Caffeine effects on cyclic AMP levels in the mouse embryonic limb and palate in vitro

Caffeine is a teratogen that causes limb and palate malformations in rodents. Since the ability to raise cyclic nucleotide levels is a known biological action of caffeine, cyclic AMP levels were measured in CD-1 mouse embryonic forelimb from whole embryo culture and embryonic limb and palate cells grown in primary culture following treatment with various concentrations of caffeine (0, 1, 3, or 10 mM). In forelimb buds from whole embryo culture, a dose-dependent response was observed. Caffeine at 1 mM concentration stimulated cyclic AMP levels to 151% of control value at 60 min. Even greater stimulation of cyclic AMP occurred at higher caffeine concentrations. A dose-dependent response was seen in both limb and palate cell culture. In limb cell culture, all caffeine concentrations significantly stimulated cyclic AMP after 10 min compared to control. In palate cell culture, there was a twofold increase in cyclic AMP at the 1-mM caffeine concentration. At higher caffeine concentrations, cyclic AMP was significantly increased after 60 min. In addition, stimulation of cyclic AMP in cultured limb and palate cells by isoproterenol, a beta-adrenergic agonist, was used as a positive control. Isoproterenol stimulated a 2.5-fold greater response in the palate cells than in the limb bud cells at isoproterenol levels of 10(-5) or 10(-4) M. The increase of cyclic AMP may be influential in the process of abnormal limb or palate development.     

Prevention of caffeine-induced limb malformations by maternal adrenalectomy

Caffeine at high doses is a known rodent teratogen and induces limb malformations along with cleft palate in various strains of rats and mice. Fujii and Nishimura ('74) postulated that caffeine was teratogenic by virtue of catecholamine release from maternal or embryonic tissue. We tested this hypothesis by surgically removing the maternal adrenal gland on day 6 of pregnancy and then administering 175 mg/kg of caffeine intraperitoneally at 1600 h day 11 and 900 h day 12. The teratogenic effects of caffeine in adrenalectomized versus nonadrenalectomized AKR mice were assessed in day 18 fetuses. Thirty percent of the surviving offspring were malformed in caffeine-treated, nonadrenalectomized dams compared to 7% of the offspring from adrenalectomized dams. Therefore we believe caffeine teratogenesis is initiated by release of catecholamines from the maternal adrenal gland.     

Reduction of caffeine teratogenicity in mice by inducing maternal drug metabolism with beta-naphthoflavone

The effect of stimulating maternal drug metabolism on caffeine teratogenicity was investigated in C57BL/6J (cytochrome P1-450 inducible) and AKR/J (cytochrome P1-450 noninducible) mice. The inducing agent, beta-naphthoflavone (beta-NF) in corn oil, was administered intraperitoneally (IP) to dams at 20 or 80 mg/kg/d on days 9 and 10 of gestation. Teratogenic injections of 175 mg/kg/d caffeine in deionized water were administered IP on days 11 and 12 of gestation. All dams were sacrificed on day 18 of gestation, and fetuses were fixed for razor blade sectioning and skeletal examination. Caffeine, without maternal metabolism stimulation, caused similar types and rates of malformations in both strains of mice. Inducing drug metabolism during pregnancy with beta-NF protected the embryos from the congenital toxicities of large injections of caffeine. Reductions in embryolethality, limb malformations, and hematoma formation were evident in the inducible strain but not in the strain incapable of being induced. A dosage of eighty mg/kg/d was more effective than 20 mg/kg/d beta-NF in decreasing malformations, suggesting that stimulation of metabolism and caffeine-induced teratogenicity are inversely related. Rapid elimination of caffeine resulting from increasing drug metabolism with the concomitant decrease in toxicity would indicate that caffeine, and not a metabolite, is the toxicant.     

Inhibitory effect of caffeine on 5-azacytidine-induced digital malformations in the rat

The effect of caffeine on 5-azacytidine (5-AC)-induced digital malformations in rat fetuses was investigated. Caffeine suppressed all types of digital defects in the fore- and hindlimbs except for syndactyly induced by 1.0 mg/kg of 5-AC; it was still effective when administered 24 hours after 5-AC treatment. However, fetal mortality increased as the frequency of malformations decreased. While the malformation results support the view that caffeine inhibits the processes leading to malformation expression, the relation between its suppressive effect on malformations and its enhancing effect on fetal mortality is unclear.     

