The kidney in diabetes

Proteomic identification of 14-3-3zeta as an adapter for IGF-1 and Akt/GSK-3beta signaling and survival of renal mesangial cells

Recently we demonstrated that IGF-1 expression is increased in the diabetic kidney and that it may involve in renal hypertrophy and extracellular matrix protein (ECM) accumulation in mesangial cells as seen in diabetic glomerulopathy. The present study investigates the molecular mechanism(s) of IGF-1 and Akt/glycogen synthase kinase-3beta (GSK-3beta) signaling pathway in the regulation of fibronectin and cyclin D1 expression and survival of renal mesangial cells. A proteomic approach is also employed to identify protein targets of IGF-1 signaling via GSK-3beta inhibition in mesangial cells. We show that IGF-1 (100 ng/ml) significantly increases the protein kinase Akt/PKB activity (1.5-2-fold, p<0.05) within 1-5 minutes, which is completely blocked by the presence of 100 nM Wortmannin (phosphatidyl-inositol 3-kinase inhibitor). Akt activation is coupled with Ser9 phosphorylation and inactivation of its down-stream target GSK-3beta. IGF-1 increases the cyclic AMP-responsive element (CRE) binding transcription factor CREB phosphorylation at Ser 133 and CRE-binding activity in mesangial cells, which parallels cyclin D1 and fibronectin expressions. Both proteins are known to have CRE-sequences in their promoter regions upstream of the transcription start site. Suppression of GSK-3beta by SB216763 (100 nM) increases CREB phosphorylation, cyclin D1 and fibronectin levels. Two dimensional gel electrophoresis followed by MALDI-TOF mass spectrometric analysis of mesangial proteins reveals that IGF-1 treatment or an inhibition of GSK-3beta increases the expression of the phosphorylated Ser/Thr binding signal adapter protein 14-3-3zeta. Immuno-precipitation of 14-3-3zeta followed by Western blotting validates the association of phosphorylated GSK-3beta with 14-3-3zeta in renal mesangial cells. Stable expression of a constitutively active GSK-3beta(Ser9Ala) induces cell death while overexpression of HA-tagged 14-3-3zeta increases cell viability as measured by MTT assays. These results indicate that the Akt/GSK-3beta pathway and the adapter protein 14-3-3zeta may play an important role in IGF-1 signaling and survival of mesangial cells in diabetic nephropathy.

Relationship between the expression of advanced glycation end-products (AGE) and the receptor for AGE (RAGE) mRNA in diabetic nephropathy

OBJECTIVE

The receptor for advanced glycation end-products (RAGE) is one of several advanced glycation end-product (AGE)-specific cellular receptors. To evaluate the relationship between AGE and RAGE in renal tissues of diabetic nephropathy (DN), we examined the levels of expression of AGE protein and of RAGE mRNA. We also investigated the relationships among the degree of mesangial expansion and the expression of AGE and RAGE mRNA.

PATIENTS AND METHODS

Renal biopsy tissues were obtained from 20 patients with DN. We performed immunohistochemical staining using monoclonal anti-AGE antibody and in situ hybridization using non-radioactive oligonucleotide RAGE probe on these tissues. We also examined five control renal samples. We evaluated the intensity of positive anti-AGE antibody staining and the percentage of cells positive for RAGE mRNA. We also measured the total glomerular area and mesangial area in glomeruli using an automatic image analyzer. We then calculated the percentage of mesangial area as a proportion of the total glomerular area (%Mes).

RESULTS

Anti-AGE antibody was detected in the expanded mesangial matrix in DN but not in control samples. RAGE mRNA expression was detected mainly in glomerular intrinsic cells, including glomerular mesangial and epithelial cells, in both DN and control. %Mes correlated significantly with both the intensity of anti-AGE antibody positive staining and the percentage of cells positive for RAGE mRNA.

CONCLUSIONS

Our findings suggest that both AGE and RAGE are associated with the development and progression of DN.

Hyperglycemia-induced TGFbeta and fibronectin expression in embryonic mouse heart

Cardiovascular defects are common in diabetic offspring, but their etiology and pathogenesis are poorly understood. Extracellular matrix accumulates in adult tissues in response to hyperglycemia, and transforming growth factor-beta1 (TGF beta1) likely mediates this effect. The objective of this study was to characterize TGF beta expression in the organogenesis-stage mouse heart and to evaluate TGF beta and fibronectin expression in embryonic mouse heart exposed to hyperglycemia. Prominent TGF beta1, and minimal TGF beta2 or TGF beta 3, protein expression was demonstrated in embryonic day (E) 9.5-E13.5 hearts. Hyperglycemia for 24 hr produced significantly increased fibronectin, slightly increased TGF beta1, and unchanged TGF beta2 or TGF beta 3, by immunohistochemistry. Increased TGF beta1 was demonstrated by enzyme-linked immunosorbent assay in embryonic fluid and isolated hearts after hyperglycemia for 24 hr, but not 48 hr. Hyperglycemia increased fibronectin protein and mRNA expression in embryonic hearts after 24 hr, and pericardial injection of TGF beta1 also increased fibronectin mRNA in the embryonic heart. It is proposed that TGF beta1 and fibronectin may play a role in diabetes-induced cardiac dysmorphogenesis.

Diabetic nephropathy: diagnosis, prevention, and treatment

Diabetic nephropathy is the leading cause of kidney disease in patients starting renal replacement therapy and affects approximately 40% of type 1 and type 2 diabetic patients. It increases the risk of death, mainly from cardiovascular causes, and is defined by increased urinary albumin excretion (UAE) in the absence of other renal diseases. Diabetic nephropathy is categorized into stages: microalbuminuria (UAE >20 microg/min and < or =199 microg/min) and macroalbuminuria (UAE > or =200 microg/min). Hyperglycemia, increased blood pressure levels, and genetic predisposition are the main risk factors for the development of diabetic nephropathy. Elevated serum lipids, smoking habits, and the amount and origin of dietary protein also seem to play a role as risk factors. Screening for microalbuminuria should be performed yearly, starting 5 years after diagnosis in type 1 diabetes or earlier in the presence of puberty or poor metabolic control. In patients with type 2 diabetes, screening should be performed at diagnosis and yearly thereafter. Patients with micro- and macroalbuminuria should undergo an evaluation regarding the presence of comorbid associations, especially retinopathy and macrovascular disease. Achieving the best metabolic control (A1c <7%), treating hypertension (<130/80 mmHg or <125/75 mmHg if proteinuria >1.0 g/24 h and increased serum creatinine), using drugs with blockade effect on the renin-angiotensin-aldosterone system, and treating dyslipidemia (LDL cholesterol <100 mg/dl) are effective strategies for preventing the development of microalbuminuria, in delaying the progression to more advanced stages of nephropathy and in reducing cardiovascular mortality in patients with type 1 and type 2 diabetes.

Clinicopathologic characteristics of nodular glomerulosclerosis in Chinese patients with type 2 diabetes

BACKGROUND

Nodular glomerulosclerosis is a distinct entity that is highly specific for diabetic glomerulopathy. However, clinicopathologic characteristics of this nodular lesion are largely undefined in patients with type 2 diabetes.

METHODS

An autopsy study was conducted to investigate the clinical, histopathologic, and histochemical characteristics of 351 consecutive cases with type 2 diabetes. In addition, immunohistochemical staining was performed in a representative subset of 50 cases.

RESULTS

Nodular glomerulosclerosis was found in 37.6%. Hypertension, elevated serum creatinine and urea levels, renal failure, myocardial infarction, low body mass index, and large glomerular matrix area were the significant risk factors for nodular glomerulosclerosis. Proteinuria (protein > 0.5 g/24 h), renal insufficiency (serum creatinine > or = 2.0 mg/dL [> or =178 micromol/L]), and renal failure were found in 28.1%, 33.6%, and 7.6% of patients with type 2 diabetes with nodular glomerulosclerosis, respectively. Glomerular matrix fractions were 42.1% +/- 13.3%, 32.3% +/- 15.3%, and 22.7% +/- 8.0% in patients with nodular glomerulosclerosis, non-nodular glomerulopathy (glomerulopathy in the absence of Kimmelstiel-Wilson nodule), and near-normal glomeruli with age-related minimal changes, respectively (analysis of variance, P < 0.001). Immunoreactivity for collagen type IV, fibronectin, and laminin was localized at the periphery of mesangial nodules. Mesangial cells at the periphery of mesangial nodules showed increased staining intensity for alpha-smooth muscle actin (alpha-SMA) and transforming growth factor-beta1 (TGF-beta1). Nodular lesions also showed a marked increase in number of glomerular CD68-positive macrophages.

