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

Distinct Ocular Surface Microbiome in Keratoconus Patients Correlate With Local Immune Dysregulation

Purpose

Keratoconus (KC) is characterized by irregular astigmatism along with corneal stromal weakness and is associated with altered immune status. Tissue resident microbiomes are known to influence the immune status in other organs, but such a nexus has not been described in ocular conditions. Therefore, we examined the ocular surface microbiome of patients with KC and correlated it to the immune cell and tear molecular factor profiles.

Methods

Sixty-two patients with KC and 21 healthy controls underwent corneal topography analysis and eye examination followed by a collection of Schirmer's strip, ocular surface wash, and ocular surface swabs. Microbiomes were analyzed by extracting DNA from the swabs followed by 16S rRNA gene V3-V4 amplicon sequencing and analyzed using QIIME. Fifty-two molecular factors from Schirmer's strip tear extracts and 11 immune cells from ocular wash were measured using multiplex ELISA and flow cytometry. Alpha diversity, linear discriminant analysis effect size (LEfSe), relative abundance and receiver operating characteristic - area under the curve (ROC-AUC) analysis were performed. Unsupervised clustering at the genus level with clinical parameters, soluble factors, and immune cells was performed.

Results

Fifty-two phyla/class, 132 order, 283 family, and 718 genera were identified in our cohort. Alpha diversity indices were comparable between patients with KC and the healthy controls. Dominant phyla across groups were Actinobacteria, Proteobacteria, Firmicutes, and Bacteroidetes. Alphaproteobacteria increased in KC eyes whereas Actinobacteria, Firmicutes_Bacilli reduced compared with the healthy controls. We found a significant positive correlation of Microbacterium, Cutibacterium, and Brevundimonas genera abundance with keratometry and corneal thickness. Levels of IL-21, IL-9, Fractalkine, and VEGF positively correlated with Tetrasphaera (P < 0.05). β2-microglobulin and CD66bhigh cells correlated with Bacteroides (P < 0.05). CD45+ cells correlated with Escherichia_Shigella (P < 0.02).

Conclusions

We discovered a unique microbiome signature of KC which correlated to disease grades and secreted molecular factors and immune cells. Therefore, the altered microbiome on the ocular surface may drive immune dysregulation in KC and provide scope for potential interventions in the future.

Protective Effect of Djulis (Chenopodium formosanum) Extract against UV- and AGEs-Induced Skin Aging via Alleviating Oxidative Stress and Collagen Degradation

Skin aging is a complex process involving photoaging and glycation stress, which share some fundamental pathways and have common mediators. They can cause skin damage and collagen degradation by inducing oxidative stress and the accumulation of reactive oxygen species (ROS). Chenopodium formosanum (CF), also known as Djulis, is a traditional cereal in Taiwan. This study investigated the protection mechanisms of CF extract against ultraviolet (UV) radiation and advanced glycation end products (AGEs)-induced stress. The results indicated that CF extract had strong antioxidant and free radical scavenging effects. It could reduce UV-induced intracellular ROS generation and initiate the antioxidant defense system by activating the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway in human skin fibroblasts. CF extract modulated mitogen-activated protein kinase (MAPK) and transformed growth factor-beta (TGF-β) signaling pathways to alleviate oxidative stress-induced skin aging. Moreover, the results revealed that CF extract not only promoted collagen synthesis but also improved aging-induced collagen degradation. CF extract attenuated AGEs-induced ROS production and the upregulation of receptor for AGEs (RAGE). The overall results suggest that CF extract provides an effective anti-aging strategy by preventing skin damage from oxidative stress and collagen loss with potent antioxidant, anti-photoaging, and antiglycation activities.

A review on mechanism of inhibition of advanced glycation end products formation by plant derived polyphenolic compounds

Advanced glycation end products (AGEs) are naturally occurring biomolecules formed by interaction of reducing sugars with biomolecules such as protein and lipids etc., Long term high blood sugar level and glycation accelerate the formation of AGEs. Unchecked continuous formation and accumulation of AGEs are potential risks for pathogenesis of various chronic diseases. Current mode of antidiabetic therapy is based on synthetic drugs that are often linked with severe adverse effects. Polyphenolic compounds derived from plants are supposed to inhibit glycation and formation of AGEs at multiple levels. Some polyphenolic compounds regulate the blood glucose metabolism by amplification of cell insulin resistance and activation of insulin like growth factor binding protein signaling pathway. Their antioxidant nature and metal chelating activity, ability to trap intermediate dicarbonyl compounds could be possible mechanisms against glycation and AGEs formation and hence, against AGEs induced health complications. Although, few species of polyphenolic compounds are being used in in vitro trials and their in vivo study is still in progress, increasing the area of research in this field may produce a fruitful approach in management of overall diabetic complications.

Advanced Glycation End-Products Suppress Mitochondrial Function and Proliferative Capacity of Achilles Tendon-Derived Fibroblasts

Debilitating cases of tendon pain and degeneration affect the majority of diabetic individuals. The high rate of tendon degeneration persists even when glucose levels are well controlled, suggesting that other mechanisms may drive tendon degeneration in diabetic patients. The purpose of this study was to investigate the impact of advanced glycation end-products on tendon fibroblasts to further our mechanistic understanding of the development and progression of diabetic tendinopathy. We proposed that advanced glycation end-products would induce limitations to mitochondrial function and proliferative capacity in tendon-derived fibroblasts, restricting their ability to maintain biosynthesis of tendon extracellular matrix. Using an in-vitro cell culture system, rat Achilles tendon fibroblasts were treated with glycolaldehyde-derived advanced glycation end-products (0, 50, 100, and 200 μg/ml) for 48 hours in normal glucose (5.5 mM) and high glucose (25 mM) conditions. We demonstrate that tendon fibroblasts treated with advanced glycation end-products display reduced ATP production, electron transport efficiency, and proliferative capacity. These impairments were coupled with alterations in mitochondrial DNA content and expression of genes associated with extracellular matrix remodeling, mitochondrial energy metabolism, and apoptosis. Our findings suggest that advanced glycation end-products disrupt tendon fibroblast homeostasis and may be involved in the development and progression of diabetic tendinopathy.

Association of Receptor for advanced glycation end products G82S polymorphism with chronic periodontitis in type II diabetic and non-diabetic South Indians

AIM The current study investigated the association of RAGE G82S polymorphism with chronic periodontitis in South Indians with and without type II Diabetes mellitus.

MATERIALS AND METHODS

405 individuals were enrolled into 3 groups-systemically and periodontally healthy with no attachment loss (n = 135), generalized chronic periodontitis (n = 135)and generalized chronic periodontitis with type II diabetes mellitus(n = 135). Periodontal clinical parameters were recorded. RFLP-PCR was utilized for genotyping.

