Evidence that modulation of glucose transporter intrinsic activity is the mechanism involved in the allose-mediated depression of hexose transport in mammalian cells

Growth inhibition of head and neck carcinomas by D-allose

BACKGROUND

An inhibitory effect of D-allose, a rare sugar, on several cancer cell lines has been reported. This study aimed to investigate the growth inhibition of head and neck squamous cell carcinoma cells by D-allose.

METHODS

We treated 3 head and neck carcinoma cell lines with D-allose, D-fructose, D-psicose, and D-glucose. Cell growth assays as well as analyses of messenger RNA (mRNA) expression, cell cycle, apoptosis, and uptake of 14C-glucose were performed.

RESULTS

D-allose had inhibitory effects on all 3 cell lines and tended to upregulate mRNA expression of glucose transporters, p21 and p53, and downregulate mRNA expression of cyclin A2, cyclin B1, and CDC2. We observed that D-allose tended to interfere with the intracellular uptake of D-glucose and induced apoptosis.

CONCLUSION

Our results indicate that D-allose inhibits the growth of head and neck squamous cell carcinoma cells. D-allose has a considerable potential as a new anticancer agent in those patients.

Is non-insulin dependent glucose uptake a therapeutic alternative? Part 1: physiology, mechanisms and role of non insulin-dependent glucose uptake in type 2 diabetes

Several decades of research for treating type 2 diabetes have yielded new drugs but the actual experience with the available oral antidiabetic compounds clearly shows that therapeutic needs are not matched. This highlights the urgent need for exploring other pathways. All cell types have the capacity to take up glucose independently of insulin, whereby basal but also hyperglycaemia-promoted glucose supply is ensured. Although poorly explored, insulin-independent glucose uptake might nevertheless represent a therapeutic target, as an alternative to the clear limits of actual drug treatments. This review not only critically examines some major pathways not requiring insulin (although they may be influenced by the hormone) but importantly, this analysis extends to the clinical applicability of these potential therapeutic principles by also considering their predictable tolerability for long-term therapy. In particular vascular safety (the ultimate problem linked with diabetes) will be envisaged because of the ubiquitous distribution of glucose transporters and some linked mechanisms. Several mechanisms can be identified which do not require insulin for their functioning. The first part of this review deals with the description, the regulation and the limits of some mechanisms representing potential pharmacological targets capable of having a highly significant impact on glucose uptake. These selected topics are: a) unmasking and/or activation of glucose transporters in cell plasma membranes, b) insulin mimetics acting at postreceptor level, c) activation of AMPK, d) increasing nitric oxide and e) increasing glucose-6P and glycogen stores.

D-allose, an all-cis aldo-hexose, suppresses development of salt-induced hypertension in Dahl rats

OBJECTIVE

D-allose, an all-cis aldo-hexose, is non-caloric and possesses antioxidant properties. We investigated the effects of oral D-allose supplementation on the development of high blood pressure and the oxidative status in two genetically hypertensive animal models: Dahl salt-sensitive hypertensive (DS) rats and spontaneously hypertensive rats.

METHODS AND RESULTS

The systolic blood pressure of DS rats fed a 4% salt diet for 4 weeks significantly increased from 122+/-8 to 161+/-5 mmHg as compared with DS rats fed a normal salt diet (138+/-5 mmHg at 4 weeks), whereas concordant supplementation of D-allose, but not D-glucose, with a dose of 2 g/kg daily to salt-loaded DS rats suppressed the development of high blood pressure (135+/-7 mmHg at 4 weeks), accompanied with decreases in superoxide production in the aorta that was determined by the lucigenin chemiluminescence and dihydroethidium staining. The increases of urinary protein secretion of salt-loaded DS rats were prevented by D-allose supplementation (DS rats fed 0.5% salt, 18.2+/-6.3 mg/day; DS rats fed 4% salt alone, 81.8+/-16.5 mg/day; DS rats fed 4% salt+D-allose, 31.3+/-11.8 mg/day; DS rats fed 4% salt+D-glucose, 85.3+/-20.5 mg/day). On the other hand, D-allose supplementation in spontaneously hypertensive rats had no significant effect on the blood pressure or the aortic superoxide production during the early developing stage of hypertension.

CONCLUSIONS

These results underscore the role of enhanced oxidative stress in the pathogenesis of high blood pressure development in DS rats, and suggest the possibility of D-allose supplementation for prevention of salt-sensitive hypertension.

