The effects of prophylactic zinc and melatonin application on experimental spinal cord ischemia–reperfusion injury in rabbits: experimental study

Melatonin, a natural antioxidant therapy in spinal cord injury

Spinal cord injury (SCI) is a sudden onset of disruption to the spinal neural tissue, leading to loss of motor control and sensory function of the body. Oxidative stress is considered a hallmark in SCI followed by a series of events, including inflammation and cellular apoptosis. Melatonin was originally discovered as a hormone produced by the pineal gland. The subcellular localization of melatonin has been identified in mitochondria, exhibiting specific onsite protection to excess mitochondrial reactive oxygen species and working as an antioxidant in diseases. The recent discovery regarding the molecular basis of ligand selectivity for melatonin receptors and the constant efforts on finding synthetic melatonin alternatives have drawn researchers' attention back to melatonin. This review outlines the application of melatonin in SCI, including 1) the relationship between the melatonin rhythm and SCI in clinic; 2) the neuroprotective role of melatonin in experimental traumatic and ischemia/reperfusion SCI, i.e., exhibiting anti-oxidative, anti-inflammatory, and anti-apoptosis effects, facilitating the integrity of the blood-spinal cord barrier, ameliorating edema, preventing neural death, reducing scar formation, and promoting axon regeneration and neuroplasticity; 3) protecting gut microbiota and peripheral organs; 4) synergizing with drugs, rehabilitation training, stem cell therapy, and biomedical material engineering; and 5) the potential side effects. This comprehensive review provides new insights on melatonin as a natural antioxidant therapy in facilitating rehabilitation in SCI.

Main Cations and Cellular Biology of Traumatic Spinal Cord Injury

Traumatic spinal cord injury is a life-changing condition with a significant socio-economic impact on patients, their relatives, their caregivers, and even the community. Despite considerable medical advances, there is still a lack of options for the effective treatment of these patients. The major complexity and significant disabling potential of the pathophysiology that spinal cord trauma triggers are the main factors that have led to incremental scientific research on this topic, including trying to describe the molecular and cellular mechanisms that regulate spinal cord repair and regeneration. Scientists have identified various practical approaches to promote cell growth and survival, remyelination, and neuroplasticity in this part of the central nervous system. This review focuses on specific detailed aspects of the involvement of cations in the cell biology of such pathology and on the possibility of repairing damaged spinal cord tissue. In this context, the cellular biology of sodium, potassium, lithium, calcium, and magnesium is essential for understanding the related pathophysiology and also the possibilities to counteract the harmful effects of traumatic events. Lithium, sodium, potassium—monovalent cations—and calcium and magnesium—bivalent cations—can influence many protein–protein interactions, gene transcription, ion channel functions, cellular energy processes—phosphorylation, oxidation—inflammation, etc. For data systematization and synthesis, we used the Preferred Reporting Items for Systematic Reviews and Meta-Analyzes (PRISMA) methodology, trying to make, as far as possible, some order in seeing the “big forest” instead of “trees”. Although we would have expected a large number of articles to address the topic, we were still surprised to find only 51 unique articles after removing duplicates from the 207 articles initially identified. Our article integrates data on many biochemical processes influenced by cations at the molecular level to understand the real possibilities of therapeutic intervention—which must maintain a very narrow balance in cell ion concentrations. Multimolecular, multi-cellular: neuronal cells, glial cells, non-neuronal cells, but also multi-ionic interactions play an important role in the balance between neuro-degenerative pathophysiological processes and the development of effective neuroprotective strategies. This article emphasizes the need for studying cation dynamics as an important future direction.

Histological Findings After Aortic Cross-Clamping in Preclinical Animal Models

Spinal cord ischemic injury and paralysis are devastating complications after open surgical repair of thoracoabdominal aortic aneurysms. Preclinical models have been developed to simulate the clinical paradigm to better understand the neuropathophysiology and develop therapeutic treatment. Neuropathological findings in the preclinical models have not been comprehensively examined before. This systematic review studies the past 40 years of the histological findings after open surgical repair in preclinical models. Our main finding is that damage is predominantly in the grey matter of the spinal cord, although white matter damage in the spinal cord is also reported. Future research needs to examine the neuropathological findings in preclinical models after endovascular repair, a newer type of surgical repair used to treat aortic aneurysms.

