Degradation of human hemoglobin by Prevotella intermedia

Ferroptosis: A New Development Trend in Periodontitis

Periodontitis is a chronic inflammatory disease associated with bacterial biofilm. It is characterized by loss of periodontal support tissue and has long been considered as a "silent disease". Because it is difficult to prevent and has a health impact that can not be ignored, researchers have been focusing on a mechanism-based treatment model. Ferroptosis is an iron-dependent regulatory form of cell death, that directly or indirectly affects glutathione peroxidase through different signaling pathways, resulting in a decrease in cell antioxidant capacity, accumulation of reactive oxygen species and lipid peroxidation, which cause oxidative cell death and tissue damage. Recently, some studies have proven that iron overload, oxidative stress, and lipid peroxidation exist in the process of periodontitis. Based on this, this article reviews the relationship between periodontitis and ferroptosis, in order to provide a theoretical reference for future research on the prevention and treatment of periodontal disease.

Iron overload induces G1 phase arrest and autophagy in murine preosteoblast cells

This study aimed to investigate the cell cycle arrest and autophagy induced by iron overload in MC3T3-E1 cells. MC3T3-E1 cells were cultured in different concentrations of ferric ammonium citrate (FAC), and Perls' Prussian blue reaction was used to detect the iron levels of the cells. CCK-8 assays were used to detect the growth of MC3T3-E1. The level of reactive oxygen species (ROS) within cells was investigated with DCFH-DA. PI staining was used to analyze the cell cycle distribution of MC3T3-E1 cells. Finally, the expression levels of cell cycle related proteins, autophagy related proteins, AKT, p38 MAPK, Stat3, and their downstream proteins were detected with Western blot assays. The results showed that the iron levels of MC3T3-E1 cells increased with increasing concentrations of FAC. High levels of ferric ion inhibited proliferation of MC3T3-E1 cells and increased their ROS levels. Additionally, iron overload induced G1arrest in MC3T3-E1 cells and down-regulated the expression of Cyclin D₁ , Cyclin D₃ , CDK2, CDK4 and CDK6, but up-regulated p27 Kip1. In addition, the expression levels of Beclin-1 and LC3 II increased, but that of p62 decreased. Further experiments showed that the phosphorylation of AKT and its downstream proteins p-GSK-3β(Ser9) and p-mTOR (Ser2448) were decreased. The levels of p-p38 and p53 were up-regulated while those of cdc25A and p-ERK 1/2 were down-regulated. Phosphorylation of Stat3 and its downstream proteins was all decreased. These results show that iron overload generates ROS, blocks the PI3K/AKT and Jak/Stat3 signal pathways, and activates p38 MAPK, subsequently inducing G1 arrest and autophagy in MC3T3-E1 cells.

Dysbiosis by neutralizing commensal mediated inhibition of pathobionts

Dysbiosis in the periodontal microbiota is associated with the development of periodontal diseases. Little is known about the initiation of dysbiosis. It was hypothesized that some commensal bacteria suppress the outgrowth of pathobionts by H₂O₂ production. However, serum and blood components released due to inflammation can neutralize this suppressive effect, leading to the initiation of dysbiosis. Agar plate, dual-species and multi-species ecology experiments showed that H₂O₂ production by commensal bacteria decreases pathobiont growth and colonization. Peroxidase and blood components neutralize this inhibitory effect primarily by an exogenous peroxidase activity without stimulating growth and biofilm formation of pathobionts directly. In multi-species environments, neutralization of H₂O₂ resulted in 2 to 3 log increases in pathobionts, a hallmark for dysbiosis. Our data show that in oral biofilms, commensal species suppress the amounts of pathobionts by H₂O₂ production. Inflammation can neutralize this effect and thereby initiates dysbiosis by allowing the outgrowth of pathobionts.

Iron and zinc exploitation during bacterial pathogenesis

Ancient bacteria originated from metal-rich environments. Billions of years of evolution directed these tiny single cell creatures to exploit the versatile properties of metals in catalyzing chemical reactions and biological responses. The result is an entire metallome of proteins that use metal co-factors to facilitate key cellular process that range from the production of energy to the replication of DNA. Two key metals in this regard are iron and zinc, both abundant on Earth but not readily accessible in a human host. Instead, pathogenic bacteria must employ clever ways to acquire these metals. In this review we describe the many elegant ways these bacteria mine, regulate, and craft the use of two key metals (iron and zinc) to build a virulence arsenal that challenges even the most sophisticated immune response.

