Medroxyprogesterone acetate inhibits the cardioprotective effect of estrogen in experimental ischemia-reperfusion injury.

OBJECTIVE: Results from recent clinical trials of estrogen and progestogen therapy (EPT) suggest that some progestogens may interfere with the cardiovascular benefits of estrogen (E). The aim of this study was to investigate whether medroxyprogesterone acetate (MPA) modifies the protective effect of E in experimental ischemia-reperfusion (IR) injury in vivo and in vitro in the rat. DESIGN: Ovariectomized female Wistar rats (250-280 g, n = 61) received E, MPA, E and MPA, or placebo subcutaneously. Fourteen days later, hearts were isolated and perfused with Krebs Henseleit for in vitro experiments or left in situ for in vivo experiments. In both cases, the left coronary artery was occluded for 45 minutes, followed by 2 hours of reperfusion. RESULTS: In vivo E significantly reduced the necrotic zone of reperfused hearts (21.8% +/- 1.7% of area at risk) compared with placebo (42.8% +/- 4.8% area at risk; P < 0.05). This protection was reversed by co-administration of MPA with E (necrotic zone 38.2% +/- 6.1% area at risk). The influence of E on neutrophil infiltration was demonstrated by its ability to reduce myocardial myeloperoxidase activity (0.2 +/- 0.1 U/g tissue) relative to placebo (1.3 +/- 0.5 U/g tissue; P < 0.05). Myocardial myeloperoxidase activity was significantly increased to 1.1 +/- 0.3 U/g tissue in rats receiving E and MPA. However, MPA also reversed the protective effect of E in neutrophil-free buffer-perfused hearts, suggesting that additional mechanisms are involved. CONCLUSION: In this study, we showed that the administration of MPA can inhibit the effects of E that lead to protection of the myocardium from reperfusion injury and that this involves both neutrophil-dependent and neutrophil-independent mechanisms.

Targeting C-reactive protein for the treatment of cardiovascular disease.

Complement-mediated inflammation exacerbates the tissue injury of ischaemic necrosis in heart attacks and strokes, the most common causes of death in developed countries. Large infarct size increases immediate morbidity and mortality and, in survivors of the acute event, larger non-functional scars adversely affect long-term prognosis. There is thus an important unmet medical need for new cardioprotective and neuroprotective treatments. We have previously shown that human C-reactive protein (CRP), the classical acute-phase protein that binds to ligands exposed in damaged tissue and then activates complement, increases myocardial and cerebral infarct size in rats subjected to coronary or cerebral artery ligation, respectively. Rat CRP does not activate rat complement, whereas human CRP activates both rat and human complement. Administration of human CRP to rats is thus an excellent model for the actions of endogenous human CRP. Here we report the design, synthesis and efficacy of 1,6-bis(phosphocholine)-hexane as a specific small-molecule inhibitor of CRP. Five molecules of this palindromic compound are bound by two pentameric CRP molecules, crosslinking and occluding the ligand-binding B-face of CRP and blocking its functions. Administration of 1,6-bis(phosphocholine)-hexane to rats undergoing acute myocardial infarction abrogated the increase in infarct size and cardiac dysfunction produced by injection of human CRP. Therapeutic inhibition of CRP is thus a promising new approach to cardioprotection in acute myocardial infarction, and may also provide neuroprotection in stroke. Potential wider applications include other inflammatory, infective and tissue-damaging conditions characterized by increased CRP production, in which binding of CRP to exposed ligands in damaged cells may lead to complement-mediated exacerbation of tissue injury.

Preventing local regeneration of glucocorticoids by 11beta-hydroxysteroid dehydrogenase type 1 enhances angiogenesis.

Angiogenesis restores blood flow to healing tissues, a process that is inhibited by high doses of glucocorticoids. However, the role of endogenous glucocorticoids and the potential for antiglucocorticoid therapy to enhance angiogenesis is unknown. Using in vitro and in vivo models of angiogenesis in mice, we examined effects of (i) endogenous glucocorticoids, (ii) blocking endogenous glucocorticoid action with the glucocorticoid receptor antagonist RU38486, and (iii) abolishing local regeneration of glucocorticoids by the enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1). Glucocorticoids, administered at physiological concentrations, inhibited angiogenesis in an in vitro aortic ring model and in vivo in polyurethane sponges implanted s.c. RU38486-enhanced angiogenesis in s.c. sponges, in healing surgical wounds, and in the myocardium of mice 7 days after myocardial infarction induced by coronary artery ligation. 11betaHSD1 knockout mice showed enhanced angiogenesis in vitro and in vivo within sponges, wounds, and infarcted myocardium. Endogenous glucocorticoids, including those generated locally by 11betaHSD1, exert tonic inhibition of angiogenesis. Inhibition of 11betaHSD1 in liver and adipose has been advocated to reduce cardiovascular risk in the metabolic syndrome: these data suggest that 11betaHSD1 inhibition offers a previously uncharacterized therapeutic approach to improve healing of ischemic or injured tissue.

Influence of scanning frequency and ultrasonic contrast agent on reproducibility of left ventricular measurements in the mouse.

BACKGROUND: Mice are now widely used as models of cardiovascular disease. Their small size and fast heart rates are technically challenging to echocardiography. This study examined the influence of different scanning frequencies and ultrasonic contrast agent (UCA) on the accuracy and reproducibility of measurements of left ventricular (LV) structure and function. METHODS: Normal mouse hearts (C57BL6) were imaged at 3 different scanning frequencies before and after intravenous injection of the UCA, Optison. Coronary artery ligation mice and sham-operated controls were scanned at 10-22 MHz with and without UCA. RESULTS: Scanning frequency had no significant effect on intraobserver or interobserver variation of LV measurements in normal mice under baseline conditions. Use of UCA significantly reduced estimated ejection fraction at 10-22 MHz compared with baseline (baseline 50.8 +/- 7.6% vs UCA 39.7 +/- 7.6%; P = .03) and significantly increased values for LV cavity dimensions (eg, LV area diastole 20.74 +/- 1.20 vs 23.23 +/- 0.98 mm 2 ; P = .002). UCA significantly reduced intraobserver and interobserver variation in LV ejection fraction. CONCLUSIONS: Scanning frequency had no significant effect on reproducibility of LV measurements in the mouse but UCA significantly reduced interobserver variation. Use of UCA could reduce the number of mice required in any given experiment to observe a statistically significant change in LV function.

Deficiency of PDK1 in cardiac muscle results in heart failure and increased sensitivity to hypoxia.

We employed Cre/loxP technology to generate mPDK1(-/-) mice, which lack PDK1 in cardiac muscle. Insulin did not activate PKB and S6K, nor did it stimulate 6-phosphofructo-2-kinase and production of fructose 2,6-bisphosphate, in the hearts of mPDK1(-/-) mice, consistent with PDK1 mediating these processes. All mPDK1(-/-) mice died suddenly between 5 and 11 weeks of age. The mPDK1(-/-) animals had thinner ventricular walls, enlarged atria and right ventricles. Moreover, mPDK1(-/-) muscle mass was markedly reduced due to a reduction in cardiomyocyte volume rather than cardiomyocyte cell number, and markers of heart failure were elevated. These results suggested mPDK1(-/-) mice died of heart failure, a conclusion supported by echocardiographic analysis. By employing a single-cell assay we found that cardiomyocytes from mPDK1(-/-) mice are markedly more sensitive to hypoxia. These results establish that the PDK1 signalling network plays an important role in regulating cardiac viability and preventing heart failure. They also suggest that a deficiency of the PDK1 pathway might contribute to development of cardiac disease in humans.