Biomedical subjects

E D Schleicher

Publications and source records attributed to E D Schleicher.

At least 19 recordsLinked to original sources

PubMed1998

High glucose-induced transforming growth factor beta1 production is mediated by the hexosamine pathway in porcine glomerular mesangial cells.

Previous studies revealed that exposure of mesangial cells to high glucose concentration induces the production of matrix proteins mediated by TGF-beta1. We tested if structural analogues of D-glucose may mimic the high glucose effect and found that D-glucosamine was strikingly more potent than D-glucose itself in enhancing the production of TGF-beta protein and subsequent production of the matrix components heparan sulfate proteoglycan and fibronectin in a time- and dose-dependent manner. D-Glucosamine also promoted conversion of latent TGF-beta to the active form. Therefore, we suggested that the hexosamine biosynthetic pathway (the key enzyme of which is glutamine:fructose-6-phosphate amidotransferase [GFAT]) contributes to the high glucose-induced TGF-beta1 production. Inhibition of GFAT by the substrate analogue azaserine or by inhibition of GFAT protein synthesis with antisense oligonucleotide prevented the high glucose-induced increase in cellular glucosamine metabolites and TGF-beta1 expression and bioactivity and subsequent effects on mesangial cell proliferation and matrix production. Overall, our study indicates that the flux of glucose metabolism through the GFAT catalyzed hexosamine biosynthetic pathway is involved in the glucose-induced mesangial production of TGF-beta leading to increased matrix production.

Animals↗

PubMed1998

Defective basement membrane in laryngeal carcinomas with heterogeneous loss of distinct components.

In this study, we evaluated immunohistochemically the composition of the tumor-associated epithelial basement membrane (BM) in a series of 66 laryngeal squamous cell carcinomas (SCC) and compared these results with those from 10 cases with laryngeal dysplasia and five cases with normal mucosa (controls). The major BM components collagen IV and VII, laminin-1, perlecan (heparan sulfate proteoglycan), and fibronectin were evaluated. The extent of the retained BM material was quantified by semiautomated morphometry. A subsequent statistical analysis correlated the immunohistochemical findings with the histopathologically evaluated degree of tumor cell differentiation. In our series, we observed a distinct correlation between the degree of tumor cell differentiation and the amount of retained BM material. The loss of BM affected the various components differently, with a more extensive loss of collagen VII even in highly differentiated tumors and a progressive loss of collagen IV immunostaining with decreasing tumor cell differentiation. With respect to the other BM components, a stepwise loss of BM material also was seen with decreasing degree of the tumor cell differentiation. This loss, however was not at a statistically significant level, so these parameters did not show further statistically relevant data. In dysplastic lesions (regardless of the degree of dysplasia), focal BM disruptions were seen that affected the various BM components to a very similar extent. Our observations provide evidence that laryngeal carcinomas show a progressive loss of BM material along with decreasing tumor cell differentiation. This loss of BM, however, affects the various BM components differently. This indicates a dysregulation of the BM, either induced by uncoordinated neosynthesis or selectively enhanced degradation by proteases or both. Finally, the BM analysis may provide information on the biological course of the tumors. The loss of collagen VII may serve as a marker for "early" invasive tumor growth, whereas the amount of collagen IV provides significant information on the loss of tumor cell differentiation.

Adult↗

PubMed1998

Expression of glutamine:fructose-6-phosphate amidotransferase in human tissues: evidence for high variability and distinct regulation in diabetes.

Recent in vitro and in vivo studies suggested that the increased flux of glucose through the hexosamine biosynthetic pathway may contribute to glucose-induced insulin resistance and to the induction of the synthesis of growth factors. Because glutamine:fructose-6-phosphate amidotransferase (GFAT) catalyzes the first and rate-limiting step in the formation of hexosamine products, this enzyme is the key regulator in this pathway and is therefore possibly also involved in the alterations occurring in preclinical or manifest diabetic patients. To study the expression of GFAT in human tissues, we produced and characterized a peptic antiserum specifically recognizing GFAT protein and a riboprobe for the detection of GFAT mRNA. Immunohistochemical and nonradioactive in situ hybridization analysis revealed high levels of expression of GFAT protein and mRNA in adipocytes and skeletal muscle. Furthermore, a marked GFAT expression was found in vascular smooth muscle cells with unexpectedly high variability and lower levels in other cells, e.g., peripheral nerve sheath cells or endocrine-active cells, including the pancreatic islet cell. GFAT protein expression was below detection level in endothelium, osteocytes, lymphocytes, granulocytes, and in most quiescent fibroblasts. In renal tissue, GFAT was expressed in tubular epithelial cells, while glomerular cells remained essentially unstained. Renal sections obtained from patients with diabetic nephropathy showed significant GFAT expression in some glomerular epithelial and mesangial cells, indicating that GFAT expression may be induced by manifest diabetes. Our data indicate that GFAT is expressed in most tissues involved in the development of diabetic late complications. Furthermore, the results suggest that GFAT gene expression is highly regulated.

