Glycation of Proteins and Its End Products: From Initiation to Natural Product-Based Therapeutic Preventions

Diabetes is a chronic metabolic disorder characterized by elevated blood glucose levels, which lead to the glycation of proteins and the formation of advanced glycation end products (AGEs). These AGEs contribute to oxidative stress, inflammation, and the development of complications such as cardiovascular disease, nephropathy, and anemia, significantly increasing mortality rates among diabetic patients. This Review focuses on the role of glycation inhibitors as a potential strategy to prevent AGE-related pathologies. While synthetic glycation inhibitors have shown promise, their adverse effects highlight the need for safer alternatives. We specifically explore a range of natural compounds-flavonoids, curcuminoids, terpenes, stilbenes, lignans, and coumarins-that have demonstrated significant antiglycating properties. The mechanisms through which these natural products inhibit glycation, including antioxidant activity, metal ion chelation, and direct interference with the glycation process, are discussed in detail. This review underscores the potential of natural products as effective and safer glycation inhibitors, offering a promising avenue for the development of therapeutic strategies against diabetes and AGE-related disorders.

Ellagic acid as potential therapeutic compound for diabetes and its complications: a systematic review from bench to bed

Diabetes mellitus (DM) is a worldwide-concerning disease with a rising prevalence. There are many ongoing studies aimed at finding new and effective treatments. Ellagic acid (EA) is a natural polyphenolic compound abundant in certain fruits and vegetables. It is the objective of this investigation to assess the effectiveness and preventive mechanisms of EA on DM and associated complications. This systematic review used PubMed, Scopus, and Google Scholar as search databases using a predetermined protocol from inception to June 2024. We assessed all related English studies, including in vitro, in vivo, and clinical trials. EA counteracted DM and its complications by diminishing inflammation, oxidative stress, hyperglycemia, apoptosis, insulin resistance, obesity, lipid profile, and histopathological alterations. Several mechanisms contributed to the anti-diabetic effect of EA, the most significant being the upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), peroxisome proliferator-activated receptor gamma (PPAR-γ), protein kinase B, and downregulation of nuclear factor-kappa-B (NF-κB) gene expression. EA also revealed protective effects against diabetes complications, such as diabetic-induced hepatic damage, testicular damage, endothelial dysfunction, muscle dysfunction, retinopathy, nephropathy, cardiomyopathy, neuropathy, and behavioral deficit. Administration of EA could have various protective effects in preventing, treating, and alleviating DM and its complications. Although it could be considered a cost-effective, safe, and accessible treatment, to fully establish the effectiveness of EA as a medication for DM, it is crucial to conduct further well-designed studies.

Effects of Ellagic Acid on Glucose and Lipid Metabolism: A Systematic Review and Meta-Analysis

Background

Abnormal glucose and lipid metabolism (GALM) serve as both a cause and an inducer for the development of the disease. Improvement and treatment of GALM are an important stage to prevent the occurrence and development of the disease. However, current clinical treatment for GALM is limited. Ellagic acid (EA), a common polyphenol present in foods, has been shown to improve abnormalities in GALM observed in patients suffering from metabolic diseases.

Objective

This study used a meta-analysis method to systematically assess the effects of EA on GALM.

Method

As of November 8, 2023, a comprehensive search was conducted across 5 databases, namely, PubMed, Embase, Web of Science, Cochrane Library, and Google Scholar to identify randomized controlled trials (RCTs) in which EA served as the primary intervention for diseases related to GALM. The risk of bias within the included studies was assessed according to the Cochrane Handbook. All statistical analyzes were performed using RevMan 5.4 software.

Results

In this study, a total of 482 articles were retrieved, resulting in the inclusion of 10 RCTs in the meta-analysis. The results showed that EA could reduce fasting blood glucose (FBG) (p = 0.008), increase insulin secretion (p = 0.01), improve insulin resistance index (HOMA-IR) (p = 0.003), decrease triglyceride (TG) (p = 0.004), and reduce cholesterol (Chol) (p = 0.04) and low-density lipoprotein (LDL-c) (p = 0.0004). EA had no significant effect on waist circumference (WC), body weight (BW), body mass index (BMI), 2 hours after prandial blood glucose (2 h-PG), total cholesterol (TC), and high-density lipoprotein (HDL-c).

Conclusions

The effect of improvement in glucose and lipids of EA was closely related to the dose and the intervention time. EA can improve GALM caused by diseases. To corroborate the findings of this study and improve the reliability of the results, EA is imperative to refine the research methodology and increase the sample size in future investigations.

