Modified cine inversion recovery pulse sequence for the quantification of myocardial T1 and gadolinium partition coefficient

Purpose:

To optimize and validate a modified cine inversion recovery sequence (MCine‐IR) for myocardial T1 quantification and gadolinium partition coefficient (λ_Gd) estimation at 1.5 T.

Materials and Methods:

The original version of the cine inversion recovery sequence was modified to allow fully transverse magnetization recovery between two successive inversion pulses. Sixty heart phases were acquired from a number of heart cycles determined on a patient heart rate basis. Phantom studies were carried out to find the optimal effective TR for myocardial and blood pool T1 quantifications in pre‐ and postcontrast studies. Four patients with myocardial infarct (MI) and 22 dilated cardiomyopathy (DCM) were investigated, as well as 11 healthy subjects used as controls.

Results:

Effective TR was identified to be 5000 msec and 2000 msec, respectively, for pre‐ and postcontrast studies. A longer precontrast (948 ± 102 msec) and shorter postcontrast (348 ± 27 msec) T1 in ischemic patients relative to DCM (815 ± 98 msec, P = 0.03 and 409 ± 42 msec, P = 0.001) were noted in delayed enhancement (DE) areas. In MI patients λ_Gd resulted higher than in DCM in DE areas (609 ± 167 vs. 422 ± 52, P = 0.01) but lower in segments not exhibiting DE (355 ± 100 vs. 398 ± 54, P = 0.02).

Conclusion:

It was feasible to measure T1 and λ_Gd with MCine‐IR and the results were in good agreement with the literature. J. Magn. Reson. Imaging 2013;37:109–118. © 2012 Wiley Periodicals, Inc.     

Solitary aorta with bilateral ductal origin of non-confluent pulmonary arteries in pulmonary atresia with intact ventricular septum

We report an exceptional case of pulmonary atresia with intact ventricular septum in which non-confluent pulmonary arteries were supplied by bilateral arterial ducts, the existence of which had been diagnosed in life. One should be aware of this arterial pattern, even when the ventricular septum is intact in the setting of pulmonary atresia, because it requires a different surgical approach than when atresia is associated with a ventricular septal defect, namely construction of bilateral shunts for palliation followed by reconstitution of the pulmonary arterial confluence for definitive repair.     

Congenital malformations of the mitral valve: clinical and morphological aspects]

The clinical, anatomic and functional features of 23 pts with congenital mitral valve malformation, seen at the University of Padua over a period of 10 years, are described. All pts underwent hemodynamic investigation and echo-Doppler evaluation. Diagnosis was confirmed at surgery in 17 cases, and at necropsy in six. In 9 pts mitral anomalies determined prevalent stenosis; the remaining 16 pts had moderate to severe mitral regurgitation. Associated cardiac malformations were present in 19 cases (82.6%). The clinical presentation occurred earlier in pts with mitral stenosis (16.9 months vs 6.55 years). The morphologic and echocardiographic features of each malformation are described. The term "valve dysplasia", as proposed by Becker et al to define the non-Ebstein malformations of the tricuspid valve, is herein applied to the congenital anomalies of the mitral valve in order to obtain a uniform and homogeneous approach to this vast spectrum of malformations.     

Human cytomegalovirus infection of the major leukocyte subpopulations and evidence for initial viral replication in polymorphonuclear leukocytes from viremic patients.

Fourteen immunocompromised patients were examined for viremia, pp65 and p72 antigenemia, and presence of viral DNA in leukocyte fractions of polymorphonuclear leukocytes (PMNL), monocytes/macrophages (M/M), and B and T lymphocytes after purification by fluorescence-activated cell sorting. Nearly all PMNL and M/M fractions were positive for DNA and pp65 antigenemia, while p72 antigenemia was detected in 73% and 62%, respectively. The virus isolation rate was 45% from PMNL and 17% from M/M. T lymphocytes were positive for DNA in 50% of cases and for pp65 and p72 antigenemia in only 11%, while B lymphocytes were DNA-positive in 43% of samples and consistently negative for antigenemia; neither T nor B lymphocytes had virus isolated. Immediate-early (IE)1 RNA was present in 23 (85.2%) of 27 dextran-enriched DNA-positive p72-positive PMNL samples and, in sequential PMNL samples from two heart-transplanted patients, was detected during peak infection in association with p72. Thus, PMNL and M/M are the subpopulations primarily involved in HCMV infection; PMNL may undergo IE replicative events and are not merely passive carriers of phagocytized viral material.     

