Norepinephrine induces glial-specific enzyme activity in cultured plasma glioma cells

Oleic Acid and Hydroxytyrosol Inhibit Cholesterol and Fatty Acid Synthesis in C6 Glioma Cells

Recently, the discovery of natural compounds capable of modulating nervous system function has revealed new perspectives for a healthier brain. Here, we investigated the effects of oleic acid (OA) and hydroxytyrosol (HTyr), two important extra virgin olive oil compounds, on lipid synthesis in C6 glioma cells. OA and HTyr inhibited both de novo fatty acid and cholesterol syntheses without affecting cell viability. The inhibitory effect of the individual compounds was more pronounced if OA and HTyr were administered in combination. A reduction of polar lipid biosynthesis was also detected, while triglyceride synthesis was marginally affected. To clarify the lipid-lowering mechanism of these compounds, their effects on the activity of key enzymes of fatty acid biosynthesis (acetyl-CoA carboxylase-ACC and fatty acid synthase-FAS) and cholesterologenesis (3-hydroxy-3-methylglutaryl-CoA reductase-HMGCR) were investigated in situ by using digitonin-permeabilized C6 cells. ACC and HMGCR activities were especially reduced after 4 h of 25 μM OA and HTyr treatment. No change in FAS activity was observed. Inhibition of ACC and HMGCR activities is corroborated by the decrease of their mRNA abundance and protein level. Our results indicate a direct and rapid downregulatory effect of the two olive oil compounds on lipid synthesis in C6 cells.

Induction of neural differentiation in rat C6 glioma cells with taxol

BACKGROUND

Glioblastoma is a common and aggressive type of primary brain tumor. Several anticancer drugs affect GBM (glioblastoma multiforme) cells on cell growth and morphology. Taxol is one of the widely used antineoplastic drugs against many types of solid tumors, such as breast, ovarian, and prostate cancers. However, the effect of taxol on GBM cells remains unclear and requires further investigation.

METHODS

Survival rate of C6 glioma cells under different taxol concentrations was quantified. To clarify the differentiation patterns of rat C6 glioma cells under taxol challenge, survived glioma cells were characterized by immunocytochemical, molecular biological, and cell biological approaches.

RESULTS

After taxol treatment, not only cell death but also morphological changes, including cell elongation, cellular processes thinning, irregular shapes, and fragmented nucleation or micronuclei, occurred in the survived C6 cells. Neural differentiation markers NFL (for neurons), β III-tubulin (for neurons), GFAP (for astrocytes), and CNPase (for oligodendrocytes) were detected in the taxol-treated C6 cells. Quantitative analysis suggested a significant increase in the percentage of neural differentiated cells. The results exhibited that taxol may trigger neural differentiation in C6 glioma cells. Increased expression of neural differentiation markers in C6 cells after taxol treatment suggest that some anticancer drugs could be applied to elimination of the malignant cancer cells as well as changing proliferation and differentiation status of tumor cells.

Type II arginine methyltransferase PRMT5 regulates gene expression of inhibitors of differentiation/DNA binding Id2 and Id4 during glial cell differentiation

PRMT5 is a type II protein arginine methyltranferase that catalyzes monomethylation and symmetric dimethylation of arginine residues. PRMT5 is functionally involved in a variety of biological processes including embryo development and circadian clock regulation. However, the role of PRMT5 in oligodendrocyte differentiation and central nervous system myelination is unknown. Here we show that PRMT5 expression gradually increases throughout postnatal brain development, coinciding with the period of active myelination. PRMT5 expression was observed in neurons, astrocytes, and oligodendrocytes. siRNA-mediated depletion of PRMT5 in mouse primary oligodendrocyte progenitor cells abrogated oligodendrocyte differentiation. In addition, the PRMT5-depleted oligodendrocyte progenitor and C6 glioma cells expressed high levels of the inhibitors of differentiation/DNA binding, Id2 and Id4, known repressors of glial cell differentiation. We observed that CpG-rich islands within the Id2 and Id4 genes were bound by PRMT5 and were hypomethylated in PRMT5-deficient cells, suggesting that PRMT5 plays a role in gene silencing during glial cell differentiation. Our findings define a role of PRMT5 in glial cell differentiation and link PRMT5 to epigenetic changes during oligodendrocyte differentiation.

Docosahexaenoic acid supplementation induces dose and time dependent oxidative changes in C6 glioma cells

In view of the promising use of n-3 polyunsaturated fatty acids (PUFAs) in the prevention and treatment of neurological diseases, it is necessary to ascertain the lack of detrimental oxidative effects. We evaluated short- and long-term effects of 25, 50 and 75 muM docosahexaenoic acid (DHA) supplementation on the oxidative status of C6 glial cells. DHA was incorporated into cells dose and time dependently without any cytotoxic effect. Reactive oxygen species (ROS) level was related to DHA dose and supplementation time. At the lowest dose no significant increase in ROS values was observed at hour 24. Low doses of DHA strengthened the cellular antioxidant defence system as highlighted by a raise in both GPX and catalase activity, and the decreased levels of lipid peroxidation. This effect was pronounced at 24 h of supplementation, almost disappeared at hour 48, while after 72 h an opposite effect was observed: lipid peroxidation increased concomitantly with DHA doses. Therefore, the final effect of DHA on cellular redox status is dependent on dose and time supplementation.

Oleic acid is a potent inhibitor of fatty acid and cholesterol synthesis in C6 glioma cells

Glial cells play a pivotal role in brain fatty acid metabolism and membrane biogenesis. However, the potential regulation of lipogenesis and cholesterologenesis by fatty acids in glial cells has been barely investigated. Here, we show that physiologically relevant concentrations of various saturated, monounsaturated, and polyunsaturated fatty acids significantly reduce [1-(14)C]acetate incorporation into fatty acids and cholesterol in C6 cells. Oleic acid was the most effective at depressing lipogenesis and cholesterologenesis; a decreased label incorporation into cellular palmitic, stearic, and oleic acids was detected, suggesting that an enzymatic step(s) of de novo fatty acid biosynthesis was affected. To clarify this issue, the activities of acetyl-coenzyme A carboxylase (ACC) and FAS were determined with an in situ digitonin-permeabilized cell assay after incubation of C6 cells with fatty acids. ACC activity was strongly reduced ( approximately 80%) by oleic acid, whereas no significant change in FAS activity was observed. Oleic acid also reduced the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR). The inhibition of ACC and HMGCR activities is corroborated by the decreases in ACC and HMGCR mRNA abundance and protein levels. The downregulation of ACC and HMGCR activities and expression by oleic acid could contribute to the reduced lipogenesis and cholesterologenesis.

