Early induction of platelet-derived growth factor ligands and receptors in acute rat renal allograft rejection

Oral Platelet-Derived Growth Factor and Vascular Endothelial Growth Factor Inhibitor Sunitinib Prevents Chronic Allograft Injury in Experimental Kidney Transplantation Model

BACKGROUND

Expression of both platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) is increased during the development of chronic rejection which remains the major reason for late allograft loss in clinical kidney transplantation. Sunitinib is a tyrosine kinase inhibitor which inhibits both VEGF and PDGF receptors. Here we investigated its effect on the development of chronic rejection.

METHODS

Rat aortic denudation model was used to define sunitinib dose. In vitro studies were done to investigate the effect of sunitinib on smooth muscle cell proliferation and migration. Kidney transplantations were performed from dark agouti rat strain (DA) to Wistar furth rat strain rats and syngenic DA-DA grafts were used as controls. Allografts were immunosuppressed either with cyclosporine or with cyclosporine and sunitinib. Grafts were harvested at 5 and 90 days for histology and immunohistochemistry. Serum creatinine levels were measured weekly to monitor graft function.

RESULTS

Sunitinib decreased neointimal formation and smooth muscle cell proliferation and migration in a dose-dependent manner. Sunitinib was well tolerated and almost completely prevented chronic rejection changes and preserved significantly better renal graft function after transplantation. Sunitinib also inhibited chronic PDGF-A and -B and VEGF-A and -B expressions.

CONCLUSIONS

These results demonstrate that combined inhibition of PGDF and VEGF with sunitinib prevents chronic rejection changes in experimental kidney transplantation which indicates that sunitinib could be a potential intervention also in clinical kidney transplantation.

Epidermal growth factor inhibition, a novel pathway to prevent chronic allograft injury

BACKGROUND

Chronic allograft injury remains a major problem in clinical kidney transplantation and different growth factors participate in its development. Epidermal growth factor (EGF) affects cell proliferation and mitogenesis through its tyrosine kinase receptor. Erlotinib is an orally administered tyrosine kinase inhibitor used in clinical oncology to inhibit EGF signaling. We investigated its effect on the development of chronic allograft injury in an experimental kidney transplantation model.

METHODS

Kidney transplantations were performed between Dark Agouti and Wistar Furth rats. Recipients were immunosuppressed either with cyclosporine A (CsA, 1.5 mg/kg/day subcutaneously) or with CsA and erlotinib (10 mg/kg/day orally). Kidney grafts were harvested after 5 and 90 days for histology and immunohistochemistry. Aorta denudation model was used for the erlotinib dose response study to define the optimal dose for the transplantation study.

RESULTS

Epidermal growth factor expression was increased in CsA-treated allografts which developed intense chronic changes on day 90. Erlotinib ameliorated neointimal formation in the dose response study. In addition, erlotinib decreased chronic rejection changes and maintained better graft function in kidney transplantation model. Late posttransplant EGF and EGF receptor levels were reduced with erlotinib.

CONCLUSION

Based on these findings, EGF mediates in part the development of chronic allograft injury. Its inhibition with erlotinib prevents chronic rejection and maintains better allograft function. Therefore, EGF blocking by erlotinib provides a novel pathway to prevent chronic allograft injury.

Detection and mechanism of action of ESM-1 in rat kidney transplantation under various immune states

OBJECTIVE

To investigate whether ESM-1 expression change reflects the impairment of endothelial cells and rejection after kidney transplantation, ESM-1 expression was detected under various immune states in this study.

METHODS

Kidney transplantations were performed from BN to LEW rats. Syngenic LEW-LEW grafts were used as controls. The LEW recipient rats were divided into acute rejection (AR) group, ciclosporin A (CsA) group and control group. In each group, 10 rats were sacrificed at 1, 5, and 7d after operation, respectively, and blood and kidney samples were collected. In the rat model of kidney transplantation, ESM-1 mRNA and ESM-1 protein expression were detected in various immune states to verify if ESM-1 can reflect endothelial cell impairment sensitively.

RESULTS

ESM-1 mRNA (1d vs. 3d, P<0.01;3d vs. 7d, P=0.018) and ESM-1 protein expression was upregulated significantly in the AR group (P<0.01, 5 and 7d), when compared to CsA group and control group. In CsA group, the cell apoptosis rate decreased when compared to AR group (P<0.01). Pathological impairment was more serious in AR group than in CsA group (P<0.01).

