, crocin and safranal administration, the total SH contents and antioxidant capacity were elevated in muscle flap. The MDA level was declined significantly in test groups. It is concluded that saffron extract and its constituents show a protective effect against lower limb I/R in rat.

Effect of Salvia leriifolia Benth. root extracts on ischemia-reperfusion in rat skeletal muscle

Background

Salvia leriifolia have been shown to decrease ischemia-reperfusion (I/R) injury in brain tissues. In this study, the effects of S. leriifolia aqueous and ethanolic extracts were evaluated on an animal model of I/R injury in the rat hind limb.

Methods

Ischemia was induced using free-flap surgery in skeletal muscle. The aqueous and ethanolic extracts of S. leriifolia (100, 200 and 400 mg/kg) root and normal saline (10 ml/kg) were administered intraperitoneally 1 h prior reperfusion. During preischemia, ischemia and reperfusion conditions the electromyographic (EMG) potentials in the muscles were recorded. The markers of oxidative stress including thiobarbituric acid reactive substances (TBARS), total sulfhydryl (SH) groups and antioxidant capacity of muscle (using FRAP assay) were measured.

Results

In peripheral ischemia, the average peak-to-peak amplitude during ischemic-reperfusion was found to be significantly larger in extracts groups in comparison with control group. Following extracts administration, the total SH contents and antioxidant capacity were elevated in muscle flap. The MDA level was also declined significantly in test groups.

Conclusion

It is concluded that S. leriifolia root extracts have some protective effects on different markers of oxidative damage in muscle tissue injury caused by lower limb ischemia-reperfusion.

Orchestration of the inflammatory response in ischemia-reperfusion injury

Ischemia to nerve can cause fiber degeneration and reperfusion following ischemia [ischemia-reperfusion (IR)] adds the additional insult of an inflammatory response and oxidative injury. Limited information is available on the molecular mediators and their endoneurial targets. In this study, using a highly reproducible animal model of IR injury to nerve and selective immunolabeling methods [for nuclear factor kappa B (NF-kappaB), intercellular adhesion molecule-1 (ICAM-1), cytokines, and inflammatory cells] over an expanded time frame, we evaluated the temporal pattern and localization of mediators of the inflammatory response. Sixty rats were used. Nine groups (N=6 each) underwent complete hind limb ischemia for 4 h, followed by reperfusion durations of 0, 3, 12, 24, and 48 h, and 7, 14, 28, and 42 days. One group underwent sham operation (N=6). The earliest change was ICAM-1 expression in the microvessel (endothelial cell) followed almost immediately by NF-kappaB activation with axonal expression (24 and 48 h), followed by endoneurial edema and ischemic fiber degeneration (7 and 14 days). Granulocytic infiltration was followed by endoneurial infiltration of mononuclear phagocytes (14 days), expression of interleukin 6 (IL-6) (microvessels), and subsequent Schwann cell NF-kappaB expression. Granulocytes, tumor necrosis factor alpha, and IL-6-positive cells were observed primarily within the epineurium. IR results in changes in a number of interacting networks of targets and inflammatory mediators. NF-kappaB activation has a central orchestrating role involving both the axon and the Schwann cell in effecting the inflammatory response.

Different degrees of fetal oxidative stress in elective and emergent cesarean section

BACKGROUND

Several studies have addressed the influence of labor and mode of delivery on oxidative stress. Still it is unclear whether oxidative stress is related to delivery itself or whether it reflects a pre-existing fetal oxidative status.

OBJECTIVE

To investigate whether the degree of fetal oxidative stress is different between distressed fetuses that were delivered by emergent cesarean section and non-distressed fetuses that were delivered by elective cesarean section.

METHODS

The protocol of this prospective study was approved by the Institutional Review Board Committee. Amniotic fluid and umbilical artery blood were prospectively collected from 21 parturients who were delivered by an emergent cesarean section for non-reassuring fetal heart rate pattern and from 21 parturients who were delivered by an elective cesarean section in a tertiary care center. Oxidative stress was evaluated in amniotic fluid, umbilical cord plasma and erythrocytes by determining malondialdehyde concentration and glutathione peroxidase (GPX) activity.

