Rapid glycation with D-ribose induces globular amyloid-like aggregations of BSA with high cytotoxicity to SH-SY5Y cells

Glycative stress as a cause of macular degeneration

People are living longer and rates of age-related diseases such as age-related macular degeneration (AMD) are accelerating, placing enormous burdens on patients and health care systems. The quality of carbohydrate foods consumed by an individual impacts health. The glycemic index (GI) is a kinetic measure of the rate at which glucose arrives in the blood stream after consuming various carbohydrates. Consuming diets that favor slowly digested carbohydrates releases sugar into the bloodstream gradually after consuming a meal (low glycemic index). This is associated with reduced risk for major age-related diseases including AMD, cardiovascular disease, and diabetes. In comparison, consuming the same amounts of different carbohydrates in higher GI diets, releases glucose into the blood rapidly, causing glycative stress as well as accumulation of advanced glycation end products (AGEs). Such AGEs are cytotoxic by virtue of their forming abnormal proteins and protein aggregates, as well as inhibiting proteolytic and other protective pathways that might otherwise selectively recognize and remove toxic species. Using in vitro and animal models of glycative stress, we observed that consuming higher GI diets perturbs metabolism and the microbiome, resulting in a shift to more lipid-rich metabolomic profiles. Interactions between aging, diet, eye phenotypes and physiology were observed. A large body of laboratory animal and human clinical epidemiologic data indicates that consuming lower GI diets, or lower glycemia diets, is protective against features of early AMD (AMDf) in mice and AMD prevalence or AMD progression in humans. Drugs may be optimized to diminish the ravages of higher glycemic diets. Human trials are indicated to determine if AMD progression can be retarded using lower GI diets. Here we summarized the current knowledge regarding the pathological role of glycative stress in retinal dysfunction and how dietary strategies might diminish retinal disease.

Development of a specific fluorescent probe to detect advanced glycation end products (AGEs)

Advanced glycation end products (AGEs) play a pivotal role in the aging process, regarded as a hallmark of aging. Despite their significance, the absence of adequate monitoring tools has hindered the exploration of the relationship between AGEs and aging. Here, we present a novel AGE-selective probe, AGO, for the first time. AGO exhibited superior sensitivity in detecting AGEs compared to the conventional method of measuring autofluorescence from AGEs. Furthermore, we validated AGO's ability to detect AGEs based on kinetics, demonstrating a preference for ribose-derived AGEs. Lastly, AGO effectively visualized glycation products in a collagen-based mimicking model of glycation. We anticipate that this study will enhance the molecular tool sets available for comprehending the physiological processes of AGEs during aging.

Revolutionizing Alzheimer's treatment: Harnessing human serum albumin for targeted drug delivery and therapy advancements

Alzheimer's disease (AD) is a neurodegenerative disorder initiated by amyloid-beta (Aβ) accumulation, leading to impaired cognitive function. Several delivery approaches have been improved for AD management. Among them, human serum albumin (HSA) is broadly employed for drug delivery and targeting the Aβ in AD owing to its biocompatibility, Aβ inhibitory effect, and nanoform, which showed blood-brain barrier (BBB) crossing ability via glycoprotein 60 (gp60) receptor and secreted protein acidic and rich in cysteine (SPARC) protein to transfer the drug molecules in the brain. Thus far, there is no previous review focusing on HSA and its drug delivery system in AD. Hence, the reviewed article aimed to critically compile the HSA therapeutic as well as drug delivery role in AD management. It also delivers information on how HSA-incorporated nanoparticles with surfaced embedded ligands such as TAT, GM1, and so on, not only improve BBB permeability but also increase neuron cell targetability in AD brain. Additionally, Aβ and tau pathology, including various metabolic markers likely BACE1 and BACE2, etc., are discussed. Besides, the molecular interaction of HSA with Aβ and its distinctive forms are critically reviewed that HSA can segregate Zn(II) and Cu(II) metal ions from Aβ owing to high affinity. Furthermore, the BBB drug delivery challenges in AD are addressed. Finally, the clinical formulation of HSA for the management of AD is critically discussed on how the HSA inhibits Aβ oligomer and fibril, while glycated HSA participates in amyloid plaque formation, i.e., β-structure sheet formation. This review report provides theoretical background on HSA-based AD drug delivery and makes suggestions for future prospect-related work.

Fenfuro®-mediated arrest in the formation of protein-methyl glyoxal adducts: a new dimension in the anti-hyperglycemic potential of a novel fenugreek seed extract

The fenugreek plant (Trigonella foenum-graecum) is traditionally known for its anti-diabetic properties owing to its high content of furostanolic saponins, which can synergistically treat many human ailments. Non-enzymatic protein glycation leading to the formation of Advanced Glycation End products (AGE) is a common pathophysiology observed in diabetic or prediabetic individuals, which can initiate the development of neurodegenerative disorders. A potent cellular source of glycation is Methyl Glyoxal, a highly reactive dicarbonyl formed as a glycolytic byproduct. We demonstrate the in vitro glycation arresting potential of Fenfuro®, a novel patented formulation of Fenugreek seed extract with clinically proven anti-diabetic properties, in Methyl-Glyoxal (MGO) adducts of three abundant amyloidogenic cellular proteins, alpha-synuclein, Serum albumin, and Lysozyme. A 0.25% w/v Fenfuro® was able to effectively arrest glycation by more than 50% in all three proteins, as evidenced by AGE fluorescence. Glycation-induced amyloid formation was also arrested by more than 36%, 14% and 15% for BSA, Alpha-synuclein and Lysozyme respectively. An increase in MW by attachment of MGO was also partially prevented by Fenfuro® as confirmed by SDS-PAGE analysis. Glycation resulted in enhanced aggregation of the three proteins as revealed by Native PAGE and Dynamic Light Scattering. However, in the presence of Fenfuro®, aggregation was arrested substantially, and the normal size distribution was restored. The results cumulatively indicated the lesser explored potential of direct inhibition of glycation by fenugreek seed in addition to its proven role in alleviating insulin resistance. Fenfuro® boosts its therapeutic potential as an effective phytotherapeutic to arrest Type 2 diabetes.

Glycated LDL generates reactive species that damage cell components, oxidize hemoglobin and alter surface morphology in human erythrocytes

Low-density lipoprotein (LDL) transports cholesterol to various tissues via the blood. Glycation of LDL occurs during hyperglycemic condition which is characterised by persistently high blood glucose level. Circulating erythrocytes can come in direct contact with glycated LDL (G-LDL). The objective of this study was to investigate the effect of G-LDL on human erythrocytes, specifically on hemoglobin, intracellular generation of reactive species and the antioxidant defence system. Isolated erythrocytes were incubated with G-LDL (3 and 6 mg/ml) and native LDL (6 mg/ml) at 37 °C for 24 h. Native LDL and G-LDL untreated erythrocytes were similarly incubated at 37 °C and served as control. G-LDL treatment increased hemolysis compared to control and native LDL-treated erythrocytes. Incubation of erythrocytes with G-LDL led to an increase in protein oxidation and lipid peroxidation while greatly decreasing the total sulfhydryl content. It also significantly enhanced hemoglobin oxidation, heme degradation, and the release of free iron moiety. Treatment with G-LDL led to an appreciable increase in the production of reactive oxygen and nitrogen species. The antioxidant power and activities of major antioxidant enzymes were drastically reduced, while critical membrane-bound enzymes were inhibited. The surface morphology of G-LDL-treated erythrocytes was altered leading to the formation of echinocytes. Importantly, treatment of erythrocytes with native LDL did not significantly affect the above-mentioned parameters and values were similar to the corresponding controls. Thus, G-LDL is cytotoxic to human erythrocytes and causes oxidative damage to cell components. This can reduce the oxygen-transporting ability of blood and also result in red cell senescence and anemia.

