The influence of a new vanadium compound, bis(2,2'-bipyridine)oxovanadium(IV) sulphate on liver golgi complexes from control and streptozotocin-diabetic rats.

Among the previously studied organic vanadium derivatives showing an anti-diabetic action, we investigated a new complex, bis(2,2'-bipyridine)oxovanadium(IV) sulphate. We tested its ability to normalise parameters previously described for streptozotocin (STZ)-diabetes, such as lower yields of Golgi-rich membrane fraction isolation, decreased activity of Golgi membrane marker enzyme - galactosyltransferase (GalT) - and altered morphology of rat liver Golgi complexes. Oral application as a drinking solution of 1.8 mmol bis(2,2'-bipyridine)oxovanadium(IV) (dissolved in 0.09 M NaCl) caused a similar dispersion of GalT activities in both vanadium treated groups, control and diabetic. Very low activities of the enzyme (characteristic for untreated diabetes) we found only in approximately 35 % of the STZ-diabetic rats treated with the new vanadium compound. The morphology of liver Golgi complexes in diabetic rats treated with bis(2,2'-bipyridine)oxovanadium(IV) sulphate was improved, which manifested itself in the reappearance of vacuoles with VLDL and coated and uncoated secretory vesicles. In view of biochemical and morphological parameters of normalised diabetic rat liver Golgi apparatus, the new vanadium complex was more effective than bis(oxalato)oxovanadium(IV) or bis(kojato)oxovanadium(IV), but in our experimental model, the best anti-diabetic, orally applied drug was the bis(maltolato)oxovanadium(IV) previously investigated.     

Influence of sodium bis(oxalato)oxovanadate(IV) on phospholipids in liver Golgi fractions from control and streptozotocin-diabetic rats

(1) Both vanadyl oxalate and streptozotocin (STZ) caused in comparison with untreated control statistically significant increase (P<0.001 and P<0.02) of PLs (μmoles of P_i per mg of protein) in rat liver Golgi-rich membrane fraction. (2) The diabetic, vanadium treated rats (D+V) showed lower than control-treated (C+V) content of PLs in these fractions. (3) Three experimental groups of rats: control-treated (P<0.01), diabetic treated with vanadium (P<0.05) and untreated diabetic (P<0.02), had a higher percentage of PI (phosphatidylinositol) in comparison with untreated-control animals.     

Effect of chronic treatment with Bis(maltolato)oxovanadium (IV) in rat model of non-insulin-dependent-diabetes

Effect of chronic treatment with Bis(maltolato)oxovanadium (IV) (BMOV) was studied in streptozotocin (STZ)-induced neonatal non-insulin-dependent-diabetic (NIDDM) rats. Intraperitoneal injection of STZ (90 mg kg(-1)) in Wistar rat pups (day 2 old) produced mild hyperglycemia, impaired glucose tolerance and insulin resistance at the age of 3 months. Treatment with BMOV (0.23 mM kg(-1)) in drinking water for 6 weeks produced a significant decrease in elevated serum glucose levels without any significant change in serum insulin levels in diabetic rats. BMOV treatment significantly decreased integrated area under the glucose curve without any significant change in integrated area under the insulin curve indicating improved glucose tolerance. Treatment also significantly increased K(ITT) value of diabetic rats indicating increased insulin sensitivity. BMOV treatment significantly reduced hypercholesterolemia in diabetic rats. Treatment also significantly decreased serum triglyceride levels in both diabetic and non-diabetic rats. The data suggest that chronic BMOV treatment improves glucose and lipid homeostasis. These effects appear to be due to the insulin sensitizing action of vanadium.     

