Liver regeneration tied to bile acids.

Bile plays an integral role in the regeneration of damaged liver tissue, a study finds.

The liver manufactures bile, which is then stored in the gall bladder. From there, it moves into the small intestine where it helps digest fats. Up to 95 percent of bile is then recycled via the blood and pumped back to the liver. It's a highly efficient system, says molecular biologist David D. Moore of the Baylor College of Medicine in Houston.

Earlier work had hinted that bile might influence the liver's capacity to repair itself. To investigate, Moore and his colleagues fed mice chow that contained a bile component. Within a week, the animals' livers grew by 30 percent.

In a separate experiment, the scientists removed parts of the livers of normal mice, which within days showed signs of regrowth. Because the gall bladder continued to release a normal amount of bile into the gut, more bile is available per gram of the undersize liver. This suggests that bile stimulated the liver regeneration, Moore says.

After similar surgery, mice lacking a gene called FXR didn't regrow liver tissue as well, the researchers report in the April 14 Science. The researchers focused on FXR because they knew that bile binds to and activates the protein encoded by the gene. Within a liver cell, this protein then switches on various genes that influence cell replication and other processes.

The finding indicates that the protein from FXR acts as a bile sensor, he says. Combined, the experiments suggest a mechanism by which the liver senses and responds to tissue loss. Further research may clarify which genes the protein switches on and how that influences cell replication, he says.--N. S.