The effects of methylxanthines on catecholamine-stimulated and normal chick embryos

Cyclic nucleotide phosphodiesterases as drug targets

Cyclic nucleotides are synthesized by adenylyl and/or guanylyl cyclase, and downstream of this synthesis, the cyclic nucleotide phosphodiesterase families (PDEs) specifically hydrolyze cyclic nucleotides. PDEs control cyclic adenosine-3',5'monophosphate (cAMP) and cyclic guanosine-3',5'-monophosphate (cGMP) intracellular levels by mediating their quick return to the basal steady state levels. This often takes place in subcellular nanodomains. Thus, PDEs govern short-term protein phosphorylation, long-term protein expression, and even epigenetic mechanisms by modulating cyclic nucleotide levels. Consequently, their involvement in both health and disease is extensively investigated. PDE inhibition has emerged as a promising clinical intervention method, with ongoing developments aiming to enhance its efficacy and applicability. In this comprehensive review, we extensively look into the intricate landscape of PDEs biochemistry, exploring their diverse roles in various tissues. Furthermore, we outline the underlying mechanisms of PDEs in different pathophysiological conditions. Additionally, we review the application of PDE inhibition in related diseases, shedding light on current advancements and future prospects for clinical intervention. SIGNIFICANCE STATEMENT: Regulating PDEs is a critical checkpoint for numerous (patho)physiological conditions. However, despite the development of several PDE inhibitors aimed at controlling overactivated PDEs, their applicability in clinical settings poses challenges. In this context, our focus is on pharmacodynamics and the structure activity of PDEs, aiming to illustrate how selectivity and efficacy can be optimized. Additionally, this review points to current preclinical and clinical evidence that depicts various optimization efforts and indications.

Effect of khat, its constituents and restraint stress on free radical metabolism of rats

The leaves of khat (Catha edulis) are found to have stimulating and pleasurable effect and are chewed habitually by people of East Africa and Arabian Peninsula. Due to various toxic and psychostimulative effect of khat the present study was undertaken to evaluate the effect of intragastric khat alone or its major constituents flavonoids/alkaloids administration and before and after 4 h of immobilization stress in terms of alteration of free radical scavenging/metabolizing enzymes, uric acid and glucose in rats. Oral khat, alkaloid administration or 4 h restraint stress resulted in the decrease of the circulating levels of superoxide dismutase, catalase, glutathione-S-transferase and glucose with enhanced uric acid concentrations as compared with control rats. Oral treatment with flavonoid fraction of khat was found to enhance the activities of GST and catalase but showed no effect on SOD while the level of glucose was decreased and uric acid increased. The levels of these biochemical parameters were more altered in post stress khat/alkaloid treated rats than pre stress khat/alkaloid treated rats. The alteration in the levels of SOD, GST, catalase and uric acid in the pre stress khat treated rats were comparable with that of khat alone, except the level of glucose which was further decreased in pre stress khat treated rats. The flavonoid fraction of khat reduced the stress induced oxidative stress in terms of above mentioned biochemical parameters. The present study suggests that khat alone or khat/alkaloid consumption preceding stress may significantly decrease the levels of free radical metabolizing/scavenging enzymes and glucose leading to enhanced free radical concentration and toxicity of khat, which could be due to its alkaloid fraction as flavonoids were found to show antioxidant properties for oxidative stress generated during restraint stress.

Slow-release theophylline in pregnant asthmatics

STUDY OBJECTIVE

Oral theophylline treatment may be helpful in controlling severe asthma during pregnancy. This treatment, however, has been suspected of causing both complications and malformations. The objective of this investigation was to study the influence of theophylline treatment on the course of pregnancy and delivery and on maternal and infant health.

SETTING

Respiratory unit, antenatal outpatient departments, and labor and delivery rooms.

DESIGN

Case-control study.

PATIENTS

The data of 212 pregnant asthmatics with theophylline treatment (AT) were compared with findings in 292 pregnant asthmatics without theophylline (A) and 237 nonasthmatic pregnant control subjects (C).

