Caffeine toxicity in zebrafish - Neurobehavioral changes, developmental defects, and oxidative stress: A review

Caffeine is one of the most widely consumed psychoactive stimulants, primarily functioning as a non-selective adenosine receptor antagonist. Its increasing detection in wastewater and surface waters reflects extensive anthropogenic use. This review synthesizes evidence from zebrafish (Danio rerio)-a genetically tractable vertebrate with rapidly developing external embryos-to assess the impact of caffeine exposure across environmentally relevant (ng-µg/L) and pharmacological/toxicological (mg/L and above) concentrations on early development and neurobehavior. Behavioral studies indicate dose- and stage-dependent alterations in locomotion, anxiety-like responses, memory performance, and sleep patterns, suggesting disruptions in neural circuitry and stress-axis regulation. Biochemical analyses frequently reveal oxidative imbalances characterized by increased reactive oxygen species and lipid peroxidation, alongside changes in antioxidant defenses (e.g., glutathione levels, superoxide dismutase (SOD) activity, and glutathione reductase activity). These findings support oxidative stress as a potential mechanistic hub, although a causal relationship has yet to be established. Embryonic exposure to caffeine is associated with developmental toxicity, including delayed hatching and concentration-dependent malformations such as edema, axial deformities, impaired angiogenesis, and neuromuscular defects at higher doses. However, cross-study comparisons are hindered by variations in units, exposure durations, and assay protocols. In summary, caffeine disrupts behavior, redox homeostasis, and developmental processes in zebrafish, highlighting the necessity for standardized methodologies to identify stage-specific vulnerabilities.