Did you know that olive leaf and fruit compounds have many pharmacological activities? In this article, we are going to show you how olive leaf and fruit extracts can promote your health and repair your body.

If you are a fan of healthy food and lifestyle, then you should have probably heard of the Mediterranean diet. Olive oil and fruit are some of the main components of this diet. Olea europaea, which is the botanical name of the olive tree, is native to the Mediterranean Region. This tree has been around for thousands of years. Olive tree products, such as olive leaf extract, have been used for centuries by local phytotherapists to treat different medical disorders.

Virgin olive oil is one of the healthiest and most expensive vegetable oils. The main active constituents of olive oil include oleic acid, phenolic constituents, and squalene. The main phenolic compounds, hydroxytyrosol, and oleuropein give extra-virgin olive oil its bitter, pungent taste. They are also present in olive leaf extract with higher concentrations. Researchers have linked these compounds to many pharmacological activities including antioxidant, anti-inflammatory, anti-atherogenic, anti-cancer activities, antimicrobial activity, antiviral activity, hypolipidemic and hypoglycemic effects.

Bioactive compounds in olive fruits and leaves

Phenolic compounds are found in all parts of the olive plant. However, their nature and concentration vary between various tissues of the plant. In Olea europaea, oleuropein is generally the most prominent phenolic compound in olives.

In the fruits, phenolic compounds represent 1– 3% of the olive dry weight. Oleuropein makes up to 19% and flavonoids can represent up to 1.8% of the dry weight of leaves. Oleuropein not only occurs in the Olea genus but also occurs in many other genera belonging to the Oleaceae family. It has even been described in Fraxinus excelsior.

Oleuropein belongs to the secoiridoids, which are abundant in Oleaceae, Gentianaceae, and Cornaleae, as well as many other plants. There are three phases in the development of the olive fruit:

a growth phase, during which accumulation of oleuropein occurs
a green maturation phase that coincides with a reduction in the levels of chlorophyll and oleuropein
a black maturation phase that is characterized by the appearance of anthocyanins and during which the oleuropein levels continue to fall.

Phenolic compounds chemistry

Oleuropein is very abundant in the early stages: in young fruits, it can reach 14% of dry matter. Although lower, its level is still very important at harvest for green-picked cultivars. In black cultivars, its level declines rapidly during maturation; in some varieties (Oeuropaea var leccino), it can even fall to zero when the fruits are completely black. During black maturation, new compounds appear such as demethyloleuropein which becomes the major constituent of black olives. The fruit of Olea europaea appears to accumulate only glucosylated derivatives of oleuropein. The decline in oleuropein also coincides with the decline in other quantitatively less important oleosides and the increase in other phenolic compounds.

Oleuropein metabolites such as elenolic acid glucoside and hydroxytyrosol are indicators for the maturation of olives. Oleuropein is also involved in the browning that occurs in green table olives after impact and wounding during harvesting or subsequent processing treatments. Therefore, the degree of browning varies considerably depending on the physiological stage of the fruit. Browning correlates with the oleuropein content.

Is oleuropein highly bioavailable?

Phenolic compounds from virgin olive oil are highly bioavailable. Their absorption level can reach 55–60% in human subjects. Our body transforms these compounds mainly into hydroxytyrosol or tyrosol and excretes them in urine. Oleuropein metabolites are rapidly absorbed, distributed, and excreted after oral administration with a maximum plasma concentration occurring 2 h after administration. Hydroxytyrosol is the most important metabolite of oleuropein.

Olive phenolic compounds health benefits

Olive phenolic compounds, especially oleuropein, have several pharmacological properties that help you keep your health. These properties include antioxidant, anti-inflammatory, anti-atherogenic, anti-cancer, antimicrobial, and antiviral activities. For these reasons, it is commercially available as a food supplement. Oleuropein is also cardioprotective against acute cardiotoxicity caused by cancer treatment drugs such as adriamycin. In addition, it exhibits anti-ischemic and hypolipidemic activities.

1 | Antioxidant activity

Oleuropein potently inhibits the induced oxidation of low-density lipoproteins (LDL) in a dose-dependent manner. It has both the ability to scavenge nitric oxide and to cause an increase in protective enzyme expression in the cell. Oleuropein scavenges oxidative substances produced at inflammation sites that can cause damage to your body.

Researchers found that the addition of oleuropein to diets increases the ability of LDL to resist oxidation and at the same time reduces the plasma levels of total, free, and esterified cholesterol. Other researchers found that oleuropein and its derivatives protect the heart against ischemia. They also reduce lipid peroxidation in a dose-dependent manner.

2 | Anti-inflammatory effect

Oleuropein increases nitric oxide (NO) production in macrophages and the overall functional activity of these immunocompetent cells. The anti-inflammatory effects of oleuropein come from its ability to inhibit hypoxygenase enzyme activity and to produce leukotriene B4.

