Glucose but Not Fructose Alters the Intestinal Paracellular Permeability in Association With Gut Inflammation and Dysbiosis in Mice

A causal correlation between the metabolic disorders associated with sugar intake and disruption of the gastrointestinal (GI) homeostasis has been suggested, but the underlying mechanisms remain unclear. To unravel these mechanisms, we investigated the effect of physiological amounts of fructose and glucose on barrier functions and inflammatory status in various regions of the GI tract and on the cecal microbiota composition. C57BL/6 mice were fed chow diet and given 15% glucose or 15% fructose in drinking water for 9 weeks. We monitored caloric intake, body weight, glucose intolerance, and adiposity. The intestinal paracellular permeability, cytokine, and tight junction protein expression were assessed in the jejunum, cecum, and colon. In the cecum, the microbiota composition was determined. Glucose-fed mice developed a marked increase in total adiposity, glucose intolerance, and paracellular permeability in the jejunum and cecum while fructose absorption did not affect any of these parameters. Fructose-fed mice displayed increased circulation levels of IL6. In the cecum, both glucose and fructose intake were associated with an increase in Il13, Ifnγ, and Tnfα mRNA and MLCK protein levels. To clarify the relationships between monosaccharides and barrier function, we measured the permeability of Caco-2 cell monolayers in response to IFNγ+TNFα in the presence of glucose or fructose. In vitro, IFNγ+TNFα-induced intestinal permeability increase was less pronounced in response to fructose than glucose. Mice treated with glucose showed an enrichment of Lachnospiracae and Desulfovibrionaceae while the fructose increased relative abundance of Lactobacillaceae. Correlations between pro-inflammatory cytokine gene expression and bacterial abundance highlighted the potential role of members of Desulfovibrio and Lachnospiraceae NK4A136 group genera in the inflammation observed in response to glucose intake. The increase in intestinal inflammation and circulating levels of IL6 in response to fructose was observed in the absence of intestinal permeability modification, suggesting that the intestinal permeability alteration does not precede the onset of metabolic outcome (low-grade inflammation, hyperglycemia) associated with chronic fructose consumption. The data also highlight the deleterious effects of glucose on gut barrier function along the GI tract and suggest that Desulfovibrionaceae and Lachnospiraceae play a key role in the onset of GI inflammation in response to glucose.

Molecular liver fingerprint reflects the seasonal physiology of the grey mouse lemur (Microcebus murinus) during winter

Grey mouse lemurs (Microcebus murinus) are a primate species exhibiting strong physiological seasonality in response to environmental energetic constraint. They notably store large amounts of lipids during early winter (EW), which are thereafter mobilized during late winter (LW), when food availability is low. In addition, they develop glucose intolerance in LW only. To decipher how the hepatic mechanisms may support such metabolic flexibility, we analyzed the liver proteome of adult captive male mouse lemurs, which seasonal regulations of metabolism and reproduction are comparable to their wild counterparts, during the phases of either constitution or use of fat reserves. We highlight profound changes that reflect fat accretion in EW at the whole-body level, however, without triggering an ectopic storage of fat in the liver. Moreover, molecular regulations would be in line with the lowering of liver glucose utilization in LW, and thus with reduced tolerance to glucose. However, no major regulation was seen in insulin signaling/resistance pathways, which suggests that glucose intolerance does not reach a pathological stage. Finally, fat mobilization in LW appeared possibly linked to reactivation of the reproductive system and enhanced liver detoxification may reflect an anticipation to return to summer levels of food intake. Altogether, these results show that the physiology of mouse lemurs during winter relies on solid molecular foundations in liver processes to adapt fuel partitioning while avoiding reaching a pathological state despite large lipid fluxes. This work emphasizes how the mouse lemur is of primary interest for identifying molecular mechanisms relevant to biomedical field.

Perinatal Effects of Metformin use in Gestational Diabetes

Background: GD is a condition in which a woman develops glucose intolerance at any time during pregnancy and may or may not resolve at the end of pregnancy. Metformin, from the group of biguanides, is considered an alternative management of gestational diabetes, included in the list of essential medicines by the OMS. Methodology: A narrative review was carried out through various databases from March 2018 to September 2021; the search and selection of articles was carried out in journals indexed in English and Spanish. The following keywords were used: metformin, macrosomia, gestational diabetes. Results: The present review offers pathophysiological measures, complications, pharmacological therapy, for a better approach in perinatals in patients with gestational diabetes. Conclusion: With the results observed, it should be noted that metformin is viable for the management of patients with gestational diabetes.

Nicotinamide Mononucleotide Prevents Free Fatty Acid-Induced Reduction in Glucose Tolerance by Decreasing Insulin Clearance

The NAD-dependent deacetylase SIRT1 improves β cell function. Accordingly, nicotinamide mononucleotide (NMN), the product of the rate-limiting step in NAD synthesis, prevents β cell dysfunction and glucose intolerance in mice fed a high-fat diet. The current study was performed to assess the effects of NMN on β cell dysfunction and glucose intolerance that are caused specifically by increased circulating free fatty acids (FFAs). NMN was intravenously infused, with or without oleate, in C57BL/6J mice over a 48-h-period to elevate intracellular NAD levels and consequently increase SIRT1 activity. Administration of NMN in the context of elevated plasma FFA levels considerably improved glucose tolerance. This was due not only to partial protection from FFA-induced β cell dysfunction but also, unexpectedly, to a significant decrease in insulin clearance. However, in conditions of normal FFA levels, NMN impaired glucose tolerance due to decreased β cell function. The presence of this dual action of NMN suggests caution in its proposed therapeutic use in humans.

Early Life Thymectomy Induces Glucose Intolerance in Middle-Aged Mice

Previously we have found that T cells contribute to age-related glucose intolerance. The purpose of this study was to test the hypothesis that early life thymectomy at 3wks of age induces T cell aging and subsequent impairments in glucose homeostasis in otherwise young animals. Male C57BL6 mice underwent thymectomy (thymex; n=7) or sham surgery (control; n=7) at 3wks of age. A glucose (2g/kg) tolerance test (GTT) was performed at 6 and 9mo via intraperitoneal injection. Following euthanasia at 9mo of age, splenic T cell phenotype was assessed by flow cytometry. Group differences were assessed by independent samples t-test or repeated measures ANOVA and Bonferroni post-hoc test. Data are presented as mean±SEM. At 6mo, the thymex animals had a significantly lower fasting glucose compared to controls (156.8±7.9mg/dl,174.1±5.8mg/dl, p=0.06). During the GTT, 6mo old thymex mice had a greater area under the curve (AUC) compared to controls (31893.8±612.3mg/dl, 28020.9±1112.9mg/dl, p=0.03). At 9mo, the thymex mice had greater fasting glucose compared to controls (215.6±11.6mg/dl, 176.3±7.9mg/dl, p=0.016), as well as a greater GTT AUC (61445.4±1949.2mg/dl, 41527.5±2530.3mg/dl, p=0.0001). The thymex group also had increased fasting and glucose stimulated insulin levels compared to controls (0=1.3±0.2ng/ml 0.3±0.1ng/ml, p=0.01; 15=1.7±0.2ng/ml,0.44±0.1ng/ml, p=0.0014). Thymex mice exhibited a blunted splenic CD4:CD8 ratio (0.5±0.2, 1.1±0.2, p=0.04) compared to controls and a trend toward a memory CD8+ T cell phenotype (23.1±11.6%, 7.1±2.6, p=0.08), both consistent with aging. This data indicates that early life thymectomy may accelerate T cell aging, resulting in impairments in glucose tolerance in otherwise young and middle aged mice.