Protocol Exchange | Community Contributed

Seeing is believing: in vivo functional real-time imaging of transplanted islets using positron emission tomography (PET)

Department of Cellular & Physiological Sciences and the Diabetes Research Group

Journal name:
Protocol Exchange
Year published:
(2006)
DOI:
doi:10.1038/nprot.2006.491
Published online

Introduction

Single time-point studies, following animal sacrifice, do not reliably reflect the status of transplanted islets and considerable efforts are now being devoted to the development of noninvasive islet imaging techniques for visualizing transplanted islets in vivo1-6. Islets are difficult to quantify in vivo, because they constitute less than 2% of total pancreatic mass, and the problem is compounded with transplants, because the number of islets is considerably less than in the native pancreas. Positron emission tomography (PET) is a well-established quantitative and noninvasive imaging modality5-14. With the PET reporter gene (PRG)/PET reporter probe (PRP) system, based on a mutant form of herpes simplex virus 1 thymidine kinase (HSV1-sr39tk), the PET signal is directly proportional to the enzymatic activity of sr39TK9-14. In this protocol, we describe in detail a method for reporter gene labeling of islets and quantitative scanning using the reporter probe 9-(4-[18F]-Fluoro-3-hydroxymethylbutyl)-guanine ([18F]FHBG). Islets expressing HSV1-sr39tk are transplanted into mice, either under the kidney capsule or into the liver, followed by injection of [18F]FHBG. PET imaging of phosphorylated, trapped, ligand enables quantification of transplant mass.

Figures at a glance

  1. Figure 1: Experimental design for the determination of islet graft survival using PET.
    91

    Mouse islets were infected with a recombinant adenovirus expressing a mutant form of herpes simplex virus 1 thymidine kinase (HSV1-sr39tk) (rAD-TK), and transplanted under the kidney capsule or liver. 9-(4-[18F] – Fluoro-3-hydroxymethylbutyl) – guanine ([18F]FHBG), was systemically administered to mice following islet transplantation, and its retention in islets quantified by PET scanning. HSV1-sr39TK specifically expressed in transplanted islets efficiently phosphorylates [18F]FHBG, following which they are retained in cells and further metabolized by cellular kinases to di- and tri-phosphates.

  2. Figure 2: Representative PET imaging of transplanted islets under the kidney capsule.
    92

    Islets, treated with 250 m.o.i. of rAD-TK, were transplanted under the kidney capsule: 85 islets under the left and 200 islets under the right kidney capsule. On the following day, the mouse was injected with 100 μCi of [18F]FHBG and scanned for 1 h. Representative transverse (a), coronal (b) and sagittal (c) MAP reconstructed slices of PET images in an islet transplanted C57 BL/6 mouse. (d) Time activity curves (TACs) of the region of interest (ROI) in the transplanted kidneys. ROIs were drawn from the microPET image data to include the transplanted area and TACs were generated. (e) PET images on each time frame. First published in ref. 19.

  3. Figure 3: Representative PET imaging of transplanted islets in the liver
    93

    1200 rAD-TK treated islets were transplanted into the liver. On the following day, the mouse was injected with 100 μCi of [18F]FHBG and scanned for 1 h. Representative transverse (a), coronal (b) and sagittal (c) MAP reconstructed slices of PET images in an islet transplanted C57 BL/6 mouse. (d) TACs of the ROIs. ROIs were drawn from the microPET image data to include the transplanted area and TACs were generated. (e) PET images on each time frame. First published in ref. 19.

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