Inhibition of nuclear factor-kappaB activation induces apoptosis in cerebellar granule cells

The nuclear factor (NF)-kappaB family of transcription factors plays important roles in the regulation of many activities of neuronal cells, such as synaptic transmission, inflammation, neuroprotection, and neurotoxicity. In resting cells, NF-kappaB activity is present both in the cytoplasm, as an inducible-inactive complex, and in the nucleus, as a constitutive form. Regulation of its inducible activity relies on processing of IkappaB(s), which occurs through the proteasome. Here we show that in cerebellar granule cells (CGC) the induction of apoptosis, by potassium withdrawal (5 mM KCl), decreases the amount of nuclear NF-kappaB. To understand whether NF-kappaB was required for CGC survival, these cells, maintained under depolarizing conditions (25 mM KCl and serum), were treated with proteasome inhibitors. The results show that these treatments reduce the nuclear amount of NF-kappaB and increase p65 cytoplasmic levels, a process partially regulated via IkappaBalpha degradation. These events are also associated with an impairment in CGC survival, with changes in nuclear morphology, induction of DNA laddering, and oligonucleosome formation, consistent with apoptosis. According to the K+ deprivation model, PSI-induced apoptosis is reversed by inhibitors of transcription and translation as well as by specific caspase inhibitors. Together our results show an important role for NF-kappaB in maintaining CGC survival. Indeed, under conditions of mild depolarization (K25) necessary for CGC survival, NF-kappaB is distributed between cytosol and nucleus, whereas, under apoptotic conditions (K5), it is depleted from the nucleus, such as after proteasome inhibitor treatment. Therefore, NF-kappaB nuclear deprivation is involved in the induction of CGC apoptosis.

[The activation of the phosphotyrosine phosphatase eta is responsible for the somatostatin inhibition of PCCl3 thyroid cell proliferation]

BACKGROUND

This study was aimed to identify possible intracellular effectors of the somatostatin (SST) antiproliferative activity, in PCCl3 thyroid cells.

METHODS

To prove the involvement of r-PTPeta in SST's effect, we studied th proliferative activity of subclones of PCCl3 cells that do or do not express this PTP.

RESULTS

SST inhibited PCCl3 TSH+insulin-dependent cell proliferation through the induction of a phosphotyrosine phosphatase (PTP) activity, detected using the synthetic substrate pNPP (+150%, p<0.01). Conversely, PCCl3 cells stably expressing the v-mos oncogene (PCmos) were completely insensitive to SST antiproliferative effects due to the incapability of SST to increase PTP activity, that correlated with the abolishment of the expression of the receptor-like PTP, r-PTPeta. In the cells in which r-PTPeta was transfected (PCmos/ PTPeta) SST inhibited cell proliferation showing a dose-dependence similar to that observed in PCCl3 cells. Conversely, the transfection of a catalytically inactive mutant of r-PTPeta did not restore the responsivity to SST. Also in PCmos/PTPeta cells SST, treatment increased membrane PTP activity.

CONCLUSIONS

SST inhibition of PCC13 cell proliferation requires the activation of r-PTPeta.

[Somatostatinergic control of Kaposi's sarcoma growth through the inhibition of angiogenesis]

Somatostatin and its analogs are active in the inhibition of the proliteration of sst receptor positive endocrine neoplasms, however their activity and mechanism in non-endocrine tumors is not clear. Somatostatin effectively inhibited the growth of a Kaposi's sarcoma xenograft in nude mice, yet in vitro the tumor cells did not express any known somatostatin receptors and were not growth inhibited by somatostatin. Histological examination revealed limited vascularization in the somatostatin treated tumors as compared to the controls. Somatostatin was a potent inhibitor of angiogenesis in an in vivo assay. In vitro, somatostatin inhibited endothelial cell growth and invasion. Migration of monocytes, important mediators of the angiogenic cascade, was also inhibited by somatostatin. Both cells types expressed somatostatin receptor mRNAs. These data demonstrate that somatostatin is a potent anti-tumor angiogenesis compound directly affecting both endothelial and monocytic cells. The debated function of somatostatin in tumor treatment and the design of therapeutic protocols should be reexamined considering these data.