Vanadium and diabetes

We demonstrated in 1985 that vanadium administered in the drinking water to streptozotocin (STZ) diabetic rats restored elevated blood glucose to normal. Subsequent studies have shown that vanadyl sulfate can lower elevated blood glucose, cholesterol and triglycerides in a variety of diabetic models including the STZ diabetic rat, the Zucker fatty rat and the Zucker diabetic fatty rat. Long-term studies of up to one year did not show toxicity in control or STZ rats administered vanadyl sulfate in doses that lowered elevated blood glucose. In the BB diabetic rat, a model of insulin-dependent diabetes, vanadyl sulfate lowered the insulin requirement by up to 75%. Vanadyl sulfate is effective orally when administered by either single dose or chronic doses. It is also effective by the intraperitoneal route. We have also been able to demonstrate marked long-terrn effects of vanadyl sulfate in diabetic animals following treatment and withdrawal of vanadyl sulfate. Because vanadyl sulfate is not well absorbed we have synthesized and tested a number of organic vanaditun compounds. One of these, bismaltolato-oxovanadiurn IV (BMOV), has shown promise as a therapeutic agent. BMOV is 2-3x more potent than vanadyl sulfate and has shown less toxicity. Recent studies from our laboratory have shown that the effects of vanadium are not due to a decrease in food intake and that while vanadium is deposited in bone it does not appear to affect bone strength or architecture. The mechanism of action of vanadium is currently under investigation. Several studies indicate that vanadiun is a phosphatase inhibitor and that vanadium can activate serine/threonine kineses distal to tbe insulin receptor presumably by preventing dephosphorylation due to inhibition of phosphatases Short-term clinical trials using inorganic vanadium compounds in diabetic patients have been promising.     

The phospholipid contents in rat liver Golgi-rich membrane fractions after streptozotocin and/or prostaglandin treatment

After dmPGE2 treatment, both alone or together with streptozotocin, the lower, statistically significant total PL contents (in mumoles P per mg of protein) in rat liver Golgi-rich membrane fractions were found. In these groups of investigated rats, the percentage of PE+PA were statistically significantly lower than in control. For the present it is impossible to certify, if there is a causal-result dependence between these two facts. The administration of streptozotocin alone (both after 6 or 11 days) caused the increase of PE+PA percentage, however not statistically significant.     

A new salicylic acid-derivatized kojic acid vanadyl complex: synthesis, characterization and anti-diabetic therapeutic potential

The molecular mechanisms of vanadium toxicity suggest that incorporation of antioxidant groups in the structure of vanadium complexes could be a preferable strategy in designing novel hypoglycemic vanadium complexes with proper efficacy and safety. By conjugating a pyrone skeleton to provide a coordination group and antioxidative motifs, we synthesized a novel complex of bis ((5-hydroxy-4-oxo-4 H-pyran-2-yl) methyl 2-hydroxy- benzoatato) oxovanadium (IV) (BSOV). Evaluation of the anti-diabetic effects of BSOV using streptozotocin (STZ)-induced diabetic rats with bis (maltolato) oxovanadium (BMOV) as a positive control showed that BSOV effectively lowered blood glucose level, ameliorated damages of hepatic and renal function in diabetic rats and improved lipid metabolism. The signs of potential alteration of renal function caused by BSOV and BMOV were observed and are discussed. Overall, the experimental results suggest BSOV as a potent hypoglycemic agent and further studies using this strategy for anti-diabetic agents.     

Comparison of bipyridyl, maltol and kojic acid action as organic vanadium ligands on activity of galactosyltransferase (EC 2.4.1.38), some physiological parameters and ultrastructure of Golgi complexes in rat hepatocytes

