Doxorubicin-induced and trastuzumab-induced cardiotoxicity in mice is not prevented by metoprolol

Aims

Our objectives were to validate a murine model of chronic cardiotoxicity induced by Doxorubicin (Dox) and Trastuzumab (Trast) and to test the potential cardio‐protective effect of metoprolol.

Methods and results

Male C57Bl6 mice were intraperitoneally injected during 2 weeks with Dox (24 mg/kg) or saline, and then with Trast (10 mg/kg) or saline for two more weeks. Half of the mice received metoprolol (100 mg/kg). Cardiotoxicity was defined by a decline in left ventricular ejection fraction (LVEF) ≥ 10 points. At Day 42, Dox + Trast‐treated mice exhibited a 13‐points decline in LVEF (74 ± 2.6% vs. 87 ± 0.8% for control mice, P < 0.001) and a severe cardiac atrophy (heart weight: 105 ± 2.7 mg vs. 119 ± 3.9 mg for control mice, P < 0.01). This cardiac atrophy resulted from an excess of cardiac necrosis (assessed by plasma cardiac troponin I level: 3.2 ± 0.4 ng/L vs. 1.3 ± 0.06 ng/L for control mice, P < 0.01), an increase in apoptosis (caspase 3 activity showing a six‐fold increase for Dox + Trast‐treated mice vs. controls, P < 0.001), and cardiomyocyte atrophy (myocyte size: 0.67 ± 0.08 μm² vs. 1.36 ± 0.10 μm² for control mice, P < 0.001). In addition, Dox + Trast‐treated mice were shown to have an increased cardiac oxidative stress (164 ± 14 dihydroethidine‐marked nuclei per area vs. 56 ± 9.5 for control mice, P < 0.01) and increased cardiac fibrosis (the semi‐quantitative fibrosis score was three‐fold higher for Dox + Trast‐treated mice as compared with controls, P < 0.01). Metoprolol was not able to prevent either the decrease in LVEF or the severe cardiac atrophy, the cardiac necrosis, and the cardiac remodelling induced by chemotherapies.

Conclusion

A murine model of chronic cardiotoxicity induced by Dox and Trast was characterized by a decrease in cardiac function, a cardiac apoptosis and necrosis leading to cardiomyocyte atrophy. Metoprolol did not prevent this cardiotoxicity.

Inhibition of circulating dipeptidyl-peptidase 3 restores cardiac function in a sepsis-induced model in rats: A proof of concept study

Sepsis is a global economic and health burden. Dipeptidyl peptidase 3 (DPP3) is elevated in the plasma of septic patients. The highest levels of circulating DPP3 (cDPP3) are found in non-survivor septic shock patients. The aim of this study was to evaluate the benefits of inhibiting cDPP3 by a specific antibody, Procizumab (PCZ), on cardiac function in an experimental model of sepsis, the caecal ligature and puncture (CLP) model. Rats were monitored by invasive blood pressure and echocardiography. Results are presented as mean ± SD, with p <0.05 considered significant. PCZ rapidly restored left ventricular shortening fraction (from 39 ± 4% to 51 ± 2% before and 30 min after PCZ administration (p = 0.004)). Cardiac output and stroke volume were higher in the CLP + PCZ group when compared to the CLP + PBS group (152 ± 33 mL/min vs 97 ± 25 mL/min (p = 0.0079), and 0.5 ± 0.1 mL vs 0.3 ± 1.0 mL (p = 0.009), respectively) with a markedly reduced plasma DPP3 activity (138 ± 70 U/L in CLP + PCZ group versus 735 ± 255 U/L (p = 0.048) in the CLP + PBS group). Of note, PCZ rapidly reduced oxidative stress in the heart of the CLP + PCZ group when compared to those of the CLP + PBS group (13.3 ± 8.2 vs 6.2 ± 2.5 UI, p = 0.005, 120 min after administration, respectively). Our study demonstrates that inhibition of cDPP3 by PCZ restored altered cardiac function during sepsis in rats.

Lythrum hyssopifolia (lesser loosestrife) poisoning of sheep in Victoria

OBJECTIVE

To document an ovine disease attributed to the consumption of Lythrum hyssopifolia (lesser loosestrife).

PROCEDURES

Historical and histological review of field and experimental cases.

RESULTS

1-20% mortality occurred in sheep flocks grazing paddocks where L. hyssopifolia was the predominant green vegetation. Well-documented disease outbreaks occurred in summer on nine farms across Victoria between 1974 and 2002. Liver damage occurred in all nine outbreaks, with kidney damage in at least eight. Hepatocyte necrosis was usually zonal to midzonal (zone 2) in the liver samples from four farms and periacinar (zone 3) in those from three farms, but some livers showed only single-cell necrosis. Multinucleate hepatocytes near necrotic areas were a feature in six cases. Proximal tubular epithelium appeared to be the primary renal target and brown granules were often present in renal tubules. Biochemical and histological evidence of liver and kidney damage was obtained from two sheep experimentally pen-fed harvested L. hyssopifolia.

CONCLUSION

Chemicals in L. hyssopifolia are toxic to ovine hepatocytes and renal tubular epithelial cells.

Oxidative stress of myosin contributes to skeletal muscle dysfunction in rats with chronic heart failure

Intrinsic muscle abnormalities affecting skeletal muscle are often reported during chronic heart failure (CHF). Because myosin is the molecular motor of force generation, we sought to determine whether its dysfunction contributes to skeletal muscle weakness in CHF and, if so, to identify the underlying causative factors. Severe CHF was induced in rats by aortic stenosis. In diaphragm and soleus muscles, we investigated in vitro mechanical performance, myosin-based actin filament motility, myosin heavy (MHC) and light (MLC) chain isoform compositions, MLC integrity, caspase-3 activation, and oxidative damage. Diaphragm and soleus muscles from CHF exhibited depressed mechanical performance. Myosin sliding velocities were 16 and 20% slower in CHF than in sham in diaphragm (1.9 ± 0.1 vs. 1.6 ± 0.1 μm/s) and soleus (0.6 ± 0.1 vs. 0.5 ± 0.1 μm/s), respectively (each P < 0.05). The ratio of slow-to-fast myosin isoform did not differ between sham and CHF. Immunoblots with anti-MLC antibodies did not detect the presence of protein fragments, and no activation of caspase-3 was evidenced. Immunolabeling revealed oxidative damage in CHF muscles, and MHC was the main oxidized protein. Lipid peroxidation and expression of oxidized MHC were significantly higher in CHF than in shams. In vitro myosin exposure to increasing ONOO−concentrations was associated with an increasing amount of oxidized MHC and a reduced myosin velocity. These data provide experimental evidence that intrinsic myosin dysfunction occurs in CHF and may be related to oxidative damage to myosin.

Cardiac myocyte neuronal nitric oxide synthase. New therapeutic target in heart failure?

Although nitric oxide-dependent regulation of contractile function is altered in the diseased and failing heart, several aspects of nitric oxide (NO) signalling in the myocardium remain poorly understood. Some apparently contrasting findings may have arisen from the use of non-isoform-specific inhibitors of NO synthase isoforms (NOS) as compared to the use of mouse models genetically deficient or overexpressing the NOS thought to be responsible for the increase in NO production in heart failure (mainly NOS2 and NOS3). In recent years, identification of the neuronal NOS (NOS1) isoform in cardiac myocytes and the recognition of the importance of its subcellular localisation have greatly advanced the understanding of the critical role of NOS1-derived NO in the control of myocardial contractility both in the normal and failing heart. The challenge is now to confirm these emerging findings on the critical role of NOS1-derived NO in human cardiac physiology and hopefully translate them into therapy.

Extracellular matrix and growth factors during heart growth

The effects of growth factors on tissue remodeling and cell differentiation depend on the nature of the extracellular matrix, the type and organization of integrins, the activation of metalloproteinases and the presence of secreted proteins associated to the matrix. These interactions are actually poorly known in the cardiovascular system. We describe here: 1) the main components of extracellular matrix within the cardiovascular system; 2) the role of integrins in the transmission of growth signals; 3) the shift in the expression of the components of the extracellular matrix (fibronectin and collagens) and the stimulation of the synthesis of metalloproteinases during normal and hypertrophic growth of the myocardium; 4) the effects of growth factors, such as Angiotensin II, Fibroblast Growth Factors (FGF), Transforming Growth Factor-beta (TGF-beta), on the synthesis of proteins of the extracellular matrix in the heart.

