Advanced Glycation End Products and Diabetic Nephropathy

Parallelism and non-parallelism in diabetic nephropathy and diabetic retinopathy

Diabetic nephropathy (DN) and diabetic retinopathy (DR), as microvascular complications of diabetes mellitus, are currently the leading causes of end-stage renal disease (ESRD) and blindness, respectively, in the adult working population, and they are major public health problems with social and economic burdens. The parallelism between the two in the process of occurrence and development manifests in the high overlap of disease-causing risk factors and pathogenesis, high rates of comorbidity, mutually predictive effects, and partial concordance in the clinical use of medications. However, since the two organs, the eye and the kidney, have their unique internal environment and physiological processes, each with specific influencing molecules, and the target organs have non-parallelism due to different pathological changes and responses to various influencing factors, this article provides an overview of the parallelism and non-parallelism between DN and DR to further recognize the commonalities and differences between the two diseases and provide references for early diagnosis, clinical guidance on the use of medication, and the development of new drugs.

Generation of autoantibodies against glycated fibrinogen: Role in diabetic nephropathy and retinopathy

The process of glycation, characterized by the non-enzymatic reaction between sugars and free amino groups on biomolecules, is a key contributor to the development and progression of both microvascular and macrovascular complications associated with diabetes, particularly due to persistent hyperglycemia. This glycation process gives rise to advanced glycation end products (AGEs), which play a central role in the pathophysiology of diabetes complications, including nephropathy. The d-ribose-mediated glycation of fibrinogen plays a central role in the pathogenesis of diabetes nephropathy (DN) and retinopathy (DR) by the generation and accumulation of advanced glycation end products (AGEs). Glycated fibrinogen with d-ribose (Rb-gly-Fb) induces structural changes that trigger an autoimmune response by generating and exposing neoepitopes on fibrinogen molecules. The present research is designed to investigate the prevalence of autoantibodies against Rb-gly-Fb in individuals with type 2 diabetes mellitus (T2DM), DN & DR. Direct binding ELISA was used to test the binding affinity of autoantibodies from patients' sera against Rb-gly-Fb and competitive ELISA was used to confirm the direct binding findings by checking the bindings of isolated IgG against Rb-gly-Fb and its native conformer. In comparison to healthy subjects, 32% of T2DM, 67% of DN and 57.85% of DR patients' samples demonstrated a strong binding affinity towards Rb-gly-Fb. Both native and Rb-gly-Fb binding by healthy subjects (HS) sera were non-significant (p > 0.05). Furthermore, the early, intermediate, and end products of glycation have been assessed through biochemical and physicochemical analysis. The biochemical markers in the patient groups were also significant (p < 0.05) in comparison to the HS group. This study not only establishes the prevalence of autoantibodies against d-ribose glycated fibrinogen in DN but also highlights the potential of glycated fibrinogen as a biomarker for the detection of DN and/or DR. These insights may open new avenues for research into novel therapeutic strategies and the prevention of diabetes-related nephropathy and retinopathy.

Vitamin C supplementation lowers advanced glycation end products (AGEs) and malondialdehyde (MDA) in patients with type 2 diabetes: A randomized, double-blind, placebo-controlled clinical trial

This study evaluated how daily vitamin C administration impacts systemic oxidative stress and inflammation and its safety in T2D patients. This randomized, double-blinded, placebo-controlled, parallel-arm clinical trial included 70 patients with T2D. They were allocated to receive either 500 mg/day of vitamin C or a matching placebo for 8 weeks. Of the 70 subjects assigned to the trial, 57 were included in the statistical analysis (vitamin C: n = 32, placebo: n = 25). Inflammatory and oxidative markers, including advanced glycation end products (AGEs), malondialdehyde (MDA), advanced oxidation protein products (AOPP), oxidized low-density lipoprotein (ox-LDL), highly sensitive C-reactive protein (hs-CRP), tumor necrosis factor-α (TNF-α), and ferric reducing ability of plasma (FRAP) were measured at baseline and the end of the trial. In addition, vitamin C tolerance was evaluated. A nutritionist visited all participants for a standard diabetic regimen. Following vitamin C supplementation, the serum levels of MDA (p-value < .001) and AGEs (p-value = .002) demonstrated a significant decrease after controlling for multiple confounders, including age, blood pressure, waist circumference, HbA1C, TG, and LDL-C, while no significant changes were observed for AOPP (p-value = .234) and ox-LDL (p-value = .480). The FRAP showed an increasing trend as an antioxidant marker but was not statistically significant (p-value = .312). The hs-CRP and TNF-α had no significant changes (p-value: .899 and .454, respectively). Also, no major adverse events were observed. Vitamin C supplementation may be beneficial in reducing AGEs and MDA in patients with T2D.

Insight into the Molecular Mechanism of Diabetic Kidney Disease and the Role of Metformin in Its Pathogenesis

Diabetic kidney disease (DKD) is one of the leading causes of death among patients diagnosed with diabetes mellitus. Despite the growing knowledge about the pathogenesis of DKD, we still do not have effective direct pharmacotherapy. Accurate blood sugar control is essential in slowing down DKD. It seems that metformin has a positive impact on kidneys and this effect is not only mediated by its hypoglycemic action, but also by direct molecular regulation of pathways involved in DKD. The molecular mechanism of DKD is complex and we can distinguish polyol, hexosamine, PKC, and AGE pathways which play key roles in the development and progression of this disease. Each of these pathways is overactivated in a hyperglycemic environment and it seems that most of them may be regulated by metformin. In this article, we summarize the knowledge about DKD pathogenesis and the potential mechanism of the nephroprotective effect of metformin. Additionally, we describe the impact of metformin on glomerular endothelial cells and podocytes, which are harmed in DKD.

