Binding of berberine to bovine serum albumin: spectroscopic approach

Interactions of three berberine mid-chain fatty acid salts with bovine serum albumin (BSA): Spectroscopic analysis and molecular docking

In this paper, the interaction of three berberine mid-chain fatty acid salts ([BBR][FAs]), viz. berberine caproate ([BBR][CAP]), berberine heptylate ([BBR][HEP]) and berberine octoate ([BBR][OCT]), with bovine serum albumin (BSA) was studied by means of UV-visible absorption spectroscopy, fluorescence spectroscopy, fourier transform infrared spectroscopy (FT-IR) and molecular docking techniques. Fluorescence experiments revealed that three berberine salts quench the fluorescence of BSA by static quenching mechanism resulted from a stable [BBR][FAs]-BSA complex formation. The stoichiometric numbers of [BBR][FAs]-BSA complexes were found to be 1:1. Synchronous and three-dimensional fluorescence spectra as well as FT-IR demonstrated that the binding of [BBR][FAs] altered the microenvironment and conformation of BSA. The binding average distance from [BBR][FAs] to BSA (3.2-3.5 nm) was determined according to Förster energy transfer theory. Site probe investigation showed that [BBR][FAs] bound to BSA active site I (sub-domain IIA). The binding promotes the esterase-like activity of BSA. The molecular docking results confirmed the fluorescence competition findings and provided the type of binding forces. Furthermore, the relationship between the anionic chain length of [BBR][FAs] and the interaction was explored, and the positive correlation was found.

Antimalarial Delivery with a Ferritin-Based Protein Cage: A Step toward Developing Smart Therapeutics against Malaria

Over the past two decades, the utilization of protein cages has witnessed exponential growth driven by their extensive applications in biotechnology and therapeutics. In the context of the recent Covid-19 pandemic, protein-cage-based scaffolds played a pivotal role in vaccine development. Beyond vaccines, these protein cages have proven valuable in diverse drug delivery applications thanks to their distinctive architecture and structural stability. Among the various types of protein cages, ferritin-based cages have taken the lead in drug delivery applications. This is primarily attributed to their ease of production, exceptional thermal stability, and nontoxic nature. While ferritin-based cages are commonly employed in anticancer drug delivery and contrast agent delivery, their efficacy in malarial drug delivery had not been explored until this study. In this investigation, several antimalarial drugs were encapsulated within horse spleen ferritin, and the binding and loading processes were validated through both experimental and computational techniques. The data unequivocally demonstrate the facile incorporation of antimalarial drugs into ferritin without disrupting its three-dimensional structure. Computational docking and molecular dynamics simulations were employed to pinpoint the precise location of the drug binding site within ferritin. Subsequent efficacy testing on Plasmodium revealed that the developed nanoconjugate, comprising the drug-ferritin conjugate, exhibited significant effectiveness in eradicating the parasite. In conclusion, the findings strongly indicate that ferritin-based carrier systems hold tremendous promise for the future of antimalarial drug delivery, offering high selectivity and limited side effects.

A new fluorescence probe for sofosbuvir analysis in dosage form and spiked human plasma

A simple, rapid, and low-cost technique was developed to allow reliable analysis of the anti-hepatitis C drug sofosbuvir in bulk, tablet form, and spiked human plasma. This method depends on the ability of sofosbuvir to quench the fluorescence of the newly synthesized 2-amino-3-cyano-4,6-dimethylpyridine (reagent 3). Elemental analysis and spectral data were used to validate the structure of the synthesized reagent. The newly synthesized reagent exhibited a satisfactory level of fluorescence emission at 365 nm after excitation at 247 nm. All experimental variables that might affect the quenching process were analyzed and optimized. Linearity, range, accuracy, precision, limit of detection (LOD), and limit of quantitation (LOQ) were all validated in accordance with the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) guidelines. The concentration range was shown to be linear between 0.1 and 1.5 μg/mL. The technique was effectively utilized for sofosbuvir analysis in both its tablet dosage form and spiked human plasma, with mean percentage recoveries of 100.13 ± 0.35 and 94.26 ± 1.69, respectively.

In Vitro Hemoglobin Binding and Molecular Docking of Synthesized Chitosan-Based Drug-Carrying Nanocomposite for Ciprofloxacin-HCl Drug Delivery System

Understanding the intermolecular interactions between antibiotic drugs and hemoglobin is crucial in biological systems. The current study aimed to investigate the preparation of chitosan/polysorbate-80/tripolyphosphate (CS-PS/TPP) nanocomposite as a potential drug carrier for Ciprofloxacin-HCl drug (CFX), intended for controlled release formulation and further used to interact with bovine hemoglobin. Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis-differential thermal analysis (TGA-DTA), scanning electron microscopy (SEM), dynamic light scattering (DLS), and X-ray diffraction analyses were used to characterize the CS-PS/TPP nanocomposite and its CFX-loaded nanocomposite. The second series of biophysical properties were performed on the Ciprofloxacin-loaded CS-PS/TPP (NCFX) for interaction with bovine hemoglobin (BHb). The interactions of (CFX and NCFX) with redox protein hemoglobin were investigated for the first time through a series of in vitro experimental techniques to provide comprehensive knowledge of the drug-protein binding interactions. Additionally, the effect of inclusion of PS-80 on the CFX-BHb interaction was also studied at different concentrations using fluorescence spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, and circular dichroism (CD) under physiological conditions. The binding process of CFX and NCFX was spontaneous, and the fluorescence of BHb was quenched due to the static mechanism formation of the (CFX/BHb) and (NCFX/BHb) complexes. Thermodynamic parameters ΔG, ΔH, and ΔS at various temperatures indicate that the hydrogen bonding and van der Waals forces play a major role in the CFX-BHb association.

