Development of diabetic nephropathy in the Milan normotensive strain, but not in the Milan hypertensive strain: possible permissive role of hemodynamics

BACKGROUND

Rats of the Milan normotensive strain develop spontaneous glomerulosclerosis, whereas those of the Milan hypertensive strain are resistant to renal disease, possibly due to intrarenal artery hypertrophy protecting from systemic hypertension. To assess the role of hemodynamic versus metabolic factors in diabetic nephropathy, we investigated whether streptozotocin-induced diabetes accelerates glomerulosclerosis in Milan normotensive and/or removes (the hemodynamic) protection in Milan hypertensive rats by reducing preglomerular vascular resistance.

METHODS

Diabetic and nondiabetic Milan normotensive, hypertensive, and progenitor Wistar rats were followed for 6 months for the assessment of renal function and structure.

RESULTS

Proteinuria increased in nondiabetic and diabetic normotensive and, to a lesser extent, in diabetic Wistar, but not hypertensive rats. Serum creatinine increased and creatinine clearance decreased in nondiabetic and diabetic normotensive rats at 6 months. At 1.5 months, diabetic normotensive, but not hypertensive rats showed increased glomerular filtration rate and filtration fraction, suggesting glomerular hypertension. Diabetic nephropathy was detected in diabetic normotensive and Wistar, but not hypertensive rats. Glomerular extracellular matrix and TGF-beta mRNA levels increased with diabetes (and age) in normotensive, but not hypertensive rats. Arterioles and interlobular arteries showed increased media thickness in hypertensive versus normotensive rats, with diabetes reducing it only in the normotensive.

CONCLUSION

These data show that Milan hypertensive rats are not susceptible to diabetic nephropathy, at variance with glomerulosclerosis-prone Milan normotensive rats, thus indicating the importance of genetic background. Our study suggests that the nature of this (genetic) protection might be hemodynamic, with intrarenal artery hypertrophy preventing diabetes-induced loss of autoregulation.

Purinergic modulation of mesangial extracellular matrix production: role in diabetic and other glomerular diseases

BACKGROUND

Extracellular adenosine triphosphate (ATP) (eATP) mediates several biologic activities via purinergic P2 receptors (P2Rs). This study aimed at (1) evaluating the role of the purinergic system in modulating mesangial extracellular matrix (ECM) and transforming growth factor-beta (TGF-beta) production and (2) its contribution to diabetes-induced mesangial ECM accumulation.

METHODS

Rat mesangial cells were grown in normal glucose (5.5 mmol/L) or high glucose (30 mmol/L) containing media and probed with purinergic agonists and antagonists for the assessment of the expression pattern and function of P2Rs; release of ATP and activity of ectoATPases; and changes in ECM and TGF-beta expression.

RESULTS

Cells cultured in normal glucose and high glucose expressed similar amounts of functional P2Rs of the P2X(2), P2X(3), P2X(4), P2X(5), P2X(7), P2Y(1), P2Y(2), P2Y(4), and P2Y(6) subtypes. Levels of eATP were higher in high glucose vs. normal glucose, with unchanged ectoATPase activity. The ATP-hydrolyzing enzymes hexokinase or apyrase reduced ECM and TGF-beta production from cells grown in high glucose, but not normal glucose. Under both normal glucose and high glucose conditions, ATP and the P2X(7) agonist benzoylbenzoylATP increased dose-dependently ECM and TGF-beta production, whereas the P2Y agonist uridine triphosphate (UTP) produced the opposite effect. The P2X(7) inhibitor oxidized ATP attenuated the ECM and TGF-beta up-regulation induced by ATP and, to a lesser extent, that caused by high glucose. A TGF-beta neutralizing antibody also prevented ATP-induced ECM up-regulation.

CONCLUSION

These data indicate a role for eATP in regulating ECM production via TGF-beta and suggest that P2XRs and P2YRs differentially modulate this process. An increased ATP release induced by hyperglycemia might contribute to mesangial matrix expansion occurring in diabetes.

Development of age-dependent glomerular lesions in galectin-3/AGE-receptor-3 knockout mice

Aging is characterized by renal functional and structural abnormalities resembling those observed in diabetes. These changes have been related to the progressive accumulation of advanced glycation end-products (AGEs) and cumulative oxidative stress occurring in both conditions. We previously reported that galectin-3 ablation is associated with increased susceptibility to diabetes- and AGE-induced glomerulopathy, thus indicating a protective role of galectin-3 as an AGE receptor. To investigate the role of the AGE/AGE receptor pathway in the pathogenesis of age-related renal disease, we evaluated the development of glomerular lesions in aging galectin-3 knockout (KO) vs. wild-type (WT) mice and their relation to the increased AGE levels and oxidative stress characterizing the aging process. KO mice showed significantly more pronounced age-dependent increases in proteinuria, albuminuria, glomerular sclerosis, and glomerular and mesangial areas, starting at 18 mo, as well as renal extracellular matrix mRNA and protein expression, starting at 12 mo vs. age-matched WT mice. Circulating and renal AGEs, plasma isoprostane 8-epi-PGF2alpha levels, glomerular content of the glycoxidation and lipoxidation products N(epsilon)-carboxymethyllysine and 4-hydroxy-2-nonenal, and renal nuclear factor-kappaB activity also increased more markedly with age in KO than WT mice. AGE levels correlated significantly with renal functional and structural parameters. These data indicate that aging galectin-3 KO mice develop more pronounced changes in renal function and structure than coeval WT mice, in parallel with a more marked degree of AGE accumulation, oxidative stress, and associated low-grade inflammation, thus supporting the concept that the AGE/AGE receptor pathway is implicated in age-related renal disease.

