Hypericin-Induced Cell Photosensitization Involves an Intracellular pH Decrease

Phenanthrenequinone antiretroviral agents

Compounds 3 and 5 are the first phenanthrenequinones to exhibit significant virucidal activity against the retrovirus equine infectious anemia virus. They differ from hypericin in that their virucidal activity is not light dependent.

Over-expression of Bcl-2 does not protect cells from hypericin photo-induced mitochondrial membrane depolarization, but delays subsequent events in the apoptotic pathway

Hypericin (HY) is a powerful photo-inducer of apoptosis in Jurkat cells as measured by caspase-3 activation, cell shrinkage, phosphatidylserine (PS) exposure and the appearance of hypoploid DNA. These processes are preceded by rapid Bcl-2-independent mitochondrial transmembrane depolarization and a drop in cytoplasmic pH. Pre-incubation of cells with inhibitors of the mitochondrial permeability transition pore, such as cyclosporin A or bongkrekic acid, does not protect cells from mitochondrial membrane potential (deltapsim) decrease. However, monitoring of mitochondrial entrapped calcein by confocal fluorescence imaging gives clear evidence of HY photo-induced mitochondrial permeability. This should be considered as the result of a non-specific alteration of mitochondrial membrane integrity brought about by lipid peroxidation. Nevertheless, synthesis of the anti-apoptotic protein Bcl-2 appears to delay the subsequent time course of PS exposure and to reduce caspase-3 activation and the fraction of cells which become hypoploid. We interpret this partially protective effect as the consequence of a direct interaction of Bcl-2 with cytosolic cytochrome c previously released from mitochondria upon deltapsim decrease and/or of Bcl-2 inhibition of the deleterious retro-effect of caspase-3 on the mitochondrial permeability transition pore and/or the mitochondrial membrane components.

Potentiation of hypericin and hypocrellin-induced phototoxicity by omeprazole

Hypericin and hypocrellin are potential antiviral and antineoplastic agents with multiple modes of light-induced biological activity connected with a production of singlet oxygen and/or excited-state proton transfer and consequent pH drop formation in the drugs environment. In present work light-induced cytotoxicity of hypericin (1 x 10(-5) - 10(-9) mol) and hypocrellin (1 x 10(-5) - 10(-9) mol) and potentiating effect of omeprazole on human leukemic cell line HL-60 was studied. Under dark condition cultivation none cytotoxicity was observed. The only one exception was hypocrellin in concentration 1 x 10(-5) mol which displayed full cytotoxic effect. However, illumination increased cytotoxic effect of hypericin and hypocrellin, both. Omeprazole, an inhibitor of H+K+-ATPase, has been used for testing the hypothetical pH decreasing effect of hypericin and hypocrellin in their cytotoxic mechanism of action. The results of our experiments have shown that in HL-60 cell line the effect of hypericin and hypocrellin at 1 x 10(-6) mol (both) was significantly potentiated by omeprazole in concentrations 1 x 10(-6) - 10(-9) mol. Our results support the hypothesis that the excited-state proton transfer and the consequent acidification of hypericin and hypocrellin environment could play a role in the biological activity of both agents.

Binding of nystatin and amphotericin B with sterol-free L-dilauroylphosphatidylcholine bilayers resulting in the formation of dichroic lipid superstructures

Interactions of multilamellar vesicles (MLV) of dilauroylphosphatidylcholine (DLPC) with the polyene antibiotics, amphotericin B (AmB) and nystatin (Ny), were followed by circular dichroism (CD). These interactions proceed with both antibiotics through a slow association with high [DLPC]/[antibiotic] stoichiometric molar ratios (> or = 130), at room temperature for which DLPC membranes are in a fluid state. Microscopic investigations of the spatial distributions of the antibiotic and the MLV in the mixtures revealed that MLV form clusters inside which the antibiotic is strongly concentrated and lipid superstructures appear. Concomitantly with the appearance of these superstructures a DLPC dichroic signal emerges. This observation indicates that the chiral properties of antibiotic oligomers can induce a chirality of the DLPC molecules which are bound to them. These results support the hypothesis of a recent molecular modeling of AmB oligomers which postulates that their chiral properties result from a chiral assemblage of antibiotic molecules (Millié et al., J. Phys. Chem. B, in press).

Sequence specific interaction of the photoactive drug hypericin depends on the structural arrangement and the stability of the structure containing its specific 5AG3 target: a resonance Raman spectroscopy study

The resonance Raman spectra of three oligonucleotides with different lengths containing a specific 5'AG3' target doublet for hypericin - a potent antiretroviral and anticancer photoactive agent, and their 1:1 and 1:2 (oligonucleotide: hypericin) complexes are reported. It is shown that the structural arrangement of the oligonucleotides, their structural stability and the local structural arrangement around the 5'AG3' hypericin target, are the factors which determine the formation of a stable, specifically bounded DNA-hypericin complexes.

