Studies on curcumin and curcuminoids. IX: Investigation of the photobiological activity of curcumin using bacterial indicator systems

UV-A-Induced Photoisomerization and Photodimerization of Curcumin: An Ion Mobility Mass Spectrometry Study

Curcumin, the bioactive compound present in spice plant turmeric, has been shown to exhibit selective phototoxic activities toward mammalian cancer cells, and it is being used extensively as a photosensitizer (PS) in photodynamic therapies (PDT). However, so far, the fate of curcumin toward photochemical transformations is not well understood. Here we report our findings of a number of novel photochemical reaction channels of curcumin in water-methanol mixture, like photoisomerization, photodimerization, and photooxidation (H2-loss). The reaction was performed by irradiating the curcumin solution with ultraviolet (UV) light of wavelength 350 nm, which is abundant in the earth's troposphere. Product identification and structure elucidation are done by employing an integrated method of drift tube ion mobility mass spectrometry (DTIMS) in combination with high-performance liquid chromatography (HPLC) and collision-induced dissociation (CID) of the mass-selected molecular ions. Two photoisomers of curcumin produced as a result of trans-cis configurational changes about C═C double bonds in the excited state have been identified, and it has been shown that they could serve as the precursors for formation of isomeric dimers via [2 + 2] cycloaddition and H2-loss products. Comparisons of the experimentally measured collision cross-section (CCS) values of the reactant and product ions obtained by the DTIMS method with those predicted by the electronic structure theory are found to be very effective for the discrimination of the produced photoisomers. The observed photochemical reaction channels are potentially significant toward uses of curcumin as a photosensitizer in photodynamic therapy.

Curcumin a Natural Phenol and Its Therapeutic Role in Cancer and Photodynamic Therapy: A Review

Cancer continues to cause an alarming number of deaths globally, and its burden on the health system is significant. Though different conventional therapeutic procedures are exploited for cancer treatment, the prevalence and death rates remain elevated. These, therefore, insinuate that novel and more efficient treatment procedures are needed for cancer. Curcumin, a bioactive, natural, phenolic compound isolated from the rhizome of the herbaceous plant turmeric, is receiving great interest for its exciting and broad pharmacological properties. Curcumin presents anticancer therapeutic capacities and can be utilized as a photosensitizing drug in cancer photodynamic therapy (PDT). Nonetheless, curcumin's poor bioavailability and related pharmacokinetics limit its clinical utility in cancer treatment. This review looks at the physical and chemical properties, bioavailability, and safety of curcumin, while focusing on curcumin as an agent in cancer therapy and as a photosensitizer in cancer PDT. The possible mechanisms and cellular targets of curcumin in cancer therapy and PDT are highlighted. Furthermore, recent improvements in curcumin's bioavailability in cancer therapy using nanoformulations and delivery systems are presented.

Photodynamic inactivation of Staphylococcus aureus by ecological antibacterial solutions associating LED (ʎ 450 ± 10 nm) with curcumin and olive leaf extracts

Antimicrobial resistance is a problem in contemporary society, with Staphylococcus aureus standing out as a threat due to its ability to colonize, its pathogenicity, and its expression of several virulence factors. In this context, antimicrobial photodynamic inactivation (aPDI) emerges as an alternative to conventional microbicidal or microbiostatic systems, enabling numerous and successive applications without developing side effects and microbial resistance. In this context, an aPDI system against cultures of S. aureus based on a water-in-oil (W/O) emulsion incorporating curcumin as the photosensitizer (PS), with and without olive leaf extract (OLE), was developed and the antibacterial efficacy evaluated under LED activation (ʎ450 ± 10 nm) by depositing an energy density of 14 J/cm². The produced emulsified systems showed no significant differences in the droplet size and morphology, remaining stable along the tested period of 30 days. The bacterial reduction achieved after the first aPDI application for the emulsions added with curcumin and curcumin combined with the OLE was 5 log10 CFU.mL^-1 and 6 log10 CFU.mL^-1, respectively, revealing a significant difference between the two groups (p < 0.0001). After the second aPDI application, an increased microbial reduction (7 log10 CFU.mL^-1) was observed for both studied groups even with a low significant difference (p < 0.05). The PS loading through an emulsified system for aPDI obtained a bactericidal action against S. aureus, increased by applying two aPDI, showing a significant synergy between photodynamic inactivation, OLE delivery and antibacterial activity. In addition, the developed solutions were produced using natural products by an ecologically correct process.

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.

Cellulose laurate films containing curcumin as photoinduced antibacterial agent for meat preservation

Hydrophobic cellulose laurate (CL) with high degree of substitution has been successfully synthesized. The mechanical property, water-resistance, antimicrobial activity, barrier properties and food decontamination of cellulose-laurate-curcumin films (CL-Cu_x, x = 0.1, 0.5, and 1) were investigated. The results showed that the mechanical properties of CL-Cu_x hardly change after soaking in water for 24 h, probably due to the strong hydrophobicity of cellulose laurate. CL-Cu₁ represented a good photoinduced antibacterial effect against S. aureus. After irradiation of white light at 60 mW·cm^-2 for 20 min, the inhibition efficiency reached to 95 ± 2.02%, probably owing to the generated active ¹O₂. In comparison with CL-Cu₁ stored in natural light, the bacteriostatic effect of CL-Cu₁ in dark storage was better, and the inhibition rate of CL-Cu₁ remained 80 ± 1.22 at 60th day. The stabler excited state of curcumin in hydrophobic cellulose laurate was probably assigned to inhibition of tautomerism or conformational transition, which was beneficial to the generation of singlet oxygen. CL-Cu₁ can significantly inhibit the growth of TVBN and TVC values of chilled meat upon white light irradiation, indicating the potential application of cellulose-laurate-curcumin films in food decontamination.

