Various short-term screening methods have been developed to detect mutagenic/carcinogenic substances. They have played important roles not only in screening suspected chemicals but in studying the mechanisms of mutagenesis/carcinogenesis, and have provided useful information for assessing the genetic effects of chemicals on humans. The micronucleus assay is an in vivo mammalian methods, which has been widely used for screening the genotoxic potency of chemical substances. By this assay, the genotoxicity of chemicals, including clastogens and spindle poisons, have been evaluated using immature bone marrow erythrocytes in mice. The use of immature erythrocytes in circulating peripheral blood instead of in bone marrow of mice has been developed in recent years and it has been determined that it gives results as relevant as those of bone marrow cells in mice. Using the peripheral blood of mice has made the micronucleus assay method more practical and useful. Recently, rats have been identified as an acceptable species for this assay, and assays using the peripheral blood of rats are often carried out concomitantly with general toxicity or carcinogenic studies. However, it must be noted that the micronucleus assays have some limitations. The activity of substances which are metabolized rapidly in mice or rats, for example, may hardly be detected by the micronucleus assay; metabolic features of the substances may affect the assay results greatly. In this review, the current status of the micronucleus assay is discussed as a short-term screening method in the context of its usefulness and its limitations.
Effects of the heavy metals cadmium and zinc on the regulation of cell destiny are reviewed in light of an apoptogenic metal of cadmium and the antiapoptotic nature of zinc. Exposure of renal cells to cadmium causes apoptotic features, DNA fragmentation and chromatin condensation in earlier stages of cadmium cytotoxicity than the cadmium-induced necrotic phase. The molecular mechanism of cadmium-induced apoptosis is poorly understood. Neither cadmium-metallothionein nor an immediate early gene such as c-myc is involved in the apoptotic pathway. In contrast, zinc can abolish cadmium-induced apoptosis. Although the mechanism underlying zinc inhibition of apoptosis remains uncertain, one possibility is that the ability of zinc to facilitate DNA synthesis might contribute to its protective effect on apoptosis.
The in vitro inhibitory effects of heavy metals, i.e., mercury, cadmium, lead, nickel and beryllium in their chloride forms, on rabbit pulmonary drug-metabolizing enzymes were studied comparatively. Microsomal and cytosolic fractions prepared from rabbit lungs were incubated in the presence of heavy metals prior to enzyme assays. Mercury was the most potent in reducing cytochrome P450 content and mixed-function oxidase activities including NADPH-cytochrome c reductase and benzo[a]pyrene hydroxylase. The addition of mercury to pulmonary microsomal preparations resulted in a spectral shift from 450 nm to 420 nm in an absorption maximum of cytochrome P450-carbon monoxide complex with mercury chloride being more potent than methylmercury. Cadmium was also inhibitory, while the effects of nickel were noted only at higher concentrations. Neither lead nor beryllium was inhibitory. Among second-phase drug-metabolizing enzymes, UDP-glucuronyltransferase and glutathione S-transferase were found to be susceptible to the adverse effects of mercury and lead, respectively. The extent of inhibition of the latter activity by mercury were highly dependent on the concentration of glutathione, implying the complex formation between them. Cadmium was slightly inhibitory to both enzyme activities, though the other metals had no effect. The results indicate that the pulmonary toxicities of airborne heavy metals could be inferred using simple in vitro assays.
The concentrations of formaldehyde, acetaldehyde, propionaldehyde, and n-butyraldehyde in water were quantitatively determined by head space-gas chromatography/mass spectrometry (HS-GC/MS). Aqueous aldehydes were treated with o-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBOA) in a sealed vial at 60°C for 60 min. Head space was then analyzed by GC/MS. In comparison with electron ionization (EI) mass spectra, negative chemical ionization (NCI) mass spectra of PFBOA derivatives gave more spectral peaks of structural origin and with simple, characteristic fragmentation patterns. HS-GC/MS is highly sensitive for aqueous aldehydes because it eliminates interference from the water sample. The concentrations of various aldehydes in tap water and commercial mineral water were determined by HS-GC/MS. The following concentration ranges were detected for the individual aldehydes; formaldehyde, not detected (N.D.)-59 μg/l; acetaldehyde, N.D.-260 μg/l; propionaldehyde, N.D.-0.9 μg/l; and n-butyraldehyde, N.D.-0.3 μg/l.
