Characterization of methylglyoxal induced advanced glycation end products and aggregates of human transferrin: Biophysical and microscopic insight

Inhibitory Potential of Carnosine and Aminoguanidine Towards Glycation and Fibrillation of Albumin: In-vitro and Simulation Studies

Carnosine is beta-alanyl histidine, a dipeptide, endogenously produced in our body by the carnosine synthase enzyme. It is an antioxidant, thus protecting from the deleterious effect of advanced glycation end products (AGEs). Similarly, aminoguanidine (AG) also prevents AGEs formation by scavenging free radicals such as reactive oxygen species (ROS)/reactive carbonyl species (RCS). This study used experimental and computational techniques to perform a comparative analysis of carnosine and AG and their inhibiting properties against glycated human serum albumin (HSA). Fructose-mediated glycation of albumin produced fluorescent structures, such as pentosidine and malondialdehyde. These AGEs were significantly reduced by carnosine and AG. At 20 mM, carnosine and AG quenches pentosidine fluorescence by 66% and 83%, respectively. A similar inhibitory effect was observed for malondialdehyde. Protein hydrophobicity and tryptophan fluorescence were restored in the presence of carnosine and AG. Aminoguanidine decreased fibrillation in HSA, while carnosine did not significantly affect aggregation/fibrillation. In addition, molecular docking study observed binding scores of -5.90 kcal/mol and -2.59 kcal/mol by HSA-aminoguanidine and HSA-carnosine complex, respectively. Aminoguanidine forms one conventional hydrogen bond with ARG A:10 and a salt bridge with ASP A:13, ASP A:259, ASP A:255, and ASP A:256 from the amine group. Similarly, carnosine forms only hydrogen bonds with GLU A:501 and GLN A:508 from the amine and hydroxy group. The root mean square deviation (RMSD) calculated from simulation studies was 1 nm upto 70 ns for the HSA-aminoguanidine complex and the spectrum of HSA-carnosine was significantly deviated and not stabilized. The superior inhibitory activity of aminoguanidine could be due to additional salt bridge bonding with albumin. Conclusively, aminoguanidine can be the better treatment choice for diabetes-associated neurological diseases.

Ropinirole reverses the effects of neuroinflammation, and cellular demise by downregulating the MARK4-NFκβ signaling system in Alzheimer's disease

Ropinirole (ROP) is a dopamine agonist that can cross the blood-brain barrier (BBB), which is crucial for drugs targeting neurological conditions like Alzheimer's disease (AD). The rationale for the current research is to investigate the potential of ROP as an inhibitor of Microtubule affinity regulating kinase 4 (MARK4)-NFκβ in neurodegenerative diseases, specifically AD. The interaction between ROP and MARK4-NFκβ holds significant promise in the realm of drug discovery and therapeutic interventions for diseases like AD. Molecular docking and biophysical characterization demonstrate how ROP effectively hinders MARK4 activity, offering detailed insights into their molecular interactions. The present research also investigates the biological aspect of MARK4 shows promise in treating AD, with neuroinflammation playing a crucial role in the disease's progression. Aβ42 and ROP were co-administered directly into the cells for the establishment of the AD model. We confirmed that ROP can inhibit the path of MARK4 activity, as evidenced by biophysical characterization, and can enhance the cell viability, lowers the expression of MARK4, decrease the rate of oxidative stress, and attenuate the expression of NFκβ, leading to reduced neuronal apoptosis in an in vitro-induced Aβ model. Overall, this research provides valuable mechanistic insights into the neuroprotective potential of ROP and its ability to target the MARK4-NFκβ pathway.

