Methylglyoxal produces more changes in biochemical and biophysical properties of human IgG under high glucose compared to normal glucose level

Elucidating the Antiglycation Effect of Creatine on Methylglyoxal-Induced Carbonyl Stress In Vitro

Advanced glycation end products (AGEs) with multiple structures are formed at the sites where carbonyl groups of reducing sugars bind to free amino groups of proteins through the Maillard reaction. In recent years, it has been highlighted that the accumulation of AGEs, which are generated when carbonyl compounds produced in the process of sugar metabolism react with proteins, is involved in various diseases. Creatine is a biocomponent that is homeostatically present throughout the body and is known to react nonenzymatically with α-dicarbonyl compounds. This study evaluated the antiglycation potential of creatine against methylglyoxal (MGO), a glucose metabolite that induces carbonyl stress with formation of AGEs in vitro. Further, to elucidate the mechanism of the cytoprotective action of creatine, its effect on the accumulation of carbonyl proteins in the cells and the MGO-induced cellular damage were investigated using neuroblastoma cells. The results revealed that creatine significantly inhibits protein carbonylation by directly reacting with MGO, and creatine added to the culture medium suppressed MGO-derived carbonylation of intracellular proteins and exerted a protective effect on MGO-induced cytotoxicity. These findings suggest that endogenous and supplemented creatine may contribute to the attenuation of carbonyl stress in vivo.

Monosaccharide-Mediated Glycoxidation of Bovine Serum Albumin and Its Prevention by Nigella sativa

The substantial rise in metabolic illnesses that has occurred in both developed and developing countries over the last three decades has been linked to an increase in sugar-added foods and sweetened beverage intake. The significance of advanced glycation end products (AGEs) in the pathophysiology of metabolic diseases related to modern nutrition is an emerging issue. Spices and herbs can potentially be potent AGE production inhibitors due to their high polyphenol content. The inhibitory activity of an aqueous extract of Nigella sativa seeds (NS) on glucose- and fructose-mediated glycation of bovine serum albumin (BSA) was investigated. The glycation of proteins and its prevention using NS were assessed using spectrophotometry, spectrofluorometrics, and electrophoretic techniques. Additionally, the NBT assay, DNPH assay, Ellman assay, and thioflavin T assay were used to observe the biochemical alterations caused by glycated BSA. Molecular docking was employed to dock the BSA active site residues with inhibitors. Our data showed that NS protects against glucose- and fructose-mediated glycation and aggregation in vitro by inhibiting the formation of fructosamine, protein carbonyl content, free sulfhydryl groups, and fluorescent AGEs. Furthermore, NS also inhibited the production of β-cross-amyloid aggregates in proteins. It was interesting to note that the inhibition was found to be significantly higher in the Glu-BSA system, although the glycation product formed in the Fru-BSA system was higher compared to the Glu-induced protein system. It can be concluded that, by inhibiting AGE production, oxidation, and aggregation of the protein, NS may be an effective antiglycation drug for the prevention of diabetes complications.

Non-enzymatic glycation and aggregation of camel immunoglobulins induce breast cancer cell proliferation

Glycation of biomolecules results in the formation of advanced glycation end products (AGEs). Immunoglobulin G (IgG) has been implicated in the progression of various diseases, including diabetes and cancer. This study purified three IgG subclasses (IgG1, IgG2, and IgG3) from Camelus dromedarius colostrum using ammonium sulfate fractionation and chromatographic procedures. SDS-PAGE was performed to confirm the purity and molecular weight of the IgG subclasses. Several biochemical and biophysical techniques were employed to study the effect of glycation on camel IgG using methylglyoxal (MGO), a dicarbonyl sugar. Early glycation measurement showed an increase in the fructosamine content by ~four-fold in IgG2, ~two-fold in IgG3, and a slight rise in IgG1. AGEs were observed in all classes of IgGs with maximum hyperchromicity (96.6%) in IgG2. Furthermore, glycation-induced oxidation of IgGs led to an increase in carbonyl content and loss of -SH groups. Among subclass, IgG2 showed the highest (39.7%) increase in carbonyl content accompanied by 82.5% decrease in -SH groups. Far UV-CD analysis illustrated perturbation of β-sheet structure during glycation reaction with MGO. Moreover, glycation of IgG proceeds to various conformational states like aggregation and increased hydrophobicity. In addition, the cytotoxicity assay (MTT) illustrated the proliferation of breast cancer cells (MCF-7) with IgG2 treatment.

