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Biomedical subjects

T Mikkelsen

Publications and source records attributed to T Mikkelsen.

At least 37 records · Page 2Linked to original sources
PubMed1995

Immunolocalization of cathepsin B in human glioma: implications for tumor invasion and angiogenesis.

The poor prognosis of patients with malignant gliomas is at least partially due to the invasive nature of these tumors. In this study, the authors investigated the possibility that the cysteine protease cathepsin B (CB) is a participant in the process of glial tumor cell invasion. To accomplish this, an immunohistochemical analysis was made of the localization of antibodies to CB in biopsies of five specimens of normal brain, 16 astrocytomas, 33 anaplastic astrocytomas, and 33 glioblastomas multiforme. Staining was scored according to the percentage of positive cells and the intensity of the stain, graded from 0 to 3+. Staining for CB was not seen in any of five samples of normal brain except for occasional neuronal cell bodies and microglia. Only five (31%) of 16 astrocytomas showed a small percentage of positive cells (0.01%-3%) that were stained in a light, diffuse cytoplasmic pattern (1+). Twenty-nine (87.8%) of 33 anaplastic astrocytomas showed positive light, granular staining in 2% to 40% of cells. In anaplastic astrocytoma, the staining within a tumor was heterogeneous with intensities of 1+ (17%), 1+ to 2+ (29%), or 2+ (55%). In contrast, all 33 (100%) glioblastomas were positive in 10% to 90% of cells. The staining was present in a coarse, granular pattern with an intensity of 2+ (12%) or 3+ (88%). Tumor cells infiltrating into brain adjacent to malignant gliomas stained positively in 26 cases that could be evaluated for glioblastoma multiforme; these invading cells frequently followed penetrating blood vessels as typical "secondary structures of Scherer." Moderate to intense CB staining associated with endothelial proliferation in high-grade tumors was also observed, especially in regions of tumor infiltration into adjacent normal brain. These results provide evidence consistent with the hypothesis that CB is functionally significant in the process of tumor invasion and angiogenesis in the clinical progression of the malignant phenotype in astrocytes.

Antibodies, Monoclonal↗
PubMed1995

Glioma cell invasion visualized by scanning confocal laser microscopy in an in vitro co-culture system.

Confrontation cultures between glioma spheroids and brain cell aggregates are well established in glioma research, and the model reflects several similarities to the in vivo brain tumour invasive process. The lipid-binding fluorescent carbocyanine dyes DiO (3,3'-dioctadecyloxacarbocyanine perchlorate) and DiI (1,1'-dioctadecyl-3,3,3,'3,'-tetramethylinocarbocyanine perchlorate) are widely used in cell biology as tracers for studying cell movement. Mature brain cell aggregates grown from fetal rat brain cells, and spheroids initiated from two glioma cell lines (GaMg and D-54Mg) were stained with DiO and DiI, respectively. Penetration of DiI and DiO into the tumour spheroids and brain aggregates was studied by confocal laser scanning microscopy (CLSM). After 48 h of dye exposures, the tracers had almost completely penetrated the tumour spheroids and brain aggregates. Light-microscopic sections of the specimens indicated that the dye incorporation had little effect on cellular morphology. Cell migration from DiI stained D-54Mg and GaMg spheroids was similar to that observed from unstained spheroids. Growth was also unaffected after 48 h of DiI exposure. Gioma cell invasion was assessed by CLSM using co-cultures of DiI -stained spheroids and DiO-stained brain cell aggregates. Optical sections revealed a gradual decrease in remaining brain volume, indicating a progressive invasive process. Single tumour cells were identified deep within the brain aggregates. In addition normal brain cells were also identified in the tumour spheroids. It is concluded that vital staining can be used to identify both normal cells and tumour cells during tumour cell invasion in vitro. The method may provide the possibility for studying the kinetics of single normal and tumour cell movement in individual tumour/brain co-cultures.

Animals↗
PubMed1994

Cathepsin B expression and localization in glioma progression and invasion.

