Upregulation of vascular endothelial growth factor expression induced by myocardial ischaemia: implications for coronary angiogenesis

OBJECTIVE

The process of coronary collateral development is poorly understood. It is assumed that particular angiogenic factors are upregulated during episodes of myocardial ischaemia and act as a trigger for neovascularisation. However, the identity of these factors is unknown. The angiogenic factor vascular endothelial growth factor (VEGF) has been shown to be hypoxia inducible, so this factor may mediate ischaemia induced angiogenesis in the heart. The aim of this study was to examine hypoxia inducibility of VEGF in cultured myocardial cells as well as in normally perfused and ischaemic porcine myocardium.

METHODS

(1) In vitro experiment: cultured rat myocardial cells were subjected to hypoxia, and steady state levels of VEGF mRNA were measured after 2 and 4 h of hypoxia. (2) In vivo experiment: myocardial ischaemia in pigs hearts was induced by repeated 2-10 min left anterior descending coronary artery occlusions, separated by 20 min of reperfusion. Hearts were retrieved after 6 h of intermittent ischaemia. Total RNA was extracted from normal and ischaemic zones of the heart and processed for RNA blot hybridisation analysis.

RESULTS

In vitro experiment: as soon as 2-4 h after exposure of cultures to hypoxia, VEGF mRNA levels were significantly raised (6-10-fold). In vivo experiment: VEGF expression was significantly augmented in the ischaemic territory of the myocardium (three- to fivefold induction). Furthermore, polymerase chain reaction amplification of the reverse transcribed mRNA showed increased production of multiple forms of differentially spliced VEGF mRNA in the ischaemic myocardium.

CONCLUSIONS

VEGF production in the myocardium is significantly upregulated by hypoxia in vitro and by ischaemia in vivo. These results suggest that VEGF is a likely mediator in the natural process of ischaemia induced myocardial neovascularisation.

Nitroxide stable radicals protect beating cardiomyocytes against oxidative damage

The protective effect of stable nitroxide radicals against oxidative damage was studied using cardiomyocyte cultures obtained from newborn rats. Monolayered cardiomyocytes were exposed to H2O2 and the effect on spontaneous beating and leakage of LDH was determined. Hydrogen peroxide irreversibly blocked rhythmic beating and resulted in a significant membrane injury as shown by release of LDH. The injury was prevented by catalase which removes H2O2 and by cell-permeable, metal-chelating agents such as desferrioxamine or bipyridine. In contrast, reagents which are excluded from the cell such as superoxide dismutase or DTPA did not protect the cells against H2O2. Five- and six-membered ring, stable nitroxide radicals which have previously been shown to chemically act as low-molecular weight, membrane-permeable, SOD-mimetic compounds provided full protection. The nitroxides prevented leakage of LDH and preserved normal cardiomyocyte contractility, presumably by intercepting intracellular O2-radicals. Alternatively, protection may result through nitroxides reacting with reduced transition metal ions or by detoxifying secondary organic radicals.

Role of iron in the potentiation of anthracycline cardiotoxicity: identification of heart cell mitochondria as a major site of iron-anthracycline interaction

The role of iron in anthracycline toxicity was studied in rats in vivo in intact animals and in vitro in heart cell cultures. In animals treated with 8 mg/kg doxorubicin, iron loading resulted in severe weight loss and a twofold increase in rate of mortality. Studies in cultured heart cells aimed at defining the subcellular target of interaction between iron and anthracycline toxicity showed no evidence of anthracycline-induced damage to sarcolemmal thiolic enzymes represented by 5'-nucleotidase and only a limited increase in lysosomal fragility as monitored by an increase in beta-hexosaminidase activity in cell homogenates and its release into the culture medium. By contrast, doxorubicin treatment resulted in a marked inhibition of mitochondrial function as monitored by a decrease in carbon 14-labeled palmitate utilization, to 33% +/- 4% of controls, and prior iron loading resulted in a further decrease in palmitate utilization, to 18% +/- 3% of controls. Conversely, iron-chelation treatment by either deferoxamine or deferiprone (L1) eliminated the harmful effects of iron loading and resulted in a partial inhibition of doxorubicin toxicity in both normal and iron-loaded cells. Our studies represent the first demonstration in intact animals of the potentiation of anthracycline toxicity by iron overload. They also indicate that mitochondria represent an important target of combined iron-anthracycline toxicity. These observations provide new insights into the mechanism of anthracycline cardiotoxicity and may be useful in developing better strategies for tumor therapy.