Spectroscopic insights with molecular docking and molecular dynamic simulation studies of anticancer drug 5-Fluorouracil targeting human pyruvate kinase m2

This study was conducted to test the efficacy of 5-fluorouracil (5-FU) as an anticancer drug against the human pyruvate kinase isozyme M2 (PKM2) using spectroscopic, molecular docking and molecular dynamic simulation studies. PKM2 fluorescence quenching studies in the presence of 5-FU performed at three different temperatures indicates dynamic quenching processes with single-set of binding (n ≈ 1) profile. The biomolecular quenching constants (kq) and the effective binding constants (Kb) obtained are shown to increase with temperature. The calculated enthalpy (ΔH) and entropy changes (ΔS) are estimated to be -118.06 kJ/mol and 146.14 kJ/mol/K respectively, which suggest the possible mode of interaction as electrostatic and hydrogen bonding. Further, these values were used to estimate the free energy changes (ΔG) and that increases with temperature. The negative ΔG values clearly indicates spontaneous binding process that stabilizes the complex formed between 5-FU and PKM2. Far-UV CD spectra of PKM2 in the presence of 5-FU shows decrease in α-helix contents which point towards the destabilization of secondary structure that weakens the biological activity of PKM2. The intrinsic fluorescence study and circular dichroism (CD) spectra showed minor conformational changes of PKM2 in the presence of 5-FU. Additionally, the results obtained from molecular docking and all-atom molecular dynamic simulation study supports the insight of the spectroscopic binding studies, and strengthens the dynamic stability of the complex between 5-FU and PKM2 through H-bonding. This study establishes a paradigm of 5-FU-PKM2 complexation and the efficacy of 5-FU that compromises the biological activity of the targeted PKM2.Communicated by Ramaswamy H. Sarma.

Profiling in-vitro release of verteporfin from VISUDYNE® liposomal formulation and investigating verteporfin binding to human serum albumin

VISUDYNE® is a liposomal formulation of verteporfin, used in the photodynamic therapy of age-related macular degeneration via intravenous administration. In this study, we developed a new in vitro method to quantify verteporfin release from VISUDYNE® under conditions that replicate in vivo conditions using human serum albumin (HSA). Verteporfin release from the liposomes was quantified using capillary electrophoresis (CE) with optical detection. Verteporfin binding to HSA was quantified by measuring HSA fluorescence that is quenched by drugs binding to specific HSA binding sites. The binding constant of verteporfin to HSA was calculated using the Stern Volmer plot and found to be 1.966 × 107 M-1 at 37 °C. Verteporfin binding to HSA involves one albumin binding site and the binding molar ratio between verteporfin and HSA is approximately 1:1. A rapid partitioning of verteporfin from VISUDYNE® onto HSA takes place within 10 min and involves the release of more than 90% of the verteporfin at physiological temperatures. This study verifies this approach of using CE to rapidly separate liposome and HSA-bound drug, thus minimizing drug release artifacts created with other methods.

Insights on the in-vitro binding interaction between donepezil and bovine serum albumin

In this work, the binding mechanism between donepezil (DNP) and bovine serum albumin (BSA) was established using several techniques, including fluorimetry, UV- spectrophotometry, synchronous fluorimetry (SF), fourier transform infrared (FTIR), fluorescence resonance energy transfer (FRET) besides molecular docking study. The fluorescence quenching mechanism of DNP-BSA binding was a combined dynamic and static quenching. The thermodynamic parameters, binding forces, binding constant, and the number of binding sites were determined using a different range of temperature settings. Van't Hoff's equation was used to calculate the reaction parameters, including enthalpy change (ΔH^ο) and entropy change (ΔS^ο). The results pointed out that the DNP-BSA binding was endothermic. It was shown that the stability of the drug-protein system was predominantly due to the intermolecular hydrophobic forces. Additionally, the site probing method revealed that subdomain IIA (Site I) is where DNP and BSA's binding occurs. This was validated using a molecular docking study with the most stable DNP configuration. This study might help to understand DNP's pharmacokinetics profile and toxicity as well as provides crucial information for its safe use and avoiding its toxicity.

