Plasma clearance and tissue distribution of recombinant human platelet-derived growth factor (B-chain homodimer) in rats

The role of the kidney in the systemic elimination of interleukin 6, platelet-derived growth factor and transforming growth factor beta

STUDY GOAL

The aim of the study was to assess the role of the kidney in systemic elimination of IL-6 and growth factors (PDGF, TGF-β) by comparison of their concentrations in renal arteries and veins, peripheral veins and urine.

MATERIAL AND METHODS

30 brain-dead kidney donors were included in the study. Samples were obtained during the harvesting procedure. 10 healthy volunteers served as controls. A mathematical model of elimination of investigated proteins from systemic circulation was developed. The elimination ratio (ER) formula indicates the predominance of renal synthesis or degradation and also quantifies the renal uptake (UR) and renal pass (PR) of investigated proteins. Serum levels of investigated proteins were estimated using an immunoenzymatic method (ELISA).

RESULTS

Renal IL-6 uptake ratio (UR) amounted to 6.6%, elimination ratio (ER) amounted to 6.4% and pass ratio (PR) amounted to 0.2%. PDGF ratios amounted to 5.1%, 5.0% and 0.1% and TGF-β ratios amounted to -9%, -9% and 0%, respectively.

CONCLUSIONS

The kidney takes part in the elimination of IL-6 and PDGF from systemic circulation. The kidney does not take part in the elimination of TGF-β.

Effect of platelet-derived growth factor-BB on root resorption after reimplantation of partially denuded tooth in dog

The prognosis for a reimplanted tooth depends largely on the condition of the root. Platelet-derived growth factor (PDGF)-BB has been shown to regenerate periodontal tissue in animal and human clinical studies. However, information regarding the effect of PDGF-BB on tooth reimplantation is limited. The objective of this study was to investigate the effect of PDGF-BB on root resorption after reimplantation of a partially denuded tooth in dog. A total of 15 healthy female beagle dogs were used. Mandibular third and fourth premolars were endodontically treated and then extracted as atraumatically as possible. The coronal portion of each root was carefully scaled and planed. The roots on the right side of the mandible were treated with PDGF-BB and reimplanted, while the roots on the left side served as controls. After 2, 4, or 8 weeks, specimens were collected and processed for histopathological examination. By the 4th week after reimplantation, new periodontal ligament (PDL)-like tissue had formed around the PDGF-BB-treated root surfaces and new bone. By the 8th week, healing of the PDGF-BB-treated roots was characterized by newly formed PDL with inserting attachment formation. In contrast, control roots showed multiple areas of replacement resorption. Immunohistochemical staining of proliferating cell nuclear antigen (PCNA) performed at 2 weeks after reimplantation showed that the number of PCNA-positive cells in the connective tissue area was statistically significantly greater in the PDGF-BB-treated group than in the control group (P < 0.001). The application of PDGF-BB resulted in a significantly lower occurrence and extent of root resorption and ankylosis. These results suggest that the use of PDGF-BB reduces occurrence of ankylosis and root resorption in tooth reimplantation.

Clinical significance of hepatocyte growth factor, platelet-derived growth factor-AB, and transforming growth factor-alpha in bone marrow and peripheral blood of patients with multiple myeloma

Angiogenesis is a process that plays an important role in the growth and progression of cancer; growing evidence suggests that neovascularization is important in hematologic malignancies. Increased angiogenic potential has been identified in multiple myeloma (MM). In this study, investigators simultaneously measured the levels of hepatocyte growth factor (HGF), platelet-derived growth factor-AB (PDGFAB), and transforming growth factor-alpha (TGF-alpha) through enzyme-linked immunosorbent assay in the bone marrow (BM) and peripheral blood (PB) of 30 patients with MM and 10 healthy controls. Differences in HGF values in BM sera were significant (P=.001) between patients and controls. In detailed analyses of HGF, PDGF-AB, and TGF-alpha, according to disease stage, a significant correlation was found between disease stage and BM HGF (P=.047), BM TGF-alpha (P=.021), and PB PDGF-AB (P=.006), respectively. When correlations between all other parameters were analyzed, significance was noted between PB TGF-alpha and lactate dehydrogenase (P=.02), PB TGF-alpha and PB HGF (P=.002), BM TGF-alpha and CD38 (P=.046), BM TGF-alpha and BM HGF (P=.000), BM TGF-alpha and BM PDGF-AB (P=.048), BM HGF and PB HGF (P=.044), and BM PDGF-AB and PB PDGF-AB (P=.000). BM HGF levels had a significant effect on overall survival, with disease severity assessed in terms of disease stage (P=.0018, log-rank test). These data show that in patients with MM, high levels of BM HGF, BM TGF-alpha, and PB PDGF-AB were associated with advanced disease stage; in addition, HGF played a significant role in disease processing and was related to disease severity. These findings have also led to the concept of a symbiotic relationship between the growth of myeloma cells and HGF, TGF-alpha, and PDGFAB in BM.

