Protective effects of Aspalathus linearis against oxidative stress in human spermatozoa: Comparison with ascorbic acid

• Aspalathus linearis extracts protect human spermatozoa from oxidative stress in vitro. • Rooibos extracts reduce oxidation-reduction potential induced by cumene hydroperoxide. • Rooibos shows comparable or superior antioxidant effects to ascorbic acid. • Treatment preserves sperm motility, viability, mitochondrial function, and DNA integrity. Oxidative stress is a major contributor to male infertility due to its detrimental effects on sperm function. This study determined the antioxidant potential of fermented and unfermented rooibos extracts compared to ascorbic acid in protecting human spermatozoa from oxidative damage induced by cumene hydroperoxide. Semen samples from 25 healthy donors were processed and exposed to 100 µM cumene hydroperoxide, with treatment groups receiving varying concentrations of rooibos extracts or ascorbic acid. Sperm parameters, including motility, viability, mitochondrial membrane potential, DNA fragmentation, reactive oxygen species, capacitation, and acrosome reaction, were assessed after 60 and 120 minutes. Human tubular fluid supplemented with bovine serum albumin was used as a negative control, while cumene hydroperoxide alone served as the positive control. Both rooibos extracts and ascorbic acid significantly reduced oxidative stress, measured by static oxidation-reduction potential, compared to the positive control ( p < 0.0001). Treatment improved sperm motility, viability, mitochondrial function, capacitation, and acrosome reaction, while decreasing DNA fragmentation and reactive oxygen species levels ( p < 0.05). Rooibos exhibited antioxidant effects comparable to ascorbic acid. Aspalathus linearis extracts effectively protect human spermatozoa against oxidative damage and preserve essential functional parameters, supporting their potential use as natural antioxidants in male fertility management.