Modulation of human gingival fibroblast cell metabolism by methyl mercaptan

Interspecies metabolite transfer fuels the methionine metabolism of Fusobacterium nucleatum to stimulate volatile methyl mercaptan production

The major oral odor compound methyl mercaptan (CH3SH) is strongly associated with halitosis and periodontitis. CH3SH production stems from the metabolism of polymicrobial communities in periodontal pockets and on the tongue dorsum. However, understanding of CH3SH-producing oral bacteria and their interactions is limited. This study aimed to investigate CH3SH production by major oral bacteria and the impact of interspecies interactions on its generation. Using a newly constructed large-volume anaerobic noncontact coculture system, Fusobacterium nucleatum was found to be a potent producer of CH3SH, with that production stimulated by metabolic interactions with Streptococcus gordonii, an early dental plaque colonizer. Furthermore, analysis of extracellular amino acids using an S. gordonii arginine-ornithine antiporter (ArcD) mutant demonstrated that ornithine excreted from S. gordonii is a key contributor to increased CH3SH production by F. nucleatum. Further study with 13C, 15N-methionine, as well as gene expression analysis, revealed that ornithine secreted by S. gordonii increased the demand for methionine through accelerated polyamine synthesis by F. nucleatum, leading to elevated methionine pathway activity and CH3SH production. Collectively, these findings suggest that interaction between S. gordonii and F. nucleatum plays a key role in CH3SH production, providing a new insight into the mechanism of CH3SH generation in oral microbial communities. A better understanding of the underlying interactions among oral bacteria involved in CH3SH generation can lead to the development of more appropriate prophylactic approaches to treat halitosis and periodontitis. An intervention approach like selectively disrupting this interspecies network could also offer a powerful therapeutic strategy.IMPORTANCEHalitosis can have a significant impact on the social life of affected individuals. Among oral odor compounds, CH3SH has a low olfactory threshold and halitosis is a result of its production. Recently, there has been a growing interest in the collective properties of oral polymicrobial communities, regarded as important for the development of oral diseases, which are shaped by physical and metabolic interactions among community participants. However, it has yet to be investigated whether interspecies interactions have an impact on the production of volatile compounds, leading to the development of halitosis. The present findings provide mechanistic insights indicating that ornithine, a metabolite excreted by Streptococcus gordonii, promotes polyamine synthesis by Fusobacterium nucleatum, resulting in a compensatory increase in demand for methionine, which results in elevated methionine pathway activity and CH3SH production. Elucidation of the mechanisms related to CH3SH production is expected to lead to the development of new strategies for managing halitosis.

Potent necrosis effect of methanethiol mediated by METTL7B enzyme bioactivation mechanism in 16HBE cell

Methanethiol is a widely existing malodorous pollutant with health effects on the human population. However, the cytotoxicity mechanism of methanethiol in vitro and its metabolic transformation (bioactivation or detoxification) have not been fully elucidated. Herein, the metabolites of methanethiol during cell culture and the cytotoxicity of methanethiol in human bronchial epithelial (16HBE) cells were investigated. Results indicate that methanethiol (10-50 μM) was partially converted into dimethyl sulfide, mainly catalyzed by thiol S-methyltransferase in the 16HBE cells, and then it induced potent cytotoxicity and cell membrane permeability. Moreover, methanethiol induced intracellular reactive oxygen species (ROS) up to 50 μM and further activated the tumor necrosis factor (TNF) signaling pathway, which eventually led to the decline in the mitochondrial membrane potential (MMP) and cell necrosis. However, all these effects were significantly alleviated with gene silencing of the methyltransferase-like protein 7B (METTL7B). These results indicate that methanethiol may induce cell necrosis in human respiratory tract cells mainly mediated by S-methyltransferase with interfering TNF and ROS induction. Non-target metabolomics results suggest that methanethiol potently affects expression of endogenous small molecule metabolites in 16HBE cells. To some extent, this work shows the possible conversion path and potential injury mechanism of human respiratory tract cells exposed to methanethiol.

