Repurposing alagebrium for diabetic foot ulcer healing: Impact on AGEs/NFκB/NOX1 signaling

BACKGROUND

Diabetic foot ulcer (DFU) is a common diabetic complication associated with disability and reduced quality of life. Available therapeutics are not sufficient to combat the spread of DFU. Here we aim to investigate the impact of alagebrium, an advanced glycation end product (AGE)-crosslink breaker, on the healing of DFU.

METHODS

Diabetes was induced in Wistar rats by STZ, and after four weeks, wound was induced on the foot. Alagebrium (10 mg/kg) was administered orally for 14 days, and wound size was measured every 3 days. Behavioral tests i.e., hot plate and footprint tests, were performed to assess sensory function and gait. Blood was collected to assess HbA1c, serum AGEs, MDA and NOX1. Tissue was collected to assess histological changes and expression of NF-κB, iNOS, TNF-α, VEGF and EGF. In a subsequent set of experiments with similar design, alagebrium was applied topically as a film-forming gel.

RESULTS

Systemic alagebrium treatment accelerated the healing of diabetic wound, improved sensory functions and gait, and ameliorated histological changes. It also reduced serum levels of AGEs, MDA and NOX1, and the tissue expression of NF-κB, iNOS, TNF-α, and increased VEGF and EGF in diabetic rats. Topical alagebrium led to similar beneficial effects i.e., accelerated diabetic wound healing, improved wound histological changes, reduced expression of NF-κB and iNOS and increased VEGF.

CONCLUSIONS

Our findings suggest repurposing of alagebrium for the management of DFU to accelerate the healing process and improve the clinical outcomes in diabetic patients.

RAGE signaling regulates the progression of diabetic complications

Diabetes, the ninth leading cause of death globally, is expected to affect 642 million people by 2040. With the advancement of an aging society, the number of patients with diabetes having multiple underlying diseases, such as hypertension, obesity, and chronic inflammation, is increasing. Thus, the concept of diabetic kidney disease (DKD) has been accepted worldwide, and comprehensive treatment of patients with diabetes is required. Receptor for advanced glycation endproducts (RAGE), a multiligand receptor, belonging to the immunoglobulin superfamily is extensively expressed throughout the body. Various types of ligands, including advanced glycation endproducts (AGEs), high mobility group box 1, S100/calgranulins, and nucleic acids, bind to RAGE, and then induces signal transduction to amplify the inflammatory response and promote migration, invasion, and proliferation of cells. Furthermore, the expression level of RAGE is upregulated in patients with diabetes, hypertension, obesity, and chronic inflammation, suggesting that activation of RAGE is a common denominator in the context of DKD. Considering that ligand–and RAGE–targeting compounds have been developed, RAGE and its ligands can be potent therapeutic targets for inhibiting the progression of DKD and its complications. Here, we aimed to review recent literature on various signaling pathways mediated by RAGE in the pathogenesis of diabetic complications. Our findings highlight the possibility of using RAGE–or ligand–targeted therapy for treating DKD and its complications.

Polysulfide-mediated sulfhydration of SIRT1 prevents diabetic nephropathy by suppressing phosphorylation and acetylation of p65 NF-κB and STAT3

Diabetic kidney disease is known as a major cause of chronic kidney disease and end stage renal disease. Polysulfides, a class of chemical agents with a chain of sulfur atoms, are found to confer renal protective effects in acute kidney injury. However, whether a polysulfide donor, sodium tetrasulfide (Na₂S₄), confers protective effects against diabetic nephropathy remains unclear. Our results showed that Na₂S₄ treatment ameliorated renal dysfunctional and histological damage in diabetic kidneys through inhibiting the overproduction of inflammation cytokine and reactive oxygen species (ROS), as well as attenuating renal fibrosis and renal cell apoptosis. Additionally, the upregulated phosphorylation and acetylation levels of p65 nuclear factor κB (p65 NF-κB) and signal transducer and activator of transcription 3 (STAT3) in diabetic nephropathy were abrogated by Na₂S₄ in a sirtuin-1 (SIRT1)-dependent manner. In renal tubular epithelial cells, Na₂S₄ directly sulfhydrated SIRT1 at two conserved CXXC domains (Cys371/374; Cys395/398), then induced dephosphorylation and deacetylation of its targeted proteins including p65 NF-κB and STAT3, thereby reducing high glucose (HG)-caused oxidative stress, cell apoptosis, inflammation response and epithelial-to-mesenchymal transition (EMT) progression. Most importantly, inactivation of SIRT1 by a specific inhibitor EX-527, small interfering RNA (siRNA), a de-sulfhydration reagent dithiothreitol (DTT), or mutation of Cys371/374 and Cys395/398 sites at SIRT1 abolished the protective effects of Na₂S₄ on diabetic kidney insulting. These results reveal that polysulfides may attenuate diabetic renal lesions via inactivation of p65 NF-κB and STAT3 phosphorylation/acetylation through sulfhydrating SIRT1.

