Streptococcus sanguis-induced platelet clotting in rabbits and hemodynamic and cardiopulmonary consequences

Type IV Pili of Streptococcus sanguinis Contribute to Pathogenesis in Experimental Infective Endocarditis

Streptococcus sanguinis is a common cause of infective endocarditis (IE). Efforts by research groups are aimed at identifying and characterizing virulence factors that contribute to the ability of this organism to cause IE. This Gram-positive pathogen causes heart infection by gaining access to the bloodstream, adhering to host extracellular matrix protein and/or platelets, colonizing the aortic endothelium, and incorporating itself into the aortic vegetation. While many virulence factors have been reported to contribute to the ability of S. sanguinis to cause IE, it is noteworthy that type IV pili (T4P) have not been described to be a virulence factor in this organism, although S. sanguinis strains typically encode these pili. Type IV pili are molecular machines that are capable of mediating diverse virulence functions and surface motility. T4P have been shown to mediate twitching motility in some strains of S. sanguinis, although in most strains it has been difficult to detect twitching motility. While we found that T4P are dispensable for direct in vitro platelet binding and aggregation phenotypes, we show that they are critical to the development of platelet-dependent biofilms representative of the cardiac vegetation. We also observed that T4P are required for in vitro invasion of S. sanguinis into human aortic endothelial cells, which indicates that S. sanguinis may use T4P to take advantage of an intracellular niche during infection. Importantly, we show that T4P of S. sanguinis are critical to disease progression (vegetation development) in a native valve IE rabbit model. The results presented here expand our understanding of IE caused by S. sanguinis and identify T4P as an important virulence factor for this pathogen.

IMPORTANCE This work provides evidence that type IV pili produced by Streptococcus sanguinis SK36 are critical to the ability of these bacteria to attach to and colonize the aortic heart valve (endocarditis). We found that an S. sanguinis type IV pili mutant strain was defective in causing platelet-dependent aggregation in a 24-h infection assay but not in a 1-h platelet aggregation assay, suggesting that the type IV pili act at later stages of vegetation development. In a rabbit model of disease, a T4P mutant strain does not develop mature vegetations that form on the heart, indicating that this virulence factor is critical to disease and could be a target for IE therapy.

The Role of the Proteasome in Platelet Function

Platelets are megakaryocyte-derived acellular fragments prepped to maintain primary hemostasis and thrombosis by preserving vascular integrity. Although they lack nuclei, platelets harbor functional genomic mediators that bolster platelet activity in a signal-specific manner by performing limited de novo protein synthesis. Furthermore, despite their limited protein synthesis, platelets are equipped with multiple protein degradation mechanisms, such as the proteasome. In nucleated cells, the functions of the proteasome are well established and primarily include proteostasis among a myriad of other signaling processes. However, the role of proteasome-mediated protein degradation in platelets remains elusive. In this review article, we recapitulate the developing literature on the functions of the proteasome in platelets, discussing its emerging regulatory role in platelet viability and function and highlighting how its functional coupling with the transcription factor NF-κB constitutes a novel potential therapeutic target in atherothrombotic diseases.

Is the Oral Microbiome Associated with Blood Pressure in Older Women?

INTRODUCTION

A possible role of the oral microbiome, specifically oral nitrate reducing flora, in blood pressure (BP) homeostasis, if proven etiologic in nature, could lead to novel mechanism-based therapy to improve hypertension prevention and control.

AIM

This cross-sectional study characterized and compared the oral microbiome between four study groups based on BP status among 446 postmenopausal women aged 53-82 years.

METHODS

Three study groups were not taking hypertension medication and were separated based on BP, as follows: normal BP (systolic < 120 and diastolic < 80; N = 179), elevated BP/Stage I hypertension (systolic 120-139 or diastolic 80-90; N = 106), Stage II hypertension (systolic > 140 or diastolic > 90; N = 42). The forth group consisted of anyone taking hypertension medications, regardless of BP (N = 119). Subgingival microbiome composition was determined using 16S rRNA sequencing with the Illumina MiSeq platform. Kruskal-Wallis tests were used to compare species-level relative abundance of bacterial operational taxonomic units across the four groups.

