Hydroxyethyl cellulose hydrogel for skin delivery of khellin loaded in ascosomes: Characterization, in vitro/in vivo performance and acute toxicity.

Aim of this work was to prepare and characterize a hydroxyethyl cellulose hydrogel loaded with ascosomes, nanovesicles based on phosphatidylcholine plus ascorbyl octanoate (ASC8) or ascorbyl decanoate (ASC1), and khellin (2 mg/mL), for topical use. ASC10 vesicles were selected for the hydrogel formulation because of the best biopharmaceutical characteristics, namely size of 115 nm, PDI of 0.26, ζ-potential of -40.1 meV, EE% of 90.2%. After 24 h the in vitro release of khellin was more than 80%, while the ex-vivo skin permeation of khellin after application of the vesicles was 42% of the dose. The hydrogel formulations had a pH value of 5, viscosity properties were different according to the different temperatures and in addition, they presented characteristics of non-Newtonian fluids with a pseudoplastic shear thinning behaviour according to the Herschel-Bulkley equation. These hydrogels combine the advantages of a suitable viscosity for dermal use (hydrogel matrix) and an increased transdermal absorption (ascosome components). The best permeability of the ASC10 ascosomes, led to select the formulation for skin irritation and corrosion tests in rats. Liver and dermal histological and pathological analyses demonstrated that hydroxyethyl cellulose hydrogels based on khellin loaded in the ASC10 ascosomes have no toxic effects.

Studies on the photobiological activity of two naturally occurring furochromones, visnagin and khellin, in Chlamydomonas reinhardtii.

Irradiation of arg-1 cells of the green alga Chlamydomonas reinhardtii with UV-A in the presence of visnagin (10 microg/ml) produced weak mutagenic effects when a fluence rate of 5.1 W/m2 and fluences of 1.5-36.7 kJ/m2 were applied. A maximum number of revertants was obtained at approximately 9.2 kJ/m2. When a fluence rate of 20.4 W/m2 was used the photomutagenicity of visnagin was markedly enhanced with fluences of > or = 36.7 kJ/m2. In survival experiments with a fluence rate of 5.1 W/m2 the surviving fraction decreased continuously to approximately 4%. In experiments with a fluence rate of 20.4 W/m2, however, higher survival rates were observed compared at equal UV-A doses. Visnagin was much less phototoxic and photomutagenic than bergapten when compared at equimolar concentrations and equal UV-A doses. Re-irradiation with UV-A in the absence of unbound visnagin did not alter survival and mutagenicity which had been induced by the first treatment. The mutation frequency plotted versus the UV-A fluence exhibited second-order kinetics. Khellin showed only marginal photosensitizing capacity and no significant mutagenicity up to a concentration of 100 microg/ml and a total UV-A fluence of 73.4 kJ/m2.

Treatment with topical khellin in combination with ultraviolet A or solar-simulated radiation is carcinogenic to lightly pigmented hairless mice.

Khellin is used together with either UVA irradiation or sun exposure in the treatment of vitiligo. The purpose of this study was to investigate the carcinogenic effect of topically applied khellin together with UVA or solar simulated radiation (SSR) in lightly pigmented C3H/Tif mice. For comparison purposes a 0.1% 8-methoxypsoralen (8-MOP) cream was also tested in combination with SSR. Fifty microliters of a 5% khellin cream, a 0.1% 8-MOP cream, or a cream without active substances were spread uniformly on the back of the mice 30 minutes before UVA or SSR irradiation. All mice were irradiated 3 times a week until age or skin tumor development necessitated killing. Treatment with topical khellin and UVA irradiation was carcinogenic to lightly pigmented hairless mice, time to 50% of the mice had developed one tumor (t50) was 507 days. This indicates that the combination of topical khellin and UVA radiation, formerly expected to be rather innocuous, is carcinogenic to mice. Also the combination of khellin and SSR (t50 = 268 days) enhanced skin tumor development significantly compared with control cream and SSR (t50 = 330 days), P < 0.05. In addition, the combination of khellin and SSR was found to have the same carcinogenic effect as treatment with 0.1% 8-MOP and SSR (t50 = 262 days). This study shows that topically applied khellin increases the carcinogenic effect of both UVA and sunlight.

Investigation of the mutagenic activity in Salmonella typhimurium of the furochromone khellin, proposed as a therapeutic agent for skin diseases.

The photomutagenicity of the furochromone khellin was tested in Ames Salmonella strains using 8-methoxypsoralen (8-MOP) and 4,5', 8-trimethylpsoralen (TMP) as positive controls. When khellin was assayed with strain TA1537, mutation induction was not detectable; in the same strain, an equitoxic dose (52-56% level of survival) of TMP (used at a concentration 12-fold lower than khellin and with a UVA dose 83-fold lower than that used with khellin) yielded an increase in revertants/plate 3-fold above the spontaneous background. In strain TA102, khellin plus UVA treatment yielded a 2-fold increase in revertants/plate above the spontaneous background (79% survival). 8-MOP, however, used at a concentration 8-fold lower than khellin with a UVA dose 13-fold lower than khellin, yielded an increase in revertants/plate about 14-fold above background (66% survival) in the same strain. These data show that khellin has a weak photomutagenic potential and, along with the previously reported low photogenotoxic potential in eukaryotic cell systems, support the notion that khellin may be safer than bifunctional psoralens for clinical use.