Differential expression of peroxiredoxin subtypes in human brain cell types.

The peroxiredoxin (Prx) protein is expressed widely in animal tissues and serves an antioxidant function associated with removal of cellular peroxides. We have cloned two Prx genes and observed differential expression of Prx-I and Prx-II (formerly NKEF-A and NKEF-B) in purified rat brain cell cultures (Sarafian et al. [1998] Mol. Chem. Neuropathol. 34:39-51). We have examined regional and cell-type-specific expression of Prx-I and Prx-II in paraffin sections of human brain using immunohistochemical methods. These studies revealed a clear segregation of expression of these two gene products in different brain cell types. In the cerebral cortex, cerebellum, basal ganglia, substantia nigra, and spinal cord, Prx-I was expressed primarily in astrocytes, while Prx-II was expressed exclusively in neurons. Prx-I was also prominently expressed in ependymal cells and subependymal matrix of substantia nigra and basal ganglia. Prx-II was not expressed at uniform density in all neurons. In general, small neurons such as cerebellar granule neurons displayed little or no staining, while large neurons, such as hippocampal pyramidal and Purkinje neurons were heavily stained. The absence of expression of Prx-I in neurons and the selective expression of Prx-II in large neurons suggest that these antioxidant enzymes serve distinct functional roles that may reflect the different functions and biochemical activities of these cell types. Restricted expression of these genes may also contribute to the selective vulnerability of these cells to a wide variety of neuropathologic conditions.

Manganese neurotoxicity: a mechanistic hypothesis.

This review provides a summary of the presentations and abstracts presented at the 15th International Neurotoxicology Conference which may contribute to an understanding of the mechanism and pathogenesis of manganese (Mn2+) neurotoxicity. We propose that an understanding of the pathogenesis of Mn2+ neurotoxicity must incorporate data on (1) the factors controlling Mn2+ uptake and distribution within the CNS, (2) account for the apparent selectivity of dopaminergic neurons, (3) analyze the role of mitochondrial dysfunction and (4) provide data to support or refute the role of oxidative injury in the genesis of toxicity. We propose a multifactor hypothesis coupling Mn2+ uptake with coincident transport of aluminum and iron. Selectivity of dopaminergic neurons is dependent upon interactions of Mn2+ with dopamine transport and the role of Mn2+ as a pro-oxidative toxicant in conjunction with changes in iron concentration. Within the synaptic milieu, Mn(2+)-mitochondrial interaction will influence mitochondrial--Ca2+ transport kinetics leading to defective mitochondrial function, decreased oxidative phosphorylation, decreased ATP and accumulation of reactive oxygen species. Under the influence of excessive depolarization, energy failure will occur leading to secondary activation of an excitotoxic state. These conceptual ideas provide for mechanistic based hypotheses and testing and are likely to lead to rational therapeutic avenues directed against Mn2+ neurotoxicity.

Estriol ameliorates autoimmune demyelinating disease: implications for multiple sclerosis.

OBJECTIVE: To evaluate the use of estriol in the treatment of experimental autoimmune encephalomyelitis (EAE) and other cell mediated autoimmune diseases. BACKGROUND: Experimental autoimmune encephalomyelitis is a T helper 1 (Th1)-mediated autoimmune demyelinating disease that is a useful model for the study of immune responses in MS. Interestingly, both EAE and MS have been shown to be ameliorated during late pregnancy. METHODS: Estriol, progesterone, and placebo pellets were implanted in mice during the effector phase of adoptive EAE. Disease scores were compared between treatment groups, and autoantigen-specific humoral and cellular responses were examined. RESULTS: Estriol treatment reduced the severity of EAE significantly compared with placebo treatment whereas progesterone treatment had no effect. Estriol doses that induced serum estriol levels that approximated estriol levels during late pregnancy were capable of ameliorating disease. Estriol-treated EAE mice had significantly higher levels of serum antibodies of the immunoglobulin (Ig) G1 isotype specific for the autoantigen myelin basic protein (MBP). Further, MBP-specific T-lymphocyte responses from estriol-treated EAE mice were characterized by significantly increased production of the Th2 cytokine interleukin 10 (IL-10). T lymphocytes were shown to be the primary source of IL-10 within antigen-stimulated splenocyte populations. CONCLUSIONS: Estriol as a hormone involved in immune changes during pregnancy may provide a basis for the novel therapeutic use of estriol for MS and other putative Th1-mediated autoimmune diseases that improve during late pregnancy.

Multiple cerebral pseudoaneurysms and hemorrhages: the expanding spectrum of metastatic cerebral choriocarcinoma.

