Structures and biological activities of novel phosphatidylethanolamine lipids of Porphyromonas gingivalis

Abstract

The Gram-negative periodontal pathogen Porphyromonas gingivalis synthesizes several classes of novel phosphorylated complex lipids, including the recently characterized phosphorylated dihydroceramides. These sphingolipids promote the interleukin-1 (IL-1)-mediated secretion of inflammatory mediators from fibroblasts, including prostaglandin E 2 and 6-keto prostaglandin F 2a , and alter gingival fibroblast morphology in culture. This report demonstrates that one additional class of phosphorylated complex lipids of P. gingivalis promotes IL-1-mediated secretory responses and morphological changes in cultured fibroblasts. Structural characterization identified the new phospholipid class as 1,2-diacyl phosphatidylethanolamine, which substituted predominantly with isobranched C 15:0 and C 13:0 fatty acids. The isobranched fatty acids, rather than unbranched fatty acids, and the phosphoethanolamine head group were identified as the essential structural elements required for the promotion of IL-1-mediated secretory responses. These structural components are also observed in specific phosphorylated sphingolipids of P. gingivalis and likely contribute to the biological activity of these substances, in addition to the phosphatidylethanolamine lipids described in this report. Supplementary key words interleukin-1b . prostaglandin E 2 . gingival fibroblast . long-chain base . gas chromatography-mass spectrometry . electrospray tandem mass spectrometry Porphyromonas gingivalis is a Gram-negative anaerobic organism that resides in the gingival sulcus surrounding the teeth, particularly at sites of chronic inflammatory or destructive periodontal diseases. A recent report demonstrated that P. gingivalis synthesizes two major phosphorylated dihydroceramides, one of which potentiates interleukin-1 (IL-1)-mediated prostaglandin E 2 (PGE 2 ) secretory responses in gingival fibroblasts and markedly alters gingival fibroblast morphology in culture (1). These lipids are also recovered from diseased tooth roots (2), and indirect evidence indicates that the phosphoglycerol dihydroceramide lipids are the primary ceramides of P. gingivalis recovered in gingival tissues at disease sites (3). Therefore, P. gingivalis produces biologically active complex lipids that are recovered at periodontal disease sites.Recent investigations have demonstrated that P. gingivalis produces one additional class of phospholipids that also demonstrate substantial capacity to promote IL-1b-mediated prostaglandin secretion from gingival fibroblasts. However, this lipid class is not a sphingolipid, because it lacks amide-linked fatty acid. This report describes the structural characterization of this new phospholipid class and demonstrates the capacity of this lipid to promote prostaglandin secretory responses and morphological changes in cultured gingival fibroblasts. Lastly, using a structural analog as a control for the bacterial lipid fraction as well as the hydrolysis products of this bacterial lipid class, this report defines the critical structura...

Macrophage Depletion Abates Porphyromonas gingivalis–Induced Alveolar Bone Resorption in Mice

“…gingivalis infection enhanced the secretion of the cytokines IL-1b, IL-6, IL-12 (p70), TNF-a, G-CSF, and GM-CSF, in addition to the chemokines eotaxin, MCP-1, MIP-1a, and MIP-b from macrophages, reflecting a proinflammatory response. These cytokines and chemokines are reported to act as proinflammatory mediators, induce monocytes to migrate from the bloodstream into gingival tissue, and act synergistically to further stimulate proinflammatory cytokine production (22,25,31,33,50,54,100). In addition, IL-10, which is produced primarily by macrophages, was detected among the vast array of cytokines induced by P. gingivalis infection.…”

“…In addition to P. gingivalis proteins and LPS penetrating gingival tissue, P. gingivalis phosphorylated dihydoceramide lipids have been isolated from gingival tissue and subgingival plaque of chronic periodontitis patients (52)(53)(54). Whole P. gingivalis cells and certain components, including the RgpA-Kgp complexes and lipids, induce secretion of a number of proinflammatory cytokines from epithelial and fibroblast cells in vitro, such as IL-1, IL-6, IL-8, PGE 2 , macrophage chemoattractant protein (MCP)-1a, and ICAM-1 (50,54,55). The elevation in levels of the proinflammatory cytokines IL-1, IL-6, IL-8, IL-12, and TNF-a is commonly found in diseased gingival tissue of chronic periodontitis (19)(20)(21)30).…”

Unique Lipids from a Common Human Bacterium Represent a New Class of Toll-Like Receptor 2 Ligands Capable of Enhancing Autoimmunity

“…Having previously demonstrated that bacterial phosphorylated dihydroceramides promote inflammatory responses in human fibroblasts in vitro, 4,5 we wanted to characterize the functional effects of these lipids in autoimmunity and used the murine model of multiple sclerosis, EAE. EAE was induced in female C57BL/6 mice and these mice were also injected intraperitoneally (i.p.)…”

“…We have previously characterized uniquely structured, non-lipopolysaccharide (LPS), phosphorylated sphingolipid classes, termed phosphorylated dihydroceramides, produced by this organism. We reported that these lipids promote inflammatory responses in human fibroblasts in vitro, 4,5 and in recent preliminary studies (F.C. Nichols, unpublished) we have successfully recovered these lipids from surgically removed human carotid atheroma.…”

“…Phosphorylated dihydroceramides have unique structural components that are not seen in mammalian lipids and that are important in mediating the observed in vitro inflammatory effects. 5 In addition to P. gingivalis, other periodontal organisms and at least one GI tract organism, Bacteroides fragilis, are known to produce simSupported by grants from the National Multiple Sclerosis Society (RG4070-A-6 to R.B.C.) NIH Training Grant (T32AI007080 to W.J.H.)…”