Infectious seeds of valve calcification: Exploring the bacterial hypothesis in the pathogenesis of calcific aortic valve disease

Background: Calcific aortic valve disease (CAVD) is a multifactorial condition characterized by progressive leaflet calcification with a potential role for bacterial colonization in its pathogenesis. This study investigates clinical, microbiological and molecular features of calcified versus non-calcified aortic regurgitation (AR) valves. Methods: This is a prospective, observational study, whose primary objective was to compare the occurrence of bacterial detection between CAVD and AR. The secondary objectives included the evaluation of bone-related calcification markers in valves from CAVD and AR patients. Results: We analysed 31 CAVD and 8 AR valves, yielding 111 leaflets (84 calcified, 27 non-calcified). Light microscopy of CAVD leaflets revealed near-complete disruption of the three-layered valve architecture, with calcified masses extending through the leaflets, sparse cellularity and focal micro-angiogenesis; no bacteria were detected by GRAM, PAS or TEM. Enrichment culture detected low-virulence bacteria in 5.95% of CAVD and 4.16% of AR leaflets; 16S rRNA PCR was positive in 22.5% of CAVD and 12.5% of AR cases, with Staphylococcus and Streptococcus spp. predominating. Calcium content was significantly higher in CAVD leaflets (p =.001) and correlated with dyslipidemia (p =.02). Osterix expression was higher in valves with positive microbiological findings (p <.0001), while ALP was increased in CAVD and bicuspid valves regardless of microbial status. Valve interstitial cells from CAVD exhibited spontaneous in vitro calcification, unlike controls. Conclusion: The early osteogenic marker osterix was found to be upregulated in patients whose valves tested positive for microbial DNA, suggesting a potential role for bacteria in driving cellular differentiation towards an osteoblastic phenotype in CAVD.