A Mechanism of Action of Metformin in the Brain: Prevention of Methylglyoxal-Induced Glutamatergic Impairment in Acute Hippocampal Slices

Metformin, a biguanide compound (N-1,1-dimethylbiguanide), is widely prescribed for diabetes mellitus type 2 (T2D) treatment. It also presents a plethora of properties, such as anti-oxidant, anti-inflammatory, anti-apoptosis, anti-tumorigenic, and anti-AGE formation activity. However, the precise mechanism of action of metformin in the central nervous system (CNS) needs to be clarified. Herein, we investigated the neuroprotective role of metformin in acute hippocampal slices exposed to methylglyoxal (MG), a highly reactive dicarbonyl compound and a key molecule in T2D developmental pathophysiology. Metformin protected acute hippocampal slices from MG-induced glutamatergic neurotoxicity and neuroinflammation by reducing IL-1β synthesis and secretion and RAGE protein expression. The drug also improved astrocyte function, particularly with regard to the glutamatergic system, increasing glutamate uptake. Moreover, we observed a direct effect of metformin on glutamate transporters, where the compound prevented glycation, by facilitating enzymatic phosphorylation close to Lys residues, suggesting a new neuroprotective role of metformin via PKC ζ in preventing dysfunction in glutamatergic system induced by MG.

Dissecting causal associations of type 2 diabetes with 111 types of ocular conditions: a Mendelian randomization study

Background

Despite the well-established findings of a higher incidence of retina-related eye diseases in patients with diabetes, there is less investigation into the causal relationship between diabetes and non-retinal eye conditions, such as age-related cataracts and glaucoma.

Methods

We performed Mendelian randomization (MR) analysis to examine the causal relationship between type 2 diabetes mellitus (T2DM) and 111 ocular diseases. We employed a set of 184 single nucleotide polymorphisms (SNPs) that reached genome-wide significance as instrumental variables (IVs). The primary analysis utilized the inverse variance-weighted (IVW) method, with MR-Egger and weighted median (WM) methods serving as supplementary analyses.

Results

The results revealed suggestive positive causal relationships between T2DM and various ocular conditions, including "Senile cataract" (OR= 1.07; 95% CI: 1.03, 1.11; P=7.77×10-4), "Glaucoma" (OR= 1.08; 95% CI: 1.02, 1.13; P=4.81×10-3), and "Disorders of optic nerve and visual pathways" (OR= 1.10; 95% CI: 0.99, 1.23; P=7.01×10-2).

Conclusion

Our evidence supports a causal relationship between T2DM and specific ocular disorders. This provides a basis for further research on the importance of T2DM management and prevention strategies in maintaining ocular health.

Inhibitory potential of N-acetylaspartate against protein glycation, AGEs formation and aggregation: Implication of brain osmolyte in glycation-related complications

Protein glycation and aggregation have a pivotal role in many diseases including diabetes and neurodegenerative disorders. N-acetyl aspartate (NAA), an osmolyte derived from L-aspartic acid, is one of the most abundant metabolites in the mammalian brain. Although NAA is supposed to be a substitute for a neuronal marker, its function is not fully elucidated. Herein, we have investigated the effect of NAA on glycation, AGEs formation and aggregation of irisin. AGE-specific fluorescence showed the strong inhibition of AGEs formation in the presence of NAA, demonstrating its anti-glycating property. The aggregates present in MG-modified irisin were also reduced by NAA, which was confirmed by Thioflavin T fluorescence and fluorescence microscopy. Further, for the explanation of the strong anti-glycating potential of NAA, the interaction between irisin and NAA was also examined. Interaction studies involving steady-state fluorescence and molecular docking demonstrated that hydrogen bonding and salt bridges by NAA stabilize the irisin. It was found that glycation-prone residues i.e., lysine and arginine are specifically involved in the interaction which might prevent them from getting modified during the process of glycation. This study for the first time reported the antiglycating potential of NAA which can be implicated in the therapeutic management of various glycation-related complications.

Characterization of advanced glycation end products and aggregates of irisin: Multispectroscopic and microscopic approaches

Glycation of proteins leading to the formation of advanced glycation end products (AGEs) has been demonstrated to contribute to the pathogenesis of several diseases. Irisin is a clinically significant protein, putatively involved in obesity, diabetes, and neurological disorders. This study aimed to monitor the methyl-glyoxal (MG) induced AGEs and aggregate formation of irisin, as a function of time, employing multispectroscopic and microscopic approaches. ANS fluorescence suggested a molten globule-like state on Day 6, followed by the formation of irisin AGEs adducts, as confirmed by AGE-specific fluorescence. Glycation of irisin led to aggregate formation, which was characterized by Thioflavin T fluorescence, CD spectroscopy, and microscopic studies. These aggregates were confirmed by exploiting fluorescence microscopy, confocal, and transmission electron microscopy. Molecular docking was performed to determine the crucial residues of irisin involved in irisin-MG interaction. Usually, MG is present in trace amounts as a metabolic by-product in the body, which is found to be elevated in diseased conditions viz. diabetes and Alzheimer's disease. This study characterized the AGEs and aggregates of clinically important protein, irisin; and since MG level has been found to be increased in various pathological conditions, this study provides a clinical perspective. There is a possibility that elevated MG concentrations might glycate irisin resulting in reduced irisin levels as reported in pathological conditions. However, further investigations are required to prove it.

