Effects of sevelamer carbonate on advanced glycation end products and antioxidant/pro-oxidant status in patients with diabetic kidney disease

Sirtuins in kidney health and disease

Sirtuins (SIRTs) are putative regulators of lifespan in model organisms. Since the initial discovery that SIRTs could promote longevity in nematodes and flies, the identification of additional properties of these proteins has led to understanding of their roles as exquisite sensors that link metabolic activity to oxidative states. SIRTs have major roles in biological processes that are important in kidney development and physiological functions, including mitochondrial metabolism, oxidative stress, autophagy, DNA repair and inflammation. Furthermore, altered SIRT activity has been implicated in the pathophysiology and progression of acute and chronic kidney diseases, including acute kidney injury, diabetic kidney disease, chronic kidney disease, polycystic kidney disease, autoimmune diseases and renal ageing. The renoprotective roles of SIRTs in these diseases make them attractive therapeutic targets. A number of SIRT-activating compounds have shown beneficial effects in kidney disease models; however, further research is needed to identify novel SIRT-targeting strategies with the potential to treat and/or prevent the progression of kidney diseases and increase the average human healthspan.

Modulation of 1,2-Dicarbonyl Compounds in Postprandial Responses Mediated by Food Bioactive Components and Mediterranean Diet

Glycoxidative stress with the consequent generation of advanced glycation end products has been implied in the etiology of numerous non-communicable chronic diseases. During the postprandial state, the levels of 1,2-dicarbonyl compounds can increase, depending on numerous factors, including characteristics of the subjects mainly related to glucose metabolism disorders and nutritional status, as well as properties related to the chemical composition of meals, including macronutrient composition and the presence of dietary bioactive molecules and macromolecules. In this review, we examine the chemical, biochemical, and physiological pathways that contribute to postprandial generation of 1,2-dicarbonyl compounds. The modulation of postprandial 1,2-dicarbonyl compounds is discussed in terms of biochemical pathways regulating the levels of these compounds, as well as the effect of phenolic compounds, dietary fiber, and dietary patterns, such as Mediterranean and Western diets.

Food-Related Carbonyl Stress in Cardiometabolic and Cancer Risk Linked to Unhealthy Modern Diet

Carbonyl stress is a condition characterized by an increase in the steady-state levels of reactive carbonyl species (RCS) that leads to accumulation of their irreversible covalent adducts with biological molecules. RCS are generated by the oxidative cleavage and cellular metabolism of lipids and sugars. In addition to causing damage directly, the RCS adducts, advanced glycation end-products (AGEs) and advanced lipoxidation end-products (ALEs), cause additional harm by eliciting chronic inflammation through receptor-mediated mechanisms. Hyperglycemia- and dyslipidemia-induced carbonyl stress plays a role in diabetic cardiovascular complications and diabetes-related cancer risk. Moreover, the increased dietary exposure to AGEs/ALEs could mediate the impact of the modern, highly processed diet on cardiometabolic and cancer risk. Finally, the transient carbonyl stress resulting from supraphysiological postprandial spikes in blood glucose and lipid levels may play a role in acute proinflammatory and proatherogenic changes occurring after a calorie dense meal. These findings underline the potential importance of carbonyl stress as a mediator of the cardiometabolic and cancer risk linked to today’s unhealthy diet. In this review, current knowledge in this field is discussed along with future research courses to offer new insights and open new avenues for therapeutic interventions to prevent diet-associated cardiometabolic disorders and cancer.

SIRT1-SIRT7 in Diabetic Kidney Disease: Biological Functions and Molecular Mechanisms

Diabetic kidney disease (DKD) is a severe microvascular complication in patients with diabetes and is one of the main causes of renal failure. The current clinical treatment methods for DKD are not completely effective, and further exploration of the molecular mechanisms underlying the pathology of DKD is necessary to improve and promote the treatment strategy. Sirtuins are class III histone deacetylases, which play an important role in many biological functions, including DNA repair, apoptosis, cell cycle, oxidative stress, mitochondrial function, energy metabolism, lifespan, and aging. In the last decade, research on sirtuins and DKD has gained increasing attention, and it is important to summarize the relationship between DKD and sirtuins to increase the awareness of DKD and improve the cure rates. We have found that miRNAs, lncRNAs, compounds, or drugs that up-regulate the activity and expression of sirtuins play protective roles in renal function. Therefore, in this review, we summarize the biological functions, molecular targets, mechanisms, and signaling pathways of SIRT1-SIRT7 in DKD models. Existing research has shown that sirtuins have the potential as effective targets for the clinical treatment of DKD. This review aims to lay a solid foundation for clinical research and provide a theoretical basis to slow the development of DKD in patients.

Systematic Review and Meta-Analyses of the Effects of Phosphate-Lowering Agents in Nondialysis CKD

BACKGROUND

Benefits of phosphate-lowering interventions on clinical outcomes in patients with CKD are unclear; systematic reviews have predominantly involved patients on dialysis. This study aimed to summarize evidence from randomized controlled trials (RCTs) concerning benefits and risks of noncalcium-based phosphate-lowering treatment in nondialysis CKD.

METHODS

We conducted a systematic review and meta-analyses of RCTs involving noncalcium-based phosphate-lowering therapy compared with placebo, calcium-based binders, or no study medication, in adults with CKD not on dialysis or post-transplant. RCTs had ≥3 months follow-up and outcomes included biomarkers of mineral metabolism, cardiovascular parameters, and adverse events. Outcomes were meta-analyzed using the Sidik-Jonkman method for random effects. Unstandardized mean differences were used as effect sizes for continuous outcomes with common measurement units and Hedge's g standardized mean differences (SMD) otherwise. Odds ratios were used for binary outcomes. Cochrane risk of bias and GRADE assessment determined the certainty of evidence.

RESULTS

In total, 20 trials involving 2498 participants (median sample size 120, median follow-up 9 months) were eligible for inclusion. Overall, risk of bias was low. Compared with placebo, noncalcium-based phosphate binders reduced serum phosphate (12 trials, weighted mean difference -0.37; 95% CI, -0.58 to -0.15 mg/dl, low certainty evidence) and urinary phosphate excretion (eight trials, SMD -0.61; 95% CI, -0.90 to -0.31, low certainty evidence), but resulted in increased constipation (nine trials, log odds ratio [OR] 0.93; 95% CI, 0.02 to 1.83, low certainty evidence) and greater vascular calcification score (three trials, SMD, 0.47; 95% CI, 0.17 to 0.77, very low certainty evidence). Data for effects of phosphate-lowering therapy on cardiovascular events (log OR, 0.51; 95% CI, -0.51 to 1.17) and death were scant.

CONCLUSIONS

Noncalcium-based phosphate-lowering therapy reduced serum phosphate and urinary phosphate excretion, but there was an unclear effect on clinical outcomes and intermediate cardiovascular end points. Adequately powered RCTs are required to evaluate benefits and risks of phosphate-lowering therapy on patient-centered outcomes.

The Influence of Sevelamer Hydrochloride and Calcium Carbonate on Markers of Inflammation and Oxidative Stress in Hemodialysis at Six Months of Follow-Up

Patients with end-stage renal disease (ESRD) present alterations in mineral and bone metabolism. Hyperphosphatemia in ESRD is considered an independent risk factor for cardiovascular disease (CVD), increasing morbidity, and mortality. Sevelamer hydrochloride is a calcium-free, non-absorbable phosphate-chelating polymer. Calcium carbonate chelator is helpful in controlling serum phosphate levels. There is insufficient information on the influence of sevelamer hydrochloride and calcium carbonate on the behavior of oxidative stress (OS) markers and inflammation in patients on hemodialysis (HD). A randomized open clinical trial was carried out on patients to evaluate sevelamer hydrochloride and calcium carbonate influence at 6 months of study follow-up. Levels of oxidants (LPO, NO, and 8-isoprostanes), antioxidants (SOD and TAC), oxidative DNA damage (8-OHdG and hOGG1), pro-inflammatory cytokines (IL-6 and TNF-α), and inflammation markers (ferritin and C-reactive protein) were measured with colorimetric and ELISA methods. We found a significant increase in oxidants LPO and NO, and antioxidants SOD and TAC, and downregulation of IL-6 and TNF-α. Ferritin decrease at 6 months follow-up in the sevelamer hydrochloride group. Increase in C-reactive protein was found in the group of patients treated with calcium carbonate. In conclusion, we found an oxidative state imbalance with increase in LPO and NO oxidants. The activity of the antioxidant enzymes (SOD and TAC) was also found to increase, suggesting a compensatory effect in the face of increase in oxidants. The same phenomenon was observed with increase in the oxidative damage marker to DNA and the increase in the DNA repair enzyme, suggesting a compensatory effect. Pro-inflammatory cytokines were predominantly downregulated by TNF-α in the group that ingested sevelamer hydrochloride in the final determination at 6 months of follow-up. Serum ferritin levels decreased significantly at the end of follow-up in patients on HD in the sevelamer hydrochloride group. The management of hyperphosphatemia with sevelamer hydrochloride appears to have obvious anti-inflammatory and antioxidant benefits.