Porphyromonas gingivalis virulence in a Drosophila melanogaster model

Porphyromonas gingivalis has been implicated in the etiology of adult periodontitis. In this study, we examined the viability of Drosophila melanogaster as a new model for examining P. gingivalis-host interactions. P. gingivalis (W83) infection of Drosophila resulted in a systemic infection that killed in a dose-dependent manner. Differences in the virulence of several clinically prevalent P. gingivalis strains were observed in the Drosophila killing model, and the results correlated well with studies in mammalian infection models and human epidemiologic studies. P. gingivalis pathobiology in Drosophila did not result from uncontrolled growth of the bacterium in the Drosophila hemolymph (blood) or overt damage to Drosophila tissues. P. gingivalis killing of Drosophila was multifactorial, involving several bacterial factors that are also involved in virulence in mammals. The results from this study suggest that many aspects of P. gingivalis pathogenesis in mammals are conserved in Drosophila, and thus the Drosophila killing model should be useful for characterizing P. gingivalis-host interactions and, potentially, polymicrobe-host interactions.

Virulence factors of the oral spirochete Treponema denticola

There is compelling evidence that treponemes are involved in the etiology of several chronic diseases, including chronic periodontitis as well as other forms of periodontal disease. There are interesting parallels with other chronic diseases caused by treponemes that may indicate similar virulence characteristics. Chronic periodontitis is a polymicrobial disease, and recent animal studies indicate that co-infection of Treponema denticola with other periodontal pathogens can enhance alveolar bone resorption. The bacterium has a suite of molecular determinants that could enable it to cause tissue damage and subvert the host immune response. In addition to this, it has several non-classic virulence determinants that enable it to interact with other pathogenic bacteria and the host in ways that are likely to promote disease progression. Recent advances, especially in molecular-based methodologies, have greatly improved our knowledge of this bacterium and its role in disease.

Development of a Compact and Simple Gas Chromatography for Oral Malodor Measurement

BACKGROUND

Volatile sulfur compounds (VSCs) in oral air are the only type of gases correlated with the strength of oral malodor. We developed a compact and simple gas chromatograph (GC) equipped with a newly invented indium oxide semiconductor gas sensor (SCS) for measuring the concentrations of VSCs in mouth air. We have assessed the correlation between measurements with a GC-SCS and those with a regular GC.

METHODS

Oral air samples from randomly selected volunteers were analyzed with both a GC-SCS and a GC with a flame photometric detector (FPD), which is specific to VSCs, and GC-SCS measurements were compared to those obtained by GC-FPD. Subsequently, oral air samples before and after mouthrinsing with 5% ethanol mouthwash were analyzed to determine the effect of ethanol on VSC measurements by GC-SCS.

RESULTS

There were strong correlations between VSC concentrations determined using these two gas chromatography methods (hydrogen sulfide, R=0.821, P<0.0001; methyl mercaptan, R=0.870, P<0.0001; and dimethyl sulfide, R=0.770, P<0.0001). Although GC-SCS can differentiate ethanol and VSCs in oral air samples after mouthrinsing, GC-SCS measurements demonstrated higher values than those obtained by GC-FPD; however, this discrepancy improved over time due to the reduced effect of ethanol.

CONCLUSION

The results suggest that GC-SCS may be useful for the diagnosis of halitosis.

Volatile sulfur compounds produced by Helicobacter pylori

GOALS

To assess the volatile sulfur compounds produced by three strains of Helicobacter pylori in broth cultures mixed with sulfur-containing amino acids.

BACKGROUND

Halitosis has been reported in H. pylori-positive patients, and volatile sulfur compounds such as hydrogen sulfide and methyl mercaptan are known to be responsible for inducing oral malodor. Whether H. pylori produces these volatile sulfur compounds has yet to be established.

STUDY

Three strains of H. pylori (ATCC 43504, SS 1, DSM 4867) were cultured with 5 mM cysteine and methionine. After 72 hours of incubation, the headspace air was aspirated and injected directly into a gas chromatograph. The concentrations of hydrogen sulfide and methyl mercaptan were analyzed and compared between experimental and control cultures

RESULTS

In broth containing 5 mM cysteine, hydrogen sulfide was increased by ATCC 43504 (P < 0.01) and SS 1 (P < 0.05), while methyl mercaptan was elevated only by SS 1 (P < 0.05). In broth containing 5 mM methionine, methyl mercaptan increases were significant for SS 1 (P < 0.05) and DSM 4867 (P < 0.05). In broth containing 5 mM cysteine and 5 mM methionine, the concentration of hydrogen sulfide was higher than in controls for all three strains (P < 0.01); that of methyl mercaptan was higher only for SS 1 (P < 0.01). Cysteine addition to cultures containing methionine increased hydrogen sulfide and methyl mercaptan for ATCC 43504 (P < 0.05) and SS 1 (P < 0.05). Conversely, addition of methionine to cultures containing cysteine increased methyl mercaptan only for DSM 4867 (P < 0.01).

