Frank Kloss

Reduced oxygen tension attenuates differentiation capacity of human mesenchymal stem cells and prolongs their lifespan

Mesenchymal stem cells (MSC) are capable of differentiating into bone, fat, cartilage, tendon and other organ progenitor cells. Despite the abundance of MSC within the organism, little is known about their in vivo properties or about their corresponding in vivo niches. We therefore isolated MSC from spongy (cancellous) bone biopsies of healthy adults. When compared with the surrounding marrow, a fourfold higher number of colony‐forming units was found within the tight meshwork of trabecular bone surface. At these sites, oxygen concentrations range from 1% to 7%. In MSC cultured at oxygen as low as 3%, rates for cell death and hypoxia‐induced gene transcription remained unchanged, while in vitro proliferative lifespan was significantly increased, with about 10 additional population doublings before reaching terminal growth arrest. However, differentiation capacity into adipogenic progeny was diminished and no osteogenic differentiation was detectable at 3% oxygen. In turn, MSC that had previously been cultured at 3% oxygen could subsequently be stimulated to successfully differentiate at 20% oxygen. These data support our preliminary finding that primary MSC are enriched at the surface of spongy bone. Low oxygen levels in this location provide a milieu that extends cellular lifespan and furthermore is instructive for the stemness of MSC allowing proliferation upon stimulation while suppressing differentiation.

Current trends and future perspectives of bone substitute materials - from space holders to innovative biomaterials.

An autologous bone graft is still the ideal material for the repair of craniofacial defects, but its availability is limited and harvesting can be associated with complications. Bone replacement materials as an alternative have a long history of success. With increasing technological advances the spectrum of grafting materials has broadened to allografts, xenografts, and synthetic materials, providing material specific advantages. A large number of bone-graft substitutes are available including allograft bone preparations such as demineralized bone matrix and calcium-based materials. More and more replacement materials consist of one or more components: an osteoconductive matrix, which supports the ingrowth of new bone; and osteoinductive proteins, which sustain mitogenesis of undifferentiated cells; and osteogenic cells (osteoblasts or osteoblast precursors), which are capable of forming bone in the proper environment. All substitutes can either replace autologous bone or expand an existing amount of autologous bone graft. Because an understanding of the properties of each material enables individual treatment concepts this review presents an overview of the principles of bone replacement, the types of graft materials available, and considers future perspectives. Bone substitutes are undergoing a change from a simple replacement material to an individually created composite biomaterial with osteoinductive properties to enable enhanced defect bridging.

Accelerated bone ingrowth by local delivery of strontium from surface functionalized titanium implants

Studies have indicated systemic treatment with strontium (Sr) as a potential route to increase bone quality and formation around osseointegrating implants. However, adverse effects are linked to such treatment. In this study we present a surface modification method designed for sustained local release of Sr from implants. The four groups used were prepared by a magnetron co-sputtering process and selected on the basis of Sr release data. The composition, morphology and mechanical stability of the coatings were analyzed and the Sr release profiles were investigated in vitro by washout experiments. Mesenchymal stem cells were cultured on the different coatings to evaluate potential cytotoxic effects and the effect on cellular proliferation. No indication of toxicity was found. A rodent study demonstrated a significant increase in direct bone-to-implant contact and peri-implant bone volume, for several of the groups, four weeks after implantation when compared to a Grade 4 titanium reference group. Median values of bone-to-implant contact and new bone formation was found to be 19% and 53%, respectively, for the best group compared to 0% for both parameters with respect to the Grade 4 titanium reference. The results indicate that this method may have applications within the orthopedic and dental industry.

The role of oxygen termination of nanocrystalline diamond on immobilisation of BMP-2 and subsequent bone formation

Medical implants are increasingly often inserted into bone of frail patients, who are advanced in years. Due to age, severe trauma or pathology-related bone changes, osseous healing at the implant site is frequently limited. We were able to demonstrate that coating of endosseous implants with nanocrystalline diamond (NCD) allows stable functionalization by means of physisorption with BMP-2. Strong physisorption was shown to be directly related to the unique properties of NCD, and BMP-2 in its active form interacted strongly when NCD was oxygen-terminated. The binding of the protein was monitored under physiological conditions by single molecule force spectroscopy, and the respective adsorption energies were further substantiated by force-field-calculations. Implant surfaces refined in such a manner yielded enhanced osseointegration in vivo, when inserted into sheep calvaria. Our results further suggest that this technical advancement can be readily applied in clinical therapies with regard to bone healing, since primary human mesenchymal stromal cells strongly activated the expression of osteogenic markers when being cultivated on NCD physisorbed with physiological amounts of BMP-2.

