This study aimed to explore the molecular mechanism in tumor invasion and metastasis. The expression of matrix metalloproteinase 2, 9 (MMP 2, MMP 9), tissue inhibitor 1 of matrix metalloproteinase (TIMP 1), c...This study aimed to explore the molecular mechanism in tumor invasion and metastasis. The expression of matrix metalloproteinase 2, 9 (MMP 2, MMP 9), tissue inhibitor 1 of matrix metalloproteinase (TIMP 1), cell adhesion molecule 44 variant 6 (CD44v6), HER2/neu and p53 was investigated in 154 patients with head and neck squamous cell carcinoma (SCC) by ABC and ImmunoMax immunohistochemical method. Their clinical relevance and correlation were analysed. The expression of MMP 2, MMP 9, TIMP 1, CD44v6, HER2/neu and p53 was found in cancer cells in 87.01%, 85.71%, 68.18%, 98.05%, 55.19% and 50.65% cases respectively. Linear regression and correlation analysis revealed that there was close positive relationship ( P <0.05) between the expression of MMP 2 and MMP 9, TIMP 1 and CD44v6, HER2/neu and MMP 9, MMP 2 and p53. Up regulation of MMP 2 was accompanied by advanced T stage ( P <0.01) . There was also a trend of MMP 2 expression being related with tumor metastasis. Increased expression of HER2/neu was found in patients with tumor recurrence( P <0.05). The expression of TIMP 1 was higher in laryngeal cancer than that in pharyngeal cancer, and higher in keratinizing and non keratinizing SCC than that in basaloid SCC( P <0.05). These findings suggested that MMP 2 and MMP 9, HER2/neu and MMP 9, MMP 2 and p53 had a coordinate function in aggression of tumor; that MMP 2 had a more important function than MMP 9 in tumor invasion and metastasis; and that HER2/neu might serve as a biomarker for poor prognosis in HNSCC.展开更多
In this study, we determined the expression levels of matrix metalloproteinase-2 and -9 and matrix metalloproteinase tissue inhibitor-1 and -2 in brain tissues and blood plasma of patients undergoing surgery for cereb...In this study, we determined the expression levels of matrix metalloproteinase-2 and -9 and matrix metalloproteinase tissue inhibitor-1 and -2 in brain tissues and blood plasma of patients undergoing surgery for cerebellar arteriovenous malformations or primary epilepsy (control group). Immunohistochemistry and enzyme-linked immunosorbent assay revealed that the expression of matrix metalloproteinase-9 and matrix metalloproteinase tissue inhibitor-1 was significantly higher in patients with cerebellar arteriovenous malformations than in patients with primary epilepsy. The ratio of matrix metalloproteinase-9 to matrix metalloproteinase tissue inhibitor-1 was significantly higher in patients with hemorrhagic cerebellar arteriovenous malformations compared with those with non-hemorrhagic malformations. Matrix metalloproteinase-2 and matrix metalloproteinase tissue inhibitor-2 levels were not significantly changed. These findings indicate that an imbalance of matrix metalloproteinase-9 and matrix metalloproteinase tissue inhibitor-I, resulting in a relative overabundance of matrix metalloproteinase-9, might be the underlying mechanism of hemorrhage of cerebellar arteriovenous malformations.展开更多
Objective: To elucidate the relation between human tissue factor pathwayinhibitor-2 (TFPI-2) expression and ovarian tumor migration and invasion. Methods: Human TFPI-2expression vector pBos-Cite-neo/TFPI-2 was transfe...Objective: To elucidate the relation between human tissue factor pathwayinhibitor-2 (TFPI-2) expression and ovarian tumor migration and invasion. Methods: Human TFPI-2expression vector pBos-Cite-neo/TFPI-2 was transfected into ovarian tumor cells line A2780- Afterthe transfected cells were selected by G418, transfected and nontransfected cells were screened forTFPI-2 mRNA and protein by reverse transcription-polymerase chain reaction and Western blotanalysis, respectively. The number of transfected or nontransfected cells passing through membraneof Boyden chamber was counted as the basis assessing tumor cells migratory and invasive behaviors.Results: Expression of mRNA and