Mitochondrial respiratory enzymes are a major target of iron toxicity in rat heart cells

Our previous studies in iron-loaded rat heart cells showed that in vitro iron loading results in peroxidative injury, manifested in a marked decrease in rate and amplitude of heart cell contractility and rhythmicity, which is correctable by treatment with deferoxamine (DF). In the present studies we explored the role of mitochondrial damage in myocardial iron toxicity. Iron loading by 24-hour incubation with 0.36 mmol/L ferric ammonium citrate resulted in a decrease in the activity of nicotinamide adenine dinucleotide (NADH)-cytochrome c oxidoreductase (complex I+III) to 35.3%+/-11.2% of the value in untreated controls; of succinate-cytochrome c oxidoreductase (complex II+III) to 57.4%+/-3.1%; and of succinate dehydrogenase to 63.5%+/-12.6% (p < 0.001 in all cases). The decrease in activity of other mitochondrial enzymes, including NADH-ferricyanide reductase, succinate ubiquinone oxidoreductase (complex II), cytochrome c oxidase (complex IV), and ubiquinol cytochrome c oxidoreductase (complex III), was less impressive and ranged from 71.5%+/-15.8% to 91.5%+/-14.6% of controls. That the observed loss of respiratory enzyme activity was a specific effect of iron toxicity was clearly demonstrated by the complete restoration of enzyme activities by in vitro iron chelation therapy. Sequential treatment with iron and doxorubicin caused a loss of complex I+III and complex II+III activity that was greater than that seen with either agent alone but was only partially correctable by DF treatment. Alterations in cellular adenosine triphosphate measurements paralleled very closely the changes observed in respiratory complex activity. These findings demonstrate for the first time the impairment of cardiac mitochondrial respiratory enzyme activity caused by iron loading at conditions formerly shown to produce severe abnormalities in contractility and rhythmicity.

Alpha- and beta-adrenergic stimulation of protein synthesis in cultured adult ventricular cardiomyocytes

The effect of the alpha 1-adrenoceptor agonist phenylephrine (PE, 1-10 microM) and the beta-adrenoceptor agonist isoprenaline (ISO, 1-10 microM) on protein synthesis and ultrastructure of ventricular cardiomyocytes from adult rat in culture (6 days in medium 199 plus 20% fetal calf serum) was studied. In these cultures cardiomyocytes were spread, but not spontaneously contractile. ISO and PE significantly increased total cell protein and incorporation of (14C)-phenylalanine within 24 h of exposure. These effects were inhibited by the antagonists propranolol and prazosin, respectively. The incorporation of (14C)-uridine was stimulated only by PE but not ISO. Induction of fetal BB-isoform of cytosolic creatine kinase was also caused only by PE but not ISO. The ultrastructure of PE-treated cardiomyocytes was altered as compared to controls, by a greater number of Golgi complexes, denser myofibrillar structures and the appearance of paracrystalline bands in mitochondrial matrices. In conclusion, in this culture model the protein synthesis of cardiomyocytes can be stimulated, independently of the contractility, by either alpha 1- or beta-adrenoceptor agonists. Catecholamines differ, however, in their effects on specific cellular proteins and structures. Only alpha 1-adrenergic stimulation leads to a "fetal shift" in the expression of CK-isoforms.

