Chaotic dynamics of graphene and graphene nanoribbons

We study the chaotic dynamics of graphene structures, considering both a periodic, defect free, graphene sheet and graphene nanoribbons (GNRs) of various widths. By numerically calculating the maximum Lyapunov exponent, we quantify the chaoticity for a spectrum of energies in both systems. We find that for all cases, the chaotic strength increases with the energy density and that the onset of chaos in graphene is slow, becoming evident after more than 10⁴ natural oscillations of the system. For the GNRs, we also investigate the impact of the width and chirality (armchair or zigzag edges) on their chaotic behavior. Our results suggest that due to the free edges, the chaoticity of GNRs is stronger than the periodic graphene sheet and decreases by increasing width, tending asymptotically to the bulk value. In addition, the chaotic strength of armchair GNRs is higher than a zigzag ribbon of the same width. Furthermore, we show that the composition of ¹²C and ¹³C carbon isotopes in graphene has a minor impact on its chaotic strength.

[Medical care unit -- a suitable instrument for ambulatory patient-adequate care and performance-related remuneration]

BACKGROUND

The question of whether a medical care unit is an appropriate tool for outpatient care has been discussed for a long time. Our aim is to investigate whether the MCU is an effective instrument for outpatient care and adequate performance-related remuneration.

MATERIAL AND METHODS

This retro- and prospective overview of the work included statements on legal foundations for medical care units, for reimbursement of services in medical care units, the development of medical care centres in Germany and a listing of the specific advantages and disadvantages of an MCU. This article focuses on the generally applicable facts and complements them with examples from general, visceral and vascular surgery. The main quantitative data on medical centre statistics come from different publications of the National Association of Statutory Health Insurance for Physicians.

RESULTS

From a legal point of view the instrument MCU allows the participating of ambulatory and stationary care in the framework of medical care contracts. This has been especially extended for stationary applications, including the spectrum of possibilities that can contribute under certain circumstances for the provision of medical care in underdeveloped regions. Freelancers can benefit primarily from financial risk and minimising bureaucratic routine. The remuneration for services performed in the MCU is analogous to that of other ambulatory care providers. Basically, there are no disadvantages, but a greater design freedom and opportunities for the generation of aggregates are visible. The number of MCU in Germany has quadrupled in the last five years, indicating an establishment of an outpatient care landscape. MCU offers from the patient's perspective, providers and policy specific advantages and disadvantages. Indeed the benefits outweigh the disadvantages, but this is not yet verified by qualitative studies.

CONCLUSION

The question of the appropriateness of medical care units as outpatient care instrumentation must be considered differentially. Under current conditions it appears suitable for ensuring the MCU and the supplement of care supply. Whether a value can be generated in the quality of care of patients, however, has to be examined separately, as there are no valid data so far. The same applies to economic assessments of costs and benefits from an economic perspective.

Numerical integration of variational equations

We present and compare different numerical schemes for the integration of the variational equations of autonomous Hamiltonian systems whose kinetic energy is quadratic in the generalized momenta and whose potential is a function of the generalized positions. We apply these techniques to Hamiltonian systems of various degrees of freedom and investigate their efficiency in accurately reproducing well-known properties of chaos indicators such as the Lyapunov characteristic exponents and the generalized alignment indices. We find that the best numerical performance is exhibited by the "tangent map method," a scheme based on symplectic integration techniques which proves to be optimal in speed and accuracy. According to this method, a symplectic integrator is used to approximate the solution of the Hamilton equations of motion by the repeated action of a symplectic map S , while the corresponding tangent map TS is used for the integration of the variational equations. A simple and systematic technique to construct TS is also presented.

Fluoreszenz-in-situ-Hybridisierung in der humangenetischen Diagnostik

Die humangenetische Diagnostik umfasst eine Vielzahl von Verfahren, die sich aufgrund ihrer spezifischen Einsatzbedingungen und Anwendungsmöglichkeiten gegenseitig ergänzen. Mit der stetigen Entwicklung neuer Methoden ist es sinnvoll und notwendig, etablierte Techniken auf den Prüfstand zu stellen. Die Fluoreszenz-in-situ-Hybridisierung (FISH) ist eine Standardmethode in der genetischen Diagnostik und Forschung. Abhängig vom Design der Sonden ist es möglich, ganz individuell DNA-Abschnitte oder auch das gesamte Genom im Fluoreszenzmikroskop in Metaphasechromosomen, in Interphasezellkernen, in Gewebeschnitten oder in lebenden Zellen sichtbar zu machen. Besonders häufig wird die FISH-Technik in der humangenetischen Diagnostik für die Darstellung und Analyse von Mikrodeletionen, Translokationen, Inversionen und Insertionen, also von Strukturaberrationen der Chromosomen, sowie für die Charakterisierung von Markerchromosomen, zur Kartierung von Chromosomenbruchpunkten und zum Aneuploidiescreening im „pränatalen FISH-Schnelltest“ eingesetzt. Die Stärke der Methode liegt dabei in der Untersuchung einzelner Zellen, sodass auch genetisch heterogene Zellpopulationen (Mosaike) im untersuchten Gewebe mit hoher Sicherheit festgestellt oder ausgeschlossen werden können. Außerdem ist es möglich, die morphologischen und immunologischen Eigenschaften der Zellen bei der Auswertung zu berücksichtigen, sodass genetische Veränderungen bestimmten Zellarten zugeordnet werden können.