Adipocytes↗

PubMed1997

1997 Volvo Award winner in basic science studies. Immunohistologic markers for age-related changes of human lumbar intervertebral discs.

STUDY DESIGN: The authors performed a correlative macroscopic, histologic, and immunohistochemical investigation on human lumbar intervertebral discs using complete motion segment slices, including all age groups and stages of degeneration. OBJECTIVES: To identify markers for age-related changes of human lumbar intervertebral discs. In particular, to investigate changes in the distribution pattern of collagen Types I, II, III, IV, V, VI, IX, and X. In addition, to study posttranslational protein modification by the immunolocalization of N-(carboxylmethyl)lysine (CML), which is regarded as a biomarker for oxidative stress. SUMMARY OF BACKGROUND DATA: Data on a correlation of age-related changes in disc morphology and disc matrix composition is sparse. So far, no comprehensive analysis considered a correlation of macroscopic, histologic, and biochemical age-related alterations using complete sections of intervertebral discs (i.e., including nucleus pulposus, anulus fibrosus, endplates, and vertebral bodies). In addition, there is need for specific markers for these disc changes to allow for a better correlation with disc function. METHODS: After photodocumentation of the macroscopic appearance, 229 sagittal lumbar motion segments obtained from 47 individuals (fetal to 86 years) during routine autopsy were processed for histologic and immunohistochemical analysis. All slices were investigated for histologic alterations of disc degeneration. A randomly selected subset of these specimens (n = 45) was used for a correlative analysis of interstitial collagens and molecular modifications of matrix proteins. RESULTS: The presence of CML-modification of extracellular matrix proteins, mainly collagen, was observed first in the nucleus pulposus of a 13-year-old individual and increased significantly with age. In elderly people, both the nucleus pulposus and the anulus fibrosus showed extensive CML deposition. This CML deposition was accentuated in areas of macroscopic and histologic disc degeneration. After the occurrence of CML in the nucleus pulposus, we found a change in the collagen type pattern. An initial increase in nuclear collagen Types II, III, and VI staining was followed by a loss of collagen Type II, the occurrence of collagen Type I, and the persistence of high collagen Type III and VI levels, which were finally decreased again. The nuclear chondrocytes revealed significant changes in their immediate pericellular matrix, indicating phenotypic changes. Thus, exclusively in the nucleus pulposus of adolescents and young adults a significant proportion of cells positively stained for the basement membrane collagen Type IV. Collagen Type X was expressed by nuclear chondrocytes at a higher age and was associated with advanced degenerative disc alterations. CONCLUSIONS: The authors present the first study in which age-related changes are correlated on a macroscopic, histologic, and molecular level using complete sections of lumbar motion segments. They reconfirm the notion that disc degeneration starts as early as in the second decade of life. Therefore, only early prevention of disc damage may inhibit disc degeneration and its sequelae. Phenotypic alterations of nuclear chondrocytes as monitored by collagen Type IV in young adults with minor lesions and collagen Type X in advanced lesions indicate distinct cellular reactions, possibly as a reaction to enhanced oxidative stress. The degree of this oxidative stress is reflected by the CML-staining pattern which, in turn, indicates that the disc undergoes an accumulative stress, possibly leading to altered properties of the collagen fibrils and, thereby, tissue destruction. The deposition of CML proved to be the best marker for ongoing age-related changes in the intervertebral disc.

Adolescent↗

PubMed1997

Increased accumulation of the glycoxidation product N(epsilon)-(carboxymethyl)lysine in human tissues in diabetes and aging.

