Noninvasive Evaluation of GIP Effects on β-Cell Mass Under High-Fat Diet

Abstract

Pancreatic β-cell mass (BCM) has an importance in the pathophysiology of diabetes mellitus. Recently, glucagon-like peptide-1 receptor (GLP-1R)-targeted imaging has emerged as a promising tool for BCM evaluation. While glucose-dependent insulinotropic polypeptide/gastric inhibitory polypeptide (GIP) is known to be involved in high-fat diet (HFD)-induced obesity, the effect of GIP on BCM is still controversial. In this study, we investigated indium 111 (111In)-labeled exendin-4 derivative ([Lys12(111In-BnDTPA-Ahx)]exendin-4) single-photon emission computed tomography/computed tomography (SPECT/CT) as a tool for evaluation of longitudinal BCM changes in HFD-induced obese mice, at the same time we also investigated the effects of GIP on BCM in response to HFD using GIP-knockout (GIP-/-) mice. 111In-exendin-4 SPECT/CT was able to distinguish control-fat diet (CFD)-fed mice from HFD-fed mice and the pancreatic uptake values replicated the BCM measured by conventional histological methods. Furthermore, BCM expansions in HFD-fed mice were demonstrated by time-course changes of the pancreatic uptake values. Additionally, 111In-exendin-4 SPECT/CT demonstrated the distinct changes in BCM between HFD-fed GIP-/- (GIP-/-+HFD) and wild-type (WT+HFD) mice; the pancreatic uptake values of GIP-/-+HFD mice became significantly lower than those of WT+HFD mice. The different changes in the pancreatic uptake values between the two groups preceded those in fat accumulation and insulin resistance. Taken together with the finding of increased β-cell apoptosis in GIP-/-+HFD mice compared with WT+HFD mice, these data indicated that GIP has preferable effects on BCM under HFD. Therefore, 111In-exendin-4 SPECT/CT can be useful for evaluating increasing BCM and the role of GIP in BCM changes under HFD conditions.

Preservation effect of imeglimin on pancreatic β-cell mass: Noninvasive evaluation using 111In-exendin-4 SPECT/CT imaging and the perspective of mitochondrial involvements

“…H1000; RRID: AB_2336789; Vector Laboratory, Newark, CA). The proliferation rate was calculated as the ratio of insulin/Ki67/DAPI co-positive cells to total insulin-positive cells ( 23 ). To examine the apoptosis rate, the slides were stained using DeadEnd™ Fluorometric TUNEL System (catalog no.…”

“…A11075; RRID: AB_2534119; Abcam). The apoptosis rate is expressed by the ratio of insulin/TUNEL/DAPI co-positive cells to total insulin-positive cells ( 23 ). For both cell proliferation and apoptosis, the calculation was made using 50 islets from each mouse ( 4 ).…”

Noninvasive quantitative evaluation of viable islet grafts using 111In‐exendin‐4 SPECT/CT

“…Tissues were immediately fixed in 10% buffered formalin phosphate at 4°C. For accurate quantification of BCM, 10 sets of serial formalin‐fixed paraffin‐embedded sections (4 μm per section; 100 μm between each set) were analyzed for each mouse, as previously reported 17–20,26 . The slides were incubated in blocking buffer supplemented with rabbit polyclonal anti‐insulin primary antibody (100‐fold dilution; catalog no.…”

“…), followed by immediate resection, weighing of the liver, and measurement of the radioactivity in the resected organ using an auto‐well γ‐counter. The liver graft uptake values were calculated by dividing the radioactivity from the organ by that of the total injection of the probe ( 111 In exendin‐4), normalized by dividing by the organ weight (%ID/g) 17–20 …”

“…In particular, a 111 Indium‐labeled exendin‐4 derivative {[Lys12(111In‐BnDTPA‐Ahx)]exendin‐4} ( 111 In‐exendin‐4) has been used for the noninvasive longitudinal evaluation of pancreatic BCM in different mouse models 14,16–21 . In the 111 In‐exendin‐4 SPECT/CT images, the radioactive isotope (RI) uptake into the pancreas is significantly correlated with histologically measured BCM, 17–20 suggesting that 111 In‐exendin‐4 may be useful for the assessment of islet graft BCM as well as pancreatic BCM. However, the utility of GLP‐1R‐targeted imaging has not been fully evaluated with respect to islet grafts, especially in intraportal transplantation, which is currently the only practical IT method available in clinical settings.…”