Effect of high glucose on type IV collagen production by cultured glomerular epithelial, endothelial, and mesangial cells

Prevention of early glomerulopathy with tolrestat in the streptozotocin-induced diabetic rat

Hyperglycemia is of central importance in the pathogenesis of the complications of diabetes mellitus. Glucose activation of the polyol pathway may lead to renal arteriolar smooth muscle and glomerular mesangial cell hypocontractility. In the streptozotocin-induced diabetic rat, the effect of the aldose reductase inhibitor, tolrestat, in preventing glomerular hyperfiltration, renal hypertrophy, extracellular matrix accumulation, and mesangial cell hypocontractility was addressed. Streptozotocin-induced diabetic rats were followed for 12 weeks and half received tolrestat (25 mg/kg per day). Increased glomerular filtration rate was prevented by tolrestat (3.1 +/- 0.3 vs. 1.8 +/- 0.2 mL/min, diabetes vs. diabetes + tolrestat, p < 0.01), in part by reduction of the filtration fraction (0.39 +/- 0.03 vs. 0.29 +/- 0.01, diabetes vs. diabetes + tolrestat, p < 0.01). Tolrestat prevented the raised albumin excretion rates (3594 +/- 1154 vs. 713 +/- 161 mg/24 h, diabetes vs. diabetes + tolrestat, p < 0.01). Endothelin-1-induced contraction of isolated glomeruli was normal in tolrestat-treated diabetic animals compared with the hypocontractile diabetic glomeruli. Tolrestat prevented glomerular hypertrophy (1.86 +/- 0.10 vs. 1.49 +/- 0.03 microns 2 x 10(5), diabetes vs. diabetes + tolrestat, p < 0.001) and attenuated the accumulation of basement-membrane-like material (50.2 +/- 0.4% vs. 46.4 +/- 0.8%, diabetes vs. diabetes+tolrestat, p < 0.001). Fractional mesangial expansion was unchanged in tolrestat-treated diabetic rats compared with untreated animals. Tolrestat prevents the functional changes of glomerular hyperfiltration, mesangial cell hypocontractility, and increased glomerular permeability to albumin. Polyol accumulation may have differential effects on glomerular growth and extracellular matrix accumulation in early diabetic nephropathy.

Left ventricular diastolic function in hypertension and role of plasma glucose and insulin. Comparison with diabetic heart

BACKGROUND

Experimental production of glucose intolerance has been associated with increased diastolic stiffness of the left ventricle, accompanied by interstitial fibrosis. Because carbohydrate metabolism is altered in hypertension, we undertook the present study to assess the relation of diastolic dysfunction in hypertension to plasma glucose and insulin concentrations. The latter are also affected by obesity. To facilitate this analysis, we studied moderately obese hypertensives. Elucidation of these relations was then sought in diabetic subjects.

METHODS AND RESULTS

Subjects undergoing catheterization for chest pain were included in the study when significant coronary disease was not present. In groups 1 (lean), 2 (obese), 3 (lean hypertensive), and 4 (obese hypertensives), intraventricular pressures and volumes were determined. Fasting plasma glucose, insulin, hemoglobinAIC, and glucose tolerance were assessed. Basal ejection fraction and end-systolic wall stress were normal in the four groups. Chamber stiffness was significantly elevated in the hypertensives and was higher in group 4 than in group 3 (P < .05). Diastolic dysfunction was correlated with fasting blood glucose (r = .69, P < .006) but not with plasma insulin or left ventricular mass. Chamber stiffness was also increased in diabetics, with a larger effect in the obese.

CONCLUSIONS

Hypertension is associated with increased diastolic stiffness of the left ventricle, which is enhanced by moderate obesity, and abnormal carbohydrate metabolism. Experimentally and in humans, hypertension is associated with interstitial fibrosis of mycardium, the presumed basis for the diastolic dysfunction. Chamber stiffness in group 4 hypertensives was similar to that in the lean diabetics but less than that in the obese diabetics. Although the latter exhibited a correlation with plasma hemoglobinAIC, the large rise in stiffness suggests a potential role for growth factors in further alteration of myocardial composition.

