The effect of hyperglycemia and hypoglycemia on glucose transport and expression of glucose transporters in human lymphocytes B and T: an in vitro study

Mast Cells are Dependent on Glucose Transporter 1 (GLUT1) and GLUT3 for IgE-mediated Activation

Mast cells (MCs) are known to have a pathological impact in a variety of settings, in particular in allergic conditions. There is also limited evidence implicating MCs in diabetes, raising the possibility that MC function may be influenced by alterations in glucose levels. However, it is not known whether MCs are directly affected by elevated glucose concentrations. Moreover, it is not known which glucose transporters that are expressed by MCs, and whether MCs are dependent on glucose transporters for activation. Here we addressed these issues. We show that MCs express high levels of both glucose transporter 1 (GLUT1/Slc2A1) and GLUT3 (Slc2A3). Further, we show that the inhibition of either GLUT1 or GLUT3 dampens both MC degranulation and cytokine induction in response to IgE receptor crosslinking, and that combined GLUT1 and GLUT3 inhibition causes an even more pronounced inhibition of these parameters. In contrast, the inhibition of GLUT1 or GLUT3, or combined GLUT1 and GLUT3 inhibition, had less impact on the ability of the MCs to respond to activation via compound 48/80. Elevated glucose concentrations did not affect MC viability, and had no stimulatory effect on MC responses to either IgE receptor crosslinking or compound 48/80. Altogether, these findings reveal that MCs are strongly dependent on glucose transport via GLUT1 and/or GLUT3 for optimal responses towards IgE-mediated activation, whereas MC functionality is minimally affected by elevated glucose levels. Based on these findings, antagonists of GLUT1 and GLUT3 may be considered for therapeutic intervention in allergic conditions.

Altered VDAC-HK association and apoptosis in mouse peripheral blood lymphocytes exposed to diabetic condition: an in vitro and in vivo study

Increased apoptotic lymphocytes have been correlated to a high incidence of infection in poorly controlled diabetes. This study aimed to determine whether altered voltage-dependent anion channel (VDAC)-hexokinase (HK) association contributes to the increase in apoptosis. Mouse peripheral blood lymphocytes (PBL) exposed to high glucose (Glc)/palmitic acid (PA) were used as the in vitro model, which was compared with PBL isolated from alloxan-induced diabetic mice (in vivo model). Our results showed a significant increase in apoptosis as indicated by the apoptotic index, caspase-3 activity, mitochondrial membrane potential and ultrastructural study. HK and glucose-6-phosphate dehydrogenase (G6PDH) activities were markedly reduced with a profound increase in glucose-6-phosphate level. Co-immunoprecipitation confirms HK interaction with VDAC, an outer mitochondrial membrane protein. Inhibited glycolytic enzyme, i.e. HK and reduced HK-VDAC interaction in our study could contribute to increased apoptosis in lymphocytes exposed to high Glc/PA. Targeting HK-VDAC interaction may therefore provide therapeutic potential for the treatment of diabetes-associated infection.

Arsenic impairs GLUT1 trafficking through the inhibition of the calpain system in lymphocytes

Exposure to arsenic is associated with increased risk of developing insulin resistance and type 2 diabetes. The proteases calpain-1 (CAPN1), calpain-2 (CAPN2) and calpain-10 (CAPN10) and their endogenous inhibitor calpastatin (CAST) regulate glucose uptake in skeletal muscle and adipocytes. We investigated whether arsenic disrupts GLUT1 trafficking and function through calpain inhibition, using lymphocytes as a cell model. Lymphocytes from healthy subjects were treated with 0.1 or 1 μM of sodium arsenite for 72 h and challenged with 3.9 or 11.1 mM of glucose. Our results showed that arsenite inhibited GLUT1 trafficking, glucose uptake, and calpain activity in the presence of 11.1 mM of glucose. These correlated with a decrease in the autolytical fragment of 50 kDa of CAPN1 and increased levels of CAST, but there were no changes in CAPN2 and CAPN10. We used a cell-free system to evaluate the effect of arsenite over CAPN1, finding that arsenite induced CAPN1 autolysis. To confirm that calpains are involved in GLUT1 trafficking and glucose uptake in lymphocytes, we generated stable CAPN1 or CAPN10 knockdowns in Jurkat cells using short hairpin RNA (shRNA). CAPN1 knockdown induced glucose uptake, while CAPN10 knockdown diminished glucose uptake, which correlated with a significant reduction of calpain activity after the pulse with 11.1 mM of glucose. These data showed that CAPN10 was responsible for the induction of calpain activity after the challenge with 11.1 mM of glucose and that CAPN1 and CAPN10 regulate glucose uptake in lymphocytes. Altogether, our results suggest that arsenite impairs GLUT1 trafficking and function through calpain dysregulation.

