Construction of Plasmid DNA Expressing Two Isoforms of Insulin-Like Growth Factor-1 and Its Effects on Skeletal Muscle Injury Models

Insulin-like growth factor-1 (IGF-1) plays a significant role in the development of various organs, and several studies have suggested that IGF-1 isoforms, IGF-1 Ea and IGF-1 Ec, are expressed in skeletal muscle to control its growth. In this study, we designed a novel nucleotide sequence, IGF-1-X10, consisting of IGF-1 exons and introns to simultaneously express both IGF-1 Ea and IGF-1 Ec. When transfected into human cells, the expression of both isoforms was observed at the transcript and protein levels. In an animal study, intramuscular injection of plasmid DNA comprising IGF-1-X10 induced the expression of IGF-1 Ea and IGF-1 Ec, leading to the production of functional IGF-1 protein. Finally, the efficacy of this plasmid DNA was tested in a cardiotoxin (CTX)-mediated muscle injury model and age-related muscle atrophy model. We found that IGF-1-X10 increased the muscle mass and controlled several key factors involved in the muscle atrophy program in both models. Taken together, these data suggest that IGF-1-X10 may be utilized in the form of gene therapy for the treatment of various muscle diseases related to IGF-1 deficiency.

Right heart adaptation to pulmonary arterial hypertension: physiology and pathobiology

Survival in patients with pulmonary arterial hypertension (PAH) is closely related to right ventricular (RV) function. Although pulmonary load is an important determinant of RV systolic function in PAH, there remains a significant variability in RV adaptation to pulmonary hypertension. In this report, the authors discuss the emerging concepts of right heart pathobiology in PAH. More specifically, the discussion focuses on the following questions. 1) How is right heart failure syndrome best defined? 2) What are the underlying molecular mechanisms of the failing right ventricle in PAH? 3) How are RV contractility and function and their prognostic implications best assessed? 4) What is the role of targeted RV therapy? Throughout the report, the authors highlight differences between right and left heart failure and outline key areas of future investigation.

Selective heart rate reduction with ivabradine unloads the left ventricle in heart failure patients

OBJECTIVES

The study aimed to determine whether isolated heart rate (HR) reduction with ivabradine reduces afterload of patients with systolic heart failure.

BACKGROUND

The effective arterial elastance (Ea) represents resistive and pulsatile afterload of the heart derived from the pressure volume relation. HR modulates Ea, and, therefore, afterload burden.

METHODS

Among the patients with systolic heart failure (ejection fraction ≤35%) randomized to either placebo or ivabradine in the SHIFT (Systolic Heart Failure Treatment With the If Inhibitor Ivabradine Trial), 275 patients (n = 132, placebo; n = 143, ivabradine 7.5 mg twice a day) were included in the echocardiographic substudy. Ea, total arterial compliance (TAC), and end-systolic elastance (Ees) were calculated at baseline and after 8 months of treatment. Blood pressure was measured by arm cuff; stroke volume (SV), ejection fraction, and end-diastolic volume were assessed by echocardiography.

RESULTS

At baseline Ea, TAC, HR, and Ees did not differ significantly between ivabradine- and placebo-treated patients. After 8 months of treatment, HR was significantly reduced in the ivabradine group (p < 0.0001) and was accompanied by marked reduction in Ea (p < 0.0001) and improved TAC (p = 0.004) compared with placebo. Although contractility remained unchanged, ventricular-arterial coupling was markedly improved (p = 0.002), resulting in a higher SV (p < 0.0001) in the ivabradine-treated patients.

CONCLUSIONS

Isolated HR reduction by ivabradine improves TAC, thus reducing Ea. Because Ees is unaltered, improved ventricular-arterial coupling is responsible for increased SV. Therefore, unloading of the heart may contribute to the beneficial effect of isolated HR reduction in patients with systolic heart failure.

Ventricular-arterial coupling, remodeling, and prognosis in chronic heart failure

OBJECTIVES

The objective of this study was to compare the physiological determinants of ejection fraction (EF)-ventricular size, contractile function, and ventricular-arterial (VA) interaction-and their associations with clinical outcomes in chronic heart failure (HF).

BACKGROUND

EF is a potent predictor of HF outcomes, but represents a complex summary measure that integrates several components including left ventricular size, contractile function, and VA coupling. The relative importance of each of these parameters in determining prognosis is unknown.

METHODS

In 466 participants with chronic systolic HF, we derived quantitative echocardiographic measures of EF: cardiac size (end-diastolic volume [EDV]); contractile function (the end-systolic pressure volume relationship slope [Eessb] and intercept [V0]); and VA coupling (arterial elastance [Ea]/Eessb). We determined the association between these parameters and the following adverse outcomes: 1) the combined endpoint of death, cardiac transplantation, or ventricular assist device (VAD) placement; and 2) cardiac hospitalization.

RESULTS

Over a median follow-up of 3.4 years, there were 76 deaths, 52 transplantations, 14 VAD placements, and 684 cardiac hospitalizations. EF was independently associated with death, transplantation, and VAD placement (adjusted hazard ratio [HR]: 3.0; 95% confidence interval [CI]: 1.8 to 5.0 comparing third and first tertiles), as were EDV (HR: 2.6; 95% CI: 1.5 to 4.2); V0 (HR: 3.6; 95% CI: 2.1 to 6.1); and Ea/Eessb (HR: 2.1; 95% CI: 1.3 to 3.3). EDV, V0, and Ea/Eessb were also associated with risk of cardiac hospitalization. Eessb was not significantly associated with any adverse outcomes in adjusted analyses.

CONCLUSIONS

Left ventricular size, V0, and VA coupling are associated with prognosis in systolic HF, but end-systolic elastance (Eessb) is not. Assessment of VA coupling via Ea/Eessb is an additional noninvasively derived metric that can be used to gauge prognosis in human HF.

Left ventricular efficiency after ligation of patent ductus arteriosus for premature infants

OBJECTIVE

The purpose of this study was to evaluate the hemodynamic changes in left ventricular function before and after patent ductus arteriosus ligation in premature infants with regard to the energetic efficiency of left ventricular pumping.

METHODS

Thirty-five premature infants who underwent patent ductus arteriosus ligation were enrolled in this study. Left ventricular efficiency was evaluated at 4 points: within 24 hours before patent ductus arteriosus ligation, within 24 hours after patent ductus arteriosus ligation, between postoperative days 2 and 4, and on postoperative day 7. The indices of contractility (end-systolic elastance) and afterload (effective arterial elastance) were approximated on the basis of the systemic blood pressure and systolic or diastolic left ventricular volume. The ratio of stroke work and pressure-volume area, representing the ventricular efficiency, was estimated using the following theoretic formula: the ratio of stroke work and pressure-volume area = 1/(1 + 0.5 ventriculoarterial coupling).

RESULTS

Left ventricular efficiency was transiently deteriorated within 24 hours after patent ductus arteriosus ligation because of the marked increase of the afterload and the slight increase of contraction, and then recovered to preoperation levels by 2 to 4 days after patent ductus arteriosus ligation.

CONCLUSIONS

Analysis of indices representing the afterload, contractility, and energetic efficiency of the left ventricle may provide practical information for the management of premature infants during the postoperative period after patent ductus arteriosus ligation.