Effect of cyclosporine during initiation of transplant arteriosclerosis. An ultrastructural study in the aorta-transplanted rabbit

Cyclosporin A and atherosclerosis--cellular pathways in atherogenesis

Cyclosporin A (CsA) is an immunosuppressant drug widely used in organ transplant recipients and people with autoimmune disorders. Long term treatment with CsA is associated with many side effects including hyperlipidemia and an increased risk of atherosclerosis. While its immunosuppressive effects are closely linked to its effects on T cell activation via the inhibition of the nuclear factor of activated T cells (NFAT) pathway, the precise mechanisms underlying its cardiovascular effects appear to involve multiple pathways additional to those relevant for immunosuppression. These include inhibition of calcineurin activity and intracellular cyclophilin peptidylprolyl isomerase and chaperone activities, inhibition of pro-inflammatory extracellular cyclophilin A, and NFAT-independent transcriptional effects. CsA demonstrates complex effects on lipoprotein metabolism and bile acid production, and affects endothelial cells, smooth muscle cells and macrophages, all of which are critical to the atherosclerotic process. Interpretation of the available data is hampered as many experimental models are used to study the effects of CsA in vivo and in vitro, leading to diverse and often contradictory findings. In this review we will describe the cellular mechanisms related to CsA-induced hyperlipidemia and atherosclerosis, with a focus on identifying pro-atherogenic pathways that are distinct from those relevant to its immunosuppressant effects. The potential of CsA analogues to avoid such sequelae will be discussed.

Therapeutic potential of VIVIT, a selective peptide inhibitor of nuclear factor of activated T cells, in cardiovascular disorders

Cardiovascular disease is the major cause of death in industrialized nations. Targeted intervention in calcineurin, a calmodulin-dependent, calcium-activated phosphatase and its substrate, nuclear factor of activated T cells (NFAT), was demonstrated to be effective in the treatment of cardiovascular diseases. Although effective in the disruption of calcineurin phosphatase activity, cyclosporin A (CsA) and FK506 also resulted in undesired side effects and toxicity, prompting the discovery of VIVIT, a novel peptide inhibitor. VIVIT selectively and potently inhibits calcineurin/NFAT interaction, but does not compromise calcineurin phosphatase activity and non-NFAT-mediated signaling. VIVIT displays a favorable therapeutic profile as a potential drug candidate and constitutes a useful tool in exploring calcineurin-NFAT functionality. This review describes the development of VIVIT peptide as a selective NFAT inhibitor and its application as a therapeutic agent in cardiovascular disorders including cardiac hypertrophy, restenosis, atherosclerosis, and angiogenesis.

Low-dose FK506 blocks collar-induced atherosclerotic plaque development and stabilizes plaques in ApoE-/- mice

Since atherosclerosis is a chronic inflammatory disease, we tested the hypothesis that the immunosuppressive drug FK506 would attenuate the development of atherosclerosis using a mouse model of collar-induced atherosclerosis. ApoE-/- mice were treated for 4 weeks with the immunosuppressive drug FK506 (0.05 mg/kg/day), yielding sustained blood levels (approximately 0.2 ng/mL) without systemic side effects. Atherosclerotic plaque development of FK506-treated mice was significantly reduced (63%) while plaque cell density was increased (52%) compared to controls. Importantly, FK506 also blocked progression of pre-existing atherosclerotic plaques. Plaque area of pre-existing plaques was 35% reduced by FK506. Cell density (35%) and collagen content (51%) were significantly increased, whereas necrotic core content was decreased (42%), indicating a more stable plaque morphology. Similar results were found during spontaneous atherosclerotic plaque development in ApoE-/- mice (treatment 17-25 weeks of age). Flow-cytometric analysis showed no peripheral effects on blood cell count or T-cell activation after FK506-treatment. In vitro, FK506 decreased vascular smooth muscle cell (VSMC) apoptosis and inhibited nuclear factor of activated T cells (NFAT)-luciferase reporter activity at concentrations in the range of the in vivo concentration. Low-dose FK506 inhibits collar-induced atherosclerotic plaque development and progression and induces more stable plaque phenotypes in ApoE-/- mice without any peripheral side effects.

