Binding of Ochratoxin A Derivatives to Human Serum Albumin

Fast, portable, selective, and ratiometric determination of ochratoxin A (OTA) by a fluorescent supramolecular sensor

Ochratoxin A (OTA), a mycotoxin found in various food items, possesses significant health risks due to its carcinogenic and toxic properties. Thus, detecting OTA is crucial to ensure food safety. Among the reported analytical methods, there has yet to be one that achieves fast, selective, and portable detection of OTA. In this study, we explore a novel supramolecular sensor, DOCE@ALB, utilizing human serum albumin as the host and a flavonoid fluorescent indicator as the guest. On the basis of indicator displacement assay, this sensor boasts an ultra-fast response time of just 5 s, high sensitivity with a limit of detection at 0.39 ppb, exceptional selectivity, and a noticeable ratiometric fluorescence response to OTA. This discernible color change and portability of the sensor make it suitable for on-site OTA detection in real food samples, including flour, beer, and wine, simply using a smartphone. In comparison to previously reported methods, our approach has showcased notable advantages in both response time and portability, addressing a critical need for food safety and regulatory compliance.

Virtual display of targets: A new level to rise the current understanding of ochratoxin A toxicity from a molecular standpoint

Ochratoxin A (OTA) is a mycotoxin spread worldwide contaminating several food and feed commodities and rising concerns for humans and animals. OTA toxicity has been thoroughly assessed over the last 60 years revealing a variety of adverse effects, including nephrotoxicity, hepatotoxicity and possible carcinogenicity. However, the underpinning mechanisms of action have yet to be completely displayed and understood. In this framework, we applied a virtual pipeline based on molecular docking, dynamics and umbrella simulations to display new OTA potential targets. The results collected consistently identified OGFOD1, a key player in protein translation, as possibly inhibited by OTA and its 2'R diastereomer. This is consistent with the current knowledge of OTA's molecular toxicology and may fill some gaps from a mechanistic standpoint. This could pave the way for further dedicated analysis focusing their attention on the OTA-OGFOD1 interaction, expanding the current understanding of OTA toxicity at a molecular level.

Interaction of the Emerging Mycotoxins Beauvericin, Cyclopiazonic Acid, and Sterigmatocystin with Human Serum Albumin

Beauvericin (BEA), cyclopiazonic acid (CPA), and sterigmatocystin (STC) are emerging mycotoxins. They appear as contaminants in food and animal feed, leading to economic losses and health risks. Human serum albumin (HSA) forms stable complexes with certain mycotoxins, including ochratoxins, alternariol, citrinin, and zearalenone. HSA binding can influence the toxicokinetics of xenobiotics, and albumin can also be considered and applied as a relatively cheap affinity protein. Therefore, we examined the potential interactions of BEA, CPA, and STC with HSA employing fluorescence spectroscopy, ultracentrifugation, ultrafiltration, and molecular modeling. Spectroscopic and ultracentrifugation studies demonstrated the formation of low-affinity BEA–HSA (K_a ≈ 10³ L/mol) and moderately strong CPA–HSA and STC–HSA complexes (K_a ≈ 10⁴ L/mol). In ultrafiltration experiments, CPA slightly displaced each site marker (warfarin, naproxen, and camptothecin) tested, while BEA and STC did not affect significantly the albumin binding of these drugs. Modeling studies suggest that CPA occupies Sudlow’s site I, while STC binds to the Heme site (FA1) on HSA. Considering the interactions of CPA with the site markers, the CPA–HSA interaction may have toxicological importance.