Differential activation of TRAIL-R1 and -2 by soluble and membrane TRAIL allows selective surface antigen-directed activation of TRAIL-R2 by a soluble TRAIL derivative

TNF-related apoptosis-inducing ligand (TRAIL) is a typical member of the tumor necrosis factor (TNF) ligand family that is expressed as a type II membrane protein (memTRAIL) and signals apoptosis via the death domain-containing receptors TRAIL-R1 and -2. Soluble recombinant derivatives of TRAIL (sTRAIL) are considered as novel tumors therapeutics because of their selective apoptosis inducing activity in a variety of human tumors but not in normal cells. Using antagonistic antigen-binding fragment (Fab) preparations of TRAIL-R1- and TRAIL-R2-specific antibodies, we demonstrate in this study that TRAIL-R1 becomes activated by both the soluble and the membrane-bound form of the ligand, whereas TRAIL-R2 becomes only activated by memTRAIL or soluble TRAIL secondarily cross-linked by antibodies. Furthermore, we show that the restricted signal capacity of sTRAIL can be readily converted into a fully signal competent memTRAIL-like molecule, i.e. a TRAIL-R2 stimulating ligand, by genetic fusion to an antibody derivative that allows antigen-dependent 'immobilization' of the fusion protein to cell surfaces. We conclude that antibody targeting-dependent activation can be used to design selective therapeutics derived of those ligands of the TNF family that are biologically inactive in their soluble form.

Generation of human high-affinity antibodies specific for the fibroblast activation protein by guided selection

Four completely human antibody derivatives [single-chain-antibody fragments (scFvs)] with specificity for the general tumor stroma marker fibroblast activation protein (FAP) were isolated by guided selection. Highly diverse IgG, IgM and IgD isotypes comprising heavy-chain variable domain libraries were generated using cDNAs derived from diverse lymphoid organs of a multitude of donors. Three of the human scFvs were converted into bivalent minibodies and expressed in eukaryotic cells for further functional characterization. Binding-competition studies and analysis by fluorescence-activated cell sorting showed high-affinity binding (10--20 nM) for two clones and recognition of the same epitope as the murine guiding antibody. The minibodies were successfully used for immunohistology of a variety of human carcinoma biopsies, revealing specific staining of stromal fibroblasts. Therefore, they should be suitable for in vivo diagnostic and tumor-targeting studies and, because of their completely human origin, be superior to murine or humanized antibody derivatives.

Blockade of A1 adenosine receptors prevents the ischaemia-induced sensitisation of adenylyl cyclase: evidence for a protein kinase C-mediated pathway

OBJECTIVE

Acute myocardial ischaemia leads to a transient sensitisation of adenylyl cyclase which may contribute to the occurrence of malignant arrhythmias and the propagation of myocardial necrosis. It is prevented by blockade of protein kinase C (PKC) which is activated in early ischaemia as shown by its translocation from the cytosol to the plasma membranes. Translocation of PKC may also occur in ischaemic preconditioning, a process thought to be induced by activation of adenosine A1 receptors. In this study it was investigated whether A1 adenosine receptors may be involved in the sensitisation of adenylyl cyclase and the activation of PKC induced by ischaemia.

METHODS

Isolated rat hearts were perfused with the specific A1 adenosine antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 1 microM) or adenosine (1 microM) prior to ischaemia induced by stop of perfusion for 5 and 10 min. Adenylyl cyclase activity was determined in plasma membranes stimulated by forskolin or stimulated via beta-receptors by isoproterenol. Total PKC activity was measured in purified plasma membranes and in the cytosolic fraction using histone III-S as a substrate.

RESULTS

Myocardial ischaemia induced a beta-receptor-independent sensitisation of adenylyl cyclase (forskolin-stimulated activity 515+/-55 vs. 384+/-30 pmol/min/mg protein) which was completely blocked by pre-perfusion with DPCPX (385+/-23 vs. 386+/-24 pmol/min/mg protein). DPCPX alone did not alter the responsiveness of adenylyl cyclase to stimulation. The stimulated adenylyl cyclase activity was increased by 20 % after pre-perfusion with adenosine, mimicking the ischaemia-induced sensitisation. The effect of adenosine was not augmented by additional ischaemia. PKC activity was translocated from the cytosol to the plasma membranes by acute ischaemia, indicating an activation of the enzyme. This effect was completely abolished by DPCPX.

CONCLUSION

These data demonstrate that in the rat heart the sensitisation of adenylyl cyclase in acute myocardial ischaemia is dependent on activation of A1 adenosine receptors. It is suggested that the sensitisation of adenylyl cyclase by adenosine or ischaemia might be mediated by an activation of PKC.

[Companionship for women dying of AIDS]

This report reflects the experience of accompanying HIV-infected women during the process of dying using their curriculi vitae as examples of different modes of dealing with fatal illness. The text contains paintings of past and contemporary art concerning death and eros and poetry as a form of therapy.

