Inhibition of Tumor Necrosis Factor- Attenuates Myocardial Remodeling in Rat Cardiac Allografts Roope K. Sihvola, MD, PhD, a,b,d Petri K. Koskinen, MD, PhD, a,b,c Ville P. Pulkkinen, MSc, a,b Jussi M. Tikkanen, MD, PhD, a,b and Karl B. Lemström, MD, PhD a,b,c Background: Tumor necrosis factor- (TNF-) elicits a wide range of pro-inflammatory activities on target cells and mediates diverse cardiovascular processes ranging from heart failure to atherosclerosis. Recently, we demonstrated that TNF- regulates the platelelet-derived growth factor (PDGF)-A/ PDGF-R activation pathway in rat cardiac allograft arteriosclerosis. The aim of this study was to determine the kinetics and biologic role of TNF- and its receptors, TNF-R1 and TNF-R2, in rat cardiac allografts. Methods: Heterotopic heart transplantations were performed from Dark Agouti to Wistar–Furth rats. In the acute rejection model, recipients were given no immunosuppression and grafts were removed 5 days after transplantation. In the chronic rejection model, cyclosporine (CsA) was administered and grafts were removed at 60 days. To investigate the functional role of TNF- in chronic rejection, recipients received recombinant human soluble TNF receptor p80/IgG1 Fc fusion protein (rhu TNF-R2:Fc). Results: During acute and chronic rejection, an increase in intragraft TNF- and TNF-R2 mRNA expression was recorded, but not TNF-R1 mRNA expression. Prominent induction of TNF- and TNF-R2 immunoreac- tivity was localized to medial cells of coronary arteries and interstitial inflammatory cells, whereas cardiomyocytes showed moderate immunoreactivity to TNF- and its receptors. Inhibition of the TNF-–mediated pathway by TNF-R2:Fc did not affect the incidence or intensity of arteriosclerotic lesions in rat cardiac allografts; however, it significantly inhibited myocardial remodeling with a concomitant decrease in myocardial TNF- expression but not intragraft PDGF immunoreactivity. Conclusions: We conclude that inhibition of TNF- attenuates myocardial remodeling but is not rate-limiting for arteriosclerotic lesion formation. J Heart Lung Transplant 2006;25:569 –78. Copyright © 2006 by the International Society for Heart and Lung Transplantation. Tumor necrosis factor- (TNF-) is a cytokine with anti-tumorigenic, cytotoxic and pro-inflammatory prop- erties. The effects of TNF- are mediated through its two cell surface receptors, a 55-kD (TNF-R1, CD120a) and a 75-kD (TNF-R2, CD120b) protein. 1 TNF- is one of the major mediators of acute immune responses in several cardiovascular and other disorders ranging from heart failure to septic shock. 2 It plays an important role in the regulation of myocardial stress response by providing early anti-apoptotic cytoprotec- tive signals and delayed signals that facilitate tissue repair and/or tissue remodeling. 3–5 TNF- is produced in the myocardium under pressure and volume over- load, but is not present in normal hearts. 6,7 With short exposure, TNF- induces negative inotropic effects, 8,9 but with long-term overexpression in the myocardium its presence leads to hypertrophy, cardiac enlargement and death. 10,11 TNF- inhibition preserves cardiac func- tion after myocardial infarction. 12 Elevated TNF- pro- duction has been associated with increased incidence of cardiac allograft arteriosclerosis and mortality in cardiac transplant recipients. 13 Simvastatin has recently been shown to decrease myocardial TNF- expression, which may explain its beneficial effect on patient survival and rejection epi- sodes. 14 However, increased TNF- production was not associated with increased risk of rejection in adult cardiac transplant recipients. 15 Studies have indicated that TNF- regulates the platelet-derived growth factor From the a Cardiopulmonary Research Group, Transplantation Labora- tory, University of Helsinki, Helsinki; Departments of b Medicine, Divi- sion of Nephrology, and c Cardiothoracic Surgery, Helsinki University Central Hospital, Helsinki, Finland; and d Department of Ophthalmol- ogy, University of Kuopio and Kuopio University Hospital, Kuopio, Finland. Submitted June 15, 2005; revised November 8, 2005; accepted January 1, 2006. Supported by grants from Helsinki University Central Hospital research funds, the University of Helsinki, the Finnish Foundation for Cardiovascular Research, the Sigrid Juselius Foundation, the Aarne Koskelo Foundation, the Emil Aaltonen Foundation and the Finnish Medical Society Duodecim, Helsinki. Reprint requests: Roope Sihvola, MD, Cardiopulmonary Research Group, Transplantation Laboratory, University of Helsinki and Hel- sinki University Central Hospital, P.O. Box 21, Haartmaninkatu 3, FIN-00014 Helsinki, Finland. Telephone: +358-9-1912-6590. Fax: +358-9-2411-227. E-mail: roope.sihvola@helsinki.fi Copyright © 2006 by the International Society for Heart and Lung Transplantation. 1053-2498/06/$–see front matter. doi:10.1016/ j.healun.2006.01.002 569 FAILING HEART—BASIC SCIENCE