Photosensitization of aqueous model systems by hypericin

Advanced theranostic nanoplatforms for hypericin delivery in the cancer treatment

Biomodified coated-lipid vesicles were obtained using the DPPC lipid (L) and F127 copolymer linked covalently with spermine (SN), biotin (BT), and folic acid (FA), resulting in LF127-SN, LF127-BT, and LF127-FA nanoplatforms. The photosensitizer hypericin (HY) was incorporated into the nanosystem by a thin-film method and characterized by dynamic light scattering, zeta potential, encapsulation efficiency, and transmission electronic microscopy. The results provided a good level of stability for all nanoplatforms for at least 5 days as an aqueous dispersion. The in vitro serum stability showed that the HY-loaded LF127-SN has a lower tendency to form complexes with BSA protein than with its analogs. LF127-SN was the most stable HY formulation, followed by LF127-BT and LF127-FA, confirmed by the association constant (Kd) values: 600 μmol L-1, 1100 μmol L-1, 515 μmol L-1, and 378 μmol L-1 for LF127, LF127 FA, LF127-BT, and LF127-SN, respectively. The photodynamic potential of HY was accessed by cytotoxicity assays using Caco-2, B16-F10, L-929, and HaCat cells. HY-loaded LF127-SN revealed a significant increase in the selectivity compared to other nanoplatforms. HY-loaded in LF127-BT and LF127-SN showed distinct uptake and biodistribution after 2 h of intravenous application. All biomodified coated-lipids showed satisfactory metabolism within 72 h after application, without significant accumulation or residue in any vital organ. These results suggest that incorporating HY-loaded in these nanosystems may be a promising strategy for future applications, even with a small amount of binders to the coating copolymer (0.02% w/v). Furthermore, these results indicate that the LF127-SN showed remarkable superiority compared to other evaluated systems, being the most distinct for future photodynamic therapy and theranostic applications.

Intestinal permeability and gut microbiota interactions of pharmacologically active compounds in valerian and St. John's wort

Phytomedicines such as valerian and St. John's wort are widely used for the treatment of sleeping disorders, anxiety and mild depression. They are perceived as safe alternatives to synthetic drugs, but limited information is available on the intestinal absorption and interaction with human intestinal microbiota of pharmacologically relevant constituents valerenic acid in valerian, and hyperforin and hypericin in St. John's wort. The intestinal permeability of these compounds and the antidepressant and anxiolytic drugs citalopram and diazepam was investigated in the Caco-2 cell model with bidirectional transport experiments. In addition, interaction of compounds and herbal extracts with intestinal microbiota was evaluated in artificial human gut microbiota. Microbiota-mediated metabolisation of compounds was assessed, and bacterial viability and short-chain fatty acids (SCFA) production were measured in the presence of compounds or herbal extracts. Valerenic acid and hyperforin were highly permeable in Caco-2 cell monolayers. Hypericin showed low-to-moderate permeability. An active transport process was potentially involved in the transfer of valerenic acid. Hyperforin and hypericin were mainly transported through passive transcellular diffusion. All compounds were not metabolized over 24 h in the artificial gut microbiota. Microbial SCFA production and bacterial viability was not substantially impaired nor promoted by exposure to the compounds or herbal extracts.

Natural antioxidants in the management of Parkinson's disease: Review of evidence from cell line and animal models

Parkinson's disease (PD) is a chronic progressive neurodegenerative disease. It results from the death of dopaminergic neurons. The pathophysiological mechanisms in idiopathic PD include the production of α-synuclein and mitochondrial respiratory function-affecting complex I, caused by reactive oxygen species. Therefore, the use of natural antioxidants in PD may provide an alternative therapy that prevents oxidative stress and reduces disease progression. In this review, the effects of hydroxytyrosol, Ginkgo biloba, Withania somnifera, curcumin, green tea, and Hypericum perforatum in PD animal and cell line models are compared and discussed. The reviewed antioxidants show evidence of protecting neural cells from oxidative stress in animal and cell models of PD. However, the clinical efficacy of these phytochemicals needs to be optimised and further investigated.