Different Forms of Vanadate on Sugar Transport in Insulin Target and Nontarget Cells

The effects of several vanadates (ie, orthovanadate, pervanadate, and two stable peroxovanadium compounds) on basal and insulin-stimulated 2-DG transport in insulin target and nontarget cell lines are reported, herein. In nontarget cells, exposure to vanadates (5 x 10(-6) to 10(-4) mol/L) resulted in 2-DG transport stimulatory responses similar to those observed in 2-DG transport post exposure to 667 nmol/L insulin alone, or insulin in combination with vanadates. In 3T3-L1 adipocytes and L6 myotubes, exposure to a vanadate compound or 67 nmol/L insulin, stimulated 2-DG transport dramatically. Again, this effect on stimulated transport was similar to 2-DG transport post-treatment with the effective vanadates in combination with insulin. While pervanadate or stable peroxovanadates stimulated 2-DG transport at 10(-5) to 10(-6) mol/L, orthovanadate up to 10(-4) mol/L was not effective in stimulating 2-DG transport in any of the cell lines tested. The data indicate that the various peroxovanadates are clearly superior insulin mimetics while a more limited insulin mimesis is observed with orthovanadate over a wide variety of cell types.

Sugar transport regulation: comparative characterization of the effect of NADH CoQ reductase deficiency in two cell culture systems

In this report, we have characterized the upregulation of glucose transport in two different respiration-deficient fibroblast cell cultures. We have demonstrated that glucose transport increases in respiration-deficient cells as measured by 2 deoxy D-glucose transport and is readily observed in both the WG750 human and G14 Chinese hamster fibroblast respiration-deficient cell lines when compared with the MCH55 normal human and V79 parental Chinese hamster cell lines, respectively. Using subcellular fractionation techniques, the GLUT 1 glucose transporter was found located predominantly in the plasma membrane-enriched fraction of the human and hamster cell lines. In human cells, the expression of the GLUT 1 glucose transporter was elevated three-fold in the plasma membrane-enriched fraction of the WG750 respiration-deficient mutant cells. In the Chinese hamster cell lines, the respiration-deficient G14 cells exhibited no such GLUT 1 glucose transporter elevation in the plasma membrane-enriched fraction, yet expressed a >2-fold increase in glucose transport. Furthermore, the G14 cells had a similar content of GLUT 1 glucose transporter in the plasma membrane fraction when compared with the V79 parental cell line. Using Western blot analysis, the GLUT 1 glucose transporter in G14 cells exhibited a different mobility on a polyacrylamide gel when compared with the mobility of the GLUT 1 glucose transporter of the V79 cell line. This differential mobility of the glucose transporters in the hamster cells appeared to be related to glycosylation differences of the glucose transporters. Although normal human and hamster cell lines exhibited significant increases in insulin-stimulated sugar transport (P < 0.05), the two respective respiration-deficient cell lines exhibited no significant increases in insulin-stimulated sugar transport (P > 0.05). Additionally, the expression of the GLUT 1 mRNA in the human WG750 mutant cells was elevated when compared with GLUT 1 mRNA in normal cells. Insulin exposure significantly increased GLUT 1 mRNA in human cells (P < 0.05). No differences in the GLUT 1 mRNA were observed between both hamster cell lines. Thus, both respiration-deficient cell lines are insulin resistant (i.e., regarding their insulin-stimulated sugar transport). The respiration-deficient mutation results in an increased sugar transport in the human and hamster cells; however, the human cells adapt to the mutation by increasing their levels of GLUT 1 mRNA and eventually membrane-located glucose transporters. On the other hand, the hamster cells adapt by apparently modifying their glucose transporters' intrinsic activity via glycosylation. We feel that these cell systems can be effective models to study the multiple factors involved in sugar transport regulation in vertebrate cells.

Structure of D-allose binding protein from Escherichia coli bound to D-allose at 1.8 A resolution

ABC transport systems for import or export of nutrients and other substances across the cell membrane are widely distributed in nature. In most bacterial systems, a periplasmic component is the primary determinant of specificity of the transport complex as a whole. We report here the crystal structure of the periplasmic binding protein for the allose system (ALBP) from Escherichia coli, solved at 1.8 A resolution using the molecular replacement method. As in the other members of the family (especially the ribose binding protein, RBP, with which it shares 35 % sequence homology), this structure consists of two similar domains joined by a three-stranded hinge region. The protein is believed to exist in a dynamic equilibrium of closed and open conformations in solution which is an important part of its function. In the closed ligand-bound form observed here, D-allose is buried at the domain interface. Only the beta-anomer of allopyranose is seen in the crystal structure, although the alpha-anomer can potentially bind with a similar affinity. Details of the ligand-binding cleft reveal the features that determine substrate specificity. Extensive hydrogen bonding as well as hydrophobic interactions are found to be important. Altogether ten residues from both the domains form 14 hydrogen bonds with the sugar. In addition, three aromatic rings, one from each domain with faces parallel to the plane of the sugar ring and a third perpendicular, make up a hydrophobic stacking surface for the ring hydrogen atoms. Our results indicate that the aromatic rings forming the sugar binding cleft can sterically block the binding of any hexose epimer except D-allose, 6-deoxy-allose or 3-deoxy-glucose; the latter two are expected to bind with reduced affinity, due to the loss of some hydrogen bonds. The pyranose form of the pentose, D-ribose, can also fit into the ALBP binding cleft, although with lower binding affinity. Thus, ALBP can function as a low affinity transporter for D-ribose. The significance of these results is discussed in the context of the function of allose and ribose transport systems.

