Rhamnan sulphate from Monostroma nitidum attenuates hepatic steatosis by suppressing lipogenesis in a diet-induced obesity zebrafish model

Rhamnan sulphate (RS) is a sulphated polysaccharide from Monostroma nitidum. Here, the effects of RS on metabolic disorders using zebrafish with diet-induced obesity (DIO) were investigated. Oral administration of RS (250 µg/g BW/day) attenuated body weight gain, dyslipidaemia (plasma triacylglycerol and low-density lipoprotein cholesterol) and hepatic steatosis in DIO. In liver tissues, RS reduced gene expression levels of CCAAT/enhancer-binding protein alpha (cebpa) and acetyl-CoA carboxylase 1 (acacb), and increased peroxisome proliferator-activated receptor alpha b (pparab) expression. However, the expression levels of downstream genes of pparab (acadm and acox1) were not increased, suggesting that the lipid-lowering effect of RS might be caused mainly by inhibition of lipogenesis. To the best of our knowledge, this is the first study to demonstrate that RS has a powerful lipid-lowering effect in vivo. Intake of RS as a functional food may be suitable for obesity prevention and for reducing the prevalence of obesity-related diseases.