Hypericin photodynamic activity in DPPC liposome. PART I: biomimetism of loading, location, interactions and thermodynamic properties

Hypericin (Hyp) is a potential photosensitizer drug for Photodynamic Therapy (PDT). However, the high lipophilicity of Hyp prevents its preparation in water. To overcome the Hyp solubility problem, this study uses the liposomal vesicle of DPPC. Otherwise liposome is also one of the most employed artificial systems that mimetizes cell membranes. Our present focus is the interaction of Hyp into DPPC liposome as biomimetic system. We studied the loading, interaction, and localization of Hyp (2.8 μmol L^-1) in DPPC (5.4 mmol L^-1) liposomes, as well as the thermodynamic aspects of Hyp-liposomes. The Hyp addition to the DPPC liposome dispersion showed a Encapsulation Efficiency for [Hyp] = 2.8 μmol L^-1 in [DPPC] = 5.3 mmol L^-1 of 74.3% and 89.3% at 30.0 and 50.0 °C, respectively. The encapsulation profile obeys a pseudo first-order kinetic law, with a rate constant of 1.26 × 10^-3 s^-1 at 30.0 °C. Also the data suggests this reaction is preceded by an extremely rapid step. A study on the binding of Hyp/DPPC liposomes (K_b), performed at several temperatures, showed results of 4.8 and 18.5 × 10³ L mol^-1 at 293 and 323 K, respectively. Additionally, a decrease was observed in the ΔG of the Hyp/DPPC interaction (-20.6 and - 26.4 kL mol^-1 at 293 and 323 K, respectively). The resulting ΔH > 0 with ΔS < 0 shows that the entropy is driven the process. Studies of Hyp location in the liposome at 298 K revealed the existence of two different Hyp populations with a Stern-Volmer constant (K_sv) of 4.65 and 1.87 L mol^-1 using iodide as an aquo-suppressor at concentration ranged from 0 to 0.025 mol L^-1 and from 0.025 to 0.150 mol L^-1, respectively. Furthermore, studies of Fluorescence Resonance Energy Transfer, using DPH as a donor and Hyp as an acceptor, revealed that Hyp is allocated in different binding sites of the liposome. This is dependent on temperature. Thermal studies revealed that the Hyp/DPPC formulation presented reasonable stability. Size and morphological investigations showed that Hyp incorporation increases the average size of DPPC liposomes from 116 to 154 nm. The study demonstrated the ability of the Hyp-DPPC liposome as an interesting system for drug delivery system that can be applied to PDT.

Interaction of a Potential Anticancer Agent Hypericin and its Model Compound Emodin with DNA and Bovine Serum Albumin

BACKGROUND/AIM

We report the incorporation of prospective anticancer agent hypericin into DNA and bovine serum albumin (BSA), respectively, with emphasis on comparison of the differences in interaction mode between hypericin and its model compound emodin.

MATERIALS AND METHODS

Spectrophotometric methods were used for determination of the binding constants of the drug complex with biomacromolecules. Differential scanning calorimetry was applied for evaluation of drug-macromolecule complex thermal stability.

RESULTS

The strength of interaction expressed by binding constants was found to be 4.0×10⁴ l/mol for hypericin-DNA and 8.1×10⁴ l/mol for emodin-DNA complex. Both molecules stabilize bovine serum albumin macromolecule and bind into the hydrophobic cavity in IIA subunit but their localization within the molecule is different.

CONCLUSION

Anticancer agent hypericin and its derivative emodin interact with DNA with medium strength and are probably incorporated into the groove of DNA by hydrogen bonds. Bovine serum albumin can serve as a transport protein for hypericin since the binding force between both molecules is adequate.

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.

High level of low-density lipoprotein receptors enhance hypericin uptake by U-87 MG cells in the presence of LDL

The dependence of the uptake of hypericin (Hyp) by human glioma U-87 MG cells on the level of expression of low-density lipoprotein (LDL) receptors has been studied in this work. A special role of the LDL receptor-pathway for Hyp delivery to U-87 MG cells in the presence of LDL was revealed by the substantial increase of Hyp uptake in the situation, when the number of LDL receptors on the cell surface was elevated. Moreover, the colocalization experiments showed the lysosomal localization of Hyp following the uptake and that the concentration of Hyp in these organelles was enhanced in the cells with elevated number of LDL receptors when the incubation medium contained LDL. Both these findings suggest that LDL and LDL receptor-pathway play an important role in the delivery and accumulation of Hyp into the cells.

