Histological changes and some in vitro biological activities induced by lipopolysaccharide from Bacteroides gingivalis

Pathological and Therapeutic Approach to Endotoxin-Secreting Bacteria Involved in Periodontal Disease

It is widely recognized that periodontal disease is an inflammatory entity of infectious origin, in which the immune activation of the host leads to the destruction of the supporting tissues of the tooth. Periodontal pathogenic bacteria like Porphyromonas gingivalis, that belongs to the complex net of oral microflora, exhibits a toxicogenic potential by releasing endotoxins, which are the lipopolysaccharide component (LPS) available in the outer cell wall of Gram-negative bacteria. Endotoxins are released into the tissues causing damage after the cell is lysed. There are three well-defined regions in the LPS: one of them, the lipid A, has a lipidic nature, and the other two, the Core and the O-antigen, have a glycosidic nature, all of them with independent and synergistic functions. Lipid A is the "bioactive center" of LPS, responsible for its toxicity, and shows great variability along bacteria. In general, endotoxins have specific receptors at the cells, causing a wide immunoinflammatory response by inducing the release of pro-inflammatory cytokines and the production of matrix metalloproteinases. This response is not coordinated, favoring the dissemination of LPS through blood vessels, as well as binding mainly to Toll-like receptor 4 (TLR4) expressed in the host cells, leading to the destruction of the tissues and the detrimental effect in some systemic pathologies. Lipid A can also act as a TLRs antagonist eliciting immune deregulation. Although bacterial endotoxins have been extensively studied clinically and in a laboratory, their effects on the oral cavity and particularly on periodontium deserve special attention since they affect the connective tissue that supports the tooth, and can be linked to advanced medical conditions. This review addresses the distribution of endotoxins associated with periodontal pathogenic bacteria and its relationship with systemic diseases, as well as the effect of some therapeutic alternatives.

Histological effects and pharmacokinetics of lipopolysaccharide derived from Porphyromonas gingivalis on rat maxilla and liver concerning with progression into non-alcoholic steatohepatitis

BACKGROUND

Non-alcoholic steatohepatitis (NASH) is one of the chronic liver diseases that can develop into hepatocirrhosis. The purpose of the present study was to investigate the impact of lipopolysaccharide (LPS) from Porphyromonas gingivalis (P. gingivalis) on NASH onset, and to determine the biodistribution of double-radiolabeled LPS (R-LPS) biosynthesized in P. gingivalis.

METHODS

Rats fed a basal diet (BD) or a high-fat diet (HD) were injected with P. gingivalis-LPS or R-LPS into the palatine gingiva around the right maxillary first molar, and were classified into the following 4 groups: BD/LPS (-), BD/LPS (+), HD/LPS (-), and HD/LPS (+) or 2 groups: BD/R-LPS and HD/R-LPS.

RESULTS

Inflammation in the gingiva of the LPS (+) groups progressed significantly more than the LPS (-) groups. Furthermore, in the HD/LPS (+) liver, histologic analysis confirmed the presence of NASH, characterized by large fat droplets, ballooning degeneration, and infiltration of inflammatory cells. When ³ H, ¹⁴ C-R-LPS was injected into the palatine gingiva, radioactivity in the right palatal mucosa of HD/R-LPS rats was the highest in comparison with other regions and was significantly elevated after 24 hours compared to BD/R-LPS rats. Autoradiographic analysis of the maxilla showed distributions from the palatal mucosa to the hard palate and the interdental region. Radioactivity in organs of both BD/R-LPS and HD/R-LPS rats were mostly localized to the liver even after 24 hours.

CONCLUSION

The present study suggests that the transfer of P. gingivalis-LPS from the oral cavity to the liver plays an important role in disease exacerbation of NASH.

Adjuvant activity of naturally occurring monophosphoryl lipopolysaccharide preparations from mucosa-associated bacteria

Natural heterogeneity in the structure of the lipid A portion of lipopolysaccharide (LPS) produces differential effects on the innate immune response. Gram-negative bacterial species produce LPS structures that differ from the classic endotoxic LPS structures. These differences include hypoacylation and hypophosphorylation of the diglucosamine backbone, both differences known to decrease LPS toxicity. The effect of decreased toxicity on the adjuvant properties of many of these LPS structures has not been fully explored. Here we demonstrate that two naturally produced forms of monophosphorylated LPS, from the mucosa-associated bacteria Bacteroides thetaiotaomicron and Prevotella intermedia, function as immunological adjuvants for antigen-specific immune responses. Each form of mucosal LPS increased vaccination-initiated antigen-specific antibody titers in both quantity and quality when given simultaneously with vaccine antigen preparations. Interestingly, adjuvant effects on initial T cell clonal expansion were selective for CD4 T cells. No significant increase in CD8 T cell expansion was detected. MyD88/Toll-like receptor 4 (TLR4) and TRIF/TLR4 signaling pathways showed equally decreased signaling with the LPS forms studied here as with endotoxic LPS or detoxified monophosphorylated lipid A (MPLA). Natural monophosphorylated LPS from mucosa-associated bacteria functions as a weak but effective adjuvant for specific immune responses, with preferential effects on antibody and CD4 T cell responses over CD8 T cell responses.

Lipopolysaccharide heterogeneity: innate host responses to bacterial modification of lipid a structure

The innate host response system is composed of various mechanisms designed to detect and facilitate host responses to microbial components, such as lipopolysaccharides (LPS). To enable this to occur, innate systems contain multiple pattern recognition receptors (i.e., LBP, CD14, and TLRs), which identify certain features within bacterial LPS that are foreign to the host, as well as essential and uniquely specific for bacteria. Innate host identification of unique bacterial components or patterns, therefore, relies on the inability of bacteria to alter these essential or critical components dramatically. Historically, LPS have been viewed as essential outer-membrane molecules containing both a highly variable outer region (O-segment) as well as a relatively conserved inner region (lipid A). However, over the last decade, new evidence has emerged, revealing that increased natural diversity or heterogeneity within specific components of LPS, such as lipid A-resulting in minor to moderate changes in lipid A structure-can produce dramatic host responses. Therefore, examples of natural lipid A heterogeneity, and the mechanisms that control it, represent a novel approach in which bacteria modulate host responses and may thereby confer specific advantages to certain bacterial species under changing environmental host conditions.