Recreating human livers, in mice for better drug testing and screening
http://blogs.discovermagazine.com/80beats/2011/07/12/a-new-way-to-test-drugs-in-mice-with-human-livers/#comment-790869832
Title-Stem cells can be used to generate a new hepatocytes for transplantation in Liver failure
By
Professor Pranab Kumar Bhattacharya MD(cal. Univ)
Professor and Head of Pathology; Calcutta school of Tropical medicine
108, CR Avenue Kolkata-73 West Bengal; India
The current consensus in the field that organ transplantation is the primary treatment for chronic liver disease like cirrhotics of liver and acute liver failure. Presently, orthotopic liver transplantation (OLTx) is the only treatment that improves the survival rate in patients with ALF.
Throughout the world, there is a significant shortage of organ donors like liver and donation of any organ depends on a persons’ motivation and will to donate his or her organ, even after his brain death and no laws in the country can force a person to donate his or her organ and not even of a corpus. The availability of an organ so depends on the local market system, though in some country like India , selling and buying of any organ is strictly prohibited by legislation. Not only are there not enough livers, but the surgery for liver transplant itself is traumatic, expensive, requires specially trained liver transplant team and these individuals who underwent liver transplant must live on immuno suppressants drugs for the rest of their lives which is again too costly. The success rate of Liver Transplant in India specially in Kolkata is also very low. Taken as a whole, the liver transplant solution is incredibly expensive with a low success rate and only helps a small number of people affected with liver disease. However, recent
research into artificial livers shows many probably show promising developments.
Biologic liver support methods are based on the use of XENOGENEIC livers or hepatocytes—parenchymatous cells of the liver—to support the failed human liver[5]. These methods exploit the
functions of biological cells, namely detoxification, metabolism(biotransformation), and biosynthesis. The foundations of biologic liver support were laid in 1932 when Krebs and Henseleit demonstratedmetabolic function in ex vivo samples of animal livers. More thantwo decades later, Otto et al became the first designers of an experimental animal extra-corporeal ex vivo liver perfusion system.
The first clinically applied biologic liver support, using a baboon liver, was reported in 1980. The contemporary era of biologic liver support began in 1975 when Wolf and Munkelt utilized isolated hepatocytes. During the past two decades, technological advances in liver cell isolation and culture and improved bio materials have formed the research base for the development of a variety of
liver-assist devices. A number of problems have not yet been fully solved,which demand further laboratory and clinical research before a truly effective liver support device can be developed; including enhancement of the cultured hepatocytes' preservation and longevity, and better understanding of thebiology of liver cell function and injury.
The first report of successful isolation of hepatocytes using collagenase perfusion dates back to 19698.Although a number of animal trials of hepatocyte transplantation have yielded encouraging results, evidence of long-term survival and function of transplanted human hepatocytes has been tantalizingly slow to come.1 Survival of isolated rat hepatocytes transplanted into the red pulp of the spleen was described in the late 1970s.[2] This and subsequent experimental studies focused on transplantation of ectopic hepatocytes—cells transplanted to non hepatic body regions such as the peritoneum, lungs, fat pads, and subcutaneous tissue. A number of studies have demonstrated that, in fact, ectopic hepatocytes are functional and able to proliferate extensively.[3,4]
The most successful transplantation of hepatocytes has been into the liver, where the engraftment
causes transitory (2–3 hours) portal hypertension.[4] The published literature suggests that
transplanting 1–5% of liver mass might be sufficient to restore adequate
functional activity and normal metabolic parameters to the failed liver.[5] Evidence of the effectiveness of the transplanted hepatocytes is typically based on anecdotal case reports.[6, 7, 8]
EXTRACORPOREAL BIOLOGIC REACTORS
Contemporary bio artificial liver support systems aim to provide adequate functional organ
replacement. This is potentially possible because perfusion through a sufficiently large number of hepatocytes could help to overcome liver failure and provide a safe bridge to OLT or recovery. This method is based on a biologic reactor containing a matrix supporting cultured cells. The patient's
blood flows through the reactor cartridge, plasma is ultra filtrated through the fibers into the cartridge's extra capillary space, and comes into contact with the hepatic cells. The exchange of metabolites is dependent on cell viability and metabolism. Human cells (allogeneic), animal cells (xenogeneic),and cell lines from immortalized liver cells or tumor cells (HepG2cells)
have been used.[8] Xenogeneic cell lines carry greater immunologic and zoonotic risks. The strategy of providing an adequate mass of human liver cells is based on the immortalization and spontaneous or genetic manipulation of human hepatocyte cultures, so that the cells maintain the full repertoire of liver functions. The possible use of these cells for transplantation is hindered by
the theoretical risk posed by the viral manipulation needed to derive the cells: the hepatocytes might rapidly lose liver-specific functions and die[8] At present there are two types of biologic reactor in use, the Extracorporeal Liver Assist Device (ELAD, Vital Therapies, Inc., San Diego, CA) and theBioartificial Liver (BAL, HepatAssist, Circe Biomedical, Lexington, MA), which
can be distinguished on the basis of the cell source used for the bioreactors.
