Cerebral penetration injury leads to H2O2 generation in microdialysis samples

Stem Cell Therapy and Thiamine Deficiency-Induced Brain Damage

Wernicke's encephalopathy (WE) is a major central nervous system disorder resulting from thiamine deficiency (TD) in which a number of brain regions can develop serious damage including the thalamus and inferior colliculus. Despite decades of research into the pathophysiology of TD and potential therapeutic interventions, little progress has been made regarding effective treatment following the development of brain lesions and its associated cognitive issues. Recent developments in our understanding of stem cells suggest they are capable of repairing damage and improving function in different maladys. This article puts forward the case for the potential use of stem cell treatment as a therapeutic strategy in WE by first examining the effects of TD on brain functional integrity and its consequences. The second half of the paper will address the future benefits of treating TD with these cells by focusing on their nature and their potential to effectively treat neurodegenerative diseases that share some overlapping pathophysiological features with TD. At the same time, some of the obstacles these cells will have to overcome in order to become a viable therapeutic strategy for treating this potentially life-threatening illness in humans will be highlighted.

The impact of oxidative stress in thiamine deficiency: a multifactorial targeting issue

Thiamine (vitamin B1) deficiency, the underlying cause of Wernicke-Korsakoff syndrome, is associated with the development of focal neuronal loss in vulnerable areas of the brain. Although the actual mechanism(s) that lead to the selective histological lesions characteristic of this disorder remain unresolved, oxidative stress has been shown to play a major role in its pathophysiology. In this review, the multifactorial influence of oxidative stress on a variety of processes known to take part in the development of structural lesions in TD including excitotoxicity, neuroinflammation, blood-brain barrier integrity, mitochondrial integrity, apoptosis, nucleic acid function, and neural stem cells will be discussed, and therapeutic strategies undertaken for treating neurodegeneration examined which may have an impact on the future treatment of this important vitamin deficiency.

Polyamine catabolism is enhanced after traumatic brain injury

Polyamines spermine and spermidine are highly regulated, ubiquitous aliphatic cations that maintain DNA structure and function as immunomodulators and as antioxidants. Polyamine homeostasis is disrupted after brain injuries, with concomitant generation of toxic metabolites that may contribute to secondary injuries. To test the hypothesis of increased brain polyamine catabolism after traumatic brain injury (TBI), we determined changes in catabolic enzymes and polyamine levels in the rat brain after lateral controlled cortical impact TBI. Spermine oxidase (SMO) catalyzes the degradation of spermine to spermidine, generating H2O2 and aminoaldehydes. Spermidine/spermine-N(1)-acetyltransferase (SSAT) catalyzes acetylation of these polyamines, and both are further oxidized in a reaction that generates putrescine, H2O2, and aminoaldehydes. In a rat cortical impact model of TBI, SSAT mRNA increased subacutely (6-24 h) after TBI in ipsilateral cortex and hippocampus. SMO mRNA levels were elevated late, from 3 to 7 days post-injury. Polyamine catabolism increased as well. Spermine levels were normal at 6 h and decreased slightly at 24 h, but were normal again by 72 h post-injury. Spermidine levels also decreased slightly (6-24 h), then increased by approximately 50% at 72 h post-injury. By contrast, normally low putrescine levels increased up to sixfold (6-72 h) after TBI. Moreover, N-acetylspermidine (but not N-acetylspermine) was detectable (24-72 h) near the site of injury, consistent with increased SSAT activity. None of these changes were seen in the contralateral hemisphere. Immunohistochemical confirmation indicated that SSAT and SMO were expressed throughout the brain. SSAT-immunoreactivity (SSAT-ir) increased in both neuronal and nonneuronal (likely glial) populations ipsilateral to injury. Interestingly, bilateral increases in cortical SSAT-ir neurons occurred at 72 h post-injury, whereas hippocampal changes occurred only ipsilaterally. Prolonged increases in brain polyamine catabolism are the likely cause of loss of homeostasis in this pathway. The potential for simple therapeutic interventions (e.g., polyamine supplementation or inhibition of polyamine oxidation) is an exciting implication of these studies.

