Citalopram and cardiac toxicity.

PURPOSE: Citalopram is a selective serotonin reuptake inhibitor (SSRI) antidepressant that is widely used in clinical practice. Recent data have indicated that high therapeutic citalopram doses may cause electrocardiographic abnormalities, and the regulatory authorities have amended its licenced dosage. The present manuscript reviews the available data concerning citalopram and cardiac toxicity. METHODS: Published data concerning the cardiac effects of citalopram were ascertained, and clinical data were considered separately between adverse effects arising from therapeutic use versus toxicity in the setting of intentional overdose. RESULTS: The occurrence of electrocardiographic abnormalities has long been recognised as a complication of acute citalopram overdose; a dose-effect relationship for QT prolongation has been described in a number of large case series, including several cases of torsades de pointes. In contrast, few data indicate the occurrence of QT prolongation and arrhythmia after therapeutic doses, and a dose-effect relationship within the therapeutic range has only recently been established. Citalopram is more likely to cause QT prolongation in patients with metabolic disturbance or pre-existing cardiac disease. CONCLUSIONS: A dose-effect relationship for QT prolongation exists across a broad range of citalopram doses, such that caution must be exercised when prescribing high doses or if there are co-existent risk factors for QT effects. The available data illustrate how clinical toxicity data may offer an earlier signal of cardiac effects than ascertained from conventional pharmacovigilance methods.

Mesenchymal differentiation propensity of a human embryonic stem cell line.

OBJECTIVES: To characterize basal differentiation tendencies of a human embryonic stem (hES) cell line, KCL-002. MATERIALS AND METHODS: In vitro specification and differentiation of hES cells were carried out using embryoid body (EB) cultures and tests of pluripotency and in vivo differentiation were performed by teratoma assays in SCID mice. Real-time PCR, immunohistochemistry, flow cytometry and histological analyses were used to identify expression of genes and proteins associated with the ectodermal, endodermal and mesodermal germ layers. RESULTS: Undifferentiated KCL-002 cells expressed characteristic markers of pluripotent stem cells such as Nanog, Sox-2, Oct-4 and TRA 1-60. When differentiated in vitro as EB cultures, expression of pluripotency, endodermal and ectodermal markers decreased rapidly. In contrast, mesodermal and mesenchymal markers such as VEGFR-2, α-actin and vimentin increased during EB differentiation as shown by qPCR, immunostaining and flow cytometric analyses. Teratoma formation in SCID mice demonstrated the potential to form all germ layers in vivo with a greater proportion of the tumours containing mesenchymal derivatives. CONCLUSIONS: The data presented suggest that the KCL-002 hES cell line is pluripotent and harbours a bias in basal differentiation tendencies towards mesodermal and mesenchymal lineage cells. Characterizing innate differentiation propensities of hES cell lines is important for understanding heterogeneity between different cell lines and for further studies aimed at deriving specific lineages from hES cells.

Neural differentiation regulated by biomimetic surfaces presenting motifs of extracellular matrix proteins.

The interaction between cells and the extracellular matrix (ECM) is essential during development. To elucidate the function of ECM proteins on cell differentiation, we developed biomimetic surfaces that display specific ECM peptide motifs in a controlled manner. Presentation of ECM domains for collagen, fibronectin, and laminin influenced the formation of neurites by differentiating PC12 cells. The effect of these peptide sequences was also tested on the development of adult neural stem/progenitor cells. In this system, collagen I and fibronectin induced the formation of beta-III-tubulin positive cells, whereas collagen IV reduced such differentiation. Biomimetic surfaces composed of multiple peptide types enabled the combinatorial effects of various ECM motifs to be studied. Surfaces displaying combined motifs were often predictable as a result of the synergistic effects of ECM peptides studied in isolation. For example, the additive effects of fibronectin and laminin resulted in greater expression of beta-III-tubulin positive cells, whereas the negative effect of the collagen IV domain was canceled out by coexpression of collagen I. However, simultaneous expression of certain ECM domains was less predictable. These data highlight the complexity of the cellular response to combined ECM signals and the need to study the function of ECM domains individually and in combination.

