Cytokine expression profile in the bone-anchored hearing system: 12-week results from a prospective randomized, controlled study

Abstract

Objective: To study the effect of implanting the percutaneous bone-anchored hearing system (BAHS) itself and inflammation of the peri-abutment skin warrant clarification. In this study, we aimed to acquire further insight into the immune responses related to BAHS surgery and peri-implant skin inflammation.

Materials and methods: During surgery and 12 weeks post-implantation, skin biopsies were obtained. If applicable, additional biopsies were taken during cases of inflammation. The mRNA expression of IL-1β, IL-6, IL-8, TNFα, IL-17, IL-10, TGF-ß, MIP-1α, MMP-9, TIMP-1, COL1α1, VEGF-A, FGF-2 TLR-2, and TLR-4 was quantified using qRT-PCR.

Results: Thirty-five patients agreed to the surgery and 12-week biopsy. Twenty-two patients had mRNA of sufficient quality for analysis. Ten were fitted with a BAHS using the minimally invasive Ponto surgery technique. Twelve were fitted with a BAHS using the linear incision technique with soft-tissue preservation. Five biopsies were obtained during episodes of inflammation. The post-implantation mRNA expression of IL-1β (P = .002), IL-8 (P = .003), MMP9 (P = .005), TIMP-1 (P = .002), and COL1α1 (P < .001) was significantly up-regulated. IL-6 (P = .009) and FGF-2 (P = .004) mRNA expression was significantly down-regulated after implantation. Within patients, no difference between post-implantation mRNA expression (at 12 weeks) and when inflammation was observed. Between patients, the expression of IL-1β (P = .015) and IL-17 (P = .02) was higher during cases of inflammation compared with patients who had no inflammation at 12-week follow-up.

Conclusions: As part of a randomized, prospective, clinical trial, the present study reports the molecular profile of selected cytokines in the soft tissue around BAHS. Within the limit of this study, the results showed that 12 weeks after BAHS implantation the gene expression of some inflammatory cytokines (IL-8 and IL-1β) is still relatively high compared with the baseline, steady-state, expression. The up-regulation of anabolic (COL1α1) and tissue-remodeling (MMP-9 and TIMP1) genes indicates an ongoing remodeling process after 12 weeks of implantation. The results suggest that IL-1β, IL-17, and TNF-α may be interesting markers associated with inflammation.

Keywords: BAHA; BAHS; Holgers index; bone anchored hearing system; cytokines; inflammation.