Over the past 3 decades, diabetes research has undergone a dramatic transformation thanks in part to the establishment of ~70 islet isolation centers around the world. These centers have provided scientists with precious islet materials for diabetes research and thereby have contributed to our deeper understanding of the underlying biological mechanisms that govern islet health and disease states. As a result, we’ve witnessed an increase in the development and commercialization of new anti-diabetic therapies, such as GLP-1R agonists, that target islets. There have also been significant improvements in the management of diabetes and the quality of life of patients. Yet despite these important advances, there are still no drugs available that can completely reverse the course of diabetes.
Progress in the field has been hindered by several limitations of human islets traditionally used in research, including:
InSphero has successfully addressed these challenges by developing a specialized process for production of highly standardized islet models. We start with gentle dissociation of primary human islets followed by scaffold-free re-aggregation to produce our 3D InSight™ Islet Microtissues, which are homogeneous in size and cellular composition, free of exocrine contaminants, and in a high-throughput-compatible cell culture format that supports long-term experiments in vitro.
Building on the convenience and uniformity of our islet models, we developed a versatile platform for diabetes research that includes multiple assays and disease models with which we aim to further upgrade human islet research and push the field forward. For example, we are now able to successfully mimic islet dysfunction observed in type 2 diabetes by exposing islets to long-term standardized glucolipotoxic conditions. This platform enables us to test and compare the efficacy of new type 2 diabetes drugs that target islets with a throughput and robustness that would not otherwise be possible.
“Expressing secretion on a per islet basis, as is frequently done, is of limited value unless the islets are characterized; some kind of normalization is necessary.”
— Jean-Claude Henquin, MD, PhD
A key advantage of working with standardized islet microtissues is the ability to quantify insulin secretion data as absolute levels of insulin secreted per islet. Historically, this has not been possible due to the heterogeneity in size and cellular composition of different islets – an issue that required investigators to normalize insulin secretion. With the most widely used normalization method, secreted insulin is expressed as a percentage of the intracellular insulin content.
To illustrate the benefits of a multiparametric approach, which obviates the need for normalization, we conducted a comprehensive islet toxicity study on effects of the ER-stress-inducing agent Tunicamycin, performed by measuring multiple multiplexable endpoints. Following 7-day treatment with a range of Tunicamycin concentrations, we observed loss of cell viability at high compound concentrations, based on decreased intracellular ATP content. This assay was followed by a multiparametric assessment of β-cell function that provided even more insight into the toxic effects of Tunicamycin.
Here, you can see normalization may mask important experimental findings and complicate the interpretation of the results. We observed that sub-toxic concentrations of Tunicamycin did not alter ATP levels, and had a negative impact not only on the insulin content, but also on insulin secretion in response to acute glucose (16.7 mM) stimulation.
Additionally, normalizing to the insulin content also decreases the statistical power of the assays due to high dilution factors typically used to measure intracellular insulin content, which amplifies the error and the variability of the data.
If you are working with insulin secretion and pancreatic islets, I highly recommend you read a paper by Jean-Claude Henquin that precisely addresses “The challenge of correctly reporting hormones content and secretion in isolated human islets.” Dr. Henquin argues that “expressing secretion on a per islet basis, as is frequently done, is of limited value unless the islets are characterized; some kind of normalization is necessary.” The standardization process and characterization of 3D InSight™ Human Islet Microtissues make the expression of insulin secretion on a per islet basis possible, thus eliminating the need for normalization.
I encourage you to watch our joint webinar with Promega Corporation on Bioluminescent Assays and 3D Models for Diabetes Research. In this webinar, I discuss our Tunicamycin case study in more detail and provide a more in depth overview of 3D InSight™ Islet Microtissues and the biochemical assays we rely on to deliver results for our pharma partners.
If there are other topics related to islet models and diabetes research that you'd like me to cover in future blogs, please share your ideas in the comments section.