Behavioral and Proteomic Studies Reveal Methylglyoxal Activate Pathways Associated with Alzheimer's Disease

Diabetes is one of the major risk factors for Alzheimer's disease (AD) development. The role of elevated levels of glucose, methylglyoxal (MGO), and advanced glycation end products (AGEs) in the pathogenesis of AD is not well understood. In this pursuit, we studied the role of methylglyoxal in the pathogenesis of AD in rat models. The elevated plus-maze (EPM) behavioral study indicated that MGO induces anxiety. Treatment of telmisartan (RAGE expression inhibitor) and aminoguanidine (MGO quencher) attenuated MGO induced anxiety. Further, hippocampal proteomics demonstrated that MGO treated rats differentially regulate proteins involved in calcium homeostasis, mitochondrial functioning, and apoptosis, which may affect neurotransmission and neuronal plasticity. The hippocampal tau phosphorylation level was increased in MGO treated rats, which was reduced in the presence of aminoguanidine and telmisartan. The plasma fructosamine level was increased upon MGO treatment. Hippocampal histochemistry showed vascular degeneration and neuronal loss upon MGO treatment. This study provides mechanistic insight into the role of MGO in the diabetes-associated development of AD.

Fermented Supernatants of Lactobacillus plantarum GKM3 and Bifidobacterium lactis GKK2 Protect against Protein Glycation and Inhibit Glycated Protein Ligation

With age, protein glycation in organisms increases continuously. Evidence from many studies shows that the accumulation of glycated protein is highly correlated with biological aging and the development of aging-related diseases, so developing a dietary agent to attenuate protein glycation is very meaningful. Previous studies have indicated that lactic acid bacteria-fermented products have diverse biological activities especially in anti-aging, so this study was aimed to investigate the inhibitory effect of the fermented supernatants of Lactobacillus plantarum GKM3 (GKM3) and Bifidobacterium lactis GKK2 (GKK2) on protein glycation. The results show that GKM3- and GKK2-fermented supernatants can significantly inhibit protein glycation by capturing a glycation agent (methylglyoxal) and/or protecting functional groups in protein against methylglyoxal-induced responses. GKM3- and GKK2-fermented supernatants can also significantly inhibit the binding of glycated proteins to the receptor for advanced glycation end products (RAGE). In conclusion, lactic acid bacteria fermentation products have the potential to attenuate biological aging by inhibiting protein glycation.

Non-inhibitory effects of the potent antioxidant C-phycocyanin from Plectonema sp. on the in vitro glycation reaction

When glucose and Amadori products are auto-oxidized, glycation occurs, resulting in the formation of early (Amadori) and late advanced glycation end products (AGEs), as well as free radicals. Glycation and an increase in free radical activity induce diabetic complications. Antioxidant and antiglycation compounds may aid in the prevention of oxidation and glycation. The goal of this study was to assess the antiglycation and antioxidant capacity of C-phycocyanin (C-PC) derived from Plectonema sp. The DPPH (1, 1-diphenyl-2-picrylhydrazyl), nitric oxide, hydroxyl radical scavenging activities and ferric ions reducing antioxidant power (FRAP) assays were used to assess antioxidant activity, while an in vitro bovine serum albumin-methyl glyoxal glycation (BSA-MG) model was used to assess glycation inhibitory potential. Glycation inhibition was measured using a variety of spectroscopic and biochemical parameters, including UV-visible & fluorescence spectroscopy, ketoamine, carbonyl and hydroxymethyl furfural content, as well as free lysine & free arginine estimations. In vitro, C-PC exhibited dose-dependent potent antioxidant activity, but lacked significant antiglycation potential. As a result, it is recommended that further studies be conducted to evaluate the antiglycation potential of C-PC.

