Lipases and phenolic aggregates : Characterization, inhibition and interaction

Sammanfattning: In recent decades, obesity has gone from being a problem of first world countries to a global one. It is considered one of the main risk factors for many serious medical conditions. In order to treat and/or prevent obesity different strategies have been considered, one of the most common being the inhibition of lipase, the enzyme that is mainly responsible for lipid digestion. Even though there is a commercial drug that can inhibit lipase (orlistat), the most accessible treatment for obesity is based on the intake of a healthy diet. For example, some studies show that a diet rich in phenolic compounds is related to a low obesity index and that this can be related to their potential to inhibit lipase. The obesity studies based on lipase inhibition make use of endogenous lipases, such as gastric and pancreatic lipase, but there have been no studies of exogenous lipases, such as from probiotics, even though there are studies that reveal that probiotics could have an effect on obesity. Thus, in the present thesis, two potential lipases from Biffidobacterium longum NCC 2705 and Lactobacillus rhamnosus GG were investigated. Both were produced and characterized. The results indicate that both are active under physiological conditions in their monomeric forms. Also, they were able to hydrolyze long‐chain acyl groups (>C10), hence they present lipase activity. The inhibition of lipase by phenolic compounds has been widely investigated. The results indicate that the inhibition takes place at molecular levels when the phenolic compounds are considered soluble. From the literature it is known that some phenolic compounds have low solubility in aqueous systems and they can form aggregates in solution. Thus, understanding the role that these phenolic aggregates play in lipase inhibition could help to comprehend their relevance in lipid digestion. For the aforementioned, the interaction between pancreatic lipase and phenolic aggregates was also investigated in the present thesis. The results suggest that, among the studied phenolic compounds, flavonoids are more prone to form aggregates in aqueous medium and that the presence of these aggregates in a solution could affect the reproducibility of lipase assays. Three flavonoids were chosen in order to study in detail their interaction with lipase (myricetin, quercetin and EGCG). All of them were able to form aggregates in water and in the presence of lipase under simulated intestinal conditions. These aggregates have shown to interact with lipase by a sequestering mechanism under the intestinal conditions that were tested, in which it was found that lipase was in its monomeric form. The results of this thesis suggest that lipase inhibition by phenolic compounds can occur both by molecular mechanism, such as non‐competitive inhibition, and by a sequestering mechanism when phenolic aggregates are formed. The phenolic concentrations used in this thesis are common values found in drinkable products, therefore, the results from this thesis suggest that the inhibition by aggregates take place in real conditions.