Noninvasive imaging of pancreatic inflammation and its reversal in type 1 diabetes

Abstract

A major stumbling block for research on and treatment of type 1 diabetes is the inability to directly, but noninvasively, visualize the lymphocytic/inflammatory lesions in the pancreatic islets. One potential approach to surmounting this impediment is to exploit MRI of magnetic nanoparticles (MNP) to visualize changes in the microvasculature that invariably accompany inflammation. MNP-MRI did indeed detect vascular leakage in association with insulitis in murine models of type 1 diabetes, permitting noninvasive visualization of the inflammatory lesions in vivo in real time. We demonstrate, in proof-of-principle experiments, that this strategy allows one to predict, within 3 days of completing treatment with an anti-CD3 monoclonal antibody, which NOD mice with recent-onset diabetes are responding to therapy and may eventually be cured. Importantly, an essentially identical MNP-MRI strategy has previously been used with great success to image lymph node metastases in prostate cancer patients. This success strongly argues for rapid translation of these preclinical observations to prediction and/or stratification of type 1 diabetes and treatment of individuals with the disease; this would provide a crucially needed early predictor of response to therapy.

Figures

Figure 1

Mapping organ-specific T2 values. Multiple-slice, multiple-echo T2-weighted spin-echo sequences were acquired, and ROIs for analysis were defined manually on the pancreas or paraspinal muscles. (A) Coronal view of a mouse visualized by MRI. Pancreas and paraspinal muscle ROIs are outlined with dotted lines. (B) T2 values for the individual tissues outlined in A were calculated by fitting a standard exponential relaxation model (Signal intensity = B0.e–(Te/T2); where B0 is initial magnetic field strength [1.5 T], Te is echo time, and T2 is T2 relaxation time) to the data within the ROIs. Values shown as blue squares were below background and were not included in analysis.

Figure 2

Tracking pancreatic inflammation during the development of autoimmune diabetes. Young female BDC2.5/NOD mice were injected with CPA to provoke autoimmune diabetes and were imaged at the indicated time points. Each group contained 4–7 mice. T2 values for pancreas (A) and paraspinal muscles (B) are shown. VVF (C and D) and microvascular leak (E and F) were estimated for each organ using formulae described in Methods. **P < 0.01.

Figure 3

Severity of insulitis revealed by noninvasive MNP-MRI. Young female BDC2.5/NOD mice were imaged on day 6 after CPA treatment and 24 hours after MNP injection. A pseudocolor was assigned to the pancreas, reflecting the T2 value of the organ. Photomicrographs show representative islet histology from these animals. Magnification, ×20.

Figure 4

Detection of pancreatic inflammation associated with spontaneous autoimmune diabetes. Female NOD mice with new-onset diabetes of less than 7 days’ duration (n = 9), nondiabetic female littermates of the diabetic animals (n = 7), and age-matched noninsulitic Eα16/NOD mice (n = 13) underwent MRI imaging according to the protocol described in Methods. (A) Mean pancreatic T2 values ± SEM for each group. (B and C) Representative islet histology from Eα16/NOD and new-onset diabetic NOD animals. Magnification, ×20.

Figure 5

Prediction of diabetes risk with noninvasive imaging. Nondiabetic female NOD mice underwent MRI scanning at 13 (A) and 20 (B) weeks according to the protocol described in Methods. Animals were followed for the spontaneous development of diabetes until 30 weeks. Correlation between T2 value of the pancreas obtained 24 hours after MNP injection and time to diagnosis of overt diabetes is shown. Circle in B indicates 3 mice with the lowest recorded pancreatic T2 values and shortest time to diabetes onset.

Figure 6

Noninvasive imaging of pancreatic inflammation can predict clinical response to anti-CD3 immunotherapy. Female NOD mice with very recent onset of diabetes were treated with either anti-CD3 or control F(ab′)2 fragments for 5 consecutive days as described in Methods. MRI was performed 24 hours after MNP injection on days 4, 8, and 18 after starting mAb immunotherapy. (A) Results from long-term responders rendered normoglycemic following F(ab′)2 treatment (triangles) are compared with those of mice failing to respond to therapy, i.e., anti-CD3 nonresponders (squares) and control antibody nonresponders (circles). Since some mice remained profoundly hyperglycemic for over 3 weeks in this experimental series, pancreas/muscle T2 ratio is presented to control for nonspecific alterations in MRI parameters induced by these global metabolic changes. Groups represent the following number of mice: day 4: responders, n = 4, nonresponders, n = 6; day 8: responders, n = 6, nonresponders, n = 4, control mAb treated, n = 3; day 18: responders, n = 4, nonresponders, n = 6. (B) Pancreas/muscle T2 ratio is plotted against the serum glucose measured at the time of scanning (n = 33), showing no correlation between pancreatic inflammation as determined by MNP-MRI and serum glucose.