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Biomedical subjects

M P Cohen

Publications and source records attributed to M P Cohen.

At least 19 recordsLinked to original sources
PubMed1998

Glycated albumin stimulates fibronectin gene expression in glomerular mesangial cells: involvement of the transforming growth factor-beta system.

Albumin modified by Amadori glucose adducts, formed in increased amounts in diabetes, stimulates collagen IV production and gene expression in renal glomerular mesangial cells, and induces mesangial matrix accumulation accompanied by increased mRNA encoding alpha 1 (IV) collagen and fibronectin in diabetic animals. These effects contribute to the pathogenesis of diabetic nephropathy, and resemble biologic activities of the cytokine TGF-beta 1, which also has been causally implicated in diabetic renal disease. We postulated that Amadori-modified glycated albumin modulates TGF-beta 1 expression in mesangial cells, and that TGF-beta 1 participates in mediating the glycated albumin-induced increases in mesangial cell matrix production. To test this hypothesis, we measured mRNA encoding TGF-beta 1, the TGF-beta Type II receptor and fibronectin, a key matrix component of the TGF-beta 1 tissue response, after incubation of mesangial cells with glycated albumin. Steady state levels of the mRNAs encoding for these proteins were stimulated when mesangial cells were cultured in the presence of albumin containing Amadori glucose adducts compared with levels in cells cultured with the nonglycated, glucose-free counterpart. The glycated protein-induced changes in mRNA expression were observed with concentrations of glycated albumin encompassing those found in clinical specimens and in media containing physiologic (5.5 mM) glucose concentrations, indicating that they were due to the glucose-modified protein and not to a hyperglycemic milieu. Further, they were accompanied by increased translated fibronectin protein, which was prevented with TGF-beta neutralizing antibody, as was the glycated albumin-induced increase in fibronectin mRNA. The findings indicate that Amadori-modified glycated albumin stimulates mesangial cell TGF-beta 1 gene expression by mechanisms that are operative under normoglycemic conditions. These data provide the first link between elevated glycated serum albumin concentrations and increased TGF-beta 1 bioactivity in the pathogenesis of mesangial matrix accumulation in diabetes.

Animals↗
PubMed1997

Glycated albumin stimulates fibronectin and collagen IV production by glomerular endothelial cells under normoglycemic conditions.

Albumin modified by Amadori glucose adducts, formed in increased amounts in diabetes, stimulates the synthesis of matrix by renal glomerular mesangial cells and has been causally linked to the pathogenesis of diabetic nephropathy. However, the effect of glycated albumin on the biology of glomerular endothelial cells, which elaborate a basement membrane that undergoes thickening in diabetes, has not been investigated. We used well-characterized rat glomerular endothelial cells to examine the influence of glycated albumin on the synthesis of extracellular matrix proteins by these cells in culture. Concentrations of glycated albumin that are present in clinical specimens stimulate fibronectin and collagen IV production by glomerular endothelial cells, and this effect is operative under normoglycemic conditions. These results support the hypothesis that increased glycated albumin contributes to glomerular basement membrane thickening in diabetes.

Animals↗
PubMed1997

RAGE mRNA expression in the diabetic mouse kidney.

Receptors for advanced glycation end products (RAGE), which bind and internalize AGE-modified proteins formed from oxidation and other products of the nonenzymatic glycation reaction, have been mechanistically implicated in the development of the chronic complications of diabetes. In the present experiments, we sought evidence for the participation of RAGE in diabetic nephropathy by analysis of steady state levels of mRNA encoding RAGE in the renal cortex of a well-defined animal model (the db/db mouse) that develops renal pathology similar to that found in human diabetes. In these animals, increased AGE-product formation was confirmed by measurement of fluorescence in serum and renal cortex proteins. Renal involvement was confirmed by demonstration of increased urine albumin excretion and elevated serum creatinine concentrations relative to nondiabetic (db/m) littermate controls. Despite elevated concentrations of circulating and tissue AGE-modified proteins, the level of RAGE mRNA expression in renal cortex of diabetic mice did not significantly differ from that in nondiabetic littermate controls. The findings militate against changes in RAGE expression in the pathogenesis of renal abnormalities in this animal model.

Albuminuria↗
PubMed1996

Glycated albumin promotes a generalized vasculopathy in the db/db mouse.

