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

Abstract

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 [¹⁴C]neutral lipid ([¹⁴C]triacylglycerol (TG) and [¹⁴C]cholesteryl ester (CE)) synthesis from [¹⁴C]oleic acid in Chinese hamster ovary-K1 (CHO-K1) cells. DPA2 inhibited [¹⁴C]TG and [¹⁴C]CE synthesis (IC₅₀s_, 0.65 and 5.6 μM, respectively), but DPA1 had no inhibitory activity on [¹⁴C]TG and [¹⁴C]CE synthesis even at 12 μM. However, a 1:1 mixture of DPA1 and DPA2 (DPA_mix) had the most potent inhibitory activity on [¹⁴C]TG and [¹⁴C]CE synthesis (IC₅₀s, 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 [¹⁴C]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 A₁, DPA_mix upregulated autophagosome turnover. These results reveal that DPA_mix enhances neutral lipid degradation together with induction of autophagy.