In vitro assessment of the toxicity of metal compounds

A review of in vitro mutagenesis assessment of metal compounds in mammalian and nonmammalian test systems has been compiled. Prokaryotic assays are ineffective or inconsistent in their detection of most metals as mutagens, with the notable exception of hexavalent chromium. Mammalian assay systems appear to be similarly inappropriate for the screening of metal compounds based upon the limited number of studies that have employed those compounds having known carcinogenic activity. Although of limited value as screening tests for the detection of potentially carcinogenic metal compounds, the well-characterized in vitro mutagenesis systems may prove to be of significant value as a means to elucidate mechanisms of metal genotoxicity.     

Design,synthesis, characterization,antibacterial and antifungal activities of a novel class of 5,7-diaryl-4,4-dimethyl-4,5,6,7-tetrahydropyridino[3,4-d]-1,2,3-selenadiazoles

Compound 26 is more potent against Escherichia coli. and 24 is more active against Staphylococcus aureus, β-Heamolytic streptococcus, Vibreo cholerae, Salmonella typhii, and Shigella flexneri than the standard drug ciprofloxacin. Moreover, of all the compounds tested, 26 is more effective against Aspergillus flavus and Mucor, than the standard drug fluconazole.     

Identification of hydrogen selenide and other volatile selenols by derivatization with 1-fluoro-2,4-dinitrobenzene

A procedure is described for the trapping and identification of hydrogen selenide and methyl selenol ( CH3SeH ). The volatile selenols were generated by reducing selenious acid or dimethyldiselenide with Zn dust and hydrochloric acid under a stream of nitrogen and passing into a trapping solution composed of 50 mM 1-fluoro-2,4-dinitrobenzene plus 83 mM sodium bicarbonate in 67% dimethylformamide:33% water. The selenols react rapidly to form stable dinitrophenyl (DNP) selenoethers that can be extracted into benzene; these are easily identified by TLC, HPLC, or mass spectrometry. Hydrogen selenide is trapped in 90-99% yield, primarily as the di-DNP- monoselenide with a trace of di-DNP- diselenide .     

Zinc,copper, selenium,and glutathione peroxidase in blood of 11-yr-old dunedin,New Zealand children

Blood was obtained from 564 11-yr-old children who had participated since birth in a multidisciplinary health and development study. Serum zinc concentration did not differ between the boys and the girls (mean±SD: 91=17 μg/100 mL,n=453). Five-6% of serum zinc values were low; although there was a weak correlation with height, none of the boys with low values were below the 10th percentile for height for this group. Serum copper concentration (112±24 μg/100 mL,n=454) was unrelated to sex, height, weight, body mass index, socioeconomic status (SES), or iron status. Blood selenium concentration (49±10 ng/mL,n=564) was lower than previously reported for Dunedin children; it was higher in children in the lower SES categories. The data represent normal values for healthy, 11-yr-old NZ children.     

Application of PIXE analysis to the study of the regional distribution of trace elements in normal human brain

A particle-induced X-ray emission (PIXE) analysis method is presented, which allows measurement of eight elements (i.e., K, Ca, Mn, Fe, Cu, Zn, Se, and Rb) in human brain samples of only a few mg dry weight. The precision and accuracy of the method were investigated by analyzing animal brain matter with both PIXE and instrumental neutron activation analysis (INAA). The method was applied to measure the 8 elements in 46 different regions of 3 human brains. The sections analyzed originated from either the left or the right cerebral hemisphere, brain stem, and cerebellum. For one of the brains, sections were also analyzed from 26 corresponding regions of both hemispheres. For all elements, similar concentrations were found in the corresponding areas of the left and right sides of the brain. The concentrations (in μg/g dry weight) of the elements K, Fe, Cu, Zn, Se, and Rb were consistently higher in cortical structures than in white matter. Deep nuclei and brain stem, which have a mixed composition, showed intermediate values for K, Zn, Se, and Rb. A hierarchical cluster analysis indicated that the various brain regions clustered into two large groups, one comprising gray and mixed matter regions and the other, white and mixed matter brain areas.     

Characteristics of human milk glutathione peroxidase

Human milk glutathione peroxidase (GPx) was purified 4500-fold using acetone precipitation and purification by repetitive ion-exchange and gel filtration chromatography with an overall yield of 34%. Homogeneity was established by gel electrophoresis. Using gel filtration, the molecular weight (mol wt) of the enzyme was estimated to be 92 kdalton (kD). The monomeric molecular weight was estimated to b 23 kD from polyacrylamide gel electrophoresis, indicating that the native enzyme consists of four identical subunits. The molecular weight of each subunit was supported by amino acid analysis. Selenium (Se) content of the purified enzyme was 0.31%, in a stoichiometry of 3.7 g-atoms/mol. Data from these studies reveal that GPx provided approximately 22% of total milk Se, but only 0.025% of the total protein.     

Temporal changes in tissue glutathione in response to chemical form,dose, and duration of selenium treatment

Selenium has been reported to affect glutathione (GSH) concentrations in short-term animal-feeding experiments. Given the central role that this tripeptide plays in maintaining cellular homeostasis, it was hypothesized that perturbations in glutathione metabolism induced by selenium might account for its cancer chemopreventive activity. In the present study, four experiments were conducted in which the effect of acute, short-, or long-term exposure to selenium was assessed. Selenium was provided as either sodium selenite or D,L-selenomethionine. Selenite was observed to induce a biphasic response in total liver GSH. Injected selenium caused an acute reduction in GSH, whereas short-term feeding (up to 8 wk) increased both total GSH and oxidized glutathione (GSSH), an effect that gradually diminished in magnitude with prolonged feeding. Our data suggest that such changes are unlikely to account for the chemopreventive activity of selenium for the following reasons: Perturbations in glutathione metabolism occurred only at doses of selenite that approached toxicity. These doses are higher than what would be required for producing cancer chemoprevention. The transient nature of these changes also contrasts with the need for a continuous supplementation of selenite in suppression of tumorigenesis. Furthermore, selenomethionine was found to have little activity in altering glutathione metabolism, even though it compares favorably with selenite as a cancer chemopreventive agent. Nonetheless, these findings do not discount the possibility that sulfhydryl compounds, such as glutathione, might be used to modify the toxicity and/or enhance the cancer prophylactic activity of selenium compounds.     

In vitro OKT3-induced mitogenesis in selenium-deficient patients on a diet for phenylketonuria

Patients with phenylketonuria (PKU) are frequently deficient in the essential trace element selenium (Se), because of their very low protein diet. Using two approaches to investigate T-cell response to proliferative signaling, viz, mitogenesis caused by the monoclonal antibody OKT3 and the plant lectin phytohaemagglutinin (PHA), we demonstrated significantly reduced responses to optimal concentrations of OKT3 in a group of PKU patients with reduced serum Se compared with a normal group (p = 0.0005) and with a group of PKU patients whose serum Se was normal (p = 0.0023). The response of the Se-deficient group to optimal levels of PHA did not differ from that of the normal controls or from that of Se-normal PKU patients. A dose-dependent relationship between serum Se levels and mitogenic response was evident for OKT3 (r = 0.34, p = 0.0154), but not for PHA (r = -0.02, p = 0.9086). We suggest that the reduced response to OKT3 mitogenesis in Se-deficient PKU patients is possibly the consequence of impaired Se-dependent metabolic activity, which affects mitogenic signaling via the T cell antigen receptor (TCR/CD3) complex.