An overview on glycation: molecular mechanisms, impact on proteins, pathogenesis, and inhibition

The formation of a heterogeneous set of advanced glycation end products (AGEs) is the final outcome of a non-enzymatic process that occurs in vivo on long-life biomolecules. This process, known as glycation, starts with the reaction between reducing sugars, or their autoxidation products, with the amino groups of proteins, DNA, or lipids, thus gaining relevance under hyperglycemic conditions. Once AGEs are formed, they might affect the biological function of the biomacromolecule and, therefore, induce the development of pathophysiological events. In fact, the accumulation of AGEs has been pointed as a triggering factor of obesity, diabetes-related diseases, coronary artery disease, neurological disorders, or chronic renal failure, among others. Given the deleterious consequences of glycation, evolution has designed endogenous mechanisms to undo glycation or to prevent it. In addition, many exogenous molecules have also emerged as powerful glycation inhibitors. This review aims to provide an overview on what glycation is. It starts by explaining the similarities and differences between glycation and glycosylation. Then, it describes in detail the molecular mechanism underlying glycation reactions, and the bio-molecular targets with higher propensity to be glycated. Next, it discusses the precise effects of glycation on protein structure, function, and aggregation, and how computational chemistry has provided insights on these aspects. Finally, it reports the most prevalent diseases induced by glycation, and the endogenous mechanisms and the current therapeutic interventions against it.

Protein Advanced Glycation End Products and Their Implications in Pancreatic Cancer

Protein advanced glycation end products (AGE) formed by nonenzymatic glycation can disrupt the normal structure and function of proteins, and stimulate the receptor for AGEs (RAGE), triggering intricate mechanisms that are etiologically related to various chronic diseases, including pancreatic cancer. Many common risk factors of pancreatic cancer are the major sources for the formation of protein AGEs and glycative stress in the human body. Abnormal accumulation of protein AGEs can impair the cellular proteome and promote AGE-RAGE driven pro-inflammatory signaling cascades, leading to increased oxidative stress, protease resistance, protein dysregulation, transcription activity of STAT, NF-κB, and AP-1, aberrant status in ubiquitin-proteasome system and autophagy, as well as other molecular events that are susceptible for the carcinogenic transformation towards the development of neoplasms. Here, we review studies to highlight our understanding in the orchestrated molecular events in bridging the impaired proteome, dysregulated functional networks, and cancer hallmarks initiated upon protein AGE formation and accumulation in pancreatic cancer.

RAGE signaling regulates the progression of diabetic complications

Diabetes, the ninth leading cause of death globally, is expected to affect 642 million people by 2040. With the advancement of an aging society, the number of patients with diabetes having multiple underlying diseases, such as hypertension, obesity, and chronic inflammation, is increasing. Thus, the concept of diabetic kidney disease (DKD) has been accepted worldwide, and comprehensive treatment of patients with diabetes is required. Receptor for advanced glycation endproducts (RAGE), a multiligand receptor, belonging to the immunoglobulin superfamily is extensively expressed throughout the body. Various types of ligands, including advanced glycation endproducts (AGEs), high mobility group box 1, S100/calgranulins, and nucleic acids, bind to RAGE, and then induces signal transduction to amplify the inflammatory response and promote migration, invasion, and proliferation of cells. Furthermore, the expression level of RAGE is upregulated in patients with diabetes, hypertension, obesity, and chronic inflammation, suggesting that activation of RAGE is a common denominator in the context of DKD. Considering that ligand–and RAGE–targeting compounds have been developed, RAGE and its ligands can be potent therapeutic targets for inhibiting the progression of DKD and its complications. Here, we aimed to review recent literature on various signaling pathways mediated by RAGE in the pathogenesis of diabetic complications. Our findings highlight the possibility of using RAGE–or ligand–targeted therapy for treating DKD and its complications.

Inhibition of AGEs formation, antioxidative, and cytoprotective activity of Sumac (Rhus typhina L.) tannin under hyperglycemia: molecular and cellular study

It is well known that accumulation of advanced glycation ends products (AGEs) lead to various diseases such as diabetes and diabetic complications. In this study we showed that hydrolysable tannin from Sumac (Rhus typhina L.)-3,6-bis-O-di-O-galloyl-1,2,4-tri-O-galloyl-β-D-glucose (C₅₅H₄₀O₃₄) inhibited generation of glycation markers in bovine serum albumin such as AGEs, dityrosine, N'-formylkynurenine and kynurenine under high glucose treatment. This effect was accompanied by stabilization of the protein structure, as was shown using ATR-FT-IR spectroscopy and fluorescence methods. C₅₅H₄₀O₃₄ exhibited also a neuroprotective effect in high glucose-exposed Neuro2A cells suppressing ROS formation and expression of phospho NF-κβ and iNOS. At the same time C₅₅H₄₀O₃₄ increased expression of heme oxygenase-1 and NAD(P)H: quinone oxidoreductase and mitochondrial complex I and V activities. Results from this study demonstrates a potent antiglycation activity of C₅₅H₄₀O₃₄ in vitro and indicates its possible therapeutic application in glycation related diseases.

Effects of d-ribose on human erythrocytes: Non-enzymatic glycation of hemoglobin, eryptosis, oxidative stress and energy metabolism

d-Ribose is not only an important component of some biomacromolecules, but also an active pentose with strong reducibility and non-enzymatic glycation ability. Previous studies reported the diverse role of d-ribose in different cells. In this study, the effects of d-ribose on non-enzymatic glycation of hemoglobin (Hb), as well as eryptosis, oxidative stress and energy metabolism of erythrocytes were observed by molecular fluorescence spectrophotometry, multi-wavelength spectrophotometry, high-pressure liquid chromatography (HPLC), mass spectrometry (MS) and flow cytometer. The results showed that d-ribose had the strongest non-enzymatic glycation ability to Hb in vitro when compared with other monosaccharides, and could enter the erythrocytes in a concentration-dependent manner, which was not inhibited by the specific glucose transporter 1 (GLUT1) inhibitor WZB117. In addition, d-ribose incubation increased the HbA1c, hemolysis, eryptosis, and ROS level of erythrocytes significantly more than that of d-glucose, however, no changes were observed in the levels of ATP, NADPH, and other intermediate energy metabolites in d-ribose treatment. Therefore, the strong non-enzymatic glycation ability of d-ribose may play an important role in erythrocyte damage.

Preoperative serum ribose concentrations may be associated with postoperative delirium in older patients with a hip fracture

BACKGROUND

Postoperative delirium (POD) is a common postoperative neurocognitive complication, especially in older patients. However, satisfactory biomarkers for predicting individual risks of POD have not been confirmed. D-ribose involvement in protein glycation and aggregation plays a pivotal role in age-related neurodegenerative disorders such as Alzheimer's disease.

OBJECTIVES

This study aimed to determine whether serum D-ribose concentrations contribute to the early diagnosis of POD. We also discuss the probable mechanisms underlying the development of POD.

METHODS

110 older patients with hip fracture who had undergone internal fixation or hip replacement under general anesthesia and had completed our assessments were selected. Preoperative venous blood (4 ml) was collected before the induction of anesthesia. Postoperative venous blood was obtained at 07:00 and 20:00 h on postoperative day 1 and at 20:00 h on postoperative day 2. On the first 2 postoperative days, the patients were assessed twice daily (at 8:00 and 20:00 h on each day) using the Confusion Assessment Method-Chinese Revision.

RESULTS

15 patients were finally diagnosed with POD. We also included 15 patients without POD who were matched with the recruited patients with POD (1:1) on the basis of age, sex, body mass index and the Mini-Mental State Examination score. Serum ribose concentrations were measured by high-performance liquid chromatography. The demographic characteristics of the groups were matched. Preoperative serum ribose concentrations were significantly higher in patients with POD than in those without POD (p < 0.05) and were also an independent risk factor for POD. Moreover, when the preoperative serum ribose concentration doubled, the risk of POD increased by 1.672 times.