Extracellular matrix and cardiac remodelling

Cardiac remodelling associated with primitive and secondary cardiomyopathy is generally associated with changes in the expression in extracellular matrix (ECM) proteins as well as their transmembrane receptors, the integrins. It emerges now that the ECM provides a structural, chemical, and mechanical substrate that is essential in cardiac function and responses to pathophysiological signals. This review will describe the various elements of the ECM, its modifications that are associated with cardiac hypertrophy and heart failure, and the molecular basis bringing a better insight into the dynamics of the ECM.

[Mechanical and functional predictive factors for restenosis and arterial remodeling after experimental angioplasty]

Arterial remodelling plays an important part in post-angioplasty restenosis but the physiopathology of this process is not fully understood. Abundant collagen synthesis and endothelial dysfunction have been demonstrated after angioplasty, but their role in restenosis and remodelling has not been studied. The aim of this study was therefore to assess endothelial function and collagen with respect to the severity of restenosis and the type of arterial remodelling. Atherosclerosis was induced by an association of endothelial abrasion and a high cholesterol diet in the femoral arteries of 22 white New Zealand rabbits. Four weeks later, angioplasty was performed. The acetylcholine endothelium-dependant vasomotricity (expressed as % inhibition of contraction to phenylephrine), collagen and morphology were assessed 28 days after angioplasty. The change in acetylcholine endothelium-dependant vasomotricity was greater in severe restenosis (r = 0.61, p = 0.02). Endothelium-dependant relaxation was not significantly altered when remodelling was expansive and very abnormal when it was constrictive (35.5 +/- 13.0 vs 3.7 +/- 7.9%; p = 0.04). Restenosis was associated with an increase in collagen (r = 0.69, p = 0.004). The density of collagen was significantly higher in constrictive remodelling than in expansive remodelling (34.5 +/- 4.5 vs 18.2 +/- 4.7%; p = 0.03). Endothelial dysfunction and collagen accumulation are correlated with the severity of restenosis and with constrictive remodelling after angioplasty in an experimental model.

Coronary microvasculature alteration in hypertensive rats. Effect of treatment with a diuretic and an ACE inhibitor

The development of hypertension is accompanied by rarefaction of arterioles and capillaries in both animal models and humans. Although many studies have examined the effects of antihypertensive therapies on hemodynamics, cardiac hypertrophy, and large vessel structure, the question of whether changes in microvascular density induced by hypertension can be restored by pharmacologic treatment has yet to be answered. We report a series of experiments performed in rats with renovascular hypertension induced by unilateral nephrectomy and renal artery stenosis (Goldblatt one-kidney, one-clip model). Animals were treated for 4 weeks, after renal artery clipping, either with an angiotensin converting enzyme inhibitor (perindopril [PER], 0.76 mg/kg/day), or with an indol derivative diuretic with specific vascular properties (indapamide [IDP], 0.24 mg/kg/day) or with the combination of both drugs at the same doses as during monotherapy. Coronary microvessel densities (arterioles and capillaries) were evaluated by double immunolabeling in nonserial cryostat sections of the left ventricular inner myocardium. After 4 weeks of hypertension (mean arterial pressure, 174+/-11 v 124+/-5 mm Hg in normotensive (NT) controls, P < .01), cardiac hypertrophy (+59%, P < .001) was associated with a significant increase in myocardial arteriolar density (+27%, P < .01), and a decrease in capillary density (-12%, P < .05). Treatment with PER prevented the increase in arterial pressure, heart weight, and arteriolar density, but did not significantly affect the low coronary capillary density in comparison with that measured in untreated hypertensive (HT) rats. Treatment with IDP preserved normal capillary myocardial density but did not significantly lower the blood pressure (BP) (169+/-9 mm Hg) and only slightly reduced the cardiac ventricular hypertrophy: - 14% v untreated HT (P < .05) and +37% v NT (P < .01). In the same way, IDP normalized the left ventricular capillary density in spontaneously HT rats (+18% v untreated rats, P < .01). The combination of both drugs, PER and IDP, at the same low doses as during monotherapy, resulted in normal levels of arterial pressure and complete normalization of cardiac hypertrophy and arteriolar and capillary myocardial densities. In conclusion, the results observed after PER suggest that blockade of the renin-angiotensin system could inhibit large coronary vessel growth but minimally affects the capillary density despite complete normalization of BP. Indapamide could have beneficial effect on myocardial capillary density. The combination of IDP and PER has additional effects and prevents the increase in BP and cardiac weight, and reverses microvascular rarefaction, specifically arteriolar and capillary densities.

Effect of pressure overload on angiotensin receptor expression in the rat heart during early postnatal life

The development of cardiac hypertrophy during neonatal life and in adults implies different processes. The angiotensin II (Ang II) system is involved in the development of cardiac hypertrophy in adults, but its role in neonates remains unclear. The aim of this study was to estimate the influence of increased hemodynamic load on the developmental pattern of the AT1/AT2 receptor expression in the heart. Two-day-old rats submitted to abdominal aortic constriction (AC) or sham operation were sacrificed 2 h, and 1, 3, and 8 days after surgery. Ang II was evaluated in sera and immunohistology was performed to define the cardiac hypertrophy process. The Ang II receptor subtypes 1 and 2 were quantified at the receptor and mRNA levels by(125)I-Ang II binding and RT-PCR, respectively. Ang II content in sera increased transiently 2 h after surgery in the AC group. In sham-operated, AT1 and AT2 decreased throughout the period studied at both mRNA and receptor levels. However, the AT1 mRNA level decrease was more pronounced than that of AT2 (by 57% and 27%, respectively). AC not only prevented the postnatal decrease in AT mRNA level but resulted in an increase in AT1 mRNA 8 days after surgery (P<0.05). Besides in the AC groups, AT2 mRNA levels but not those of AT1 mRNA were linearly correlated with the left ventricular mass. At the receptor level, a significant transient (1 day after surgery) increase in both AT1 and AT2 was observed. In conclusion, our data demonstrated that imposition of pressure overload soon after birth altered the pattern of AT receptor expression.

Specific cellular features of atheroma associated with development of neointima after carotid endarterectomy: the carotid atherosclerosis and restenosis study

BACKGROUND

The purpose of this study was to investigate whether some cellular and molecular features of tissue retrieved at carotid endarterectomy are associated with the extent of neointima formation at ultrasound follow-up.

METHODS AND RESULTS

One hundred fifty patients were studied. Endarterectomy specimens were tested by immunocytochemistry with the use of (1) monoclonal antibodies that identify smooth muscle cells (SMCs) and fetal-type SMCs on the basis of smooth muscle and nonmuscle myosin content, (2) the anti-macrophage HAM 56, and (3) the anti-lymphocyte CD45RO. The maximum intima-media thickness (M-IMT) of the revascularized vessel was assessed by the use of B-mode ultrasonography 6 months after surgery. The M-IMT values were related positively to the number of SMCs (r=0.534, P<0.0005) and negatively to that of macrophages and lymphocytes (r=-0.428, P<0.0005, and -0.538, P=0.001, respectively). Patients were classified as class 1 (M-IMT </=1.0 mm), class 2 (1. 0<M-IMT</=1.3 mm), and class 3 (M-IMT >1.3 mm). An abundance of SMCs, mostly of fetal type, was found in the plaque of class 3 patients, whereas lesions from class 1 patients were rich in macrophages and lymphocytes. In the multivariate analysis, factors related to M-IMT were the number of SMCs and the percentage of fetal-type SMCs present in the plaque.

CONCLUSIONS

Although the classic risk factors did not play a role, an abundance of SMCs and a scarcity of macrophages characterized the primary lesion of patients in whom neointima developed after surgery. In patients in whom neointima did not develop, lesions were rich in macrophages and lymphocytes. This approach can be useful in defining patients at risk of restenosis.

Comparison of the effects of fetal cardiomyocyte and skeletal myoblast transplantation on postinfarction left ventricular function

OBJECTIVES

Transplantation of fetal cardiomyocytes improves function of infarcted myocardium but raises availability, immunologic, and ethical issues that justify the investigation of alternate cell types, among which skeletal myoblasts are attractive candidates.

METHODS

Myocardial infarction was created in rats by means of coronary artery ligation. One week later, the animals were reoperated on and intramyocardially injected with culture growth medium alone (controls, n = 15), fetal cardiomyocytes (5 x 10(6) cells, n = 11), or neonatal skeletal myoblasts (5 x 10(6) cells, n = 16). The injections consisted of a 150-microL volume and were made in the core of the infarct, and the animals were immunosuppressed. Left ventricular function was assessed by echocardiography immediately before transplantation and 1 month thereafter. Myoblast-transplanted hearts were then immunohistologically processed for the expression of skeletal muscle-specific embryonic myosin heavy chain and cardiac-specific connexin 43.

