Stabilization of diketo tautomer of curcumin by premicellar anionic surfactants: UV-Visible, fluorescence, tensiometric and TD-DFT evidences

Curcumin loaded hydrogel with double ROS-scavenging effect regulates microglia polarization to promote poststroke rehabilitation

Cyclodextrins are used to include curcumin to form complex, which is subsequently loaded into a reactive oxygen species (ROS) responsive hydrogel (Cur gel). This gel exhibits a dual ROS scavenging effect. The gel can neutralize extracellular ROS to lead to a ROS-sensitive curcumin release. The released curcumin complex can eliminate intracellular ROS. Furthermore, the Cur gel effectively downregulates the expression of CD16 and IL-1β while upregulating CD206 and TGF-β in oxygen and glucose-deprived (OGD) BV2 cells. Additionally, it restores the expression of synaptophysin and PSD95 in OGD N2a cells. Upon injection into the stroke cavity, the Cur gel reduces CD16 expression and increases CD206 expression in the peri-infarct area of stroke mice, indicating an in vivo anti-inflammatory polarization of microglia. Colocalization studies using PSD95 and VGlut-1 stains, along with Golgi staining, reveal enhanced neuroplasticity. As a result, stroke mice treated with the Cur gel exhibit the most significant motor function recovery. Mechanistic investigations demonstrate that the released curcumin complex scavenges ROS and suppresses the activation of the ROS-NF-κB signaling pathway by inhibiting the translocation of p47-phox and p67-phox to lead to anti-inflammatory microglia polarization. Consequently, the Cur gel exhibits promising potential for promoting post-stroke rehabilitation in clinics.

Theoretical studies on the photo protective mechanism of curcuminoids

In this work, the deactivation pathways of curcuminoids after photoexcitation was studied by employing density functional theory to explore their UVA radiation screening capacity. A comprehensive computational characterization of the excited-state processes of curcumin, demethoxycurcumin, and bis-demethoxycurcumin was done. The molecules exist in diketo and enol forms which are in equilibrium and interconvertible through keto-enol tautomerism. The enolic forms of each of the studied molecules have eight geometric cis-trans isomers as a result of torsion rotation about three different carbon-carbon double bonds across the aliphatic chain. For each geometric isomer, sixteen possible rotamers are found to exist due to rotation about five different carbon-carbon single bond rotations, also across the skeleton of the aliphatic chain. Upon photoexcitation, the studied molecules follow three main pathways of radiationless decay: (a) rotamerism and interconversion between rotamers of comparable energies which are in equilibrium, (b) interconversion between the cis-trans geometrical isomers where an efficient vibrational relaxation path is formed at ∼90° during torsion rotation about carbon-carbon double bond, and (c) excited state intramolecular proton transfer in a single O-H stretching vibration through a cyclic intramolecular hydrogen bonded ring formed at the centre of the molecule giving back the original structure. The absorption and emission spectra of the molecules were also simulated where the theoretically obtained absorption and emission maxima are close to the reported experimental values.

Enhancement of the chemical stability of nanoemulsions loaded with curcumin by unsaturated mannuronate oligosaccharide

Unsaturated mannuronate oligosaccharide (MOS) is an acidic oligosaccharide prepared from alginate-derived polymannuronate by enzymatic depolymerization, followed by double bond formation between C-4 and C-5 at the nonreducing end. In this study, MOS was used as a stabilizer to fabricate O/W nanoemulsions loaded with curcumin (MOS-CUR) for the first time. The results revealed that the MOS-CUR showed small droplet sizes and narrow size distributions and was slightly more stable than normal oil-in-water (O/W) curcumin nanoemulsions (water-CUR). Additionally, MOS can improve the superoxide anion scavenging ability and iron ion reducing ability of the curcumin nanoemulsion system. Although the digestion behaviour of MOS-CUR and water-CUR was similar, the bioavailability of curcumin in MOS-CUR was significantly higher than that in water-CUR. All these results indicated that MOS could be used as a stabilizer for preparing nanoemulsions to easily encapsulate labile nutrients and to enhance the bioavailability and antioxidant capacity of these nutrients.