Injection of amniotic fluid stem cells delays progression of renal fibrosis

Injection of amniotic fluid stem cells ameliorates the acute phase of acute tubular necrosis in animals by promoting proliferation of injured tubular cells and decreasing apoptosis, but whether these stem cells could be of benefit in CKD is unknown. Here, we used a mouse model of Alport syndrome, Col4a5(-/-) mice, to determine whether amniotic fluid stem cells could modify the course of progressive renal fibrosis. Intracardiac administration of amniotic fluid stem cells before the onset of proteinuria delayed interstitial fibrosis and progression of glomerular sclerosis, prolonged animal survival, and ameliorated the decline in kidney function. Treated animals exhibited decreased recruitment and activation of M1-type macrophages and a higher proportion of M2-type macrophages, which promote tissue remodeling. Amniotic fluid stem cells did not differentiate into podocyte-like cells and did not stimulate production of the collagen IVa5 needed for normal formation and function of the glomerular basement membrane. Instead, the mechanism of renal protection was probably the paracrine/endocrine modulation of both profibrotic cytokine expression and recruitment of macrophages to the interstitial space. Furthermore, injected mice retained a normal number of podocytes and had better integrity of the glomerular basement membrane compared with untreated Col4a5(-/-) mice. Inhibition of the renin-angiotensin system by amniotic fluid stem cells may contribute to these beneficial effects. In conclusion, treatment with amniotic fluid stem cells may be beneficial in kidney diseases characterized by progressive renal fibrosis.     

Direct three-dimensional visualization of membrane disruption by amyloid fibrils

Protein misfolding and aggregation cause serious degenerative conditions such as Alzheimer’s, Parkinson, and prion diseases. Damage to membranes is thought to be one of the mechanisms underlying cellular toxicity of a range of amyloid assemblies. Previous studies have indicated that amyloid fibrils can cause membrane leakage and elicit cellular damage, and these effects are enhanced by fragmentation of the fibrils. Here we report direct 3D visualization of membrane damage by specific interactions of a lipid bilayer with amyloid-like fibrils formed in vitro from β₂-microglobulin (β₂m). Using cryoelectron tomography, we demonstrate that fragmented β₂m amyloid fibrils interact strongly with liposomes and cause distortions to the membranes. The normally spherical liposomes form pointed teardrop-like shapes with the fibril ends seen in proximity to the pointed regions on the membranes. Moreover, the tomograms indicated that the fibrils extract lipid from the membranes at these points of distortion by removal or blebbing of the outer membrane leaflet. Tiny (15–25 nm) vesicles, presumably formed from the extracted lipids, were observed to be decorating the fibrils. The findings highlight a potential role of fibrils, and particularly fibril ends, in amyloid pathology, and report a previously undescribed class of lipid–protein interactions in membrane remodelling.The failure of molecular chaperones to prevent the accumulation of misfolded proteins results in protein aggregation and amyloid formation, processes associated with severe human degenerative diseases (1, 2). Despite the attention focused on these problems during the century since these disorders were first identified (3–5) and advances in understanding the structure of the cross-β conformation of amyloid fibrils in atomic detail (6, 7), the basic pathological mechanisms of amyloidosis remain poorly understood and therapeutic intervention is lacking. The identity of the toxic species and the mechanisms of cytotoxicity remain major unsolved problems. In some systems, there is evidence suggesting that prefibrillar oligomers, rather than the fully formed fibrils, are the source of toxicity (8, 9). In these cases, cytotoxicity is thought to result from the formation of specific membrane pores (10, 11) although alternative models including membrane destabilization or membrane thinning have also been proposed (12–15). In other cases, toxicity may reside with the amyloid fibrils themselves. Evidence that toxicity correlates with fibrillar assemblies has been reported for yeast and mammalian prion proteins (16, 17), human lysozyme (18), Huntingtin exon 1, α-synuclein (19), and Amyloid-β (Aβ) (20, 21). Furthermore, Aβ plaques have been shown to form rapidly in vivo and to precede neuropathological changes in a mouse model (22). The end surfaces of fibrils (herein termed “fibril ends”) are unusually reactive entities: they play a key role in catalyzing recruitment and conformational conversion of amyloid-forming proteins (23, 24) and provide the sites for templated elongation of amyloid fibril growth (25, 26). Recently, Xue et al. (27) showed that short fibrils of β₂-microglobulin (β₂m), α-synuclein, and hen lysozyme, each prepared by fragmentation of longer fibrils, cause increased damage to membranes and disruption to cellular function compared with the initial long fibrils. Short and long fibril preparations differ in the number of fibril ends at a given protein concentration. Because these are known to be reactive sites, the above observations suggest a role for fibril ends in amyloid–lipid interaction and possibly in amyloid pathogenesis (23, 24, 27). Fragmented fibrils of all three proteins were also found to induce dye leakage from negatively charged liposomes, the most susceptible of which contain a mixture of the cellular lipids phosphatidylcholine (PC) and phosphatidylglycerol (PG), but liposomes with a variety of compositions were damaged by the fibrils in all cases (27).Here, we use β₂m amyloid fibrils formed in vitro as a model system to investigate the structural basis of membrane damage by amyloid fibrils (27, 28). Previous studies have shown that these fibrils possess a parallel in register cross-β structure (29, 30) assembled into multidomain filaments coiled together, described by cryo-EM (28). These fibrils bind amyloid-specific ligands such as serum amyloid P component with a similar affinity to their ex vivo counterparts (31). Using the conditions under which β₂m amyloid fibrils induce dye release from liposomes (pH 7.4), we examined the effects of both long (∼1,400 nm) and fragmented (∼400 nm) β₂m fibrils (27), as well as various control preparations, on the 3D structures of the liposomes by confocal microscopy, cryo-EM, and tomography. We found pronounced distortions in the liposomes, interruptions to the bilayer structure, and extraction of lipids that were induced by the presence of amyloid fibrils. The most severe distortions were seen in proximity to the fibril ends, which are enriched in the fragmented fibril samples. This type of membrane remodelling appears distinct from the actions of other previously described proteins that induce membrane breakage, as in the action of membrane pore-forming proteins (32). The results suggest a role of fibrils in membrane damage that could contribute to the cellular dysfunction associated with amyloid disease.     