The formation of nitrated pyrenes was investigated on nine metallic oxides as soil components with pyrene and various nitrogen sources under xenon lamp irradiation. The metallic oxides studied were CaO, Al2O3, MgO, Fe2O3, SiO2 (quartz, silicic anhydride, and silica gel forms), and TiO2 (rutile and anatase forms). Nitrated pyrene as a reaction product was extracted with benzene: ethanol (4 : 1, v/v) and analyzed by GC/MS selected ion monitoring (SIM). In the presence of indoor air, 1-nitropyrene (1-NP) was produced in all nine metallic oxides, and the yield of 1-NP was high on silicon dioxide (SiO2; silicic anhydride and silica gel forms) and titanium dioxide (TiO2; rutile and anatase forms). 2-Nitropyrene (2-NP) and 4-nitropyrene (4-NP) were produced in aluminum oxide (Al2O3), magnesium oxide (MgO), and TiO2 (rutile form). In the presence of nitrogen dioxide gas (NO2 gas), nitrite ion (NO2-) or nitrate ion (NO3-), 1-NP was produced in SiO2 (silicic anhydride and silica gel forms), TiO2 (rutile and anatase forms), Al2O3, and MgO. 2- and 4-NP were produced in most samples of Al2O3 and MgO. Accordingly, NO2 gas, NO2-, and NO3- were shown to be nitrogen sources for the formation of nitrated pyrenes in these metallic oxides. In addition, in the presence of these nitrogen sources, 2- and 4-NP were produced on metallic oxides as soil components. The yields and formation patterns of the three types of mononitrated pyrenes differed in the various metallic oxides, as well as with the type of nitrogen source (NO2 gas, NO2- or NO3-). Hence, the nature of the photochemical reaction in the formation of the nitrated pyrenes differed depending on the type of metallic oxide and source of nitrogen. The yields of nitrated pyrenes depended on the amount of NO2- in Al2O3 and MgO and on the amount of NO3- in Al2O3 and SiO2 (silicic anhydride form). In these experiments, dinitropyrenes were not detected in all cases.
The manifestation of toxicity by certain environmental compounds requires enzymatic activation. It is well known that chlorinated ethylenes (CEs) are metabolized by intracellular enzymes represented by cytochromes P450 (CYPs) to the urinary secreted forms via epoxide intermediates, which are responsible for their toxicities by forming complexes with intracellular components including CYPs. In order to study the roles of CYPs in the metabolic activation of tetrachloroethylene (PCE), trichloroethylene (TCE) or 1, 1-dichloroethylene (1, 1-DCE), the cytotoxicity of individual CEs were tested in primary hepatocyte cultures established from animals treated with various CYP-inducers such as 3-methylchoranthrene (inducer of CYPlAl/2), phenobarbital (CYP2B1/2) and pyridine (CYP2E1). The cytotoxicity of CEs measured by lactate dehydrogenase leakage after 24 hr was enhanced in different fashions, depending on the CYP inducers used. The results are summarized as follows: CYP1A1/2 and 2B1/2 raised the cytotoxicity of PCE;CYP2B1/2 was exclusively associated with the enhanced cytotoxicity of TCE; and CYP2E1 and 2B1/2 were proved to potentiate 1, 1-DCE. Based on these observations, CEs differing in the number of chlorine substitutions were disclosed to have divergent preferences for CYPs, by which they were metabolically activated.
The effect of zinc and vitamin K2 (menaquinone-7) on bone components in the femoral tissue of female elderly rats was investigated. Rats were orally administrated either vehicle (distilled water), zinc sulfate (1.0 mg Zn/100 g body weight), menaquinone-7 (MK-7, 0.5 mg/100 g) or zinc (1.0 mg/100 g) plus MK-7 (0.5 mg/100 g) once a day for 7 days. Femoral dry weight was significantly increased by the administration of both zinc and MK-7, although a significant change was not seen by zinc or MK-7 alone. Calcium content in the femoral-diaphyseal and metaphyseal tissues was significantly increased by zinc administration. Such an increase was not found by MK-7. Bone calcium content was synergistically enhanced by the administration of both zinc and MK-7. Alkaline phosphatase activity and deoxyribonucleic acid (DNA) content in the diaphyseal and metaphyseal tissues were significantly increased by zinc or MK-7 administration; these increases were additively enhanced by both zinc and MK-7. Moreover, the intake of supplement containing both zinc (1.675 mg/100 g) and MK-7 (168.8 μg/100 g) once a day for 15 days caused a significant increase in femoral dry weight, alkaline phosphatase activity, DNA, calcium and zinc contents in the diaphyseal and metaphyseal tissues. This study demonstrates that the administration of both zinc and MK-7 can enhance additively or synergistically bone components in female elderly rats, suggesting a role in the prevention of osteoporosis with increasing age.
