Effects of a Commercial Standardized Green Rooibos (Aspalathus linearis) Extract on Caenorhabditis elegans and Zebrafish Anxiety-Like Behavior.

Abstract

Anxiety-related disorders are among the most prevalent mental health conditions worldwide, driving interest in novel, plant-based interventions. This study aimed to evaluate the antioxidant activity and capacity to alleviate anxiety-like behavior of a commercially standardized green rooibos (Aspalathus linearis) powdered extract (GRE) in vivo. The GRE was chemically characterized using liquid and gas chromatography. Antioxidant capacity (survival and ROS levels upon oxidative stress) and anxiety-like behavior reduction (octanol avoidance test) were evaluated in the Caenorhabditis elegans model, and additionally in adult zebrafish (Danio rerio) by a Novel Tank Test after 4 months of GRE ingestion. Analytical results of GRE confirmed the presence of dihydrochalcones (aspalathin, nothofagin) and flavones (orientin, isoorientin, isovitexin) as the major phenolic constituents. In C. elegans, GRE supplementation improved survival under oxidative stress conditions and significantly reduced intracellular ROS levels in a dose-dependent manner. Additionally, GRE exposure mitigated anxiety-like behavior in nematodes subjected to serotonin-deficiency conditions induced by starvation. GRE-fed fish exhibited a significant increase in time spent in the upper zone of the tank, reduced latency to reach this zone, and fewer individuals displaying bottom-dwelling behavior, while locomotor parameters (speed and distance traveled) remained unaffected, indicating reduced anxiety-like behavior levels. Data support the potential of GRE to reduce anxiety-related behavior in both invertebrate and vertebrate models, possibly mediated by its antioxidant properties and polyphenolic profile. These findings underscore the potential of A. linearis as a functional botanical candidate for future dietary interventions for anxiety support.