Development of an 125I-postlabeling assay as a simple, rapid, and sensitive index of DNA-protein cross-links

A rapid, simple, and sensitive 125I-postlabeling technique has been developed to allow detection of DNA-protein cross-links induced by environmental contaminants and carcinogens. This method is based on specific incorporation of 125I into tyrosine residues associated with DNA. Cultured Chinese hamster ovary cells were exposed to various crosslinking agents, e.g., UV light, K2CrO4, or NiCl2. DNA was isolated by proteinase K/phenol/chloroform. The residual peptides cross-linked to DNA were radioiodinated with Na125I and chloramine T. After repeated precipitation with ethanol, the radioactivity was determined. The 125I method was compared with a 3[H]-tyrosine prelabeling method and found to be of similar sensitivity.

The role of nickel and nickel-mediated reactive oxygen species in the mechanism of nickel carcinogenesis

Increasing evidence demonstrates the reactive oxygen species (ROS) are implicated in metal carcinogenesis. Exposure of cultured Chinese hamster ovary (CHO) cells to several nickel compounds, i.e. NiS, Ni3S2, NiO (black and green), and NiCl2 has been shown to increase oxidation of 2',7-dichlorofluorescein to the fluorescent 2',7-dichlorofluorescein (DCF), suggesting that nickel compounds increased the concentration of oxidants in CHO cells. This fluorescence can be attenuated by addition of exogenous catalase to the extracellular media, indicating that H2O2 is one of the formed oxidants in this system. Fluorimetric measurements of chromogens following thiobarbituric acid reaction showed that nickel compounds also induce lipid peroxidation with a decreasing potency NiS, Ni3S2 > black NiO > green NiO > NiCl2. These results suggest that lipid hydroperoxides may also be produced through the action of nickel in intact cells. MgCl2, an antagonist of Ni-induced DNA strand breaks and cell transformation, has no effect on the formation of DCF fluorescence induced in CHO cells by nickel. The results suggest that nickel is an active inducer of ROS in intact mammalian cells and that the molecular mechanism of nickel carcinogenesis may involve multiple steps of nickel-mediated ROS.

Detection of the von Hippel-Lindau gene deletion in cytologic specimens using microdissection and the polymerase chain reaction

Previous studies have demonstrated von Hippel-Lindau (VHL) gene abnormalities in renal cell carcinoma. Archival cytologic samples of renal cell carcinomas (RCCs) from two patients were evaluated for allelic loss of the VHL gene. Small clusters of renal carcinoma cells were dissected from cytocentrifuge preparations under direct microscopic visualization followed by single-step DNA extraction and subsequent polymerase chain reaction (PCR). Amplification of DNA from the harvested tumor cells demonstrated a loss of heterozygosity at the VHL gene in five RCC specimens obtained from two patients. The combination of microdissection and PCR enabled DNA studies to be performed on a pure population of tumor cells isolated from heterogeneous samples containing admixed normal cellular elements. Selected genetic studies performed on microscopically targeted cells will help to further the biologic and cytomorphologic characterization of the targeted cell population.

Molecular mechanisms of nickel carcinogenesis

Carcinogenic, water-insoluble Ni compounds are phagocytized by cells; and the particles undergo dissolution inside the cell, releasing Ni ions that interact with chromatin. Ni produces highly selective damage to heterochromatin. The longest contiguous region of heterochromatin in the Chinese hamster genome is found on the q arm of the X chromosome, and this region is selectively damaged by Ni. More than half of the male mice in which there were Ni-induced transformations of Chinese hamster cells exhibited complete deletion of the long arm of the X chromosome. The introduction of a normal X chromosome into these cells resulted in cellular senescence, suggesting that the Ni interacted with Chinese hamster genome to inactivate a senescence gene. Investigations were conducted into the mechanisms by which Ni produced damage to chromatin. Ni ions have a much higher affinity for proteins and amino acids than for DNA (by five to seven orders of magnitude). Therefore, Ni interacted with chromatin because of the protein present, not because of its reactivity for DNA. Studies have shown that Ni produced an increase in oxidative products in cells as indicated by oxidation of the fluorescent dye dichlorofluorescein; Ni has also been shown to produce oxidation of proteins in cells, as measured by carbonyl formation. Ni cross-linked certain amino acids and proteins to DNA. These covalent cross-links were not dissociated by EDTA and are inconsistent with direct Ni involvement, but they are consistent with Ni acting catalytically. Using subtractive hybridization, we have isolated a number of clones that are expressed in normal but not in Ni-transformed cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular mechanisms of nickel carcinogenesis

Nickel treatment of intact cultured cells oxidized dichlorofluorescin to a fluorescent product indicating that nickel elevated the level of oxidants in cells. Nickel also caused an increase in crosslinking of amino acids to DNA and these complexes did not appear to involve the direct participation of Ni2+. Histidine, cysteine and tyrosine were prominent among the amino acids crosslinked to DNA. Nickel selectively damaged heterochromatin and this resulted in deletions of heterochromatic regions during nickel carcinogenesis. Thrombospondin was one of the genes expressed in normal cells that was not expressed in nickel-transformed cells. Other aspects of the molecular mechanism of nickel carcinogenesis are discussed.