RESULTS

Sixty-five bacterial species demonstrated significant differences in relative abundance in women with elevated BP or using hypertension medication as compared to those with normal BP. After correction for multiple testing, two species, Prevotella oral (species 317) and Streptococcus oralis, remained significant and were lower in abundance among women taking antihypertension medications compared to those with normal BP (corrected P < 0.05).

CONCLUSIONS

These data provide novel description of oral subgingival bacteria grouped according to BP status. Additional larger studies including functional analysis and prospective designs will help further assess the potential role of the oral microbiome in BP regulation and hypertension.

Activated protein C ameliorates Bacillus anthracis lethal toxin-induced lethal pathogenesis in rats

BACKGROUND

Lethal toxin (LT) is a major virulence factor of Bacillus anthracis. Sprague Dawley rats manifest pronounced lung edema and shock after LT treatments, resulting in high mortality. The heart failure that is induced by LT has been suggested to be a principal mechanism of lung edema and mortality in rodents. Since LT-induced death occurs more rapidly in rats than in mice, suggesting that other mechanisms in addition to the heart dysfunction may be contributed to the fast progression of LT-induced pathogenesis in rats. Coagulopathy may contribute to circulatory failure and lung injury. However, the effect of LT on coagulation-induced lung dysfunction is unclear.

METHODS

To investigate the involvement of coagulopathy in LT-mediated pathogenesis, the mortality, lung histology and coagulant levels of LT-treated rats were examined. The effects of activated protein C (aPC) on LT-mediated pathogenesis were also evaluated.

RESULTS

Fibrin depositions were detected in the lungs of LT-treated rats, indicating that coagulation was activated. Increased levels of plasma D-dimer and thrombomodulin, and the ameliorative effect of aPC further suggested that the activation of coagulation-fibrinolysis pathways plays a role in LT-mediated pathogenesis in rats. Reduced mortality was associated with decreased plasma levels of D-dimer and thrombomodulin following aPC treatments in rats with LT-mediated pathogenesis.

CONCLUSIONS

These findings suggest that the activation of coagulation in lung tissue contributes to mortality in LT-mediated pathogenesis in rats. In addition, anticoagulant aPC may help to develop a feasible therapeutic strategy.

Ecto-5'-nucleotidase: a candidate virulence factor in Streptococcus sanguinis experimental endocarditis

Streptococcus sanguinis is the most common cause of infective endocarditis (IE). Since the molecular basis of virulence of this oral commensal bacterium remains unclear, we searched the genome of S. sanguinis for previously unidentified virulence factors. We identified a cell surface ecto-5′-nucleotidase (Nt5e), as a candidate virulence factor. By colorimetric phosphate assay, we showed that S. sanguinis Nt5e can hydrolyze extracellular adenosine triphosphate to generate adenosine. Moreover, a nt5e deletion mutant showed significantly shorter lag time (P<0.05) to onset of platelet aggregation than the wild-type strain, without affecting platelet-bacterial adhesion in vitro (P = 0.98). In the absence of nt5e, S. sanguinis caused IE (4 d) in a rabbit model with significantly decreased mass of vegetations (P<0.01) and recovered bacterial loads (log₁₀CFU, P = 0.01), suggesting that Nt5e contributes to the virulence of S. sanguinis in vivo. As a virulence factor, Nt5e may function by (i) hydrolyzing ATP, a pro-inflammatory molecule, and generating adenosine, an immunosuppressive molecule to inhibit phagocytic monocytes/macrophages associated with valvular vegetations. (ii) Nt5e-mediated inhibition of platelet aggregation could also delay presentation of platelet microbicidal proteins to infecting bacteria on heart valves. Both plausible Nt5e-dependent mechanisms would promote survival of infecting S. sanguinis. In conclusion, we now show for the first time that streptococcal Nt5e modulates S. sanguinis-induced platelet aggregation and may contribute to the virulence of streptococci in experimental IE.

Effect of Streptococcus sanguinis/Porphyromonas gingivalis single and combined biofilms upon platelet aggregation

OBJECTIVE

To assess the effect of two oral bacteria Streptococcus sanguinis and Porphyromonas gingivalis upon platelet aggregation.

