Date on Master's Thesis/Doctoral Dissertation

5-2010

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physiology and Biophysics

Committee Chair

Dawn, Buddhadeb

Author's Keywords

Transgenic inhibition; Cardiac remodeling; Cardiomyopathy; Doxorubicin; Apoptosis

Subject

Heart failure--Treatment

Abstract

Background The anthracycline doxorubicin (DOX) is widely used as an effective antineoplastic drug. Cardiotoxicity leading to congestive heart failure is the primary factor limiting the clinical use of DOX. However, although a variety of approaches to protect the heart against DOX-induced cardiotoxicity have been attempted; treatment to prevent short and long term DOX-induced cardiac damage remains limited. Currently, there is no specific therapeutic strategy against this severe disease. Cardiac inflammation and myocardial apoptosis is known to contribute to DOX-induced cardiomyopathy. The nuclear factor-kappaB (NF-?B) is a part of the innate immune system and is involved in cardiac stress reactions. Since NF-?B might play a significant role in cardiac inflammatory signaling and apoptosis, we investigated whether or not NF-?B is involved in DOX-induced cardiotoxicity. Methods and results Age-matched wild-type (WT), nontransgenic littermates (NTg) and inhibitory kappaB transgenic mice (I?B Tg) mice were divided into six groups based on whether the mice receive either DOX or vehicle. DOX was injected at a dose of 7.5 mg/kg intraperitoneally (i.p.) 2 times over 2 wks. Group I, WT (vehicle, n=6); group II, NTg (vehicle, n=6); group III, Tg (vehicle, n=6); group IV, WT (DOX, n=14); group V, NTg (DOX, n=14); and group VI, Tg (DOX, n=11). Groups I, II and Ill served as control mice and received injections of saline as vehicle. 14 days after DOX therapy, cardiac function was assessed by echocardiography and hemodynamics using a micro conductance Millar catheter. Following invasive hemodynamics, the mice were euthanized and heart and lung weights were noted and hearts were perfusion fixed for pathology and morphometry. The left ventricular (LV) tissue was harvested for myocardial protein expression of proinflammatory cytokines and proapopotic markers. DOX injection in WT and NTg mice resulted in significant impairment in LV function as evidenced by a decrease in LV ejection fraction (LVEF), LV systolic pressure (LVSP), LV rate of pressure development and pressure decay (±dP/dt) and an increase in LV end-diastolic and end-systolic diameters, LV end-diastolic pressure and LV end-diastolic volume (LVEDV). Furthermore, WT and NTg mice after DOX therapy showed signs of congestive heart failure as evidenced by an increase in lung weight and development of pulmonary edema, which was also associated with signs of adverse ventricular remodeling (increase in chamber diameters and decrease in wall thickness). In contrast to these findings, the heart weight, LVEDP, LV intrinsic diameters, LVEDV and lung weight were reduced, whereas the ± dP/dt, LVSP and LVEF were increased towards normal levels in I?B Tg group. In order to examine the effects of cardiac specific inhibition of NF-?B on inflammatory response and myocardial apoptosis, LV samples were analyzed for the protein expression of key inflammatory cytokines [tumor necrosis factor-a (TNF-a), interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS)] and proapoptotic proteins (Bax and p53) after DOX therapy. In WT and NTg hearts, therapy with DOX was associated with an increase in inflammation and apoptosis, as indicated by an up-regulation of TNF-a, IL-6, iNOS, Bax and p53. In contrast, I?B Tg mice showed decreased expression of proinflammatory cytokines and proapoptotic proteins. Furthermore, survival rate was significantly higher in I?B Tg mice than in WT and NTg mice 14 days after DOX injection (73% vs 43%, P < 0.05). Conclusions Cardiac specific inhibition of NF-?B improves LV function and attenuates adverse cardiac remodeling in DOX-induced cardiomyopathy. These beneficial effects of inhibition of NF-?B may be due to the decrease in the development of cardiac inflammation and myocardial apoptosis in DOX-induced cardiotoxicity. These findings may have important therapeutic implications of NF-?B in DOX-induced congestive heart failure.

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