Cerebral metastases occur in 10-20% of patients with choriocarcinoma. Although single oncotic and pseudoaneurysms have been reported, multiple pseudoaneurysms and hemorrhages are rare. A 33-year-old woman developed 10 intracerebral hemorrhages over a 30-day period. Angiogram showed multiple focal areas of delayed contrast washout in distal vessels. Autopsy revealed intravascular choriocarcinoma without true aneurysm formation. A diagnosis of choriocarcinoma should be considered for women of childbearing age presenting with cerebrovascular syndromes, especially those found to have cerebral aneurysm pseudoaneurysm and/or hemorrhage.

Expression of oligodendrocytic mRNAs in glial tumors: changes associated with tumor grade and extent of neoplastic infiltration.

We examined the expression of glial- and neuronal-specific mRNAs within human gliomas using in situ hybridization. We found that low-grade astrocytomas contained a high number of proteolipid protein (PLP) mRNA-positive cells and that the number of PLP-stained cells decreased markedly with increasing tumor grade. Interestingly, the ratio of PLP mRNA-stained cells:myelin basic protein (MBP) mRNA-stained cells in normal white matter and low-grade astrocytoma was about 2:1 but approached 1:1 with increasing tumor grade. This parameter appeared to be a good indicator of tumor infiltration in astrocytomas, so we tested this in the analysis of other gliomas. Unlike astrocytomas, oligodendrogliomas were found consistently to contain few PLP mRNA- or MBP mRNA-expressing cells. In contrast, gemistocytic astrocytomas, typically highly invasive tumors, contained high numbers of PLP-positive cells and a ratio of PLP mRNA:MBP mRNA-stained cells of about 1.5:1, similar to low-grade astrocytomas. Nonradioactive in situ hybridization also enabled the morphological identification of specific cells. For example, gemistocytic astrocytes, which were found to be strongly vimentin mRNA positive, contained little glial fibrillary acidic protein mRNA and did not stain for PLP or MBP mRNAs. Neuronal mRNAs, such as neurofilament 68, were observed in small numbers of entrapped neurons within gliomas but were uninformative with respect to predicting tumor grade. Our results suggest that oligodendrocytes survive low-grade tumor infiltration and that glial tumor cells, unlike cell lines derived from them, do not express oligodendrocyte or neuronal mRNAs. In addition, the expression of mRNAs for the two major myelin protein genes, PLP and MBP, could be used to predict the grade and extent of tumor infiltration in astrocytomas.

Cellular resistance to methylmercury.

The destructive pathologic and biochemical consequences of methyl mercury have been extensively described. Relatively little is known, however, about the defensive mechanisms neurons employ to protect themselves against mercurial injury. Studies using a variety of cell types have disclosed several inducible biochemical responses to heavy metal and pro-oxidant insult. These responses include modulation of cellular levels of glutathione, metallothionein, hemoxygenase, and other stress proteins. With few exceptions, however, neurons appear to be markedly deficient in these responses. This suggests the possibility that the phenomenon of selective vulnerability of cells in the nervous system to mercury and other heavy metals may arise from a critical absence of inherent protective mechanisms. Transfection of neural cells with the anti-apoptotic gene, bcl-2, confers partial resistance to a variety of neurotoxins, including methyl mercury. This approach to providing neuroprotection may represent an efficacious strategy for combating tenacious neurotoxins such as methyl mercury.

bcl-2 expression decreases methyl mercury-induced free-radical generation and cell killing in a neural cell line.

Methyl mercury neurotoxicity is associated with a broad range of neuropathologic and biochemical disturbances which include induction of oxidative injury. Treatment of the hypothalamic neural cell line GT1-7 with 10 microM methyl mercury (MeHg) for 3 h resulted in increased formation of reactive oxygen species (ROS), and decreased levels of reduced glutathione (GSH), associated with 20% cell death. Cells transfected with an expression construct for the anti-apoptotic proto-oncogene, bcl-2, displayed attenuated ROS induction and negligible cell death. Twenty-four-h exposure to 5 microM MeHg killed 56% of control cells, but only 19% of bcl-2-transfected cells. By using diethyl maleate to deplete cells of GSH, we demonstrate that the differential sensitivity to MeHg was not due solely to intrinsically different GSH levels. The data suggest that MeHg-mediated cell killing correlates more closely with ROS generation than with GSH levels and that bcl-2 protects MeHg-treated cells by suppressing ROS generation.

Lidocaine delays cortical ischemic depolarization: relationship to electrophysiologic recovery and neuropathology.

