High-glucose administration induces glucose intolerance in mice: a critical role of toll-like receptor 4

Excess glucose alone depress young mesenchymal stromal/stem cell osteogenesis and mitochondria activity within hours/days via NAD+/SIRT1 axis

BACKGROUND

The impact of global overconsumption of simple sugars on bone health, which peaks in adolescence/early adulthood and correlates with osteoporosis (OP) and fracture risk decades, is unclear. Mesenchymal stromal/stem cells (MSCs) are the progenitors of osteoblasts/bone-forming cells, and known to decrease their osteogenic differentiation capacity with age. Alarmingly, while there is correlative evidence that adolescents consuming greatest amounts of simple sugars have the lowest bone mass, there is no mechanistic understanding on the causality of this correlation.

METHODS

Bioinformatics analyses for energetics pathways involved during MSC differentiation using human cell information was performed. In vitro dissection of normal versus high glucose (HG) conditions on osteo-/adipo-lineage commitment and mitochondrial function was assessed using multi-sources of non-senescent human and murine MSCs; for in vivo validation, young mice was fed normal or HG-added water with subsequent analyses of bone marrow CD45- MSCs.

RESULTS

Bioinformatics analyses revealed mitochondrial and glucose-related metabolic pathways as integral to MSC osteo-/adipo-lineage commitment. Functionally, in vitro HG alone without differentiation induction decreased both MSC mitochondrial activity and osteogenesis while enhancing adipogenesis by 8 h' time due to depletion of nicotinamide adenine dinucleotide (NAD+), a vital mitochondrial co-enzyme and co-factor to Sirtuin (SIRT) 1, a longevity gene also involved in osteogenesis. In vivo, HG intake in young mice depleted MSC NAD+, with oral NAD+ precursor supplementation rapidly reversing both mitochondrial decline and osteo-/adipo-commitment in a SIRT1-dependent fashion within 1 ~ 5 days.

CONCLUSIONS

We found a surprisingly rapid impact of excessive glucose, a single dietary factor, on MSC SIRT1 function and osteogenesis in youthful settings, and the crucial role of NAD+-a single molecule-on both MSC mitochondrial function and lineage commitment. These findings have strong implications on future global OP and disability risks in light of current worldwide overconsumption of simple sugars.

Glucosamine substituted sulfonylureas: IRS-PI3K-PKC-AKT-GLUT4 insulin signalling pathway intriguing agent

Normally, skeletal muscle accounts for 70-80% of insulin-stimulated glucose uptake in the postprandial hyperglycemia state. Consequently, abnormalities in glucose uptake by skeletal muscle or insulin resistance (IR) are deemed as initial metabolic defects in the pathogenesis of type 2 diabetes mellitus (T2DM). Globally, T2DM is growing in exponential proportion. The majority of T2DM patients are treated with sulfonylureas in combination with other drugs to improve insulin sensitivity. Glycosylated sulfonylureas (sulfonylurea-glucosamine analogues) are modified analogues of sulfonylurea that have been previously reported to possess antidiabetic activity. The aim of this study was to evaluate the impact of glycosylated sulfonylureas on the insulin signalling pathway at the molecular level using L6 skeletal muscle cell (in vitro) and extracted soleus muscle (ex vivo) models. To create an in vitro model, insulin resistance was established utilizing a high insulin-glucose approach in differentiated L6 muscle cells from Rattus norvegicus. Additionally, for the ex vivo model, extracted soleus muscles, adult Sprague-Dawley rats were subjected to a solution containing 25 mmol L-1 glucose and 100 mmol L-1 insulin for 24 hours to induce insulin resistance. After insulin resistance, compounds under investigation and standard medicines (metformin and glimepiride) were tested. The differential expression of PI3K, IRS-1, PKC, AKT2, and GLUT4 genes involved in the insulin signaling pathway was evaluated using qPCR. The evaluated glycosylated sulfonylurea analogues exhibited a significant increase in the gene expression of insulin-dependent pathways both in vitro and ex vivo, confirming the rejuvenation of the impaired insulin signaling pathway genes. Altogether, glycosylated sulfonylurea analogues described in this study represent potential therapeutic anti-diabetic drugs.

Clinical significance of high mobility group box 1/toll-like receptor 4 in obese diabetic patients

High mobility group box 1 (HMGB1) is an alarmin that may link to obesity and type 2 diabetes mellitus (T2DM). The present study analyzed the correlation between HMGB1/ Toll-like receptor 4 (TLR4) and certain biochemical parameters in obese (OB) diabetic patients. 40 normal glucose tolerant subjects (NGT) and 40 patients with newly diagnosed T2DM were enrolled. All patients were further divided into non-obese NGT (NGT-NOB), obese NGT (NGT-OB), non-obese T2DM (T2DM-NOB) and obese T2DM (T2DM-OB) groups according to body mass index (BMI).The levels of HMGB1 in serum were quantified using ELISA, whereas the mRNA expression levels of TLR4 in peripheral blood mononuclear cells were assessed using reverse transcription-quantitative PCR. The results suggested that the levels of HMGB1 and TLR4 were higher in NGT-OB and T2DM-NOB groups compared with those in NGT-NOB group. Similarly, the levels of these two markers were higher in T2DM-OB group compared with those in NGT-OB group. Correlation analysis indicated that the levels of HMGB1 and TLR4 were positively correlated with triglyceride (TG), fasting plasma glucose (FPG) levels and BMI, whereas a negative correlation between HMGB1 and high density lipoprotein (HDL) was noted. Linear regression analysis suggested that HMGB1 was associated with FPG and TG levels, whereas TLR4 was strongly associated with TG levels and BMI. The results demonstrated that the expression levels of HMGB1 and TLR4 in patients with T2DM or obesity were increased, which were associated with glycolipid metabolism disorders. Therefore, the HMGB1/TLR4 may serve a role in inflammatory process associated with obesity and T2DM.