Staphylococcus aureus host cell invasion and post-invasion events

Staphylococcus aureus is now recognized as a facultative intracellular pathogen. The aim of this review is to discuss novel data regarding the invasion mechanism and post-invasion events with a focus on the fate of the infected phagosome in non-professional phagocytes and the role of S. aureus alpha-toxin.

Expression of Pls (plasmin sensitive) in Staphylococcus aureus negative for pls reduces adherence and cellular invasion and acts by steric hindrance

BACKGROUND

The methicillin-resistant Staphylococcus aureus (MRSA) surface protein Pls (plasmin sensitive) reduces adhesion to host proteins and cellular invasiveness by an unknown mechanism that requires Pls expression. Here, we tested the effect of Pls expression using different pls-negative backgrounds.

METHODS

Three pls-negative strains (the methicillin-susceptible Staphylococcus aureus strains Cowan I and 6850 and the MRSA strain ST239-635/93, which harbors staphylococcal cassette chromosome [SCC] mec type III) were transformed. Constructs used were full-length pls (pPLS4), pls-DeltaLPDTG (no sortase motif; pPLS5), and pls-DeltaSD (no serine-aspartic acid [SD] repeats; pPLS6). Adherence, invasiveness, gene expression, and surface expression were quantified by photometry, flow cytometry, real-time reverse-transcription polymerase chain reaction, and a modified enzyme-linked immunosorbent assay, respectively.

RESULTS

In Pls-expressing strains (those with pPLS4), adherence to immobilized fibronectin (Fn) and binding of soluble Fn was reduced by approximately 20% and approximately 25%, respectively. Invasion of 293 cells and EA.hy 926 cells was reduced by up to 85%. Surprisingly, transcription of fnbA and spa was up-regulated, but transcription of clfA and hla was down-regulated. Pls and Fn-binding protein (FnBP) surface expression was increased. Competition with purified FnBPA, but not with Pls, reduced invasiveness by approximately 90%. The invasiveness of 6850 (pPLS5) and of 6850 (pPLS6) was reduced by only approximately 20% and approximately 15%, respectively.

CONCLUSION

Expression of cell wall-anchored Pls reduces adherence and invasiveness independently of the MRSA/SCCmec background. This occurs despite early up-regulation of fnbA transcription and FnBP surface expression. Thus, Pls acts by steric hindrance rather than another mechanism.

Assessment of partial nitrification reactor performance through microbial population shift using quinone profile, FISH and SEM

In engineered systems, biological nitrogen removal through partial nitrification to nitrite is of great interest. Accordingly, effect of operating parameters such as pH, DO and temperature on the accumulation of ammonia-oxidizers was investigated. pH of 8, DO of 0.3-0.5mg/l and temperature of 35 degrees C yielded a ratio of 0.9-1.5 of NO(2)N:NH(4)N in the effluent suitable as a feed for Anammox reactor. Microbial population shift during start-up was assessed using quinone profile, SEM and FISH. UQ-8 in the biomass, which is the predominant quinone in ammonia-oxidizers, increased from 24.8% on Day 1 to 61.2% on Day 136. Fluorescence in situ hybridization analysis in the reactor showed that ammonia-oxidizing bacteria gradually outcompeted other bacteria and was the dominant population. The morphology and inner structure of the granular sludge was observed using SEM and the photographs indicated that the aerobic granular sludge showed a shift towards spherical and small rod-shaped clusters.

Staphylococcal infections impair the mesothelial fibrinolytic system: the role of cell death and cytokine release

Bacterial peritonitis is a serious complication of peritoneal dialysis patients and of patients after abdominal surgery. Especially episodes due to Staphylococcus aureus can harm the peritoneum severely, resulting in peritoneal fibrosis. Human peritoneal mesothelial cells play a critical role in maintaining the integrity of the peritoneum, as they release components of the fibrinolytic system and regulate the influx of immune cells by expressing chemokines and adhesion molecules. Using cultured human peritoneal mesothelial cells (HMCs) and blood mononuclear cells, we analyzed the effect of different staphylococcal strains on mesothelial fibrinolysis and on inflammatory reactions and show that only S. aureus strains with an invasive and hemolytic phenotype decrease the production of fibrinolytic system components, most likely via cell death induction. Furthermore, HMCs react to invading staphylococci by enhanced expression of chemokines and adhesion molecules. Mononuclear cells were activated by all staphylococcal strains tested, and their culture supernatants impaired mesothelial fibrinolysis. Simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, efficiently enhanced the mesothelial fibrinolytic capacity under these inflammatory conditions, but did not protect HMCs against S. aureus-induced cell death. We conclude that only selected S. aureus strains decrease the release of fibrinolytic system components and provoke a mesothelial inflammatory response. These factors most likely contribute to peritoneal fibrosis and might account for the severe clinical presentation of S. aureus peritonitis.

A feasibility study of an intensive combined modality smoking cessation program in the radiation oncology clinic

19604

Background: Radiotherapy (RT) patients present for daily treatment over many weeks, often accompanied by friends and family. This represents a unique opportunity for intensive smoking intervention concurrently with RT in both cancer patients and their companions. Methods: Eligible participants included smoking cancer patients scheduled to receive = 3 weeks of RT and their smoking family/friends. All participants received bupropion and 9 individualized behavioral interventions (BI) in the RT clinic with an addiction professional, followed by 9–12 scheduled intensive relapse prevention encounters (in person or by telephone). The primary endpoint was feasibility determined by accrual and program completion. Other endpoints included carbon-monoxide (CO) confirmed and participant-reported tobacco abstinence. During 4 months of enrollment, smoking and basic eligibility data were prospectively collected on consultations seen in clinic. Results: Over 8 months 20 cancer patients and 3 family members were enrolled. Based on our sampling, this represented greater than 40% of eligible smokers seen in clinic. Six cancer patients withdrew, all on or before the third BI. 13 participants completed all 9 BIs while 4 patients completed 7–8 BIs. 11 participants reported compliance with bupropion therapy. One participant discontinued bupropion citing increased depression. No other possible adverse events to bupropion or BI were discovered. At the completion of BI, 16 participants had exhaled CO concentrations < 10ppm and 14 participants self-reported tobacco abstinence. Of the 17 participants completing 7–9 behavioral interventions, the median number of relapse prevention sessions was 4 (range 0–8). With a median follow-up of 5.85 months, the 3-month crude self-reported abstinence rate was 41% (7/17). Conclusions: Tobacco cessation with bupropion and intensive BI for cancer patients and their companions during RT was feasible. A significant number of eligible smokers enrolled and completed BI during RT. However, few participants completed scheduled prevention encounters following RT.