MATERIALS AND METHODS

Streptococcus sanguinis, P. gingivalis, S. sanguniis+P. gingivalis were added to platelet-rich plasma and platelet aggregation measured using a platelet aggregometer. Platelets were passed through a flow chamber with S. sanguinis, P. gingivalis or a biofilm of S. sanguinis and P. gingivalis coated with saliva. Platelet adhesion to the chamber was observed under a fluorescence microscope for 15min. The positive control was platelets treated with adrenaline; the negative control was platelets treated with phosphate-buffered saline.

RESULTS

The mean (± s.e.) aggregation magnitude of S. sanguinis and P. gingivalis was 77.7±7.4% and 79.3±9.9%, respectively. The aggregation magnitude of S. sanguinis+P. gingivalis was 51.3±12.9%, which was significantly lower than that for S. sanguinis/P. gingivalis (P<0.05). In the flow chamber system, platelets adhered to S. sanguinis/P.gingivalis respectively within 3min, and reached a plateau at 5-15min. Under the condition of the S. sanguinis- and P. gingivalis-saliva biofilm, platelet adhesion to the biofilm was significantly reduced at 5-15min (P<0.05).

CONCLUSIONS

In the static or dynamic flow system, platelets adhered to S. sanguinis or P. gingivalis. However, if S. sanguinis was mixed with P. gingivalis, the aggregation magnitude (%) was significantly reduced.

Mechanism of adhesion maintenance by methionine sulphoxide reductase in Streptococcus gordonii

Methionine sulphoxide reductase maintains adhesin function during oxidative stress. Using Streptococcus gordonii as a model, we now show the mechanistic basis of adhesin maintenance provided by MsrA. In biofilms, S. gordonii selectively expresses the msrA gene. When the wild-type strain was grown with exogenous hydrogen peroxide (H(2)O(2)), msrA-specific mRNA expression significantly increased, while acid production was unaffected. In the presence of H(2)O(2), a msrA-deletion mutant (ΔMsrA) showed a 6 h delay in lag phase growth, a 30% lower yield of H(2)O(2), significantly greater inhibition by H(2)O(2) on agar plates (reversed by complementation), 30% less adhesion to saliva-coated hydroxyapatite, 87% less biofilm formation and an altered electrophoretic pattern of SspAB protein adhesins. Using mass spectrometry, methionine residues in the Met-rich central region of SspB were shown to be oxidized by H(2)O(2) and reduced by MsrA. In intact wild-type cells, MsrA colocalized with a cell wall-staining dye, and MsrA was detected in both cell wall and cytosolic fractions. To maintain normal adhesion and biofilm function of S. gordonii in response to exogenous oxidants therefore msrA is upregulated, methionine oxidation of adhesins and perhaps other proteins is reversed, and adhesion and biofilm formation is maintained.

Molecular basis for Staphylococcus aureus-mediated platelet aggregate formation under arterial shear in vitro

OBJECTIVE

Staphylococcus aureus is the most frequent causative organism of infective endocarditis (IE) and is characterized by thrombus formation on a cardiac valve that can embolize to a distant site. Previously, we showed that S. aureus clumping factor A (ClfA) and fibronectin-binding protein A (FnBPA) can stimulate rapid platelet aggregation.

METHODS AND RESULTS

In this study we investigate their relative roles in mediating aggregate formation under physiological shear conditions. Platelets failed to interact with immobilized wild-type S. aureus (Newman) at shear rates <500 s(-1) but rapidly formed an aggregate at shear rates >800 s(-1). Inactivation of the ClfA gene eliminated aggregate formation at any shear rate. Using surrogate hosts that do not interact with platelets bacteria overexpressing ClfA supported rapid aggregate formation under high shear with a similar profile to Newman whereas bacteria overexpressing FnBPA did not. Fibrinogen binding to ClfA was found to be essential for aggregate formation although fibrinogen-coated surfaces only allowed single-platelets to adhere under all shear conditions. Blockade of the platelet immunoglobulin receptor Fc gammaRIIa inhibited aggregate formation.

