(R)-α-Lipoic acid inhibits fructose-induced myoglobin fructation and the formation of advanced glycation end products (AGEs) in vitro

The effect of a-Lipoic acid (ALA) on oxidative stress, inflammation, and apoptosis in high glucose-induced human corneal epithelial cells

PURPOSE

Oxidative stress and inflammation had been proved to play important role in the progression of diabetic keratopathy (DK). The excessive accumulation of AGEs and their bond to AGE receptor (RAGE) in corneas that cause the formation of oxygen radicals and the release of inflammatory cytokines, induce cell apoptosis. Our current study was aimed to evaluate the effect of ALA on AGEs accumulation as well as to study the molecular mechanism of ALA against AGE-RAGE axis mediated oxidative stress, apoptosis, and inflammation in HG-induced HCECs, so as to provide cytological basis for the treatment of DK.

METHODS

HCECs were cultured in a variety concentration of glucose medium (5.5, 10, 25, 30, 40, and 50 mM) for 48 h. The cell proliferation was evaluated by CCK-8 assay. Apoptosis was investigated with the Annexin V- fluorescein isothiocyanate (V-FITC)/PI kit, while, the apoptotic cells were determined by flow cytometer and TUNEL cells apoptosis Kit. According to the results of cell proliferation and cell apoptosis, 25 mM glucose medium was used in the following HG experiment. The effect of ALA on HG-induced HCECs was evaluated. The HCECs were treated with 5.5 mM glucose (normal glucose group, NG group), 5.5 mM glucose + 22.5 mM mannitol (osmotic pressure control group, OP group), 25 mM glucose (high glucose group, HG group) and 25 mM glucose + ALA (HG + ALA group) for 24 and 48 h. The accumulation of intracellular AGEs was detected by ELISA kit. The RAGE, catalase (CAT), superoxide dismutase 2 (SOD2), cleaved cysteine-aspartic acid protease-3 (Cleaved caspase-3), Toll-like receptors 4 (TLR4), Nod-like receptor protein 3 (NLRP3) inflammasome, interleukin 1 beta (IL-1 ß), and interleukin 18 (IL-18) were quantified by RT-PCR, Western blotting, and Immunofluorescence, respectively. Reactive oxygen species (ROS) production was evaluated by fluorescence microscope and fluorescence microplate reader.

RESULTS

When the glucose medium was higher than 25 mM, cell proliferation was significantly inhibited and apoptosis ratio was increased (P < 0.001). In HG environment, ALA treatment alleviated the inhibition of HCECs in a dose-dependent manner, 25 μM ALA was the minimum effective dose. ALA could significantly reduce the intracellular accumulation of AGEs (P < 0.001), activate protein and genes expression of CAT and SOD2 (P < 0.001), and therefore inhibited ROS-induced oxidative stress and cells apoptosis. Besides, ALA could effectively down-regulate the protein and gene level of RAGE, TLR4, NLRP3, IL-1B, IL-18 (P < 0.05), and therefore alleviated AGEs-RAGE-TLR4-NLRP3 pathway-induced inflammation in HG-induced HCECs.

CONCLUSION

Our study indicated that ALA could be a desired treatment for DK due to its potential capacity of reducing accumulation of advanced glycation end products (AGEs) and down-regulating AGE-RAGE axis-mediated oxidative stress, cell apoptosis, and inflammation in high glucose (HG)-induced human corneal epithelial cells (HCECs), which may provide cytological basis for therapeutic targets that are ultimately of clinical benefit.

Understanding the role of glycation in the pathology of various non-communicable diseases along with novel therapeutic strategies

Glycation refers to carbonyl group condensation of the reducing sugar with the free amino group of protein, which forms Amadori products and advanced glycation end products (AGEs). These AGEs alter protein structure and function by configuring a negative charge on the positively charged arginine and lysine residues. Glycation plays a vital role in the pathogenesis of metabolic diseases, brain disorders, aging, and gut microbiome dysregulation with the aid of 3 mechanisms: (i) formation of highly reactive metabolic pathway-derived intermediates, which directly affect protein function in cells, (ii) the interaction of AGEs with its associated receptors to create oxidative stress causing the activation of transcription factor NF-κB, and (iii) production of extracellular AGEs hinders interactions between cellular and matrix molecules affecting vascular and neural genesis. Therapeutic strategies are thus required to inhibit glycation at different steps, such as blocking amino and carbonyl groups, Amadori products, AGEs-RAGE interactions, chelating transition metals, scavenging free radicals, and breaking crosslinks formed by AGEs. The present review focused on explicitly elaborating the impact of glycation-influenced molecular mechanisms in developing and treating noncommunicable diseases.

