Korean J Orthod.  2013 Dec;43(6):294-301. 10.4041/kjod.2013.43.6.294.

Role of interleukin-6 in orthodontically induced inflammatory root resorption in humans

• Kunii R
• Yamaguchi
• Tanimoto Y
• Asano M
• Yamada K
• Goseki T
• Kasai K

• KMID: 2273423
• DOI: http://doi.org/10.4041/kjod.2013.43.6.294

Abstract

OBJECTIVE
To determine the interleukin (IL)-6 levels in gingival crevicular fluid (GCF) of patients with severe root resorption after orthodontic treatment and investigate the effects of different static compressive forces (CFs) on IL-6 production by human periodontal ligament (hPDL) cells and the influence of IL-6 on osteoclastic activation from human osteoclastic precursor (hOCP) cells in vitro.
METHODS
IL-6 levels in GCF samples collected from 20 patients (15 and 5 subjects without and with radiographic evidence of severe root resorption, respectively) who had undergone orthodontic treatment were measured by ELISA. The levels of IL-6 mRNA in hPDL cells and IL-6 protein in conditioned medium after the application of different uniform CFs (0, 1.0, 2.0, or 4.0 g/cm2 for up to 72 h) were measured by real-time PCR and ELISA, respectively. Finally, the influence of IL-6 on mature osteoclasts was investigated by using hOCP cells on dentin slices in a pit-formation assay.
RESULTS
Clinically, the IL-6 levels were significantly higher in the resorption group than in the control group. In vitro, IL-6 mRNA expression significantly increased with increasing CF. IL-6 protein secretion also increased in a time- and magnitude-dependent manner. Resorbed areas on dentin slices were significantly greater in the recombinant human IL-6-treated group and group cultured in hPDL cell-conditioned medium with CF application (4.0 g/cm2) than in the group cultured in hPDL cell-conditioned medium without CF application.
CONCLUSIONS
IL-6 may play an important role in inducing or facilitating orthodontically induced inflammatory root resorption.

Keyword

Interleukin-6; Osteo/odontoclastogenesis; Orthodontic force; Root resorption

MeSH Terms

Culture Media, Conditioned
Dentin
Enzyme-Linked Immunosorbent Assay
Gingival Crevicular Fluid
Humans*
Interleukin-6*
Interleukins
Osteoclasts
Periodontal Ligament
Real-Time Polymerase Chain Reaction
RNA, Messenger
Root Resorption*
Culture Media, Conditioned
Interleukin-6
Interleukins
RNA, Messenger

Figure

• 

  Figure 1 Sampling of gingival crevicular fluid from the mesial and distal aspects of the maxillary central incisors.

• 

  Figure 2 Illustration of the method used for uniform compressive force (CF) application in vitro. A confluent layer of cultured human periodontal ligament cells in one well of a six-well plate was compressed continuously by using a glass cylinder containing lead granules. The number of lead granules in the cylinder controlled the magnitude of CF applied.

• 

  Figure 3 Concentrations of interleukin (IL)-6 protein detected by ELISA in gingival crevicular fluid samples from the control and resorption groups. The data represent means ± standard deviation. *p < 0.01 by Mann-Whitney U-test.

• 

  Figure 4 Relative levels of interleukin (IL)-6 mRNA expression determined by real-time PCR in human periodontal ligament cells subjected to different uniform compressive forces (0, 1.0, 2.0, or 4.0 g/cm2) for 24 h. The data represent means ± standard deviation of 4 independent experiments. *p < 0.01 by Mann-Whitney U-test and p < 0.01 by one-way ANOVA.

• 

  Figure 5 Levels of interleukin (IL)-6 protein release determined by ELISA using cultured human periodontal ligament cells subjected to different uniform compressive forces (0, 1.0, 2.0, or 4.0 g/cm2) for up to 72 h. The data represent means ± standard deviation of four independent experiments. *p < 0.01 by Mann-Whitney U-test and p < 0.01 by one-way ANOVA.

• 

  Figure 6 Percent resorbed areas on dentin slices determined by the pit-formation assay using human osteoclastic precursor cells cultured in commercial medium containing recombinant human interleukin (rhIL)-6 or human periodontal ligament (hPDL) cell-conditioned medium without or with uniform compressive force (CF) application (4.0 g). The data represent means ± standard deviation of four independent experiments. *p < 0.01 by Mann-Whitney U-test.

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