The effect of impaired thyroid function during development on the mechanical properties of avian bone

Thyroid hormones show fluctuating levels during the post-hatching development of birds. In this paper we report the results of the first mechanical tests to quantify the effect of hypothyroidism, during post-natal development, on the skeletal properties of a precocial bird, the barnacle goose, as determined by microhardness testing. The effect of hypothyroidism is tissue-specific; bone from the femora of birds is not significantly affected by induced hypothyroidism, however, there is a strong positive relationship between the levels of circulating thyroid hormones and the mechanical properties of bone from humeri. In the barnacle goose the development of the wing skeleton and musculature depends on an increase in circulating thyroid hormones and our analysis shows that, in its absence, the mechanical competence of the bone mineral itself is reduced in addition to the decreased bone length and muscle development previously reported in the literature. (C) 2004 Wiley-Liss, Inc.

Analysis of creep strain during tensile fatigue of cortical bone

During fatigue tests of cortical bone specimens, at the unload portion of the cycle (zero stress) non-zero strains occur and progressively accumulate as the test progresses. This non-zero strain is hypothesised to be mostly, if not entirely, describable as creep. This work examines the rate of accumulation of this strain and quantifies its stress dependency. A published relationship determined from creep tests of cortical bone (Journal of Biomechanics 21 (1988) 623) is combined with knowledge of the stress history during fatigue testing to derive an expression for the amount of creep strain in fatigue tests. Fatigue tests on 31 bone samples from four individuals showed strong correlations between creep strain rate and both stress and “normalised stress” (σ/E) during tensile fatigue testing (0–T). Combined results were good (r2=0.78) and differences between the various individuals, in particular, vanished when effects were examined against normalised stress values. Constants of the regression showed equivalence to constants derived in creep tests. The universality of the results, with respect to four different individuals of both sexes, shows great promise for use in computational models of fatigue in bone structures.

Targeting stem cell niches and trafficking for cardiovascular therapy.

Regenerative cardiovascular medicine is the frontline of 21st-century health care. Cell therapy trials using bone marrow progenitor cells documented that the approach is feasible, safe and potentially beneficial in patients with ischemic disease. However, cardiovascular prevention and rehabilitation strategies should aim to conserve the pristine healing capacity of a healthy organism as well as reactivate it under disease conditions. This requires an increased understanding of stem cell microenvironment and trafficking mechanisms. Engagement and disengagement of stem cells of the osteoblastic niche is a dynamic process, finely tuned to allow low amounts of cells move out of the bone marrow and into the circulation on a regular basis. The balance is altered under stress situations, like tissue injury or ischemia, leading to remarkably increased cell egression. Individual populations of circulating progenitor cells could give rise to mature tissue cells (e.g. endothelial cells or cardiomyocytes), while the majority may differentiate to leukocytes, affecting the environment of homing sites in a paracrine way, e.g. promoting endothelial survival, proliferation and function, as well as attenuating or enhancing inflammation. This review focuses on the dynamics of the stem cell niche in healthy and disease conditions and on therapeutic means to direct stem cell/progenitor cell mobilization and recruitment into improved tissue repair.

Care in the community? Interpretations of a fractured goat bone from Neolithic Jarmo, Iraq

A case study of a goat metatarsal exhibiting a complex diaphyseal fracture from Pottery Neolithic Jarmo in the Central Zagros region of the eastern Fertile Crescent is here described and analysed. The Central Zagros is one of the areas with the earliest evidence for goat domestication. The significance of the pathology may be viewed within the context of domestic goat ecology in the landscape of Jarmo, potentially impacting browsing behaviour (goats raise themselves on their hind limbs to browse) and movement with the herd in the landscape (the terrain around Jarmo is very steep in places, which would be difficult for an animal to navigate on three legs). In the light of this, possible levels of care that the Neolithic human community may have afforded this animal are discussed – from a situation where therapeutic intervention may have occurred, to one of stall confinement of the animal to allow the pathology to heal, to a position of simple awareness of the condition – and how this impacts on our understanding of changes in attitudes towards animals through the process of domestication.

Translational research and therapeutic applications of neural crest-derived stem cells in regenerative periodontology

Regeneration of periodontal tissues aims to utilize tissue engineering techniques to restore lost periodontal tissues including the cementum, periodontal ligament and alveolar bone. Regenerative dentistry and its special field regenerative periodontology represent relatively new and emerging branches of translational stem cell biology and regenerative medicine focusing on replacing and regenerating dental tissues to restore or re-establish their normal function lost during degenerative diseases or acute lesions. The regeneration itself can be achieved through transplantation of autologous or allogenic stem cells, or by improving the tissue self-repair mechanisms (e.g. by application of growth factors). In addition, a combination of stem cells or stem cell-containing tissue with bone implants can be used to improve tissue integration and the clinical outcome. As the oral cavity represents a complex system consisting of teeth, bone, soft tissues and sensory nerves, regenerative periodontology relies on the use of stem cells with relatively high developmental potential. Notably, the potential use of pluripotent stem cell types such as human embryonic stem cells or induced pluripotent stem cells is still aggravated by ethical and practical problems. Thus, other cellular sources such as those readily available in the postnatal craniofacial area and particularly in oral structures offer a much better and realistic alternative as cellular regenerative sources. In this review, we summarize current knowledge on the oral neural crest-derived stem cell populations (oNCSCs) and discuss their potential in regenerative periodontology.