Hepatopac Model: The Truth Revealed
The HEPATOPAC® model is a bioengineered, in vitro co-culture of primary hepatocytes and 3T3 murine fibroblasts. The cultures are arranged into a precise cyto-architecture that optimizes liver-specific functions and extends hepatocyte viability for several weeks, mimicking the in vivo liver. HEPATOPAC cultures secrete albumin, synthesize urea, display functional bile canaliculi, and metabolize compounds using active Phase I and Phase II enzymes at higher levels than other in vitro liver models.
The longevity of the HEPATOPAC platform and its in vivo-like expression of biochemical and metabolic machinery enable accurate drug disposition, safety, and efficacy assessments. Despite the demonstrated utility of the HEPATOPAC platform for liver metabolism and toxicity studies, it is yet to see industry-wide adoption. To promote a better understanding of the HEPATOPAC model, we have addressed some of the questions that new clients typically ask below.
Are the stromal cells in HEPATOPAC an advantage or a disadvantage?
Mouse 3T3 fibroblasts are the optimal cell type to stabilize hepatic function in vitro. Cytotoxicity assessments performed in HEPATOPAC culture allows for the evaluation of hepatocyte-specific markers such as albumin, urea, ALT, GLDH, mir-122 among others. Additionally, our clients have exploited the difference in species between the stromal cells and the hepatocytes by using ELISA kits to measure non-liver specific markers. For markers such as ATP, cellular ATP levels are also determined in stromal-only controls and subtracted from HEPATOPAC cultures ATP content to calculate hepatocyte-specific ATP content. Microscopy assessment of hepatic markers is observed within the micropatterned areas which are segregated from the 3T3 cells. Indeed, the presence of the stromal cells in the co-cultures are an advantage, allowing for the determination of both the cytotoxic and hepatotoxic effects of test compounds.
Are the number of hepatocytes in a well of a HEPATOPAC plate enough for my assays?
Functional characterization of HEPATOPAC cultures show high levels and retention of CYP450 and phase II enzyme activity (> 50% of freshly isolated hepatocytes)1. Not only that, comparisons of activities of several enzymes across different in vitro models, including other next-generation liver models, show that the metabolic activity of the HEPATOPAC model was consistently better than all the other models when averaged across 11 enzyme markers2. In addition, the HEPATOPAC model outperformed both suspension and monolayer cultures in accurately predicting the in vivo clearance of 23 reference compounds (87% and 96% within 2-fold and 3-fold respectively)3. Therefore, it is all about quality versus quantity. The data shows that, on a per hepatocyte basis, the cells in HEPATOPAC cultures are more productive and have higher activity for a longer period of time compared to other hepatocyte systems.
Is the HEPATOPAC model qualified for regulatory use?
Although the HEPATOPAC platform is a non-GLP in vitro liver model, data from the HEPATOPAC model has been submitted to regulatory agencies including the U.S. FDA. The data submitted has included (but is not limited to) metabolite identification and clearance data for IND submissions, and toxicology data as part of a larger package used to remove a clinical hold.
Are HEPATOPAC cultures as good as a 3D models?
Current 3D models cannot reproduce the structural and anatomical complexities of the liver. Indeed the HEPATOPAC platform has been shown to be functionally better than most 3D models. It has demonstrated functional similarity with the liver, recapitulating in vivo metabolic profiles and key biochemical mechanisms and pathways. In a study by Pfizer scientists, HEPATOPAC multispecies plates, differentiated compound turnover across multiple species, demonstrating species-specific metabolism4. Additionally, HEPATOPAC cultures have been used in lead optimization and identification to determine the safety profiles of drug candidates, with in vitro data correlating with in vivo findings. Moreover, the HEPATOPAC platform permits real-time, longitudinal, non-invasive monitoring of cultures, providing important mechanistic information whereas optical attenuation in 3D models limits visualization to the periphery of these micro-tissues.
Are HEPATOPAC plates easy to handle?
Although manufacturing HEPATOPAC cultures involve the use of complex microfabrication tools, using and handling these plates is as easy as pie. HEPATOPAC cultures are available in high-throughput, ready-to-use, easy-to-handle, industry-standard 96-well and 24-well plate formats. For customers who want to run their studies at their sites (i.e., in-house), HEPATOPAC plates are shipped as kits. Kits contain everything you need to run your studies/assays: HEPATOPAC cultures, media, and protocols. Our protocols have straightforward and easy-to-follow instructions. Our prime concerns are to have user-friendly kits and satisfied customers. HEPATOPAC kits are backed by scientific support, with our team available to provide technical and logistical support throughout the entire process – from ordering, plate delivery and study execution – to fit each customer’s unique needs.