Synergism among oxidants, proteinases, phospholipases, microbial hemolysins, cationic proteins, and cytokines

A striking similarity exists between the pathogenetic properties of group A streptococci and those of activated mammalian professional phagocytes (neutrophils, macrophages). Both types of cells are endowed by the ability to adhere to target cells; to elaborate oxidants, hydrolases, and membrane-active agents (hemolysins, phospholipases); and to freely invade tissues and destroy cells. From the evolutionary point of view, streptococci might justifiably be considered the forefathers of "modern" leukocytes. Our earlier findings that synergy between a streptococcal hemolysin (streptolysin S, SLS) and a streptococcal thiol-dependent proteinase and between cytotoxic antibodies+complement and streptokinase-activated plasmin readily killed tumor cells, led us to hypothesize that by analogy to the pathogenetic mechanisms of streptococci, the mechanisms of tissue destruction initiated by activated leukocytes in inflammatory sites, as well as in tissues undergoing episodes of ischemia and reperfusion, might also be the result of the synergistic effects among leukocyte-derived oxidants, phospholipases, proteinases, cytokines, and cationic proteins. The current report extends our previous synergy studies with endothelial cells to two additional cell types--monkey kidney epithelial cells and rat beating heart cells. Monolayers of 51Cr-labeled cells that had been treated by combinations of sublytic amounts of hydrogen peroxide (generated either by glucose oxidase, xanthine-xanthine oxidase, or by paraquat) and with sublytic amounts of a variety of membrane-active agents (streptolysin S, phospholipases A2 and C, lysophosphatides, histone, chlorhexidine) were killed in a synergistic manner (double synergy). Crystalline trypsin markedly enhanced cell killing by combinations of oxidant and the membrane-active agents (triple synergy). Injury to the cells was characterized by the appearance of large membrane blebs that detached from the cells and floated freely in the media, looking like lipid droplets. Cytotoxicity induced by the various combinations of agonists was depressed, to a large extent, by scavengers of hydrogen peroxide (catalase, dimethyl thiourea, and by Mn2+) but not by SOD or by deferoxamine. When cationic agents were employed together with hydrogen peroxide, polyanions (heparin, polyanethole sulfonate) were also found to inhibit cell killing. It is proposed that in order to effectively combat the deleterious toxic effects of leukocyte-derived agonists on cells and tissues, antagonistic "cocktails" comprised of cationized catalase, cationized SOD, dimethylthiourea, Mn(2+)+glycine, proteinase inhibitors, putative inhibitors of phospholipases, and polyanions might be concocted. The current literature on synergistic phenomena pertaining to mechanisms of cell and tissue injury in inflammation is selectively reviewed.

Changes in cytoplasmic and lysosomal enzyme activities in cultured rat heart cells: the relationship to cell differentiation and cell population in culture

Postnatal rat heart cells in culture enriched with respect to muscle cells were obtained by either high density seeding or by the replating technique. [3H]Thymidine incorporation to DNA and the enzymatic pattern of cytoplasmic and lysosomal enzymes have been studied as a function of the culture's age, of seeding density, and replating. It was shown that replating maintains predominance of myocyte population for at least 2 wk in culture; heavy seeding density allows homogeneous myocyte population for the 1st wk in culture; and the enzyme profile of the culture may serve as an indicator for the type of cell population in culture and its state of differentiation.

Exposure to endocrine disrupting chemicals and neurodevelopmental alterations

The developing brain is remarkably malleable as neural circuits are formed and these circuits are strongly dependent on hormones for their development. For those reasons, the brain is very vulnerable to the effects of endocrine-disrupting chemicals (EDCs) during critical periods of development. This review focuses on three ubiquitous endocrine disruptors that are known to disrupt the thyroid function and are associated with neurobehavioral deficits: polychlorinated biphenyls, polybrominated diphenyl ethers, and bisphenol A. The human and rodent data suggesting effects of those EDCs on memory, cognition, and social behavior are discussed. Their mechanisms of action go beyond relative hypothyroidism with effects on neurotransmitter release and calcium signaling.