Alagebrium Mitigates Metabolic Insults in High Carbohydrate and High Fat Diet Fed Wistar Rats

Background: Metabolic syndrome (MS) is characterized by sustained hyperglycemia that triggers advanced glycation end products (AGEs) generation. Alagebrium (ALA) is an advanced glycation end products (AGEs) cross-links breaker.Methods: 32 Wistar rats were divided into normal control (NC) group (8 rats) and MS groups (24 rats) received a high carbohydrate high fat diet (HCFD) for 10 weeks. Rats with established MS were equally divided into 3 subgroups remained on HCFD for further 6 weeks: MS control (MSC), ALA treated received 10 mg/kg/day ALA orally and metformin treated (MF) (a reference drug) received 50 mg/kg/day MF orally. The studied parameters were systolic blood pressure (SBP), body and liver weights (BW, LW), LW/BW% ratio, fasting blood glucose (FBG), serum insulin, lipid profile, liver enzymes, serum AGEs, hepatic Interleukin-17 (IL-17), adipokines, pAkt/Akt ratio, and liver histopathology.Results: HCFD elevated SBP, BW, LW and LW/BW% ratio, FBG, serum insulin, and AGEs. It also deteriorated lipid profile and liver enzymes, induced inflammation, insulin resistance and histopathological derangements. ALA ameliorated the elevated SBP, FBG, lipid profile, liver enzymes, mitigated insulin resistance, hepatic IL-17, serum AGEs, modulated adipokines levels and improved liver histopathology. However, MF had better effects than ALA in all studied parameters except AGEs.Conclusion: ALA is protective against dietary-induced MS via ameliorating the inflammatory process and serum AGEs that implicated in MS pathogenesis, which makes it a promising new tool in MS treatment.

Salusin-β mediates tubular cell apoptosis in acute kidney injury: Involvement of the PKC/ROS signaling pathway

Salusin-β is abundantly expressed in many organs and tissues including heart, blood vessels, brain and kidneys. Recent studies have identified salusin-β as a bioactive peptide that contributes to various diseases, such as atherosclerosis, hypertension, diabetes and metabolic syndrome. However, the role of salusin-β in the pathogenesis of acute kidney injury (AKI) is largely unclear. In the present study, we investigated the roles of salusin-β in cisplatin or lipopolysaccharide (LPS)-induced renal injury. Herein, we found that salusin-β expression was upregulated in both renal tubular cells and kidney tissues induced by both cisplatin and LPS. In vitro, silencing of salusin-β diminished, whereas overexpression of salusin-β exaggerated the increased PKC phosphorylation, oxidative stress, histone γH2AX expression, p53 activation and apoptosis in either cisplatin or LPS-challenged renal tubular cells. More importantly, salusin-β overexpression-induced tubular cell apoptosis were abolished by using the PKC inhibitor Go 6976, reactive oxygen species (ROS) scavenger NAC, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin (Apo) or p53 inhibitor Pifithrin-α. In animals, blockade of salusin-β alleviated PKC phosphorylation, ROS accumulation, DNA damage, and p53 activation as well as renal dysfunction in mice after administration of cisplatin or LPS. Taken together, these results suggest that overexpressed salusin-β is deleterious in AKI by activation of the PKC/ROS signaling pathway, thereby priming renal tubular cells for apoptosis and death.

Alagebrium and Complications of Diabetes Mellitus

Glycation is the process of linking a sugar and free amino groups of proteins. Cross-linking of glycation products to proteins results in the formation of cross-linked proteins that inhibit the normal functioning of the cell. Advanced glycation end products (AGEs) are risk molecules for the cell aging process. These ends products are increasingly synthesized in diabetes and are essentially responsible for diabetic complications. They accumulate in the extracellular matrix and bind to receptors (receptor of AGE [RAGE]) to generate oxidative stress and inflammation. particularly in the cardiovascular system. Treatment methods targeting the AGE system may be of clinical importance in reducing and preventing the complications induced by AGEs in diabetes and old age. The AGE cross-link breaker alagebrium (a thiazolium derivative) is the most studied anti-AGE compound in the clinical field. Phase III clinical studies with alagebrium have been successfully conducted, and this molecule has positive effects on cardiovascular hypertrophy, diabetes, hypertension, vascular sclerotic pathologies, and similar processes. However, the mechanism is still not fully understood. The primary mechanism is that alagebrium removes newly formed AGEs by chemically separating α-dicarbonyl carbon-carbon bonds formed in cross-linked structures. However, it is also reported that alagebrium is a methylglyoxal effective inhibitor. It is not yet clear whether alagebrium inhibits copper-catalyzed ascorbic acid oxidation through metal chelation or destruction of the AGEs. It is not known whether alagebrium has a direct association with RAGEs. The safety profile is favorably in humans, and studies have been terminated due to financial insufficiency and inability to license as a drug.

