Protection and potentiation of radiation clastogenesis by caffeine: nature of possible initial events

Melatonin-Caffeine Combination Modulates Gamma Radiation-induced Sperm Malformations in C57BL/6 Male Mice at Sublethal Dose of Gamma Radiation

Aims:

The aim of this study was to assess the protective effect of the melatonin–caffeine combination against γ radiation-induced alterations in the morphological characteristics of sperms.

Settings and Design:

C57BL/6 male mice (n = 30) were randomly divided into five groups: control, radiation (2 Gy), melatonin (100 mg/kg body wt.) + radiation (2 Gy), caffeine (30 mg/kg body wt.) + radiation (2 Gy), melatonin–caffeine (100–30 mg/kg body wt.) + radiation (2 Gy).

Materials and Methods:

All the mice were sacrificed 24 h postirradiation, and cauda epididymis was collected. In this study, sperm concentration along with any abnormality in their morphology (amorphous heads, pinheads, hookless, coiled tails, midpiece defect, and tail-less) was observed in the control and treatment group of animals.

Results:

Radiation exposure (2 Gy) considerably decreases the sperm count when compared with the control group. However, pretreatment with melatonin and melatonin–caffeine combination before gamma irradiation increased the sperm count (P < 0.05), but with caffeine alone could not produce a significant difference. The higher rate of abnormal sperms was observed in the γ-irradiated mice when compared with the control group (P < 0.05). Besides, the numbers of sperm that are hookless and coiled tails were significantly increased after irradiation. Melatonin significantly reduced the number of sperm with amorphous heads and coiled tails. Melatonin–caffeine combination further reduced sperm malformations when compared with the melatonin + 2 Gy radiation and caffeine + 2 Gy radiation group.

Conclusions:

This study suggests that caffeine exerts a protective effect when given in combination with melatonin against gamma irradiation in sperms of C57BL/6 mice and could be a potent combination for the development of radioprotector.

Pharmacology of natural radioprotectors

Radiotherapy is one of the most efficient ways to treat cancer. However, deleterious effects, such as acute and chronic toxicities that reduce the quality of life, may result. Naturally occurring compounds have been shown to be non-toxic over wide dose ranges and are inexpensive and effective. Additionally, pharmacological strategies have been developed that use radioprotectors to inhibit radiation-induced toxicities. Currently available radioprotectors have several limitations, including toxicity. In this review, we present the mechanisms of proven radioprotectors, ranging from free radical scavenging (the best-known mechanism of radioprotection) to molecular-based radioprotection (e.g., upregulating expression of heat shock proteins). Finally, we discuss naturally occurring compounds with radioprotective properties in the context of these mechanisms.

Neocarzinostatin as a probe for DNA protection activity--molecular interaction with caffeine

Neocarzinostatin (NCS), a potent mutagen and carcinogen, consists of an enediyne prodrug and a protein carrier. It has a unique double role in that it intercalates into DNA and imposes radical-mediated damage after thiol activation. Here we employed NCS as a probe to examine the DNA-protection capability of caffeine, one of common dietary phytochemicals with potential cancer-chemopreventive activity. NCS at the nanomolar concentration range could induce significant single- and double-strand lesions in DNA, but up to 75 ± 5% of such lesions were found to be efficiently inhibited by caffeine. The percentage of inhibition was caffeine-concentration dependent, but was not sensitive to the DNA-lesion types. The well-characterized activation reactions of NCS allowed us to explore the effect of caffeine on the enediyne-generated radicals. Postactivation analyses by chromatographic and mass spectroscopic methods identified a caffeine-quenched enediyne-radical adduct, but the yield was too small to fully account for the large inhibition effect on DNA lesions. The affinity between NCS chromophore and DNA was characterized by a fluorescence-based kinetic method. The drug-DNA intercalation was hampered by caffeine, and the caffeine-induced increases in DNA-drug dissociation constant was caffeine-concentration dependent, suggesting importance of binding affinity in the protection mechanism. Caffeine has been shown to be both an effective free radical scavenger and an intercalation inhibitor. Our results demonstrated that caffeine ingeniously protected DNA against the enediyne-induced damages mainly by inhibiting DNA intercalation beforehand. The direct scavenging of the DNA-bound NCS free radicals by caffeine played only a minor role.