Production of type IV collagen and 72-kDa gelatinase by human endothelial cells cultured in high glucose. Effects of a protein kinase C inhibitor, GF 109203X

Since diabetic microangiopathy and macroangiopathy are characterized by type IV collagen accumulation in vascular basement membranes, it was of interest to study type IV collagen production and type IV collagenase secretion by endothelial cells (EC) cultured in high glucose and to evaluate the role of protein kinase C (PKC) activation in the alterations induced by high glucose. Primary cultures of human umbilical vein EC were exposed to high glucose concentration for 3 days at the beginning of confluence. The number of EC decreased with glucose concentration from 5 to 50 mM. At 16.7 mM glucose concentration, the amount of type IV collagen, determined by a two-step ELISA, increased in the culture supernatant and in the insoluble fraction associated with the extracellular matrix and cells; proline incorporation was more markedly elevated in the collagenous than in the total proteins of the culture supernatant and of the extracellular matrix and cell extracts. Gelatin zymography of the culture supernatant showed that EC mainly produce a 72-kDa gelatinase known to degrade type IV collagen. At 16.7 mM glucose concentration, total gelatinase activity per millilitre of culture supernatant was reduced and the 72-kDa gelatinase activity measured on the zymogram scan was lowered. When EC were exposed to 16.7 mM glucose, the specific PKC inhibitor GF 109203X corrected the increases in type IV collagen concentration and in proline incorporation into the collagenous or total proteins present in he culture supernatant or in the extract of the insoluble fraction, including the extracellular matrix and cells. Our results show that soluble and insoluble type IV collagen accumulation by EC cultured at high glucose concentration is not only associated with increased synthesis of the collagenous and total proteins but also with decreased total 72-kDa gelatinase activity in the extracellular fluid. The observed effects of GF 109203X are in favor of the involvement of PKC activation in the type IV collagen accumulation.

Proteoglycan synthesis by bovine myocardial endothelial cells is increased by long-term exposure to high concentrations of glucose

The role of the metabolic milieu in control of proteoglycan synthesis was investigated using bovine myocardial endothelial cells (BMEC) grown for six to eight passages in media containing either 5.6 or 25 mM glucose. Macromolecular Na[35S]sulfate incorporation into proteoglycans was increased by exposure to 25 mM when compared with 5.6 mM glucose (7.05 +/- 0.40 [SD] vs. 3.5 +/- 0.50 x 10(-4) dpm/microgram DNA). In contrast, [3H]leucine incorporation was unaffected by glucose (11.27 +/- 0.85 vs. 9.88 +/- 1.23 x 10(-5) dpm/microgram DNA). The distribution of isotopes between media and cell layer fractions was not different in the two conditions. Addition of 19.4 mM mannitol to 5.6 mM glucose containing media had no effect on isotope incorporation. The HPLC-DEAE and Sepharose CL-6B elution profiles of media 35S-proteoglycans synthesized under each condition were similar. A Sepharose CL-4B Kav 0.08 heparan sulfate proteoglycan accounted for 20% of the total 35S-incorporation. Perlecan domain III mRNA was identified by Northern analysis and domain 1 by the polymerase chain reaction (PCR) in total BMEC RNA. A mixture of chondroitin/dermatan sulfate proteoglycans accounted for 67% of 35S-incorporation. They eluted from Sepharose CL-6B at Kav 0 and 0.22. Two [3H]leucine labeled core proteins of 135 and 50 kD were identified in each of these 35S-proteoglycan peaks. Biglycan but not decorin mRNAs were detected by Northern analysis and by PCR. These data demonstrate that prolonged exposure to high glucose concentrations in vitro stimulate the accumulation of [35S]sulfate into microvascular endothelial cell proteoglycans without significant alterations in their overall hydrodynamic or charge related properties. Modulation of proteoglycan synthesis by glucose may participate in the pathogenesis of the small vessel complications of diabetes.

