Anti-Glucotoxicity Effect of Phytoconstituents via Inhibiting MGO-AGEs Formation and Breaking MGO-AGEs

The therapeutic benefits of phytochemicals in the treatment of various illnesses and disorders are well documented. They show significant promise for the discovery and creation of novel medications for treating a variety of human diseases. Numerous phytoconstituents have shown antibiotic, antioxidant, and wound-healing effects in the conventional system. Traditional medicines based on alkaloids, phenolics, tannins, saponins, terpenes, steroids, flavonoids, glycosides, and phytosterols have been in use for a long time and are crucial as alternative treatments. These phytochemical elements are crucial for scavenging free radicals, capturing reactive carbonyl species, changing protein glycation sites, inactivating carbohydrate hydrolases, fighting pathological conditions, and accelerating the healing of wounds. In this review, 221 research papers have been reviewed. This research sought to provide an update on the types and methods of formation of methylglyoxal-advanced glycation end products (MGO-AGEs) and molecular pathways induced by AGEs during the progression of the chronic complications of diabetes and associated diseases as well as to discuss the role of phytoconstituents in MGO scavenging and AGEs breaking. The development and commercialization of functional foods using these natural compounds can provide potential health benefits.

Aspalathin and Other Rooibos Flavonoids Trapped α-Dicarbonyls and Inhibited Formation of Advanced Glycation End Products In Vitro

The excessive dietary intake of simple sugars and abnormal metabolism in certain diseases contribute to the increased production of α-dicarbonyls (α-DCs), such as methylglyoxal (MGO) and glyoxal (GO), the main precursors of the formation of advanced glycation end products (AGEs). AGEs play a vital role, for example, in the development of cardiovascular diseases and diabetes. Aspalathus linearis (Burman f.) R. Dahlgren (known as rooibos tea) exhibits a wide range of activities beneficial for cardio-metabolic health. Thus, the present study aims to investigate unfermented and fermented rooibos extracts and their constituents for the ability to trap MGO and GO. The individual compounds identified in extracts were tested for the capability to inhibit AGEs (with MGO or GO as a glycation agent). Ultra-high-performance liquid chromatography coupled with an electrospray ionization mass spectrometer (UHPLC-ESI-MS) was used to investigate α-DCs' trapping capacities. To evaluate the antiglycation activity, fluorescence measurement was used. The extract from the unfermented rooibos showed a higher ability to capture MGO/GO and inhibit AGE formation than did the extract from fermented rooibos, and this effect was attributed to a higher content of dihydrochalcones. The compounds detected in the extracts, such as aspalathin, nothofagin, vitexin, isovitexin, and eriodictyol, as well as structurally related phloretin and phloroglucinol (formed by the biotransformation of certain flavonoids), trapped MGO, and some also trapped GO. AGE formation was inhibited the most by isovitexin. However, it was the high content of aspalathin and its higher efficiency than that of metformin that determined the antiglycation and trapping properties of green rooibos. Therefore, A. linearis, in addition to other health benefits, could potentially be used as an α-DC trapping agent and AGE inhibitor.

Glycation Interferes with the Expression of Sialyltransferases in Meningiomas

Meningiomas are the most common non-malignant intracranial tumors and prefer, like most tumors, anaerobic glycolysis for energy production (Warburg effect). This anaerobic glycolysis leads to an increased synthesis of the metabolite methylglyoxal (MGO) or glyoxal (GO), which is known to react with amino groups of proteins. This reaction is called glycation, thereby building advanced glycation end products (AGEs). In this study, we investigated the influence of glycation on sialylation in two meningioma cell lines, representing the WHO grade I (BEN-MEN-1) and the WHO grade III (IOMM-Lee). In the benign meningioma cell line, glycation led to differences in expression of sialyltransferases (ST3GAL1/2/3/5/6, ST6GAL1/2, ST6GALNAC2/6, and ST8SIA1/2), which are known to play a role in tumor progression. We could show that glycation of BEN-MEN-1 cells led to decreased expression of ST3Gal5. This resulted in decreased synthesis of the ganglioside GM3, the product of ST3Gal5. In the malignant meningioma cell line, we observed changes in expression of sialyltransferases (ST3GAL1/2/3, ST6GALNAC5, and ST8SIA1) after glycation, which correlates with less aggressive behavior.