Crowding modulates the glycation of plasma proteins: In vitro analysis of structural modifications to albumin and transferrin and identification of sites of modification

Protein modification occurs in biological milieus that are characterized by high concentrations of (macro)molecules (i.e. heterogeneous and packed environments). Recent data indicate that crowding can modulate the extent and rate of protein oxidation, however its effect on other post-translational modifications remains to be explored. In this work we hypothesized that crowding would affect the glycation of plasma proteins. Physiologically-relevant concentrations of albumin (35 mg mL^-1) and transferrin (2 mg mL^-1) were incubated with methylglyoxal and glyoxal (5 μM-5 mM), two α-oxoaldehyde metabolites that are elevated in the plasma of people with diabetes. Crowding was induced by adding dextran or ficoll polymers. Electrophoresis, electron microscopy, fluorescence spectroscopy and mass spectrometry were employed to investigate the structural consequences of glycation under crowded conditions. Our data demonstrate that crowding modulates the extent of formation of transferrin cross-links, and also the modification pathways in both albumin and transferrin. Arginine was the most susceptible residue to modification, with lysine and cysteine also affected. Loss of 0.48 and 7.28 arginine residues per protein molecule were determined on incubation with 500 μM methylglyoxal for albumin and transferrin, respectively. Crowding did not influence the extent of loss of arginine and lysine for either protein, but the sites of modification, detected by LC-MS, were different between dilute and crowded conditions. These data confirm the relevance of studying modification processes under conditions that closely mimic biological milieus. These data unveil additional factors that influence the pattern and extent of protein modification, and their structural consequences, in biological systems.

Sensitive Detection of Rosmarinic Acid Using Peptide-Modified Graphene Oxide Screen-Printed Carbon Electrode

Peptides have been used as components in biological analysis and fabrication of novel sensors due to several reasons, including well-known synthesis protocols, diverse structures, and acting as highly selective substrates for enzymes. Bio-conjugation strategies can provide a simple and efficient way to convert peptide-analyte interaction information into a measurable signal, which can be further used for the manufacture of new peptide-based biosensors. This paper describes the sensitive properties of a peptide-modified graphene oxide screen-printed carbon electrode for accurate and sensitive detection of a natural polyphenol antioxidant compound, namely rosmarinic acid. Glutaraldehyde was chosen as the cross-linking agent because it is able to bind nonspecifically to the peptide. We demonstrated that the strong interaction between the immobilized peptide on the surface of the sensor and rosmarinic acid favors the addition of rosmarinic acid on the surface of the electrode, leading to an efficient preconcentration that determines a high sensitivity of the sensor for the detection of rosmarinic acid. The experimental conditions were optimized using different pH values and different amounts of peptide to modify the sensor surface, so that its analytical performances were optimal for rosmarinic acid detection. By using cyclic voltammetry (CV) as a detection method, a very low detection limit (0.0966 μM) and a vast linearity domain, ranging from 0.1 µM to 3.20 µM, were obtained. The novelty of this work is the development of a novel peptide-based sensor with improved performance characteristics for the quantification of rosmarinic acid in cosmetic products of complex composition. The FTIR method was used to validate the voltammetric method results.

Advanced Glycation End Products and Their Effect on Vascular Complications in Type 2 Diabetes Mellitus

Diabetes is well established as a chronic disease with a high health burden due to mortality or morbidity from the final outcomes of vascular complications. An increased duration of hyperglycemia is associated with abnormal metabolism. Advanced glycation end products (AGEs) are nonenzymatic glycated forms of free amino acids that lead to abnormal crosslinking of extra-cellular and intracellular proteins by disrupting the normal structure. Furthermore, the interaction of AGEs and their receptors induces several pathways by promoting oxidative stress and inflammation. In this review, we discuss the role of AGEs in diabetic vascular complications, especially type 2 DM, based on recent clinical studies.