Revealing the effects of ligands of silver nanoclusters on the interactions between them and ctDNA: Abstraction to visualization

Silver nanoclusters (AgNCs) have been widely applied in the field of biology, drug therapy and cell imaging in the last decade. In order to study the biosafety of AgNCs, GSH-AgNCs and DHLA-AgNCs were synthesized using glutathione (GSH) and dihydrolipoic acid (DHLA) as ligands, and their interactions with calf thymus DNA (ctDNA) from abstraction to visualization were studied. The results of spectroscopy, viscometry and molecular docking demonstrated that GSH-AgNCs mainly bound to ctDNA in a groove mode, while DHLA-AgNCs were both groove and intercalation binding. Fluorescence experiments suggested that the quenching mechanism of both AgNCs to the emission of ctDNA-probe were both in static mode, and thermodynamic parameters demonstrated that the main forces between GSH-AgNCs and ctDNA were hydrogen bonds and van der Waals forces, while hydrogen bonds and hydrophobic forces contributed to the binding of DHLA-AgNCs to ctDNA. The binding strength demonstrated that DHLA-AgNCs bound to ctDNA more strongly than that of GSH-AgNCs. The results of circular dichroism (CD) spectroscopy reflected small effects of both AgNCs on the structure of ctDNA. This study will support the theoretical foundation for the biosafety of AgNCs and have a guiding significance for the preparation and application of AgNCs.

Calix[4]Resorcinarene Carboxybetaines and Carboxybetaine Esters: Synthesis, Investigation of In Vitro Toxicity, Anti-Platelet Effects, Anticoagulant Activity, and BSA Binding Affinities

As a result of bright complexation properties, easy functionalization and the ability to self-organize in an aqueous solution, amphiphilic supramolecular macrocycles are being actively studied for their application in nanomedicine (drug delivery systems, therapeutic and theranostic agents, and others). In this regard, it is important to study their potential toxic effects. Here, the synthesis of amphiphilic calix[4]resorcinarene carboxybetaines and their esters and the study of a number of their microbiological properties are presented: cytotoxic effect on normal and tumor cells and effect on cellular and non-cellular components of blood (hemotoxicity, anti-platelet effect, and anticoagulant activity). Additionally, the interaction of macrocycles with bovine serum albumin as a model plasma protein is estimated by various methods (fluorescence spectroscopy, synchronous fluorescence spectroscopy, circular dichroic spectroscopy, and dynamic light scattering). The results demonstrate the low toxicity of the macrocycles, their anti-platelet effects at the level of acetylsalicylic acid, and weak anticoagulant activity. The study of BSA-macrocycle interactions demonstrates the dependence on macrocycle hydrophilic/hydrophobic group structure; in the case of carboxybetaines, the formation of complexes prevents self-aggregation of BSA molecules in solution. The present study demonstrates new data on potential drug delivery nanosystems based on amphiphilic calix[4]resorcinarenes for their cytotoxicity and effects on blood components.

Exploring the molecular interaction of mebendazole with bovine serum albumin using multi-spectroscopic approaches and molecular docking

This article presents the binding interaction between mebendazole (MBZ) and bovine serum albumin. The interaction has been studied using different techniques, such as fluorescence quenching spectroscopy, UV–visible spectroscopy, synchronous fluorescence spectroscopy, fourier transform infrared, and fluorescence resonance energy transfer in addition to molecular docking. Results from Stern Volmer equation stated that the quenching for MBZ-BSA binding was static. The fluorescence quenching spectroscopic study was performed at three temperature settings. The binding constant (k_q), the number of binding sites (n), thermodynamic parameters (ΔH^ο, ΔS^ο and ΔG^ο), and binding forces were determined. The results exhibited that the interaction was endothermic. It was revealed that intermolecular hydrophobic forces led to the stabilization of the drug-protein system. Using the site marker technique, the binding between MBZ and BSA was found to be located at subdomain IIA (site I). This was furtherly approved using the molecular docking technique with the most stable MBZ configuration. This research may aid in understanding the pharmacokinetics and toxicity of MBZ and give fundamental data for its safe usage to avoid its toxicity.

Cationic polythiophene-anionic fullerene pair in water and water-dioxane: studies on hydrogen bonding capabilities, kinetic and thermodynamic properties

Despite the vast array of solution- and solid-state bio-analytical, bioelectronic and optoelectronic applications of cationic polythiophenes (CPTs), the number of studies focused on the role of hydrogen bonding (H-bonding) between these and other molecules is scarce, regardless of whether H-bonding is expected to play an important role in several such applications. Also, despite the advantages of using cosolvents to systematically examine the molecular interactions, there are no such studies for CPTs to our knowledge. This work presents a steady-state UV-vis/fluorescence spectroscopic, kinetic and thermodynamic study on the H-bonding interactions between a water-soluble, cationic-anionic (isothiouronium-tetraphosphonate), polythiophene-fullerene donor-acceptor pair with two-point, charge-assisted H-bonding (CAHB) capabilities, tuned using water or a 1,4-dioxane-water mixture (W-DI). Both solvents generate photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET), spontaneous binding, H-bonding, ground-state complexing via multiple site binding, formation of micelle-like aggregates and equivalence points at a similar concentration of the quencher. However, in comparison with water, W-DI promotes less-ordered, less packed micellar aggregates, due to hydrophobic desolvation of the H-bond and larger solvent displacement during the PT1-4Fo complexation. This would decrease the extent of charge-transfer and the size of the sphere-of-quenching, mainly by displacements or rotations of the H-bonds, instead of elongations, together with a possible larger extent of diffusion-controlled static quenching. At [4Fo] larger than the equivalence point the micelles formed in water do not have available binding sites due to a tighter aggregation, causing a decrease in the quenching efficiency, while the micelles formed in W-DI start showing larger quenching efficiencies, possibly due to an increase in entropy that overcomes the desolvation of the H-bonding. These results could be useful when analyzing outputs from systems including CPTs with H-bonding capabilities, operating in (or casted from) solvents with clear differences in polarity and/or H-bonding capacity.