The preferential homing of a platelet derived growth factor receptor-recognizing macromolecule to fibroblast-like cells in fibrotic tissue

Platelet derived growth factor (PDGF) is a key factor in the induction and progression of fibrotic diseases with the activated fibroblast as its target cell. Drug targeting to the PDGF-receptor is explored as a new approach to treat this disease. Therefore, we constructed a macromolecule with affinity for the PDGF-beta receptor by modification of albumin with a small peptide that recognises this PDGF-beta receptor. The binding of the peptide-modified albumin (pPB-HSA) to the PDGF-beta receptor was confirmed in competition studies with PDGF-BB using NIH/3T3-fibroblasts and activated hepatic stellate cells. Furthermore, pPB-HSA was able to reduce PDGF-BB-induced fibroblast proliferation in vitro, and proved to be devoid of proliferation-inducing activity itself. We assessed the distribution of pPB-HSA in vivo in two models of fibrosis and related the distribution of pPB-HSA to PDGF-beta receptor density. In rats with liver fibrosis (bile duct ligation model), pPB-HSA quickly accumulated in the liver in contrast to unmodified HSA (P<0.001). The major part of pPB-HSA in the fibrotic liver was localized in hepatic stellate cells. In rats with renal fibrosis (anti-Thy1.1 model), pPB-HSA also homed to the cells that expressed the PDGF-beta receptor, i.e. the mesangial cells in the glomeruli of the kidney. These results indicate that pPB-HSA may be applied as a macromolecular drug-carrier that accumulates specifically in cells expressing the PDGF-beta receptor, thus allowing a selective delivery of anti-fibrotic agents to these cells.

Periodontal Regeneration in Humans Using Recombinant Human Platelet- Derived Growth Factor-BB (rhPDGF-BB) and Allogenic Bone

BACKGROUND

Purified recombinant human platelet-derived growth factor BB (rhPDGF-BB) is a potent wound healing growth factor and stimulator of the proliferation and recruitment of both periodontal ligament (PDL) and bone cells. The hypothesis tested in this study was that application of rhPDGF-BB incorporated in bone allograft would induce regeneration of a complete new attachment apparatus, including bone, periodontal ligament, and cementum in human interproximal intrabony defects and molar Class II furcation lesions.

METHODS

Nine adult patients (15 sites) with advanced periodontitis exhibiting at least one tooth requiring extraction due to an extensive interproximal intrabony and/or molar Class II furcation defect were entered into the study. Eleven defects were randomly selected to receive rhPDGF-BB. Following full-thickness flap reflection and initial debridement, the tooth roots were notched at the apical extent of the calculus, the osseous defects were thoroughly debrided, and the tooth root(s) were planed/prepared. The osseous defects were then filled with demineralized freeze-dried bone allograft (DFDBA) saturated with one of three concentrations of rhPDGF-BB (0.5 mg/ml, 1.0 mg/ml, or 5.0 mg/ml). Concurrently, four interproximal defects were treated with a well accepted commercially available graft (anorganic bovine bone in collagen, ABB-C) and a bilayer collagen membrane. Radiographs, clinical probing depths, and attachment levels were obtained preoperatively (at baseline) and 9 months later. At 9 months postoperatively, the study tooth and surrounding tissues were removed en bloc. Clinical and radiographic data were analyzed for change from baseline by defect type and PDGF concentration. The histologic specimens were analyzed for the presence of regeneration of a complete new attachment apparatus coronal to the reference notch.

RESULTS

The post-surgical wound rapidly healed and was characterized by firm, pink gingivae within 7 to 10 days of surgery. There were no unfavorable tissue reactions or other safety concerns associated with the treatments throughout the course of the study. In rhPDGF/allograft sites, the vertical probing depth (vPD) reduction for interproximal defects was 6.42 +/- 1.69 mm (mean +/- SD) and clinical attachment level (CAL) gain was 6.17 +/- 1.94 mm (both P < 0.01). Radiographic fill was 2.14 +/- 0.85 mm. Sites filled with ABB-C had a PD reduction and CAL gain of 5.75 +/- 0.5 and 5.25 +/- 1.71, respectively. Furcation defects treated with rhPDGF/allograft exhibited a mean horizontal and vertical PD reduction of 3.40 +/- 0.55 mm (P < 0.001) and 4.00 +/- 1.58 mm (P < 0.005), respectively. The CAL gain for furcation defects was 3.2 +/- 2.17 mm (P < 0.030). Histologic evaluation revealed regeneration of a complete periodontal attachment apparatus, including new cementum, PDL, and bone coronal to the root notch in four of the six interproximal defects and all evaluable (four of four) furcation defects treated with PDGF. Two of the four interproximal intrabony defects treated with ABB-C and membrane exhibited regeneration.

