Involvement of beta 2-microglobulin modified with advanced glycation end products in the pathogenesis of hemodialysis-associated amyloidosis. Induction of human monocyte chemotaxis and macrophage secretion of tumor necrosis factor-alpha and interleukin-1

Osteoarticular disorders of renal origin: disease-related and iatrogenic

Osteoarticular disorders significantly limit the quality of long-term survival with chronic renal failure. beta 2M amyloidosis is a complication of chronic renal failure that has been recognized mostly in patients receiving long-term haemodialysis. Patients with beta 2M amyloidosis typically present with the triad of shoulder periarthritis, carpal tunnel syndrome, and flexor tenosynovitis of the hands. Other musculoskeletal manifestations of beta 2M amyloidosis include destructive spondyloarthropathy, cervico-occipital pseudotumours, bone cysts, and pathological fractures. At present, only renal transplantation may slow or halt the progession of beta 2M amyloidosis. Crystal-induced arthropathy, most commonly caused by basic calcium phosphate crystals, is an important cause of acute joint inflammation in the patient with renal failure. The incidence of bone and joint infection is increased in patients undergoing dialysis. Haemodialysis and peritoneal dialysis are also associated with an erosive or destructive arthropathy of finger joints, which is not explained by local amyloid deposition.

Role of interleukin-6 in beta2-microglobulin-induced bone mineral dissolution

BACKGROUND

beta2-microglobulin (beta2m) amyloidosis is commonly seen in patients undergoing long-term dialysis. beta2m has been shown to induce in vitro bone mineral dissolution. The present study was designed to investigate the effect of beta2m on osteoblast function and the role of interleukin-6 (IL-6) on beta2m-induced bone resorption.

METHODS

Using neonatal mouse calvariae as well as primary osteoblasts and MC 3T3 osteoblast-like cells, IL-6 production, release, and gene expression were investigated with enzyme-linked immunosorbent assay (ELISA) and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) techniques, respectively.

RESULTS

In calvariae, beta2m induced a time- and dose-dependent calcium release, which was maximum following a 48-hour incubation at a concentration of 10-5 mol/L. beta2m (10-6 mol/L) also induced a significant release of IL-6 from calvarial and primary osteoblastic cultures. Using 10-6 mol/L beta2m, the amount of IL-6 mRNA in MC 3T3 cells increased in a time-dependent fashion, which peaked at 3 hours and declined to baseline by 12 hours. In primary osteoblast cells, beta2m maximally increased IL-6 mRNA levels at 6 hours; however, they remained elevated up to 24 hours. Compared with control, the presence of beta2m significantly increased cell proliferation of both primary osteoblasts and MC 3T3 cells. To investigate osteoblastic function further, osteocalcin mRNA was quantitated. Incubation with beta2m for 3 to 24 hours did not alter the amount of osteocalcin mRNA in the MC 3T3 osteoblast cells.

CONCLUSION

beta2m affects bone metabolism by mechanisms that include increasing IL-6 gene expression and release, and enhancing osteoblast proliferation without affecting osteocalcin gene expression.

Glycoxidative modification of AA amyloid deposits in renal tissue

BACKGROUND

N(epsilon)-carboxymethyllysine (CML) is a product of the oxidative modification of glycated proteins, which damages proteins with ageing, diabetes, uraemia and Alzheimer's disease. In contrast, pyrraline is one of the advanced glycation end products, which is independent of oxidative processes. CML has been identified in beta-amyloid of Alzheimer's disease and beta(2)-microglobulin-associated amyloid. We investigated whether CML and pyrraline are formed in AA and AL amyloid of the kidney.

METHOD

Renal specimens from 19 cases of AA amyloidosis and 14 cases of AL amyloidosis were investigated for immunolocalization of CML, pyrraline, collagen type IV and laminin in amyloid deposits. Renal biopsies of 10 age-matched cases with thin basement membrane disease and normal renal function were used as controls. The fractional areas of amyloid, CML, laminin and collagen IV in glomeruli and interstitium (%amyloid, %CML, %laminin and %collagen, respectively) were calculated using the point counting method. The correlation between these parameters was evaluated using Spearman's rank correlation test.

RESULTS

CML colocalized with AA amyloid, but not AL amyloid, except in two cases of the latter with a long history of nephropathy exceeding 14 years. In contrast, pyrraline was not observed in either type of amyloid. Mean %CML in AA amyloid was significantly higher than %collagen and %laminin in glomeruli and interstitium, indicating that AA amyloid is modified by CML independent of colocalized extracellular matrix. %CML significantly correlated with %amyloid both in glomeruli and interstitium in AA amyloidosis. AL amyloid cases with a long history of nephropathy showed positive staining for CML in glomeruli and interstitium but no staining for collagen IV and laminin in amyloid deposits.

CONCLUSION

CML modification may occur in amyloid deposits of AA amyloidosis, independent of extracellular matrix components. Glycoxidative modification may have a functional link to AA amyloid deposition in renal tissues.

Transforming growth factor-beta is involved in the pathogenesis of dialysis-related amyloidosis

BACKGROUND

Advanced glycation end product-modified beta2-microglobulin (AGE-beta2m) is an important component of dialysis-related amyloidosis (DRA). Its presence induces monocyte chemotaxis and the release of the proinflammatory cytokines through macrophage activation. Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that also has chemotactic activity for monocytes at very low (0.1 to 10 pg/mL) concentrations and inhibits proinflammatory cytokine production of macrophages. In this study, we investigated the role of TGF-beta in the pathogenesis of DRA.

METHODS

We performed an immunohistochemical study of DRA tissues (8 cases) to confirm the existence of TGF-betas and their receptors; we also performed a chemotaxis assay of human monocytes as well as enzyme-linked immunosorbent assay (ELISA) of TGF-beta1, tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and interleukin-1 receptor antagonist (IL-1Ra) in the supernatant of human monocyte-derived macrophage cell culture under varying conditions of incubation with TGF-beta1, AGE-beta2m, and TGF-beta1 antibody additions.

RESULTS

There was positive staining for TGF-betas (types 1, 2, and 3) and their receptors (types I, II, and III) in infiltrated macrophages (CD68+), synovial lining cell, as well as vascular walls around amyloid deposition. AGE-beta2m also induced TGF-beta1 production by macrophages in a dose-dependent manner (410 +/- 80 pg/mL at 12.5 microg/mL, 621 +/- 62 pg/mL at 25 microg/mL, and 776 +/- 62 pg/mL at 50 microg/mL of AGE-beta2m). AGE-beta2m induced significant TNF-alpha and IL-1Ra production by macrophage. The addition of exogenous TGF-beta1 (0.1 to 10 ng/mL) decreased AGE-beta2m-induced TNF-alpha production and increased IL-1Ra production in a dose-dependent fashion. IL-1beta production was not effected by any experimental conditions. In chemotaxis assay, anti-TGF-beta1 antibody (0.1 to 10 microg/mL) attenuated AGE-beta2m-induced monocyte chemotaxis.

CONCLUSIONS

These results provide the first evidence to our knowledge for the presence of TGF-beta in DRA tissue, as well as the stimulatory action of AGE-beta2m on tissue macrophages. In turn, TGF-beta suppresses the proinflammatory activation of macrophages, suggesting a dual role for TGF-beta in the inflammatory process of DRA. These observations may provide a pathophysiologic link between TGF-beta and DRA.

Glucose degradation product methylglyoxal enhances the production of vascular endothelial growth factor in peritoneal cells: role in the functional and morphological alterations of peritoneal membranes in peritoneal dialysis

Peritoneal membrane permeability deteriorates in peritoneal dialysis (PD) patients. We test whether glucose degradation products (GDPs) in PD fluids, glyoxal, methylglyoxal and 3-deoxyglucosone, stimulate the production of vascular endothelial growth factor (VEGF), a factor known to enhance vascular permeability and angiogenesis. VEGF increased in cultured rat mesothelial and human endothelial cells exposed to methylglyoxal, but not to glyoxal or 3-deoxyglucosone. VEGF also increased in peritoneal tissue of rats given intraperitoneally methylglyoxal. VEGF and carboxymethyllysine (CML) (formed from GDPs) co-localized immunohistochemically in mesothelial layer and vascular walls of the peritoneal membrane of patients given chronic PD. By contrast, in the peritoneum of non-uremic subjects, VEGF was identified only in vascular walls, in the absence of CML. VEGF production induced by GDPs may play a role in the progressive deterioration of the peritoneal membrane.

