Transthyretin Binding Heterogeneity and Anti-amyloidogenic Activity of Natural Polyphenols and Their Metabolites

A Preliminary Analysis of the Influence of Elderberry Juice Consumption on Thyroid Metabolism in Mice and Humans Fed High-Fat Diets

BACKGROUND/OBJECTIVES

Elderberry juice (EBJ) consumption prevents weight gain in mice fed a high-fat diet and increases fat oxidation in response to a meal challenge in overweight humans. Thyroid hormones influence metabolism and substrate oxidation, and the impact of EBJ consumption on thyroid homeostasis remains unexplored. Thus, the primary objective of this analysis was to investigate whether elderberry consumption in mice and humans affects serum thyroid biomarkers.

METHODS

Serum samples from a previous trial incorporating an EBJ intervention were analyzed for thyroxine (T4), thyroid stimulating hormone (TSH), and thyroglobulin (Tg). The samples are from a meal-tolerance test in 18 humans who followed a 7-day diet-controlled crossover design. Samples from 33 male mice were collected after 13 weeks following a high-fat diet with or without EBJ powder, and with or without free wheel running.

RESULTS

Short-term EBJ consumption in humans resulted in significant increases in T4 (PL: 42.3 ± 3.2 vs. EBJ: 49.3 ± 4.1 ng/mL, p < 0.05), and TSH (PL: 0.094 ± 0.012 vs. EBJ: 0.104 ± 0.011 ng/mL, p < 0.05), with no change in Tg (p > 0.05). Whereas supplementation with EBJ powder in rodents resulted in a non-significant reduction in T4 (p = 0.07).

CONCLUSIONS

These findings suggest that elderberry juice consumption may influence thyroid metabolism, contributing to the observed metabolic benefits, such as improved fat oxidation, body composition, and protection against high-fat diet-induced weight gain. The increased T4 and TSH in humans align with enhanced metabolic rate, while the reduction in T4 in rodents indicates potential long-term adaptations requiring further exploration.

Optimization of the Search for Neuroprotectors among Bioflavonoids

For the first time, to optimize the creation of new neuroprotective agents based on bioflavonoids, we applied information technologies; these include docking analysis to calculate the binding of candidate molecules to the pharmacological target protein transthyretin as well as a program of virtual screening of NO scavengers. As a result of this approach, the substance catechin was isolated from candidate molecules-quercetin, catechin, Epicatechin gallate, Epicatechin, Procyanidin B1, Procyanidin B2, Procyanidin B3, and Catechin-3-gallate-according to docking analysis. As a result of virtual screening, catechin was identified as a potential NO scavenger (55.15% prediction). The results of the prediction were confirmed by in vitro experiments. Course administration of catechin to animals with experimental multiple sclerosis (MS) against the background of methylprednisolone administration completely eliminated lethal cases, reduced the number of diseased animals by 20% as well as prevented the development of severe neurological symptoms by 20% (compared to the methylprednisolone group) and by 60% compared to the control group. Course administration of catechin with methylprednisolone leads to a decrease in the neurodegradation markers in the cytosol of rats, with EAE: NSE by 37% and S-100 by 54.8%. The combined administration of methylprednisolone significantly exceeds the combination of methylprednisolone with the reference drug mexidol by the degree of NSE reduction. The obtained results indicate a significant neuroprotective effect of ocular combinations of methylprednisolone and catechin. The above-mentioned confirms the correctness of the bioflavonoid selection with the help of a virtual screening program.

Understanding the prion-like behavior of mutant p53 proteins in triple-negative breast cancer pathogenesis: The current therapeutic strategies and future directions

Breast cancer (BC) is viewed as a significant public health issue and is the primary cause of cancer-related deaths among women worldwide. Triple-negative breast cancer (TNBC) is a particularly aggressive subtype that predominantly affects young premenopausal women. The tumor suppressor p53 playsa vital role in the cellular response to DNA damage, and its loss or mutations are commonly present in many cancers, including BC. Recent evidence suggests that mutant p53 proteins can aggregate and form prion-like structures, which may contribute to the pathogenesis of different types of malignancies, such as BC. This review provides an overview of BC molecular subtypes, the epidemiology of TNBC, and the role of p53 in BC development. We also discuss the potential implications of prion-like aggregation in BC and highlight future research directions. Moreover, a comprehensive analysis of the current therapeutic approaches targeting p53 aggregates in BC treatment is presented. Strategies including small molecules, chaperone inhibitors, immunotherapy, CRISPR-Cas9, and siRNA are discussed, along with their potential benefits and drawbacks. The use of these approaches to inhibit p53 aggregation and degradation represents a promising target for cancer therapy. Future investigations into the efficacy of these approaches against various p53 mutations or binding to non-p53 proteins should be conducted to develop more effective and personalized therapies for BC treatment.

Inhibitors of Transthyretin Amyloidosis: How to Rank Drug Candidates Using X-ray Crystallography Data

Amyloidosis is a group of protein misfolding diseases, which include spongiform encephalopathies, Alzheimer's disease and transthyretin (TTR) amyloidosis; all of them are characterized by extracellular deposits of an insoluble fibrillar protein. TTR amyloidosis is a highly debilitating and life-threatening disease. Patients carry less stable TTR homotetramers that are prone to dissociation into non-native monomers, which in turn rapidly self-assemble into oligomers and, ultimately, amyloid fibrils. Liver transplantation to induce the production of wild-type TTR was the only therapeutic strategy until recently. A promising approach to ameliorate transthyretin (TTR) amyloidosis is based on the so-called TTR kinetic stabilizers. More than 1000 TTR stabilizers have already been tested by many research groups, but the diversity of experimental techniques and conditions used hampers an objective prioritization of the compounds. One of the most reliable and unambiguous techniques applied to determine the structures of the TTR/drug complexes is X-ray diffraction. Most of the potential inhibitors bind in the TTR channel and the crystal structures reveal the atomic details of the interaction between the protein and the compound. Here we suggest that the stabilization effect is associated with a compaction of the quaternary structure of the protein and propose a scoring function to rank drugs based on X-ray crystallography data.