RESULTS

The left ventricular ejection fraction markedly increased in the fetal and myoblast groups from 39.3% +/- 3.9% to 45% +/- 3.4% (P =.086) and from 40.4% +/- 3.6% to 47.3% +/- 4.4% (P =.034), respectively, whereas it decreased in untreated animals from 40.6% +/- 4% to 36.7% +/- 2.7%. Transplanted myoblasts could be identified in all animals by the positive staining for skeletal muscle myosin. Conversely, clusters of connexin 43 were not observed on these skeletal muscle cells.

CONCLUSIONS

These results support the hypothesis that skeletal myoblasts are as effective as fetal cardiomyocytes for improving postinfarction left ventricular function. The clinical relevance of these findings is based on the possibility for skeletal myoblasts to be harvested from the patient himself.

Expression of laminin alpha2 chain during normal and pathological growth of myocardium in rat and human

OBJECTIVES

Fibrosis is a classical feature of cardiac hypertrophy. To date changes within the basal lamina during normal and pathological cardiac growth have been poorly investigated. The goal of the present study was to determine if the expression of the muscle specific subunit of merosin (laminin alpha2 chain) together with that of fibronectin (FN) is modified in the diseased human heart. Laminin alpha2 chain expression was also investigated during physiological and pathological cardiac growth in the rat.

METHODS

In ten normal human hearts and ten hearts with idiopathic dilated cardiomyopathy (IDCM), the laminin-alpha2 and FN mRNA levels were quantified by slot-blot using total RNA and the protein distribution was analysed using an immunofluorescence approach. In Wistar rats, laminin alpha2 and FN mRNA expression was analyzed using RNase protection assay (RPA) and slot-blot assays.

RESULTS

The amount of laminin alpha2 mRNA did not vary in normal and pathological human hearts whereas it was significantly decreased in renovascular hypertensive rats (-20%) P<0.05 versus normal tissue). The amount of fibronectin mRNA increased in IDMC patients (x2, P<0.05 versus normal tissue), but was unchanged in hypertensive rats. A negative correlation was found between the cardiac laminin-alpha2 level and the age of the patients whatever the cardiac status. During postnatal development in the rat, a similar decrease in cardiac laminin-alpha2 level was observed between 3 and 30 weeks of age. Finally, the immunofluorescent approach failed to detect any alteration in laminin alpha2 distribution within the human myocardium.

CONCLUSION

These data indicate that an imbalance between myocyte hypertrophy and the level of laminin-alpha2 might contribute to alterations in sarcolemmal properties, which occur during the development of cardiac hypertrophy and its transition to cardiac failure.

Modulation of angiotensin II receptor expression during development and regression of hypoxic pulmonary hypertension

Lung vessel muscularization during hypoxic pulmonary hypertension is associated with local renin-angiotensin system activation. The expression of angiotensin II (Ang II) AT1 and AT2 receptors in this setting is not well known and has never been investigated during normoxia recovery. We determined both chronic hypoxia and normoxia recovery patterns of AT1 and AT2 expression and distal muscularization in the same lungs using in situ binding, reverse transcriptase/polymerase chain reaction, and histology. We also used an isolated perfused lung system to evaluate the vasotonic effects of AT1 and AT2 during chronic exposure to hypoxia with and without subsequent normoxia recovery. Hypoxia produced right ventricular hypertrophy of about 100% after 3 wk, which reversed with normoxia recovery. Hypoxia for 2 wk was associated with simultaneous increases (P<0.05) in AT1 and AT2 binding (16-fold and 18-fold, respectively) and in muscularized vessels in alveolar ducts (2. 8-fold) and walls (3.7-fold). An increase in AT2 messenger RNA (mRNA) (P<0.05) was also observed, whereas AT1 mRNA remained unchanged. After 3 wk of hypoxia, muscularization was at its peak, whereas all receptors and transcripts showed decreases (P<0.05 versus hypoxia 2 wk for AT1 mRNA), which became significant after 1 wk of normoxia recovery (P<0.05 versus hypoxia 2 wk). Significant reversal of muscularization (P<0.01) was found only after 3 wk of normoxia recovery in alveolar wall vessels. Finally, the AT1 antagonist losartan completely inhibited the vasopressor effect of Ang II in hypoxic and normoxia-restored lungs, whereas the AT2 agonist CGP42112A had no effect. Our data indicate that in lungs, chronic hypoxia-induced distal muscularization is associated with early and transient increases in AT2 and AT1 receptors probably owing to hypoxia- dependent transcriptional and post-transcriptional regulatory mechanisms, respectively. They also indicate that the vasotonic response to Ang II is mainly due to the AT1 subtype.

Expression and localization of the annexins II, V, and VI in myocardium from patients with end-stage heart failure

Annexins II, V, and VI belong to a family of Ca(2+)-dependent phospholipid-binding proteins that have been involved mainly in signal transduction, differentiation, membrane trafficking events, or binding to the extracellular matrix, or that might be effective as Ca(2+)-channels. They are abundant in the mammalian myocardium and might play a role in ventricular remodeling and altered calcium handling during heart failure. To test this hypothesis, we compared the expression and distribution of these annexins in nonfailing (n = 9) and failing human hearts with idiopathic dilated cardiomyopathy (n = 11). Northern blot and slot blot analysis were used to determine the annexin mRNA levels and Western blots were used to quantify the amounts of annexin proteins. Distribution of annexins was studied by immunohistofluorescence labeling and compared with that of a sarcolemmal marker (Na+/K(+)-ATPase) and of a myofibrillar protein (alpha-actinin). We showed that nonfailing hearts contained a higher amount of annexin VI than of annexin V or II (13.5 +/- 1.8, 3.7 +/- 0.2, and 2.5 +/- 0.5 microg/mg protein, respectively). In failing hearts, there was a parallel increase in both mRNA and protein levels of annexin II (146% and 132%, p < 0.05, respectively) and annexin V (152%, p < 0.01, 147%, p < 0.005, respectively); the protein level of annexin VI was also increased (117%, p < 0.05), whereas the increase of its mRNA level was statistically insignificant. We observed a predominant localization of annexin II in interstitium, and of annexins V and VI in cardiomyocytes at the level of the sarcolemma, T-tubules, and intercalated disks in nonfailing hearts, whereas in failing hearts enlarged interstitium contained all three annexins. Furthermore, annexin V staining at the level of cardiomyocytes almost disappeared. In conclusion, we showed that heart failure is accompanied by marked overexpression of annexins II and V, as well as translocation of annexin V from cardiomyocytes to interstitial tissue. The data suggest that annexins may contribute to ventricular remodeling and annexin V to impaired Ca2+ handling in failing heart.

Thyroid hormones differentially modulate enolase isozymes during rat skeletal and cardiac muscle development

During muscle development, an isozymic transition of the glycolytic enzyme enolase occurs from the embryonic and ubiquitous alphaalpha-isoform to the muscle-specific betabeta-isoform. Here, we demonstrate a stimulatory role of thyroid hormones on these two enolase genes during rat development in hindlimb muscles and an inhibitory effect on the muscle-specific enolase gene in cardiac muscle. In hindlimb muscles the ubiquitous alpha-transcript level is diminished by hypothyroidism, starting at birth. On the contrary, the more abundant muscle-specific beta-transcript is insensitive to hypothyroidism before establishment of the functional diversification of fibers and is greatly decreased thereafter. Our data support the hypothesis of a role of thyroid hormones in coordinating the expressions of contractile proteins and metabolic enzymes during muscle development. The subcellular localization of isoenolases, established here, is not modified by hypothyroidism. Our results underline the specificity of action of thyroid hormones, which modulate differentially two isozymes in the same muscle and regulate, in opposite directions, the expression of the same gene in two different muscles.

Self-protection by cardiac myocytes against hypoxia and hyperoxia

Cardiac muscle must maintain a continuous balance between its energy supply and work performed. An important mechanism involved in achievement of this balance is cross talk via chemical signals between cardiac myocytes and the cardiac muscle vascular system. This has been demonstrated by incubating isolated cardiac myocytes in different concentrations of oxygen and then assaying the conditioned media for vasoactive substances on isolated aortic rings and small-resistance arteries. With increasing oxygen concentrations above 6%, cardiac myocytes produce increasing amounts of angiotensin I, which is converted to angiotensin II by the blood vessel. The angiotensin II stimulates vascular endothelial cells to secrete endothelin and increase vascular tone. Below 6% oxygen, cardiac myocytes secrete adenosine, which acts directly on vascular smooth muscle to block the effect of alpha-adrenergic agonists and reduce vascular tone. In an intact heart, the net effect of these 2 regulatory systems would be the maintenance of oxygen concentration within a narrow range at the cardiac myocytes. By acting as oxygen sensors, cardiac myocytes modulate vascular tone according to the needs of the myocytes and reduce potential problems of hypoxia and extensive formation of reactive oxygen species.