The biochemical activity and morphology of control and streptozotocin-diabetic rat liver Golgi complexes were previously investigated by us under influence of some vanadium [V(IV)] compounds. The effectiveness of these derivatives depends on the kind of complexing ligands. This paper presents the investigation of the effect of bipyridyl, the ligand of a new vanadium compound, tested by us with maltol and kojic acid (two ligands studied by the present and other authors). The three ligands alone action was tested under the same experimental conditions as in the case of whole compounds with vanadium and applied to liver Golgi complexes of control rats. A preliminary study for maltol and kojic acid had been previously carried out by us parallel with tests of whole vanadium complexes, but valuable differences in biological action found in our condition of experiments suggested the extension of studies to include the two above-mentioned ligands and to compare the effects of the three investigated ligands. The supplementary part of the experiment focused mainly on the ultrastructure of Golgi complexes in hepatocytes. Four groups of animals were used: C - control rats, C + M (maltol), C + (ka)2 (kojic acid) and C + (bpy)2 (bipyridyl). The control rats received 0.09M NaCl as drinking liquid; all the other animals were given 3.6 mmol/L of appropriate ligand solution in 0.09M NaCl during 7 days. All the animals survived the experiments. Only in group C + (bpy)2 did the authors observe statistically significant differences as compared with the controls (group C). The differences were detected in physiological studies and manifested as body weight decreased by approximately 20% during the experiment, lower liquid (p<0.001) and food (p<0.01) intake and increase of free blood sugar level (p<0.01). The yield of Golgi membrane isolation decreased in this group (p<0.01). The main investigated biochemical parameter, i.e. the activity of liver Golgi marker enzyme - galactosyltransferase - was not statistically significantly changed in comparison with the controls in all the investigated groups of rats; a similar dispersion of individual results were found in the four groups. In the three experimental groups, ultrastructural observations demonstrated a predominance of cylindrical Golgi structures, which were haphazardly twisted in the majority of cases. Typically shaped structures were encountered sporadically. The ligands alone evoked numerous subcellular changes in hepatocytes; these alterations most frequently involved the mitochondria and endoplasmic reticulum. No such changes had been seen, or else they had been less advanced when complex vanadium compounds were employed in our earlier experiments. As it follows, the ligands alone were demonstrated to be much more toxic to morphology of control liver Golgi apparatus as compared to complex compounds, which showed the ability of the former to normalize Golgi complexes of diabetic animals.     

The activity of Golgi-membrane galactosyltransferase in the liver of streptozotocin-diabetic rats.

The Golgi-rich membrane fraction isolated from streptozotocin-diabetic rat liver had a lower protein content than the corresponding fraction from normal liver. Its UDPgalactose-N-acetylglucosamine galactosyltransferase activity calculated per 1 g of liver or whole liver was decreased. The electron-microscopic examination of the negatively stained fraction revealed morphological changes. The morphology of the Golgi complex in thin sections of diabetic liver was also changed.     

Differences in plasma homocysteine levels between Zucker fatty and Zucker diabetic fatty rats following 3 weeks oral administration of organic vanadium compounds

