Photo-ionization and photo-excitation of curcumin investigated by laser flash photolysis

Predicting pKa Values of Para-Substituted Aniline Radical Cations vs. Stable Anilinium Ions in Aqueous Media

The focus of pKa calculations has primarily been on stable molecules, with limited studies comparing radical cations and stable cations. In this study, we comprehensively investigate models with implicit solvent and explicit water molecules, direct and indirect calculation approaches, as well as methods for calculating free energy, solvation energy, and quasi-harmonic oscillator approximation for para-substituted aniline radical cations (R-PhNH2•+) and anilinium cations (R-PhNH3+) in the aqueous phase. Properly including and positioning explicit H2O molecules in the models is important for reliable pKa predictions. For R-PhNH2•+, precise pKa values were obtained using models with one or two explicit H2O molecules, resulting in a root mean square error (RMSE) of 0.563 and 0.384, respectively, for both the CBS-QB3 and M062X(D3)/ma-def2QZVP methods. Further improvement was achieved by adding H2O near oxygen-containing substituents, leading to the lowest RMSE of 0.310. Predicting pKa values for R-PhNH3+ was more challenging. CBS-QB3 provided an RMSE of 0.349 and the M062X(D3)/ma-def2QZVP method failed to calculate pKa accurately (RMSE > 1). However, by adopting the double-hybrid functional method and adding H2O near the R substituent group, the calculations were significantly improved with an average absolute difference (ΔpKa) of 0.357 between the calculated and experimental pKa values. Our study offers efficient and reliable methods for pKa calculations of R-PhNH2•+ (especially) and R-PhNH3+ based on currently mature quantum chemistry software.

Shedding light on curcumin stability

The stability of molecular curcumin (purcumin, 1a) in solution is strongly light-dependent. Under laboratory artificial light, a relative stability is observed only at neutral pH, while more intense light and/or solar light can trigger degradation via a combination of hydrolytic and oxidative fragmentation of the heptadiendione moiety. Minor curcuminoids in commercial curcumin (purcuminoids) can improve the stability of molecular curcumin, but only under conditions of low irradiation. While confirming earlier observations alerting to the instability of purcumin, our results provide new rationales for unexplained differences between previous studies, question the biological relevance of a non-enzymatic degradation for the bioactivity profiles that have been reported for purcumin, and highlight the need of a better characterization of the degradation of purcuminoids under visible light irradiation.

Treatment of breast cancer in vivo by dual photodynamic and photothermal approaches with the aid of curcumin photosensitizer and magnetic nanoparticles

Breast cancer is a neoplastic disease with a high mortality rate among women. Recently, photodynamic therapy (PDT) and photothermal therapy (PTT) attracted considerable attention because of their minimal invasiveness. The PTT approach works based on hyperthermia generation, and PDT approach employs laser irradiation to activate a reagent named photosensitizer. Therefore, in the current paper, a dual-functioned nanocomposite (NC) was designed for the treatment of breast cancer model in Balb/c mice with the combination of photodynamic and photothermal approaches. Transmission electron microscopy, UV-visible spectroscopy, FTIR, and XRD were employed to validate the nanostructure and silica coating and curcumin (CUR) immobilization on the Fe3O4 nanoparticles. The effect of Fe3O4/SiO2-CUR combined with PDT and PTT was assessed in vivo on the breast tumor mice model, and immunohistochemistry (IHC) was employed to evaluate the expression of apoptotic Bax and Caspase3 proteins. The TEM images, UV-visible absorption, and FTIR spectra demonstrated the successful immobilization of curcumin molecules on the surface of Fe3O4/SiO2. Also, MTT assay confirmed the nontoxic nature of Fe3O4/SiO2 nanoparticles in vitro. In the breast tumor mice model, we have assessed six treatment groups, including control, CUR + PDT, Blue + NIR (near-infrared) lasers, NC, NC + PTT, and NC + PDT + PTT. The tumor volume in the NC + PDT + PTT group showed a significant reduction compared to other groups (p < 0.05). More interestingly, the tumor volume of NC + PDT + PTT group showed a 27% decrease compared to its initial amount. It should be noted that no detectable weight loss or adverse effects on the vital organs was observed due to the treatments. Additionally, the IHC data represented that the expression of proapoptotic Bax and Caspase3 proteins were significantly higher in the NC + PDT + PTT group compared to the control group, indicative of apoptosis. To conclude, our data supported the fact that the NC + PDT + PTT strategy might hold a promising substitute for chemotherapy for the treatment of triple-negative breast cancers.

Enhanced photosensitizing properties of protein bound curcumin

AIMS

The naturally occurring compound curcumin has been proposed for a number of pharmacological applications. In spite of the promising chemotherapeutic properties of the molecule, the use of curcumin has been largely limited by its chemical instability in water. In this work, we propose the use of water soluble proteins to overcome this issue in perspective applications to photodynamic therapy of tumors.

MATERIALS AND METHODS

Curcumin was bound to bovine serum albumin and its photophysical properties was studied as well as its effect on cell viability after light exposure through MTT assay and confocal imaging.