A quantitative ultrastructural study of juxtaglomerular arterioles in IDDM patients with micro- and normoalbuminuria

Hyalinization of juxtaglomerular arterioles is prominent in advanced diabetic nephropathy and may have important functional consequences. We studied the early stages of diabetic renal disease using kidney biopsy material from insulin-dependent diabetic patients, 8 with normal albumin excretion rate (< 15 micrograms/min) and 16 with microalbuminuria (15-200 micrograms/min). Ten living non-diabetic kidney donors served as a control group. Median duration of diabetes was 9.5 years (range 5-31) in patients with normoalbuminuria, and 12 years (7-22) in patients with microalbuminuria (p = 0.27). The tissue was sectioned systematically, 1-micron thick sections for light microscopy at 10-micron intervals, and thin sections for electron microscopy taken at 60-micron intervals. The arterioles were identified as afferent or efferent, and total profiles were photographed (magnification 7500x), providing a systematic independent sample for measurements using standard stereological methods. Patients with microalbuminuria had significantly increased arteriole parameters compared with the control group: for afferent and efferent arterioles the volume fraction of matrix/media, means and (co-efficient of variation, CV), was 0.47 (0.16) vs 0.33 (0.19) (p = 0.0009), and 0.62 (0.14) vs 0.45 (0.23) (p = 0.0004) and matrix-T, expressing amount of matrix per unit arteriolar surface, 2.38 (0.38) micron vs 1.44 (0.30) micron (p = 0.004), and 1.62 (0.28) micron vs. 1.03 (0.34) (p = 0.0009). Patients with normoalbuminuria showed no significant differences from the control group, and had lower values than microalbuminuric patients for all parameters except the afferent matrix-T. In the normoalbuminuric group a correlation was found between parameters for afferent arterioles and those for glomerular structure. In conclusion there is arteriolar accumulation of extracellular material in the early phase of diabetic nephropathy, concomitant with early glomerulopathy.

Overexpression of glucose transporters in rat mesangial cells cultured in a normal glucose milieu mimics the diabetic phenotype

An environment of high glucose concentration stimulates the synthesis of extracellular matrix (ECM) in mesangial cell (MC) cultures. This may result from a similar increase in intracellular glucose concentration. We theorized that increased uptake, rather than glucose concentration per se is the major determinant of exaggerated ECM formation. To test this, we compared the effects of 35 mM glucose on ECM synthesis in normal MCs with those of 8 mM glucose in the same cells overexpressing the glucose transporter GLUT1 (MCGT1). Increasing medium glucose from 8 to 35 mM caused normal MCs to increase total collagen synthesis and catabolism, with a net 81-90% increase in accumulation. MCs transduced with the human GLUT1 gene (MCGT1) grown in 8 mM glucose had a 10-fold greater GLUT1 protein expression and a 1.9, 2.1, and 2.5-fold increase in cell myo-inositol, lactate production, and cell sorbitol content, respectively, as compared to control MCs transduced with bacterial beta-galactosidase (MCLacZ). MCGT1 also demonstrated increased glucose uptake (5-fold) and increased net utilization (43-fold), and greater synthesis of individual ECM components than MCLacZ. In addition, total collagen synthesis and catabolism were also enhanced with a net collagen accumulation 111-118% greater than controls. Thus, glucose transport activity is an important modulator of ECM formation by MCs; the presence of high extracellular glucose concentrations is not necessarily required for the stimulation of matrix synthesis.

[Lys(B28), Pro(B29)]-human insulin: effect of injection time on postprandial glycemia

BACKGROUND

[Lys(B28), Pro(B29)]-human insulin (lispro) is an insulin analogue with a reduced capacity for self-association and faster absorption from subcutaneous injection sites. We hypothesized that administration of lispro closer to a meal would result in better glucose control than that achieved with regular insulin.

METHODS

This trial used a randomized crossover design that consisted of a period of metabolic stabilization lasting 9 days followed by an evaluation period lasting 5 days. The patients received weight-maintenance diets, and insulin doses were adjusted as needed. Calorie intake, insulin dose, and activities were kept constant once the evaluation period began. During the evaluation period, we varied the time between insulin injection and mealtime and assessed glucose control.

RESULTS

During the evaluation period, the lowest mean glucose concentrations were 117.9 mg/dl for lispro and 119.8 mg/dl (p = 0.817) for regular insulin. To obtain these, we gave lispro, on average, 22.5 minutes before meals and regular insulin 63.8 minutes before meals (p = 0.006). A similar pattern was evident throughout the glucose control parameters. The exception was mean amplitude of glucose excursion, which was lower after lispro (59 versus 75 mg/dl; p = 0.007) compared with regular insulin.

