Advanced glycation end products stimulate angiotensinogen production in renal proximal tubular cells.
Impact Factor: 1.911
Level of Evidence: III
Sample Size/Population: 11 mice (6 controls, 5 streptozotocin-induced DM mice)
Introduction: The augmentation of angiotensinogen (AGT) in proximal tubular cells (PTC) plays a role in the development of diabetic nephropathy. This study investigated the hypothesis that AGE stimulates AGT production in PTC.
Protocol: Rat PTC was treated with 0-200 μg/ml AGE-BSA for 24 hours and cultured before AGT expression and secretion were evaluated. An ELISA assay was used to measure urinary AGT and AGE levels in streptozotocin-induced diabetes mellitus (DM) mice. qRT-PCR was used to evaluate AGT mRNA expression. Western blot analysis evaluated AGT levels, phosphorylation levels of p47phox, and activities of signal transducers and transcription factors. The expression of RAGE protein in PTC was confirmed by immunostaining.
Statistical analysis: Data was expressed as means ± standard error. Student t-test, 1-way ANOVA, post hoc Bonferroni/Dunn multiple comparison test. P <0.05 was considered statistically significant.
Type of Study: Mouse study.
Limitations: The sample size was relatively small at 11 mice in total.
Results: DM mice showed greeted urinary AGT and AGE levels compared to control mice. In cultured PCT, treatment with AGE-BSA enhanced AGT mRNA expression, intracellular AGT protein levels, and secreted AGT levels. AGT levels were not altered in PTC receiving nonglycated BSA. Recombinant soluble AGE receptor, which competes with endogenous AGE receptor, diminished the AGE-induced AGT upregulation, suggesting that AGE-BSA stimulates AGT expression via activation of the AGE receptor. Enhanced phosphorylation of ERK ½ and c-JUN, were observed in AGE-BSA treated PTC. AGE-induced AGT augmentation was attenuated by an ERK inhibitor.
Discussion/Conclusions: AGE was found to enhance proximal tubular AGT expression via ERK ½ , which can exacerbate the development of diabetic related kidney injury. These findings provide a rationale for targeting AGE/RAGE pathway axis to suppress intrarenal RAS activity and prevent or treat kidney injury in DM.
Garagliano JM, Katsurada A, Miyata K, Derbenev AV, Zsombok A, Navar LG, Satou R. Advanced Glycation End Products Stimulate Angiotensinogen Production in Renal Proximal Tubular Cells. Am J Med Sci. 2019 Jan;357(1):57-66. doi: 10.1016/j.amjms.2018.10.008. Epub 2018 Oct 24. PMID: 30466736; PMCID: PMC6778966.
Restricted intake of dietary advanced glycation end products retards renal progression in the remnant kidney model.
Impact Factor: 8.945
Level of Evidence: VII
Sample Size/Population: 90 rats with ⅚ nephrectomy (⅔ removal of left kidney) divided into 3 groups of 30 rats each (standard rat diet, low AGE diet (LAD), and high AGE diet (HAD)), 30 control rats (sham surgery); Each of the 4 groups of 30 was further divided into groups of 10 rats which were harvested at 5, 9, or 13 weeks.
Protocol: ELISA and fluorospectrometry to measure concentration of AGEs in all specimens, histochemistry to determine extent of glomerular sclerosis, immunohistochemistry and RT-PCR to determine macrophage, TGF-β (involved in fibrosis) and MCP-1 (proinflammatory chemokine) levels and distribution in kidney tissue.
Statistical Analysis: A one-way ANOVA followed by Least Significant Difference method, independent sample t-test, Pearson correlation analysis, significance defined as P≤0.05.
Study type: Rat study.
Results: Serum AGE levels were significantly higher in rats with ⅚ nephrectomy compared to controls who had sham surgery. Rats in the HAD group had higher serum AGE levels than rats in the standard diet group, and rats in the LAD group had lower serum AGE levels than the standard diet group. The HAD group had increased weight of the remnant kidney and increased glomerular volume. The HAD group showed an increased glomerulosclerosis index and interstitial fibrosis score, while the LAD group had improved glomerulosclerosis and interstitial fibrosis. They found a close correlation between serum AGE levels and macrophages in glomeruli and interstitium of the kidneys. LAD rats had slowed renal dysfunction and decreased proteinuria, as well as decreased levels of MCP-1 and TGF-β in tubular cells and glomeruli. HAD rats had higher levels of renal oxidation reactions.