RESULTS

Malondialdehyde concentration was higher in amniotic fluid (mean +/- SEM) (2.2 +/- 0.7 nmol/l vs. 0.6 +/- 0.02 nmol/l, p < 0.05), in umbilical cord plasma (1.2 +/- 0.2 nmol/l vs. 0.7 +/- 0.3 nmol/l, p < 0.05) and in umbilical cord erythrocytes (159.6 +/- 48.6 nmol/g Hb vs. 85.8 +/- 5.2 nmol/g Hb, p < 0.05) in women delivering by emergent cesarean compared to those delivering by elective cesarean. GPX activity was enhanced in amniotic fluid (12.4 +/- 2.2 U/l vs. 5.1 +/- 0.6 U/l, p < 0.05) and GPX activity/hemoglobin ratio was higher in cord blood (22.0 +/- 0.8 U/g Hb vs. 18.7 +/- 0.9 U/g Hb, p < 0.05) in women delivering by emergent cesarean compared to those delivering by elective cesarean.

CONCLUSION

Distressed fetuses delivered by emergency cesarean exhibited increased malondialdehyde concentrations, an indicative parameter for oxidative damage, and enhanced GPX activity an antioxidant enzyme, in amniotic fluid and umbilical cord blood compared to non-distressed fetuses delivered by elective cesarean section. This is probably an indication of higher fetal oxidative stress.

Ischemic preconditioning reduces the severity of ischemia-reperfusion injury of peripheral nerve in rats

Background and aim

Allow for protection of briefly ischemic tissues against the harmful effects of subsequent prolonged ischemia is a phenomennon called as Ischemic Preconditioning (IP). IP has not been studied in ischemia-reperfusion (I/R) model of peripheral nerve before. We aimed to study the effects of acute IP on I/R injury of peripheral nerve in rats.

Method

70 adult male rats were randomly divided into 5 groups in part 1 experimentation and 3 groups in part 2 experimentation. A rat model of severe nerve ischemia which was produced by tying iliac arteries and all idenfiable anastomotic vessels with a silk suture (6-0) was used to study the effects of I/R and IP on nerve biochemistry. The suture technique used was a slip-knot technique for rapid release at time of reperfusion in the study. Cytoplasmic vacuolar degeneration was also histopathologically evaluated by light microscopic examination in sciatic nerves of rats at 7th day in part 2 study.

Results

3 hours of Reperfusion resulted in an increase in nerve malondialdehyde levels when compared with ischemia and non-ischemia groups (p < 0.001 and p < 0.0001 respectively). IP had significantly lower nerve MDA levels than 3 h reperfusion group (p < 0.001). The differences between ischemic, IP and non-ischemic control groups were not significant (p > 0.05). There was also a significant decrease in vacoular degeneration of sciatic nerves in IP group than I/R group (p < 0.05).

Conclusion

IP reduces the severity of I/R injury in peripheral nerve as shown by reduced tissue MDA levels at 3 th hour of reperfusion and axonal vacoulization at 7 th postischemic day.

Effects of antineoplastic agents on the peripheral nerves under a surgical tissue expansion procedure: An experimental study

BACKGROUND

Elongation of peripheral nerve by the use of a tissue expander is helpful to repair nerve defects. This study was designed to investigate the effects of some antineoplastic agents on the peripheral nerves under a surgical tissue expansion procedure.

MATERIALS AND METHODS

Twenty-five Wistar rats were used in this study. Following the exposition of the sciatic nerve and placement of two 10/0-nylon sutures in the epineurium 20 mm apart, a tissue expander was then placed under it. Inflation of the expander was immediately accomplished by the separate percutaneous injections of 6, 6, and 8 ml for every 3 min under general anesthesia. The expander was fully deflated at the end of each 3 min The distance between two sutures was measured 1 h later to measure the rate of elongation. Rats were randomly divided into five groups (according to the administered drugs), each consisting of five rats (10 sciatic nerves). Normal saline (1 ml) in the control group (group I), cyclophosphamide (15 mg/kg) in the group II, cisplatinum (3 microg/kg) in the group III, mitomycin-C (0.5 mg/kg) in the group IV and 5-fluorouracil (10 mg/kg) in the group V were injected intravenously. Intravenous injections of drugs were performed via the tail vein 30 min before expansion, 48 and 96 h after removal of expander. The incision was reopened on the third and seventh postoperative days, and five sciatic nerves of each group were exposed and then the pinching test was performed to measure regeneration distance. Electroneurographic changes were recorded. The expanded portion of the sciatic nerve between two sutures was harvested for histological evaluation.