AGE/RAGE in diabetic kidney disease and ageing kidney

Diabetic kidney disease (DKD) is the primary cause of chronic kidney disease that inevitably progress to end-stage kidney disease. Intervention strategies such as blood glucose control is effective for preventing DKD, but many patients with DKD still reach end-stage kidney disease. Although comprehensive mechanisms shed light on the progression of DKD, the most compelling evidence has highlighted that hyperglycemia-related advanced glycation end products (AGEs) formation plays a central role in the pathogenesis of DKD. Pathologically, accumulation of AGEs-mediated receptor for AGEs (RAGE) triggers oxidative stress and inflammation, which is the major deleterious effect of AGEs in host and intestinal microenvironment of diabetic and ageing conditions. The activation of AGEs-mediated RAGE could evoke nicotinamide adenine dinucleotide phosphate oxidase-induced reactive oxygen and nitrogen species production and subsequently give rise to oxidative stress in DKD and ageing kidney. Therefore, targeting RAGE with its ligands mediated oxidative stress and chronic inflammation is considered as an additional intervention strategy for DKD and ageing kidney. In this review, we summarize AGEs/RAGE-mediated oxidative stress and inflammation signaling pathways in DKD and ageing kidney, discussing opportunities and challenges of targeting at AGEs/RAGE-induced oxidative stress that could hold the promising potential approach for improving DKD and ageing kidney.

New progress in drugs treatment of diabetic kidney disease

Diabetic kidney disease (DKD) is not only one of the main complications of diabetes, but also the leading cause of the end-stage renal disease (ESRD). The occurrence and development of DKD have always been a serious clinical problem that leads to the increase of morbidity and mortality and the severe damage to the quality of life of human beings. Controlling blood glucose, blood pressure, blood lipids, and improving lifestyle can help slow the progress of DKD. In recent years, with the extensive research on the pathological mechanism and molecular mechanism of DKD, there are more and more new drugs based on this, such as new hypoglycemic drugs sodium-glucose cotransporter 2 (SGLT2) inhibitors, glucagon-like peptide-1 (GLP-1) inhibitors, and dipeptidyl peptidase-4 (DPP-4) inhibitors with good efficacy in clinical treatment. Besides, there are some newly developed drugs, including protein kinase C (PKC) inhibitors, advanced glycation end product (AGE) inhibitors, aldosterone receptor inhibitors, endothelin receptor (ETR) inhibitors, transforming growth factor-β (TGF-β) inhibitors, Rho kinase (ROCK) inhibitors and so on, which show positive effects in animal or clinical trials and bring hope for the treatment of DKD. In this review, we sort out the progress in the treatment of DKD in recent years, the research status of some emerging drugs, and the potential drugs for the treatment of DKD in the future, hoping to provide some directions for clinical treatment of DKD.

Protective effects of dietary carnosine during in-vitro digestion of pork differing in fat content and cooking conditions

Muscle carnosine represents an important health advantage of meat. Ground pork samples with intrinsic or added carnosine; fat content; and cooked under low or high intensity as a 2 × 2 × 2 factorial were digested in-vitro. Changes in free carnosine and in markers of lipid (hexanal, 4-hydroxynonenal (4-HNE), malondialdehyde (MDA) and protein (protein-carbonyls, thiols) oxidation, and of advanced glycation end-products (AGEs) N^ε -(carboxymethyl)lysine (CML) were determined in the saliva, gastric, and duodenal digests. During digestion, the different markers overall indicated increased oxidation and decreased free carnosine. Increasing pork carnosine level significantly reduced protein carbonyls, loss of thiols, and 4-HNE during in-vitro gastric digestion, irrespective of fat and cooking level of the meat. Increased carnosine also significantly reduced hexanal, MDA and CML up to the duodenum phase in moderately cooked lean pork. Besides substantiating the formation of AGEs during digestion, these results show a potentially important role of dietary carnosine occurring in the gastrointestinal tract. PRACTICAL APPLICATIONS: The ailments epidemiologically associated with red meat consumption could be counteracted by ingesting carnosine into meat. The health advantages of dietary carnosine, however, have never been demonstrated during digestion, a unique and complex oxidative environment compounded by the composition and cooking of the meat. The results obtained substantiated that AGEs formation occurred in-vitro in the GIT. They also showed that increased carnosine had an immediate health beneficial role during pork digestion in reducing the formation of different harmful molecules, including AGEs, modulated by the composition and cooking of the meat. However, in exerting this protective role in the GIT, the remaining free level of carnosine, gradually decreased during digestion. Carnosine, as an important meat compositional factor may, depending on the fat content and cooking conditions, change the image of meat from representing a health risk to a health benefit. Carnosine level may also explain discrepancies observed in the literature.

Advanced Glycation End Products: New Clinical and Molecular Perspectives

Diabetes mellitus (DM) is considered one of the most massive epidemics of the twenty-first century due to its high mortality rates caused mainly due to its complications; therefore, the early identification of such complications becomes a race against time to establish a prompt diagnosis. The research of complications of DM over the years has allowed the development of numerous alternatives for diagnosis. Among these emerge the quantification of advanced glycation end products (AGEs) given their increased levels due to chronic hyperglycemia, while also being related to the induction of different stress-associated cellular responses and proinflammatory mechanisms involved in the progression of chronic complications of DM. Additionally, the investigation for more valuable and safe techniques has led to developing a newer, noninvasive, and effective tool, termed skin fluorescence (SAF). Hence, this study aimed to establish an update about the molecular mechanisms induced by AGEs during the evolution of chronic complications of DM and describe the newer measurement techniques available, highlighting SAF as a possible tool to measure the risk of developing DM chronic complications.

The impact of phosphate lowering agents on clinical and laboratory outcomes in chronic kidney disease patients: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Besides reducing hyperphosphatemia in chronic kidney disease (CKD) patients, phosphate lowering agents might provide beneficial effects on clinical and laboratory parameters. This meta-analysis was conducted to comprehensively examine the impact of all phosphate lowering agents on various aspects of clinical and laboratory outcomes in CKD patients.

METHOD

A systematic literature search was performed in MEDLINE, Scopus, and the Cochrane Register of Controlled Trials until July 2020 to identify randomized controlled trials (RCTs) which compared the effects of each phosphate lowering agent with controls, comprising placebo and all other phosphate lowering agents. Various clinical and laboratory outcomes were analyzed. Random effects model was used to compute the standardized mean difference for continuous variables and the risk ratio (RR) for binary variables.

RESULTS

This meta-analysis included 127 RCTs with 20,215 patients. Sevelamer and lanthanum significantly reduced all-cause mortality (RR 0.610, 95% CI 0.401-0.929 and 0.467, 95% CI 0.337-0.647, respectively) but not cardiovascular (CV) mortality or CV events. Hospitalization rates were significantly diminished by sevelamer (RR 0.527; 95% CI 0.308-0.902). Certain phosphate lowering agents improved biochemical parameters including serum phosphate, calcium, coronary artery calcium scores, fibroblast growth factor-23, bone biomarkers, and lipid profiles. Intact parathyroid hormone and bone mineral density were not significantly changed.

CONCLUSIONS

In addition to decreasing serum phosphate levels, various beneficial effects on clinical and laboratory parameters of phosphate lowering agents might play potential roles in diminishing morbidity and mortality in CKD patients.