Insights into cyclosporine A-induced atherosclerotic risk in transplant recipients: macrophage scavenger receptor regulation

Clinical monitoring of organ-transplant recipients suggests that administration of cyclosporine (CsA) may increase the risk of atherosclerosis when compared with the general population. The purpose of this work is to demonstrate the utility of the in vitro Tamm-Horsfall protein (THP)-1 human monocyte cell culture model for determining drug-related atherosclerotic potential in macrophages. The effect of CsA on the mRNA expression of macrophage scavenger receptor genes including CD36, CD68, scavenger receptor (SR)-A, SR-BII, and lectin-like oxidized low-density lipoprotein receptor (LOX-1); the nuclear hormone receptors, including peroxisome-proliferator activated receptor (PPAR)gamma and liver-X-receptor (LXR)alpha; and the cholesterol efflux pump ABCA1 were investigated as markers of atherosclerotic progression. The THP-1 cells were cultured and differentiated into macrophages. The macrophages were then treated with CsA to assess gene expression. Time- (1, 2, 4, 8, and 24 hours) and dose- (concentrations [mg/L] corresponding to the trough [0.5], peak [1.25] and 4x peak [5]) dependency of CsA was assessed. The treated macrophage mRNA gene expression of CD36, CD68, and PPARgamma were up-regulated in the presence of CsA. Interestingly, SR-A, SR-BII, LOX-1, and LXRalpha expression appeared to be slightly down-regulated, and ABCA1 was relatively unchanged. Immunoblotting studies demonstrated that the protein expression of CD36 was unchanged or increased, PPARgamma was unchanged, and ABCA1 was unchanged or decreased at 4 and 8 hours. The results document CsA-induced mRNA and protein changes in receptors relevant to lipid-laden foam cell formation and demonstrate the utility of THP-1 macrophages for screening of atherosclerotic risk potential.

Ultrastructural evidence of early endothelial damage in coronary arteries of rat cardiac allografts

BACKGROUND

Events that occur early after transplantation, particularly immune recognition of allo-endothelium, initiate transplant vascular disease (TVD). Previous work suggests an important compromise of endothelial integrity as the allo-immune milieu evolves, although mechanisms by which integrity is altered remain unclear. Increased vascular permeability caused by endothelial damage may allow inflammatory cells, lipoproteins, other proteins, and plasma fluid to enter the sub-endothelial space, thereby contributing to the initiation of atherosclerosis. In this study, we examined endothelial integrity in coronary arteries and the proximal aorta after cardiac transplantation in rats.

METHODS

We used Lewis-to-Lewis and Lewis-to-F344 rat heterotopic cardiac transplant models. We studied the effects of cyclosporine (5mg/kg/day) therapy compared with saline-treated controls. En face silver nitrate staining was performed to demonstrate endothelial cell borders and gaps. We used scanning electron microscopy to extend silver nitrate findings and to further define the presence and nature of endothelial disruptions. We used transmission electron microscopy to further characterize immune cell identity and interaction with endothelium.

RESULTS

Syngrafts and cyclosporine-treated allografts showed normal-looking endothelium similar to that observed in arteries from native hearts. However, saline-treated allografts displayed progressive endothelial destruction, including large intercellular gaps, missing cells, and areas of bare extracellular matrix. Exfoliated surfaces were covered by platelets at various stages of adhesion, activation, and spreading. Similarly, we observed numerous leukocytes as either adherent to the endothelial lining or transmigrating into the sub-endothelial space. Cessation of cyclosporine therapy was associated with the development of similar abnormalities.

CONCLUSIONS

Our findings indicate that, especially when immunosuppression is insufficient, early endothelial damage may promote vascular permeability and thereby initiate TVD.

Temporal changes in myocardial endothelial nitric oxide synthase expression following human heart transplantation

BACKGROUND

The incidence of cardiac allograft vasculopathy increases with time after heart transplantation. Allograft vasculopathy is associated with endothelial dysfunction and reduced endothelium-dependent nitric oxide-mediated vascular effects. In this study, temporal changes in endothelial nitric oxide synthase (NOS3) expression in human myocardial biopsies were investigated during the first 3 years after heart transplantation.