Discussion/Conclusion: In the setting of renal insufficiency, the consumption of AGEs by rats was associated with accelerated progression of renal damage, whereas a reduction of dietary AGE consumption slowed this progression. The increase in AGEs in the kidneys of HAD rats suggests that dietary AGE intake is an important contributor to the AGE burden particularly when there is impaired excretion of AGEs. The finding of less tubulointerstitial fibrosis in LAD rats may explain the more preserved glomerular filtration rate. This model showed that intrarenal oxidative stress and proinflammatory reactions can be largely inhibited by restricting dietary AGE consumption, potentially preventing the proposed positive feedback loop between AGE formation and oxidative stress.
Feng JX, Hou FF, Liang M, Wang GB, Zhang X, Li HY, Xie D, Tian JW, Liu ZQ. Restricted intake of dietary advanced glycation end products retards renal progression in the remnant kidney model. Kidney Int. 2007 May;71(9):901-11. doi: 10.1038/sj.ki.5002162. PMID: 17342181.
Advanced glycation end-products: implications for diabetic and non-diabetic nephropathies.
Impact Factor: 4.731
Level of Evidence: I
Introduction: This review is an update of recent advances of diabetic nephropathy (DN), non-diabetic renal disease and renal aging.
Sample Size: N/A
Study Type: Review article
Summary: Chronic hyperglycemia promotes the formation of modified molecular species such as AGEs, which forms through glycation, the polyol pathway, and glycoxidation. AGEs are found in many renal structures, including atheromatous plaques within arteries. Their concentration in plaques correlates with the degree of atherosclerosis, seen even higher in diabetic patients with renal failure. Aside from DN, renal disorders including chronic renal failure, chronic inflammatory disease, high dietary AGE, and aging involve AGEs.
Further, AGE deposition is found in aterionephrosclerosis, IgA nephropathy, lupus nephritis, uraemia and the experimental murine model of focal sclerosis mediated by adriamycin. Still, it is uncertain to what extent kidney AGE accumulation is a cause or consequence of kidney disease, and AGEs could exert effects through a vicious cycle. Regarding renal ageing, it can be promoted through AGE accumulation, in situ glycation and RAGE activation. In terms of treatment, diet may play a key role in the prevention of AGE-linked pathologies. At this point, AGE inhibitors have been targeted for therapy including, aminoguanidine, 2-isopropylidenehydrazono-4-oxo-thiazolidin-5-ylacetalinide (OPB-9195), LR-90, LR-9, LR-74, pyridoxamine, and benfotiamine, with the most promising being the ‘LR’ inhibitors, pyridoxamine, and benfotiamine. Alagebrium (ALT-711), an AGE cross-link breaker, has also been studied for its role in limiting tissue AGE accumulation and reduction of AGE deleterious effects. ACE inhibitors, ARBs, statins, and some oral antidiabetics and antioxidative molecules are current treatments used for their ‘anti-AGE’ properties. The most promising therapies currently used for basic research include sRAGE and anti-RAGE antibody.
Daroux M, Prévost G, Maillard-Lefebvre H, Gaxatte C, D'Agati VD, Schmidt AM, Boulanger E. Advanced glycation end-products: implications for diabetic and non-diabetic nephropathies. Diabetes Metab. 2010 Feb;36(1):1-10. doi: 10.1016/j.diabet.2009.06.005. Epub 2009 Nov 22. PMID: 19932633.
The modern western diet rich in Advanced Glycation End-Products (AGEs): An overview of its impact on obesity and early progression of renal pathology.
Impact Factor: 4.546
Level of Evidence: II
Sample Size: N/A
Study Type: Review article
Statistical analysis: N/A
Results: AGE-induced kidney damage is a result of multiple interconnected factors which can lead to fibrotic damage in the ECM and sub-ECM components in the kidney. AGE’s are capable of increasing expression of monocyte chemoattractant protein-1 (MCP-1), particularly in the mesangial cells of the vascular region of the renal corpuscle. MCP-1 will recruit monocytes and macrophages which can lead to fibrotic changes in the kidney. Additionally, AGE’s can lead to TGF-b secretion through activation of RAGE which can lead to further fibrotic changes. As collagen is laid down in the ECM and sub-ECM, AGE is able to interact with type IV collagen to create proteoglycans which can increase permeability of the glomerulus, thus leading to the development of proteinuria and kidney disease.
As a part of the pro-inflammatory effects of AGE’s, the NF-KB pathway is upregulated which can lead to Zinc finger E-box binding homeobox 2 (ZEB2) gene upregulation in the kidney tissue. ZEB2 is known to decrease E-cadherin, P-cadherin, and nephrin expression in renal podocytes which can reduce podocyte count and damage the glomerulus.
