Unexpected crosslinking and diglycation as advanced glycation end-products from glyoxal

Glyoxal-derived advanced glycation end products (GO-AGEs) with UVB critically induce skin inflammaging: in vitro and in silico approaches

Advanced glycation end products (AGEs) have potential implications on several diseases including skin inflammation and aging. AGEs formation can be triggered by several factors such as UVB, glyoxal and methylglyoxal etc. However, little attention has been paid to glyoxal-derived AGEs (GO-AGEs) and UVB-induced skin inflammaging, with none have investigated together. This study aimed to investigate the possible role of GO-AGEs and UVB in skin inflammaging focusing on revealing its molecular mechanisms. The effects of GO-AGEs in the presence or absence of UVB were studied by using enzyme linked immunosorbent assay, western blotting, qPCR, flow cytometry and in silico approaches. In HaCaT cells, GO-AGEs in the presence of UVB irradiation (125 mJ/cm2) dramatically enhanced the release of different pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) with further activation of RAGE signaling pathways (NF-κB, COX 2, and IL- 1β) and increased oxidative stress also noticed in NHEK cells. In NHDF cells, extracellular matrix disruption noted via increasing matrix metalloproteinase release and decreasing collagen type 1 and SIRT1 expression. Besides that, the docking scores obtained from the molecular docking study support the above-mentioned results. This study strongly suggests the pivotal role of GO-AGEs in skin inflammaging and illuminates novel molecular pathways for searching most effective and updated anti-aging therapy.

Protective effect of thymoquinone on glycation of human myoglobin induced by d-ribose

Nonenzymatic glycation and the subsequent accumulation of advanced glycation end-products (AGEs) in proteins are factors underlying long-term pathogenesis in diabetes. The study of protein glycation is crucial for elucidating their relationship with diabetes mellitus and related disorders. This study explores the interaction between d-ribose and human myoglobin (HMb), as well as the protective effect of thymoquinone (TQ) on glycation. A time-dependent in-vitro glycation study was performed to investigate the mechanism of d-ribose-induced structural interference of HMb in the absence and presence of TQ. Spectroscopic and proteomic analysis indicated that the presence of TQ significantly reduced the total amount of AGEs while maintaining structural characteristics of HMb. 14 glycated sites on HMb were further identified via liquid chromatography-tandem mass spectrometry (LC-MS/MS) after incubation with d-ribose for 12 h, predominantly interacting with lysine residues. TQ was found to disrupt this interaction, reducing the glycated sites from 14 to 12 sites and the percentage of glycated peptides from 26.50 % to 12.97 %. Additionally, there was a significant decrease in the degree of glycation at the same sites. In summary, our findings suggest that TQ has the potential to act as an anti-glycation agent and provide a comprehensive understanding underlying the inhibition mechanism of glycation.

Glycated bovine serum albumin for use in feeding trials with animal models - In vitro methodology and characterization of a glycated substrate for modifying feed pellets

This study investigated different methods to produce N^ε-carboxymethyl-lysine (CML)-enriched bovine serum albumin (BSA) as alternatives to the classical approach using glyoxylic acid (GA) and sodium cyanoborohydride (NaBH₃CN) which results in toxic hydrogen cyanide (HCN). The reaction of GA (6 mmol/L) and NaBH₃CN (21 mmol/L) to produce CML remained the most effective with CML yields of 24-35%, followed by 13-24% using 300 mmol/L glyoxal (GO). GA promoted specific modification of lysine to CML, and fewer structural modifications of the BSA molecule compared with GO, as evidenced by fluorescence and proteomic analyses. GO promoted greater arginine modification compared with GA (76 vs 23%). Despite structural changes to BSA with GO, murine fecal clearance of CML was similar to literature values. Hence, BSA glycation with 300 mmol/L glyoxal is a suitable alternative to GA and NaBH₃CN for generating CML-enriched protein free of HCN, but a CML-only fortification model remains to be described.

Glyoxal-derived advanced glycation end-products, Nε-carboxymethyl-lysine, and glyoxal-derived lysine dimer induce apoptosis-related gene expression in hepatocytes

BACKGROUND

Advanced glycation end-products (AGEs) are proteins or lipids that have been glycated nonenzymatically by reducing sugars and their derivatives such as methylglyoxal. AGEs are known to cause inflammation, oxidative stress, and diseases in the human body. The toxic effects of AGEs and their structures on the origin of the protein being modified have not been well studied.

METHODS AND RESULTS

Five different types of AGEs: AGE1 (glucose-derived), AGE2 (glyceraldehyde-derived), AGE3 (glycolaldehyde-derived), AGE4 (methylglyoxal-derived), and AGE5 (glyoxal-derived); were used to examine the effect of AGEs on HepG2 cells. AGE2 through 5 increase the production of reactive oxygen species (ROS) in liver cells, an initiating factor for apoptosis. At the mRNA and protein levels, AGE5 treatment showed the greatest increase in expression of apoptosis-related factors such as Bax, p53, and Caspase 3. Quantitative analysis revealed that N^ε-carboxymethyl-lysine (CML) and glyoxal-lysine dimer (GOLD) were the important types of AGE5. The ROS generation and the expression of apoptotic factors both increased when cells were treated with CML and GOLD.

CONCLUSION

These findings suggest that AGE5 treatment activates the apoptosis-related gene expression in hapatocytes, with CML and GOLD as potential major AGE compounds.