Comparative genome analysis of Prevotella intermedia strain isolated from infected root canal reveals features related to pathogenicity and adaptation

Background

Many species of the genus Prevotella are pathogens that cause oral diseases. Prevotella intermedia is known to cause various oral disorders e.g. periodontal disease, periapical periodontitis and noma as well as colonize in the respiratory tract and be associated with cystic fibrosis and chronic bronchitis. It is of clinical significance to identify the main drive of its various adaptation and pathogenicity. In order to explore the intra-species genetic differences among strains of Prevotella intermedia of different niches, we isolated a strain Prevotella intermedia ZT from the infected root canal of a Chinese patient with periapical periodontitis and gained a draft genome sequence. We annotated the genome and compared it with the genomes of other taxa in the genus Prevotella.

Results

The raw data set, consisting of approximately 65X-coverage reads, was trimmed and assembled into contigs from which 2165 ORFs were predicted. The comparison of the Prevotella intermedia ZT genome sequence with the published genome sequence of Prevotella intermedia 17 and Prevotella intermedia ATCC25611 revealed that ~14% of the genes were strain-specific. The Preveotella intermedia strains share a set of conserved genes contributing to its adaptation and pathogenic and possess strain-specific genes especially those involved in adhesion and secreting bacteriocin. The Prevotella intermedia ZT shares similar gene content with other taxa of genus Prevotella. The genomes of the genus Prevotella is highly dynamic with relative conserved parts: on average, about half of the genes in one Prevotella genome were not included in another genome of the different Prevotella species. The degree of conservation varied with different pathways: the ability of amino acid biosynthesis varied greatly with species but the pathway of cell wall components biosynthesis were nearly constant. Phylogenetic tree shows that the taxa from different niches are scarcely distributed among clades.

Conclusions

Prevotella intermedia ZT belongs to a genus marked with highly dynamic genomes. The specific genes of Prevotella intermedia indicate that adhesion, competing with surrounding microbes and horizontal gene transfer are the main drive of the evolution of Prevotella intermedia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1272-3) contains supplementary material, which is available to authorized users.

Contribution of hly homologs to the hemolytic activity of Prevotella intermedia

Prevotella intermedia is a periodontal pathogen that requires iron for its growth. Although this organism has hemolytic activity, the precise nature of its hemolytic substances and their associated hemolytic actions are yet to be fully determined. In the present study, we identified and characterized several putative hly genes in P. intermedia ATCC25611 which appear to encode hemolysins. Six hly genes (hlyA, B, C, D, E, and hlyI) of P. intermedia were identified by comparing their nucleotide sequences to those of known hly genes of Bacteroides fragilis NCTC9343. The hlyA-E, and hlyI genes were overexpressed individually in the non-hemolytic Escherichia coli strain JW5181 and examined its contribution to the hemolytic activity on sheep blood agar plates. E. coli cells expressing the hlyA and hlyI genes exhibited hemolytic activity under anaerobic conditions. On the other hand, only E. coli cells stably expressing the hlyA gene were able to lyse the red blood cells when cultured under aerobic conditions. In addition, expression of the hlyA and hlyI genes was significantly upregulated in the presence of red blood cells. Furthermore, we found that the growth of P. intermedia was similar in an iron-limited medium supplemented with either red blood cells or heme. Taken together, our results indicate that the hlyA and hlyI genes of P. intermedia encode putative hemolysins that appear to be involved in the lysis of red blood cells, and suggest that these hemolysins might play important roles in the iron-dependent growth of this organism.

Biofilms of black tooth stains: PCR analysis reveals presence of Streptococcus mutans

This study investigated the presence of the black-pigmented bacteria Prevotella nigrescens and Prevotella intermedia, the non-black-pigmented bacteria Actinomyces spp and particularly the cariogenic pathogen Streptococcus mutans in the dental biofilms of patients with or without black extrinsic tooth stains, using the multiplex polymerase chain reaction (PCR) technique. Analysis of the dental biofilms of patients with (n=26) or without (n=26) black tooth stains was performed using duplex PCR for the 16S ribosomal RNA gene (P. nigrescens, P. intermedia, Actinomyces spp) and glucosyltransferase-I gene for S. mutans. P. nigrescens and S. mutans were the most frequent bacteria detected in both groups. The least frequently detected were P. intermedia and Actinomyces spp. The similar bacterial composition of dental biofilms of black tooth stains and healthy tooth surfaces indicates that black tooth stains are not free of cariogenic bacteria.