Agonists calcitonin, corticotropin-releasing hormone, and vasoactive intestinal peptide, but not prostaglandins or beta-adrenergic agonists, elevate cyclic adenosine monophosphate levels in oligodendroglial cells

Although 3',5'-cyclic AMP (cAMP) is known to regulate oligodendrocyte development in vitro, little is known about the identity of agonists that induce cAMP synthesis in oligodendroglia. To identify such agonists, we used a novel immunohistochemical method of visualizing cAMP within single cells to screen compounds that are known to activate cAMP synthesis in other cellular systems. Calcitonin, corticotropin-releasing hormone, and vasoactive intestinal peptide elevated cAMP in oligodendroglial cells but not in other cell types present in the cultures (i.e., astrocytes and microglia). In contrast, prostaglandins and the beta-adrenergic agonist isoproterenol, which have previously been reported to induce modest increases in oligodendroglial cell cAMP from biochemical assay of cell homogenates, did not induce a detectable cAMP response in individually identified oligodendroglial cells but instead induced a robust cAMP response in nonoligodendroglial cells.

Transcriptional regulation of 2',3'-cyclic nucleotide 3'-phosphodiesterase gene expression by cyclic AMP in C6 cells

It was recently shown that the two transcripts encoding the isoforms of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP1 and CNP2) are differentially regulated during the process of oligodendrocyte maturation. In oligodendrocyte precursors, only CNP2 mRNA is present, whereas in differentiating oligodendrocytes, both CNP1 and CNP2 mRNAs are expressed. This pattern of CNP expression is likely due to stage-specific transcriptional regulation of the two CNP promoters during the process of oligodendrocyte differentiation. Here, we report the influence of increased intracellular cyclic AMP (cAMP) levels on the transcription of both CNP1 and CNP2 mRNAs in rat C6 glioma cells. We found that the transcription of CNP1 mRNA was significantly increased in comparison with that of CNP2 mRNA in cells treated with cAMP analogues to elevate intracellular cAMP levels. This up-regulation of CNP1 expression (a) is due to an increase of transcription, (b) requires de novo protein synthesis, and (c) requires the activity of protein kinase A. These results are physiologically significant and support the idea that a cAMP-mediated pathway is part of the molecular mechanisms regulating the expression of CNP1 in oligodendrocytes. The regulation of CNP1 promoter activity by cAMP was then investigated in stably transfected C6 cell lines containing various deletions of the CNP promoter directing the bacterial chloramphenicol acetyltransferase gene. We showed that the sequence between nucleotides -126 and -102 was essential for the cAMP-dependent induction of CNP1 expression. Gel retardation analysis showed that two protein-DNA complexes are formed between this sequence and nuclear factors from C6 cells treated or not treated with cAMP. This suggests that the induction of CNP1 mRNA transcription is not mediated by changes in binding of nuclear factors that interact directly with the -126/-102 sequence. Sequence analysis of this region revealed the presence of a putative activator protein-2 (AP-2) binding site. It is interesting that mutagenesis of this region resulted in a significant reduction in transcriptional responses to cAMP, implying a possible role for the AP-2 factor in the expression of CNP1. In addition, we have shown that putative binding sites for activator protein-4 and nuclear factor-1 adjacent to the AP-2 site are required for efficient induction of CNP1 expression by cAMP. Taken together, our results show that the cAMP-dependent accumulation of CNP1 mRNA appears to depend on the synergistic interaction of several regulatory elements.

C-terminal CTII motif of 2',3'-cyclic nucleotide 3'-phosphodiesterase undergoes carboxylmethylation

Eukaryotic proteins with a carboxyl-terminal CaaX motif are modified by isoprenylation and subsequently processed by proteolysis of the three terminal amino acids and carboxylmethylation of the exposed cysteine residue. The myelination-associated 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) has a C-terminal CTII sequence and is isoprenylated; however, no examples of subsequent processing exist when threonine, a polar residue, is located adjacent to the cysteine. Here we show that CNP is capable of being carboxylmethylated in both insect cells and glioma cells. This processing is dependent upon isoprenylation of the cysteine and can be inhibited with the isoprenylated cysteine derivative, N-acetyl-S-farnesyl-L-cysteine. Although the role of the methyl group at the C-terminus of other isoprenylated proteins is not fully understood, modulation of signal transduction pathways is strongly indicated. This modification of CNP may similarly regulate cell biological processes in myelinogenesis.

Patterns of reactivity with anti-glycolipid antibodies in human primary brain tumors

Antibodies against carbohydrates of three glycolipids were used to determine patterns of immunohistochemical reactivity of histologically identifiable cell subpopulations in 101 human primary brain tumors. For all tumor types fibrillary cells, polar cells, and gemistocytes (commonly seen in astrocytomas and ependymomas) stained more frequently for galactosylcerebroside with mAbO1 than small tumor cells and macrophages. Frequency of staining for sulfatide with mAbO4 was fibrillary > polar > small cells = macrophages. Gemistocytes stained more frequently with mAbO4 than polar cells in all tumors except low grade astrocytomas. These data indicate that tumors classified on histological grounds as astrocytic are often stained with antibodies that recognize oligodendrocytes and their progenitors. Thus, anti-glycolipid antibodies used in the study of developmental lineage may offer useful tools for classification of human brain tumors. Staining of fibrillary cells, polar cells, and gemistocytes for paragloboside directly with mAb F1H11 was much less common than with mAbO1, but this increased by pretreatment of the tissues with neuraminidase (F1H11 + N). Of particular note was the finding that small tumor cells frequently stained with F1H11 + N. Evidence that these were not macrophages was obtained using double immunostaining with F1H11 + N and anti-macrophage antibodies. In astrocytomas the frequency of small tumor cells immunostained with F1H11 + N was high grade > anaplastic > low grade, demonstrating a correlation of this tumor cell population with more aggressive astrocytomas. Thus, immunostaining with F1H11 + N may be of value in identifying small, anaplastic tumor cells, especially in small biopsies or tissue taken adjacent to the main tumor mass.

