Journal of Hepatology
Volume 34, Issue 1 , Pages 148-149, January 2001

Bioencapsulated hepatocytes for experimental liver support

Artificial Cells & Organs Research Centre, Medicine and Biomedical Engineering, Faculty of Medicine, McGill University, Montreal, Quebec, CanadaH3G 1Y6

Received 5 July 2000; received in revised form 10 August 2000; accepted 6 November 2000.

See Article, pages 11–18

Article Outline

 

In this issue, Canaple et al. [1] describe their finding on ‘Maintenance of Primary Murine Hepatocyte Functions in Multicomponent Polymer Capsules – In vitro Cryopreservation Studies’. They use specially designed multicomponent microcapsules to encapsulate primary culture of murine hepatocytes without causing any cytotoxicity to the hepatocytes. Furthermore, they show that it is possible to cryopreserve the encapsulated hepatocytes for up to four months. What does this finding mean in term of current knowledge and future perspectives of hepatocyte preparations for liver support systems?

Bioencapsulation of hepatocytes is based on the basic principle of artificial cells or semipermeable microcapsules [2] and the use of a drop method for the bioencapsulation of intact cells to isolate the cells from immunological processes [3]. Intraperitoneal injection of bioencapsulated hapatocytes were effective in increasing the survival time of galactosamine induced fulminant hepatic failure rats [4], [5], [6]. Implantation of bioencapsulated hepatocytes can efficiently lower bilirubin levels in Gunn rats, an animal model for human non-haemolytic hyperbilirubinemia (CriglerNajjar type I) [7], [8], [9], [10].

Encouraged by these in-vivo results, extensive studies are being carried out by a number of groups to develop this approach towards possible clinical applications [11], [12], [13], [14], [15], [16]. These include improving the biocompatibility, the longer-term survival and the possibility for longer term storage using cryopreservation. The paper by Canaple et al. [1] in this issue is part of the important ongoing research in the above areas to bring this approach towards clinical application The following is a discussion and analysis of the ongoing approaches.

After intraperitoneal implantation into mice, rat hepatocytes in free-floating microcapsules can stay viable and can be immunoprotected [17]. Thus, rat hepatocytes implanted into CD-1 Swiss mice were rejected and by the 14th day, there were no intact hepatocytes detected in the mice. In the case of bioencapsulated hepatocytes, the hepatocytes retained their viability [17]. Furthermore, hepatotrophic factors secreted by the hepatocytes are retained inside the microcapsules [18], [19]. Unfortunately, the biocompatibility of the microcapsules varies from batch to batch and only a variable proportion of the microcapsules remained free-floating after implantation. A large proportion are coated by fibrin and fibroblasts resulting in adhesion and death of the enclosed hepatocytes. For any future potential clinical applications, it would be very important to have a high proportion of the microcapsules with sufficient biocompatibility so that they can remain free-floating and functioning after implantation. As a result, extensive studies [12], [13], [14], [15], [16] including those of Canaple et al. [1] in this issue are being carried out to improve the biocompatibility of the microcapsule membrane with increasing success. Thus, Canaple et al. [1] in this issue reported their successful use of polyelectrolyte complexation between sodium alginate, cellulose sulphate and poly(methlene-co-guanidine) hydrochloride. This membrane would be much stronger than the standard alginate–polylysine–alginate membrane. Furthermore, they have shown that this material is less cytotoxic to the encapsulated hepatocytes. Another related problem is that in microencapsulating a high concentration of dispersed cells like hepatocytes, some hepatocytes are incorporated into the membrane matrix with weakening of the membrane and others are exposed on the surface of the membrane [20]. When these microcapsules are implanted, the hosts immediately recognize the protruding cells on the surface resulting in acute cell mediated host immune response and rejection. To prevent the above problem, we worked out a 2-step method that prevents this from happening [21]. Thus, contribution from different laboratories can now be combined together to prepare bioencapsulated hepatocytes that are closer for potential clinical applications.

Even with the successful preparation of microencapsulated hepatocytes that can stay free floating and viable for long periods of time, there is another potential problem. This is the availability of bioencapsulated hepatocytes when needed. Isolation of hepatocytes followed by bioencapsulation is a laborious procedure that needs to be carried out by persons with much experience. They cannot be prepared by untrained personnel on demand. Thus, it would be important to have these preparations appropriately stored so that they can become available as needed. Cryopreservation of bioencapsulated hepatocytes is a possible solution [22], [23]. Canaple et al. [1] in this issue has described a method of cryopreservation that can preserve the bioencapsulated hapatocytes for 4 months. This progress is very important since a 4 month storage period would allow the preparation to be more readily available when needed.

Permeability of the membrane can be adjusted. Detailed analysis has been carried out using HPLC analysis of a large spectrum of molecular weight dextran [24]. The permeability can be adjusted to have different cut off molecular weight depending on the applications. Thus, for bioencapsulation of hepatocytes, it can be adjusted to allow albumin to pass through but not immunoglobulin nor leucocytes.This immunoprotection would avoid the need for immunosuppressants. However, it should be kept in mind that this would only be potentially suitable for allograft since proteins secreted by the bioencapsulated hepatocytes, like albumin, are human proteins. On the other hand, this may not be suitable for xenograft, since proteins secreted by the xenograft would no longer be human proteins and could be antigenic when they are released continuously from the bioencapsulated hepatocytes.

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References 

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PII: S0168-8278(00)00061-1

doi:10.1016/S0168-8278(00)00061-1

Journal of Hepatology
Volume 34, Issue 1 , Pages 148-149, January 2001

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