Teratogenicity of paraxanthine (1,7-dimethylxanthine) in C57BL/6J mice

The teratogenicity of caffeine, as well as two of its three dimethylated metabolites (theobromine and theophylline), has been established in animal studies. The third metabolite, paraxanthine, has not been reported as being tested for teratogenicity even though it is actually the major demethylated metabolite of caffeine metabolism in man. Pregnant C57BL/6J mice were treated i.p. with 175 or 300 mg/kg/day paraxanthine (1,7-dimethylxanthine) dissolved in deionized water at 4 p.m. on day 11 and 9 a.m. on day 12 of gestation. All dams were sacrificed on day 18, and fetuses were fixed for Wilson's razor blade sectioning or double-staining skeletal examination. A dose-related increase in total malformations, primarily cleft palate and limb malformations, was found. The pattern of malformations was similar to that reported for caffeine, theobromine, and theophylline, i.e., an asymmetric response with the left forelimb most often affected. A 21% resorption and a 46% malformation rate was observed at 300 mg/kg/day of paraxanthine, indicating that paraxanthine was slightly less toxic to the embryo than caffeine. Therefore, the parent compound, caffeine, as well as all three of its dimethylated metabolites--paraxanthine, theophylline, and theobromine--are teratogenic.     

Histological study of cell death in digital malformations induced by 5-azacytidine: suppressive effect of caffeine

The present study investigated microscopically the process of 5-azacytidine (5-AC)-induced digital teratogenesis and caffeine's suppressive effect on this process. Three distinct zones of programmed cell death were observed in control and caffeine-treated embryos 3 hours after 5-AC injection: the preaxial and postaxial ectodermal regions and the central part of the mesodermal regions. 5-AC temporarily suppressed programmed cell death in the ectoderm and mesoderm 3 hours after it was injected. However, caffeine promoted programmed cell death; normal programmed cell death was observed in the limb buds of embryos whose dams were treated with 5-AC and caffeine. The percentage of total cell death in hindlimb buds of embryos treated with 5-AC and caffeine was higher than that from embryos treated with 5-AC, whereas 5-AC-induced digital malformations were reduced by post-treatment with caffeine. Cell death reached a maximum 12 hours after the injection in limb buds from 5-AC and caffeine-treated embryos and at 24 hours in the 5-AC treated embryos. Furthermore, in the 5-AC and caffeine-treated embryos, the frequency of cell deaths at 12 hours increased almost linearly with the doses of caffeine in parallel with the reduction of 5-AC-induced malformation frequency by caffeine. These results suggest that although induced cell death may be one of the factors leading to digital malformations produced by 5-AC, it is not essential, and the existence of other factors affecting the pattern formation of the limb bud is proposed.     

Rapid development of functional tolerance to caffeine-induced seizures in rats

The concentration and time dependence of caffeine-induced neurotoxicity was determined by infusing rats intravenously with caffeine at a rate of about 5, 12.5, and 25 mg kg-1 min-1 until the onset of generalized seizures which occurred at about 82, 28, and 11 min, respectively. The concentration of caffeine in the serum, brain, and cerebrospinal fluid at onset of seizures increased with decreasing infusion rate; the concentrations of caffeine metabolites were negligible and serum protein binding was not affected by the infusion rate. In another experiment, one group of rats was infused with caffeine for 60 min at about 2.2 mg kg-1 min-1 whereas another group was infused with solvent only. Both groups were then immediately infused with caffeine at about 22 mg kg-1 min-1 until onset of seizures. Caffeine concentrations at that time in serum, brain, and cerebrospinal fluid were significantly higher in the caffeine-pretreated animals than in the solvent-pretreated controls. The same pretreatment 17 hr before the fast infusion of caffeine had no apparent effect on caffeine concentrations at onset of seizures. These results show that functional tolerance to the seizure-inducing effect of caffeine in rats develops within minutes and that it is reversible within hours or less.     

