Periodontal innate immune mechanisms relevant to atherosclerosis and obesity

Breaking bad: manipulation of the host response by Porphyromonas gingivalis

Recent metagenomic and mechanistic studies are consistent with a new model of periodontal pathogenesis. This model proposes that periodontal disease is initiated by a synergistic and dysbiotic microbial community rather than by a select few bacteria traditionally known as "periopathogens." Low-abundance bacteria with community-wide effects that are critical for the development of dysbiosis are now known as keystone pathogens, the best-documented example of which is Porphyromonas gingivalis. Here, we review established mechanisms by which P. gingivalis interferes with host immunity and enables the emergence of dysbiotic communities. We integrate the role of P. gingivalis with that of other bacteria acting upstream and downstream in pathogenesis. Accessory pathogens act upstream to facilitate P. gingivalis colonization and co-ordinate metabolic activities, whereas commensals-turned pathobionts act downstream and contribute to destructive inflammation. The recent concepts of keystone pathogens, along with polymicrobial synergy and dysbiosis, have profound implications for the development of therapeutic options for periodontal disease.

Advances in immune-modulating therapies to treat atherosclerotic cardiovascular diseases

In addition to hypercholesterolemia, innate and adaptive immune mechanisms play a critical role in atherogenesis, thus making immune-modulation therapy a potentially attractive way of managing atherosclerotic cardiovascular disease. These immune-modulation strategies include both active and passive immunization and confer beneficial reduction in atherosclerosis. Preclinical studies have demonstrated promising results and we review current knowledge on the complex role of the immune system and the potential for immunization as an immune-modulation therapy for atherosclerosis.

PPARγ gene polymorphism, C-reactive protein level, BMI and periodontitis in post-menopausal Japanese women

BACKGROUND

Several studies have reported inconsistent results regarding the association between the PPARγPro12Ala polymorphism and obesity. Obese individuals had higher C-reactive protein (CRP) levels compared with those of normal weight, and PPARγ activation could significantly reduce serum high-sensitive CRP level. We have previously suggested that the Pro12Ala polymorphism represents a susceptibility factor for periodontitis, which is a known risk factor for increased CRP level.

OBJECTIVES

The aim was to investigate associations between PPARγ gene polymorphism, serum CRP level, BMI and/or periodontitis among post-menopausal Japanese women.

MATERIALS AND METHODS

The final sample in this study comprised 359 post-menopausal Japanese women. Periodontal parameters, including PD, CAL and BOP, were measured per tooth. PPARγPro12Ala genotype was determined by PCR-RFLP. Hs-CRP value was measured by a latex nephelometry assay.

RESULTS

No significant differences in age, BMI or periodontal parameters were found between the genotypes. The percentages of sites with PD ≥ 4 mm were significantly higher among the hsCRP ≥ 1 mg/l group than the hsCRP < 1 mg/l group (p = 0.003). Positive correlations were found between serum hsCRP levels and the percentages of sites with PD ≥ 4 mm (p = 0.043) in PPARγ Ala allele carriers, and BMI (p = 0.033) in non-carriers. After adjustment for model covariates, BMI was significantly associated with serum hsCRP level.

CONCLUSION

The PPARγPro12Ala polymorphism was not independently associated with periodontitis, serum CRP level or BMI in post-menopausal Japanese women. However, serum hsCRP level correlated with periodontitis in Ala allele carriers, and with BMI in non-carriers.

Immune cells link obesity-associated type 2 diabetes and periodontitis

The clinical association between obesity-associated type 2 diabetes (T2D) and periodontitis, coupled with the increasing prevalence of these diseases, justifies studies to identify mechanisms responsible for the vicious feed-forward loop between systemic and oral disease. Changes in the immune system are critical for both obesity-associated T2D and periodontitis and therefore may link these diseases. Recent studies at the intersection of immunology and metabolism have greatly advanced our understanding of the role the immune system plays in the transition between obesity and obesity-associated T2D and have shown that immune cells exhibit similar functional changes in obesity/T2D and periodontitis. Furthermore, myeloid and lymphoid cells likely synergize to promote obesity/T2D-associated periodontitis despite complexities introduced by disease interaction. Thus the groundwork is being laid for researchers to exploit existing models to understand immune cell dysfunction and break the devastating relationship between obesity-associated T2D and oral disease.

