Investigation of the Interactions of Silibinin with 2-Hydroxypropyl-β-cyclodextrin through Biophysical Techniques and Computational Methods

Highly robust quantum mechanics and umbrella sampling studies on inclusion complexes of curcumin and β-cyclodextrin

The poor aqueous solubility of curcumin (CUR) obstructs its wide utilization in nutraceuticals, cosmetics, and pharmaceutical companies. This study is dedicated to investigate the stability of CUR inside the hydrophobic pocket of β-cyclodextrin (β-CD), hydroxypropyl-β-CD (HP-β-CD), and 2,6-Di-O-methyl-β-CD (DM-β-CD). Initially, molecular mechanics (MM) calculations and subsequently quantum mechanical (QM) calculations were performed on inclusion complexes to strengthen the MM results. We performed microsecond timescale MD simulations to observe the structural dynamics of CUR inside the cavity of CDs. We elucidated the most stable binding orientations of CUR inside the cavity of CDs based on binding free energy obtained from the Molecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA) and umbrella sampling simulations. Furthermore, the two-layered ONIOM (B3LYP/6-311+G(2d,p):PM7) method with CPCM implicit water model was used to derive the complete energetics and thermodynamics of inclusion complexes at 1:1 stoichiometry. Each inclusion reaction was exothermic and spontaneous. The chemical reactivity and kinetic stability of inclusion complexes were described by HOMO-LUMO molecular orbital energies. In conclusion, our studies revealed that HP-β-CD had the highest binding affinity for CUR with the most negative complexation energy (-6520.69 kJ/mol) and Gibb's free energy change (-6448.20 kJ/mol). The atomic-level investigation of noncovalent interactions between CUR and the hydroxypropyl groups in HP-β-CD/CUR complex may be helpful to drive new derivatives of HP-β-CD with better host capacity. The computational strategy adopted here might serve as a benchmark for increasing the solubility of numerous clinically significant molecules.

Estimation of the Controlled Release of Antioxidants from β-Cyclodextrin/Chamomile (Matricaria chamomilla L.) or Milk Thistle (Silybum marianum L.), Asteraceae, Hydrophilic Extract Complexes through the Fast and Cheap Spectrophotometric Technique

This is the first study on the modeling of the controlled release of the estimated antioxidants (flavonoids or flavonolignans) from β-cyclodextrin (β-CD)/hydrophilic vegetable extract complexes and the modeling of transdermal pharmaceutical formulations based on these complexes using an overall estimation by the spectrophotometric method. The Korsmeyer-Peppas model was chosen for evaluating the release mechanisms. β-CD/chamomile (Matricaria chamomilla L., Asteraceae) ethanolic extract and β-CD/milk thistle (Silybum marianum L., Asteraceae) ethanolic extract complexes were obtained by the co-crystallization method with good recovering yields of 55-76%, slightly lower than for β-CD/silibinin or silymarin complexes (~87%). According to differential scanning calorimetry (DSC) and Karl Fischer water titration (KFT), the thermal stability of complexes is similar to β-CD hydrate while the hydration water content is lower, revealing the formation of molecular inclusion complexes. In the Korsmeyer-Peppas model, β-CD/M. chamomilla flower extract complexes reveal Case II transport mechanisms, while the corresponding complexes with leaf extracts indicate non-Fickian diffusion for the controlled release of antioxidants in ethanol 60 and 96%. The same non-Fickian diffusion was revealed by β-CD/S. marianum extract and β-CD/silibinin complexes. On the contrary, almost all model transdermal pharmaceutical formulations based on β-CD/M. chamomilla extract complexes and all those based on β-CD/S. marianum extract complexes revealed non-Fickian diffusion for the antioxidant release. These results indicate that H-bonding is mainly involved in the diffusion of antioxidants into a β-CD based matrix, while the controlled release of antioxidants in model formulations is mainly due to hydrophobic interactions. Results obtained in this study can be further used for studying the particular antioxidants (namely rutin or silibinin, quantified, for example, by liquid chromatographic techniques) for their transdermal transport and biological effects in innovatively designed pharmaceutical formulations that can be obtained using "green" methods and materials.

Novel Topical Anandamide Formulation for Alleviating Peripheral Neuropathic Pain

Peripheral neuropathy (PN) is a condition of peripheral nerve damage leading to severe pain. The first line therapies are associated with adverse psychotropic effects (PSE) and second line therapies are not efficient enough to relieve pain. There is an unmet drug need for relieving pain effectively without PSE in PN. Anandamide, an endocannabinoid activates cannabinoid receptors to relieve the pain due to peripheral neuropathy (PN). Anandamide has a very short biological half-life as they are extensively metabolized by fatty acid amide hydrolase enzyme (FAAH). Regional delivery of safe FAAH inhibitor (FI) with anandamide would be beneficial for PN without psychotropic effects. The objective of the study is to identify a safe FAAH inhibitor and deliver the anandamide in combination with the FAAH inhibitor topically for the management of PN. The FAAH inhibition potential of silymarin constituents was evaluated by molecular docking and in vitro studies. The topical gel formulation was developed to deliver anandamide and FI. The formulation was assessed in chemotherapeutic agent-induced peripheral neuropathy rat models to relieve mechanical-allodynia and thermal-hyperalgesia. The molecular docking studies demonstrated that the Prime MM-GBSA free energy of silymarin constituents were in the order of silybin > isosilybin > silychristin > taxifolin > silydianin. In in vitro studies, silybin 20 µM inhibited >61.8% of FAAH activity and increased the half-life of anandamide. The developed formulation increased permeation of anandamide and silybin across the porcine skin. Furthermore, on the application of anandamide and anandamide-silybin gel to rat paws, there was a significant increase in the pain threshold for allodynic and hyperalgesic stimulus up to 1 h and 4 h, respectively. The topical anandamide with silybin delivery approach could serve to alleviate peripheral neuropathy efficiently and thus could minimize unwanted CNS side effects of synthetic or natural cannabinoids in patients.