Study of alkaloid berberine and its interaction with the human telomeric i-motif DNA structure

The alkaloid berberine presents many biological activities related to its potential to bind DNA structures, such as duplex or G-quadruplex. Recently, it has been proposed that berberine may interact with i-motif structures formed from the folding of cytosine-rich sequences. In the present work, the interaction of this alkaloid with the i-motif formed by the human telomere cytosine-rich sequence, as well as with several positive and negative controls, has been studied. Molecular fluorescence and circular dichroism spectroscopies, as well as nuclear magnetic resonance spectrometry and competitive dialysis, have been used with this purpose. The results shown here reveal that the interaction of berberine with this i-motif is weak, mostly electrostatics in nature and takes place with bases not involved in C·C⁺ base pairs. Moreover, this ligand is not selective for i-motif structures, as binds equally to both, folded structure, and unfolded strand, without producing any stabilization of the i-motif. As a conclusion, the development of analytical methods based on the interaction of fluorescent ligands, such as berberine, with i-motif structures should consider the thermodynamic aspects related with the interaction, as well as the selectivity of the proposed ligands with different DNA structures, including unfolded strands.

Spectrofluorimetric analysis of the binding of a target molecule to serum albumin: tricky aspects and tips

Protein binding heavily modulates drug activity. Therefore, the binding features need to be elucidated when chemistry researchers study new molecules (metal complexes) to be used as drugs. This paper concerns the experimental and data treatment aspects of the mechanistic analysis of the binding to a fluorescent protein (the golden standard serum albumin) by using direct fluorescence titrations. Fluorescence data are not rarely only qualitatively used, neglecting further treatments which could offer a precious detailed picture of the behavior of the drug. We aim to spread a mechanistic approach, discussing the critical aspects for correctly designing the experiments and treating the data. The researcher may confirm adduct formation and evaluate binding constants (Stern-Volmer K_SV or other types of K). Also, we discuss here, with the help of literature examples, the correct use of temperature dependence of K to extract thermodynamic parameters, comment on enthalpy-entropy compensation, together with the use of synchronous spectra and exchange experiments to gain information on the binding type and site. We think that this tutorial/critical synopsis can be of help for the increasing community dealing with these experiments, which are valuable but often much more tricky than it might appear at first sight.

Multi spectroscopy and molecular modeling aspects related to drug interaction of aspirin and warfarin with pepsin; structural change and protease activity

This study evaluates the biochemical interactions between two widely used anticoagulants agents, Aspirin and Warfarin, with the Pepsin as the main stomach protease. These two drugs usually prescribe orally for long period daily use to reduce cardiovascular and thrombi death which leads to being in close contact with Pepsin. This interaction could induce related gastrointestinal problems such as peptic ulcer. In this regard, the conformational changes and enzymatic activity of the Pepsin induced by Aspirin and Warfarin were studied by using several spectroscopic methods along with molecular modeling approaches. Results confirm the formation of stable complexes between protein and drugs which leads to slight subsequent conformational changes of protein structure. The quenching mechanisms for both drug-Pepsin interactions are static. In the case of Warfarin, the hydrophobic interactions are the most important interactions. Also for Aspirin, hydrogen bond and van der Waals forces are mainly involved in the binding process. The Warfarin shows the induction of some conformational changes resulted in suppressing the protease activity and the Aspirin reversely enhanced the enzyme activity function. This study provides useful information regarding the effects of Warfarin and Aspirin on Pepsin which are helpful for the choosing of therapeutics depending on the patients' condition.

Mechanistic interaction study of 5,6-Dichloro-2-[2-(pyridin-2-yl)ethyl]isoindoline-1,3-dione with bovine serum albumin by spectroscopic and molecular docking approaches

A synthesized and promising biologically hypoglycemic compound 5,6-Dichloro-2-[2-(pyridin-2-yl)ethyl]isoindoline-1,3-dione (5e) was studied for its binding to a model protein (bovine serum albumin; BSA) by spectroscopic and molecular simulation approaches. Fluorescence studies revealed that 5e quenched BSA's intrinsic fluorescence by static quenching. The experiments were performed at three different temperatures and the quenching constants and binding constants were evaluated. Stern-Volmer constant (Ksv) values decreased from 1.36 × 104 to 1.20 × 104 as the temperature increased suggesting static quenching involvement in the interaction. Decreased binding constants from 1.70 × 104 to 4.57 × 103 at higher temperatures indicated instability of the complex at rising temperatures. Site I (subdomain IIA) of BSA was found to interact with 5e. The thermodynamic results showed the binding interaction was spontaneous and enthalpy driven. The secondary structure alterations in BSA due to interaction with 5e were studied by UV-visible, synchronous fluorescence, and three-dimensional fluorescence spectra. The results indicate the 5e binds effectively to the BSA and thus, this study can be useful in further exploring the pharmacokinetics and pharmacodynamics of 5e.