No significant financial relationships to disclose.

Staphylococcal Chromosomal CassettemecType I,spaType, and Expression of Pls Are Determinants of Reduced Cellular Invasiveness of Methicillin‐ResistantStaphylococcus aureusIsolates

We have shown previously that pls, which codes for the surface protein Pls of methicillin-resistant Staphylococcus aureus (MRSA), reduces adhesion to immobilized fibronectin, fibrinogen, laminin, and immunoglobulin G as well as invasion of host cells. Here, we tested a collection of 66 clinical MRSA isolates--48 negative for pls/Pls (pls(-)/Pls(-)), 15 positive for pls/Pls (pls(+)/Pls(+)), and 3 harboring the pls gene but not expressing Pls (pls(+)/Pls(-))--for cellular invasiveness. Invasion of 293 cells by pls(+)/Pls(+) strains was lower than that by the pls(-)/Pls(-) strains (median [range], 36% [22%-70%] vs. 93% [25%-162%]). The 3 pls(+)/Pls(-) strains (median [range], 95% [63%-103%]) were as invasive as the pls(-)/Pls(-) strains. In addition, we identified a pls(+)/Pls(+) staphylococcal chromosomal cassette mec (SCCmec) IV strain. In conclusion, 3 properties--pls/Pls, SCCmec type, and spa type--strongly predicted the cellular invasiveness of MRSA strains, as indicated by good clustering. In contrast, the spa type-deduced multilocus sequence typing clonal complex (MLST-CC) was not able to predict the invasiveness of MRSA strains equally well. The underlying mechanism remains to be elucidated.

Staphylococcus aureus fibronectin binding protein-A induces motile attachment sites and complex actin remodeling in living endothelial cells

Staphylococcus aureus fibronectin binding protein-A (FnBPA) stimulates alpha5beta1-integrin signaling and actin rearrangements in host cells. This eventually leads to invasion of the staphylococci and their targeting to lysosomes. Using live cell imaging, we found that FnBPA-expressing staphylococci induce formation of fibrillar adhesion-like attachment sites and translocate together with them on the surface of human endothelial cells (velocity approximately 50 microm/h). The translocating bacteria recruited cellular actin and Rab5 in a cyclic and alternating manner, suggesting unsuccessful attempts of phagocytosis by the endothelial cells. Translocation, actin recruitment, and eventual invasion of the staphylococci was regulated by the fibrillar adhesion protein tensin. The staphylococci also regularly produced Neural Wiskott-Aldrich syndrome protein-controlled actin comet tails that further propelled them on the cell surface (velocity up to 1000 microm/h). Thus, S. aureus FnBPA produces attachment sites that promote bacterial movements but subvert actin- and Rab5 reorganization during invasion. This may constitute a novel strategy of S. aureus to postpone invasion until its toxins become effective.

Fibronectin binding proteins contribute to the adherence of Staphylococcus aureus to intact endothelium in vivo

Staphylococcal adhesins mediate attachment to matrix proteins and endothelial cells in vitro, yet, their role in primary adherence to the physiologic vessel wall has not been studied in vivo, and complex endocarditis models yielded ambiguous results. Recently, we developed a hamster model to study interaction kinetics of S. aureus with intact microvasculature using intravital fluorescence microscopy (Laschke et al. J Infect Dis 2005; 191: 435-443) providing the basis for this study. S. aureus Cowan 1 wild type (WT) log phase cells adhered to postcapillary venules to a significantly larger extent compared to stationary phase staphylococci, a finding in congruence with the fact that the staphylococcal adhesin repertoire largely depends on the growth phase. In comparison, the adherence rate of the fnbA deleted mutant (DU5895) to the vessel wall was significantly reduced to approximately 40% of WT. These DU5895 attachment rates were similar to those of an S. carnosus strain (TM300). In contrast, upon heterologous complementation of TM300 with either fnbA and fnbB, adherence of these transformants to the microvasculature increased, an increase found to be significant for fnbA transformant single cocci and clusters at 30 and 60 min when compared to S. carnosus TM300 WT. In conclusion, these results demonstrate that staphylococcal FnBPs significantly contribute to primary interaction with intact endothelium under physiologic conditions. Accordingly, this attribution of staphylococcal FnBPs provide a rationale for novel intervention strategies such as the use of anti-FnBP antibodies in endovascular S. aureus disease.

Staphylococcus aureus induces caspase-independent cell death in human peritoneal mesothelial cells

Bacterial peritonitis remains a serious complication of peritoneal dialysis. Although Staphylococcus epidermidis is the most common pathogen involved, infections with Staphylococcus aureus lead to severe peritoneal damage and are often associated with a dramatic loss of mesothelial cells. Induction of cell death appears to be involved in peritoneal damage and mesothelial cell loss during bacterial infections. Using cultured human peritoneal mesothelial cells (HMCs), we investigated the ability of different S. epidermidis and S. aureus strains to damage the HMC monolayer and to trigger cell death. We show that only a subgroup of live S. aureus isolates, characterized by an invasive and alpha-hemolysin-producing phenotype, induces cell death. None of the tested S. epidermidis strains, which were not invasive or hemolytic, had a cytotoxic effect. After host cell invasion, S. aureus resided within phagocytic vacuoles, and HMCs were apparently able to degrade staphylococci. However, even after prolonged infection, a high percentage of S. aureus remained alive within HMCs and might be released after host cell death. Cell death induced by S. aureus was accompanied by apoptotic alterations, such as DNA fragmentation, but was independent of endogenous FasL and tumor necrosis factor-alpha death ligand expression. Moreover, caspases were not involved in S. aureus-induced mesothelial cell death. In conclusion, our data indicate that mesothelial cell death might represent a major mechanism of S. aureus-induced damage of the peritoneum during bacterial peritonitis.

The anchorless adhesin Eap (extracellular adherence protein) from Staphylococcus aureus selectively recognizes extracellular matrix aggregates but binds promiscuously to monomeric matrix macromolecules

Besides a number of cell wall-anchored adhesins, the majority of Staphylococcus aureus strains produce anchorless, cell wall-associated proteins, such as Eap (extracellular adherence protein). Eap contains four to six tandem repeat (EAP)-domains. Eap mediates diverse biological functions, including adherence and immunomodulation, thus contributing to S. aureus pathogenesis. Eap binding to host macromolecules is unusually promiscuous and includes matrix or matricellular proteins as well as plasma proteins. The structural basis of this promiscuity is poorly understood. Here, we show that in spite of the preferential location of the binding epitopes within triple helical regions in some collagens there is a striking specificity of Eap binding to different collagen types. Collagen I, but not collagen II, is a binding substrate in monomolecular form. However, collagen I is virtually unrecognized by Eap when incorporated into banded fibrils. By contrast, microfibrils containing collagen VI as well as basement membrane-associated networks containing collagen IV, or aggregates containing fibronectin bound Eap as effectively as the monomeric proteins. Therefore, Eap-binding to extracellular matrix ligands is promiscuous at the molecular level but not indiscriminate with respect to supramolecular structures containing the same macromolecules. In addition, Eap bound to banded fibrils after their partial disintegration by matrix-degrading proteinases, including matrix metalloproteinase 1. Therefore, adherence to matrix suprastructures by S. aureus can be supported by inflammatory reactions.

