Mette Madsen

Dwarfism and Impaired Gut Development in Insulin-Like Growth Factor II mRNA-Binding Protein 1-Deficient Mice

ABSTRACT Insulin-like growth factor II mRNA-binding protein 1 (IMP1) belongs to a family of RNA-binding proteins implicated in mRNA localization, turnover, and translational control. Mouse IMP1 is expressed during early development, and an increase in expression occurs around embryonic day 12.5 (E12.5). To characterize the physiological role of IMP1, we generated IMP1-deficient mice carrying a gene trap insertion in the Imp1 gene. Imp1−/− mice were on average 40% smaller than wild-type and heterozygous sex-matched littermates. Growth retardation was apparent from E17.5 and remained permanent into adult life. Moreover, Imp1−/− mice exhibited high perinatal mortality, and only 50% were alive 3 days after birth. In contrast to most other organs, intestinal epithelial cells continue to express IMP1 postnatally, and Imp1−/− mice exhibited impaired development of the intestine, with small and misshapen villi and twisted colon crypts. Analysis of target mRNAs and global expression profiling at E12.5 indicated that Igf2 translation was downregulated, whereas the postnatal intestine showed reduced expression of transcripts encoding extracellular matrix components, such as galectin- 1, lumican, tenascin-C, procollagen transcripts, and the Hsp47 procollagen chaperone. Taken together, the results demonstrate that IMP1 is essential for normal growth and development. Moreover, IMP1 may facilitate intestinal morphogenesis via regulation of extracellular matrix formation.

Molecular characterization of the haptoglobin.hemoglobin receptor CD163. Ligand binding properties of the scavenger receptor cysteine-rich domain region.

CD163 is the macrophage receptor for endocytosis of haptoglobin·hemoglobin complexes. The extracellular region consisting of nine scavenger receptor cysteinerich (SRCR) domains also circulates in plasma as a soluble protein. By ligand binding analysis of a broad spectrum of soluble CD163 truncation variants, the amino-terminal third of the SRCR region was shown to be crucial for the binding of haptoglobin·hemoglobin complexes. By Western blotting of the CD163 variants, a panel of ten monoclonal antibodies was mapped to SRCR domains 1, 3, 4, 6, 7, and 9, respectively. Only the two antibodies binding to SRCR domain 3 exhibited effective inhibition of ligand binding. Furthermore, analysis of purified native CD163 revealed that proteolytic cleavage in SRCR domain 3 inactivates ligand binding. Calcium protects against cleavage in this domain. Analysis of the calcium sensitivity of ligand binding to CD163 demonstrated that optimal ligand binding requires physiological plasma calcium concentrations, and an immediate ligand release occurs at the low calcium concentrations measured in acidifying endosomes. In conclusion, SRCR domain 3 of CD163 is an exposed domain and a critical determinant for the calcium-sensitive coupling of haptoglobin·hemoglobin complexes.

Peripheral flow response to transient arterial forearm occlusion does not reflect myocardial perfusion reserve.

Background —Ultrasonographic evaluation of systemic arterial function is widely available, and a close relation of endothelial function in the coronary and brachial arteries has been documented. It is unknown, however, whether a similar correlation exists for their 2 microcirculatory territories and thus whether assessment of the systemic microcirculation can be used similarly as a surrogate marker of myocardial perfusion. Methods and Results —Twenty-three patients with documented coronary artery disease (CAD; 66±9 years old, 18 men), 16 patients with syndrome X (SX; 56±5 years old, 13 women), and 45 healthy control subjects (C; 34±9 years old, 22 men) were studied. Myocardial perfusion was measured at rest and after dipyridamole (0.56 mg · kg−1 · min−1 over 4 minutes) by PET, and brachial artery blood flow was measured at rest and after transient forearm ischemia by standard Doppler ultrasound techniques. Dipyridamole increased myocardial perfusion in all groups (mL · g−1 · min−1: CAD, 0.89±0.27 versus 1.62±0.67, P <0.001; SX, 0.82±0.16 versus 1.67±0.49, P <0.001; and C, 0.82±0.15 versus 2.32±0.64, P <0.001). Postocclusion forearm flow increased similarly in all groups (CAD, 52±18 versus 174±77 mL/min, P <0.001; SX, 49±29 versus 202±82 mL/min, P <0.001; and C, 61±34 versus 229±108 mL/min, P <0.001). No significant correlations were found between peripheral and myocardial microcirculatory beds for either resting flow, hyperemic flow, or flow reserve in any of the groups (r2<0.1, P =NS). Conclusions —The peripheral perfusion responses to transient forearm ischemia do not correlate with dipyridamole-induced myocardial hyperemia. The lack of correlation indicates different mechanisms of microvascular activation or regulation and confirms that extrapolations between findings in the 2 vascular beds are not suitable.

