Glucose Transport In Cells Research Articles

Expression and Purification of Rat Glucose Transporter 1 in Pichia pastoris.

Large amounts of pure and homogenous protein are a prerequisite for several biochemicaland biophysical analyses, and in particular if aiming at resolving the three-dimensional protein structure. Here we describe the production of the rat glucose transporter 1 (GLUT1), a membrane protein facilitating the transport of glucose in cells. The protein is recombinantly expressed in the yeast Pichia pastoris. It is easily maintained and large-scale protein production in shaker flasks, as commonly performed in academic research laboratories, results in relatively high yields of membrane protein. The purification protocol describes all steps needed to obtain a pure and homogenous GLUT1 protein solution, including cell growth, membrane isolation, and chromatographic purification methods.

Orchestration of the mammalian host cell glucose transporter proteins-1 and 3 by Chlamydia contributes to intracellular growth and infectivity.

Chlamydia are gram-negative obligate intracellular bacteria that replicate within a discrete cellular vacuole, called an inclusion. Although it is known that Chlamydia require essential nutrients from host cells to support their intracellular growth, the molecular mechanisms for acquiring these macromolecules remain uncharacterized. In the present study, it was found that the expression of mammalian cell glucose transporter proteins 1 (GLUT1) and glucose transporter proteins 3 (GLUT3) were up-regulated during chlamydial infection. Up-regulation was dependent on bacterial protein synthesis and Chlamydia-induced MAPK kinase activation. GLUT1, but not GLUT3, was observed in close proximity to the inclusion membrane throughout the chlamydial developmental cycle. The proximity of GLUT1 to the inclusion was dependent on a brefeldin A-sensitive pathway. Knockdown of GLUT1 and GLUT3 with specific siRNA significantly impaired chlamydial development and infectivity. It was discovered that the GLUT1 protein was stabilized during infection by inhibition of host-dependent ubiquitination of GLUT1, and this effect was associated with the chlamydial deubiquitinase effector protein CT868. This report demonstrates that Chlamydia exploits host-derived transporter proteins altering their expression, turnover and localization. Consequently, host cell transporter proteins are manipulated during infection as a transport system to fulfill the carbon source requirements for Chlamydia.

Microcystin-LR disrupts insulin signaling by hyperphosphorylating insulin receptor substrate 1 and glycogen synthase.

Microcystin-LR (MC-LR) is a cyanobacteria-derived heptapeptide that has been commonly characterized as a hepatotoxin. Although the liver is a primary organ in glucose homeostasis, the effect of MC-LR on glucose metabolism remains unclear. In this study, the human liver cell line HL7702 and ICR mice were exposed to various concentrations of MC-LR for 24 h, and the proteins involved in insulin signaling were investigated. The results showed that MC-LR treatment induced the hyperphosphorylation of insulin receptor substrate 1 (IRS1) at several serine sites, S307, S323, S636/639, and S1101 in HL7702 cells, and S302, S318, S632/635, and S1097 in mice livers. In addition, the activation of S6K1 was demonstrated to play an important role in MC-LR-induced IRS1 hyperphosphorylation at several serine sites. Decreased levels of total IRS1 were observed in the mice livers, but there was no significant change in HL7702 cells. MC-LR also induced glycogen synthase (GS) hyperphosphorylation at S641 (inactivating GS) both in vitro and in vivo, even glycogen synthase kinase 3, a well-known GS kinase, was inactivated after MC-LR treatment. Moreover, MC-LR could block insulin-induced GS activation. In addition, glucose transport in liver cells was not impacted by MC-LR either with or without insulin stimulation. Our study implies that MC-LR can interfere with the actions of IRS1 and GS in insulin signaling and may have a toxic effect on glucose metabolism in the liver.

Repin1 deficiency in adipose tissue improves whole-body insulin sensitivity, and lipid metabolism.