Both hydroxylamine and nitroxide protect cardiomyocytes from oxidative stress

The unique anti-oxidative activity of nitroxide radicals protecting against reactive oxygen-derived species (ROS) has been recently demonstrated in several model systems. The present study focuses on the activity of nitroxide and of its reduced form in cultured rat ventricular cardiomyocytes exposed to O2.- and H2O2 generated by hypoxanthine (HX) and xanthine oxidase (XO). To evaluate cell injury, spontaneous beating, leakage of lactate dehydrogenase (LDH), and depletion of cellular ATP were determined. The protective effect of 4-OH-2,2,6,6-tetramethyl-piperidine-N-oxyl (TPL) was compared with that of 4-OH-2,2,6,6-tetramethyl-1-hydroxypiperidine (TPL-H) and of several common anti-oxidants. A rapid exchange between TPL and TPL-H, is mediated by cellular metabolism and through reactions with ROS. In particular, TPL under O2.- flux is oxidized to oxo-ammonium cation (TPL+) which comproportionates with TPL-H yielding two nitroxide radicals. Because this exchange limits the distinction between the biological activities of TPL and TPL-H, NADH which can reduce TPL+ was included in order to maintain the nitroxide in its reduced form. The results demonstrate that both TPL and TPL-H protect cardiomyocytes against beating loss and LDH leakage. Conversely, cellular ATP depletion induced by HX/XO is inhibited by TPL-H, though not by TPL, suggesting that different mechanisms underlie their protective activities. Through a flip-flop between the two forms, which coexist in the system, the levels of TPL-H and TPL are continuously replenished. The conversion, upon reaction, of each antioxidant into the other one enables them, contrary to common antioxidants which operate in a stoichiometric mode, to act catalytically.

Prevention of anthracycline cardiotoxicity by iron chelation

The use of anthracycline antineoplastic drugs is limited by a cumulative, dose-dependent toxicity to the heart. Of the cellular organelles proposed as possible primary sites of anthracycline toxicity, the mitochondrial membrane appears to be most likely target. Cardiolipin, a major phospholipid component of the inner mitochondrial membrane is rich in polyunsaturated fatty acids and is particularly susceptible to peroxidative injury by harmful radicals produced by redox cycling of anthracyclines. This, in turn, leads to the inactivation of key enzymes in the mitochondrial respiratory chain. Since the formation of free radicals is catalyzed by iron through the Haber-Weiss reaction, it was hypothesized that iron depletion by deferoxamine (DFO) may limit anthracycline cardiotoxicity. Recent studies indicate that iron-loading aggravates doxorubicin cardiotoxicity by enhancing mitochondrial damage, and this can be prevented by prior DFO treatment. Although these observations are intriguing, further studies are required to show that the cardioprotective effects of DFO do not interfere with the therapeutic, antitumoral action of anthracyclines.

Proteins of seminal fluid and spermatozoa in the trout (Oncorhynchus mykiss): Partial characterization and variations

The protein composition of seminal fluid, blood serum, sperm plasma membrane and flagellum of rainbow trout were analysed by SDS-polyacrylamide gel electrophoresis. Immunological identity between proteins of the 2 fluids and sperm components was studied using crossed immunoelectrophoresis, rocket immunoelectrophoresis and immunoblotting. Results indicate that many seminal proteins are antigenically-related to serum proteins, proteins of sperm origin are present in seminal fluid in varying amounts, depending on the animals and sampling time, and several serum-like seminal proteins are bound to spermatozoa.Lipoproteins were isolated from seminal fluid (mean level: 33 μg/ml) and characterized. They were identified as being HDL-like lipoproteins. A possible physiological role is proposed for these seminal lipoproteins.

The role of iron and iron chelators in anthracycline cardiotoxicity

The redox cycling of anthracyclines promotes the formation of free radicals which are believed to play a central role in their cardiotoxicity. A number of observations indicate that the mechanism of the antineoplastic effect of anthracyclines is independent of their cardiotoxic effect and that it may be possible to prevent toxicity without interfering with therapeutic effect. Iron plays an important role in anthracycline toxicity by promoting the conversion of superoxide into highly toxic hydroxyl radicals through the Haber-Weiss reaction. Conversely, iron deprivation by its high-affinity binding to iron chelating compounds may inhibit anthracycline toxicity by interfering with free radical formation. ICRF-187, a bispiperazonedione which is hydrolyzed intracellularly into a bidentate chelator resembling EDTA, is able to decrease adriamycin-induced free hydroxyl radical formation and to prevent the development of clinical cardiac toxicity in patients receiving long-term anthracycline therapy. Our studies in rat heart cell cultures have shown that iron overload aggravates anthracycline toxicity and that this interaction can be prevented by prior iron chelating treatment. Since iron overload caused by multiple blood transfusions and bone marrow failure is a common condition in patients requiring anthracycline therapy, these observations may have significant clinical implications to the prevention of anthracycline cardiotoxicity.