Increased protein glycation has been mechanistically linked to accelerated vascular pathobiology in diabetes. Because glycated albumin induces biosynthetic abnormalities in cultured aortic endothelial cells that resemble those associated with macrovascular disease, we sought evidence that increased glycated albumin is operative in the genesis of diabetic vasculopathy in vivo. Plasma concentrations of fibronectin, a sensitive marker of endothelial cell damage, were increased two-fold in diabetic db/db mice compared with their nondiabetic db/m littermates. Treatment with monoclonal antibodies specifically reactive with albumin modified by Amadori glucose adducts normalized fibronectin in diabetic animals despite persistent hyperglycemia. These findings suggest that increased glycated albumin causally contributes to diabetic vasculopathy, and that blocking this influence ameliorates vascular damage.

Aging↗
PubMed1996

Prevention of decline in renal function in the diabetic db/db mouse.

We recently reported that when diabetic db/db mice, which develop glomerular pathology resembling that in human diabetes mellitus, are treated with monoclonal antibodies (A717) that neutralize the effects of excess glycated albumin, there is an amelioration of mesangial expansion, renal overexpression of mRNAs encoding for the extracellular matrix proteins collagen IV and fibronectin and proteinuria. These findings suggested that A717 might also retard the development of compromised renal function in this animal model. To examine this possibility, serum creatinine and blood urea nitrogen (BUN) were measured in diabetic db/db mice and their non-diabetic db/m littermates before and after an 8-week course of treatment with A717 or irrelevant murine immunoglobulin (MIg). Early in the course of diabetes, BUN and serum creatinine concentrations did not significantly differ from those in the db/m littermates, but were significantly increased after 10 weeks of sustained hyperglycaemia. Treatment of db/db mice with A717 prevented the rise in creatinine and attenuated the elevation in BUN. A717 also prevented the decrease in creatinine clearance observed in diabetic compared with non-diabetic animals (2.2 +/- 0.8 vs 4.1 +/- 0.3 vs 5.0 +/- 1.1 ml/h in db/db vs db/db-A717 vs db/m, respectively). MIg did not alter the change in renal function with time in db/db mice. Taken together with our previous results, the present findings indicate that the diabetic db/db mouse develops changes in renal function and structure that parallel the course of human diabetic nephropathy in nature and chronology and demonstrate, for the first time, that therapy directed against increased glycated albumin can prevent the decline in renal function in this rodent model of genetic diabetes.

Analysis of Variance↗
PubMed1996

The design and synthesis of substituted biphenyl libraries.

A novel scaffold system for the generation of diversity libraries has been designed which allows for rapid modification not only of functional groups, but their spatial arrangements as well. The biphenyl scaffold allows for display of three or four diverse functional groups in a wide variety of spatial arrangements depending on the substitution pattern selected. The libraries are generated by a combination of solution and solid-phase chemistries and are cleaved off the solid-support for screening.

Biphenyl Compounds↗
PubMed1996

Role of Amadori-modified nonenzymatically glycated serum proteins in the pathogenesis of diabetic nephropathy.

Accelerated nonenzymatic glycation in diabetes, resulting in Amadori-modified proteins and the later-developing advanced glycation end-products, has been mechanistically linked to the pathogenesis of diabetic nephropathy. Recent focus on putative AGE-induced pathophysiology has shifted attention from the possible role of Amadori-modified proteins in the development of diabetic complications. Ample experimental evidence has demonstrated that Amadori-modified serum proteins adversely affect renal glomerular capillary function, structure, and metabolism. Previous studies from the laboratories of this study's authors have shown that human serum containing diabetic concentrations of albumin modified by Amadori-glucose adducts inhibits the replication of murine mesangial cells in culture and stimulates the production and gene expression of type IV collagen. Monoclonal antibodies (A717) specific for Amadori-glycated albumin prevent these abnormalities. In other studies, it has also been shown that in vivo administration of A717 (Fab fragments) retards the progression of diabetic nephropathy in diabetic db/db mice. Neutralizing the effects of the elevated circulating glycated albumin concentration is associated with reduction in proteinuria and mesangial matrix expansion, and prevention of the overexpression of mRNA encoding type IV collagen and fibronectin in the renal cortex. The renoprotective effects of A717 are independent of any change in blood glucose concentrations. These studies implicate Amadori-modified glycated albumin in the pathogenesis of diabetic nephropathy. It is proposed in this study that abrogating the biologic effects of increased glycated albumin in diabetes has novel therapeutic potential in the management of diabetic renal complications.

