Exploring the binding mechanism of ondansetron hydrochloride to serum albumins: spectroscopic approach

In silico and in vitro studies confirm Ondansetron as a novel acetylcholinesterase and butyrylcholinesterase inhibitor

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is growing rapidly among the elderly population around the world. Studies show that a lack of acetylcholine and butyrylcholine due to the overexpression of enzymes Acetylcholinesterase (AChE) and Butyrylcholinesterase (BChE) may lead to reduced communication between neuron cells. As a result, seeking novel inhibitors targeting these enzymes might be vital for the future treatment of AD. Ondansetron is used to prevent nausea and vomiting caused by chemotherapy or radiation treatments and is herein shown to be a potent inhibitor of cholinesterase. Comparison is made between Ondansetron and FDA-approved cholinesterase inhibitors Rivastigmine and Tacrine. Molecular docking demonstrates that interactions between the studied ligand and aromatic residues in the peripheral region of the active site are important in binding. Molecular dynamics simulations and binding pose metadynamics show that Ondansetron is highly potent against both enzymes and far better than Rivastigmine. Inhibitor activities evaluated by in vitro studies confirm that the drug inhibits AChE and BChE by non-competitive and mixed inhibition, respectively, with IC₅₀ values 33 µM (AChE) and 2.5 µM (BChE). Based on the findings, we propose that Ondansetron may have therapeutic applications in inhibiting cholinesterase, especially for BChE.

Guide to development of compound files for PBPK modeling in the Simcyp population-based simulator

The Simcyp Simulator is a software platform for population physiologically‐based pharmacokinetic (PBPK) modeling and simulation. It links in vitro data to in vivo absorption, distribution, metabolism, excretion and pharmacokinetic/pharmacodynamic outcomes to explore clinical scenarios and support drug development decisions, including regulatory submissions and drug labels. This tutorial describes the different input parameters required, as well as the considerations needed when developing a PBPK model within the Simulator, for a small molecule intended for oral administration. A case study showing the development and application of a PBPK model for ondansetron is herein used to aid the understanding of different PBPK model development concepts.

Spectroscopic analysis of 2-(5-mercapto-1,3,4-oxadiazol-2-yl)-6-methylquinolin-4-ol binding to blood plasma albumin

Binding of 2-(5-mercapto-1,3,4-oxadiazol-2-yl)-6-methylquinolin-4-ol (C1), a biologically active substance, to bovine blood plasma albumin (BSA) at 293, 298, and 303 K was studied using fluorescence (steady state, synchronous, excitation/emission matrix) and FT-IR spectroscopy methods. The experimental results showed that C1 causes fluorescence quenching of BSA through both static and dynamic quenching mechanisms. The thermodynamic parameters, enthalpy and entropy change, for the static quenching were calculated to be - 35.73 kJ mol-1 and - 35.34 J mol-1 K-1, which indicated that hydrogen bonding and van der Waals interactions were the predominant intermolecular forces regulating C1-BSA interactions. Distance between donor and acceptor (2.14, 2.26, and 2.30 nm) depending on the temperature, obtained from intrinsic Förster resonance energy transfer calculations, revealed the static quenching mechanism of BSA fluorescence in 0-3.0 × 10-5 mol/dm3 concentration range of C1. The micro-environmental and conformational changes in BSA structure, established by synchronous, excitation/emission matrices and FT-IR spectra showed the changes in the BSA secondary structure.

Graphical abstract

Investigation of binding interaction behavior between antiemetic drugs and Trypsin by spectroscopy and molecular docking

Antiemetic drugs are used to control excessive vomiting and nausea and generally absorbed through gastrointestinal tract. In present study, the in-vitro binding interactions two of the antiemetic drugs (dimenhydrinate and ondansetron) between Trypsin (Tsn) secreted from pancreas to small intestine for protein digestion were investigated by fluorescence emission spectroscopy (FES), UV-VIS spectroscopy, synchronous fluorescence spectroscopy (SFS), FT-IR spectroscopy and molecular modeling methods. Also, the effect of these drugs on the catalytic activity of Tsn was determined. The fluorescence quenching experiments indicated that each drugs quenched the intrinsic fluorescence of Tsn with their increased concentrations. The results of SFS and UV-VIS spectra proved the interaction of dimenhydrinate and ondansetron with Tsn. FT-IR spectra showed that the secondary structure of enzyme was altered in the presence of the drugs. All these spectroscopy results were validated and explained by molecular docking studies. Both drugs have inhibition effect on the catalytic activity of Tsn and the IC₅₀ values were determined as 2.6 × 10^-4 M and 6.4 × 10^-4 M for dimenhydrinate and ondansetron, respectively. Docking results revealed that the hydrogen bond interaction of dimenhydrinate with active-site residue Ser195 and ondansetron with active-site residues His57 and Ser195 hydrogen bonds might be cause the inhibition of enzyme activity. The results of this study can provide valuable information in the field of pharmacokinetics and pharmacodynamics.

