The role of oral
bacterial infections including
periodontal disease in the pathogenesis of
rheumatoid arthritis (RA) has gained increasing interest. Among the major periodontal pathogens, Porphyromonas gingivalis has been mostly associated with RA pathogenesis. The aim of this study was to analyze the effect of P. gingivalis total
lipid (TL) fraction and dihydroceramides, as potent
virulence factors, on human primary chondrocytes. Primary chondrocyte cultures were incubated with P. gingivalis phosphoglycerol
dihydroceramide (PG DHC)
lipids, the TL fraction or
phosphoethanolamine dihydroceramide. Cell morphology changes were determined by phase contrast light microscopy. Early and late apoptosis cell analysis was performed by
Annexin-V, active
caspases, and
7-Aminoactinomycin D staining, and examined by flow cytometry, and cell
necrosis was evaluated by
lactate dehydrogenase release.
Procaspase-3 activation was determined by Western blot analysis. Microscopic analysis showed altered cell morphology and cell shrinkage following incubation with P. gingivalis TLs and PG DHC
lipids. Flow cytometry demonstrated an increase of
Annexin-V positive and active
caspases positive chondrocytes after incubation with TL and PG DHC fractions but not after
phosphoethanolamine dihydroceramide (control
lipid) treatment or in untreated control cells. Furthermore, Western blot analysis showed an early cleavage of
procaspase-3 after 1 hr. Significant
lactate dehydrogenase release following incubation with P. gingivalis
lipids was demonstrated. The present data demonstrate that P. gingivalis
lipids promote apoptosis in primary human chondrocytes, and thereby may contribute to the joint damage seen in the pathogenesis of RA.