Positron emission tomography and single photon emission computed tomography imaging of tertiary lymphoid structures during the development of lupus nephritis.

Lymphoid neogenesis occurs in tissues targeted by chronic inflammatory processes, such as infection and autoimmunity. In systemic lupus erythematosus (SLE), such structures develop within the kidneys of lupus-prone mice ((NZBXNZW)F1) and are observed in kidney biopsies taken from SLE patients with lupus nephritis (LN). The purpose of this prospective longitudinal animal study was to detect early kidney changes and tertiary lymphoid structures (TLS) using in vivo imaging. Positron emission tomography (PET) by tail vein injection of 18-F-fluoro-2-deoxy-D-glucose (18F-FDG)(PET/FDG) combined with computed tomography (CT) for anatomical localization and single photon emission computed tomography (SPECT) by intraperitoneal injection of 99mTC labeled Albumin Nanocoll (99mTC-Nanocoll) were performed on different disease stages of NZB/W mice (n = 40) and on aged matched control mice (BALB/c) (n = 20). By using one-way ANOVA analyses, we compared two different compartmental models for the quantitative measure of 18F-FDG uptake within the kidneys. Using a new five-compartment model, we observed that glomerular filtration of 18FFDG in lupus-prone mice decreased significantly by disease progression measured by anti-dsDNA Ab production and before onset of proteinuria. We could not visualize TLS within the kidneys, but we were able to visualize pancreatic TLS using 99mTC Nanocoll SPECT. Based on our findings, we conclude that the five-compartment model can be used to measure changes of FDG uptake within the kidney. However, new optimal PET/SPECT tracer administration sites together with more specific tracers in combination with magnetic resonance imaging (MRI) may make it possible to detect formation of TLS and LN before clinical manifestations.

The role of endoplasmic reticulum in in vivo cancer FDG kinetics.

A recent result obtained by means of an in vitro experiment with cancer cultured cells has configured the endoplasmic reticulum as the preferential site for the accumulation of 2-deoxy-2-[18F]fluoro-D-glucose (FDG). Such a result is coherent with cell biochemistry and is made more significant by the fact that the reticular accumulation rate of FDG is dependent upon extracellular glucose availability. The objective of the present paper is to confirm in vivo the result obtained in vitro concerning the crucial role played by the endoplasmic reticulum in FDG cancer metabolism. This study utilizes data acquired by means of a Positron Emission Tomography scanner for small animals in the case of CT26 models of cancer tissues. The recorded concentration images are interpreted within the framework of a three-compartment model for FDG kinetics, which explicitly assumes that the endoplasmic reticulum is the dephosphorylation site for FDG in cancer cells. The numerical reduction of the compartmental model is performed by means of a regularized Gauss-Newton algorithm for numerical optimization. This analysis shows that the proposed three-compartment model equals the performance of a standard Sokoloff's two-compartment system in fitting the data. However, it provides estimates of some of the parameters, such as the phosphorylation rate of FDG, more consistent with prior biochemical information. These results are made more solid from a computational viewpoint by proving the identifiability and by performing a sensitivity analysis of the proposed compartment model.

G6Pase location in the endoplasmic reticulum: Implications on compartmental analysis of FDG uptake in cancer cells.

The favourable kinetics of 18F-fluoro-2-deoxyglucose (FDG) permits to depict cancer glucose consumption by a single evaluation of late tracer uptake. This standard procedure relies on the slow radioactivity loss, usually attributed to the limited tumour expression of G6P-phosphatase (G6Pase). However, this classical interpretation intrinsically represents an approximation since, as in all tissues, cancer G6Pase activity is remarkable and is confined to the endoplasmic reticulum (ER), whose lumen must be reached by phosphorylated FDG to explain its hydrolysis and radioactivity release. The present study tested the impact of G6Pase sequestration on the mathematical description of FDG trafficking and handling in cultured cancer cells. Our data show that accounting for tracer access to the ER configures this compartment as the preferential site of FDG accumulation. This is confirmed by the reticular localization of fluorescent FDG analogues. Remarkably enough, reticular accumulation rate of FDG is dependent upon extracellular glucose availability, thus configuring the same ER as a significant determinant of cancer glucose metabolism.

Anthropometric and glucometabolic changes in an aged mouse model of lipocalin-2 overexpression.

BACKGROUND: Lipocalin-2 (LCN2) is widely expressed in the organism with pleiotropic roles. In particular, its overexpression correlates with tissue stress conditions including inflammation, metabolic disorders, chronic diseases and cancer. OBJECTIVES: To assess the effects of systemic LCN2 overexpression on adipose tissue and glucose metabolism. SUBJECTS: Eighteen-month-old transgenic mice with systemic LCN2 overexpression (LCN2-Tg) and age/sex-matched wild-type mice. METHODS: Metabolic cages; histology and real-time PCR analysis; glucose and insulin tolerance tests; ELISA; flow cytometry; microPET and serum analysis. RESULTS: LCN2-Tg mice were smaller compared to controls but they ate (P = 0.0156) and drank (P = 0.0057) more and displayed a higher amount of visceral adipose tissue. Furthermore, LCN2-Tg mice with body weight ≥20 g showed adipocytes with a higher cell area (P < 0.0001) and altered expression of genes involved in adipocyte differentiation and inflammation. In particular, mRNA levels of adipocyte-derived Pparg (P ≤ 0.0001), Srebf1 (P < 0.0001), Fabp4 (P = 0.056), Tnfa (P = 0.0391), Il6 (P = 0.0198), and Lep (P = 0.0003) were all increased. Furthermore, LCN2-Tg mice displayed a decreased amount of basal serum insulin (P = 0.0122) and a statistically significant impaired glucose tolerance and insulin sensitivity consistent with Slc2a2 mRNA (P ≤ 0.0001) downregulated expression. On the other hand, Insr mRNA (P ≤ 0.0001) was upregulated and correlated with microPET analysis that demonstrated a trend in reduced whole-body glucose consumption and MRGlu in the muscles and a significantly reduced MRGlu in brown adipose tissue (P = 0.0247). Nevertheless, an almost nine-fold acceleration of hexokinase activity was observed in the LCN2-Tg mice liver compared to controls (P = 0.0027). Moreover, AST and ALT were increased (P = 0.0421 and P = 0.0403, respectively), which indicated liver involvement also demonstrated by histological staining. CONCLUSIONS: We show that LCN2 profoundly impacts adipose tissue size and function and glucose metabolism, suggesting that LCN2 should be considered as a risk factor in ageing for metabolic disorders leading to obesity.