Pivotal role of NOD2 in inflammatory processes affecting atherosclerosis and periodontal bone loss

The purpose of this study was to elucidate the role of nucleotide binding oligomerization domain-containing protein 2 (NOD2) signaling in atherosclerosis and periodontal bone loss using an Apolipoprotein E(-/-) (ApoE(-/-)) mouse model based on the proposed role of NOD2 in inflammation. NOD2(-/-)ApoE(-/-) and ApoE(-/-) mice fed a standard chow diet were given an oral gavage of Porphyromonas gingivalis for 15 wk. NOD2(-/-)ApoE(-/-) mice exhibited significant increases in inflammatory cytokines, alveolar bone loss, cholesterol, and atherosclerotic lesions in the aorta and the heart compared with ApoE(-/-) mice. In contrast, ApoE(-/-) mice injected i.p. with Muramyl DiPeptide (MDP) to stimulate NOD2 and given an oral gavage of P. gingivalis displayed a reduction of serum inflammatory cytokines, alveolar bone loss, cholesterol, and atherosclerotic lesions in the aorta and aortic sinus compared with ApoE(-/-) mice orally challenged but injected with saline. A reduction in body weight gain was observed in ApoE(-/-) mice fed a high-fat diet (HFD) and injected with MDP compared with ApoE(-/-) mice fed a high-fat diet but injected with saline. MDP treatment of bone marrow-derived macrophages incubated with P. gingivalis increased mRNA expressions of NOD2, Toll-like receptor 2, myeloid differentiation primary response gene 88, and receptor-interacting protein-2 but reduced the expressions of inhibitor of NF-κB kinase-β, NF-κB, c-Jun N-terminal kinase 3, and TNF-α protein levels compared with saline control, highlighting pathways involved in MDP antiinflammatory effects. MDP activation of NOD2 should be considered in the treatment of inflammatory processes affecting atherosclerosis, periodontal bone loss ,and possibly, diet-induced weight gain.

Porphyromonas gingivalis promotes neointimal formation after arterial injury through toll-like receptor 2 signaling

We previously demonstrated that Porphyromonas gingivalis infection induces neointimal hyperplasia with an increase in monocyte chemoattractant protein (MCP)-1 after arterial injury in wild-type mice. Toll-like receptor (TLR) 2 is a key receptor for the virulence factors of P. gingivalis. The aim of this study was to assess whether TLR2 plays a role in periodontopathic bacteria-induced neointimal formation after an arterial injury. Wild-type and TLR2-deficient mice were used in this study. The femoral arteries were injured, and P. gingivalis or vehicle was injected subcutaneously once per week. Fourteen days after arterial injury, the murine femoral arteries were obtained for histopathologic and immunohistochemical analyses. The immunoglobulin-G levels of the P. gingivalis-infected groups were significantly increased in comparison with the level in the corresponding noninfected groups in both wild-type and TLR2-deficient mice. TLR2 deficiency negated the P. gingivalis-induced neointimal formation in comparison with the wild-type mice, and reduced the number of positive monocyte chemoattractant protein-1 cells in the neointimal area. These findings demonstrate that P. gingivalis infection can promote neointimal formation after an arterial injury through TLR2 signaling.