Exploring Steroidal Surfactants as Potential Drug Carriers for an Anticancer Drug Curcumin: An Insight into the Effect of Surfactants' Structure on the Photophysical Properties, Stability, and Activity of Curcumin

Despite having tremendous medicinal benefits, the practical applications of curcumin are limited, owing to two major challenges: poor aqueous solubility and lack of bioavailability. In this regard, biosurfactant-based micellar systems have surged recently for the development of novel and more effective formulations because of their biological relevance. This study deals with a comprehensive and comparative investigation on the effect of seven structurally different steroidal surfactants on the photophysical properties of curcumin and also evaluates these steroidal surfactants as possible drug delivery media for curcumin. The photophysical properties of curcumin exhibited a strong dependence on the structure of the steroidal surfactant; the extent of excited-state proton transfer between curcumin and the surfactants depends strongly on the type of the side chain in the surfactants, which mostly dictates the photophysics of curcumin in the presence of these structural variants. The solubility of curcumin and its stability at different pHs and temperatures and in the presence of salt are significantly enhanced in the presence of these surfactants. Furthermore, the curcumin-loaded micelles exhibited improved intracellular uptake and cytotoxicity against MCF-7 cancer cells than pristine curcumin. Among these steroidal surfactants, CHAPS, the zwitterionic derivative of cholic acid, was the most efficient one to offer better solubility and stability to curcumin under all conditions, and the death rate of MCF-7 cells by curcumin was found to be the highest in the presence of CHAPS, indicating the enhanced bioavailability of curcumin. Therefore, CHAPS-based colloids are found to be promising candidates as potential drug carriers for curcumin.

Click synthesis of novel dendronized curcumin and analogs. Strengthening of physicochemical properties toward biological applications

Curcumin and its analogs, chalcones, and C5-monocarbonyl are molecules of great therapeutic potential, but their poor stability and hydrophobicity have hampered their extensive use in clinical trials. Therefore, significant efforts have been made in materials science to improve their physicochemical properties. In this study, we propose dendronization as a synthetic strategy to strengthen some physicochemical properties such as solubility and stability of curcumin and analogs, taking advantage of the click chemistry (CuAAC) to attach second-generation polyester dendrons to the unsaturated cores. The dendronization, with the subsequent formation of aromatic triazole groups as linkers, not only modified the solubility and stability of the molecular systems but also favored the diketo tautomeric form of curcumin, as demonstrated spectroscopically. This result is significant since the diketo tautomer, which preserves the antioxidant properties of curcumin, is the most biologically active form. The hydrophobic/hydrophilic balance, achieved after dendronization, allowed the solubilization of the chromophoric molecules in buffered solutions at relevant pH values (7.4 and 6.4). Furthermore, the stability of all molecules was also upgraded since UV-vis absorption spectra did not exhibit modified profiles after 7 days at physiologic pH. From photochemical stability experiments irradiating at 415 nm, the dendritic derivatives containing triazole linkers were more susceptible to being degraded. All derivatives exhibited emission properties according to the length of each conjugate fragment. Fluorescence experiments evidenced the role of dendrons in preventing emission quenching by aggregation and exhibited differentiated emission behavior depending on the linker type (triazole or ester) between the chromophoric core and the polyester dendrons.

A Novel Curcumin-Based Drug Powder Inhalation Medicine for Chronic Obstructive Pulmonary Disease

The dry powder inhaler is a new form of drug delivery that is widely used as an alternative to traditional drug delivery methods, addressing the shortcomings of traditional drug delivery methods and obtaining better therapeutic results. This mode of delivery is also one of the most rational ways to treat pulmonary diseases such as chronic obstructive pulmonary disease (COPD). Curcumin, a natural polyphenol, has been shown to be effective in the treatment of COPD. In this study, different concentrations of curcumin ethanol solution were spray dried with mannitol as a carrier to obtain dry powder particles with different particle size distribution for the preparation of curcumin dry powder inhaler. The solubility and physicochemical properties were further characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy. The characterization results showed that the product obtained in the experiment had reasonable particle size distribution and excellent solubility properties, which were positive for the treatment of COPD or other pulmonary diseases.

