The Effect of Solvent on Tautomerism, Acidity and Radical Stability of Curcumin and Its Derivatives Based on Thermodynamic Quantities

First-Principles Study of the Dispersion Effects in the Structures and Keto-Enol Tautomerization of Curcumin

Noncovalent interactions, such as dispersion, play a significant role in the stability of flexible molecules, such as curcumin. This study revealed the importance of dispersion correction in the structure and keto-enol tautomerization of curcumin, which has rarely been addressed in computational studies. We rigorously constructed all possible unique curcumin conformers in the enol and keto forms within the first-principles framework. Regardless of the different environments, we carefully explained the agreement between the computational geometry (in the gas phase) and the experimental measurement (in the polymorph) by using dispersion correction. The calculation results for the aqueous solution of conformational abundance, thermochemistry, and reaction kinetics support the experimental observations after considering the dispersion correction. The study also suggests a water-catalyzed mechanism for keto-enol tautomerization, where dispersion correction plays a role in decreasing the energy barrier and making the keto form thermochemically and kinetically favorable. Our results could be helpful in future computational studies to find a method for increasing the aqueous solubility of curcumin; hence, the potential of curcumin as a multifunctional medicine can be fully achieved.

High Yield Synthesis of Curcumin and Symmetric Curcuminoids: A "Click" and "Unclick" Chemistry Approach

The worldwide known and employed spice of Asian origin, turmeric, receives significant attention due to its numerous purported medicinal properties. Herein, we report an optimized synthesis of curcumin and symmetric curcuminoids of aromatic (bisdemethoxycurcumin) and heterocyclic type, with yields going from good to excellent using the cyclic difluoro-boronate derivative of acetylacetone prepared by reaction of 2,4-pentanedione with boron trifluoride in THF (ca. 95%). The subsequent cleavage of the BF₂ group is of significant importance for achieving a high overall yield in this two-step procedure. Such cleavage occurs by treatment with hydrated alumina (Al₂O₃) or silica (SiO₂) oxides, thus allowing the target heptanoids obtained in high yields as an amorphous powder to be filtered off directly from the reaction media. Furthermore, crystallization instead of chromatographic procedures provides a straightforward purification step. The ease and efficiency with which the present methodology can be applied to synthesizing the title compounds earns the terms "click" and "unclick" applied to describe particularly straightforward, efficient reactions. Furthermore, the methodology offers a simple, versatile, fast, and economical synthetic alternative for the obtention of curcumin (85% yield), bis-demethoxycurcumin (78% yield), and the symmetrical heterocyclic curcuminoids (80-92% yield), in pure form and excellent yields.

Effect of curcumin on acute chronic kidney disease due to ischemia-reperfusion syndrome

OBJECTIVE

To evaluate the effect of curcumin on renal function, hemodynamics, and renal oxidative profile of rats with chronic kidney disease (CKD) subjected to renal ischemia-reperfusion injury (IRI).

METHODS

Wistar rats, 250-300 g, distributed in four groups: Sham (n = 5), CKD simulation; CKD (n = 5), 5/6 renal ablation for CKD induction; CKD + IRI (n = 5), CKD and renal pedicle clamping for 30 minutes; and CKD + IRI+curcumin (n = 5), CKD + IRI, curcumin administration 30 mg/kg/day, orally, for 10 days. Renal function (inulin clearance, urine flow, plasma creatinine), hemodynamics (blood pressure), and oxidative profile (peroxides, TBARS, and urine nitrate, non-protein soluble thiols in renal tissue) were evaluated.

RESULTS

The CKD + IRI + curcumin group showed increased inulin clearance and reduced plasma creatinine, decreased RVR and increased RBF, decreased oxidative metabolites in urine and increased thiols in renal tissue when compared with the CKD + IRI group.

CONCLUSION

The treatment with curcumin preserved renal function and hemodynamics of animals with acute CKD, improving oxidative profile, with reduction of oxidants and preservation of antioxidant reserve.

