Table 6.

In vitro endpoints commonly evaluated for predicting acute toxicity

Test Category/Topic	Example	Rationale (for acute toxicity)
1. General
Physico-chemical Properties	cLogP, pKa, H-bond donors/acceptors, MW, PSA	Influence biophysical effects: 1) can relate directly to toxicity (e.g., corrosives); 2) can modify expression of toxicity (e.g., through effects on ADME properties) Are often included as chemical descriptors used to develop in silico (Q)SAR models
	Michael-Acceptor	Chemical reactivity (e.g., adduct formation)
Cytotoxicity/Cytolethality	Non-specific (i.e., basal) cell	Toxicity resulting in cell death generally (i.e., without regard to effects that may be limited to specific tissues or cell types)
	Specific cell lineages	Specificity of toxicity directed toward certain tissues/organs (e.g., cardiomyocytes, hematopoietic cells)
Cell Growth and Proliferation	Non-specific or specific for certain cell lineages	Effects related to cell stasis without necessarily causing death (e.g., CDK inhibition)
Cell Energetics	ATP depletion	Ability to provide energy for cellular processes
	Mitochondrial function	Ability to conduct oxidative (aerobic) metabolism
	Ox-Phos uncoupling	Ability to capture and store energy from electron transport (oxidative metabolism)
Other Cell Functions	Protein synthesis
	DNA, RNA synthesis
	Cell-cell signaling	Ability of cells to interact with their environment (e.g., ligand-receptor interaction)
	Secretory function	Production of major secretory substances (e.g., hormones)
Cell/Tissue Morphology	Vacuolation; Accumulation	Detection of morphologic abnormalities
	Membrane Integrity	Effects on plasma membrane function (e.g., cell homeostasis involving compartmentalization, maintenance of gradients, etc.)
Test Article Metabolism	GSH Depletion and/or Adduct Formation	Effects on normal detoxification pathways.
2. Targeted Mechanisms
Specific Enzymes	Acetylcholinesterase	Cholinergic effects
	Cytochrome P450 (CYP) enzymes	Drug/toxicant metabolism
Receptors and Ion Channels	hERG (hERG): Potassium voltage-gated channel subfamily H member 2	Cardiac function
	Cav1.2 (CACNA1C): Voltage-dependent L-type calcium channel subunit alpha-1C	Cardiac and neurologic function
	Nav1.5 (SCN5A): Sodium channel protein type 5 subunit alpha	Cardiac function
	Kv4.3 (KCND3): Potassium voltage-gated channel subfamily D member 3	Cardiac function
	KCNQ1: Potassium voltage-gated channel subfamily KQT member 1	Cardiac function
	KCNE1: Potassium voltage-gated channel subfamily E member 1	Cardiac function
	Kir2.1 (KCNJ2): Inward rectifier potassium channel 2	Cardiac function
	5HT2B: 5-hydroxytryptamine receptor 2B	CNS function
	B-AR, PDE: Beta adrenergic receptor; Phosphodiesterase	Cardiac function
	Purkinjie fiber assay	Cardiac function
Nervous System	GABA Receptor(s)	CNS function (GABA receptors are the predominant inhibitory neurotransmitter receptors)
	GABA Benzodiazepine Site	CNS function
	NMDA Receptor	CNS function (glutamate receptors are the predominant excitatory neurotransmitter receptors)
	D2 Receptor (DRD2): D(2) dopamine receptor	CNS function