Dual effects of extracellular Ca2+ on cardiotoxin-induced cytotoxicity and cytosolic Ca2+ changes in cultured single cells of rabbit aortic endothelium

Fetoplacental vasculature as a model to study human cardiovascular endocrine disruption

Increasing evidence has associated the exposure of endocrine-disrupting chemicals (EDCs) with the cardiovascular (CV) system. This exposure is particularly problematic in a sensitive window of development, pregnancy. Pregnancy exposome can affect the overall health of the pregnancy by dramatic changes in vascular physiology and endocrine activity, increasing maternal susceptibility. Moreover, fetoplacental vascular function is generally altered, increasing the risk of developing pregnancy complications (including cardiovascular diseases, CVD) and predisposing the foetus to adverse health risks later in life. Thus, our review summarizes the existing literature on exposures to EDCs during pregnancy and adverse maternal health outcomes, focusing on the human placenta, vein, and umbilical artery associated with pregnancy complications. The purpose of this review is to highlight the role of fetoplacental vasculature as a model for the study of human cardiovascular endocrine disruption. Therefore, we emphasize that the placenta, together with the umbilical arteries and veins, allows a better characterization of the pregnant woman's exposome. Consequently, it contributes to the protection of the mother and foetus against CV disorders in life.

Cardiovascular Effects of Snake Toxins: Cardiotoxicity and Cardioprotection

Snake venoms, as complex mixtures of peptides and proteins, affect various vital systems of the organism. One of the main targets of the toxic components from snake venoms is the cardiovascular system. Venom proteins and peptides can act in different ways, exhibiting either cardiotoxic or cardioprotective effects. The principal classes of these compounds are cobra cardiotoxins, phospholipases A2, and natriuretic, as well as bradykinin-potentiating peptides. There is another group of proteins capable of enhancing angiogenesis, which include, e.g., vascular endothelial growth factors possessing hypotensive and cardioprotective activities. Venom proteins and peptides exhibiting cardiotropic and vasoactive effects are promising candidates for the design of new drugs capable of preventing or constricting the development of pathological processes in cardiovascular diseases, which are currently the leading cause of death worldwide. For example, a bradykinin-potentiating peptide from Bothrops jararaca snake venom was the first snake venom compound used to create the widely used antihypertensive drugs captopril and enalapril. In this paper, we review the current state of research on snake venom components affecting the cardiovascular system and analyse the mechanisms of physiological action of these toxins and the prospects for their medical application.

Suppression of cardiomyocyte functions by β-CTX isolated from the Thai king cobra (Ophiophagus hannah) venom via an alternative method

Background

Beta-cardiotoxin (β-CTX), the three-finger toxin isolated from king cobra (Ophiophagus hannah) venom, possesses β-blocker activity as indicated by its negative chronotropy and its binding property to both β-1 and β-2 adrenergic receptors and has been proposed as a novel β-blocker candidate. Previously, β-CTX was isolated and purified by FPLC. Here, we present an alternative method to purify this toxin. In addition, we tested its cytotoxicity against different mammalian muscle cell types and determined the impact on cardiac function in isolated cardiac myocyte so as to provide insights into the pharmacological action of this protein.

Methods

β-CTX was isolated from the crude venom of the Thai king cobra using reverse-phased and cation exchange HPLC. In vitro cellular viability MTT assays were performed on mouse myoblast (C2C12), rat smooth muscle (A7r5), and rat cardiac myoblast (H9c2) cells. Cell shortening and calcium transient dynamics were recorded on isolated rat cardiac myocytes over a range of β-CTX concentration.

Results

Purified β-CTX was recovered from crude venom (0.53% w/w). MTT assays revealed 50% cytotoxicity on A7r5 cells at 9.41 ± 1.14 µM (n = 3), but no cytotoxicity on C2C12 and H9c2 cells up to 114.09 µM. β-CTX suppressed the extend of rat cardiac cell shortening in a dose-dependent manner; the half-maximal inhibition concentration was 95.97 ± 50.10 nM (n = 3). In addition, the rates of cell shortening and re-lengthening were decreased in β-CTX treated myocytes concomitant with a prolongation of the intracellular calcium transient decay, indicating depression of cardiac contractility secondary to altered cardiac calcium homeostasis.

Conclusion

We present an alternative purification method for β-CTX from king cobra venom. We reveal cytotoxicity towards smooth muscle and depression of cardiac contractility by this protein. These data are useful to aid future development of pharmacological agents derived from β-CTX.

