The influence of mildronate on peripheral neuropathy and some characteristics of glucose and lipid metabolism in rats with the streptozotocin model of diabetes mellitus

Rats with the streptozotocin (STZ) model of diabetes mellitus were treated with mildronate (100 mg/kg daily, per os or intraperitoneally) for 6 weeks. Body weight, blood glucose, triglycerides, ketone body concentrations, percent of glycated hemoglobin (HbA1c%), glucose tolerance, and the development of neuropathic pain were monitored throughout the whole experiment. The mildronate treatment completely prevented the development of the diabetic neuropathy from the first week up to the end of experiment. In the group of diabetic animals treated with mildronate a significant decrease of blood glucose was observed on the fourth week of the treatment, the level of triglycerides decreased from the third to sixth weeks. Mildronate also decreased accumulation of glycated hemoglobin on the sixth week and improved glucose tolerance compared with untreated animals. The data obtained confirm applicability of mildronate for therapy of diabetes mellitus and its complications.     

Changes in glucose transporter expression and nitric oxide production are associated with liver injury in diabetes

In diabetes mellitus (DM), both hyperglycaemia and hyperlipidaemia can initiate accumulation of fat in the liver, which might be further mediated by inducible nitric oxide synthase. We have studied changes in GLUT1, nitric oxide (NO^·) concentration and liver damage in two rat DM models. STZ model was induced by strepozotocin 50 mg/kg. HS model was induced by high‐fat diet and 30 mg/kg streptozotocin. GLUT1 expression was studied by means of real‐time RT‐PCR and immunohistochemistry. Production of NO^· was monitored by means of erythrocyte sedimentation rate spectroscopy of Fe‐DETC‐NO complex. Liver damage was assessed using histological activity index (HAI). NO^· concentration was increased in the liver of STZ rats, but it did not change in HS rats (control 36.8 ± 10.3; STZ 142.1 ± 31.1; HS 35.4 ± 9.8 ng/g). Liver HAI was higher in STZ group, 8.6 ± 0.17 versus HS 4.7 ± 0.31, p < 0.05. GLUT1 protein expression was elevated only in STZ group, 16 ± 3 cells/mm² versus Control 5 ± 2 cells/mm², p = 0.007. Hyperglycaemia sooner causes severe liver damage in rat models of DM, compared with hyperlipidaemia, and is associated with increased NO^· production. GLUT1 transporter expression might be involved in toxic effects of glucose in the liver. We have obtained novel data about association of GLUT1 expression and NO^· metabolism in the pathogenesis of liver injury in DM. Increased GLUT1 expression was observed together with overproduction of NO^· and pronounced liver injury in severely hyperglycaemic rats. On the contrary, moderately hyperglycaemic hyperlipidaemic rats developed only moderate liver steatosis and no increase in GLUT1 and NO^·. GLUT1 overexpression might be implicated in the toxic effects of glucose in the liver. Glycotoxicity is associated with oxidative stress and NO^· hyperproduction. GLUT1 and NO^· metabolism might become novel therapeutic targets in liver steatosis. Copyright © 2015 John Wiley & Sons, Ltd.     

1,4‐Dihydropyridine derivatives without Ca2+‐antagonist activity up‐regulate Psma6 mRNA expression in kidneys of intact and diabetic rats

