Inhibition of Porphyromonas gingivalis proteinases (gingipains) by chlorhexidine: synergistic effect of Zn(II)

Limonium brasiliense rhizomes extract against virulence factors of Porphyromonas gingivalis: Inhibition of gingipains, bacterial adhesion, and biofilm formation

Periodontitis is clinically characterized by destruction of the tooth support system and tooth loss. Porphyromonas gingivalis (Pg) plays a dominant role in periodontitis. Fractions and isolated compounds from an acetone-water extract of the roots of Limonium brasiliense (Lb) were tested in vitro for their anti-adhesive capacity against Pg on human KB buccal cells, influence on gingipains, the main virulence factors of Pg, and biofilm formation. Fractions EAF and FLB7 (50 μg/mL) reduced the bacterial adhesion of Pg to KB cells significantly (63 resp. 70%). The proanthocyanidin samarangenin A inhibited the adhesion (72%, 30 μM), samarangenin B (71%, 20 μM), and the flavan-3-ol epigallocatechin-3-O-gallate (79%, 30 μM). Fraction AQF, representing hydrophilic compounds, reduced the proteolytic activity of Arginin-specific gingipain (IC50 12.78 μg/mL). Fractions EAF and FLB7, characterized by lipohilic constituents, inhibited Arg-gingipain (IC50 3 μg/mL). On Lysine-specific gingipain, AQF has an IC50 15.89, EAF 14.15, and FLB7 6 μg/mL. The reduced bacterial adhesion is due to a strong interaction of proanthocyanidins with gingipains. AQF, EAF, and FLB7 significantly inhibited biofilm formation: IC50 11.34 (AQF), 11.66 (EAF), and 12.09 μg/mL (FLB7). In silico analysis indicated, that the polyphenols act against specific targets of Pg, not affecting mammalian cells. Therefore, Lb might be effective for prevention of periodontal disease by influencing virulence factors of Pg.

Coordination chemistry suggests that independently observed benefits of metformin and Zn2+ against COVID-19 are not independent

Independent trials indicate that either oral Zn2+ or metformin can separately improve COVID-19 outcomes by approximately 40%. Coordination chemistry predicts a mechanistic relationship and therapeutic synergy. Zn2+ deficit is a known risk factor for both COVID-19 and non-infectious inflammation. Most dietary Zn2+ is not absorbed. Metformin is a naked ligand that presumably increases intestinal Zn2+ bioavailability and active absorption by cation transporters known to transport metformin. Intracellular Zn2+ provides a natural buffer of many protease reactions; the variable "set point" is determined by Zn2+ regulation or availability. A Zn2+-interactive protease network is suggested here. The two viral cysteine proteases are therapeutic targets against COVID-19. Viral and many host proteases are submaximally inhibited by exchangeable cell Zn2+. Inhibition of cysteine proteases can improve COVID-19 outcomes and non-infectious inflammation. Metformin reportedly enhances the natural moderating effect of Zn2+ on bioassayed proteome degradation. Firstly, the dissociable metformin-Zn2+ complex could be actively transported by intestinal cation transporters; thereby creating artificial pathways of absorption and increased body Zn2+ content. Secondly, metformin Zn2+ coordination can create a non-natural protease inhibitor independent of cell Zn2+ content. Moderation of peptidolytic reactions by either or both mechanisms could slow (a) viral multiplication (b) viral invasion and (c) the pathogenic host inflammatory response. These combined actions could allow development of acquired immunity to clear the infection before life-threatening inflammation. Nirmatrelvir (Paxlovid®) opposes COVID-19 by selective inhibition the viral main protease by a Zn2+-independent mechanism. Pending safety evaluation, predictable synergistic benefits of metformin and Zn2+, and perhaps metformin/Zn2+/Paxlovid® co-administration should be investigated.

Interplay between Porphyromonas gingivalis Hemophore-Like Protein HmuY and Kgp/RgpA Gingipains Plays a Superior Role in Heme Supply

To acquire heme as a source of iron and protoporphyrin IX, Porphyromonas gingivalis uses gingipains, Hmu, and Hus systems. The aim of this study was to assess the correlation between the production and function of the most important virulence factors of P. gingivalis involved in heme supply, namely, hemophore-like proteins (HmuY and HusA) and gingipains. Respective mutant strains were used, and the expression of genes at the transcript and protein levels, as well as the importance of these genes' products for virulence potential, was examined. We found that HmuY and Kgp/RgpA gingipains are among the main P. gingivalis virulence factors synergistically engaged in heme supply. Their expression is related mainly when P. gingivalis grows in conditions rich in iron and heme sources, resembling those found in severe periodontitis. We confirmed that HmuY production is strictly dependent on the availability of heme and iron in the external environment, whereas we did not observe such dependence in the production of HusA. Moreover, we found that the HmuY protein can easily sequester heme from the HusA protein. The only correlation in the production of HmuY and HusA hemophore-like proteins could occur in P. gingivalis grown in conditions rich in iron and heme sources, mimicking an environment typical for severe periodontitis. Based on our observations, we suggest that HmuY is the major heme-binding protein produced by P. gingivalis, especially in iron- and heme-depleted conditions, typical for healthy periodontium and the initial stages of infection. The HusA protein could play a supporting role in P. gingivalis heme uptake. IMPORTANCE Altered or disturbed mutualism between oral microbiome members results in dysbiosis with local injuries and subsequently in systemic diseases. Periodontitis belongs to a group of multifactorial infectious diseases, characterized by inflammation and destruction of tooth-supporting tissues. Porphyromonas gingivalis is considered the main etiologic agent and keystone pathogen responsible for developing advanced periodontitis. As part of the infective process, P. gingivalis must acquire heme to survive and multiply at the infection site. Analysis of the mutual relationship between its main virulence factors showed that heme acquisition in P. gingivalis is a complex process in which mainly the Hmu system, with the leading role played by the HmuY hemophore-like protein, and Kgp and RgpA gingipains prefer cooperative interplay. It seems that the Hus system, including HusA hemophore-like protein, could be involved in another, so far uncharacterized, stage of iron and heme supply.