Bio-Actives from Natural Products with Potential Cardioprotective Properties: Isolation, Identification, and Pharmacological Actions of Apigenin, Quercetin, and Silibinin

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. As a result, pharmaceutical and non-pharmaceutical interventions modifying risk factors for CVDs are a top priority of scientific research. Non-pharmaceutical therapeutical approaches, including herbal supplements, have gained growing interest from researchers as part of the therapeutic strategies for primary or secondary prevention of CVDs. Several experimental studies have supported the potential effects of apigenin, quercetin, and silibinin as beneficial supplements in cohorts at risk of CVDs. Accordingly, this comprehensive review focused critically on the cardioprotective effects/mechanisms of the abovementioned three bio-active compounds from natural products. For this purpose, we have included in vitro, preclinical, and clinical studies associated with atherosclerosis and a wide variety of cardiovascular risk factors (hypertension, diabetes, dyslipidemia, obesity, cardiac injury, and metabolic syndrome). In addition, we attempted to summarize and categorize the laboratory methods for their isolation and identification from plant extracts. This review unveiled many uncertainties which are still unexplored, such as the extrapolation of experimental results to clinical practice, mainly due to the small clinical studies, heterogeneous doses, divergent constituents, and the absence of pharmacodynamic/pharmacokinetic analyses.

A Review of Applications of Solid-State Nuclear Magnetic Resonance (ssNMR) for the Analysis of Cyclodextrin-Including Systems

Cyclodextrins, cyclic oligosaccharides composed of five or more α-D-glucopyranoside units linked by α-1,4 glycosidic bonds, are widely used both in their native forms as well as the components of more sophisticated materials. Over the last 30 years, solid-state nuclear magnetic resonance (ssNMR) has been used to characterize cyclodextrins (CDs) and CD-including systems, such as host-guest complexes or even more sophisticated macromolecules. In this review, the examples of such studies have been gathered and discussed. Due to the variety of possible ssNMR experiments, the most common approaches have been presented to provide the overview of the strategies employed to characterize those useful materials.

Development of silymarin topical formulation: In vitro and ex vivo dermal kinetics of silymarin

Silymarin constituents are extensively investigated in the treatment of skin disorders. The main constituents of silymarin include taxifolin (TX), silychristin (ST), silydianin (SDN), silybin A (SA), silybin B (SB), isosilybin A (ISA) and isosilybin B (ISB). The objective of the present study was to determine in-vitro dermal kinetics of individual silymarin constituents in human skin models and to develop a silymarin topical formulation. In-vitro studies indicate human skin binding of silymarin was in the range of 2.09 to 12.3% and half-life of silymarin constituents was > 15.5 h in epidermal and dermal cells. Topical silymarin cream was prepared using sulfobutylether-β-cyclodextrins as solubilizer and propylene glycol as permeation enhancer. The cream was subjected to ex-vivo human skin permeation studies. In ex-vivo studies, cumulative amount of TX, ST, SDN, SA, SB, ISA and ISB permeated across human cadaver skin at 24 h was 921 ± 13.5, 1992 ± 67.6, 345 ± 39.2, 1089 ± 45.0, 1770 ± 100, 1469 ± 81.5 and 1285 ± 33.1 ng/cm², respectively. The amount TX, ST, SDN, SA, SB, ISA and ISB retained after 24 h was 60.7 ± 8.2, 376 ± 45.5, 72.3 ± 6.9, 66.4 ± 8.0, 208 ± 31.3, 154 ± 12.4 and 102 ± 6.3 ng/mg of human cadaver skin, respectively. The study results demonstrate silymarin topical formulation could deliver significant amount of silymarin constituents into skin. The developed silymarin formulation could be beneficial for treatment or management of a broad spectrum of dermatological disorders.

Molecular simulations of fluoxetine in hydrated lipid bilayers, as well as in aqueous solutions containing β-cyclodextrin

Fluoxetine, which is a well-known antidepressant drug, is studied in hydrated cholesterol-free and cholesterol-containing lipid bilayers through unbiased and biased atomistic molecular dynamics simulations. The latter are conducted for the calculation of the potential of mean force (PMF) of fluoxetine along an axis perpendicular to the two leaflets of the bilayer. The PMF indicates that the drug prefers to reside inside the lipid phase and allows us to calculate important thermodynamic properties, such as the Gibbs energy difference of partitioning from the water to the lipid phase and the Gibbs energy barrier for hopping events between the two leaflets of the bilayer. The results from the biased simulations are in accord with the mass density profiles calculated from the unbiased simulations. Moreover, we estimate the effect of fluoxetine mole fraction on the order parameters of the lipid alkyl chains and on the area per lipid. It is also found that fluoxetine forms a hydrogen bond network with lipids and water molecules penetrating into the lipid phase. In addition, fluoxoetine is studied in detail in aqueous solutions containing β-cyclodextrin. It is observed from unbiased molecular dynamics simulations that the two aforementioned molecules form a noncovalent complex spontaneously and the calculated binding free energy is in agreement with the literature.

Comparative Interaction Studies of Quercetin with 2-Hydroxyl-propyl-β-cyclodextrin and 2,6-Methylated-β-cyclodextrin

Quercetin (QUE) is a well-known natural product that can exert beneficial properties on human health. However, due to its low solubility its bioavailability is limited. In the present study, we examine whether its formulation with two cyclodextrins (CDs) may enhance its pharmacological profile. Comparative interaction studies of quercetin with 2-hydroxyl-propyl-β-cyclodextrin (2HP-β-CD) and 2,6-methylated cyclodextrin (2,6Me-β-CD) were performed using NMR spectroscopy, DFT calculations, and in silico molecular dynamics (MD) simulations. Using T1 relaxation experiments and 2D DOSY it was illustrated that both cyclodextrin vehicles can host quercetin. Quantum mechanical calculations showed the formation of hydrogen bonds between QUE with 2HP-β-CD and 2,6Μe-β-CD. Six hydrogen bonds are formed ranging between 2 to 2.8 Å with 2HP-β-CD and four hydrogen bonds within 2.8 Å with 2,6Μe-β-CD. Calculations of absolute binding free energies show that quercetin binds favorably to both 2,6Me-β-CD and 2HP-β-CD. MM/GBSA results show equally favorable binding of quercetin in the two CDs. Fluorescence spectroscopy shows moderate binding of quercetin in 2HP-β-CD (520 M-1) and 2,6Me-β-CD (770 M-1). Thus, we propose that both formulations (2HP-β-CD:quercetin, 2,6Me-β-CD:quercetin) could be further explored and exploited as small molecule carriers in biological studies.

