Salomon Amar

Macrophage polarization: an opportunity for improved outcomes in biomaterials and regenerative medicine.

The host response to biomaterials has been studied for decades. Largely, the interaction of host immune cells, macrophages in particular, with implanted materials has been considered to be a precursor to granulation tissue formation, the classic foreign body reaction, and eventual encapsulation with associated negative impacts upon device functionality. However, more recently, it has been shown that macrophages, depending upon context dependent polarization profiles, are capable of affecting both detrimental and beneficial outcomes in a number of disease processes and in tissue remodeling following injury. Herein, the diverse roles played by macrophages in these processes are discussed in addition to the potential manipulation of macrophage effector mechanisms as a strategy for promoting site-appropriate and constructive tissue remodeling as opposed to deleterious persistent inflammation and scar tissue formation.

Periodontal Disease Is Associated With Brachial Artery Endothelial Dysfunction and Systemic Inflammation

Objective—The purpose of this study was to determine whether periodontal disease is associated with endothelial dysfunction and systemic inflammation. Epidemiological studies suggest that severe periodontal disease is associated with increased cardiovascular disease risk, but the mechanisms remain unknown. Methods and Results—We assessed flow-mediated dilation and nitroglycerin-mediated dilation of the brachial artery using vascular ultrasound in 26 subjects with advanced periodontal disease and 29 control subjects. The groups were matched for age and sex, and patients with hypercholesterolemia, diabetes mellitus, hypertension, and history of cigarette smoking were excluded. We also examined serum levels of C-reactive protein using an established high-sensitivity method. Subjects with advanced periodontal disease had lower flow-mediated dilation compared with control patients (7.8±4.6% versus 11.7±5.3%, P =0.005). Nitroglycerin-mediated dilation was equivalent in the two groups. Subjects with advanced periodontitis exhibited higher serum levels of high-sensitivity C-reactive protein compared with healthy controls patients (2.3±2.3 versus 1.0±1.0 mg/L, P =0.03). Conclusions—Subjects with advanced periodontal disease exhibit endothelial dysfunction and evidence of systemic inflammation, possibly placing them at increased risk for cardiovascular disease.

Periodontal disease and systemic conditions: a bidirectional relationship

For decades, physicians and dentists have paid close attention to their own respective fields, specializing in medicine pertaining to the body and the oral cavity, respectively. However, recent findings have strongly suggested that oral health may be indicative of systemic health. Currently, this gap between allopathic medicine and dental medicine is quickly closing, due to significant findings supporting the association between periodontal disease and systemic conditions such as cardiovascular disease, type 2 diabetes mellitus, adverse pregnancy outcomes, and osteoporosis. Significant effort has brought numerous advances in revealing the etiological and pathological links between this chronic inflammatory dental disease and these other conditions. Therefore, there is reason to hope that the strong evidence from these studies may guide researchers towards greatly improved treatment of periodontal infection that would also ameliorate these systemic illnesses. Hence, researchers must continue not only to uncover more information about the correlations between periodontal and systemic diseases but also to focus on positive associations that may result from treating periodontal disease as a means of ameliorating systemic diseases.

Deep sequencing of the oral microbiome reveals signatures of periodontal disease.

The oral microbiome, the complex ecosystem of microbes inhabiting the human mouth, harbors several thousands of bacterial types. The proliferation of pathogenic bacteria within the mouth gives rise to periodontitis, an inflammatory disease known to also constitute a risk factor for cardiovascular disease. While much is known about individual species associated with pathogenesis, the system-level mechanisms underlying the transition from health to disease are still poorly understood. Through the sequencing of the 16S rRNA gene and of whole community DNA we provide a glimpse at the global genetic, metabolic, and ecological changes associated with periodontitis in 15 subgingival plaque samples, four from each of two periodontitis patients, and the remaining samples from three healthy individuals. We also demonstrate the power of whole-metagenome sequencing approaches in characterizing the genomes of key players in the oral microbiome, including an unculturable TM7 organism. We reveal the disease microbiome to be enriched in virulence factors, and adapted to a parasitic lifestyle that takes advantage of the disrupted host homeostasis. Furthermore, diseased samples share a common structure that was not found in completely healthy samples, suggesting that the disease state may occupy a narrow region within the space of possible configurations of the oral microbiome. Our pilot study demonstrates the power of high-throughput sequencing as a tool for understanding the role of the oral microbiome in periodontal disease. Despite a modest level of sequencing (∼2 lanes Illumina 76 bp PE) and high human DNA contamination (up to ∼90%) we were able to partially reconstruct several oral microbes and to preliminarily characterize some systems-level differences between the healthy and diseased oral microbiomes.

