Influence of high glucose concentrations on the expression of glycosaminoglycans and N-deacetylase/N-sulphotransferase mRNA in cultured skin fibroblasts from diabetic patients with or without nephropathy

A Glucose-Dependent Pharmacokinetic/ Pharmacodynamic Model of ACE Inhibition in Kidney Cells

Diabetic kidney disease (DKD) is a major cause of renal failure. Podocytes are terminally differentiated renal epithelial cells that are key targets of damage due to DKD. Podocytes express a glucose-stimulated local renin-angiotensin system (RAS) that produces angiotensin II (ANG II). Local RAS differs from systemic RAS, which has been studied widely. Hyperglycemia increases the production of ANG II by podocyte cells, leading to podocyte injury. Angiotensin-converting enzyme (ACE) is involved in the production of ANG II, and ACE inhibitors are drugs used to suppress elevated ANG II concentration. As systemic RAS differs from the local RAS in podocytes, ACE inhibitor drugs should act differently in local versus systemic contexts. Experimental and computational studies have considered the pharmacokinetics (PK) and pharmacodynamics (PD) of ACE inhibition of the systemic RAS. Here, a PK/PD model for ACE inhibition is developed for the local RAS in podocytes. The model takes constant or dynamic subject-specific glucose concentration input to predict the ANG II concentration and the corresponding effects of drug doses locally and systemically. The model is developed for normal and impaired renal function in combination with different glucose conditions, thus enabling the study of various pathophysiological conditions. Parameter uncertainty is also analyzed. Such a model can improve the study of the effects of drugs at the cellular level and can aid in development of therapeutic approaches to slow the progression of DKD.

N-sulfation of heparan sulfate is critical for syndecan-4-mediated podocyte cell-matrix interactions

Previous research has shown that podocytes unable to assemble heparan sulfate on cell surface proteoglycan core proteins have compromised cell-matrix interactions. This report further explores the role of N-sulfation of intact heparan chains in podocyte-matrix interactions. For the purposes of this study, a murine model in which the enzyme N-deacetylase/N-sulfotransferase 1 (NDST1) was specifically deleted in podocytes and immortalized podocyte cell lines lacking NDST1 were developed and used to explore the effects of such a mutation on podocyte behavior in vitro. NDST1 is a bifunctional enzyme, ultimately responsible for N-sulfation of heparan glycosaminoglycans produced by cells. Immunostaining of glomeruli from mice whose podocytes were null for Ndst1 (Ndst1(-/-)) showed a disrupted pattern of localization for the cell surface proteoglycan, syndecan-4, and for α-actinin-4 compared with controls. The pattern of immunostaining for synaptopodin and nephrin did not show as significant alterations. In vitro studies showed that Ndst1(-/-) podocytes attached, spread, and migrated less efficiently than Ndst1(+/+) podocytes. Immunostaining in vitro for several markers for molecules involved in cell-matrix interactions showed that Ndst1(-/-) cells had decreased clustering of syndecan-4 and decreased recruitment of protein kinase-Cα, α-actinin-4, vinculin, and phospho-focal adhesion kinase to focal adhesions. Total intracellular phospho-focal adhesion kinase was decreased in Ndst1(-/-) compared with Ndst1(+/+) cells. A significant decrease in the abundance of activated integrin α5β1 on the cell surface of Ndst1(-/-) cells compared with Ndst1(+/+) cells was observed. These results serve to highlight the critical role of heparan sulfate N-sulfation in facilitating normal podocyte-matrix interactions.

Dehydroepiandrosterone sulfate (DHEAS) as an endocrine marker of aging in calorie restriction studies

The adrenal steroid, dehydroepiandrosterone sulfate (DHEAS), is generally regarded as being a reliable endocrine marker of aging, because in humans and nonhuman primates its circulating concentrations are very high during young adulthood, and the concentrations then decline markedly during aging. Despite promising results from early studies, we were recently surprised to find that caloric restriction (CR) did little to prevent or delay the decline of DHEAS concentrations in old rhesus macaques. Here we summarize the use of circulating DHEAS concentrations as a biomarker of aging in CR studies and suggest reasons for its limited value. Although DHEAS can reliably predict aging in animals maintained on a standard diet, dietary manipulations may affect liver enzymes involved in the metabolism of steroid hormones. Consequently, in CR studies the reliability of using DHEAS as a biomarker of aging may be compromised.