Carvacrol protects against carbonyl osmolyte-induced structural modifications and aggregation to serum albumin: Insights from physicochemical and molecular interaction studies

The robust use of osmolytes (i.e., polyols and sugars) in the key therapeutic regimens/formulations has questioned their impact beyond the stability of therapeutic proteins as these osmolytes trigger structural alterations into proteins including misfolding and subsequent aggregation into amyloid fibrils. Therefore, the current study is the first to delineate the inhibitory effect of carvacrol (CRV) on the carbonyl osmolyte-induced aggregation as well as structural alterations to the bovine serum albumin (BSA) via a set of physicochemical as well as artificial intelligence (AI)-based molecular docking studies. Our initial findings from physicochemical investigations revealed that CRV exhibits substantial protection to BSA under carbonyl osmolyte stress as evident by the compromised hyperchromicity, Schiff's bases, carbonyl and hydroxymethyl furfural content, reduced fluorescent signals, low Rayleigh scattering and prevention of covalent modifications at Lys and Arg residues. The protection against aggregate formation by CRV was further confirmed through the reduced amyloid-specific congo red absorbance as well as fluorescent signals recorded after adding the fibril-specific extrinsic fluorophore probes (i.e., ThT and ANS). The AI-based molecular docking analysis further revealed that CRV (ΔG: -4.96 kcal/mol) competes with d-fructose (ΔG: -4.40 kcal/mol) to mask the Lys and Arg residues to restrict the osmolyte-mediated protein modifications. In conclusion, CRV exhibits substantial protective impact against carbonyl osmolyte-induced structural alterations and protein misfolding and aggregation.

The Impact of a Plant-Based Diet on Gestational Diabetes: A Review

Gestational diabetes mellitus (GDM) represents a challenging pregnancy complication in which women present a state of glucose intolerance. GDM has been associated with various obstetric complications, such as polyhydramnios, preterm delivery, and increased cesarean delivery rate. Moreover, the fetus could suffer from congenital malformation, macrosomia, neonatal respiratory distress syndrome, and intrauterine death. It has been speculated that inflammatory markers such as tumor necrosis factor-alpha (TNF-α), interleukin (IL) 6, and C-reactive protein (CRP) impact on endothelium dysfunction and insulin resistance and contribute to the pathogenesis of GDM. Nutritional patterns enriched with plant-derived foods, such as a low glycemic or Mediterranean diet, might favorably impact on the incidence of GDM. A high intake of vegetables, fibers, and fruits seems to decrease inflammation by enhancing antioxidant compounds. This aspect contributes to improving insulin efficacy and metabolic control and could provide maternal and neonatal health benefits. Our review aims to deepen the understanding of the impact of a plant-based diet on oxidative stress in GDM.

Attenuation of methylglyoxal-induced glycation and cellular dysfunction in wound healing by Centella cordifolia