N(epsilon)-(Carboxymethyl)lysine (CML), a major product of oxidative modification of glycated proteins, has been suggested to represent a general marker of oxidative stress and long-term damage to proteins in aging, atherosclerosis, and diabetes. To investigate the occurrence and distribution of CML in humans an antiserum specifically recognizing protein-bound CML was generated. The oxidative formation of CML from glycated proteins was reduced by lipoic acid, aminoguanidine, superoxide dismutase, catalase, and particularly vitamin E and desferrioxamine. Immunolocalization of CML in skin, lung, heart, kidney, intestine, intervertebral discs, and particularly in arteries provided evidence for an age-dependent increase in CML accumulation in distinct locations, and acceleration of this process in diabetes. Intense staining of the arterial wall and particularly the elastic membrane was found. High levels of CML modification were observed within atherosclerotic plaques and in foam cells. The preferential location of CML immunoreactivity in lesions may indicate the contribution of glycoxidation to the processes occurring in diabetes and aging. Additionally, we found increased CML content in serum proteins in diabetic patients. The strong dependence of CML formation on oxidative conditions together with the increased occurrence of CML in diabetic serum and tissue proteins suggest a role for CML as endogenous biomarker for oxidative damage.

Adult↗

PubMed1996

Elevated glucose levels stimulate transforming growth factor-beta 1 (TGF-beta 1), suppress interleukin IL-2, IL-6 and IL-10 production and DNA synthesis in peripheral blood mononuclear cells.

The molecular mechanisms leading to impaired immune response in less well controlled diabetic patients are unclear. In this study we have analyzed the effects of elevated glucose concentration on both DNA synthesis and the production of transforming growth factor-beta 1 (TGF-beta 1) and the interleukins (IL) IL-2, IL-6 and IL-10 in stimulated peripheral blood mononuclear cells (PBMC) obtained from normal individuals. PBMC were stimulated by pokeweed mitogen or anti-CD3-antibody which binds specifically to the CD3-surface protein of T-lymphocytes. High glucose concentrations significantly inhibited DNA synthesis in PWM- as well as anti-CD3-stimulated PBMC. Exposure to elevated glucose levels caused a significant and dose-dependent increase in the production of latent TGF-beta 1 by (PWM)-stimulated PBMC at 24 and 48 h. Production of the cytokines IL-2, IL-6 and IL-10 was suppressed by elevated glucose concentration dose- and time-dependently. In contrast to the time-dependent decreased effect of glucose-induced TGF-beta 1 production the effects of elevated glucose levels on IL-2, IL-6 and IL-10 production increased with time indicating that TGF-beta 1 production is preceding the reduced IL production. These data demonstrate for the first time that elevated glucose levels significantly alter cytokine production in stimulated peripheral mononuclear cells and concomitantly inhibit cellular proliferation. Our results indicate that high glucose-induced TGF-beta 1 production may suppress immune response by inhibiting the endogenous production of IL-2, IL-6 and IL-10.

CD3 Complex↗

PubMed1996

High glucose-induced TGF-beta 1 regulates mesangial production of heparan sulfate proteoglycan.

Previous investigations have demonstrated that growing mesangial cells in high glucose concentration stimulates extracellular matrix synthesis and also increases the expression of transforming growth factor-beta (TGF-beta). We examined the effects of hyperglycemia on mesangial proliferation and heparan sulfate proteoglycan (HSPG) and fibronectin production. Prolonged exposure of mesangial cells to increasing glucose concentrations resulted in dose-dependent effects on growth inhibition and stimulation of matrix production. Treatment of mesangial cells with high glucose-conditioned medium or with TGF-beta 1 mimicked the effects of high-glucose incubation. Furthermore, TGF-beta 1 caused a dose-dependent increase in HSPG mRNA levels. The high-glucose effects on mesangial cells were preceded by an increase in total TGF-beta 1 protein. The presence of TGF-beta 1 antisense oligonucleotide attenuated the glucose-mediated effects on mesangial proliferation and matrix production. The data show that even moderately elevated glucose concentrations appear to affect the mesangial cells. The results indicate that 1) TGF-beta 1 protein production is necessary to obtain the high glucose-induced effects and 2) TGF-beta 1 stimulates mesangial HSPG expression and production. Because these effects may be attenuated by oligonucleotides antisense to TGF-beta 1, the results suggest a possible way for effective intervention in TGF-beta-mediated glomerulosclerosis.

Animals↗

PubMed1995

Localization of extracellular matrix components in congenital nephrotic syndromes.

