Compartmentation of lysosomes in neurones and neuropil and a new neuronal marker

Brain lysosomal hydrolases in neuronal ceroid-lipofuscinoses

Although the neuronal ceroid-lipofuscinoses (NCLs) are often referred to as lysosomal storage disorders, information on brain lysosomal hydrolases in NCLs is not available. We have determined the specific activities of several acid hydrolases in postmortem brain gray matter of infantile (INCL), late infantile (LINCL), juvenile (JNCL), and adult (ANCL) forms of NCL, patients affected with other neurological disorders (ON), and normal controls. The specific activities of beta-hexosaminidase A and B were significantly high in JNCL gray matter, whereas in LINCL, the increase is significant only in beta-hexosaminidase compared to the controls. A significant increase in the activities of alpha-mannosidase, beta-glucuronidase, and acid phosphatase was also observed in LINCL and JNCL patients compared to the control values. beta-galactosidase activity was also found to be elevated in JNCL brains over the controls. In contrast, activities of beta-glucosidase and sialidase appeared to be lowered in INCL and LINCL. On the other hand, alpha-fucosidase, beta-mannosidase, and sulfatase were unaffected in NCLs brains. Thus, the present data indicate NCLs related abnormalities in some of the acid hydrolases in brain gray matter, which are primarily glycoproteins of lysosomal origin. These data in conjuction with the reported association of sphingolipid activator proteins (SAP) A and D and lysosomal glycoproteins with NCL storage bodies imply abberations in the glycoconjugate metabolism and lysosomal function.

Eicosanoid formation in the rat cerebral cortex. Contribution of neurons and glia

Despite the extensive literature on brain eicosanoids, no information is available on the cellular source of individual compounds in the mature organ and the relative contribution of different cell types to the total synthetic product. To address this problem, neurons and glia were isolated from the cerebral cortex of the adult rat by a process comprising, in order, trypsinization, selective sieving, differential centrifugation, and density gradient centrifugation. Enrichment of cells in the appropriate fractions was verified by morphological, immunocytochemical, and biochemical criteria. Both neuron- and glia-rich fractions retained synthetic activity throughout the period of incubation (max. 60 min). Among the eicosanoids examined, prostaglandin (PG) E2 was the predominant compound, followed by leukotriene (LT) E4 and thromboxane (TX) B2, whereas LTC4 occurred in minimal amounts. Although the rank order of eicosanoids did not vary with the cell type, absolute values of PGE2 and TXB2 were greater with neurons. PGE2 synthesis was increased by supplementation of the medium with arachidonic acid (2.6 microM), whereas indomethacin (5.6 microM) had the opposite effect. Conversely, LT synthesis was not altered by arachidonic acid and was only marginally reduced by the 5-lipoxygenase inhibitor, U-60,257 (10 microM). Several agonists (12-O-tetradecanoyl-phorbol-13-acetate, TPA; Ca ionophore A23187; platelet-activating factor; endotoxin; recombinant IL-1) were tested on both neuron- and glia-rich fractions but none of them had an effect. We conclude that freshly isolated neurons and glia are viable insofar as the basal rate of eicosanoid synthesis is concerned. No qualitative difference was noted between the two cell types in the spectrum of products formed and the spectrum itself accorded with early data on the biosynthetic activity of the intact tissue in vivo. Our isolation procedure appears useful for the analysis of the cellular source of eicosanoids under resting conditions, although it cannot be applied to the study of the site and mode of action of activators.

Changes of phospholipid-metabolizing and lysosomal enzymes in hypoglossal nucleus and ventral horn motoneurons during regeneration of craniospinal nerves