Modification of beta 2-microglobulin with D-glucose or 3-deoxyglucosone inhibits A beta 2M amyloid fibril extension in vitro

beta 2-microglobulin (beta 2M) is a major constituent of amyloid fibrils (fA beta 2M) deposited in patients with A beta 2M amyloidosis. Recently, advanced glycation end products (AGE) of beta 2M and fA beta 2M have been suggested to play an important role in the pathogenesis of A beta 2M amyloidosis. We first characterized the states of AGE modification of fA beta 2M. Western blot analysis with a monoclonal anti-AGE antibody showed that purified fA beta 2M was naturally modified with AGE. Immunohistochemical studies of amyloid-deposited tissue have revealed a patchy distribution of the AGE-modified area in the amyloid deposits. Then we modified beta 2-m either with D-glucose or with 3-deoxyglucosone (3-DG) and investigated the effect of these modification on fA beta 2M extension in vitro, using the recently established first-order kinetic model of fA beta 2M extension in vitro. Western blot analysis and enzyme linked immunosorbent assay with a monoclonal anti-AGE antibody showed that these sugar-modified beta 2M contained AGE. During the incubation of fA beta 2M with native beta 2-m at 37 degrees C, the fluorescence of thioflavin T increased without a lag phase and proceeded to equilibrium. On the contrary, only a slight increase in fluorescence was observed during the incubation of fA beta 2M with sugar-modified beta 2M. Moreover, sugar-modified beta 2M exhibited a dose-dependent inhibitory effect on the extension reaction of fA beta 2M with native beta 2M. These results may suggest that in some in vivo situations, the modification of beta 2-m with AGE could play an inhibitory role for the formation of fA beta 2M.

Extraskeletal problems and amyloid

The major clinical manifestations of dialysis-associated A beta 2M amyloidosis are chronic arthralgias, destructive arthropathy and the carpal tunnel syndrome. For dialysis patients who have been maintained on renal replacement therapy for more than 10-15 years, this complication may become a major physical handicap. It may even be life-threatening in some instances due to cervical cord compression. Amyloid deposits in joint areas precede clinical symptoms and signs by several years. Systemic deposits may also occur but their clinical manifestations are infrequent. The diagnosis of dialysis arthropathy associated with beta 2-microglobulin-associated (A beta 2M) amyloidosis mostly relies on indirect clinical and radiological evidence. Histologic proof is rarely obtained in vivo. The pathogenesis of the disease is complex. It includes reduced elimination of beta 2M and potentially also as impaired degradation of A beta 2M as well as enhanced production of A beta 2M amyloid fibrils. Non enzymatic modifications of beta 2M probably play a role, including beta 2M protein modification with advanced glycation end-products (AGE) and advanced oxidation protein products. Modified beta 2M, collagen and proteoglycans appear actively involved in the induction of a local inflammatory response and beta 2M amyloid formation. There is also evidence in favor of treatment-related factors such as the type of hemodialysis membrane and the purity of dialysis water. Hopefully, the translation of our improving knowledge of all the factors involved will lead to a better treatment and eventually to the prevention of this dramatic complication of dialysis.

Increased oxidative stress in mouse kidneys with unilateral ureteral obstruction

BACKGROUND

Unilateral ureteral obstruction (UUO) is a well-established experimental model of renal injury leading to interstitial fibrosis. The molecular and cellular mechanism(s) of interstitial fibrosis in UUO kidney is beginning to be elucidated. Oxidative stress has been implicated in the pathogenesis of various forms of renal injury; however, little is known about its involvement in the setting of ureteral obstruction.

METHODS

To investigate the possible involvement of oxidative stress in the obstructive nephropathy, we studied the occurrence and distribution of Nepsilon-carboxymethyl-lysine (CML) in the kidneys after ureteral obstruction. CML is an integrative biomarker of the cumulative protein damage induced by glycoxidation. Heme oxygenase-1 (HO-1) mRNA and protein expression, which is a sensitive and reliable indicator of oxidative stress, were also examined.

RESULTS

CML immunoreactivity was found in the interstitium of UUO kidneys 10 days after the onset ureteral obstruction. HO-1 mRNA was up-regulated as early as 12 hours after ureteral obstruction. HO-1 immunoreactivity was observed in the periglomerular and peritubular interstitium two days after ureteral obstruction.

CONCLUSIONS

These results strongly suggested the presence of increased oxidative stress in the interstitium of UUO kidneys. The oxidative stress and the formation of various kind of biological active oxidative products in the interstitium are supposed to play significant roles in UUO kidney.

Protein aging by carboxymethylation of lysines generates sites for divalent metal and redox active copper binding: relevance to diseases of glycoxidative stress

Aging and age-related diseases are associated with the production of reactive oxygen species which modify lipids, proteins and DNA. Here we hypothesized the glyco- and lipoxidation product N(epsilon)-(carboxymethyl)lysine (CML) in proteins should bind divalent and redox active transition metal binding. CML-rich poly-L-lysine and bovine serum albumin (BSA) were chemically prepared and found to bind non-dialyzable Cu(2+), Zn(2+) and Ca(2+). CML-BSA-copper complexes oxidized ascorbate and depolymerized protein in the presence of H(2)O(2). CML-rich tail tendons implanted for 25 days into the peritoneal cavity of diabetic rats had a 150% increase in copper content and oxidized ascorbate three times faster than controls. CML-rich proteins immunoprecipitated from serum of uremic patients oxidized four times more ascorbate than control and generated spin adducts of DMPO in the presence of H(2)O(2). The chelator DTPA suppressed ascorbate oxidation thereby implicating transition metals in the process. In aging and disease, CML accumulation may result in a deleterious vicious cycle since CML formation itself is catalyzed by lipoxidation and glycoxidation.

Increased carbonyl modification by lipids and carbohydrates in diabetic nephropathy

BACKGROUND

In diabetic nephropathy (DN), possible mediators of untoward effects of hyperglycemia include the advanced glycation end products (AGEs). Indeed, an AGE, carboxymethyllysine (CML), accumulates in expanded mesangial matrix and nodular lesions. An advanced lipoxidation end product (ALE), malondialdehyde-lysine (MDA-lysine), generated on proteins during lipid peroxidation also accumulates in these lesions. As both ALEs and AGEs are formed by carbonyl amine chemistry between protein and carbonyl compounds derived from autoxidation of lipids and carbohydrates, their colocalization suggests an increased carbonyl modification of proteins.

METHODS

To address this hypothesis, human diabetic renal tissues were examined to characterize carbonyl modification of proteins by lipids and carbohydrates: (a) ALEs, MDA-lysine and 4-hydroxynonenal (HNE) protein adduct, derived from lipids, and (b) AGEs, pentosidine and CML, derived from carbohydrates. Furthermore, to elucidate the biological effect of carbonyl modification on primary cultured human and rat mesangial cells, the intracellular protein phosphorylation was examined in the presence of various kinds of carbonyl compounds.

RESULTS

The ALE and AGE adducts examined were identified in expanded mesangial matrix and nodular lesions. The exposure of cultured mesangial cells to carbonyl compounds resulted in phosphorylation of tyrosine residues of a number of intracellular proteins.

CONCLUSIONS

These data suggest a broad derangement in nonenzymatic biochemistry involving both lipids and carbohydrates exists in diabetic glomerular lesions ("carbonyl stress").

Influence of hemodialysis membrane type on pentosidine plasma level, a marker of "carbonyl stress"

Influence of hemodialysis membrane type on pentosidine plasma level, a marker of "carbonyl stress."

BACKGROUND

The accumulation of advanced glycation end products (AGEs) in uremia has been ascribed to the retention of carbonyl precursors of AGEs. Pentosidine plasma level has been identified as a surrogate marker of carbonyl precursors ("carbonyl stress"). The influence of hemodialysis (HD) membrane type and residual diuresis on carbonyl stress has not been studied.

METHODS

We measured protein-linked and free plasma pentosidine (a surrogate marker of carbonyl stress) by high-performance liquid chromatography in patients on HD with low-flux cellulose (N = 29), high-flux polysulfone (PS; N = 57), polymethylmethacrylate (PMMA) (N = 25), and AN69 (N = 15).

