Supraadditive formation of micronuclei in preimplantation mouse embryos in vitro after combined treatment with X-rays and caffeine

The influence of caffeine (0.1 or 2 mM), X-rays (0.24 Gy [= 25 R] or 0.94 Gy [= 100 R]), or of a combination of both on the formation of micronuclei in early stages of preimplantation mouse embryos in vitro was studied. X-rays as well as caffeine induced micronuclei. The dose-effect curve after irradiation was linear for the dose range measured (0-3.76 Gy; = 0-400 R). Caffeine did not induce micronuclei if the concentration was 1 mM or less; between 1 mM and 7 mM, however, there was a linear increase in the number of micronuclei. A considerable enhancement of the number of radiation-induced micronuclei was observed when irradiation of the embryos was followed by a treatment with caffeine. Not only was the sum of the single effects exceeded by the combination effects, but the combination results even lay in the range of supraadditivity of the envelope of additivity.

The effects of fasting on the acute oral toxicity of nine chemicals in the rat

Nine chemicals, with a range from extremely to slightly toxic, were used to measure the oral LD50 in both fasted (24-h) and non-fasted rats. Each chemical was tested as a solution or suspension in corn oil, responses within 14 days post-treatment were evaluated, and LD50S were calculated. Hexachlorophene was more toxic in non-fasted rats. The LD50 values for tetraethyl lead, methomyl and hexamethylenediamine were essentially the same in both fasted and non-fasted rats. Adiponitrile, bromobenzene, caffeine, carbon tetrachloride and N-butyl-1,6-hexamediamine yielded lower LD50 values in fasted rats. The use of non-fasted rats in acute oral toxicity determinations allows both the establishment of relative potency and the estimation of dosage levels for further repeated dose oral studies. The LD50 values obtained were generally (7 of 9) higher in non-fasted rats, but the magnitude of the differences was not great enough to suggest routine use of both fasted and non-fasted rats in oral toxicity studies.

[Pharmacological correction of disordered function of the myocardial contractile proteins]

The ability of some drugs to normalize the disturbed interaction of myocardial contractile proteins with ATP determined by superprecipitation of myocyte actomyosin was studied in experimental allergic and caffeine-adrenaline-induced injury to the rabbit myocardium. Ethimizole (2.5 mg/kg) appeared the most effective, while isolanide (0.005 mg/kg), contrykal (500 Units/kg), propranolol (1 mg/kg) and amidopyrine (10 mg/kg) were less effective. The action of prednisolone (5 mg/kg) appeared especially demonstrable in allergic myocardial injury.

Two-year toxicity/carcinogenicity study of fresh-brewed coffee in rats initially exposed in utero

Fresh-brewed regular coffee at concentrations of 25, 50, and 100% was consumed ad libitum as the sole fluid intake of F1 Sprague-Dawley rats (55 male and 55 female/group), derived from P0-treated females which were provided 50% coffee for about 5 weeks prior to copulation and throughout gestation and lactation. P0 males, P0 control females, and two groups of F1 control rats received tap water. Ten rats/sex/level were killed and examined after 1 year; survivors were killed after 2 years. Smaller mean body weights (50 and 100% coffee concentrations) occurred with increased feed and liquid consumption. Mean serum alkaline phosphatase, bilirubin, BUN, and calcium values occasionally were elevated. Serum cholesterol levels at 2 years were elevated in males (25 and 100%) and at 1 and 2 years in females (100%). Bone calcium was slightly reduced in females consuming 25 or 100% coffee for 1 year, but not after 2 years. Treatment-related increases in relative weights of lungs, kidneys, liver, and epididymides were recorded. Significantly increased mortality was observed in females receiving 50 or 100% coffee. There also was some evidence of a relationship between coffee consumption and the number of primary tumor-bearing animals; however, this finding appeared ambiguous, dependent on the assumption that tumors were the probable cause of death.

Estimation of creatine kinase isoenzymes: the effects of caffeine and retinoic acid on CK levels in fetal mouse limbs

Caffeine and retinoic acid were examined for effects upon limb morphogenesis and upon creatine kinase (CK) as a measure of limb myogenesis. Caffeine at 200 mg/kg, i.p., on E11 produced a low level of forelimb (1.2%) and hindlimb (2.0%) defects. Retinoic acid, at 50 mg/kg given orally as an oily suspension, induced a high level of reduction deformities. Hindlimbs (100%) were affected more than forelimbs (88%). Limbs (E16) were examined for CK isoenzymes using DEAE-Sephacel column chromatography. Untreated limbs had 88.04% skeletal muscle (MM), 6.98% hybrid (MB) and 5.08% brain (BB) CK isoenzyme. Caffeine had no effect. However, retinoic acid increased MM-CK to 92.67%, and decreased BB-CK to 2.24%. This is the first evidence that suggests that retinoic acid may modify the phenotypic expression of developing muscle.