Prebiotic-like cyclodextrin assisted silybin on NAFLD through restoring liver and gut homeostasis

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease with no currently approved treatment. The natural compound silybin (SLN) has versatile hepatoprotective efficacy with negligible adverse effects; however, poor absorption limits its clinical applications. Gut microbiota has been proposed to play a crucial role in the pathophysiology of NAFLD and targeted for disease control. Cyclodextrins, the cyclic oligosaccharides, were documented to have various health benefits with potential prebiotic properties. This study aimed to develop a silybin-2-hydroxypropyl-β-cyclodextrin inclusion (SHβCD) to improve the therapeutic efficacy of SLN and elucidate the mechanisms of improvement. The results showed that SLN formed a 1:1 stoichiometric inclusion complex with HP-β-CD. The solubility of SLN was increased by generating SHβCD, resulting in improved drug permeability and bioavailability. In high-fat diet (HFD)-fed hamsters, SHβCD modulated gut health by restoring the gut microbiota and intestinal integrity. SHβCD showed superior anti-lipid accumulation, antioxidant, and anti-inflammatory effects compared with SLN alone. Transcriptome analysis in the liver tissue implied that the improved inflammation and/or energy homeostasis was the potential mechanism. Therefore, SHβCD may be a promising alternative for the treatment of NAFLD, attributing to the dual functions of HβCD on drug absorption and gut microbial homeostasis.

A Comprehensive Review of the Cardiovascular Protective Properties of Silibinin/Silymarin: A New Kid on the Block

Silibinin/silymarin has been used in herbal medicine for thousands of years and it is well-known for its hepato-protective properties. The present comprehensive literature review aimed to critically summarize the pharmacological properties of silymarin extract and its main ingredient silibinin in relation to classical cardiovascular risk factors (e.g., diabetes mellitus, etc.). We also assessed their potential protective and/or therapeutic application in cardiovascular diseases (CVDs), based on experimental and clinical studies. Pre-clinical studies including in vitro tests or animal models have predominantly implicated the following effects of silymarin and its constituents: (1) antioxidant, (2) hypolipidemic, (3) hypoglycemic, (4) anti-hypertensive and (5) cardioprotective. On the other hand, a direct amelioration of atherosclerosis and endothelial dysfunction after silymarin administration seems weak based on scarce data. In clinical trials, the most important findings are improved (1) glycemic and (2) lipid profiles in patients with type 2 diabetes mellitus and/or hyperlipidemia, while (3) the anti-hypertensive effects of silibinin/silymarin seem very modest. Finally, the changes in clinical endpoints are not robust enough to draw a firm conclusion. There are significant limitations in clinical trial design, including the great variety in doses and cohorts, the underlying conditions, the small sample sizes, the short duration and the absence of pharmacokinetic/pharmacodynamic tests prior to study commitment. More data from well-designed and high-quality pre-clinical and clinical studies are required to firmly establish the clinical efficacy of silibinin/silymarin and its possible therapeutic application in cardiovascular diseases.

Losartan Interactions with 2-Hydroxypropyl-β-CD

Losartan potassium salt (LSR) is a well-known antihypertensive drug with proven beneficial effects on human health. Its formulation with the non-toxic 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) could improve its pharmacological profile. Thus, its molecular interactions are studied using a combination of Differential Scanning Calorimetry (DSC), Nuclear Magnetic Resonance (NMR) and Molecular Dynamics (MD). First, its complexation is shown through Differential Scanning Calorimetry as lyophilization provided distinct thermal properties in comparison to the mixture. The complexation is further proved by utilizing the chemical shift changes in the complexation and T1 values. Furthermore, the reversible favorable complexation was shown by MD calculations. Such physical chemical properties provide evidence that this formulation must be further explored through biological experiments.

Pro-inflammatory cytokines/chemokines, TNF-α, IL-6 and MCP-1, as biomarkers for the nephro- and pneumoprotective effect of silibinin after hepatic ischemia/reperfusion: confirmation by immunihistochemistry and qRT-PCR

The present study investigated the potential nephro- and pneumoprotective effect of silibinin (Si) after hepatic ischemia-reperfusion (I/R) injury, by measuring pro-inflammatory factors. Sixty-three rats were randomly assigned into three groups, as follows: (a) the sham group (n=7 rats), subjected to opening and closing the abdomen; (b) the control group (n = 28 rats), subjected to 45-min hepatic ischemia followed by reperfusion; and (c) the silibinin group (n=28), subjected to 45-min hepatic ischemia followed by intravenous administration of lyophilized SLB-HP-β-CD before reperfusion. Control and silibinin groups were further subdivided into time-point groups, according to the duration of reperfusion. TNF-α, IL-6 and MCP-1 expressions were determined immunihistochemically and by qrT-PCR at each time-point. Kidney TNF-α expression was significantly lower at 180 and 240 min, while lung TNF-α expression was significantly lower at 240 min. Comparison between the control and Si group at the same time-points, showed very strong evidence of difference at 240 min, with the levels of IL-6 shifting towards lower values in the Si group. Finally, we found a high MCP-1 expression after 120 min. We conclude that hepatic I/R injury remotely increases proinflammatory mediators in the kidney and lung, whereas silibinin shows a time-dependent nephro- and pneumoprotective effect.

Effect of silibinin on the expression of MMP2, MMP3, MMP9 and TIMP2 in kidney and lung after hepatic ischemia/reperfusion injury in an experimental rat model

PURPOSE

The protective effect of silibinin on kidney and lung parenchyma during hepatic ischemia/reperfusion injury (IRI) is explored.

METHODS

Sixty-three Wistar rats were separated into three groups: sham; control (45 min IRI); and silibinin (200 μL silibinin administration after 45 min of ischemia and before reperfusion). Immunohistochemistry and real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) were used to evaluate the expression levels of MMP2, MMP3, MMP9, and TIMP2 on kidney and lung.

RESULTS

Comparing sham vs. control groups, confirmed that hepatic IRI increased both renal and lung MMP2, MMP3, MMP9 and TIMP2 expressions starting at 180 min (p<0.001). Comparison of the control vs. silibinin groups showed a statistically significant decrease in the expression levels of MMP2, MMP3, and MMP9 and increase of TIMP2 in kidney and lung parenchyma. The starting point of this decrease was at 120 min after reperfusion, both for kidney and lung parameters, and it was statistically significant at 240 min (p<0.001) for kidney, while silibinin showed a peak of lung protection at 180 min after hepatic reperfusion (p<0.001).

