Pyridocarbazole alkaloids from Ochrosia borbonica: lipid-lowering agents inhibit the cell proliferation and adipogenesis of 3T3-L1 adipocyte via intercalating into supercoiled DNA.

Bioassay-guided fractionation of an ethanolic extract of Ochrosia borbonica led to the isolation of two known pyridocarbazole alkaloids, ellipticine (1) and 9-methoxyellipticine (2), and six known monoterpenoid indole alkaloids (3-8). Lipid-lowering assay in 3T3-L1 cell model revealed that 1 and 2 could significantly inhibit the lipid droplet formation (EC50 = 0.41 and 0.92 µmol·L-1, respectively) and lower triglyceride levels by 50%-60% at the concentration of 1 µmol·L-1, being more potent than the positive drug luteolin (EC50 = 2.63 µmol·L-1). A mechanistic study indicated that 1 and 2 could intercalate into supercoiled DNA, which consequently inhibited the mitotic clonal expansion of 3T3-L1 cells at the early differentiation phase, leading to the retardance of following adipogenesis and lipogenesis. These findings suggest that 1 and 2 may serve as promising leads for further development of anti-obesity drugs.

Discovery of natural alkaloid bouchardatine as a novel inhibitor of adipogenesis/lipogenesis in 3T3-L1 adipocytes.

Bouchardatine (1), a naturally occurring ß-indoloquinazoline alkaloid, was synthesized. For the first time, the lipid-lowering effect and mechanism of 1 was investigated in 3T3-L1 adipocytes. Our study showed that 1 could significantly reduce lipid accumulation without cytotoxicity and mainly inhibited early differentiation of adipocyte through proliferation inhibition and cell cycle arrested in dose-dependent manner. Furthermore, the inhibition of early differentiation was reflected by down-regulation of key regulators of adipogenesis/lipogenesis, including CCAAT enhancer binding proteins (C/EBPß, C/EBPδ, C/EBPα), peroxisome proliferator-activated receptors γ (PPARγ) and sterol-regulatory element binding protein-1c (SREBP-1c), in both of mRNA and protein levels. Subsequently decreasing the protein levels of acetyl CoA carboxylase (ACC), fatty acid synthase (FAS), and stearyl coenzyme A desaturated enzyme 1 (SCD-1), the rate-limited metabolic enzymes of fatty acid synthesis, were also observed. Further studies revealed that 1 persistently activated adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) during differentiation, suggesting that the AMPK may be an upstream mechanism for the effect of 1 on adipogenesis and lipogenesis. Our data suggest that 1 can be a candidate for the development of new therapeutic drugs against obesity and related metabolic disorders.