Diet-induced obesity in mice causes changes in immune responses and bone loss manifested by bacterial challenge

Obesity has been suggested to be associated with an increased susceptibility to bacterial infection. However, few studies have examined the effect of obesity on the immune response to bacterial infections. In the present study, we investigated the effect of obesity on innate immune responses to Porphyromonas gingivalis infection, an infection strongly associated with periodontitis. Mice with diet-induced obesity (DIO) and lean control C57BL/6 mice were infected orally or systemically with P. gingivalis, and periodontal pathology and systemic immune responses were examined postinfection. After oral infection with P. gingivalis, mice with DIO had a significantly higher level of alveolar bone loss than the lean controls. Oral microbial sampling disclosed higher levels of P. gingivalis in mice with DIO vs. lean mice during and after infection. Furthermore, animals with DIO exposed to oral infection or systemic inoculation of live P. gingivalis developed a blunted inflammatory response with reduced expression of TNF-α, IL-6, and serum amyloid A (SAA) at all time points compared with lean mice. Finally, peritoneal macrophages harvested from mice with DIO and exposed to P. gingivalis exhibited reduced levels of proinflammatory cytokines compared with lean mice and when exposed to P. gingivalis LPS treatment had a significantly reduced recruitment of NF-κB to both TNF-α and IL-10 promoters 30 min after exposure. These data indicate that obesity interferes with the ability of the immune system to appropriately respond to P. gingivalis infection and suggest that this immune dysregulation participates in the increased alveolar bone loss after bacterial infection observed in mice with DIO.

Cytokine Profiling of Macrophages Exposed to Porphyromonas gingivalis, Its Lipopolysaccharide, or Its FimA Protein

ABSTRACT To characterize the roles of Porphyromonas gingivalis and its components in the disease processes, we investigated the cytokine profile induced by live P. gingivalis, its lipopolysaccharides (LPS), and its major fimbrial protein, fimbrillin (FimA). Using cytokine antibody arrays, we found that P. gingivalis LPS and FimA induced a similar profile of cytokine expression when exposed to mouse peritoneal macrophages but that this profile differed significantly in response to live P. gingivalis. In vitro, mouse peritoneal macrophages were stimulated to produce interleukin-6 (IL-6), granulocyte colony-stimulating factor, and lymphotactin by live P. gingivalis, but not by P. gingivalis LPS or FimA, while RANTES, gamma interferon, IL-17, vascular cell adhesion molecule 1 (VCAM-1), and vascular endothelial growth factor were induced by P. gingivalis LPS or FimA, but not by live P. gingivalis. In vivo, IL-6 mRNA was strongly induced only by live P. gingivalis while monocyte chemoattractant protein 1 mRNA was strongly induced only by P. gingivalis LPS and FimA in mouse calvarial scalp, further confirming the differences of cytokine profile induced in vitro. Cytokine antibody arrays using toll-like receptor 2 (TLR2)- and TLR4-deficient macrophages revealed that most of the cytokines induced by P. gingivalis LPS or FimA signal through TLR2, while most of cytokines induced by live P. gingivalis signal through both TLR2 and TLR4. Interestingly, the activation of TLR2 by live P. gingivalis inhibited the release of RANTES, VCAM-1, and IL-1α from mouse peritoneal macrophages. A tumor necrosis factor alpha enzyme-linked immunosorbent assay further confirmed that P. gingivalis LPS and FimA activate mouse peritoneal macrophages via TLR2. These results indicate that host immune cells sense live P. gingivalis and its components differently, which translates into the expression of different inflammatory cytokine profiles.

Interleukin-1 Receptor Signaling Mediates Atherosclerosis Associated With Bacterial Exposure and/or a High-Fat Diet in a Murine Apolipoprotein E Heterozygote Model Pharmacotherapeutic Implications

