Spirogyra neglecta inhibits the absorption and synthesis of cholesterol in vitro

BACKGROUND Spirogyra neglecta (SN) has many nutritional benefits and it is commonly used to ameliorate different human conditions including inflammation, gastric ulcer, hyperglycemia, and hyperlipidemia. However, the mechanism of the hypocholesterolemic effect of SN still remains unclear. Therefore, the present study was aimed to evaluate the effect of SN extract particularly on cholesterol absorption and synthesis mechanisms. METHODS For cholesterol absorption, the uptake of cholesterol was measured by using tritium radiolabeling of cholesterol in Caco-2 cells. Bile acid binding, micelles size, and cholesterol solubility were analyzed in in vitro assays, while cholesterol synthesis was evaluated by using a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase assay kit. RESULTS SN extract was found to decrease cholesterol uptake in Caco-2 cells and decreased the solubility of cholesterol in micelles. The SN extract bound to taurocholate, taurodeoxycholate, and glycodeoxycholate bile acids, and increased micelles size. SN has also demonstrated an inhibitory effect on HMG-CoA reductase (HMGR) enzymatic activity. For further experimentation, the treatment combination of SN and ezetimibe (0.04 mg/mL) showed a greater significant reduction in cholesterol uptake than the extract alone. CONCLUSION These observations suggested that inhibitory cholesterol absorption effects of SN could be mediated through the modulation of size and solubility of cholesterol micelles, resulting in interference of cholesterol uptake. In addition, SN inhibited the rate limiting step of cholesterol synthesis. This study provides supporting evidence for the potential usage of SN as a cholesterol lowering agent.