Effects of Common H1-Antihistamines on IL-6 and RANKL Expression in Osteoblasts

OBJECTIVE H1-antihistamines are the treatment of choice for prevention and relief of symptoms associated with allergic rhinoconjunctivitis which affects 18.9% of children and 25.7% of adults in the United States. The purpose of this study is to evaluate the expression of RANKL, OPG and IL-6 in human osteoblasts, G-292 osteosarcoma cell line, following treatment with varying concentrations of histamine and common second-generation H1-antihistamines including fexofenadine (Allegra), cetirizine (Zyrtec), and loratadine (Claritin) METHODS In this in vitro study, G-292 cells were cultured in 6-well plates with McCoy’s medium. The cells were treated with histamine at a concentration of 0.01, 0.1, 1 or 10 µM and then incubated for 24- or 6-hours prior to mRNA isolation. mRNA expression of HRH1, RANKL, OPG and IL-6 were measured using quantitative PCR. To compare the effects of antihistamine treatment on G-292 cells, cell cultures were treated with 1 µM of histamine and fexofenadine, cetirizine and loratadine were added at concentrations of 0.01, 0.1, or 1 µM. mRNA expression of RANKL and IL-6 were measured using quantitative PCR. Luminex Milliplex assay was completed on extracted media from the samples to evaluate protein expression of IL-6. Mann-Whitney U Test was completed to determine statistical significance (P value < 0.05). RESULTS Stimulation of G-292 cells with varying concentrations of histamine does not result in a statistically significant change in mRNA expression of HRH1, RANKL or OPG at both treatment times of 6- and 24-hours. The increased expression of IL-6 is statistically significant at higher concentrations of 10 µM after incubation at 24-hours and 1 and 10 µM at 6-hours. The results suggest that there is a positive correlation between histamine concentration and IL-6 expression. Treatment of G-292 cells with histamine and different types and concentrations of fexofenadine, cetirizine and loratadine did not result in statistically significant changes in RANKL mRNA expression. The results suggest that there is a negative correlation between antihistamine concentration and IL-6 mRNA expression for fexofenadine and cetirizine. At the concentration closest to Cmax for each antihistamine, there is a statistically significant decrease in IL-6 expression for fexofenadine and cetirizine, but no change is observed for loratadine. The data from the Milliplex assay evaluating protein expression of IL-6 supports the qPCR results. CONCLUSIONS The results from this in vitro study suggest that loratadine may be a better option compared to fexofenadine and cetirizine with regards to maintaining the rate of orthodontic tooth movement since there were no significant changes in IL-6 expression noted between the treated cells and the positive control.