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

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

Mitofusin 2 attenuates the histone acetylation at collagen IV promoter in diabetic nephropathy

Extracellular matrix (ECM) increase in diabetic nephropathy (DN) is closely related to mitochondrial dysfunction. The mechanism of protective function of mitofusin 2 (Mfn2) for mitochondria remains largely unknown. In this study, the molecular mechanisms for the effect of Mfn2 on mitochondria and subsequent collagen IV expression in DN were investigated. Ras-binding-deficient mitofusin 2 (Mfn2-Ras(Δ)) were overexpressed in rat glomerular mesangial cells, and then the cells were detected for mitochondrial morphology, cellular reactive oxygen species (ROS), mRNA and protein expression of collagen IV with advanced glycation end-product (AGE) stimulation. Preliminary results reveal that the mitochondrial dysfunction and the increased synthesis of collagen IV after AGE stimulation were reverted by Mfn2-Ras(Δ) overexpression. Bioinformatical computations were performed to search transcriptional factor motifs in the promoter region of collagen IV. Three specific regions for TFAP2A binding were identified, followed by validation with chromatin immunoprecipitation experiments. Knocking down TFAP2A significantly decreased the TF binding in the first two regions and the gene expression of collagen IV. Furthermore, results reveal that Mfn2-Ras(Δ) overexpression significantly mitigated TFAP2A binding and also reverted the histone acetylation at Regions 1 and 2 after AGE stimulation. In streptozotocin-induced diabetic rats, Mfn2-Ras(Δ) overexpression also ameliorated glomerular mesangial lesions with decreased collagen IV expression, accompanied by decreased acetylation and TFAP2A binding at Region 1. In conclusion, this study highlights the pathway by which mitochondria affect the histone acetylation of gene promoter and provides a new potential therapy approach for DN.

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.

Novel Therapies for Diabetic Kidney Disease: Storied Past and Forward Paths

IN BRIEF Current therapeutic approaches are only moderately efficacious at preventing the progression of diabetic kidney disease (DKD). As the number of people with DKD continues to rise worldwide, there is an urgent need for novel therapies. A better understanding of the root causes and molecular mechanisms of DKD pathogenesis has enabled the identification of numerous new therapeutic targets, including advanced glycation end products, reactive oxygen species, protein kinase C, and serum amyloid A. Although experimental studies have illustrated the potential of such approaches, challenges in clinical translation remain a barrier in therapeutic development. Advances in preclinical safety and efficacy evaluations and improved delivery systems may aid in clinical translation of novel DKD therapies.

Augmented renal prostacyclin by intrarenal bicistronic cyclo-oxygenase-1/prostacyclin synthase gene transfer attenuates renal ischemia-reperfusion injury

BACKGROUND

We elucidated the protective mechanism of increased prostacyclin (PGI2) derived from adenoviral cyclo-oxygenase (COX)-1/prostacyclin synthase (PGIS) (Adv-COPI) gene transfer in rat kidneys with ischemia-reperfusion (I/R) injury.

METHODS

We tended to augment PGI2 production by intrarenal arterial Adv-COPI administration with renal venous clamping in female Wistar rats. After Adv-COPI transfection, we evaluated the renal COX-1 and PGIS protein expression and PGI2 and prostaglandin E2 (PGE2) levels in the kidney and renal venous plasma. We evaluated the protective effect of PGI2 on hypoxia/reoxygenation-induced tubular cells injury or I/R kidneys by measuring oxidative stress, necrosis, apoptosis, and autophagy in tubules and kidneys and determining renal function, microcirculation, and accumulation of tubular 4-hydroxynonenal in the kidney in vivo.

RESULTS

Adv-COPI treatment selectively augmented COX-1 and PGIS protein expression in the renal proximal and distal tubules and significantly increased PGI2, not PGE2, production in the renal venous plasma and kidney at the baseline level. I/R markedly depressed renal blood flow and increased the production in O2, PGE2, the expression in P47 and Rac-1 expression of two nicotinamide adenine dinucleotide phosphate oxidase subunits, cytosolic cytochrome C release, proapoptotic marker lamin expression, the pathologic appearance of necrosis, apoptosis, and autophagy, and blood urea nitrogen and creatinine levels in the damaged kidneys. Adv-COPI protected distal and proximal tubules against hypoxia/reoxygenation-enhanced oxidative stress and autophagic, apoptotic, and necrotic cell death. Adv-COPI significantly improved renal function by restoring renal blood flow, reducing nicotinamide adenine dinucleotide phosphate oxidase-derived and mitochondria-derived oxidative stress, and necrosis, apoptosis, and autophagy.

