Salivary Hemoglobin Protects against Erosive Tooth Wear in Gastric Reflux Patients

Objective: Saliva is the most important biological factor to protect against erosive tooth wear (ETW). Gastroesophageal reflux disease (GERD) patients have an increased risk of ETW due to the frequent presence of intrinsic acids in the oral cavity. Remarkably, not all GERD patients suffer from ETW, which might be due to differences in the composition of the saliva. Methods: This study compared the proteomic profile of saliva in patients (1) with GERD and ETW (basic erosive wear examination, BEWE, score >= 9; GE group) and (2) with GERD without ETW (BEWE = 0; GNE group) using shotgun label-free quantitative proteomic analysis nLC-ESI-MS/MS. The ability of hemoglobin (Hb) to protect against initial enamel erosion caused by a daily 10-s immersion of enamel specimens in 0.01 M HCl (pH 2.3) for 3 days was evaluated in vitro for proof of concept. Surface hardness change was used as response variable. Results: The differential expression of Hb subunits was significantly increased in the GNE group versus the GE group, in particular the Hb alpha-subunit that showed a >22-fold increase. Expressions of serum albumin (4.5-fold) and isoforms of cytoskeletal keratin type II (>3-fold) were also increased in the GNE group. Proteinase inhibitors, such as alpha(1)-antitrypsin and alpha(2)-macroglobulin, were only identified in the GNE group. In vitro, Hb (1.0 and 4.0 mg/mL) significantly reduced initial enamel erosion compared to a negative control after 3 days. Conclusions: Our results indicate that many proteins, with special emphasis on Hb, may be involved in the resistance of GERD patients to the occurrence of ETW. These proteins may be candidates for inclusion in dental products to protect against ETW.