Low density, but not high density, C6 glioma cells support dorsal root ganglion and sympathetic ganglion neurite growth

Accumulating evidence suggests that an inhibitory influence of the environment on growth cones plays a crucial role in development and regeneration of neuronal projections. Oligodendrocyte-associated neurite growth inhibiting substance is one of the most extensively studied molecules. Molecular biological studies, however, remain slow in progress. Although finding clonal cells that express such factors would facilitate the analysis of inhibitory influences on neurite growth, few cell lines have been reported to express neurite growth inhibitor. We therefore investigated the possibility of a clonal glial cell line to differentiate and express inhibitory or non-permissive features for neurite outgrowth in culture. We chose the C6 glioblastoma cell line and examined neurite extension from chick dorsal root ganglion (DRG) explants. Neurites from embryonic day 9 DRG extensively grew on C6 cells that were cultured at low cell density, while they failed to grow on C6 cells cultured at high density, even in the presence of nerve growth factor in high concentrations. Membrane extract from high density C6 cells, when used as culture substratum, was less permissive for neurite outgrowth compared to extract from low density cells. Treatment of the membrane extract derived from high density C6 cells with trypsin made it less non-permissive for neurite growth. These results suggest that C6 cells are induced to express a non-permissive property for neurite outgrowth by culturing them at high density.

Epinephrine induces beta-adrenergic desensitization and differentiation of HL-60 cells

The HL-60 cell line was cultured in a serum-free medium and exposed to various concentrations of EPI. The effects on cell growth, differentiation and beta-adrenergic response were followed during the culture period of 72 h. Short-term exposure (3 min) to EPI (1 nM-1 mM) in the presence of theophylline (4 mM) caused a dose-dependent increase of cAMP levels with a maximum of 1500% above basal levels. When the cells were exposed to EPI (1 nM-10 microM) for 72 h, a dose-dependent increase of cAMP levels with a maximum of 60% above basal levels. Sustained exposure to EPI generated a dose-dependent desensitization of the beta-adrenergic signal system. After EPI treatment for 72 h, IPR (10 microM for 3 min) in the presence of theophylline (4 mM) increased cAMP-levels by only 80% above baseline level (cAMP levels after maintained exposure to EPI), compared to 1080% above unstimulated level in control cells. The alpha-adrenergic receptor blocker PHENT (10 microM) did not affect baseline cAMP level or IPR-dependent cAMP response, but a mixture of EPI and PHENT increased the response to IPR. The HL-60 cell growth was not influenced by EPI. However, after repeated exposure to EPI for 72 h a concentration-dependent increase of HL-60 differentiation was demonstrated. Differentiation was not influenced by PHENT. These results suggest a differentiation induction due to a beta-adrenergic-induced cAMP elevation.

Synthesis of glial fibrillary acidic protein in rat C6 glioma in chemically defined medium: cyclic AMP-dependent transcriptional and translational regulation

Glial fibrillary acidic protein (GFA) expression was induced in rat C6 glioma in chemically defined medium by the addition of N6, O2'-dibutyryl cyclic AMP (dbcAMP). Induction was dependent on the increase in intracellular cyclic AMP (cAMP), which was linearly correlated with added dbcAMP. Contrary to GFA mRNA synthesis, which can be obtained by cAMP-dependent and -independent pathways, translation of mRNA into GFA was observed only above a cellular cAMP concentration of approximately 0.2 fmol/cell. dbcAMP stimulation did not affect the vimentin concentration, which remained at a low level, but changed the cellular morphology from a bipolar to a stellate shape. A similar morphological change was observed after stimulation of C6 with lipopolysaccharide (LPS). However, LPS did not significantly increase the intracellular concentration of cAMP and the LPS-induced mRNA was not translated into GFA. Our results indicate that GFA synthesis is regulated at the mRNA level and at the translational level and that a cAMP-dependent mechanism determines the ultimate synthesis of GFA by a yet unknown mechanism.

Expression of multiple integrins and extracellular matrix components by C6 glioma cells

We have investigated the expression of integrins in C6 glioma, a chemically-induced glial tumor cell line from rat brain. Immunochemical analysis revealed that C6 cells express sets of integrin receptor complexes which immunologically and electrophoretically are indistinguishable from those expressed by normal rat skin fibroblasts. These include the well-characterized fibronectin (alpha 5 beta 1) and the multi-specific laminin, collagen and fibronectin (alpha 3 beta 1) receptors. Assay of cell adhesion indicated that C6 cells adhere to fibronectin-coated surfaces or matrix deposited by the C6 glioma cells (CGM) in an RGD- and divalent cation-dependent fashion. However, anti-fibronectin antibodies, which are able to inhibit fibroblast adhesion to fibronectin, did not inhibit adhesion of the C6 cells to fibronectin or CGM. This may reflect differences in functional properties and/or distribution patterns of integrins in C6 cells and normal fibroblasts.

A histochemical study of the activity of nonspecific cholinesterase in C6 glioma cells in culture

The activity of nonspecific cholinesterase (nChE) was revealed histochemically in a small number of C6 glioma cells under conditions of spontaneous growth in culture. The nChE-positive cells (nChE+) first appeared in 4-day-old cultures. They occurred solitarily or in small groups with a cluster- or chain-like arrangement. The incidence of nChE+ cells increased with in vitro age and/or higher population densities of cultures but it never exceeded 3% of the whole population. These results indicate the necessity of histochemical as well as biochemical data on nChE activity in glioma cells both in situ and in culture for the discovery of the heterogeneous distribution of this enzyme. db-cAMP induced a decrease in the proportion of nChE+ cells to total number of cells. These changes suggest that the original C6 glioma cell seed stock contains a small subclone of less differentiated cells exhibiting nChE activity. The greater number of nChE+ cells in older cultures is probably due to recovery and multiplication of initially scarce subclone cells. C6 glioma cells in culture form a suitable model for investigation of changes in nChE activity of glial cells provided that a histochemical method of detection is applied.

A review of the aetiology of multiple sclerosis: an ecological approach

Multiple sclerosis (MS) is a disease of unknown aetiology characterized by myelin destruction. Approaches to the aetiology of the condition have noted its differential geographic and demographic distribution; a tentative and inconsistent link with infectious agents; a genetic susceptibility; and a tendency to track with dietary lipids. This review proposes a multidisciplinary approach to the aetiology of MS, emphasizing the interlocking and interdependent nature of current aetiological arguments. We suggest that the most profitable interpretation of current empirical data on the aetiology of MS can be accomplished through this kind of analysis.