Nano-Derived Therapeutic Formulations with Curcumin in Inflammation-Related Diseases

Due to its vast therapeutic potential, the plant-derived polyphenol curcumin is utilized in an ever-growing number of health-related applications. Here, we report the extraction methodologies, therapeutic properties, advantages and disadvantages linked to curcumin employment, and the new strategies addressed to improve its effectiveness by employing advanced nanocarriers. The emerging nanotechnology applications used to enhance CUR bioavailability and its targeted delivery in specific pathological conditions are collected and discussed. In particular, new aspects concerning the main strategic nanocarriers employed for treating inflammation and oxidative stress-related diseases are reported and discussed, with specific emphasis on those topically employed in conditions such as wounds, arthritis, or psoriasis and others used in pathologies such as bowel (colitis), neurodegenerative (Alzheimer's or dementia), cardiovascular (atherosclerosis), and lung (asthma and chronic obstructive pulmonary disease) diseases. A brief overview of the relevant clinical trials is also included. We believe the review can provide the readers with an overview of the nanostrategies currently employed to improve CUR therapeutic applications in the highlighted pathological conditions.

Photoinduced Antimicrobial Activity of Curcumin-Containing Coatings: Molecular Interaction, Stability and Potential Application in Food Decontamination

Polyvinyl acetate (PVAc) and curcumin (Cu) were utilized for preparing new protecting PVAc-Cu x (x = 1, 5 and 10) coatings exerting antimicrobial photodynamic activity upon white light irradiation. Toward Salmonella typhimurium or Staphylococcus aureus, the killing efficiency represented the dependence on the Cu concentration and irradiation intensity. Toward S. aureus, the killing efficiency of PVAc-Cu 10 coating reached 93% at an energy density of 72 J/cm2. With the change in storage time of coating, the results implied significant stability of photosterilization efficiency within 60 days. Compared with the control experiment, lower total viable counts (TVCs) and total volatile basic nitrogen (TVB-N) values in fresh meat packaged by PVDC films with PVAc-Cu 10 coatings during storage at 4 °C demonstrated the practicability of the PVAc-Cu x coatings in decontaminating fresh pork. PVAc packed curcumin tightly within polymer chains, thus preventing tautomerization or, more probably, conformational transition, which is advantageous for improving photostability and emission lifetime.

Role of Photoactive Phytocompounds in Photodynamic Therapy of Cancer

Cancer is one of the greatest life-threatening diseases conventionally treated using chemo- and radio-therapy. Photodynamic therapy (PDT) is a promising approach to eradicate different types of cancers. PDT requires the administration of photosensitisers (PSs) and photoactivation using a specific wavelength of light in the presence of molecular oxygen. This photoactivation exerts an anticancer effect via apoptosis, necrosis, and autophagy of cancer cells. Recently, various natural compounds that exhibit photosensitising potentials have been identified. Photoactive substances derived from medicinal plants have been found to be safe in comparison with synthetic compounds. Many articles have focused on PDT mechanisms and types of PSs, but limited attention has been paid to the phototoxic activities of phytocompounds. The reduced toxicity and side effects of natural compounds inspire the researchers to identify and use plant extracts or phytocompounds as a potent natural PS candidate for PDT. This review focusses on the importance of common photoactive groups (furanocoumarins, polyacetylenes, thiophenes, curcumins, alkaloids, and anthraquinones), their phototoxic effects, anticancer activity and use as a potent PS for an effective PDT outcome in the treatment of various cancers.

Identification of carbonylated proteins in a bactericidal process induced by curcumin with blue light irradiation on imipenem-resistant Acinetobacter baumannii

RATIONALE

Antimicrobial photodynamic treatment is potentially an alternative to antibiotics and is also effective against viruses, fungi and some cancers. Our previous studies have shown that blue light combined with curcumin, a chemical from the turmeric plant, exerted effective antimicrobial activity via photodynamic treatment. The study reported in this paper investigates which target proteins are affected after the treatment.

METHODS

We treated imipenem-resistant Acinetobacter baumannii with blue light and curcumin and used protein carbonylation as a marker for oxidative damage. After treatment, the bacterial proteins were extracted and the protein carbonyls marked using dinitrophenylhydrazide. After enzyme digestion, we used liquid chromatography/nano-electrospray ionization (LC/nano-ESI) ion trap mass spectrometry to identify bacterial peptides from a customized database. The functional enrichment analyses of the identified proteins were performed using gene ontology annotation and the STRING protein-protein interaction network.

RESULTS

The application of curcumin with blue light showed good antibacterial activity against imipenem-resistant A. baumannii. Using a shotgun proteomics approach, the carbonylated proteins in A. baumannii caused by the photolytic curcumin were identified. The results showed that the proteins related to membrane structures, translation and response to oxidative stress were preferentially modified.

CONCLUSIONS

The photolytic curcumin treatment could be a potential alternative to antibiotics for bacterial infection. In this study, the shotgun proteomics strategy allows us to explore the possible bactericidal mechanisms under this oxidative stress. The result provides a reference for future studies on the enhancement of the action of photolytic curcumin.

