Disruption of mitochondrial calcium homeostasis after chronic alpha-naphthylisothiocyanate administration: relevance for cholestasis.
BACKGROUND
Hepatocyte dysfunction caused by impaired mitochondrial function has been pointed out as a probable leading cause of cholestatic liver injury. The aim of this study was to evaluate liver mitochondrial bioenergetics that followed repeated in vivo administration of alpha-naphthylisothiocyanate, a known cholestatic agent.


METHODS
Serum markers of liver injury and endogenous adenine nucleotides were measured in alpha-naphthylisothiocyanate-treated rats (intraperitoneally, 100 mg/Kg/wk x 6 wk). Changes in membrane potential, mitochondrial respiration, as well as alterations in mitochondrial calcium homeostasis were monitored.


RESULTS
In rats injected with alpha-naphthylisothiocyanate, liver injury with cholestasis developed within 48 hours, as indicated by both serum enzyme activities and total bilirubin concentration. However, 1 week after the last injection, serum enzyme activity returned to control levels. In addition, after chronic alpha-naphthylisothiocyanate administration, no alterations in mitochondrial respiratory function and membrane potential were observed. Associated with these parameters, mitochondria from treated animals exhibited increased susceptibility to disruption of mitochondrial calcium homeostasis by calcium phosphate and by bile acids, which was probably caused by induction of permeability transition pore.


CONCLUSIONS
Our data suggest that chronic cholestasis in rats leads to impaired mitochondrial function due to the disruption of mitochondrial calcium homeostasis. The initiating event is the induction of a cyclosporine A-sensitive release of calcium. This event may be an important determinant of the progression of cholestatic liver injury and associated liver cirrhosis. In addition, in the present study we observed that impairment of mitochondrial function is potentiated by chenodeoxycholate, a bile acid that is known to be toxic. Ursodeoxycholate (the beta- epimer of chenodeoxycholate) is approved for the treatment of chronic cholestatic liver disease. Interestingly, we show that the susceptibility to the cyclosporine A-sensitive release of calcium was increased by the combination of both bile acids. These results indicate that the reported improvement of biochemical parameters in cholestatic patients treated with ursodeoxycholate would not prevent the associated mitochondrial dysfunction. This may explain the progression of the histological stage and the maintenance of symptoms during cholestasis.
Rolo
Anabela P
AP
Department of Zoology, Center for Neurosciences and Cell Biology of Coimbra, University of Coimbra, Portugal.
Oliveira
Paulo J
PJ
Seiça
Raquel
R
Santos
Maria S
MS
Moreno
Antonio J
AJ
Palmeira
Carlos M
CM
D015058:1-Naphthylisothiocyanate / Q000008:administration & dosage / Q000633:toxicity; D000227:Adenine Nucleotides / Q000378:metabolism; D000410:Alanine Transaminase / Q000097:blood; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002635:Chenodeoxycholic Acid / Q000633:toxicity; D002779:Cholestasis / Q000139:chemically induced / Q000378:metabolism*; D004734:Energy Metabolism / Q000187:drug effects; D005260:Female; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006706:Homeostasis / Q000502:physiology; D007274:Injections, Intraperitoneal; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D000227:Adenine Nucleotides; D002635:Chenodeoxycholic Acid; D015058:1-Naphthylisothiocyanate; D000410:Alanine Transaminase; D002118:Calcium