RESUMEN

Orthopaedic implants are designed to promote biocompatibility and hence their integration with surrounding tissue. This involves influencing cell-implant interactions through changes in both surface topography and surface roughness. However, the large range of machining techniques used in implant manufacture and inconsistencies in the measurement techniques used for surface characterization make it difficult to measure the impact of surface characteristics on cell-implant interactions. Here, we describe a new in vitro multi-parametric approach that uses commercially available arrays of engineered surfaces that linearly increase in roughness, as measured by Ra, and that can be used to obtain quantitative measurements of cell attachment, differentiation and bone formation. Using this model, we demonstrate that cell attachment above 50% confluency occurs over a narrow range of roughness (Ra from 0.0125 microm to 6.3 microm) and that promotion of cell differentiation and bone development, while significantly influenced by surface topography, does not correlate directly with initial levels of cell attachment. These results compare well with published in vivo implant biocompatibility data indicating that this approach has the potential to offer a rapid, reliable and reproducible in vitro prediction of in vivo implant biocompatibility.

Asunto(s)

RESUMEN

We recently found that estrogen deficiency leads to a lowering of thiol antioxidant defenses in rodent bone. Moreover, administration of agents that increase the concentration in bone of glutathione, the main intracellular antioxidant, prevented estrogen-deficiency bone loss, whereas depletion of glutathione by buthionine sulfoximine (BSO) administration provoked substantial bone loss. It has been shown that the estrogen-deficiency bone loss is dependent on TNFalpha signaling. Therefore, a model in which estrogen deficiency causes bone loss by lowering antioxidant defenses predicts that the osteopenia caused by lowering antioxidant defenses should similarly depend on TNFalpha signaling. We found that the loss of bone caused by either BSO administration or ovariectomy was inhibited by administration of soluble TNFalpha receptors and abrogated in mice deleted for TNFalpha gene expression. In both circumstances, lack of TNFalpha signaling prevented the increase in bone resorption and the deficit in bone formation that otherwise occurred. Thus, depletion of thiol antioxidants by BSO, like ovariectomy, causes bone loss through TNFalpha signaling. Furthermore, in ovariectomized mice treated with soluble TNFalpha receptors, thiol antioxidant defenses in bone remained low, despite inhibition of bone loss. This suggests that the low levels of antioxidants in bone seen after ovariectomy are the cause, rather than the effect, of the increased resorption. These experiments are consistent with a model for estrogen-deficiency bone loss in which estrogen deficiency lowers thiol antioxidant defenses in bone cells, thereby increasing reactive oxygen species levels, which in turn induce expression of TNFalpha, which causes loss of bone.

Asunto(s)

RESUMEN

Specialised phytophagous arthropods often display high levels of specificity to particular sites on their host plant. In this paper we examine the occupation of microhabitats and aggregation patterns of the eriophyoid mite, Acalitus essigi (Hassan), on its host plant, European blackberry (Rubus fruticosus L. aggregate), a plant that undergoes significant seasonal changes in its morphology. A. essigi was found to be a refuge inhabiting species. It resided in bud and leaf axil microhabitats on both primocanes and fructocanes and also occupied berry and bract microhabitats on fructocanes. Population fluctuations within the different microhabitats were evident across seasons. From summer to winter, populations significantly declined in bract and leaf axil microhabitats, but significantly increased within bud microhabitats where overwintering took place as slowly reproducing colonies. Live fruit and young shoots were also identified as overwintering sites. A. essigi populations displayed an aggregated distribution both within and between individual blackberry canes. Within primocanes A. essigi were aggregated in the lower 20% of cane length. On fructocanes aggregation of A. essigi was in the lower 20% and especially in the upper 20% of cane length. In spring A. essigi was confirmed to emerge from bud overwintering sites and colonise shoots mainly in the lower third of the previous season's primocanes, suggesting limited dispersal away from overwintering sites. It is proposed that biotic factors such as tissue age, microhabitat morphology and limited ambulatory dispersal capabilities are responsible for the aggregation pattems of this mite.

Asunto(s)

RESUMEN

Generic taxon-specific DNA probes that target an internal region of the gene (rbcL) encoding the large subunit of ribulose-1, 5-bisphosphate carboxylase/oxygenase (RubisCO) were developed for two groups of marine phytoplankton (diatoms and prymnesiophytes). The specificity and utility of the probes were evaluated in the laboratory and also during a 1-month mesocosm experiment in which we investigated the temporal variability in RubisCO gene expression and primary production in response to inorganic nutrient enrichment. We found that the onset of successive bloom events dominated by each of the two classes of chromophyte algae was associated with marked taxon-specific increases in rbcL transcription rates. These observations suggest that measurements of RubisCO gene expression can provide an early indicator of the development of phytoplankton blooms and may also be useful in predicting which taxa are likely to dominate a bloom.

Asunto(s)

Asunto(s)

Asunto(s)