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Cardiac-Specific Overexpression of a Dominant Negative (DN) p67phox Mutant Shows Reduction in Mouse Heart Size
The 12th Annual Scientific Meeting
HFSA
S1
Jay N. Cohn New Investigator Award: Basic Science 001 GLP-1(7-36) and GLP-1(9-36) Protect Murine Hearts from Post-Ischemic Contractile Dysfunction Christopher P. Kolibash1, Christine A. Chen1, Anbin Mu1, Suzanne B. Brown1, Richard P. Shannon1; 1Cardiovascular Medicine, University of Pennsylvania, Philadelphia, PA Background: Increasing evidence suggests that glycemic control is necessary but insufficient to alter cardiovascular complications in Type 2 DM. Glucagon like peptide1(GLP-1) is a novel anti-glycemic agent that possesses both insulinotropic and insulinomimetic actions and has been shown to be cardio-protective in both animals and humans. However, it is uncertain as to whether the protective effects are mediated by the native peptide, GLP-1(7-36) or its active metabolite, GLP-1(9-36). The goal of the present study was to determine the effects of GLP-1 (7-36) versus GLP1(9-36) on post-ischemic contractile dysfunction. Methods: Thirty C57BL/6 mice (age 8e12 weeks) were anesthetized and hearts were extracted, immediately suspended in a Langendorff preparation and perfused at constant flow (3.3 ml/min) with a standard KH buffer containing 11 mM glucose and 5 mM pyruvate. A pressure transducing balloon was placed in the LV and filled to generate 5 mmHg in LVEDP and hearts were paced at 480 mine1. After a 15 min stabilization period, GLP-1(7-36) [400 pM] or GLP-1 (9-36) [800 pM] were added to the perfusate for 10 min before low flow ischemia was induced for 20 min followed by 40 min of reperfusion. LV developed pressure (LVDev), LVdP/dt, and LVEDP were monitored and compared to buffer alone. Results: GLP-1(7-36) had a more rapid (Con:40 min; GLP-1(7-36): 10 min, p ! 0.01) and complete recovery of function (Con:54 6 12%; GLP1(7-36):78 6 5%, p ! 0.001). The effect was abolished by pre-treatment with the GLP-1 receptor antagonist, exendin(9-39) [30 nM]. Notably, GLP-1(9-36) was also associated with a similar rapid (Con: 40 min; GLP-1 (9-36): 10 min, p ! 0.01) and more complete recovery (Con: 41 6 8%; GLP-1 (9-36):67 6 6%, p ! 0.001). Conclusion: Both GLP-1(7-36) and GLP-1(9-36) mitigate post-ischemic contractile dysfunction in isolated mouse hearts. GLP-1 appears to act independent of the GLPe1 receptor.
Adoptive Transfer of Regulatory T Cells Protects Against CoxsackievirusInduced Myocarditis Yu Shi1, Masahiro Fukuoka1, Guohua Li1, Youan Liu1, Mayin Chen1, Michael Konvisor1, Peter P. Liu1; 1Department of Cardiology, Toronto General Hospital Research Institute, Toronto, ON, Canada
95
89
0.9
71
72
64
67%
67 96 68
64 95 68
6.2 0.9 68
65 54 68
66 47 68
65 40 68
66 41% 68
004
Drug Baseline Run-in
Ischemia
Reperfusion
10% Flow
10 min 20 min 40 min % recovery
96
94
4
79
80
75
78%
65 102 67
65 94 68
61 8 63
66 49 69
66 53 611
65 55 69
65 54% 612
LVDev mmHg LV Functional Recovery GLP-1(9-36) vs Control
Drug Baseline Run-in GLP-1(9-36) n56 SEM Control n 5 7 SEM
003