RESULTS

Both protein-linked and free pentosidine were similar on low-flux cellulose, high-flux PMMA, and AN69, but were lower (P < 0.01) on high-flux PS. Pentosidine levels were virtually identical on Fresenius and Asahi PS in Japanese and Belgian patients. By multivariate analysis, only the type of HD membrane and residual diuresis proved to be independent determinants (P < 0.001) of pentosidine levels. During a single HD session, the clearance of free pentosidine was similar with all membranes. In three patients who were switched from AN69 to PS, the protein-linked pentosidine level dropped to the control level after resumption of the AN69 membrane.

CONCLUSIONS

Both HD membrane type and residual diuresis are independent determinants of pentosidine plasma level, which is a marker of carbonyl stress.

Pathogenesis and management of dialysis-related amyloid bone disease

Dialysis-related amyloidosis (DRA) is a major complication of chronic renal failure and long-term renal replacement therapy. Beta2-Microglobulin is a major constituent of amyloid fibrils in DRA. Amyloid deposition can present as carpal tunnel syndrome, destructive arthropathy, or subchondral bone erosions and cysts. A definitive diagnosis of DRA can only be made using histological findings, but various analytical imaging methods often support diagnosis. Therapy of an established DRA is limited to symptomatic approaches and surgical removal of amyloid deposits. High-flux biocompatible dialysis membranes can be used to delay DRA development. Recent studies have suggested a pathogenic role for a new modification of beta2-microglobulin in DRA. Increased carbonyl compounds modify proteins, which leads to the augmentation of advanced glycation and lipoxidation end products. Thus, uremia might be a state of carbonyl overload with potentially damaging proteins, leading to a new modification of beta2-microglobulin in amyloid fibrils and development of DRA.

Membrane proteins of human erythrocytes are modified by advanced glycation end products during aging in the circulation

Recent immunological studies demonstrated that proteins in vivo in several diseases are subjected to post-translational modification by advanced glycation end products (AGEs), suggesting a potential role of AGEs in aging and age-enhanced disease processes such as diabetic complications, atherosclerosis and Alzheimer's disease. Nvarepsilon-(Carboxymethyl)lysine (CML) is one of the major AGE-structures demonstrated in vivo so far. In the present study, membrane proteins from young erythrocyte population were compared with those from senescent erythrocytes separated from the same individual in their CML-contents using a monoclonal antibody for CML (6D12). SDS-polyacrylamide gel electrophoresis and subsequent Western blot showed that 6D12 bound to the band 1, 2, 3, 4.2, 5, 6 and 7 proteins from senescent erythrocytes, but not to those from young erythrocytes. Furthermore, quantitative estimation of the reactivity of 6D12 to these erythrocyte membranes by ELISA showed that the reactivity of 6D12 to senescent erythrocyte membranes was 3- to 6-fold higher than that of young erythrocyte membranes. These results indicate that membrane proteins of circulating erythrocytes undergo CML-modification, and the modified proteins accumulated in an age-dependent manner during the life span of erythrocytes.

Immunohistochemical evidence for an increased oxidative stress and carbonyl modification of proteins in diabetic glomerular lesions

Advanced glycation end products (AGE) include a variety of protein adducts whose accumulation has been implicated in tissue damage associated with diabetic nephropathy (DN). It was recently demonstrated that among AGE, glycoxidation products, whose formation is closely linked to oxidation, such as carboxymethyllysine (CML) and pentosidine, accumulate in expanded mesangial matrix and nodular lesions in DN, in colocalization with malondialdehyde-lysine (MDA-lysine), a lipoxidation product, whereas pyrraline, another AGE structure whose deposition is rather independent from oxidative stress, was not found within diabetic glomeruli. Because CML, pentosidine, and MDA-lysine are all formed under oxidative stress by carbonyl amine chemistry between protein amino group and carbonyl compounds, their colocalization suggests a local oxidative stress and increased protein carbonyl modification in diabetic glomerular lesions. To address this hypothesis, human renal tissues from patients with DN or IgA nephropathy were examined with specific antibodies to characterize most, if not all, carbonyl modifications of proteins by autoxidation products of carbohydrates, lipids, and amino acids: CML (derived from carbohydrates, lipids, and amino acid), pentosidine (derived from carbohydrates), MDA-lysine (derived from lipids), 4-hydroxynonenal-protein adduct (derived from lipids), and acrolein-protein adduct (derived from lipids and amino acid). All of the protein adducts were identified in expanded mesangial matrix and nodular lesions in DN. In IgA nephropathy, another primary glomerular disease leading to end-stage renal failure, despite positive staining for MDA-lysine and 4-hydroxynonenal-protein adduct in the expanded mesangial area, CML, pentosidine, and acrolein-protein adduct immunoreactivities were only faint in glomeruli. These data suggest a broad derangement in nonenzymatic biochemistry in diabetic glomerular lesions, and implicate an increased local oxidative stress and carbonyl modification of proteins in diabetic glomerular tissue damage ("carbonyl stress").

Transplantation, not dialysis, corrects azotemia-dependent priming of the neutrophil oxidative burst

The oxidative burst of neutrophils from patients with renal failure before the initiation of dialysis is primed for an enhanced response after stimulation by phagocytosis or chemoattractants. This study shows that phagocytosis-stimulated oxidative burst activity remains primed in patients treated with both high-efficiency hemodialysis and continuous ambulatory peritoneal dialysis (CAPD), but it is normal in patients with a functioning renal transplant. Incubation of normal neutrophils or HL-60 granulocytes in azotemic plasma results in increased resting and phagocytosis-stimulated H2O2 production, which is rapidly reversible on removal of the plasma. Priming of the oxidative burst by azotemic plasma is independent of changes in opsonization and phagocytosis and does not require protein synthesis. These results suggest that azotemic plasma contains a substance or substances capable of reversibly priming oxidative burst activity in neutrophils and neutrophil-like cell lines. The Inability of high-efficiency hemodialysis and CAPD to normalize oxidative burst activity suggests that this substance is of higher molecular weight.

2-Isopropylidenehydrazono-4-oxo-thiazolidin-5-ylacetanilide (OPB-9195) treatment inhibits the development of intimal thickening after balloon injury of rat carotid artery: role of glycoxidation and lipoxidation reactions in vascular tissue damage

We have pursued the hypothesis that the carbonyl modification of proteins by glycoxidation and lipoxidation reactions plays a role in atherogenesis. Human atherosclerotic tissues with fatty streaks and uremic arteriosclerotic tissues were examined, with specific antibodies, to detect protein adducts formed with carbonyl compounds by glycoxidation or lipoxidation reactions, i.e. advanced glycation end products (AGEs) or glycoxidation products, such as carboxymethyllysine (CML) and pentosidine, and lipoxidation products, such as malondialdehyde (MDA)-lysine and 4-hydroxy-nonenal (HNE)-protein adduct. All the four adducts were identified in the proliferative intima and in macrophage-rich fatty streaks. If the carbonyl modification is not a mere result but is a contributor to atherogenesis, inhibition of glycoxidation and lipoxidation reactions might prevent vascular tissue damage. We tested this hypothesis in rats following balloon injury of their carotid arteries, a model exhibiting a remarkable intimal thickening, which are stained positive for all the four adducts. Oral administration of 2-isopropylidenehydrazono-4-oxo-thiazolidin-5-ylacetanili de (OPB-9195), an inhibitor of both glycoxidation and lipoxidation reactions, in rats following balloon injury effectively prevented the intimal thickening. These data suggest a role for the carbonyl modification of proteins by glycoxidation and lipoxidation reactions in most, if not all, types of vascular tissue damage ('carbonyl stress'), and the usefulness of inhibitors of carbonyl reactions for the treatment of vascular tissue damage.