PURPOSE: Recently, our laboratory group has reported that rats with Type 1 diabetes have decreased plasma homocysteine and cysteine levels compared to non-diabetic controls and that organic vanadium treatment increased plasma homocysteine concentrations to non-diabetic concentrations. However, to date, no studies have been done investigating the effects of organic vanadium compounds on plasma homocysteine and its metabolites in Type 2 diabetic animal model. These studies examined the effect of organic vanadium compounds [bis(maltolato)oxovanadium(IV) and bis(ethylmaltolato)oxovanadium(IV); BMOV and BEOV] administered orally on plasma concentrations of homocysteine and its metabolites (cysteine and cysteinylglycine) in lean, Zucker fatty (ZF) and Zucker diabetic fatty (ZDF) rats. ZF rats are a model of pre-diabetic Type 2 diabetes characterized by hyperinsulinemia and normoglycemia. The ZDF rat is a model of Type 2 diabetes characterized by relative hypoinsulinemia and hyperglycemia. METHODS: Zucker lean and ZF rats received BMOV in the drinking water at a dose of 0.19 +/- 0.02 mmol/kg/day. Lean and ZDF rats received BEOV by oral gavage daily at dose of 0.1 mmol/kg. The treatment period for both studies was 21 days. At termination, animals were fasted overnight (approximately 16 h) and blood samples were collected by cardiac puncture for determination of plasma glucose, insulin and homocysteine levels. Plasma homocysteine and its metabolites levels were determined using high-pressure liquid chromatography. Plasma glucose was determined using a Glucose Analyzer 2. Plasma insulin levels were determined by radioimmunoassay. Plasma triglycerides were determined by an enzymatic assay methodology. RESULTS: ZF (n = 4) and ZDF (n = 10) rats had significantly lower plasma homocysteine as compared to their respective lean groups (ZF 0.78 +/- 0.1 micromol/L vs. Zucker lean 2.19 +/- 0.7 micromol/L; ZDF 1.71 +/- 0.2 micromol/L vs. Zucker lean 3.02 +/- 0.3 micromol/L; p < 0.05). BMOV treatment in ZF rats restored plasma homocysteine levels to those observed in lean untreated rats (ZF treated: 2.04 +/- 0.2 micromol/L; lean 2.19 +/- 0.7 micromol/L). There was a modest effect of BMOV treatment on plasma glucose levels in ZF rats. BEOV treatment significantly decreased the elevated plasma glucose levels in the ZDF rats (lean 7.9 +/- 0.1 mmol/L; lean + vanadium 7.7 +/- 0.2 mmol/L; ZDF 29.9 +/- 0.4 mmol/L; ZDF + vanadium 17.4 +/- 0.3 mmol/L, p < 0.05). Organic vanadium treatment reduced cysteine levels in both ZF and ZDF rats. No differences in total plasma cysteinylglycine concentrations were observed. CONCLUSION: Plasma homocysteine levels are significantly reduced in a pre-diabetic model of Type 2 diabetes, which was restored to lean levels upon vanadium treatment; however, this restoration of plasma homocysteine levels was not seen in ZDF Type 2 diabetic rats following vanadium treatment. In the latter case vanadium treatment may not have totally overcome the insulin resistance seen in these animals.     

Bis(maltolato)oxovanadium(IV) (BMOV) Attenuates Apoptosis in High Glucose-Treated Cardiac Cells and Diabetic Rat Hearts by Regulating the Unfolded Protein Responses (UPRs)

Endoplasmic reticulum stress (ERS)-induced unfolded protein response (UPR) and the subsequent cell deaths are essential steps in the pathogenesis of diabetic cardiomyopathy (DCM), a main cause of diabetics’ morbidity and mortalities. The bis(maltolato)oxovanadium(IV) (BMOV), a potent oral vanadium complex with anti-diabetic properties and insulin-mimicking effects, was shown to improve cardiac dysfunctions in diabetic models. Here, we examined the effects of BMOV on UPR pathway protein expression and apoptotic cell deaths in both high glucose-treated cardiac H9C2 cells and in the hearts of diabetic rats. We show that in both the high glucose-treated cardiac cells and in the hearts of streptozotocin (STZ) diabetic rats, there was an overall activation of the UPR signaling, including both apoptotic (e.g., the cascades of PERK/EIf2α/ATF4/CHOP and of IRE1/caspase 12/caspase 3) and pro-survival (GRP78 and XBP1) signaling. A high amount of apoptotic cell deaths was also detected in both diabetic conditions. The administration of BMOV suppressed both the apoptotic and pro-survival UPR signaling and significantly attenuated apoptotic cell deaths in both conditions. The overall suppression of UPR signaling by BMOV suggests that the drug protects diabetic cardiomyopathy by counteracting reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress. Our findings lend support to promote the use of BMOV in the treatment of diabetic heart diseases.     

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.     