Photophysics and Multifunctionality of Hypericin-Like Pigments in Heterotrich Ciliates: A Phylogenetic Perspective

In this paper, we review the literature and present some new data to examine the occurrence and photophysics of the diverse hypericin-like chromophores in heterotrichs, the photoresponses of the cells, the various roles of the pigments and the taxa that might be studied to advance our understanding of these pigments. Hypericin-like chromophores are known chemically and spectrally so far only from the stentorids and Fabrea, the latter now seen to be sister to stentorids in the phylogenetic tree. For three hypericin-like pigments, the structures are known but these probably do not account for all the colors seen in stentorids. At least eight physiological groups of Stentor exist depending on pigment color and presence/absence of zoochlorellae, and some species can be bleached, leading to many opportunities for comparison of pigment chemistry and cell behavior. Several different responses to light are exhibited among heterotrichs, sometimes by the same cell; in particular, cells with algal symbionts are photophilic in contrast to the well-studied sciaphilous (shade-loving) species. Hypericin-like pigments are involved in some well-known photophobic reactions but other pigments (rhodopsin and flavins) are also involved in photoresponses in heterotrichs and other protists. The best characterized role of hypericin-like pigments in heterotrichs is in photoresponses and they have at least twice evolved a role as photoreceptors. However, hypericin and hypericin-like pigments in diverse organisms more commonly serve as predator defense and the pigments are multifunctional in heterotrichs. A direct role for the pigments in UV protection is possible but evidence is equivocal. New observations are presented on a folliculinid from deep water, including physical characterization of its hypericin-like pigment and its phylogenetic position based on SSU rRNA sequences. The photophysics of hypericin and hypericin-like pigments is reviewed. Particular attention is given to how their excited-state properties are modified by the environment. Dramatic changes in excited-state behavior are observed as hypericin is moved from the homogeneous environment of organic solvents to the much more structured surroundings provided by the complexes it forms with proteins. Among these complexes, it is useful to consider the differences between environments where hypericin is not found naturally and those where it is, notably, for example, in heterotrichs. It is clear that interaction with a protein modifies the photophysics of hypericin and understanding the molecular basis of this interaction is one of the outstanding problems in elucidating the function of hypericin and hypericin-like chromophores.

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.

Toxicity and drug interactions associated with herbal products: ephedra and St. John's Wort

Health care providers are being increasingly confronted with the use of herbal medications by their patients. It is imperative that patients be questioned regarding herbal preparation use and that health care providers become familiar with these agents. Research into the active components and mechanisms of action of various herbals is ongoing [350]. Long-range studies need to be performed to follow patients for efficacy or toxicity in chronic use [351,352]. Adverse reactions to herbal remedies should be reported to the FDA MedWatch at http://www.fda.gov/medwatch. As withany therapeutic agent, risk of use must always be weighed against potential benefits.

Fluorescence Spectroscopic Study of Hypericin-photosensitized Oxidation of Low-density Lipoproteins

By means of UV-VIS absorption and fluorescence spectroscopy, we demonstrate that the photosensitizer hypericin (Hyp) interacts nonspecifically with low-density lipoproteins (LDL), most probably with the lipid fraction of LDL. The molar ratio of monomeric Hyp binding to nonoxidized LDL and mildly oxidized LDL is 30:1. Increasing the Hyp concentration further leads to the formation of Hyp aggregates inside the LDL molecule. We also demonstrate that photoactivated Hyp oxidizes LDL in a light dose and excitation wavelength dependent manner. The level of oxidation of LDL depends on the amount of Hyp inside the LDL molecule. The maximum of the photosensitized oxidation of the LDL by Hyp is achieved for a 30:1 molar ratio, which corresponds to the maximum concentration of monomeric form of Hyp in LDL.

