Obesity is recognized as an energy balance disorder in which energy input exceeds energy output. Recent medications approved for the treatment of obesity attempt to restore energy balance by reducing energy input by suppressing appetite or inhibiting lipid lipase to interfere with lipid absorption from the small intestine. Another potential strategy for the treatment is to block the synthesis of triacylglycerol (TG), the final storage form of free long-chain fatty acid. Therefore, inhibitors of TG synthesis are expected to be therapeutic agents for obesity. We established a high content assay to observe the TG biosynthetic pathway using intact animal cells.
During our screening for microbial inhibitors of TG synthesis in the cell-based assay utilizing Chinese hamster ovary (CHO-K1) cells, a new biaryl dihydronaphtopyranone, named dinapinone A was first isolated from the culture broth of Penicillium pinophilum FKI-3864. Dinapinone A showed to be a very potent inhibitor of TG synthesis in CHO-K1 cells with an IC₅₀ of 0.097 μM. We then elucidated the structure of dinapinone A by spectroscopic analyses including various NMR experiments, suggesting that dainapinone A was a mixture of isomers. Accordingly, HPLC by using a C30 column enables the separation of dinapinone A to atropisomer dinapinones A1 and A2 by circular dichroism spectral analysis. Dinapinone A1 did not inhibit TG synthesis even at 12 μM and dinapinone A2 showed less potent inhibition (IC₅₀; 0.65 μM) than dinapinone A. Interestingly, a mixture of isolated dinapinones A1 and A2 (1:1) recovered the potent TG inhibitory activity (IC₅₀; 0.054 μM).