METHODS

In each patient (n = 7), the immunohistochemical presence of NOS3 and inducible nitric oxide synthase were examined in serial biopsies taken at 1, 4, and 26 weeks and at 1, 2, and 3 years after transplantation.

RESULTS

Endothelial nitric oxide synthase was present in vascular endothelial cells in all biopsies at the time of transplantation. A rapid fall within the first months in the number of NOS3-positive biopsies was observed, with a possible difference in the rate of disappearance among the capillaries, the arterial endothelium, and the venous endothelium. After 2 years, very little NOS3 could be detected. Inducible nitric oxide synthase was present in vascular smooth muscle cells throughout the study period and did not change.

CONCLUSION

Endothelial nitric oxide synthase immunoreactivity is gradually lost after heart transplantation. These changes may be responsible for the coronary endothelial dysfunction often seen after human cardiac transplantation.

Effect of cyclosporine on arterial balloon injury lesions in cholesterol-clamped rabbits: T lymphocyte-mediated immune responses not involved in balloon injury-induced neointimal proliferation

Restenosis after balloon dilatation of stenosed coronary arteries is a major clinical problem. Because T lymphocytes occur in neointima and because cyclosporine inhibits T-lymphocyte proliferation, we tested the hypothesis that cyclosporine would attenuate neointimal proliferation after balloon dilation injury. Rabbits with a balloon-injured aorta, randomized to cyclosporine in the human therapeutic range (n=13) or vehicle (n=14) were followed up for 5 weeks; as a control for the effect of cyclosporine, half the rabbits received in addition an aorta allograft. Rabbits were clamped at a human plasma cholesterol level of 5 to 7 mmol/L. Cyclosporine did not affect aorta cholesterol accumulation or neointimal proliferation in balloon-injured aortas; however, it attenuated both in transplanted aortas. Likewise, cyclosporine had no effect on endothelial cells at balloon-injured sites, but protected these cells in the transplanted aortas. Infiltration of smooth muscle cells, T lymphocytes, and macrophages were unaffected by cyclosporine in balloon-injured aortas; however, in transplanted aortas, cyclosporine reduced the relative number of T lymphocytes and macrophages but increased the relative number of smooth muscle cells. Finally, in balloon-injured aortas, cyclosporine did not affect expression of vascular adhesion molecule-1, intercellular adhesion molecule-1, or major histocompatibility complex II, but all these cellular activation markers were attenuated by cyclosporine in transplanted aortas. These results suggest that cyclosporine does not attenuate neointimal proliferation after balloon dilatation, and that T lymphocyte--mediated immune responses are not involved in neointimal proliferation after balloon dilatation.

Heart allograft vascular disease: an obliterative vascular disease in transplanted hearts

More than 30 years have passed since the first human heart transplantation was performed. Since then, short-term survival after heart transplantation has been markedly improved, but this development has not been paralleled with a similar improvement in long-term survival. One of the major reasons for this is the subsequent development of heart allograft vascular disease, an obliterative disease in the coronary arteries of the transplanted heart. The dubious effect of re-vascularization in this disease, the less favorable outcome after repeat heart transplantation, and the low donor supply have called for intensified research for new and efficient prophylactic therapies against heart allograft vascular disease. This research has lead to improved knowledge about diagnosis, etiology, pathogenesis, prophylaxis, and treatment possibilities. The most important among these seem to be: (i) the introduction of intravascular ultrasound for early detection of the disease; (ii) evidence to suggest that hyperlipidemia, insufficient immunosuppressive therapy, human leukocyte antigen (HLA)-mismatch, and infection with cytomegalovirus (CMV) all may promote allografts vascular disease; and (iii) the introduction of at least two promising prophylactic therapies in humans namely 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors and calcium entry blockers, and others potentially promising e.g. angiotensin-converting enzyme-inhibitors, angiopeptin, mycophenolate mofetil and rapamycin. This review summarizes present knowledge on the possibilities of inhibiting or treating heart allograft vascular disease incorporating evidence from both human and experimental studies.