CONCLUSIONS

The production of volatile sulfur compounds by H. pylori is not only very complicated but also strain-specific. Nevertheless, H. pylori was shown to produce hydrogen sulfide and methyl mercaptan, which suggests that this microorganism can contribute to the development of halitosis.

Proinflammatory cytokine profiles in pulp fibroblasts stimulated with lipopolysaccharide and methyl mercaptan

Pulpal disease is intimately associated with the immune system's response to bacteria products. Clinical pathology is mediated in part by the production of pyrogenic cytokines, especially interleukin (IL)-1, tumor necrosis factor (TNF)-alpha, and IL-6. Methyl mercaptan (CH3SH), a volatile sulfur compound produced by anaerobic Gram-negative bacteria, has been shown to contribute to the production of IL-1 by human mononuclear cells. In this report, we investigated the production of IL-1, TNF-alpha, and IL-6 by human pulp fibroblasts when stimulated for various periods of time with lipopolysaccharide (LPS) with or without the presence of CH3SH. We found that LPS and CH3SH had no effect on the production of IL-1 or TNF-alpha. However, LPS stimulated IL-6 production, and this production was augmented when CH3SH was present. We conclude that the volatile sulfur compound CH3SH plays a role in activation and modulation of the immune response through its role in production of IL-6.

Monitoring ammonia to assess halitosis

OBJECTIVE

This study examined the applicability of ammonia monitoring for assessing halitosis.

STUDY DESIGN

The actual degree of halitosis was determined by using an organoleptic test in 61 subjects aged 28 +/- 10 years (mean +/- SD). Levels of volatile sulfur compounds and ammonia were determined by using gas chromatography and ammonia monitoring, respectively. Levels of ammonia and methyl mercaptan produced by bacteria in dental plaque and tongue-coating samples obtained from 25 subjects were quantified. In addition, changes in ammonia levels were measured before and after removing tongue coating or dental plaque.

RESULTS

There was no significant correlation between the organoleptic score and the ammonia level measured with ammonia monitoring, whereas there was a significant correlation between ammonia level and the total level of volatile sulfur compounds measured with gas chromatography. Significant correlations were also observed between ammonia level and levels of methyl mercaptan produced by bacteria in dental plaque and tongue coating. Furthermore, the ammonia level decreased after the removal of tongue coating and dental plaque.

CONCLUSION

These results indicate that measuring ammonia levels is useful for assessing halitosis, specifically for halitosis arising from a lack of oral hygiene.

The effects of methyl mercaptan on epithelial cell growth and proliferation

AIM

Previous studies have demonstrated that methyl mercaptan (CH3SH), one of the main causes of oral malodour, might contribute to the initiation and progression of periodontal disease. These studies suggested that CH3SH may affect the epithelial cells of the gingival crevice, which form a barrier to the penetration of microbial substances. In this study, the effects of CH3SH on the epithelial cells and gingival fibroblasts were investigated.

METHOD

Human oral epithelial carcinoma cell line (KB), human oral squamous cell carcinoma cell line (HSC-2), and human gingival fibroblasts (HGF) derived from healthy gingiva were used in this study. These cells were cultured in conditions of 5% CO2/95% air with or without CH3SH (10 ng/ml or 50 ng/ml) for 5 days. Cell numbers, proliferation and cytotoxicity were evaluated.

RESULTS

CH3SH inhibited epithelial cell growth and proliferation at the concentration of 50 ng/ml, and a cytotoxic effect of CH3SH was also noted. On the other hand, HGF cells were not affected by 50 ng/ml CH3SH.

CONCLUSION

High concentrations of CH3SH such as 50 ng/ml have an inhibitory effect on the growth and proliferation of epithelial cells, but not on those of fibroblasts.

Association between oral malodor and adult periodontitis: a review

BACKGROUND

Bad breath has a significant impact on our daily social life to those who suffer from it. The majority of bad breath originates within the oral cavity. However, it is also possible that it can come from other sources such as gastric-intestine imbalance. The term "oral malodor" is used to describe a foul or offensive odor emanating from the oral cavity, in which proteolysis, metabolic products of the desquamating cell, and bacterial putrefaction are involved. Recent evidence has demonstrated a link between oral malodor and adult periodontitis. The process of developing bad breath is similar to that noted in the progression of gingivitis/periodontitis. Oral malodor is mainly attributed to volatile sulfur compounds (VSC) such as hydrogen sulfide, methyl mercaptan and dimethyl sulfide. The primary causative microbes are gram-negative, anaerobic bacteria that are similar to the bacteria causing periodontitis. These bacteria produce the VSC by metabolizing different cells/tissues (i.e., epithelial cells, leukocytes, etc.) located in saliva, dental plaque, and gingival crevicular fluid. Tongue surface is composed of blood components, nutrients, large amounts of desquamated epithelial cells and bacteria, suggesting that it has the proteolytic and putrefactive capacity to produce VSC. One of the challenges in dealing with oral malodor is to identify a reliable test for detecting bad breath.

