Table 3 Tiered Testing Strategy to support the HARN IATA. Recommended methods and models to address each IATA decision node are set-out according to the appropriate tier of testing.
Can HARN deposit in the distal lung? | Does the HARN dissolve very slowly in lung lining fluid (pH7.4)? | Does the HARN dissolve very slowly in lysosomal fluid (pH4.5)? | Is HARN length > 5 µm? | Is HARN rigid and maintain a needle-like morphology? | Does HARN cause frustrated phagocytosis? |
|---|---|---|---|---|---|
Tier 1 | |||||
Review existing data sets | |||||
Estimation of aerodynamic diameter from diameter and density of HARN | Batch dissolution test or dissolution in continuous flow system in lung lining fluid | Batch dissolution test or dissolution in continuous flow system in lysosomal fluid | Length distribution profile from TEM/SEM images | Mean diameter of HARN from TEM/SEM. Include supporting images | Inflammasome activation in macrophage exposed to HARN: IL-1β release |
Tier 2 | |||||
Review existing data sets | |||||
Measurement of mass median aerodynamic diameter (MMAD) from airborne dispersion of material | Â | Durability in cellular systems | HARN length measurement from airborne dispersion of material from TEM/SEM images | HARN size measurement from airborne dispersion of material from TEM/SEM images. Include supporting images | In vitro granuloma formation |
Tier 3 | |||||
Review existing data sets | |||||
Quantification of lung deposition during in vivo inhalation studies | Quantification of lung burden and clearance kinetics during in vivo inhalation studies | Â | Â | Fibre rigidity of HARN demonstrated by morphological assessment and/or size measurements after incubation with macrophages in vitro or in vivo | Evidence of frustrated phagocytosis and granuloma formation from in vivo exposure (OECD GD 39) |