Probing the binding of phenolic aldehyde vanillin with bovine serum albumin: Evidence from spectroscopic and docking approach

The interactions of bovine serum albumin (BSA) with vanillin (VAN) were studied using UV-vis absorption, fluorescence, synchronous fluorescence, three dimensional fluorescence spectroscopy (3D), Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), and molecular docking techniques. The results revealed that VAN causes the static quenching of BSA by forming BSA-VAN complex. The thermodynamic parameters obtained using isothermal titration calorimetry (ITC) showed that the interaction between BSA and VAN is spontaneous and hydrogen bonding, van der Waals forces are mainly involved in stabilizing the complex. The distance between the donor and the acceptor was analyzed using fluorescence resonance energy transfer (FRET) which showed Forster distance of 2.58 nm. Molecular docking technique was applied to study the modes of interaction between BSA-VAN system and it was found that VAN bound to the sub-domain IIA of BSA. Structural analysis using 3D, synchronous fluorescence FTIR, and CD showed that upon binding of VAN, BSA exhibits small micro-environmental changes around tryptophan amino acid residue.

Ultrafast Spectroscopic Dynamics of Quinacrine-Riboflavin Binding Protein Interactions

Redox active cofactors play a dynamic role inside protein binding active sites because the amino acids responsible for binding participate in electron transfer (ET) reactions. Here, we use femtosecond transient absorption (FsTA) spectroscopy to examine the ultrafast ET between quinacrine (Qc), an antimalarial drug with potential anticancer activity, and riboflavin binding protein (RfBP) with a known K_d = 264 nM. Steady-state absorption reveals a ∼ 10 nm red-shift in the ground state when QcH₃²⁺ is titrated with RfBP, and a Stern-Volmer analysis shows ∼84% quenching and a blue-shift of the QcH₃²⁺ photoluminescence to form a 1:1 binding ratio of the QcH₃²⁺-RfBP complex. Upon selective photoexcitation of QcH₃²⁺ in the QcH₃²⁺-RfBP complex, we observe charge separation in 7 ps to form ¹[QcH_{3_red}^•+-RfBP^•+], which persists for 138 ps. The FsTA spectra show the spectroscopic identification of QcH_{3_red}^•+, determined from spectroelectrochemical measurements in DMSO. We correlate our results to literature and report lifetimes that are 10-20× slower than the natural riboflavin, Rf-RfBP, complex and are oxygen independent. Driving force (ΔG) calculations, corrected for estimated dielectric constants for protein hydrophobic pockets, and Marcus theory depict a favorable one-electron ET process between QcH₃²⁺ and nearby redox active tyrosine (Tyr) or tryptophan (Trp) residues.

In vitro evaluation of the cytotoxic and bactericidal mechanism of the commonly used pesticide triphenyltin hydroxide

Triphenyltin hydroxide (TPTH) is a widely used pesticide that is highly toxic to a variety of organisms including humans and a potential contender for the environmental pollutant. In the present study, the cytotoxic mechanism of TPTH on mammalian cells was analyzed using HeLa cells and the antibacterial activity was analyzed using B. subtilis and E. coli cells. TPTH inhibited the growth of HeLa cells with a half-maximal inhibitory concentration of 0.25 μM and induced mitotic arrest. Immunofluorescence microscopy analysis showed that TPTH caused strong depolymerization of interphase microtubules and spindle abnormality with the appearance of colchicine type mitosis and condensed chromosome. TPTH exhibited high affinity for tubulin with a dissociation constant of 2.3 μM and inhibited the in vitro microtubule assembly in the presence of glutamate as well as microtubule-associated proteins. Results from the molecular docking and in vitro experiments implied that TPTH may have an overlapping binding site with colchicine on tubulin with a distance of about 11 Å between them. TPTH also binds to DNA at the A-T rich region of the minor groove. The data presented in the study revealed that the toxicity of TPTH in mammalian cells is mediated through its interactions with DNA and its strong depolymerizing activity on tubulin. However, its antibacterial activity was not through FtsZ, the prokaryotic homolog of tubulin but perhaps through its interactions with DNA.