Galectin-3/AGE-receptor 3 knockout mice show accelerated AGE-induced glomerular injury: evidence for a protective role of galectin-3 as an AGE receptor

We previously showed that mice lacking galectin-3/AGE-receptor 3 develop accelerated diabetic glomerulopathy. To further investigate the role of galectin-3/AGE-receptor function in the pathogenesis of diabetic renal disease, galectin-3 knockout (KO) and coeval wild-type (WT) mice were injected for 3 months with 30 microg/day of N(epsilon)-carboxymethyllysine (CML)-modified or unmodified mouse serum albumin (MSA). Despite receiving equal doses of CML, KO had higher circulating and renal AGE levels and showed more marked renal functional and structural changes than WT mice, with significantly higher proteinuria, albuminuria, glomerular, and mesangial area and glomerular sclerosis index. Renal 4-hydroxy-2-nonenal content and NFkappaB activation were also more pronounced in KO-CML vs. WT-CML. Kidney mRNA levels of fibronectin, laminin, collagen IV, and TGF-beta were up-regulated, whereas those of matrix metalloproteinase-2 and -14 were down-regulated, again more markedly in KO-CML than WT-CML mice. Basal and CML-induced RAGE and 80K-H mRNA levels were higher in KO vs. WT mice. MSA injection did not produce any significant effect in both genotypes. The association of galectin-3 ablation with enhanced susceptibility to AGE-induced renal disease, increased AGE levels and signaling, and altered AGE-receptor pattern indicates that galectin-3 is operating in vivo as an AGE receptor to afford protection toward AGE-dependent tissue injury.

Oxidative stress in diabetes-induced endothelial dysfunction involvement of nitric oxide and protein kinase C

Reactive oxygen species (ROS) formation plays a major role in diabetes-induced endothelial dysfunction, though the molecular mechanism(s) involved and the contribution of nitric oxide (NO) are still unclear. This study using bovine retinal endothelial cells was aimed at assessing (i) the role of oxygen-dependent vs. NO-dependent oxidative stress in the endothelial cell permeability alterations induced by the diabetic milieu and (ii) whether protein kinase C (PKC) activation ultimately mediates these changes. Superoxide, lipid peroxide, and PKC activity were higher under high glucose (HG) vs. normal glucose throughout the 30 d period. Nitrite/nitrate and endothelial NO synthase levels increased at 1 d and decreased thereafter. Changes in monolayer permeability to 125I-BSA induced by 1 or 30 d incubation in HG or exposure to advanced glycosylation endproduct were reduced by treatment with antioxidants or PKC inhibitors, whereas NO blockade prevented only the effect of 1 d HG. HG-induced changes were mimicked by a PKC activator, a superoxide generating system, an NO and superoxide donor, or peroxynitrite (attenuated by PKC inhibition), but not a NO donor. The short-term effect of HG depends on a combined oxidative and nitrosative stress with peroxynitrite formation, whereas the long-term effect is related to ROS generation; in both cases, PKC ultimately mediates permeability changes.

Role of galectin-3 in diabetic nephropathy

The advanced glycosylation end products (AGE) participate in the pathogenesis of nephropathy and other diabetic complications through several mechanisms, including their binding to cell surface receptors. The AGE receptors include RAGE, the macrophage scavenger receptors, OST-48 (AGE-R1), 80K-H (AGE-R2), and galectin-3 (AGE-R3). Galectin-3 interacts with the beta-galactoside residues of cell surface and matrix glycoproteins via the carbohydrate recognition domain and with intracellular proteins via peptide-peptide associations mediated by its N-terminus domain. These structural properties enable galectin-3 to exert multiple functions, including the mRNA splicing activity, the control of cell cycle, the regulation of cell adhesion, the modulation of allergic reactions, and the binding of AGE. The lack of transmembrane anchor sequence or signal peptide suggests that it is associated with other AGE receptors, possibly AGE-R1 and AGE-R2, to form an AGE-receptor complex, rather than playing an independent role. In target tissues of diabetic vascular complications, such as the endothelium and mesangium, galectin-3 is weakly expressed under basal conditions and is markedly upregulated by the diabetic milieu (and to a lesser extent by aging). Galectin-3-deficient mice were found to develop accelerated diabetic glomerulopathy versus the wild-type animals, as evidenced by the more pronounced increase in proteinuria, mesangial expansion, and matrix gene expression. This was associated with a more marked renal/glomerular AGE accumulation, suggesting that it was attributable to the lack of galectin-3 AGE-receptor function. These data indicate that galectin-3 is upregulated under diabetic conditions and is operating in vivo to provide protection toward AGE-induced tissue injury, as opposed to RAGE.

Glomerular cell replication and cell loss through apoptosis in experimental diabetes mellitus

AIM

To evaluate changes in the glomerular cell balance between replication and apoptosis in experimental diabetes mellitus (DM) in relation to morphometric data.

METHODS

Adult Sprague-Dowley rats with streptozotocin-induced DM and controls of the same age and strain were sacrificed 4 and 8 weeks and 6 months after disease onset. Cell replication was demonstrated with MIB-5, and apoptosis with the terminal uridine nick end labeling technique. Glomerular size and glomerular cell population were estimated morphologically.

RESULTS

Diabetic and control rats showed irrelevant MIB-5 positivity at all time points. Glomerular apoptosis was minimal in rats with 4 and 8 weeks of DM and in controls. Rats with 6 months of DM showed significantly higher glomerular apoptosis values than controls (2.49 +/- 0.25 vs. 0.65 +/- 0.16%; p < 0.001). The mean cell count per glomerular profile was significantly lower in these diabetic rats (64.02 +/- 1.93 vs. 78.27 +/- 0.99; p < 0.001), a change that correlated with that in apoptosis. The glomerular cell density was further decreased in diabetic rats because of the diabetic increase in mean glomerular volume (1.598 vs. 0.927 10(6) microm).