Bruton's tyrosine kinase is at the crossroads of metabolic adaptation in primary malignant human lymphocytes

In this work we explored metabolic aspects of human primary leukemic lymphocytes that hold a potential impact on the treatment of Bruton tyrosine kinase (BTK)-driven diseases. Our results suggest that there is crosstalk between Bruton tyrosine kinase (BTK) signaling and bioenergetic stress responses. In primary chronic lymphocytic leukemia (CLL) lymphocytes, pharmacological interference with mitochondrial ATP synthesis or glucose metabolism affects BTK activity. Conversely, an inhibitor of BTK used clinically (ibrutinib) induces bioenergetic stress responses that in turn affect ibrutinib resistance. Although the detailed molecular mechanisms are still to be defined, our work shows for the first time that in primary B cells, metabolic stressors enhance BTK signaling and suggest that metabolic rewiring to hyperglycemia affects ibrutinib resistance in TP53 deficient chronic lymphocytic leukemia (CLL) lymphocytes.

Hyperglycemia Suppresses RANKL-Induced Osteoclast Differentiation through LXRβ Expression in RAW264.7 Cells

There have been reports that hyperglycemia suppresses osteoclast (OCL) differentiation, although the underlying mechanism is poorly understood. Here we demonstrated that high glucose suppresses OCL differentiation through activation of liver X receptor (LXR) β, a recently reported glucose-sensing nuclear receptor. The effect of hyperglycemia on osteoclastogenesis was tested in RAW264.7 cells, a murine macrophage cell line. Cells were treated with receptor activator of NF-κB ligand (RANKL) under normoglycemic (5.5 mM glucose), normoglycemic with high osmotic pressure (5.5 mM glucose + 10.0 mM mannitol), and hyperglycemic (15.5 mM glucose) conditions. RANKL-induced osteoclastogenesis was significantly suppressed by high-glucose treatment. Mannitol treatment also significantly suppressed osteoclastogenesis, but the inhibitory effect was lower than for high-glucose treatment. The suppression of mRNA expression of Lxrβ by RANKL was significantly restored by high glucose, but not mannitol. Additionally, the deactivation of Lxrβ by siRNA attenuated high-glucose-induced suppression of osteoclastogenesis. Although further validation of the underlying pathway is necessary, targeting LXRβ is a potential therapeutic approach to treating osteoporosis.

The structural and functional changes of blood cells and molecular components in diabetes mellitus

It is known fact that diabetes mellitus (DM) affects blood cells. Changes in the erythrocyte membrane, disorder in hemoglobin oxygen-binding and modification in mechanical characteristics, are effects of hyperglycemia on red blood cells. Altered susceptibility infection of patients with diabetes has been ascribed to a depression in the function of polymorphonuclear leukocytes. Neutrophil function in patients with diabetes with good glucose control is slightly different than in healthy ones. DM causes significant changes in lymphocytes metabolism and their functions. Patients with diabetes, presenting with acute coronary syndrome, are at higher risk of cardiovascular complications and recurrent ischemic events in comparison to non-diabetic counterparts. Various mechanisms, including endothelial dysfunction, platelet hyperactivity, and abnormalities in coagulation and fibrynolysis have been implicated for this increased atherothrombotic risk. There are many other alterations of blood cells due to DM. In the present review we focused on modifications of blood cells due to DM. Then, as a second point, we explored how the changes affect functions of red blood cells, white blood cells and platelets.

Usefulness of the plasma glucose concentration-to-HbA1c ratio in predicting clinical outcomes during acute illness with extreme hyperglycaemia

AIMS

To evaluate the correlation between the plasma glucose-to-glycated haemoglobin ratio (GAR) and clinical outcome during acute illness.

METHODS

This retrospective observational cohort study enrolled 661 patients who visited the emergency department of our hospital between 1 July 2008 and 30 September 2010 with plasma glucose concentrations>500mg/dL. Systolic blood pressure, heart rate, white blood cells, neutrophils, haematocrit, blood urea nitrogen, serum creatinine, liver function and plasma glucose concentration were recorded at the initial presentation to the emergency department. Data on glycated haemoglobin over the preceding 6 months were reviewed from our hospital database. The glucose-to-HbA_1c ratio (GAR) was calculated as the plasma glucose concentration divided by glycated haemoglobin.

