Alterations in mRNA for inducible and endothelial nitric oxide synthase and plasma nitric oxide with rejection and/or infection of allotransplanted lungs

Comparison of FK 506, mycophenolate mofetil, and aminoguanidine effects on delay of corneal allograft rejection in an experimental model of low-risk and high-risk keratoplasty

The purpose of our study was to compare the effectiveness of immunosuppressive drugs on the prevention of allograft rejection in a murine model of low-risk and high-risk keratoplasty. The therapy included FK 506 (tacrolimus; 0.2 mg/kg), mycophenolate mofetil (30 mg/kg), aminoguanidine (0.1 g/kg), and combination of FK506 + mycophenolate mofetil or FK506 + aminoguanidine. The results obtained from the Gray's survival model stratified according to the type of subjects suggest that a major rejection risk reduction was achieved using FK506; good results also were obtained for mycophenolate mofetil. Although the point estimates of both the survival and relative risk of rejection suggest a deferred effect of the combination FK506 + mycophenolate mofetil, this finding did not prove statistically significant.

FK 506 and aminoguanidine suppress iNOS induction in orthotopic corneal allografts and prolong graft survival in mice

The aim of this study was to compare the effectiveness of immunosuppressant FK 506 and the specific inhibitor of inducible nitric oxide synthase (iNOS) aminoguanidine (AG) in prevention of corneal graft rejection and to investigate the iNOS expression in the rejection process. Orthotopic corneal allografting in mice was performed (C57BL/10; H-2(b) to BALB/c; H-2(d)). FK 506 (0.3 mg/kg per day) or AG (100 mg/kg per day) was injected intraperitoneally for 4 weeks. Grafted mice without therapy served as controls. Immunohistological evaluation of iNOS-positive cells and macrophage infiltration in grafts 27th day after grafting was performed. Within 4 weeks FK 506 prevented graft rejection in 71% and AG in 57% of animals compared to 29% of clear grafts in controls. A significant proportion of iNOS-positive cells was detected in the rejected grafts of the control and AG-treated groups. The treatment with FK 506 resulted in the inhibition of iNOS expression to a high degree in the rejected corneas. Non-rejected corneas of all groups and non-transplanted corneas exhibited no iNOS-positive cells. A massive infiltration of macrophages was detected in the rejected grafts, whereas non-rejected grafts exhibited only slight infiltration of macrophages. The presented data suggest that overexpression of iNOS and/or activation of iNOS is one of the several influential factors that contribute to the rejection process and that iNOS suppression delays corneal allograft rejection. FK 506 and AG are effective drugs in preventing corneal allograft rejection. Higher beneficial effect of FK 506 on graft survival could be explained by its well-known selective T-cell immunosuppression.

Prolonging organ allograft survival: potential role of nitric oxide scavengers

A growing number of studies suggest a key role of nitric oxide (NO) derived from the inducible NO synthase (iNOS) isoform as a signalling molecule leading to acute organ transplant rejection. Current theory suggests that NO targets certain tissue proteins for nitrosylation or nitration leading to inhibition of enzyme/protein function and to cell death via apoptosis. Gene expression of iNOS and formation of nitrotyrosine residues have been confirmed in biopsies of rejecting grafts in humans. Experimental attempts to delay graft rejection by treatment with iNOS enzyme inhibitors have yielded conflicting results. An alternative strategy to alter rejection mediated by NO is to scavenge and/or neutralise the actions of excess NO, thereby by-passing the inhibition of iNOS enzyme activity. This review summarises recent laboratory evidence that new experimental NO scavengers/neutralisers have potential value to prolong graft survival. To date, various metal-based NO scavenging/neutralising compounds have been shown to enhance cardiac allograft survival in the absence of immunosuppression. When used in combination with low-dose cyclosporin, these agents produce a synergistic action to enhance graft survival or even to produce "permanent graft survival" under certain prolonged drug regimens. A portion of this benefit may be accounted for by the property of some of these compounds to display immunosuppressant and anti-inflammatory activity in vivo. These properties are based on findings including the following: (i) attenuating cell infiltration into the graft; (ii) attenuating activation of NFkappaB (a transcription factor important for upregulation of various inflammatory genes); (iii) attenuating cyclin D3 gene expression (a marker of cell proliferation; (iv) antagonising autoimmune activation (as determined by attenuated cytokine gene expression in splenocytes isolated from treated animals but stimulated for several days ex vivo in mixed lymphocyte cultures).