CONCLUSIONS

Thus, fibrinogen and IgG binding to ClfA is essential for aggregate formation under arterial shear conditions and may explain why S. aureus is the major cause of IE.

[Relationship between coronary artery disease and periodontal disease. What the cardiologist must know]

In this review, we will present the recent works, which shows a link between arterial lesions, particularly in coronary arteries, and periodontal disease. The pathways are those of chronic infection, and several studies have revealed a relationship between arterial lesions and buccal bacteraemia. Though the mechanism that links them is still unclear, the first hypotheses suggest that the presence of the bacteria in the bloodstream triggers a direct reaction (bacteria on the target organ), and/or an indirect immune reaction. This immune response could be induced by an increase in the secretion of pro-inflammatory cytokines (IL1, IL6, TNF), which are also involved in atherogenesis. Indeed, these cytokines have been found in higher concentrations in patients with periodontal disease, whereas reduced levels have been found in patients who have had deep gum pockets thoroughly cleaned. Cardiologists need to have access to such information not only because of the similarity of the populations, but also because of the therapeutic consequences. The future development of simple dental scores will provide an important tool for epidemiological studies of primary and secondary prevention.

Periodontal infections and cardiovascular disease: the heart of the matter

BACKGROUND

Oral infection models have emerged as useful tools to study the hypothesis that infection is a cardiovascular disease (CVD) risk factor. Periodontal infections are a leading culprit, with studies reporting associations between periodontal disease and CVD. The results, however, have varied, and it often is unclear what conclusions can be drawn from these data.

SUMMARY

An association exists between periodontal disease and CVD. It is unknown, however, whether this relationship is causal or coincidental. Early studies predominantly used nonspecific clinical and radiographic definitions of periodontal disease as surrogates for infectious exposure. While most studies demonstrated positive associations between periodontal disease and CVD, not all studies were positive, and substantial variations in results were evident. More recent studies have enhanced the specificity of infectious exposure definitions by measuring systemic antibodies to selected periodontal pathogens or by directly measuring and quantifying oral microbiota from subgingival dental plaque. Results from these studies have shown positive associations between periodontal disease and CVD.

CONCLUSIONS

Evidence continues to support an association among periodontal infections, atherosclerosis and vascular disease. Ongoing observational and focused pilot intervention studies may inform the design of large-scale clinical intervention studies. Recommending periodontal treatment for the prevention of atherosclerotic CVD is not warranted based on scientific evidence. Periodontal treatment must be recommended on the basis of the value of its benefits for the oral health of patients, recognizing that patients are not healthy without good oral health. However, the emergence of periodontal infections as a potential risk factor for CVD is leading to a convergence in oral and medical care that can only benefit the patients and public health.

Antimicrobial peptides versus invasive infections

It has been estimated that there are more microorganisms within and upon the human body than there are human cells. By necessity, every accessible niche must be defended by innate mechanisms to prevent invasive infection, and ideally that precludes the need for robust inflammatory responses. Yet the potential for pathogens to transcend the integument actively or passively and access the bloodstream emphasizes the need for rapid and potent antimicrobial defense mechanisms within the vascular compartment. Antimicrobial peptides from leukocytes have long been contemplated as being integral to defense against these infections. Recently, platelets are increasingly recognized for their likely multiple roles in antimicrobial host defense. Platelets and leukocytes share many structural and functional archetypes. Once activated, both cell types respond in specific ways that emphasize key roles for their antimicrobial peptides in host defense efficacy: (a) targeted accumulation at sites of tissue injury or infection; (b) direct interaction with pathogens; and (c) deployment of intracellular (leukocyte phagosomes) or extracellular (platelet secretion) antimicrobial peptides. Antimicrobial peptides from these cells exert rapid, potent, and direct antimicrobial effects against organisms that commonly access the bloodstream. Experimental models in vitro and in vivo show that antimicrobial peptides from these cells significantly contribute to prevent or limit infection. Moreover, certain platelet antimicrobial proteins are multifunctional kinocidins (microbicidal chemokines) that recruit leukocytes to sites of infection, and potentiate the antimicrobial mechanisms of these cells. In turn, pathogens pre-decorated by kinocidins may be more efficiently phagocytosed and killed by leukocytes and their antimicrobial peptide arsenal. Hence, multiple and relevant interactions between platelets and leukocytes have immunologic functions yet to be fully understood. A clearer definition of these interactions, and the antimicrobial peptide effectors contributing to these functions, will significantly advance our understanding of antimicrobial host defense against invasive infection. In addition, this knowledge may accelerate development of novel anti-infective agents and strategies against pathogens that have become refractory to conventional antimicrobials.