CONCLUSIONS

We achieved equal or slightly better glucose control, as reflected by mean amplitude of glucose excursion, with insulin lispro given much closer to meal time than that achieved with regular insulin. As a result of these findings, we propose that a rapidly absorbed analogue of insulin is capable of achieving better control of postprandial glucose at a more convenient injection time.

Glucose-induced alteration of integrin expression and function in cultured human mesangial cells

Alteration in mesangial volume, due to an increase of the matrix surrounding mesangial cells, is a hallmark indicator of nephropathy in diabetes. Mesangial cells may also play a significant role in the development of nephropathy. Therefore, we examined the effect of glucose on the expression of integrins by cultured human mesangial cells and their ability to interact with collagen IV, a major component of the mesangial matrix. Human mesangial cells were grown in 5 and 25 mM glucose and their integrin profile was examined by immunoprecipitation and flow cytometry in each experimental condition. The results indicate that when mesangial cells were grown in 25 mM glucose, the expression of integrin subunit alpha 2, was increased, while the alpha 1 subunit was considerably decreased, as compared to cells grown in 5 mM glucose. Additionally, mesangial cells were tested for their ability to adhere to collagen IV in a solid-phase assay in the presence of neutralizing antibodies to integrin subunits. The results of these experiments indicate that both alpha 1 and alpha 2 complexed to beta 1 (alpha 2 beta 1 and alpha 1 beta 1) are major mesangial cell receptors for adhesion to collagen IV both in 5 and 25 mM glucose. The two receptors act in concert to mediate adhesion of mesangial cells to type IV collagen. When cell surface expression of the alpha 1 subunit in 25 mM glucose was reduced, the alpha 2 subunit was involved in adhesion to a greater extent than it was in 5 mM glucose. Immunoperoxidase histochemical studies localized both alpha 1 and alpha 2 integrin subunits in the mesangium of normal adult kidneys, suggesting that in vivo interaction with collagen IV could involve both of these receptors. These observations suggest that glucose-induced alterations in integrin expression may modify the ability of mesangial cells to interact with collagen IV.

PDGF and TGF-beta mediate collagen production by mesangial cells exposed to advanced glycosylation end products

Deposition of type III collagen protein is increased when cultured rat mesangial cells are cultured in media containing high glucose concentrations. Possible mechanisms for this effect include the production of growth factors, such as PDGF and TGF-beta, and the formation of abnormal glucose-protein adducts called advanced glycosylation end products (AGEs). In our studies, neutralizing antibodies to PDGF and TGF-beta prevented increased type III collagen deposition by mesangial cells exposed either to high glucose media or to low glucose media containing AGEs. Daily addition of PDGF or TGF-beta stimulated type III collagen production. However, while co-incubation with the TGF-beta Ab prevented PDGF-stimulated type III collagen production, the PDGF Ab did not prevent TGF-beta-stimulated type III collagen production. Daily addition of PDGF or TGF-beta stimulated, while AGEs inhibited, mesangial cell proliferation after 96 hours. We propose that high extracellular glucose and AGEs stimulate type III collagen production by pathways that involve the intermediate formation of PDGF and TGF-beta by mesangial cells. PDGF may increase type III collagen production by stimulating the intermediate production of TGF-beta. Exposure to high glucose, AGEs, or TGF-beta also leads to impaired mesangial cell proliferation. The autocrine effects of TGF-beta and PDGF play important roles in the effects of high extracellular glucose and AGEs on cultured mesangial cells.