RESULTS

Frequencies of genotype GG, GA and AA were 133, 2, 0 in group I respectively, 131, 4, 0 in group II respectively and 118, 13, 4 in group III respectively. Pearson's Chi squared test demonstrated a significant difference in the genotype distribution between the three groups (χ² = 19.88,P < 0.001). Fischer exact-test showed that the variant GA/AA genotype was associated with a significantly increased risk for generalized chronic periodontitis in type II diabetics when compared with the GG genotype of systemically and periodontally healthy subjects (OR-9.58, 95% CI 2.168-42.339, P < 0.001) and non-diabetic chronic periodontitis subjects (OR- 4.71, 95% CI: 1.54-14.42, P < 0.05). No association and increased susceptibility to chronic periodontitis was observed in subjects with GA/AA genotype when compared with systemically and periodontally healthy subjects (OR- 2.031, 95% CI: 0.366-11.277 P > 0.05). Furthermore, comparison of clinical parameters based on genotype distribution revealed statistically significant higher mean plaque (P < 0.05) and sulcus bleeding score (P < 0.001) in group-III subjects.

CONCLUSION

RAGE G82S gene polymorphism confers susceptibility to generalized chronic periodontitis in type II diabetic subjects of South Indian Tamilian ethnicity.

Advanced Glycation End Products (AGEs), Receptor for AGEs, Diabetes, and Bone: Review of the Literature

Diabetes compromises bone cell metabolism and function, resulting in increased risk of fragility fracture. Advanced glycation end products (AGEs) interact with the receptor for AGEs (RAGE) and can make a meaningful contribution to bone cell metabolism and/or alter function. Searches in PubMed using the key words "advanced glycation end-product," "RAGE," "sRAGE," "bone," and "diabetes" were made to explain some of the clinical outcomes of diabetes in bone metabolism through the AGE-RAGE signaling pathway. All published clinical studies were included in tables. The AGE-RAGE signaling pathway participates in diabetic complications, including diabetic osteopathy. Some clinical results in diabetic patients, such as reduced bone density, suppressed bone turnover markers, and bone quality impairment, could be potentially due to AGE-RAGE signaling consequences. However, the AGE-RAGE signaling pathway has some helpful roles in the bone, including an increase in osteogenic function. Soluble RAGE (sRAGE), as a ligand decoy, may increase in either conditions of RAGE production or destruction, and then it cannot always reflect the AGE-RAGE signaling. Recombinant sRAGE can block the AGE-RAGE signaling pathway but is associated with some limitations, such as accessibility to AGEs, an increase in other RAGE ligands, and a long half-life (24 hours), which is associated with losing the beneficial effect of AGE/RAGE. As a result, sRAGE is not a helpful marker to assess activity of the RAGE signaling pathway. The recombinant sRAGE cannot be translated into clinical practice due to its limitations.

Atorvastatin prevents advanced glycation end products (AGEs)-induced cardiac fibrosis via activating peroxisome proliferator-activated receptor gamma (PPAR-γ)

BACKGROUND

Previous studies have shown that the activation of advanced glycation end products (AGEs) contributed to the cardiac fibrosis in diabetic patients. Although it had been reported that statins have beneficial effects on cardiac fibrosis in hypertension and myocardial ischemia models, their effects on AGEs models have not been studied. We aimed to investigate the effects of atorvastatin (Ator) on the AGEs-induced cardiac fibrosis both in vitro and vivo.

METHODS

Male Sprague-Dawley rats were randomly divided into four groups: Control, AGEs, Ator or AGEs+Ator. The cardiac function was evaluated with the echocardiography at the second and the third month. Fibrosis area, α-SMA and RAGE expression in cardiac tissue were measured. For in vitro study, rat cardiac fibroblasts were treated with PD98059 (ERK inhibitor), Ator or Ator+GW9662 (PPAR-γ antagonist), and then were stimulated with AGEs. Fibroblasts proliferation, ERK1/2, phosphorylated ERK1/2, α-SMA, and RAGE expression were studied.

RESULTS

Compared with the control group, in vivo treatment with Ator significantly retarded the AGEs-induced diastolic function and attenuated cardiac fibrosis, α-SMA, and RAGE over expression induced by AGEs. Consistently, Ator prominently downregulated RAGE and α-SMA, while inhibited phosphorylation of ERK1/2 and fibroblast proliferation induced by AGEs in vitro. The GW9662 neutralized these effects of Ator on cardiac fibroblasts stimulated by AGEs.

CONCLUSION

In this study, we demonstrated that AGEs-induced fibroblast proliferation and differentiation were dependent on AGEs-RAGE-ERK1/2 pathway and that atorvastatin could block this pathway via activating PPAR-γ.

AGE-RAGE signal generates a specific NF-κB RelA "barcode" that directs collagen I expression

Advanced glycation end products (AGEs) are sugar-modified biomolecules that accumulate in the body with advancing age, and are implicated in the development of multiple age-associated structural and functional abnormities and diseases. It has been well documented that AGEs signal via their receptor RAGE to activate several cellular programs including NF-κB, leading to inflammation. A large number of stimuli can activate NF-κB; yet different stimuli, or the same stimulus for NF-κB in different cellular settings, produce a very different transcriptional landscape and physiological outcome. The NF-κB barcode hypothesis posits that cellular network dynamics generate signal-specific post-translational modifications, or a “barcode” to NF-κB, and that a signature “barcode” mediates a specific gene expression pattern. In the current study, we established that AGE-RAGE signaling results in NF-κB activation that directs collagen Ia1 and Ia2 expression. We further demonstrated that AGE-RAGE signal induces phosphorylation of RelA at three specific residues, T254, S311, and S536. These modifications are required for transcription of collagen I genes and are a consequence of cellular network dynamics. The increase of collagen content is a hallmark of arterial aging, and our work provides a potential mechanistic link between RAGE signaling, NF-κB activation, and aging-associated arterial alterations in structure and function.

Biological Effects Induced by Specific Advanced Glycation End Products in the Reconstructed Skin Model of Aging

Advanced glycation end products (AGEs) accumulate in the aging skin. To understand the biological effects of individual AGEs, skin reconstructed with collagen selectively enriched with N^ɛ-(carboxymethyl)-lysine (CML), N^ɛ-(carboxyethyl)-lysine (CEL), methylglyoxal hydroimidazolone (MG-H1), or pentosidine was studied. Immunohistochemistry revealed increased expression of α6 integrin at the dermal epidermal junction by CEL and CML (p<0.01). Laminin 5 was diminished by CEL and MG-H1 (p<0.05). Both CML and CEL induced a robust increase (p<0.01) in procollagen I. In the culture medium, IL-6, VEGF, and MMP1 secretion were significantly decreased (p<0.05) by MG-H1. While both CEL and CML decreased MMP3, only CEL decreased IL-6 and TIMP1, while CML stimulated TIMP1 synthesis significantly (p<0.05). mRNA expression studies using qPCR in the epidermis layer showed that CEL increased type 7 collagen (COL7A1), β1, and α6 integrin, while CML increased only COL7A1 (p<0.05). MG-H1-modified collagen had no effect. Importantly, in the dermis layer, MMP3 mRNA expression was increased by both CML and MG-H1. CML also significantly increased the mRNAs of MMP1, TIMP1, keratinocyte growth factor (KGF), IL-6, and monocyte chemoattractant protein 1 (MCP1) (p<0.05). Mixed effects were present in CEL-rich matrix. Minimally glycoxidized pentosidine-rich collagen suppressed most mRNAs of the genes studied (p<0.05) and decreased VEGF and increased MCP1 protein expression. Taken together, this model of the aging skin suggests that a combination of AGEs tends to counterbalance and thus minimizes the detrimental biological effects of individual AGEs.