CONCLUSIONS

Use of purified rhPDGF-BB mixed with bone allograft results in robust periodontal regeneration in both Class II furcations and interproximal intrabony defects. This is the first report of periodontal regeneration demonstrated histologically in human Class II furcation defects.

Platelet-derived growth factor BB secreted from osteoclasts acts as an osteoblastogenesis inhibitory factor

Osteoclasts and osteoblasts are responsible for strict bone maintenance with a balance between bone formation and resorption by interacting with each other. Recently, it has been revealed that osteoblasts/stromal cells regulate differentiation of osteoclasts/hematopoietic cells by two factors, the receptor activator of nuclear factor-kappaB (NF-kappaB) ligand (RANKL) on the plasma membrane, and secreted osteoprotegerin (OPG). However, no factors have yet been reported by which osteoclasts/hematopoietic cells regulate osteoblasts/stromal cells. To elucidate the possibility of signal transduction from osteoclasts to osteoblasts, we studied the conditioned medium of mouse osteoclast-like myeloma cell line RAW264.7 treated with RANKL. We found that this medium contains a factor that inhibits differentiation of mouse osteoblast precursor-like cell line MC3T3-E1 to osteoblasts induced by bone morphogenetic protein 4 (BMP-4) and named this factor osteoblastogenesis inhibitory factor (OBIF). OBIF was purified by successive three-step chromatography by heparin affinity, anion exchange, and reversed-phase columns. Osteoblastogenesis inhibitory activity made one peak in each chromatography step, showing the factor is a single entity. Active fractions were loaded on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and bands of proteins were excised, digested by trypsin, and analyzed by liquid chromatography equipped with tandem mass spectrometry (LC/MS/MS). Consequently, we have identified this factor to be platelet-derived growth factor BB (PDGF BB) homodimer. Furthermore, this identification of PDGF BB as OBIF was confirmed by neutralization of the inhibitory activity of the medium with anti-PDGF antibody. These results show, for the first time, that osteoclasts regulate osteoblasts directly and suggest that PDGF BB is a key factor in bone remodeling.

Uptake of 125I-PDGF-AB to the blood after extravascular administration in mice

The kinetics of exogenously given 125I-platelet-derived growth factor-AB (PDGF-AB) was studied in mice. 125I-PDGF-AB was injected either intraperitoneally, intramuscularly or subcutaneously and the resulting concentrations of 125I-radioactivity monitored in the blood at different times. The serum levels of 125I-radioactivity rose to a maximum 2-4 hours after injection, before decreasing. Precipitation of serum with trichloroacetic acid demonstrated that 50 per cent or more of the 125I remained in macromolecular form. Further, gel chromatography studies showed that the molecular size of the labelled material in serum, three hours after injection, was the same as that of the original 125I-PDGF-AB. In addition, a low-molecular weight fraction was observed, indicating the presence of degradation products. The largest proportion of degraded material was obtained after subcutaneous administration. The absence of partially degraded 125I-labelled fragments, e.g. 125I oligopeptides, indicates complete rather than limited degradation and suggests that the 125I-PDGF-AB had been processed by cellular uptake. It is concluded that extra-vascularly given PDGF-AB in mice is taken up into the blood in intact macromolecular form. This finding suggests that it is possible to administer PDGF extravascularly to obtain a prolonged increase in the concentration of intact PDGF in the blood.

Temporal expression of PDGF receptors and PDGF regulatory effects on osteoblastic cells in mineralizing cultures

Platelet-derived growth factor (PDGF) is mitogenic and chemotactic for osteoblastic cells in vitro. It is expressed during osseous wound healing and stimulates formation of new bone in vivo. PDGF stimulates cells by binding to specific cell surface receptors. The purpose of this study was to examine the effects of PDGF on osteoblastic proliferation and differentiation in long-term mineralizing cultures. Utilizing Northern blot analysis, we found that continuous PDGF treatment increased histone expression, indicative of enhanced proliferation, but suppressed osteoblast differentiation, demonstrated by inhibition of alkaline phosphatase, type I collagen, and osteocalcin expression. The inhibitory effect of PDGF on the differentiated function of osteoblasts was further established by findings that PDGF significantly inhibited nodule formation. The expression of PDGF receptors varied at different stages of culture. PDGF receptor mRNA expression increased when the cells had achieved a mature phenotype, during the stage of matrix maturation, and then decreased. However, as demonstrated by thymidine incorporation assays, the capacity of PDGF to stimulate DNA synthesis actually decreased during osteoblast maturation, as receptor expression increased. To investigate this apparent contradiction, tyrosyl phosphorylation and immunoblot assays were performed to assess changes in PDGF activation of their cognate receptors. The pattern of PDGF-induced tyrosyl phosphorylation remained relatively constant. This suggests that the diminished mitogenic activity of PDGF that occurs after osteoblast differentiation is regulated at a postreceptor level.