[Methyl-D3]2hypericin as internal standard for quantification in human plasma

The multistep synthesis and negative ion-ESI fragmentation pattern of [methyl-D(3)](2)hypericin (1-D(6)) is described. The application of 1-d(6) as internal standard for the quantification of hypericin (1) in the ng mL(-1) range in human plasma by isotope-dilution LC-MS is demonstrated. The hypericin-containing plasma samples are spiked with 1-D(6), deproteinized and extracted with ethyl acetate. The extracts are injected into a HPLC-ESI-ion-trap system and the mass-separated negative ions from 1 and 1-D(6) are analysed. From their intensities linear standard curves over the concentration range from 1 to 10 ng mL(-1) are obtained. Accuracy, precision and recovery are discussed.

Influence of GSTT1 and GSTM1 genotypes on sunburn sensitivity

BACKGROUND

Exposure to sunlight may cause sunburn, skin cancer or phototoxic reactions to certain drugs such as Hypericum extract. All these are ultraviolet B (UVB)-mediated reactions which may be modulated by individual genetic susceptibility. UVB exposure results in oxidative stress. Many products of oxidative stress are detoxified by glutathione-S-transferases mu 1 (GSTM1) and theta 1 (GSTT1). Deletion polymorphisms (genotype *0/*0) of GSTM1 and GSTT1 occur in 50% and 20% of Caucasians, respectively. By affecting the individual ability to detoxify oxidative stress-related products, they may influence the severity of the cutaneous photoreaction.

METHODS

Minimal erythema doses (MED) of UVB irradiation on the skin were determined in 110 subjects who were selected according to their GSTT1 genotype (28 GSTT1*0/*0, 54 GSTT1*A/*0, and 28 GSTT1*A/*A). Genotypes were detected with novel polymerase chain reaction (PCR) assays that allow the differentiation between homozygous and heterozygous GSTT1 and GSTM1 deletions.

RESULTS

In the absence of GSTT1 enzyme, the susceptibility of individuals to UVB-induced inflammatory skin reactions increased significantly (p = 0.02, ANCOVA). 'Gene-equivalents' were calculated from the number of functional GSTM1 and GSTT1 alleles as a measure of the gene-dose. UVB sensitivity correlated with gene dose up to a threshold above which additional GSTT1 or GSTM1 alleles did not provide additional protection. Volunteers who were homozygously deficient in GSTT1 and GSTM1 were most sensitive to UVB. Interestingly, individuals with high GSTM1 gene-doses showed increased photosensitization after administration of Hypericum extract (St. John's wort).

CONCLUSION

Individuals harboring the *0/*0 genotype of GSTT1 and/or GSTM1 showed enhanced UVB-induced cutaneous damage. Moreover, GST genotypes modulated Hypericum-induced photosensitization.

Photobleaching of hypericin bound to human serum albumin, cultured adenocarcinoma cells and nude mice skin

Hypericin is a promising photosensitizer for photodynamic therapy (PDT) characterized by a high yield of singlet oxygen. Photobleaching of hypericin has been studied by means of absorption and fluorescence spectroscopy in different biological systems: in human serum albumin solution, in cultured human adenocarcinoma WiDr cells and in the skin of nude mice. Prolonged exposure to light (up to 95 min, 100 mW/cm2) of wavelength around 596 nm induced fluence-dependent photobleaching of hypericin in all studied systems. The photobleaching was not oxygen dependent, and singlet oxygen probably played no significant role. Emission bands in the spectral regions 420-560 nm and above 600 nm characterize the photoproducts formed. An emission band at 615-635 nm was observed after irradiation of cells incubated with hypericin or of mouse skin in vivo but not in albumin solution. The excitation spectrum of these products resembled that of hypericin. Hypericin appears to be more photostable than most sensitizers used in PDT, including mTHPC and Photofrin.

Interaction of hypericin with serum albumins: surface-enhanced Raman spectroscopy, resonance Raman spectroscopy and molecular modeling study

