Caffeine: its action on purine metabolizing enzymes

Caffeine affects the biological responses of human hematopoietic cells of myeloid lineage via downregulation of the mTOR pathway and xanthine oxidase activity

Correction of human myeloid cell function is crucial for the prevention of inflammatory and allergic reactions as well as leukaemia progression. Caffeine, a naturally occurring food component, is known to display anti-inflammatory effects which have previously been ascribed largely to its inhibitory actions on phosphodiesterase. However, more recent studies suggest an additional role in affecting the activity of the mammalian target of rapamycin (mTOR), a master regulator of myeloid cell translational pathways, although detailed molecular events underlying its mode of action have not been elucidated. Here, we report the cellular uptake of caffeine, without metabolisation, by healthy and malignant hematopoietic myeloid cells including monocytes, basophils and primary acute myeloid leukaemia mononuclear blasts. Unmodified caffeine downregulated mTOR signalling, which affected glycolysis and the release of pro-inflammatory/pro-angiogenic cytokines as well as other inflammatory mediators. In monocytes, the effects of caffeine were potentiated by its ability to inhibit xanthine oxidase, an enzyme which plays a central role in human purine catabolism by generating uric acid. In basophils, caffeine also increased intracellular cyclic adenosine monophosphate (cAMP) levels which further enhanced its inhibitory action on mTOR. These results demonstrate an important mode of pharmacological action of caffeine with potentially wide-ranging therapeutic impact for treating non-infectious disorders of the human immune system, where it could be applied directly to inflammatory cells.

Enhancement of cellular adenosine triphosphate levels in PC12 cells by 2,5-dideoxyadenosine, a P-site inhibitor of adenylate cyclase

To elucidate the biological significance of the P-site inhibitor of adenylate cyclase, the effect of 2,5-dideoxyadenosine (DDA) on cellular levels of adenine compounds in PC12 cells was studied. The addition of DDA and deoxyadenosine (deoxyAdo), P-site inhibitors of adenylate cyclase, as well as the addition of adenosine (Ado) to the incubation medium containing glucose as the sole nutrient significantly enhanced cellular ATP levels in PC12 cells. N6-Methyladenosine and N6-cyclohexyladenosine did not augment the ATP levels. The ATP level-enhancing effect of DDA was further enhanced by Ado. After pretreatment of PC12 cells with theophylline, DDA-induced ATP enhancement was potentiated by theophylline but the effect of Ado was suppressed. cAMP levels in PC12 cells were markedly reduced by DDA but the levels were not changed by Ado. These results suggest for the first time that P-site inhibitors of adenylate cyclase may stimulate ATP synthesis via glycolysis by decreasing cAMP levels and the mode of action of the ATP level-enhancing effect of DDA may be different from that of Ado.

Effect of caffeine and zinc on DNA and protein synthesis of neonatal rat cardiac muscle cell in culture

The effect of caffeine and/or zinc on DNA and protein synthesis of purified neonatal-rat ventricular cardiac myocytes was studied. Caffeine (0.2-2 mM) inhibited both DNA and protein synthesis of the cells. Addition of EDTA in the growth medium inhibited both DNA and protein synthesis. Without caffeine and in the presence of lower concentrations of caffeine (0.2 mM) in the growth medium, 10 microM of zinc concentration reversed DNA synthesis, which was inhibited by the chelating agent (EDTA). Higher concentrations of caffeine (2 mM) in the growth medium completely abolished sensitivity of cardiac myocytes to zinc. Additional zinc supplementation to the growth medium of cardiac myocytes did not alter the rate of protein synthesis. The present results suggest that the effect of caffeine on cardiac myocytes may be associated with the zinc-dependent enzymes involved in DNA synthesis.