Differentially expressed genes in human esophageal carcinoma/normal tissue pairs were identified by means of a modified differential display technique to overcome the limitations of the conventional technique. Out of the eight cDNAs isolated, three were novel. The other five clones consisted of cDNA encoding cytokeratin 13, complement 7, KIAA1160, expression sequence tag (EST)-Hs110855 and EST-Hs13662. Quantitative reverse transcription-PCR (RT-PCR) for 10 carcinoma/normal tissue pairs confirmed down-regulation of cytokeratin 13, complement 7 and KIAA1160 mRNAs in carcinoma tissue and up-regulation of EST-Hs110855 mRNA. EST-Hs13662 mRNA also seemed to increase in carcinoma tissues but not to a statistically significant extent. In situ hybridization confirmed that cytokeratin 13 mRNAs localized in differentiating keratinocytes of normal epithelia and had disappeared in carcinomas, suggesting that tihs down-regulation reflects de-differentiation during carcinogenesis. The functions of complement 7 and KIAA1160 mRNAs are unclear in normal tissue but their down-regulation in carcinoma tissue may help the development of esophageal carcinoma. The expression of EST-Hs110855 mRNA reportedly observed in carcinomas of different origins suggests that tihs EST is a carcinogenesis-related gene. Our modified technique, which eliminates the source of false-positives, reduces the screening time, and dispense with the radioisotope, was found to be useful for isolating differentially expressed genes from clinical specimens with apparently genetically distant cellular populations and a very limited mass.
Defatted seeds effectively adsorbed organochlorine compounds such as chloroform, dichloromethane and trichloroethylene. The amounts of these compounds adsorbed was plotted against the equilibrium concentration of substances in solution on a logarithmic scale. A linear relationship was obtained, indicating that the adsorption reactions were Freundlich type. The adsorption of these compounds by defatted seed was observed over the range of pH 1-11. Chloroform was successfully removed from tap water with an average removal efficiency of 70% after 60 min when rapeseed was added to tap water that contained 0.0073 mg/l chloroform. The removal of these organochlorine compounds by defatted seed was attributed to the uptake by intracellular particles called spherosomes.
Okadaic acid, a tumor promoter derived from a black sponge, dose-dependently suppressed human chorionic gonadotropin (hCG)-stimulated testosterone production in primary cultured mouse Leydig cells. Okadaic acid at 10 nM caused a 70% reduction in testosterone production, and this inhibition was not due to cell damage. Okadaic acid did not affect basal testosterone production. Our results suggest that okadaic acid may inhibit the hCG-stimulated signaling pathway. We found that okadaic acid suppressed the expression of mRNA for two steroidogenic enzymes, cytochrome P450 cholesterol side-chain cleavage (P450scc) and 3β-hydroxysteroid dehydrogenase (3β-HSD), which catalyze cholesterol conversion to testosterone. It is interesting to analyze the mechanisms by which okadaic acid, which inhibits protein phosphatase 1 and 2A, suppressed steroidogenesis.
The concentration of nitrate in biological fluids was determined using nitrate reductase (NR) in a flow system. A merging zone method was applied, in which a zone of NR and that of nitrate in separate streams were merged, and allowed to react. The decrease in NADPH caused by the reaction between NR and nitrate was measured at 340 nm. The conditions were as follows: length of the reaction coil used for the enzymatic reaction was 250 cm; 0.1 M PIPES buffer (pH 7.5) was used as the first carrier (C1); 0.1 M PIPES buffer (pH 7.5) containing 0.1 mM NADPH was used as the second carrier (C2); the reaction coil was immersed in a water bath maintained at 32°C. Under these conditions, a linear calibration curve (r = 0.994) was plotted for the concentration of nitrate between 1 and 100 μM with a detection limit (S/N = 3) of 0.2 μM. The present method was applied to determine the amount of nitrate in serum, plasma and urine using samples that had not been deproteinized. The concentration of nitrate within each sample was calculated from differences observed in the peak areas obtained in the absence or presence of nitrate reductase. The recovery test of the nitrate added to biological fluids indicated the applicability of the present method to the determination of nitrate in them. The nitrate concentrations determined using this technique correspond well with those of other methods.