Glyoxal induced glycative insult suffered by immunoglobulin G and fibrinogen proteins: A comparative physicochemical characterization to reveal structural perturbations

Glycation of proteins results in structural alteration, functional deprivation, and generation of advanced glycation end products (AGEs). Reactive oxygen species (ROS) that are generated during in vivo autoxidation of glucose induces glycoxidation of intermediate glycation-adducts, which in turn give rise to aldehyde and/or ketone groups containing dicarbonyls or reactive carbonyl species (RCS). RCS further reacts non-enzymatically and starts the glycation-oxidation vicious cycle, thus exacerbating oxidative, carbonyl, and glycative stress in the physiological system. Glyoxal (GO), a reactive dicarbonyl that generates during glycoxidation and lipid peroxidation, contributes to glycation. This in vitro physicochemical characterization study focuses on GO-induced glycoxidative damage suffered by immunoglobulin G (IgG) and fibrinogen proteins. The structural alterations were analyzed by UV-vis, fluorescence, circular dichroism, and Fourier transform infrared (FT-IR) spectroscopy. Ketoamines, protein carbonyls, hydroxymethylfurfural (HMF), free lysine, free arginine, carboxymethyllysine (CML), and protein aggregation were also quantified. Structural perturbations, increased concentration of ketoamines, protein carbonyls, HMF, and malondialdehyde (MDA) were reported in glycated proteins. The experiment results also validate increased oxidative stress and AGEs formation i.e. IgG-AGEs and Fib-AGEs. Thus, we can conclude that AGEs formation during GO-mediated glycation of IgG and fibrinogen could hamper normal physiology and might play a significant role in the pathogenesis of diabetes-associated secondary complications.

The Neoepitopes on Methylglyoxal- (MG-) Glycated Fibrinogen Generate Autoimmune Response: Its Role in Diabetes, Atherosclerosis, and Diabetic Atherosclerosis Subjects

OBJECTIVES

In diabetes mellitus, hyperglycemia-mediated nonenzymatic glycosylation of fibrinogen protein plays a crucial role in the pathogenesis of micro- and macrovascular complications especially atherosclerosis via the generation of advanced glycation end products (AGEs). Methylglyoxal (MG) induces glycation of fibrinogen, resulting in structural alterations that lead to autoimmune response via the generation of neoepitopes on protein molecules. The present study was designed to probe the prevalence of autoantibodies against MG-glycated fibrinogen (MG-Fib) in type 2 diabetes mellitus (T2DM), atherosclerosis (ATH), and diabetic atherosclerosis (T2DM-ATH) patients. Design and Methods. The binding affinity of autoantibodies in patients' sera (T2DM, n = 100; ATH, n = 100; and T2DM-ATH, n = 100) and isolated immunoglobulin G (IgG) against native fibrinogen (N-Fib) and MG-Fib to healthy subjects (HS, n = 50) was accessed by direct binding ELISA. The results of direct binding were further validated by competitive/inhibition ELISA. Moreover, AGE detection, ketoamines, protein carbonyls, hydroxymethylfurfural (HMF), thiobarbituric acid reactive substances (TBARS), and carboxymethyllysine (CML) concentrations in patients' sera were also determined. Furthermore, free lysine and free arginine residues were also estimated.

RESULTS

The high binding affinity was observed in 54% of T2DM, 33% of ATH, and 65% of T2DM-ATH patients' samples with respect to healthy subjects against MG-Fib antigen in comparison to N-Fib (p < 0.05 to p < 0.0001). HS sera showed nonsignificant binding (p > 0.05) with N-Fib and MG-Fib. Other biochemical parameters were also found to be significant (p < 0.05) in the patient groups with respect to the HS group.

CONCLUSIONS

These findings in the future might pave a way to authenticate fibrinogen as a biomarker for the early detection of diabetes-associated micro- and macrovascular complications.

