Extracellular vesicles from water kefir can interact with human neurons in vitro: a potential explanation for the role of probiotics consumption in mental health.

Major depressive disorder is one of the most burdensome mental health disorders. Probiotics have been shown to ameliorate depressive symptoms, though the mechanism remains unclear. This study was conducted to investigate whether extracellular vesicles (EVs) extracted from the probiotic beverage water kefir could influence gene and protein expression in human-derived neuroblastoma cells in vitro. EVs were extracted from lab-cultured water kefir and a control solution without water kefir grains by ultracentrifugation. Water kefir vesicles were imaged via electron microscopy. Neuroblastoma, microglia, and neuroblastoma-microglia co-cultures were exposed to water kefir EVs or negative control medium. Uptake of water kefir EVs was identified by microscopy. All conditions were quantified for brain derived neurotrophic factor, fractalkine, and synaptophysin RNA and protein. Data were analyzed using factorial ANOVAs with significance set at 0.05. Water kefir vesicles were taken up by neuroblastoma cells, and incubation in neuroblastoma-microglia co-culture resulted in significantly higher levels of fractalkine protein compared to media-only control (p = 0.029). To our knowledge, this is the first study to identify potential interactions between EVs derived from the probiotic beverage water kefir and human neuronal cells. Further research is needed to fully elucidate the role played by probiotic-derived EVs in human health.