Zinc promotes autophagy and inhibits apoptosis through AMPK/mTOR signaling pathway after spinal cord injury

Autophagy is a intracellular biological process that controls the homeostasis of nutrition deprivation and starvation and has been associated with the development of traumatic diseases. Zinc, an important chemical element involved in life activities, has improved nerve recovery effects through intraperitoneal injection. The purpose of this study was to probe the possible modulation of autophagy and apoptosis from the injured spinal cord and neurons by zinc administration. It was shown that zinc significantly induced the level of Beclin1 and LC3B by activating adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling pathway. In addition, zinc suppressed apoptosis in the injured spinal cord. Taken together, these findings suggested that zinc through promoting neurons autophagy and inhibiting apoptosis.

Quantification of surviving neurons after contusion, dislocation, and distraction spinal cord injuries using automated methods

This study proposes and validates an automated method for counting neurons in spinal cord injury (SCI) and then uses it to examine and compare the surviving cells in common types of SCI mechanisms. Moderate contusion, dislocation, and distraction SCIs were surgically induced in Sprague Dawley male rats (n = 6 for each type of injury). Their spinal cords were harvested 8 weeks post injury with 5 normal weight-matched rats. The spinal cords were cut, stained with anti-NeuN antibody and fluorescent Nissl, and imaged in the dorsal and ventral horns at various distances to the epicenter. Neurons in the images were automatically counted using an algorithm that was designed to filter non-soma-like objects based on morphological characteristics (size, solidity, circular pattern) and check the remaining objects for the double-stained nucleus/cell body features (brightness variation, brightness distribution, color). To validate the automated method, some of the images were randomly selected for manual counting. The number of surviving cells that were automatically measured by the algorithm was found to be correlated with the values that were manually measured by 2 observers (P < .001) with similar differences (P > .05). Neurons in the dorsal and ventral horns were reduced after the SCIs (P < .05). Dislocation and distraction, respectively, caused the most severe damage to the ventral horn neurons especially near the epicenter and the most extensive and uniform damage to the dorsal horn neurons (P < .05). Our method was proved to be reliable, which is suitable for studying different types of SCI.

Melatonin for the treatment of spinal cord injury

Spinal cord injury (SCI) from trauma or disease severely impairs sensory and motor function. Neurorehabilitation after SCI is a complex medical process that focuses on improving neurologic function and repairing damaged connections in the central nervous system. An increasing number of preclinical studies suggest that melatonin may be useful for the treatment of SCI. Melatonin is an indolamine that is primarily secreted by the pineal gland and known to be regulated by photoperiodicity. However, it is also a versatile hormone with antioxidative, antiapoptotic, neuroprotective, and anti-inflammatory properties. Here, we review the neuroprotective properties of melatonin and the potential mechanisms by which it might be beneficial in the treatment of SCI. We also describe therapies that combine melatonin with exercise, oxytetracycline, and dexamethasone to attenuate the secondary injury after SCI and limit potential side effects. Finally, we discuss how injury at different spinal levels may differentially affect the secretion of melatonin.

Effect of N-acetylcysteine and allopurinol combination to protect spinal cord ischemia/reperfusion injury induced by aortic cross-clamping in rat model

Purpose

The aim of this experimental study was to determine whether combination of N-acetylcysteine and allopurinol can reduce the ischemia/reperfusion injury of spinal cord in a rat model.

Methods

Twenty-seven Spraque Dawley rats, all male, weighing between 220 to 370 (mean 325) gr were used in the study. 27 rats were divided into three groups: sham group, control group and experimental group. Abdominal aortic occlusion between the renal arteries and iliac bifurcations was carried out for 60 min with proximal and distal clip in control and experimental groups. Hindlimb motor functions were evaluated at 24, and 48 h using the Tarlov Scale. Besides, spinal cord samples were taken for determination of superoxide dismutase, and catalase activities as antioxidant enzymes, and malondialdehyde as an indicator of lipid peroxidation and xanthine oxidase levels as source hydroxyl radical for biochemical studies. Also, histopathological evaluation was made from cord tissue samples.

Results

The experimental group subjects had better neurological functions than control group subjects. In experimental group; superoxide dismutase and catalase levels increased, while malondialdehyde and xantine oxidase levels decreased as compared with control group. Histopathological examination showed that experimental group had less cell degeneration, hemorrhage, edema and inflammation loss than control group.

Conclusions

This study offers that combined use of N-acetylcysteine and allopurinol might help protect the spinal cord against ischemia/reperfusion injury.

Effects of iloprost and piracetam in spinal cord ischemia-reperfusion injury in the rabbit

STUDY DESIGN

Experimental Study.

OBJECTIVES

The aim of this study was to investigate the neuroprotective effects of iloprost and piracetam on spinal cord ischemia/reperfusion (I/R) injury in the rabbit.

SETTINGS

The Experimental Research Center of Selcuk University, Konya, Turkey.