Current pre-clinical evidences of Centella focus on its pharmacological effects on normal wound healing but there are limited studies on the bioactivity of Centella in cellular dysfunction associated with diabetic wounds. Hence we planned to examine the potential of Centella cordifolia in inhibiting methylglyoxal (MGO)-induced extracellular matrix (ECM) glycation and promoting the related cellular functions. A Cell-ECM adhesion assay examined the ECM glycation induced by MGO. Different cell types that contribute to the healing process (fibroblasts, keratinocytes and endothelial cells) were evaluated for their ability to adhere to the glycated ECM. Methanolic extract of Centella species was prepared and partitioned to yield different solvent fractions which were further analysed by high performance liquid chromatography equipped with photodiode array detector (HPLC-PDA) method. Based on the antioxidant [2,2-diphenyl-1-picrylhydrazyl (DPPH) assay] screening, anti-glycation activity and total phenolic content (TPC) of the different Centella species and fractions, the ethyl acetate fraction of C. cordifolia was selected for further investigating its ability to inhibit MGO-induced ECM glycation and promote cellular distribution and adhesion. Out of the three Centella species (C. asiatica, C. cordifolia and C. erecta), the methanolic extract of C. cordifolia showed maximum inhibition of Advanced glycation end products (AGE) fluorescence (20.20 ± 4.69 %, 25.00 ± 3.58 % and 16.18 ± 1.40 %, respectively). Its ethyl acetate fraction was enriched with phenolic compounds (3.91 ± 0.12 mg CAE/μg fraction) and showed strong antioxidant (59.95 ± 7.18 μM TE/μg fraction) and antiglycation activities. Improvement of cells spreading and adhesion of endothelial cells, fibroblasts and keratinocytes was observed for ethyl acetate treated MGO-glycated extracellular matrix. Significant reduction in attachment capacity of EA.hy926 cells seeded on MGO-glycated fibronectin (41.2%) and attachment reduction of NIH3t3 and HaCaT cells seeded on MGO-glycated collagen (33.7% and 24.1%, respectively) were observed. Our findings demonstrate that ethyl acetate fraction of C. cordifolia was effective in attenuating MGO-induced glycation and cellular dysfunction in the in-vitro wound healing models suggesting that C. cordifolia could be a potential candidate for diabetic wound healing. It could be subjected for further isolation of new phytoconstituents having potential diabetic wound healing properties.

Alpha-lipoic acid and its protective role in fructose induced endocrine-metabolic disturbances

In recent decades a worldwide increase has been reported in the consumption of unhealthy high calorie diets associated with marked changes in meal nutrient composition, such as a higher intake of refined carbohydrates, which leads to the speculatation that changes in food habits have contributed to the current epidemic of obesity and type 2 diabetes. Among these refined carbohydrates, fructose has been deeply investigated and murine models of high fructose diet have emerged as useful tools to study dietary-induced insulin resistance, impaired glucose tolerance, dyslipidemia and alterations in glucose metabolism. Since oxidative stress has been demonstrated to play a key pathogenic role in the alterations described above, several lines of research have focused on the possible preventive effects of antioxidant/redox state regulation therapy, among which alpha-lipoic acid has been extensively investigated. The following references discussed support the fact that co-administration of alpha-lipoic acid normalized the changes generated by fructose rich diets, thereby making this compound a good therapeutic tool, also administered as a food supplement, to prevent endocrine-metabolic disturbances triggered by high fructose associated with obesity and type 2 diabetes at an early stage of development (prediabetes).

Attenuation of Glucose-Induced Myoglobin Glycation and the Formation of Advanced Glycation End Products (AGEs) by (R)-α-Lipoic Acid In Vitro

High-carbohydrate containing diets have become a precursor to glucose-mediated protein glycation which has been linked to an increase in diabetic and cardiovascular complications. The aim of the present study was to evaluate the protective effect of (R)-α-lipoic acid (ALA) against glucose-induced myoglobin glycation and the formation of advanced glycation end products (AGEs) in vitro. Methods: The effect of ALA on myoglobin glycation was determined via the formation of AGEs fluorescence intensity, iron released from the heme moiety of myoglobin and the level of fructosamine. The extent of glycation-induced myoglobin oxidation was measured via the levels of protein carbonyl and thiol. Results: The results showed that the co-incubation of ALA (1, 2 and 4 mM) with myoglobin (1 mg/mL) and glucose (1 M) significantly decreased the levels of fructosamine, which is directly associated with the decrease in the formation of AGEs. Furthermore, ALA significantly reduced the release of free iron from myoglobin which is attributed to the protection of myoglobin from glucose-induced glycation. The results also demonstrated a significant protective effect of ALA on myoglobin from oxidative damage, as seen from the decreased protein carbonyls and increased protein thiols. Conclusion: The anti-glycation properties of ALA suggest that ALA supplementation may be beneficial in the prevention of AGEs-mediated diabetic and cardiovascular complications.