Solvent Effects on the Photophysical Properties of a Donor-acceptor Based Schiff Base

In this work, a donor-acceptor substituted aromatic system ((E)-N-((E)-3-(4 (dimethylamino)phenyl) allylidene)-4-(trifluoromethyl) benzenamine (DPATB) has been synthesized and its detailed photophysics of intramolecular charge transfer process have been explored on the basis of steady state absorption, fluorescence and time resolved spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring from the donor group to the acceptor moiety in the excited state. Effect on addition of acid and pH on steady state spectral properties further reveals excited state charge transfer character. Quantum chemical calculations were performed in order to study the conformation and polarity of DPATB at their ground as well as excited electronic states. The HOMO and LUMO molecular orbital pictures are obtained at DFT level using B3LYP functional and 6-311 + g(d,p) basis set which clearly support excited state intramolecular charge transfer process. The molecular electrostatic potential maps for the optimized ground state, donor twisted and acceptor twisted geometry shed insight on the electrostatic potential and charge distribution in a system which gives information about the reacting site of the probe and nature of the reaction. In this work, detailed photophysics of excited state intramolecular charge transfer process in donor-acceptor system (DPATB) was evaluated using steady state and time-resolved fluorescence spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring in DPATB. Molecular orbital pictures as obtained from DFT based computational analysis reveals a significant change in the distribution of electron density upon transition from HOMO to LUMO which confirms an ICT process occurring from the donor group to the acceptor moiety in the excited state.

Nordihydroguaiaretic Acid in Therapeutics: Beneficial to Toxicity Profiles and the Search for its Analogs

Nordihydroguaiaretic acid (NDGA) is a plant lignan obtained from creosote bush, Larrea tridentata and is known to possess antioxidant, anticancer activities and is used in traditional medicine in North America and Mexico. However, its prolonged consumption leads to liver damage and kidney dysfunction. Despite its toxicity and side effects, there is little awareness to forbid its consumption and its use in the treatment of medical ailments has continued over the years. Several reports discuss its therapeutic efficiency and its medical applications have tremendously been on the rise to date. There has been a recent surge of interest in the chemical synthesis of NDGA derivatives for therapeutic applications. NDGA derivatives have been developed as better alternatives to NDGA. Although several NDGA derivatives have been chemically synthesized as evidenced by recent literature, there is a paucity of information on their therapeutic efficacies. This review is to highlight the medicinal applications of NDGA, its toxicity evaluations and discuss the chemical derivatives of NDGA synthesized and studied so far and suggest to continue research interests in the development of NDGA analogs for therapeutic applications. We suggest that NDGA derivatives should be investigated more in terms of chemical synthesis with preferred conformational structures and exploit their biological potentials with future insights to explore in this direction to design and develop structurally modified NDGA derivatives for potential pharmacological properties.

Probing the Interactions of Ochratoxin B, Ochratoxin C, Patulin, Deoxynivalenol, and T-2 Toxin with Human Serum Albumin

Ochratoxins, patulin, deoxynivalenol, and T-2 toxin are mycotoxins, and common contaminants in food and drinks. Human serum albumin (HSA) forms complexes with certain mycotoxins. Since HSA can affect the toxicokinetics of bound ligand molecules, the potential interactions of ochratoxin B (OTB), ochratoxin C (OTC), patulin, deoxynivalenol, and T-2 toxin with HSA were examined, employing spectroscopic (fluorescence, UV, and circular dichroism) and ultrafiltration techniques. Furthermore, the influence of albumin on the cytotoxicity of these xenobiotics was also evaluated in cell experiments. Fluorescence studies showed the formation of highly stable OTB–HSA and OTC–HSA complexes. Furthermore, fluorescence quenching and circular dichroism measurements suggest weak or no interaction of patulin, deoxynivalenol, and T-2 toxin with HSA. In ultrafiltration studies, OTB and OTC strongly displaced the Sudlow’s site I ligand warfarin, while other mycotoxins tested did not affect either the albumin binding of warfarin or naproxen. The presence of HSA significantly decreased or even abolished the OTB- and OTC-induced cytotoxicity in cell experiments; however, the toxic impacts of patulin, deoxynivalenol, and T-2 toxin were not affected by HSA. In summary, the complex formation of OTB and OTC with albumin is relevant, whereas the interactions of patulin, deoxynivalenol, and T-2 toxin with HSA may have low toxicological importance.