Binding Studies of Caffeic and p-Coumaric Acid with α-Amylase: Multispectroscopic and Computational Approaches Deciphering the Effect on Advanced Glycation End Products (AGEs)

Alpha-amylase (α-amylase) is a key player in the management of diabetes and its related complications. This study was intended to have an insight into the binding of caffeic acid and coumaric acid with α-amylase and analyze the effect of these compounds on the formation of advanced glycation end-products (AGEs). Fluorescence quenching studies suggested that both the compounds showed an appreciable binding affinity towards α-amylase. The evaluation of thermodynamic parameters (ΔH and ΔS) suggested that the α-amylase-caffeic/coumaric acid complex formation is driven by van der Waals force and hydrogen bonding, and thus complexation process is seemingly specific. Moreover, glycation and oxidation studies were also performed to explore the multitarget to manage diabetes complications. Caffeic and coumaric acid both inhibited fructosamine content and AGE fluorescence, suggesting their role in the inhibition of early and advanced glycation end-products (AGEs). However, the glycation inhibitory potential of caffeic acid was more in comparison to p-coumaric acid. This high antiglycative potential can be attributed to its additional –OH group and high antioxidant activity. There was a significant recovery of 84.5% in free thiol groups in the presence of caffeic acid, while coumaric attenuated the slow recovery of 29.4% of thiol groups. In vitro studies were further entrenched by in silico studies. Molecular docking studies revealed that caffeic acid formed six hydrogen bonds (Trp 59, Gln 63, Arg 195, Arg 195, Asp 197 and Asp 197) while coumaric acid formed four H-bonds with Trp 59, Gln 63, Arg 195 and Asp 300. Our studies highlighted the role of hydrogen bonding, and the ligands such as caffeic or coumaric acid could be exploited to design antidiabetic drugs.

Plasma glycation adducts and various RAGE isoforms are intricately associated with oxidative stress and inflammatory markers in type 2 diabetes patients with vascular complications

BACKGROUND

The secondary vascular complications in diabetes mellitus (DM) are contributed by acute as well as inflammatory responses which get activated due to interaction between glycation adducts and respective receptors.

AIM

The present work was performed to understand the relationship between Advanced glycation end products (AGEs)-receptor for advanced glycation end products (RAGE) interaction with oxidative stress and inflammation in vascular complications.

METHODS

For the present work we recruited 103 controls, 200 patients with type 2 DM, and 200 patients with Diabetic complications. Different Plasma glycation adducts (fructosamine, carbonyls, AGEs, β-amyloid content, free amino groups, and free thiol groups); RAGE isoforms, level of antioxidant such as glutathione, catalase activity, nitric oxide level, total antioxidant capacity, and superoxide dismutase activity, as well as oxidative markers, and expression of Nε-carboxymethyl-lysine (CML), different isoforms of RAGE, NF-κB, and inflammatory markers were analyzed.

RESULTS

Glycation adducts were higher in DM patients and more elevated in nephropathy patients where free amino groups and thiol groups lowered as compared to controls. sRAGE levels and expression were increased mainly in nephropathy. CML expression was higher in nephropathy patients. The antioxidant profile indicates a reduced level of different antioxidants while increased lipid peroxidation and intracellular ROS generation in DM and much higher in nephropathy patients. Expression of membrane RAGE, NF-κB, and inflammatory markers showed a remarkably increased level in DM patients with nephropathy.

CONCLUSION

This work provides the first evidence of four different RAGE isoforms in diabetes and in complications. The glycation via the activation of RAGE, oxidative stress, and resultant inflammation plays a crucial role in the development of diabetic complications.