To determine if the previously reported limitation of i.v. lidocaine in facilitating recovery from cerebral ischemia was related to an effect on ischemic depolarization, we recorded cortical DC potential, electrocorticogram (ECoG) or EEG, and evoked potentials in rabbits subjected to either 3 or 5 min of complete ischemia. Three control animals undergoing 3 min of ischemia and all animals subjected to 5 min of ischemia were continuously monitored under anesthesia for 24 h, at which time the brains were processed for neocortical histology. Complete ischemia was produced by occlusion of the basilar artery and cervical collateral vessels followed by transient snare occlusion of the brachiocephalic trunk. In control animals of either ischemic duration, the onset of ischemic depolarization occurred at 102 +/- 5 s (n = 18). In animals receiving 0.2 mg/kg/min lidocaine infusion, the negative DC shift was delayed to 182 +/- 28 s (n = 7) in animals with 3-min ischemia and 195 +/- 15 s (n = 9) in lidocaine animals with 5 min ischemia (p < .01 and p < .0005 respectively, compared to controls of the same ischemic duration). In 3-min ischemia, lidocaine also reduced the amplitude of the DC shift from 8.9 +/- 0.4 mV to 4.6 +/- 1.1 mV (p < .005), whereas in 5-min ischemia there was no significant difference in the amplitude of the shift between lidocaine and control animals (11.1 +/- 1.4 and 12.7 +/- 1.0 mV, respectively). Lidocaine shortened the isoelectric EEG duration and hastened the recovery of evoked potentials in animals with 3-min ischemia; with 5-min ischemia, however, there was no significant difference in the recovery of either type of electrical activity between control and lidocaine-treated animals. Significant correlations were found between the recovery of cortical electrical activity (both spontaneous and evoked) and the amplitude or integral of the ischemic depolarization shift (p < .001 in each case). Postischemic epileptiform bursts accompanied by negative DC shifts occurred in 3/7 controls and 4/7 lidocaine animals after reperfusion for > 12 h following 5-min ischemia. There was no significant difference in the degree of cortical neuronal injury or status spongiosus found between lidocaine and control animals subjected to 5-min ischemia and 24 h reperfusion. Cortical injury in control animals with 3-min ischemia was negligible and not significantly different from sham-operated animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Posterior cortical atrophy. Neuropathologic correlations.

OBJECTIVE: A subgroup of patients with progressive dementia has been reported with a marked predominance of symptoms attributed to the dysfunction of the posterior parieto-occipital cortex. These cases have been referred to as posterior cortical atrophy. The objective of this study was to determine whether posterior cortical atrophy is associated with distinct, uniform neuropathologic findings. DESIGN: Three individuals with progressive dementia that began with higher visual dysfunction (posterior cortical atrophy) were followed up to definitive neuropathologic diagnosis. RESULTS: Three separate neuropathologic entities were discovered: subcortical gliosis, Alzheimer's disease, and Creutzfeldt-Jakob disease. CONCLUSION: Posterior cortical atrophy is a clinically homogeneous but pathologically heterogeneous syndrome.

Phospholipase A2 stimulation by methyl mercury in neuron culture.

In primary prelabeled cultures of cerebellar granule cells, methyl mercury (MeHg) induced a concentration- and time-dependent release of [3H]arachidonic acid. MeHg-induced [3H]arachidonate release was partially dependent on the extracellular Ca2+ concentration. MeHg at 10-20 microM also stimulated basal 45Ca2+ uptake after 20 min of incubation at 37 degrees C, and at 10 microM inhibited K+ depolarization-stimulated uptake. MeHg stimulated [3H]arachidonate uptake, but had no effect on the rate of phospholipid reacylation. Phospholipase A2 (PLA2) activation preceded cytotoxicity, but at higher concentrations of MeHg such dissociation was not evident. Inhibition of MeHg-induced PLA2 activation by 100 microM mepacrine failed to modify cytotoxicity. MeHg-induced lipoperoxidation, measured as the production of thiobarbituric acid-reacting products, was inhibited by alpha-tocopherol without inhibition of [3H]arachidonate release. The absence of alpha-tocopherol inhibition of MeHg-induced arachidonate release precludes a causal role for lipoperoxide-induced PLA2 activation in this system. Moreover, MeHg induced an increased susceptibility of unilamellar vesicles to exogenous PLA2 in the presence of low Ca2+ concentrations without evidence of lipid peroxidation. [3H]Arachidonate incorporation into granule neuron phospholipids was analyzed by isocratic HPLC analysis. Relatively high proportional incorporation was found in the combined phosphatidylcholine fractions and phosphatidylinositol. With MeHg, an increase in the relative specific activity of incorporation was found in the phosphatidylinositol fraction, indicating a preferential turnover in this phospholipid species in the presence of MeHg.