METHODS

A total of 24 rabbits were divided into four groups of six rabbits each, as follows: group 1 (n = 6) sham, laparotomy only; group 2 (n = 6) I/R; group 3 (n = 6) I/R+iloprost; and group 4 (n = 6) I/R+piracetam. I/R was established in groups 2, 3 and 4. Subsequently, they were followed up neurologically for 24 h until the rabbits were killed; biochemical and histopathological examinations of samples from the spinal cord were carried out.

RESULTS

Neurological examination results were significantly better in the iloprost and piracetam groups compared with the I/R group (P < 0.05). Neuroprotection was achieved with iloprost and piracetam by suppressing malondialdehyde (P < 0.05), increasing glutathione peroxidase activity (P < 0.05) and decreasing the xanthine oxidase level. In histopathological assessment, iloprost and piracetam groups were statistically different from the I/R group in terms of the number of apoptotic neurons in gray matter and white matter, as well as in terms of degenerated neurons and glial cells (P < 0.05). No statistical difference was determined between the four groups in the number of degenerated glial cells (P > 0.05).

CONCLUSION

This study has shown that iloprost and piracetam have neuroprotective effects in I/R injury both neurologically and histopathologically because of inhibition of lipid peroxidation.

Synergistic effect of melatonin on exercise-induced neuronal reconstruction and functional recovery in a spinal cord injury animal model

Nitric oxide (NO) may aggravate neuronal damage after spinal cord injury (SCI). We hypothesized that NO produced by inducible nitric oxide synthase (iNOS) accelerates secondary damage to spinal tissue, which may be reversed by the neuroprotectant, melatonin. This study investigated the effects of combination therapy with melatonin (10 mg/kg) and exercise (10 m/min) on recovery from SCI caused by contusion. We examined locomotor recovery, iNOS gene expression, autophagic and apoptotic signaling, including Beclin-1, LC3, p53 and IKKalpha protein expression and histological alterations in the ventral horn of the spinal cord. Melatonin in combination with exercise resulted in significantly increased hindlimb movement (P < 0.05), a reduced level of iNOS mRNA (P < 0.05) and more motor neurons in the ventral horn, versus control SCI and SCI plus exercise alone, with no effect on the other signaling molecules examined. This study shows that combined therapy with melatonin and exercise reduces the degree of secondary damage associated with SCI in rats and supports the possible use of melatonin in combination with exercise to reduce the side effects related to exercise-induced fatigue and impairment.

Therapeutic potential of melatonin in traumatic central nervous system injury

A vast literature extolling the benefits of melatonin has accumulated during the past four decades. Melatonin was previously considered of importance to seasonal reproduction and circadian rhythmicity. Currently, it appears to be a versatile anti-oxidative and anti-nitrosative agent, a molecule with immunomodulatory actions and profound oncostatic activity, and also to play a role as a potent neuroprotectant. Nowadays, melatonin is sold as a dietary supplement with differential availability as an over-the-counter aid in different countries. There is a widespread agreement that melatonin is nontoxic and safe considering its frequent, long-term usage by humans at both physiological and pharmacological doses with no reported side effects. Endeavors toward a designated drug status for melatonin may be enormously rewarding in clinics for treatment of several forms of neurotrauma where effective pharmacological intervention has not yet been attained. This mini review consolidates the data regarding the efficacy of melatonin as an unique neuroprotective agent in traumatic central nervous system (CNS) injuries. Well-documented actions of melatonin in combating traumatic CNS damage are compiled from various clinical and experimental studies. Research on traumatic brain injury and ischemia/reperfusion are briefly outlined here as they have been recently reviewed elsewhere, whereas the studies on different animal models of the experimental spinal cord injury have been extensively covered in this mini review for the first time.

Application of zinc-bis-(DL-hydrogensaspartate) does not reduce apoptotic cell death in myocardial infarction in the rat heart

BACKGROUND

Early studies in different stress models have shown potential beneficial effects of exogenous zinc application with reduction in the rate of apoptotic cell death. This has not been shown in models of myocardial infarction.

METHODS

Rats were exposed to either brief episodes of acute ischemia followed by reperfusion (phase 1) or chronic coronary occlusion (phase 2). Animals were either treated with zinc or vehicle. Groups 1 and 3 received zinc-bis-(DL-hydrogenaspartate) 10 mg/kg body weight as a single 5-mL bolus administered intraperitoneally 24 hours prior to coronary occlusion, groups 2 and 4 received saline. The infarct sizes were determined by triphenyltetrazolium chloride staining and expressed at relative areas to areas of ischemia. Histological slices of the rat's myocardium at the border zones of the infarcts were stained with the TUNEL method to assess for apoptosis. Animals in groups 5, 7, and 9 received zinc, given once before and then repeated every 4 days after coronary occlusion, whereas groups 6, 8, and 10 received saline. Animals were observed for observation periods of 13 (groups 9 and 10), 16 (groups 7 and 8), or 19 weeks (groups 5 and 6), respectively. Two-dimensional echocardiography was performed to measure ejection fraction (EF) at baseline and at the end of the observation periods. TUNEL staining was used to detect and quantify apoptosis rate in the border zones of infarcts after the hearts were excised.