Design of a Binary Grating with Subwavelength Features that Acts as a Polarizing Beam Splitter

A binary diffractive optical element, acting as a polarizing beam splitter, is proposed and analyzed. It behaves like a transmissive blazed grating, working on the first or the second diffraction order, depending on the polarization state of the incident radiation. The grating-phase profile required for both polarization states is obtained by means of suitably sized subwavelength groups etched in an isotropic dielectric medium. A rigorous electromagnetic analysis of the grating is presented, and numerical results concerning its performances in terms of diffraction efficiency as well as frequency and angular bandwidths are provided.

HIV-1 Tat causes apoptotic death and calcium homeostasis alterations in rat neurons

We investigated the role of the HIV-1 protein Tat in AIDS-associated dementia, by studying its toxicity on rat cortical and hippocampal neurons in vitro. We evaluated the involvement of astroglial cells and of caspase transduction pathway in determining Tat toxicity. Here we report that synthetic Tat(1-86) induced apoptotic death on cultured rat neurons in a time-dependent manner that was not influenced by glial coculture, and that was abolished by blocking caspase transduction pathway. A microfluorimetric analysis on the Tat excitatory properties on neurons, and its effect on intracellular calcium concentrations, revealed that Tat(1-86) induced increase in cytoplasmic free calcium concentrations in rat hippocampal and cortical neurons. This effect required extracellular calcium and was differently reduced by voltage dependent calcium channel blockers and both NMDA and non-NMDA glutamate receptors antagonists. Furthermore, we observed that Tat(1-86)-treated neurons showed increased sensitivity to the glutamate excitotoxicity. Thus, the Tat-induced neuronal injury seems to occur through a direct interaction of the protein with neurons, requires activation of caspases, and is likely to derive from Tat(1-86)-induced calcium loads and disruption of glutamatergic transmission.

The activation of the phosphotyrosine phosphatase eta (r-PTP eta) is responsible for the somatostatin inhibition of PC Cl3 thyroid cell proliferation

The aim of this study was the characterization of the intracellular effectors of the antiproliferative activity of somatostatin in PC Cl3 thyroid cells. Somatostatin inhibited PC Cl3 cell proliferation through the activation of a membrane phosphotyrosine phosphatase. Conversely, PC Cl3 cells stably expressing the v-mos oncogene (PC mos) were completely insensitive to the somatostatin antiproliferative effects since somatostatin was unable to stimulate a phosphotyrosine phosphatase activity. In PC mos cells basal phosphotyrosine phosphatase activity was also reduced, suggesting that the expression of a specific phosphotyrosine phosphatase was impaired in these transformed cells. We suggested that this phosphotyrosine phosphatase could be r-PTP eta whose expression was abolished in the PC mos cells. To directly prove the involvement of r-PTP eta in somatostatin's effect, we stably transfected this phosphatase in PC mos cells. This new cell line (PC mos/PTP eta) recovered somatostatin's ability to inhibit cell proliferation, showing dose-dependence and time course similar to those observed in PC Cl3 cells. Conversely, the transfection of a catalytically inactive mutant of r-PTP eta did not restore the antiproliferative effects of somatostatin. PC mos/PTP eta cells showed a high basal phosphotyrosine phosphatase activity which, similarly to PC Cl3 cells, was further increased after somatostatin treatment. The specificity of the role of r-PTP eta in somatostatin receptor signal transduction was demonstrated by measuring its specific activity after somatostatin treatment in an immunocomplex assay. Somatostatin highly increased r-PTP eta activity in PCCl3 and PC mos/PTP eta (+300%, P < 0.01) but not in PCmos cells. Conversely, no differences in somatostatin-stimulated SHP-2 activity, (approximately +50%, P < 0.05), were observed among all the cell lines. The activation of r-PTP eta by somatostatin caused, acting downstream of MAPK kinase, an inhibition of insulin-induced ERK1/2 activation with the subsequent blockade of the phosphorylation, ubiquitination, and proteasome degradation of the cyclin-dependent kinase inhibitor p27(kip1). Ultimately, high levels of p27(kip1) lead to cell proliferation arrest. In conclusion, somatostatin inhibition of PC Cl3 cell proliferation requires the activation of r-PTP eta which, through the inhibition of MAPK activity, causes the stabilization of the cell cycle inhibitor p27(kip1).