CONCLUSIONS

Hepatic IRI causes distant kidney and lung damage, while a statistically significant protective action, both on kidney and lung parenchyma, is conveyed by the intravenous administration of silibinin.

Application of Molecular Dynamics Simulations in the Analysis of Cyclodextrin Complexes

Cyclodextrins (CDs) are highly respected for their ability to form inclusion complexes via host-guest noncovalent interactions and, thus, ensofance other molecular properties. Various molecular modeling methods have found their applications in the analysis of those complexes. However, as showed in this review, molecular dynamics (MD) simulations could provide the information unobtainable by any other means. It is therefore not surprising that published works on MD simulations used in this field have rapidly increased since the early 2010s. This review provides an overview of the successful applications of MD simulations in the studies on CD complexes. Information that is crucial for MD simulations, such as application of force fields, the length of the simulation, or solvent treatment method, are thoroughly discussed. Therefore, this work can serve as a guide to properly set up such calculations and analyze their results.

Enantioseparation of mandelic acid and substituted derivatives by high-performance liquid chromatography with hydroxypropyl-β-cyclodextrin as chiral mobile additive and evaluation of inclusion complexes by molecular dynamics

The enantioseparation and resolution mechanism of mandelic acid (MA), 4-methoxymandelic acid (MMA), and 4-propoxymandelic acid (PMA) were investigated by reversed-phase high-performance liquid chromatography (HPLC) with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) as a chiral mobile-phase additive and molecular dynamics simulation. The suitable chromatographic conditions for the enantioseparation of MA, MMA, and PMA were obtained. Under the selected chromatographic conditions, these enantiomers could achieve baseline separation. The results of thermodynamic parameter analysis revealed that the main driven forces for the enantioseparation of MA, MMA, and PMA could be van der Waals forces and hydrogen-bonding interactions and the chromatographic retention of these chiral compounds was an enthalpy-driven process. The results of the molecular simulation revealed that their chiral resolution mechanism on HP-β-CD was responsible for the formation of inclusion complexes of enantiomers with HP-β-CD with different conformations and binding energies. And the binding energy of HP-β-CD with (S)-isomer was larger than that with (R)-isomer, which is consistent with the experimental results of the first elution of (S)-isomer. Additionally, it is also confirmed that the interaction energies included the van der Waals energy (∆E_vdw ), electrostatic energy (∆E_elec ), polar solvation energy, and SASA energy (∆E_sasa ), and the separation factor (α) was closely connected with the disparity in the binding energies of optical isomers and HP-β-CD complexes. Meanwhile, from molecular dynamics simulation, it can be found that the ∆(∆E_binding ), (∆(∆E_binding ) = ∆E_binding,R  - ∆E_binding,S ) value was in order of MA-HP-β-CD complex > MMA-HP-β-CD complex > PMA-HP-β-CD complex, which was consistent with the order of Δ(ΔG) values obtained from van't Hoff plot. This indicated that the molecular dynamics simulation has predictive function for chiral resolution.

The hepatoprotective effect of silibinin after hepatic ischemia/reperfusion in a rat model is confirmed by immunohistochemistry and qRT-PCR

OBJECTIVES

We investigated the positive effect of silibinin after IV administration as silibinin-hydroxypropyl-β-cyclodextrin lyophilized product, by measuring gene expression and liver tissue protein levels of tumor necrosis factor-α, interleukin-6, monocyte chemoattractant protein-1, matrix metalloproteinases matrix metalloproteinases and tissue inhibitor of matrix metalloproteinases-2.

METHODS

63 Wistar rats of age 13.24±4.40 weeks underwent ischemia/reperfusion (I/R) injury of the liver. The animals were randomized into three groups: Sham (S; n = 7); Control (C; n-28); silibinin (Si; n-28). The C and Si groups underwent 45 min ischemia. Si received silibinin-hydroxypropyl-β-cyclodextrin intravenously immediately before reperfusion at a dose of 5 mg/kg. Both groups were further divided into 4 subgroups, based on euthanasia time (i.e., 60, 120, 180 and 240 min).

KEY FINDINGS

qRT-PCR results confirmed the statistically significant reduction of the expression of the pro-inflammatory factors at 240 min after I/R injury (tumor necrosis factor-α: P < 0.05; MCR1: P < 0.05) and matrix metalloproteinases (matrix metalloproteinases 2: P < 0.05; matrix metalloproteinases 3: P < 0.05) and the increase of tissue inhibitor of matrix metalloproteinases-2 in liver tissue in the Si group. Moreover, results of immunohistochemistry levels confirmed that at 240 min pro-inflammatory factors (tumor necrosis factor-α: P < 0.05; MCR1: P < 0.05) and matrix metalloproteinases ( matrix metalloproteinases 2: P < 0.05; matrix metalloproteinases 3: P < 0.05) had a statistically significantly lower expression in the Si group while tissue inhibitor of matrix metalloproteinases-2 had a higher expression.

CONCLUSIONS

Silibinin may have a beneficial effect on the protection of the liver.

Advancing the Therapeutic Efficacy of Bioactive Molecules by Delivery Vehicle Platforms

Drugs have to overcome numerous barriers to reach their desired therapeutic targets. In several cases, drugs, especially the highly lipophilic molecules, suffer from low solubility and bioavailability and therefore their desired targeting is hampered. In addition, undesired metabolic products might be produced or off-targets could be recognized. Along these lines, nanopharmacology has provided new technological platforms, to overcome these boundaries. Specifically, numerous vehicle platforms such as cyclodextrins and calixarenes have been widely utilized to host lipophilic drugs such as antagonists of the angiotensin II AT1 receptor (AT₁R), as well as quercetin and silibinin. The encapsulation of these drugs in supramolecules or other systems refines their solubility and metabolic stability, increases their selectivity and therefore decreases their effective dose and improves their therapeutic index. In this mini review we report on the formulations of silibinin and AT₁R antagonist candesartan in a 2-HP-β-cyclodextrin host molecule, which displayed enhanced cytotoxicity and increased silibinin's and candesartan's stability, respectively. Moreover, we describe the encapsulation of quercetin in gold nanoparticles bearing a calixarene supramolecular host. Also, the encapsulation of temozolomide in a calixarene nanocapsule has been described. Finally, we report on the activity enhancement that has been achieved upon using these formulations as well as the analytical and computational methods we used to characterize these formulations and explore the molecular interactions between the host and quest molecules.