3-O-Methyltolcapone and Its Lipophilic Analogues Are Potent Inhibitors of Transthyretin Amyloidogenesis with High Permeability and Low Toxicity

Transthyretin (TTR) is an amyloidogenic homotetramer involved in the transport of thyroxine in blood and cerebrospinal fluid. To date, more than 130 TTR point mutations are known to destabilise the TTR tetramer, leading to its extracellular pathological aggregation accumulating in several organs, such as heart, peripheral and autonomic nerves, and leptomeninges. Tolcapone is an FDA-approved drug for Parkinson's disease that has been repurposed as a TTR stabiliser. We characterised 3-O-methyltolcapone and two newly synthesized lipophilic analogues, which are expected to be protected from the metabolic glucuronidation that is responsible for the lability of tolcapone in the organism. Immunoblotting assays indicated the high degree of TTR stabilisation, coupled with binding selectivity towards TTR in diluted plasma of 3-O-methyltolcapone and its lipophilic analogues. Furthermore, in vitro toxicity data showed their several-fold improved neuronal and hepatic safety compared to tolcapone. Calorimetric and structural data showed that both T4 binding sites of TTR are occupied by 3-O-methyltolcapone and its lipophilic analogs, consistent with an effective TTR tetramer stabilisation. Moreover, in vitro permeability studies showed that the three compounds can effectively cross the blood-brain barrier, which is a prerequisite for the inhibition of TTR amyloidogenesis in the cerebrospinal fluid. Our data demonstrate the relevance of 3-O-methyltolcapone and its lipophilic analogs as potent inhibitors of TTR amyloidogenesis.

Resveratrol Derivatives Inhibit Transthyretin Fibrillization: Structural Insights into the Interactions between Resveratrol Derivatives and Transthyretin

Hereditary ATTR amyloidosis is a disease caused by the deposition of amyloid fibrils formed by mutated transthyretin (TTR), a protein that binds to thyroid hormone in the serum, in the organs. The development of a small molecule that binds to and stabilizes TTR is a promising strategy for the treatment of ATTR amyloidosis. In the present study, we demonstrated that the resveratrol derivatives including pterostilbene available as a dietary supplement inhibit the fibrillization of V30M-TTR to the same extent as the approved drug tafamidis. Furthermore, based on a thermodynamic and X-ray crystallographic analysis, the binding of the resveratrol derivative to TTR was shown to be enthalpy-driven, with the binding enthalpy being acquired by hydrogen bonding to S117. Moreover, direct observation of hydrogen atoms by neutron crystallography provided details of the hydrogen bond network by S117 and emphasized the importance of the CH···π interaction by L110 in the ligand binding.

Gut microbial metabolites of dietary polyphenols and their potential role in human health and diseases

Polyphenols contribute as one of the largest groups of compounds among all the phytochemicals. Common sources of dietary polyphenols are vegetables, fruits, berries, cereals, whole grains, etc. Owing to their original form, they are difficult to get absorbed. Dietary polyphenols after undergoing gut microbial metabolism form bioaccessible and effective metabolites. Polyphenols and derived metabolites are all together a diversified group of compounds exhibiting pharmacological activities against cardiovascular, cancer, oxidative stress, inflammatory, and bacterial diseases. The formed metabolites are sometimes even more bioavailable and efficacious than the parent polyphenols. Studies on gut microbial metabolism of dietary polyphenols have introduced new approach for the use of polyphenol-rich food in the form of supplementary diet. This review provides insights on various aspects including classification of polyphenols, gut microbiota-mediated metabolism of polyphenols, chemistry of polyphenol metabolism, and pharmacological actions of gut microbial metabolites of polyphenols. It also suggests the use of polyphenols from marine source for the microbial metabolism studies. Till date, gut microbial metabolism of polyphenols from terrestrial sources is extensively studied as compared to marine polyphenols. Marine ecosystem is a profound but partially explored source of phytoconstituents. Among them, edible seaweeds contain high concentration of polyphenols, especially phlorotannins. Hence, microbial metabolism studies of seaweeds can unravel the pharmacological potential of marine polyphenol-derived metabolites.

Detection of Dietary Chalcone and Flavonoid Metabolites in Mice Using UPLC-MS/MS and Their Modulatory Effects on Amyloid β Aggregation

Amyloid β-protein (Aβ42) aggregates have been demonstrated to induce cognitive decline and neurodegeneration in Alzheimer's disease (AD). Thus, functional food ingredients that inhibit Aβ42 aggregation are valuable for AD prevention. Although several food ingredients have been studied for their anti-aggregation activity, information on their bioavailability in the brain, incorporated forms, and relevance to AD etiology is limited. Here, we first detected the sulfate- and glucuronic-acid-conjugated forms of green perilla-derived chalcone (1) and taxifolin (2), which inhibit Aβ42 aggregation, in the brain, small intestine, and plasma of mice (1 and 2 were administered orally) using ultra-performance liquid chromatography-tandem mass spectrometry. We observed that the conjugated metabolites (sulfate (4) and glucuronide (5)) of 1 prevented the fibrillization and oligomerization of Aβ42. These findings imply that the conjugated metabolites of 1 can prove beneficial for AD treatment.

Transthyretin Binding Mode Dichotomy of Fluorescent trans-Stilbene Ligands

The orientations of ligands bound to the transthyretin (TTR) thyroxine (T4) binding site are difficult to predict. Conflicting binding modes of resveratrol have been reported. We previously reported two resveratrol based trans-stilbene fluorescent ligands, (E)-4-(2-(naphthalen-1-yl)vinyl)benzene-1,2-diol (SB-11) and (E)-4-(2-(naphthalen-2-yl)vinyl)benzene-1,2-diol (SB-14), that bind native and misfolded protofibrillar TTR. The binding orientations of these two analogous ligands to native tetrameric TTR were predicted to be opposite. Herein we report the crystal structures of these TTR:ligand complexes. Opposite binding modes were verified but were different than predicted. The reverse binding mode (SB-14) placing the naphthalene moiety toward the opening of the binding pocket renders the fluorescent ligand pH sensitive due to changes in Lys15 amine protonation. Conversely, the forward binding mode (SB-11) placing the naphthalene inward mediates a stabilizing conformational change, allowing intersubunit H-bonding between Ser117 of different monomers across the dimer interface. Our structures of TTR complexes answer important questions in ligand design and interpretation of trans-stilbene binding modes to the TTR T4 binding site.

