Liver cell co-cultures can offer a more comprehensive in vitro model to study the effects of intercellular signaling on xenobiotic metabolism. Non-parenchymal cells (NPC) of the liver such as Kupffer, sinusoidal, endothelial, and stellate cells can be co-cultured with hepatocytes to more accurately mimic in vivo conditions.Kupffer cells are a type of macrophage located within the liver sinusoid that are of particular interest because of their key role in the modulation of drug-metabolizing enzymes following immunological response. Hepatocyte/Kupffer cell co-cultures can be seeded at ratios with increasing Kupffer cell content to allow investigators to compare inflammation versus normal-state response. Stimulation of the co-cultures with lipopolysaccharide (LPS) results in the release of a variety of soluble factors, such as nitric oxide (NO) or pro-inflammatory cytokines, such as IL-6 and TNF-α. The response to inflammation and infection can lead to altered gene expression, down-regulation of cytochrome P450 (CYP) enzymes, and depression of the mechanisms underlying drug clearance.
The use of hepatocyte/Kupffer cell co-cultures is also important in the screening of therapeutic proteins and biologics. These drugs are more heterogeneous in composition, follow different pathways of elimination, and have greater potential to elicit an immune response. Their impact on CYP enzyme suppression and the potential to cause small molecule toxicity should be thoroughly studied before reaching clinical trials.
Other advantages to culturing hepatocytes with NPCs are longer maintenance in culture and higher liver-specific function. Fresh and cryopreserved hepatocytes and non-parenchymal cells from the same donor or pool of donors allow researchers to reconstitute compatible cells in a physiologically relevant format that is most appropriate for their experiment.