The Circadian Clock Regulates the Expression of the Nuclear Factor Erythroid 2-Related Factor 2 in Acute Kidney Injury following Myocardial Ischemia-Reperfusion in Diabetic Rat

Cardiac surgery-associated acute kidney injury (AKI) is a serious and frequent complication with poor prognosis, and disruption in circadian rhythm shall adversely influence cardiovascular and renal functions via oxidative stress mechanisms. However, the role of circadian clock genes (circadian locomotor output cycle kaput (CLOCK) and brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein-1 (BMAL1)) and its interaction with nuclear factor erythroid 2-related factor 2 (Nrf2) in AKI following myocardial ischemia-reperfusion (MIR) in the diabetic rat has not yet been explored. In this study, rats were divided into the sham (S) group, MIR (M) group, diabetic (D) group, and diabetic+MIR (DM) group. At light (zeitgeber time (ZT) 0) and dark time points (ZT12), rat MIR model was established by occlusion of the left anterior descending coronary artery for 30 min followed by 2 -hour reperfusion, and then renal injury was evaluated. The renal histological changes in the DM group were significantly high compared to other groups; serum creatinine, blood urea nitrogen, and neutrophil gelatinase-associated lipocalin levels, as well as malondialdehyde and 8-iso-prostaglandin-F2α levels in renal tissues of M ZT12 and DM ZT12 subgroups, were significantly higher than those of M ZT0 and DM ZT0 subgroups, individually indicating increased oxidative stress at a dark cycle. Further, Nrf2 protein accumulated in a circadian manner with decreasing levels at night in the DM and M groups. In conclusion, renal injury following MIR was exacerbated in the diabetic rat at night through molecular mechanisms involving transcriptional control of the circadian clock on light-dark activation of Nrf2.

An updated pharmacological insight of resveratrol in the treatment of diabetic nephropathy

As one of the most common complications of diabetes, nephropathy develops in approximately 40% of diabetic individuals. Although end stage kidney disease is known as one of the most consequences of diabetic nephropathy, the majority of diabetic individuals might die from cardiovascular diseases and infections before renal replacement treatment. Moreover, the routine medical treatments for diabetes hold undesirable side effects. The explosive prevalence of diabetes urges clinicians and scientists to investigate the complementary or alternative therapies. Phytochemicals are emerging as alternatives with a wide range of therapeutic effects on various pathologies, including diabetic kidney disease. Of those phytochemicals, resveratrol, a natural polyphenolic stilbene, has been found to exert a broad spectrum of health benefits via various signaling molecules. In particular, resveratrol has gained a great deal of attention because of its anti-oxidative, anti-inflammatory, anti-diabetic, anti-obesity, cardiovascular-protective, and anti-tumor properties. In the renal system, emerging evidence shows that resveratrol has already been used to ameliorate chronic or acute kidney injury. This review critically summarizes the current findings and molecular mechanisms of resveratrol in diabetic renal damage. In addition, we will discuss the adverse and inconsistent effects of resveratrol in diabetic nephropathy. Although there is increasing evidence that resveratrol affords great potential in diabetic nephropathy therapy, these results should be treated with caution before its clinical translation. In addition, the unfavorable pharmacokinetics and/or pharmacodynamics profiles, such as poor bioavailability, may limit its extensive clinical applications. It is clear that further research is needed to unravel these limitations and improve its efficacy against diabetic nephropathy. Increasing investigation of resveratrol in diabetic kidney disease will not only help us better understand its pharmacological actions, but also provide novel potential targets for therapeutic intervention.

Systematic review of the nuclear factor erythroid 2-related factor 2 (NRF2) system in human chronic kidney disease: alterations, interventions, and relation to morbidity

BACKGROUND

NRF2 and its effectors NAD(P)H:quinoneoxidoreductase 1 (NQO1) and heme oxygenase 1 (HO-1) are of interest in kidney disease. We therefore reviewed studies about their status in patients with chronic kidney disease (CKD).

METHODS

We undertook systematic searches of PubMed and EMBASE databases. Alterations of NRF2, NQO1 and HO-1 in CKD, their responses to interventions and their relation to clinically relevant parameters were reported.

RESULTS

We identified 1373 articles, of which 32 studies met the inclusion criteria. NRF2 levels were decreased in the majority of analyses of CKD patients. Half of the analyses showed a similar or increased NQO1 level vs. control, whereas NQO1 was decreased in half of the analyses. Most of the studies reported either an increased or similar HO-1 level in CKD patients compared to controls. For patients with CKD stages 1-4, studies reported positive correlations to markers of kidney disease severity. Also, positive associations of NQO1/HO-1 levels to inflammation and comorbidities were reported. One third of the studies showed discordant changes between gene expression and protein level of NRF2 system components. Two thirds of intervention studies (50% dietary, such as using resistant starch) reported an increase of NRF2, NQO1, or HO-1.

CONCLUSIONS

In patients with CKD, NRF2 expression was downregulated, while NQO1 and HO-1 showed varying alterations related to inflammation, comorbidities, and severity of kidney damage. Interventions that increased NRF2 system components were described, but their effectiveness and clinical relevance require further clinical studies of high quality. Research on gene expression together with protein analyses is indispensable to understand NRF2 system alterations in CKD.

AgeR deletion decreases soluble fms-like tyrosine kinase 1 production and improves post-ischemic angiogenesis in uremic mice

Peripheral arterial disease occurs more frequently and has a worse prognosis in patients with chronic kidney disease (CKD). The receptor for advanced glycation end products (RAGE) is involved in multiple aspects of uremia-associated vasculopathy. Previous data suggest that the RAGE pathway may promote soluble fms-like tyrosine kinase 1 (sFlt1) production, an anti-angiogenic molecule. Thus, we tested the hypothesis that the deletion of AgeR would decrease sFlt1 production and improve post-ischemic revascularization in uremic condition. We used a well-established CKD model (5/6 nephrectomy) in WT and AgeR-/- C57/Bl6 mice. Hindlimb ischemia was induced by femoral artery ligation. Revascularization was evaluated by complementary approaches: ischemic limb retraction, LASCA imagery, and capillary density. The production of sFlt1 was assessed at both RNA and protein levels. After hindlimb ischemia, uremic mice showed slower functional recovery (p < 0.01), decreased reperfusion (p < 0.01), lower capillary density (p = 0.02), and increased circulating sFlt1 levels (p = 0.03). AgeR deletion restored post-ischemic angiogenesis and was protective from sFlt1 increase in uremic mice. These findings show the main role of RAGE in post-ischemic angiogenesis impairment associated with CKD. RAGE may represent a key target for building new therapeutic approaches to improve the outcome of CKD patients with PAD.

Sevelamer Use in End-Stage Kidney Disease (ESKD) Patients Associates with Poor Vitamin K Status and High Levels of Gut-Derived Uremic Toxins: A Drug-Bug Interaction?

Gut microbial metabolism is not only an important source of uremic toxins but may also help to maintain the vitamin K stores of the host. We hypothesized that sevelamer therapy, a commonly used phosphate binder in patients with end-stage kidney disease (ESKD), associates with a disturbed gut microbial metabolism. Important representatives of gut-derived uremic toxins, including indoxyl sulfate (IndS), p-Cresyl sulfate (pCS), trimethylamine N-oxide (TMAO), phenylacetylglutamine (PAG) and non-phosphorylated, uncarboxylated matrix-Gla protein (dp-ucMGP; a marker of vitamin K status), were analyzed in blood samples from 423 patients (65% males, median age 54 years) with ESKD. Demographics and laboratory data were extracted from electronic files. Sevelamer users (n = 172, 41%) were characterized by higher phosphate, IndS, TMAO, PAG and dp-ucMGP levels compared to non-users. Sevelamer was significantly associated with increased IndS, PAG and dp-ucMGP levels, independent of age, sex, calcium-containing phosphate binder, cohort, phosphate, creatinine and dialysis vintage. High dp-ucMGP levels, reflecting vitamin K deficiency, were independently and positively associated with PAG and TMAO levels. Sevelamer therapy associates with an unfavorable gut microbial metabolism pattern. Although the observational design precludes causal inference, present findings implicate a disturbed microbial metabolism and vitamin K deficiency as potential trade-offs of sevelamer therapy.

Changes in oxidative nucleic acid modifications and inflammation following one-week treatment with the bile acid sequestrant sevelamer: Two randomised, placebo-controlled trials

AIMS

Sevelamer has been reported to have anti-oxidative and anti-inflammatory effects as well as effects on glycaemic control and plasma lipids. The aim of this study was to determine the effects of one-week treatment with sevelamer on oxidative nucleic acid modifications and inflammation markers.

METHODS

Two double-blinded studies including 30 patients with type 2 diabetes (T2D) and 20 healthy individuals were conducted. Participants were randomised to one week of treatment with sevelamer (1600 mg three times daily) or placebo. RNA and DNA oxidation, measured by urinary excretion of 8-oxo-7,8-dihydroguanosine(8-oxoGuo) and (8-oxo-7,8-dihydro-2'-deoxyguanosine(8-oxodG), and markers of inflammation were determined before and after the intervention.