Optical spectroscopy study of the interaction between curcumin and acrylic polymers

This paper presents the results of a study conducted on the interaction between curcumin, a compound with several biomedical applications in traditional and modern medicine, and the acrylic polymers poly(methyl methacrylate), poly(ethyl methacrylate), and poly(n-butyl methacrylate), through photophysical experiments in curcumin/acrylic polymers casting films. Optical absorption intensity at ~340 nm increases relatively to its maximum at ~417 nm when the amount of curcumin in the polymeric film decreases, due to a significant change in the concentration of the isomers cis- or trans-form of curcumin, regardless of the acrylic polymer. Fluorescence (FL) spectra of the films depend on the curcumin concentration in the matrix with well-resolved line shape. They show two distinct bands, one at ~525 nm, for higher curcumin concentration (5.00 mmol.L^-1), related to the aggregated curcumin species, and another at ~465 nm, for lower concentration of curcumin (0.10 mmol.L^-1), related to the effects of the solvent on the conformational structure of the curcumin molecule and the presence of the trans-form of curcumin. The parameter K_agg, related to the contribution of the aggregated curcumin, shows the influence of the polymeric lateral chain length of the matrix in the de-aggregation of the curcumin. The Huang-Rhys factor indicates that curcumin aggregated species are conformationally more stable, and that the isolate species depends on the chemical environment and the matrix/curcumin interaction, decreasing its conformational degrees of freedom. Arrhenius plots, obtained via FL experiment in function of the sample temperature, show that, for higher curcumin concentration, the value for the relaxation energy process is not well defined, due the decrease in the interaction between the matrix and the curcumin molecules. With these results, it is possible to infer that the interaction matrix/curcumin must occur via lateral chemical alkyl groups.

Formulation Development of a Food-Graded Curcumin-Loaded Medium Chain Triglycerides-Encapsulated Kappa Carrageenan (CUR-MCT-KC) Gel Bead Based Oral Delivery Formulation

In recent years, curcumin has been a major research endeavor in food and biopharmaceutical industries owing to its miscellaneous health benefits. There is an increasing amount of research ongoing in the development of an ideal curcumin delivery system to resolve its limitations and further enhance its solubility, bioavailability and bioactivity. The emergence of food-graded materials and natural polymers has elicited new research interests into enhanced pharmaceutical delivery due to their unique properties as delivery carriers. The current study is to develop a natural and food-graded drug carrier with food-derived MCT oil and a seaweed-extracted polymer called k-carrageenan for oral delivery of curcumin with improved solubility, high gastric resistance, and high encapsulation of curcumin. The application of k-carrageenan as a structuring agent that gelatinizes o/w emulsion is rarely reported and there is so far no MCT-KC system established for the delivery of hydrophobic/lipophilic molecules. This article reports the synthesis and a series of in vitro bio-physicochemical studies to examine the performance of CUR-MCT-KC as an oral delivery system. The solubility of CUR was increased significantly using MCT with a good encapsulation efficiency of 73.98 ± 1.57% and a loading capacity of 1.32 ± 0.03 mg CUR/mL MCT. CUR was successfully loaded in MCT-KC, which was confirmed using FTIR and SEM with good storage and thermal stability. Dissolution study indicated that the solubility of CUR was enhanced two-fold using heated MCT oil as compared to naked or unformulated CUR. In vitro release study revealed that encapsulated CUR was protected from premature burst under simulated gastric environment and released drastically in simulated intestinal condition. The CUR release was active at intestinal pH with the cumulative release of >90% CUR after 5 h incubation, which is the desired outcome for CUR absorption under human intestinal conditions. A similar release profile was also obtained when CUR was replaced with beta-carotene molecules. Hence, the reported findings demonstrate the potencies of MCT-KC as a promising delivery carrier for hydrophobic candidates such as CUR.

Improved oral delivery of quercetin with hyaluronic acid containing niosomes as a promising formulation

Quercetin, a substance from nature has various biological effects; while, some challenges like low solubility in water and absorption, and high first-pass metabolism hindered its clinical efficiencies. So, various strategies using novel nanocarriers have been designed to overcome these obstacles. This study aimed to fabricate the polymeric niosomes by incorporating hyaluronic acid to deliver quercetin. After preparation, quercetin entrapped niosomes were investigated in terms of size, zeta potential, quercetin entrapment, CTAB turbidimetric assay, AFM, TEM, differential scanning Calorimetry, X-Ray diffraction, DPPH antioxidant determination, and in vivo anti-inflammatory analysis. The analysis of the results exhibited that size of niosomes containing quercetin and hyaluronic acid was 231.07 ± 8.39 nm with a zeta potential of -34.00 ± 0.95 mV. Moreover, quercetin entrapment efficiency and loading were 94.67 ± 1.62% and 1.65 ± 0.37%, respectively. TEM and AFM showed that polymeric niosomes were spheres. The release data presented that the Higuchi model was the best-fitted model. DPPH antioxidant determination displayed that 80 µl of polymeric niosomes with 7.46 × 10^-8mol of quercetin had a remarkable antioxidant potency. According to the in vivo oedema evaluation, the potency of polymeric formulations was superior to the simple suspension of quercetin to control inflammation in rats by oral administration.