Alterations in nonenzymatic biochemistry in uremia: origin and significance of "carbonyl stress" in long-term uremic complications

Advanced glycation end products (AGEs), formed during Maillard or browning reactions by nonenzymatic glycation and oxidation (glycoxidation) of proteins, have been implicated in the pathogenesis of several diseases, including diabetes and uremia. AGEs, such as pentosidine and carboxymethyllysine, are markedly elevated in both plasma proteins and skin collagen of uremic patients, irrespective of the presence of diabetes. The increased chemical modification of proteins is not limited to AGEs, because increased levels of advanced lipoxidation end products (ALEs), such as malondialdehydelysine, are also detected in plasma proteins in uremia. The accumulation of AGEs and ALEs in uremic plasma proteins is not correlated with increased blood glucose or triglycerides, nor is it determined by a decreased removal of chemically modified proteins by glomerular filtration. It more likely results from increased plasma concentrations of small, reactive carbonyl precursors of AGEs and ALEs, such as glyoxal, methylglyoxal, 3-deoxyglucosone, dehydroascorbate, and malondialdehyde. Thus, uremia may be described as a state of carbonyl overload or "carbonyl stress" resulting from either increased oxidation of carbohydrates and lipids (oxidative stress) or inadequate detoxification or inactivation of reactive carbonyl compounds derived from both carbohydrates and lipids by oxidative and nonoxidative chemistry. Carbonyl stress in uremia may contribute to the long-term complications associated with chronic renal failure and dialysis, such as dialysis-related amyloidosis and accelerated atherosclerosis. The increased levels of AGEs and ALEs in uremic blood and tissue proteins suggest a broad derangement in the nonenzymatic biochemistry of both carbohydrates and lipids.

Induction of cyclooxygenase-2 in human synovial cells by beta 2-microglobulin

BACKGROUND

Prostaglandins (PGs) are important mediators of inflammation in arthritis. We evaluated the role of the cycloxygenase-2 (COX-2) enzyme, which regulates PG biosynthesis, in osteoarthropathy associated with hemodialysis-associated amyloidosis (HAA) by characterizing COX-2 expression in beta 2-microglobulin-treated human synovial cells.

METHODS

We examined the effects of beta 2-microglobulin (beta 2m), a major constituent protein of amyloid fibrils in HAA, on the COX-2 protein and mRNA expression in human synovial cells using Western blot and reverse transcriptase-polymerase chain reaction.

RESULTS

beta 2m selectively increased the biosynthesis of COX-2 protein and induction of COX-2 mRNA in a dose-dependent manner. Immunoabsorption of beta 2m-containing media by anti-beta 2m-specific antibody abrogated beta 2m-mediated COX-2 expression on synovial cells. On the other hand, dexamethasone markedly suppressed the induction of COX-2 protein and mRNA in beta 2m-stimulated synovial cells.

CONCLUSIONS

Our results suggest that induction of COX-2 expression by beta 2m may be an important component of the inflammatory process in hemodialysis-associated osteoarthropathy.

[Non-enzymatic glycation and oxidative stress in chronic illnesses and diabetes mellitus]

New approaches in biochemistry and molecular biology have increased the knowledge on the pathophysiology of chronic diseases as late diabetic complications, Alzheimer's disease, arteriosclerosis and vascular disease by defining the concept of "AGE-formation and oxidative stress." Nonenzymatic glycation, in which reducing sugars are covalently bound to free aminogroups of macromolecules, results in the formation of Advanced Glycation End products (AGEs) which accumulate during aging and at accelerated rate during the course of diabetes. Glycation accompanying oxidation processes support AGE-formation. AGE-formation changes the physicochemical properties of proteins, lipids and nucleic acids. In addition, binding of AGEs to specific surface receptors induces cellular signalling and cell activation. Interaction of AGEs with one of the receptors, RAGE, generates intracellular oxidative stress, which results in activation of the transcription factor NF-kappa B and subsequent gene expression, which might be relevant in late diabetic complications.

CONCLUSION

Knowledge of the basis molecular mechanisms allows to understand the interplay of different inducers such as redicals, cytokines, AGE-proteins and amyloid-beta-peptids and to define oxidative stress as a "common endpoint" of cell dysfunction. With respect to therapeutic options it is now possible not only to optimize blood glycemic control, but also to design drugs such as AGE-inhibitors and AGE-"cross-link" breakers. In addition patients with chronic disease associated with increased oxidative stress ay benefit from an antioxidant rich (and AGE protein poor?) nutrition.

Lixelle adsorbent to remove inflammatory cytokines

A beta2-microglobulin (beta2M) selective adsorbent (Lixelle) for direct hemoperfusion has been used for the treatment of hemodialysis patients with the long-term complication of dialysis related amyloidosis (DRA), but there is no significant correlation between the serum level of beta2M and the occurrence of DRA. Inflammatory cytokines such as interleukin (IL)-1, IL-6, and tumor necrosis factor alpha (TNFalpha) are related to the development of DRA. We studied the adsorptive rates of cytokines in vitro using the Lixelle adsorbent. The adsorptive rates were 98.5% for IL-1beta 98.0% for interleukin-1 receptor antagonist (IL-1RA), 82.9% for IL-6, 99.9% for IL-8, 31.2% for TNFalpha, and 46.1% for soluble TNF receptor (sTNFr), respectively. As the molecular weights of cytokines increase, the adsorptive rates decrease. The Lixelle column adsorbed beta2M and various inflammatory cytokines as well. Therefore, the removal of both beta2M and inflammatory cytokines may play an important role in the treatment of DRA.

Immunohistochemical and ELISA assays for biomarkers of oxidative stress in aging and disease

Oxidative stress is apparent in pathology associated with aging and many age-related, chronic diseases, including atherosclerosis, diabetes mellitus, rheumatoid arthritis, and neurodegenerative diseases. Although it cannot be measured directly in biological systems, several biomarkers have been identified that provide a measure of oxidative damage to biomolecules. These include amino acid oxidation products (methionine sulfoxide, ortho-tyrosine (o-tyr) and dityrosine, chlorotyrosine and nitrotyrosine), as well as chemical modifications of protein following carbohydrate or lipid oxidation, such as N epsilon-(carboxymethyl)lysine and N epsilon-(carboxyethyl)lysine, and malondialdehyde and 4-hydroxynonenal adducts to amino acids. Other biomarkers include the amino acid cross-link pentosidine, the imidazolone adducts formed by reaction of 3-deoxyglucosone or methylglyoxal with arginine, and the imidazolium cross-links formed by the reaction of glyoxal and methylglyoxal with lysine residues in protein. These compounds have been measured in short-lived intracellular proteins, plasma proteins, long-lived extracellular proteins, and in urine, making them valuable tools for monitoring tissue-specific and systemic chemical and oxidative damage to proteins in biological systems. They are normally measured by sensitive high-performance liquid chromatography or gas chromatography-mass spectrometry methods, requiring both complex analytical instrumentation and derivatization procedures. However, sensitive immunohistochemical and ELISA assays are now available for many of these biomarkers. Immunochemical assays should facilitate studies on the role of oxidative stress in aging and chronic disease and simplify the evaluation of therapeutic approaches for limiting oxidative damage in tissues and treating pathologies associated with aging and disease. In this article we summarize recent data and conclusions based on immunohistochemical and ELISA assays, emphasizing the strengths and limitations of the techniques.

Autoxidation products of both carbohydrates and lipids are increased in uremic plasma: is there oxidative stress in uremia?

BACKGROUND

Advanced glycation end products (AGEs), formed by non-enzymatic glycation and oxidation (glycoxidation) reactions, have been implicated in the pathogenesis of several diseases, including normoglycemic uremia. AGE research in uremia has focused on the accumulation of carbohydrate-derived adducts generated by the Maillard reaction. Recent studies, however, have demonstrated that one AGE, the glycoxidation product carboxymethyllysine (CML), could be derived not only from carbohydrates but also from oxidation of polyunsaturated fatty acids in vitro, raising the possibility that both carbohydrate and lipid autoxidation might be increased in uremia.

METHODS

To address this hypothesis, we applied gas chromatography-mass spectrometry and high performance liquid chromatography to measure protein adducts formed in uremic plasma by reactions between carbonyl compounds and protein amino groups: pentosidine derived from carbohydrate-derived carbonyls, malondialdehyde (MDA)-lysine derived from lipid-derived carbonyls, and CML originating possibly from both sources.

RESULTS

All three adducts were elevated in uremic plasma. Plasma CML levels were mainly (>95%) albumin bound. Their levels were not correlated with fructoselysine levels and were similar in diabetic and non-diabetic patients on hemodialysis, indicating that their increase was not driven by glucose. Pentosidine and MDA-lysine were also increased in plasma to the same extent in diabetic and non-diabetic hemodialysis patients. Statistical analysis indicated that plasma levels of CML correlated weakly (P < 0.05) with those of pentosidine and MDA-lysine, but that pentosidine and MDA-lysine varied independently (P > 0.5).

CONCLUSIONS

These data suggest that the increased levels of AGEs in blood, and probably in tissues, reported in uremia implicate a broad derangement in non-enzymatic biochemistry involving alterations in autoxidation of both carbohydrates and lipids.

