The accumulation of visceral adipose tissue usually results from an energy imbalance involving the combination of excessive calorie consumption with insufficient energy expenditure. Increased visceral adiposity can induce insulin resistance and lead to type 2 diabetes mellitus, dyslipidemia, hypertension, and cardiovascular disease.1) "Metabolic syndrome" is the combination of multiple cardiovascular risk factors, including visceral obesity, dyslipidemia, glucose intolerance, and hypertension in one individual.2,3) Obesity resulting from an accumulation of visceral adiposity is a primary cause of metabolic syndrome.Propolis is a sticky, resinous substance collected by honey bees (Apis mellifera) from the sap, leaves, and buds of plants, and then mixed with secreted beeswax. The chemical constituents of propolis are mainly flavonoids, phenolic compounds, caffeoylquinic acids, cinnamic acid derivatives, diterpenoic acid, lignan, coumarin acid and other compounds. 4,5) Propolis has been used as a folk medicine in many countries from ancient times especially in Brazil and Eastern Europe. It has been characterized variously as an anti-bacterial, 6,7) anti-viral, 8) anti-inflammatory, 9-11) anti-oxidant, 12) and anti-carcinogenesis agent. 13,14) Obesity is caused by various environmental and genetic factors.15) One of the main environmental factors causing obesity is the intake of a high-fat diet, now common in many populations. A diet-induced obesity animal model has been developed to investigate human obesity, replicating the effects of human obesity more accurately than genetic obesity models.16) Mice that are fed a high-fat diet, develop obesity, hyperglycemia, and hyperlipidemia, and differ from those fed a normal diet in the expression levels of specific genes transcripts.17) Recent studies have reported that propolis prevented and mitigated diabetes and hypertension, [18][19][20][21][22] but it remains unclear whether propolis similarly prevents and mitigates the accumulation of visceral adipose tissues and hyperlipidemia. In this study we examined the effect of propolis on visceral fat and hyperlipidemia induced in a high-fat dietinduced obesity mouse model, and analyzed hepatic gene expression involved in lipid metabolism.
MATERIALS AND METHODS
Preparation of Propolis ExtractPropolis used in this study was obtained from Apiai, Sao Paulo in Brazil. Propolis (1 kg) was treated with 50% ethanol (3 l) at room temperature for 24 h, and filtered. This extract included 10.8% of solid contents of propolis. Total flavonoids content in the extract was determined as amounts of quercetin by using the aluminum nitrate method as described previously.23) In addition, the extract was subjected to reversed-phase column chromatography using following conditions: column, Shim Pack CLC-ODS (6 mm i.d.ϫ150 mm, Shimadzu, Japan); column temperature, 50°C; gradient system, A solvent (30% MeOH, 70% H 2 O and 1% AcOH) and B solvent (75% MeOH, 25% H 2 O and 1% AcOH), 0-20 min 100% A isocratic, 20-55 min 100% B isocratic, 55-75 min 100% ...
