Effects of bleaching on osteoclast activity and their modulation by osteostatin and fibroblast growth factor 2

Six-month Follow-up of the Effect of Nonvital Bleaching on IL-1β and RANK-L: A Randomized Clinical Trial

Objectives:

It has been reported that bleaching generates an increase in the activity of osteoclasts in vitro. We quantified the RANK-L and IL-1β biomarkers in a double-blind, randomized clinical trial evaluating the in vivo effect of hydrogen peroxide (35%) and peroxide carbamide (37%) six months after whitening.

Methods and Materials:

Fifty volunteers participated, each with color change in a nonvital tooth. Fifty teeth were randomly divided into two groups (n=25), and the teeth were bleached using either 35% hydrogen peroxide (G1) or 37% carbamide peroxide (G2). Intracoronal bleaching was carried out by a technical “walking bleach” over four sessions. Gingival crevicular fluid samples were collected and used to quantify the IL-1β and RANK-L secreted levels. Samples of six periodontal sites (three vestibular and three palatal) were collected for up to six months (at the beginning of the study [baseline] and at one week, one month, and six months posttreatment). The color change was visually monitored using the Vita Bleached Guide (ΔSGU).

Results:

Comparing each time to baseline assessment, a significant increase in the levels of IL-1β and RANK-L across time points was detected (p<0.05). The color change was 4 in G1 and G2, and a statistically significant difference (p<0.05) was found at the month time point between the groups. Using the Spearman test, a strong correlation (>0.8) between the IL-1β and RANK-L levels in both groups at all time points was detected.

Conclusions:

Nonvital bleaching using a technical walking bleach induces an increase in the IL-1β and RANKL production in periodontal tissues, which persists for six months after treatment. Both biomarkers were highly correlated in both groups and at all time points.

High glucose alters the secretome of mechanically stimulated osteocyte-like cells affecting osteoclast precursor recruitment and differentiation

Diabetes mellitus (DM) induces bone deterioration, while mechanical stimulation promotes osteocyte-driven bone formation. We aimed to evaluate the interaction of acute exposure (24 h) to high glucose (HG) with both the pro-survival effect conferred to osteocytic MLO-Y4 cells and osteoblastic MC3T3-E1 cells by mechanical stimulation and the interaction of these cells with osteoclast precursor RAW264.7 cells. We found that 24 h of HG (25 mM) pre-exposure prevented both cell survival and ERK and β-catenin nuclear translocation upon mechanical stimulation by fluid flow (FF) (10 min) in both MLO-Y4 and MC3T3-E1 cells. However, migration of RAW 264.7 cells was inhibited by MLO-Y4 cell-conditioned medium (CM), but not by MC3T3-E1 cell-CM, with HG or FF. This inhibitory effect was associated with consistent changes in VEGF, RANTES, MIP-1α, MIP-1β MCP-1, and GM-CSF in MLO-Y4 cell-CM. RAW264.7 proliferation was inhibited by MLO-Y4 CM under static or HG conditions, but it increased by FF-CM with or without HG. In addition, both FF and HG abrogated the capacity of RAW 264.7 cells to differentiate into osteoclasts, but in a different manner. Thus, HG-CM in static condition allowed formation of osteoclast-like cells, which were unable to resorb hydroxyapatite. In contrast, FF-CM prevented osteoclastogenesis even in HG condition. Moreover, HG did not affect basal RANKL or IL-6 secretion or their inhibition induced by FF in MLO-Y4 cells. In conclusion, this in vitro study demonstrates that HG exerts disparate effects on osteocyte mechanotransduction, and provides a novel mechanism by which DM disturbs skeletal metabolism through altered osteocyte-osteoclast communication.