Growth factors and receptors in allograft arteriosclerosis

[Solutions for organ preservation and other cardioplegic liquid formulations. Role of the hospital pharmacist]

Solid organ transplantation is an increasing need and a well-established activity which requires maintaining the quality of the transplant from procurement through the entire, storage, transport and graft procedure. Solutions for organ preservation play a key role in this procedure, by minimizing the deleterious effects of both ischemia and reperfusion. As such, their qualitative and quantitative compositions have to be optimized and validated. The development strategy and formulations proposed for these solutions are analyzed in this review as well as the results of the clinical studies which have set up the relevant pharmacological and physicochemical criteria. The French regulatory status of these products is also discussed. A clear distinction has to be made between solutions for organ preservation which are classified as produits thérapeutiques annexes (therapeutic ancillary products) and cardioplegic liquid formulations which are considered as medicinal products and are subject to marketing approval. Finally, the roles of the hospital pharmacist in the evaluation, selection, purchase and proper use of these products are described.

Differentiated expression patterns of growth factors in routine formalin-fixed endomyocardial biopsies in the early postoperative phase after heart transplantation

BACKGROUND

Platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) seem to play a key role in immunological reactions shortly after heart transplantation (HTx). The aim of this study was to analyze the time course of the expression of PDGF A and B, PDGF-receptor alpha (PDGF-Ralpha) and beta, aFGF, and bFGF on formalin-fixed routine endomyocardial biopsies.

PATIENTS AND METHODS

Right ventricular endomyocardial biopsies were obtained from 36 heart transplant recipients up to 2 weeks after HTx. According to the clinical course in the first postoperative year, 3 groups were formed: (1) clinically uneventful course (n = 12); (2) cardiac/systemic infections (n = 12); (3) acute rejection (n = 12). The growth factor expression was examined immunohistochemically.

RESULTS

In the early phase after HTx, PDGF A, PDGF B, PDGF-Ralpha, and PDGF-Rbeta were predominantly expressed in endothelial cells. The main expression of PDGF-Ralpha and bFGF was found in cardiomyocytes, endothelial cells, and smooth muscle cells. During the first 2 postoperative weeks, PDGF A, PDGF B, and PDGF-Rbeta showed a similar time course of expression: A significantly elevated expression in the first week was followed by a decrease in the second week. In the rejection group, PDGF A was significantly elevated after the first week.

CONCLUSIONS

The increased expression of PDGF in the first postoperative week can be interpreted as an unspecific reaction to peritransplant injury. The prolonged expression of PDGF A, PDGF B, and PDGF-Rbeta showed that there were ongoing immunological reactions in the transplant during week 2. The persistence of elevated PDGF A expression might be of prognostic value in terms of a risk factor for either infection or rejection.

The FcgammaRIIa polymorphism in patients with chronic kidney graft rejection

The FcgammaRIIa receptors, which provide a crucial link between cellular and humoral components of the immune response, display allelic polymorphism. Individuals are homozygous for either arginine 131 (RR131) or histidine 131 (HH131) or are heterozygous for these two alleles (RH131). The HH131 genotype binds human IgG2 with high RR131 with low, and RH131 with intermediate affinity. The aim of the study was to evaluate the FcgammaRIIa polymorphism in patients with chronic kidney graft rejection. The study included 121 renal transplant recipients: 53 patients with long-term stable graft function and 68 with chronic allograft rejection. The distribution of FcgammaRIIa genotypes in patients with chronic kidney graft rejection did not differ significantly from that in patients with stable graft function. The results suggest that the FcgammaRIIa polymorphism is not an important genetic risk factor for chronic rejection of kidney allografts.

alpha4beta1-integrin blockade and cyclosporine decreases the prevalence and severity of transplant vasculopathy in a rat transplant model

BACKGROUND

Transplant vasculopathy leads to neointimal proliferation of allograft arteries, and alpha4beta1-integrin (very late antigen-4 [VLA-4]) seems to play an important role in the pathogenesis. This study evaluates the effect of a new, synthetic, VLA-4 blocker (S3429) on transplant vasculopathy in a rat cardiac transplant model.