While renal tissue from one fetus and a newborn with congenital nephrotic syndrome, Finnish type (FCNS), showed a normal basement membrane (BM) localization and composition, in another type of congenital nephrotic syndrome, diffuse mesangial sclerosis (DMS), most glomeruli demonstrated a completely disorganized matrix. In the latter, hyalinized glomerular segments were composed of irregular deposits of interstitial collagens I, III, V, and extensive deposits of heparin sulphate proteoglycan (HSPG), while collagen IV and laminin were completely absent in those areas. Apart from these sclerosed glomerular areas, normal capillarly loops revealed a matrix composition that was comparable to normal glomeruli. The additional immunolocalization of various extracellular matrix components during the development of normal human glomeruli revealed some significant age-dependent changes both in the localization of interstitial collagens and BM components: interstitial collagens I and III disappeared after the first S-shaped indentations appeared, while the interstitial collagen V remained along the glomerular BM and within the mesangium. The BM components showed no significant qualitative changes, but quantitative changes, with a post-natal relative decrease in the collagen IV and laminin content when compared with the level of BM-associated HSPG. Our results provide circumstantial evidence that the composition of the extracellular matrix (and in particular of the BM) shows age-dependent quantitative changes which may be associated with functional adaptation processes of the developing kidney. The observed matrix composition in the two different congenital nephrotic syndromes suggests various pathomechanisms which may be located either in the molecular structure of the negatively charged molecules (e.g. abnormal sulphatation of HSPG in FCNS) or in the dysregulated synthesis of various matrix components (DMS).

Adult↗

PubMed1994

Immunohistochemical localization of collagen VI in diabetic glomeruli.

Late stage diabetic nephropathy is histologically characterized by either diffuse or nodular expansion of the glomerular matrix. This is presumed to represent the morphological correlate for the functional impairment of the kidney. The exact matrix composition of the nodular glomerulosclerosis lesion of end-stage diabetic nephropathy is not known. Biochemical studies have provided evidence that the microfibrillar collagen type VI is increased in diabetic nephropathy. Consequently, this immunohistochemical study was designed to evaluate the extent and exact morphologic location of increased collagen VI deposition at various stages of diabetic glomerulosclerosis (GS). An irregular, sometimes spot-like staining of collagen VI was observed in diffuse GS in the mesangial portion. The uninterrupted staining which was evident along the glomerular basement membrane in normal glomeruli was discontinuous in diffusely sclerotic glomeruli. In nodular GS, the markedly increased deposition of collagen VI appeared to be evenly distributed throughout the entire nodular lesion. At the same time, mesangial staining for collagen IV was reduced in nodular GS, suggesting that in the expanded mesangial matrix collagen IV is progressively substituted by collagen VI during the transition from diffuse to nodular GS. The colocalization of PAS staining with collagen VI deposition in nodular GS suggests that the typical Kimmelstiel-Wilson lesions at least in part consist of collagen VI. Biochemical analysis confirmed the increased collagen VI deposition in glomeruli extracted from diabetic patients with nodular GS. Application of two antisera, recognizing primarily the alpha 1(VI)- and alpha 2(VI)-chains and the N-terminal part of alpha 3(VI)-chain, respectively, revealed no difference in staining pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

In-vitro carboxymethylation of low density lipoprotein alters its metabolism via the high-affinity receptor.

Carboxymethylation of lysine residues has been shown to result from oxidation of glycated proteins in vivo and in vitro leading to an augmentation of proteins' net negative charge. The metabolism of carboxymethylated low density lipoprotein (LDL) was studied in cultured human fibroblasts and mouse peritoneal macrophages. In vitro carboxymethylation was achieved by incubation of LDL with glyoxylic acid in the presence of Na(CN)BH3. Carboxymethylation inhibited metabolism of LDL via the high affinity receptor in fibroblasts as did methylation. The uptake of LDL into mouse peritoneal macrophages via the scavenger receptor, which was stimulated by acetylation, was not affected.

Acetylation↗

PubMed1993

Upregulation of myo-inositol transport compensates for competitive inhibition by glucose. An explanation for the inositol paradox?