Induction of oligodendrocyte differentiation by activators of adenylate cyclase

Oligodendrocyte differentiation is accelerated by analogs of cyclic AMP (cAMP), such as N6,2-'O-dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP) or 8-bromo cAMP, in developing rat glial cell cultures (Raible and McMorris, 1989). However, it is not known whether the immature developing oligodendrocytes have G protein-coupled adenylate cyclase capable of generating cAMP, as would be required if development of the cells is normally regulated by endogenous cAMP. In the present study, we demonstrate that the diterpene forskolin, a potent activator of adenylate cyclase, or cholera toxin, which activates adenylate cyclase through G protein modification, can induce a precocious increase in oligodendrocyte number. When both forskolin and cholera toxin are added together, oligodendrocyte differentiation is induced to a level similar to that observed in response to cAMP analogs. These results establish for the first time that modulation of the endogenous cAMP regulatory system alters the schedule of oligodendrocyte differentiation.

Analysis of the calcium-modulated proteins, S100 and calmodulin, and their target proteins during C6 glioma cell differentiation

We have analyzed the levels, subcellular distribution, and target proteins of two calcium-modulated proteins, S100 and calmodulin, in differentiated and undifferentiated rat C6 glioma cells. Undifferentiated and differentiated C6 cells express primarily the S100 beta polypeptide, and the S100 beta levels are four-fold higher in differentiated compared to undifferentiated cells. Double fluorescent labeling studies of undifferentiated cells demonstrated that S100 beta staining localized to a small region of the perinuclear cytoplasm and colocalized with the microtubule organizing center and Golgi apparatus. Analysis of differentiated C6 cells demonstrated that S100 beta distribution and S100 beta-binding protein profile changed significantly upon differentiation. In addition, the brain-specific isozyme of one S100-binding protein, fructose-1,6-bisphosphate aldolase C, can be detected in differentiated but not undifferentiated C6 cells. While changes in the subcellular distribution of calmodulin were not observed during differentiation, calmodulin levels and calmodulin-binding protein profiles did change. Altogether these data suggest that S100 beta and calmodulin regulate different processes in glial cells and that the regulation of the expression, subcellular distribution, and target proteins of S100 beta and calmodulin during differentiation is a complex process which involves multiple mechanisms.

Expression of glial fibrillary acidic protein in rat C6 glioma relates to vimentin and is independent of cell-cell contact

Glial fibrillary acidic protein (GFAP) was induced in rat C6 glioma cells grown in M199 and HAM F10 media by addition of 1 mM dibutyryl cyclic AMP. The amount of GFAP per cell increased 7- and 33-fold in M199 and HAM F10 media, respectively. GFAP could be induced in each phase of the cell culture except for the lag phase, where GFAP synthesis was delayed until the onset of the logarithmic growth. The induction took place under conditions where the total protein content of the cell decreased. Measurement of the amount of vimentin indicated that GFAP was induced under conditions of low vimentin concentration. Our results do not support the hypothesis that GFAP induction depends on cell-cell contact or cell proliferation. They indicate a shift from vimentin to GFAP synthesis by an as yet unknown mechanism.

Control of glial cell volume in anoxia. In vitro studies on ischemic cell swelling

Volume regulation of C6 glial cells was studied in anoxia in vitro to improve the understanding of ischemic cell swelling in the brain. Contrary to in vivo conditions, anoxia or anoxia plus iodoacetate for additional inhibition of anaerobic energy metabolism did not induce glial swelling. However, intracellular K+ was markedly decreased while intracellular Na+ increased. Induction of energy failure by anoxia plus iodoacetate was found to prevent the regulatory volume decrease on hyposmotic exposure of the cells, which is regularly observed in normoxic control conditions. Hyposmotic exposure in anoxia plus iodoacetate led only to an initial tendency of cell volume normalization followed by secondary cell swelling. This was associated with a net increase of intracellular Na+ that may explain the failure of volume regulation under these circumstances. Maintenance of a normal glial cell size during complete energy deprivation by anoxia plus iodoacetate in isotonic medium strongly indicates that energy failure per se does not suffice to induce cell swelling. Cell swelling in cerebral ischemia in vivo thus is likely to require additional mechanisms, most likely an increase of membrane permeability to Na+, which may be caused by release and accumulation of excitotoxins such as glutamate or by an extracellular release of K+. Such a mechanism would hardly influence the extracellular homeostasis in vitro due to the large medium-to-cell volume ratio. The findings demonstrate, nonetheless, the significance of a competent energy metabolism to support cell volume regulation. This is concluded from the failure of regulatory volume decrease of hypotonically suspended glial cells in anoxia plus iodoacetate.(ABSTRACT TRUNCATED AT 250 WORDS)

Capacity for substrate utilization in oxidative metabolism by neurons, astrocytes, and oligodendrocytes from developing brain in primary culture

Neuron, astrocyte, and oligodendrocyte cultures which were established from developing rat brain were examined for their utilization of glucose, ketone bodies, and free fatty acids by oxidative processes. 14CO2 production was measured in these cells from [1-14C] or [6-14C]glucose; [1-14C]octanoate and [1-14C], [6-14C], or [16-14C]palmitate; and [3-14C]acetoacetate and D(-)-3-hydroxy[3-14C]butyrate. Pyruvate dehydrogenase (EC 1.2.4.1.) and 3-oxoacid-CoA transferase (EC 2.8.3.5) activities were found at high levels in each of the cell populations. Astrocytes and oligodendrocytes produced much more 14CO2 from [1-14C]glucose than from [6-14C]glucose, indicating substantial hexose monophosphate shunt activity. This process was not as active in neurons. All three cell populations readily utilized the ketone bodies for oxidative metabolism at rates 7-9 times greater than they utilized glucose. Only astrocytes were able to utilize fatty acids for 14CO2 production, and the rate of utilization was greater than that of the ketone bodies. We found that the metabolic patterns of these brain cells which were derived from the developing brain complement the nature of the diet of the suckling animal which is rich in fat and low in carbohydrate. They readily utilized the ketone bodies or fatty acids and spared glucose for processes that metabolites of fat cannot fulfill.

Differential expression of 2':3'-cyclic nucleotide 3'-phosphodiesterase in cultured central, peripheral, and extraneural cells

The relative levels of the central nervous system myelin marker enzyme 2':3'-cyclic nucleotide 3'-phosphodiesterase (EC 3.1.4.37, CNPase) were determined in neuroblastoma, astrocyte, oligodendrocyte and Schwann cell cultures and in freshly isolated human lymphocytes and platelets. The highest specific activities were associated with the cells that elaborate myelin membrane in the central and peripheral nervous system, oligodendrocytes and Schwann cells, respectively. Antiserum to bovine CNPase recognized both CNP1 and CNP2 in CNS myelin and human oligodendroglioma. In addition, a 53,000 dalton protein was evident on autoradiographs of immunoblotted PNS myelin and human oligodendroglioma proteins. Cultured rat oligodendrocyte, C6 and mouse NA neuroblastoma CNPase appear to share common determinants with the corresponding normal rat CNS enzyme.

