Christiane Petzold

The peroxisome proliferator-activated receptor (PPAR) alpha agonist fenofibrate maintains bone mass, while the PPAR gamma agonist pioglitazone exaggerates bone loss, in ovariectomized rats

BackgroundActivation of peroxisome proliferator-activated receptor (PPAR)gamma is associated with bone loss and increased fracture risk, while PPARalpha activation seems to have positive skeletal effects. To further explore these effects we have examined the effect of the PPARalpha agonists fenofibrate and Wyeth 14643, and the PPARgamma agonist pioglitazone, on bone mineral density (BMD), bone architecture and biomechanical strength in ovariectomized rats.MethodsFifty-five female Sprague-Dawley rats were assigned to five groups. One group was sham-operated and given vehicle (methylcellulose), the other groups were ovariectomized and given vehicle, fenofibrate, Wyeth 14643 and pioglitazone, respectively, daily for four months. Whole body and femoral BMD were measured by dual X-ray absorptiometry (DXA), and biomechanical testing of femurs, and micro-computed tomography (microCT) of the femoral shaft and head, were performed.ResultsWhole body and femoral BMD were significantly higher in sham controls and ovariectomized animals given fenofibrate, compared to ovariectomized controls. Ovariectomized rats given Wyeth 14643, maintained whole body BMD at sham levels, while rats on pioglitazone had lower whole body and femoral BMD, impaired bone quality and less mechanical strength compared to sham and ovariectomized controls. In contrast, cortical volume, trabecular bone volume and thickness, and endocortical volume were maintained at sham levels in rats given fenofibrate.ConclusionsThe PPARalpha agonist fenofibrate, and to a lesser extent the PPARaplha agonist Wyeth 14643, maintained BMD and bone architecture at sham levels, while the PPARgamma agonist pioglitazone exaggerated bone loss and negatively affected bone architecture, in ovariectomized rats.

Sinus Graft With Safescraper: 5-Year Results

PURPOSE In the procedure of sinus floor elevation, autogenous bone, allogenic grafts, and several other bone substitutes are used. However, autogenous bone is still considered the gold standard. Donor sites for autogenous bone are generally the iliac crest, oral cavity, calvarium bone, and tibia. In this work the experience with the use of a Safescraper device for harvesting of autogenous bone is reported and a decision-making algorithm for grafting in sinus floor elevation procedures is proposed. MATERIALS AND METHODS Forty sinus augmentation procedures were performed in 34 patients. All sinuses were filled with a mixture of autogenous bone and bovine hydroxyapatite. A Safescraper device was used to harvest autologous bone from the maxillary area. Platelet-rich plasma was used to sustain bone placement. Sixty-five dental implants were placed at 4 months with a flapless procedure. A clinical and radiological 5-year retrospective case series of a cohort is reported. RESULTS In all cases new bone formation was confirmed radiologically and implant placement was performed successfully. Analysis of samples obtained by biopsy with histology and microcomputed tomography showed the presence of mature bone. Healing problems were observed in only 1 case. CONCLUSIONS Sinus augmentation with bone grafts obtained from oral cavity with a bone scraper device has the advantage of providing autogenous bone without the need for an extra surgical approach. This procedure yields satisfactory results in bone formation, implant survival, and patient satisfaction. When combined with a flapless approach for implant placement, a decrease in the morbidity of the entire process is achieved.

The Skeletal Phenotype of Chondroadherin Deficient Mice

Chondroadherin, a leucine rich repeat extracellular matrix protein with functions in cell to matrix interactions, binds cells via their α2β1 integrin as well as via cell surface proteoglycans, providing for different sets of signals to the cell. Additionally, the protein acts as an anchor to the matrix by binding tightly to collagens type I and II as well as type VI. We generated mice with inactivated chondroadherin gene to provide integrated studies of the role of the protein. The null mice presented distinct phenotypes with affected cartilage as well as bone. At 3–6 weeks of age the epiphyseal growth plate was widened most pronounced in the proliferative zone. The proteome of the femoral head articular cartilage at 4 months of age showed some distinct differences, with increased deposition of cartilage intermediate layer protein 1 and fibronectin in the chondroadherin deficient mice, more pronounced in the female. Other proteins show decreased levels in the deficient mice, particularly pronounced for matrilin-1, thrombospondin-1 and notably the members of the α1-antitrypsin family of proteinase inhibitors as well as for a member of the bone morphogenetic protein growth factor family. Thus, cartilage homeostasis is distinctly altered. The bone phenotype was expressed in several ways. The number of bone sialoprotein mRNA expressing cells in the proximal tibial metaphysic was decreased and the osteoid surface was increased possibly indicating a change in mineral metabolism. Micro-CT revealed lower cortical thickness and increased structure model index, i.e. the amount of plates and rods composing the bone trabeculas. The structural changes were paralleled by loss of function, where the null mice showed lower femoral neck failure load and tibial strength during mechanical testing at 4 months of age. The skeletal phenotype points at a role for chondroadherin in both bone and cartilage homeostasis, however, without leading to altered longitudinal growth.