Mechanistic Insights of Polyphenolic Compounds from Rosemary Bound to Their Protein Targets Obtained by Molecular Dynamics Simulations and Free-Energy Calculations

Rosemary represents an important medicinal plant that has been attributed with various health-promoting properties, especially antioxidative, anti-inflammatory, and anticarcinogenic activities. Carnosic acid, carnosol, and rosmanol, as well as the phenolic acid ester rosmarinic acid, are the main compounds responsible for these actions. In our earlier research, we carried out an inverse molecular docking at the proteome scale to determine possible protein targets of the mentioned compounds. Here, we subjected the previously identified ligand-protein complexes with HIV-1 protease, K-RAS, and factor X to molecular dynamics simulations coupled with free-energy calculations. We observed that carnosic acid and rosmanol act as viable binders of the HIV-1 protease. In addition, carnosol represents a potential binder of the oncogene protein K-RAS. On the other hand, rosmarinic acid was characterized as a weak binder of factor X. We also emphasized the importance of water-mediated hydrogen-bond networks in stabilizing the binding conformation of the studied polyphenols, as well as in mechanistically explaining their promiscuous nature.

Anticancer Therapeutic Strategies Targeting p53 Aggregation

p53 is a tumor suppressor protein that is mutated in more than 50% of cancer cases. When mutated, it frequently results in p53 oncogenic gain of function (GOF), resulting in a greater tendency to aggregate in the phase separation and phase transition pathway. GOFs related to p53 aggregation include chemoresistance, which makes therapy even more difficult. The therapies available for the treatment of cancer are still quite limited, so the study of new molecules and therapeutic targets focusing on p53 aggregates is a promising strategy against cancer. In this review, we classify anticancer molecules with antiaggregation properties into four categories: thiol alkylating agents, designed peptides, agents with chaperone-based mechanisms that inhibit p53 aggregation, and miscellaneous compounds with anti-protein aggregation properties that have been studied in neurodegenerative diseases. Furthermore, we highlight autophagy as a possible degradation pathway for aggregated p53. Here, considering cancer as a protein aggregation disease, we review strategies that have been used to disrupt p53 aggregates, leading to cancer regression.

Deep blue autofluorescence reflects the oxidation state of human transthyretin

Human transthyretin (TTR) is a tetrameric protein transporting thyroid hormones and retinol. TTR is a neuroprotective factor and sensor of oxidative stress which stability is diminished due to mutations and aging, leading to amyloid deposition. Adverse environmental conditions, such as redox and metal ion imbalances, induce destabilization of the TTR structure. We have previously shown that the stability of TTR was disturbed by Ca²⁺ and other factors, including DTT, and led to the formation of an intrinsic fluorophore(s) emitting blue light, termed deep blue autofluorescence (dbAF). Here, we show that the redox state of TTR affects the formation dynamics and properties of dbAF. Free thiols lead to highly unstable subpopulations of TTR and the frequent ocurrence of dbAF. Oxidative conditions counteracted the destabilizing effects of free thiols to some extent. However, strong oxidative conditions led to modifications of TTR, which altered the stability of TTR and resulted in unique dbAF spectra. Riboflavin and/or riboflavin photoproducts bound to TTR and crosslinked TTR subunits. Riboflavin-sensitized photooxidation increased TTR unfolding, while photooxidation, either in the absence or presence of riboflavin, increased proteolysis and resulted in multiple oxidative modifications and dityrosine formation in TTR molecules. Therefore, oxidation can switch the role of TTR from a protective to pathogenic factor.

Quercetin binding accelerates prion fibrillation into proteinase sensitive and loosely structured amyloids

Amyloidoses are caused by the deposition of amyloid fibrils ascribed to protein misfolding. In this study, we examined the antiamyloidogenic and antioxidative activities of quercetin, a plant flavonol from the flavonoid group of polyphenols, on mouse prion protein (moPrP) with biophysical approaches. As the results show, quercetin binds to the C-terminal region of moPrP, and quercetin binding does not affect the structure of moPrP. However, quercetin binding accelerates moPrP fibrillation and changes the structure of moPrP fibrils. Unlike typical prion fibrils, quercetin-bound fibrils are sensitive to proteinase K and are loosely structured. Moreover, due to high antioxidant activity of flavonoid, quercetin-bound fibrils lack imbalance of free radicals and, therefore, they are nontoxic towards neuroblastoma cells. The quercetin shows its uniqueness from typical antiamyloidogenic drugs which either suppress the development of amyloid or eliminate formed amyloids. Quercetin binding converts moPrP into protease-sensitive and non-cytotoxic fibrils. This work provides a powerful resolution in the advancement of antiamyloidogenic treatment.

The Transthyretin/Oleuropein Aglycone Complex: A New Tool against TTR Amyloidosis

The release of monomers from the homotetrameric protein transthyretin (TTR) is the first event of a cascade, eventually leading to sporadic or familial TTR amyloidoses. Thus, ligands able to stabilize TTR and inhibit monomer release are subject of intense scrutiny as potential treatments against these pathologies. Here, we investigated the interaction between TTR and a non-glycated derivative of the main olive polyphenol, oleuropein (OleA), known to interfere with TTR aggregation. We coupled fluorescence studies with molecular docking to investigate the OleA/TTR interaction using wild-type TTR, a monomeric variant, and the L55P cardiotoxic mutant. We characterized a fluorescence band emitted by OleA upon formation of the OleA/TTR complex. Exploiting this signal, we found that a poorly specific non-stoichiometric interaction occurs on the surface of the protein and a more specific stabilizing interaction takes place in the ligand binding pocket of TTR, exhibiting a K_D of 3.23 ± 0.32 µM, with two distinct binding sites. OleA interacts with TTR in different modes, stabilizing it and preventing its dissociation into monomers, with subsequent misfolding. This result paves the way to the possible use of OleA to prevent degenerative diseases associated with TTR misfolding.

