Similarities in the phenotypic expression of pericytes and bone cells

Role of periosteum in alveolar bone regeneration comparing with collagen membrane in a buccal dehiscence model of dogs

To investigate the role of periosteum on the treatment of buccal dehiscence defects comparing with collagen membrane in canine model. Bilateral dehiscence-type defects at the buccal side on the distal root of the lower 3rd/4th premolars were created in six beagle dogs with a total of 24 defects and assigned into three groups: Group A: blood clot in an untreated defect; Group B: deproteinized bovine bone material (DBBM) covered with an absorbable membrane; Group C: DBBM covered with the periosteum. The structural parameters for trabecular architecture and vertical bone regeneration were evaluated. Histological and histomorphometric evaluation were carried out to observe new bone formation and mineralization in the graft site. Immunohistochemical analysis was performed to identify the expression of osteopontin (OPN) and osteocalcin (OCN) at postoperative 3 months. Group C achieved greater vertical alveolar bone gain than that of group A and group B. The periosteum-covered group showed significantly greater new bone formation and accelerated mineralization. The greater immunolabeling for OPN and OCN was observed in group C than in group A. Periosteal coverage has explicit advantages over collagen membranes for the quality and quantity of new bone regeneration in dehiscence defects repairing.

The periosteum: a simple tissue with many faces, with special reference to the antler-lineage periostea

Periosteum is a thin membrane covering bone surfaces and consists of two layers: outer fibrous layer and inner cambium layer. Simple appearance of periosteum has belied its own complexity as a composite structure for physical bone protection, mechano-sensor for sensing mechanical loading, reservoir of biochemical molecules for initiating cascade signaling, niche of osteogenic cells for bone formation and repair, and "umbilical cord" for nourishing bone tissue. Periosteum-derived cells (PDCs) have stem cell attributes: self-renewal (no signs of senescence until 80 population doublings) and multipotency (differentiate into fibroblasts, osteoblasts, chondrocytes, adipocytes and skeletal myocytes). In this review, we summarized the currently available knowledge about periosteum and with special references to antler-lineage periostea, and demonstrated that although periosteum is a type of simple tissue in appearance, with multiple faces in functions; antler-lineage periostea add another dimension to the properties of somatic periostea: capable of initiation of ectopic organ formation upon transplantation and full mammalian organ regeneration when interacted with the covering skin. Very recently, we have translated this finding into other mammals, i.e. successfully induced partial regeneration of the amputated rat legs. We believe further refinement along this line would greatly benefit human health.

Bone Marrow Microvasculature

The skeleton is highly vascularized due to the various roles blood vessels play in the homeostasis of bone and marrow. For example, blood vessels provide nutrients, remove metabolic by-products, deliver systemic hormones, and circulate precursor cells to bone and marrow. In addition to these roles, bone blood vessels participate in a variety of other functions. This article provides an overview of the afferent, exchange and efferent vessels in bone and marrow and presents the morphological layout of these blood vessels regarding blood flow dynamics. In addition, this article discusses how bone blood vessels participate in bone development, maintenance, and repair. Further, mechanical loading-induced bone adaptation is presented regarding interstitial fluid flow and pressure, as regulated by the vascular system. The role of the sympathetic nervous system is discussed in relation to blood vessels and bone. Finally, vascular participation in bone accrual with intermittent parathyroid hormone administration, a medication prescribed to combat age-related bone loss, is described and age- and disease-related impairments in blood vessels are discussed in relation to bone and marrow dysfunction. © 2020 American Physiological Society. Compr Physiol 10:1009-1046, 2020.

The response of host blood vessels to graded distribution of macro-pores size in the process of ectopic osteogenesis

Angiogenesis is of great importance to bone regeneration, but it remains a significant challenge to induce sufficient angiogenesis and osteogenesis within bone grafts for large bone defect healing. The aim of this study is to investigate the effects of hydroxyapatite (HA) scaffold via a novel graded pore distribution approach on vascularization and osteoinduction. Two types of graded porous scaffolds were fabricated by sugar templates-leaching techniques: (1) one with large pores of 1100-1250 μm in the center and small pores of 500-650 μm at the periphery (HALS); (2) the other with small pores of 500-650 μm in the center and large pores of 1100-1250 μm at the periphery (HASL). In vivo data showed different pore size distribution had a remarkable impact on blood vessel formation during bone formation, which led to distinct localization of new bone within the defects. After one month of implantation, the diameters of the blood vessels infiltrated on the periphery of HASL were substantially larger than those in the center though the host blood vessels were successful in infiltrating throughout the whole scaffold. In contrast, vascularization within HALS appeared to be poor with very few blood vessels formed in the center, indicating heterogeneous vascularization in the scaffolds. After 3 months of implantation, we found that HASL induced more homogeneous bone formation in the whole bone graft but new bone was only found at the periphery of HALS. This study suggests that the pores size distribution in graded scaffolds cannot only affected early stage vascularization, but also influence late stage bone formation and remodeling. The architecture of larger pores at the periphery of graded scaffold may be capable of enhancing angiogenesis and osteogenesis during large size bone defect healing.

The role of pericytes in brain disorders: from the periphery to the brain

It is becoming increasingly apparent that disorders of the brain microvasculature contribute to many neurological disorders. In recent years it has become clear that a major player in these events is the capillary pericyte which, in the brain, is now known to control the blood-brain barrier, regulate blood flow, influence immune cell entry and be crucial for angiogenesis. In this review we consider the under-explored possibility that peripheral diseases which affect the microvasculature, such as hypertension, kidney disease and diabetes, produce central nervous system (CNS) dysfunction by mechanisms affecting capillary pericytes within the CNS. We highlight how cellular messengers produced peripherally can act via signalling pathways within CNS pericytes to reshape blood vessels, restrict blood flow or compromise blood-brain barrier function, thus causing neuronal dysfunction. Increased understanding of how renin-angiotensin, Rho-kinase and PDGFRβ signalling affect CNS pericytes may suggest novel therapeutic approaches to reducing the CNS effects of peripheral disorders.

Gingival crevicular fluid and plasma oxidative stress markers and TGM-2 levels in chronic periodontitis

OBJECTIVE

This study was aimed to evaluate the gingival crevicular fluid (GCF) and plasma transglutaminase-2 (TGM-2), total antioxidant capacity (TAC), total oxidant status (TOS), ferric reducing antioxidant power (FRAP) and thiobarbituric acid reactive substances (TBARS) in patients with chronic periodontal disease.

MATERIALS AND METHODS

Twenty patients with chronic periodontitis (CP), 20 patients with gingivitis and 20 healthy subjects were enrolled in the study. Clinical periodontal parameters including probing depth, clinical attachment level, plaque index and papillary bleeding index were recorded. GCF and plasma levels of TGM-2, TAC, TOS, TBARS and FRAP were analyzed.