Identification of Immunoreactive Peptides of Toxins to Simultaneously Assess the Neutralization Potency of Antivenoms against Neurotoxicity and Cytotoxicity of Naja atra Venom

Assessing the neutralization capability of nonlethal but medically relevant toxins in venom has been a challenging task. Nowadays, neutralization efficacy is evaluated based simply on the survival rates of animals injected with antivenom together with a predefined dose of venom, which can determine potency against neurotoxicity but not validate the capability to neutralize cytotoxin-induced complications. In this study, a high correlation with in-vivo and in-vitro neutralization assays was established using the immunoreactive peptides identified from short-chain neurotoxin and cytotoxin A3. These peptides contain conserved residues associated with toxin activities and a competition assay indicated that these peptides could specifically block the antibody binding to toxin and affect the neutralization potency of antivenom. Moreover, the titers of peptide-specific antibody in antivenoms or mouse antisera were determined by enzyme-linked immunosorbent assay (ELISA) simultaneously, and the results indicated that Taiwanese bivalent antivenom (BAV) and Vietnamese snake antivenom-Naja (SAV-Naja) exhibited superior neutralization potency against the lethal effect of short-chain neurotoxin (sNTX) and cytotoxicity of cardiotoxin/cytotoxin (CTX), respectively. Thus, the reported peptide ELISA shows not only its potential for antivenom prequalification use, but also its capability of justifying the cross-neutralization potency of antivenoms against Naja atra venom toxicity.

Bone marrow-derived cells do not engraft into skeletal muscle microvasculature but promote angiogenesis after acute injury

The skeletal muscle is supported by a vast network of microvessels with the capacity to regenerate in response to injury. However, the dynamics of microvascular repair and the origin of reconstituted endothelial cells in the skeletal muscle are poorly understood. A growing body of literature exists to indicate bone marrow (BM)-derived cells engraft into regenerating vascular endothelium and muscle macrovasculature. Therefore, we investigated the extent of BM contribution to skeletal muscle microvasculature after acute injury. Because reporters and markers commonly used to trace donor BM cells are not endothelial specific but are also expressed by leukocytes, we generated novel BM chimeras utilizing Tie2-green fluorescent protein BM cells transplanted into CD31 and Caveolin-1 knockout recipients. In turn, we surveyed BM vascular contribution, not just by the presence of green fluorescent protein, but also CD31 and Caveolin-1, respectively. After stable BM reconstitution, chimera limb muscles were cardiotoxin (CTX) injured and examined 21 days post-injury for the presence of green fluorescent protein, CD31, and Caveolin-1. Acute muscle injury by CTX is characterized by initial microvasculature death followed by rapid endothelial regeneration within 14 days post-damage. Histological analysis of injured and uninjured contralateral limb muscles revealed a complete absence of BM engraftment in the muscle vasculature of wild-type and CD31/Caveolin-1 knockout chimeras. In contrast, F4/80(+) cells isolated from CTX-injured muscle, expressed endothelial-related markers and promoted angiogenesis in vitro. Therefore, despite the absence of BM engraftment to regenerated skeletal muscle microvasculature, macrophages recruited after injury promote angiogenesis and, in turn, vascular regeneration.

Rapid action of pesticides on cytosolic calcium concentrations in cultures of human umbilical vein endothelial cells

Persistent metabolites of pesticides such as p,p'-DDE, at environmentally relevant concentrations, have been shown to have a rapid effect on intracellular calcium [Ca2+]i concentrations in human granulosa-lutein cells. Since endocrine disrupting substances can be transferred from the maternal circulation to the fetus the present study examined whether the pesticides, kepone, o,p-DDE, p,p'-DDE and methoxychlor, could alter cytoplasmic calcium [Ca2+]cyt concentrations in human umbilical vein endothelial (HUVE) cells. Cultured HUVE cells were loaded with Fura-2 AM and changes in [Ca2+]cyt of single cells were studied using a dynamic digital Ca2+ imaging system. Kepone and methoxychlor consistently increased [Ca2+]cyt concentrations, similar to the effects of estradiol and progesterone. p,p'-DDE increased [Ca2+]cyt concentrations in 80% of experiments whereas o,p-DDE stimulated its increases in 42%. Estrone, estriol, pregnenolone and cortisol were not effective. These results demonstrate that pesticides can have a rapid effect on HUVE cells probably through a nongenomic mechanism of action.

Non-genomic action of estradiol and progesterone on cytosolic calcium concentrations in primary cultures of human granulosa-lutein cells

BACKGROUND

The present study examined whether the sex steroids, estradiol and progesterone, could alter cytoplasmic calcium concentrations ([Ca(2+)](cyt)) in human granulosa-lutein cells.

METHODS

Human granulosa cells were obtained at the time of oocyte retrieval for IVF and cultured for 3-7 days. Cells were loaded with Fura-2 AM and changes in [Ca(2+)](cyt) of single cells were studied using a dynamic digital Ca(2+) imaging system.