Mechanism and consequences of invasion of endothelial cells by Staphylococcus aureus

It has become clear that Staphylococcus aureus is a facultative intracellular microorganism. Adherence and invasion are a prerequisite for endovascular infections caused by S. aureus, such as infective endocarditis. These phenomena may also be involved in the pathogenesis of invasive and metastatic infection upon hematogenous dissemination, such as osteomyelitis and abscess formation. The underlying molecular mechanism has been elucidated in detail, including its likely relevance in vivo. However, the mode of action of recently identified modulators of invasion, such as pls/Pls have not yet been clarified. The potential outcome for host cells and S. aureus following invasion are diverse. Surprisingly, induction of apoptosis in human endothelial cells is more complex than previously thought, since it appears to involve multiple virulence factors. In the light of increasing resistance to antimicrobial therapy, understanding the multifacetted pathogenesis of S. aureus infection in detail is needed for a better prevention and therapy.

Staphylococcus aureus ClpC is required for stress resistance, aconitase activity, growth recovery, and death

The ability of Staphylococcus aureus to adapt to various conditions of stress is the result of a complex regulatory response. Previously, it has been demonstrated that Clp homologues are important for a variety of stress conditions, and our laboratory has shown that a clpC homologue was highly expressed in the S. aureus strain DSM20231 during biofilm formation relative to expression in planktonic cells. Persistence and long-term survival are a hallmark of biofilm-associated staphylococcal infections, as cure frequently fails even in the presence of bactericidal antimicrobials. To determine the role of clpC in this context, we performed metabolic, gene expression, and long-term growth and survival analyses of DSM20231 as well as an isogenic clpC allelic-replacement mutant, a sigB mutant, and a clpC sigB double mutant. As expected, the clpC mutant showed increased sensitivity to oxidative and heat stresses. Unanticipated, however, was the reduced expression of the tricarboxylic acid (TCA) cycle gene citB (encoding aconitase), resulting in the loss of aconitase activity and preventing the catabolization of acetate during the stationary phase. clpC inactivation abolished post-stationary-phase recovery but also resulted in significantly enhanced stationary-phase survival compared to that of the wild-type strain. These data demonstrate the critical role of the ClpC ATPase in regulating the TCA cycle and implicate ClpC as being important for recovery from the stationary phase and also for entering the death phase. Understanding the stationary- and post-stationary-phase recovery in S. aureus may have important clinical implications, as little is known about the mechanisms of long-term persistence of chronic S. aureus infections associated with formation of biofilms.

Multiple virulence factors are required for Staphylococcus aureus-induced apoptosis in endothelial cells

Staphylococcus aureus infections can result in sepsis and septic shock associated with vascular damage and multiple organ failure. Apoptosis appears to play a key role during sepsis, and the ability of S. aureus to induce apoptosis in endothelial cells might contribute to metastatic infection. In contrast to leukocytes, in human umbilical vein endothelial cells and two endothelial cell lines neither purified alpha-toxin nor staphylococcal supernatants were sufficient to induce apoptosis. Apoptosis induction instead required staphylococcal invasion as well as signals from metabolically active intracellular staphylococci. Only strongly haemolytic and invasive staphylococci, but not non-invasive strains induced apoptosis that was caspase-dependent but Fas-independent. However, only a subgroup of clinical isolates with an invasive and haemolytic phenotype induced apoptosis. Expression of alpha-toxin in a non-haemolytic strain partially restored apoptosis induction, suggesting a role of alpha-toxin as a trigger of apoptosis. Furthermore, infection of endothelial cells with isogenic mutants of various regulator genes revealed that apoptosis induction was dependent on the global regulator agr and the alternative sigma factor sigB, but not influenced by sarA. Together, our results indicate that the ability of S. aureus to induce apoptosis in endothelial cells is determined by multiple virulence factors.

Fibrinogen and fibronectin binding cooperate for valve infection and invasion in Staphylococcus aureus experimental endocarditis

The expression of Staphylococcus aureus adhesins in Lactococcus lactis identified clumping factor A (ClfA) and fibronectin-binding protein A (FnBPA) as critical for valve colonization in rats with experimental endocarditis. This study further analyzed their role in disease evolution. Infected animals were followed for 3 d. ClfA-positive lactococci successfully colonized damaged valves, but were spontaneously eradicated over 48 h. In contrast, FnBPA-positive lactococci progressively increased bacterial titers in vegetations and spleens. At imaging, ClfA-positive lactococci were restricted to the vegetations, whereas FnBPA-positive lactococci also invaded the adjacent endothelium. This reflected the capacity of FnBPA to trigger cell internalization in vitro. Because FnBPA carries both fibrinogen- and fibronectin-binding domains, we tested the role of these functionalities by deleting the fibrinogen-binding domain of FnBPA and supplementing it with the fibrinogen-binding domain of ClfA in cis or in trans. Deletion of the fibrinogen-binding domain of FnBPA did not alter fibronectin binding and cell internalization in vitro. However, it totally abrogated valve infectivity in vivo. This ability was restored in cis by inserting the fibrinogen-binding domain of ClfA into truncated FnBPA, and in trans by coexpressing full-length ClfA and truncated FnBPA on two separate plasmids. Thus, fibrinogen and fibronectin binding could cooperate for S. aureus valve colonization and endothelial invasion in vivo.

