Artificial Cells for Replacement of Metabolic Organ Functions

Abstract

Artificial cells are being actively investigated for use in the replacement of cell and organ functions, especially related to metabolic functions. The earliest routine clinical use of artificial cells is in the form of coated activated charcoal for hemoperfusion. Implantation of encapsulated cells are being studied for the treatment of diabetes, liver failure, kidney failure and the use of encapsulated genetically engineered cells for gene therapy. Blood substitutes based on modified hemoglobin are already in Phase III clinical trials in patients with as much as 20 units infused into each patient during trauma surgery. Artificial cells containing enzymes are being developed for clinical trial in hereditary enzyme deficiency diseases and other diseases. Artificial cell is also being investigated for drug delivery and for other uses in biotechnology, chemical engineering and medicine.

• Hybrid artificial organs
• Enzyme therapy
• Cell therapy
• Liver support
• Kidney support
• Gene therapy
• Blood substitutes
• Bioencapsulation
• Artificial cells

Introduction

Artificial cells evolves from Chang's initial studies to prepare artificial structures for bioencapsulation of enzymes, cells and other biologically active materials ((Chang, [1964], [1966], [1972]; Chang et al., [1966])). Once bioencapsulated, biologically active materials inside the artificial cells are prevented from coming into contact with external materials like leucocytes, antibodies or tryptic enzymes. Smaller molecules can equilibrate rapidly across the ultrathin membrane with large surface to volume relationship. A number of potential medical applications using artificial cells have been proposed ((Chang, [1966], [1972]; Chang et al., [1966])). The first of these developed successfully for routine clinical use is hemoperfusion ((Chang, [1972])). After initial clinical trails for poisoning, kidney failure, and liver failure ((Chang, [1975])), it is now in routine clinical uses ((Winchester, [1988])). Some exciting recent developments include their use in the replacement of the metabolic functions of cells and organs ((Chang, [1997a])) This review will highlight some examples.

Artificial Cells Containing Enzymes for Inborn Errors of Metabolism and Other Conditions

Chang and Poznanksy have earlier implanted artificial cells containing catalase into acatalesemic mice, animals with a congenitical deficiency in catalase ((Chang and Poznansky, [1968])). This replaces the deficient enzymes and prevented the animals from the damaging effects of oxidants. The artificial cells protect the enclosed enzyme from immunological reactions ((Poznansky and Chang, [1974])). It was also showed that artificial cells containing asparaginase implanted into mice with lymphosarcoma delayed the onset and growth of lymphosarcoma ((Chang, [1971a])). The single problem preventing the clinical application of enzyme artificial cells is the need to repeatedly inject these enzyme artificial cells. To solve this problem, Bourget and Chang found that microencapsulated phenylalanine ammonia lyase given orally can lower the elevated phenylalanine levels in phenylketonuria[[PKU]] rats ((Bourget and Chang, [1986])). This is because of our more recent finding of an extensive recycling of amino acids between the body and the intestine ((Chang et al., [1995])). This is now being developed for clinical trial in PKU ((Liu et al., [2002]; Sarkissian et al., [1999])). In addition to PKU other examples our recent studies shows that oral artificial cells containing tyrosinase is effective in lowering systemic tyrosine levels in rats ((Chang and Yu, [2002]; Yu and Chang, [2002])). This has much potential for the treatment of the fatal skin cancer, melanoma. We are encouraged in this oral approach because of our preliminary clinical testing of oral microencapsulated xanthine oxidase as experimental therapy in Lesch‐‐Nyhan Disease ((Palmour et al., [1989])).

Artificial Cells Encapsulated Cells for Liver Failure, Endocrine Replacement and Other Replacements

Chang et al reported the encapsulation of biological cells in 1966 based on a drop method and proposed that “protected from immunological process, encapsulated endocrine cells might survive and maintain an effective supply of hormone” ((Chang, [1972]; Chang et al., [1966])) Chang approached Conaught Laboratory to develop this for use in islet transplantation for diabetes. Sun from Conaught and his collaborators have developed this drop‐‐method by using milder physical crosslinking ((Lim and Sun, [1980])). This resulted in alginate‐‐polylysine‐‐alginate [[APA]] microcapsules containing cells. They show that after implantation, the islets inside artificial cells remain viable and continued to secrete insulin to control the glucose levels of diabetic rats ((Chang, [1995])). Cell encapsulation for cell therapy has been extensively developed by many groups especially using artificial cells containing endocrine tissues, hepatocytes and other cells for cell therapy ((Aebischer et al., [1996]; Chang, [1995], [1997a]; Chang and Prakash, [1998], [2001a]; Dionne et al., [1996]; Hunkeler et al., [1999]; Kulitreibez et al., [1999]; Lim and Sun, [1980]; Orive et al., [2003])). Microencapsulated genetically engineered cells has been carried out by many groups ((Aebischer et al., [1996]; Chang, [1995]; Chang and Prakash, [1998], [2001a]; Dionne et al., [1996]; Hunkeler et al., [1999]; Kulitreibez et al., [1999]; Orive et al., [2003])). This has been studied for potential applications in amyotrophic lateral sclerosis, Dwarfism, pain treatment, IgG₁ plasmacytosis, Hemophilia B, Parkinsonism and axotomized septal cholinergic neurons. We have also studied the oral use of microencapsulated genetically engineered nonpathogenic E.coli DH5 cells containing Klebsiella aerogenes urease gene in renal failure rats ((Chang, [1997b]; Chang and Prakash, [2001b], [c]; Prakash and Chang, [1996], [1999])). We have been studying the use of implantation of encapsulated hepatocytes for liver support ((Bruni and Chang, [1989]; Chang, [2001]; Chang and Wong, [1992]; Liu and Chang, [2000]; Wong and Chang, [1986], [1988], [1991a], [b])) This included acute liver failure ((Chang, [2001])) and hyperbilirubinemia in Gunn rats ((Bruni and Chang, [1989])). We developed a two step cell encapsulation method to improve the APA method resulting in improved survival of implanted cells ((Chang and Wong, [1992]; Wong and Chang, [1991b])). Using this two step methods plus the use of co‐‐encapsulation of stem cells and hepatocytes we have further increased the viability of encapsulated hepatocytes both in culture and also after implantation ((Liu and Chang, [2000], [2002])).