protein of TFPI-2 was detectable in transfected cells. In invasionassay, the number of TFPI-2-expressing cells to traverse a Matrigel-coated membrane was obviouslydecreased compared with that of nonexpressing cells (59.3±6.5 vs 109.7±5.5, P 【 0.01); While inmigration assay, no significant difference through a noncoated membrane was observed amongtransfected and nontransfected cells (114.7±8.6 vs 127.3±7.1, P 】 0.05). Conclusion: Expression ofTFPI-2 may strongly inhibit the invasive ability of ovarian tumor cells in vitro, but has no effecton the migratory ability which provides an experimental basis for genotherapy of human ovariantumor.展开更多
The action mechanism of matrix metalloproteinases-2 (MMP-2) and tissue inhibitor of metalloproteinases-2 (TIMP-2) in the genesis, development and degeneration of haemangioma was investigated by detecting their exp...The action mechanism of matrix metalloproteinases-2 (MMP-2) and tissue inhibitor of metalloproteinases-2 (TIMP-2) in the genesis, development and degeneration of haemangioma was investigated by detecting their expression in the tissue of haemangioma in different phases by using the immunohistochemistry. Fifty paraffin-embedded specimens of skin capillary haemangioma were collected, which were documented in the Department of Pathology, Renmin Hospital of Wuhan University from 2000 to 2006. All samples were stained by regular HE method, and proliferative cell nuclear antigen (PCNA) was tested by immunohistochemical S-P method. The samples were classified according to the Mulliken criteria and the expression pattern of PCNA. Immunohistochemical S-P method was ap- plied to detect the expression of MMP-2 and TIMP-2 in proliferative and degenerative phases of cutaneous capillary haemangioma, and in normal skin tissues. In combination with the detection of the expression of factor Ⅷ-related antigen, it was verified that in haemangioma tissues, the cells expressing MMP-2 and TIMP-2 were vascular endothelial cells. The MMP-2 and TIMP-2 expression was quantitatively analyzed by image analysis system (HPIAS-1000), and one-way ANOVA(107) and SNK(q) test were done to analyze average absorbance (A) and positive area rate of immunohistochemically positive particles by using SPSS11.5. The results showed: (1) Among 50 samples of haemangioma, there were 26 proliferative haemangiomas, and 24 degenerative haemangiomas, respectively; (2) The expression of MMP-2 was weak in normal vascular endothelial cells, cytoplasm of connective tissues and extracellular matrix around blood vessels. The expression of MMP-2 in proliferative group was significantly higher than in degenerative group and control group (normal skin) (P〈0.05), but there was no statistically significant difference between the latter two groups; (3) TIMP-2 was highly expressed in normal tissues, degenerative vascular endothelial cells, cytoplasm of connective tissues and extracellular matrix around blood vessels. The expression level of TIMP-2 in proliferative phase was significantly lower than in degenerative phase (P〈0.05), and the expression of TIMP-2 in proliferative phase was significantly different from that in degenerative phase and normal tissues (P〈0.05). It was concluded that in proliferative phase of haemangioma, MMP-2 may promote over-proliferation of endothelial cells of haemangioma, and in degenerative phase, TIMP-2 can inhibit the proliferation of endothelial cells of haemangioma. The two substances play important roles in the genesis, development and degeneration of haemangiomas.展开更多
In this study, genes of two distinct tissue inhibitors of metalloproteinases-2 (TIMP-2) from Japanese puffer fishFugu rubripes, Fugu TIMP-2a and TIMP-2b, were cloned. The open reading frames of Fugu TIMP-2a and TIMP-2...In this study, genes of two distinct tissue inhibitors of metalloproteinases-2 (TIMP-2) from Japanese puffer fishFugu rubripes, Fugu TIMP-2a and TIMP-2b, were cloned. The open reading frames of Fugu TIMP-2a and TIMP-2b cDNAsare composed of 660 and 657 nucleotides and 220 and 219 amino acids, respectively. Both Fugu TIMP-2s contain 12 cysteineresidues, which might form six disulfide bonds as in other animals’ TIMP-2s. Reverse-transcribed polymerase chain reactionanalysis showed the mRNAs of Fugu TIMP-2a and TIMP-2b to be expressed in some tissues examined with different expres-sion patterns. These findings suggest that the two distinct Fugu TIMP-2s might perform different functions in Fugu tissues.展开更多