Enhanced cell attachment using a novel cell culture surface presenting functional domains from extracellular matrix proteins.

Many factors contribute to the creation and maintenance of a realistic environment for cell growth in vitro, e.g. the consistency of the growth medium, the addition of supplements, and the surface on which the cells grow. The nature of the surface on which cells are cultured plays an important role in their ability to attach, proliferate, migrate and function. Components of the extracellular matrix (ECM) are often used to coat glass or plastic surfaces to enhance cell attachment in vitro. Fragments of ECM molecules can be immobilised on surfaces in order to mimic the effects seen by whole molecules. In this study we evaluate the application of a novel technology for the immobilisation of functional domains of known ECM proteins in a controlled manner on a surface. By examining the adherence of cultured PC12 cells to alternative growth surfaces, we show that surfaces coated with motifs from collagen I, collagen IV, fibronectin and laminin can mimic surfaces coated with the corresponding whole molecules. Furthermore, we show that the adherence of cells can be controlled by modifying the hydropathic properties of the surface to either enhance or inhibit cell attachment. Collectively, these data demonstrate the application of a new technology to enable optimisation of cell growth in the tissue culture laboratory.

Growth of teratomas derived from human pluripotent stem cells is influenced by the graft site.

Pluripotent stem cells transplanted into immune-deficient mice form complex teratomas. Although such tumors are generally haphazard in their organization, they do contain some structures that resemble tissues normally seen in the embryo. As a consequence, the teratoma model is useful for exploring the developmental potential of stem cells and studying certain aspects of tissue development. To further our understanding of this process, we examined whether the anatomical location into which human pluripotent stem cells were grafted influenced their growth in situ. Here we report that cells grafted into the liver rapidly produced large tumors containing predominantly immature cells. In contrast, subcutaneous implants were significantly slower growing and eventually formed tumors composed of differentiated tissues. The alternative growth patterns recorded between these two graft sites indicates how environmental cues affect stem cell behavior. This approach may lead to the identification of new ways to control stem cell growth and differentiation.

Purine modulation of dizocilpine effects on spontaneous alternation.

The Y-maze was used to assess spontaneous alternation behaviour in mice to examine possible interactions between the N-methyl-D-aspartate receptor channel blocker dizocilpine and purine receptor agonists and antagonists. Scopolamine reduced spontaneous alternation. Dizocilpine also produced a dose-dependent reduction in alternation scores, which was accompanied by an increase in locomotion. The selective A1 adenosine receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX) had no effect when administered alone, or in combination with scopolamine. However, when co-administered with dizocilpine, CPX reversed both the deficit in alternation behaviour and also the increase in locomotion induced by dizocilpine. The A1 selective agonist N6-cyclopentyladenosine (CPA) had no effect on either locomotion or alternation scores when administered alone, but in combination with scopolamine, CPA attenuated the scopolamine-induced deficit. CPA had no significant effect on the dizocilpine-induced deficit. The A2 selective agonist N6-[2-(3, 5-dimethoxyphenyl)-2(2-methylphenyl)-ethyl]adenosine (DPMA), had no effect on spontaneous alternation when administered alone, but did cause a depression of locomotion. DPMA had no significant effect when co-administered with scopolamine, but reversed the deficit in spontaneous alternation, and the increase in locomotion induced by dizocilpine. The A2 selective antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) had no effect when given alone or in combination with scopolamine, but when co-administered with dizocilpine, DMPX reversed the reduction in spontaneous alternation caused by dizocilpine. It is concluded that dizocilpine has a detrimental effect on spontaneous alternation which is mediated partly by A1 and A2 adenosine receptors.

The involvement of adenosine receptors in the effect of dizocilpine on mice in the elevated plus-maze.

