Elevated serum levels of visfatin in gestational diabetes: a comparative study across various degrees of glucose tolerance.

AIMS/HYPOTHESIS: Concentrations of visfatin are increased in insulin-resistant conditions, but the relationship between visfatin and insulin and/or insulin resistance indices in pregnancy remains unclear. Insulin resistance in pregnancy is further accentuated in women with gestational diabetes mellitus (GDM). Thus we assessed serum levels of visfatin in pregnant women with varying degrees of glucose tolerance. MATERIALS AND METHODS: Fasting visfatin levels were measured at 28 weeks of gestation in 51 women divided according to their response to a 50-g glucose challenge test (GCT) and a 75-g OGTT: control subjects (n = 20) had normal responses to both a GCT and an OGTT; the intermediate group (IG; n = 15) had a false-positive GCT, but a normal OGTT; the GDM group (n = 16) had abnormal GCTs and OGTTs. RESULTS: There were no age or BMI differences between analysed groups. Across the subgroups there was a progressive increase in glucose and insulin at 120 min of the OGTT (p < 0.01). This was accompanied by an increase in visfatin, from 76.8 +/- 14.1 ng/ml in the control subjects, to 84.0 +/- 14.7 ng/ml in the IG group and 93.1 +/- 12.3 ng/ml in the GDM group (p < 0.01 for GDM vs control subjects). There was a positive correlation between visfatin and fasting insulin (r = 0.38, p = 0.007) and insulin at 120 min of the OGTT (r = 0.39, p = 0.006). CONCLUSIONS/INTERPRETATION: An increase in fasting visfatin, the levels of which correlate with both fasting and post-glucose-load insulin concentrations, accompanies worsening glucose tolerance in the third trimester of pregnancy. However, the significance of these findings, and in particular the role of visfatin in the regulation of insulin sensitivity during pregnancy, remains to be elucidated.

Activation of red blood cell glutathione peroxidase and morphological transformation of erythrocytes under the action of tert-butyl hydroperoxide.

Susceptibility of control and diabetic erythrocytes to oxidative stress was measured after incubation with various concentration of tert-butyl hydroperoxide (t-BHP). TBA-reactive substances (TBARS) formed were determined by the method of Stocks & Dormady modified by Jain. GSH and total glutathione were estimated by the procedure of Ellman and Akerboom and Sies. Activity of GSH peroxidase was determined by the method of Martinez et al. Protein SH groups were determined after membrane isolation by the method of Dodge et al. Cell morphology was viewed under phase contrast microscope with a magnification of 500x. All results were analyzed by the unpaired two tailed Student's t-test. Oxidative treatment of erythrocytes with tert-butyl hydroperoxide significantly increases the reaction rate but decreases the affinity for substrate (tert-butyl hydroperoxide). The susceptibility of the enzyme from diabetic erythrocytes to oxidation is higher in comparison with normal cells. The oxidation of cellular reduced glutathione (GSH) is not correlated with oxidation of membranous protein SH-groups. Oxidative damage of erythrocytes induces significant cell morphological transformations.

Acetylcholinesterase activity of normal and diabetic human erythrocyte membranes: the effect of oxidative agents.

The activity characteristics of membrane acetylcholinesterase from red blood cells of diabetic patients are very different from those of healthy donors: the limiting enzyme reaction rate is 17.2 +/- 0.8 mumol acetylthiocholine per ml packed cells per min compared with 13.1 +/- 0.8 mumol for control cells. This Michaelis constants for substrate are the same: 0.061 +/- 0.007 mM for diabetic and 0.061 +/- 0.004 mM for control cells. Cell exposure to oxidative agent (t-butyl hydroperoxide) significantly changes the enzyme activity parameters. The limiting enzyme reaction rate increases but the affinity for the substrate decreases at lower oxidant concentrations (up to 0.1 mM for the "diabetic" erythrocytes and up to 0.4 mM for the control ones). At higher oxidant concentrations both the limiting reaction rate and the Michaelis constant decrease. The susceptibility of erythrocyte membranes of diabetic patients to oxidative stress is much higher in comparison with control erythrocyte membranes.

Human red blood cell membrane potential and fluidity in glucose solutions.