Impaired degradation of proteins by the ubiquitin–proteasome system (UPS) is observed in numerous pathologies including diabetes mellitus (DM) and its complications. Dysregulation of proteasomal degradation might be because of altered expression of genes and proteins involved in the UPS. The search for novel compounds able to normalize expression of the UPS appears to be a topical problem. A novel group of 1,4‐dihydropyridine (1,4‐DHP) derivatives lacking Ca2+‐antagonists activities, but capable to produce antidiabetic, antioxidant and DNA repair enhancing effects, were tested for ability to modify Psma6 mRNA expression levels in rat kidneys and blood in healthy animals and in rats with streptozotocin (STZ) induced DM. Psma6 gene was chosen for the study, as polymorphisms of its human analogue are associated with DM and cardiovascular diseases. 1,4‐DHP derivatives (metcarbatone, etcarbatone, glutapyrone, J‐9‐125 and AV‐153‐Na) were administered per os for three days (0.05 mg/kg and/or 0.5 mg/kg). Psma6 gene expression levels were evaluated by quantitative PCR. Psma6 expression was higher in kidneys compared to blood. Induction of diabetes caused increase of Psma6 expression in kidneys, although it was not changed in blood. Several 1,4‐DHP derivatives increased expression of the gene both in kidneys and blood of control and model animals, but greater impact was observed in kidneys. The observed effect might reflect coupling of antioxidant and proteolysis‐promoting activities of the compounds. Copyright © 2015 John Wiley & Sons, Ltd.     

Routine enzymes in the monitoring of type 2 diabetes mellitus

We examined the relationships of glucose and HbA1c levels with the routinely screened serum enzyme activities in type 2 diabetes mellitus, and we designed an in vitro study to evaluate the direct effect of glucose levels on enzyme activities. The study was performed on a consecutive series of outpatients with type 2 diabetes who were followed up at Dicle University Medical Faculty Hospital from May 2009 to May 2010 for the first time. Effects of aspartate transaminase, aminotransferase, gamma‐glutamyl transferase (GGT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) activities, glucose and HbA1c levels and in vitro glucose (492, 287, 184, 131, 82 mg dl⁻¹, respectively) on enzymes were determined. The patients were categorized on the basis of glucose and HbA1c levels and grouped according to a range of values. In patients with high HbA1c levels (>10.1%), ALP, GGT activities and creatine kinase (CK)‐MB/CK (p = 0.008, 0.026, 0.014) ratio were increased significantly when compared with those in the control group. In patients with high glucose levels (>200 mg dl⁻¹), ALP, GGT activities and CK‐MB/CK ratio (p = 0.003, 0.001, 0.001) were increased significantly when compared with those in the control group. Glucose, which was added to serum in different concentrations in vitro, did not directly affect enzyme activities such as ALP, GGT and CK. We concluded that increased glucose levels could damage the liver and the heart muscle cells. Monitoring of blood glucose levels is a more valuable parameter than monitoring HbA1c in the momentary evaluation of diabetes. Copyright © 2011 John Wiley & Sons, Ltd.     

Mitochondria as the target for mildronate's protective effects in azidothymidine (AZT)-induced toxicity of isolated rat liver mitochondria

Previously mildronate, an aza-butyrobetaine derivative, was shown to be a cytoprotective drug, through its mechanism of action of inhibition of carnitine palmitoyltransferase-1, thus protecting mitochondria from long-chain fatty acid accumulation and subsequent damage. Recently in an azidothymidine (AZT)-induced cardiotoxicity model in vivo (in mice), we have found mildronate's ability of protecting heart tissue from nuclear factor kappaB abnormal expression. Preliminary data also demonstrate cerebro- and hepatoprotecting properties of mildronate in AZT-toxicity models. We suggest that mildronate may target its action predominantly to mitochondria. The present study in isolated rat liver mitochondria was designed to clarify mitochondrial targets for mildronate by using AZT as a model compound. The aim of this study was to investigate: (1) whether mildronate may protect mitochondria from AZT-induced toxicity; and (2) which is the most critical target in mitochondrial processes that is responsible for mildronate's regulatory action. The results showed that mildronate protected mitochondria from AZT-induced damage predominantly at the level of complex I, mainly by reducing hydrogen peroxide generation. Significant protection of AZT-caused inhibition of uncoupled respiration, ADP to oxygen ratio, and transmembrane potential were also observed. Mildronate per se had no effect on the bioenergetics, oxidative stress, or permeability transition of rat liver mitochondria. Since mitochondrial complex I is the first enzyme of the respiratory electron transport chain and its damage is considered to be responsible for different mitochondrial diseases, we may account for mildronate's effectiveness in the prevention of pathologies associated with mitochondrial dysfunctions.     