The Complement Pathway: New Insights into Immunometabolic Signaling in Diabetic Kidney Disease

Significance: The metabolic disorder, diabetes mellitus, results in microvascular complications, including diabetic kidney disease (DKD), which is partly believe to involve disrupted energy generation in the kidney, leading to injury that is characterized by inflammation and fibrosis. An increasing body of evidence indicates that the innate immune complement system is involved in the pathogenesis of DKD; however, the precise mechanisms remain unclear. Recent Advances: Complement, traditionally thought of as the prime line of defense against microbial intrusion, has recently been recognized to regulate immunometabolism. Studies have shown that the complement activation products, Complement C5a and C3a, which are potent pro-inflammatory mediators, can mediate an array of metabolic responses in the kidney in the diabetic setting, including altered fuel utilization, disrupted mitochondrial respiratory function, and reactive oxygen species generation. In diabetes, the lectin pathway is activated via autoreactivity toward altered self-surfaces known as danger-associated molecular patterns, or via sensing altered carbohydrate and acetylation signatures. In addition, endogenous complement inhibitors can be glycated, whereas diet-derived glycated proteins can themselves promote complement activation, worsening DKD, and lending support for environmental influences as an additional avenue for propagating complement-induced inflammation and kidney injury. Critical Issues: Recent evidence indicates that conventional renoprotective agents used in DKD do not target the complement, leaving this web of inflammatory stimuli intact. Future Directions: Future studies should focus on the development of novel pharmacological agents that target the complement pathway to alleviate inflammation, oxidative stress, and kidney fibrosis, thereby reducing the burden of microvascular diseases in diabetes. Antioxid. Redox Signal. 37, 781-801.

Comparison of metabolic fate, target organs, and microbiota interactions of free and bound dietary advanced glycation end products

Increased intake of Western diets and ultra-processed foods is accompanied by increased intake of advanced glycation end products (AGEs). AGEs can be generated exogenously in the thermal processing of food and endogenously in the human body, which associated with various chronic diseases. In food, AGEs can be divided into free and bound forms, which differ in their bioavailability, digestion, absorption, gut microbial interactions and untargeted metabolites. We summarized the measurements and contents of free and bound AGE in foods. Moreover, the ingestion, digestion, absorption, excretion, gut microbiota interactions, and metabolites and metabolic pathways between free and bound AGEs based on animal and human studies were compared. Bound AGEs were predominant in most of the selected foods, while beer and soy sauce were rich in free AGEs. Only 10%-30% of AGEs were absorbed into the systemic circulation when orally administered. The excretion of ingested free and bound AGEs was approximately 90% and 60%, respectively. Dietary free CML has a detrimental effect on gut microbiota composition, while bound AGEs have both detrimental and beneficial impacts. Free and bound dietary AGEs changed amino acid metabolism, energy metabolism and carbohydrate metabolism. And besides, bound dietary AGEs altered vitamin metabolism, and glycerolipid metabolism.

Advanced glycation end products activated endothelial-to-mesenchymal transition in pancreatic islet endothelial cells and triggered islet fibrosis in diabetic mice

Advanced glycation end products (AGEs) are associated with the pathogenesis of diabetic vascular complications. Induction of the endothelial-to-mesenchymal transition (EndMT) is associated with the pathogenesis of fibrotic diseases. The roles of AGEs in islet EndMT induction and diabetes-related islet microvasculopathy and fibrosis remain unclear. This study investigated the pathological roles of AGEs in islet EndMT induction and fibrosis in vitro and in vivo. Non-cytotoxic concentrations of AGEs upregulated the protein expression of fibronectin, vimentin, and α-smooth muscle actin (α-SMA) (mesenchymal/myofibroblast markers) and downregulated the protein expression of vascular endothelial (VE)-cadherin and cluster of differentiation (CD) 31 (endothelial cell markers) in cultured mouse pancreatic islet endothelial cells, which was prevented by the AGE cross-link breaker alagebrium chloride. In streptozotocin-induced diabetic mice, the average islet area and islet immunoreactivities for insulin and CD31 were decreased and the islet immunoreactivities for AGEs and α-SMA and fibrosis were increased, which were prevented by the AGE inhibitor aminoguanidine. Immunofluorescence double staining showed that α-SMA-positive staining co-localized with CD31-positive staining in the diabetic islets, which was effectively prevented by aminoguanidine. These results demonstrate that AGEs can induce EndMT in islet endothelial cells and islet fibrosis in diabetic mice, suggesting that AGE-induced EndMT may contribute to islet fibrosis in diabetes.

WITHDRAWN: Effect of 2-dodecyl-6-methoxycyclohexa-2, 5-diene-1, 4-dione, isolated from Averrhoa carambola L. (Oxalidaceae) roots, on advanced glycation end-product-mediated renal injury in type 2 diabetic KKAy mice

The Publisher regrets that this article is an accidental duplication of an article that has already been published in [Toxicology Letters, 339C (2021) 88–96], https://doi.org/10.1016/j.toxlet.2020.11.022. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal

Mitochondrial Dysfunctions: A Thread Sewing Together Alzheimer's Disease, Diabetes, and Obesity

Metabolic disorders are severe and chronic impairments of the health of many people and represent a challenge for the society as a whole that has to deal with an ever-increasing number of affected individuals. Among common metabolic disorders are Alzheimer's disease, obesity, and type 2 diabetes. These disorders do not have a univocal genetic cause but rather can result from the interaction of multiple genes, lifestyle, and environmental factors. Mitochondrial alterations have emerged as a feature common to all these disorders, underlining perhaps an impaired coordination between cellular needs and mitochondrial responses that could contribute to their development and/or progression.

Antidiabetic effects of extracts of red and yellow fruits of cornelian cherries (Cornus mas L.) on rats with streptozotocin-induced diabetes mellitus

The effects of extracts of red and yellow fruits of cornelian cherries have been evaluated in rats with streptozotocin-induced diabetes mellitus.

Corn silk (Zea mays L.), a source of natural antioxidants with α-amylase, α-glucosidase, advanced glycation and diabetic nephropathy inhibitory activities

The oxidative stress plays a critical role in the progression of diabetes mellitus (DM) and its complications. Corn silk is a traditional medicine used to treat DM. The aim of this study is to investigate the antioxidant capacity of corn silk, as well as its inhibitory potential on DM and diabetic nephropathy (DN). The ethanol extract of corn silk (CS) was liquid-liquid fractionated to get petroleum ether fraction (PCS), ethyl acetate fraction (ECS), n-butanol fraction (BCS) and water fraction (WCS). The Folin-Ciocalteu and AlCl₃ assay showed that silk corn contained considerable amount of phenolics and flavonoids, ECS and BCS were the two phenolic-enriched fractions with highest TPC and TFC values. The ECS and BCS showed the highest total antioxidant activity and reducing power, as well as the strongest scavenging activity against DPPH and hydroxyl radicals, compared to CS and other fractions. The ECS and BCS displayed appreciable anti-hyperglycaemic effect indicated by the significant inhibition on α-amylase and α-glucosidase in enzymatic assays. In BSA-glucose model, ECS and BCS effectively inhibited the formation of advanced glycation end products (AGEs). In addition, the anti-diabetic nephropathy activity assay displayed that CS, ECS and BCS significantly inhibited the production of Col IV, FN and IL-6 in high-glucose stimulated mesangial cells at 200 μg/mL. These findings suggested the antioxidant activities of corn silk could contribute, at least in part, to its traditionally claimed therapeutic benefits on DM and DN. The phenolic-enriched CS fractions could be considered as a source of natural antioxidants and further developed for the prevention and treatment of DM and its complications including DN.