CONCLUSIONS

These results indicate that the serum D-ribose concentration may be a potential predictive molecular biomarker for POD, and provide useful information for further pathological mechanism studies.

Metabolite Profiling of Antioxidant Rich Fractions of Punica granatum L. Mesocarp and CD36 Expression Regulation

OBJECTIVE

It was aimed at determining which polyphenolic compound(s) in pomegranate mesocarp extract (PME) is liable for the antioxidant, anti-glycation and anti-CD36 activities.

METHODS

The PME was fractionated using liquid-liquid extraction method. The fractions were tested for their polyphenolic content, antioxidant potency, anti-glycation activity and anti-CD36 potential. The metabolite compositions of PME and derived fractions were investigated in an untargeted manner using metabolomics in relation to its antioxidant and anti-glycation activities.

RESULTS

The ethyl acetate and n-butanol fractions of the pomegranate mesocarp demonstrated highest antioxidant and anti-glycation potencies. These fractions, represented by gallic and ellagic acids monomers, were enriched in tannins and phenolic acids. Orthogonal partial least squares discriminate analysis (OPLS-DA) modeling of ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) metabolite profiles from the different pomegranate mesocarp fractions indicated that gallic and ellagic acids were potential contributors to the antioxidant and anti-glycation effects of the pomegranate mesocarp. At cellular level, the polyphenolic-rich crude extract as well as the ethyl acetate, n-butanol and aqueous residual fractions suppressed the protein expression of CD36. The anti-CD36 activity of these extracts and fractions was attributed to the presence of punicalagin, the ellagitannins that occurred in equal amount in the different fractions.

CONCLUSION

This work demonstrated the protective effect of the non-edible part of the pomegranate fruit and showed that gallic and ellagic acids account for the antioxidant and anti-glycation activities while punicalagin is liable for the anti-CD36 activity of PME.

Non-enzymatic glycation of human angiogenin: Effects on enzymatic activity and binding to hRI and DNA

The effects of non-enzymatic glycation on the structural and functional properties of human angiogenin (hAng) have been investigated with respect to the formation of advanced glycated end products (AGEs), on prolonged treatment with d-Glucose, d-Fructose and d-Ribose at 37 °C. Fluorescence studies show the formation of fluorescent AGEs which exhibit emission maxima at 406 nm and 435 nm. Glycation of hAng with ribose leads to the maximum loss of its functional characteristic properties, as compared to fructose and glucose, along with the formation of higher oligomers. An increase in the incubation time results in the formation of higher oligomers with a concomitant decrease in the ribonucleolytic activity. The increase in the hydrodynamic radii of the glycated samples compared to native hAng is indicative of structural perturbations. The ribonucleolytic activity and the DNA binding ability of glycated hAng has been investigated by an agarose gel-based assay. Glycated hAng was unable to bind with human placental ribonuclease inhibitor (hRI), otherwise known to form one of the strongest protein-protein interaction systems with an affinity in the femtomolar range.

D-Ribose-Induced Glycation and Its Attenuation by the Aqueous Extract of Nigella sativa Seeds

Background and Objectives: Glycation and oxidative stress are the major contributing factors responsible for diabetes and its secondary complications. Aminoguanidine, a hydrazine derivative, is the only approved drug that reduces glycation with its known side effects. As a result, research into medicinal plants with antioxidant and antiglycation properties is beneficial in treating diabetes and its consequences. This investigation aimed to examine the efficacy of the aqueous extract of Nigella sativa seeds against the D-ribose-induced glycation system. Materials and Methods: The suppression of α-amylase and α-glucosidase enzymes were used to assess the antidiabetic capacity. UV-Visible, fluorescence, and FTIR spectroscopy were used to characterize the Nigella sativa seed extract and its efficacy in preventing glycation. The inhibition of albumin glycation, fluorescent advanced glycation end products (AGEs) formation, thiol oxidation, and amyloid formation were used to evaluate the extracts' antiglycation activity. In addition, the extent of glycoxidative DNA damage was analyzed using agarose gel electrophoresis. Results: The IC₅₀ for the extract in the α-amylase and α-glucosidase enzyme inhibition assays were approximately 1.39 ± 0.016 and 1.01 ± 0.022 mg/mL, respectively. Throughout the investigation, it was found that the aqueous extract of Nigella sativa seeds (NSAE) inhibited the level of ketoamine, exerted a considerable drop in fluorescence intensity, and reduced carbonyl production and thiol modification when added to the D-ribose-induced glycation system. In addition, a reduction in the BSA-cross amyloid formation was seen in the Congo red, thioflavin T assay, and electrophoretic techniques. NSAE also exhibited a strong capability for DNA damage protection. Conclusion: It can be concluded that Nigella sativa could be used as a natural antidiabetic, antiglycation treatment and a cost-effective and environmentally friendly source of powerful bioactive chemicals.

Ribose Intake as Food Integrator: Is It a Really Convenient Practice?

Reports concerning the beneficial effects of D-ribose administration in cardiovascular and muscle stressful conditions has led to suggestions for the use of ribose as an energizing food supplement for healthy people. However, this practice still presents too many critical issues, suggesting that caution is needed. In fact, there are many possible negative effects of this sugar that we believe are underestimated, if not neglected, by the literature supporting the presentation of the product to the market. Here, the risks deriving from the use of free ribose as ATP source, forcing ribose-5-phosphate to enter into the pentose phosphate pathway, is emphasized. On the basis of the remarkable glycation capacity of ribose, the easily predictable cytotoxic effect of the molecule is also highlighted.

d-ribose-mediated glycation of fibrinogen: Role in the induction of adaptive immune response

A nonenzymatic reaction between reducing sugars and amino groups of proteins results in the formation of advanced glycation end products, which are linked to a number of chronic progressive diseases with macro- and microvascular complications. In this research, we sought to ascertain the immunological response to d-ibose-glycated fibrinogen. New Zealand White female rabbits were immunized with native and d-ribose-glycated (Rb-gly-Fb) fibrinogen and used for studying the immunological response. Serum from these rabbits analyzed using direct binding and competitive inhibition ELISA was found to contain a high titer of antibodies against Rb-gly-Fb; Rb-gly-Fb was much more immunogenic than its native form. The IgG against Rb-gly-Fb (Rb-gly-Fb-IgG) was highly specific against the immunogenic protein. Moreover, histopathology and immunofluorescence studies revealed the deposition of the Rb-gly-Fb-IgG immune complex in the glomerular basement membrane of the kidneys of immunized rabbits. Furthermore, immunization with Rb-gly-Fb increased the expression of genes encoding proinflammatory cytokines, tumour necrosis factor α, interleukin-6, interleukin-1β, and interferon-gamma, which is indicative of increased inflammation and the antigenic role of Rb-gly-Fb in provoking an immune response.

Urine D-ribose levels correlate with cognitive function in community-dwelling older adults

Background

D-ribose is involved in the pathogenesis of Alzheimer’s Disease. The study aimed to determine the association between D-ribose and cognitive function in a sample of community-dwelling older adults.

Methods

A cross-sectional study was conducted in Chaoyang District, Beijing in 2019–2020. Eligible participants were community-based older adults aged 60 years and above. D-ribose was analyzed from the morning urine. Cognitive function, subjective cognitive decline, and depressive symptoms were measured by a battery of neuropsychological tests. Linear regressions were performed to determine the relationship between the urine D-ribose levels and cognitive performance.