Physico-chemical Changes Induced in the Serum Proteins Immunoglobulin G and Fibrinogen Mediated by Methylglyoxal

BACKGROUND

Non-enzymatic glycation of proteins plays a significant role in the pathogenesis of secondary diabetic complications via the formation of advanced glycation end products (AGEs) and increased oxidative stress. Methylglyoxal (MG), a highly reactive dicarbonyl of class α-oxoaldehyde that generates during glucose oxidation and lipid peroxidation, contributes to glycation.

OBJECTIVE

This comparative study focuses on methylglyoxal induced glycoxidative damage suffered by immunoglobulin G (IgG) and fibrinogen, and to unveil implication of structural modification of serum proteins in diabetes-associated secondary complications.

METHODS

The methylglyoxal induced structural alterations in IgG and fibrinogen were analyzed by UVvis, fluorescence, circular dichroism and Fourier transform infrared (FT-IR) spectroscopy. Ketoamine moieties, carbonyl contents, 5-Hydroxymethylfurfural (HMF) and malondyaldehyde were also quantified. Free lysine and arginine estimation, detection of non-fluorogenic carboxymethyllysine (CML) and fibril formation were confirmed by thioflavin T (ThT) assay.

RESULTS

Structural alterations, increased carbonyl contents and ketoamines were reported in MG glycated IgG and fibrinogen against their native analogues.

CONCLUSION

The experiment results validate structural modifications, increased oxidative stress and AGEs formation. Thus, we can conclude that IgG-AGEs and Fib-AGEs formed during MG induced glycation of IgG and fibrinogen could impede normal physiology and might initiates secondary complications in diabetic patients.

Methylglyoxal mediated glycation leads to neo-epitopes generation in fibrinogen: Role in the induction of adaptive immune response

In diabetes mellitus, hyperglycemia mediated non-enzymatic glycosylation of proteins results in the pathogenesis of diabetes-associated secondary complications via the generation of advanced glycation end products (AGEs). The focus of this study is to reveal the immunological aspects of methylglyoxal (MG) mediated glycation of fibrinogen protein. The induced immunogenicity of modified fibrinogen is analyzed by direct binding and inhibition ELISA. Direct binding ELISA confirmed that MG glycated fibrinogen (MG-Fib) is highly immunogenic and induces a high titer of antibodies in comparison to its native analog. Cross-reactivity and antigen-binding specificity of induced antibodies were confirmed by inhibition ELISA. The enhanced affinity of immunoglobulin G (IgG) from immunized rabbits' sera and MG glycated fibrinogen is probably the aftermath of neo-epitopes generation in the native structure of protein upon modification. Thus, we deduce that under the glycative stress, MG-mediated structural alterations in fibrinogen could induce the generation of antibodies which might serve as a potential biomarker in diabetes mellitus and its associated secondary disorders.

An in vitro approach to unveil the structural alterations in d-ribose induced glycated fibrinogen

Plasma proteins persistently bear non-enzymatic post-translational modifications (NEPTM) that proceeds with nucleophilic addition between free amino groups of proteins, and carbonyl group of reducing sugars. Glycation, a prevalent NEPTM rush by the high availability of reducing sugars results in the generation of advanced glycation end products (AGEs). Plasma proteins are more vulnerable to glycation because of the presence of multiple glycation sites and are widely studied. However, fibrinogen glycation is less studied. Therefore, it was designed as an in vitro study to elucidate d-ribose mediated glycative damage suffered by fibrinogen protein at secondary and tertiary structure level. The glycation induced structural alterations were analyzed by UV-vis, fluorescence, circular dichroism, scanning electron microcopy and Fourier transform infrared spectroscopy. Glycation induced protein aggregation and fibrils formation was confirmed by thioflavin T and congo red assay. Moreover, molecular docking study was performed to further validate physicochemical characterization. Structural alterations, increased ketoamines, protein carbonyls and HMF contents were reported in d-ribose glycated fibrinogen against their native analogues. The results validate structural perturbations, increased glycoxidative stress and AGEs formation, which might influence normal function of fibrinogen especially blood coagulation cascade. Thus, we can conclude that under diabetes induced hyperglycemic state in physiological systems, d-ribose induced fibrinogen glycation might play a crucial role in the onset of micro- and macro-vascular complications, thereby worsen the diabetes associated secondary disorders. Moreover, this in vitro study might pave a path to choose fibrinogen as a future biomarker for the early detection of diabetes mediated vascular complications.Communicated by Ramaswamy H. Sarma.