RESULTS

The GAR of those who died was significantly higher than that of the survivors (81.0±25.9 vs 67.6±25.0; P<0.001). There was a trend towards a higher 90-day mortality rate in patients with higher GARs (log-rank test P<0.0001 for trend). On multivariate Cox regression analysis, the GAR was significantly related to 90-day mortality (hazard ratio [HR] for 1 standard deviation [SD] change: 1.41, 95% confidence interval [CI]: 1.22-1.63; P<0.001), but not to plasma glucose (HR: 0.89, 95% CI: 0.70-1.13; P=0.328). Rates of intensive care unit (ICU) admission and mechanical ventilator use were also higher in those with higher GARs.

CONCLUSION

GAR independently predicted 90-day mortality, ICU admission and use of mechanical ventilation. It was also a better predictor of patient outcomes than plasma glucose alone in patients with extremely high glucose levels.

Chronic pistachio intake modulates circulating microRNAs related to glucose metabolism and insulin resistance in prediabetic subjects

PURPOSE

To assess the effects of a pistachio-enriched diet on the profile of circulating microRNAs (miRNAs) related to glucose metabolism and insulin resistance (IR).

METHODS

Randomized crossover clinical trial in 49 subjects with prediabetes was performed. Subjects consumed a pistachio-supplemented diet (PD, 50 % carbohydrates, 33 % fat, including 57 g/day of pistachios) and an isocaloric control diet (CD, 55 % carbohydrates and 30 % fat) for 4 months each, separated by a 2-week washout period. The plasma profile of a set of seven predefined miRNAs related to glucose and insulin metabolism was analyzed by quantitative RT-PCR.

RESULTS

After the PD period, subjects have shown significant lower circulating levels of miR-192 and miR-375 compared to CD period, whereas miR-21 nonsignificantly increased after PD compared with CD (47 vs. 2 %, P = 0.092). Interestingly, changes in circulating miR-192 and miR-375 were positively correlated with plasma glucose, insulin and HOMA-IR.

CONCLUSION

Chronic pistachio consumption positively modulates the expression of some miRNA previously implicated on insulin sensitivity.

Pairing nuts and dried fruit for cardiometabolic health

Certain dietary patterns, in which fruits and nuts are featured prominently, reduce risk of diabetes and cardiovascular disease. However, estimated fruit consumption historically in the U.S. has been lower than recommendations. Dried fruit intake is even lower with only about 6.9 % of the adult population reporting any consumption. The 2015 Dietary Guidelines Advisory Committee identified a gap between recommended fruit and vegetable intakes and the amount the population consumes. Even fewer Americans consume tree nuts, which are a nutrient-dense food, rich in bioactive compounds and healthy fatty acids. Consumption of fruits and nuts has been associated with reduced risk of cardiometabolic disease. An estimated 5.5 to 8.4 % of U.S. adults consume tree nuts and/or tree nut butter. This review examines the potential of pairing nuts and dried fruit to reduce cardiometabolic risk factors and focuses on emerging data on raisins and pistachios as representative of each food category. Evidence suggests that increasing consumption of both could help improve Americans’ nutritional status and reduce the risk of chronic diseases.

Hyperglycemia Differentially Affects Maternal and Fetal DNA Integrity and DNA Damage Response

Objective: Investigate the DNA damage and its cellular response in blood samples from both mother and the umbilical cord of pregnancies complicated by hyperglycemia. Methods: A total of 144 subjects were divided into 4 groups: normoglycemia (ND; 46 cases), mild gestational hyperglycemia (MGH; 30 cases), gestational diabetes mellitus (GDM; 45 cases) and type-2 diabetes mellitus (DM2; 23 cases). Peripheral blood mononuclear cell (PBMC) isolation and/or leukocytes from whole maternal and umbilical cord blood were obtained from all groups at delivery. Nuclear and mitochondrial DNA damage were measured by gene-specific quantitative PCR, and the expression of mRNA and proteins involved in the base excision repair (BER) pathway were assessed by real-time qPCR and Western blot, respectively. Apoptosis was measured in vitro experiments by caspase 3/7 activity and ATP levels. Results: GDM and DM2 groups were characterized by an increase in oxidative stress biomarkers, an increase in nuclear and mitochondrial DNA damage, and decreased expression of mRNA (APE1, POLβ and FEN1) and proteins (hOGG1, APE1) involved in BER. The levels of hyperglycemia were associated with the in vitro apoptosis pathway. Blood levels of DNA damage in umbilical cord were similar among the groups. Newborns of diabetic mothers had increased expression of BER mRNA (APE1, POLβ and FEN1) and proteins (hOGG1, APE1, POLβ and FEN1). A diabetes-like environment was unable to induce apoptosis in the umbilical cord blood cells. Conclusions: Our data show relevant asymmetry between maternal and fetal blood cell susceptibility to DNA damage and apoptosis induction. Maternal cells seem to be more predisposed to changes in an adverse glucose environment. This may be due to differential ability in upregulating multiple genes involved in the activation of DNA repair response, especially the BER mechanism. However if this study shows a more effective adaptive response by the fetal organism, it also calls for further studies to determine the limit of this response that definitely changes the fate of a fetus under these conditions of cellular stress.

