Bacterioruberin-Rich Carotenoid Extract Protects Human PBMCs Against UV-Induced Oxidative Stress and Apoptosis: Insights into Mitochondrial and Cell Survival Mechanisms

Ultraviolet (UV) radiation is a major environmental stressor that disrupts cellular integrity by inducing oxidative stress, impairing mitochondrial function, and altering immune cell activity, ultimately compromising cellular homeostasis. In this context, carotenoids are widely recognized for their antioxidant and immunomodulatory properties, with C50 carotenoids emerging as a promising subgroup with enhanced biological activity compared with classical C40 carotenoids. Among them, bacterioruberin (BR), a red-pigmented C50 carotenoid mainly produced by haloarchaea, has attracted increasing interest due to its strong antioxidant and cytoprotective potential. Accordingly, this study investigated the mechanisms underlying the protective effects of a bacterioruberin-rich carotenoid extract (BRCE) against UV-induced damage in human peripheral blood mononuclear cells (PBMCs). PBMCs were pre-incubated with BRCE prior to UV exposure and intracellular reactive oxygen species (ROS), mitochondrial membrane potential (Δψm), caspase-3 activation, and the expression of B cell lymphoma 2 (Bcl-2) and granzyme A were evaluated using fluorescence-based assays via confocal microscopy and flow cytometry. BRCE attenuated oxidative stress, preserved mitochondrial membrane potential, reduced caspase-3 activation, and modulated Bcl-2 and granzyme A expression, with more pronounced effects observed at low concentrations. Overall, BRCE exerted a coordinated cytoprotective effect through modulation of oxidative stress, mitochondrial integrity, and apoptosis-related signaling pathways. These findings provide novel insight into the cellular effects associated with the bioactivity of bacterioruberin and support the growing interest in C50 carotenoids as promising photoprotective and immunomodulatory compounds.