Activation of Macrophages and Microglia by Interferon-γ and Lipopolysaccharide Increases Methylglyoxal Production: A New Mechanism in the Development of Vascular Complications and Cognitive Decline in Type 2 Diabetes Mellitus?

Methylglyoxal (MGO), a dicarbonyl compound derived from glucose, is elevated in diabetes mellitus and contributes to vascular complications by crosslinking collagen and increasing arterial stiffness. It is known that MGO contributes to inflammation as it forms advanced glycation end products (AGEs), which activate macrophages via the receptor RAGE. The aim of study was to investigate whether inflammatory activation can increase MGO levels, thereby completing a vicious cycle. In order to validate this, macrophage (RAW264.7, J774A.1) and microglial (N11) cells were stimulated with IFN-γ and LPS (5 + 5 and 10 + 10 IFN-γ U/ml or μg/ml LPS), and extracellular MGO concentration was determined after derivatization with 5,6-Diamino-2,4-dihydroxypyrimidine sulfate by HPLC. MGO levels in activated macrophage cells (RAW264.7) peaked at 48 h, increasing 2.86-fold (3.14±0.4 μM) at 5 U/ml IFN-γ+5 μg/ml LPS, and 4.74-fold (5.46±0.30 μM) at 10 U/ml IFN-γ+10 μg/ml LPS compared to the non-activated controls (1.15±0.02 μM). The other two cell lines, J774A.1 macrophages and N11 microglia, showed a similar response. We suggest that inflammation increases MGO production, possibly exacerbating arterial stiffness, cardiovascular complications, and diabetes-related cognitive decline.

Kidney, heart and brain: three organs targeted by ageing and glycation

Advanced glycation end-product (AGE) is the generic term for a heterogeneous group of derivatives arising from a non-enzymatic reaction between reducing sugars and proteins. In recent years, evidence has accumulated that incriminates AGEs in pathogenic processes associated with both chronic hyperglycaemia and age-related diseases. Regardless of their exogenous or endogenous origin, the accumulation of AGEs and their derivatives could promote accelerated ageing by leading to protein modifications and activating several inflammatory signalling pathways via AGE-specific receptors. However, it remains to be demonstrated whether preventing the accumulation of AGEs and their effects is an important therapeutic option for successful ageing. The present review gives an overview of the current knowledge on the pathogenic role of AGEs by focusing on three AGE target organs: kidney, heart and brain. For each of these organs we concentrate on an age-related disease, each of which is a major public health issue: chronic kidney disease, heart dysfunction and neurodegenerative diseases. Even though strong connections have been highlighted between glycation and age-related pathogenesis, causal links still need to be validated. In each case, we report evidence and uncertainties suggested by animal or epidemiological studies on the possible link between pathogenesis and glycation in a chronic hyperglycaemic state, in the absence of diabetes, and with exogenous AGEs alone. Finally, we present some promising anti-AGE strategies that are currently being studied.

Hyperglycemia and advanced glycation end products (AGEs) suppress the differentiation of 3T3-L1 preadipocytes

Aging is characterized by mild hyperglycemia and accumulation of advanced glycation end products (AGEs). Effects of chronic exposure to hyperglycemia or AGEs on the adipogenic differentiation of 3T3-L1 preadipocytes remain unclear. We examined the chronic effect of AGEs and high glucose on the differentiation of 3T3-L1 cells by culturing 3T3-L1 cells in the presence of AGEs or 25 mM glucose for 1 month. Chronic incubation of 3T3-L1 cells with AGEs or high glucose blocked their differentiation into mature adipocytes as evidenced by reduced levels of adipocyte markers such as accumulated oil droplets, GPDH, aP2, adiponectin and of adipogenesis regulators PPARγ and C/EBPα. Levels or activities of Src, PDK1, Akt, and NF-κB were higher in AGEs- and high glucose-treated cells than those in 3T3-L1 cells. Levels of Bcl-2 were elevated in AGEs- and high glucose-treated cells, and were attenuated by inhibitors of PI3-kinase, Akt and NF-κB. Moreover, adipogenesis was attenuated in 3T3-L1 cells stably expressing Bcl-2 or YAP. These results suggest that chronic AGEs and high glucose treatments up-regulate Bcl-2 and YAP via the Akt-NF-κB pathway and impair adipogenesis.

RAGE-Aptamer Blocks the Development and Progression of Experimental Diabetic Nephropathy

The interaction of advanced glycation end products (AGEs) and their receptor (RAGE) plays a central role in diabetic nephropathy. We screened DNA aptamers directed against RAGE (RAGE-aptamers) in vitro and examined the effects on the development and progression of diabetic nephropathy in streptozotocin-induced diabetic rats. RAGE-aptamer bound to RAGE with a K_d of 5.68 nmol/L and resultantly blocked the binding of AGEs to RAGE. When diabetic rats received continuous intraperitoneal injection of RAGE-aptamer from week 7 to 11 of diabetes, the increases in renal NADPH oxidase activity, oxidative stress generation, AGE, RAGE, inflammatory and fibrotic gene and protein levels, macrophage and extracellular matrix accumulation, and albuminuria were significantly suppressed, which were associated with improvement of podocyte damage. Two-week infusion of RAGE-aptamer just after the induction of diabetes also inhibited the AGE-RAGE-oxidative stress system and MCP-1 levels in the kidneys of 8-week-old diabetic rats and simultaneously ameliorated podocyte injury and albuminuria. Moreover, RAGE-aptamer significantly suppressed the AGE-induced oxidative stress generation and inflammatory and fibrotic reactions in human cultured mesangial cells. The findings suggest that continuous infusion of RAGE-aptamer could attenuate the development and progression of experimental diabetic nephropathy by blocking the AGE-RAGE axis.

