Differential effects of methoxy group on the interaction of curcuminoids with two major ligand binding sites of human serum albumin

Assesment of polyphenolic compounds against biofilms produced by clinical Acinetobacter baumannii strains using in silico and in vitro models

Several types of microbial infections are caused by Acinetobacter baumanii that has developed resistance to antimicrobial agents. We therefore investigated the role of plant polyphenols against A. baumannii using in silico and in vitro models. The clinical strains of A. baumannii were investigated for determination of resistance pattern and resistance mechanisms including efflux pump, extended spectrum beta lactamase, phenotype detection of AmpC production, and Metallo-β-lactamase. The polyphenolic compounds were docked against transcription regulator BfmR (PDB ID 6BR7) and antimicrobial, antibiofilm, and anti-quorum sensing activities were performed. The antibiogram studies showed that all isolated strains were resistant. Strain A77 was positive in Metallo-β-lactamase production. Similarly, none of strains were producers of AmpC, however, A77, A76, A75 had active efflux pumps. Molecular docking studies confirmed a strong binding affinity of Rutin and Catechin towards transcription regulator 6BR7. A significant antimicrobial activity was recorded in case of quercetin and syringic acid (MIC 3.1 µg/mL) followed by vanillic acid and caffeic acid (MIC 12.5 µg/mL). All tested compounds presented a strong antibiofilm activity against A. baumanii strain A77 (65 to 90%). It was concluded that all tested polyphenols samples posess antimicrobial and antibiofilm activities, and hence they may be utilized to treat multidrug resistance A. baumannii infections.

Structural modification of the Pseudomonas aeruginosa alkylquinoline cell-cell communication signal, HHQ, leads to benzofuranoquinolines with anti-virulence behaviour in ESKAPE pathogens

Microbial populations have evolved intricate networks of negotiation and communication through which they can coexist in natural and host ecosystems. The nature of these systems can be complex and they are, for the most part, poorly understood at the polymicrobial level. The Pseudomonas Quinolone Signal (PQS) and its precursor 4-hydroxy-2-heptylquinoline (HHQ) are signal molecules produced by the important nosocomial pathogen Pseudomonas aeruginosa . They are known to modulate the behaviour of co-colonizing bacterial and fungal pathogens such as Bacillus atropheaus, Candida albicans and Aspergillus fumigatus. While the structural basis for alkyl-quinolone signalling within P. aeruginosa has been studied extensively, less is known about how structural derivatives of these molecules can influence multicellular behaviour and population-level decision-making in other co-colonizing organisms. In this study, we investigated a suite of small molecules derived initially from the HHQ framework, for anti-virulence activity against ESKAPE pathogens, at the species and strain levels. Somewhat surprisingly, with appropriate substitution, loss of the alkyl chain (present in HHQ and PQS) did not result in a loss of activity, presenting a more easily accessible synthetic framework for investigation. Virulence profiling uncovered significant levels of inter-strain variation among the responses of clinical and environmental isolates to small-molecule challenge. While several lead compounds were identified in this study, further work is needed to appreciate the extent of strain-level tolerance to small-molecule anti-infectives among pathogenic organisms.

All Polyphenols Are Not Created Equal: Exploring the Diversity of Phenolic Metabolites

Dietary intake of plant polyphenols is significant, and many of them enter a human body as a highly diverse pool of ring-fission phenolic metabolites arising from digestion and microbial catabolism of the parental structures. Difficulty in designing the uniform intervention studies and limited tools calibrated to detect and quantify the inherent complexity of phenolic metabolites hindered efforts to establish and validate protective health effects of these molecules. Here, we highlight the recent findings that describe novel complex downstream metabolite profiles with a particular focus on dihydrophenolic (phenylpropanoic) acids of microbial origin, ingested and phase II-transformed methylated phenolic metabolites (methylated sinks), and small phenolic metabolites derived from the breakdown of different classes of flavonoids, stilbenoids, and tannins. There is a critical need for precise identification of the individual phenolic metabolite signatures originating from different polyphenol groups to enable future translation of these findings into break-through nutritional interventions and dietary guidelines.

