Graphene nanoribbons as a drug delivery agent for lucanthone mediated therapy of glioblastoma multiforme

We report use of PEG-DSPE coated oxidized graphene nanoribbons (O-GNR-PEG-DSPE) as agent for delivery of anti-tumor drug Lucanthone (Luc) into Glioblastoma Multiformae (GBM) cells targeting base excision repair enzyme APE-1 (Apurinic endonuclease-1). Lucanthone, an endonuclease inhibitor of APE-1, was loaded onto O-GNR-PEG-DSPEs using a simple non-covalent method. We found its uptake by GBM cell line U251 exceeding 67% and 60% in APE-1-overexpressing U251, post 24h. However, their uptake was ~38% and 29% by MCF-7 and rat glial progenitor cells (CG-4), respectively. TEM analysis of U251 showed large aggregates of O-GNR-PEG-DSPE in vesicles. Luc-O-GNR-PEG-DSPE was significantly toxic to U251 but showed little/no toxicity when exposed to MCF-7/CG-4 cells. This differential uptake effect can be exploited to use O-GNR-PEG-DSPEs as a vehicle for Luc delivery to GBM, while reducing nonspecific cytotoxicity to the surrounding healthy tissue. Cell death in U251 was necrotic, probably due to oxidative degradation of APE-1.

Mitigation effect of an FGF-2 peptide on acute gastrointestinal syndrome after high-dose ionizing radiation

PURPOSE

Acute gastrointestinal syndrome (AGS) resulting from ionizing radiation causes death within 7 days. Currently, no satisfactory agent exists for mitigation of AGS. A peptide derived from the receptor binding domain of fibroblast growth factor 2 (FGF-P) was synthesized and its mitigation effect on AGS was examined.

METHODS AND MATERIALS

A subtotal body irradiation (sub-TBI) model was created to induce gastrointestinal (GI) death while avoiding bone marrow death. After 10.5 to 16 Gy sub-TBI, mice received an intramuscular injection of FGF-P (10 mg/kg/day) or saline (0.2 ml/day) for 5 days; survival (frequency and duration) was measured. Crypt cells and their proliferation were assessed by hematoxylin, eosin, and BrdU staining. In addition, GI hemoccult score, stool formation, and plasma levels of endotoxin, insulin, amylase, interleukin (IL)-6, keratinocyte-derived chemokine (KC) monocyte chemoattractant protein 1 (MCP-1) and tumor necrosis factor (TNF)-alpha were evaluated.

RESULTS

Treatment with FGF-P rescued a significant fraction of four strains of mice (33-50%) exposed to a lethal dose of sub-TBI. Use of FGF-P improved crypt survival and repopulation and partially preserved or restored GI function. Furthermore, whereas sub-TBI increased plasma endotoxin levels and several pro-inflammation cytokines (IL-6, KC, MCP-1, and TNF-alpha), FGF-P reduced these adverse responses.

CONCLUSIONS

The study data support pursuing FGF-P as a mitigator for AGS.

Radiation resistance in glioma cells determined by DNA damage repair activity of Ape1/Ref-1

Since radiation therapy remains a primary treatment modality for gliomas, the radioresistance of glioma cells and targets to modify their radiation tolerance are of significant interest. Human apurinic endonuclease 1 (Ape1, Ref-1, APEX, HAP1, AP endo) is a multifunctional protein involved in base excision repair of DNA and a redox-dependent transcriptional co-activator. This study investigated whether there is a direct relationship between Ape1 and radioresistance in glioma cells, employing the human U87 and U251 cell lines. U87 is intrinsically more radioresistant than U251, which is partly attributable to more cycling U251 cells found in G2/M, the most radiosensitive cell stage, while more U87 cells are found in S and G1, the more radioresistant cell stages. But observed radioresistance is also related to Ape1 activity. U87 has higher levels of Ape1 than does U251, as assessed by Western blot and enzyme activity assays (approximately 1.5-2 fold higher in cycling cells, and approximately 10 fold higher at G2/M). A direct relationship was seen in cells transfected with CMV-Ape1 constructs; there was a dose-dependent relationship between increasing Ape1 overexpression and increasing radioresistance. Conversely, knock down by siRNA or by pharmacological down regulation of Ape1 resulted in decreased radioresistance. The inhibitors lucanthone and CRT004876 were employed, the former a thioxanthene previously under clinical evaluation as a radiosensitizer for brain tumors and the latter a more specific Ape1 inhibitor. These data suggest that Ape1 may be a useful target for modifying radiation tolerance.

