Transplant Graft Vasculopathy

Progenitor cell mobilizing treatments prevent experimental transplant arteriosclerosis

OBJECTIVE

Vascular rejection after organ transplantation is characterized by an arterial occlusive lesion, resulting from intimal proliferation occurring in response to arterial wall immune aggression. Our hypothesis is that an early endothelial repair may prevent vascular graft rejection. The aim of the current study was to compare different pharmacologic progenitor cell mobilizing treatments for their protective effects against vascular rejection.

METHODS AND RESULTS

Aortic transplants were made from balb/c donor to C57Bl/6 recipient mice. Three different mobilizing pharmacologic agents were used: low molecular weight fucoidan (LMWF), simvastatin, and AMD3100. The circulating levels of progenitor cells were found to be increased by all three treatments, as determined by flow cytometry. For each treatment, the design was: treated allografts, nontreated allografts, treated isografts, and nontreated isografts. After 21 d, morphometric and immunohistochemical analyses were performed. We found that the three treatments significantly reduced intimal proliferation, compared with nontreated allografts. This was associated with intimal re-endothelialization of the grafts. Further, in chimeric mice that had previously received GFP-transgenic bone marrow transplantation, GFP-positive cells were found in the vascular allograft intima, indicating that re-endothelialization was, at least partly, due to the recruitment of bone marrow-derived, presumably endothelial progenitor circulating cells.

CONCLUSIONS

In this aortic allograft model, three different mobilizing treatments were found to partially prevent vascular transplant rejection. Bone marrow-derived progenitor cells mobilized by the three treatments may play a direct role in the endothelial repair process and in the suppression of intimal proliferation.

Low Molecular Weight Fucoidan Prevents Neointimal Hyperplasia After Aortic Allografting

BACKGROUND

Fucoidan, a new low molecular weight sulfated polysaccharide (LMWF), has previously been shown to mobilize bone marrow-derived progenitors cells via stimulation of stromal derived factor (SDF)-1 release. Mobilized progenitor cells have been suggested to repair intimal lesions after immune-mediated endothelial injury and thus prevent intimal proliferation. The aim of this study was to evaluate the effect of LMWF treatment in a rat aortic allograft model of transplant arteriosclerosis (TA).

METHODS

Aortic grafts were performed in Brown Norway (BN, donor) and Lewis (Lew, recipient) rats. The recipient rats were treated with LMWF (5 mg/kg/day) and sacrificed at 30 days. To determine the role of SDF-1 in mediating the effects of LMWF, a specific inhibitor of the SDF-1 receptor CXCR4, AMD 3100 (20 microg/kg/day), was used. The grafted segments were evaluated by morphometric (histochemical) analyses.

RESULTS

Untreated aortic allografts exhibited severe intimal proliferation, indicative of TA. In contrast, LMWF treatment significantly prevented allograft intimal proliferation as compared with controls (5.7+/-3 vs. 66.2+/-6 microm, P<0.01) and permitted a normalization of the intima/media ratio (0.1+/-0.1 vs. 1.7+/-0.3, P<0.01). Further, LMWF treatment stimulated allograft reendothelialization, as evidenced by strong intimal endothelial nitric oxide synthase antibody and CD31 signals. Unexpectedly, AMD treatment failed to prevent the protective effect of LMWF on intimal thickening and AMD treatment alone was found to reduced intimal proliferation in allografts.

CONCLUSIONS

We found that LMWF treatment reduced intimal thickness and induced the presence of an endothelial cell lining in the vascular graft at 30 days. Our findings may suggest a novel therapeutic strategy in the prevention of TA.

Endothelial Progenitor Cells in Chronic Renal Insufficiency

There is growing evidence for a role of endothelial progenitor cells (EPCs) in the repair of damaged endothelium. It remains unclear which cell populations are most useful for clinical trials. Administration of drugs increasing EPC numbers and/or improving functional properties seems attractive. Further basic research is necessary to understand the mechanisms of mobilization, differentiation and homing of EPC in general and in particular under uremic conditions. Nephrologists should search for strategies to ameliorate EPC dysfunction of uremia. In this way it might be possible to test whether improved EPC biology is associated with decreased cardiovascular mortality in uremic humans. In any such studies the difficulties are going to be related to the complex procedures for EPC isolation, the testing of their identity and differentiation and their propagation before use.

Biology of the smooth muscle cells in human atherosclerosis

The aim of this study was to reconstruct dynamic biological steps of human atherosclerosis at different ages of life and, in particular, to clarify the role of the smooth muscle cells (SMCs) by means of evaluation of several markers implicated in proliferative diseases (c-fos, proliferating cell nuclear antigen: PCNA, apoptosis, chromosome 7). We examined the biological features of 67 atherosclerotic arterial lesions obtained from fetuses, infants, young people and adults. From each case serial sections were stained for histological examination, PCNA, c-fos and apoptosis detection by immunohistochemical methods and for chromosome 7 number evaluation by fluorescence in situ hybridization. In coronary specimens of fetuses we observed SMCs with c-fos positivity. In infant lesions the predominant result was positivity for PCNA. Similar results were obtained from the plaques from young subjects with a greater presence of PCNA-positive cells. In adult subjects numerous apoptotic cells were present in the stable plaques, whereas in the unstable plaques we frequently detected joint positivity for both PCNA and c-fos gene and supernumerary chromosomes 7. During the evolution of the atherosclerotic process we observed a biological modulation of SMC proliferation, which begins after activation of the c-fos gene, increases during progression of the lesion and declines in stable plaques, when apoptosis increases. In unstable plaques, the same early steps observed in fetus and infant arteries occur. The observation in some cases of chromosome 7 alterations, markers of tumorigenesis, suggests the possible transformation of an advanced atherosclerotic plaque into a neoplastic-like process.