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Hydrogen peroxide produced by oral Streptococci induces macrophage cell death.

Okahashi N, Nakata M, Sumitomo T, Terao Y, Kawabata S - PLoS ONE (2013)

Bottom Line: Although the cytotoxicity of H2O2 has been widely recognized, the effects of H2O2 produced by oral streptococci on host defense systems remain unknown.Catalase, an enzyme that catalyzes the decomposition of H2O2, inhibited the cytotoxic effect of S. oralis.Furthermore, H2O2 alone was capable of inducing cell death.

View Article: PubMed Central - PubMed

Affiliation: Department of Oral Frontier Biology, Osaka University Graduate School of Dentistry, Suita-Osaka, Japan. okahashi@dent.osaka-u.ac.jp

ABSTRACT
Hydrogen peroxide (H2O2) produced by members of the mitis group of oral streptococci plays important roles in microbial communities such as oral biofilms. Although the cytotoxicity of H2O2 has been widely recognized, the effects of H2O2 produced by oral streptococci on host defense systems remain unknown. In the present study, we investigated the effect of H2O2 produced by Streptococcus oralis on human macrophage cell death. Infection by S. oralis was found to stimulate cell death of a THP-1 human macrophage cell line at multiplicities of infection greater than 100. Catalase, an enzyme that catalyzes the decomposition of H2O2, inhibited the cytotoxic effect of S. oralis. S. oralis deletion mutants lacking the spxB gene, which encodes pyruvate oxidase, and are therefore deficient in H2O2 production, showed reduced cytotoxicity toward THP-1 macrophages. Furthermore, H2O2 alone was capable of inducing cell death. The cytotoxic effect seemed to be independent of inflammatory responses, because H2O2 was not a potent stimulator of tumor necrosis factor-α production in macrophages. These results indicate that streptococcal H2O2 plays a role as a cytotoxin, and is implicated in the cell death of infected human macrophages.

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THP-1 macrophage cell death induced by oral streptococci.Differentiated THP-1 macrophages were infected with viable S. mutans MT8148, S. salivarius HHT, and S. oralis ATCC35037 for 2 h; washed with PBS to remove non-adherent extracellular bacteria; and cultured in fresh medium containing antibiotics for 18 h. As a control, macrophages were also infected with S. sanguinis SK36 [17]. Macrophage viability was determined by a trypan blue dye exclusion method. Data are shown as the mean ± SD of triplicate samples. *p<0.05 as compared with untreated control (None).
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pone-0062563-g001: THP-1 macrophage cell death induced by oral streptococci.Differentiated THP-1 macrophages were infected with viable S. mutans MT8148, S. salivarius HHT, and S. oralis ATCC35037 for 2 h; washed with PBS to remove non-adherent extracellular bacteria; and cultured in fresh medium containing antibiotics for 18 h. As a control, macrophages were also infected with S. sanguinis SK36 [17]. Macrophage viability was determined by a trypan blue dye exclusion method. Data are shown as the mean ± SD of triplicate samples. *p<0.05 as compared with untreated control (None).

Mentions: We previously reported that infection with S. sanguinis induces THP-1 macrophage cell death, with reactive oxygen species apparently contributing to this process. [17]. In the present study, we first examined whether other oral streptococcal species also induce macrophage cell death. Differentiated THP-1 macrophages were exposed to viable oral streptococcal strains, S. mutans MT8148, S. salivarius HHT, and S. oralis ATCC35037. Macrophages were then stained with trypan blue to determine their viability (Figure 1). At an MOI of more than 100, viable S. oralis induced cell death of macrophages at a level comparable to S. sanguinis[17]. Exposure to S. mutans or S. salivarius showed little effects on the viability of the macrophages even at MOIs of 200. During infection at an MOI of over 500, all tested streptococci steadily induced cell death (data not shown). This was likely due to acidification of culture medium and/or accumulation of cytotoxic products such as formic and acetic acids [1], [2], [24].


