Interaction of nitrite with catalase in the perfused rat liver

Health and environment in the context of urbanization

This paper introduces a series of research projects designed to fulfill the societal role of environmental health studies by investigating (1) the dynamic and complex relationships between environmental conditions and (2) health in an urban setting. Research in this first category has revealed the existence of the combined influence of multiple physical environmental factors on health and its mechanisms. In the second category, there have been a number of studies of the integrated influence of social environmental factors on health employing an aggregate modeling of multiple determinants of health and studies of individual topics related to social determinants of health. These research projects have contributed to the formulation of specific remedies and the development of comprehensive health policies. Participatory approaches have been used to enhance capacity building opportunities and to ensure that research results reflect the actual conditions in urban societies. Healthy Cities projects and programs have been developed in close collaboration with this type of research. Urban societies have become interdependent and share the same issues globally. Further research into the relationships between health and the environment in the context of urbanization will expand the base of evidence applicable to the complex realities in modern societies.

High-performance liquid chromatography ultraviolet assay for human erythrocytic catalase activity by measuring glutathione as o-phthalaldehyde derivative

The most frequently used catalase (CAT) activity assay is based on the spectrophotometric measurement of hydrogen peroxide (H(2)O(2)) absorbance decrease at 240 nm. Here we report an alternative high-performance liquid chromatography (HPLC) assay for human erythrocytic CAT (heCAT) activity measurement based on glutathione (GSH) analysis as a highly stable, H(2)O(2)-insensitive o-phthalaldehyde (OPA) derivative. The method was developed and validated using an isolated heCAT in phosphate-buffered saline at pH 7.4 and was applied to measure CAT activity in lysed human erythrocytes. heCAT activity was measured at initial concentrations of 5 nM for heCAT, 5mM for H(2)O(2), and 10mM for GSH, and the incubation time was 10 min. Nitrite (NO(2)(-)) was found to be an uncompetitive inhibitor of heCAT activity (IC(50)=9 μM) and of CAT activity in hemolysate (IC(50)∼750 μM). Nitrate (NO(3)(-)) at concentrations up to 100 μM did not inhibit heCAT activity. Azide (N(3)(-)) was found to be a very strong inhibitor of the heCAT (IC(50)=0.2 nM) but a relatively weak CAT inhibitor (IC(50)∼10 μM) in human hemolysates. The novel CAT activity assay works under redox conditions that more closely resemble those prevailing in cells and allows high-throughput analysis despite the required HPLC step.

Metabolism and detoxification of nitrite by trout hepatocytes

Nitrite (NO2-) is one of the most important toxicants to fish. Freshwater fish are especially sensitive, particularly salmonids. Nitrite uptake is thought to occur via the HCO3-, Cl- -exchanger at the gill epithelia with nitrite substituting for chloride. In this way freshwater fish accumulate nitrite in the blood up to 100-fold from the surrounding water. Another source, endogenous nitrite as a degradation product of nitric oxide, rarely leads to pharmacologically relevant concentrations. We developed a new method for the determination of nitrate (NO3-) in biological samples and used it to measure nitrite oxidation in isolated rainbow trout (Oncorhynchus mykiss) hepatocytes which were found to detoxify nitrite to the almost non-toxic nitrate. Detoxification is inhibited by 0.05 mM bumetanide and 0.1 mM furosemide but not by SITS and DITS, suggesting the involvement of the Na+, K+, 2Cl- -cotransporter with nitrite or nitrate substituting for chloride. Oxidation of nitrite is strongly accelerated by 0.05 mM uric acid. The efficacy of this antioxidant suggests that similar reactions are involved as known for haemoglobin [33]. However, in the case of trout liver also membrane bound detoxificating activity can be observed which is also enhanced by uric acid. ATP concentrations remained constant in the hepatocytes during all experiments demonstrating that hepatocyte energy status was not influenced by nitrite oxidation. Thus nitrite resistance in fish is governed by at least two mechanisms, nitrite uptake and the rate of detoxification. It is unknown whether fish actually differ in their ability to distinguish between chloride and nitrite during branchial uptake, but evidence presented in this paper suggests a significant contribution of detoxification pathways to a possible nitrite tolerance of fish.

Effect of ethanol on nitrite oxidation in the perfused rat liver

The effect of ethanol on nitrite oxidation was investigated in the perfused rat liver. Real-time spectral changes in catalase were obtained using a reflectance scanning spectrophotometer in rat liver perfused with Krebs-Henseleit bicarbonate buffer in a non-recirculating system. The nitrite oxidation rate and nitrate production rate were calculated from the differences in concentrations between the influx and efflux perfusates and from the flow rate/g liver weight. Nitrite infusion caused an increase in absorbance difference delta A (640-660 nm), indicating decomposition of catalase compound I to the free form. Administration of ethanol during the nitrite infusion caused a further increase in delta A (640-660 nm) and significant decreases in both the nitrite oxidation rate and the nitrate production rate. Both the nitrite oxidation rate and nitrate production rate decreased, depending on the concentration of ethanol administered. At 10 mM ethanol, they reached about half the rates before the ethanol infusion. In conclusion, ethanol inhibits nitrite oxidation by catalase in the perfused rat liver at relatively low concentrations that can be realized in blood by daily alcohol consumption.