Chemo-Preventive Action of Resveratrol: Suppression of p53-A Molecular Targeting Approach

Extensive experimental, clinical, and epidemiological evidence has explained and proven that products of natural origin are significantly important in preventing and/or ameliorating various disorders, including different types of cancer that researchers are extremely focused on. Among these studies on natural active substances, one can distinguish the emphasis on resveratrol and its properties, especially the potential anticancer role. Resveratrol is a natural product proven for its therapeutic activity, with remarkable anti-inflammatory properties. Various other benefits/actions have also been reported, such as cardioprotective, anti-ageing, antioxidant, etc. and its rapid digestion/absorption as well. This review aims to collect and present the latest published studies on resveratrol and its impact on cancer prevention, molecular signals (especially p53 protein participation), and its therapeutic prospects. The most recent information regarding the healing action of resveratrol is presented and concentrated to create an updated database focused on this topic presented above.

Transthyretin Misfolding, A Fatal Structural Pathogenesis Mechanism

Transthyretin (TTR) is an essential transporter of a thyroid hormone and a holo-retinol binding protein, found abundantly in human plasma and cerebrospinal fluid. In addition, this protein is infamous for its amyloidogenic propensity, causing various amyloidoses in humans, such as senile systemic amyloidosis, familial amyloid polyneuropathy, and familial amyloid cardiomyopathy. It has been known for over two decades that decreased stability of the native tetrameric conformation of TTR is the main cause of these diseases. Yet, mechanistic details on the amyloidogenic transformation of TTR were not clear until recent multidisciplinary investigations on various structural states of TTR. In this review, we discuss recent advancements in the structural understanding of TTR misfolding and amyloidosis processes. Special emphasis has been laid on the observations of novel structural features in various amyloidogenic species of TTR. In addition, proteolysis-induced fragmentation of TTR, a recently proposed mechanism facilitating TTR amyloidosis, has been discussed in light of its structural consequences and relevance to acknowledge the amyloidogenicity of TTR.

Molecular insights into a mechanism of resveratrol action using hybrid computational docking/CoMFA and machine learning approach

A phytoalexin, Resveratrol remains a legendary anticancer drug candidate in the archives of scientific literature. Although earlier wet-lab experiments rendering its multiple biological targets, for example, epidermal growth factors, Pro-apoptotic protein p53, sirtuins, and first apoptosis signal (Fas) receptor, Mouse double minute 2 (MDM2) ubiquitin-protein ligase, Estrogen receptor, Quinone reductase, etc. However, notwithstanding some notable successes, identification of an appropriate Resveratrol target(s) has remained a major challenge using physical methods, and hereby limiting its translation into an effective therapeutic(s). Thus, computational insights are much needed to establish proof-of-concept towards potential Resveratrol target(s) with minimum error rate, narrow down the search space, and to assess a more accurate Resveratrol signaling pathway/mechanism at the starting point. Herein, a brute-force technique combining computational receptor-, ligand-based virtual screening, and classification-based machine learning, reveals the precise mechanism of Resveratrol action. Overall, MDM2 ubiquitin-protein ligase (4OGN.pdb) and co-crystallized quinone reductases 2 (4QOH.pdb) were found two suitable drug targets in the case of Resveratrol derivatives. Indeed, carotenoid cleaving oxygenase together with later twos gave gigantic momentum in guiding the rational drug design of Resveratrol derivatives. These molecular modeling insights would be useful for Resveratrol lead optimization into a more precise science.Communicated by Ramaswamy H. Sarma.

The effects of polyphenols-rich tropical fruit juice on cognitive function and metabolomics profile - a randomized controlled trial in middle-aged women

Objectives: Polyphenols, particularly anthocyanins, have received attention in improving health issues during old age, including decline in cognitive function and other health parameters. We aimed to determine the effects of polyphenols-rich tropical fruit TP 3-in-1™ juice towards improving cognitive function, oxidative stress and metabolomics profiles among middle-aged women.Methods: This clinical trial involved 31 subjects with signs of poor cognitive function, as assessed using the Rey Auditory Verbal Learning Test (RAVLT). They were randomized to receive either TP 3-in-1™ juice (n = 16) or placebo (n = 15). Study subjects consumed 500 ml of beverages for three times per day, three days per week, for a period of ten weeks. Juice supplementation provided 9135 mg GAE of total phenolic content and 194.1 mg cyanidin-3-glucoside of total anthocyanin monomer.Results: There was a significant interaction effects on RAVLT immediate recall (p < 0.05) and Comprehensive Trail Making Test (CTMT) Trail 4 (p < 0.05). Metabolomics analysis showed the presence of metabolites related to polyphenols intake and cognitive functions with the intervention group showed increased urinary excretion of thyroxine and 3-methyladenine. Thyroxine and 3-methyladenine give stability to human transthyretin (TTR) and activate autophagy, respectively, which are associated with the pathogenesis of Alzheimer's disease.Conclusion: The result shows the potential of TP 3-in-1™ juice which is rich in anthocyanins in improving cognitive function, particularly learning, memory, processing speed, sequencing, mental flexibility and visual-motor skills domains, among middle-aged women.