Measurement of energy landscape roughness of folded and unfolded proteins

The dynamics of protein conformational changes, from protein folding to smaller changes, such as those involved in ligand binding, are governed by the properties of the conformational energy landscape. Different techniques have been used to follow the motion of a protein over this landscape and thus quantify its properties. However, these techniques often are limited to short timescales and low-energy conformations. Here, we describe a general approach that overcomes these limitations. Starting from a nonnative conformation held by an aromatic disulfide bond, we use time-resolved spectroscopy to observe nonequilibrium backbone dynamics over nine orders of magnitude in time, from picoseconds to milliseconds, after photolysis of the disulfide bond. We find that the reencounter probability of residues that initially are in close contact decreases with time following an unusual power law that persists over the full time range and is independent of the primary sequence. Model simulations show that this power law arises from subdiffusional motion, indicating a wide distribution of trapping times in local minima of the energy landscape, and enable us to quantify the roughness of the energy landscape (4–5 k_BT). Surprisingly, even under denaturing conditions, the energy landscape remains highly rugged with deep traps (>20 k_BT) that result from multiple nonnative interactions and are sufficient for trapping on the millisecond timescale. Finally, we suggest that the subdiffusional motion of the protein backbone found here may promote rapid folding of proteins with low contact order by enhancing contact formation between nearby residues.     

Repair of congenital mitral valve dysplasia in infants and children: is it always possible?

OBJECTIVES: Surgical management of congenital malformation of the mitral valve (MV) in the pediatric age group remains a therapeutic challenge for the wide spectrum of the morphological abnormalities and the high incidence of associated cardiac anomalies. We reviewed our experience so as to assess whether MV conservative surgery is always advisable and its results are superior to MV replacement. METHODS: Thirty-four consecutive children (20 male and 14 female) with a mean age of 5.9 years (range 45 days-18 years) treated surgically for congenital MV disease between January 1987 and June 1999. Four patients (11.7%) were under 12 months of age, while 21 patients (62%) were younger than 5 years. Twenty-two patients presented with MV incompetence (or prevalent incompetence), while 12 presented with stenosis (or prevalent stenosis). Associated cardiac lesions were present in 22 patients (62.8%). RESULTS: Mitral valve reconstruction was possible in all. There were no operative deaths. Three patients required reoperation for MV restenosis (a re-repair in one and MV replacement with mechanical prosthesis in two) 4 months, 27 months and 5.6 years after repair with no operative deaths. There was only one late death for prosthetic valve thrombosis. Follow-up data reveal that the 33 surviving patients are asymptomatic and well 4 months-12 years (mean 72 months) after surgery. At 12 years, actuarial survival and freedom from reoperation are 96.8 and 85.9%, respectively. Echocardiography performed in all of them shows no or mild incompetence or stenosis in 26 (78%), while residual moderate MV incompetence persists in six. CONCLUSIONS: Our experience indicates that MV reconstructive procedures in infants and children with congenital MV dysplasia may be effective and reliable with low mortality and low incidence of reoperation rate. Mitral valve repair should always be attempted, especially in infants, despite the frequent severity of MV dysplasia, to avoid the drawbacks of the currently available prostheses.