Benefits of PEGylation in the early post-transplant period of intraportal islet transplantation as assessed by magnetic resonance imaging of labeled islets

Figures & data

Figure 1. (A) Dithizone stain of untreated (a) and PEGylated (b) islets, and acridine orange and propidium iodide stain of untreated (c) and PEGylated (d) islets. Purple indicates dithizone-stained β cells (a, b). Green indicates acridine orange-stained live cells and red indicates propidium iodide-stained dead cells (c, d). Scale bars indicate 50μm. (B) Glucose-stimulated insulin secretion of control (n = 8) and PEGylated islets (n = 8). (C) Ex vivo imaging of PEGylated islets labeled with ferucarbotran. Islets in 1% agarose gel are in the left panel while corresponding magnetic resonance images are in the right panel. The scale bar indicates 50 μm. (D) Representative MR images of PEGylated (PEG) and non-PEGylated (control) islets. The images were obtained 7 d after islet transplantation. Arrows indicate hypointense spots representing SPIO-labeled islets.

Figure 2. (A–B) Comparison of the total area of all hypointense spots (A) and the number of large (> 1.758 mm²) hypointense spots (B) between control and PEGylated islet groups 1, 7, and 14 d post-transplantation. There were six animals in the control islet group and eight in the PEGylated islet group on day 1 (animals that showed conglomerated hypointense spots were excluded from the image analysis). *P < 0.05. (C) Comparison of blood glucose levels between control and PEGylated islet groups during 4 wk post-transplantation. (D) The cumulative proportion of recipients that achieved normoglycemia in the PEGylated and control islet groups.

Figure 3. Histologic analyses of transplanted islets 1 wk after the islet transplantation and the counterpart MR images. (A) An example of insulin-stained islet which was co-stained with more than 10 Prussian blue-stained spots. Low power field histology and its counterpart MR image (left-hand side), and the high power field image of the area indicated by rectangle in the MRI and low power image (right-hand side). This example was from the recipient of control islets. (B) An example of insulin-stained islet which was co-stained with less than 10 Prussian blue-stained spots (right-hand side). Low power field histology and its counterpart MR image (left-hand side), and the high power field image of the area indicated by rectangle in the MRI and low power image (right-hand side). This example was from the recipient of PEGylated islets. (C) Representative high power field images of control islets. (D) Representative high power field images of PEGylated islets. Scale bars indicate 50 μm in each figure (A–D).

Figure 4. Validation of MRI parameters in syngeneic islet transplantation. (A–B) Total area of hypointense spots (A) and number of large hypointense spots (B) on T2* MRI 1, 7, and 14 d post-transplantation. There were 6 animals in the hyperglycemia group and 8 in the normoglycemia group 1 DPT. Animals that showed conglomerated hypointense spots were excluded from the image analysis. (C–D) Correlation between the total area of hypointense spots (C) and number of large (> 1.758 mm²) hypointense spots (D) 1 wk post-transplantation and blood glucose levels 4 wk post-transplantation in PEGylated (PEG) and non-PEGylated (control) islets. (E–F) Comparison of the total area of hypointense spots (E) and number of large (> 1.758 mm²) hypointense spots (F) 1 wk post-transplantation between hyperglycemic and euglycemic recipients transplanted with PEGylated islets. *P < 0.05; **P < 0.01; ***P < 0.001.

Table 1. The predictive value of the MRI parameters 1,7, and 14 DPT for classification of recipients to the normoglycemia group*

MRI parameter	Area under the ROC curve (95% confidence interval)	P value
1 d after islet transplantation
Total area of all hypointense spots	0.917 (0.751–1.000)	0.010
Number of large^† hypointense spots	0.896 (0.727–1.000)	0.014
Number of all hypointense spots	0.417 (0.057–0.776)	0.606
7 d after islet transplantation
Total area of all hypointense spots	0.967 (0.897–1.000)	< 0.001
Number of large^† hypointense spots	0.960 (0.878–1.000)	< 0.001
Number of all hypointense spots	0.543 (0.310–0.777)	0.718
14 d after islet transplantation
Total area of all hypointense spots	0.940 (0.833–1.000)	< 0.001
Number of large^† hypointense spots	0.940 (0.833–1.000)	< 0.001
Number of all hypointense spots	0.473 (0.244–0.703)	0.824

Area under the receiver-operator characteristics (ROC) curve is 0.5 if the parameter has no predictive value, and 1.0 if the parameter perfectly predicts the outcome. *The normoglycemia group was defined as those recipients with 2 consecutive blood glucose levels < 200 mg/dL by 4 wk post-transplantation. ^† > 1.758 mm² in diameter