Solubility, spectroscopic properties and photostability of Rhein/cyclodextrin inclusion complex

Reducing the water quenching processes using heavy water in capillary electrophoresis with fluorescence detection

Water, ubiquitous in analytical methods, is renowned for its fluorescence quenching properties, influencing techniques like fluorescence spectrophotometry or techniques with fluorescence detection. This study explores the impact of water (H₂O) substitution for heavy water (D₂O) on the fluorescence behavior of anthraquinones and anthracyclines. Anthraquinones and anthracyclines play crucial roles in pharmacy, serving as essential components in various therapeutic formulations, particularly in cancer treatment and other pharmacological interventions. Capillary electrophoresis (CE) with heavy water as the background electrolyte (BGE) solvent offers superior sensitivity to the separation and detection of these analytes. Experimental results demonstrate the improved detection limits and separation efficiency of selected anthraquinones rhein (RH), aloe-emodin (AE), and anthracyclines doxorubicin (DOX), epirubicin (EPI) and daunorubicine (DAU) in heavy water-based buffers, highlighting the potential of heavy water in advancing analytical chemistry.

The shape-dependent inhibitory effect of rhein/silver nanocomposites on porcine reproductive and respiratory syndrome virus

Traditional Chinese medicines (TCMs)/nanopreparations as viral antagonists exhibited a structure-function correlation, i.e., the differences in surface area/volume ratio caused by the variations in shape and size could result in different biochemical properties and biological activities, suggesting an important impact of morphology and structure on the antiviral activity of TCM-based nanoparticles. However, few studies paid attention to this aspect. Here, the effect of TCM-based nanoparticles with different morphologies on their antiviral activity was explored by synthesizing rhein/silver nanocomposites (Rhe@AgNPs) with spherical (S-Rhe/Ag) and linear (L-Rhe/Ag) morphologies, using rhein (an active TCM ingredient) as a reducing agent and taking its self-assembly advantage. Using porcine reproductive and respiratory syndrome virus (PRRSV) as a model virus, the inhibitory effects of S-Rhe/Ag and L-Rhe/Ag on PRRSV were compared. Results showed that the product morphology could be regulated by varying pH values, and both S- and L-Rhe/Ag exhibited good dispersion and stability, but with a smaller size for L-Rhe/Ag. Antiviral experiments revealed that Rhe@AgNPs could effectively inhibit PRRSV infection, but the antiviral effect was morphology-dependent. Compared with L-Rhe/Ag, S-Rhe/Ag could more effectively inactivate PRRSV in vitro and antagonize its adsorption, invasion, replication, and release stages. Mechanistic studies indicated that Rhe@AgNPs could reduce the production of reactive oxygen species (ROS) induced by PRRSV infection, and S-Rhe/Ag also had stronger ROS inhibitory effect. This work confirmed the inhibitory effect of Rhe@AgNPs with different morphologies on PRRSV and provided useful information for treating PRRSV infection with metal nanoparticles synthesized from TCM ingredients.

Therapeutically important bioactive compounds of the genus Polygonum L. and their possible interventions in clinical medicine

OBJECTIVES

Increasing literature data have suggested that the genus Polygonum L. possesses pharmacologically important plant secondary metabolites. These bioactive compounds are implicated as effective agents in preclinical and clinical practice due to their pharmacological effects such as anti-inflammatory, anticancer, antidiabetic, antiaging, neuroprotective or immunomodulatory properties among many others. However, elaborate pharmacological and clinical data concerning the bioavailability, tissue distribution pattern, dosage and pharmacokinetic profiles of these compounds are still scanty.

KEY FINDINGS

The major bioactive compounds implicated in the therapeutic effects of Polygonum genus include phenolic and flavonoid compounds, anthraquinones and stilbenes, such as quercetin, resveratrol, polydatin and others, and could serve as potential drug leads or as adjuvant agents. Data from in-silico network pharmacology and computational molecular docking studies are also highly helpful in identifying the possible drug target of pathogens or host cell machinery.

SUMMARY

We provide an up-to-date overview of the data from pharmacodynamic, pharmacokinetic profiles and preclinical (in-vitro and in-vivo) investigations and the available clinical data on some of the therapeutically important compounds of genus Polygonum L. and their medical interventions, including combating the outbreak of the COVID-19 pandemic.

