Photophysics of Hypericin and Hypocrellin A in Complex with Subcellular Components: Interactions with Human Serum Albumin

Photophysical properties of Radachlorin photosensitizer in solutions of different pH, viscosity and polarity

We present a thorough experimental investigation of fluorescence properties of Radachlorin photosensitizer in solutions of different acidity, viscosity and polarity. Experiments were performed using time-resolved fluorescence lifetime imaging and time-resolved analysis of polarized fluorescence. Variations of solution acidity resulted in considerable changes of Radachlorin fluorescence quantum yield and lifetime in the pH range from 4 to 7, but did not affect the rotational diffusion time, and almost did not change the quantum yield and characteristic times of singlet oxygen phosphorescence. Variations of solution polarity and viscosity were achieved by changing ethanol or methanol fraction in aqueous solution. The decrease of solution polarity resulted in nonlinear rise of Radachlorin fluorescence quantum yield and lifetime up to alcohol concentration of 50%-65%, as well as in considerable rise of singlet oxygen quantum yield and significant changes in characteristic times of its phosphorescence. Variations of solution viscosity resulted in changes of rotational diffusion time of Radachlorin molecules, which appeared to be in perfect correlation with methanol solution viscosity. Good correspondence with ethanol solution viscosity was observed only up to 50% alcohol fraction. Deviations of rotational diffusion time of Radachlorin molecules from direct proportionality with solution viscosity at higher ethanol concentrations were suggested to be due to different solvation conditions. The data obtained can give important reference points for analysis of microenvironment of Radachlorin molecules, their intracellular localization and performance in singlet oxygen generation.

Analysis of Radachlorin localization in living cells by fluorescence lifetime imaging microscopy

Intracellular localization of photosensitizer molecules is influential on cell death pathway at photodynamic treatment and is thus an important aspect in achieving enhanced efficacy of photodynamic therapy. In this paper we performed thorough studies of the distribution of Radachlorin photosensitizer in three established cell lines: HeLa, A549, and 3T3 with fluorescence lifetime imaging microscopy through the analysis of lifetime distributions. Experiments carried out in Radachlorin solutions in phosphate buffered saline revealed the pronounced dependence of the fluorescence quantum yield and lifetime on solution pH. This finding was used for analysis of lifetime images of living cells and their phasor plot representations and allowed us to suggest that Radachlorin localized predominantly in lysosomes, known to have acidic pH values. Experiments on co-localization of Radachlorin fluorescence lifetimes and LysoTracker fluorescence intensity supported this suggestion. The results obtained show that the inhomogeneity of fluorescence quantum yield within a cell can be significant due to lower pH values in lysosomes than in other intracellular compartments. This finding suggests that the actual amount of accumulated Radachlorin can be underestimated if being evaluated solely by comparison of fluorescence intensities.

Photoactivity of hypericin: from natural product to antifungal application

Considering the multifaceted and increasing application of photodynamic therapy (PDT), in recent years the antimicrobial employment of this therapy has been highlighted, because of the antiviral, antibacterial, antiparasitic, and antifungal activities that have already been demonstrated. In this context, research focussed on antimycological action, especially for treatment of superficial infections, presents promising growth due to the characteristics of these infections that facilitate PDT application as new therapeutic options are needed in the field of medical mycology. Among the more than one hundred classes of photosensitizers the antifungal action of hypericin (Hyp) stands out due to its ability to permeate the lipid membrane and accumulate in different cytoplasmic organelles of eukaryotic cells. In this review, we aim to provide a complete overview of the origin, physicochemical characteristics, and optimal alternative drug deliveries that promote the photodynamic action of Hyp (Hyp-PDT) against fungi. Furthermore, considering the lack of a methodological consensus, we intend to compile the best strategies to guide researchers in the antifungal application of Hyp-PDT. Overall, this review provides a future perspective of new studies and clinical possibilities for the advances of such a technique in the treatment of mycoses in humans.