In order to study the biochemical changes associated with the cell body response to axonal crush injury, two systems, hypoglossal nucleus and spinal cord ventral horn, were used. The time intervals chosen were 7, 14, and 28 days after unilateral crushing of the right hypoglossal nerve and cervicothoracic nerves of the rabbit. Non-crushed, contralateral nerves were used as controls. Three groups of enzyme activities were tested: (a) phospholipase A2, acyl CoA:2-acyl-sn-glycero-3-phosphocholine acyltransferase, and choline phosphotransferase, as indicators of phospholipid degradation and biosynthesis; (b) seven hydrolases, namely, beta-D-glucuronidase, beta-N-acetyl-D-hexosaminidase, arylsulfatase A, galactosylceramidase, GM1-ganglioside beta-galactosidase, and acid RNase, as indicators of lysosomal activity; and (c) free and inhibitor-bound alkaline RNase, as an index of RNA metabolism. Changes could be grouped into three distinct patterns. Compared to contralateral control, choline phosphotransferase showed a slight increase, whereas phospholipase A2 and most lysosomal hydrolases showed a significant increase of activity, especially evident in the ventral spinal cord neurons 14-28 days after crushing. These changes correlate with known increases of membrane and organelle numbers, including lysosomes, in motor and sensory neurons during peripheral regeneration. In contrast, free and acid alkaline RNase activity significantly decreased in the injured sides compared to the controls. This change can probably be correlated with a stabilization of RNAs needed for increased protein synthesis. No changes in total alkaline RNase and acyltransferase activities in either regeneration model were observed.

Subcellular pathology of human neurodegenerative disorders: Alzheimer-type dementia and Huntington's disease

Activities of enzyme markers of subcellular organelles have been measured in brain tissue from subjects with Alzheimer-type dementia (ATD) and Huntington's disease (HD). Significant increases in the activity of the lysosomal enzyme beta-glucuronidase were observed in both ATD temporal cortex and HD putamen. It is suggested that beta-glucuronidase activity may be a useful biochemical indicator of cellular damage in the CNS. A significant reduction in neutral alpha-glucosidase activity was observed in ATD temporal cortex and HD putamen. This change may reflect an alteration in glycoconjugate processing and may relate to the susceptibility of neurones to the degenerative processes of ATD and HD.

beta-Glucosidase and beta-galactosidase in primary cultures of rat astrocytes: comparison to the brain enzymes

In primary astrocyte cultures beta-glucosidase (EC 3.2.1.21) and beta-galactosidase (EC 3.2.1.23) showed pH optima and Km values identical to rat brain enzymes, using methylumbelliferyl glycosides and labeled gluco- and galactocerebrosides as substrates. The activities of both glycosidases increased in culture up to 3-4 weeks. In rat brain only galactosidase increased; glucosidase activity declined between 12-20 days after birth. The specific activities were two- to sixfold higher in astrocyte cultures than in rat brain. These activities were not due to uptake of enzymes from the growth medium. Secretion of beta-galactosidase, but not beta-glucosidase nor acid phosphatase could be demonstrated. These results support the suggestion of a degradative function for astrocytes in the brain.

Isolation of protoplasmic astrocytes: a procedure based on controlled trypsin digestion

Trypsinization of rat brain tissue for shorter (10 min) and longer (60-90 min) periods is shown to yield two distinctly different types of dissociated cell populations. The over-all yield of intact dissociated cells declines when the period of trypsinization exceeds 10 min. Comparison of the types of dissociated cells obtained after different lengths of trypsinization indicates that the protoplasmic astrocytes, which represent the bulk of the neuroglial cells in brain, are highly susceptible to degradation during tissue trypsinization. Based on this observation, a new procedure involving controlled trypsin digestion for tissue disruption and Percoll gradient centrifugation has been developed for the isolation of virtually pure populations of intact protoplasmic astrocytes (97-98% particle purity). Identification of the purified cells is based on morphological, histochemical staining, and biochemical (marker enzyme) characteristics.