The influence of caffeine on tumour incidence in Sprague-Dawley rats

Food-grade natural caffeine was given in the drinking-water (available ad lib.) to barrier-maintained specified-pathogen free Sprague-Dawley rats for 2 yr. Groups of 50 animals per sex received levels of 200, 430, 930 and 2000 mg caffeine/litre, while two control groups, each of 50 animals per sex, received plain water. No unusual tumours or sites of origin for neoplastic growth were found in any animal receiving caffeine. Neoplasms found in various organs showed incidences not exceeding those seen in controls. Thus, exposure to caffeine for 2 yr did not enhance or induce neoplasia in the Sprague-Dawley rats.

Influence of caffeine and 3-aminobenzamide in G2 on the frequency of chromosomal aberrations induced by thiotepa, mitomycin C and N-methyl-N-nitro-N'-nitrosoguanidine in human lymphocytes

The effects of post-treatments with caffeine in G2 on the frequency of chromosomal aberrations induced by thiotepa, mitomycin C and N-methyl-N-nitro-N'-nitrosoguanidine were studied in human lymphocytes. Caffeine was found to potentiate the frequency of chromatid aberrations induced by all 3 S-dependent agents tested; the most striking enhancement being obtained when caffeine was present during the last 1.5 h before harvesting. Post-treatments in G2 with 3-aminobenzamide had no influence on the aberration frequency induced by thiotepa and N-methyl-N-nitro-N'-nitrosoguanidine.

In vivo and in vitro effects of caffeine on hepatic mixed-function oxidases in rodents and chicks

Administration of caffeine, ip 100 mg/kg/day for 1-5 days, to adult male rats resulted in a significant increase in hepatic cytochrome P-450 and b5 concentrations and in cytochrome c reductase, aminopyrine N-demethylase and acetanilide hydroxylase activities. No change was seen in relative liver weight but microsomal protein content was increased after treatment for 1 day and decreased after treatment for 3 or 5 days. In adult rats given 25, 100 or 150 mg caffeine/kg for 3 days, maximum stimulation of mixed-function oxidases was seen with the 100-mg/kg dose. Caffeine treatment (100 mg/kg for 3 days) increased relative liver weight in female guinea-pigs and decreased it in chicks and female mice, and decreased microsomal protein content in male mice, female guinea-pigs and young rats, and increased it in chicks. A significant increase in hepatic cytochrome P-450 content was seen in all species studied. Cytochrome b5 content was increased in chicks and young rats, while cytochrome c reductase activity was increased in male and female mice, young rats and chicks and decreased in female guinea-pigs. Aminopyrine N-demethylase activity was increased in young rats and female guinea-pigs, and acetanilide hydroxylase was increased in all test species except male mice. In vitro addition of 2.5 mM-caffeine to microsomal incubations from untreated rats, guinea-pigs, mice and chicks inhibited aminopyrine N-demethylase activity, although only to a significant extent in male mice; addition of caffeine to incubations containing microsomes from caffeine-treated animals produced significant inhibition of aminopyrine N-demethylase activity in microsomes from adult and young rats and female guinea-pigs. Aminopyrine N-demethylase inhibition did not increase with increasing concentration of added caffeine, although acetanilide hydroxylase activity was progressively inhibited in the microsomal incubates from both control and caffeine-treated animals.

Mutagenic activity of some clastogenic chemicals at the hypoxanthine guanine phosphoribosyl transferase locus of Chinese hamster ovary cells

4 presumptive clastogens (caffeine, dimethyl sulfoxide, diethylstilbestrol and p,p'-DDE) and 4 chemicals thought to induce chromosomal mutations in L5178Y mouse lymphoma cells (procarbazine X HCl, epichlorohydrin, hycanthone and iodomethane) were tested in the CHO/HGPRT gene mutation assay for the induction of 6-thioguanine-resistant ( 6TGR ) mutants. Of the clastogens, p,p'-DDE was mutagenic at several concentrations and diethylstilbestrol (DES) increased the 6TGR mutant frequency over control levels at the 6.7 and 8.0 micrograms/ml doses, but the results for DES were neither convincing nor significant. Caffeine was not mutagenic although at very high concentrations (6667-8000 micrograms/ml) there was a slight elevation in mutant frequency over background. This was probably due to a selective effect of caffeine against the HGPRT+ phenotype, for 2 different HGPRT- cell lines were refractory to the toxic effects of caffeine at the highest test level (8000 micrograms/ml). All 4 'chromosomal mutagens' produced dose-related increases in mutant frequencies at the HGPRT locus of these CHO cells. 6TGR colonies were generally uniform in size when normal precautions were taken to prevent the formation of satellite (secondary) colonies. Excepting DES, dimethyl sulfoxide, and caffeine, these data demonstrate that 5 of 8 clastogenic chemicals reproducibly induce mutations at the HGPRT locus of CHO cells which lack the small colony-forming potential of 3.7.2C L5178Y cells.