Caffeine and D2O medium interact in affecting the expression of radiation-induced potentially lethal damage

Earlier work (Ben-Hur et al. 1980) has been extended to compare the killing of log-phase V79 Chinese hamster cells by ionizing radiation when they are treated immediately after irradiation with medium containing either caffeine or 90% D2O. The object was to determine if the enhanced killing due to post-treatment with caffeine, or D2O, resulted from action on the same sector of potentially lethal damage as appeared to be the case for hypertonic shock and D2O medium. The treatments by themselves were not toxic to unirradiated cells. We found that the enhanced expression of potentially lethal damage by post-treatment with caffeine or D2O medium is similar. For example, the kinetics of the repair of the potentially lethal damage expressible by either post-treatment was similar, and an additive enhancement of potentially lethal damage occurred when the two treatments were administered sequentially. These findings suggest that caffeine and D2O medium affect the same sector of potentially lethal damage. When the two treatments were combined, however, they competed with each other. That is, exposures to caffeine, which by themselves did not enhance killing (up to 1 mM for 2 h), decreased the enhanced killing due to D2O medium, Reciprocally, D2O medium reduced the enhanced killing due to high concentrations of caffeine (greater than 1 mM). Thus, although caffeine and D2O medium act on the same sector of potentially lethal damage they do so differently, suggesting that more than one pathway of the expression of radiation damage can result in the same phenotypic effect.

Caffeine reverses the cytotoxic and cell kinetic effects of Novantrone (mitoxantrone)

Caffeine is known to potentiate the cytotoxicity of a variety of DNA damaging agents presumably by reducing the ability of the cells to repair potentially lethal lesions. However, in the present study we observe that 5 mM caffeine reverses the cell kinetic and cytotoxic effects of the intercalating drug Novantrone (mitoxantrone) on L1210, HL-60 and CHO cells. Novantrone alone, at a concentration of 20-30 ng/ml, given to cultures for 1 h, inhibits cell growth by about 50% and causes cells to accumulate in S and G2 phase and to enter a higher DNA ploidy level. Treatment of these cell lines with 5 mM caffeine alone for 1 h has a minimal effect on cell proliferation; suppression of cell growth varies from 5 to 10%. Exposure of cells to Novantrone for 1 h in the presence of caffeine results in a significant reduction of the Novantrone effects; the cell growth rate is partially restored (e.g. caffeine reduces suppression of L1210 cell growth from 48 to 83% of control) and in each of the cell lines studied, the Novantrone-induced cell accumulation in S and G2 is abolished. Combined treatment with caffeine and Novantrone also increases the clonogenicity of CHO cells 8.5 times over that seen in cultures treated with Novantrone alone. In contrast to the combined treatment with caffeine + Novantrone, pretreatment of cells with caffeine provides no protection. Likewise, post-treatment with caffeine provides little reversal of growth inhibition and G2 cell accumulation, especially if the post-treatment is delayed in time. The present data, in conjunction with evidence in the literature that caffeine protects cells against the cytotoxic effects of doxorubicin, suggest that caffeine may play a more general role in protecting cells against planar aromatic molecules such as intercalating agents.

Abrogation of the effects of aphidicolin on NIH3T3 and V79 cells by caffeine

In this communication I show that caffeine (1,3,7-trimethylxanthine) stimulates [3H]thymidine incorporation in aphidicolin-treated V79 and NIH3T3 cells. Flow microfluorometric analysis showed that caffeine, partially or fully, abrogates the cell cycle progression block produced by aphidicolin. Increased cell growth is also observed in cultures treated with both aphidicolin and caffeine compared to cultures treated with aphidicolin only. Microscopic examination of V79 cultures treated with aphidicolin for 8 h showed a marked reduction in the frequency of round mitotic cells, as is expected from a drug which inhibits progression through the cell cycle by inhibiting DNA replication; this effect of aphidicolin was also reduced by caffeine. Biochemical analysis showed that caffeine did not directly interfere with the inhibition of DNA polymerase-alpha by aphidicolin. Analysis of dNTP pools indicated that caffeine increased the level of dCTP in V79 cells. In aphidicolin-treated V79 cells, the increase in the dCTP level due to exogenous cytidine was almost completely blocked; caffeine also substantially overcame this effect of aphidicolin. These results indicate that caffeine produces its effects on aphidicolin-treated cells by altering the dCTP metabolism.