Intrinsic "Turn-On" Aptasensor Detection of Ochratoxin A Using Energy-Transfer Fluorescence

Ochratoxin A (OTA) is an intrinsically fluorescent phenolic mycotoxin that contaminates a wide range of food products and is a serious health threat to animals and humans. An OTA binding aptamer (OTABA) that folds into an antiparallel G-quadruplex (GQ) in the absence and presence of target OTA has been incorporated into a vast variety of aptasensor platforms for OTA detection. The development of a simple, aptamer-based approach would allow for detection of the toxin without the use of complex analytical instrumentation, which has been the gold standard for OTA detection thus far. However, to date, none of the aptasensor platforms have utilized the natural fluorescence of the phenolic toxin for detection. Herein, we report that OTA binding to OTABA involves π-stacking interactions that lead to GQ-to-toxin energy transfer (ET), which affords a "turn-on" fluorescence self-signaling platform in which the emission of the aptamer-target complex is enhanced in comparison to the free toxin alone. Selective excitation of the GQ-OTA complex at 256 nm leads to a 4-fold enhancement in OTA fluorescence. The GQ-OTA ET detection platform boasts a limit of detection ∼2 ng/mL, which is comparable to a previously demonstrated fluorescence resonance energy transfer immunoassay platform for OTA detection, and displays excellent OTA selectivity and recovery from red wine samples.

Interaction of Mycotoxin Alternariol with Serum Albumin

Alternariol (AOH) is a mycotoxin produced by Alternaria species. In vitro studies suggest the genotoxic, mutagenic, and endocrine disruptor effects of AOH, and an increased incidence of esophageal cancer has been reported related to higher AOH exposure. Human serum albumin (HSA) is the most abundant plasma protein in the circulation, it is able to affect toxicokinetic properties of numerous xenobiotics. HSA forms stable complexes with several mycotoxins, however, the interaction of AOH with albumin has not been examined. In this study, the complex formation of AOH with HSA was tested, employing fluorescence spectroscopy, ultrafiltration, and molecular modeling. Each spectroscopic measurement shows the formation of stable AOH-HSA complexes (K = 4 × 10⁵ L/mol). Investigations with site markers (in spectroscopic and ultrafiltration models) as well as modeling studies suggest that AOH occupies Sudlow’s site I as a high-affinity binding site in HSA. The binding affinity of AOH towards bovine, porcine, and rat albumins was also tested, suggesting that AOH binds to rat albumin with considerably higher affinity than other albumins tested. Our results demonstrate the strong interaction of AOH with serum albumins, suggesting the potential in vivo importance of these interactions.

Fluorescence Spectroscopic Investigation of Competitive Interactions between Quercetin and Aflatoxin B₁ for Binding to Human Serum Albumin

Aflatoxin B₁ (AFB₁) is a highly toxic mycotoxin found worldwide in cereals, food, and animal feeds. AFB₁ binds to human serum albumin (HSA) with high affinity. In previous experiments, it has been revealed that reducing the binding rate of AFB₁ with HSA could speed up the elimination rate of AFB₁. Therefore, we examined the ability of quercetin to compete with AFB₁ for binding HSA by fluorescence spectroscopy, synchronous spectroscopy, ultrafiltration studies, etc. It was shown that AFB₁ and quercetin bind to HSA in the same Sudlow site Ӏ (subdomain IIA), and the binding constant (K_a) of the quercetin-HSA complex is significantly stronger than the complex of AFB₁-HSA. Our data in this experiment showed that quercetin is able to remove the AFB₁ from HSA and reduce its bound fraction. This exploratory work may be of significance for studies in the future regarding decreasing its bound fraction and then increasing its elimination rate for detoxification. This exploratory study may initiate future epidemiological research designs to obtain further in vivo evidence of the long-term (potential protective) effects of competing substances on human patients.