Coxsackievirus (CVB) infection is a significant cause of myocarditis and dilated cardiomyopathy (DCM). The virus imparts autoimmunity through antigenic mimicry, cryptic epitopes, and adjuvant effect. Therefore an approach designed to reduce the immunopathological effects without impairing the development of anti-viral immunity would be beneficial in treating this or other infection-associated autoimmune disorders. Regulatory T cells (Tregs), play an important role in the negative regulation of immune responses. In this study, we attempted to test protective effect by adoptively transferring naturally occurring Tregs isolated from spleen to mice prior to infection with CVB3. CFSE-labeled CD4 + CD25 + Tregs of splenocytes were adoptively i.v. injected once every two weeks for 3 times to mice starting age of 5 weeks. The mice were then i.p. challenged with CVB3 immediately after the last cell transfer. Control groups were injected with CD4 + T cells or PBS only. Adoptive transfer of Tregs significantly reduced mortality of infected mice compared to CD4 + T cells injection group (P 5 0.0136) and PBS injection group (P 5 0.0589). Tregs also significantly decreased virus titer and inflammatory scores in the heart. Tregs were not only detected in the recipient spleen but also present n the infected heart. Both plasma cytokine levels and local inflammation in the heart and pancreas were suppressed in Treg group. Splenocytes proliferated equally in Tregs, CD4 + T cell, and PBS group when stimulated with heat-inactivated virus; whereas, Tregs significantly reduced proliferation rate (P ! 0.05 vs CD4 + T cell and PBS groups) when stimulated with heart homogenate, suggesting Tregs increased threshold of immune response which could tolerate self antigen. Tregs transfer also upregulated the TGFb expression in the heart and prosurvival gene expression of phospho-AKT (pAKT) compared to control groups. Although expression of LCK and ERK1/2 in the heart was not apparently changed, Coxsackievirus-adenovirus receptor (C AR) was decreased in the Tregs group. Pancreas as the virus reservoir also showed moderately reduced virus titer and inflammation in Tregs group. Conclusions: Adoptive transfer of Tregs protected against CVB3-induced myocarditis by suppressing immune response to the heart tissue and reduced CAR expression and virus titers probably by decreasing the inflammatory milieu favorite for virus replication and through increased expression of p-AKT to promote survival.
LV Functional Recovery GLP-1(7-36) vs Control
GLP-1(7-36) n56 SEM Control n 5 7 SEM
cardiac myosin immunization, one group of rats was treated with disodium cromoglycate (DSCG), a mast cell stabilizer, at 24 mg/Kg until sacrifice (n 5 17). Another group of animals was treated with vehicle for the same period (n 5 13). Evaluations of cardiac hypertrophy, myocardial fibrosis, mast cell density and their degranulation were performed by histopathology, immunostaining and immunoblotting and also cardiac functions by echocardiography and hemodynamic analysis. Results: Increase in mast cell density, cardiac hypertrophy and myocardial fibrosis was observed in the hearts of vehicle-treated postmyocarditis rats. Elevated levels of stem cell factor and tumor necrosis factor-a were found in the hearts of vehicle-treated animals. Decline in myocardial function was observed in the vehicle-treated rats. Importantly, stabilization of mast cells by DSCG reversed all these effects. Conclusions: Our data suggest that cardiac mast cells can be possible therapeutic target in postmyocarditis heart failure.