Prunin from Poncirus trifoliata (L.) Rafin Inhibits Aldose Reductase and Glucose-Fructose-Mediated Protein Glycation and Oxidation of Human Serum Albumin

Diabetes complications are associated with aldose reductase (AR) and advanced glycation end products (AGEs). Using bioassay-guided isolation by column chromatography, 10 flavonoids and one coumarin were isolated from Poncirus trifoliata Rafin and tested in vitro for an inhibitory effect against human recombinant AR (HRAR) and rat lens AR (RLAR). Prunin, narirutin, and naringin inhibited RLAR (IC50 0.48-2.84 μM) and HRAR (IC50 0.68-4.88 μM). Docking simulations predicted negative binding energies and interactions with the RLAR and HRAR binding pocket residues. Prunin (0.1 and 12.5 μM) prevented the formation of fluorescent AGEs and nonfluorescent Nε-(carboxymethyl) lysine (CML), as well as the fructose-glucose-mediated protein glycation and oxidation of human serum albumin (HSA). Prunin suppressed the formation of the β-cross-amyloid structure of HSA. These results indicate that prunin inhibits oxidation-dependent protein damage, AGE formation, and AR, which may help prevent diabetes complications.

Mechanistic role of Syzygium cumini (L.) Skeels in glycation induced diabetic nephropathy via RAGE-NF-κB pathway and extracellular proteins modifications: A molecular approach

ETHNOPHARMACOLOGY RELEVANCE

Syzygium cumini (L.) Skeels (SC), an ancient medicinal plant, is used as a complementary and alternative medicine for treating diabetes mellitus and its associated complications, such as diabetic nephropathy (DN). Phytochemicals present in SC homeopathic formulations possess anti-glycemic, anti-glycation, anti-inflammatory, and antioxidant properties. Additionally, the non-enzymatic formation of advanced glycation end products (AGEs) increases during hyperglycemia in diabetes. AGEs interaction with their receptor of AGEs (RAGE) promotes inflammation via Nuclear Factor-κB (NF-κB) and the accumulation of Extracellular Matrix (ECM) proteins, contributing to the renal dysfunction in DN. However, the molecular mechanism through which SC formulations interact with the AGEs-RAGE-NF-κB pathway has not yet been investigated.

AIM

This study aims to examine the impact of SC formulations on the RAGE-NF-κB pathway and ECM protein modifications in glycation-induced DN using a molecular approach.

MATERIALS AND METHODS

Human serum albumin (10 mg/ml) was glycated with MGO (55 mM) in the presence of SC formulations - Mother tincture (MT), 30C, 200C for 7 days. Glycated samples were added to renal cells (HEK 293) for 24 h. Subsequently, cellular gene and protein expressions of RAGE, NF-κB, vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), collagen IV (Col IV), and fibronectin were determined using RT-qPCR and Western blot analysis. The immunofluorescence, luciferase assay, and chromatin immunoprecipitation techniques were employed to gain insights into glycation-induced NF-κB nuclear translocation, transcriptional activity, and its effect on RAGE promoter activity in SC-treated cells.

RESULTS

SC formulations significantly downregulated glycation-induced elevated levels of RAGE and NF-κB. Mechanistically, SC formulations prevented NF-κB nuclear translocation, transcriptional activity, and RAGE promoter activity. Also, SC formulations significantly attenuated glycation-enhanced expressions of inflammatory cytokines (IL-6, TNF-α, and VEGF) and ECM proteins (Col IV and fibronectin).

CONCLUSION

Our findings enlighten the molecular mechanism of SC in DN by targeting the AGEs-RAGE-NF-κB signaling pathway, inflammatory responses, and ECM accumulation. Hence, the study validates the protective role of SC formulations and signifies its novel potential for treating DN.

Non-enzymatic glycation and diabetic kidney disease

Chronic diabetes leads to various complications including diabetic kidney disease (DKD). DKD is a major microvascular complication and the leading cause of morbidity and mortality in diabetic patients. Varying degrees of proteinuria and reduced glomerular filtration rate are the cardinal clinical manifestations of DKD that eventually progress into end-stage renal disease. Histopathologically, DKD is characterized by renal hypertrophy, mesangial expansion, podocyte injury, glomerulosclerosis, and tubulointerstitial fibrosis, ultimately leading to renal replacement therapy. Amongst the many mechanisms, hyperglycemia contributes to the pathogenesis of DKD via a mechanism known as non-enzymatic glycation (NEG). NEG is the irreversible conjugation of reducing sugars onto a free amino group of proteins by a series of events, resulting in the formation of initial Schiff's base and an Amadori product and to a variety of advanced glycation end products (AGEs). AGEs interact with cognate receptors and evoke aberrant signaling cascades that execute adverse events such as oxidative stress, inflammation, phenotypic switch, complement activation, and cell death in different kidney cells. Elevated levels of AGEs and their receptors were associated with clinical and morphological manifestations of DKD. In this chapter, we discussed the mechanism of AGEs accumulation, AGEs-induced cellular and molecular events in the kidney and their impact on the pathogenesis of DKD. We have also reflected upon the possible options to curtail the AGEs accumulation and approaches to prevent AGEs mediated adverse renal outcomes.