Chondroitin sulfate-functionalized lipid nanoreservoirs: a novel cartilage-targeting approach for intra-articular delivery of cassic acid for osteoarthritis treatment

Novel intra-articular nanoreservoirs were implemented employing different cartilage targeting approaches to improve cartilage bioavailability of a chondroprotective drug, cassic acid (CA), for effective amelioration of cartilage deterioration off-targeting CA gastrointestinal disorders. Herein, we compared active cartilage-targeting approach via chondroitin sulfate (CHS) functionalization versus passive targeting using positively charged nanoparticles to target negatively charged cartilage matrix. Firstly, CA integrated nanoreservoirs (CA-NRs) were fabricated based on ionic conjugation between CA and cationic hydrophobic surface modifier octadecylamine (ODA) and were further functionalized with CHS to develop CHS-CA-NRs. Confocal laser microscope was used to visualize the accumulation of nanoparticles into the cartilage tissue. Both targeting approaches promoted CA local cartilage availability and prolonged its residence time. Compared to passive targeted CA-NRs, active targeted CHS-CA-NRs showed higher fluorescence signals in proximity to and inside chondrocytes which lasted for up to 21 days. In MIA-osteoarthritic rats, CHS-CA-NRs showed superior antiosteoarthritic activity, exhibiting highest cartilage repair compared to CA-NRs. Additionally, CHS-CA-NRs significantly inhibited OA inflammatory cytokine, degradation enzyme and oxidative stress and improved cartilage matrix biosynthesis. Conclusively, CHS-CA-NRs improved OA repair showing a superior efficacy for articular cartilage targeting with CHS which could be a potential advance for OA therapy.

Cationic nanocarrier of rhein based on hydrophobic ion pairing approach as intra-articular targeted regenerative therapy for osteoarthritis

Cartilage deterioration is the hallmark of osteoarthritis (OA). Rapid clearance of intra-articularly injected drugs and inherent cartilage barrier properties represent enormous challenges facing the effective local OA therapy. Rhein (RH), a dihydroxy-anthraquinone acid molecule, possess a potential chondroprotective effect. However, RH suffers from poor oral bioavailability besides its gastrointestinal side effects. Herein, for the first time, we exploited cationic carriers to target anionic cartilage matrix to create a RH-reservoir within the cartilage matrix, improving RH therapeutic efficacy with reduced side effects. Firstly, we improved RH lipophilic characteristics employing hydrophobic ion pairing (HIP) to be efficiently loaded within lipid nanoparticles with slow-release properties. RH-HIP integrated solid lipid nanoparticles (RH-SLNs) rapidly penetrated through cartilage tissue and lasted for 3 weeks into healthy and arthritic rat joints. Furthermore, RH-SLNs significantly inhibited inflammatory response, oxidative stress and cartilage deterioration in MIA-arthritic rats. In conclusion, intra-articular cationic RH-SLNs represented a meaningful step towards OA therapy.

Novel rhein integrate transphytosomes as non-invasive local therapy for osteoarthritis to ameliorate cartilage deterioration in MIA-arthritic rats

Rhein (RH), a natural chondroprotective agent, suffers from poor systemic availability (20-25%) after oral administration concomitant to side effects on the gastrointestinal tract and liver. We present a new approach for non-invasive local targeted delivery of rhein to ameliorate cartilage deterioration employing cartilage-homing phospholipids nanocarriers. This is the first work to elaborate RH loaded transphytosome (RH-T-PHY) as novel nanovesicular systems for transdermal drug delivery based on an advantageous hybrid between phytosomes and transfersomes or bilosomes. Here, we developed transphytosomes through incorporating various edge activators (EAs) such as Tween 80, Span 80 and sodium deoxycholate into the lipid bilayer of RH phytosomes to affix the flexibility. RH-T-PHY with high flexibility and entrapment efficacy showed the highest significant skin permeation compared to conventional phytosomes. Additionally, RH-T-PHY have a magnificent potential in maintaining high chondroprotective activity as demonstrated by enhanced repair, regeneration of chondrocytes and GAG formation in MIA-induced osteoarthritis (OA) rat model. Besides, histological examination of vital organs revealed the formulation safety. Confocal laser microscopy images revealed the highest drug availability in the articular cartilage of RH-T-PHY treated group. Conclusively, novel RH-T-PHY can serve as a promising alternative means for delivery of chondroprotective drugs for effective non-invasive local therapy of OA.

