Cardiac-Specific Overexpression of Oxytocin Receptor Leads to Cardiomyopathy in Mice.

BACKGROUND: Oxytocin (Oxt) and its receptor (Oxtr) gene system has been implicated in cardiomyogenesis and cardioprotection; however, effects of chronic activation of Oxtr are not known. We generated and investigated transgenic (TG) mice that overexpress Oxtr specifically in the heart. METHODS AND RESULTS: Cardiac-specific overexpression of Oxtr was obtained by having the α-major histocompatibility complex promoter drive the mouse Oxtr gene (α-Mhc-Oxtr). Left ventricular (LV) function and remodeling were assessed by magnetic resonance imaging and echocardiography. In α-Mhc-Oxtr TG mice, LV ejection fraction was severely compromised at 14 weeks of age compared with wild-type (WT) littermates (25 ± 6% vs 63 ± 3%; P < .001). LV end-diastolic volume was larger in the TG mice (103 ± 6 µL vs 67 ± 5 µL; P < .001). α-Mhc-Oxtr TG animals displayed cardiac fibrosis, atrial thrombus, and increased expression of pro-fibrogenic genes. Mortality of α-Mhc-Oxtr TG animals was 45% compared with 0% (P < .0001) of WT littermates by 20 weeks of age. Most cardiomyocytes of α-Mhc-Oxtr TG animals but not WT littermates (68.0 ± 12.1% vs 5.6 ± 2.4%; P = .008) were positive in staining for nuclear factor of activated T cells (NFAT). To study if thrombin inhibitor prevents thrombus formation, a cohort of 7-week-old α-Mhc-Oxtr TG mice were treated for 12 weeks with AZD0837, a potent thrombin inhibitor. Treatment with AZD0837 reduced thrombus formation (P < .05) and tended to attenuate fibrosis and increase survival. CONCLUSIONS: Cardiac-specific overexpression of Oxtr had negative consequences on LV function and survival in mice. The present findings necessitate further studies to investigate potential adverse effects of chronic Oxt administration. We provide a possible mechanism of Oxtr overexpression leading to heart failure by nuclear factor of activated T cell signaling. The recapitulation of human heart failure and the beneficial effects of the antithrombin inhibitor render the α-Mhc-Oxtr TG mice a promising tool in drug discovery for heart failure.

Evaluation of systemic exposure of nanoparticle suspensions subcutaneously administered to mice regarding stabilization, volume, location, concentration and size.

Different routes of administration are likely to result in very different outcomes due to different availability or plasma profile. The objective of the present study was to evaluate the pharmacokinetic profile after different subcutaneous (s.c.) administration of nanoparticle suspensions of a lipophilic compound to mice. Pharmacokinetics of the selected test compound and the effect of drug concentration, particle size, location of administration, volume given and particle stabilizers were studied. Adding PEGylated lipids or pluronic F-127 to the negatively charged surface of the nanoparticles increased the stability of the particles and the bioavailability. The in vivo studies demonstrated linear absorption kinetics for the selected model compound up to at least 500 µmol/kg. Absorption from upper-neck resulted in different systemic exposure compared to administration in the hip. The former was preferred if a prolonged Cmax was desired while the latter ensured a flat profile for approximately 24 hours. Administering the double volume (but the same dose) had no effect on the pharmacokinetics, whereas smaller particle size significantly increased the exposure.

Phospholamban antisense oligonucleotides improve cardiac function in murine cardiomyopathy.

Heart failure (HF) is a major cause of morbidity and mortality worldwide, highlighting an urgent need for novel treatment options, despite recent improvements. Aberrant Ca2+ handling is a key feature of HF pathophysiology. Restoring the Ca2+ regulating machinery is an attractive therapeutic strategy supported by genetic and pharmacological proof of concept studies. Here, we study antisense oligonucleotides (ASOs) as a therapeutic modality, interfering with the PLN/SERCA2a interaction by targeting Pln mRNA for downregulation in the heart of murine HF models. Mice harboring the PLN R14del pathogenic variant recapitulate the human dilated cardiomyopathy (DCM) phenotype; subcutaneous administration of PLN-ASO prevents PLN protein aggregation, cardiac dysfunction, and leads to a 3-fold increase in survival rate. In another genetic DCM mouse model, unrelated to PLN (Cspr3/Mlp-/-), PLN-ASO also reverses the HF phenotype. Finally, in rats with myocardial infarction, PLN-ASO treatment prevents progression of left ventricular dilatation and improves left ventricular contractility. Thus, our data establish that antisense inhibition of PLN is an effective strategy in preclinical models of genetic cardiomyopathy as well as ischemia driven HF.

Measurement of MR signal and T2* in lung to characterize a tight skin mouse model of emphysema using single-point imaging.

PURPOSE: To evaluate whether MRI signal and T2* measurements of lung tissue acquired at ultrashort detection times (tds) can detect emphysematous changes in lungs. MATERIALS AND METHODS: MR signal intensity of in vivo mouse lungs was measured at 4.7 T at tds of 0.2 and 0.4 msec using single-point imaging (SPI). T2* was calculated from the measurements obtained at the two tds. Two groups of 8- and 30-week-old Tight Skin (TS) and aged-matched CB57BL/6 mice were examined. The TS mice spontaneously developed emphysema-like alveolar enlargement. In vivo micro-computed tomography (microCT) scanning and histology were used as reference methods. RESULTS: MR signal and T2* were significantly lower in the lungs of TS mice than in controls. There were no significant differences between the different age groups. MR signal in lung parenchyma correlated linearly (P < 0.0001, r = 0.89) with microCT mass density, and T2* correlated linearly (P < 0.0001, r = -0.91) with the alveoli size (mean linear intercept [MLI]). CONCLUSION: The MR signal intensity and T2* measured at short tds can be used as imaging biomarkers to characterize parenchyma density and alveolar size, respectively.