A PET Tracer That Can See the Insulin Cells Diabetes Destroys

Kyoto University

How much insulin-producing tissue does a person with type 1 diabetes still have? It is a deceptively simple question, and right now, clinicians cannot answer it directly. Blood-based markers give indirect estimates that fluctuate with glucose conditions. There is no routine imaging test that shows how many beta cells remain in the pancreas. As therapies aimed at preserving or restoring those cells advance, this blind spot has become a real problem.

A team at Kyoto University may have found a way to fill it. In a study published March 12 in Diabetes, they report that a PET tracer targeting the GLP-1 receptor can distinguish between the pancreatic tissue of people with type 1 diabetes and those without it - and that the signal correlates with clinical markers of disease severity.

Targeting the receptor, not the cell

The tracer, designated [18F]FB(ePEG12)12-exendin-4, is a fluorine-18-labeled molecule designed to bind the GLP-1 receptor, which is expressed on the surface of beta cells. The logic is straightforward: if beta cells are disappearing, the number of GLP-1 receptors should decline in proportion. A PET scan that lights up where those receptors are could, in principle, produce a direct readout of remaining beta cell mass.

The researchers conducted a prospective study at Kyoto University Hospital. Adults with type 1 diabetes received an intravenous injection of the tracer, then underwent combined PET and CT imaging. The pancreatic uptake was quantified using standardized measures and compared with data from participants without diabetes.

Lower signal, higher disease burden

The results showed what the team had hypothesized. Pancreatic tracer uptake was lower in participants with type 1 diabetes than in those without diabetes. But the more interesting finding was the correlation with clinical markers: the imaging signal was inversely related to hemoglobin A1c (a measure of average blood glucose over two to three months) and to the total daily insulin dose used for treatment.

In other words, people with less tracer uptake - suggesting fewer remaining beta cells - tended to have worse glucose control and higher insulin requirements. The imaging measurement appeared to track with disease severity in a clinically meaningful way.

No serious side effects were observed among the participants.

From snapshot to treatment compass

If validated in larger studies, beta cell-targeted PET could serve several clinical purposes. It could help define the stage of type 1 diabetes more precisely than blood tests alone. It could track changes in beta cell mass over time, providing a direct measure of whether a therapy is preserving or restoring those cells. And it could serve as an objective endpoint in clinical trials - something the field has lacked.

First author Kentaro Sakaki noted that the study was driven by a key gap in type 1 diabetes research and care, and expressed hope that the approach could provide an objective readout for therapeutic evaluation.

Team leader Takaaki Murakami added that many decisions in type 1 diabetes treatment would benefit from a clearer picture of remaining beta cell mass, and that the tracer may provide a noninvasive, quantitative readout to support disease staging and treatment monitoring.

Small study, big caveats

This is a prospective study, but it is small. The exact number of participants is not specified in the press release, which is itself a limitation of the available information. Larger studies are needed to confirm whether the tracer reliably measures beta cell mass across diverse patient populations.

Longitudinal studies - following the same patients over time - will be essential to determine whether changes in the PET signal actually predict clinical outcomes. A cross-sectional correlation between tracer uptake and A1c is suggestive, but it does not prove that imaging changes will track with disease progression or treatment response in individual patients.

There is also the question of specificity. The GLP-1 receptor is not expressed exclusively on beta cells. If other cell types in or near the pancreas express the receptor, the signal could be confounded. The researchers will need to demonstrate that changes in tracer uptake reflect beta cell loss specifically, not changes in other GLP-1 receptor-expressing tissues.

And there are practical barriers. PET imaging requires specialized equipment, radioactive tracers, and trained personnel. Even if the tracer proves reliable, it is unlikely to become a routine clinical tool in the way a blood test is. Its greatest value may be in research settings and clinical trials, where precise measurement of beta cell mass could accelerate the development of new therapies.

A missing measurement, partially found

Type 1 diabetes therapies are evolving rapidly. Immunotherapies like teplizumab can delay onset. Stem cell-derived beta cell transplants are in clinical trials. But evaluating whether these interventions actually preserve or restore beta cell mass has required indirect proxies that are imprecise and sometimes unreliable.

This PET tracer will not solve that problem overnight. But it represents a concrete step toward giving clinicians and researchers something they have not had: a direct, noninvasive window into how much insulin-producing tissue remains. If subsequent studies confirm its utility, it could change how type 1 diabetes is staged, monitored, and treated.