Effects of high glucose on caveolin-1 and insulin signaling in 3T3-L1 adipocytes

Adipocytes exposed to high glucose concentrations exhibit impaired metabolic function, including an increase of oxidative and proinflammatory factors that might favor the development of insulin resistance. Caveolin-1 (Cav-1) is a key mediator of the insulin transduction pathway whose expression is significantly enhanced during adipocyte differentiation. In this work, we studied the effects of high glucose concentration on the regulation of Cav-1 expression and activation and its relation to the insulin signaling pathway during the adipogenic process and in long-term differentiated adipocytes. Both, long-term high glucose exposure during adipogenesis and short-term glucose incubation of mature adipocytes, promoted triglyceride accumulation in 3T3-L1 cells. The short-term exposure of mature adipocytes to high glucose significantly reduced the sensitivity to insulin of Cav-1, insulin receptor (IR) and potein kinase B (AKT-2) phosphorylation, as well as insulin-induced deoxyglucose uptake. Adipocytes differentiated in the presence of high glucose lost Cav-1 and IR response to insulin-stimulated phosphorylation, but maintained the insulin sensitivity of AKT-2 phosphorylation and deoxyglucose uptake. Although long-term high glucose exposure increased DNA methylation in Cav-1 promoter, Cav-1 expression was not affected. Moreover, these cells showed an increase of Cav-1, IR and AKT-2 protein content, pointing to an adaptive response induced by the long-term high glucose exposure.

Leptin at gender-specific concentrations does not affect glucose transport, expression of glucose transporters and leptin receptors in human lymphocytes

Leptin shows pleiotropic effects in organisms including an important role in the regulation of glucose homeostasis. Elevated serum leptin, particularly in obese individuals, is a warning sign of energy imbalance, hyperinsulinemia, insulin resistance and other metabolic risk factors that are strongly associated with type 2 diabetes. Obesity is also related to a higher rate of infections and immune function deterioration may in part ensue from decreased glucose uptake as the main energy source for lymphocytes. The aim of this study was to investigate the effect of physiologic and low pathophysiologic gender-specific leptin concentration found in lean and obese subjects on glucose transport, the expression of glucose transporters and leptin receptors in human peripheral blood lymphocytes. Isolated lymphocytes were incubated with human leptin at gender-specific concentrations observed in normal weight and obese subjects. Glucose uptake in lymphocytes was determined using nonmetabolizable radiolabeled deoxy-D-glucose. The expression of GLUT1, 3, 4 and leptin receptors was investigated using methods of immunocytochemistry and flow cytometry. Leptin at concentrations used in the study does not change glucose transport into lymphocytes and seems to have no influence on the expression of glucose transporters and leptin receptors. Further studies are necessary to address the relationship between leptin, glucose transport and the lymphocytes' function in obesity.

Transport of deoxy-D-glucose into lymphocytes of patients with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is linked to increased risk of insulin resistance and diabetes mellitus in patients' later life. The aim of this study was to investigate uptake of deoxy-D-glucose by peripheral blood lymphocytes of PCOS patients with normal fasting plasma glucose and normal glucose tolerance test. The study involved 20 patients with PCOS with normal fasting plasma glucose and normal glucose in 60 and 120 min of oral glucose tolerance test, aged 18-32 (mean 23), BMI between 20 and 30 (mean 26). A control group consisted of 20 healthy women matched for glucose level (normoglycemia), aged 18-28 years (mean 23), BMI 20-25 (mean 23). Blood for the studies was collected in fasting conditions onto heparin. Lymphocytes were isolated within 2 h from collection by centrifuging. The intracellular transport into lymphocytes was studied using tritium-labeled deoxy-D-glucose and measured with a liquid scintillation counter. Radioactivity in curie per minute (cpm) was evaluated after 24 h. An initial examination was performed to check the presence of GLUT4 in peripheral blood lymphocytes of PCOS women. In all of the studied time points, the value of cpm for lymphocytes of PCOS patients was statistically significantly lower in comparison with the value obtained for lymphocytes of healthy women. However, the profile of deoxy-D-glucose uptake (d cpm) was the same for lymphocytes in both studied groups without statistically significant differences. In lymphocytes of PCOS patients, GLUT4 was detected. The obtained results indicate that PCOS affects the intracellular transport of deoxy-D-glucose into lymphocytes of PCOS patients with normal glucose level.