Curcumin derivatives as photosensitizers in photodynamic therapy: photophysical properties and in vitro studies with prostate cancer cells

Photodynamic therapy (PDT) is a minimally invasive approach to treat various forms of cancer, based on the ability of certain non-toxic molecules (photosensitizers) to generate reactive oxygen species (ROS) after excitation by light of a certain wavelength and eventually induce strong phototoxic reactions against malignant cells and other pathogens. Curcumin is one of the most extensively investigated phytochemicals with a wide range of therapeutic properties and has been shown to induce strong photocytotoxic effects in micromolar concentrations against a variety of cancer cell lines. Curcumin (1) is comparatively evaluated with the naturally occurring bisdemethoxy Curcumin (2), which lacks the two methoxy groups, as well as two newly synthesized curcuminoids, the cinnamaldehyde derivative (3) and the dimethylamino one (4), designed to increase the absorption maximum and hence the tissue penetration. The synthetic curcuminoids were successfully synthesized in sufficient amounts and their photophysical properties such as absorption, fluorescence, photobleaching and free radical generation were investigated. Compound 4 exhibited a significant increase in peak absorption (497 nm) and strong fluorescent emission signals were recorded for all curcuminoids. Photobleaching of 4 was comparable to 1 whereas 2 and 3 showed more extended photobleaching but much higher ROS production in very short irradiation times. Compounds 2 and 4 exhibited specific intracellular localization. After dark and light cytotoxicity experiments against LNCaP prostate cancer cell line for all curcuminoids, concentration of 3 μM and irradiance of 6 mW cm-2 were selected for the PDT application which resulted in remarkable results with very short LD50. Curcuminoids 2 and 4 exhibited a significant dose-dependent PDT effect. The biphasic dose-response photodynamic effect observed for 1 and 3 may provide a strategy against prolonged and sustained photosensitivity.

A Detailed Insight of the Anti-inflammatory Effects of Curcumin with the Assessment of Parameters, Sources of ROS and Associated Mechanisms

Background:

Curcumin is an active constituent ofCurcuma longa,which belongs to Zingiberaceae family. It is derived from the Rhizome of a perennial plant having molecular formula C21H20O6and chemically it is (1, 7- bis (4- hydroxy - 3 methoxyphenyl) -1, 6 - heptadine - 3, 5 - diene), also known as diferuloylmethane. Curcumin has been extensively used as a herbal constituent for curing several diseases and is scientifically proven to show major effects as an anti-inflammatory agent.

Objective:

Inflammation is an important factor for numerous diseases including diabetes neuropathy, cancer, asthma, arthritis, and other diseases. Prophylaxis of inflammatory diseases through synthetic medications tends to have major toxicity and side effects on a large number of population. The foremost aim of this review paper is to assess the natural anti-inflammatory effect of curcumin, source, and mechanism of action, potential therapeutic effect and models associated. Additionally, this paper aims to scrutinize inflammation, sources of reactive oxygen species, and pathways of reactive oxygen species generation and potential side effects of curcumin.

Methods:

Selection of data has been done by studying the combination of research and review papers from different databases like PubMed, Medline and Web of science from the year 1985- 2018 by using search keywords like “curcumin”, “anti-inflammatory”, “ROS”, “Curcuma longa”, “medicinal uses of curcumin”, “assessing parameters”, “inflammation”, “anti-oxidant”

Results:

On the basis of our interpretation, we have concluded that curcumin has potential therapeutic effects in different inflammatory diseases, it inhibits the inflammatory mediators, oxidation processes, and oxidative stress and has no severe toxicity on animals and humans.

Conclusion:

Oxidative stress is a major cause of inflammation and curcumin has a good potential for blocking it. Curcumin is also easily accessible herbal source and should be consumed in the form of food, antioxidant, anti-inflammatory agents and further observation should be done on its therapeutic parameters, risk factors, and toxicity studies and oral viability.

Anti-infective Properties of the Golden Spice Curcumin

The search for novel anti-infectives is one of the most important challenges in natural product research, as diseases caused by bacteria, viruses, and fungi are influencing the human society all over the world. Natural compounds are a continuing source of novel anti-infectives. Accordingly, curcumin, has been used for centuries in Asian traditional medicine to treat various disorders. Numerous studies have shown that curcumin possesses a wide spectrum of biological and pharmacological properties, acting, for example, as anti-inflammatory, anti-angiogenic and anti-neoplastic, while no toxicity is associated with the compound. Recently, curcumin’s antiviral and antibacterial activity was investigated, and it was shown to act against various important human pathogens like the influenza virus, hepatitis C virus, HIV and strains of Staphylococcus, Streptococcus, and Pseudomonas. Despite the potency, curcumin has not yet been approved as a therapeutic antiviral agent. This review summarizes the current knowledge and future perspectives of the antiviral, antibacterial, and antifungal effects of curcumin.

Low-dose blue light irradiation enhances the antimicrobial activities of curcumin against Propionibacterium acnes

Propionibacterium acnes (P. acnes) is an opportunistic infection in human skin that causes acne vulgaris. Antibiotic agents provide the effective eradication of microbes until the development of drug-resistant microbes. Photodynamic inactivation (PDI) is a non-antibiotic therapy for microbial eradication. In this study, the visible blue light (BL, λ_max = 462 nm) was used to enhance the antimicrobial activities of curcumin, a natural phenolic compound. Individual exposure to curcumin or BL irradiation does not generate cytotoxicity on P. acnes. The viability of P. acnes was decreased significantly in 0.09 J/cm² BL with 1.52 μM of curcumin. Furthermore, the low-dose blue light irradiation triggers a series of cytotoxic actions of curcumin on P. acnes. The lethal factors of photolytic curcumin were investigated based on the morphology of P. acnes by SEM and fluorescent images. The membrane disruption of microbes was observed on the PDI against P. acnes. Chromatography and mass spectrometry techniques were also used to identify the photolytic metabolites. Curcumin could be photolysed into vanillin through BL irradiation, which presents a strong linear relationship in quantitation. Because the safety of blue light in mammalian cell has been proven, the photolytic curcumin treatment could support non-antibiotic therapy to eradicate P. acnes on clinical dermatology.

