Neurochemical pathology最新文献

Definitive evidence of oxygen radical-mediated lipid peroxidation as a cause of tissue injury in the setting of brain ischemia has proven elusive. We review the experimental data from our own and other laboratories on this subject. Spectroscopic detection of the conjugated diene structure, the earliest structural alteration produced by fatty acid radicalization, is an inconstant and highly focal observation in the recirculated ischemic brain. Alterations of lipid-soluble antioxidants offer an indirect indication of possible free radical reactions. Other inferences of lipid peroxidation have derived from studies of selective disappearance of free fatty acids. Recent studies of tissue conjugated diene in two rat models of thrombotic infarction with acute reperfusion yielded inconsistent evidence for lipid peroxidation, and in rats subjected to 25 min of diffuse forebrain ischemia, no evidence of conjugated diene formation was observed during early recirculation. We conclude that evolving parenchymal injury in these settings is unlikely to derive from spectroscopically observable lipid autoxidation.

Several aspects of the relationships between glycolipids, gliomas, and problems involved in studying these are reviewed. Major problems that currently must be addressed include developing a classification scheme that more accurately predicts the biological behavior of these tumors, obtaining samples representative of the patient's glioma, and identifying appropriate control specimens. Results of analytical studies indicate that the patterns of gangliosides in human glioma tissues generally correlate with the degree of histological malignancy. Some gliomas contain unusual, and perhaps unique, glycolipids. Exogenous glycosphingolipids can alter cell shape and growth, which may involve modulation of growth factor receptors and protein kinases. Tumor glycolipids may also modulate immune functions in patients harboring gliomas. Transfection of nonneural cells with some oncogenes can alter glycolipid metabolism, which may be part of the mechanism through which these oncogenes exert their effects.

Neuroblastomas from children presenting with tumors at various ages and different primary sites (abdominal, adrenals, pelvic, and thoracic) were studied. Analysis of the ganglioside patterns of 53 tumors indicated that patients who were either disease positive 2 yr following surgery or dead of disease, had significantly (p less than 0.005) less GT1b plus GD1b than tumors from patients that were disease free 2 yr post surgery. The presence of GD2 in 45 of the tumors correlates well with the suggestion that it can be used as a marker in neuroblastoma diagnosis. Children with thoracic neuroblastomas have a significantly better prognosis than children with tumors in other anatomic sites. Analysis of the ganglioside composition of these tumors only, indicated that they had a significantly higher (p less than 0.005) concentration of GT1b and GD1b and a significantly lower concentration (p less than 0.025) of monosialogangliosides than those patients who were dead of disease or had persistent disease. These results suggest that low levels of GT1b and GD1b correlate with a poor prognosis. The thoracic neuroblastomas may be comprised of more "differentiated" neuroblastoma cells (ganglioside patterns more similar to the CNS), and this may contribute to the fact that about 85% of children with thoracic neuroblastoma recover. To understand why the ganglioside pattern may serve as a prognostic indicator for neuroblastoma, it is necessary to know whether gangliosides have specific roles in neuronal differentiation. Our approach to this question is to compare the effect(s) of added ganglioside or the corresponding oligosaccharide on neuroblastoma cells. Results obtained suggest that the oligosaccharide from GM1 is able to enhance neuritogenesis by S20Y murine neuroblastoma cells to the same extent that GM1 does.

The availability of specific antibodies and cDNA probes for lysosomal hydrolases has revealed unexpected heterogeneity among the human inherited lysosomal storage diseases. Using alpha-fucosidase and N-acetyl-beta-D-hexosaminidase deficiency variants as examples, it has been determined that a lysosomal hydrolase deficiency can result from DNA deletion mutations, failure to synthesize mRNA because of defective splicing, posttranslational defects in assembly, and synthesis of a precursor enzyme that is prematurely proteolytically degraded through lack of a protective protein. In some cases (fucosidosis), the different genotypes cannot be distinguished phenotypically, whereas in others (beta-hexosaminidoses) the phenotypes can range from infantile neurodegeneration through juvenile motor neuron disease to adult neurodysfunction. Biochemical studies on both diseases have revealed several distinct genotypes. We show that some forms of fucosidosis result from unstable enzyme that can be stabilized by protease inhibitors, whereas partial beta-hexosaminidase deficiencies cannot be corrected by these protease inhibitors.

IgM monoclonal gammopathy has been reported in some patients with motor neuron disease. The monoclonal IgMs in several of the patients bind to the carbohydrate epitope Gal (beta 1-3) GalNAc, which is shared by gangliosides GM1 and GD1b and glycoproteins in the nervous system and crossreacted with Gal (beta 1-3) GlcNAc. They also immunostain spinal cord and gray matter and presynaptic terminals of motor neurons at the neuromuscular junction. The role and mechanisms of action of these antibodies in motor neuron disease is under investigation.

The studies were performed on autopsy material of 18 patients who died between the ages of 70-89 y, and of 5 patients who died between 23-44 ys of age. White matter of the frontal lobe and of oerebellum was submitted for histological and biochemical analysis. The neuropathological data provided a rationale for dividing the material into two subgroups: one including patients mainly with vascular changes in the brain, and the other consisting of patients with senile atrophy of the Alzheimer type. Chemical alterations noted both in frontal lobe and in cerebellum were an increase in lysophosphatidylcholine content and a marked decrease in myelin yield. Additionally, in cerebellum a decrease in sulphatide content was observed. The chemical results were almost identical in the two subgroups of patients, although they differ in neuropathological patterns of lesions. It is emphasized that the general decrease in myelin yield as well as some minor changes in myelin lipid pattern seem to be a sign of aging and are not connected with atrophy of the Alzheimer type.