RESULTS

GCF TGM-2 was significantly lower in CP group than in gingivitis patients (P=0.006). GCF FRAP in CP and gingivitis groups was significantly lower than in healthy subjects (P<0.001). Plasma FRAP level was lower in gingivitis group when compared to healthy subjects (P=0.003). There was no significant difference in GCF and plasma TAC, TOS, TBARS and plasma TGM-2 levels among the study groups (P>0.05). GCF TGM-2 level was positively correlated with GCF TAC and negatively correlated with CAL.

CONCLUSIONS

Decreased FRAP in GCF and plasma indicating lower antioxidant status of CP patients might suggest the role of oxidative stress in periodontitis. GCF TGM-2 data might suggest that TGM2 is associated with stabilization of the extracellular matrix and wound healing in periodontium rather than gingival inflammation.

Toll-like receptors as a key regulator of mesenchymal stem cell function: An up-to-date review

Understanding the role of toll-like receptors (TLRs) in the immunomodulation potential, differentiation, migration, and survival of mesenchymal stem cells (MSCs) is absolutely vital to fully exploiting their MSC-based therapeutic potential. Furthermore, through recognition of exogenous or endogenous ligands produced upon injury, TLRs have been linked to allograft rejection and maintenance of chronic inflammatory diseases, including Crohn's disease, rheumatoid arthritis. Characterizing the effect of TLRs in biological control of MSCs fate and function could improve our knowledge about the MSC-based cell therapy and immunotherapy. In this paper, we outline the impacts of TLR activation and mechanisms on MSCs immunomodulatory functions, differentiation, migration, and survivability. Moreover, we indicate that the expression patterns of TLRs in MSCs from different sources.

Ectopic osteogenesis and angiogenesis regulated by porous architecture of hydroxyapatite scaffolds with similar interconnecting structure in vivo

The macro-pore sizes of porous scaffold play a key role for regulating ectopic osteogenesis and angiogenesis but many researches ignored the influence of interconnection between macro-pores with different sizes. In order to accurately reveal the relationship between ectopic osteogenesis and macro-pore sizes in dorsal muscle and abdominal cavities of dogs, hydroxyapatite (HA) scaffolds with three different macro-pore sizes of 500–650, 750–900 and 1100–1250 µm were prepared via sugar spheres-leaching process, which also had similar interconnecting structure determined by keeping the d/s ratio of interconnecting window diameter to macro-pore size constant. The permeability test showed that the seepage flow of fluid through the porous scaffolds increased with the increase of macro-pore sizes. The cell growth in three scaffolds was not affected by the macro-pore sizes. The in vivo ectopic implantation results indicated that the macro-pore sizes of HA scaffolds with the similar interconnecting structure have impact not only the speed of osteogenesis and angiogenesis but also the space distribution of newly formed bone. The scaffold with macro-pore sizes of 750–900 µm exhibited much faster angiogenesis and osteogenesis, and much more uniformly distribution of new bone than those with other macro-pore sizes. This work illustrates the importance of a suitable macro-pore sizes in HA scaffolds with the similar interconnecting structure which provides the environment for ectopic osteogenesis and angiogenesis.

Stem cells sources for intervertebral disc regeneration

Intervertebral disc regeneration field is rapidly growing since disc disorders represent a major health problem in industrialized countries with very few possible treatments. Indeed, current available therapies are symptomatic, and surgical procedures consist in disc removal and spinal fusion, which is not immune to regardable concerns about possible comorbidities, cost-effectiveness, secondary risks and long-lasting outcomes. This review paper aims to share recent advances in stem cell therapy for the treatment of intervertebral disc degeneration. In literature the potential use of different adult stem cells for intervertebral disc regeneration has already been reported. Bone marrow mesenchymal stromal/stem cells, adipose tissue derived stem cells, synovial stem cells, muscle-derived stem cells, olfactory neural stem cells, induced pluripotent stem cells, hematopoietic stem cells, disc stem cells, and embryonic stem cells have been studied for this purpose either in vitro or in vivo. Moreover, several engineered carriers (e.g., hydrogels), characterized by full biocompatibility and prompt biodegradation, have been designed and combined with different stem cell types in order to optimize the local and controlled delivery of cellular substrates in situ. The paper overviews the literature discussing the current status of our knowledge of the different stem cells types used as a cell-based therapy for disc regeneration.

[The Use of Stem Cells in the Treatment of Intervertebral Disc Degeneration]

The paper presents a review of current data on the use of stem cells in the treatment of intervertebral disc degeneration. Acute spinal pain is often a consequence of the pathology affecting the intervertebral disc. Many applied therapeutic techniques do not provide effective results as expected because most of them address symptoms, but do not treat the underlying disease. We have outlined current findings on the molecular mechanisms of intervertebral disc degeneration, analyzed international experimental studies demonstrating the feasibility of a stem cell therapy for intervertebral disc degeneration. The conducted studies reported on the clinical application of mesenchymal stem cells or stem cells derived from adipose, synovium, and bone marrow tissue. The most pressing and undetermined issues that require further experimental and clinical studies are indicated and defined in the article.

Pericytes: multitasking cells in the regeneration of injured, diseased, and aged skeletal muscle

Pericytes are perivascular cells that envelop and make intimate connections with adjacent capillary endothelial cells. Recent studies show that they may have a profound impact in skeletal muscle regeneration, innervation, vessel formation, fibrosis, fat accumulation, and ectopic bone formation throughout life. In this review, we summarize and evaluate recent advances in our understanding of pericytes' influence on adult skeletal muscle pathophysiology. We also discuss how further elucidating their biology may offer new approaches to the treatment of conditions characterized by muscle wasting.

Differential expression of transglutaminase genes in patients with chronic periodontitis

OBJECTIVE

Gingival epithelium plays a key role in the protection of oral tissues from microbial challenge, especially during the periodontal disease. This study was aimed to evaluate levels of mRNA transcripts of different forms of transglutaminase in the human gingival tissues from patients with chronic periodontitis and relative controls.

SUBJECTS AND METHODS

This study included 22 patients with chronic periodontitis (CP) and 22 healthy controls. For each patient, the values of probing depth (PD), clinical attachment level (CAL), and bleeding on probing (BOP) were recorded. Gene expression of transglutaminase 1, transglutaminase 2, transglutaminase 3, and metalloprotease 2 was evaluated by real-time PCR, while that of Factor XIIIA and metalloprotease 9 by RT-PCR.