Natural compounds as inhibitors of transthyretin amyloidosis and neuroprotective agents: analysis of structural data for future drug design

Natural compounds, such as plant and fruit extracts have shown neuroprotective effect against neurodegenerative diseases. It has been reported that several natural compounds binding to transthyretin (TTR) can be useful in amyloidosis prevention. TTR is a transporter protein that under physiological condition carries thyroxine (T4) and retinol in plasma and in cerebrospinal fluid (CSF); it also has a neuroprotective role against Alzheimer's disease (AD). However, TTR also is an amyloidogenic protein responsible for familial amyloid polyneuropathy (FAP) and familial amyloid cardiomyopathy (FAC). The TTR amyloidogenic potential is speeded up by several point mutations. One therapeutic strategy against TTR amyloidosis is the stabilisation of the native tetramer by natural compounds and small molecules. In this review, we examine the natural products that, starting from 2012 to present, have been studied as a stabiliser of TTR tetramer. In particular, we discussed the chemical and structural features which will be helpful for future drug design of new TTR stabilisers.

Interactions of tolcapone analogues as stabilizers of the amyloidogenic protein transthyretin

Transthyretin (TTR) is an amyloidogenic homotetramer involved in the transport of thyroxine and retinol in blood and cerebrospinal fluid. TTR stabilizers, such as tolcapone, an FDA approved drug for Parkinson's disease, are able to interact with residues of the thyroxine-binding sites of TTR, both wild type and pathogenic mutant forms, thereby stabilizing its tetrameric native state and inhibiting amyloidogenesis. Herein, we report on the synthesis of 3-deoxytolcapone, a novel stabilizer of TTR. The high-resolution X-ray analyses of the interactions of 3-O-methyltolcapone and 3-deoxytolcapone with TTR were performed. In the two TTR-ligand complexes the tolcapone analogues establish mainly H-bond and hydrophobic interactions with residues of the thyroxine-binding site of the TTR tetramer. Both compounds are capable of high and selective stabilization of TTR in the presence of plasma proteins, despite their markedly different 'forward' and 'reverse' binding mode, respectively. In fact, the loss or the weakening of stabilizing interactions with protein residues of 3-deoxytolcapone in comparison with tolcapone and 3-O-methyltolcapone is compensated by new interactions established at the dimer-dimer interface. Our data, coupled with previously reported data on the pharmacokinetics properties in humans of tolcapone and 3-O-methyltolcapone, further support the relevance of the latter tolcapone analogue as TTR stabilizer.

Native Mass Spectrometry Based Method for Studying the Interactions between Superoxide Dismutase 1 and Stilbenoids

To inhibit the abnormal aggregation of Cu, Zn-superoxide dismutase (SOD1) is regarded as a potential therapeutic strategy of SOD1-linked amyotrophic lateral sclerosis (ALS). Herein the interactions between SOD1 and four stilbene-based polyphenols, namely, resveratrol, oxyresveratrol, polydatin, and 2,3,4',5-tetrahydroxystilbene-2-O-β-d-glycoside (THSG), were investigated using electrospray ionization mass spectrometry (ESI-MS) combined with ion mobility (IM) spectrometry. The addition of tandem MS to the study of SOD1-ligand complexes provides further insight into their gas-phase stability. Monitoring the unfolding of SOD1-ligand complexes using IM-MS allows observation of subtle changes in the protein stability upon ligand binding. From the MS/MS and IM-MS measurements, polydatin and THSG were highlighted as the strongest bound compounds in the gas phase, and both of them appear to provide a stabilizing effect on the SOD1 dimer conformation. In addition, the data of fluorescence assays clearly show the ability of the ligands to inhibit apoSOD1 from aggregation, and polydatin was found to have the strongest inhibitory effect. Overall, the method described here can be an effective approach to investigate the interactions between SOD1 and other drug-like molecules.

Structural Stabilization of Human Transthyretin by Centella asiatica (L.) Urban Extract: Implications for TTR Amyloidosis

Transthyretin is responsible for a series of highly progressive, degenerative, debilitating, and incurable protein misfolding disorders known as transthyretin (TTR) amyloidosis. Since dissociation of the homotetrameric protein to its monomers is crucial in its amyloidogenesis, stabilizing the native tetramer from dissociating using small-molecule ligands has proven a viable therapeutic strategy. The objective of this study was to determine the potential role of the medicinal herb Centella asiatica on human transthyretin (huTTR) amyloidogenesis. Thus, we investigated the stability of huTTR with or without a hydrophilic fraction of C. asiatica (CAB) against acid/urea-mediated denaturation. We also determined the influence of CAB on huTTR fibrillation using transmission electron microscopy. The potential binding interactions between CAB and huTTR was ascertained by nitroblue tetrazolium redox-cycling and 8-anilino-1-naphthalene sulfonic acid displacement assays. Additionally, the chemical profile of CAB was determined by liquid chromatography quadruple time-of-flight mass spectrometry (HPLC-QTOF-MS). Our results strongly suggest that CAB bound to and preserved the quaternary structure of huTTR in vitro. CAB also prevented transthyretin fibrillation, although aggregate formation was unmitigated. These effects could be attributable to the presence of phenolics and terpenoids in CAB. Our findings suggest that C. asiatica contains pharmaceutically relevant bioactive compounds which could be exploited for therapeutic development against TTR amyloidosis.

Uncovering the Neuroprotective Mechanisms of Curcumin on Transthyretin Amyloidosis

Transthyretin (TTR) amyloidoses (ATTR amyloidosis) are diseases associated with transthyretin (TTR) misfolding, aggregation and extracellular deposition in tissues as amyloid. Clinical manifestations of the disease are variable and include mainly polyneuropathy and/or cardiomyopathy. The reasons why TTR forms aggregates and amyloid are related with amino acid substitutions in the protein due to mutations, or with environmental alterations associated with aging, that make the protein more unstable and prone to aggregation. According to this model, several therapeutic approaches have been proposed for the diseases that range from stabilization of TTR, using chemical chaperones, to clearance of the aggregated protein deposited in tissues in the form of oligomers or small aggregates, by the action of disruptors or by activation of the immune system. Interestingly, different studies revealed that curcumin presents anti-amyloid properties, targeting multiple steps in the ATTR amyloidogenic cascade. The effects of curcumin on ATTR amyloidosis will be reviewed and discussed in the current work in order to contribute to knowledge of the molecular mechanisms involved in TTR amyloidosis and propose more efficient drugs for therapy.