RESULTS

Infarct sizes were 49% + 22% in group 1 (zinc + 30 minutes ischemia + 30 minutes reperfusion); 48% + 10% in group 2 (vehicle + 30 minutes ischemia + 30 minutes reperfusion); 42% + 11% in group 3 (zinc + 60 minutes ischemia + 30 minutes reperfusion); and 41% + 23% in group 4 (vehicle + 60 minutes ischemia + 60 minutes reperfusion). In group 1, 11% + 6% of cells were apoptotic compared to 12% + 4% in group 2, 16% + 9% in group 3, and 17% + 7% in group 4 (P > .05). In phase 2, echocardiography revealed a significant reduction in EF in all groups after coronary occlusion. There were no significant differences in EF between the 5 groups at baseline and at follow-up. TUNEL staining did not reveal any significant apoptosis after 13 to 19 weeks.

CONCLUSION

Application of zinc failed to result in reduction of infarct size after temporary coronary occlusion followed by reperfusion and did not demonstrate any reduction in apoptotic cell death. In chronic coronary occlusion, zinc also did not improve EF compared to controls in the presented model in rats. The mechanisms involved in antiapoptotic effects seem to be more complex and might not be inducible by simple zinc injections.

Melatonin reduces stress-activated/mitogen-activated protein kinases in spinal cord injury

Permanent functional deficits following spinal cord injury (SCI) arise from both mechanical injury and from secondary tissue reactions involving inflammation. The mitogen-activated protein kinases (MAPKs) play a critical role in cell signaling and gene expression. MAPK family includes three major members: extracellular signal regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK), representing three different signaling cascades. Moreover, various studies have clearly shown that high-mobility group box 1 (HMGB1) protein is implicated as a putative danger signal involved in the pathogenesis of a variety of inflammatory conditions including autoimmunity, cancer, trauma and hemorrhagic shock, and ischemia-reperfusion injury. Recently, we have reported that the pineal secretory product melatonin exerts important anti-inflammatory effects in an experimental model of SCI induced by the application of vascular clips (force of 24 g) to the dura after a four-level T5-T8 laminectomy. However, no reports are available on the effect of melatonin on MAPK signaling pathways and HMGB1 expression in SCI. The aim of the present study was to evaluate whether the melatonin protective effect observed in SCI is related to the regulation of MAPK signaling pathways and HMGB1 in mice. In this study we demonstrate the efficacy of treatment with the melatonin in SCI in mice in reducing (a) motor recovery, (b) activation of MAPKs p38, JNK and ERK1/2, (c) tumor necrosis factor-alpha expression, and (d) expression of HMGB1. We propose that melatonin's ability to reduce SCI in mice is also related to a reduction in MAPK signaling pathways and HMGB1 expression.

Melatonin regulates matrix metalloproteinases after traumatic experimental spinal cord injury

The matrix metalloproteinases (MMPs) are important enzymes that regulate developmental processes, maintain normal physiology in adulthood and have reparative roles at specific stages after an insult to the nervous system. MMPs, particularly MMP-9/gelatinase B, promote early inflammation and barrier disruption after spinal cord injury (SCI). Recently, we have reported that the pineal secretory product melatonin exerts important anti-inflammatory effects in an experimental model of SCI induced by the application of vascular clips (force of 24 g) to the dura after a four-level T5-T8 laminectomy. However, no reports are available on the relationship between the activity of MMPs and melatonin's anti-inflammatory effects. The aim of the present study was to evaluate whether the protective effect of melatonin observed in SCI is related to the regulation of MMP-9 and MMP-2 in mice. Biochemical and zymographic methods were used to analyze MMP-9 and -2 expression and activities in spinal cord tissue from SCI-treated mice at 24 hr after the trauma. Our studies reveal that melatonin reduced SCI and lipid peroxidation in spinal cord at 24 hr after SCI. Melatonin also diminished proMMP-9 and -2 activities that were induced in the spinal cord tissues at 24 hr after SCI. The reduced activities of MMP-9 and -2 were associated with depressed expression of TNF-alpha. We propose that melatonin's ability to reduce SCI in mice is also related to a reduction in MMP-9 and MMP-2 activity and expression.