When Albumin Meets Liposomes: A Feasible Drug Carrier for Biomedical Applications

Albumin, the most abundant protein in plasma, possesses some inherent beneficial structural and physiological characteristics that make it suitable for use as a drug delivery agent, such as an extraordinary drug-binding capacity and long blood retention, with a high biocompatibility. The use of these characteristics as a nanoparticle drug delivery system (DDS) offers several advantages, including a longer circulation time, lower toxicity, and more significant drug loading. To date, many innovative liposome preparations have been developed in which albumin is involved as a DDS. These novel albumin-containing liposome preparations show superior deliverability for genes, hydrophilic/hydrophobic substances and proteins/peptides to the targeting area compared to original liposomes by virtue of their high biocompatibility, stability, effective loading content, and the capacity for targeting. This review summarizes the current status of albumin applications in liposome-based DDS, focusing on albumin-coated liposomes and albumin-encapsulated liposomes as a DDS carrier for potential medical applications.

Multitargeting Antibacterial Activity of a Synthesized Mn2+ Complex of Curcumin on Gram-Positive and Gram-Negative Bacterial Strains

Curcumin is an important molecule with a plethora of pharmacological activities and therapeutic potentials. Despite its efficacy, it remained a potential drug candidate owing to hydrolytic instability and poor aqueous solubility. To overcome the limitations related to low solubility, low bioavailability, and the fact that curcumin is never present in solution as a "single unit", its complex was prepared with MnII with the idea that binding to a metal ion might help to resolve these issues. The complex was characterized by elemental and spectral analysis. The structure of the complex was determined by density functional theory calculations. The complex was stable at physiological buffer conditions, unlike curcumin. It did not have any detrimental effect on mammalian cells. There was a significant enhancement in the antibacterial activity of the complex compared to curcumin against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. It showed a strong affinity for deoxyribonucleic acid (DNA) evident from a high binding constant value with calf thymus DNA and also from the retarded electrophoretic mobility of bacterial plasmid DNA. The complex showed "superoxide dismutase-like" activity leading to the generation of reactive oxygen species (ROS). The complex caused bacterial membrane perturbation evident from calcein leakage assay, which was further corroborated by scanning and transmission electron microscopic experiments. Overall, the present study shows improved stability and antibacterial potency of a nontoxic complex over curcumin. Its multitargeting mode of action such as ROS-production, effective binding with DNA, and permeabilization of bacterial membrane together allows it to be an effective antibacterial agent that could be taken further for therapeutic use against bacterial infections.

Multi-spectroscopic studies of the interaction of new synthesized platin complex with human carrier protein of serum albumin

Previous reports have shown that protein-drug interaction helps to improve the pharmacokinetics of the drugs. Human serum albumin (HSA) is one of the basic components of blood plasma and it serves as a storage and carrier protein. In the present study, the interaction of a new synthesized Pt [iso]2 complex (cis - [Pt(NH₂-Isopentylamine)₂(Isopentylglycine)]NO₃₎ with HSA was studied using the spectroscopic methods of fluorescence and circular dichroic (CD) at two different temperatures of 25 and 37 °C. Analysis of the quenching mechanism via Stern-Volmer curve, determination of HSA binding parameters (0.65 × 10⁴ and 2.27 × 10⁴) and standard Gibbs free energy (-25.8, and 21.77) at 25 and 37 °C, respectively, carried out using fluorescence quenching data. Data analysis showed that the static mechanism has the main role in fluorescence quenching. Also, the number of protein binding sites for complex indicated one binding site at two temperatures of 25 and 37 °C. The secondary structure of protein in the presence of different concentrations of Pt(II) complex did not show any significant alterations. Whereas, thermal stability of the HSA was reduced in the presence of complex. Also, thermal analysis obtained the values of ΔG°₂₅ for HSA and HSA in presence of Pt [Iso]₂ 20, 13, respectively. According to the above results, we concluded that the new synthesized Pt complex can bind to the blood carrier protein of HSA and change the stability of it which can be considered in the design of new drugs.Communicated by Ramaswamy H. Sarma.