CONCLUSION

In patients with type 2 diabetes, nodular glomerulosclerosis is related to hypertension, advanced renal disease, and prevalent myocardial infarction. Glomerular macrophage infiltration, expression of alpha-SMA by mesangial cells, and overexpression of TGF-beta1 are the cellular changes associated with abnormal extracellular matrix deposition in nodular glomerulosclerosis.

Activation of the Smad Pathway in Glomeruli from a Spontaneously Diabetic Rat Model, OLETF Rats

BACKGROUND/AIMS

Transforming growth factor-beta (TGF-beta) mediates the excess accumulation of extracellular matrix in the diabetic kidney. Smad family proteins have been identified as signal transducers for the TGF-beta superfamily. We sought to characterize the role of Smad proteins in mediating TGF-beta responses in the development of diabetic nephropathy.

METHODS

We evaluated the time course of TGF-beta1 fibronectin, Smad2 and Smad3 protein expression and Smad3 activation in glomeruli from spontaneously diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats, using immunohistochemistry and Western blot analysis.

RESULTS

The glomeruli of diabetic OLETF rats showed not only accelerated activation of Smad3, but also enhanced protein expression of Smad2 and Smad3, which occurred in parallel to the increased expression of TGF-beta and fibronectin compared with glomeruli of control, Long-Evans Tokushima Otsuka (LETO) rats at 30 weeks of age. No differences were found in TGF-beta1 fibronectin, Smad2 and Smad3 protein expression and Smad3 activation in glomeruli between the two strains at 12 weeks of age when OLETF rats were not diabetic.

CONCLUSIONS

The enhancement of Smad protein expression and activation may be involved in the TGF-beta signaling cascade that plays an important role in the development of diabetic nephropathy through progressive expansion of the mesangial matrix.

Hexosamines and TGF-beta1 use similar signaling pathways to mediate matrix protein synthesis in mesangial cells

Hyperglycemia-induced alterations in mesangial (MES) cell function and extracellular matrix (ECM) protein accumulation are seen in diabetic glomerulopathy. Transforming growth factor-beta1 (TGF-beta1) mediates high-glucose-induced matrix production in the kidney. Recent studies demonstrated that some of the effects of high glucose on cellular metabolism are mediated by the hexosamine biosynthesis pathway (HBP) in which fructose-6-phosphate is converted to glucosamine (GlcN) 6-phosphate. We previously showed that the high-glucose-mediated fibronectin and laminin synthesis in MES cells is mediated by the HBP and that GlcN is more potent than glucose in inducing TGF-beta1 promoter luciferase activity. In this study, we investigated the hypothesis that the effects of glucose on MES matrix production occur via hexosamine regulation of TGF-beta1. Culturing simian virus (SV)-40-transformed rat kidney MES cells in 25 mM glucose (HG) for 48 h increases cellular fibronectin and laminin levels about twofold on Western blots compared with low glucose (5 mM). GlcN (1.5 mM) or TGF-beta1 (2.5-5 ng/ml) for 24-48 h also increases ECM synthesis. However, the effects of HG or GlcN with TGF-beta1 are not additive. The presence of anti-TGF-beta1 antibodies (20 microg/ml) blocks both TGF-beta1- and GlcN-induced fibronectin synthesis. TGF-beta1 increased ECM levels via PKA (laminin and fibronectin) and PKC (fibronectin) pathways. Similarly, TGF-beta1 and hexosamines led to nonadditive increases in phosphorylation of the cAMP responsive element binding transcription factor. These results suggest that the effects of excess glucose on MES ECM synthesis occur via HBP-mediated regulation of TGF-beta1.

Diabetic kidney disease in the db/db mouse

Diabetic nephropathy is increasing in incidence and is now the number one cause of end-stage renal disease in the industrialized world. To gain insight into the genetic susceptibility and pathophysiology of diabetic nephropathy, an appropriate mouse model of diabetic nephropathy would be critical. A large number of mouse models of diabetes have been identified and their kidney disease characterized to various degrees. Perhaps the best characterized and most intensively investigated model is the db/db mouse. Because this model appears to exhibit the most consistent and robust increase in albuminuria and mesangial matrix expansion, it has been used as a model of progressive diabetic renal disease. In this review, we present the findings from various studies on the renal pathology of the db/db mouse model of diabetes in the context of human diabetic nephropathy. Furthermore, we discuss shortfalls of assessing functional renal disease in mouse models of diabetic kidney disease.

Ultrastructural morphometry of capillary basement membrane thickness in normal and transgenic diabetic mice

Capillary basement membrane (CBM) thickening is an ultrastructural hallmark in diabetic patients and in animal models of diabetes. However, the wide variety of tissues sampled and diverse methods employed have made the interpretation of thickness data difficult. We showed previously that acellular glomerular BMs in OVE26 transgenic diabetic mice were thickened beyond normal age-related thickening, and in the current study we hypothesized that other microvascular BMs likewise would show increased widths relative to age-matched controls. Accordingly, a series of tissues, including skeletal and cardiac muscle, ocular retina and choriod, peripheral nerve, lung, pancreas, and renal glomerulus was collected from 300-350-day-old normal and transgenic mice. Transmission electron micrographs of cross sections through capillary walls were prepared, and CBM thickness (CBMT) was determined by the "orthogonal intercept" method. Morphometric analyses showed highly variable transgene-related BMT increases in the sampled tissues, with glomerular BM showing by far the greatest increase (+87%). Significant thickness increases were also seen in the retina, pulmonary alveolus, and thoracoabdominal diaphragm. BMT increases were not universal; however, most were modestly widened, and those that were thickest in controls generally showed the greatest increase. Although the pathogenesis of diabetes-related increases in CBM is poorly understood, data in the current study showed that in OVE26 transgenic mice increased BMT was a frequent concomitant of hyperglycemia. Accordingly, it seems likely that hyperglycemia-induced microvascular damage may be a contributing factor in diabetic BM disease, and that microvessel cellular and extracellular heterogeneity may limit the extent of CBM thickening in diverse tissues.

Overexpression of the complementary DNA for human glutamine:fructose-6-phosphate amidotransferase in mesangial cells enhances glucose-induced fibronectin synthesis and transcription factor cyclic adenosine monophosphate-responsive element binding phosphorylation

Hyperglycemia-induced alterations in mesangial cell function and extracellular matrix protein (ECM) accumulation are seen in diabetic glomerulopathy. The hexosamine biosynthesis pathway (HBP) is implicated in mediating several metabolic effects of high glucose (HG) in cells. This pathway converts fructose-6-phosphate to glucosamine (GlcN)-6-phosphate by the rate-limiting enzyme glutamine:fructose-6-phosphate amidotransferase (GFA). We have previously shown that metabolism of glucose through the HBP regulates the effects of glucose on ECM (fibronectin) synthesis and transcription factor (cyclic adenosine monophosphate-responsive element binding [CREB]) phosphorylation in SV-40-transformed rat kidney mesangial cells. UDP-N-acetyl-GlcN is the end product of the HBP and serves as a precursor for O-linked serine/threonine glycosylation of cytoplasmic and nuclear proteins. Here we show that culturing mesangial cells in HG and GlcN increases the level of O-N-acetylglucosamine in several cytoplasmic and nuclear proteins. Inhibition of O-glycosylation by benzyl-2-acetamido-2-deoxy-alpha-D-galactopyranoside blocks both HG and GlcN-induced fibronectin synthesis and CREB phosphorylation. To further support the hypothesis that the HBP mediates HG-induced ECM synthesis, a complementary deoxyribonucleic acid (DNA) for human GFA was stably expressed in mesangial cells. Mesangial and GFA-overexpressing cells were cultured in 5 to 25 mM glucose for 48 hours. GFA-overexpressing cells were more sensitive to glucose as they demonstrated increases in fibronectin and CREB phosphorylation at lower glucose concentrations than seen In control cells. In addition, the response to 25 mM glucose for both proteins was increased in GFA when compared with controls. There is no difference in DNA synthesis and cellular adenosine triphosphate levels between the two cell lines. These results suggest that the HBP is a glucose sensor and mediator of the effects of hyperglycemia in the diabetic mesangium.