Background—Current data demonstrate that progressive atherosclerosis is associated with activation of the inflammatory process, as evidenced by systemic elevations of molecules such as tumor necrosis factor, interleukin (IL)-6, and IL-1. It has been postulated that inflammatory events within an atherogenic lesion are induced by oxidized LDL. Recent evidence suggests that infectious agents, including those that cause periodontal disease, may also play an important role. Studies presented here tested the hypothesis that IL-1 receptor (IL-1R1) signaling plays a crucial role in bacteria- and/or high-fat diet (HFD)–enhanced atherogenesis. Methods and Results—Ten-week-old ApoE+/− mice lacking either 1 IL-1R1 allele (ApoE+/−/IL-1R1+/−) or 2 IL-1R1 alleles (ApoE+/−/IL-1R1−/−) fed either an HFD or regular chow were inoculated intravenously with live Porphyromonas gingivalis (P gingivalis) (107 CFU), an important periodontal pathogen, or vehicle once per week for 14 or 24 consecutive weeks. Histomorphometry of plaque cross-sectional area in the proximal aortas, en face measurement of plaque area over the aortic trees, and ELISA for systemic proinflammatory mediators were performed. Atherosclerotic lesions of proximal aortas and aortic tree were substantially reduced in ApoE+/−/IL-1R1−/− mice than in ApoE+/−/IL-1R1+/− mice challenged with P gingivalis. At 24 weeks after P gingivalis inoculation, proximal aortic lesion size quantified by histomorphometry was 5-fold–reduced in chow-fed ApoE+/−/IL-1R1−/− mice than in ApoE+/−/IL-1R1+/− mice (P<0.05). In the HFD group, ApoE+/−/IL-1R1−/− mice exhibited marked attenuation of the progression of atherosclerotic lesions (78% to 97%), with and without P gingivalis inoculation (P<0.05) Conclusion—Ablation of IL-1R1 under P gingivalis challenge and/or an HFD reduced the progression of atherosclerotic plaques. These results indicate that IL-1 plays a crucial role in bacteria- and/or HFD-enhanced atherogenesis.

LPS-induced TNF-α factor (LITAF)-deficient mice express reduced LPS-induced cytokine: Evidence for LITAF-dependent LPS signaling pathways

Previously we identified a transcription factor, LPS-Induced TNF-α Factor (LITAF), mediating inflammatory cytokine expression in LPS-induced processes. To characterize the role of LITAF in vivo, we generated a macrophage-specific LITAF-deficient mouse (macLITAF−/−). Our data demonstrate that in macrophages (i) several cytokines (such as TNF-α, IL-6, sTNF-RII, and CXCL16) are induced at lower levels in macLITAF−/− compared with LITAF+/+ control macrophages; (ii) macLITAF−/− mice are more resistant to LPS-induced lethality. To further identify LITAF signaling pathways, we tested mouse TLR-2−/−, -4−/−, and -9−/− and WT peritoneal macrophages exposed to LPS. Using these cells, we now show that LITAF expression can be induced after challenge either with LPS from Porphyromonas gingivalis via agonism at TLR-2, or with LPS from Escherichia coli via agonism at TLR-4, both requiring functional MyD88. We also show that, in response to LPS, the MyD88-dependent LITAF pathway differs from the NF-κB pathway. Furthermore, using a kinase array, p38α was found to mediate LITAF phosphorylation and the inhibition of p38α with a p38-specific inhibitor (SB203580) blocked LITAF nuclear translocation and reduced LPS-induced TNF-α protein levels. Finally, macLITAF−/− macrophages rescued by LITAF cDNA transfection restored levels of TNF-α similar to those observed in WT cells. We conclude that LITAF is an important mediator of the LPS-induced inflammatory response that can be distinguished from NF-κB pathway and that p38α is the specific kinase involved in the pathway linking LPS/MyD88/LITAF to TNF.

Animal models for Porphyromonas gingivalis-mediated periodontal disease

Porphyromonas gingivalis is one of the principal pathogens in the development of adult periodontitis. Several different animal models have been used to evaluate the complex interactions between P. gingivalis and the host and these have been an important research tool for studying the pathogenesis of P. gingivalis-mediated periodontal diseases.

Inflammation and Tissue Loss Caused by Periodontal Pathogens Is Reduced by Interleukin-1 Antagonists

Periodontal disease is a significant cause of tooth loss among adults. It is initiated by pathogenic bacteria, which trigger an inflammatory response that is effective in preventing significant microbial colonization of the gingival tissues. In some individuals, the reaction to bacteria may lead to an excessive host response, resulting in periodontal tissue destruction. Recent developments suggest that interleukin (IL)-1 genetic polymorphisms may identify certain individuals who have a predisposed susceptibility to periodontal breakdown and that elevated levels of IL-1 are found in individuals with periodontal disease. However, there is no direct evidence that IL-1 per se is responsible for the critical events that occur in periodontitis. We investigated the role of IL-1 in periodontal disease in a Macaca fascicularis primate model, using human soluble IL-1 receptor type I as a specific inhibitor. The results indicate that inhibition of IL-1 alone significantly reduces inflammation, connective tissue attachment loss, and bone resorption that are induced by periodontal pathogens.