It has been claimed that blockade of receptors for N-methyl-D-aspartate (NMDA) can enhance adenosine receptor function on single neurones. Previous work has also indicated that the NMDA channel blocker dizocilpine, and the A1 selective agonist N6-cyclopentyladenosine (CPA) both had anxiolytic profiles in the elevated plus-maze. The anxiolytic effect of dizocilpine was accompanied by an increase in locomotor activity. In the present study, the elevated plus-maze has been used to determine whether dizocilpine's effects on behaviour are mediated through activation of adenosine receptors. When co-administered with dizocilpine (0.05 mg/kg), CPA (0.05 mg/kg) reduced the anxiolytic and locomotor effects of dizocilpine. The A1 selective antagonist 1,3-dipropyl-8-cyclopentylxanthine (CPX, 0.05 mg/kg) had no effect when administered alone. When co-administered with dizocilpine, CPX reversed the anxiolytic and increased locomotor effects induced by dizocilpine. The A2 receptor selective agonist N6-[2-(3,5-dimethoxyphenyl)-2(2-methylphenyl)ethyladenosine (DPMA) (1 mg/kg) reversed both the anxiolytic effect and the increased locomotion induced by dizocilpine, while the A2 selective antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) (1 mg/kg) did not. It is concluded that at least part of the anxiolytic and locomotor stimulant properties of dizocilpine may be explained by the release of endogenous adenosine acting at A1, but not A2 receptors.

Interactions between ifenprodil and dizocilpine on mouse behaviour in models of anxiety and working memory.

The N-methyl-D-aspartate (NMDA) receptor polyamine site antagonist, ifenprodil, had no effect on spontaneous alteration or locomotor activity in the Y-maze when given alone. The NMDA receptor/ion channel blocker, dizocilpine, induced a deficit in spontaneous alteration, but when ifenprodil was co-administered with dizocilpine, it showed a strong tendency to attenuate the dizocilpine-induced deficit. In the plus-maze, ifenprodil had an anxiolytic profile which was accompanied by an increase in locomotion. Dizocilpine had an anxiolytic profile in this model and increased locomotor activity. When co-administered with dizocilpine, ifenprodil reduced both the anxiolytic and locomotor effects of dizocilpine. When co-administered with ifenprodil, cyclopentyladenosine (CPA) and 1,3-dipropyl-8-cyclopentylxanthine (CPX) reduced the anxiolytic effect of ifenprodil. CPA and CPX in combination did not reverse the anxiolytic effect of ifenpropil. It is concluded that NMDA antagonists with different sites of action can show distinct behavioural profiles, with dizocilpine but not ifenprodil inducing a deficit in working memory, while both are anxiolytic. Blockade of NMDA receptors by ifenprodil, however, can preclude any response to dizocilpine. The anxiolytic activity of ifenprodil may involve the release of purines acting at adenosine receptors.

Field trial of metrifonate in the treatment and prevention of schistosomiasis infection in man.

A field trial was set up to test the prophylactic properties of the organophosphorous drug metrifonate (Bilarcil Bayer AG). Subjects were rural African children living in an area of Rhodesia where Schistosoma haematobium and S. mansoni are highly endemic. The trial was conducted in three stages, a preliminary period of therapy followed by two six-month periods of prophylaxis. Parasitological and haematological tests were carried out monthly and major assessments (including clinical examinations) were carried out prior to the start of the trial and at the end of each of the three stages. Drug was given to the appropriate groups at a dose rate of 7-5 mg/kg once per fortnight for three doses during the therapy stage and four-weekly during the prophylaxis stage. Results with S. haematobium were very good. A 60% cure-rate was observed six weeks aection was obtained in those children continuing to receive the drug as a prophylactic, even during the season of highest transmission; intensities of infection in those who became infected were very low. Infection rates in the treated but unprotected group rose steadily from 40% at week 11 to 95% at week 70. There was a sigificant effect upon the intensity of S. mansoni infections only when pre- and post-trial data were compared. Apart from the anticipated (and previously reported) depression of plasma cholinesterase values no side effects were recorded. Drug tolerance and acceptibility were very high. It is likely that the costs of a year's protection against S. Haematobium using metrifonate will be significantly lower than protection by molluscicidal techniques or single courses of treatment with established drugs.