Replication initiator 1 (Repin1) gene encodes for a zinc-finger protein and has been implicated in the regulation of adipocyte cell size and glucose transport in vitro. Here, we investigate the consequences of reduced adipose tissue (AT) Repin1 expression in vivo. We have inactivated the Repin1 gene in adipose tissue (iARep-/-) at an age of 4 weeks using tamoxifen-inducible gene targeting strategies on the background of C57BL/6NTac mice. Furthermore, we differentiated human primary adipocytes derived from subcutaneous AT in vitro and knocked down REPIN1 using siRNA technique to measure glycerol release. Conditional Repin1 inactivation results in decreased AT mass, smaller adipocytes in both, subcutaneous and epigonadal AT compared to controls. Compared to controls, iARep-/- mice were more insulin sensitive, had better glucose tolerance and lower LDL-, HDL- and total cholesterol. Significantly lower AT expression of the Repin1 target genes Cd36 and Lcn2 may contribute to the phenotype of iARep-/- mice. Knockdown of REPIN1 in human in vitro differentiated adipocytes revealed an increased glycerol release. In conclusion, deficiency of Repin1 in AT causes alterations in AT morphology and function, which may underlay lower body weight and improved parameters of insulin sensitivity, glucose and lipid metabolism.

CREB1 regulates glucose transport of glioma cell line U87 by targeting GLUT1.

Glioma is stemmed from the glial cells in the brain, which is accounted for about 45% of all intracranial tumors. The characteristic of glioma is invasive growth, as well as there is no obvious boundary between normal brain tissue and glioma tissue, so it is difficult to resect completely with worst prognosis. The metabolism of glioma is following the Warburg effect. Previous researches have shown that GLUT1, as a glucose transporter carrier, affected the Warburg effect, but the molecular mechanism is not very clear. CREB1 (cAMP responsive element-binding protein1) is involved in various biological processes, and relevant studies confirmed that CREB1 protein regulated the expression of GLUT1, thus mediating glucose transport in cells. Our experiments mainly reveal that the CREB1 could affect glucose transport in glioma cells by regulating the expression of GLUT1, which controlled the metabolism of glioma and affected the progression of glioma.

Role of glucose metabolism related gene GLUT1 in the occurrence and prognosis of colorectal cancer.

Colorectal cancer (CRC) ranks the third most commonly diagnosed cancer in males and the second in females worldwide. However, the functional and causal SNPs for CRC remain to be mined. Glucose transporter 1 (GLUT1), a pivotal rate-limiting element in the transport of glucose in malignancy cells, has been identified to be associated with many cancers. Here, we aim to explore the role of GLUT1 in the occurrence and prognosis of colorectal cancer in a Chinese population. We found that GLUT1 expression levels in CRC tumor tissues were significantly higher than those in the corresponding adjacent normal tissues, and Cox multivariate analysis demonstrated that the GLUT1 expression was an independent prognostic factor for CRC (HR = 2.11, 95% CI = 1.33–3.34, P=0.001). For a functional polymorphism of GLUT1 (rs710218), we found that individuals with TT genotype (OR = 1.68, 95% CI = 1.02-2.75, P = 0.041) or AT genotype (OR = 1.47, 95% CI = 1.09-1.99, P = 0.012) of rs710218 had a significantly increased risk of CRC compared to those with AA homozygote. These findings strongly suggest that glucose metabolism related gene GLUT1, and its functional SNP, rs710218 might contribute to CRC susceptibility and prognosis, and the exact biological mechanism awaits further research.

Expression of glucose transporter 1 and prognosis in non-small cell lung cancer: a pooled analysis of 1665 patients.