CONCLUSIONS

Apoptosis is associated with loss of glomerular cells in rats with long-term, streptozotocin-induced DM and - to a considerably lower degree - in controls of the same age and strain. These changes could be relevant to glomerulosclerosis associated with long-term, streptozotocin-induced DM.

Increased retinal endothelial cell monolayer permeability induced by the diabetic milieu: role of advanced non-enzymatic glycation and polyol pathway activation

BACKGROUND

Increased vascular permeability could be involved in the pathogenesis of diabetic retinopathy. The present study was aimed at assessing whether high glucose concentrations can impair retinal endothelial cell barrier function directly, irrespective of changes in other determinants of permeability, and the role of non-enzymatic glycation and polyol pathway activation in these alterations.

METHODS

Bovine retinal endothelial cells (BREC) were exposed for various periods to high glucose vs iso-osmolar mannitol and normal glucose containing media+/-agents mimicking or inhibiting advanced glycation end product (AGE) formation and polyol pathway activation. Monolayer permeability was assessed by measuring the transendothelial passage of (125)I-labeled proteins.

RESULTS

Permeability increased significantly (up to +70%) in BREC exposed to high glucose, but not to mannitol, for 1-30 days, vs normal glucose control cells. Exposure to AGE-modified bovine serum albumin (BSA) (> or = 90%) and, to a lesser extent, sorbitol (+28%) mimicked the high glucose effect. The AGE formation and nitric oxide synthase (NOS) inhibitor aminoguanidine significantly reduced (by 60%) changes induced by 30-day exposure to high glucose, whereas methylguanidine, which inhibits only NOS activity, did not affect permeability. Aldose reductase or sorbitol dehydrogenase inhibitors decreased (by approximately 40%) the enhanced leakage produced by 1-day, but not 30-day, incubation in high glucose.

CONCLUSIONS

The present results indicate that high glucose is capable of impairing retinal endothelial cell barrier function directly and that non-enzymatic glycation and polyol pathway activation may mediate these changes, with AGEs participating in the long-term alterations and increased flux through the sorbitol pathway in the short-term effect.

Accelerated diabetic glomerulopathy in galectin-3/AGE receptor 3 knockout mice

Several molecules were shown to bind advanced glycation end products (AGEs) in vitro, but it is not known whether they all serve as AGE receptors and which functional role they play in vivo. We investigated the role of galectin-3, a multifunctional lectin with (anti)adhesive and growth-regulating properties, as an AGE receptor and its contribution to the development of diabetic glomerular disease, using a knockout mouse model. Galectin-3 knockout mice obtained by gene ablation and the corresponding wild-type mice were rendered diabetic with streptozotocin and killed 4 months later, together with age-matched nondiabetic controls. Despite a comparable degree of metabolic derangement, galectin-3-deficient mice developed accelerated glomerulopathy vs. the wild-type animals, as evidenced by the more pronounced increase in proteinuria, extracellular matrix gene expression, and mesangial expansion. This was associated with a more marked renal/glomerular AGE accumulation, indicating it was attributable to the lack of galectin-3 AGE receptor function. The galectin-3-deficient genotype was associated with reduced expression of receptors implicated in AGE removal (macrophage scavenger receptor A and AGE-R1) and increased expression of those mediating cell activation (RAGE and AGE-R2). These results show that the galectin-3-regulated AGE receptor pathway is operating in vivo and protects toward AGE-induced tissue injury in contrast to that through RAGE.

Role of galectin-3 as a receptor for advanced glycosylation end products

The advanced glycosylation end product (AGE)-binding proteins identified so far include the components of the AGE-receptor complex p60, p90 and galectin-3, receptor for advanced glycosylation end products (RAGE), and the macrophage scavenger receptor types I and II. Galectin-3 interacts with beta-galactoside residues of several cell surface and matrix glycoproteins through the carbohydrate recognition domain and is also capable of peptide-peptide associations mediated by its N-terminus domain. These structural properties enable galectin-3 to exert multiple functions, including the modulation of cell adhesion, the control of cell cycle, and the mRNA splicing activity. Moreover, in macrophages, astrocytes, and endothelial cells, galectin-3 has been shown to exhibit a high-affinity binding for AGEs; the lack of a transmembrane anchor sequence or signal peptide suggests that it associates with other AGE-receptor components rather than playing an independent role as AGE-receptor. In tissues that are targets of diabetic vascular complications, such as the mesangium and the endothelium, galectin-3 is not expressed or only weakly expressed under basal conditions, at variance with p90 and p60 but becomes detectable with aging and is induced or up-regulated by the diabetic milieu, which only slightly affects the expression of p90 or p60. This (over)expression of galectin-3 may in turn modulate AGE-receptor-mediated events by modifying the function of the AGE-receptor complex, which could play a role in the pathogenesis of target tissue injury. Up-regulated galectin-3 expression may also exert direct effects on tissue remodeling, independently of AGE ligands, by virtue of its adhesive and growth regulating properties.