The effect of ellagic acid on the metabolic syndrome: A review article

Objective

(s): Metabolic syndrome is a collection of metabolic abnormalities that includes hyperglycemia, dyslipidemia, hypertension, and obesity. Ellagic acid is found in various fruits and vegetables. It has been reported to have several pharmacological properties, such as antibacterial, antifungal, antiviral, anti-inflammatory, hepatoprotective, cardioprotective, chemopreventive, neuroprotective, gastroprotective, and antidiabetic. Our current study aims to shed light on the probable efficiency of ellagic acid in managing metabolic syndrome and its complications.

Materials and methods

To prepare the present review, the databases or search engines utilized included Scopus, PubMed, Science Direct, and Google Scholar, and relevant articles have been gathered with no time limit until March 2023.

Results

Several investigations indicated that ellagic acid could be a potent compound for the treatment of many disorders such as diabetes, hypertension, and hyperlipidemia by various mechanisms, including increasing insulin secretion, insulin receptor substrate protein 1 expression, regulating glucose transporter 4, triglyceride, total cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), attenuating tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), reactive oxygen species (ROS), malondialdehyde (MDA), and oxidative stress in related tissues. Furthermore, ellagic acid ameliorates mitochondrial function, upregulates uncoupling protein 1 (found in brown and white adipose tissues), and regulates blood levels of nitrate/nitrite and vascular relaxations in response to acetylcholine and sodium nitroprusside.

Conclusion

Ellagic acid can treat or manage metabolic syndrome and associated complications, according to earlier studies. To validate the beneficial effects of ellagic acid on metabolic syndrome, additional preclinical and clinical research is necessary.

Potential roles of ellagic acid on metabolic variables in diabetes mellitus: A systematic review

Diabetes mellitus is a widespread endocrine disorder globally. Due to its antioxidant and anti-inflammatory properties, ellagic acid has the potential to improve the metabolic effects of chronic non-communicable diseases. This systematic review summarizes current evidence about the potential effects of ellagic acid on metabolic variables in diabetes mellitus. A comprehensive systematic literature search was conducted in databases such as PubMed, Scopus, EMBASE, ProQuest and Google Scholar from inception until March 2022. All animal studies and clinical trials were eligible for inclusion. Studies using in vitro models or published in a non-English language were excluded. Of 1320 articles, 23 were selected for assessment, including 21 animal studies and two randomized controlled trial studies. Following ellagic acid administration, findings reported improvement in FBS, HbA1c, insulin (20, 8 and 12 studies, respectively), TG, TC, HDL-C (13, 10 and 5 studies, respectively), MDA, GSH, CAT, SOD (11, 6, 3 and 4 studies, respectively), and TNF-α and IL-6 (6 and 3 studies, respectively). In conclusion, ellagic acid may improve glycaemic indicators, dyslipidaemia, oxidative stress and inflammation in diabetes mellitus. However, further clinical trials are needed to explore the mechanisms more precisely and to observe the applied consequences.

The Use of Ellagic Acid and Annona Muricata Improves Semen Quality in Men with High-Risk Papillomavirus Infection

Background: Few data are currently available on the treatment of patients with HPV infection. In particular, there is no agreement on the use of antioxidants in these patients. Ellagic acid and annona muricata appear to improve HPV clearance in infected women. However, it is presently unknown whether they could enhance the clearance of HPV infection in infertile male patients. Aim: To evaluate the effects of a commercially available combined compound containing ellagic acid and annona muricata on semen quality in patients with documented papillomavirus (HPV) infection, and on the frequency of HPV DNA detection in seminal fluid after treatment. In addition, anti-sperm antibodies and the percentage of spermatozoa with fragmented DNA were evaluated. Materials and methods: This was a retrospective case-control study including patients attending our center for infertility. Fifty selected patients who were positive for high risk (HR)-HPV with available semen analysis results were consecutively enrolled. Patients were classified into two groups, according to the clinician’s decision to either administer ellagic acid 100 mg and annona muricata 100 mg (combined tablet formulation) for a period of three months (Group A; 25 patients), or to re-evaluate HPV DNA after a period of active surveillance only (protected sexual intercourse) (Group B; 25 patients). Results: Group A patients had a mean age of 31.0  ±  11.0 years, while Group B was 33.0  ±  8.0 years old (p  > 0.05). After three months of treatment with ellagic acid and annona muricata, all conventional seminal parameters improved more significantly in Group A than in Group B patients: sperm concentration = 45 mil/mL vs. 20 mil/mL (p < 0.05); sperm progressive motility = 45% vs. 18% (p < 0.05); and normal sperm morphology = 18% vs. 6% (p < 0.05). After the treatment, the frequency of persistence of HPV DNA in the seminal fluid was significantly lower in Group A patients compared to those in Group B (12/25 = 48% vs. 22/25 = 88%; p < 0.05). Finally, after 3 months, Group A showed a significant reduction in anti-sperm antibodies and in the percentage of spermatozoa with fragmented DNA. Conclusion: The results of this study demonstrate, for the first time, the effects of a commercially available combined compound containing ellagic acid and annona muricata on semen quality in patients with HR-HPV infection, and that this therapy is also associated with a significant reduction in the persistence of HPV DNA in the seminal fluid.