RESULTS

In patients with T2D there was no significant placebo-corrected reduction in 8-oxoGuo or 8-oxodG. However, a reduction in 8-oxoGuo was observed within the group treated with sevelamer (∆8-oxoGuo/creatinine (median[IQR]): -0.04 [-0.24; 0.01] nmol/mmol, p = 0.02). A sevelamer-mediated reduction in interleukin-2 (p = 0.04) and a trend towards reduction in interleukin-6 (p = 0.053) were found in patients with T2D.

CONCLUSIONS

This study reveals a potential effect of sevelamer treatment on inflammation and possible oxidative RNA modifications. The potential protective effects of sevelamer in terms of cardiovascular disease in patients with T2D need further investigation.

Phosphate Binders and Nonphosphate Effects in the Gastrointestinal Tract

Phosphate binders are commonly prescribed in patients with end-stage kidney disease to prevent and treat hyperphosphatemia. These binders are usually associated with gastrointestinal distress, may bind molecules other than phosphate, and may alter the gut microbiota, altogether having systemic effects unrelated to phosphate control. Sevelamer is the most studied of the available binders for nonphosphate-related effects including binding to bile acids, endotoxins, gut microbiota-derived metabolites, and advanced glycation end products. Other binders (calcium- and noncalcium-based binders) may bind vitamins, such as vitamin K and folic acid. Moreover, the relatively new iron-based phosphate binders may alter the gut microbiota, as some of the iron or organic ligands may be used by the gastrointestinal bacteria. The objective of this narrative review is to provide the current evidence for the nonphosphate effects of phosphate binders on gastrointestinal function, nutrient and molecule binding, and the gut microbiome.

Carbotoxicity-Noxious Effects of Carbohydrates

Modern nutrition is often characterized by the excessive intake of different types of carbohydrates ranging from digestible polysaccharides to refined sugars that collectively mediate noxious effects on human health, a phenomenon that we refer to as "carbotoxicity." Epidemiological and experimental evidence combined with clinical intervention trials underscore the negative impact of excessive carbohydrate uptake, as well as the beneficial effects of reducing carbs in the diet. We discuss the molecular, cellular, and neuroendocrine mechanisms that link exaggerated carbohydrate intake to disease and accelerated aging as we outline dietary and pharmacologic strategies to combat carbotoxicity.

Does the Administration of Sevelamer or Nicotinamide Modify Uremic Toxins or Endotoxemia in Chronic Hemodialysis Patients?

BACKGROUND

Hyperphosphatemia control is a major issue in hemodialysis patients. Both sevelamer and nicotinamide are prescribed for this purpose. In addition, they exert pleiotropic effects such as an improvement of inflammatory status and potentially enhanced clearance of uremic toxins. In the present secondary analysis of the NICOREN trial, we investigated the impact of sevelamer and nicotinamide on uremic toxins, toxin precursors, and endotoxemia in chronic hemodialysis patients.

METHODS

Circulating uremic toxins (including phenylacetylglutamine, trimethylamine-N-oxide, p-cresyl sulfate, indoxyl sulfate, kynurenine, hippuric acid, indole-3-acetic acid, 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid, kynurenic acid, and p-cresyl glucuronide) and precursors were measured by ultra-performance liquid chromatography-tandem mass spectrometry, and urea, uric acid, phosphate, C-reactive protein, and intact parathyroid hormone by routine biochemistry methods. Serum endotoxin (evaluated by lipopolysaccharide levels) and C-terminal fibroblast growth factor-23 levels were measured using enzyme-linked immunosorbent assay kits.

RESULTS

One hundred hemodialysis patients were randomized to receive either nicotinamide or sevelamer treatment. Among them, 63% were male, mean (± standard deviation) age was 65 ± 14 years, 47% had diabetes mellitus, and 51% had a history of cardiovascular disease. In the sevelamer group, but not the nicotinamide group, serum levels of urea, uric acid, and fibroblast growth factor-23 were significantly reduced after 6 months of treatment. The other circulating uremic toxins and toxin precursors remained unchanged in response to either phosphate-lowering agent. Sevelamer treatment led to a marked decrease in serum lipopolysaccharide (p < 0.001) whereas nicotinamide treatment induced an only modest decrease of borderline significance (p = 0.057). There was no change in C-reactive protein levels.

CONCLUSION

In contrast to sevelamer, nicotinamide did not reduce circulating levels of low-molecular-weight uremic toxins other than phosphate, and neither agent reduced circulating uremic toxins of high-molecular-weight or protein-bound toxins. Sevelamer, but not nicotinamide, reduced serum endotoxin levels. Despite no change in serum C-reactive protein, the endotoxin-lowering effect of sevelamer may help to attenuate the inflammatory status of patients with chronic kidney disease.

Effects of Sevelamer Carbonate in Patients With CKD and Proteinuria: The ANSWER Randomized Trial

RATIONALE & OBJECTIVE

Hyperphosphatemia is associated with increased risk for chronic kidney disease (CKD) progression and reduced antiproteinuric effects of renin-angiotensin system (RAS) blockers. We investigated whether the phosphate binder sevelamer carbonate may enhance the antiproteinuric effect of RAS inhibitors in patients with CKD.

STUDY DESIGN

Phase 2, randomized, controlled, open-label, crossover trial.

SETTING & PARTICIPANTS

Between November 2013 and December 2014, we enrolled 53 patients with CKD with estimated glomerular filtration rates (eGFRs)>15mL/min/1.73m² and residual proteinuria with protein excretion≥0.5g/24h despite maximal tolerated ramipril and/or irbesartan therapy from 2 nephrology units in Italy.

INTERVENTION

After stratification by serum phosphate level, ≤4 or>4mg/dL, patients were randomly assigned to 3 months of sevelamer (1,600mg thrice daily) treatment followed by 3 months without sevelamer separated by a 1-month washout period or 3 months without sevelamer followed by 3 months with sevelamer, also separated by a 1-month washout period.

OUTCOMES

The primary outcome was 24-hour proteinuria (n=49patients). Secondary outcomes included measured GFR (using iohexol plasma clearance), office blood pressure (BP), serum lipid levels, levels of inflammation and bone metabolism biomarkers, urinary electrolyte levels, and arterial stiffness.

RESULTS

Changes in proteinuria during the 3-month treatment with (from 1.36 [IQR, 0.77-2.51] to 1.36 [IQR, 0.77-2.60] g/24h) or without (from 1.36 [IQR, 0.99-2.38] to 1.48 [IQR, 0.81-2.77] g/24h) sevelamer were similar (P=0.1). Sevelamer reduced urinary phosphate excretion without affecting serum phosphate levels. Sevelamer reduced C-reactive protein (CRP), glycated hemoglobin, and total and low-density lipoprotein cholesterol levels and increased high-density lipoprotein cholesterol levels without affecting levels of office BP, measured GFR, fibroblast growth factor 23, klotho, intact parathyroid hormone, serum vitamin D, or other urinary electrolytes. Results were similar in the low- and high-phosphate groups. Sevelamer was well tolerated. Adverse events were comparable between treatment periods. One case of transient hypophosphatemia was observed during treatment with sevelamer.

LIMITATIONS

Short treatment duration, lower pretreatment proteinuria than expected.

CONCLUSIONS

3-month sevelamer treatment did not reduce proteinuria in patients with CKD on maximal RAS blockade. Amelioration of inflammation and dyslipidemia with sevelamer treatment raises the possibility that it may confer benefit in patients with CKD beyond reduction of proteinuria.

FUNDING

Sanofi (Milan, Italy).

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with study number NCT01968759.

Mediterranean Diet Supplemented With Coenzyme Q10 Modulates the Postprandial Metabolism of Advanced Glycation End Products in Elderly Men and Women

Advanced glycation end products (AGEs) and oxidative stress are elevated with aging and dysmetabolic conditions. Because a Mediterranean (Med) diet reduces oxidative stress, serum AGEs levels, and gene expression related to AGEs metabolism in healthy elderly people, we studied whether supplementation with coenzyme Q10 (CoQ) was of further benefit. Twenty participants aged ≥ 65 (10 men and 10 women) were randomly assigned to each of three isocaloric diets for successive periods of 4 weeks in a crossover design: Med diet, Med + CoQ, and a Western high-saturated-fat diet (SFA diet). After a 12-hour fast, volunteers consumed a breakfast with a fat composition similar to the previous diet period. Analyses included dietary AGEs consumed, serum AGEs and AGE receptor-1 (AGER1), receptor for AGEs (RAGE), glyoxalase I (GloxI), and estrogen receptor α (ERα) mRNA levels. Med diet modulated redox-state parameters, reducing AGEs levels and increasing AGER1 and GloxI mRNA levels compared with the SFA diet. This benefit was accentuated by adding CoQ, in particular, in the postprandial state. Because elevated oxidative stress/inflammation and AGEs are associated with clinical disease in aging, the enhanced protection of a Med diet supplemented with CoQ should be assessed in a larger clinical trial in which clinical conditions in aging are measured.