Discussion: AGE’s lead to chronic inflammation in the kidney which can accelerate fibrotic processes and podocyte degeneration leading to chronic kidney disease. Additionally, AGE’s can play a role in the development of obesity, which can further chronic inflammation and impact renal health through separate pathways.
Bettiga A, Fiorio F, Di Marco F, Trevisani F, Romani A, Porrini E, Salonia A, Montorsi F, Vago R. The Modern Western Diet Rich in Advanced Glycation End-Products (AGEs): An Overview of Its Impact on Obesity and Early Progression of Renal Pathology. Nutrients. 2019 Jul 30;11(8):1748. doi: 10.3390/nu11081748. PMID: 31366015; PMCID: PMC6724323.
Uremic toxicity of advanced glycation end products in CKD.
Impact Factor: 9.274
Level of Evidence: V
Sample Size: N/A
Study Type: Review article
Statistical Analysis: N/A
Results: AGEs have been shown to accumulate as a result of inflammation, oxidative stress, and diet, and are themselves proinflammatory and pro-oxidative compounds. The accumulation of AGEs is involved in the cardiovascular complications seen in patients with Chronic Kidney Disease (CKD) through their contribution to endothelial dysfunction, arterial stiffness, myocardial changes, immune system dysregulation, and atherosclerosis. AGEs have also been shown to increase inflammation in patients with CKD by activating the NF-kB pathway which produces inflammatory cytokines. There are many potential strategies for therapeutic interventions to counteract the effects of AGEs, which include decreasing dietary intake, inhibiting gastrointestinal absorption, dialysis, kidney transplantation, agents that can break down AGEs, RAGE inhibitors, among others.
Discussion/Conclusion: AGEs can be high in chronic diseases with elevated levels of oxidative stress, such as CKD. Additional studies are needed to determine the role of AGEs in vascular function and the immune system in patients CKD, as well as what therapeutics could be used to decrease their detrimental effects.
Stinghen AE, Massy ZA, Vlassara H, Striker GE, Boullier A. Uremic Toxicity of Advanced Glycation End Products in CKD. J Am Soc Nephrol. 2016 Feb;27(2):354-70. doi: 10.1681/ASN.2014101047. Epub 2015 Aug 26. PMID: 26311460; PMCID: PMC4731113.
Knockout of receptor for advanced glycation end-products attenuates age-related renal lesions.
Impact factor: 7.238
Level of evidence: VII
Sample size: n=3 for 3 month old mice, n=10 for 20 month old mice.
Protocol: They used histologic markers of aging (immunohistochemistry followed by HPLC/MS) in wild-type (WT) mice and RAGE knockout mice (RAGE-/-) over 18 months, on a diet rich in AGEs (CML) and a control diet; RT-qPCR and Western blot to measure gene/protein expression associated with kidney injury
Statistical Analysis: Kruskal-Wallis test followed by a Dunn’s multiple comparison test for multiple comparisons, two-tailed T-Test for samples with n=10, Mann-Whitney test for smaller samples (for both: P<0.05 was considered significant).
Study Type: In vivo using a mouse model.
Results: Accumulation of AGEs (CML) in proximal tubular cells and along renal arteries was found in both WT and RAGE-/- mice fed the CML-enriched diet. RAGE-/- mice fed the control diet were found to have significantly less endothelial dysfunction, tubular atrophy, interstitial fibrosis, and amyloidosis-linked glomerulosclerosis than WT mice fed the control diet. Certain inflammatory and oxidation markers increased less as RAGE-/- mice aged compared to WT.
Discussion/Conclusion: This study demonstrates that the RAGE receptor may play a role in the aging of kidney cells, however AGE-enriched diet was not found to have a significant effect on AGE accumulation and renal injury, and AGE accumulation seemed to be RAGE-independent. It is important to note that the sample sizes used in this study are small, which may have exaggerated the significance of the differences between groups. Also, some of the histologic data was not quantified, it is presented in percentages as assessed by an anatomopathologist and nephrologist.
Teissier T, Quersin V, Gnemmi V, Daroux M, Howsam M, Delguste F, Lemoine C, Fradin C, Schmidt AM, Cauffiez C, Brousseau T, Glowacki F, Tessier FJ, Boulanger E, Frimat M. Knockout of receptor for advanced glycation end-products attenuates age-related renal lesions. Aging Cell. 2019 Apr;18(2):e12850. doi: 10.1111/acel.12850. Epub 2019 Feb 22. PMID: 30794349; PMCID: PMC6413655.
Advanced glycation end products (AGE) and receptor for AGE (RAGE) in patients with active tuberculosis, and their relationship between food intake and nutritional status.