RAGE, receptor of advanced glycation endoproducts, negatively regulates chondrocytes differentiation

RAGE, receptor for advanced glycation endoproducts (AGE), has been characterized as an activator of osteoclastgenesis. However, whether RAGE directly regulates chondrocyte proliferation and differentiation is unclear. Here, we show that RAGE has an inhibitory role in chondrocyte differentiation. RAGE expression was observed in chondrocytes from the prehypertrophic to hypertrophic regions. In cultured cells, overexpression of RAGE or dominant-negative-RAGE (DN-RAGE) demonstrated that RAGE inhibited cartilaginous matrix production, while DN-RAGE promoted production. Additionally, RAGE regulated Ihh and Col10a1 negatively but upregulated PTHrP receptor. Ihh promoter analysis and real-time PCR analysis suggested that downregulation of Cdxs was the key for RAGE-induced inhibition of chondrocyte differentiation. Overexpression of the NF-κB inhibitor I-κB-SR inhibited RAGE-induced NF-κB activation, but did not influence inhibition of cartilaginous matrix production by RAGE. The inhibitory action of RAGE was restored by the Rho family GTPases inhibitor Toxin B. Furthermore, inhibitory action on Ihh, Col10a1 and Cdxs was reproduced by constitutively active forms, L63RhoA, L61Rac, and L61Cdc42, but not by I-κB-SR. Cdx1 induced Ihh and Col10a1 expressions and directly interacted with Ihh promoter. Retinoic acid (RA) partially rescued the inhibitory action of RAGE. These data combined suggests that RAGE negatively regulates chondrocyte differentiation at the prehypertrophic stage by modulating NF-κB-independent and Rho family GTPases-dependent mechanisms.

Potential of the angiotensin receptor blockers (ARBs) telmisartan, irbesartan, and candesartan for inhibiting the HMGB1/RAGE axis in prevention and acute treatment of stroke

Stroke is a major cause of mortality and disability worldwide. The main cause of stroke is atherosclerosis, and the most common risk factor for atherosclerosis is hypertension. Therefore, antihypertensive treatments are recommended for the prevention of stroke. Three angiotensin receptor blockers (ARBs), telmisartan, irbesartan and candesartan, inhibit the expression of the receptor for advanced glycation end-products (RAGE), which is one of the pleiotropic effects of these drugs. High mobility group box 1 (HMGB1) is the ligand of RAGE, and has been recently identified as a lethal mediator of severe sepsis. HMGB1 is an intracellular protein, which acts as an inflammatory cytokine when released into the extracellular milieu. Extracellular HMGB1 causes multiple organ failure and contributes to the pathogenesis of hypertension, hyperlipidemia, diabetes mellitus, atherosclerosis, thrombosis, and stroke. This is the first review of the literature evaluating the potential of three ARBs for the HMGB1-RAGE axis on stroke therapy, including prevention and acute treatment. This review covers clinical and experimental studies conducted between 1976 and 2013. We propose that ARBs, which inhibit the HMGB1/RAGE axis, may offer a novel option for prevention and acute treatment of stroke. However, additional clinical studies are necessary to verify the efficacy of ARBs.

Periodontal disease and type 2 diabetes mellitus: is the HMGB1-RAGE axis the missing link?

Periodontitis is a major chronic inflammatory disease associated with increased production of numerous proinflammatory cytokines, which leads to the destruction of the periodontal tissue and ultimately loss of teeth. Periodontitis has powerful and multiple influences on the occurrence and severity of systemic conditions and diseases, such as diabetes mellitus, cardiovascular disease and respiratory disease. Meanwhile, diabetes is associated with increased prevalence, severity and progression of periodontal disease. There is also abundant evidence showing that diabetes plays important etiological roles in periodontitis. High mobility group box 1 (HMGB1) was recently identified as a lethal mediator of severe sepsis and comprises a group of intracellular proteins that function as inflammatory cytokines when released into the extracellular milieu. From a clinical perspective, extracellular HMGB1 can cause multiple organ failure and contribute to the pathogenesis of sepsis, rheumatoid arthritis, cardiovascular disease and diabetes. We recently reported that HMGB1 expression in periodontal tissues was elevated in patients with severe periodontitis. In addition, the receptor for advanced glycation end-products (RAGE), a receptor for HMGB1, was strongly expressed in gingival tissues obtained from patients with type 2 diabetes and periodontitis compared with systemically healthy patients with chronic periodontitis patients. From these data, we hypothesize that HMGB1 might play a role in the development of diabetes-associated periodontitis.

Arthroplasty in veterans: analysis of cartilage, bone, serum, and synovial fluid reveals differences and similarities in osteoarthritis with and without comorbid diabetes

Osteoarthritis patients with diabetes who receive total knee arthroplasty are more vulnerable to complications, including aseptic loosening and need for revision surgery. To elucidate mechanisms related to arthroplasty failure in diabetes, we examined serum and synovial fluid markers as well as collagen crosslinks in bone and cartilage of 20 patients (10 with diabetes, 10 controls without) undergoing this procedure. Hemoglobin A1c, body mass index, bone alkaline phosphatase, leptin, osteocalcin, and pyridinium were analyzed along with tissue content of the crosslinks hydroxylysylpyridinoline, lysylpyridinoline, and pentosidine. Pentosidine levels in tissue specimens from diabetic subjects were higher than in control subjects. Osteocalcin levels negatively correlated with hydroxylysylpyridinoline levels in cartilage. Osteocalcin levels also negatively correlated with pentosidine levels in cartilage, but only in subjects with diabetes. This study suggests potential metabolic mechanisms for arthroplasty failure in patients with diabetes.

Natural history of age-related retinal lesions that precede AMD in mice fed high or low glycemic index diets

PURPOSE

Epidemiologic data indicate that people who consume low glycemic index (GI) diets are at reduced risk for the onset and progression of age-related macular degeneration (AMD). The authors sought corroboration of this observation in an animal model.