Estimating mean glomerular volume using two arbitrary parallel sections

The most reliable method for estimation of mean glomerular volume (MGV), the disector/Cavalieri method, is technically demanding and time consuming. Other methods suffer either from a lack of precise correlation with the gold standard or from the need for a large number of glomeruli in the sample. Here, a new method (the 2-profile method) is described; it provides a reliable estimate of MGV by measuring the profile area of glomeruli in two arbitrary parallel sections. MGV was estimated in renal biopsies from 16 diabetic patients and 13 normal subjects using both the Cavalieri and the 2-profile methods. The range of individual glomerular volumes based on the Cavalieri measurements was 0.31 to 4.02 x10(6) micro m(3). There was a high correlation between the two methods for MGV (r = 0.97; P < 0.0001). However, the 2-profile method systematically overestimated MGV (P = 0.0005, paired t test). This overestimation was corrected by introducing a multiplication factor of 0.91, after which statistical criteria of interchangeability with the Cavalieri method were met. The optimal distance between two sections was determined as 20 micro m with a coefficient of variation of 7.4% in repeated measurements of MGV. On the basis of findings that values for MGV stabilize after ten glomeruli are measured by the disector/Cavalieri method, it was determined that the accuracy of MGV by the 2-profile method obtained by eight glomeruli was less than 7% different from ten in all cases. Thus, the 2-profile method is a practical alternative to the disector/Cavalieri method for estimating MGV, especially in small samples and blocks with limited residual tissue.

Biochemical study on the effects of some Egyptian herbs in alloxan-induced diabetic rats

The present study was carried out to investigate the effects of Lupinus albus, L. (Lupinus termis), family L. leguminosae, Cymbopogon proximus, (Halfa barr), family Gramineae, and Zygophyllum coccineum L. (Kammun quaramany), family L. Zygophyllacae on biochemical parameters in alloxan-induced diabetic rats. A dose of 1.5 ml of aqueous suspension of each herb/100 g body weight (equivalent to 75 mg/100 g b.wt.) was orally administered daily to alloxan-diabetic rats for 4 weeks. The levels of glucose, urea, creatinine and bilirubin were significantly (P<0.05) increased in plasma of alloxan-diabetic rats compared with the control group. In contrast, total protein and albumin were significantly decreased by 25 and 46%, respectively, versus control. Treatment of the diabetic rats with repeated doses of any one of the three herb suspensions could restore the changes of the above parameters to their normal levels after 4 weeks of treatment. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) and alkaline phosphatase (AlP) activities were significantly (P<0.05) increased in the plasma of alloxan-diabetic rats. However, acetylcholinesterase activity was significantly (P<0.05) decreased in the plasma compared with the control group, whereas, such activity did not change in brain. The activities of AST, ALT and LDH were significantly (P<0.05) decreased in the liver of alloxan-diabetic rats by 58, 21 and 40%, respectively, and such activities increased in testes by 39, 26 and 26%, respectively, compared with the control group. Also, brain LDH was significantly (P<0.05) increased. Treatment of the diabetic rats with the aqueous suspension of the tested herbs restored the activities of the above enzymes to their normal level in plasma, liver and testes. The present results showed that the herb suspensions exerted antihyperglycemic effects and consequently may alleviate liver and renal damage caused by alloxan-induced diabetes.

Association of transforming growth factor-beta1 T29C polymorphism with the progression of diabetic nephropathy

Diabetes mellitus is a leading cause of end-stage renal disease in the Western world. Histologically, mesangial expansion with increased extracellular matrix protein is observed in patients with diabetic nephropathy. Because transforming growth factor (TGF)-beta promotes extracellular matrix production in response to high glucose, TGF-beta is considered to play a central role in the pathogenesis of diabetic nephropathy. We investigated the association of TGF-beta1 T29C polymorphism and the progression of diabetic nephropathy. Forty patients with type 2 diabetes mellitus were enrolled. All patients had had diabetes for more than 10 years. DNA was extracted from peripheral blood cells, and genotype was determined using real-time polymerase chain reaction method. Patients were classified into three groups according to genotype: TT, TC, and CC. Grade of diabetic nephropathy was determined using the amount of urinary excretion of albumin. Demographic characteristics of the patients with each genotype were not statistically different. No differences in the glycemic control and the mode of therapy were observed. Among patients with three genotypes, the severity of diabetic nephropathy was not statistically different. The patients with TT genotype tended to have a higher rate of progression of nephropathy; however, no statistically significant difference was observed among the three groups. Our results suggest that TGF-beta1 T29C polymorphism is not associated with the progression of diabetic nephropathy. Further studies are required to determine the exact role of this polymorphism in the progression of diabetic nephropathy.

Hexosamine-induced fibronectin protein synthesis in mesangial cells is associated with increases in cAMP responsive element binding (CREB) phosphorylation and nuclear CREB: the involvement of protein kinases A and C

Hyperglycemia-induced alterations in mesangial (MES) cell function and extracellular matrix protein accumulation are seen in diabetic glomerulopathy. Recent studies have demonstrated that some of the effects of high glucose (HG) on cellular metabolism are mediated by the hexosamine biosynthesis pathway (HBP), in which fructose-6-phosphate is converted to glucosamine 6-phosphate by the rate-liming enzyme glutamine:fructose-6-phosphate amidotransferase (GFA). In this study, we investigated the role of HBP on HG-stimulated fibronectin protein synthesis, a matrix component, in SV-40-transformed rat kidney MES cells. Treatment of MES cells with 25 mmol/l glucose (HG) for 48 h increases cellular fibronectin levels by two- to threefold on Western blots when compared with low glucose (5 mmol/l). Glucosamine (GlcN; 1.5 mmol/l), which enters the hexosamine pathway distal to GFA action, also increases fibronectin synthesis. Azaserine (AZA; 0.5 micromol/l), an inhibitor of GFA, blocks the HG- but not the GlcN-induced fibronectin synthesis. Fibronectin contains cAMP responsive element (CRE) consensus sequences in its promoter and the phosphorylation of CRE-binding protein (CREB) may regulate its expression. On Western blots, HG and GlcN stimulate two- to threefold the phosphorylation of CREB at Ser 133, whereas CREB protein content was unaltered by either HG or GlcN. In addition, nuclear CREB activity was increased by HG and GlcN on gel-shift assays using (32)P-CRE oligonucleotides. AZA impeded the HG-enhanced CREB phosphorylation and CRE binding but had no effect on GlcN-mediated CREB phosphorylation and CRE binding. Pharmacologic inhibition of protein kinase C (PKC) and protein kinase A (PKA), which are involved in hexosamine-mediated matrix production, blocked the CREB phosphorylation and fibronectin synthesis seen in HG and GlcN conditions. We conclude that the effects of HG on fibronectin synthesis in the mesangium are mediated by the HBP possibly via hexosamine regulation of CREB and PKC/PKA signaling pathways. These results support the hypothesis that the HBP is a sensor and regulator of the actions of glucose in the kidney.

