Fatty Acid Modulated Human Serum Albumin Binding of the β-Carboline Alkaloids Norharmane and Harmane

Simple naturally occurring β-carboline alkaloids – role in sustainable theranostics

This review is a brief treatise on some simple β-carboline alkaloids that are abundantly available in plants, animals and foodstuff. These alkaloids are well known for their pharmacological action as well as their allelopathic behaviour. The focus of this review is on sustainable use of naturally occurring compounds in safeguarding human health and protecting our environment at large i.e. the prospective applications of these molecules for Sustainable Theranostics. The review commences with an initial introduction to the β-carboline alkaloids, followed by an outlay of their geographical distribution and natural abundance, then the basic structure and building units of the simplest β-carboline alkaloids have been mentioned. This is followed by a discussion on the important methods of extraction from natural sources both plants and animals. Then the foundation for the use of these alkaloids in Sustainable Theranostics has been built by discussing their interesting photophysics, interactions with important biological molecules and an extensive survey of their therapeutic potential and allelopathic behaviour. Finally the review ends with a silver lining mentioning the future prospective applications of these alkaloids with special relevance to sustainability issues.

Interactive multiple binding of oleic acid, warfarin and ibuprofen with human serum albumin revealed by thermal and fluorescence studies

Human serum albumin binds a wide variety of drugs with different structure and affinity to two main binding sites, drug site 1 (DS1) and drug site 2 (DS2), which partially or totally overlap with fatty acid (FA) sites. Although multiple binding sites are available for endogenous compounds, FAs are the primary physiological ligands of albumin and their competition in the occupancy of DS1 and DS2 affects the binding of exogenous molecules, with a possible impact on drug delivery. In this work, we have investigated the simultaneous binding of oleic acid, warfarin and ibuprofen to albumin using differential scanning calorimetry and fluorescence to evaluate the impact on the conformational stability of the protein. The two drugs are widely used for their anticoagulant (warfarin) and anti-inflammatory (ibuprofen) properties, and can be also considered as site markers to probe DS1 and DS2, respectively. Oleic acid is one of the most important fatty acids from a physiological point of view for its role as a source of energy for cells, and also it binds albumin with the highest association constant. When complexed with oleic acid the calorimetric profile of albumin shows a biphasic trend whose line shape depends on the ligand concentration. The binding capacity of either warfarin or ibuprofen to albumin is modulated by oleate molecules in a concentration-dependent mode being synergic cooperative (warfarin) or competitive-like (ibuprofen). The overall results provide insights on the dynamics of albumin/ligands complex, which in turn may have important pharmacokinetic and pharmacodynamic implications.

Alkaloids as Photosensitisers for the Inactivation of Bacteria

Antimicrobial photodynamic therapy has emerged as a powerful approach to tackle microbial infections. Photodynamic therapy utilises a photosensitiser, light, and oxygen to generate singlet oxygen and/or reactive oxygen species in an irradiated tissue spot, which subsequently react with nearby biomolecules and destroy the cellular environment. Due to the possibility to irradiate in a very precise location, it can be used to eradicate bacteria, fungus, and parasites upon light activation of the photosensitiser. In this regard, natural products are low-cost molecules capable of being obtained in large quantities, and some of them can be used as photosensitisers. Alkaloids are the largest family among natural products and include molecules with a basic nature and aromatic rings. For this study, we collected the naturally occurring alkaloids used to treat microorganism infections using a photodynamic inactivation approach. We gathered their main photophysical properties (excitation/emission wavelengths, quantum yields, and oxygen quantum yield) which characterise the ability to efficiently photosensitise. In addition, we described the antibacterial activity of alkaloids upon irradiation and the mechanisms involved in the microorganism killing. This review will serve as a reference source to obtain the main information on alkaloids used in antimicrobial photodynamic therapy.

Probe into the Molecular Mechanism of Ibuprofen Interaction with Warfarin Bound to Human Serum Albumin in Comparison to Ascorbic and Salicylic Acids: Allosteric Inhibition of Anticoagulant Release

The release of anticoagulant drugs such as warfarin from human serum albumin (HSA) has been important not only mechanistically but also clinically for patients who take multiple drugs simultaneously. In this study, the role of some commonly used drugs, including s-ibuprofen, ascorbic acid, and salicylic acid, was investigated in the release of warfarin bound to HSA in silico. The effects of the aforementioned drugs on the HSA-warfarin complex were investigated with molecular dynamics (MD) simulations using two approaches; in the first perspective, molecular docking was used to model the interaction of each drug with the HSA-warfarin complex, and in the second approach, drugs were positioned randomly and distant from the binary complex (HSA-warfarin) in a physiologically relevant concentration. The results obtained from both approaches indicated that s-ibuprofen and ascorbic acid both displayed allosteric effects on the release of warfarin from HSA. Although ascorbic acid aided in warfarin release, leading to destabilization of HSA, ibuprofen demonstrated a stabilizing effect on releasing the anticoagulant drug through several noncovalent interactions, including hydrophobic, electrostatic, and hydrogen-bonding interactions with the protein. The calculated binding free energy and energy contribution of involved residues using the molecular mechanics-Poisson Boltzmann surface area (MM-PBSA) method, along with root mean square deviation (RMSD) values, protein gyration, and free energy surface (FES) mapping of the protein, provided valuable details on the nature of the interactions of each drug on the release of warfarin from HSA. These results can provide important information on the mechanisms of anticoagulant release that has not been revealed in molecular details previously.