Regulation of cerebroside and sulfatide metabolism in glia cells

Mouse oligodendroglioma cells, G-26 clone 20 and 24, contain galactosylceramide (cerebroside) and sulfogalactosylceramide (sulfatide) as determined by an HPLC technique. The synthesis of both these lipids was stimulated by 10(-6) M hydrocortisone (cortisol) and also by the removal of serum from the culture medium. Forty-eight hours after the addition of cortisol the incorporation of H235SO4 into sulfatide, the level of sulfatide and the specific activity of the enzyme 3'-phosphoadenosine 5'-phosphosulfate:galactosylceramide sulfotransferase in the cells increased three- to fourfold. The level of cerebroside and the specific activity of UDP-galactose:hydroxyacyl sphingosine galactosyltransferase also increased threefold in the cells on treatment with cortisol. The effect of the hormone on the synthesis of cerebroside preceded the increase in sulfatide synthesis. Experiments with cycloheximide and actinomycin D showed that the effect of the hormone on glycolipid synthesis in these cells were mediated through de novo messenger RNA and protein synthesis. Removal of serum from the culture medium resulted in an approximately twofold enhancement of H235SO4 incorporation into sulfatide within 24 h. The levels of sulfatide and cerebroside and the specific activity of the galactosyltransferase and sulfotransferase also increased significantly after serum removal. However, in contrast to the effect of the steroid, the sulfotransferase activity and the level of sulfatide increased prior to elevations in galactosyltransferase and cerebroside. The effect of serum removal was also found to be mediated by de novo RNA and protein synthesis. The effects of cortisol and serum removal on the synthesis of cerebroside and sulfatide were strictly additive.

Expression of hyaluronectin by C-6 glial cells at high density

Hyaluronectin, a brain glycoprotein that has been localized to the nodes of Ranvier in vivo and to oligodendrocytes in primary cultures of neonatal rat brain cells, was shown by using an unlabeled immunoperoxidase method to be present in C-6 glial cells grown to high density. The density-dependent expression of this glycoprotein is in accordance with the known properties of the glial stem cells, i.e., induction of differentiated properties such as 2',3'-cyclic nucleotide-3'-phosphohydrolase, glutamine synthetase, S-100 protein, and glial fibrillary acidic protein.

Induction of myelin components: cyclic AMP increases the synthesis rate of 2',3'-cyclic nucleotide 3'-phosphohydrolase in C6 glioma cells

In an effort to determine the factors that stimulate myelin synthesis, we investigated the mechanism by which dibutyryl cyclic AMP induces the activity of the myelin enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP; EC 3.1.4.37), in C6 glioma cells. Immunotitration experiments and measurements of the accumulation of [35S]methionine-labeled CNP showed that dibutyryl cyclic AMP increased the amount of CNP in the cells but not the catalytic activity per molecule of the enzyme. Moreover, inhibition of protein synthesis with cycloheximide abolished induction of enzyme activity. Dibutyryl cyclic AMP doubled the rate of CNP synthesis but had no effect on the half-life of the enzyme (approximately 33 h). The induction was partially blocked by the inhibitors of mRNA synthesis, cordycepin or alpha-amanitin. Thus, cyclic AMP induces the synthesis of CNP.

Modulation of beta-adrenergic response in rat brain astrocytes by serum and hormones

Purified astrocyte cultures from neonatal rat cerebrum respond to isoproterenol, a beta-adrenergic agonist, with a transient rise in cAMP production. This astroglial property was regulated by serum, a chemically defined medium (serum-free medium plus hydrocortisone, putrescine, prostaglandin F2 alpha, insulin, and fibroblast growth factor) and epidermal growth factor. Compared to astrocytes grown in serum-supplemented medium, astrocytes grown in the chemically defined medium were nonresponsive to isoproterenol stimulation, and this difference did not appear to be due to selection of a subpopulation of cells by either medium. The data suggest that a decreased beta-adrenergic receptor number and an increased degradation of cAMP may account for the reduced response to beta-adrenergic stimulation. The nonresponsive state of astrocytes in the defined medium was reversible when the medium was replaced with serum-supplemented medium. An active substance(s) in serum was responsible for restoring the responsiveness of astrocytes. Each of the five components of the defined medium had little effect by itself; however, together they acted synergistically to desensitize astrocytes to beta-adrenergic stimulation. On the other hand, epidermal growth factor, a potent mitogen for astrocytes, was very competent by itself in reducing the cAMP response of astrocytes to beta-adrenergic stimulation. Thus purified astrocytes grown in the chemically defined medium appear to be a good model for the study of hormonal interactions and of serum factors which may modulate the beta-adrenergic response.

Galactosyltransferases: physical, chemical, and biological aspects

Galactosyltransferases (GTs) are one of the members of a family of enzymes called glycosyltransferases involved in the biosynthesis of complex carbohydrates. These enzymes catalyze the transfer of galactose from UDP-galactose to an acceptor (glycoprotein, glycolipid) containing terminal N-acetylglucosamine or N-acetylgalactosamine residue. GTs occur in soluble (milk, serum, effusions, etc.) and insoluble (membrane) forms. The GT activities on the outer surface of the cells have been correlated with a host of cellular interactions, including fertilization, cell migration, embryonic induction, chondrogenesis, contact inhibition of growth, cell adhesion, hemostasis, intestinal cell differentiation, and immune recognition. GTs have been purified to homogeneity using affinity chromatography. Most GTs are found active in the pH range 6 to 8 and at temperatures between 35 to 40 degrees C. Manganese is an essential co-factor for GT activity. Isoenzymes of GT have been recognized, especially in tumor tissues, malignant effusions, and sera of cancer patients using polyacrylamide gel electrophoresis in the presence and absence of SDS. Depending on the source of the enzyme, the molecular weights of GTs range between 40,000 to 80,000 daltons. Carcinoma-associated GT isoenzyme has been reported to have a higher molecular weight than the normal GT isoenzyme. Development of monoclonal antibody against the cancer-specific GT isoenzyme will provide help in the development of an immunoassay for the measurement of this isoenzyme in the sera and an aid in the radioimmunolocalization of the tumors in cancer patients.

