Risk assessment of workers exposed to crystalline silica aerosols

This study was conducted to determine the concentration of airborne respirable crystalline silica (ARCS) particles and to evaluate its risk level among workers employed in eight different workplaces in Iran. They included sandblasting operations, ceramic production, sand and gravel work, brick production, asphalt manufacturing, foundry operation, glass making, and stone cutting. Personal exposure to ARCS was measured in randomly selected samples from each workplace. The maximum and minimum average of ARCS concentration in the eight workplaces were observed in foundry operation (0.338 ± 0.110 mg/m³) and glass manufacturing (0.125 ± 0.093 mg/m³), respectively. The average concentration of ARCS in all assessed working conditions were higher than the permitted limit of occupational contact recommended by Technical Committee of the Iranian Ministry of Health, treatment and medical education (0.025 mg/m³). Overall, the results showed a serious lack of control in Iranian industries with respect to workers' exposures to ARCS.     

Induction of SOS-response of cells exposed to autoregulatory factors of microorganisms

Among examined microbial growth regulators of alkyl hydroxybenzene group (hexylresorcinol, methylresorcinol, and hydroxyethylphenol), only hexylresorcinol induces cellular SOS response, demonstrating a dose-dependent increase of the induction factor in the SOS chromotest with the Escherichia coli PQ37 strain. At the highest of used concentrations (100 micrograms/ml), hydroxyethylphenol and nonalkylated resorcinol were shown to exert a weak toxic effect, reducing the activity of constitutive alkaline phosphatase, but did not induce SOS response. Nontoxic methylresorcinol did not induce genome damage, which can trigger SOS functions. It is concluded that substitutions in phenolic ring affect genotoxic activity of alkylresorcinols.     

Significance of characteristics of microorganisms in the pathogenesis B. pyocyaneus infection (an experimental study)

The experimental Pseudomonas Sepsis was induced by various strains. Biological features of these strains were different and various forms of sepsis were induced. The authors suggested that biological features of microorganisms cause the development of different and various forms of sepsis.     

Barophiles: deep-sea microorganisms adapted to an extreme environment

The deep-sea environment is characterized by high pressure and low temperature but in the vicinity of hydrothermal vents regions of extremely high temperature exist. Deep-sea microorganisms have specially adapted features that enable them to live and grow in this extreme environment. Recent research on the physiology and molecular biology of deep-sea barophilic bacteria has identified pressure-regulated operons and shown that microbial growth is influenced by the relationship between temperature and pressure in the deep-sea environment.     

Meiotic competence and DNA damage of porcine oocytes exposed to an elevated temperature

The present study was conducted to investigate the effects of the length of exposure to an elevated temperature (41 degrees C) on the meiotic competence and DNA damage of porcine oocytes. Oocytes were recovered from ovaries, loaded into straws, and then exposed at 41.0 or 38.5 degrees C (sham control) for 0, 0.5, 1.0, or 1.5h, followed by culture for 44 h. The proportion of oocytes reaching the metaphase II (MII) stage gradually decreased with increasing exposure time, irrespective of the exposure temperature. A higher proportion of oocytes stored at 38.5 degrees C reached MII (57-63%) than those exposed to 41 degrees C (14-29%; P<0.01). The proportion of total oocytes with DNA fragmentation gradually increased with increasing exposure time, irrespective of the exposure temperature. The proportion of DNA fragmentation in total oocytes exposed to 41 degrees C (37-57%) was higher (P<0.01) than that in total oocytes stored at 38.5 degrees C (14-24%). When the oocytes were stored at 38.5 degrees C for up to 1.5 h, there were no differences in the proportions of MII-stage oocytes, with DNA-fragmented nuclei among all groups (P>0.05). However, a higher proportion of MII-stage oocytes exposed to 41 degrees C for more than 1h exhibited DNA-fragmented nuclei, compared with MII-stage oocytes stored at 38.5 degrees C (P<0.05). In conclusion, exposure of porcine oocytes to an elevated temperature had a detrimental effect on the meiotic competence and quality of oocytes; furthermore, the effect was dependent on the duration of exposure.     

Survival of subsurface microorganisms exposed to UV radiation and hydrogen peroxide.

Aerobic and microaerophilic subsurface bacteria were screened for resistance to UV light. Contrary to the hypothesis that subsurface bacteria should be sensitive to UV light, the organisms studied exhibited resistance levels as efficient as those of surface bacteria. A total of 31% of the aerobic subsurface isolates were UV resistant, compared with 26% of the surface soil bacteria that were tested. Several aerobic, gram-positive, pigmented, subsurface isolates exhibited greater resistance to UV light than all of the reference bacterial strains tested except Deinococcus radiodurans. None of the microaerophilic, gram-negative, nonpigmented, subsurface isolates were UV resistant; however, these isolates exhibited levels of sensitivity similar to those of the gram-negative reference bacteria Escherichia coli B and Pseudomonas fluorescens. Photoreactivation activity was detected in three subsurface isolates, and strain UV3 exhibited a more efficient mechanism than E. coli B. The peroxide resistance of four subsurface isolates was also examined. The aerobic subsurface bacteria resistant to UV light tolerated higher levels of H2O2 than the microaerophilic organisms. The conservation of DNA repair pathways in subsurface microorganisms may be important in maintaining DNA integrity and in protecting the organisms against chemical insults, such as oxygen radicals, during periods of slow growth.     

Analysis of DNA fragmentation in mouse embryos exposed to an extremely low-frequency electromagnetic field

Effects of extremely low-frequency electromagnetic fields (ELF-EMFs) on DNA damage in biological systems are still a matter of dispute. The aim of the present study was to investigate the possible effect of electromagnetic field exposure on DNA fragmentation in cells (blastomers) of mouse blastocysts.

