Science Editor

Worldwide, almost 800,000 people die from liver cirrhosis each year, which is caused most frequently, though not exclusively, by excess alcohol or hepatitis C infection.

There currently is no treatment for cirrhosis, but its molecular causes are fairly well worked out. Cirrhosis results from fibrosis, or the excessive formation of scar tissue. Molecularly, fibrosis occurs when a type of liver cell, the hepatic stellate cell, is activated to secrete excess collagen, which leads to the buildup of extracellular matrix and scar tissue.

Hepatic stellate cells, in turn, are activated by a kinase known as RSK, which phosphorylates the protein C/EBP-beta. In the Dec. 26 issue of PLoS One, researchers from the University of California in San Diego reported that by blocking the interaction of RSK and C/EBP-beta, they were able to induce cell death selectively in activated stellate cells, and prevent and even reverse liver fibrosis in animals.

The researchers first tested whether mice bearing a transgenic version of C/EBP-beta that could not be phosphorylated would develop cirrhosis in response to a liver toxin. Despite the fact that the normal version of C/EBP-beta is still around and could, in theory, be phosphorylated, the transgene is dominant.

"We've shifted the kinetics on our favor," said Martina Buck, assistant professor of medicine at UCSD and the Veterans Affairs San Diego Healthcare System. She added that the transgenic version binds RSK more easily but cannot be phosphorylated, so RSK is, in effect, not available to phosphorylate the normal protein.

Buck and senior author Mario Chojkier found that three months of toxin administration led to severe liver cirrhosis in normal mice but little to no cirrhosis in transgenic animals. Transgenic animals had less collagen, less of an inflammatory response and their hepatic stellate cells did not show the activation that is typical in liver fibrosis.

"Our treatment was in the presence of continuing damage," Buck stressed. "So it is very realistic" for modeling the situation in cirrhotic patients. Blocking C/EBP-beta phosphorylation induced apoptosis by activating caspase 8.

In cell culture, the researchers then used a peptide that inhibits the activity of RSK to test whether it could stimulate apoptosis of activated stellate cells and prevent cirrhosis. The peptide inhibited RSK activation, stopped hepatic stellate cells from proliferating and activated caspase 8 in proliferating cells, which killed the cells responsible for liver fibrosis but not normal hepatic stellate cells.

"All control mice had severe liver fibrosis, while all mice that received the RSK-inhibitory peptide had minimal or no liver fibrosis," Buck said. The treatment was actually able to reverse liver fibrosis, which Buck added was not entirely unexpected. "There are natural [collagen] degrading processes that happen all the time," she told BioWorld Today. "So if you can stop the buildup, you can allow those to happen."

Buck and Chojkier also tested human liver biopsies from patients with hepatitis C-induced liver fibrosis. All four samples tested had a high level of active RSK and phosphorylated C/EBP-beta.

The researchers caution in their paper that, to date, it is unclear whether the same mechanisms are at fault for liver fibrosis resulting from other causes. They wrote, "It would be important to determine whether RSK and phosphorylation of C/EBPâ are also critical in other animal models that reflect other causes of human liver fibrosis, such as biliary cirrhosis, alcoholic liver disease, immune liver injury and genetic iron overload. Any one of these studies will require as extensive an analysis as that performed with the [toxin] model of liver fibrosis."

Nevertheless, it is certainly reasonable to assume that different types of liver damage might have the same underlying cause. In the meantime, Buck said that they are "actively engaged in discussion and hoping to get a collaboration with one or more pharma or biotech companies" to further clinical development of the discoveries.