Antimicrobial coatings on polyethylene terephthalate based on curcumin/cyclodextrin complex embedded in a multilayer polyelectrolyte architecture

Bacterial contamination is a growing concern worldwide. The aim of this work was to develop an antimicrobial coating based on curcumin-cyclodextrin inclusion complex and using polyethylene terephthalate (PET) film as a support matrix. After a pre-treatment aimed to provide sufficient electric charge to the PET surface, it was electrostatically coated with repeated multilayers comprising alternately deposited positively-charged poly-l-lysine (PLL) and negatively-charged poly-l-glutamic acid (PLGA) and carboxymethyl-β-cyclodextrin (CMBCD). The coatings had an architecture (PLL-PLGA)₆-(PLL-PLGA-PLL-CMBCD)_n, with the number of repeated multilayers n varying from 5 to 20. The CMBCD molecules were either covalently cross-linked using carbodiimide crosslinker chemistry or left unbound. The surface morphology, structure and elemental composition of the coatings were analysed by scanning electron microscopy and energy dispersive x-ray spectroscopy. To impart antimicrobial properties to the coatings they were loaded with a natural phenolic compound curcumin forming inclusion complexes with β-cyclodextrin. The non-cross-linked coatings showed bactericidal activity towards Escherichia coli in the dark, and this activity was further enhanced upon illumination with white light. Curcumin was released from the non-cross-linked coatings into an aqueous medium in the form of cyclodextrin inclusion complex. After the cross-linking, the coating lost its dark antimicrobial activity but retained the photodynamic properties. Stabilized cross-linked curcumin-loaded coatings can serve a basis for developing photoactivated antimicrobial surfaces controlling bacterial contamination and spread.

Excited state dynamics of bis-dehydroxycurcumin tert-butyl ester, a diketo-shifted derivative of the photosensitizer curcumin

Bis-dehydroxycurcumin tert-butyl ester (K2T23) is a derivative of the natural spice curcumin. Curcumin is widely studied for its multiple therapeutic properties, including photosensitized cytotoxicity. However, the full exploitation of curcumin phototoxic potential is hindered by the extreme instability of its excited state, caused by very efficient non radiative decay by means of transfer of the enolic proton to the nearby keto oxygen. K2T23 is designed to exhibit a tautomeric equilibrium shifted toward the diketo conformers with respect to natural curcumin. This property should endow K2T23 with superior excited-state stability when excited in the UVB band, i.e., in correspondence of the diketo conformers absorption peaks, making this compound an interesting candidate for topical photodynamic therapy of, e.g., skin tumors or oral infections. In this work, the tautomeric equilibrium of K2T23 between the keto-enolic and diketo conformers is assessed in the ground state in several organic solvents by UV-visible absorption and by nuclear magnetic resonance. The same tautomeric equilibrium is also probed in the excited-state in the same environments by means of steady-state fluorescence and time-correlated single-photon counting measurements. These techniques are also exploited to elucidate the excited state dynamics and excited-state deactivation pathways of K2T23, which are compared to those determined for several other curcuminoids characterized in previous works of ours. The ability of K2T23 in photosensitizing the production of singlet oxygen is compared with that of curcumin.

Modes of antibacterial action of curcumin under dark and light conditions: A toxicoproteomics approach

Curcumin is a potent natural food-grade antimicrobial compound. Exposure to light further enhances its antimicrobial capacity. Proteomic methods were used in this study for investigating the mechanistic aspects of the antibacterial curcumin effects in the dark and upon illumination. Escherichia coli cells exposed to water-dispersible curcumin-methyl-β-cyclodextrin inclusion complex under dark and light conditions were compared with the non-treated cells kept under the same illumination regimes. Curcumin treatment in the dark evoked adaptive responses aimed at mitigation of oxidative stress, DNA protection, proteostasis, modulation of redox state via changing NADH level, and gasotransmitter (H₂S and NH₃) biosynthesis. Although part of these phenomena were also present in E. coli treated under light, the light-induced curcumin toxicity was prevailed by maladaptive responses. The ROS burst induced upon curcumin treatment under light overrode the cellular adaptive mechanisms disrupting the iron metabolism, deregulating the iron-sulfur cluster biosynthesis and eventually leading to cell death. The toxicoproteomic findings were validated by transcriptomic analysis and by assessment of intracellular ROS, NADH, NADPH and iron levels.

SIGNIFICANCE

The results of this study elucidate putative mechanistic basis of antibacterial effects of curcumin, suggesting ways towards more efficient contamination control. In particular, the antimicrobial efficacy of curcumin can be potentiated by targeting bacterial systems that remediate its dark toxicity by free radical detoxification and modulation of cell redox status. To the best of the authors' knowledge, this is the first proteomic study differentiating between the dark and light-induced antimicrobial activity of curcumin.

Ambient light induced antibacterial action of curcumin/graphene nanomesh hybrids

Antibacterial curcumin/graphene nanomesh hybrids are synthesized and tested.