RESULTS

There is no significant difference between the elongation rates of all groups (P < 0.05). Histologic evaluation showed that inflammatory changes, vacuolization, intraneural edema, demyelination, axonal changes in the control group, the cisplatinum group, and the mitomycin-C group. These changes were significantly decreased in the cyclophosphamide group and the 5-fluorouracil group. In the cyclophosphamide group and the 5-fluorouracil group, the amplitude of compound action potential (CAP) values were significantly higher and the latency was significantly shorter (P > 0.05).

CONCLUSION

We believed that cyclophosphamide and 5-fluorouracil may be helpful in tissue expansion of peripheral nerves, by decreasing the effects of the ischemia-reperfusion injury on the expanded peripheral nerves.

Roles of nitric oxide, malondialdehyde, and fibronectin in an experimental peripheral nerve ischemia-reperfusion model

Although there are many studies of the neuropathology of the ischemic degeneration of peripheral nerves, the pathogenesis is not well-understood. The roles of several biomolecules on this process were previously reported. An adhesion molecule, fibronectin, which is applied locally (as a conduit material), is very effective in nerve recovery. This study was carried out to evaluate the roles of fibronectin, lipid peroxidation, and nitric oxide (NO) in an experimental model of peripheral nerves. Ischemia and reperfusion injury of sciatic nerves was rendered by clamping the femoral artery and vein. Rats were divided into nine groups. Ischemia and reperfusion were not applied to group 1. In group 2, only ischemia was performed, but reperfusion was not accomplished. For groups 3-9, 1, 2, and 24 h and 1, 2, 3, and 4 weeks of reperfusion were applied following 3 h of ischemia. Then NO, malondialdehyde (MDA), and fibronectin levels were observed in serum samples of rats. Colorimetric and nephelometric assays were used for determination of the levels of these parameters. In this study, all biochemical parameters were found to be increased in the ischemia groups when compared with the control group 1 (P < 0.05). A significant difference was observed between study groups with respect to MDA, NO, and fibronectin levels (P < 0.05). Also, some correlations were established between biochemical parameters in the same group, depending on the varying reperfusion time (r > 0.50). Ischemia causes some important changes in biochemical parameters, and depending on the reperfusion time, nerve injury continues for a while. In our study, we observed that serum levels of MDA decreased in the periods when NO and fibronectin simultaneously increased. Such increases may contribute to neural recovery, and there may be interactions among them.

Ischemia-reperfusion injury causes oxidative stress and apoptosis of Schwann cell in acute and chronic experimental diabetic neuropathy

Mild ischemia-reperfusion (IR) injury to diabetic peripheral nerve is known to cause severe ischemic fiber degeneration. Little information is available on its effects on Schwann cell (SC). In this study, we evaluated oxidative stress and apoptosis of SC following mild IR, using immunohistochemistry in streptozotocin (STZ)- induced diabetic rats. Twenty-six rats were divided into four groups according to the duration of diabetes: 1- month STZ-induced diabetic group (n=7) and age-matched control group (n=7); 4-month STZ-induced diabetic group (n=6) and age-matched control group (n=6). Using our established IR model of 3 h of ischemia followed by 7 days of reperfusion, sciatic and tibial nerves were harvested and labeled with 8-hydroxydeoxyguanosine (8-OHdG; oxidative stress marker), caspase-3 (apoptotic executor), and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) activity (apoptotic indicator). Marked positive staining with 8-OHdG, caspase-3, and TUNEL were found in diabetic ischemic nerves (right side) following IR in both 1-month and 4-month groups. Only mild positive staining or no staining was seen in the nonischemic side (left side) of diabetic and age-matched control groups. Co-labeling with S-100 confirmed that the cells labeled with 8-OHdG, caspase3, and TUNEL were SC. SC was susceptible to oxidative injury and apoptosis in experimental diabetic neuropathy when subjected to mild IR injury.