Tissue-sparing effect of x-ray microplanar beams particularly in the CNS: is a bystander effect involved?

OBJECTIVE

Normal tissues, including the central nervous system, tolerate single exposures to narrow planes of synchrotron-generated x-rays (microplanar beams; microbeams) up to several hundred Gy. The repairs apparently involve the microvasculature and the glial system. We evaluate a hypothesis on the involvement of bystander effects in these repairs.

METHODS

Confluent cultures of bovine aortic endothelial cells were irradiated with three parallel 27-microm microbeams at 24 Gy. Rats' spinal cords were transaxially irradiated with a single microplanar beam, 270 microm thick, at 750 Gy; the dose distribution in tissue was calculated.

RESULTS

Within 6 hours following irradiation of the cell culture the hit cells died, apparently by apoptosis, were lost, and the confluency was maintained. The spinal cord study revealed a loss of oligodendrocytes, astrocytes, and myelin in 2 weeks, but by 3 months repopulation and remyelination was nearly complete. Monte Carlo simulations showed that the microbeam dose fell from the peak's 80% to 20% in 9 microm.

CONCLUSIONS

In both studies the repair processes could have involved "beneficial" bystander effects leading to tissue restoration, most likely through the release of growth factors, such as cytokines, and the initiation of cell-signaling cascades. In cell culture these events could have promoted fast disappearance of the hit cells and fast structural response of the surviving neighboring cells, while in the spinal cord study similar events could have been promoting angiogenesis to replace damaged capillary blood vessels, and proliferation, migration, and differentiation of the progenitor glial cells to produce new, mature, and functional glial cells.

Augmentation of osseous phenotypes in vivo with a synthetic peptide

The synthetic peptide B2A2-K-NS augmented the in vitro expression of osseous phenotypes when cells were stimulated with BMP-2, an osteoinductive growth factor. B2A2-K-NS significantly enhanced the effects of BMP-2-induced alkaline phosphatase activity and mineralization. In the absence of BMP-2, B2A2-K-NS did not have an effect on these endpoints. Based on these observations, in vivo studies were conducted to evaluate if B2A2-K-NS could augment osseous phenotypes in an osteoinductive environment in which BMP-2 should be present. In one study, human demineralized bone matrix (DBM) was used to generate an osteoinductive environment and the effects of B2A2-K-NS on ectopic mineralization of subcutaneous implants evaluated. In the second study, a noncritical sized defect in rabbit ulnas with inherent reparative capacity was used as the osteoinductive environment and was treated with or without B2A2-K-NS. In the DBM studies, B2A2-K-NS augmented mineralization as determined using a combination of radiographic analysis and von Kossa staining at 4 weeks postimplant. In the rabbit ulna model, B2A2-K-NS significantly increased the radiographic bone density in the defects compared to carrier-only or no-treatment controls after 6 weeks. Histological staining confirmed that B2A2-K-NS generated a pronounced bone repair response. The results are consistent with the hypothesis that B2A2-K-NS augments osseous phenotypes in an osteoinductive environment, and suggests that B2A2-K-NS may have clinical utility.

Augmentation of demineralized bone matrix (DBM) mineralization by a synthetic growth factor mimetic

These studies evaluated whether F2A4-K-NS, a peptide mimetic of FGF-2, could augment ectopic bone production following the subcutaneous implant of human demineralized bone matrix (DBM). DBM was formulated into a gel with and without F2A4-K-NS, and injected subcutaneously into athymic rats. After 28 days the resultant tissue was excised and fixed. The tissue was examined with soft X-rays and microcomputerized tomography (micro-CT), and by histological methods. Inclusion of F2A4-K-NS with DBM resulted in an increased mineral deposition as determined by soft X-ray and micro-CT analysis and von Kossa staining. DBM-containing tissues showed extensive mineralization compared to the carrier alone, which was poorly mineralized. The mineralization was qualitatively and quantitatively the most extensive in the samples containing F2A4-K-NS plus DBM. Additionally, the highest amount of von Kossa staining for calcium was observed in tissues from animals that had received DBM plus F2A4-K-NS. In these studies, 100 ng of peptide per 0.2 mL of injectable DBM gel generated the most optimal results. The synthetic peptide F2A4-K-NS augmented DBM-induced ectopic mineralization in athymic animals.

