Abstract
BackgroundVisceral fat accumulation is one of the most important predictors of mortality in obese populations. Administration of green tea extract (GTE) can reduce body fat and reduce the risk of obesity-related diseases in mammals. In this study, we investigated the effects and mechanisms of GTE on adiposity in diet-induced obese (DIO) zebrafish.MethodsZebrafish at 3.5 to 4.5 months post-fertilization were allocated to four groups: non-DIO, DIO, DIO + 0.0025%GTE, and DIO + 0.0050%GTE. The non-DIO group was fed freshly hatched Artemia once daily (5 mg cysts/fish daily) for 40 days. Zebrafish in the three DIO groups were fed freshly hatched Artemia three times daily (60 mg cysts/fish daily). Zebrafish in the DIO + 0.0025%GTE and DIO + 0.0050%GTE groups were exposed to GTE after the start of feeding three times daily for 40 days.ResultsThree-dimensional microcomputed tomography analysis showed that GTE exposure significantly decreased the volume of visceral but not subcutaneous fat tissue in DIO zebrafish. GTE exposure increased hepatic expression of the lipid catabolism genes ACOX1 (acyl-coenzyme A oxidase 1, palmitoyl), ACADM (acyl-coenzyme A dehydrogenase, c-4 to c-12 straight chain), and PPARA (peroxisome proliferator-activated receptor alpha). GTE exposure also significantly decreased the visceral fat expression of SOCS3 (suppressor of cytokine signaling 3b) which inhibits leptin signaling.ConclusionsThe present results are consistent with those seen in mammals treated with GTE, supporting the validity of studying the effects of GTE in DIO zebrafish. Our results suggest that GTE exerts beneficial effects on adiposity, possibly by altering the expression of lipid catabolism genes and SOCS3.
Highlights
Visceral fat accumulation is one of the most important predictors of mortality in obese populations
This effect was accompanied by increase hepatic expression of lipid catabolism genes. These results are very consistent with the findings of previous studies in humans [12,14] and rodents [10,11,13,14,35,36,37]. It is unclear whether the functions of visceral and subcutaneous fat in zebrafish are homologous to those in mammals, our findings indicate that body fat distribution is present in zebrafish as well as in humans and animals and that the site-specific effects of green tea extract (GTE) are similar to those in mammals
High-fat diet in wild-type rodents and is reduced in obese humans [39]. Their results help support the notion that adipose tissue gene expression profiles differ among species, and the lack of consistency between our data and those of Park et al our present results suggest that the mechanism by which GTE suppresses body fat accumulation, at least in the liver, in zebrafish is similar to that in rodents
Summary
Visceral fat accumulation is one of the most important predictors of mortality in obese populations. Lipid metabolism in zebrafish is very similar to that in humans in terms of intestinal absorption with the aid of bile produced in the liver [26], transport of fat and cholesterol by lipoproteins [27], β-oxidation [28], and storage as triacylglycerols in visceral, subcutaneous, and intramuscular adipocyte depots [26,29] Because of these similarities and advantages, zebrafish are used in lipid metabolism research as a model for lipid-related diseases, including atherosclerosis induced by high-cholesterol diets [30] and obesity induced by overexpression of the endogenous melanocortin antagonist agouti-related protein (AgRP) [29]. DIO zebrafish have been used to validate the antiobesity effects of natural products [32]
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