Development of a Potential Gallium-68-Labelled Radiotracer Based on DOTA-Curcumin for Colon-Rectal Carcinoma: From Synthesis to In Vivo Studies

Colorectal cancer is the third most commonly occurring cancer in men and the second most commonly occurring cancer in women worldwide. We have recently reported that curcuminoid complexes labelled with gallium-68 have demonstrated preferential uptake in HT29 colorectal cancer and K562 lymphoma cell lines compared to normal human lymphocytes. In the present study, we report a new gallium-68-labelled curcumin derivative (⁶⁸Ga-DOTA-C21) and its initial validation as marker for early detection of colorectal cancer. The precursor and non-radioactive complexes were synthesized and deeply characterized by analytical methods then the curcuminoid was radiolabelled with gallium-68. The in vitro stability, cell uptake, internalization and efflux properties of the probe were studied in HT29 cells, and the in vivo targeting ability and biodistribution were investigated in mice bearing HT29 subcutaneous tumour model. ⁶⁸Ga-DOTA-C21 exhibits decent stability (57 ± 3% after 120 min of incubation) in physiological media and a curcumin-mediated cellular accumulation in colorectal cancer cell line (121 ± 4 KBq of radiotracer per mg of protein within 60 min of incubation). In HT29 tumour-bearing mice, the tumour uptake of ⁶⁸Ga-DOTA-C21 is 3.57 ± 0.3% of the injected dose per gram of tissue after 90 min post injection with a tumour to muscle ratio of 2.2 ± 0.2. High amount of activity (12.73 ± 1.9% ID/g) is recorded in blood and significant uptake of the radiotracer occurs in the intestine (13.56 ± 3.3% ID/g), lungs (8.42 ± 0.8% ID/g), liver (5.81 ± 0.5% ID/g) and heart (4.70 ± 0.4% ID/g). Further studies are needed to understand the mechanism of accumulation and clearance; however, ⁶⁸Ga-DOTA-C21 provides a productive base-structure to develop further radiotracers for imaging of colorectal cancer.

Further Evidence Regarding the Important Role of Chlorine Atoms of Aripiprazole on Binding to the Site II Area of Human Albumin

Previously, we reported on the high-affinity binding of aripiprazole (ARP), an antipsychotic drug, to human albumin and the role of the chlorine atom of ARP on this binding. In this study, we investigated the binding mode of ARP to human albumin in detail using ARP derivatives and several animal-derived albumins. ARP bound strongly to human and dog albumin. The circular dichroism (CD) spectra of ARP bound to human and dog albumin were also similar. Deschloro-ARP bound less strongly to all of the albumin species compared to ARP, and the shapes of CD spectra were similar for all albumin species. CD spectra of dimethyl-ARP, for which chlorine atoms were substituted methyl groups, were quite similar to that of deschloro-ARP. In displacement experiments, competitive binding was observed between ARP and deschloro-ARP. These results suggest that the chlorine atoms in ARP are involved in the binding modes of ARP for human and dog albumins, whereas ARP and deschloro-ARP appear to share the same binding region in site II. The aforementioned results imply that compounds having a chlorine atom bind more strongly to plasma proteins, resulting in a long blood retention time. Therefore, findings reported here may provide the basically useful data for drug design.

Superior anticancer activity is demonstrated by total extract of Curcuma longa L. as opposed to individual curcuminoids separated by centrifugal partition chromatography

Three curcuminoids: bisdemethoxycurcumin, demethoxycurcumin, and curcumin from turmeric were successfully separated by a high capacity solvent system composed of heptane: chloroform: methanol: water mixture (5: 6: 3: 2 v/v/v/v) tailored for centrifugal partition chromatographs at K-values of 0.504, 1.057, 1.644, respectively. These three ferulic acid derivatives obtained at a purity rate exceeding 95% were analysed by an HPLC-MS spectrometer. Turmeric extract inhibited the proliferation/viability of A549 human lung cancer, HT29 colon cancer, and T98G glioblastoma cell lines in (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) tetrazolium reduction assay (MTT). Single curcuminoids significantly decreased the viability/proliferation of lung cancer cells in a dose-dependent manner. However, total extract displayed the superior anticancer activity in the investigated cell lines. Crude extract in combination with cisplatin augmented the decrease in the viability of cancer cells compared with single compound treatment in A549 lung cancer cells. Total extract of Curcuma longa could be regarded as being more effective against lung cancer cells in vitro than its separated compounds.