Dietary Advanced Glycation End Products: Digestion, Metabolism and Modulation of Gut Microbial Ecology

The formation of advanced glycation end products (AGEs) in foods is accelerated with heat treatment, particularly within foods that are cooked at high temperatures for long periods of time using dry heat. The modern processed diet is replete with AGEs, and excessive AGE consumption is thought to be associated with a number of negative health effects. Many dietary AGEs have high molecular weight and are not absorbed in the intestine, and instead pass through to the colon, where they are available for metabolism by the colonic bacteria. Recent studies have been conducted to explore the effects of AGEs on the composition of the gut microbiota as well as the production of beneficial microbial metabolites, in particular, short-chain fatty acids. However, there is conflicting evidence regarding the impact of dietary AGEs on gut microbiota reshaping, which may be due, in part, to the formation of alternate compounds during the thermal treatment of foods. This review summarises the current evidence regarding dietary sources of AGEs, their gastrointestinal absorption and role in gut microbiota reshaping, provides a brief overview of the health implications of dietary AGEs and highlights knowledge gaps and avenues for future study.

The role of advanced glycation end-products in the development of coronary artery disease in patients with and without diabetes mellitus: a review

Background

Traditional risk factors are insufficient to explain all cases of coronary artery disease (CAD) in patients with diabetes mellitus (DM). Advanced glycation end-products (AGEs) and their receptors may play important roles in the development and progression of CAD.

Body

Hyperglycemia is the hallmark feature of DM. An increase in the incidence of both micro-and macrovascular complications of diabetes has been observed with increased duration of hyperglycemia. This association persists even after glycemic control has been achieved, suggesting an innate mechanism of “metabolic memory.” AGEs are glycated proteins that may serve as mediators of metabolic memory due to their increased production in the setting of hyperglycemia and generally slow turnover. Elevated AGE levels can lead to abnormal cross linking of extracellular and intracellular proteins disrupting their normal structure and function. Furthermore, activation of AGE receptors can induce complex signaling pathways leading to increased inflammation, oxidative stress, enhanced calcium deposition, and increased vascular smooth muscle apoptosis, contributing to the development of atherosclerosis. Through these mechanisms, AGEs may be important mediators of the development of CAD. However, clinical studies regarding the role of AGEs and their receptors in advancing CAD are limited, with contradictory results.

Conclusion

AGEs and their receptors may be useful biomarkers for the presence and severity of CAD. Further studies are needed to evaluate the utility of circulating and tissue AGE levels in identifying asymptomatic patients at risk for CAD or to identify patients who may benefit from invasive intervention.

Pharmacologic control of oxidative stress and inflammation determines whether diabetic glomerulosclerosis progresses or decreases: A pilot study in sclerosis-prone mice

Diabetic kidney disease (DKD) is characterized by progressive glomerulosclerosis (GS). ROP mice have a sclerosis-prone phenotype. However, they develop severe, rapidly progressive GS when rendered diabetic. Since GS also develops in aged C57Bl6 mice, and can be reversed using bone marrow from young mice which have lower oxidative stress and inflammation (OS/Infl), we postulated that this might also apply to DKD. Therefore, this pilot study asked whether reducing OS/Infl in young adult sclerosis-prone (ROP) diabetic mice leads to resolution of existing GS in early DKD using safe, FDA-approved drugs.After 4 weeks of stable streptozotocin-induced hyperglycemia 8-12 week-old female mice were randomized and treated for 22 weeks as follows: 1) enalapril (EN) (n = 8); 2) pyridoxamine (PYR)+EN (n = 8); 3) pentosan polysulfate (PPS)+EN (n = 7) and 4) PPS+PYR+EN (n = 7). Controls were untreated (non-DB, n = 7) and hyperglycemic (DB, n = 8) littermates. PPS+PYR+EN reduced albuminuria and reversed GS in DB. Treatment effects: 1) Anti-OS/Infl defenses: a) PPS+PYR+EN increased the levels of SIRT1, Nrf2, estrogen receptor α (ERα) and advanced glycation endproduct-receptor1 (AGER1) levels; and b) PYR+EN increased ERα and AGER1 levels. 2) Pro-OS/Infl factors: a) PPS+PYR+EN reduced sTNFR1, b) all except EN reduced MCP1, c) RAGE was reduced by all treatments. In summary, PYR+PPS+EN modulated GS in sclerosis-prone hyperglycemic mice. PYR+PPS+EN also decreased albuminuria, OS/Infl and the sclerosis-prone phenotype. Thus, reducing OS/Infl may reverse GS in early diabetes in patients, and albuminuria may allow early detection of the sclerosis-prone phenotype.

Phosphate binders for preventing and treating chronic kidney disease-mineral and bone disorder (CKD-MBD)

BACKGROUND

Phosphate binders are used to reduce positive phosphate balance and to lower serum phosphate levels for people with chronic kidney disease (CKD) with the aim to prevent progression of chronic kidney disease-mineral and bone disorder (CKD-MBD). This is an update of a review first published in 2011.

OBJECTIVES

The aim of this review was to assess the benefits and harms of phosphate binders for people with CKD with particular reference to relevant biochemical end-points, musculoskeletal and cardiovascular morbidity, hospitalisation, and death.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 12 July 2018 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) or quasi-RCTs of adults with CKD of any GFR category comparing a phosphate binder to another phosphate binder, placebo or usual care to lower serum phosphate. Outcomes included all-cause and cardiovascular death, myocardial infarction, stroke, adverse events, vascular calcification and bone fracture, and surrogates for such outcomes including serum phosphate, parathyroid hormone (PTH), and FGF23.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion and extracted study data. We applied the Cochrane 'Risk of Bias' tool and used the GRADE process to assess evidence certainty. We estimated treatment effects using random-effects meta-analysis. Results were expressed as risk ratios (RR) for dichotomous outcomes together with 95% confidence intervals (CI) or mean differences (MD) or standardised MD (SMD) for continuous outcomes.