[Somatostatin and its receptors. Role in the control of cell proliferation]

A number of studies have been carried out over the past year to characterise the physiological functions and possible therapeutic applications of somatostatin (sst). Somatostatin is one of the most widespread peptides in the body and it fulfils a very wide spectrum of actions in the various organs and tissues. The aim of this review is to make a critical analysis of knowledge of the structure and physiology of sst and its receptors, together with the possible role played by this peptide in cell proliferation in animal models and the treatment of human tumours. In particular, the authors discuss the most recent findings on cell and intracell mechanisms regulated by somatostatin receptors and how this knowledge may encourage the development of more effective and selective new molecules in terms of therapy.

Chemokines and their receptors in the central nervous system

Chemokines are a family of proteins associated with the trafficking of leukocytes in physiological immune surveillance and inflammatory cell recruitment in host defence. They are classified into four classes based on the positions of key cystiene residues: C, CC, CXC, and CX3C. Chemokines act through both specific and shared receptors that all belong to the superfamily of G-protein-coupled receptors. Besides their well-established role in the immune system, several recent reports have demonstrated that these proteins also play a role in the central nervous system (CNS). In the CNS, chemokines are constitutively expressed by microglial cells, astrocytes, and neurons, and their expression can be increased after induction with inflammatory mediators. Constitutive expression of chemokines and chemokine receptors has been observed in both developing and adult brains, and the role played by these proteins in the normal brain is the object of intense study by many research groups. Chemokines are involved in brain development and in the maintenance of normal brain homeostasis; these proteins play a role in the migration, differentiation, and proliferation of glial and neuronal cells. The chemokine stromal cell-derived factor 1 and its receptor, CXCR4, are essential for life during development, and this ligand-receptor pair has been shown to have a fundamental role in neuron migration during cerebellar formation. Chemokine and chemokine receptor expression can be increased by inflammatory mediators, and this has in turn been associated with several acute and chronic inflammatory conditions. In the CNS, chemokines play an essential role in neuroinflammation as mediators of leukocyte infiltration. Their overexpression has been implicated in different neurological disorders, such as multiple sclerosis, trauma, stroke, Alzheimer's disease, tumor progression, and acquired immunodeficiency syndrome-associated dementia. An emerging area of interest for chemokine action is represented by the communication between the neuroendocrine and the immune system. Chemokines have hormone-like actions, specifically regulating the key host physiopathological responses of fever and appetite. It is now evident that chemokines and their receptors represent a plurifunctional family of proteins whose actions on the CNS are not restricted to neuroinflammation. These molecules constitute crucial regulators of cellular communication in physiological and developmental processes.

The beta-amyloid precursor protein APP is tyrosine-phosphorylated in cells expressing a constitutively active form of the Abl protoncogene

The cytosolic domain of the beta-amyloid precursor protein APP interacts with three PTB (phosphotyrosine binding domain)-containing adaptor proteins, Fe65, X11, and mDab1. Through these adaptors, other molecules can be recruited at the cytodomain of APP; one of them is Mena, that binds to the WW domain (a protein module with two conserved tryptophans) of Fe65. The enabled and disabled genes of Drosophila, homologues of the mammalian Mena and mDab1 genes, respectively, are genetic modulators of the phenotype observed in flies null for the Abl tyrosine kinase gene. The involvement of Mena and mDab1 in the APP-centered protein-protein interaction network suggests the possibility that Abl plays a role in APP biology. We show that Fe65, through its WW domain, binds in vitro and in vivo the active form of Abl. Furthermore, in cells expressing the active form of Abl, APP is tyrosine-phosphorylated. Phosphopeptide analysis and site-directed mutagenesis support the hypothesis that Tyr(682) of APP(695) is the target of this phosphorylation. Co-immunoprecipitation experiments demonstrate that active Abl and tyrosine-phosphorylated APP also form a stable complex, which could result from the interaction of the pYENP motif of the APP cytodomain with the SH2 domain of Abl. These results suggest that Abl, Mena, and mDab1 are involved in a common molecular machinery and that APP can play a role in tyrosine kinase-mediated signaling.