Enhanced Loading Efficiency and Mucoadhesion Properties of Gellan Gum Thin Films by Complexation with Hydroxypropyl-β-Cyclodextrin

Polymeric oral thin films (OTFs) were prepared by the casting method, combining gellan gum (GG), a water-soluble polysaccharide, and glycerol (Gly) as a plasticizing agent. GG-Gly films were investigated as potential systems for buccal drug delivery using fluconazole (Class I of the Biopharmaceutical Classification System) as a model drug. At a low concentration of Gly drug precipitation occurred while, for higher concentrations of Gly, a significant deterioration of mucoadhesive and mechanical properties was observed. One possible way to overcome all these problems could be the addition of hydroxypropyl-β-cyclodextrin (HP-β-CD) to the GG-Gly formulation as a drug-precipitation inhibitor. In this work the effect of cyclodextrin addition on the mechanical, mucoadhesive, swelling and release properties of GG-Gly films was investigated. In-vitro drug release studies were carried out using the paddle type dissolution apparatus (USP II) and the millifluidic flow-through device (MFTD). A moving-boundary model for swelling dynamics and release in USP II is proposed to estimate the effective diffusivity of the solvent, HP-β-CD, fluconazole and complex fluconazole/HP-β-CD in the swelling film. Experimental results, supported by theoretical modeling, confirmed that gellan gum-low glycerol thin films including HP-β-CD represent a suitable formulation for fluconazole drug delivery. A sustained release was observed when GG-Gly film is loaded with a preformed complex fluconazole/HP-β-CD.

Novel rhein-phospholipid complex targeting skin diseases: development, in vitro, ex vivo, and in vivo studies

Rhein (RH), an anthraquinone derivative, has proven to be a promising molecule for treating several skin disorders thanks to its pleiotropic pharmacological activities like antimicrobial, antifungal, antioxidant, and anticancer. However, RH's low water and oil solubility and poor skin permeability halted its topical delivery. This is the first work to investigate the expediency of tailoring a rhein-phospholipid complex (RH-PLC) to improve RH challenging physicochemical and skin permeability properties. The phospholipid complex was prepared by employing different methods and different RH/PL molar ratios. RH-PLC was successfully developed at a stoichiometric ratio of 1:1 using a novel pH-dependent method where at a certain pH, it exhibits the highest complexation efficiency (95%). RH-PLC formation was confirmed using FTIR, DSC, and XRPD analysis. RH-PLC showed a significant increase in water and n-octanol solubility. RH-PLC was self-assembled upon dispersion into water forming nano-sized particles (196.6 ± 1.6 nm) with high negatively charged surface (- 29.7 ± 2.45 mV). RH-PLC exhibited a significant 3.3- and 2.46-fold increase in ex vivo and in vivo skin permeability when compared with RH suspension, respectively. Confocal microscopy study confirmed the ability of RH-PLC to penetrate deeply into rat skin. Besides, skin irritation test on healthy rats indicated compatibility and safety of RH-PLC. Conclusively, phospholipid complex might be a suitable approach to improve permeability of RH and other promising abandoned poor-permeable drugs. The proposed RH-PLC is expected to be a major progressive step toward the development of a topical RH formulation. Graphical abstract.

Therapeutic Emergence of Rhein as a Potential Anticancer Drug: A Review of Its Molecular Targets and Anticancer Properties

According to the World Health Organization (WHO), cancer is the second-highest cause of mortality in the world, and it kills nearly 9.6 million people annually. Besides the fatality of the disease, poor prognosis, cost of conventional therapies, and associated side-effects add more burden to patients, post-diagnosis. Therefore, the search for alternatives for the treatment of cancer that are safe, multi-targeted, effective, and cost-effective has compelled us to go back to ancient systems of medicine. Natural herbs and plant formulations are laden with a variety of phytochemicals. One such compound is rhein, which is an anthraquinone derived from the roots of Rheum spp. and Polygonum multiflorum. In ethnomedicine, these plants are used for the treatment of inflammation, osteoarthritis, diabetes, and bacterial and helminthic infections. Increasing evidence suggests that this compound can suppress breast cancer, cervical cancer, colon cancer, lung cancer, ovarian cancer, etc. in both in vitro and in vivo settings. Recent studies have reported that this compound modulates different signaling cascades in cancer cells and can prevent angiogenesis and progression of different types of cancers. The present review highlights the cancer-preventing and therapeutic properties of rhein based on the available literature, which will help to extend further research to establish the chemoprotective and therapeutic roles of rhein compared to other conventional drugs. Future pharmacokinetic and toxicological studies could support this compound as an effective anticancer agent.