The therapeutic window of hypothermic neuroprotection in experimental ischemic neuropathy: Protection in ischemic phase and potential deterioration in later reperfusion phase

Hypothermia will neuroprotect peripheral nerve from ischemia-reperfusion (IR) injury, but the therapeutic window of hypothermic neuroprotection has not been defined. Unilateral IR injury was produced by the ligation and release of nooses tied around supplying arteries to the right sciatic-tibial nerve of the rat. Using this model, 114 rats were divided into 12 groups according to the delay (0, 1, 3, and 4 h) and the depth of hypothermia (28, 32, and 35 degrees C). All rats were subjected to 3 h ischemia and 7 days reperfusion followed by behavioral, electrophysiological, and pathological evaluations. We demonstrated significant hypothermic neuroprotection with both deep (28 degrees C) and mild (32 degrees C) hypothermia initiated during ischemia (0 and 1 h delay), but not hypothermia initiated during reperfusion (3 and 4 h delay) in both behavioral and electrophysiological evaluations. In addition, the pathologically significant differences were observed between deep hypothermia (28 degrees C) and normothermia (35 degrees C) initiated during ischemia. We conclude that the therapeutic window of hypothermic neuroprotection is optimal during the intraischemic period and that mild and deep hypothermia provide neuroprotection. Prolonged delay of hypothermic treatment results in worsening of IR injury.

Ischemia–reperfusion injury of peripheral nerve in experimental diabetic neuropathy

The pathogenesis of human diabetic neuropathy likely involves the interplay of hyperglycemia, ischemia, and oxidative stress. Mild-moderate ischemia-reperfusion to streptozotocin (STZ)-induced diabetes results in florid fiber degeneration in diabetic but not in normal nerves. Uncertainty exists as to the influence of duration of diabetes on this susceptibility. We therefore studied diabetic tibial and sciatic nerves using a rat ischemia-reperfusion (IR) model after 1 month and 4 months of diabetes utilizing electrophysiological, behavioral, and neuropathological methods. Electrophysiological abnormalities were present in 1-month diabetic rats (D) and persisted over 4 months. Behavioral scores were decreased markedly at 4 months (p<0.05). Endoneurial edema and ischemia fiber degeneration (IFD) were observed at both the 1-month (p<0.01 and p<0.001) and 4-month (p<0.001) durations in diabetic nerves, whereas only mild or no damage was observed in age-matched control nerves. These findings demonstrate that STZ-induced diabetes exacerbates the morphological and electrophysiological pathology in peripheral nerve to IR injury both in the early timepoint of 1 month and late timepoint of 4 months, although there was a gradation of injury, which is more severe at the later timepoint. Reperfusion exaggerated morphological pathology in 1-month STZ-induced diabetic peripheral nerve.

Beneficial effects of melatonin on reperfusion injury in rat sciatic nerve

Studies have shown that ischemia-reperfusion (I/R) produces free radicals leading to lipid peroxidation and to damage of the nervous tissue. Melatonin, a main secretory product of the pineal gland, has free radical scavenging and antioxidant properties and has been shown to diminish I/R injury in many tissues. There are a limited number of studies related to the effects of melatonin on I/R injury in the peripheral nervous system. Therefore, in the present study, the protective effect of melatonin was investigated in rats subjected to 2 hr of sciatic nerve ischemia followed by 3 hr of reperfusion. Following reperfusion, nerve tissue samples were collected for quantitative assessment of malondialdehyde (MDA), an oxidative stress marker, and superoxide dismutase (SOD), a principal antioxidant enzyme. Samples were further evaluated at electron microscopic level to examine the neuropathological changes. I/R elevated the concentration of MDA significantly while there was a reduction at SOD levels. Melatonin treatment reversed the I/R-induced increase and decrease in MDA and SOD levels, respectively. Furthermore, melatonin salvaged the nerve fibers from ischemic degeneration. Histopathologic findings in the samples of melatonin-treated animals indicated less edema and less damage to the myelin sheaths and axons than those observed in the control samples. Our results suggest that administration of melatonin protects the sciatic nerve from I/R injury, which may be attributed to its antioxidant property.

