The role of glucose transporters in brain disease: diabetes and Alzheimer’s Disease

Can Tea Consumption be a Safe and Effective Therapy Against Diabetes Mellitus-Induced Neurodegeneration?

Diabetes mellitus (DM) is a metabolic disease that is rapidly increasing and has become a major public health problem. Type 2 DM (T2DM) is the most common type, accounting for up to 90-95% of the new diagnosed DM cases. The brain is very susceptible to glucose fluctuations and hyperglycemia-induced oxidative stress (OS). It is well known that DM and the risk of developing neurodegenerative diseases are associated. Tea, Camellia sinensis L., is one of the most consumed beverages. It contains several phytochemicals, such as polyphenols, methylxanthines (mainly caffeine) and L-theanine that are often reported to be responsible for tea's health benefits, including in brain. Tea phytochemicals have been reported to be responsible for tea's significant antidiabetic and neuroprotective properties and antioxidant potential. Epidemiological studies have shown that regular consumption of tea has positive effects on DM-caused complications and protects the brain against oxidative damage, contributing to an improvement of the cognitive function. Among the several reported benefits of tea consumption, those related with neurodegenerative diseases are of great interest. Herein, we discuss the potential beneficial effects of tea consumption and tea phytochemicals on DM and how their action can counteract the severe brain damage induced by this disease.

Modeling of hypo/hyperglycemia and their impact on breast cancer progression related molecules

Breast cancer (BC) arises commonly in women with metabolic dysfunction. The underlying mechanism by which glycemic load can exert its action on tumor metastasis is under investigated. In this study we showed that glycemic microenvironment alters the expression of three classes of proteins, VEGF and its receptors, cell to cell, and cell to extracellular matrix (ECM) adhesion proteins in MDA-MB-231 parental cells and its two metastatic variants to the bone and brain (MDA-MB-231BO and MDA-MB-231BR, respectively). Using western blotting, we showed that VEGFR2 levels were higher in these variant cells and persisted in the cells under extreme hypoglycemia. Hypoglycemia did not alter VEGFR2 expression per se but rather suppressed its posttranslational glycosylation. This was reversed rapidly upon the restoration of glucose, and cyclohexamide (CHX) treatment demonstrated that this deglycosylated VEGFR2 was not a product of de-novo protein synthesis. VEGFR2 co-receptor Neuropilin-1 was up-regulated four-fold in all MDA-MB-231 cells (parental and two variants) compared to VEGFR2 expression, and was also susceptible to glycemic changes but resistant to CHX treatment for up to 72 hrs. Hypoglycemia also resulted in a significant decrease in specific catenin, cadherin, and integrin proteins, as well as cellular proliferation and colony forming ability. However, MDA-MB-231BR cells showed a unique sensitivity to hypo/hyperglycemia in terms of morphological changes, colony formation ability, integrin β3 expression and secreted VEGF levels. In conclusion, this study can be translated clinically to provide insight into breast cancer cell responses to glycemic levels relevant for our understanding of the interaction between diabetes and cancer.

Pertussis toxin administered spinally induces a hypoglycemic effect on normal and diabetic mice

BACKGROUND/AIMS

To show whether intrathecal (i.t.) treatment with pertussis toxin (PTX) produces a hypoglycemic effect in ICR, db/db and streptozotocin-treated mice.

METHODS

The blood glucose level (BGL) was measured after i.t. treatment with PTX, AB5 toxins and PTX subunits. Insulin or leptin levels were measured after PTX injection. The effect of PTX on the BGL was examined in adrenalectomized (ADX) mice. Glucose transporter (GLUT) levels were determined by Western blotting.