Effect of high glucose on formation of extracellular matrix components by cultured rat heart endothelial cells

In an attempt to define the basis for the microvascular changes observed in diabetic myocardium, a study was undertaken on the effect of elevated glucose on the synthesis by rat heart endothelial cells of the extracellular matrix components, types VI, IV and I collagen, as well as fibronectin. Confluent cultures of these cells, isolated by fluorescence-activated cell sorting after treatment with rhodamine-labelled acetylated low density lipoprotein, showed a three to fivefold enhancement in the synthesis of type VI collagen after exposure for 48 h to high glucose (20 to 30 mmol/l), as determined by immunoblot analysis. Increased production of type IV collagen and fibronectin was also observed, but the change was smaller and no effect on type I collagen was found. Measurement of mRNA levels by hybridization with cDNA probes indicated that 48-h exposure to high glucose significantly increased the level of transcripts for type VI and IV collagens but not for type I collagen. While glucose consumption by endothelial cells in high glucose doubled in the initial 24-h period, utilization returned to normal by 48 h, concomitant with a reduction in GLUT1 transcript levels, suggesting that signals for stimulation of collagen synthesis must be active during the initial period of exposure to elevated glucose levels.

Glucose entry into rat mesangial cells is mediated by both Na(+)-coupled and facilitative transporters

Since previous studies from our laboratory have demonstrated that increased glucose consumption by cultured rat mesangial cells is accompanied by an accelerated production of type IV and type VI collagen, we have now examined the manner by which glucose is transported into these cells. A progressive stimulation of glucose uptake by the mesangial cells was observed with increasing concentrations of NaCl so that at 145 mmol/l about twice as much glucose entered the cells as in its absence (substituted by choline chloride). Moreover, since phlorizin inhibited the NaCl-promoted uptake of glucose and this salt was found to increase the accumulation of alpha-methylglucoside in a manner which could not be duplicated by KCl or mannitol, both Na(+)-coupled and facilitative glucose transporters appeared to be present in the cells. Km values of 1.93 mmol/l and 1.36 mmol/l were determined for the co-transport and facilitated transport pathways, respectively, with their Vmax being 29.5 and 18.0 nmol.mg protein-1.h-1. Both uptake activities were found to be down-regulated by exposure of the cells to high glucose and furthermore the Na(+)-dependent transport could no longer be detected after about 12 passages of the cells. Hybridization of mesangial cell mRNA with cDNA probes revealed transcripts for the Na+/glucose co-transporter as well as GLUT1 and to a lesser extent GLUT4.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycated albumin modified by Amadori adducts modulates aortic endothelial cell biology

Increased protein glycation has been mechanistically linked to accelerated vascular pathobiology in diabetes. To test the influence of protein modified by Amadori glucose adducts on vascular cell biology, we examined the effect of glycated albumin on replicative capacity and basement membrane collagen production by aortic endothelial cells in culture. Relative to carbohydrate-free albumin, which supported cell proliferation and Type IV collagen synthesis, glycated albumin significantly inhibited 3H-thymidine incorporation and Type IV collagen production. The glycated albumin-induced effects were prevented by monoclonal antibodies (A717) that specifically react with Amadori-modified albumin, but not by IgG that was unreactive with glycated albumin. A717 had no effect on thymidine incorporation or collagen synthesis by cells cultured in the presence of nonglycated albumin. The findings indicate that the interaction of glycated albumin with endothelial cells, which have been shown to display dose-responsive, saturable receptors, limits cell replication and triggers maladaptive biosynthetic programs, which may contribute to degenerative macrovascular disease in diabetes.

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.

Expression of transforming growth factor-beta 1 during diabetic renal hypertrophy

Experimental type I diabetes mellitus is characterized by an early increase in kidney weight and glomerular volume, but changes in gene expression accompanying diabetic renal growth have not been fully elucidated. In the current study, total RNA was extracted from renal cortex and isolated glomeruli of streptozotocin-induced diabetic rats 24 hours, 48 hours, 96 hours, one and two weeks after the onset of hyperglycemia (blood glucose > 15 mmol/liter), insulin-treated diabetic rats (blood glucose < 6.0 mmol/liter), and normal rats. RNA samples were reverse transcribed (RT) and subjected to polymerase chain reaction (PCR) amplication with specific 5' and 3' primers for rat transforming growth factor (TGF-beta 1) and beta-actin. RT-PCR analysis revealed that glomerular TGF-beta 1 mRNA levels increased relative to beta-actin as early as 24 hours after the onset of hyperglycemia, reaching a plateau after 96 hours that was sustained at one and two weeks. In cortical samples, TGF-beta 1 mRNA levels increased less abruptly, reaching a peak one week after the onset of hyperglycemia. Intensive insulin treatment to normalize blood glucose levels attenuated the rise in glomerular and renal cortical TGF-beta 1 mRNA. Cryostat sections of rat kidneys were immunostained for TGF-beta 1 utilizing a polyclonal anti-porcine TGF-beta 1 antibody and semiquantitative scoring of TGF-beta 1 immunostaining revealed a twofold increase in diabetic glomeruli after two weeks compared to normal glomeruli. Increased segmental immunostaining for TGF-beta 1 was also evident in cortical tubules of diabetic rats. These studies establish that TGF-beta 1 expression in the kidney increases during the phase of rapid renal hypertrophy in diabetic rats. Normalization of blood glucose levels with insulin treatment attenuates the increase in TGF-beta 1 expression.