Results

A sample of 1725 participants (67.1% female) aged 60 to 85 years (69.40 ± 5.87 years, mean ± SD) was enrolled in the analysis. The urine D-ribose concentrations ranged from 1.53 to 208.89 μmol/L (median 38.10 μmol/L; interquartile range 22.52—64.96 μmol/L). Higher levels of D-ribose were associated with worse performance on Mini-Mental State Examination and verbal fluency when age, gender, education, depressive symptoms, and cardiovascular risk factors were included as covariates.

Conclusions

The urine D-ribose was negatively correlated with cognitive function in community-dwelling older adults. The findings suggest that the dysmetabolism of D-ribose may play a role at the early stage of cognitive impairment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-022-03288-w.

Antiglycation and antioxidant activities of the crude extract and saponin fraction of Tribulus terrestris before and after microcapsule release

OBJECTIVE

The present study investigated antiglycation and antioxidant activities of crude dry extract and saponin fraction of Tribulus terrestris. It also developed a method of microencapsulation and evaluated antiglycation and antioxidant activities of crude dry extract and saponin fraction before and after microcapsule release.

METHODS

Antiglycation activity was determined by relative electrophoretic mobility (REM), free amino groups and inhibition of advanced glycation end-product (AGE) formation. Antioxidant activity was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric ion-reducing antioxidant power (FRAP), nitric oxide (NO) and thiobarbituric acid reactive species (TBARS) tests. Microcapsules were prepared using maltodextrin as wall material and freeze-drying as encapsulation technique. Morphological characterization of microcapsules was evaluated by scanning electron microscopy, and encapsulation efficiency and microcapsule release were determined by total saponins released. Antiglycation and antioxidant assays were performed using crude dry extract and saponin fraction of T. terrestris before and after release.

RESULTS

Saponin fraction showed an increase of 32.8% total saponins. High-performance liquid chromatography-mass spectrometry analysis showed the presence of saponins in the obtained fraction. Antiglycation evaluation by REM demonstrated that samples before and after release presented antiglycation activity similar to bovine serum albumin treated with aminoguanidine. Additionally, samples inhibited AGE formation, highlighting treatment with saponin fraction after release (89.89%). Antioxidant tests demonstrated antioxidant activity of the samples. Crude dry extract before encapsulation presented the highest activities in DPPH (92.00%) and TBARS (32.49%) assays. Saponin fraction before encapsulation in FRAP test (499 μmol Trolox equivalent per gram of dry sample) and NO test (15.13 μmol nitrite formed per gram of extract) presented the highest activities.

CONCLUSION

This study presented antiglycation activity of crude dry extract and saponin fraction of T. terrestris, besides it demonstrated promising antioxidant properties. It also showed that the encapsulation method was efficient and maintained biological activity of bioactive compounds after microcapsule release. These results provide information for further studies on antidiabetic and antiaging potential, and data for new herbal medicine and food supplement formulations containing microcapsules with crude extract and/or saponin fraction of T. terrestris.

Glycation modulates alpha-synuclein fibrillization kinetics: a sweet spot for inhibition

Glycation is a nonenzymatic posttranslational modification (PTM) known to be increased in the brains of hyperglycemic patients. Alpha-synuclein (αSN), a central player in the etiology of Parkinson’s disease, can be glycated at lysine residues, thereby reducing αSN fibril formation in vitro and modulating αSN aggregation in cells. However, the molecular basis for these effects is unclear. To elucidate this, we investigated the aggregation of αSN modified by eight glycating agents, namely the dicarbonyl compound methylglyoxal (MGO) and the sugars ribose, fructose, mannose, glucose, galactose, sucrose, and lactose. We found that MGO and ribose modify αSN to the greatest extent, and these glycation products are the most efficient inhibitors of fibril formation. We show glycation primarily inhibits elongation rather than nucleation of αSN and has only a modest effect on the level of oligomerization. Furthermore, glycated αSN is not significantly incorporated into fibrils. For both MGO and ribose, we discovered that a level of ∼5 modifications per αSN is optimal for inhibition of elongation. The remaining sugars showed a weak but optimal inhibition at ∼2 modifications per αSN. We propose that this optimal level balances the affinity for the growing ends of the fibril (which decreases with the extent of modification) with the ability to block incorporation of subsequent αSN subunits (which increases with modification). Our results are not only relevant for other αSN PTMs but also for understanding PTMs affecting other fibrillogenic proteins and may thus open novel avenues for therapeutic intervention in protein aggregation disorders.

Comparison of bovine serum albumin glycation by ribose and fructose in vitro and in vivo

Advanced glycation end products (AGEs) play a critical pathogenic role in the development of diabetic complications. Recent studies have shown that diabetes is associated with not only abnormal glucose metabolism but also abnormal ribose and fructose metabolism, although glucose is present at the highest concentration in humans. The glycation ability and contribution of ribose and fructose to diabetic complications remain unclear. Here, the glycation ability of ribose, fructose and glucose under a mimic physiological condition, in which the concentration of ribose or fructose was one-fiftieth that of glucose, was compared. Bovine serum albumin (BSA) was used as the working protein in our experiments. Ribose generated more AGEs and was markedly more cytotoxic to SH-SY5Y cells than fructose. The first-order rate constant of ribose glycation was found to be significantly greater than that of fructose glycation. LC-MS/MS analysis revealed 41 ribose-glycated Lys residues and 12 fructose-glycated residues. Except for the shared Lys residues, ribose reacted selectively with 17 Lys, while no selective Lys was found in fructose-glycated BSA. Protein conformational changes suggested that ribose glycation may induce BSA into amyloid-like monomers compared with fructose glycation. The levels of serum ribose were correlated positively with glycated serum protein (GSP) and diabetic duration in type 2 diabetes mellitus (T2DM), respectively. These results indicate that ribose has a greater glycation ability than fructose, while ribose largely contributes to the production of AGEs and provides a new insight to understand in the occurrence and development of diabetes complications.

miR-141-5p Affects the Cell Proliferation and Apoptosis by Targeting BTG1 in Cervical Cancer

Background: MicroRNAs have been discovered to have the possibility to play a significant role in cancer development. It has been found that miR-141-5p is upregulated in various cancers. However, the functions of miR-141-5p in cervical cancer have rarely been reported. Methods: The expression level of miR-141-5p was assessed in cervical cancer tissues and cell lines by RT-qPCR. The function of miR-141-5p in C33A and HeLa cells was detected by CCK-8, and colony formation, wound-healing, transwell chamber, and flow cytometry assays. Dual luciferase reporter was carried out to identify the interaction between miR-141-5p and BTG antiproliferation factor 1 (BTG1). Results: miR-141-5p was upregulated in cervical cancer and was negatively associated with the prognosis of patients with cervical cancer. Functional analyses demonstrated that silenced miR-141-5p expression inhibited the cell proliferation, migration, and invasion, and alleviated apoptosis of C33A and HeLa cells. In addition, miR-141-5p suppresses the activity of BTG1-3'-UTR. Rescue assays demonstrated that the cervical cancer progression is suppressed by miR-141-5p inhibitor and retrieved by sh-BTG1. Conclusions: The authors' findings reveal that miR-141-5p exerts its role through targeting BTG1 in cervical cancer progression, indicating that miR-141-5p may represent a promising target for the treatment of cervical cancer patients. The Clinical Trial Registration number: (2019-KY013).

