Short‐Chain Carboxylic Acids Produced by Gram‐Negative Anaerobic Bacteria Can Accelerate or Delay Polymorphonuclear Leukocyte Apoptosis in Vitro

Background: Short‐chain carboxylic acids (SCCA) are metabolic byproducts of anaerobic subgingival bacteria associated with human periodontal disease. We examined the effect of 4 SCCA (butyric, propionic, succinic, and lactic acids) on human polymorphonuclear leukocyte (PMN) apoptosis over the range of concentrations (1 to 30 mM) found in the diseased periodontium. Methods: PMN suspensions were incubated at 37°C with medium alone (control) or one of the 4 SCCA at concentrations of 1, 5, or 30 mM. Aliquots were withdrawn hourly to assess apoptosis and viability by fluorescence microscopy. Results: Relative to untreated controls, PMN incubated for at least 5 hours with 1 mM butyric or propionic acids exhibited significant delays in apoptosis ( P <0.05), while those incubated with succinic or lactic acids exhibited no significant differences from controls ( P >0.05). At a concentration of 5 mM, propionic, succinic, and lactic acids had little effect on apoptosis ( P >0.05), but butyric acid significantly accelerated apoptotic changes ( P <0.05). At 30 mM, all SCCA except lactic acid significantly accelerated apoptosis ( P <0.05). Incubation with SCCA did not adversely affect cell viability (typically >98%). Lysates from PMN incubated 6 hours with 30 mM butyric or propionic acids contained significantly more caspase‐3 activity than lysates from untreated control PMN ( P <0.05). Moreover, pretreatment with a specific inhibitor of caspase‐3 blocked acceleration of PMN apoptosis by butyric or propionic acids ( P <0.05). Conclusion: Low concentrations of butyric or propionic acids delay PMN apoptosis and extend their functional lifespan, while higher concentrations accelerate apoptosis through a mechanism that appears to involve caspase‐3. J Periodontol 2001;72:1059‐1063.