Obesity has been increasing worldwide and has become a major factor contributing to health complications for millions of people. The accelerating obesity rate raises more concerns, for nutritionists and physicians now know that obesity is related directly or indirectly to diseases such as diabetes, cancer, hypertension, and osteoarthritis, and with some cardiovascular diseases.
Adipocyte differentiation, known as adipogenesis, is the process of fat cell development, accompanied by dramatic alteration in the cellular pattern of gene expression and protein synthesis. It is well-known that the adipocyte differentiation and the extent of subsequent fat accumulation are closely related to obesity. For these reasons, many studies have been conducted to find food ingredients for weight control without a side effect from natural resources using 3T3-L1 as a useful in vitro model to assess the adipogenic regulatory mechanism. Traditional edible marine algae are also a valuable source for finding new food ingredients.
Ecklonia cava is a member of the family of Laminariaceae and is widely recognized as a very prolific source of biologically active compounds. The collected samples of E. cava were extracted for 3 hours under reflux. Their crude extracts were partitioned between CH2Cl2 and water. The organic layer was further partitioned between 85% aq MeOH and n-hexane and then the aqueous layer was fractionated with n-BuOH and H2O, repectively. Among the solvent fractions from E. cava, the n-BuOH fractions most effectively reduced the levels of triglyceride accumulation, of glucose consumption, and of adipogenesis-related genes. Further purification of the n-BuOH fraction led to the isolation of six phlorotannins. Their chemical structures were determined by extensive 2D NMR experiments such as 1H gDQCOSY, TOCSY, NOESY, gHMQC, and gHMBC, and by comparison with published spectral data.
Potential inhibitory effects of these phlorotannins on adipogenic differentiation were also estimated in 3T3-L1 cells. Intracellular lipid accumulation levels were compared by measuring triglyceride accumulation in adipocytes, and glucose consumption, glycerol and leptin secretions in the cultured medium. All phlorotannins suppressed lipid accumulation in a dose-dependent manner. The expression levels of several genes related to adipogenesis including transcription factors were examined using reverse-transcription polymerase chain reaction (RT-PCR). Among compounds tested, dieckol (6) exhibited the highest down-regulation for most genes related to adipogenesis such as adipogenic transcription factors (C/EBPα, PPARγ, and SREBP1) and adipocyte-specific genes (FABP4, FATP1, FAS, LPL, ACS1, perilipin, and TNF-α) at the concentration of 50 μM, followed by eckol (3).
Taken together, our findings suggest that phlorotannins may serve as the useful molecules in both basic and clinical research on adipocyte differentiation and as a potential lead compound for the treatment of obesity.