A2 noradrenergic nerve cell metabolic transducer and nutrient transporter adaptation to hypoglycemia: impact of estrogen.

CNS neurons exhibit sustained activation by recurring hypoglycemia in the presence of estrogen. We investigated the impact of estradiol on fuel uptake and detection of energy imbalance by hindbrain A2 metabolosensory neurons during acute vs. chronic hypoglycemia. A2 neurons were laser dissected from estradiol benzoate (EB)- and oil (O)-implanted ovariectomized rats after single or serial injection of neutral protamine Hagedorn (NPH) insulin for single-cell qPCR or high-sensitivity Western blotting. Acute NPH increased A2 GLUT3 mRNA but not protein in EB, but decreased both profiles in O rats. Single insulin dosing did not alter monocarboxylate transporter-2 (MCT2) mRNAs in EB or O, but increased MCT2 protein in EB. Preceding hypoglycemia augmented baseline transporter mRNA and protein in O, but decreased GLUT4 and increased MCT2 proteins in EB. Chronic NPH increased A2 MCT2 and GLUT3 proteins in EB, but elevated GLUT4 protein in O. A2 phospho-AMPK (pAMPK) protein was progressively diminished by acute and chronic hypoglycemia in EB, but elevated in O after serial NPH. Dopamine-ß-hydroxylase (DßH) transcripts were decreased in EB during acute and chronic hypoglycemia, but unaltered by serial NPH dosing in O. These results suggest that estrogen enhances A2 lactate utilization during acute hypoglycemia, thereby lessening AMPK activation relative to euglycemic controls. Cellular adaptation to chronic hypoglycemia may involve estrogen-dependent augmentation of lactate and GLUT3-mediated glucose uptake and hormone-independent increases in GLUT4 expression, coincident with diminished pAMPK-mediated signaling of energy deficiency. The data also imply that increased lactate and glucose uptake during recurring hypoglycemia may be required for sustained DßH transcriptional reactivity to this metabolic stress.

Differential effects of 5-fluorouracil on glucose transport and expressions of glucose transporter proteins in gastric cancer cells.

Although 5-fluorouracil (5-FU) is a widely used chemotherapeutic agent in the treatment of gastric cancer, the underlying mechanism for 5-FU resistant phenotype, has yet to be elucidated. We hypothesized that the sensitivity of gastric cancer to 5-FU treatment might be related to the rate of glucose transport (GLUT), and investigated the expressions of GLUT1, 2, 3, and 4 in two different gastric cancer cells (SNU-216, moderately differentiated gastric adenocarcinoma; and SNU-668, signet ring cell gastric carcinoma). Immunohistochemistry of GLUT1 and GLUT4 and immunoblot analysis of glycogen synthase kinase 3 were also performed. Hexokinase activity was measured. We found that 5-FU suppressed glucose uptake in SNU-216, while it stimulated GLUT in SNU-668. Further analysis revealed that 5-FU decreased the expression levels of GLUT1, 2, and 4 in SNU-216 cells and increased the expression levels of GLUT1, 2, and 4 in SNU-668 cells. Consistent with GLUT expression levels, immunohistochemistry analysis showed that 5-FU increased GLUT1 and GLUT4 levels in SNU-216 and decreased GLUT1 and GLUT4 levels in SNU-668. We also observed that glycogen synthase kinase 3 activity was decreased in SNU-216 and increased in SNU-668 with 5-FU treatment. No significant difference in hexokinase activities was observed with 5-FU treatment. Taken together, these results suggest that 5-FU exerts differential effects on GLUT depending on gastric cancer cell types, which may indicate a possible explanation, at least in part, for the differing responses to 5-FU chemotherapy in gastric cancer.

Oleanolic acid derivative NPLC441 potently stimulates glucose transport in 3T3-L1 adipocytes via a multi-target mechanism.

The natural product oleanolic acid (OA) has been discovered to exhibit varied pharmacological functions including anti-inflammation, anti-tumor and anti-diabetes, while appropriate synthetic oleanolic acid derivatives seem to possess more potent activities. Here we identified a new oleanolic acid derivative, 3-beta-(2-carboxybenzoyloxy)-oleanolic acid (NPLC441), which functioned as a competitive PTP1B inhibitor and enhanced insulin-stimulated phosphorylation of IR and AKT in HepG2 cells. As an RXRalpha antagonist, it could selectively activate LXRalpha:RXRalpha heterodimer and increase the promoter activities of ABCA1 and ABCG1 genes in transient transfection assays. Quantitative RT-PCR and Western blot analyses suggested that NPLC441 could up-regulate GLUT4 expression in 3T3-L1 adipocytes, and such effect was further proved to be dependent on LXRalpha:RXRalpha activation. Moreover, 2-deoxyglucose uptake technology-based characterization demonstrated that this compound could stimulate glucose uptake in 3T3-L1 adipocytes. Finally, NPLC441 was observed to be able to suppress 11beta-HSD(1) expression in HepG2 cells, following the discovery that activation of LXRalpha:RXRalpha could repress the expression of 11beta-HSD(1). Compared with NPLC441, OA showed no effects on the transactivation of either LXRalpha:RXRalpha heterodimer or RXRalpha-LBD. Our work is thus expected to provide a new insight into the anti-diabetic application for oleanolic acid derivatives via multi-target mechanism, and NPLC441 could be used as a potential lead compound for further research.