Synthetic peptide F2A4-K-NS mimics fibroblast growth factor-2 in vitro and is angiogenic in vivo

A multi-domain synthetic peptide, F2A4-K-NS, mimicked the action of recombinant human FGF-2 (rhFGF-2) in vitro and in an in vivo model of angiogenesis. Like rhFGF-2, F2A4-K-NS was quantitatively shown to bind to FGF receptors in a cell-free receptor binding assay using a chimeric FGFR1 (IIIc)/Fc as monitored by surface plasmon resonance (SPR), and also shown to bind to heparin using biotinylated low-molecular weight heparin in a similar SPR assay. In vitro, F2A4-K-NS triggered signal transduction as monitored by the stimulation of ERK1/2 phosphorylation in human umbilical cord endothelial cells. In cell based assays, it increased cell migration, cell proliferation, and gelatinase secretion; endpoints associated with FGF-2 stimulation. Furthermore, these in vitro effects were mediated with quantities of F2A4-K-NS that were similar to those of rhFGF-2. In vivo, F2A4-K-NS was angiogenic at doses of 40 and 400 ng/implant in a subcutaneous implant assay as determined by morphologic scoring, hemoglobin content, and histology. These results support the hypothesis that F2A4-K-NS is a mimetic of FGF-2 that can substitute for FGF-2 in vitro and in vivo. A synthetic mimetic of FGF-2, such as F2A4-K-NS, could be a useful tool in studying mechanisms of cell activation and potentially in various therapeutic applications.

Multidomain synthetic peptide B2A2 synergistically enhances BMP-2 in vitro

A multidomain, synthetic peptide designated B2A2 synergizes the activity of BMP-2. B2A2 interacts with BMP receptor isoforms, potentiating the action of BMP-2 in activating alkaline phosphatase and triggering Smad and MAPK signaling. B2A2's design permits its delivery as a local surface coating as well as a soluble co-factor, thus broadening potential bioengineering applications.

INTRODUCTION

BMP-2 induces osteogenic differentiation and accelerates bone repair. Although BMP-2 inhibitors have been discovered, no BMP-2 mimetics or enhancers that function in the physiological range have yet been found. Here we report that a synthetic peptide designated B2A2, consisting of (1) a BMP receptor-targeting sequence, (2) a hydrophobic spacer, and (3) a heparin-binding sequence, is a positive modulator of recombinant BMP-2.

MATERIALS AND METHODS

Cultures of mesenchymal cell lines C2C12 and C3H10T1/2 were given B2A2, recombinant BMP-2, or both. Alkaline phosphatase (ALP) activity was assayed by conversion of paranitrophenol phosphate (PNPP). Signaling through Smad and MAP kinase pathways was monitored by Western blot. Receptor binding was assessed by incubating immobilized B2A2 with soluble recombinant receptor-Fc chimeras and detecting bound receptor by anti-Fc antibody ELISA. Surface coating of medical device materials was done by first dip-coating with silyl-heparin, followed by B2A2.

RESULTS AND CONCLUSIONS

Treatment of cells with B2A2 alone marginally increased ALP activity. However, B2A2 plus BMP-2 resulted in 5- to 40-fold augmentation of ALP compared with BMP-2 alone in C3H10T1/2 or C2C12 cells, respectively. This synergistic enhancement was observed over a broad concentration range (4-1000 ng/ml BMP-2). B2A2 interacted directly with BMP receptor isoforms (preferentially to BMPR-Ib and ActivinR-II). In cells, B2A2 + BMP-2 led to a repression of MAP kinase and an increase of Smad activation, consistent with known activation pathways of BMP-2. B2A2 was ineffective when paired with other cytokine/growth factors (basic fibroblast growth factor [FGF-2], TGF-beta1, vascular endothelial growth factor [VEGF]). Simultaneous co-administration was not strictly required. Pulse-chase experiments revealed that temporal separations up to 1 h were still effective. B2A2 was also effective when delivered in a polystyrene- or stainless steel-coated surface through a heparin platform (silyl-heparin) while BMP-2 was added exogenously in solution. These results suggest that B2A2 might promote aggregation of receptor subunits, enabling BMP-2 to activate signaling pathways at effectively lower concentrations. Synthetic multidomain constructs like B2A2 may be useful to accelerate bone repair/deposition through augmentation of endogenous levels of BMP-2 or through local BMP-2 contained in artificial or engineered matrices.

