Deoxycholic acid modulates cell death signaling through changes in mitochondrial membrane properties.
Cytotoxic bile acids, such as deoxycholic acid (DCA), are responsible for hepatocyte cell death during intrahepatic cholestasis. The mechanisms responsible for this effect are unclear, and recent studies conflict, pointing to either a modulation of plasma membrane structure or mitochondrial-mediated toxicity through perturbation of mitochondrial outer membrane (MOM) properties. We conducted a comprehensive comparative study of the impact of cytotoxic and cytoprotective bile acids on the membrane structure of different cellular compartments. We show that DCA increases the plasma membrane fluidity of hepatocytes to a minor extent, and that this effect is not correlated with the incidence of apoptosis. Additionally, plasma membrane fluidity recovers to normal values over time suggesting the presence of cellular compensatory mechanisms for this perturbation. Colocalization experiments in living cells confirmed the presence of bile acids within mitochondrial membranes. Experiments with active isolated mitochondria revealed that physiologically active concentrations of DCA change MOM order in a concentration- and time-dependent manner, and that these changes preceded the mitochondrial permeability transition. Importantly, these effects are not observed on liposomes mimicking MOM lipid composition, suggesting that DCA apoptotic activity depends on features of mitochondrial membranes that are absent in protein-free mimetic liposomes, such as the double-membrane structure, lipid asymmetry, or mitochondrial protein environment. In contrast, the mechanism of action of cytoprotective bile acids is likely not associated with changes in cellular membrane structure.
Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal.
Tânia
T
Sousa
Research Institute for Medicines (iMed.ULisboa), Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal.
Rui E
RE
Castro
Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal.
Sandra N
SN
Pinto
Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal Departamento de Química e Bioquímica, Faculty of Sciences, University of Lisbon, Lisbon, Portugal.
Ana
A
Coutinho
Research Institute for Medicines (iMed.ULisboa), Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal.
Susana D
SD
Lucas
Research Institute for Medicines (iMed.ULisboa), Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal.
Rui
R
Moreira
Research Institute for Medicines (iMed.ULisboa), Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal.
Cecília M P
CM
Rodrigues
Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal.
Manuel
M
Prieto
Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal.
Fábio
F
Fernandes
D000818:Animals; D017209:Apoptosis; D002470:Cell Survival; D002478:Cells, Cultured; D003840:Deoxycholic Acid / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008560:Membrane Fluidity; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000378:metabolism*; D010539:Permeability; D051381:Rats; D015398:Signal Transduction
D003840:Deoxycholic Acid
apoptosis; bile acids and salts; bile acids and salts/physical chemistry; fluorescence microscopy; membranes; membranes/fluidity; mitochondria