Stromal cell-derived factor-1alpha induces astrocyte proliferation through the activation of extracellular signal-regulated kinases 1/2 pathway

Stromal cell-derived factor-1 (SDF-1), the ligand of the CXCR4 receptor, is a chemokine involved in chemotaxis and brain development that also acts as co-receptor for HIV-1 infection. We previously demonstrated that CXCR4 and SDF-1alpha are expressed in cultured type-I cortical rat astrocytes, cortical neurones and cerebellar granule cells. Here, we investigated the possible functions of CXCR4 expressed in rat type-I cortical astrocytes and demonstrated that SDF-1alpha stimulated the proliferation of these cells in vitro. The proliferative activity induced by SDF-1alpha in astrocytes was reduced by PD98059, indicating the involvement of extracellular signal-regulated kinases (ERK1/2) in the astrocyte proliferation induced by CXCR4 stimulation. This observation was further confirmed showing that SDF-1alpha treatment selectively activated ERK1/2, but not p38 or stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK). Moreover, both astrocyte proliferation and ERK1/2 phosphorylation, induced by SDF-1alpha, were inhibited by pertussis toxin (PTX) and wortmannin treatment indicating the involvement of a PTX sensitive G-protein and of phosphatidyl inositol-3 kinase in the signalling of SDF-1alpha. In addition, Pyk2 activation represent an upstream components for the CXCR4 signalling to ERK1/2 in astrocytes. To our knowledge, this is the first report demonstrating a proliferative effect for SDF-1alpha in primary cultures of rat type-I astrocytes, and showing that the activation of ERK1/2 is responsible for this effect. These data suggest that CXCR4/SDF-1 should play an important role in physiological and pathological glial proliferation, such as brain development, reactive gliosis and brain tumour formation.

Amino-terminal modification and tyrosine phosphorylation of [corrected] carboxy-terminal fragments of the amyloid precursor protein in Alzheimer's disease and Down's syndrome brain

The carboxy-terminal fragments (CTFs) of the amyloid precursor protein (APP) are considered beta-amyloid (Abeta) precursors as well as molecular species possibly amyloidogenic and neurotoxic by [corrected] in vitro or in animal models. The CTF's role in the pathogenesis of Alzheimer's disease (AD) is however relatively unexplored in human brain. In this study, we analyzed brain extracted CTFs in subjects with AD, non-AD control, and Down's syndrome (DS) cases. Our data indicate that: (i) In fetal DS subjects CTFs levels are increased in comparison to age-matched control, suggesting that the enhanced CTFs formation is important for the early occurrence of plaques deposition in DS. No significant difference in CTFs level [corrected] between AD and age-matched control cases. (ii) CTFs modified at their N-terminus are the direct precursors of similarly N-terminally modified Abeta peptides, which constitute the most abundant species in AD and DS plaques. This observation suggests that N-truncated Abeta peptides are formed directly at beta-secretase level and not through a progressive proteolysis of full-length Abeta1-40/42. (iii) Among the differently cleaved CTFs, only the 22- and 12.5-kDa CTF polypeptides are tyrosine phosphorylated in both AD and control brain while the full-length APP and the CTFs migrating below the 12.5-kDa marker are not phosphorylated, suggesting that APP and CTFs may be involved in different pathways depending on their length and sequences. This study provides evidence that CTFs constitute in human brain a molecular species directly involved in AD pathogenesis and in the development of the AD-like pathology in DS subjects.

