An Efficient Method for Converting Fat Cells to Liver Cells


I have a friend whose wife has systemic lupus erythematosis, and her liver has taken a beating as a result of this disease. She has never had a drop of alcohol for decades and yet she has a liver that looks like the liver of a 70-year-old alcoholic. The scarring of the liver as result of repeated damage and healing has seriously compromised her liver function. She is now a candidate for a liver transplant. Wouldn’t it be nice to simply give her liver cells to heal her liver?

This dream came a little closer to becoming reality in October of this year when scientists at Stanford University developed a fast and efficient way to convert fat cells isolated from routine liposuction into liver cells. Even though these experiments used mice, the stem cells were isolated from human liposuction procedures.

This experiment did not use embryonic stem cells or induced pluripotent stem cells to generate liver cells. Instead it used adult stem cells from fat.

Fat-based stem cells

The liver builds complex molecules, filters and breaks down waste products and toxic substances that might otherwise accumulate to dangerous concentrations.

The liver, unlike other organs, has a capacity to regenerate itself to a significant extent, but the liver’s regenerative abilities cannot overcome the consequences of acute liver poisoning, or chronic damage to the liver, as a result of hepatitis, alcoholism, or drug abuse.

For example, acetaminophen (Tylenol) is a popular pain-reliever, but abusing acetaminophen can badly damage the liver. About 500 people die each year from abuse of acetaminophen, and some 60,000 emergency-room visits and more than 25,000 hospitalizations annually are due to acetaminophen abuse. Other environmental toxins, such as poisonous mushrooms, contribute more cases of liver damage.

Fortunately, the fat-to-liver protocol is readily adaptable to human patients, according to Gary Peltz, professor of anesthesia and senior author of this study. The procedure takes about nine days, which is easily fast enough to treat someone suffering from acute liver poisoning, who might die within a few weeks without a liver transplant.

Some 6,300 liver transplants are performed annually in he United States, and approximately 16,000 patients are on the waiting list for a liver. Every year more than 1,400 people die before a suitable liver can be found for them.

Even though liver transplantations save the lives of patients, the procedure is complicated, not without risks, and even when successful, is fraught with after effects. The largest problem is the immunosuppressant drugs that live patients must take in order to prevent their immune system from rejecting the transplanted liver. Acute rejection is an ongoing risk in any solid organ transplant, and improvements in immunosuppressive therapy have reduced rejection rates and improved graft survival. However, acute rejection still develops in 25% to 50% of liver transplant patients treated with immunosuppressants. Chronic rejection is somewhat less frequent and is declining and occurs in approximately 4% of adult liver transplant patients.

Peltz said, “We believe our method will be transferable to the clinic, and because the new liver tissue is derived from a person’s own cells, we do not expect that immunosuppressants will be needed.”

Peltz also noted that fat-based stem cells do not normally differentiate into liver cells. However, in 2006, a Japanese laboratory developed a technique for converting fat-based stem cells into induced liver cells (called “i-Heps” for short). This method, however, is inefficient, takes 30 days, and relies on chemical stimulation. In short, this technique would not provide enough material to regenerate a liver.

The Stanford University group built upon the Japanese work and improved it. Peltz’s group used a spherical culture and were able to convert fat-bases stem cells into i-Heps in nine days and with 37% efficiency (the Japanese group only saw a 12% rate). Since the publication of their paper, Peltz said that workers in his laboratory have increased the efficiency to 50%.

Dan Xu, a postdoctoral scholar and the lead author of this study, adapted the spherical culture methodology from early embryonic-stem-cell literature. However, instead of growing on flat surfaces in a laboratory dish, the harvested fat cells are cultured in a liquid suspension in which they form spheroids. Peltz noted that the cells were much happier when they were grown in small spheres.

Once they had enough cells, Peltz and his co-workers injected them into immune-deficient laboratory mice that accept human grafts. These mice were bioengineered in 2007 as a result of a collaboration between Peltz and Toshihiko Nishimura from the Tokyo-based Central Institute for Experimental Animals. These mice had a viral thymidine kinase gene inserted into their genomes and when treated with the drug gancyclovir, the mice experienced extensive liver damage.

