Proteomic Analysis on Sequential Samples of Cystic Fluid Obtained from Human Brain Tumors

Cystic formation in human primary brain tumors is a relatively rare event whose incidence varies widely according to the histotype of the tumor. Composition of the cystic fluid has mostly been characterized in samples collected at the time of tumor resection and no indications of the evolution of cystic content are available. We characterized the evolution of the proteome of cystic fluid using a bottom-up proteomic approach on sequential samples obtained from secretory meningioma (SM), cystic schwannoma (CS) and cystic high-grade glioma (CG). We identified 1008 different proteins; 74 of these proteins were found at least once in the cystic fluid of all tumors. The most abundant proteins common to all tumors studied derived from plasma, with the exception of prostaglandin D2 synthase, which is a marker of cerebrospinal fluid origin. Overall, the protein composition of cystic fluid obtained at different times from the same tumor remained stable. After the identification of differentially expressed proteins (DEPs) and the protein-protein interaction network analysis, we identified the presence of tumor-specific pathways that may help to characterize tumor-host interactions. Our results suggest that plasma proteins leaking from local blood-brain barrier disruption are important contributors to cyst fluid formation, but cerebrospinal fluid (CSF) and the tumor itself also contribute to the cystic fluid proteome and, in some cases, as with immunoglobulin G, shows tumor-specific variations that cannot be simply explained by differences in vessel permeability or blood contamination.

Increased L1CAM (CD171) levels are associated with glioblastoma and metastatic brain tumors

L1 cell adhesion molecule (L1CAM) is a member of the immunoglobulin-like cell-adhesion molecule family that was shown to be associated with a worse prognosis in several human cancers. L1 ectodomain shedding via vesicles or exosomes has been detected in extracellular fluids after cleavage from the cell surface by metalloproteases. We evaluated the presence of L1CAM in cyst fluid and tissue from glioblastomas or brain metastases.The amount of L1CAM in cyst fluid of 9 glioblastomas and 11 brain metastases was assessed using enzyme-linked immunosorbent assay (ELISA). Corresponding tumor tissue slices were stained immunohistochemically for L1CAM. Cerebrospinal fluid of 20 non-tumor patients served as controls.Mean levels of L1CAM in tumor cyst fluid were significantly higher in glioblastoma (6118 ± 4095 ng/mL) and metastasis patients (8001 ± 6535 ng/mL) than in CSF of control patients (714 ± 22 ng/mL). The immunohistochemical expression of L1CAM in corresponding tissue was significantly higher in metastases than in glioblastomas.The present study demonstrates high levels of L1CAM in cyst fluid of glioblastoma and metastatic brain tumors. Soluble L1CAM may represent a motility promoting molecule in cancer progression, a co-factor for development of tumor cysts and a target for new treatment strategies.

SELDI-TOF analysis of glioblastoma cyst fluid is an approach for assessing cellular protein expression

OBJECTIVES

In about 10% of glioblastoma patients, preoperative MRI discloses the presence of tumor cysts. Whereas the impact of cystic appearance on prognosis has been discussed extensively, only little is known about the tumor cyst fluid. In this study, we tested the feasibility of the surface enhanced laser desorption ionization time of flight (SELDI-TOF) technique to detect cyst fluid proteins.

METHODS

Cyst fluid was collected from 21 glioblastoma patients for SELDI-TOF analysis and compared to control cerebrospinal fluids from 15 patients with spinal stenosis. Resulting protein peaks with significant differences between groups were further described, using the molecular weight in an internet search of protein databases and publications. Two potential cyst fluid proteins, basigin and ferritin light chain, were selected for immunohistological detection in the histologic slides of the patients, metallothionein (MT) served as negative control.

RESULTS

As supposed from the results of the SELDI-TOF analysis, basigin and ferritin were detected immunohistochemically in the cyst wall, whereas MT was more equally distributed between the cyst wall and the surrounding tumor tissue. Median survival time of the patients was 20 months (range 2 to 102 months) and correlated with age, but not with expression of the three proteins.

DISCUSSION

The SELDI-TOF approach reveals a number of proteins, potentially present in glioblastoma cyst fluid. Identification of these proteins in tumor cells may help understand the pathogenetic pathways and the prognostic value of cystic changes.

Magnetic resonance spectroscopic imaging associated with analysis of fluid in cystic brain tumors

OBJECTIVE

There is a growing interest in cystic lesions of the brain. Examining the cyst content of brain tumors may contribute in determining the malignancy of the given tumor accompanied by a cyst.

METHODS

In this work, samples of cyst fluid from 18 patients with brain tumor were collected and studied biochemically regarding their protein, lactate contents and pH values; magnetic resonance spectroscopic images of these patients were also compared. We investigated the relation between the grade of malignancy and the lactate concentration and the discrepancy between the high levels of lactate in cysts and their alkaline environment.