METHODS

After transplantation (Lewis to Fisher), rats were divided randomly into 6 therapy groups: Group 1, n = 14, saline solution (vehicle); Group 2, n = 14, 3 mg/kg/day cyclosporine; Group 3, n = 21, 10 mg/kg/day S3429 + 3 mg/kg/day cyclosporine; Group 4, n = 21, 5 mg/kg/day S3429 + 3 mg/kg/day cyclosporine; Group 5: n = 21, 10 mg/kg/day S3429; Group 6, n = 21, 5 mg/kg/day S3429. Cyclosporine was given continuously until rats were killed. S3429 was either given for the entire study time or was discontinued after 20 days and animals were killed at Day 80. Twenty-eighty days after grafting, we assessed vasculopathy prevalence and mean vessel occlusion in coronary arteries.

RESULTS

Cyclosporine decreased the prevalence of vasculopathy and mean vessel occlusion compared with controls. We observed a further decrease in prevalence and mean vessel occlusion with 80 days of therapy with S3429 and cyclosporine. After discontinuing S3429 therapy at Day 20, prevalence and mean vessel occlusion increased to values seen in cyclosporine-treated animals at Day 80. S3429 alone decreased mean vessel occlusion only within the first 20 days compared with controls but had no effect on the prevalence of vasculopathy.

CONCLUSION

Because of the further decrease with S3429 therapy and the dramatic increase after discontinuation of S3429 therapy, we conclude that blocking VLA-4 receptors may prevent the development of transplant vasculopathy.

Inhibition of aortic allograft vasculopathy by local delivery of platelet-derived growth factor receptor tyrosine-kinase blocker AG-1295

BACKGROUND

Signal transduction through the platelet-derived growth factor (PDGF)/PDGF-receptor (PDGFR) system has been linked to vascular smooth muscle cell migration and proliferation leading to allograft vasculopathy. This study describes the effect of the tyrphostin AG-1295, a specific PDGFR tyrosine-kinase inhibitor, on neointimal formation in this disease.

METHODS AND RESULTS

Rat aortic allografts transplanted from dark agouti (RT1 ) donors to Wistar-Furth (RT1 ) recipients were assessed in a new treatment model for local drug delivery from polymeric carrier matrices precoated with AG-1295. Matrices were wrapped around the graft immediately after transplantation. The recipients received no background immunosuppression. At day 80 posttransplantation, intimal thickness in AG-1295-treated grafts was reduced when compared to controls (11.8+/-9.1% intimal thickness vs. 23.7+/-6.4% intimal thickness; P=0.042). This finding corresponded to inhibition of intimal PDGFR-beta expression in AG-1295-treated grafts at day 20 posttransplantation (P =0.029 vs. allogeneic controls).

CONCLUSIONS

The tyrphostin AG-1295 reduces neointimal formation in aortic allograft vasculopathy by inhibition of PDGFR-beta-triggered tyrosine phosphorylation. Local drug release of specific tyrosine-kinase inhibitors from perivascularly co-implanted polymeric carrier matrices is effective in the prophylaxis of allograft vasculopathy under selected experimental conditions.

Recipient selection in cardiac transplantation: contraindications and risk factors for mortality

Currently the only acknowledged, definitive treatment for refractory heart failure is heart transplantation (HTx). During the past 10 years, selection criteria for heart transplant recipients have been developed that use an analysis of risk factors associated with mortality, which were identified by consensus opinion and by single-center and multi-center database review. A number of other studies also have been designed to evaluate specific risk factors for transplant such as advanced age, diabetes, and sex. This review identifies variables that continue to provoke controversy during the candidate selection process or variables that have changed from absolute to relative contraindications for HTx. Clinicians may use the data summarized in this review as a guide to making decisions about patient candidacy for HTx. One could conclude from this analysis that a more formalized and objective scale to select patients and to assess risk of death after HTx is necessary. Moreover, as alternative therapies to HTx become reality, a better instrument for triaging patients to one form of therapy or another may be necessary.