Cell attachment and biocompatibility of polytetrafluoroethylene (PTFE) treated with glow-discharge plasma of mixed ammonia and oxygen

The plasma generated from a gas mixture of NH3 plus O2 (NH3 + O2) has been used to impart unique chemical and biological characteristics to polytetrafluoroethylene (PTFE). PTFE treated with NH3 + O2 plasma was physiochemically distinct from surfaces treated with plasma of either NH3 or O2 alone, as determined by electron spectroscopy for chemical analysis (ESCA). The contact angle analysis revealed that the PTFE surfaces became less hydrophobic after plasma treatments. ESCA results indicate the presence of oxygen-containing groups and nitrogen-containing groups at the plasma-treated surfaces. PTFE treated with NH3 + O2 plasma resisted the attachment of platelets and leukocytes in a manner similar to untreated PTFE; however, the attachment of bovine aorta endothelial cells was substantially increased. Once attached, these cells grew to confluency. The increased endothelial cell attachment was higher than that observed following plasma treatment with each gas used separately, which could be attributed to the considerable amount of CF(OR)2-CF2 formed on the NH3 + O2 plasma-treated PTFE surface. At 14 days after subcutaneous implantation in rats, the PTFE wafers treated with NH3 + O2 plasma demonstrated less encapsulation and lower levels of inflammatory cells compared to controls. Collectively, the results suggest that NH3 + O2 plasma treatment imparts a unique character to PTFE and could be useful in certain in vivo applications.

Local delivery of basic fibroblast growth factor (bFGF) using adsorbed silyl-heparin, benzyl-bis(dimethylsilylmethyl)oxycarbamoyl-heparin

A growth factor delivery system was developed that is based on the use of silyl-heparin, a chemically modified analogue of heparin. The silyl-heparin was adsorbed onto surfaces by hydrophobic interaction via the prosthetic unit and can then be used as a solid-phase adsorbent for bFGF. All the coating steps were performed by adsorption, a process that allowed preparation of surfaces by immersion or "dip-coating". In this study a series of silyl-heparins were synthesized and each of the analogues found to function similar to unmodified heparin relative to their binding of antithrombin III and also the binding of bFGF. The silyl-heparins were found to be adsorbed onto a wide variety of substrates including polystyrene and lactide:glycolide copolymer. Enzyme-linked immumosorbant assay (ELISA) was used to establish that bFGF was readily bound to surface adsorbed silyl-heparin, and that the amount bound was directly related to amount offered for binding. Once adsorbed the silyl-heparin/FGF was able to induce capillary tube formation of endothelial cells and to increase the growth of endothelial cells. When coated onto suture material and implanted in muscle, the FGF/silyl-heparin coating caused an increased density of mesenchymal cells in the area of the implant. This coating method could prove to be useful in a number of tissue engineering applications for the local delivery of FGF and other growth factors.

Response of rat intracranial 9L gliosarcoma to microbeam radiation therapy

Radiotherapeutic doses for malignant gliomas are generally palliative because greater, supposedly curative doses would impart clinically unacceptable damage to nearby vital CNS tissues. To improve radiation treatment for human gliomas, we evaluated microbeam radiation therapy, which utilizes an array of parallel, microscopically thin (<100 microm) planar beams (microbeams) of synchrotron-generated X rays. Rats with i.c. 9L gliosarcoma tumors were exposed laterally to a single microbeam, 27 pm wide and 3.8 mm high, stepwise, to produce irradiation arrays with 50, 75, or 100 microm of on-center beam spacings and 150, 250, 300, or 500 Gy of in-slice, skin-entrance, single-exposure doses. The resulting array size was 9 mm wide and 10.4 mm high (using three 3.8-mm vertical tiers); the beam's median energy was -70 keV. When all data were collated, the median survival was 70 days; no depletion of nerve cells was observed. However, when data from the highest skin-entrance dose and/or the smallest microbeam spacings were excluded, the median survival time of the subset of rats was 170 days, and no white matter necrosis was observed. Others have reported unilateral single-exposure broad-beam irradiation of i.c. 9L gliosarcomas at 22.5 Gy with a median survival of only -34 days and with severe depletion of neurons. These results suggest that the therapeutic index of unidirectional microbeams is larger than that of the broad beams and that an application for microbeam radiation therapy in treating certain malignant brain tumors may be found in the future.