Computational simulations determining disulfonic stilbene derivative bioavailability within human serum albumin

Disulfonic stilbene (DS) derivatives are a member of the large family of compounds widely employed in medicine and biology as modulators for membrane transporters or inhibitors of a protein involved in DNA repair. They constitute interesting compounds that have not yet been investigated within the bioavailability framework. No crystallographic structures exist involving such compounds embedded in the most common drug carrier, human serum albumin (HSA). The present work studies, for the first time, the physico-chemical features driving the inclusion of three DS derivatives (amino, nitro and acetamido, named DADS, DNDS and DATDS, respectively) within the four common HSA binding sites using combined molecular docking and molecular dynamics simulations. A careful analysis of each ligand within each of the studied binding sites is carried out, highlighting specific interactions and key residues playing a role in stabilizing the ligand within each pocket. The comparison between DADS, DNDS and DATDS reveals that depending on the binding site, the conclusions are rather different. For instance, the IB binding site shows a specificity to DADS compounds while IIIA is the most favorable site for DNDS and DATDS.

Interaction of 2'R-ochratoxin A with Serum Albumins: Binding Site, Effects of Site Markers, Thermodynamics, Species Differences of Albumin-binding, and Influence of Albumin on Its Toxicity in MDCK Cells

Ochratoxin A (OTA) is a nephrotoxic mycotoxin. Roasting of OTA-contaminated coffee results in the formation of 2′R-ochratoxin A (2′R-OTA), which appears in the blood of coffee drinkers. Human serum albumin (HSA) binds 2′R-OTA (and OTA) with high affinity; therefore, albumin may influence the tissue uptake and elimination of ochratoxins. We aimed to investigate the binding site of 2′R-OTA (verses OTA) in HSA and the displacing effects of site markers to explore which molecules can interfere with its albumin-binding. Affinity of 2′R-OTA toward albumins from various species (human, bovine, porcine and rat) was tested to evaluate the interspecies differences regarding 2′R-OTA-albumin interaction. Thermodynamic studies were performed to give a deeper insight into the molecular background of the complex formation. Besides fluorescence spectroscopic and modeling studies, effects of HSA, and fetal bovine serum on the cytotoxicity of 2′R-OTA and OTA were tested in MDCK kidney cell line in order to demonstrate the influence of albumin-binding on the cellular uptake of ochratoxins. Site markers displaced more effectively 2′R-OTA than OTA from HSA. Fluorescence and binding constants of 2′R-OTA-albumin and OTA-albumin complexes showed different tendencies. Albumin significantly decreased the cytotoxicity of ochratoxins. 2′R-OTA, even at sub-toxic concentrations, increased the toxic action of OTA.

Interactions of zearalenone and its reduced metabolites α-zearalenol and β-zearalenol with serum albumins: species differences, binding sites, and thermodynamics

Zearalenone (ZEN) is a mycotoxin produced by Fusarium species. ZEN mainly appears in cereals and related foodstuffs, causing reproductive disorders in animals, due to its xenoestrogenic effects. The main reduced metabolites of ZEN are α-zearalenol (α-ZEL) and β-zearalenol (β-ZEL). Similarly to ZEN, ZELs can also activate estrogen receptors; moreover, α-ZEL is the most potent endocrine disruptor among these three compounds. Serum albumin is the most abundant plasma protein in the circulation; it affects the tissue distribution and elimination of several drugs and xenobiotics. Although ZEN binds to albumin with high affinity, albumin-binding of α-ZEL and β-ZEL has not been investigated. In this study, the complex formation of ZEN, α-ZEL, and β-ZEL with human (HSA), bovine (BSA), porcine (PSA), and rat serum albumins (RSA) was investigated by fluorescence spectroscopy, affinity chromatography, thermodynamic studies, and molecular modeling. Our main observations are as follows: (1) ZEN binds with higher affinity to albumins than α-ZEL and β-ZEL. (2) The low binding affinity of β-ZEL toward albumin may result from its different binding position or binding site. (3) The binding constants of the mycotoxin-albumin complexes significantly vary with the species. (4) From the thermodynamic point of view, the formation of ZEN-HSA and ZEN-RSA complexes are similar, while the formation of ZEN-BSA and ZEN-PSA complexes are markedly different. These results suggest that the toxicological relevance of ZEN-albumin and ZEL-albumin interactions may also be species-dependent.