RESULTS

There appears to be a positive relation between the grade of malignancy and the concentration of lactate in the cysts' fluid. A significant two-fold increase in lactate concentration in malignant tumors cysts has been found as compared with the more benign tumor cysts (p<0.001). This increase in lactate level is probably because of aerobic glycolysis, which causes lactate production by the tumor.

DISCUSSION

High lactate levels found through magnetic resonance spectroscopy are positively related to the grade of tumor malignancy. The pH values in the cyst fluids were above normal, resulting to a discrepancy in high levels of lactate in the cyst and the alkaline environment. This suggests efflux of H+ ions by a Na/H exchange mechanism to compensate for the change of pH.

Migration of human glioma cells in response to tumour cyst fluids

Glial tumours often show high degrees of local invasion that lead to local recurrence of the disease. Extracellular matrix components as well as soluble factors may play a critical role in this poorly understood process. Cyst fluid from human brain tumours may accumulate such autocrine produced factors and may represent a source were those factors may be easily obtained and studied. We have studied the effect of cyst fluids harvested from 17 glial tumours, 3 meningiomas, and three metastases on the motility of established human glioma cell lines. Both cyst fluids of high grade and low grade gliomas contained varying degrees of motility enhancing activity. No such activity was identified in cyst fluids obtained from meningiomas. The relation of mitogenic and motogenic activity in three selected cyst fluids was analysed using a quantitative monolayer migration assay. Quantitative analysis of cyst fluid effects on both proliferation and migration indicate that tumour cyst fluids contain factors that strongly stimulate cell migration and that maximum stimulation of migration did not occur at concentrations optimal for cell proliferation. Our findings indicate that glial tumours in fact produce and secrete soluble factors that may contribute to their dissemination in brain tissue.

Insulin-like growth factors and IGF binding proteins in cyst fluid from patients with craniopharyngioma prior to intracavitary irradiation with Yttrium and thereafter

Aim-To examine a series of cyst fluid samples from patients with craniopharyngioma at various stages of treatment in order to evaluate the use of insulin-like growth factors (IGFs) and IGF binding proteins as tumour markers or indicators of successful treatment, or both.Methods-Cyst fluid samples were obtained by stereotactic puncture prior to the intracavitary application of (90)Yttrium and at subsequent occasions. Analysis was performed by gel chromatography, radio-immunoassays, binding studies, and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) with subsequent western blotting.Results-IGF-I, -II and IGF binding protein-1 concentrations were measured in three craniopharyngioma cyst fluid samples. Immunoreactive IGF-I and IGF binding protein-1 concentrations in these three samples were between 6 and 29 ng/ml, and 17 and 48 ng/ml, respectively. In contrast, the IGF-II concentrations measured in 19 cyst fluid samples from seven patients with craniopharyngioma at various stages of treatment were much higher at 25-671 ng/ml. SDS-PAGE and subsequent western blotting using [(125)I]IGF-II as the ligand gave bands with estimated molecular weights of 330, 220, 135, 96, 46, 43, 34, 29, and 13.5 kDa in one adult, and identical bands at 220, 41.5, 37.5, 32, and 19 kDa in three cyst fluid samples from three children with craniopharyngioma.Conclusions-These results suggest that IGFs and IGF binding proteins are secreted by craniopharyngiomas and that they may alter the growth characteristics of these tumours. Furthermore, the distinct pattern of IGF binding protein sizes might be used as a tool for the differential diagnosis of tumours of the central nervous system.

Identification and characterization of an anti-tyrosine kinase factor in cystic gliomas

In view of the frequent activation of the epidermal growth factor receptor (EGF-R) in gliomas and autocrine hypothesis, we searched for 'EGF-like' factor(s) in cystic fluids (CFs) associated with gliomas. Membranes of A431 cells, which overexpress EGF-R, were used to explore such activity in 20 CFs. In all cases CFs induced inhibition of EGF-R phosphorylation. Biochemical analysis revealed an anti-tyrosine kinase activity which was identified as a 18 kDa proteic factor. Effectiveness at high dilution and anti-proliferative effect on living cells in culture suggest that this factor may be involved in the negative regulation of glial oncogenesis.

Human brain tumor cyst fluid is mitogenic for primary astrocytes in culture

Tumor cyst fluid from five patients with malignant glial neoplasms was assayed for mitogenic activity by measuring [3H]thymidine uptake by rat astrocyte cultures in serum-free defined media. Cyst fluid from all patients stimulated [3H]thymidine uptake three- to fourfold in astrocyte cultures in comparison with untreated controls. Mitogenic activity was found to be soluble and resistant to freezing, but inactivated by heat and trypsin. The activity was retained by ultrafiltration through a 100-kd molecular weight filter. It appears from these results that mitogenic factor(s) for nonneoplastic astrocytes are present in human brain tumor cyst fluid and that such factors appear to be protein in nature and associated with a complex of molecular weight greater than 100,000.