The diabetic milieu modulates the advanced glycation end product-receptor complex in the mesangium by inducing or upregulating galectin-3 expression

Nonenzymatic glycation has been implicated in the pathogenesis of the dysregulated tissue remodeling that characterizes diabetic glomerulopathy, via the formation of advanced glycation end products (AGEs) and their binding to cell surface receptors. Several AGE-binding proteins have been identified so far, including p60, p90, and the adhesive and growth-regulating lectin galectin-3 (Gal-3), the components of the so-called AGE-receptor complex. This study aimed to evaluate the mesangial expression of the AGE-receptor complex and its modulation by the diabetic milieu, both in vivo, in non-diabetic versus streptozotocin-induced diabetic rats, and in vitro, in mesangial cells exposed to either normal glucose (NG) levels (5.5 mmol/l), as compared with high glucose (HG) levels (30 mmol/l) and iso-osmolar mannitol (M), or to native bovine serum albumin (BSA), as compared with glycated BSA with AGE formation (BSA-AGE) and glycated BSA in which AGE formation was prevented by aminoguanidine (BSA-AM). In vivo, Gal-3 protein and mRNA were not detectable in glomeruli from nondiabetic rats until 12 months after initiating the study. On the contrary, in diabetic rats, Gal-3 expression was observed at 2 months of disease duration, and it increased thereafter. Both p60 and p90 immunoreactivities were observed at the glomerular level with slightly increased expression of p90, but not p60, in diabetic versus nondiabetic animals. In vitro, Gal-3 was not detectable in mesangial cells cultured in NG (although it became evident after a certain number of passages in culture), whereas Gal-3 was detectable in cells grown on BSA. Prolonged exposure (2-4 weeks) of mesangial cells to HG but not to M, as well as growing cells on BSA-AGE and, to a lesser extent, BSA-AM, induced or significantly increased the expression of Gal-3, both protein (up to 2.65-fold) and mRNA (up to 3.10-fold) and its secretion in the medium (by approximately 50%). Both p60 and p90 were demonstrated in mesangial cells under NG conditions, and the expression of p90, but not p60, was upregulated by approximately 20% by HG or BSA-AGE. These results indicate that 1) under basal conditions, Gal-3, unlike p90 and p60, is not detectable in the mesangium but becomes expressed with aging and 2) the diabetic milieu induces or upregulates Gal-3 production, whereas it increases only slightly the expression of p90, but not p60. Gal-3 expression or overexpression may modulate the AGE-receptor-mediated events by modifying the function of the AGE-receptor complex. Additionally, it may exert direct effects on tissue remodeling by virtue of its adhesive and growth-regulating properties.

The circulating insulin-like growth factor system in children with coeliac disease: an additional marker for disease activity

BACKGROUND

Chronic undernutrition resulting from coeliac disease (CD) could be associated with changes in the circulating insulin-like growth factor (IGF) system, which may participate in the pathogenesis of growth retardation occurring in these patients.

METHODS

We performed a cross-sectional study in CD subjects attempting to (1) document the pattern of serum IGF-I and IGF binding protein (IGFBP) 1 and 3 at diagnosis and (2) assess the response of circulating IGF system to dietary treatments, in comparison with the response of clinical and laboratory findings utilized for the diagnosis of CD. Thirty-two prepubertal CD children were divided into three groups based on the dietetic treatment: at diagnosis (D, n=18); on gluten-free diet for at least 6 months (GFD, n=7); and on gluten challenge for at least 3 months (CH, n=7). Six postpubertal CD patients were also studied at diagnosis.

RESULTS

In prepubertal children IGF-I levels were significantly reduced (by 29%) in D vs sex- and age-matched normal control (NC) subjects, with reductions being more pronounced before 3 years of age. Likewise, serum IGFBP-3 concentrations were decreased by 22%, whereas circulating IGFBP-1 levels were increased by 60%, compared with NC, with more marked IGFBP changes in older children. Similar alterations were observed in postpubertal patients. Changes in the circulating IGF system disappeared in GFD subjects and reappeared in CH children, as positivity of disease-specific antibodies. Body mass index (BMI) also improved in GFD subjects, but did not decrease in CH children. Changes in IGF-I and IGFBPs did not correlate with each other. Levels of IGF-I, but not of IGFBPs, maintained the relation with age and correlated significantly with BMI and positivity of antibodies.

CONCLUSIONS

These results demonstrate that CD patients show significant changes in serum IGF-I, in younger children, and IGFBPs (particularly IGFBP-1), in older children and adolescents, correlating with clinical course and response to dietary treatments. The alteration in the circulating IGF system could be implicated in the pathogenesis of growth retardation occurring in CD and may provide an additional tool in monitoring of the disease.

Eicosanoid synthesis in peripheral blood monocytes: a marker of disease activity in lupus nephritis

A typical feature of lupus nephritis is glomerular and interstitial leukocyte infiltration. In search of a serological marker of renal disease activity, we examined prostaglandin endoperoxide synthetase (PGHS) activity in peripheral-blood monocytes isolated from 5 healthy subjects and 11 untreated patients with biopsy-proven lupus nephritis, using radioimmunoassay of prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) released during 24-hour cultures with selective stimuli/inhibitors. Unstimulated basal PGE2 and TxB2 synthesis, reflecting in vivo PGHS activity, was greater in the five patients with active renal involvement (World Health Organization [WHO] classes IVb-c) and the six lupus patients without active disease than in the five healthy subjects (TxB2, 2,643+/-198 [standard error], 2,015+/-190, 1,548+/-295 pg/10(6) cells, respectively). Escherichia coli lipopolysaccharide (LPS; 10 microg/mL) potently induced TxB2 or PGE2 synthesis in healthy controls (+255%+/-76% and +611%+/-190%, +688%+/-234% and +3,189%+/-154%; 4 to 24 hours, respectively), an effect abolished by 5 micromol/L of dexamethasone (DEX) or by 5 micromol/L of the protein synthesis inhibitor cycloheximide (CHX). Responses to LPS were reduced in lupus patients without disease activity and reduced even further in those with active nephritis. This may be related to substrate depletion or feedback functional inhibition of the inducible isoform of PGHS. Our assay may prove useful in the early detection of kidney disease activity in lupus erythematosus.