The mode of antimicrobial action of curcumin depends on the delivery system: monolithic nanoparticles vs. supramolecular inclusion complex

Formulation determines curcumin antimicrobial effect: curcumin–cyclodextrin complexes are bactericidal, induce ROS, and target electron transport; monolithic nanoparticles are bacteriostatic, and target membranes and ATP.

Photodynamic inactivation of a multispecies biofilm using curcumin and LED light

This study evaluated the potential of curcumin-mediated antimicrobial photodynamic inactivation (API) on multispecies biofilms of Candida albicans, Candida glabrata, and Streptococcus mutans of different ages. Acrylic samples (n = 480) were made with standardized rough surfaces and incubated with bacteria and yeast for 24 or 48 h. API was performed with curcumin (80, 100, 120 μM) and LED light. Additional acrylic samples were treated with curcumin or LED light only. Positive control samples received neither light nor curcumin. After API, colony counts were quantified (CFU/mL), cell metabolism was determined by means of XTT assay, and the total biofilm biomass was evaluated using Crystal Violet (CV) staining assay and images were obtained by confocal laser scanning microscopy (CLSM). The data were analyzed by nonparametric two-way ANOVA and post hoc Tukey tests (α < 0.05). For 24-h biofilm, API resulted in statistically significant difference (ρ < 0.001) of viability of C. albicans compared with control (P-L-) for all Cur concentrations. For 48-h biofilm, API resulted in statistically significant difference (ρ < 0.001) compared with control only when Cur at 120 μM was used. API promoted statistically significant difference (ρ ≤ 0.001) in the viability of S. mutans and C. glabrata for all Cur concentrations in the two biofilm ages. In addition, API produced a statistically significant difference (ρ < 0.001) of metabolic activity and of total biomass (ρ < 0.001) of multispecies biofilms compared with control for all Cur concentrations. It can be concluded that both 24- and 48-h biofilms were susceptible to API mediated by Cur; however, 24-h biofilm was more sensitive than the 48-h biofilm.

Determining whether curcumin degradation/condensation is actually bioactivation (Review)

Curcumin has been shown to exert therapeutic or protective effects against a variety of diseases, such as cancer, pulmonary diseases, neurological, liver, metabolic, autoimmune, cardiovascular diseases and numerous other chronic ailments. Over 116 clinical studies on curcumin in humans were registered with the US National Institutes of Health in 2015. However, it is mystifying how curcumin can be so effective in the treatment of many diseases since it has very low water solubility and bioavailability. Furthermore, curcumin is not stable under various conditions; its degradation or condensation into different bioactive compounds may be responsible for its biological activities rather than curcumin itself. In this review, we provide evidence of curcumin degradation and condensation into different compounds which have or may have health benefits themselves. Literature reviews strongly suggest that these molecules contribute to the observed health benefits, rather than curcumin itself.

Evaluation of Antimicrobial Photodynamic Therapy against Streptococcus mutans Biofilm in situ

AIM

This study investigated the effect of antimicrobial photo-dynamic therapy (aPDT) over Streptococcus mutans biofilm.

MATERIALS AND METHODS

Eighteen (n = 18) patients were selected and one palatine device with dental blocks was used. The biofilm was treated by curcumin and Photogem® with a LED and the effect was analyzed by CFU/ml.

RESULTS

Although, statistical analysis showed significant reductions for aPDT mainly with Photogem® (p = 0.02), these were low.

CONCLUSION

The results suggest a low antimicrobial effect of aPDT over S. mutans biofilm. Some parameters used need to be improved.

CLINICAL SIGNIFICANCE

This technique can be a promising in Dentistry.

Bactericidal activity of curcumin I is associated with damaging of bacterial membrane

Curcumin, an important constituent of turmeric, is known for various biological activities, primarily due to its antioxidant mechanism. The present study focused on the antibacterial activity of curcumin I, a significant component of commercial curcumin, against four genera of bacteria, including those that are Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa). These represent prominent human pathogens, particularly in hospital settings. Our study shows the strong antibacterial potential of curcumin I against all the tested bacteria from Gram-positive as well as Gram-negative groups. The integrity of the bacterial membrane was checked using two differential permeabilization indicating fluorescent probes, namely, propidium iodide and calcein. Both the membrane permeabilization assays confirmed membrane leakage in Gram-negative and Gram-positive bacteria on exposure to curcumin I. In addition, scanning electron microscopy and fluorescence microscopy were employed to confirm the membrane damages in bacterial cells on exposure to curcumin I. The present study confirms the broad-spectrum antibacterial nature of curcumin I, and its membrane damaging property. Findings from this study could provide impetus for further research on curcumin I regarding its antibiotic potential against rapidly emerging bacterial pathogens.

Trichophyton rubrum is inhibited by free and nanoparticle encapsulated curcumin by induction of nitrosative stress after photodynamic activation

Antimicrobial photodynamic inhibition (aPI) utilizes radical stress generated from the excitation of a photosensitizer (PS) with light to destroy pathogens. Its use against Trichophyton rubrum, a dermatophytic fungus with increasing incidence and resistance, has not been well characterized. Our aim was to evaluate the mechanism of action of aPI against T. rubrum using curcumin as the PS in both free and nanoparticle (curc-np) form. Nanocarriers stabilize curcumin and allow for enhanced solubility and PS delivery. Curcumin aPI, at optimal conditions of 10 μg/mL of PS with 10 J/cm² of blue light (417 ± 5 nm), completely inhibited fungal growth (p<0.0001) via induction of reactive oxygen (ROS) and nitrogen species (RNS), which was associated with fungal death by apoptosis. Interestingly, only scavengers of RNS impeded aPI efficacy, suggesting that curcumin acts potently via a nitrosative pathway. The curc-np induced greater NO^• expression and enhanced apoptosis of fungal cells, highlighting curc-np aPI as a potential treatment for T. rubrum skin infections.