Antimicrobial behavior of titanium coating with chlorhexidine-doped thin film exposed to a biofilm supplemented with nicotine

Because nicotine upregulates the growth of most oral bacteria, this in vitro study investigated the antimicrobial effect of chlorhexidine-doped thin film on commercially pure titanium against Fusobacterium nucleatum (F. nucleatum) biofilm supplemented with different concentrations of nicotine (0, 1, and 2 mg/mL). Biofilms were formed on a chlorhexidine-doped thin film on commercially-pure-titanium discs and compared to the control groups. Biofilm viability, total biofilm growth using a spectrophotometer, extracellular polysaccharide content, and pH variations were assessed as dependent variables. Data were submitted to ANOVA and Tukey honest significant difference tests (α=0.05). F. nucleatum biofilm growth was inhibited when exposed to chlorhexidine-doped thin film (p<0.05). Biofilm supplemented with nicotine did not impact the synthesis of EPS on the same type of treatment (p>0.05). The pH values were significantly increased with the increase of nicotine concentration (p<0.05). Chlorhexidine-doped thin film was effective in reducing F. nucleatum biofilm supplemented with nicotine.

Implications of Porphyromonas gingivalis peptidyl arginine deiminase and gingipain R in human health and diseases

Porphyromonas gingivalis is a major pathogenic bacterium involved in the pathogenesis of periodontitis. Citrullination has been reported as the underlying mechanism of the pathogenesis, which relies on the interplay between two virulence factors of the bacterium, namely gingipain R and the bacterial peptidyl arginine deiminase. Gingipain R cleaves host proteins to expose the C-terminal arginines for peptidyl arginine deiminase to citrullinate and generate citrullinated proteins. Apart from carrying out citrullination in the periodontium, the bacterium is found capable of citrullinating proteins present in the host synovial tissues, atherosclerotic plaques and neurons. Studies have suggested that both virulence factors are the key factors that trigger distal effects mediated by citrullination, leading to the development of some non-communicable diseases, such as rheumatoid arthritis, atherosclerosis, and Alzheimer’s disease. Thus, inhibition of these virulence factors not only can mitigate periodontitis, but also can provide new therapeutic solutions for systematic diseases involving bacterial citrullination. Herein, we described both these proteins in terms of their unique structural conformations and biological relevance to different human diseases. Moreover, investigations of inhibitory actions on the enzymes are also enumerated. New approaches for identifying inhibitors for peptidyl arginine deiminase through drug repurposing and virtual screening are also discussed.

Antibiofilm effect of ozonized physiological saline solution on peri-implant-related biofilm

BACKGROUND

Removal of dental plaque and local application of local chemical adjuncts, such as chlorhexidine (CHX), have been used to control and treat peri-implant disease. However, these methods can damage the surface properties of the implants or promote bacterial resistance. The application of ozone as an adjunctive treatment represents a new approach in the management of peri-implantitis. Thus, the purpose of this study was to evaluate the antimicrobial effect of ozonized physiological saline solution in different concentrations against oral biofilms developed on titanium surface.

METHODS

Single and multi-species biofilms of Porphyromonas gingivalis, Fusobacterium nucleatum, and Streptococcus oralis were formed on titanium specimens for 5 days in anaerobic conditions. Biofilms were treated with ozonized saline solution at different concentrations (25, 50, and 80 μg/NmL), for 30 seconds and 1 minute. CHX (0.12%) and saline solution (0.89% NaCl) were used as positive and negative controls, respectively. Bacterial viability was quantified by colony forming units (CFU mL^-1 ), and biofilm images were acquired by confocal laser scanning microscopy (CLSM). Data were analyzed by parametric test (ANOVA) with Tukey post-hoc test (P < 0.05).

RESULTS

Ozonized saline solution showed antibiofilm activity at a concentration of 80 μg/NmL for 30 seconds and 1 minute, reducing, mainly, Porphyromonas gingivalis viability, with 2.78 and 1.7 log₁₀ CFU mL^-1 of reduction in both single and multi-species biofilms, respectively, when compared to the control (saline), whereas CHX reduced 1.4 and 1.2 log₁₀ CFU mL^-1 .

CONCLUSION

Ozonized saline solution has antibiofilm activity, with better effect when applied for 1 minute at 80 μg/NmL, being a promising candidate therapy for the treatment of peri-implant diseases.

Synthesis of multifunctional chlorhexidine-doped thin films for titanium-based implant materials