CONCLUSIONS

Peripheral blood ESM-1 mRNA and ESM-1 protein expression in kidney grafts can reflect the severity of endothelial cell impairment. Thus, ESM-1 may be used as a new indicator for AR prediction and diagnosis. Nevertheless, further investigation is required to test if it meets the criteria for clinical utility.

PLATELET-DERIVED GROWTH FACTOR, TRANSFORMING GROWTH FACTOR-β, AND CONNECTIVE TISSUE GROWTH FACTOR IN A PORCINE BRONCHIAL MODEL OF OBLITERATIVE BRONCHIOLITIS

The expression of platelet-derived growth factor (PDGF), transforming growth factor (TGF)-beta, and connective tissue growth factor (CTGF) and the effect of imatinib, an agent inhibiting PDGF receptors, were assessed in a porcine bronchial transplantation model of obliterative bronchiolitis (OB). Up-regulation of PDGF-A, PDGF receptors alpha and beta, and TGF-beta expression occurred in allografts, whereas PDGF-B and CTGF expression was similar in allo- and autografts. Imatinib modified the inflammatory responses and expression patterns of PDGF-A and PDGF receptors. This study further confirms PDGF and TGF-beta as mediators of OB and supports the concept of the importance of the pathways signaled through PDGF receptors in post-transplant OB.

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 Effect of FK778 on Acute Rat Renal Allograft Rejection and Expression of Platelet-Derived Growth Factor and Transforming Growth Factor-Beta

BACKGROUND

Acute rejection is the single most important risk factor for the development of subsequent chronic allograft nephropathy (CAN). Both platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) are major mitogens mediating mesenchymal cell proliferation and epithelial to mesenchymal cell transition. Early posttransplant induction of these growth factors may start molecular mechanisms leading to CAN. A new promising immunosuppressive drug, FK778, is an analogue of the active metabolite of leflunamide, which inhibits de novo pyrimidine biosynthesis. Herein we investigated the effect of FK778 on acute rejection and on the expression of PDGF and TGF-beta both alone and in combination with cyclosporine (CsA) or tacrolimus (Tac).

METHODS

Kidney transplantations were performed from Dark Agouti (DA) to Wistar-Furth (WF) rats with syngeneic controls between DA rats. No immunosuppression was given to syngeneic grafts. Allografts were immunosuppressed with FK778 alone or in combination with CsA or Tac. Grafts were harvested on day 5 for histology and immunohistochemistry (PDGF-A, -B, PDGFR-alpha, -beta, TGF-beta1, and TGF-betaR1).

RESULTS

FK778 ameliorated the inflammatory response and reduced PDGF and TGF-beta expression in a dose-dependent manner. It also showed synergy with calcineurin inhibitors, an effect that was stronger with Tac than with CsA.

CONCLUSIONS

Our results indicated that FK778 decreased PDGF and TGF-beta expression early in acute rejection, suggesting it to be a promising therapy for CAN.

Role of Activated Growth Factors in Lumbar Spinal Fusions

BACKGROUND

The concentration of platelets into an activated growth factor (AGF) gel may stimulate graft consolidation into a fusion mass. Preoperative hemodilution and intraoperative clot activation may also reduce the overall blood loss. Consequently, the need for postoperative transfusions may also be reduced.

OBJECTIVE

The objective of this work was to report our experience with AGF platelet gels in transforaminal lumbar interbody fusion (TLIF) procedures.

METHODS

A consecutive series of patients between 1996 and 1999 undergoing one- and two-level TLIFs with AGF were compared with a consecutive series of TLIF patients who did not receive AGF. Sixty-two control subjects who did not receive AGF and 22 patients who received an AGF platelet gel were compared after 41 and 34 months of follow-up, respectively.

RESULTS

On average, the AGF group required 18 minutes of additional preincision anesthesia (P = 0.0001). No statistical differences in the operative times, estimated blood loss, postoperative drainage, percentage of patients requiring a transfusion, or length of hospitalization were appreciated between the two groups. The 19% decrease in the arthrodesis rate of the AGF group, as compared with the control group, did not reach statistical significance. Platelet counts from the AGF platelet concentrates demonstrated an average 3.5-fold increase compared with preoperative serum levels.

