Mechanism of Caffeine Enhancement of Mutations Induced by Sublethal Ultraviolet Dosages

Abstract

Certain chemical compounds increase mutation frequency of Escherichia coli B/r significantly when used in conjunction with nonlethal ultraviolet (UV) dosages. Studies were done to elucidate the mechanism of this enhancing mutational effect. Dark survival curves showed that 500 ,ug of caffeine per ml in the postirradiation medium markedly decreased survival to 60 ergs/mm2 of UV in strain B/r. Caffeine did not markedly decrease survival to UV in strain B/r WP-2 hcr-. At least 90% of the mutations induced to streptomycin resistance by UV and 85 % of those induced by UV with caffeine could be photoreversed. Experiments with thymine analogues suggested that thymine dimerization at the streptomycin locus was the primary premutational photoproduct induced by sublethal UV dosages. Caffeine did not interfere with the photoreversal of induced mutants, indicating that it probably does not bind to the photoreactivating enzyme or to a UV-induced lesion in the DNA. Addition of DNA or irradiated DNA with 500 ,g of caffeine per ml resulted in no loss of the caffeine activity. The excision of UV-induced thymine-containing dimers from E. coli B/r Twas investigated in the presence and absence of caffeine. Our results indicated that caffeine prevents excision of thymine dimers, presumably by binding to the excising enzyme. This binding results in an impairment of repair, which produces the increase in mutant numbers. Caffeine, theophylline, and theobromine, as well as acridine dyes, increase the frequency of mutations induced by lethal and sublethal ultraviolet (UV) light when they are added to the postirradiation medium of Escherichia coli strain B/r (3, 14, 23, 29, 30). Bacterial killing is increased when bacteria irradiated with lethal and sublethal dosages are plated on a medium containing acriflavine (1, 7, 30) or caffeine (7, 17, 29). These compounds decrease the survival of UV-irradiated phage by inhibiting host cell reactivation (5). The increase in both killing and mutation can be attributed to inhibition of a "dark repair" process that repairs UV photoproducts in the irradiated bacteria. Irradiation of bacteria with high dosages of UV light produces a variety of pyrimidine dimers in the deoxyribonucleic acid of these organisms (DNA) (21). Pyrimidine dimers can be repaired either by photoreactivation, in which the photoreactivating enzyme splits dimers in situ (35), or by excision of pyrimidine dimers from the DNA in the dark (2, 20, 25). Numerous UVsensitive mutants of E. coli have been isolated 198 Vol. 96, No. I

Structural alterations in Candida albicans by caffeine and caffeine salts

“…According to Downes et al [12], caffeine overcomes a restriction point associated with DNA replication, but does not accelerate mitosis. With ultraviolet radiation (which was not applied here), caffeine is a specific inhibitor of excision repair, for instance in Escherichia coli [ 13,14 ]; but in the recovery of Candida albicans in the dark, no involvement of DNA repair was detected [15]. As a result of experiments with caffeine-sensitive and caffeineresistant strains of Candida albicans, Sarachek et al…”

UV Survival of Human Mycoplasmas: Evidence of Dark Reactivation in Mycoplasma buccale

“…However, there are some differences in the mode of action of caffeine on repair processes between prokaryotes and eukaryotes [see review by Kihlman (20)]. In E. coli caffeine inhibits the excision of pyrimidine dimers from UV-damaged DNA (19,32,33,38), whereas caffeine does not inhibit the postreplication repair in excision-deficient strains of E. coli (22). Fabre (7,8) has reported that two pathways, excision and recombinational repair, act to repair UV-lesions in the yeast S.pombe with the latter pathway sensitive to caffeine but not the former.…”

Antimutagenesis in microbial systems.

“…In view of the findings (119) that caffeine is one of the most effective mutagens and darkrepair inhibitors (42) of several methylated purines tested, it would be extremely interesting to compare the relative antimutagenic activities of a series of methylated purines. If all three activities of methylated purines -mutagenesis of replicating bacterial DNA (57), repair inhibition (65,144), and antimutagenesis-depend on weak binding to DNA (41), then the same rank order for the various purines might be expected for the above three types of activities. Any deviation from this expectation might well provide clues as to a more specific mode of antimutagenic action of methylated purines.…”