Extraction and Application of Natural Rutin From Sophora japonica to Prepare the Novel Fluorescent Sensor for Detection of Copper Ions

Rutin (R), a representative flavonoid found in various biomasses, can be used to prepare different fluorescent sensors for environmental, biological and medical fields. In this work, the natural R in Sophora japonica was extracted and purified to prepare fluorescent-responding sensor systems intended to recognize copper ions with both strong selectivity as well as appropriate sensitivity. Results showed that neat R had no obvious fluorescent emission peak in PBS buffer solution. However, when R and (2-hydroxypropyl)-β-cyclodextrin (CD) were introduced within buffer solution, fluorescent emission intensity was significantly increased due to the resultant R-CD inclusion complex. In addition, the formed R-CD inclusion complex was shown to behave as the aforementioned fluorescent sensor for copper ions through a mechanism of quenched fluorescent emission intensity when R-CD became bound with copper ions. The binding constant value for R-CD with copper ions was 1.33 × 10⁶, allowing for quantification of copper ions between the concentration range of 1.0 × 10^–7–4.2 × 10^–6mol⋅L^–1. Furthermore, the minimum detection limit was found to be 3.5 × 10^–8mol⋅L^–1. This work showed the prepared R-CD inclusion complex was both highly selective and strongly sensitive toward copper ions, indicating that this system could be applied into various fields where copper ions are of concern.

Molecular Dynamics Protocols for the Study of Cyclodextrin Drug Delivery Systems

Hypertension treatment is a current therapeutic priority as there is a constantly increasing part of the population that suffers from this risk factor, which may lead to cardiovascular and encephalic episodes and eventually to death. A number of marketed medicines consist of active ingredients that may be relatively potent; however, there is plenty of room to enhance their pharmacological profile and therapeutic index by improving specific physicochemical properties. In this work, we focus on a class of blood pressure regulators, called sartans, and we present the computational scheme for the pharmacological improvement of irbesartan (IRB) as a representative example. IRB has been shown to exert increased pharmacological action compared with other sartans, but it appears to be highly lipophilic and violates Lipinski rule (MLogP >4.15). To circumvent this drawback, proper hydrophilic molecules, such as cyclodextrins, can be used as drug carriers. This chapter describes the combinatory use of computational methods, namely molecular docking, quantum mechanics, molecular dynamics, and free energy calculations, to study the interactions and the energetic contributions that govern the IRB:cyclodextrin association. We provide a detailed computational protocol, which aims to assist the improvement of the pharmacological properties of sartans. This protocol can also be applied to any other drug molecule with diminished hydrophilic character.

Unveiling the Thermodynamic Aspects of Drug-Cyclodextrin Interactions Through Isothermal Titration Calorimetry

Due to their low toxicity and high aqueous solubility, cyclodextrins have emerged as a distinctive class of supramolecules with wide application in the pharmaceutical and food industry. Their ability to improve the water solubility, stability and pharmacokinetic profile of small molecules has established them as a rich toolkit for drug formulation. In order to improve the physicochemical characteristics and the pharmacokinetic profile of a drug through cyclodextrin inclusion, the proper cyclodextrin type has to be selected among the existing great variety consisting of both natural and synthetic variants. The selection of the most proper cyclodextrin variant comes after drug-cyclodextrin screening studies targeting the characterization of the complex formation and evaluation of the affinity and interaction forces participating in the complexation. Numerous analytical, spectroscopic, separation and electrochemical techniques have been applied to elucidate the interaction profile in a cyclodextrin-drug complex. Herein, we describe the application of Isothermal Titration Calorimetry (ITC) on cyclodextrin-drug complexes that enables the charting of the binding affinity and the thermodynamic profile of the inclusion complexes. We focus on the experimental design and present technical tips of the ITC application. To better illustrate the technique's rationale, the interaction between 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and the antihypertensive drug losartan is investigated.

Application of Neutralization and Freeze-Drying Technique for the Preparation of the Beneficial in Drug Delivery 2-Hydroxypropyl-β-Cyclodextrin Complexes with Bioactive Molecules

Bioavailability of active substances is of great importance for the formulation of a drug product, as it actually reflects drug absorption and achievement of the optimum pharmacological effect. A great number of chemical compounds with excellent pharmacological properties possess low solubility and permeability values, ending in low bioavailability in the human body after administration (especially after per os administration). CDs are oligosaccharides that possess biological properties similar to their linear counterparts, but some of their physicochemical properties differ. They are enhancing bioavailability and solving problems of absorption for poorly soluble lipophilic drugs by forming water-soluble inclusion complexes. For this reason, they are widely used in drug delivery systems (Carrier et al. J Control Release 123:78-99, 2007; Kurkov and Loftsson, Int J Pharm 453:167-80, 2013). The main purpose of this chapter is to show a protocol for the preparation of drug:CD_complex delivery systems.

Silibinin-hydroxypropyl-β-cyclodextrin (SLB-HP-β-CD) complex prevents apoptosis in liver and kidney after hepatic ischemia-reperfusion injury

BACKGROUND

We investigated the protective effect of silibinin on rat liver and kidney after hepatic inschemia/reperfusion (I/R) injury.

METHODS AND MATERIALS

Sixty three male Wistar-type rats (median age 13 weeks; average weight 314 g) were subjected to I/R injury of the liver. They were randomly divided into three groups: Sham (n = 7), Control (C, n = 28) and Silibinin (Si, n = 28). The last group received intravenously silibinin. The C and Si groups were each subdivided in four subgroups according to euthanasia times (i.e., 60, 120, 180, 240 min). We assessed expression of caspase-3 and TUNEL assay, and biochemical and histological parameters.

RESULTS

At 240 min, expression of caspase-3 and TUNEL assay were statistically significantly lower in the Si compared to the C group for both liver and kidney. SGOT and SGPT were also statistically significantly lower in the Si than in the C group at all time points. Histological parameters of the liver were also improved in the Si group.

