Bioconversion of Citrus unshiu peel extracts with cytolase suppresses adipogenic activity in 3T3-L1 cells

Background/objectives: Citrus flavonoids have a variety of physiological properties such as anti-oxidant, anti-inflammation, anti-cancer, and anti-obesity. We investigated whether bioconversion of Citrus unshiu with cytolase (CU-C) ameliorates the anti-adipogenic effects by modulation of adipocyte differentiation and lipid metabolism in 3T3-L1 cells.

Materials/methods: Glycoside forms of Citrus unshiu (CU) were converted into aglycoside forms with cytolase treatment. Cell viability of CU and CU-C was measured at various concentrations in 3T3L-1 cells. The anti-adipogenic and lipolytic effects were examined using Oil red O staining and free glycerol assay, respectively. We performed real time-polymerase chain reaction and western immunoblotting assay to detect mRNA and protein expression of adipogenic transcription factors, respectively.

Results: Treatment with cytolase decreased flavanone rutinoside forms (narirutin and hesperidin) and instead, increased flavanone aglycoside forms (naringenin and hesperetin). During adipocyte differentiation, 3T3-L1 cells were treated with CU or CU-C at a dose of 0.5 mg/ml. Adipocyte differentiation was inhibited in CU-C group, but not in CU group. CU-C markedly suppressed the insulin-induced protein expression of CCAAT/enhancer-binding protein α (C/EBPα) and peroxisome proliferator-activated receptor gamma (PPARγ) as well as the mRNA levels of CEBPα, PPARγ, and sterol regulatory element binding protein 1c (SREBP1c). Both CU and CU-C groups significantly increased the adipolytic activity with the higher release of free glycerol than those of control group in differentiated 3T3-L1 adipocytes. CU-C is particularly superior in suppression of adipogenesis, whereas CU-C has similar effect to CU on stimulation of lipolysis.

Conclusions: These results suggest that bioconversion of Citrus unshiu peel extracts with cytolase enhances aglycoside flavonoids and improves the anti-adipogenic metabolism via both inhibition of key adipogenic transcription factors and induction of adipolytic activity.