Inhibition of human phospholipase C by aurothiomalate and (triethylphosphine) gold complexes.

The effect of several gold complexes on the activity of phospholipase C from human blood platelets was studied in vitro. Aurothiomalate and auranofin--2 agents used for the chrysotherapy of rheumatoid arthritis--, gold chloride, (triethylphosphine)gold chloride, and 5 newly synthesized (triethylphosphine)gold complexes dose-dependently inhibited the enzyme with IC50 values between 0.8 mumol/l ((triethylphosphine)gold chloride) and over 100 mumol/l (auranofin). None of the compounds affected phospholipase A2 from human polymorphonuclear leukocytes at concentrations up to 100 mumol/l. Inhibition of phospholipase C by (triethylphosphine)gold chloride, aurothiomalate, and compound 3 was not significantly different at substrate concentrations of 20 and 100 mumol/l phosphatidylinositol, suggesting that these gold complexes do not inhibit phospholipase C by competing with the substrate. After confirming the Ca2+ dependence of the human platelet phospholipase C by demonstrating inhibition by the Ca2+ chelators EDTA and EGTA--but no inhibition by the Zn2+ chelator 1,10-phenanthroline--the inhibition of the enzyme by (triethylphosphine)gold chloride, aurothiomalate, and compound 3 was studied at 3 different concentrations of Ca2+ in the range of 0.2 to 2 mmol/l. Inhibition by (triethylphosphine)gold chloride was not affected by changes of Ca2+, whereas inhibition by aurothiomalate and compound 3 was markedly suppressed by increasing the Ca2+ concentration.(ABSTRACT TRUNCATED AT 250 WORDS)