DURHAM, N.C. -- After noticing -- almost entirely by chance -- the striking cellular similarities between the damage that occurs to donor livers awaiting transplantation and the very early stages of tumor growth, Duke University Medical Center researchers believe they have found a novel way of extending the amount of time livers can remain safely outside the body before transplantation.
Using Interferon (IFN)-alpha, an agent used in cancer treatment, the researchers not only extended the preservation time of the liver, but also found that treated livers showed improved function compared to untreated organs.
"These findings clearly represent a new approach to preserving livers prior to transplantation, which could significantly help future liver transplant patients," said Dr. Pierre-Alain Clavien, lead researcher and chief liver transplant surgeon at Duke. "With more time, we can do more with livers, such as segmenting them to help two people with one organ."
The results of Clavien's research were published as the cover article today (Oct. 24) in the November issue of the journal Gastroenterology.
While investigating the phenomenon of cold preservation injury two years ago, Clavien said one of those rare moments in science occurred when happenstance is the catalyst for scientific discovery. A relative of one of Clavien's collaborators had been diagnosed with breast cancer, so the collaborator was gathering as much information as possible to better understand the disease.
"As we were looking at the mechanisms of breast cancer, we noticed the striking similarities between what was occurring during the very early stages of tumor development and cold preservation injury to the livers," Clavien.
After removal from the donor, livers are immersed in a special cold solution to preserve the function of hepatocytes, cells which have complex functions, producing as many as 5,000 different proteins, according to Clavien. However, the low temperature (1 degree C or 34 degrees F) required to effectively preserve hepatocytes also causes sinusoidal cells -- which act as a detoxifying filter between the blood and hepatocytes -- to become deformed, slough off and die after transplantation.
The same physical changes in endothelial cells -- deformation and sloughing -- occur during the initial stages of tumor growth. Also, in both processes, researchers observe large numbers of scavenging immune cells know as macrophages.
"If you looked at the sinusoidal cells and the endothelial cells in cancer tissue under a microscope, you couldn't tell the difference," Clavien said.
Since the cellular changes appeared the same, the researchers tested three agents known to inhibit angiogenesis, a process in the initial stages of tumor growth when new capillaries sprout to nourish the growing tumor. They discovered that all three agents provided protection, but one agent, IFN-alpha, provided significant protection to livers prior to transplantation in animal models by preserving the sinusoidal cells, Clavien said.
Researchers have long known that the proliferation of new capillaries usually occurs when oxygen levels are low in the tissue involved and also in the presence of macrophages. Likewise, while the cold solution reduces the metabolic needs of the organ, the liver does not receive the optimal oxygenation it received while in the body
"The beginning of angiogenesis is marked by the detachment, change of shape and proliferation of endothelial cells," Clavien said. "Since the injuries that occur to the liver during preservation look so much like the initial stages of angiogenesis, and since both occur in the presence of these macrophages, it appeared to us that the damage to the sinusoidal cells was an angiogeneic response to the low oxygen levels."
The only difference between the two processes is that when sinusoidal cells slough off, they die; in cancer, the cells multiply and proliferate. While researchers don't know for sure what causes these processes -- possibly factors released by macrophages or cancer cells -- they do know that certain agents, the most potent being IFN-alpha, can retard angiogenesis.
Clavien's team added IFN-alpha to liver preservation solutions, injected it into animals at various times before organ harvest and tested it on isolated liver models. They found that IFN-alpha provided protection in all models.
"Because IFN-alpha reached peak levels between two and six hours after injection, we believe that a single dose of IFN-a, given a few hours prior to organ recovery and addition of the drug in the preservation solution, can dramatically prevent injuries to the liver," Clavien said.
Clavien's lab currently is investigating what actually triggers the changes evident in the sinusoidal cells before embarking on tests involving humans. Once these studies are complete, clinical trials need to be conducted, Clavien said.
Joining Clavien in the study, which was supported by Duke's department of surgery, were Dr. Wenshi Gao, Dr. Mary Washington and Dr. Rex Bentley.