Biomedical subjects

L G Ellies

Publications and source records attributed to L G Ellies.

24 records · Page 2Linked to original sources

PubMed1992

Crystallographic changes in calcium phosphates during plasma-spraying.

Coating hydroxyapatite (HA) onto metal implant surfaces using the plasma-spraying technique has been investigated in several laboratories as a means of improving the mechanical properties of the bulk ceramic. This study describes crystallographic changes which can occur during the plasma-spraying of calcium phosphate powders. A precipitated calcium-deficient apatite and a high temperature near-stoichiometric HA were each sprayed onto metal substrate in an argon plasma using several hydrogen gas flow conditions at various temperatures. The surfaces were examined by X-ray diffraction and scanning electron microscopy. The plasma-sprayed products were identified as a mixture of calcium phosphates including HA, beta-tricalcium phosphate (beta-TCP) and calcium oxide. Stoichiometric HA when plasma-sprayed showed the least (5%) degradation. Since beta-TCP is more resorbable than HA in vivo, varying the HA/beta-TCP ratio on the plasma-sprayed surface may provide a method to control surface dissolution of the coating.

Biocompatible Materials↗

PubMed1991

Interleukin-1 alpha stimulates the release of prostaglandin E2 and phospholipase A2 from fetal rat calvarial cells in vitro: relationship to bone nodule formation.

We have shown previously that interleukin-1 (IL-1) has biphasic effects on the formation of bone nodules in long-term cultures of fetal rat calvarial (RC) cells (Ellies and Aubin, Cytokine 2:430-437, 1990). To determine the role of arachidonic acid metabolism in this process, we have examined the release of prostaglandin E2 (PGE2) and phospholipase A2 (PLA2) from RC cells under conditions that allowed concomitant analysis of the formation of bone nodules. Recombinant human IL-1 alpha (rhIL-1 alpha) stimulated PGE2 and PLA2 release in a time- and dose-dependent manner. PGE2 release was highest in preconfluent cultures (days 1-6) and was stimulated up to 8.5-fold in response to 50 U/ml of rhIL-1 alpha. In contrast, extracellular PLA2 activity was maximal in postconfluent cultures, with 50 U/ml of rhIL-1 alpha causing a 20-fold increase by day 15. PLA2 release by RC cells was not significantly affected by PGE2, the glucocorticoid dexamethasone, or the cyclooxygenase inhibitor indomethacin. Indomethacin partially blocked the inhibition of bone nodule formation caused by rhIL-1 alpha, and exogenous PGE2 reversed this effect. Addition of group I PLA2 from Naja naja venom to RC cells had no effect on bone nodule development; however, group II PLA2 from Crotalus adamanteus venom inhibited the formation of bone nodules in a dose range similar to that induced by rhIL-1 alpha. These results indicate that PGE2 release does not have a direct temporal correlation with increases in PLA2 activity. In addition, the data show that only part of the inhibition of bone formation seen with rhIL-1 alpha is mediated by PGE2 and suggest that extracellular PLA2 also accounts for part of the inhibition.

Animals↗

PubMed1991

Extracellular phospholipase A2 secretion is a common effector pathway of interleukin-1 and tumour necrosis factor action.

Inflammatory processes are characterized by increased levels of extracellular phospholipase A2 (PLA2) and cytokines such as interleukin 1 (IL-1) and tumour necrosis factor (TNF). IL-1, TNF and PLA2 share a number of proinflammatory, arthritogenic effects. The sequential induction, first of the cytokines followed by PLA2, suggests that these cytokines may regulate synthesis and secretion of PLA2. To test this postulate, foetal rat calvarial bone-forming cells (FRCC) were treated with recombinant human IL-1 and TNF and extracellular PLA2 release was quantitated. Both IL-1 and TNF induced the de novo synthesis of PLA2 in a concentration-dependent manner. Continuous exposure of FRCC in primary culture to IL-1 (50 units/ml) over 15 days resulted in as much as 100-fold increase in PLA2 secretion. IL-1 (50 units/ml) added to post-confluent cultures for a 48-h pulse increased PLA2 activity 9.4-fold. The combination of IL-1 (50 units/ml) and TNF (500 units/ml) was synergistic with an observed increase in extracellular PLA2 secretion of 146-fold following a 48-h pulse. Interleukin-6, alone or in combination with IL-1 or TNF, did not further enhance PLA2 synthesis of secretion. Cytokine-induced synthesis of PLA2 was inhibited 80% by 10 microM cycloheximide but not by dexamethasone over the range of 10(-6) to 10(-8) M. FRCC-derived PLA2 was neutral-active with a pH optimum of 6-7.5 and was calcium-dependent with optimal activity in the presence of 2-7 mM calcium. It had absolute 2-acyl specificity using micellar phosphatidylcholine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Temporal sequence of interleukin 1 alpha-mediated stimulation and inhibition of bone formation by isolated fetal rat calvaria cells in vitro.