Ischemia
Reperfusion
10% Flow
10 min 20 min 40 min % Recovery
LVDev mmHg
002 Mast Cells, the Allergic Responders, a Target of Heart Failure Therapy? Suresh S. Palaniyandi1, Kenichi Watanabe2, Daria Mochly-Rosen1; 1Department of Chemical and Systems Biology, Stanford University, Stanford, CA; 2Department of Clinical Pharmacology, Niigata University of Pharmacy and Applied Life Sciences, Niigata, Japan Introduction: Increased cardiac demand leads to an adaptive and compensatory remodeling. The presence of continual stress such as pressure overload, volume overload, cardiac injury and metabolic stress leads to a maladaptive cardiac remodeling and heart failure (HF). The different causes of cardiac maladaptive remodeling likely share common molecular, biochemical, and mechanical pathways. Cardiomyocytes, fibroblasts, inflammatory cells, coronary vasculature and extra cellular matrix participate in the remodeling events. Here we focus on mast cells in the remodeling process using a model of HF after cardiac injury, i.e., autoimmune myocarditis. Methods: Rats were immunized with pig cardiac myosin to develop experimental autoimmune myocarditis, which eventually resulted in HF. Twenty eight days after
Cardiac-Specific Overexpression of a Dominant Negative (DN) p67phox Mutant Shows Reduction in Mouse Heart Size Qiong Zhao Dalia Urboniene1, Magdalena Ornatowska1, R. John Solaro1, John W. Christman1, Lei Xiao; 1University of Illinois, Chicago, IL The role of NADPH oxidase (NOX) was recently suggested in cardiac hypertrophy. Overexpression of a DN mutant of p67phox, a cytosolic subunit of NOX, DN-p67 with a V204A point mutation completely inhibited NOX enzymatic function of superoxide generation in vitro. We recently found that overexpression of DN-p67 in adult rat cardiomyocytes attenuated a1-adrenoceptor-induced hypertrophy in vitro, thus hypothesized that NOX plays a critical role in cardiac hypertrophy and remodeling. In order to investigate the role of cardiac NOX/p67phox in vivo, we created a transgenic (Tg) mouse model with cardiac-specific overexpression of the above DN-p67 mutant along with a downstream independently-translated fluorescent tag gene EGFP led by an initiation sequence IRES. The DN-p67/IRES-EGFP sequence was then linked to a cardiac-specific a-MHC promoter generating a 9.1-Kb transgene containing a-MHC/DN-p67/IRES-EGFP, which was microinjected into the C57BL/6 mouse zygotes to generate Tg founder mice. Hearts from 1.5-, 3- and 6-month (M) old heterozygous Tg mice and their Non-Tg (NTg) littermates were harvested and compared. The heart weight /body weight (HW/BW) ratio in Tg group (n 5 23) was significantly (p ! 0.01) smaller (overall: 14%Y; 1.5-M: 10%Y; 3-M: 16%Y; 6-M: 12%Y) vs. NTg group (n 5 19). This result was confirmed by 2D echocardiography
S2 Journal of Cardiac Failure Vol. 14 No. 6S Suppl. 2008 measuring the left ventricular myocardial area (LVMA) determined by subtracting endocardial area from epicardial area in short axis view at the end diastole. The LVMA (mm2) in 3-M and 6-M mice was significantly (p ! 0.05) smaller in Tg (0.44 6 0.02, n 5 21) vs. NTg (0.50 6 0.02, n 5 13) with equal BW. LV internal dimensions and systolic function were preserved without difference in Tg vs. NTg. The LV wall thickness also appeared to be smaller in LV cross-sections in Tg vs. NTg by hematoxylin/eosin staining, and no change in fibrosis was detected in both groups by trichrome staining (n 5 4). Interestingly, the expression of NOX catalytic subunit gp91phox in Tg hearts was significantly decreased (3-foldY, n 5 5) vs. NTg by Western blot, whereas the cardiac expression of other NOX subunits p47phox and p22phox remained the same in both groups. In summary, we have generated a Tg mouse model with cardiac-specific overexpression of a DN p67phox, which shows significant reduction in myocardial mass/size and gp91phox expression with normal cardiac function and development. This study indicates that normal cardiac size and growth is dependent on the expression of a functional NOX/p67phox.
