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.

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.

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.

Comparative in vivo and in vitro genotoxicity studies of airborne particle extract in mice

The genotoxicity of an acetone extract of locally collected airborne particles was evaluated both in vitro and in vivo using the sister-chromatid exchange (SCE) assay in mice. At the highest concentration (5.36 mg/5 ml culture), the extract caused approximately a 3-fold increase in SCEs over controls in mouse bone marrow and spleen primary cells in vitro. However, the same airborne particle extract did not induce a significant increase in the SCE level over controls in vivo in mouse bone marrow and spleen cells when administered intraperitoneally or through oral gavage. This indicates that bone marrow and spleen primary cell cultures can be used in in vitro genotoxicity studies of complex mixtures, and that the genotoxicity of airborne particles detected in the in vitro system cannot always be detected in vivo with the same cell types. In addition, the same acetone extract of airborne particles caused dose-related his+ revertants in the strain TA98 of Salmonella typhimurium, both with and without S9 activation. The significant finding of this study is that the in vitro genotoxicity results of airborne particle extract may not be very meaningful in an in vivo situation.

Inhibition of overall protein and RNA synthesis as a mechanism for the tunicamycin induced decrease in cytochrome P-450 in rat hepatocytes

In rat hepatocytes maintained in culture, cytochrome P-450 and NADPH cytochrome c reductase activities were decreased by tunicamycin in a dose and time dependent fashion. The effect of tunicamycin was mainly due to inhibition of protein synthesis. Tunicamycin decreased L-[35S] methionine incorporation into many proteins, including a 52 kDa cytochrome P-450 isozyme. Tunicamycin also reduced RNA synthesis. These results indicate that tunicamycin decreased cytochrome P-450 levels in hepatocytes by inhibiting protein and RNA synthesis.

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.

Inhibition of cyclophosphamide and mitomycin C-induced sister chromatid exchanges in mice by vitamin C

Ascorbic acid (vitamin C) is known to act as an antimutagen and anticarcinogen in several test systems. However, there is no report of its effect on carcinogen-induced chromosomal damage in vivo in animals. The present study was performed to determine whether or not ascorbic acid affects sister chromatid exchanges (SCEs) induced by cyclophosphamide (CPA) and mitomycin C (MMC) in bone marrow and spleen cells in mice. The results indicate that ascorbic acid per se did not cause a significant increase in SCEs in mice. However, increasing concentrations of ascorbic acid caused decreasing levels of CPA- and MMC-induced SCEs in both cell types in vivo. At the highest concentration of ascorbic acid, 6.68 g/kg, approximately 75 and 40% SCE inhibition in both cell types was noted for CPA and MMC, respectively. Likewise, under in vivo/in vitro conditions (exposure of animals to experimental chemicals followed by culturing of cells), ascorbic acid caused a dose-related decrease in CPA- and MMC-induced SCEs, up to a dose of 3.34 g/kg At this concentration, approximately 50% CPA- and MMC-induced SCE inhibition was observed in both cell types studied. Thus, ascorbic acid acts as an anti-SCE agent in both in vivo and in vivo/in vitro conditions in mice.

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.

Genetic expression of cyclic GMP phosphodiesterase activity defines abnormal photoreceptor differentiation in neurological mutants of inherited retinal degeneration

We have examined cyclic GMP concentrations, guanylate cyclase activities, and cyclic GMP phosphodiesterase (PDE) activities in developing retinas of congenic mice with different allelic combinations at the retinal degeneration (rd) and retinal degeneration slow (rds) loci. Although guanylate cyclase activities were found to be uniformly low in the mutant retinas, striking differences in PDE activity and cyclic GMP levels were observed in retinas of the various genotypes. Homozygous rds mice, which lack receptor outer segments, showed reduced retinal PDE activity and cyclic GMP concentration in comparison to normal animals. In heterozygous rds/+ mice with abnormal outer segments, the levels were intermediate. In retinas of homozygous rd mice, PDE activity was lower than in rds retinas and cyclic GMP levels were much higher. In mice homozygous for both rd and rds genes, retinal PDE activities were even lower than in single homozygous rd mice; the cyclic GMP level reached the same high value as in the rd animals, persisted for a longer time at this high level, and did not correlate with the rate of photoreceptor cell loss. Thus, a marked variation in PDE activity appears to be the major manifestation of abnormal outer segment differentiation and eventual degeneration of photoreceptor cells in these neurological mutants. An increased cyclic GMP level seems to be an essential corollary in the expression of the rd gene even in the absence of outer segments, but it appears unlikely that an abnormally high nucleotide level in itself causes photoreceptor cell death.

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.

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.

Increased sensitivity of the isometric contraction of the neonatal isolated rat atria to halothane, isoflurane, and enflurane

Isolated atria from neonatal (0-5 day old) and adult (50 +/- 5 day old) rats were perifused in oxygenated Kreb's Henseleit solution at 30 +/- 0.5 degrees C and exposed to four different concentrations of halothane, isoflurane, or enflurane while isometric contractile tension was recorded and compared with control atria. ED50 values (mM of anesthetic required to produce 50% reduction in contractile tension) of neonates for halothane (0.18 +/- 0.01), isoflurane (0.41 +/- 0.05), and enflurane (0.41 +/- 0.04) were significantly lower than those of adults (0.35 +/- 0.02, 0.80 +/- 0.05, and 1.15 +/- 0.05, respectively). Furthermore, neonatal ED50 calculated as per cent of adult ED50 was significantly less for enflurane (35%) than for halothane (54%) or isoflurane (51%).