The glycocalyx and cardiovascular disease in diabetes: should we judge the endothelium by its cover?

Patients with diabetes mellitus are characterized by an extraordinary vascular vulnerability. Traditionally, glucose-induced damage to the vascular endothelium is believed to be one of the first steps in the development of vascular damage. However, in the healthy vessel the endothelium is protected by a matrix layer of highly glycosylated proteins that form a physical barrier between the endothelium and the blood flowing past. Although its presence has been known for half a century, this so-called glycocalyx earned little attention from researchers in the past because of an underestimation of its size. In the last decade it has become clear that its full thickness actually exceeds that of the vascular endothelium. Accumulating research into the functional relevance of the endothelial glycocalyx suggests an important role for this layer in the development of cardiovascular disease in diabetes mellitus. Here we will present an overview of the biochemistry of the intact glycocalyx, current methods to assess the glycocalyx, and its possible role in the pathophysiology of cardiovascular disease in diabetes.

Effects of intensive glycemic control on serum levels of insulin-like growth factor-I and dehydroepiandrosterone sulfate in Type 2 diabetes mellitus

BACKGROUND

Although accumulating evidence shows that aging hormones are involved in glucose metabolism, effects of glycemic control on serum IGF-I and DHEAS levels are still unclear.

OBJECTIVE AND METHODS

To investigate the effects of glycemic control on these hormone levels, we conducted a 1-month longitudinal study of 49 Japanese patients with Type 2 diabetes mellitus. We measured serum levels of IGF-I and DHEA-S before and after 1-month glycemic control and analyzed the association of changes in IGF-I and DHEA-S with glycated hemoglobin (HbA1c).

RESULTS

HbA1c was decreased at 1 month with mean changes of -1.2% (p<0.001). Serum IGF-I was increased with mean changes of 11 ng/ml (p<0.05), while serum DHEA-S was decreased with mean changes of -19 μg/dl (p<0.05). Multiple regression analysis showed that changes in DHEA-S were inversely associated with changes in fasting plasma glucose (β=-0.36, p=0.027) and HbA1c (β=-0.33, p=0.028), while changes in IGF-I were not.

CONCLUSION

The present longitudinal study showed that intensive glycemic control for 1 month increased serum IGF-I level and decreased serum DHEA-S level in Japanese patients with poorly controlled Type 2 diabetes. Further studies are needed to clarify the hormonal changes in IGF-I and DHEA-S after intensive glycemic control would affect diabetic complications.

No change in glomerular heparan sulfate structure in early human and experimental diabetic nephropathy

Heparan sulfate (HS) proteoglycans are major anionic glycoconjugates of the glomerular basement membrane and are thought to contribute to the permeability properties of the glomerular capillary wall. In this study we evaluated whether the development of (micro) albuminuria in early human and experimental diabetic nephropathy is related to changes in glomerular HS expression or structure. Using a panel of recently characterized antibodies, glomerular HS expression was studied in kidney biopsies of type I diabetic patients with microalbuminuria or early albuminuria and in rat renal tissue after 5 months diabetes duration. Glomerular staining, however, revealed no differences between control and diabetic specimens. A significant (p < 0.05) approximately 60% increase was found in HS N-deacetylase activity, a key enzyme in HS sulfation reactions, in diabetic glomeruli. Structural analysis of glomerular HS after in vivo and in vitro radiolabeling techniques revealed no changes in HS N-sulfation or charge density. Also HS chain length, protein binding properties, as well as disaccharide composition did not differ between control and diabetic glomerular HS samples. These results indicate that in experimental and early human diabetic nephropathy, increased urinary albumin excretion is not caused by loss of glomerular HS expression or sulfation and suggest other mechanisms to be responsible for increased glomerular albumin permeability.