Peripheral nerve ischemia: reperfusion injury and fiber regeneration

We continued our studies of ischemia-reperfusion (IR) injury, extending the reperfusion duration to 42 days to capture the fiber regeneration process. We used a rat model for IR injury produced by ligation and release of nooses around supplying vessels to the sciatic nerve. Fifty-six rats were used. One group (control N = 8) underwent sham ischemia; the other six groups (N = 8 each) underwent complete hind limb ischemia for 4 h followed by reperfusion durations of 0 h (ischemia alone), 3 h, 7 days, 14 days, 28 days, and 42 days. Behavioral and electrophysiological data were obtained immediately before euthanasia. Pathologically, three phases were identifiable: Phase 1 (0-3 h)-minimal pathological changes, minimal edema; phase 2 (7 days, 14 days)-prominent fiber degeneration, endoneurial edema; phase 3 (28 days, 42 days)-abundant small regenerating fiber clusters, minimal edema. Compound muscle action potential (CMAP) was the most sensitive index of neural deficits and recovery, showing progressive recovery beyond 14 days. Severe functional deficits developed immediately and persisted with a trend to recovery at the 42-day time-point. It was concluded that reperfusion, by oxidative injury, worsened nerve function and aggravated fiber degeneration, but in the longer time frame, permitted fiber regeneration to occur.

Neuroprotective effects of nitrone radical scavenger S-PBN on reperfusion nerve injury in rats

The nitrone-based free radical scavengers have potent neuroprotective activities in models of stroke in which oxidative stress plays a key role in its development. We examined the effects of S-PBN (sodium 4-[(tert-butylimino) methyl]benzene-3-sulfonate N-oxide), a spin trap nitrone, on reperfusion injury in rat peripheral nerves. Immediately after the onset of 4-h ischaemia in rat right hindlimb, S-PBN was administered via mini-osmotic pumps, containing 2 ml of S-PBN (1.2 M), inserted subcutaneously. S-PBN, in addition, was given by a single injection (50 mg/kg BW, i.p.). Mean plasma concentrations of S-PBN were significantly greater in S-PBN-treated rats than in controls after 24, 48 and 72 h of reperfusion. Pump and dosing solution analysis indicated that the rats received between 82 and 99% of the target S-PBN concentration. Morphology in sciatic, tibial and peroneal nerves was assessed after 4 h of ischaemia followed by 72 h and 7 days of reperfusion. After 72 h of reperfusion, saline-treated control rats showed endoneurial oedema at the thigh level and diffuse axonal degeneration of myelinated nerve fibres distally. S-PBN-treated nerves were normal or revealed less severe abnormalities in myelinated fibres after 72 h and 7 days of reperfusion, when compared with those in saline-treated control nerves. Morphometrically, the frequency of abnormal myelinated fibres at calf levels was significantly less in S-PBN-treated nerves than in controls. In conclusion, post-ischaemic administration of S-PBN exhibits substantial neuroprotective properties in ischemia/reperfusion nerve injury.

How does glucose generate oxidative stress in peripheral nerve?

Diabetes-associated oxidative stress is clearly manifest in peripheral nerve, dorsal root, and sympathetic ganglia of the peripheral nervous system and endothelial cells and is implicated in nerve blood flow and conduction deficits, impaired neurotrophic support, changes in signal transduction and metabolism, and morphological abnormalities characteristic of peripheral diabetic neuropathy (diabetic peripheral neuropathy). Hyperglycemia has a key role in oxidative stress in diabetic nerve, whereas the contribution of other factors, such as endoneurial hypoxia, transition metal imbalance, and hyperlipidemia, has not been rigorously proven. It has been suggested that oxidative stress, particularly mitochondrial superoxide production, is responsible for sorbitol pathway hyperactivity, nonenzymatic glycation/glycooxidation, and activation of protein kinase C. However, this concept is not supported by in vivo studies demonstrating the lack of any inhibition of the sorbitol pathway activity in peripheral nerve, retina, and lens by antioxidants, including potent superoxide scavengers. Its has been also hypothesized that aldose reductase (AR) detoxifies lipid peroxidation products, and therefore, the enzyme inhibition in diabetes is detrimental rather than benefical. However, the role for AR in lipid peroxdation product metabolism has never been demonstrated in vivo, and the effects of aldose reductase inhibitors and antioxidants on diabetic peripheral neuropathy are unidirectional, i.e., both classes of agents prevent and correct functional, metabolic, neurotrophic, and morphological changes in diabetic nerve. Growing evidence indicates that AR has a key role in oxidative stress in the peripheral nerve and contributes to superoxide production by the vascular endothelium. The potential mechanisms of this phenonmenon are discussed.