Ultraviolet blocking and antioxidant polyvinyl alcohol films incorporated with baicalin extraction from Scutellaria baicalensis Georgi

Baicalin, an active flavonoid ingredient of Scutellaria baicalensis Georgi, was extracted by heat reflux extraction and showed the same significance UV absorption property with standard baicalin. Active films were prepared from polyvinyl alcohol (PVA) containing baicalin extract by casting method. The effect of baicalin extracts on the UV-blocking, optical, antioxidant property, water vapor permeability, swelling and mechanical properties of the films were studied. UV–vis transmittance spectra showed that PVA films incorporated with baicalin extract blocked ultraviolet light range from 280–400 nm even with low concentration of baicalin (0.5 wt%) and maintain the high transparency in visible spectrum. The outstanding UV-blocking properties of PVA films incorporated with baicalin extract were also confirmed by Rhodamine B degradation. Baicalin conferred antioxidant properties to PVA films as determined by DPPH radical scavenging activity. Due to the interaction between hydroxy groups of baicalin and PVA molecule, water vapor permeability, swelling and elongation at break of the films were decreased accompanied with the increasing in tensile strength and Young’s modulus. FTIR reveal that the interaction between PVA molecules was significant changed by the introduction of baicalin. These results suggest that PVA film incorporated with baicalin extract can be used for the development of functional protective film.

The interaction mechanism between fludarabine and human serum albumin researched by comprehensive spectroscopic methods and molecular docking technique

Fludarabine (Flu) is widely used to treat B-cell chronic lymphocytic leukemia. HSA is of the essence to human, especially in blood circulation system. The interaction mechanism between Flu and HSA was studied by comprehensive spectroscopic methods and molecular docking technique. UV-vis and FL spectrum results indicated that Flu bond with HSA, and there was a new complex produced at the binding site I in subdomain IIA. Association constants at 298 K were 1.637 × 10⁴ M^-1 and 1.552 × 10⁴ M^-1 at 310 K, respectively. The negative enthalpy (ΔH) and positive entropy (ΔS) values for the interaction revealed that the binding behavior was driven by hydrophobic forces and hydrogen bonds. The results obtained from UV, RLS spectra, 3D fluorescence and CD spectrum illustrated that Flu could change the secondary structure of HSA. According to molecule docking result, the binding energy of interaction is -11.15 kcal/mol.

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.

Association of iminium and alkanolamine forms of the benzo[c]phenanthridine alkaloid chelerythrine with human serum albumin: photophysical, thermodynamic and theoretical approach

Association of isoforms of chelerythrine (CHL) with HSA.

Human plasma lipocalins and serum albumin: Plasma alternative carriers?

Lipocalins are an evolutionarily conserved family of proteins that bind and transport a variety of exogenous and endogenous ligands. Lipocalins share a conserved eight anti-parallel β-sheet structure. Among the different lipocalins identified in humans, α-1-acid glycoprotein (AGP), apolipoprotein D (apoD), apolipoprotein M (apoM), α1-microglobulin (α1-m) and retinol-binding protein (RBP) are plasma proteins. In particular, AGP is the most important transporter for basic and neutral drugs, apoD, apoM, and RBP mainly bind endogenous molecules such as progesterone, pregnenolone, bilirubin, sphingosine-1-phosphate, and retinol, while α1-m binds the heme. Human serum albumin (HSA) is a monomeric all-α protein that binds endogenous and exogenous molecules like fatty acids, heme, and acidic drugs. Changes in the plasmatic levels of lipocalins and HSA are responsible for the onset of pathological conditions associated with an altered drug transport and delivery. This, however, does not necessary result in potential adverse effects in patients because many drugs can bind both HSA and lipocalins, and therefore mutual compensatory binding mechanisms can be hypothesized. Here, molecular and clinical aspects of ligand transport by plasma lipocalins and HSA are reviewed, with special attention to their role as alterative carriers in health and disease.