Modulation of methotrexate-induced cytogenotoxicity in mouse spermatogonia and its transmission in the male germline by caffeine

Apart from its own controversial cytogenotoxic effects, caffeine (CAF), one of the most commonly consumed alkaloids worldwide, is found potentiative to and so also protective from the cytogenotoxic effects of numerous chemical and physical mutagens. It also has modulated the actions of several antineoplastic agents. Additionally, it has been tested as a chemopreventive of cancer and is reportedly associated inversely with different cancer risks. Therefore, in the present study, three different sub-lethal doses of CAF, 25, 50 and 100mg/kg, were tested in mouse to assess their cytogenotoxic effects on dividing spermatogonia at 24h post-treatment, and transmission of such effects in the male germline from the primary spermatocytes and sperm at week 4 and week 8 post-treatment, respectively. CAF was found to be weakly clastogenic to mouse spermatogonia and the effects were also found transmitted in the male germline. Interestingly, such induced effects were quantitatively related to the dose of CAF tested. On the other hand, methotrexate (MTX), an antifolate antimetabolite, is prescribed frequently for the treatment of various types of cancers. However, MTX is reportedly clastogenic. Modulation of the said three different pre-treated doses of CAF on MTX 10mg/kg-induced cytogenotoxic effects, tested in the same experimental protocol, indicated that CAF pre-treatment was decreasing the MTX-induced clastogenicity in spermatogonia, and was lowering the concurrent transmission of such effects in the male germline of mice, significantly. Such decreases were related to the dose of CAF tested, i.e. higher the dose of CAF more was the decrease in the MTX-induced cytogenotoxic effects and in their transmission. The possible mechanisms that might have caused the manifestation of a weak clastogenic action of CAF on spermatogonia and in its transmission in the male germline, and the CAF modulation of MTX-induced cytogenotoxic effects in spermatogonia and in their transmission have been discussed.

Modulatory effects of caffeine on methotrexate-induced cytogenotoxicity in mouse bone marrow

Caffeine (CAF), a widely used and extensively studied chemical, is known for the reports on its controversial and inconsistent genotoxic effects, potentiative and protective effects from the genotoxicity of chemical and physical mutagens, and its modulatory effects on the action of antineoplastic drugs. Methotrexate (MTX), an antifolate antimetabolite, is a widely prescribed antineoplastic drug with significant clastogenic effects. In the present study, in addition to the assessment of cytogenotoxicity of CAF 25, 50 or 100mg/kg in mouse bone marrow, their modulatory effects on the cytogenotoxicity of MTX 10mg/kg was assessed from the induced frequencies of aberrant metaphases, chromosomal aberrations (CAs) and percentages of dividing cells at 24h post-treatment and the induced frequency of micronuclei (MN) at 30h post-treatment. All the three doses of CAF induced higher percentages of aberrant metaphases, high frequency of CAs and MN and increased percentages of dividing cells, but the increase in the aberrant metaphases and CAs was statistically significant only with the highest dose of CAF. Thus, CAF was weakly clastogenic to mouse bone marrow cells. However, pre-treatment of each of the three doses of CAF reduced the frequency of MTX 10mg/kg-induced aberrant metaphases, CAs, MN and also the percentage of dividing cells, but significantly only by the two higher doses of CAF. Thus, the higher doses of CAF protected mouse bone marrow cells from the cytogenotoxicity of MTX. The possible mechanisms involved in bringing about the weak clastogenic action of CAF and its protection from the cytogenotoxic effects of MTX have been discussed, and bio-modulation of the effects of antineoplastic drugs has been highlighted.

Caffeine ameliorates radiation-induced skin reactions in mice but does not influence tumour radiation response

Intramuscular administration of caffeine at a dose of 80 mg kg(-1) body weight to the gastrocnemius muscles of Swiss mice 5 min prior to local irradiation (35 Gy) of the leg delayed the progression of radiation-induced skin reactions in such animals. While 90% epilation with reddening of the skin was noted in animals treated with radiation alone, animals pretreated with caffeine suffered only partial hair loss with slight reddening of the skin on the 16th and 20th days post-irradiation. Beyond the 28th day, damage scores in irradiated feet for both the groups were similar (score 3) and remained unchanged until the 32nd day and then decreased and disappeared completely in both treatment groups by the 40th day after irradiation. In addition, the effect of caffeine on the radiation response of a mouse fibrosarcoma was investigated. Results showed that intratumoral administration of caffeine at a dose of 80 mg kg(-1) body weight 5 min prior to local exposure of tumours to 10 Gy of 60Co gamma-rays did not influence the response of tumours to radiation. The present study thus showed that although caffeine ameliorated radiation-induced skin reactions in the mouse leg, it did not affect the tumour radiation response, indicating its potential application in cancer radiotherapy.