AIMS

The purposes of this review article were: (1) to correlate the relationship between oral malodor and adult periodontitis; (2) to analyze current malodor tests and discuss available treatment regimens.

Relationship of sulcular sulfide level to severity of periodontal disease and BANA test

BACKGROUND

Volatile sulfur compounds (VSC), such as hydrogen sulfide and methyl mercaptan, are toxic metabolites produced by periodontal pathogens. Their relationship to periodontal disease severity is not yet fully understood. Hence, the aims of this study were to: 1) examine the relationship between sulcular sulfide (pS) levels and severity of periodontal disease and 2) examine the link between pS level and the BANA (benzoyl-DL-arginine-naphthylamide) test.

METHODS

Seventy systemically healthy subjects with a mean age of 53.0 +/- 13.8 years participated. Three sites were selected from each subject based upon radiographic bone loss (RBL): RBL < 2 mm, healthy; RBL > or = 2 to < 4, low to moderate; RBL > or = 4 mm, severe. Periodontal parameters, probing depth (PD), clinical attachment level (CAL), and bleeding on probing (BOP), were recorded. The pS level was measured using a portable sulfide monitor in a digital score ranging from 0.0 (< 10(-7) M of S) to 5.0 (> or = 10(-2) M of S) in increments of 0.5. The presence of specific bacteria in subgingival plaque was detected using BANA test.

RESULTS

The mean pS level was 0.10 +/- 0.23, 0.36 +/- 0.48, and 1.10 +/- 0.87 for healthy, low to moderate, and severe disease sites, respectively, and was statistically different (P<0.001). The pS level was positively correlated with the BANA test, and was higher in untreated subjects than maintenance subjects (P<0.01).

CONCLUSIONS

The pS level may be a potential indicator for detecting severity of periodontal disease and identifying bacteria that are capable of hydrolyzing BANA.

Formation of methyl mercaptan from L-methionine by Porphyromonas gingivalis

Methyl mercaptan production by oral bacteria is thought to be one of the main causes of oral malodor. We examined the ability of periodontopathic Porphyromonas gingivalis to produce methyl mercaptan from L-methionine and found that the invasive strains W83 and W50 produced large amounts of methyl mercaptan. We cloned and sequenced the mgl gene encoding L-methionine-alpha-deamino-gamma-mercaptomethane-lyase (METase) from P. gingivalis W83. The structural mgl gene consisted of 1,200 bp and encoded a 43.3-kDa protein. To examine the role of methyl mercaptan in the pathogenesis of P. gingivalis, a METase-deficient mutant of P. gingivalis W83 was constructed. The methionine degradation activity and virulence of the mutant (M1217) and the parent strain (W83) in mice were compared. M1217 showed a marked decrease in the formation of methyl mercaptan from L-methionine and decreased virulence compared with the wild-type strain W83. These results suggest that methyl mercaptan not only is one of the sources of oral malodor, but may also play a role in the pathogenicity of P. gingivalis.

The relationship between oral malodor, gingivitis, and periodontitis. A review

Volatile sulfur compounds (VSC) are a family of gases which are primarily responsible for halitosis, a condition in which objectionable odors are present in mouth air. Although most patients perceive this condition as primarily a cosmetic problem, an increasing volume of evidence is demonstrating that extremely low concentrations of many of these compounds are highly toxic to tissues. VSC may, therefore, play a role in the pathogenesis of inflammatory conditions such as periodontitis. Since these compounds result from bacterial putrefaction of protein, investigations have been conducted to determine whether specific bacteria are associated with odor production. Two members of this family, hydrogen sulfide (H2S) and methyl mercaptan (CH3SH), are primarily responsible for mouth odor. Although many bacteria produce H2S, the production of CH3SH, especially at high levels, is primarily restricted to periodontal pathogens. Direct exposure to either of these metabolites adversely affects protein synthesis by human gingival fibroblasts in culture. However, methyl mercaptan has the greatest effect. Other in vitro experiments have demonstrated that cells exposed to methyl mercaptan synthesize less collagen, degrade more collagen, and accumulate collagen precursors which are poorly cross-linked and susceptible to proteolysis. CH3SH also increases permeability of intact mucosa and stimulates production of cytokines which have been associated with periodontal disease. VSC, and in particular methyl mercaptan, are therefore capable of inducing deleterious changes in both the extracellular matrix and the local immune response of periodontal tissues to plaque antigens. This article reviews these data and emphasizes the potential importance of VSC in the transition of periodontal tissues from clinical health to gingivitis and then to periodontitis.