METHODS

Five- and 16-month-old C57BL/6 mice were fed high or low GI diets until they were 17 and 23.5 months of age, respectively. Retinal lesions were evaluated by transmission electron microscopy, and advanced glycation end products (AGEs) were evaluated by immunohistochemistry.

RESULTS

Retinal lesions including basal laminar deposits, loss of basal infoldings, and vacuoles in the retinal pigment epithelium were more prevalent in the 23.5- than in the 17-month-old mice. Within each age group, consumption of a high GI diet increased the risk for lesions and the risk for photoreceptor abnormalities and accumulation of AGEs.

CONCLUSIONS

Consuming high GI diets accelerates the appearance of age-related retinal lesions that precede AMD in mice, perhaps by increasing the deposition of toxic AGEs in the retina. The data support the hypothesis that consuming lower GI diets, or simulation of their effects with nutraceuticals or drugs, may protect against AMD. The high GI-fed C57BL/6 mouse is a new model of age-related retinal lesions that precede AMD and mimic the early stages of disease and may be useful for drug discovery.

The effects of the receptor for advanced glycation end products (RAGE) on bone metabolism under physiological and diabetic conditions

It has been reported that AGEs and the receptor for AGEs (RAGEs) have been linked to the pathogenesis of diabetic microangiopathy. However, the relationship between RAGE and alteration in bone metabolism is unclear. Therefore, in order to determine the role of RAGE in bone metabolism, we investigated the effects of RAGE deletion on bone metabolism under physiological and diabetic conditions using RAGE knockout mice (RAGE-KO). Eight-week-old male RAGE-KO and wild-type littermates (WT) were intraperitoneally injected with either streptozotocin or vehicle. Mice were classified into four groups: (1) nondiabetic WT; (2) nondiabetic RAGE-KO; (3) diabetic WT; and (4) diabetic RAGE-KO. After 12 weeks of streptozotocin or vehicle treatment, the physical properties of femora and the static and dynamic parameters of bone histomorphometry of tibiae were assessed. The deletion of RAGE affected neither body weights nor hemoglobin A1c levels. RAGE deletion resulted in increased bone mineral density due to decreased osteoclast function under physiological conditions that is no accumulation of AGEs. In contrast, lacking RAGE did not affect the alteration in bone metabolism under diabetic conditions, suggesting that AGEs-RAGE interaction may not be involved in the pathogenesis of diabetic osteopenia, although RAGE plays a crucial role in bone metabolism.

Advanced glycation end-products activate extracellular signal-regulated kinase via the oxidative stress-EGF receptor pathway in renal fibroblasts

Advanced glycation end-products (AGEs), epidermal growth factor receptor (EGFR), reactive oxygen species (ROS), and extracellular signal-regulated kinases (ERK) are implicated in diabetic nephropathy (DN). Therefore, we asked if AGEs-induced ERK protein phosphorylation and mitogenesis are dependent on the receptor for AGEs (RAGE)-ROS-EGFR pathway in normal rat kidney interstitial fibroblast (NRK-49F) cells. We found that AGEs (100 microg/ml) activated EGFR and ERK1/2, which was attenuated by RAGE short-hairpin RNA (shRNA). AGEs also increased RAGE protein and intracellular ROS levels while RAGE shRNA and N-acetylcysteine (NAC) attenuated AGEs-induced intracellular ROS. Hydrogen peroxide (5-25 microM) increased RAGE protein level while activating both EGFR and ERK1/2. Low-dose hydrogen peroxide (5 microM) increased whereas high-dose hydrogen peroxide (100 microM) decreased mitogenesis at 3 days. AGEs-activated EGFR and ERK1/2 were attenuated by an anti-oxidant (NAC) and an EGFR inhibitor (Iressa). Moreover, AGEs-induced mitogenesis was attenuated by RAGE shRNA, NAC, Iressa, and an ERK1/2 inhibitor (PD98059). In conclusion, it was found that AGEs-induced mitogenesis is dependent on the RAGE-ROS-EGFR-ERK1/2 pathway whereas AGEs-activated ERK1/2 is dependent on the RAGE-ROS-EGFR pathway in NRK-49F cells.

Advanced glycation end products inhibit the expression of collagens type I and III by human gingival fibroblasts

BACKGROUND

It is evident that diabetes and periodontal disease are closely interrelated. Accumulation of advanced glycation end products (AGEs), coupled with exaggerated host responses to bacterial infection, may account for the increased periodontal destruction observed in patients with uncontrolled diabetes. The present study investigated the effects of AGEs on the viability of human gingival fibroblasts (HGFs) and the expression of types I and III collagen in HGFs.

METHODS

The cell viability of HGFs was examined by methylthiazolet-etrazolium assay, whereas the expression of types I and III collagen message and protein was detected by real-time quantitative reverse transcription-polymerase chain reaction and sandwich enzyme-linked immunosorbent assay, respectively.

RESULTS

AGEs significantly suppressed the cell viability of HGFs from 24 to 72 hours (P <0.01). A high concentration of glucose (25 mmol/l) in the culture media exaggerated the inhibition of the survival rate of HGFs (P <0.01). The expression of collagen types I and III messages and proteins was significantly downregulated at 72 hours by AGEs in a concentration-dependent manner (P <0.05). Moreover, the synthesis of intracellular types I and III collagen protein was markedly inhibited by AGEs (P <0.05).

CONCLUSIONS

AGEs may suppress the cell viability of HGFs and downregulate the expression of types I and III collagen by the cells. Further investigations are warranted to clarify the molecular mechanisms of AGEs in the regulation of cell function and collagen metabolism in patients with diabetes and periodontitis.

Mapping mechanisms and charting the time course of premature cell senescence and apoptosis: lysosomal dysfunction and ganglioside accumulation in endothelial cells

Endothelial cells subjected to glycated collagen I develop premature senescence within 3-5 days, as revealed by increased senescence-associated beta-galactosidase activity, decreased proliferation, and an increase in cell size. Here, we analyzed the time course and possible mechanisms of this process. Lysosomal integrity studies revealed a rapid collapse of pH gradient and lysosomal permeabilization, detectable after 30 min, and preceded by the increased production of reactive oxygen species. Measurement of mitochondrial membrane potential after application of glycated collagen demonstrated that depolarization was delayed by 4 h compared with changes in lysosomal pH and permeability. Based on the above findings of lysosomal permeabilization, we hypothesized that the reduced activity of senescence-associated beta-galactosidase could be responsible for the cellular accumulation of gangliosides, previously shown to induce cell senescence. After 5 days of exposure to glycated collagen, there was an increase in the levels of gangliosides GM3, GD1b, and GT1b, coincident with development of cell senescence. Treatment of endothelial cells with d-threo-EtDOP4, an inhibitor of glucosylceramide synthase, inhibited apoptosis, but not the development of senescence. In conclusion, collagen I modified by advanced glycation initially induces apoptosis of human umbilical vein endothelial cells. This process is initiated by the collapse of lysosomal pH and an increase in lysosomal permeability, with the subsequent mitochondrial depolarization and accumulation of gangliosides. Blockade of ganglioside synthesis suppresses apoptosis, but not senescence, which develops after 3 days of exposure to glycated collagen. These data imply a critical role for lysosomal permeabilization in triggering apoptosis of endothelial cells exposed to the diabetic milieu.