Tissue factor expression of human monocytes is suppressed by lysophosphatidylcholine

The expression of tissue factor (TF), the principal initiator of coagulation, is increased during inflammation and atherosclerosis. Both conditions are promoted by lysophosphatidylcholine (lysoPC). We observed in the present study that lysoPC (1 to 10 micromol/L) dose-dependently reduced TF activity in human monocytes, as elicited by lipopolysaccharide (LPS). Lysophosphatidylethanolamine (lysoPE) and other lysophospholipids did not affect LPS-induced TF activity of human monocytes. TF antigen expression as elicited by LPS was also lowered by lysoPC. Phospholipid analyses indicated a selective increase in the lysoPC content of the monocytes after preincubation with the lysophospholipid. LysoPC inhibited the TF activity of Mono Mac-6 cells to a similar extent as in the monocytes. LPS binding to plasma membrane receptors and internalization of LPS into monocytes were not affected by lysoPC. In contrast, LPS-mediated nuclear binding of nuclear factor-kappaB/Rel to a TF-specific kappaB site was inhibited by lysoPC. Induction of TF mRNA expression by LPS tended to be partially reduced by the lysophospholipid. Preincubation with lysoPC increased monocytic cAMP levels. Inhibition of adenylyl cyclase by pretreatment with 2'-deoxy-3'-adenosine monophosphate partially reversed the inhibition of TF activity promoted by lysoPC. In conclusion, lysoPC markedly decreases LPS-mediated TF expression of human monocytes, the effect probably being mediated by both transcriptional and posttranscriptional mechanisms. LysoPC may thus attenuate activation of coagulation during inflammation and atherosclerosis.

Hydroxyethyl starch antibodies in humans: incidence and clinical relevance

Hydroxyethyl starch (HES) is a plasma expander used for perioperative i.v. fluid management, as well as for resuscitation from trauma and shock. HES is very well tolerated, and the incidence of anaphylactic reactions is lower than with dextran or gelatin. Dextran anaphylaxis is caused by circulating dextran-reactive antibodies (ABs) of the immunoglobin G (IgG) class found in most adults. Histamine release from mast cells induces adverse reactions after gelatin infusion. The cause of adverse reactions due to HES is not yet clear. To investigate AB formation due to HES, we collected sera of 1004 patients at least 14 days after starch administration. Using a highly sensitive enzyme-linked immunoabsorbent assay technique, we found one patient with a low 1:10 titer of HES-reactive ABs (immunoglobin M [IgM] class). Despite repeated HES infusions, no clinical reaction could be detected in this patient. On the basis of a binomial distribution, a one-tailed confidence interval (99%) was used to calculate the percentage of the occurrence of ABs in general with maximum of 33 in 10,000 persons (IgM) and 23 in 10,000 persons (IgG). We suggest that HES-reactive ABs are extremely rare and that they do not necessarily induce anaphylaxis. Other mechanisms may be responsible for adverse reactions due to HES.

IMPLICATIONS

The frequency of antibody formation due to hydroxyethyl starch, a commonly used plasma expander, was prospectively investigated in 1004 patients. Only one patient showed transient antibody formation, which was not harmful to the patient. This low antigenicity could explain the excellent tolerance of hydroxyethyl starch compared with other plasma expanders.

ACE-inhibition prevents postischemic coronary leukocyte adhesion and leukocyte-dependent reperfusion injury

OBJECTIVE

Polymorphonuclear leukocytes (PMN), retained in the microvascular bed, can contribute to postischemic myocardial reperfusion injury. Since a beneficial effect of ACE-inhibition on reperfusion injury has been reported, we investigated the impact of cilazaprilat on PMN dependent reperfusion injury in isolated guinea pig hearts.

METHODS

Hearts (n = 5 per group) were subjected to 15 min of ischemia. Immediately thereafter, a bolus of PMN was injected into the coronary system. External heart work (EHW) and total cardiac nitric oxide release were measured. For microscopic evaluation, hearts received rhodamine 6G labelled PMN after ischemia, were arrested 5 min later and further perfused with FITC dextran (0.1%). Localization of retained PMN was assessed by fluorescence microscopy. Leukocyte activation was studied by FACS analysis of the adhesion molecule CD11b before and after coronary passage of the PMN. The ACE-inhibitor cilazaprilat (Cila, 2 microM) and the NO-synthase inhibitor nitro-L-arginine (NOLAG, 10 microM) were used to modulate nitric oxide formation of the heart.

RESULTS

Postischemic EHW recovered to 67 +/- 5% (controls) and 64 +/- 6% (Cila) of the preischemic value. Addition of PMN severely depressed recovery of EHW (39 +/- 2%) and NO release (39 +/- 6% of the preischemic value). Simultaneously, ischemia led to a substantial increase in postcapillary PMN adhesion (from 21 +/- 5 to 172 +/- 27 PMN/mm2 surface) and CD11b-expression of the recovered PMN (3-fold). Cila attenuated postischemic PMN adhesion (83 +/- 52 PMN/mm2) and activation of PMN, whereas it improved recovery of work performance (64 +/- 4%) and NO release (65 +/- 4%) in the presence of PMN. Conversely, NOLAG increased PMN adhesion (284 +/- 40 PMN/mm2) and myocardial injury. We conclude that ACE-inhibition prevents leukocyte dependent reperfusion injury mainly by inhibition of postcapillary leukocyte adhesion. The effect may be mediated by NO, given the proadhesive effect of NOLAG.

