Impact of Increased Oxygen Delivery via Bovine Red Blood Cell Supplementation of Culturing Media on Select Metabolic and Synthetic Functions of C3A Hepatocytes Maintained within a Hollow Fiber Bioreactor

Use of perfluorocarbons to enhance the performance of perfused three-dimensional hepatic cultures

Bioartificial liver devices (BALs) are extracorporeal systems designed to temporarily bridge patients until a suitable donated liver is available for transplantation and also have value for pharmaceutical testing applications. Yet critical issues exist that limit the functional performance of their current designs. One of these concerns scale up issues connected to oxygen (O2 ) delivery to the cells housed within their three-dimensional (3D) configurations, and its consequences to device performance. As primary blood substitute candidates with extraordinarily high O2 capacity, perfluorocarbons (PFCs) offer hope as one strategy for addressing the O2 delivery issue encountered when scaling up the tissue space of current BAL designs. This study utilizes a PFC-based second-generation O2 carrier OXYCYTE®, as an additive to regular nutrient medium, for augmenting O2 delivery in a customized 3D tissue assembly system. The results demonstrate that the addition of PFCs significantly increases the O2 capacity of regular medium and that net cytochrome P450 activity levels are considerably increased under flow in PFC-treated systems, as compared to controls. This work thus clarifies the benefits of using PFCs to enhance the functional performance of 3D liver systems.

Current development of bioreactors for extracorporeal bioartificial liver (Review)

The research and development of extracorporeal bioartificial liver is gaining pace in recent years with the introduction of a myriad of optimally designed bioreactors with the ability to maintain long-term viability and liver-specific functions of hepatocytes. The design considerations for bioartificial liver are not trivial; it needs to consider factors such as the types of cell to be cultured in the bioreactor, the bioreactor configuration, the magnitude of fluid-induced shear stress, nutrients' supply, and wastes' removal, and other relevant issues before the bioreactor is ready for testing. This review discusses the exciting development of bioartificial liver devices, particularly the various types of cell used in current reactor designs, the state-of-the-art culturing and cryopreservation techniques, and the comparison among many today's bioreactor configurations. This review will also discuss in depth the importance of maintaining optimal mass transfer of nutrients and oxygen partial pressure in the bioreactor system. Finally, this review will discuss the commercially available bioreactors that are currently undergoing preclinical and clinical trials.

Hemoglobin regulates the metabolic, synthetic, detoxification, and biotransformation functions of hepatoma cells cultured in a hollow fiber bioreactor

Hepatic hollow fiber (HF) bioreactors constitute one type of extracorporeal bioartificial liver assist device (BLAD). Ideally, cultured hepatocytes in a BLAD should closely mimic the in vivo oxygenation environment of the liver sinusoid to yield a device with optimal performance. However, most BLADs, including hepatic HF bioreactors, suffer from O2 limited transport toward cultured hepatocytes, which reduces their performance. We hypothesize that supplementation of hemoglobin-based O2 carriers into the circulating cell culture medium of hepatic HF bioreactors is a feasible and effective strategy to improve bioreactor oxygenation and performance. We examined the effect of bovine hemoglobin (BvHb) supplementation (15g/L) in the circulating cell culture medium of hepatic HF bioreactors on hepatocyte proliferation, metabolism, and varied liver functions, including biosynthesis, detoxification, and biotransformation. It was observed that BvHb supplementation supported the maintenance of a higher cell mass in the extracapillary space, improved hepatocyte metabolic efficiency (i.e., hepatocytes consumed much less glucose), improved hepatocyte capacity for drug metabolism, and conserved both albumin synthesis and ammonia detoxification functions compared to controls (no BvHb supplementation) under the same experimental conditions.

Transport advances in disposable bioreactors for liver tissue engineering

Acute liver failure (ALF) is a devastating diagnosis with an overall survival of approximately 60%. Liver transplantation is the therapy of choice for ALF patients but is limited by the scarce availability of donor organs. The prognosis of ALF patients may improve if essential liver functions are restored during liver failure by means of auxiliary methods because liver tissue has the capability to regenerate and heal. Bioartificial liver (BAL) approaches use liver tissue or cells to provide ALF patients with liver-specific metabolism and synthesis products necessary to relieve some of the symptoms and to promote liver tissue regeneration. The most promising BAL treatments are based on the culture of tissue engineered (TE) liver constructs, with mature liver cells or cells that may differentiate into hepatocytes to perform liver-specific functions, in disposable continuous-flow bioreactors. In fact, adult hepatocytes perform all essential liver functions. Clinical evaluations of the proposed BALs show that they are safe but have not clearly proven the efficacy of treatment as compared to standard supportive treatments. Ambiguous clinical results, the time loss of cellular activity during treatment, and the presence of a necrotic core in the cell compartment of many bioreactors suggest that improvement of transport of nutrients, and metabolic wastes and products to or from the cells in the bioreactor is critical for the development of therapeutically effective BALs. In this chapter, advanced strategies that have been proposed over to improve mass transport in the bioreactors at the core of a BAL for the treatment of ALF patients are reviewed.

