Faculty Bibliography

Short chain fatty acids (SCFA) are metabolic by-products of anaerobic bacteria present in the periodontal pocket. We examined the effect of SCFA on cultured human periodontal ligament fibroblasts (PDLF). PDLF were challenged with propionate, butyrate and succinate. A dose dependent inhibition of fibroblast adhesion and proliferation was observed. These results indicate that SCFA present in the periodontal pockets could interfere with periodontal wound healing and repair in patients affected by periodontal infections.

The results reported here indicate that the short-chain carboxylic acids acetate and propionate stimulate cytoplasmic calcium mobilization in human polymorphonuclear leukocytes, while butyrate and lactate do not. Together with the results of previous work, this indicates that there are at least three classes of short-chain carboxylic acids: those which can alter only cytoplasmic pH (e.g., lactic acid), those which can alter cytoplasmic pH and actin (e.g., butyric acid), and those which can alter cytoplasmic pH, actin, and calcium (e.g., acetate and propionate).

Short-chain carboxylic acids (SCCA) are metabolic by-products of bacterial pathogens which can alter cytoplasmic pH and inhibit a variety of polymorphonuclear leukocyte (PMN) motile functions. Since cytoskeletal F-actin alterations are central to PMN mobility, in this study we examined the effects of SCCA on cytoskeletal F-actin. Initially, we tested nine SCCA (formate, acetate, propionate, butyrate, valerate, caproate, lactate, succinate, and isobutyrate). We document here that while eight altered cytoplasmic pH, only six altered cytoskeletal F-actin. We then selected one SCCA that altered both F-actin and cytoplasmic pH (propionate) and one SCCA that altered only cytoplasmic pH (lactate) for further study. Propionate, but not lactate, caused an irregular cell shape and F-actin distribution. Furthermore, propionate, but not lactate, inhibited formylmethionyl-leucyl-phenylalanine (fMLP)-stimulated PMN polarization, F-actin localization, and cytoplasmic pH oscillation. Propionate-induced changes in cytoskeletal F-actin and cytoplasmic acidification were not affected by the fMLP receptor antagonist N-t-BOC-1-methionyl-1-leucyl-1-phenylalanine; however, alkalinization was affected. Pertussis toxin treatment completely inhibited propionate-induced changes in F-actin but had no effect on propionate-induced cytoplasmic pH oscillation. These results indicate that propionate (i) bypasses the fMLP receptor and G protein(s) to induce cytoplasmic pH oscillation, (ii) operates through G protein(s) to induce actin oscillation, cell shape changes (to irregular), and F-actin localization, and (iii) inhibits fMLP-stimulated cytoplasmic pH and actin oscillation, PMN polarization, and F-actin localization.

Ammonium, a weak base produced as a metabolic by-product of urea metabolism by bacterial pathogens, inhibits a variety of motile polymorphonuclear leukocyte (PMN) functions. It was initially assumed that the mechanism of leukocyte inhibition was due to cytoplasmic alkalinization. However, while it is clear that ammonium can effect cytoplasmic alkalinization, current data indicate that alterations in chemotaxis, degranulation, and receptor recycling occur independently of cytoplasmic alkalinization. Since these are motility-related events, we examined the possibility that alterations in cytoskeletal actin may account for the effects of ammonium on PMN function. The results indicate that ammonium can inhibit degranulation, decrease cytoskeletal actin, and increase actin depolymerization rates. These findings are supported by five lines of evidence. First, formylmethionyl-leucyl-phenylalanine (fMLP)-induced elastase release was inhibited by 85% +/- 3% in the presence of ammonium, and ammonium by itself did not stimulate elastase release. Second, ammonium treatment of resting PMNs caused a rapid 38% +/- 6% decrease in cytoskeletal actin. Third, ammonium treatment accelerated the fMLP-induced depolymerization phase of the cytoskeletal actin transient by 150% +/- 12%. Fourth, in resting PMNs treated with cytochalasin B or D, ammonium induced a 21% +/- 4% and a 25% +/- 5% decrease in cytoskeletal actin, respectively. Conversely, ammonium did not affect the ability of the cytochalasins to inhibit an fMLP-induced cytoskeletal actin transient. Fifth, pertussis toxin treatment of neutrophils did not affect the ammonium-stimulated decrease in cytoskeletal actin. These results suggest that ammonium can inhibit neutrophil function by altering cytoskeletal actin and therefore provide new information regarding potential pathogenic mechanisms for bacterial pathogens.

The effects of short chain carboxylic acids (SCCA), namely succinic, butyric, and iso-butyric, on neutrophil metabolic activation were assessed. SCCA induced a significant decrease in O2.- recovery and chemiluminescent response in neutrophils activated with the diacylglycerol analog tetradecanoyl-phorbol-acetate (TPA). SCCA did not alter O2 consumption, H2O2 production, or the calorimetrically determined energy expenditure occurring during the metabolic burst. SCCA also induced a significant acidification of intracellular pH (pHi). These results are consistent with an increased divalent versus univalent O2 reduction performed by the NADPH oxidase at a more acidic intracellular pH.

Cytoplasmic alkalinization has received considerable attention as a regulatory event In cell growth, transformation and signal transduction (Busa, W.B. (1986) Annu. Rev. Physiol. 48, 389-402 and Moolenar, W.H. (1986) Annu. Rev. Physiol. 48, 363-376). In contrast the current paper presents evidence for the role of an early cytoplasmic acidification, during signal transduction in the polymorphonuclear leukocyte (PMN). Following PMN stimulation with a chemotactic peptide, there is a significant decrease in cytoplasmic pH concomitant with a dramatic increase in cytoskeletal actin. The data indicate that this drop in pHi is necessary, but not sufficient, for signal transduction leading to cytoskeletal reorganization in these cells.