Inhibitory effect of synthetic histatin 5 on leukotoxin from Actinobacillus actinomycetemcomitans

Preventive effects of the novel antimicrobial peptide Nal-P-113 in a rat Periodontitis model by limiting the growth of Porphyromonas gingivalis and modulating IL-1β and TNF-α production

Background

P-113 (AKRHHGYKRKFH-NH2) is a 12-amino-acid histidine-rich peptide derived from histatin 5 that is highly degradable in high salt concentrations and biological fluids such as serum, plasma and saliva. Nal-P-113, a novel antimicrobial peptide whose histidine residues are replaced by the bulky amino acids β-naphthylalanine, causes the antimicrobial peptide to retain its bactericidal activity even in physiological environments. This study evaluated the effect of the novel antimicrobial peptide Nal-P-113 in a rat periodontitis model and the mechanisms of action of Nal-P-113 for suppressing periodontitis.

Methods

Periodontitis was induced in mandibular first molars in rats receiving a ligature and infected with Porphyromonas gingivalis. Animals were randomly divided into six groups: a, P. gingivalis W83 alone; b, P. gingivalis W83 with 6.25 μg/mL of Nal-P-113; c, P. gingivalis W83 with 25 μg/mL of Nal-P-113; d, P. gingivalis W83 with 100 μg/mL of Nal-P-113; e, P. gingivalis W83 with 400 μg/mL of Nal-P-113; and f, control without P. gingivalis W83 or Nal-P-113. Morphometric analysis was used to evaluate alveolar bone loss. Microbiological assessment of the presence of Porphyromonas gingivalis and total bacteria was performed using absolute quantitative real-time PCR and scanning electron microscopy. Gingival tissue was collected for western blot and immunohistochemical assays of IL-1β and TNF-α levels.

Results

Alveolar bone loss was inhibited by 100 μg/mL or 400 μg/mL of Nal-P-113 compared to the control group (P < 0.05). Lower amounts of P. gingivalis and total bacteria were found in groups d and e compared with group a (P < 0.05). A decrease in the levels of IL-1β and TNF-α was detected in group d and group e compared to the control group (P < 0.05). The amount of P. gingivalis was positively correlated with IL-1β and TNF-α expression in periodontal tissue (P < 0.05).

Conclusions

Nal-P-113 exhibited protective effects on Porphyromonas gingivalis-induced periodontitis in rats by limiting the amount of bacteria and modulating IL-1β and TNF-α production. The use of Nal-P-113 in vivo might serve as a beneficial preventive or therapeutic approach for periodontitis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-017-1931-9) contains supplementary material, which is available to authorized users.

Innate Humoral Defense Factors

Although innate immunity came into the research spotlight in the late 1990s when its instructive role in the adaptive immune response was recognized, innate humoral defense factors have a much older history. The exocrine secretions of the body contain a plethora of distinct soluble factors (lysozyme, lactoferrin, peroxidases, proline-rich proteins, histatins, etc.) that protect the body from mucosal microbial pathogens. More recent studies have established that the humoral arm of innate immunity contains a heterogeneous group of pattern-recognition molecules (e.g., pentraxins, collectins, and ficolins), which perform diverse host-defense functions, such as agglutination and neutralization, opsonization, control of inflammation, and complement activation and regulation. These pattern-recognition molecules, which act as functional predecessors of antibodies (“ante-antibodies”), and the classic soluble innate defense factors form an integrated system with complementary specificity, action, and tissue distribution, and they are the subject of this chapter.

The diagnostic potential of salivary protease activities in periodontal health and disease

Periodontal disease is characterised by proteolytic processes involving enzymes that are released by host immune cells and periodontal bacteria. These enzymes, when detectable in whole saliva, may serve as valuable diagnostic markers for disease states and progression. Because the substrate specificities of salivary proteases in periodontal health and disease are poorly characterised, we probed these activities using several relevant substrates: (i) gelatin and collagen type IV; (ii) the Arg/Lys-rich human salivary substrate histatin-5; and (iii) a histatin-derived synthetic analog benzyloxycarbonyl-Arg-Gly-Tyr-Arg-methyl cumaryl amide (Z-RGYR-MCA). Substrate degradation was assessed in gel (zymography) and in solution. Whole saliva supernatant enzyme activities directed at gelatin, quantified from the 42 kDa, 92 kDa and 130 kDa bands in the zymograms, were 1.3, 1.4 and 2.0-fold higher, respectively, in the periodontal patient group (P < 0.01), consistent with enhanced activities observed towards collagen type IV. On the other hand, histatin 5 degraded equally fast in healthy and periodontal patients' whole saliva supernatant samples (P > 0.10). Likewise, the hydrolysis rates of the Z-RGYR-MCA substrate were the same in the healthy and periodontal patient groups (P > 0.10). In conclusion, gelatinolytic/collagenolytic activities but not trypsin-like activities in human saliva differentiate health from periodontal disease and may thus provide an adjuvant to diagnosis for monitoring disease activity.

