The worldwide prevalence of metabolic diseases such as obesity, metabolic syndrome and type 2 diabetes shows an upward trend in recent decades. A characteristic feature of these diseases is hyperglycemia which can be associated with hyperphagia. Absorption of glucose in the small intestine physiologically contributes to the regulation of blood glucose levels, and hence, appears as a putative target for treatment of hyperglycemia. In fact, recent progress in understanding the molecular and cellular mechanisms of glucose absorption in the gut and its reabsorption in the kidney helped to develop a new strategy of diabetes treatment. Changes in blood glucose levels are also involved in regulation of appetite, suggesting that glucose absorption may be relevant to hyperphagia in metabolic diseases. In this review we discuss the mechanisms of glucose absorption in the small intestine in physiological conditions and their alterations in metabolic diseases as well as their relevance to the regulation of appetite. The key role of SGLT1 transporter in intestinal glucose absorption in both physiological conditions and in diabetes was clearly established. We conclude that although inhibition of small intestinal glucose absorption represents a valuable target for the treatment of hyperglycemia, it is not always suitable for the treatment of hyperphagia. In fact, independent regulation of glucose absorption and appetite requires a more complex approach for the treatment of metabolic diseases.
Lactic acid bacteria (LAB) are often used for prevention and treatment of dysbiosis.
However, the action of various strains of LAB on metabolism and digestion under these
conditions are poorly understood. The purpose of this study was to investigate the
influence of probiotic LAB on metabolism, digestion and microbiota in animals with
dysbiosis. After administration of ampicillin and metronidazole male Wistar rats, were fed
products containing Enterococcus faecium L3 (E.f.), Lactobacillus
fermentum Z (L.f.) or milk (control 1). Animals in control
group 2 were fed milk, after water instead of antibiotics. Dyspeptic symptoms disappeared
after administration of probiotic compared with control 1. At the end of the experiment,
an increase in the content of enterococci and lactobacilli in the proximal part of the
small intestine was found in the animals treated with E.f. and
L.f., respectively. After the introduction of probiotic enterococci,
the quantity of lactobacilli and bifidobacteria in the intestines of rats increased, and
the content of Klebsiella spp. and Escherichia coli
decreased in comparison with the control group 1 and the group fed lactobacilli. The
activity of alkaline phosphatase and aspartate transaminase was greater in blood serum of
rats with dysbiosis receiving milk and lactobacilli. Intestinal alkaline phosphatase
activity increased in the epithelium and chyme in the jejunum of the animals treated with
L. f. and in the chyme only in the animals treated with E.
f. Thus, the specific effects of different strains of probiotic LAB on the
microbiota, and on metabolism and digestion of various nutrients were demonstrated.
The distribution of cytoskeleton elements (microtubules and actin filaments) and glucose trans porters SGLT1 or GLUT2 in enterocyte of rat intestine and Caco2 cells during hexose absorption was stud ied. Confocal microscopy revealed that the distribution of SGLT1 and GLUT2 transporters in absorptive cells of the intestinal villus was altered depending on maltose concentration. The transporters were colocal ized with actin. An increased number of vesicles close to microtubules in the apical cell part during absorption of high hexoze concentration was observed with electron microscopy. This observation, as well as uncovered colocalization of the transporters and actin, as well as actin and α tubulin, suggests that elements of the cytoskeleton participate in the translocation of glucose transporters to the apical cell membrane.
Previous studies have shown two components of glucose absorption in the small intestine: a secondary active transport through SGLT1, and unsaturated component, recently attributed mainly to the facilitated diffusion through GLUT2, but the relationship between these two components under physiological conditions remains controversial. In chronic experiments on nonanesthetized rats we investigated for the first time the kinetics of maltose hydrolysis and glucose absorption in the isolated loop of the small intestine in a wide range of maltose and glucose concentrations (25 -200 mmol/l glucose). The processes were simulated on mathematical models which took into account the current views about mechanisms of hydrolysis and transport of nutrients and geometric characteristics of the intestinal surface. The results of chronic experiments and mathematical simulation have shown that under the close to physiological conditions the glucose transport mediated by SGLT1 is the main mechanism of its absorption in comparison with the unsaturated component. This was demonstrated not only at low, but also at high substrate concentrations. We conclude that correct evaluation of the relative contribution of different mechanisms in glucose transport through the intestinal epithelium requires taking into account the geometric specificities of its surface.
In recent years, great interest has arisen in the use of autoprobiotics (indigenous bacteria isolated from the organism and introduced into the same organism after growing). This study aimed to evaluate the effects of indigenous bifidobacteria on intestinal microbiota and digestive enzymes in a rat model of antibiotic-associated dysbiosis. Our results showed that indigenous bifidobacteria (the Bf group) accelerate the disappearance of dyspeptic symptoms in rats and prevent an increase in chyme mass in the upper intestine compared to the group without autoprobiotics (the C1 group), but significantly increase the mass of chyme in the colon compared to the C1 group and the control group (healthy animals). In the Bf group in the gut microbiota, the content of opportunistic bacteria (Proteus spp., enteropathogenic Escherichia coli) decreased, and the content of some beneficial bacteria (Bifidobacterium spp., Dorea spp., Blautia spp., the genus Ruminococcus, Prevotella, Oscillospira) changed compared to the control group. Unlike the C1 group, in the Bf group there was no decrease in the specific activities of maltase and alkaline phosphatase in the mucosa of the upper intestine, but the specific activity of maltase was decreased in the colon chyme compared to the control and C1 groups. In the Bf group, the specific activity of aminopeptidase N was reduced in the duodenum mucosa and the colon chyme compared to the control group. We concluded that indigenous bifidobacteria can protect the microbiota and intestinal digestive enzymes in the intestine from disorders caused by dysbiosis; however, there may be impaired motor function of the colon.
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