The Role of Glyoxalase in Glycation and Carbonyl Stress Induced Metabolic Disorders

Glycation refers to the covalent binding of sugar molecules to macromolecules, such as DNA, proteins, and lipids in a non-enzymatic reaction, resulting in the formation of irreversibly bound products known as advanced glycation end products (AGEs). AGEs are synthesized in high amounts both in pathological conditions, such as diabetes and under physiological conditions resulting in aging. The body's anti-glycation defense mechanisms play a critical role in removing glycated products. However, if this defense system fails, AGEs start accumulating, which results in pathological conditions. Studies have been shown that increased accumulation of AGEs acts as key mediators in multiple diseases, such as diabetes, obesity, arthritis, cancer, atherosclerosis, decreased skin elasticity, male erectile dysfunction, pulmonary fibrosis, aging, and Alzheimer's disease. Furthermore, glycation of nucleotides, proteins, and phospholipids by α-oxoaldehyde metabolites, such as glyoxal (GO) and methylglyoxal (MGO), causes potential damage to the genome, proteome, and lipidome. Glyoxalase-1 (GLO-1) acts as a part of the anti-glycation defense system by carrying out detoxification of GO and MGO. It has been demonstrated that GLO-1 protects dicarbonyl modifications of the proteome and lipidome, thereby impeding the cell signaling and affecting age-related diseases. Its relationship with detoxification and anti-glycation defense is well established. Glycation of proteins by MGO and GO results in protein misfolding, thereby affecting their structure and function. These findings provide evidence for the rationale that the functional modulation of the GLO pathway could be used as a potential therapeutic target. In the present review, we summarized the newly emerged literature on the GLO pathway, including enzymes regulating the process. In addition, we described small bioactive molecules with the potential to modulate the GLO pathway, thereby providing a basis for the development of new treatment strategies against age-related complications.

Glycation of benign meningioma cells leads to increased invasion

Meningiomas are the most common non-malignant intracranial tumors. Like most tumors, meningiomas prefer anaerobic glycolysis for energy production (Warburg effect). This leads to an increased synthesis of the metabolite methylglyoxal (MGO). This metabolite is known to react with amino groups of proteins. This reaction is called glycation, thereby building advanced glycation endproducts (AGEs). In this study, we investigated the influence of glycation on two meningioma cell lines, representing the WHO grade I (BEN-MEN-1) and the WHO grade III (IOMM-Lee). Increasing MGO concentrations led to the formation of AGEs and decreased growth in both cell lines. When analyzing the influence of glycation on adhesion, chemotaxis and invasion, we could show that the glycation of meningioma cells resulted in increased invasive potential of the benign meningioma cell line, whereas the invasive potential of the malignant cell line was reduced. In addition, glycation increased the E-cadherin- and decreased the N-cadherin-expression in BEN-MEN-1 cells, but did not affect the cadherin-expression in IOMM-Lee cells.

Characterization of Reaction Products and Mechanisms between Serotonin and Methylglyoxal in Model Reactions and Mice

Serotonin is an important endogenous regulatory neurotransmitter and has also been found in fruits, vegetables, and nuts. Methylglyoxal (MGO) is a reactive dicarbonyl metabolite and also a food toxin that modifies protein and DNA to cause the development of many chronic diseases. The objective of this study is to understand the reaction mechanisms between serotonin and MGO and determine whether serotonin could trap MGO in vivo. Five products were detected in phosphate buffer (pH 7.4) at 37 °C. Four products (compounds 2 and 4-6) were purified from the reaction mixture, and their structures were characterized by the analysis of their high-resolution mass and one- and two-dimensional nuclear magnetic resonance spectra. One product (compound 3), as a result of its instability, could not be properly purified and was tentatively characterized on the basis of its high-resolution mass spectrum and corresponding mass fragments. On the basis of the structures of these five products, two reaction pathways were proposed. Compounds 2, 3, 5, and 6 were produced through the Pictet-Spengler condensation pathway between the primary amine of serotonin and the ketone of MGO, and compound 3 was identified as the intermediate product to form products 2, 5, and 6, whereas compound 4 was formed through nucleophilic substitution by the benzene ring of serotonin, which is a new reaction pathway between biogenic amines and reactive carbonyl species. More importantly, the detection of adducts 2 and 4-6 in mice supports our hypothesis that the reaction between serotonin and MGO also happens in vivo through the same pathways as those in model reactions, suggesting that dietary or endogenous serotonin has the capacity to trap MGO in vivo.