005 The Mechanism of Cardiac Failure in Experimental Myocardial Infarction Nicholas T. Befera1, Karen R. Wasiluk1, James M. Berry2, Sylvester Black1, Erik G. Strungs1, John E. Foker1; 1Cardiovascular Surgery, University of Minnesota, Minneapolis, MN; 2Pediatric Cardiology, University of Minnesota, Minneapolis, MN Introduction: Following myocardial infarction (MI), the uninvolved, remote myocardium (RM) may fail. The most general cause would seem to be either a failure of the contractile apparatus due to the increased load placed on the RM or a fall in myocardial energy levels because demand exceeds supply. To distinguish between the two, we infused ribose, the rate limiting component for AMP synthesis and hence ATP levels, but not itself a fuel, in a rat model of MI. The RM which fails would be structurally normal. Function was assessed by echocardiography and at the conclusion of the experiment, RM biopsies were taken. Hypotheses: (1) An energy supply/demand imbalance causes failure of the RM following an MI and (2) dysfunction can be at least partially prevented by increased AMP synthesis. Methods: Lewis rats (N 5 7 for each group) had central venous infusion pumps placed and 1 day later, the left anterior descending artery was ligated just distal to the circumflex artery, resulting in infarction of 35% of the LV. Ribose was infused for 2 weeks. Echo analysis was carried out at 0, 2, and 4 weeks. ATP was determined by NADP reduction. Results: In this model, MI produced LV dysfunction with thinning and dilation. Ribose reduced RM and LV dysfunction following MI as shown. Myocardial ATP levels were better preserved with ribose. Weeks 0 Ribose Control LVV s (mL) Ribose Control LVV d (mL) Ribose Control PTW d (cm) Ribose Control ATP concentration(umol/mg) Ribose Control EF (%)
60 65 0.90 .071 0.22 0.22 0.12 0.13
6 6 6 6 6 6 6 6
2 14 14 0.03 0.03 0.03 0.06 0.05 0.06
56 29 0.17 0.43 0.38 0.61 0.13 0.09
6 6 6 6 6 6 6 6
4 13* 3 0.06* 0.08 0.08* 0.11 0.03 0.06
46 26 0.31 0.53 0.57 0.71 0.10 0.08 12.6 9.02
6 6 6 6 6 6 6 6 6 6
8.0* 4.6 0.17* 0.19 0.24 0.25 0.01* 0.02 3.30 1.92
EF 5 ejection fraction; LVV 5 LV volume; s 5 systolic; d 5 diastolic; PWT 5 posterior wall thickness; *p ! 0.05.
Conclusions: 1) Ribose significantly reduced the RM dysfunction following experimental MI. 2) Ribose was continued for only 2 weeks and some functional deterioration occurred by 4 weeks. 3) These data suggest that the mechanism of failure is a decrease in energy levels, not a primary breakdown of the contractile apparatus.
HFSA
S1
Jay N. Cohn New Investigator Award: Basic Science 001 GLP-1(7-36) and GLP-1(9-36) Protect Murine Hearts from Post-Ischemic Contractile Dysfunction Christopher P. Kolibash1, Christine A. Chen1, Anbin Mu1, Suzanne B. Brown1, Richard P. Shannon1; 1Cardiovascular Medicine, University of Pennsylvania, Philadelphia, PA Background: Increasing evidence suggests that glycemic control is necessary but insufficient to alter cardiovascular complications in Type 2 DM. Glucagon like peptide1(GLP-1) is a novel anti-glycemic agent that possesses both insulinotropic and insulinomimetic actions and has been shown to be cardio-protective in both animals and humans. However, it is uncertain as to whether the protective effects are mediated by the native peptide, GLP-1(7-36) or its active metabolite, GLP-1(9-36). The goal of the present study was to determine the effects of GLP-1 (7-36) versus GLP1(9-36) on post-ischemic contractile dysfunction. Methods: Thirty C57BL/6 mice (age 8e12 weeks) were anesthetized and hearts were extracted, immediately suspended in a Langendorff preparation and perfused at constant flow (3.3 ml/min) with a standard KH buffer containing 11 mM glucose and 5 mM pyruvate. A pressure transducing balloon was placed in the LV and filled to generate 5 mmHg in LVEDP and hearts were paced at 480 mine1. After a 15 min stabilization period, GLP-1(7-36) [400 pM] or GLP-1 (9-36) [800 pM] were added to the perfusate for 10 min before low flow ischemia was induced for 20 min followed by 40 min of reperfusion. LV developed pressure (LVDev), LVdP/dt, and LVEDP were monitored and compared to buffer alone. Results: GLP-1(7-36) had a more rapid (Con:40 min; GLP-1(7-36): 10 min, p ! 0.01) and complete recovery of function (Con:54 6 12%; GLP1(7-36):78 6 5%, p ! 0.001). The effect was abolished by pre-treatment with the GLP-1 receptor antagonist, exendin(9-39) [30 nM]. Notably, GLP-1(9-36) was also associated with a similar rapid (Con: 40 min; GLP-1 (9-36): 10 min, p ! 0.01) and more complete recovery (Con: 41 6 8%; GLP-1 (9-36):67 6 6%, p ! 0.001). Conclusion: Both GLP-1(7-36) and GLP-1(9-36) mitigate post-ischemic contractile dysfunction in isolated mouse hearts. GLP-1 appears to act independent of the GLPe1 receptor.