Characterization of L-cysteine desulfhydrase from Prevotella intermedia

INTRODUCTION

Hydrogen sulfide is responsible for lysis of red blood cells and is a major compound for oral malodor. To clarify the production mechanism of hydrogen sulfide in Prevotella intermedia, we found an L-cysteine desulfhydrase gene (lcs) homologue on the genome database of P. intermedia ATCC25611 and characterized its gene product.

METHODS

The lcs gene homologue cloned into pGEX6p-1 vector was expressed in Escherichia coli and purified. Lcs activity was assayed by detection of the reaction products (hydrogen sulfide and pyruvate) or its derivatives from L-cysteine. Site-directed mutagenesis was used to convert an amino acid of the Lcs molecule.

RESULTS

The purified lcs gene product catalysed the degradation of L-cysteine to pyruvate, ammonia, and hydrogen sulfide, indicating that the protein is L-cysteine desulfhydrase. The enzyme required pyridoxal 5'-phosphate as a cofactor, and it was highly active at pH 7.0 and completely inhibited by ZnCl(2). The K(m) and V(max) of the enzyme were 0.7 mm and 4.2 micromol/min/mg, respectively. Replacement of Tyr-59, Tyr-118, Asp-198, and Lys-233 with any of the amino acids resulted in the complete disappearance of Lcs activity, implying that these amino acids are essential for enzyme activity. In addition, hydrogen sulfide produced by this enzyme lysed sheep red blood cells and modified hemoglobin.

CONCLUSION

These results show the enzymatic properties of L-cysteine desulfhydrase from P. intermedia ATCC25611 and also suggest that the Lcs enzyme, which produces hydrogen sulfide from L-cysteine, is closely associated with the pathogenesis of P. intermedia.

Role of the cysteine protease interpain A of Prevotella intermedia in breakdown and release of haem from haemoglobin

The gram-negative oral anaerobe Prevotella intermedia forms an iron(III) protoporphyrin IX pigment from haemoglobin. The bacterium expresses a 90 kDa cysteine protease, InpA (interpain A), a homologue of Streptococcus pyogenes streptopain (SpeB). The role of InpA in haemoglobin breakdown and haem release was investigated. At pH 7.5, InpA mediated oxidation of oxyhaemoglobin to hydroxymethaemoglobin [in which the haem iron is oxidized to the Fe(III) state and which carries OH- as the sixth co-ordinate ligand] by limited proteolysis of globin chains as indicated by SDS/PAGE and MALDI (matrix-assisted laser-desorption ionization)-TOF (time-of-flight) analysis. Prolonged incubation at pH 7.5 did not result in further haemoglobin protein breakdown, but in the formation of a haemoglobin haemichrome (where the haem Fe atom is co-ordinated by another amino acid ligand in addition to the proximal histidine residue) resistant to degradation by InpA. InpA-mediated haem release from hydroxymethaemoglobin-agarose was minimal compared with trypsin at pH 7.5. At pH 6.0, InpA increased oxidation at a rate greater than auto-oxidation, producing aquomethaemoglobin (with water as sixth co-ordinate ligand), and resulted in its complete breakdown and haem loss. Aquomethaemoglobin proteolysis and haem release was prevented by blocking haem dissociation by ligation with azide, whereas InpA proteolysis of haem-free globin was rapid, even at pH 7.5. Both oxidation of oxyhaemoglobin and breakdown of methaemoglobin by InpA were inhibited by the cysteine protease inhibitor E-64 [trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane]. In summary, we conclude that InpA may play a central role in haem acquisition by mediating oxyhaemoglobin oxidation, and by degrading aquomethaemoglobin in which haem-globin affinity is weakened under acidic conditions.