RESULTS

There were no significant differences among groups as to age, height, age of onset of asthma, lung function, parity, or smoking. In the AT group, 19% were treated for acute exacerbations of the asthma as compared with 6% in the A group (p < 0.001). The incidence of preeclampsia was higher in the AT (15.6%) than in the C (6.4%) group (p < 0.03). Theophylline treatment at term was not associated with premature contractions or premature rupture of membranes, hemorrhage, placenta previa, abruption of the placenta, abnormal fetus position, frequent induction or augmentation of labor, prolonged third phase of delivery, or increased hemorrhage post partum. No differences among groups were seen with regard to gestational age, birth weight, Apgar scores, or perinatal deaths. Jaundice in the newborn, necessitating treatment with blue light, was more common in the AT (15.0%) than in the C group (7.8%) (p < 0.05). Three infants of 121 patients treated with theophylline during the first trimester were born with malformations; in the 91 patients treated with theophylline only during the second and third trimester, and the asthmatic control group, the corresponding figures were 4 and 3.

CONCLUSIONS

During the second and third trimesters until term, theophylline treatment using moderate doses can be considered safe. The safety of theophylline treatment during the first trimester with regard to teratogenicity remains to be determined.

Evaluation of teratogenic potential of khat (Catha edulis Forsk.) in rats

The embryotoxic and teratogenic effects of khat (Catha edulis Forsk.), a plant chewed by the people of Eastern Africa and Southern Arabia to attain a state of euphoria and stimulation, was studied in Wistar rats. Methanolic extract of khat was administered orally by gavage to rats during days from 6 to 15 of gestation at doses of 0, 125, 250 and 500 mg/kg. body weight/day. Khat reduced the food consumption and maternal weight gain and also lowered the food efficiency index, as compared to control mothers. On day 20 of gestation, all dams were sacrificed by cervical dislocation, cesarean sections were performed and maternal and fetal toxicities were assessed. The administration of khat had no effect on fetal sex ratio. However, at a dose of 125 mg/kg body weight and above, it produced a significant increase in resorptions and fetal wastage. Khat administration in utero also reduced the litter size and caused intrauterine growth retardation. External, visceral and skeletal examination of the fetus of treated dams showed several types of malformations and variations in all the groups of animals. However, a consistent tendency of abnormalities was observed in the highest dosed (500 mg/kg) group. The data of the present study revealed that khat retarded fetal growth and induced terata. The present observations indicate that khat possesses both embryotoxic as well as teratogenic properties. The developmental toxicities of khat are dose-related.

Potentiating effects of forskolin on the cardiovascular teratogenicity of ephedrine in chick embryos

The effects of forskolin on the teratogenicity of ephedrine in the developing chick heart were studied. Forskolin was administered to 4-day chick embryos (Hamburger-Hamilton stage 24) together with ephedrine at doses at which each agent alone caused minimal embryotoxicity. The embryos were examined for malformations on day 14 of incubation. The frequency of malformed embryos exposed to ephedrine (0.5 or 5 mumol) alone was 8 and 26%, respectively, and significantly increased to 47-72% in the presence of 1 nmol forskolin. Forskolin (1 nmol) alone did not induce a significant number of cardiac malformations. These results suggest that the increase in cAMP through stimulation of adenylate cyclase by forskolin is associated with the potentiation of ephedrine-induced cardiovascular malformations in the chick.

The induction of dominant lethal mutations upon chronic administration of khat (Catha edulis) in albino mice

The mutagenicity of a methanolic extract of khat has been evaluated on male germ cells using the dominant lethal test in albino mice. An aqueous solution of khat extract was administered orally in doses of 50, 100 and 200 mg/kg body wt., respectively, to 3 different groups of male mice for a period of 6 weeks. At the end of treatment each male mouse was allowed to mate with 2 different groups of 3 females each, on 2 consecutive weeks. These females were necropsied on the 13th day of their presumptive mating, and the number of implants in each female and the ratio of live and dead embryos were determined. The results of this study showed that the treatment of male mice over a period of 6 weeks produced a dose-dependent reduction in the rate of fertility in the first week after mating, which was irreversible in the second week at the highest dose (200 mg/kg). Khat extract also induced post-implantation loss during the first week following treatment. However, a comparison of the results of the first and second weeks showed a reversible pattern of dominant lethality.