Endothelial dysfunction and collagen accumulation: two independent factors for restenosis and constrictive remodeling after experimental angioplasty

BACKGROUND

Constrictive remodeling plays a prominent role in restenosis after balloon angioplasty, but its regulation remains unclear. Because endothelial dysfunction and changes in extracellular matrix have been reported after angioplasty, this study was designed to simultaneously evaluate endothelial function and collagen and elastin changes after restenosis and arterial remodeling.

METHODS AND RESULTS

Atherosclerosis was induced in femoral arteries of 22 New Zealand White rabbits by air-desiccation and a high-cholesterol diet. One month later, angioplasty was performed. Histomorphometry and in vitro assessment of endothelial function were performed 4 weeks after angioplasty. Restenosis correlated with constrictive remodeling (r=0.60, P=0.01) but not with neointimal growth (r=-0.06, P=0.79). Restenosis correlated with an impaired relaxation to acetylcholine (ACh; r=0.61, P=0.02) but not with the response to the endothelium-independent vasodilator sodium nitroprusside (r=-0.25, P=0.40). Restenosis correlated positively with collagen accumulation (r=0.69, P=0.004) and inversely with elastin density (r=-0.48, P=0.05). Relaxations to ACh were significantly more decreased in arteries with constrictive remodeling than in those with enlargement remodeling (3.7+/-7.9% versus 35.5+/-15.0%, P=0.04). Neointimal collagen density was significantly higher in arteries with constrictive remodeling than in those with enlargement remodeling (34.5+/-4.5% versus 18.2+/-4.7%, P=0.03). Endothelial function and collagen and elastin density were independent predictors of restenosis in the study.

CONCLUSIONS

These results demonstrate that the severity of restenosis after angioplasty correlated with both defective endothelium-dependent relaxation and increased collagen density.

Localization and quantitation of cardiac annexins II, V, and VI in hypertensive guinea pigs

Annexins are characterized by Ca2+-dependent binding to phospholipids. Annexin II mainly participates in cell-cell adhesion and signal transduction, whereas annexins V and VI also seem to regulate intracellular calcium cycling. Their abundance and localization were determined in left ventricle (LV) and right ventricle (RV) from hypertensive guinea pigs, during the transition from compensatory hypertrophy to heart failure. Immunoblot analysis of annexins II, V, and VI revealed an increased accumulation (2.6-, 1.45-, and 2.3-fold, respectively) in LV from hypertensive guinea pigs and no modification in RV. Immunofluorescent labeling of annexins II, V, and VI; of Na+-K+-ATPase; and of sarcomeric alpha-actinin showed that in control LV and RV, 1) annexin II is present in nonmuscle cells; 2) annexins V and VI are mainly observed in the sarcolemma and intercalated disks of myocytes; 3) annexins II, V, and VI strongly label endothelial cells and adventitia of coronary arteries; and 4) annexin VI is present in the media. At the onset of heart failure, the most striking changes are the increased protein accumulation in LV and the very strong labeling of annexins II, V, and VI in interstitial tissue, suggesting a role in fibrosis development and cardiac remodeling.

Collagen I and III and mechanical properties of conduit arteries in rats with genetic hypertension

Conduit arteries of hypertensive rats are thicker and stiffer than those of normotensive controls. The possible role played by collagen type I and II subtypes in the mechanism of arterial stiffness remains unknown. The carotid and aortic arterial wall of rats of Japanese (Wistar-Kyoto and spontaneously hypertensive rats) and Lyon (normotensive and hypertensive rats) origin were studied. The stiffness of the carotid wall material (ultrasound), the histomorphometry of the aortic wall with the content in collagen I and III subtypes and their corresponding mRNA were analyzed. Independently of hypertension, the Japanese group differed from the Lyon group by a stiffer carotid wall material at any given value of wall stress; a lesser degree of aortic hypertrophy with a higher percentage of elastin, and a higher density of collagen III but not of collagen I. All other hemodynamic and histomorphometric parameters were affected by both the origin of the rats (Japanese vs. Lyon) and the presence of hypertension. Large artery stiffness in genetically hypertensive rats was not only influenced by hypertension itself, but also by differences in the contents of collagen subtypes which are also found in their corresponding normotensive controls.

Vascular endothelial cell-cardiac myocyte crosstalk in achieving a balance between energy supply and energy use

In isolated perfused hearts, endothelial cells in the coronary arterial vascular system release substances that can alter the contractility of the cardiac myocytes. There are at least two different substances, one that increases and another that decreases the contractility of cardiac myocytes. The rate of release of these endothelial-derived cardioactive substances depends on the oxygen tension in the immediate vicinity of the cardiac myocytes. As the local oxygen tension increases the contractility changes in the same direction. The oxygen sensor in this regulatory system is the cardiac myocyte, which then releases substances that regulate the secretion of endothelin and a relaxant by endothelial cells. The result is a loop involving cross talk between coronary endothelial cells and cardiac myocytes to modulate cardiac contractility in accordance with the oxygen supply to the cardiac myocytes. Preliminary data suggest that the change in contractility is related to a change in structure and position of the cross bridge due to phosphorylation of a protein in the thick filament.

Cellular distribution of Ca2+ pumps and Ca2+ release channels in rat cardiac hypertrophy induced by aortic stenosis

BACKGROUND

The response of ventricular myocytes to pressure overload is heterogeneous and not spatially coordinated. We investigated whether or not the alterations in SERCA and RyR gene expression are homogeneous within the myocardium.

METHODS AND RESULTS

The cellular distribution of mRNAs and proteins encoding the 2 sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) isoforms (SERCA 2a and 2b) and 2 Ca2+ release channels (the ryanodine receptor, RyR, and the IP3 receptor, IP3R) were analyzed by in situ hybridization and immunofluorescence, respectively. Analyses were performed during early (1 and 5 days) and late (1 month) stages of cardiac hypertrophy induced in rat by thoracic aortic stenosis (AS). The results indicated that 1 and 5 days after AS, the cellular distribution of SERCA 2a and RyR2 mRNAs in right ventricle and atrium was similar to controls but the mRNA levels appeared to decrease in some areas of the left ventricle (LV). One month after AS, the distribution of SERCA 2a mRNA and protein became heterogeneous throughout the LV, whereas RyR2 mRNA and protein levels were decreased in a homogeneous manner. SERCA 2b, poorly expressed in both cardiomyocytes and vessels of controls, was increased 4-fold 1 month after AS in coronary arteries only. In both sham (Sh) and AS, SERCA 3 and IP3R mRNAs were mainly found in the vessels.

CONCLUSIONS

In severe hypertrophy, decreased accumulation of SERCA 2a was heterogeneous and not compensated by an induction of SERCA 2b in the cardiomyocytes. Decrease in RyR2 expression was more homogeneous and not compensated by an increased IP3R expression.

Can cellular transplantation improve function in doxorubicin-induced heart failure?

BACKGROUND

Transplantation of fetal cardiomyocytes has been shown to improve function of regionally infarcted myocardium, but its effects on global heart failure are still unknown.

METHODS AND RESULTS

Heart failure was induced in female mice by intraperitoneal injection of doxorubicin (2 mg/kg twice per week over 2 cycles of 2 weeks separated by a 2-week drug-free period). One week after the end of treatment, left ventricular function was assessed by transthoracic echocardiography (baseline). Animals were then randomized into 3 groups: The treated group (n = 12) received an intramyocardial injection of fetal cardiomyocytes (1 x 10(6) in 10 microL) harvested from transgenic mice expressing the gene of beta-galactosidase, the control group (n = 15) received an equivalent volume of culture medium alone, and 10 sham mice had no surgery. Two weeks and 1 month after transplantation, function was again assessed echocardiographically. At baseline, fractional shortening was not significantly different between the 3 groups. It then significantly increased in cell-treated mice at 2 weeks and 1 month after transplantation (P < 0.002 and P < 0.03 versus baseline, respectively), whereas it did not change in untreated animals. Transplanted cells could not be identified by beta-galactosidase activity or presence of Y chromosome (with 1 exception).

CONCLUSIONS

Cellular transplantation can improve function of globally failing hearts by a mechanism that might not necessarily involve the sustained presence of transplanted cells but rather the effects of cardioprotective factors released by them.