目的 探讨急性肺栓塞(APE)患者血浆金属蛋白酶组织抑制因子-1(TIMP-1)、血管内皮生长因子(VEGF)及潜在转化生长因子结合蛋白2(LTBP-2)水平与危险分层和死亡的关系。方法 选取2022年1月~2024年1月海口市第三人民医院收治的APE患者110例...目的 探讨急性肺栓塞(APE)患者血浆金属蛋白酶组织抑制因子-1(TIMP-1)、血管内皮生长因子(VEGF)及潜在转化生长因子结合蛋白2(LTBP-2)水平与危险分层和死亡的关系。方法 选取2022年1月~2024年1月海口市第三人民医院收治的APE患者110例进行危险分层,分为低危组(n=28)、中危组(n=43)和高危组(n=39);根据APE患者发生死亡情况分为存活组(n=79)和死亡组(n=31)。采用酶联免疫吸附法(ELISA)测定血浆TIMP-1,VEGF及LTBP-2水平;应用多元Logistic回归分析影响APE患者死亡的危险因素,绘制ROC曲线分析血浆TIMP-1,VEGF及LTBP-2水平预测APE患者死亡的价值;采用Pearson相关分析血浆TIMP-1,VEGF及LTBP-2水平与APE患者临床指标的相关性。结果 死亡组心率、B型脑钠肽(BNP)、D-二聚体、TIMP-1(207.15±62.84pg/ml vs 152.48±41.62pg/ml),VEGF(726.35±190.46pg/ml vs 419.27±115.28pg/ml)及LTBP-2(29.17±6.38ng/ml vs 13.26±3.70ng/ml)水平均明显高于存活组,差异具有统计学意义(t=5.386~21.194,均P<0.05)。高危组和中危组血浆TIMP-1(204.15±60.17 pg/ml,178.18±51.30pg/ml vs 148.20±34.80pg/ml),VEGF(720.83±204.18pg/ml,580.16±158.37pg/ml vs 412.15±109.26pg/ml)及LTBP-2(28.40±6.41ng/ml,21.37±5.26ng/ml vs 12.84±3.12ng/ml)水平均明显高于低危组(t=8.417~19.850),且高危组高于中危组(t=7.964,9.381,11.470),差异具有统计学意义(均P<0.05)。多元Logistic回归分析显示,血浆BNP,D-二聚体,TIMP-1,VEGF及LTBP-2水平升高是影响APE患者死亡的危险因素(均P<0.05)。ROC曲线分析显示,TIMP-1,VEGF及LTBP-2三项联合预测APE患者死亡的AUC(95%CI)最大[0.938(0.881~0.997)],其准确度为88.2%。Pearson相关分析显示,APE患者血浆TIMP-1,VEGF及LTBP-2水平与BNP及D-二聚体均呈正相关(r=0.416~0.753,均P<0.05)。结论 血浆TIMP-1,VEGF及LTBP-2水平升高与APE高危和死亡有关,三项联合对APE患者死亡具有较好的预测价值。展开更多
Background The cholesterol-lowering statin drugs have some non-lipid-lowering effects, such as inhibiting myocardial remodeling. However, the underlying mechanism is still unclear. Methods The left anterior descending...Background The cholesterol-lowering statin drugs have some non-lipid-lowering effects, such as inhibiting myocardial remodeling. However, the underlying mechanism is still unclear. Methods The left anterior descending coronary artery was ligated to establish a rat model of heart failure, and the rats were divided into a sham operation (SO) group, myocardial infarction model (MI) group, and MI-atorvastatin group. Changes in hemodynamic parameters were recorded after the final drug administration. Histological diagnosis was made by reviewing hematoxylin and eosin (HE) stained tissue. Real-time quantitative polymerase chain reaction (PCR) was performed to determine the expressions of type I and type III collagen, matrix metalloproteinase-2 (MMP-2), and tissue matrix metalloproteinase inhibitor-2 (TIMP-2). Further, primary rat cardiac fibroblasts were cultured and the MTT assay was performed to determine the effect of atorvastatin on cardiac fibroblast proliferation. Results The model of heart failure was established and the results of HE staining and Masson's trichrome staining revealed that the rats in the heart failure group showed obvious hyperplasia of fibrotic tissue, which was significantly reduced in the atorvastatin group. Real-time quantitative PCR showed that the MI group showed a significantly increased expression of type I and type III coltagen, MMP-2, and TIMP-2, but a significantly reduced MMP-2/T'IMP- 2 ratio. Compared with the MI group, the atorvastatin group showed significantly reduced expression of type I and III collagen, unchanged expression of MMP-2, significantly reduced expression of TIMP-2, and an increased MMP-2/ TIMP-2 ratio. We further found that atorvastatin significantly inhibited the Ang II-induced fibroblast proliferation and the expression of type I and type III collagen in cardiac fibroblasts while increasing the MMP-2/TIMP-2 ratio. Conclusions These data suggest that atorvastatin can inhibit cardiac fibroblast proliferation and enhance collagen degradation by increasing the MMP-2/TIMP-2 ratio, thereby inhibiting the formation of myocardial fibrosis in rats with heart failure after myocardial infarction.展开更多