MAIN RESULTS

We included 104 studies involving 13,744 adults. Sixty-nine new studies were added to this 2018 update.Most placebo or usual care controlled studies were among participants with CKD G2 to G5 not requiring dialysis (15/25 studies involving 1467 participants) while most head to head studies involved participants with CKD G5D treated with dialysis (74/81 studies involving 10,364 participants). Overall, seven studies compared sevelamer with placebo or usual care (667 participants), seven compared lanthanum to placebo or usual care (515 participants), three compared iron to placebo or usual care (422 participants), and four compared calcium to placebo or usual care (278 participants). Thirty studies compared sevelamer to calcium (5424 participants), and fourteen studies compared lanthanum to calcium (1690 participants). No study compared iron-based binders to calcium. The remaining studies evaluated comparisons between sevelamer (hydrochloride or carbonate), sevelamer plus calcium, lanthanum, iron (ferric citrate, sucroferric oxyhydroxide, stabilised polynuclear iron(III)-oxyhydroxide), calcium (acetate, ketoglutarate, carbonate), bixalomer, colestilan, magnesium (carbonate), magnesium plus calcium, aluminium hydroxide, sucralfate, the inhibitor of phosphate absorption nicotinamide, placebo, or usual care without binder. In 82 studies, treatment was evaluated among adults with CKD G5D treated with haemodialysis or peritoneal dialysis, while in 22 studies, treatment was evaluated among participants with CKD G2 to G5. The duration of study follow-up ranged from 8 weeks to 36 months (median 3.7 months). The sample size ranged from 8 to 2103 participants (median 69). The mean age ranged between 42.6 and 68.9 years.Random sequence generation and allocation concealment were low risk in 25 and 15 studies, respectively. Twenty-seven studies reported low risk methods for blinding of participants, investigators, and outcome assessors. Thirty-one studies were at low risk of attrition bias and 69 studies were at low risk of selective reporting bias.In CKD G2 to G5, compared with placebo or usual care, sevelamer, lanthanum, iron and calcium-based phosphate binders had uncertain or inestimable effects on death (all causes), cardiovascular death, myocardial infarction, stroke, fracture, or coronary artery calcification. Sevelamer may lead to constipation (RR 6.92, CI 2.24 to 21.4; low certainty) and lanthanum (RR 2.98, CI 1.21 to 7.30, moderate certainty) and iron-based binders (RR 2.66, CI 1.15 to 6.12, moderate certainty) probably increased constipation compared with placebo or usual care. Lanthanum may result in vomiting (RR 3.72, CI 1.36 to 10.18, low certainty). Iron-based binders probably result in diarrhoea (RR 2.81, CI 1.18 to 6.68, high certainty), while the risks of other adverse events for all binders were uncertain.In CKD G5D sevelamer may lead to lower death (all causes) (RR 0.53, CI 0.30 to 0.91, low certainty) and induce less hypercalcaemia (RR 0.30, CI 0.20 to 0.43, low certainty) when compared with calcium-based binders, and has uncertain or inestimable effects on cardiovascular death, myocardial infarction, stroke, fracture, or coronary artery calcification. The finding of lower death with sevelamer compared with calcium was present when the analysis was restricted to studies at low risk of bias (RR 0.50, CI 0.32 to 0.77). In absolute terms, sevelamer may lower risk of death (all causes) from 210 per 1000 to 105 per 1000 over a follow-up of up to 36 months, compared to calcium-based binders. Compared with calcium-based binders, lanthanum had uncertain effects with respect to all-cause or cardiovascular death, myocardial infarction, stroke, fracture, or coronary artery calcification and probably had reduced risks of treatment-related hypercalcaemia (RR 0.16, CI 0.06 to 0.43, low certainty). There were no head-to-head studies of iron-based binders compared with calcium. The paucity of placebo-controlled studies in CKD G5D has led to uncertainty about the effects of phosphate binders on patient-important outcomes compared with placebo.It is uncertain whether the effects of binders on clinically-relevant outcomes were different for patients who were and were not treated with dialysis in subgroup analyses.

AUTHORS' CONCLUSIONS

In studies of adults with CKD G5D treated with dialysis, sevelamer may lower death (all causes) compared to calcium-based binders and incur less treatment-related hypercalcaemia, while we found no clinically important benefits of any phosphate binder on cardiovascular death, myocardial infarction, stroke, fracture or coronary artery calcification. The effects of binders on patient-important outcomes compared to placebo are uncertain. In patients with CKD G2 to G5, the effects of sevelamer, lanthanum, and iron-based phosphate binders on cardiovascular, vascular calcification, and bone outcomes compared to placebo or usual care, are also uncertain and they may incur constipation, while iron-based binders may lead to diarrhoea.

Plasma p-cresol lowering effect of sevelamer in non-dialysis CKD patients: evidence from a randomized controlled trial

BACKGROUND

The accumulation of p-cresol, a metabolic product of aromatic amino acids generated by intestinal microbiome, increases the cardiovascular risk in chronic kidney disease (CKD) patients. Therefore, therapeutic strategies to reduce plasma p-cresol levels are highly demanded. It has been reported that the phosphate binder sevelamer (SEV) sequesters p-cresol in vitro, while in vivo studies on dialysis patients showed controversial results. Aim of our study was to evaluate the effect of SEV on p-cresol levels in non-dialysis CKD patients.

METHODS

This was a single-blind, randomized placebo-controlled trial (Registration number NCT02199444) carried on 69 CKD patients (stage 3-5, not on dialysis), randomly assigned (1:1) to receive either SEV or placebo for 3 months. Total p-cresol serum levels were evaluated at baseline (T0), and 1 (T1) and 3 months (T3) after treatment start. The primary end-point was to evaluate the effect of SEV on p-cresol levels.

RESULTS

Compared to baseline (T0, 7.4 ± 2.7 mg/mL), p-cresol mean concentration was significantly reduced in SEV patients after one (- 2.06 mg/mL, 95% CI - 2.62 to - 1.50 mg/mL; p < 0.001) and 3 months of treatment (- 3.97 mg/mL, 95% CI - 4.53 to - 3.41 mg/mL; p < 0.001); no change of plasma p-cresol concentration was recorded in placebo-treated patients. Moreover, P and LDL values were reduced after 3 months of treatment by SEV but not placebo.

CONCLUSIONS

In conclusion, our study represents the first evidence that SEV is effective in reducing p-cresol levels in CKD patients in conservative treatment, and confirms its beneficial effects on inflammation and lipid pattern.

In Silico Analysis of Putrefaction Pathways in Bacteria and Its Implication in Colorectal Cancer

Fermentation of undigested proteins in human gastrointestinal tract (gut) by the resident microbiota, a process called bacterial putrefaction, can sometimes disrupt the gut homeostasis. In this process, essential amino acids (e.g., histidine, tryptophan, etc.) that are required by the host may be utilized by the gut microbes. In addition, some of the products of putrefaction, like ammonia, putrescine, cresol, indole, phenol, etc., have been implicated in the disease pathogenesis of colorectal cancer (CRC). We have investigated bacterial putrefaction pathways that are known to be associated with such metabolites. Results of the comprehensive in silico analysis of the selected putrefaction pathways across bacterial genomes revealed presence of these pathways in limited bacterial groups. Majority of these bacteria are commonly found in human gut. These include Bacillus, Clostridium, Enterobacter, Escherichia, Fusobacterium, Salmonella, etc. Interestingly, while pathogens utilize almost all the analyzed pathways, commensals prefer putrescine and H₂S production pathways for metabolizing the undigested proteins. Further, comparison of the putrefaction pathways in the gut microbiomes of healthy, carcinoma and adenoma datasets indicate higher abundances of putrefying bacteria in the carcinoma stage of CRC. The insights obtained from the present study indicate utilization of possible microbiome-based therapies to minimize the adverse effects of gut microbiome in enteric diseases.

Sevelamer reduces endothelial inflammatory response to advanced glycation end products

Background

Advanced glycation end products (AGEs) have been related to the pathogenesis of cardiovascular diseases (CVD), chronic kidney disease (CKD) and diabetes mellitus. We sought to investigate the binding capacity of sevelamer to both AGEs and uremic serum in vitro and then test this pharmaceutical effect as a potential vascular anti-inflammatory strategy.

Methods

AGEs were prepared by albumin glycation and characterized by absorbance and electrophoresis. Human endothelial cells were incubated in culture media containing AGEs and uremic serum with or without sevelamer. Receptor for advanced glycation end product (RAGE) expression was evaluated through immunocytochemistry and western blot to explore the interactions between AGEs and the endothelium. Inflammatory and endothelial dysfunction biomarkers, such as interleukin 6 (IL-6) and IL-8, monocyte chemoattractant protein-1 (MCP-1), plasminogen activator inhibitor-1 (PAI-1) and serum amyloid A (SAA) were also measured in cell supernatant. The chemotactic property of the supernatant was evaluated.

Results

AGEs significantly induced the expression of RAGE, inflammatory and endothelial activation biomarkers [IL-6, (P < 0.005); IL-8, MCP-1, PAI-1 and SAA (P < 0.001)] and monocyte chemotaxis as compared with controls. In addition, AGEs increased the levels of inflammatory biomarkers, which were observed after 6 h of endothelial cell incubation with uremic serum [IL-6 (P < 0.001) IL-8, MCP-1 and PAI-1 (P < 0.05)]. On the other hand, after 6 h of endothelial cell treatment with sevelamer, RAGE expression (P < 0.05) and levels of inflammatory biomarkers [IL-6 and IL-8 (P < 0.001), MCP-1 (P < 0.01), PAI-1 and SAA (P < 0.005)] significantly decreased compared with the AGEs/uremic serum treatment alone.

Conclusions

Sevelamer decreased both endothelial expression of RAGE and endothelial dysfunction biomarkers, induced by AGEs, and uremic serum. Further studies are necessary for a better understanding of the potential protective role of sevelamer on uremic serum and AGEs-mediated endothelial dysfunction.

