MERC Proteins in Saliva and GCF in Periodontal Disease (ELISA Study)

Expression of Mitochondria-Endoplasmic Reticulum Contact Proteins in Saliva and Gingival Crevicular Fluid in Patients With Periodontal Disease: ELISA and Calcium Analysis

This observational cross-sectional study investigates the levels of mitochondria-endoplasmic reticulum contact site (MERC) proteins in saliva and gingival crevicular fluid (GCF) of individuals with different periodontal conditions. MERCs are specialized regions where mitochondria and the endoplasmic reticulum physically connect, and they play important roles in calcium signaling, oxidative stress regulation, and cell death (apoptosis). Disruption of these contact sites has been linked to inflammatory diseases, including periodontal disease.

The study includes 48 systemically healthy, non-smoking adults divided into three groups: periodontally healthy (n=16), gingivitis (n=16), and Stage III Grade B periodontitis (n=16). Five MERC-associated proteins (VAPB, PTPIP51, IP3R, GRP75, and VDAC) are measured in GCF and saliva samples using ELISA. Additionally, caspase-3 (a marker of apoptosis), reactive oxygen species (a marker of oxidative stress), and calcium levels are measured to explore relationships between MERC proteins and key cellular processes involved in periodontal tissue destruction.

The purpose of this study is to determine whether MERC protein levels differ across periodontal conditions and to evaluate their associations with clinical periodontal parameters, oxidative stress, calcium metabolism, and apoptosis.

Mitochondria-endoplasmic reticulum contact sites (MERCs) are specialized structural domains that physically link mitochondria and the endoplasmic reticulum. These contact sites are enriched with functional proteins that coordinate calcium transfer between the two organelles, regulate lipid metabolism, modulate oxidative stress responses, and control apoptotic signaling pathways. Key MERC-associated proteins include VAPB (vesicle-associated membrane protein-associated protein B), PTPIP51 (protein tyrosine phosphatase-interacting protein 51), IP3R (inositol 1,4,5-trisphosphate receptor), GRP75 (glucose-regulated protein 75), and VDAC (voltage-dependent anion channel). The IP3R-GRP75-VDAC complex facilitates calcium transfer from the ER to mitochondria, while the VAPB-PTPIP51 complex modulates this process and influences ATP production and autophagy. Disruption of MERC homeostasis has been implicated in neurodegenerative diseases, metabolic disorders, and periodontal disease. Periodontal disease is a chronic inflammatory condition driven by microbial dental plaque, leading to destruction of periodontal tissues and alveolar bone. Previous studies demonstrated dysregulation of MERC-related gene expression (MFN1, IP3R, GRP75, PINK1, SIGMAR1) in human gingival fibroblasts exposed to Porphyromonas gingivalis and Fusobacterium nucleatum.

The present study measures the concentrations and total amounts of five MERC proteins-VAPB, PTPIP51, IP3R, GRP75, and VDAC-together with caspase-3 (an apoptosis marker), reactive oxygen species (ROS, an oxidative stress marker), and calcium levels in gingival crevicular fluid (GCF) and unstimulated whole saliva obtained from systemically healthy, non-smoking participants. Participants are classified into three groups according to the 2017 World Workshop classification: periodontally healthy (n=16), gingivitis (n=16), and Stage III Grade B periodontitis (n=16), with equal sex distribution (8 males and 8 females per group). GCF samples are collected from three single-rooted teeth per participant using standardized paper strips (Periopaper), with absorbed volume measured using a Periotron 8000. Saliva samples are collected using the passive drooling method. Biomarker levels are quantified using commercially available ELISA kits. Clinical periodontal parameters recorded include Plaque Index (PI), Gingival Index (GI), Probing Depth (PD), Bleeding on Probing (BOP%), and Clinical Attachment Level (CAL). Correlations between biomarker levels and clinical parameters are analyzed. Receiver operating characteristic (ROC) curve analysis is performed to evaluate the diagnostic potential of the biomarkers.

Inclusion Criteria:

• Systemically healthy individuals aged 18-65 years
• Non-smokers or smoking cessation more than 5 years ago
• Healthy group: No history of periodontal disease, ≥20 teeth, probing depth (PD) ≤3 mm at all sites, bleeding on probing (BOP) <10%, radiographic CEJ-to-alveolar bone crest distance ≤3 mm in ≥95% of teeth
• Gingivitis group: No history of periodontal disease, ≥20 teeth, PD ≤3 mm at all sites, BOP ≥30%, radiographic CEJ-to-alveolar bone crest distance ≤3 mm in ≥95% of teeth
• Periodontitis group: ≥15 teeth, >30% of teeth affected by periodontal disease, PD ≥6 mm, clinical attachment loss (CAL) ≥5 mm, vertical bone loss ≥3 mm, Class II or III furcation involvement, radiographic alveolar bone loss extending to the middle third or beyond (≥33%), bone loss-to-age ratio between 0.25 and 1.00

Exclusion Criteria:

• Periodontal treatment or antibiotic use within the past 6 months
• Fewer than 20 teeth (excluding third molars)
• Presence of any systemic disease
• Current smoking or cessation within the past 5 years
• Use of immunosuppressive medication
• Alcohol consumption
• Regular medication use
• Pregnancy or lactation
• Need for antibiotic prophylaxis prior to dental procedures
• Prosthetic restorations on the teeth selected for sampling