A Fatty Diet Induces a Jejunal Ketogenesis Which Inhibits Local SGLT1-Based Glucose Transport via an Acetylation Mechanism—Results from a Randomized Cross-Over Study between Iso-Caloric High-Fat versus High-Carbohydrate Diets in Healthy Volunteers

Abstract

Background and aims: Insights into the nature of gut adaptation after different diets enhance the understanding of how food modifications can be used to treat type 2 diabetes and obesity. The aim was to understand how diets, enriched in fat or carbohydrates, affect glucose absorption in the human healthy jejunum, and what mechanisms are involved. Methods: Fifteen healthy subjects received, in randomised order and a crossover study design, two weeks of iso-caloric high-fat diet (HFD) and high-carbohydrate diet (HCD). Following each dietary period, jejunal mucosa samples were retrieved and assessed for protein expression using immunofluorescence and western blotting. Functional characterisation of epithelial glucose transport was assessed ex vivo using Ussing chambers. Regulation of SGLT1 through histone acetylation was studied in vitro in Caco-2 and human jejunal enteroid monolayer cultures. Results: HFD, compared to HCD, decreased jejunal Ussing chamber epithelial glucose transport and the expression of apical transporters for glucose (SGLT1) and fructose (GLUT5), while expression of the basolateral glucose transporter GLUT2 was increased. HFD also increased protein expression of the ketogenesis rate-limiting enzyme mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (HMGCS2) and decreased the acetylation of histone 3 at lysine 9 (H3K9ac). Studies in Caco-2 and human jejunal enteroid monolayer cultures indicated a ketogenesis-induced activation of sirtuins, in turn decreasing SGLT1 expression. Conclusion: Jejunal glucose absorption is decreased by a fat-enriched diet, via a ketogenesis-induced alteration of histone acetylation responsible for the silencing of SGLT1 transcription. The work relates to a secondary outcome in ClinicalTrials.gov (NCT02088853).

Morphological Adaptation in the Jejunal Mucosa after Iso-Caloric High-Fat versus High-Carbohydrate Diets in Healthy Volunteers: Data from a Randomized Crossover Study

“…Apparently, the HCD induced enlargement of the basal parts of the microvilli which carry the transport capacity, mainly for sugars. This goes hand in hand with our previous report that also showed an increased ability of glucose uptake via the sodium glucose transporter 1 (SGLT1) following HCD compared to HFD [ 8 ].…”

“…On day 14 in each dietary period, the volunteers underwent enteroscopy with biopsy sampling from the jejunum. The jejunal epithelial monosaccharide transporters in these biopsies have been reported elsewhere [ 8 ].…”

“…We have recently shown that the jejunum of the small intestine can express the rate-limiting ketogenic enzyme mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (HMGCS2) and produce ketone bodies during prolonged consumption of a diet high in fat [ 17 ]. In another of our previous studies, we showed that expression of jejunal HMGCS2 was increased after HFD [ 8 ]. To investigate if the amount of HMGCS2 expression in the enterocytes is linked to the number of mitochondria, we performed confocal scanning microscopy along the villus-axis in a number of experiments.…”

“…Intra-individual comparisons of the HCD- and the HFD-exposed mucosae were carried out at the end of the dietary period. Two reports have already been published regarding this study: a first report on the systemic glucose clearance following a mixed meal test performed on day 12 for each diet [ 7 ], and a second on glucose transport in jejunal biopsies taken on day 14 for each diet [ 8 ]. The present third paper is a morphological report with the aim to describe the epithelial enlargement of the jejunal villi comparing the HCD and HFD, including immunohistochemical aspects of the proliferation and apoptosis.…”

“…We also studied the ultrastructural aspects of the surface enterocytes and their mitochondria. In the previous study, we concluded that jejunal glucose absorption is decreased by the HFD via the ketogenesis rate-limiting enzyme mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (HMGCS2) [ 8 ]. Therefore, as a final aim, we wanted to study the co-location of HMGCS2 and mitochondria following each diet.…”