[Cellular cardiomyoplasty: state of the art, evaluation, and future possibilities]

Cellular cardiomyoplasty, or the transplantation of myogenic cells into the myocardial tissues, could emerge as a therapeutic alternative in patients with cardiac failure. It depends on several procedures: implantation of cell types, syngenic embryonic cardiomycocytes, allogenic and autogenic cardiac muscle cells. These cells carne into contact with host cardiomyocytes and could contract in a synchronous fashion. Experimental data suggests that this technique could improve global left ventricular function in the post-infarction period or in dilated cardiomyopathy even though the precise mechanism of this improvement is not fully understood. Many difficulties remain, the cell types have an oncogenic potential; syngenic foetal cells are weakly immunogenic but their use is limited by ethical and problems of supply. Therefore, auto-transplantation either of cardiomycocytes obtained by endomyocardial biopsy or of adult skeletal muscle, could be a potential clinical option.

Increased compliance in diaphragm muscle of the cardiomyopathic Syrian hamster

We investigated the hypothesis that diaphragm compliance was abnormal in cardiomyopathic Syrian hamsters (CSH), an experimental model of myopathy. The passive elastic properties of isolated diaphragm muscles were analyzed at both the muscle and sarcomere levels. We used the following passive exponential relationship between stress (sigma) and strain (epsilon): sigma = (Eo/beta) (ebetaepsilon - 1), where Eo is the initial elastic modulus and beta is the stiffness constant. Immunocytochemistry procedures were used to analyze the distribution of two key elastic components of muscle, extracellular collagen and intracellular titin elastic components, as well as the extracellular matrix glycoprotein laminin. Muscle and sarcomere values of beta were nearly twofold lower in CSH (8.7 +/- 1.9 and 8.3 +/- 1.4, respectively) than in control animals (19.7 +/- 1.7 and 16.8 +/- 2.1, respectively) (P < 0.01 for each). Compared with controls, Eo was higher in CSH. Sarcomere slack length was significantly longer in CSH than in control animals (2.1 +/- 0.1 vs. 1.9 +/- 0.1 micrometer, P < 0.05). The surface area of collagen I was significantly larger in CSH (17.4 +/- 1.8%) than in control animals (12.4 +/- 0.7%, P < 0.05). There was no change in the distribution of titin or laminin labelings between the groups. These results demonstrate increased diaphragm compliance in cardiomyopathic hamsters. The increase in CSH diaphragm compliance was observed despite an increase in the surface area of collagen and was not associated with an abnormal distribution of titin or laminin.

Microvasculature in angiotensin II-dependent cardiac hypertrophy in the rat

The long-lasting effect of angiotensin II (Ang II) on the microvasculature in the rat left ventricle was studied. Immunolabeling of ventricular cryosections combined with morphometric analysis allowed us to (1) distinguish between capillaries and arterioles and (2) precisely evaluate their respective densities in the endomyocardium. Ang II-induced hypertensive cardiac hypertrophy was associated with an 18% decrease in capillary density (P<0.05) and an increase in arteriole density (+54%, P<0.001). Treatments with losartan or PD123319, the respective antagonists of the angiotensin subtype 1 and subtype 2 receptors, prevented the increase in arteriolar density, whereas only losartan, which restored normal arterial pressure, prevented changes in capillary density. Taken together, these results indicate that Ang II-induced cardiac hypertrophy was associated with capillary rarefaction and arteriolar growth, the 2 processes being independently regulated.

Cytoskeleton and mitochondrial morphology and function

It has been well established that the cytoskeleton is an essential modulator of cell morphology and motility, intracytoplasmic transport and mitosis, however cytoskeletal linkage to the organelles has not been unequivocally demonstrated. Indeed, cytoskeleton appears to be essential in determining and modulating gene phenotype as a function of cellular environment. According to recent studies, the organization of the cytoskeleton network together with associated protein(s) could be essential in regulating mitochondrial function and particularly the permeability of the mitochondrial outer membrane to ADP. The aim of this chapter is to summarize the main properties of the cytoskeletal environment of mitochondria and the possible role(s) of this network in mitochondrial function in myocytes.

Cardiac senescence is associated with enhanced expression of angiotensin II receptor subtypes

Recent studies have pointed out the differential role of angiotensin II (Ang II) receptor subtypes, AT1 and AT2, in cardiac hypertrophy and fibrosis during pathological cardiac growth. Because senescence is characterized by an important cardiovascular remodeling, we examined the age-related expression of cardiac Ang II receptors in rats. AT1 and AT2 receptor subtype messenger RNA (mRNA) levels were quantitated by RT-PCR. In parallel, specific Ang II densities were determined in competition binding experiments using specific antagonists. AT1a and AT1b mRNA levels were markedly up-regulated (5.6-fold) in the left ventricle of 24-month-old rats compared with 3-month-old rats, but not in the right ventricle. In contrast, AT2 gene expression was increased in both ventricles of senescent rats (4.2- and 2.8-fold in the left and right ventricles, respectively). Similarly, AT1 and AT2 gene expression was increased 2.3- and 2-fold, respectively, in freshly isolated cardiomyocytes from aged rats. Furthermore, AT1 and AT2 specific binding was increased in the aged left ventricular myocardium. Even though the mechanistic pathway of this up-regulation of Ang II receptor subtype gene expression might be intrinsic to developmental gene reprogramming, the up-regulation of AT1 mRNA accumulation in the left ventricle during aging could also be secondary to age-related hemodynamic changes, whereas increased AT2 gene expression in both ventricles may depend upon hormonal and humoral factors.

Study of regulation of mitochondrial respiration in vivo. An analysis of influence of ADP diffusion and possible role of cytoskeleton

The purpose of this work was to investigate the mechanism of regulation of mitochondrial respiration in vivo in different muscles of normal rat and mice, and in transgenic mice deficient in desmin. Skinned fiber technique was used to study the mitochondrial respiration in the cells in vivo in the heart, soleus and white gastrocnemius skeletal muscles of these animals. Also, cardiomyocytes were isolated from the normal rat heart, permeabilized by saponin and the "ghost" (phantom) cardiomyocytes were produced by extraction of myosin with 800 mM KCl. Use of confocal immunofluorescent microscopy and anti-desmin antibodies showed good preservation of mitochondria and cytoskeletal system in these phantom cells. Kinetics of respiration regulation by ADP was also studied in these cells in detail before and after binding of anti-desmine antibodies with intermediate filaments. In skinned cardiac or soleus skeletal muscle fibers but not in fibers from fast twitch skeletal muscle the kinetics of mitochondrial respiration regulation by ADP was characterized by very high apparent Km (low affinity) equal to 300-400 microM, exceeding that for isolated mitochondria by factor of 25. In skinned fibers from m. soleus, partial inhibition of respiration by NaN3 did not decrease the apparent Km for ADP significantly, this excluding the possible explanation of low apparent affinity of mitochondria to ADP in these cells by its rapid consumption due to high oxidative activity and by intracellular diffusion problems. However, short treatment of fibers with trypsin decreased this constant value to 40-70 microM, confirming the earlier proposition that mitochondrial sensitivity to ADP in vivo is controlled by some cytoplasmic protein. Phantom cardiomyocytes which contain mostly mitochondria and cytoskeleton and retain the normal shape, showed also high apparent Km values for ADP. Therefore, they are probably the most suitable system for studies of cellular factors which control mitochondrial function in the cells in vivo. In these phantom cells anti-desmin antibodies did not change the kinetics of respiration regulation by ADP. However, in skinned fibers from the heart and m. soleus of transgenic desmin-deficient mice some changes in kinetics of respiration regulation by ADP were observed: in these fibers two populations of mitochondria were observed, one with usually high apparent Km for ADP and the second one with very low apparent Km for ADP. Morphological observations by electron microscopy confirmed the existence of two distinct cellular populations in the muscle cells of desmin-deficient mice. The results conform to the conclusion that the reason for observed high apparent Km for ADP in regulation of oxidative phosphorylation in heart and slow twitch skeletal muscle cells in vivo is low permeability of mitochondrial outer membrane porins but not diffusion problems of ADP into and inside the cells. Most probably, in these cells there is a protein associated with cytoskeleton, which controls the permeability of the outer mitochondrial porin pores (VDAC) for ADP. Desmin itself does not display this type of control of mitochondrial porin pores, but its absence results in appearance of cells with disorganised structure and of altered mitochondrial population probably lacking this unknown VDAC controlling protein. Thus, there may be functional connection between mitochondria, cellular structural organisation and cytoskeleton in the cells in vivo due to the existence of still unidentified protein factor(s).

Does transplantation of cardiomyocytes improve function of infarcted myocardium?

BACKGROUND

The feasibility of successfully grafting fetal cardiomyocytes into infarcted myocardium is now established, but the functional effects of such a procedure still remain elusive.