CONCLUSIONS

The theoretical benefits of AGF platelet gel technology were not clinically appreciated. The cost of implementing this technology may therefore outweigh its theoretical benefits.

Expression of NHERF-1, NHERF-2, PDGFR-alpha, and PDGFR-beta in normal human kidneys and in renal transplant rejection

Sodium-hydrogen exchanger regulatory factor-1 and -2 (NHERF-1 and NHERF-2) are adaptor proteins that regulate renal electrolyte transport and interact with the platelet-derived growth factor receptors (PDGFR). The distribution of the NHERF proteins and PDGFR was studied in normal human kidneys and in renal transplant rejection using immunocytochemistry. In normal kidneys, NHERF-1 was detected in proximal tubules. NHERF-2 was detected in glomeruli, peritubular capillaries, and collecting duct principal cells. NHERF-2 was also weakly detected in the proximal tubule. PDGFR-beta was detected in glomeruli but not in tubules while PDGFR-alpha was detected in renal tubules and minimally in glomeruli. Acute and chronic transplant rejection was associated with increased expression of PDGFR-alpha in tubules and expression in the glomeruli. PDGFR-beta expression in the glomeruli was increased in transplant rejection and became detectable in tubules. Expression of NHERF-1 and NHERF-2 was not different in the patient groups. These results indicate that in contrast to the rat, both NHERF isoforms are detected in the human proximal tubule. In renal transplant rejection, there is increased expression of both PDGFR subtypes consistent with a role for PDGF in injury or repair.

Obstructive Uropathy in Mice and Humans: Potential Role for PDGF-D in the Progression of Tubulointerstitial Injury

ABSTRACT. Tubulointerstitial fibrosis is a major characteristic of progressive renal diseases. Platelet-derived growth factor (PDGF) is a family of growth regulatory molecules consisting of PDGF-A and -B, along with the newly discovered PDGF-C and -D. They signal through cell membrane receptors, PDGF receptor α (PDGF-Rα) and receptor β (PDGF-Rβ). Involvement of PDGF-B and PDGF-Rβ in the initiation and progression of renal fibrosis has been well documented. The authors studied the localization of PDGF ligands and receptors by immunohistochemistry, with emphasis on the role of PDGF-D in murine renal fibrosis induced by unilateral ureteral obstruction (UUO). In mice with UUO,de novoexpression of PDGF-D was detected in interstitial cells at day 4, which increased to maximal expression at day 14. Increased expression of PDGF-B by interstitial cells and in some tubules was observed after day 4. The diseased mice did not show augmentation of PDGF-A or PDGF-C proteins in the areas of fibrosis. PDGF-Rα and -Rβ protein expression was increased in interstitial cells after day 4 and reached maximal expression at day 14. Human renal nephrectomies (n= 10) of chronic obstructive nephropathy demonstrated similarde novoexpression of PDGF-D in interstitial cells, correlating with expression of PDGF-Rβ and PDGF-B, as it did in the murine model. These observations suggest that PDGF-D plays an important role in the pathogenesis of tubulointerstitial injury through binding of PDGF-Rβ in both human obstructive nephropathy and the corresponding murine model of UUO. E-mail: calp@u.washington.edu

Hypertension increases expression of growth factors and MHC II in chronic allograft nephropathy

BACKGROUND

Hypertension of the recipient is strongly associated with chronic allograft nephropathy. It is unclear, however, whether hypertension is the cause or the consequence of chronic allograft nephropathy.

METHODS

The present study was performed in the Fisher to Lewis rat kidney transplant model. Transplanted rats (N = eight in each group) received either no treatment or were made hypertensive by administration of deoxycorticosteron acetate (DOCA) and salt. Proteinuria and systolic blood pressure was measured monthly, grafts were harvested at 3 and 6 months for semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and for immunohistology.

RESULTS

Systolic blood pressure was markedly elevated in rats receiving DOCA/salt. Allografts of hypertensive animals contained significantly more cells expressing the proliferating cell nuclear antigen compared to isografts and to allografts from normotensive animals (P < 0.05). Histologic staining and mRNA expression of major histocompatibility complex (MHC) II was markedly increased in allografts of hypertensive animals compared to all other groups (P < 0.05). Expression of mRNA for platelet-derived growth factor-B (PDGF-B), transforming growth factor-beta (TGF-beta) and collagen was higher in allografts than in isografts and was highest in hypertensive animals.