High glucose alters proteoglycan expression and the glycosaminoglycan composition in placentas of women with gestational diabetes mellitus and in cultured trophoblasts

Impaired glucose metabolism with diabetes may alter the expressions of proteoglycans (PGs), which may impair the biological functions of placenta. In this study, we investigated the expression of PGs and their conjugated glycosaminoglycan (GAG) composition in the placentas of mothers with gestational diabetes mellitus (GDM) and trophoblasts cultured in a high-glucose condition. The PGs by guanidine/HCl extraction and DEAE Sepharose fractionation followed by GAG degradation enzyme digestion analyses showed that the expression of chondroitin sulfate and/or dermatan sulfate (CS/DS) PGs was increased whereas the heparan sulfate (HS) PG was decreased in GDM placentas compared to controls. Western blot analyses demonstrated that the increased CS/DS PGs in GDM placentas were predominantly the small leucine-rich proteoglycans (SLRPs), decorin and biglycan. Increased mRNA expression level was consistently shown by quantitative real-time PCR. Immunohistochemistry indicated intensive staining of decorin and biglycan in the diabetic placenta with different localizations. Additionally, the basement membrane HSPG, perlecan was found to contain both CS/DS and HS in GDM placentas and plain HS in controls. Similar findings of PG alterations induced by hyperglycemia were observed in cultured trophoblast in a high-glucose condition. This study demonstrated that hyperglycemia induced not only the gene expressions of PGs but also alterations in the carried GAG type and composition.

Loss of heparan N-sulfotransferase in diabetic liver: role of angiotensin II

The basis for accelerated atherosclerosis in diabetes is unclear. Diabetes is associated with loss of heparan sulfate (HS) from the liver, which may impede lipoprotein clearance and thereby worsen atherosclerosis. To study hepatic HS loss in diabetes, we examined regulation of HS N-deacetylase/N-sulfotransferase-1 (NDST), a key enzyme in hepatic HS biosynthesis. Hepatic NDST mRNA, protein, and enzymatic activity were suppressed by >50% 2 weeks after induction of type 1 diabetes in rats. Treatment of diabetic rats with enalapril, an ACE inhibitor, had no effect on hyperglycemia or hepatic NDST mRNA levels, yet increased hepatic NDST protein and enzymatic activity. Similar results were obtained in diabetic animals treated with losartan, which blocks the type 1 receptor for angiotensin II (AngII). Consistent with these findings, diabetic livers exhibited increased ACE expression, and addition of AngII to cultured hepatoma cells reduced NDST activity and protein. We conclude that diabetes substantially suppresses hepatic NDST mRNA, protein, and enzymatic activity. AngII contributes to suppression of NDST protein and enzymatic activity, whereas mRNA suppression occurs independently. Suppression of hepatic NDST may contribute to diabetic dyslipidemia, and stimulation of NDST activity by AngII inhibitors may provide cardiovascular protection.

Confirmation of a susceptibility locus for diabetic nephropathy on chromosome 3q23-q24 by association study in Russian type 1 diabetic patients

Family-based studies and segregation analyses suggest that inherited factors play a significant role in susceptibility to diabetic nephropathy (DN). Moczulski et al. [Diabetes 47 (1998) 1164-1169] found a susceptibility locus for DN in type 1 diabetes covering a 20cM region on chromosome 3q, with a peak of linkage close to the angiotensin II type 1 receptor (AT1) gene. We examined eight polymorphic markers (D3S1512, D3S1550, D3S1557, D3S1744, D3S2326, D3S3599, D3S3694, and a (CA)(n) dinucleotide repeat polymorphism in the 3' flanking region of the AT1 gene) spanning about 6.2 megabases (Mb) in the region of maximal linkage with DN on chromosome 3q23-q24. The markers were used to genotype a total of 381 Russian type 1 diabetic subjects, 195 of whom had DN and 186 had no clinical nephropathy. Four of the markers tested, D3S1512, D3S1550, D3S2326, and D3S3599, showed an association with DN in type 1 diabetes mellitus. These markers are located within a 1.0Mb interval that starts about 4.4Mb centromeric to the AT1 gene. Thus, our results suggest the existence of the DN susceptibility locus previously described by Moczulski et al. on chromosome 3q.