文摘This study aimed to explore the molecular mechanism in tumor invasion and metastasis. The expression of matrix metalloproteinase 2, 9 (MMP 2, MMP 9), tissue inhibitor 1 of matrix metalloproteinase (TIMP 1), cell adhesion molecule 44 variant 6 (CD44v6), HER2/neu and p53 was investigated in 154 patients with head and neck squamous cell carcinoma (SCC) by ABC and ImmunoMax immunohistochemical method. Their clinical relevance and correlation were analysed. The expression of MMP 2, MMP 9, TIMP 1, CD44v6, HER2/neu and p53 was found in cancer cells in 87.01%, 85.71%, 68.18%, 98.05%, 55.19% and 50.65% cases respectively. Linear regression and correlation analysis revealed that there was close positive relationship ( P <0.05) between the expression of MMP 2 and MMP 9, TIMP 1 and CD44v6, HER2/neu and MMP 9, MMP 2 and p53. Up regulation of MMP 2 was accompanied by advanced T stage ( P <0.01) . There was also a trend of MMP 2 expression being related with tumor metastasis. Increased expression of HER2/neu was found in patients with tumor recurrence( P <0.05). The expression of TIMP 1 was higher in laryngeal cancer than that in pharyngeal cancer, and higher in keratinizing and non keratinizing SCC than that in basaloid SCC( P <0.05). These findings suggested that MMP 2 and MMP 9, HER2/neu and MMP 9, MMP 2 and p53 had a coordinate function in aggression of tumor; that MMP 2 had a more important function than MMP 9 in tumor invasion and metastasis; and that HER2/neu might serve as a biomarker for poor prognosis in HNSCC.
文摘In this study, we determined the expression levels of matrix metalloproteinase-2 and -9 and matrix metalloproteinase tissue inhibitor-1 and -2 in brain tissues and blood plasma of patients undergoing surgery for cerebellar arteriovenous malformations or primary epilepsy (control group). Immunohistochemistry and enzyme-linked immunosorbent assay revealed that the expression of matrix metalloproteinase-9 and matrix metalloproteinase tissue inhibitor-1 was significantly higher in patients with cerebellar arteriovenous malformations than in patients with primary epilepsy. The ratio of matrix metalloproteinase-9 to matrix metalloproteinase tissue inhibitor-1 was significantly higher in patients with hemorrhagic cerebellar arteriovenous malformations compared with those with non-hemorrhagic malformations. Matrix metalloproteinase-2 and matrix metalloproteinase tissue inhibitor-2 levels were not significantly changed. These findings indicate that an imbalance of matrix metalloproteinase-9 and matrix metalloproteinase tissue inhibitor-I, resulting in a relative overabundance of matrix metalloproteinase-9, might be the underlying mechanism of hemorrhage of cerebellar arteriovenous malformations.
文摘Objective: To elucidate the relation between human tissue factor pathwayinhibitor-2 (TFPI-2) expression and ovarian tumor migration and invasion. Methods: Human TFPI-2expression vector pBos-Cite-neo/TFPI-2 was transfected into ovarian tumor cells line A2780- Afterthe transfected cells were selected by G418, transfected and nontransfected cells were screened forTFPI-2 mRNA and protein by reverse transcription-polymerase chain reaction and Western blotanalysis, respectively. The number of transfected or nontransfected cells passing through membraneof Boyden chamber was counted as the basis assessing tumor cells migratory and invasive behaviors.Results: Expression of mRNA and protein of TFPI-2 was detectable in transfected cells. In invasionassay, the number of TFPI-2-expressing cells to traverse a Matrigel-coated membrane was obviouslydecreased compared with that of nonexpressing cells (59.3±6.5 vs 109.7±5.5, P 【 0.01); While inmigration assay, no significant difference through a noncoated membrane was observed amongtransfected and nontransfected cells (114.7±8.6 vs 127.3±7.1, P 】 0.05). Conclusion: Expression ofTFPI-2 may strongly inhibit the invasive ability of ovarian tumor cells in vitro, but has no effecton the migratory ability which provides an experimental basis for genotherapy of human ovariantumor.