Mechanistic insight of diabetic nephropathy and its pharmacotherapeutic targets: An update

Diabetic nephropathy (DN), a chronic complication of diabetes, is charecterized by glomerular hypertrophy, proteinuria, decreased glomerular filtration, and renal fibrosis resulting in the loss of renal function. Although the exact cause of DN remains unclear, several mechanisms have been postulated, such as hyperglycemia-induced renal hyper filtration and renal injury, AGEs-induced increased oxidative stress, activated PKC-induced increased production of cytokines, chemokines, and different inflammatory and apoptotic signals. Among various factors, oxidative stress has been suggested to play a major role underlying the onset and propagation of DN. It triggers several signaling pathways involved in DN, like AGEs, PKC cascade, JAK/STAT signaling, MAPK, mTOR, and SMAD. Oxidative stress-induced activation of both inflammatory and apoptotic signals are two major problems in the pathogenesis of DN. The FDA approved pharmacotherapeutic agents affecting against polyol pathway principally include anti-oxidants, like α-lipoic acid, vitamin E, and vitamin C. Kremezin and benfotiamine are the FDA approved AGEs inhibitors, another therapeutic target against DN. Ruboxistaurin, telmizartan, rapamycin, fenofibrate, aliskiren, and manidipine are some FDA approved pharmacotherapeutics effective against DN via diverse mechanisms. Beside this, some therapeutic agents are still waiting for FDA approval and few drugs without FDA approval are also prescribed in some countries for the management of DN. Despite the medications available in the market to treat DN, the involvement of multiple mechanisms makes it difficult to choose an optimum therapeutic agent. Therefore, much research is required to find out new therapeutic agent/strategies for an adequate pharmacotherapy of DN.

Non-enzymatic glycation mediated structure–function changes in proteins: case of serum albumin

Albumin, a major plasma protein with extraordinary ligand binding properties, transports various ligands ranging from drugs, hormones, fatty acids, and toxins to different tissues and organs in the body.

Carbonyl scavenging and chemical chaperon like function of essential amino acids attenuates non-enzymatic glycation of albumin

Essential amino acids showed potent antiglycation activity by preventing formation of both early and advanced glycation end products (AGEs).

Recent advances in detection of AGEs: Immunochemical, bioanalytical and biochemical approaches

Advanced glycation end products (AGEs) are a cohort of heterogeneous compounds that are formed after the nonenzymatic glycation of proteins, lipids and nucleic acids. Accumulation of AGEs in the body is implicated in various pathophysiological conditions like diabetes, cardiovascular diseases and atherosclerosis. Numerous studies have reported the connecting link between AGEs and the various complications associated with diseases. Hence, detection and measurement of AGEs becomes centrally important to understand and manage the menace created by AGEs inside the body. In recent years, an increasing number of immunotechniques as well as bioanalytical techniques have been developed to efficiently measure the levels of AGEs, but most of them are still far away from being clinically consistent, as relative disparity and ambiguity masks their standardization. This article is designed to critically review the recent advances and the emerging techniques for detection of AGEs. It is an attempt to summarize the major techniques that exist currently for the detection of AGEs both qualitatively and quantitatively. This review primarily focuses on the detection and quantification of AGEs which are formed in vivo. Immunochemical approach though costly but most effective and accurate method to measure the level of AGEs. Literature review suggests that detection of autoantibody targeting AGEs is a promising way that can be utilized for detection of AGEs. Future research efforts should be dedicated to develop this method in order to push forward the clinical applications of detection of AGEs.

Carboxymethyl lysine induces EMT in podocytes through transcription factor ZEB2: Implications for podocyte depletion and proteinuria in diabetes mellitus

Advanced glycation end-products (AGEs) are implicated in the pathogenesis of diabetic nephropathy (DN). N-carboxymethyl-lysine (CML) is one of the predominant AGEs that accumulate in all renal compartments of diabetic patients. Nevertheless, the direct effect of CML on podocyte biology has not been explored. In this study, we demonstrate the induction of the transcription factor Zeb2 in podocytes upon exposure to CML through activation of NF-kB signaling cascade. Zeb2 orchestrates epithelial-mesenchymal transformation (EMT), during which cell-cell and cell-extracellular matrix interactions are feeble and enable epithelial cells to become invasive. CML treatment induced both NF-kB and Zeb2 promoter activity and suppressed E-cadherin promoter activity. Inhibition of NF-kB activity prevented CML dependent induction of Zeb2 and loss of E-cadherin. While the exposure of podocytes to CML results in increased podocyte permeability, shRNA-mediated knockdown of Zeb2 expression abrogated CML-mediated podocyte permeability. Further, in vivo findings of elevated CML levels concurrent with increased expression of ZEB2 in glomeruli and proteinuria in diabetic rats confirm that CML-mediated manifestations in the kidney under chronic diabetes conditions. These in vitro and in vivo results envisage the novel axis of NFkB-ZEB2 in podocytes playing a significant role in eliciting EMT and pathogenesis of DN.

Esculin improves dyslipidemia, inflammation and renal damage in streptozotocin-induced diabetic rats

Background

Increasing studies have shown that dyslipidemia and inflammatory responses play important roles in the progression of microvascular diabetic complications. Esculin (ES), a coumarin derivative, was extracted from Fraxinus rhynchophylla. The present study was to evaluate the potential effects of ES on lipid metabolism, inflammation responses and renal damage in streptozotocin (STZ)-induced experimental diabetic rats and explore the possible mechanism.

Methods

Diabetic rat model was established by administration high-glucose-fat diet and intraperitoneal injection of STZ 45 mg/kg. ES was administrated to diabetic rats intragastrically at 10, 30 and 90 mg/kg for 10 weeks respectively. The levels of triglycerides (TG), total cholesterol (T-CHO), low density lipoproteins (LDL), and high-density-cholesterol (HDL-C) in serum were measured. IL-1, IL-6, ICAM-1, NO, NAGL, and AGEs level in serum were detected by ELISA assay. The accumulation of AGEs in kidney tissue was examined by immunohistochemistry assay.

Results

The results showed that ES could decrease TG, T-CHO, LDL levels in serum of diabetic rats in a dose dependent manner. ES also decreased IL-1, IL-6, ICAM-1, NO and NGAL levels in serum of diabetic rats in a dose dependent manner. Furthermore, ES at 30 and 90 mg/kg significantly decreased AGEs level in serum and alleviated AGEs accumulation in renal in diabetic rats.