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.

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.

A simple method for the extraction of mutagens from airborne particles

Organic materials were extracted with acetone from filters of airborne particles by soaking, shaking, soxhletion, and sonication. These extracts were tested with and without S9 for mutagenicity using Ames assay and arabinose-resistant assay of Salmonella typhimurium. Among the extraction methods, soaking extract had the highest mutagenic activity followed by sonication, shaking, and soxhletion in both the assays. With the samples studied, it was concluded that soaking with acetone for 1/2 hr is the simplest and an efficient procedure for the extraction of mutagens from airborne particles.

Inhibition of protein synthesis: a basis for tunicamycin-induced decrease in rat liver cytochrome P-450

Tunicamycin caused a dose and time dependent decrease in cytochrome P-450 in rat liver. A dose of 50 micrograms/kg caused a decrease of about 50% in 72 hours. A similar decrease in the activities of rat liver microsomal aniline hydroxylase, aminopyrine N-demethylase and ethoxycoumarin O-deethylase were also seen after the tunicamycin treatment. Tunicamycin also suppressed food and water intake but the decrease in cytochrome P-450 was not related to these effects. NADPH cytochrome c reductase was not markedly decreased by tunicamycin. A decrease in cytochrome P-450 was also observed in cultured rat hepatocytes treated with tunicamycin. It decreased incorporation of [35S]-methionine into total proteins as well as into various cytochrome P-450 isozymes of rat hepatocytes. This indicates that a decrease in protein synthesis may be responsible for the tunicamycin-induced decrease in cytochrome P-450 and drug metabolism.

In vivo cytogenetic studies on mice exposed to ethylene dibromide

The pesticide, ethylene dibromide (EDB), was evaluated with in vivo cytogenetic assays to determine its genotoxicity. CD1 male mice were exposed to EDB through intraperitoneal injections. Bone marrow cells isolated from femora were analyzed for sister-chromatid exchange (SCE), chromosome aberration and micronucleus formation. The results showed that only certain concentrations of EDB tested caused a slight but significant increase in SCEs and chromosome aberrations. However, these increases were not dose-related. No increase in the polychromatic erythrocytes with micronuclei was observed following EDB exposure. Also, EDB did not cause cell-cycle delay in comparison with controls. Thus, it appears that EDB is not an effective genotoxic agent in vivo in mice.

A simple and sensitive method for monitoring drug-induced cell injury in cultured cells

A simple, sensitive method has been developed for evaluating cell injury noninvasively in monolayer cells in culture. The cell ATP pool was radiolabeled by incubating the cells with [14C]adenine. The uptake and incorporation of [14C]adenine was shown to proportional to the number of cells. As determined by HPLC, about 65-70% of the incorporated 14C label was in the ATP pool, 15-20% was in the ADP pool, and the rest was in the 5'-AMP pool. When prelabeled cells were exposed to toxic drugs (acetaminophen, calcium ionophore A-23187, or daunomycin) there was a marked decrease in cell ATP with a concomitant increase in leakage of labeled nucleotides, mainly 5'-AMP and 5'IMP. We have shown that leakage of 14C label into the medium from the prelabeled cells may be employed for quantitation of cell injury. This new measure of toxicity was shown to correlate very well with LDH leakage from the cells, which is a well accepted measure of cell injury. The leakage of 5'-[14C]AMP also correlated very well with the reduction of cell ATP in cardiac myocytes. This method has been used for monitoring drug-induced toxicity in liver cells, cardiac myocytes, and LB cells.

The calcium ionophore A23187 evokes and potentiates antiviral activity of interferon

Calcium ionophore A23187, which causes a rapid efflux of Ca2+ from cells, evokes an antiviral response in mouse LB, simian COS-1, Hela, human amniotic (U), baby hamster kidney (BHK), and VERO cells against Sindbis (SBV) and vesicular stomatitis (VSV) viruses. The degree of antiviral activity depends on the type of cell, virus, and the dose of A23187. A23187 inhibits the production of infectious VSV; however, VSV particle production was not significantly inhibited as measured by viral RNA and viral proteins. The VSV released from the A23187-treated cells is deficient in VSV glycoprotein (G) and membrane (M) protein. A23187 potentiates the antiviral activity of interferon (IFN) against SBV and VSV in mouse LB and human U cells. It is possible to postulate that a change in intracellular Ca2+ may play an important role in the antiviral activity of IFN.

Dopamine reverses cardiovascular depression of toxic doses of pentobarbitone in dogs

Pentobarbitone, 20 mg X kg-1 IV followed by infusion of 25 mg X kg-1 X hr-1, produced a progressive decrease in mean arterial pressure in dogs from 113 +/- 17 mmHg (SD) after one hour of infusion to 82 +/- 21 mmHg after 3.5 hours and to 49 +/- 22 mmHg after 5.5 hours. EEG silence occurred at 3.6 +/- 0.6 hours. In dogs similarly treated with pentobarbitone, a two hour infusion of dopamine 5 micrograms X kg-1 X min-1 beginning at the time of EEG silence prevented the further decrease in pressure and restored pressure to 87 +/- 18 mmHg. The mechanism for this effect of dopamine was an increase in cardiac output as systemic vascular resistance was unaffected by dopamine. The cardiac output increase was mainly the result of an increase in stroke volume as heart rate increased only slightly. Since reduced stroke volume was the main reason why pentobarbitone lowered blood pressure, the effect of dopamine on stroke volume and thus on blood pressure makes it an appropriate antagonist to the cardiovascular effects of toxic doses of pentobarbitone.