The Extracorporeal Liver-Assist Device[8]
Over the past two decades, researchers around the world have
made significant progress in the creation of a functioning artificial liver. In
particular, there have been many successes in engineering artificially grown
liver cells that replicate the liver’s functions with designs functioning both
inside and outside of the body. The extracorporeal liver assist device, or
ELAD, is one such achievement. Connecting this machine to individuals with
liver failure has allowed many individuals to survive long enough until an
organ becomes available and has even been successful in treating acute liver
failure . It also provides extra support to the liver, giving the organ time to
regenerate itself. As ELAD undergoes more clinical trials, an increasing number
of hospitals across the United States are beginning to offer it as a therapy
for liver disease patients. The FDA is asking for three to 10 days of ELAD
liver support to improve the 30-day survival that the similarly ill get with
today’s standard supportive care.The ELAD system uses the C3A
clone of the HepG2 cellline. Clinical testing of this system began in 1996 and indicated the need for
better prognostic indices arecently published trial demonstrated how the ELAD was part of a successfulbridge to OLT in five patientsPatientsare connected to the ELAD by standard dual-lumen hemodialysis catheters forcentral access; blood is drawn at a rate of 200 ml/min and pumped into achamber containing ELAD cartridges (four cartridges are used for an adult patient and two for a child weighing less than 40 kg). Each of the cartridgescontains approximately 100 g of C3A cells within the extra capillaryspace surrounding the hollow fibers. The ultrafiltrate passes through the lumen of the fibers, in which the biochemical transport occurs.
ELAD is easily reproducible and its use is typically straightforward. The system's
current design provides greater metabolic activity, and incorporates an
oxygenator and a glucose infusion pump to support the hepatocytes. The clinical
safety results obtained so far have been encouraging. The limited number of patients treated so far does not, however,allow us to ascertain the device's full safety profile and potential efficacy.
AtBioEngine, a rising firm in biotechnology, researchers created a similar device
designed to function within the human body. This structure would theoretically
provide a bio artificial scaffold for human liver cells to grow and function
normally. In other aspects of the field, biologists have been able to grow
artificial liver cells from embryonic stem cells, human hepatocytes, and
porcine hepatocytes. Although these technological advances are large steps
towards developing a solution to liver failure, scientists still have a long
way to go, as there are many biological, ethical, and economic reasons that are
hindering artificial liver development.
The world's first artificial liver had been grown from stem cells
by British scientists in 2006. The resulting "mini-liver" is the size
of a small coin; the same technique will be further developed to create a
full-size liver. The mini-liver is useful as it is; within two years it can be
used to test new drugs, reducing the number of animal experiments as well as
providing results based on a human (rather than animal) liver. The stem cells used by Drs. McGucklin and Forraz in this research are gathered from umbilical cords ("cord blood"), seen by
some as a more ethical alternative to stem cells created from human embryo.
However Liver cells could be grown from Induced Skin stem cells or even bone marrow stem cells. The creation of efficient human liver cells requires a large
amount of time, money, and resources, which adds to the overall costs of these
therapies for a small yield of available cells. As a result, many of these
therapies are not economically sound and cannot be available to the general
public. Many scientists believe that developing more cost effective designs
will be the focus of artificial liver research over the next decade. There is
already an ongoing public debate on the ethical issues of using embryonic stem
cells for research.. From a biological point of view, there are concerns of
porcine cells possibly transferring viruses from pigs to humans. Addressing
these concerns in these current technologies will allow for further progress
within artificial liver research.disease.
References
1Chowdhury JR et al. (1998) Human hepatocyte transplantation: gene therapy and more? Pediatrics 102: 647–648 | Article | PubMed | ISI | ChemPort |
2 Mito M et al. (1979) Studies on ectopic liver utilizing hepatocyte
transplantation into the rat spleen. Transpl Proc 11: 585–591 | ChemPort |
3.Darby H et al. (1986) Observations on ratspleen reticulum during the development of syngeneic hepatocellular implants. Br J Exp Pathol 67: 329–339 | PubMed | ChemPort |
4.Selden AC et al. (1991) Further observations
on the survival, proliferation and function of ectopically implanted syngeneic
and allogeneic liver cells in rat spleen. Eur J Hepatol Gastroenterol 3: 607–611
5.
Selden C and Hodgson H (2004) Cellular therapies for liver replacement. Transpl Immunol 12:
273–288 | PubMed | ChemPort |
6. Soriano H (2002) Liver cell transplantation: human applications in adults and
children. In: Hepatocyte transplantation: proceedings of Falk Symposium 126 (Progress in
Gastroenterology and Hepatology Part III) held in Hannover,Germany, October 2–3, 2001, 99–105 (Eds Gupta S et al.) Dordrecht,
Boston, London: Kluwer Academic Publishers
7.
Strom SC et al. (1997) Hepatocyte transplantation as a bridge to orthotopic liver transplantation in terminalliver failure. Transplantation 63:559–569 | Article | PubMed | ISI | ChemPort |
8. JMichael Millis* and Julian E Losanoff Technology Insight: liver
support systems Nature Clinical Practice Gastroenterology & Hepatology (2005) 2, 398-405
doi:10.1038/ncpgasthep0254
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The opinions expressed in this article is of author’s only. Copy Right of the article belongs toProf.Pranab kumar Bhattacharya-the author and only to his first degree blood relatives under Copy Right Rules /301/3D/ 107/1201 (a) (b)/ RDF of Intellectual Property Right Act and SPARC Copy Right rules-2006 and PIP Copy Right Rules-2012 of USA. For Permission for reproducing, citation, references , further research work, for self use and for implementation of more than three words or any meaning full sentences in any health care system either in any state of India or in any other countries or in any pvt care & cure Institute /hospital or translating in other languages please mail to profpkb@ yahoo.co.in to avoid infringement and plagiarism from your end to avoid copy right damage suit in million US dollar for injury to author.
Sd/ Professor Pranab Kumar Bhattacharya MD(Calcutta Univ) - Professor and Head, Department of Pathology , School of Tropical Medicine, Kolkata-700073