Our goal was to create bio-functional chlorhexidine (CHX)-doped thin films on commercially pure titanium (cpTi) discs using the glow discharge plasma approach. Different plasma deposition times (50, 35 and 20 min) were used to create bio-functional surfaces based on silicon films with CHX that were compared to the control groups [no CHX and bulk cpTi surface (machined)]. Physico-chemical and biological characterizations included: 1. Morphology, roughness, elemental chemical composition, film thickness, contact angle and surface free energy; 2. CHX-release rate; 3. Antibacterial effect on Streptococcus sanguinis biofilms at 24, 48 and 72 h; 4. Cytotoxicity and metabolic activity using fibroblasts cell culture (NIH-F3T3 cells) at 1, 2, 3 and 4 days; 5. Protein expression by NIH-F3T3 cells at 1, 2, 3 and 4 days; and 6. Co-culture assay of fibroblasts cells and S. sanguinis to assess live and dead cells on the confocal laser scanning microscopy, mitochondrial activity (XTT), membrane leakage (LDH release), and metabolic activity (WST-1 assay) at 1, 2 and 3 days of co-incubation. Data analysis showed that silicon films, with or without CHX coated cpTi discs, increased surface wettability and free energy (p < 0.05) without affecting surface roughness. CHX release was maintained over a 22-day period and resulted in a significant inhibition of biofilm growth (p < 0.05) at 48 and 72 h of biofilm formation for 50 min and 20 min of plasma deposition time groups, respectively. In general, CHX treatment did not significantly affect NIH-F3T3 cell viability (p > 0.05), whereas cell metabolism (MTT assay) was affected by CHX, with the 35 min of plasma deposition time group displaying the lowest values as compared to bulk cpTi (p < 0.05). Moreover, data analysis showed that films, with or without CHX, significantly affected the expression profile of inflammatory cytokines, including IL-4, IL-6, IL-17, IFN-y and TNF-α by NIH-F3T3 cells (p < 0.05). Co-culture demonstrated that CHX-doped film did not affect the metabolic activity, cytotoxicity and viability of fibroblasts cells (p > 0.05). Altogether, the findings of the current study support the conclusion that silicon films added with CHX can be successfully created on titanium discs and have the potential to affect bacterial growth and inflammatory markers without affecting cell viability/proliferation rates.

PgFur participates differentially in expression of virulence factors in more virulent A7436 and less virulent ATCC 33277 Porphyromonas gingivalis strains

Background

Porphyromonas gingivalis is considered a keystone pathogen responsible for chronic periodontitis. Although several virulence factors produced by this bacterium are quite well characterized, very little is known about regulatory mechanisms that allow different strains of P. gingivalis to efficiently survive in the hostile environment of the oral cavity, a typical habitat characterized by low iron and heme concentrations. The aim of this study was to characterize P. gingivalis Fur homolog (PgFur) in terms of its role in production of virulence factors in more (A7436) and less (ATCC 33277) virulent strains.

Results

Expression of a pgfur depends on the growth phase and iron/heme concentration. To better understand the role played by the PgFur protein in P. gingivalis virulence under low- and high-iron/heme conditions, a pgfur-deficient ATCC 33277 strain (TO16) was constructed and its phenotype compared with that of a pgfur A7436-derived mutant strain (TO6). In contrast to the TO6 strain, the TO16 strain did not differ in the growth rate and hemolytic activity compared with the ATCC 33277 strain. However, both mutant strains were more sensitive to oxidative stress and they demonstrated changes in the production of lysine- (Kgp) and arginine-specific (Rgp) gingipains. In contrast to the wild-type strains, TO6 and TO16 mutant strains produced larger amounts of HmuY protein under high iron/heme conditions. We also demonstrated differences in production of glycoconjugates between the A7436 and ATCC 33277 strains and we found evidence that PgFur protein might regulate glycosylation process. Moreover, we revealed that PgFur protein plays a role in interactions with other periodontopathogens and is important for P. gingivalis infection of THP-1-derived macrophages and survival inside the cells. Deletion of the pgfur gene influences expression of many transcription factors, including two not yet characterized transcription factors from the Crp/Fnr family. We also observed lower expression of the CRISPR/Cas genes.

Conclusions

We show here for the first time that inactivation of the pgfur gene exerts a different influence on the phenotype of the A7436 and ATCC 33277 strains. Our findings further support the hypothesis that PgFur regulates expression of genes encoding surface virulence factors and/or genes involved in their maturation.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1511-x) contains supplementary material, which is available to authorized users.

Biguanide is a modifiable pharmacophore for recruitment of endogenous Zn2+ to inhibit cysteinyl cathepsins: review and implications

Excessive activities of cysteinyl cathepsins (CysCts) contribute to the progress of many diseases; however, therapeutic inhibition has been problematic. Zn²⁺ is a natural inhibitor of proteases with CysHis dyads or CysHis(Xaa) triads. Biguanide forms bidentate metal complexes through the two imino nitrogens. Here, it is discussed that phenformin (phenylethyl biguanide) is a model for recruitment of endogenous Zn²⁺ to inhibit CysHis/CysHis(X) peptidolysis. Phenformin is a Zn²⁺-interactive, anti-proteolytic agent in bioassay of living tissue. Benzoyl-L-arginine amide (BAA) is a classical substrate of papain-like proteases; the amide bond is scissile. In this review, the structures of BAA and the phenformin-Zn²⁺ complex were compared in silico. Their chemistry and dimensions are discussed in light of the active sites of papain-like proteases. The phenyl moieties of both structures bind to the "S2" substrate-binding site that is typical of many proteases. When the phenyl moiety of BAA binds to S2, then the scissile amide bond is directed to the position of the thiolate-imidazolium ion pair, and is then hydrolyzed. However, when the phenyl moiety of phenformin binds to S2, then the coordinated Zn²⁺ is directed to the identical position; and catalysis is inhibited. Phenformin stabilizes a "Zn²⁺ sandwich" between the drug and protease active site. Hundreds of biguanide derivatives have been synthesized at the 1 and 5 nitrogen positions; many more are conceivable. Various substituent moieties can register with various arrays of substrate-binding sites so as to align coordinated Zn²⁺ with catalytic partners of diverse proteases. Biguanide is identified here as a modifiable pharmacophore for synthesis of therapeutic CysCt inhibitors with a wide range of potencies and specificities. Phenformin-Zn²⁺ Complex.

