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In vitro TNF-alpha release from THP-1 monocytes in response to dental casting alloys exposed to lipopolysaccharide
S K Nelson1, J C Wataha, R M Cibirka
1School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1260, USA. snelson@mail.mg.edu
Statement Of Problem:
Studies have found that lipopolysaccharide (LPS) attaches to and is eluted from dental alloys, but the biologic effects of LPS are not known.
Purpose:
This study evaluated the ability of dental casting alloys pre-exposed to LPS to activate human monocytes with and without subsequent elution of the LPS.
Material And Methods:
Eight types of casting alloys (n = 6 specimens per type) were exposed to LPS (Escherichia coli @ 100 micrograms/mL) for 24 hours. Controls were not exposed to LPS. Teflon (Tf) (+/- LPS) served as the material control. Treated alloys were transferred to THP-1 human monocytes for 24 hours or placed into phosphate-buffered saline (PBS) solution for 120 hours before monocyte exposure. Monocyte activation was assessed by tumor necrosis factor alpha (TNF-alpha) secretion into the medium. Alloys without LPS, with LPS but without PBS elution, and with LPS and elution were compared with ANOVA and Turkey intervals (alpha=.05).
Results:
Specimens without LPS exposure but with elution caused no detectable TNF-alpha secretion from monocytes. Specimens without elution into PBS caused low-to-moderate TNF-alpha secretion, indicating a possible false-positive result from the alloy conditioning solution used. After LPS exposure but no elution, high levels of TNF-alpha were found. When alloys were eluted for 120 hours after LPS exposure, there was no detectable TNF-alpha released.
Conclusion:
In this in vitro system as in past studies, LPS appeared to adhere to and elute from the alloys. Monocytes were activated initially but not after elution into PBS for 120 hours. Alloy conditioning solutions may also have an artifactual effect on cytokine release.
