Study of pyridoxamine against glycation and reactive oxygen species production in human serum albumin as model protein: An in vitro & ex vivo approach

Increased therapeutic effect of nanotized silibinin against glycation and diabetes: An in vitro and in silico-based approach

BACKGROUND

The global prevalence of diabetes has increased sharply, with the number of cases expected to rise from 424.9 million in 2017 to 628.6 million by 2045. Flavonoids are plant derived molecules with well-established antioxidant potential in addition to other therapeutic properties. Silibinin is a naturally occurring flavonoid with antioxidant and antidiabetic properties. However, its rapid metabolism and low bioavailability limit its therapeutic effects.

AIMS & OBJECTIVES

In this study, we have synthesized the nanoformulation of silibinin and compared its antiglycating and antidiabetic potential with the soluble form.

METHODOLOGY

The inhibitory effect was tested on carbohydrate-hydrolyzing enzymes as well as glycation of human serum albumin (HSA). The structural and biochemical changes in HSA were assessed by spectroscopic analyses and different assays.

KEY FINDINGS

The nanoforms were found to be better inhibitors of α-amylase and α-glucosidase compared to the bulk forms. Glycation of HSA in the presence of nano-silibinin resulted in the formation of lower level of early and advanced glycation products. This was also confirmed by spectroscopic studies and by estimating protein oxidation and free lysine residues. Molecular docking studies further supported the experimental outcomes. These results indicate that the nano form has significantly stronger antidiabetic and antiglycating effects than the bulk form. Nano-silibinin could therefore be recommended as a dietary supplement for diabetics to help control glycation and other associated complications.

4-Chloro-orthophenylenediamine alters DNA integrity and affects cell survival: inferences from a computational, biophysical/biochemical, microscopic and cell-based study

The deleterious impact of toxic constituents of hair dyes over the human health has gained immense attention in the recent past. Their oncogenicity, mutagenicity, role in protein modification, impact on cellular metabolism has been documented. There is little information on the mechanism of reactivity of hair dye components with the nucleic acids and its implications. This work, therefore, uses computational, biophysical/biochemical, microscopic and cell-based study to analyze the interaction of monocyclic aromatic amine and a hair dye component, 4-chloro-orthophenylenediamine (4-Cl-OPD) with the DNA, its impact on DNA structure and cell survival. The results suggest that 4-Cl-OPD binds with the DNA in minor groove of the duplex involving three base pairs preferentially the G-C residues, induces strand breaks and makes DNA thermally labile through loss of hydrogen bonding/base unstacking. 4-Cl-OPD causes fragmentation of DNA, reduction in size of the molecule, alters B-DNA conformation and disrupts its secondary structure. The modified DNA gives fragmented appearance, shows broken strands and aggregation in ultra-structural analysis. 4-Cl-OPD induces ROS generation in lymphocytes, increases the comet's average tail length and reduces the viability of lymphocytes. This study forms a base for establishing the direct toxicity of 4-Cl-OPD at the molecular and cellular level through direct production of superoxide radicalCommunicated by Ramaswamy H. Sarma.

4-Chloro-1,2-phenylenediamine induced structural perturbation and genotoxic aggregation in human serum albumin

4-Chloro-1,2-phenylenediamine (4-Cl-OPD) is a halogenated aromatic diamine used as a precursor in permanent hair color production. Despite its well-documented mutagenic and carcinogenic effects in various in vitro and in vivo models, its role in fibrillar aggregate formation and their genotoxic effect in therapeutic proteins has received less attention. The significance of human serum albumin (HSA) arises from its involvement in bio-regulatory and transport processes. HSA misfolding and aggregation are responsible for some of the most frequent neurodegenerative disorders. We used various complementary approaches to track the formation of amyloid fibrils and their genotoxic effect. Molecular dynamics study demonstrated the complex stability. The impact of 4-Cl-OPD on the structural dynamics of HSA was confirmed by Raman spectroscopy, X-ray diffraction, HPLC and SDS-PAGE. Fibrilllar aggregates were investigated using Congo red assay, DLS, and SEM. The genotoxic nature of 4-Cl-OPD was confirmed using plasmid nicking assay and DAPI staining, which revealed DNA damage and cell apoptosis. 4-Cl-OPD provides a model system for studying fibrillar aggregation and their genotoxic potential in the current investigation. Future studies should investigate the inhibition of the aggregation/fibrillation process, which may yield valuable clinical insights.