CONCLUSION

Silibinin was found to exhibit a protective effect on liver and kidney after hepatic I/R injury. The present results are encouraging for further studies and future clinical application.

Antihypertensive activity and molecular interactions of irbesartan in complex with 2-hydroxypropyl-β-cyclodextrin

Irbesartan (IRB) exerts beneficial effects either alone or in combination with other drugs on numerous diseases, such as cancer, diabetes, and hypertension. However, due to its high lipophilicity, IRB does not possess the optimum pharmacological efficiency. To circumvent this problem, a drug delivery system with 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) was explored. The 1:1 complex between IRB and 2-HP-β-CD was identified through ESI QTF HRMS. Dissolution studies showed a higher dissolution rate of the lyophilized IRB-2-HP-β-CD complex than the tablet containing IRB at pH = 1.2. DSC results revealed the differences of the thermal properties between the complex and various mixtures consisting of the two components, namely IRB and 2-HP-β-CD. Interestingly, depending on the way the mixture preparation was conducted, different association between the two components was observed. Molecular dynamics (MD) simulations predicted the favorable formation of the above complex and identified the dominant interactions between IRB and 2-HP-β-CD. In vitro pharmacological results verified that the inclusion complex not only preserves the binding affinity of IRB for AT1R receptor, but also it slightly increases it. As the complex formulation lacks the problems of the tablet, our approach is a promising new way to improve the efficiency of IRB.

Charting the structural and thermodynamic determinants in phenolic acid natural product - cyclodextrin encapsulations

Cyclodextrins are pliable platforms that have served to optimize the pharmaceutic profile of numerous compounds and to enhance the stability of natural food additives. Caffeic and rosmarinic acid are natural products with proven health benefits, though their full therapeutic potential has not been exploited. To enhance their pharmaceutic profile, we developed cyclodextrin-based formulates and unveiled their thermodynamic and structural principles. The complexes' stoichiometry was determined by ESI-MS. Solid-state and liquid NMR spectroscopy revealed the interactions and the topographical location of the caffeic and rosmarinic acid inside the cyclodextrin cavity. The theoretically analyzed HP-β-CD's degree of substitution (DS) of caffeic and rosmarinic acids can explain the intensities obtained by 2D NOESY experiments. The thermodynamics and the affinity of the complexes were evaluated through isothermal titration calorimetry. In addition, the rosmarinic and caffeic acids as, also, their complexes showed considerable antimicrobial activity against common food spoilage and pathogenic bacteria. The generated data could provide the basis to understand the structural and thermodynamic determinants implicated in natural products - CD recognition and to develop platforms for the optimization of their pharmaceutical and stability profiles in order to be utilized as safe and stable natural antimicrobial food additives.Communicated by Ramaswamy H. Sarma.

Glycoprotein non-metastatic melanoma B expression after hepatic ischemia reperfusion and the effect of silibinin

Background

Glycoprotein non-metastatic melanoma B (GPNMB) is a transmembrane glycoprotein with various roles in inflammation regulation, tissue remodeling and oncogenesis. Clinical situations implicating alterations in its expression include ischemic injury, cirrhosis and fatty liver disease amongst other. We examine its expression in hepatic and renal tissue following hepatic ischemia-reperfusion (I/R) in a rat model, with and without intravenous silibinin administration, as a silibinin-hydroxypropyl-β-cyclodextrin lyophilized complex (SLB-HP-β-CD).

Methods

Sixty-three Wistar rats were divided into 3 groups: sham group (virtual intervention; 7 animals), control (C) group (45 min of ischemia, followed by reperfusion and euthanasia at 60, 120, 180 and 240 min; 28 animals equally divided), and silibinin (Si) group (45 min of ischemia, intravenous administration of SLB-HP-β-CD, reperfusion and euthanasia at the same time points; 28 animals equally divided). GPNMB expression was examined in liver and kidney tissue.

Results

GPNMB expression was significantly increased following hepatic I/R in the control group, in kidney tissue, in a time dependent manner. In the silibinin group, GPNMB expression significantly decreased with time compared to the control group in both liver and kidney tissue (P<0.05).

Conclusions

Hepatic I/R causes increase of GPNMB levels both in liver and kidney tissues, which may reflect tissue injury. Silibinin seems to act protectively on both liver and kidney, and can be potentially used as a therapeutic approach against hepatic I/R injury.

Nanotherapeutic silibinin: An insight of phytomedicine in healthcare reformation

Most of the herbal origin drugs possess water insoluble active constituents which lower the bioavailability and increase systemic clearance after administration of repeated or higher dose of drug. Silymarin is extracted from the seeds and fruits of milk thistle plant Silybum marianum which consists of main biologically active component as silibinin. However, the clinical applications of silibinin show some limitations due to low aqueous solubility, poor penetration into the epithelial cells of intestine, high metabolism and rapid systemic elimination. But nanotechnology-based drug delivery system explores great potential for phytochemicals to enhance the aqueous solubility and bioavailability of BCS class II and IV drugs, improve stability and modify the pharmacological activity. This review focuses on the therapeutic properties of silibinin and discusses the benefits, challenges and applications of silibinin nanoformulations. Such nanotherapeutic system as a regular medicine will be an attractive approach to reduce the adverse events and toxicities of current therapies.

Formulation Strategies for Enhancing the Bioavailability of Silymarin: The State of the Art

Silymarin, a mixture of flavonolignan and flavonoid polyphenolic compounds extractable from milk thistle (Silybum marianum) seeds, has anti-oxidant, anti-inflammatory, anti-cancer and anti-viral activities potentially useful in the treatment of several liver disorders, such as chronic liver diseases, cirrhosis and hepatocellular carcinoma. Equally promising are the effects of silymarin in protecting the brain from the inflammatory and oxidative stress effects by which metabolic syndrome contributes to neurodegenerative diseases. However, although clinical trials have proved that silymarin is safe at high doses (>1500 mg/day) in humans, it suffers limiting factors such as low solubility in water (<50 μg/mL), low bioavailability and poor intestinal absorption. To improve its bioavailability and provide a prolonged silymarin release at the site of absorption, the use of nanotechnological strategies appears to be a promising method to potentiate the therapeutic action and promote sustained release of the active herbal extract. The purpose of this study is to review the different nanostructured systems available in literature as delivery strategies to improve the absorption and bioavailability of silymarin.

