Transmyocardial laser revascularization induced angiogenesis correlated with the expression of matrix metalloproteinases and platelet-derived endothelial cell growth factor

Thymidine Phosphorylase Promotes the Formation of Abdominal Aortic Aneurysm in Mice Fed a Western Diet

Aims

The precise molecular drivers of abdominal aortic aneurysm (AAA) remain unclear. Thymidine phosphorylase (TYMP) contributes to increased platelet activation, thrombosis, and inflammation, all of which are key factors in AAA development. Additionally, TYMP suppresses the proliferation of vascular smooth muscle cells (VSMCs), which are central to the development and progression of AAA. We hypothesize that TYMP plays a key role in AAA development.

Methods and Results

We conducted a histological study using human AAA samples and normal abdominal aortas, revealing heightened levels of TYMP in human AAA vessel walls. To validate this observation, we utilized an Ang II perfusion-induced AAA model in wild-type C57BL/6J (WT) and Tymp-/- mice, feeding them a Western diet (TD.88137) starting from 4 weeks of age. We found that Tymp-/- mice were protected from Ang II perfusion-induced AAA formation. Furthermore, by using TYMP-expressing VSMCs as well as primarily cultured VSMCs from WT and Tymp-/- mice, we elucidated the essential role of TYMP in regulating MMP2 expression and activation. TYMP deficiency or inhibition by tipiracil, a selective TYMP inhibitor, led to reduced MMP2 production, release, and activation in VSMCs. Additionally, TYMP was found to promote pro-inflammatory cytokine expression systemically, and its absence attenuates TNF-α-stimulated activation of MMP2 and AKT. By co-culturing VSMCs and platelets, we observed that TYMP-deficient platelets had a reduced inhibitory effect on VSMC proliferation compared to WT platelets. Moreover, TYMP appeared to enhance the expression of activated TGFβ1 in cultured VSMCs in vitro and in human AAA vessel walls in vivo. TYMP also boosted the activation of thrombospondin-1 type 1 repeat domain-enhanced TGFβ1 signaling, resulting in increased connective tissue growth factor production.

Conclusion

Our findings collectively demonstrated that TYMP serves as a novel regulatory force in vascular biology, exerting influence over VSMC functionality and inflammatory responses that promote the development of AAA.

Thymidine Phosphorylase Deficiency or Inhibition Preserves Cardiac Function in Mice With Acute Myocardial Infarction

Background Ischemic cardiovascular disease is the leading cause of death worldwide. Current pharmacologic therapy has multiple limitations, and patients remain symptomatic despite maximal medical therapies. Deficiency or inhibition of thymidine phosphorylase (TYMP) in mice reduces thrombosis, suggesting that TYMP could be a novel therapeutic target for patients with acute myocardial infarction (AMI). Methods and Results A mouse AMI model was established by ligation of the left anterior descending coronary artery in C57BL/6J wild-type and TYMP-deficient (Tymp-/-) mice. Cardiac function was monitored by echocardiography or Langendorff assay. TYMP-deficient hearts had lower baseline contractility. However, cardiac function, systolic left ventricle anterior wall thickness, and diastolic wall strain were significantly greater 4 weeks after AMI compared with wild-type hearts. TYMP deficiency reduced microthrombus formation after AMI. TYMP deficiency did not affect angiogenesis in either normal or infarcted myocardium but increased arteriogenesis post-AMI. TYMP deficiency enhanced the mobilization of bone marrow stem cells and promoted mesenchymal stem cell (MSC) proliferation, migration, and resistance to inflammation and hypoxia. TYMP deficiency increased the number of larger MSCs and decreased matrix metalloproteinase-2 expression, resulting in a high homing capability. TYMP deficiency induced constitutive AKT phosphorylation in MSCs but reduced expression of genes associated with retinoid-interferon-induced mortality-19, a molecule that enhances cell death. Inhibition of TYMP with its selective inhibitor, tipiracil, phenocopied TYMP deficiency, improved post-AMI cardiac function and systolic left ventricle anterior wall thickness, attenuated diastolic stiffness, and reduced infarct size. Conclusions This study demonstrated that TYMP plays an adverse role after AMI. Targeting TYMP may be a novel therapy for patients with AMI.