Liquid chromatographic determination of caffeine in biologic fluids

A high-performance liquid chromatographic procedure was developed for the determination of caffeine in various biologic fluids and coffee. A reversed-phase column and UV detection at 254 nm were used to obtain a sensitivity of 0.1 μg/ml caffeine in serum and saliva using a sample volume of 0.1 ml. Caffeine metabolites and commonly ingested xanthines do not interfere with the assay. The within-day coefficients of variation were 9.8 and 9.9% at plasma caffeine concentrations of 2 and 10 μg/ml, respectively. The day-to-day coefficients of variation were 6.8 and 6.6% at plasma caffeine concentrations of 2 and 10 μg/ml, respectively. Serum and saliva caffeine concentrations were determined following a single oral dose of coffee and an intravenous infusion of caffeine in one subject. Computer estimates of caffeine pharmacokinetic parameters in one subject are in excellent agreement with previously published values.     

咖啡因体内代谢及其应用的研究进展

咖啡因是从茶叶、咖啡果中提取出来的一种生物碱,常用于治疗神经衰弱和昏迷复苏。咖啡因体内代谢过程复杂,现已发现咖啡因的15种代谢产物,参与代谢过程的酶类也被逐一证实。尿液咖啡因代谢产物比率(UCMRs)常用于多种药物代谢酶活性的评估,主要包括CYP1A2、CYP2A6、N-乙酰转移酶和黄嘌呤氧化酶,咖啡因及其代谢产物检测方法也逐步得到改进与更新。总之,咖啡因与人类健康密切相关,以及其重要的科研应用价值,一直受到普遍关注。     

Caffeine decreases the occurrence of cadmium-induced forelimb ectrodactyly in C57BL/6J mice

BACKGROUND: Cadmium is a well-known animal teratogen. Caffeine is an alkaloid widely consumed by humans. Interactions between teratogens and nonteratogenic doses of other agents are becoming widely studied, as they may shed light on understanding mechanisms of teratogenicity or possible prevention of teratogenic effects. METHODS: C57BL/6JBK mice were injected intraperitoneally (ip) with cadmium sulfate (Cd) at 0, 1.00 (LDCd), 2.50 (MDCd), or 5.00 (HDCd) mg/kg, immediately followed by subcutaneous (sc) administration of 0 or 50 mg/kg caffeine (CAFF) on gestation day (GD) 9. Fetuses were examined on GD 18 for ectrodactyly and other gross morphological malformations. RESULTS: Amelioration of cadmium-induced forelimb ectrodactyly by CAFF was seen in both the high-dose cadmium (HDCd = 65.4%, HDCd+CAFF = 39.2%) and medium-dose cadmium (MDCd = 46.2%, MDCd+ CAFF = 20.8%) treatment groups (P < 0.025). Bilateral expression of ectrodactyly was also decreased in the presence of caffeine. A statistically significant reduction in Cd-induced abnormalities, including: eye, abdominal, and other skeletal defects, was not seen with caffeine addition, although they did trend downward in the caffeine-supplemented groups. Litter size, fetal weight, fetal mortality, and dam weight also were not affected by co-treatment with caffeine. CONCLUSIONS: This study provides evidence that a subteratogenic dose of caffeine can ameliorate cadmium-induced forelimb ectrodactyly in the Cd-sensitive C57BL/6J inbred mouse strain.     

Effect of Naturally Occurring Xanthines on Bacteria: I. Antimicrobial Action and Potentiating Effect on Antibiotic Spectra

The effect of xanthines on various microorganisms was studied. The antibacterial effect was not high; most of the test organisms could easily withstand a concentration of 2,500 μg/ml. Caffeine was more antibacterial than theophylline, and the latter more than theobromine. Caffeine citrate exhibited greater inhibitory effect than did pure caffeine. The effect was both bacteriostatic and bactericidal against susceptible organisms. The susceptibility of organisms to xanthines differed greatly even in related species. The morphology of Aerobacter aerogenes and A. cloacae was affected under the influence of caffeine; filamentation of cells followed sublethal doses. Potentiation was seen with antibiotics and caffeine; resistant strains were killed with a lower dose of drug in the presence of caffeine. This potentiating effect was pronounced with the tetracyclines; with streptomycin, the effect was the contrary.     