Response of rat intracranial 9L gliosarcoma to microbeam radiation therapy

Radiotherapeutic doses for malignant gliomas are generally palliative because greater, supposedly curative doses would impart clinically unacceptable damage to nearby vital CNS tissues. To improve radiation treatment for human gliomas, we evaluated microbeam radiation therapy, which utilizes an array of parallel, microscopically thin (<100 microm) planar beams (microbeams) of synchrotron-generated X rays. Rats with i.c. 9L gliosarcoma tumors were exposed laterally to a single microbeam, 27 pm wide and 3.8 mm high, stepwise, to produce irradiation arrays with 50, 75, or 100 microm of on-center beam spacings and 150, 250, 300, or 500 Gy of in-slice, skin-entrance, single-exposure doses. The resulting array size was 9 mm wide and 10.4 mm high (using three 3.8-mm vertical tiers); the beam's median energy was -70 keV. When all data were collated, the median survival was 70 days; no depletion of nerve cells was observed. However, when data from the highest skin-entrance dose and/or the smallest microbeam spacings were excluded, the median survival time of the subset of rats was 170 days, and no white matter necrosis was observed. Others have reported unilateral single-exposure broad-beam irradiation of i.c. 9L gliosarcomas at 22.5 Gy with a median survival of only -34 days and with severe depletion of neurons. These results suggest that the therapeutic index of unidirectional microbeams is larger than that of the broad beams and that an application for microbeam radiation therapy in treating certain malignant brain tumors may be found in the future.

Prevalence of serological markers against measles, rubella, varicella, hepatitis B, hepatitis C, and human immunodeficiency virus among medical residents in Mexico

BACKGROUND

Vaccination programs among health care workers are based on seroprevalence studies, which seldom include medical residents or students. The objective of this study was to determine the seroprevalence of antibodies against measles, rubella, varicella, hepatitis B (HBV), hepatitis C (HCV), and human immunodeficiency virus (HIV) among medical residents.

METHODS

This study was designed as a prospective survey. A self-reported questionnaire was used to obtain the information. Serum samples were tested for antibodies by commercial immunoenzymatic assays. Statistical analysis was descriptive; history of exposure was evaluated as a diagnostic test and sensitivity, specificity, and predictive values were calculated according to Bayes theorem.

RESULTS

Eighty-nine residents were included, the median age was 27 years, and 58 (65.2%) were female. Seventy-two (79.7%) had been vaccinated against HBV, but vaccination was complete in only 30/72 (41.6%). All were positive for measles and varicella, with the exception of one case for each. The serology for rubella was negative in 12 residents (10 women). Three residents had anti-core against HBV, with negative surface antigen. One positive case for HCV was confirmed by Western blot. All were negative for HIV. A history of prior varicella had a 100% positive predictive value; in contrast, the negative predictive value was quite low (7%).

CONCLUSIONS

Negative serology for rubella among women and incomplete vaccination against HBV support the implementation of vaccination programs in medical schools in Mexico.

Radiation-induced apoptosis of endothelial cells in the murine central nervous system: protection by fibroblast growth factor and sphingomyelinase deficiency