Effects of denervation and axotomy on nervous system-specific protein, ornithine decarboxylase, and other enzyme activities in the superior cervical sympathetic ganglion of the rat

The time courses of changes of three enolase isozymes (alpha alpha, alpha gamma, and gamma gamma), S-100 protein, 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), ornithine decarboxylase (ODC), beta-galactosidase, and glucose-6-phosphate dehydrogenase (G6PDH) were examined from 1 to 14 days after cutting of the preganglionic nerve (denervation) or the postganglionic nerve (axotomy) of the superior cervical sympathetic ganglion (SCG) of the rat. The wet weight and protein content in the axotomized SCG increased continuously, to nearly twice those of the denervated SCG for 1-2 weeks after the operations. Among enolase isozymes in the SCG, neuron-specific gamma gamma-enolase decreased rapidly after denervation and stayed at a low level for 2 weeks, whereas the isozyme remained almost unchanged after axotomy. On the contrary, ganglionic alpha alpha-enolase and the alpha gamma-hybrid form increased remarkably to reach a maximum at the second day after axotomy, and remained above control for 1 to 2 weeks; these two enolase isozymes showed little change after denervation. Denervation caused a much larger increase than did axotomy in the ganglionic S-100 protein, an astrocyte-specific protein, during the first week after the operation, while the protein content decreased after 2 weeks of either denervation or axotomy. CNPase, a myelin-associated enzyme, rose suddenly 2 days after axotomy, and remained at a rather high level compared with the denervated ganglion, which showed little variation.(ABSTRACT TRUNCATED AT 250 WORDS)

Subcellular distribution of diacylglycerol lipase in rat and mouse brain

Rat Brain has a lipase which hydrolyzes diacylglycerol at an optimal pH of 4.8 (1). The subcellular distribution of this acid diacylglycerol lipase was studied in brain tissue of rats and mice; in the latter case neurological mutants and their normal controls were used. Several other acidic hydrolases were employed as normal controls were used. Several other acidic hydrolases were employed as lysosomal markers. In mouse brain, the specific activity which is about 50-100 times lower than in rat brain, was greatest in the lysosomal fraction. In contrast, no enrichment of DG-lipase was observed in any subcellular fraction of the active enzyme of rat brain. Activities were about equally distributed in the microsomal, myelin-synaptosomal and lysosomal fractions.

DNA content and enzymic activities in the auditory regions of seizure-susceptible and non-susceptible strains of mice

The developmental profiles of four glycosidase enzymes (beta-D-glucosidase, beta-D-glucuronidase, beta-D-N-acetylglucosaminidase and beta-D-galactosidase) in the cochleas, cochlear nuclei and inferior colliculi of four strains of mice were investigated. The strains used were an audiogenically seizure-susceptible strain (DBA/2) and three non-susceptible strains (BALB/c, C3H/He and Swiss/A2G). The enzymic activities fell to varying degrees from 7 to 28 days of age. Two significant observations were made--beta-D-glucuronidase was low in the regions of the C3H/He strain, and beta-D-galactosidase was particularly low in the regions of the DBA/2 strain. The very low activity of beta-D-galactosidase in the DBA/2 mice is discussed in relation to the ganglioside patterns known to be present in these seizure-susceptible mice. Studies on the DNA contents of these auditory regions in the four strains showed no correlation with seizure sensitivity.

Selective loss of Purkinje cells from the rat cerebellum caused by acrylamide and the responses of beta-glucuronidase and beta-galactosidase

Acrylamide (30 mg/kg) given daily to rats five times each week for 3 weeks leads to progressive loss of Purkinje cells. The necrotic cells begin to be visible from the third day and their numbers reach a peak at the time when the dosing ceases at 18 days. They are less frequent thereafter, but are still visible almost 3 weeks later in small numbers. The density of Purkinje cells per millimeter falls to about 70% of normal at the 7th day, and a similar degree of reduction of the neuronal marker enzyme, beta-galactosidase, is found over the same time scale. By contrast, while there is a brisk macrophage/microglial response in the molecular layer to the loss of the Purkinje cell dendrites, the increase in beta-glucuronidase activity is relatively minor and is not significantly different from normal until after the 21st day. These responses are discussed in the context of the use of lysosomal enzyme activities in the assay of certain neurotoxic lesions.