KEY FINDINGS

Bovine serum albumin binds curcumin with moderate affinity and solubilizes the hydrophobic compound preserving its photophysical properties for several hours. Cell viability assays demonstrate that when bound to serum albumin, curcumin is an effective photosensitizer for HeLa cells, with better performance than curcumin alone. Confocal fluorescence imaging reveals that when curcumin is delivered alone, it preferentially associates with mitochondria, whereas curcumin bound to bovine serum albumin is found in additional locations within the cell, a fact that may be related to the higher phototoxicity observed in this case.

SIGNIFICANCE

The higher bioavailability of the photosensitizing compound curcumin when bound to serum albumin may be exploited to increase the efficiency of the drug in photodynamic therapy of tumors.

Comparison of different laser-based photochemical systems for periodontal treatment

PURPOSE

The main aim in periodontitis treatment is to remove supragingival and subgingival biofilm. Mechanical treatment to eliminate pathogenic bacteria is limited by morphological conditions on the root surface. This study assessed the antibacterial effectiveness of different laser-based photochemical systems, particularly a novel curcumin-based option.

METHODS

Ninety-one titanium bars were inoculated with an artificial biofilm of common pathogenic periodontal bacteria and inserted into an artificial periodontal pocket model. The following groups (n = 13) were tested: 1, curcumin solution plus SLB laser irradiation (C + L; 445 nm, 0.6 W, 25% duty cycle, 100 Hz, 10 s); 2, curcumin solution (Cur); 3, dimethyl sulfoxide solution (DMSO); 4, SiroLaser Blue (SLB) - laser irradiation (445 nm, 0.6 W, 25% duty cycle, 100 Hz, 10 s); 5, antimicrobial photodynamic therapy (aPDT); 6, antimicrobial photothermal therapy (aPTT); 7, control. The samples were stored in Eppendorf tubes and analyzed microbiologically using quantitative real-time polymerase chain reaction (PCR). The main parameter for analyzing group differences was the total bacterial load. Statistical analysis was performed with nonparametric methods.

RESULTS

Statistically significant reductions in bacterial count were observed in all experimental groups (p < 0.05). The mean percentage reductions were as follows: SLB, 95.03%; aPDT, 83.91%; DMSO, 95.69%; C + L, 97.15%. No statistically significant differences in bacteria reduction were observed for laser alone (SLB), DMSO, or curcumin with or without additional laser irradiation.

CONCLUSIONS

The greatest antibacterial efficacy was observed in samples treated with aPTT. Using curcumin as a photosensitizing agent for 445 nm laser irradiation did not result in improved antibacterial effectiveness in comparison with laser alone.

Effects of LED-Based photodynamic therapy using red and blue lights, with natural hydrophobic photosensitizers on human glioma cell line

Photodynamic therapy (PDT) has received high attention in cancer treatment due to its minimal side effects, specific cancer-targeting, non-invasion and low cost. It utilizes a specific group of anti-cancer drugs called photosensitizers (PS), which can be only activated under a certain wavelength light illumination and kills cancer cells. To screen the potential of PS and setup of PDT treatment protocol, it is essential to assess the PDT efficacy in vitro. In this study, a light-emitting diode- (LED-) based illumination system at two wavelengths (red & blue) with homogeneous and stable irradiation, and constant temperature conditions in 96-well plates was provided. The photodynamic effect of curcumin (CUR) and methyl ester of 5-aminolevulinic acid (MAL) using LED light on human glioma cell line was investigated. The obtained results indicate that this homemade LED-based illumination system is a favorable light source for in vitro PDT in 96-well plates. The PDT using CUR and MAL was efficient at final concentrations of 25μM and 2mM, and light doses of 60J/cm² and 40J/cm² respectively. The blue PDT efficiency was dependent on the light and PS doses. MAL-PDT and CUR-PDT using blue LED significantly decreased cell viability in the treatment groups compared with control groups. Furthermore, MAL-PDT using blue LEDs was more effective in comparison with conventional red LEDs on the human glioma cell line.

Transient spectra study on photo-dynamics of curcumin

A novel mechanism of DNA damage induced by photosensitized curcumin (Cur) was explored using laser flash photolysis, pulse radiolysis and gel electrophoresis. Cur neutral radical (Cur) was confirmed as an identical product in photo-sensitization of Cur by laser flash photolysis and pulse radiolysis. A series of reaction rate constants between Cur and nucleic acid bases/nucleotides were determined by pulse radiolysis. Gel electrophoresis was carried out to investigate damage induced by photosensitized Cur to biologically active DNA. The results indicate that the damage to DNA may be caused by Cur produced from the photosensitization of Cur.

The triplet state of tanshinone I and its synergic effect on the phototherapy of cancer cells with curcumin

The excited triplet state of tanshinone I (Tan I) extracted from the traditional Chinese medicine Salvia miltiorrhiza Bunge was characterized by laser flash photolysis. The synergic effect of Tan I on the phototherapy of cancer cells with curcumin (Cur) was also investigated by MTT assay because the excited energy transfer from the triplet state of Tan I ((3)Tan I(∗)) to Cur occurred. At the same time, the characteristic absorption spectra of (3)Tan I(∗) were recorded, and its molar absorption coefficient and rate constants for several excited energy transfers were obtained. The photo-therapeutic effect of Cur is enhanced by combination with Tan I.

A new role of curcumin: as a multicolor photoinitiator for polymer fabrication under household UV to red LED bulbs

Curcumin can act as a multicolor photoinitiator in free radical photopolymerization under air upon exposure to household LED bulbs.