Hypoxia and high glucose cause exaggerated mesangial cell growth and collagen synthesis: role of osteopontin

The effect of hypoxia on the proliferation and collagen synthesis of cultured rat mesangial cells was examined under normal-glucose (NG, 5 mM) and high-glucose (HG, 25 mM)-media conditions. In addition, a role for osteopontin (OPN) in mediating these processes was assessed. Quiescent cultures were exposed to hypoxia (3% O(2)) and normoxia (18% O(2)) in a serum-free medium with NG or HG, and cell proliferation, collagen synthesis, and OPN expression were assessed. Cells exposed to hypoxia in NG medium resulted in significant increases in [(3)H]thymidine incorporation, cell number, and [(3)H]proline incorporation, respectively. HG incubations also produced significant stimulation of these parameters under normoxic conditions, which were markedly enhanced in cells exposed to hypoxia in HG medium. In addition, hypoxia and HG stimulated the mRNA levels of type IV collagen, and the combination of hypoxia and HG resulted in additive increases in type IV collagen expression. Hypoxia and HG also stimulated OPN mRNA and protein levels in an additive fashion. A neutralizing antibody to OPN or its beta(3)-integrin receptor significantly blocked the effect of hypoxia and HG on proliferation and collagen synthesis. In conclusion, these results demonstrate for the first time that hypoxia in HG medium produces exaggerated mesangial cell growth and type IV collagen synthesis. In addition, OPN appears to play a role in mediating the accelerated mesangial cell growth and collagen synthesis found in a hyperglycemic and hypoxic environment.

Hexosamine regulation of glucose-mediated laminin synthesis in mesangial cells involves protein kinases A and C

Hyperglycemia leads to alterations in mesangial cell function and extracellular matrix (ECM) protein accumulation. These adverse effects of glucose may be mediated by glucose metabolism through the hexosamine biosynthesis pathway (HBP). The HBP converts fructose-6-phosphate to glucosamine-6-phosphate via the rate-limiting enzyme, glutamine:fructose-6-phosphate amidotransferase (GFA). We have investigated the effects of high glucose (HG, 25 mM) and glucosamine (GlcN, 1.5 mM) on the synthesis of the ECM protein laminin in a SV-40-transformed rat kidney mesangial (MES) cell line. The roles of protein kinases C (PKC) and A (PKA) in mediating laminin accumulation were also investigated. Treatment of MES cells with HG or GlcN for 48 h increased laminin levels in cellular extracts more than twofold compared with 5 mM glucose (low glucose; LG). The presence of the GFA inhibitor diazo-oxo-norleucine (DON, 10 microM) blocked HG but not GlcN-induced laminin synthesis. HG resulted in a time-dependent increase in total PKC and PKA activities, 57+/-11.3 (P < 0.01 vs. LG) and 85+/-17.4% (P < 0.01 vs. LG), respectively. GlcN had no effect on the total PKC activity; however, both glucose and glucosamine increased membrane-associated PKC activity by twofold compared with LG. GlcN stimulated total PKA activity by 47+/-8.4% (P < 0.01 vs. LG). Similarly, membrane- associated PKA activity was also increased by HG and GlcN approximately 1.8 and 1.5-fold, respectively. HG and GlcN increased cellular cAMP levels 2.2- and 3. 4-fold, respectively. Pharmacological downregulation of PKC by long-term incubation of MES cells with 0.5 microM phorbol 12-myristate 13-acetate (PMA) or inhibition of PKA activity by 2 microM H-8 blocked the effects of HG and GlcN on laminin synthesis. These results demonstrate that glucose-induced laminin synthesis in MES cells is mediated by flux through the HBP and that this stimulation involves PKC and PKA signaling pathways.

Role of vascular endothelial growth factor in diabetic nephropathy

BACKGROUND

Vascular endothelial growth factor (VEGF) is a potent cytokine that is considered to be an important mediator in the pathogenesis of endothelial dysfunction in diabetes.

METHODS

This study investigates the effect of high glucose on the signaling and production of VEGF in rat mesangial cells in culture and measures the urinary VEGF level in patients with different stages of diabetic nephropathy. To elucidate the role of VEGF in vivo further, expression of VEGF in control and diabetic kidneys was examined using immunohistochemistry.

RESULTS

A high ambient glucose concentration in the culture medium increased VEGF mRNA expression and protein production within 3 h in a concentration-dependent manner. A protein kinase C (PKC) inhibitor and PKC down-regulation inhibited glucose-induced increases in VEGF production. Urinary excretion of VEGF significantly increased according to the degree of proteinuria in patients with diabetes. A weak but significant correlation was found between urinary VEGF excretion and the levels of serum creatinine, creatinine clearance, microalbuminuria, and proteinuria. Immunohistochemistry revealed marked differences in the extent of mesangial VEGF staining between diabetic and control kidneys. Pronounced up-regulation of VEGF was observed in the glomerular epithelial cell in the early phase of diabetic kidney disease, whereas widespread expression of VEGF was found in the tubular segments, especially the proximal segment, in advanced diabetic nephropathy.

CONCLUSIONS

These results suggest that VEGF may play a role in the pathogenesis of diabetic nephropathy.

Pyridine nucleotides in glucose metabolism and diabetes: a review

Nicotinamide adenine dinucleotide (NAD) and its derivatives NADH, NADP and NADPH have regulatory functions in the generation of triose phosphates and pyruvate from glucose. In many studies of the influence of the diabetic state on relationships between pyridine nucleotide and glucose metabolism, the focus has been on the sorbitol pathway. Less attention has been paid to other aspects of the role of pyridine nucleotides in pyruvate formation from glucose, in particular the effects of the NAD precursors nicotinamide and nicotinic acid on glucose metabolism. This paper reviews current knowledge of the involvement of pyridine nucleotides and their precursors in glucose catabolism in the normal and diabetic state. Reference is also made to the following three current hypotheses for mechanisms underlying diabetic microangiopathy: 1. Chronic glucose overutilization, caused by hyperglycemia, in tissues which lack insulin receptors and therefore are freely permeable to glucose. 2. Enhancement of sorbitol pathway activity with an ensuing decrease in the ratio of NAD/NADH. 3. Enhanced utilization of both glucose and pyridine nucleotides in formation of triose phosphates and pyruvate. Therapy with NAD precursors like nicotinamide might have corrective effects on these proposed biochemical aberrations, thereby retarding progression of microangiopathy.

Nesidioblastosis, myelodysplastic syndrome and nodular diabetic glomerulosclerosis in an elderly nondiabetic woman: an autopsy report

Nesidioblastosis as the cause of hyperinsulinaemic hypoglycaemia in an adult is rare. We report here an additional case of nesidioblastosis, which resulted in fatal hyperinsulinaemic hypoglycaemia in a 72-year-old woman with an underlying myelodysplastic syndrome. The diagnosis of nesidioblastosis was established only after post-mortem examination with a careful exclusion of minute insulinoma. To our surprise, the renal pathology disclosed typical diabetic nodular glomerulosclerosis in the same patient who had no previous history of diabetes mellitus (DM). Nesidioblastosis has been reported to cause 'reversal' of Type 1 DM and insulinoma causing 'reversal' of Type 2 disease. We therefore hypothesize that our patient might have had an undiagnosed DM in the past, which resulted in the typical diabetic nodular glomerulosclerosis. The nesidioblastosis caused a 'reversal' of DM and even the ultimate development of hyperinsulinaemic hypoglycaemia.

Urinary albumin excretion rate is independently related to autonomic neuropathy in type 2 diabetes mellitus

OBJECTIVE

To evaluate if urinary albumin excretion rate (UAER) is independently related to subclinical autonomic neuropathy in type 2 diabetes.

DESIGN

A controlled cross-sectional study.

SETTING

Primary health care centre.

SUBJECTS

Consecutive recently diagnosed (< 1 year) type 2 diabetic patients (group A, n = 150) and patients with long-standing (median 11 years) type 2 diabetes (group B, n = 146) chosen at random. A nondiabetic control group (group C, n = 150) matched for age and gender to group A.

MAIN OUTCOME MEASURES

Neuropathy by cardiovascular reflex tests and UAER by nephelometry.

METHODS

Univariate statistics in group A + B (t-test chi 2- or McNemars test) with Valsalva and breathing ratios as categorical grouping variables and the independent variables gender, smoking, systolic and diastolic blood pressure, fasting serum cholesterol, HDL cholesterol, triglycerides, haemoglobin A1c, glucagon stimulated C-peptide, fasting and postload 1 and 2 h blood glucose and serum insulin, UAER, coronary heart disease and congestive heart failure. Logistic regression analyses in group A + B with Valsalva and breathing ratios as dependent categorical variables and age, systolic blood pressure, congestive heart failure, coronary heart disease, fasting blood glucose, serum triglycerides and UAER as independent variables.

