The mechanisms of interaction between furanochromones and DNA. A heteronuclear Overhauser effect study on the khellin-thymidine model system

Development of Gel-in-Oil Emulsions for Khellin Topical Delivery

Hypopigmentation is a progressive dermatological condition caused by a reduction in the skin pigment, melanin. Its treatment is considered a challenge due to the lack of a highly efficient single therapy. Currently, the main treatments include photochemotherapy, application of corticosteroids and immunosuppressants, and laser. Khellin-based gel-in-oil emulsions appear as a promising alternative since they ensure a concentration of the drug, a natural furanochromone, at the desired location, skin surface. Khellin promotes repigmentation as it forms a dark colored complex after solar irradiation. The aim of this study was the development and characterization (e.g., rheological behaviour, droplet size, tackiness, adhesion and spreadability) of three topical gel-in-oil emulsions prepared with different emollients, formulated through a cold emulsification process, and suitable for the incorporation of khellin. In vitro studies were performed to evaluate the drug release and permeation profiles across artificial membranes and excised human skin, respectively, using Franz-type vertical diffusion cells. The W/O emulsions developed showed macroscopic appearance, shear-thinning behavior with a mean droplet size from 3.28 to 4.28 μm, suitable for topical application. In vitro studies revealed permeation values of about 1% of khellin across the stratum corneum, making these gel-in-oil emulsions promising for preclinical and clinical studies. The cold process, being an easy and low energy production method, represents an innovative strategy to produce khellin-based gel-in-oil emulsions to treat patients with hypopigmentation.

Influence of growing conditions on metabolite profile of Ammi visnaga umbels with special reference to bioactive furanochromones and pyranocoumarins

The medicinal plant Ammi visnaga is a valuable source of furanochromones and pyranocoumarins used as vasodilator agents. Its ability to germinate under unfavourable growth conditions, such as saline soil and hypoxia characterizing clay soils and marshes ecosystems, prompted us to qualitatively characterize secondary metabolites in umbels of A. visnaga plants grown under different conditions (in field, hydroponically controlled, and contrasted by salinity and/or hypoxia) by HPLC-ESI/IT/MS(n) analysis. Subsequently, the quantitative analysis of the bioactive compounds, above all furanochromones and pyranocoumarins, was carried out by HPLC-ESI/QqQ/MS/MS. The results show the influence of growing conditions on the quali-quantitative profile of A. visnaga secondary metabolites and evidence that hydroponic culture leads to increased level of A. visnaga active principles. Furthermore, two furanochromones never reported before were identified and characterized by 1D- and 2D-NMR analysis.

Furanochromone radical cations: generation, characterization and interaction with DNA

The radical cations of naturally occurring furanochromones visnagin (VI) and khellin (KH) have been generated and identified for the first time by use of laser flash photolysis and pulse radiolysis techniques. The lifetimes of VI(.+) and KH(.+) are determined as approximately 6 and approximately 35 micros under these conditions, respectively. Direct 308-nm excitation of VI in aqueous buffer at physiological pH results in monophotonic photoionization to generate VI(.+), with a quantum yield of 0.075, which is much higher than that of 8-methoxypsoralen and KH under identical conditions. Though VI(.+) is a more powerful oxidant than KH(.+), both of them react with guanosine mononucleotide (k=1.2x10(9) and 3.8x10(7) dm(3) mol(-1) s(-1), respectively) via electron transfer to give the guanine radical cation. Furthermore, selective oxidation of guanine in single and double strand DNA by VI(.+) was also observed. These novel findings suggest that electron transfer reactions involving furanochromone radical cations may be of considerable importance in furanochromone photochemotherapy.

Photosensitizing action of furocoumarins on membrane components and consequent intracellular events

The photodamage induced in membrane components by furocoumarins is reviewed. The oxygen-dependent photoreactions between furocoumarins and cell membrane constituents lead mainly to lipid peroxidation and the formation of cross-linking in ghost proteins, whereas the oxygen-independent photoreactions lead essentially to a C4 cycloaddition between the furocoumarin and the unsaturated fatty acids. In the latter, cycloadducts are formed between the 3,4 double bond of the furocoumarin and the olefinic double bond of the unsaturated fatty acid. The stereochemical structures of these cycloadducts and the reaction mechanism of the cycloaddition are discussed. Finally, the modulation of several membrane systems by furocoumarins and the consequent intracellular events are reviewed.

Photosensitization of DNA of defined sequence by furochromones, khellin and visnagin

The sequence specificity in the in vitro DNA photobinding of khellin and visnagin, two naturally occurring furochromones proposed for chemotherapy of vitiligo, was investigated by using DNA sequencing methodology. The 3'-5' exonuclease associated with the T4 DNA polymerase served as a tool for determining photoadducts distribution on DNA fragments of the lac I gene of Escherichia coli. The photoadduct distribution of psoralen is also studied for comparison. Upon UVA irradiation, visnagin mainly forms monoadducts with thymine and to a lower extent with cytosine. Alternating (A-T)n sequences are hot spots for visnagin photoaddition. This is a property shared with furocoumarins. TTT sites are also quite reactive to visnagin, as they are to methylated angelicins. In contrast, with psoralen derivatives, there is no preferential photobinding in 5'-TpA sites, and 5'-ApT sites react as well. Furthermore, many sites such as T in the GC context, and C in any context, react, although weakly. The visnagin photoadduct distribution resembles very much the photoadduct distribution of methylated angelicins as described by Miolo et al. The photoreaction of these two series of compounds is less sequence dependent than the photobinding of psoralen derivatives as described by Sage and Moustacchi and by Boyer et al. The sequence specificity in khellin-DNA photobinding is the same as for visnagin, even though it forms much fewer photoadducts. The absence of photo-oxidation of DNA after treatment with visnagin or khellin plus UVA suggests that furochromones do not present any photodynamic effect on DNA.

Solvent spin-labelling for investigating the interaction of biological ligands with macromolecules. A 1H paramagnetic relaxation study

The paramagnetic contributions to the spin-lattice relaxation rates of khellin protons, induced by the presence in an aqueous solution of TEMPO nitroxide, have been analyzed in the interaction of the furochromone with DNA. The relaxation data obtained at different temperatures, nitroxide and DNA concentrations indicate that the average solvent exposure of the furanic moiety of khellin is lower than that of the pyranic group. This feature suggests that the former is the main site of approach of khellin to DNA.

Treatment of vitiligo with khellin and ultraviolet A

Twenty-eight patients with vitiligo were treated with a new photochemotherapeutic regimen using khellin, a furanochromone, as photosensitizer, together with ultraviolet A (UVA) irradiation. Twenty-five patients received khellin orally and three patients were treated with topical khellin. Treatments were given three times weekly. As opposed to psoralens, khellin did not induce skin phototoxicity with UVA but it induced repigmentation similar to psoralens. The treatment success strongly depended on the number of treatments. More than 70% repigmentation was achieved in 41% of the patients who had received 100 to 200 treatments. This success rate is comparable to the rate obtained with psoralens. Seven patients experienced a mild elevation of liver transaminases within the early treatment phase and their treatments were discontinued. No long-term internal organ or skin toxicity was observed. The major advantage of khellin is that it does not lead to phototoxic skin erythema and thus can be considered safe for home treatment. Because of its photochemistry it may be considered less hazardous than psoralens regarding mutagenicity and carcinogenicity.