Protection of Endothelial Cell Death by a Specific NOS–II Inhibitor During Acute Corneal Graft Rejection

Abstract

Abstract: : Purpose: To evaluate the protective effect of 1400W, an inhibitor of inducible nitric oxide synthase, on corneal graft endothelial cells survival during the acute rejection episode. Methods: Corneal buttons (3mm) from Brown–Norway rats were transplanted into Lewis rat recipients. Rats (n=11) were randomized in two groups that received intraperitoneal injections of saline (group I, n=5) or 0.5 mg/kg/day 1400W (group II; n=6). Clinical scores of rejection were assessed at day 2, 5, 10 and 13 in three clinical categories: 1– No signs of graft rejection; 2– Partial rejection; and 3– Total rejection. On day 13 after transplantation, animals were sacrificed. Flat–mount of the recipient bed and the transplanted graft were prepared. DAPI and phalloidin staining were used to evaluate the integrity of nuclear and cytoplasmic membranes of endothelial cells. The aqueous humor was collected and pooled in each group to dose the nitrite level. Results: By day 13 after transplantation, one graft in each group had no signs of rejection. One graft in group I and 3 grafts in group II had only partial graft rejection and 3 grafts in group I and 2 grafts in group II developed a clinically evident total rejection before sacrifice. Despite the lack of significant clinical scores rejection between the two groups, a sparing of the endothelial cells of animals in group II was observed.The mean endothelial cell count/field (ECC) was 237cells (+/–84.7) on the grafts and 433 cells (+/–32.65) on the recipient corneas in group I (p=0.008). In group II, this ECC was respectively 397 cells (+/–107) and 551 cells (+/–42.2)(NS, p>0.1). While the endothelial cell counts on the recipient corneas was not significantly different in both groups (p=0.33), the endothelial cell number in the graft corneas differed significantly and was higher in group II (p<0.05). In group I corneas, larger areas did not stain with DAPI or Phalloidin illustrating the total loss of endothelial cells. Nitrite levels were higher in the aqueous humor of saline injected rats than in eyes of rats treated with 1400W. Conclusions: Treatment with iNOS inhibitor (1400W) reduces markedly the endothelial cell loss in the graft (and in the recipient corneas) during the rejection process. This strategy may have some therapeutic potential for the prevention of corneal endothelial cell loss during episodes of graft rejection.

Keywords: cornea: endothelium • drug toxicity/drug effects • antioxidants