Interaction of PGBx and peroxides with cytochrome c and inhibition of lipid peroxidation

Mechanism(s) of cytoprotective and anti-inflammatory activity of PGB1 oligomers: PGBx has potent anti-phospholipase A2 and anti-oxidant activity

We postulate that the anti-PLA2 and anti-oxidant activities may account for the broad spectrum protective effects of PGBx that were previously described. These dual properties are demonstrable in vitro, in situ and in vivo, and would have profound effects on stabilization of membrane structure and function, which in turn, would protect organelles, cells, tissues, and organs from inflammation and injury, and possibly alter patterns of aging involving senescence and cell death.

Oligomers of prostaglandin B1 inhibit in vitro phospholipase A2 activity

Oligomers of prostaglandin B1 inhibited phospholipase A2 extracted from human neutrophils in a dose-dependent manner (IC50 = 5 microM), while the monomer was not inhibitory at concentrations of 10 microM or less. The inhibitory activity of PGB1 oligomers increased with increasing polymer size; PGB dimer had approximately one-half the maximal inhibitory activity of PGBx, while a trimer was almost as inhibitory as a tetramer and PGBx (n = 6). PGBx as an oil or as a water-soluble sodium-salt-inhibited Ca2(+)-dependent phospholipase A2 from snake venom, bovine pancreas, human neutrophil and platelet, human synovial fluid, and human sperm with IC50 values ranging from 0.5-7.5 microM. Inhibition was independent of added Ca2+ and was independent of substrate phospholipid concentration. Interaction of purified snake venom phospholipase A2 (Naja mocambique) with PGBx resulted in dose-dependent quenching of the enzyme's tryptophan fluorescence; 50% quench was noted with a molar ratio of PGBx/enzyme of 1.5. Inhibition of phospholipase A2 activity by PGBx was relieved in a dose-dependent manner by either defatted or untreated bovine serum albumin. PGBx is a potent in vitro inhibitor of a wide spectrum of phospholipases A2, and as illustrated in the accompanying paper, has profound inhibitory effects on arachidonic acid mobilization in human neutrophils and vascular endothelial cells. Modulation of cellular and extracellular phospholipases A2, and the bioactive transmitters generated by this catalytic event, may be a basic mechanism by which oligomers of prostaglandin B1 exert their reported membrane-protective effects.

Hydroperoxide-dependent folic acid degradation by cytochrome c

Folic acid is degraded by cytochrome c in the presence of hydrogen peroxide/tert-butyl hydroperoxide at the C9-N10 bond. The degradation is increased with increasing temperature. When guanidine HCl or benzoate are included in the reaction medium, the amount of folic acid degradation is enhanced. Catalase, formate, and thiourea inhibited hydrogen peroxide-dependent folic acid degradation only, and not tert-butyl hydroperoxide dependent degradation. Cyanide and azide markedly inhibited both the hydroperoxide-dependent degradations. Superoxide dismutase, EDTA, ethanol, mannitol, and dimethyl sulfoxide did not inhibit the degradation. The mechanism of cytochrome c-catalyzed folic acid degradation is discussed.