Protein oxidation and amino acid-DNA crosslinking by nickel compounds in intact cultured cells

Oxidative damage induced by NiCl2 to protein has been investigated. We found that nickel induced a dose-dependent increase in the oxidation of bovine serum albumin (BSA) as detected by carbonyl formation in the presence of H2O2 in vitro, as well as producing carbonyl of proteins in intact cultured Chinese hamster ovary (CHO) cells. Other metals capable of producing oxidative damage to BSA in the presence of H2O2 included Cu, Co, Fe, and chromate. However, Cd2+, Hg2+, and Pb2+ were not active even in the presence of H2O2. As an indicator of nickel-induced genotoxic damage, the crosslinking of amino acids to DNA was also examined. Cysteine, histidine, and tyrosine were increased in their association with DNA based upon their persistent binding to DNA following washes with EDTA or SDS. The results suggest that DNA-protein or DNA-amino acids crosslinks induced by nickel may result from interaction of the nickel-oxidized carbonyl group of protein, peptides, and free amino acids.

Cognition-activated low-frequency modulation of light absorption in human brain

Animal model studies indicate light-absorption changes of the exposed animal brain in response to visual stimulation. Here we report observations of red-light absorbance changes, attributable to repetitive blood concentration changes in response to stimulation in the human brain frontal region by a cognitive process. These responses are observed as low-frequency recurrence of changes by Fourier transform analysis and are attributed to blood concentration change stimulated by the increased metabolic rate of brain tissue in cognitive function. A simple, portable dual wavelength spectrophotometer was attached noninvasively to the human forehead to measure the low frequency and power spectra of fluctuations of absorbances attributed to variations of brain blood concentration in the frontal region. The responses are associated with brain activity in responses to problem solving of analogies presented visually that require an associative function in the frontal region. The method of subtraction of test -rest Fourier transforms minimizes the arterial pulse frequency contributions and identifies specific frequencies--for example, 0.8, 1.6, 1.8 Hz in 24 of 28 tests of nine individuals (85%). Tests in which no increased brain activity was elicited (rest-rest) showed small differences. It is concluded that low-frequency recurrences of brain activity linked to blood concentration increases can be detected in human subjects with an optical device of potentially for simplified tests of cognitive function in the 0- to 3-Hz region and with modifications for wider band recordings in localized tissue volumes by time-resolved spectroscopy.

Analysis of residual amino acid--DNA crosslinks induced in intact cells by nickel and chromium compounds

Chinese hamster ovary cells were incubated with radioactive amino acids, the DNA was isolated by standard proteinase K/phenol/chloroform extraction and residual amino acids complexed to the DNA were examined as an index of metal induced DNA-protein crosslinks. Using this method, both chromate and nickel caused residual histidine and cysteine to be complexed with the DNA isolated from metal-treated cells. In the case of chromate, a number of amino acids were studied and Tyr, Thr and Cys were found to be complexed to DNA at a level (above the untreated control) that was statistically significant. Stability studies indicated that some of the chromate-induced DNA-protein complexes were mediated by direct participation of chromium(III), whereas others that were resistant to dissociation by EDTA and mercaptoethanol did not seem to involve direct chromium(III) participation. A significant portion of the cysteine complexed to DNA by chromate was believed to involve glutathione since treatment of cells with cycloheximide did not decrease chromate-induced cysteine-DNA crosslinks. In the case of nickel, most of the stable DNA-protein crosslinks did not involve direct metal participation and were probably oxidatively mediated by Ni(II)/Ni(III) redox cycling. These findings present new methodology for analysis of DNA-protein crosslinks by examination of residual amino acids associated with the DNA. This method should be highly sensitive and will yield important information about the mechanism of metal-induced DNA-protein crosslinks.

[Common tumors of the fourth ventricle and cerebellum in childhood: evaluation of CT differential diagnosis]

Forty pediatric patients with infratentorial cerebellar astrocytomas, medulloblastomas and ependymomas were evaluated. In most cases it was possible to predict the histological type of these tumors by CT. The search for the residual fourth ventricle cavity and defining its location were the first step in differential diagnosis. The density of tumor on plain scans was of value to distinguish medulloblastomas from astrocytomas. Cerebellar astrocytomas had an obvious tendency to develop cystic change. Especially, the configuration of "Cyst-with-mural nodule" was the most specific characteristic in diagnosis. Just like medulloblastomas and ependymomas, cerebellar astrocytomas may have also the tendency to arise at the midline in childhood. The incidence of calcification was rather high in ependymomas.

The in vitro insertion of monoamine oxidase B into mitochondrial outer membranes

Bovine monoamine oxidase (MAO) B has been synthesized in vitro using a reticulocyte lysate translation system directed by bovine liver poly(A)+ RNA. The newly synthesized enzyme apparently lacks a cleavable N-terminal extension, but MAO B is readily incorporated into mitochondria or isolated mitochondrial outer membranes prepared from rat liver. ATP is not required for the binding of the newly synthesized enzyme to the outer membranes, but is necessary for the insertion of MAO B into these membrane vesicles. The ATP is not required to generate a mitochondrial membrane potential as assembly occurs under conditions that preclude either the formation or the maintenance of the potential. MAO B will bind to but not become incorporated into outer membrane vesicles which have been treated with trypsin, suggesting that the insertion of MAO B also depends on protein factors present on the outer membranes.

Plasmid deoxyribonucleic acid replication in Streptomyces griseus

A series of electron micrographs showing the presence of different molecular forms representing various replication stages of plasmid deoxyribonucleic acid from Streptomyces griseus was obtained. Based upon an analysis of these electron micrographs, a tentative model for plasmid deoxyribonucleic acid replication in S. griseus is proposed.