Activation of amiloride-sensitive sodium transport in C6 glioma cells

We have characterized, in C6 cells, an amiloride-sensitive Na+ entry pathway that can exchange for H+. In this report we demonstrate that this cation-exchange system can be induced within 24-36 h by either serum removal or by dibutyryl cyclic AMP; however, these modes of induction are not additive and are manifest only after activation by serum. In these glioma cells we found that activation by serum can be mimicked in part by specific serum factors, i.e., epidermal growth factor and bradykinin. We attempted to characterize this activation process further using several cell biologic probes. We had previously shown that that activation process involves a calcium-dependent step with full activation obtained in the presence of the calcium ionophore A23187. The activation by serum was inhibited by preincubation with colchicine but not with dihydrocytochalasin B, suggesting a cytoskeletal involvement in the activation process. Activation by epidermal growth factor and bradykinin was found to be unaffected by colchicine, suggesting that other factors must be present in serum that confer sensitivity to colchicine. Incubation of the cells with phorbol myristoyl acetate results in the activation of amiloride-sensitive transport, suggesting that stimulation of protein kinase C may be integral to the activation process. Unlike the effects of serum, activation by phorbol myristoyl acetate is not inhibited by colchicine, indicating that this drug works in a way that bypasses the cytoskeletal-dependent step. Since diacylglycerol is the presumed endogenous activator of protein kinase C, we studied the effects of dioleylglycerol. This intermediate of phospholipid turnover was found to increase specifically the amiloride-sensitive sodium pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation of cholesterol to astrocytic differentiation in C-6 glial cells

The relation of cellular cholesterol content to a biochemical expression of astrocytic differentiation was investigated in cultured C-6 glial cells. The astrocytic marker, glutamine synthetase, was studied. Cellular sterol content was perturbed with compactin, a specific inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase and, thereby, cholesterol biosynthesis. Depletion of cellular sterol resulted in 72 h in a more than twofold increase in glutamine synthetase activity. Production of various degrees of sterol depletion with different concentrations of compactin demonstrated a striking inverse relationship between glutamine synthetase activity and the cellular sterol/phospholipid molar ratio. That the effect of compactin, in fact, is mediated by depletion of sterol was shown further by prevention of the compactin-induced increase in synthetase activity by simultaneous addition of exogenous cholesterol. Moreover, addition of cholesterol alone to the culture medium led to both a decrease in glutamine synthetase activity and an increase in the sterol/phospholipid molar ratio. The possibility that the compactin-induced increase in glutamine synthetase activity is caused by an increase in synthesis of the enzyme was suggested by prevention of the increase by cycloheximide. The data suggest that astrocytic differentiation is stimulated by a decrease in cellular sterol content. When considered with our previous observation that oligodendroglial differentiation is inhibited by such a decrease, the findings suggest that cellular sterol content is a critical determinant of the direction of glial differentiation, i.e., whether along astrocytic or oligodendroglial lines.

Schwann cell galactocerebroside induced by derivatives of adenosine 3',5'-monophosphate

Indirect immunofluorescence was used to show the presence of galactocerebroside (galC), a lipid found in myelin, on the surface of about half of the Schwann cells isolated from neonatal rat sciatic nerves and cultured for 1 day without neurons. By day 4 in vitro, the Schwann cells had all lost their surface galC. Three days after beginning treatment with 10(-3) molar 8-bromo-adenosine 3',5'-monophosphate (8-bromo cyclic AMP) or N6,O2'-dibutyryl adenosine 3',5'-monophosphate (dibutyryl cyclic AMP), galC reappeared on the Schwann cells, and 2 days later 48 percent of the cultured Schwann cells showed surface galC. Tritium from tritiated D-galactose was incorporated into galC by the 8-bromo cyclic AMP-and dibutyryl cyclic AMP-treated cultures at a rate 15 times the control rate.

Cytoskeletal structures and oligodendroglial differentiation in C-6 glial cells

The relationship of the cytoskeleton to a biochemical expression of oligodendroglial differentiation was studied in cultured C-6 glial cells. Specifically, we investigated the effect of the cytoskeletal perturbants, colchicine and cytochalasin D, on the induction of the oligodendroglial marker enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP), caused by removal of serum from the culture medium. Each drug inhibited CNP induction in a concentration-dependent manner, and essentially complete inhibition of induction was observed with 0.25 microM colchicine or 2.0 microM cytochalasin D. Detailed study of the effect of colchicine was carried out. This antimicrotubular agent not only totally prevented induction if added at the onset of serum removal, but also prevented further induction when added at various times after serum removal. That the effect of colchicine related to the drug's effect on microtubules was supported by the demonstration that lumicolchicine, a colchicine isomer which has no effect on microtubules, had no effect on the CNP induction. Moreover, colchicine, but not lumicolchicine, prevented the morphological signs of differentiation provoked by serum removal. The effect of colchicine was reversible and relatively specific. Thus, no concomitant effect of colchicine on the activity of another plasma membrane enzyme of C-6 cells, i.e., (Na+ + K+)-activated ATPase, or on the rate of incorporation of [3H]leucine into total protein of intact cells could be discerned. The possibility that the site of the effect of colchicine is on intracellular events was suggested by the observation that the drug inhibited the induction of CNP by dibutyryl cyclic AMP. The data suggest that the cytoskeleton is involved in oligodendroglial differentiation.

Synergistic enzyme induction by glucocorticoids and cyclic AMP observed in glioma x hepatoma cell hybrids but not in their parents

Enzyme induction by hydrocortisone (HC) and dibutyryl cyclic AMP (dbcAMP) was studied in C6 rat glioma cells, FU5AH rat hepatoma cells, and five C6 x FU5AH hybrids. Hormone responsive enzymes from both parental lines were studied, including: tyrosine aminotransferase (TAT), alanine aminotransferase (AAT), glycerol phosphate dehydrogenase (GPDH), lactate dehydrogenase (LDH), and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP). There was no overall dominance of one parental phenotype over the other in expression of uninduced or induced enzyme activity after fusion, and the hybrids possessed some enzymatic properties characteristic of both parents. GPDH was induced by dbcAMP in all five hybrids, and TAT was induced by dbcAMP in four of the hybrids, although neither of these enzymes were induced by dbcAMP in the parents. Furthermore, synergistic induction of these enzymes by HC and dbcAMP was observed in the hybrids but not in the parents. These hybrids provide a model system to study hormone interaction in enzyme induction.