Identification of multiple genes in bovine retinal pericytes altered by exposure to elevated levels of glucose by using mRNA differential display

Loss of capillary pericytes, a characteristic finding in diabetic retinopathy, is strongly associated with hyperglycemia. The pathologic aberrations associated with diabetic retinopathy are localized primarily in the retinal capillaries and are only poorly reversed by subsequent euglycemic control. Since hyperglycemia significantly inhibits pericyte growth in culture, we investigated the regulation of gene expression in retinal pericytes exposed to physiologic (5.5mM) and pathologic (20 mM) glucose concentrations. By utilizing modifications of the mRNA differential display technique, over 14,000 mRNA species were screened, and 35 candidate clones were obtained. Partial DNA sequence demonstrated that 25 of these were distinct genes, including 7 known, 16 previously unreported, and 2 sequences with known homologues. Northern blot analysis demonstrated altered gene expression in 10 (40%), undetectable signals in 12 (48%), and nonregulation in 3 (12%). Genes with glucose-regulated expression included those encoding fibronectin (51% +/- 15%, P = 0.003; mean percentage of control +/- SD), caldesmon (68% +/- 18%; P = 0.026), two ribosomal proteins (201% +/- 72%, P = 0.011; 136% +/- 16%, P = 0.036), Rieske FeS reductase (66% +/- 17%; P = 0.029), three previously unreported sequences (57%, 167%, 271%), and molecules homologous to autoantigens (213%) and tyrosine kinases (down 16- to 33-fold). Caldesmon protein concentrations in pericytes and smooth muscle cells demonstrated decreases by Western blot analysis concordant with mRNA levels. These studies identify genes whose expression is significantly altered after 7 days of exposure to elevated glucose levels and provide new targets for understanding the adverse effects of hyperglycemia on vascular cells. In addition, this study provides strong support for the use of differential mRNA display as a method to rapidly isolate differentially expressed genes in metabolic systems.

Amelioration of diabetic nephropathy by treatment with monoclonal antibodies against glycated albumin

The pathogenesis of diabetic nephropathy is incompletely understood, but increased nonenzymatic glycation of proteins is considered an important contributory factor. Glycated albumin, which is increased in diabetic sera and is preferentially transported into the renal glomerulus, induces an increase in Type IV collagen production and a decrease in proliferative capacity by mesangial cells in culture. These effects resemble the abnormalities that characterize the glomerular mesangium in diabetes and are prevented by monoclonal antibodies that specifically react with Amadori adducts in glycated albumin. To explore the possibility that the in vitro effects of glycated albumin on mesangial cell biology pertain to the in vivo situation, we examined the effect of treatment with the A717 monoclonal antibodies on glomerular functional and structural changes in a rodent model of genetic diabetes, the db/db mouse. Weekly parenteral antibody administration reduced the elevated albumin excretion and attenuated the mesangial expansion that were observed in the untreated db/db mice that served as controls. Monoclonal antibody treatment also was shown to lower plasma concentrations of glycated albumin in diabetic mice. Thus, reducing glycated albumin concentrations and/or blocking its biologically active epitopes has a salutary influence on the pathogenesis of diabetic nephropathy. The findings indicate that glycated albumin participates in the development of the glomerular lesion in the db/db mouse, and suggest a new approach to the therapy of this complication of diabetes.