Flavonoid-Modified Surfaces: Multifunctional Bioactive Biomaterials with Osteopromotive, Anti-Inflammatory, and Anti-Fibrotic Potential

Flavonoids are small polyphenolic molecules of natural origin with antioxidant, anti-inflammatory, and antibacterial properties. Here, a bioactive surface based on the covalent immobilization of flavonoids taxifolin and quercitrin on titanium substrates is presented, using (3-aminopropyl)triethoxysilane (APTES) as coupling agent. FTIR and XPS measurements confirm the grafting of the flavonoids to the surfaces. Using 2-aminoethyl diphenylborinate (DPBA, a flavonoid-specific dye), the modified surfaces are imaged by fluorescence microscopy. The bioactivity of the flavonoid-modified surfaces is evaluated in vitro with human umbilical cord derived mesenchymal stem cells (hUC-MSCs) and human gingival fibroblasts (HGFs) and compared to that of simple flavonoid coatings prepared by drop casting. Flavonoid-modified surfaces show anti-inflammatory and anti-fibrotic potential on HGF. In addition, Ti surfaces covalently functionalized with flavonoids promote the differentiation of hUC-MSCs to osteoblasts--enhancing the expression of osteogenic markers, increasing alkaline phosphatase activity and calcium deposition; while drop-casted surfaces do not. These findings could have a high impact in the development of advanced implantable medical devices like bone implants. Given the broad range of bioactivities of flavonoid compounds, these surfaces are ready to be explored for other biomedical applications, e.g., as stent surface or tumor-targeted functionalized nanoparticles for cardiovascular or cancer therapies.

UV photoactivation of 7-dehydrocholesterol on titanium implants enhances osteoblast differentiation and decreases Rankl gene expression.

Vitamin D plays a central role in bone regeneration, and its insufficiency has been reported to have profound negative effects on implant osseointegration. The present study aimed to test the in vitro biological effect of titanium (Ti) implants coated with UV-activated 7-dehydrocholesterol (7-DHC), the precursor of vitamin D, on cytotoxicity and osteoblast differentiation. Fourier transform infrared spectroscopy confirmed the changes in chemical structure of 7-DHC after UV exposure. High-pressure liquid chromatography analysis determined a 16.5±0.9% conversion of 7-DHC to previtamin D(3) after 15min of UV exposure, and a 34.2±4.8% of the preD(3) produced was finally converted to 25-hydroxyvitamin D(3) (25-D(3)) by the osteoblastic cells. No cytotoxic effect was found for Ti implants treated with 7-DHC and UV-irradiated. Moreover, Ti implants treated with 7-DHC and UV-irradiated for 15min showed increased 25-D(3) production, together with increased ALP activity and calcium content. Interestingly, Rankl gene expression was significantly reduced in osteoblasts cultured on 7-DHC-coated Ti surfaces when UV-irradiated for 15 and 30min to 33.56±15.28% and 28.21±4.40%, respectively, compared with the control. In conclusion, these findings demonstrate that UV-activated 7-DHC is a biocompatible coating of Ti implants, which allows the osteoblastic cells to produce themselves active vitamin D, with demonstrated positive effects on osteoblast differentiation in vitro.

Decreased bone mineral density and reduced bone quality in H+/K+ATPase beta‐subunit deficient mice

Proton pump inhibitors (PPIs) are widely used against gastroesophageal reflux disease. Recent epidemiological studies suggest that PPI users have an increased risk of fractures, but a causal relationship has been questioned. We have therefore investigated the skeletal phenotype in H+/K+ATPase beta‐subunit knockout (KO) female mice. Skeletal parameters were determined in 6‐ and 20‐month‐old KO mice and in wild‐type controls (WT). Whole body bone mineral density (BMD) and bone mineral content (BMC) were measured by dual energy X‐ray absorptiometry (DXA). Femurs were examined with µCT analyses and break force were examined by a three‐point bending test. Plasma levels of gastrin, RANKL, OPG, osteocalcin, leptin, and PTH were analyzed. KO mice had lower whole body BMC at 6 months (0.53 vs. 0.59 g, P = 0.035) and at 20 months (0.49 vs. 0.74 g, P < 0.01) compared to WT as well as lower BMD at 6 months (0.068 vs. 0.072 g/cm2, P = 0.026) and 20 months (0.067 vs. 0.077 g/cm2, P < 0.01). Mechanical strength was lower in KO mice at the age of 20 months (6.7 vs. 17.9 N, P < 0.01). Cortical thickness at 20 months and trabecular bone volume% at 6 months were significantly reduced in KO mice. Plasma OPG/RANKL ratio and PTH was increased in KO mice compared to controls. H+/K+ATPase beta subunit KO mice had decreased BMC and BMD, reduced cortical thickness and inferior mechanical bone strength. Whereas the mechanism is uncertain, these findings suggest a causal relationship between long‐term PPI use and an increased risk of fractures. J. Cell. Biochem. 113: 141–147, 2012.