Periodontal innate immune mechanisms relevant to obesity

Obesity affects over 35% of the adult population of the USA, and obesity-related illnesses have emerged as the leading cause of preventable death worldwide, according to the World Health Organization. Obesity's secondary morbidities include increased risk of cardiovascular disease, type II diabetes, and cancer, in addition to increased occurrence and severity of infections. Sedentary lifestyle and weight gain caused by consumption of a high-fat diet contribute to the development of obesity, with individuals having a body mass index (BMI) score > 30 being considered obese. Genetic models of obesity (ob/ob mice, db/db mice, and fa/fa rats) have been insufficient to study human obesity because of the overall lack of genetic causes for obesity in human populations. To date, the diet-induced obese (DIO) mouse model best serves research studies relevant to human health. Periodontal disease presents with a wide range of clinical variability and severity. Research in the past decade has shed substantial light on both the initiating infectious agents and host immunological responses in periodontal disease. Up to 46% of the general population harbors the microorganism(s) associated with periodontal disease, although many are able to limit the progression of periodontal disease or even clear the organism(s) if infected. In the last decade, several epidemiological studies have found an association between obesity and increased incidence of periodontal disease. This review focuses on exploring the immunological consequences of obesity that exacerbate effects of infection by pathogens, with focus on infection by the periodontal bacterium Porphyromonas gingivalis as a running example.

Polymicrobial infection with major periodontal pathogens induced periodontal disease and aortic atherosclerosis in hyperlipidemic ApoE(null) mice

Periodontal disease (PD) and atherosclerosis are both polymicrobial and multifactorial and although observational studies supported the association, the causative relationship between these two diseases is not yet established. Polymicrobial infection-induced periodontal disease is postulated to accelerate atherosclerotic plaque growth by enhancing atherosclerotic risk factors of orally infected Apolipoprotein E deficient (ApoE^null) mice. At 16 weeks of infection, samples of blood, mandible, maxilla, aorta, heart, spleen, and liver were collected, analyzed for bacterial genomic DNA, immune response, inflammation, alveolar bone loss, serum inflammatory marker, atherosclerosis risk factors, and aortic atherosclerosis. PCR analysis of polymicrobial-infected (Porphyromonas gingivalis [P. gingivalis], Treponema denticola [T. denticola], and Tannerella forsythia [T. forsythia]) mice resulted in detection of bacterial genomic DNA in oral plaque samples indicating colonization of the oral cavity by all three species. Fluorescent in situ hybridization detected P. gingivalis and T. denticola within gingival tissues of infected mice and morphometric analysis showed an increase in palatal alveolar bone loss (p<0.0001) and intrabony defects suggesting development of periodontal disease in this model. Polymicrobial-infected mice also showed an increase in aortic plaque area (p<0.05) with macrophage accumulation, enhanced serum amyloid A, and increased serum cholesterol and triglycerides. A systemic infection was indicated by the detection of bacterial genomic DNA in the aorta and liver of infected mice and elevated levels of bacterial specific IgG antibodies (p<0.0001). This study was a unique effort to understand the effects of a polymicrobial infection with P. gingivalis, T. denticola and T. forsythia on periodontal disease and associated atherosclerosis in ApoE^null mice.

Obesity prevention and intervention in dental practice

Dentists have an important role in preventing and detecting oral and systemic diseases because of their diagnostic and screening abilities and the frequency of patient visits. These skills and practice paradigms should be considered in solving the obesity epidemic. The well-described connection between periodontal disease and diabetes is a reason for dentists to intervene in the rise of obesity. Dentists are in a unique position to identify and aid in treatment of obstructive sleep apnea, a condition associated with obesity and diabetes. Dentists can play a role in raising awareness of overweight status and obesity risk behaviors in children.

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.

Mast cells squeeze the heart and stretch the gird: their role in atherosclerosis and obesity

Mast cells are crucial for the development of allergic and anaphylactic reactions, but they are also involved in acquired and innate immunity. Increasing evidence now implicates mast cells in inflammatory diseases through activation by non-allergic triggers such as neuropeptides and cytokines. This review discusses how mast cells contribute to the inflammatory processes associated with coronary artery disease and obesity. Animal models indicate that mast cells, through the secretion of various vasoactive mediators, cytokines and proteinases, contribute to coronary plaque progression and destabilization, as well as to diet-induced obesity and diabetes. Understanding how mast cells participate in these inflammatory processes could help in the development of unique inhibitors with novel therapeutic applications for these diseases, which constitute the greatest current threat to global human health and welfare.