Cerium oxide nanoparticles promote HSA fibrillation in vitro

Physicochemical characterization of CeO₂NPs using UV-vis, FTIR and XRD have confirmed the characteristic identity and fluorite phase of their crystalline nature. The interaction studies between cerium oxide nanoparticles (CeO₂NPs) and HSA were investigated using fluorescence emission and synchronous spectra, UV-vis absorbance, FTIR, FT-Raman and Circular Dichroism spectroscopy. Thermodynamic parameters and Stern-Volmer plot has conveyed the existence of the ground state complex raised due to static quenching. Synchronous and Three-Dimensional fluorescence spectra have conveyed the affinity of CeO₂NPs towards Trp and Tyr residues. Results obtained from the FTIR and FT-Raman studies have evidenced minor changes in the amide and amino acid residues band position. Circular Dichroism studies have quantified the conformational changes due to the loss in their alpha helical contents of the secondary structures. Fibrillation studies using Congo red (CR), Thioflavin T (ThT) and Tryptophan emission (Trp) assay have suggested the promoting role of CeO₂NPs against HSA fibrillation. CD studies have shown the enhanced percentage of beta sheet structures in the fibrillar samples that reconfirm the increased effect of CeO₂NPs during the fibrillation process.

A Comprehensive Spectroscopic and Computational Investigation to Probe the Interaction of Antineoplastic Drug Nordihydroguaiaretic Acid with Serum Albumins

Exogenous drugs that are used as antidote against chemotheray, inflammation or viral infection, gets absorbed and interacts reversibly to the major serum transport protein i.e. albumins, upon entering the circulatory system. To have a structural guideline in the rational drug designing and in the synthesis of drugs with greater efficacy, the binding mechanism of an antineoplastic and anti-inflammatory drug Nordihydroguaiaretic acid (NDGA) with human and bovine serum albumins (HSA & BSA) were examined by spectroscopic and computational methods. NDGA binds to site II of HSA with binding constant (Kb) ~105 M-1 and free energy (ΔG) ~ -7.5 kcal.mol-1. It also binds at site II of BSA but with lesser binding affinity (Kb) ~105 M-1 and ΔG ~ -6.5 kcal.mol-1. The negative value of ΔG, ΔH and ΔS for both the albumins at three different temperatures confirmed that the complex formation process between albumins and NDGA is spontaneous and exothermic. Furthermore, hydrogen bonds and hydrophobic interactions are the main forces involved in complex formation of NDGA with both the albumins as evaluated from fluorescence and molecular docking results. Binding of NDGA to both the albumins alter the conformation and causes minor change in the secondary structure of proteins as indicated by the CD spectra.

Interaction of cinnamic acid derivatives with serum albumins: a fluorescence spectroscopic study

Cinnamic acid (CA) derivatives are known to possess broad therapeutic applications including anti-tumor activity. The present study was designed to determine the underlying mechanism and thermodynamic parameters for the binding of two CA based intramolecular charge transfer (ICT) fluorescent probes, namely, 4-(dimethylamino) cinnamic acid (DMACA) and trans-ethyl p-(dimethylamino) cinnamate (EDAC), with albumins by fluorescence spectroscopy. Stern-Volmer analysis of the tryptophan fluorescence quenching data in presence of the added ligand reveals fluorescence quenching constant (κ(q)), Stern-Volmer constant (K(SV)) and also the ligand-protein association constant (K(a)). The thermodynamic parameters like enthalpy (ΔH) and entropy (ΔS) change corresponding to the ligand binding process were also estimated. The results show that the ligands bind into the sub-domain IIA of the proteins in 1:1 stoichiometry with an apparent binding constant value in the range of 10(4) dm(3) mol(-1). In both the cases, the spontaneous ligand binding to the proteins occur through entropy driven mechanism, although the interaction of DMACA is relatively stronger in comparison with EDAC. The temperature dependence of the binding constant indicates the induced change in protein secondary structure.