Ultra-High to Ultra-Low Drug-Loaded Micelles: Probing Host-Guest Interactions by Fluorescence Spectroscopy

Polymer micelles are an attractive means to solubilize water insoluble compounds such as drugs. Drug loading, formulations stability and control over drug release are crucial factors for drug-loaded polymer micelles. The interactions between the polymeric host and the guest molecules are considered critical to control these factors but typically barely understood. Here, we compare two isomeric polymer micelles, one of which enables ultra-high curcumin loading exceeding 50 wt.%, while the other allows a drug loading of only 25 wt.%. In the low capacity micelles, steady-state fluorescence revealed a very unusual feature of curcumin fluorescence, a high energy emission at 510 nm. Time-resolved fluorescence upconversion showed that the fluorescence life time of the corresponding species is too short in the high-capacity micelles, preventing an observable emission in steady-state. Therefore, contrary to common perception, stronger interactions between host and guest can be detrimental to the drug loading in polymer micelles.

Curcumin entrapped hyaluronan containing niosomes: preparation, characterisation and in vitro/in vivo evaluation

Curcumin, a natural polyphenolic compound, has numerous pharmacological activities; while it faces several bioavailability problems, due to its poor solubility and stability. So, many nanostructures have been designed to overcome these drawbacks. The aim of this study was to prepare a polymeric niosomal structure by incorporating hyaluronan to improve curcumin efficiencies. Hyaluronan containing niosomes were prepared by thin film hydration medium with slight modifications. In the formulation of hyaluronan containing niosomes size and zeta potential studies, Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), in-vitro release test, DPPH antioxidant assay and in-vivo anti-inflammatory test were investigated. The results showed that hyaluronan containing niosomes were 249.83 ± 6.38 nm and the entrapment of curcumin was 98.28 ± 0.278% (w/w). In addition, the shape of the hyaluronan containing niosomes was spherical. 500 µl of the prepared formulation with 4.002 × 10^-7 moles of curcumin showed 100% antioxidant effect. Moreover, the anti-inflammatory effect of the hyaluronan containing niosomes was higher than the anti-inflammatory effect of the simple suspension of curcumin.

Just add sugar for carbohydrate induced self-assembly of curcumin

In nature, self-assembly processes based on amphiphilic molecules play an integral part in the design of structures of higher order such as cells. Among them, amphiphilic glycoproteins or glycolipids take on a pivotal role due to their bioactivity. Here we show that sugars, in particular, fructose, are capable of directing the self-assembly of highly insoluble curcumin resulting in the formation of well-defined capsules based on non-covalent forces. Simply by mixing an aqueous solution of fructose and curcumin in an open vessel leads to the generation of capsules with sizes ranging between 100 and 150 nm independent of the initial concentrations used. Our results demonstrate that hydrogen bonding displayed by fructose can induce the self-assembly of hydrophobic molecules such as curcumin into well-ordered structures, and serving as a simple and virtually instantaneous way of making nanoparticles from curcumin in water with the potential for template polymerization and nanocarriers.

Keto-Enol Tautomerism of Temperature and pH Sensitive Hydrated Curcumin Nanoparticles: Their Role as Nanoreactors and Compatibility with Blood Cells

In order to provide a solution for the poor aqueous solubility and poor bioavailability of curcumin, we present the synthesis and characteristic features of water-soluble curcumin hydrated nanoparticles (CNPs). They are stable and nearly monodisperse in the aqueous phase where the keto form of curcumin self-assembles into spherical CNPs, which are highly sensitive to temperature and pH variations. The CNPs are quite stable up to 40 °C and at neutral pH. A higher temperature range reduces their hydration and makes them unstable, thereby disintegrating them into smaller aggregates. Similarly, a higher pH converts the keto form of CNPs into the enol form by promoting their interparticle fusions driven by hydrogen bonding with a remarkable color change from yellow to bright orange-red which demonstrates their excellent photophysical behavior. The stable keto form CNPs are highly efficient nonreactors for the in situ synthesis of Au, Ag, and Pd NPs which are simultaneously entrapped in curcumin aggregates, thus promoting the metal NP carrying ability of curcumin aggregates. The CNPs also demonstrate their excellent dose-dependent biocompatibility with blood cells. A concentration range up to 5 mM of CNPs is quite safe for their applications in biological systems.