Amadori glucose adducts modulate mesangial cell growth and collagen gene expression

Diabetic serum contains increased concentrations of glycated proteins, which are preferentially transported into the renal glomerulus. We investigated effects of Amadori glucose adducts in serum proteins, the predominant form in which circulating glycated proteins exist in vivo, on glomerular mesangial cells, where the lesion of diabetic nephropathy originates. [3H]-thymidine incorporation by murine mesangial cells was significantly inhibited when cells were grown in the presence of serum glycated by incubation for four days with 28 mM glucose or when cells were cultured in microtiter plates that had been precoated with glycated serum. This effect was prevented by a monoclonal antibody immunoreactive with Amadori adducts in glycated albumin, and unreactive with other glycated serum proteins or with advanced glycation end (AGE) products. Glycated serum stimulated Type IV collagen gene expression and increased Type IV collagen secretion, an effect also prevented by monoclonal antibodies reactive with Amadori adducts in glycated albumin. The glycation-induced changes in proliferation, collagen synthesis and collagen gene expression were observed in media containing normal glucose concentration and were exaggerated in media containing high glucose concentration. The data indicate that Amadori products of glycated serum proteins induce mesangial cell abnormalities that are highly relevant to the pathogenesis of diabetic nephropathy, and that these effects are accentuated when glycated serum proteins are presented in a hyperglycemic milieu. The data also suggest that mesangial cells specifically recognize Amadori adducts in glycated albumin.

Stimulation of collagen gene expression and protein synthesis in murine mesangial cells by high glucose is mediated by autocrine activation of transforming growth factor-beta

Previous investigations have demonstrated that growing mesangial cells in high glucose concentration stimulates extracellular matrix synthesis and also increases the expression of TGF-beta. We tested whether the stimulation of extracellular matrix production is mediated by autocrine activation of TGF-beta, a known prosclerotic cytokine. Addition of neutralizing anti-TGF-beta antibody, but not normal rabbit IgG, significantly reduced the high glucose-stimulated incorporation of 3[H]proline. Denaturing SDS-PAGE revealed that mainly collagen types I and IV were stimulated by high (450 mg/dl) D-glucose. This high glucose-mediated increase in collagen synthesis was reduced by the anti-TGF-beta antibody. Treatment of mesangial cells grown in normal (100 mg/dl) D-glucose with 2 ng/ml recombinant TGF-beta 1 mimicked the effects of high glucose. Furthermore, the anti-TGF-beta antibody significantly reduced the increase in mRNA levels encoding alpha 2(I) and alpha 1(IV) collagens induced by high glucose. Thus, the high glucose-stimulated increase of collagen production in mesangial cells is mediated, at least in part, by autocrine TGF-beta activation. We postulate that the interception of the glomerular activity of TGF-beta may be an effective intervention in the management of diabetic nephropathy.

The extracellular matrix in diabetic nephropathy

In the subgroup of diabetic patients who are destined to develop the full spectrum of the clinical syndrome of diabetic nephropathy, the kidney is afflicted with a series of distinct structural lesions principally involving the extracellular matrices. Diabetic nephropathy is characterized by hypertrophy of both glomerular and tubular elements, progressive accumulation of extracellular matrix components in the glomerular mesangium, and thickening of the glomerular and tubular basement membranes. Albeit less well recognized, progressive tubulointerstitial fibrosis is also a feature of the syndrome. Irrespective of pathogenetic mechanisms (be they metabolic, hemodynamic, or genetic), the structural changes involving the renal extracellular matrix compartments are believed to be the basis for the appearance of overt dysfunction, namely, proteinuria, hypertension, and renal failure. Therefore, a full understanding of the mechanisms that culminate in irreversible kidney failure requires a closer inspection of the status of the extracellular matrix in diabetes. This review outlines the different structural changes that typically occur during the course of the disease. Both glomerular and tubulointerstitial changes are reviewed. Valuable structural-functional correlations have been derived from examining kidney specimens obtained from patients with a wide spectrum of disease stages. Experimental animal models, supplanted with recent investigations in tissue culture on the effect of high ambient glucose levels, have increased our understanding of the cellular mechanisms that underlie the disordered matrix composition. Alterations in the metabolism of the collagens, proteoglycans, and other matrix constituents are reviewed.(ABSTRACT TRUNCATED AT 250 WORDS)