Phytochemical thymoquinone prevents hemoglobin glycoxidation and protofibrils formation: A biophysical aspect

d-ribose, a reducing sugar, in diabetic hyperglycemia provokes non-enzymatic glycoxidation of hemoglobin (Hb), an abundant protein of red blood cells (RBCs). Different types of intermediates adduct formation occur during glycoxidation, such as advanced glycation end-products (AGEs) which lead to amyloid formation due to structural and conformational alterations in protein. Therefore, the study of these intermediate adducts plays a pivotal role to discern their relationship with diabetes mellitus and related disorders. Here, we investigated the interaction mechanism of d-ribose with Hb, and Hb prebound phytochemical thymoquinone (TQ). Our investigation reveals that the interaction of TQ with histidine residues of Hb interferes with the interaction of d-ribose with glycine residues at the glycation-site. Based on that, we had performed a time-based (21-days) in-vitro glycoxidation study at 37 °C to investigate the structural perturbation mechanism of Hb at different time-intervals in absence/presence of TQ. We found that prolonged glycoxidation induces amyloid formation in absence of TQ but in its presence, the process was prohibited. In summary, this study examined and characterized biophysically different intermediate-states of protein carrying glycoxidation-modification. Our findings suggested that TQ potentially affects interaction of d-ribose with Hb that prevents glycoxidation and protofibril formation, which establishes TQ as a potential therapeutic agent.

Amyloid-like aggregation of bovine serum albumin at physiological temperature induced by cross-seeding effect of HEWL amyloid aggregates

BSA can form amyloid-like aggregates in vitro at 65 °C. Heterologous amyloid can proposedly cross-seed other protein's aggregation, however, general mechanisms and driving conditions remain to be vividly elucidated. Here, we examined if pre-formed HEWL amyloid can cross-seed the aggregation of BSA at physiological temperature, 37 °C, and whether the efficacy depends on the BSA conformation. We find that at pH 3.0, 37 °C where BSA manifests exposure of abundant hydrophobic patches, HEWL amyloid efficiently drives BSA into ThT-positive, sarkosyl-resistant, β-sheet rich amyloid-like aggregates exhibiting fibrils in TEM. On the contrary, HEWL amyloid fails to cross-seed the BSA aggregation at pH 7.0, 37 °C where BSA has largely internalized hydrophobic patches. Strikingly, human lysozyme amyloid could also cross-seed human serum albumin aggregation at pH 3.0, 37 °C. Thus, heterologous amyloid cross-seeding can help overcome the energy-barrier for aggregation of other proteins that, for any reason, may have perturbed and promiscuous structural conformation at physiological temperatures.

Structural and Functional Characterization of Covalently Modified Proteins Formed By a Glycating Agent, Glyoxal

Glycation, the main consequence of hyperglycemia, is one of the major perpetrators of diabetes and several other conditions, including coronary and neurodegenerative complications. Such a hyperglycemic condition is represented by a large increase in levels of various glycation end products including glyoxal, methylglyoxal, and carboxymethyl-lysine among others. These glycation end products are known to play a crucial role in diabetic complications due to their ability to covalently modify important proteins and enzymes, specifically at lysine residues (a process termed as glycation), making them non-functional. Previous studies have largely paid attention on characterization and identification of these reactive glycating agents. Structural and functional consequences of proteins affected by glycation have not yet been critically investigated. We have made a systematic investigation on the early conformational changes and functional alterations brought about by a glycating agent, glyoxal, on different proteins. We found that the early event in glycation includes an increase in hydrodynamic diameter, followed by minor structural alterations sufficient to impair enzyme activity. The study indicates the importance of glyoxal-induced early structural alteration of proteins toward the pathophysiology of hyperglycemia/diabetes and associated conditions.

Evidence of Anti-amyloid Characteristics of Plumbagin via Inhibition of Protein Aggregation and Disassembly of Protein Fibrils

The biological consequences associated with the conversion of soluble proteins into insoluble toxic amyloids are not only limited to the onset of neurodegenerative diseases but also to the potential health risks associated with supplements of protein therapeutic agents as well. Hence, finding inhibitors against amyloid formation is important, and natural product-based anti-amyloid compounds have gained much interest because of their higher efficacy and biocompatibility. Plumbagin has been identified as a potential natural product with multiple medical benefits; however, it remains largely unclear whether plumbagin can act against amyloid formation of proteins. Here, we show that plumbagin can effectively inhibit the temperature-induced amyloid aggregation of important proteins (insulin and serum albumin). Both experimental and computational data revealed that the presence of plumbagin in protein solutions, under aggregating conditions, promotes a direct protein-plumbagin interaction, which is predominantly stabilized by stronger H-bonds and hydrophobic interactions. Plumbagin-mediated retention of the native structures of proteins appears to play a crucial role in preventing their conversion into insoluble β-sheet-rich amyloid aggregates. More importantly, the addition of plumbagin into a suspension of protein fibrils triggered their spontaneous disassembly, promoting the release of soluble proteins. The results highlight that a possible synergistic effect via both the stabilization of protein structures and the restriction of the monomer recruitment at the fibril growth sites could be important for the mechanism of plumbagin's anti-aggregation effect. These findings may inspire the development of plumbagin-based formulations to benefit both the prevention and treatment of amyloid-related health complications.

Understanding the Role of Protein Glycation in the Amyloid Aggregation Process

Protein function and flexibility is directly related to the native distribution of its structural elements and any alteration in protein architecture leads to several abnormalities and accumulation of misfolded proteins. This phenomenon is associated with a range of increasingly common human disorders, including Alzheimer and Parkinson diseases, type II diabetes, and a number of systemic amyloidosis characterized by the accumulation of amyloid aggregates both in the extracellular space of tissues and as intracellular deposits. Post-translational modifications are known to have an active role in the in vivo amyloid aggregation as able to affect protein structure and dynamics. Among them, a key role seems to be played by non-enzymatic glycation, the most unwanted irreversible modification of the protein structure, which strongly affects long-living proteins throughout the body. This study provided an overview of the molecular effects induced by glycation on the amyloid aggregation process of several protein models associated with misfolding diseases. In particular, we analyzed the role of glycation on protein folding, kinetics of amyloid formation, and amyloid cytotoxicity in order to shed light on the role of this post-translational modification in the in vivo amyloid aggregation process.

Revealing Advanced Glycation End Products Associated Structural Changes in Serum Albumin

Structural alterations in proteins have a significant impact on their function and body physiology. Glycation via nonenzymatic forms of cross-linking leads to proteins' conformational changes, the macromolecule being recognized as a stable fibrillary structure, oligomerization, and becoming advanced glycation end products (AGEs). Protein that undergoes glycation-related modifications, namely, β-sheet enriched structural changes, are recognized as amyloid. In the current study, we characterized a single protein modified in vitro under physiological conditions to represent a protein glycation model. The glycation altered the helical conformation of serum albumin (SA) and promoted the formation of a β-sheet enriched with amyloid fibrils detected at multidimensional levels. The nanoscale resolution by spectroscopy in the presence of thioflavin-T (ThT) and 8-anilinonaphthalene-1-sulfonic acid (8-ANS) showed binding of the fibrils formed in the presence of glucose (GLU) and the carbonyl metabolites methylglyoxal (MGO) and glycolaldehyde (GAD). In the presence of MGO and GAD, the SA becomes insoluble aggregates, demonstrated by TEM microscopy and dynamic light scattering (DLS). The protein oligomerization was visualized when separated via SDS gel electrophoresis and mass photometry (MP) assays. Following the glycation, eventually, the material polymerized and became stiffer. The level of stiffness was analyzed by a rheometer that revealed a quick alteration under MGO and GAD. This is the first study to combine multiple spectroscopy assays, imaging, and rheology measurements of SA and to demonstrate a resolution on a nanoscale structural toward better resolution of the conformational changes of glycated SA, oligomerization, and protein aggregations under physiological conditions.

Affinity Diversification of a Polymer Probe for Pattern-recognition-based Biosensing Using Chemical Additives

Pattern-recognition-based sensing has attracted attention as a promising alternative to conventional sensing methods that rely on selective recognition. Here, we report on novel strategy using chemical additives with the ability to modulate probe/analyte interactions to more easily construct pattern-recognition-based sensing systems for proteins and cells. The fluorescence of dansyl-modified cationic poly-L-lysine (PLL-Dnc) is enhanced upon binding to proteins in aqueous solution, while the addition of salts, inert polymers, or alcohols modulates the protein/PLL-Dnc interactions via a variety of mechanisms. Subsequent readout of the fluorescence changes produces response patterns that reflect the characteristics of the analytes. Multivariate analysis of the response patterns allowed for accurate identification of not only eight structurally similar albumin homologues, but also four mammalian cells. This strategy, which uses inexpensive and common additives, significantly improves the accessibility of pattern-recognition-based sensing, which will offer new opportunities for the detection of various bioanalytes.