Distribution of the receptor for advanced glycation end products in the human male reproductive tract: prevalence in men with diabetes mellitus

BACKGROUND

Diabetics have a significantly higher percentage of sperm with nuclear DNA (nDNA) fragmentation and increased levels of advanced glycation end products (AGEs), in their testis, epididymis and sperm. As the receptor for AGEs (RAGE) is important to oxidative stress and cell dysfunction, we hypothesise, that it may be involved in sperm nDNA damage.

METHODS

Immunohistochemistry was performed to determine the presence of RAGE in the human testis and epididymis. A comparison of the receptor's incidence and localization on sperm from 10 diabetic and 11 non-diabetic men was conducted by blind semi-quantitative assessment of the immunostaining. Enzyme-linked immunosorbent assay analysis ascertained RAGE levels in seminal plasma and sperm from 21 diabetic and 31 non-diabetic subjects. Dual labelling immunolocalization was employed to evaluate RAGE's precise location on the sperm head.

RESULTS

RAGE was found throughout the testis, caput epididymis, particularly the principle cells apical region, and on sperm acrosomes. The number of sperm displaying RAGE and the overall protein amount found in sperm and seminal plasma were significantly higher in samples from diabetic men (P < 0.01, P < 0.0001 and P < 0.0001, respectively).

CONCLUSIONS

The presence of RAGE implies that it may play a central role in sperm nDNA damage particularly in diabetic men where the levels are elevated.

The induction of surface β-amyloid binding proteins and enhanced cytotoxicity in cultured PC-12 and IMR-32 cells by advanced glycation end products

During aging the non-enzymatic glycation of proteins and other molecules increases significantly, leading to the accumulation of advanced glycation end-products (AGEs). These AGEs enhance inflammatory and autoimmune reactions with resultant cytotoxicity. We noted in an earlier study that individuals with Alzheimer's disease exhibit enhanced expression of the receptor for advanced glycation end-products (RAGE) on the surface of their leukocytes. In order to better understand the relationship between AGEs and the cell surface binding of amyloid-beta protein (Abeta) 42 we studied the effect of two AGEs: glycated bovine serum albumin (BSA), and epsilon-carboxymethyllysine-BSA (CML), a glycoxidation product, on the binding of Abeta42 to rat PC-12 and IMR-32 cells. We measured the expression of three potential cell surface receptors binding Abeta42: RAGE, beta-amyloid precursor protein (beta-APP), and the alpha7 subtype of the nicotinic acetylcholine receptor (alpha7nAChR) by using specific antibody probes. Incubation of PC-12 or IMR-32 cells with bovine serum albumin-advanced glycation end-product (BSA-AGE) or with CML induced small but significant concentration-dependent increases in the expression of beta-APP, RAGE, and alpha7nAChRs as measured by flow cytometry or by ELISA. Incubation of the cells with 48 microM of either of the AGEs combined with varying concentrations (138-1100 nM) of Abeta42 resulted in the enhanced binding of the Abeta42 to the cell surface as compared with cells not exposed to the AGE co-treatment. The combination of AGE and Abeta treatment also resulted in the heightened expression of all three potential Abeta binding sites as well as their gene precursors. Exposure of cells to the same regimen of AGE plus Abeta resulted in the production of reactive oxygen species and mitochondrial toxicity. These results are consistent with the ability of AGEs to enhance the cell surface expression of diverse Abeta42 binding sites, a factor that can lead to the enhanced binding of amyloid and subsequent cell death.

Receptor for advanced glycation end products and the cardiovascular complications of diabetes and beyond: lessons from AGEing

The presence of elevated blood glucose levels characterizes the diabetic state. Hyperglycemia may be caused by a number of underlying factors; however, the consequences of chronically elevated glucose are similar. Both the macrovasculature and microvasculature are exquisitely sensitive to the long-term effects of elevated blood glucose. Cardiovascular disease remains the leading cause of morbidity and mortality in diabetes, regardless of the underlying cause of hyperglycemia. Although other substrates, such as DNA, are susceptible to glycation, this article addresses the impact of nonenzymatic glycation on the proteome. The impact of Advanced Glycation End products (AGEs) on alteration of protein function and signal transduction mechanisms contributes to the pathogenesis of diabetes complications. This suggests that blocking the generation or molecular impact of AGEs may modulate the complications of diabetes.

Relationship of serum advanced glycation end products with deterioration of periodontitis in type 2 diabetes patients

BACKGROUND

A close relationship between diabetes and chronic periodontitis has been demonstrated. We previously found that Porphyromonas gingivalis with the type II fimA gene is an infectious factor closely associated with the deterioration seen in diabetic periodontitis patients. In the present study, we examined whether other biomarkers are related to the development and deterioration of periodontitis often seen in type 2 diabetic individuals.

METHODS

A total of 97 type 2 diabetes patients with and without periodontitis were recruited, and their periodontal and diabetic conditions were analyzed. The ratio (%) of teeth with an attachment loss >5 mm among all teeth in each subject was used as an index of periodontal deterioration. Peripheral blood was tested for levels of glycated hemoglobin (HbA1c), advanced glycation end products (AGEs), C-reactive protein (CRP), and cytokines (tumor necrosis factor [TNF]-alpha and interleukin [IL]-1beta). Subgingival plaque samples were also examined for the occurrences of Actinobacillus actinomycetemcomitans, Tannerella forsythensis, Treponema denticola, and Prevotella intermedia.

RESULTS

Serum AGEs were significantly associated with deterioration of periodontitis, whereas no other serum biochemical marker or bacterial occurrence showed a clear relationship with that condition.

CONCLUSION

AGEs may be factors associated with diabetic periodontitis and may be useful as biomarkers that reflect such deterioration.

Diabetes-enhanced inflammation and apoptosis--impact on periodontal pathology

Diabetes, particularly type 2 diabetes, is a looming health issue with many ramifications. Because diabetes alters the cellular microenvironment in many different types of tissues, it causes myriad untoward effects, collectively referred to as 'diabetic complications'. Two cellular processes affected by diabetes are inflammation and apoptosis. This review discusses how diabetes-enhanced inflammation and apoptosis may affect the oral environment. In particular, dysregulation of tumor necrosis factor and the formation of advanced glycation products, both of which occur at higher levels in diabetic humans and animal models, potentiate inflammatory responses and induce apoptosis of matrix-producing cells. The enhanced loss of fibroblasts and osteoblasts through apoptosis in diabetics could contribute to limited repair of injured tissue, particularly when combined with other known deficits in diabetic wound-healing. These findings may shed light on diabetes-enhanced risk of periodontal diseases.