Ten-year follow-up after combined coronary artery bypass grafting and transmyocardial laser revascularization in patients with disseminated coronary atherosclerosis

Coronary artery disease involving heavily calcified lesions has been associated with worse short- and long-term outcomes including increased mortality. This paper aims to evaluate long-term survival benefit when CABG + transmyocardial laser revascularization (TMLR) are performed on the hearts of patients with disseminated coronary atherosclerosis (DCA). This novel retrospective study was conducted between 1997 and 2002 and followed 86 patients with ischemic heart disease and severe DCA who underwent TMLR using a Holmium:YAG laser and/or CABG. There were 46 patients who had CABG plus TMLR on at least one heart wall ("combined therapy group") and 40 patients who had CABG or TMLR separately on at least one heart wall ("single therapy group"). For the whole group, actuarial survival at 10 years was 78.3% in the combined group compared to 72.5% in the single therapy group (p = 0.535). Ten-year survival in the combined vs. single therapy group for the anterior heart walls was 100 vs. 72.2% (p = 0.027). For the lateral and posterior heart walls were 73.7 vs. 73.3% (p = 0.97) and 84.2 vs. 72% (p = 0.27), respectively. Kaplan-Meier survival analysis showed benefit only for the anterior heart wall (F Cox test, p = 0.103). Single therapy procedures on all heart walls (odds ratio 1.736, p = 0.264) or on the anterior heart wall only (odds ratio 3.286, p = 0.279) were found to be predictors of 10-year late mortality. Combined therapy (TMLR + CABG) provides benefit for perioperative mortality and long-term survival only when provided on the anterior heart wall. For patients with disseminated coronary atherosclerosis, cardiac mortality was found to be increased when followed up 6 years later, regardless of the therapy applied.

Angiogenic growth factors in myocardial infarction: a critical appraisal

In the recent past, substantial advances have been made in the treatment of myocardial infarction (MI). Despite the impact of these positive developments, MI remains to be a leading cause of morbidity as well as mortality. An interesting hypothesis is that the development of new blood vessels (angiogenesis) or the remodeling of preexisting collaterals may form natural bypasses that could compensate for the occlusion of an epicardial coronary artery. A number of angiogenic factors are proven to be elicited during MI. Exogenous supplementation of these growth factors either in the form of recombinant protein or gene would enhance the collateral vessel formation and thereby improve the outcome after MI. The aim of this review is to describe the nature and potentials of different angiogenic factors, their expression, their efficacy in animal studies, and clinical trials pertaining to MI.

Paraoxonase 2 prevents the development of heart failure

BACKGROUND

Mitochondrial oxidation is a major source of reactive oxygen species (ROS) and mitochondrial dysfunction plays a central role in development of heart failure (HF). Paraoxonase 2 deficient (PON2-def) mitochondria are impaired in function. In this study, we tested whether PON2-def aggravates HF progression.

METHODS AND RESULTS

Using qPCR, immunoblotting and lactonase activity assay, we demonstrate that PON2 activity was significantly decreased in failing hearts despite increased PON2 expression. To determine the cardiac-specific function of PON2, we performed heart transplantations in which PON2-def and wild type (WT) donor hearts were implanted into WT recipient mice. Beating scores of the donor hearts, assessed at 4 weeks post-transplantation, were significantly decreased in PON2-def hearts when compared to WT donor hearts. By using a transverse aortic constriction (TAC) model, we found PON2 deficiency significantly exacerbated left ventricular remodeling and cardiac fibrosis post-TAC. We further demonstrated PON2 deficiency significantly enhanced ROS generation in heart tissues post-TAC. ROS generation was measured through dihydroethidium (DHE) using high-pressure liquid chromatography (HPLC) with a fluorescent detector. By using neonatal cardiomyocytes treated with CoCl₂ to mimic hypoxia, we found PON2 deficiency dramatically increased ROS generation in the cardiomyocytes upon CoCl₂ treatment. In response to a short CoCl₂ exposure, cell viability and succinate dehydrogenase (SDH) activity assessed by MTT assay were significantly diminished in PON2-def cardiomyocytes compared to those in WT cardiomyocytes. PON2-def cardiomyocytes also had lower baseline SDH activity. By using adult mouse cardiomyocytes and mitochondrial ToxGlo assay, we found impaired cellular ATP generation in PON2-def cells compared to that in WT cells, suggesting that PON2 is necessary for proper mitochondrial function.