Advanced Oxidation Protein Products as Novel Mediators of Inflammation and Monocyte Activation in Chronic Renal Failure1, 2

We previously demonstrated the presence of advanced oxidation protein products (AOPP), a novel marker of oxidative stress in the plasma of uremic patients receiving maintenance dialysis. The present study in a cohort of 162 uremic patients showed that plasma concentrations of AOPP increased with progression of chronic renal failure and were closely related to advanced glycation end products (AGE)-pentosidine (r = 0.52, p &lt; 0.001), taken as a marker of AGE. In vivo, the relevance of AOPP and AGE-pentosidine in monocyte-mediated inflammatory syndrome associated with uremia was evidenced by close correlations between AOPP or AGE-pentosidine and monocyte activation markers, including neopterin, IL-1R antagonist, TNF-α, and TNF soluble receptors (TNF-sR55 and TNF-sR75). To determine the mechanisms by which AOPP and AGE could be directly involved in monocyte activation, AOPP-human serum albumin (HSA) and AGE-HSA were produced in vitro by treating HSA with oxidants or glucose, respectively. Spectroscopic analysis confirmed that AOPP-HSA contains carbonyls and dityrosine. Both AOPP-HSA and AGE-HSA, but not purified dityrosine, were capable of triggering the oxidative burst of human monocytes in cultures. The AOPP-HSA-induced respiratory burst was dependent on the chlorinated nature of the oxidant and on the molar ratio HSA/HOCl. Collectively, these data first demonstrate that AOPP act as a mediator of oxidative stress and monocyte respiratory burst, which points to monocytes as both target and actor in the immune dysregulation associated with chronic uremia.

Increased aggregation of human platelets produced by advanced glycation end products in vitro

Advanced glyco-oxidation end products (AGEs) generate oxygen free radicals that potentiate the development of atherosclerosis. Thus, AGEs may potentiate the aggregation of human platelets through oxidative stress. AGE-bovine serum albumin (BSA) and AGE-poly-L-lysine were evaluated for aggregation of human platelets. Superoxide in platelet-rich plasma (PRP) was measured using lucigenin-derived chemiluminescence. The platelet aggregation induced by ADP or U46619 was potentiated by preincubation with AGE-BSA, by 40% and by 59%, P < .05, respectively, vs BSA. Aggregation was increased by AGEs in a dose-dependent manner. The production of superoxide was significantly greater in PRP incubated with AGE-BSA vs BSA. The other Maillard reaction products, such as Amadori-, pentosidine-, and carboxymethyl lysine (CML)-BSA had no effect. Superoxide dismutase or indomethacin abolished the enhancing effect of AGEs on the platelet aggregation. AGEs potentiate platelet aggregation possibly with superoxide anions and prostanoids. AGE-induced potentiation of platelet aggregation may be involved in the development of atherosclerosis.

Accelerated formation of N epsilon-(carboxymethyl) lysine, an advanced glycation end product, by glyoxal and 3-deoxyglucosone in cultured rat sensory neurons

The formation of advanced glycation end products (AGEs) is associated with pathophysiological changes with aging and disease processes. In the neurodegeneration in Alzheimer's disease and other neurodegenerative diseases. AGEs are speculated to play a role in their pathogenesis. We provide the first evidence for the induction of AGEs in cultured neuronal cells. Glyoxal and 3-deoxyglucosone (3-DG), AGE precursors, induced N epsilon-(carboxymethyl) lysine (CML), a well characterized and major AGE structure, in cultured rat sensory neurons in a time- and dose-dependent manner. CML formation was prevented by addition of aminoguanidine, an inhibitor of AGE formation. This culture system provides a useful model to analyze the role of the glycoxidation reaction in neuronal aging and neurodegenerative disorder.

Treatment of amyloidosis and the rheumatologist. State of the art and perspectives for the future

The rheumatologist must be prepared to face diagnostic and therapeutic problems related to different categories of amyloidosis. This applies to the systemic AA amyloidosis that complicates chronic inflammatory arthropathies like adult and juvenile rheumatoid arthritis, causing nephropathy and various internal manifestations. Other types of amyloidosis are essential because they may localize to structures of the locomotor system and cause rheumatic complaints. At present, there is no cure for amyloidosis. But adequate and especially early therapeutic intervention is helpful in many cases. This review focuses on treatment of the categories of amyloidosis which are most relevant to the rheumatologist. In addition to treatments that are available today, more effective therapeutic modalities which hopefully will be available in the near future are also reviewed.

Beta 2-microglobulin modified with advanced glycation end products modulates collagen synthesis by human fibroblasts

Beta 2-microglobulin amyloidosis (A beta 2m) is a serious complication for patients undergoing long-term dialysis. beta 2-microglobulin modified with advanced glycation end products (beta 2m-AGE) is a major component of the amyloid in A beta 2m. It is not completely understood whether beta 2m-AGE plays an active role in the pathogenesis of A beta 2m, or if its presence is a secondary event of the disease. beta 2-microglobulin amyloid is mainly located in tendon and osteo-articular structures that are rich in collagen, and local fibroblasts constitute the principal cell population in the synthesis and metabolism of collagen. Recent identification of AGE binding proteins on human fibroblasts lead to the hypothesis that the fibroblast may be a target for the biological action of beta 2m-AGE. The present study demonstrated that two human fibroblast cell lines exhibited a decrease in procollagen type I mRNA and type I collagen synthesis after exposure to beta 2m-AGE for 72 hours. Similar results were observed using AGE-modified albumin. Antibody against the RAGE, the receptor for AGE, attenuated this decrease in synthesis, indicating that the response was partially mediated by RAGE. In addition, antibody against epidermal growth factor (EGF) attenuated the decrease in type I procollagen mRNA and type I collagen induced by beta 2m-AGE, suggesting that EGF acts as an intermediate factor. These findings support the hypothesis that beta 2m-AGE actively participates in connective tissue and bone remodeling via a pathway involving fibroblast RAGE, and at least one interposed mediator, the growth factor EGF.

Implication of altered redox regulation by antioxidant enzymes in the increased plasma pentosidine, an advanced glycation end product, in uremia

Pentosidine is an advanced glycation end product (AGE) formed during Maillard or browning reaction by non-enzymatic glycation and oxidation (glycoxidation). Recent studies demonstrated the increased plasma pentosidine levels not only in diabetic patients with hyperglycemia but also in normoglycemic uremic patients. The mechanism of increased glycoxidation reaction in uremia, however, remains unknown. As superoxide dismutases (SODs) and glutathione peroxidase (GPx) are antioxidant enzymes involved in the metabolism of H2O2 which accelerates the glycoxidation reaction, we measured their activities by enzymatic assays in the plasma of normal and non-diabetic hemodialysis patients and examined a link between redox regulation by antioxidant enzymes and glycoxidation reaction. The activities of GPx were significantly lower in the plasma of hemodialysis patients than in normal subjects, whereas those of SODs were higher in the former than in the latter. As plasma SODs comprise three isozymes, i.e., Cu/Zn-SOD, Mn-SOD, and extracellular (EC)-SOD, we determined the levels of each SOD isozyme by ELISAs. The plasma concentrations of Cu/Zn-SOD and EC-SOD were significantly higher in hemodialysis patients than in normal subjects, whereas those of Mn-SOD did not differ between the two groups. It is of note that GPx activities correlated inversely with pentosidine in the plasma of hemodialysis patients (r2 = 0.262, P < 0.01). There was no significant correlation between total SOD activities and pentosidine levels in the plasma of hemodialysis patients, but, among the three SOD isozymes, the plasma EC-SOD levels correlated with the levels of pentosidine in hemodialysis patients (r2 = 0.286, P < 0.05). As decreased GPx and increased SOD activities result in the increased H2O2 generation, which accelerates the glycoxidation of protein, these data suggest a link of altered redox regulation by antioxidant enzymes to increased glycoxidation reaction in the uremic plasma. This paper provides the first time evidence for the possible involvement of enzymatic redox regulation in the non-enzymatic glycoxidation reaction in vivo.