Comparative toxicities of dietary caffeine and theobromine in the rat

Caffeine, incorporated into pulverized Purina Rat Chow at a concentration of 0.5%, was fed to male Sprague-Dawley rats for 7 or 8 wk and the effects were compared with those of 0.8% dietary theobromine, fed to male rats for 7 wk. Both dietary methylated xanthines produced significant decreases in food consumption and body-weight gain when compared to their respective control groups. Food consumption of caffeine-fed rats was 57.2% of controls and for theobromine-fed rats it was 77.9% of the respective controls. Theobromine produced significant decreases in thymus weights, with caffeine producing smaller decreases. The theobromine-fed rats showed severe testicular atrophy with extensive spermatogenic cell degeneration and necrosis, while the testes of rats fed caffeine for 7 or 8 wk showed only scattered vacuolar degeneration of spermatogenic cells. Caffeine appears to be more potent than theobromine as an anorexic agent in rats, but to be equivalent to theobromine in its potential for inducing thymic atrophy and spermatogenic cell destruction with testicular atrophy.

Enhancement of induced sister chromatid exchange and chromosomal aberrations by inhibitors of DNA repair processes

The effect of post-treatment with inhibitors of DNA synthesis (hydroxyurea, aphidicolin) and repair (caffeine, 3-aminobenzamide) on the frequencies of chromosomal aberrations and sister chromatid exchange (SCE) induced by mitomycin C and decarbamoyl mitomycin C both in Chinese hamster cells and in human lymphocytes in vitro has been studied. The data show that in the case of Chinese hamster and human lymphocytes mitomycin C-treated cells there is an increased frequency of both chromosomal aberrations and SCE after a G2 post-treatment with the inhibitors, while no increase is observed for decarbamoyl mitomycin C-treated cells. Since SCE are DNA synthesis-dependent phenomenon, an increase in the frequency of SCE also in the G2 phase might suggest that after mitomycin C treatment there is a residual DNA synthesis still going on very late in the cell cycle.

Interstrain variation in acute toxic response to caffeine among inbred mice

Acute toxic dosage-dependent behavioral effects of caffeine were compared in adult males from seven inbred mouse strains (A/J, BALB/cJ, CBA/J, C3H/HeJ, C57BL/6J, DBA/2J, SWR/J). C57BL/6J, chosen as a "prototypic" mouse strain, was used to determine behavioral responses to a broad range (5-500 mg/kg) of caffeine doses. Five phenotypic characteristics--locomotor activity, righting ability, clonic seizure induction, stress-induced lethality, death without external stress--were scored at various caffeine doses in drug-naive animals under empirically optimized, rigidly constant experimental conditions. Mice (n = 12 for each point) received single IP injections of a fixed volume/g body weight of physiological saline carrier with or without caffeine in doses ranging from 125-500 mg/kg. Loss of righting ability was scored at 1, 3, 5 min post dosing and at 5 min intervals thereafter for 20 min. In the same animals the occurrence of clonic seizures was scored as to time of onset and severity for 20 min after drug administration. When these proceeded to tonic seizures, death occurred in less than 20 min. Animals surviving for 20 min were immediately stressed by a swim test in 25 degrees C water, and death-producing tonic seizures were scored for 2 min. In other animals locomotor activity was measured 15 or 60 min after caffeine administration. By any single behavioral criterion or a combination of these criteria, marked differences in response to toxic caffeine doses were observed between strains. These results indicate that behavioral toxicity testing of alkylxanthines in a single mouse strain may be misleading and suggest that toxic responses of the central nervous system to this class of compounds are genetically influenced in mammals.

