Primary hepatocytes are the main cells of the liver, making up about 70-80% of its total cell population. Derived directly from liver tissue, whether human or animal, these specialized cells are responsible for the liver’s metabolic and detoxification functions, including processing nutrients, synthesizing proteins, and breaking down harmful substances.
What Primary Hepatocytes Are
Primary hepatocytes are cells freshly isolated from liver tissue, distinguishing them from immortalized cell lines that can divide indefinitely. This direct isolation means they retain many biological pathways and characteristics of liver cells. Their defining features include high metabolic activity, various enzyme systems, and the ability to perform intricate liver-specific tasks.
Cytochrome P450 (CYP) enzymes are abundant in hepatocytes, metabolizing a wide range of substances, including drugs and toxins. The smooth endoplasmic reticulum within hepatocytes, where these CYP enzymes reside, is extensive, reflecting their detoxification capacity. Hepatocytes also synthesize important proteins like albumin and clotting factors, and regulate carbohydrate, lipid, and protein metabolism.
Unique Value in Scientific Study
Primary hepatocytes are highly valued in scientific research because they closely mimic the physiological environment of the liver. Unlike other cell models, primary hepatocytes maintain intact metabolic pathways, detoxification capabilities, and gene expression profiles that accurately represent the liver’s functions. This physiological relevance makes them a valuable tool for studies where other cell lines might not fully replicate biological responses.
They exhibit native-like metabolic zonation, where different regions of the liver lobule have distinct metabolic functions, such as periportal hepatocytes specializing in albumin synthesis and urea secretion, while pericentral hepatocytes handle cytochrome P450 activity. This ability to replicate the liver’s intricate functions, including drug-metabolizing enzymes and transporters, makes them a preferred model in various research applications. The integrity of these functions allows researchers to gain insights that are predictive of how the liver behaves in vivo.
Applications in Research and Drug Development
Primary hepatocytes are widely used in drug discovery and development, serving as a benchmark for understanding how new compounds interact with the liver. In drug metabolism studies, they help researchers understand how drugs are processed by the body’s enzymatic systems. This includes identifying metabolic pathways, the resulting metabolites, and predicting potential drug-drug interactions, where one drug can alter the metabolism of another.
Hepatocytes are also widely used for toxicity testing, particularly for assessing potential drug-induced liver injury (DILI). By exposing them to new compounds, scientists can screen for liver damage early in the drug development process, identifying issues that might otherwise not be detected until clinical trials. Three-dimensional culture systems, such as spheroids or liver-on-a-chip platforms, can maintain liver cell functions for extended periods, allowing for long-term toxicity studies and more accurate predictions of DILI.
Primary hepatocytes are also used for disease modeling, creating in vitro systems to study liver conditions like metabolic dysfunction-associated steatotic liver disease (MASLD), cholestasis, and viral hepatitis. These models allow researchers to investigate the underlying mechanisms of liver diseases and test new therapeutic strategies in a setting that closely resembles human liver biology. In regenerative medicine, primary hepatocytes show potential for liver tissue engineering and cell transplantation, contributing to the development of bioartificial liver platforms that mimic liver zonation and functions.
Challenges in Their Utilization
Despite their value, working with primary hepatocytes presents several challenges. One limitation is their relatively short lifespan in standard two-dimensional culture systems, typically lasting only two to three days. This rapid loss of function in vitro restricts the duration of experiments, making long-term studies, such as those for chronic toxicity, difficult.
Primary hepatocytes also tend to dedifferentiate over time in culture, losing some specialized liver-specific functions and characteristics. Variability between different batches of cells, often due to differences between individual donors, can also complicate research outcomes. The isolation and maintenance of these cells require specialized techniques and equipment, which can add to the complexity and cost of their utilization in research.