A protein involved in one of the liver’s most basic functions also sounds the alarm when liver cells get hurt, according to new research with mice.
The findings point to a potential way to better monitor the health of patients who have suffered the damage, treat the damage, and even prevent the damage from happening.
On a normal day, the cells of a human liver do what they do best—make key blood proteins, clear toxins from the blood, and send their remains down the digestive tract in a stream of bile.
But when something badly injures enough of these cells—such as an overdose of pain medicine—this vital work can come to a screeching halt. With few good treatment options available, more than 2,000 Americans develop acute liver failure each year.
The alarm, however, and the help that it summons from the immune system, can help protect the liver from further damage, the researchers report. It can even spur the repair of a damaged liver after injury, says Bishr Omary, a professor in the molecular and integrative physiology department and the gastroenterology and hepatology division at the University of Michigan Medical School.
Doing good in times of need
Omary and colleagues discovered an unexpected function for the enzyme CPS1, short for carbamoyl phosphate synthetase-1.
Normally, CPS1 plays a key role in breaking down ammonia, a waste product the body needs to get rid of. It does this in the mitochondria of the major cells of the liver, called hepatocytes.
A few years ago, Omary and his team discovered CPS1 in an unexpected place: the blood of animals and humans with acute liver injury. They showed that the amount of CPS1 in the blood served as an indicator of the extent of the damage—but also found that it left the blood quickly. That made it a potential early marker for recovery from liver injury.
In the new paper, they report that CPS1 is normally released into bile but ends up in blood upon acute liver injury. They were surprised to learn that CPS1 had reached the inside of white blood cells called monocytes. There, they found, it performs a good deed.
“CPS1 that is cleared from blood reprograms monocytes to become anti-inflammatory and move to the liver,” says Omary.
“This cytokine-like function, which is entirely unrelated to its usual enzymatic function, provides a mechanism for the protective effect we observed.
“It’s very exciting since it offers a potential pathway to develop new treatments,” Omary says.
Min-Jung Park, a research scientist in the College of Veterinary Medicine at Chonnam National University in South Korea, led the painstaking work of studying CPS1 in the blood, bone marrow, liver, and bile of mice and then increasing its levels in the blood by injecting mice with an extra supply she generated in the lab.
The researchers gave this exogenous CPS1 to mice before they exposed them to acetaminophen—the pain reliever in Tylenol, the over-the-counter medication that millions of people take. The medication holds the potential to damage the liver in high doses and in combination with other substances.
Even when the mice received doses high enough to cause acute injury, those that received added CPS1 beforehand did not suffer major liver damage.
On the mend
When the researchers injected CPS1 into mice after giving them the high dose of acetaminophen, the animals’ livers showed significant signs of recovery.
“The amount of CPS1 released to blood naturally is not sufficient to cope with injury, which is why the boost becomes very helpful,” says Park. “In contrast, if too much is spilled to blood by the liver, then this means too many liver cells have died to have a chance to recover.”
Omary notes that since CPS1 is a fairly large protein, determining which of its components are most important for triggering the anti-inflammatory response might improve any effort to use and understand its therapeutic capacity.
He and his team are working to assess exactly how it works in mice and to determine if they can ultimately use it as a therapeutic in humans. However, he cautions that significantly more work is necessary to determine the feasibility of its human use.
The research appears in the Proceedings of the National Academy of Sciences.
The National Institutes of Health funded the research, including a Postdoctoral Translational Scholars Program award to Park through the Michigan Institute for Clinical & Health Research. The University of Michigan has applied for patents on the use of CPS1 as an anti-inflammatory biologic, as well as for its potential utility as a biomarker to predict the severity of acute liver failure.
Source: University of Michigan