Injury to the central nervous system (CNS) by ionizing radiation may be a consequence of damage to the vascular endothelium. Recent studies showed that radiation-induced apoptosis of endothelial cells in vitro and in the lung in vivo is mediated by the lipid second messenger ceramide via activation of acid sphingomyelinase (ASM). This apoptotic response to radiation can be inhibited by basic fibroblast growth factor or by genetic mutation of ASM. In the CNS, single-dose radiation has been shown to result in a 15% loss of endothelial cells within 24 h, but whether or not this loss is associated with apoptosis remains unknown. In the present studies, dose- and time-dependent induction of apoptosis was observed in the C57BL/6 mouse CNS. Apoptosis was quantified by terminal deoxynucleotidyl transferase-mediated nick end labeling, and specific endothelial apoptosis was determined by histochemical double labeling with terminal deoxynucleotidyl transferase-mediated nick end labeling and Lycopersicon esculentum lectin. Beginning at 4 h after single-dose radiation, apoptosis was ongoing for 24 h and peaked at 12 h at an incidence of 0.7-1.4% of the total cells in spinal cord sections. Up to 20% of the apoptotic cells were endothelial. This effect was also seen in multiple regions of the brain (medulla, pons, and hippocampus). A significant reduction of radiation-induced apoptosis was observed after i.v. basic fibroblast growth factor treatment (0.45-4.5 microg/mouse). Identical results were noted in C3H/HeJ mice. Furthermore, irradiated ASM knockout mice displayed as much as a 70% reduction in endothelial apoptosis. This study demonstrates that ionizing radiation induces early endothelial cell apoptosis throughout the CNS. These data are consistent with recent evidence linking radiation-induced stress with ceramide and suggest approaches to modify the apoptotic response in control of radiation toxicity in the CNS.

Niemann-Pick human lymphoblasts are resistant to phthalocyanine 4-photodynamic therapy-induced apoptosis

Stress-induced activation of sphingomyelinase (SMase) leading to generation of ceramide, a lipid mediator, has been associated with apoptosis in several malignant and nonmalignant cell lines. Photodynamic therapy (PDT), with the phthalocyanine photosensitizer Pc 4 [HOSiPcOSi(CH3)2(CH2)3N(CH3)2], is an oxidative stress associated with increased ceramide generation and subsequent induction of apoptosis in various cell types. We assessed the role of SMase in photocytotoxicity. Normal human lymphoblasts accumulated ceramide and underwent apoptosis after Pc 4-PDT. In contrast, Niemann-Pick disease (NPD) lymphoblasts, which are deficient in acid sphingomyelinase (ASMase) activity, failed to respond to Pc 4-PDT with ceramide accumulation and apoptosis, suggesting that ASMase may be a Pc 4-PDT target. NPD lymphoblasts were exposed to exogenous bacterial sphingomyelinase (bSMase) to test whether these defects are reversible. Treatment of NPD cells with bSMase itself led to elevated ceramide formation, which did not translate into induction of apoptosis. However, a combination of Pc 4-PDT + bSMase induced a significant apoptotic response. Thus, the combined treatment of Pc 4-PDT + bSMase, rather than bSMase alone, was required to restore apoptosis in NPD cells. These data support the hypothesis that SMase is a proapoptotic factor determining responsiveness of cells to Pc 4-PDT.

[Evaluation of diagnostic tests for hypocalcemia in critically ill newborns]

OBJECTIVE

To determine sensitivity (Sn), specificity (Sp), positive and negative predictive values (PPV, NPV) of total and calculated calcium and of QTc and QoTc intervals for the diagnosis of hypocalcemia in critically ill newborns.

SETTING

A neonatal intensive care unit.

METHODS

We included all newborn less than 28 days of age; we excluded those with calcium treatment, hypomagnesemia or congenital heart disease. Serum levels of total calcium, albumin and ionic calcium were measured as well as the QTc and QoTc intervals. Values for Sn, Sp, PPV and NPV were calculated according to cutoff points of the literature and with those of our receptor operating curves (ROC). Ionic calcium was considered the gold standard (hypocalcemia < 1.10 mmol/L).

RESULTS

We included 53 newborns; 21/53 (40%) had hypocalcemia. Clinical features were similar among patients with or without hypocalcemia. For total calcium the Sn was 47%; Sp = 87%; PPV = 71% and NPV = 72%. For calculated calcium there values were: 55, 75, 57 and 73; for QoTc: 47, 81, 61 and 70%; and for QTc: 19, 87, 50 and 62% respectively. With the ROC values the Sn for total calcium and QTc was improved.

CONCLUSIONS

Among critical ill newborns, total and calculated calcium were better in identifying patients with hypocalcemia whereas QTc and QoTc were better in those without hypocalcemia.