Upregulation of mesangial growth factor and extracellular matrix synthesis by advanced glycation end products via a receptor-mediated mechanism

Enhanced advanced glycosylation end product (AGE) formation has been shown to participate in the pathogenesis of diabetes-induced glomerular injury by mediating the increased extracellular matrix (ECM) deposition and altered cell growth and turnover leading to mesangial expansion. These effects could be exerted via an AGE-receptor-mediated upregulation of growth factors, such as the IGFs and transforming growth factor-beta (TGF-beta). We tested this hypothesis in human and rat mesangial cells grown on nonglycated or native bovine serum albumin (BSA), glycated BSA with AGE formation (BSA-AGE), or glycated BSA in which AGE formation was prevented by the use of aminoguanidine (BSA-AM), in the presence or absence of an antibody, alpha-p60, directed against the p60/OST protein named AGE-receptor 1 (AGE-R1), or normal control (pre-immune) serum. The mRNA and/or protein levels of IGF-I, IGF-II, IGF receptors, IGF binding proteins (IGFBPs), TGF-beta1 and the ECM components fibronectin, laminin, and collagen IV were measured, together with cell proliferation. Both human and rat mesangial cells grown on BSA-AGE showed increased IGF-I and total and bioactive TGF-beta medium levels and enhanced IGF-I, IGF-II, and TGF-beta1 gene expression, compared with cells grown on BSA, whereas total IGFBP and IGFBP-3 medium content, IGF receptor density and affinity, and IGF-I receptor transcripts were unchanged. Moreover, cells grown on BSA-AGE showed increased ECM protein and mRNA levels versus cells cultured on BSA, whereas cell proliferation was unchanged in human mesangial cells and slightly reduced in rat mesangial cells. Growing cells on BSA-AM did not affect any of the measured parameters. Co-incubation of BSA-AGE with anti-AGE-R1, but not with pre-immune serum, prevented AGE-induced increases in IGF-I, TGF-beta1, and ECM production or gene expression; anti-AGE-R1 also reduced growth factor and matrix synthesis in cells grown on BSA. These results demonstrate that mesangial IGF and TGF-beta1 synthesis is upregulated by AGE-modified proteins through an AGE-receptor-mediated mechanism. The parallelism with increased ECM production raises the speculation that the enhanced synthesis of these growth factors resulting from advanced nonenzymatic glycation participates in the pathogenesis of hyperglycemia-induced mesangial expansion.

Early, but not advanced, glomerulopathy is reversed by pancreatic islet transplants in experimental diabetic rats: correlation with glomerular extracellular matrix mRNA levels

In this study, we investigated 1) whether long-term restoration of euglycemia by means of pancreatic islet transplants is capable of preventing and/or reversing renal functional and structural alterations in an experimental model of insulin-deficient diabetes, and 2) whether changes in extracellular matrix (ECM) and cell turnover at the glomerular level and biochemical abnormalities associated with hyperglycemia correlate with the renal outcome after transplantation. Male Lewis rats, rendered diabetic by intravenous injection of streptozotocin, underwent homologous islet transplantation via the portal vein at 2 weeks (study A), at 4 months (study B), and at 8 months (study C) after the induction of diabetes and killed 12 months after transplantation in study A and 4 months after transplantation in studies B and C. Age-matched nondiabetic and untreated diabetic rats were used as control animals and were studied at 4, 8, and 12 months. In the untreated diabetic animals, metabolic derangement was associated with increased erythrocyte polyol and fructose levels, tail-tendon content of advanced glycation end products (AGEs), total proteinuria, albuminuria, kidney weight, and mean glomerular volume as well as with marked glomerular and extraglomerular lesions. Glomerular gene expression for the ECM components fibronectin and collagen IV and for TGF-beta was also increased, whereas glomerular cell proliferation was unaffected by diabetes. In study A, changes in renal function and structure observed in diabetic rats at 12 months were completely prevented by successful islet transplants. In study B, all functional and structural abnormalities detected in diabetic rats at 4 months of disease duration were virtually reversed by 4 months of euglycemia in transplanted animals, whereas they progressed further in untreated diabetic rats. In study C, the course of functional and structural changes observed in untreated diabetic rats was not reversed by islet transplantation. Likewise, tissue AGE accumulation and particularly upregulation of glomerular ECM and transforming growth factor (TGF)-beta gene expression, which are believed to play a role in the pathogenesis of altered renal function and structure in diabetes, were normalized in transplanted rats from study A and study B, but not in those from study C. These experiments show that restoration of euglycemia by islet transplants is capable of preventing experimental diabetic glomerulopathy and reversing early changes in renal function and structure induced by diabetes. In a later phase of the disease, when glomerular matrix gene expression becomes independent of hyperglycemia, possibly because of the persistent increase in tissue AGE accumulation, metabolic control is not capable of reversing renal abnormalities.