Involvement of interleukin-8 in dialysis-related arthritis

To elucidate the role of interleukin (IL)-8, a chemotactic factor for neutrophils, in dialysis-related arthritis (DRA) of patients on long-term hemodialysis, the concentration of IL-8 was measured in the synovial fluids of DRA patients with acute arthralgia and joint swelling, and was compared with those in patients with rheumatoid arthritis (RA) and patients with osteoarthritis (OA). We noted a marked elevation of IL-8 in the joint fluids of patients with DRA and RA as compared with OA. Furthermore, to determine the role of IL-8 in synovitis, we examined the in vivo effect of intra-articular injection of human recombinant IL-8 on leukocyte infiltration into the joint space of rabbits. A single injection of IL-8 to the joints of rabbits induced rapid infiltration of neutrophils into the joint space and synovial tissues, which reached a maximum in four hours. The oral administration of indometacin farnesil (a prodrug that is converted to indomethacin after intestinal absorption) before the injection of IL-8 alleviated the infiltration of neutrophils. When human synovial cells were incubated with tumor necrosis factor (TNF)-alpha, the expression of IL-8 mRNA and IL-8 production in the cultured synovial cells were increased. The TNF-alpha-stimulated expression of IL-8 mRNA and IL-8 production in the cultured synovial cells were markedly inhibited by dexamethasone. In conclusion, IL-8 levels were markedly elevated in the joint fluids of patients with DRA. Interleukin-8 released from synovial cells may be an important factor to induce acute inflammation in DRA. Dexamethasone and indomethacin may be effective for DRA by inhibiting the production and chemotactic actions of IL-8, respectively.

Increased pentosidine, an advanced glycation end product, in plasma and synovial fluid from patients with rheumatoid arthritis and its relation with inflammatory markers

Pentosidine is an advanced glycation end product (AGE) formed by combined processes of glycation and oxidation (glycoxidation) between carbohydrate-derived carbonyl group and protein amino group. Recent studies demonstrated the increased pentosidine levels not only in diabetic patients with hyperglycemia but also in normoglycemic uremic patients due to increased oxidative stress. Rheumatoid arthritis (RA) is a state of increased oxidative stress associated with chronic inflammation. This suggested an enhanced glycoxidation reaction and increased AGE levels in RA patients. In the present study, we therefore determined, by high performance liquid chromatographic (HPLC) assay, the concentrations of pentosidine in plasma and synovial fluid from 22 patients with rheumatoid arthritis (RA) and compared their levels with those in 17 patients with osteoarthritis (OA), 26 diabetic patients, and 25 normal subjects. The levels of inflammatory markers and markers of tissue destruction, metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), were also measured in the same samples. Pentosidine levels in plasma and synovial fluid from RA patients were significantly higher than those in OA patients, diabetic patients, and normal subjects. There was a significant correlation between the pentosidine levels in plasma and those in synovial fluid. Among markers of inflammation and matrix destruction, pentosidine levels in plasma from RA patients were correlated with the levels of C-reactive protein (CRP), erythrocyte sedimentation rate, white blood cell count, and platelet count. Multiple stepwise regression analysis reveals an independent influence of CRP on plasma pentosidine levels. In conclusion, pentosidine levels are significantly higher in plasma and synovial fluid from RA patients and may be useful as a biomarker of chronic inflammation in RA patients.

Synovial inflammatory cells captured 131I-beta 2-microglobulin in patients with dialysis related amyloidosis

Dialysis related amyloidosis (DRA) is a major complication of long term hemodialysis therapy. It is well recognized that scintigraphic study using radioisotope-labeled beta 2-microglobulin (beta 2M) as a tracer is a sensitive and specific technique to diagnose DRA non-invasively. The aim of this study is to clarify the mechanism of 131I-beta 2M accumulation around the amyloid tissue. Three dialysis patients with carpal tunnel syndromes were examined for consecutive 131I-beta 2M scintigraphies every 24 hours for 3 days till the carpal tunnel synovectomy. Removed synovial tissues were processed for histological study. The scintigraphic study demonstrated tracer accumulations in the joints involved with DRA and the intensity increased in a time dependent fashion. Microscopic observations revealed many inflammatory cells presenting CD68-monocytes/macrophages antigen infiltrated into the synovial tissues. 131I-beta 2M was evident in the cytoplasm of the infiltrating cells, while no radioactivity was detected above background in the amyloid tissues. In conclusion, the tracer accumulations observed in the 131I-beta 2M scintigraphic studies were the consequence of circulating beta 2M assimilated by the infiltrating monocytes/macrophages. Thus, the undetermined elimination pathway of circulating beta 2M in the dialysis patients was identified as the storage pool in those inflammatory cells. The inflammatory change may play a crucial role in the local progression of DRA through the accumulation of circulating beta 2M around the established amyloid tissues.

Renal catabolism of advanced glycation end products: the fate of pentosidine

Advanced glycation end products (AGEs) generated through the Maillard reaction significantly alter protein characteristics. Their accumulation has been incriminated in tissue injury associated with aging, diabetes, and renal failure. However, little is known about their clearance from the body. The present study delineates the catabolic pathway of a well-defined AGE product, pentosidine. Synthesized pentosidine given intravenously in rats with normal renal function was rapidly eliminated from the circulation through glomerular filtration, but was undetectable in the urine by chemical analysis. Immunohistochemistry with anti-pentosidine antibody disclosed that pentosidine accumulated transiently in the proximal renal tubule one hour after its administration, but had disappeared from the kidney at 24 hours. After an intravenous load of radiolabeled pentosidine, radioactivity peaked in the kidney at one hour and subsequently decreased, whereas it rose progressively in the urine. Over 80% of the radioactivity was recovered in the 72-hour collected urine. However, only 20% of urine radioactivity was associated with intact pentosidine chemically or immunochemically. In gentamicin-treated rats with tubular dysfunction, up to 30% of the pentosidine load was recovered as intact pentosidine in the urine. The present study suggests that free pentosidine (and possibly other AGEs) is filtered by renal glomeruli, reabsorbed in the proximal tubule where it is degraded or modified, and eventually excreted in the urine. Kidney thus plays a key role in pentosidine disposal.

Immunohistochemical colocalization of glycoxidation products and lipid peroxidation products in diabetic renal glomerular lesions. Implication for glycoxidative stress in the pathogenesis of diabetic nephropathy

Advanced glycation end products (AGEs) include a variety of protein adducts whose accumulation alters the structure and function of tissue proteins and stimulates cellular responses. They have been implicated in tissue damage associated with diabetic complications. To assess the possible link between AGE accumulation and the development of diabetic nephropathy (DN), we have examined the immunohistochemical localization of various AGE structures postulated to date, i.e., pentosidine, Nepsilon-(carboxymethyl)lysine (CML), and pyrraline, in diabetic and control kidneys. CML and pentosidine accumulate in the expanded mesangial matrix and thickened glomerular capillary walls of early DN and in nodular lesions and arterial walls of advanced DN, but were absent in control kidneys. By contrast, pyrraline was not found within diabetic glomeruli but was detected in the interstitial connective tissue of both normal and diabetic kidneys. Although the distribution of pyrraline was topographically identical to type III collagen, distribution of pentosidine and CML was not specific for collagen type, suggesting that difference in matrix protein composition per se could not explain heterogeneous AGE localization. Since oxidation is linked closely to the formation of pentosidine and CML, we also immunostained malondialdehyde (MDA), a lipid peroxidation product whose formation is accelerated by oxidative stress, assuming that local oxidative stress may serve as a mechanism of pentosidine and CML accumulation. Consistent with our assumption, diabetic nodular lesions were stained positive for MDA. These findings show that AGE localization in DN varies according to AGE structure, and suggest that the colocalization of markers of glycoxidation (pentosidine and CML) with a marker of lipid peroxidation reflects a local oxidative stress in association with the pathogenesis of diabetic glomerular lesions. Thus, glycoxidation markers may serve as useful biomarkers of oxidative damage in DN.

Beta 2-microglobulin induces stromelysin production by human synovial fibroblasts

beta 2-Microglobulin (beta 2-m) is a major constituent of amyloid fibrils in hemodialysis-associated amyloidosis (HAA), a serious complication in patients on long-term hemodialysis. The most distinctive pathological feature of HAA is the deposition of amyloid fibrils with subsequent articular inflammation and destruction. However, the pathological role of beta 2-m is not well known at present. We investigated the effects of beta 2-m on the production of proteinases from synovial fibroblasts isolated from patients with rheumatoid arthritis. beta 2-m stimulated synovial fibroblasts to produce stromelysin, a neutral matrix metalloproteinase (MMP-3). The production of MMP-2 and of a tissue inhibitor of metalloproteinase-1 (TIMP-1) were not enhanced by beta 2-m-treated synovial fibroblasts. Stromelysin is capable of degrading several components of the extracellular matrix and believed to be the key enzyme causing articular destruction in inflammatory joint diseases. Our results suggest a novel role for beta 2-m in articular inflammation and destruction mediated by stromelysin in HAA.