C60 carboxyfullerene exerts a protective activity against oxidative stress-induced apoptosis in human peripheral blood mononuclear cells

C60 carboxyfullerene is a novel buckminsterfullerene-derived compound that behaves as a free-radical scavenger. In the present report, we investigated whether this drug exerts a protective activity against oxidative stress-induced apoptosis. Human peripheral blood mononuclear cells (PBMCs) were challenged by 2-deoxy-d-ribose (dRib) or TNF-alpha plus cycloheximide as agents that trigger apoptosis by interfering with the redox status of cell and mitochondrial membrane potential. We found that carboxyfullerene was able to protect quiescent PBMCs from apoptosis caused either by 2-deoxy-d-ribose or TNF-alpha plus cycloheximide by a mechanism partially involving the mitochondrial membrane potential integrity, known to be associated with early stages of apoptosis. These results represent the first indication for a target activity of buckminsterfullerenes on cells of the immune system and their mitochondria.

Carboxyfullerenes protect human keratinocytes from ultraviolet-B-induced apoptosis

Carboxyfullerene, a water-soluble carboxylic acid derivative of a fullerene, which acts as a free-radical scavenger, was investigated as a protective agent against ultraviolet-light-induced damage in human keratinocytes. First, we demonstrate that carboxyfullerene is not cytotoxic for these cells. In addition, this compound significantly reduces the ultraviolet-B-induced inhibition of keratinocyte proliferation and protects keratinocytes from apoptosis caused by ultraviolet B irradiation in a time- and dose-dependent fashion. Furthermore, the percentage of cells with depolarized mitochondria is significantly lower in ultraviolet-B-irradiated keratinocytes pretreated with carboxyfullerene than in cells provided with diluent alone. Carboxyfullerene also protects human keratinocytes from apoptosis induced by exposure to deoxy-D-ribose, a sugar that causes cell death through a pathway involving oxidative stress. On the other hand, ultraviolet B downregulates bcl-2 levels in human keratinocytes, and carboxyfullerene fails to prevent this effect. These results suggest that carboxy- fullerene protects human keratinocytes from ultraviolet B damage possibly via a mechanism interfering with the generation of reactive oxygen species from depolarized mitochondria without the involvement of bcl-2.

Generation of an apoptotic intracellular peptide by gamma-secretase cleavage of Alzheimer's amyloid beta protein precursor

The amyloid beta protein precursor (AbetaPP) is sequentially processed by beta- and gamma-secretases to generate the Abeta peptide. The biochemical path leading to Abeta formation has been extensively studied since extracellular aggregates of amyloidogenic forms of Abeta peptide (Abeta42) are considered the culprit of Alzheimer's disease. Aside from its pathological relevance, the biological role of AbetaPP proteolysis is unknown. Although never previously described, cleavage of AbetaPP by gamma-secretase should release, together with Abeta, a COOH-terminal AbetaPP Intracellular Domain, herein termed AID. We have now identified AID-like peptides in brain tissue of normal control and patients with sporadic Alzheimer's disease and demonstrate that AID acts as a positive regulator of apoptosis. Thus, overproduction of AID may add to the toxic effect of Abeta42 aggregates and further accelerate neurodegeneration.

Apoptotic cell death and impairment of L-type voltage-sensitive calcium channel activity in rat cerebellar granule cells treated with the prion protein fragment 106-126

Prion diseases are neurodegenerative pathologies characterized by the accumulation, in the brain, of altered forms of the prion protein (PrP), named PrP(Sc). A synthetic peptide homologous to residues 106-126 of PrP (PrP106-126) was reported to maintain the neurodegenerative characteristics of PrP(Sc). We investigated the intracellular mechanisms involved in PrP106-126-dependent degeneration of primary cultures of cerebellar granule neurons. Prolonged exposure of such neurons to PrP106-126 induced apoptotic cell death. The L-type voltage-sensitive calcium channel blocker nicardipine reproduced this effect, suggesting that blockade of Ca(2+) entry through this class of calcium channels may be responsible for the granule cell degeneration. Microfluorometric analysis showed that PrP106-126 caused a reduction in cytosolic calcium levels, elicited by depolarizing K(+) concentrations in these neurons. Electrophysiological studies demonstrated that PrP106-126 and nicardipine selectively reduce the L-type calcium channel current. These data demonstrate that PrP106-126 alters the activity of L-type voltage-sensitive calcium channels in rat cerebellar granule cells and suggest that this phenomenon is related to the cell death induced by the peptide.