CONCLUSION

Our study suggests a cardioprotective role for PON2 in both experimental and human heart failure, which may be associated with the ability of PON2 to improve mitochondrial function and diminish ROS generation.

Thymidine phosphorylase: A potential new target for treating cardiovascular disease

We recently found that thymidine phosphorylase (TYMP), also known as platelet-derived endothelial cell growth factor, plays an important role in platelet activation in vitro and thrombosis in vivo by participating in multiple signaling pathways. Platelets are a major source of TYMP. Since platelet-mediated clot formation is a key event in several fatal diseases, such as myocardial infarction, stroke and pulmonary embolism, understanding TYMP in depth may lead to uncovering novel mechanisms in the development of cardiovascular diseases. Targeting TYMP may become a novel therapeutic for cardiovascular disorders. In this review article, we summarize the discovery of TYMP and the potential molecular mechanisms of TYMP involved in the development of various diseases, especially cardiovascular diseases. We also offer insights regarding future studies exploring the role of TYMP in the development of cardiovascular disease as well as in therapy.

Transmyocardial Revascularization: Peril and Potential

Transmyocardial laser revascularization is a technique for the treatment of patients with chronic angina pectoris that is refractory to medical therapy and who are not eligible for surgical intervention. Percutaneous myocardial revascularization is a less-invasive catheter-based procedure that has been adapted from transmyocardial laser revascularization. Six prospective randomized clinical trials have been performed with transmyocardial laser revascularization and 5 have been performed using percutaneous myocardial revascularization. All of the transmyocardial laser revascularization and 4 of the percutaneous myocardial revascularization studies showed a significant improvement in angina class; however, results for improved survival, increased exercise tolerance, improved ejection fraction, and improved myocardial perfusion were less definitive. Transmyocardial laser revascularization has significant potential for morbidity and mortality. This article summarizes the results of the randomized trials, explains the current theories for the mechanism of transmyocardial laser revascularization, and discusses its current role in treatment for patients, considering the evidence that currently exists.

Transmyocardial revascularization devices: technology update

Transmyocardial laser revascularization (TMR) emerged as treatment modality for patients with diffuse coronary artery disease not amendable to percutaneous or surgical revascularization. The procedure entails the creation of laser channels within ischemic myocardium in an effort to better perfuse these areas. Currently, two laser devices are approved by the US Food and Drug Administration for TMR – holmium:yttrium–aluminum–garnet and CO₂. The two devices differ in regard to energy outputs, wavelengths, ability to synchronize with the heart cycle, and laser–tissue interactions. These differences have led to studies showing different efficacies between the two laser devices. Over 50,000 procedures have been performed worldwide using TMR. Improvements in angina stages, quality of life, and perfusion of the myocardium have been demonstrated with TMR. Although several mechanisms for these improvements have been suggested, evidence points to new blood vessel formation, or angiogenesis, within the treated myocardium, as the major contributory factor. TMR has been used as sole therapy and in combination with coronary artery bypass grafting. Clinical studies have demonstrated that TMR is both safe and effective in angina relief long term. The objective of this review is to present the two approved laser devices and evidence for the safety and efficacy of TMR, along with future directions with this technology.