RESULTS

Compared to nondiabetic subjects the diabetic patients of both groups were at increased risk of neuropathy as judged by the Valsalva ratio (P < 0.01). In known diabetic patients with a UAER > or = 30 mg 24-1 h neuropathy was more common than amongst their normoalbuminuric counterparts (Valsalva test P = 0.007, breathing test P = 0.02). In logistic regression analysis UAER independently explained abnormal Valsalva (P = 0.015) and breathing tests (P = 0.04) in the group A + B.

CONCLUSIONS

UAER is independently related to subclinical autonomic neuropathy in type 2 diabetes.

Circadian variation of urinary microalbumin excretion and ambulatory blood pressure in patients with essential hypertension

OBJECTIVE

To investigate the relationship between circadian changes in urinary microalbumin excretion (UAE), blood pressure (BP) and physical activity in patients with essential hypertension.

DESIGN AND METHODS

The subjects were 45 patients with essential hypertension (EH group: 26 male and 19 female, age 56+/-12 years (mean +/- SD)) and 25 patients with diabetes mellitus (DM group: 14 male and 11 female, age 61+/-10 years). Their BP and physical activity (acceleration) were measured at 30-min intervals for 24 h by means of a multi-biomedical recorder (TM2425). Urine samples were collected during each of four 4-h daytime periods and one 8-h night-time period. From these samples, per-h UAE (UAE/h) was measured. Mean values for mean blood pressure (MBP) and acceleration were calculated for corresponding time periods. Plasma hormones were measured during an early morning rest period.

RESULTS

In the EH group, a significant positive correlation was observed between circadian variation of UAE/h and MBP in 35 (78%) subjects, and the mean coefficient of correlation (r) was 0.86+/-0.12. A significant positive correlation was observed between circadian variation of UAE/h and mean acceleration value (Gh) in 25 (56%) subjects, and the mean r value was 0.70+/-0.26. Multivariate linear regression analysis showed that MBP exerted a greater influence on UAE/h than Gh. Significant positive correlations were observed between UAE/day and plasma human atrial natriuretic peptide and plasma aldosterone concentration (r = 0.50, P < 0.01; r = 0.36, P< 0.05). None of these relations, however, was observed in the DM group.

CONCLUSIONS

In patients with essential hypertension, circadian changes in activity and variation of BP influence UAE/h, but no definite relationship of this kind was observed in patients with diabetes mellitus. Measurement of circadian changes in UAE or UAE/day may be useful in estimating the degree of daily stress in non-diabetic patients with essential hypertension.

Na+-dependent glucose uptake and collagen synthesis by cultured bovine retinal pericytes

This study was performed to clarify the presence of sodium-dependent glucose uptake and its role in the synthesis of type IV and type VI collagen by cultured bovine retinal pericytes. The glucose uptake by retinal pericytes and retinal endothelial cells was measured using 3H-D-glucose in the presence or absence of sodium. Glucose uptake in the presence of sodium was twice as high as that observed in the presence of phlorizin and sodium or in the absence of sodium. Sodium-dependent glucose uptake was observed at different sodium concentrations, and its half-maximal stimulation occurred at 48 mM. These findings were not observed in retinal endothelial cells. Levels of type IV and type VI collagen produced by retinal pericytes were significantly increased at glucose concentrations higher than 20 mM. Phlorizin decreased both collagen synthesis and glucose consumption by retinal pericytes incubated with 30 mM of glucose to the levels observed with 5 mM of glucose. These data suggest that sodium-dependent glucose uptake is present in retinal pericytes and that excessive glucose entry into the cell is an important factor for overproduction of collagen. Phlorizin normalized the synthesis of type IV and type VI collagen with decreasing glucose consumption under high glucose conditions.

The nonspecificity of focal segmental glomerulosclerosis. The defining characteristics of primary focal glomerulosclerosis, mesangial proliferation, and minimal change

We performed a detailed clinical review and pathologic analysis of the kidney biopsies of 134 children with nephrotic syndrome or asymptomatic proteinuria. This analysis challenges some of our concepts about the classification of conditions associated with these disorders. The presence of focal segmental sclerotic lesions does not define a unique disorder in childhood. Some children with such lesions will have unaffected glomeruli that are ultrastructurally completely normal. These patients, predominately black adolescents, present either with nephrotic syndrome or asymptomatic proteinuria. We classify this disorder as primary focal segmental glomerulosclerosis (FSGS) and have never found it to recur after transplantation. Most other children with FSGS have 1 of 2 specific glomerulopathies. Those with minimal change have generalized fusion of podocyte foot processes. Those with mesangial proliferation have similar foot process changes combined with mesangial expansion and proliferation and, frequently, thinning of the lamina densa and tubuloreticular inclusions. The presence of segmental lesions in these glomerulopathies appears to be nothing more than a marker of severity. Children with these glomerulopathies are generally younger white children, virtually all of whom have nephrotic syndrome. These disorders have a strong propensity to recur after transplantation. The presence of mesangial labeling of IgM or C1q has no significance in any of these 3 disorders. The classification of disorders associated with nephrotic syndrome or asymptomatic proteinuria must concentrate less on the presence or absence of focal sclerosis and more on the histologic appearance of the rest of the glomeruli.

Ultrastructural and functional analyses of nephropathy in calmodulin-induced diabetic transgenic mice

BACKGROUND

Previous animal models of diabetic nephropathy have used diabetic animals for which the underlying defect was either uncertain or the diabetes was induced by potentially specific toxins. In this report, we describe the renal abnormalities in a transgenic mouse model that develops early-onset diabetes due to overexpression of calmodulin in pancreatic beta cells.

METHODS

Renal tissues were collected from normal and transgenic mice at 112, 182, and 300 days. These were prepared for light microscopic observation, stained with polyethylenimine (for anionic sites), or rendered acellular by detergent extraction prior to observation by transmission and scanning electron microscopy. Morphometric analysis of glomerular basement membrane thickness was carried out by the "orthogonal intercept" method. Twelve-hour urine samples of fed and fasting mice were collected for urine volume and glucose and protein analyses. Blood glucose, blood urea nitrogen, serum insulin, and creatinine were determined in 60-90-day-old and 255-day-old mice by established methods.

RESULTS

Morphometric analyses revealed age-related and transgene-related increases in glomerular basement membrane thickness. A 22% increase in transgenic diabetics over controls was seen at 112 days of age that developed to increases of 43% and 37% at 182 and 300 days of age, respectively. Mesangial matrix area was also increased markedly in transgenic mice. Surprisingly, even in the oldest diabetic mice, there was no reduction in anionic sites. Moreover, despite an eightfold increase in urine volume, these mice did not become significantly proteinuric.

CONCLUSIONS

These results indicate that proteinuria of diabetes may be delayed or prevented by maintenance of a normal complement of glomerular basement membrane anionic sites. They also demonstrate that transgenic mice can provide a valuable model for discriminating between different aspects of diabetic nephropathy.

Immunofluorescence staining of renal biopsy samples in patients with diabetic nephropathy in non-insulin-dependent diabetes mellitus using monoclonal antibody to reduced glycated lysine

This is the first report on immunofluorescence staining of renal biopsy samples in human diabetic nephropathy (DN) using monoclonal antibodies to reduced glycated lysine. In order to detect the localization of glycated lysine in the mesangial matrix and/or the glomerular basement membrane (GBM), we examined immunofluorescence staining using antibodies against reduced glycated lysine in the glomeruli of 16 patients with DN and ten age-matched patients with diffuse mesangial proliferative glomerulonephritis without IgA deposition (DPGN) as controls. In the early stage of DN, immunofluorescence microscopy revealed the presence of intense staining for reduced glycated lysine in the GBM as well as in part of the tubular basement membrane, but not in the mesangial area. In contrast, immunofluorescence microscopy revealed less staining for glycated lysine in the GBM in the advanced stage of DN, and no reaction with any part of the renal tissue in patients with DPGN. It was concluded that detection of reduced glycated lysine in GBM in the early stage of DN might be associated with the initial pathogenesis of this disease.