Electric magnetic resonance and spectrophotometry evidence on the photodynamic activity of a new perylenequinonoid pigment

Di-cysteine substituted hypocrellin B (DCHB) is a new water-soluble photosensitizer with significantly enhanced red absorption at wavelengths longer than 600 nm over the parent compound hypocrellin B (HB). The photosensitizing properties (Type I and/or Type II mechanisms) of DCHB have been investigated in dimethylsulfoxide (DMSO) and aqueous solution (pH 7.4) using electron paramagnetic resonance (EPR) and spectrophotometric methods. In anaerobic DMSO solution, the semiquinone anion radical of DCHB (DCHB-) is predominantly photoproduced via self-electron transfer between excited- and ground-state DCHB species. The presence of an electron donor significantly promotes the formation of the reduced form of DCHB. When a deoxygenated aqueous solution of DCHB and an electron door are irradiated with 532 nm light, the hydroquinone of DCHB (DCHBH2) is formed via the disproportionation of the first-formed DCHB- and second electron transfer to DCHB- and second electron transfer to DCHB- from the electron donor. When oxygen is present, singlet oxygen (1 O2), superoxide anion radical (O2-) and hydroxyl radical (OH) are produced. The quantum yield of 1 O2 generation by DCHB photosensitization is estimated to be 0.54 using Rose Bengal as a reference, a little lower than that of HB (0.76). The superoxide anion radical is also significantly enhanced by the presence of electron donors. Moreover, O2- upon disproportionation generated H2O2 and ultimately the highly reactive OH via the Haber-Weiss reaction pathway. The efficiency of O2- generation by DCHB is obviously enhanced over that of HB. These findings suggest that the photodynamic actions of DCHB may proceed via type I and Type II mechanisms and that this new photosensitizer retains photosensitizing activity after photodynamic therapy-oriented chemical modification.

The effect of hypericin and hypocrellin-A on lipid membranes and membrane potential of 3T3 fibroblasts

Hypericin (HY) and Hypocrellin-A (HA) photosensitization induce rapid depolarization of plasma membrane in 3T3 cells as revealed by confocal microspectrofluorimetry using diO-C5(3) fluorescent probe. HY and HA are also able to rigidify the lipid membrane of DMPC liposomes as indicated by the decrease of pyrene excimer fluorescence used as a marker of the lipid membrane fluidity. We have also observed a nonspecific inhibition of Na+,K+-ATPase activity due to the HY and HA photosensitization. The described effects are concentration- and light dose-dependent and generally more pronounced for HA than for HY. All these observations suggest that the lipid membranes can play an important role in the photosensitization process induced by HY and HA at the cellular level. It can be hypothesized that for HA and HY the secondary mechanism following type I or type II photosensitization process can be the peroxidation of membrane lipids as well, and thus intracellular membranes seem to be one of the most important targets of these photosensitizers.

The role of oxygen in the antiviral activity of hypericin and hypocrellin

The light-induced antiviral activity of hypericin and hypocrellin in the presence and absence of oxygen was examined under experimental conditions where the effect of oxygen depletion could be quantified. There was a significant reduction of light-induced antiviral activity of hypericin and hypocrellin under hypoxic conditions. Interestingly, antiviral activity of hypocrellin was not observed at low oxygen levels at which hypericin retained measurable virucidal activity. This suggests that additional pathways, such as the generation of protons from excited states of hypericin, may enhance the biological activity of activated oxygen species.

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.

Hypocrellin A photosensitization involves an intracellular pH decrease in 3T3 cells

The fluorescent pH probe carboxy-seminaphtorhodafluor-1 (C-Snarf-1) has been used for laser microspectro-fluorometric assays of intracellular pH in 3T3 mouse fibroblasts treated with hypocrellin A. These results are compared to those previously obtained with the structurally related hydroxylated polycyclic quinone, hypericin (Sureau et al., J. Am. Chem. Soc. 118, 9484-9487, 1996). A mean local intracellular pH drop of 0.6 units has been observed in the presence of 1 microM hypocrellin A after 90 s of exposure to 0.1 microW of laser irradiation at 514.5 nm. The time evolution of the cytoplasm acidification for hypocrellin A-treated cells is faster than that for cells treated by hypericin. Thus, release of protons from an excited state of hypocrellin A appears to be more efficient than that from hypericin. In addition, the pH dependence of the quenching of C-Snarf-1 fluorescence in 3T3 cells under continuous irradiation has been observed. It is shown here that under continuous illumination, a pH decrease is able to induce a modification of the intracellular binding equilibrium of C-Snarf-1 that results in an increase of C-Snarf-1 fluorescence intensity. This latter observation suggests that the protons generated upon the photoexcitation of hypericin or its analogs may be involved in the production of other photoreactive species. Finally, we suggest that, just as for hypericin, this pH drop may be involved in the antiviral and antitumor activity of hypocrellin A.

Sequence specific interaction of the antiretrovirally active drug hypericin with 5'ATGGCAGGATAT3' oligonucleotide: a resonance Raman spectroscopy study

The resonance Raman spectra of two oligonucleotides and their complexes with potent antiretrovirally and antineoplastic active photochemical drug hypericin are reported. The Raman spectra of two oligonucleotides containing twelve base pairs on addition of hypericin (one and two molecules per one oligonucleotide) were compared. The first one contains the first nine base pairs of the "rev" gene coming from HIV genome with three base pairs added to stabilize the duplex (5'ATGGCAGGATAT3') and the second one consists of the same content of the nucleotide bases but in changed sequence order which serves as a control sequence (5'ACGTGATGATGA3'). Differences in the spectra of the "rev" gene sequence and control sequence in interaction with the drug indicate that: i) the AG and GA nucleotide doublets are structurally specific targets for hypericin and ii) the hypericin interaction with 5'AG3' target is stronger than with 5'GA3' one.