Blood pool activity on F-18 FDG PET/CT as a possible imaging biomarker of metabolic syndrome

Evaluation of [18F]F-TZ3108 for PET Imaging of Metabolic-Associated Fatty Liver Disease

PURPOSE

Sigma-1 receptor (Sig-1R), a chaperone that resides at the mitochondrion-associated endoplasmic reticulum (ER) membrane, is an ER stress biomarker. It is thought that ER stress plays a critical role in the progression of metabolic-associated fatty liver disease (MAFLD). The aim of this study was to evaluate a positron emission tomography (PET) tracer [¹⁸F]F-TZ3108 targeting Sig-1R for MAFLD.

PROCEDURES

The mouse model of MAFLD was established by feeding high-fat diet (HFD) for 12 weeks. Dynamic (0-60 min) PET/CT scans were performed after intravenous injection of 2-deoxy-2[¹⁸F]fluoro-D-glucose ([¹⁸F]-FDG) and [¹⁸F]F-TZ3108. Tracer kinetic modeling was performed for quantification of the PET/CT imaging of the liver. Post-PET biodistribution, the liver tissue western blotting (WB), and immunofluorescence (IF) were performed to compare the expression of Sig-1R levels in the organs harvested from both MAFLD and age-matched control mice.

RESULTS

The micro PET/CT imaging revealed a significantly decreased uptake of [¹⁸F]F-TZ3108 in the livers of the MAFLD group compared to the healthy controls, while the uptake of [¹⁸F]-FDG in the livers was not significantly different between the two groups. Based on the tracer kinetic modeling, the binding disassociate rate (k₄) for [¹⁸F]F-TZ3108 was significantly increased in MAFLD group compared to healthy controls. The volume distribution (V_T), and the non-displacement binding potential (BP_ND) revealed significantly decrease in MAFLD compared to healthy controls respectively. The post-PET biodistribution (%ID/g) of [¹⁸F]F-TZ3108 in the livers of MAFLD mice was significantly reduced nearly twofold than that in the livers of control mice. WB and IF experiments further confirmed the reduction of Sig-1R expression in the MAFLD group.

CONCLUSIONS

The expression of Sig-1R in the liver, measured by the PET tracer, [¹⁸F]F-TZ3108, was significantly decreased in mouse model of MAFLD. The [¹⁸F]F-TZ3108 PET/CT imaging may provide a novel means of visualization for ER stress in MAFLD or other diseases in vivo.

Changes of macrophage and CD4+ T cell in inflammatory response in type 1 diabetic mice

Immune cells play an important role in the development of inflammation in type 1 diabetes mellitus, so we want to explore the changes of CD4+ T cells and macrophages in vivo, which can provide an experimental basis for immunotherapy based on CD4+ T cells and macrophages. The intraperitoneal injection of streptozocin was used to induce a type 1 diabetes mellitus mouse model; the blood glucose, body weight, and the expression of inflammatory factors in the kidney were measured. Immunohistochemistry was applied to determine and analyze the infiltration of CD4+ T cells and macrophages in the spleen, pancreas, and kidney. The subtypes of macrophages in the kidney and CD4+ T cells in the spleen were analyzed by flow cytometry. Our study suggests that CD4+ T cells and macrophages increase, while the inflammatory immune response system is activated in the development of T1DM. CD4+ T cells positively correlated with macrophages in the pancreas and kidney of T1DM. CD4+ T cells turn to pro-inflammatory subtypes in the spleen of T1DM, while macrophages turn to pro-inflammatory subtypes in the kidney of T1DM. Therefore, regulation of CD4+ T cells and macrophages may be a potential target for T1DM and kidney complications.