Soluble Guanylate Cyclase Inhibitors Discovered among Natural Compounds

Soluble guanylate cyclase (sGC) is the human receptor of nitric oxide (NO) in numerous kinds of cells and produces the second messenger 3',5'-cyclic guanosine monophosphate (cGMP) upon NO binding to its heme. sGC is involved in many cell signaling pathways both under healthy conditions and under pathological conditions, such as angiogenesis associated with tumor growth. Addressing the selective inhibition of the NO/cGMP pathway is a strategy worthwhile to be investigated for slowing down tumoral angiogenesis or for curing vasoplegia. However, sGC inhibitors are lacking investigation. We have explored a chemical library of various natural compounds and have discovered inhibitors of sGC. The selected compounds were evaluated for their inhibition of purified sGC in vitro and sGC in endothelial cells. Six natural compounds, from various organisms, have IC₅₀ in the range 0.2-1.5 μM for inhibiting the NO-activated synthesis of cGMP by sGC, and selected compounds exhibit a quantified antiangiogenic activity using an endothelial cell line. These sGC inhibitors can be used directly as tools to investigate angiogenesis and cell signaling or as templates for drug design.

Biophysical Characterization and Anticancer Activities of Photosensitive Phytoanthraquinones Represented by Hypericin and Its Model Compounds

Photosensitive compounds found in herbs have been reported in recent years as having a variety of interesting medicinal and biological activities. In this review, we focus on photosensitizers such as hypericin and its model compounds emodin, quinizarin, and danthron, which have antiviral, antifungal, antineoplastic, and antitumor effects. They can be utilized as potential agents in photodynamic therapy, especially in photodynamic therapy (PDT) for cancer. We aimed to give a comprehensive summary of the physical and chemical properties of these interesting molecules, emphasizing their mechanism of action in relation to their different interactions with biomacromolecules, specifically with DNA.

Hypericin photodynamic activity in DPPC liposomes - part II: stability and application in melanoma B16-F10 cancer cells

Hypericin (Hyp) is considered a promising photosensitizer for Photodynamic Therapy (PDT), due to its high hydrophobicity, affinity for cell membranes, low toxicity and high photooxidation activity. In this study, Hyp photophysical properties and photodynamic activity against melanoma B16-F10 cells were optimized using DPPC liposomes (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) as a drug delivery system. This nanoparticle is used as a cell membrane biomimetic model and solubilizes hydrophobic drugs. Hyp oxygen singlet lifetime (τ) in DPPC was approximately two-fold larger than that in P-123 micelles (Pluronic™ surfactants), reflecting a more hydrophobic environment provided by the DPPC liposome. On the other hand, singlet oxygen quantum yield values (Φ_Δ¹O₂) in DPPC and P-123 were similar; Hyp molecules were preserved as monomers. The Hyp/DPPC liposome aqueous dispersion was stable during fluorescence emission and the liposome diameter remained stable for at least five days at 30 °C. However, the liposomes collapsed after the lyophilization/rehydration process, which was resolved by adding the lyoprotectant Trehalose to the liposome dispersion before lyophilization. Cell viability of the Hyp/DPPC formulation was assessed against healthy HaCat cells and high-metastatic melanoma B16-F10 cells. Hyp incorporated into the DPPC carrier presented a higher selectivity index than the Hyp sample previously solubilized in ethanol under the illumination effect. Moreover, the IC₅₀ was lower for Hyp in DPPC than for Hyp pre-solubilized in ethanol. These results indicate the potential of the formulation of Hyp/DPPC for future biomedical applications in PDT treatment.

Importance of Hypericin-Bcl2 interactions for biological effects at subcellular levels