Drug Displacement Strategy for Treatment of Acute Liver Injury with Cyclodextrin-Liposome Nanoassembly

Biofunctional supramolecular assemblies that combine macrocyclic receptors and amphiphiles are potent drug delivery systems, but optimization and implementation challenges remain. We herein describe a cooperative drug displacement strategy exemplified by the use of cyclodextrin-liposome supramolecular nanoassemblies as a therapy for acute liver injury. The hepatoprotective drug silibinin was solubilized in phosphotyramine-modified β-cyclodextrin, and subsequent encapsulation of the silibinin-cyclodextrin complex in phosphatidylcholine liposomes gave uniformly sized and stable nanoassemblies that accumulated preferentially in the liver of mice. Enzymatic cleavage of the phosphate ester of the β-cyclodextrin resulted in rapid release of the encapsulated silibinin. Significantly, silibinin could be readily displaced by cytotoxic bile acids, thus leading to the removal of excess bile acids from the bodies of mice and the recovery of liver function. Our results demonstrate that cyclodextrin-based nanoassemblies with a dual role of solubilizing a drug and removing toxins constitute a promising therapy for hepatic injury.

Host-Guest Interactions between Candesartan and Its Prodrug Candesartan Cilexetil in Complex with 2-Hydroxypropyl-β-cyclodextrin: On the Biological Potency for Angiotensin II Antagonism

Renin-angiotensin aldosterone system inhibitors are for a long time extensively used for the treatment of cardiovascular and renal diseases. AT1 receptor blockers (ARBs or sartans) act as antihypertensive drugs by blocking the octapeptide hormone Angiotensin II to stimulate AT1 receptors. The antihypertensive drug candesartan (CAN) is the active metabolite of candesartan cilexetil (Atacand, CC). Complexes of candesartan and candesartan cilexetil with 2-hydroxylpropyl-β-cyclodextrin (2-HP-β-CD) were characterized using high-resolution electrospray ionization mass spectrometry and solid state ¹³C cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS NMR) spectroscopy. The ¹³C CP/MAS results showed broad peaks especially in the aromatic region, thus confirming the strong interactions between cyclodextrin and drugs. This experimental evidence was in accordance with molecular dynamics simulations and quantum mechanical calculations. The synthesized and characterized complexes were evaluated biologically in vitro. It was shown that as a result of CAN's complexation, CAN exerts higher antagonistic activity than CC. Therefore, a formulation of CC with 2-HP-β-CD is not indicated, while the formulation with CAN is promising and needs further investigation. This intriguing result is justified by the binding free energy calculations, which predicted efficient CC binding to 2-HP-β-CD, and thus, the molecule's availability for release and action on the target is diminished. In contrast, CAN binding was not favored, and this may allow easy release for the drug to exert its bioactivity.

Investigating molecular interactions of high-loaded glipizide-HPMCAS microparticles by integrated experimental and modeling techniques

Molecular interactions between drug and polymeric carriers are believed to be the key for high drug loading and better physical stability of micro-particles. However, molecular interactions between drug and polymer are still difficult to investigate using only experimental tools. In this study, high-loaded glipizide (GLP)/hydroxypropyl methylcellulose acetate succinate (HPMCAS) (1/1 w/w) micro-particles were prepared using an in situ pH-dependent solubility method. Molecular interactions within the micro-particles were investigated by integrated experimental and modeling techniques. The dissolution rate of GLP/HPMCAS micro-particles was significantly better than those of solid dispersions and physical mixtures. Scanning electron microscopy images showed that the polymer inhibited GLP recrystallization. Experimental (FTIR spectroscopy, differential scanning calorimetry, powder X-ray diffraction and nuclear magnetic resonance spectroscopy) and molecular dynamics simulation revealed that hydrogen-bonding was the key to the properties of the micro-particles. Our research developed high drug-loading GLP/HPMCAS micro-particles and investigated the interactions between drug and polymer at the molecular level. This integrated approach could be practical methodology for future formulation design.

Sensitive fluorescent assay for copper(ii) determination in aqueous solution using quercetin-cyclodextrin inclusion

Environmentally friendly probe materials for detecting copper ions were studied in this research. Fluorescent emission of quercetin (Q) was observed in the buffer solution (pH = 7.40), and (2-hydroxypropyl)-β-cyclodextrin (CD) could enhance the fluorescence intensity of Q. The UV/Vis spectrum showed that the Q-CD system was formed. After adding copper ions into the Q-CD system, the fluorescent emission intensity of Q-CD system generated quenching, and other metal ions could not bring change, which meant the Q-CD system showed good selectivity to copper ions. The fluorescence titration spectra showed that the concentration of copper ions was inversely proportional to fluorescence intensity, and gave a good linear change in fluorescence emission intensity in response to the concentration of copper ions ranging from 5.0 × 10-8 to 8.3 × 10-6 mol L-1. The calibration curve of the relationship between the intensity and copper ions concentration was y = -9.24x + 844.51 (R 2 = 0.997). The detection limit of copper ions was measured to be 2.3 × 10-8 mol L-1. The probable mechanism was studied by UV/Vis spectrum and Job's plot method. The results indicated that Q-CD-Cu(ii) complex was formed and intramolecular charge transfer (ICT) took place. At last, the probe was successfully applied for determination of copper ions in water bodies, vegetables and fruits with good recovery. The study showed that Q-CD system could detect copper ions as a fluorescent probe with high selectivity, sensitivity and larger linearity range.

Silibinin Improves TNF-α and M30 Expression and Histological Parameters in Rat Kidneys After Hepatic Ischemia/Reperfusion

BACKGROUND

Remote kidney damage is a sequel of hepatic ischemia-reperfusion (I/R) injury. Silibinin is the main ingredient of the milk thistle plant seed extract with known antioxidant and hepatoprotective activity. Our study investigates the nephroprotective potential of intravenously administered silibinin, as a lyophilized SLB-hydoxypropyl-beta-cyclodextrin product, in hepatic I/R injury.

MATERIAL AND METHODS

63 Wistar rats were divided into three groups: Sham (virtual intervention); Control (45 min ischemia and reperfusion); and Silibinin (200 μL intravenous silibinin administration after 45 min of ischemia). Kidney tissues were collected to determine TNF-α, M30 and histopathological changes at predetermined time intervals.

