Cytoprotection by fructose and other ketohexoses during bile salt‐induced apoptosis of hepatocytes

Toxic bile salts cause hepatocyte necrosis at high concentrations and apoptosis at lower concentrations. Although fructose prevents bile salt‐ induced necrosis, the effect of fructose on bile salt‐induced apoptosis is unclear. Our aim was to determine if fructose also protects against bile salt‐induced apoptosis. Fructose inhibited glycochenodeoxycholate (GCDC)‐induced apoptosis in a concentration‐dependent manner with a maximum inhibition of 72% ± 10% at 10 mmol/L. First, we determined if fructose inhibited apoptosis by decreasing adenosine triphosphate (ATP) and intracellular pH (pH i ). Although fructose decreased ATP to <25% of basal values, oligomycin (an ATP synthase inhibitor) did not inhibit apoptosis despite decreasing ATP to similar values. Fructose (10 mmol/L) decreased intracellular pH (pH i ) by 0.2 U. However, extracellular acidification (pH 6.8), which decreased hepatocyte pH i 0.35 U and is known to inhibit necrosis, actually potentiated apoptosis 1.6‐fold. Fructose cytoprotection also could not be explained by induction of bcl‐2 transcription or metal chelation. Because we could not attribute fructose cytoprotection to metabolic effects, alterations in the expression of bcl‐2, or metal chelation, we next determined if the poorly metabolized ketohexoses, tagatose and sorbose, also inhibited apoptosis; unexpectedly, both ketohexoses inhibited apoptosis. Because bile salt‐induced apoptosis and necrosis are inhibited by fructose, these data suggest that similar processes initiate bile salt‐induced hepatocyte necrosis and apoptosis. In contrast, acidosis, which inhibits necrosis, potentiates apoptosis. Thus, ketohexose‐sensitive pathways appear to initiate both bile salt‐induced cell apoptosis and necrosis, whereas dissimilar, pH‐sensitive, effector mechanisms execute these two different cell death processes.