Tissue and plasma levels of a teratogenic dose of dopamine in the chick embryo following pretreatment with metoprolol or phosphate buffered saline

Metoprolol pretreatment has been shown to reduce the cardiovascular malformation rate produced by topical doses of dopamine in the stage 24 chick embryo. We report on the tissue and plasma levels and teratogenic effect of dopamine hydrochloride following topical application of a teratogenic dose in stage 24 chick embryos pretreated with either metoprolol tartrate or phosphate buffered saline (PBS). Pretreatment with either metoprolol or PBS resulted in similar patterns of dopamine distribution in the head, body, and heart, with peak levels occurring at 12 hours after dopamine treatment. Plasma concentrations of dopamine were similar for both PBS and metoprolol pretreated embryos, with plasma levels exceeding tissue concentrations, but also peaking at 12 hours after dopamine treatment. Pretreatment with PBS followed by a teratogenic dose of dopamine resulted in a decrease in the teratogenic effect of dopamine similar to that found in previous work in our lab with pretreatment with metoprolol. The developing chick cardiovascular system experiences peak susceptibility to the teratogenic effects of dopamine at stage 24 during development, which represents a time frame of about 12 hours. A delay in the peak levels of dopamine to 12 hours after dopamine treatment as compared to previous work in our lab reporting peak levels of dopamine at 1 hour, suggests that the previously reported antiteratogenic effects of metoprolol may be due, at least in part, to a delayed absorption of dopamine past the time of peak susceptibility of the embryo to the teratogen.

The teratogenic effect of forskolin on cardiovascular development in the chick embryo

The cardiovascular teratogenicity and embryotoxicity of forskolin, a potent activator of adenylate cyclase, was studied in the chick embryo. The drug was topically applied to the surface of the chorioallantoic membrane in the vicinity of the embryonic heart on the 4th day of incubation (Hamburger-Hamilton developmental stage 24). Cardiovascular malformations were induced in 51% of embryos treated with forskolin doses larger than 1 x 10(-8) mol/egg. Major malformations included remnant of the left 4th aortic arch and ventricular septal defect. These results indicate that forskolin induces cardiovascular malformations in the chick embryo and suggest that increased levels of cyclic 3',5'-adenosine monophosphate produced by forskolin may be related to the malformations observed.

Cytological effects of khat (Catha edulis) in somatic and male germ cells of mice

Cytological effects of khat (Catha edulis), a popular drug of abuse from Southern Arabia and Eastern Africa, have been studied in Swiss albino mice. The studies on the somatic system involved the use of micronucleus test and the cytological analysis of the mitotic index in the femoral cells of mice. In the micronucleus test, the mice were treated with different doses of khat extract (125, 250 and 500 mg/kg, p.o.) 30 and 6 hours before sacrificing the animals. The polychromatic erythrocytes were screened for the induction of micronuclei. For the analysis of bone marrow cytotoxicity, the mice were treated with the dose of 125, 250 and 500 mg/kg, body weight, p.o. daily for 5 consecutive days. The animals were sacrificed and the femoral cells were microscopically examined for the mitoses. Following the same schedule of treatment, studies on the cytogenetic analysis of meiotic chromosomal aberrations and the sperm head abnormality were undertaken. Khat extract significantly increased the frequency of micronucleated polychromatic erythrocytes, induced bone marrow depression and reduced the mitotic index of the somatic cells. It induced significant chromosomal aberrations viz., aneuploids, autosomal univalents, univalents of the sex chromosomes and polyploids. The frequency of abnormal sperms was also increased.

The effects of cardioteratogenic doses of caffeine on cardiac function in the 3-day chick embryo

The effects on embryonic cardiac function of caffeine administration (two non-cardioteratogenic and two cardioteratogenic doses) to Hamburger-Hamilton stage 19 (3-3 1/2 days of incubation) chick embryos were investigated. Using microcinephotoanalysis, we have determined that caffeine (1.0-4.7 mg/egg), within the initial three hours after treatment, produced a dose-dependent decrease in end diastolic volume, stroke volume, cardiac output, and ejection fraction. These effects were sustained for a longer period of time following dosing at a cardioteratogenic level (3.5-4.7 mg/egg). Caffeine (1.0-4.7 mg/egg) also increased cardiac rate with a maximum increase of 30% seen 60 minutes after treatment with doses of 2.7 mg and 3.5 mg. However, the increase in cardiac rate was not related to dose. At 20 hours after treatment, caffeine increased stroke volume, ejection fraction and cardiac output relative to the controls. End-diastolic volume and cardiac rate were not changed. These results are evidence for a biphasic effect of cardioteratogenic dosing with caffeine during the first 20 hours after treatment--initially a sustained decrease in cardiac output, suggesting decreased flow through the embryonic heart, followed by an increase in ejection fraction, suggesting increased cardiac workload.