Surface-enhanced Raman spectroscopy, resonance Raman spectroscopy and molecular modeling were employed to study the interaction of hypericin (Hyp) with human (HSA), rat (RSA) and bovine (BSA) serum albumins. The identification of the binding site of Hyp in serum albumins as well as the structural model for Hyp/HSA complex are presented. The interactions mainly reflect: (1) a change of the strength of H bonding at the N1-H site of Trp; (2) a change of the Trp side-chain conformation; (3) a change of the hydrophobicity of the Trp environment; and (4) a formation of an H-bond between the carbonyl group of Hyp and a proton donor in HSA and RSA which leads to a protonated-like carbonyl in Hyp. Our results indicate that Hyp is rigidly bound in IIA subdomain of HSA close to Trp214 (distance 5.12 A between the centers of masses). In the model presented the carbonyl group of Hyp is hydrogen bonded to Asn458. Two other candidates for hydrogen bonds have been identified between the bay-region hydroxyl group of Hyp and the carbonyl group of the Trp214 peptidic link and between the peri-region hydroxyl group of Hyp and the Asn458 carbonyl group. It is shown that the structures of the Hyp/HSA and Hyp/RSA complexes are similar to, and in some aspects different from, those found for the Hyp/BSA complex. The role of aminoacid sequence in the IIA subdomains of HSA, RSA and BSA is discussed to explain the observed differences.

A photodynamic pathway to apoptosis and necrosis induced by dimethyl tetrahydroxyhelianthrone and hypericin in leukaemic cells: possible relevance to photodynamic therapy

The mechanism of cell death induction by dimethyl tetrahydroxyhelianthrone (DTHe), a new second-generation photodynamic sensitizer, is analysed in human leukaemic cell lines in comparison with the structurally related hypericin. DTHe has a broad range of light spectrum absorption that enables effective utilization of polychromatic light. Photosensitization of HL-60 cells with low doses of DTHe (0.65 microM DTHe and 7.2 J cm(-2) light energy) induced rapid apoptosis of > or =90% of the cells. At doses > or =2 microM, dying cells assumed morphological necrosis with perinucleolar condensation of chromatin in HL-60 and K-562 cell lines. Although nuclear fragmentation that is characteristic to apoptosis was prevented, DNA digestion to oligonucleosomes proceeded unhindered. Such incomplete apoptosis was more prevalent with the related analogue hypericin throughout most doses of photosensitization. Despite hypericin being a stronger photosensitizer, DTHe exhibited advantageous phototoxic properties to tumour cells, initiating apoptosis at concentrations about threefold lower than hypericin. Photosensitization of the cells induced dissociation of the nuclear envelope, releasing lamins into the cytosol. DTHe also differed from hypericin in effects exerted on the nuclear lamina, causing release of an 86-kDa lamin protein into the cytosol that was unique to DTHe. Within the nucleus, nuclear envelope lamin B underwent covalent polymerization, which did not affect apoptotic nuclear fragmentation at low doses of DTHe. At higher doses, polymerization may have been extensive enough to prevent nuclear collapse. Hut-78, CD4+ cells were resistant to the photodynamically activated apoptotic pathway. Beyond the tolerated levels of photodynamic damage, these cells died exclusively via necrosis. Hut-78 cells overexpress Bcl-X(L) as well as a truncated Bcl-X(L)tr isoform that could contribute to the observed resistance to apoptosis.

Photocytotoxic effect of pseudohypericin versus hypericin

Pseudohypericin and hypericin, the major photosensitizing constituents of Hypericum perforatum, are believed to cause hypericism. Since hypericin has been proposed as a photosensitizer for photodynamic cancer therapy, the photocytotoxicity of its congener pseudohypericin has been investigated. The presence of foetal calf serum (FCS) or albumin extensively inhibits the photocytotoxic effect of pseudohypericin against A431 tumour cells, and is associated with a large decrease in cellular uptake of the compound. These results suggest that pseudohypericin, in contrast to hypericin, interacts strongly with constituents of FCS, lowering its interaction with cells. Since pseudohypericin is two to three times more abundant in Hypericum than hypericin and the bioavailabilities of pseudohypericin and hypericin after oral administration are similar, these results suggest that hypericin, and not pseudohypericin, is likely to be the constituent responsible for hypericism. Moreover, the dramatic decrease of photosensitizing activity of pseudohypericin in the presence of serum may restrict its applicability in clinical situations.