High glucose level inhibits capacitative Ca2+ influx in cultured rat mesangial cells by a protein kinase C-dependent mechanism

In cultured mesangial cells (MC), capacitative Ca2+ influx via store-operated channels (SOC) is potentiated by agents that release Ca2+ from intracellular stores, and inhibited by protein kinase C (PKC). Cells grown under high glucose conditions, as a model of the diabetic microenvironment, display reduced Ca2+ signalling in response to vasoconstrictors, probably due to downregulation by elevated PKC activity. Since SOC might be relevant to this phenomenon, we assessed Ca2+ influx by microfluorometry of fura-2-loaded rat MC cultured for 5 days in normal (5.5 mmol/l, NG) or high glucose (30 mmol/l, HG). The addition of 1-10 mmol/l Ca2+ to NG cells equilibrated in Ca(2+)-free media induced an immediate Ca2+ influx with a free cytosolic Ca2+ ([Ca2+]i) plateau of 155 +/- 50 and 318 +/- 114 nmol/l, respectively. Basal influx was reduced to 88 +/- 8 and 145 +/- 17 nmol/l [Ca2+]i (1-10 mmol/l Ca2+, p < 0.01) by 30 mmol/l D-glucose. This effect of HG was confirmed by Mn2+ quenching of fura-2, indicating reduced entry of divalent cations via the capacitative pathway. Equimolar L-glucose had no effect on Ca2+ influx, consistent with a non-osmotic mechanism. Arginine vasopressin (10 mumol/l) elicited weaker release of stored Ca2+ and subsequent influx in HG cells (191 +/- 33 vs 153 +/- 24 nmol/l, 400 +/- 76 vs 260 +/- 33 nmol/l, 1-10 mmol/l Ca2+, NG/HG, p < 0.05). To examine the involvement of PKC in the effect of HG on capacitative Ca2+ influx, the enzyme was activated or downregulated by treatment with 0.1 mumol/l phorbol myristate acetate (PMA) for 3 min or 24 h, respectively. PMA acutely inhibited Ca2+ influx in NG cells, while PKC downregulation restored it in HG cells. Similarly, the PKC inhibitors staurosporin or H-7 normalized SOC activity in HG cells. In summary, impairment of Ca2+ influx via SOC by HG is one mechanism of the reduced MC [Ca2+]i responsiveness to vasoconstrictors. This event is mediated by PKC and may contribute to the glomerular haemodynamic changes in the initial stages of diabetes mellitus.

High glucose level unmasks a genetic predisposition to enhanced extracellular matrix production in mesangial cells from the Milan normotensive strain

A growing body of evidence indicates that the individual genetic background plays a role in the pathogenesis of diabetic glomerular disease by either favoring or protecting against injury produced by hyperglycemia. Two genetically related rat strains, the Milan normotensive strain (MNS) and the Milan hypertensive strain (MHS) display different susceptibilities to develop glomerulosclerosis with age. Glomerular sclerosing lesions occur in the MNS rats, which remain normotensive throughout their entire life-span, but not in the MHS rats, despite the presence of arterial hypertension. Previous studies have reported that extracellular matrix production and cell proliferation increased with donor-aging in mesangial cells isolated from MNS rats, but not in those from MHS rats, thus suggesting the existence of an inherited defect in the regulation of cell and matrix turnover, which translates into an abnormal response to growth-promoting stimuli favoring the development of glomerulosclerosis. In the study presented here, it was hypothesized that, in addition to donor-aging, other independent risk factors for the development of glomerular disease, such as metabolic injury by hyperglycemia, would be able to trigger and/or precipitate the occurrence of these changes in mesangial cells from the susceptible normotensive strain, but not in those from the protected hypertensive strain. To test this hypothesis, mesangial cells obtained from these rat strains (before the onset of either glomerulosclerosis or hypertension) were used to assess the effects of prolonged (4 wk) exposure to high (30 mmol/L) versus normal (5.5 mmol/L) glucose concentrations on extracellular matrix and cytokine production and cell proliferation. The accumulation and/or gene expression of the matrix components fibronectin, laminin, and collagen IV, and of the cytokines insulin-like growth factor-I (IGF-I) and transforming growth factor-beta (TGF-beta) did not change under normal glucose and increased progressively in response to high glucose in both MNS and MHS cells. These increases, with the exception of the increment in TGF-beta gene expression, were significantly more pronounced in MNS cells than in MHS cells. In contrast, the proliferative response to serum was not affected by high glucose, but increased in MNS cells, and decreased, although not significantly, in MHS cells during the 4-wk period, thus mimicking the changes previously observed in these rat strains as a function of age. These results indicate that high glucose unmasks a genetic tendency to produce increasing amounts of extracellular matrix, not yet evident under normal glucose conditions, and suggest that a genetically determined propensity of mesangial cells to hyperrespond to chronic hyperglycemia may be implicated in the pathogenesis of diabetic glomerular disease.

Regulatory role of eicosanoids in extracellular matrix overproduction induced by long-term exposure to high glucose in cultured rat mesangial cells

Accumulation of extracellular matrix in the mesangium and altered renal eicosanoid synthesis are two prominent features of diabetic glomerular disease. We investigated the relationship between eicosanoid and extracellular matrix production in rat mesangial cells cultured under high glucose vs normal glucose conditions. Long-term exposure of rat mesangial cells to high glucose, but not to iso-osmolar mannitol, significantly increased extracellular matrix accumulation and gene expression and transforming growth factor-beta (TGF-beta) mRNA levels, and decreased prostaglandin (PG) E2 synthesis without affecting production of either thromboxane (TX) B2 or PGF2 alpha, with respect to cells incubated in normal glucose. Addition of exogenous PGE2 resulted in a dose-dependent reduction of matrix protein and mRNA levels and TGF-beta gene expression in cells cultured in either normal or high glucose conditions, whereas exposure to exogenous PGF2 alpha produced a significant increment in matrix production and matrix and TGF-beta gene expression in cells grown in normal glucose, but only a slight increase in those cultured in high glucose. Stimulation of endogenous endoperoxide metabolism towards PGE2 and PGF2 alpha synthesis with FCE-22,178, a drug originally developed as TXA2 synthase inhibitor, resulted in a dose-dependent decrease in matrix accumulation and matrix and TGF-beta gene expression which was suppressed by coincubation with the cyclo-oxygenase inhibitor fenoprofen blocking the FCE-22,178-enhanced PG production. In both cell lines, the rate of synthesis of TXA2 was very low and the selective blockade of its synthesis (by two other TXA2 synthase inhibitors, OKY-046 and Ridogrel) or action (by the TXA2 receptor antagonist BM-13,177) did not alter matrix production or TGF-beta mRNA levels. These results suggest that the cyclo-oxygenase pathway is involved in the regulation of matrix changes induced by high glucose in rat mesangial cells; the reduced production of PGE2 may enhance the synthesis or potentiate the effect of stimulators of ECM formation such as TGF-beta, whereas TXA2 does not appear to be involved. These data also indicate that glucose-enhanced mesangial matrix accumulation may be prevented by exogenous PGE2 or by drugs capable of increasing endogenous PGE2 synthesis.