Combination of Curcumin and Photodynamic Therapy Based on the Use of Red Light or Near-Infrared Radiation in Cancer: a Systematic Review

BACKGROUND

Photodynamic therapy (PDT) is a therapeutic intervention that can be applied to the treatment of cancer. The interaction between a photosensitizer (PS), ideal wavelength radiation and tissue molecular oxygen, triggers a series of photochemical reactions that are responsible for the production of reactive oxygen species. These highly reactive species can decrease proliferation and induce tumor cell death. The search for PS of natural origin extracted from plants becomes relevant, as they have photoactivation capacity, preferentially targeting tumor cells and because they do not present any or little toxicity to healthy cells.

OBJECTIVE

Our work aimed to carry out a qualitative systematic review to investigate the effects of curcumin (CUR), a molecule considered as PS of natural origin, on PDT, using red light or near infrared radiation, in tumor models.

METHODS

A systematic search was performed in three databases (PubMed, Scopus, and Web of Science) using the PICOT method, retrieving a total of 1,373 occurrences. At the end of the peer screening, using inclusion, exclusion, and eligibility criteria, 25 eligible articles were included in this systematic review.

RESULTS

CUR, whether in its free state, associated with metal complexes or other PS, and in a nanocarrier system, was considered a relevant PS for PDT using red light or near-infrared against tumoral models in vitro and in vivo, acting by increasing cytotoxicity, inhibiting proliferation, inducing cell death mainly by apoptosis, and changing oxidative parameters.

CONCLUSION

The results found in this systematic review suggest the potential use of CUR as a PS of natural origin to be applied in PDT against many neoplasms, encouraging further search in the field of PDT against cancer and serving as an investigative basis for upcoming pre-clinical and clinical applications.

Tautomers and Rotamers of Curcumin: A Combined UV Spectroscopy, High-Performance Liquid Chromatography, Ion Mobility Mass Spectrometry, and Electronic Structure Theory Study

The structures of tautomers and rotameric forms of curcumin, the bioactive compound present in spice plant turmeric, have been investigated using ion mobility mass spectrometry (IMMS) in conjunction with high-performance liquid chromatography (HPLC) and UV-visible spectroscopy. Two tautomeric forms of this β-diketone compound, keto-enol and diketo, have been chromatographically separated, and the electronic absorption spectra for these two tautomeric forms in methanol solution have been recorded separately for the first time. The molecular identity of the HPLC-separated solution fractions is established unambiguously by recording the mass and fragmentation spectra simultaneously. The ion mobility spectrum for the deprotonated curcumin anion, [Cur-H]^-, corresponding to the diketo tautomer, displays only one peak (P), and the collision cross-section (CCS) value is measured to be 185.9 Ų. However, the ion mobility spectrum corresponding to the HPLC-separated keto-enol tautomer shows three distinctly separated peaks, P, Q, and R, with CCS values of 185.9, 194.8, and 203.4 Ų, respectively, whereby peak R appears to be the most intense one, followed by peaks P and Q. The theoretically calculated CCS values of different isomers of [Cur-H]^-, optimized by electronic structure theory methods, display satisfactory correlation with the experimentally observed values, corroborating our assignments. The spectral attributes also indicate the occurrence of structural rearrangements in the electrospray ionization process. With the aid of the electronic structure calculation, low-energy pathways for the occurrence of the structural isomerization to surpass the energy barrier are suggested, which are consistent with the assignments of the peaks observed in the IM spectra.

Mono-Dendronized β-Cyclodextrin Derivatives as Multitasking Containers for Curcumin. Impacting Its Solubility, Loading, and Tautomeric Form

In this study, three mono-dendronized β-cyclodextrin (βCD) derivatives (βCD-1G, βCD-2G, and βCD-3G) were used as multitasking containers of curcumin (CUR) to influence its aqueous solubility and tautomerism, both of which are related to its biological activity. We evaluated the relevant physicochemical properties of these containers associated with their potential hosting capacity. All mono-dendronized derivatives exhibited enhanced solubility in different solvents, including water, in comparison with native βCD. Gas-phase geometry optimizations by density functional theory (DFT) confirmed that none of the dendrons blocked the passage of CUR into the βCD cavity, and depending on the generation, different preorganization scenarios were promoted before complexation. Phase solubility diagrams showed that all the dendronized containers have superior performance for solubilizing CUR compared to native βCD. We proved that coprecipitation is most efficient than lyophilization for forming inclusion complexes (ICs) with dendronized containers. Even though βCD-3G with the largest 3G dendron exhibited the highest CUR loading, the complexation of CUR with βCD-2G provided the supramolecular system that contains CUR preferentially in its diketo tautomer, which is known for its antioxidant activity.