Effects of ACE-inhibition on redox status and expression of P-selectin of endothelial cells subjected to oxidative stress

Redox stress during post-ischemic reperfusion may be the prime signal for processes leading to myocardial remodelling and hypertrophy. Nitric oxide (NO) is antioxidative, antiadhesive for neutrophils (PMN) and antiproliferative. Thus, enhancing endothelial production of NO, e.g. by inhibiting breakdown of endogenous bradykinin via angiotensin converting enzyme (ACE), could be beneficial. The effect of cilazaprilat (CILA, 10 micro M), an ACE inhibitor, on redox status, expression of the adhesion molecule P-selectin, and PMN adhesion under conditions of oxidative stress was investigated in cultured human umbilical vein endothelial cells (HUVECs). Incubation of the cells with H2O2 (0.1 and 1 mm) for 15 min served as oxidative stimulus. The intra- and extracellular concentrations of reduced and oxidized glutathione (GSH and GSSG) were measured by HPLC as indicators of endothelial redox status. Expression of P-selectin was measured by flow cytometry. Furthermore, firm leukocyte adhesion to HUVECs was assessed. In controls, the intracellular ratio GSH/GSSG averaged 47 and dropped to 30 after incubation with 0.1 mm H2O2. The ratio declined to 6.5 with 1 mm H2O2. CILA blocked the effects of 0.1 mm H2O2, but was ineffective against 1 mm peroxide. The extracellular ratio did not discriminate between 0.1 and 1 mm H2O2, falling from 18 to 1 in both situations. P-selectin expression rose from 100% (control) to 146% after 1 mm H2O2 without CILA, but only to 114% in the presence of CILA. PMN adhesion was enhanced from about 1600 PMN per microwell (control) to 4300/well by 1 mm H2O2. CILA had no significant effect on adhesion (3900 PMN/well). Exposure of HUVECs to 0.1 mm H2O2 affected neither P-selectin expression nor PMN adhesion. Consequently, ACE inhibition can mitigate mild (0.1 mm H2O2) but not more severe redox stress in HUVECs. Irrespectively, CILA reduced the upregulation of P-selectin at the higher H2O2 concentration, indicating that this process is regulated independently of the cellular redox status. The firm adhesion of PMN to HUVECs was independent of P-selectin expression.

A TNF receptor antagonistic scFv, which is not secreted in mammalian cells, is expressed as a soluble mono- and bivalent scFv derivative in insect cells

Single chain antibodies (scFv) are usually produced in E. coli, but generation of certain scFv derivatives, such as complex fusion proteins or glycosylated forms of scFv is restricted to eukaryotic expression systems. We investigated the production of soluble mono- and bivalent single chain antibodies (scFv) in eukaryotic cells and describe a cassette vector system for mammalian and baculovirus expression which is compatible with an established vector system for bacterial expression and phage display selection of scFvs. The applied model scFv was derived from a murine antibody (H398) against human tumor necrosis factor receptor 1 (TNFR60), known to be a potent antagonist of TNF action in its monomeric form and a potential therapeutic agent for treatment of TNF-mediated diseases. Surprisingly, the monomeric scFv form of H398 (scFv H398) is expressed but not secreted in different mammalian cells. In contrast, in insect cells using recombinant baculovirus, a monovalent scFv H398 and a bivalent scFv fusion protein with an human IgG1 Fc region were expressed and secreted with correctly processed signal sequence. Concerning the influence of valency of the model Ab and its derivatives on antigen binding affinity and neutralisation of TNF activity, we found that the mono- and bivalent form of scFv H398 possesses the same characteristics as proteolytically produced Fab H398 and original mAb H398, respectively. Furthermore, fusion of the Ig Fc protein to scFv H398 increase the in vitro half-life at 37 degrees C. We conclude that the described cassette vectors readily allow the eukaryotic expression of mono- and bivalent scFv derivatives to analyse the influence of valency of scFv molecules on antigen binding and biological activity.

Hemodynamic effects of isoprostanes (8-iso-prostaglandin F2alpha and E2) in isolated guinea pig hearts

Isoprostanes are a family of prostaglandin-related compounds formed from arachidonic acid in a cyclooxygenase-independent manner as products of free radical-initiated lipid peroxidation. To elucidate the biological activity of the F2-and E2-isoprostanes, 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha) and 8-iso-prostaglandin E2 (8-iso-PGE2), we measured hemodynamic effects in isolated perfused guinea pig hearts after cumulative administration (3 x 10(-9)-10(-5) M) of these compounds into the coronary system. Coronary flow (CF), left ventricular pressure (LVP), maximal rate of pressure development (dP/dt(max)), and heart rate were determined continuously. Furthermore, net release of lactate into the coronary venous effluent and myocardial pyruvate consumption were measured. Comparative studies were performed with the known potent vasoconstrictor endothelin-1 (6 x 10(-12)-2 x 10(-9) M). Both 8-iso-PGF2alpha and 8-iso-PGE2 induced concentration-dependent decreases in CF, which declined maximally to approximately 50% of the baseline level. The potencies of the two compounds were almost identical. Alterations in CF were associated in both groups with parallel reductions of LVP and dP/dt(max); heart rate was not influenced. Furthermore, the diminished CF caused enhanced lactate release and a reduced pyruvate consumption. All isoprostane-induced hemodynamic changes were prevented by coapplication of the thromboxane A2-receptor antagonist SQ 29548 (1 microM). Endothelin-1 caused CF reductions associated with loss of myocardial contractility, just like the isoprostanes. We conclude that in isolated guinea pig hearts, 8-iso-PGF2alpha and 8-iso-PGE2 are potent vasoconstrictors. The action appears to be mediated by SQ 29548-responsive thromboxane receptors. The accompanying loss of contractility is a secondary phenomenon, elicited by infringed oxygen supply.