Increased activity of the insulin-like growth factor system in mesangial cells cultured in high glucose conditions. Relation to glucose-enhanced extracellular matrix production

Recent evidence suggests that several growth factors participate in diabetic glomerular disease by mediating increased extracellular matrix accumulation and altered cell growth and turnover leading to mesangial expansion. Transforming growth factor (TGF)-beta has been demonstrated to be upregulated both in vivo and in vitro, whereas studies on the activity of the renal insulin-like growth factor (IGF) system in experimental diabetes have provided conflicting results. We investigated the effects of prolonged exposure (4 weeks) of cultured human and rat mesangial cells to high (30 mmol/l) glucose vs iso-osmolar mannitol or normal (5.5 mmol/l) glucose levels on: 1) the autocrine/paracrine activity of the IGF system (as assessed by measuring IGF-I and II, IGF-I and II receptors, and IGF binding proteins); and, in parallel, on 2) TGF-beta 1 gene expression; 3) matrix production; and 4) cell proliferation. High glucose levels progressively increased the medium content of IGF-I and the mRNA levels for IGF-I and IGF-II, increased IGF-I and IGF-II binding and IGF-I receptor gene expression, and reduced IGF binding protein production. TGF-beta 1 transcripts and matrix accumulation and gene expression were increased in parallel, whereas cell proliferation was reduced. Iso-osmolar mannitol did not affect any of the above parameters. These experiments demonstrated that high glucose levels induce enhanced mesangial IGF activity, together with enhanced TGF-beta 1 gene expression, increased matrix production, and reduced cell proliferation. It is possible that IGFs participate in mediating diabetes-induced changes in matrix turnover leading to mesangial expansion, by acting in a paracrine/autocrine fashion within the glomerulus.

Insulin-like growth factors I and II stimulate extracellular matrix production in human glomerular mesangial cells. Comparison with transforming growth factor-beta

An enhanced paracrine/autocrine activity of the insulin-like growth factor (IGF) system within the glomerulus has been implicated together with up-regulation of transforming growth factor-beta (TGFbeta) in the pathogenesis of diabetic glomerular disease. This would imply their ability to modulate extracellular matrix (ECM) and cell turnover at the mesangial level, but the direct effects of IGFs on ECM production have not been demonstrated to date. These experiments in cultured human mesangial cells were aimed at assessing the effects of IGF-I and IGF-II, compared with those of TGFbeta, on 1) ECM medium accumulation and gene expression, and 2) total protein synthesis and cell proliferation. Human mesangial cells were grown to subconfluence, growth arrested for 48 h, and then exposed for 4-24 h to serum-free medium containing IGF-I (10(-7) - 10(-11) M), IGF-II (10(-7) - 10(-11) M), TGFbeta (10(-9) - 10(-11) M), or various combinations of two of these growth factors (10(-9)M). All three growth factors dose dependently increased ECM protein and messenger RNA levels. The combination of either IGF-I or IGF-II with TGFbeta, but not the two IGFs together, produced additive effects on matrix production. Total protein synthesis was also increased by IGF-I, IGF-II, and TGFbeta, although to a lesser extent than ECM production, whereas cell proliferation was enhanced by IGFs but not by TGFbeta. These results demonstrate that IGF-I and IGF-II are effective, although less potent than TGFbeta, in stimulating the production of the ECM components that accumulate in the mesangial region during the course of diabetic glomerular disease.

Role of advanced glycation end-products (AGE) in late diabetic complications

To evaluate accumulation of advanced glycation end-products (AGE) in diabetes and its possible correlation with late diabetic complications, AGE levels were measured by spectrofluorimetry in eye lens and sciatic nerve proteins and isolated tail tendon collagen of rats with experimental diabetes of 3- and 6-month duration. The values obtained were compared to those from age-matched control rats and correlated with cataract presence and somatosensory evoked potential (SEP) alterations. Diabetic animals had increased AGE levels in all tissues at both times; cataract developed in 29% of diabetic rats at 3 months and in 57% at 6 months; SEP conduction velocity was reduced in diabetic animals both at 3 (54.5 +/- 1.8 S.E.M. m/s vs. 73.9 +/- 1.0, P < 0.0001) and 6 months (59.5 +/- 1.4 vs. 71.5 +/- 1.6, P < 0.0001) from diabetes induction. No eye lens AGE level differences were observed when cataract presence was considered. Interestingly, in diabetic rats, increased sciatic nerve AGE levels were associated with reduced SEP. These data show that: (1) AGE levels are increased as early as 3 months from development of hyperglycemia; (2) other factors, in addition to an enhanced rate of fluorescent AGE formation, might play important roles in the pathogenesis of diabetic cataract; (3) increased peripheral nerve AGE levels are associated with SEP alterations.