Accumulation of pro-apolipoprotein A-II in mouse senile amyloid fibrils

Apolipoprotein A-II (apoA-II), the major apoprotein of serum high-density lipoprotein, is deposited as amyloid fibrils (AApoAII) in murine senile amyloidosis. We have identified and purified a more basic amyloid protein from old-mouse liver. N-terminal sequencing of the protein revealed that the pro-segment of five amino acid residues (Ala-Leu-Val-Lys-Arg) extended from the N-terminal glutamine residue of mature apoA-II protein. MS analysis revealed the deposit of intact pro-apoA-II protein (molecular mass 9319 Da). Antiserum was prepared for staining of the AApoAII amyloid deposition. The relative abundance of pro-apoA-II to mature apoA-II in the amyloid-fibril fraction isolated from livers of mice with severe amyloidosis was 14.1%. The similar abundance of pro-apoA-II in the amyloid fibril fraction from the spleen (16.3%) suggested that deposited pro-apoA-II originated from the blood. The concentration of pro-apoA-II was much lower in the serum (1.5% of mature apoA-II) than in the amyloid-fibril fraction. There was no difference in the content of pro-apoA-II between the amyloidogenetic R1.P1-Apoa2c and amyloid-resistant SAMR1 strains at the age of 3 months. The abundance of pro-apoA-II in the amyloid-fibril fraction compared with the serum suggested that it plays a key role in the initialization of mouse senile amyloidosis.

HMG-CoA reductase inhibitors suppress macrophage growth induced by oxidized low density lipoprotein

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors ameliorate atherosclerotic diseases in several models of vascular disease. This is largely due to their ability to reduce plasma cholesterol levels in vivo. Proliferation of cellular components is one of the major events in the development and progression of atherosclerotic lesions. We recently demonstrated that oxidized low density lipoprotein (Ox-LDL), a likely atherogenic lipoprotein present in vivo, is capable of inducing macrophage growth in vitro. In the present study, we investigated the effect of HMG-CoA reductase inhibitors, simvastatin and pravastatin, on Ox-LDL-induced macrophage growth. Our results demonstrated that these inhibitors effectively suppressed Ox-LDL-induced macrophage growth with concentrations required for 50% inhibition by simvastatin and pravastatin being 0.1 and 80 microM, respectively, and that this inhibitory effect was reversed by mevalonate but not by squalene. Under these conditions, simvastatin did not affect the endocytic degradation of Ox-LDL, nor subsequent accumulation of intracellular cholesteryl esters. Our results suggest that a non-cholesterol metabolites(s) of mevalonate pathway may play an important role in Ox-LDL-induced macrophage growth. Since it is well known that macrophage-derived foam cells are the key cellular element in the early stage of atherosclerosis, a significant inhibition of Ox-LDL-induced macrophage growth by HMG-CoA reductase inhibitors in vitro, particularly simvastatin, may also explain, at least in part, their anti-atherogenic action in vivo.

Synthesis and secretion of tumour necrosis factor-alpha by human monocytic THP-1 cells and chemotaxis induced by human serum albumin derivatives modified with methylglyoxal and glucose-derived advanced glycation endproducts

Human serum albumin minimally-modified by methylglyoxal (MGmin-HSA) stimulated the synthesis and secretion of tumour necrosis factor-alpha (TNF-alpha) from human monocytic THP-1 cells in vitro. Human serum albumin minimally-modified by glucose-derived advanced glycation endproducts (AGEmin-HSA) and human serum albumin highly-modified by glucose-derived advanced glycation endproducts (AGE-HSA) stimulated markedly lower synthesis and secretion of TNF-alpha from THP-1 cells than did MGmin-HSA. The median effective concentration EC50 value of MGmin-HSA for the secretion of TNF-alpha was 5.8 +/- 0.3 microM and the maximal secretion was 0.28 +/- 0.01 ng TNF-alpha/ml (n = 12) for incubations containing 5 x 10(5) cells/ml. MGmin-HSA (0.2-2.0 microM) also stimulated chemotaxis of THP-1 cells in vitro but AGE-HSA did not in this concentration range. The EC50 value of MGmin-HSA for the chemotactic response was 0.44 +/- 0.07 microM (n = 15). Similar induction of the synthesis and secretion of TNF-alpha and chemotaxis by monocytes in response to MGmin-HSA in vivo may contribute to atherosclerosis in macro- and micro-angiopathy, particularly in the development of chronic clinical complications of diabetes mellitus.

Immunohistochemical localization of advanced glycation end products, pentosidine, and carboxymethyllysine in lipofuscin pigments of Alzheimer's disease and aged neurons

Lipofuscins are intracellular fluorescent pigments accumulating in the central nervous system (CNS) with aging and degenerative processes such as Alzheimer's disease (AD). Although they are thought to be lipid peroxidation products derived from malondialdehyde, their biogenesis remains controversial. We further characterize the chemical nature of lipofuscins in brain tissues from AD patients and normal aged subjects. Advanced glycation end products (AGEs), pentosidine and carboxymethyllysine (CML), were identified by appropriate specific antibodies. They have physicochemical properties similar to those of lipofuscin and also increase with aging. Pentosidine and CML were identified in the neuronal perikarya and the extraneuroperikaryal deposits of both the AD and aged brain. Pentosidine, but not CML, was present in the fiber-like structure within the neuropil and the core of classical senile plaque. In the brain of young subjects without CNS disease, pentosidine and CML staining was faint. Pentosidine and CML co-localized with lipofuscin pigments in the neuronal perikarya of both the AD and aged brain. We demonstrate for the first time that lipofuscin is constituted not only of lipid peroxidation products but also from glycation products which may be the origin of fluorescent pigments. Lipofuscins should thus be considered as fluorescent pigments generated by lipid- and sugar-derived Schiff base-protein polymers.

Advanced glycation endproducts stimulate the MAP-kinase pathway in tubulus cell line LLC-PK1

Advanced glycation endproducts (AGEs) are suggested to play an important role in diabetic nephropathy. They induce specific cellular responses such as the release of cytokines in different cell lines. The effect of AGEs on signal transduction pathways was investigated in the renal tubulus cell line LLC-PK1. Using a serine-phosphate-specific antibody AGE-induced cellular responses associated with phosphorylation/dephosphorylation events were demonstrated. In particular, the p42MAP kinase and its downstream target, the AP-1 complex, are shown to be activated by AGE-BSA but not by BSA. In contrast, only partial phosphorylation is observed for the p70S6-kinase. Thus, AGEs appear to induce specific signal transduction pathways.

Characterization and functional analysis of the promoter of RAGE, the receptor for advanced glycation end products

The receptor for advanced glycation end products, RAGE, is a member of the immunoglobulin superfamily of cell surface molecules differentially expressed on a range of cell types. Ligation of RAGE perturbs homeostatic mechanisms and, potentially, provides a basis for cellular dysfunction in pathologic situations in which its ligands accumulate. To understand factors underlying RAGE expression, we cloned the 5'-flanking region of the RAGE gene and characterized putative regulatory motifs. Analysis of the putative promoter region revealed the presence of three potential NF-kappaB-like and two SP1 binding sites. Transient transfection of vascular endothelial and smooth muscle cells using chimeric 5'-deletion constructs linked to luciferase reporter revealed that the region -1543/-587 contributed importantly to both basal and stimulated expression of the RAGE gene. This region of the RAGE gene contained three putative NF-kappaB-like binding sites and was responsible for increased luciferase activity observed when endothelial or smooth muscle cells were stimulated with lipopolysaccharide. DNase I footprinting assays and electrophoretic mobility shift assay revealed that two of the three NF-kappaB-like binding sites (1 and 2) were likely functional and responsive to stimuli. Upon simultaneous mutation of NF-kappaB-like sites 1 and 2, both basal promoter expression and response to stimulation with LPS, as measured by relative luciferase activity, were significantly diminished. These results point to NF-kappaB-dependent mechanisms regulating cellular expression of RAGE and suggest a means of linking RAGE to the inflammatory response.