Oxidative damage and repair in the developing nervous system.

Excessive production of reactive oxygen species (ROS) is a recognized cause of cell injury. In contrast to such well recognized cell injury, oxidative stress plays a role in cell proliferation, differentiation and tumor promotion. This review examines the role of oxidative stress in initiating and promoting the establishment of normal or abnormal neuronal patterns and subsequent neurogenesis within the central and peripheral nervous system. In particular, the role of apoptosis in both normal and abnormal neuronal development and maturation will be examined with special reference to the induction of apoptotic cell death following abusive ligand-induced ion movements. The interaction of oxidant stress and immediate-early response gene activation is discussed with further reference to the induction of apoptosis. While glutamate receptor activation appears mandatory for coordinate maturation and neuritogenesis, such neuronal survival and differentiation is intimately dependent upon the intracellular glutathione redox potential, maintained by cystine uptake. Selected examples of reactive oxygen species induced injury pertaining to developmental neurotoxicology are presented and include starvation, irradiation injury and glutamate excitotoxicity.

Primary pineal melanoma: case report.

Primary melanomas of the central nervous system are unusual, and those in the pineal region are exceedingly rare. We present a case of primary pineal melanoma in a 60-year-old man. The lesion was subtotally resected through an infratentorial, supracerebellar approach. The clinical features and the histological findings are discussed. Eight previous case reports are reviewed.

Assay of acyl-CoA dehydrogenase activity in frozen muscle biopsies: application to medium-chain acyl-CoA dehydrogenase deficiency.

The acyl-CoA dehydrogenases (ACDs) are mitochondrial enzymes that dehydrogenate acyl-coenzyme A esters of different chain lengths. Inherited deficiencies of these dehydrogenases are commonly associated with muscle weakness and lipid storage. Numerous assays including spectrophotometric, fluorometric, chemical, and radiochemical procedures have been used, but there is need for a rapid, reproducible assay for the different acyl-CoA dehydrogenases in small frozen samples of human muscle biopsies. We describe a comparative study of dye-linked spectrophotometric assays of the long, medium, and short chain acyl-CoA dehydrogenases in frozen rat and human muscle samples. An optimal procedure is described confirming the value of glass-glass homogenization and assay of a 600g supernatant. Higher activities for all acyl-CoA dehydrogenases, citrate synthase, and cytochrome c oxidase were obtained in rat in contrast to human. The substrate-linked dye reduction method was found superior to the ferricenium or electron transfer flavoprotein acceptor systems. Application of the phenazine ethosulfate-DCPIP-linked method to medium-chain acyl-CoA dehydrogenase (MCAD) was studied in detail and the effect of immunoprecipitation of MCAD allowed for the determination of substrate specificity and the degree of crossover between long-, medium-, and short-chain ACD activity following immunoprecipitation. Finally, a comparison of the specificity and validity of the assay in a patient with MCAD deficiency was performed.

Environmental neurotoxicity of chemicals and radiation.

Epidemiologic and societal concerns continue to stimulate studies in the field of environmental neurotoxicology. Although the role of heavy metals, aluminum, and iron are unclear in the etiology of human neurodegenerative disorders, these toxins have provided fertile ground for in vivo and in vitro experimental studies to elucidate their role in neurotoxic injury. Experimental models of clinical syndromes are discussed with special relevance to developmental neurotoxicology. Cycloleucine, tellurium, and 1,3-dinitrobenzene provide models of subacute combined degeneration, primary peripheral nerve demyelination, and thiamine deficiency-like lesions, respectively. Increasing attention is being given to irradiation neurotoxicity, especially in the developing or young central nervous system. A fuller understanding of the pathogenesis of low-dose irradiation injury allows for a clearer understanding of its neurobiology and also provides a more rational approach to understanding an interventional therapy associated with brain irradiation for childhood neoplasia.

Late onset primary systemic carnitine deficiency exacerbated by carnitine-free parenteral nutrition.

We describe a 21-year-old male with previously normal plasma total and free carnitine levels who developed a deficiency manifest by decreased plasma and muscle total and free carnitine, decreased urine carnitine, severe hepatic steatosis, mediastinal lipomatosis, progressively impaired triglyceride clearance, myopathy and intermittent hypoglycemia. This case demonstrates that systemic carnitine deficiency may occur in some patients receiving long term carnitine-free TPN. Carnitine may be an essential element of the diet in this patient population.