The Effect of Cell-Free Metabolites of Vaginal Lactobacilli on HeLa Cells Is Independent of Lactic Acid Concentration.

It remains unclear how metabolites produced by vaginal peroxide-producing lactobacilli influence parameters supporting cervical cancer cell survival. The aim of our study was to investigate the functional response of HeLa cells to cell-free metabolites of vaginal lactobacilli producing peroxide under conditions of oxidative stress. HeLa cells were treated with cell-free metabolites of lactobacilli isolated from the vaginal fluid of healthy women. Subsequently, their resistance to oxidative stress (total number of surviving, apoptotic, and necrotic cells), dehydrogenase activity with the MTT assay, and mitochondrial potential were measured. Pretreatment with cell-free lactobacilli metabolites significantly reduced HeLa cell survival under oxidative stress in most cases; dehydrogenase activity and mitochondrial potential changed to a lesser extent. All HeLa cells pretreated with cell-free lactobacillus metabolites that died due to oxidative stress died apoptotic death. These effects of cell-free lactobacilli metabolites are not always determined by lactic acid levels. These data reveal a new mechanism by which vaginal lactobacilli exert local antitumor protection by inducing controlled cell death in transformed cells.