In Vitro Assessment of Factors Affecting the Apparent Diffusion Coefficient of Jurkat Cells Using Bio-phantoms

It is well known that many tumor tissues show lower apparent diffusion coefficient (ADC) values, and that several factors are involved in the reduction of ADC values. The aim of this study was to clarify how much each factor contributes to decreases in ADC values. We investigate the roles of cell density, extracellular space, intracellular factors, apoptosis and necrosis in ADC values using bio-phantoms. The ADC values of bio-phantoms, in which Jurkat cells were encapsulated by gellan gum, were measured by a 1.5-Tesla magnetic resonance imaging device with constant diffusion time of 30sec. Heating at 42℃ was used to induce apoptosis while heating at 48℃ was used to induce necrosis. Cell death after heating was evaluated by flow cytometric analysis and electron microscopy. The ADC values of bio-phantoms including non-heated cells decreased linearly with increases in cell density, and showed a steep decline when the distance between cells became less than 3μm. The analysis of ADC values of cells after destruction of cellular structures by sonication suggested that approximately two-thirds of the ADC values of cells originate from their cellular structures. The ADC values of bio-phantoms including necrotic cells increased while those including apoptotic cells decreased. This study quantitatively clarified the role of the cellular factors and the extracellular space in determining the ADC values produced by tumor cells. The intermediate diffusion time of 30msec might be optimal to distinguish between apoptosis and necrosis

β-Secretase Inhibitor Potency Is Decreased by Aberrant β-Cleavage Location of the “Swedish Mutant” Amyloid Precursor Protein

The amyloid-β (Aβ) peptide, widely known as the causative molecule of Alzheimer disease (AD), is generated by the sequential cleavage of amyloid precursor protein (APP) by the aspartyl proteases BACE1/β-secretase and presenilin/γ-secretase. Inhibition of BACE1, therefore, is a promising strategy for preventing the progression of AD. However, β-secretase inhibitors (BSIs) exhibit unexpectedly low potency in cells expressing “Swedish mutant” APP (APPswe) and in the transgenic mouse Tg2576, an AD model overexpressing APPswe. The Swedish mutation dramatically accelerates β-cleavage of APP and hence the generation of Aβ; this acceleration has been assumed to underlie the poor inhibitory activity of BSI against APPswe processing. Here, we studied the mechanism by which the Swedish mutation causes this BSI potency decrease. Surprisingly, decreased BSI potency was not observed in an in vitro assay using purified BACE1 and substrates, indicating that the accelerated β-cleavage resulting from the Swedish mutation is not its underlying cause. By focusing on differences between the cell-based and in vitro assays, we have demonstrated here that the potency decrease is caused by the aberrant subcellular localization of APPswe processing and not by accelerated β-cleavage or the accumulation of the C-terminal fragment of β-cleaved APP. Because most patients with sporadic AD express wild type APP, our findings suggest that the wild type mouse is superior to the Tg2576 mouse as a model for determining the effective dose of BSI for AD patients. This work provides novel insights into the potency decrease of BSI and valuable suggestions for its development as a disease-modifying agent

Additional file 1 of Evaluating the safety profile of calcineurin inhibitors: cancer risk in patients with systemic lupus erythematosus from the LUNA registry—a historical cohort study

Additional file 1: Figure S1. Design diagram to clarify the key points of each item