Self-assembly, photoresponsive behavior and transport potential of azobenzene grafted dendronized polymeric amphiphiles

An azobenzene based light responsive polymeric system was developed to study the transport potential and photo-controlled release of encapsulated guests.

The chemistry of curcumin: from extraction to therapeutic agent

Curcumin, a pigment from turmeric, is one of the very few promising natural products that has been extensively investigated by researchers from both the biological and chemical point of view. While there are several reviews on the biological and pharmacological effects of curcumin, chemistry reviews are comparatively scarcer. In this article, an overview of different aspects of the unique chemistry research on curcumin will be discussed. These include methods for the extraction from turmeric, laboratory synthesis methods, chemical and photochemical degradation and the chemistry behind its metabolism. Additionally other chemical reactions that have biological relevance like nucleophilic addition reactions, and metal chelation will be discussed. Recent advances in the preparation of new curcumin nanoconjugates with metal and metal oxide nanoparticles will also be mentioned. Directions for future investigations to be undertaken in the chemistry of curcumin have also been suggested.

Elucidation of the relationships between H-bonding patterns and excited state dynamics in cyclovalone

Cyclovalone is a synthetic curcumin derivative in which the keto-enolic system is replaced by a cyclohexanone ring. This modification of the chemical structure might in principle result in an excited state that is more stable than that of curcumin, which in turn should produce an enhanced phototoxicity. Indeed, although curcumin exhibits photosensitized antibacterial activity, this compound is characterized by very fast excited-state dynamics which limit its efficacy as a photosensitizer. In previous works we showed that the main non-radiative decay pathway of keto-enolic curcuminoids is through excited-state transfer of the enolic proton to the keto-oxygen. Another effective deactivation pathway involves an intermolecular charge transfer mechanism occurring at the phenyl rings, made possible by intramolecular H-bonding between the methoxy and the hydroxyl substituent. In this paper we present UV-Vis and IR absorption spectra data with the aim of elucidating the intramolecular charge distribution of this compound and its solvation patterns in different environments, with particular focus on solute-solvent H-bonding features. Moreover, we discuss steady state and time-resolved fluorescence data that aim at characterizing the excited-state dynamics of cyclovalone, and we compare its decay photophysics to that of curcumin. Finally, because during the characterization procedures we found evidence of very fast photodegradation of cyclovalone, its photostability in four organic solvents was studied by HPLC and the corresponding relative degradation rates were calculated.

Formulation and characterization of lyophilized curcumin solid dispersions for antimicrobial photodynamic therapy (aPDT): studies on curcumin and curcuminoids LII

CONTEXT

Bacterial resistance to antibiotics is increasing and alternative antibacterial treatments like antimicrobial photodynamic therapy (aPDT) are needed. Curcumin is under investigation as a potential photosensitizer in aPDT.

OBJECTIVE

The purpose of this study was to develop rapidly dissolving formulations of curcumin that could photoinactivate both Gram-positive and Gram-negative bacteria.

MATERIALS AND METHODS

Curcumin solid dispersions with methyl-β-cyclodextrin and hyaluronic acid (HA), hydroxypropyl methylcellulose (HPMC) or both HA and HPMC were prepared through lyophilization. The lyophilizates were characterized by curcumin drug load [% (w/w)], differential scanning calorimetry, photostability, thermal stability, their ability to form supersaturated solutions and by in vitro photoinactivation of Enterococcus faecalis and Escherichia coli.

RESULTS AND DISCUSSION

The lyophilizates were amorphous solid dispersions with a curcumin drug load in the range of 1.4-5.5% (w/w) depending on the included polymer and the ratio between curcumin and the cyclodextrin. The lyophilizates were photolabile, but thermally stable and dissolved rapidly in contact with water to form supersaturated solutions. Selected lyophilizates demonstrated >log 6 reduction of colony forming units/ml of both E. faecalis and E. coli after exposure to low curcumin concentrations (0.5-10 µM) and blue light dose (11-16 J/cm(2)). The high drug load of the lyophilizates, rapid dissolution, ability to form relatively stable supersaturated solutions and the very high phototoxicity towards both E. faecalis and E. coli make these lyophilizates suitable for in vivo aPDT.

CONCLUSIONS

This treatment with optimized curcumin formulations should be explored as an alternative to topical antibiotics in the treatment of wound infections.

Visible light is a better co-inducer of apoptosis for curcumin-treated human melanoma cells than UVA

Curcumin attracts worldwide scientific interest due to its anti-proliferative and apoptosis inducing effects on different tumor cells at concentrations ranging from 10 to 150 µM (3.7-55 µg/ml). Unfortunately, because of a low oral bioavailability, only low and pharmacologically ineffective serum levels are achievable. In this study, an alternative treatment concept consisting of low concentration curcumin (0.2-5 µg/ml) and irradiation with UVA or visible light (VL) has been tested. The experimental results show clearly that this treatment decreases the proliferation and the viability of human melanoma cells while the cell membrane integrity remains intact. We identified the onset of apoptosis characterized by typical markers such as active caspases 8, 9 and 3 as well as DNA fragmentation accompanied by the loss of cell adhesion. The mitochondrial apoptosis signaling pathway is predominant due to an early activation of caspase-9. The present data indicate a higher efficacy of a combination of curcumin and VL than curcumin and UVA. Reduced effects as a result of light absorption by heavily pigmented skin are unlikely if VL is used. These results indicate that a combination of curcumin and light irradiation may be a useful additional therapy in the treatment of malignant disease.