Assessment methods for angiogenesis and current approaches for its quantification

Angiogenesis is a physiological process which describes the development of new blood vessels from the existing vessels. It is a common and the most important process in the formation and development of blood vessels, so it is supportive in the healing of wounds and granulation of tissues. The different assays for the evaluation of angiogenesis have been described with distinct advantages and some limitations. In order to develop angiogenic and antiangiogenic techniques, continuous efforts have been resulted to give animal models for more quantitative analysis of angiogenesis. Most of the studies on angiogenic inducers and inhibitors rely on various models, both in vitro, in vivo and in ova, as indicators of efficacy. The angiogenesis assays are very much helpful to test efficacy of both pro- and anti- angiogenic agents. The development of non-invasive procedures for quantification of angiogenesis will facilitate this process significantly. The main objective of this review article is to focus on the novel and existing methods of angiogenesis and their quantification techniques. These findings will be helpful to establish the most convenient methods for the detection, quantification of angiogenesis and to develop a novel, well tolerated and cost effective anti-angiogenic treatment in the near future.

Atrazine-induced changes in the myocardial structure of peripubertal rats

The aim of the present study was to investigate the effect of atrazine (6-chloro-N(2)-ethyl-N(4)-isopropyl-1,3,5-triazine-2,4-diamine) on the left ventricle myocardium in juvenile/peripubertal male Wistar rats. Atrazine was administered orally at 50 or 200 mg/kg of body weight dose for 28 consecutive days. In order to assess possible structural alterations, tissue sections were examined histologically and then subjected to quantification analysis using stereological methods. The tissue specimens were routinely processed and stained with Mallory trichrome method in order to clearly distinguish muscle cells from the connective tissue components. A toluidine blue staining method was additionally used for the demonstration of mast cells. Statistically significant increase in length density and numerical density of capillaries were found at both the investigated doses of atrazine compared with the control. The increase in surface density and volume density of capillaries found at lower dosage of atrazine was significant in comparison with the control. The extensive mast cell degranulation was noted on the histological examination at both doses of the applied chemical. No significant changes were demonstrated for the stereological parameters of cardiomyocytes. Based on the available published data and the present results, it can be concluded that atrazine promoted angiogenesis in the rat myocardium, which might be partially mediated by mast cells.

Experimentally induced puromycine aminonucleoside nephrosis (PAN) in rats: evaluation of angiogenic protein platelet-derived endothelial cell growth factor (PD-ECGF) expression in glomeruli

BACKGROUND

In experimentally induced puromycine aminonucleoside nephrosis (PAN) animal models, nephrotic syndrome with minimal change disease and focal and segmental sclerosis-like nephritis similar to that in human is demonstrated; however, the real mechanism of PAN is not yet elucidated. Platelet derived endothelial cell growth factor (PD-ECGF), an endothelial mitogen protein, is believed to take part in microvessel formation and in stimulation of angiogenesis and its expression has not been totally demonstrated in PAN rats yet. In this study, we aimed to examine PD-ECGF expression in acute and chronic PAN induced in rats and find out the association between its expression and the stages of angiogenesis in kidney.

METHODS

For the experiment, twenty-four Male Wistar Albino rats were used and divided into four groups; control group (n = 6), pre-proteinuria group (n = 6), acute group (n = 6) and chronic group (n = 6). We compared statistically all data by One-way ANOVA Test followed by Dunn Multiple Comparison Test.

RESULTS

Proteinurea levels in control and pre-proteinuria groups were not statistically different; however, it was remarkably higher in the acute nephrosis group and significantly greater in the chronic nephrosis group than control group (p < 0.0025). In pre-proteinuria group, the serum albumin and creatinine clearances also did not significantly differ from the control group. On the other hand, in the acute and chronic nephrosis groups, serum albumin and creatinine clearances progressively decreased (p < 0.05). In our immunohistochemical studies, we showed elevated PD-ECGF expression in glomeruli of acute and chronic PAN rats. Microscopic and ultrastructural appearances of the glomeruli of acute and chronic PAN showed various sequential steps of angiogenesis, macrophages and immature capillaries with primitive lumens and apoptotic endothelial cells in the increased mesangial matrix.

CONCLUSIONS

It is reported that acute and chronic PAN progressively increase PD-ECGF expression and following induction of angiogenesis in the affected glomeruli.

