Autophagy induction by the 30-100kDa fraction of areca nut in both normal and malignant cells through reactive oxygen species

Abstract

Areca nut (AN) is an addictive carcinogen used by about 200-600 million people worldwide. Some AN components are shown to induce apoptosis; however, we previously demonstrated that AN extract (ANE) and the 30-100kDa fraction of ANE (ANE 30-100K) induced autophagy-like responses, such as swollen cell morphology, empty cytoplasm, acidic vesicles, and LC3-II accumulation, in an oral cancer cell line, OECM-1. To further assess the responses of other cell types to ANE 30-100K, we used both normal and malignant cells as the targets of ANE 30-100K and found that normal oral fibroblasts (CMT415), peripheral blood lymphocytes (PBLs), Jurkat leukemia T cells, and esophageal carcinoma cells (CE81T/VGH) exhibited similar responses after ANE 30-100K challenge. ANE 30-100K drastically increased acidic vesicle-containing PBLs isolated from two independent donors (from 0.1% to 92.1% and 2.9% to 64.2%). Furthermore, both ANE- and ANE 30-100K-induced LC3-II accumulation in CMT415 and CE81T/VGH was further increased in the presence of the lysosomal protease inhibitors (pepstatin A, E64d, and leupeptin). On the other hand, ANE 30-100K also increased the level of intracellular reactive oxygen species (ROS), and the ROS scavengers, N-acetylcysteine (NAC) and Tiron, inhibited ANE 30-100K-induced cell death and LC3-II accumulation. Collectively, these results suggest the existence of an autophagy-inducing AN ingredient (AIAI) in ANE 30-100K, which renders ANE as an autophagic flux inducer through ROS in both normal and malignant cells.