GPR21 Inhibition Increases Glucose-Uptake in HepG2 Cells.

GPR21 is a constitutively active, orphan, G-protein-coupled receptor, with in vivo studies suggesting its involvement in the modulation of insulin sensitivity. However, its precise contribution is not fully understood. As the liver is both a major target of insulin signalling and critically involved in glucose metabolism, the aim of this study was to examine the role of GPR21 in the regulation of glucose uptake and production in human hepatocytes. In particular, HepG2 cells, which express GPR21, were adopted as cellular models. Compared with untreated cells, a significant increase in glucose uptake was measured in cells treated with siRNA to downregulate GPR21 expression or with the GPR21-inverse agonist, GRA2. Consistently, a significantly higher membrane translocation of GLUT-2 was measured under these conditions. These effects were accompanied by an increased ratio of phAKT(Ser473)/tot-AKT and phGSK-3ß(Ser9)/tot-GSK-3ß, thus indicating a marked activation of the insulin signalling pathway. Moreover, a significant reduction in ERK activation was observed with GPR21 inhibition. Collectively, these results indicate that GPR21 mediates the negative effects on glucose uptake by the liver cells. In addition, they suggest that the pharmacological inhibition of GPR21 could be a novel strategy to improve glucose homeostasis and counteract hepatic insulin resistance.

G protein-coupled receptor 21 in macrophages: An in vitro study.

GPR21 is an orphan and constitutively active receptor belonging to the superfamily of G-Protein Coupled Receptors (GPCRs). GPR21 couples to the Gq family of G proteins and is expressed in macrophages. Studies of GPR21 knock-out mice indicated that GPR21 may be involved in promoting macrophage migration. The aim of this study was to evaluate the role of GPR21 in human macrophages, analyzing (i) its involvement in cell migration and cytokine release and (ii) the consequence of its pharmacological inhibition by using the inverse agonist GRA2. THP-1 cells were activated and differentiated into either M1 or M2 macrophages. GPR21 expression was evaluated at gene and protein level, the signalling pathway was investigated by an IP1 assay, and cytokine release by ELISA. Cell migration was detected by the Boyden chamber migration assay, performed on macrophages derived from both the THP-1 cell line and human peripheral blood monocytes. In addition, we compared the effect of the pharmacological inhibition of GPR21 with the effect of the treatment with a specific GPR21 siRNA to downregulate the receptor expression, thus confirming that GRA2 acts as an inverse agonist of GPR21. GRA2 does not affect cell viability at the tested concentrations, but significantly reduces the release of TNF-α and IL-1ß from M1 macrophages. The analysis of the migratory ability highlighted opposite effects of GRA2 on M1 and M2 macrophages since it decreased M1, while it promoted M2 cell migration. Therefore, the pharmacological inhibition of GPR21 could be of interest for pathological conditions characterized by low grade chronic inflammation.

Sedentariness and Urinary Metabolite Profile in Type 2 Diabetic Patients, a Cross-Sectional Study.

Recent findings indicate a significant association between sedentary (SED)-time and type 2 diabetes mellitus(T2DM). The aim of this study was to investigate whether different levels of SED-time could impact on biochemical and physiological processes occurring in sedentary and physically inactive T2DM patients. In particular, patients from the "Italian Diabetes and Exercise Study (IDES)_2 trial belonging to the first and fourth quartile of SED-time were compared. Urine samples were analyzed by comprehensive two-dimensional gas chromatography(GC×GC) with parallel detection by mass spectrometry and flame ionization detection(GC×2GC-MS/FID). This platform enables accurate profiling and fingerprinting of urinary metabolites while maximizing the overall information capacity, quantitation reliability, and response linearity. Moreover, using advanced pattern recognition, the fingerprinting process was extended to untargeted and targeted features, revealing diagnostic urinary fingerprints between groups. Quantitative metabolomics was then applied to analytes of relevance for robust comparisons. Increased levels of glycine, L-valine,L-threonine, L-phenylalanine, L-leucine, L-alanine, succinic acid, 2-ketoglutaric acid, xylitol, and ribitol were revealed in samples from less sedentary women. In conclusion, SED-time is associated with changes in urine metabolome signatures. These preliminary results suggest that reducing SED-time could be a strategy to improve the health status of a large proportion of diabetic patients.

PPARgamma stimulation promotes neurite outgrowth in SH-SY5Y human neuroblastoma cells.

Several evidences indicate that PPARgamma stimulation promotes neuronal differentiation. However, to date, no data describe the effects of PPARgamma agonists on neurite outgrowth. Here we have evaluated the effects of pioglitazone, a synthetic PPARgamma agonist, on differentiation and neurite outgrowth in SH-SY5Y human neuroblastoma cells. Our results show that pioglitazone promotes cell differentiation and the outgrowth of cell processes in a concentration-dependent manner with the maximal effect at 100 nM-1 microM. It significantly increases both the mean process length and the percentage of neurite-bearing cells. In addition, these effects are accompanied by significant activation of p42 and p44 mitogen-activated protein kinases. In conclusion, albeit preliminary, these findings suggest the possibility that PPARgamma stimulation may contribute to the development and maintenance of a proper neuronal connectivity within neuronal networks.

Effects of amine oxidases in allergic and histamine-mediated conditions.

This review provides an update on histamine, on diamine oxidase (DAO) and on their implications in allergy and various conditions or affections, such as food histaminosis, ischemia and inflammatory bowel diseases (IBD). The review also presents, in brief, patent coverage on therapies for allergy and IBD with the focus on histamine-related treatments.

PPARgamma stimulation promotes mitochondrial biogenesis and prevents glucose deprivation-induced neuronal cell loss.

Peroxisome proliferator-activated receptor (PPAR)gamma stimulation provides protection in several models of neurological disorders, but the mechanisms underlying these effects remain to be fully elucidated. Here we have studied whether two PPARgamma agonists, pioglitazone and rosiglitazone, prevent loss of differentiated SH-SY5Y cells transiently exposed to glucose deprivation (GD). Nanomolar drug concentrations prevented GD-induced cell loss in a concentration- and time-dependent manner. These effects were abolished by malonate, a reversible mitochondrial Complex II inhibitor, while significantly potentiated by pyruvate, thus suggesting that they are related to mitochondrial function. During cell pretreatment, PPARgamma agonists promoted biogenesis of functional mitochondria, as indicated by the up-regulation of PPARgamma coactivator (PGC)-1alpha, NRF1, TFAM, cytochrome c oxidase subunit (CO) I and CO IV, and the increased level of mtDNA, while did not significantly change mitochondrial membrane potential. In addition, the analysis of the concentration-response and time-course curves for the protective effects and the up-regulation of mitochondrial biogenesis markers suggests that mitochondrial biogenesis and cell loss prevention are related effects. In conclusion our data indicate that a prolonged PPARgamma stimulation, by repeated administration of nanomolar pioglitazone or rosiglitazone concentrations, decreases GD-induced loss of differentiated SH-SY5Y cells. In addition, they suggest that mitochondrial biogenesis may contribute to these effects.