Molecular damage and responses of oral keratinocyte to hydrogen peroxide

Kuan-Yu Lin,Pei-Wen Wang,Ching-Hung Chung,Tzu-Chueh Wang,Pei-Fang Su,Jheng-Sian Ciou,Dar-Bin Shieh

doi:10.1186/s12903-018-0694-0

Abstract

BackgroundHydrogen peroxide (H2O2)-based tooth bleaching reagents have recently increased in popularity and controversy. H2O2 gel (3%) is used in a Nightguard for vital bleaching; transient tooth sensitivity and oral mucosa irritation have been reported. Genotoxicity and carcinogenicity have also been significant concerns.MethodsWe used primary cultured normal human oral keratinocytes (NHOKs) as an in vitro model to investigate the pathological effects to mitochondria functions on human oral keratinocytes exposed to different doses of H2O2 for different durations.ResultsAn MTT assay showed compromised cell viability at a dose over 5 mM. The treatments induced nuclear DNA damage, measured using a single-cell gel electrophoresis assay. A real-time quantitative polymerase chain reaction showed H2O2 induced significant increase in mitochondrial 4977-bp deletion. Mitochondrial membrane potential and apoptosis assays suggested that oxidative damage defense mechanisms were activated after prolonged exposure to H2O2. Reduced intracellular glutathione was an effective defense against oxidative damage from 5 mM of H2O2.ConclusionOur study suggests the importance for keratinocyte damage of the dose and the duration of the exposure to H2O2 in at-home-bleaching. A treatment dose ≥100 mM directly causes severe cytotoxicity with as little as 15 min of exposure.

Highlights

Hydrogen peroxide (H2O2)-based tooth bleaching reagents have recently increased in popularity and controversy
Nuclear DNA damage and cell cytotoxicity were higher in cells treated with H2O2 Cell viability based on the dose of H2O2 was analyzed by MTT assay, which showed that regardless of the incubation period; the H2O2-treated normal human oral keratinocytes (NHOKs) were > 90% viable when treated with 0.01–1 mM of H2O2
After we exposed NHOKs to H2O2, we comprehensively evaluated the effects on cell viability, DNA damage, cellular defense response to oxidative damage, and apoptosis in the estimated basal cell level exposure dose range of 0.01~100 mM, which is about 1/10 that of the H2O2 in the bleaching gel

Summary

Introduction

Hydrogen peroxide (H2O2)-based tooth bleaching reagents have recently increased in popularity and controversy. H2O2 gel (3%) is used in a Nightguard for vital bleaching; transient tooth sensitivity and oral mucosa irritation have been reported. Normal tooth color is determined by the optical and chromatic properties of dentine and enamel: hue, value, chroma, thickness, texture, and translucency [1]. Both intrinsic and extrinsic factors in dentin or enamel, or in both, can cause tooth discoloration [1,2,3]. The most noteworthy side effects associated with at-home-bleaching are tooth sensitivity and oral mucosa irritation. Safety for exposure to a long-term H2O2 bleaching agent has been a concern in more recent studies [9, 10]. The inappropriate application or abuse of H2O2 during cleaning treatments has other potential adverse effects [13]

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Discussion

Conclusion