Polypharmacology or Promiscuity? Structural Interactions of Resveratrol With Its Bandwagon of Targets

Resveratrol (3, 4', 5-trihydroxy-trans-stilbene) is a natural phytoalexin found in grapes and has long been thought to be the answer to the "French Paradox." There is no shortage of preclinical and clinical studies investigating the broad therapeutic activity of resveratrol. However, in spite of many comprehensive reviews published on the bioactivity of resveratrol, there has yet to be a report focused on the variety and complexity of its structural binding properties, and its multi-targeted role. An improved understanding of disease mechanisms at the systems level has enabled targeted polypharmacology to mature into a rational drug discovery approach. Unlike traditional hit-to-lead campaigns that typically optimize activity and selectivity for a single target, polypharmacological drugs aim to selectively target multiple proteins, while avoiding critical off target interactions. This strategy bears promise of improved efficacy and reduced clinical attrition. This review seeks to investigate whether the bioactivity of resveratrol is due to a polypharmacological effect or promiscuity of the phenolic small molecule by examining the modes of binding with its diverse collection of protein targets. We focused on annotated targets, identified via the ChEMBL database, and matched these targets to a representative structure deposited in the Protein Data Bank (PDB), as crystal structures are most informative in understanding modes of binding at the atomic level. We discuss the structural aspects of resveratrol itself that permits binding to multiple proteins in various signaling pathways. Furthermore, we suggest that resveratrol's bioactivity is a result of scaffold promiscuity rather than polypharmacology, and the variety of binding modes across targets display little similarity in the pattern of target interaction.

Inhibition of protein misfolding and aggregation by natural phenolic compounds

Protein misfolding and aggregation into fibrillar deposits is a common feature of a large group of degenerative diseases affecting the central nervous system or peripheral organs, termed protein misfolding disorders (PMDs). Despite their established toxic nature, clinical trials aiming to reduce misfolded aggregates have been unsuccessful in treating or curing PMDs. An interesting possibility for disease intervention is the regular intake of natural food or herbal extracts, which contain active molecules that inhibit aggregation or induce the disassembly of misfolded aggregates. Among natural compounds, phenolic molecules are of particular interest, since most have dual activity as amyloid aggregation inhibitors and antioxidants. In this article, we review many phenolic natural compounds which have been reported in diverse model systems to have the potential to delay or prevent the development of various PMDs, including Alzheimer's and Parkinson's diseases, prion diseases, amyotrophic lateral sclerosis, systemic amyloidosis, and type 2 diabetes. The lower toxicity of natural compounds compared to synthetic chemical molecules suggest that they could serve as a good starting point to discover protein misfolding inhibitors that might be useful for the treatment of various incurable diseases.

Resveratrol prevents p53 aggregation in vitro and in breast cancer cells

One potential target for cancer therapeutics is the tumor suppressor p53, which is mutated in more than 50% of malignant tumors. Loss of function (LoF), dominant negative (DN) and gain of function (GoF) mutations in p53 are associated with amyloid aggregation. We tested the potential of resveratrol, a naturally occurring polyphenol, to interact and prevent the aggregation of wild-type and mutant p53 in vitro using fluorescence spectroscopy techniques and in human breast cancer cells (MDA-MB-231, HCC-70 and MCF-7) using immunofluorescence co-localization assays. Based on our data, an interaction occurs between resveratrol and the wild-type p53 core domain (p53C). In addition, resveratrol and its derivatives pterostilbene and piceatannol inhibit mutant p53C aggregation in vitro. Additionally, resveratrol reduces mutant p53 protein aggregation in MDA-MB-231 and HCC-70 cells but not in the wild-type p53 cell line MCF-7. To verify the effects of resveratrol on tumorigenicity, cell proliferation and cell migration assays were performed using MDA-MB-231 cells. Resveratrol significantly reduced the proliferative and migratory capabilities of these cells. Our study provides evidence that resveratrol directly modulates p53, enhancing our understanding of the mechanisms involved in p53 aggregation and its potential as a therapeutic strategy for cancer treatment.

Structural aspects of thyroid hormone binding to proteins and competitive interactions with natural and synthetic compounds

Thyroid hormones and their metabolites constitute a vast class of related iodothyronine compounds that contribute to the regulation of metabolic activity and cell differentiation. They are in turn transported, transformed and recognized as signaling molecules through binding to a variety of proteins from a wide range of evolutionary unrelated protein families, which renders these proteins and their iodothyronine binding sites an example for extensive convergent evolution. In this review, we will briefly summarize what is known about iodothyronine binding sites in proteins, the modes of protein/iodothyronine interaction, and the ligand conformations. We will then discuss physiological and synthetic compounds, including popular drugs and food components, that can interfere with iodothyronine binding and recognition by these proteins. The discussion also includes compounds persisting in the environment and acting as endocrine disrupting chemicals.

Structural and dynamics evidence for scaffold asymmetric flexibility of the human transthyretin tetramer

The molecular symmetry of multimeric proteins is generally determined by using X-ray diffraction techniques, so that the basic question as to whether this symmetry is perfectly preserved for the same protein in solution remains open. In this work, human transthyretin (TTR), a homotetrameric plasma transport protein with two binding sites for the thyroid hormone thyroxine (T4), is considered as a case study. Based on the crystal structure of the TTR tetramer, a hypothetical D2 symmetry is inferred for the protein in solution, whose functional behavior reveals the presence of two markedly different Kd values for the two T4 binding sites. The latter property has been ascribed to an as yet uncharacterized negative binding cooperativity. A triple mutant form of human TTR (F87M/L110M/S117E TTR), which is monomeric in solution, crystallizes as a tetrameric protein and its structure has been determined. The exam of this and several other crystal forms of human TTR suggests that the TTR scaffold possesses a significant structural flexibility. In addition, TTR tetramer dynamics simulated using normal modes analysis exposes asymmetric vibrational patterns on both dimers and thermal fluctuations reveal small differences in size and flexibility for ligand cavities at each dimer-dimer interface. Such small structural differences between monomers can lead to significant functional differences on the TTR tetramer dynamics, a feature that may explain the functional heterogeneity of the T4 binding sites, which is partially overshadowed by the crystal state.