Effect of pH on the structure and function of cyclin-dependent kinase 6

Cyclin-dependent kinase 6 (CDK6) is an important protein kinase that regulates cell growth, development, cell metabolism, inflammation, and apoptosis. Its overexpression is associated with reprogramming glucose metabolism through alternative pathways and apoptosis, which ultimately plays a significant role in cancer development. In the present study, we have investigated the structural and conformational changes in CDK6 at varying pH employing a multi-spectroscopic approach. Circular dichroism (CD) spectroscopy revealed at extremely acidic conditions (pH 2.0–4.0), the secondary structure of CDK6 got significantly disrupted, leading to aggregates formation. These aggregates were further characterized by employing Thioflavin T (ThT) fluorescence. No significant secondary structural changes were observed over the alkaline pH range (pH 7.0–11.0). Further, fluorescence and UV spectroscopy revealed that the tertiary structure of CDK6 was disrupted under extremely acidic conditions, with slight alteration occurring in mild acidic conditions. The tertiary structure remains intact over the entire alkaline range. Additionally, enzyme assay provided an insight into the functional aspect of CDK at varying pH; CDK6 activity was optimal in the pH range of 7.0–8.0. This study will provide a platform that provides newer insights into the pH-dependent dynamics and functional behavior of CDK6 in different CDK6 directed diseased conditions, viz. different types of cancers where changes in pH contribute to cancer development.

Bioflavonoid (Hesperidin) Restrains Protein Oxidation and Advanced Glycation End Product Formation by Targeting AGEs and Glycolytic Enzymes

Alpha-amylase (α-amylase) not long ago has acquire recognition as a possible drug target for the management of diabetes. Here, we have investigated the binding and enzyme activity of α-amylase by hesperidin; a naturally occurring flavanone having wide therapeutic potential. Hesperidin exerted an inhibitory influence on α-amylase activity with an IC50 value of 16.6 µM. Hesperidin shows a significant binding toward α-amylase with a binding constant (Ka) of the order of 104 M-1. The evaluation of thermodynamic parameters (∆H and ∆S) suggested that van der Waals force and hydrogen bonding drive seemingly specific hesperidin-α-amylase complex formation. Glycation and oxidation studies were performed using human serum albumin (HSA) as ideal protein. Hesperidin inhibited fructosamine content ≈40% at 50 µM and inhibited advanced glycation end products (AGEs) formation by 71.2% at the same concentration. Moreover, significant recovery was evident in free -SH groups and carbonyl content of HSA. Additionally, molecular docking also entrenched in vitro observations and provided an insight into the important residues (Trp58, Gln63, His101, Glu233, Asp300, and His305) at the heart of hesperidin-α-amylase interaction. This study delineates mechanistic insight of hesperidin-α-amylase interaction and provides a platform for use of hesperidin to treat AGEs directed diseases.

Insight into the In Vitro Antiglycation and In Vivo Antidiabetic Effects of Thiamine: Implications of Vitamin B1 in Controlling Diabetes

Hyperglycemia is considered to be a driving factor for advanced glycated end products (AGEs) formation. Inhibition of this process plays a vital role in reducing the problems of diabetes. This study aimed to explore the in vitro antiglycation and in vivo antidiabetic effect of thiamine. Human serum albumin (HSA) was used as a model protein to delineate the antiglycation potential of thiamine. Fructosamine levels were low in the presence of thiamine, implying the inhibition of early stages of glycation by thiamine. Furthermore, HSA-glucose assays depict the inhibition of post-Amadori products by thiamine. CD spectroscopy suggested fewer alterations in the secondary structure in the presence of thiamine. It was found that the administration of thiamine to diabetic rats leads to an increase in hexokinase activity and increased insulin secretion coupled with glycolysis utilization of glucose. Moreover, the activity of glucose-6-phosphatase and fructose- 1-6-phosphatase (increased in the liver and kidney of diabetic rats) is restored to near-normal levels upon thiamine administration. Histopathological studies also advocated that thiamine supplementation decreases the pathological abnormalities associated with diabetes in the liver and kidney. This study provides a rationale that vitamins can be implicated in controlling diabetes.