AGE/RAGE in diabetic kidney disease and ageing kidney

Diabetic kidney disease (DKD) is the primary cause of chronic kidney disease that inevitably progress to end-stage kidney disease. Intervention strategies such as blood glucose control is effective for preventing DKD, but many patients with DKD still reach end-stage kidney disease. Although comprehensive mechanisms shed light on the progression of DKD, the most compelling evidence has highlighted that hyperglycemia-related advanced glycation end products (AGEs) formation plays a central role in the pathogenesis of DKD. Pathologically, accumulation of AGEs-mediated receptor for AGEs (RAGE) triggers oxidative stress and inflammation, which is the major deleterious effect of AGEs in host and intestinal microenvironment of diabetic and ageing conditions. The activation of AGEs-mediated RAGE could evoke nicotinamide adenine dinucleotide phosphate oxidase-induced reactive oxygen and nitrogen species production and subsequently give rise to oxidative stress in DKD and ageing kidney. Therefore, targeting RAGE with its ligands mediated oxidative stress and chronic inflammation is considered as an additional intervention strategy for DKD and ageing kidney. In this review, we summarize AGEs/RAGE-mediated oxidative stress and inflammation signaling pathways in DKD and ageing kidney, discussing opportunities and challenges of targeting at AGEs/RAGE-induced oxidative stress that could hold the promising potential approach for improving DKD and ageing kidney.

Hydroxyl radical induced structural perturbations make insulin highly immunogenic and generate an auto-immune response in type 2 diabetes mellitus

Reactive oxygen species (ROS) cause oxidative damage to proteins and generate deleterious by-products which induce a breakdown of immune tolerance and produce antibodies against host macromolecules with implication in human diseases. This study characterizes the hydroxyl radical (OH) modifications of insulin, evaluates its cytotoxicity and immunogenicity, and probes its role in type 2 diabetes (T2DM) autoimmunity. The results demonstrate susceptibility of insulin to modifications induced by OH, causing exposure of its chromophoric aromatic amino acid residues, quenching of tyrosine fluorescence intensity, loss of α-helix and gain in β content. Modification causes re-arrangement of native interactions of the aromatic residues in insulin. It enhanced the carbonyl content in insulin, exposed its hydrophobic patches and generated non-fibrillar, amorphous type of aggregates that are cytotoxic in nature. Native insulin induced low titre antibodies in immunized rabbits, whereas OH modified insulin generated a strong immune response. Competitive ELISA studies showed high specificity of antibodies generated against OH modified insulin towards the modified protein. Cross reaction studies showed the presence of common antigenic determinants on various oxidised proteins. Since T2DM patients show increased ROS production, oxidation of insulin is expected to occur, which might amplify autoimmune reactions against insulin. True to the assumption, direct binding ELISA showed the presence of anti-OH insulin circulating antibodies in T2DM patients which are specific for the oxidized insulin. In conclusion, insulin loses structural integrity to OH, forms cytotoxic amorphous aggregates, turns highly immunogenic and elicits humoral response in T2DM patients.

Effects of High Intakes of Fructose and Galactose, with or without Added Fructooligosaccharides, on Metabolic Factors, Inflammation, and Gut Integrity in a Rat Model

SCOPE

A high fructose and galactose intake show adverse metabolic effects in animal models and in humans, but it is yet unknown if addition of fermentable dietary fiber can mitigate such effects. This study investigate the effects of high intakes of fructose and galactose, with/without added fructooligosaccharides (FOS), on metabolic factors, inflammation, and gut integrity markers in rats.

METHODS AND RESULTS

Rats (n = 6/group) receive different carbohydrates at isocaloric conditions for 12 weeks as follows: 1) starch (control), 2) fructose, 3) galactose, 4) starch + FOS (FOS control), 5) fructose + FOS, and 6) galactose + FOS, together with a high amount of n-6 polyunsaturated fatty acids (n-6 PUFA) in all diets except for in 7) starch + olive oil (negative control). The rats fed the galactose and galactose + FOS diets exhibit lower body weight than other groups. High-galactose diets has more pronounced effects on metabolic factors and gut permeability than high-fructose diets. High-fructose diets show less pronounced effect on these selected markers. No differences in inflammatory markers are detected for any of the diets.

CONCLUSIONS

The results suggest potential adverse effects of high galactose and fructose on metabolic factors and gut integrity markers, but not on inflammation. However, several mechanisms are at play, and general net effects are difficult to determine conclusively for the conditions tested.