Evaluating the effect of mutations and ligand binding on transthyretin homotetramer dynamics

Native transthyretin (TTR) homotetramer dissociation is the first step of the fibrils formation process in amyloid disease. A large number of specific point mutations that destabilize TTR quaternary structure have shown pro-amyloidogenic effects. Besides, several compounds have been proposed as drugs in the therapy of TTR amyloidosis due to their TTR tetramer binding affinities, and therefore, contribution to its integrity. In the present paper we have explored key positions sustaining TTR tetramer dynamical stability. We have identified positions whose mutations alter the most the TTR tetramer equilibrium dynamics based on normal mode analysis and their response to local perturbations. We have found that these positions are mostly localized at β-strands E and F and EF-loop. The monomer-monomer interface is pointed out as one of the most vulnerable regions to mutations that lead to significant changes in the TTR-tetramer equilibrium dynamics and, therefore, induces TTR amyloidosis. Besides, we have found that mutations on residues localized at the dimer-dimer interface and/or at the T4 hormone binding site destabilize the tetramer more than the average. Finally, we were able to compare several compounds according to their effect on vibrations associated to the ligand binding. Our ligand comparison is discussed and analyzed in terms of parameters and measurements associated to TTR-ligand binding affinities and the stabilization of its native state.

Cancer Chemoprevention by Resveratrol: The p53 Tumor Suppressor Protein as a Promising Molecular Target

Increasing epidemiological and experimental evidence has demonstrated an inverse relationship between the consumption of plant foods and the incidence of chronic diseases, including cancer. Microcomponents that are naturally present in such foods, especially polyphenols, are responsible for the benefits to human health. Resveratrol is a diet-derived cancer chemopreventive agent with high therapeutic potential, as demonstrated by different authors. The aim of this review is to collect and present recent evidence from the literature regarding resveratrol and its effects on cancer prevention, molecular signaling (especially regarding the involvement of p53 protein), and therapeutic perspectives with an emphasis on clinical trial results to date.

Novel trans-Stilbene-based Fluorophores as Probes for Spectral Discrimination of Native and Protofibrillar Transthyretin

Accumulation of misfolded transthyretin (TTR) as amyloid fibrils causes various human disorders. Native transthyretin is a neurotrophic protein and is a putative extracellular molecular chaperone. Several fluorophores have been shown in vitro to bind selectively to native TTR. Other compounds, such as thioflavin T, bind TTR amyloid fibrils. The probe 1-anilinonaphthalene-8-sulfonate (ANS) binds to both native and fibrillar TTR, becoming highly fluorescent, but with indistinguishable emission spectra for native and fibrillar TTR. Herein we report our efforts to develop a fluorescent small molecule capable of binding both native and misfolded protofibrillar TTR, providing distinguishable emission spectra. We used microwave synthesis for efficient production of a small library of trans-stilbenes and fluorescence spectral screening of their binding properties. We synthesized and tested 22 trans-stilbenes displaying a variety of functional groups. We successfully developed two naphthyl-based trans-stilbenes probes that detect both TTR states at physiological concentrations. The compounds bound with nanomolar to micromolar affinities and displayed distinct emission maxima upon binding native or misfolded protofibrillar TTR (>100 nm difference). The probes were mainly responsive to environment polarity providing evidence for the divergent hydrophobic structure of the binding sites of these protein conformational states. Furthermore, we were able to successfully use one of these probes to quantify the relative amounts of native and protofibrillar TTR in a dynamic equilibrium. In conclusion, we identified two trans-stilbene-based fluorescent probes, (E)-4-(2-(naphthalen-1-yl)vinyl)benzene-1,2-diol (11) and (E)-4-(2-(naphthalen-2-yl)vinyl)benzene-1,2-diol (14), that bind native and protofibrillar TTR, providing a wide difference in emission maxima allowing conformational discrimination by fluorescence spectroscopy. We expect these novel molecules to serve as important chemical biology research tools in studies of TTR folding and misfolding.

Human TTR conformation altered by rhenium tris-carbonyl derivatives

Transthyretin (TTR) is a 54 kDa homotetrameric serum protein that transports thyroxine (T4) and retinol. TTR is potentially amyloidogenic due to homotetramer dissociation into monomeric intermediates that self-assemble as amyloid deposits and insoluble fibrils. Most crystallographic structures, including those of amyloidogenic variants show the same tetramer without major variations in the monomer-monomer interface nor in the volume of the interdimeric cavity. Soaking TTR crystals in a solution containing rhenium tris-carbonyl derivatives yields a TTR conformer never observed before. Only one of the two monomers of the crystallographic dimer is significantly altered, and the inner part of the T4 binding cavity is expanded at one end and shrunk at the other. The result redefines the mechanism of allosteric communication between the two sites, suggesting that negative cooperativity is a function of dimer asymmetry, which can be induced through internal or external binding. An aspect that remains unexplained is why the conformational changes are ubiquitous throughout the crystal although the heavy metal content of the derivatized crystals is relatively low. The conformational changes observed, which include Leu(82), may represent a form of TTR better at scavenging β-Amyloid. At a resolution of 1.69Å, with excellent refinement statistics and well defined electron density for all parts of the structure, it is possible to envisage answering important questions that range from protein cooperative behavior to heavy atom induced protein conformational modifications that can result in crystallographic non-isomorphism.

Resveratrol: How Much Wine Do You Have to Drink to Stay Healthy?