A biochemical assessment of the neurotoxicity of the radiosensitizing drug misonidazole in the rat

We have obtained biochemical evidence that misonidazole when administered in large doses to rats produces a sparse dying-back peripheral neuropathy and degenerative changes in the trigeminal ganglia and cerebellum. In our experience these neurotoxic effects of misonidazole cannot be detected reliably by the use of simple behavioural and functional tests, e.g., inclined plane and narrowing bridge tests (Rose and Dewar, unpublished results). Therefore, these methods would be of limited use in the neurotoxicity screening of misonidazole analogues. On the other hand, the biochemical approach provides a convenient quantitative method which could be used as the basis for comparing the neurotoxicity of other candidate radiosensitizing drugs.

Glycerophospholipid metabolism in neuronal and glial cell-enriched fractions

The metabolism of phospholipids in separated glial and neuronal cells has been reviewed in this paper. Lipids are more abundant in glia; on the other hand, in vivo experiments performed with labeled precursors have indicated that lipid turnover is faster in neurons (with the possible exception of oligodendroglia). Biosynthetic and catabolic enzymes of lipid metabolism have been studied in separated cells (mainly in neurons and astroglia) and have been shown to be almost always more active in neurons. Also base exchange is probably more active in these cells. Therefore the results of in vitro and in vivo experiments indicate that neurons are more active than astroglia in metabolizing glycerophospholipids.

Transported enzymes in sciatic nerve and sensory ganglia of rats exposed to maternal antibodies against nerve growth factor

The accumulations by axoplasmic transport of selected enzyme activities proximal and distal to a ligature placed on the sciatic nerve were monitored in rats exposed in utero to maternal antibodies to nerve growth factor (NGF) and in control rats. Littermates of the animals exposed to anti-NGF were shown elsewhere to have had a 70% reduction in the number of sensory neurons in dorsal root ganglia and a 90% reduction in number of neurons in superior cervical (sympathetic) ganglion. The accumulation of F(-)-sensitive acid phosphatase activity was depressed 75% both proximal and distal to the tie. Accumulation of F(-)-resistant acid phosphatase activity was depressed nearly 50% proximal to the tie. Distal accumulation of this activity did not occur in either group of rats. Accumulation of acetylcholinesterase activity was depressed 30%. Distal accumulation of the activities of beta-glucuronidase and hexokinase was depressed 50%. In the lumbar dorsal root ganglia, dry weight was reduced 40%, and the activities of peroxide-sensitive, F(-)-resistant acid phosphatase and of the mitochondrial enzymes hexokinase, glutamic dehydrogenase, glutamic-oxalacetic transaminase, and NAD-dependent isocitric dehydrogenase were all reduced a little more, 45--50% per ganglion. However, the activities of the lysosomal enzymes, F(-)-sensitive acid phosphatase and beta-glucuronidase, of the peroxide-resistant, F(-)-resistant acid phosphatase, and of the mitochondrial enzyme glutaminase were all reduced about 60% per ganglion. The results of these measurements were interpreted to suggest that much, and perhaps all, of the F(-)-sensitive acid phosphatase activity in motion in peripheral nerve in rat is confined to sensory axons.

A biochemical method for assessing the neurotoxic effects of misonidazole in the rat

A proven biochemical method for assessing chemically induced neurotoxicity has been applied to the study of the toxic effects of misonidazole (MISO) in the rat. This involves the fluorimetric measurement of beta-glucuronidase and beta-galactosidase activities in homogenates of rat nervous tissue. The tissues analysed were sciatic/posterior tibial nerve (SPTN) cut into 4 sections, trigeminal ganglia and cerebellum. MISO administered i.p. to Wistar rats in doses greater than 300 mg/kg/day for 7 consecutive days produced maximal increases in both beta-glucuronidase and beta-galactosidase activities in th SPTN at 4 weeks (140-180% of control values). The highest increases were associated with the most distal secretion of the nerve. Significant enzyme-activity changes were also found in the trigeminal ganglia and cerebellum of MISO-dosed rats. The greatest activity occurred 4-5 weeks after dosing, and was dose-related. It is concluded that, in the rat, MISO can produce biochemical changes consistent with a dying-back peripheral neuropathy, and biochemical changes suggestive of cerebellar damage. This biochemical approach would appear to offer a convenient quantitative method for the detection of neurotoxic effects of other potential radio-sensitizing drugs.

