Use of the PET ligand florbetapir for in vivo imaging of pancreatic islet amyloid deposits in hIAPP transgenic mice

Neuroinflammation induced by amyloid-forming pancreatic amylin: Rationale for a mechanistic hypothesis

Amylin is a systemic neuroendocrine hormone co-expressed and co-secreted with insulin by pancreatic β-cells. In persons with thype-2 diabetes, amylin forms pancreatic amyloid triggering inflammasome and interleukin-1β signaling and inducing β-cell apoptosis. Here, we summarize recent progress in understanding the potential link between amyloid-forming pancreatic amylin and Alzheimer's disease (AD). Clinical data describing amylin pathology in AD alongside mechanistic studies in animals are reviewed. Data from multiple research teams indicate higher amylin concentrations are associated with increased frequency of cognitive impairment and amylin co-aggregates with β-amyloid in AD-type dementia. Evidence from rodent models further suggests cerebrovascular amylin accumulation as a causative factor underlying neurological deficits. Analysis of relevant literature suggests that modulating the amylin-interleukin-1β pathway may provide an approach for counteracting neuroinflammation in AD.

RIPK3 promotes islet amyloid-induced β-cell loss and glucose intolerance in a humanized mouse model of type 2 diabetes

OBJECTIVE

Aggregation of human islet amyloid polypeptide (hIAPP), a β-cell secretory product, leads to islet amyloid deposition, islet inflammation and β-cell loss in type 2 diabetes (T2D), but the mechanisms that underlie this process are incompletely understood. Receptor interacting protein kinase 3 (RIPK3) is a pro-death signaling molecule that has recently been implicated in amyloid-associated brain pathology and β-cell cytotoxicity. Here, we evaluated the role of RIPK3 in amyloid-induced β-cell loss using a humanized mouse model of T2D that expresses hIAPP and is prone to islet amyloid formation.

METHODS

We quantified amyloid deposition, cell death and caspase 3/7 activity in islets isolated from WT, Ripk3-/-, hIAPP and hIAPP; Ripk3-/- mice in real time, and evaluated hIAPP-stimulated inflammation in WT and Ripk3-/- bone marrow derived macrophages (BMDMs) in vitro. We also characterized the role of RIPK3 in glucose stimulated insulin secretion (GSIS) in vitro and in vivo. Finally, we examined the role of RIPK3 in high fat diet (HFD)-induced islet amyloid deposition, β-cell loss and glucose homeostasis in vivo.

RESULTS

We found that amyloid-prone hIAPP mouse islets exhibited increased cell death and caspase 3/7 activity compared to amyloid-free WT islets in vitro, and this was associated with increased RIPK3 expression. hIAPP; Ripk3-/- islets were protected from amyloid-induced cell death compared to hIAPP islets in vitro, although amyloid deposition and caspase 3/7 activity were not different between genotypes. We observed that macrophages are a source of Ripk3 expression in isolated islets, and that Ripk3-/- BMDMs were protected from hIAPP-stimulated inflammatory gene expression (Tnf, Il1b, Nos2). Following 52 weeks of HFD feeding, islet amyloid-prone hIAPP mice exhibited impaired glucose tolerance and decreased β-cell area compared to WT mice in vivo, whereas hIAPP; Ripk3-/- mice were protected from these impairments.

CONCLUSIONS

In conclusion, loss of RIPK3 protects from amyloid-induced inflammation and islet cell death in vitro and amyloid-induced β-cell loss and glucose intolerance in vivo. We propose that therapies targeting RIPK3 may reduce islet inflammation and β-cell loss and improve glucose homeostasis in the pathogenesis of T2D.

Imaging in experimental models of diabetes

Translational medicine, experimental medicine and experimental animal models, in particular mice and rats, represent a multidisciplinary field that has made it possible to achieve, in the last decades, important scientific progress. In this review, we have summarized the most frequently used imaging animal models, such as ultrasound (US), micro-CT, MRI and the optical imaging methods, and their main implications in diagnostic and therapeutic fields, with a particular focus on diabetes mellitus, a multifactorial disease extremely widespread among the general population.

The β Cell in Diabetes: Integrating Biomarkers With Functional Measures

The pathogenesis of hyperglycemia observed in most forms of diabetes is intimately tied to the islet β cell. Impairments in propeptide processing and secretory function, along with the loss of these vital cells, is demonstrable not only in those in whom the diagnosis is established but typically also in individuals who are at increased risk of developing the disease. Biomarkers are used to inform on the state of a biological process, pathological condition, or response to an intervention and are increasingly being used for predicting, diagnosing, and prognosticating disease. They are also proving to be of use in the different forms of diabetes in both research and clinical settings. This review focuses on the β cell, addressing the potential utility of genetic markers, circulating molecules, immune cell phenotyping, and imaging approaches as biomarkers of cellular function and loss of this critical cell. Further, we consider how these biomarkers complement the more long-established, dynamic, and often complex measurements of β-cell secretory function that themselves could be considered biomarkers.