Glucose transporter 1 (GLUT1) plays an important role in the transport and metabolism of glucose in cancer cells. An increasing number of studies have explored the connection between GLUT1 expression and prognosis in non-small cell lung cancer (NSCLC), but the results have been controversial. Therefore, we conducted a meta-analysis to obtain a comprehensive evaluation of the prognostic value of GLUT1 in NSCLC. Relevant studies from PubMed, Embase, and Web of Science were searched. Hazard ratios (HRs) and odds ratios (ORs) with their 95% confidence intervals (CIs) were used as the effective measures. A total of 10 studies involving 1,665 patients were included in this meta-analysis. The results showed that GLUT1 overexpression was associated with poor overall survival (HR = 2.21; 95% CI, 1.42–3.42; p < 0.001) and disease-free survival (HR = 1.73; 95% CI, 1.35–2.23; p < 0.001). Furthermore, elevated GLUT1 expression correlated with sex (OR = 2.29; 95% CI, 1.17–4.49; p = 0.015), advanced tumor stage (OR = 2.46; 95% CI, 1.79–3.38; p < 0.001), histology (OR = 6.99; 95% CI, 4.71–10.38; p < 0.001), and large tumor size (OR = 2.77; 95% CI, 1.73–4.44; p < 0.001). This meta-analysis revealed overexpression of GLUT1 to be a biomarker of worse prognosis in NSCLC.

Puerariae Lobatae Radix elevated expression levels of OB-R, IRS2, GLUT1 and GLUT2 to regulate glucose metabolism in insulin-resistance HepG2 cells

To observe the anti-hyperglycemic effect of Puerariae Lobatae Radix in hepatocyte insulin resistance(IR) models, and investigate its preliminary molecular mechanism. IR-HepG2 cell model was stably established with 1×10-9 mol•L⁻¹ insulin plus 3.75×10-6 mol•L-1 dexamethasone treatment for 48 h according to optimized protocol in our research group. After IR-HepG2 cells were treated with different concentrations(5%,10% and 15%) of Puerariae Lobatae Radix-containing serum, cell viability was detected by CCK-8 assay; the glucose consumptions in IR-HepG2 cells were separately detected at different time points (12, 15, 18, 21, 24, 30, 36 h) by using glucose oxidase method; intracellular glycogen content was detected by anthrone method; and the protein expression levels of leptin receptor (Ob-R), insulin receptor substrate-2 (IRS2), glucose transporter 1(GLUT1) and GLUT2 were detected by Western blot assay. The results showed that Puerariae Lobatae Radix-containing serum (5%, 10% and 15%) had no significant effect on IR-HepG2 cell viability; 5% and 10% Puerariae Lobatae Radix-containing serum significantly increased glucose consumption of IR-HepG2 cells (P<0.01) at 18, 21 and 24 h; 15% Puerariae Lobatae Radix-containing serum elevated the glucose consumption of IR-HepG2 cells at 15 h (P<0.05), and significantly elevated the glucose consumption at 18, 21, 24 and 30 h (P<0.01) in a dose-dependent manner. The optimized time of anti-hyperglycemic effect was defined as 24 h, and further study showed that Puerariae Lobatae Radix-containing serum could increase intracellular glycogen content after 24 h treatment (P<0.01), and up-regulate IRS2, Ob-R, GLUT1 and GLUT2 protein expression levels. Our results indicated that Puerariae Lobatae Radix-containing serum could achieve the anti-hyperglycemic effect through important PI3K/PDK signaling pathway partially by up-regulating the expression levels of Ob-R and IRS2, GLUT1 and GLUT2 in IR-HepG2 cells, accelerating the glucose transport into hepatocytes and increasing hepatic glycogen synthesis to enhance the anti-hyperglycemic effect of IR-HepG2 cells.

Glucose transporter GLUT1 expression and clinical outcome in solid tumors: a systematic review and meta-analysis.

