Construction and transplantation of an engineered hepatic tissue using a polyaminourethane-coated nonwoven polytetrafluoroethylene fabric.
Soto-Gutierrez A, Navarro-Alvarez N, Rivas-Carrillo JD, Tanaka K, Chen Y, Misawa H, Okitsu T, Noguchi H, Tanaka N, Kobayashi N.
Transplantation. 2007 Jan 27;83(2):129-37.
Acute liver failure (ALF) is a serious disease with a high mortality rate. In severe cases, treatment of the disease, even when it is transient, requires transplantation and lifelong immune suppression. However, due to the shortage of donors, high costs, and the associated risks, treatments that involve temporary liver support are preferred over transplantation. Current bioartificial livers deal with issues of platelet consumption and hemodynamic instability. The researchers here have developed a new bioartificial device in which cells are grown on a polyaminourethane (
The experiments that the researchers ran can fall into two sections: before transplantation and after transplantion into mice (transplantation occurred after 2 weeks). Several visual experiments were done to confirm the morphology and viability of cells that were grown on the PAU-coated PTFE fabric vs. cells grown on collagen IV. After 72 hours, cells on the fabric were uniformly distributed and showed spherical aggregates. Transmission electron microscopy revealed that these cells showed gap junctions and bile canaliculi. Mitochondrial viability, determined using an absorption assay, was better on the fabric than on collagen IV. The addition of a deleted-variant hepatocyte growth factor (dHGF) improved the viability of all three types of cells on both surfaces after 14 days.
Metabolic rate of ammonia and diazepam were also measured by introducing these into the cultures and measuring how much remained after 4 hours. Significantly higher rates of metabolism were measured in cells grown on fabric than cells on collagen. The addition of dHGF increased metabolic rates for all cells on both substrates. Albumin production was measured daily using ELISA. Cells on fabric maintained the level of albumin production, while cells on collagen showed no production on day 14. Addition of dHGF improved production for both sets.
The next step was to transplant the PAU-coated PTFE fabrics onto the surface of the spleens of mice suffering from ALF. Mice treated with various control transplants showed hypoglycemia, hyperammonemia, and encephalopathy, and died quickly of ALF. However, mice treated with the engineered hepatic tissue (EHT) device, which incorporated hepatocytes grown on PAU-coated PTFE fabric, showed improved survival rate. After 30 days, survival rate of mice with the EHT transplant was 60%, whereas survival rate for control mice was 0%. EHT also improved blood glucose and ammonia levels and reversed encephalopathy. The surviving mice were then sacrificed and histological examination of their livers showed normal structure, appropriate attachment, and strong expression of albumin.
The researchers have developed a device that can act as a functional artificial liver, at least in the short term. I think this article is interesting because of how thorough the research is. The researchers make several measurements, both pre- and post-transplantation, to fully determine the functionality of their device. It was also interesting because of the fact that the device showed such big improvements over growth on collagen substrates or over other control devices. Mainly, though, I chose it because liver tissue engineering interests me.
4 comments:
I was wondering if the paper had any hypothesis as to why the PTFE fabric worked so well in comparison to the collagen IV scaffolds. I know that PTFE is extremely chemically inert, but collagen IV shouldn't cause a significant immune response either in the short time frame of these experiments. I'm a little rusty on hepatocytes, but I'm wondering if it was improved physical properties (better cell attachment/proliferation?) or maybe improved microscructure that simulates liver ECM? I'm always curious to see the motivation behind which synthetic materials are used.
Are there any biocompatibility issues associated with PAU or PTFE?
I think that it is pretty interesting that a relatively simple bioartificial scaffold (once seeded with hepatocytes) is mostly all that is necessary to make such a big difference in tissue function. While a 60% survival rate is certainly significant, I'm not sure how this compares to success rates corresponding to transplantation, so perhaps this is one of those instances where calling it a "functional" artificial liver is somewhat imprecisely defined. It would also be interesting to look at success rates with and without dHGF.
Mitochondrial viability is a measure of the metabolic activity of cells. Since the liver performs many metabolic functions, it is an important test to determine if cells are still functional after transplantation.
The paper doesn't specifically mention why they thought the PTFE fabric would be better, other than that they used it previously in a bioartificial pancreas designed to control blood glucose. The PAU-PTFE promotes cell adhesion, and cell-cell contact is important in hepatocyte function, so that might be why they tried it. As far as biocompatibility, neither material seemed to have biocompatibility issues in the experiments.
60% survival rate is much better than the 0% they observed with collagen fibers. I, too, am not sure what survival rate is with current transplants, but the hope with this device is that it would counter the shortage of donor organs as well as biocompatibility issues.
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