Comparative Study on Beneficial Effects of Hydroxytyrosol- and Oleuropein-Rich Olive Leaf Extracts on High-Fat Diet-Induced Lipid Metabolism Disturbance and Liver Injury in Rats

Oleuropein and hydroxytyrosol, as major compounds of olive leaves, have been reported to exert numerous pharmacological properties, including anticancer, antidiabetic, and anti-inflammatory activities. The purpose of this study is to evaluate and compare the protective effect of oleuropein- and hydroxytyrosol-rich extracts, derived from olive leaves, on high-fat diet-induced lipid metabolism disturbance and liver injury in rats. In this respect, four groups of male rats (8 per group) were used: control group (Control), group treated with high-fat diet (HFD), group treated with HFD and oleuropein (HFD + OLE), and group treated with HFD and hydroxytyrosol (HFD + HYD). The current research showed that the treatment with the HFD increased the body weight and adipose tissue mass in male rats. Moreover, the plasma levels of triglycerides, total cholesterol, LDL-cholesterol, AST, ALT, LDH, and TNF-α were also raised. The hepatic immunohistochemical analysis revealed a significant increase in the expression of inflammatory genes (COX-2, NF-κB, and TNF-α). Equally, it showed a rise of the apoptotic markers (a decrease in the expression of the Bcl-2 and an increase of the P53). In addition, the oral administration of oleuropein- and hydroxytyrosol-rich olive leaf extracts at 16 mg/kg similarly reduced the body weight and adipose tissue mass and improved the lipid profile. Moreover, these extracts, mainly the hydroxytyrosol-rich extract, reduced the elevated liver enzymes, enhanced the antioxidant status, and attenuated the liver inflammation and apoptosis. These findings suggest that the oleuropein- and hydroxytyrosol-rich olive leaf extracts possessed hypolipidemic and hepatoprotective effects against the HFD-induced metabolic disorders by enhancing the antioxidative defense system and blocking the expression of the proteins involved in inflammation and liver damage.