Myocardial expression of PDECGF is associated with extracellular matrix remodeling in experimental myocardial infarction in rats

Platelet-derived endothelial cell growth factor (PDECGF) is a potent angiogenic peptide with anti-apoptotic activity expressed widely in tumours. However, its expression in myocardial infarction (MI) is not yet established. This study aimed to assess the myocardial expression of PDECGF in rats after MI. Extracellular matrix (ECM) remodeling plays an important role in angiogenesis; hence, changes in the ECM components were investigated in the myocardium after MI, which was induced in rats by coronary artery ligation (CAL) and verified using biochemical markers and histopathology. Immunohistochemistry, RT-PCR, and activity assays identified the expression pattern of PDECGF on days 1, 2, 4, 8, 16, and 32 after CAL. The levels of TNF-alpha, MMP-2, collagen, and glycosaminoglycans in the ECM were assessed. Studies on immunohistochemistry, RT-PCR, and PDECGF activity demonstrated elevated levels of PDECGF expression from day 2 after CAL. Macrophages, endothelial cells, fibroblasts, and cardiomyocytes, especially at the border region of the lesion, showed an enhanced expression for PDECGF. Remodeling of the ECM was depicted by changes in the levels of TNF-alpha, MMP-2, collagen, and GAG. Hence, this study clearly indicated PDECGF as an important angiogenic molecule expressed during MI and the alterations in ECM components facilitated the process of angiogenesis.

Long-term effect of gene therapy for chronic ischemic myocardium using platelet-derived endothelial cell growth factor in dogs

BACKGROUND

We previously reported the 2-week benefits of platelet-derived endothelial cell growth factor (PD-ECGF) gene therapy in chronically ischemic myocardium. However, the long-term effects and safety using this gene have not been reported.

METHODS

Chronic myocardial ischemia was created in 24 dogs by stenosing the origin of the left anterior descending coronary artery (LAD) using an ameroid constrictor. Two weeks later, the PD-ECGF gene, the LacZ gene, or saline was infused directly into the myocardium in the LAD area. The myocardial blood volume and myocardial function were examined prior to ischemia, immediately before gene injection, and for 6 months following injection, and then the organs were harvested for histological and molecular examination.

RESULTS

PD-ECGF gene treatment significantly attenuated endocardial infarction at 6 months. Myocardial blood volume and myocardial function decreased in all three groups after ameroid implantation, but recovered after 2 weeks in the PD-ECGF-treated group, and maintained a higher level of function during the examination period. Histological analysis demonstrated that angiogenesis and arteriogenesis occurred after PD-ECGF gene treatment. There was a decreased expression of the pro-apoptotic proteins, active caspase-3 and Bax, and the number of apoptotic myocardial cells was lower in the PD-ECGF-treated group. Histological examination demonstrated that no abnormal histological changes or neoplasms were found in any organs.

CONCLUSIONS

We conclude that gene targeting of ischemic myocardium using PD-ECGF generated long-term improvement in cardiac function by causing angiogenesis, arteriogenesis and inhibiting apoptosis, but did not induce neoplasms in the remote organs, and may be a promising therapy.

Transmyocardial laser revascularization

It has been almost a decade since transmyocardial laser revascularization (TMR) was approved for clinical use in the United States. The safety of TMR was demonstrated initially with nonrandomized studies in which TMR was used as the only treatment for patients with severe angina. TMR efficacy was proven after multiple randomized controlled trials. These revealed significant angina relief compared to maximum medical therapy in patients with diffuse coronary disease not amenable to conventional revascularization. In light of these results, TMR has been used as an adjunct to coronary artery bypass grafting (CABG). By definition, patients treated with this combined therapy have more severe coronary disease and comorbidities that are associated with end-stage atherosclerosis. Combination CABG + TMR has resulted in symptomatic improvement without additional risk. The likely mechanism whereby TMR has provided benefit is the angiogenesis engendered by the laser-tissue interaction. Improved perfusion and concomitant improvement in myocardial function have been observed post-TMR. Additional therapies to enhance the angiogenic response include combining TMR with stem cell-based treatments, which appear to be promising future endeavors.

