Reduction of FK-506 requirements by combination with polyethylene glycol superoxide dismutase in orthotopic rat liver transplantation☆,☆☆,★,★★

Presented in part at the Scientific Session of the American Academy of Allergy and Immunology Annual Meeting, Anaheim, California, March 4-9, 1995.
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Abstract

Reperfusion after ischemia results in endothelial cell injury and Kupffer cell activation. Inflammatory cytokines thus released can induce major histocompatibility complex antigens and increase the immunogenecity of the graft. An orthotopic rat liver allotransplant model was used to test the hypothesis that prevention of reperfusion injury by infusion of polyethylene glycol superoxide dismutase (PEG-SOD) would result in long-term allograft survival in the presence of subthreshold immunosuppressive dosages. ACI rats were used as donors, and Lewis strain rats as recipients. Orthotopic liver transplantation was initially performed to identify a subthreshold dose of the immunosuppressant FK-506, which would be unable to extend survival longer than control untreated rats with this strain combination. After testing three intramuscular FK-506 doses of 0.04, 0.08, and 0.16 mg/kg, it was observed that an FK-506 dose of 0.04 mg/kg/day for 14 days was unable to extend survival longer than in untreated recipients. This dose of FK-506 was used in combination with PEG-SOD at doses of 1000, 3000, 10,000, or 30,000 units. Recipient animals were treated intravenously with PEG-SOD as a loading dose to facilitate tissue penetration on day 1, and beginning on the day of transplantation, every 2 days for the duration of the study. Results of histologic studies and mean survival time were compared in untreated recipients and in rats treated with PEG-SOD plus 0.04 mg/kg/day FK-506. Mean survival time was increased significantly in these animals (p < 0.007) to 40.6 ± 25.6 days as compared with either untreated rats (10.0 ± 2.7 days) or rats treated with 0.04 mg/kg FK-506 alone (13.7 ± 4.2 days). Histologic examination demonstrated a significant reduction in the cellular infiltrate in rats treated with PEG-SOD plus FK-506, as compared with recipients treated with either agent alone or left untreated. Our results therefore suggest a potential approach to reducing immunosuppression in transplantation. (J ALLERGY CLIN IMMUNOL 1995;95:1276-81.)

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METHODS

An orthotopic liver transplant (OLTX) model was used. Inbred male rats were used in all experiments. ACI (RT1) rats, weighing approximately 225 to 250 gm, were used as donors; and Lewis rats (RT1) rats, weighing 275 to 300 gm, were used as recipients. The procedure for OLTX was that of Kamada and Calne.18 In our experience, this procedure exposes the donor liver to a warm ischemia period of approximately 45 minutes. OLTXs were performed in a randomized fashion. FK-506 was given for

Survival

TABLE I, TABLE II show the relationship between FK dosage and graft survival. MST in rats treated with 0.04 mg/kg/day of FK-506 was 13.7 ± 4.2 days and was not significantly different from that of control (untreated) animals (10.00 ± 2.7 days). Treatment with PEG-SOD alone at a dose of 1000, 3000, 10,000, or 30,000 U/kg also did not result in significantly prolonged survival, although some improvement was observed. No improvement in survival was observed when PEG-albumin was used alone. When

DISCUSSION

The results suggest that the addition of 30,000 U/kg of PEG-SOD to subthreshold doses of FK-506 causes a significant amelioration of orthotopic rat liver rejection. A nonsignificant prolongation of survival was observed with a PEG-SOD dose of 30,000 U/kg used alone. No such prolongation was observed with PEG-albumin either alone or in combination with FK-506 (0.04 mg/kg). We hypothesize that this benefit is caused by a decrease in reperfusion injury caused by PEG-SOD.

We and others have

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    • Cited by (0)

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    From the Departments of aSurgery, bPharmaceutical Sciences, and cPathology, University of Pittsburgh, d the Department of Surgery, Duke University, Durham; c The Sterling Research Group Inc., Malvern; and fthe Department of Medicine, Louisiana State University Medical Center, New Orleans.

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    Supported by grants from the Department of Veterans Affairs, National Institutes of Health (DK 29961), HL 46810, and HL 52297), and Sterling Winthrop Research, Inc.

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    Reprint requests: Prakash N. Rao, PhD. Department of Medicine, Section of Allergy and Clinical Immunology, Louisiana State University Medical Center, 1542 Tulane Ave., New Orleans, LA 70112-2822.

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