Histological prevalence of beta 2-microglobulin amyloidosis in hemodialysis: a prospective post-mortem study

The histological prevalence of beta-2 microglobulin amyloidosis (A beta 2m) was evaluated in a prospective study of joint samples obtained at autopsy in 54 patients on hemodialysis (HD) for 2 to 163 (median 47) months, aged 20 to 80 (median 63) years at HD onset. Carpal tunnel syndrome surgery or radiological signs of A beta 2m were present in 2 and 4% of them, respectively. A control group of 34 patients without end-stage renal disease, autopsied during the same period was used as a reference. The 153 sampled joints (1 to 8, median 2 per patient) were sternoclavicular joints (N = 77), shoulders (N = 35), knees (N = 28), others (N = 13). A beta 2m was diagnosed (positive Congo red with typical birefringence and positive immunostaining of deposits for beta 2m) in 26 of 54 (48%) patients. Prevalence reached respectively 21%, 33%, 50%, 90% and 100% within two years, after 2 to 4 years, 4 to 7 years, 7 to 13 years and more than 13 years HD. The calculated sensitivity of the various joints for A beta 2m detection is significantly higher (P < 0.03) for sternoclavicular joints (97%) and knees (91%) than for shoulders (57%). Multivariate stepwise logistic regression with discriminant analysis identified both HD duration (P = 0.0008) and age at HD onset (P = 0.0093) but not diabetic nephropathy (P = 0.23) or gender (P = 0.25) as independent risk factors for A beta 2m. The probability of joint A beta 2m was quantitated as a function of age and HD duration. In conclusion, A beta 2m may be observed in the large joints early after HD onset. Overall prevalence reaches 48% of the patients on HD for a median of 47 months. It is much higher than that reported on the basis of clinical or radiological evidence. The sternoclavicular and knee joints are more frequently (P < 0.03) involved than the shoulder. The easily accessible sternoclavicular joint therefore appears to be the best site for the early detection of A beta 2m. Both HD duration and age at HD onset, but not diabetic nephropathy, are independent risk factors for A beta 2m.

Implication of an increased oxidative stress in the formation of advanced glycation end products in patients with end-stage renal failure

Recent studies have demonstrated a marked increase in the level of advanced glycation end products (AGEs) in the plasma, skin and amyloid fibrils of hemodialysis (HD) patients. The presence of AGEs in (beta2m) forming amyloid fibrils has been established in a previous immunochemical study relying on a monoclonal anti-AGE antibody. In the present study, Western blot analysis and immunohistochemistry reveal that the epitope recognized by this antibody is N epsilon-(carboxymethyl)lysine (CML) and that CML is one of the AGE structures present in amyloid fibrils. Thus, two AGE structures, CML and pentosidine, are now recognized in dialysis-related amyloidosis. AGE accumulation in uremia is not accounted for by elevated glucose levels. Since CML and pentosidine formation are closely linked to oxidative processes, we tested the hypothesis that a high oxidative stress enhanced AGE formation in HD patients. We focused on ascorbic acid (AA) because AA is easily oxidized under oxidative stress and its oxidized form (oxiAA) is a source of CML and pentosidine. In vitro incubation of beta2m with AA under atmospheric oxygen resulted in: (1) the rapid appearance of characteristic physicochemical properties of AGEs (brown color, fluorescence, polymerization tendency); (2) the transformation of beta2m into AGE-modified beta2m recognized by a specific monoclonal antibody; and (3) the accelerated formation of CML in beta2m and beta2m-peptide, recognized by mass spectrometry. A similar in vitro incubation of human serum albumin disclosed a parallel production of pentosidine measured by high-performance liquid chromatographic assay. In HD patients, the degree of AA oxidation, assessed as the ratio of oxiAA to total ascorbate, was more than twice as high as that of normal subjects (0.87 +/- 0.16 vs. 0.35 +/- 0.11, P < 0.0001), suggesting the presence of an increased oxidative stress. Interestingly, plasma level of oxiAA was correlated with the plasma levels of protein linked (P < 0.01, r2 = 0.25) and free (P < 0.05, r2 = 0.22) pentosidine. Altogether these results demonstrate that AGE, that is, CML and pentosidine, production is accelerated under oxidative stress, even in the absence of glucose. They suggest that, in uremia, CML and pentosidine production is determined both by an increased oxidative stress and the availability of precursors such as oxiAA. Finally, both CML and pentosidine contribute to the AGEs present in dialysis-related amyloid fibrils.

Immunohistochemical detection of imidazolone, a novel advanced glycation end product, in kidneys and aortas of diabetic patients

To investigate the role of the Maillard reaction in the pathogenesis of diabetic complications, we produced several clones of monoclonal antibodies against advanced glycation end products (AGEs) by immunizing mice with AGE-modified keyhole limpet hemocyanin, and found that one clone (AG-1) of the anti-AGE antibodies reacted specifically with imidazolones A and B, novel AGEs. Thus, the imidazolones, which are the reaction products of the guanidino group of arginine with 3-deoxyglucosone (3-DG), a reactive intermediate of the Maillard reaction, were found to be common epitopes of AGE-modified proteins produced in vitro. We determined the erythrocyte levels of imidazolone in diabetic patients using ELISA with the monoclonal anti-imidazolone antibody. The imidazolone levels in the erythrocytes of diabetic patients were found to be significantly increased as compared with those of healthy subjects. Then we studied the localization of imidazolone in the kidneys and aortas obtained from diabetic patients by immunohistochemistry using the antibody. Specific imidazolone immunoreactivity was detected in nodular lesions and expanded mesangial matrix of glomeruli, and renal arteries in an advanced stage of diabetic nephropathy, as well as in atherosclerotic lesions of aortas. This study first demonstrates the localization of imidazolone in the characteristic lesions of diabetic nephropathy and atherosclerosis. These results, taken together with a recent demonstration of increased serum 3-DG levels in diabetes, strongly suggest that imidazolone produced by 3-DG may contribute to the progression of long-term diabetic complications such as nephropathy and atherosclerosis.

Clearance of pentosidine, an advanced glycation end product, by different modalities of renal replacement therapy

We recently demonstrated that pentosidine, an advanced glycation end product, accumulates markedly as albumin-linked form (Palb) and in free-form (Pfree) in the plasma of patients with end-stage renal failure. The present study was undertaken to examine the clearance of Palb and Pfree by different modalities of renal replacement therapy, that is, hemodialysis (HD), continuous ambulatory peritoneal dialysis (CAPD), and renal transplantation. HD cleared Pfree (9.4 +/- 4.3 nmol/kg/HD) but not Palb, by diffusion but not by membrane adsorption, whereas CAPD cleared both Palb (4.03 +/- 2.01 nmol/kg/day) and Pfree (2.43 +/- 1.24 nmol/kg/day). Plasma total pentosidine levels were significantly (P < 0.05) lower in CAPD (0.97 +/- 0.41 nmol/ml) than in HD (1.19 +/- 0.41 nmol/ml), as the result of a lower serum albumin level in the former patients. Indeed, Palb expressed per mg albumin was virtually identical in HD and CAPD. By contrast, Pfree was significantly lower in CAPD than in HD. Palb levels were significantly correlated with plasma Pfree levels in both HD and CAPD patients, but not in the CAPD dialysate. Pentosidine transport across the peritoneum occurs mainly by diffusion, both as Palb and Pfree. Interestingly, peritoneal Palb clearance (0.17 +/- 0.07 ml/min) significantly (P < 0.00001) exceeded albumin clearance (0.11 +/- 0.05 ml/min). Palb levels being significantly higher (P < 0.0005) in the peritoneal fluid (36.28 +/- 18.55 pmol/mg) than in the serum (27.12 +/- 11.71 pmol/mg), thus raises the possibility of a facilitated diffusion of Palb or an active transport mechanism for protein-linked pentosidine into the peritoneal cavity. After renal transplantation, plasma Pfree fell rapidly, remained barely detectable after one month, and returned to normal at six months. By contrast, Palb fell more slowly and remained significantly above normal at six months, but returned eventually to normal levels. These findings demonstrate that: (1) both HD and CAPD remove Pfree; (2) the peritoneal clearance of Palb, might contribute to the lower level of plasma pentosidine in CAPD than in HD patients; and (3) renal transplantation is the best therapeutic modality to normalize both Palb and Pfree levels.