After gancyclovir treatment, Peltz and his coworkers injected 5 million i-Heps into the livers of these mice, using ultrasound-guided injection procedures, which is typically used for biopsies.

Four weeks later, the mice expressed human blood proteins and 10-20 percent of the mouse livers were repopulated with human liver cells. Blood tests also showed that the mouse livers, which were greatly damaged previous to the transplantation, were processing nitrogenous wastes properly. Structurally, the mouse livers contained human cells that made human bile ducts, and expressed mature human liver cells.

Other tests established that the i-Heps made from fat-based stem cells were more liver-like than i-Heps made from induced pluripotent stem cells.

Two months are injection of the i-Heps, there was no evidence of tumor formation.

Peltz said, “To be successful, we must regenerate about half of the damaged liver’s original cell count.” With the spherical culture, Peltz is able to produce close to one billion injectable i-Heps from 1 liter of liposuction aspirate. The cell replication that occurs after injection expands that number further to over 100 billion i-Heps.

If this is possible, then this procedure could potentially replace liver transplants. Stanford University’s Office of Technology Licensing has filed a patent on the use of spherical culture for hepatocyte (liver cell) induction. Peltz’s group is optimizing this culture and injection techniques,talking to the US Food and Drug Administration, and gearing up for safety tests on large animals. Barring setbacks, the new method could be ready for clinical trials within two to three years, according the estimations by Peltz.

Induced Pluripotent Stem Cells Replace Liver Function in Mice


Liver transplants save lives and in the United States there is a shortage of livers for transplantation. Between July 1, 2008 and June 30, 2011, well over 14,601 adult donor livers were recovered and transplanted. Of these livers that were transplanted, many other patients died from liver failure. If there was a way to restore liver function in patients with liver failure without dependence on a liver from a liver donor, then we might be able to extend their lives.

A paper from the laboratory of Hossein Baharvand at the University of Science and Culture in Tehran, Iran provides a step towards doing just that. In this paper, Baharvand and his colleagues used human induced pluripotent stem cells to make hepatocyte-like cells or HLCs. Hepatocyte is a fancy word for a liver cell. These HLCs were then transplanted into the spleen of mice that have damaged livers, and they rescued liver function in these mice.

The liver is a vital organ. It processes molecules absorbed by the digestive system, processes foreign chemicals to make them more easily excreted. It also produces bile, which helps dispose of fat-soluble waste and solubilize fats for degradation in the small intestine during digestion. It also produces blood plasma proteins, cholesterol and special proteins to cholesterol and fat transport, converts excess glucose into glycogen for storage, regulates blood levels of amino acids (the building blocks of proteins), processes used hemoglobin to recycle its iron content, converts poisonous ammonia to urea, regulates blood clotting, and helps the body resist infections by producing immune factors and removing bacteria from the bloodstream. Thus without a functioning liver, you are in deep weeds.

Induced pluripotent stem cells or iPSCs are made from adult cells that have been genetically engineered to de-differentiate into embryonic-like stem cells. They can be grown in culture to large numbers, and can also be differentiated into, potentially, any cell type in the adult body.

In this paper, Baharvand and his colleagues grew human iPSCs in “matrigel,” and then grew them in suspension. Matrigel is gooey and the cells stick to it and grow, and they were grown in matrigel culture for 1 week. After one week, the cells were grown in liquid suspension for 1-2 weeks. The cells have better access to soluble growth factors in liquid culture and tend to grow faster. After this they were grown in a stirred culture (known as a spinner).  This expanded the cells into large numbers for further use.