Adolescents with clinical type 1 diabetes display reduced red blood cell glucose transporter isoform 1 (GLUT1)

Type 1 diabetic (T1D) adolescent children on insulin therapy suffer episodes of both hyper- and hypoglycemic episodes. Glucose transporter isoform GLUT1 expressed in blood-brain barrier (BBB) and red blood cells (RBC) compensates for perturbed circulating glucose toward protecting the supply to brain and RBCs. We hypothesized that RBC-GLUT1 concentration, as a surrogate for BBB-GLUT1, is altered in T1D children. To test this hypothesis, we measured RBC-GLUT1 by enzyme-linked immunosorbent assay (ELISA) in T1D children (n = 72; mean age 15.3 ± 0.2 yr) and control children (CON; n = 11; mean age 15.6 ± 0.9 yr) after 12 h of euglycemia and during a hyperinsulinemic-hypoglycemic clamp with a nadir blood glucose of ~3.3 mmol/L for 90 min (clamp I) or ~3 mmol/L for 45 min (clamp II). Reduced baseline RBC-GLUT1 was observed in T1D (2.4 ± 0.17 ng/ng membrane protein); vs. CON (4.2 ± 0.61 ng/ng protein) (p < 0.0001). Additionally, baseline RBC-GLUT1 in T1D negatively correlated with hemoglobin A1c (HbA1c) (R = -0.23, p < 0.05) but not in CON (R = 0.06, p < 0.9). Acute decline in serum glucose to 3.3 mmol/L (90 min) or 3 mmol/L (45 min) did not change baseline RBC-GLUT1 in T1D or CON children. We conclude that reduced RBC-GLUT1 encountered in T1D, with no ability to compensate by increasing during acute hypoglycemia over the durations examined, may demonstrate a vulnerability of impaired RBC glucose transport (serving as a surrogate for BBB), especially in those with the worst control. We speculate that this may contribute to the perturbed cognition seen in T1D adolescents.

Glucose transporter 1-mediated glucose uptake is limiting for B-cell acute lymphoblastic leukemia anabolic metabolism and resistance to apoptosis

The metabolic profiles of cancer cells have long been acknowledged to be altered and to provide new therapeutic opportunities. In particular, a wide range of both solid and liquid tumors use aerobic glycolysis to supply energy and support cell growth. This metabolic program leads to high rates of glucose consumption through glycolysis with secretion of lactate even in the presence of oxygen. Identifying the limiting events in aerobic glycolysis and the response of cancer cells to metabolic inhibition is now essential to exploit this potential metabolic dependency. Here, we examine the role of glucose uptake and the glucose transporter Glut1 in the metabolism and metabolic stress response of BCR-Abl+ B-cell acute lymphoblastic leukemia cells (B-ALL). B-ALL cells were highly glycolytic and primary human B-ALL samples were dependent on glycolysis. We show B-ALL cells express multiple glucose transporters and conditional genetic deletion of Glut1 led to a partial loss of glucose uptake. This reduced glucose transport capacity, however, was sufficient to metabolically reprogram B-ALL cells to decrease anabolic and increase catabolic flux. Cell proliferation decreased and a limited degree of apoptosis was also observed. Importantly, Glut1-deficient B-ALL cells failed to accumulate in vivo and leukemic progression was suppressed by Glut1 deletion. Similarly, pharmacologic inhibition of aerobic glycolysis with moderate doses of 2-deoxyglucose (2-DG) slowed B-ALL cell proliferation, but extensive apoptosis only occurred at high doses. Nevertheless, 2-DG induced the pro-apoptotic protein Bim and sensitized B-ALL cells to the tyrosine kinase inhibitor Dasatinib in vivo. Together, these data show that despite expression of multiple glucose transporters, B-ALL cells are reliant on Glut1 to maintain aerobic glycolysis and anabolic metabolism. Further, partial inhibition of glucose metabolism is sufficient to sensitize cancer cells to specifically targeted therapies, suggesting inhibition of aerobic glycolysis as a plausible adjuvant approach for B-ALL therapies.