Clastogenic evaluation of cathinone and amphetamine in somatic cells of mice

Clastogenic effects of cathinone, the active principle from khat (Catha edulis) and amphetamine, a compound having similar chemical structure and pharmacological activity, have been studied on the somatic cells of mice. Both of them produced marked clastogenic activity and affected the cell proliferation in the bone marrow of mice. They induced a significant increase in the frequency of micronucleated polychromatic erythrocytes at higher doses. These results substantiate our earlier observations on the clastogenic and mitodepressive activity of cathinone on the meristematic region of Allium cepa, and indicate that cathinone may be responsible for the mutagenic effect of khat reported by other workers. The clastogenic effects of amphetamine are being reported for the first time. Further studies are required to substantiate these findings and to study whether cathinone and amphetamine produce a direct clastogenic effect or whether they act as spindle poisons.

Routine teratogenicity test that uses chick embryos in vitro

An in vitro culture of chicken embryo is described: the embryos at the stage of gastrulation are explanted from eggs into transparent silicone chambers where they continue to develop normally under controlled conditions for additional 3 d. This period corresponds to 2-5 wk of postconceptional age in the human embryo. In both the chick and man, this period is very sensitive to physicochemical perturbations which can lead to surviving malformations. Six chemical agents were tested with this culture: methotrexate, cadmium chloride, caffeine, phenobarbital, aspirin, and saccharin. Survival scores, growth perturbations, and early signs of anomalies of the nervous, skeletomotor, and cardiovascular systems were analyzed with respect to the used concentrations. The dose-response curves were obtained with good precision and allowed a discrimination between the teratogenetic and unspecific toxic effects and a comparison of the toxic potency of the six drugs. The evaluation of one drug took, roughly, 3 wk, one technician, and about 150 eggs. The advantages (simplicity, rapidity, reproducibility, specificity, economy, no suffering, and no use of mature animals) and disadvantages (nonmammalian species, absence of detoxicating organs) of the method are discussed. The method is proposed as a routine teratogenicity and embryotoxicity test which allows primary screening of many compounds and which can thus substantially reduce the ultimate experiments that use pregnant mammalian females.

The teratogenic effect of phenobarbital on the embryonic chick heart

Phenobarbital was observed to produce cardiovascular malformations in embryonic chicks. Malformations included simple ventricular septal defect, ventricular septal defect associated with dextroposition of the aorta, double outlet right ventricle, and several types of aortic arch anomalies. Embryos were exposed to phenobarbital at doses of 1-25 mumol on day 4 of incubation (Hamburger-Hamilton developmental stage 24). Doses equal to and greater than 5 mumol phenobarbital (26 mg/kg egg) significantly increased the frequency of embryos with cardiovascular malformations compared with lesser doses and with saline. A significant reduction in heart rate and abnormal rhythm of the heart were observed in embryos treated with teratogenic doses of phenobarbital. No arrhythmia nor significant changes in heart rate were observed in embryos exposed to subteratogenic doses of phenobarbital or to saline.

Potentiating effects of caffeine on the cardiovascular teratogenicity of ephedrine in chick embryos

Ephedrine was administered to 3-day chick embryos (Hamburger-Hamilton developmental stage 19) together with caffeine at doses where each agent alone caused minimal embryotoxicity. Embryos were examined for malformations on day 14 of incubation. The teratogenicity of ephedrine in the chick cardiovascular system was significantly potentiated by caffeine at a dose as low as 0.5 mumol (0.1 mg/egg; 2 mg/kg egg).

An aborted human fetus with truncus arteriosus communis--possible teratogenic effect of Tedral

We recently performed a detailed anatomicopathologic examination on an aborted human embryo whose mother had taken four tablets of Tedral (one tablet of Tedral contains 130 mg theophylline, 25 mg ephedrine, 8 mg phenobarbital) for an upper respiratory tract infection when the embryo was at approximately 30 days of development. On the same day, the mother developed acute chest pain and a fast, irregular heart beat. The abortion occurred at approximately 80 days of gestation. The heart of the fetus showed truncus arteriosus (Van Praagh type A1). Although no direct cause and effect relationship was proven in this case, the possibility of a teratogenic effect of Tedral during early pregnancy is considered.