Zinc-mediated diastereoselective assembly of a trinuclear circular helicate

We have designed a triptycene-based ditopic ligand H₂L, which is able to adopt an adequate topology required for optimal binding to naked Zn²⁺ leading to a neutral trinuclear circular helicate Zn₃L₃.

Green synthesis of curcumin conjugated nanosilver for the applications in nucleic acid sensing and anti-bacterial activity

Silver nanoparticles (Ag NPs) are often synthesized by chemical and physical methods. Natural and non-toxic molecules are recently being replaced for nanoparticles preparation. In this paper we have used curcumin, which interacts with Ag+ and subsequently synthesizes silver nanoparticles. Further continuation of the reaction often makes aggregation and forms dark brown/black silver oxide. Presence of glycerol in the reaction mixture gives mono-disperse curcumin conjugated Ag NPs, which can be made stable by capping with polyvinylpyrolidone (PVP). XRD data confirm that curcumin conjugated Ag NPs are crystalline in nature with a mean crystalline size of 13.27 nm. The Ag NPs are spherical and in the range of 10-50 nm though their hydrodynamic radius is found to be higher, ∼294 nm, due to polyvinylpyrolidone capping and aggregation of nanoparticles in solution. The production of curcumin conjugated Ag NPs follows first order kinetics and the effect of curcumin concentration during formation of Ag NPs indicates a linear enhancement in the production of Ag NPs with an increase in concentration of curcumin. These curcumin conjugated silver nanoparticles show anti-bacterial activity and can successfully determine nucleic acid (DNA and RNA) in the concentration range 100-1000 ng/mL with a linear regression coefficient >0.997 using Resonance Rayleigh Scattering spectra.

Synthesis and controlled curcumin supramolecular complex release from pH-sensitive modified gum-arabic-based hydrogels

Delivery of a curcumin supramolecular complex from pH-responsive gum arabic-based hydrogels.

The effect of the water on the curcumin tautomerism: a quantitative approach

The tautomerism of curcumin has been investigated in ethanol/water binary mixtures by using UV-Vis spectroscopy and advanced quantum-chemical calculations. The spectral changes were processed by using advanced chemometric procedure, based on resolution of overlapping bands technique. As a result, molar fractions of the tautomers and their individual spectra have been estimated. It has been shown that in ethanol the enol-keto tautomer only is presented. The addition of water leads to appearance of a new spectral band, which was assigned to the diketo tautomeric form. The results show that in 90% water/10% ethanol the diketo form is dominating. The observed shift in the equilibrium is explained by the quantum chemical calculations, which show that water molecules stabilize diketo tautomer through formation of stable complexes. To our best knowledge we report for the first time quantitative data for the tautomerism of curcumin and the effect of the water.

Fluorescence behavior of cis-methyl orange stabilized in cationic premicelles

The cis-isomer of methyl orange (MO), stabilized in cationic premicelles, has been found to be fluorescence active when excited at wavelength ≤270nm. An intense fluorescence band with maximum at 575nm along with a broad moderate intensity band in the range of 370-530nm and a low intensity band at 361nm have been observed. The major band at 575nm has been attributed to S1→S0 (n-π(*)) fluorescence unlike the other azobenzenes where the S2→S0 (π-π(*)) fluorescence is usually reported. UV-Vis spectral and surface tension study indicate that the dye exists in the trans form in dye-surfactant ionpair (DSIP) at very dilute concentrations of the surfactant. But the polar cis-isomer is stabilized by micellization of the DSIPs as the concentration of the surfactant is increased. The fluorescence and hence the cis-isomer again disappear when normal micelles are formed above the normal CMC of the surfactant. It has been suggested that the symmetry forbidden S1→S0 (n-π(*)) transition of MO becomes allowed due to the formation of the twisted cis-form. TD-DFT calculations have been used as an auxiliary tool to identify the possible structures and electronic transitions responsible for the specific absorption and fluorescence properties of MO observed in presence of premicellar cationic surfactants.