Aging↗
PubMed1995

Albumin modified by Amadori glucose adducts activates mesangial cell type IV collagen gene transcription.

The direct relationship between elevated glucose concentrations and accelerated protein glycation has implicated increased glycation as a potential mechanistic link between hyperglycemia and the pathogenesis of diabetic nephropathy. Albumin modified by Amadori glucose adducts has been shown to stimulate collagen secretion by mesangial cells in vitro, and to contribute to the overproduction of glomerular mesangial matrix in vivo. To delineate mechanisms responsible for these effects, we examined the influence of glycated albumin on transcriptional activation of the alpha 1 (IV) collagen gene in renal glomerular mesangial cells. These experiments used a stably transfected reporter mesangial cell line that exhibits responses to media manipulations that are directionally parallel with those of non-transformed mesangial cells, and that expresses luciferase driven by 5'-flanking and first intron regions of the alpha 1 (IV) collagen gene. In these cells, purified glycated albumin stimulated collagen IV gene transcription, whereas glucose-free albumin did not. Further, glycated albumin induced a significant increase in mesangial cell collagen IV mRNA, assessed by Northern blot analysis and quantified by calculation of the ratio of collagen IV mRNA to 18S ribosomal RNA after densitometric scanning. The stimulation of collagen gene transcription and mRNA expression were both prevented by monoclonal antibodies known to specifically recognize Amadori-modified albumin. The findings indicate that glycated albumin promotes mesangial cell transcriptional activation and mRNA expression of the alpha 1 (IV) collagen gene and further implicate increased glycated albumin in diabetes in the pathogenesis of diabetic nephropathy.

Animals↗
PubMed1995

Evidence for a ligand receptor system mediating the biologic effects of glycated albumin in glomerular mesangial cells.

Mesangial cells cultured with albumin modified by Amadori glucose adducts exhibit decreased proliferation in association with increased elaboration of Type IV collagen. To test the hypothesis that this modulation of mesangial cell biology is linked to ligand binding, we examined renal glomerular mesangial cells for the expression of receptors that interact with Amadori-modified albumin. Murine mesangial cells bound glycated albumin in a dose-dependent and saturable manner, displaying high and low affinity binding sites. Binding of glycated but not nonglycated albumin was inhibited by monoclonal antibodies that specifically react with albumin containing fructosyllysine groups. LDL containing Amadori glucose adducts did not compete with glycated albumin for binding. These results are consistent with ligand selectively of the binding sites for an Amadori-modified sequence within an albumin domain and suggest that a ligand receptor system mediates the effects of glycated albumin on mesangial cell proliferation and matrix production.

Animals↗
PubMed1995

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.

Animals↗
PubMed1995

Treatment with acarbose, an alpha-glucosidase inhibitor, reduces increased albumin excretion in streptozotocin-diabetic rats.

1. We examined the effect of the alpha-glucosidase inhibitor acarbose on urinary albumin excretion (UAE) in streptozotocin diabetic rats. 2. Treatment with acarbose for 8 weeks after induction of diabetes prevented the significant increase in UAE observed in untreated diabetic rats relative to nondiabetic controls. 3. Acarbose significantly reduced integrated glycemia, which correlated with albumin excretion rates, and exerts a salutary effect on diabetic renal dysfunction.

Acarbose↗
PubMed1995

Prevention of diabetic nephropathy in db/db mice with glycated albumin antagonists. A novel treatment strategy.

