Background-Mesenchymal stem cells (MSCs) have the potential to replace infarct scar, but the long-term effects are unknown. We studied short-and long-term effects of MSC transplantation on left ventricular (LV) function in a rat myocardial infarction model. Methods and Results-Saline (nϭ46) or MSCs labeled with 1,1Ј-dioctadecyl-3,3,3Ј3Ј-testramethylindocarbocyanine perchlorate (DiI; nϭ49, 2ϫ10 6 cells each) were injected into the scar of a 1-week-old myocardial infarction in Fischer rats. The presence and differentiation of engrafted cells and their effect on LV ejection fraction was assessed. At 4 weeks, LV stroke volume was significantly greater in the MSC-treated group (145Ϯ9 L) than in the saline group (122Ϯ3 L, Pϭ0.032), and LV ejection fraction was significantly greater in MSC-treated animals (43.8Ϯ1.0%) than in the saline group (38.8Ϯ1.1%, Pϭ0.0027). However, at 6 months, these benefits of MSC treatment were lost. DiI-positive cells were observed in the MSC group at 2 weeks and at 3 and 6 months. Expression of the muscle-specific markers ␣-actinin, myosin heavy chain, phospholamban, and tropomyosin was not observed at 2 weeks in DiI-positive cells. At 3 and 6 months, the DiI-positive cells were observed to express the above muscle-specific markers, but they did not fully evolve into an adult cardiac phenotype. Some of the DiI-positive cells expressed von Willebrand factor. Conclusions-Allogeneic

It is clear that cocaine has cardiotoxic effects. Acute doses of cocaine suppress myocardial contractility, reduce coronary caliber and coronary blood flow, induce electrical abnormalities in the heart, and in conscious preparations increase heart rate and blood pressure. These effects will decrease myocardial oxygen supply and may increase demand (if heart rate and blood pressure rise). Thus, myocardial ischemia and/or infarction may occur, the latter leading to large areas of confluent necrosis. Increased platelet aggregability may contribute to ischemia and/or infarction. Young patients who present with acute myocardial infarction, especially without other risk factors, should be questioned regarding use of cocaine. As recently pointed out by Cregler, cocaine is a new and sometimes unrecognized risk factor for heart disease. Acute depression of LV function by cocaine may lead to the presence of a transient cardiomyopathic presentation. Chronic cocaine use can lead to the above problems as well as to acceleration of atherosclerosis. Direct toxic effects on the myocardium have been suggested, including scattered foci of myocyte necrosis (and in some but not all studies, contraction band necrosis), myocarditis, and foci of myocyte fibrosis. These abnormalities may lead to cases of cardiomyopathy. Left ventricular hypertrophy associated with chronic cocaine recently has been described. Arrhythmias and sudden death may be observed in acute or chronic use of cocaine. Miscellaneous cardiovascular abnormalities include ruptured aorta and endocarditis. Most of the cardiac toxicity with cocaine can be traced to two basic mechanisms: one is its ability to block sodium channels, leading to a local anesthetic or membrane-stabilizing effect; the second is its ability to block reuptake of catecholamines in the presynaptic neurons in the central and peripheral nervous system, resulting in increased sympathetic output and increased catecholamines. Other potential mechanisms of cocaine cardiotoxicity include a possible direct calcium effect leading to contraction of vessels and contraction bands in myocytes, hypersensitivity, and increased platelet aggregation (which may be related to increased catecholamine). The correct therapy for cocaine cardiotoxicity is not known. Calcium blockers, alpha-blockers, nitrates, and thrombolytic therapy show some promise for acute toxicity. Beta-Blockade is controversial and may worsen coronary blood flow. In patients who develop cardiomyopathy, the usual therapy for this entity is appropriate.

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