Production of soluble autocrine inhibitory factors by human glioma cell lines

Gliomas in vitro exhibit density-limited growth upon the attainment of confluency, an effect usually attributed to cell-cell contact inhibition. Since gliomas have been demonstrated to secrete an array of soluble factors which can enhance tumor growth, we undertook this study to ascertain whether production of soluble factors by the tumor may also inhibit growth in an autocrine manner, and whether production of such factors is associated with the growth phase of the glioma. We observed that cell-conditioned medium (supernatants) from non-confluent glioma cultures induced growth, while confluent culture supernatants produced pronounced growth suppression. These latter supernatants enhanced proliferation of non-transformed astrocytes. Supernatants derived from all stages of confluency produced inhibition of lymphocyte proliferation. To characterize these factors, dialyzed supernatant was tested and found to continue to produce lymphocyte suppression but no glioma growth limitation. Growth of tumors in indomethacin or in acetylsalicylic acid to abolish prostanoid synthesis abrogated the inhibitory influence on glioma growth but only partially reversed the lymphocyte suppressive capacity. These studies suggest that gliomas do produce a growth phase dependent autocrine inhibitory factor(s), and that the production of these small molecular weight factors is at least partially under control of the cyclooxygenase pathway.

Eicosanoid production by brain tumours in vivo--evidence for intracranial compartmentation

Brain tumours produce prostaglandins in vitro; their in vivo production has been studied by determining the levels of prostaglandin F2 alpha, prostaglandin E2, 6-ketoprostaglandin F1 alpha and thromboxane B2 in tumour cyst fluid and ventricular CSF taken from 21 patients with a variety of intracranial tumours. The levels were high in tumour cyst fluid but there was no overall increase in ventricular CSF. Hence, brain tumours do not produce a consistent pattern of abnormality of eicosanoid concentrations in the ventricular CSF that would be useful for diagnosis. If brain tumours produce excess quantities of these prostaglandins in vivo as they do in vitro, these prostaglandins may be rapidly cleared by the cerebral microvasculature unless compartmentalized within a tumour cyst.

Radioimmunoassay of insulin-like growth factors in cyst fluid of central nervous system tumors

Tumor cells are characterized by abnormalities in growth and metabolism, including the autocrine secretion of certain growth factors. The authors have previously shown the presence of insulin-like growth factor receptors in tumors of the central nervous system (CNS) and in this study examine whether CNS tumors are capable of autocrine secretion of insulin-like growth factors in situ. To investigate the production of insulin-like growth factors I and II by CNS tumors, the authors have developed specific radioimmunoassays for these growth factors. In situ production of insulin-like growth factors was studied by immunoassay of CNS tumor cyst fluid aspirated at the time of surgery from 12 cystic tumors: seven primary brain tumors, four metastatic tumors, and one spinal schwannoma. For immunoassay, cyst fluid was treated overnight with acetic acid, then insulin-like growth factors were separated from binding proteins by a refined solid-phase technique, then dried and reconstituted in immunoassay buffer. Normal human serum and cerebrospinal fluid served as controls. Insulin-like growth factor I was detected in all 12 tumors studied. In contrast, insulin-like growth factor II was detected only in three low-grade astrocytomas, the spinal schwannoma (which had the highest insulin-like growth factor II level of all tumors studied), and three metastatic lung cancers. These results suggest that CNS tumors may be capable of autocrine production of insulin-like growth factors in situ. Furthermore, there appears to be a difference in the type of insulin-like growth factors produced by different types of CNS tumors. Preferential production of insulin-like growth factors may be an important marker of tumor differentiation and useful as a diagnostic tool.

Acidic fibroblast growth factor (aFGF) is present in the fluid of brain tumour pseudocysts

Fluid samples from brain tumour pseudocysts were examined for the presence of Fibroblast Growth Factor (FGF). Fluids were collected from 6 patients with differentiated low grade gliomas (group A), 3 anaplastic gliomas (group B) and 3 metastases (group C). For FGF assays pooled fluids from group A, B, and C were subjected to affinity chromatography on a Heparin-Sepharose column. Each pool contained endothelial cell mitogenic activity which eluted in the 1.2 M NaCl fraction and to a lesser degree in the 0.6 M fraction of Heparin-Sepharose high affinity chromatography. Mitogenic activity in the 1.2 M NaCl fraction of Heparin-Sepharose chromatography suggests the presence of acidic FGF (aFGF).