Effects of selected chelating agents and metals on the stability of liver lysosomes

Abstract

Diethyldithiocarbamate (DDC), penicillamine and sodium ethyldiaminetetraacetate (Na-EDTA) in 1 mM concentrations significantly stabilized the membrane of isolated liver lysosomes, as shown by a decreased release of β-glucuronidase upon incubation at 37° and pH 5·0. Thiol compounds which are readily auto-oxidized (cysteine, glutathione and dithiothreitol) did not affect lysosomal fragility when subjected to 1 mM concentration; at a higher concentration (5 mM), these substances increased the release of β-glucuronidase. Stabilization by DDC and penicillamine, both of which contain sulphydryl-like groups, may be related to their nonauto-oxidizability, although their chelation effect cannot be excluded. Various chelating agents relatively specific for Fe 2+ or Fe 3+, such as l,10-phenanthroline, 5,6-dimethyl-l,10-phenanthroline, 2-2′-dipyridyl, Desferal, and pyrocatechol-3,5-disulfonic acid (Tiron), had no effect on lysosomal stability. Zinc ions (0·05–2·5 mM) significantly stabilized lysosomal membranes; this stabilization was concentration dependent, was not affected by thiol compounds, and was potentiated by equimolar complex with 8-hydroxyquinoline (8-HQ) ; 8-HQ alone (1 mM) labilized lysosomes. Calcium ions had no effect, whereas Cu 2+ and Hg 2+ labilized the lysosomes. Labilization by Cu 2+ was reversed by chelating agents and decreased by thiol compounds. Incubation of lysosomes in nitrogen and dark prevented labilization by copper, and did not affect stabilization by zinc. The effects of certain chelating agents (8-HQ, DDC, penicillamine, EDTA) or metals (Zn 2+, Cu 2+, Hg 2+) on the stability of the lysosomal membranes are discussed in terms of the reactivity of these agents with components of the membrane, or interference with metal-catalyzed lipid peroxidation.