 Expansion and characterization of human induced pluripotent stem cells (hiPSCs) in a dynamic suspension culture. (A) Schematic representation of the suspension culture and expansion of human pluripotent stem cells (hPSCs) from adherent to stirred bioreactor. The cells were transferred to bacterial dishes to adapt to three-dimensional (3D) environment and then transferred into the dynamic phase, stirred flask. (B) Morphology of a tested hiPSC line (hiPSC1) after passage in a stirred suspension bioreactor as monitored by dark-field microscopy. (C) Immunostaining of cross sections of spheroids for OCT4 and TRA-1-81. Scale bar: 50 μm. (D) Flow cytometry analysis and (E) normal karyotype of suspended cells in the bioreactor.
Expansion and characterization of human induced pluripotent stem cells (hiPSCs) in a dynamic suspension culture. (A) Schematic representation of the suspension culture and expansion of human pluripotent stem cells (hPSCs) from adherent to stirred bioreactor. The cells were transferred to bacterial dishes to adapt to three-dimensional (3D) environment and then transferred into the dynamic phase, stirred flask. (B) Morphology of a tested hiPSC line (hiPSC1) after passage in a stirred suspension bioreactor as monitored by dark-field microscopy. (C) Immunostaining of cross sections of spheroids for OCT4 and TRA-1-81. Scale bar: 50 μm. (D) Flow cytometry analysis and (E) normal karyotype of suspended cells in the bioreactor.

Getting cells to grow in liquid suspension tends to be a bit of an art form, but these iPSCs grew rather well. Also, the iPSCs were differentiated into definitive endoderm, which is the first step in bringing cells to the liver cell stage. The drug Rapamycin and activin (50 ng / L for those who are interested) were used to bring the growing iPSCs to the definitive endoderm.  The cells expressed all kinds of endoderm-specific genes.  Endoderm is the embryonic germ layer from which the digestive system and its accessory organs forms.

 Induction of hiPSCs into definitive endoderm. (A) Diagrammatic representation of the experimental groups for endoderm induction of hiPSCs in the bacterial dish static suspension, which include rapamycin (Rapa) “priming” and activin A “inducing” phases, and positive control groups of hiPSCs cultured in the absence of Rapa in suspension or adherent cultures in the presence of activin A. (B) Gene expression analysis of hiPSCs induced into endodermal cells. Quantitative reverse transcriptase–polymerase chain reaction (qRT-PCR) showed no significant differences in SOX17 and FOXA2 [definitive endoderm (DE) markers], and BRA (mesoendoderm marker) in all groups. SOX7 (visceral endoderm marker) was expressed at a low level. Influence of the refreshment strategy of the induction medium on DE formation in suspension cultures by qRT-PCR (C), immunostaining (D), and flow cytometry (E). We compared single (SR), double (DR), and triple (TR) refreshment of induction medium per 24 h for 4 days after Rapa administration in the static suspension of hiPSCs. Scale bar: 100 μm. The target gene expression level in qRT-PCR was normalized to GAPDH and calibrated with (presented relative to) hiPSCs. Data are presented as mean±SD. Statistical analysis as determined by one-way ANOVA with Tukey's post hoc test, n=3 for B, C, and E. *P<0.05, **P<0.01.
Induction of hiPSCs into definitive endoderm. (A) Diagrammatic representation of the experimental groups for endoderm induction of hiPSCs in the bacterial dish static suspension, which include rapamycin (Rapa) “priming” and activin A “inducing” phases, and positive control groups of hiPSCs cultured in the absence of Rapa in suspension or adherent cultures in the presence of activin A. (B) Gene expression analysis of hiPSCs induced into endodermal cells. Quantitative reverse transcriptase–polymerase chain reaction (qRT-PCR) showed no significant differences in SOX17 and FOXA2 [definitive endoderm (DE) markers], and BRA (mesoendoderm marker) in all groups. SOX7 (visceral endoderm marker) was expressed at a low level. Influence of the refreshment strategy of the induction medium on DE formation in suspension cultures by qRT-PCR (C), immunostaining (D), and flow cytometry (E). We compared single (SR), double (DR), and triple (TR) refreshment of induction medium per 24 h for 4 days after Rapa administration in the static suspension of hiPSCs. Scale bar: 100 μm. The target gene expression level in qRT-PCR was normalized to GAPDH and calibrated with (presented relative to) hiPSCs. Data are presented as mean±SD. Statistical analysis as determined by one-way ANOVA with Tukey’s post hoc test, n=3 for B, C, and E. *P<0.05, **P<0.01.
After the cells went through this culture protocol, they were grown in a stirred liquid culture called a “spinner.” The culture system contain a cocktail of growth factors that differentiated the definitive endoderm cells into HLCs.  The cells formed little spheres that expressed a host of liver-specific genes.