Dietary interventions to contrast the onset and progression of diabetic nephropathy: A critical survey of new data

This article is a critical overview of recent contributions on the dietary corrections and the foods that have been claimed to delay or hinder the onset of diabetic nephropathy (DN) and its progression to end-stage renal disease. Innovative dietary and behavioral approaches to the prevention and therapy of DN appear to be the most captivating in consideration of the rather well-established protocols for glucose and blood pressure control in use. In addition to restricted caloric intake to contrast obesity and the metabolic syndrome, adjustments in the patient's macronutrients intake, and in particular some degree of reduction in protein, have been long considered in the prevention of DN progression. More recently, the focus has shifted to the source of proteins and the content of glycotoxins in the diet as well as to the role of specific micronutrients. Few clinical trials have specifically addressed the role of those micronutrients associated with diet proteins that show the most protective effect against DN. Research on clinical outcome and mechanisms of action of such micronutrients appears the most promising in order to develop both effective intervention on nutritional education of the patient and selection of functional foods capable of contrasting the onset and progression of DN.

Dietary fat quantity and quality modifies advanced glycation end products metabolism in patients with metabolic syndrome

SCOPE

Advanced glycation end products (AGEs) increase in dysmetabolic conditions. Lifestyle, including diet, has shown be effective in preventing the development of metabolic syndrome (MetS). We investigated whether AGE metabolism is affected by diets with different fat quantity and quality in MetS patients.

METHODS AND RESULTS

A randomized, controlled trial assigned 75 MetS patients to one of four diets: high SFA (HSFA), high MUFA (HMUFA), and two low-fat, high-complex carbohydrate diets (LFHCC) supplemented with long-chain n-3 PUFA or placebo for 12-weeks each. Dietary and serum AGE [methylglyoxal (MG: lysine-MG-H1) and N-carboxymethyllysine] levels and gene expression related to AGE metabolism in peripheral blood mononuclear cells (AGER1, RAGE, GloxI, and Sirt1 mRNA) were determined. HMUFA diet reduced serum AGE (sAGE) and RAGE mRNA, increased AGER1 and GloxI mRNA levels compared to the other diets. LFHCC n-3 diet reduced sAGE levels and increased AGER1 mRNA levels compared to LFHCC and HSFA diets. Multiple regression analyses showed that sMG and AGER1 mRNA appeared as significant predictors of oxidative stress/inflammation-related parameters.

CONCLUSIONS

Low AGE content in HMUFA diet reduces sAGEs and modulates the gene expression related to AGE metabolism in MetS patients, which may be used as a therapeutic approach to reduce the incidence of MetS and related chronic diseases.

Glycative Stress and Its Defense Machinery Glyoxalase 1 in Renal Pathogenesis

Chronic kidney disease is a major public health problem around the world. Because the kidney plays a role in reducing glycative stress, renal dysfunction results in increased glycative stress. In turn, glycative stress, especially that due to advanced glycated end products (AGEs) and their precursors such as reactive carbonyl compounds, exacerbates chronic kidney disease and is related to premature aging in chronic kidney disease, whether caused by diabetes mellitus or otherwise. Factors which hinder a sufficient reduction in glycative stress include the inhibition of anti-glycation enzymes (e.g., GLO-1), as well as pathogenically activated endoplasmic reticulum (ER) stress and hypoxia in the kidney. Promising strategies aimed at halting the vicious cycle between chronic kidney disease and increases in glycative stress include the suppression of AGE accumulation in the body and the enhancement of GLO-1 to strengthen the host defense machinery against glycative stress.

Estrogen receptor subtype ratio change protects against podocyte damage

Women are relatively protected against the development and progression of glomerulosclerosis (GS) prior to menopause. However, the "female advantage" is lost in women who are either diabetic, post-menopausal or both. We showed that 17β-estradiol (E₂) was effective in prevention of diabetic GS development in part through the stabilization of podocyte cytoskeleton and a change in estrogen receptor (ER) subtype ratio. The objective of this study was to examine whether resveratrol (RSV), reported to have estrogen-like action and renoprotective activity against diabetic GS, would affect similar pathways. After in vitro treatment with RSV we found a change in the ERα and ERβ expression ratio in favor of ERβ, suppression of heat shock protein 25 (Hsp25) expression and increase in β1-integrin expression, important for maintaining podocyte cytoskeleton. We noted a reduction of insulin-like growth factor 1 receptor (IGFR1) expression, decrease in extracellular signal-regulated kinase (ERK) activation, decrease in reactive oxygen species (ROS), and decrease in cleaved-caspase 3 expression. We found an increase in [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT) and an increase in matrix metalloproteinases (MMP-2 and MMP-9) activity. Using cre-loxP strategy we developed podocyte-specific ERα knockout mice to show the importance of ERβ. In isolated podocytes, we confirmed reduction of ERα expression in conjunction with a decrease in IGFR1 expression, ERK and increase of MMP-2 similar to that of our in vitro treatment with RSV. Taken together these data suggest an important role for ERβ and ER subtype ratio in podocyte stabilization. Therefore RSV or other regulators of ER pathways could offer protection against diabetic and age-related podocyte changes.

Iridoid glycoside from Cornus officinalis ameliorated diabetes mellitus-induced testicular damage in male rats: Involvement of suppression of the AGEs/RAGE/p38 MAPK signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Cornus officinalis (CO) has been widely used as a traditional Chinese medicine for treating diabetes mellitus (DM) and its complications. Iridoid glycoside from C. officinalis (IGCO) can resist apoptosis, hyperglycemia, oxidation and so on. The aim of this study was to investigate the therapeutic effects of IGCO on DM-induced testicular damage through inhibition of the AGEs/RAGE/p38 MAPK signaling pathway.

MATERIALS AND METHODS

A DM model of male Wistar rats was induced with streptozotocin injection (30mg/kg, i.p.) and high-fat diet. The DM rats were administrated with IGCO at low and high doses (15 and 30mg/kg, p.o.) for 12 weeks. Testicular damage was evaluated by estimating relative testicular weights, testicular pathohistology, sperm count, live sperm rate, endogenous sex hormone level and activity of testicular marker enzymes. Besides, general diabetic symptoms, renal function, oxidative stress parameters and testicular apoptosis marker were also determined. Finally, the mechanism was explored based on the AGEs/RAGE/p38 MAPK pathway.

RESULTS

IGCO effectively mitigated the general symptoms of DM rats including weight loss, polydipsia, polyphagia, polyuria, elevated blood glucose level and low serum insulin level. Nourishing the kidney evidently, IGCO reduced serum creatinine, urea nitrogen and urine protein excretion, and also markedly protected against DM-induced testicular damage by increasing testis/body weight ratio and live sperm rate, improving the histomorphology of testes, upregulating testosterone, LH, FSH and GnRH levels and preventing the decrease of testicular marker enzymes LDH, ACP and γ-GT. Moreover, IGCO showed considerable anti-oxidative and anti-apoptotic effects, which downregulated the increase of ROS and MDA levels, restored SOD and CAT activities, and decreased spermatogenic cell apoptosis and Bax/Bcl-2 ratio. In the end, the increased AGEs, RAGE and p-p38 MAPK protein levels in DM rats were also reversed by IGCO significantly.

CONCLUSIONS

The kidney tonic IGCO well protected DM rats from testicular damage, which may be related to suppression of the AGEs-RAGE-p38 MAPK pathway.

Renal Aging: Causes and Consequences

Individuals age >65 years old are the fastest expanding population demographic throughout the developed world. Consequently, more aged patients than before are receiving diagnoses of impaired renal function and nephrosclerosis-age-associated histologic changes in the kidneys. Recent studies have shown that the aged kidney undergoes a range of structural changes and has altered transcriptomic, hemodynamic, and physiologic behavior at rest and in response to renal insults. These changes impair the ability of the kidney to withstand and recover from injury, contributing to the high susceptibility of the aged population to AKI and their increased propensity to develop subsequent progressive CKD. In this review, we examine these features of the aged kidney and explore the various validated and putative pathways contributing to the changes observed with aging in both experimental animal models and humans. We also discuss the potential for additional study to increase understanding of the aged kidney and lead to novel therapeutic strategies.

