Nitric oxide production by a murine macrophage cell line (RAW264.7 cells) stimulated with Aggregatibacter actinomycetemcomitans surface-associated material

Salivary and serum nitric oxide synthase, macrophage inflammatory protein 1 alpha and macrophage migration inhibitory factor levels in periodontal disease

Objective

Periodontal disease is multifactorial inflammatory disease involving both gingivitis and periodontitis. Inducible nitric oxide synthase (iNOS), macrophage inflammatory protein 1 alpha (MIP-1α) and macrophage migration inhibitory factor (MIF) are mediators contributing to the progression of periodontal diseases with distinct functions. The aim of this study is to evaluate the local and systemic iNOS, MIP-1α and MIF concentrations in patients having periodontal disease with different severities.

Design

The study was conducted on 88 individuals equally divided into four groups; 1) Periodontally Healthy 2) Gingivitis 3) Stage I-II Periodontitis 4) Stage III-IV Periodontitis. Saliva and serum samples were obtained from each individual and then periodontal examinations were performed. Plaque and bleeding on probing indexes, probing depths and clinical attachment levels were measured on each tooth to determine the periodontal status. Concentrations of iNOS, MIP-1α and MIF were measured with enzyme-linked immunosorbent assay.

Results

Patients with stage I-II and stage III-IV periodontitis had more iNOS levels than periodontally healthy people in serum and saliva (p ≤ 0,001 for serum; p < 0,05 for saliva). Stage III-IV periodontitis group had significantly more serum-iNOS levels than that in gingivitis group (p = 0,005). When compared with periodontally healthy individuals, MIP-1α levels in stage III-IV periodontitis patients were measured significantly more in saliva; (p = 0,016) but less in serum (p = 0,006) samples. More serum-MIF concentrations were observed in stage I-II periodontitis groups than that in periodontally healthy individuals (p < 0,05).

Conclusion

Increased salivary and serum iNOS and serum-MIF levels in different stages of periodontitis suggest that these molecules might be involved in periodontal disease pathogenesis. Also, oral microenvironment may stimulate the enhanced MIP-1α concentration in advanced periodontitis cases.

The cytolethal distending toxin of Aggregatibacter actinomycetemcomitans inhibits macrophage phagocytosis and subverts cytokine production

Aggregatibacter actinomycetemcomitans is an important periodontal pathogen that can participate in periodontitis and other non-oral infections. The cytolethal distending toxin (Cdt) is among the virulence factors produced by this bacterium. The Cdt is also secreted by several mucosa-associated Gram-negative pathogens and may play a role in perpetuating the infection by modulating the immune response. Although the toxin targets a wide range of eukaryotic cell types little is known about its activity on macrophages which play a key part in alerting the rest of the immune system to the presence of pathogens and their virulence factors. In view of this, we tested the hypothesis that the A. actinomycetemcomitans Cdt (AaCdt) disrupts macrophage function by inhibiting phagocytic activity as well as affecting the production of cytokines. Murine macrophages were co-cultured with either wild-type A. actinomycetemcomitans or a Cdt(-) mutant. Viable counts and qPCR showed that phagocytosis of the wild-type strain was significantly reduced relative to that of the Cdt(-) mutant. Addition of recombinant Aa(r)Cdt to co-cultures along with the Cdt(-) mutant diminished the phagocytic activity similar to that observed with the wild type strain. High concentrations of Aa(r)Cdt resulted in decreased phagocytosis of fluorescent bioparticles. Nitric oxide production was modulated by the presence of Cdt and the levels of IL-1β, IL-12 and IL-10 were increased. Production of TNF-α did not differ in the co-culture assays but was increased by the presence of Aa(r)Cdt. These data suggest that the Cdt may modulate macrophage function in A. actinomycetemcomitans infected sites by impairing phagocytosis and modifying the pro-inflammatory/anti-inflammatory cytokine balance.

Inhibition of inducible nitric oxide synthase prevents lipid peroxidation in osteoarthritic chondrocytes

Nitric oxide (NO) and the lipid peroxidation (LPO) product 4-hydroxynonenal (HNE) are considered to be key mediators of cartilage destruction in osteoarthritis (OA). NO is also known to be an important intermediary in LPO initiation through peroxynitrite formation. The aim of the present study was to assess the ability of the inducible NO synthase (iNOS) inhibitor N-iminoethyl-L-lysine (L-NIL) to prevent HNE generation via NO suppression in human OA chondrocytes and cartilage explants. Human OA chondrocytes and cartilage explants were treated with L-NIL and thereafter with or without interleukin-1beta (IL-1β) or HNE at cytotoxic or non-cytotoxic concentrations. Parameters related to oxidative stress, apoptosis, inflammation, and catabolism were investigated. L-NIL stifled IL-1β-induced NO release, iNOS activity, nitrated proteins, and HNE generation in a dose-dependent manner. It also blocked IL-1β-induced inactivation of the HNE-metabolizing glutathione-s-transferase (GST). L-NIL restored both HNE and GSTA4-4 levels in OA cartilage explants. Interestingly, it also abolished IL-1β-evoked reactive oxygen species (ROS) generation and p47 NADPH oxidase activation. Furthermore, L-NIL significantly attenuated cell death and markers of apoptosis elicited by exposure to a cytotoxic dose of HNE as well as the release of prostaglandin E(2) and metalloproteinase-13 induced by a non-cytotoxic dose of HNE. Altogether, our findings support a beneficial effect of L-NIL in OA by (i) preventing the LPO process and ROS production via NO-dependent and/or independent mechanisms and (ii) attenuating HNE-induced cell death and different mediators of cartilage damage.