The spontaneous occurrence of aortic arch and cardiac malformations in the white Leghorn chick embryo (Gallus domesticus)

Spontaneous aortic arch and cardiac malformations occur in White Leghorn chick embryos at a relatively high rate. Although this breed of Gallus domesticus is widely used for biomedical and biological research, no previous study has recorded the incidence of these defects. We found aortic arch malformations in 7.1% (14 of 196) and ventricular septal defects in 11.7% (23 of 196) of living embryos. Defects occurred alone or as a combined pattern. Our findings suggest that the cardiovascular defects in the chick embryo documented in past studies may, in some cases, have been part of normal spontaneous occurrence, rather than the major result of experimental manipulation.

External malformations in chick embryos following concomitant administration of methylxanthines and beta-adrenomimetic agents: 1. Gross pathologic features

The objectives of this report are to document external malformations observed in chick embryos following concomitant administration of methylxanthines (caffeine, theophylline) and beta-adrenomimetic agents (isoproterenol, epinephrine) and to suggest reasonable explanations for the anomalies. Administration of caffeine or theophylline alone (2.5-5.0 mg/egg) retarded growth in a dose-dependent fashion. Doses of 5.0 mg caffeine and theophylline produced beak malformations in 4.9% and 57.1% of embryos, respectively. Limb malformations, seen in low frequency (3.6% in 56 embryos) after administration of 1 microgram isoproterenol, were not seen in 224 methylxanthine-treated embryos. Structural defects following coadministration of methylxanthines and beta-adrenomimetics were frequently observed in limbs (primarily lower limbs with predilection for left-sided oligodactyly) and beak. Other findings included limb hematomas, hygromas in the nuchal region, and prominent generalized edema. The most dramatic effects observed in this study were those induced by concomitant administration of 2.5 mg caffeine and 1 microgram isoproterenol. This combination produced at least one of the embryopathies listed above in 87.9% of treated embryos and frequently induced beak (24.2%) and lower limb defects (75.8%) in addition to nuchal hygromas (9.1%). Similar severe malformations were observed following administration of 3.8 mg theophylline with 1 microgram epinephrine. Embryos that died within 12-48 hours following drug insult demonstrated marked cardiac dilation, apparently due to congestive heart failure. The results of this study suggest that methylxanthines and beta-adrenomimetic agents are synergistic in their action in the developing chick. Doses of alpha-adrenomimetic agents that were used in this study were not synergistic with methylxanthines. Increased intracellular cyclic adenosine monophosphate (AMP) is offered as an explanation for digital anomalies due to inhibition of proximodistal development of limbs. Increased intracellular cyclic AMP may also explain limb hypoplasia and loss of intermediate limb structures as a result of inhibited mitosis and/or necrosis of embryonic tissue.

Reduction of catecholamine-induced cardiovascular malformations in the chick embryo with metoprolol

It has been documented that activation of the beta 1-adrenergic receptor mechanism is directly related to cardiovascular malformations associated with the heart and great vessels of the embryonic chick. These adrenergic receptors are believed to be present and functional in the innervated and noninnervated embryonic heart at early stages of development. The present study examined the effects of four sympathomimetic cardioactive amines on chick cardiovascular morphogenesis at Hamburger and Hamilton stage 24. Special attention was directed toward understanding dopamine teratogenicity. In order of decreasing potency at the maximum teratogenic dose (dopamine greater than isoproterenol greater than epinephrine greater than norepinephrine) each drug was found capable of producing aortic arch anomalies of the third, fourth, and sixth aortic arches and ventricular septal defects (VSD). A new specific beta 1-adrenergic antagonist, metoprolol tartrate, was employed in an attempt to lower the incidence of these cardiovascular malformations. Pretreatment with this selective beta 1-blocker profoundly reduced the incidence of malformations within any amine-treated group. These experiments demonstrate that dopamine, as well as the other sympathomimetic amines, is a potent teratogen and most likely produces these cardiovascular malformations by primarily stimulating the beta 1-adrenoreceptor in the embryonic chick.