Early neuroendocrine disruption in hypothalamus and hippocampus: developmental effects including female sexual maturation and implications for endocrine disrupting chemical screening

The timing of puberty has been mainly studied in females for several reasons, including the possible evaluation of a precise timer (i.e. menarcheal age) and concerns with respect to the high prevalence of precocity in females as opposed to males. Human evidence of altered female pubertal timing after exposure to endocrine disrupting chemicals (EDCs) is equivocal. Among the limiting factors, most studies evaluate exposure to single EDCs at the time of puberty and hardly assess the impact of lifelong exposure to mixtures of EDCs. Some rodent and ovine studies indicate a possible role of foetal and neonatal exposure to EDCs, in accordance with the concept of an early origin of health and disease. Such effects possibly involve neuroendocrine mechanisms because the hypothalamus is a site where homeostasis of reproduction, as well as control of energy balance, is programmed and regulated. In our previous studies, pulsatile gonadotrophin-releasing hormone (GnRH) secretion control via oestrogen, glutamate and aryl hydrocarbon receptors was shown to be involved in the mechanism of sexual precocity after early postnatal exposure to the insecticide dichlorodiphenyltrichloroethane. Very recently, we have shown that neonatal exposure to the potent synthetic oestrogen diethylstilbestrol (DES) is followed by early or delayed puberty depending on the dose, with consistent changes in developmental increase of GnRH pulse frequency. Moreover, DES results in reduced leptin stimulation of GnRH secretion in vitro, an effect that is additive with prenatal food restriction. Thus, using puberty as an endpoint of the effects of EDC, it appears necessary to consider pre- and perinatal exposure to low doses and to pay attention to the other conditions of prenatal life, such as energy availability, keeping in mind the possibility that puberty could not only be advanced, but also delayed through neuroendocrine mechanisms.

Iron chelation

Adequate iron chelation in thalassaemia has resulted in a striking improvement in survival, with a reduction of cardiac mortality at age 15 years from 14-3%, and a predicted survival at age 36 years of 85%. Long term desferrioxamine (DF) therapy in thalassaemic children should be started between 2-4 years of age. In addition to daily 8-12 h subcutaneous infusions, intermittent high dose (9-16 g) i.v. supplementation over 24-48 h may be given on the occasion of blood transfusions. In established myocardiopathy continuous i.v. DF infusion at 100-125 mg/kg/d may result in improved myocardial function. In addition, there is considerable current interest in the use of DF in conditions unrelated to iron overload by preventing the formation of free-radicals in inflammatory reactions, or by S-phase inhibition of cell proliferation. Although at present highly experimental, this novel approach may have important implications for the management of patients with inflammatory conditions and perhaps in the control of protozoal infections. Over the last decade several hundred candidate compounds have been studied in cell cultures and in animal models and a number of orally effective iron chelators have been identified, all of which are superior to DF in their in vivo iron chelating effect. Although we do not yet have a new drug which is immediately available for replacing DF in clinical practice, significant progress has already been made, and some of the most promising candidate drugs are currently undergoing extensive toxicity tests in anticipation of their development for large-scale clinical use.

Do nitroxides protect cardiomyocytes from hydrogen peroxide or superoxide?