Structure Related Inhibition of Enzyme Systems in Cholinesterases and BACE1 In Vitro by Naturally Occurring Naphthopyrone and Its Glycosides Isolated from Cassia obtusifolia

Cassia obtusifolia Linn. have been used to improve vision, inflammatory diseases, and as hepatoprotective agents and to promote urination from ancient times. In the present study, we investigated the influence of glycosylation of components of C. obtusifolia and structure-activity relationships (SARs) with respect to the inhibition of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and β-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1), which are related to Alzheimer’s disease (AD). All six C. obtusifolia-derived compounds, rubrofusarin (1), rubrofusarin 6-O-β-d-glucopyranoside (2), rubrofusarin 6-O-β-d-gentiobioside (3), nor-rubrofusarin 6-O-β-d-glucoside (4), isorubrofusarin 10-O-β-d-gentiobioside (5), and rubrofusarin 6-O-β-d-triglucoside (6) showed promising inhibitory activity against AChE/BACE1. Compounds 3 and 4 showed most significant inhibition against AChE and BACE1, respectively. The SARs results emphasized the importance of gentiobiosyl moiety in the rubrofusarin for AChE inhibition, whereas the presence of hydroxyl group at C-8 and the glucosyl moiety at the C-6 position in the nor-rubrofusarin appeared to largely determine BACE1 inhibition. Kinetics and docking studies showed the lowest binding energy and highest affinity for mixed-type inhibitors, 3 and 4. Hydrophobic bonds interactions and the number of hydrogen bonds determined the strength of the protein-inhibitor interaction. These results suggest that C. obtusifolia and its constituents have therapeutic potential, and that the SARs of its active components are further explored with a view towards developing a treatment for AD.

Investigating the affinity of BDE154 and 3OH-BDE154 with HSA: Experimental and simulation validation

The physicochemical properties of polybrominated diphenyl ethers are important for modeling their transport, but these data are often missing. Here, satisfactory bioactivity results were obtained using human serum albumin as the carrier, 2,2',4,4',5,6'-hexabromodiphenyl ether (BDE154) and 3-hydroxy-2,2',4,4', 5,6'-hexabromodiphenyl ether (3OH-BDE154) as the ligands, using UV-visible absorbance, fluorescence, circular dichroism, molecular docking, and molecular dynamics methods. The interactions between human serum albumin and BDE154 or 3OH-BDE154 were verified, consistent with the static quenching procedure. At pH 7.4, the binding constants of the complexes for site I were relatively comparable and increased in the order BDE154<3OH-BDE154. Then, the secondary structure and kinetic parameters of albumin were analyzed using the circular dichroism spectra and GROMACS software. The data obtained from these simulations indicate that hydrophobic attraction might be the key factor for the stability of complexes. The docking experiments provided further insight into the hydrophobic pocket and showed that 3OH-BDE154 has a stronger binding affinity to human serum albumin than BDE154. The experimental spectral data were obtained and compared with the simulation results, showing good agreement. A detailed analysis of PBDEs-HSA interactions would provide valuable information to better understand the interaction on this class of compounds.

The Binding of Silibinin, the Main Constituent of Silymarin, to Site I on Human Serum Albumin

Silibinin is the main constituent of silymarin, an extract from the seeds of milk thistle (Silybum marianum). Because silibinin has many pharmacological activities, extending its clinical use in the treatment of a wider variety of diseases would be desirable. In this study, we report on the binding of silibinin to plasma proteins, an issue that has not previously been extensively studied. The findings indicated that silibinin mainly binds to human serum albumin (HSA). Mutual displacement experiments using ligands that primarily bind to sites I and II clearly revealed that silibinin binds tightly and selectively to site I (subsites Ia and/or Ic) of HSA, which is located in subdomain IIA. Thermodynamic analyses suggested that hydrogen bonding and van der Waals interactions are major contributors to silibinin-HSA interactions. Furthermore, the binding of silibinin to HSA was found to be decreased with increasing ionic strength and detergent concentration of the media, suggesting that electrostatic and hydrophobic interactions are involved in the binding. Trp214 and Arg218 were identified as being involved in the binding of silibinin to site I, based on binding experiments using chemically modified- and mutant-HSAs. In conclusion, the available evidence indicates that silibinin binds to the region close to Trp214 and Arg218 in site I of HSA with assistance by multiple forces and can displace site I drugs (e.g., warfarin or iodipamide), but not site II drugs (e.g., ibuprofen).