Cytolethal distending toxin from Shiga toxin-producing Escherichia coli O157 causes irreversible G2/M arrest, inhibition of proliferation, and death of human endothelial cells

Recently, cytolethal distending toxin V (CDT-V), a new member of the CDT family, was identified in Shiga toxin-producing Escherichia coli (STEC) O157 and particular non-O157 serotypes. Here we investigated the biological effects of CDT-V from STEC O157:H(-) (strain 493/89) on human endothelial cells, which are believed to be major pathogenetic targets in severe STEC-mediated diseases. CDT-V caused dose-dependent G(2)/M cell cycle arrest leading to distension, inhibition of proliferation, and death in primary human umbilical vein endothelial cells (HUVEC) and two endothelial cell lines, EA.hy 926 cells (HUVEC derived) and human brain microvascular endothelial cells (HBMEC). The cell cycle effects of CDT-V were cell type specific. In HUVEC and EA.hy 926 cells, CDT-V caused a slowly developing but persistent G(2)/M block which resulted in delayed nonapoptotic cell death. In contrast, in HBMEC, CDT-V induced a rapidly evolving but transient G(2)/M block which was followed by progressive, mostly apoptotic cell death. In both HBMEC and EA.hy 926 cells, G(2)/M arrest was preceded by the early accumulation of a phosphorylated inactive form of cdc2 kinase. Significant G(2)/M arrest and inhibition of proliferation in both HUVEC and each of the endothelial cell lines were induced by 2 to 15 min of exposure to CDT-V, indicating that the effects of the toxin are irreversible. CDT-V-treated HBMEC and EA.hy 926 cells displayed fragmented nuclei and expressed phosphorylated histone protein H2AX, indicative of DNA damage followed by a DNA repair response. Our data demonstrate that CDT-V causes irreversible damage to human endothelial cells and thus may contribute to the pathogenesis of STEC-mediated diseases.

Birth hypoxia and spinal reflex in newborn babies

Birth hypoxia is detrimental to neuronal function. In this study, its effect on spinal monosynaptic reflex was investigated on two different age groups of human newborn babies using few non-invasive electrophysiological parameters. A total of 57 newborns (25 hypoxic + 32 non-hypoxic) were the study subject. Out of which, 31 newborns (11 hypoxic + 20 non-hypoxic) were examined within 48 hours of birth, and the rest 26 (14 hypoxic + 12 non-hypoxic) were examined between 48h and 120h (five days) of birth. H-reflex latency (HRL), distal motor latency (DL), and H-reflex conduction velocity (HRCV), were estimated for understanding the transmission of impulse in the monosynaptic reflex pathway. Moreover, Hmax, Mmax, and H/M ratio were observed for studying the spinal motor neuronal excitability. The injurious effect of hypoxia was detected on HRL, HRCV, Hmax and H/M ratio in babies who were examined within 48h of birth. The HRL was significantly increased and other parameters were significantly reduced. In the older group of babies, however, Hmax was the only parameter affected by hypoxia. The relatively older babies of hypoxic or non-hypoxic group had higher Hmax and H/M ratio compared to younger ones of their own group.

Truncation of fibronectin-binding proteins in Staphylococcus aureus strain Newman leads to deficient adherence and host cell invasion due to loss of the cell wall anchor function

Staphylococcus aureus fibronectin-binding proteins (FnBPs) play a critical role in S. aureus pathogenesis. FnBPs mediate adhesion to fibronectin and invasion of mammalian cells, including epithelial, endothelial, and fibroblastic cells, by fibronectin bridging to the host cell fibronectin receptor integrin (alpha(5))beta(1). Strain Newman is a laboratory strain frequently used for genetic, functional, and in vivo studies. However, despite pronounced production of FnBPs, strain Newman is only weakly adherent to immobilized Fn and weakly invasive. We examined whether these effects are due to a structural difference of FnBPs. Here, we show that both fnbA(Newman) and fnbB(Newman) contain a centrally located point mutation resulting in a stop codon. This leads to a truncation of both FnBPs at the end of the C domain at identical positions. Most likely, the stop codon occurred first in fnbB(Newman) and was subsequently transferred to fnbA(Newman) by replacement of the entire region encompassing the C, D, and W domains with the respective sequence of fnbB(Newman). Using heterologous expression in Staphylococcus carnosus, we found that truncated FnBPs were completely secreted into the culture medium and not anchored to the cell wall, since they lack the sortase motif (LPETG). Consequently, this led to a loss of FnBP-dependent functions, such as strong adhesion to immobilized fibronectin, binding of fibrinogen, and host cell invasion. This mutation may explain some of the earlier reported conflicting data with strain Newman. Thus, care should be taken when drawing negative conclusions about the role of FnBPs as a virulence factor in a given model.

Staphylococcus aureus fibronectin-binding protein (FnBP)-mediated adherence to platelets, and aggregation of platelets induced by FnBPA but not by FnBPB

BACKGROUND

The ability of Staphylococcus aureus to adhere to platelets and to induce aggregation of platelets is considered to be a critical factor in S. aureus-associated infective endocarditis.

METHODS

To identify and characterize further bacterial factors involved in the S. aureus-platelet interaction, we generated a phage-display library of S. aureus genomic DNA by use of the improved phagemid vector pG8SAET. The library was affinity-panned against gel-filtered, immobilized platelets.

RESULTS

Repeatedly isolated clones contained overlapping DNA fragments encoding a portion of the S. aureus fibronectin (Fn)-binding proteins (FnBPs). In a flow cytometric adherence assay, Staphylococcus carnosus that heterologously expressed either fnbA or fnbB, which encode FnBPA and FnBPB, respectively, showed increased adherence to activated, gel-filtered platelets. Adherence was promoted by the addition of Fn or fibrinogen (Fg), which most likely act as bridging molecules. Interestingly, promotion of adherence mediated by Fn was in the same range with S. carnosus producing either FnBPA or FnBPB, whereas promotion of adherence mediated by Fg was significantly more pronounced with S. carnosus that produce FnBPA than with S. carnosus that produce FnBPB. Furthermore, FnBPA, but not FnBPB, mediated aggregation of platelets when present on S. carnosus cells.

CONCLUSION

Our results indicate a substantial functional difference between FnBPA and FnBPB in the S. aureus-platelet interaction.

Reduced adherence and host cell invasion by methicillin-resistant Staphylococcus aureus expressing the surface protein Pls

Pls, the surface protein of methicillin-resistant Staphylococcus aureus (MRSA), prevents adhesion of clinical strain 1061 to immobilized fibronectin (Fn) and immunoglobulin G (IgG). Invasion of mammalian cells by S. aureus depends on Fn-mediated binding of staphylococcal Fn-binding proteins to host cell beta (1)-integrins. In the present study, we show that, for 10 clinical Pls-positive (Pls(+)) MRSA strains, adhesion to immobilized Fn, fibrinogen (Fg), IgG, and laminin, as well as binding to soluble Fn and Fg, was less efficient than adhesion and binding associated with 4 Pls-negative (Pls(-)) MRSA strains. However, binding to soluble IgG was comparable among both types of strains. For 293 cells, Pls(+) strains were less invasive than were Pls(-) strains (median [range], 35% [22%-70%] and 110% [89%-141%], respectively, compared with strain Cowan 1). Disruption of the pls gene of strain 1061 increased invasiveness, but it did not affect binding of soluble Fn, Fg, and IgG. Complementation restored the low level of invasiveness, but it did not restore the low level of adhesion to immobilized Fn. In conclusion, the reduced adhesiveness and invasiveness of MRSA appear to generally correlate with expression of Pls.

