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

Quantitative imaging using [18F]F-TZ3108 to assess metabolic-associated fatty liver disease progression and low-carbohydrate diet efficacy

OBJECTIVE

The Sigma-1 receptor (Sig-1R), located in the mitochondrion-associated membranes (MAMs), is an important biomarker for endoplasmic reticulum (ER) stress and plays a crucial role in the advancement of metabolic-associated fatty liver disease (MAFLD). Despite its significance, current methods to monitor MAFLD progression and treatment response are limited. This study aims to address this gap by utilizing [18F]F-TZ3108, an effecient tracer targeting Sig-1R, to quantitatively assess MAFLD progression and the efficacy of a low-carbohydrate diet (LCD) as a potential therapeutic intervention.

METHODS

The C57 BL/6 J mice were fed either a high-fat diet (HFD) or regular diet (CTR) for 12 weeks, and the progression of MAFLD was continuously monitored at 0, 4, 8, 12 weeks via [18F]F-TZ3108 positron emission tomography/computed tomography (PET/CT) and ex vivo assessment. After confirming successful induction, LDC intervention was administered in the HFD group for 2 weeks. And relevant post-treatment evaluations were also performed.

RESULTS

PET/CT revealed a continuous decline in the hepatic binding potential (BPND) of [18F]F-TZ3108 in mice in the HFD group during the induction period, when compared with the BPND in the CTR group. This reduction was significant after the 4th week of induction (p < 0.05). Furthermore, following intervention with LCD, there was a significant improvement in BPND (LCD vs HFD, p = 0.001).

CONCLUSIONS

The results of this study demonstrate that LCD therapy effectively mitigates MAFLD progression. Furthermore, the use of PET imaging with [18F]F-TZ3108 provides a reliable, non-invasive method for monitoring the progression and treatment response of MAFLD, offering significant potential for early detection and personalized treatment evaluation.

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.