The aim of the research was to study the role played by extracellular O2-radicals, which are implicated in cardiac cell damage and the protective effect by cell-permeable, nitroxide, superoxide dismutase-mimics. Cardiomyocytes cultures from 1-day-old rats served as the test-system. Experiments were performed since 5th day in culture when > 80% of the cells were beating myocardial cells. Oxidative damage was induced by 0.5 mM hypoxanthine and 0.06 U/ml xanthine oxidase or by 10 mM glucose and 0.15 U/ml glucose oxidase. The parameters used to evaluate damages were spontaneous beating, lactate dehydrogenase release and ATP level. The rhythmic pulsation was followed microscopically. To determine the kinetics of cytosolic enzyme release from the cells, media samples were collected at various points of time and assayed for enzyme activity. To determine the cellular ATP, cells were washed with sodium phosphate buffer, scraped off and boiled for 3 min with sodium phosphate buffer. Following centrifugation the supernatant was collected and ATP was determined by the chemiluminogenic assay using firefly tails. The present results indicate that nitroxide stable free radicals in the millimolar concentration range, provide full protection without toxic side-effect. Unlike exogenously added SOD that failed to protect, exogenous catalase provided almost full protection. In addition, the metal-chelating agent dipyridyl, but not diethylene-triamine-pentaacetate or desferrioxamine, protected the cultured cells. The present results suggest that H2O2 is the predominant toxic species mediating the oxidative damage whereas extracellular superoxide radical does not contribute to cultured cardiomyocyte damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on oxygen and extracellular fluid restrictions in cultured heart cells: high energy phosphate metabolism

Although cultured heart cells are increasingly used for the study of cardiac metabolism, relatively little is known about their energy turnover. We studied the effects of anoxia with simultaneous restrictions of the volume of the extracellular medium ("ischaemia") on high energy phosphate catabolism in cells from neonatal rat ventricles, cultured for 5 days. The cells were incubated for up to 4 h in Ham-F10 medium either in the presence or in the absence of glucose. High energy phosphates in cell extracts and AMP catabolites in the incubation medium were measured by high pressure liquid chromatography. ATP and creatine phosphate content in normoxic cells did not change significantly, either in the presence or absence of glucose, and the values were similar to those found in the heart in vivo. Energy rich phosphates decreased during anoxia, and were more rapidly depleted during simultaneous oxygen deprivation and volume restriction. Glucose delayed the decline in high energy phosphates. In the presence of glucose, hypoxanthine uptake was higher during normoxia than in anoxia, whereas in "ischaemic" conditions some hypoxanthine was produced. In the absence of glucose, only minor changes were observed in hypoxanthine levels during anoxia, but hypoxanthine production was marked when anoxia was coupled with extracellular volume restriction. Adenosine levels were below the limit of detection. Inosine release was relatively low under all conditions, Xanthine release did not show variation, and anoxia suppressed urate production. Oxygen and glucose deprivation thus led to various degrees of ATP and creatine phosphate breakdown in cultured neonatal heart cells both during anoxia and in simulated "ischaemia".

Interactions of cardiac glycosides with cultured cardiac cells. II. Biochemical and electron microscopic studies on the effects of ouabain on muscle and non-muscle cells

Electron microscopic and biochemical studies revealed a salient difference in the response to toxic doses of ouabain by cultured cardiac muscle and non-muscle cells from neonatal rats. Progressive cellular injury in myocytes incubated with 1 . 10(-4)--1 . 10(-3) M ouabain ultimately leads to swelling and necrosis. The morphological damage in myocytes was accompanied by a drastic decrease in 14CO2 formation from 14C-labeled stearate or acetate but not glucose. Neither morphological nor biochemical impairments were observed in non-muscle cells. The interaction between ouabain and the cultured cells, using therapeutic doses of ouabain (i.e., less than 1 . 10(-7) M), was characterized. Two binding sites were described in both classes of cells, one site is a saturable K+-sensitive site whereas the other is non-saturable and K+-insensitive. The complexes formed between the sarcolemma receptor(s) and ouabain, at low concentrations of the drug (e.g., 7.52 . 10(-9) M), had Kd values of 8.9 . 10(-8) and 2.3 . 10(-8) M for muscle and non-muscle cells, respectively. The formation and dissociation of the complexes were affected by temperature and potassium ions.