To evaluate the genetic toxicity of 1, 4-dichlorobenzene (p-DCB), DNA adducts of p-DCB were analyzed in in vitro and in in vivo. In the in vitro study, calf thymus DNA (400 μg/ml) was mixed with p-DCB (100 μM), liver microsome (1 mg protein/ml) and an NADPH-regenerating system. After incubation at 37°C for 1 hr, DNA was isolated and purified for DNA adduct analysis. There were no DNA adducts detected when p-DCB was metabolized by rat, mouse or human liver microsomes. In the in vivo study, Fischer 344 rats were given different kinds of cytochrome P450 (CYP) inducers and then injected with p-DCB. Twenty-four hr after injection, livers were collected from the rats for DNA adducts analysis. We did not find any p-DCB DNA adducts in rat livers pre-treated with ethanol, phenobarbital or 3-methylcholanthrene, respectively. In conclusion, no p-DCB DNA adducts were found either the in vitro or in vivo studies. In this study, we demonstrated that p-DCB is not genotoxic.
Three healthy volunteers were exposed to 1, 4-dichlorobenzene (p-DCB) vapor (2.4-2.8 ppm) for 1 hr, peripheral blood was taken before and after exposure. Serum was collected and incubated with calf thymus DNA to examine whether there are any DNA-binding metabolites persisting in human serum. Among the 3 subjects we detected 4, 2, and 0 DNA adducts respectively, no differences were found in adduct profiles before or after p-DCB inhalation. The result reflects that qualities and quantities of DNA-reactive metabolites in human sera are different, depending upon individual exposure to environmental carcinogens and their metabolism ability. There were no additional DNA-reactive metabolites found after inhalation exposure to p-DCB.
The toxic solution used at the Tokyo Subway Sarin Incident was purified by vacuum distillation. We were thus able to obtain sarin with high purity. We conducted a quantitative analysis of sarin using 31P-NMR spectrometry. High-purity sarin was examined by trimethyl phosphate as an internal standard. In comparison with 1H nondecoupling, the relative intensity between sarin and the internal standard did not change in 1H decoupling. Trimethyl phosphate is a good internal standard substance. A 31P-NMR chemical shift of trimethyl phosphate is separate from those of sarin and related compounds. Trimethyl phosphate has one phosphorus atom in the molecule, as does sarin. Since it is advantageous in the conversion of quantitative value, the molecular weight of trimethyl phosphate (m.w. 140.08) is close to that of sarin (m.w. 140.09). By using trimethyl phosphate as an internal standard, it is possible to conduct a quantitative analysis of sarin through 1H decoupled 31P-NMR spectrometry.
Cadmium (Cd) induces apoptosis in vitro and in vivo. However, the mode of action is unclear. Cytochrome C (Cyt c) release from mitochondria into cytoplasm is a key event in apoptosis. In this study, we examined the effects of Cd on the release of Cyt c from mitochondria using human leukemia HL-60 cells and isolated mitochondria. Cd induced apoptosis in HL-60 cells in a dose-dependent manner, in accordance with increases in cytosolic Cyt c. Cd at 25 μM also induced the release of Cyt c from isolated mitochondria. Mitochondrial swelling induced by permeability transition is known to cause outer membrane rupture and Cyt c release from mitochondria. Cd induced a swelling of mitochondria in vitro, as did calcium, a classical inducer of mitochondrial permeability transition. These results suggest that apoptosis induced by Cd appears to be involved in a mitochondria-dependent pathway and in the release of Cyt c from mitochondria by swelling.
Despite advances in cardiovascular medicine, the endogenous mechanisms responsible for positive inotropic state of the heart is poorly understood. We have assessed surgical transposition of the portal vein (portacaval shunt) as a procedure providing total systemic delivery of portal venous effluent in six dogs. The animals recovered rapidly from the surgery maintaining euglycemia. Four days after surgery the serum enzymes such as alkaline phosphatase, alanine aminotransferase and gamma glutamyl transferase returned to normal values, whereas all the animals had significantly higher values of urine volume and left ventricular dP/dt. Pre and postoperative left ventricular pressure was unchanged. Our results indicate that portacaval shunt plays an endogenous role in the positive inotropic state of the heart, and suggest that this surgical procedure may provide an insight into its beneficial role in heart failure.
Chinese hamster ovary (CHO) K1 cells were treated with 2.5 μM Mitomycin C (MMC) for one hour and incubated in Ham’s F12 medium containing 10% fetal bovine serum or in the medium supplemented with the extract from Cassia nomame pods, leaves and stems. The frequency of cells with chromosome aberrations was significantly lowered by the extract. Proliferation of CHO cells was suppressed by a 1-hr MMC treatment, but the suppression was nullified by the presence of the extract. These findings suggest that the extract can prevent the physiological damage caused by MMC.
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