RESULTS

The values of all the clinical parameters were significantly higher in the CP group than in the healthy control group (P < 0.05). In the CP group, the mRNA expression of transglutaminase 1 and transglutaminase 3 was significantly decreased in comparison with healthy control group. A slight nonsignificant changes of transglutaminase 2 gene expression were observed in samples from CP patients in comparison with controls.

CONCLUSIONS

These observations suggest that transglutaminase gene expression may be modified in response to chronic injury in the damaged gingival and emphasizes the key role of these enzymes in gingival remodelling/healing and adaptive processes.

Impaired coronary microvascular and left ventricular diastolic function in patients with inflammatory bowel disease

BACKGROUND AND AIM

Increased incidence of coronary vascular events in patients with inflammatory bowel disease (IBD) is known. However, the association between coronary microvascular function and IBD has not been fully defined. We aimed to investigate whether coronary flow reserve (CFR) and left ventricular diastolic function were impaired in IBD patients.

METHODS

Seventy-two patients with IBD (36 patients with ulcerative colitis [UC] and 36 Crohn's disease [CD]) were registered. Each subject was evaluated after a minimum 15-day attack-free period. For the control group, 36 age- and sex-matched healthy volunteers were included into the study. IBD clinical disease activity in UC was assessed by the Truelove-Witts Index (TWAS) and in CD by the Crohn's Disease Activity Index (CDAI). In each subject, CFR was measured through transthoracic Doppler echocardiography.

RESULTS

Compared to the controls, the CD group and UC group had significantly higher high-sensitivity C-reactive protein (hs-CRP) and erythrocyte sedimentation rate. Baseline diastolic peak flow velocity (DPFV) of the left anterior descending artery (LAD) was significantly higher in the IBD group (24.1±3.9 vs. 22. 4±2.9, p<0.05), and hyperemic DPFV (56.1±12.5 vs. 70.6±15.3, p<0.05) and CFR (2.34±0.44 vs. 3.14±0.54, p<0.05) were significantly lower in the IBD group than in the control group. In stepwise linear regression analysis, hs-CRP and lateral Em/Am ratio were independently correlated with CFR.

CONCLUSION

CFR, reflecting coronary microvascular function, is impaired in patients with IBD. CFR and left ventricular diastolic function parameters are well correlated with hs-CRP.

Periosteum: biology and applications in craniofacial bone regeneration

The bone-regenerative potentials of the periosteum have been explored as early as the 17th century. Over the past few years, however, much has been discovered in terms of the molecular and cellular mechanisms that control the periosteal contribution to bone regeneration. Lineage tracing analyses and knock-in transgenic mice have helped define the relative contributions of the periosteum and endosteum to bone regeneration. Additional studies have shed light on the critical roles that BMP, FGF, Hedgehog, Notch, PDGF, Wnt, and inflammation signaling have or may have in periosteal-mediated bone regeneration, fostering the path to novel approaches in bone-regenerative therapy. Thus, by examining the role that each pathway has in periosteal-mediated bone regeneration, in this review we analyze the status of the current research on the regenerative potential of the periosteum. The provided analysis aims to inform both clinician-scientists who may have interest in the current studies about the biology of the periosteum as well as dental surgeons who may find this review useful to perform periosteal-harnessing bone-regenerative procedures.

Inhibition of cellular senescence by developmentally regulated FGF receptors in mesenchymal stem cells

Bone-derived mesenchymal stem cells (MSCs) are important cells for use in cell therapy, tissue engineering, and regenerative medicine, but also to study bone development, homeostasis, and repair. However, little is known about their developmental ontology and in vivo identity. Because fibroblast growth factors (FGFs) play key roles in bone development and their receptors are developmentally regulated in bones, we hypothesized that MSCs should express FGF receptors (FGFRs), reflecting their developmental origin and potential. We show here that FGFR1/2 are expressed by rare mesenchymal progenitors in putative MSC niches in vivo, including the perichondrium, periosteum, and trabecular marrow. FGFR1⁺ cells often appeared as pericytes. These cells display a characteristic MSC phenotype in vitro when expanded with FGF-2, which appears to maintain MSC stemness by inhibiting cellular senescence through a PI3K/AKT-MDM2 pathway and by promoting proliferation. FGFRs may therefore be involved in MSC self-renewal. In summary, FGFR1/2 are developmentally regulated markers of MSCs in vivo and in vitro and are important in maintaining MSC stemness.

Rapid vascularization of starch-poly(caprolactone) in vivo by outgrowth endothelial cells in co-culture with primary osteoblasts

The successful integration of in vitro-generated tissues is dependent on adequate vascularization in vivo. Human outgrowth endothelial cells (OECs) isolated from the mononuclear cell fraction of peripheral blood represent a potent population of circulating endothelial progenitors that could provide a cell source for rapid anastomosis and scaffold vascularization. Our previous work with these cells in co-culture with primary human osteoblasts has demonstrated their potential to form perfused vascular structures within a starch-poly(caprolactone) biomaterial in vivo. In the present study, we demonstrate the ability of OECs to form perfused vascular structures as early as 48 h following subcutaneous implantation of the biomaterial in vivo. The number of OEC-derived vessels increased throughout the study, an effect that was independent of the OEC donor. This finding of rapid and thorough OEC-mediated scaffold vascularization demonstrates the great potential for OEC-based strategies to promote vascularization in tissue engineering. OECs have the potential to contribute to host-derived scaffold vascularization, and formed vascular structures at a similar density as those arising from the host. Additionally, immunohistochemical evidence demonstrated the close interaction between OECs and the co-cultured osteoblasts. In addition to the known paracrine activity osteoblasts have in modulating angiogenesis of co-cultured OECs, we demonstrate the potential of osteoblasts to provide additional structural support for OEC-derived vessels, perhaps acting in a pericyte-like role.

Potential of chemically modified hydrophilic surface characteristics to support tissue integration of titanium dental implants

In the past, several modifications of specific surface properties such as topography, structure, chemistry, surface charge, and wettability have been investigated to predictably improve the osseointegration of titanium implants. The aim of the present review was to evaluate, based on the currently available evidence, the impact of hydrophilic surface modifications of titanium for dental implants. A surface treatment was performed to produce hydroxylated/hydrated titanium surfaces with identical microstructure to either acid-etched, or sand-blasted, large grit and acid-etched substrates, but with hydrophilic character. Preliminary in vitro studies have indicated that the specific properties noted for hydrophilic titanium surfaces have a significant influence on cell differentiation and growth factor production. Animal experiments have pointed out that hydrophilic surfaces improve early stages of soft tissue and hard tissue integration of either nonsubmerged or submerged titanium implants. This data was also corroborated by the results from preliminary clinical studies. In conclusion, the present review has pointed to a potential of hydrophilic surface modifications to support tissue integration of titanium dental implants.