Further studies on tetracycline-induced mutation in V79 Chinese hamster cells

The interaction between ultraviolet light and tetracycline in producing cell killing and mutation has been studied in V79 Chinese hamster cells. It has been established that these agents act independently of each other. Cycloheximide altered the response to tetracycline in the fractionation experiment: when cycloheximide was not present, fractionation of TC treatment resulted in a higher mutation yield but no change in survival level; in the presence of cycloheximide, however, mutation was greatly reduced but survival increased. The results were taken to indicate that for tetracycline action to take place, de novo protein synthesis during tetracycline treatment was necessary. Caffeine had no influence on tetracycline-induced lethality or mutagenicity. This observation was considered to suggest that tetracycline did not affect cellular repair processes.

Some methodological issues in the conduct of caffeine research

The caffeine literature of the past 10 years shows the frequent recurrence of several weaknesses--the use of weak or erroneous hypotheses in experimental design, design flaws (e.g. the use of excessively high doses) that prevent the derivation of any meaningful implication for humans, the violation of ordinary rules of logic in extrapolating experimental results to human situations (e.g. the application of findings in naive animals to caffeine-tolerant human subjects) and the biased selection of literature citations to support a hypothesis and ignore opposing evidence. Workers who review the literature dispassionately, who use dosages relevant to human caffeine consumption when they wish to extrapolate from animal studies to man, who distinguish carefully between acute and chronic effects and who include proper controls in feeding studies to prevent confusion of the effects of dietary deprivation with the pharmacological effects should succeed in advancing our understanding of caffeine's effects in the human body.

The toxicology of chemical interactions during pregnancy in the mouse: caffeine and phenytoin

The toxic interaction of caffeine and phenytoin during pregnancy was investigated in mice of the ICR strain on E10 of gestation. Caffeine, over a range of dosages, showed limited embryotoxic activity. Phenytoin was also weakly teratogenic and dosages needed to elicit embryotoxicity were accompanied by a significant increase in maternal lethality. Pretreatment with caffeine enhanced phenytoin-induced toxicity and teratogenicity and these observations confirm that caffeine has the ability to function as a co-teratogen. Pretreatment with phenytoin produced a significant increase in maternal lethality following caffeine administration but no co-teratogenic effect. It is suggested that these results are the consequence of a yet undefined interaction at critical receptor sites in the maternal-embryo unit.

Induction of hepatic ornithine decarboxylase by intraperitoneal administration of caffeine in rats

I.p. administration of caffeine led to a significant increase in hepatic ornithine decarboxylase activity in rats. The enzyme activity reached approximately 10-fold above the control level 5 h after the injection of caffeine at a dose of 150 mg/kg body weight. The high level of ornithine decarboxylase activity remained for 3 h and then decreased rapidly. The enzyme activity of the kidney, however, was not significantly enhanced by the administration of caffeine. The possible mechanism of the caffeine-mediated hepatic ornithine decarboxylase induction is discussed.

Comparative analysis of caffeine and 3-aminobenzamide as DNA repair inhibitors in Syrian baby hamster kidney cells

The effects of caffeine and 3-aminobenzamide (3-AB) on Syrian baby hamster kidney cells treated with DNA-alkylating agents and ultraviolet-light suggest that two different DNA-repair mechanisms are involved. Both these agents enhanced the cell kill after methyl methanesulfonate (MMS) treatment. However, enhanced lethality was observed only with caffeine post-treatment when cells were exposed to nitrogen mustard (HN2) or ultraviolet light (UV); 3-AB did not appreciably change cell killing by these agents. With MMS-treated cultures, the effect of caffeine was maximal about 16 h later. The effect of 3-AB on the other hand, was exerted during the first 4 h after exposure to MMS. Caffeine's effect on cell survival could be abolished by low concentrations of cycloheximide, whereas 3-AB's effect could not. Furthermore, the G2 block in cell cycle progression, after MMS treatment, was not observed if the cells were post-treated with caffeine. In the presence of 3-AB, MMS-treated cells were arrested in G2 phase at a much earlier time compared to cells not treated with 3-AB. Finally caffeine post-treatment produced a 10-fold increase in nuclear fragmentation in MMS-treated cells. 3-AB did not cause nuclear fragmentation by itself but further enhanced the nuclear fragmenting effect of caffeine when both agents were present during the posttreatment. Therefore, we propose that 3-AB and caffeine each prevent a different repair mechanism from being effective.