Glucose transporter 1 (GLUT1), the uniporter protein encoded by the SLC2A1 gene, is a key rate-limiting factor in the transport of glucose in cancer cells, and frequently expressed in a significant proportion of human cancers. Numerous studies have reported paradoxical evidence of the relationship between GLUT1 expression and prognosis in solid human tumors. To address this discrepancy, we conducted a thorough search of Pubmed and Web of Science for studies evaluating the expression of GLUT1 and overall survival (OS) and disease-free survival (DFS) in patients with solid cancer from 1993 to April 2016. Data from published researches were extracted and computed into odds ratio (OR). A total of 26 studies including 2948 patients met our search criteria and were evaluated. Overexpression of GLUT1 was found to significantly correlate with poor 3-year OS (OR: 2.86; 95% CI, 1.90–4.32, P < 0.00001) and 5-year OS (OR: 2.52; 95% CI, 1.75–3.61, P < 0.00001) of solid tumors. Similar results were observed when analysis of DFS was performed. Subgroup analysis revealed that elevated GLUT1 expression was associated with worse prognosis of oral squamous cell carcinoma and breast cancer. Taken together, overexpression of GLUT1 is correlated with poor survival in most solid tumors, suggesting that the expression status of GLUT1 is a vital prognostic indicator and promising therapeutic target in solid tumors.

The expression and regulation of glucose transporters in tumor cells

&lt;p&gt;Glucose transporter proteins are involved in many physiological and biochemical processes. In particular, the high expressions of sodium-glucose cotransporter and glucose transporter proteins in tumor cells show that these two transporters play a key role in tumor cell metabolism. Studying the crystal structure and conformation of human glucose transporter proteins has enabled the development of drugs based on specific binding sites, opening up a new path towards more effective cancer treatments. This mini review serves to summarize our existing understanding of the metabolic pathways of tumor cells, focusing on the roles of glucose transporter proteins.&lt;/p&gt;

Acute Effects of Sugars and Artificial Sweeteners on Small Intestinal Sugar Transport: A Study Using CaCo-2 Cells As an In Vitro Model of the Human Enterocyte.

BackgroundThe gastrointestinal tract is responsible for the assimilation of nutrients and plays a key role in the regulation of nutrient metabolism and energy balance. The molecular mechanisms by which intestinal sugar transport are regulated are controversial. Based on rodent studies, two models currently exist that involve activation of the sweet-taste receptor, T1R2/3: an indirect model, whereby luminal carbohydrates activate T1R2/3 expressed on enteroendocrine cells, resulting in the release of gut peptides which in turn regulate enterocyte sugar transport capacity; and a direct model, whereby T1R2/3 expressed on the enterocyte regulates enterocyte function.AimsTo study the direct model of intestinal sugar transport using CaCo-2 cells, a well-established in vitro model of the human enterocyte.MethodsUptake of 10mM 14C D-Glucose and D-Fructose into confluent CaCo-2/TC7 cells was assessed following 3hr preincubation with sugars and artificial sweeteners in the presence and absence of the sweet taste receptor inhibitor, lactisole. Expression of the intestinal sugar transporters and sweet-taste receptors were also determined by RT-PCR.ResultsIn response to short term changes in extracellular glucose and glucose/fructose concentrations (2.5mM to 75mM) carrier-mediated sugar uptake mediated by SGLT1 and/or the facilitative hexose transporters (GLUT1,2,3 and 5) was increased. Lactisole and artificial sweeteners had no effect on sugar transport regulated by glucose alone; however, lactisole increased glucose transport in cells exposed to glucose/fructose. RT-PCR revealed Tas1r3 and SGLT3 gene expression in CaCo-2/TC7 cells, but not Tas1r2.ConclusionsIn the short term, enterocyte sugar transport activities respond directly to extracellular glucose levels, but not fructose or artificial sweeteners. We found no evidence of a functional heterodimeric sweet taste receptor, T1R2/3 in CaCo-2 cells. However, when glucose/fructose is administered together there is an inhibitory effect on glucose transport possibly mediated by T1R3.

Effect of nordihydroguaiaretic acid on cell viability and glucose transport in human leukemic cell lines.

The polyphenol nordihydroguaiaretic acid (NDGA) has antineoplastic properties, hence it is critical to understand its action at the molecular level. Here, we establish that NDGA inhibits glucose uptake and cell viability in leukemic HL‐60 and U‐937 cell lines. We monitored hexose uptake using radio‐labeled 2‐deoxyglucose (2DG) and found that the inhibition by NDGA followed a noncompetitive mechanism. In addition, NDGA blocked hexose transport in human red blood cells and displaced prebound cytochalasin B from erythrocyte ghosts, suggesting a direct interaction with the glucose transporter GLUT1. We propose a model for the mechanism of action of NDGA on glucose uptake. Our study shows for the first time that NDGA can act as inhibitor of the glucose transporter GLUT1.