Gut microbiota drives age-related oxidative stress and mitochondrial damage in microglia via the metabolite N6-carboxymethyllysine

Microglial function declines during aging. The interaction of microglia with the gut microbiota has been well characterized during development and adulthood but not in aging. Here, we compared microglial transcriptomes from young-adult and aged mice housed under germ-free and specific pathogen-free conditions and found that the microbiota influenced aging associated-changes in microglial gene expression. The absence of gut microbiota diminished oxidative stress and ameliorated mitochondrial dysfunction in microglia from the brains of aged mice. Unbiased metabolomic analyses of serum and brain tissue revealed the accumulation of N⁶-carboxymethyllysine (CML) in the microglia of the aging brain. CML mediated a burst of reactive oxygen species and impeded mitochondrial activity and ATP reservoirs in microglia. We validated the age-dependent rise in CML levels in the sera and brains of humans. Finally, a microbiota-dependent increase in intestinal permeability in aged mice mediated the elevated levels of CML. This study adds insight into how specific features of microglia from aged mice are regulated by the gut microbiota.

Effects of Shenkang Pills on Early-Stage Diabetic Nephropathy in db/db Mice via Inhibiting AURKB/RacGAP1/RhoA Signaling Pathway

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease, so there is an urgent need to suppress its development at early stage. Shenkang pills (SKP) are a hospital prescription selected and optimized from effective traditional Chinese medicinal formulas for clinical treatment of DN. In the present study, liquid chromatography-quadrupole-time of flight-mass spectrometry (LC-Q-TOF-MS) and total contents qualification were applied to generate a quality control standard of SKP. For verifying the therapeutic effects of SKP, db/db mice were administered intragastrically with SKP at a human-equivalent dose (1.82 g/kg) for 4 weeks. Moreover, the underlying mechanism of SKP were analyzed by the renal RNA sequencing and network pharmacology. LC-Q-TOF-MS identified 46 compounds in SKP. The total polysaccharide and organic acid content in SKP were 4.60 and 0.11 mg/ml, respectively, while the total flavonoid, saponin, and protein content were 0.25, 0.31, and 0.42 mg/ml, respectively. Treatment of SKP significantly reduced fasting blood glucose, improved renal function, and ameliorated glomerulosclerosis and focal foot processes effacement in db/db mice. In addition, SKP protected podocytes from injury by increasing nephrin and podocin expression. Furthermore, transcriptome analyses revealed that 430 and 288 genes were up and down-regulated in mice treated with SKP, relative to untreated controls. Gene ontology enrichment analysis revealed that the differentially expressed genes mainly involved in modulation of cell division and chromosome segregation. Weighted gene co-expression network analysis and network pharmacology analysis indicated that aurora kinase B (AURKB), Rac GTPase activating protein 1 (RacGAP1) and SHC binding, and spindle associated 1 (shcbp1) might be the core targets of SKP. This protein and Ras homolog family member A (RhoA) were found overexpression in db/db mice, but significantly decreased with SKP treatment. We conclude that SKP can effectively treat early-stage DN and improve renal podocyte dysfunction. The mechanism may involve down-regulation of the AURKB/RacGAP1/RhoA pathway.

Physicochemical Characterization of In Vitro LDL Glycation and Its Inhibition by Ellagic Acid (EA): An In Vivo Approach to Inhibit Diabetes in Experimental Animals

Hundreds of millions of people around the globe are afflicted by diabetes mellitus. The alteration in glucose fixation process might result into hyperglycaemia and could affect the circulating plasma proteins to undergo nonenzymatic glycation reaction. If it is unchecked, it may lead to diabetes with increase in advanced glycation end products (AGEs). Therefore, the present study was designed to inhibit the diabetes and glycation by using natural antioxidant “ellagic acid” (EA). In this study, we explored the antidiabetes and antiglycation potential of EA in both in vitro (EA at micromolar concentration) and in vivo systems. The EA concentrations of 10 and 20 mg kg⁻¹B.W./day were administered orally for 25 days to alloxan-induced diabetic rats, a week after confirmation of stable diabetes in animals. Intriguingly, EA supplementation in diabetic rats reversed the increase in fasting blood sugar (FBS) and hemoglobin A1c (HbA1c) level. EA also showed an inhibitory role against glycation intermediates including dicarbonyls, as well as AGEs, investigated in a glycation mixture with in vitro and in vivo animal plasma samples. Additionally, EA treatment resulted in inhibition of lipid peroxidation-mediated malondialdehyde (MDA) and conjugated dienes (CD). Furthermore, EA exhibited an antioxidant property, increased the level of plasma glutathione (GSH), and also helped to decrease histological changes evaluated by histoimmunostaining of animal kidney tissues. The results from our investigation clearly indicates the antiglycative property of EA, suggesting EA as an adequate inhibitor of glycation and diabetes, which can be investigated further in preclinical settings for the treatment and management of diabetes-associated complications.