Unveiling the interaction mechanism of alogliptin benzoate with human serum albumin: Insights from spectroscopy, microcalorimetry, and molecular docking and molecular dynamics analyses

The interaction between a DPP-4 inhibitor, alogliptin benzoate (AB), and human serum albumin (HSA) was systematically investigated via spectroscopy, microcalorimetry and molecular simulations. Steady-state fluorescence and time-resolved fluorescence spectrometry illustrated that the fluorescence quenching type of AB to HSA was static and caused by the formation of ground state AB-HSA complex. Isothermal titration calorimetry (ITC) combined with fluorescence spectra revealed that the affinity of AB to the subdomain IIA of HSA was moderate with a binding constant in the order of 10⁴. Molecular docking analysis and thermodynamic parameters demonstrated that this combination was maintained by hydrogen bonding along with van der Waals force and hydrophobic force. Circular dichroism and three-dimensional (3D) fluorescence showed that AB increased the hydrophobicity of Trp residue and the α-helix content of HSA by 1.99%. Microdifferential scanning calorimetry revealed that the addition of AB enhanced the thermal stability of HSA. The action forces, binding stability, binding sites, and protein structure of the AB-HSA system were evaluated via molecular dynamics analysis in the simulated environment. On the basis of molecular docking, MD simulation constructed a more reliable 3D model of the AB-HSA complex in terms of spatial structure.

Protective actions of bioactive flavonoids chrysin and luteolin on the glyoxal induced formation of advanced glycation end products and aggregation of human serum albumin: In vitro and molecular docking analysis

The post-translational modification of proteins by nonenzymatic glycation (NEG) and the accumulation of AGEs are the two underlying factors associated with the long-term pathogenesis in diabetes. Glyoxal (GO) is a reactive intermediate which has the ability to modify proteins and generate AGEs at a faster rate. Human serum albumin (HSA) being the most abundant serum protein has a higher chance to be modified by NEG. The key objective of the present study is to investigate the potency of chrysin and luteolin as antiglycating and antifibrillating agents in the GO-mediated glycation and fibril formation of HSA. AGEs formation were confirmed from the absorption and fluorescence spectral measurements. Both the flavonoids were able to quench the AGEs fluorescence intensity in vitro indicating the antiglycating nature of the molecules. The formation of fibrils in the GO-modified HSA was confirmed by the Thioflavin T (ThT) fluorescence assay and the flavonoids were found to exihibit the antifibrillation properties in vitro. Docking results suggested that both the flavonoids interact with various amino acid residues of subdomain IIA including glycation prone lysines and arginines via non-covalent forces and further stabilized the structure of HSA, which further explains their mechanisms of action as antiglycating and antifibrillating agents.

Effects of piceatannol on the structure and activities of bovine serum albumin: A multi-spectral and molecular modeling studies

Piceatannol (PIC) displays a wide spectrum of biological activities, such as antioxidation, antibacterial activity and anti-inflammation, but the biochemical and molecular mechanism is not fully understood. In this study, the interaction of PIC with bovine serum albumin (BSA) was studied by fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, circular dichroism spectroscopy and molecular simulation. The effects of PIC on BSA non-enzymatic glycosylation, fibrillation, thermal stability, and structure information were also studied. The results showed that the formation of PIC-BSA complex by mainly hydrogen-bonding forces resulted in the conformational changes of protein. PIC inhibited the formation of β-sheets structures of BSA. BSA still maintained the esterase-like good activity in the presence of PIC. In addition, PIC significantly reduced the degree of BSA glycosylation. These results provided a basis for the molecular interaction between PIC and protein, and suggested the potential effect of PIC in preventing the progression of diabetes mellitus.

Glyoxal Induced Transition of Transferrin to Aggregates: Spectroscopic, Microscopic and Molecular Docking Insight

BACKGROUND & OBJECTIVE

The present study was aimed at characterizing the conformational alterations induced in human transferrin, the iron regulatory protein by glyoxal. Since protein aggregation is at the core of many disorders, thus interest in this domain has increased significantly during the past years.

METHODS

In our present study, the effect of glyoxal was monitored on human transferrin using multispectroscopic and multi-microscopic studies.

RESULTS

Intrinsic fluorescence spectroscopy suggested changes in native conformation of human transferrin evident by decreased fluorescence and blue shift in the presence of glyoxal. Further, extrinsic fluorescence was retorted and the results showed the formation of aggregates; apparent by increased Congo red (CR) absorbance, Thioflavin T (ThT) and ANS fluorescence and TEM of human transferrin in the presence of glyoxal. Molecular docking was also employed to see which residues are at core of human transferrin and glyoxal interaction. Reactive oxygen species (ROS) generation assays revealed enhanced ROS levels by human transferrin after treatment with glyoxal.