Trifolium pratense (Red Clover) Improve SIRT1 Expression and Glycogen Content in High Fat Diet‐Streptozotocin Induced Type 2 Diabetes in Rats

Flowering tops of Trifolium pratense L. (Fabaceae) are known for its traditional medicinal values. In present study, our aim was to investigate effect of standardized aqueous extract of flowering tops of Trifolium pratense L. on insulin resistance and SIRT1 expression in type 2 diabetic rats. Type 2 diabetes was induced by feeding high fat diet and administering low dose of streptozotocin. Diabetic animals were treated with standardized aqueous extract at three different doses. Parameters such as blood glucose, lipid profile, glycohemoglobin, insulin sensitivity, HOMA‐IR and liver glycogen content were measured. Changes in morphology and expression of SIRT1 in pancreatic tissue were measured in histopathological and immunohistological studies. Aqueous extract treatment showed reduction in hyperglycemia and improved insulin sensitivity. Extract treatment also showed reduction in formation of glycated hemoglobin and improved liver glycogen level. Histopathological study revealed protecting effect of extract in pancreatic tissue against hyperglycemia induced damage. Treatment increased expression of SIRT1 in rat pancreatic tissue. Results indicate that the aqueous extract of Trifolium pratense had beneficial role in improving insulin sensitivity and SIRT1 expression.     

Gender‐dimorphic regulation of DJ1 and its interactions with metabolic proteins in streptozotocin‐induced diabetic rats

Regulation of DJ1 is associated with a number of human diseases. To determine the involvement of DJ1 in progression of diabetes in a gender‐dependent manner, we investigated its tissue‐specific expression in streptozotocin (STZ)‐induced diabetic male and female rats in this study. In animal experiments, females showed greater susceptibility towards developing diabetes because of lower insulin secretion and higher blood glucose levels as compared to male diabetic rats upon exposure to STZ. Immunoblotting confirmed sexually dimorphic regulation of DJ1 in various metabolic tissues such as the liver, pancreas and skeletal muscle. Immunofluorescence analysis revealed the location as well as reinforced the gender‐dependent expression of DJ1 in hepatic tissue. Co‐immunoprecipitation assay identified several interacting proteins with DJ1 whose functions were shown to be involved in various metabolic pathways viz. antioxidative and stress defence system, protein and methionine metabolism, nitrogen metabolism, urea metabolism, etc. Using GeneMANIA, a predictive web interface for gene functions, we showed for the first time that DJ1 may regulate T1DM via the JNK1 pathway, suggesting DJ1 interacts with other proteins from various metabolic pathways. We anticipate that the current data will provide insights into the aetiology of T1DM.     

Blockade of cannabinoid 1 receptor improves glucose responsiveness in pancreatic beta cells

Cannabinoid 1 receptors (CB1Rs) are expressed in peripheral tissues, including islets of Langerhans, where their function(s) is under scrutiny. Using mouse β‐cell lines, human islets and CB1R‐null (CB1R^?/?) mice, we have now investigated the role of CB1Rs in modulating β‐cell function and glucose responsiveness. Synthetic CB1R agonists diminished GLP‐1‐mediated cAMP accumulation and insulin secretion as well as glucose‐stimulated insulin secretion in mouse β‐cell lines and human islets. In addition, silencing CB1R in mouse β cells resulted in an increased expression of pro‐insulin, glucokinase (GCK) and glucose transporter 2 (GLUT2), but this increase was lost in β cells lacking insulin receptor. Furthermore, CB1R^?/? mice had increased pro‐insulin, GCK and GLUT2 expression in β cells. Our results suggest that CB1R signalling in pancreatic islets may be harnessed to improve β‐cell glucose responsiveness and preserve their function. Thus, our findings further support that blocking peripheral CB1Rs would be beneficial to β‐cell function in type 2 diabetes.     