Evidence that Chemical Chaperone 4-Phenylbutyric Acid Binds to Human Serum Albumin at Fatty Acid Binding Sites

Endoplasmic reticulum stress elicits unfolded protein response to counteract the accumulating unfolded protein load inside a cell. The chemical chaperone, 4-Phenylbutyric acid (4-PBA) is a FDA approved drug that alleviates endoplasmic reticulum stress by assisting protein folding. It is found efficacious to augment pathological conditions like type 2 diabetes, obesity and neurodegeneration. This study explores the binding nature of 4-PBA with human serum albumin (HSA) through spectroscopic and molecular dynamics approaches, and the results show that 4-PBA has high binding specificity to Sudlow Site II (Fatty acid binding site 3, subdomain IIIA). Ligand displacement studies, RMSD stabilization profiles and MM-PBSA binding free energy calculation confirm the same. The binding constant as calculated from fluorescence spectroscopic studies was found to be k_PBA = 2.69 x 10⁵ M^-1. Like long chain fatty acids, 4-PBA induces conformational changes on HSA as shown by circular dichroism, and it elicits stable binding at Sudlow Site II (fatty acid binding site 3) by forming strong hydrogen bonding and a salt bridge between domain II and III of HSA. This minimizes the fluctuation of HSA backbone as shown by limited conformational space occupancy in the principal component analysis. The overall hydrophobicity of W214 pocket (located at subdomain IIA), increases upon occupancy of 4-PBA at any FA site. Descriptors of this pocket formed by residues from other subdomains largely play a role in compensating the dynamic movement of W214.

Supramolecular interaction of a cancer cell photosensitizer in the nanocavity of cucurbit[7]uril: A spectroscopic and calorimetric study

The interaction of small biologically active molecules in the nanocavity of supramolecular host is very interesting and thriving research area. In the presence of supramolecular host the absorption and emission properties of small biologically active molecules were modulated several folds compared to bulk solution. In this study we have investigated the supramolecular interaction of a cancer cell photosensitizer molecule harmane in the presence of cucurbit[7]uril (CB7) as host in aqueous buffer solution (pH∼7.2). We have used steady state absorption, emission and time resolved fluorescence spectroscopy techniques. The thermodynamics of the binding between harmane in the nanochannel of CB7 were studied by using isothermal titration calorimetry (ITC) method. The emission properties of harmane are modulated several fold in the presence of CB7. ITC study indicates that the complexation between harmane and CB7 are enthalpically favourable.

The janus facet of nanomaterials

Application of nanoscale materials (NMs) displays a rapidly increasing trend in electronics, optics, chemical catalysis, biotechnology, and medicine due to versatile nature of NMs and easily adjustable physical, physicochemical, and chemical properties. However, the increasing abundance of NMs also poses significant new and emerging health and environmental risks. Despite growing efforts, understanding toxicity of NMs does not seem to cope with the demand, because NMs usually act entirely different from those of conventional small molecule drugs. Currently, large-scale application of available safety assessment protocols, as well as their furthering through case-by-case practice, is advisable. We define a standard work-scheme for nanotoxicity evaluation of NMs, comprising thorough characterization of structural, physical, physicochemical, and chemical traits, followed by measuring biodistribution in live tissue and blood combined with investigation of organ-specific effects especially regarding the function of the brain and the liver. We propose a range of biochemical, cellular, and immunological processes to be explored in order to provide information on the early effects of NMs on some basic physiological functions and chemical defense mechanisms. Together, these contributions give an overview with important implications for the understanding of many aspects of nanotoxicity.

Synthesis and serum protein binding of novel ring-substituted harmine derivatives

Potential anticancer derivatives of the β-carboline alkaloid harmine exhibit substituent dependent serum protein binding.

Insight into the binding mechanism of imipenem to human serum albumin by spectroscopic and computational approaches

The mechanism of interaction between imipenem and HSA was investigated by various techniques like fluorescence, UV.vis absorbance, FRET, circular dichroism, urea denaturation, enzyme kinetics, ITC, and molecular docking. We found that imipenem binds to HSA at a high affinity site located in subdomain IIIA (Sudlow's site I) and a low affinity site located in subdomain IIA.IIB. Electrostatic interactions played a vital role along with hydrogen bonding and hydrophobic interactions in stabilizing the imipenem.HSA complex at subdomain IIIA, while only electrostatic and hydrophobic interactions were present at subdomain IIA.IIB. The binding and thermodynamic parameters obtained by ITC showed that the binding of imipenem to HSA was a spontaneous process (ΔGD⁰(D)= -32.31 kJ mol(-1) for high affinity site and ΔGD⁰(D) = -23.02 kJ mol(-1) for low affinity site) with binding constants in the range of 10(4)-10(5) M(-1). Spectroscopic investigation revealed only one binding site of imipenem on HSA (Ka∼10(4) M(-1)). FRET analysis showed that the binding distance between imipenem and HSA (Trp-214) was optimal (r = 4.32 nm) for quenching to occur. Decrease in esterase-like activity of HSA in the presence of imipenem showed that Arg-410 and Tyr-411 of subdomain IIIA (Sudlow's site II) were directly involved in the binding process. CD spectral analysis showed altered conformation of HSA upon imipenem binding. Moreover, the binding of imipenem to subdomain IIIA (Sudlow's site II) of HSA also affected its folding pathway as clear from urea-induced denaturation studies.