Increased Glucose Transport into Neurons Rescues Aβ Toxicity in Drosophila

SummaryGlucose hypometabolism is a prominent feature of the brains of patients with Alzheimer’s disease (AD). Disease progression is associated with a reduction in glucose transporters in both neurons and endothelial cells of the blood-brain barrier. However, whether increasing glucose transport into either of these cell types offers therapeutic potential remains unknown. Using an adult-onset Drosophila model of Aβ (amyloid beta) toxicity, we show that genetic overexpression of a glucose transporter, specifically in neurons, rescues lifespan, behavioral phenotypes, and neuronal morphology. This amelioration of Aβ toxicity is associated with a reduction in the protein levels of the unfolded protein response (UPR) negative master regulator Grp78 and an increase in the UPR. We further demonstrate that genetic downregulation of Grp78 activity also protects against Aβ toxicity, confirming a causal effect of its alteration on AD-related pathology. Metformin, a drug that stimulates glucose uptake in cells, mimicked these effects, with a concomitant reduction in Grp78 levels and rescue of the shortened lifespan and climbing defects of Aβ-expressing flies. Our findings demonstrate a protective effect of increased neuronal uptake of glucose against Aβ toxicity and highlight Grp78 as a novel therapeutic target for the treatment of AD.

Ketoisocaproic acid, a metabolite of leucine, suppresses insulin-stimulated glucose transport in skeletal muscle cells in a BCAT2-dependent manner.

Although leucine has many positive effects on metabolism in multiple tissues, elevated levels of this amino acid and the other branched-chain amino acids (BCAAs) and their metabolites are implicated in obesity and insulin resistance. While some controversies exist about the direct effect of leucine on insulin action in skeletal muscle, little is known about the direct effect of BCAA metabolites. Here, we first showed that the inhibitory effect of leucine on insulin-stimulated glucose transport in L6 myotubes was dampened when other amino acids were present, due in part to a 140% stimulation of basal glucose transport (P < 0.05). Importantly, we also showed that α-ketoisocaproic acid (KIC), an obligatory metabolite of leucine, stimulated mTORC1 signaling but suppressed insulin-stimulated glucose transport (-34%, P < 0.05) in an mTORC1-dependent manner. The effect of KIC on insulin-stimulated glucose transport was abrogated in cells depleted of branched-chain aminotransferase 2 (BCAT2), the enzyme that catalyzes the reversible transamination of KIC to leucine. We conclude that although KIC can modulate muscle glucose metabolism, this effect is likely a result of its transamination back to leucine. Therefore, limiting the availability of leucine, rather than those of its metabolites, to skeletal muscle may be more critical in the management of insulin resistance and its sequelae.

Diabetes and exposure to peritoneal dialysis solutions alter tight junction proteins and glucose transporters of rat peritoneal mesothelial cells