Lysosomal acid hydrolases in developing human brain regions

beta-D-Glucosidase, beta-D-glucosaminidase, acid phosphatase, and beta-D-galactosidase were monitored in the human foetal brain at different gestational periods. Glucosidase specific activity in all brain regions exhibits two peaks, at 8 g and 32 g foetal weights. Acid phosphatase exhibits very high specific activity in all brain regions at 5 g, but the cerebellar activity forms a peak at 220 g foetal weight, the midbrain at 135 g, and the spinal activity at 760 g. beta-D-Glucosaminidase has a peak at 220 g and 660 g in the midbrain, and beta-D-galactosidase specific activity is highest in the cortex and cerebellum in late gestation (neuronal differentiation phase). The midbrain medulla and the spinal cord show peak activity at 8 g and 220 g foetal weight. The results suggest an inter- and intraregional heterogeneity of acquisition for these enzymes in human brain ontogeny.

Lysosomal enzymes in cerebral atrophy

In seven patients with cerebral atrophy due to pre-senile dementia and/or cerebrovascular disease, the activity of acid phosphatase in lumbar cerebrospinal fluid (CSF) was higher (p less than 0.05) than in six controls. The activity of arylsulphatase and beta-galactosidase in CSF was the same in the two groups. In the serum, the activities of acid phosphatase and arylsulphatase were the same in the two groups but the activity of beta-galactosidase was lower (p less than 0.02) in patients with cerebral atrophy.

Neurochemical and morphological changes during the development of cobalt-induced epilepsy in the rat

Following the implantation of cobalt-gelatine pellets into the frontal cortex, epileptiform spikes in both primary and secondary foci developed and reached a peak between 7-12 days post implantation. Histological examination showed a necrotic lesion with terminal and fibre degeneration in brain areas connected with the frontal cortex. Golgi staining at 60 days showed a loss of pyramidal cells in the primary focal area. In the lesion and primary focal areas GABA, glutamate and aspartate were significantly reduced between 5--10 days post implantation. No changes in glutamine and glycine were found in either the lesion or pulmonary focus. No changes in amino acid content were found in the secondary focus or in glass implanted controls at any time. In cobalt-treated rats there were significant reductions in the transmitter related enzymes, glutamate decarboxylase, acetylcholinesterase, choline acetyltransferase and aromatic amino acid decarboxylase in the lesion area and primary and secondary foci at 4--8 days post implantation. Levels of these enzymes had recovered to normal by 24 days. Lactate dehydrogenase was reduced only in the lesion area. Beta-Galactosidase was reduced in the lesion area at 4 days but subsequent rose rapidly paralleling increasing gliosis around the lesion. It is concluded that cobalt-induced epilepsy is associated with relatively selective loss of neuronal tissue and provides a useful model for further investigation relevant to clinical epilepsy.

Cellular compartmentation of brain metabolism and its functional significance

This paper reviews work from our laboratory on the metabolism and interrelations of isolated neuronal and neuropil fractions. The cell preparations are evaluated according to criteria of yield, purity, and integrity. Differences in the levels of activity of six groups of enzymes, of glucose metabolism, amino-acid metabolism, transmitter metabolism, acid hydrolysis, alkaline hydrolysis, and carbonic anhydrase have been followed, and neuronal and glial marker enzymes are proposed. Lysosomes and their enzymes are concentrated in neuronal perikarya. Metabolically, although no major differences in glucose oxidation have been found, there is considerable evidence of compartmentation of amino acids and their metabolism. At short times after injection of 3H-lysine as precursor in vivo, neuronal incorporation is high as compared with neuropil; at longer times the ratio is reversed, and we interpret this as evidence for the presence of a rapidly labeling protein fraction present in the neuromal perikarya but subsequently transported out. Neuronal protein incorporation is suppressed in the visual but not the motor cortex of dark-reared rats and is switched on following exposure to light; there is evidence that the suppressed fraction of neuronal protein synthesis includes the rapidly labeling component. A model for neuronal-glial metabolic interaction and its state-dependence in response to changes in the organism's environment and behavior is sketched out.