High glucose concentrations inhibit the uptake of myo-inositol into cells. However, whether this leads to a depletion of intracellular myo-inositol levels has been debated, because unchanged, decreased, and increased cellular myo-inositol levels all have been reported for diabetic tissues. To evaluate whether cells are capable of counterregulating impaired uptake, we have investigated myo-inositol uptake in porcine aortic endothelial cells under short- and long-term hyperglycemic conditions. Although increasing glucose concentrations inhibited acute myo-inositol uptake competitively, the uptake was increased markedly, when cells were already preincubated in a high glucose medium for > 6 h. The stimulation was maximal at 20 mM of glucose with no further increase at 40 mM glucose. The same stimulation of uptake could be induced by 5 mM of glucose plus 35 mM of raffinose, whereas 35 mM of sorbitol or mannitol, which do not compete for myo-inositol uptake, were ineffective. Lineweaver-Burk analysis revealed an increased Vmax for the induced myo-inositol transport activity, whereas the Km for myo-inositol remained constant (18 microM). The upregulated inositol transporter was still Na+ and ATP dependent, indicating that the same carrier system was operating. Uptake returned to control values when cells were again exposed to normoglycemic medium conditions for an additional 24 h. When endothelial cells were incubated with D-[U-14C]glucose and 10 microM myo-[2-3H]inositol of equal specific radioactivity for 24 h, no 14C radioactivity was found in intracellular myo-inositol, indicating that conversion of glucose to myo-inositol was rather low.

Animals↗

PubMed1993

Specific glycation of albumin depends on its half-life.

Some suggest that measurements of plasma fructosamine concentration should be corrected for the plasma protein (or albumin) concentration because the extent of glycation per volume depends on both protein and glucose concentrations. Several reports, however, demonstrate a poor correlation between plasma fructosamine and albumin concentrations in diabetic patients. In vitro kinetic and in vivo studies have shown that glycation is also dependent on the half-lives of plasma proteins. Because a decrease in plasma albumin diminishes its catabolism, we speculated that low albumin concentrations are associated with a greater extent of glycation on a molar basis (specific glycation) and vice versa. To test this hypothesis, we studied plasma albumin, total protein, and fructosamine in 63 nondiabetic subjects with normal plasma fasting glucose concentrations and hemoglobin A1c between 5.1% and 5.9%. Plasma fructosamine was poorly correlated with albumin concentration (r = 0.348) but a logarithmic plot of the specific glycation of albumin vs albumin concentration showed a better correlation (r = -0.842), suggesting that the kinetic considerations were operating in vivo. Therefore, because lower specific glycation of plasma albumin "compensates" for higher concentration, correction of fructosamine for albumin content in patients will overestimate mean blood glucose when albumin is low and underestimate it when albumin is high.

Blood Glucose↗

PubMed1992

Elevated glucose decreases the content of a basement membrane associated heparan sulphate proteoglycan in proliferating cultured porcine mesangial cells.

The effect of elevated glucose concentrations on the synthesis of basement membrane components was investigated in proliferating cultured porcine mesangial cells. Basement membrane associated heparan sulphate proteoglycan was determined by enzyme immunoassay with a specific antiserum recognizing the core protein of the heparan sulphate proteoglycan. When cells were exposed to increasing glucose concentrations up to 40 mmol/l, the heparan sulphate proteoglycan content was concomitantly decreased to 53% when compared to cells cultured under normal glucose concentrations or in the presence of 40 mmol/l sorbitol. The fibronectin content was essentially unchanged under these conditions. No significant effect of insulin on these basement membrane components was found. The results indicate that hyperglycaemia may be responsible for a decrease of mesangial heparan sulphate proteoglycan content in diabetes mellitus. This supports the view that loss of heparan sulphate proteoglycan may be an important step or even an initial event of mesangial alterations in diabetic glomerulopathy.

Animals↗

PubMed1992

Glomerular changes in diabetes mellitus.

Ultrastructural, immunohistochemical and biochemical studies have improved our knowledge on the events occurring during the development of diabetic late complications. Immunohistochemical investigations of diabetic kidneys, using antibodies against various components of the extracellular matrix, showed increased collagen type IV (alpha 1,alpha 2-chain) deposition in the mesangial matrix, and a decrease of heparan sulphate proteoglycan in the mesangial matrix and glomerular basement membrane. Changes in matrix components seem to be the underlying cause of the alterations in renal function, as reflected by albuminuria and proteinuria. The occurrence of collagen type III in late diffuse glomerulosclerosis has been interpreted as an irreversible change in glomerular structure. The extent of alteration of the extracellular matrix correlates to a certain extent with the severity of nephropathy of the individual subject. The studies performed to date support the hypothesis that hyperglycaemia, whatever its origin, is the primary cause of diabetic late complications, although the pathobiochemical mechanisms are not yet fully understood. Increased intra- and extracellular levels of glucose and its derivatives are thought to contribute to diabetic tissue dysfunction. Three pathobiochemical theories are favoured in the current discussion: i) the polyol pathway ii) non-enzymatic glycation of proteins iii) direct influence of hyperglycaemia on the synthesis of matrix components. The evidence for the participation of the polyol pathway in the pathogenesis of diabetic nephropathy comes mainly from animal data using aldose reductase inhibitors, but only limited data are available for humans, so that the significance of this pathomechanism cannot yet be determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

High concentrations of low density lipoprotein decrease basement membrane-associated heparan sulfate proteoglycan in cultured endothelial cells.