Investigation of the interaction between berberine and nucleosomes in solution: Spectroscopic and equilibrium dialysis approach

Berberine is a natural plant alkaloid with high pharmacological potential. Although its interaction with free DNA has been the subject of several reports, to date there is no work concerning the effect of berberine on nucleoprotein structure of DNA, the nucleosomes. The present study focuses on the binding affinity of berberine to nucleosomes and histone H1 employing various spectroscopic techniques, fluorescence, circular dichroism, thermal denaturation as well as equilibrium dialysis. The results showed that the binding of berberine to nucleosomes is positive cooperative with Ka=5.57×10³M^-1. Berberine quenched with the chromophores of protein moiety of nucleosomes and reduced fluorescence emission intensity at 335nm with Ksv value of 0.135. Binding of berberine to nucleosomes decreased the absorbance at 210 and 260nm, produced hypochromicity in thermal denaturation profiles and its affinity to nucleoprotein structure of nucleosomes was much higher than to free DNA. Berberine also exhibited high affinity to histone H1 in solution and the binding was positive cooperative with. Ka=3.61×10³M^-1. Moreover berberine decreased fluorescence emission intensity of H1 by quenching with tyrosine residue in its globular core domain. The circular dichroism profiles demonstrated that the binding of drug induced secondary structural changes in both DNA stacking and histone H1. It is concluded that berberine is genotoxic drug, interacts with nucleosomes and in this process histone H1 is involved to exert its anticancer activity.

Antimicrobial photodynamic effect of extracts and oxoaporphine alkaloid isomoschatoline from Guatteria blepharophylla

Photodynamic Therapy, a tumor therapy idealized at the beginning of the last century, emerges nowadays as a promising treatment alternative against infectious diseases. In this study we report a bioguided study of Guatteria blepharophylla phytoderivatives for antimicrobial PDT. Crude extracts and fraction from the species bark were obtained and further fractionated for substances isolation. All samples were evaluated in relation to their photophysical (absorbance and fluorescence) and photochemical properties (1,3-DPBF bleaching method). Then, bioassays were conducted using as biological models bacteria and yeast strains and a diode laser as a light source. Phytochemical analyses lead to the isolation of 5 isoquinoline alkaloids from oxoaporphine subclass, denominated GB1 to GB5. Photophysical and photochemical analysis showed that extracts, fraction and GB1 (isomoschatoline) presented absorption profile with bands at 600-700nm and were positive for singlet oxygen production. Photobiological assays indicate that these samples presented photodynamic antimicrobial activity against both gram-positive and gram-negative bacterial and some Candida ssp. yeast strains at sub-inhibitory concentrations. The susceptibility of gram-negative bacteria was significantly enhanced when CaCl2 or MgCl2 were employed. Greater energy doses and double sample's dosage also decreased microbial survival. It is suggested that GB1 photodynamic activity happens through both types I and II photochemical mechanisms, but with a predominance of the latter. Phytoderivatives of G. blepharophylla promoted antimicrobial effect, however more detailed study concerning chemical composition of the crude extracts and fractions as also photophysical and photochemical characteristics of GB1 are necessary to ensure their potential as photosensitizers at antimicrobial photodynamic inactivation.

Spectroscopic analysis on the binding interaction of biologically active pyrimidine derivative with bovine serum albumin

A biologically active antibacterial reagent, 2-amino-6-hydroxy-4-(4-N, N-dimethylaminophenyl)-pyrimidine-5-carbonitrile (AHDMAPPC), was synthesized. It was employed to investigate the binding interaction with the bovine serum albumin (BSA) in detail using different spectroscopic methods. It exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus which are common food poisoning bacteria. The experimental results showed that the fluorescence quenching of model carrier protein BSA by AHDMAPPC was due to static quenching. The site binding constants and number of binding sites (n≈1) were determined at three different temperatures based on fluorescence quenching results. The thermodynamic parameters, enthalpy change (ΔH), free energy (ΔG) and entropy change (ΔS) for the reaction were calculated to be 15.15 kJ/mol, -36.11 kJ/mol and 51.26 J/mol K according to van't Hoff equation, respectively. The results indicated that the reaction was an endothermic and spontaneous process, and hydrophobic interactions played a major role in the binding between drug and BSA. The distance between donor and acceptor is 2.79 nm according to Förster's theory. The alterations of the BSA secondary structure in the presence of AHDMAPPC were confirmed by UV-visible, synchronous fluorescence, circular dichroism (CD) and three-dimensional fluorescence spectra. All these results indicated that AHDMAPPC can bind to BSA and be effectively transported and eliminated in the body. It can be a useful guideline for further drug design.

Natural isoquinoline alkaloids: binding aspects to functional proteins, serum albumins, hemoglobin, and lysozyme

The putative anticancer alkaloids berberine, palmatine, jatrorrhizine, and sanguinarine are known to bind to nucleic acids. To develop them as potential drugs for therapeutic use, their binding affinity to functional proteins and mode of transport in the circulatory system need to be clearly understood. Towards this, many studies on their binding aspects to proteins have been reported and a considerable amount of data, mostly of biophysical nature, exists in the literature. The importance of these natural isoquinoline alkaloids and the recent literature on their interaction phenomena with functional proteins, serum albumins, hemoglobin, and lysozyme are presented in this review.

