Tumor-targeted induction of intrinsic apoptosis in colon cancer cells by Lactobacillus plantarum and Lactobacillus rhamnosus strains.

Abstract

Colorectal cancer is one of the widespread and lethal types of malignancies. Recently, antineoplastic attributes of probiotics have attracted lots of attention. Here, we investigated anti-proliferative potential of the non-pathogenic strains Lactobacillus plantarum ATCC 14,917 and Lactobacillus rhamnosus ATCC 7469 on human colorectal adenocarcinoma-originated Caco-2 cells. Caco-2 and HUVEC control cells were treated with ethyl acetate extracts of the two Lactobacillus strains to assess cell viability by MTT assay. Annexin/PI staining flow cytometry, and caspase-3, -8 and - 9 activity assays were performed to determine the type of cell death induced in extract-treated cells. Expression levels of apoptosis-related genes were evaluated by RT-PCR. Extracts from both L. plantarum and L. rhamnosus specifically targeted the Caco-2 cells and not HUVEC controls, and significantly affected the viability of the colon cancer cell line in a time- and dose-dependent manner. This effect was shown to occur through activation of the intrinsic apoptosis pathway, as indicated by the increased caspase-3 and - 9 activities. While there are limited and conflicting data about the mechanisms underlying the specific antineoplastic attributes of Lactobacillus strains, we clarified the overall induced mechanism. The Lactobacillus extracts specifically down-regulated the expression of the anti-apoptotic bcl-2 and bcl-xl, and simultaneously up-regulated the pro-apoptotic bak, bad, and bax genes in treated Caco-2 cells. Ethyl acetate extracts of L. plantarum and L. rhamnosus strains could be considered as targeted anti-cancer treatments specifically inducing the intrinsic apoptosis pathway in colorectal tumor cells.