Trehalose Restrains the Fibril Load towards α-Lactalbumin Aggregation and Halts Fibrillation in a Concentration-Dependent Manner

Protein aggregation and misfolding are some of the most challenging obstacles, customarily studied for their association with amyloid pathologies. The mechanism of amyloid fibrillation development is a dynamic phenomenon involving various factors such as the intrinsic properties of protein and the physical and chemical environmental conditions. The purpose of this study was to see the thermal aggregation profile of alpha-lactalbumin (α-LA) and to delineate the effect of trehalose on its aggregation profile. α-LA was subjected to thermal aggregation at high concentrations. UV-Vis spectroscopy, a turbidity assay, intrinsic fluorescence, Rayleigh scattering and a thioflavin T (ThT) assay explained the steady outcomes that 1 M trehalose repressed α-LA aggregation in the most effective way followed by 0.75 M and 0.5 M and to a significantly lesser degree by 0.25 M. Multi spectroscopic obser Sania Bashir ations were further entrenched by microscopy. Transmission electron microscopy confirmed that in the presence of its higher concentration, trehalose hinders fibril development in α-LA. In vitro studies were further validated by in silico studies. Molecular docking analysis indicated that trehalose occupied the binding pocket cavity of α-LA and offered several significant interactions, including H-bonds with important residues. This study provides a platform for trehalose in the therapeutic management of protein aggregation-related diseases.

Evaluation of Binding of Rosmarinic Acid with Human Transferrin and Its Impact on the Protein Structure: Targeting Polyphenolic Acid-Induced Protection of Neurodegenerative Disorders

Rosmarinic acid (RA) is a natural compound that is gaining wide popularity owing to its broad-spectrum biological activities. RA is known for its wide range of medicinal properties and therapeutic applications in a vast range of neurodegenerative disorders thus making it a vital natural compound. Human transferrin (hTf) is a clinically significant protein that plays a pivotal role in maintaining iron homeostasis. The importance of studies pertaining to hTf is attributable to the pivotal role of iron deposition in CNS in neurodegenerative disorders. The study was intended to have an insight into the interaction between RA and hTf employing multispectroscopic approach, molecular docking, and molecular dynamic simulation studies. Fluorescence quenching studies revealed that RA shows an excellent binding affinity to hTf with a binding constant (K) of 107 M-1 and is guided by static mode of quenching. Isothermal titration calorimetry (ITC) further validated the spontaneous nature of binding. The estimation of enthalpy change (∆H) and entropy change (∆S) suggested that the RA-hTf complex formation is driven by hydrogen bonding, thereby making this process seemingly specific. Further, Fourier transform infrared (FTIR) and circular dichroism (CD) spectra suggested that RA induces conformational and structural changes in hTf. Additionally, molecular dynamics (MD) studies were carried out to investigate the stability of the hTf and hTf-RA system and suggested that binding of RA induces structural alteration in hTf with free hTf being more stable. This study provides a rationale to use RA in drug development against neurodegenerative disorders by designing novel functional foods containing RA.

Influence of Ascorbic Acid on the Structure and Function of Alpha-2- macroglobulin: Investigations using Spectroscopic and Thermodynamic Techniques

Background:

Ascorbic acid is a classic dietary antioxidant which plays an important role in the body of human beings. It is commonly found in various foods as well as taken as dietary supplement.

Objective:

The plasma ascorbic acid concentration may range from low, as in chronic or acute oxidative stress to high if delivered intravenously during cancer treatment. Sheep alpha-2- macroglobulin (α2M), a human α2M homologue is a large tetrameric glycoprotein of 630 kDa with antiproteinase activity, found in sheep’s blood.

Methods:

In the present study, the interaction of ascorbic acid with alpha-2-macroglobulin was explored in the presence of visible light by utilizing various spectroscopic techniques and isothermal titration calorimetry (ITC).

Results:

UV-vis and fluorescence spectroscopy suggests the formation of a complex between ascorbic acid and α2M apparent by increased absorbance and decreased fluorescence. Secondary structural changes in the α2M were investigated by CD and FT-IR spectroscopy. Our findings suggest the induction of subtle conformational changes in α2M induced by ascorbic acid. Thermodynamics signatures of ascorbic acid and α2M interaction indicate that the binding is an enthalpy-driven process.

Conclusion:

It is possible that ascorbic acid binds and compromises antiproteinase activity of α2M by inducing changes in the secondary structure of the protein.