Search PubMed⌕ Search

Biomedical subjects

G Krishna

Publications and source records attributed to G Krishna.

At least 91 records · Page 5Linked to original sources
PubMed1988

In vivo and in vivo/in vitro kinetics of cyclophosphamide-induced sister-chromatid exchanges in mouse bone marrow and spleen cells.

In several acute and chronic exposures to various chemicals in vivo and in vitro, the average sister-chromatid exchange (SCE) frequencies in human, mouse, rat, and rabbit lymphocytes generally decrease with time following treatment. The rate of this decline varies, but little data have been published pertaining to the comparative kinetics of SCEs both in vivo and in vivo/in vitro (exposure of animals to the test compound and culturing of cells) simultaneously in the same tissues. In this study, a single dose of cyclophosphamide (40 mg/kg) was injected for varying periods (6-48 h) and its effects, as assessed by the induction of SCEs, were analyzed under both in vivo and in vivo/in vitro conditions in mouse bone marrow and spleen cells. In vivo, the cyclophosphamide-induced SCEs increased with increasing time up to 12 h, stayed at approximately the same level until 24 h, and then decreased with increase in post-exposure time. However, the SCE levels remained significantly higher than controls at 48 h post-exposure time in both bone marrow and spleen cells. Under in vivo/in vitro conditions, the SCEs in bone marrow decreased with increase in post-exposure time until reaching control values by 48 h post exposure. However, in spleen cells, the decrease in SCE level was gradual, and by 48 h post-exposure time, the cells still had approximately 6 times higher SCEs than the control values. These results suggest that there are pharmacokinetic differences for cyclophosphamide in mouse bone marrow and spleen. Also, there is a differential SCE response to cyclophosphamide under in vivo and in vivo/in vitro conditions.

Animals↗
PubMed1988

Sister-chromatid exchanges induced by triethylenemelamine: in vivo and in vivo/in vitro studies in mouse and Chinese hamster bone marrow and spleen cells.

This study was designed to obtain sister-chromatid exchange (SCE) frequencies in bone marrow and spleen cells of mice and Chinese hamsters under in vivo and in vivo/in vitro systems following treatment of animals with varying doses (15-405 micrograms/kg) of triethylenemelamine (TEM). A dose-related SCE response was found in both species, tissues, and systems analyzed following TEM treatment. In vivo, similar responses were noted for both tissues in both species. However, in vivo/in vitro, the response was lower than in vivo and it varied with the tissue. The spleen cells were more sensitive and gave higher numbers of SCEs than bone marrow of both species at the two highest doses tested (135 and 405 micrograms/kg). These differences may be attributed to cell-culturing effects, type of cells analyzed, species and tissue specificities, and pharmacokinetic properties of the chemical. This study lends support to recently established in vivo/in vitro cell culture methodologies employing mice and Chinese hamsters for comparative cytogenetic analysis.

Animals↗
PubMed1987

Daunomycin inhibits the uptake of adenine, amino acids, and glucose into cardiac myocytes.

Daunomycin and adriamycin are widely used antitumor agents which induce dose-dependent cardiotoxicity. The mechanisms by which daunomycin causes cardiotoxicity have been investigated in neonatal rat cardiac myocytes maintained in tissue culture. Daunomycin inhibited the uptake of adenine, amino acids, and deoxyglucose in a dose-dependent fashion. The uptake of both adenine and methionine was inhibited without any delay while the glucose uptake (deoxyglucose) was inhibited after a delay of 2 hr. Since daunomycin affected the uptake of both adenine and amino acids without any delay and since daunomycin did not affect the incorporation of adenine into nucleotide and amino acids into proteins once these were transported into the cell, it is possible the daunomycin exerted these effects by acting directly on the cell membrane. Thus, one of the early toxic manifestations of anthracycline antibiotics may be on the transport of nutrients such as amino acids, glucose, and adenine.

Adenine↗
PubMed1987

Mitomycin C-induced sister chromatid exchanges in vivo and in vivo/in vitro in mice and Chinese hamsters.