Combined transmyocardial revascularization and cell-based angiogenic gene therapy increases transplanted cell survival

We hypothesized that pretreatment of an infarcted heart by mechanical transmyocardial revascularization (TMR) before transplantation of bone marrow cells (BMCs) or BMC-expressing angiogenic growth factors would increase transplanted BMC survival and enhance myocardial repair. Female Lewis rats underwent coronary ligation 3 wk before creation of 10 needle TMR channels (3 groups) or no TMR (3 groups), followed by transplantation of 3 × 106male donor BMCs, BMC transfected with vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and insulin-like growth factor-1 (IGF-1) (BMC + VBI), or medium alone. At 1, 3, and 7 days, we evaluated transplanted cell survival, vascular densities, and left ventricular (LV) function ( N = 4 per group × 6 groups × 3 time points). At 3 days, vascular densities in the scar were increased by TMR + BMC + VBI and by BMC + VBI ( P < 0.05), and at 7 days, vascular densities were greatest in rats receiving TMR + BMC + VBI ( P < 0.05). Transplanted cell survival at 3 and 7 days was increased by TMR and by BMC + VBI. Combined therapy with TMR + BMC + VBI resulted in the greatest cell survival at 3 days ( P < 0.05) versus BMC. After 7 days, LV ejection fraction (LVEF) was lowest in rats receiving neither BMC nor TMR and greatest in rats receiving TMR + BMC + VBI ( P = 0.004). We concluded that mechanical pretreatment of infarcted myocardium by TMR enhances the effect of subsequent cell-based gene therapy on transplanted cell survival, angiogenesis, and LV function. Scar pretreatment with TMR combined with cell-based multigene therapy may maximize myocardial repair.

Thymidine phosphorylase gene transfer inhibits vascular smooth muscle cell proliferation by upregulating heme oxygenase-1 and p27KIP1

OBJECTIVE

Thymidine phosphorylase (TP) reportedly promotes endothelial cell migration and induces heme oxygenase (HO)-1 expression. However, its effect on vascular smooth muscle cells (VSMCs) is poorly understood. In this study, we examined the effect of TP on VSMCs in vitro and in vivo.

METHODS AND RESULTS

Phagemid vector encoding human TP gene was transfected into rat VSMCs, and a clone overexpressing TP was selected (C2). C2 showed a slower migration and proliferation than VSMCs cloned with empty vector (pC) under basal, serum-stimulated, and hypoxic conditions. This decrease in proliferation correlated with TP-induced HO-1 expression and was reversed by inhibitors of either TP or HO activity. Furthermore, in C2, the cyclin-dependent kinase inhibitor (p27KIP1) was much more abundant than in pC, and the cell cycle was arrested at the G1 phase. TP or HO activity inhibitors decreased p27(KIP1) expression in C2 to the level seen in pC. Adventitial TP gene delivery significantly reduced neointimal VSMC migration and neointima formation in balloon-injured rat carotid arteries.

CONCLUSIONS

TP overexpression upregulated HO-1 expression and consequently increased p27(KIP1) in cultured VSMCs, and inhibited VSMC migration and proliferation in vitro and in vivo. TP represents a promising target for treating vascular obstructive disease.

Improvement of myocardial contractility in a porcine model of chronic ischemia using a combined transmyocardial revascularization and gene therapy approach

OBJECTIVES

The purpose of this study was to investigate whether a novel fibroblast growth factor-2 gene formulation, providing a localized and sustained availability of the adenoviral vector from a collagen-based matrix, in combination with CO 2 transmyocardial laser revascularization would lead to an enhanced angiogenic response and improved myocardial function.

METHODS

Fibroblast growth factor-2 gene was delivered by means of an adenoviral vector (adenoviral fibroblast growth factor-2) formulated in a collagen-based matrix. The ischemic areas of 33 animals were then treated. Group 1 was treated with CO 2 transmyocardial laser revascularization; group 2 was treated with intramyocardial injections of adenoviral fibroblast growth factor-2 in a collagen-based matrix; group 3 had a combination treatment of matrix adenoviral fibroblast growth factor-2 and CO 2 transmyocardial laser revascularization; and group 4 received injections with saline-formulated adenoviral fibroblast growth factor-2. Baseline left ventricular function was assessed by echocardiography and cine magnetic resonance imaging. Studies were repeated 6 weeks after treatment. Vascular development was assessed using anti-alpha-actin immunohistochemistry.