MSC frequency correlates with blood vessel density in equine adipose tissue

Mesenchymal stem cells (MSCs) are multipotent cells that have the capacity to develop into different mature mesenchymal cell types. They were originally isolated from bone marrow, but MSC-like cells have also been isolated from other tissues. The common feature of all of these tissues is that they all house blood vessels. It is, thus, possible that MSCs are associated with perivascular locations. The objective of this work was to test the hypothesis that MSCs are associated with blood vessels by verifying if MSC frequency positively correlates with blood vessel density. To this end, samples from highly and poorly vascularized adipose tissue sites of two equine donors were collected and processed for histology and cell isolation. MSC frequency in these samples was estimated by means of CFU-F assays, which were performed under MSC conditions. Culture-adherent cells from equine adipose tissue and bone marrow were culture expanded, tested for differentiation into mesenchymal cell types in vitro, and implanted in vivo in porous ceramic vehicles to assess their osteogenic capacity, using human MSCs and brain pericytes as controls. The differentiation assays showed a difference between adipose tissue-derived cells as compared to equine bone marrow MSCs. While differences in CFU-F frequencies between both donors were evident, the CFU-F numbers correlated directly with blood vessel densities (r(2) = 0.86). We consider these preliminary data as further evidence linking MSCs to blood vessels.

Bone regeneration in dehiscence-type defects at non-submerged and submerged chemically modified (SLActive) and conventional SLA titanium implants: an immunohistochemical study in dogs

OBJECTIVES

The aim of the present study was to evaluate bone regeneration in dehiscence-type defects at non-submerged and submerged titanium implants with chemically modified (mod) and conventional sandblasted/acid-etched (SLA) surfaces.

MATERIAL AND METHODS

Standardized buccal dehiscence defects were surgically created following implant site preparation in both the upper and lower jaws of 12 beagle dogs. Both types of implants were randomly assigned to either a non-submerged or a submerged healing procedure. After 1, 2, 4, and 8 weeks, dissected blocks were processed for histomorphometrical [e.g. new bone height (NBH), per cent linear fill (PLF), percentage of bone to implant contact (BIC-D), area of new bone fill (BF)] and immunohistochemical analysis.

RESULTS

At 8 weeks, non-submerged and submerged SLA implants revealed significantly lower mean NBH (1.1+/-0.8-1.9+/-1.2 mm), PLF (27.7+/-20.3-46.0+/-28.5%), BIC-D (26.8+/-10.4-46.2+/-16.2%), and BF (1.3+/-0.9-3.4+/-2.8 mm(2)) values than respective modSLA implants [NBH (2.6+/-0.8-4.3+/-0.1 mm), PLF (64.2+/-19.4-107.2+/-4.7%), BIC-D (67.5+/-18.8-82.1+/-14.8%), BF (2.9+/-1.0-6.7+/-1.1 mm(2))]. Within modSLA groups, significantly highest BF values were observed at submerged implants.

CONCLUSION

It was concluded that (i) modSLA titanium surfaces promoted bone regeneration in acute-type buccal dehiscence defects and (ii) a submerged healing procedure improved the outcome of healing additionally.

Effect of thrombin peptide 508 (TP508) on bone healing during distraction osteogenesis in rabbit tibia

Thrombin-related peptide 508 (TP508) accelerates bone regeneration during distraction osteogenesis (DO). We have examined the effect of TP508 on bone regeneration during DO by immunolocalization of Runx2 protein, a marker of osteoblast differentiation, and of osteopontin (OPN) and bone sialoprotein (BSP), two late markers of the osteoblast lineage. Distraction was performed in tibiae of rabbits over a period of 6 days. TP508 (30 or 300 μg) or vehicle was injected into the distraction gap at the beginning and end of the distraction period. Two weeks after active distraction, tissue samples were harvested and processed for immunohistochemical analysis. We also tested the in vitro effect of TP508 on Runx2 mRNA expression in osteoblast-like (MC3T3-E1) cells by polymerase chain reaction analysis. Runx2 and OPN protein were observed in preosteoblasts, osteoblasts, osteocytes of newly formed bone, blood vessel cells and many fibroblast-like cells of the soft connective tissue. Immunostaining for BSP was more restricted to osteoblasts and osteocytes. Significantly more Runx2- and OPN-expressing cells were seen in the group treated with 300 μg TP508 than in the control group injected with saline or with 30 μg TP508. However, TP508 failed to increase Runx2 mRNA levels significantly in MC3T3-E1 cells after 2–3 days of exposure. Our data suggest that TP508 enhances bone regeneration during DO by increasing the proportion of cells of the osteoblastic lineage. Clinically, TP508 may shorten the healing time during DO; this might be of benefit when bone regeneration is slow.

Histological and immunohistochemical analysis of initial and early osseous integration at chemically modified and conventional SLA titanium implants: preliminary results of a pilot study in dogs

OBJECTIVES

The aim of the present pilot study was to investigate initial and early tissue reactions to modified (mod) and conventional sand-blasted, large grit and acid-etched (SLA) titanium implants.

MATERIAL AND METHODS

Implantation of modSLA and SLA implants was performed bilaterally in both the mandible and maxilla of dogs. The animals were sacrificed after a healing period of 1, 4, 7 and 14 days, respectively. Peri-implant tissue reactions were assessed in non-decalcified tissue sections using conventional histology (Toluidine blue-TB and Masson Goldner Trichrome stain-MG) and immunohistochemistry using monoclonal antibodies to transglutaminase II (TG) (angiogenesis) and osteocalcin (OC). Bone density (BD) and bone to implant contact (BIC) were assessed histomorphometrically.

RESULTS

Day 1 revealed an early TG antigen reactivity in the provisional fibrin matrix adjacent to both implant surfaces. Day 4 was characterized by the formation of a collagen-rich connective tissue (MG), which revealed the first signs of OC synthesis adjacent to modSLA surfaces. Immunohistochemical staining for TG revealed a direct correlation between angiogenesis and new bone formation, which was clearly identifiable after 7 days by means of increasing BD, BIC and OC values. After 14 days, modSLA surfaces seemed to be surrounded by a firmly attached mature, parallel-fibered woven bone.

CONCLUSIONS

Within the limits of the present study, it might be concluded that the combination of immunohistochemical and conventional histological stainings in non-decalcified tissue sections is a valuable technique to evaluate the initial and early stages of wound healing around endosseous titanium implants.

Chemisch modifizierte, ultra-hydrophile Titanimplantatoberflächen

Recently, a chemically modified ultra-hydrophilic sand-blasted, large grit and acid-etched (modSLA) titanium surface has been introduced in order to enhance bone apposition. Indeed, preliminary preclinical and clinical data have indicated that modSLA implants may enhance bone apposition during early stages of wound healing. These positive effects on bone regeneration might be probably mainly due to the hydrophilic surface properties noted for modSLA which ensured a stabilization of the blood clot. The aim of the present review article is to evaluate, based on the currently available evidence, the potential impact of modSLA surfaces for implant dentistry.