Signal transduction of stress via ceramide

The sphingomyelin (SM) pathway is a ubiquitous, evolutionarily conserved signalling system analogous to conventional systems such as the cAMP and phosphoinositide pathways. Ceramide, which serves as second messenger in this pathway, is generated from SM by the action of a neutral or acidic SMase, or by de novo synthesis co-ordinated through the enzyme ceramide synthase. A number of direct targets for ceramide action have now been identified, including ceramide-activated protein kinase, ceramide-activated protein phosphatase and protein kinase Czeta, which couple the SM pathway to well defined intracellular signalling cascades. The SM pathway induces differentiation, proliferation or growth arrest, depending on the cell type. Very often, however, the outcome of signalling through this pathway is apoptosis. Mammalian systems respond to diverse stresses with ceramide generation, and recent studies show that yeast manifest a form of this response. Thus ceramide signalling is an older stress response system than the caspase/apoptotic death pathway, and hence these two pathways must have become linked later in evolution. Signalling of the stress response through ceramide appears to play a role in the development of human diseases, including ischaemia/reperfusion injury, insulin resistance and diabetes, atherogenesis, septic shock and ovarian failure. Further, ceramide signalling mediates the therapeutic effects of chemotherapy and radiation in some cells. An understanding of the mechanisms by which ceramide regulates physiological and pathological events in specific cells may provide new targets for pharmacological intervention.

Stress-induced apoptosis and the sphingomyelin pathway

The sphingomyelin pathway is a ubiquitous, evolutionarily conserved signaling system initiated by hydrolysis of the plasma membrane phospholipid sphingomyelin to generate the second messenger ceramide. Sphingomyelin degradation is catalyzed by acid and neutral sphingomyelinase (SMase) isoforms. Most, if not all mammalian cells, appear capable of signaling though the sphingomyelin pathway. Diverse receptor types and environmental stresses utilize the sphingomyelin pathway as a downstream effector system. In some cellular systems, ceramide initiates differentiation or cell proliferation, while in other systems, ceramide signals apoptosis. Recent investigations link the activation of neutral SMase to the extracellular signal regulated kinase (ERK) cascade and pro-inflammatory responses, and acid SMase to the stress-activated protein kinase/c-jun kinase (SAPK/JNK) cascade and apoptotic responses. Environmental stresses act directly on membrane to activate acid pH-dependent sphingomyelinase (ASMase), whereas cytokine receptors signal ASMase activation through motifs termed death domains. The present review focuses on mechanisms of activation of ASMase and on ceramide signaling of the apoptotic response.

Acid sphingomyelinase-deficient human lymphoblasts and mice are defective in radiation-induced apoptosis

Stress is believed to activate sphingomyelinase to generate ceramide, which serves as a second messenger in initiating the apoptotic response. Conclusive evidence for this paradigm, however, is lacking. In the present study, we used a genetic approach to address this issue directly. We show that lymphoblasts from Niemann-Pick patients, which have an inherited deficiency of acid sphingomyelinase activity, fail to respond to ionizing radiation with ceramide generation and apoptosis. These abnormalities are reversible up on restoration of acid sphingomyelinase activity by retroviral transfer of human acid sphingomyelinase cDNA. Acid sphingomyelinase knockout mice also expressed defects in radiation-induced ceramide generation and apoptosis in vivo. Comparison with p53 knockout mice revealed that acid sphingomyelinase-mediated apoptosis and p53-mediated apoptosis are likely distinct and independent. These genetic models provide definitive evidence for the involvement of acid sphingomyelinase in one form of stress-induced apoptosis.

beta-Amyloid regulates gene expression of glial trophic substance S100 beta in C6 glioma and primary astrocyte cultures

S100 beta, a calcium-binding protein synthesized by CNS astrocytes, has trophic effects in vitro (neurite extension and glial proliferation). In Alzheimer's disease and Down's syndrome, severely afflicted brain regions exhibit up to 20-fold higher levels of S100 beta protein, and astrocytes surrounding neuritic plaques exhibit highly elevated levels of S100 beta immunostaining. A major constituent of plaques, beta-amyloid, has been reported to have neurotoxic and neurotrophic effects in vitro. In our study we examined the responses of CNS glia to beta-amyloid. C6 glioma cells and primary rat astrocyte cultures were treated with beta A(1-40) peptide at doses up to 1 microM. Weak mitogenic activity, measured by [3H]thymidine incorporation, was observed. Northern blot analysis revealed increases of S100 beta mRNA within 24 h in a dose-dependent manner. Nuclear run-off transcription assays showed that beta A(1-40) specifically induced new synthesis of S100 beta mRNA in cells maintained in serum, but under serum-free conditions, there was a general elevation of several mRNA species. Corresponding increases of S100 beta protein synthesis were observed by immunoprecipitation of 35S-labeled cellular proteins. To evaluate whether this effect of beta-amyloid was mediated via neurokinin receptors or by calcium fluxes, various agonists and antagonists were tested and found to be ineffective at stimulating S100 beta synthesis. In sum, these in vitro data suggest that in neuropathological conditions, beta-amyloid itself is an agent which may provoke chronic gliosis and the production of trophic substances by astrocytes.