Hypericin (Hyp) is a naturally occurring compound used as photosensitizer in photodynamic therapy and diagnosis. Recently, we have shown that Hyp presence alone, without illumination, resulted in substantial biological effects at several sub-cellular levels. Hyp induced changes in cellular ultrastructure, mitochondria function and metabolism, and distribution of Bcl2 proteins in malignant and non-malignant cells. The molecular mechanisms that underlie Hyp light-independent effects are still elusive. We have hypothesized that Bcl2-Hyp interactions might be one possible mechanism. We performed molecular docking studies to determine the Hyp-Bcl2 interaction profile. Based on the interaction profiles small Bcl2 peptide segments were selected for further study. We designed small peptides corresponding to Bcl2 BH3 and BH1 domains and tested the binding of Hyp and Bcl2 known inhibitor, ABT263, to the peptides in computer modeling and in vitro binding studies. We employed endogenous tryptophan and tyrosine in the BH3 and BH1 peptides, respectively, and their fluorescent properties to show interaction with Hyp and ABT263. Overall, our results indicate that Hyp can interact with Bcl2 protein at its BH3-BH1 hydrophobic groove, and this interaction may trigger changes in intracellular distribution of Bcl2 proteins. In addition, our computer modeling results suggest that Hyp also interacts with other anti-apoptotic members of Bcl2 family similar to the known BH3 mimetics. Our findings are novel and might contribute to understanding Hyp light-independent effects. In addition, they may substantiate the therapeutic use of Hyp as a BH3 mimetic molecule to enhance other cancer treatments.

A Hypericin Delivery System Based on Polydopamine Coated Cerium Oxide Nanorods for Targeted Photodynamic Therapy

Photodynamic therapy (PDT) as a non-aggressive therapy with fewer side effects has unique advantages over traditional treatments. However, PDT still has certain limitations in clinical applications, mainly because most photosensitizers utilized in PDT are hydrophobic compounds, which will self-aggregate in the aqueous phase and cause undesirable effects. In order to resolve this, we utilized the self-polymerization of dopamine molecules under alkaline conditions to coat cerium oxide nanorods (CeONR) with a dense polydopamine (PDA) film. Thereafter, thiolated galactose (Gal-SH) and hypericin (Hyp) were modified and loaded onto the surface to construct CeONR@PDA-Gal/Hyp, respectively, which can be used for targeted photodynamic therapy of human hepatoma HepG2 cells. CeONR@PDA-Gal/Hyp was characterized by transmission electron microscope (TEM), Zeta potential, Ultraviolet-visible (UV-Vis), and fluorescence spectroscopy, respectively. This hypericin delivery system possesses good biocompatibility and specific targeting ability, where the galactose units on the surface of CeONR@PDA-Gal/Hyp can specifically recognize the asialo-glycoprotein receptors (ASGP-R), which overexpress on HepG2 cell membrane. Furthermore, Hyp will detach from the surface of CeONR@PDA-Gal/Hyp after the nanorods enter cancer cells, and shows excellent PDT effect under the irradiation of light with a wavelength of 590 nm. Our work exemplifies a novel targeted delivery of hydrophobic photosensitizers for cancer treatment.

Hypericin-Apomyoglobin: An Enhanced Photosensitizer Complex for the Treatment of Tumor Cells

Bioavailability of photosensitizers for cancer photodynamic therapy is often hampered by their low solubility in water. Here, we overcome this issue by using the water-soluble protein apomyoglobin (apoMb) as a carrier for the photosensitizer hypericin (Hyp). The Hyp-apoMb complex is quickly uptaken by HeLa and PC3 cells at submicromolar concentrations. Fluorescence emission of Hyp-apoMb is exploited to localize the cellular distribution of the photosensitizer. The plasma membrane is rapidly and efficiently loaded, and fluorescence is observed in the cytoplasm only at later times and to a lesser extent. Comparison with cells loaded with Hyp alone demonstrates that the uptake of the photosensitizer without the protein carrier is a slower, less efficient process, that involves the whole cell structure without preferential accumulation at the plasma membrane. Cell viability assays demonstrate that the Hyp-apoMb exhibits superior performance over Hyp. Similar results were obtained using tumor spheroids as three-dimensional cell culture models.

Ultrafast dynamics of the antibiotic Rifampicin in solution

Ultrafast time-resolved studies demonstrate that intra- and intermolecular H-bonds with water molecules act synergistically to stabilize the active zwitterionic form of Rifampicin, an effective antibiotic against mycobacterial infections.