Effect of antianginal medication on resting myocardial perfusion and pharmacologically induced hyperemia

BackgroundPatients scheduled for myocardial perfusion imaging are often taking several antianginal drugs. There is presently no consensus concerning a regimen of discontinuation before either rest or pharmacologic stress myocardial perfusion imaging. Whether antianginal treatment affects diagnostic sensitivity and specificity is not well documented.Methods and ResultsThe effect of the three most commonly used antianginal drugs (nitroglycerin, 400 μg [NTG]; metoprolol, 50 mg [MET]; and amlodipine, 5 mg [AML]) on myocardial perfusion was tested in 49 patients (age, 63 α 8 years; 43 men) allocated prospectively to one of the treatments (NTG, n = 25; MET, n = 14; and AML, n = 10). All patients had documented coronary artery disease and were scheduled for elective percutaneous coronary intervention. Patients were studied once on treatment and once off treatment with an interval of 1 to 3 weeks. For NTG, the measurements were performed on the same day with an interval of 1 hour. The MET and AML groups were also studied during dipyridamole-induced hyperemia (0.56 mg.kg−1.min−1 for 4 minutes). So that a quantitative value of myocardial perfusion in milliliters per gram per minute could be obtained, myocardial perfusion was quantified with nitrogen 13 ammonia positron emission tomography as an average of the midventricular perfusion in each of the 3 vascular territories. NTG treatment increased the overall resting perfusion (0.75 ± 0.18 vs 0.86 ± 0.22, P < .05), whereas resting perfusion was reduced after MET treatment (0.92 ± 0.14 vs 0.82 ± 0.17, P < .05). AML treatment did not alter resting perfusion (0.87 ± 0.22 vs 0.87 ± 0.23, P = NS). Dipyridamole-induced hyperemia was reduced after treatment with MET (2.02 ± 0.66 vs l.57 ± 0.52, P < .001), whereas the hyperemic response was unchanged after treatment with AML (1.54 ± 0.49 vs 1.86 ± 0.91, P = NS).ConclusionsAntianginal medication can alter both resting and hyperemic myocardial perfusion and might affect the ability to detect flow-limiting stenosis. NTG increases perfusion, MET reduces perfusion, and AML does not affect perfusion. Larger-scale trials are warranted to establish a consensus for optimal antianginal medication for patients undergoing perfusion imaging.

Effect of oral nitroglycerin and cold stress on myocardial perfusion in areas subtended by stenosed and nonstenosed coronary arteries

Physical obstruction and coronary vasoconstriction mediated by adrenergic stress are believed to be responsible for episodes of myocardial hypoperfusion and angina. Nitroglycerin relieves symptoms by reducing preload and dilating epicardial vessels. The net perfusion change and relation to stenosis severity of nitroglycerin and adrenergic stress have been debated. This study aimed to evaluate whether oral nitroglycerin and adrenergic stress alters perfusion in myocardial segments subtended by stenosed and nonstenosed coronary arteries. Myocardial perfusion was quantified (using N-13-ammonia positron emission tomography [PET]) at rest, after oral nitroglycerin 400 microg, and after cold stress in 25 patients with coronary artery disease (62 +/- 9 years, 21 men) and in 30 controls (34 +/- 9 years, 22 men). Myocardial perfusion was quantified in areas supplied by stenosed (>70%) and nonstenosed (<30%) coronary arteries. The cold pressor test did not significantly alter myocardial perfusion in any of the groups. However, when normalized for rate-pressure product, the response in stenosed areas showed a significantly more pronounced reduction compared with nonstenosed areas (0.78 +/- 0.18 vs 0.64 +/- 0.19 ml/g/min, p <0.005 and 0.86 +/- 0.19 vs 0.73 +/- 0.24 ml/g/min, p <0.05, p <0.05) for intergroup comparison. In both stenosed areas and nonstenosed areas nitroglycerin increased perfusion (0.51 +/- 0.14 vs 0.60 +/- 0.17 ml/g/min, p <0.05 and 0.56 +/- 0.14 vs 0.61 +/- 0.17 ml/g/min, p <0.05). Nitroglycerin did not alter myocardial perfusion in the control group. There was a negative correlation between the cold pressor test response and stenosis severity (r(2) = 0.17, p <0.046), whereas this was not the case for nitroglycerin. In patients with coronary artery disease, myocardial segments supplied by stenosed coronary arteries showed an altered perfusion response to adrenergic stress. Oral nitroglycerin increased myocardial perfusion irrespective of the presence of a stenosis.

