[Comparison of photomutagenic activities of 5-mop (bergapten) and 8-mop (xanthotoxin) in chlamydomonas reinhardii (author's transl)]

Protective effect of furocoumarins against 254-nm ultraviolet in Staphylococcus aureus

For Staphylococcus aureus, pretreatment with furocoumarins (FCs) protect cells against killing by far ultraviolet light (FUV; approximately 254 nm). This protective effect was evident in the repair-proficient, parental strain as well as in the repair-deficient variants in the following order of efficacy: 4,5'',8-trimethylpsoralen << 8-methoxypsoralen congruent with angelicin < 3-carbethoxypsoralen. The extent of protection was greater in the parental strain, indicating that despite the protective effect, a certain number of lethal lesions are nevertheless produced, which would be repaired with greater efficiency in such a strain than in the repair-deficient ones. This protective effect could be attribute to the inhibition of the formation of cyclobutyl pyrimidine dimers. Although the energy-transfer concept could explain the inhibition of pyrimidine dimer formation, and thus the protective effect of FC against FUV, we cannot rule out the possibility that the differences in degree of protection afforded by the FC employed here are related to a subtle and complex combination of effects.

Furoquinoline alkaloids as photosensitizers in Chlamydomonas reinhardtii

Seven naturally occurring furoquinoline alkaloids were investigated for their photobiological activity using arg-1 cells of Chlamydomonas reinhardtii. UV-A-mediated toxicity of the compounds was calculated from the colony-forming ability of the treated cells. The UV-A-mediated mutagenicity was measured by counting the number of Arg+ revertants induced by the treatment. Dictamnine was found to be the strongest mutagen as well as the most toxic compound of the group. The mutagenic activities were measured as mutation frequencies at equal substance concentration and ranked in the following order: An increase in the number of substituents on the lateral aromatic nucleus greatly decreased the photomutagenicity. Except for evolitrine, a similar ranking order was found as reported for the dark mutagenicity of these compounds in Salmonella typhimurium strain TA98. Based on the result that furoquinolines are able to intercalate into DNA, we assume that the different mutagenic potencies may reflect differences in the geometry of the intercalation complex, which is important for the subsequent photochemical reaction.

Mutagenic compounds in an extract from Rutae Herba (Ruta graveolens L.). II. UV-A mediated mutagenicity in the green alga Chlamydomonas reinhardtii by furoquinoline alkaloids and furocoumarins present in a commercial tincture from Rutae Herba

A commercial tincture prepared from Rutae Herba (Ruta graveolens L.) exhibited a moderate photomutagenicity in an arginine-requiring mutant strain of Chlamydomonas reinhardtii. In the tincture some furocoumarins, e.g., bergapten, psoralen, imperatorin, and 3 furoquinoline alkaloids (dictamnine, gamma-fagarine, skimmianine) were detected. All compounds revealed photomutagenic properties but their activities were quite different. Bergapten was the most potent furocoumarin. Dictamnine, the furoquinoline with the strongest effect, reached only about 10% of the activity of bergapten. Based on the amount of these compounds in the tincture and their activities we conclude that bergapten is mainly responsible for the photomutagenicity of the tincture. The lower phototoxicity and photomutagenicity of the furoquinoline alkaloids may be due to the fact that furoquinolines form only monoadducts with DNA in the presence of UV-A in contrast to furocoumarins which also form biadducts.

The clastogenic effect of 5-methoxypsoralen plus UV-A in human lymphocytes in vitro and its modification by the anticlastogen beta-aminoethylisothiouronium

The treatment of human lymphocytes in vitro with 5-methoxypsoralen (5-MOP) plus UV-A induces a dose-dependent increase in the SCE rate and in structural chromosome aberrations. We carried out tests to see whether the clastogenic effect of 5-MOP plus UV-A could be reduced by the anticlastogen beta-aminoethylisothiouronium (AET). The occurrence of a protective effect proved to be dependent upon the conditions of treatment. When AET was present over a long period of time (22 h) in cultures with 5-MOP, the number of breaks was reduced compared with such cultures without AET (reduction factor 0.5-0.6). On the other hand, a short period of action by AET (1.5 h) in the presence of 5-MOP produced no reduction of breaks. Posttreatment with AET (20 h) yielded an obvious protective effect (reduction factor 0.2-0.4). The possible mechanisms of the protective effect of AET are discussed.

Chromosome damage induced in human lymphocytes by 5-methoxypsoralen and 8-methoxypsoralen plus UV-A

The induction of structural chromosome aberrations and sister chromatid exchanges (SCE) was studied in human lymphocytes in vitro after treatment with the two bifunctional furocoumarins 5-methoxypsoralen (5-MOP) and 8-methoxypsoralen (8-MOP) in the presence of UV-A. The results show that both psoralens induce a dose-dependent increase in the SCE rate as well as in structural chromosome aberrations. 5-MOP was 2.0-2.5 times more effective for the induction of chromosome breaks and had a slightly stronger effect with respect to SCE induction. A significant influence on proliferation kinetics could be observed only with 5-MOP plus UV-A.

Mutagenicity of a furocoumarin epoxide, heraclenin, in Chlamydomonas reinhardii

Treatment of arg- or strd mutant cells of Chlamydomonas reinhardii with a furocoumarin epoxide, heraclenin, plus UV-A resulted in a decrease in survival and a UV-A dose-dependent increase in induced Arg+ or Strs revertants. Imperatorin, a furocoumarin with a very similar structure but lacking an epoxide group showed a very similar phototoxic and photomutagenic activity in these mutant strains. Treating the mutant cells with heraclenin or imperatorin in the dark neither influenced survival nor mutation induction. The results are discussed with respect to the involvement of the epoxide moiety of heraclenin in mutagenicity.

Genotoxic effects and DNA photoadducts induced in Chinese hamster V79 cells by 5-methoxypsoralen and 8-methoxypsoralen

The induction of lethal effects and 6-thioguanine-resistant (6-TGr) mutants were studied in Chinese hamster V79 cells after treatment with the two bifunctional furocoumarins 5- and 8-methoxypsoralens (5-MOP, 8-MOP) in the presence of 365-nm radiation (UVA). The in vivo DNA-photobinding capacity of these two compounds was measured and in parallel the cross-linking capacities of 5-MOP and 8-MOP were determined using the alkaline elution technique. The results show that 5-MOP plus UVA was about 2.5 times more effective than 8-MOP plus UVA for inhibiting cell survival and for inducing the same frequency of 6-TGr mutants (10(-4]. The total number of photoinduced lesions by 5-MOP plus UVA was about 6 times higher than that induced by 8-MOP plus UVA. However, the cross-linking capacities of 5-MOP and 8-MOP were found to be within the same range at equal doses of UVA. At equal number of DNA photoadducts produced, the lesions induced by 5-MOP appeared to be less genetically active than those induced by 8-MOP. The apparently weaker genotoxicity of 5-MOP-induced lesions is likely to be due to the induction of a lower proportion of cross-links by 5-MOP at a given number of photoadducts.