Cytotoxicity testing

Cytotoxicity testing is an in vitro cell-culture assay that exposes cultured mammalian cells to a test substance or its extract and compares cell survival with untreated controls, serving as a sensitive, low-cost early-warning screen for harmful contaminants rather than proof of safety. It can flag contaminants - including residual solvents, heavy metals, plasticizers, cleaning agents, or synthesis by-products - even where chemical assays show no problem.

Cytotoxicity testing procedure and the ISO 10993-5 70% threshold

Cytotoxicity testing is performed by exposing cultured mammalian cells - commonly mouse fibroblast L929 or human hepatoma lines such as HepG2 - to a test substance and comparing survival to untreated controls; under ISO 10993-5, viability at or above 70% of the control is classified as non-cytotoxic. Cell health is assessed across three areas: morphology (physical structure), growth, and metabolism.

Common validated methods in cytotoxicity testing and what each measures:

• MTT/XTT: measure metabolic activity
• Neutral Red Uptake: measures lysosomal function
• LDH release: measures membrane damage
• Qualitative microscopy scoring

Limits of cytotoxicity testing and common test confusions

Cytotoxicity testing is a screening test with clear limits: it cannot confirm identity or purity, cannot detect chronic or organ-specific toxicity, and cannot catch every contaminant. It is distinct from sterility testing, endotoxin or pyrogen testing, and genotoxicity testing. When reviewing a cytotoxicity report, check the cell line used, the method applied, the viability percentage, and whether the 70% ISO 10993-5 threshold was met.

Sources

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