Impact Factor: 3.673
Sample Size/Population: 35 tuberculosis (TB) patients and 35 controls. Patients and controls were individually matched for sex and age in a 1:1 matching ratio.
Protocol: TB patients selected from the hospital and members of the control group (healthy volunteers selected from the TB patients family to account for same daily exposures) were interviewed using a standardized questionnaire. Subjects then completed a series of diagnostic tests including: blood samples to test CML and sRAGE levels, chest x-rays evaluated by an independent physician for evidence of active TB, and a nutritional assessment. The outcome of hospitalization (discharge or death) was also recorded.
Statistical Analysis: Shapiro-Wilk test for normality, chi-square test for categorical comparisons, paired t-test or Wilcoxon test for continuous variables, Pearson’s correlations used to evaluate potential relationships. Considering a confidence level of 95% and a power of 80%, sample size was calculated based on the expected difference of sRAGE levels between survivors and non-survivors and estimated to be a sample of 30 individuals per group.
Study Type: Case-Control Study.
Results: The most common symptoms TB patients experienced according to the questionnaire were weight loss (94.3%), cough (88.6%), night sweats (65.7%), and fever (62.9%). Within the TB patient sample group: 40.0% were HIV positive, 80.0% were sputum smear TB positive, and 80.0% had a positive Mycobacterium tuberculosis complex culture. White race was more common in the control group as 82.9% of the control group were of white race, and 54.3% of the TB patients were of white race. 74.3% of TB the patients had a typical chest x-ray, and 80% of the sample group were survivors.
The mean sRAGE levels were higher in TB patients than the controls (68.5 ± 28.1 pg/mL vs 57.5 ± 24.0 pg/mL, p = 0.046). BMI was significantly lower in TB patients than in controls (p<0.0001). Malnutrition measured by MUAC, MAMC, and TSF were each more frequent in TB patients than in controls. There was no statistically significant difference in CML levels and diet CML content between TB patients and controls. There was no statistical significance between serum CML levels and diet CML levels, or between BMI and CML levels, or between BMI and sRAGE levels. Malnutrition measured by MUAC, MAMC, and TSF were also not correlated with CML or sRAGE levels. There was also no statistical significance between CML in diet content between TB patients and controls. No statistical difference was found in serum CML levels, diet CML content, or sRAGE levels between survivors and non-survivors. Among the individuals that were current smokers, lower levels of sRAGE were statistically associated with mortality (sRAGE levels [mean ± SD] = 58.0 ± 36.5 pg/mL [non-survivors] vs 71.3 ± 25.6 pg/mL [survivors], p = 0.006; odds ratio 1.053 [CI95% 1.006–1.103]). Lower sRAGE levels were associated with weight loss in TB patients (sRAGE levels [mean ± SD] = 65.6 ± 27.4 pg/mL [weight loss] vs 98.6 ± 16.7 pg/mL [no weight loss], p = 0.034).
Conclusion: The study found that sRAGE levels were higher in TB patients than in controls, however it is unclear if that difference is clinically relevant because sRAGE is a competitive inhibitor of RAGE. One possible hypothesis is that the enhanced RAGE expression and cellular damage that comes with disease increases sRAGE generation and release. In that instance sRAGE could be used to measure RAGE hyperactivity. There was no statistical evidence of a difference between TB patients and control CML levels. The authors suspect that this could be due to the fact that the sample size was limited and the fact that RAGE is capable of binding multiple ligands other than AGEs. Contrastingly, lower sRAGE levels were associated with weight loss and mortality among the individuals who were current smokers.
da Silva LF, Skupien EC, Lazzari TK, Holler SR, de Almeida EGC, Zampieri LR, Coutinho SE, Andrades M, Silva DR. Advanced glycation end products (AGE) and receptor for AGE (RAGE) in patients with active tuberculosis, and their relationship between food intake and nutritional status. PLoS One. 2019 Mar 14;14(3):e0213991. doi: 10.1371/journal.pone.0213991. PMID: 30870511; PMCID: PMC6417785.
Clinical studies of advanced glycation end product inhibitors and diabetic kidney disease.
Impact Factor: 3.686
Level of Evidence: II
Type of Study: Review article.