Differentiation of hepatocyte-like cells (HLCs) from hiPSCs in the stirred bioreactor. (A) Stepwise protocol for differentiation of hiPSCs into HLCs. (B) The morphology and cross section of spheroids at day 21. The spheroids in this step were observed as cystic and dense spheroids. Hematoxylin and eosin (H&E) staining of spheroid cross sections indicated cystic and dense epithelioid appearances in the transplant and dense spheroids, respectively. Scale bar: 100 μm. (C) Comparative relative mRNA expression in cystic and dense spheroids normalized to GAPDH and calibrated to undifferentiated hiPSCs. Transplant and dense spheroids expressed more early and late hepatic lineage markers, respectively. Data are presented as mean. n=3. (D) Transmission electron microscopy (TEM) of differentiated cells in dense spheroids at day 21. Nucleus (N), nucleoli (n), mitochondria (M), Golgi apparatus (G), lysosomes (Ly), rough endoplasmic reticuli (arrowhead), glycogen granules (GR), intermediate filaments (CK), tight junctions (TJ), gap junctions (GJ), fascia adherens (FA), junctional complex (JC), microvilli (MV), and bile-like canaliculus (BLC). Scale bar: 1 μm.
Differentiation of hepatocyte-like cells (HLCs) from hiPSCs in the stirred bioreactor. (A) Stepwise protocol for differentiation of hiPSCs into HLCs. (B) The morphology and cross section of spheroids at day 21. The spheroids in this step were observed as cystic and dense spheroids. Hematoxylin and eosin (H&E) staining of spheroid cross sections indicated cystic and dense epithelioid appearances in the transplant and dense spheroids, respectively. Scale bar: 100 μm. (C) Comparative relative mRNA expression in cystic and dense spheroids normalized to GAPDH and calibrated to undifferentiated hiPSCs. Transplant and dense spheroids expressed more early and late hepatic lineage markers, respectively. Data are presented as mean. n=3. (D) Transmission electron microscopy (TEM) of differentiated cells in dense spheroids at day 21. Nucleus (N), nucleoli (n), mitochondria (M), Golgi apparatus (G), lysosomes (Ly), rough endoplasmic reticuli (arrowhead), glycogen granules (GR), intermediate filaments (CK), tight junctions (TJ), gap junctions (GJ), fascia adherens (FA), junctional complex (JC), microvilli (MV), and bile-like canaliculus (BLC). Scale bar: 1 μm.

From the figure above, we can see that these HLCs, not only express liver-specific genes, but when they are examined in the electron microscope they look, for all intents and purposes, like liver cells.  Functional tests of these spheres of HLCs showed that they 1) took up low-density lipoprotein; 2) produced albumin (a major blood plasma protein); 3) expressed cytochrome P450s, which are the major enzymes used to process drugs; 4) produced urea from amino acids, just like real liver cells; 5) accumulated glycogen; 6) and made liver proteins (HNF4a, ALB, etc).

So it looks like liver, quacks like liver, but can it replace liver?  These HLCs were transplanted into the spleen of mice whose livers had been treated with carbon tetrachloride.  Carbon tetrachloride tends to make mincemeat of the liver, and these mice are in trouble, since their livers are toast.  Transplantation of the iPSC-derived HLCs into the spleens of these mice increased their survival rate and decreased the blood levels of liver enzymes that are usually present when there is liver damage.

This paper is significant because the procedure used provides an example of a “scalable” protocol for making large quantities of iPSCs, and their mass differentiation into definitive endoderm and then liver cells,  Because this can potentially provide enough cells to replace a nonfunctional liver, it represents a major step forward in regenerative medicine.