From ice to neurons: investigating the neuroprotective effects of Antarctic microalgae Chlorella variabilis and Chlorella pyrenoidosa extracts

In this study, it was aimed to examine the neuroprotective effects of ethanolic extracts of <i>Chlorella variabilis</i> YTU.ANTARCTIC.001 and <i>Chlorella pyrenoidosa</i> OZCIMEN.001 microalgae that were isolated from Antarctica in a H₂O₂-induced oxidative stress model using SH-SY5Y cell line. In this context, first, Antarctic microalgae were cultivated and characterized. It was determined that <i>C. pyrenoidosa</i> and <i>C. variabilis</i> had specific growth rates of 0.093 and 0.097 day^-1, respectively, and doubled their cell concentration in 7 days. With the antioxidant and phenolic content analysis, it was found that 1 mg/mL <i>C. pyrenoidosa</i> and <i>C. variabilis</i> ethanolic extracts had 33-37% radical scavenging activity and 102-107 mg GAE/mg extract phenolic content, respectively. Then, the cytotoxic effects of the microalgae extracts on SH-SY5Y cells were assessed across a concentration range of 6.25-125 µg/mL. The results indicated a concentration-dependent effect on cell viability, with no observed cytotoxicity within the tested range. Notably, the highest neuroprotective activity was recorded with <i>C. variabilis</i> extract at a concentration of 75 µg/mL, which maintained cell viability at 73.7% ± 0.3. These findings showed the significant neuroprotective potential of <i>C. pyrenoidosa</i> and <i>C. variabilis</i> ethanolic extracts, attributed to their substantial antioxidant properties and non-cytotoxic nature at effective concentrations. The promising neuroprotective efficacy of these extracts highlights their potential for therapeutic applications in neurodegenerative disease prevention and treatment.