Cabergoline modulation of alpha-subunits and FSH secretion in a gonadotroph adenoma

Most non-functioning pituitary adenomas respond poorly to medical therapy. We describe the case of a 62-year-old man who presented with clinical features of an invasive macroadenoma. Baseline hormonal evaluation revealed increased FSH and alpha-subunit (alpha-SU) levels. Transsphenoidal exeresis followed by radiotherapy (RT) was performed. Almost all neoplastic cells were intensely immunoreactive for alpha-SU. On PCR analysis, specific amplification products were observed for somatostatin 2, 3 and 5 receptors as well as for both short and long isoforms of the dopamine D2 receptor. In vitro, alpha-SU and FSH were released into the medium by adenoma cells and increased after TRH stimulation. After surgery, alpha-SU and FSH levels were still elevated. Short-term slow-release lanreotide treatment did not modify either alpha-SU or FSH levels. Cabergoline was started and a fast and long-lasting decrease in alpha-SU and, to a lesser extent, in FSH was observed. The tumor remnant was unmodified on magnetic resonance imaging 3 years after surgery and RT. This case report shows that the in vitro expression of somatostatin receptors may not be directly associated to the in vivo response of alpha-SU and FSH to lanreotide, probably because of a functional uncoupling of the receptors. Cabergoline should be considered as an effective therapy for hormonal, and perhaps proliferative, control of gonadotroph adenoma remnants before the effects of RT are fully effective.

Intracellular mechanisms mediating the neuronal death and astrogliosis induced by the prion protein fragment 106-126

Prion encephalopathies include fatal diseases of the central nervous system of men and animals characterized by nerve cell loss, glial proliferation and deposition of amyloid fibrils into the brain. During these diseases a cellular glycoprotein (the prion protein, PrP(C)) is converted, through a not yet completely clear mechanism, in an altered isoform (the prion scrapie, PrP(Sc)) that accumulates within the brain tissue by virtue of its resistance to the intracellular catabolism. PrP(Sc) is believed to be responsible for the neuronal loss that is observed in the prion disease. The PrP 106-126, a synthetic peptide that has been obtained from the amyloidogenic portion of the prion protein, represents a suitable model for studying the pathogenic role of the PrP(Sc), retaining, in vitro, some characteristics of the entire protein, such as the capability to aggregate in fibrils, and the neurotoxicity. In this work we present the results we have recently obtained regarding the action of the PrP 106-126 in different cellular models. We report that the PrP 106-126 induces proliferation of cortical astrocytes, as well as degeneration of primary cultures of cortical neurons or of neuroectodermal stable cell lines (GH(3) cells). In particular, these two opposite effects are mediated by the same attitude of the peptide to interact with the L-type calcium channels: in the astrocytes, the activity of these channels seems to be activated by PrP 106-126, while, in the cortical neurons and in the GH(3) cells, the same treatment causes a blockade of these channels causing a toxic effect.

Immunofluorescence and biochemical techniques to detect nuclear localization of ciliary neurotrophic factor in glial cells

Ciliary neurotrophic factor (CNTF) promotes the survival of several populations of neurons, including sensory and motor neurons. It is mainly produced by Schwann cells and astrocytes and exerts its biological function via a specific membrane receptor. We recently determined the nuclear localization of CNTF in producing cells, after transfection and in the heterologous system of Xenopus oocytes. In the present paper, we describe in detail the techniques for the detection of CNTF in the nucleus of rat astrocytes, transfected cells, isolated nuclei and injected Xenopus oocytes.