Effect of platelet-derived growth factor-BB on bone formation in calvarial defects: an experimental study in rabbits

The effect of recombinant human platelet-derived growth factor-BB (rhPDGF-BB) on bone healing was examined in calvarial defects in rabbits. Bicortical circular (critical size) defects were prepared in the calvarial bone of 16 rabbits. The defects were closed on the dural side and covered externally with expanded polytetrafluoroethylene membranes to prevent interference with osteogenesis within the defect by the surrounding tissue and to keep the growth factor in place. A single dose of methylcellulose gel (4.4%) with (n = 8) or without rhPDGF-BB (50 micrograms/ml) (n = 8) was applied to the defects, and the bone formation was evaluated after 8 weeks. Healing of defects in both groups was characterized by the presence of newly formed bone along the edges of the original defect and by a central area of fibrous connective tissue. The newly formed bone in the rhPDGF-BB treated defects had a trabecular structure; in contrast, a more compact structure was found in the control defects. In the rhPDGF-BB-treated defects, the bone ingrowth was 51.8 +/- 7.1% compared to 30.5 +/- 3.3% in the control defects. Furthermore, the amount of mineralized tissue was increased 112% in the rhPDGF-BB group. The amount of bone marrow was increased 75% in the rhPDGF-BB-treated defect. The porosity of cortical lamella in the newly formed bone was 84% higher in the rhPDGF-BB-treated defects compared to the control. These results show that administration of a single dose of rhPDGF-BB stimulates bone formation in critical size calvarial defects.

Platelet-derived growth factor inhibits bone regeneration induced by osteogenin, a bone morphogenetic protein, in rat craniotomy defects

Platelet-derived growth factor (PDGF) is a potent moderator of soft tissue repair through induction of the inflammatory phase of repair and subsequent enhanced collagen deposition. We examined the effect of recombinant BB homodimer PDGF (rPDGF-BB) applied to rat craniotomy defects, treated with and without bovine osteogenin (OG), to see if bone regeneration would be stimulated. Implants containing 0, 20, 60, or 200 micrograms rPDGF-BB, reconstituted with insoluble rat collagenous bone matrix containing 0, 30, or 150 micrograms OG, were placed into 8-mm craniotomies. After 11 d, 21 of the 144 rats presented subcutaneous masses superior to the defect sites. The masses, comprised of serosanguinous fluid encapsulated by fibrous connective tissue, were larger and occurred more frequently in rats treated with 200 micrograms rPDGF-BB, and were absent in rats not treated with rPDGF-BB. The masses underwent resorption within 28 d after surgery. OG (2-256 micrograms) caused a dose-dependent increase in radiopacity and a marked regeneration of calcified tissue in a dose-dependent fashion within defect sites. However, OG-induced bone regeneration was inhibited 17-53% in the presence of rPDGF-BB. These results suggest that rPDGF-BB inhibited OG-induced bone regeneration and stimulated a soft tissue repair wound phenotype and response.

Platelet-derived endothelial cell growth factor. Pharmacokinetics, organ distribution and degradation after intravenous administration in rats

Platelet-derived endothelial cell growth factor (PD-ECGF) stimulates chemotaxis of endothelial cells in vitro and has angiogenic activity in vivo. Recently PD-ECGF was shown to have thymidine phosphorylase activity. In order to study possible therapeutic applications of PD-ECGF we used a rat model to determine its pharmacokinetics and tissue distribution after intravenous injection. [125I]PD-ECGF disappeared from the plasma in a biphasic manner, with estimated distribution and elimination half-lives of 17 min and 7 h, respectively. PD-ECGF was metabolized in the liver, excreted via the bile, and not accumulated in any organ system. The stability and long half-life in the circulation, together with the specificity for endothelial cells, suggest that PD-ECGF may be useful as a therapeutic agent to stimulate re-endothelialization in vivo, or, in view of its thymidine phosphorylase activity, in chemotherapy, by decreasing the pool of available thymidine.