A novel synaptic transmission mediated by a PACAP-like neuropeptide in Drosophila

Neuropeptide-mediated transmission was analyzed at Drosophila larval body-wall neuromuscular junctions. Focal application of vertebrate pituitary adenylyl cyclase-activating polypeptide (PACAP38) to the neuromuscular junction region triggered two temporally distinct muscle responses: an immediate depolarization followed by a large enhancement of K+ current. This late enhancement occurred many minutes after the early depolarization. High frequency stimulation of motor nerve fibers evoked a postsynaptic response mimicking that induced by PACAP38. This evoked response was desensitized by preincubation of the preparation with PACAP38. PACAP38-like immunoreactivity was also found in the Drosophila CNS and at almost all larval neuromuscular junctions. Moreover, an immunoreactive band that compares well with PACAP38 in size was identified in Western blot. These results demonstrate that a PACAP-like peptide may function in invertebrates and that a neuropeptide can evoke two distinct postsynaptic responses, each separated by up to 15 min. In addition, this initial electrophysiological study provides a basis for genetic analysis of neuropeptide function in Drosophila.

CNS glial cells express neurotrophin receptors whose levels are regulated by NGF

Normal CNS glial cells manufacture neurotrophin receptors and are competent to respond to NGF. Neurotrophins bind a common receptor (LNGFR) and ligand-specific, tyrosine kinase-containing subunits (TrkA, TrkB, or TrkC). Northern blots and transcription assays reveal complex transcriptional regulation of LNGFR in astrocytes; from undetectable basal levels, NGF dramatically induces LNGFR within 4-6 h. Oligodendrocytes' relatively high basal levels are unaffected by NGF. TrkA mRNA was undetectable, however, TrkB was present and upregulated by NGF in astrocytes but not oligodendrocytes. The results are consistent with receptor autoregulation by its ligand and suggest that NGF plays a role in normal glial functions.

Characterization of functional nerve growth factor-receptors in a CNS glial cell line: monoclonal antibody 217c recognizes the nerve growth factor-receptor on C6 glioma cells

The biological effects of nerve growth factor (NGF) have been shown to be mediated by the high-affinity form of the nerve growth factor receptor (NGF-R) in sympathetic and sensory neurons, and in PC12 cells. We report here that the central nervous system C6 rat glioma cell line likewise expresses functional high-affinity NGF-Rs. The expression of NGF-R mRNA in C6 cells can be up-regulated by cycloheximide and its own ligand, NGF; and it can be rapidly down-regulated by epidermal growth factor (EGF). Furthermore, C6 cells display NGF responsiveness by expressing c-fos mRNA within 30 minutes of treatment with NGF; and after 4-5 days of NGF exposure, C6 cells cease dividing as measured by [3H]-thymidine uptake, change shape, and reveal neurite-like processes. Scatchard analysis of [125I]-labelled NGF bound to solubilized C6 cells confirms the presence of both high- and low-affinity receptor protein. Crosslinking radiolabeled NGF to its receptor in the presence or absence of excess unlabeled NGF, followed by immunoprecipitation with monoclonal antibody (mAb) 192-IgG (a known anti-NGF-R antibody) and SDS-PAGE reveals a 100 kD band corresponding to the NGF/NGF-R complex. An identical band is observed when the immunoprecipitation is carried out with mAb 217c, suggesting that the 217c epitope is related to NGF-R. The 217c antibody was generated against C6 cells and shown to be a cell surface antibody (Peng et al., Science 215:1102-4, 1982); several investigators have used it subsequently as an immunocytochemical marker for Schwann cells. The significance of NGF-Rs in a CNS glial cell line is unclear, but association of NGF with the control of proliferation and/or differentiation of primitive glial cells is suggested.