The influence of Pluronics® on dark cytotoxicity, photocytotoxicity, localization and uptake of curcumin in cancer cells: studies of curcumin and curcuminoids XLIX

In order to apply curcumin as a photosensitizer in photodynamic therapy (PDT) one needs a formulation that can solubilize and stabilize the compound. Pluronics® (Pluronic) are reported to both solubilize and stabilize curcumin against hydrolytic degradation. The aim of the present work was therefore to investigate the influence of Pluronic formulation on the photocytotoxicity of curcumin. Interactions between curcumin and Pluronics were investigated by fluorescence emission and absorption spectroscopy. Cell survival was measured with the MTT assay. The location of curcumin in the cells was investigated with fluorescence microscopy, and the cellular uptake was measured with fluorescence emission spectroscopy. Pluronics P123 and F127 in contrast to Pluronic P85 and PEG 400 may solubilize curcumin under non-cytotoxic conditions. An inverse relationship between the concentration of Pluronic and the photocytotoxicity of curcumin was observed. Curcumin could rapidly translocate across the cell membrane by passive diffusion. The fluorescence from curcumin in the cells (in the cytoplasm) after 1 hour of incubation was lowered by the presence of Pluronics in the formulation. However, the absolute amount of cell-bound curcumin after 1 hour of incubation was independent of the presence of Pluronics. Curcumin was bound more strongly to cells when incubated with formulations without Pluronics compared to cells incubated with curcumin formulations with Pluronics. Incubation of WiDr cells with curcumin for 6 hours resulted in lysosomal accumulation of curcumin independent of the presence of Pluronics. Lysosomally located curcumin could not be observed in HT1080 cells after 6 hours of incubation. The Pluronics P123 and F127 were found to be suitable for solubilizing and stabilizing curcumin, but inhibited photocytotoxic effects of curcumin unless the Pluronic concentration during treatment of the cells was less than 5-10× above the critical micellar concentration.

Curcumin: an orally bioavailable blocker of TNF and other pro-inflammatory biomarkers

TNFs are major mediators of inflammation and inflammation-related diseases, hence, the United States Food and Drug Administration (FDA) has approved the use of blockers of the cytokine, TNF-α, for the treatment of osteoarthritis, inflammatory bowel disease, psoriasis and ankylosis. These drugs include the chimeric TNF antibody (infliximab), humanized TNF-α antibody (Humira) and soluble TNF receptor-II (Enbrel) and are associated with a total cumulative market value of more than $20 billion a year. As well as being expensive ($15 000-20 000 per person per year), these drugs have to be injected and have enough adverse effects to be given a black label warning by the FDA. In the current report, we describe an alternative, curcumin (diferuloylmethane), a component of turmeric (Curcuma longa) that is very inexpensive, orally bioavailable and highly safe in humans, yet can block TNF-α action and production in in vitro models, in animal models and in humans. In addition, we provide evidence for curcumin's activities against all of the diseases for which TNF blockers are currently being used. Mechanisms by which curcumin inhibits the production and the cell signalling pathways activated by this cytokine are also discussed. With health-care costs and safety being major issues today, this golden spice may help provide the solution.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

Curcumin and its derivatives: their application in neuropharmacology and neuroscience in the 21st century

Curcumin (diferuloylmethane), a polyphenol extracted from the plant Curcuma longa, is widely used in Southeast Asia, China and India in food preparation and for medicinal purposes. Since the second half of the last century, this traditional medicine has attracted the attention of scientists from multiple disciplines to elucidate its pharmacological properties. Of significant interest is curcumin's role to treat neurodegenerative diseases including Alzheimer's disease (AD), and Parkinson's disease (PD) and malignancy. These diseases all share an inflammatory basis, involving increased cellular reactive oxygen species (ROS) accumulation and oxidative damage to lipids, nucleic acids and proteins. The therapeutic benefits of curcumin for these neurodegenerative diseases appear multifactorial via regulation of transcription factors, cytokines and enzymes associated with (Nuclear factor kappa beta) NFκB activity. This review describes the historical use of curcumin in medicine, its chemistry, stability and biological activities, including curcumin's anti-cancer, anti-microbial, anti-oxidant, and anti-inflammatory properties. The review further discusses the pharmacology of curcumin and provides new perspectives on its therapeutic potential and limitations. Especially, the review focuses in detail on the effectiveness of curcumin and its mechanism of actions in treating neurodegenerative diseases such as Alzheimer's and Parkinson's diseases and brain malignancies.

Excited-state dynamics of bis-dehydroxycurcumin carboxylic acid, a water-soluble derivative of the photosensitizer curcumin

Bis-dehydroxycurcumin carboxylic acid (K2A23) is a synthetic curcuminoid designed to exhibit enhanced water solubility and photosensitizing potential with respect to natural curcumin. In this work, the tendency of the compound to form intra- and intermolecular hydrogen bonds in the ground state is studied by UV-visible absorption and by nuclear magnetic resonance (NMR). The excited-state dynamics of the drug are probed in different environments by means of time-correlated single-photon counting measurements and related to its hydrogen bonding affinity in the excited state.

Susceptibility of clinical isolates of Candida to photodynamic effects of curcumin

BACKGROUND AND OBJECTIVE

The resistance of Candida species to antifungals represents a major challenge for therapeutic and prophylactic strategies. This study evaluated photodynamic therapy (PDT) mediated by Curcumin (CUR) against clinical isolates of C. albicans, C. tropicalis, and C. glabrata, both in planktonic and biofilm forms.