Structural and photodynamic properties of the anti-cancer drug irinotecan in aqueous solutions of different pHs

This work reports on photophysical studies of the irinotecan (IRT) anti-cancer drug in water solutions of different acidities (pH = 1.11-9.46). We found that IRT co-exists as mono-cationic (C1), di-cationic (C2), or neutral (N) forms. The population of each prototropic species depends on the pH of the solution. At pH = 1.11-3.01, the C1 and C2 structures are stabilized. At pH = 7.00, the most populated species is C1, while at pH values larger than 9.46 the N form is the most stable species. In the 1.11-2.61 pH range, the C1* emission is efficiently quenched by protons to give rise to the emission from C2*. The dynamic quenching constant, KD, is ∼32 M-1. While the diffusion governs the rate of excited-state proton-transfer (ESPT) under these conditions, the reaction rate increases with the proton concentration. A two-step diffusive Debye-Smoluchowski model was applied at pH = 1.11-2.61 to describe the protonation of C1*. The ESPT time constants derived for C1* are 382 and 1720 ps at pH = 1.11 and 1.95, respectively. We found that one proton species is involved in the protonation of C1* to give C2*, in the analyzed acidic pH range. Under alkaline conditions (pH = 9.46), the N form is the most stable structure of IRT. These results indicate the influence of the pH of the medium on the structural and dynamical properties of IRT in water solution. They may help to provide a better understanding on the relationship between the structure and biological activity of IRT.

Subdiffraction localization of a nanostructured photosensitizer in bacterial cells

Antibacterial treatments based on photosensitized production of reactive oxygen species is a promising approach to address local microbial infections. Given the small size of bacterial cells, identification of the sites of binding of the photosensitizing molecules is a difficult issue to address with conventional microscopy. We show that the excited state properties of the naturally occurring photosensitizer hypericin can be exploited to perform STED microscopy on bacteria incubated with the complex between hypericin and apomyoglobin, a self-assembled nanostructure that confers very good bioavailability to the photosensitizer. Hypericin fluorescence is mostly localized at the bacterial wall, and accumulates at the polar regions of the cell and at sites of cell wall growth. While these features are shared by Gram-negative and Gram-positive bacteria, only the latter are effectively photoinactivated by light exposure.

Binding interaction of hypocrellin B to myoglobin: a spectroscopic and computational study

Hypocrellin B (Hyp B), a perylenequinone naturally present in Hypocrella bambusae, is commonly used to treat a variety of diseases. Its versatile role in different biomedical applications necessitates a thorough investigation of its interaction with different biomolecules, particularly enzymes. To address this need, the binding mode of Hyp B to myoglobin (Mb) was studied using UV-visible absorption, emission, and synchronous fluorescence spectroscopies, as well as flexible docking simulations. Analyses of the absorbance and fluorescence data establish that Hyp B quenches tyrosine (Tyr) and tryptophan (Trp) fluorescence via the formation of two unique ground-state complexes on the surface of Mb, with one site being more energetically preferred than the other (the fraction of fluorophores accessible by Hyp B is 0.32). Molecular modeling simulations demonstrate preferential Hyp B binding at the Tyr103 site first, followed by the Trp7 site. In both cases, a ground-state complex is generated through H-bonding interaction between Hyp B and the respective residues, with the Tyr103 complex being more stable than that of the Trp7 complex. Synchronous fluorescence measurements indicate that the microenvironment surrounding Trp7 becomes more hydrophilic upon Hyp B interaction. This is evidenced by a red-shift of the band associated with this residue, while that of Tyr103 remains the same. Electrostatic potential surfaces reveal a more pronounced shift in electron density of Trp7 upon Hyp B binding compared to Tyr103. The binding constant of Hyp B to Mb is 1.21×10(5)M(-1), suggesting a relatively strong interaction between the ligand and enzyme.

Femtosecond Fluorescence Upconversion Investigations on the Excited-State Photophysics of Curcumin