基金supported by a grant from the National Natural Sciences Foundation of China (No.30872688)
文摘The action mechanism of matrix metalloproteinases-2 (MMP-2) and tissue inhibitor of metalloproteinases-2 (TIMP-2) in the genesis, development and degeneration of haemangioma was investigated by detecting their expression in the tissue of haemangioma in different phases by using the immunohistochemistry. Fifty paraffin-embedded specimens of skin capillary haemangioma were collected, which were documented in the Department of Pathology, Renmin Hospital of Wuhan University from 2000 to 2006. All samples were stained by regular HE method, and proliferative cell nuclear antigen (PCNA) was tested by immunohistochemical S-P method. The samples were classified according to the Mulliken criteria and the expression pattern of PCNA. Immunohistochemical S-P method was ap- plied to detect the expression of MMP-2 and TIMP-2 in proliferative and degenerative phases of cutaneous capillary haemangioma, and in normal skin tissues. In combination with the detection of the expression of factor Ⅷ-related antigen, it was verified that in haemangioma tissues, the cells expressing MMP-2 and TIMP-2 were vascular endothelial cells. The MMP-2 and TIMP-2 expression was quantitatively analyzed by image analysis system (HPIAS-1000), and one-way ANOVA(107) and SNK(q) test were done to analyze average absorbance (A) and positive area rate of immunohistochemically positive particles by using SPSS11.5. The results showed: (1) Among 50 samples of haemangioma, there were 26 proliferative haemangiomas, and 24 degenerative haemangiomas, respectively; (2) The expression of MMP-2 was weak in normal vascular endothelial cells, cytoplasm of connective tissues and extracellular matrix around blood vessels. The expression of MMP-2 in proliferative group was significantly higher than in degenerative group and control group (normal skin) (P〈0.05), but there was no statistically significant difference between the latter two groups; (3) TIMP-2 was highly expressed in normal tissues, degenerative vascular endothelial cells, cytoplasm of connective tissues and extracellular matrix around blood vessels. The expression level of TIMP-2 in proliferative phase was significantly lower than in degenerative phase (P〈0.05), and the expression of TIMP-2 in proliferative phase was significantly different from that in degenerative phase and normal tissues (P〈0.05). It was concluded that in proliferative phase of haemangioma, MMP-2 may promote over-proliferation of endothelial cells of haemangioma, and in degenerative phase, TIMP-2 can inhibit the proliferation of endothelial cells of haemangioma. The two substances play important roles in the genesis, development and degeneration of haemangiomas.
基金partially supported by a grant from the Ministry of Education,Culture,Sports,Science and Technology of Japan.
文摘In this study, genes of two distinct tissue inhibitors of metalloproteinases-2 (TIMP-2) from Japanese puffer fishFugu rubripes, Fugu TIMP-2a and TIMP-2b, were cloned. The open reading frames of Fugu TIMP-2a and TIMP-2b cDNAsare composed of 660 and 657 nucleotides and 220 and 219 amino acids, respectively. Both Fugu TIMP-2s contain 12 cysteineresidues, which might form six disulfide bonds as in other animals’ TIMP-2s. Reverse-transcribed polymerase chain reactionanalysis showed the mRNAs of Fugu TIMP-2a and TIMP-2b to be expressed in some tissues examined with different expres-sion patterns. These findings suggest that the two distinct Fugu TIMP-2s might perform different functions in Fugu tissues.