Accelerated protein glycation in diabetes has been mechanistically linked to the pathogenesis of diabetic nephropathy. Because glycated albumin induces abnormalities in cultured mesangial cells that resemble those characterizing the glomerular mesangium in diabetes, and monoclonal antibodies (A717) specific for Amadori-modified glycated albumin prevent these abnormalities, we postulated that in vivo administration of A717 could retard the progression of diabetic nephropathy. To test this hypothesis, diabetic db/db mice and their nondiabetic db/m littermates were treated with eight consecutive weekly injections of 150 micrograms of A717 (Fab fragments) to reduce the elevated plasma glycated albumin concentration, or with irrelevant murine IgG (MIg). Relative to nondiabetics, diabetic mice (MIg treated) manifested proteinuria (3.35 +/- 0.15 vs 0.87 +/- 0.1 mg albumin/mg creatinine), 3.8-fold increase in mesangial matrix fraction, and renal cortical overexpression of mRNAs encoding alpha 1(IV) collagen (2.6-fold increase) and fibronectin (3.8-fold increase). Treatment of db/db mice with A717 significantly reduced the proteinuria (1.52 +/- 0.3 mg/mg creatinine), inhibited mesangial matrix expansion, and attenuated overexpression of matrix mRNAs. The nephropathic protective effects of A717 were independent of any change in blood glucose concentrations. Antibodies unreactive with glycated albumin did not duplicate the beneficial effects of A717. Thus, abrogating the biologic effects of increased glycated albumin with A717 has a salutary influence on the pathogenesis of diabetic nephropathy and has novel therapeutic potential in its management.

Albuminuria↗
PubMed1994

Receptors specific for Amadori-modified glycated albumin on murine endothelial cells.

Albumin modified by Amadori glucose adducts has been shown to modulate endothelial and glomerular mesangial cell biology. Recognizing that circulating proteins may trigger cellular events through ligand binding, we examined murine aortic endothelial cells for the expression of a receptor system that recognizes fructosyllysine epitopes in glycated albumin. Endothelial cells contain membrane-associated polypeptides that bind Amadori-modified glycated albumin and exhibit traditional receptor characteristics of dose-responsivity, saturability and ligand specificity. Nonglycated albumin does not compete for binding to the receptor, and the interaction of glycated albumin with its receptor is blocked by a monoclonal antibody that selectively reacts with the Amadori adduct in glycated albumin. The findings suggest that a ligand-receptor system specific to Amadori glucose adducts mediates the biologic effects of glycated albumin.

Animals↗
PubMed1994

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.

Albuminuria↗
PubMed1994

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.

Animals↗
PubMed1994

Glycated albumin: a marker of glycaemic status in rats with experimental diabetes.

Monoclonal antibodies that specifically recognize non-enzymatically glycated epitopes residing in albumin were used to measure levels of glycated albumin in the plasma of control and streptozotocin diabetic rats. Standard or sample was incubated with monoclonal antibody immobilized onto preactivated tubes, and binding was detected with enzyme-conjugated polyclonal antibody to rat albumin and substrate. Rat glycated albumin exhibited a linear dose response in the assay, and plasma samples contained between 30-100 micrograms/50 microliters. Levels were significantly increased in diabetic compared with control rats, and correlated positively and significantly with mean blood glucose concentrations measured in the fasting and fed states. The results indicate that glycated albumin levels measured by immunoassay reflect recent integrated glycaemia and provide and objective index of glycaemic status in the rat experimental model of diabetes.

Animals↗
PubMed1993

Effects of glycated albumin on mesangial cells: evidence for a role in diabetic nephropathy.

Nonenzymatically glycated proteins are preferentially transported across the glomerular filtration barrier, and the glomerular mesangium in diabetes is bathed with serum containing increased concentrations of glycated albumin. We investigated effects of glycated albumin on mesangial cells, which are involved in diabetic nephropathy. [3H]-thymidine incorporation was significantly inhibited when murine mesangial cells were grown in culture media containing human serum that had been nonenzymatically glycated by incubation for 4 days with 28 mM glucose. This inhibition was reversed when monoclonal antibodies that selectively react with Amadori products of glycated albumin were added to the culture media. Purified glycated albumin containing Amadori adducts of the glycation reaction induced significant inhibition of thymidine incorporation and stimulation of Type IV collagen secretion compared with cells cultured in the presence of purified nonglycated albumin. These changes were prevented when monoclonal antibodies specifically reactive with fructosyl-lysine epitopes in glycated albumin were added to the cultures. The antibodies had no effect on growth or collagen production in the presence of nonglycated albumin. The results provide the first evidence directly implicating Amadori adducts in glycated albumin in the pathogenesis of diabetic nephropathy, which is characterized by decreased cellularity in association with expansion of the mesangial matrix.

Animals↗