Comparison of Posttranslational Modification and the Functional Impairment of Human Serum Albumin in Commercial Preparations

On account of its long circulating half-life, human serum albumin (HSA) is susceptible to posttranslational modifications that can alter its functions. Here, we comprehensively compared the degree of posttranslational modifications with the functional impairment of HSA derived from 5 different commercially available albumin preparations and clarified their relationships. We used electrospray ionization-time of flight mass spectrometry to evaluate the degree of posttranslational modification of the entire HSA molecule that was associated with disease development and found that the fraction of Cys34-cysteinylated HSA (Cys-Cys34-HSA), a major form of oxidative modification, varied substantially among the albumin preparations. Meanwhile, no remarkable difference was found in the degree of glycated or N-terminal truncated HSA among the preparations tested. The nonosmotic pressure maintenance functions of HSA, such as its antioxidative and ligand-binding activities significantly differed among the preparations. Interestingly, the alternations of these functions showed a significantly negative correlation only with the Cys-Cys34-HSA fraction. These findings suggest that the Cys-Cys34-HSA fraction, as estimated by electrospray ionization-time of flight mass spectrometry can be used as a predictive marker for the functional impairment of albumin preparations and that it would be preferable to use albumin preparations with higher contents of functionally effective albumin that correspond to a lower degree of cysteinylation of Cys34 in clinical practice.

N-acetyl-L-methionine is a superior protectant of human serum albumin against post-translational oxidation as compared to N-acetyl-L-tryptophan

Sodium octanoate and N-acetyl-L-tryptophan (N-AcTrp) are widely used as stabilizers during pasteurization and storage of albumin products. However, as compared with N-AcTrp, N-acetyl-L-methionine (N-AcMet) is superior in protecting albumin exposed to light during storage. Here, we examine, whether N-AcMet also is better than N-AcTrp to protect albumin against oxidation. Recombinant human serum albumin (rHSA) without and with N-AcMet or N-AcTrp was oxidized by using chloramine-T (CT) as a model compound for mimicking oxidative stress. Oxidation of rHSA was examined by determining carbonyl groups and advanced oxidation protein products. Structural changes were studied by native-PAGE, circular dichroism, intrinsic fluorescence and differential scanning calorimetry. The anti-oxidant capacity of CT-treated rHSA was quantified by its ability to scavenge peroxynitrite and the hydroxyl radical. The pharmacokinetics of indocyanine green-labeled albumin preparations was studied in male mice. We found that the number of chemical modifications and the structural changes of rHSA were significantly smaller in the presence of N-AcMet than in the presence of N-AcTrp. The anti-oxidant properties of CT-exposed rHSA were best protected by adding N-AcMet. Finally, N-AcMet is superior in preserving the normal pharmacokinetics of rHSA. Thus, N-AcMet is superior to N-AcTrp in protecting albumin preparations against oxidation. In addition, N-AcMet is probable also useful for protecting other proteins. Therefore, N-AcMet should be useful as a new and effective stabilizer and antioxidant for albumin isolated from blood, rHSA, albumin-fusion proteins and for preparations of rHSA-therapeutic complexes.

The increased binding affinity of curcumin with human serum albumin in the presence of rutin and baicalin: A potential for drug delivery system

The impacts of rutin and baicalin on the interaction of curcumin (CU) with human serum albumin (HSA) were investigated by fluorescence and circular dichroism (CD) spectroscopies under imitated physiological conditions. The results showed that the fluorescence quenching of HSA by CU was a simultaneous static and dynamic quenching process, irrespective of the presence or absence of flavonoids. The binding constants between CU and HSA in the absence and presence of rutin and baicalin were 2.268×10(5)M(-1), 3.062×10(5)M(-1), and 3.271×10(5)M(-1), indicating that the binding affinity was increased in the case of two flavonoids. Furthermore, the binding distance determined according to Förster's theory was decreased in the presence of flavonoids. Combined with the fact that flavonoids and CU have the same binding site (site I), it can be concluded that they may simultaneously bind in different regions in site I, and formed a ternary complex of flavonoid-HSA-CU. Meanwhile, the results of fluorescence quenching, CD and three-dimensional fluorescence spectra revealed that flavonoids further strengthened the microenvironmental and conformational changes of HSA induced by CU binding. Therefore, it is possible to develop a novel complex involving CU, flavonoid and HSA for CU delivery. The work may provide some valuable information in terms of improving the poor bioavailabiliy of CU.

Quantum molecular modelling of ibuprofen bound to human serum albumin

The total interaction energies of the ibuprofen complexed with FA3/FA4 and FA6 binding sites of human serum albumin are in agreement with the hypothesis that the Sudlow's site II is the main binding pocket for ibuprofen.