Exposure of periodontal ligament cells to methyl mercaptan reduces intracellular pH and inhibits cell migration

Volatile sulfur compounds such as hydrogen sulfide and methyl mercaptan have been associated with adult periodontitis as well as with healing surgical wounds. To examine the effects of these compounds on the periodontium, we assayed periodontal ligament (PDL) cells for changes in intracellular pH, total protein, and cell migration following chronic exposure to CH3SH. Intracellular pH was quantitated by fluorescence measurements of cells loaded with BCECF, a pH-sensitive dye. Data show that 48-hour exposure to mercaptan lowered resting intracellular pH but did not consistently alter activity of the Na/H exchanger. This effect was seen in PDL cells from three different patients. Lowered pH was accompanied by decreases in both total protein and mature alpha 1 and alpha 2 chains of type I collagen. Since reductions in intracellular pH and total protein have been associated with inhibition of cell motility, migration was quantitated by sequential computer imaging, which measured the increase in size of plated cell circles at different times of migration. Incubation of PDL cells in pH 7.4 and 6.6 buffers reversibly altered intracellular pH. Migration was reversibly inhibited in pH 6.8 buffer. Exposure to CH3SH reduced intracellular pH in pH 7.4 buffer and in three independent assays inhibited enlargement of cell circles in pH 7.4 medium. These effects were therefore not related to alterations of extracellular pH, which remained at 7.4. The results support the hypothesis that gases such as methyl mercaptan may play a role in both surgical wound healing and periodontal disease by adversely affecting cell function and suggest that alterations in intracellular pH may be part of the mechanism for these changes.

Effect of methyl mercaptan on synthesis and degradation of collagen

Measurements of the conversion of [14C]-proline to [14C]-hydroxyproline were employed to assess the effect of methyl mercaptan on intra- and extracellular metabolism of collagenous proteins in human gingival fibroblast cultures. Following a 30-min pulse, 10 ng of methyl mercaptan per ml of 95% air/5% CO2 head-space suppressed collagen synthesis by 39% and increased the intracellular degradation of newly synthesized collagen from 26% to 42%. Parallel cultures assayed for proline transport demonstrated a 29% inhibition of [14C]-proline uptake. A similar analysis of cultures exposed to methyl mercaptan for 12 h revealed an increase in intracellular degradation (20% control vs. 30% test) and a marked increase in extracellular collagenolysis (4% control vs. 55% test). While pulsing, collagen synthesis was decreased by 39%. Slab gel electrophoresis also demonstrated that treatment with methyl mercaptan caused reductions both in mature alpha 1 and alpha 2 chains of type I collagen and in type III procollagen. Identities of the procollagen species were confirmed by pepsin digestion. Reverse transcribed polymerase chain reaction was utilized to compare expression of alpha 1 chains of type I procollagen with type III procollagen and indicated suppression of mRNA synthesis for type III procollagen in cultures exposed to methyl mercaptan.

Stimulation of enzyme and cytokine production by methyl mercaptan in human gingival fibroblast and monocyte cell cultures

The volatile sulphur compound methyl mercaptan (CH3SH) is a by-product of protein metabolism and a principal component of oral malodour. This investigation examines the effect of CH3SH on the enzymatic activities of cathepsins B and G and elastase, and on the production by human gingival fibroblasts of two key factors, prostaglandin E (PGE) and cAMP, of the PGE2-cAMP-dependent pathway, which may contribute to the increased production of collagenase and tissue destruction in human periodontal disease. The results demonstrate that CH3SH alone, or in combination with interleukin-1 (IL-1) or lipopolysaccharide, can significantly enhance the secretion of PGE2, cAMP and procollagenase by human gingival fibroblasts. CH3SH also stimulated mononuclear cells to produce IL-1, which can increase cAMP production, and act in synergism with the direct effect of CH3SH on cAMP. CH3SH also significantly enhanced the activity of cathepsin B, moderately suppressed that of cathepsin G, but did not significantly affect elastase. These results provide evidence that CH3SH could be a contributing factor in the enzymatic and immunological cascade of events leading to tissue degradation in periodontal diseases.