Increased potency of vanadium using organic ligands

Thein vivo glucose lowering effect of orally administered inorganic vanadium compounds in diabetes was first reported in our laboratory in 1985. While both vanadate and vanadyl forms of vanadium are orally active, they are still not well absorbed. We have synthesized several organic vanadium compounds and one compound, bis(maltolato)oxovanadium(IV) or BMOV, has been extensively investigated. BMOV proved effective in lowering plasma glucose and lipids in STZ-diabetic rats when administered in drinking water over a 25 week period. The maintenance dose (0.18 mmol/kg/day) was approximately 50% of that required for vanadyl sulfate (VS). Secondary complications of diabetes were prevented by BMOV and no marked toxicity was noted. Oral gavage of STZ-diabetic rats with BMOV also reduced blood glucose levels. The ED₅₀ for BMOV was 0.5 mmol/kg, while for VS the estimated ED₅₀ was 0.9 mmol/kg. BMOV was also effective by the intraperitoneal route in STZ-diabetic rats. The ED₅₀ was 0.08 mmol/kg compared to 0.22 mmol/kg for VS. Some animals treated p.o. or i.p. remained euglycemic for up to 14 weeks. An i.v. infusion of BMOV of 0.05 mmol/kg over a 30 min period reduced plasma glucose levels by 50% while VS was not effective.     

Modulation of prolactin binding sites in vitro by membrane fluidizers. IV. Differential effects on plasma membrane and Golgi fractions of male prostate and female liver in the rat

In vitro treatment of crude particulate fractions of male rat ventral prostate and female rat liver with membrane fluidizers (aliphatic alcohols) has been previously reported by us to increase prolactin (PRL) receptor levels, presumably by unmasking cryptic prolactin receptors. The objective of this study was to determine if similar in vitro treatment of purified plasma membrane- and Golgi-rich fractions of male rat prostate and female rat liver with ethanol produced differential effects on prolactin binding in these two subcellular fractions. The degree of fluidization was monitored by a fluorescence polarization method using 1,6-diphenylhexatriene. 125I-PRL specific binding to Golgi-rich fractions of male ventral prostate and female liver was approximately 4-fold higher than that observed in plasma membrane-rich fractions. The microviscosity parameter, inversely related to lipid fluidity, was consistently lower in Golgi-rich fractions than that in plasma membrane-rich fractions in both prostate and liver. In vitro ethanol treatment of prostatic and hepatic plasma membrane fractions produced a dose-related increase and then decline in prolactin binding and a maximal (60-75%) increase in prolactin binding was observed at 4.8% and 2.0% ethanol in prostatic and hepatic membranes, respectively. This in vitro treatment also produced a significant increase in apparent lipid fluidity of plasma membrane-rich fractions of prostate gland and liver. However, similar in vitro ethanol treatment of Golgi fractions of both prostate gland and liver exhibited little increase in prolactin binding without changing microviscosity. Our observations are consistent with the direct relationship between membrane fluidity and prolactin receptor levels. The changes in prostatic and hepatic plasma membrane fractions following in vitro ethanol treatment suggest that prolactin receptors located on the plasma membranes may be modulated (via membrane lipid microviscosity changes) in vivo to a greater extent by various physiological agents than those located within the Golgi fraction.     

The topographical location and unique nature of a glucokinase associated with the Golgi apparatus of rat liver.

A particulate glucokinase was recovered in the Golgi-rich fraction of rat liver prepared by the method of Morré [Methods Enzymol. (1971) 22, 130-148], thus extending the demonstration by Berthillier et al. [Biochim. Biophys. Acta (1973), 293, 370-378] of particulate glucokinase activity in a microsomal subfraction that showed enrichment in Golgi characteristics. The purity of this fraction was examined and it was then subjected to several treatments, the action of Triton X-100, freezing and thawing, and sonication to establish the topographical location of the glucokinase activity thus solubilized. The evidence suggests that the glucokinase activity is either soluble in the lumen of the Golgi apparatus or loosely associated with the inside of the Golgi membranes.     