Eighty female NMRI mice were randomly divided into 2 groups of 40 animals each. The control group was left unexposed whereas the animals in the EMF-group were exposed to a 50-Hz EMF at 0.5 mT 4 h per day, 6 days a week for a duration of 2 weeks. After the 8^th day of exposure, the female mice in both groups were superovulated (with injections of pregnant mare serum gonadotropin and human chorionic gonadotropin) and then mated overnight. At approximately 4 days after mating (102 h after the human chorionic gonadotropin treatment), blastocysts were obtained by flushing the uterus horns. The mean numbers of pregnant mice, blastocysts after flushing, blastomers within the blastocysts, and the DNA fragmentation index following staining in both groups were compared using statistical methods (SPSS, the Chi-square test, the Student's t-test and the Mann-Whitney U-test, P < 0.05). The results showed that the mean number of blastocysts after flushing was significantly decreased in the EMF-group compared to that of the control group (P < 0.03). The DNA fragmentation index was significantly increased in the EMF-group compared to control (10.53% vs. 7.14%; P < 0.001). However, there was no significant difference in the mean numbers of blastomers and numbers of pregnant mice between the EMF-exposed and control group. Our findings indicate that the EMF exposure in preimplantation stage could have detrimental effects on female mouse fertility and embryo development by decreasing the number of blastocysts and increasing the blastocysts DNA fragmentation.     

Analysis of DNA fragmentation in mouse embryos exposed to an extremely low-frequency electromagnetic field

Effects of extremely low-frequency electromagnetic fields (ELF-EMFs) on DNA damage in biological systems are still a matter of dispute. The aim of the present study was to investigate the possible effect of electromagnetic field exposure on DNA fragmentation in cells (blastomers) of mouse blastocysts. Eighty female NMRI mice were randomly divided into 2 groups of 40 animals each. The control group was left unexposed whereas the animals in the EMF-group were exposed to a 50-Hz EMF at 0.5?mT 4?h per day, 6 days a week for a duration of 2 weeks. After the 8(th) day of exposure, the female mice in both groups were superovulated (with injections of pregnant mare serum gonadotropin and human chorionic gonadotropin) and then mated overnight. At approximately 4 days after mating (102?h after the human chorionic gonadotropin treatment), blastocysts were obtained by flushing the uterus horns. The mean numbers of pregnant mice, blastocysts after flushing, blastomers within the blastocysts, and the DNA fragmentation index following staining in both groups were compared using statistical methods (SPSS, the Chi-square test, the Student's t-test and the Mann-Whitney U-test, P?相似文献   

Adsorption of DNA to mica mediated by divalent counterions: a theoretical and experimental study

The adsorption of DNA molecules onto a flat mica surface is a necessary step to perform atomic force microscopy studies of DNA conformation and observe DNA-protein interactions in physiological environment. However, the phenomenon that pulls DNA molecules onto the surface is still not understood. This is a crucial issue because the DNA/surface interactions could affect the DNA biological functions. In this paper we develop a model that can explain the mechanism of the DNA adsorption onto mica. This model suggests that DNA attraction is due to the sharing of the DNA and mica counterions. The correlations between divalent counterions on both the negatively charged DNA and the mica surface can generate a net attraction force whereas the correlations between monovalent counterions are ineffective in the DNA attraction. DNA binding is then dependent on the fractional surface densities of the divalent and monovalent cations, which can compete for the mica surface and DNA neutralizations. In addition, the attraction can be enhanced when the mica has been pretreated by transition metal cations (Ni(2+), Zn(2+)). Mica pretreatment simultaneously enhances the DNA attraction and reduces the repulsive contribution due to the electrical double-layer force. We also perform end-to-end distance measurement of DNA chains to study the binding strength. The DNA binding strength appears to be constant for a fixed fractional surface density of the divalent cations at low ionic strength (I < 0.1 M) as predicted by the model. However, at higher ionic strength, the binding is weakened by the screening effect of the ions. Then, some equations were derived to describe the binding of a polyelectrolyte onto a charged surface. The electrostatic attraction due to the sharing of counterions is particularly effective if the polyelectrolyte and the surface have nearly the same surface charge density. This characteristic of the attraction force can explain the success of mica for performing single DNA molecule observation by AFM. In addition, we explain how a reversible binding of the DNA molecules can be obtained with a pretreated mica surface.     

Design, synthesis, and DNA binding properties of photoisomerizable azobenzene-distamycin conjugates: an experimental and computational study

Here, we present the synthesis, photochemical, and DNA binding properties of three photoisomerizable azobenzene-distamycin conjugates in which two distamycin units were linked via electron-rich alkoxy or electron-withdrawing carboxamido moieties with the azobenzene core. Like parent distamycin A, these molecules also demonstrated AT-specific DNA binding. Duplex DNA binding abilities of these conjugates were found to depend upon the nature and length of the spacer, the location of protonatable residues, and the isomeric state of the conjugate. The changes in the duplex DNA binding efficiency of the individual conjugates in the dark and with their respective photoirradiated forms were examined by circular dichroism, thermal denaturation of DNA, and Hoechst displacement assay with poly[d(A-T).d(T-A)] DNA in 150 mM NaCl buffer. Computational structural analyses of the uncomplexed ligands using ab initio HF and MP2 theory and molecular docking studies involving the conjugates with duplex d[(GC(AT)10CG)]2 DNA were performed to rationalize the nature of binding of these conjugates.