Liesbeth Frederix

Fumagillin reduces adipose tissue formation in murine models of nutritionally induced obesity.

The effect of fumagillin (a methionine aminopeptidase‐type 2 (Met‐AP2) inhibitor, with antiangiogenic properties) was investigated in murine models of diet‐induced obesity. Eleven‐week‐old male C57Bl/6 mice (group 1) were given fumagillin by oral gavage at a dose of 1 mg/kg/day during 4 weeks while fed a high‐fat diet (HFD) (20.1 kJ/g), and control mice (group 2) received solvent and were pair‐fed. At the end of the experiment, body weights in group 1 were significantly lower as compared to group 2 (P < 0.0005). The subcutaneous (SC) and gonadal (GON) fat mass was also significantly lower in group 1 (P < 0.005 and P < 0.05, respectively). Adipocytes were smaller in adipose tissues of mice in group 1, associated with higher adipocyte density. Blood vessel density normalized to adipocyte density was lower in group 1 adipose tissues. However, in mice with established obesity monitored to maintain the same body weight and fat mass as controls, short‐term fumagillin administration was also associated with adipocyte hypotrophy (P = 0.01) without affecting blood vessel size or density. Thus, treatment with fumagillin impaired diet‐induced obesity in mice, associated with adipocyte hypotrophy but without marked effect on adipose tissue angiogenesis.

Deficiency of plasminogen activator inhibitor‐2 impairs nutritionally induced murine adipose tissue development

Background: A functional role for several components of the fibrinolytic (plasminogen/plasmin) system in development of adipose tissue has been demonstrated. No information is available, however, on a potential role of plasminogen activator inhibitor‐2 (PAI‐2) in obesity. Methods: In vitro, 3T3‐F442A murine pre‐adipocytes were differentiated into mature adipocytes. In vivo, 5‐week‐old male PAI‐2‐deficient (PAI‐2−/−) mice and wild‐type (WT) controls of the same genetic background (C57Bl/6) were kept on a high fat diet (HFD, caloric value of 20.1 kJ g−1) for 15 weeks. Results: Semi‐quantitative reverse transcription‐polymerase chain reaction (RT‐PCR) revealed expression of PAI‐2 mRNA during in vitro differentiation of pre‐adipocytes and in vivo in s.c. and gonadal (GON) adipose tissues of WT mice, where it was localized both in the stromal/vascular cell fraction and in adipocytes. During HFD feeding, food intake and body weight gain were comparable for WT and PAI‐2−/− mice. Subcutaneous plus GON fat mass was, however, significantly lower in PAI‐2−/− mice (3.15 ± 0.21 vs. 3.91 ± 0.18 g; P < 0.05). Immunohistochemical analysis of adipose tissues revealed significant adipocyte hypotrophy in s.c. fat of PAI‐2−/− mice (about 25% reduction in size; P < 0.01). Blood vessel density, normalized to adipocyte number, was comparable in s.c. fat, but was lower (P < 0.05) in GON fat of PAI‐2−/− mice. Adipose tissue‐associated fibrinolytic activity was not affected by PAI‐2 deficiency. Conclusion: PAI‐2 promotes adipose tissue development in mice via a mechanism independent of its antifibrinolytic effect.

Tiplaxtinin impairs nutritionally induced obesity in mice

To investigate the effect of tiplaxtinin, designed as a synthetic inhibitor of plasminogen activator inhibitor-1 (PAI-1), on obesity, male C57Bl/6 mice (13-14 weeks old) were kept on a high-fat diet (20.1 kJ/g) for four weeks without or with addition of tiplaxtinin (PAI-039) at a dose of 2 mg/g food. At the time of sacrifice, body weights were significantly lower in the inhibitor-treated mice (p < 0.0005). The weights of the isolated subcutaneous and gonadal fat deposits were also significantly lower (both p < 0.0005), associated with adipocyte hypotrophy. Inhibitor-treated adipose tissues displayed similar blood vessel size, but a higher blood vessel density. Fasting glucose and insulin levels, as well as glucose-tolerance tests were not significantly affected by the inhibitor treatment, whereas plasma triglyceride levels were significantly reduced (p = 0.02) and LDL-cholesterol levels significantly enhanced (p = 0.0002). Insulin-tolerance tests revealed significantly lower glucose levels at the end of the test in the inhibitor treated mice (p = 0.03). Thus, in this model of diet-induced obesity in mice administration of tiplaxtinin resulted in impaired adipose tissue development.