Butyric acid induces apoptosis in both human monocytes and lymphocytes equivalently

Short-chain fatty acids (SCFAs) are metabolites from anaerobic periodontopathic bacteria that induce apoptosis in immune cells such as lymphocytes, monocytes and macrophages. However, it remains unclear if SCFAs from pathogens induce apoptosis in monocytes/macrophages similarly with lymphocytes. This study investigated whether SCFAs-induced apoptosis is equal among the immunoregulatory cells. Cell apoptosis of the employed human cells was evaluated after treatment with culture supernatants from various periodontopathic bacteria or sodium butyrate. Apoptosis and viability were determined by detection of DNA fragmentation and using an MTS assay kit, respectively. Porphyromonas gingivalis and Fusobacterium nucleatum culture filtrates strongly induced apoptosis whereas Prevotella nigrescens and Prevotella intermedia culture filtrates failed to induce apoptosis in the THP-1 and U937 human monocyte and macrophage cell lines. Healthy gingival fibroblasts and oral epithelial cells were resistant to all the culture filtrates. Gas-liquid chromatography detected butyric acid in P. gingivalis (21.0-34.0 mM) and F. nucleatum (36.0 mM) in culture filtrates, whereas, only trace levels were seen in P. nigrescens and P. intermedia. These results suggest that butyric acid produced by periodontopathic bacteria severely damages immunoregulatory cells in a consistent manner and, likewise, could be involved in mediating periodontal chronic inflammation.

Antimicrobial peptides and periodontal disease

AIMS

The goal of this review is to identify the antimicrobial proteins in the oral fluids, saliva and gingival crevicular fluid and identify functional families and candidates for antibacterial treatment.

RESULTS

Periodontal biofilms initiate a cascade of inflammatory and immune processes that lead to the destruction of gingival tissues and ultimately alveolar bone loss and tooth loss. Treatment of periodontal disease with conventional antibiotics does not appear to be effective in the absence of mechanical debridement. An alternative treatment may be found in antimicrobial peptides and proteins, which can be bactericidal and anti-inflammatory and block the inflammatory effects of bacterial toxins. The peptides have co-evolved with oral bacteria, which have not developed significant peptide resistance. Over 45 antibacterial proteins are found in human saliva and gingival crevicular fluid. The proteins and peptides belong to several different functional families and offer broad protection from invading microbes. Several antimicrobial peptides and proteins (AMPs) serve as templates for the development of therapeutic peptides and peptide mimetics, although to date none have demonstrated efficacy in human trials.

CONCLUSIONS

Existing and newly identified AMPs may be developed for therapeutic use in periodontal disease or can serve as templates for peptide and peptide mimetics with improved therapeutic indices.

Salivary proteome and its genetic polymorphisms

Salivary diagnostics for oral as well as systemic diseases is dependent on the identification of biomolecules reflecting a characteristic change in presence, absence, composition, or structure of saliva components found under healthy conditions. Most of the biomarkers suitable for diagnostics comprise proteins and peptides. The usefulness of salivary proteins for diagnostics requires the recognition of typical features, which make saliva as a body fluid unique. Salivary secretions reflect a degree of redundancy displayed by extensive polymorphisms forming families for each of the major salivary proteins. The structural differences among these polymorphic isoforms range from distinct to subtle, which may in some cases not even affect the mass of different family members. To facilitate the use of modern state-of-the-art proteomics and the development of nanotechnology-based analytical approaches in the field of diagnostics, the salient features of the major salivary protein families are reviewed at the molecular level. Knowledge of the structure and function of salivary gland-derived proteins/peptides has a critical impact on the rapid and correct identification of biomarkers, whether they originate from exocrine or non-exocrine sources.

Human antimicrobial peptides: defensins, cathelicidins and histatins

Antimicrobial peptides, which have been isolated from many bacteria, fungi, plants, invertebrates and vertebrates, are an important component of the natural defenses of most living organisms. The isolated peptides are very heterogeneous in length, sequence and structure, but most of them are small, cationic and amphipathic. These peptides exhibit broad-spectrum activity against Gram-positive and Gram-negative bacteria, yeasts, fungi and enveloped viruses. A wide variety of human proteins and peptides also have antimicrobial activity and play important roles in innate immunity. In this review we discuss three important groups of human antimicrobial peptides. The defensins are cationic non-glycosylated peptides containing six cysteine residues that form three intramolecular disulfide bridges, resulting in a triple-stranded beta-sheet structure. In humans, two classes of defensins can be found: alpha-defensins and beta-defensins. The defensin-related HE2 isoforms will also be discussed. The second group is the family of histatins, which are small, cationic, histidine-rich peptides present in human saliva. Histatins adopt a random coil conformation in aqueous solvents and form alpha-helices in non-aqueous solvents. The third group comprises only one antimicrobial peptide, the cathelicidin LL-37. This peptide is derived proteolytically from the C-terminal end of the human CAP18 protein. Just like the histatins, it adopts a largely random coil conformation in a hydrophilic environment, and forms an alpha-helical structure in a hydrophobic environment.