Bone regeneration in dehiscence-type defects at chemically modified (SLActive�) and conventional SLA titanium implants: a pilot study in dogs

OBJECTIVES

The aim of the present study was to evaluate bone regeneration in dehiscence-type defects at titanium implants with chemically modified (mod) and conventional sand-blasted/acid-etched (SLA) surfaces.

MATERIAL AND METHODS

Standardized buccal dehiscence defects (height: 3 mm, width: 3 mm) were surgically created following implant site preparation in both the upper and lower jaws of four beagle dogs. modSLA and SLA implants were inserted bilaterally according to a split-mouth design. The animals were sacrificed after 2 and 12 weeks (n=2 animals each). Dissected blocks were processed for histomorphometrical analysis: defect length, new bone height (NBH), percent linear fill (PLF), percent of bone-to-implant contact (BIC-D) and area of new bone fill (BF).

RESULTS

Wound healing at SLA implants was predominantly characterized by the formation of a dense connective tissue at 2 and 12 weeks, without significant increases in mean NBH, PLF, BIC-D or BF values. In contrast, modSLA implants exhibited a complete defect fill at 12 weeks following implant placement. In particular, histomorphometrical analysis revealed the following mean values at 12 weeks: NBH (3.2+/-0.3 mm), PLF (98%), BIC-D (82%) and BF (2.3+/-0.4 mm(2)).

CONCLUSION

Within the limits of the present study, it was concluded that modSLA titanium surfaces may promote bone regeneration in acute-type buccal dehiscence defects at submerged implants.

Angiogenesis pattern of native and cross-linked collagen membranes: an immunohistochemical study in the rat

The aim of the present study was to immunohistochemically evaluate angiogenesis pattern of native and cross-linked collagen membranes after subcutaneous implantation in rats. Five commercially available and three experimental membranes (VN) were included: (1) BioGide (BG), (2) BioMend (BM), (3) BioMend Extend (BME), (4) Ossix (OS), (5) TutoDent (TD), and (6-8) VN(1-3). Specimens were randomly allocated in unconnected subcutaneous pouches (n=4) separated surgically on the back of 40 wistar rats, which were divided into five groups (2, 4, 8, 16, and 24 weeks), including eight animals each. Pattern of angiogenesis was labelled using primary mouse monoclonal antibody to transglutaminase II. For each membrane, the period of time, needed for a complete and homogeneous transmembraneous vascularization, was assessed immunohistomorhometrically. Differences between the membranes were found regarding the initial pattern of transmembraneous angiogenesis, as evaluated 2 weeks following implantation. Mean cross- and longitudinal-sectional area of blood vessels (%) was highest for VN(3) (5.27+/-2.73), followed by BG (2.45+/-0.88), VN(1) (2.07+/-0.29), VN(2) (1.91+/-0.55), TD (1.44+/-0.53), BME (0.35+/-0.29) and BM (0.25+/-0.4). In contrast to BG and VN(1-3), BM, BME and TD exhibited a homogeneous transmembraneous formation of blood vessels merely 4-8 weeks following implantation. OS, however, exhibited no signs of angiogenesis throughout the whole study period. Within the limits of the present study, it may be concluded that pattern of transmembraneous angiogenesis markedly differs among the membranes investigated.

Formation of new bone during vertical distraction osteogenesis of the human mandible is related to the presence of blood vessels

We examined the effect of distraction rate on blood vessel growth in intramembraneous ossification after vertical distraction osteogenesis in the human mandible. Six edentulous patients (aged 60+/-9 years) with a severely atrophic mandible underwent bone augmentation with distraction osteogenesis. Two distraction rates (0.5 and 1 mm/day) were compared and for each group three patients were analyzed. Vascular histomorphometry was carried out in two different areas in the distraction gap: (1) in the first and (2) in the second 1 mm area from the osteotomy line, representing the oldest and younger new-bone area, respectively. Correlation analysis was performed between blood vessel parameters and the amount of new bone formed during distraction. Histological analysis demonstrated the presence of blood vessels throughout the soft connective tissue in the distraction gap. The volume density of blood vessels between the two investigated areas was significantly lower in the 1 mm/day groups, suggesting a delay in angiogenesis in this group of patients. A positive correlation between blood vessel volume and bone volume density was found in the younger new-bone area but not in the oldest new-bone area. This correlation was due to a higher number of blood vessels rather than to a larger size of the blood vessels. Our data suggest that the lower blood vessel density found in the patients with 1 mm/day distraction rate may be related to disruption of angiogenesis in the soft connective tissue of the gap or to a less optimal mechanical stimulation of cells involved in angiogenesis. This probably results in the slower rate of osteogenesis seen at the 1 mm/day distraction rate compared with the 0.5 mm/day distraction rate. The data support the concept that a positive relationship exists between the density of blood vessels and the formation of bone. For distraction of the human mandible in elderly patients, a distraction rate of 0.5 mm/day seems beneficial.

CNS microvascular pericytes exhibit multipotential stem cell activity

It has been suggested that a vascular-like cell has multipotent regenerative and mesenchymal lineage relationships. The identity of this stem/progenitor cell has remained elusive. We report here that adult central nervous system (CNS) capillaries contain a distinct population of microvascular cells, the pericyte that are nestin/NG2 positive and in response to basic fibroblast growth factor (bFGF) differentiate into cells of neural lineage. In their microvascular location, pericytes express nestin and NG2 proteoglycan. In serum containing media primary (0 to 7 day old) CNS pericytes are nestin positive, NG2 positive, alpha smooth muscle actin (alphaSMA) positive, and do not bind the endothelial cell specific griffonia symplicifolia agglutinin (GSA). In serum containing media, pericytes do not undergo neurogenesis but are induced to express alphaSMA. In bFGF containing media without serum, CNS pericytes form small clusters and multicellular spheres. Differentiated spheres expressed neuronal and glial cell markers. After disruption and serial dilution, differentiated spheres were capable of self-renewal. When differentiated spheres were disrupted and cultured in the presence of serum, multiple adherent cell populations were identified by dual and triple immunocytochemistry. Cells expressing markers characteristic of pericytes, neurons, and glial cells were generated. Many of the cells exhibited dual expression of differentiation markers. With prolonged culture fully differentiated cells of neural lineage were present. Results indicate that adult CNS microvascular pericytes have neural stem cell capability.