Synergistic killing of HeLa cells by hydroxyurea and caffeine

Synchronous populations of HeLa S3 cells suffer synergistic killing during S phase in the presence of 0.5-5 mM hydroxyurea together with 5-10 mM caffeine. Both the rate and the extent of killing are greater than expected for independent action of the two drugs. Only simultaneous treatment is effective. The dependence of the synergistic killing on cell age resembles the age dependence for killing by hydroxyurea alone (greater than 3 mM), but not that by high concentrations of caffeine. In addition, rapid killing occurs if caffeine is added to cultures that have been incubated in the presence of hydroxyurea from early G1 and are blocked at the beginning of S, although such cells are killed only slowly on continued incubation in greater than or equal to 10 mM hydroxyurea alone. Furthermore, cells that are incubated with the two drugs from early G1 begin to undergo synergistic killing at about 12 h after mitotic collection, but they do not commence DNA replication for another 2-3 h if the drugs are removed. It is concluded that cells that have reached a point in the cycle identical with or close to the end of G1 are sensitive to the combination whether or not they are able to synthesize DNA, and whether or not they are sensitive to hydroxyurea alone. A tentative model is proposed: hydroxyurea is postulated to kill cells by interacting with sites of replication in DNA, and the synergism is attributed to the extra replication points that caffeine is known to induce.

Induction at high frequency of a unique phenotypic class of Bacillus subtilis mutants by methylxanthines

Caffeine and theophylline are mutagenic at high concentration in the B. subtilis multigene sporulation test for mutagens; caffeine is a stronger mutagen than theophylline in this test. An unusually high fraction of the mutant colonies appear to be phenotypically identical, as judged by colonial morphology and microscopic appearance of the vegetative cells. These mutants do not bring about the pH increase normally associated with sporulation of B. subtilis; such behavior is frequently associated with lack of a functional tricarboxylic acid (TCA) cycle, essential for normal sporulation of this species. Similar mutants have not been noted in the course of screening a variety of well-known mutagens, including acriflavine. Caffeine is maximally effective in inducing these mutants about 10 min after germination commences. Adenosine greatly reduces the ability of caffeine to induce these mutants.

Mechanism of caffeine-induced inhibition of DNA synthesis in escherichia coli

Caffeine inhibited DNA synthesis in toluene-treated Escherichia coli K12 strains to the same extent as in intact cells using the incorporation of [3H]thymidine as a measure of DNA synthesis. The inhibition was found to be competitive with ATP, and it was not influenced by the concentrations of deoxynucleoside triphosphates to any extent. When caffeine was added together with other DNA synthesis inhibitors such as novobiocin, nalidixic acid or actinomycin D, the inhibition in all cases was non-additive. It is suggested that caffeine inhibits one of the ATP-requiring enzymes in the DNA replication machinery, possibly DNA polymerase III or one of the DNA helicases.

Growth and death of HeLa cells in the presence of caffeine

Proliferation and death were measured in synchronously growing cultures of HeLa S3 cells during treatment with up to 30 mM caffeine. Changes in the number of colony-forming cells were determined by single-cell plating, while changes in the total number of cells were measured both by electronic counting and by monitoring cell division and physiological death cinemicrographically. At concentrations between 2 and 5 mM, cell killing occurs over several days during which the cells traverse the generation cycle once or a few times before losing colony-forming ability, with consequent proliferation of non-colony-forming cells. This indicates that lethal damage is accumulated with time. Death occurs more rapidly at higher concentrations, without proliferation, the kinetics of inactivation being strongly dependent on the phase of the cycle (cell age) at which treatment is initiated. G1 cells are killed more slowly in 10 mM caffeine than are S cells, but G1 cells respond rapidly to 20 mM caffeine, suggesting the inception of an additional mode of killing. The incidence of sister-cell fusion increases with increasing caffeine concentration above 1 mM. On addition of 10 mM caffeine to a culture prepared from collected mitotic cells, the cells undergo a transient rounding and then respread after several hours; with 20 mM, they never respread. The generation cycle is prolonged in a concentration-dependent fashion, as is the duration of G1; the generation time is doubled in 5-6 mM caffeine. G2 and M are also prolonged at concentrations above 3 mM, but S is not prolonged even by 10 mM caffeine.