Adoptive Transfer of Regulatory T Cells Protects Against CoxsackievirusInduced Myocarditis Yu Shi1, Masahiro Fukuoka1, Guohua Li1, Youan Liu1, Mayin Chen1, Michael Konvisor1, Peter P. Liu1; 1Department of Cardiology, Toronto General Hospital Research Institute, Toronto, ON, Canada
95
89
0.9
71
72
64
67%
67 96 68
64 95 68
6.2 0.9 68
65 54 68
66 47 68
65 40 68
66 41% 68
004
Drug Baseline Run-in
Ischemia
Reperfusion
10% Flow
10 min 20 min 40 min % recovery
96
94
4
79
80
75
78%
65 102 67
65 94 68
61 8 63
66 49 69
66 53 611
65 55 69
65 54% 612
LVDev mmHg LV Functional Recovery GLP-1(9-36) vs Control
Drug Baseline Run-in GLP-1(9-36) n56 SEM Control n 5 7 SEM
003
Coxsackievirus (CVB) infection is a significant cause of myocarditis and dilated cardiomyopathy (DCM). The virus imparts autoimmunity through antigenic mimicry, cryptic epitopes, and adjuvant effect. Therefore an approach designed to reduce the immunopathological effects without impairing the development of anti-viral immunity would be beneficial in treating this or other infection-associated autoimmune disorders. Regulatory T cells (Tregs), play an important role in the negative regulation of immune responses. In this study, we attempted to test protective effect by adoptively transferring naturally occurring Tregs isolated from spleen to mice prior to infection with CVB3. CFSE-labeled CD4 + CD25 + Tregs of splenocytes were adoptively i.v. injected once every two weeks for 3 times to mice starting age of 5 weeks. The mice were then i.p. challenged with CVB3 immediately after the last cell transfer. Control groups were injected with CD4 + T cells or PBS only. Adoptive transfer of Tregs significantly reduced mortality of infected mice compared to CD4 + T cells injection group (P 5 0.0136) and PBS injection group (P 5 0.0589). Tregs also significantly decreased virus titer and inflammatory scores in the heart. Tregs were not only detected in the recipient spleen but also present n the infected heart. Both plasma cytokine levels and local inflammation in the heart and pancreas were suppressed in Treg group. Splenocytes proliferated equally in Tregs, CD4 + T cell, and PBS group when stimulated with heat-inactivated virus; whereas, Tregs significantly reduced proliferation rate (P ! 0.05 vs CD4 + T cell and PBS groups) when stimulated with heart homogenate, suggesting Tregs increased threshold of immune response which could tolerate self antigen. Tregs transfer also upregulated the TGFb expression in the heart and prosurvival gene expression of phospho-AKT (pAKT) compared to control groups. Although expression of LCK and ERK1/2 in the heart was not apparently changed, Coxsackievirus-adenovirus receptor (C AR) was decreased in the Tregs group. Pancreas as the virus reservoir also showed moderately reduced virus titer and inflammation in Tregs group. Conclusions: Adoptive transfer of Tregs protected against CVB3-induced myocarditis by suppressing immune response to the heart tissue and reduced CAR expression and virus titers probably by decreasing the inflammatory milieu favorite for virus replication and through increased expression of p-AKT to promote survival.
