Eventual fibrosis [2,14]. Our model recapitulated many of these findings. Recruited inflammatory cells were observed within the kidneys of the antiGBM PS 1145 custom synthesis nephritis mice, VCAM-1 expression was elevated and renal 
failure ultimately developed. We selected two parameters, tmax and AUC, that could be conveniently derived from the quantitative analysis of clinically acquired PET images to evaluate the nephrographs as a potential indication of the status of anti-GBM induced nephritis. The trends of tmax and AUC changes within the 21-day study period were parallel to the changes in renal function and pathological changes in the anti-GBM nephritic mice, but most importantly the FDG uptake peak preceded the clinical disease peak by ,1 week. As shown in Figure 1, the clinical phenotype 23977191 (proteinuria, serumFigure 3. Quantitative analysis of PET-CT images. Time-activity curves of FDG in kidneys (left and right kidneys pooled) reconstructed at short time intervals (0? min: 30 s; 1? min: 15 s; 5?0 min: 30 s; 20?40 min: 60 s; 40?0 min: 120 s). Day 0, 7, 14, and 21: n = 4?. Error bars are the standard deviation. The defined nephritis characteristic phase is visualized in 0?0 min. doi:10.1371/journal.pone.0057418.gcreatinine) and pathological phenotype (GN score) peaked on day 14 and subsequently exhibited a self-limiting course as reported [15,16]. In comparison, the FDG renal retention peaked on day 7 (Table 2) where both tmax and AUC were greatest over our study period. Of particular interest, the occurrence of these changes in renal FDG retention coincided with systemic endothelial cell activation and inflammation and the early phase of renal inflammation, as marked by the rapid increase in serum and urine VCAM-1 by day 7 (Table 2). To our knowledge this is the first study showing a correlation between VCAM-1 expression and FDG uptake/retention in the kidneys. The mechanism of FDG handling in the kidney is complex and is not fully understood [13,17]. Like glucose, FDG accumulates in the kidney and then undergoes glomerular filtration. Unlike glucose, the two-stage 
reabsorption of FDG in the renal tubular proximal segment is incomplete with some excreted through the urine [18]. Nephrographs or TACs reflect the perfusion of the kidney at the earliest time points followed by impact of glomerular filtration, tubular reabsorption and secretion, and finally clearance from the renal pelvis. As is evident from the nephrograph on day 0, FDG accumulated then rapidly cleared through kidneys followed by a prolonged plateau phase. In contrast, on day 7 the anti-GBM nephritic mice showed a delayed uptake with peak shift, increased tmax (8.7 min on day 7 vs. 1.9 min on day 0), prolonged tubular concentration phase, less rapid excretion rate leading to delayed onset of the plateau phase. This contributes to the increased AUC. In our model, many factors could have contributed to the alteration of FDG retention. For example, focusing on the day 7 nephrographs, the shift in tmax may be an effect of decreased glomerular filtration and the increased in the AUC might be the consequence of uptake by inflammatory infiltrate within the kidney. Additionally nephritic edema, shown by increased kidney wet PLV-2 biological activity weight and a significant enlargement of the kidney size on CT images, might have raised the interstitial pressure, which could subsequently narrow the tubules thereby restricting the urine flow and leading to the slower rate of clearance during the excretion phase. While our exper.Eventual fibrosis [2,14]. Our model recapitulated many of these findings. Recruited inflammatory cells were observed within the kidneys of the antiGBM nephritis mice, VCAM-1 expression was elevated and renal failure ultimately developed. We selected two parameters, tmax and AUC, that could be conveniently derived from the quantitative analysis of clinically acquired PET images to evaluate the nephrographs as a potential indication of the status of anti-GBM induced nephritis. The trends of tmax and AUC changes within the 21-day study period were parallel to the changes in renal function and pathological changes in the anti-GBM nephritic mice, but most importantly the FDG uptake peak preceded the clinical disease peak by ,1 week. As shown in Figure 1, the clinical phenotype 23977191 (proteinuria, serumFigure 3. Quantitative analysis of PET-CT images. Time-activity curves of FDG in kidneys (left and right kidneys pooled) reconstructed at short time intervals (0? min: 30 s; 1? min: 15 s; 5?0 min: 30 s; 20?40 min: 60 s; 40?0 min: 120 s). Day 0, 7, 14, and 21: n = 4?. Error bars are the standard deviation. The defined nephritis characteristic phase is visualized in 0?0 min. doi:10.1371/journal.pone.0057418.gcreatinine) and pathological phenotype (GN score) peaked on day 14 and subsequently exhibited a self-limiting course as reported [15,16]. In comparison, the FDG renal retention peaked on day 7 (Table 2) where both tmax and AUC were greatest over our study period. Of particular interest, the occurrence of these changes in renal FDG retention coincided with systemic endothelial cell activation and inflammation and the early phase of renal inflammation, as marked by the rapid increase in serum and urine VCAM-1 by day 7 (Table 2). To our knowledge this is the first study showing a correlation between VCAM-1 expression and FDG uptake/retention in the kidneys. The mechanism of FDG handling in the kidney is complex and is not fully understood [13,17]. Like glucose, FDG accumulates in the kidney and then undergoes glomerular filtration. Unlike glucose, the two-stage reabsorption of FDG in the renal tubular proximal segment is incomplete with some excreted through the urine [18]. Nephrographs or TACs reflect the perfusion of the kidney at the earliest time points followed by impact of glomerular filtration, tubular reabsorption and secretion, and finally clearance from the renal pelvis. As is evident from the nephrograph on day 0, FDG accumulated then rapidly cleared through kidneys followed by a prolonged plateau phase. In contrast, on day 7 the anti-GBM nephritic mice showed a delayed uptake with peak shift, increased tmax (8.7 min on day 7 vs. 1.9 min on day 0), prolonged tubular concentration phase, less rapid excretion rate leading to delayed onset of the plateau phase. This contributes to the increased AUC. In our model, many factors could have contributed to the alteration of FDG retention. For example, focusing on the day 7 nephrographs, the shift in tmax may be an effect of decreased glomerular filtration and the increased in the AUC might be the consequence of uptake by inflammatory infiltrate within the kidney. Additionally nephritic edema, shown by increased kidney wet weight and a significant enlargement of the kidney size on CT images, might have raised the interstitial pressure, which could subsequently narrow the tubules thereby restricting the urine flow and leading to the slower rate of clearance during the excretion phase. While our exper.
