G. Vallés

Modulation of the cross-talk between macrophages and osteoblasts by titanium-based particles

Titanium (Ti) and its alloys have widespread uses as implant materials for orthopaedic and dental applications. To improve their surface characteristics, modifications that give rise to an outer ceramic layer of rutile have been developed. It is expected that after a long period of service, rutile particles will arise from these modified surfaces. Rutile particles have recently been proposed as reinforcement agents of substrates designed for bone tissue engineering applications. In this study, the ability of Ti and rutile particles to modulate secretion of soluble factors involved in bone turnover has been assayed in an in vitro co-culture system of macrophages and human osteoblasts that allows the exchange of soluble factors between both cell types without direct cell contact. Exposure of co-cultured macrophages to sub-cytotoxic doses of Ti or rutile particles did not modify the osteoblastic expression of surface RANKL or the secretion of OPG into the media. Both IL-6 and PGE2 levels increased to a similar extent after treatment with rutile or Ti particles. M-CSF and GM-CSF levels were lower after treatment with rutile particles than with Ti. Experiments employing neutralising antibodies indicate that exposure of co-cultured macrophages to both Ti-based particles induces the release of M-CSF, GM-CSF, IL-6 and PGE2 through up-regulation of IL-1beta and TNF-alpha. We comparatively examined the response of co-cultured macrophages, osteoblasts or both types of cells after exposure to particles. The results indicate that interactions of osteoblasts with particles can modulate the extent of the response initiated by macrophages. Maximal levels of secretions of all tested factors were reached after exposure of co-cultured cells to Ti particles, which is suggestive of the lower bioreactivity of rutile particles.

Effects of polyethylene and α-alumina particles on IL-6 expression and secretion in primary cultures of human osteoblastic cells

The effect of two biomaterials, polyethylene and alpha-alumina, on interleukin-6 (IL-6) secretion and expression has been studied in human osteoblasts in primary culture. Human osteoblastic cells were derived from fresh trabecular bone explants removed during total knee arthroplasty. On reaching confluence, cells were subcultured in 6 well plates; the resulting subcultures were incubated until confluence and polyethylene or alpha-alumina particles were added to some while the rest were left as controls. The IL-6 mRNA levels were assessed by reverse transcription (RT) followed by polymerase chain reaction (PCR). IL-6 secretion was measured in the conditioned medium. The IL-6 expression was higher in the presence of both biomaterials. Maximum expression occurred in response to a dose of 50 mg particles well with both biomaterials and was greater after polyethylene particle addition than after alpha-alumina particle addition at this dose. The maximum IL-6 secretion elicited by alpha-alumina was produced at 10 mg particles well while maximum response with polyethylene required 50 mg well. At a dose of 10 mg/well, alpha-alumina particles induced more secretion than 10 mg of polyethylene particles. Nevertheless, at a dose of 50 mg/well maximum secretion was produced with polyethylene particles. In conclusion and in our experimental conditions, polyethylene as well as alpha-alumina increased both the expression and the secretion of IL-6 in human osteoblastic cells in primary culture and stimulation from polyethylene appears stronger than that from alpha-alumina at the same dose.