Acute regulation of glucose transport in a monocyte-macrophage cell line: Glut-3 affinity for glucose is enhanced during the respiratory burst

Activation of the respiratory burst imposes acute metabolic demands on phagocytic cells. These are met by mobilizing internal energy stores and by increasing the utilization of exogenous energy, including glucose in the circulation. To determine whether the increased glucose uptake that is known to be associated with the respiratory burst involves the regulation of glucose transporter molecules, the intrinsic transport properties of glucose transporters on the macrophage cell line RAW 264.7 were determined after activation with PMA, N-formyl-methionine-leucine-phenylalanine (fMLP) and the cytokines granulocyte/macrophage colony-stimulating factor (GM-CSF) and interleukin 3 (IL-3). Treatment with PMA resulted in a 2-fold increase in respiratory burst activity within 10 min; this was associated with a 30-50% increase in 2-deoxyglucose uptake and a 4-fold increase in transporter affinity for glucose. Similarly, fMLP, GM-CSF and IL-3 treatments stimulated 2-deoxyglucose uptake that was associated with a 3-4-fold increase in transporter affinity for glucose. To determine whether the changes observed in 2-deoxyglucose uptake in response to PMA, fMLP and growth factors were influenced by phosphorylation of the sugar, 3-O-methylglucose, which is not phosphorylated, was used. Increased 3-O-methylglucose uptake and increased transporter affinity for glucose were also observed after PMA, fMLP and GM-CSF treatments. Whereas both fMLP and GM-CSF stimulated superoxide production, IL-3 failed to activate respiratory burst activity. The protein kinase inhibitors genistein and staurosporine inhibited the increase in 2-deoxyglucose uptake observed with fMLP and GM-CSF, and partly reversed the affinity increase towards that of untreated control cells. In contrast, the phosphatidylinositol 3-kinase inhibitor wortmannin had little effect on 2-deoxyglucose uptake in response to these activators. Western blotting with subtype-specific antisera showed that Glut-3 was the predominant transporter on RAW 264.7 cells. These studies demonstrate that acute regulation of glucose transporters occurs in response to activators that promote respiratory burst activity, and show that this regulation involves both tyrosine kinases and protein kinase C activity.

Acylation-stimulating protein (ASP) regulates glucose transport in the rat L6 muscle cell line

Acylation-stimulating protein (ASP), a human plasma protein, is a potent stimulator of triglyceride synthesis and glucose transport in both human adipocytes and fibroblasts. The purpose of the present in vitro study was to examine the effect of ASP on glucose transport in muscle cells. ASP stimulated 2-deoxy-glucose transport (2-DG) in differentiated rat L6 myotubes in a time (30 min to 24 h) and concentration dependent manner (97% increase). The magnitude of the ASP effect on glucose transport was comparable to the time- and concentration-dependent effects seen with insulin (125% increase), but was additive to insulin, pointing to involvement of differential signalling pathways. ASP stimulation was dependent on cell differentiation in that glucose transport increased by only 12% in myoblasts, comparable to the effect of insulin in myoblasts (15% increase) demonstrating selective responsiveness of the differentiated myotubes to ASP and insulin. The mechanism for the ASP induced increase in glucose transport was also examined. ASP increased the Vmax for 2-DG transport by 183% (4.02 vs. 1.42 nmol/mg cell protein/30 s; ASP vs. Control, respectively). This could be explained by an increased translocation of glucose transporters (GLUT 1, GLUT 4 and GLUT 3) to the plasma membrane surface as demonstrated by Western analysis (+43% P < 0.05, +30% P < 0.05, and +49% P < 0.05, respectively). The effects of ASP were equal to those of insulin (+47%, +26% and +53% for GLUT 1, GLUT 4 and GLUT 3, respectively) and in all cases were paralleled by comparable glucose transport increases under the same incubation conditions. After long-term stimulation (24 h), Western analysis indicated that ASP had a permissive effect on insulin stimulated increases in total GLUT3 and GLUT4 cellular transporter content. These results suggest that muscle is also responsive to ASP and that ASP may play a role in glucose metabolism in both muscle and adipose tissue.