Adhesion, apoptosis and cytokine release of human mononuclear cells cultured on degradable poly(urethane urea), polystyrene and titanium in vitro.

Early interactions between materials and mononuclear cells may influence the viability and secretory response of the cells. Such effects may in turn influence the subsequent inflammatory and repair phases around the materials. In the present study, it was examined if mononuclear cells cultured in vitro either unstimulated or stimulated with lipopolysaccharide (LPS) (10ng/ml) revealed differences regarding cell viability and apoptosis. A major interest was to study the influence of different material properties on the parameters of the inflammatory response upon cell adhesion to materials with widely different surface chemical properties but similar surface topography: degradable poly(urethane urea) (PUUR), cell culture treated polystyrene (PS) surfaces, and commercially pure (c.p.) titanium (Ti). Finally, the secretion of the proinflammatory tumor necrosis factor-a (TNF-alpha) and the downregulating interleukin-10 (IL-10) cytokines was examined in the supernatants from 24h mononuclear cell cultures. No differences in cell viability as measured by lactate dehydrogenas (LDH) were observed between the three materials. The number of material-surface adherent cells was higher on PUUR than the more hydrophilic PS and Ti as judged by quantification of material surface-associated DNA, light microscopic morphological examination of DAPI-stained cells and SEM. LPS increased the number of adherent cells, irrespective of the type of material. The lowest number of apoptotic (annexin-V) and necrotic (propidium iodide) mononuclear cells was detected on PUUR. LPS decreased the number of both apoptotic and necrotic cells, irrespective of material. Low TNF-alpha levels were detected in unstimulated conditions, irrespective of material types. A significantly lower amount of TNF-alpha was found with unstimulated cells on PUUR than on Ti. A significantly higher IL-10 level was detected in unstimulated Ti cultures compared with PUUR and PS. Secretion of IL-10 was predominantly stimulated by LPS on PUUR and Ti. The data indicate that material-related differences are expressed in differences in cell adherence, apoptosis and cytokine secretion. Further, degradable PUUR has equal or less cell-activating properties than Ti and PS under in vitro conditions.

Effects of local changes in the helix flexibility on electrophoretic migration of DNA in agarose gel.

We present a study of how kinks, flexible bends, and flexible joints in the DNA helix, induced by binding cis-diamminedichloroplatinum(II) (cis-DDP), transdiamminedichloroplatinum(II) (trans-DDP), and chlorodiethylenetriammineplatinum(II) (dien-Pt) to the DNA, affect the electrophoretic migration of DNA in agarose gels. For long DNA the conformation oscillates between extended and compact states during the migration, as for native DNA. The presence of flexible joints decreases both the length of time and the step length of the cycles, but in a compensatory manner so that there is no net effect on the mobility. This demonstrates that in some cases mobility alone cannot detect pertubations in the DNA helix. Kinks and flexible bends reduce the mobility because they both lead to longer time periods of the cycles. With kinks the reduction is strongest at low fields because at high fields the kinks are straightened out; the steps thus become even longer than for native DNA. The results suggest that a combination of mobility and orientation measurements on reptating DNA can be used for distinguishing different kinds of structural alterations in the DNA.