Axl Deficiency Does Not Affect Adipogenesis or Adipose Tissue Development

To evaluate a potential role of Axl, the high‐affinity receptor of growth arrest‐specific protein 6 (GAS6) in adiposity, murine embryonic fibroblasts (MEF) derived from mice with genetic deficiency of Axl (Axl−/−) or wild‐type littermates (Axl+/+) were differentiated into mature adipocytes. In addition, Axl−/− and Axl+/+ mice were kept on standard fat diet (SFD) or on high‐fat diet (HFD) for 15 weeks. Deficiency of Axl in MEF did not affect differentiation, as shown by a similar uptake of Oil Red O and expression of the adipogenic markers aP2 and peroxisome proliferator activator receptor γ (PPARγ) at the end of the differentiation. In the first 7 weeks of HFD feeding, Axl−/− mice gained less weight than their wild‐type littermates. Weight gain for both genotypes on either SFD of HFD over 15 weeks was, however, not significantly different, resulting in comparable body weights, as well as subcutaneous (s.c.) and gonadal (GON) fat mass. Adipocyte size in the fat tissues was not affected by Axl deficiency. Gene expression analysis indicated that the absence of Axl in vivo may be compensated for by the other TAM family members Mer and Tyro3. Glucose and insulin tolerance tests (ITT) in Axl−/− and Axl+/+ mice did not reveal significant differences in glucose homeostasis. Thus, Axl deficiency had no significant effect on adipogenesis in vitro or in vivo.

Deficiency of vascular endothelial growth factor-D does not affect murine adipose tissue development

Vascular endothelial growth factor (VEGF)-D deficiency had no significant effect on total body weight or on subcutaneous (SC) or gonadal (GON) adipose tissue mass of mice kept on a standard fat (SFD) or a high fat diet (HFD) for 15 weeks. The composition of SC and GON adipose tissues of VEGF-D deficient mice in terms of size and density of adipocytes or blood vessels was also comparable to that of wild-type control mice. Staining of lymphatic vessels in adipose tissue sections did not reveal marked differences between both genotypes. The absence of an effect of VEGF-D deficiency could not be explained by compensatory increases of VEGF-C expression in adipose tissues of the deficient mice. Thus, our data do not support an important role of VEGF-D in (lymph) angiogenesis or in adipose tissue development.

Role of thrombospondin-2 in murine adipose tissue angiogenesis and development.

Expression of thrombospondin‐2 (TSP‐2), a matricellular protein with anti‐angiogenic properties, is modulated in developing adipose tissue. To investigate a potential functional role of TSP‐2 in adipose tissue angiogenesis and growth, TSP‐2 deficient (TSP‐2−/−) and wild‐type littermate (TSP‐2+/+) mice were kept on normal chow (standard fat diet (SFD)) or on high fat diet (HFD) for 15 weeks. TSP‐2−/− mice kept on HFD had a significantly lower total body weight throughout the experimental period. Subcutaneous (SC) and gonadal (GON) fat mass were, however, not different, and their composition in terms of size and density of adipocytes and blood vessels was also comparable in both genotypes. Macrophage infiltration in SC or GON adipose tissues was not affected by TSP‐2 deficiency. TSP‐2 deficiency had no effect on adipose tissue mRNA expression of gelatinase A (MMP‐2), whereas gelatinase B (MMP‐9) was downregulated in SC and GON adipose tissues of TSP‐2−/− mice on HFD. Glucose tolerance and insulin resistance tests were comparable for TSP‐2+/+ and TSP‐2−/− mice. TSP‐2 deficiency was not compensated by increased expression of TSP‐1 in the TSP‐2−/− mice. These data suggest that TSP‐2, despite its reported anti‐angiogenic properties, does not play an important functional role in adipose tissue related angiogenesis or associated fat development in mice.

Monitoring reperfused myocardial infarction with delayed left ventricular systolic dysfunction in rabbits by longitudinal imaging