AimTo evaluate alterations in tight junction (TJ) proteins and glucose transporters in rat peritoneal mesothelial cells (RPMC) from diabetic rats and after treatment with peritoneal dialysis solutions (PDS) in vitro. MethodsDiabetes was induced in female Wistar rats by streptozotocin (STZ)-injection. Twenty-one days after STZ-injection, peritoneal thickness and mesothelial cell morphology were studied by light microscopy and microvilli length and density by atomic force microscopy. RPMC were obtained from healthy and diabetic rats. Mesothelial phenotype, evaluated by cytokeratin and pan-cadherin, epithelial to mesenchymal transition (EMT), evaluated by alpha-smooth muscle action (α-SMA) and vimentin, TJ proteins, claudins-1 and -2, and occludin, and glucose transporters, sodium and glucose co-transporters (SGLT) -1 and -2 and facilitative glucose transporters (GLUT) -1 and -2 were analyzed. Also, transepithelial electrical resistance (TER) was measured. Oxidative stress was estimated by measuring reactive oxygen species production, and protein carbonylation, receptor for advanced glycation end products (RAGE), nuclear factor erythroid related factor-2 (Nrf-2), and expression of antioxidant enzymes. Key findingsPeritoneal damage was present 21days after STZ-injection. Diabetes induced changes in TJ and glucose transporters in RPMC together with decreased TER. RPMC from diabetic rats showed oxidative stress, which was enhanced by exposure to PDS. In addition, RPMC from diabetic rats showed early EMT. SignificanceTo our knowledge, this is the first study that shows changes in TJ proteins and glucose transporters of RPMC from diabetic rats. All these alterations might explain the increased peritoneal permeability observed in diabetic patients undergoing peritoneal dialysis.

Targeting Iron in Colon Cancer via Glycoconjugation of Thiosemicarbazone Prochelators.

The implication of iron in the pathophysiology of colorectal cancer is documented at both the biochemical and epidemiological levels. Iron chelators are therefore useful molecular tools for the study and potential treatment of this type of cancer characterized by high incidence and mortality rates. We report a novel prochelation strategy that utilizes a disulfide redox switch to connect a thiosemicarbazone iron-binding unit with carbohydrate moieties targeting the increased expression of glucose transporters in colorectal cancer cells. We synthesized three glycoconjugates (GA2TC4, G6TC4, and M6TC4) with different connectivity and/or carbohydrate moieties, as well as an aglycone analog (ATC4). The sugar conjugates present increased solubility in neutral aqueous solutions, and the ester-linked conjugates M6TC4 and G6TC4 compete as effectively as d-glucose for transporter-mediated cellular uptake. The glycoconjugates show improved selectivity compared to the aglycone analog and are 6-11 times more toxic in Caco-2 colorectal adenocarcinoma cells than in normal CCD18-co colon fibroblasts.

A bioluminescent assay for measuring glucose uptake

Identifying activators and inhibitors of glucose uptake is critical for both diabetes management and anticancer therapy. To facilitate such studies, easy-to-use nonradioactive assays are desired. Here we describe a bioluminescent glucose uptake assay for measuring glucose transport in cells. The assay is based on the uptake of 2-deoxyglucose and the enzymatic detection of the 2-deoxyglucose-6-phosphate that accumulates. Uptake can be measured from a variety of cell types, it can be inhibited by known glucose transporter inhibitors, and the bioluminescent assay yields similar results when compared with the radioactive method. With HCT 116 cells, glucose uptake can be detected in as little as 5000 cells and remains linear up to 50,000 cells with signal-to-background values ranging from 5 to 45. The assay can be used to screen for glucose transporter inhibitors, or by multiplexing with viability readouts, changes in glucose uptake can be differentiated from overall effects on cell health. The assay also can provide a relevant end point for measuring insulin sensitivity. With adipocytes and myotubes, insulin-dependent increases in glucose uptake have been measured with 10- and 2-fold assay windows, respectively. Significant assay signals of 2-fold or more have also been measured with human induced pluripotent stem cell (iPSC)-derived cardiomyocytes and skeletal myoblasts.

Effect of polyphenols on glucose and lactate transport by breast cancer cells.