LV Functional Recovery GLP-1(7-36) vs Control
GLP-1(7-36) n56 SEM Control n 5 7 SEM
cardiac myosin immunization, one group of rats was treated with disodium cromoglycate (DSCG), a mast cell stabilizer, at 24 mg/Kg until sacrifice (n 5 17). Another group of animals was treated with vehicle for the same period (n 5 13). Evaluations of cardiac hypertrophy, myocardial fibrosis, mast cell density and their degranulation were performed by histopathology, immunostaining and immunoblotting and also cardiac functions by echocardiography and hemodynamic analysis. Results: Increase in mast cell density, cardiac hypertrophy and myocardial fibrosis was observed in the hearts of vehicle-treated postmyocarditis rats. Elevated levels of stem cell factor and tumor necrosis factor-a were found in the hearts of vehicle-treated animals. Decline in myocardial function was observed in the vehicle-treated rats. Importantly, stabilization of mast cells by DSCG reversed all these effects. Conclusions: Our data suggest that cardiac mast cells can be possible therapeutic target in postmyocarditis heart failure.
Ischemia
Reperfusion
10% Flow
10 min 20 min 40 min % Recovery
LVDev mmHg
002 Mast Cells, the Allergic Responders, a Target of Heart Failure Therapy? Suresh S. Palaniyandi1, Kenichi Watanabe2, Daria Mochly-Rosen1; 1Department of Chemical and Systems Biology, Stanford University, Stanford, CA; 2Department of Clinical Pharmacology, Niigata University of Pharmacy and Applied Life Sciences, Niigata, Japan Introduction: Increased cardiac demand leads to an adaptive and compensatory remodeling. The presence of continual stress such as pressure overload, volume overload, cardiac injury and metabolic stress leads to a maladaptive cardiac remodeling and heart failure (HF). The different causes of cardiac maladaptive remodeling likely share common molecular, biochemical, and mechanical pathways. Cardiomyocytes, fibroblasts, inflammatory cells, coronary vasculature and extra cellular matrix participate in the remodeling events. Here we focus on mast cells in the remodeling process using a model of HF after cardiac injury, i.e., autoimmune myocarditis. Methods: Rats were immunized with pig cardiac myosin to develop experimental autoimmune myocarditis, which eventually resulted in HF. Twenty eight days after
Cardiac-Specific Overexpression of a Dominant Negative (DN) p67phox Mutant Shows Reduction in Mouse Heart Size Qiong Zhao Dalia Urboniene1, Magdalena Ornatowska1, R. John Solaro1, John W. Christman1, Lei Xiao; 1University of Illinois, Chicago, IL The role of NADPH oxidase (NOX) was recently suggested in cardiac hypertrophy. Overexpression of a DN mutant of p67phox, a cytosolic subunit of NOX, DN-p67 with a V204A point mutation completely inhibited NOX enzymatic function of superoxide generation in vitro. We recently found that overexpression of DN-p67 in adult rat cardiomyocytes attenuated a1-adrenoceptor-induced hypertrophy in vitro, thus hypothesized that NOX plays a critical role in cardiac hypertrophy and remodeling. In order to investigate the role of cardiac NOX/p67phox in vivo, we created a transgenic (Tg) mouse model with cardiac-specific overexpression of the above DN-p67 mutant along with a downstream independently-translated fluorescent tag gene EGFP led by an initiation sequence IRES. The DN-p67/IRES-EGFP sequence was then linked to a cardiac-specific a-MHC promoter generating a 9.1-Kb transgene containing a-MHC/DN-p67/IRES-EGFP, which was microinjected into the C57BL/6 mouse zygotes to generate Tg founder mice. Hearts from 1.5-, 3- and 6-month (M) old heterozygous Tg mice and their Non-Tg (NTg) littermates were harvested and compared. The heart weight /body weight (HW/BW) ratio in Tg group (n 5 23) was significantly (p ! 0.01) smaller (overall: 14%Y; 1.5-M: 10%Y; 3-M: 16%Y; 6-M: 12%Y) vs. NTg group (n 5 19). This result was confirmed by 2D echocardiography
S2 Journal of Cardiac Failure Vol. 14 No. 6S Suppl. 2008 measuring the left ventricular myocardial area (LVMA) determined by subtracting endocardial area from epicardial area in short axis view at the end diastole. The LVMA (mm2) in 3-M and 6-M mice was significantly (p ! 0.05) smaller in Tg (0.44 6 0.02, n 5 21) vs. NTg (0.50 6 0.02, n 5 13) with equal BW. LV internal dimensions and systolic function were preserved without difference in Tg vs. NTg. The LV wall thickness also appeared to be smaller in LV cross-sections in Tg vs. NTg by hematoxylin/eosin staining, and no change in fibrosis was detected in both groups by trichrome staining (n 5 4). Interestingly, the expression of NOX catalytic subunit gp91phox in Tg hearts was significantly decreased (3-foldY, n 5 5) vs. NTg by Western blot, whereas the cardiac expression of other NOX subunits p47phox and p22phox remained the same in both groups. In summary, we have generated a Tg mouse model with cardiac-specific overexpression of a DN p67phox, which shows significant reduction in myocardial mass/size and gp91phox expression with normal cardiac function and development. This study indicates that normal cardiac size and growth is dependent on the expression of a functional NOX/p67phox.