Pharmacokinetics and pharmacodynamics of metformin in healthy subjects and patients with noninsulin-dependent diabetes mellitus

This study was conducted to assess the effect of noninsulin-dependent diabetes mellitus (NIDDM) and gender on the pharmacokinetics of metformin and to investigate whether or not metformin exhibits dose-dependent pharmacokinetics. The pharmacodynamic effects (on plasma glucose and insulin) of metformin in patients with NIDDM and in healthy subjects also were assessed. Nine patients with NIDDM and 9 healthy subjects received 4 single-blind single-dose treatments of metformin HCL (850 mg, 1,700 mg, 2,550 mg, and placebo) and a multiple-dose treatment of 850 mg metformin HCL (3 times daily for 19 doses). After each single-dose treatment and the final dose of the multiple-dose phase, multiple plasma and urine samples were collected for 48 hours and assayed for metformin levels. Plasma samples were also assayed for glucose and insulin levels. There were no significant differences in metformin kinetics in patients with NIDDM compared with healthy subjects, in men compared with women, or during multiple-dose treatment versus single-dose treatment. Plasma concentrations of metformin increase less than proportionally to dose, most likely due to a decrease in percent absorbed. In patients with NIDDM, single doses of 1,700-mg or higher of metformin significantly decrease postprandial, but not preprandial, glucose concentrations and do not influence insulin concentrations. With multiple doses, both preprandial and postprandial glucose concentrations and preprandial insulin concentrations were significantly lower than with placebo. The effect of metformin on glucose level is correlated with the average fasting plasma glucose level without drug. In healthy subjects, single and multiple doses of metformin showed no effect on plasma glucose, but significantly attenuated the rise in immediate postprandial insulin levels.

Quantification of glomerular TGF-beta 1 mRNA in patients with diabetes mellitus

Transforming growth factor-beta 1 (TGF-beta 1) is a primary determinant of the mesangial expansion observed in diabetic nephropathy. In this study, we quantitated the levels of intraglomerular TGF-beta 1 mRNA in patients with diabetes mellitus using a competitive polymerase chain reaction (PCR) method. Renal biopsy specimens were obtained from 29 patients with non-insulin-dependent diabetes mellitus. Total RNA was extracted from the glomeruli and reverse transcribed into cDNA with reverse transcriptase. To prepare samples containing identical amounts of beta-actin cDNA (8 pg), we performed competitive PCR by co-amplifying mutant templates of beta-actin with a unique EcoRI site. We also used this competitive PCR method to measure TGF-beta 1 cDNA by co-amplifying mutant templates of TGF-beta 1. We observed higher expression of TGF-beta 1 mRNA in glomeruli of patients with diabetic nephropathy as compared with normal glomeruli. Intraglomerular TGF-beta 1 mRNA was elevated, even in the early stage of diabetic nephropathy. Moreover, levels of intraglomerular TGF-beta 1 mRNA correlated with values of HbA1c. These data suggest that hyperglycemia induces intraglomerular TGF-beta 1 mRNA expression in vivo, and that TGF-beta 1 overproduction may be associated with the progression of diabetic nephropathy.

Renal TGF-beta regulation in spontaneously diabetic NOD mice with correlations in mesangial cells

Diabetic nephropathy is characterized by excessive glomerular matrix accumulation, basement membrane thickening and sclerosis. Although it is clear that systemic metabolic disturbances precipitate such renal changes, the signals and pathways involved in this process are not fully elucidated. Recent evidence suggests that growth factors/cytokines are intimately involved in the pathogenesis of diabetic nephropathy. Because of its prosclerotic properties, transforming growth factor-beta (TGF-beta) is a prime candidate mediator of diabetic nephrosclerosis. We examined perfused kidney tissues isolated from spontaneously diabetic, non-obese diabetic mice (NOD) for TGF-beta content. By using murine isotype specific TGF-beta probes, we demonstrate that within 5 to 10 days of hyperglycuria renal TGF-beta 2 mRNA and protein content increases. By immunohistochemical analysis, de novo TGF-beta immunoreactivity was detected within both glomeruli and the interstitium. In order to determine the signals involved in promoting kidney TGF-beta content in vivo, TGF-beta regulation was examined in renal mesangial cells in vitro. Murine mesangial cells stimulated with glycosylated protein secrete bioactive TGF-beta and demonstrate a disproportionate increase in the steady state levels of TGF-beta 2 mRNA. These data suggest that a major early renal response in NOD mice to hyperglycemia or to glycosylated proteins is characterized by increases in TGF-beta.

Differential modulation of mitogenic and metabolic actions of insulin-like growth factor I in rat glomerular mesangial cells in high glucose culture

In order to explore the possible contribution of insulin-like growth factor I to the development of diabetic nephropathy, the effect of glucose on the mitogenic and metabolic actions of insulin-like growth factor I in cultured rat glomerular mesangial cells was examined. The stimulation of [3H]-thymidine incorporation by insulin-like growth factor I in the cells exposed to high concentrations (55 mmol/l) of glucose (4.6 +/- 1.3 fold stimulation) was significantly suppressed as compared with that in the cells cultured in 11 mmol/l glucose (17.5 +/- 0.8 fold). In contrast, [3H]-amino-isobutylic acid uptake into the mesangial cells was significantly enhanced by glucose (2.03 +/- 0.03 nmol.mg protein-1. 15 min-1 at 55 mmol/l glucose vs 0.59 +/- 0.01 at 11 mmol/l glucose), while 2-deoxyglucose uptake remained unchanged. [125I]-insulin-like growth factor I binding was slightly but significantly increased in the cells exposed to high concentrations of glucose. Thus, glucose may modulate the mitogenic and metabolic actions of insulin-like growth factor I differently in cultured mesangial cells probably at the post-insulin-like growth factor I receptor level. These results may indicate that the differential modulation of the actions of insulin-like growth factor I by glucose could result in the increase in amino acid uptake and decrease in the cell proliferation in the mesangial cells, possibly leading to enhanced mesangial matrix synthesis with a relatively small increase in mesangial cell volume as seen in diabetic nephropathy.

Widening of capillary neck and alteration of extracellular matrix ultrastructure in diabetic rat glomerulus as revealed by computer morphometry and improved tissue processing

Morphological and morphometric studies of glomeruli were carried out in streptozotocin-induced diabetic rats using improved tissue processing and computerized morphometry. Increased mesangial matrix, occupying the enlarged diabetic mesangium, contained an abundance of dark granular material in addition to the microfibrils which were usually found in the control glomeruli. In the diabetic glomeruli, the lamina densa was thick and heterogeneous showing a dense layer both on its epithelial and endothelial aspects, and the lamina rara externa contained more fibrils than in control rats. Detailed estimation of the absolute values of the various compartments of the diabetic glomeruli by using perfusion-fixed materials and a computer-assisted digitizer revealed that the volume and surface area of the mesangium were increased more extensively than those of the capillary; the enlargement of the mesangial-capillary interface area was the most pronounced among the morphometric changes of the diabetic glomeruli; and that the moderate increase in capillary volume was associated with an increased radius. Our quantitative results showed that capillaries in the diabetic glomeruli had an extensively wider neck which may be the first sign of structural damage to the glomerular tuft.

An overview of renal pathology in insulin-dependent diabetes mellitus in relationship to altered glomerular hemodynamics

Clinical diabetic nephropathy in man is the consequence of the development of a specific constellation of glomerular, tubular, vascular, and interstitial structural abnormalities accompanied by highly characteristic immunohistochemical alterations that, together, are unique to diabetes. Because changes resembling the specific pathology of diabetes do not develop in patients with conditions that lead to long-standing glomerular hyperfunction (such as unilateral nephrectomy), it is unlikely that glomerular hemodynamic abnormalities per se can be the cause of diabetic nephropathy. Whether hemodynamic abnormalities represent a risk factor that, in the presence of the diabetic state, can accelerate the rate of development of the basic lesions of diabetic nephropathy is currently unclear. However, there is considerable evidence that when the renal lesions of diabetes are far advanced, factors such as systemic hypertension can determine the rate of renal functional deterioration in diabetes as in other disorders. Although the diabetic rat may be a useful model for the study of aspects of the pathogenesis of diabetic nephropathy, much confusion has resulted from the inclusion of focal segmental glomerular sclerosis as a diabetic lesion. Similarly, the acceptance of all increases in urinary protein excretions in this model as resulting from or reflecting of diabetic nephropathology can be misleading. It is concluded that treatment aimed at manipulating renal hemodynamics in diabetic patients without evidence of renal disease should remain in the realm of clinical research.

