Effects of calcium channel blockers on the development of early rat postimplantation embryos in culture

Management of tachyarrhythmias in pregnancy - A review

The most common arrhythmias detected during pregnancy include sinus tachycardia, sinus bradycardia, and sinus arrhythmia, identified in 0.1% of pregnancies. Isolated premature atrial or ventricular arrhythmias are observed in 0.03% of pregnancies. Arrhythmias may become more frequent during pregnancy or may manifest for the first time.

Calcium channel blockers and risk of breast cancer: a meta-analysis of 17 observational studies

PURPOSE

Studies on the association between the use of calcium channel blockers (CCBs) and breast cancer risk have reported inconsistent results. We quantitatively assessed this association by conducting a meta-analysis based on the evidence from observational studies.

METHODS

We searched PubMed, MEDLINE, EMBASE and the Cochrane Library for relevant studies published up to and including December 31, 2013. We calculated pooled risk ratios (RRs) for cancer risk.

RESULTS

A total of 17 studies (9 cohort studies, 8 case-control studies) were selected for further study. These studies included 149,607 female subjects, of which 53,812 were CCBs users, who were followed for 2-16 years. The risks of breast cancer among patients receiving CCBs were significantly different for the pooled RRs (95% confidence interval) of cohort studies 1.08 (0.95, 1.20) and case-control studies 0.98 (0.86, 1.09). Differences were also noted for cancer risk, for CCBs use of <5 years 0.96 (0.78, 1.15), and for >5 years 1.01 (0.74, 1.28), as well as for ever used 1.08 (0.95, 1.20), and for current use 1.13 (0.83, 1.42). The RR for studies longer than 10 years was 1.71 (1.01, 2.42), and for studies evaluating nifedipine was 1.10 (0.87, 1.33) and diltiazem was 0.75 (0.40, 1.10).

CONCLUSIONS

The long-term use of CCBs appears to have a significant relationship with breast cancer. Well-designed clinical trials are needed to optimize the doses and types of these drugs needed to minimize their carcinogenic potential.

Calcium channel blockade in embryonic cardiac progenitor cells disrupts normal cardiac cell differentiation

We suggest that characterization of processes involved in differentiation of the pluripotential cardiac precursor cells in their embryonic environment will permit identifying pathways important for induction of diverse stem cells toward the cardiac phenotype. Phenotypic characteristics of cardiac cells are their contractile and electrical properties. The objective of the present study was to define whether calcium (Ca(++)) has a regulatory role in the pluripotential precursor cell population during commitment into cardiomyocytes. We used the chick embryo model because of ease of staging the embryos and visibility of heart development. Using the Ca(++) indicator Fluo-3/acetoxymethyl and confocal microscopy, we demonstrated the existence of higher free Ca(++) levels in the cardiogenic precursor cells than in neighboring cell populations outside of the heart fields. Subsequently, gastrulation stage 4/5 chick embryos were set up in modified New cultures in the medium containing either the L-type Ca channel blocker, diltiazem, or the N-type Ca channel inhibitor, ω-conotoxin. The embryos were incubated for 22-24 h during which time the control embryos developed, beating looping hearts. At the end of incubation, exposure to the L-type channel blockade with diltiazem resulted in an inhibition of cardiomyogenesis in the most posterior, uncommitted, part of the heart fields. N-type channel blockade with ω-conotoxin was less intense. Cells in the most anterior cardiogenic regions that were already committed at time of exposure continued to differentiate. Thus, regulation and maintenance of normal cytosolic Ca levels are necessary for the early steps of cardiomyocyte specification and commitment leading to differentiation.

Intracellular calcium plays an essential role in cardiac development

Intracellular calcium signaling plays an essential role in cardiac physiology and modulates cardiac gene expression. However, the role that intracellular calcium signaling plays during cardiac development is not known. To address this issue, we examined the effects of altered intracellular calcium levels on cardiac morphogenesis. In acutely cultured mouse embryos, L-type calcium channel blockade decreased resting intracellular calcium levels and inhibited calcium transients. Embryos cultured at embryonic day (E) 7.5-8.5 in the presence of the L-type calcium channel blockers nifedipine and verapamil developed hearts that had a large left ventricle, lacked a right ventricle and had a long, thin outflow tract. If embryos were cultured at E7.5, calcium channel blockade also induced an abnormal, anterior cardiac loop. These alterations in development were not due to altered cardiac function, as heart rates at the end of the culture period were not affected by calcium channel blockade and blood flow was observed. Treatment with nifedipine altered the mRNA expression of the transcription factor Gata4, which was absent in the developing ventricles, and the sarcomeric protein Mylpc (myosin light chain 2V), which was decreased distal to the left ventricle and was absent at the site of the developing right ventricle. In contrast, the expression pattern of other cardiac transcription factor (Hand1, Hand2, Mef2c, Nkx2-5) and cytoskeletal protein (Myhca, Tagln) mRNA did not change with calcium channel blockade. These data demonstrate that proper intracellular calcium signaling is essential for normal cardiac looping, gene expression, and organ development.