Mechanisms of glucose-enhanced extracellular matrix accumulation in rat glomerular mesangial cells

In view of the importance of mesangial extracellular matrix (ECM) accumulation in the pathogenesis of diabetic glomerulosclerosis, we investigated 1) the effects of high glucose on ECM production by rat glomerular mesangial cells in culture (study A) and 2) the mechanisms underlying these effects, particularly the role of high sugar levels irrespective of intracellular metabolism (study B1) and of excess glucose disposal via the polyol pathway and associated biochemical alterations (study B2). Cells were cultured for 4 weeks, through six to eight passages, under the experimental conditions indicated below and, at each passage, the levels of fibronectin (FN), laminin (LAM), and collagen types I (C-I), III (C-III), IV (C-IV), and VI (C-VI) in media and cell extracts were quantified by an enzyme immunoassay. In study A, medium and cell content of matrix were assessed, together with [3H]leucine and [3H]thymidine incorporation into monolayers, polyol, fructose, and myo-inositol levels and the cytosolic redox state, in cells grown in high (30 mM) D-glucose or iso-osmolar mannitol versus cells cultured in normal (5.5 mM) D-glucose. FN, LAM, C-IV, and C-VI accumulation, but not C-I and C-III accumulation, was increased by 30 mM glucose, but not by iso-osmolar mannitol, when compared with 5.5 mM glucose, starting at week 2 and, except for C-VI, persisting throughout the remaining 2 weeks, whereas no change was observed in the measured indexes of total protein synthesis and DNA synthesis/cell proliferation. At any time point, polyol levels were increased, whereas myo-inositol was reduced by high glucose; in cells grown under elevated glucose concentrations, the lactate/pyruvate (L/P) ratio, an index of the cytosolic redox state, progressively increased. In study B1, the effects of high D-glucose were compared with those of iso-osmolar concentrations of sugars that are partly or not metabolized but are capable of inducing nonenzymatic glycosylation, such as D-galactose and L-glucose, and of mannitol, which does not enter the cell. Both D-galactose and L-glucose, but not mannitol, partly mimicked D-glucose-induced ECM overproduction. Although D-galactose is metabolized via the polyol pathway and alters the cytosolic redox state, ECM changes induced by high galactose were not prevented by the use of an aldose reductase inhibitor (ARI), Alcon 1576 (14 microM).(ABSTRACT TRUNCATED AT 400 WORDS)

High glucose inhibits cytosolic calcium signaling in cultured rat mesangial cells

Glomerular vasodilatation in the early stages of type I diabetes mellitus apparently results from arteriolar insensitivity to vasoconstrictors. Since cytosolic free calcium ([Ca2+]i) is a major signaling mechanism for smooth muscle contraction, we studied whether growth of smooth muscle-like rat glomerular mesangial cells in media with high glucose concentration affects [Ca2+]i responses to vasoconstrictors. In cells grown for five days in 22 mM glucose, we observed blunted responsiveness to three structurally unrelated vasoconstrictors that elevate [Ca2+]i via a phospholipase C-dependent mechanism, angiotensin II, prostaglandin F2 alpha, and arginine vasopressin. Inhibition of [Ca2+]i responses was not due to an osmotic effect of high glucose, since it was not mimicked by hypertonic mannitol. While the size of intracellular Ca2+ pools was unaffected by elevated glucose, Na+/Ca2+ exchange was markedly inhibited, thus ruling out both impaired filling of Ca2+ stores and enhanced counter-regulatory mechanisms. Impaired myoinositol transport or intracellular sorbitol accumulation were not responsible for the effects of high glucose, since supplementation of media with myo-inositol or with the aldose reductase inhibitor. Alcon 1576, failed to reverse insensitivity to vasoconstrictors. On the other hand, down-regulation or pharmacological inhibition of protein kinase C completely reversed the effects of high glucose, thus indicating involvement of this signal transduction pathway. These data suggest a possible intracellular mechanism for the impaired vascular sensitivity underlying early renal hemodynamic changes in diabetes mellitus.

Advanced nonenzymatic glycation endproducts (AGE): their relevance to aging and the pathogenesis of late diabetic complications

Several studies in the last decade have highlighted the importance of the hexose sugars and especially glucose, as being responsible for alterations to living protein and other molecules. The phenomenon of nonenzymatic glycation--by which the carbonyl group of glucose can directly condense with a free amino group--may be relevant for the process of aging and for the pathogenesis of late diabetic complications. Thus life-long exposure to normoglycemia in non diabetic subjects or a shorter exposure but continued association with a hyperglycemic milieu, as in diabetes mellitus, have both been shown to lead to the formation and accumulation of irreversible and highly reactive advanced glycation endproducts (AGE) over long-lived, fundamental molecules such as the constituents of arterial wall collagen, basement membranes, nerve myelin, DNA and others. For example, the introduction of foreign AGE groups into proteins might alter their tertiary structure and therefore modify their function or activity. By increasing protein-to-protein cross-links AGE could reduce protein turnover, with consequential increases in levels of modified and thus less reactive molecules. Moreover, AGE could initiate an immune response with the production of specific antibodies. Reducing the extent of nonenzymatic glycation could effectively reduce the accumulation of AGE. Many authors are experimenting with methods to achieve this aim. Amongst the products tested are aspirin and aminoguanidine which compete with glucose for the same protein amino group. D-lysine is also being investigated on the principle that by reacting with glucose in circulation, it could effectively prevent it from reaching the amino group on the protein.(ABSTRACT TRUNCATED AT 250 WORDS)