MRI biomarkers for Alzheimer's disease: the impact of functional connectivity in the default mode network and structural connectivity between lobes on diagnostic accuracy.

BACKGROUND: At present, clinical use of MRI in Alzheimer's disease (AD) is mostly focused on the assessment of brain atrophy, namely in the hippocampal region. Despite this, multiple biomarkers reflecting structural and functional brain connectivity changes have shown promising results in the assessment of AD. To help identify the most relevant ones that may stand a chance of being used in clinical practice, we compared multiple biomarker in terms of their value to discriminate AD from healthy controls and analyzed their age dependency. METHODS: 20 AD patients and 20 matched controls underwent MRI-scanning (3T GE), including T1-weighted, diffusion-MRI, and resting-state-fMRI (rsfMRI). Whole brain, white matter, gray matter, cortical gray matter and hippocampi volumes were measured using icobrain. rsfMRI between regions of the default-mode-network (DMN) was assessed using group independent-component-analysis. Median diffusivity and kurtosis were determined in gray and white-matter. DTI data was used to evaluate pairwise structural connectivity between lobar regions and the hippocampi.Logistic-Regression and Random-Forest models were trained to classify AD-status based on, respectively different isolated features and age, and feature-groups combined with age. RESULTS: Hippocampal features, features reflecting the functional connectivity between the medial-Pre-Frontal-Cortex (mPFC) and the posterior regions of the DMN, and structural interhemispheric frontal connectivity showed the strongest differences between AD-patients and controls. Structural interhemispheric parietal connectivity, structural connectivity between the parietal lobe and hippocampus in the right hemisphere, and mPFC-DMN-features, showed only an association with AD-status (p < 0.05) but not with age. Hippocampi volumes showed an association both with age and AD-status (p < 0.05).Smallest-hippocampus-volume was the most discriminative feature. The best performance (accuracy:0.74, sensitivity:0.74, specificity:0.74) was obtained with an RF-model combining the best feature from each feature-group (smallest hippocampus volume, WM volume, median GM MD, lTPJ-mPFC connectivity and structural interhemispheric frontal connectivity) and age. CONCLUSIONS: Brain connectivity changes caused by AD are reflected in multiple MRI-biomarkers. Decline in both the functional DMN-connectivity and the parietal interhemispheric structural connectivity may assist sepparating healthy-aging driven changes from AD, complementing hippocampal volumes which are affected by both aging and AD.

Direct isolation of human central nervous system stem cells.

Stem cells, which are clonogenic cells with self-renewal and multilineage differentiation properties, have the potential to replace or repair damaged tissue. We have directly isolated clonogenic human central nervous system stem cells (hCNS-SC) from fresh human fetal brain tissue, using antibodies to cell surface markers and fluorescence-activated cell sorting. These hCNS-SC are phenotypically 5F3 (CD133)(+), 5E12(+), CD34(-), CD45(-), and CD24(-/lo). Single CD133(+) CD34(-) CD45(-) sorted cells initiated neurosphere cultures, and the progeny of clonogenic cells could differentiate into both neurons and glial cells. Single cells from neurosphere cultures initiated from CD133(+) CD34(-) CD45(-) cells were again replated as single cells and were able to reestablish neurosphere cultures, demonstrating the self-renewal potential of this highly enriched population. Upon transplantation into brains of immunodeficient neonatal mice, the sorted/expanded hCNS-SC showed potent engraftment, proliferation, migration, and neural differentiation.

Fluorescent cationic probes of mitochondria. Metrics and mechanism of interaction.

Mitochondria strongly accumulate amphiphilic cations. We report here a study of the association of respiring rat liver mitochondria with several fluorescent cationic dyes from differing structural classes. Using gravimetric and fluorometric analysis of dye partition, we find that dyes and mitochondria interact in three ways: (a) uptake with fluorescence quenching, (b) uptake without change in fluorescence intensity, and (c) lack of uptake. For dyes that quench upon uptake, the extent of quenching correlates with the degree of aggregation of the dye to dimers, as predicted by theory (Tomov, T.C. 1986. J. Biochem. Biophys. Methods. 13:29-38). Also predicted is the relationship observed between quenching and the mitochondria concentration when constant dye is titrated with mitochondria. Not predicted is the relationship observed between quenching and dye concentration when constant mitochondria are titrated with dye. Because a limit to dye uptake exists, in this case, the degree of quenching decreases as dye is added. A Langmuir isotherm analysis gives phenomenological parameters that predict quenching when it is observed as a function of dye concentration. By allowing for a decrease in membrane potential, caused by incorporation of cationic dye into the lipid bilayer, a modification of the Tomov theory predicts the dye titration data. We present a model of cationic dye-mitochondria interaction and discuss the use of these as probes of mitochondrial membrane potential.

Platelet attachment and spreading on polystyrene surfaces: dependence on fibronectin and plasma concentration.

Fibronectin promoted platelet attachment and spreading on polystyrene surfaces but was not essential if the surfaces were coated with plasma. The dependence of platelet adhesion on plasma concentration was complex. The extent of attachment and spreading was increased on surfaces treated with up to 1.0% plasma and decreased at higher plasma concentrations. The results support the hypothesis that protein adsorption is not directly related to protein concentration when surfaces are exposed to complex protein mixtures.

Deposition of fibronectin on material surfaces exposed to plasma: quantitative and biological studies.

Experiments were carried out to characterize plasma fibronectin deposition onto material surfaces exposed to plasma solutions. Under nonclotting conditions, the amount of fibronectin adsorption on the surfaces, determined by an indirect radioactive antibody assay, was maximal at low plasma concentrations (0.1%). At higher concentrations of plasma, other plasma proteins appeared to compete with and inhibit adsorption of fibronectin. Biological activity (fibronectin-promoted cell spreading) was also greatest at low plasma concentrations and decreased as the plasma concentration was raised. When surfaces were exposed to plasma under clotting conditions (i.e., addition of Ca2+ and thrombin), fibronectin deposition on the surfaces and biological activity remained constant or increased as the plasma concentration was raised. Based on indirect immunofluorescent antibody assays, the fibronectin deposited from clotting plasma appeared to be in a punctate distribution over the entire material surface and occasionally was associated with discrete fibrillar structures. The increased deposition of fibronectin from clotting plasma compared to nonclotting plasma (approximately a 10-fold difference with 10% plasma) was partially a result of covalent crosslinking of fibronectin to fibrin based upon studies with putrescine added to inhibit crosslinking during clotting. On the other hand, the increase in biological activity that occurred if the surfaces were exposed to clotting plasma was completely inhibited by putrescine, indicating that fibronectin had to be crosslinked to fibrin to have biological activity under these conditions. Finally, fibronectin deposition also occurred on surfaces exposed to whole blood and was markedly enhanced when clotting occurred.