Modern biologics used in orthopaedic surgery

PURPOSE OF REVIEW

In this review we summarize some of the most recent research in the area of local bone regeneration. These innovations may be relevant in the orthopaedic treatment of patients with rheumatoid arthritis, or other inflammatory arthridities, as such patients often present with inadequate bone stock.

RECENT FINDINGS

Bone grafting remains the standard treatment for bone deficiency. Several new approaches, such as the use of concentrated blood products or osteoprogenitor cells in conjunction with grafts, have been developed but remain to be tested clinically. Experimental studies have elucidated important aspects of the biology of bone graft remodeling and osteoprogenitor cell differentiation. Materials that can serve as graft alternatives continue to be developed. Positive experimental findings have resulted from combinations of such materials with osteoprogenitor cells or osteoinductive factors such as bone morphogenetic proteins.

SUMMARY

While few studies to date have examined the specific use of these new strategies in the setting of rheumatoid arthritis, many hold promise for patients with rheumatoid arthritis and other inflammatory and metabolic conditions that affect bone quality and quantity.

Rapid isolation, expansion, and differentiation of osteoprogenitors from full-term umbilical cord blood

There is an urgent clinical requirement for appropriate bone substitutes that can be used for the repair and regeneration of diseased or damaged skeletal tissues. Cell-sourcing limitations in particular have affected progress, largely because of the shortage of accessible tissues capable of yielding sufficient numbers of viable osteoprogenitor cells. Previous work has suggested that umbilical cord blood (UCB) contains circulating progenitor cells (mesenchymal stem cells) capable of osteogenic differentiation, although a comparable number of reports refute this claim. From a screen of more than 20 different culture conditions, we have identified an optimal, simple, and reliable technique to generate, from full-term human UCB, stromal cells with the ability to undergo rapid osteogenic differentiation. By comparing different sorting and culture strategies, we demonstrated that early exposure of mononuclear UCB cells to medium conditioned by osteoblastic cells in the presence of osteogenic supplements and human plasma, markedly increased the frequency of stromal cell growth, the rate of osteogenic differentiation, and their attachment to and spreading on calcium phosphate scaffolds. These findings suggest that full-term UCB may act as an appropriate source of osteoprogenitor cells, which will impact significantly on the development of autologous tissue- engineered bone constructs.

Isolated primary osteocytes express functional gap junctions in vitro

The osteocyte is the most abundant cell type in bone and is embedded in mineralized bone matrix. Osteocytes are still poorly characterized because of their location and the lack of primary osteocyte isolation methods. Data on the cell biology of osteocytes is especially limited. We have isolated primary osteocytes from rat cortical bone by applying repeated enzymatic digestion and decalcification. The isolated osteocytes expressed typical osteocytic morphology with cell-cell contacts via long protrusions after a 1-day culture. These cells were negative or faintly positive for alkaline phosphatase but expressed high levels of osteocalcin, PHEX (phosphate-regulating gene with homology to endopeptidases on the X chromosome), and DMP1 (dentin matrix protein 1). These cells also revealed patchy membrane staining for connexin43. For studying the function of gap junctions in isolated osteocytes, we microinjected rhodamine-labeled dextran (MW: 10,000) and Lucifer yellow (MW: 457) and found that Lucifer yellow was rapidly transmitted to several surrounding cells, whereas dextran remained in the injected cells. Heptanol and 18alpha-glycyrrhetinic acid inhibited the transfer of Lucifer yellow. This clearly showed the existence of functional gap junctions in cultured osteocytes. Enveloped viruses, such as vesicular stomatitis virus and influenza A virus, were used for studying cell polarity. We were unable to demonstrate plasma membrane polarization with enveloped viruses in isolated primary osteocytes in culture. Our results suggest that osteocytes do not possess apical and basolateral plasma membrane domains as do osteoblasts, which are their precursors.

Efficacy of rhBMP-2 during distraction osteogenesis

BACKGROUND

Osteoinductive ability of bone morphogenetic protein-2 (BMP-2) has been studied in recent reports. In this study, we evaluated the efficacy of BMP-2 during distraction osteogenesis.

METHODS

A group of 24 Japanese white rabbits were divided into four groups randomly and underwent lengthening of the right femur. Distraction was performed for 2 weeks (1.0 mm/day). Group A began distraction following a 7-day waiting period after surgery. For all other groups (B-D), distraction was started immediately after surgery. Groups A and B did not undergo any surgical intervention at the osteotomy site, as a control. The delivery system for rhBMP-2 used a polymer-coated gelatin sponge (PGS). Buffer/PGS was implanted into the osteotomy site in group C, and group D received rhBMP-2/PGS. Callus was evaluated radiographically at 1, 2, 4, and 6 weeks after the surgery, and all rabbits were killed at 6 weeks. One rabbit from each group was examined histologically; the remaining five rabbits underwent biomechanical testing.

RESULTS

A significant increase in callus formation was evident in group D compared with that in other groups. In group D, regenerative changes were evident during the earlier phase. Formation of bone cortex and bone marrow cavity was almost complete in group D, and the cortex was thicker than that in the other groups. Torsional strength values (10(-2) Nm) of each group were as follows: A, 118.7 +/- 52.4; B, 160.0 +/- 40.7; C, 106.8 +/- 8.1; D, 266.1 +/- 93.1. Stiffness values (10(-3) Nm/degree) were as follows: A, 390.2 +/- 137.2; B, 391.8 +/- 158.4; C, 183.1 +/- 78.5; D, 624.4 +/- 214.2. Group D exhibited the highest values for both torsional strength and stiffness.

CONCLUSIONS

Acceleration of the regenerative changes during the early phase occurred in the BMP-2-treated group. The efficacy of BMP-2 in distraction osteogenesis was recognized radiographically, histologically, and by biomechanical testing (torsional strength and stiffness).

Effect of vascularity on canine distracted tibial callus consolidation

In the consolidation period of distraction osteogenesis, mineralization occurs before corticalization. We hypothesized that the increased rate of bone mineral density correlates to the density of vascularity in the callus. We unilaterally lengthened the tibia in eight adult beagles. After a waiting period of 7 days, tibiae were lengthened for 30 days. After a consolidation period of an additional 60 days, all animals were euthanized. Just before euthanasia, blood vessels were perfused with 50% w/v barium sulfate solution, and soft radiographs of the distracted callus and the control tibiae were taken. Bone mineral density of the regenerated bones was measured preoperatively by quantitative computed tomography on Days 37, 68, and 98. Increases of the percent bone mineral density (from Day 37 to Day 98 and from Day 68 to Day 98) correlated with the blood vessel volume density ratios on Day 98. Our results suggest that preservation of the higher density of blood vessels in the consolidation period could lead to the better mineralization of the distracted callus.