Background An experimental imaging platform for longitudinal monitoring and evaluation of cardiac morphology-function changes has been long desired. We sought to establish such a platform by using a rabbit model of reperfused myocardial infarction (MI) that develops chronic left ventricle systolic dysfunction (LVSD) within 7 weeks. Methods Fifty-five New Zeeland white (NZW) rabbits received sham-operated or 60-min left circumflex coronary artery (LCx) ligation followed by reperfusion. Cardiac magnetic resonance imaging (cMRI), transthoracic echocardiography (echo), and blood samples were collected at baseline, in acute (48 hours or 1 week) and chronic (7 weeks) stage subsequent to MI for in vivo assessment of infarct size, cardiac morphology, LV function, and myocardial enzymes. Seven weeks post MI, animals were sacrificed and heart tissues were processed for histopathological staining. Results The success rate of surgical operation was 87.27%. The animal mortality rates were 12.7% and 3.6% both in acute and chronic stage separately. Serum levels of the myocardial enzyme cardiac Troponin T (cTnT) were significantly increased in MI rabbits as compared with sham animals after 4 hours of operation (P<0.05). According to cardiac morphology and function changes, 4 groups could be distinguished: sham rabbits (n=12), and MI rabbits with no (MI_NO_LVSD; n=10), moderate (MI_M_LVSD; n=9) and severe (MI_S_LVSD; n=15) LVSD. No significant differences in cardiac function or wall thickening between sham and MI_NO_LVSD rabbits were observed at both stages using both cMRI and echo methods. cMRI data showed that MI_M_LVSD rabbits exhibited a reduction of ejection fraction (EF) and an increase in end-systolic volume (ESV) at the acute phase, while at the chronic stage these parameters did not change further. Moreover, in MI_S_LVSD animals, these observations were more striking at the acute stage followed by a further decline in EF and increase in ESV at the chronic stage. Lateral wall thickening determined by cMRI was significantly decreased in MI_M_LVSD versus MI_NO_LVSD animals at both stages (P<0.05). As for MI_S_LVSD versus MI_M_LVSD rabbits, the thickening of anterior, inferior and lateral walls was significantly more decreased at both stages (P<0.05). Echo confirmed the findings of cMRI. Furthermore, these in vivo outcomes including those from vivid cine cMRI could be supported by exactly matched ex vivo histomorphological evidences. Conclusions Our findings indicate that chronic LVSD developed over time after surgery-induced MI in rabbits can be longitudinally evaluated using non-invasive imaging techniques and confirmed by the entire-heart-slice histomorphology. This experimental LVSD platform in rabbits may interest researchers in the field of experimental cardiology and help strengthen drug development and translational research for the management of cardiovascular diseases.

Prolonged High-Fat Diet Feeding of WHHLMI Rabbits does Not Aggravate Metabolic or Cardiac Dysfunction

Myocardial infarction (MI)-prone Watanabe hereditary hyperlipidemic (WHHLMI) rabbits were reported to spontaneously but slowly develop MI, associated with enhanced coronary atherosclerosis and metabolic syndrome features. Our aim was to accelerate these processes by exposing the rabbits to a high-fat diet (HFD) that was previously shown to induce insulin resistance and cardiac injury in rabbits. HFD feeding for one year was indeed associated with development of obesity (37% increases in body weight, as compared to 3.7% for control standard-fat diet, SFD). On HFD, liver weight and hepatic triglyceride content were significantly higher as compared to SFD, with mild steatosis. Glucose and insulin levels were not markedly different on SFD or HFD, however after 1 year of diet treatment, HFD-fed animals were more glucose intolerant as compared to SFD-fed rabbits. On SFD, the rabbits developed marked thoracic aorta stenosis and calcification of atherosclerotic lesions, which were not aggravated by HFD feeding. Cardiac function analysis by MRI and transthoracic echocardiography did not reveal significant differences between SFDand HFDfed rabbits. Thus, the metabolic and cardiac phenotype of WHHLMI rabbits was not aggravated by HFD feeding for one year, and the rabbits did not spontaneously develop diabetes or myocardial infarction.

Evaluation of cardiac arrhythmic risks using a rabbit model of left ventricular systolic dysfunction

ABSTRACT Patients with heart disease have a higher risk to develop cardiac arrhythmias, either spontaneously or drug‐induced. In this study, we have used a rabbit model of myocardial infarction (MI) with severe left ventricular systolic dysfunction (LVSD) to study potential drug‐induced cardiac risks with N‐(piperidin‐2‐ylmethyl)‐2,5‐bis(2,2,2‐trifluoroethoxy)benzamide (flecainide). Upon ligation of the left circumflex arteries, male New Zealand White rabbits developed a large MI and moderate or severe LVSD 7 weeks after surgery, in comparison to SHAM‐operated animals. Subsequently, animals were exposed to escalating doses of flecainide (0.25–4 mg/kg) or solvent. Electrocardiograms (ECG) were recorded before surgery, 1 and 7 weeks after surgery and continuously during the drug protocol. The ECG biomarker iCEB (index of Cardio‐Electrophysiological Balance = QT/QRS ratio) was calculated. During the ECG recording at week 1 and week 7 post MI, rabbits had no spontaneous cardiac arrhythmias. When rabbits were exposed to escalating doses of flecainide, 2 out of 5 rabbits with MI and moderate LVSD versus 0 out of 5 solvent‐treated rabbits developed arrhythmias, such as ventricular tachycardia/ventricular fibrillation. These were preceded by a marked decrease of iCEB just before the onset (from 4.09 to 2.42 and from 5.56 to 2.25, respectively). Furthermore, 1 out of 5 MI rabbits with moderate LVSD and 1 out of 7 MI rabbits with severe LVSD developed total atrioventricular block after flecainide infusion and died. This rabbit model of MI and severe LVSD may be useful for preclinical evaluation of drug (similar mechanism as flecainide)‐induced arrhythmic risks, which might be predicted by iCEB.