Interpain A, a cysteine proteinase from Prevotella intermedia, inhibits complement by degrading complement factor C3

Periodontitis is an inflammatory disease of the supporting structures of the teeth caused by, among other pathogens, Prevotella intermedia. Many strains of P. intermedia are resistant to killing by the human complement system, which is present at up to 70% of serum concentration in gingival crevicular fluid. Incubation of human serum with recombinant cysteine protease of P. intermedia (interpain A) resulted in a drastic decrease in bactericidal activity of the serum. Furthermore, a clinical strain 59 expressing interpain A was more serum-resistant than another clinical strain 57, which did not express interpain A, as determined by Western blotting. Moreover, in the presence of the cysteine protease inhibitor E64, the killing of strain 59 by human serum was enhanced. Importantly, we found that the majority of P. intermedia strains isolated from chronic and aggressive periodontitis carry and express the interpain A gene. The protective effect of interpain A against serum bactericidal activity was found to be attributable to its ability to inhibit all three complement pathways through the efficient degradation of the alpha-chain of C3 -- the major complement factor common to all three pathways. P. intermedia has been known to co-aggregate with P. gingivalis, which produce gingipains to efficiently degrade complement factors. Here, interpain A was found to have a synergistic effect with gingipains on complement degradation. In addition, interpain A was able to activate the C1 complex in serum, causing deposition of C1q on inert and bacterial surfaces, which may be important at initial stages of infection when local inflammatory reaction may be beneficial for a pathogen. Taken together, the newly characterized interpain A proteinase appears to be an important virulence factor of P. intermedia.

A new autocatalytic activation mechanism for cysteine proteases revealed by Prevotella intermedia interpain A

Prevotella intermedia is a major periodontopathogen contributing to human gingivitis and periodontitis. Such pathogens release proteases as virulence factors that cause deterrence of host defenses and tissue destruction. A new cysteine protease from the cysteine-histidine-dyad class, interpain A, was studied in its zymogenic and self-processed mature forms. The latter consists of a bivalved moiety made up by two subdomains. In the structure of a catalytic cysteine-to-alanine zymogen variant, the right subdomain interacts with an unusual prodomain, thus contributing to latency. Unlike the catalytic cysteine residue, already in its competent conformation in the zymogen, the catalytic histidine is swung out from its active conformation and trapped in a cage shaped by a backing helix, a zymogenic hairpin, and a latency flap in the zymogen. Dramatic rearrangement of up to 20A of these elements triggered by a tryptophan switch occurs during activation and accounts for a new activation mechanism for proteolytic enzymes. These findings can be extrapolated to related potentially pathogenic cysteine proteases such as Streprococcus pyogenes SpeB and Porphyromonas gingivalis periodontain.

Passively released heme from hemoglobin and myoglobin is a potential source of nutrient iron for Bordetella bronchiseptica

Colonization by Bordetella bronchiseptica results in a variety of inflammatory respiratory infections, including canine kennel cough, porcine atrophic rhinitis, and a whooping cough-like disease in humans. For successful colonization, B. bronchiseptica must acquire iron (Fe) from the infected host. A vast amount of Fe within the host is sequestered within heme, a metalloporphyrin which is coordinately bound in hemoglobin and myoglobin. Utilization of hemoglobin and myoglobin as sources of nutrient Fe by B. bronchiseptica requires expression of BhuR, an outer membrane protein. We hypothesize that hemin is acquired by B. bronchiseptica in a BhuR-dependent manner after spontaneous loss of the metalloporphyrin from hemoglobin and/or myoglobin. Sequestration experiments demonstrated that direct contact with hemoglobin or myoglobin was not required to support growth of B. bronchiseptica in an Fe-limiting environment. Mutant myoglobins, each exhibiting a different affinity for heme, were employed to demonstrate that the rate of growth of B. bronchiseptica was directly correlated with the rate at which heme was lost from the hemoprotein. Finally, Escherichia coli cells expressing recombinant BhuR had the capacity to remove hemin from solution. Collectively, these experiments provided strong experimental support for the model that BhuR is a hemin receptor and B. bronchiseptica likely acquires heme during infection after passive loss of the metalloporphyrin from hemoglobin and/or myoglobin. These results also suggest that spontaneous hemin loss by hemoglobin and myoglobin may be a common mechanism by which many pathogenic bacteria acquire heme and heme-bound Fe.