The poor prognosis of human malignant gliomas is due to their invasion and recurrence, the molecular mechanisms of which remain poorly characterized. We have accumulated substantial evidence implicating the cysteine protease cathepsin B in human glioma malignancy. Increases in cathepsin B expression were observed throughout progression. In primary brain tumor tissue, transcript abundance (Northern blot analysis) increased in low-grade astrocytoma to high-grade glioblastoma from 3- to 6-fold, respectively, above normal brain levels. This increase correlated with increases in protein abundance (from + to ) as measured by immunohistochemistry. Furthermore, in glioblastoma cell lines increases in transcript abundance (ranging from 3- to 12-fold) were accompanied by increases in enzyme activity (44-133 nmol/min x mg protein). Altered subcellular localization was observed both immunohistochemically and by indirect immunofluorescence confocal microscopy and was found to correlate with increased grade. In addition, this increase in cathepsin B expression and altered subcellular localization correlated with histomorphological invasion and clinical evidence of invasion as detected by magnetic resonance imaging. These data support the hypothesis that cathepsin B plays a role in human glioma progression and invasion.

Animals↗
PubMed1994

Development of a non-selecting, non-perturbing method to study human brain tumor cell invasion in murine brain.

The infiltrative nature of glial and some meningeal neoplasms is responsible for the failure of surgical removal and high recurrence rate of these tumors. Modeling of this process in vitro and in vivo will lead to a better understanding of the pathophysiology of this process and identify targets for novel therapy directed towards this phenotype. We present the results of the development and refinement of two model systems of tumor invasion: one in vitro barrier assay using the basement membrane extract Matrigel, and one in vivo where molecular detection of tumor cells allows single cell discrimination by in situ hybridization histochemistry. These techniques have strong correlations which validate their utility as measures of nervous system tumor invasion.

Animals↗
PubMed1994

Recent advances in brain tumor molecular biology.

Work in the field of molecular neuro-oncology has evolved from a purely descriptive catalogue of regional mutations to the implication of specific genes in the malignant process. Reverse genetic strategies have resulted in the cloning of the neurofibromatosis-1 and neurofibromatosis-2 genes, the molecular physiology of the p53 gene, and work is in progress toward identifying specific genes in each of the other major genomic regions in which genetic events accumulate during malignant progression in human gliomas. Current studies are examining the functional role of genes implicated in glioma malignancy and investigating the mechanisms of their dysregulation in the generation of the malignant phenotype.

Animals↗
PubMed1992

Increasing incidence of primary malignant brain tumors: influence of diagnostic methods.

BACKGROUND: The incidence of brain cancer has increased dramatically over the last decades in most developed countries. Whether these trends can be attributed to improved diagnosis is not clear. PURPOSE: To determine the effect of new imaging technology on increased rates of brain cancer, we assessed the level of detection for neurological disorders when computed tomography (CT) and magnetic resonance imaging (MRI) results were not available. METHODS: A neurologist performed a blind review of hospital charts from 356 randomly selected patients, hospitalized between 1985 and 1989 for neurological disorders, including brain cancer. All prediagnosis information except CT and MRI results was used as a basis for diagnostic re-evaluation. Also, a random sample of 151 brain cancer patients diagnosed between 1960 and 1965 was selected for a description of diagnostic methods used during that period. RESULTS: A comparison between the original diagnoses and the re-evaluations for patients in the 1985-1989 sample indicated that there was, among the diseases selected, a 24% misclassification when CT scans and MRI were not available. In particular, 20% of brain tumors were undetected (95% confidence interval = 15%-25%), and 10% of non-tumor disorders were inaccurately labeled as brain tumors in the absence of these tests. The repeatability of the re-evaluations was 86%. CONCLUSIONS: Among elderly North Americans, at least twofold increases in brain cancer incidence were observed over the last two decades. Since our findings show that CT scans and MRI are responsible for the detection of about 20% of brain tumors, we conclude that other factors also are responsible for the observed trends.

Adolescent↗
PubMed1992

Clonal expansion of p53 mutant cells is associated with brain tumour progression.

Tumour progression is a fundamental feature of the biology of cancer. Cancers do not arise de novo in their final form, but begin as small, indolent growths, which gradually acquire characteristics associated with malignancy. In the brain, for example, low-grade tumours (astrocytomas) evolve into faster growing, more dysplastic and invasive high-grade tumours (glioblastomas). To define the genetic events underlying brain tumour progression, we analysed the p53 gene in ten primary brain tumour pairs. Seven pairs consisted of tumours that were high grade both at presentation and recurrence (group A) and three pairs consisted of low-grade tumours that had progressed to higher grade tumours (group B). In group A pairs, four of the recurrent tumours contained a p53 gene mutation; in three of them, the same mutation was found in the primary tumour. In group B pairs, progression to high grade was associated with a p53 gene mutation. A subpopulation of cells were present in the low-grade tumours that contained the same p53 gene mutation predominant in the cells of the recurrent tumours that had progressed to glioblastoma. Thus, the histological progression of brain tumours was associated with a clonal expansion of cells that had previously acquired a mutation in the p53 gene, endowing them with a selective growth advantage. These experimental observations strongly support Nowell's clonal evolution model of tumour progression.