Cardiovascular malformations associated with administration of prenalterol to young chick embryos

Prenalterol (levo-1-[4-hydroxyphenoxy]-3-isopropyl-amino-2-propanol), a new stimulant of cardiac beta-adrenergic receptors in man, induces cardiovascular malformations when topically administered to 2 1/2- through 5 1/2-day chick embryos (Hamburger-Hamilton stages 17-27). Ventricular septal defects (VSD) located in the middle portion of the conal septum and classified as the simple, punched-out type VSD without septal malalignment were the predominant malformations observed throughout the developmental period tested. Arch malformations of the aortic circulation were also observed throughout the test interval, while anomalies of the pulmonary system were observed only at Hamburger-Hamilton stages 17 and 26-27. At stage 25 prenalterol demonstrated an acute toxicity significantly less than (1/50-1/20) epinephrine (P = .035 at concentrations of 8-10 mM) but was relatively equipotent with epinephrine in producing cardiovascular malformations. The effective median concentrations of the two agents were comparable (0.5-1.0 mM). The spectra of malformations induced by prenalterol and epinephrine were qualitatively similar. Malformations included absence of the right and/or left third aortic arch (innominate arteries), persistent remnant of the left fourth aortic arch, and VSD. These results support a previously proposed theory by these investigators that hyperstimulation of cardiac beta-adrenergic receptors in the chick embryo produces cardiovascular malformations.

Pharmacology of dextroamphetamine-induced cardiovascular malformations in the chick embryo

We have observed dextroamphetamine sulfate to cause cardiovascular malformations in the 4-day-old chick embryo. Essentially all malformations were of the heart and great vessels. About one-half of these were the abnormal persistence of the left fourth aortic arch. Ventricular septal defects comprised the vast majority of the other malformations. Since d-amphetamine has both a direct and, more importantly, an indirect mode of alpha and beta adrenergic stimulation, three drugs were used to try to inhibit malformation production: alpha-methyl-p-tyrosine (AMT), a catecholamine synthesis inhibitor; metoprolol, a beta 1 blocker; and phentolamine, an alpha blocker. When given with d-amphetamine, all three drugs significantly reduced the malformation rate resulting from d-amphetamine alone. We speculate that the embryonic chick is capable of responding to the alpha and/or beta properties of dextroamphetamine sulfate. These properties may be causally related to the malformations observed.

Embryopathic effects of caffeine in the chick

There is increasing concern about the potential teratogenic effects of caffeine. Laboratory rodents were widely used for the teratological evaluation of caffeine. However, few studies have been carried out in non-mammalian organisms. Caffeine, dissolved in sterile water, was injected into the air sacs of fertile White Leghorn chick eggs at doses of 100, 200, 300, 400, 500, 700, 900, and 1,100 micrograms per egg. Control eggs were injected with an equivalent volume of sterile water (0.1 ml/egg). The embryos were treated at either 48, 72, or 96 hours incubation. On day 9, live embryos were recovered and examined for external malformations after staging and weighing. Treatment with 400 and 1,100 micrograms caffeine at 48 hours incubation resulted in a significantly high incidence of abnormal embryos, compared to the controls. The most common malformations included reduced body, microphthalmia, exencephaly, everted viscera and short neck. A significant number of embryos died following treatment with 1,100 micrograms caffeine at 48 hours incubation, and 400 and 700 micrograms at 72 hours incubation. Embryonic growth was not affected. Even though it is not possible to extrapolate these findings directly to humans, moderation in the consumption of caffeine-containing beverages during pregnancy is recommended.

Caffeine and pregnancy outcome

Caffeine is a drug which easily crosses the placental barrier and enters the fetal circulation. To date, most studies that demonstrate caffeine's teratogenic potential have been conducted in animal models. Although no definite relationship in humans has been confirmed, it is suggested that a pregnant woman should limit or discontinue her intake of caffeine.

Acetylsalicylic acid-induced morphological changes in the ductus arteriosus of the chick embryo

The effect of acetylsalicyclic acid upon the ducti arteriosi of the embryonic chick was studied. A spectrum of gross malformations and histological findings associated with premature closure of the right ductus arteriosus is presented.