Human Bone Marrow Hosts Polyfunctional Memory CD4+ and CD8+ T Cells with Close Contact to IL-15–Producing Cells

Recently, a key role in memory T cell homing and survival has been attributed to the bone marrow (BM) in mice. In the human BM, the repertoire, function, and survival niches of CD4+ and CD8+ T cells have not yet been elucidated. In this study, we demonstrate that CD4+ and CD8+ effector memory T cells accumulate in the human BM and are in a heightened activation state as revealed by CD69 expression. BM-resident memory T cells produce more IFN-γ and are frequently polyfunctional. Immunofluorescence analysis revealed that CD4+ and CD8+ T cells are in the immediate vicinity of IL-15–producing BM cells, suggesting a close interaction between these two cell types and a regulatory role of IL-15 on T cells. Accordingly, IL-15 induced an identical pattern of CD69 expression in peripheral blood CD4+ and CD8+ T cell subsets. Moreover, the IL-15–inducible molecules Bcl-xL, MIP-1α, MIP-1β, and CCR5 were upregulated in the human BM. In summary, our results indicate that the human BM microenvironment, in particular IL-15–producing cells, is important for the maintenance of a polyfunctional memory CD4+ and CD8+ T cell pool.

The impact of aging on memory T cell phenotype and function in the human bone marrow.

Recently, the BM has been shown to play a key role in regulating the survival and function of memory T cells. However, the impact of aging on these processes has not yet been studied. We demonstrate that the number of CD4+ and CD8+ T cells in the BM is maintained during aging. However, the composition of the T cell pool in the aged BM is altered with a decline of naïve and an increase in TEM cells. In contrast to the PB, a highly activated CD8+CD28– T cell population, which lacks the late differentiation marker CD57, accumulates in the BM of elderly persons. IL‐6 and IL‐15, which are both increased in the aged BM, efficiently induce the activation, proliferation, and differentiation of CD8+ T cells in vitro, highlighting a role of these cytokines in the age‐dependent accumulation of highly activated CD8+CD28– T cells in the BM. Yet, these age‐related changes do not impair the maintenance of a high number of polyfunctional memory CD4+ and CD8+ T cells in the BM of elderly persons. In summary, aging leads to the accumulation of a highly activated CD8+CD28– T cell population in the BM, which is driven by the age‐related increase of IL‐6 and IL‐15. Despite these changes, the aged BM is a rich source of polyfunctional memory T cells and may thus represent an important line of defense to fight recurrent infections in old age.

Impact of Dental Implant Surface Modifications on Osseointegration.

Objective. The aim of this paper is to review different surface modifications of dental implants and their effect on osseointegration. Common marketed as well as experimental surface modifications are discussed. Discussion. The major challenge for contemporary dental implantologists is to provide oral rehabilitation to patients with healthy bone conditions asking for rapid loading protocols or to patients with quantitatively or qualitatively compromised bone. These charging conditions require advances in implant surface design. The elucidation of bone healing physiology has driven investigators to engineer implant surfaces that closely mimic natural bone characteristics. This paper provides a comprehensive overview of surface modifications that beneficially alter the topography, hydrophilicity, and outer coating of dental implants in order to enhance osseointegration in healthy as well as in compromised bone. In the first part, this paper discusses dental implants that have been successfully used for a number of years focusing on sandblasting, acid-etching, and hydrophilic surface textures. Hereafter, new techniques like Discrete Crystalline Deposition, laser ablation, and surface coatings with proteins, drugs, or growth factors are presented. Conclusion. Major advancements have been made in developing novel surfaces of dental implants. These innovations set the stage for rehabilitating patients with high success and predictable survival rates even in challenging conditions.

