Glycyrrhizic Acid Scavenges Reactive Carbonyl Species and Attenuates Glycation-Induced Multiple Protein Modification: An In Vitro and In Silico Study

The current study is aimed at studying the inhibitory effect of glycyrrhizic acid (GA) on D-ribose-mediated protein glycation via various physicochemical analyses and in silico approaches. Being a potent free radical scavenger and a triterpenoid saponin, GA plays a vital role in diminishing the oxidative stress and thus could be an effective inhibitor of the nonenzymatic glycation process. Our data showed that varying concentrations of GA inhibited the in vitro BSA-AGEs via inhibiting the formation of fructosamines, fluorescent AGEs, scavenging protein carbonyl and hydroxymethyl furfural (HMF) content, and protection against D-ribose-induced modification of BSA as evident by increased free Arg and Lys residues in GA-treated Gly-BSA samples. Moreover, GA also attenuated D-ribose-induced alterations in the secondary structure of BSA by protecting the α-helix and β-sheet conformers and amide-I band delocalization. In addition, GA attenuated the modification in β-cross amyloid structures of BSA and in silico molecular interaction study too showed strong binding of GA with higher number of Lys and Arg residues of BSA and binding energy (ΔG) of -8.8 Kcal/mol, when compared either to reference standard aminoguanidine (AG)-BSA complex (ΔG: -4.3 Kcal/mol) or D-ribose-BSA complex (ΔG: -5.2 Kcal/mol). Therefore, GA could be a new and favorable inhibitor of the nonenzymatic glycation process that ameliorates AGEs-related complications via attenuating the AGE formation and glycation-induced multiple protein modifications with a reduced risk of adverse effects on protein structure and functionality; hence, it could be investigated at further preclinical settings for the treatment and management of diabetes and age-associated complications.

How Does Glycation Affect Binding Parameters of the Albumin-Gliclazide System in the Presence of Drugs Commonly Used in Diabetes? In Vitro Spectroscopic Study

In this research, the selected drugs commonly used in diabetes and its comorbidities (gliclazide, cilazapril, atorvastatin, and acetylsalicylic acid) were studied for their interactions with bovine serum albumin—native and glycated. Two different spectroscopic methods, fluorescence quenching and circular dichroism, were utilized to elucidate the binding interactions of the investigational drugs. The glycation process was induced in BSA by glucose and was confirmed by the presence of advanced glycosylation end products (AGEs). The interaction between albumin and gliclazide, with the presence of another drug, was confirmed by calculation of association constants (0.11–1.07 × 104 M−1). The nature of changes in the secondary structure of a protein depends on the drug used and the degree of glycation. Therefore, these interactions may have an influence on pharmacokinetic parameters.

Non-Enzymatic Glycation and Formation of Advanced Glycation End-Products Alters the Activity and Related Kinetic Properties of Aldose Reductase

Aldose reductase was incubated with and without either fructose or glucose for 42 days to initiate the glycation process. The concentrations of fructosamine were measured on every 7th day using the standard nitroblue tetrazolium reagent assay. Carboxymethyllysine formed was determined using enzyme linked immunosorbent assay-based methods, fluorescent end-products were measured using spectrofluorometric methods. Activities were assayed by measuring the absorbance of co-factor nicotinamide adenine dinucleotide phosphate hydrogen at 340 nm. Fructosamine, carboxymethyllysine protein adducts and fluorescent end-products were significantly higher (p < 0.001) when aldose reductase was incubated with fructose or glucose than without. Although the glycation of aldose reductase did not result in the alteration of both the optimum pH and temperature of the enzyme, both the activity and Vmax were increased, whereas Km was decreased. Non-enzymatic glycation of aldose reductase increases both its activity and Vmax, while decreasing its Km. Additionally, glycation did not affect the pH of enzyme and temperature optima.