Energy cost and cardiorespiratory changes during the practice of Surya Namaskar

Surya Namaskar (SN), a group of Yogic exercise consists of a set of twelve postures which is practiced by some of the yoga practitioners. The present study was undertaken to observe critically the energy cost and different cardiorespiratory changes during the practice of SN. Twenty-one male volunteers from the Indian Army practiced selected Yogic exercises for six days in a week for three months duration. The Yogic practice schedule consisted of Hatha Yogic Asanas (28 min), Pranayama (10.5 min) and Meditation (5 min). In the Yogic practice schedule 1st they practiced Kapal Bhathi (breathing maneuvers) for 2 min then Yogamudra (yogic postural exercise) for 2 min, after that they took rest until oxygen consumption and heart rate (HR) came to resting value. Subsequently subjects performed SN for 3 min 40 seconds on an average. After three months of training at the beginning of the fourth month subjects performed entire Yogic practice schedule in the laboratory as they practiced during their training session and experiments were carried out. Their pulmonary ventilation, carbondioxide output, Oxygen consumption, HR and other cardiorespiratory parameters were measured during the actual practice of SN. Oxygen consumption was highest in the eighth posture (1.22+/-0.073 1 min(-1)) and lowest in the first posture (0.35+/-0.02 1 min(-1)). Total energy cost throughout the practice of SN was 13.91 kcal and at an average of 3.79 kcal/min. During its practice highest HR was 101+/-13.5 b.p.m. As an aerobic exercise SN seemed to be ideal as it involves both static stretching and slow dynamic component of exercise with optimal stress on the cardiorespiratory system.

Carcinoma metastasis to unexpected synchronous lymphoproliferative disorder: report of three cases and review of literature

Metastasis of one cancer to another cancer is rare. This report describes three cases in which low grade non-Hodgkin lymphomas were incidentally detected during the examination of lymph nodes removed as part of treatment of a previously diagnosed malignancy.

agr-dependent bacterial interference has no impact on long-term colonization of Staphylococcus aureus during persistent airway infection of cystic fibrosis patients

The agr specificity group distribution of persistent Staphylococcus aureus clones recovered from the airways of cystic fibrosis (CF) patients did not differ from that of isolates recovered from various clinical infections and healthy nasal carriers. The success of CF clones in terms of cocolonization and/or infection with S. aureus, prevalence of clones, or persistence appeared to be independent of agr group specificity.

The adhesive and immunomodulating properties of the multifunctional Staphylococcus aureus protein Eap

Adherence of Staphylococcus aureus to the host tissue is an important step in the initiation of pathogenesis. At least 10 adhesins produced by S. aureus have been described and it is becoming clear that the expression of these adhesins and their interactions with eukaryotic cells involve complex processes. Some of these, such as the fibronectin-binding proteins (FnBPs) and Clumping Factor A, are well characterized. However, in the last 10 years a number of novel S. aureus adhesins have been described. Functional analyses of these proteins, one of which is Eap (extracellular adherence protein, also known as Map and p70), are revealing important information on the pathogenesis of staphylococcal disease. More than 10 years after the first report of Eap, we are beginning to understand that this protein, which has a broad spectrum of functions, may be a critical factor in the pathogenesis of S. aureus. This review will focus on the interactions of Eap with eukaryotic cells, plasma proteins and the extracellular matrix as well as on the recently recognized role of Eap as an important mediator in the immune response to staphylococcal infection.

Staphylococcus aureus alpha-toxin-induced cell death: predominant necrosis despite apoptotic caspase activation

Recent data suggest that alpha-toxin, the major hemolysin of Staphylococcus aureus, induces cell death via the classical apoptotic pathway. Here we demonstrate, however, that although zVAD-fmk or overexpression of Bcl-2 completely abrogated caspase activation and internucleosomal DNA fragmentation, they did not significantly affect alpha-toxin-induced death of Jurkat T or MCF-7 breast carcinoma cells. Caspase inhibition had also no effect on alpha-toxin-induced lactate dehydrogenase release and ATP depletion. Furthermore, whereas early assessment of apoptosis induction by CD95 resulted solely in the generation of cells positive for active caspases that were, however, not yet permeable for propidium iodide, a substantial proportion of alpha-toxin-treated cells were positive for both active caspases and PI. Finally, electron microscopy demonstrated that even in the presence of active caspases, alpha-toxin-treated cells displayed a necrotic morphology characterized by cell swelling and cytoplasmic vacuolation. Together, our data suggest that alpha-toxin-induced cell death proceeds even in the presence of activated caspases, at least partially, in a caspase-independent, necrotic-like manner.

["Problem-based learning--inflammation and transplantation": an integrated, subject-centred course in the clinical section of the medical curriculum at the medical school of the University of Muenster]

Conventional medical curricula present information pertinent to chronic inflammatory diseases, infectious diseases and transplantation, via systematic lectures and courses in medical specialties without any integrated approach. The authors report on a 3-week model course that attempts to provide students with an overview of clinical presentation, diagnostics, and therapy of representative disease entities with particular emphasis on the interdisciplinary approach to these problems in hospital practice. In addition to problem-based learning in small groups, the model course comprises interdisciplinary concept lectures, practical demonstrations of specific diagnostic procedures, and bedside teaching. In the meantime, the course "Problem-Based Learning--Inflammation and Transplantation" has been held twice successfully as a mandatory course in the clinical part of the curriculum at the Muenster Medical School.

Staphylococcus aureus alpha-toxin induces apoptosis in peripheral blood mononuclear cells: role of endogenous tumour necrosis factor-alpha and the mitochondrial death pathway

Staphylococcus aureus infections can result in septic and toxic shock with depletion of immune cells and massive cytokine production. Recently, we showed that, in S. aureus-infected Jurkat T cells, alpha-toxin is the major mediator of caspase activation and apoptosis. Here, we investigated the mechanisms of cell death induced by alpha-toxin in peripheral blood mononuclear cells (MNC). We show that alpha-toxin is required and sufficient for S. aureus-induced cell death not only in transformed Jurkat T cells but also in MNC. Low alpha-toxin doses (3-30 ng ml-1) dose- and time-dependently induced apoptosis in both cell types, which was completely blocked by the caspase inhibitor zVAD-fmk. In Jurkat T cells and MNC, alpha-toxin induced the breakdown of the mitochondrial membrane potential and the intrinsic activation of caspase-3, -8 and -9. Interestingly, unlike in Jurkat T cells, apoptosis in MNC was additionally mediated by a caspase-9-independent component. MNC, but not Jurkat T cells, produced tumour necrosis factor (TNF)-alpha upon alpha-toxin stimulation. Blocking endogenous TNF-alpha with a TNF-alpha receptor antagonist partially decreased apoptosis in MNC. Our data therefore suggest that, whereas in Jurkat T cells apoptosis is solely mediated by the mitochondrial pathway, in MNC endogenous TNF-alpha and a death receptor-dependent pathway are also involved, which may contribute to depletion of immune cells during S. aureus infection.