Results: The study discusses the clinical trial results of 3 AGE inhibitors. In a phase 3 clinical trial, Pimagedine (a competitive inhibitor of the AGE pathway) was not found to be more efficacious than placebo in reducing serum creatinine in patients with type I diabetes, but it did reduce urinary protein excretion and lipid levels. However, the study was suspended due to adverse events, particularly the development of crescentic glomerulonephritis in several participants. Pyridoxamine, a vitamin B6 derivative that has been shown to inhibit AGE formation in animal models, had promising results in a phase 2 trial and is awaiting a phase 3 trial. Its proposed mechanisms of AGE formation inhibition include carbonyl trapping and scavenging of metal ions in vivo, and it can inhibit the degradation of protein-Amadori products into AGEs. Alagebrium is a cross-link breaker, and thus an AGE inhibitor since AGEs mediate protein cross-linking. Current clinical trials with this drug are focused on its potential for reducing vascular stiffness caused by increased collagen cross-links, but it may also have effects on the increased collagen cross-links associated with diabetes and needs to be studied further. Another pharmacological target for reducing diabetic kidney disease is glycated albumin, which may be inhibited in a similar way to AGE inhibition.
Discussion/Conclusion: There are several AGE inhibitors currently in different stages of development and clinical trials. Further research is needed to find pharmacological agents that can reduce the impact of AGE formation on diabetic nephropathy and other pathology associated with AGEs.
Williams ME. Clinical studies of advanced glycation end product inhibitors and diabetic kidney disease. Curr Diab Rep. 2004 Dec;4(6):441-6. doi: 10.1007/s11892-004-0054-0. PMID: 15539009.
Endothelial dysfunction in patients with chronic kidney disease results from advanced glycation end products.
Impact Factor: 6.628
Level of Evidence: III
Sample Size: 51
Protocol: Cross-sectional study of ambulatory patients without diabetes and with different stages of CKD (compared with gender- and age-matched healthy subjects).
Statistical Analysis: The Kolmogorov-Smirnov goodness-of-fit test.
Type of Study: Cross-sectional study.
Results: There was a correlation between glomerular filtration rate and serum AGEs, mRNA receptor for AGE levels, postocclusive reactive hyperemia, and thermal hyperemia. Serum AGE product was correlated with the receptor for AGEs and was inversely correlated with postocclusive reactive hyperemia. Serums from chronic kidney disease that were rich with AGE were found to suppress endothelial nitric oxide synthase expression of human aortic endothelial cells when compared to serums of healthy subjects.
Discussion/Conclusion: Excess AGE product burden with increased peripheral blood mononuclear cell mRNA receptor for advanced glycation end product and in vivo endothelial dysfunction in patients with chronic kidney disease. Endothelial dysfunction in chronic kidney disease may be, in part, mediated by AGE product–induced inhibition of endothelial nitric oxide synthase through receptor for advanced glycation end product activation.
Linden E, Cai W, He JC, Xue C, Li Z, Winston J, Vlassara H, Uribarri J. Endothelial dysfunction in patients with chronic kidney disease results from advanced glycation end products (AGE)-mediated inhibition of endothelial nitric oxide synthase through RAGE activation. Clin J Am Soc Nephrol. 2008 May;3(3):691-8. doi: 10.2215/CJN.04291007. Epub 2008 Feb 6. PMID: 18256374; PMCID: PMC2386710.
Pathophysiology and therapeutics of premature ageing in chronic kidney disease, with a focus on glycative stress.
Impact Factor: 2.456
Level of Evidence: V
Study Type: Review article
Results: High levels of FGF23 and angiotensin II are frequently detected in CKD patients. These high levels can accelerate aging directly or through hyperphosphatemia and hypertension. Renal hypoxia, which can be induced by renal hypoxia, can increase glycative stress due to increased oxidative stress. Many factors are involved in premature ageing in CKD, including hormonal imbalance, glycative stress, nitrogenous metabolites, and oxidative stress. Of these, the most important role in premature ageing in CKD is played by glycative stress, namely a massive and unfavourable glycation state, since the kidney is responsible for the clearance of advanced glycation endproducts (AGEs).
Discussion/Conclusion: Factors such as FGF23, angiotensin II and indoxyl sulphate are often found at high levels in patients with CKD, which can accelerate premature aging in the patient. Interventions that target the glycative stress caused by these factors, such as enforcing overexpression of glyoxalase (GLO-1) can detoxify advanced glycation endproducts (AGEs) and can help alleviate premature aging in the kidneys. These strategies can only be carried out when there is a greater understanding of what is needed in the field. Clinical trials focused on the anti-aging effect of drugs can also lead to further research and studies in this field.
Hirakawa Y, Jao TM, Inagi R. Pathophysiology and therapeutics of premature ageing in chronic kidney disease, with a focus on glycative stress. Clin Exp Pharmacol Physiol. 2017 Dec;44 Suppl 1:70-77. doi: 10.1111/1440-1681.12777. Epub 2017 Sep 20. PMID: 28467603.