METHODS AND RESULTS

Twenty-three female rats underwent 45 minutes of coronary artery occlusion followed by 30 minutes of reperfusion. At this time point, 13 animals received intramyocardial injections of fetal cardiomyocytes (6 x 10(6) cells in 60 microL of culture medium) in the once ischemic area, whereas the 10 control rats were injected with an equivalent volume of culture medium alone. One month after transplantation, left ventricular function was assessed by two-dimensional (2D) and Doppler echocardiography using a short focus 10- to 13-MHz transducer, and a numeric acquisition of 2D images up to 65.5 frames/second. Explanted hearts were then processed for histological assessment of infarct size. The presence of male donor cells into female recipient myocardium was detected by fluorescent in situ hybridization using a deoxyribonucleic acid probe specific for Y chromosome. Cellular transplantation resulted in an improved left ventricular function, as demonstrated by significantly higher 2D ejection fraction and cardiac output (P<.02 and P<.02 versus control hearts, respectively). The histological sections of female recipient myocardium were Y-positive in all but one heart, thereby suggesting that this improvement of function was causally related to the presence of transplanted cells.

CONCLUSIONS

These data suggest that transplantation of cardiomyocytes might be an effective means of improving function of infarcted myocardium.

Trophic effect of human pericardial fluid on adult cardiac myocytes. Differential role of fibroblast growth factor-2 and factors related to ventricular hypertrophy

Pericardial fluid (PF) may contain myocardial growth factors that exert paracrine actions on cardiac myocytes. The aims of this study were (1) to investigate the effects of human PF and serum, collected from patients undergoing cardiac surgery, on the growth of cultured adult rat cardiac myocytes and (2) to relate the growth activity of both fluids to the adaptive changes in overloaded human hearts. Both PF and serum increased the rate of protein synthesis, measured by [14C]phenylalanine incorporation in adult rat cardiomyocytes (PF, +71.9 +/- 8.2% [n = 17]; serum, +14.9 +/- 6.5% [n = 13]; both P < .01 versus control medium). The effects of both PF and serum on cardiomyocyte growth correlated positively with the respective left ventricular (LV) mass. However, the magnitude of change with PF was 3-fold greater than with serum (P < .01). These trophic effects of PF were mimicked by exogenous basic fibroblast growth factor (FGF2) and inhibited by anti-FGF2 antibodies and transforming growth factor-beta (TGF-beta), suggesting a relationship to FGF2. In addition, FGF2 concentration in PF was 20 times greater than in serum. On the other hand, the LV mass-dependent trophic effect, present in both fluids, was independent of FGF2 concentration or other factors, such as angiotensin II, atrial natriuretic factor, and TGF-beta. These data suggest that FGF2 in human PF is a major determining factor in normal myocyte growth, whereas unidentified LV mass-dependent factor(s), present in both PF and serum, participates in the development of ventricular hypertrophy.

Increased expression of fibronectin isoforms after myocardial infarction in rats

Fibronectin is a known chemoattractant for several cell types which play a role in the wound healing process, like fibroblasts, endothelial cells and macrophages. In addition, fibronectin generates a scaffold to which other extracellular matrix components can attach. The possible involvement of fibronectin in the wound healing process after myocardial infarction (MI) was investigated by studying the expression of fibronectin isoforms after induction of a MI in the rat. Deposition of plasma (pFN) and cellular fibronectin (cFN) protein was determined immunohistochemically, using monoclonal antibodies specific for cFN and polyclonal anti-human total FN (tFN antibodies). Expression of the mRNAs of total cFN and the embryonic isoforms EIIIA and EIIIB was investigated, using in situ hybridization (ISH). The ratio between EIIIA containing fibronectin (EIIIA+-FN) mRNA and total cFN mRNA was determined using a semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). cFN protein was present from day 4 until day 35 after infarction and was located around the area of infarction, in the epi- and endomyocardium and in the wall of larger vessels. pFN was found in the infarcted cardiomyocytes 1 day after the induction of the MI. From day 4 on pFN protein deposition was found in the border zone of the infarction and in the wall of larger vessels. pFN immunoreactivity remained present at high levels around the area of infarction and in the vessel wall throughout the entire period of investigation (90 days). From day 35 after the infarction pFN protein was detected in cardiomyocytes of the right ventricle and septum. cFN mRNA, determined by in situ hybridization, was present in the border zone of the infarcted area as early as 1 day after MI, and its expression peaked at 4 days after MI. Four days after MI the mRNA's coding for both the embryonic isoforms EIIIA and EIIIB could also be detected in the same area. Because expression of the EIIIA isoform was more abundant than the EIIIB isoform we only determined the percentage of the EIIIIA containing isoform from total FN. EIIIA+ mRNA was elevated 1 day after MI. We conclude that various fibronectin isoforms including the embryonic isoforms accumulate in the heart after MI. This suggests that these isoforms may play a role in the wound healing process in the left ventricle of the infarcted heart.

Primary culture of human atrial myocytes is associated with the appearance of structural and functional characteristics of immature myocardium

We examined changes in the structural and physiological characteristics of human atrial myocytes during primary culture in the presence of serum. Action potentials and ionic currents were recorded in freshly dissociated (FM) and cultured (CM) whole-cell patch-clamped myocytes, alpha-smooth muscle actin, sarcomeric alpha-actinin and beta-myosin heavy chains (beta-MHC) were stained with monoclonal antibodies. From day 5 to day 21, myocytes lost their rod shape, spread and exhibited reorganized sarcomeres. These morphological changes were associated with a marked increase in membrane capacitance (+266%). Both beta-MHC and alpha-smooth muscle actin were expressed in CM but not in FM, indicating a dedifferentiation process. CM were characterized by a lower resting potential (-30 +/- 2 v -60 +/- 4 mV, P < 0.05) and, when repolarized, by a shorter action potential duration (APD) than FM (APD-60: 126.9 v 159.6 ms, P < 0.05). The inward rectifier K+ current was absent in CM, thus explaining the low resting potential. The density of the transient component of the voltage-activated K+ current Ito1 was not modified during culture, while that of the sustained component Isus was increased fourfold. The amplitude of ICa was increased, but its density was unchanged, indicating that CM maintained a normal density of functional calcium channels. Neither the voltage dependence nor the inactivation of ICa was modified in CM. The time constants of inactivation of ICa were unchanged, although the amplitude of the rapidly inactivating component of ICa was increased in CM compared to FM. Moreover, ICa was increased by the beta-adrenergic agonist isoproterenol (1 microM) throughout the culture period. Our results demonstrate that in long-term serum-supplemented culture, adaptation of human atrial myocytes to their new environment is associated with differential alterations of the main ionic currents and phenotypic changes characteristic of immature myocardium.

Alteration of flow-induced dilatation in mesenteric resistance arteries of L-NAME treated rats and its partial association with induction of cyclo-oxygenase-2

1. We investigated the response to pressure (myogenic tone) and flow of rat mesenteric resistance arteries cannulated in an arteriograph which allowed the measurement of intraluminal diameter for controlled pressures and flows. Rats were treated for 3 weeks with NG-nitro-L-arginine methyl ester (L-NAME, 50 mg kg-1 day-1) or L-NAME plus the angiotensin I converting enzyme inhibitor (ACEI) quinapril (10 mg kg-1 day-1). 2. Mean blood pressure increased significantly in chronic L-NAME-treated rats (155 +/- 4 mmHg, n = 8, vs control 121 +/- 6 mmHg, n = 10; P < 0.05). L-NAME-treated rats excreted significantly more dinor-6-keto prostaglandin F1 alpha (dinor-6-keto PGF1 alpha), the stable urinary metabolite of prostacyclin, than control rats. The ACEI prevented the rise in blood pressure and the rise in urinary dinor-6-keto PGF1 alpha due to L-NAME. 3. Isolated mesenteric resistance arteries, developed myogenic tone in response to stepwise increases in pressure (42 +/- 6 to 847 +/- 10 mN mm-1, from 25 to 150 mmHg, n = 9). Myogenic tone was not significantly affected by the chronic treatment with L-NAME or L-NAME + ACEI. 4. Flow (100 microliters min-1) significantly attenuated myogenic tone by 50 +/- 6% at 150 mmHg (n = 10). Flow-induced dilatation was significantly attenuated by chronic L-NAME to 22 +/- 6% at 150 mmHg (n = 10, p = 0.0001) and was not affected in the L-NAME + ACEI group. 5. Acute in vitro NG-nitro-L-arginine (L-NOARG, 10 microM) significantly decreased flow-induced dilation in control but not in L-NAME or L-NAME + ACEI rats. Both acute indomethacin (10 microM) and acute NS 398 (cyclo-oxygenase-2 (COX-2) inhibitor, 1 microM) did not change significantly flow-induced dilatation in controls but they both decreased flow-induced dilatation in the L-NAME and L-NAME + ACEI groups. Acute Hoe 140 (bradykinin receptor inhibitor, 1 microM) induced a significant contraction of the isolated mesenteric arteries which was the same in the 3 groups. 6. Immunofluorescence analysis of COX-2 showed that the enzyme was expressed in resistance mesenteric arteries in L-NAME and L-NAME + ACEI groups but not in control. COX-1 expression was identical in all 3 groups. 7. We conclude that chronic inhibition of nitric oxide synthesis is associated with a decreased flow-induced dilatation in resistance mesenteric arteries which was compensated by an overproduction of vasodilator prostaglandins resulting in part from COX-2 expression. The decrease in flow-induced dilatation was prevented by the ACEI, quinapril.

