N-acetylglucosamine: more than a silent partner in insulin resistance

In-depth investigation of the therapeutic effect of Tribulus terrestris L. on type 2 diabetes based on intestinal microbiota and feces metabolomics

ETHNOPHARMACOLOGICAL RELEVANCE

The fruit of Tribulus terrestris L. (TT) is extensively documented in the Tibetan medical literature 'Si Bu Yi Dian', has been used to treat diabetes mellitus for more than a thousand years. However, the underlying mechanisms and comprehensive effects of TT on diabetes have yet to be investigated.

AIM OF THE STUDY

The aim of the study was to systemically elucidate the potential mechanisms of TT in treating diabetes mellitus, and further investigate the therapeutic effects of the water extract, small molecular components and saccharides from TT.

MATERIALS AND METHODS

Fecal metabolomics was employed to draw the metabolic profile based on UHPLC-Q-TOF-MS/MS. The V3-V4 hypervariable regions of the bacteria 16S rRNA gene were amplified to explore the structural changes of the intestinal microbiome after TT intervention and to analyze the differential microbiota. The microbial metabolites SCFAs were determined by GC-MS, and the BAs and tryptophan metabolites were quantified by UPLC-TQ-MS. Spearman correlation analysis was carried out to comprehensively investigate the relationship among the endogenous metabolites profile, intestinal microbiota and their metabolites.

RESULTS

TT exhibited remarkably therapeutic effect on T2DM rats, as evidenced by improved glucolipid metabolism and intestinal barrier integrity, ameliorated inflammation and remission in insulin resistance. A total of 24 endogenous biomarkers were screened through fecal metabolomics studies, which were mainly related to tryptophan metabolism, fatty acid metabolism, bile acid metabolism, steroid hormone biosynthesis and arachidonic acid metabolism. Investigations on microbiomics revealed that TT significantly modulated 18 differential bacterial genera and reversed the disordered gut microbial in diabetes rats. Moreover, TT notably altered the content of gut microbiota metabolites, both in serum and fecal samples. Significant correlation among microbial community, metabolites and T2DM-related indicators was revealed.

CONCLUSIONS

The multiple components of TT regulate the metabolic homeostasis of the organism and the balance of intestinal microbiota and its metabolites, which might mediate the anti-diabetic capacity of TT.

Galectins in epithelial-mesenchymal transition: roles and mechanisms contributing to tissue repair, fibrosis and cancer metastasis

Galectins are soluble glycan-binding proteins that interact with a wide range of glycoproteins and glycolipids and modulate a broad spectrum of physiological and pathological processes. The expression and subcellular localization of different galectins vary among tissues and cell types and change during processes of tissue repair, fibrosis and cancer where epithelial cells loss differentiation while acquiring migratory mesenchymal phenotypes. The epithelial-mesenchymal transition (EMT) that occurs in the context of these processes can include modifications of glycosylation patterns of glycolipids and glycoproteins affecting their interactions with galectins. Moreover, overexpression of certain galectins has been involved in the development and different outcomes of EMT. This review focuses on the roles and mechanisms of Galectin-1 (Gal-1), Gal-3, Gal-4, Gal-7 and Gal-8, which have been involved in physiologic and pathogenic EMT contexts.

Gut Microbiota and Blood Metabolites Related to Fiber Intake and Type 2 Diabetes

BACKGROUND

Consistent evidence suggests diabetes-protective effects of dietary fiber intake. However, the underlying mechanisms, particularly the role of gut microbiota and host circulating metabolites, are not fully understood. We aimed to investigate gut microbiota and circulating metabolites associated with dietary fiber intake and their relationships with type 2 diabetes (T2D).

METHODS

This study included up to 11 394 participants from the HCHS/SOL (Hispanic Community Health Study/Study of Latinos). Diet was assessed with two 24-hour dietary recalls at baseline. We examined associations of dietary fiber intake with gut microbiome measured by shotgun metagenomics (350 species/85 genera and 1958 enzymes; n=2992 at visit 2), serum metabolome measured by untargeted metabolomics (624 metabolites; n=6198 at baseline), and associations between fiber-related gut bacteria and metabolites (n=804 at visit 2). We examined prospective associations of serum microbial-associated metabolites (n=3579 at baseline) with incident T2D over 6 years.

RESULTS

We identified multiple bacterial genera, species, and related enzymes associated with fiber intake. Several bacteria (eg, Butyrivibrio, Faecalibacterium) and enzymes involved in fiber degradation (eg, xylanase EC3.2.1.156) were positively associated with fiber intake, inversely associated with prevalent T2D, and favorably associated with T2D-related metabolic traits. We identified 159 metabolites associated with fiber intake, 47 of which were associated with incident T2D. We identified 18 of these 47 metabolites associated with the identified fiber-related bacteria, including several microbial metabolites (eg, indolepropionate and 3-phenylpropionate) inversely associated with the risk of T2D. Both Butyrivibrio and Faecalibacterium were associated with these favorable metabolites. The associations of fiber-related bacteria, especially Faecalibacterium and Butyrivibrio, with T2D were attenuated after further adjustment for these microbial metabolites.

CONCLUSIONS

Among United States Hispanics/Latinos, dietary fiber intake was associated with favorable profiles of gut microbiota and circulating metabolites for T2D. These findings advance our understanding of the role of gut microbiota and microbial metabolites in the relationship between diet and T2D.

