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The conventional imaging geometry for small animal cone beam computed tomography (CBCT) is that a detector panel rotates around the head-to-tail axis of an imaged animal (‘tubular’ geometry). Another unusual but possible imaging geometry is that the detector panel rotates around the anterior-to-posterior axis of the animal (‘pancake’ geometry). The small animal radiation research platform developed at Johns Hopkins University employs the pancake geometry where a prone-positioned animal is rotated horizontally between an x-ray source and detector panel. This study is to assess the CBCT image quality in the pancake geometry and investigate potential methods for improvement. We compared CBCT images acquired in the pancake geometry with those acquired in the tubular geometry when the phantom/animal was placed upright simulating the conventional CBCT geometry. Results showed signal-to-noise and contrast-to-noise ratios in the pancake geometry were reduced in comparison to the tubular geometry at the same dose level. But the overall spatial resolution within the transverse plane of the imaged cylinder/animal was better in the pancake geometry. A modest exposure increase to two folds in the pancake geometry can improve image quality to a level close to the tubular geometry. Image quality can also be improved by inclining the animal, which reduces streak artifacts caused by bony structures. The major factor resulting in the inferior image quality in the pancake geometry is the elevated beam attenuation along the long axis of the phantom/animal and consequently increased scatter-to-primary ratio in that orientation. Not withstanding, the image quality in the pancake-geometry CBCT is adequate to support image guided animal positioning, while providing unique advantages of non-coplanar and multiple mice irradiation. This study also provides useful knowledge about the image quality in the two very different imaging geometries, i.e. pancake and tubular geometry, respectively. [ABSTRACT FROM AUTHOR]

The molecular mechanisms responsible for the development of proteinuria and glomerulosclerosis in radiation nephropathy remain largely unknown. Podocytes are increasingly recognized as key players in the pathogenesis of proteinuria in primary and secondary glomerular disorders. The lipid-modulating enzyme sphingomyelin phosphodiesterase acid-like 3B (SMPDL3b) is a key determinant of podocyte injury and a known off target of the anti-CD20 antibody rituximab (RTX). The current study investigates the role of sphingolipids in radiation-induced podocytopathy. After a single dose of radiation (8 Gy), several ceramide species were significantly elevated. In particular, C16:00, C24:00, and C24:1 ceramides were the most abundant ceramide species detected. These changes were paralleled by a time-dependent drop in SMPDL3b protein, sphingosine, and sphingosine-1-phosphate levels. Interestingly, SMPDL3b-overexpressing podocytes had higher basal levels of sphingosine-1-phosphate and maintained basal ceramide levels after irradiation. Morphologically, irradiated podocytes demonstrated loss of filopodia and remodeling of cortical actin. Furthermore, the actin binding protein ezrin relocated from the plasma membrane to the cytosol as early as 2 h after radiation. In contrast, SMPDL3b overexpressing podocytes were protected from radiation-induced cytoskeletal remodeling. Treatment with RTX before radiation exposure partially protected podocytes from SMPDL3b loss, cytoskeletal remodeling, and caspase 3 cleavage. Our results demonstrate that radiation injury induces early cytoskeletal remodeling, down-regulation of SMPDL3b, and elevation of cellular ceramide levels. Overexpression of SMPDL3b and pretreatment with RTX confer a radioprotective effect in cultured podocytes. These findings indicate a potential role for SMPDL3b and RTX in radiation-induced podocytopathy. [ABSTRACT FROM AUTHOR]

Radiation-induced gastroin-testinal (GI) syndrome currently has no effective prophylactic or therapeutic treatment. Previous studies and our data have demonstrated the important role of p53 in acute radiation-induced GI syndrome in mice. Many cytokines, such as tumor necrosis factor-α and fibroblast growth factor (bFGF), have been found to protect against radiation-induced intestinal injury, although the underlying mechanisms remain to be identified. Here, we report blockage of p53 through a protein kinase B (Akt) pathway in intestinal progenitor/stem cells or crypt cells as a novel molecular mechanism of growth factor-mediated intestinal radioprotection. Treatment with platelet-derived growth factor (PDGF-BB) or bFGF activated Akt phosphor-ylation in the intestinal crypt, lessened intestinal crypt p53 expression, decreased radiation-induced apoptosis in mouse intestinal progenitor/ stem cell marker leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5)-positive cells by an average of 50%, and increased the survival rate of mice with abdominal radiation by 3 days in average. Conversely, the Akt inhibitor perifosine obstructed growth factor-simulated Akt phosphorylation while promoting radiation-in-duced p53 expression in intestinal crypts. Importantly, reduced Akt phosphorylation and elevated p53 expression due to the Akt inhibitor perifosine impaired intestinal progenitor/stem cells radioprotection provided by PDGF-BB and bFGF. Consistently, PDGF-BB and bFGF both upregulated Akt activation, suppressed radiation-induced p53 expression, and abrogated radiation-induced apoptosis in IEC-6 cells, although p53 overexpression in IEC-6 cells partially counteracted the radioprotection of PDGF-BB and bFGF. Our data suggest that intestinal crypt radioprotection by PDGF-BB and bFGF is dependent on regulation of Akt/p53 signaling. [ABSTRACT FROM AUTHOR]