Biomedical subjects

Reinhard Gruber

Publications and source records attributed to Reinhard Gruber.

23 records · Page 2Linked to original sources

PubMed2002

Platelet-released supernatants stimulate formation of osteoclast-like cells through a prostaglandin/RANKL-dependent mechanism.

Platelets are activated at fracture sites or upon the insertion of implants as a consequence of vascular disruption and secrete the contents of their granules into the developing hematoma. The regeneration of injured tissue requires bone remodeling and the resorbing activity of osteoclasts. To test our hypothesis that platelets can stimulate osteoclastogenesis, we examined the effects of supernatants released from thrombin-activated platelets on osteoclast-like cell formation in murine bone marrow cultures. Histochemical analysis indicated the presence of bone-resorbing, tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells. Transcripts that are characteristically expressed in native osteoclasts were increased in these cultures, as determined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis. The inhibition of both cyclooxygenases with indomethacin, as well as the addition of the cyclooxygenase-2 (COX-2)-selective antagonist, NS398, completely blocked osteoclast-like cell formation and decreased endogenous prostaglandin E(2) production. Platelet-released supernatants stimulated the expression of receptor activator of NF-kappaB ligand (RANKL), whereas mRNA levels of osteoprotegerin (OPG) were decreased. The formation of osteoclast-like cells was prevented by recombinant OPG. Our results suggest that COX-2 activity is necessary for osteoclast-like cell formation in response to platelet-released supernatants, and that endogenously produced prostaglandin E(2) can, in turn, increase the RANKL:OPG ratio, indicating that platelets can contribute to bone remodeling by stimulation of osteoclastogenesis.

Animals↗

PubMed2002

Platelets stimulate proliferation of bone cells: involvement of platelet-derived growth factor, microparticles and membranes.

Platelets have been implicated in accelerated bone regeneration in grafting applications. The beneficial effects of platelets may involve their ability to stimulate the proliferation of osteoblasts. We therefore determined the mitogenic response of human trabecular bone-derived cells to human platelets and supernatants of thrombin-activated platelets. We can show a approximately 50-fold increase in DNA-synthesis of bone cells (BC) cultured in the presence of platelets as determined by [3H]-thymidine incorporation. Preventing cell-to-cell contact by a membrane filter did not abrogate the stimulatory effect, indicating the release of soluble factor(s) that are mitogenic for BC. The lipid fraction of the platelets had no effect on [3H]-thymidine uptake into the DNA of BC. Platelet-released supernatant (PRS) increased the rate of [3H]-thymidine incorporation to approximately 20-fold and retained 56% of their activity after incubation at 56 degrees C, and 27% at 100 degrees C, respectively. Neutralizing antibodies raised against platelet-derived growth factor (PDGF) partially suppressed the mitogenic potential of PRS. Gel exclusion chromatography analysis showed that molecules ranging from 25 kDa to more than 70 kDa within the PRS can stimulate BC proliferation. The highest amount of PDGF was detected in fractions corresponding to a molecular weight of 28-37 kDa as determined by immunoassay. The mitogenic activity was not restricted to soluble growth factors because microparticles in the PRS and platelet membranes also increased BC proliferation. Our data indicate that native platelets, the respective PRS, microparticles, and platelet membranes can stimulate the mitogenic activity of BC, thereby contributing to the regeneration of mineralized tissue.

Aged↗

PubMedDate not supplied

BMP-6-induced osteogenic differentiation of mesenchymal cell lines is not modulated by sex steroids and resveratrol.

Bone morphogenetic protein-6 (BMP-6) is a potent inducer of osteogenic differentiation and its expression is stimulated by 17beta-estradiol. The existence of a regulatory loop between sex steroids and BMP-6 is therefore reasonable to hypothesize. Here we determined whether the sex steroids 17beta-estradiol and dihydrotestosterone, and the phytoestrogen resveratrol can modulate BMP-6-induced alkaline phosphatase activity and osteocalcin expression. Mesenchymal cells of murine (osteoblastic MC3T3-E1 cells, preadipogenic ST2 cells, prechondrogenic ATDC5 cell) and human origin (osteosarcoma SaOS and HOS cells, primary bone marrow stromal cells) were cultured in the presence of recombinant BMP-6 under serum-free conditions. BMP-6 dose-, and time-dependently increased alkaline phosphatase activity in murine cell lines, but not in human cells. Osteocalcin expression was also increased upon stimulation with BMP-6. The presence of 17beta-estradiol, dihydrotestosterone, and resveratrol had no effect on BMP-6-induced alkaline phosphatase activity and osteocalcin expression. These data suggest that osteogenic differentiation in response to BMP-6 occurs independent of steroid hormones and resveratrol in mesenchymal cells that express basal receptor levels.

Alkaline Phosphatase↗

PubMedDate not supplied

Bone marrow stromal cells can provide a local environment that favors migration and formation of tubular structures of endothelial cells.

Findings suggest that mesenchymal progenitor cells can support the process of blood vessel formation, which may be relevant during granulation tissue formation at defect sites. The aim of this study was to investigate possible mechanisms of the angiogenic process that can be stimulated by mesenchymal progenitor cells. In the in vivo-like model of the chick embryo chorioallantoic membrane assay, we observed blood vessel ingrowth into collagen sponges containing conditioned medium from undifferentiated bone marrow stromal cells. In the Boyden chamber assay, the conditioned medium was chemotactic for human umbilical vascular endothelial cells and human uterus microvascular endothelial cells, and when cells were placed on Matrigel-coated culture dishes, formation of tubular structures was enhanced. The presence of vascular endothelial growth factor-neutralizing antibodies did not affect the outcome of the two in vitro assays. Bone marrow stromal cell-conditioned medium had no effect on proliferation of endothelial cells, as determined by measuring [3H]thymidine incorporation, and on matrix metalloproteinase 2 expression, as evaluated by reverse transcription-polymerase chain reaction and gelatin zymography. These data indicate that mesenchymal progenitor cells can provide a local environment that supports the ingrowth of blood vessels into a defect site.

Adult↗

PubMedDate not supplied

Enhanced bone-to-implant contact by platelet-released growth factors in mandibular cortical bone: a histomorphometric study in minipigs.

PURPOSE: To determine the effects of platelet-released growth factors (PRGF) on bone-to-implant contact (BIC) in minipig cortical bone. MATERIALS AND METHODS: In each of 8 adult minipigs, 2 implants were placed in the facial wall of the mandible, one implant with and one without PRGF. PRGF was defined as the supernatant from washed, thrombin-activated, allogenic, platelet-rich plasma cells obtained after centrifugation. Four animals were sacrificed at 4 weeks, and the remaining 4 were sacrificed at 8 weeks. For histomorphometric analyses, undecalcified ground specimens were prepared and stained with the Levai-Laczko stain. RESULTS: For the entire follow-up time, 55.30% BIC was found with PRGF versus 38.91% without PRGF (P = .0198). At 4 weeks, BIC was 44.20% with PRGF versus 29.62% without PRGF (P = .0632), and at 8 weeks there was 70.36% BIC with PRGF versus 48.20% without PRGF (P = .1221). DISCUSSION: Growth factors and other molecules released upon activation of platelet-rich plasma cells can enhance implant anchorage in cortical bone. PRGF obtained from allogenic sources does not impair healing. CONCLUSION: The results indicated that a single application of PRGF before implant placement can be sufficient to increase the percent BIC in minipig cortical bone.

Animals↗