This study aimed to investigate the membrane potential and fluidity changes of human red blood cells subjected to isotonic glucose solutions. For the control erythrocytes a membrane potential value of -10.1 +/- 1.8 mV was obtained, whereas erythrocyte membranes in diabetic cells were hyperpolarized, with a potential of -13.9 +/- 2.3 mV. Incubation of both types of red blood cells with increasing glucose concentrations resulted in a substantial hyperpolarization of the cell membranes. Glucose solutions in water had a much stronger effect on membrane potential than glucose dissolved in phosphate-buffered saline. Red blood cell membrane fluidity measurements using the fluorescent label TMADPH did not reveal any significant changes upon incubation with glucose.

[High energy substance and late complications of diabetes]. / Zwiazki bogatoenergetyczne a pózne powiklania cukrzycy.

All the vital processes in cels are dependent on its energetic metabolism. The substances of most importance are adenine phosphates. We present update knowledge about their metabolism. We noted also importance of enzymes involved in these processes. In diabetes disturbance in energetic state of the cell are obvious. We tried to find up theoretically what is the influence of diabetes on metabolism of high energetic adenine phosphates. We present probable role of these substances in development of late complications of diabetes.

Estimation of cholesterol sulphate in blood plasma and in erythrocyte membranes from individuals with Down's syndrome or diabetes mellitus type I.

OBJECTIVES: Plasma and erythrocyte membrane cholesterol sulphate (CS) were measured in patients suffering from diabetes and Down's syndrome. DESIGN AND METHODS: The procedure for separation and determination of CS comprised HPTLC (high-performance thin-layer chromatography) and densitometry. RESULTS: The mean plasma and RBC membranes CS concentrations (+/- SD) of the control group (n = 16) was 188 +/- 47 micrograms/dL and 343 +/- 57 micrograms/10(12) RBC, respectively. In 15 patients with diabetes and 12 Down's syndrome patients substantially higher CS levels were found (diabetes: plasma-348 +/- 60 micrograms/dL; RBC membranes-646 +/- 113 micrograms/10(12) RBC; Down's syndrome: plasma-245 +/- 54 micrograms/dL; RBC membranes 427 +/- 74 micrograms/10(12) RBC). Analysis of variance and multiple comparison (Newman-Keuls test) show statistically significant differences between all samples both for erythrocytes, F(2.41) = 52.24, p < 0.05, and plasma, F(2.41) = 34.92, p < 0.05. CONCLUSIONS: It is postulated that differences in CS levels may contribute to changes of erythrocyte properties in these pathological states.

Oxidative processes in red blood cells from normal and diabetic individuals.

The oxidation processes in normal and diabetic erythrocytes after cell exposure to H2O2 and t-butyl hydroperoxide, as well as the effect of malondialdehyde (a stable end product of lipid peroxidation) on erythrocyte membrane structure and stability were studied. The malondialdehyde level began to increase only after oxidation of most of the red blood cell glutathione by peroxides. The activation energy of malondialdehyde was 53 +/- 7 kj/mol. Sodium azide inhibited the oxidation processes induced by t-butyl hydroperoxide. The modification of erythrocytes by malondialdehyde decreased the fluidity of the membrane lipid bilayer measured by fluorescence anisotropy and increased the osmotic stability of the cells. The level of endogenous thiobarbituric acid-reactive species was higher and antioxidative activity was lower in diabetic cells. It seems likely that oxidation processes and accumulation of malondialdehyde can contribute directly to changes in the properties of ¿diabetic¿ red blood cells and may cause the development of long-term complications.

Abnormal degradation of red cell membrane proteins in diabetes.

The degradation of main membrane proteins, spectrin and band 3 protein, was studied in erythrocyte membranes of elderly diabetic patients and of healthy donors of various ages. In general, the rates of proteolysis were higher in diabetics. The degradation intensity depended on the sex of the diabetic patients and on the age of healthy donors.

Association between the glycation of erythrocyte membrane proteins and membrane fluidity.

Erythrocyte membrane ghosts prepared from normal individuals were incubated in vitro at different glucose concentrations for 72 h. Incubation with increasing concentrations of glucose resulted in increased glycation (nonenzymatic glycosylation) of membrane proteins and a decrease of erythrocyte membrane fluidity measured by the use of the fluorescent label pyrene. It would therefore seem likely that the changes in erythrocyte membrane fluidity previously reported in diabetic subjects (1-3) are related to in vivo glycation of membrane proteins as well as to changes in lipid composition, as was previously suggested (2).