Enhancing signal detectability in learning-based CT reconstruction with a model observer inspired loss function.

Deep neural networks used for reconstructing sparse-view CT data are typically trained by minimizing a pixel-wise mean-squared error or similar loss function over a set of training images. However, networks trained with such pixel-wise losses are prone to wipe out small, low-contrast features that are critical for screening and diagnosis. To remedy this issue, we introduce a novel training loss inspired by the model observer framework to enhance the detectability of weak signals in the reconstructions. We evaluate our approach on the reconstruction of synthetic sparse-view breast CT data, and demonstrate an improvement in signal detectability with the proposed loss.

The neuroprotective N-terminal amyloid-ß core hexapeptide reverses reactive gliosis and gliotoxicity in Alzheimer's disease pathology models.

BACKGROUND: Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by accumulation of extracellular amyloid beta (Aß) and intracellular neurofibrillary tangles, leading to chronic activation of astrocytes and microglia and persistent neuroinflammation. Aß-linked activation of microglia and astrocytes leads to increased intracellular calcium and production of proinflammatory cytokines, impacting the progression of neurodegeneration. An N-terminal Aß fragment (Aß1-15) and a shorter hexapeptide core sequence within the N-Aß fragment (N-Aßcore: Aß10-15) have previously been shown to protect against Aß-induced mitochondrial dysfunction, oxidative stress and apoptosis in neurons and rescue synaptic and spatial memory deficits in an APP/PSEN1 mouse model. Here, we hypothesized that the N-Aß fragment and N-Aßcore are protective against Aß-induced gliotoxicity, promoting a neuroprotective environment and potentially alleviating the characteristically persistent neuroinflammation present in AD. METHODS: We treated ex vivo organotypic brain slice cultures from an aged familial AD mouse model, 5xFAD, with the N-Aßcore and used immunocytochemistry to assess the impact on astrogliosis and microgliosis and alterations in synaptophysin-positive puncta engulfed by microglia. Isolated neuron/glia cultures, mixed glial cultures or a microglial cell line were treated with oligomeric human Aß at concentrations mimicking the pathogenic concentrations (µM) observed in AD in the absence or presence of the non-toxic N-terminal Aß fragments. Resultant changes in synaptic density, gliosis, oxidative stress, mitochondrial dysfunction, apoptosis, and the expression and release of proinflammatory markers were then determined. RESULTS: We demonstrate that the N-terminal Aß fragments mitigated the phenotypic switch leading to astrogliosis and microgliosis induced by pathological concentrations of Aß in mixed glial cultures and organotypic brain slice cultures from the transgenic 5xFAD mouse model, while protecting against Aß-induced oxidative stress, mitochondrial dysfunction and apoptosis in isolated astrocytes and microglia. Moreover, the addition of the N-Aßcore attenuated the expression and release of proinflammatory mediators in microglial cells activated by Aß and rescued microglia-mediated loss of synaptic elements induced by pathological levels of Aß. CONCLUSIONS: Together, these findings indicate the protective functions of the N-terminal Aß fragments extend to reactive gliosis and gliotoxicity induced by Aß, by preventing or reversing glial reactive states indicative of neuroinflammation and synaptic loss central to AD pathogenesis.

Anti-Neuroinflammatory Effects of a Semi-Synthetic Isoorientin-Based Glycogen Synthase Kinase-3ß Inhibitor in Lipopolysaccharide-Activated Microglial Cells.

