Photosensitisation and photoinduced DNA cleavage by four naturally occurring anthraquinones

Effect of Substituents on the Photodynamic Action of Anthraquinones: EPR, Computational and In Vitro Studies

Anthraquinone class of compounds possesses a broad spectrum of therapeutic applications. Cancer cell targeting ability, together with photogeneration of reactive oxygen species, renders anthraquinones an interesting class of photosensitizers for photodynamic therapy (PDT). Screening of newer compounds for better singlet oxygen generation is of current interest to improve the practical usability in PDT. In this study, we investigate the photodynamic activity of nine commercially available anthraquinones, using EPR spectroscopy and computational techniques, to identify the role of substituents on singlet oxygen yield. Three anthraquinone derivatives, 1,5-diaminoanthraquinone, 15-dihydroxyanthraquinone and 1,2,7-trihydroxyanthraquinone, showed highest singlet oxygen quantum yield (0.21, 0.18 and 0.15, respectively) relative to Rose Bengal. Time-dependent density functional theory calculations indicate the singlet oxygen quantum yield of anthraquinones inversely correlate well with the excited singlet-triplet (S1-T1) energy gap. Electron-donating substituents present at positions 1, 2 and 5 of anthraquinone seem to reduce the S1-T1 energy gap, facilitating inter-system crossing and the production of singlet oxygen. This would greatly aid in the design of newer anthraquinone-based photosensitizers. This study also highlights the suitability of 1,5-diaminoanthraquinone for PDT applications as demonstrated by in vitro experiments of photoinduced DNA cleavage and photocytotoxicity in Dalton's lymphoma ascites.

Health functions and structure-activity relationships of natural anthraquinones from plants

Anthraquinone compounds with the anthraquinone ring structure are widely found in traditional Chinese medicines and they are attracting a lot of attention due to their good pharmacological activity. Diversities of anthraquinones depend on their chemical structures, such as the number of anthraquinone rings and the substituents; what's more, the difference in chemical structure determines the difference in physiological activity. Based on results of previous studies, this review summarizes several natural anthraquinones identified from Chinese herbal medicines and their physiological activities including anti-cancer, anti-pathogenic microorganisms, anti-inflammatory, anti-oxidation, anti-osteoporosis, anti-depression, and anti-constipation. The source, effect, model, and action mechanism of the active anthraquinones are described in detail, from which their structure-activity relationship is summarized. By analyzing the relationship between anthraquinone structure and function, we found that, on the whole structure, the anthraquinone ring and anthraquinone glycosides have significant anticancer activity and anti-constipation activity, while for their substituents, anthraquinones substituted by alizarin have significant antioxidant activity and the polarity of the substituents is closely related to their antibacterial activities.

A Review of the Botany, Phytochemistry, Pharmacology and Toxicology of Rubiae Radix et Rhizoma

Rubia cordifolia Linn (Rubiaceae) is a climbing perennial herbal plant, which is widely distributed in China and India. Its root and rhizome, Rubiae Radix et Rhizoma (called Qiancao in China and Indian madder in India), is a well known phytomedicine used for hematemesis, epistaxis, flooding, spotting, traumatic bleeding, amenorrhea caused by obstruction, joint impediment pain, swelling and pain caused by injuries from falls. In addition, it is a kind of pigment utilized as a food additive and a dye for wool or fiber. This review mainly concentrates on studies of the botany, phytochemistry, pharmacology and toxicology of this Traditional Chinese Medicine. The phytochemical evidences indicated that over a hundred chemical components have been found and isolated from the medicine, such as anthraquinones, naphthoquinones, triterpenoids, cyclic hexapeptides and others. These components are considered responsible for the various bioactivities of the herbal drug, including anti-oxidation, anti-inflammation, immunomodulation, antitumor, effects on coagulation-fibrinolysis system, neuroprotection and other effects. Additionally, based on these existing results, we also propose some interesting future research directions. Consequently, this review should help us to more comprehensively understand and to more fully utilize the herbal medicine Rubiae Radix et Rhizoma.