The effect of increasing low density lipoprotein (LDL) concentrations on the synthesis of basement membrane components was investigated in proliferating porcine aortic endothelial cells (PAEC) in culture. Basement membrane-associated heparan sulfate proteoglycan (HSPG) and fibronectin were determined by enzyme immunoassay. Low extracellular LDL-levels increase, high extracellular LDL-levels decrease the HSPG content of PAEC. Fibronectin synthesis was only slightly affected while proliferation and metabolic activity as assessed by lactate production were constant. Insulin or high extracellular glucose did not influence the effect of LDL on basement membrane components.

Animals↗

PubMed1990

Competitive inhibition by glucose of myo-inositol incorporation into cultured porcine aortic endothelial cells.

To explore the significance of hyperglycaemia as a causal factor for the appearance of diabetic angiopathies we investigated aspects of myo-inositol metabolism in porcine aortic endothelial cells. myo-Inositol was shown to be a long-living metabolite. Its uptake into the cells was mediated by a high-affinity, Na(+)-dependent uptake system inhibitable by ouabain with an apparent KM of 18.6 mumols/l, which was responsible for more than 80% of total uptake at physiological myo-inositol concentrations. Inhibition of inositol uptake by D-glucose was exclusively competitive with an apparent Ki of 24 mmol/l as shown by Lineweaver-Burk- and Dixon-plot analysis. The specificity of competitive inhibition was studied. L-Glucose which is stereochemically related to myo-inositol in the same way as the D-isomer proved to be an equally potent inhibitor. The hexoses D-galactose, D-mannose and D-fructose inhibited myo-inositol uptake to a minor extent. D-allose and 3-O-methyl-D-glucose had no inhibitory effect indicating that the OH-group of the carbon atom in 3 position is essential for the interaction with the carrier. The acyclic hexitol sorbitol also did not compete. As expected, the aldose reductase blocker sorbinil did not influence the carrier since there is no polyol pathway operating in porcine aortic endothelial cells. In accordance with the results of the uptake experiments, the incorporation of exogenous myo-inositol into membrane phosphatidylinositol was reduced at elevated extracellular glucose levels. The results raise the possibility that hyperglycaemia impairs endothelial inositol supply.

Aldehyde Reductase↗

PubMed1990

Standardization of serum fructosamine assays.

We have calibrated a secondary serum protein standard by use (as primary standards) of samples of albumin and polylysine glycated with [14C]glucose in vitro, the glycation of which was assessed by radioactivity measurements and by elementary analysis for C and N. Using this standard for calibration in our improved fructosamine assay, one obtains an average fructosamine value of 247 mumol/L for nondiabetic individuals (or, in terms of total serum protein, 3.2 mumol/g)--about a tenth the value we obtained when we used the fructosamine assay of Johnson et al. (Clin Chim Acta 1983;127:87-95), standardized with desoxymorpholinofructose. In contrast, results corresponded well with the value for mean glycation of serum proteins, 3 mumol/g, determined by a furosine/HPLC method. Evidently the proposed procedure, in which a standard sharing the binding characteristics of endogenous glycated proteins is used together with our modified new fructosamine assay, leads to more realistic values for the concentrations of glycated serum proteins.

Carbon↗

PubMed1990

Differential kinetics of glucose metabolism in porcine retinal and aortic endothelial cells.

Rates of glucose utilization, measured by steady state lactate production, and the rates of initial uptake of [14C]glucose were determined in cultured porcine retinal endothelial cells. The apparent Km for the steady state process proved to be lower than that determined for the uptake step (0.20 vs. 0.86 mmol/l glucose), suggesting that the carrier-mediated uptake of glucose into retinal endothelial cells cannot be the rate limiting step of overall glucose consumption. Thus, porcine retinal endothelial cells differ from porcine aortic endothelial cells, in that the aortic endothelial cell membrane acts as a barrier for the uptake of glucose into the cell. Accordingly, dexamethasone, which is known to reduce glucose uptake and degradation in aortic endothelial cells, does not influence glucose utilization in the retinal cells.

Animals↗