RESULTS

Comparing Sham vs. Control groups, proved that hepatic I/R injury increased renal TNF-α and M30 expression. Deterioration was observed in hyperemia/filtration of renal parenchyma and tubules, cortical filtration, tubular necrosis and edema (tissue swelling index). Intravenous silibinin administration and comparison of the Control vs. Silibinin groups showed a statistically significant decrease in TNF-α levels at 240 min following I/R (p < 0.0001), and in M30 at 180 min (p = 0.03) and 240 min (p < 0.0001). Renal parameters have significantly decreased in: hyperemia/filtration of renal parenchyma at 120 min (p = 0.003), 180 min (p = 0.0001) and 240 min (p = 0.0002); hyperemia/filtration of renal tubules at 120 min (p = 0.02), 180 min (p = 0.0001) and 240 min (p = 0.0005); cortical filtration (240 min - p = 0.005); tubular necrosis (240 min - p = 0.021); and edema (240 min - p = 0.001).

CONCLUSION

Our study confirms that hepatic I/R injury causes remote renal damage while the intravenous administration of silibinin leads to statistically significant nephroprotective action.

Exploring the interactions of irbesartan and irbesartan-2-hydroxypropyl-β-cyclodextrin complex with model membranes

The interactions of irbesartan (IRB) and irbesartan-2-hydroxypropyl-β-cyclodextrin (HP-β-CD) complex with dipalmitoyl phosphatidylcholine (DPPC) bilayers have been explored utilizing an array of biophysical techniques ranging from differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), ESI mass spectrometry (ESI-MS) and solid state nuclear magnetic resonance (ssNMR). Molecular dynamics (MD) calculations have been also conducted to complement the experimental results. Irbesartan was found to be embedded in the lipid membrane core and to affect the phase transition properties of the DPPC bilayers. SAXS studies revealed that irbesartan alone does not display perfect solvation since some coexisting irbesartan crystallites are present. In its complexed form IRB gets fully solvated in the membranes showing that encapsulation of IRB in HP-β-CD may have beneficial effects in the ADME properties of this drug. MD experiments revealed the topological and orientational integration of irbesartan into the phospholipid bilayer being placed at about 1nm from the membrane centre.

Compilation of Data and Modelling of Nanoparticle Interactions and Toxicity in the NanoPUZZLES Project

The particular properties of nanomaterials have led to their rapidly increasing use in diverse fields of application. However, safety assessment is not keeping pace and there are still gaps in the understanding of their hazards. Computational models predicting nanotoxicity, such as (quantitative) structure-activity relationships ((Q)SARs), can contribute to safety evaluation, in line with general efforts to apply alternative methods in chemical risk assessment. Their development is highly dependent on the availability of reliable and high quality experimental data, both regarding the compounds' properties as well as the measured toxic effects. In particular, "nano-QSARs" should take the nano-specific characteristics into account. The information compiled needs to be well organized, quality controlled and standardized. Integrating the data in an overarching, structured data collection aims to (a) organize the data in a way to support modelling, (b) make (meta)data necessary for modelling available, and (c) add value by making a comparison between data from different sources possible.Based on the available data, specific descriptors can be derived to parameterize the nanomaterial-specific structure and physico-chemical properties appropriately. Furthermore, the interactions between nanoparticles and biological systems as well as small molecules, which can lead to modifications of the structure of the active nanoparticles, need to be described and taken into account in the development of models to predict the biological activity and toxicity of nanoparticles. The EU NanoPUZZLES project was part of a global cooperative effort to advance data availability and modelling approaches supporting the characterization and evaluation of nanomaterials.

Deconvoluting the Dual Antiplatelet Activity of a Plant Extract

A thorough evaluation of the antiplatelet activity profile of hexane olive leaf extract in human platelets indicated a potent activity accomplished through a two axis inhibition of platelet activation triggered both by ADP and thrombin. To delineate the extract components responsible for this dual activity, an NMR based method was established to determine and quantify the triterpenoid content leading to the characterization of uvaol, erythrodiol, and oleanolic acid. The antiplatelet profile of the total extract and of the 3 determined triterpenoids was evaluated against in vitro platelet aggregation induced by several platelet agonists as also on PAC-1 binding and P-selectin membrane expression both in healthy volunteers and in platelets from patients with an acute coronary syndrome receiving dual antiplatelet therapy with aspirin and ticagrelor. The extract was identified to inhibit ADP-induced platelet activation due to its erythrodiol content and TRAP-induced platelet activation due to the activity of uvaol and oleanolic acid.

Chemical and pharmaceutical evaluation of the relationship between triazole linkers and pore size on cyclodextrin–calixarene nanosponges used as carriers for natural drugs

Nanosponges based nanocarriers with three different cavities were used to encapsulate and release bioactive compounds.

Serum and tissue pharmacokinetics of silibinin after per os and i.v. administration to mice as a HP-β-CD lyophilized product

Silibinin, the main active component of Silybum marianum is a hepatoprotective and antioxidant agent with antitumor effect, exhibiting very low aqueous solubility and oral bioavailability limiting its use in therapeutics. We characterized serum and tissue pharmacokinetics of SLB, calculated its absolute bioavailability and developed an open loop physiologically based pharmacokinetic (PBPK) model, after oral (per os, p.o) and intravenous (i.v.) administration in mice as water-soluble silibinin-hydroxypropyl-beta-cyclodextrin (SLB-HP-β-CD) lyophilized product. 60 C57Bl/6J mice were divided into groups of 5, each group representing one sampling time point. SLB-HP-β-CD lyophilized product was administered orally (50mg/kg) and i.v. (20mg/kg) after reconstitution with water for injection. Blood and tissue samples were collected at selected time points after animal sacrificed, properly treated and analyzed with HPLC-PDA for non-metabolized and total SLB. NONMEM pharmacokinetic analysis revealed a 2-compartment PK model to describe serum SLB pharmacokinetics, with zero order absorption after oral administration and was applied as forcing function to an open loop PBPK model incorporating heart, liver, kidneys and lungs. Tissue/plasma Kp values were estimated using i.v. data and can be used to predict tissue SLB distribution after oral administration. Absolute oral bioavailability of SLB from the lyophilized SLB-HP-β-CD product was 10 times higher than after administration of pure SLB.