Biology of developmental and regenerative skeletogenesis

Embryonic skeletal development involves the recruitment, commitment, differentiation, and maturation of mesenchymal cells into those in the skeletal tissue lineage, specifically cartilage and bone along the intramembranous and endochondral ossification pathways. The exquisite control of skeletal development is regulated at the level of gene transcription, cellular signaling, cell-cell and cell-matrix interactions, as well as systemic modulation. Mediators include transcription factors, growth factors, cytokines, metabolites, hormones, and environmentally derived influences. Understanding the mechanisms underlying developmental skeletogenesis is crucial to harnessing the inherent regenerative potential of skeletal tissues for wound healing and repair, as well as for functional skeletal tissue engineering. In this review, a number of key issues are discussed concerning the current and future challenges of the scientific investigation of developmental skeletogenesis in the embryo, specifically limb cartilage development, and how these challenges relate to regenerative or reparative skeletogenesis in the adult. Specifically, a more complete understanding the biology of skeletogenic progenitor cells and the cellular and molecular mechanisms governing tissue patterning and morphogenesis should greatly facilitate the development of regenerative approaches to cartilage repair.

Physiologic weight-bearing increases new vessel formation during distraction osteogenesis: a micro-tomographic imaging study

During distraction osteogenesis, large volumes of new bone are formed through the slow distraction of fracture callus. The newly formed bone is closely linked to angiogenesis and positively influenced by physiologic loading. In this study, a rat model was used to explore the correlation between these two observations. Unilateral femoral lengthenings were performed in 18 male Sprague-Dawley rats (400-500 g, age<6 months). Half of the animals were allowed to bear weight freely (WB) while the remaining animals were made non-weight-bearing via a through-knee amputation (NWB). After a seven-day latency period, femurs were lengthened 7 mm over 21 days. Animals were sacrificed at 7, 21, 35, and 49 days (0, 4.7, 7, and 7 mm of distraction) at which time lower extremity vessels were perfused with a 60% (w/v) barium sulfate suspension. High-resolution three-dimensional images of the vascular architecture were generated using a fan-beam micro-tomography machine by digitally separating the contrast-filled vessels from surrounding tissue. For two subvolumes, VOI(1), which included vessels in the medullary canal, cortex, and periosteum, and VOI(2), which included only vessels in the canal and cortex, the total tissue volume (TV), the volume of vessels (VV), and vessel diameter (VD) were determined. For the larger subvolume (VOI(1)), VV and vessel density (VV/TV) increased as a function of time (p<0.001) in WB animals. In NWB animals, VV increased significantly with time (p=0.029), while VV/TV did not (p=0.36). Increases in VV and VV/TV were significantly greater in WB animals than in NWB animals (p<0.01 and 0.05, respectively). VD was similar in both groups and did not change with time. Our data suggest that weight bearing stimulates new vessel formation during distraction osteogenesis.

Multilineage mesenchymal differentiation potential of human trabecular bone-derived cells

Explant cultures of adult human trabecular bone fragments give rise to osteoblastic cells, that are known to express osteoblast-related genes and mineralize extracellular matrix. These osteoblastic cells have also been shown to undergo adipogenesis in vitro and chondrogenesis in vivo. Here we report the in vitro developmental potential of adult human osteoblastic cells (hOB) derived from explant cultures of collagenase-pretreated trabecular bone fragments. In addition to osteogenic and adipogenic differentiation, these cells are capable of chondrogenic differentiation in vitro in a manner similar to adult human bone marrow-derived mesenchymal progenitor cells. High-density pellet cultures of hOB maintained in chemically defined serum-free medium, supplemented with transforming growth factor-beta1, were composed of morphologically distinct, chondrocyte-like cells expressing mRNA transcripts of collagen types II, IX and X, and aggrecan. The cells within the high-density pellet cultures were surrounded by a sulfated proteoglycan-rich extracellular matrix that immunostained for collagen type II and proteoglycan link protein. Osteogenic differentiation of hOB was verified by an increased number of alkaline phosphatase-positive cells, that expressed osteoblast-related transcripts such as alkaline phosphatase, collagen type I, osteopontin and osteocalcin, and formed mineralized matrix in monolayer cultures treated with ascorbate, beta-glycerophosphate, and bone morphogenetic protein-2. Adipogenic differentiation of hOB was determined by the appearance of intracellular lipid droplets, and expression of adipocyte-specific genes, such as lipoprotein lipase and peroxisome proliferator-activated receptor gamma2, in monolayer cultures treated with dexamethasone, indomethacin, insulin and 3-isobutyl-1-methylxanthine. Taken together, these results show that cells derived from collagenase-treated adult human trabecular bone fragments have the potential to differentiate into multiple mesenchymal lineages in vitro, indicating their developmental plasticity and suggesting their mesenchymal progenitor nature.

Relationships between trabecular bone remodeling and bone vascularization: a quantitative study

Beside its well-known role in bone development, vascularization plays a major role in bone cell migration for bone remodeling and metastatic tumor invasion. However, the various techniques used to identify vessels in bone have never been tested for trabecular bone vessel quantification, whereas bone remodeling quantitative parameters are commonly assessed. In this context, we developed and compared various histological techniques used to visualize blood vessels in rat bone in order to quantify them. First, several products were tested by intracardiac infusion to opacify the bone vascular network. The best results were obtained using either an India ink-1% agarose solution or an India ink-saturated barium sulfate solution followed by X-ray microradiography. Second, to identify the types of vessels, we also performed histoenzymology and immunohistochemistry stainings. Neither alkaline phosphatase (for endothelial cells) nor adenosine triphosphatase (ATPase) stainings (for smooth muscle cells) provided a low enough background to allow for vessel identification and quantification. For immunohistochemistry, various specific vessel constituents were analyzed: laminin, smooth muscle cell alpha-actin, factor VIII, and lectin Griffonia simplifolia. Anti-laminin and anti-smooth muscle cell alpha-actin antibodies gave the best results for quantification. Third, after optimization of these techniques, we performed quantitative bone and vessel histomorphometry on two groups of 12 rats each, for which bone remodeling and vessel number and area parameters were measured. No statistical differences were observed between the two groups, confirming the reproducibility of our measurements. A significant relationship was found between vessel number and histodynamic parameters; that is, bone formation rate correlated positively with India ink-positive vessel area (p < 0.009, r2 = 0.54) and alpha-actin-positive vessel number (p < 0.05, r2 = 0.66). Furthermore, we report reproducible techniques for visualization and quantification of vessels in bone that also allowed for simultaneous conventional bone histomorphometry. This methodology should help researchers to better understand the functional and anatomical relationship between trabecular bone and its vascularization during normal or pathological processes.