Red Blood Cell Substitutes

Polyhemoglobin as blood substitutes: Chang has extended his original approach of artificial cells containing hemoglobin and enzymes ((Chang, [1964])) to form polyhemoglobin–a molecular version of artificial cells. This is based on his use of bifunctional agents like diacid ((Chang, [1964], [1972])) or later glutaraldehyde ((Chang, [1971b])) to crosslink hemoglobin molecules into polyhemoglobin. This gluataradehyde crosslinked polyhemoglonin approach has been extensively developed more recently ((Chang, [1997c], [2000], [2002])). One example is the recent report by Gould et al on their ongoing clinical trials using pyridoxalated glutaraldehyde human polyhemoglobin in trauma surgery. They show that this can successfully replace blood loss by maintaining the hemoglobin level with no reported side effects ((Gould et al., [1998a], [[b]]. More recently, they have infused up to 20 units into individual trauma surgery patients. Another example is glutaraldehyde crosslinked bovine polyhemoglobin that has been extensive tested in Phase III clinical trials ((Pearce and Gawryl, [1998])). This has been approved for veterinary medicine in the U.S. and for routine clinical use in South Africa. An o‐‐raffinose polyhemoglobin is also being developed and being tested for surgery that needs only low volume replacement ((Adamson and Moore, [1998])). All the above three polyhemoglobins have been approved for compassionate uses in human and they are waiting for regulatory approval for routine clinical uses in human. For the resuscitation of sustained severe hemorrhagic shock or in reperfusion of ischemic organs as in stroke or in organ trasnplantation, we are using a crosslinked polyhemoglobin‐‐superoxide dismutase‐‐catalase ((PolyHb‐‐SOD‐‐CAT)) ((Chang, [1997c]; D'Agnillo and Chang, [1997], [1998a], [[b]]; Powanda and Chang, [2002]; Razack et al., [1997])). Reperfusion studies in a rat model of intestinal ischemia, shows that PolyHb‐‐SOD‐‐CAT resulted in negligible increase in oxygen radicals, unlike the high level that resulted from reperfusion using polyHb ((Razack et al., [1997])). More recently ((Powanda and Chang, [2002])), in a transient global cerebral ischemia rat model, we found that after 60 minutes of ischemia, reperfusion with polyHb resulted in significant increases in blood‐‐brain barrier and the breakdown of blood‐‐brain barrier. On the otherhand, polyHb‐‐SOD‐‐CAT did no result in these adverse changes.

There are other modified hemoglobins ((Chang, [1997c], [1999], [2002]; Chang and Yu, [1997], [1998]; Yu and Chang, [1996])). Chang's original idea of a complete artificial red blood cell ((Chang, [1964]; Chang et al., [1966])) is now being developed as third generation blood substitute ((Chang, [1997c], [1999], [2002])). Hemoglobin lipid vesicles is one of these approaches ((Rudolph et al., [1997]; Tsuchida, [1998])). We are using a new system based on biodegradable polymer and nanotechnology resulting in hemoglobin nanocapsules of 80 to 150 nanometre diameter ((Chang and Yu, [1997], [1998]; Chang et al., [2002]; Yu and Chang, [1996])) Our recent studies show that using a polyethylene‐‐glycol‐‐polylactide copolymer we are able to increase the circulation time of these Hb nanocapsules to double that of polyHb ((Chang et al., [2002])).

General

The above review contains a very brief overview of this rather large area. For more specific details, please refer to the references given. Artificial Cells Biotechnology is a rapidly evolving area and rapidly updating can be found at our McGill University website: www.artcell.mcgill.ca.

Uncited references

Bunn and Jandl, [1968]

Djordjevich and Miller, [1980]

Doherty et al., [1998]

Dudziak and Bonhard, [1980]

Freytag and Templeton, [1997]

[[Hoffman, et al.,]

Nelson, [1998]

Philips et al., [1999]

Winslow et al., [1997]

Acknowledgments

This author acknowledges the supports of the Canadian Institutes of Health Research, the “Virage” Centre of Excellence in Biotechnology from the Quebec Ministry, the MSSS‐‐FRSQ Research Group award on Blood Substitutes in Transfusion Medicine from the Quebec Ministry of Health and the Bayer//Canadian Blood Agency//Hema Quebec//Canadian Institutes of Health Research Partnership Fund.