Conclusions

Our findings indicate that ES could improve dyslipidemia, inflammation responses, renal damage in STZ-induced diabetic rats and the possible mechanism might be associated with the inhibition of AGEs formation.

Role of RAGE in Alzheimer's Disease

Receptor for advanced glycation end products (RAGE) is a receptor of the immunoglobulin super family that plays various important roles under physiological and pathological conditions. Compelling evidence suggests that RAGE acts as both an inflammatory intermediary and a critical inducer of oxidative stress, underlying RAGE-induced Alzheimer-like pathophysiological changes that drive the process of Alzheimer's disease (AD). A critical role of RAGE in AD includes beta-amyloid (Aβ) production and accumulation, the formation of neurofibrillary tangles, failure of synaptic transmission, and neuronal degeneration. The steady-state level of Aβ depends on the balance between production and clearance. RAGE plays an important role in the Aβ clearance. RAGE acts as an important transporter via regulating influx of circulating Aβ into brain, whereas the efflux of brain-derived Aβ into the circulation via BBB is implemented by LRP1. RAGE could be an important contributor to Aβ generation via enhancing the activity of β- and/or γ-secretases and activating inflammatory response and oxidative stress. However, sRAGE-Aβ interactions could inhibit Aβ neurotoxicity and promote Aβ clearance from brain. Meanwhile, RAGE could be a promoting factor for the synaptic dysfunction and neuronal circuit dysfunction which are both the material structure of cognition, and the physiological and pathological basis of cognition. In addition, RAGE could be a trigger for the pathogenesis of Aβ and tau hyper-phosphorylation which both participate in the process of cognitive impairment. Preclinical and clinical studies have supported that RAGE inhibitors could be useful in the treatment of AD. Thus, an effective measure to inhibit RAGE may be a novel drug target in AD.

HMGB1 Enhances the AGE-Induced Expression of CTGF and TGF-β via RAGE-Dependent Signaling in Renal Tubular Epithelial Cells

BACKGROUND/AIMS

Advanced glycation end products (AGEs) induce epithelial mesenchymal transition (EMT) in renal proximal tubular epithelial cells (PTECs) by promoting the two EMT regulators, transforming growth factor beta (TGF-β) and connective tissue growth factor (CTGF). However, the exact signaling mechanism remains largely unclear.

METHODS

We investigated the promotion to high mobility group box 1 (HMGB1) in renal tubular epithelial HK-2 cells by AGE-BSA with quantitative PCR and western blot assay, and then determined the regulatory role of HMGB1 in the AGE-BSA-induced CTGF and TGF-β. In addition, the dependence of the receptor of advanced glycation end products (RAGE) was also examined in the CTGF and TGF-β promotion by AGEs and HMGB1 in HK-2 cells using the RNAi method.

RESULTS

It was demonstrated that AGEs induced translocation and release of HMGB1 from tubular epithelial HK-2 cells, and the released HMGB1 enhanced the promotion to CTGF and TGF-β by AGEs in HK-2 cells. On the other side, the HMGB1 knockdown by siRNA attenuated the AGE-BSA-induced expression of TGF-β. Moreover, the CTGF and TGF-β promotion in HK-2 cells by AGEs and HMGB1 was RAGE-dependent.

CONCLUSION

Our results indicated that AGEs induced HMGB-1 and promoted the CTGF and TGF-β in renal epithelial HK-2 cells RAGE-dependently. And there was a synergism between AGEs and HMGB1 in the RAGE signaling activation. The in vitro data suggested that the AGE-RAGE and HMGB-1-RAGE signaling might play an important role in the promotion of CTGF and TGF-β in the renal fibrosis process of diabetic nephropathy.

Advanced glycation end-products induce apoptosis in pancreatic islet endothelial cells via NF-κB-activated cyclooxygenase-2/prostaglandin E2 up-regulation

Microvascular complications eventually affect nearly all patients with diabetes. Advanced glycation end-products (AGEs) resulting from hyperglycemia are a complex and heterogeneous group of compounds that accumulate in the plasma and tissues in diabetic patients. They are responsible for both endothelial dysfunction and diabetic vasculopathy. The aim of this study was to investigate the cytotoxicity of AGEs on pancreatic islet microvascular endothelial cells. The mechanism underlying the apoptotic effect of AGEs in pancreatic islet endothelial cell line MS1 was explored. The results showed that AGEs significantly decreased MS1 cell viability and induced MS1 cell apoptosis in a dose-dependent manner. AGEs dose-dependently increased the expressions of cleaved caspase-3, and cleaved poly (ADP-ribose) polymerase in MS1 cells. Treatment of MS1 cells with AGEs also resulted in increased nuclear factor (NF)-κB-p65 phosphorylation and cyclooxygenase (COX)-2 expression. However, AGEs did not affect the expressions of endoplasmic reticulum (ER) stress-related molecules in MS1 cells. Pretreatment with NS398 (a COX-2 inhibitor) to inhibit prostaglandin E₂ (PGE₂) production reversed the induction of cleaved caspase-3, cleaved PARP, and MS1 cell viability. Moreover, AGEs significantly increased the receptor for AGEs (RAGE) protein expression in MS1 cells, which could be reversed by RAGE neutralizing antibody. RAGE Neutralizing antibody could also reverse the induction of cleaved caspase-3 and cleaved PARP and decreased cell viability induced by AGEs. These results implicate the involvement of NF-κB-activated COX-2/PGE₂ up-regulation in AGEs/RAGE-induced islet endothelial cell apoptosis and cytotoxicity. These findings may provide insight into the pathological processes within the pancreatic islet microvasculature induced by AGEs accumulation.

Human recombinant lysozyme downregulates advanced glycation endproduct-induced interleukin-6 production and release in an in-vitro model of human proximal tubular epithelial cells

Diabetic nephropathy is the leading cause of chronic renal disease and one of the major causes of cardiovascular mortality. Evidence suggests that its progression is due to the chronic hyperglycemia consequent to the production and accumulation of advanced glycation endproducts (AGEs). Lysozyme was shown to posses AGE-sequestering properties and the capacity to reduce the severity of the early stage manifestations of the diabetic nephropathy. This study was aimed to contribute to the understanding the molecular mechanisms of lysozyme effectiveness in the diabetic nephropathy, using an in-vitro cellular model, represented by the HK-2 cells, human proximal tubular epithelial cells. Lysozyme significantly reduced the AGE-induced IL-6 mRNA and an ELISA assay showed also a decreased release of the functional protein with a dose-dependent trend. In addition, lysozyme prevented macrophage recruitment, suggesting its capacity to elicit an anti-inflammatory action. We may conclude that the protective action of lysozyme on the nephrotoxic effects of AGE may depend, at least in part, on its ability to prevent the production and release of inflammatory mediators, such as IL-6 and to reduce macrophage recruitment in the inflammatory sites.