Controlling Streptococcus mutans and Staphylococcus aureus biofilms with direct current and chlorhexidine

Microbial biofilms formed on biomaterials are major causes of chronic infections. Among them, Gram-positive bacteria Streptococcus mutans and Staphylococcus aureus are important pathogens causing infections associated with dental caries (tooth-decay) and other medical implants. Unfortunately, current antimicrobial approaches are ineffective in disrupting established biofilms and new methods are needed to improve the efficacy. In this study, we report that the biofilm cells of S. mutans and S. aureus can be effectively killed by low-level direct current (DC) and through synergy in concurrent treatment with DC and chlorhexidine (CHX) at low concentrations. For example, after treatment with 28 µA/cm² DC and 50 µg/mL CHX for 1 h, the viability of biofilm cells was reduced by approximately 4 and 5 logs for S. mutans and S. aureus, respectively. These results are useful for developing more effective approaches to control pathogenic biofilms.

Effects of octenidine mouth rinse on apoptosis and necrosis of human fibroblasts and epithelial cells - an in vitro study

This study aimed at comparing the cytotoxicity of a new octenidine mouth rinse (MR) on gingival fibroblasts and epithelial cells using different established MRs. Octenidol (OCT), Chlorhexidine 0.2% (CHX), Meridol (MER), Oral B (OB), and control (PBS only) were used. Human primary gingival fibroblasts (HGFIBs) and human primary nasal epithelial cells (HNEPCs) were cultivated in cell-specific media (2 × 10⁵ cells/well) and treated with a MR or PBS for 1, 5, and 15 min. All tests were performed in duplicate and repeated 12 times. The apoptosis and necrosis were determined using a Caspase-3/7 assay and LDH assay, respectively. The data were analyzed using two-way analysis of variance with subsequent Mann-Whitney U-test. No significant differences could be found between the incubation times of the MR, neither for apoptosis nor necrosis (p > 0.05). Regarding apoptosis of HGFIBs, MRs had no influence at all. In HNEPCs, OCT induced relevantly lower apoptosis than CHX (p = 0.01). Considering necrosis, MER showed the lowest numbers of necrotic HGFIBs and HNEPCs, whereas OB induced the highest number of necrotic cells. The differences between both MR were statistically relevant (p < 0.01). OCT did neither differ from the other MRs nor from the control (PBS) in induction of necrosis in both cell types. In conclusion, the slightly negative effect of OCT considering apoptosis and necrosis of HGFIBs and HNEPCs is nearly the same or even lower compared to the established MRs included in this study. The results confirm that OCT is a potential alternative to CHX.

Contribution of cationic amino acids toward the inhibition of Arg-specific cysteine proteinase (Arg-gingipain) by the antimicrobial dodecapeptide, CL(14-25), from rice protein

CL(14-25), a dodecapeptide, exhibits antimicrobial activity against Porphyromonas gingivalis with the 50% growth-inhibitory concentration (IC50 ) value of 145 µM, and arginine-specific gingipain (Rgp)-inhibitory activity. Kinetic analysis revealed that CL(14-25) is a mixed-type inhibitor, with inhibition constants (Ki and Ki ' values) of 1.4 × 10(-6) M and 4.3 × 10(-6) M, respectively. To elucidate the contributions of four cationic amino acid residues at the N- and C-termini of CL(14-25) toward Rgp-inhibitory activity, we investigated the Rgp-inhibitory activities of truncated and alanine-substituted analogs of CL(14-25). Rgp-inhibitory activities significantly decreased by truncated analogs, CL(15-25) and CL(16-25), whereas those of CL(14-24) and CL(14-23) were almost as high as that of CL(14-25). Rgp-inhibitory activities of alanine-substituted analogs, CL(R14A) and CL(R14A, R15A) also significantly decreased, whereas those of CL(K25A) and CL(R24A, K25A) were higher than that of CL(14-25). These results suggest that the arginine residue at position 15 substantially contributes to the Rgp-inhibitory activity and that the arginine residue at position 14 plays important roles in exerting Rgp-inhibitory activity. In this study, we demonstrated that CL(K25A) was a potent, dual function, peptide inhibitor candidate, exhibiting Rgp-inhibitory activity with Ki and Ki ' of 9.6 × 10(-7) M and 1.9 × 10(-6) M, respectively, and antimicrobial activity against P. gingivalis with an IC50 value of 51 µM.

Polymeric nanoarchitectures on Ti-based implants for antibacterial applications

Because of the excellent mechanical properties and good biocompatibility, titanium-based metals are widely used in hard tissue repair, especially load-bearing orthopedic applications. However, bacterial infection and complication during and after surgery often causes failure of the metallic implants. To endow titanium-based implants with antibacterial properties, surface modification is one of the effective strategies. Possessing the unique organic structure composed of molecular and functional groups resembling those of natural organisms, functionalized polymeric nanoarchitectures enhance not only the antibacterial performance but also other biological functions that are difficult to accomplish on many conventional bioinert metallic implants. In this review, recent advance in functionalized polymeric nanoarchitectures and the associated antimicrobial mechanisms are reviewed.

In vitro activity of Carvacrol against titanium-adherent oral biofilms and planktonic cultures

OBJECTIVE

The aim of this study was to test the effect of Carvacrol against oral pathogens and their preformed biofilms on titanium disc surface.

METHODS

Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and biofilm inhibitory concentration (BIC) were performed to evaluate Carvacrol antibacterial activity, while flow cytometry (FCM) was used to verify the Carvacrol effect on esterase activity and membrane permeability. Carvacrol was tested in vitro on single- and multi-species biofilms formed on titanium disc by Streptococcus mutans ATCC 25175, Porphyromonas gingivalis ATCC 33277 or Fusobacterium nucleatum ATCC 25586, in different combinations, comparing its effect to that of chlorhexidine.