CONCLUSION

We conclude that hypertension augments the expression of growth factors in the allograft possibly aggravating the intimal hyperplasia observed in chronic allograft nephropathy. By increasing the expression of MHC II antigens, hypertension may render the allograft more susceptible to alloantigen-dependent damage. Hypertension and alloantigen-dependent factors appear to exert additive or synergistic effects on inflammatory pathways leading to graft injury.

Chronic allograft nephropathy is prevented by inhibition of platelet-derived growth factor receptor: tyrosine kinase inhibitors as a potential therapy

BACKGROUND

Chronic allograft nephropathy (CAN) is the primary reason for late allograft loss in kidney transplantation, and currently there is no treatment available for it. Platelet-derived growth factor (PDGF) is suggested to be a major mitogen mediating mesenchymal cell proliferation in CAN. It has been shown that PDGF is already induced at acute renal allograft rejection, indicating a link between acute rejection and subsequent development of CAN. However, the definite effect of PDGF on the pathogenesis of CAN is still unknown. We investigated the role of PDGF in CAN by inhibiting PDGF by imatinib (STI571), a selective PDGF receptor tyrosine kinase inhibitor.

METHODS

Kidney transplantations were performed from Dark Agouti (DA) to Wistar-Furth rats, and syngenic control transplantations were performed from DA to DA rats. All allograft recipients were immunosuppressed with cyclosporine A (1.5 mg/kg/day subcutaneously). One group of the animals was also treated with imatinib (10 mg/kg/day orally). Serum creatinine levels and cyclosporine A concentrations were measured once per week until the animals were killed. Grafts were harvested 5 and 90 days after transplantation for histology and immunohistochemistry.

RESULTS

Only very few histologic chronic changes, similar to syngenic grafts, were seen in imatinib-treated allografts compared with control allografts. Creatinine values of imatinib-treated allograft recipients and infiltration of inflammatory cells, PDGF ligand, and receptor induction were also at the same level as in syngenic grafts.

CONCLUSIONS

Our results demonstrate that imatinib prevents CAN almost completely, indicating that PDGF plays an important role in its pathogenesis. On the basis of our findings, imatinib could be a potential intervention in preventing CAN in clinical kidney transplantation.

The effect of acute rejection and cyclosporin A-treatment on induction of platelet-derived growth factor and its receptors during the development of chronic rat renal allograft rejection

BACKGROUND

In the development of chronic kidney allograft rejection acute rejection (AR) is the single most important risk factor. Although Cyclosporin A (CsA) medication has decreased the incidence of AR, chronic rejection (CR) is still the major reason for late allograft loss. Platelet-derived growth factor (PDGF) is a major mitogen mediating mesenchymal cell proliferation in CR. We have investigated the impact of AR and different doses of CsA on the expression of PDGF ligands and receptors in the development of CR.

METHODS

Kidney transplantations were performed from DA to WF rats and syngenic controls were done from DA to DA rats. Two groups of allografts were treated daily with CsA either at low dose (1.5 mg/kg) or high dose (5 mg/kg). Third group of allografts was treated with CsA 5 mg/kg/day for 1 week and then left untreated until the development of AR. AR episodes were treated with CsA 5 mg/kg/day. Grafts were harvested 3 months after transplantation for histology and immunohistochemistry (PDGF-AA, -BB and PDGFR-alpha, -beta).

RESULTS

In syngenic grafts no histological signs of CR were seen and the expression of PDGF ligands and receptors remained almost nonexistent. AR episodes increased the chronic rejection changes. High-dose CsA-treatment ameliorated inflammation compared to low-dose CsA-treatment, although it failed to inhibit the development of chronic changes. More fibrosis was even seen in high-dose than in low-dose CsA-treated grafts. CR in each allograft group was associated with induction of all PDGF ligands and receptors (P<0.05 compared with syngenic controls) in interstitial inflammatory cells, capillary endothelium, and arterial smooth muscle cells. In the group with AR episodes the expression was further increased.

CONCLUSIONS

Our results demonstrate that CsA treatment cannot inhibit the expression of PDGF ligands and receptors in the development of chronic kidney allograft rejection and that AR episodes induce even more PDGF and its receptors in the graft indicating a link between AR and subsequent development of CR.