Tacrolimus Inhibits the Revascularization of Isolated Pancreatic Islets

<div><p>Aims</p><p>Immunosuppressive drugs could be crucial factors for a poor outcome after islet allotransplantation. Unlike rapamycin, the effects of tacrolimus, the current standard immunosuppressant used in islet transplantation, on graft revascularization remain unclear. We examined the effects of tacrolimus on islet revascularization using a highly sensitive imaging system, and analyzed the gene expression in transplanted islets by introducing laser microdissection techniques.</p><p>Methods</p><p>Islets isolated from C57BL/6-Tg (CAG-EGFP) mice were transplanted into the nonmetallic dorsal skinfold chamber on the recipients. Balb/c athymic mice were used as recipients and were divided into two groups: including a control group (n = 9) and tacrolimus-treated group (n = 7). The changes in the newly-formed vessels surrounding the islet grafts were imaged and semi-quantified using multi-photon laser-scanning microscopy and a Volocity system. Gene expression in transplanted islets was analyzed by the BioMark dynamic system.</p><p>Results</p><p>The revascularization process was completed within 14 days after pancreatic islet transplantation at subcutaneous sites. The newly-formed vascular volume surrounding the transplanted islets in the tacrolimus-treated group was significantly less than that in the control group (p<0.05). Although the expression of <i>Vegfa</i> (p<0.05) and <i>Ccnd1</i> (p<0.05) was significantly upregulated in the tacrolimus-treated group compared with that of the control group, no differences were observed between the groups in terms of other types of gene expression.</p><p>Conclusions</p><p>The present study demonstrates that tacrolimus inhibits the revascularization of isolated pancreatic islets without affecting the characteristics of the transplanted grafts. Further refinements of this immunosuppressive regimen, especially regarding the revascularization of islet grafts, could improve the outcome of islet allotransplantation.</p></div

The increasing rate of newly-formed vascular volume surrounding the transplanted islets with and without tacrolimus.

<p>The increasing rate (against day 1) of newly-formed vascular volume surrounding the islets at 4, 7, 11, and 14 days after transplantation in the control group (black bar) and the tacrolimus-treated group (white bar) was calculated. All values are expressed as the means ± SEM. *P<0.05 in comparison to the control group.</p

The time-dependent changes of newly-formed vascular volume for the transplanted pancreatic islets.

<p>Newly-formed vascular volume surrounding the islets at 4, 7, 11, 14, 18, and 21 days after transplantation was measured by using a Volocity system. All values are expressed as the means ± SEM.</p

Imaging of the transplanted islets and surrounding blood vessels.

<p>Overlay of GFP fluorescence (pancreatic islets) and Texas Red fluorescence (blood vessels). Upper row: islets in the control group, Lower row: islets in the tacrolimus-treated group. GFP and Texas Red were excited at 890 nm. The scale bar indicated 51.0 μm/unit.</p

Relative gene expression in the transplanted pancreatic islets with and without tacrolimus.

<p>Relative gene expression of <i>Hif1a</i> (A), <i>Hnf4a</i> (B), <i>Vegfa</i> (C), <i>Mmp14</i> (D), <i>Mapk</i> (E), <i>Mbip</i> (F), <i>Mif</i> (G), <i>F3</i> (H),<i>Il1b</i> (I), <i>Ccnd1</i> (J), <i>Cdk4</i> (K), <i>AldoA</i> (L), <i>Eno1</i> (M), <i>Cs</i> (N), and <i>Pdha1</i> (O) in islets before transplantation (gray bar), the control group (black bar), and the tacrolimus-treated group (white bar). The values in the control and tacrolimus treated-group were represented as the ratio to the values in islets before transplantation. *P<0.05 in comparison to the islets before transplantation, **P<0.01 in comparison to the islets before transplantation, and #P<0.05 in comparison to the control group.</p

The increasing rate of islet graft volume with and without tacrolimus.

<p>The increasing rate (against day 1) of islet graft volume at 4, 7, 11, and 14 days after transplantation in the control group (black bar: n = 9) and the tacrolimus-treated group (white bar: n = 4) was calculated. All values are expressed as the means ± SEM.</p

The time-dependent changes of newly-formed vascular volume surrounding the transplanted islets with and without tacrolimus.

<p>The newly-formed vascular volume in the control group (closed circles) and the tacrolimus-treated group (open circles). All values are expressed as the means ± SEM. *P<0.05 in comparison to the control group.</p