Extinction coefficient of polymerized diaminobenzidine complexed with cobalt as final reaction product of histochemical oxidase reactions

Intracellular free radical production in synovial T lymphocytes from patients with rheumatoid arthritis

OBJECTIVE

To investigate the cellular and molecular sources of oxidative stress in patients with rheumatoid arthritis (RA) through analysis of the production of reactive oxygen species (ROS) in synovium.

METHODS

Cytochemical procedures based on the 3,3'-diaminobenzidine (DAB)-Mn2+ deposition technique were used on unfixed cryostat sections of synovium from RA patients and rheumatic disease controls. For immunophenotyping, sections were incubated, fixed, and stained with fluorescein isothiocyanate-labeled antibodies. Fluorescence-activated cell sorter analysis of the ROS-reactive dye 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate-di(acetoxymethyl ester) was used to measure intracellular ROS in T lymphocytes from peripheral blood and synovial fluid. To determine which enzymes produced ROS, different inhibitors were tested.

RESULTS

Large quantities of DAB precipitated in the majority of RA synovial T lymphocytes, indicative of intracellular ROS production. These ROS-producing T lymphocytes were observed throughout the synovium. Polymerization of DAB was observed to a lesser extent in other forms of chronic arthritis, but was absent in osteoarthritis. DAB staining of cytospin preparations of purified RA synovial fluid T cells confirmed the presence of ROS-producing cells. One of the ROS involved appeared to be H2O2, since catalase suppressed intracellular ROS production. Superoxide dismutase, which uses superoxide as a substrate to form H2O2, diphenyleneiodonium (an inhibitor of NADPH oxidase), N(G)-monomethyl-L-arginine (an inhibitor of nitric oxide synthesis), nordihydroguaiaretic acid (an inhibitor of lipoxygenase), and rotenone (an inhibitor of mitochondrial ROS production) failed to suppress ROS production.

CONCLUSION

Our findings show that chronic oxidative stress observed in synovial T lymphocytes is not secondary to exposure to environmental free radicals, but originates from intracellularly produced ROS. Additionally, our data suggest that one of the intracellularly generated ROS is H2O2, although the oxidase(s) involved in its generation remains to be determined.

In situ heterogeneity of peroxisomal oxidase activities: an update

Oxidases are a widespread group of enzymes. They are present in numerous organisms and organs and in various tissues, cells, and subcellular compartments, such as mitochondria. An important source of oxidases, which is investigated and discussed in this study, are the (micro)peroxisomes. Oxidases share the ability to reduce molecular oxygen during oxidation of their substrate, yielding an oxidized product and hydrogen peroxide. Besides the hydrogen peroxide-catabolizing enzyme catalase, peroxisomes contain one or more hydrogen peroxide-generating oxidases, which participate in different metabolic pathways. During the last four decades, various methods have been developed and elaborated for the histochemical localization of the activities of these oxidases. These methods are based either on the reduction of soluble electron acceptors by oxidase activity or on the capture of hydrogen peroxide. Both methods yield a coloured and/or electron dense precipitate. The most reliable technique in peroxisomal oxidase histochemistry is the cerium salt capture method. This method is based on the direct capture of hydrogen peroxide by cerium ions to form a fine crystalline, insoluble, electron dense reaction product, cerium perhydroxide, which can be visualized for light microscopy with diaminobenzidine. With the use of this technique, it became clear that oxidase activities not only vary between different organisms, organs, and tissues, but that heterogeneity also exists between different cells and within cells, i.e. between individual peroxisomes. A literature review, and recent studies performed in our laboratory, show that peroxisomes are highly differentiated organelles with respect to the presence of active enzymes. This study gives an overview of the in situ distribution and heterogeneity of peroxisomal enzyme activities as detected by histochemical assays of the activities of catalase, and the peroxisomal oxidases D-amino acid oxidase, L-alpha-hydroxy acid oxidase, polyamine oxidase and uric acid oxidase.