Maternal ante-natal parameters as predictors of persistent postnatal glucose intolerance: a comparative study between Afro-Caribbeans, Asians and Caucasians

AIMS

To measure the prevalence of persistent glucose intolerance at 6-12 weeks postpartum in various ethnic groups to assess the value of targeted postpartum screening.

METHODS

A retrospective study was performed using computerized databases from two large maternity units within one UK region. Both units used the same screening strategy for gestational diabetes mellitus (GDM) and the same postpartum follow-up at 6-12 weeks using a 75-g oral glucose tolerance test (OGTT). A total of 221 women with a diagnosis of GDM/impaired glucose tolerance (IGT) in the index pregnancy in addition to a completed postpartum 75-g OGTT were studied. Of these, 91 were Caucasian, 89 were of Indo-Asian (Asian) origin and 41 were of Afro-Caribbean origin.

RESULTS

The study showed that 35% Indo-Asians had persistent postpartum glucose intolerance compared with 7% Caucasians and 5% Afro-Caribbeans (P < 0.003). Insulin requirement during pregnancy and a diagnosis of gestational diabetes prior to 20 weeks of pregnancy were predictive for persistent postpartum glucose intolerance amongst Indo-Asians.

CONCLUSIONS

The frequency of postpartum glucose intolerance among Indo-Asian women is significantly greater than among age-matched Caucasian and Afro-Caribbean women. We suggest that all Indo-Asian women with gestational diabetes should undergo postpartum screening for persistent glucose intolerance. However, in non-Asian women selective screening may be more cost effective.

Expression of 11beta-hydroxysteroid dehydrogenase type 1 in adipose tissue is not increased in human obesity

Central obesity is associated with increased morbidity and mortality. Preadipocyte proliferation and differentiation contribute to increases in adipose tissue mass, yet the mechanisms that underlie these processes remain unclear. Patients with glucocorticoid excess develop a reversible form of central obesity, but circulating cortisol levels in idiopathic obesity are invariably normal. We have hypothesized that the enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), by converting inactive cortisone to active cortisol in adipose tissue, might be an important autocrine regulator of fat mass. Paired omental and sc fat biopsies were obtained from 32 women (median age, 43 yr; range, 28-65; median body mass index, 27.5 kg/m(2); range, 19.7-39.2) undergoing elective abdominal surgery. 11beta-HSD1 activity and mRNA levels were assessed in whole tissue and in isolated preadipocytes and adipocytes using specific enzyme assays and real-time PCR. Preadipocyte proliferation was measured using tritiated thymidine incorporation. Whole adipose tissue 11beta-HSD1 mRNA levels did not differ between omental and sc samples (P = 0.73). In addition, mRNA levels did not correlate with body mass index (omental: r = 0.1; P = 0.6; sc: r = 0.15; P = 0.4). In keeping with earlier studies, 11beta-HSD1 mRNA levels were higher in omental compared with sc preadipocytes. However, in cultured omental preadipocytes, 11beta-HSD1 activity inversely correlated with body mass index (r = -0.47; P = 0.03). In omental preadipocytes, both cortisol and cortisone decreased proliferation (P < 0.05). Inhibition of 11beta-HSD1 with glycyrrhetinic acid partially reversed the cortisone-induced decrease in preadipocyte proliferation (P < 0.05). Enhanced preadipocyte proliferation within omental adipose tissue as a consequence of decreased 11beta-HSD1 mRNA levels and activity may contribute to increases in visceral adipose tissue mass in obese patients.

Aerobic capacity & perceived exertion after practice of Hatha yogic exercises

BACKGROUND & OBJECTIVES

Reports on the effect of yogic exercises on aerobic capacity are few. There is also no literature available on the effect of yogic exercise on perceived exertion (PE) after maximal exercise. In this study the effect of training in Hatha yogic exercises on aerobic capacity and PE after maximal exercise was observed.

METHODS

Forty men from the Indian army (aged 19-23 yr) were administered maximal exercise on a bicycle ergometer in a graded work load protocol. The oxygen consumption, carbon dioxide output, pulmonary ventilation, respiratory rate, heart rate (HR) etc., at maximal exercise and PE score immediately thereafter were recorded. The subjects were divided into two equal groups. Twelve subjects dropped out during the course of study. One group (yoga, n = 17) practiced Hatha yogic exercises for 1 h every morning (6 days in a week) for six months. The other group (PT, n = 11) underwent conventional physical exercise training during the same period. Both groups participated daily in different games for 1 h in the afternoon. In the 7th month, tests for maximal oxygen consumption (VO2Max) and PE were repeated on both groups of subjects.

RESULTS

Absolute value of VO2Max increased significantly (P < 0.05) in the yoga group after 6 months of training. The PE score after maximal exercise decreased significantly (P < 0.001) in the yoga group after 6 months but the PT group showed no change.

INTERPRETATION & CONCLUSION

The practice of Hatha yogic exercises along with games helps to improve aerobic capacity like the practice of conventional exercises (PT) along with games. The yoga group performed better than the PT group in terms of lower PE after exhaustive exercise.

alpha-Toxin is a mediator of Staphylococcus aureus-induced cell death and activates caspases via the intrinsic death pathway independently of death receptor signaling

Infections with Staphylococcus aureus, a common inducer of septic and toxic shock, often result in tissue damage and death of various cell types. Although S. aureus was suggested to induce apoptosis, the underlying signal transduction pathways remained elusive. We show that caspase activation and DNA fragmentation were induced not only when Jurkat T cells were infected with intact bacteria, but also after treatment with supernatants of various S. aureus strains. We also demonstrate that S. aureus-induced cell death and caspase activation were mediated by alpha-toxin, a major cytotoxin of S. aureus, since both events were abrogated by two different anti-alpha-toxin antibodies and could not be induced with supernatants of an alpha-toxin-deficient S. aureus strain. Furthermore, alpha-toxin-induced caspase activation in CD95-resistant Jurkat sublines lacking CD95, Fas-activated death domain, or caspase-8 but not in cells stably expressing the antiapoptotic protein Bcl-2. Together with our finding that alpha-toxin induces cytochrome c release in intact cells and, interestingly, also from isolated mitochondria in a Bcl-2-controlled manner, our results demonstrate that S. aureus alpha-toxin triggers caspase activation via the intrinsic death pathway independently of death receptors. Hence, our findings clearly define a signaling pathway used in S. aureus-induced cytotoxicity and may provide a molecular rationale for future therapeutic interventions in bacterial infections.