Convection and hemoglobin-based oxygen carrier enhanced oxygen transport in a hepatic hollow fiber bioreactor

Hepatic hollow fiber bioreactors are a promising class of bioartificial liver assist device (BLAD). The development of this type of device is currently hindered by limited oxygen transport to cultured hepatocytes, due to low solubility of oxygen in aqueous media. In order to increase the oxygen spectrum to cultured hepatocytes housed within a hollow fiber bioreactor, several different engineering strategies were explored in this study. These included: supplementing the circulating media stream of the hollow fiber bioreactor with a hemoglobin-based oxygen carrier (bovine red blood cells) with defined oxygen binding and release kinetics and operating the bioreactor with media flow through the hollow fiber membrane into the extracapillary space (ECS). We hypothesize that these two strategies can be used to improve hepatocyte oxygenation and possibly attain an in vivo-like pO(2) spectrum, similar to that observed in vivo in the liver sinusoid. This work is significant, since provision of an in vivo-like pO(2) spectrum should create a fully functional BLAD that could potentially bridge thousands of liver failure patients towards native liver regeneration of damaged tissue or, if necessary, orthotopic liver transplantation.

Targeted Oxygen Delivery within Hepatic Hollow Fiber Bioreactors via Supplementation of Hemoglobin-Based Oxygen Carriers

Hepatic hollow fiber bioreactors are considered a promising class of bioartificial liver assist device (BLAD). Unfortunately, limited oxygen (O(2)) transport to hepatocytes within this device hinders further development. Hepatocytes in vivo (in the liver sinusoid) experience a wide range of oxygen tensions (pO(2) = 25-70 mmHg), which is important for development of proper differentiated function (zonation). Previously, we observed that bovine red blood cell (bRBC) supplementation of the circulating media stream enhanced oxygenation of cultured C3A hepatoma cells compared to a culture with no O(2) carrier (Gordon, J.; Palmer, A. F. Artif. Cells, BloodSubstitutes, Biotechnol. 2006, 33 (3), 297-306). Despite this success, the cells were not exposed to the desired in vivo O(2) spectrum (Sullivan, J.; Gordon, J.; Palmer, A. Biotechnol. Bioeng. 2006, 93 (2) 306-317). We hypothesize that altering the kinetics of O(2) binding/release to/from hemoglobin-based O(2) carriers (HBOCs) could potentially target O(2) delivery to cell cultures. High P(50) (low O(2) affinity) HBOCs preferentially targeted O(2) delivery at high inlet pO(2) values. Conversely, low P(50) (high O(2) affinity) HBOCs targeted O(2) delivery at low inlet pO(2) values. Additionally, inlet pO(2), flow rate, and HBOC concentration were varied to find optimal bioreactor operating conditions. Our results demonstrate that HBOCs can enhance O(2) delivery to cultured hepatocytes, while exposing them to in vivo-like O(2) tensions, which is critical to create a fully functional BLAD.

Enhancing oxygen tension and cellular function in alginate cell encapsulation devices through the use of perfluorocarbons

Encapsulation devices are often hindered by the inability to achieve sufficient oxygen levels for sustaining long-term cell survival both in vivo and in vitro. We have investigated the use of synthetic oxygen carriers in alginate gels to improve metabolic activity and viability of HepG2 cells over time. Perfluorocarbons (PFCs), specifically perfluorotributylamine (PFTBA) and perfluorooctylbromide (PFOB), were emulsified with alginate and used to encapsulate HepG2 cells in a spherical geometry. Cellular state was assessed using the MTT assay and Live/Dead stain as well as through analysis of both lactate and lactate dehydrogenase (LDH) levels which are indirect indicators of oxygen availability. Addition of 1% surfactant resulted in stable emulsions with evenly dispersed PFC droplets of the order of 1-2 microm in diameter, with no influence on cell viability. Both PFCs evaluated were effective in increasing cellular metabolic activity over alginate-only gels. The presence of 10% PFOB significantly increased cellular growth rate by 10% and reduced both intracellular LDH and extracellular lactate levels by 20-40%, improving glucose utilization efficiency. The characteristic drop in cellular metabolic activity upon encapsulation was eliminated with addition of 10% PFC and viability was better maintained throughout the bead, with a significant decrease in necrotic core size. Results were consistent under a physiologically relevant 5% oxygen environment. The incorporation of PFC synthetic oxygen carriers into encapsulation matrices has been successfully applied to improve cell function and viability with implication for a variety of tissue engineering applications.

Simulation of oxygen carrier mediated oxygen transport to C3A hepatoma cells housed within a hollow fiber bioreactor

A priori knowledge of the dissolved oxygen (O2) concentration profile within a hepatic hollow fiber (HF) bioreactor is important in developing an effective bioartificial liver assist device (BLAD). O2 provision is limiting within HF bioreactors and we hypothesize that supplementing a hepatic HF bioreactor's circulating media with bovine red blood cells (bRBCs), which function as an O2 carrier, will improve oxygenation. The dissolved O2 concentration profile within a single HF (lumen, membrane, and representative extra capillary space (ECS)) was modeled with the finite element method, and compared to experimentally measured data obtained on an actual HF bioreactor with the same dimensions housing C3A hepatoma cells. Our results (experimental and modeling) indicate bRBC supplementation of the circulating media leads to an increase in O2 consumed by C3A cells. Under certain experimental conditions (pO2,IN) = 95 mmHg, Q = 8.30 mL/min), the addition of bRBCs at 5% of the average in vivo human red blood cell concentration (% hRBC) results in approximately 50% increase in the O2 consumption rate (OCR). By simply adjusting the operating conditions (pO2,IN) = 25 mmHg, Q = 1.77 mL/min) and increasing bRBC concentration to 25% hRBC the OCR increase is approximately 10-fold. However, the improved O2 concentration profile experienced by the C3A cells could not duplicate the full range of in vivo O2 tensions (25-70 mmHg) typically experienced within the liver sinusoid with this particular HF bioreactor. Nonetheless, we demonstrate that the O2 transport model accurately predicts O2 consumption within a HF bioreactor, thus setting up the modeling framework for improving the design of future hepatic HF bioreactors.