Buccal cells show reduced mitochondrial complex i expression in Brugada syndrome

Introduction Brugada syndrome (BrS) is an inherited arrhythmia syndrome associated with an increased risk of sudden cardiac death (SCD). Pathogenic variants in SCN5A, which encodes the α-subunit of the cardiac sodium channel Nav1.5, represent the most common genetic substrate. However, this accounts for only 20% of cases, leaving most patients without a defined molecular diagnosis. The absence of reliable validated tissue or circulating biomarkers limits diagnostic precision. Buccal smears have recently emerged as a risk-free, non-invasive surrogate for myocardial tissue in arrhythmogenic cardiomyopathy. Aim We aimed to identify novel biomarkers and dysregulated pathways in BrS buccal cells. Methods Buccal cell suspensions from 2 BrS patients and 2 age-matched controls underwent subcellular proteome fractionation followed by quantitative mass spectrometry (MS). Both patients presented with a spontaneous type 1 ECG pattern and had ICDs implanted. One patient (no variant identified) manifested with syncope, while the other patient (SCN5A variant identified) manifested with cardiac arrest. Buccal smears from 5 BrS patients and 9 age-matched controls were then analysed by immunocytochemistry (ICC) and confocal microscopy to validate candidate biomarkers identified by MS-based pathway enrichment. All the BrS patients had a spontaneous type 1 ECG pattern although none had an SCN5A variant. Results MS revealed dysregulation of the respiratory chain complex I (beta subunit) mitochondrial pathway. The most affected protein within the pathway was NADH dehydrogenase (ubiquinone) 1 beta subcomplex subunit 8 (NDUFB8), which was selected for validation. Immunostaining was optimized to yield a binary outcome; presence versus near/total absence of NDUFB8 in buccal smears. In control buccal smears, NDUFB8 was strongly localized to the cytoplasm. However, in buccal smears obtained from BrS patients, NDUFB8 expression was near absent in 4/5 (80%) of cases (Figure 1). Conclusions Our results indicate reduced mitochondrial Complex I expression in buccal cells from BrS patients. These findings implicate mitochondrial dysfunction and metabolic remodelling as potential contributors to disease pathogenesis. Mitochondrial ROS has previously been shown to downregulate cardiac Nav1.5. Further studies are required to define the mechanistic and clinical implications of this observation.