The demonstration of curcumin as a photodynamic therapy agent has generated a high level of interest in understanding the photoinduced chemical and physical properties of this naturally occurring, yellow-orange medicinal compound. Important photophysical processes that may be related to photodynamic therapy effects including excited-state intramolecular hydrogen atom transfer (ESIHT) occur within the femtosecond to picosecond time scales. Femtosecond fluorescence upconversion spectroscopy has sufficient time resolution to resolve and investigate these important photophysical processes. In this review, recent advances in using femtosecond fluorescence upconversion to reveal ultrafast solvation and ESIHT of curcumin are presented. The excited-state photophysics of curcumin has been investigated in alcohols and micellar solutions. The results of curcumin in methanol and ethylene glycol reveal the presence of two decay components in the excited-state kinetics with time scales of 12–20 ps and ∼100 ps. Similarly, in a micellar solution, biphasic kinetics are present with the fast decay component having a time constant of 3–8 ps, the slow decay component 50–80 ps. Deuteration of curcumin in both media leads to a pronounced isotope effect in the slow decay component, which suggests that ESIHT is an important photophysical process on this time scale. The results of multiwavelength fluorescence upconversion studies show that the fast component in the excited-state kinetics is due to ultrafast solvation. These advances form a part of the continuing efforts to elucidate the photodynamic therapy properties of curcumin.

Study of interaction of hypericin and its pharmaceutical preparation by fluorescence techniques

We report the detection of interactions between a photosensitizer, hypericin (HY), and its solvent system prepared with a formulation additive, polyvinylpyrrolidone (PVP), a commonly used pharmaceutical excipient. Fluorescence correlation spectroscopy (FCS) and fluorescence lifetime imaging microscopy (FLIM) were used to study aggregation and binding of HY in the presence of PVP. Digitized fluorescence endoscopic imaging (DFEI) was used to study the effect of the pharmaceutical formulation in the in vivo tumor implanted chick chorioallantoic membrane (CAM) model. The results presented reveal the coordination of HY-PVP binding, HY disaggregation in the presence of PVP, and strengthened HY tumor uptake selectivity. PVP is thus suggested as a potential adjuvant to previously investigated N-methyl pyrrolidone (NMP) in the HY delivery system as well as a replacement for the conventionally used albumin in the HY bladder instillation fluids preparation for clinical use.

Accumulation and interaction of hypericin in low-density lipoprotein--a photophysical study

The accumulation and interaction of hypericin with the biologically important macromolecule, low-density lipoprotein (LDL), is investigated using various steady-state and time-resolved fluorescence measurements. It is concluded that multiple hypericins can penetrate considerably deeply into the LDL molecule. Up to approximately 20 nonaggregated hypericin molecules can enter LDL; but upon increasing the hypericin concentration, the fluorescence lifetime of hypericin decreases drastically, suggesting most likely the self-quenching of aggregated hypericin. There is also evidence of energy transfer from tryptophans of the constituent protein, apoB-100, to hypericin in LDL. The results demonstrate the ability of LDL to solubilize hypericin (a known photosensitizer) in nonaggregated form, which has implications for the construction of drug delivery systems.

Target Analysis of Primary Photoprocesses Involved in the Oxyblepharismin-Binding Protein

Target analysis is performed on previously published transient absorption spectra of the 200-kDa oxyblepharismin-binding protein (OBIP) thought to trigger the photophobic response of the ciliate Blepharisma japonicum. The OBIP sample is considered as heterogeneous and made of two distinct classes of chromophore-protein complexes. A so-called nonreactive class is seen to be comparable to free oxyblepharismin in organic solution. Another, reactive, class is shown to undergo a fast picosecond photocycle involving the formation in 4 ps of an intermediate state noted Y1. The spectrum associated to Y1 bears striking similarities with that of the oxyblepharismin radical cation. This element favors the hypothesis that an excited-state intermolecular electron-transfer could be the primary step of the sensory transduction chain of B. japonicum. Proton release is also considered as a possible secondary step. These possibilities support the idea that reactive OBIP functions like an electron or proton pump. We alternatively propose a new hypothesis stating that the fast photocycle of reactive OBIP actually does not generate any photoproduct or protein change of conformation but is involved in another biological function. It would act as a kind of solar screen, providing additional protection to the light-adapted form of B. japonicum in case of excessive illumination.