Immunologic role of nitric oxide in acute rejection of golden hamster to rat liver xenotransplantation

AIM: To evaluate the immunologic role and expression significances of nitric oxide (NO), nitric oxide synthase (NOS), and its isoenzyme in acute rejection to liver xenografts from golden hamster in rat.

METHODS: Liver transplantations were randomly divided into five groups (n = 6-9):isografts (group I); xenografts (group II); xenografts plus cyclosporine treatment (group III), xenografts plus cyclophosphamide treatment combined with splenectomy (group IV), and xenografts using cyclophosphamide in combination with splenectomy (group IV) and xenografts using splenectomy in addition to cyclophosphamide and cyclosporine treatments (group V). The levels of ALT, TNF-α, and nitric oxide production (NOx) in serum of reciprents were examined, and expressions of type II (iNOS) and type III (cNOS) nitric oxide synthase (NOS)-inducible NOS (iNOS) and constitutive NOS (cNOS) were observed by NADPH diaphorase histochemical and immunohistochemical staining.

RESULTS: The level of serum ALT, activity of serum TNF-α and systemic levels of NO metabolite in groups II and IV were higher than those of groups I and V (serum ALT, 2416 ± 475, 2540 ± 82.5) nkat•L⁻¹^-1vs (556.8 ± 43.5, 677.30 ± 38.2) nkat•L⁻¹^-1, P < 0.01; (serum TNF-α, 353.5 ± 16.1, 444.6 ± 28.1) ng•L^-1, vs 38.5 ± 5.2, 52.0 ± 5.7) ng•L^-1, P < 0.01; (serum NOx 514.6 ± 18.1, 336.0 ± 43.0) nmol•g⁻¹, vs 26.1 ± 5.7, 27.7 ± 6.0) nmol•g⁻¹, P < 0.01. Cyclosporine in group III can repress the cellular immune response and the synthesis of nitric oxide and the expression of NO synthase, but not prolong the liver xenograft survival. The over-expression of NOS, iNOS and cNOS in liver xenograft rejection in groups II and IV were detected by NADPH diaphorase histochemical and immunohistochemical staining.

CONCLUSION: The degrees of acute rejection can be effectively repressed in golden hamster to rat liver xenografts with splenectomy and cyclosporine. Nitric oxide metabolites, and nitric oxide synthase and its isoenzymes, above all inducible NOS (iNOS) can be used as potential diagnostic markers for acute rejection in liver transplantation. The cellular localization of nitric oxide varies according to the immunologic status of liver xenografts, thus thinking that hepatocyte derived nitric oxide may be protective in the hyporesponsive state, but hepatic injury is likely triggered by centrilobular iNOS expression in the superresponsive state.

Inducible nitric oxide synthase transcription in human lung transplantation

BACKGROUND

Recent animal data suggest that inducible nitric oxide synthase (iNOS) mRNA expression in the bronchoalveolar lavage (BAL) may be useful for the diagnosis of lung rejection. The aim of this study was to evaluate iNOS mRNA transcription in the BAL fluid of human lung allografts.

METHODS

iNOS mRNA transcription was quantified by competitive reverse transcription-polymerase chain reaction in 51 BAL cell pellets of lung transplant patients. According to bacteriological and histological results, BAL samples were divided into three groups: normal (n=21), acute rejection (AR, n=15), and infection (INF, n=15).

RESULTS

Compared with the control group, iNOS transcription increased significantly with INF (P=0.0005) but only slightly with AR (P>0.05). INF values were significantly higher than AR values (P=0.0029).

CONCLUSION

BAL iNOS mRNA transcript determination by competitive reverse transcription-polymerase chain reaction may be useful in differentiating infected from normal and/or acutely rejecting allografts.

