Titanium Oxide Nanotube Platforms for Bioartificial Livers and for Transplantation of Hepatocytes Derived from Human Embryonic Stem Cells
The liver is the largest organ in the human body. It is essential for life. The production of blood proteins involved in coagulation and the detoxification of poisons that enter the body are among the most important functions of the liver. Serious health consequences occur when the liver fails to perform these functions. For example, human beings born with defective coagulation proteins acquire Hemophilia (a genetic disease). Or humans with livers destroyed by incurable infections (hepatitis) or work-related chemicals often contract liver failure and fibrosis. When Hemophilia, liver failure and liver fibrosis are uncontrollable, these people often die of ‘end-stage liver disease’ (ESLD).
ESLDs such as chronic hepatitis and liver cancer are rampant in California and clinical treatments are becoming increasingly strained. A recent study (2005) found that chronic liver disease ranked as one of the leading causes of death in California, resulting in 3,725 deaths in 2002; it was also found that minorities suffered disproportionately from ESLD.
Liver organ transplantation is the current therapy for ESLD. However, it is very costly and complex, it depends upon the availablity of donor livers, and there are many associated problems. Donor livers are rare, transplant waiting lists are long, and transplant waiting times are long (so long that some patients die before a donor liver is available). The major problem -- unless the donor comes from an identical twin – is that patients reject the donor liver. To prevent rejection, patients are currently treated lifelong with drugs, but often these drugs fail or are themselves dangerously toxic and life-threatening.
The research in this proposal will lay the groundwork for the development of a device that can replace a failing liver (without drugs), much as dialysis machines can save the lives of people with kidney failure. This device is called a BAL (bioartificial liver).
A prototype BAL will be made by a team of biologists, physicians and bioengineers. Federally approved human embryonic stem cells (hESCs), which can be converted into liver cells, will be placed on ‘computer-like’ chips made from titanium (a metal harmless to the body) designed to simulate small livers. To see if hESC-derived liver cells-on-chips (LCOCs) maintain liver functions and survive transplantation, LCOCs will be put into special mice (which do not reject human cells) for up to a month. During this time, the LCOCs will be removed and tests for liver cell functions (e.g. production of blood proteins) will be made.
If these experiments work, future research will be geared to (a) designing LCOCs that cure liver disease in animals, and (b) producing hESCs that resist rejection. If these problems are solved, studies will move into human trials. If human trials work, we hope to build universal, inexpensive, LCOCs to cure ESLD in California and worldwide, without resorting to liver transplantation and drugs.
End-stage liver diseases (ESLDs) such as chronic hepatitis and liver cancer are rampant in California and therapeutic modalities are becoming increasingly strained. Many afflicted die of these conditions including those associated with alcoholic liver disease. According to the California DHS and Center for Health Statistics (Data Summary No. DS05-05000, May, 2005, pp. 1-11), in a study entitled “End Stage Liver Disease (ESLD): Morbidity, Mortality, and Transplantation California, 1999-2003”, chronic liver disease and cirrhosis ranked as one of the leading causes of death in California, resulting in 3,725 deaths statewide in 2002. Not surprisingly, minorities suffered disproportionately: American Indians, Alaska Natives, Hispanics and Latinos had significantly higher ESLD death and hospitalization rates, but lower liver transplant rates, despite many Adult Liver Transplant centers in the State (11 of 91 throughout the US, as determined 5/30/06 [https://www.cms.hhs.gov/ApprovedTransplantCenters/downloads/liver_list.pdf]). More surprisingly, the incidence of ESLD in California was higher than the incidence of newly diagnosed Parkinson’s disease cases as judged from a 1994–1995 study using information from Kaiser Permanente of Northern California (Van Den Eeden SK et al. Amer. J. Epidemiol. 2003;157:1015-1022).
Current cures for ESLD depend mainly upon liver transplantation. However, liver donor organs are limited, matched organs rarely exist, and the medical costs for transplantation and post-operative care are prohibitive. Transplantation of suspensions of committed liver stem cells is one future option; but scientific controversy and technical issues plague isolation, culture, directed and stable differentiation of these cells, as well as the universal problems of (a) transplantation without rejection, and (b) provision of sufficient liver function to sustain normal life.
State-of-the art materials science and nanotechnology, coupled with recent advances in the hepatocyte-directed differentiation of human embryonic stem cells (hESCs) in vitro, may provide tissue and biomedical engineering approaches that can lead to breakthroughs towards curing ESLDs without resorting to organ transplantation. These breakthroughs may well come from functional extracorporeal and transplantable hESC-based bioartificial livers (BALs), constructed from inexpensive TiO2 chips carrying liver acinar-like stacks of hESC-drived hepatocytes, to assist or cure human beings suffering from ESLDs of infectious (hepatitis), genetic (Hemophilia A and B) or chemical origin (alcohol abuse).
Apart from therapeutic transplantation devices, significant benefits from these novel BALs would be quickly evident, as they would provide normal, homogeneous cell sources for robotic screening of potential specificities, metabolism, polymorphisms and toxicities of new or experimental drugs, chemicals, and therapeutics developed by pharmaceutical and chemical industries.