Retention of leucocytes in reperfused, isolated hearts does not cause haemodynamically relevant permanent capillary plugging

Effects of microspheres (5 microns or 10 microns diameter) and polymorphonuclear leucocytes (PMN) on coronary resistance were compared in beating, non-working isolated guinea-pig hearts (Langendorff preparation). The hearts were buffer perfused (5 ml/min, constant flow) and particles or cells were infused into the coronary system as a bolus (1 ml, 1 min). Coronary perfusion pressure, coronary flow and formation of epicardial transudate were measured before and after bolus administration. Coronary resistance was estimated from these parameters. Retention of particles or cells was monitored by quantifying the numbers emerging in the coronary effluent in relation to the number administered. The effects of PMN were also studied after 15 min of global ischemia. Coronary resistance correlated with the number of 10-micron particles infused, which were almost quantitatively retained. In contrast, 5-micron beads had no such effect and were not retained in the coronary system. Though considerable numbers of PMN were retained in the hearts (about 21% under control conditions and 35% after ischaemia), coronary resistance was not increased in either case. Blockage of the CD18 adhesion complex by monoclonal antibodies lowered basal retention to 11% and completely prevented the elevation of retention by ischaemia. We conclude that, in this experimental model, PMN, permanently retained in the hearts under normal flow conditions and especially after brief ischaemia, do not cause acute, haemodynamically relevant capillary plugging, but adhere to postcapillary venules via CD18.

The catalytic domain of activated collagenase I (MMP-1) is absolutely required for interaction with its specific inhibitor, tissue inhibitor of metalloproteinases-1 (TIMP-1)

Here, we describe the production of recombinant human tissue inhibitor of metalloproteinases-1 (rTIMP-1) and wild-type and mutant human collagenase type I (rMMP-1) proteins in SF9 cells by the baculovirus expression system. Wild-type MMP-1, as well as the MMP-1 mutant lacking the C-terminal hemopexin-like domain [des-(248-450)-MMP-1], exhibit enzymatic activity upon cleavage of the prodomain by treatment with trypsin or 4-aminophenylmercuric acetate. Enzyme activity of both proteins can be inhibited by addition of rTIMP. Deletion of the complete active-site [des-(161-228)-MMP-1] within the catalytic domain, or mutation of a single His residue of the Zn2+ binding domain (His199), generates stable forms of MMP-1 proteins which are unable to digest collagen type I or beta-casein. In addition to co-immunoprecipitation analysis, we have established a rapid and sensitive ELISA assay using immobilized rTIMP to determine the structural requirements of MMP-1 to form complexes with its inhibitor. Only the activated and not the latent forms of wild-type and C-terminal mutant des-(248-450)-MMP-1 proteins are able to form complexes with TIMP. Neither mutation of His199, nor deletion mutants des-(161-228)-MMP-1 and des-(161-228/248-450)-MMP-1, interact with TIMP. This demonstrates that the C-terminal hemopexin domain of MMP-1, in contrast to the corresponding regions of gelatinase A and gelatinase B, does not interact with TIMP-1. In summary, we have shown that the integrity of the catalytic domain of MMP-1 and its ability to bind Zn2+ is absolutely required for complex formation with TIMP-1, which further underlines the importance of this region for proper regulation of enzymatic activity of MMP-1.

Cardioprotection by cyclosporine A in experimental ischemia and reperfusion--evidence for a nitric oxide-dependent mechanism mediated by endothelin

The acute effect of cyclosporine A (CSA) on myocardial function after ischemia and reperfusion and the mechanism of action was investigated in isolated working guinea-pig hearts. Myocardial function was experimentally infringed by imposing short-term global ischemia and reperfusion (15 min each). External heart work (EHW), determined before and after ischemia, served as the criterion for quantitation of recovery. Control hearts were perfused with modified Krebs-Henseleit buffer, other hearts received buffer supplemented with CsA +/- an endothelin receptor antagonist or exogenous endothelin +/- an inhibitor of nitric oxide (NO) synthesis. To assess the importance of endothelial production of mediators directly, NO release in coronary effluent (continuously measured with an amperometric sensor) and release of 6-keto-prostaglandin F1, (6-keto-PGFb), a stable metabolite of prostacyclin (PGI2), were determined in non-working. Langendorff hearts. Oxidative stress during reperfusion was assessed by measuring glutathione release in coronary venous effluent. Cyclosporine A (0.8 microM) improved post-ischemic function significantly (59% recovery of EHW nu 31% for controls). At 0.08 microM. CsA was without beneficial effect (30% recovery). The endothelin (ET)A- and ETB-receptor antagonist bosentan inhibited the protective action of 0.8 microM CsA (32% recovery). Exogenous ET-1 (80 pM) improved recovery to 53%, an effect which was blocked by the inhibitor of NO-synthase, NG-nitro-L-arginine (NOLAG. 1 microM. 31% recovery. In the control group, post-ischemic NO release in coronary effluent recovered from zero to about 100% of the pre-ischemic value by 10 min. but then decreased rapidly during the subsequent 15 min of reperfusion. In hearts treated with 0.8 microM CsA, NO release stayed at 100% of the pre-ischemic value throughout reperfusion, the difference between controls and CsA-treated hearts being significant after 20 min of reperfusion. On the other hand, coronary venous release of 6-keto-PGF1a was not different between the groups. Release of glutathione during early reperfusion first 5 min) was significantly lowered (P < 0.05) to about 50% in CsA (0.8 microMI- and ET-I-treated compared with controls (8.8 nmol/min). Cyclosporine A acts as a cardioprotective agent in our model of ischemia and reperfusion, presumably by elevating the level of endogenous nitric oxide and thereby reducing oxidative stress.

