Acute systemic toxicity studies evaluate adverse effects occurring after a single exposure, or repeated exposure within a short acute window, and the main in vivo readouts are mortality, moribund condition, clinical signs, body-weight change, and gross pathological findings; acute oral toxicity methods were developed to replace classical LD50 testing with reduced-animal designs such as fixed-dose procedure, acute toxic class method, and up-and-down procedure. The fixed-dose procedure classifies acute toxicity by administering predefined dose levels and observing evident toxicity rather than using death as the primary endpoint, whereas the acute toxic class method uses sequential groups of three animals per step and the up-and-down procedure doses animals sequentially to estimate an LD50 with fewer animals than conventional LD50 testing.
Toxicology Studies
Toxicology experiments are scientific research that studies the effects of poisons on living organisms, reveals their toxicity mechanisms, and evaluates potential health risks. This field includes research on acute toxicity, subacute toxicity, chronic toxicity, mutagenicity and carcinogenicity. Experiments usually use models such as mice, rats, and cell culture, and adopt various toxicity assessment methods, such as biochemical testing, histopathology, and gene expression analysis. Toxicology experiments provide key information for drug safety assessment, environmental pollution research, and toxicology research.
Related Experimental Schemes
This protocol assesses dermal irritation using reconstructed human epidermis (RhE) models such as EpiDerm, EPISKIN, and SkinEthic RHE, in which a test substance is applied topically and tissue viability is measured after exposure; reduced viability reflects cytotoxic injury associated with skin irritation potential. The primary readout is MTT reduction, where viable cells convert tetrazolium salt into colored formazan measured by spectrophotometry; this signal is used as a quantitative viability endpoint for classifying irritant versus non-irritant responses. The historical in vivo comparator is the Draize rabbit skin irritation method, which scores erythema and edema after topical exposure, but validated RhE assays were developed to replace or reduce reliance on this animal-based endpoint.
A carcinogenicity bioassay detects whether long-term exposure to a test substance increases benign or malignant tumor incidence, changes tumor spectrum, or shortens tumor latency in experimental animals; the classical rodent design exposes rats and/or mice to multiple dose levels for most of their lifespan, followed by complete necropsy and histopathologic diagnosis of neoplastic and non-neoplastic lesions. The readout is tumor incidence by organ, sex, species, dose group, and survival status; interpretation requires concurrent controls, dose-response assessment, survival-adjusted tumor statistics, and pathology review because mortality, spontaneous tumor background, and body-weight effects can influence apparent tumor rates.
A subchronic/chronic oral toxicity study detects systemic adverse effects caused by repeated administration of a test article, using mortality, clinical signs, body weight, food/water intake, ophthalmology, urinalysis, hematology, serum biochemistry, organ weights, gross necropsy, and histopathology as integrated readouts. The readout reflects dose-related physiological injury, target-organ pathology, reversibility after recovery, and derivation of NOAEL, LOAEL, or related point-of-departure values when the dataset supports them.
A repeated-dose oral toxicity study evaluates systemic toxic effects after daily oral exposure to a test substance for a defined period, commonly 28 days, 6 weeks, 90 days, or 13 weeks in rodent studies. The readout is generated by integrating mortality, clinical signs, body-weight change, food and water intake, functional or behavioral observations, hematology, serum biochemistry, urinalysis, organ weights, necropsy, and histopathology to identify dose-related adverse effects, target organs, and the no-observed-adverse-effect level (NOAEL).
This protocol evaluates hepatotoxicity using complementary in vivo mouse APAP acute liver injury and in vitro hepatocyte-based cytotoxicity readouts. In vivo APAP injury is assessed by serum ALT/AST, liver histology, hepatic glutathione, protein adducts, necrosis, inflammation, and regeneration-related endpoints. In vitro hepatotoxicity is assessed by loss of viability, leakage of ALT/AST/LDH, oxidative-stress markers, mitochondrial function, nuclear morphology, intracellular calcium, and high-content imaging endpoints.
Inhalation toxicity studies expose rodents to a controlled aerosol, vapor, gas, or smoke atmosphere and assess respiratory and systemic toxicity using exposure-atmosphere characterization, clinical observations, body and organ weights, bronchoalveolar lavage fluid, histopathology, blood chemistry, hematology, and, when included, molecular endpoints such as transcriptomics, proteomics, lipidomics, or tissue burden analysis. The primary biological readouts are airway irritation, pulmonary inflammation, cytotoxicity, altered surfactant or lipid homeostasis, impaired particle clearance, and tissue remodeling, reflected by BALF cell differentials, BALF protein, LDH, phosphatase activities, cytokines, lung weight, microscopic respiratory-tract lesions, and retained lung burden.
The bacterial reverse mutation assay detects point mutations that restore amino-acid prototrophy in auxotrophic Salmonella typhimurium or Escherichia coli tester strains; after exposure to a test article, mutagenic activity is read out as an increased number of revertant colonies on minimal agar compared with the vehicle control. The assay uses tester strains with different mutation targets so that base-substitution and frameshift mutagens can be detected, and testing is performed with and without exogenous mammalian metabolic activation because some chemicals require biotransformation to become mutagenic.
Reproductive and developmental toxicity studies detect adverse effects of prenatal or peri/postnatal exposure on maternal condition, pregnancy maintenance, embryo-fetal survival, fetal growth, structural development, and offspring reproductive or developmental endpoints; classic rat protocols generate readouts by comparing treated groups with vehicle, pair-fed, or untreated controls for implantation, resorption, fetal weight, crown-rump length, external morphology, visceral morphology, skeletal ossification, anogenital distance, nipple/areola retention, and postnatal cohort outcomes.
This protocol assesses in vitro neurotoxicity by combining neuronal viability, mitochondrial/metabolic activity, neurite outgrowth, and optional neuronal network function readouts. Calcein-AM or resazurin/PrestoBlue readouts estimate viable or metabolically active cells; βIII-tubulin immunofluorescence detects neuronal morphology and neurite networks; TMRE detects mitochondrial membrane potential; and MEA recordings detect functional changes in neuronal network activity.
This protocol assesses nephrotoxicity by combining functional kidney injury readouts, urinary/tissue injury biomarkers, and renal histopathology. Serum creatinine and BUN reflect impaired kidney function, while KIM-1, NGAL, clusterin, osteopontin, IL-18, cystatin C, nephrin, Oat5, urinary protein, glucose, and alkaline phosphatase have been used to detect tubular injury in cisplatin-, gentamicin-, and acetaminophen-induced nephrotoxicity models.
