Ca2+ elevation exacerbates oxidative stress (OS)-induced hepatocellular damage by facilitating formation of mitochondrial permeability transition pore (MPTP), via Ca2+-calmodulin (CM)

PÉREZ L.M.; OCHOA J.E.; SÁNCHEZ POZZI E.J.; ROMA M.G.

Vilamoura

Congreso; XXV Congreso de Gastrenterologia e Endoscopia Digestiva; 2005

Sociedad de Gastrenterología y Endoscopía Digestiva de Portugal

OS is a common event in most hepatopathies, leading to MPTP formation and membrane lipid peroxidation, among other alterations. Although Ca2+ plays a permissive role in these events, the underlying mechanisms involved in this phenomenon are largely unknown. We examined here whether Ca2+-dependent signaling events, including PKC activation or CM formation, are involved in Ca2+ pro-oxidizing effect, by assessing the capability of specific signaling Ca2+ antagonists to counteract both lipid peroxidation and MPTP formation induced by the model, oxidizing compound, tert-butyl hydroperoxide (tBOOH). tBOOH (500 µM, 15 min) induced lipid peroxidation, as evidenced by a 723 % increase (p<0.001) in the generation of thiobarbituric acid reactive species (TBARS); cyclosporin A (5 µM), a MPTP inhibitor, partially prevented this effect (-22%, p<0.025). Sequestration of intracellular Ca2+ with BAPTA/AM (50 µM) or inhibition of CM with W7 (100 µM) reduced in a similar extent tBOOH-induced TBARS formation (-28 %; p<0.01). tBOOH-induced MPTP formation, as assessed by measuring mitochondrial membrane depolarisation as a surrogate MPTP marker using tetra-methyl-rhodamine methyl ester as a fluorescent probe, was also similarly counteracted by these two compounds (approx. ?30%, p<0.025). Neither the PKC inhibitor, staurosporine (100 µM), the inhibitor of the CM-dependent PKII, calmidazolium (5 µM), nor the calpain inhibitor I (50 µM) modified tBOOH-induced TBARS generation or MPTP formation. We concluded that Ca2+ exacerbates oxidative hepatocellular damage via CM formation. As yet unidentified CM-dependent molecules other than PKII or calpain seem to be involved. Further investigation to identify these downstream CM effectors is in progress.