Bacterial Profile and Burden of Periodontal Infection in Subjects With a Diagnosis of Acute Coronary Syndrome

BACKGROUND

Periodontitis has been identified as a potential risk factor in cardiovascular diseases. It is possible that the stimulation of host responses to oral infections may result in vascular damage and the inducement of blood clotting. The aim of this study was to assess the role of periodontal infection and bacterial burden as an explanatory variable to the activation of the inflammatory process leading to acute coronary syndrome (ACS).

METHODS

A total of 161 consecutive surviving cases admitted with a diagnosis of ACS and 161 control subjects, matched with cases according to their gender, socioeconomic level, and smoking status, were studied. Serum white blood cell (WBC) counts, high- and low-density lipoprotein (HDL/LDL) levels, high-sensitivity C-reactive protein (hsC-rp) levels, and clinical periodontal routine parameters were studied. The subgingival pathogens were assayed by the checkerboard DNA-DNA hybridization method.

RESULTS

Total oral bacterial load was higher in the subjects with ACS (mean difference: 17.4x10(5); SD: 10.8; 95% confidence interval [CI]: 4.2 to 17.4; P<0.001), and significant for 26 of 40 species including Porphyromonas gingivalis, Tannerella forsythensis, and Treponema denticola. Serum WBC counts, hsC-rp levels, Streptococcus intermedius, and Streptococcus sanguis, were explanatory factors to acute coronary syndrome status (Nagelkerke r2=0.49).

CONCLUSION

The oral bacterial load of S. intermedius, S. sanguis, Streptococcus anginosus, T. forsythensis, T. denticola, and P. gingivalis may be concomitant risk factors in the development of ACS.

Oral streptococci and cardiovascular disease: searching for the platelet aggregation-associated protein gene and mechanisms of Streptococcus sanguis-induced thrombosis

BACKGROUND

Pathogenic mechanisms in infective endocarditis, disseminated intravascular coagulation, and cardiovascular events involve the aggregation of platelets into thrombi. Attendant infection by oral bacteria contributes to these diseases. We have been studying how certain oral streptococci induce platelet aggregation in vitro and in vivo. Streptococcus sanguis expresses a platelet aggregation-associated protein (PAAP), which contributes little to adhesion to platelets. When specific antibodies or peptides block PAAP, S. sanguis fails to induce platelet aggregation in vitro or in vivo.

METHODS

We used subtractive hybridization to identify the gene encoding for PAAP.

RESULTS

After subtraction of strain L50 (platelet aggregation-negative), four strain 133-79 specific sequences were characterized. Sequence agg4 encoded a putative collagen-binding protein (CbpA), which was predicted to contain two PAAP collagen-like octapeptide sequences. S. sanguis CbpA- mutants were constructed and tested for induction of platelet aggregation in vitro. Platelet aggregation was substantially inhibited when compared to the wild-type using platelet-rich plasma from the principal donor, but adhesion was unaffected. Other donor platelets responded normally to the CbpA- strain, suggesting additional mechanisms of response to S. sanguis. In contrast, CshA- and methionine sulfoxide reductase-negative (MsrA-) strains neither adhered nor induced platelet aggregation.

CONCLUSIONS

CbpA was suggested to contribute to site 2 interactions in our two-site model of platelet aggregation in response to S. sanguis. Platelet polymorphisms were suggested to contribute to the thrombogenic potential of S. sanguis.