Effect of trapidil in ischemia/reperfusion injury of peripheral nerves

OBJECTIVE

Ischemia plays an important role in the development of pathological changes in nerve tissue, and restoration of blood flow results in injury (ischemia/reperfusion [I/R] injury) mediated by toxic oxygen free radicals. Trapidil is currently used as a coronary artery vasodilating agent and is also used for the prevention of ischemic symptoms of cerebral vasospasm. The purpose of this study was to determine the effects of trapidil on I/R injury and the ischemic tolerance of rat peripheral nerves.

METHODS

Preischemia or prereperfusion administration of trapidil (8 mg/kg) was evaluated in the rat sciatic nerve I/R injury model. Nerve tissue samples from the I/R injury site were assayed for malondialdehyde (MDA), nitrites, and nitrates, as markers of I/R injury, and pathological changes were evaluated by electron microscopy.

RESULTS

I/R resulted in an increase in MDA levels, which remained elevated for 2 weeks in control nerves. Rats that received trapidil before ischemia exhibited decreased MDA levels, and rats that received trapidil after the standard 3 hours of ischemia demonstrated increased tolerance to reperfusion, as reflected in significantly decreased MDA levels. Nitrite and nitrate levels in trapidil-treated rats were significantly higher than those in control animals. Histological evaluations of the sciatic nerve segments demonstrated that preischemia and postischemia trapidil treatments had a sparing effect against the myelin damage and axonal edema that are consistently noted in untreated ischemic reperfused nerves.

CONCLUSION

The results confirm that pretreatment with trapidil before the ischemic insult or before reperfusion provides marked protection against I/R injury in peripheral nerves.

Aggravated reperfusion injury in STZ-diabetic nerve

The streptozocin (STZ)-diabetic nerve manifests increased morphological susceptibility to a superimposed acute ischemic injury, and reperfusion injury exaggerates ischemic nerve pathology. To determine whether STZ-diabetic nerves are susceptible to reperfusion, we evaluated the pathological consequences after 2.5 hours of ischemia followed by 3 and 24 hours of reperfusion in a 20-week STZ-diabetic rat sciatic nerve. After 3 hours of reperfusion, endoneurial edema developed in diabetic nerves, whereas non-diabetic controls showed mild or no edema. Morphometric analysis of endoneurial edema, quantified by the total transverse fascicular area and the point-count score of endoneurial structureless space, confirmed significantly more reperfusion-induced edema at thigh and knee levels in diabetic nerves than in controls. Reperfusion caused a significant increase in the number of endoneurial mast cells at the thigh level in diabetic nerves. After 24 hours of reperfusion, there were striking morphological anomalies of myelinated nerve fibers in diabetic nerves, without any observable changes in control nerves. In conclusion, we have demonstrated that STZ-diabetes exacerbates the morphological change to reperfusion. Diabetes therefore renders the microvasculature more vulnerable to the deleterious effects of ischemia/reperfusion.

A functional model system of an hypoxic nerve injury and its evaluation

OBJECTIVES/HYPOTHESIS

Develop an hypoxic peripheral nerve injury model with a controlled injury type and two types of clinically relevant physiological measurements of function during and after recovery. The model, controlling for injury and measurement variables, would have predictable outcomes in function. The functional model could test potential therapeutic interventions with greater sensitivity.

STUDY DESIGN

Twenty-one rats were used in preliminary studies evaluating peroneal nerve injury types and functional model evaluation. Forty-eight rats were used in a controlled and blinded evaluation of the injury model followed by treatment with hyperbaric oxygen (HBO) as a potential therapeutic intervention and evaluated with functional models.

METHODS

Preliminary studies compared nerve injuries: epineurectomy, epineurectomy with crush and transection with autograft for rate of return of function and final extent of return of function. The gait analysis model was also evaluated and modified to decrease variability. The final study evaluated peroneal epineurectomy and nerve crush injury with serial gait analysis during recovery, final elicited maximum force measurements, and histological analysis. Half of the animals were treated with HBO during recovery (ANOVA or regression statistical analysis were used to determine group differences.).

RESULTS

Preliminary studies suggested that the peroneal nerve injury model of an epineurectomy with crush of specified length and a modification of the gait analysis model would yield a useful and predictable injury outcome. The final study resulted in predicted and consistent injury outcomes. In the HBO treatment group, a 12% improvement in function 5 days after HBO treatment was demonstrated (P < .03), but no long-term or histological benefit was seen.