Vanadium increases GLUT4 in diabetic rat skeletal muscle

The effect of vanadium in lowering blood glucose in diabetic animals is well established; however, the exact mechanism of action of vanadium still eludes us. There are several reports from in vitro studies indicating that vanadium increases enzyme activity in insulin signalling pathways, however these findings have not been duplicated in vivo. Glucose transporters (GLUT) have a major role to play in any glucoregulatory effects. Insulin dependent GLUT4 is a major glucose transporter present in skeletal muscle, adipocytes and heart. In the present study we found that the plasma glucose in streptozotocin (STZ) diabetic animals was restored to normal following treatment with a single dose of BMOV, an organic vanadium compound, given by oral gavage (0.6 mmol/kg), similar to the response with chronic BMOV treatment. The response to BMOV by oral gavage was rapid and the animals were normoglycemic within 24 h of treatment and still demonstrated a significant effect even after 72 h. Using a specific antibody against GLUT4 we found an overall reduction in the GLUT4 in the total membrane fraction in skeletal muscle of diabetic animals. However, with a single dose of BMOV the GLUT4 level was restored to normal. This is the first report that establishes a direct effect of vanadium on the regulation of GLUT4 expression in diabetic animals in vivo, and may at least partially explain the glucoregulatory effects of vanadium.     

Suppression of GLUT1; A new strategy to prevent diabetic complications

High blood glucose results in high glucose levels in retina, because GLUT1, the sole glucose transporter between blood and retina, transports more glucose when blood glucose is high. This is the ultimate cause of diabetic retinopathy. Knockdown of GLUT1 by intraocular injections of a pool of siRNAs directed against SLC2A1 mRNA which codes for GLUT1 significantly reduced mean retinal glucose levels in diabetic mice. Systemic treatment of diabetic mice with forskolin or genistein, which bind GLUT1 and inhibit glucose transport, significantly reduced retinal glucose to the same levels seen in non‐diabetics. 1,9‐Dideoxyforskolin, which binds GLUT1 but does not stimulate adenylate cyclase had an equivalent effect to that of forskolin regarding lowering retinal glucose in diabetics indicating that cyclic AMP is noncontributory. GLUT1 inhibitors also reduced glucose and glycohemoglobin levels in red blood cells providing a peripheral biomarker for the effect. In contrast, brain glucose levels were not increased in diabetics and not reduced by forskolin. Treatment of diabetics with forskolin prevented early biomarkers of diabetic retinopathy, including elevation of superoxide radicals, increased expression of the chaperone protein β2 crystallin, and increased expression of vascular endothelial growth factor (VEGF). These data identify GLUT1 as a promising therapeutic target for prevention of diabetic retinopathy. J. Cell. Physiol. 228: 251–257, 2013. © 2012 Wiley Periodicals, Inc.     