Antithrombotic effect of the type III collagen-related octapeptide (KOGEOGPK) in the mouse

Platelet adhesion to subendothelial types I and III collagens exposed upon vascular injury plays a crucial role in hemostasis and thrombosis. We previously identified a KOGEOGPK sequence (O for hydroxyproline) within type III collagen interacting with platelets, and demonstrated a strong inhibitory effect of the KOGEOGPK peptide on human platelet interactions with type III collagen in vitro. In the present study, we tested the antithrombotic effect of KOGEOGPK in vivo. In a mouse model of pulmonary thromboembolism induced by intravenous injection of type III collagen and epinephrine, prior administration of 80 mg/kg KOGEOGPK reduced by 50% the size of thrombi embolized in lungs, compared to vehicle-treated mice (p<0.0001). In a mouse model of photochemically induced lesion of caecum venules and arterioles, intravenous injection of 80 mg/kg KOGEOGPK decreased by 76% the occurrence of arteriole occlusion 45 min after vascular injury (p<0.05). A moderate antithrombotic effect of KOGEOGPK was also observed in the injured venules. In addition, intracardiac injection of KOGEOGPK had no effect on the tail bleeding time. These findings demonstrate a substantial contribution of platelet interactions with the type III collagen-related KOGEOGPK sequence in thrombus formation in vivo with preferential involvement in arterial thrombosis.

Analysis of periodontal risk profiles in adults with or without a history of myocardial infarction

BACKGROUND

An association between periodontitis and cardiovascular diseases has been suggested.

AIMS

To study whether a combination of clinical variables in a functional risk diagram enhanced the ability to differentiate between subjects with or without an immediate history of acute myocardial infarction (AMI).

MATERIAL AND METHODS

A functional periodontal pentagon risk diagram (PPRD) with five periodontal risk vectors was created. The surface of individual PPRDs was calculated using data from 88 subjects with recent AMI and 80 matched control subjects with no history of AMI.

RESULTS

Age, gender, number of remaining teeth (mean value: 21.1 versus 21.6 teeth), smoking status, and pocket probing depth (PPD) distribution did not differ by group. Gingival recession was greater in control subjects (mean difference: 5.7, SD: +/- 1.9, p<0.01, 95% CI: 1.8-9.6). Bone loss > or = 4.0 mm was at all levels studied was significantly greater in subjects with AMI and bone loss > or = 50% (> or = 4 mm) was the best individual predictor of AMI (beta = 2.99, p < 0.000, 95% CI: 7.5-53.4). Only PPRD scores were associated with AMI status when factors not included in the PPRD were studied (beta = 22.1, SE: 5.9, p < 0.0001, 95% CI: 10.3-33.7). The best association between AMI status and study variables was the combination of > or = 4 mm of bone loss > or = 50%, proportion of bleeding on probing (%BOP), %PPDs > or = 6 mm, and tooth loss (Nagelkirke r2 = 0.46).

CONCLUSIONS

The combination of five periodontal parameters in a PPRD added predictive value, suggesting that comprehensive data should be used in studies of associations between periodontitis and heart diseases. Radiographic evidence of bone loss was the best individual parameter.

Chronic infection and coronary artery disease

On a variety of fronts, chronic infection has been found to be significantly associated with the development of atherosclerosis and the clinical complications of unstable angina, myocardial infarction, and stroke. For the most part, these relationships are still just associations. Failure to confirm initial reports of serologic associations also has been common. Specific causative relationships on par with that determined between H pylori and peptic ulcer disease have not yet been established. Potential mechanisms whereby chronic infections may play a role in atherogenesis are myriad. In the case of C pneumoniae, the effect may result from direct vessel wall colonization that may damage the vessel either directly or indirectly by initiating immunologic responses. In other cases the effect may simply be that of enhancing the pre-existing chronic inflammatory response of the body to standard risk factors such as hyperlipidemia. Even though the infectious agent may not directly infect the vessel wall, it may perform its critical role from afar. Chronic infection might also influence pre-existing plaque by enhancing T-cell activation or other inflammatory responses that may participate in the destabilization of the intimal cap. Hence chronic infection may play a role either in the initiation, progression, or the destabilization of atherosclerotic plaques. The infectious agents with the most evidence to support an etiologic role in atherosclerosis include C pneumoniae and cytomegalovirus. Evidence is mounting for a variety of other potential agents including other herpes viruses, influenza, other specific bacteria (such as M pneumoniae), and chronic infections with common bacterial agents (periodontal disease, chronic bronchitis, and chronic urinary tract infection, among others) [191]. Future studies are expected to elucidate further the pathophysiologic relationship between chronic infection and atherosclerosis and to evaluate further the potential of a variety of treatment approaches, including antibiotics.

