The Effect of Experimentally Induced Redox Changes on Human Rheumatoid and Non-Rheumatoid Synovial Tissue in vitro

Abstract

This study has confirmed that the lysosomal membranes in the synovial lining cells of human rheumatoid synovial tissue are abnormally labile; that the cytoplasmic redox balance, as measured by the proportion of dithiol to disulphide groups, is exceptionally reductive; and that there is an excessive rate of generation of reduced NADP despite little change in its rate of oxidation. These results suggested that the increased reductive conditions in the cytoplasm might contribute to the state of the lysosomes. To test this, human synovial tissue was maintained in vitro , in adult maintenance culture, and hydrogendonating or hydrogen-accepting molecules were added to the culture medium. It was shown that ascorbate acts as a hydrogen-donor. In non-rheumatoid cells it increased the proportion of cytoplasmic sulphydryl groups (which indicates a more reductive redox balance) and also increased the lability of the lysosomal membranes. Hydrogen-accepting molecules, such as dehydroascorbate and particularly menadione, produced the reverse effect. Similar effects occurred in rheumatoid synovial lining cells, in which menadione also diminished the rate of generation of NADPH. It seems likely, therefore, that redox systems in the cytoplasm and in the extra-cellular space, can influence the cytoplasmic dithiol: disulphide balance and the functional state of lysosomal membranes in synovial lining cells. In rheumatoid synovial tissue, menadione diminishes the excessively reductive conditions in these cells and stabilizes lysosomal membranes. In der vorliegenden Arbeit werden neue Hinweise aufgeführt, daß die Membranen von Lysosomen in Synoviazellen bei der rheumatoiden Arthritis des Menschen gesteigert labil sind; der Redoxquotient des Zytoplasmas gemessen am Quotienten Dithiol zu Disulfidgruppen liegt stark im Reduktiven. Reduziertes NADP wird in vermehrtem Maß gebildet, bei fast normaler Oxydationsfähigkeit. Möglicherweise bedingen die vermehrt reduktiven Kräfte im Zytoplasma den Zustand der Lysosomen. Um diese Hypothese zu überprüfen, werden menschliche Synoviazellen in vitro gehalten, Moleküle den Kulturen zugesetzt, die entweder Wasserstoffdonatoren oder Wasserstoffakzeptoren sind, z.B. Ascorbat wirkt als Wasserstoffdonator. In nichtrheumatoiden Synoviazellen erhöht es die Anzahl zytoplasmatischer Sulphydrylgruppen und steigert somit die Labilität lysosomaler Membranen in den Synoviazellen und erhöht