After incubating the MPs for 24 h with 1 μM hypericin) or 5 μM hypericin), the highest concentration of the lipophilic hypericin was found in samples where no cells have been added.
Including polyvinylpyrrolidone- (PVP-) hypericin allows for the direct comparison between the hydrophobic PS hypericin and a water-soluble formulation of this compound.
Both substances differ in their hydrophilic character: AlPCS4 is hydrophilic per se; PVP-hypericin is made water soluble by the addition of polyvinylpyrrolidone to hypericin [ 13], resulting in a different behavior at the higher concentrations employed.
To date, the relation between the content of hypericins and their proto-forms accumulated in the nodules, and morphological characters of the plant parts containing these structures has not been sufficiently explained.
The high level of neuronal death (∼90%) detected after hypericin-mediated PDT showed that the lack of neuronal cell death after mTHPC-mediated PDT was not due to an inability to detect neuronal death in this system.
This negative selectivity is the highest (more than double) after 0.5 mM ALA incubation, about double after hypericin treatment, with both concentrations, and reduced after 1 mM ALA– 15(d)).
The high cost and environmental harms of these dyes turned the attention toward natural pigments like anthocyanins, chlorophylls, and hypericin [7, 8, 9] extracted from plant leaves, roots, flowers, seeds, and fruits [10, 11, 12, 13, 14, 15, 16].
An almost linear but smaller decrease of viable cells is found if only plate-adhered hypericin was available, with an LD50 of 1.0 J·cm−2; although even with this protocol, cells completely deceased after the highest light dose was applied.
With a higher PVP-hypericin concentration of 5 μM), the phototoxic effect is intensified for cells directly incubated with the PS, with a fast decrease of viability for illumination up to 1.3 J·cm−2 and no viable cells at higher fluences.
They too reported that a continuous source of external radiation resulted in more effective target cell cytotoxicity and suggested that this may be related to suboptimal proximity between the luciferin and the hypericin.