Mouse and Chinese hamster models have been extensively used for assessing the cytogenetic effects of environmental carcinogens and mutagens. However, there is little information on comparative analysis of chromosomal damage in these species under in vivo and in vivo/in vitro (culturing of cells from animals exposed to the test compound) systems. To obtain such information, mice and Chinese hamsters were injected with varying concentrations (0.5-6.0 mg/kg) of mitomycin C, an antineoplastic drug. The bone marrow and spleen cells were analyzed for the number of sister chromatid exchanges (SCEs) under in vivo and in vivo/in vitro conditions. The results indicated a dose-related SCE response that varied with species, tissues, and assay conditions. The mouse cells appeared more sensitive to the effects of mitomycin C than did Chinese hamster cells. In general, the SCE frequencies were relatively higher under in vivo conditions than under in vivo/in vitro conditions in both species. The spleen cells had higher SCE values than bone marrow cells under in vivo/in vitro conditions in both species. These differences may be related to the pharmacokinetic properties of the drug in different species and tissues, to treatment conditions, or to the repair capabilities of the cells. This study also indicates the usefulness of recently established bone marrow and spleen in vivo/in vitro cell cultures for comparative cytogenetic analysis.

Animals↗
PubMed1987

Cyclophosphamide-induced cytogenetic effects in mouse bone marrow and spleen cells in in vivo and in vivo/in vitro assays.

Sister chromatid exchange (SCE) and chromosomal aberration studies have been used to monitor human populations for genotoxic exposure to chemical substances. These monitoring techniques involve collection of blood and/or bone marrow from the exposed subjects and culturing cells for one or two cell cycles with various treatments in culture. The results obtained from such in vivo/in vitro studies may lead to an over- or underestimation of the damage that could occur in vivo. In the present study, which uses a mouse model, the in vivo/in vitro cytogenetic assays (SCEs and chromosomal aberrations) have been compared with similar in vivo systems in bone marrow and spleen cells treated with various doses of cyclophosphamide (CPA). The results indicate a significant difference in CPA-induced cytogenetic endpoints between in vivo and in vivo/in vitro conditions in both organs. However, linear relationships were found between CPA dose and cytogenetic end point analyzed under both conditions. Based on these results it appears that the in vivo/in vitro assay is a useful technique for indicating potential in vivo damage of chemicals.

Animals↗
PubMed1987

In vivo induction of sister chromatid exchanges in mice by nitrosated coal dust extract.

The genotoxicity of coal dust extract nitrosated with sodium nitrite (NaNO2) was investigated in mice with the in vivo sister chromatid exchange (SCE) assay system. The SCEs in bone marrow cells of mice were examined following single and double oral dosings of coal dust extract, NaNO2, and nitrosated coal dust extract. Coal dust extract and NaNO2 separately did not cause significant increases of SCEs either in single or in double dosings. Nitrosated coal dust extract in single doses did not increase SCEs but in two doses significant increases in SCEs were observed (P less than 0.02). The mutagenicity of the same extracts was tested in Salmonella typhimurium with the Ames tester strain TA98. Coal dust extract was either non- or weakly mutagenic and NaNO2 was nonmutagenic. The nitrosated coal dust extract caused pronouced increases in his+ revertants both with and without rat liver S9 activation. These findings provide additional evidence that nitrosation of ingested coal dust which may occur in the stomach environment could be one of the factors leading to the higher incidence of gastric cancer in coal miners.

Animals↗
PubMed1987

Valproic acid-induced increase in carnitine acetyltransferase in rat hepatocytes is not due to an induction of peroxisomes.

Valproic acid induced a dose-dependent increase in carnitine acetyltransferase (CAT) activity in rat hepatic mitochondrial fractions isolated by differential centrifugation. An increase in CAT and carnitine palmitoyltransferase (CPT) also occurred in cultured rat hepatocytes in a concentration-and time-dependent fashion. A maximal increase of 8-fold in the activity of CAT and 2-fold in the activity of CPT was induced by 3 mM valproic acid in 72 h. Valproic acid had no effect on cytochrome P-450 levels in cultured rat hepatocytes. Electron-microscopic examination of rat hepatocytes showed that there was no increase in the number of peroxisomes but there was a marked proliferation of mitochondria in parallel with an increase in glutathione level and succinic dehydrogenase in the liver cells after incubation with valproic acid in vitro.

Acetyltransferases↗
PubMed1987

Immunoelectron microscopic localization of photoreceptor-specific markers in the monkey retina.