Evaluation of regional myocardial perfusion in patients with severe left ventricular dysfunction: Comparison of 13N-ammonia PET and 99mTc sestamibi SPECT

ObjectivePositron emission tomography (PET) scanning with 13N-ammonia and 18FDG is well established for the detection of myocardial viability. Due to the limited availability of PET facilities, recent studies have combined technetium 99m sestamibi single photon emission computed tomography (SPECT) with 18FDG PET or 18FDG SPECT. This approach enables simultaneous assessment of regional myocardial blood flow and metabolism and substantially increases the capacity for viability detection. To validate whether 99mTc-Sestamibi SPECT can replace 13N-ammonia PET, we compared these two modalities in patients with severe left ventricular dysfunction due to coronary artery disease.Materials and MethodsThirty-one patients (mean age 57±8 years; mean ejection fraction 27%±8%) with angiographically verified coronary artery disease were included. In random order, ammonia-PET and sestamibi-SPECT scans were performed. In a 20-segment model of the left ventricle, two blinded observers scored a total of 610 segments on a five-point scale. In a subset of 20 patients, 400 segments were scored twice to evaluate the observer variations of the two techniques. Segmental score differences were used to compare the imaging modalities. The impact on viability detection was assessed by combining the two flow tracers with FDG PET.ResultsSegmental comparison of the PET and SPECT studies yielded similar (difference ≤1) results in 74% of segments, reflecting regional concordance values in the lateral, apical, anterior, septal, and inferior myocardial walls of 86%, 82%, 71%, 66%, and 63%, respectively. The differences in the septal and inferior walls were primarily due to overestimation of perfusion defects by sestamibi SPECT, which yielded a higher proportion of mismatch patterns in those regions. The overall observer variations of the PET and SPECT studies were 7.5% and 5.8%.ConclusionMyocardial perfusion imaging with 13N-ammonia PET and 99mTc-sestamibi SPECT yielded similar results in patients with severe left ventricular dysfunction, except for the septal and inferior regions. In these regions, SPECT tended to overestimate perfusion defects. Hence, attenuation correction should be considered when combining FDG PET and sestamibi SPECT for diagnosing myocardial viability to avoid overestimation of mismatch patterns in those regions.

Incidence and prevalence of multiple endocrine neoplasia 2B in Denmark: a nationwide study

Multiple endocrine neoplasia 2B (MEN2B) is an autosomal dominant inherited cancer syndrome associating medullary thyroid carcinoma (MTC), pheochromocytoma (PHEO), ganglioneuromatosis of the aerodigestive tract and facial, ophthalmologic and skeletal abnormalities. MEN2B is caused by the M918T and A883F mutation of the REarranged during Transfection (RET) proto-oncogene in approximately 95% and <5% of cases, respectively. Only very few other mutations have been reported to cause MEN2B. In approximately 75% of MEN2B patients, mutations occur as de novo (Wells et al. 2015). The epidemiology of MEN2B is poorly defined. A nationwide study from Northern Ireland reported of three MEN2B patients and 1,824,000 inhabitants alive at April 21, 2012, yielding a point prevalence of 1.65 per million (Znaczko et al. 2014). However, it is unclear if this is representative of larger populations. A German study reported an MEN2B incidence (M918T carriers only) of 1.4 per million live births per year from 1991 to 2000 and estimated that at least half of all German RET carriers were captured (Machens et al. 2013). Meanwhile, the incidence of MEN2B and M918T carriers in a complete population is undisclosed. We conducted a nationwide study of the incidence and prevalence of MEN2B in Denmark from 1941 to 2014. This retrospective cohort study included 12 unique MEN2B patients identified through the following sources:

Impact of hydrochloric acid instillation on salvage of infected central venous catheters in children with acute lymphoblastic leukaemia