Protection of diabetes-induced kidney injury by phosphocreatine via the regulation of ERK/Nrf2/HO-1 signaling pathway

Diabetic nephropathy is the most common long-term complication of diabetes mellitus. The Methylglyoxal (MGO) production is mainly by metabolic pathways, such as lipolysis and glycolysis, its increases in the DM enhances oxidative stress and plays a crucial role in the diabetic nephrotic pathogenesis. Phosphocreatine (PCr) can improve lipopolysaccharide, ox-LDL-induced atherosclerosis, and alleviate vascular endothelial cell injury in diabetes. The aim of our present study is to examine the potential role of phosphocreatine (PCr) as a molecule protects against diabetes-induced Kidney Injury in-vitro and in-vivo through ERK/Nrf2/HO-1 signaling pathway. NRK-52E cells treatment with PCr obviously suppressed MGO-induced change of viability, apoptosis, coupled with decreased Bax/Bcl-2ratio, casapse-9 and caspase-3expressions. We determined the generation of reactive oxygen species (ROS) using membrane permeable fluorescent probe DCFH-DA as well as intracellular calcium by flow cytometry. ERK, Nrf2 and HO-1 expressions were determined by Western blot. PCr pretreatment significantly returned the oxidative stress enzymes to normal condition in-vitro and in-vivo. PCr pretreatment significantly reduced apoptosis, calcium and ROS production, induced by MGO, in NRK-52E cells. Moreover, pretreatment with PCr significantly inhibited cleaved caspase-3, cleaved caspase-9 and p-ERK expressions, while increased Nrf-2 and HO-1 expressions. Furthermore, PCr pretreatment significantly decreased p-ERK expression of MGO-induced injury in NRK-52E cells transfected with p-ERK cDNA. In conclusion, the renal protective effect of PCr in-vitro and in-vivo depends on suppressing apoptosis and ROS generation through ERK mediated Nrf-2/HO-1 pathway, suggesting that PCr may be a novel therapeutic candidate for the diabetic nephropathy treatment.

Inhibitory Effects of Bioassay-Guided Isolation of Anti-Glycation Components from Taraxacum coreanum and Simultaneous Quantification

Inhibition of the formation of advanced glycation end products (AGEs) is an attractive strategy in diabetes treatment. Taraxacum coreanum extracts were suggested to have antidiabetic effects. However, studies on the components of T. coreanum are lacking, and there is no report on the inhibitory effects of T. coreanum on the formation of AGEs. Therefore, T. coreanum extracts and fractions were tested for their inhibitory effects on α-glucosidase and AGEs formation in two systems (bovine serum albumin (BSA)⁻glucose and BSA⁻methylglyoxal (MGO)). Bioassay-guided isolation of compounds from T. coreanum led to six flavones (1⁻6) and four hydroxycinnamic acid derivatives (7⁻11). Compound 11 exhibited the highest inhibitory activity against α-glucosidase and AGEs formation and had the highest content in T. coreanum extract. All compounds except compound 9 showed a stronger inhibition than the positive control in the BSA-glucose and BSA-MGO system. In addition, T. coreanum showed a higher content of bioactive compounds and stronger inhibition of AGE formation and α-glucosidase activity than T. officinale. Our study demonstrated the preventive and therapeutic efficacy of T. coreanum and its potential use as a cost-effective phytopharmaceutical in complementary therapy against type-2 diabetes and its complications.