Maillard Browning Inhibition by Ellagic Acid via Its Adduct Formation with the Amadori Rearrangement Product

The Maillard reaction performed under a stepwise increase of temperature was applied for researching the inhibition of Maillard browning caused by ellagic acid. Ellagic acid was found effective for the inhibition of melanoidin formation in the xylose-glycine Maillard reaction but depended on its dosage and the point of time it was added in the reaction system. The lightest color of the Maillard reaction products was observed when ellagic acid was added at the 90th min, which was the point of time when the Amadori rearrangement product (ARP) developed the most. LC-ESI-MS/MS analysis results showed a significant tendency of the ellagic acid hydrolysis product to react with the predominant intermediate ARP to yield an adduct. The adduct stabilized the ARP and delayed its decomposition and inhibited the downstream reactions toward browning. After the ARP was depleted, ellagic acid also showed an effect on scavenging some short-chain dicarbonyls which contributed to the inhibition of Maillard browning.

Deciphering nutritional interventions for podocyte structure and function

Despite increasing awareness and therapeutic options chronic kidney disease (CKD) is still and important health problem and glomerular diseases constitute and important percentage of CKD. Proteinuria/albuminuria is not just a marker; but it also plays a direct pathogenic role in renal disease progression of CKD. Glomerular filtration barrier (GFB) which consists of fenestrated endothelial cells, fused basal membrane and interdigitating podocyte foot process and filtration slits between foot process is the major barrier for proteinuria/albuminuria. Many glomerular diseases are characterized by disruption of GFB podocytes, foot process and slit diaphragm. Many proteinuric diseases are non-specifically targeted by therapeutic agents such as steroids and calcineurin inhibitors with systemic side effects. Thus, there is unmet need for more efficient and less toxic therapeutic options to treat glomerular diseases. In recent years, modification of dietary intake, has been gained to treat pathologic processes introducing the concept of 'food as a medicine'. The effect of various nutritional products on podocyte function and structure is also trending, especially in recent years. In the current review, we summarized the effect of nutritional interventions on podocyte function and structure.

Natural Products as a Source of Inspiration for Novel Inhibitors of Advanced Glycation Endproducts (AGEs) Formation

Protein glycation, a post-translational modification found in biological systems, is often associated with a core defect in glucose metabolism. In particular, advanced glycation endproducts are complex heterogeneous sugar-derived protein modifications implicated in the progression of pathological conditions such as atherosclerosis, diabetic complications, skin diseases, rheumatism, hypertension, and neurodegenerative diseases. Undoubtedly, there is the need to expand the knowledge about antiglycation agents that can offer a therapeutic approach in preventing and treating health issues of high social and economic importance. Although various compounds have been under consideration, little data from clinical trials are available, and there is a lack of approved and registered antiglycation agents. Next to the search for novel synthetic advanced glycation endproduct inhibitors, more and more the efforts of scientists are focusing on researching antiglycation compounds from natural origin. The main purpose of this review is to provide a thorough overview of the state of scientific knowledge in the field of natural products from plant origin (e.g., extracts and pure compounds) as inhibitors of advanced glycation endproduct formation in the period between 1990 and 2019. Moreover, the objectives of the summary also include basic chemistry of AGEs formation and classification, pathophysiological significance of AGEs, mechanisms for inhibiting AGEs formation, and examples of several synthetic anti-AGEs drugs.

Subclinical hypothyroidism contributes to poor glycemic control in patients with type 2 diabetes mellitus, and ellagic acid attenuates methimazole-induced abnormal glucose metabolism in mice model

Subclinical hypothyroidism (SCH) as mild thyroid disorder or comorbidity in patients with endocrine disorders is closely related with insulin resistance (IR) and poor glycemic control. The present study attempted to investigate the effect of SCH on IR and glycemic control in patients with type 2 diabetes mellitus (T2DM). In addition, the effects of ellagic acid (EA) on SCH C57BL/6J and db/db mice were also investigated to explore potential therapeutic drug against SCH-induced abnormal glucose metabolism. T2DM patients were recruited in our study and categorized into two groups according to thyroid stimulating hormone (TSH) value: T2DM without SCH group (TSH ≤4 μIU/ml; n = 30) and T2DM with SCH group (TSH >4μIU/ml; n = 60). Methimazole (MMI; 0.08 mg kg^-1  day^-1 ) was intragastrically administrated for 12 weeks to establish SCH in C57BL/6J and db/db mice. Compared with T2DM patients without SCH, poor glycemic and cholesterol control were emerged in T2DM patients with SCH and that were prominent in patients with TSH more than 10 μIU/ml. In addition, a significant positive correlation between serum TSH and fasting plasma-glucose (FPG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), or glycated hemoglobin (HbA1c) was observed in T2DM patients with SCH. Moreover, abnormal glucose metabolism in C57BL/6J and db/db mice with SCH has been attenuated by EA administration. Our findings provided data regarding the positive correlation between high TSH level with poor glycemic control in T2DM patients with SCH. EA might be a supportive strategy for preventing SCH-induced abnormal glucose metabolism. PRACTICAL APPLICATIONS: Subclinical hypothyroidism (SCH) is a potential risk factor associated with abnormal glucose metabolism in patients with type 2 diabetes mellitus (T2DM). A clinical theory of a positive correlation between high TSH level and poor glycemic control was validated in type 2 diabetes mellitus patients and mouse models. Ellagic acid (EA) might be a supportive strategy for preventing SCH-induced abnormal glucose metabolism that provided a treatment option in T2DM patients with subclinical hypothyroidism in clinical practice.