Differential roles of AT1 and AT2 receptor subtypes in vascular trophic and phenotypic changes in response to stimulation with angiotensin II

The aim of this study was to investigate the roles of angiotensin II (Ang II) receptor subtypes 1 (AT1) and 2 (AT2) in producing vascular wall hypertrophy and qualitative changes in smooth muscle cell gene expression. Wistar rats were treated for 23 days with osmotic minipumps containing solvent and either Ang II (120 ng.kg-1.min-1) or PD123319 (30 mg.kg-1.d-1), an AT2 receptor antagonist. In addition, rats receiving solvent and either Ang II or PD123319 were given losartan, an AT1 receptor antagonist, in the drinking water (10 mg.kg-1.d-1). Vascular wall hypertrophy and smooth muscle phenotype were characterized by morphometric analysis combined with immunohistochemistry. Ang II-induced hypertension was associated with the development of medial hypertrophy of the aorta and coronary arteries accompanied by reversion of vascular smooth muscle cells (VSMCs) toward an immature phenotype, as shown by the expression of cellular fibronectin and nonmuscle myosin. Losartan treatment, which restored normal arterial pressure, prevented all these changes. PD123319 treatment, which had no effect on blood pressure, prevented only vascular hypertrophy, with no effect on VSMC phenotype. Administration of only losartan to normal rats reproduced the Ang II-induced vascular hypertrophy, with no effect on VSMC phenotype. Taken together, these results suggest that (1) the trophic effect of Ang II on VSMCs is mediated via AT2 receptor subtypes and (2) changes in VSMC phenotypes are triggered mainly through AT1 receptor subtypes.

HR 720, a novel angiotensin receptor antagonist inhibits the angiotensin II-induced trophic effects, fibronectin release and fibronectin-EIIIA+ expression in rat aortic vascular smooth muscle cells in vitro

The aim of this study was to evaluate the direct trophic effects of angiotensin II (AII) on rat vascular smooth muscle cells obtained from a single cellular isolate. Cell volume, protein synthesis, fibronectin (FN) release and FN-EIIIA+ mRNA isoform expression were analyzed in parallel. The effects of HR 720, a novel AT1 angiotensin receptor antagonist with some AT2 receptor affinity, were compared with those of selective AT1 antagonist EXP 3174. Both HR 720 and EXP 3174 inhibited in a concentration-dependent manner the maximum increase in cell volume induced by 10(-9) M Sar1-All (IC50 = 0.49 x 10(-9) M and 0.79 x 10(-9) M, respectively). Maximum [3H]leucine incorporation was also achieved at 10(-9) M All. HR 720 blocked the increase in protein synthesis with potency similar to EXP 3174; the respective IC50 values were 1.04 x 10(-9) M and 1.36 x 10(-9) M. All dose-dependently increased FN release, which was also equally inhibited by about 50% with both compounds at 10(-6) M. Furthermore, All enhanced FN-EIIIA+ mRNA in rat vascular smooth muscle cells (VSMC), which indicated a modulation of FN isoform expression which was inhibited by angiotensin II antagonists. In conclusion, All induced parallel and concentration-dependent increases in cell volume, protein synthesis, FN release and FN-EIIIA+ mRNA expression in vascular smooth muscle cells. These effects appeared to be essentially mediated by AT1 receptor stimulation as indicated by the equal inhibitory effects of HR 720 and EXP 3174.

Can grafted cardiomyocytes colonize peri-infarct myocardial areas?

BACKGROUND

Cell transplantation is emerging as a potential means of improving repair of damaged organs. This preliminary study tests the feasibility of grafting allogenic cells into the border zone of a myocardial infarct (MI).

METHODS AND RESULTS

Neonatal cardiomyocytes were obtained from fetuses of female rats 20 days pregnant. They were then injected at three different sites (2 x 10(6) cells per site) into the left ventricular (LV) myocardium of control rats (n = 10) or of rats in which MI had been created by proximal occlusion of the left coronary artery (n = 10). In the latter case, injections were placed along the peri-infarct border zone. Half of each batch of cells was grown in culture to provide a control for cell morphology and viability. Six additional rats were injected with the culture medium alone. Forty-eight hours after injection, LV slices were processed for histological (hematoxylin-eosin) and immunohistological (sarcomeric alpha-actinin transplantation and laminin staining) techniques. Examination of serial sections from injected regions showed that grafted myocytes were harbored into the host LV myocardium in all control animals and at the border zone in 50% of the infarcted rats. Grafted cells were identified by their morphological characteristics and an immunohistological pattern of loose myofibrillar organization similar to that seen in cells concomitantly grown in culture. Injection of the culture medium alone had no effect but allowed us to rule out needle-related injury.

CONCLUSIONS

These initial results suggest the feasibility of transplanting allogeneic cardiomyocytes into the border zone of MI areas, a prerequisite for this approach to successfully improve the function of ischemically damaged hearts.

Differential regulation of voltage-activated potassium currents in cultured human atrial myocytes

To examine whether the two components of the voltage-activated outward K+ current, an initially rapidly inactivating component (Ito,1) and a slowly inactivating sustained component (Isus), in human atrial myocytes are distinct currents differentially regulated, we studied their behavior during serum-induced growth of cultured myocytes. Currents were recorded in whole cell patch clamped myocytes. After 1 wk of culture (day 8), membrane capacitance was twice the value in freshly dissociated myocytes (178.7 +/- 23 vs. 83.1 +/- 5.5 pF; P < 0.001). Ito,1 density did not differ from that in freshly dissociated myocytes (at +40 mV: 4.38 +/- 0.8 vs. 3.71 +/- 0.6 pA/pF), whereas that of Isus was markedly increased (at +40 mV: 9.76 +/- 2 vs. 2.21 +/- 0.29 pA/pF; P < 0.001). After inactivation of Ito,1 by a prepulse, sustained depolarization elicited in cultured myocytes an Isus with a density of 10.22 +/- 1.18 pA/pF and an apparent tail current reversal potential of -73.5 +/- 3.2 mV, indicating high K+ selectivity. Isus was highly sensitive to 4-aminopyridine (55.4 +/- 4.4% inhibition in 50 microM) and to D-600 (with a concentration inhibiting 50% of maximal response of 34.2 x 10(-6) M). Addition of 5-10 nM staurosporine at day 3 prevented cell growth and reduced Ito,1 density but not the increase in Isus density, which was inhibited by 10 microM staurosporine. Our results indicate that Ito,1 and Isus are regulated independently during in vitro myocyte growth in human atrial myocytes and that the increase in Isus density is not mediated by a protein kinase C-dependent pathway.

Atrial natriuretic factor (ANF) and ANF receptor C gene expression and localization in the respiratory system: effects induced by hypoxia and hemodynamic overload

Atrial natriuretic factor (ANF) and ANF receptor C (ANF.RC) expression have been investigated in healthy and cardiomyopathic hamsters (CMPH) with widespread necrosis of the diaphragm and myocardium leading to respiratory and heart failure. ANF- and ANF.RC-producing cells were localized in different structures of the respiratory system, and the regulation of their expression by the individual and/or combined action of hypoxia and hemodynamic overload was analyzed. The study was performed in 20-, 90-, and 150-day-old animals using immunohistochemistry, in situ hybridization, Northern blot, and RIA analyses. ANF was shown to be expressed in the tracheo-bronchial epithelium and muscle and, to a lesser extent, in the alveolar wall and muscular media of the pulmonary arteries and extraparenchymal pulmonary veins in both healthy hamsters and CMPH. In 150-day-old CMPH, hypoxia (PaO2 < 50 mm Hg) induced a 10-fold increase in ANF messenger RNA accumulation and a 6-fold increase in the immunoreactive ANF (IR-ANF) concentration in lungs, as quantitated by RIA. As plasma IR-ANF concentrations were elevated in all CMPH age groups, it was most likely produced by the myocardium. ANF.RC messenger RNA was homogeneously distributed throughout the entire respiratory system and was increased 2-fold in hypoxic 150-day-old CMPH only. These results suggest that ANF originating in the respiratory system exerts only paracrine effects on different structures of the respiratory system in addition to the action of circulating ANF. Hemodynamic overload (left ventricular end-diastolic pressure, 17.20 +/- 3.80 mm Hg) might contribute to enhanced ANF gene expression only in extraparenchymal pulmonary vein walls of 150-day-old CMPH. We also propose that ANF.RC overexpression might be a protective mechanism operated via either ANF clearance or inhibition of adenylate cyclase activity to counteract exaggerated smooth muscle relaxation.