RESULTS

The pathogens were sensitive to Carvacrol with MICs and MBCs values of 0.25 % and 0.50 % and BICs of 0.5 % for S. mutans ATCC 25175 and 1 % for P. gingivalis ATCC 33277 and F. nucleatum ATCC 25586. FCM analysis showed that treatment of planktonic cultures with Carvacrol caused an increase of damaged cells and a decrement of bacteria with active esterase activity. Moreover, Carvacrol demonstrated greater biofilm formation preventive property compared to chlorhexidine against titanium-adherent single- and multi-specie biofilms, with statistically significant values.

CONCLUSIONS

Carvacrol showed inhibitory activity against the tested oral pathogens and biofilm formation preventive property on their oral biofilm; then, it could be utilized to control and prevent the colonization of microorganisms with particular significance in human oral diseases.

CLINICAL RELEVANCE

This natural compound may be proposed in daily hygiene formulations or as an alternative agent supporting traditional antimicrobial protocols to prevent periodontal diseases in implanted patients.

Removing bacteria from rough surface titanium discs with chlorhexidine and additional brushing with dentifrice

OBJECTIVES

This in vitro study was conducted: (i) to evaluate the effect of using cotton pellets soaked with chlorhexidine (CHX) on titanium surface roughness; (ii) to assess the removal of Porphyromonas gingivalis (P. gingivalis) from resorbable blast material (RBM) titanium surfaces using CHX pellets; and (iii) to evaluate the effects of additional brushing on bacterial removal efficiency.

MATERIALS AND METHODS

RBM titanium discs were treated with CHX-soaked cotton pellets, and change in surface roughness was measured using confocal microscopy. After the titanium discs were incubated with P. gingivalis for 2 days, the discs were cleaned with CHX pellets for 40 s. The quantity of remaining adherent bacteria was measured using crystal violet assay. Additional brushing was performed with dentifrice for a total of 40 s, and bacterial removal efficiency with brushing and dentifrice was evaluated using crystal violet assay and scanning electron microscopy.

RESULTS

The changes in surface roughness after treatment were observed by confocal microscopy. Statistically significant decrease in surface roughness was seen in CHX 40-s group (p < 0.05). Cleaning with CHX-soaked pellets resulted in significant decrease in remaining adherent bacteria. Brushing the bacteria-incubated discs with dentifrice reduced adhering bacteria. There were fewer bacteria left on the CHX-pre-treated discs compared with the brushing-only group, but there were no significant differences when compared with the brushing-only group (p > 0.05).

CONCLUSIONS

This study clearly showed that burnishing with CHX influenced the RBM titanium surface, and burnishing with CHX pellets and brushing with dentifrice were efficient in removing bacteria from the contaminated titanium surface.

Assessment of cytogenetic and cytotoxic effects of chlorhexidine digluconate on cultured human lymphocytes

OBJECTIVE

The aim of this study was to assess the genetic and cellular toxicity of Chlorhexidine digluconate (CHX) on peripheral human lymphocytes in vitro.

MATERIALS AND METHODS

Micronucleus assay was used to investigate the genotoxicity, while the cell viability and proliferation were evaluated by Trypan blue exclusion test and Nuclear Division Index in control and CHX-treated (0.05, 0.1, 0.2, 0.4, 0.5 mg/ml) human blood cultures.

RESULTS

A dose-dependent toxic effect was found depending on CHX incubation on the genetic and cell viability of the lymphocytes. Micronucleus frequency was found to be statistically higher at 0.5 mg/ml concentration compared to lower doses and the control group (p < 0.05). A significant reduction was shown in the cell viability and cell proliferation of the exposed lymphocytes at the concentrations of 0.4 and 0.5 mg/ml (p < 0.05), while no significant toxicity was found at lower concentrations compared to control (p > 0.05).

CONCLUSION

This study showed dose-dependent genotoxic and cytotoxic effects of CHX on human lymphocytes in vitro. It should be considered during periodontal irrigation or novel CHX products at lower concentrations should be manufactured for clinical usage.

Inhibition of acetylpolyamine and spermine oxidases by the polyamine analogue chlorhexidine

Acetylpolyamine and spermine oxidases are involved in the catabolism of polyamines. The discovery of selective inhibitors of these enzymes represents an important tool for the development of novel anti-neoplastic drugs. Here, a comparative study on acetylpolyamine and spermine oxidases inhibition by the polyamine analogue chlorhexidine is reported. Chlorhexidine is an antiseptic diamide, commonly used as a bactericidal and bacteriostatic agent. Docking simulations indicate that chlorhexidine binding to these enzymes is compatible with the stereochemical properties of both acetylpolyamine oxidase and spermine oxidase active sites. In fact, chlorhexidine is predicted to establish several polar and hydrophobic interactions with the active site residues of both enzymes, with binding energy values ranging from -7.6 to -10.6 kcal/mol. In agreement with this hypothesis, inhibition studies indicate that chlorhexidine behaves as a strong competitive inhibitor of both enzymes, values of Ki being 0.10 μM and 0.55 μM for acetylpolyamine oxidase and spermine oxidase, respectively.

