Heat inactivation of catalase from Staphylococcus aureus MF-31

P19-derived neuronal cells express H1, H2, and H3 histamine receptors: a biopharmaceutical approach to evaluate antihistamine agents

Histamine is a biogenic amine implicated in various biological and pathological processes. Convenient cellular models are needed to screen and develop new antihistamine agents. This report aimed to characterize the response of neurons differentiated from mouse P19 embryonal carcinoma cells to histamine treatment, and to investigate the modulation of this response by antihistamine drugs, vegetal diamine oxidase, and catalase. The exposure of P19 neurons to histamine reduced cell viability to 65% maximally. This effect involves specific histamine receptors, since it was prevented by treatment with desloratadine and cimetidine, respectively, H₁ and H₂ antagonists, but not by the H₃ antagonist ciproxifan. RT-PCR analysis showed that P19 neurons express H₁ and H₂ receptors, and the H₃ receptor, although it seemed not involved in the histamine effect on these cells. The H₄ receptor was not expressed. H₁ and H₂ antagonists as well as vegetal diamine oxidase diminished the intracellular Ca²⁺ mobilization triggered by histamine. The treatment with vegetal diamine oxidase or catalase protected against mortality and a significant reduction of H₂O₂ level, generated from the cells under the histamine action, was found upon treatments with desloratadine, cimetidine, vegetal diamine oxidase, or catalase. Overall, the results indicate the expression of functional histamine receptors and open the possibility of using P19 neurons as model system to study the roles of histamine and related drugs in neuronal pathogenesis. This model is less expensive to operate and can be easily implemented by current laboratories of analysis and by Contract Research Organizations.

Platelet-Rich Fibrin Can Neutralize Hydrogen Peroxide-Induced Cell Death in Gingival Fibroblasts

Hydrogen peroxide is a damage signal at sites of chronic inflammation. The question arises whether platelet-rich fibrin (PRF), platelet-poor plasma (PPP), and the buffy coat can neutralize hydrogen peroxide toxicity and thereby counteract local oxidative stress. In the present study, gingival fibroblasts cells were exposed to hydrogen peroxide with and without lysates obtained from PRF membranes, PPP, heated PPP (75 °C for 10 min), and the buffy coat. Cell viability was examined by trypan blue staining, live-dead staining, and formazan crystal formation. Cell apoptosis was assessed by cleaved caspase-3 Western blot analysis. Reverse transcription-quantitative polymerase chain reaction (RT-PCR) was utilized to determine the impact of PRF lysates on the expression of catalase in fibroblasts. It was reported that lysates from PRF, PPP, and the buffy coat—but not heated PPP—abolished the hydrogen peroxide-induced toxicity in gingival fibroblasts. Necrosis was confirmed by a loss of membrane integrity and apoptosis was ruled out by the lack of cleavage of caspase-3. Aminotriazole, an inhibitor of catalase, reduced the cytoprotective activity of PRF lysates yet blocking of glutathione peroxidase by mercaptosuccinate did not show the same effect. PRF lysates had no impact on the expression of catalase in gingival fibroblasts. These findings suggest that PRF, PPP, and the buffy coat can neutralize hydrogen peroxide through the release of heat-sensitive catalase.

Synergistic effect of thermal energy on bactericidal action of photolysis of H₂O₂ in relation to acceleration of hydroxyl radical generation

The purpose of the present study is to evaluate the effect of thermal energy on the yield of and the bactericidal action of hydroxyl radical generated by photolysis of H(2)O(2). Different concentrations of H(2)O(2) (250, 500, 750, and 1,000 mM) were irradiated with light-emitting diodes (LEDs) at a wavelength of 400 ± 20 nm at 25°C to generate hydroxyl radical. The 500 mM H(2)O(2) was irradiated with the LEDs at different temperatures (25, 35, 45, and 55°C). Electron spin resonance spin trapping analysis showed that the yield of hydroxyl radicals increased with the temperature, as well as the concentration of H(2)O(2). Streptococcus mutans and Enterococcus faecalis were used in the bactericidal assay. The LED-light irradiation of the bacterial suspensions in 500 mM H(2)O(2) at 25°C could hardly kill the bacteria within 3 min, while the bactericidal effect was markedly enhanced with the temperature rise. For instance, a temperature increase to 55°C resulted in >99.999% reduction of viable counts of both bacterial species only within 1 min. The photolysis of 500 mM H(2)O(2) at 55°C could reduce the viable counts of bacteria more efficiently than did the photolysis of 1,000 mM H(2)O(2) at 25°C, although the yields of hydroxyl radical were almost the same under the both conditions. These findings suggest that the thermal energy accelerates the generation of hydroxyl radical by photolysis of H(2)O(2), which in turn results in a synergistic bactericidal effect of hydroxyl radical and thermal energy.