RESULTS

Matrix adenoviral fibroblast growth factor-2 + transmyocardial laser revascularization-treated areas had a 105% increase in arteriolar development versus either treatment alone ( P < .05) and a 390% increase compared with saline-formulated adenoviral fibroblast growth factor-2 treatment alone ( P < .05). Contractility was significantly improved in matrix adenoviral fibroblast growth factor-2 + transmyocardial laser revascularization-treated areas as measured by myocardial wall thickening. This functional improvement was confirmed by cine magnetic resonance imaging, in which a 90% increase in the contractility of the treated segments was demonstrated after matrix adenoviral fibroblast growth factor-2 + transmyocardial laser revascularation. The other treatments provided significantly less restoration of myocardial function.

CONCLUSIONS

The increase in angiogenesis as a result of matrix adenoviral fibroblast growth factor-2 gene therapy in combination with CO 2 transmyocardial laser revascularization is greater than that seen in either therapy alone. A concomitant improvement in myocardial function was seen as a result of this angiogenic response.

Digital Radiographic Quantification of Myocardial Blood Flow Around a Transmyocardial Laser Channel in Rabbit Hearts

BACKGROUND

A mechanism underlying the benefits of transmyocardial laser revascularization (TMLR) has been presumed to be improvement in perfusion. We evaluated myocardial blood flow around a laser channel using digital radiography combined with a 3H-labeled desmethylimipramine ([3H]DMI) deposition.

METHODS AND RESULTS

A laser channel was created in the left ventricular wall using a YAG-laser in 6 non-ischemic rabbit hearts. After 8 weeks, [3H]DMI(1.11 MBq) was injected into the left atrium and the TMLR-treated myocardium was sectioned. Another 6 hearts were examined as controls. We measured [3H]DMI density in arbitrary units with digital radiography in the channel remnant, the surrounding area and a remote area. Flow distribution was quantified by the coefficient of variation of flows (CV). The surrounding area had the highest density (p < 0.001) and the lowest CV (p < 0.001), and had higher density (p < 0.001) and lower CV (p < 0.001) than the controls. There was no transmural difference in the density in all domains. The CV increased with depth in the remote area, as well as in controls (p < 0.001), but there was no transmural difference in the surrounding area.

CONCLUSIONS

The TMLR increases myocardial blood flow and decreases flow heterogeneity in the surrounding area. The disappearance of transmural difference in flow heterogeneity might indicate the remodeling of microcirculation to improve regional oxygen delivery.

Gene therapy for chronic myocardial ischemia using platelet-derived endothelial cell growth factor in dogs

Platelet-derived endothelial cell growth factor (PD-ECGF), also known as thymidine phosphorylase (TP), has been reported to possess angiogenic activity and to inhibit apoptosis. This study was performed to determine whether PD-ECGF/TP can be used to ameliorate chronic myocardial ischemia. Myocardial ischemia was created in 40 mongrel dogs by placement of an ameroid constrictor on the proximal left anterior descending coronary artery (LAD). Plasmid vector encoding human PD-ECGF/TP cDNA (pCIhTP group; n = 12), empty vector pCI (pCI group; n = 12), or saline (Saline group; n = 12) was directly injected into the LAD territory 3 wk after ameroid constrictor implantation. Myocardial blood flow was detected using PET at baseline, 3 wk after ameroid constrictor implantation, and 2 wk after therapeutic treatment. At the end of the experiment, the hearts were isolated for biological and histological analysis. In the pCIhTP group, the transfected heart strongly expressed PD-ECGF/TP. The size of the infarct was smaller in the pCIhTP group than in the pCI or Saline group. The number of apoptotic myocardial cells was decreased in the pCIhTP group compared with the control groups based on triple immunohistochemical staining for von Willebrand factor, alpha-actin smooth muscle cells, and single-strand DNA. The level of proapoptotic protein Bax markedly decreased in the pCIhTP group compared with the other groups. Double immunohistochemical staining for von Willebrand factor and alpha-actin smooth muscle cells demonstrated that angiogenesis and arteriogenesis occurred, and paralleled the changes in myocardial blood flow and myocardial function in the pCIhTP group. We conclude that genetic approaches using PD-ECGF/TP to target the myocardium are effective for alleviating chronic myocardial ischemia.