Ramipril inhibits AGE-RAGE-induced matrix metalloproteinase-2 activation in experimental diabetic nephropathy

BACKGROUND

Advanced glycation end products (AGE)-receptor for AGE (RAGE) axis and renin-angiotensin system (RAS) play a role in diabetic nephropathy (DN). Matrix metalloproteinase-2 (MMP-2) activation also contributes to DN. However, the pathological interaction among AGE-RAGE, RAS and MMP-2 in DN remains unknown. We examined here the involvement of AGE and RAS in MMP-2 activation in streptozotocin (STZ)-induced diabetic rats and in AGE-exposed rat renal proximal tubular cells (RPTCs).

METHODS

Experimental diabetes was induced in 6-week-old male Sprague-Dawley (SD) rats by intravenous injection of STZ. Diabetic rats received ramipril (3 mg/kg body weight/day) or vehicle for 32 weeks. AGE-modified rat serum albumin (AGE-RSA) or RSA was intraperitoneally administrated to 6-week-old male SD rats for 16 weeks. RPTCs were stimulated with 100 μg/ml AGE-modified bovine serum albumin (AGE-BSA) or BSA in the presence or absence of 10(-7) M ramiprilat, an inhibitor of angiotensin-converting enzyme or 100 nM BAY11-7082, an IκB-α phosphorylation inhibitor.

RESULTS

AGE and RAGE expression levels and MMP-2 activity in the tubules of diabetic rats was significantly increased in association with increased albuminuria, all of which were blocked by ramipril. AGE infusion induced tubular MMP-2 activation and RAGE gene expression in SD rats. Ramiprilat or BAY11-7082 inhibited the AGE-induced MMP-2 activation or reactive oxygen species generation in RPTCs. Angiotensin II increased MMP-2 gene expression in RPTCs, which was blocked by BAY11-7082.

CONCLUSIONS

Our present study suggests the involvement of AGE-RAGE-induced, RAS-mediated MMP-2 activation in experimental DN. Blockade of AGE-RAGE axis by ramipril may protect against DN partly via suppression of MMP-2.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

AGEs, rather than hyperglycemia, are responsible for microvascular complications in diabetes: a "glycoxidation-centric" point of view

AIMS

Advanced glycation end products (AGE) excess is one of the most important mechanisms involved in the pathophysiology of chronic diabetic complications. This review first summarizes the role of these compounds in microvascular pathogenesis, particularly in the light of recently proposed biochemical mechanisms for diabetic retinopathy, nephropathy and neuropathy. Then we focus on the relationship between AGE and metabolic memory, trying to clarify the former's role in the missing link between micro- and macrovascular complications.

DATA SYNTHESIS

An excessive AGE formation has been demonstrated in the newly disclosed biochemical pathways involved in the microvascular pathobiology of type 2 diabetes, confirming the central role of AGE in the progression of diabetic neuropathy, retinopathy and nephropathy. As shown by recent studies, AGE seem to be not "actors", but "directors" of processes conducting to these complications, for at least two main reasons: first, AGE have several intra- and extracellular targets, so they can be seen as a "bridge" between intracellular and extracellular damage; secondly, whatever the level of hyperglycemia, AGE-related intracellular glycation of the mitochondrial respiratory chain proteins has been found to produce more reactive oxygen species, triggering a vicious cycle that amplifies AGE formation. This may help to explain the clinical link between micro- and macrovascular disease in diabetes, contributing to clarify the mechanisms behind metabolic memory.

CONCLUSIONS

The pathophysiological cascades triggered by AGE have a dominant, hyperglycemia-independent role in the onset of the microvascular complications of diabetes. An effective approach to prevention and treatment must therefore focus not only on early glycemic control, but also on reducing factors related to oxidative stress, and the dietary intake of exogenous AGE in particular.

DNA aptamer raised against AGEs blocks the progression of experimental diabetic nephropathy

Advanced glycation end products (AGEs) and their receptor (RAGE) play a role in diabetic nephropathy. We screened DNA aptamer directed against AGEs (AGEs-aptamer) in vitro and examined its effects on renal injury in KKAy/Ta mice, an animal model of type 2 diabetes. Eight-week-old male KKAy/Ta or C57BL/6J mice received continuous intraperitoneal infusion of AGEs- or control-aptamer for 8 weeks. AGEs-aptamer was detected and its level was increased in the kidney for at least 7 days. The elimination half-lives of AGEs-aptamer in the kidney were about 7 days. Compared with those in C57BL/6J mice, glomerular AGEs levels were significantly increased in KKAy/Ta mice, which were blocked by AGEs-aptamer. Urinary albumin and 8-hydroxy-2'-deoxy-guanosine levels were increased, and glomerular hypertrophy and enhanced extracellular matrix accumulation were observed in KKAy/Ta mice, all of which were prevented by AGEs-aptamer. Moreover, AGEs-aptamer significantly reduced gene expression of RAGE, monocyte chemoattractant protein-1, connective tissue growth factor, and type IV collagen both in the kidney of KKAy/Ta mice and in AGE-exposed human cultured mesangial cells. Our present data suggest that continuous administration of AGEs-aptamer could protect against experimental diabetic nephropathy by blocking the AGEs-RAGE axis and may be a feasible and promising therapeutic strategy for the treatment of diabetic nephropathy.