Neuroinflammation contributes to the pathogenesis of several neurodegenerative disorders. Glycogen synthase kinase-3ß (GSK-3ß) regulates the release of proinflammatory cytokines and promotes inflammatory responses in immune cells. Microglia are the resident mononuclear immune cells of the central nervous system. Here, we investigated the anti-neuroinflammatory effects of (2S,3S,4R,5R,6S)-6-(2-(3,4-dimethoxyphenyl)-5,7-dimethoxy-4-oxo-4H-chromen-6-yl)-3,4,5-trihydroxy-N-((S)-1,1,1-trifluoropropan-2-yl)tetrahydro-2H-pyran-2-carboxamide (TFGF-18), a semisynthetic GSK-3ß inhibitor, in lipopolysaccharide (LPS) activation of spontaneously immortalized SIM-A9 microglial cells and of mouse cortical microglia. TFGF-18 at 2.5 µM concentration inhibited LPS-induced production of nitric oxide by 56.3% and the proinflammatory cytokines TNF-α and IL-1ß by 28.3 and 59.2% in SIM-A9 cells, respectively, relative to the LPS treatment control group. Pretreatment of mouse primary microglial cells with TFGF-18 at 2.5 µM concentration led to a reduction of 58.7% in TNF-α+ microglial cells at 24 h post-LPS stimulation. The migration of LPS-activated SIM-A9 cells was also reduced by 26.7% with pretreatment of TFGF-18 in a scratch assay. Analyses of signaling pathways demonstrated that TFGF-18 led to the suppression of LPS-induced GSK-3ß activation and p65/NF-κB activity. Furthermore, the co-culture of SIM-A9 with SH-SY5Y neuroblastoma cells showed the suppression of TFGF-18 to microglia-mediated neurotoxicity in vitro. The findings indicate strong inhibitory effects of TFGF-18 on LPS-induced microglia activation via regulation of GSK-3ß and downstream p65/NF-κB signaling. The results suggest a potential role of TFGF-18 in neuroprotection via its anti-neuroinflammatory effect.

Transcriptome Profile of Nicotinic Receptor-Linked Sensitization of Beta Amyloid Neurotoxicity.

Understanding the specific gene changes underlying the prodromic stages of Alzheimer's disease pathogenesis will aid the development of new, targeted therapeutic strategies for this neurodegenerative disorder. Here, we employed RNA-sequencing to analyze global differential gene expression in a defined model nerve cell line expressing α4ß2 nicotinic receptors (nAChRs), high-affinity targets for beta amyloid (Aß). The nAChR-expressing neuronal cells were treated with nanomolar Aß1-42 to gain insights into the molecular mechanisms underlying Aß-induced neurotoxicity in the presence of this sensitizing target receptor. We identified 15 genes (out of 15,336) that were differentially expressed upon receptor-linked Aß treatment. Genes up-regulated with Aß treatment were associated with calcium signaling and axonal vesicle transport (including the α4 nAChR subunit, the calcineurin regulator RCAN3, and KIF1C of the kinesin family). Downregulated genes were associated with metabolic, apoptotic or DNA repair pathways (including APBA3, PARP1 and RAB11). Validation of the differential expression was performed via qRT-PCR and immunoblot analysis in the defined model nerve cell line and primary mouse neurons. Further verification was performed using immunocytochemistry. In conclusion, we identified apparent changes in gene expression on Aß treatment in the presence of the sensitizing nAChRs, linked to early-stage Aß-induced neurotoxicity, which may represent novel therapeutic targets.

Linker Variation and Structure-Activity Relationship Analyses of Carboxylic Acid-based Small Molecule STAT3 Inhibitors.

The molecular determinants for the activities of the reported benzoic acid (SH4-54), salicylic acid (BP-1-102), and benzohydroxamic acid (SH5-07)-based STAT3 inhibitors were investigated to design optimized analogues. All three leads are based on an N-methylglycinamide scaffold, with its two amine groups condensed with three different functionalities. The three functionalities and the CH2 group of the glycinamide scaffold were separately modified. The replacement of the pentafluorobenzene or cyclohexylbenzene, or replacing the benzene ring of the aromatic carboxylic or hydroxamic acid motif with heterocyclic components (containing nitrogen and oxygen elements) all decreased potency. Notably, the Ala-linker analogues, 1a and 2v, and the Pro-based derivative 5d, all with (R)-configuration at the chiral center, had improved inhibitory activity and selectivity against STAT3 DNA-binding activity in vitro, with IC50 of 3.0 ± 0.9, 1.80 ± 0.94, and 2.4 ± 0.2 µM, respectively. Compounds 1a, 2v, 5d, and other analogues inhibited constitutive STAT3 phosphorylation and activation in human breast cancer and melanoma lines, and blocked tumor cell viability, growth, colony formation, and migration in vitro. Pro-based analogue, 5h, with a relatively polar tetrahydropyranyl (THP) ring, instead of the cyclohexyl, showed improved permeability. In general, the (R)-configuration Pro-based analogs showed the overall best profile, including physicochemical properties (e.g., microsomal metabolic stability, Caco-2 permeability), and in particular, 5d showed improved tumor-cell specificity.