Involvement of periodontopathic biofilm in vascular diseases

Oral bacteria inhabit biofilms, which are firm clusters adhering in layers to surfaces and are not easily eliminated by immune responses and are resistant to antimicrobial agents. Dental plaque is one such biofilm. In the past 10 years, subgingival plaque bacteria forming biofilms have been increasingly reported to be involved in systemic diseases. A close relationship between microbial infections and vascular disease has also been reported in the past two decades. The present review discusses the significance of the ecologic characteristics of biofilms formed by periodontopathic bacteria in order to further clarify the associations between periodontal disease and systemic disease. We focus on the relationships between periodontal disease-associated bacteria forming biofilms and vascular diseases including atherosclerosis and carotid coronary stenotic artery disease, and we discuss the direct and indirect effects on vascular diseases of lipopolysaccharides as well as heat shock proteins produced by periodontopathic bacteria.

Coagulation and thrombosis in cardiovascular disease: plausible contributions of infectious agents

An occlusive thrombus in the coronary arteries is the critical pathological event that immediately precedes most cases of myocardial infarction. Often the thrombus originates with a bleed from a fissured atheroma. Atheroma formation, therefore, creates risk of thrombosis; asymptomatic episodes of thrombosis and healing contribute to the pathogenesis of atherosclerosis and the development of atherosclerotic plaques. Based largely on in vitro and animal model evidence, infectious agents and their products can activate the coagulation cascade enzymatically or by up-regulating tissue factor. By initiating a procoagulant response, infectious agents can indirectly trigger a prothrombotic response. Alternatively, some microbes can directly trigger platelet aggregation in vitro and in animal models, suggesting direct prothrombotic potential in human cardiovascular disease. Activation of coagulation and thrombosis characterizes the pathological response to infectious agents in human disseminated intravascular coagulation and infective endocarditis. Given the underlying biological plausibility, the cumulative lifetime burden of chronic pathogens may be expected to create risk of atherosclerosis and thrombosis, and, indirectly, signs of cardiovascular disease.

Periodontal infections and cardiovascular disease--how strong is the association?

In the past decade there has been renewed interest in the old hypothesis that infections increase the risk of developing cardiovascular disease and stroke. There is now a convincing body of evidence that atherosclerosis has a major inflammatory component and is much more than the simple vascular accumulation of lipids. Infectious agents that have been linked to an increased risk of coronary heart disease (CHD) include Chlamydia pneumoniae, Helicobacter pylori, cytomegalovirus, and herpesviruses. The concept has emerged that each of these agents is an independent risk factor for CHD and that common chronic infections are important. In addition, periodontal infections have also been implicated as one of several factors contributing to the development of CHD. Evidence supporting a causative role of chronic infections in CHD is largely circumstantial. However, the evidence is sufficiently strong to warrant further examination of the possible link between chronic infections and CHD. In this review the lines of evidence for a causative role of C. pneumoniae in the development of CHD are summarized and contrasted with the lines of evidence suggesting a periodontal infection--CHD association. If common or widespread chronic infections are truly important risk factors for CHD, it is unlikely that a single infection will be shown to be causative. It is likely that the entire microbial burden of the patient from several simultaneous chronic infections is more important (e.g., H. pylori-caused gastric ulcers + C. pneumoniae-caused bronchitis + periodontitis). Increased cooperation between cardiologists and periodontists will be required to determine if, and what, combinations of common chronic infections are important in the pathogenesis of CHD and stroke.

