Primary human hepatocytes vs. cell lines in researh

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Understanding the distinction between primary cells vs cell lines is essential for selecting the appropriate in vitro model in biomedical research. While cell line establishment has been crucial to prompt advances in fields such as drug development, primary human cells offer a close resemblance to human physiology that should not be overlooked.

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What is the difference between primary cells and cell lines?

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Primary cells are derived directly from human or animal tissues and retain many of the functional characteristics of the tissue of origin, thanks to their genotypical and phenotypical stability. Human primary cells allow the study population heterogeneity by utilizing cells from a diverse range of donors. 

In contrast, cell lines are immortalized cells that can proliferate indefinitely under controlled conditions. Continuous cell lines are easier to maintain and provide a consistent supply for experimentation but often lack the full spectrum of physiological functions. A comparison of the molecular and functional characteristics of cell lines vs primary cells shows that cell lines prioritize functions that support growth and division. This is especially true for cell lines derived from advanced-stage cancers, which are prone to genetic changes over time as they are repeatedly cultured. 

This distinction underpins the debate of primary cells vs cell lines in experimental design. A primary cell culture is differentiated from a cell line by longevity and biological relevance. While primary cells provide a more accurate representation of in vivo biology, their finite lifespan poses challenges.

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In the specific context of primary human hepatocytes vs hepatic cell lines, primary human hepatocytes closely mimic human liver tissue’s metabolic and enzymatic processes, making them invaluable for preclinical drug metabolism and toxicity studies. 

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What are the advantages of cell lines in research?

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Cell line development has provided a versatile tool for easily culturing human liver cells. Cell lines can grow continuously with the appropriate cell line media, making them cost-effective and accessible. This fact supports large-scale and long-term experiments in high-throughput drug screening. Moreover, they are well-suited for gene-editing techniques, providing a platform for studying specific pathways.

However, these benefits come at the cost of physiological relevance, which brings us back to the debate of primary vs cell line: how closely do they reflect in vivo conditions?

Popular hepatocyte cell lines like HepG2 and HepaRG, derived from hepatocellular carcinoma, are commonly used for in vitro assessment of liver toxicity. Nevertheless, a recent study has revealed these cell lines’ limitations in drug metabolism studies. Focusing on Phase I protein expression, basal cytochrome P450-dependent activity, and utility in P450 induction studies, HepG2 cells are severely compromised, lacking key proteins and drug-metabolizing capacity. 

HepG2 cells also show deficiencies in bile acid synthesis and transport and show a reduced expression of liver transporters, which may lead to misleading results in drug interactions and toxicity studies. 

While differentiated HepaRG cells are more hepatocyte-like and have a potential utility in drug metabolism studies, their utility is hindered by the variable and complex differentiation protocols. 

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Primary human hepatocytes: main characteristics 

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Human primary hepatocytes are considered the gold standard for drug metabolism, toxicity, or liver disease studies. They offer a significant advantage in research due to their ability to retain the expression of essential liver-specific enzymes and proteins, including the complete cytochrome P450 enzyme family. This capability enables more precise investigations into drug metabolism and interactions, yielding data with a higher likelihood of translating to human clinical outcomes. 

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Primary human hepatocytes maintain typical liver cell structure and functions, such as albumin production and urea synthesis, which are vital for exploring liver physiology and disease mechanisms. Another key strength of primary hepatocytes is their capacity to respond to external stimuli in a manner that closely reflects in vivo conditions. This includes their reactions to inflammatory cytokines, hormones, and other signaling molecules, making them indispensable for research into liver inflammation, fibrosis, and related diseases.

Difficult access to primary human hepatocytes used to be one of their main drawbacks. At BeCytes, we have mastered the isolation protocols to grant you access to primary liver cells, including non-parenchymal cells. Our proprietary protocol allows us to obtain human primary hepatocytes, plateable or in suspension, with a granted post-thawing viability superior to 85%.

Our liver cells are ethically sourced from donor tissues and meticulously characterized. The Certificate of Analysis (CoA) includes donor demographic information (HLA, age, gender, diseases…), number of cells and viability after thawing, and days in culture, among others. You’ll also find details on spheroid and organoid formation and the induction of cytochrome phases I and II.

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References

Guo L, Dial S, Shi L, Branham W, Liu J, Fang JL, et al. Similarities and differences in the expression of drug-metabolizing enzymes between human hepatic cell lines and primary human hepatocytes. Drug Metab Dispos. 2011 Mar;39(3):528–38. doi: 10.1124/dmd.110.035873

Rodríguez-Antona C, Donato MT, Boobis A, Edwards RJ, Watts PS, Castell JV, et al. Cytochrome P450 expression in human hepatocytes and hepatoma cell lines: molecular mechanisms that determine lower expression in cultured cells. Xenobiotica. 2002 Jun;32(6):505–20. doi: 10.1080/00498250210128675

Stanley LA, Wolf CR. Through a glass, darkly? HepaRG and HepG2 cells as models of human phase I drug metabolism. Drug Metab Rev. 2022 Feb;54(1):46-62. doi: 10.1080/03602532.2022.2039688.

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