We examined the effects of age on RNA and lipid formation by whole retina and optic nerve in vitro. Male Wistar rats, aged 4, 12, and 24 mo, were used. From the results obtained the following conclusions may be drawn: 1. In assaying the lipid biosynthesis during aging, a striking difference between the retina and optic nerve clearly emerged; 2. In isolated retina, [3H]uridine incorporation into RNA was relatively constant at the three ages, whereas both [14C]palmitate and [3H]choline incorporation into lipids showed a substantial increase in rats at 24 mo of age compared with those at 4 mo; 3. In contrast, in the optic nerve of the oldest rats, compared with the youngest, a significant decrease of [14C]acetate and [14C]palmitate incorporation into acylglycerols, cerebrosides, and phospholipids was found. Each fatty acid precursor label was incorporated to a proportion that reflected the typical acyl group composition of individual lipids; 4. Following labeling of the optic nerve with [3H]choline, the specific radioactivity of choline-containing phospholipids was drastically decreased with increasing rat age; and 5. The incorporation of [2-3H]glycerol into optic nerve diacylglycerols, PtdEtn, and PtdIns declined with age, whereas no significant change took place in the incorporation into PtdCho. The results strongly support the concept that RNA metabolism of rat retina (most likely photoreceptor cell layer) is not altered during aging; on the contrary, phospholipid synthesis is stimulated in comparison with that of the optic nerve, for which a serious impairment was concomitantly observed. The physiological significance of these responses, and the mechanism by which retinal tissue is spared from the general age derangement of the nervous system, remain to be defined.

The neurological mutant of the paralytic tremor "pt" rabbit is characterized by a reduced amount of myelin to 25-30% of control with no change in specific activity for 2',3'-cyclic nucleotide phosphodiesterase. The ratio of total lipids to protein was higher in "pt" rabbit myelin than in control by about 20%. Analysis of the lipid composition of "pt" rabbit myelin indicated a significantly lower level of galactolipids (by about 30%) and a higher level of gangliosides compared to control. The percentage composition of phospholipids in "pt" myelin was characterized by a lower proportion of acidic phospholipids (polyphosphoinositides, phosphatidic acid, phosphatidylserine). The protein-lipid complex in "pt" rabbit myelin was decreased by about 10-15% compared to control. The ratio by weight of protein to lipid in myelin was 0.24 and 0.20 in control and "pt" rabbit, respectively, but in protein-lipid complex isolated from myelin it was 1.73 in control and 0.72 in "pt" rabbit. Protein-lipid complex isolated from myelin of "pt" rabbit brain contained about 34% less protein and about 16% less acidic phospholipids but neutral phospholipids were increased by 24%. The lipid abnormalities in "pt" rabbit myelin and in the composition of protein-lipid complex may be responsible for the disturbances of myelin formation and compaction in "pt" rabbit.

Chronic systemic exposure of rats to the neuronotoxic compound trimethyltin (TMT) results in increased incorporation of radioactive precursors into retinal proteins and glycoproteins. Because this increased metabolic activity is accompanied by minimal subcellular pathological alterations and almost no neuronal necrosis, we suggested that it may represent an early, reactive (compensatory) response (Brain Res. 398, 298-304; 1986). We have now investigated the development of this metabolic response to TMT in more detail. Beginning at 30 d of age, rats received weekly doses of TMT (4 mg/kg body wt) by gavage for up to 7 wk; rates of incorporation of [35S]methionine and [3H]fucose into retinal proteins and glycoproteins, respectively, were then determined using in vitro retinal incubations. The apparent rates of protein synthesis and glycoprotein glycosylation in retinas from TMT-treated animals were normal or slightly decreased after 1-3 wkly doses, but were increased after 4 doses and more markedly increased after 7 doses. Glycoprotein glycosylation was increased to a greater degree (192% of control after 7 wk of dosing) than was protein synthesis (134% of control). The increased incorporation in retinas from TMT-treated animals persisted when retinas were incubated with "flooding" concentrations of precursor (1 mM), suggesting that these increases were not owing to alterations in the size of retinal precursor pools. The preferential increase in glycoprotein glycosylation was partially owing to a selective increase in glycosylation of two molecular species with apparent mol wt of 32 and 45 KDa. Quantitative autoradiographic analysis of newly synthesized proteins and glycoproteins indicated that the TMT-induced increase in metabolic activity was not specific or selective for any retinal layer or cell type. We suggest that the preferential activation of glycoprotein glycosylation, and in particular the increased glycosylation of the 32 and 45 KDa glycoprotein species, may represent part of a compensatory metabolic response of retinal neurons to TMT-induced neuronal injury.

The effect of fatty acids and lysophospholipids on calcium-activated neutral protease (CANP) was investigated. mu CANP, low calcium ion (microM concentration)-requiring CANP is more strongly inhibited by unsaturated fatty acids than is mCANP--the high calcium ion (mM concentration)-requiring form. Lysophospholipids in concentrations ranging from 10(-5) M to 10(-3) M inhibit mu CANP exclusively, whereas mCANP activity is unaffected or even slightly increased. Calpastatin decreases the activity of mCANP and, in the presence of polyunsaturated fatty acids such as docosahexaenoic acid, the inhibition is not increased. In the presence of lysophosphatidyl-ethanolamine, however, the inhibition of mCANP by calpastatin does not occur. The results indicate that fatty acids and lysocompounds liberated under different physiological and pathological conditions may modulate calcium-activated neutral protease.