Cyclodextrin complexation studies as the first step for repurposing of chlorpromazine

The antipsychotic drug chlorpromazine (CPZ) has potential for the treatment of acute myeloid leukemia, if central nervous system side-effects resulting from its passage through the blood-brain barrier can be prevented. A robust drug delivery system for repurposed CPZ would be drug-in-cyclodextrin-in-liposome that would redirect the drug away from the brain while avoiding premature release in the circulation. As a first step, CPZ complexation with cyclodextrin (CD) has been studied. The stoichiometry, binding constant, enthalpy, and entropy of complex formation between CPZ and a panel of CDs was investigated by isothermal titration calorimetry (ITC). All the tested CDs were able to include CPZ, in the form of 1:1, 1:2 or a mixture of 1:1 and 1:2 complexes. In particular, a substituted γ-CD, sugammadex (the octasodium salt of octakis(6-deoxy-6-S-(2-carboxyethyl)-6-thio)cyclomaltooctaose), formed exclusively 1:2 complexes with an extremely high association constant of 6.37 × 10⁹ M^-2. Complexes were further characterized by heat capacity changes, one- and two-dimensional (ROESY) nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics simulations. Finally, protection of CPZ against photodegradation by CDs was assessed. This was accelerated rather than reduced by complexation with CD. Altogether these results provide a molecular basis for the use of CD in delayed release formulations for CPZ.

A novel β-cyclodextrin-rhein conjugate for improving the water solubility and bioavailability of rhein

Rhein is a potential antitumor agent, but the poor water-solubility restricts its clinical applicability. β-cyclodextrin-drug conjugates provide a possibility to improve the water-solubility of rhein and thereby enhance its bioavailability. A novel β-cyclodextrin-rhein conjugate (β-CD-RH) was synthesized by covalently link β-cyclodextrin with rhein through a 1,8-diamino-3,6-dioxaoctane linker. The structure of β-CD-RH was characterized by ¹H NMR, FT-IR, Maldi-tof MS etc. The inclusion style of β-CD-RH in water was detected by 2D NMR. The 2D ROESY spectrum provided details of the rhein moiety encapsulated in the β-CD cavity. The water-solubility of β-CD-RH is up to 3.24 μmol/mL β-CD-RH exhibited higher cytotoxicity than rhein and rhein/β-CD mixture against Hela cells. Our work provides a new way for the preparation of novel β-CD-drug conjugate.

Effects of cyclodextrins on the chemical stability of drugs

Cyclodextrins (CDs) are enabling pharmaceutical excipients that can enhance both solubility and stability of wide variety of drugs in aqueous solutions through formation of drug/CD inclusion complexes where apolar moieties of the drug molecules are located inside the CD cavity. In properly designed pharmaceutical formulations CDs will improve physiochemical properties of lipophilic drugs without affecting their intrinsic ability to permeate biological membranes. Here the effect of CD complexes on the chemical stability of drugs is reviewed. Numerous studies shown that in aqueous solutions CD complexation can hamper hydrolysis, oxidation, photodegradation, isomerization and enzyme catalyzed degradation of dissolved drugs. However, some drugs, such as β-lactam antibiotics, can under certain conditions undergo CD catalyzed degradation in aqueous solutions. Also, some drugs that are stabilized by CDs in aqueous solutions are destabilized by the same CDs in solid dosage forms. Thus, the effects of CDs on drug stability have to be tested and verified in the final drug formulation and under the recommended storage conditions.

Preparation, characterization, and in vivo study of rhein solid lipid nanoparticles for oral delivery

In this study, rhein-SLNs were successfully produced by hot homogenization followed by ultrasonication. Precirol ATO5 in which rhein exhibited higher partition coefficient was selected for preparation of SLNs. In the dynamic light scattering, the rhein-SLNs showed a smaller size with a mean value of 120.8 ± 7.9 nm and with zeta potential of -16.9 ± 2.3 mV. SLNs exhibited a good stability during the period of 2 months. The SLNs indicated faster drug release with a burst release within 2 hr and followed by a sustained release with a biphasic drug-release pattern. Comparing with the same concentration (free drug), the cellular cytotoxicity of rhein-loaded SLNs increased significantly at the same incubation condition. In vivo, the AUC_0-t of rhein in the form of SLNs was significantly increased and was 2.06-fold that of suspensions group. The results showed an increased oral absorption and improved the oral bioavailability of rhein by the formulation of SLNs.