Connective tissue progenitors: practical concepts for clinical applications

Tissue engineering can be defined as any effort to create or induce the formation of a specific tissue in a specific location through the selection and manipulation of cells, matrices, and biologic stimuli. The biologic concepts and the biochemical and biophysical principles on which these efforts are based have become an exciting and rapidly evolving field of biomedical research. More importantly, tissue engineering is becoming a clinical reality in the practice of orthopaedic surgery, providing patients and physicians with an expanding set of practical tools for effective therapy. New and improved matrices and bioactive factors inevitably will play important roles in the evolution of orthopaedic tissue engineering. However, tissue engineering never can stray far from fundamental biologic principles, and one of these is that cells do all the work. No new tissue forms except through the activity of living cells. No bone graft, no matrix, no growth factor, no cytokine can contribute to the generation or integration of new tissue, except through the influence it has on the behavior of cells. The efficacy of all current clinical tools depends entirely on the cells in the grafted site, particularly the small subset of stem cells and progenitor cells that are capable of generating new tissue. The current authors review a series of key biologic concepts related to the rational design and selection of composites of cells and matrices in contemporary bone grafting and tissue engineering efforts. The functional paradigms of stem cell biology are reviewed, including self renewal, asymmetric and symmetric mitosis, and lineage restriction. Several potential sources for autogenous stem cells for connective tissues are discussed. Finally, a simple mathematical model is introduced as a tool for understanding the functional demands placed on stem cells and progenitors in a graft site and to provide a conceptual framework for the rational design of cell matrix composite grafts.

Cultivation of rat marrow-derived mesenchymal stem cells in reduced oxygen tension: effects on in vitro and in vivo osteochondrogenesis

Rat mesenchymal stem cells (rMSCs) represent a small portion of the cells in the stromal compartment of bone marrow and have the potential to differentiate into bone, cartilage, fat, and fibrous tissue. These mesenchymal progenitor cells were maintained as primary isolates and as subcultured cells in separate closed modular incubator chambers purged with either 95% air and 5% CO(2) (20% or control oxygen) or 5% oxygen, 5% CO(2), and 90% nitrogen (5% or low oxygen). At first passage, some cells from each oxygen condition were loaded into porous ceramic vehicles and implanted into syngeneic host animals in an in vivo assay for osteochondrogenesis. The remaining cells were continued in vitro in the same oxygen tension as for primary culture or were switched to the alternate condition. The first passage cells were examined for in vitro osteogenesis with assays involving the quantification of alkaline phosphatase activity and calcium and DNA content as well as by von Kossa staining to detect mineralization. Cultures maintained in low oxygen had a greater number of colonies as primary isolates and proliferated more rapidly throughout their time in vitro, as indicated by hemacytometer counts at the end of primary culture and increased DNA values for first passage cells. Moreover, rMSCs cultivated in 5% oxygen produced more bone than cells cultured in 20% oxygen when harvested and loaded into porous ceramic cubes and implanted into syngeneic host animals. Finally, markers for osteogenesis, including alkaline phosphatase activity, calcium content, and von Kossa staining, were elevated in cultures which had been in low oxygen throughout their cultivation time. Expression of these markers was usually increased above basal levels when cells were switched from control to low oxygen at first passage and decreased for cells switched from low to control oxygen. We conclude that rMSCs in culture function optimally in an atmosphere of reduced oxygen that more closely approximates documented in vivo oxygen tension.

Thromboprophylaxis using a low molecular weight heparin delays fracture repair

Low molecular weight heparins are significantly superior to unfractionated heparin or warfarin in the prevention of thromboembolic episodes associated with orthopaedic surgery. Therapeutic doses of heparin and warfarin have been shown to delay bone repair in a rabbit model. The current study investigated the effect of prophylactic administration of a low molecular weight heparin, enoxaparin, on the healing of a closed rabbit rib fracture. Fracture healing was assessed using histomorphometric, histologic, and immunohistochemical methods at 3, 7, and 14 days, and biomechanical testing with torsional loading was assessed after 21 days. Bone repair was significantly attenuated at all times in animals receiving subcutaneous enoxaparin compared with that of the control animals. Numerous putative mechanisms for this phenomenon are discussed, and additional studies are proposed to elucidate the effects of this pharmacologically diverse group of compounds on all aspects of bone physiology and repair.

Osteoprogenitor cells within skeletal muscle

The formation of ectopic bone within skeletal muscle is a widely observed phenomenon. However, the source of the osteoprogenitor cells responsible for ectopic bone formation remains unknown. This study was designed to test for osteogenic differentiation among cells isolated from skeletal muscle tissue. Different subpopulations of cells derived from an adult mouse skeletal muscle were tested for induction of alkaline phosphatase activity after exposure to bone morphogenetic protein-2 in vitro. A responsive subpopulation was identified, transduced with a retrovirus encoding for beta-galactosidase (Rv-lacZ) and an adenoviral construct encoding for one bone morphogenetic protein-2, and injected into the hindlimb of immune compromised (severe combined immunodeficient, or SCID) mice. The injected cells appeared to actively participate in the ectopic bone formation. The existence of lacZ-positive muscle-derived cells colocalized with osteocalcin-producing cells within lacunae of newly formed bone matrix suggests osteoblast and osteocyte differentiation. Although a specific cell was not isolated, these data support the contentions that osteoprogenitor cells reside within skeletal muscle and that muscle may represent a source other than bone marrow for the harvest of these cells.

Vascular proliferation and blood supply during distraction osteogenesis: a scanning electron microscopic observation

This scanning electron microscopic study examined the spatial and temporal features of proliferating vessels of regenerating bone tissue and blood supply during distraction osteogenesis. A rat model of tibial lengthening was used with a protocol divided into a latency period of 7 days, a distraction period that lasted 14 days with a daily distraction rate of 0.5 mm in two steps, and a consolidation period of 21 days. Vascular casting was done on the hindlimbs before osteotomy and on postoperative days 7, 14, 21, 28, and 42. Scanning electron microscopic findings were correlated with radiological and histological observations. On days 7 and 14, the proliferation of periosteal vessels was pronounced and there was distinct subperiosteal bone formation on the osteotomized surfaces. On day 21, vascular branches from the medullary canal of the host bone formed a vascular network, which gave rise to multiple axial, straight vascular branches, running parallel to the direction of distraction, toward the interzone, in accordance with the progress of mineralization. On day 28, the periosteum provided vascularization to the peripheral side of the interzone whereas the center of the interzone was still relatively avascular. On day 42, the periosteal and medullary vascular channels were completely connected at the distraction site including the interzone, which was occupied by developing and mature bone trabeculae. These results suggest that vascular proliferation occurs actively during the latency and distraction periods and then gradually decreases over time. A close temporal and spatial relationship exists between formation of regenerated bone and vascular proliferation of the periosteum and medullary canal.