Upper gastrointestinal mucosal disease in pediatric Crohn disease and ulcerative colitis: a blinded, controlled study

BACKGROUND

Upper gastrointestinal endoscopic biopsies often show histologic abnormalities in Crohn disease. Consequently, it has been proposed that routine endoscopy could help to distinguish Crohn disease from ulcerative colitis. Surprisingly, however, recent case reports and an uncontrolled study suggested that similar abnormalities may occur in ulcerative colitis. Therefore, a blinded, controlled study was performed.

METHODS

Esophageal, gastric antral, and duodenal biopsies from children with Crohn disease (n = 28) and ulcerative colitis (n = 14) were compared with those from controls undergoing endoscopy for suspected reflux esophagitis (n = 22). Two pathologists, unaware of patient identity and diagnosis, agreed on a consensus report. Severity of inflammation was scored semiquantitatively. Helicobacter pylori colonization was an exclusion criterion.

RESULTS

Inflammation was reported as follows: esophagitis: controls 91%; Crohn disease: 72%; ulcerative colitis: 50%; gastritis: controls: 27%; Crohn disease: 92% (P < 0.001); ulcerative colitis: 69%; duodenitis: controls: 9%; Crohn disease: 33%; ulcerative colitis: 23%. In Crohn disease, granulomas were noted in 40% of patients (P = 0.001). Duodenal cryptitis was noted in 26% of patients with Crohn disease but not ulcerative colitis. In one patient with ulcerative colitis, neutrophilic infiltration of gastric glands was seen. Abnormalities seen in Crohn disease and ulcerative colitis included gastroduodenal ulceration (Crohn disease, 7%; ulcerative colitis, 8%), villus atrophy (Crohn disease, 11%; ulcerative colitis, 15%), and increased intraepithelial lymphocytes (Crohn disease, 15%; ulcerative colitis, 31% [P < 0.05]). None of these abnormalities was noted in the controls.

CONCLUSION

Although the presence of granulomas can support a diagnosis of Crohn disease, severe inflammation and other abnormalities occur in the proximal gastrointestinal tract in Crohn disease and ulcerative colitis.

Heterologously expressed Staphylococcus aureus fibronectin-binding proteins are sufficient for invasion of host cells

Staphylococcus aureus invasion of mammalian cells, including epithelial, endothelial, and fibroblastic cells, critically depends on fibronectin bridging between S. aureus fibronectin-binding proteins (FnBPs) and the host fibronectin receptor integrin alpha(5)beta(1) (B. Sinha et al., Cell. Microbiol. 1:101-117, 1999). However, it is unknown whether this mechanism is sufficient for S. aureus invasion. To address this question, various S. aureus adhesins (FnBPA, FnBPB, and clumping factor [ClfA]) were expressed in Staphylococcus carnosus and Lactococcus lactis subsp. cremoris. Both noninvasive gram-positive microorganisms are genetically distinct from S. aureus, lack any known S. aureus surface protein, and do not bind fibronectin. Transformants of S. carnosus and L. lactis harboring plasmids coding for various S. aureus surface proteins (FnBPA, FnBPB, and ClfA) functionally expressed adhesins (as determined by bacterial clumping in plasma, specific latex agglutination, Western ligand blotting, and binding to immobilized and soluble fibronectin). FnBPA or FnBPB but not of ClfA conferred invasiveness to S. carnosus and L. lactis. Invasion of 293 cells by transformants was comparable to that of strongly invasive S. aureus strain Cowan 1. Binding of soluble and immobilized fibronectin paralleled invasiveness, demonstrating that the amount of accessible surface FnBPs is rate limiting. Thus, S. aureus FnBPs confer invasiveness to noninvasive, apathogenic gram-positive cocci. Furthermore, FnBP-coated polystyrene beads were internalized by 293 cells, demonstrating that FnBPs are sufficient for invasion of host cells without the need for (S. aureus-specific) coreceptors.

A mammalian H+ channel generated through alternative splicing of the NADPH oxidase homolog NOH-1

Voltage-gated proton (H+) channels are found in many human and animal tissues and play an important role in cellular defense against acidic stress. However, a molecular identification of these unique ion conductances has so far not been achieved. A 191-amino acid protein is described that, upon heterologous expression, has properties indistinguishable from those of native H+ channels. This protein is generated through alternative splicing of messenger RNA derived from the gene NOH-1 (NADPH oxidase homolog 1, where NADPH is the reduced form of nicotinamide adenine dinucleotide phosphate).

Fibronectin-binding protein acts as Staphylococcus aureus invasin via fibronectin bridging to integrin alpha5beta1

The ability of Staphylococcus aureus to invade mammalian cells may explain its capacity to colonize mucosa and to persist in tissues after bacteraemia. To date, the underlying molecular mechanisms of cellular invasion by S. aureus are unknown, despite its high prevalence and difficulties in treatment. Here, we show cellular invasion as a novel function for an S. aureus adhesin, previously implicated solely in attachment. S. aureus, but not S. epidermidis, invaded epithelial 293 cells in a temperature- and F-actin-dependent manner. Formaldehyde-fixed and live bacteria were equally invasive, suggesting that no active bacterial process was involved. All clinical S. aureus isolates analysed, but only a subset of laboratory strains, were invasive. Fibronectin-binding proteins (FnBPs) acted as S. aureus invasins, because: (i) FnBP deletion mutants of invasive laboratory strains lost invasiveness; (ii) expression of FnBPs in noninvasive strains conferred invasiveness; and (iii) the soluble isolated fibronectin-binding domain of FnBP (D1-D4) completely blocked invasion. Integrin alpha5beta1 served as host cell receptor, which interacted with staphylococcal FnBPs through cellular or soluble fibronectin. FnBP-deficient mutants lost invasiveness for epithelial cells, endothelial cells and fibroblasts. Thus, fibronectin-dependent bridging between S. aureus FnBPs and host cell integrin alpha5beta1 is a conserved mechanism for S. aureus invasion of human cells. This may prove useful in developing new therapeutic and vaccine strategies for S. aureus infections.