CONCLUSION

A reliable hypoxic nerve injury model has been developed and tested utilizing two functional methods as the primary outcome variables.

Ischaemia-reperfusion injury of the peripheral nerve: An experimental study

Although the neuropathology of ischaemic fibre degeneration is relatively well known, its pathogenesis is poorly understood. One of the presumed mechanisms is oxidative stress, causing the breakdown of the blood-nerve barrier (BNB) and ending in lipid peroxidation. We evaluated the effect of ischaemia and reperfusion on the sciatic-tibial nerve of the rat and investigated the biochemical, pathological, and functional evidence of BNB disruption and lipid peroxidation. The distal portion and trifurcation of the sciatic nerve were rendered ischaemic by clamping the femoral vessels for 3 h and followed by varying durations of reperfusion. Reperfusion resulted in an increase in lipid peroxidation beginning from the first hour and increasing until the seventh day, followed by a gradual decline over the following weeks. Nerve oedema and ischaemic fibre degeneration (IFD) consistently became more severe and prominent with reperfusion, indicating that oxidative stress damages the BNB and causes IFD. Results of functional testing by the sciatic function index correlated with other parameters as walking track analysis results got worse as reperfusion periods increased. Impairment of walking patterns was more striking after the first day and continued up to the third week. These data indicate that severe ischaemia of the peripheral nerve results in reperfusion injury, functional impairment, and disruption of the BNB. Microvascular events, which may occur during reperfusion, may be important in amplifying the nerve fibre degeneration that initiated during ischaemia.

Protein carbonyl formation and tyrosine nitration as markers of oxidative damage during ischaemia-reperfusion injury to rat sciatic nerve

We have investigated the role of oxidative damage in peripheral nerve ischaemia-reperfusion injury using a rat sciatic nerve model. After 5 h ischaemia blood flow to the sciatic nerve was restarted and markers of oxidative damage measured after various times of reperfusion. As a marker of protein oxidative damage, protein carbonyl formation was measured using a sensitive enzyme-linked immunosorbent assay. Protein carbonyl content was unaffected by ischaemia alone, but increased by 55% after 12-18 h reperfusion, correlating with the onset of nerve pathology. Pretreatment with the xanthine oxidase inhibitor allopurinol prevented these abnormalities, suggesting that xanthine oxidase activity is proximal to oxidative damage during reperfusion injury. To determine whether formation of the potent oxidant peroxynitrite from nitric oxide and superoxide contributed to ischaemia-reperfusion injury, we measured the accumulation of 3-nitrotyrosine residues in proteins. Only one protein of 49,000 mol. wt contained significant amounts of 3-nitrotyrosine residues which was shown to be glial fibrillary acidic protein, an abundant cytoskeletal protein in Schwann cells. However glial fibrillary acidic protein contained 3-nitrotyrosine residues prior to ischaemia-reperfusion, and the amount of nitrated tyrosine residues in total glial fibrillary acidic protein did not increase significantly during reperfusion, therefore it was not possible to draw conclusions about the role of peroxynitrite in nerve reperfusion injury.

The expression of proinflammatory cytokine mRNA in the sciatic-tibial nerve of ischemia-reperfusion injury

We evaluated the proinflammatory cytokines, TNF-alpha and IL-1beta, mRNA expression in the rat sciatic and tibial nerves following ischemia-reperfusion (IR) injury, using competitive RT-PCR, to explore the role of cytokines in IR injury. The expressions of both TNF-alpha and IL-1beta mRNA were related to severity of ischemia and occurred with reperfusion rather than ischemia alone. TNF-alpha gene expression peaked at 24 h of reperfusion, while that of IL-1beta peaked at 12 h. These data support the notion that the proinflammatory cytokines TNF-alpha and IL-1beta are involved in the inflammatory response of IR injury to the peripheral nervous system and may be involved in the pathophysiology of ischemic fiber degeneration.