Spectroscopic study on interaction between three cationic surfactants with different alkyl chain lengths and DNA

In this study, the interaction between cationic surfactants with different alkyl chain lengths, such as hexyltrimethyl ammonium bromide (HTAB), dodecyltrimethyl ammonium bromide (DTAB) and cetyltrimethyl ammonium bromide (CTAB), and DNA was investigated by UV-vis spectroscopy, fluorescence spectroscopy and viscosity techniques. The results showed that these three cationic surfactants with different hydrocarbon chain lengths could all interact with DNA. Their binding modes were estimated and their interaction strength was compared. In addition, the effects of the surfactant, NaCl and phosphate ion concentrations on the interaction were reviewed. It is wished that this work would provide some valuable references to investigate the influence of cationic surfactants with different alkyl chain lengths on DNA.

Spectroscopic analyses on interaction of melamine, cyanuric acid and uric acid with DNA

In this work, the interaction of DNA with melamine (MEL), cyanuric acid (CYA) and uric acid (UA) were studied, respectively, by means of UV-vis, fluorescence, circular dichroism (CD) spectroscopy, viscosity and gel electrophoresis methods. The fluorescence quenching was used to study the interaction models of MEL, CYA and UA with DNA, respectively, and the bimolecular quenching constant (Kq), apparent quenching constant (Ksv), effective binding constant (KA) and corresponding dissociation constant (KD) and binding site number (n) were calculated by adopting Stern-Volmer, Lineweaver-Burk and Double logarithm equations. The results show that MEL, CYA and UA are all able to markedly bind to DNA, and the binding strength order is DNA-UA>DNA-CYA>DNA-MEL. It is wished that these researches would facilitate the understanding of the formation of kidney stones and gout in the body after ingesting excess MEL.

Biophysical study on the interaction of etomidate and the carrier protein in vitro

Etomidate is a unique drug used for induction of general anesthesia and sedation, and is usually used through intravenous injection clinically. Before targeting to the receptor, etomidate binds proteins in blood when it comes into veins. Thus to study the interaction of etomidate and serum albumin would be of great toxicological and pharmacological importance. In this study, the interaction between etomidate and human serum albumin (HSA) was studied using fluorescence spectroscopy, UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FT-IR), circular dichroism (CD) spectroscopy, site maker displacement and molecular modeling methods. Investigations of the binding constant (K = 3.55 × 10(5 )M(-1), 295 K), the number of binding sites (n = 1.16), thermodynamic parameters (ΔG = 3.13 × 10(4 )J·mol(-1), ΔS = 364 J·mol(-1)·K(-1) and ΔH = -6.85 × 10(5 )J·mol(-1)) for the reaction and changes to the binding sites and conformation in HSA in response to etomidate were presented. Results show that etomidate can bind HSA tightly through electrostatic forces, and the protein skeleton conformation and secondary structure changes thereby. This is the first spectroscopic report for etomidate-HSA interactions which illustrates the complex nature of this subject.

Separation and identification of anthocyanin extracted from mulberry fruit and the pigment binding properties toward human serum albumin

Purple pigments were isolated from mulberry extracts using preparative high-speed countercurrent chromatography (HSCCC) and identified by ESI-MS/MS and high performance liquid chromatography (HPLC) techniques. The solvent system containing methyl tert-butyl ether, 1-butanol, acetonitrile, water, and trifluoroacetic acid (10:30:10:50:0.05; %, v/v) was developed in order to separate anthocyanins with different polarities. Cyanidin 3-O-(6″-O-α-rhamnopyranosyl-β-galactopyranoside) (also known as keracyanin) is the major component present in mulberry (41.3%). Other isolated pigments are cyanidin 3-O-(6″-O-α-rhamnopyranosyl-β-glucopyranoside) and petunidin 3-O-β-glucopyranoside. The binding characteristics of keracyanin with human serum albumin (HSA) were investigated by fluorescence and circular dichroism (CD) spectroscopy. Spectroscopic analysis reveals that HSA fluorescence quenched by keracyanin follows a static mode. Binding of keracyanin to HSA mainly depends on van der Waals force or H-bonds with average binding distance of 2.82 nm. The results from synchronous fluorescence, three-dimensional fluorescence, and CD spectra show that adaptive structure rearrangement and decrease of α-helical structure occur in the presence of keracyanin.

Spectroscopic investigation on sonodynamic and sonocatalytic damage of BSA molecules by Thymol Blue (TB) derivants under ultrasonic irradiation

In this paper, the Thymol Blue derivants including Thymol Blue (thymolsulfonphthalein), Thymol Blue-DA (3,3'-Bis [N,N-bis (carboxymethyl) aminomethyl] thymolsulfonphthalein) and Thymol Blue-DA-Fe(III) (3,3'-Bis [N,N-bis (carboxymethyl) aminomethyl] thymolsulfonphthalein-Ferrous(III)) were adopted as sonosensitizers to study the sonodynamic and sonocatalytic activities under ultrasonic irradiation. At first, the interaction of Thymol Blue derivants with bovine serum albumin (BSA) was studied by fluorescence spectroscopy. On that basis, the sonodynamic and sonocatalytic damages of Thymol Blue derivants to BSA under ultrasonic irradiation were investigated by the combination of UV-vis, circular dichroism (CD) and fluorescence spectroscopy. Meanwhile, some influenced factors (ultrasonic irradiation time, Thymol Blue derivants concentration and ionic strength) on the damaging degree of BSA molecules were also reviewed. In addition, synchronous fluorescence spectra were used to estimate the binding and damage sites of Thymol Blue derivants to BSA. Finally, the generation of ROS during sonodynamic and sonocatalytic processes was confirmed by the method of Oxidation-Extraction Spectrometry (OEP). Perhaps, this paper may offer some important subjects for the study of Thymol Blue derivants in sonodynamic therapy (SDT) and sonocatalytic therapy (SCT) technologies for tumor treatment and the effect of the amino acid and central metal.