Caffeine protects mice against whole-body lethal dose of gamma-irradiation

Administration of caffeine (1,3,7-trimethylxanthine), a major component of coffee, to Swiss mice at doses of 80 or 100 mg/kg body weight 60 min prior to whole-body lethal dose of gamma-irradiation (7.5 Gy) resulted in the survival of 70 and 63% of animals, respectively, at the above doses in contrast to absolutely no survivors (LD-100/25 days) in the group exposed to radiation alone. Pre-treatment with a lower concentration of caffeine (50 mg/kg) did not confer any radioprotection. The protection exerted by caffeine (80 mg/kg), however, was reduced from 70 to 50% if administered 30 min prior to irradiation. The trend statistics reveal that a dose of 80 mg/kg administered 60 min before whole-body exposure to 7.5 Gy is optimal for maximal radioprotection. However, caffeine (80 mg/kg) administered within 3 min after irradiation offered no protection. While there is documentation in the literature that caffeine is an antioxidant and radioprotector against the oxic pathway of radiation damage in a wide range of cells and organisms, this is the first report demonstrating unequivocally its potent radioprotective action in terms of survival of lethally whole-body irradiated mice.

Caffeine as an antioxidant: inhibition of lipid peroxidation induced by reactive oxygen species

Caffeine (1,3,7-trimethyl xanthine), an ingredient of coffee, has been investigated for its potential antioxidant activity against oxidative damage to rat liver microsomes. Such damage was induced by three reactive oxygen species of cardinal importance in causing membrane damage in vivo namely hydroxyl radical (.OH), peroxyl radical (ROO.) and singlet oxygen (1O2). The results obtained showed that caffeine was an effective inhibitor of lipid peroxidation, at millimolar concentrations, against all the three reactive species. The extent of inhibition was high against peroxidation induced by .OH, medium against 1O2 and low against ROO. In general, the antioxidant ability of caffeine was similar to that of the established biological antioxidant glutathione and significantly higher than ascorbic acid. Investigations into the possible mechanisms involved in the observed antioxidant effect reveal that the quenching of these reactive species by caffeine may be one of the possible factor responsible. The rate constant of caffeine with .OH was 7.3 x 10(9) M-1 s-1 and with 1O2 it was 2.9 x 10(7) M-1 s-1. Considering their potential for damage, half-life estimates and generation in biological systems, the ability of caffeine to inhibit oxidative damage induced by these reactive species in membranes suggest one more positive attribute of caffeine, whose daily intake as coffee may be considerable in most populations.

Caffeine potentiates or protects against radiation-induced DNA and chromosomal damage in human lymphocytes depending on temperature and concentration

The effect of caffeine on radiation-induced chromosomal aberrations and DNA strand breaks in unstimulated human lymphocytes was investigated. When present prior to and during the radiation exposure, caffeine treatment was found to cause either potentiation or protection against induction of chromosomal aberrations depending on the concentration and temperature. When the nucleoid sedimentation technique was applied, enhancement or reduction of radiation-induced DNA strand breaks by caffeine was also found to be dependent on temperature and caffeine concentration. It is proposed that caffeine, in addition to its suspected ability to influence DNA repair, can also influence the induction of DNA damage, leading to alterations in the yield of chromosomal aberrations.

Radioprotection by caffeine pre- and post-treatment in the bone marrow chromosomes of mice given whole-body gamma-irradiation

The effect of caffeine given as pre- and post-treatment in mice exposed to whole-body gamma-irradiation (1.5 Gy 60Co gamma-rays) was studied. The pre-treatment was either acute or chronic. The acute dose (5 mg/kg and 15 mg/kg body weight) was in the form of an injection given intraperitoneally, 30 min before irradiation. The chronic administration was in the form of caffeine solution (4.208 x 10(-3) M and 7.72 x 10(-4) M) contained in the drinking water that mice had had ad libitum access to instead of plain drinking water for 5 weeks prior to radiation exposure. The acute pre-treatment with caffeine reduced the radiation-induced frequency of chromosomal aberrations discernibly, whereas the chronic pre-treatment afforded a much more significant degree of radioprotection. The caffeine post-treatment (5 mg/kg and 15 mg body weight) was given in the form of an intraperitoneal injection to the mice immediately following whole-body gamma-irradiation. It is noted that both post-treatment concentrations of caffeine also significantly reduced the frequency of chromosomal aberrations induced by gamma-rays. These data are briefly discussed in terms of possible mechanistic considerations.