One of the cancer molecular hallmarks is a deviant energetic metabolism, known as the Warburg effect, whereby the rate of glucose uptake is significantly increased and a high rate of glycolysis and lactic acid production occurs even when oxygen is present-"aerobic lactatogenesis". Accordingly, GLUT1 and MCT1, which are the main glucose and lactate transporters in cancer cells, respectively, have been proposed as oncogenes and are currently seen as potential therapeutic targets in cancer treatment. Polyphenols, commonly contained in fruits and vegetables, have long been associated with a protective role against cancer. Generally considered as nontoxic, dietary polyphenols are considered ideal chemopreventive and possibly chemotherapeutic agents. Several mechanisms of action of polyphenols in breast cancer cells have been proposed including modulation of intracellular signaling, induction of apoptosis through redox regulation or modulation of epigenetic alterations. Additionally, in vitro studies have shown that several polyphenols act as specific inhibitors of glucose transport in breast cancer cell lines and an association between their anticarcinogenic effect and inhibition of glucose cellular uptake has been described. Also, some polyphenols were found to inhibit lactate transport. Importantly, some polyphenols behave as inhibitors of both glucose and lactate cellular uptake by breast cancer cells and these compounds are thus very interesting in the context of a chemopreventive effect, because they deplete breast cancer cells of their two most important energy suppliers. So, the antimetabolic effect of polyphenols should be regarded as a mechanism of action contributing to their chemopreventive/chemotherapeutic potential in relation to breast cancer.

Oat β-glucan depresses SGLT1- and GLUT2-mediated glucose transport in intestinal epithelial cells (IEC-6)

Oat β-glucan consumption is linked to reduced risk factors associated with diabetes and obesity by lowering glycemic response and serum level of low-density lipoproteins. The purpose of this study was to identify the mechanism of action of oat β-glucan at the interface between the gut wall and the lumen responsible for attenuating glucose levels. We proposed that viscous oat β-glucan acts as a physical barrier to glucose uptake in normally absorptive gut epithelial cells IEC-6 by affecting the expression of intestinal glucose transporters. Concentration and time-dependent changes in glucose uptake were established by using a nonmetabolizable glucose analog 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-d-glucose. The effectiveness of nutrient transport in IEC-6 cells was shown by significant differences in glucose uptake and corresponding transporter expression. The expressions of glucose transporters sodium-glucose–linked transport protein 1 (SGLT1) and glucose transporter 2 (GLUT2) increased with time (0-60 minutes) and glucose levels (5-25 mmol/L). The suppression of glucose uptake and SGLT1 and GLUT2 expression by increasing concentrations (4-8 mg/mL) of oat β-glucan demonstrated a direct effect of the physical properties of oat β-glucan on glucose transport. These results affirmed oat β-glucan as a dietary agent for minimizing postprandial glucose and showed that modulating the activity of the key intestinal glucose transporters with oat β-glucan could be an effective way of lowering blood glucose levels in patients with diabetes.

Expression of the semicarbazide-sensitive amine oxidase in articular cartilage: its role in terminal differentiation of chondrocytes in rat and human

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the oxidation of primary amines into ammonia and reactive species (hydrogen peroxide, aldehydes). It is highly expressed in mammalian tissues, especially in vascular smooth muscle cells and adipocytes, where it plays a role in cell differentiation and glucose transport. The study aims at characterizing the expression and the activity of SSAO in rat and human articular cartilage of the knee, and to investigate its potential role in chondrocyte terminal differentiation. SSAO expression was examined by immunohistochemistry and western blot. Enzyme activity was measured using radiolabeled benzylamine as a substrate. Primary cell cultures of rat chondrocytes were treated for 21 days by a specific SSAO inhibitor, LJP 1586. Terminal chondrocyte differentiation markers were quantified by RT-qPCR. The basal and IL1β-stimulated glucose transport was monitored by the entrance of (3)[H]2-deoxyglucose in chondrocytes. SSAO was expressed in chondrocytes of rat and human articular cartilage. SSAO expression was significantly enhanced during the hypertrophic differentiation of chondrocytes characterized by an increase in MMP13 and in alkaline phosphatase (ALP) expressions. SSAO inhibition delayed the late stage of chondrocyte differentiation without cell survival alteration and diminished the basal and IL1β-stimulated glucose transport. Interestingly, SSAO activity was strongly increased in human osteoarthritic cartilage. SSAO was expressed as an active form in rat and human cartilage. The results suggest the involvement of SSAO in rat chondrocyte terminal differentiation via a modulation of the glucose transport. In man, the increased SSAO activity detected in osteoarthritic patients may trigger hypertrophy and cartilage degeneration.