Replicative DNA synthesis in permeable fibroblasts from normal individuals and ataxia-telangiectasia patients

Replicative DNA synthesis in normal human fibroblasts was inhibited by 50% when they were X-irradiated (8 Gy) and made permeable 30 min later, whereas only a slight inhibition (20%) was observed in similarly treated ataxia-telangiectasia cells. Treatment of irradiated normal cells with caffeine (2 mM) before permeabilization reversed the inhibitory effects of X-rays, buf caffeine had no effect on DNA synthesis in permeable ataxia-telangiectasia cells. Diadenosine tetraphosphate (0.1 mM) did not affect DNA synthesis in permeable normal fibroblasts.

Effect of caffeine on nucleotide pools in Escherichia coli

The influence of caffeine on the intracellular concentration of various nucleoside triphosphates in addition do dTMP and dTDP, in Escherichia coli has been investigated. For most of the nucleoside triphosphates the presence of 10 mM caffeine in the medium resulted in a small increase in pool size 5 min after addition, followed by a slow decrease to the initial concentration. In the case of dTTP, however, the pool size reached a maximum, 2-fold higher than the initial value, 30 min after caffeine addition. This increase in dTTP level is probably due to an effect of caffeine on the DNA synthesis process and synthesis of dTDP-sugars.

Stimulation of sporulation of Clostridium perfringens by papaverine

Papaverine induced sporulation in Clostridium perfringens, strains FD-1 and PS52; growth was markedly slowed under these conditions. Papaverine induced sporulation in the presence of glucose, a sporulation repressor, although increasing glucose concentrations overcame the papaverine effect. Papaverine induced sporulation of strain FD-1 more effectively than did theophylline.

Induction of sister chromatic exchanges and inhibition of cellular proliferation in vitro. I. Caffeine

Cytogenetic assay systems based on the detection of sister chromatid exchanges (SCE) are widely advocated as a sensitive screening method for assessing genotoxic potential. While many agents have been examined for their ability to induce SCE's, complete dose-response information has often been lacking. We have reexamined the ability of one such compound-caffeine-to induce SCEs and also to inhibit cellular proliferation in human peripheral lymphocytes in vitro. An acute exposure to caffeine prior to the DNA synthetic period did not affect either SCE frequency or the rate of cellular proliferation. Chronic exposure to caffeine throughout the culture period lead to both a dose-dependent increase in SCEs (SCEd or doubling dose = 2.4 mM; SCE10 or the dose capable of inducing 10 SCE = 1.4 mM) and a dose-dependent inhibition of cellular proliferation (IC50 or the 50% inhibition concentration = 2.6 mM). The relative proportion of first generation metaphase cels, an assessment of proliferative inhibition, increased linearly with increasing caffeine concentrations. However, SCE frequency increased nonlinearly over the same range of caffeine concentrations. Examination of the ratio of nonsymmetrical to symmetrical SCEs in third generation metaphase cells indicated that caffeine induced SCEs in equal frequency in each of three successive generations. The dependency of SCE induction and cellular proliferative inhibition on caffeine's presence during the DNa synthetic period suggests that caffeine may act as an antimetabolite in normal human cells. The significance of these results in regard to both caffeine's genotoxic potential and to the reliability of the SCE assay system are discussed.

The structure of methylated xanthines in relation to their effects on DNA synthesis and cell lethality in nitrogen mustard-treated cells

The variation in cellular response to alkylated xanthines possessing different side chains has been used to evaluate more fully the effect of caffeine on both survival and DNA synthesis in cells with DNA damage. A correlation is observed between the ability of these xanthines to reverse the inhibitory effects of nitrogen mustard damage on DNA synthesis and their ability to enhance nitrogen mustard lethality in human HT-29 cells. These findings are consistent with our theory that regulation of damaged replicon initiation protects against potentially lethal damage in the form of unrepaired DNA alkylations. Enhancement of nitrogen mustard lethality is observed to have a maximum limit, which can be reduced by highly toxic xanthine concentrations. The lethal effects of xanthines alone at higher concentrations are unrelated to the effects of caffeine specific to nitrogen mustard treated cells, and appear to be related to an immediate reduction in thymidine incorporation most likely caused by inhibition of other enzyme systems influencing DNA synthesis such as de novo and salvage pathways for purine biosynthesis.