Hypericin in phototherapy

We describe the first local use of hypericin as photosensitizer for photodynamic therapy in a patient with recurrent malignant mesothelioma. Hypericin is a polycyclic quinone, which has been shown to possess in vivo and in vitro antiretroviral and photosensitizing activity; moreover, it is used in depressive disorders. The semiquinone radical, singlet oxygen, and superoxide anion radical are reported to be the toxic agents in hypericin phototherapy. Our first experience with locally applied hypericin in a superficial tumor-plate was performed 8 weeks after the systemic administration of hematoporphyrin derivatives. For tumor light illumination we used an argon pumped dye laser tuned to 632 nm. Owing to satisfactory results, we repeated the same therapy 4 weeks later- and no therapeutic effect was noted. Following this, we proved the interstitial application of HPD and the combination of interstitial HDP and superficially applied hypericin. The subsequent light illumination 6 hours later had no efficacy in the HDP-photosensitized area but there was tumor destruction in the field with both administered photosensitizers. Our first experience suggests a potentiation of two photosensitizers: hematoporphyrin derivatives and hypericin.

Wavelength-dependent photoresponse of biological and aqueous model systems using the photodynamic plant pigment hypericin

Photodynamic eradication of tumour cells in vivo depends on the presence of a photosensitizer, light delivery to the cells, and an oxygen supply. Hypericin, a polycyclic quinone with absorption maxima in the ultraviolet and visible ranges, was prepared for clinical use as a photosensitizer. Due to antitumoral and antineoplastic activities as well as the generation of singlet oxygen after photoexcitation, hypericin was applied in clinical oncology and photodynamic therapy. Hypericin was administered subcutaneously (20 micrograms hypericin in 200 microliters Nacl/pyridine solution) into the ante brachium (forearm) of two volunteers. After the diffusion and equilibration of 120 min phototesting was carried out using outdoor light exposure, halogen lamp, laser 514 nm (argon), laser 632 nm (argon dye) and laser 670 nm (diode laser), from 60 to 120 J cm-2. Positive phototests to outdoor light exposure, halogen lamp and laser 514 nm were characterized by rubescence, oozing, vesiculation and darting pain. Phototests with laser 632 nm and 670 nm showed no effects after irradiation. When hypericin was administered topically on skin, erythema and flaring could not be induced by any irradiation. These results suggest that hypericin is a potent photosensitizer only within the UV and green light ranges. This characteristic photoresponse could also be obtained in guinea pig papillary muscle (GPPM) bioassay, which may be established as a model for photosensitizer testing. Irradiation of hypericin-incubated GPPM with 514 nm (20 J cm-2) led to a decrease of the contractile force of about 31%. However, excitation with 632 nm and 670 nm did not cause inotropic effects on GPPM. In addition, hypericin and Photosan 3 were shown to be capable of sensitizing the photo-oxidation of sodium linoleate. This assay should be established for testing interactions between photosensitizers and light sources in vitro.

Single-dose and steady-state pharmacokinetics of hypericin and pseudohypericin

Single-dose and steady-state pharmacokinetics of antivirally acting hypericin (H) and pseudohypericin (PH) were studied in 13 healthy volunteers by administration of St. John's Wort extract LI 160, a plantal antidepressant. Oral administration of 250, 750, and 1,500 micrograms of H and 526, 1,578, and 3,156 micrograms of PH resulted in median peak levels in plasma (Cmax) of 1.3, 7.2, and 16.6 micrograms/liter for H and 3.4, 12.1, and 29.7 micrograms/liter for PH, respectively. The Cmax and the area under the curve values for the lowest dose were disproportionally lower than those for the higher doses. A lag time of 1.9 h for H was remarkably longer than the 0.4-h lag time for PH. Median half-lives for absorption, distribution, and elimination were 0.6, 6.0, and 43.1 h after 750 micrograms of H and 1.3, 1.4, and 24.8 h after 1,578 micrograms of PH, respectively. Fourteen-day treatment with 250 micrograms of H and 526 micrograms of PH three times a day resulted in median steady-state trough levels of 7.9 micrograms/liter for H and 4.8 micrograms/liter for PH after 7 and 4 days, respectively; the corresponding Cssmax levels were 8.8 and 8.5 micrograms/liter, respectively. Kinetic parameters after intravenous administration of Hypericum extract (115 and 38 micrograms for H and PH, respectively) in two subjects corresponded to those estimated after an oral dosage. Both H and PH were initially distributed into a central volume of 4.2 and 5.0 liter, respectively. The mean distribution volumes at steady state were 19.7 liters for H and 39.3 liters for PH, and the mean total clearance rates were 9.2 ml/min for H and 43.3 ml/min for PH. The systemic availability of H and PH from LI 160 was roughly estimated to be 14 and 21%, respectively. Treatment with Hypericum extract, even in high doses, was well tolerated.