Extractionless method for the determination of urinary caffeine metabolites using high-performance liquid chromatography coupled with tandem mass spectrometry

Caffeine is metabolised in humans primarily by cytochromes P450 1A2 and 2A6, xanthine dehydrogenase/oxidase, and N-acetyltransferase 2. The activities of these enzymes show a large variation due to genetic polymorphisms and/or induction by xenobiotics. Ratios of different caffeine metabolites in urine or other body fluids are frequently used to characterise the individual/actual activity of these enzymes. The common analytical method involves extensive sample preparation, followed by HPLC-UV. The presence of numerous other UV-absorbing chemicals in body fluids affects the sensitivity and selectivity of this method. We have developed an HPLC-electrospray-MS-MS method for the determination of 11 caffeine metabolites and two internal standards after a simple, extractionless preparation. Blank urine, obtained after 5 days on a methylxanthine-free diet, contained small amounts of some caffeine metabolites, but no other components producing any confounding signals. Eleven metabolites and internal standards were recovered at 90 to 110% after addition to the blank urine (0.1 to 2.5 micro M in the final sample involving a 20-fold dilution of urine) in the 0.1-2.5 micro M concentration range. Other metabolites, 5-acetylamino-6-amino-3-methyluracil (AAMU) and 5-acetylamino-6-formylamino-3-methyluracil (AFMU), were detected with similar recovery and precision, but required higher concentrations (3 to 30 micro M). AFMU was completely converted into AAMU by a short alkalisation of urine. The method was explored in six healthy individuals after consuming coffee (4 mg caffeine per kg body mass). These experiments demonstrated the simplicity, high sensitivity and selectivity of the method under conditions used for phenotyping.     

Hind limb malformations in free-living northern leopard frogs (Rana pipiens) from Maine, Minnesota, and Vermont suggest multiple etiologies

BACKGROUND: Reports of malformed frogs have increased throughout the North American continent in recent years. Most of the observed malformations have involved the hind limbs. The goal of this study was to accurately characterize the hind limb malformations in wild frogs as an important step toward understanding the possible etiologies. METHODS: During 1997 and 1998, 182 recently metamorphosed northern leopard frogs (Rana pipiens) were collected from Minnesota, Vermont, and Maine. Malformed hind limbs were present in 157 (86%) of these frogs, which underwent necropsy and radiographic evaluation at the National Wildlife Health Center. These malformations are described in detail and classified into four major categories: (1) no limb (amelia); (2) multiple limbs or limb elements (polymelia, polydactyly, polyphalangy); (3) reduced limb segments or elements (phocomelia, ectromelia, ectrodactyly, and brachydactyly; and (4) distally complete but malformed limb (bone rotations, bridging, skin webbing, and micromelia). RESULTS: Amelia and reduced segments and/or elements were the most common finding. Frogs with bilateral hind limb malformations were not common, and in only eight of these 22 frogs were the malformations symmetrical. Malformations of a given type tended to occur in frogs collected from the same site, but the types of malformations varied widely among all three states, and between study sites within Minnesota. CONCLUSIONS: Clustering of malformation type suggests that developmental events may produce a variety of phenotypes depending on the timing, sequence, and severity of the environmental insult. Hind limb malformations in free-living frogs transcend current mechanistic explanations of tetrapod limb development.     

Determination of caffeine and its metabolites by micellar electrokinetic capillary electrophoresis

The determination of caffeine and its analogues is important for a wide variety of analyses and is performed in an assortment of matrices ranging from food to clinical samples. While reversed-phase HPLC has become the standard analysis protocol in most laboratories, capillary electrophoresis has the advantages of higher separation efficiency and shorter separation time. The micellar capillary electrophoresis (MECC) separation of caffeine and its metabolites, theobromine, paraxanthine, theophylline and 1,3,7-trimethyluric acid was investigated using sodium dodecyl sulphate (SDS) as the micellar phase. The effects of pH, micelle concentration, buffer concentration, ionic strength, buffer salts, applied voltage and injection time were studied to select the optimum conditions for the determination of caffeine and its four analogues in drugs, foods and body fluids. Caffeine and its three analogues were resolved within 120 s with detection limits less than 1 μg/ml. Samples could be analyzed utilizing direct injection with satisfactory resolution and reproducibility.     