The function of neutrophils isolated by a magnetic antibody cell separation technique is not altered in comparison to a density gradient centrifugation method

Most comparative studies on neutrophil (PMN) isolation techniques have shown either activation or functional impairment of the cells due to the different separation processes. We have established a preparation method for PMN from human whole blood employing iron tagged, magnetizable antibodies against the cell surface antigen CD15. The aim of our study was to test whether this magnetic separation (MACS) alters cellular functions of PMN in comparison to a conventional density gradient technique (Percoll). The purity, cell yield, and pre-activation of the cells were evaluated. The latter was assessed by quantifying the expression of the integrin CD11b using flow cytometry. Furthermore, as functional tests, cell morphology and the oxidative burst reaction were investigated. We have shown that the use of 'magnetic' antibodies leads to highly purified PMN (> 99% of isolated leukocytes), while there is still contamination by eosinophils (about 6%) after Percoll separation. Platelet contamination was about the same in both procedures (approx. one platelet per two PMN). The basal expression of CD11b and, hence, neutrophil activation, was significantly lower and the upregulation of CD11b in response to FMLP was more pronounced after magnetic separation, as compared to density gradient centrifugation. The MACS technique did not lead to polarisation of PMN, nor did it affect the oxidative burst. This study suggests that magnetic separation is a simple, time-saving technique, yielding highly purified and functionally intact PMN.

Halothane, isoflurane, and sevoflurane reduce postischemic adhesion of neutrophils in the coronary system

BACKGROUND

Polymorphonuclear neutrophils (PMNs) contribute to postischemic reperfusion damage in many organs and tissues, a prerequisite being adhesion of PMNs to vascular endothelial cells. Because adhesion processes involve orderly interactions of membrane proteins, it appeared possible that "membrane effects" of volatile anesthetics could interfere. We investigated the effects of halothane, isoflurane, and sevoflurane on postischemic adhesion of human PMNs in the intact coronary system of isolated perfused guinea pig hearts.

METHODS

The hearts (n = 7-10 per group) were perfused in the "Langendorff" mode under conditions of constant flow (5 ml/min) using modified Krebs-Henseleit buffer equilibrated with 94.4% oxygen and 5.6% carbon dioxide. Global myocardial ischemia was induced by interrupting perfusion for 15 min. In the second minute of reperfusion (5 ml/min), a bolus dose of 6 x 10(5) PMNs was injected into the coronary system. The number of cells reemerging in the coronary effluent was expressed as a percentage of the total number of applied PMNs. Halothane, isoflurane, and sevoflurane, each at 1 and 2 minimal alveolar concentration (MAC), were vaporized in the gas mixture and applied from 14 min before ischemia until the end of the experiment.

RESULTS

Under nonischemic conditions, 24.7 +/- 1.3% of the injected neutrophils did not reemerge from the perfused coronary system. Subjecting the hearts to global ischemia augmented retention (36.4 +/- 2.8%, P < .05). Application of halothane reduced adhesion of neutrophils to 22.6 +/- 2.1% and 24.2 +/- 1.8% at 1 and 2 MAC, respectively (P < .05). Exposure to 1 and 2 MAC isoflurane was similarly effective, whereas basal adhesion was not significantly influenced. Sevoflurane-treated hearts (1 and 2 MAC) also showed decreased adhesion of PMNs (23 +/- 2.3% and 24.8 +/- 1.8%, respectively; P < .05) and an identical reduction resulted when sevoflurane (1 MAC) was applied only with the onset of reperfusion.

CONCLUSIONS

Although the mechanism of action of volatile anesthetics remains unclear in these preliminary studies, their inhibitory effect on ischemia-induced adhesion of PMNs may be beneficial for the heart during general anesthesia.

Characterization of different soluble TNF receptor (TNFR80) derivatives: positive influence of the intracellular domain on receptor/ligand interaction and TNF neutralization capacity

Different soluble human TNFR80 derivatives, a solubilized form of the complete TNFR80, the TNFR80 extracellular domain, a secretory TNFR80 mutant (TR80TM-) with a deleted transmembrane region, and a TNFR80 immunoadhesin were produced in insect cells and characterized side by side with a recombinant human TNFR60 extracellular domain with respect to TNF binding affinity and neutralization of TNF bioactivity. The construct TR80TM- and the solubilized complete TNFR80 revealed a similar TNF binding and neutralization capacity, which was superior to the monovalent TNFR80 extracellular domain and comparable to the bivalent TNFR80 immunoadhesin, already known as a potent TNF antagonist. Determination of ligand off rate constants of the various receptor constructs by surface plasmon resonance revealed a correlation of low off rates with a high TNF neutralization capacity. We propose that the high TNF binding and neutralization capacity of the solubilized complete TNFR80 and TR80TM- in comparison with the monovalent extracellular TNR80 domain is due to a noncovalent self-aggregation of the receptors via their intracellular domain. This finding suggests that efficient soluble TNF antagonists can be derived from TNFR themselves without the need of construction of TNFR Ig Fc fusion proteins.