CONCLUSION

Thus, our study proposes that glyoxal induces the formation of aggregates in human transferrin. These aggregates further generate ROS which are key players in the complications associated with diabetes mellitus, giving our study clinical perspective.

The expression of four pyridoxal kinase (PDXK) human variants in Drosophila impacts on genome integrity

In eukaryotes, pyridoxal kinase (PDXK) acts in vitamin B₆salvage pathway to produce pyridoxal 5′-phosphate (PLP), the active form of the vitamin, which is implicated in numerous crucial metabolic reactions. In Drosophila, mutations in the dPdxk gene cause chromosome aberrations (CABs) and increase glucose content in larval hemolymph. Both phenotypes are rescued by the expression of the wild type human PDXK counterpart. Here we expressed, in dPdxk¹ mutant flies, four PDXK human variants: three (D87H, V128I and H246Q) listed in databases, and one (A243G) found in a genetic screening in patients with diabetes. Differently from human wild type PDXK, none of the variants was able to completely rescue CABs and glucose content elicited by dPdxk¹ mutation. Biochemical analysis of D87H, V128I, H246Q and A243G proteins revealed reduced catalytic activity and/or reduced affinity for PLP precursors which justify this behavior. Although these variants are rare in population and carried in heterozygous condition, our findings suggest that in certain metabolic contexts and diseases in which PLP levels are reduced, the presence of these PDXK variants could threaten genome integrity and increase cancer risk.

How Does Pyridoxamine Inhibit the Formation of Advanced Glycation End Products? The Role of Its Primary Antioxidant Activity

Pyridoxamine, one of the natural forms of vitamin B6, is known to be an effective inhibitor of the formation of advanced glycation end products (AGEs), which are closely related to various human diseases. Pyridoxamine forms stable complexes with metal ions that catalyze the oxidative reactions taking place in the advanced stages of the protein glycation cascade. It also reacts with reactive carbonyl compounds generated as byproducts of protein glycation, thereby preventing further protein damage. We applied Density Functional Theory to study the primary antioxidant activity of pyridoxamine towards three oxygen-centered radicals (•OOH, •OOCH3 and •OCH3) to find out whether this activity may also play a crucial role in the context of protein glycation inhibition. Our results show that, at physiological pH, pyridoxamine can trap the •OCH3 radical, in both aqueous and lipidic media, with rate constants in the diffusion limit (>1.0 × 108 M - 1 s - 1 ). The quickest pathways involve the transfer of the hydrogen atoms from the protonated pyridine nitrogen, the protonated amino group or the phenolic group. Its reactivity towards •OOH and •OOCH3 is smaller, but pyridoxamine can still scavenge them with moderate rate constants in aqueous media. Since reactive oxygen species are also involved in the formation of AGEs, these results highlight that the antioxidant capacity of pyridoxamine is also relevant to explain its inhibitory role on the glycation process.

Anti-diabetic study of vitamin B6 on hyperglycaemia induced protein carbonylation, DNA damage and ROS production in alloxan induced diabetic rats

Oxidative stress performs an imperative role in the onset and progression of diabetes. Metabolic enzymes and cellular organelles are detrimental to increased levels of free radicals and the subsequent reduction in anti-oxidant defence. Pyridoxamine (vitamin B6) is an indispensible nutrient for humans and is considered to be an important food additive too. The aim of this research was to examine the effect of vitamin B6 in a diabetic environment. This study reports the effects of pyridoxamine supplementation in alloxan induced diabetic rats. Diabetes was induced by the single intra peritoneal dose of alloxan (120 mg per kg body weight). Diabetic rats were treated with pyridoxamine (10 and 15 mg per kg body weight) and compared with a control set of diabetic rats without supplementation. Pyridoxamine treatment showed dose dependent recovery in all parameters. A notable decline in oxidative stress parameters and ROS production with reductions in fasting blood glucose levels along with normal patterns of the glucose tolerance test has been reported here. Histological studies reveal damage recovery in the liver as well as kidney tissues. A notable amount of recovery was observed in cellular DNA distortion and damage. It is thus advocated that pyridoxamine might help in reducing problems associated with diabetes. A probable mechanism pertaining to the action of pyridoxamine is proposed as well.