Preparation of Aptamer Responsive DNA Functionalized Hydrogels for the Sensitive Detection of α-Fetoprotein Using SERS Method

Hepatocellular carcinoma (HCC), which is one of the three major cancers, has attracted growing attention due to its high mortality, health care cost, and circumscribed therapeutic methods. Hence, the development of a fast, accurate, and flexible method to detect α-fetoprotein (AFP), the specific marker of HCC, is significant for diagnosis and treatment of cancer. Here, we constructed a novel SERS biosensing platform combining the target-responsive DNA hydrogel for the sensitive detection of AFP. The linker strand in DNA hydrogel is an aptamer that can specifically recognize AFP and accurately control the release of immunoglobulin G (IgG) encapsulated in hydrogel. In the presence of AFP, the hydrogels were disentangled and the IgG was released. Thereafter, the released IgG was captured by SERS probes and biofunctional magnetic beads through formation of sandwich-like structures, resulting in the signal of Raman tags decreasing in the supernatant after magnetic separation. Due to the ultrahigh sensitivity of the SERS biosensor, the proposed method has a wide detection linear range (50 pg/mL to 0.5 μg/mL) and a detection limit down to 50 pg/mL. Moreover, the sequence of the linker strand in the DNA hydrogel can be specifically encoded into a new aptamer that responds to other cancer markers. This convenient and inexpensive detection method provides a new strategy for the detection of tumor markers.

Carnosine Prevents Different Structural Damages Induced by Methylglyoxal in Lens Crystallins

The elevated lenticular level of methylglyoxal (MGO) in diabetic patients is an important risk factor for the development of age-related (senile) cataract disorders. Carnosine (β-alanyl L-histidine), a natural antioxidant dipeptide product, has been indicated to prevent the development of cataract diseases. Therefore, it is possible that the anti-cataract activity of this naturally occurring compound is mediated by its anti-glycoxidation effect. In this study, the eye lens proteins were treated with MGO in the presence of carnosine. Then, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis and several spectroscopic evaluations were used with the aim to investigate the possible inhibitory activity of carnosine against the MGO-induced structural damages of eye lens proteins. Our results indicated that MGO causes a substantial structural alteration in the lens proteins. The results of fluorescence assessments also suggested that MGO-induced structural changes were accompanied with the formation of additional chromophores in the protein structure. Also, in the presence of carnosine, a notable reduction in the protein structural damages was observed. Our results may highlight an important protective role of carnosine against MGO-induced structural insults in the lens proteins. This study suggests carnosine supplementation as a possible preventive strategy against development of the diabetic cataracts in human.

A Bowman-Birk Inhibitor from the Seeds of Luetzelburgia auriculata Inhibits Staphylococcus aureus Growth by Promoting Severe Cell Membrane Damage

Staphylococcus aureus is a multidrug-resistant bacterium responsible for several cases of hospital-acquired infections, which constitute a global public health problem. The introduction of new healthcare strategies and/or the discovery of molecules capable of inhibiting the growth or killing S. aureus would have a huge impact on the treatment of S. aureus-mediated diseases. Herein, a Bowman-Birk protease inhibitor ( LzaBBI), with strong in vitro antibacterial activity against S. aureus, was purified to homogeneity from Luetzelburgia auriculata seeds. LzaBBI in its native form is a 14.3 kDa protein and has a pI of 4.54, and its NH₂-terminal sequence has high identity with other Bowman-Birk inhibitors. LzaBBI showed a mixed-type inhibitory activity against both trypsin and chymotrypsin, respectively, and it remained stable after both boiling at 98 °C for 120 min and incubation at various pHs. Scanning electron microscopy revealed that LzaBBI disrupted the S. aureus membrane integrity, leading to bacterial death. This study suggests that LzaBBI is a powerful candidate for developing a new antimicrobial to overcome drug resistance toward reducing hospital-acquired infections caused by S. aureus.