Mycophenolate mofetil and its mechanisms of action

Mycophenolate mofetil (MMF, CellCept(R)) is a prodrug of mycophenolic acid (MPA), an inhibitor of inosine monophosphate dehydrogenase (IMPDH). This is the rate-limiting enzyme in de novo synthesis of guanosine nucleotides. T- and B-lymphocytes are more dependent on this pathway than other cell types are. Moreover, MPA is a fivefold more potent inhibitor of the type II isoform of IMPDH, which is expressed in activated lymphocytes, than of the type I isoform of IMPDH, which is expressed in most cell types. MPA has therefore a more potent cytostatic effect on lymphocytes than on other cell types. This is the principal mechanism by which MPA exerts immunosuppressive effects. Three other mechanisms may also contribute to the efficacy of MPA in preventing allograft rejection and other applications. First, MPA can induce apoptosis of activated T-lymphocytes, which may eliminate clones of cells responding to antigenic stimulation. Second, by depleting guanosine nucleotides, MPA suppresses glycosylation and the expression of some adhesion molecules, thereby decreasing the recruitment of lymphocytes and monocytes into sites of inflammation and graft rejection. Third, by depleting guanosine nucleotides MPA also depletes tetrahydrobiopterin, a co-factor for the inducible form of nitric oxide synthase (iNOS). MPA therefore suppresses the production by iNOS of NO, and consequent tissue damage mediated by peroxynitrite. CellCept(R) suppresses T-lymphocytic responses to allogeneic cells and other antigens. The drug also suppresses primary, but not secondary, antibody responses. The efficacy of regimes including CellCept(R) in preventing allograft rejection, and in the treatment of rejection, is now firmly established. CellCept(R) is also efficacious in several experimental animal models of chronic rejection, and it is hoped that the drug will have the same effect in humans.

Effects of estrogen on nitric oxide synthase expression in rat aorta allograft and smooth muscle cells

BACKGROUND

We find that chronic estradiol treatment inhibits the development of transplant arteriosclerosis (TA). The mechanism of this inhibition remains unclear. The objective of this study is to investigate in a non-cyclosporin-requiring TA model whether estradiol-17beta treatment modulates the expression of both endothelial nitric oxide synthase (ecNOS) and inducible nitric oxide synthase (iNOS) in the early phase following transplantation.

METHODS

Orthotopic abdominal aorta allograft transplantation was performed in male rats using Brown-Norway rats as donors and Lewis rats as recipients. The recipients (n = 50) were treated with estradiol 20 microg/kg/day or placebo by osmotic minipump from 2 days prior to surgery until sacrifice on post-operative days 1, 3, 7, 14, and 21. The allografts were harvested and cross-sections of the vascular tissues were used for immunohistochemical staining of ecNOS and iNOS. The effects of estradiol on cytokine-induced (tumor necrosis factor-alpha and interleukin-1 beta iNOS protein and messenger RNA (mRNA) expression were also evaluated on rat aorta smooth muscle cells by Western blotting and RT-PCR in vitro, respectively.

RESULTS

The expression of ecNOS and iNOS was graded semiquantitatively from 0 to +3. Estrogen elevates ecNOS expression in the intima in the early phase following transplantation, 0.85 +/- 0.14 (day 7) and 1.08 +/- 0.11 (day 14) vs 1.53 +/- 0.25 (day 7) and 1.60 +/- 0.17 (day 14) for placebo and estradiol treated groups respectively, p < 0.01. Estrogen suppresses iNOS expression in neointima (0.67 +/- 0.17 vs 0.24 +/- 0.04, p < 0.01, day 14), media (1.03 +/- 0.15 vs 0.4 +/- 0.09, p < 0.01, day 7), and adventitia (1.55 +/- 0.12 vs 1.02 +/- 0.10, p < 0.05, day 14) in the same phase. Estradiol treatment inhibits cytokine-induced iNOS mRNA expression in cultured smooth muscle cells.

CONCLUSIONS

Chronic estrogen treatment modulates both ecNOS and iNOS expression in the early phase following transplantation. This is associated with the estrogen-protective effects on TA.

Induction and cDNA sequence of inducible nitric oxide synthase from canine aortic smooth muscle cells

An inducible isoform of nitric oxide synthase (type II, iNOS) is expressed in cardiac and vascular smooth muscle in response to inflammatory cytokines. The dog is an important large animal used for cardiovascular research including effects of exercise, heart failure, and allograft rejection. However, molecular probes for iNOS developed in other mammals have not been reliable for the study of iNOS induction in canine vascular smooth muscle. Experiments were designed to develop a molecular probe for canine iNOS. Smooth muscle cells were isolated from canine aortas. The cells (passages 3-10) were incubated for 1, 3, 6, 12, 24, 48, or 72 h in the absence and presence of Escherichia coli lipopolysaccharide (LPS) to induce iNOS. Total RNA was isolated from the cells using standard techniques. RT-PCR with primers against conserved regions of all known iNOS enzyme was used to clone the iNOS cDNA. RT-PCR showed a single band only from cells treated with LPS. Cloned cDNA from cultured canine aortic smooth muscle cells has 84% homology to human, 81% to rat, and 81% to mouse iNOS gene. Identification of the cDNA for canine iNOS will be useful in the study of differential, transcriptional regulation of inducible (type II) compared with constitutive endothelial (type III) NOS in canine studies of allograft rejection and cardiovascular disease.