Cytokines released at sites of inflammation and infection may alter normal bone remodeling processes resulting in pathologic bone destruction or bone formation. Interleukin 1, an inflammatory mediator, has been shown to stimulate as well as inhibit parameters associated with bone formation. In this study we have examined temporal aspects of the biphasic effects of recombinant interleukin 1 alpha (IL 1 alpha) on the differentiation of osteoprogenitor cells into bone-forming osteoblasts (bone nodules) in vitro. A dose-dependent stimulation of bone formation over a concentration range of 0.5 to 50 U/mL (1.4 x 10(-12) to 1.4 x 10(-10) M) was observed when preconfluent, primary cultures of fetal rat calvaria (RC) cells were pulsed with IL 1 alpha for 72 to 96 hr from the beginning of the culture period. This was correlated with a stimulation of cell proliferation and alkaline phosphatase activity measured during the late log phase of growth. In contrast, continuous exposure to IL 1 alpha or exposure to IL 1 alpha after confluency resulted in inhibition of bone nodule formation and alkaline phosphatase activity. IL 1 alpha-stimulated prostaglandin E2 (PGE2) production until the RC cells became multilayered, but the addition of the cyclooxygenase inhibitor indomethacin had no effect in reducing the IL 1 alpha-mediated stimulation of cell proliferation or bone nodule formation. However, in cultures continuously exposed to IL 1 alpha, added indomethacin partially reduced the inhibition of bone formation, suggesting that prostaglandin production may play a role in the inhibitory effects of IL 1 alpha on bone formation.

Alkaline Phosphatase↗

PubMed1988

Quantitative analysis of early in vivo tissue response to synthetic apatite implants.

Studies have shown synthetic calcium phosphates such as hydroxyapatite and beta tricalcium phosphate to be biocompatible in vivo. However, few studies have quantitated histological responses to the implants. The aim of this study was to develop a method for the quantitative assessment of tissue biocompatibility to ceramic materials in vivo and to use this method to compare noncarbonated and carbonated apatite implants. Synthetic sintered apatites of 0, 3, and 6% carbonate by weight were prepared and cut into implants 4 X 4 X 1 mm. These were placed 2 mm into the medial aspect of rat femurs. Following sacrifice at 4 weeks, the femurs were fixed in formalin, demineralized in formic acid, and embedded in glycol methacrylate. Sections were cut on an ultramicrotome set at 1.5 micron and stained with toluidine blue. A point counting technique using standard stereological grids and a low-power microscope was used to measure areas of new bone formation. The width of the connective tissue zone adjacent to muscle was measured using an image analyzer. All implants were well accepted by the host tissues judging from criteria of minimal inflammation and degree of fixation. Results showed an increase in new bone formed in the marrow cavity with increasing carbonate content. This may improve stability of the implant in the host bone, particularly during the initial healing period. A technique which should enable quantitative histological evaluation of different ceramic materials has been developed. The use of this method indicates that further studies are warranted to investigate carbonated apatite as an implant material.

Animals↗

PubMed1988

Crystallographic structure and surface morphology of sintered carbonated apatites.

Densely sintered synthetic hydroxyapatite (HA) is used as an implant material because of its excellent tissue biocompatibility. In order to maximize the biological potential of this calcium phosphate, we have investigated the incorporation of carbonate into HA to make a material which more closely resembles the mineral found in bones and teeth. The aim of the present study was to determine the conditions under which sintered carbonated apatites of specific carbonate content could be produced. The apatites were prepared by heating compressed pellets of precipitated carbonated apatite under a carbon dioxide/steam or nitrogen/steam atmosphere between 825 and 1050 degrees C. The products were analyzed chemically and the surfaces examined by x-ray diffraction, infrared spectroscopy, reflected light microscopy, and scanning electron microscopy. The results showed that carbonate loss during sintering could be reliably predicted, making it possible to produce materials with specific carbonate content, and with specific physical and chemical composition.

Carbonates↗