Environmental regulation of glycosidase and peptidase production by Streptococcus gordonii FSS2

The synthesis of cell-associated and secreted proteins by Streptococcus gordonii FSS2, an infective endocarditis (IE) isolate, was influenced by both environmental pH and carbon source. Controlling the pH at 7.5 in stirred batch cultures showed that cell-associated and secreted protein concentrations were increased during late exponential and stationary phase by 68% and 125%, respectively, compared with similar cultures without pH control. The expression of five glycosidase and eight peptidase activities were examined using fluorogen-labelled synthetic substrates. Enzyme activities were significantly down-regulated during exponential growth, increasing during stationary phase (P<0.01) whether the culture pH was controlled at pH 7.5 or allowed to fall naturally to pH 4.4. Culture-supernatant activities were significantly increased (P<0.05) when the pH was maintained at 6.0 or 7.5, indicating modulation of enzyme activity by pH. Growth under nitrogen-limitation/glucose-excess conditions resulted in a significant repression of cell-associated glycosidase activities (P<0.01), whilst in the supernatant, activities were generally reduced. The expression of peptidase activities in the culture supernatant did not significantly change. The results suggest a possible role for catabolite repression by glucose in regulating enzyme expression. When S. gordonii FSS2 was cultured with 50% (v/v) added heat-inactivated foetal bovine serum, several cell-associated enzyme activities increased initially but were then reduced as the culture time was extended to 116 h. Culture-supernatant enzyme activities (N-acetyl-beta-D-glucosaminidase, N-acetyl-beta-D-galactosaminidase, thrombin, Hageman factor, collagenase and chymotrypsin), however, were significantly increased (P<0.01) over the same time period. The findings indicated that most of the important glycosidases synthesized by S. gordonii FSS2 were down-regulated by acid growth conditions and may also be subject to catabolite repression by glucose but conversely may be up-regulated by growth in serum. These results may have implications for streptococcal growth in an IE vegetation and in the mouth between meals or during sleep.

Periodontal disease: bacterial virulence factors, host response and impact on systemic health

Teeth are coated with a biofilm that contains periodontal pathogens. Pathogens express virulence factors which enable them to invade and replicate within epithelial cells and to invade the underlying connective tissue. This stimulates production of prostaglandins and cytokines that induce tissue loss. In addition, these bacteria have the potential to modulate the course of systemic diseases such as atherosclerosis and to contribute to low birthweight and preterm labor.

Chronic infection and coronary artery disease

On a variety of fronts, chronic infection has been found to be significantly associated with the development of atherosclerosis and the clinical complications of unstable angina, myocardial infarction, and stroke. For the most part, these are still just associations. Specific causative relationships on par with that determined between H. pylori and peptic ulcer disease have not yet been established. Potential mechanisms whereby chronic infections may play a role in atherogenesis are myriad. In the case of C. pneumoniae, the effect may result from direct vessel wall colonization, which may damage the vessel directly or indirectly by initiating immunologic responses. In other cases, the effect may simply be that of enhancing the preexisting chronic inflammatory response of the body to standard risk factors, such as hyperlipidemia. Even though the infectious agent may not directly infect the vessel wall, it may perform its critical role from afar. Chronic infection might also influence preexisting plaque by enhancing T cell activation or other inflammatory responses that may participate in the destabilization of the intimal cap. Chronic infection may play a role in the initiation, progression, or destabilization of atherosclerotic plaques. The infectious agents with the most evidence to support a causative role in atherosclerosis include C. pneumoniae and cytomegalovirus. Evidence is mounting for a variety of other potential agents, including H. pylori, various periodontal agents, and even hepatitis A. Future studies are expected to elucidate further the pathophysiologic relationship between chronic infection and atherosclerosis and to evaluate the potential of a variety of treatment approaches, including antibiotics.

Infective endocarditis: new concepts in pathogenesis

Gram-positive cocci account for the large majority of cases of infective endocarditis. Pathogenesis investigations of endocarditis have therefore focused on purported virulence factors in staphylococci, viridans group streptococci and enterococci. In addition to novel molecular techniques that have been adapted for use in the examination of gram-positive cocci, animal models of experimental endocarditis have been employed to support or discount the role of specific bacterial components in production of infective endocarditis. This review details recent work that addresses endocarditis pathogenesis and highlights pertinent findings from these investigations.