STUDY DESIGN/MATERIALS AND METHODS

Suspensions of Candida were treated with three CUR concentrations and exposed to four LED fluences. The protocol that showed the best outcomes for inactivation of the planktonic phase was selected to be evaluated against Candida biofilms. In addition, two higher CUR concentrations were tested. The metabolic activity of biofilms was evaluated by means of XTT reduction assay and the biofilm biomass was evaluated using crystal violet (CV) staining assay. Data were analyzed in a mixed model nested ANOVA, Wilcoxon's nonparametric tests, and the Kruskal-Wallis test (α = 5%).

RESULTS

The use of CUR in association with light was able to promote a significant antifungal effect against the planktonic form of the yeasts. When using 40 µM of CUR, the metabolic activity of C. albicans, C. glabrata, and C. tropicalis biofilms was reduced by 85%, 85%, and 73%, respectively, at 18 J/cm(2) . CUR-mediated PDT also decreased the biofilm biomass of all species evaluated. In addition, CV staining showed that C. albicans isolates were strong biofilm-forming strains, when compared with C. glabrata and C. tropicalis isolates.

CONCLUSION

The results from the present investigation showed that low CUR concentrations can be highly effective for inactivating Candida isolates when associated with light excitation.

Properties of lewis lung carcinoma cells surviving curcumin toxicity

The anti-inflammatory agent curcumin can selectively eliminate malignant rather than normal cells. The present study examined the effects of curcumin on the Lewis lung carcinoma (LLC) cell line and characterized a subpopulation surviving curcumin treatments. Cell density was measured after curcumin was applied at concentrations between 10 and 60 μM for 30 hours. Because of the high cell loss at 60 μM, this dose was chosen to select for surviving cells that were then used to establish a new cell line. The resulting line had approximately 20% slower growth than the original LLC cell line and based on ELISA contained less of two markers, NF-κB and ALDH1A, used to identify more aggressive cancer cells. We also injected cells from the original and surviving lines subcutaneously into syngeneic C57BL/6 mice and monitored tumor development over three weeks and found that the curcumin surviving-line remained tumorigenic. Because curcumin has been reported to kill cancer cells more effectively when administered with light, we examined this as a possible way of enhancing the efficacy of curcumin against LLC cells. When LLC cells were exposed to curcumin and light from a fluorescent lamp source, cell loss caused by 20 μM curcumin was enhanced by about 50%, supporting a therapeutic use of curcumin in combination with white light. This study is the first to characterize a curcumin-surviving subpopulation among lung cancer cells. It shows that curcumin at a high concentration either selects for an intrinsically less aggressive cell subpopulation or generates these cells. The findings further support a role for curcumin as an adjunct to traditional chemical or radiation therapy of lung and other cancers.

Curcumin nanoformulations: a future nanomedicine for cancer

Curcumin, a natural diphenolic compound derived from turmeric Curcuma longa, has proven to be a modulator of intracellular signaling pathways that control cancer cell growth, inflammation, invasion and apoptosis, revealing its anticancer potential. In this review, we focus on the design and development of nanoparticles, self-assemblies, nanogels, liposomes and complex fabrication for sustained and efficient curcumin delivery. We also discuss the anticancer applications and clinical benefits of nanocurcumin formulations. Only a few novel multifunctional and composite nanosystem strategies offer simultaneous therapy as well as imaging characteristics. We also summarize the challenges to developing curcumin delivery platforms and up-to-date solutions for improving curcumin bioavailability and anticancer potential for therapy.

Investigation of the photodynamic effects of curcumin against Candida albicans

This study describes the association of curcumin with light emitting diode (LED) for the inactivation of Candida albicans. Suspensions of Candida were treated with nine curcumin concentrations and exposed to LED at different fluences. The protocol that showed the best outcomes for Candida inactivation was selected to evaluate the effect of the preirradiation time (PIT) on photodynamic therapy (PDT) effectiveness, the uptake of curcumin by C. albicans cells and the possible involvement of singlet oxygen in the photodynamic action. Curcumin-mediated PDT was also assessed against biofilms. In addition to the microbiological experiments, similar protocols were tested on a macrophage cell line and the effect was evaluated by Methyltetrazolium assay (MTT) and SEM analysis. The optical properties of curcumin were investigated as a function of illumination fluence. When compared with the control group, a statistically significant reduction in C. albicans viability was observed after PDT (P < 0.05), for both planktonic and biofilm cultures. Photodynamic effect was greatly increased with the presence of curcumin in the surrounding media and the PIT of 20 min improved PDT effectiveness against biofilms. Although PDT was phototoxic to macrophages, the therapy was more effective in inactivating the yeast cell than the defense cell. The spectral changes showed a high photobleaching rate of curcumin.

Studies on curcumin and curcuminoids. XXXIX. Photophysical properties of bisdemethoxycurcumin

The steady-state absorption and fluorescence, as well as the time-resolved fluorescence properties of bisdemethoxycurcumin dissolved in several solvents differing in polarity and H-bonding capability were measured. The photodegradation quantum yield of the compound in acetonitrile and methanol was determined. The bisdemethoxycurcumin decay mechanisms from the S(1) state were discussed and compared with those of curcumin. The differences in S(1) dynamics observed between bisdemethoxy-curcumin and curcumin could be ascribed to a difference in H-bond acceptor/donor properties of the phenolic OH and a difference in strength of the intramolecular H-bond in the keto-enol moiety within the two molecules.