Blood—Brain Barrier Glucose Transporter

Abstract : The transport of glucose across the blood-brain barrier (BBB) is mediated by the high molecular mass (55-kDa) isoform of the GLUT1 glucose transporter protein. In this study we have utilized the tritiated, impermeant photolabel 2-N-[4-(1-azi-2,2,2-trifluoroethyl)[2-³H]propyl]-1,3-bis(d -mannose-4-yloxy)-2-propylamine to develop a technique to specifically measure the concentration of GLUT1 glucose transporters on the luminal surface of the endothelial cells of the BBB. We have combined this methodology with measurements of BBB glucose transport and immunoblot analysis of isolated brain microvessels for labeled luminal GLUT1 and total GLUT1 to reevaluate the effects of chronic hypoglycemia and diabetic hyperglycemia on transendothelial glucose transport in the rat. Hypoglycemia was induced with continuous-release insulin pellets (6 U/day) for a 12- to 14-day duration ; diabetes was induced by streptozotocin (65 mg/kg i.p.) for a 14- to 21-day duration. Hypoglycemia resulted in 25-45% increases in regional BBB permeability-surface area (PA) values for d -[¹⁴C]glucose uptake, when measured at identical glucose concentration using the in situ brain perfusion technique. Similarily, there was a 23 ± 4% increase in total GLUT1/mg of microvessel protein and a 52 ± 13% increase in luminal GLUT1 in hypoglycemic animals, suggesting that both increased GLUT1 synthesis and a redistribution to favor luminal transporters account for the enhanced uptake. A corresponding (twofold) increase in cortical GLUT1 mRNA was observed by in situ hybridization. In contrast, no significant changes were observed in regional brain glucose uptake PA, total microvessel 55-kDa GLUT1, or luminal GLUT1 concentrations in hyperglycemic rats. There was, however, a 30-40% increase in total cortical GLUT1 mRNA expression, with a 96% increase in the microvessels. Neither condition altered the levels of GLUT3 mRNA or protein expression. These results show that hypoglycemia, but not hyperglycemia, alters glucose transport activity at the BBB and that these changes in transport activity result from both an overall increase in total BBB GLUT1 and an increased transporter concentration at the luminal surface.     

Streptozotocin-Induced Diabetes Mellitus and Further Nimodipine Treatment Do Not Change Calcium Currents in Rat Sensory Neurons within Early Stages of the Disease

Earlier, considerable prolongation of the depolarization-induced Ca²⁺ transients was demonstrated in primary sensory neurons of rats with streptozotocin (STZ)-induced diabetes mellitus. To analyze the nature of this effect, we examine possible changes in the characteristics of voltage-operated calcium channels. Neither the amplitude of Ca²⁺ currents provided by both high- and low-voltage activated calcium channels nor the respective current densities significantly changed within the early stages of diabetes mellitus. In rats treated with nimodipine, also no significant changes in the calcium channel activity were observed. Only in the case of a decrease in the external calcium concentration was some drop in the Ca²⁺ current amplitude observed. We conclude that within the early stages of diabetes mellitus there are no significant modifications in the structure of the membrane of primary sensory neurons manifested in the expression of Ca²⁺ channels, which might be responsible for the observed rapidly occurring changes in calcium signalling, cytosolic Ca²⁺ accumulation, and synaptic plasticity.     

成纤维细胞生长因子21对1型糖尿病动物模型的肝糖代谢影响及机制研究

成纤维细胞生长因子(FGF)-21是FGF家族的成员之一.作为近年发现的一种新的糖代谢调节因子,大量研究表明,FGF-21是一种不依赖胰岛素,能够独立降糖的2型糖尿病治疗潜力型药物.但是,能否应用于1型糖尿病的治疗,国内外目前尚无报道.通过改良传统造模方法,诱导小鼠缓慢产生糖耐量异常,研究FGF-21对此类模型的糖代谢影响及肝糖代谢机制.通过检测FGF-21短期注射和长期注射后模型动物血糖的变化,研究FGF-21在模型动物上对血糖的调控效果.采用实时定量PCR检测FGF-21对模型动物肝脏中葡萄糖转运蛋白(GLUT)1、4 mRNA的表达影响.利用蒽酮法检测模型动物肝脏中糖原合成量.实验结果显示,FGF-21能够调节1型糖尿病动物的血糖水平,并呈剂量依赖性.同时,首次在1型糖尿病动物模型上证实了低剂量FGF-21(0.125 mg/kg)与胰岛素的协同作用效果优于相同剂量FGF-21和胰岛素单独注射的效果.治疗结果表明,FGF-21能够维持1型糖尿病动物模型血糖在正常范围,效果优于胰岛素.实时定量PCR结果发现,与胰岛素上调GLUT4 mRNA表达量不同的是,FGF-21作用动物模型8周后,GLUT1 mRNA表达量显著提高,长期的FGF-21与胰岛素协同注射使GLUT1、4 mRNA表达量同时显著提高.长期FGF-21与胰岛素协同注射组和高剂量FGF-21注射均可显著提高模型动物肝糖原的合成.结果表明,FGF-21促进动物模型糖代谢机制与增加GLUT1表达、增加糖原合成作用有关.为临床应用FGF-21治疗1型糖尿病,增加胰岛素敏感性提供了理论依据.     