Efeito da curcumina na doença renal crônica agudizada pela síndrome isquemia-reperfusão

RESUMO Objetivo: Avaliar o efeito da curcumina na função renal, hemodinâmica e perfil oxidativo renal de ratos com doença renal crônica (DRC) submetidos a isquemia-reperfusão renal (I/R). Métodos: Ratos Wistar, 250–300 g, distribuídos em quatro grupos: Sham (n = 5), simulação da DRC; DRC (n = 5), ablação de 5/6 dos rins para indução de DRC; DRC + I/R (n = 5), DRC e clampeamento do pedículo renal por 30 minutos; DRC + I/R + curcumina (n = 5) e DRC + I/R, administração de curcumina 30 mg/kg/dia, via oral, por 10 dias. Foram avaliadas a função renal (clearance de inulina, fluxo urinário, creatinina plasmática), hemodinâmica (pressão arterial) e perfil oxidativo (peróxidos, TBARS e nitrato urinário, tióis solúveis não proteicos no tecido renal). Resultados: O grupo DRC + I/R + curcumina apresentou elevação do clearance de inulina e redução da creatinina plasmática, diminuição da RVR e aumento do FSR, diminuição de metabólitos oxidativos na urina e aumento dos tióis no tecido renal quando comparado ao grupo DRC + I/R. Conclusão: O tratamento com curcumina preservou a função e hemodinâmica renal dos animais com DRC agudizada, promovendo melhora no perfil oxidativo, com redução de oxidantes e preservação de reserva antioxidante.

Phenylboronic acid-based core-shell drug delivery platform clasping 1,3-dicarbonyl compounds by a coordinate interaction

Along with the successful commercialization of chemotherapeutics, such as doxorubicin and paclitaxel, numerous natural compounds have been investigated for clinical applications. Recently, curcumin (CUR), a natural compound with various therapeutic effects, has attracted attention for cancer immunotherapy. Most chemotherapeutics, however, have poor water solubility due to their hydrophobicity, which makes them less suited to biomedical applications; CUR is no exception because of its low bioavailability and extremely high hydrophobicity. In the present study, we developed an easy but effective strategy using the interaction between the 1,3-dicarbonyl groups of drugs and phenylboronic acid (PBA) to solubilize hydrophobic drugs. First, we verified the coordinate interaction between 1,3-dicarbonyl and PBA using 3,5-heptanedione as a model compound, followed by CUR as a model drug. A PBA-grafted hydrophilic polymer was used to form a nanoconstruct by coordination bonding with CUR, which then made direct administration of the nanoparticles possible. The nanoconstruct exhibited remarkable loading capability, uniform size, colloidal stability, and pH-responsive drug release, attributed to the formation of core-shell nanoconstructs by coordinate interaction. The therapeutic nanoconstructs successfully showed both chemotherapeutic and anti-PD-L1 anticancer effects in cellular and animal models. Furthermore, we demonstrated the applicability of this technique to other 1,3-dicarbonyl compounds. Overall, our findings suggest a facile, but expandable strategy by applying the coordinate interaction between 1,3-dicarbonyl and PBA, which enables high drug loading and stimuli-responsive drug release.

Encapsulation of Curcumin in Polystyrene-Based Nanoparticles-Drug Loading Capacity and Cytotoxicity

Nanoparticles made of amphiphilic block copolymers are commonly used in the preparation of nano-sized drug delivery systems. Poly(styrene)-block -poly(acrylic acid) (PS-PAA) copolymers have been proposed for drug delivery purposes; however, the drug loading capacity and cytotoxicity of PS-PAA nanoparticles are still not fully recognized. Herein, we investigated the accumulation of a model hydrophobic drug, curcumin, and its spatial distribution inside the PS-PAA nanoparticles. Experimental methods and atomistic molecular dynamics simulations were used to understand the molecular structure of the PS core and how curcumin molecules interact and organize within the PS matrix. The hydrophobic core of the PS-PAA nanoparticles consists of adhering individually coiled polymeric chains and is compact enough to prevent post-incorporation of curcumin. However, the drug has a good affinity for the PS matrix and can be efficiently enclosed in the PS-PAA nanoparticles at the formation stage. At low concentrations, curcumin is evenly distributed in the PS core, while its aggregates were observed above ca. 2 wt %. The nanoparticles were found to have relatively low cytotoxicity to human skin fibroblasts, and the presence of curcumin further increased their biocompatibility. Our work provides a detailed description of the interactions between a hydrophobic drug and PS-PAA nanoparticles and information on the biocompatibility of these anionic nanostructures which may be relevant to the development of amphiphilic copolymer-based drug delivery systems.