Adrenalectomy of rats results in hypomyelination of the central nervous system

The effect of adrenalectomy on CNS myelin accumulation was investigated to determine whether glucocorticoids play a role in regulating myelination. When 14-day-old rats were adrenalectomized and sacrificed 7-8 days later, the amount of bulk-isolated myelin in whole brain, as expressed per gram wet weight of brain or per milligram DNA-phosphate, was reduced to about 75% that of sham-operated controls. Both brain weight and DNA content were unchanged by adrenalectomy. Examination of individual brain regions also revealed decreased amounts of myelin in adrenalectomized animals. Brain glycerol 3-phosphate dehydrogenase specific activity was reduced in adrenalectomized animals to 40-60% that of controls, and serum corticosterone levels were less than 0.6% of control levels. The amount of cerebral myelin in animals adrenalectomized on day 21 and sacrificed 9 days later was not significantly reduced. This suggests a possible role of glucocorticoids during the early period of rapid myelination.

Cyclic AMP induction of the myelin enzyme 2',3'-cyclic nucleotide 3'-phosphohydrolase in rat oligodendrocytes

Cyclic AMP (cAMP) is known to induce the activity of the myelin enzyme 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP; EC 3.1.4.37) in C6 rat glioma cells. This report shows that CNP is also inducible in oligodendrocytes explanted from 1-day-old rat cerebrum and grown in tissue culture. Induction was observed after a 1-day treatment with 1 mM N6, O2-dibutyryl cyclic AMP (dbcAMP) and was maximal after 5 days, reaching 200-240% of control. Induction was observed both in mixed cerebral cell cultures containing oligodendrocytes and astrocytes, and in purified cultures of oligodendrocytes prepared by a differential shakeoff procedure. Addition of dbcAMP to the cultures 3-9 days after the cells were explanted from rat brain induced CNP activity, but no induction was observed when dbcAMP treatment was begun 13 or more days after explanation. These results demonstrate that one component of myelin, CNP, is inducible in oligodendrocytes by a cAMP-mediated mechanism, and suggest a role for cAMP in the regulation of the myelin-associated functions of oligodendrocytes.

Relation of cholesterol to oligodendroglial differentiation in C-6 glial cells

The relation of cellular cholesterol content of a biochemical expression of oligodendroglial differentiation was studied in cultured C-6 glial cells. Induction of the oligodendroglial marker enzyme 2':3'-cyclic nucleotide 3'-phosphohydrolase (CNP) was determined after alteration of the sterol content of cellular membranes by exposure to compactin, a specific inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol synthesis. The sterol content and, as a consequence, the sterol/phospholipid molar ratio of C-6 glial cells were decreased by treating the cells, in 10% lipoprotein-poor serum, with various concentrations of compactin for 24 h. The degrees of sterol depletion thus produced were maintained for 48 h after removal of the compactin if the cells were maintained in serum-free medium, the culture conditions necessary for induction of CNF in untreated cells. Forty-eight hours after removal of serum, no induction of CNP occurred in cells previously treated with 0.5 micrograms/ml of compactin, whereas untreated cells exhibited a three- to fourfold increase in CNP activity. Intermediate degree of sterol depletion resulted in intermediate degrees of inhibition of the CNP induction. Moreover, the morphological expressions of glial differentiation observed in the untreated cells did not occur in the sterol-depleted cells. That the effect of compactin on the induction of CNP relates to depletion of sterol was indicated by the finding that when low-density lipoprotein was added to the compactin-treated cells, the induction of CNP, the morphological expressions of differentiation, and the sterol/phospholipid molar ratios were preserved. The degree of sterol depletion that totally prevented the induction of CNP had no effect on (Na+ R K+)-activated ATPase activity, total protein synthesis, and cell viability. The data define a critical role for sterol in oligodendroglial differentiation in this model system.

Induction of glutamine synthetase by dibutyryl cyclic AMP in C-6 glioma cells

Glutamine synthetase was found to be increased in C-6 glioma cells as a result of increasing culture passage and N-6,2'-O-dibutyryl cyclic AMP (dbcAMP) treatment. At low passage dbcAMP produced a 2.5-fold increase in glutamine synthetase activity per unit of cellular protein. At high passage control glutamine synthetase was approximately double that seen at low passage, but dbcAMP produced an additional 65% increase. Lactate dehydrogenase activity was also increased by dbcAMP treatment at both low and high passage, but culture passage produced no change in the lactate dehydrogenase. With increasing culture passage, the ratio of cellular protein to DNA doubled. Therefore, expression of data per unit of protein tended to minimize the apparent changes in activity. The maximum increase in glutamine synthetase activity produced by both dbcAMP and increasing culture passage and expressed on a DNA basis was 5.6-fold. The increase in glutamine synthetase activity was generally linear during the first 20 h of drug treatment, after which enzyme activity remained nearly constant up to 72 h. Ninety percent or more of the dbcAMP remained in the medium at the end of 48-h exposure of cells to dbcAMP. 8-br-Cyclic AMP also increased glutamine synthetase activity of C-6-cels, but n-butyrate did not. Isoproterenol, which increases cyclic AMP in C-6-cells, increased glutamine synthetase activity. The effect of isoproterenol on glutamine synthetase was inhibited by the beta-adrenergic blocking agent sotalol. Cycloheximide (10 micrograms/ml) inhibited the dbcAMP effect on glutamine synthetase activity and also decreased the control enzyme activity by 60%.

On the role of calcium ions in the regulation of glycogenolysis in mouse brain cortical slices

Using mouse brain cortical slices, we investigated the relative roles of cyclic AMP and of calcium ions as the intracellular messengers for the activation of glycogen phosphorylase (EC 2.4.1.1; alpha-1,4-glucan:orthophosphate glucosyltransferase) induced by noradrenaline and by depolarization. Activation of phosphorylase by 100 microM noradrenaline is mediated by beta-adrenergic receptors and does not require the copresence of adenosine. The role of the concomitant small increase in cyclic AMP is questioned. Short-term treatment with EGTA or LaCl3 abolishes the noradrenaline activation of phosphorylase, pointing to a critical role of extracellular calcium. Depolarization by 25 mM K+ or 100 microM veratridine produces a rapid and large (fourfold) activation of phosphorylase. Only veratridine increases the cyclic AMP levels; exogenous adenosine deaminase essentially blocks this cyclic AMP accumulation but not the phosphorylase activation. A half-maximal activation of phosphorylase occurs at about 12 mM K+. Addition of EGTA or LaCl3 reduces the effect of both depolarizations to a slight and transient activation of phosphorylase. These results indicate that activation of glycogen phosphorylase by K+ or veratridine occurs by a cyclic AMP-independent and calcium-dependent mechanism. The calcium dependency of brain phosphorylase kinase renders this kinase the prime target enzyme for regulation of glycogenolysis by calcium ions.