Nephroprotective potential of Quercus infectoria galls against experimentally induced diabetic nephropathy in rats through inhibition of renal oxidative stress and TGF-β

Diabetic nephropathy (DN) is the leading cause of death in diabetic patients and the current treatment options available have a limited significance. The insect galls of Quercus infectoria are traditionally important in the treatment of numerous diseases including diabetes. Hence, the present study was undertaken to evaluate the effect of Q. infectoria gall extract (QIGE) against experimental DN. Type 2 diabetes was induced by feeding rats with a high-fat diet (HFD) initially for 5 weeks, followed by a single intraperitoneal injection of streptozotocin (STZ, 35?mg/kg?bw/day). QIGE was administered to the rats orally at doses of 100 and 200?mg/kg?bw/day, respectively. At the end of the experimental period, various glycemic and renal function parameters were evaluated in the serum, urine and kidney tissues. The QIGE treatment significantly (p?p?via the inhibition of hyperglycemia-induced oxidative stress and renal TGF-β expression and is, therefore, a potential therapeutic agent in the treatment of diabetic complications, especially DN.     

Petalonia improves glucose homeostasis in streptozotocin-induced diabetic mice

The anti-diabetic potential of Petalonia binghamiae extract (PBE) was evaluated in vivo. Dietary administration of PBE to streptozotocin (STZ)-induced diabetic mice significantly lowered blood glucose levels and improved glucose tolerance. The mode of action by which PBE attenuated diabetes was investigated in vitro using 3T3-L1 cells. PBE treatment stimulated 3T3-L1 adipocyte differentiation as evidenced by increased triglyceride accumulation. At the molecular level, peroxisome proliferator-activated receptor γ (PPARγ) and terminal marker protein aP2, as well as the mRNA of GLUT4 were up-regulated by PBE. In mature adipocytes, PBE significantly stimulated the uptake of glucose and the expression of insulin receptor substrate-1 (IRS-1). Furthermore, PBE increased PPARγ luciferase reporter gene activity in COS-1 cells. Taken together, these results suggest that the in vivo anti-diabetic effect of PBE is mediated by both insulin-like and insulin-sensitizing actions in adipocytes.     

Carnitine depletion in rat pups from mothers given mildronate: a model of carnitine deficiency in late fetal and neonatal life

Mildronate (3-(2,2,2,-trimethylhydrazinium)propionate), is a butyrobetaine analogue that is known to inhibit gamma-butyrobetaine hydroxylase, the enzyme catalyzing the last step of carnitine biosynthesis. When administered to adult rats it determines a systemic carnitine deficiency and may therefore serve as an animal model for human carnitine depletion. The aim of this study was to evaluate the effect of mildronate administration to pregnant and lactating rats on tissue carnitine concentrations in 4- and 13-day-old rat pups. At 14 days of gestation female rats began to receive mildronate in the diet (200 mg/kg/d) and this continued for entire lactation period. Mildronate treatment determined a large reduction of carnitine levels in the milk of lactating dams. Because organ carnitine concentrations in neonatal rats are directly related to dietary supply, pups from mildronate group had significantly depleted levels of total carnitine in serum, heart, liver, muscle, brain and pancreas relative to controls, at 4 and 13 days of age. Correspondingly, an increase in triglyceride levels was observed in liver, heart and muscle of mildronate pups. This is in agreement with a reduction of basal rate of oxidation of [U-(14)C]-palmitate to (14)CO(2) and (14)C-acid-soluble products observed in liver homogenates from carnitine-deficient pups. All functional and biochemical modifications were compatible with a carnitine deficiency status. In conclusion our results describe a model of carnitine depletion in pups, suitable for the investigation of carnitine deficiency in fetal-neonatal nutrition, without any concomitant mildronate-mediated metabolic alterations.     