Intracellular localization of GDP-l-fucose: Glycoprotein and CMP-sialic acid: Apolipoprotein glycosyltransferases in rat and pork livers

A GDP-l-fucose:glycoprotein fucosyltransferase which transfers l-fucose to terminal β-N-acetyl-d-glucosaminyl residues of sialidase-, β-galactosidase-treated α₁-acid glycoprotein and a CMP-sialic acid:glycoprotein sialyltransferase acting on sialidase-treated apolipoprotein-Ala₁ from human very low density lipoprotein have been shown to be concentrated in rat liver Golgi apparatus preparations at enrichments of 40- and 45-fold, respectively, and in pork liver Golgi-rich fractions at enrichments of 35- and 20-fold, respectively. A second fucosyltransferase acting on sialidase-treated α₁-acid glycopretein was absent from rat liver and was enriched only 13-fold in a pork liver Golgi-rich fraction. The smooth-surfaced microsome fraction was the only other rat liver subcellular fraction with appreciable levels of the GDP-l-fucose: β-N-acetyl-d-glucosaminide fucosyltransferase and the lipoprotein sialyltransferase (enrichments of 2.6- and 5.2-fold, respectivley). This enrichment could not be attributed to the plasma membrane content of the smooth microsome fraction since plasma membrane fractions from rat liver were shown to have relatively low concentrations of these two transferases (enrichments of 0.3 or less). Rat liver plasma membrane was also shown to have similarly low relative specific activities for three other glycosyltransferases (sialyl-, galactosyl-, and N-acetylglucosaminyl-). The accurate determination of the glycosyltransferase activities of the plasma membrane fraction required the use of relatively low concentrations of plasma membrane and relatively high concentrations of nucleotide-sugars in order to avoid interference by the high nucleotide-sugar pyrophosphatase and hydrolase activities of this fraction.     

Demonstration of GTP-binding proteins and ADP-ribosylated proteins in rat liver Golgi fraction

A Golgi-rich fraction isolated from rat liver was found to contain GTP-binding proteins with 20-25 kDa, which were tightly bound to the Golgi membrane. The Golgi fraction also contained two species of proteins which were ADP-ribosylated by bacterial toxins. Protein(s) which was ADP-ribosylated by botulinum toxin had a similar molecular mass as those with GTP-binding activity but was easily released from the membrane. Another protein with 46 kDa which was ADP-ribosylated by pertussis toxin was tightly bound to the membrane but had no significant GTP-binding activity under conditions tested here. These proteins were much less or negligible in the plasma membrane and the endoplasmic reticulum.     

Modulation of GalT1 and SialT1 sub-Golgi localization by SialT2 expression reveals an organellar level of glycolipid synthesis control

Ganglioside glycosyltransferases organize as multienzyme complexes that localize in different sub-Golgi compartments. Here we studied whether in CHO-K1 cells lacking CMP-NeuAc: GM3 sialyltransferase (SialT2), the sub-Golgi localization of UDP-Gal:glucosylceramide beta-1,4-galactosyltransferase (GalT1) and CMP-NeuAc:lactosylceramide sialyltransferase (SialT1) complex is affected when SialT2, another member of this complex, is coexpressed. GalT1 and SialT1 sub-Golgi localization was determined by studying the effect of brefeldin A (BFA) and monensin on the synthesis of glycolipids and on the sub-Golgi localization of GalT1(1-52)-CFP (cyan fluorescent protein) and SialT1(1-54)-YFP (yellow fluorescent protein) chimeras by single cell fluorescence microscopy and by isopycnic subfractionation. We found that BFA, and also monensin, impair the synthesis of glycolipids beyond GM3 ganglioside in wild type (WT) cells but beyond GlcCer in SialT2(+) cells. Although BFA redistributed GalT1-CFP and SialT1-YFP to the endoplasmic reticulum in WT cells, a fraction of these chimeras remained associated with a distal Golgi compartment, enriched in trans Golgi network, and recycling endosome markers in SialT2(+) cells. In BFA-treated cells, the percentage of GalT1-CFP and SialT1-YFP associated with Golgi-like membrane fractions separated by isopycnic subfractionation was higher in SialT2(+) cells than in WT cells. These effects were reverted by knocking down the expression of SialT2 with specific siRNA. Results indicate that sub-Golgi localization of glycosyltransferase complexes may change according to the relative levels of the expression of participating enzymes and reveal a capacity of the organelle to adapt the topology of the glycolipid synthesis machinery to functional states of the cell.     