A phage display selected 7-mer peptide inhibitor of the Tannerella forsythia metalloprotease-like enzyme Karilysin can be truncated to Ser-Trp-Phe-Pro

Tannerella forsythia is a gram-negative bacteria, which is strongly associated with the development of periodontal disease. Karilysin is a newly identified metalloprotease-like enzyme, that is secreted from T. forsythia. Karilysin modulates the host immune response and is therefore considered a likely drug target. In this study peptides were selected towards the catalytic domain from Karilysin (Kly18) by phage display. The peptides were linear with low micromolar binding affinities. The two best binders (peptide14 and peptide15), shared the consensus sequence XWFPXXXGGG. A peptide15 fusion with Maltose Binding protein (MBP) was produced with peptide15 fused to the N-terminus of MBP. The peptide15-MBP was expressed in E. coli and the purified fusion-protein was used to verify Kly18 specific binding. Chemically synthesised peptide15 (SWFPLRSGGG) could inhibit the enzymatic activity of both Kly18 and intact Karilysin (Kly48). Furthermore, peptide15 could slow down the autoprocessing of intact Kly48 to Kly18. The WFP motif was important for inhibition and a truncation study further demonstrated that the N-terminal serine was also essential for Kly18 inhibition. The SWFP peptide had a Ki value in the low micromolar range, which was similar to the intact peptide15. In conclusion SWFP is the first reported inhibitor of Karilysin and can be used as a valuable tool in structure-function studies of Karilysin.

Chlorhexidine decreases the risk of ventilator-associated pneumonia in intensive care unit patients: a randomized clinical trial

BACKGROUND AND OBJECTIVE

The aim was to evaluate whether oral swabbing with 0.2% chlorhexidine gluconate (CHX) decreases the risk of ventilator-associated pneumonia (VAP) in intensive care unit (ICU) patients.

MATERIAL AND METHODS

Sixty-one dentate patients scheduled for invasive mechanical ventilation for at least 48 h were included in this randomized, double-blind, controlled study. As these patients were variably incapacitated, oral care was provided by swabbing the oral mucosa four times/d with CHX in the CHX group (29 patients) and with saline in the control group (32 patients). Clinical periodontal measurements were recorded, and lower-respiratory-tract specimens were obtained for microbiological analysis on admission and when VAP was suspected. Pathogens were identified by quantifying colonies using standard culture techniques.

RESULTS

Ventilator-associated pneumonia developed in 34/61 patients (55.7%) within 6.8 d. The VAP development rate was significantly higher in the control group than in the CHX group (68.8% vs. 41.4%, respectively; p = 0.03) with an odds ratio of 3.12 (95% confidence interval = 1.09-8.91). Acinetobacter baumannii was the most common pathogen (64.7%) of all species identified. There were no significant differences between the two groups in clinical periodontal measurements, VAP development time, pathogens detected or mortality rate.

CONCLUSION

The finding of the present study, that oral care with CHX swabbing reduces the risk of VAP development in mechanically ventilated patients, strongly supports its use in ICUs and indeed the importance of adequate oral hygiene in preventing medical complications.

Chlorhexidine delivery system from titanium/polybenzyl acrylate coating: evaluation of cytotoxicity and early bacterial adhesion

OBJECTIVES

The formation of biofilms on titanium dental implants is one of the main causes of failure of these devices. Streptococci are considered early colonizers that alter local environment favouring growing conditions for other colonizers. Chlorhexidine (CHX) is so far the most effective antimicrobial treatment against a wide variety of Gram-positive and Gram-negative organisms as well as fungi. This study was designed to develop a CHX delivery system appropriate for healing caps and abutments, with suitable drug release rate, effective as antimicrobial agent, and free of cytotoxic effects.

METHODS

Polybenzyl acrylate (PBA) coatings with and without CHX (Ti/PBA and Ti/PBA-CHX, respectively) and different drug loads (0.35, 0.70, and 1.40%, w/w) were assayed. The cytotoxic effect of CHX released from the different substrates on UMR106 cells was tested by alkaline phosphatase specific activity (ALP), and microscopic evaluation of the cells. Non-cytotoxic drug load (0.35%, w/w) was selected to evaluate the antimicrobial effectiveness of the system using a microbial consortium of Streptococcus species.

RESULTS

The kinetic profile of CHX delivered by Ti/PBA-CHX showed an initial fast release rate followed by a monotonic increase of delivered mass over 48 h. The number of attached bacteria decreased in the following order: Ti>Ti/PBA>Ti/PBA-0.35.

CONCLUSIONS

PBA-0.35 coating is effective to inhibit the adhesion of early colonizers on Ti without any cytotoxic effect on UMR-106 cells.

Microbial and fungal protease inhibitors--current and potential applications

Proteolytic enzymes play essential metabolic and regulatory functions in many biological processes and also offer a wide range of biotechnological applications. Because of their essential roles, their proteolytic activity needs to be tightly regulated. Therefore, small molecules and proteins that inhibit proteases can be versatile tools in the fields of medicine, agriculture and biotechnology. In medicine, protease inhibitors can be used as diagnostic or therapeutic agents for viral, bacterial, fungal and parasitic diseases as well as for treating cancer and immunological, neurodegenerative and cardiovascular diseases. They can be involved in crop protection against plant pathogens and herbivorous pests as well as against abiotic stress such as drought. Furthermore, protease inhibitors are indispensable in protein purification procedures to prevent undesired proteolysis during heterologous expression or protein extraction. They are also valuable tools for simple and effective purification of proteases, using affinity chromatography. Because there are such a large number and diversity of proteases in prokaryotes, yeasts, filamentous fungi and mushrooms, we can expect them to be a rich source of protease inhibitors as well.

Diagnostic evaluation of a nanobody with picomolar affinity toward the protease RgpB from Porphyromonas gingivalis

Porphyromonas gingivalis is one of the major periodontitis-causing pathogens. P. gingivalis secretes a group of proteases termed gingipains, and in this study we have used the RgpB gingipain as a biomarker for P. gingivalis. We constructed a naive camel nanobody library and used phage display to select one nanobody toward RgpB with picomolar affinity. The nanobody was used in an inhibition assay for detection of RgpB in buffer as well as in saliva. The nanobody was highly specific for RgpB given that it did not bind to the homologous gingipain HRgpA. This indicated the presence of a binding epitope within the immunoglobulin-like domain of RgpB. A subtractive inhibition assay was used to demonstrate that the nanobody could bind native RgpB in the context of intact cells. The nanobody bound exclusively to the P. gingivalis membrane-bound RgpB isoform (mt-RgpB) and to secreted soluble RgpB. Further cross-reactivity studies with P. gingivalis gingipain deletion mutants showed that the nanobody could discriminate between native RgpB and native Kgp and RgpA in complex bacterial samples. This study demonstrates that RgpB can be used as a specific biomarker for P. gingivalis detection and that the presented nanobody-based assay could supplement existing methods for P. gingivalis detection.