The Effect of Tigecycline on the Binding of Fluoroquinolones to Human Serum Albumin

The co-administration of several drugs in multidrug therapy may alter the binding of each drug to human serum albumin (HSA) and, thus, their pharmacology effect. Therefore, in this study, the interaction mechanism between HSA and two fluoroquinolones (FQs), sparfloxacin (SPF) and levofloxacin (LVF), was investigated using fluorescence and absorption methods in the absence and presence of the competing drugtigecycline (TGC). The the UV-Vis and fluorescence spectroscopy results showed that the fluorescence quenching of HSA was a result of the formation of the HSA-SPF and HSA-LVF complexes. The fluorescence quenching of HSA-TGC revealed that tigecycline can regulate the binding sites, binding mode and binding affinity of fluoroquinolones. The binding constants (KA) and binding sites (n) of the interaction systems were calculated. The results confirmed that the KA values of the HSA-FQ system decreased in the presence of TGC, indicating that TGC can affect the binding ability of FQ for HSA. This interaction may increase the free plasma concentration of unbound FQ and enhance their pharmacology effect.

Competitive binding of (-)-epigallocatechin-3-gallate and 5-fluorouracil to human serum albumin: A fluorescence and circular dichroism study

Combination therapy with more than one therapeutic agent can improve therapeutic efficiency and decrease drug resistance. In this study, the interactions of human serum albumin (HSA) with individual or combined anticancer drugs, (-)-epigallocatechin-3-gallate (EGCG) and 5-fluorouracil (FU), were investigated by fluorescence and circular dichroism (CD) spectroscopy. The results demonstrated that the interaction of EGCG or FU with HSA is a process of static quenching and EGCG formed a more stable complex. The competitive experiments of site markers suggested that both anti-carcinogens mainly bound to site I (subdomain IIA). The interaction forces which play important roles in the binding process were discussed based on enthalpy and entropy changes. Moreover, the competition binding model for a ternary system was proposed so as to precisely calculate the binding parameters. The results demonstrated that one drug decreased the binding affinity of another drug with HSA, resulting in the increasing free drug concentration at the action sites. CD studies indicated that there was an alteration in HSA secondary structure due to the binding of EGCG and FU. It can be concluded that the combination of EGCG with FU may enhance anticancer efficacy. This finding may provide a theoretical basis for clinical treatments.

Measuring the bioactivity and molecular conformation of typically globular proteins with phenothiazine-derived methylene blue in solid and in solution: A comparative study using photochemistry and computational chemistry

Methylene blue is a phenothiazine agent, that possesses a diversity of biomedical and biological therapeutic purpose, and it has also become the lead compound for the exploitation of other pharmaceuticals such as chlorpromazine and the tricyclic antidepressants. However, the U.S. Food and Drug Administration has acquired cases of detrimental effects of methylene blue toxicities such as hemolytic anemia, methemoglobinemia and phototoxicity. In this work, the molecular recognition of methylene blue by two globular proteins, hemoglobin and lysozyme was characterized by employing fluorescence, circular dichroism (CD) along with molecular modeling at the molecular scale. The recognition of methylene blue with proteins appears fluorescence quenching via static type, this phenomenon does cohere with time-resolved fluorescence lifetime decay that nonfluorescent protein-drug conjugate formation has a strength of 10(4)M(-1), and the primary noncovalent bonds, that is hydrogen bonds, π-conjugated effects and hydrophobic interactions were operated and remained adduct stable. Meantime, the results of far-UV CD and synchronous fluorescence suggest that the α-helix of hemoglobin/lysozyme decreases from 78.2%/34.7% (free) to 58.7%/23.8% (complex), this elucidation agrees well with the elaborate description of three-dimensional fluorescence showing the polypeptide chain of proteins partially destabilized upon conjugation with methylene blue. Furthermore, both extrinsic fluorescent indicator and molecular modeling clearly exhibit methylene blue is situated within the cavity constituted by α1, β2 and α2 subunits of hemoglobin, while it was located at the deep fissure on the lysozyme surface and Trp-62 and Trp-63 residues are nearby. With the aid of computational analyses and combining the wet experiments, it can evidently be found that the recognition ability of proteins for methylene blue is patterned upon the following sequence: lysozyme<hemoglobin<albumin. Basically, the distinction originates from different spatial structures of proteins and noncovalent interactions between proteins and methylene blue. In addition, biological relevance of the biorecognition of methylene blue with proteins was briefly discussed. We hope that this study could provide further standpoint so that one explore the biological activity of methylene blue and also phenothiazines.