Role of secretory phospholipase a(2) in CNS inflammation: implications in traumatic spinal cord injury

Secretory phospholipases A(2) (sPLA(2)s) are a subfamily of lipolytic enzymes which hydrolyze the acyl bond at the sn-2 position of glycerophospholipids to produce free fatty acids and lysophospholipids. These products are precursors of bioactive eicosanoids and platelet-activating factor (PAF). The hydrolysis of membrane phospholipids by PLA(2) is a rate-limiting step for generation of eicosanoids and PAF. To date, more than 10 isozymes of sPLA(2) have been found in the mammalian central nervous system (CNS). Under physiological conditions, sPLA(2)s are involved in diverse cellular responses, including host defense, phospholipid digestion and metabolism. However, under pathological situations, increased sPLA(2) activity and excessive production of free fatty acids and their metabolites may lead to inflammation, loss of membrane integrity, oxidative stress, and subsequent tissue injury. Emerging evidence suggests that sPLA(2) plays a role in the secondary injury process after traumatic or ischemic injuries in the brain and spinal cord. Importantly, sPLA(2) may act as a convergence molecule that mediates multiple key mechanisms involved in the secondary injury since it can be induced by multiple toxic factors such as inflammatory cytokines, free radicals, and excitatory amino acids, and its activation and metabolites can exacerbate the secondary injury. Blocking sPLA(2) action may represent a novel and efficient strategy to block multiple injury pathways associated with the CNS secondary injury. This review outlines the current knowledge of sPLA(2) in the CNS with emphasis placed on the possible roles of sPLA(2) in mediating CNS injuries, particularly the traumatic and ischemic injuries in the brain and spinal cord.

Non-protein-bound iron in brain interstitium of newborn pigs after hypoxia

Oxidative damage is implied in perinatal hypoxic-ischemic brain injury, most importantly in white matter. Nonprotein-bound iron (NPBI) catalyzes the formation of toxic hydroxyl radicals. We measured the extracellular level of NPBI through microdialysis in the cortex, striatum, and periventricular white matter before, during and after severe hypoxia in newborn pigs. NPBI was analyzed by a new spectrophotometric method in which ferrous iron is chelated by bathophenanthroline. NPBI was present in all brain areas under baseline conditions and increased in white matter from 0.97 (0.69) to 2.75 (1.85) micromol/l (not corrected for recovery rate) during early reoxygenation. NPBI may contribute to oxidative injury after perinatal hypoxic insults.

Stem cells for neurodegenerative disorders: where can we go from here?

The use of stem cells in cell replacement therapy for neurodegenerative diseases has received a great deal of scientific and public interest in recent years. This is due to the remarkable pace at which paradigm-changing discoveries have been made regarding the neurogenic potential of embryonic, fetal, and adult cells. Over the last decade, clinical fetal tissue transplants have demonstrated that dopaminergic neurons can survive long term and provide functional clinical benefits for patients with Parkinson's disease. Pluripotent embryonic stem cells and multipotent neural stem cells may provide renewable sources that could replace these primary fetal grafts. Considerable advancement has been made in generating cultures with high numbers of neurons in general and of dopaminergic neurons using a varied array of techniques. However, much of this encouraging progress still remains to be tested on long-term expanded human cultures. Further problems include the low survival rate of these cells following transplantation and the tumorigenic tendencies of embryo-derived cells. However, pre-differentiation or genetic modification of stem cell cultures prior to transplantation may help lead to the generation of high numbers of cells of the desired phenotype following grafting. Boosting particular factors or substrates in the culture media may also protect grafted neurons from oxidative and metabolic stress, and provide epigenetic trophic support. Possible endogenous sources of cells for brain repair include the transdifferentiation of various types of adult cells into neurons. Despite the excitement generated by examples of this phenomenon, further work is needed in order to identify the precise instructive cues that generate neural cells from many other tissue types, and whether or not the new cells are functionally normal. Furthermore, issues such as cell homogeneity and fusion need to be addressed further before the true potential of transdifferentiation can be known. Endogenous stem cells also reside in the neurogenic zones of the adult brain (ventricle lining and hippocampus). Further elucidation of the mechanisms that stimulate cell division and migration are required in order to learn how to amplify the small amount of new cells generated by the adult brain and to direct these cells to areas of injury or degeneration. Finally, a more fundamental understanding of brain injury and disease is required in order to circumvent local brain environmental restrictions on endogenous cell differentiation and survival.

Oxidative damage after severe head injury and its relationship to neurological outcome

OBJECTIVE

We sought to establish the time course of reactive oxygen species after severe head injuries in humans and to investigate their relationship with clinical outcomes.