文摘目的 探讨急性肺栓塞(APE)患者血浆金属蛋白酶组织抑制因子-1(TIMP-1)、血管内皮生长因子(VEGF)及潜在转化生长因子结合蛋白2(LTBP-2)水平与危险分层和死亡的关系。方法 选取2022年1月~2024年1月海口市第三人民医院收治的APE患者110例进行危险分层,分为低危组(n=28)、中危组(n=43)和高危组(n=39);根据APE患者发生死亡情况分为存活组(n=79)和死亡组(n=31)。采用酶联免疫吸附法(ELISA)测定血浆TIMP-1,VEGF及LTBP-2水平;应用多元Logistic回归分析影响APE患者死亡的危险因素,绘制ROC曲线分析血浆TIMP-1,VEGF及LTBP-2水平预测APE患者死亡的价值;采用Pearson相关分析血浆TIMP-1,VEGF及LTBP-2水平与APE患者临床指标的相关性。结果 死亡组心率、B型脑钠肽(BNP)、D-二聚体、TIMP-1(207.15±62.84pg/ml vs 152.48±41.62pg/ml),VEGF(726.35±190.46pg/ml vs 419.27±115.28pg/ml)及LTBP-2(29.17±6.38ng/ml vs 13.26±3.70ng/ml)水平均明显高于存活组,差异具有统计学意义(t=5.386~21.194,均P<0.05)。高危组和中危组血浆TIMP-1(204.15±60.17 pg/ml,178.18±51.30pg/ml vs 148.20±34.80pg/ml),VEGF(720.83±204.18pg/ml,580.16±158.37pg/ml vs 412.15±109.26pg/ml)及LTBP-2(28.40±6.41ng/ml,21.37±5.26ng/ml vs 12.84±3.12ng/ml)水平均明显高于低危组(t=8.417~19.850),且高危组高于中危组(t=7.964,9.381,11.470),差异具有统计学意义(均P<0.05)。多元Logistic回归分析显示,血浆BNP,D-二聚体,TIMP-1,VEGF及LTBP-2水平升高是影响APE患者死亡的危险因素(均P<0.05)。ROC曲线分析显示,TIMP-1,VEGF及LTBP-2三项联合预测APE患者死亡的AUC(95%CI)最大[0.938(0.881~0.997)],其准确度为88.2%。Pearson相关分析显示,APE患者血浆TIMP-1,VEGF及LTBP-2水平与BNP及D-二聚体均呈正相关(r=0.416~0.753,均P<0.05)。结论 血浆TIMP-1,VEGF及LTBP-2水平升高与APE高危和死亡有关,三项联合对APE患者死亡具有较好的预测价值。
文摘Background The cholesterol-lowering statin drugs have some non-lipid-lowering effects, such as inhibiting myocardial remodeling. However, the underlying mechanism is still unclear. Methods The left anterior descending coronary artery was ligated to establish a rat model of heart failure, and the rats were divided into a sham operation (SO) group, myocardial infarction model (MI) group, and MI-atorvastatin group. Changes in hemodynamic parameters were recorded after the final drug administration. Histological diagnosis was made by reviewing hematoxylin and eosin (HE) stained tissue. Real-time quantitative polymerase chain reaction (PCR) was performed to determine the expressions of type I and type III collagen, matrix metalloproteinase-2 (MMP-2), and tissue matrix metalloproteinase inhibitor-2 (TIMP-2). Further, primary rat cardiac fibroblasts were cultured and the MTT assay was performed to determine the effect of atorvastatin on cardiac fibroblast proliferation. Results The model of heart failure was established and the results of HE staining and Masson's trichrome staining revealed that the rats in the heart failure group showed obvious hyperplasia of fibrotic tissue, which was significantly reduced in the atorvastatin group. Real-time quantitative PCR showed that the MI group showed a significantly increased expression of type I and type III coltagen, MMP-2, and TIMP-2, but a significantly reduced MMP-2/T'IMP- 2 ratio. Compared with the MI group, the atorvastatin group showed significantly reduced expression of type I and III collagen, unchanged expression of MMP-2, significantly reduced expression of TIMP-2, and an increased MMP-2/ TIMP-2 ratio. We further found that atorvastatin significantly inhibited the Ang II-induced fibroblast proliferation and the expression of type I and type III collagen in cardiac fibroblasts while increasing the MMP-2/TIMP-2 ratio. Conclusions These data suggest that atorvastatin can inhibit cardiac fibroblast proliferation and enhance collagen degradation by increasing the MMP-2/TIMP-2 ratio, thereby inhibiting the formation of myocardial fibrosis in rats with heart failure after myocardial infarction.