Glucose promotes epithelial‐mesenchymal transitions in bladder cancer by regulating the functions of YAP1 and TAZ

Glucose levels and type 2 diabetes (T2D) are both associated with tumorigenesis and epithelial‐mesenchymal transitions (EMTs). EMTs facilitate bladder cancer (BC) metastasis development, but the mechanism by which high‐glucose levels promote these EMTs in BC remains unclear. Therefore, we sought to elucidate the mechanism underlying EMT promotion due to increased glucose levels. T24 and UMUC‐3 cells were cultured in media containing different glucose concentrations. YAP1, TAZ, GLUT1 and EMT‐associated marker expression was analysed via Western blotting and qPCR. BC cell proliferation and invasion were assessed using MTT and Transwell assays, respectively. A xenograft nude mouse model of diabetes was used to evaluate tumour growth and metastasis in vivo. T2D was positively associated with pathologic grade (P = .016) and TNM stage (P < .001) in BC. High glucose triggered BC cell proliferation and invasion in both in vitro and in vivo conditions. High‐glucose levels also promoted EMTs in BC cells and increased YAP1 and TAZ expression. YAP1 or TAZ knockdown altered EMT marker expression and decreased GLUT1 expression. Overall, our results suggest that high‐glucose levels promote EMTs in BC cells via YAP1 and TAZ regulation. These effector molecules may be promising therapeutic targets for BC cases comorbid with T2D.     

Possible mechanisms underlying calcium signal changes in murine sensory neurons at experimental diabetes

Numerous investigations indicate thatdiabetes mellitus is associated with pronounced changes in calcium homeostasis, which in turn lead to substantial complications in most systemic functions. However, similar combined investigations of possible alterations in calcium signalling in the nerve cells are lacking, although pathological changes in nervous functions, including paresthesia and increased pain sensitivity, are common complications ofdiabetes mellitus in humans. Therefore, we studied the changes in calcium homeostasis in sensory neurons of mice with streptozotocin (STZ)-induced and genetically determineddiabetes mellitus.     

lncRNA NBR2 modulates cancer cell sensitivity to phenformin through GLUT1

Biguanides, including metformin (widely used in diabetes treatment) and phenformin, are AMP-activated protein kinase (AMPK) activators and potential drugs for cancer treatment. A more in-depth understanding of how cancer cells adapt to biguanide treatment may provide important therapeutic implications to achieve more effective and rational cancer therapies. NBR2 is a glucose starvation-induced long non-coding RNA (lncRNA) that interacts with AMPK and regulates AMPK activity upon glucose starvation. Here we show that phenformin treatment induces NBR2 expression, and NBR2 deficiency sensitizes cancer cells to phenformin-induced cell death. Surprisingly, unlike glucose starvation, phenformin does not induce NBR2 interaction with AMPK, and correspondingly, NBR2 deficiency does not affect phenformin-induced AMPK activation. We further reveal that NBR2 depletion attenuates phenformin-induced glucose transporter GLUT1 expression and glucose uptake. GLUT1 deficiency sensitizes cancer cells to phenformin-induced cell death, whereas GLUT1 restoration in NBR2 deficient cells rescues the increased cell death upon phenformin treatment. Together, the results of our study reveal that NBR2-GLUT1 axis may serve as an adaptive response in cancer cells to survive in response to phenformin treatment, and identify a novel mechanism coupling lncRNA to biguanide-mediated biology.