Mechanisms and Results of Transmyocardial Laser Revascularization

Transmyocardial laser revascularization (TMR) is a technique that has been performed on over 10,000 patients around the world. Most of the patients were not suffering from heart failure. TMR is principally used for the treatment of angina, but in patients with significant reversible ischemia that is not amenable to conventional therapy, TMR may also improve myocardial function. The results of using TMR as a treatment for angina show a dramatic improvement in symptoms and quality of life. This paper reviews the current status of TMR techniques, mechanisms and results.

Role of MMPs and plasminogen activators in angiogenesis after transmyocardial laser revascularization in dogs

We examined the role of matrix metalloproteinases (MMPs), tissue inhibitors of MMP (TIMPs), and plasminogen activator (PA) in transmyocardial laser revascularization (TMLR)-induced angiogenesis. TMLR was accomplished with a carbon dioxide laser in seven dogs whose left anterior descending coronary artery (LAD) was ligated. Seven control dogs underwent only LAD ligation, and four dogs underwent a sham operation, consisting only of a left thoracotomy. Two weeks later, transmural myocardial samples were harvested from the distributions of the LAD and the left circumflex artery for substrate zymography, immunohistochemical staining, and in situ zymography. MMP-1, MMP-2, TIMP-1, TIMP-2, and urokinase-type PA levels in the distribution of the LAD were higher in the laser group than in the control or sham group. Counts of von Willebrand factor-positive microvessels and smooth muscle alpha-actin-positive arterioles demonstrated that the angiogenesis and ateriogenesis was promoted in the laser group and correlated directly with the number of MMP-stained microvessels. We conclude that TMLR induces the expression of MMPs, TIMPs, and urokinase-type PA and that these proteinases play an important role in angiogenesis after TMLR.

Influence of transmyocardial laser revascularization (TMLR) on regional cardiac function and metabolism in an isolated hemoperfused working pig heart

The mechanism of an indirect revascularization in ischemic myocardium by transmyocardial laser revascularization (TMLR) is not yet fully understood. An improvement of clinical symptoms caused by TMLR is reported in many clinical trials with patients in which a direct revascularization is not possible. An increase of myocardial perfusion through laser channels is doubtful, because the myocardial pressure in the wall is higher than in the cavum. Therefore we measured the local cardiac function (intramyocardial pressure, wall thickness, pressure-length curves) and acute metabolic changes (tissue lactate content, tissue pO2) in ischemic and nonischemic regions before and after TMLR in isolated hemoperfused pig hearts. An isolated heart was chosen because it enabled us to separate coronary flow from flow through ventricular channels. The ischemia was induced by coronary occlusion or microembolization (eight hearts each). It should be noted that microembolization leads to conditions which are more comparable with those found in patients selected for TMLR. In the isolated working heart, the coronary perfusion can be controlled independently from perfusion through the ventricular cavum. Under the ischemic conditions mentioned above, we observed that the intramyocardial pressure in the ischemic region decreased below the left ventricular pressure, so one premise for indirect perfusion was met. TMLR after microembolization led to a significant improvement of regional cardiac work and the tissue oxygen pressure. These acute effects demonstrate the possibility of functional and metabolic amelioration by TMLR after ischemia induced by microembolization in an isolated hemoperfused pig heart.

35 years of experimental research in transmyocardial revascularization: what have we learned?

In the past 35 years many experimental studies have been performed to investigate the revascularization potential of transmyocardial revascularization and the possible working mechanisms underlying the observed clinical improvement in angina pectoris after this treatment. In this review of the experimental literature, the various methods that have been used to create transmyocardial channels and the most supported hypotheses on the working mechanism (channel patency, angiogenesis and myocardial denervation) are discussed and evaluated.