In Vitro Osteogenic Properties of Two Dental Implant Surfaces

Current dental implant research aims at understanding the biological basis for successful implant therapy. The aim of the study was to perform a full characterization of the effect of two commercial titanium (Ti) surfaces, OsseoSpeed and TiOblast, on the behaviour of mouse preosteoblast MC3T3-E1 cells. The effect of these Ti surfaces was compared with tissue culture plastic (TCP). In vitro experiments were performed to evaluate cytotoxicity, cell morphology and proliferation, alkaline phosphatase activity, gene expression, and release of a wide array of osteoblast markers. No differences were observed on cell viability and cell proliferation. However, changes were observed in cell shape after 2 days, with a more branched morphology on OsseoSpeed compared to TiOblast. Moreover, OsseoSpeed surface increased BMP-2 secretion after 2 days, and this was followed by increased IGF-I, BSP, and osterix gene expression and mineralization compared to TiOblast after 14 days. As compared to the gold standard TCP, both Ti surfaces induced higher osteocalcin and OPG release than TCP and differential temporal gene expression of osteogenic markers. The results demonstrate that the gain of using OsseoSpeed surface is an improved osteoblast differentiation and mineralization, without additional effects on cell viability or proliferation.

Clinical color intensity of white spot lesions might be a better predictor of enamel demineralization depth than traditional clinical grading.

INTRODUCTION The aims of this study were to calculate the volume of white spot lesions by using microcomputed tomography and to determine which clinical attribute of the white spot lesion could better predict its volume: the clinically visible white spot lesion surface area or its color intensity. METHODS White spot lesions were induced in 8 patients in vivo on 23 healthy premolars destined for extraction during orthodontic treatment by using specially designed plaque-retaining orthodontic bands. After 7 weeks, the premolars were extracted. After extraction, the resulting white spot lesions were photographed and clinically graded. The teeth were analyzed with microcomputed tomography. RESULTS After 7 weeks, 70% of the teeth developed clinical white spot lesions. Clinically, the size of the lesions varied from minor to severe. Their volumes varied from 0 to 1.2931 mm(3). The traditional grades for white spot lesions correlated significantly with color intensity. A significant correlation was found between white spot lesion color intensity and lesion volume. This correlation was found to be better than that between the white spot lesion clinical score and lesion volume. CONCLUSIONS Our results indicate that white spot lesion color intensity might predict the depth of enamel demineralization as well as or better than traditional white spot lesion scoring. Therefore, the dentist could use this information when planning treatment for white spot lesions.

In vivo performance of titanium implants functionalized with eicosapentaenoic acid and UV irradiation

The aim of this study was to design implant surfaces that attach less to bone but at the same time improve osseous healing for use as temporary bone fracture plates. The strategy was to combine the nonadhesive properties of smooth titanium (Ti) surfaces with the differentiative and anti-inflammatory properties of eicosapentaenoic acid (EPA). Machined Ti implant surfaces coated with a layer of EPA, with or without UV irradiation, were characterized by X-ray photoelectron spectroscopy, and their in vivo performance was evaluated in New Zealand White rabbits. The performance of the functionalised implants was analyzed after 10 weeks of healing by mechanical pull-out testing, molecular biology, and histological and microcomputed tomography analysis. The results indicate that surface functionalization with UV light can reduce bone attachment and volumetric bone mineral density in the peri-implant bone tissue. The presence of EPA on the surfaces enhanced this effect further. Gene expression of bone formation markers showed a trend toward higher mRNA levels in all EPA treated groups. The histological analyses demonstrated lower inflammation in the UV-irradiated group and immature bone formation in all the groups. In conclusion, surface functionalization of Ti implants with UV light and EPA could be a biocompatible coating for reduced bone bonding ability of Ti while promoting bone formation.

Effect of proline-rich synthetic peptide-coated titanium implants on bone healing in a rabbit model.

PURPOSE Previous studies have demonstrated the capacity of a designed proline-rich synthetic peptide to stimulate osteoblast differentiation and biomineralization in vitro. Therefore, the aim of the present study was to evaluate the osseointegration capacity of titanium (Ti) implants coated with these peptides in a rabbit model. MATERIALS AND METHODS Four calibrated defects were prepared in the tibiae of three New Zealand rabbits, and the defects were randomized into a test group (peptide-modified machined Ti implant) and a control group (unmodified machined Ti implant). The performance in vivo was investigated after 4 weeks of implantation by real-time reverse transcriptase polymerase chain reaction of bone and inflammatory markers, microcomputed tomographic analysis of mineralized bone, and histologic examination. RESULTS The peptides adsorbed in agglomerates on Ti and underwent a change in secondary structure upon adsorption, which induced an increase in surface wettability. Gene expression markers indicated that peptide-coated Ti implants had significantly decreased mRNA levels of tartrate-resistant acid phosphatase. A trend toward increased osteocalcin in the peri-implant bone tissue was also seen. Bone morphometric and histologic parameters did not show significant differences, although the peptide group showed a higher percentage of new bone histologically. CONCLUSIONS Proline-rich peptides have potential as a biocompatible coating for promoting osseointegration of Ti implants by reducing bone resorption.