Autophagy induction by a natural ingredient of areca nut.

We recently identified an autophagy-inducing areca nut ingredient (AIAI) in the partially purified 30-100 kDa fraction of areca nut extract (ANE), designated as ANE 30-100K. Before disintegration, most ANE 30-100K-treated cells exhibit rounding morphology, cytoplasmic clearance, and nuclear shrinkage, distinct from arecoline- and cisplatin-induced cellular apoptosis. This unique death pattern is verified to be autophagy by LC3-I cleavage, acidic vesicles, and autophagic vacuoles. As analyzed by Molish's Test, Selinowaff's Test, and thin-layer chromatography, most of the ANE 30-100K constituents are carbohydrates, whereas the protein content of this fraction is less than 1% as assessed by protein assay reagent. The cytotoxicity of ANE 30-100K is further shown to be sensitive to cellulase and proteinase K digestion suggesting AIAI in ANE 30-100K to be a proteoglycan (or glycoprotein). Thus, although ANE contains apoptosis-inducing ingredients such as arecoline, it predominantly triggers autophagic cell death by this natural AIAI.