Somatostatin receptor 1 (SSTR1)-mediated inhibition of cell proliferation correlates with the activation of the MAP kinase cascade: role of the phosphotyrosine phosphatase SHP-2

The mitogen activated protein (MAP) kinase cascade represents one of the major regulator of cell growth by hormones and growth factors. However, although the activation of this intracellular pathway has been often regarded as mediator of cell proliferation, in many cell types the increase in MAP kinase (also called extra-cellular signal regulated kinase: ERK) activity may result in cell growth arrest, depending on the length or the intensity of the stimulation. In this review we examine recent data concerning the effects of somatostatin on the MAP kinase cascade through one of its major receptor subtype, the somatostatin receptor 1 (SSTR1), stably expressed in CHO-K1 cells. Somatostatin inhibits the proliferative effects of basic FGF (bFGF) in CHO-SSTR1 cell line. However, in these cells, somatostatin robustly activates the MAP kinase and augments bFGF-induced stimulation of ERK. We show that the activation of ERK via SSTR1 is mediated by the betagamma subunit of a pertussis toxin-sensitive G-protein and requires both the small G protein Ras and the serine/threonine kinase Raf-1. Moreover the phosphatidyl inositol-3kinase and the cytosolic tyrosine kinase c-src participate in the signal transduction regulated by SSTRI to activate ERK, as well as it is involved the protein tyrosine phosphatase (PTP) SHP-2. Previous studies have suggested that somatostatin-stimulated PTP activity mediates the growth inhibitory actions of somatostatin, in CHO-SSTR1 cells. Thus, the activation of SHP-2 by SSTR1 may mediate the antiproliferative activity of somatostatin. SHP-2 may. in turn, regulate the activity of kinases upstream of ERK that require tyrosine dephosphorylation to be activated, such as c-src. Finally, the synergism between somatostatin and bFGF in the activation of ERK results in an increased expression of the cyclin-dependent kinase inhibitor p21cip/WAF1 as molecular effector of the antiproliferative activity of somatostatin.

The role of MRI in the surgical selection of cerebral metastases

BACKGROUND

About one third of patients operated on for a "single" cerebral metastasis diagnosed by CT scan have probably more than one lesion. In fact, Gd-DTPA enhanced MRI has proved to be more sensitive than CT in detecting the number of cerebral metastases, reducing the number of patients candidate to surgery.

METHODS

Thirty-five patients with a CT scan picture of a single cerebral neoplasm of presumable metastatic nature performed a Gd-DTPA enhanced cerebral MRI. In 25 cases MR images confirmed a single lesion, while in other 10 (28.6%) showed a number of metastases ranging from 2 to 6. In order to assess the utility of MRI in surgical selection of patients and then to reconsider the concept of operability limited to single brain metastases only, we compared the survival of the 25 cases who preoperatively performed MRI (MRI group) with that of other 25 consecutive patients operated on in pre-MR era (during a 24-month period), with a CT picture of single cerebral metastasis (non-MRI group).

RESULTS

The median survival was 36 +/- 5 weeks for MRI group and 40 +/- 15 for non-MRI group. The Kaplan-Meier product-limit survival analysis and the log-rank test do not reveal any statistically significative difference of survival between the two groups.

CONCLUSIONS

Even if the number of patients is limited for definitive considerations, our preliminary results seem to suggest that the further selection of surgical cases obtained with MRI could not impact significatively the survival. Therefore, in selected patients with multiple cerebral metastases a surgical treatment could be reasonable.

The importance of surgery in supratentorial ependymomas. Long-term survival in a series of 23 cases