Drug-loading capacity of polylactide-based micro- and nanoparticles - Experimental and molecular modeling study

Micro- and nanostructures prepared from biodegradable homopolymers and amphiphilic block copolymers (AmBCs) have found application as drug-delivery systems (DDSs). The ability to accumulate a drug is a very important parameter characterizing a given DDS. This work focuses on the impact of DDS size, the packing of polymer chains in the DDS, and drug - polymer matrix compatibility on the hydrophobic drug - loading capacity (DLC) of nano/microcarriers prepared from a biodegradable polymer or its copolymer. Using experimental measurements in combination with atomistic molecular dynamics simulations, an analysis of curcumin encapsulation in microspheres (MSs) from polylactide (PLA) homopolymer and nanoparticles (NPs) from PLA-block-poly(2-methacryloyloxyethylphosphorylcholine) AmBC was performed. The results show that curcumin has good affinity for the PLA matrix due to its hydrophobic nature. However, the DLC value is limited by the fact that curcumin only accumulates in the peripheral part of these structures. Such uneven drug distribution in the PLA matrix results from the non-homogeneous density of MSs (non-uniform packing of the polymer chains in the coil). The results also indicate that the MSs can retain a greater amount of hydrophobic drug compared to the NPs, which is associated with the formation of drug aggregates inside the PLA microparticles.

Interplay between conformational and solvent effects in UV-visible absorption spectra: curcumin tautomers as a case study

We present a combined theoretical and experimental study on the UV-vis spectra of enol-keto (EK) and keto-keto (KK) tautomeric forms of curcumin dissolved in aqueous solution. Solvent effects have been investigated by resorting to the implicit polarizable continuum model (QM/PCM) and non-polarizable and fully polarizable QM/MM approaches, the latter based on the fluctuating charges (FQ) force-field. In particular, all methods are challenged to rationalize the contribution of conformational, electrostatic and polarization effects in the calculation of the vertical excitation spectra of curcumin tautomers. The obtained results highlight that for both tautomers specific solute-solvent hydrogen-bond interactions play a minor role with respect to conformational and electrostatic effects.

Ethnopharmacological Approaches for Dementia Therapy and Significance of Natural Products and Herbal Drugs

Dementia is a clinical syndrome wherein gradual decline of mental and cognitive capabilities of an afflicted person takes place. Dementia is associated with various risk factors and conditions such as insufficient cerebral blood supply, toxin exposure, mitochondrial dysfunction, oxidative damage, and often coexisting with some neurodegenerative disorders such as Alzheimer's disease (AD), Huntington's disease (HD), and Parkinson's disease (PD). Although there are well-established (semi-)synthetic drugs currently used for the management of AD and AD-associated dementia, most of them have several adverse effects. Thus, traditional medicine provides various plant-derived lead molecules that may be useful for further medical research. Herein we review the worldwide use of ethnomedicinal plants in dementia treatment. We have explored a number of recognized databases by using keywords and phrases such as “dementia”, “Alzheimer's,” “traditional medicine,” “ethnopharmacology,” “ethnobotany,” “herbs,” “medicinal plants” or other relevant terms, and summarized 90 medicinal plants that are traditionally used to treat dementia. Moreover, we highlight five medicinal plants or plant genera of prime importance and discuss the physiological effects, as well as the mechanism of action of their major bioactive compounds. Furthermore, the link between mitochondrial dysfunction and dementia is also discussed. We conclude that several drugs of plant origin may serve as promising therapeutics for the treatment of dementia, however, pivotal evidence for their therapeutic efficacy in advanced clinical studies is still lacking.