Recognition of various biomolecules by the environment-sensitive spectral responses of hypocrellin B

In this work, the spectral responses of hypocrellin B (HB) to the microenvironments of various biomolecules were studied, with human serum albumin (HSA), bovine serum albumin (BSA) and ovalbumin (OVA) used as the models for proteins, sodium alginate (SOA) and hyaluronan (HYA) for polysaccharides and liposomes for lipid membranes. Generally, compared to those in aqueous solution, the absorbance and fluorescence of HB were all strengthened in the model systems except for the fluorescence in HYA. Specially, according to the spectral responses of HB, the microenvironments in biomolecules and liposomes could be set in a sequence of hydrophobic grades, i.e., liposomes > proteins > polysaccharides. Further, R(F/A), a parameter defined as the ratio of the fluorescence intensity to the absorbance, was proposed to identify the microenvironment quantitatively. It was found that the R(F/A) could not only distinguish various types of biomolecules but also identify specific binding from nonspecific binding to proteins or polysaccharides.

Comparative analysis of naphthodianthrone and phloroglucine derivatives in St. John's Wort extracts by near infrared spectroscopy, high-performance liquid chromatography and capillary electrophoresis

A near infrared spectroscopic (NIRS) method is established for quantitative determination of naphthodianthrones and phloroglucine derivatives in St. John's Wort extracts. The validated NIRS method is compared with optimised liquid chromatography (LC) and capillary electrophoresis (CE), applying UV as a detection tool. Optimisation of stationary and mobile phase conditions in reversed-phase liquid chromatography (RP-LC) allow separating the derivatives of interest with high peak symmetry and robustness. Elution takes 15 and 25 min on non-porous or porous silica C18 with different porosities, respectively. Capillary electrophoresis (CE) is used for cross-validation of RP-LC. CE enables baseline separation of hypericine and pseudohypericine in less than 2min, but is ten times less sensitive. The validated RP-LC is chosen as a reference method for calibration of the NIRS-system. Analysis of 80 St. John's Wort extracts (320 NIR spectra) and the subsequent chemometric calculations of the best regression model show that NIRS is suitable for analysis of hypericine, pseudohypericine and hyperforine. RP-LC or CE must be employed for the other remaining lower concentrated naphthodianthrone and phloroglucine derivatives. Hypericine and hyperforine are analysed via NIRS with a standard error of estimation (SEE) of 0.52 and 0.50 microg mL(-1) and standard error of prediction (SEP) of 0.64 and 0.71 microg mL(-1) within few seconds. The current study demonstrates the suitability of NIRS as an alternative to LC and CE for St. John's Wort producing phytopharmaceutical industry. The short analysis time of few seconds' assures high sample throughput in routine analysis.

Fluorescence imaging and phototoxicity effects of new formulation of chlorin e6–polyvinylpyrrolidone

Evaluations of the efficiency of a new formulation of chlorin consisting of a complex of trisodium salt chlorin e6 (Ce6) and polyvinylpyrrolidone (PVP) in photodynamic therapy (PDT) and fluorescence diagnosis was performed on poorly differentiated human bladder carcinoma murine model with the following specific aims: (i) to qualitatively evaluate the fluorescence accumulation in human bladder tumor, (ii) to determine fluorescence distribution of Ce6-PVP using the tissue extraction technique and fluorescence imaging technique, (iii) to compare the fluorescence distribution of Ce6, Ce6-PVP and Photofrin in skin of nude mice, and (iv) to investigate phototoxicity caused by different parameters (drug-light interval, drug dose, irradiation fluence rate and total light fluence) in PDT. The fluorescence of the Ce6-PVP formulation was determined either by fluorescence imaging measurements or by chemical extraction from the tissues displaying similar trends of distribution. Our results demonstrated that the Ce6-PVP formulation possesses less in vivo phototoxic effect compared to Ce6 alone. The phototoxicity revealed a strong dependence on the drug and light dosimetry as well as on the drug-light interval. In PDT, the Ce6-PVP compound was most toxic at the 1h drug-light interval at 200J/cm(2), while Ce6 alone was most toxic at a light dose of more that 50J/cm(2) at the 1 and 3h drug-light interval. We also confirmed that Ce6-PVP has a faster clearance compared to Ce6 alone or Photofrin. This eliminates the need for long-term photosensitivity precautions. In conclusion, the Ce6-PVP formulation seems to be a promising photosensitizer for fluorescence imaging as well as for photodynamic treatment.