METHODS

Both the markers of oxidative damage-malonylaldehyde (MDA) and the enzymatic and nonenzymatic antioxidant defenses (i.e., superoxide dismutase [SOD] and vitamin E [VE], respectively)-were studied. To assess the time course of MDA, SOD, and VE, jugular bulb (JB) and peripheral venous blood samples were obtained from 30 patients within 8 hours of severe head trauma onset (T(0)) and 6 (T(1)), 12 (T(2)), 24 (T(3)), and 48 hours (T(4)) after trauma onset. Patients were divided into good and poor outcome groups according to their 6-month neurological outcome as determined on the basis of their Glasgow Outcome Scale scores and biochemical profiles.

RESULTS

In JB samples, MDA levels increased significantly at T(1), T(2), T(3), and T(4) as compared with T(0); SOD activity increased significantly at T(2) and T(3) as compared with T(0); and VE levels decreased significantly at T(1), T(2), and T(3) as compared with T(0). The same variables did not change significantly over time in peripheral venous blood samples. Moreover, the MDA levels and SOD activity detected in JB samples were significantly higher in the poor outcome group at T(1) and T(2). No significant difference in VE levels was observed between the two outcome groups.

CONCLUSION

Reactive oxygen species-mediated oxidative damage can play an important role in determining the prognosis of severe brain injury in humans.

Subcellular localization of a glutathione-dependent dehydroascorbate reductase within specific rat brain regions

Recently, we described the occurrence of a dehydroascorbate reductase within the rat CNS. This enzyme regenerates ascorbate after it is oxidized during normal aerobic metabolism. In this work, we describe the neuronal compartmentalization of the enzyme, using transmission electron microscopy of those brain areas in which the enzyme was most densely present when observed under light microscopy. In parallel biochemical studies, we performed immunoblotting and measured the enzyme activity of the cytoplasm and different nuclear fractions. Given the abundance of ascorbate in the caudate-putamen, we focused mostly on the occurrence of dehydroascorbate reductase at the striatal subcellular level. We also studied cerebellar Purkinje cells, hippocampal CA3 pyramidal cells and giant neurons in the magnocellular part of the red nucleus. In addition to neurons, immunolabeling was found in striatal endothelial cells, in the basal membrane of blood vessels and in perivascular astrocytes. In neuronal cytosol, the enzyme was observed in a peri-nuclear position and on the nuclear membrane. In addition, in both the striatum and the cerebellum, we found the enzyme within myelin sheets. Dehydroascorbate reductase was also present in the nucleus of neurons, as further indicated by measuring enzyme activity and by immunoblotting selected nuclear fractions. Immunocytochemical labeling confirmed that the protein was present in isolated pure nuclear fractions. Given the great amount of free radicals which are constantly generated in the CNS, the discovery of a new enzyme with antioxidant properties which translocates into neuronal nuclei appears to be a potential starting point to develop alternative strategies in neuroprotection.

Non-invasive measurement of chemotherapy drug concentrations in tissue: preliminary demonstrations of in vivo measurements

Measurements of the tissue concentrations of two chemotherapy agents have been made in vivo on an animal tumour model. The method used is based on elastic scattering spectroscopy (ESS) and utilizes a fibre-optic probe spectroscopic system. A broadband light source is used to acquire data over a broad range of wavelengths and, therefore, to facilitate the separation of absorptions from various chromophores. The results of the work include measurements of the time course of the drug concentrations as well as a comparison of the optical measurements with high performance liquid chromatography (HPLC) analysis of the drug concentrations at the time of sacrifice. It is found that the optical measurements correlate linearly with HPLC measurements, but give lower absolute values.

Kainic acid causes redox changes in cerebral cortex extracellular fluid: NMDA receptor activity increases ascorbic acid whereas seizure activity increases uric acid

Kainic acid (KA) causes seizures and extensive brain damage in rats. To study the effects of KA on the redox state in cerebral cortex extracellular fluid (ECF), ascorbic and uric acid concentrations were measured in intracerebral microdialysis samples before and after systemic KA administration (ip). During seizures, concentrations of ascorbic and uric acid increased 500 and 100%, respectively. When midazolam was given with KA to prevent seizures, ascorbic acid still increased 400%, but uric acid increased only transiently. When the NMDA receptor antagonist aminophosphonovaleric acid (APV) was included in the microdialysis perfusion media, ascorbic acid levels decreased during baseline perfusion in a concentration-dependent manner. APV then suppressed the KA-induced increase in ascorbic acid levels, without blocking seizure activity. In summary, increased uric acid levels in brain ECF activity after KA administration are related to the induced seizure, but ascorbic acid levels are associated with NMDA receptor activity.