Hypothermic neuroprotection of peripheral nerve of rats from ischemia-reperfusion injury: intraischemic vs. reperfusion hypothermia

The pathophysiology of ischemic fiber degeneration (IFD) is not known, but mechanisms involved during nerve ischemia differ from those during reperfusion. We have previously demonstrated hypothermic neuroprotection of peripheral nerve from IFD. We now evaluate the efficacy of hypothermia in the intraischemic vs. the reperfusion period, using our established model of ischemia-reperfusion injury. Intraischemic hypothermia resulted in significant recovery of all indices (behavior score, electrophysiology and histology, P<0.01 or 0.05) while hypothermia during reperfusion period showed less improvement, significant only for the histological score compared to normothermia group (IFD index, P<0.05). Once hypothermia was applied in the ischemic period, the resultant neuroprotection continued into the reperfusion period, even if nerve temperature was then raised during the reperfusion period. These results indicate that hypothermic neuroprotection is more efficacious during the intraischemic period than during reperfusion, when a lesser degree of neuroprotection ensued.

Alpha-lipoic acid provides neuroprotection from ischemia-reperfusion injury of peripheral nerve

BACKGROUND

Reperfusion aggravates nerve ischemic fiber degeneration, likely by the generation of reduced oxygen species. We therefore evaluated if racemic alpha-lipoic acid (LA), a potent antioxidant, will protect peripheral nerve from reperfusion injury, using our established model of ischemia-reperfusion injury.

METHODS

We used male SD rats, 300+/-5 g. Ischemia was produced by the ligature of each of the supplying arteries to the sciatic-tibial nerve of the right hind-limb for predetermined periods of time (either 3 or 5 h), followed by the release of the ligatures, resulting in reperfusion. LA was given intraperitoneally daily for 3 days for both pre- and post-surgery. Animals received either LA, 100 mg/kg/day, or the same volume of saline intraperitoneally. Clinical behavioral score and electrophysiology of motor and sensory nerves were obtained at 1 week after ischemia-reperfusion. After electrophysiological examination, the sciatic-tibial nerve was fixed in situ and embedded in epon. We evaluated for ischemic fiber degeneration (IFD) and edema, as we described previously.

RESULTS

Distal sensory conduction (amplitude of sensory action potential and sensory conduction velocity (SCV) of digital nerve) was significantly improved in the 3-h ischemia group, treated with LA (P<0.05). LA also improved IFD of the mid tibial nerve (P=0.0522). LA failed to show favorable effects if the duration of ischemia was longer (5-h ischemia).

CONCLUSION

These results suggest that alpha-lipoic acid is efficacious for moderate ischemia-reperfusion, especially on distal sensory nerves.

Hypothermic neuroprotection of peripheral nerve of rats from ischaemia-reperfusion injury

Although there is much information on experimental ischaemic neuropathy, there are only scant data on neuroprotection. We evaluated the effectiveness of hypothermia in protecting peripheral nerve from ischaemia-reperfusion injury using the model of experimental nerve ischaemia. Forty-eight male Sprague-Dawley rats were divided into six groups. We used a ligation-reperfusion model of nerve ischaemia where each of the supplying arteries to the sciatic-tibial nerves of the right hind limb was ligated and the ligatures were released after a predetermined period of ischaemia. The right hind limbs of one group (24 rats) were made ischaemic for 5 h and those of the other group (24 rats) for 3 h. Each group was further divided into three and the limbs were maintained at 37 degrees C (36 degrees C for 5 h of ischaemia) in one, 32 degrees C in the second and 28 degrees C in the third of these groups for the final 2 h of the ischaemic period and an additional 2 h of the reperfusion period. A behavioural score was recorded and nerve electrophysiology of motor and sensory nerves was undertaken 1 week after surgical procedures. At that time, entire sciatic-tibial nerves were harvested and fixed in situ. Four portions of each nerve were examined: proximal sciatic nerve, distal sciatic nerve, mid-tibial nerve and distal tibial nerve. To determine the degree of fibre degeneration, each section was studied by light microscopy, and we estimated an oedema index and a fibre degeneration index. The groups treated at 36-37 degrees C underwent marked fibre degeneration, associated with a reduction in action potential and impairment in behavioural score. The groups treated at 28 degrees C (for both 3 and 5 h) showed significantly less (P < 0.01; ANOVA, Bonferoni post hoc test) reperfusion injury for all indices (behavioural score, electrophysiology and neuropathology), and the groups treated at 32 degrees C had scores intermediate between the groups treated at 36-37 degrees C and 28 degrees C. Our results showed that cooling the limbs dramatically protects the peripheral nerve from ischaemia-reperfusion injury.