RAGE and glyoxalase in kidney disease

Glycation is an important reaction in the regulation of physiological state. When poorly controlled, however, glycation can also result in the accumulation of glycated proteins (advanced glycation endproducts; AGEs) in the body. This AGE accumulation is termed glycative stress, and is an established pathological factor: to date, glycative stress has been closely associated with not only kidney diseases, but also kidney aging. Accumulating evidence demonstrates that the progression of renal tubular damage and tubular aging are often correlated with activation of the receptor for the AGE (RAGE)-AGE pathway or decreased activity of glyoxalase 1, which is an anti-glycation enzyme to lower glycative stress. Further, glycative stress exacerbates the derangement of protein homeostasis: the posttranslationally modified proteins by glycation often lose or gain their functions. Such deranged protein homeostasis leads to endoplasmic reticulum (ER) stress, a state of ER dysfunction in which the quality control of proteins is defective, as well as to induction of its stress signal, the unfolded protein response (UPR), in the kidney. The lowering of glycative stress via modulation of RAGE-AGE axis or glyoxalase 1 activity is beneficial for tubular homeostasis and the subsequent prevention and treatment of kidney disease, suggesting the possibility of novel therapeutic approaches which target glycative stress. In this review, we focused on the impact of glycative stress in the kidney, especially the role of RAGE and glyoxalase 1. Further we also discuss the crosstalk between glycative stress and ER stress in their effect on protein homeostasis.

Diabetic kidney disease: a role for advanced glycation end-product receptor 1 (AGE-R1)?

Diabetic patients are postulated to be in a perpetual state of oxidative stress and inflammation at sites where chronic complications occur. The accumulation of AGEs derived from both endogenous and exogenous sources (such as the diet) have been implicated in the development and progression of diabetic complications, particularly nephropathy. There has been some interest in investigating the potential for reducing the AGE burden in chronic disease, through the action of AGE "clearance" receptors, such as the advanced glycation end-product receptor 1 (AGE-R1). Reducing the burden of AGEs has been linked to attenuation of inflammation, slower progression of diabetic complications (in particular vascular and renal complications) and has been shown to extend lifespan. To date, however, there have been no direct investigations into whether AGE-R1 has any role in modulating normal kidney function, or specifically during the development and progression of diabetes. This mini-review will focus on the recent advances in knowledge around the mechanistic function of AGE-R1 and the implications of this for the pathogenesis of diabetic kidney disease.

Pathologic role of dietary advanced glycation end products in cardiometabolic disorders, and therapeutic intervention

Reactive derivatives from nonenzymatic glucose-protein condensation reactions, as well as lipids and nucleic acids exposed to reducing sugars, form a heterogeneous group of irreversible adducts called AGEs (advanced glycation end products). The glycation process begins with the conversion of reversible Schiff base adducts to more stable, covalently bound Amadori rearrangement products. Over the course of days to weeks, these Amadori products undergo further rearrangement and condensation reactions to form irreversibly cross-linked macroprotein derivatives known as AGEs. The formation and accumulation of AGEs have been known to progress in a physiological aging process and at an accelerated rate under hyperglycemic and oxidative stress conditions. There is growing evidence that AGEs play a pathologic role in numerous disorders. Indeed, glycation and/or cross-linking modification of circulating or organic matrix proteins by AGEs the senescence of moieties and deteriorate their physiological function and structural integrity in multiple organ systems. Moreover, AGEs elicit oxidative stress and inflammatory reactions through the interaction with the receptor for advanced glycation products in a variety of cells, thereby contributing to the development and progression of various aging- or diabetes-related disorders, such as cardiovascular disease, chronic kidney disease, insulin resistance, and Alzheimer's disease. Recently, diet has been recognized as a major environmental source of AGEs that could cause proinflammatory reactions and organ damage in vivo. Therefore, this review summarizes the pathophysiological role of dietary AGEs in health and disease, especially focusing on cardiometabolic disorders. We also discuss the potential utility in targeting exogenously derived AGEs for therapeutic intervention.

Uremic Toxicity of Advanced Glycation End Products in CKD

Advanced glycation end products (AGEs), a heterogeneous group of compounds formed by nonenzymatic glycation reactions between reducing sugars and amino acids, lipids, or DNA, are formed not only in the presence of hyperglycemia, but also in diseases associated with high levels of oxidative stress, such as CKD. In chronic renal failure, higher circulating AGE levels result from increased formation and decreased renal clearance. Interactions between AGEs and their receptors, including advanced glycation end product-specific receptor (RAGE), trigger various intracellular events, such as oxidative stress and inflammation, leading to cardiovascular complications. Although patients with CKD have a higher burden of cardiovascular disease, the relationship between AGEs and cardiovascular disease in patients with CKD is not fully characterized. In this paper, we review the various deleterious effects of AGEs in CKD that lead to cardiovascular complications and the role of these AGEs in diabetic nephropathy. We also discuss potential pharmacologic approaches to circumvent these deleterious effects by reducing exogenous and endogenous sources of AGEs, increasing the breakdown of existing AGEs, or inhibiting AGE-induced inflammation. Finally, we speculate on preventive and therapeutic strategies that focus on the AGE-RAGE axis to prevent vascular complications in patients with CKD.

Improvements in the Management of Diabetic Nephropathy

The burden of diabetes mellitus is relentlessly increasing. Diabetic nephropathy is the most common cause of end-stage renal disease (ESRD) worldwide and a major cause of morbidity and mortality in patients with diabetes. The current standard therapy of diabetic nephropathy involves intensive treatment of hyperglycemia and strict blood pressure control, mainly via blockade of the renin-angiotensin system (RAS). Attention has been drawn to additional beneficial effects of oral hypoglycemic drugs and fibrates on other aspects of diabetic nephropathy. On the other hand, antiproteinuric effects of RAS combination therapy do not seem to enhance the prevention of renal disease progression, and it has been associated with an increased rate of serious adverse events. Novel agents, such as bardoxolone methyl, pentoxifylline, inhibitors of protein kinase C (PKC), sulodexide, pirfenidone, endothelin receptor antagonists, vitamin D supplements, and phosphate binders have been associated with controversial outcomes or significant side effects. Although new insights into the pathogenetic mechanisms have opened new horizons towards novel interventions, there is still a long way to go in the field of DN research. The aim of this review is to highlight the recent progress made in the field of diabetes management based on the existing evidence. The article also discusses novel targets of therapy, with a special focus on the major pathophysiologic mechanisms implicated in the initiation and progression of diabetic nephropathy.

Effect of PKC-β Signaling Pathway on Expression of MCP-1 and VCAM-1 in Different Cell Models in Response to Advanced Glycation End Products (AGEs)

Advanced glycation end products (AGEs) are compounds classified as uremic toxins in patients with chronic kidney disease that have several pro-inflammatory effects and are implicated in the development of cardiovascular diseases. To explore the mechanisms of AGEs–endothelium interactions through the receptor for AGEs (RAGE) in the PKC-β pathway, we evaluated the production of MCP-1 and VCAM-1 in human endothelial cells (HUVECs), monocytes, and a coculture of both. AGEs were prepared by albumin glycation and characterized by absorbance and electrophoresis. The effect of AGEs on cell viability was assessed with an MTT assay. The cells were also treated with AGEs with and without a PKC-β inhibitor. MCP-1 and VCAM-1 in the cell supernatants were estimated by ELISA, and RAGE was evaluated by immunocytochemistry. AGEs exposure did not affect cell viability, but AGEs induced RAGE, MCP-1, and VCAM-1 expression in HUVECs. When HUVECs or monocytes were incubated with AGEs and a PKC-β inhibitor, MCP-1 and VCAM-1 expression significantly decreased. However, in the coculture, exposure to AGEs and a PKC-β inhibitor produced no significant effect. This study demonstrates, in vitro, the regulatory mechanisms involved in MCP-1 production in three cellular models and VCAM-1 production in HUVECs, and thus mimics the endothelial dysfunction caused by AGEs in early atherosclerosis. Such mechanisms could serve as therapeutic targets to reduce the harmful effects of AGEs in patients with chronic kidney disease.

The low AGE diet: a neglected aspect of clinical nephrology practice?

Increasing evidence in the literature suggests an important role for advanced glycation end products (AGEs) in the generation of a state of increased oxidative stress and chronic subclinical inflammation, which underlies most modern chronic diseases, including diabetes, cardiovascular disease and chronic kidney disease (CKD). Although AGEs were originally thought to form only endogenously, primarily as the result of the hyperglycemia of diabetes, it is now clear that exogenous AGEs, specially incorporated in foods, are an important contributor to the body pool of AGEs. Over the past decade, several clinical trials have been performed in a variety of conditions demonstrating that the application of an AGE-restricted diet reduces not only the systemic levels of AGEs but also the levels of markers of oxidative stress and inflammation. This has been shown in CKD patients before and after the initiation of dialysis and either in the presence or absence of coexistent diabetes. Reduction of the AGE content in food is obtained by simple changes in culinary techniques and appears to be a feasible, easily applicable and safe intervention, even in advanced CKD patients.