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

Abstract

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.

Antidiabetic effect of olive leaf extract on streptozotocin-induced diabetes mellitus in experimental animals

“…(2020) reported that olive leaf therapy exhibited hepatoprotective effects by decreasing ALT and AST levels due to its antioxidant properties (11). Although our findings are in agreement with the study by Fki et al, the decrease in ALT and AST levels was not significant in our treated diabetic rats (Fig.…”

“…In the previous studies, oleuropein has been reported to be a peroxisome proliferator-activated receptor α (PPARα) ligand, and oleuropein treatment reduces in rat hepatocytes the activity of the rate(HMG-CoA) reductase (28,29). Moreover, it was reported that treatment with olive leaves significantly decreased serum cholesterol and triglyceride levels in rats fed a high fat diet(11). Similarly, we found that treatment with low-dose olive leaf extract significantly reduced serum total cholesterol (p < 0.01), but resulted in no significant improvement in triglyceride levels (Fig.…”

Oleuropein protects against lipopolysaccharide‐induced sepsis and alleviates inflammatory responses in mice

“…In our study, LPS challenge resulted in a 100% mortality rate at the seventh day, whereas, OLE pretreatment increased the survival rate to 66.3%. Oleuropein has been recorded to have valuable cardioprotective, antioxidant, 22,23 and anti-inflammatory effects. 24 Sepsis can induce disorders in many organs and lead to death.…”

Functional compounds from olive pomace to obtain high‐added value foods – a review

“…Olive leaves constitute 10% of the raw material sent to oil mills, 7‐10 and are a source of antioxidant compounds with different uses and properties (i) as ingredients to obtain functional foods 11‐16 ; (ii) as natural preservatives, as substitutes for chemical ones, exploiting their antioxidant and antimicrobial effects to increase the shelf‐life of foods and then reduce the food lost; 13‐18 (iii) in the biomedical field with studies on genotoxicity, antinflammatory, anti‐carcinogenic, and other health‐related effects 19,20 …”