Photodynamic effects of hypericin on lipid peroxidation and antioxidant status in melanoma cells

Photodynamic-induced cytotoxicity by hypericin (HYP) was studied on three human melanoma cell lines: one pigmented cell line (G361) and two amelanotic cell lines (M18 and M6). No significant variation in the rate of uptake and in the maximum level of HYP incorporation for the different cells was observed. In the dark, no cytotoxicity was observed in the range 0-10-6 M HYP for the three cell lines. Amelanotic cells were found to be more sensitive than pigmented cells to irradiation of HYP with visible light (lambda > 590 nm). In addition, for the three cell lines HYP-induced photocytotoxicity was found to be drug-dose and light-dose dependent. Under the conditions used, thiobarbituric acid-reacting substances (TBARs) were significantly increased in amelanotic cells after irradiation (P < 0.0001). By contrast, the amount of TBARS remained unchanged in pigmented cells. Antioxidant defenses including enzymes and glutathione (GSH) were assayed before and after HYP photosensitization. Significantly increased total SOD activity was observed after photosensitizaton for amelanotic cells (P < 0.05), while glutathione peroxidase (GSHPx) and catalase (Cat) activities but also GSH levels were significantly decreased (P < 0.01). In pigmented cells a significantly increased Cat activity was found (P < 0.05), whereas GSHPx was unaffected after irradiation. It can be inferred that (a) HYP may be an effective PDT agent for melanoma and (b) there is a relationship between melanin content and sensitivity to HYP phototoxicity in human melanoma cells.

Hypericin-induced phototoxicity in cultured fibroblasts and swine erythrocytes

Hypericin is a naturally occurring photosensitizer, whose presence in plants has been responsible for cutaneous phototoxicity in grazing animals. The photosensitizing properties of this agent have recently been exploited in models for anti-tumor and anti-viral activity. The cytotoxicity of hypericin and light was assessed in 3T3 mouse fibroblasts using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide)] assay and the lactate dehydrogenase (LDH) leakage assay. Membrane damage was assessed in swine erythrocytes using hemolysis, potassium (K+) leakage and formation of lipid hydroperoxides. Concentration- and light-dependent decreases in fibroblast viability were seen starting at hypericin concentrations of 1.25 microM and light power flux levels of 24 J/cm2 using a visible light source and at 0.417 microM hypericin and a similar light dose using a solar simulator. No LDH leakage was observed at hypericin concentrations up to 30 microM and visible light up to 144 J/cm2. Light-and/or concentration-dependent increases in hemolysis, K+ leakage and formation of lipid hydroperoxides in red blood cell (RBC) membranes were observed, but at concentrations and light doses much greater than those required to induce cytotoxicity in fibroblasts. Lipid peroxidation and hemolysis occurred at 15 microM hypericin and 24 J/cm2 (visible light source). Potassium ion leakage occurred at concentrations and light levels as low as 5 microM and 12 J/cm2 or 15 microM and 4.8 J/cm2 (visible light source) but was still a less sensitive indicator than fibroblast cytotoxicity. Evidence for both type I and type II reactions was shown in RBC membranes by TLC analysis of cholesterol products. In the absence of light, hypericin appears to be relatively nontoxic in the models tested.

Sensitization of photohemolysis by hypericin and Photofrin

Sensitization of post-irradiation (delayed) photohemolysis (DPH) and "during irradiation" (continuous) photohemolysis (CPH) were investigated for sodium hypericin and Photofrin. The photohemolysis rate and relative steepness of the photohemolysis curves were measured for a range of sensitizer concentrations and DPH irradiation times. The data are analyzed by a multihit model based on the assumption that photohemolysis requires thermal activation of light-activated damage. A key result of the model is the photohemolysis rate has a power dependence of 1 or more on the irradiation time and sensitizer concentration for DPH and a power dependence of less than 1 on sensitizer concentration for CPH. The data for sodium hypericin are consistent with the predictions and indicative of a square dependence of photohemolysis rate on the absorbed light dose. The results for Photofrin led to an approximately square dependence of the photohemolysis rate on DPH irradiation time and an apparently anomalous 1.24 power dependence on sensitizer concentration. The model predicts also that the relative steepness of the photohemolysis curves is independent of the light dose and sensitizer concentration for DPH and almost independent of the sensitizer concentration for CPH. This prediction is confirmed to within +/- 10% for all sets of DPH and CPH curves. The relationship of the multihit kinetics model to detailed photohemolysis mechanisms is discussed.