Comparative in vitro study among the effects of different laser and LED irradiation protocols and conventional chlorhexidine treatment for deactivation of bacterial lipopolysaccharide adherent to titanium surface

OBJECTIVE AND BACKGROUND

The present in vitro study was designed to evaluate and compare the efficacy of: 1) different dental laser devices used in photoablative (PA) mode, namely commercial CO(2), Er:YAG, and Nd:YAG lasers and a prototype diode laser (wavelength = 810  nm); 2) prototype low-energy laser diode or light-emitting diode (LED) (wavelength = 630  nm), used in photodynamic (PD) mode together with the photoactivated agent methylene blue; and 3) chlorhexidine, used as reference drug, to reduce the activation of macrophages by lipopolysaccharide (LPS), a major pro-inflammatory gram-negative bacterial endotoxin, adherent to titanium surface.

METHODS

RAW 264-7 macrophages were cultured on titanium discs, cut from commercial dental implants and precoated with Porphyromonas gingivalis LPS. Before cell seeding, the discs were treated or not with the noted lasers and LED in PA and PD modes, or with chlorhexidine. The release of nitric oxide (NO), assumed to be a marker of macrophage inflammatory activation, in the conditioned medium was related to cell viability, evaluated by the MTS assay and ultrastructural analysis.

RESULTS

PA laser irradiation of the LPS-coated discs with Er:YAG, Nd:YAG, CO(2,) and diode (810  nm) significantly reduced NO production, with a maximal inhibition achieved by Nd:YAG and diode (810  nm). Similar effects were also obtained by PD treatment with diode laser and LED (630  nm) and methylene blue. Notably, both treatments were superior to chlorhexidine in terms of efficiency/toxicity ratio.

CONCLUSIONS

These findings suggest that laser and LED irradiation are capable of effectively reducing the inflammatory response to LPS adherent to titanium surface, a notion that may have clinical relevance.

Porphyromonas gingivalis cysteine proteinase inhibition by kappa-casein peptides

Porphyromonas gingivalis is a major pathogen associated with chronic periodontitis, an inflammatory disease of the supporting tissues of the teeth. The Arg-specific (RgpA/B) and Lys-specific (Kgp) cysteine proteinases of P. gingivalis are major virulence factors for the bacterium. In this study κ-casein(109-137) was identified in a chymosin digest of casein as an inhibiting peptide of the P. gingivalis proteinases. The peptide was synthesized and shown to inhibit proteolytic activity associated with P. gingivalis whole cells, purified RgpA-Kgp proteinase-adhesin complexes, and purified RgpB proteinase. The peptide κ-casein(109-137) exhibited synergism with Zn(II) against both Arg- and Lys-specific proteinases. The active region for inhibition was identified as κ-casein(117-137) using synthetic peptides. Kinetic studies revealed that κ-casein(109-137) inhibits in an uncompetitive manner. A molecular model based on the uncompetitive action and its synergistic ability with Zn(II) was developed to explain the mechanism of inhibition. Preincubation of P. gingivalis with κ-casein(109-137) significantly reduced lesion development in a murine model of infection.

Antimicrobial activity of Rosmarinus officinalis against oral pathogens: relevance of carnosic acid and carnosol

The in vitro inhibitory activity of crude EtOH/H2O extracts from the leaves and stems of Rosmarinus officinalis L. was evaluated against the following microorganisms responsible for initiating dental caries: Streptococcus mutans, S. salivarius, S. sobrinus, S. mitis, S. sanguinis, and Enterococcus faecalis. Minimum inhibitory concentrations (MIC) were determined with the broth microdilution method. The bioassay-guided fractionation of the leaf extract, which displayed the higher antibacterial activity than the stem extract, led to the identification of carnosic acid (2) and carnosol (3) as the major compounds in the fraction displaying the highest activity, as identified by HPLC analysis. Rosmarinic acid (1), detected in another fraction, did not display any activity against the selected microorganisms. HPLC Analysis revealed the presence of low amounts of ursolic acid (4) and oleanolic acid (5) in the obtained fractions. The results suggest that the antimicrobial activity of the extract from the leaves of R. officinalis may be ascribed mainly to the action of 2 and 3.

Differential effects of periopathogens on host protease inhibitors SLPI, elafin, SCCA1, and SCCA2

Objective

Secretory leukocyte peptidase inhibitors (SLPI), elafin, squamous cell carcinoma antigen 1 and 2 (SCCA1 and SCCA2) are specific endogenous serine protease inhibitors expressed by epithelial cells that prevent tissue damage from excessive proteolytic enzyme activity due to inflammation. To determine the effects of various periopathogens on these protease inhibitors, we utilized human gingival epithelial cells (GECs) challenged with cell-free bacteria supernatants of various periopathogens Porphyromonas gingivalis, Tannerella forsythia, Aggregatibacter actinomycetemcomitans, and Fusobacterium nucleatum.

Design

The gene expression and secretion of SLPI, elafin, SCCA1, and SCCA2 were determined using real-time PCR and ELISA, respectively. The direct effects of periopathogens and P. gingivalis gingipain mutants on these inhibitors were examined in vitro by Western Blot. The effect on the innate immune response of GECs was measured by expression of antimicrobial peptides: human beta-defenisin-2 (hBD2) and chemokine (C-C motif) ligand 20 (CCL20).