Development of Novel PET Imaging Probes for Detection of Amylin Aggregates in the Pancreas

The deposition of islet amyloid is associated with β-cell mass dysfunction in type 2 diabetes mellitus (T2DM). Since the amylin aggregate is the main component of islet amyloid, in vivo imaging of amylin may be useful for diagnosis and elucidation of the pathogenic mechanism of T2DM. In the present study, we newly designed, synthesized, and evaluated two ¹⁸F labeled compounds ([¹⁸F]DANIR-F 2b and [¹⁸F]DANIR-F 2c) as positron emission tomography (PET) probes targeting amylin aggregates. In an in vitro binding study, DANIR-F 2b and DANIR-F 2c showed binding affinity for amylin aggregates (K_i = 160 and 29 nM, respectively). In addition, [¹⁸F]DANIR-F 2b and [¹⁸F]DANIR-F 2c clearly labeled islet amyloids in in vitro autoradiography of T2DM pancreatic sections. In the biodistribution study using normal mice, [¹⁸F]DANIR-F 2b and [¹⁸F]DANIR-F 2c displayed favorable pharamacokinetics in the pancreas and some organs located near the pancreas. Furthermore, in an ex vivo autoradiographic study, [¹⁸F]DANIR-F 2c also bound to amylin aggregates in the pancreas of the amylin transplanted mice. The results of this study suggest that [¹⁸F]DANIR-F 2c shows fundamental properties as a PET imaging probe targeting amylin aggregates in the T2DM pancreas.

Blood-based protein mediators of senility with replications across biofluids and cohorts

Dementia severity can be quantitatively described by the latent dementia phenotype 'δ' and its various composite 'homologues'. We have explored δ's blood-based protein biomarkers in the Texas Alzheimer's Research and Care Consortium. However, it would be convenient to replicate them in the Alzheimer's Disease Neuroimaging Initiative. To that end, we have engineered a δ homologue from the observed cognitive performance measures common to both projects [i.e. 'd:Texas Alzheimer's Research and Care Consortium to Alzheimer's Disease Neuroimaging Initiative' (dT2A)]. In this analysis, we confirm 13/22 serum proteins as partial mediators of age's effect on dementia severity as measured by dT2A in the Texas Alzheimer's Research and Care Consortium and then replicate 4/13 in the Alzheimer's Disease Neuroimaging Initiative's plasma data. The replicated mediators of age-specific effects on dementia severity are adiponectin, follicle-stimulating hormone, pancreatic polypeptide and resistin. In their aggregate, the 13 confirmed age-specific mediators suggest that 'cognitive frailty' pays a role in dementia severity as measured by δ. We provide both discriminant and concordant support for that hypothesis. Weight, calculated low-density lipoprotein and body mass index are partial mediators of age's effect in the Texas Alzheimer's Research and Care Consortium. Biomarkers related to other disease processes (e.g. cerebrospinal fluid Alzheimer's disease-specific biomarkers in the Alzheimer's Disease Neuroimaging Initiative) are not. It now appears that dementia severity is the sum of multiple independent processes impacting δ. Each may have a unique set of mediating biomarkers. Age's unique effect appears to be at least partially mediated through proteins related to frailty. Age-specific mediation effects can be replicated across cohorts and biofluids. These proteins may offer targets for the remediation of age-specific cognitive decline (aka 'senility'), help distinguish it from other determinants of dementia severity and/or provide clues to the biology of Aging Proper.

Fibrillation of human islet amyloid polypeptide and its toxicity to pancreatic β-cells under lipid environment

BACKGROUND

Previous studies suggested that fibrillar human IAPP (hIAPP) is more likely to deposit in β-cells, resulting in β-cell injury. However, the changes in the conformation of hIAPP in lipid environment and the mechanism involved in β-cell damage are unclear.

METHODS

Synthetic hIAPP was incubated with five types of free fatty acids and phospholipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (POPS), which constitute the cell membrane. Thioflavin-T fluorescence assay was conducted to analyze the degree of hIAPP fibrosis, and circular dichroism spectroscopy was performed to detect the β-fold formation of hIAPP. Furthermore, INS-1 cells were infected with human IAPP delivered by a GV230-EGFP plasmid. The effects of endogenous hIAPP overexpression induced by sodium palmitate on the survival, endoplasmic reticulum (ER) stress, and apoptosis of INS-1 cells were evaluated.

RESULTS

The five types of free fatty acids can accelerate the fibrosis of hIAPP. Sodium palmitate also maintained the stability of fibrillar hIAPP. POPS, not POPC, accelerated hIAPP fibrosis. Treatment of INS-1 cells with sodium palmitate increased the expression of hIAPP, activated ER stress and ER stress-dependent apoptosis signaling pathways, and increased the apoptotic rate.

CONCLUSION

Free fatty acids and anionic phospholipid can promote β-fold formation and fibrosis in hIAPP. High lipid induced the overexpression of hIAPP and aggravated ER stress and apoptosis in INS-1 cells, which caused β-cell death in high lipid environment.

GENERAL SIGNIFICANCE

Our study reveals free fatty acids and hIAPP synergistically implicated in endoplasmic reticulum stress and apoptosis of islet β-cells.

Characterization of Novel 18F-Labeled Phenoxymethylpyridine Derivatives as Amylin Imaging Probes

Deposition of islet amyloid consisting of amylin constitutes one of pathological hallmarks of type 2 diabetes mellitus (T2DM), and it may be involved in the development and progression of T2DM. However, the details about the relationship between the deposition of islet amyloid and the pathology of T2DM remain unclear, since no useful imaging tracer enabling the visualization of pancreatic amylin is available. In the present study, we synthesized and evaluated six novel ¹⁸F-labeled phenoxymethylpyridine (PMP) derivatives as amylin imaging probes. All ¹⁸F-labeled PMP derivatives showed not only affinity for islet amyloid in the post-mortem T2DM pancreatic sections but also excellent pharmacokinetics in normal mice. Furthermore, ex vivo autoradiographic studies demonstrated that [¹⁸F]FPMP-5 showed intense labeling of islet amyloids in the diabetes model mouse pancreas in vivo. The preclinical studies suggested that [¹⁸F]FPMP-5 may have potential as an imaging probe that targets amylin aggregates in the T2DM pancreas.