Resveratrol is a naturally occurring stilbene endowed with multiple health-promoting effects. It is produced by certain plants including several dietary sources such as grapes, apples, raspberries, blueberries, plums, peanuts, and products derived therefrom (e.g., wine). Resveratrol can be isolated and purified from these biological sources or synthesized in a few steps with an overall high yield. This compound and its glucoside, the trans-polydatin piceid, have received worldwide attention for their beneficial effects on cardiovascular, inflammatory, neurodegenerative, metabolic, and age-related diseases. These health-promoting effects are particularly attractive given the prevalence of resveratrol-based nutraceuticals and the paradoxical epidemiologic observation that wine consumption is inversely correlated to the incidence of coronary heart disease. However, the notion of resveratrol as a "magic bullet" was recently challenged by clinical trials showing that this polyphenol does not have a substantial influence on health status and mortality risk. In the present review, we discuss the proposed therapeutic attributes and the mode of molecular actions of resveratrol. We also cover recent pharmacologic efforts to improve the poor bioavailability of resveratrol and influence the transition between body systems in humans. We conclude with some thoughts about future research directions that might be meaningful for resolving controversies surrounding resveratrol.

Resveratrol administration increases Transthyretin protein levels ameliorating AD features- importance of transthyretin tetrameric stability

Previous in vivo work showed that resveratrol has beneficial effects in the AD pathology, resulting in increased expression of transthyretin (TTR). TTR binds Aβ peptide avoiding its aggregation and toxicity, and is reduced in the CSF and plasma, in AD. Further, resveratrol binds TTR, stabilizing the native TTR tetrameric structure. To further explore the mechanism of neuroprotection conferred by TTR in AD, resveratrol was administrated, in the diet, to 5-8 months old AD transgenic female mice carrying just one copy of the mouse TTR gene, for two months. Effects in brain Aβ burden were evaluated by immunohistochemistry, and in total brain Aβ levels by ELISA, showing a striking decrease in both parameters in treated animals. In addition, total brain LRP1 protein levels were increased in treated animals, although its gene expression was unaltered. To further understand the mechanism(s) underlying such improvement in AD features, we measured TTR plasma levels showing that TTR increased in resveratrol-treated mice, whereas liver TTR gene transcription was not altered. These results strengthen the stability hypothesis, which postulates that TTR is unstable in AD leading to accelerated clearance and lower levels. Therefore, resveratrol which stabilizes the TTR tetramer results in TTR normalized clearance, thus increasing the protein plasma levels. In turn, stabilized TTR binds more strongly to Aβ peptide, avoiding its aggregation. Our results represent a step forward to the understanding of the mechanism underlying TTR protection in AD and highlight the possibility of using TTR stabilization as a therapeutic target in AD.

Targeting Different Transthyretin Binding Sites with Unusual Natural Compounds

Misfolding and aggregation of the transthyretin (TTR) protein leads to certain forms of amyloidosis. Some nutraceuticals, such as flavonoids and natural polyphenols, have recently been investigated as modulators of the self-assembly process of TTR, but they generally suffer from limited bioavailability. To discover innovative and more bioavailable natural compounds able to inhibit TTR amyloid formation, a docking study was performed using the crystallographic structure of TTR. This computational strategy was projected as an ad hoc inspection of the possible relationship between binding site location and modulation of the assembly process; interactions with the as-yet-unexplored epigallocatechin gallate (EGCG) sites and with the thyroxine (T4) pocket were simultaneously analyzed. All the compounds studied seem to prefer the traditional T4 binding site, but some interesting results emerged from the screening of an in-house database, used for validating the computational protocol, and of the Herbal Ingredients Targets (HIT) catalogue available on the ZINC database.

Modifications of the 7-Hydroxyl Group of the Transthyretin Ligand Luteolin Provide Mechanistic Insights into Its Binding Properties and High Plasma Specificity

Amyloid formation of the plasma protein transthyretin (TTR) has been linked to familial amyloid polyneuropathy and senile systemic amyloidosis. Binding of ligands within its natural hormone binding site can stabilize the tetrameric structure and impair amyloid formation. We have recently shown that the flavonoid luteolin stabilizes TTR in human plasma with a very high selectivity. Luteolin, however, is inactivated in vivo via glucuronidation for which the preferred site is the hydroxy group at position 7 on its aromatic A-ring. We have evaluated the properties of two luteolin variants in which the 7-hydroxy group has been exchanged for a chlorine (7-Cl-Lut) or a methoxy group (7-MeO-Lut). Using an in vitro model, based on human liver microsomes, we verified that these modifications increase the persistence of the drug. Crystal structure determinations show that 7-Cl-Lut binds similarly to luteolin. The larger MeO substituent cannot be accommodated within the same space as the chlorine or hydroxy group and as a result 7-MeO-Lut binds in the opposite direction with the methoxy group in position 7 facing the solvent. Both 7-Cl-Lut and 7-MeO-Lut qualify as high-affinity binders, but in contrast to luteolin, they display a highly non-specific binding to other plasma components. The binding of the two conformations and the key-interactions to TTR are discussed in detail. Taken together, these results show a proof-of-concept that the persistence of luteolin towards enzymatic modification can be increased. We reveal two alternative high-affinity binding modes of luteolin to TTR and that modification in position 7 is restricted only to small substituents if the original orientation of luteolin should be preserved. In addition, the present work provides a general and convenient method to evaluate the efficacy of TTR-stabilizing drugs under conditions similar to an in vivo environment.

A new crystal form of human transthyretin obtained with a curcumin derived ligand

Transthyretin (TTR), a 54kDa homotetrameric protein that transports thyroxine (T4), has been associated with clinical cases of TTR amyloidosis for its tendency to aggregate to form fibrils. Many ligands with a potential to inhibit fibril formation have been studied by X-ray crystallography in complex with TTR. Unfortunately, the ligand is often found in ambiguous electron density that is difficult to interpret. The ligand validation statistics suggest over-interpretation, even for the most active compounds like diflunisal. The primary technical reason is its position on a crystallographic 2-fold axis in the most common crystal form. Further investigations with the use of polyethylene glycol (PEG) to crystallize TTR complexes have resulted in a new trigonal polymorph with two tetramers in the asymmetric unit. The ligand used to obtain this new polymorph, 4-hydroxychalcone, is related to curcumin. Here we evaluate this crystal form to understand the contribution it may bring to the study of TTR ligands complexes, which are often asymmetric.