Nitric oxide mitigates leukocyte adhesion and vascular leak after myocardial ischemia

Tissue edema is a facet of ischemia/reperfusion injury in many organs, polymorphonuclear leukocytes (PMN) presumably playing a contributory role. We studied the intracoronary adhesion of PMN and its effect on vascular permeability during reperfusion in isolated guinea-pig hearts. After a global ischemia of 15 min duration. PMN (10(7)) were infused into the coronary system during the first minute of reperfusion. PMN adhesion was measured as difference of applied PMN and those recovered in the effluent perfusate. Coronary permeability was assessed by measuring the rate of transudate formation (TF) on the epicardial surface, before as well as 5, 15 and 30 min after ischemia. Experiments were also performed in the presence of the NO-synthase inhibitor nitro-L-arginine (10 microM) and the ACE-inhibitor ramiprilat (2 microM), the latter known to enhance endogenous nitric oxide formation. Furthermore, the radical scavenger uric acid (0.5 mM) was applied either before and during ischemia or starting after PMN application. Ischemia/reperfusion increased coronary PMN adherence from 23 +/- 1% (basal) to 33 +/- 2%. Whereas ischemia alone did not influence TF (about 100 microliters/min during reperfusion), postischemic PMN infusion led to progressive TF. With nitro-L-arginine, PMN adhesion rose to 45 +/- 3%; TF increased to 212 +/- 30 microliters/min. In contrast, ramiprilat caused post-ischemic adhesion and TF to decline to basal values. In the presence of uric acid (UA) PMN adhesion declined to 26 +/- 2%, however, the subsequent increase in TF after withdrawal of UA was not markedly attenuated. On the other hand, infusion of UA after application of PMN caused a significant decrease of TF. The extracellular antioxidants SOD/catalase were without effect. As shown using luminol enhanced chemiluminescence. No was able to scavenge oxygen free radicals released by activated PMN. These findings indicate that enhanced PMN adhesion in reperfusion leads to an increase in coronary permeability. Scavenging of oxygen free radicals with NO or UA appears to mitigate both, postischemic PMN adhesion and PMN-induced vascular injury, even after adhesion.

A bivalent immunoadhesin of the human interferon-gamma receptor is an effective inhibitor of IFN-gamma activity

We describe here the bioengineering of a bivalent IFN-gamma-RFc immunoadhesin consisting of the extracellular domain of the human IFN-gamma receptor alpha chain (IFN-gamma-R) fused to a human IgG1 Fc region (encoding hinge, CH2 and CH3 domain) that was efficiently expressed as a covalently linked homodimer in insect cells and purified in a one-step purification procedure. The IFN-gamma-RFc fusion protein exerted a 3-fold higher ligand binding affinity in binding competition studies in vitro compared with the monovalent extracellular IFN-gamma-R domain. In addition, the in vitro antagonistic activity of IFN-gamma-RFc, as determined by inhibition of IFN-gamma-induced virus protection and HLA-DR expression, was more than 30-fold higher in comparison with the monovalent soluble receptor. The described IFN-gamma-R immunoadhesin is a potential therapeutic reagent to interfere with the disease-promoting activities of IFN-gamma in several autoimmune diseases.

Preischaemic as well as postischaemic application of a calcium antagonist affords cardioprotection in the isolated guinea pig heart

OBJECTIVE

The aim was to answer the following questions: (1) Does treatment with calcium antagonists have to be begun before ischaemia or is postischaemic application also protective? (2) When applied before ischaemia, do calcium antagonists have to depress preischaemic cardiac function in order to elicit protection? (3) Is cardioprotection a matter of improved reflow or do the agents influence the degree of oxidative injury during reperfusion?

METHODS

Isolated working guinea pig hearts underwent ischaemia (15 min) and reperfusion (15 min). The calcium antagonist gallopamil was given either before (0.1 nM and 1 nM) or after ischaemia (0.1 nM) during early reperfusion (first 5 min). Recovery was defined as postischaemic compared to preischaemic external heart work, expressed in percent. Oxidative stress was assessed by the release of glutathione (GSH). Lactate release served as a measure of the ischaemic challenge. The ability of gallopamil to scavenge oxygen radicals directly was investigated in an in vitro chemiluminescence assay.

RESULTS

Pump function of control hearts recovered to only 28% after reperfusion. Pretreatment with 0.1 and 1 nM gallopamil improved recovery to the same extent (48.7% and 43.4%, respectively); however, postischaemic application of 0.1 nM gallopamil afforded equal protection (45.4% recovery). Only the higher concentration of 1 nM gallopamil depressed preischaemic external heart work (by 11%). During earliest reperfusion (1-5 min), release of GSH only tended to be lower in treated hearts. During the subsequent minutes of reperfusion (5-15 min), release of GSH was significantly less in hearts postischaemically treated with 0.1 nM gallopamil (40 pmol.min-1 v 940 pmol.min-1 for controls). In contrast, ischaemia-induced lactate release did not differ between the groups. Gallopamil did not scavenge reactive oxygen species in vitro.

CONCLUSIONS

Short term postischaemic application of the calcium antagonist gallopamil is almost as effective at restoring pump function as preischaemic application which, in turn, does not have to depress preischaemic cardiac function in order to elicit protection. A reduction of oxidative stress during reperfusion seems to contribute to the beneficial effects of postischaemic application of gallopamil, but a direct oxygen radical scavenging activity of gallopamil is not involved.