Craniomaxillofacial Trauma: Synopsis of 14,654 Cases with 35,129 Injuries in 15 Years

Craniomaxillofacial (CMF) trauma occurs in isolation or in combination with other serious injuries, including intracranial, spinal, and upper- and lower-body injuries. It is a major cause of expensive treatment and rehabilitation requirements, temporary or lifelong morbidity, and loss of human productivity. The aim of this study was to evaluate patterns of CMF trauma in a large patient sample within a 15-year time frame. Between 1991 and 2005, CMF trauma data were collected from 14,654 patients with 35,129 injuries at the Department of Cranio-Maxillofacial and Oral Surgery in Innsbruck, assessing a plethora of parameters such as injury type and mechanism as well as age and gender distribution over time. Three main groups of CMF trauma were evaluated: facial bone fractures, dentoalveolar trauma, and soft tissue injuries. Statistical comparisons were carried out using a chi-square test. This was followed by a logistic regression analysis to determine the impact of the five main causes for CMF injury. Older people were more prone to soft tissue lesions with a rising risk of 2.1% per year older, showing no significant difference between male and female patients. Younger patients were at higher risk of suffering from dentoalveolar trauma with an increase of 4.4% per year younger. This number was even higher (by 19.6%) for female patients. The risk of sustaining facial bone fractures increased each year by 4.6%. Male patients had a 66.4% times higher risk of suffering from this type of injury. In addition, 2550 patients (17.4%) suffered from 3834 concomitant injuries of other body parts. In summary, we observed changing patterns of CMF trauma over the last 15 years, paralleled by advances in refined treatment and management options for rehabilitation and reconstruction of patients suffering from CMF trauma.

Bone and aging: Effects on the maxillofacial skeleton

The originally balanced system of normal bone metabolism with an equilibrium of bone resorption and bone formation experiences involutionary changes along with increasing age. This article provides an overview on the effects of aging on bone, in particular on the bone of the maxillofacial skeleton. It explains differences between the postmenopausal type and the senile type of osteoporosis, deals with age-related morphologic changes of bone, mechanisms leading to age-related changes, depicts bones at high fracture risk in aging persons, analyses the reduced bone quantity and quality in cranial bone, and discusses the preservation of maxillofacial bone dimensions by implants. Therefore, research on wound healing, in particular bone healing, and on the regenerative potential of tissue of mesenchymal origin is of major interest and will eventually translate into improved care for patients during daily clinical routine.

In vivo investigation on connective tissue healing to polished surfaces with different surface wettability

OBJECTIVES Connective tissue in contact to transgingival/-dermal implants presents itself as tight scar formation. Although rough surfaces support the attachment they increase bacterial colonisation as well. In contrast to surface roughness, little is known about the influence of surface wettability on soft-tissue healing in vivo. We therefore investigated the influence of different surface wettabilities on connective tissue healing at polished implant surfaces in vivo. MATERIAL AND METHODS Three polished experimental groups (titanium, titanium coated with hydrophobic nano-crystalline diamond (H-NCD) and titanium coated with hydrophilic nano-crystalline diamond (O-NCD) were inserted into the subcutaneous connective tissue of the abdominal wall of 24 rats. Animals were sacrificed after 1 and 4 weeks resulting in eight specimen per group per time point. Specimen were subjected to histological evaluation (van Giessons staining) and immunohistochemistry staining for proliferating cell nuclear antigen (PCNA), fibronectin and tumour necrosis factor-alpha (TNF-α). RESULTS Histological evaluation revealed dense scar formation at the titanium and H-NCD surfaces. In contrast, the connective tissue was loose at the O-NCD surface with a significantly higher number of cells after 4 weeks. O-NCD demonstrated a strong expression of PCNA and fibronectin but a weak expression of TNF-α. In contrast, the PCNA and fibronectin expression was low at the titanium and H-NCD, with a strong signal of TNF-α at the H-NCD surface. CONCLUSIONS Hydrophilicity influences the connective tissue healing at polished implant surfaces in vivo positively. The attachment of connective tissue and the number of cells in contact to the surface were increased. Moreover, the inflammatory response is decreased at the hydrophilic surface.