On the Diffusion of Hypericin in Dimethylsulfoxide/Water Mixtures—The Effect of Aggregation

Abstract

Hypericin (Hyp) is a natural photosensitizing pigment with a possible application in the photodynamic therapy of cancer. Hyp is readily dissolved in dimethylsulfoxide (DMSO) but forms nonsoluble aggregates in an aqueous environment. Fluorescence spectroscopy and diffusion coefficient measurements are used to investigate the self-association of Hyp molecules in DMSO/water mixtures. Fluorescence measurements reveal that Hyp remains in its monomeric form in DMSO/water mixtures containing up to ∼20-30 wt % water. At higher water concentration, Hyp starts to form nonfluorescent aggregates. To determine the size of the aggregates, the diffusion coefficient of Hyp is determined for different DMSO/water mixtures both experimentally and theoretically. Our data indicate that the size of the aggregates increases as more water is added into DMSO. At 50 wt % water content, the effective diffusion coefficient is about 30% smaller than the calculated value for the stacked Hyp tetramer. The results indicate that in an aqueous environment, Hyp presumably produces large molecular weight stacked H-aggregates. We have also confirmed that in an aqueous environment at alkaline pH, molecules of Hyp remain in the monomeric state.

Photodynamic Effect of Hypericin after Topical Application in the Ex Ovo Quail Chorioallantoic Membrane Model

“…Photochemical and photophysical properties are characterized by multiple fluorescence excitation peaks in the range 400-600 nm, which induces fluorescence emission at about 600 nm [1]. Hypericin is a hydrophobic molecule and, consequently, in aqueous solution, at physiological pH, forms nonfluorescent aggregates that interfere with the biological activity of this compound [2][3][4]. Cosolvents such as ethanol, glycerol, dimethyl sulphoxide, N-methyl pyrrolidone, polyethylene glycol 400 (PEG-400), or human serum albumin have been used to reduce aggregation [5][6][7].…”

“…Disruption of CAM tissue was also observed after PDT. Hypericin exhibits a relatively high quantum yield and low photobleaching characteristics compared to some other photosensitizers [4]. Despite promising photodynamic properties of hypericin, there are problems in some photophysical behaviors of this molecule.…”

“…Hypericin in a polar water environment is almost insoluble and at physiological pH forms nonfluorescent high molecular weight aggregates. The forms of aggregation have been proposed as stacked face-to-face association forming H-aggregates and planar association forming J-aggregates [4]. Microscopic examinations of tissue sections in the study of van de Putte et al [2] revealed that the size of coarse particles of aggregated hypericin ranged from 5 to 30 µm.…”

Estimation of PKCδ autophosphorylation in U87 MG glioma cells: combination of experimental, conceptual and numerical approaches

“…Fluorescence spectrum of NBDC 6 in PBS solution is plotted in the Figure 3 in the absence and in the presence of hypericin. It should be noted, that hypericin in the aqueous solutions quickly forms non-fluorescent aggregates [27,28]. Significant decrease of NBDC 6 fluorescence intensity can be observed after hypericin addition.…”

Necrosis-targeted combinational theragnostic approach to treat cancer

“…Besides, with nearly planar conformation, Hyp is poorly soluble and forms nonfluorescent aggregates in aqueous environment [18], which strongly hindered its selective accumulation in necrotic tumor [19]. The coarse aggregates are intercepted by pulmonary capillary network and small ones are cleaned by reticuloendothelial system and substantially retained in the liver and spleen.…”