Molecular pathogenicity of the oral opportunistic pathogen Actinobacillus actinomycetemcomitans

Periodontitis is mankind's most common chronic inflammatory disease. One severe form of periodontitis is localized aggressive periodontitis (LAP), a condition to which individuals of African origin demonstrate an increased susceptibility. The main causative organism of this disease is Actinobacillus actinomycetemcomitans. A member of the Pasteurellaceae, A. actinomycetemcomitans produces a number of interesting putative virulence factors including (a) an RTX leukotoxin that targets only neutrophils and monocytes and whose action is influenced by a novel type IV secretion system involved in bacterial adhesion; (b) the newly discovered toxin, cytolethal distending toxin (CDT); and (c) a secreted chaperonin 60 with potent leukocyte-activating and bone resorbing activities. This organism also produces a plethora of proteins able to inhibit eukaryotic cell cycle progression and proteins and peptides that can induce distinct forms of proinflammatory cytokine networks. A range of other proteins interacting with the host is currently being uncovered. In addition to these secreted factors, A. actinomycetemcomitans is invasive with an unusual mechanism for entering, and traveling within, eukaryotic cells. This review focuses on recent advances in our understanding of the molecular and cellular pathogenicity of this fascinating oral bacterium.

Human salivary gland-specific daily variations in histatin concentrations determined by a novel quantitation technique

Histatins constitute a distinct family of human salivary antimicrobial peptides, of which histatins 1, 3 and 5 are the most abundant. To evaluate salivary gland-specific differences in histatin secretion, we used the recently developed histatin-zinc precipitation method to quantify histatins and to assess daily variations in secretions. Stimulated pure secretions from parotid glands (HPS) and submandibular/sublingual glands (SMSL) were collected from 10 different subjects at four different times of the day (9:35 a.m.; 12:40 p.m.; 2:50 p.m. and 5:00 p.m.). Zinc precipitation and subsequent reversed phase HPLC analysis were performed to determine concentrations of histatins 1, 3 and 5 with reference to purified histatin standards. Both HPS and SMSL secretions displayed daily variations in histatin concentrations. HPS values showed a maximum at mid-day and SMSL samples showed a maximum in the morning. Mean daily histatin concentrations were almost three fold higher in SMSL than in HPS. Mean histatin 1, 3 and 5 concentrations in HPS from 10 subjects ranged from 0.7 to 2.8, 0.6 to 4.3 and 1.0 to 4.3mg%, respectively. The corresponding means in SMSL were 2.8-12.2, 1.5-7.5 and 2.6-9.0mg%, respectively. Remarkably, although histatins constitute only 3-10% of total protein in these secretions, an almost perfect correlation between total protein and total histatin concentrations was observed for both glands. Despite a broad range in histatin concentrations between individuals, this study demonstrated a hitherto unidentified daily variation in histatin concentrations in HPS and SMSL secretions and a differential expression pattern which might have functional implications.

A new method for the isolation of histatins 1, 3, and 5 from parotid secretion using zinc precipitation

Histatins, a family of small-molecular-weight, histidine-rich cationic salivary proteins, have been difficult to isolate in an efficient way by conventional procedures due to their anomalous interactions with chromatographic resins. In the present study we explored the possibility of developing a new isolation procedure based on recent observations that histatins associate with various metal ions, including zinc. Since solubility studies showed that histatin 5 forms precipitates with zinc under alkaline conditions, we investigated whether this characteristic could be exploited for the preparative isolation of histatins from salivary secretions. A fast and efficient two-step procedure was developed using zinc precipitation of histatins from human parotid secretion followed by final purification using reversed-phase high-performance liquid chromatography (HPLC). Analysis of zinc precipitates by Tricine-SDS-PAGE, cationic PAGE, HPLC, and mass spectrometry revealed the presence of the three major histatins, 1, 3, and 5, as well as statherin. The histatin yield obtained by the precipitation step was approximately 90%. Therefore, zinc precipitation of histatins from glandular salivary secretions is a novel, rapid, and effective means for the isolation of these proteins.