Effect of 2-dodecyl-6-methoxycyclohexa-2,5-diene-1,4-dione, isolated from Averrhoa carambola L. (Oxalidaceae) roots, on advanced glycation end-product-mediated renal injury in type 2 diabetic KKAy mice

The roots of Averrhoa carambola L. (Oxalidaceae) have a long history of medical use in traditional Chinese medicine for treating diabetes and diabetic nephropathy. 2-Dodecyl-6-methoxycyclohexa-2,5-diene-1,4-dione (DMDD) was isolated from the tuberous roots of A. carambola L. The purpose of this study was to investigate the beneficial effect of DMDD on the advanced glycation end-product-mediated renal injury in type 2 diabetic KKAy mice with regard to prove its efficacy by local traditional practitioners in the treatment of kidney frailties in diabetics. KKAy mice were orally administrated DMDD (12.5, 25, 50mg/kg body weight/d) or aminoguanidine (200mg/kg body weight/d) for 8 weeks. Hyperglycemia, renal AGE formation, and the expression of related proteins, such as the AGE receptor, nuclear factor-κB, transforming growth factor-β1, and N(ε)-(carboxymethyl)lysine, were markedly decreased by DMDD. Diabetes-dependent alterations in proteinuria, serum creatinine, creatinine clearance, and serum urea-N and glomerular mesangial matrix expansion were attenuated after treatment with DMDD for 8 weeks. The activities of superoxide dismutase and glutathione peroxidase, which are reduced in the kidneys of KKAy mice, were enhanced by DMDD. These findings suggest that DMDD may inhibit the progression of diabetic nephropathy and may be a therapeutic agent for regulating several pharmacological targets to treat or prevent of diabetic nephropathy.

Alagebrium reduces glomerular fibrogenesis and inflammation beyond preventing RAGE activation in diabetic apolipoprotein E knockout mice

Advanced glycation end products (AGEs) are important mediators of diabetic nephropathy that act through the receptor for AGEs (RAGE), as well as other mechanisms, to promote renal inflammation and glomerulosclerosis. The relative contribution of RAGE-dependent and RAGE-independent signaling pathways has not been previously studied in vivo. In this study, diabetic RAGE apoE double-knockout (KO) mice with streptozotocin-induced diabetes were treated with the AGE inhibitor, alagebrium (1 mg/kg/day), or the ACE inhibitor, quinapril (30 mg/kg/day), for 20 weeks, and renal parameters were assessed. RAGE deletion attenuated mesangial expansion, glomerular matrix accumulation, and renal oxidative stress associated with 20 weeks of diabetes. By contrast, inflammation and AGE accumulation associated with diabetes was not prevented. However, treatment with alagebrium in diabetic RAGE apoE KO mice reduced renal AGE levels and further reduced glomerular matrix accumulation. In addition, even in the absence of RAGE expression, alagebrium attenuated cortical inflammation, as denoted by the reduced expression of monocyte chemoattractant protein-1, intracellular adhesion molecule-1, and the macrophage marker cluster of differentiation molecule 11b. These novel findings confirm the presence of important RAGE-independent as well as RAGE-dependent signaling pathways that may be activated in the kidney by AGEs. This has important implications for the design of optimal therapeutic strategies for the prevention of diabetic nephropathy.

Natural compounds containing a catechol group enhance the formation of Nε-(carboxymethyl)lysine of the Maillard reaction

Inhibition of advanced glycation end-product (AGE) formation is a potential strategy for the prevention of clinical diabetes complications. Screening for new AGE inhibitors revealed several natural compounds that inhibited the formation of N(ε)-(carboxymethyl)lysine (CML), a major antigenic AGE structure, whereas natural compounds containing a catechol group, such as gallic acid and epicatechin, significantly enhanced CML formation. A similar enhancing effect was also observed by culturing THP-1 macrophages in the presence of catechol compounds. Although 4-methylcatechol significantly enhanced CML formation from glycated HSA (gHSA), a model for Amadori proteins, analogues of catechol such as 5-methylresorcinol and methylhydroquinone showed no enhancing effect. Even though 1mM 4-methylcatechol, epicatechin, and gallic acid significantly enhanced CML formation from gHSA, it was significantly inhibited by decreasing their concentration. The enhancing effect of 1mM catechol compounds was inhibited in the presence of the glutathione peroxidase system, thus demonstrating that hydrogen peroxide generated from catechol compounds plays an important role in the enhancement of CML formation. Furthermore, administration of 500mg/kg/day epicatechin to STZ-induced diabetic mice for 45days enhanced CML accumulation at the surface area of gastric epithelial cells in the stomach. This study provides the first evidence that high amounts of catechol-containing structures enhance oxidative stress, thus leading to enhanced CML formation, and this phenomenon may explain the paradoxical effect that some flavonoids have on redox status.

Modulation of advanced glycation end products by candesartan in patients with diabetic kidney disease--a dose-response relationship study

Advanced glycation end products (AGEs) are proinflammatory mediators implicated in the pathogenesis of diabetic kidney disease (DKD). In this study, dose-dependent effects of angiotensin receptor blockade on urinary AGEs were evaluated in patients with DKD. Patients with type 2 diabetes and proteinuria ≥500 mg/d (n = 11) were compared with diabetic controls without DKD (n = 10) and normal controls (n = 11). After a 2-week washout period, DKD participants were treated with candesartan doses progressively increasing from 8, 16, 32, to 64 mg/d every 3 weeks for a total of 12 weeks. Other antihypertensive agents were adjusted to maintain stable blood pressure. At baseline and after each dosing period, blood pressure measurements and 24-hour urine collections were obtained. Urinary carboxymethyl lysine, an AGE biomarker, was reduced over the 12-week dose escalation protocol (r = 0.38, P = 0.01) in DKD participants. Creatinine clearance increased slightly, but albuminuria was unaffected by candesartan administration. Baseline urinary transforming growth factor-β₁ excretion was lower in DKD participants than in controls and did not change during the study period. Reducing kidney exposure to AGEs may be a mechanism of protection by angiotensin receptor blockade in DKD. AGEs may also impact the diabetic kidney through mechanisms independent of transforming growth factor-β₁.

Effects of pancreas transplantation on oxidative stress in pulmonary tissue from alloxan-induced diabetic rats

PURPOSE

There is considerable evidence that cellular oxidative stress caused by hyperglycemia plays an important role in the genesis and evolution of chronic diabetic lesions. In this study, we determined the effectiveness of pancreas transplantation (PT) in preventing the imbalance caused by excessive production of reactive oxygen species over antioxidant defenses in lungs of rats rendered diabetic by alloxan injection.

METHODS

Sixty inbred male Lewis rats, weighing 250-280 g, were randomly assigned to 3 experimental groups: NC, 20 nondiabetic control rats; DC, 20 untreated diabetic control rats; and PT, 20 diabetic rats that received syngeneic PT from normal donor Lewis rats. Each group was further divided into 2 subgroups of 10 rats each which were killed after 4 and 12 weeks of follow-up. Plasma glucose, glycosylated hemoglobin, and insulin levels were determined in all rats. Lipid hydroperoxide (LPO) concentrations and enzyme activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) were measured in the pulmonary tissue of all rats.