Antibodies for several molecules that function in the visual process were used to localize these molecules in primate rod and cone cells. These antibodies (monoclonal or polyclonal) were prepared against Interphotoreceptor Retinoid-binding Protein (IRBP), S-antigen (S-Ag), opsin, alpha-transducin and also against cyclic GMP (cGMP). Lowicryl-embedded tissues were labeled with secondary antibodies linked to colloidal gold. Although IRBP is predominantly an extracellular protein, the relatively small amount found intracellularly was localized mainly in rods, with little in cones. Opsin, S-Ag and cGMP were found mainly in rod cell outer segments. A polyclonal antiserum raised against transducin-alpha purified from rod outer segments predominantly labeled rod cells, but an antiserum against the carboxyterminal decapeptide of transducin-alpha labeled both rod and cone cells. Thus, most of these specialized molecules are present predominantly in rod cells, confirming major differences in components of the visual cycle in rods and cones.

Animals↗
PubMed1986

Structural requirements for inducing cardiotoxicity by anthracycline antibiotics: studies with neonatal rat cardiac myocytes in culture.

Neonatal rat cardiac myocytes maintained in tissue culture were utilized to screen cardiotoxicity induced by a number of adriamycin and daunomycin analogs. Cell toxicity was assessed by leakage of cytoplasmic enzymes and was confirmed by electron microscopy. A number of modifications of structure of adriamycin and daunomycin markedly altered the incidence of toxicity caused by these drugs. Even though some of these structural alterations markedly altered lipid solubility or reactivity of quinone function, these changes did not always account for the differences in the toxicity induced by anthracycline analogs. The cardiomyocyte culture system used in this simple screening technique should be useful in the development of active anthracycline analog with least cardiotoxic potential.

Adenosine Triphosphate↗
PubMed1986

Formation of superoxide and hydroxyl radicals from 1-methyl-4-phenylpyridinium ion (MPP+): reductive activation by NADPH cytochrome P-450 reductase.

Formation of free radical intermediates from 1--methyl-4-phenylpyridinium ion(MPP+) has been studied using spin-trapping techniques. Incubation of MPP+ with purified NADPH cytochrome P-450 reductase and NADPH under anaerobic conditions failed to produce any detectable radical intermediates. However, in the presence of air and a spin-trap, a significant stimulation of superoxide and hydroxyl radicals was detected. Formation of these toxic radicals from MPP+ was inhibited by superoxide dismutase, catalase, and ethanol. Under identical conditions, however, considerably less of these radicals were formed with MPP+ in comparison to paraquat, a lung toxin containing two pyridinium moieties.

1-Methyl-4-phenylpyridinium↗
PubMed1986

A comparison of baseline and cyclophosphamide-induced sister chromatid exchanges in bone marrow and spleen cells of mouse and Chinese hamster.

Baseline sister chromatid exchange (SCE) frequencies were investigated in bone marrow and spleen cells of mice and Chinese hamsters. No significant difference in SCE frequency was noted for bone marrow in both species and for bone marrow and spleen in mice on per cell and per pg DNA basis. However, a significant difference was noted between species in spleen and between cell types in Chinese hamsters. Also, statistically significant differences were noted between species for both cell types when the same data were expressed on per chromosome basis. SCE levels in cultured bone marrow and spleen cells after intraperitoneal administration of the antineoplastic drug cyclophosphamide (10 and 20 mg/kg) differed significantly in mice and Chinese hamsters on per cell, per pg DNA content, and per chromosome basis. The spleen cells were much more sensitive to the effects of cyclophosphamide than bone marrow cells in both species. The replicative indices did not differ significantly between treated and control animals in either bone marrow or spleen cells of both species. Since SCE frequency is a sensitive measure of DNA damage, and bone marrow and lymphocytes are the most widely used cell types in human and animal in vivo assays, the methodologies and results reported here may be useful for comparative mammalian cytogenetic studies.

Animals↗
PubMed1986

Comparative in vivo and in vitro sister chromatid exchange studies in Chinese hamster bone marrow and spleen cells.