Acetazolamide: maternal toxicity, pattern of malformations, and litter effect

Thirty litters of C57BL 6J mice were administered intraperitoneally one of four doses (0, 500, 750, and 1,000 mg/kg maternal weight) of acetazolamide on day 9 of gestation. The fetuses were removed on day 18 and fixed, stained, cleared, and examined for the pattern of malformations. The forelimb postaxial limb deficiency was the most common abnormality, but forelimb postaxial polydactyly and a postaxial deficiency in the hindlimb were also observed. Males were significantly more likely to be malformed than females at all doses, in contrast to the predominance of females observed in rat fetuses exposed to acetazolamide (Scott et al.: Teratology 6:239-240, '73). The occurrence of limb malformations did not correlate with maternal weight loss, the birth weight of the fetus, or the position of the fetus in the uterus. A "litter effect" was demonstrated in that there was a nonuniform distribution of litters with different proportions of malformed fetuses.     

Time effect of rutaecarpine on caffeine pharmacokinetics in rats

Rutaecarpine is reported as a potent inducer of CYP1A2 enzyme in rats. There are natural herbal supplements containing rutaecarpine that are designed to enhance the CYP1A2-dependent removal of caffeine from blood so that people can have coffee later in the day without causing sleep interference. This study aimed to determine the minimum amount of time needed from oral rutaecarpine administration until the observed effect of rutaecarpine on caffeine pharmacokinetics (PK) in 15 male Sprague-Dawley rats. PK parameters for caffeine and its metabolites in the control and rutaecarpine groups were calculated using WinNonlin®. Results showed that orally administered rutaecarpine at 100 mg/kg dose as early as 3 h before oral caffeine administration significantly decreased the oral systemic exposure and mean residence time of caffeine and its metabolites due to decreased caffeine bioavailability (by up to 75%) and increased clearance. The systemic exposure of caffeine and its metabolites were also decreased when caffeine was given intravenously, though this effect was less pronounced than when caffeine was given orally. Although plasma level of rutaecarpine was undetectable (less than 10 ng/mL), rutaecarpine still induced hepatic CYP1A2 activity. Results from 7-methoxyresorufin O-demethylation activity, which is specific to CYP1A2, showed that 3 h after one rutaecarpine oral dose, CYP1A2 activity in rat liver tissue was increased by 3- fold. This finding suggested that rutaecarpine effectively induced CYP1A2 activity in the liver.     

New 3-substituted xanthines : Potent inhibitors of cell plate formation

Caffeine and some related compounds are known to inhibit cell plate formation (CPF), but little is known about their mechanism of action. In this connection, the effects of xanthine derivatives on CPF in Tradescantia stamen hair cells were examined. Caffeine (1,3,7-trimethylxanthine) and 1,3-dimethyl-xanthine were more effective inhibitors of CPF than 1-methyl- or 1,7-dimethyl-xanthine. Four compounds with a substituent at the three position of 1,7-dimethyl-xanthine were found to be more effective than caffeine as inhibitors of CPF. Among them, 1,7-dimethyl-3-(3-ethylbutyl) xanthine was the most effective and the concentration required for inhibition of CBF was one tenth of that of caffeine. Breakdown of cell plates could be partially reversed using guanosine or adenosine, but reversibility was not detected using cytokinins.     

Caffeine metabolism in Coffea arabica and other species of coffee

High performance liquid chromatography has been used to measure the quantities of caffeine, theobromine, and theophylline in aqueous extracts of endosperm from immature and mature fruits of Coffea arabica and six other species of Coffea. Caffeine was the alkaloid present in largest amounts and, with one exception, in concentrations that were broadly similar in immature and mature fruit. The highest concentrations of caffeine were found in C. canephora at 35.1 and 24.5 mg g⁻¹, respectively, in immature and mature endosperm. The lowest concentrations were in C. bengalensis, where caffeine was not detected in extracts from mature fruit. [8-³H]Caffeine was metabolised relatively slowly by immature endosperm of C. arabica and C. canephora. In contrast, C. dewevrei, C. eugenioides, C. stenophylla, C. salvatrix and C. bengalensis all appeared to metabolise [8-³H]caffeine much more rapidly, as the percentage recovery of the applied label was much lower and there was more extensive incorporation of radioactivity into theobromine, theophylline, 3-methylxanthine and two unidentified polar metabolites. The endogenous caffeine concentrations and the metabolism data indicate that there may be marked differences in the rate of turnover of caffeine in the various species of Coffea. Potential sources of material for the production of naturally decaffeinated coffee are discussed.