Jounal of Negative and No Positive Results (Mar 2020)
Influence of olive polyphenols on glucose and cholesterol levels in medaka fish
Abstract
Background. Polyphenol-rich olive extracts are non-toxic and have anti-inflammatory, neuroprotective and antiadipogenic effects in cell and animal models. Objective. To evaluate the potential influence of olive extracts on the mechanisms of digestion and absorption of polysaccharides and fats by quantifying amylase, glucose, phospholipase, and cholesterol in the medaka fish model. Material and methods. For each assay, six adult fish were placed in a tank with an extract (0.01% concentration), performing three replicates per extract. A control group with standard feeding was used. The same procedure was followed to study glucose, adding a polysaccharide-rich diet and a corresponding overfed control. The fish were maintained under these conditions for five days. Five olive extracts were used without attempting to purify the polyphenols due to possible synergistic effects. Total concentrations were between 2-116mg/g (mainly oleuropein and hydroxytyrosol). On completion, amylase, phospholipase A2, glucose and cholesterol were quantified in each group. All assays were conducted in triplicate. Enzyme activities were also studied in juveniles. Non-parametric tests were used to determine possible differences, considering p<0.05 to denote statistical significance. Results. Polyphenol extracts were not toxic at a concentration of 0.1%, ten times higher than the concentration used. An overall decrease in glucose levels was observed in fish overfed with carbohydrates with the addition of the extracts, but without returning to the levels in the control group with standard feeding (between 15-40% decrease). There was no impact on amylase in adults or juveniles, an overall but not significant decrease in cholesterol, and an overall increase in phospholipase in the juveniles. Conclusion. Olive extracts rich in polyphenols lower glucose levels in overfed fish.
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