Quantification of mechanical ventricular dyssynchrony: direct comparison of velocity-encoded and cine magnetic resonance imaging.

PURPOSE: The preoperative assessment of mechanical dyssynchrony can help to improve patient selection in candidates for cardiac resynchronization therapy (CRT). The present study compared the performance of velocity-encoded (VENC) MRI to cine-magnetic resonance imaging (MRI) for quantifying mechanical ventricular dyssynchrony. MATERIALS AND METHODS: VENC-MRI and cine-MRI were performed in 20 patients with heart failure NYHA class III and reduced ejection fraction (median: 24 %, interquartile range: 18 - 28 %) before CRT device implantation. The interventricular mechanical delay (IVMD) was assessed by VENC-MRI as the temporal difference between the onset of aortic and pulmonary flow. Intraventricular dyssynchrony was quantified by cine-MRI, using the standard deviation of time to maximal wall thickening in sixteen left ventricular segments (SDt-16). The response to CRT was assessed in a six-month follow-up. RESULTS: 14 patients (70 %) clinically responded to CRT. A similar accuracy was found to predict the response to CRT by measurements of the IVMD and SDt-16 (75 vs. 70 %; p = ns). The time needed for data analysis was significantly shorter for the IVMD at 1.69 min (interquartile range: 1.66 - 1.88 min) compared to 9.63 min (interquartile range: 8.92 - 11.63 min) for the SDt-16 (p < 0.0001). CONCLUSION: Measurements of the IVMD by VENC-MRI and the SDt-16 by cine-MRI provide a similar accuracy to identify clinical responders to CRT. However, data analysis of the IVMD is significantly less time-consuming compared to data analysis of the SDt-16.

Epidermal aminopeptidase activity and metabolism as observed in an organized HaCaT cell sheet model.

Metabolism studies on organized HaCaT keratinocyte cell sheets are reported. Cells were grown on porous membranes to form organized cell sheets of several cell layers, which were considered as a model of viable epidermis. Metabolism was studied by reflection kinetics, with the top side of the cell sheets in contact with a donor solution and the basal side closed by an impermeable backing layer. Metabolite formation was followed by HPLC of substrate and metabolite in the donor. For comparison, studies with homogenized HaCaT cells were also performed. Model substrates were amino acid amides of 4-methoxy-2-naphthylamine (MNA) (i.e., Ala-MNA, Arg-MNA, Glu-MNA, and Leu-MNA). Also Leu-enkephalin was studied as a model peptide. Except for Glu-MNA, all substrates were metabolized in both the organized cell sheet and in the homogenates. In homogenate studies, saturation of the metabolic reaction was reached at <100 nmol mL(-1) substrate, whereas metabolism in organized cell sheets was below saturation (up to 500 nmol mL(-1)) except for Leu-enkephalin that showed saturation at >100 nmol mL(-1). In homogenates, substrate inhibition was found with Leu-MNA (> approximately 20 nmol mL(-1)) but not with Ala-MNA and Arg-MNA, both of which showed saturation. Differences of homogenates versus organized cell sheets are due to the intact organization and enzyme compartmentation of the cell sheets as opposed to the loss of organization and compartmentation in homogenates. Also, diffusion of substrate into cell sheets may be rate limiting.

Melatonin inhibits LDL receptor activity and cholesterol synthesis in freshly isolated human mononuclear leukocytes.

There is some indirect evidence that the pineal hormone melatonin can suppress plasma levels of cholesterol in hypercholesterolemic rats. We have examined the effects of the hormone on cellular cholesterol metabolism in freshly isolated human mononuclear leukocytes. Incubation of cells for up to 20 h in a lipid-free medium resulted in an increase in the rate of cholesterol synthesis from [14C]acetate and the high affinity accumulation and degradation of [125I]labeled low density lipoprotein (LDL). Addition of melatonin in increasing concentrations to the incubation medium at zero time inhibited cholesterol synthesis and the specific accumulation and degradation of [125I]labeled LDL; at a concentration of 100 microM, the inhibitions were 38%, 42%, and 48%, respectively. Similar results were obtained using [14C]mevalonate as precursor. Fatty acid synthesis was not altered under these conditions. In contrast to cholesterol, the synthesis of the first cyclic compound lanosterol was not affected by the pineal hormone. These results implicate that melatonin inhibits this pathway between lanosterol and cholesterol. The action of melatonin on LDL receptor activity appeared to be mediated by a decrease in the number of LDL receptors and not by a change in binding affinity. Pharmacological characterization of the potential melatonin receptor site using several analogs like tryptamine, 5-hydroxytryptamine,N-acetyl-5-hydroxytryptamine, 5-methoxytryptamine, and 6-chloromelatonin indicated that the 5-methoxy group is indispensible for the hormone action on cholesterol synthesis. The data provide evidence that melatonin can modulate cholesterol metabolism in human cells.