High glucose-induced proliferation in mesangial cells is reversed by autocrine TGF-beta

We investigated the effects of glucose concentration in serum-free media on the proliferative growth response of a cultured murine mesangial cell line. Raising the ambient D-glucose concentration from 100 mg/dl to 450 mg/dl stimulated cell proliferation after 24 to 48 hours but had a growth inhibitory effect after 72 to 96 hours of incubation. This biphasic proliferative response to high glucose concentration was not mediated by the elevated osmolarity of the medium and did not occur when L-glucose was used. The early phase of glucose-induced proliferation was associated with increased expression of the immediate early genes c-myc and egr-1 as well as with induction of the S-phase related proliferating nuclear cell antigen (PCNA). Several lines of evidence indicated that the late phase of glucose-induced growth inhibition was mediated by the bioactivation of endogenous transforming growth factor beta (TGF-beta). Neutralizing antibody against TGF-beta prevented the late inhibitory effects of glucose on proliferation. On the other hand, exogenous TGF-beta (1 ng/ml) significantly inhibited basal proliferation in mesangial cells. Furthermore, Northern blot analysis revealed that TGF-beta 1 mRNA was induced by 450 mg/dl glucose in the medium after 48 to 72 hours, but not after 24 hours. Cell cycle analysis demonstrated that mesangial cells incubated in high glucose for 24 hours have a higher percentage of cells in the S-G2 phase of the cell cycle compared with cells grown in normal glucose concentration. After 48 hours of culture in elevated glucose concentration, the percentage of cells in S-G2 phase was decreased, and became comparable to that of cells in normal glucose concentration. However, the addition of neutralizing anti-TGF-beta antibody stimulated the progression of cells towards S-G2 in high glucose medium after 48 hours. The findings of this study demonstrate a biphasic growth response of mesangial cells when they were cultured in high glucose concentration; initially there was a transient stimulation of replication for 24 to 48 hours followed by a sustained inhibition after longer incubation periods. This inhibition may be mediated by the glucose-induced synthesis and/or bioactivation of TGF-beta which can inhibit proliferation of mesangial cells in an autocrine fashion.

Effects of high glucose on cellular proliferation and fibronectin production by cultured human mesangial cells

Diabetic glomerulosclerosis is characterized by the accumulation of the matrix protein fibronectin in the glomerular mesangium and could result from increased mesangial cell fibronectin synthesis induced by hyperglycemia. To test this hypothesis, we cultured human mesangial cells for up to 14 days in media containing normal (5 mM) or high glucose (20 to 115 mM) concentrations and assessed cellular proliferation and fibronectin synthesis. When compared to 5 mM glucose, high glucose levels significantly inhibited cellular proliferation in a dose dependent fashion, as assessed by direct cell counting and thymidine incorporation. After eight days in culture, tissue culture supernatant fibronectin levels, as assessed by ELISA, were significantly higher from cells cultured under high glucose conditions than cells exposed to normal glucose levels. After 14 days and when compared to 5 mM glucose, matrix fibronectin levels and fibronectin mRNA expression (by Northern analysis) were also increased by 20 mM glucose. To control for the osmotic effects of high glucose, mesangial cells were also cultured in the presence of 20 mM or 50 mM mannitol. Mannitol had no effect on cellular proliferation but significantly increased tissue culture supernatant fibronectin levels and fibronectin gene expression. These studies demonstrate that, in vitro, high glucose suppresses human mesangial cell proliferation and stimulates fibronectin synthesis. The increase in fibronectin synthesis may in part result from changes in osmolality induced by high glucose. These data suggest that increased mesangial cell fibronectin synthesis may play a role in the accumulation of glomerular fibronectin common to diabetic glomerulosclerosis.

A thromboxane A2 synthetase inhibitor retards hypertensive rat diabetic nephropathy

Spontaneously hypertensive rats (SHR) were injected with streptozotocin (STZ-SHR) to induce diabetes. The effect of DP-1904, a thromboxane A2 synthetase inhibitor, on diabetic nephropathy was then studied by administering it for 5 months (1 or 10 mg/kg). DP-1904 did not affect renal 6-keto prostaglandin (PG)F1 alpha production in STZ-SHR, but markedly inhibited renal thromboxane (TX) B2 production, so that the 6-keto PGF1 alpha/TXB2 ratio was significantly increased (P less than 0.05). STZ-SHR showed significant uraemia and proteinuria, plus increases in urinary gamma-glutamyl-transpeptidase and urinary N-acetyl-beta-glucosaminidase. DP-1904 significantly decreased (P less than 0.01) the urinary changes. STZ-SHR also showed an increase in mesangial periodic acid-Schiff-positive substance and in relative renal weight, both of which were significantly inhibited by DP-1904 (P less than 0.05). Thus, DP-1904 inhibited both TXB2 production and the progression of renal damage in STZ-SHR.

Global glomerular sclerosis and glomerular arteriolar hyalinosis in insulin dependent diabetes

We studied the lesions of global glomerular sclerosis and arteriolar hyalinosis in 43 (29 females) insulin-dependent diabetes mellitus (IDDM) patients whose creatinine clearance (CCr) was greater than or equal to 45 ml/min/1.73 m2 and whose renal biopsies had at least 20 glomeruli available for study. These patients, ages 17 to 55 years, had IDDM for 7 to 32 (20 +/- 6, means +/- SD) years. CCr ranged from 47 to 139 (91 +/- 25) ml/min/1.73 m2 and urinary albumin excretion (UAE) from 5 to 3386 (median = 127) mg/24 hrs. Eighteen patients were hypertensive. Thus, these patients represented a broad clinical range from normal renal function through overt diabetic nephropathy. The percent of glomeruli which were globally sclerosed was strongly correlated with CCr (r = -0.64, P less than 0.0001) and log UAE (r = +0.67, P less than 0.001). Hypertension was more common in patients with more than 10% sclerosed glomeruli (chi square = 9.5, P less than 0.002). Percent sclerosed glomeruli was highly significantly correlated with the index of severity of the arteriolar hyalinosis lesion (r = +0.66, P less than 0.0001) and mesangial volume fraction (r = +0.61, P less than 0.0001). We hypothesize that arteriolar hyalinosis could contribute to global glomerular sclerosis through severe compromise of glomerular blood flow. Alternately, global glomerular sclerosis may result from marked mesangial expansion and capillary occlusion. However, in this broad range of patients it appeared that global glomerular sclerosis and mesangial expansion were not infrequently independent diabetic renal lesions which could contribute separately to the ultimate development of overt diabetic nephropathy.

Insulin-like growth factor I (IGF-I) stimulates glucose and amino acid uptake in cultured glomerular mesangial cells

Cultured mesangial cells possess a large number of receptors specific to IGF-I with a small number of insulin receptors. Physiological concentrations of IGF-I increased the uptakes of aminoisobutyric acid and 2-deoxyglucose in mesangial cells, while insulin exhibited similar effects only with unphysiologically high concentration. These findings suggest that, in cultured mesangial cells, IGF-I may regulate cellular metabolic functions such as glucose and amino acid uptakes through its own receptors rather than insulin receptors.

Diabetic nephropathy: new directions in management

Approximately 6 million people in the United States are known to be diabetic, with an estimated 4 million individuals having undiagnosed diabetes mellitus. The metabolic derangements of both insulin-dependent diabetes mellitus (IDDM) and noninsulin-dependent diabetes mellitus (NIDDM) result in widespread end-organ damage, including progressive kidney failure. Since its initial description in 1936, the incidence of diabetic nephropathy has progressively increased, and it is now the most common cause of newly diagnosed end-stage renal disease (ESRD) requiring renal replacement therapy in the United States. While basic research efforts into pathogenesis continue, there is significant interest in clinical interventions that may slow the progression of diabetic renal disease. In addition, the options available for renal replacement therapy have increased and improved substantially in recent years.