Effect of methylglyoxal on the alteration in structure and digestibility of α-lactalbumin, and the formation of advanced glycation end products under simulated thermal processing

α-Dicarbonyl compounds (α-DCs) are a class of compounds generated during the thermal processing of food. Due to the high reactivity, α-DCs were endowed with the ability to react with food components thus lowering nutrition value and even leading to a potential risk for food safety. In this study, methylglyoxal (MG), the most abundant α-DCs, was selected to investigate the alteration effects on the structure and digestibility of α-lactalbumin (αLA) under thermal processing (60-100°C). The results showed that the modification degree of αLA by MG increased with the rise of processing temperature, accompanied by the significant changes in molecular weight, intrinsic fluorescence, and secondary structures of αLA. High-resolution mass spectrometry analysis identified that lysine (Lys) and arginine (Arg) are the modification sites, and Nε-(carboxyethyl)-L-lysine is the main modification type. Since the Lys and Arg are also the cleavage sites of trypsin, the digestibility of MG modified αLA (MG-αLA) by trypsin correspondingly decreased with an increase of processing temperature. The reacted Lys and Arg residues, and the protein-bound AGEs were quantified, and the contents were found to be highly dependent on the temperature.

D-ribose: Potential clinical applications in congestive heart failure and diabetes, and its complications (Review)

The quality of life of patients with certain diseases may be improved through the development of technologies and advancements in pharmacology, with the aim of prolonging their life. However, congestive heart failure (CHF), as well their complications, continue to be the leading cause of disease-associated death. The mechanisms underlying the development and progression of diabetes and CHF have been uncovered in a stepwise manner and the understanding of these mechanisms has improved the management of these diseases, resulting in reduced mortality and morbidity rates; however, CHF remains the leading cause of death worldwide, particularly in developed countries. In the past decades, research has indicated that several supplements and naturally occurring compounds may be used to treat muscle weakness, for cardiac failure management, rehabilitation following myocardial ischemia-reperfusion and various complications of diabetes. D-ribose is an essential component of the respiratory, skeletal and nervous systems and is a popular compound, as its supplementation may have beneficial effects. In the present review, the physiological roles, toxic reactions and the potential use of D-ribose in the management of clinical diseases are summarized.

Osmoprotectant Coated Thermostable Gold Nanoparticles Efficiently Restrict Temperature-Induced Amyloid Aggregation of Insulin

Naturally occurring osmoprotectants are known to prevent aggregation of proteins under various stress factors including extreme pH and elevated temperature conditions. Here, we synthesized gold nanoparticles coated with selected osmolytes (proline, hydroxyproline, and glycine) and examined their effect on temperature-induced amyloid-formation of insulin hormone. These uniform, thermostable, and hemocompatible gold nanoparticles were capable of inhibiting both spontaneous and seed-induced amyloid aggregation of insulin. Both quenching and docking experiments suggest a direct interaction between the osmoprotectant-coated nanoparticles and aggregation-prone hydrophobic stretches of insulin. Circular-dichroism results confirmed the retention of insulin's native structure in the presence of these nanoparticles. Unlike the indirect solvent-mediated effect of free osmolytes, the inhibition effect of osmolyte-coated gold nanoparticles was observed to be mediated through their direct interaction with insulin. The results signify the protection of the exposed aggregation-prone domains of insulin from temperature-induced self-assembly through osmoprotectant-coated nanoparticles, and such effect may inspire the development of osmolyte-based antiamyloid nanoformulations.

The concept of protein folding/unfolding and its impacts on human health

Proteins have evolved in specific 3D structures and play different functions in cells and determine various reactions and pathways. The newly synthesized amino acid chains once depart ribosome must crumple into three-dimensional structures so can be biologically active. This process of protein that makes a functional molecule is called protein folding. The protein folding is both a biological and a physicochemical process that depends on the sequence of it. In fact, this process occurs more complicated and in some cases and in exposure to some molecules like glucose (glycation), mistaken folding leads to amyloid structures and fatal disorders called conformational diseases. Such conditions are detected by the quality control system of the cell and these abnormal proteins undergo renovation or degradation. This scenario takes place by the chaperones, chaperonins, and Ubiquitin-proteasome complex. Understanding of protein folding mechanisms from different views including experimental and computational approaches has revealed some intermediate ensembles such as molten globule and has been subjected to biophysical and molecular biology attempts to know more about prevalent conformational diseases.

The Prophylactic Activity of Punica granatum L. mesocarp Protects Preadipocytes against Ribosylated BSA-Induced Toxicity

OBJECTIVE

It was aimed at comparing the glycating capacities of glucose and ribose in bovine serum albumin (BSA) and anti-glycation activity of pomegranate mesocarp extract (PME). The protective mechanism of PME against ribosylated BSA (BSA_RIB)-induced toxicity was also investigated.

METHODS

BSA was incubated with glucose or ribose in the presence or absence of PME for 15 days. In preadipocytes pretreated with PME, cell viability, ROS production, lipid peroxidation and mitochondrial membrane potential were investigated following 1, 6, 12, 18 and 24 h exposure to BSA_RIB. Nuclear translocation of NFκB was assessed at 1 h and 24 h of BSA_RIB insult. Accumulation of oxidized proteins, activities of intrinsic antioxidant enzymes and IL-6 secretion were also determined after 24 h exposure to BSA_RIB.

RESULTS

Ribose was a harsher glycating agent as compared to glucose and PME showed strong anti-glycation activity by suppressing (P < 0.05) the increase in levels of fluorescent AGEs, Amadori products, protein carbonyl and advanced oxidation protein products (AOPP). In preadipocytes, BSA_RIB potentiated pro-apoptotic activity by inhibiting the nuclear translocation of NFκB. BSA_RIB induced a time dependent decrease in cell viability, which was significantly suppressed (P < 0.05) by PME. The extract also significantly reduced (P < 0.05) the time dependent increase in ROS level and associated lipid peroxidation as well as loss in mitochondrial membrane potential caused by BSA_RIB. PME also counteracted the BSA_RIB-induced accumulation of oxidized proteins, decrease in intrinsic antioxidant activity and IL-6 over-secretion.

CONCLUSIONS

PME showed anti-glycation activity and afforded protection against BSA_RIB-induced toxicity, oxidative stress and inflammation in preadipocytes.

Chronic D-ribose and D-mannose overload induce depressive/anxiety-like behavior and spatial memory impairment in mice

The effects of different forms of monosaccharides on the brain remain unclear, though neuropsychiatric disorders undergo changes in glucose metabolism. This study assessed cell viability responses to five commonly consumed monosaccharides-D-ribose (RIB), D-glucose, D-mannose (MAN), D-xylose and L-arabinose-in cultured neuro-2a cells. Markedly decreased cell viability was observed in cells treated with RIB and MAN. We then showed that high-dose administration of RIB induced depressive- and anxiety-like behavior as well as spatial memory impairment in mice, while high-dose administration of MAN induced anxiety-like behavior and spatial memory impairment only. Moreover, significant pathological changes were observed in the hippocampus of high-dose RIB-treated mice by hematoxylin-eosin staining. Association analysis of the metabolome and transcriptome suggested that the anxiety-like behavior and spatial memory impairment induced by RIB and MAN may be attributed to the changes in four metabolites and 81 genes in the hippocampus, which is involved in amino acid metabolism and serotonin transport. In addition, combined with previous genome-wide association studies on depression, a correlation was found between the levels of Tnni3k and Tbx1 in the hippocampus and RIB induced depressive-like behavior. Finally, metabolite-gene network, qRT-PCR and western blot analysis showed that the insulin-POMC-MEK-TCF7L2 and MAPK-CREB-GRIN2A-CaMKII signaling pathways were respectively associated with RIB and MAN induced depressive/anxiety-like behavior and spatial memory impairment. Our findings clarified our understanding of the biological mechanisms underlying RIB and MAN induced depressive/anxiety-like behavior and spatial memory impairment in mice and highlighted the deleterious effects of high-dose RIB and MAN as long-term energy sources.