Amino Acid Sequence↗
PubMed1991

Tagging the genome of the murine leukemia retrovirus SL3-3 by a bacterial lac operator sequence.

The bacterial lactose operator (lacO) was introduced into the PstI site of the long terminal repeat of the SL3-3 murine leukemia virus, generating a virus, SL3-3lacO, that can replicate in NIH3T3 cell cultures. DNA sequences harboring the lacO sequence might be recovered by molecular cloning in Escherichia coli lac+ lacZ+ using bacteriophage lambda or plasmid vectors. The high copy numbers of the lacO sequence titrate out the lac repressor, leading to the induction of the lac operon in the host. We show here that the lacO and the proviral sequences are carried stably together in the genomes of SL3-3lacO-infected cell cultures and in viral particles. This system is designed to facilitate studies on the provirus and the site of viral integration.

3T3 Cells↗
PubMed1991

Genetics of the malignant progression of astrocytoma.

The tendency of human cancers to progress towards a more malignant state over time is a well described biological phenomenon. Recent investigations elucidating the genetic nature of malignancy and the possible mechanisms responsible for this evolution have suggested that a sequential pathway may exist whereby a cell population accumulates a nested set of genetic aberrations which endow it with the ability to overwhelm other populations and dominate the tumor. Human astrocytomas are a dramatic case in point, where specific genetic events of amplification and deletion are seemingly related to the stages of malignancy. The identification of these aberrations represents the first stage in the dissection of the temporal process of this cancer. Its augmentation with functional analyses will likely allow a fuller genetic description of in vivo transformation.

Astrocytoma↗
PubMed1990

DNA cytosine methylation in brain of patients with Alzheimer's disease.

We developed a novel quantitative assay to test the hypothesis that defects in DNA cytosine methylation might be responsible for the brain chromatin abnormalities and transcriptional alterations observed in patients with Alzheimer's disease (AD). We found no significant difference in percent methylation of CCGG sites from brain DNA of 44 patients with AD compared with 20 normal subjects. These results, however, would not exclude genomic redistribution of methylcytosine in AD, or disturbed methylation of a limited population of critical brain-specific genes.

Aged↗
PubMed1990

Loss of genetic information in central nervous system tumors common to children and young adults.

The clonal loss of genetic information as revealed by the comparison of normal and tumor DNA restriction fragment length alleles has permitted the determination of the genomic positions of cancer-recessive mutations. Here we have applied this approach to the analysis of 19 central nervous system tumors that constitute four histologic groups and occur most frequently in children and young adults. The detectable loss of genetic information from cases of medulloblastoma (11 examined) indicates that among such tumors, loss occurs most frequently from the short arm of chromosome 17. For the ependymomas examined (four cases), chromosome 22 was the preferred site for detectable loss. Analysis of pilocytic astrocytomas of the cerebellum (three cases) failed to reveal genetic alterations of any type among such tumors, a finding unique to this histologic group. The single choroid plexus papilloma examined demonstrated loss of genetic information from chromosome 3. Among the 19 tumors, multiple cases of loss were observed from chromosomes 10, 11, 13, and 22, and from the short arm of chromosome 17. Therefore, with regard to the chromosomal locations of implied tumor suppressor genes, these results are consistent with those described for intracranial tumors occurring more commonly in adults of middle to advanced age.

Adult↗
PubMed1990

Molecular genetic aspects of glial tumour evolution.

Cancer can be viewed as a dynamic process driven by the cellular accumulation of genetic alterations that provide selective growth advantage. Such alterations can be classified as one of two fundamental types: acquired (cancer-affective, dominant) or eliminated (cancer suppressive, recessive). This review considers genetic alterations that occur during the development of the most common type of central nervous system tumour, glioma.

Brain Neoplasms↗