Catalase and superoxide dismutase activities after heat injury of Listeria monocytogenes

Four strains of Listeria monocytogenes were examined for catalase (CA) and superoxide dismutase (SOD) activities. The two strains having the highest CA activities (LCDC and Scott A) also possessed the highest SOD activities. The CA activity of heated cell extracts of all four strains examined decreased sharply between 55 and 60 degrees C. SOD was more heat labile than CA. Two L. monocytogenes strains demonstrated a decline in SOD activity after heat treatment at 45 degrees C, whereas the other two strains demonstrated a decline at 50 degrees C. Sublethal heating of the cells at 55 degrees C resulted in increased sensitivity to 5.5% NaCl. Exogenous hydrogen peroxide was added to suspensions of L. monocytogenes; strains producing the highest CA levels showed the greatest H2O2 resistance.

Synthesis of catalase in Staphylococcus aureus MF-31

During the growth of Staphylococcus aureus MF-31, initial catalase activity dropped to a reduced level at the onset of exponential phase before increasing. When S. aureus was grown at 25, 32, or 37 degrees C, catalase activity was found to decrease by 80 to 90% within 1 h of inoculation. Two catalase-negative mutants and wild-type S. aureus MF-31 cells were exposed to exogenous 20 mM H2O2 for 15 min. For wild-type S. aureus, there was no effect from H2O2 until min 15, at which time a 10% decrease in CFU was observed. Both mutants showed increased sensitivity to the H2O2, with 56 and 71% reductions in the CFU for mutants C3 and C4, respectively, after a 15-min exposure. Cells of mutant and wild-type S. aureus were subjected to sublethal heating at 52 degrees C for 20 min. The lack of catalase activity in the mutants resulted in large decreases in enumeration.

Effect of free-radical scavengers on enumeration of thermally stressed cells of Staphylococcus aureus MF-31

Exposure of crude cell lysates of Staphylococcus aureus MF-31 to 5 or 10 mM hydrogen peroxide resulted in a linear decrease in superoxide dismutase activity. Approximately 13% of the superoxide dismutase activity was lost after 16 min. Thermally stressed and nonstressed cells were exposed to a photochemically generated exogenous flux of superoxide radicals (O2.-). The death of thermally stressed cells was linear with time. Addition of superoxide dismutase or catalase to the O2.- generating system resulted in protection of thermally stressed and nonstressed cells, with the protective effect being greater for thermally stressed cells. Incorporation of O2-, hydroxyl radical, or singlet oxygen scavengers or antioxidants to tryptic soy agar containing 7.5% NaCl did not increase the enumeration of thermally stressed cells.

Superoxide dismutase activity during recovery of thermally stressed Staphylococcus aureus MF-31

Superoxide dismutase (SOD) activity was determined during the growth cycle of unheated and heat-injured cells of Staphylococcus aureus MF-31. SOd activity levels dropped in unheated cells during the lag phase, increased during logarithmic phase, and became constant in the stationary phase. Cells which were sublethally heated (52 degrees c, 20 min) in 100 mM phosphate buffer and subsequently allowed to recover in tryptic soy broth demonstrated an 85% decrease in SOD activity upon inoculation into recovery medium. As the injured cells repaired the heat-induced lesions and entered logarithmic growth, SOD levels rapidly increased. Heat-injured cells allowed to recover in tryptic soy broth plus 10% NaCl showed similar decreases in SOD activity levels. However, no subsequent increase was observed when specific activity was calculated based on milligrams of protein.

Superoxide dismutase activity in thermally stressed Staphylococcus aureus

The effects of heat and NaCl on the activity of superoxide dismutase from Staphylococcus aureus were examined. A linear decrease in superoxide dismutase activity occurred when S. aureus MF-31 cells were thermally stressed for 90 min at 52% C in 100 mM potassium phosphate buffer (pH 7.2). After 20 min of heating, only 5% of the superoxide dismutase activity was lost. Heating for 60, 90 and 120 min resulted in decreases of approximately 10, 22, and 68%, respectively. The rates of thermal inactivation of superoxide dismutase from S. aureus strains 196E and 210 were similar and slightly greater than those of strains MF-31, S-6, and 181. The addition of NaCl before or after heating resulted in increased losses of superoxide dismutase activity.