CONCLUSIONS

Increased PGI2 by Adv-COPI protects the kidney against I/R-induced oxidative stress, necrosis, apoptosis and autophagy.

Potential clinical utility of advanced glycation end product cross-link breakers in age- and diabetes-associated disorders

Reducing sugars can react nonenzymatically with the amino groups of proteins to form Amadori products. These early glycation products undergo further complex reactions, such as rearrangement, dehydration, and condensation, to become irreversibly cross-linked, heterogeneous fluorescent derivatives, termed advanced glycation end products (AGEs). The formation and accumulation of AGEs have been known to progress in a normal aging process and at an accelerated rate under diabetes. Nonenzymatic glycation and cross-linking of proteins not only leads to an increase in vascular and myocardial stiffness, but also deteriorates structural integrity and physiological function of multiple organ systems. Furthermore, there is accumulating evidence that interaction of AGEs with a cell-surface receptor, receptor for AGEs (RAGE), elicits oxidative stress generation and subsequently evokes inflammatory, thrombogenic, and fibrotic reactions, thereby being involved in atherosclerosis, diabetic microvascular complications, erectile dysfunction, and pancreatic β-cell apoptosis. Recently, AGE cross-link breakers have been discovered. Therefore, removal of the preexisting AGEs by the breakers has emerged as a novel therapeutic approach to various types of diseases that develop with aging. This article summarizes the potential clinical utility of AGE cross-link breakers in the prevention and management of age- and diabetes-associated disorders.

Aldolase B knockdown prevents high glucose-induced methylglyoxal overproduction and cellular dysfunction in endothelial cells

We used cultured endothelial cells as a model to examine whether up-regulation of aldolase B and enhanced methylglyoxal (MG) formation play an important role in high glucose-induced overproduction of advanced glycosylation endproducts (AGEs), oxidative stress and cellular dysfunction. High glucose (25 mM) incubation up-regulated mRNA levels of aldose reductase (an enzyme converting glucose to fructose) and aldolase B (a key enzyme that catalyzes MG formation from fructose) and enhanced MG formation in human umbilical vein endothelial cells (HUVECs) and HUVEC-derived EA. hy926 cells. High glucose-increased MG production in EA. hy926 cells was completely prevented by siRNA knockdown of aldolase B, but unaffected by siRNA knockdown of aldolase A, an enzyme responsible for MG formation during glycolysis. In addition, inhibition of cytochrome P450 2E1 or semicarbazide-sensitive amine oxidase which produces MG during the metabolism of lipid and proteins, respectively, did not alter MG production. Both high glucose (25 mM) and MG (30, 100 µM) increased the formation of N(ε)-carboxyethyl-lysine (CEL, a MG-induced AGE), oxidative stress (determined by the generation of oxidized DCF, H₂O₂, protein carbonyls and 8-oxo-dG), O-GlcNAc modification (product of the hexosamine pathway), membrane protein kinase C activity and nuclear translocation of NF-κB in EA. hy926 cells. However, the above metabolic and signaling alterations induced by high glucose were completely prevented by knockdown of aldolase B and partially by application of aminoguanidine (a MG scavenger) or alagebrium (an AGEs breaker). In conclusion, efficient inhibition of aldolase B can prevent high glucose-induced overproduction of MG and related cellular dysfunction in endothelial cells.

Catalase deficiency accelerates diabetic renal injury through peroxisomal dysfunction

Mitochondrial reactive oxygen species (ROS) play an important role in diabetes complications, including diabetic nephropathy (DN). Plasma free fatty acids (FFAs) as well as glucose are increased in diabetes, and peroxisomes and mitochondria participate in FFA oxidation in an interconnected fashion. Therefore, we investigated whether deficiency of catalase, a major peroxisomal antioxidant, accelerates DN through peroxisomal dysfunction and abnormal renal FFA metabolism. Diabetes was induced by multiple injections of low-dose streptozotocin into catalase knock-out (CKO) and wild-type (WT) C57BL/6 mice. Murine mesangial cells (MMCs) transfected with catalase small interfering RNA followed by catalase overexpression were used to further elucidate the role of endogenous catalase. Despite equivalent hyperglycemia, parameters of DN, along with markers of oxidative stress, were more accelerated in diabetic CKO mice than in diabetic WT mice up to 10 weeks of diabetes. CKO mice and MMCs showed impaired peroxisomal/mitochondrial biogenesis and FFA oxidation. Catalase deficiency increased mitochondrial ROS and fibronectin expression in response to FFAs, which were effectively restored by catalase overexpression or N-acetylcysteine. These data provide unprecedented evidence that FFA-induced peroxisomal dysfunction exacerbates DN and that endogenous catalase plays an important role in protecting the kidney from diabetic stress through maintaining peroxisomal and mitochondrial fitness.