The Receptor for Advanced Glycation End Products Is Highly Expressed in the Skin and Upregulated by Advanced Glycation End Products and Tumor Necrosis Factor-Alpha

Advanced glycation end products (AGEs) form non-enzymatically from reactions of proteins with reducing sugars. In the skin, AGEs were reported to accumulate in dermal elastin and collagens and to interact nonspecifically with the cell membrane of dermal fibroblasts. Therefore, AGEs may influence the process of skin aging. We investigated the presence of the AGE receptor RAGE in skin and the influence of AGEs on receptor expression and the formation of extracellular matrix (ECM). Sections of sun-protected and sun-exposed skin were analyzed with monoclonal antibodies against (RAGE), heat-shock protein 47, factor XIIIa, CD31, and CD45. RAGE was mainly expressed in fibroblasts, dendrocytes, and keratinocytes and to a minor extent in endothelial and mononuclear cells. Human foreskin fibroblasts (HFFs) highly expressed RAGE on the protein and mRNA level when analyzed by quantitative Western blotting and real-time PCR. Incubation of HFFs with the specific RAGE ligand Nepsilon-(carboxymethyl)lysine-modified BSA (CML-BSA) and tumor necrosis factor-alpha resulted in significant upregulation of RAGE expression. CML-BSA induced a mildly profibrogenic pattern, increasing connective tissue growth factor, transforming growth factor-beta (TGF-beta) 1, and procollagen-alpha1(I) mRNA, whereas expression of matrix metalloproteinase (MMP)-1, -2, -3, and -12 was unaffected. We conclude that in HFFs, AGE-RAGE interactions may influence the process of skin aging through mild stimulation of ECM gene expression.

ε-Glycation, APP and Aβ in ageing and Alzheimer disease: A hypothesis

The post-translational modifications of protein molecules include glycation, which may not only occur enzymatically controlled in N and O position, but also wherever proteins meet reducing sugars non-enzymatically in epsilon position at lysines (non-enzymatic (epsilon) glycation (NEG)). The formation of keto-amines from the amine-sugar compounds (Amadori re-arrangement) and further processing of the largely undigestible Amadori compounds eventually results in insoluble advanced glycation end products (AGEs). The latter can induce or favour disease including mental disorders. Preferential targets of NEG include large cell surface proteins. Ample evidence has been provided that NEG also occurs in the brain where cross-linking of epsilon-glycated proteins, induction of oxidative stress and signalling of AGEs through their specific receptor (RAGE) likely play a role in (brain) ageing and Alzheimer disease (AD). This is underscored by the demonstration of particular interactions between AGE/RAGE and amyloid-beta (Abeta) that favour the aggregation and deposition of Abeta and, perhaps, the formation of Abeta itself. The close relationship between NEG and Abeta, as well as other facts foster the hypothesis that NEG of the large trans-membrane amyloid precursor protein (APP) might be a significant factor in the induction of aberrant APP cleavage with production of Abeta, not only in normal ageing, but also in AD. Blockade of lysine cleavage sites on APP by sugar chains or marker effects induced by NEG akin to ubiquitination of proteins for degradation at lysines could be expected to contribute to altered processing of APP. The hypothesis of epsilon-glycation in APP proposed here and the review of evidences for the significance of NEG in brain ageing and AD are aimed at the stimulation of investigations into the still open question which role NEG plays with respect to APP and its abnormal processing in AD. It can be rendered likely that such research might open new avenues towards decreasing the risk of AD and/or slowing its progression through the prevention of NEG in APP with aberrant APP processing, increased generation of Abeta and the formation of AGEs from epsilon-glycated APP.

Importance of measuring products of non-enzymatic glycation of proteins

Non-enzymatic glycation products are a complex and heterogeneous group of compounds which accumulate in plasma and tissues in diabetes and renal failure. There is emerging evidence that these compounds may play a role in the pathogenesis of chronic complications associated with diabetes and renal failure. So measurement of the products of non-enzymatic glycation has a twofold meaning: on one hand, measurement of early glycation products can estimate the extent of exposure to glucose and the subject's previous metabolic control; on the other hand, measurement of intermediate and late products of the glycation reaction is a precious instrument in verifying the relationship between glycation products and tissue modifications. This review summarizes current knowledge about the diagnostic utility of measuring non-enzymatic glycation products.

Advanced glycation end products and RAGE: a common thread in aging, diabetes, neurodegeneration, and inflammation

The products of nonenzymatic glycation and oxidation of proteins and lipids, the advanced glycation end products (AGEs), accumulate in a wide variety of environments. AGEs may be generated rapidly or over long times stimulated by a range of distinct triggering mechanisms, thereby accounting for their roles in multiple settings and disease states. A critical property of AGEs is their ability to activate receptor for advanced glycation end products (RAGE), a signal transduction receptor of the immunoglobulin superfamily. It is our hypothesis that due to such interaction, AGEs impart a potent impact in tissues, stimulating processes linked to inflammation and its consequences. We hypothesize that AGEs cause perturbation in a diverse group of diseases, such as diabetes, inflammation, neurodegeneration, and aging. Thus, we propose that targeting this pathway may represent a logical step in the prevention/treatment of the sequelae of these disorders.

Advanced glycation endproducts--role in pathology of diabetic complications

Diabetes mellitus is a common endocrine disorder characterised by hyperglycaemia and predisposes to chronic complications affecting the eyes, blood vessels, nerves and kidneys. Hyperglycaemia has an important role in the pathogenesis of diabetic complications by increasing protein glycation and the gradual build-up of advanced glycation endproducts (AGEs) in body tissues. These AGE form on intra- and extracellular proteins, lipids, nucleic acids and possess complex structures that generate protein fluorescence and cross-linking. Protein glycation and AGE are accompanied by increased free radical activity that contributes towards the biomolecular damage in diabetes. There is considerable interest in receptors for AGEs (RAGE) found on many cell types, particularly those affected in diabetes. Recent studies suggest that interaction of AGEs with RAGE alter intracellular signalling, gene expression, release of pro-inflammatory molecules and free radicals that contribute towards the pathology of diabetic complications. This review introduces the chemistry of glycation and AGEs and examines the mechanisms by which they mediate their toxicity. The role of AGEs in the pathogenesis of retinopathy, cataract, atherosclerosis, neuropathy, nephropathy, diabetic embryopathy and impaired wound healing are considered. There is considerable interest in anti-glycation compounds because of their therapeutic potential. The mechanisms and sites of action of selected inhibitors, together with their potential in preventing diabetic complications are discussed.