Behavioral and physical development of rats chronically exposed to caffeinated fluids

Coffee and caffeine solutions were administered as the sole source of fluid to male and female Sprague-Dawley rats (F0) beginning 60 days before breeding and continuing until the litters (F1) from these animals were weaned. Treatments were administered as 100% brewed coffee (COF-100), and a 25% dilution of coffee (COF-25), together with solutions of caffeine in water that paralleled the caffeine content of the coffee groups, 0.056% caffeine (CAF-100) and 0.014% (CAF-25). Controls received measured amounts of plain water (CNL) and another group received vitamin A (40,000 IU/kg) on Days 7-20 of gestation (positive control treatment). During pregnancy all groups receiving COF and CAF consumed significantly more fluid than CNLs. Offspring from the COF-100 and CAF-100 dams were significantly lower in weight than CNLs. No abnormalities of reproductive performance were observed. Of 10 preweaning tests, COF-100 and CAF-100 litters displayed delayed incisor eruption, delayed swimming development, and altered activity. On 7 postweaning measures, these groups showed decreased running wheel activity and increased open-field ambulation and/or defecation. The CAF-25 group, by contrast, showed an increase in running wheel activity. Vitamin A (Vit-A) offspring showed multiple effects, including delayed incisor eruption, increased pre- and postweaning open-field activity, and reduced running wheel activity. COF and CAF produced effects on tests for psychoteratogenesis that appear consistent with the morphological consequences (delayed development) known to be associated with pre- and neonatal administration of caffeine, alone or in coffee, at high doses. The data indicate that most of the behavioral effects observed from caffeine exposure were consistent with the expected effects of concurrent administration of this agent, while the postweaning exposure effects suggest a longer-term change in activity. No effects of caffeine were found, however, on measures of learning, memory, or motoric functioning.

Antagonism of caffeine-induced seizures in mice by Ro15-1788

The effect of the benzodiazepine antagonist Ro15-1788 has been tested against caffeine (200-300 mg/kg i.p.) induced convulsions in mice. It offered protection in lower doses (10 mg/kg i.p.) than had been effective previously against other convulsants such as bicuculline and leptazol. In contrast, diazepam was much less active against caffeine than against the other convulsants and offered no significant protection in doses up to 1 mg/kg i.p. If Ro15-1788 only acts on benzodiazepine receptors then one explanation for the increased activity of Ro15-1788 compared with diazepam against caffeine is that caffeine exerts its convulsant action through a direct effect on benzodiazepine receptors but is more potent at displacing diazepam than Ro15-1788 or alternatively it acts on a sub-class of benzodiazepine receptors that bind Ro15-1788 more effectively than diazepam.

Cerebral hemorrhage associated with phenylpropanolamine in combination with caffeine

Phenylpropanolamine (PPA) is a drug that has been associated with serious side effects including stroke. It is often combined with caffeine in diet preparations and "look-alike" pills. In order to determine if PPA/caffeine can lead to stroke in normotensive and/or hypertensive rats, we administered the combination in six times the allowed human dose calculated on a per weight basis for the rats two times per day for five days. Subarachnoid and cerebral hemorrhage was noted in 18% of the hypertensive rats. A single PPA/caffeine administration (same dose) lead to acute hypertension in both the normotensive and hypertensive animals. These results suggest that PPA/caffeine can lead to cerebral hemorrhage in previously hypertensive animals when administered in greater than the allowed dosage. An acute elevation in blood pressure may be a contributing factor.

Acute and chronic caffeine exposure effects on play fighting in the juvenile rat

Effects of acute and chronic exposure to caffeine on the behavior of juvenile rats were assessed in three experiments. In Experiment 1, two indices of play fighting--pin frequency and duration--were decreased and locomotor activity was increased in dose dependent fashions by caffeine. Social investigation of another juvenile was not affected by the drug. In Experiment 2, juvenile rats were isolated and given caffeine in their drinking fluid for 10-11 days. Play fighting was increased by all except the highest caffeine dose. In Experiment 3, juveniles were housed in groups of four and received either tap water or caffeine in their drinking fluid. Pin frequency of caffeine treated subjects was lower than controls on days 2-4, and higher than controls on days 9-11 after caffeine treatment was initiated. Evidently, caffeine has inhibitory and facilitatory effects on juvenile play fighting behavior, contingent on duration of exposure to the drug.

Influence of caffeine on arecoline-induced SCE in mouse bone-marrow cells in vivo

The effect of exposure of mice for 5, 10 and 15 days to arecoline or/and caffeine on the frequency of sister-chromatid exchanges (SCEs) in bone-marrow cells was evaluated by using the fluorescence plus Giemsa technique. There was a significant increase in the frequency of SCEs after exposure to either arecoline or caffeine. When these two alkaloids were given in combination, the SCE frequency-enhancing effect was additive. The implications of coffee/tea drinking and betel chewing on oral cancer are discussed.