Antiglycation Activity of Aucubin In Vitro and in Exogenous Methylglyoxal Injected Rats

Advanced glycation end products (AGEs) is a causative factor of various chronic diseases, including chronic kidney disease and atherosclerosis. AGE inhibitors, such as aminoguanidine and pyridoxamine, have the therapeutic activities for reversing the increase in AGEs burden. This study evaluated the inhibitory effects of aucubin on the formation of methylglyoxal (MGO)-modified AGEs in vitro. We also determined the potential activity of aucubin in reducing the AGEs burden in the kidney, blood vessel, heart, and retina of exogenously MGO-injected rats. Aucubin inhibited the formation of MGO-modified AGE-bovine serum albumin (IC₅₀ = 0.57 ± 0.04 mmol/L) and its cross-links to collagen (IC₅₀ = 0.55 ± 0.02 mmol/L) in a dose-dependent manner. In addition, aucubin directly trapped MGO (IC₅₀ = 0.22 ± 0.01 mmol/L) in vitro. In exogenous MGO-injected rats, aucubin suppressed the formation of circulating AGEs and its accumulation in various tissues. These activities of aucubin on the MGO-derived AGEs in vitro and in vivo showed its pharmacological potential for inhibiting AGEs-related various chronic diseases.

d-Ribose contributes to the glycation of serum protein

d-Ribose is active in glycation and rapidly produces advanced glycation end products, leading to cell death and to cognitive impairment in mice. Glycated serum protein (GSP) is a relatively short-term biomarker for glycemic control in diabetes mellitus. However, whether d-ribose is related to GSP is unclear. The aim of this work was to identify the contribution of d-ribose to GSP compared to d-glucose. Here, we showed that the yield of glycated human serum albumin with d-ribose was at least two-fold higher than that with d-glucose in a 2-week incubation. The glycation of human serum albumin (HSA) with d-ribose was much faster than that with d-glucose, as determined by monitoring changes in the fluorescent intensity of glycation products with time. Liquid chromatography-mass spectrometry/mass spectrometry revealed that 17 and 7 lysine residues on HSA were glycated in the presence of d-ribose and d-glucose, respectively, even when the concentration ratio [d-ribose]/[d-glucose] was 1/50. The intraperitoneal injection of d-ribose significantly increased the GSP levels in Sprague Dawley rats, but the injection of d-glucose did not. The level of d-ribose was more positively associated with GSP than the level of d-glucose in streptozotocin-treated rats. In diabetic patients, the levels of both d-ribose and d-glucose were closely related to the level of GSP. Together, these in vitro and in vivo findings indicated that d-ribose is an important contributor to the glycation of serum protein, compared to d-glucose. To assess GSP levels in diabetes mellitus, we should consider the contribution from d-ribose, which plays a nonnegligible role.

Ethyl Pyruvate Prevents Renal Damage Induced by Methylglyoxal-Derived Advanced Glycation End Products

The renal accumulation of advanced glycation end products (AGEs) is a causative factor of various renal diseases, including chronic kidney disease and diabetic nephropathy. AGE inhibitors, such as aminoguanidine and pyridoxamine, have the therapeutic activities for reversing the increase in renal AGE burden. This study evaluated the inhibitory effects of ethyl pyruvate (EP) on methylglyoxal- (MGO-) modified AGE cross-links with proteins in vitro. We also determined the potential activity of EP in reducing the renal AGE burden in exogenously MGO-injected rats. EP inhibited MGO-modified AGE-bovine serum albumin (BSA) cross-links to collagen (IC₅₀ = 0.19 ± 0.03 mM) in a dose-dependent manner, and its activity was stronger than aminoguanidine (IC₅₀ = 35.97 ± 0.85 mM). In addition, EP directly trapped MGO (IC₅₀ = 4.41 ± 0.08 mM) in vitro. In exogenous MGO-injected rats, EP suppressed AGE burden and MGO-induced oxidative injury in renal tissues. These activities of EP on the MGO-mediated AGEs cross-links with protein in vitro and in vivo showed its pharmacological potential for inhibiting AGE-induced renal diseases.

Identification and characterization of reaction products of 5-hydroxytryptamine with methylglyoxal and glyoxal by liquid chromatography/tandem mass spectrometry

RATIONALE

Methylglyoxal (MGO) and glyoxal (GO) are known to be at high levels in humans with diabetes. They react with amine-containing proteins and amino acids to form advanced glycation end products, however, their reactivity with other amine-containing metabolites, such as neurotransmitters, has not been explored. In this study, we aimed at studying the reactivity of 5-hydroxytryptamine (5-HT) with MGO or GO, which may alter the metabolic function of 5-HT.

METHODS

Stock solutions of 5-HT, MGO and GO were made in PBS buffer at pH 7.4 and 5-HT was incubated with MGO or GO at different concentrations. The reactions were also performed at physiological concentrations. The reaction mixtures collected at different incubation times were analyzed by direct ESI-HRMS, LC/MS and LC/MS/MS to detect/characterize the products. Agilent 6545 Q-TOF and Agilent 6420 triple quadrupole mass spectrometers were used for the study, and LC separations were performed on a C18 column.

RESULTS

The direct ESI-HRMS data of the reaction mixtures showed formation of three and four reaction products when 5-HT was reacted with MGO and GO, respectively. All the products showed dominant [M + H]⁺ ions. The products were characterized by HRMS, LC/MS/MS and literature reports on similar compounds. The products can easily be identified by LC/MS based on the accurate mass values together with retention time information. The MS/MS of the reaction products showed structure-indicative fragment ions.

CONCLUSIONS

5-HT reacts with one or two MGO/GO to form a set of reaction products. The reaction between 5-HT and MGO or GO was faster at higher concentrations of MGO/GO (<10 min), and the same products were found even at physiological concentrations (<48 h). The LC/MS/MS (SRM) method can be used to screen the reaction products when present at low levels.