3 | Anti-atherogenic effect

Researchers reported that oleuropein reduces monocytoid cell adhesion to endothelium. In ischemic hearts, oleuropein prevented membrane lipid peroxidation, a key factor in the pathogenesis of atherosclerosis.

4 | Antimicrobial effect

Oleuropein has a strong antimicrobial activity against both Gram-negative and Gram-positive bacteria as well as mycoplasma. Phenolic structures similar to oleuropein seem to produce an antibacterial effect by damaging the bacterial membrane. However, the exact mechanism of the antimicrobial activity of oleuropein is still not completely established. The antimicrobial activity mechanism is probably related to the direct stimulation of phagocytosis as a response of the immune system to microbes of all types.

Oleuropein and hydrolysis products are able to inhibit the development and production of enterotoxin B by Staphylococcus aureus, the development of Salmonella enteritidis, and the germination and consequent development of spores of Bacillus cereus. Oleuropein and other phenolic compounds completely inhibit the development of Klebsiella pneumoniae, Escherichia coli, and B. cereus. They also inhibit the development of Campylobacter jejuni, Helicobacter pylori, and methicillin-resistant Staphylococcus aureus (MRSA). These compounds may also play a role in regulating the composition of the gastric flora by selectively reducing levels of H. pylori and C. jejuni.

5 | Antiviral effect

Oleuropein has potent antiviral activities against herpes mononucleosis, hepatitis virus, rotavirus, bovine rhinovirus, canine parvovirus, and feline leukemia virus. Studies have also shown that oleuropein exhibits significant antiviral activity against the respiratory syncytial virus and para-influenza type 3 virus.

Researchers have demonstrated that oleuropein inhibits cell-to-cell transmission and replication of HIV in a dose-dependent manner. One of the suspected targets for olive leaf extract (mainly oleuropein) action is a glycoprotein responsible for HIV entry into normal cells.

6 | Anti-cancer effect

A plethora of constituents in olive leaves and fruits are effective agents in mitigating the initiation, promotion, and progression of multistage carcinogenesis.

A group of researchers showed that oleuropein inhibits the growth of glioblastoma cells and tumor cells derived from advanced-grade human tumors. Oleuropein aglycone is the most potent phenolic compound in decreasing breast cancer cell viability. They also found that cells amplified with HER2, a gene responsible for the development of breast cancer, are 5 times more sensitive to oleuropein aglycone than HER2-negative cells.

Another group of researchers found that olive secoiridoids induce strong tumoricidal effects by selectively triggering high levels of apoptotic cell death in breast carcinomas. These compounds markedly deplete HER2 protein in a dose- and time-dependent manner. Oleuropein also inhibits the rate of cell proliferation and induces cancerous cell apoptosis. These cells include breast adenocarcinoma cells, urinary bladder carcinoma cells, and brain capillary endothelial cells.

7 | Skin protectant

Phenol components of olive oil have a direct antioxidant action on the skin. Oleuropein, which acts as a free radical scavenger at the skin level, is the most potent antioxidant compound. Researchers reported that olive leaf extracts and oleuropein can protect against chronic UVB-induced skin damage, carcinogenesis, and tumor growth.

8 | Anti-aging

Recent studies demonstrated that oleuropein enhances anti-aging enzyme activities in vitro more effectively than other known chemical activators. Moreover, continuous treatment with oleuropein decreases the intracellular levels of reactive oxygen species (ROS). Importantly, oleuropein-treated cell cultures exhibit a delay in the appearance of senescence morphology, and their life span is extended by approximately 15%.

9 | Neuroprotective activity

Mitochondrial membranes are very sensitive to free radical attacks which leads to the production of cognitive and neurodegenerative diseases. A study has reported that oleuropein decreases or even prevent sequels of Alzheimer’s disease. The potential effect of oleuropein on brain function is analogous to atherosclerosis because they both are age-dependent diseases. Polyphenolic natural extracts, such as oleuropein, are effective against age-dependent diseases.

Other activities

Olive phenolic compounds have other diverse healing properties including vasodilatory, anti-platelet aggregation, hypotensive, anti-rheumatic, diuretic, and antipyretic effects. Prevention of free radical formation by oleuropein occurs through its inhibitory effect on several inflammatory enzymes. Oleuropein has also an anti-hyperglycemic effect. Additionally, it inhibits hyperglycemia and oxidative stress induced by diabetes. Therefore, the administration of oleuropein is helpful in the prevention of diabetes with oxidative stress complications.

Conclusion

Oleuropein, the main bioactive compound present in olives and olive leaves, and hydroxytyrosol, the principal degradation product of oleuropein, protect against coronary heart disease and many types of cancers. They also exhibit many pharmacological activities including antioxidant, anti-inflammatory, anti-atherogenic, anti-cancer activities, antimicrobial activity, antiviral activity, hypolipidemic and hypoglycemic effects.