Selective enrichment of ochratoxin A using human serum albumin bound magnetic beads as the concentrating probes for capillary electrophoresis/electrospray ionization-mass spectrometric analysis

Ochratoxin A (OTA) is a toxicant commonly present in many food products. Conventionally, immuno-affinity analysis is applied to rapidly screen the presence of OTA in food. However, antibodies are expensive. In this study, we present a new approach for selectively enriching OTA from aqueous samples using human serum albumin (HSA) bound magnetic beads as the affinity probes, followed by the analysis of CE/ESI-MS. In addition to demonstrating the feasibility of using the affinity probes to concentrate OTA, we also propose a rapid concentration and elution method for extraction, that is, OTA are extracted from aqueous samples by pipetting the samples in and out of a sample vial for 1 min followed by elution with pipetting for another minute. On the basis of the magnetic property, the affinity magnetic probe-target species could be rapidly isolated from the solution during the process of extraction and elution by magnetic separation. CE/ESI-MS, coupled by the electrodeless/sheathless interface, is used for the analysis of the samples. As this method features speed and cost-effectiveness, it is suitable for the purpose of rapid screening. In fact, the lowest detection limit for OTA is approximately 4 x 10(-3) mg/L.

Binding of Warfarin Influences the Acid-Base Equilibrium of H242 in Sudlow Site I of Human Serum Albumin

Sudlow Site I of human serum albumin (HSA) is located in subdomain IIA of the protein and serves as a binding cavity for a variety of ligands. In this study, the binding of warfarin (W) is examined using computational techniques and isothermal titration calorimetry (ITC). The structure of the docked warfarin anion (W-) to Site I is similar to that revealed by X-ray crystallography, with a calculated binding constant of 5.8 x 10(5) M(-1). ITC experiments (pH 7.13 and I = 0.1) carried out in three different buffers (MOPs, phosphate and Tris) reveal binding of W- is accompanied by uptake of 0.30+/-0.02 protons from the solvent. This measurement suggests that the binding of W- is stabilized by an ion-pair interaction between protonated H242 and the phenoxide group of W-.

Interaction of colchicine with human serum albumin investigated by spectroscopic methods

We investigated the interaction between colchicine and human serum albumin (HSA) by fluorescence and UV-vis absorption spectroscopy. In the mechanism discussion, it was proved that the fluorescence quenching of HSA by colchicine is a result of the formation of colchicines-HSA complex; van der Waals interactions and hydrogen bonds play a major role in stabilizing the complex. The modified Stern-Volmer quenching constant K(a) and corresponding thermodynamic parameters deltaH, deltaG, deltaS at different temperatures were calculated. The distance r between donor (Trp214) and acceptor (colchicine) was obtained according to fluorescence resonance energy transfer (FRET).

Fluorometric investigation of the interaction between methylene blue and human serum albumin

The interaction between methylene blue (MB) and human serum albumin (HSA) was investigated by fluorescence spectroscopy and UV-vis absorbance spectroscopy. In the mechanism discussion, it was proved that the fluorescence quenching of HSA by MB is a result of the formation of MB-HSA complex and electrostatic interactions play a major role in stabilizing the complex. The Stern-Volmer quenching constant K(SV) and corresponding thermodynamic parameters DeltaH, DeltaG and DeltaS were calculated. Binding studies concerning the number of binding sites n and apparent binding constant Kb were performed by fluorescence quenching method. The distance r between the donor (HSA) and the acceptor (MB) was obtained according to fluorescence resonance energy transfer (FRET). Wavelength shifts in synchronous fluorescence spectra showed the conformation of HSA molecules is changed in the presence of MB.