A Mixture of Atropisomers Enhances Neutral Lipid Degradation in Mammalian Cells with Autophagy Induction

Atropisomers with a biaryl dihydronaphthopyranone structure, dinapinones A1 (DPA1) (M position) and A2 (DPA2) (P position), were isolated from the fungus culture broth of Talaromyces pinophilus FKI-3864 as inhibitors of [(14)C]neutral lipid ([(14)C]triacylglycerol (TG) and [(14)C]cholesteryl ester (CE)) synthesis from [(14)C]oleic acid in Chinese hamster ovary-K1 (CHO-K1) cells. DPA2 inhibited [(14)C]TG and [(14)C]CE synthesis (IC(50)s(,) 0.65 and 5.6 μM, respectively), but DPA1 had no inhibitory activity on [(14)C]TG and [(14)C]CE synthesis even at 12 μM. However, a 1:1 mixture of DPA1 and DPA2 (DPA(mix)) had the most potent inhibitory activity on [(14)C]TG and [(14)C]CE synthesis (IC(50)s, 0.054 and 0.18 μM, respectively). The mechanism of action of DPA(mix) was investigated. DPA(mix) had no effects on the enzymes involved in neutral lipid synthesis, while DPA(mix) enhanced the degradation of [(14)C]neutral lipids with concomitant decrease in cytosolic lipid droplets accumulated in CHO-K1 cells. From analysis of autophagy marker proteins, DPA(mix) caused dose-dependent induction of microtubule-associated protein light chain 3-II (LC3-II) and degradation of p62. In the autophagic flux assay using bafilomycin A(1), DPA(mix) upregulated autophagosome turnover. These results reveal that DPA(mix) enhances neutral lipid degradation together with induction of autophagy.