Effects of methadone on ornithine decarboxylase and cyclic nucleotide phosphohydrolase in neuronal and glial cell cultures

Mixed neuronal and nonneuronal cell cultures were obtained from 8-day-old chick embryos cerebral hemispheres and glial-enriched cultures were obtained from fifteen-day-old chick embryo cerebral hemispheres. Cultures were exposed to methadone, a narcotic drug, from days four to six. The activity of ornithine decarboxylase (ODC) was determined at day eight and the activity of cyclic nucleotide phosphohydrolase (CNP) was determined at day fifteen. Both ODC and CNP activity were higher in mixed neuronal-nonneuronal cell cultures treated with methadone as compared to control. No effect was observed in the neuronal-enriched or glial-enriched cultures. These findings are interpreted to reflect that neuronal-glial interaction is important in the response of primary neural cells to methadone.

Biosynthesis of galactocerebrosides and glucocerebrosides in glial cell lines

UDP-galactose:ceramide galactosyltransferase (CGalT, EC 2.4.1.45) and UDP-glucose:ceramide glucosyltransferase (CGlcT, EC 2.4.1.80) were determined in the glial cell lines G26-20, G26-24, C6, and C6TK-. The enzymatic assay for CGalT in cultured glial cells was complicated by a rapid conversion of UDP-galactose to UDP-glucose, due to the elevated UDP-galactose-4'-epimerase activity in certain glial cell clones. It seems that mechanisms regulating UDP-galactose-4'-epimerase activity and levels of UDP sugars in the glial cell lines differ from those in brain tissue. Compared with the maximum activity of CGalT in the myelinating rat brain, the enzyme activities in the oligodendroglioma clonal cell lines G26-20 and G26-24 were 16-30 times lower. On the other hand, CGalT levels in G26-20 and G26-24 cells were comparable to the values found in young rat brain before myelination starts. No CGalT activity could be detected in C6 or C6TK- cells by the method used in this study, whereas CGlcT activity was found in all glial cell lines tested and its levels were close to the values observed in the young rat brain.

Vimentin: a phosphoprotein under hormonal regulation

Past studies of norepinephrine-stimulated protein phosphorylation in intact C-6 glioma cells had identified a 58,000 molecular weight, 5.7 isoelectric point protein (58K-5.7) as a cyclic AMP-dependent phosphoprotein and had shown that 58K-5.7 was one of the most abundant proteins of the nuclear fraction. Initial experiments of present studies showed that the 58K-5.7 protein remained with the nuclear ghost, or matrix structure, after removal of chromatin. Based on the size, acidity, abundance, nonsolubilization by nonionic detergent and salt, and solubilization by urea, the hypothesis was advanced that the 58K-5.7 protein was the vimentin-type intermediate filament protein. The hypothesis was tested by two types of immunochemical experiments. Antisera against hamster vimentin reacted selectively with only the 58K-5.7 protein in polyacrylamide gels of urea-solubilized cellular residues (i.e., nonionic detergent and 0.6 M salt-insoluble material) as determined by immunoautoradiography. Antisera against the pure 58K-5.7 protein of C-6 cells bound selectively to a fibrous array of cellular material typical of vimentin filaments as determined by indirect immunofluorescence. It is concluded that the 58K-5.7 protein is vimentin.

Alcohol inhibits morphological and biochemical differentiation of C6 glial cells in culture

Cultures of glial cell lines (C6) were exposed to 10-micromilligram Dexamethasone which is known to cause morphological differentiation and induction of 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) in these cells. Ethanol in a concentration of 1.5% abolished these responses, and at 1% diminished them.

The development of brain tumours produced in rats by the intracerebral injection of neoplastic glial cells: a fine structural study

Tumours were produced by the intracerebral injection of a clone of glial cells derived from a glioma induced transplacentally by N-ethyl-N-nitrosourea in a BD-IX rat. The injection of 5 X 10(5) cells into the left frontal lobe resulted in a 100% incidence of tumours. To follow the development of the neoplasms, the brains were studied from 1 day to 4 weeks after injection. The tumours maintained their glial characters throughout, but their features changed with time. Ultrastructurally, they were pleomorphic: the proportion of fibrillary astrocytes, undifferentiated and intermediate cell types varied according to tumour size. When smaller (1 and 2 weeks), fibrillary astrocytes predominated, but when larger (3 and 4 weeks), the number of undifferentiated astrocytes considerably increased. A reproducible brain tumour model with a short latency has thus been established and characterized, which may be of use for chemo- and radiotherapeutic studies and for examining the mechanisms of cerebral oedema.

Morphological analysis of malignancy: a comparative study of transplanted brain tumours

A comparative study of the cellular composition and ultrastructural features of rat brain tumours produced by early and late passage of neoplastic glial cells was carried out. The cells injected intracerebrally were of a clone neoplastic astrocytes (A15A5) derived from a mixed glioma induced transplacentally by N-ethyl-N-nitrosourea (ENU) in a BD-IX rat. The neoplastic cells were maintained for various lengths of time in vitro and then injected (5 X 10(5) cells) into the left frontal lobe of the brains of syngeneic rats, resulting in a 100% tumour yield. Gliomas produced by cells of earlier passages were less malignant and contained better differentiated astrocytes than those produced by cells of later passages. There were also differences in size, shape, extracellular space, presence of haemorrhage and necrosis, vascularity and invasion of the surrounding tissues. Thus the morphological features of transplanted tumours in vivo correlated well with the in vitro behaviour of neoplastic glial cells.

C-6 glioma growth in rats: suppression with a beta-adrenergic agonist and a phosphodiesterase inhibitor

Rat C-6 glioma possesses a beta-adrenergic receptor which, when activated, raises intracellular levels of cyclic adenosine monophosphate (cAMP) in cultured C-6 glioma cells. The present study shows that growth of C-6 glioma is suppressed in rats treated with the beta-adrenergic agonist isoproterenol. Addition of papaverine, a cAMP phosphodiesterase inhibitor, to the treatment schedule augments this effect. Pharmacological agents that elevate intracellular cAMP levels may retard the growth of neural tumors in vivo.