Bioartificial liver

Bioreactor Developments for Tissue Engineering Applications by the Example of the Bioartificial Liver... 

Keywords. Bioartificial liver, cell culture, hollow fiber bioreactor, flat membrane bioreactor, spheroids... 

There have already been clinical trials of porcine hepatocyte-based bioartificial livers [5, 6]. However, we believe these systems to represent temporary and short-lived approaches. Compelling evidence from recent experiments show that primary porcine liver cells express and release endogenous retroviral particles that are able to infect human cells. However, long term in vivo investigations of patients previously exposed to porcine tissues over a period of 12 year did not show any porcine endogenous retrovirus (PERV) viremia [7]. Therefore, we consider the further pursuit of porcine bioartificial livers the only solution at present with regard to the cell source. However, as an intermediate term alternative human cell sources are in development [8]. Expansion technologies for human fetal cells may contribute to resolve these limitations in the future. 

Hepatocyte-based bioartificial livers will have two major uses to provide a) short term support for liver-failure patients in the clinic and b) a tool for the pharmaceutical industry to produce drug metabolites for subsequent toxicological studies in vitro. 

To be useful to both, clinicians and the pharmaceutical industry, a bioartificial liver will need to maintain a large number of hepatocytes at high cell densities and in a fully differentiated state for prolonged periods of time. Development of such a system has been impeded by three principal problems a) a requirement for large numbers of cells (>25 10 ) b) loss of liver-specific functions in cultured cells (primary and immortalized) c) nutrient and waste product gradients in high density cultures leading to lowered cell viability and impaired function. 

A bioartificial liver will need to maintain a large number of hepatocytes at high cell densities over a prolonged period of time. The metabolic requirements of hepatocytes, particularly the high rates of oxygen consumption, place strin-... 

One method of culturing anchorage-dependent tissue cells is to use a bed of packings, on the surface of which the cells grow and through which the culture medium can be passed. Hollow fibers can also be used in this role here, as the medium is passed through either the inside or the outside of the hollow fibers, the cells grow on the other side. These systems have been used to culture liver cells to create a bioartificial liver (Section 15.4.2). 

Hollow Fibers. The general configuration of the hollow-fiber apparatus is similar to that of hemodialyzers and blood oxygenators. Hepatocytes or microcarrier-attached hepatocytes are cultured either inside the hollow fibers or in the extra-fiber spaces, and the patient s blood is passed outside or inside the fibers. A bioartificial liver of this type, using 1.5 mm o.d. hollow fibers with 1.5 mm clearance between them, and with tissue-like aggregates of animal hepatocytes cultured in the extra-fiber spaces, can maintain liver functions for a few months [20]. 

Naruse, K., Sakai, Y, Nagashima, I., Jaing, G., Suzuki, M., and Muto, T. Development of a new bioartificial liver module filled with porcine hepatocytes cocultured in a microchannel flat plate bioreactor. Inter. J. art if. Organs 19, 347, 1996. 

Mazariegos, G.. Kramer, D.. Lopez, R., Shjakil, A., Rosenbloom, A., DeVera, M., Giraldo, M., Grogan, T, Zhu. Y. Fulmer, M., Amiot, B., Patzer, J. Safety observations in phase I clini cal evaluation of Excorp medical bioartificial liver support system after the first four patients. ASAIO J. 47, 471, 2001. 

DESIGN OF IDEAL SCAFFOLD FOR EXTRACORPOREAL BIOARTIFICIAL LIVER (BAL) OR IMPLANTABLE ARTIFICIAL ORGAN... 

The so-called UCLA bioartificial liver involves the direct hemoperfusion of microencapsulated porcine hepatocytes in an extracorporeal chamber (Eigure 7.3). Since it permits perfusion with whole blood, it has an advantage over the hollow fiber technique that has to be perfused with plasma. The hepatocytes are isolated from pig livers and microencapsulated in an alginate-polylysine membrane. Microencapsulated hepatocytes are approximately 300 to 700 pm in diameter. 

As liver performs multiple and complex functions, artificial organ or bioartifidal organ exploiting a synthetic cartridge to host biological components such as cells (hepatocytes in the case of a bioartificial liver) have been investigated. Among all of these potentialities, we only focus here on purely artificial systems. Membrane-based bioartificial livers (BAL) will not be described here, but could be found in other reviews [22-25] and in another chapter in the present book. 

As seen above, the artificial systems are only able to supply detoxication functions of the liver. In some cases, this might not be enough to save patients. An alternative is the design of bioartificial liver. A simplistic approach consists in considering such a device as a bioreactor based on synthetic elements able to offer an adequate environment to the liver cells. This environment would in turn lead to the maintenance of efficient functions of the cells aiming at liver supply, when placed in a bioreactor located in an extracorporeal circuit. The mandatory requirements for acceptable cell viability and functions in a bioartificial liver (BAL) are tentatively listed below, according to a biotechnological point of view ... 

Up to now, none of the presented system can claim its ability to fully replace all liver functions in an extracorporeal circuit. On the one hand, purely artificial techniques can only cover some detoxification aspects, which is already crucial in many clinical cases to save patients. On the other hand, bioartificial livers have not proven their full efficiency yet, mainly because both regulatory and logistic aspects limit, for the moment, the inclusion of significant numbers of patients to draw statistically relevant conclusions. 

First clinical use of a novel bioartificial liver support system (BLSS). Amer. X Transplant. 2002 2 260—266... 

Tsiaonssis, X, Newsome, P.N., Nelson, L.X, Hayes, P.C., Plevis, XN. Which hepatocyte will it be Hepatocyte choice for bioartificial liver support systems. Liver Transplant. 2001 7 2-10... 

The encapsulation of hepatocytes for a bioartificial liver, and cell therapy for the treatment of other hormone deficiencies or neurodegenerative diseases, such as Alzheimer s and Parkinson s, are also under investigation. Additional examples of cell encapsulation in polymer-polymer coacervates include non-autologous gene therapy,blood substitutes as well as the treatment of prostate cancer. Pharmaceutical applications of microcapsules encompass, in addition, trans-dermal drug delivery and protein delivery such as is required in anti-inflammatory therapy for arthritis. 

Hoekstra R, Nibourg GA, van der Hoeven TV et al (2013) Phase 1 and phase 2 drug metabolism and bile acid production of HepaRG cells in a bioartificial liver in absence of dimethyl sulfoxide. Drug Metab Dispos 41 562-567... 

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