Mechanisms of trichloramine removal with activated carbon: stoichiometric analysis with isotopically labeled trichloramine and theoretical analysis with a diffusion-reaction model.

This study investigated the mechanism by which activated carbon removes trichloramine, a byproduct of water treatment that has a strongly offensive chlorinous odor. A stoichiometrical mass balance for ¹5N before and after activated carbon treatment of laboratory-prepared ¹5N-labeled trichloramine solutions clearly revealed that the mechanism of trichloramine removal with activated carbon was not adsorption but rather reductive decomposition to nitrogen gas. There was a weak positive correlation between the surface decomposition rate constant of trichloramine and the concentration of basic functional groups on the surface of the carbon particles, the suggestion being that the trichloramine may have been reduced by sulfhydryl groups (-SH) on the activated carbon surface. Efficient decomposition of trichloramine was achieved with super powdered activated carbon (SPAC), which was prepared by pulverization of commercially available PAC into very fine particles less than 1 µm in diameter. SPAC could decompose trichloramine selectively, even when trichloramine and free chlorine were present simultaneously in water, the indication being that the strong disinfection capability of residual free chlorine could be retained even after trichloramine was effectively decomposed. The residual ratio of trichloramine after carbon contact increased somewhat at low water temperatures of 1-5 °C. At these low temperatures, biological treatment, the traditional method for control of a major trichloramine precursor (ammonium nitrogen), is inefficient. Even at these low temperatures, SPAC could reduce the trichloramine concentration to an acceptable level. A theoretical analysis with a diffusion-reaction model developed in the present study revealed that the increase in the trichloramine residual with decreasing water temperature was attributable to the temperature dependence of the rate of the reductive reaction rather than to the temperature dependence of the diffusive mass transfer rate.

Protective effects of amino acids against gabexate mesilate-induced cell injury in porcine aorta endothelial cells.

Gabexate mesilate (GM), a serine protease inhibitor, often causes severe vascular injury. We previously reported that GM induced necrotic cell death via injury of the cell membrane in porcine aorta endothelial cells (PAECs). In the present study, we investigated the protective effects of amino acids against this GM-induced cell injury in PAECs. L-Cysteine (Cys), glycine (Gly), L-serine, L-glutamine (Gln), L-glutamate (Glu), L-proline, L-methionine, L-threonine, and L-isoleucine significantly inhibited the GM-induced decrease of cell viability. Gly showed the most potent effect among these amino acids. Gly, L-Cys, L-Glu, and L-Gln also inhibited the GM-induced increase in the number of necrotic cells stained by propidium iodide (PI). However, these amino acids had no effect on the GM-induced inhibition of trypsin activity. Strychnine, MK-801, or dichlorokynurenic acid did not affect the protective effect of Gly. Gly completely suppressed the GM-induced increase in PI uptake, which occurred immediately after exposure to GM. These findings suggest that Gly exerts protection against GM-induced cellular membrane injury, and several amino acids such as Gly may be useful for prophylaxis of the GM-induced severe vascular injury.

Characteristics of gabexate mesilate-induced cell injury in porcine aorta endothelial cells.

Gabexate mesilate (GM), a serine protease inhibitor, often causes severe vascular injury, when injected in high concentration. In the present study, we investigated the mechanisms for the cytotoxicity of GM on porcine aorta endothelial cells (PAECs). GM (0.5 - 5.0 mM) decreased cell viability in a dose-dependent manner and caused cell injury, whilst nafamostat mesilate (NM), another serine protease inhibitor, or mesilate itself had no effect on cell viability. zVAD-fmk, a pancaspase inhibitor, or zDEVD-fmk, a caspase-3 inhibitor, did not affect the GM (1.5 mM)-induced decrease of cell viability. Apoptotic cells or DNA fragmentation were also not observed after GM treatment. Moreover, Ca(2+) chelators, a nitric oxide (NO) synthase inhibitor, antioxidants, and radical scavengers had no effect on the GM-induced cell injury. On the other hand, cellular ATP content was decreased in the GM (2.0 mM)-treated cells. Surprisingly, GM (2.0 mM) immediately increased cellular uptake of propidium iodine. These findings suggest that GM induces necrotic cell death via injury of the cell membrane.