Teratogenicity of the I(Kr)-blocker cisapride: relation to embryonic cardiac arrhythmia

Cisapride and mosapride are structurally and pharmacologically related prokinetic agents. In contrast to mosapride, cisapride causes embryonic lethality in teratology studies, and has been related to fatal cardiac arrhythmia in the adult. The arrhythmogenic potential of cisapride is linked to its potential to inhibit a specific ion channel (I(Kr)) as a side effect. Mosapride lacks I(Kr)-blocking properties. The aims of this study were (1) to compare the effects of cisapride and mosapride on embryonic heart rhythm in vitro and (2) to investigate if cisapride in vivo, has potential to induce hypoxia-related teratogenic effects as has been shown for selective I(Kr)-blockers. Cisapride induced severe embryonic bradycardia (approximately 60% decrease), and arrhythmia in 94% of the cultured rat embryos at 1000 ng/ml. Mosapride did not induce any bradycardia or arrhythmia up to 2000 ng/ml. In vivo, single dose administration of cisapride to rats on gestational day (GD) 13 caused digital reductions (8/108 fetuses, 4/9 litters) at 75 mg/kg and high incidence of embryonic death (55-82%) at 100-200 mg/kg. Identical developmental toxic effects have been described after temporary interruption of oxygen supply, and after single dose administration of selective I(Kr)-blockers, on the same GD. The results support the idea that all potent I(Kr)-blocking agents have the potential to cause embryolethality and teratogenicity, and that the adverse effects are mediated via hypoxic episodes due to embryonic arrhythmia.

Establishment of an in vitro reporter gene assay for developmental cardiac toxicity

This study is based on the unique potential of pluripotent embryonic stem (ES) cells to differentiate in vitro into embryoid bodies containing cell lineages representative of most cell types found in the mammalian fetus. However, the use of wild type ES cells as an in vitro assay for embryotoxicological studies is complicated by the simultaneous development of various cellular phenotypes. This prevents a quantitative assessment of drug effects on one specific cell type. Here we report the effects of 15 chemicals on cardiac differentiation as determined by various specific toxicological endpoints such as morphological inspection (contractile activity), quantitative mRNA analysis and cardiac-specific expression of green fluorescent protein (GFP), used as a quantitative reporter. The data from the different endpoints have been subjected to a statistical analysis, and a preliminary prediction model is proposed. The results demonstrate that genetically-engineered ES cells could provide a valuable tool for estimating the developmental cardiotoxic potential of compounds in vitro and form the basis for automated analysis in a high-throughput system.

A calcium agonist, Bay k 8644, suppresses the embryotoxic effects induced by dihydropyridines calcium channel blockers in cultured rat embryos

Day 9 rat embryos were exposed to 1,4-dihydropyridine calcium channel blockers; nifedipine (NIF), nicardipine (NIC) or nitrendipine (NIT), for 48 hr in the whole embryo culture system. There were dose-dependent growth retardation and abnormalities, predominantly in cardiovascular system. The three compounds exhibited very similar pattern of dysmorphogenic effects, but the potency of these compounds were quantitatively different. The incidences of embryos with the abnormalities were 100%, 100% and 85% following either exposure of NIF, NIC or NIT at concentration of 300, 8 and 15 microM, respectively. This study was to investigate whether these blocker-induced embryotoxicity was due to calcium channel blocking properties themselves in the embryos. Day 9 rat embryos were co-exposed to 1,4-dihydropyridine calcium channel agonist, Bay k 8644 (BAY) and each calcium channel blocker under the same culture condition. The retarded embryonic growth induced by 200 or 300 microM of NIF, 8 microM of NIC and 15 microM of NIT nearly of completely ameliorated when embryos were co-exposed with BAY at one-third or half concentration of each calcium channel blocker. Supplementation of BAY reduced the incidence of abnormalities by NIF-, NIC- and NIT-alone. These results suggested that one of mechanisms for embryotoxicity induced by calcium channel blocker was directly related to channel blocking property of the chemicals.

Calcium-channel blockade and incidence of cancer in aged populations

BACKGROUND

Calcium-channel blockers can alter apoptosis, a mechanism for destruction of cancer cells. We examined whether the long-term use of calcium-channel blockers is associated with an increased risk of cancer.

