Contribution of non-ionic interactions on bile salt sequestration by chitooligosaccharides: Potential hypocholesterolemic activity

abstract

Chitooligosaccharides have been suggested as cholesterol reducing ingredients mostly due to their ability to sequestrate bile salts. The nature of the chitooligosaccharides-bile salts binding is usually linked with the ionic interaction. However, at physiological intestinal pH range (6.4 to 7.4) and considering chitooligosaccharides pKa, they should be mostly uncharged. This highlights that other type of interaction might be of relevance. In this work, aqueous solutions of chitooligosaccharides with an average degree of polymerization of 10 and 90 % deacetylated, were characterized regarding their effect on bile salt sequestration and cholesterol accessibility. Chitooligosaccharides were shown to bind bile salts to a similar extent as the cationic resin colestipol, both decreasing cholesterol accessibility as measured by NMR at pH 7.4. A decrease in the ionic strength leads to an increase in the binding capacity of chitooligosaccharides, in agreement with the involvement of ionic interactions. However, when the pH is decreased to 6.4, the increase in charge of chitooligosaccharides is not followed by a significant increase in bile salt sequestration. This corroborates the involvement of non-ionic interactions, which was further supported by NMR chemical shift analysis and by the negative electrophoretic mobility attained for the bile salt-chitooligosaccharide aggregates at high bile salt concentrations. These results highlight that chitooligosaccharides non-ionic character is a relevant structural feature to aid in the development of hypocholesterolemic ingredients.

authors

Filipe Coreta-Gomes, Inês M.V. Silva, Claudia Nunes, Ildefonso Marin-Montesinos, Dmitry Evtuguin, Carlos F.G.C. Geraldes, Maria João Moreno, Manuel A. Coimbra

our authors

acknowledgements

This research was funded by Fundaç ̃ao para a Ciˆencia e a Tecnologia (FCT)/MCTES for the support to the research units QOPNA (FCT UID/ QUI/00062/2019), LAQV-REQUIMTE (UIDB/50006/2020 & UIDP/ 50006/2020), CICECO (UIDB/50011/2020; UIDP/50011/2020 & LA/ P/0006/2020) and CQC (UIDB/00313/2020 & UIDP/00313/2020); and also supported by the projects PTDC/QUI-OUT/29373/2017 and POCI 01-0145-FEDER-031032, through national funds (OE) and where applicable co-financed by the FEDER, by the Operational Program of Competitiveness and Internationalization (POCI), within the PT2020 Partnership Agreement. I.M.V.S and F.M.C.G. were supported by master fellow and research contract framed on PTDC/QUI-OUT/29373/2017 and LAQV-REQUIMTE (UIDB/50006/2020) projects. C.N. was funded by national funds (OE), through FCT, I.P., within the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19.

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