Comparison of anti-hyperglycemic effect amongst vanadium, molybdenum and other metal maltol complexes

A wide variety of vanadium-containing complexes have been tested, both in vivo and in vitro, as possible therapeutic agents for the oral treatment of type 2 diabetes mellitus. None so far has surpassed bis(maltolato)oxovanadium(IV) (BMOV) for glucose- and lipid-lowering in an orally available formulation. Ligand choice is clearly an important factor in pharmacological efficacy of vanadium compounds as insulin enhancing agents. In this study, we kept the ligand and dose the same, varying instead the metal ion bound to the maltolato ligand in a series of binary complexes of neutral charge. A requirement for vanadyl ion as the metal ion of choice was apparent; no other metal ion tested served as a suitable substitute. Amongst [MoO(2)](2+), Co(II), Cu(II), Cr(III), and Zn(II), only [MoO(2)](2+) and Co(II) showed any hypoglycemic activity at the ED(50) dose for bis(maltolato)oxovanadium(IV), 0.6 mmolkg(-1) by oral gavage in streptozotocin (STZ)-diabetic rats within 72 h of administration of compound.     

Ganglioside glycosyltransferases organize in distinct multienzyme complexes in CHO-K1 cells

The synthesis of gangliosides is compartmentalized in the Golgi complex. In most cells, glycosylation of LacCer, GM3, and GD3 to form higher order species (GA2, GM2, GD2, GM1, GD1b) is displaced toward the most distal aspects of the Golgi and the trans-Golgi network, where the involved transferases (GalNAcT and GalT2) form physical and functional associations. Glycosylation of the simple species LacCer, GM3, and GD3, on the other hand, is displaced toward more proximal Golgi compartments, and we investigate here whether the involved transferases (GalT1, SialT1, and SialT2) share the property of forming physical associations. Co-immunoprecipitation experiments from membranes of CHO-K1 cells expressing epitope-tagged versions of these enzymes indicate that GalT1, SialT1, and SialT2 associate physically in a SialT1-dependent manner and that their N-terminal domains participate in these interactions. Microscopic fluorescence resonance energy transfer and fluorescence recovery after photobleaching in living cells confirmed the interactions, and in addition to showing a Golgi apparatus localization of the complexes, mapped their formation to the endoplasmic reticulum. Neither co-immunoprecipitation nor fluorescence resonance energy transfer detected interactions between either GalT2 or GalNAcT and GalT1 or SialT1 or SialT2. These results, and triple color imaging of Golgi-derived microvesicles in nocodazole-treated cells, suggest that ganglioside synthesis is organized in distinct units each formed by associations of particular glycosyltransferases, which concentrate in different sub-Golgi compartments.     

Effects of decavanadate and insulin enhancing vanadium compounds on glucose uptake in isolated rat adipocytes

The effects of different vanadium compounds namely pyridine-2,6-dicarboxylatedioxovanadium(V) (V5-dipic), bis(maltolato) oxovanadium(IV) (BMOV) and amavadine, and oligovanadates namely metavanadate and decavanadate were analysed on basal and insulin stimulated glucose uptake in rat adipocytes. Decavanadate (50 μM), manifest a higher increases (6-fold) on glucose uptake compared with basal, followed by BMOV (1 mM) and metavanadate (1 mM) solutions (3-fold) whereas V5 dipic and amavadine had no effect. Decavanadate (100 μM) also shows the highest insulin like activity when compared with the others compounds studied. In the presence of insulin (10 nM), only decavanadate increases (50%) the glucose uptake when compared with insulin stimulated glucose uptake whereas BMOV and metavanadate, had no effect and V5 dipic and amavadine prevent the stimulation to about half of the basal value. Decavanadate is also able to reduce or eradicate the suppressor effect caused by dexamethasone on glucose uptake at the level of the adipocytes. Altogether, vanadium compounds and oligovanadates with several structures and coordination spheres reveal different effects on glucose uptake in rat primary adipocytes.