Antiglycation and antitumoral activity of Tribulus terrestris dry extract

OBJECTIVE

Investigation of the antiglycation and antitumoral potential of standardized and saponins-enriched extracts of Tribulus terrestris herbal medicine.

MATERIALS AND METHODS

The procedures for the evaluation of the antiglycation activity of the standardized (TtSE) and saponins-enriched (TtEE) extracts of T. terrestris were: determination of relative mobility in electrophoresis (RME), free amino groups using OPA method and advanced glycation end-products (AGEs) fluorescence. Antioxidant activity was determined by DPPH radical scavenging test. In vitro antitumor activity of TtSE and TtEE was evaluated in human tumor cell lines.

RESULTS

The results were obtained by antiglycation tests (RME, OPA method and AGEs fluorescence determination), using BSA as protein and ribose as glycation agent, and antioxidant assay (DPPH test); it was verified that both extracts of T. terrestris have antiglycation and antioxidant activity. In addition, the extracts were able to induce death of more than 50% of human tumor cell lines.

CONCLUSION

The present study showed that standardized and saponins-enriched extracts of T. terrestris herbal medicine present antiglycation and antioxidant and antiproliferative action in human tumor cells lines. The saponins-enriched extract proved a greater antiglycation and antioxidant activity in comparison to the standardized type.

Inhibitory Effect of Antidesma bunius Fruit Extract on Carbohydrate Digestive Enzymes Activity and Protein Glycation In Vitro

Antidesma bunius (L.) spreng (Mamao) is widely distributed in Northeastern Thailand. Antidesma bunius has been reported to contain anthocyanins, which possess antioxidant and antihypertensive actions. However, the antidiabetic and antiglycation activity of Antidesma bunius fruit extract has not yet been reported. In this study, we investigated the inhibitory activity of anthocyanin-enriched fraction of Antidesma bunius fruit extract (ABE) against pancreatic α-amylase, intestinal α-glucosidase (maltase and sucrase), protein glycation, as well as antioxidant activity. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) chromatogram revealed that ABE contained phytochemical compounds such as cyanidin-3-glucoside, delphinidin-3-glucoside, ellagic acid, and myricetin-3-galactoside. ABE inhibited intestinal maltase and sucrase activity with the IC₅₀ values of 0.76 ± 0.02 mg/mL and 1.33 ± 0.03 mg/mL, respectively. Furthermore, ABE (0.25 mg/mL) reduced the formation of fluorescent AGEs and the level of N^ε-carboxymethyllysine (N^ε-CML) in fructose and glucose-induced protein glycation during four weeks of incubation. During the glycation process, the protein carbonyl and β-amyloid cross structure were decreased by ABE (0.25 mg/mL). In addition, ABE exhibited antioxidant activity through DPPH radical scavenging activity and Trolox equivalent antioxidant capacity (TEAC) with the IC₅₀ values 15.84 ± 0.06 µg/mL and 166.1 ± 2.40 µg/mL, respectively. Meanwhile, ferric reducing antioxidant power (FRAP) showed an EC₅₀ value of 182.22 ± 0.64 µg/mL. The findings suggest that ABE may be a promising agent for inhibiting carbohydrate digestive enzyme activity, reducing monosaccharide-induced protein glycation, and antioxidant activity.

Comparative assessment of neurotoxicity impacts induced by alkyl tri-n-butyl phosphate and aromatic tricresyl phosphate in PC12 cells

Organophosphate flame retardants (OPFRs) have become a growing concern due to their potential environmental and health risk. However, limited studies have described the toxicity, particularly neurotoxicity of alkyl and aromatic OPFRs. This study investigated the neurotoxicity of alkyl tri-n-butyl phosphate (TnBP) and aromatic tricresyl phosphate (TCP) to rat adrenal pheochromocytoma (PC12) cells for 24 h. Viability detection showed dose-response toxicity effect of TCP and TnBP to PC12 cells. The half-maximal inhibitory concentration of 24 h (24 h-IC₅₀ ) of TCP and TnBP were 2415.61 and 338.09 μM, respectively. Both TnBP and TCP significantly changed the acetylcholinesterase (AChE) activity, and TnBP is more likely to cause neurotoxicity to PC12 cells compared to TCP. Also, The results of LDH and caspase-3 activity detection as well as Hoechst staining suggested that cell apoptosis induced by TCP and TnBP may be the primary pathway. These findings provide a toxicity data of aromatic and alkyl-substituted OPFRs to PC12 cells, and a new insight into the toxicity of OPFRs on health risk assessment.

Consequence of macromolecular crowding on aggregation propensity and structural stability of haemoglobin under glycating conditions

Cell interiors are extremely congested with biological macromolecules exerting crowding effect, influencing various physiognomies of protein life. Present work deals with effect of crowding on folding behaviour of haemoglobin (Hb) under glycating conditions. Macromolecular crowding was mimicked by concentrated solutions of dextran 70. Hb with 0.2 M fructose and ribose was incubated separately for 96 h in dilute and crowded solution to analyse conformational changes. Reduced intrinsic and ANS fluorescence, decreased Soret absorbance, enhanced turbidity, browning of protein, red shift in ThT and Congo red spectra significantly unveiled protein aggregation. FTIR and CD results revealed transition from α-helix to β-sheets confirming aggregation. Transmission electron microscopy exhibited incidence of aggregates. Macromolecular crowding was witnessed to defend conformational stability of native Hb under stress condition at 100 mg/ml dextran, noticeably indicating deceleration of aggregation. Stabilising effect of crowding was marginally better in fructosylated Hb than with ribose due to difference in their glycation potential. Contrarily, in over-crowded solution where dextran concentration was 500 mg/ml, heightened aggregation was perceived implying concentration dependant, dual nature of macromolecular crowding. The novelty of this study lies in idea of considering macromolecular crowding as a key player in regulation of protein stability which was safely ignored previously.

Ribosylation-Derived Advanced Glycation End Products Induce Tau Hyperphosphorylation Through Brain-Derived Neurotrophic Factor Reduction

Advanced glycation end products (AGEs) have been implicated in the disease process of diabetes mellitus. They have also been found in senile plaques and neurofibrillary tangles in the brains of Alzheimer's disease patients. Furthermore, abnormally high levels of D-ribose and D-glucose were found in the urine of patients with type 2 diabetes mellitus, suggesting that diabetic patients suffer from dysmetabolism of not only D-glucose but also D-ribose. In the present study, intravenous tail injections of ribosylated rat serum albumin (RRSA) were found to impair memory in rats, but they did not markedly impair learning, as measured by the Morris water maze test. Injections of RRSA were found to trigger tau hyperphosphorylation in the rat hippocampus via GSK-3β activation. Tau hyperphosphorylation and GSK-3β activation were also observed in N2a cells in the presence of ribosylation-derived AGEs. Furthermore, the administration of ribosylation-derived AGEs induced the suppression of brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase B (TrkB). Both GSK-3β inhibition and BDNF treatment decreased the levels of phosphorylated tau in N2a cells. In particular, the administration of BDNF could rescue memory failure in ribosylated AGE-injected rats. Ribosylation-derived AGEs downregulated the BDNF-TrkB pathway in rat brains and N2a cells, leading to GSK-3β activation-mediated tau hyperphosphorylation, which was involved in the observed rat memory loss. Targeting ribosylation may be a promising therapeutic strategy to prevent Alzheimer's disease and diabetic encephalopathies.

