Research groups from Okayama University Graduate School of Medicine have made remarkable breakthroughs in liver transplantation. One team found that mouse induced pluripotent stem cells can form liver cells. The second group showed that transplantation of liver cells from another animal species could reverse the symptoms of liver failure in mice.
The first research team use mouse induced pluripotent stem cells (iPSCs) and subjected them to a protocol to convert them into liver cells. They cultured the iPSCs in free-floating cultures to form embryoid bodies. Embryoid bodies (EBs) are cell aggregates derived from embryonic stem cells when they are grown in non-attached, free floating cultures, like a hanging drop. EBs can also be induced by plating embryonic stem cells (ESCs) on non-tissue culture treated plates or by growing them in spinner flasks. Once the cells aggregate, they differentiate to a limited extent to roughly recapitulate embryonic development. EBs are composed of a large variety of differentiated cell types. However, EB differentiation is largely disorganized.
The EBs were then treated with a growth factor called “fibroblast growth factor” and activin for three days to induce the formation of endodermal tissues. On the eighth day of differentiation, they treated the cells with “hepatic growth factor” for eight days. After 16 days, they had functional liver cells, and this protocol seemed to work quite well.
A variety of genetic and metabolic tests showed that these cells were liver cells. They expressed liver-specific enzymes like urea cycle enzymes, the iron transport protein transferrin, asialoglycoprotein receptor (ASGR), and the all-important liver-specific protein, albumin. Metabolically, the iPSC-made liver cells also metabolized ammonium, which is a liver-specific activity.
A major limitation for cell-based therapies for the treatment of liver diseases is the shortage of livers for transplantation, and the risk of rejection by the immune system if the transplanted tissue is not well matched with that of the donor is also a stark problem. This technology, however, provides the means to make transplantable liver cells from someone else’s own somatic cells.
The lead author of this study, Masaya Iwamuro said, “The ability to make iPS cells from somatic cells has implications for overcoming both immunological rejection and ethical issues associated with embryonic stem cells… Our study will be an important step in generating hepatocytes from human iPS cells as a new source for liver-targeted cell therapies…In the future, studies will generate new therapies that include the transplantation of iPS cell-derived hepatocytes without immunological barrier, in vitro determination of toxicity, and the development of personalized health care by evaluating drugs for efficacy and toxicity on patient-specific hepatocytes,”
The second study used pig liver cells for mice with failed livers. Because of the lack of suitable livers for transplantation, Naoya Kobayashi argued that the greater supply of pig liver cells suggest that once technical issues are overcome, pig liver cells might be transplanted successfully into human livers. In their recent study, Kobayashi and colleagues successfully transplanted pig liver cells into mice with acute liver failure. Their transplantations caused the mice with liver failure to survive and their symptoms subsided.
Kobayashi provided this statement: “Using xenogenic hepatocytes from animals such as pigs might be advantageous for treating acute liver failure in humans…. Hepatocytes are the main active cells in the liver. However, removal from the liver causes hepatocytes major stress and potential loss of function. We tested a scaffold to improve the success of hepatocyte xenotransplantation…. In this xenotransplantation model, we found that the SAPNF has an excellent ability to promote hepatocyte engraftment and maintains tremendous hepatocyte functions capable of rescuing mice from acute liver failure. Dr. Kobayashi collaborated with colleagues from the Baylor (Texas) University Institution for Immunology Research.