Phytochemicals against anti-diabetic complications: targeting the advanced glycation end product signaling pathway

The role of advanced glycation end products (AGEs) is not limited to diabetes and diabetes-related complications. There are multiple modulators, including the receptor for advanced glycation end products, high mobility group box 1, glyoxalase 1, nuclear factor-kappa B, tumor necrosis factor-α, chronic unpredictable stress, reactive oxygen species, and inflammatory cytokines, which interact with AGE signaling and control diabetes, modulating these interacting modulators. The progression of diabetes, as well as related complications, can be controlled and treated. Natural products rich in bioactive constituents can interact with AGEs and their related mediators through various signaling cascades, thereby controlling and preventing the progression of diabetes. This review provides a deeper assessment of the signaling pathway, interactions between phytochemicals and AGEs, and its mediators, to develop a multifold therapeutic approach to prevent and treat diabetes and its related complications.

Ellagic Acid Affects Metabolic and Transcriptomic Profiles and Attenuates Features of Metabolic Syndrome in Adult Male Rats

Ellagic acid, a natural substance found in various fruits and nuts, was previously shown to exhibit beneficial effects towards metabolic syndrome. In this study, using a genetic rat model of metabolic syndrome, we aimed to further specify metabolic and transcriptomic responses to ellagic acid treatment. Adult male rats of the SHR-Zbtb16^Lx/k.o. strain were fed a high-fat diet accompanied by daily intragastric gavage of ellagic acid (50 mg/kg body weight; high-fat diet–ellagic acid (HFD-EA) rats) or vehicle only (high-fat diet–control (HFD-CTL) rats). Morphometric and metabolic parameters, along with transcriptomic profile of liver and brown and epididymal adipose tissues, were assessed. HFD-EA rats showed higher relative weight of brown adipose tissue (BAT) and decreased weight of epididymal adipose tissue, although no change in total body weight was observed. Glucose area under the curve, serum insulin, and cholesterol levels, as well as the level of oxidative stress, were significantly lower in HFD-EA rats. The most differentially expressed transcripts reflecting the shift induced by ellagic acid were detected in BAT, showing downregulation of BAT activation markers Dio2 and Nr4a1 and upregulation of insulin-sensitizing gene Pla2g2a. Ellagic acid may provide a useful nutritional supplement to ameliorate features of metabolic syndrome, possibly by suppressing oxidative stress and its effects on brown adipose tissue.

Potential effect of tropical fruits Phyllanthus emblica L. for the prevention and management of type 2 diabetic complications: a systematic review of recent advances

Phyllanthus emblica is a fruit widely consumed in subtropical areas, which is rich in polyphenols and other nutrients. There are increasing evidences that as a daily and nutritious fruit, it may have a positive role in controlling diabetic complications. According to the new study, its mechanisms include enhancing the functioning of insulin, reducing insulin resistance, activating the insulin-signaling pathway, protecting β-cells, scavenging free radicals, alleviating inflammatory reactions, and reducing the accumulation of advanced glycation end products. Owing to its few side effects, and low price, it should be easily accepted by patients and has potential for preventing diabetes. Taken together, Phyllanthus emblica may be an ideal fruit for controlling diabetic complications. This review highlights the latest findings of the role of Phyllanthus emblica in anti-diabetes and its complications, especially clarifies the molecular mechanism of the chemical components related to this effect, and prospects some existing problems and future research directions.

Ellagic Acid as a Tool to Limit the Diabetes Burden: Updated Evidence

Oxidative stress contributes not only to the pathogenesis of type 2 diabetes (T2D) but also to diabetic vascular complications. It follows that antioxidants might contribute to limiting the diabetes burden. In this review we focus on ellagic acid (EA), a compound that can be obtained upon intestinal hydrolysis of dietary ellagitannins, a family of polyphenols naturally found in several fruits and seeds. There is increasing research on cardiometabolic effects of ellagitannins, EA, and urolithins (EA metabolites). We updated research conducted on these compounds and (I) glucose metabolism; (II) inflammation, oxidation, and glycation; and (III) diabetic complications. We included studies testing EA in isolation, extracts or preparations enriched in EA, or EA-rich foods (mostly pomegranate juice). Animal research on the topic, entirely conducted in murine models, mostly reported glucose-lowering, antioxidant, anti-inflammatory, and anti-glycation effects, along with prevention of micro- and macrovascular diabetic complications. Clinical research is incipient and mostly involved non-randomized and low-powered studies, which confirmed the antioxidant and anti-inflammatory properties of EA-rich foods, but without conclusive results on glucose control. Overall, EA-related compounds might be potential agents to limit the diabetes burden, but well-designed human randomized controlled trials are needed to fill the existing gap between experimental and clinical research.