RESULTS

PTX attenuated the elevated BGL in the D-glucose-fed model in a long-term manner. Heat-labile toxin (HLT), HLT subunit B or Shiga toxin, which belong to the AB5 toxins, administered i.t. did not affect the BGL. PTX A protomer (PTX-A) or PTX B oligomers (PTX-B) injected i.t. did not have an effect on the BGL as well. However, combined treatment with PTX-A and PTX-B subunits caused a hypoglycemic effect. The leptin level was gradually reduced by PTX for up to 6 days, without affecting the insulin level. PTX administered i.t. significantly decreased the BGL further in ADX mice. Moreover, GLUT-2 (hypothalamus and pituitary gland), GLUT-4 (muscle) and GLUT-3 (adrenal gland) expression levels were increased, whereas GLUT-1 (brain cortex, liver, muscle and spinal cord), GLUT-2 (liver) and GLUT-3 (brain cortex and pituitary gland) expression levels were decreased.

DISCUSSION

Our data suggest that PTX administered spinally produces a hypoglycemic effect in a long-term manner, and PTX-induced hypoglycemia appears to be mediated by the reduction in activity of the glucocorticoid system. Furthermore, PTX may modulate the insulin level during hypoglycemia. Among GLUTs, GLUT-4 in muscle, GLUT-2 in the liver, hypothalamus and pituitary gland as well as GLUT-1 in the adrenal gland may be responsible for PTX-induced hypoglycemia.

The prelude on novel receptor and ligand targets involved in the treatment of diabetes mellitus

Metabolic disorders are a group of disorders, due to the disruption of the normal metabolic process at a cellular level. Diabetes Mellitus and Tyrosinaemia are the majorly reported metabolic disorders. Among them, Diabetes Mellitus is a one of the leading metabolic syndrome, affecting 5 to 7 % of the population worldwide and mainly characterised by elevated levels of glucose and is associated with two types of physiological event disturbances such as impaired insulin secretion and insulin resistance. Up to now, various treatment strategies are like insulin, alphaglucosidase inhibitors, biguanides, incretins were being followed. Concurrently, various novel therapeutic strategies are required to advance the therapy of Diabetes mellitus. For the last few decades, there has been an extensive research in understanding the metabolic pathways involved in Diabetes Mellitus at the cellular level and having the profound knowledge on cell-growth, cell-cycle, and apoptosis at a molecular level provides new targets for the treatment of Diabetes Mellitus. Receptor signalling has been involved in these mechanisms, to translate the information coming from outside. To understand the various receptors involved in these pathways, we must have a sound knowledge on receptors and ligands involved in it. This review mainly summarises the receptors and ligands which are involved the Diabetes Mellitus. Finally, researchers have to develop the alternative chemical moieties that retain their affinity to receptors and efficacy. Diabetes Mellitus being a metabolic disorder due to the glucose surfeit, demands the need for regular exercise along with dietary changes.

Insulin therapy modulates mitochondrial dynamics and biogenesis, autophagy and tau protein phosphorylation in the brain of type 1 diabetic rats

The main purpose of this study was to examine whether streptozotocin (STZ)-induced type 1 diabetes (T1D) and insulin (INS) treatment affect mitochondrial function, fission/fusion and biogenesis, autophagy and tau protein phosphorylation in cerebral cortex from diabetic rats treated or not with INS. No significant alterations were observed in mitochondrial function as well as pyruvate levels, despite the significant increase in glucose levels observed in INS-treated diabetic rats. A significant increase in DRP1 protein phosphorylated at Ser616 residue was observed in the brain cortex of STZ rats. Also an increase in NRF2 protein levels and in the number of copies of mtDNA were observed in STZ diabetic rats, these alterations being normalized by INS. A slight decrease in LC3-II levels was observed in INS-treated rats when compared to STZ diabetic animals. An increase in tau protein phosphorylation at Ser396 residue was observed in STZ diabetic rats while INS treatment partially reversed that effect. Accordingly, a modest reduction in the activation of GSK3β and a significant increase in the activity of phosphatase 2A were found in INS-treated rats when compared to STZ diabetic animals. No significant alterations were observed in caspases 9 and 3 activity and synaptophysin and PSD95 levels. Altogether our results show that mitochondrial alterations induced by T1D seem to involve compensation mechanisms since no significant changes in mitochondrial function and synaptic integrity were observed in diabetic animals. In addition, INS treatment is able to normalize the alterations induced by T1D supporting the importance of INS signaling in the brain.