Abstract Background: Bacteraemia associated with indwelling central venous catheters (CVC) causes significant morbidity in children with cancer. Hydrochloric acid (HCl) instillations have been reported to salvage CVCs with antibiotic-refractory infection. We implemented this treatment in 2002. The impact on the survival of CVCs has been evaluated in a retrospective cohort study of children with acute lymphoblastic leukaemia (ALL). Methods: Children with newly diagnosed ALL during 1999–2005 having their first CVC inserted before (n = 16) and after (n = 24) the introduction of the procedure were studied. All bacteraemic episodes were reviewed, recording bacteriological findings and treatment, and the time to premature or planned removal of the CVC was determined. Results: In the comparison cohort, 31.0% (9/29) of bacteraemic episodes led to removal of the CVC, compared to 5.5% (2/36) in the intervention cohort (p = 0.01). Thus, the rate of catheter loss due to infection fell from 56.3% (9/16) to 8.3% (2/24) after introducing HCl treatment (p = 0.0025). Overall, the premature catheter removal rate fell from 75.0% (12/16) to 45.8% (11/24) (p = 0.10). Analysed in a CUSUM plot the reduced frequency of premature CVC removal evidently coincided with the introduction of the procedure. In a subgroup analysis of 21 monobacterial infections with coagulase-negative staphylococci, a decrease in systemic and lock antibiotic therapy was found. No adverse events were noted. Conclusions: HCl instillations significantly reduced the need to remove and replace CVCs. The procedure is practical, appears to be safe, and may reduce the consumption of antibiotics.

Altered Regulation of the Myocardial Microcirculation in Young Smokers

Smoking is known to affect microcirculatory function in a middle-aged population. However, the effects of smoking on myocardial perfusion in young smokers have not been studied. Myocardial perfusion was measured in 15 smokers (24 ± 2 years) and 15 nonsmokers (24 ± 3 years) using positron emission tomography. Myocardial perfusion was measured at rest, during cold stress and during dipyridamole. Resting myocardial blood flow was similar in the two groups. The well-described correlation between rate-pressure product and myocardial blood flow was present only in the nonsmokers (r2 = 0.61, p < 0.001). Myocardial blood flow corrected for the rate-pressure product declined during cold by 20% in the smokers [1.11 ± 0.28 vs. 0.92 ± 0.20 ml·g–1·min–1 (p = 0.012)], but remained unchanged in nonsmokers [1.11 ± 0.25 vs. 1.09 ± 0.30 ml·g–1·min–1 (p = NS)]. Dipyridamole-induced hyperemia was similar in the two groups [2.23 ± 0.78 vs. 2.42 ± 0.65 ml·g–1·min–1 (p = NS)]. In conclusion, smoking induces abnormalities in myocardial microcirculatory regulation in young otherwise healthy smokers. The coronary flow reserve, however, is not significantly altered.

Impact of type 2 diabetes on nitric oxide and adrenergic modulation of myocardial perfusion

Type 2 diabetic patients are characterized by a reduced adenosine-induced hyperemic myocardial perfusion, which may contribute to their increased cardiovascular morbidity. We hypothesized that the reduced hyperemia can be explained by functional changes in endothelial or autonomic nervous regulation. In 12 type 2 diabetic patients without signs of ischemic heart disease and 14 age-matched control subjects, myocardial perfusion was measured at rest, during adenosine, and during adenosine and α-receptor blockade (phentolamine) using positron emission tomography on two separate days: 1) with, and 2) without nitric oxide (NO) inhibition with NG-nitro-l-arginine methyl ester. Myocardial perfusion during adenosine was lower in type 2 diabetic patients compared with control subjects (P = 0.05). No significant effect of NO inhibition on myocardial perfusion during adenosine was found in any of the groups. In control subjects, α-receptor blockade increased hyperemic myocardial vascular resistance during NO inhibition, whereas no effect was observed in type 2 diabetic patients. At rest, a significant correlation was observed between rate-pressure product and myocardial perfusion in control subjects. NO inhibition and type 2 diabetes abolished this correlation. Endothelial and cardiac autonomic nerve function seems to play only a minimal role in the reduced hyperemic myocardial perfusion in type 2 diabetic patients. However, the linear correlation between resting perfusion and cardiac work appears to be abolished in type 2 diabetes and during NO synthase inhibition.