Bioassay-guided fractionation of the fermentation broth of Arctic Streptomyces nitrosporeus YBH10-5 resulted in the isolation of seven new compounds named nitrosporeunols A-G (1-7), together with seven known analogues (8-14). Their structures were determined based on extensive spectroscopic analysis. Compounds 1-14 were evaluated for the lowering lipid effects, while two compounds (10 and 12) remarkably decreased lipid levels including total cholesterol (TC) and triglycerides (TG) in HepG2 cells. Quantitative realtime PCR and Western blot indicated that farnesylquinone (12) increased the expression of the key proteins including peroxisome proliferator-activated receptor-α (PPARα), peroxisome proliferator-activated receptor-γ, and coactivator 1α (PGC-1α), as well as their downstream genes carnitine palmitoyltransterase-1 (CPT-1), acyl-coenzyme A oxidase 1 (ACOX), malonyl CoA decarboxylase 1 (MCD1), pyruvate dehydrogenase kinase 4 (PDK4), and cholesterol 7α -hydroxylase (CYP7A1). Luciferase assay showed that 12 increased the transcriptional activity of PPARα, while its lipid-lowering effect was abolished by PPARα inhibitor, MK886, in HepG2 cells. These findings suggested that 12 is a potent lipid-lowering agent which may decrease lipid levels through upregulation of PPARα pathway.
Keywords: Farnesylquinone; Lowering lipid effect; Nitrosporeunols A–G; PPARα pathway; Streptomyces nitrosporeus.
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