Protective effect of exendin-4 treatment on erectile dysfunction induced by chronic methylglyoxal administration in rats

OBJECTIVE

The aim of this study was to investigate the effect of chronic exendin-4 (Ex-4) treatment on corpus cavernosum (CC) dysfunction in methylglyoxal (MGO) administered rats.

METHODS

Male rats were divided into four groups as control, MGO (75 mg/kg/day in drinking water for 12 weeks), MGO + low-dose Ex-4 (0.1 μg/kg twice daily subcutaneously for 12 weeks concomitant with MGO), and MGO + high-dose Ex-4 (1 μg/kg twice daily subcutaneously for 12 weeks concomitant with MGO). Nitric oxide (NO)-mediated endothelium-dependent and neurogenic CC relaxations were evaluated by acetylcholine (ACh) and electrical field stimulation (EFS), respectively. Apoptosis was determined by TUNEL. Endothelial nitric oxide synthase (eNOS), phosphorylated eNOS (p-eNOS), NADPH oxidase subunit gp91phox (NOX2), and Rho kinase (ROCK2) expressions in CC were investigated by immunohistochemistry. Levels of the malondialdehyde (MDA) and advanced oxidation protein products (AOPP) were also measured.

RESULTS

In MGO administered rats, both endothelium-dependent and neurogenic CC relaxations were significantly impaired as compared to controls. Apoptotic cell death and levels of MDA and AOPP increased significantly in MGO administered rats. eNOS and p-eNOS expressions decreased significantly in MGO group, while gp91phox expressions increased significantly. The diminished relaxation in response to ACh or EFS as well as the changes in expression of proteins in MGO groups were significantly improved by exendin-4 treatment. TUNEL-positive cells, and levels of MDA and AOPP in MGO group rats were also significantly reduced by exendin-4.

CONCLUSION

Exendin-4 treatment improves NO-mediated CC relaxations in MGO administered rats probably by inhibiting NADPH oxidase.

Methylglyoxal-augmented manuka honey as a topical anti-Staphylococcus aureus biofilm agent: safety and efficacy in an in vivo model

BACKGROUND

Bacterial biofilms are thought to contribute to recalcitrance in chronic rhinosinusitis (CRS) patients. Manuka honey (MH) and its active component methylglyoxal (MGO) have demonstrated antibiofilm activity in vitro. This study evaluated the safety and efficacy of these agents in an in vivo model.

METHODS

To assess safety, ovine frontal sinuses were flushed twice daily for 14 days. In each sheep, 1 sinus was flushed with a panel of MGO concentrations ranging from 0.5 to 7.2 mg/mL alone and flushed with a panel of with 16.5% wt/vol MH enriched with MGO at the same range of concentrations (0.5-7.2 mg/mL; designated MH/MGO). Contralateral sinuses were flushed with saline control. Tissue morphology was assessed histologically and with scanning electron microscopy. Efficacy was tested by developing Staphylococcus aureus biofilms in sheep sinuses. Twice-daily irrigation for 5 days was commenced with either saline, MGO (0.5-3.6 mg/mL) alone, or MH/MGO (with 0.5-3.6 mg/mL MGO). Biofilm biomass was compared between the groups (n = 4) using LIVE/DEAD BacLight staining and confocal scanning laser microscopy.

RESULTS

The results of the safety assessment, for normal sinuses treated with MGO alone or with MH/MGO (≤1.8 mg/mL) showed normal pseudostratified epithelium and cilia structure; however, higher concentrations caused cilia denudation and squamous metaplasia. As for efficacy, when compared to saline flush, treatment with MH/MGO at 0.9 mg/mL (0.608 ± 0.110 vs 0.316 ± 0.197 μm(3) /μm(2) , respectively; p = 0.015) and 1.8 mg/mL (0.676 ± 0.079 vs 0.114 ± 0.033 μm(3) /μm(2) , respectively; p = 0.001) significantly reduced biofilm biomass.

CONCLUSION

Sinus irrigation with MH/MGO at MGO concentrations between 0.9 and 1.8 mg/mL is both safe to mucosa and efficacious against S. aureus biofilm. MH/MGO irrigation could represent a viable treatment option for recalcitrant CRS.