Action of natural bioactive compounds on the enteroendocrine system
- Autores: Àngela Casanova Martí
- Directores de la Tesis: Montserrat Pinent Armengol (dir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Montserrat Pinent Armengol (presid.), J. E. Fortune (secret.), Brian Desmond Green (voc.)
- Programa de doctorado: Programa de Doctorado en Nutrición y Metabolismo por la Universidad Rovira i Virgili
- Materias:
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- Resumen
The dramatically increased prevalence of overweight and obesity, in both developing and developed societies, highlights the need to find preventive and management treatment of obesity and its metabolic-associated diseases. The gastrointestinal tract represents the largest endocrine organ in the body, comprising by enteroendocrine cells scattered throughout the gut mucosa, which secrete peptide hormones involved in the control of metabolism. At least 15 types of enteroendocrine cells have been described, which produces and secretes a variety of hormones or signaling molecules, including ghrelin, cholecystokinin (CCK) glucose-dependent insulinotropic peptide (GIP) glucagon-like peptides (GLPs) and peptide YY (PYY). These hormones act notably as intermediate markers in the regulation of glucose homeostasis and food intake. The focus of type 2 diabetes mellitus (T2DM) treatments is keeping blood glucose levels within the normal physiological range. With regards to body weight management, focusing on the regulation of food intake is one potential strategy as it is well known that the main causes of obesity is increased food intake coupled with decreases energy expenditure. Hence, the regulation of enteroendocrine system offers a substantial therapeutic target to maintain and improve health. In the last decade, scientific advances have aided the investigation of natural bioactive compounds to reduce obesity and related pathologies. Therefore, complementary strategies using natural bioactive compounds focused on the modulation of gut hormone profile might be a potential strategy to prevent or/and management of obesity and one of the most associated disease, T2DM.
This doctoral thesis was focused on defining the mechanisms of a known bioactive compound at intestinal level, i.e. grape seed proanthocyanidin extract (GSPE), specifically on the different mechanisms involved in enteroendocrine system modulation, as well as finding new ones, i.e. bioactive peptides derived from chicken leg, that might act through modulation of these intestinal mechanisms. To achieve our objective different models of study, including in vitro, ex vivo and in vivo models, were used.
The in vivo release of enterohormone occurs through direct sensing of luminal components, and also indirectly by vagal and humoral stimulation. Therefore, the first objective proposed was whether a grape-seed proanthocyanidin extract directly affect the release of the main enterohormones. Our results in ex vivo model demonstrated that GSPE act at several regions of GI tract and directly modulate the release of the main enterohormones. GSPE treatment decreased CCK release in duodenal segments and increased active GLP-1 levels in ileum segments, in agreement with previously observed in plasma levels of acute in vivo studies. Our results also indicated that GSPE directly act on GIP and PYY secretion in duodenal and ileum segments, respectively. GSPE is composed by different molecules that present distinct bioavailability; some of them are well absorbed in upper intestine, in front of others that reach the colon and are subjected to microbial catabolism. For this reason, microbiota-metabolized polyphenols of GSPE were used to treat ex vivo colon segments. The results suggested that molecules of GSPE that are well absorbed in the upper intestine are the responsible for direct inhibition of CCK release, as well as unabsorbed polyphenols (high degree of polymerization) and microbiota-metabolized polyphenols of GSPE directly act on endocrine cells to promote GLP-1 secretion.
Once we determined the direct modulation of enterohormone release by acute dose of GSPE, we wanted to determine, as second and third objectives, the mid-term effects of GSPE on enteroendocrine system. The organoids culture system was used to elucidate whether GSPE affect intestinal differentiation and an in vivo model was employed to clarify whether GSPE modulate intestinal gut microbiota and whether such modulation influence enteroendocrine system.
From results obtained in ileum organoids, we observed that GSPE up-regulated Chga gene expression, as well as gene expression of the main enterohormones associated with L- cells, GLP-1 and PYY. Accordingly, basal GLP-1 release was increased in mid-term treatment, but no changes were observed in PYY release. Moreover, our results point out that the stimulation of L-cell differentiation induced by GSPE is due to the modulation of the early-transcription factors (Ngn3) and late-transcription factors (Pax4, Pax6, Foxa1/2, and ARX). The effect of GSPE on markers of L-cell differentiation is also extended to others markers of epithelial cell lines, such as goblet, enterocyte, and stem cells.
GSPE could also affect the entroendocrine system in mid-term treatments through affecting gut micobiota, which is an important element of the intestinal environment and could be subject to alterations by diet components in a mid or long-term consumption. Several studies reported that flavanols unabsorbed by the upper intestine reaching the colon where they accumulate at high concentrations and are metabolised by gut microbiota. Therefore, it is described that the gut microbiota act on flavanols, but few information has been published about the inverse relation, the effect of flavanols on gut microbiota. The results obtained in this thesis revealed that the dose of 0.5g/kg BW of GSPE changed the gut microbial composition after mid-term treatment (8 days) in animals fed a standard diet. We demonstrated that 0.5g/kg BW of GSPE decrease Firmicutes/Bacteroidetes ratio in agreement with the general results obtained with polyphenols. Moreover, our results indicated that GSPE acts on lower levels of microbiome classification, altering specific genera. In this study, we described that new target taxonomic groups are influenced by proanthocyanidins, including Sutterella, Pharscolarctobacterium, Parabacteroides, Bilophila, and Ruminococcus. The correlation analysis showed some interaction where alterations in gut microbiota induced by GSPE are correlated with some metabolism parameters, especially with the increased active GLP-1 plasma levels.
In our fourth objective, we hypothesized that new natural bioactive compounds can also exert beneficial effect acting at different intestinal levels helping to prevent obesity and T2DM. In the screening of new compounds, bioactive peptides derived from protein hydrolyzates might be good candidates due to their structural characteristics and the effects that they exert in other points of the body. Accordingly with this, our fourth objective was to evaluate whether bioactive peptides derived from chicken leg modulate the incretin system through affecting GLP-1 cleavage and secretion. The in vitro results determine that chicken leg hydrolyzate inhibit DPP-IV. Moreover, the potential as natural DPP-IV inhibitor was employed to screen an array of different chicken leg hydrolyzate obtained by different enzymatic treatments. Although the inhibition of DPP-IV activity to enhance active GLP-1 plasma levels is important, the promotion of GLP-1 release by direct action on EECs is also a considerable strategy. The results obtained in vitro (STC-1 cell line) and ex-vivo models elucidated the direct effect of selected chicken leg hydrolyzate on GLP-1 release. The results determined that a chicken leg hydrolyzate inhibits DPPIV, and thereby chicken leg hydrolyzate affects GLP-1 cleavage and secretion. Both mechanisms of chicken leg hydrolyzate action explain the in vivo results obtained that show an improvement of glucose levels in disrupted-glucose homeostasis animals.
In conclusion, the findings obtained in this thesis point out that natural bioactive compounds act through different mechanisms on the enteroendocrine system in acute and mid-term treatments, and thereby could be good therapeutic agents to treat obesity and glucose homeostasis disruption.