Hydrogen peroxide produced by oral Streptococci induces macrophage cell death.

Okahashi N, Nakata M, Sumitomo T, Terao Y, Kawabata S - PLoS ONE (2013)

THP-1 macrophage cell death induced by oral streptococci.Differentiated THP-1 macrophages were infected with viable S. mutans MT8148, S. salivarius HHT, and S. oralis ATCC35037 for 2 h; washed with PBS to remove non-adherent extracellular bacteria; and cultured in fresh medium containing antibiotics for 18 h. As a control, macrophages were also infected with S. sanguinis SK36 [17]. Macrophage viability was determined by a trypan blue dye exclusion method. Data are shown as the mean ± SD of triplicate samples. *p<0.05 as compared with untreated control (None).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3643943&req=5

pone-0062563-g001: THP-1 macrophage cell death induced by oral streptococci.Differentiated THP-1 macrophages were infected with viable S. mutans MT8148, S. salivarius HHT, and S. oralis ATCC35037 for 2 h; washed with PBS to remove non-adherent extracellular bacteria; and cultured in fresh medium containing antibiotics for 18 h. As a control, macrophages were also infected with S. sanguinis SK36 [17]. Macrophage viability was determined by a trypan blue dye exclusion method. Data are shown as the mean ± SD of triplicate samples. *p<0.05 as compared with untreated control (None).
Mentions: We previously reported that infection with S. sanguinis induces THP-1 macrophage cell death, with reactive oxygen species apparently contributing to this process. [17]. In the present study, we first examined whether other oral streptococcal species also induce macrophage cell death. Differentiated THP-1 macrophages were exposed to viable oral streptococcal strains, S. mutans MT8148, S. salivarius HHT, and S. oralis ATCC35037. Macrophages were then stained with trypan blue to determine their viability (Figure 1). At an MOI of more than 100, viable S. oralis induced cell death of macrophages at a level comparable to S. sanguinis[17]. Exposure to S. mutans or S. salivarius showed little effects on the viability of the macrophages even at MOIs of 200. During infection at an MOI of over 500, all tested streptococci steadily induced cell death (data not shown). This was likely due to acidification of culture medium and/or accumulation of cytotoxic products such as formic and acetic acids [1], [2], [24].

Bottom Line: Although the cytotoxicity of H2O2 has been widely recognized, the effects of H2O2 produced by oral streptococci on host defense systems remain unknown.Catalase, an enzyme that catalyzes the decomposition of H2O2, inhibited the cytotoxic effect of S. oralis.Furthermore, H2O2 alone was capable of inducing cell death.

View Article: PubMed Central - PubMed

Affiliation: Department of Oral Frontier Biology, Osaka University Graduate School of Dentistry, Suita-Osaka, Japan. okahashi@dent.osaka-u.ac.jp

ABSTRACT
Hydrogen peroxide (H2O2) produced by members of the mitis group of oral streptococci plays important roles in microbial communities such as oral biofilms. Although the cytotoxicity of H2O2 has been widely recognized, the effects of H2O2 produced by oral streptococci on host defense systems remain unknown. In the present study, we investigated the effect of H2O2 produced by Streptococcus oralis on human macrophage cell death. Infection by S. oralis was found to stimulate cell death of a THP-1 human macrophage cell line at multiplicities of infection greater than 100. Catalase, an enzyme that catalyzes the decomposition of H2O2, inhibited the cytotoxic effect of S. oralis. S. oralis deletion mutants lacking the spxB gene, which encodes pyruvate oxidase, and are therefore deficient in H2O2 production, showed reduced cytotoxicity toward THP-1 macrophages. Furthermore, H2O2 alone was capable of inducing cell death. The cytotoxic effect seemed to be independent of inflammatory responses, because H2O2 was not a potent stimulator of tumor necrosis factor-α production in macrophages. These results indicate that streptococcal H2O2 plays a role as a cytotoxin, and is implicated in the cell death of infected human macrophages.

Show MeSH
Related in: MedlinePlus