Elsevier

Food Chemistry

Volume 88, Issue 1, November 2004, Pages 11-15
Food Chemistry

Involvement of oleuropein in (some) digestive metabolic pathways

https://doi.org/10.1016/j.foodchem.2004.01.029Get rights and content

Abstract

Olive oil is the principal source of fats in the Mediterranean diet and it has been postulated that the components in olive oil can contribute to a lower incidence of coronary heart disease and cancers (prostate, colon, breast, and skin). The positive effects on human health can be attributed to the high level of phenolic compounds present in olive oil, the major ones being oleuropein, hydroxytyrosol and tyrosol. The aim of the present study was to evaluate the effect of oleuropein on enzymes involved in specific pathways of metabolism of proteins, carbohydrates and lipids.

In particular, the effects of oleuropein on enzymes, such as trypsin, pepsin, lipase, glycerol dehydrogenase, glycerol-3-phosphate dehydrogenase, and glycerokinase, were investigated.

Results demonstrate that oleuropein is able to activate pepsin and shows an inhibitory effect toward all the other enzymes tested, which suggests a new role for this polyphenol. In addition, a new method for lipase activity assay is presented.

Introduction

Since antiquity, oil obtained from the fruit of the olive (Olea europaea) has been considered to have many medicinal properties (Holy Bible). In recent years, various researches have shown that polyphenols, or sec-iridoids, present in olive oil act as antihypertensive, antithrombotic, antibacterial, antiviral, antidepressant, antioxidant (Manna et al., 2002), antiatherosclerotic, hypoglycemic (Le Tutor & Guedon, 1992; Gonzalez et al., 1992; Driss, Duranthon, & Viard, 1996) hypocholesterolemic (Ficarra, Ficarra, de Pasquale, Monforte, & Calabro, 1991) and antiatherogenic (Visioli & Galli, 2001) agents. The constitution of olive oil is primarily triacylglycerols and ∼0.5–1.0% non-glyceridic constituents. It is also the source of at least 30 phenolic compounds, its phenolic content depending on a number of factors, the main one being the production and storage of the oil (Brenes, Garcia, Garcia, & Garrido, 2001). The major phenolic compounds in olive oil are oleuropein, hydroxytyrosol and tyrosol. Other polyphenols, such as vanillic acid, p-coumaric acid, vanillin, demethyloleuropein, homoorientin, verbascoside, rutin, luteolin 7-O-glucoside, apigenin 7-O-rutinoside, apigenin 7-O-glucoside, luteolin, oleuropein aglycone, cyanidin 3-O-glucoside, and finally cyanidin 3-O-rutinoside, are present, both in the leaves and in the olive oil (Romani, Mulinacci, Vinceri, & Cimato, 1999). Even if at lower activities, they have the same pharmacological properties as oleuropein (Gonzalez et al., 1992).

Recent studies have demonstrated that the average oleuropein content in olive oil from Apulia varies between 3.1 and 11 mg oleuropein/kg of oil and that it depends on cultivar (Perri, Raffaelli, & Sindona, 1999; Owen et al., 2000).

The aim of the present work is to investigate the possible effects of oleuropein on trypsin and pepsin, lipase, glycerol dehydrogenase, glycerol-3-phosphate dehydrogenase, and glycerolkinase, enzymes involved in glucidic, proteic, and lipidic metabolism.

Section snippets

Materials

Oleuropein was supplied from Extrasynthese; 3-Palmitoyl-sn-glycerol and glycerol were from Fluka. All other chemical reagents were from Sigma.

Enzyme activities assay

Trypsin, glycerol dehydrogenase and glycerol-3-phosphate dehydrogenase activities were calculated by continuous direct spectrophotometer assays, while pepsin activity was measured by a discontinuous direct spectrophotometer assay. All these assays were performed in a thermostatically controlled Varian DMS-90 spectrophotometer.

A discontinuous direct HPLC

Oleuropein effect on pepsin enzymatic activity

Pepsin shows, for hemoglobin, a Km=9.6 μM and a Vmax=0.0075 M min−1. As shown in Fig. 1, oleuropein proves to be an activator of pepsin activity.

Oleuropein effect on trypsin activity

The kinetic parameters of trypsin for the synthetic substrate N-benzoyl-DL-arginine p-nitroanilide were calculated and resulted in Km=0.434 mM and a Vmax=0.868 mM min−1. Furthermore, the effect of oleuropein on trypsin activity was investigated: the phenolic compound proved to be a competitive inhibitor toward trypsin with Ki=0.85 mM (Fig. 2).

Oleuropein effect on glycerol dehydrogenase activity

Glycerol

Discussion

In recent years, the number of reports describing the beneficial properties of olive oil has increased. These reports suggest that the components in olive oil may have more health benefits than previously thought and consequently there have been numerous experiments investigating the fate of olive oil constituents. We focussed our attention on oleuropein, one of the major polyphenols present in olive oil. Although many researchers have investigated its positive effects on human health, here we

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