Verapamil prolongs atrial fibrillation by evoking an intense sympathetic neurohumoral effect

BACKGROUND

Verapamil is an effective drug to slow ventricular rate in atrial fibrillation (AF). Clinically, however, i.v. verapamil enhances AF despite experimental evidence suggesting favorable effects of the drug on AF-induced electrical remodeling of the atria.

METHODS AND RESULTS

To clarify this controversy, i.v. verapamil's effects were determined in 41 anesthetized dogs, including 6 after beta-blockade. Intravenous verapamil (0.20 mg/kg, bolus, and 0.20 mg/kg/h, infusion) increased the duration of AF (induced by a single extrastimulus), from 19 +/- 6 to 130 +/- 24 s, P < 0.001, and slowed its ventricular response, from 246 +/- 25 to 110 +/- 15 min-1, P < 0.001. Mean aortic pressure, P = 0.002, and systemic vascular resistance, P < 0.035, decreased, and mean right atrial pressure increased, P < 0.001. Plasma norepinephrine concentration increased by 502 +/- 83 pg/mL, P < 0.001, plasma epinephrine concentration by 804 +/- 206 pg/mL, P = 0.002, and plasma total catecholamine concentration by 1606 +/- 366 pg/mL, P = 0.001. Prolongation of AF was related to an increase in mean right atrial pressure, R = 0.49, P = 0.014, right atrial wall tension, R = 0.45, P = 0.044, and plasma norepinephrine concentration, R = 0.83, P < 0.001, with plasma norepinephrine concentration remaining as an independent predictor of AF lengthening on multivariable analysis. In the presence of beta-blockade, verapamil produced comparable or more exaggerated hemodynamic effects, but it did not promote AF.

CONCLUSION

The prolongation of AF by verapamil can be related directly to the intense sympathetic neurohumoral effect that occurs following the drug's administration.

Nitric oxide downregulates tumour necrosis factor in mRNA in RAW 264.7 cells

Nitric oxide (NO) and tumour necrosis factor (TNF) are essential mediators in a number of biological processes, including the immune response. TNF stimulates NO production via expression of inducible NO synthase (iNOS), with L-arginine being the only substrate. Previously, we demonstrated that, inversely, NO inhibits lipopolysaccharide (LPS)-induced TNF synthesis. We have now investigated whether this reduction of TNF bioactivity is also reflected at the level of TNF mRNA in the murine macrophage cell line RAW 264.7. TNF mRNA was quantified by Northern analysis using an alpha[33P]dCTP-labelled probe. Cells stimulated with 10 microg/ml LPS in the absence of L-arginine, in order to prevent endogenous NO formation, contained more TNF mRNA than cells supplied with 1 mM L-arginine at 14 h and 20 h after stimulation. By contrast, no difference was observed at 4 h. This time course is compatible with the involvement of iNOS. The half-life of TNF mRNA in the presence of NO was roughly half that observed under L-arginine-free conditions (41 min versus 77 min, respectively). L-citrulline (1 mM), which has been shown to be recycled in RAW 264.7 cells to L-arginine, completely restored attenuation of TNF bioactivity and TNF message to control levels obtained with 1 mM L-arginine. Together, these findings suggest that endogenous NO regulates TNF mRNA, mainly by reducing its half-life. In addition, a distinct additional band (approximately 1.4 kb) hybridizing with the TNF probe was consistently observed in non-stimulated cells. This may correspond to TNF mRNA specifically hydrolysed at the AU-rich region, possibly reflecting another control point for TNF expression.

Role of ras oncogene in adriamycin resistance in human prostate tumor cells

We have previously isolated a drug-resistant, [PC3(R)], variant of human prostate PC3 cell line, which showed significant resistance (>10-fold) to adriamycin. No known mechanisms of drug resistance were found; however, resistant cells expressed more bcl2, c-myc, and ms oncogenes compared to the sensitive cells. In this study, we found that buthionine sulfoximine (BSO), an inhibitor of gamma-glutamyl-cysteine synthetase, decreased glutathione levels by 80-90% in both cell lines. BSO treatment down-modulated Ras protein only in PC3(R) cells and caused a 4-fold sensitization of PC3(R) cells to adriamycin without affecting PC3(W) cells. Farnesol treatment also inhibited expression of Ras protein and concomitantly reversed adriamycin resistance in PC3(R) cells, indicating that altered levels of ras expression plays an important role in drug resistance in PC3(R) cells.

Taming TNF: strategies to restrain this proinflammatory cytokine

Recent studies have demonstrated the essential role of tumor necrosis factor alpha (TNF-alpha) in rheumatoid arthritis and Crohn's disease. This article discusses agents known to suppress the formation or activity of TNF-alpha, and summarizes clinical studies using anti-TNF-alpha antibodies.

Endogenous adenosine curtails lipopolysaccharide-stimulated tumour necrosis factor synthesis

Recent studies have demonstrated the inhibitory effect of exogenous adenosine on TNF production. During inflammation endogenous adenosine levels are elevated and may be one of several anti-inflammatory mediators that reduce TNF synthesis. In the present study the authors investigated this role of adenosine in freshly isolated human PBMC. The effect of endogenous adenosine on TNF formation was studied by four different approaches. First, adenosine deaminase was added to LPS-stimulated mononuclear cells. This enzyme specifically deaminates extracellular adenosine to the inactive metabolite inosine. TNF production was augmented from baseline stimulation (LPS alone) of 3.5 +/- 0.4 ng ml-1 -5.2 +/- 0.9 ng ml-1 in the presence of 10 U ml-1 adenosine deaminase. Second, TNF production was determined after stimulation in the presence of dipyridamole, an inhibitor of cellular re-uptake of adenosine which increases extracellular concentrations. TNF synthesis was reduced dose-dependently from 3.1 +/- 0.9 ng ml-1 -1.1 +/- 0.2 ng ml-1 by 10 microM dipyridamole. Third, the adenosine A2 receptor antagonist 8-(3-chlorostyryl)caffeine (100 nM) enhanced TNF synthesis from a baseline of 3.7 +/- 0.5 ng ml-1 -5.5 +/- 0.9 ng ml-1. In contrast, no increase resulted from the addition of 100 nM of the specific A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. Finally, the authors were able to show that suppression of TNF formation by the specific type IV phosphodiesterase inhibitor rolipram can be completely reversed by adenosine deaminase or by the application of the A2 receptor antagonist. The authors conclude that endogenous adenosine controls TNF production. This effect of adenosine may not only have a physiological role but also appears to contribute to the pharmacological inhibition of TNF synthesis by exogenous agents such as the specific type IV phosphodiesterase inhibitor rolipram.