Mechanism of Selenium Nanoparticles Inhibiting Advanced Glycation End Products

Selenium nanoparticles (SeNPs) have been applied in fields of nanobiosensors, environment, nanomedicine, etc. as a result of their excellent characteristics. Early studies had shown that SeNPs have certain inhibition ability against glycation, but the inhibition mechanism, especially for the influence of SeNPs on the reaction activity of glycation sites, remains unclear. The aim of the presented research was to reveal the effects of SeNPs on the β-lactoglobulin (β-Lg)/d-ribose glycation system at the molecular level and explore the possible inhibitory mechanism of SeNPs on the formation of advanced glycation end products (AGEs) by analyzing the glycation sites via high-performance liquid chromatography (HPLC)-Orbitrap-tandem mass spectrometry (MS/MS). Changes in contents of AGE formation and free amino acid contents had indicated that SeNPs could significantly slow the glycation process, thus attenuating the formation of AGEs. HPLC-Orbitrap-MS/MS analysis revealed that, at 6, 12, and 24 h, the number of glycation sites of glycated β-Lg decreased from 7, 7, and 9 to 5, 5, and 6 after the intervention of SeNPs, respectively. The glycation extent of each glycation site was controlled, and the dual-glycation ability of K8, K14, K47, K91, and K101 was changed. All of these results confirmed that SeNPs could indeed slow the process of protein glycation at the molecular level. This may be the reason for SeNPs reducing the formation of AGEs during glycation. Therefore, this study shed light on the insight of how SeNPs reduce the formation of AGEs.

Ribosylation induced structural changes in Bovine Serum Albumin: understanding high dietary sugar induced protein aggregation and amyloid formation

Non-enzymatic glycation of proteins is believed to be the root cause of high dietary sugar associated pathophysiological maladies. We investigated the structural changes in protein during progression of glycation using ribosylated Bovine Serum Albumin (BSA). Non enzymatic attachment of about 45 ribose molecules to BSA resulted in gradual reduction of hydrophobicity and aggregation as indicated by red-shifted tryptophan fluorescence, reduced ANS binding and lower anisotropy of FITC-conjugated protein. Parallely, there was a significant decrease of alpha helicity as revealed by Circular Dichroism (CD) and Fourier transformed-Infra Red (FT-IR) spectra. The glycated proteins assumed compact globular structures with enhanced Thioflavin-T binding resembling amyloids. The gross structural transition affected by ribosylation led to enhanced thermostability as indicated by melting temperature and Transmission Electron Microscopy. At a later stage of glycation, the glycated proteins developed non-specific aggregates with increase in size and loss of amyloidogenic behaviour. A parallel non-glycated control incubated under similar conditions indicated that amyloid formation and associated changes were specific for ribosylation and not driven by thermal denaturation due to incubation at 37 °C. Functionality of the glycated protein was significantly altered as probed by Isothermal Titration Calorimetry using polyphenols as substrates. The studies demonstrated that glycation driven globular amyloids form and persist as transient intermediates during formation of misfolded glycated adducts. To the best of our knowledge, the present study is the first systematic attempt to understand glycation associated changes in a protein and provides important insights towards designing therapeutics for arresting dietary sugar induced amyloid formation.

Sunset yellow degradation product, as an efficient water-soluble inducer, accelerates 1N4R Tau amyloid oligomerization: In vitro preliminary evidence against the food colorant safety in terms of "Triggered Amyloid Aggregation"

Today, Alzheimer's disease (AD) as the most prevalent type of dementia turns into one of the most severe health problems. Neurofibrillary tangle (NFT), mostly comprised of fibrils formed by Tau, is a hallmark of a class of neurodegenerative diseases. Tau protein promotes assembly and makes stable microtubules that play a role in the appropriate function of neurons. Polyanionic cofactors such as heparin, and azo dyes, can induce aggregation of tau protein in vitro. Sunset Yellow is a food colorant used widely in food industries. In the current work, we introduced degradation product (DP) of Sunset Yellow as an effective inducer of Tau aggregation. Two Tau aggregation inducers were produced, and then the aggregation kinetics and the structure of 1N4R Tau amyloid fibrils were characterized using ThT fluorescence spectroscopy, X-Ray Diffraction (XRD), circular dichroism (CD) and atomic force microscopy (AFM). Also, the toxic effects of the induced aggregates on RBCs and SH-SY5Y cells were demonstrated by hemolysis and LDH assays, respectively. Both inducers efficiently accelerated the formation of the amyloid fibril. Along with the confirmation of the β-sheets structure in Tau aggregates by Far-UV CD spectra, X-ray diffractions revealed the typical cross-β diffraction pattern. The oligomer formation in the presence of DPs was also confirmed by AFM. The possible in vivo effect of artificial azo dyes on Tau aggregation should be considered seriously as a newly opened dimension in food safety and human health.

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.

Glycated albumin precipitation using aptamer conjugated magnetic nanoparticles

To develop a strategy for the elimination of prefibrillar amyloid aggregates, a three-step non-modified DNA aptamer conjugation on silica-coated magnetic nanoparticles was carried out to achieve aptamer conjugated on MNP (Ap-SiMNP). Prefibrillar amyloid aggregates are generated under a diabetic condition which are prominently participated in developing diabetic complications. The binding properties of candidate DNA aptamer against serum albumin prefibrillar amyloid aggregates (AA20) were verified using electrophoretic mobility shift assay (EMSA) and surface plasmon resonance spectroscopy (SPR) analysis. The chloro-functionalized silica-coated MNPs were synthesized then a nano-targeting structure as aptamer conjugated on MNP (Ap-SiMNP) was constructed. Finally, Ap-SiMNP was verified for specific binding efficiency and AA20 removal using an external magnetic field. The candidate aptamer showed a high binding capacity at EMSA and SPR analysis (KD = 3.4 × 10─9 M) and successfully used to construct Ap-SiMNP. Here, we show a proof of concept for an efficient bio-scavenger as Ap-SiMNP to provide a promising opportunity to consider as a possible strategy to overcome some diabetic complications through specific binding/removal of toxic AA20 species.

An Azidoribose Probe to Track Ketoamine Adducts in Histone Ribose Glycation

Reactive cellular metabolites can modify macromolecules and form adducts known as nonenzymatic covalent modifications (NECMs). The dissection of the mechanisms, regulation, and consequences of NECMs, such as glycation, has been challenging due to the complex and often ambiguous nature of the adducts formed. Specific chemical tools are required to directly track the formation of these modifications on key targets in order to uncover their underlying physiological importance. Here, we present the novel chemoenzymatic synthesis of an active azido-modified ribose analog, 5-azidoribose (5-AR), as well as the synthesis of an inactive control derivative, 1-azidoribose (1-AR), and their application toward understanding protein ribose-glycation in vitro and in cellulo. With these new probes we found that, similar to methylglyoxal (MGO) glycation, ribose glycation specifically accumulates on histones. In addition to fluorescent labeling, we demonstrate the utility of the probe in enriching modified targets, which were identified by label-free quantitative proteomics and high-resolution MS/MS workflows. Finally, we establish that the known oncoprotein and hexose deglycase, fructosamine 3-kinase (FN3K), recognizes and facilitates the removal of 5-AR glycation adducts in live cells, supporting the dynamic regulation of ribose glycation as well as validating the probe as a new platform to monitor FN3K activity. Altogether, we demonstrate this probe's utilities to uncover ribose-glycation and deglycation events as well as track FN3K activity toward establishing its potential as a new cancer vulnerability.