A multi-photoresponsive supramolecular hydrogel with dual-color fluorescence and dual-modal photodynamic action

We have developed an engineered supramolecular hydrogel, formed in the absence of any toxic solvents or reagents, by the self-assembly of four different components: a poly-β-cyclodextrin polymer, a hydrophobically modified dextran, a commercial zinc phthalocyanine and a tailored nitric oxide photodonor. The formation of this supramolecular assembly is based on a "lock-and-key" mechanism in which the alkyl side chains of the modified dextran form inclusion complexes with the cyclodextrin cavities of the poly-β-cyclodextrin polymer. The multivalent character of the interactions between all the components ensures the stability of the hydrogel and the negligible leaching of the photoactive components from the gel network under physiological conditions, even in the absence of protective coating agents. The combination of steady-state and time-resolved spectroscopic techniques together with photoamperometric measurements shows that the two chromo-fluorogenic components do not interfere with each other while being enclosed in their supramolecular matrix and can thus be operated in parallel under the control of light stimuli. Specifically, excitation with visible light results in the red and green fluorescence emission typical of the two photoactive centers and in their capability to generate singlet oxygen and nitric oxide, two cytotoxic species playing a key role in photodynamic cancer and bacterial therapies.

Metal-mediated DNA damage and cell death: mechanisms, detection methods, and cellular consequences

Metal ions cause various types of DNA damage by multiple mechanisms, and this damage is a primary cause of cell death and disease.

Simultaneous preconcentration and analysis of anthraquinones based on ultrasound emulsification ionic liquid microextraction

An ultrasensitive method of ultrasound emulsification ionic liquid microextraction (UEILME) coupled with high-performance liquid chromatography (HPLC) has been developed and introduced for the preconcentration and analysis of anthraquinone additives in cosmetic samples and five anthraquinone compounds (aloe-emodin, rhein, emodin, chrysophanol and physcion) in traditional Chinese medicines. Several parameters affecting the extraction efficiency were investigated and optimized, such as the type and amount of extraction solvent, sample pH, ultrasound time and temperature, centrifugation speed and time and ionic strength. The most favorable results were obtained using 60 mg of 1-hexyl-3-methylimidazolium hexafluorophosphate as extraction solvent. The anthraquinones were extracted from the aqueous solution (pH 2.0) by ultrasound at 40°C for 7 min and centrifuged at 2,500 rpm for 6 min. Under optimal conditions, acceptable linearity of the five anthraquinone compounds was obtained with correlation coefficients > 0.99. The limits of detection (LODs) and limits of quantitation (LOQs) ranged from 0.01 to 0.09 µg/L and 0.05 to 0.25 µg/L, respectively. The relative standard deviations (n = 3) were less than 9.8%. Moreover, the enrichment factors ranged from 80 to 197-fold. Compared with conventional dispersive liquid-liquid microextraction, the UEILME technique exhibited lower LODs and LOQs. The results demonstrated that the UEILME coupled with HPLC is a simple, environmentally friendly, sensitive and efficient method for the extraction, concentration and analysis of anthraquinone compounds.

Toxic effects of anthraquinone and phenanthrenequinone upon Scenedesmus strains (green algae) at low and elevated concentration of CO2

Short-term (24h) experiments were performed to examine the effect of anthraquinone (ANTQ) and phenanthrenequinone (PHEQ) on two Scenedesmus armatus strains (B1-76 and 276-4d) grown in a batch culture system aerated with CO2 at a low (0.1%) or elevated (2%) concentration. ANTQ at concentrations within the range of 0.156-1.250 mg dm-3 inhibited the growth of B1-76 population in a concentration-dependent manner, and calculated EC50 for low-CO2 cells was 0.56 mg dm-3. The toxic effect of ANTQ on this strain was more pronounced in high-CO2 cells, where not only growth but also photosynthesis, respiration and SOD activity were significantly inhibited. In contrast, except for SOD activity, no ANTQ effects on strain 276-4d were found. PHEQ at concentrations within the range of 0.063-0.125 mg dm-3 inhibited the growth of B1-76 population in a concentration-dependent manner. The value of EC50 for low-CO2 B1-76 cells was 0.10 mg dm-3. PHEQ inhibited the growth of both strains regardless of CO2 concentration. In B1-76 cells affected by PHEQ, inhibition of photosynthesis was independent of the CO2 level, whereas the SOD activity was much higher in cultures aerated with 2% than with 0.1% CO2. Higher toxicity of PHEQ to strain 276-4d grown at 2% CO2 was accompanied by strong inhibition of photosynthesis, while in low-CO2 cells this process was slightly stimulated. The SOD activity in both low- and high-CO2 cells of strain 276-4d treated with PHEQ was 2-3 times higher compared with the controls. The pattern of SOD isoforms (PAGE analysis) obtained from cells exposed to ANTQ or PHEQ did not change compared with the controls, but the location of the SOD isoforms bands on gel was affected by the concentration of CO2. The results suggest that the strain-specific toxicity of ANTQ and PHEQ may result from oxidative stress. In addition, carbon dioxide appears to play an important role in the toxicity of quinones to algae.