METHODS

Between 1988 and 1992 we carried out a prospective cohort study of 5052 people aged 71 years or more and who lived in three regions of Massachusetts, Iowa, and Connecticut USA. Those taking calcium-channel blockers (n = 451) were compared with all other participants (n = 4601). The incidence of cancer was assessed by survey of hospital discharge diagnoses and causes of death. These outcomes were validated by the cancer registry in the one region where it was available. Demographic variables, disability, cigarette smoking, alcohol consumption, blood pressure, body-mass index, use of other drugs, hospital admissions for other causes, and comorbidity were all assessed as possible confounding factors.

FINDINGS

The hazard ratio for cancer associated with calcium-channel blockers (1549 person-years, 47 events) compared with those not taking calcium-channel blockers (17225 person-years, 373 events) was 1.72 (95% CI 1.27-2.34, p = 0.0005), after adjustment for confounding factors. A significant dose-response gradient was found. Hazard ratios associated with verapamil, diltiazem, and nifedipine did not differ significantly from each other. The results remained unchanged in community-specific analyses. The association between calcium-channel blockers and cancer was found with most of the common cancers.

INTERPRETATION

Calcium-channel blockers were associated with a general increased risk of cancer in the study populations, which suggested a common mechanism. These observational findings should be confirmed by other studies.

Embryotoxic effects of L-691,121, a class III antiarrhythmic agent, in rats

L-691,121 is a class III antiarrhythmic agent which blocks potassium currents, leading to prolongation of cardiac potential and prevention of cardiac arrhythmia. In a developmental toxicity study in rats, there was a dose-dependent decrease in embryonic/fetal survival, and death of the entire litter was seen at an oral dose of 0.8 mg/kg per day. The critical period for embryolethality was determined as gestational days (GD) 10-13. In a study where females received 1 mg/kg on a critical day (GD 10 or 12) and were killed at 24-h intervals, a high embryonic mortality was seen at 72 h (GD 10 treatment) or 48 h (GD 12 treatment) after dosing. The surviving embryos had morphological abnormalities such as enlarged cardiac tube and pericardium, generalized edema, and hematoma. In order to investigate a possible mechanism for the embryolethality, GD 11 embryos were dissected from females at 4 h after dosing of 1 mg/kg and incubated for 5 h in vitro. The embryonic heart rates were decreased for the first 2 h after incubation but tended to recover to control levels thereafter. When GD 11 embryos were incubated for 4 h with the drug, there were decreases in the heart rates during the entire observation period. In a washout study where the embryos were transferred to drug-free medium after 1-h exposure, decreased heart rates recovered to control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the class III antiarrhythmic, dofetilide (UK-68,798) on the heart rate of midgestation rat embryos, in vitro

Gestation day 11 (GD11) and 14 (GD14) embryos were cultured for up to 4 hours in the presence of Dofetilide (0.01-0.50 microgram/ml), a potent Class III Antiarrhythmic which selectively inhibits the rapid component of the time dependent outward potassium current (IKr). Significant (P < or = 0.05) reductions in heart rate (HR) as measured over a 4 hour period were dose dependent and reversible. The sensitivity of the GD11 embryos was greater than GD14 embryos (14-64% decrease in HR vs. an 11-43% decrease in HR, respectively) at the same concentrations tested. These in vitro results support the hypothesis that the embryo-lethality of Class III Antiarrhythmics observed in vivo may be a class effect of the IKr subtype potassium channel blockers. The data suggest a possible mechanism of embryotoxicity is to lower embryonic HR resulting in subsequent hypoxia and death. Dofetilide's effects on GD11 HR were partially reversible by the sequential addition of Isoproterenol or Theophylline.

Whole embryo culture: interpretation of abnormal development in vitro

An overview will be given of a number of problems that arise when we attempt an interpretation of data obtained with the whole embryo culture method (WEC). The following aspects will be considered: 1) Types of deviation from normal development in the whole-embryo culture system: (a) problem of "artifacts" (for example, due to preparation mistakes and suboptimal culture conditions), (b) types and frequency of abnormal development in controls, retardation as an abnormal outcome, and the difficulty of assessing its significance, (c) gross-structural defects and, specifically, attempts to answer the following questions: (i) What are the limitations for an assessment of abnormal development with the WEC? (ii) Is a specific abnormality pattern recognizable under specific pathologic conditions? (iii) Is the rate of induced abnormal development concentration-dependent? (2) Problems encountered when interpreting concentration-effect relationships (for example, statistical and pharmacokinetic aspects). (3) Necessity of verifying in vitro effects with in vivo studies.