Biochemical effects of heat shock and caffeine on post-irradiation oxic and anoxic damage in barley seeds of low and high water content

Wet heat shock (60 degrees C, 90 s) and caffeine (3.8 X 10(-4) M) afford significant radioprotection against post-irradiation O2-dependent damage which develops in seeds of approximately 3.5% moisture content. The damage was assessed in terms of seedling injury on the eighth day of growth. An increase in seedling injury is clearly seen, associated with a parallel increase in the peroxidase activity. There is a concomitant decrease in the content of total peroxides. Both these post-irradiation treatments potentiate the O2-independent component of seedling injury, irrespective of the seed moisture content. Analysis of the peroxidase activity in the seedlings using non-denaturing polyacrylamide gel electrophoresis reveals that two additional bands appear with the post-irradiation oxic damage. Radioprotection against this damage by caffeine, heat shock and O2-free post-irradiation hydration is accompanied by the disappearance of these two additional bands. However there is no appearance of the two additional bands in the peroxidase family even though the enzyme activity is substantially increased due to the action of caffeine and/or heat shock on the post-irradiation O2-independent pathway of damage. The probable mechanisms of radioprotection are discussed in this paper.

Chemical modification of postirradiation damage under varying oxygen concentrations in barley seeds

The influence of ascorbic acid, potassium permanganate and caffeine on the postirradiation seedling injury of dry barley seeds was studied, irradiated (350 Gy 60Co gamma-rays) in vacuo and post-hydrated with varying oxygen concentrations in the soaking medium. The oxygen concentration in the post-hydration medium (OCHG) was adjusted at 0%, 10%, 30%, 50%, 80% and 100%. A linear response between the seedling injury and O2 concentration in the range of 0-80% was observed. These chemicals potentiated, protected or exerted no effect, depending upon the OCHG. Thus, ascorbic acid did not exert any effect on seeds post-hydrated at OCHG of less than or equal to 30%, but afforded radio-protection at OCHG of greater than or equal to 50%. Caffeine, on the other hand, potentiated the postirradiation injury at OCHG of less than or equal to 30%, exerted no influence at OCHG of approximately 50% and afforded radioprotection at OCHG of greater than or equal to 80%. Potassium permanganate enhanced the injury at OCHG of less than or equal to 10%, exerted no effect at OCHG of approximately 30% and afforded radioprotection at OCHG of greater than or equal to 50%. The possible radiation-chemical events in the dry irradiated seeds following their post-hydration containing different OCHG and the three test chemicals which are known free radical scavengers are discussed.

Increased frequency of spontaneous and X-ray-induced chromosomal aberrations in lymphocytes from neonates and the influence of caffeine--an in vitro study

We have examined lymphocytes from human preterm (PT) and fullterm (FT) babies for an effect of gestational age (GA) on chromosomal aberrations either occurring spontaneously or induced by treatment with X-rays (1 Gy) alone; or with caffeine (1,3,7-trimethylxanthine) supplementation (5 X 10(-4) M), in comparison to the lymphocytes of healthy adults (AD). Percent of abnormal cells (%Abn) was used as an indicator of chromosome sensitivity to the different treatments. PT babies had significantly higher spontaneous and X-ray-induced %Abn values than AD, but were comparable to FT. After X-irradiation + caffeine the yield of aberrations in any 2 groups was not significantly different. Chromosomal sensitivity may result from factors other than GA. This in vitro model may permit study of the mechanisms of chromosomal damage repair and prevention of free radical damage of DNA during the perinatal period.

Purine and its analogues and radiation damage in Bacillus megaterium spores

As an extension of results obtained from radiation studies on caffeine both in other laboratories and more recently in this laboratory using the bacterial spore as the test system, six compounds with chemical structures closely resembling that of caffeine were tested as radiation modifiers. Of these compounds, purine, adenine and hypoxanthine resembled caffeine in sensitizing spores to radiation, while theobromine, xanthine and theophylline did not. These responses are discussed in relation to the electron sequestration hypothesis of cellular sensitization to high-energy radiation.