Host-guest inclusion system of rhein with polyamine-modified β-cyclodextrins: characterization and cytotoxicity

We report the preparation of inclusion complexes between rhein and four polyamine-modified β-cyclodextrins, namely amino-β-cyclodextrins (NH₂-βCD), ethylenediamine-β-cyclodextrins (EN-βCD), diethylenetriamine-β-cyclodextrins (DETA-βCD) and triethylenetetramine-β-cyclodextrins (TETA-βCD) using suspension method. The solution and solid state forms of the inclusion complexes of rhein with polyamine-β-cyclodextrins were characterized by multiple techniques. Additionally, saturated solution and MTT methods were implemented to assess the water solubilization and in vitro cytotoxicity of the inclusion complexes, respectively. The results suggested that rhein was encapsulated within the CD cavity to form a 1:1 host-guest inclusion complex. Notably, a significant enhancement of the water solubility and in vitro cytotoxicity of rhein was found in the form of inclusion complex with polyamine-β-cyclodextrin.

Solubility and solution thermodynamics of rhein in eight pure solvents from (288.15 to 313.15) K

Solubility of rhein in water, dichloroethane, glycol, ethanol, methanol, ethyl acetate, propanol, and butanol was measured. Two equations including the modified Apelblat equation, and λh equation can correlate the solubilities of rhein.

Spectroscopic characterization of both aqueous and solid-state diacerhein/hydroxypropyl-β-cyclodextrin inclusion complexes

Diacerhein, a poorly water soluble antirheumatic prodrug, was spectroscopically characterized to form inclusion complexes with hydroxypropyl-β-cyclodextrin (HPβCD) in both aqueous solution and in solid phase. Complexation with the hydrophilic carriers was used to improve the solubility and dissolution rate of the compound. The kinetics of the prodrug degradation to the active rhein in aqueous buffer solution were also investigated as a function of HPβCD concentration. The solid complexes prepared by different methods such as physical mixture, kneading, co-evaporation method and freeze dried method in 1:1M ratio, were characterized by DSC and FTIR. The dissolution profiles of solid complexes were determined and compared with diacerhein alone and their physical mixture, in the simulated intestinal fluid at 37°C. The accurate molecular spectroscopic characterization of diacerhein in the presence of different amounts of aqueous cyclodextrins was essential to determine the correct binding constants for the diacerhein/HPβCD system. The binding constants were also validated by UV spectrometry and HPLC procedure in order to compare the values from the different methods. Higuchi-Connors phase solubility method has proved not suitable when either the free or/and the complexed prodrug degrade in aqueous solution.

Advanced technologies for oral controlled release: cyclodextrins for oral controlled release

Cyclodextrins (CDs) are used in oral pharmaceutical formulations, by means of inclusion complexes formation, with the following advantages for the drugs: (1) solubility, dissolution rate, stability, and bioavailability enhancement; (2) to modify the drug release site and/or time profile; and (3) to reduce or prevent gastrointestinal side effects and unpleasant smell or taste, to prevent drug-drug or drug-additive interactions, or even to convert oil and liquid drugs into microcrystalline or amorphous powders. A more recent trend focuses on the use of CDs as nanocarriers, a strategy that aims to design versatile delivery systems that can encapsulate drugs with better physicochemical properties for oral delivery. Thus, the aim of this work was to review the applications of the CDs and their hydrophilic derivatives on the solubility enhancement of poorly water-soluble drugs in order to increase their dissolution rate and get immediate release, as well as their ability to control (to prolong or to delay) the release of drugs from solid dosage forms, either as complexes with the hydrophilic (e.g., as osmotic pumps) and/or hydrophobic CDs. New controlled delivery systems based on nanotechnology carriers (nanoparticles and conjugates) have also been reviewed.

Structure-based in silico model profiles the binding constant of poorly soluble drugs with β-cyclodextrin

Cyclodextrin inclusion complexation technique is the key method to enhance the solubility and absorption of poorly soluble drugs in the early development stage, and thus it is essential to predict the binding constant between drug molecules and cyclodextrin. Structure-based in silico model was constructed for a data set of 86 poorly soluble drugs and used to profile the binding constant of drug-β-cyclodextrin inclusion complex. The stepwise regression was employed to select the optimum subset of the independent variables. The in silico model was built by the multiple linear regression method and validated by the residual analysis, the normal Probability-Probability plot and Williams plot. For the entire data set, the R(2) and Q(2) of the model were 0.78 and 0.67, respectively. The results indicated that the fitted model is robust, stable and satisfies all the prerequisites of the regression models. The chemical space position and important contributors were compared between selected drug molecules and organic compounds available in the literature. It was suggested that the binding behavior of drug molecules with β-CD should differ from that of the common organic compounds. Focusing on structurally diverse drugs, the in silico model can be used as an efficient tool to rapidly screen the drug-β-cyclodextrin inclusion complex stability and to rationally design the new drug delivery system of poorly soluble drugs.