RESULTS

The DC rats showed elevated blood glucose and glycosylated hemoglobin levels, with insulin blood levels significantly lower than the NC rats (P < .001). They also showed significantly increased LPO concentrations in the lungs (P < .01) after 4 and 12 weeks of follow-up. In contrast, SOD, CAT, and GSH-Px antioxidant activities were significantly reduced in these periods (P < .01) 12 weeks after diabetes induction. Successful PT corrected all clinical and metabolic changes in the diabetic rats, with sustained normoglycemia throughout the study. Excessive lung LPO production and low SOD, CAT, and GSH-Px antioxidant activities were already back to normal 4 weeks after PT.

CONCLUSION

PT can control oxidative stress in pulmonary tissue of diabetic rats. It may be the basis for preventing chronic diabetic lesions in lungs.

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.

Ethnic differences in anemia among patients with diabetes mellitus: the Diabetes Study of Northern California (DISTANCE)

To examine ethnic differences in hemoglobin testing practices and to test the hypothesis that ethnicity is an independent predictor of anemia among patients with diabetes mellitus. We conducted a panel study to assess the rate of hemoglobin testing during 1999-2001 and the period prevalence and incidence of anemia among 79,985 adults with diabetes mellitus receiving care within Kaiser Permanente of Northern California. Anemia was defined as hemoglobin <13.0 g/dL in men or < 12.0 g/dL in women. Overall, 82.1% of the cohort was tested for anemia at least once during the 3-year study period. Mixed ethnicity patients were most likely to be tested, followed by whites, blacks, Latinos, and Asians (P < 0.0001). Fifteen percent of the cohort had prevalent anemia at baseline, and an additional 22% of those tested developed anemia during the study period. Anemia was more prevalent among blacks and mixed ethnicity persons compared with other racial/ethnic groups. Anemia was also more prevalent among those >/=70 years of age or with estimated glomerular filtration rate <60 ml/min/1.73 m(2). In multivariable models, blacks had higher and Asians had lower odds of prevalent anemia and hazard ratios of incident anemia compared with whites. Within a large, diverse cohort with diabetes, ethnicity was predictive of anemia, even after adjustment for age, level of kidney function, and other potential confounders. Blacks with diabetes are at increased risk of anemia relative to whites. These differences may account for some of the observed ethnic disparities in diabetes complications.

Advanced glycation end-products induce tubular CTGF via TGF-beta-independent Smad3 signaling

Advanced glycation end-products (AGEs) can induce expression of connective tissue growth factor (CTGF), which seems to promote the development of diabetic nephropathy, but the exact signaling mechanisms that mediate this induction are unknown. Here, AGEs induced CTGF expression in tubular epithelial cells (TECs) that either lacked the TGF-beta1 gene or expressed dominant TGF-beta receptor II, demonstrating independence of TGF-beta. Furthermore, conditional knockout of the gene encoding TGF-beta receptor II from the kidney did not prevent AGE-induced renal expression of CTGF and collagen I. More specific, AGEs induced CTGF expression via the receptor for AGEs-extracellular signal-regulated kinase (RAGE-ERK)/p38 mitogen-activated protein kinase-Smad cross-talk pathway because inhibition of this pathway by several methods (anti-RAGE antibody, specific inhibitors, or dominant negative adenovirus to ERK1/2 and p38) blocked this induction. Overexpressing Smad7 abolished AGE-induced Smad3 phosphorylation and CTGF expression, demonstrating the necessity for activation of Smad signaling in this process. More important, knockdown of either Smad3 or Smad2 demonstrated that Smad3 but not Smad2 is essential for CTGF induction in response to AGEs. In conclusion, AGEs induce tubular CTGF expression via the TGF-beta-independent RAGE-ERK/p38-Smad3 cross-talk pathway. These data suggest that overexpression of Smad7 or targeting Smad3 may have therapeutic potential for diabetic nephropathy.

XLF-III-43, a novel coumarin-aspirin compound, prevents diabetic nephropathy in rats via inhibiting advanced glycation end products

Advanced glycation end products (AGE) have been implicated in the pathogenesis of diabetic complications. The purpose of this study was to examine the novel coumarin-aspirin compound XLF-III-43 in the inhibition of AGE formation in diabetic nephropathy. In vitro analysis showed XLF-III-43 in a dose-dependent manner decreased glucose induced formation of glycation adducts on albumin and inhibited AGE-lysozyme crosslinking. The streptozotocin-induced diabetic rats were used to investigate the beneficial effects of XLF-III-43 treatment on diabetic nephropathy. Administration of XLF-III-43 significantly decreased (P<0.05) blood urea nitrogen and urinary albumin excretion. Moreover, XLF-III-43 ameliorated kidney hypertrophy, mesangial expansion and glomerulosclerosis in diabetic rats relative to untreated model group. These data correlated with decreased both AGE and downstream markers of AGE stress (TGF-beta1, CTGF, fibronectin and collagen IV fibrolysis) in kidneys of diabetic rats. These data support further development of XLF-III-43 for prevention of nephropathy via inhibition of AGE formation consequent to chronic hyperglycemia.

Dietary carbohydrates and dental-systemic diseases

Two contradictory hypotheses on the role of dietary carbohydrates in health and disease shape how dental-systemic associations are regarded. On one side, Cleave and Yudkin postulated that excessive dietary fermentable carbohydrate intake led-in the absence of dental interventions such as fluorides-first to dental diseases and then to systemic diseases. Under this hypothesis, dental and systemic diseases shared-as a common cause-a diet of excess fermentable carbohydrates. Dental diseases were regarded as an alarm bell for future systemic diseases, and restricting carbohydrate intake prevented both dental and systemic diseases. On the opposite side, Keys postulated the lipid hypothesis: that excessive dietary lipid intake caused systemic diseases. Keys advocated a diet high in fermentable carbohydrate for the benefit of general health, and dental diseases became regarded as local dietary side effects. Because general health takes precedence over dental health when it comes to dietary recommendations, dental diseases became viewed as local infections; interventions such as fluorides, sealants, oral hygiene, antimicrobials, and dental fillings became synonymous with maintaining dental health, and carbohydrates were no longer considered as a common cause for dental-systemic diseases. These opposing dietary hypotheses have increasingly been put to the test in clinical trials. The emerging trial results favor Cleave-Yudkin's hypothesis and may affect preventive approaches for dental and systemic diseases.