Tannins and vascular complications of Diabetes: An update

BACKGROUND

Diabetes mellitus is a chronic metabolic disorder associated with persistent increased level of glucose in the blood. According to a report by World Health Organisation (WHO), prevalence of diabetes among adults over 18 years of age had reached to 8.5% in year 2014 which was 4.7% in 1980s. The Prolong increased level of glucose in blood leads to development of microvascular (blindness, nephropathy and neuropathy) and macrovascular (cardiovascular and stroke) degenerative complications because of uncontrolled level of glucose in blood. This also leads to the progression of oxidative stress and affecting metabolic, genetic and haemodynamic system by activation of polyol pathway, protein kinase C pathway, hexosamine pathway and increases advanced glycation end products (AGEs) formation. Diabetes mellitus and its associated complications are one of the major leading causes of mortality worldwide. Various natural products like alkaloids, glycosides, flavonoids, terpenoids and polyphenols are reported for their activity in management of diabetes and its associated diabetic complications. Tannins are systematically studied by many researchers in past few decades for their effect in diabetes and its complications.

AIM

The present review was designed to compile the data of tannins and their beneficial effects in the management of diabetic complications.

METHOD

Literature search was performed using various dataset like pubmed, EBSCO, proQuest Scopus and selected websites including the National Institutes of Health (NIH) and the World Health Organization (WHO).

RESULTS

Globally, more than 400 natural products have been investigated in diabetes and its complications. Tannins are the polyphenolic compounds present in many medicinal plants and various dietary sources like fruits, nuts, grains, spices and beverages. Various reports have shown that compounds like gallic acid, ellagic acid, catechin, epicatechin and procynidins from medicinal plants play major role in controlling progression of diabetes and its related complications by acting on molecular pathways and key targets involved in progression. Many chemists used above mentioned phyto-constituents as a pharmacophore for the developing new chemical entities having higher therapeutic benefits in management of diabetic complications.

CONCLUSION

This review focuses on the role of various tannins in prevention and management of diabetic complications like diabetic nephropathy, diabetic neuropathy, diabetic retinopathy and diabetic cardiomyopathy. It will help researchers to find some leads for the development of new cost effective therapy using dietary source for the management of diabetic complications.

Cordyceps militaris polysaccharides exerted protective effects on diabetic nephropathy in mice via regulation of autophagy

The present study is designed to investigate the protective effects of Cordyceps militaris polysaccharides (CMP) on STZ-treated DN mice.

Antioxidant Activity and In Vitro Antiglycation of the Fruit of Spondias purpurea

Hyperglycemia in diabetes mellitus causes irreversible life-threatening micro- and macrovascular complications. There is evidence that the glycation reaction leads to a chemical modification of the proteins contributing to the complications of diabetes. It is known that advanced glycation end products (AGEs) are formed by glycation and oxidation reactions called glycoxidation. CML, a nonfluorescent AGE, has become a biomarker of glycoxidative damage; other AGEs appear to induce oxidative stress, which results in cytotoxicity. To determine antioxidant activity, the FRAP, DPPH, and TEAC tests were used, as well as the polyphenols content using Folin-Ciocalteu's method. To evaluate the antiglycation activity, the BSA/glucose system was used, and the fructosamine concentration, protein carbonyl content, thiol, and CML groups were determined. The results obtained show that the hexane extract of the fruit of Spondias purpurea (CFH) effectively inhibits the glycation reaction, in addition to increasing the thiol groups and decreasing levels of fructosamine, protein carbonyl, and CML. In addition, CFH presented significant antioxidant activity. CFH inhibits the glycation reaction; therefore, it can help prevent complications related to AGEs in diabetes mellitus; it also reduces oxidative stress and is effective in protecting proteins from oxidative damage.

Progestin and AdipoQ Receptor 3 Upregulates Fibronectin and Intercellular Adhesion Molecule-1 in Glomerular Mesangial Cells via Activating NF-κB Signaling Pathway Under High Glucose Conditions

BACKGROUND

Progestin and adipoQ receptor 3 (PAQR3), is a Golgi-anchored membrane protein containing seven transmembrane helices. It has been demonstrated that PAQR3 mediates insulin resistance, glucose and lipid metabolism, and inflammation. In addition, kidney inflammatory fibrosis is an important pathological feature of diabetic nephropathy (DN). Therefore, we aimed to investigate the role of PAQR3 in diabetic kidney fibrosis as well as inflammation in DN.