RESULTS

Both estradiol and progesterone stimulated elevations of [Ca(2+)](cyt) in Ca(2+)-containing medium within seconds of exposure of the granulosa-lutein cells to the steroid, but only estradiol caused an increase in [Ca(2+)](cyt) in Ca(2+)-free medium. Both ICI-182780 and RU 486 stimulated [Ca(2+)](cyt) increases and inhibited the effects of estradiol and progesterone, respectively. Tamoxifen also induced transient increases in [Ca(2+)](cyt) concentrations but inhibited the effects of both estradiol and progesterone. The inhibitory effects of tamoxifen, ICI-182780 and RU 4486 on [Ca(2+)](cyt) responses to estradiol and progesterone could be reversed with higher concentrations of estradiol and progesterone, respectively. The [Ca(2+)](cyt) effects induced with tamoxifen could not be eliminated by prior treatment with RU 486 or ICI-182780.

CONCLUSION

These results provide strong evidence that both estradiol and progesterone as well as the steroid antagonists, tamoxifen, RU 486 and ICI-182780, can act on human granulosa-lutein cells through a non-genomic mechanism.

Effect of calcium on the vascular contraction induced by cobra venom cardiotoxin

1. The cytotoxic effects of cardiotoxin (CTX) purified from Cobra venom were tested in endothelium-denuded rat aortic ring preparations in tissue organ baths and the effect of extracellular Ca2+ on the cytotoxic effect of CTX was investigated using a digital dynamic calcium imaging technique. 2. At 10 micromol/L, CTX induced a slowly developing and sustained contraction that amounted to approximately 50% of the maximal contraction induced by 80 mmol/L KCl. At high concentrations (> 15 micromol/L), CTX caused irreversible damage to the smooth muscle contractile function. However, washout of CTX at its peak contraction did not affect the subsequent contraction to either KCl or phenylephrine. 3. Contraction induced by CTX was dependent on the Ca2+ concentration in the external solution. A maximal contractile response to CTX was obtained in medium containing 1-2.5 mmol/L Ca2+. This contractile response induced by CTX decreased with higher Ca2+ concentrations and was completely diminished when 7 mmol/L Ca2+, 3 mmol/L Ni2+ or 30 micromol/L tetrandrine (a non-selective calcium channel blocker) was present in the external solution before addition of CTX to the bath. 4. The above observations were supported by the calcium imaging work performed with cultured aortic smooth muscle cells from Wistar-Kyoto rats, in which CTX was shown to induce the elevation of cytosolic Ca2+ in the presence, but not in the absence, of 2.5 mmol/L extracellular Ca2+. Increasing the extracellular Ca2+ concentration to 7 mmol/L, the addition of 3 mmol/L Ni2+ or inclusion of 30 micro mol/L tetrandrine inhibited the elevation of cytosolic Ca2+ induced by CTX. 5. These results suggest that: (i) a CTX-sensitive internal calcium store does not exist in rat aortic smooth muscle; (ii) the contractile effect CTX is associated with a Ca2+ influx process; and (iii) CTX interacts extracellularly with the plasma membrane at the level of the calcium channels, as well as anionic sites to which Ca2+ and other inorganic cations bind.

Perturbation by lysophosphatidylcholine of membrane permeability in cultured vascular smooth muscle and endothelial cells

Lysophosphatidylcholine (LPC), a major component of oxidized low-density lipoprotein found in atherosclerotic arterial walls, has been shown to have insignificant effect on arterial contraction but cause an impairment of endothelium-dependent relaxation (EDR). The aim of this study was to compare the degree of LPC-induced perturbation in the plasma membrane of cultured aortic smooth muscle cells (SMC) and endothelial cells (EC). In contractility studies phenylephrine (PE) elicited a sustained contraction and a subsequent addition of acetylcholine (ACh) caused an almost complete relaxation. Preincubation of endothelium-intact aortic rings with LPC did not significantly affect PE-elicited contraction but substantially inhibited ACh-triggered relaxation. Such inhibition by LPC was both concentration- and time-dependent. LPC also inhibited relaxation triggered by extracellular ATP and cyclopiazonic acid. Exposure of cultured EC to LPC (30 microM) resulted in an elevation of [Ca2+]i with a lag period of some 25 min. Following [Ca2+]i elevation, addition of Ni2+ resulted in a rapid entry of this ion into the cell. In addition, fura-2 leak-out was observed. Exposure of cultured SMC to 30 microM LPC also resulted in [Ca2+]i elevation and Ni2+ entry. However, LPC did not cause fura-2 leak-out in SMC. Also, LPC raised [Ca2+]i at a slower rate in SMC than in EC. Our results suggest that the plasma membrane of EC is more susceptible to LPC-induced derangement than that of SMC. This may contribute in part to the selective impairment of EDR by LPC.