Chronic blockade of AT2-subtype receptors prevents the effect of angiotensin II on the rat vascular structure

Angiotensin II (Ang II) is both a vasoactive and a potent growth-promoting factor for vascular smooth muscle cells. Little is known about the in vivo contribution of AT1 and AT2 receptor activation to the biological action of Ang II. Therefore, we investigated the effect of AT1 or AT2 subtype receptor chronic blockade by losartan or PD123319 on the vascular hypertrophy in rats with Ang II-induced hypertension. Normotensive rats received for 3 wk subcutaneous infusions of Ang II (120 ng/kg per min), or Ang II + PD 123319 (30 mg/kg per d), or Ang II + losartan (10 mg/kg per d) or PD 123319 alone, and were compared with control animals. In normotensive animals, chronic blockade of AT2 receptors did not affect the plasma level of angiotensin II and the vascular reactivity to angiotensin II mediated by the AT1 receptor. Chronic blockade of AT1I in rats receiving Ang II resulted in normal arterial pressure, but it induced significant aortic hypertrophy and fibrosis. Chronic blockade of AT2 receptors in Ang II-induced hypertensive rats had no effect on arterial pressure, but antagonized the effect of Ang II on arterial hypertrophy and fibrosis, suggesting that in vivo vasotrophic effects of Ang II are at least partially mediated via AT2 subtype receptors.

On the regulation of cellular energetics in health and disease

Very recent experimental data, obtained by using the permeabilized cell technique or tissue homogenates for investigation of the mechanisms of regulation of respiration in the cells in vivo, are shortly summarized. In these studies, surprisingly high values of apparent Km for ADP, exceeding that for isolated mitochondria in vitro by more than order of magnitude, were recorded for heart, slow twitch skeletal muscle, hepatocytes, brain tissue homogenates but not for fast twitch skeletal muscle. Mitochondrial swelling in the hypo-osmotic medium resulted in the sharp decrease of the value of Km for ADP in correlation with the degree of rupture of mitochondrial outer membrane, as determined by the cytochrome c test. Very similar effect was observed when trypsin was used for treatment of skinned fibers, permeabilized cells or homogenates. It is concluded that, in many but not all types of cells, the permeability of the mitochondria outer membrane for ADP is controlled by some cytoplasmic protein factor(s). Since colchicine and taxol were not found to change high values of the apparent Km for ADP, the participation of microtubular system seems to be excluded in this kind of control or respiration but studies of the roles of other cytoskeletal structures seem to be of high interest. In acute ischemia we observed rapid increase of the permeability of the mitochondrial outer membrane for ADP due to mitochondrial swelling and concomitant loss of creatine control of respiration as a result of dissociation of creatine kinase from the inner mitochondrial membrane. The extent of these damages was decreased by use of proper procedures of myocardial protection showing that outer mitochondrial membrane permeability and creatine control of respiration are valuable indices of myocardial preservation. In contrast to acute ischemia, chronic hypoxia seems to improve the cardiac cell energetics as seen from better postischemic recovery of phosphocreatine, and phosphocreatine overshoot after inotropic stimulation. In general, adaptational possibilities and pathophysiological changes in the mitochondrial outer membrane system point to the central role such a system may play in regulation of cellular energetics in vivo.

Pressure and angiotensin II synergistically induce aortic fibronectin expression in organ culture model of rabbit aorta. Evidence for a pressure-induced tissue renin-angiotensin system

Aortic fibronectin (FN) expression is augmented in hypertension. Increasing evidence suggests that both angiotensin II (Ang II) and mechanical factors may induce vascular remodeling in response to hypertension. We have previously shown that, in vitro, increased transmural pressure enhances FN expression in rabbit aortic media. To investigate the existence of a link between the effects of pressure and Ang II and to explore the mechanisms underlying such a relationship, we quantified the effect of Ang II and Ang II inhibitors on the pressure-dependent FN expression in a 3-day organ culture model of rabbit aorta using immunolabeling analysis and detected FN mRNAs by in situ hybridization. A dose-dependent effect of Ang II on FN expression was observed at both 80 and 150 mm Hg but not at 0 mm Hg (relaxed vessels). One mumol/L Ang II increased the media cross-sectional surface, showing FN expression from 7.9 +/- 0.7% (n = 9) to 18.9 +/- 1.1% (n = 4) at 80 mm Hg (P < .01) and from 17.4 +/- 1.8% (n = 9) to 56.6% +/- 3.6 (n = 4) at 150 mm Hg (P < .001). In situ hybridization revealed that Ang II and pressure upregulated FN mRNA expression. Losartan, an AT1 antagonist, not only blocked the Ang II effect but also inhibited the transmural pressure effect. Angiotensin-converting enzyme inhibition abolished the pressure-dependent FN expression and significantly diminished the effect of pressure in the presence of Ang II. The effect of renin-angiotensin system inhibitors was specific for FN, since neither bFGF nor laminin expression was affected by these agents. Taken together, the results demonstrate that (1) the effect of transmural pressure is mediated by the stimulation of a local renin-angiotensin system, resulting in a net Ang II production in the culture medium, (2) transmural pressure and Ang II act synergistically to enhance vascular FN expression, (3) AT1 receptors mediate both the effects of pressure and of exogenous Ang II, and (4) the effect of Ang II on FN expression is regulated at a pretranslational level.

Expression of fibronectin ED-A+ and ED-B+ isoforms by human and experimental colorectal cancer. Contribution of cancer cells and tumor-associated myofibroblasts

Alternative splicing of primary fibronectin (FN) mRNA results in the synthesis of different isoforms. ED-A+ and ED-B+ FN isoforms are absent from plasma FN and are representative of cellular FN. Their expression was studied in human and rat normal colon, in human colorectal carcinomas, and in transplanted tumors derived from a chemically-induced rat colon cancer. In normal colon, only the ED-A+ FN isoform was expressed as a thin deposit between crypt colonocytes and pericryptal myofibroblasts. Conversely, heavy ED-A+ FN deposits and lighter ED-B+ FN expression were found in the stroma of colorectal tumors in association with myofibroblasts surrounding tumor glands. Some colonic cancer cells also contained intracellular FN isoform granules and expressed FN mRNA. Tumor-associated myofibroblasts and some cancer cell lines were able to synthesize and deposit extracellular ED-A+ and ED-B+ FN in vitro. FN isoform deposition by tumor-associated myofibroblasts was not modulated by colon cancer cell-conditioned medium, but was strongly enhanced when myofibroblasts were cultured on colon cancer cell extracellular matrix or on laminin. These results show that the ED-A+ and ED-B+ FN isoforms were overexpressed in colorectal cancer. Cancer cells can deposit these FN isoforms directly and also stimulate their deposition by tumor-associated myofibroblasts.

Differential expression of alpha- and beta-enolase genes during rat heart development and hypertrophy

We have analyzed the transition between isoforms of the glycolytic enzyme enolase (2-phospho-D-glycerate hydrolyase; EC 4.2.1.11) in rat heart during normal and pathological growth. A striking fall in embryonic alpha-enolase gene expression occurs during cardiac development, mostly controlled at pretranslational steps. In fetal and neonatal hearts, muscle-specific beta-enolase gene expression is a minor contributor to total enolase. Control mechanisms of beta-enolase gene expression must include posttranscriptional steps. Aortic stenosis induces a rapid and drastic decrease in beta-enolase transcript level in cardiomyocytes, followed by the fall in beta-subunit level. In contrast, alpha-enolase transcript level is not significantly altered, although the corresponding subunit level increases in nonmuscle cells. We conclude that, like fetal heart, hypertrophic heart is characterized by a high ratio of alpha- to beta-enolase subunit concentrations. This study indicates that the decrease in beta-enolase gene expression may be linked to beneficial energetic changes in contractile properties occurring during cardiac hypertrophy.