Activation of receptor for advanced glycation end products in osteoarthritis leads to increased stimulation of chondrocytes and synoviocytes

OBJECTIVE

The major risk factor for osteoarthritis (OA) is aging, but the mechanisms underlying this risk are only partly understood. Age-related accumulation of advanced glycation end products (AGEs) could be one of these mechanisms. We undertook this study to investigate the role of the receptor for AGEs (RAGE) in mediating the cellular effects of AGEs on chondrocytes and fibroblast-like synoviocytes (FLS).

METHODS

AGE levels in human cartilage were determined by fluorescence, browning, and pentosidine levels. Chondrocyte activation by AGEs was assessed as the release of proteoglycans and the synthesis of matrix metalloproteinase 1 (MMP-1) and type II collagen messenger RNA (mRNA). The activation of FLS by AGEs was measured by MMP-1 production and invasion through matrix proteins.

RESULTS

Patients with focal degeneration of cartilage showed increased AGE levels in their healthy cartilage compared with the levels in healthy cartilage from donors without cartilage degeneration (P < 0.01 for both fluorescence and browning; P not significant for pentosidine content). Stimulation of bovine chondrocytes with glycated albumin increased the release of proteoglycans by 110% (P < 0.001) and the production of MMP-1 mRNA by 200% (P = 0.028). In addition, OA FLS produced 240% more MMP-1 when stimulated with glycated albumin (P < 0.001). Glycated matrix or albumin increased the catabolic activity of OA FLS, which was assessed as invasive behavior, by 150% and 140% (P = 0.001 and P = 0.010), respectively. Effects of stimulation with AGEs were blocked by a neutralizing antibody against RAGE, but not by an isotype control.

CONCLUSION

This study shows that AGEs trigger RAGE on chondrocytes and FLS, leading to increased catabolic activity and therefore to cartilage degradation. AGEs, via RAGE, could therefore contribute to the development and/or progression of OA.

Advanced glycation end products enhance expression of pro-apoptotic genes and stimulate fibroblast apoptosis through cytoplasmic and mitochondrial pathways

Both aging and diabetes are characterized by the formation of advanced glycation end products (AGEs). Both exhibit other similarities including deficits in wound healing that are associated with higher rates of fibroblast apoptosis. In order to investigate a potential mechanism for enhanced fibroblast apoptosis in diabetes and aged individuals, experiments were carried out to determine whether the predominant advanced glycation end product in skin, N-epsilon-(carboxymethyl) lysine (CML)-collagen, could induce fibroblast apoptosis. In vivo experiments established that CML-collagen but not unmodified collagen induced fibroblast apoptosis and that apoptosis was dependent upon caspase-3, -8, and -9 activity. In vitro experiments demonstrated that CML-collagen but not control collagen induced a time- and dose-dependent increase in fibroblast apoptosis. By use of blocking antibodies, apoptosis was shown to be mediated through receptor for AGE signaling. AGE-induced apoptosis was largely dependent on the effector caspase, caspase-3, which was activated through both cytoplasmic (caspase-8-dependent) and mitochondrial (caspase-9) pathways. CML-collagen had a global effect of enhancing mRNA levels of pro-apoptotic genes that included several classes of molecules including ligands, receptors, adaptor molecules, mitochondrial proteins, and others. However, the pattern of expression was not identical to the pattern of apoptotic genes induced by tumor necrosis factor alpha.

Use of topical sRAGE in diabetic wounds increases neovascularization and granulation tissue formation

Advanced glycation end products (AGEs) accumulate in diabetic wounds as a result of the glycosylation of various proteins. Interaction of AGEs with the receptor for AGEs (RAGE) results in an exaggerated inflammatory response and compromised collagen production. These changes lead to impaired wound healing. A soluble form of RAGE (sRAGE) has been shown to bind AGEs and thereby blunt their pathogenetic effects. Using genetically diabetic C57BLks-db/db mice, the authors applied sRAGE topically to standardized full-thickness wounds to improve diabetic wound healing. They measured various parameters of wound healing such as neovascularization, reepithelialization, collagen formation, and granulation tissue area. Their results showed a statistically significant increase in granulation tissue area and microvascular density in the sRAGE group compared with untreated wounds. There was a trend toward a smaller epithelial gap in the sRAGE-treated group that did not reach statistical significance. The authors conclude that sRAGE may be a powerful treatment of accelerating diabetic wound healing.

RAGE and its ligands: a lasting memory in diabetic complications?

The complications of diabetes are myriad and represent a rising cause of morbidity and mortality, particularly in the Western world. The update of the Diabetes Control and Clinical Trials Group/Epidemiology of Diabetes Interventions and Complications Research Group (DCCT/EDIC) suggested that previous strict control of hyperglycaemia was associated with reduced carotid atherosclerosis compared to conventional treatment, even after levels of glycosylated haemoglobin between the two treatment groups became indistinguishable. These intriguing findings prompt the key question, why does the blood vessel 'remember'? This review focuses on the hypothesis that the ligand/RAGE axis contributes importantly to glycaemic 'memory'. Studies in rodent models of diabetes suggest that blockade or genetic modification of RAGE suppress diabetes-associated progression of atherosclerosis, exaggerated neointimal expansion consequent to acute arterial injury, and cardiac dysfunction. We propose that therapeutic RAGE blockade will intercept maladaptive diabetes-associated memory in the vessel wall and provide cardiovascular protection in diabetes.

Anabolic Potential of Fibroblasts from Chronically Inflamed Gingivae Grown in a Hyperglycemic Culture Medium in the Presence or Absence of Insulin and Nicotine

BACKGROUND

Impaired fibroblast function due to hyperglycemia shows reversal in response to insulin. The aim of this investigation was to use a hyperglycemic cell-culture model to study the anabolic products of androgen metabolism in fibroblasts in response to insulin and nicotine.

METHODS

Human gingival fibroblasts were derived from chronically inflamed gingivae of six nondiabetic periodontal patients with no history of smoking. Six cell lines were established in monolayer culture in 24 well multiwell plates, and duplicate incubations were performed with each cell line for all three experiments. Eagle's minimum essential medium was used in a range of individual experiments, with radiolabeled testosterone as substrate, in the presence or absence of (1) glucose (1 to 4,000 microg/ml); (2) insulin (1 to 100 microg/ml) independently; (3) an effective concentration of glucose (500 microg/ml) with serial concentrations of insulin (1 to 100 microg/ml); and (4) effective concentrations of nicotine (250 microg/ml), glucose, and their combinations in response to insulin (5 microg/ml). The controls contained no agents other than the radiolabeled substrate. At the end of a 24-hour incubation period, the medium was solvent extracted with ethyl acetate, and androgen metabolites were separated by thin-layer chromatography and were quantified using a radioisotope scanner.