In view of the widely recognized correlation between extent of surgical resection and length of survival of children with intracranial ependymoma and the statement that total resection is more likely to be achieved in supratentorial than infratentorial primaries, we decided to review our experience with supratentorial ependymomas and the pertinent literature to verify the importance of surgery in treating this subgroup of pediatric ependymal neoplasms. Of 23 patients operated on, 12 are still alive without evidence of disease 72-357 months after surgery (mean 227, median 237 months). One girl treated by surgery alone was lost to follow-up after 234 months when she, and 7 other patients in the series, had already passed the end of the period of risk for recurrence according to Collins' law. Six surviving patients (2 with subependymoma and 4 with ependymoma) were treated by surgery alone and only 1, the oldest in the series, had to undergo a second operation for recurrence after 10 years. The idea of treating intracranial ependymoma by surgery alone was favored by eminent neurosurgeons in the past and has recently received renewed attention. This was in part the consequence of recognizing that unlike diffuse astrocytoma, in which neoplastic cells can be found up to several centimeters away from the apparent tumor borders, ependymoma has more or less well-defined margins and grows mainly by expansion. Early experience with the policy of electively deferring adjuvant therapy after radiologically controlled total resection of ependymoma seems encouraging, although postoperative MRI does not yet indicate absolute certainty. Close surveillance is recommended. The majority of ependymomas so far treated by surgery alone, with relatively good success, have been supratentorial. In conclusion, on the basis of our experience and a review of the literature we favor a change in attitude to the management of intracranial ependymomas, especially of the cerebrum, with radiologically controlled radical surgery alone followed by close surveillance with periodic MR imaging until the child passes the period of risk for recurrence according to Collins' law as the initial option. In children less than 3 years old the period of surveillance should be doubled. In case of recurrence, reoperation should be considered first, particularly for supratentorial primaries. Radiotherapy continues to be a major option in malignant ependymoma and unresectable primary or recurrent benign ependymoma.

C3-fullero-tris-methanodicarboxylic acid protects cerebellar granule cells from apoptosis

Buckminsterfullerenols were recently investigated for their protective properties in different models of acute and chronic neurodegeneration. We tested C3-fullero-tris-methanodicarboxylic acid in our in vitro model of apoptotic neuronal death, which consists of shifting the culture K+ concentration from 25 to 5 mM for rat cerebellar granule cells. The impairment of mitochondrial respiratory function as well as chromatin derangement and fragmentation of DNA in apoptotic oligonucleosomes that occur in these conditions were protected by this compound in a concentration-dependent way. To assess whether antioxidant activity could account for the rescue of cerebellar granule cells from apoptosis, we tested the fullerene derivative under FeSO4-induced oxidative stress and found significant protection. Thus, we visualized membrane and cytoplasmic peroxides and reactive oxygen species and found a significant reduction of the species after 24 h in 5 mM K+ with the fullerene derivative. Such evidence suggests that this compound exerts a protective role in cerebellar granule cell apoptosis, likely reducing the oxidative stress.

A novel mechanism for the melatonin inhibition of testosterone secretion by rat Leydig cells: reduction of GnRH-induced increase in cytosolic Ca2+

The site of inhibition, by melatonin, of GnRH-dependent testosterone secretion was investigated in adult rat Leydig cells cultured in vitro. The various effects downstream of the binding of GnRH to its own receptor were isolated and mimicked by specific drugs. Testosterone secretion was then evaluated after 3 h stimulation with GnRH, thapsigargin (1 microM), phorbol-12-myristate-13-acetate (100 nM), arachidonic acid (20 microM), and ionomycin (1 microM) in the presence or absence of melatonin (215 nM). The effect of melatonin on the GnRH-induced changes in cytoplasmic calcium concentration ([Ca(2+)](i)) was also studied, using Fura-2 as fluorescent Ca(2+) indicator. Melatonin attenuated the increase in [Ca(2+)](i) and inhibited the testosterone secretion induced by GnRH, but not that induced by ionomycin. Both ionomycin and thapsigargin potentiated GnRH-induced testosterone secretion; however, ionomycin, but not thapsigargin, partially prevented the inhibitory effect of melatonin on cells stimulated with GnRH. The effect of melatonin was probably dependent on the binding of melatonin to its Gi-protein-coupled receptor, as the inhibitory effect on GnRH-induced secretion was supressed in cells pretreated with pertussis toxin in a concentration of 180 ng/ml for 20 h. Assay of 17-hydroxy-progesterone showed that, irrespective of the treatment, cells cultured with melatonin secreted greater amounts than controls. We conclude that melatonin reduces GnRH-induced testosterone secretion by 1) decreasing [Ca(2+)](i), through impairment of the GnRH-dependent release of Ca(2+) from intracellular stores and 2) blocking 17-20 desmolase enzymatic activity, an effect that occurs irrespective of changes in [Ca(2+)](i).