Results

We found that SLPI, SCCA2, elafin, hBD2, and CCL20 gene expression levels were significantly induced (p<0.001) in response to P. gingivalis, whose virulence factors include cysteine proteases, but not in response to stimulation by other bacteria. P. gingivalis reduced the secretion of SLPI and elafin significantly in GECs, and degraded recombinant SLPI, elafin, SCCA1, and SCCA2. Differential degradation patterns of SLPI, elafin, SCCA1, and SCCA2 were observed with different bacteria as well as P. gingivalis mutants associated with the loss of specific gingipains secreted by P. gingivalis. In addition, pretreatment of GECs with SLPI, SCCA1, or SCCA2 partially blocked hBD2 and CCL20 mRNA expression in response to P. gingivalis, suggesting a protective effect.

Conclusion

Our results suggest that different periopathogens affect the host protease inhibitors in a different manner, suggesting host susceptibility may differ in the presence of these pathogens. The balance between cellular protease inhibitors and their degradation may be an important factor in susceptibility to periodontal infection.

A randomized trial of chlorhexidine gluconate on oral bacterial pathogens in mechanically ventilated patients

INTRODUCTION

Dental plaque biofilms are colonized by respiratory pathogens in mechanically-ventilated intensive care unit patients. Thus, improvements in oral hygiene in these patients may prevent ventilator-associated pneumonia. The goal of this study was to determine the minimum frequency (once or twice a day) for 0.12% chlorhexidine gluconate application necessary to reduce oral colonization by pathogens in 175 intubated patients in a trauma intensive care unit.

METHODS

A randomized, double-blind, placebo-controlled clinical trial tested oral topical 0.12% chlorhexidine gluconate or placebo (vehicle alone), applied once or twice a day by staff nurses. Quantitation of colonization of the oral cavity by respiratory pathogens (teeth/denture/buccal mucosa) was measured.

RESULTS

Subjects were recruited from 1 March, 2004 until 30 November, 2007. While 175 subjects were randomized, microbiologic baseline data was available for 146 subjects, with 115 subjects having full outcome assessment after at least 48 hours. Chlorhexidine reduced the number of Staphylococcus aureus, but not the total number of enterics, Pseudomonas or Acinetobacter in the dental plaque of test subjects. A non-significant reduction in pneumonia rate was noted in groups treated with chlorhexidine compared with the placebo group (OR = 0.54, 95% CI: 0.23 to 1.25, P = 0.15). No evidence for resistance to chlorhexidine was noted, and no adverse events were observed. No differences were noted in microbiologic or clinical outcomes between treatment arms.

CONCLUSIONS

While decontamination of the oral cavity with chlorhexidine did not reduce the total number of potential respiratory pathogens, it did reduce the number of S. aureus in dental plaque of trauma intensive care patients.

Degradation of collagen-guided tissue regeneration membranes by proteolytic enzymes of Porphyromonas gingivalis and its inhibition by antibacterial agents

Previous studies have shown that whole cells of several periodontal pathogenic bacteria including Porphyromonas gingivalis may degrade the clinically used regeneration membranes Biomend Extend and Bio-Gide. Fractionation of P. gingivalis cells revealed that cell membrane-associated proteases are responsible for the in vitro degradation of the collagen membranes. In the present study, the specific role of extracellular vesicles and the purified Arg-gingipain enzyme of P. gingivalis in the degradation of three differently cross-linked collagen membranes (Ossix; Bio-Gide and Biomend Extend) was examined. In addition, the inhibitory effect of antibacterial agents and antibiotics used in local periodontal therapy on the enzymatic degradation was evaluated. The data presented show that while all tested collagen membranes, are prone to lysis by oral bacterial proteases, cross-linked membranes are more resistant to proteolysis. Furthermore, therapeutical concentrations of the antibacterial and antibiotic agents chlorhexidine, cetylpyridiniumchloride, minocycline and doxycycline were found to partially inhibit the enzymatic breakdown of the membranes, while metronidazole had no such effect. These results suggest that the presence of P. gingivalis cells, extracellular vesicles and enzymes in the vicinity of regeneration membranes in the periodontium, may change their physical structure and therefore alter their biological properties. Furthermore, the use of cross-linked collagen membranes and antibacterial agents may significantly inhibit this proteolytic process.

Effect of chlorhexidine digluconate on different cell types: a molecular and ultrastructural investigation

Although several studies have shown that chlorhexidine digluconate (CHX) has bactericidal activity against periodontal pathogens and exerts toxic effects on periodontal tissues, few have been directed to evaluate the mechanisms underlying its adverse effects on these tissues. Therefore, the aim of the present study was to investigate the in vitro cytotoxicity of CHX on cells that could represent common targets for its action in the surgical procedures for the treatment of periodontitis and peri-implantitis and to elucidate its mechanisms of action. Osteoblastic, endothelial and fibroblastic cell lines were exposed to various concentrations of CHX for different times and assayed for cell viability and cell death. Also analysis of mitochondrial membrane potential, intracellular Ca2+ mobilization and reactive oxygen species (ROS) generation were done in parallel, to correlate CHX-induced cell damage with alterations in key parameters of cell homeostasis. CHX affected cell viability in a dose and time-dependent manners, particularly in osteoblasts. Its toxic effect consisted in the induction of apoptotic and autophagic/necrotic cell deaths and involved disturbance of mitochondrial function, intracellular Ca2+ increase and oxidative stress. These data suggest that CHX is highly cytotoxic in vitro and invite to a more cautioned use of the antiseptic in the oral surgical procedures.