RESULTS

The androgen substrate 14C-testosterone was metabolized mainly to 5alpha-dihydrotestosterone (DHT) and 4-androstenedione. (1) Glucose at a concentration of 500 microg/ml reduced yields of DHT by 36% (n = 6; P < 0.01). (2) Insulin caused a small but significant inhibition of DHT in normoglycemic cells. (3) Serial concentrations of insulin significantly counteracted the inhibitory effects of glucose on the yields of DHT (n = 6; P < 0.01). (4) The independent inhibitory effects of nicotine and glucose on metabolic yields of DHT were marginally more pronounced in combination but significantly overcome in the presence of insulin.

CONCLUSION

Human gingival fibroblasts obtained from chronically inflamed tissue of nondiabetic patients demonstrated that the inhibitory effects of glucose and nicotine on androgen metabolism can be overcome by insulin, in varying degrees.

Stimulation of osteoclastic bone resorption in a model of glycerol-induced acute renal failure: evidence for a parathyroid hormone-independent mechanism

This study was undertaken to evaluate the bone changes occurring in rats with acute renal failure (ARF). Acute renal failure was induced in rats 24 hours after dehydration by an intramuscular injection of glycerol. After induction of ARF, the rats were divided into two groups, one of which underwent parathyroidectomy (PTX). Rats with normal renal function, matched for age and weight, were used as controls and divided into two groups, one of them for PTX. At termination of the study blood and urine chemistry and bone histomorphometry were analyzed. Rats with glycerol-induced ARF developed bone changes compatible with mild hyperparathyroid bone disease, characterized mainly by increased osteoclastic bone resorption when compared with control rats having normal renal function. Rats with normal renal function following PTX developed bone disease showing complete suppression of forming and resorptive parameters. Rats with glycerol-induced ARF and PTX showed abolishment of all bone forming parameters, but a dramatic increase in osteoclastic resorption was apparent. Based on these observations we suggest that, in this model of glycerol-induced ARF, osteoclastic bone resorption may develop in the absence of parathyroid hormone, probably stimulated by other potent osteoclastogenic factors.

Photosensitized growth inhibition of cultured human skin cells: mechanism and suppression of oxidative stress from solar irradiation of glycated proteins

Chronic exposure to sunlight plays a role in skin aging and carcinogenesis. The molecular mechanisms of photodamage by ultraviolet A, the sunlight's major ultraviolet constituent, are poorly understood. Here we provide evidence that advanced glycation end products on proteins are sensitizers of photo-oxidative stress in skin cells. Glycation is a process of protein damage by reducing sugars and other reactive carbonyl species leading to the formation of advanced glycation end products, which accumulate on long-lived proteins such as dermal elastin and collagen during skin aging. Growth inhibition as a result of advanced glycation end product photosensitization of ultraviolet A and solar-simulated light was demonstrated in human keratinocytes and fibroblasts. Using advanced glycation end product bovine serum albumin and advanced glycation end product collagen as model photosensitizers, ultraviolet A-induced formation of H2O2 was identified as the key mediator of skin cell growth inhibition as evidenced by complete protection by catalase treatment and equivalent growth inhibition of unirradiated cells treated with pre-irradiated advanced glycation end product protein. D-penicillamine protected against advanced glycation end product-photosensitized growth inhibition even when added following irradiation, suggesting the feasibility of therapeutic approaches for protection against skin ultraviolet A damage. Photosensitized growth inhibition increased with the degree of advanced glycation end product modification paralleled by the amount of H2O2 formed upon solar-simulated light irradiation of the protein. Photosensitization was not observed using bovine serum albumin modified with the major advanced glycation end product, Nepsilon-carboxymethyl-L-lysine, ruling out effects of cellular advanced glycation end product receptor (RAGE) stimulation. In contrast to bovine serum albumin, unglycated collagen showed photosensitization in CF3 fibroblasts and generation of H2O2 upon solar-simulated light irradiation. This study supports the hypothesis that advanced glycation end product-modified proteins are endogenous sensitizers of photo-oxidative cell damage in human skin by ultraviolet A-induced generation of reactive oxygen species contributing to photoaging and photocarcinogenesis.

Beta 2-microglobulin amyloidosis: role of monocytes/macrophages

PURPOSE OF REVIEW

Macrophage infiltration is a distinctive histological characteristic of beta2-microglobulin amyloidosis. Studies reported during the past years have helped to clarify the role of monocytes/macrophages in the fibrillar precipitation of beta2-microglobulin and in the pathogenesis of osteoarticular pathology.

RECENT FINDINGS

Contrary to the original view, macrophage infiltration is more likely a secondary phenomenon of amyloidosis rather than an initiating event. The observation that macrophages are associated with a later stage of beta2-microglobulin amyloidosis suggests a possible role of these cells in transformation of clinical silent deposits into symptomatic osteoarticular destruction. Accumulating evidence suggests that beta2-microglobulin modified with advanced glycation end products plays a key role in recruitment and activation of macrophages through an advanced glycation end products receptor-mediated pathway, and thus may contribute to the development of local cellular inflammation in beta2-microglobulin amyloidosis.

SUMMARY

Beta 2-microglobulin amyloidosis arthropathies may result from progressive accumulation of advanced glycation end products in long-lived amyloid linked to a heightened cellular response. Antagonism of the interaction between advanced glycation end products and their receptor may be a relevant strategy for cellular inflammation in beta2-microglobulin amyloidosis.

Receptor for advanced glycation end products on human synovial fibroblasts: role in the pathogenesis of dialysis-related amyloidosis

An important component of amyloid fibrils in dialysis-related amyloidosis (DRA) is beta(2)-microglobulin (beta(2)m) modified with advanced glycation end products (AGE). The amyloid deposits are located principally in joint structures, with adjacent chronic inflammatory reaction characterized by monocyte infiltration. This study examined the interaction of AGE-beta(2)m with human synovial fibroblasts and investigated the proinflammatory effects of that interaction. It was demonstrated that human synovial fibroblasts constitutively expressed the receptor for AGE (RAGE). RAGE expression was detected mainly in synovial intima and was upregulated in DRA synovium. (125)I-AGE-beta(2)m bound to immobilized human synovial fibroblasts in a specific, dose-dependent manner (K(d) of approximately 138.0 nM), and binding was inhibited by anti-RAGE IgG. Incubation of human synovial fibroblasts with AGE-beta(2)m induced degradation of this AGE-modified protein, as well as increased monocyte chemoattractant protein-1 (MCP-1) mRNA and protein expression. The amount of MCP-1 produced by AGE-beta(2)m-stimulated human synovial fibroblasts was sufficient to induce the chemotaxis of monocytes. MCP-1 synthesis resulted from engagement of RAGE, because the increase in MCP-1 synthesis was attenuated by preincubation of human synovial fibroblasts with anti-RAGE IgG. These data provide evidence of RAGE-mediated perturbation of human synoviocytes, which may be involved in the pathogenesis of inflammatory processes associated with DRA.