By Kristina Fiore, Staff Writer, MedPage Today
Published: October 31, 2010
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco
BOSTON -- Researchers reported here that they have pared down animal livers to their basic vascular structure and repopulated them with human liver progenitor and endothelial cells -- taking a small step toward ultimately creating completely bioartificial livers.
After a week in a bioreactor, human liver cells placed onto this liver "scaffolding" began to express signature proteins such as albumin, and the endothelial cells expressed von Willebrand factor -- clues that the cells were functioning normally, according to Pedro Baptista, PhD, PharmD, of Wake Forest University in Winston-Salem, N.C., and colleagues.
Baptista reported the group's findings during an oral session at the American Association for the Study of Liver Diseases meeting.
"We're looking into organ scaffolding because it offers a vascular system, and you can't really tissue engineer an organ without a vascular system," Baptista told MedPage Today.
"It's amazing because the cells recognize the chemistry of the matrix on their own and localize and attach in what we think are their native niches -- the endothelial cells attach to vascular structures and the hepatocytes attach in more parenchymal areas," he added.
Yet Baptista cautioned that the work is still very preliminary and his group is currently working on increasing the percentage of organ that gets repopulated with cells -- which currently stands at about 30%.
The purpose of creating bioartificial livers is to mitigate the organ donor shortage -- a persistent and growing problem in the U.S. During his talk, Baptista said the most recent statistics show that 109,000 people are awaiting organ transplants, 16,000 of whom are waiting for a donor liver.
Generating a liver scaffold has been done in the past -- and the technique can also be applied to other organs including the kidney and lungs -- but the organs had only been repopulated with animal cells.
To test the ability of growing human cells on these animal matrices, the researchers removed all existing cells from ferret livers with a detergent solution (Triton X-100 with a bit of ammonium hydroxide) to wash away cellular components such as membranes, nucleic acids, and cellular proteins.
That left behind an extracellular matrix that retains most of its microarchitecture, Baptista explained.
Next, the group seeded 70 million human liver progenitor cells and 30 million endothelial cells onto the matrix through the portal vein or vena cava, and left the organs in a bioreactor for a week.
During that time they found that the endothelial cells attached to the existing vascular channels, and the liver progenitor cells clustered throughout the bioscaffolding.
Baptista said that the "seeding is not quite there" at a 30% level, but his group is now looking at increasing the number of human cells initially infused -- perhaps to 300 or 400 million instead of 100 million.
The results still show, however, that the liver scaffold is biocompatible and can provide a sufficient substrate.
"It shows the cells are really able to recognize the native tissues and attach and engraft in those selected tissues," he said.
In fact, the liver cells were excreting higher levels of signature proteins including albumin and urea, and the endothelial cells expressed higher levels of von Willebrand factor and nitric oxide than comparator cells grown in Petri dishes, Baptista said.
He said a next step is to transplant the new organs back into animals to measure function and survival.
Another group, from Massachusetts General Hospital in Boston, Mass., which presented its findings during a poster session at the AASLD meeting, used the same scaffolding technology and retransplanted the livers back into rats.
They found similar 30% function in the new organs, but the transplanted animals only survived for eight hours, Basak Uygun, PhD, told MedPage Today.
She said in an interview that her team used large doses of blood thinner to prevent the clotting that's typical when a scaffolded organ is reperfused, which may have had an effect on mortality.
But when the livers remained outside of the animals, they functioned well for 24 hours but were not followed-up longer, she added.
The next step is to reperfuse greater than 30% of the matrix with functioning cells, Uygun added.
Arun Sanyal, MD, of Virginia Commonwealth University Medical Center in Richmond, Va., and president of the AASLD, remarked that the findings of both groups "are in a very early stage, but they provide proof-of-concept that you can take these extracellular matrices and create functioning artificial livers."
"It's very interesting even though these are emerging technologies," Sanyal added.
Baptista said he can't forecast when these bioartificial organs would be available for use in the general population, though he predicted porcine livers would be good candidates for providing the extracellular matrices for human transplants.
In the meantime, he said the engineered livers could be used for drug discovery and development.
"I hope in the future," Baptista said, "there will be some type of bioengineered livers that will be suitable for transplant."
Baptista and Uygun said they had no disclosures.
The Wake Forest University work was supported by the Portuguese Foundation for Science and Technology.
Primary source: American Association for the Study of Liver Diseases
Source reference:
Baptista PM, et al "The use of whole organ decellularization for the bioengineering of a human vascularized liver" AASLD 2010; Abstract 12.
Additional source: American Association for the Study of Liver Diseases meeting
Source reference:
Uygyn BE, et al "Engineering of a transplantable liver graft" AASLD 2010; Abstract 293.
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