Brain death induces apoptosis in donor liver of the rat

Abstract

Background: A difference in short- and long-term function between living-related and cadaveric donor organs is consistently shown in kidney- and liver-transplant studies. We hypothesize that this is caused by induction of apoptosis and inflammation of the potential graft because of the phase of brain death (BD) in the cadaveric donor that predisposes for additional transplant injury. Previously, we have shown inflammation in the liver of brain-dead donors by increased expression of cell adhesion molecules and influx of leukocytes. The key inflammatory mediator in inflammation is tumor necrosis factor (TNF)-alpha. In addition to being involved in inflammation, TNF-alpha also activates the potential detrimental process of apoptosis and, on the other hand, activates an antiapoptotic survival pathway by way of NF-kB. The aim of the present study was to investigate whether the inflammatory response in the liver of brain-dead donors is accompanied by changes in apoptosis and in expression of apoptosis-related proteins, in particular those regulated by NF-kB.

Methods: BD was induced by inflation of an intracranially placed balloon. Apoptosis was assessed by caspase-3 enzyme activity and terminal deoxynucleotide transferase-mediated dUTP nick-end labeling (TUNEL) assay. Changes in expression of proteins involved in pathways leading to apoptosis were studied by determination of mRNA levels using semiquantitative reverse-transcriptase polymerase chain reaction followed by image analysis. TNF-receptor (TNFR), Fas, and Fas-ligand (FasL) were used as indicators for activation of the death receptor mediated pathway. Bcl-2, Bax, Bak, Bid, and A1 were used as indicators for activation of the mitochondrial pathway.

Results: After 6 hours of normotensive BD, the number of apoptotic cells and caspase-3 activity were significantly increased compared with non-brain-dead control rats. TUNEL staining revealed that the apoptotic cells were primarily hepatocytes. mRNA levels of all NF-kappaB induced activators (Fas, bid) and inhibitors (A1, BCl-xl, cIAP2) of both apoptotic pathways were significantly increased in liver tissue of BD donors versus non-BD controls.

Conclusions: The phase of BD in the donor induces increased apoptosis of hepatocytes despite an enhanced expression of NF-kB-dependent antiapoptotic genes.