Drug Safety Science
Liver Toxicity Screening and DILI Testing
A scientific overview of in vitro liver toxicity screening, why standard models are insufficient for DILI detection, and how multicellular microphysiological systems improve predictive accuracy.
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Definition
What is Liver Toxicity and Drug-Induced Liver Injury (DILI)?
Drug-induced liver injury (DILI) refers to hepatic damage caused by a pharmaceutical compound, its metabolites, or reactive intermediates generated during hepatic metabolism. DILI is a leading cause of drug development failure, clinical trial discontinuation, and post-market drug withdrawal.
DILI is classified into two broad categories:
Intrinsic (dose-dependent)
Predictable liver injury directly related to compound concentration. Examples include paracetamol (acetaminophen) overdose. More reliably modelled in vitro.
Idiosyncratic (dose-independent)
Unpredictable, immune-mediated or metabolic reactions that occur in susceptible individuals at therapeutic doses. Notoriously difficult to predict in standard models.
For more background on in vitro liver models, see the What is MPS? page and the Glossary.
Model Limitations
Why Traditional Models Fail to Predict DILI
2D Hepatocyte Cultures
Standard 2D cultures of primary human hepatocytes (PHH) or hepatocyte cell lines (e.g., HepG2, HepaRG) are the most widely used models for liver safety assessment. However, they have significant limitations:
- Rapid loss of hepatocyte-specific function within 24–72 hours in standard 2D culture (CYP enzyme activity, albumin secretion)
- Absence of non-parenchymal cells — Kupffer cells, liver sinusoidal endothelial cells (LSECs), and stellate cells — which mediate immune-inflammatory DILI mechanisms
- Static culture conditions fail to replicate the zonation and flow dynamics of the liver sinusoid
- Cell lines (HepG2) have significantly reduced metabolic competence compared to primary hepatocytes
Animal Models
Animal models (typically rodent) are standard in preclinical safety packages but have fundamental limitations for liver toxicity prediction:
- Significant species differences in CYP enzyme expression, metabolite profiles, and immune responses
- Poor predictors of human idiosyncratic DILI — most idiosyncratic hepatotoxins are not toxic in rodents
- Ethical and cost burden associated with in vivo studies
- Limited throughput for early-stage compound screening
Model Requirements
What Makes a Good In Vitro Liver Model for Toxicity Screening?
A high-quality liver model for DILI screening should recapitulate the key cellular and architectural features of the human liver sinusoid:
Key requirements for a predictive liver model
- Primary human hepatocytes (PHH) or metabolically competent iPSC-derived hepatocytes
- Inclusion of non-parenchymal cells: Kupffer cells (resident macrophages), liver sinusoidal endothelial cells, and hepatic stellate cells
- Dynamic culture conditions that maintain hepatocyte phenotype and metabolic activity over extended periods
- Defined and reproducible cell-type composition for quantitative, comparable results
- Compatibility with standard analytical readouts (ELISA, imaging, metabolomics)
- Sensitivity to both intrinsic and immune-mediated DILI mechanisms
NANOSTACKS™ Approach
How NANOSTACKS™ Supports Liver Toxicity Screening
Revivocell's Liver MPS platform uses NANOSTACKS™ inserts to build anatomically inspired multi-layer liver sinusoid models in standard 24-well plates. Dynamic culture conditions are provided by orbital shaking — generating physiological shear stress without external pumps or microfluidic hardware.
Three validated configurations are available, each adding progressive cellular complexity:
Monoculture
Hepatocytes only
Phase I/II metabolism studies, basic cytotoxicity, CYP induction/inhibition assays.
Triculture
Hepatocytes + Liver Sinusoidal Endothelial Cells + Kupffer cells
Improved DILI sensitivity, inflammatory DILI mechanisms, endothelial function.
Tetraculture
Hepatocytes + LSECs + Kupffer cells + Hepatic Stellate Cells
Fibrosis and chronic liver injury modelling, steatohepatitis, long-term hepatotoxicity.
Cell Biology
Cell Types and Their Roles
| Cell Type | Location in Sinusoid | Role in Toxicity |
|---|---|---|
| Hepatocytes | Parenchymal (basal) | Primary site of drug metabolism; generate reactive metabolites responsible for direct toxicity |
| Liver Sinusoidal Endothelial Cells (LSECs) | Sinusoidal lining (apical) | Regulate compound access to hepatocytes; fenestrated structure affects drug bioavailability |
| Kupffer Cells | Sinusoidal (apical) | Resident macrophages; mediate inflammatory and immune-mediated DILI through cytokine release |
| Hepatic Stellate Cells | Perisinusoidal (basal) | Activated by chronic injury; key mediators of hepatic fibrosis and steatohepatitis |
Analytical Endpoints
Key Readouts and Endpoints
The following analytical endpoints can be measured using standard laboratory equipment with NANOSTACKS™ Liver MPS:
Hepatocyte viability and function
- ALT / AST (hepatocyte injury markers)
- LDH release (membrane integrity)
- Albumin secretion (synthetic function)
- Urea synthesis (nitrogen metabolism)
- CYP enzyme activity (CYP1A2, CYP3A4, CYP2D6)
Inflammation and immune activation
- Pro-inflammatory cytokines (IL-6, IL-8, TNF-α) by ELISA
- Kupffer cell activation markers
- NF-κB pathway activation (imaging-based)
Morphology and structure
- Brightfield and phase contrast imaging
- Fluorescence confocal imaging (Z-stacks through layers)
- Bile canaliculi morphology (CDFDA assay)
- Lipid accumulation (Oil Red O, BODIPY)
Metabolism and transport
- Drug metabolite profiling (LC-MS/MS)
- CYP induction/inhibition assays
- Efflux transporter activity (MRP2, BSEP)
- Reactive metabolite trapping assays
Drug Discovery Use Cases
Applications in Drug Discovery
Early-stage DILI screening
Rank-order hepatotoxicity risk of compound series during lead optimisation to deprioritise hepatotoxic candidates before resource-intensive animal studies.
Mechanistic DILI investigation
Distinguish between mitochondrial toxicity, reactive metabolite-mediated injury, cholestatic mechanisms, and immune-mediated DILI to inform structural modifications.
Chronic and repeated-dose studies
Assess cumulative toxicity over 14–28 day dosing regimens — critical for oncology, CNS, and chronic disease therapeutics where prolonged exposure is expected.
ADME and metabolite profiling
Generate human-relevant intrinsic clearance and metabolite data for PBPK modelling and IVIVE. Supports IND-enabling package development.
New Approach Methodology (NAM) packages
Generate human-relevant liver safety data under the FDA Modernization Act 2.0 framework as a complement or alternative to in vivo toxicology studies.
Discuss a liver toxicity study
Our team can advise on model selection, study design, and interpretation of liver safety data for your compounds.