Renal disease in noninsulin-dependent diabetes mellitus

Diabetic nephropathy now accounts for approximately one-third of all patients who develop end-stage renal disease. The estimated cost to supply renal replacement therapy for this population now exceeds $750 million. The relatively recent realization that half of these individuals suffer from noninsulin-dependent diabetes mellitus has sparked increased interest in attempts to understand the pathologic processes involved and how they may be similar or different from those alterations seen in insulin-dependent diabetes mellitus. Basic and clinical investigation continues in an attempt to solve the puzzle of pathogenesis, as well as answer questions about the clinical usefulness of microalbuminuria and the appropriate management of hypertension in this population.

A non-mammalian in vivo model for cellular and molecular analysis of glucose-mediated thickening of basement membranes

An increase of basement membrane thickness in renal glomeruli, blood vessels, and other tissues is a consistent pathological observation in individuals with diabetes mellitus. Although a number of pathological complications of the disease are thought to result from this structural abnormality in basement membranes, the mechanism(s) responsible for this glucose-mediated process remain unknown. The current study was designed to develop a non-mammalian in vivo epithelial/basement membrane model which would facilitate detailed analysis of the cellular and molecular processes which lead to thickening of basement membrane under hyperglycaemic conditions. The system developed utilizes the Cnidarian, Hydra vulgaris. Hydra lends itself to such studies because of (1) its simplified body structure which is composed of an epithelial bilayer with an intervening basement membrane (mesoglea) and (2) its extensive regenerative capacity which allows cell pellets (Hydra cell aggregates), formed from isolated Hydra cells, to develop into adult Hydra within 72-96 h. This process involves reformation of an epithelial bilayer and de novo biosynthesis of a basement membrane. Our studies indicate that exposure of developing Hydra cell aggregates to levels of D-glucose which mimic that observed in the human diabetic patient (15 mmol/l) induces a doubling of Hydra basement membrane thickness within 72-96 h of pellet formation. The same results were obtained using 15 mmol/l D-Ribose which is a highly efficient glycating agent. The data presented support the use of the Hydra cell aggregate system as a potentially powerful non-mammalian in vivo model to investigate the cellular and molecular mechanism(s) underlying glucose-mediated basement membrane thickening.

Diabetic microangiopathy in KK mice. VI. Effect of glycemic control on renal glycoprotein metabolism and established glomerulosclerosis

Twenty-three nonobese KK mice with abnormal tolerance to glucose, hyperinsulinemia with insulin resistance and human diabetic-like nephropathy were treated with either saline (12 mice) or glipizide, an oral hypoglycemic compound, 1 mg/kg, (11 mice) from 120 to 360 days of age. These mice develop significant increases in mesangial volume and matrix by 40 days of age. Oral glucose tolerance (OGTT), glucosyltransferase and N-acetyl-beta-glucosaminidase (enzymes involved in synthesis and degradation of kidney glycoproteins, respectively) in the kidney and serum, 24-hr proteinuria, and light microscopy studies of the kidney were performed. Glipizide-treated mice improved their OGTT. There was no difference in body weight; however, a 16% decrease (P less than 0.05) in kidney weight was observed in glipizide-treated mice. Both enzymes were significantly increased in the kidneys of mice treated with glipizide. No difference in serum enzymes was found between the two groups of mice. About 58% of the saline-treated mice had moderate glomerulosclerosis. By contrast, only 27% of glipizide-treated mice had moderate glomerulosclerosis. Also, a significant decrease in proteinuria was found in glipizide-treated mice. These data suggest that glipizide improves glucose metabolism, decreases kidney size, prevents kidney glycoprotein and mesangial matrix accumulation, and reduces proteinuria in type II diabetic KK mice. This indicates that good glycemic control prevents further progression of established diabetic nephropathy in animals.

Should there be an expanded role for kidney biopsy in the management of patients with type I diabetes?

Diabetic nephropathy is the single most important cause of end-stage renal disease (ESRD) in the United States. Further, the increased risk of mortality from type I diabetes is almost entirely confined to patients developing clinical diabetic nephropathy. Nonetheless, kidney biopsy has had little role in the clinical assessment of diabetic patients or in the design of clinical research in diabetic nephropathy. The development of dipstick-positive proteinuria in patients with type I diabetes of more than 10 years' duration is regularly associated with advanced structural changes of diabetic nephropathology; in these patients, clinical parameters, especially the rate of decline of glomerular filtration rate (GFR), are accurate monitors of disease progression. Microalbuminuria indicates a very high risk of overt proteinuria and thus ESRD. This increased risk is associated with levels of urinary albumin excretion (UAE; greater than 30 micrograms/min [45 mg/24 h]), which are frequently accompanied by hypertension and reduced or decreasing GFR. At this stage, lesions of diabetic nephropathy are usually already well established. Thus, microalbuminuria is more a marker of early nephropathy than a predictor of later renal injury. Before these clinical stages of nephropathy, there are no accurate predictors of renal risk. Renal biopsy may serve this role by indicating those patients who are developing significant lesions during the "silent" phase of the disease. In large measure, this value of the biopsy derives from evidence that the lesions tend to develop linearly over time and can be measured by techniques that are relatively easily established in standard surgical pathology environments. Renal biopsies can serve to assure the majority of diabetic patients that they are developing serious lesions slowly, if at all.(ABSTRACT TRUNCATED AT 250 WORDS)

Can management strategies alter the course of diabetic nephropathy?

End Stage Renal Disease (ESRD) is a common consequence of diabetic nephropathy (DN). DN is the major cause of death in patients with IDDM, accounting for greater than 40% of deaths with this form of diabetes. There is no clearly documented therapeutic technique that will prevent or reverse progressive renal damage in IDDM. While pancreatic transplantation and "cure" of diabetes in experimental animals may be associated with some histological reversal of renal pathology, this has not been documented in humans. Most studies agree that once diabetic renal disease is present (as documented by proteinuria), progression is inevitable, albeit the rate of progression may be altered by different therapeutic methods. There is considerable hope that "tight metabolic control" will prevent the initial damage that leads to DN and ESRD, but evidence remains inconclusive. There is some evidence that careful monitoring for microalbuminuria will allow for very early detection of damage and alterations in therapy. Our studies have documented a decrease in both morbidity and mortality in IDDM in patients who have been competitive athletes, suggesting that promotion of physical fitness may be a valuable means of delaying progression of renal disease while control of BP delays progression. Early detection and aggressive therapy is recommended. Some studies utilizing diets low in sodium and/or protein appear beneficial but more studies are needed before pediatric application.

Prognosis in diabetic nephropathy

OBJECTIVE

To assess the effect of long term antihypertensive treatment on prognosis in diabetic nephropathy.

DESIGN

Prospective study of all insulin dependent diabetic patients aged under 50 with onset of diabetes before the age of 31 who developed diabetic nephropathy between 1974 and 1978 at Steno Memorial Hospital.

SETTING

Outpatient diabetic clinic in tertiary referral centre.

PATIENTS

Forty five patients (20 women) with a mean age of 30 (SD 7) years and a mean duration of diabetes of 18 (7) years at onset of persistent proteinuria were followed until death or for at least 10 years.

INTERVENTIONS

Antihypertensive treatment was started a median of three (0-13) years after onset of nephropathy. Four patients (9%) received no treatment, and 9 (20%), 13 (29%), and 19 (42%) were treated with one, two, or three drugs, respectively. The median follow up was 12 (4-15) years.

MAIN OUTCOME MEASURES

Arterial blood pressure and death.

RESULTS

Mean blood pressure at start of antihypertensive treatment was 148/95 (15/50) mm Hg. Systolic blood pressure remained almost unchanged (slope -0.01 (95% confidence interval -0.39 to 0.37) mm Hg a year) while diastolic blood pressure decreased significantly (0.87 (0.65 to 1.10) mm Hg a year) during antihypertensive treatment. The cumulative death rate was 18% (8 to 32%) 10 years after onset of nephropathy, in contrast to previous reports of 50% to 77% 10 years after onset of nephropathy. As in previous studies, uraemia was the main cause of death (9 patients; 64%).

CONCLUSIONS

The prognosis of diabetic nephropathy has improved during the past decade largely because of effective antihypertensive treatment.