Community mobilisation and empowerment interventions as part of HIV prevention for female sex workers in Southern India: a cost-effectiveness analysis

BACKGROUND

Most HIV prevention for female sex workers (FSWs) focuses on individual behaviour change involving peer educators, condom promotion and the provision of sexual health services. However, there is a growing recognition of the need to address broader societal, contextual and structural factors contributing to FSW risk behaviour. We assess the cost-effectiveness of adding community mobilisation (CM) and empowerment interventions (eg. community mobilisation, community involvement in programme management and services, violence reduction, and addressing legal policies and police practices), to core HIV prevention services delivered as part of Avahan in two districts (Bellary and Belgaum) of Karnataka state, Southern India.

METHODS

An ingredients approach was used to estimate economic costs in US$ 2011 from an HIV programme perspective of CM and empowerment interventions over a seven year period (2004-2011). Incremental impact, in terms of HIV infections averted, was estimated using a two-stage process. An 'exposure analysis' explored whether exposure to CM was associated with FSW's empowerment, risk behaviours and HIV/STI prevalence. Pathway analyses were then used to estimate the extent to which behaviour change may be attributable to CM and to inform a dynamic HIV transmission model.

FINDINGS

The incremental costs of CM and empowerment were US$ 307,711 in Belgaum and US$ 592,903 in Bellary over seven years (2004-2011). Over a 7-year period (2004-2011) the mean (standard deviation, sd.) number of HIV infections averted through CM and empowerment is estimated to be 1257 (308) in Belgaum and 2775 (1260) in Bellary. This translates in a mean (sd.) incremental cost per disability adjusted life year (DALY) averted of US$ 14.12 (3.68) in Belgaum and US$ 13.48 (6.80) for Bellary--well below the World Health Organisation recommended willingness to pay threshold for India. When savings from ART are taken into account, investments in CM and empowerment are cost saving.

CONCLUSIONS

Our findings suggest that CM and empowerment is, at worst, highly cost-effective and, at best, a cost-saving investment from an HIV programme perspective. CM and empowerment interventions should therefore be considered as core components of HIV prevention programmes for FSWs.

Bioavailability and activity of natural food additive triterpenoids as influenced by protein

Triterpenoids were thought to be biologically ineffective for a very long time, but aggregating proof on their widely ranging pharmacological activities paired with a dubious toxicity portrait has motivated regenerated attraction for human health and disease. In the current contribution, our central goal was to integratively dissect the biointeraction of two typical triterpenoids, ursolic acid and oleanolic acid, by the most fundamental macromolecule bovine serum albumin (BSA) by employing molecular modeling, steady state and time-resolved fluorescence, and circular dichroism spectra at the molecular scale. Based on molecular modeling, subdomain IIA, which matches Sudlow's site I, was allocated to retain high affinity for triterpenoids, but the affinity of ursolic acid with subdomain IIA is somewhat inferior compared to that of oleanolic acid, probably because the affinity differentiation arises from the different positions of the methyl group on the E-ring in the two triterpenoids. This sustains the site-specific ligands, and hydrophobic 8-anilino-1-naphthalenesulfonic acid probe results in arranging the triterpenoids at the warfarin-azapropazone site. The data of steady state and time-resolved fluorescence indicated that the recognition of triterpenoids by BSA produced quenching by a static type, in other words, the ground state BSA-triterpenoid complex formation with the affinities of 1.507/1.734, 1.042/1.186, and 0.8395/0.9863 × 10(4) M(-1) at 298, 304, and 310 K for ursolic acid/oleanolic acid, respectively. Thermodynamic analyses show that the basic forces acting between BSA and triterpenoids are hydrogen bonds, van der Waals forces, and hydrophobic interactions; this occurrence provoked the alterations of the BSA spatial structure with a noticeable decline of α-helix evoking perturbation of the protein, as stemmed from circular dichroism, synchronous fluorescence, and three-dimensional fluorescence measurements. We anticipate that the complexation of plant triterpenoids with protein delineated here may be exploited as a biologically relevant model for evaluating the physiologically applicable noncovalent complexes in in vivo examination of triterpenoid properties such as accumulation, bioavailability, and distribution.

Investigation the interaction of Daphnin with human serum albumin using optical spectroscopy and molecular modeling methods

The interaction between Daphnin with human serum albumin has been studied for the first time by spectroscopic methods including fluorescence quenching technology, circular dichroism (CD) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy under simulative physiological conditions. The results of fluorescence titration revealed that Daphnin can quench the intrinsic fluorescence of HSA by static quenching and there is a single class of binding site on HSA. In addition, the studies of CD spectroscopy and FT-IR spectroscopy showed that the protein secondary structure changed with increases of α-helices at the drug to protein molar ratio of 2. Furthermore, the thermodynamic functions ΔH(0) and ΔS(0) for the reaction were calculated to be 11.626 kJ mol(-1) and 118.843 J mol(-1)K(-1) according to Van't Hoff equation. The thermodynamic parameters (ΔH(0) and ΔS(0)) and the molecular modeling study indicated that hydrophobic force played an important role to stabilize the Daphnin-HSA complex, and Daphnin could bind within the subdomain IIA of the HSA.