Nitric oxide system in needle-induced transmyocardial revascularization

Recent advances in the understanding of the role of nitric oxide in cardiovascular homeostasis

Nitric oxide synthases (NOS) are the enzymes responsible for nitric oxide (NO) generation. To date, 3 distinct NOS isoforms have been identified: neuronal NOS (NOS1), inducible NOS (NOS2), and endothelial NOS (NOS3). Biochemically, NOS consists of a flavin-containing reductase domain, a heme-containing oxygenase domain, and regulatory sites. NOS catalyse an overall 5-electron oxidation of one Nomega-atom of the guanidino group of L-arginine to form NO and L-citrulline. NO exerts a plethora of biological effects in the cardiovascular system. The basal formation of NO in mitochondria by a mitochondrial NOS seems to be one of the main regulators of cellular respiration, mitochondrial transmembrane potential, and transmembrane proton gradient. This review focuses on recent advances in the understanding of the role of enzyme and enzyme-independent NO formation, regulation of NO bioactivity, new aspects of NO on cardiac function and morphology, and the clinical impact and perspectives of these recent advances in our knowledge on NO-related pathways.

Reduction of Myocardial Scar Size after Implantation of Mesenchymal Stem Cells in Rats: What Is the Mechanism?

The use of a cellular therapy offers a promising approach for the treatment of heart disease. Besides other precursor cells, bone marrow (BM)-derived stem cells were discovered that migrate into ischemic myocardium and participate in myogenesis as well as angiogenesis. A subpopulation of those are the mesenchymal stem cells (MSC), which may be potential candidates for repairing ischemic heart tissue. MSC are easy to prepare and can be used in an autologous strategy. Here we demonstrate the effect of transplanted MSC in our autologous rat model of myocardial injury. BM was isolated from tibiae and femurs of Wistar rats. After 24 h, the adhering MSC were separated, expanded, retrovirally transduced using green fluorescent protein (GFP), and cloned. A cryo-infarct was generated in the rat hearts, and immediately after this the cells were injected into the border zone of the lesion. After a 10-week follow up, the hearts were excised and the myocardial scar areas were measured using computer-guided morphometry. When comparing transplanted rats (n = 8) with control animals (n = 5) treated rats demonstrated a significant reduction in the width (p < 0.05) of the myocardial scar area. The depth of the scars of the cell therapy rats was less extended (p > 0.05) and the myocardium of these animals was thicker than in the controls (p > 0.05). Immunohistochemical analyses revealed neither evidence of MSC transdifferentiation into cardiomyocytes, nor could an increased neovascularization be found. In conclusion, MSC are responsible for a remarkable reduction of the myocardial scar size in the treated animals. But, whether this strategy is directly transferable to the patient suffering from heart disease has to be determined. In addition, the mechanism by which MSC act in the ischemic heart remains to be determined.

Effects of intramyocardial pVEGF165 delivery on regional myocardial blood flow: evidence for a spatial ‘delivery–efficacy’ mismatch

The aim of this study was to determine the effects of direct intramyocardial pVEGF165 gene transfer on regional myocardial blood flow in a porcine model of chronic myocardial ischaemia. Pigs underwent placement of an ameroid constrictor around the left circumflex coronary artery. After 3 weeks, animals received direct intramyocardial injections of pVEGF165 (20 x 50 microl at 1 microg/microl, n=11) or a plasmid vector encoding chloramphenicol acetyltransferase (20 x 50 microl at 1 microg/microl, n=11) into a specified target area (TA) of the left lateral wall. At 3 weeks after gene transfer, animals underwent final evaluation including a systematic assessment of regional myocardial blood flow (MBF) under resting and stress conditions. In all, 20 animals (10 per group) reached final studies. There was no change in mean arterial blood pressure or Rentrop collateral score from gene delivery to final studies in either group, nor were there differences between study groups. MBF was significantly higher in the areas adjacent to the TA in the VEGF group under resting (P<0.001) and stress conditions (P<0.05). In addition, pVEGF165 gene transfer abolished flow differences between the adjacent areas and the septum. MBF was not different between study groups in the TA, the anterior wall, or the septum. In conclusion, direct intramyocardial pVEGF165 gene transfer significantly improves myocardial blood flow. However, this effect is limited to the myocardial segments adjacent to the area of gene delivery. These data, therefore, demonstrate a spatial 'delivery-efficacy' mismatch with implications for myocardial gene delivery sites and detection of treatment effects in vivo.

Bone marrow mononuclear cell transplantation had beneficial effects on doxorubicin-induced cardiomyopathy

BACKGROUND

Cell transplantation is a promising therapy for treating end-stage heart failure. Bone marrow mononuclear cells (BMMNC) have been used to enhance angiogenesis in ischemic heart disease. However, the effect of BMMNC transplantation in non-ischemic dilated cardiomyopathy is unknown. In this study, we evaluated the efficacy of BMMNC transplantation in doxorubicin-induced cardiomyopathy in a rat model.

METHODS

Doxorubicin (15 mg/kg, IP) was introduced into 52 Lewis rats. They were divided into 3 groups at 4 weeks after injection: transplant group (TX, BMMNC [1 x 10(6)] implantation, n = 18), control group (CN, saline injection, n = 18), and sham group (SH, thoracotomy, n = 16). At 4 weeks after surgery, we used echocardiography to measure systolic left ventricular diameter (LVDs), diastolic left ventricular diameter (LVDd), fractional shortening (FS), and left ventricular wall thickness/LVDs. We used a Langendorff apparatus to measure systolic, diastolic, and developed pressures. We used radioimmunoassay to measure circulating atrial natriuretic peptide concentration, and we performed histologic study, including electron-microscopic study.

RESULTS

Left ventricular wall thickness/LVDs in the TX group was the largest of all groups (p < 0.05). Systolic and developed pressures in the TX group were the greatest (p < 0.005). Systolic left ventricular diameter, FS, and end-diastolic pressure in the TX group were smaller than in the SH group (p < 0.05). These cardiac parameters did not differ significantly between TX and CN groups, but secondary changes (decreased heart weight, developed ascites, and increased atrial natriuretic peptide concentration) caused by doxorubicin-induced heart failure were most attenuated in the TX group. In the TX group, vascular density was greatest (p < 0.05) in the left ventricular free wall and in the septum. In addition, electron microscopy showed that myocardium in the TX group was most maintained.

CONCLUSION

Bone marrow mononuclear cell transplantation had beneficial effects in doxorubicin-induced cardiomyopathy.