In Vitro Antioxidant and Anti-Glycation Activity of Resveratrol and Its Novel Triester with Trolox

Resveratrol (RSV) is well known for its many beneficial activities, but its unfavorable physicochemical properties impair its effectiveness after systemic and topical administration; thus, several strategies have been investigated to improve RSV efficacy. With this aim, in this work, we synthesized a novel RSV triester with trolox, an analogue of vitamin E with strong antioxidant activity. The new RSV derivative (RSVTR) was assayed in vitro to evaluate its antioxidant and anti-glycation activity compared to RSV. RSVTR chemical stability was assessed at pH 2.0, 6.8, and 7.2 and different storage temperatures (5 °C, 22 °C, and 37 °C). An influence of pH stronger than that of temperature on RSVTR half-life values was pointed out, and RSVTR greatest stability was observed at pH 7.2 and 5 °C. RSVTR showed a lower antioxidant ability compared to RSV (determined by the oxygen radical absorbance capacity assay) while its anti-glycation activity (evaluated using the Maillard reaction) was significantly greater than that of RSV. The improved ability to inhibit the glycation process was attributed to a better interaction of RSVTR with albumin owing to its increased topological polar surface area value and H-bond acceptor number compared to RSV. Therefore, RSVTR could be regarded as a promising anti-glycation agent worthy of further investigations.

Cholinesterase and Glycation Inhibition Assay of Several Metabolites Obtained from Plant and Fungi

Cholinesterase inhibition is one of the major strategies to develop better quality anti-Alzheimer’s drug, while inhibition of glycation pathway is a useful therapeutic strategy to treat diabetic complications. This study was designed to evaluate the anti-acetylcholinesterase, anti-butyrylcholinesterase and anti-glycation activities of 8 secondary metabolites namely, RS-8, RS-22C (arborinine), CL-1 (betulinic acid), CL-2 (ursolic acid), CCL-1 (cajaninstilbene acid), CP-1 (beta-sitosterol), HS-1 (anhydrofusarubin) and HS-2 (methylether of fusarubin). It was found that RS-8 and arborinine showed promising activity in inhibiting acetylcholinesterase with IC50 values of 24.40 ± 0.39 and 13.14 ± 0.07, respectively. Anhydrofusarubin and methyl ether of fusarubin exhibited moderate activities with IC50 values of 47.82 ± 0.54 and 44.58 ± 0.8. Arborinine and cajaninstilbene acid potentially inhibited butyrylcholinesterase with IC50 values of 26.34 ± 0.31 and 25.82 ± 0.34, respectively, but other metabolites did not show such inhibitory activities. Inhibition of glycation process was evaluated by bovine serum albumin assay but none of the metabolites significantly inhibited the glycation pathway. Dhaka Univ. J. Pharm. Sci. 18(1): 31-38, 2019 (June)

Guiding the Differentiation Direction of Pancreatic Islet-Derived Stem Cells by Glycated Collagen

The microenvironment is an important factor of stem cells regulating their maintenance, survival, and differentiation. The glycation of proteins with reducing sugars through nonenzymatic reactions induces the collagen cross-linking, which causes tissue stiffening, which is enhanced during aging and diabetes. In this study, we aimed to analyze the effect of glycated collagen on the stem cell culture and differentiation. The collagen type 1 was modified by glycation with mannose, rhamnose, arabinose, and glucose. After the culture of mesenchymal stem cells on the coated surfaces with glycated collagen, the differences in cell adhesion, proliferation, and differentiation were compared. The results showed that the modifications did not induce apoptosis or cause cell death. However, the culture of cells on modified collagens improved the proliferation. It was found that the mannose-modified collagen stimulated the adipogenic differentiation of stem cells, and rhamnose-modified collagen supports the differentiation into both osteogenic and insulin-producing cells. The low concentration of monosaccharides during glycation process improved the characteristics of the matrix protein in favor of stem cell differentiation. Modification of the collagen by glycation might be used as a tool to improve natural polymers for material-induced stem cell differentiation in the future.

GLYCATION STRESS AND PHOTOAGING OF THE SKIN

The study of foreign researchers on glycation mechanisms and the effect of this non-enzymatic reaction on photodamaged skin are presented. The final products of enhanced glycation - AGEs and their pathogenetic role in skin aging are described. AGEs inhibiting substances, focusing on the prevention of the glycation process, are described.