005 The Mechanism of Cardiac Failure in Experimental Myocardial Infarction Nicholas T. Befera1, Karen R. Wasiluk1, James M. Berry2, Sylvester Black1, Erik G. Strungs1, John E. Foker1; 1Cardiovascular Surgery, University of Minnesota, Minneapolis, MN; 2Pediatric Cardiology, University of Minnesota, Minneapolis, MN Introduction: Following myocardial infarction (MI), the uninvolved, remote myocardium (RM) may fail. The most general cause would seem to be either a failure of the contractile apparatus due to the increased load placed on the RM or a fall in myocardial energy levels because demand exceeds supply. To distinguish between the two, we infused ribose, the rate limiting component for AMP synthesis and hence ATP levels, but not itself a fuel, in a rat model of MI. The RM which fails would be structurally normal. Function was assessed by echocardiography and at the conclusion of the experiment, RM biopsies were taken. Hypotheses: (1) An energy supply/demand imbalance causes failure of the RM following an MI and (2) dysfunction can be at least partially prevented by increased AMP synthesis. Methods: Lewis rats (N 5 7 for each group) had central venous infusion pumps placed and 1 day later, the left anterior descending artery was ligated just distal to the circumflex artery, resulting in infarction of 35% of the LV. Ribose was infused for 2 weeks. Echo analysis was carried out at 0, 2, and 4 weeks. ATP was determined by NADP reduction. Results: In this model, MI produced LV dysfunction with thinning and dilation. Ribose reduced RM and LV dysfunction following MI as shown. Myocardial ATP levels were better preserved with ribose. Weeks 0 Ribose Control LVV s (mL) Ribose Control LVV d (mL) Ribose Control PTW d (cm) Ribose Control ATP concentration(umol/mg) Ribose Control EF (%)
60 65 0.90 .071 0.22 0.22 0.12 0.13
6 6 6 6 6 6 6 6
2 14 14 0.03 0.03 0.03 0.06 0.05 0.06
56 29 0.17 0.43 0.38 0.61 0.13 0.09
6 6 6 6 6 6 6 6
4 13* 3 0.06* 0.08 0.08* 0.11 0.03 0.06
46 26 0.31 0.53 0.57 0.71 0.10 0.08 12.6 9.02
6 6 6 6 6 6 6 6 6 6
8.0* 4.6 0.17* 0.19 0.24 0.25 0.01* 0.02 3.30 1.92
EF 5 ejection fraction; LVV 5 LV volume; s 5 systolic; d 5 diastolic; PWT 5 posterior wall thickness; *p ! 0.05.
Conclusions: 1) Ribose significantly reduced the RM dysfunction following experimental MI. 2) Ribose was continued for only 2 weeks and some functional deterioration occurred by 4 weeks. 3) These data suggest that the mechanism of failure is a decrease in energy levels, not a primary breakdown of the contractile apparatus.