Insights into in vitro binding of parecoxib to human serum albumin by spectroscopic methods

Herein, we report the effect of parecoxib on the structure and function of human serum albumin (HSA) by using fluorescence, circular dichroism (CD), Fourier transforms infrared (FTIR), three-dimensional (3D) fluorescence spectroscopy, and molecular docking techniques. The Stern-Volmer quenching constants K(SV) and the corresponding thermodynamic parameters ΔH, ΔG, and ΔS have been estimated by the fluorescence quenching method. The results indicated that parecoxib binds spontaneously with HSA through van der Waals forces and hydrogen bonds with binding constant of 3.45 × 10(4) M(-1) at 298 K. It can be seen from far-UV CD spectra that the α-helical network of HSA is disrupted and its content decreases from 60.5% to 49.6% at drug:protein = 10:1. Protein tertiary structural alterations induced by parecoxib were also confirmed by FTIR and 3D fluorescence spectroscopy. The molecular docking study indicated that parecoxib is embedded into the hydrophobic pocket of HSA.

Understanding the fate of an anesthetic, nalorphine upon interaction with human serum albumin: a photophysical and mass-spectroscopy approach

Nalorphine is an injectable opioid agonist–antagonist.

Insights into the selective binding and toxic mechanism of microcystin to catalase

Microcystin is a sort of cyclic nonribosomal peptides produced by cyanobacteria. It is cyanotoxin, which can be very toxic for plants and animals including humans. The present study evaluated the interaction of microcystin and catalase, under physiological conditions by means of fluorescence, three-dimensional (3D) fluorescence, circular dichroism (CD), Fourier Transform infrared (FT-IR) spectroscopy, and enzymatic reactionkinetic techniques. The fluorescence data showed that microcystin could bind to catalase to form a complex. The binding process was a spontaneous molecular interaction procedure, in which electrostatic interactions played a major role. Energy transfer and fluorescence studies proved the existence of a static binding process. Additionally, as shown by the three-dimensional fluorescence, CD and FT-IR results, microcystin could lead to conformational and microenvironmental changes of the protein, which may affect the physiological functions of catalase. The work provides important insights into the toxicity mechanism of microcystin in vivo.

Berberine acutely inhibits the digestion of maltose in the intestine

ETHNOPHARMACOLOGICAL RELEVANCE

The Chinese Goldthread Rhizome has been used in the Traditional Chinese Medicine as an important ingredient of many formulas for the treatment of diabetes mellitus. Berberine, the main effective composition of Chinese Goldthread Rhizome, is also effective in treating diabetes in today's clinical practice of Traditional Chinese Medicine.

AIM OF THE STUDY

To evaluate the hypoglycemic activity of berberine which treats acutely on the postprandial blood glucose, and to explore the mechanism of this activity.

MATERIALS AND METHODS

1. One-dose preprandial intragastric administrations of berberine were given to normal animals (dogs and rats), and the postprandial blood glucose concentration curves were measured. Serum insulin enzyme linked immunosorbent assay (ELISA) was only performed in rats. 2. The euglycemic clamp test was performed to evaluate the effect of one-dose berberine intragastric administration on the blood glucose transformation and utilization rate in rats. 3. In the Caco-2 cell monolayer test, the changes of glucose concentration on the apical and basolateral sides were measured when the maltose solution containing berberine was added to the apical side. 4. The inhibition ratio of berberine against α-glucosidase was measured in vitro. 5. The effect of berberine on the fluorescence emission spectrums of α-glucosidase was studied.

RESULTS

One-dose preprandial intragastric administration of berberine delayed the rise of post-maltose blood glucose, did not affect postprandial blood glucose after glucose meal, and did not affect the insulin level in normal rats; reduced post-maltose blood glucose in normal dogs. 2. The result of euglycemic clamp test showed that one-dose intragastric administration of berberine had no effect on the blood glucose transformation and utilization rate in rats. 3. Berberine added to the maltose solution on the apical side of Caco-2 cell monolayer reduced the glucose concentration on the apical side. Glucose in basolateral side of all groups cannot be detected. 4. Berberine inhibited the activity of α-glucosidase in vitro. 5. Berberine significantly and concentration dependently quenched the fluorescence emission spectrum of α-glucosidase.

CONCLUSION

Our findings suggest an additional mechanism of the hypoglycemic activity of berberine by demonstrating its ability to acutely inhibit the α-glucosidase, and support the traditional use of berberine and Chinese Goldthread Rhizome for the treatment of diabetes mellitus.