OBJECT

The effect of PAQR3 on NF-κB signaling pathway, expressions of fibronectin (FN) and intercellular adhesion molecule-1 (ICAM-1) in glomerular mesangial cells (GMCs) cultured by high glucose (HG) were examined.

METHOD

Diabetic mouse and rat models were induced by streptozotocin (STZ). GMCs were treated with HG and transfected with PAQR3 plasmids or small-interfering RNA targeting PAQR3 or NF-κB. The protein levels of FN and ICAM-1 were examined by Western blotting, and the transcriptional activity and DNA binding activity of NF-κB were measured by dual luciferase reporter assay and electrophoretic mobility shift assay (EMSA). The interaction between PAQR3 and IKKβ (inhibitor of nuclear factor κB kinase β) was analyzed by co-immunoprecipitation.

RESULTS

PAQR3 was increased in both STZ-induced diabetic models and HG-treated GMCs. PAQR3 overexpression further increased HG-induced FN and ICAM-1 upregulation. In contrast, silencing of PAQR3 suppressed the expressions of FN and ICAM-1. PAQR3 overexpression promoted the nuclear accumulation, DNA binding activity, and transcriptional activity of NF-κB. Mechanically, PAQR3 directly interacted with IKKβ. The upregulation effect of PAQR3 overexpression on the expressions of FN and ICAM-1 was abolished by the treatment of NF-κB siRNA or PDTC (ammonium pyrrolidinedithiocarbamate) in HG-treated GMCs.

CONCLUSION

PAQR3 promotes the expressions of FN and ICAM-1 via activating NF-κB signaling pathway. Mechanistically, PAQR3 activates NF-κB signaling pathway to mediate kidney inflammatory fibrosis through direct interaction with IKKβ in DN.

Attenuation of diabetic retinopathy in rats by ellagic acid through inhibition of AGE formation

Diabetic retinopathy (DR) is a major concern for blindness all over the world. Diabetic retinopathy is associated with thickening of basement membrane, retinal thinning, retinal detachment, and pericyte death. Advanced glycation end products (AGEs) mediate the progression of DR by stimulating the expression of RAGE and VEGF which subsequently damages the blood-retinal barrier. Employing a set of in vitro protein glycation systems, earlier we demonstrated antiglycating potential of ellagic acid (EA). In this study, we evaluated the efficacy of EA to prevent in vivo accumulation of AGE and to ameliorate retinal changes in diabetic rats. Streptozotocin-induced diabetic rats were fed either with 0.2 or 2% EA in the diet for 12 weeks. Effect of EA on retinal function was assessed with electroretinogram (ERG). At the end of the experiment, rats were scarified and retina was collected. Histology was carried out with H&E staining and immunohistochemistry. Formation of AGE product (CML) and activation of RAGE was analyzed by immunoblotting and immunohistochemistry. Expression of GFAP, VEGF, Bax and HIF-1α was assessed by qRT-PCR and immunoblotting. Dietary supplementation of EA to diabetic rats resulted in: (1) inhibition of accumulation of CML and activation of RAGE in retina, (2) attenuation of expression of GFAP, VEGF, and HIF-1α in retina, (3) attenuation of cell death by reducing proapoptic mediator Bax and (4) amelioration of retinal thickness and function. In conclusion, EA attenuated the retinal abnormalities including angiogenesis, hypoxia and cell death by inhibiting AGE-RAGE mediated cellular events.

Advanced glycation end products mediated cellular and molecular events in the pathology of diabetic nephropathy

Diabetic nephropathy (DN) is a major cause of morbidity and mortality in diabetic patients and a leading cause of end-stage renal disease (ESRD). Degenerative changes such as glomerular hypertrophy, hyperfiltration, widening of basement membranes, tubulointerstitial fibrosis, glomerulosclerosis and podocytopathy manifest in various degrees of proteinuria in DN. One of the key mechanisms implicated in the pathogenesis of DN is non-enzymatic glycation (NEG). NEG is the irreversible attachment of reducing sugars onto free amino groups of proteins by a series of events, which include the formation of Schiff’s base and an Amadori product to yield advanced glycation end products (AGEs). AGE modification of client proteins from the extracellular matrix induces crosslinking, which is often associated with thickening of the basement membrane. AGEs activate several intracellular signaling cascades upon interaction with receptor for AGEs (RAGE), which manifest in aberrant cellular responses such as inflammation, apoptosis and autophagy, whereas other receptors such as AGE-R1, AGE-R3 and scavenger receptors also bind to AGEs and ensue endocytosis and degradation of AGEs. Elevated levels of both serum and tissue AGEs are associated with adverse renal outcome. Increased evidence supports that attenuation of AGE formation and/or inhibition of RAGE activation manifest(s) in improving renal function. This review provides insights of NEG, discusses the cellular and molecular events triggered by AGEs, which manifest in the pathogenesis of DN including renal fibrosis, podocyte epithelial-mesenchymal transition and activation of renin-angiotensin system. Therapies designed to target AGEs, such as inhibitors of AGEs formation and crosslink breakers, are discussed.