The sister chromatid exchange (SCE) assay in bone marrow and spleen cells of Chinese hamsters was used to evaluate the differences between in vivo and in vivo/in vitro (exposure of animals to chemical followed by culturing of cells) conditions. Cyclophosphamide, a mutagenic carcinogen, caused dose-related SCEs both in vivo and in vivo/in vitro. In the in vivo group, both bone marrow and spleen cells showed approximately a five-fold increase in SCEs over controls following 40 mg cyclophosphamide/kg treatment. The same dose, under in vivo/in vitro conditions, caused about three- and six-fold increases in SCEs over controls in bone marrow and spleen cells, respectively. While the extent of cyclophosphamide-induced SCEs (after subtraction of baseline level) in bone marrow is approximately the same under both conditions, the response was significantly higher in spleen cells in vivo/in vitro than in vivo. Under in vitro conditions, treatment of bone marrow and spleen primary cell cultures with a direct acting mutagen, trinitrofluorenone, caused significant dose-related increases in SCEs in both cell types in an equivalent manner. The replicative indices under these experimental conditions remained almost the same. Thus, this study indicates the potential usefulness of Chinese hamster bone marrow and spleen cells for in vivo and in vitro comparative studies with the same tissue to better assess the genotoxic hazard of chemicals.

Animals↗
PubMed1986

Murine bone marrow culture system for cytogenetic analysis.

A mouse bone marrow culture system for examining genotoxicity of agents by first exposing animals in vivo then growing cells in vitro is presented. This assay can also be used for in vitro and/or for the in vivo and in vitro comparative cytogenetic studies. The protocol involves culturing of approximately 1,000,000 nucleated cells obtained from mice tibia and femora in 5 ml of Ham's F-12 medium containing 20% fetal bovine serum, 10% whole uterus extract from pregnant mice and 1% penicillin-streptomycin. The use of flasks and mouse uterus extract for culturing are important steps for higher mitotic yield. The addition of 20 microM BrdU for 24 h helps in the differentiation of sister chromatids for sister-chromatid exchange (SCE) analysis. Cyclophosphamide, given to mice through intraperitoneal injection, induced significant dose-related SCEs in culture. Trinitrofluorenone, a direct-acting mutagen, caused dose-related SCEs in in vitro bone marrow cell culture.

Animals↗
PubMed1986

Retinoblastoma. A clinical, immunohistochemical, and electron microscopic case report.

A 4-year, 9-month-old boy had a history of leukocoria of the right eye for approximately six months prior to admission. The other eye was normal. There was no family history of retinoblastoma. Funduscopy disclosed a large white mass extending from the nasal pars plana to the mid-pupillary zone and the posterior pole with a near total retinal detachment in the superior temporal quadrant. A B-scan ultrasound showed an echo dense area of the anterior portion of the mass. A CT scan showed intraocular tissue densities with no evidence of optic nerve involvement or extraocular extension. Immunohistochemistry of a fresh frozen portion of tumor revealed reactivity with antibodies directed against interphotoreceptor retinoid-binding-protein (IRBP), neuron-specific enolase, glial fibrillary acidic protein, S-antigen, focal reactivity with opsin, and scattered cytoplasmic staining for cyclic GMP and cyclic GMP phosphodiesterase. Biochemical analysis of fresh frozen tissue samples confirmed the presence of IRBP. Transmission electron microscopy disclosed occasional Flexner-Wintersteiner rosettes connected by zonula adherens-like junctions. These showed inner segment-like structures containing prominent mitochondria, portions of cilia and fragments of outer segment material. These data, along with the immunocytochemistry indicates a predominant neuronal nature of the tumor cells with significant photoreceptor-like differentiation.

Child, Preschool↗
PubMed1986

Comparative mutagenicity studies of azo dyes and their reduction products in Salmonella typhimurium.

The arabinose-resistant and Ames assay systems of Salmonella typhimurium were used to evaluate the mutagenic potential of azo dyes and their aromatic amine reduction products. Azo dyes, namely direct black 38, direct blue 15, and direct red 2, were mutagenic in the arabinose-resistant and Ames assays with both hamster and rat liver S9 activation. Both assays gave relatively higher mutagenic responses with hamster S9. Reduction products of these dyes, namely benzidine, o-dianisidine, and o-tolidine, were mutagenic in the Ames assay. Benzidine was weakly mutagenic and o-dianisidine and o-tolidine were nonmutagenic in the arabinose-resistant assay. These results indicate that both arabinose-resistant tester SV50 and Ames tester TA98 were sensitive in detecting mutagenicity of azo dyes. The use of the standard plate protocol with Ames tester TA98 is more efficient than the modified azo dye protocol in detecting mutagenicity of aromatic amine reduction products. Additional modifications in either the standard plate or modified azo dye protocols may improve detection of mutagenicity of these compounds in the arabinose-resistant assay system.

Animals↗