Composition of the gut microbiome, role of diet, lifestyle, and antioxidant therapies in diabetes mellitus and diabetic retinopathy

The gut microbiome is a complex ecosystem in the gastrointestinal tract composed of trillions of bacteria, viruses, fungi, and protozoa. Disruption of this delicate ecosystem, formally called "dysbiosis", has been linked to a variety of metabolic and inflammatory pathologies. Several studies have focused on abnormal microbiome composition and correlated these findings with the development of type 2 diabetes mellitus (T2DM) and diabetic retinopathy (DR). However, given the complexity of this ecosystem, the current studies are narrow in design and present variable findings. Composition of the gut microbiome in patients with DR significantly differs from patients with diabetes without retinopathy as well as from healthy controls. Additionally, the gut microbiome has been shown to modify effects of medication, diet, exercise, and antioxidant use on the development and progression of DR. In this paper, we present a comprehensive review of literature on the effect of oxidative stress, antioxidant therapies, and dysbiosis on DR.

Determination and Correlation of Solubility of N-Acetylglucosamine in Four Aqueous Binary Solvents from 283.15 to 323.15 K

N-Acetylglucosamine (NAG) is a significant novel functional monosaccharide with a wide range of potential applications, such as in the medical and cosmetic fields. A gravimetric technique was used to assess the solubility of NAG in water, methanol, N,N-dimethylformamide, water + methanol, water + n-propanol, water + N,N-dimethylformamide, and water + acetonitrile at temperatures ranging from 283.15 to 323.15 K. The outcomes of the experiment demonstrated that the temperature and water content were positively correlated with the solubility of NAG in four experimental binary solvents. The order of solubility in the four aqueous solvent mixtures is water + DMF > water + methanol > water + n-propanol > water + acetonitrile. The solubility data was well correlated using the modified Apelblat model, the CNIBS/R-K model, and the Apelblat-Jouyban-Acree model. Experimental data from NAG will help guide the design of cooling and dissolution in crystallization processes.

Sardinian Infants of Diabetic Mothers: A Metabolomics Observational Study

Gestational diabetes mellitus (GDM) is a condition characterized by glucose intolerance, with hyperglycemia of varying severity with onset during pregnancy. An uncontrolled GDM can lead to an increased risk of morbidity in the fetus and newborn, and an increased risk of obesity or developing type 2 diabetes, hypertension or neurocognitive developmental impairment in adulthood. In this study, we used nuclear magnetic resonance (NMR) spectroscopy and gas chromatography-mass spectrometry (GS-MS) to analyze the urinary metabolomic profile of newborns of diabetic mothers (NDMs) with the aim of identifying biomarkers useful for the monitoring of NDMs and for early diagnosis of predisposition to develop related chronic diseases. A total of 26 newborns were recruited: 21 children of diabetic mothers, comprising 13 in diet therapy (NDM-diet) and 8 in insulin therapy (NDM-insulin), and 5 control children of non-diabetic mothers (CTR). Urine samples were collected at five time points: at birth (T1), on the third day of life (T2), one week (T3), one month (T4) and six months postpartum (T5). At T1, variations were observed in the levels of seven potential biomarkers (acetate, lactate, glycylproline/proline, isocitrate, N,N-dimethylglycine, N-acetylglucosamine and N-carbamoyl-aspartate) in NMD-insulin infants compared to NDM-diet and CTR infants. In particular, the altered metabolites were found to be involved in several metabolic pathways such as citrate metabolism, glycine, serine and threonine metabolism, arginine and proline metabolism, amino sugar and nucleotide sugar metabolism, and pyruvate metabolism. In contrast, these changes were not visible at subsequent sampling times. The impact of early nutrition (maternal and formula milk) on the metabolomic profile was considered as a potential contributing factor to this finding.

AMPK differentially alters sulphated glycosaminoglycans under normal and high glucose milieu in proximal tubular cells

Glycosaminoglycans (GAGs) and AMP-activated protein kinase (AMPK) are two critical molecular players involved in cellular homeostasis. Both of them are altered due to hyperglycaemia in the kidney, leading to the pathogenesis of diabetic nephropathy. Here, we have looked into the effect of AMPK modulation on sulphated GAG (sGAG) levels of tubular cells of proximal and distal origin to understand the mechanism of hyperglycaemia-mediated pathogenesis of the diabetic nephropathy. In MDCK cells (distal tubular cell) and NRK-52E (proximal tubular cell), AMPK inhibition resulted in increased sGAG levels under normal glucose conditions characteristically of heparan sulphate class, whereas AMPK activation did not have any effect. High glucose (HG) condition did not alter sGAG levels in MDCK cell despite a decrease in AMPK phosphorylation. Subjecting NRK-52E cells to HG milieu significantly decreased sGAG levels more so of chondroitin/dermatan sulphate, which is significantly prevented when HG is co-treated with AMPK activator. Interestingly, knockdown of AMPK by AMPKα1/α2 siRNA showed increased sGAG levels in NRK-52E. Our results suggest that changes in sGAG level, in particular, as a result of AMPK modulation is differentially regulated and is dependent on cell type as well as its physiological status. Furthermore, activation of AMPK is beneficial in preventing the HG-mediated decrease in sGAGs in proximal tubular cells.