Hypericin inhibits cell growth and induces apoptosis in retinal pigment epithelial cells: possible involvement of protein kinase C

Proliferative vitreoretinopathy (PVR) is characterized by the proliferation and migration of retinal pigment epithelial (RPE) cells in the vitreous cavity. The drug hypericin, which is already in clinical use as an antidepressant, has shown promise as an antiviral and antineoplastic agent. To investigate the therapeutic potential of hypericin in PVR, we incubated RPE cells in standard medium with various serum concentrations containing 0.5 to 5 microM hypericin. In some experiments we studied the effects of hypericin in conjunction with the RPE growth stimulating cytokine tumor necrosis factor alpha (TNF-alpha). Dose-dependent inhibition of RPE cell proliferation with IC50 values of 0.7 microM and 3.3 microM in 1% and 5% serum respectively, was found. Even in conjunction with TNF-alpha, hypericin inhibited RPE proliferation with an IC50 value of 1.5 microM. The drug inhibited PKC activity in cells treated with a 2.5 microM dose by 72% after 30 min and by 100% after 180 min. Finally, hypericin induced RPE cells to undergo apoptotic cell death, as shown by the presence of DNA laddering. These results suggest that hypericin may have potential as a therapeutic drug for PVR and that its antiproliferative and apoptotic effects on RPE cells in vitro are in part mediated by PKC.

Spectroscopic and photoacoustic studies of hypericin embedded in liposomes as a photoreceptor model

In photoresponsive ciliates, like Blepharisma japonicum and Stentor coeruleus, the photoreceptor pigments responsible for photomotile reactions are hypericin-type chromophores packed in highly osmiophilic subpellicular granules. Lipopsomes loaded with hypericin can constitute a simple model system, appropriate for understanding the primary light-induced molecular events triggering the sensory chain in these microorganisms. Optical absorption, steady-state and time-resolved fluorescence and pulsed photoacoustic calorimetry have been used to measure spectral distributions, fluorescence lifetimes, radiative and radiationless transition quantum yields of hypericin when assembled into egg L-alpha-phosphatidylcholine liposomes. With respect to hypericin ethanol solutions, both absorption and fluorescence maxima are 5 nm red shifted when the pigment is inserted into the lipidic microenvironment, regardless of the hypericin local concentration. Increasing by 100 times the hypericin local concentration decreases the relative fluorescence quantum yield by a factor of around 150 and the fraction of thermally released energy, conversely, increases from 0.6 to 0.9. From the analysis of fluorescence lifetimes and their relative amplitudes it appears that a subnanosecond living component is predominant at the highest hypericin local concentrations.

Photoactivated inhibition of superoxide generation and protein kinase C activity in neutrophils by blepharismin, a protozoan photodynamically active pigment

Blepharismin is an endogenous photosensitizing pigment found in the protozoan Blepharisma. This pigment inhibited the generation of superoxide anion (O2-.) in neutrophils not only via a diacylglycerol-induced protein kinase C (PKC)-dependent reaction but also by an arachidonate-induced PKC-independent reaction. The inhibition was light and concentration dependent for both reactions. Light-activated inhibition was strong at wavelengths between 520 and 570 nm but not above 610 nm. PKC activity in neutrophils and from rat brain was inhibited by blepharismin in a light- and concentration-dependent manner. Moreover, arachidonate-activated NADPH oxidase activity in a cell-free system was also inhibited by the pigment in a light- and concentration-dependent manner. These results suggest that blepharismin inhibits NADPH oxidase activation through the non-specific inhibition of various membrane-bound enzymes and that this inhibition may also be correlated with that of PKC.