Nitric oxide accounts for postischemic cardioprotection resulting from angiotensin-converting enzyme inhibition: indirect evidence for a radical scavenger effect in isolated guinea pig heart

The cardioprotective effect of angiotensin-converting enzyme (ACE) inhibitors in cardiac ischemia/reperfusion damage is assumed to result largely from inhibition of the enzymatic breakdown of endogenous bradykinin (BK). We assessed the role of nitric oxide (NO) in mediating the beneficial actions of BK and the possible mechanism of the effect of NO. We experimentally infringed myocardial function in a working guinea pig heart preparation by ischemia (15 min) and reperfusion. The parameter external heart work (EHW), determined before and after ischemia, served as criterion for quantitation of recovery. We assessed oxidative stress during reperfusion by measuring glutathione release in coronary venous effluent; lactate release was used as a measure of ischemic challenge. The principal ability of NO to scavenge oxygen radicals was separately investigated in a chemiluminescence (CL) assay with the NO-donor sodium nitroprusside (SNP) and lucigenin. The ACE inhibitor ramiprilat (RT 25 microM) improved postischemic function significantly (55% recovery of EHW vs. 29% for controls). BK 1 nM was even more cardioprotective (71% recovery). The NO-synthase inhibitor Ng-nitro-L-arginine (NOLAG 10 microM) inhibited the effects of RT and BK (18% recovery each). SNP (0.3 microM) improved recovery to 57%, the prostacyclin analogue iloprost (ILO, 0.1 and 3 nM) had no beneficial effect (21 and 20% recovery, respectively). With 8-bromo-cyclicGMP, a membrane-permeable cGMP analogue, function was not better than control (30% recovery). Release of glutathione during reperfusion was decreased by the three compounds known to increase NO concentration in the heart; lactate release was the same in all groups.(ABSTRACT TRUNCATED AT 250 WORDS)

No association of antibodies to glutamic acid decarboxylase and diabetic complications in patients with IDDM

OBJECTIVE

To evaluate the association of antibodies to glutamic acid decarboxylase (GAD-ab) and diabetic complications (neuropathy, retinopathy, and nephropathy) in patients with insulin-dependent diabetes mellitus (IDDM).

RESEARCH DESIGN AND METHODS

We examined the prevalence of GAD-ab (immunoprecipitation assay) and islet cell antibodies (ICAs) (indirect immunofluorescence) in a representative sample of IDDM patients (n = 146) with different disease duration (2-52 years, median 13.2 years). Of all patients characterized for the existence of diabetic complications, 56 of 146 had peripheral neuropathy, 24 of 142 had autonomic neuropathy, 67 of 141 had retinopathy, and 39 of 146 had nephropathy.

RESULTS

GAD-ab (> 2 SD) were detected more frequently than ICA (> 5 Juvenile Diabetes Foundation units) in IDDM patients of different disease duration (GAD-ab+ 37% [54 of 146] vs. ICA+ 22% [32 of 146], P = 0.011; diabetes duration less than median: GAD-ab+ 47% vs. ICA+ 23%, P = 0.0046; diabetes duration greater than median: GAD-ab+ 27% vs. ICA+ 22%, P > 0.05). For GAD-ab and for ICA, respectively, no difference was observed in frequency of positivity or titers between patients with or without diabetic complications.

CONCLUSIONS

Both GAD-ab and, to a lesser extent, ICA persist for a long time in several individuals. This persistence is not related to diabetic neuropathy or any other diabetic complication.

Coexpression of the human TNF receptors TR60 and TR80 in insect cells: analysis of receptor complex formation

For investigation of a possible physical interaction between the two human tumor necrosis factor receptors, TR60 (type I) and TR80 (type II), the baculovirus expression system was used. Each of the receptors was expressed as a membrane-integrated protein in insect cells, able to specifically bind the two ligands, tumor necrosis factor (TNF) and lymphotoxin (LT alpha). Typically, about 150,000 membrane receptors per cell could be detected 40 h after infection, exerting high affinity ligand binding capacity with Kd values virtually identical to that of human cell lines. The baculovirus system allowed coexpression of both TNF membrane receptors at very high and about equal numbers to investigate the existence of heteromultimeric receptor complexes, either formed spontaneously or ligand induced. Neither saturation binding studies nor immunoprecipitation experiments gave an indication for the existence of TNF receptor heteromers. These data are in accordance with the current view of TNF signaling, in which homonultimerization, rather than heteromer formation of TNF receptors is the initial activating event.

Stimulation of endothelial adenosine A1 receptors enhances adhesion of neutrophils in the intact guinea pig coronary system

OBJECTIVE

The primary aim was to determine the action of pathophysiologically relevant adenosine concentrations (0.1-1 microM) on adhesion of neutrophils to coronary endothelium. Further aims were to evaluate the nature and localisation of the adenosine receptor involved, and to assess the effect of endogenous adenosine.

METHODS

Adhesion was studied in isolated perfused guinea pig hearts by determining the number of cells emerging in the coronary effluent after intracoronary bolus injections of 600,000 neutrophils prepared from guinea pig or human blood. The system was characterised by the use of the proadhesive stimulus thrombin.

RESULTS

A 5 min infusion of adenosine (0.1-0.3 microM) or the A1 receptor agonist N6-cyclopentyladenosine (CPA, 0.01 microM) significantly increased adhesion from about 20% (control) to 30%. This effect was prevented by the A1 receptor antagonist dipropyl-8-cyclopentylxanthine (DPCPX, 0.1 microM). It was not diminished by cessation of adenosine infusion 90 s prior to neutrophil injection. At a higher concentration of adenosine (1 microM), adhesion did not seem to be enhanced. However, coinfusion of the A2 receptor antagonist 3,7-dimethyl-1-propargylxanthine (DMPX, 0.1 microM) with 1 microM adenosine unmasked the A1 action, adhesion rising to 39%. Adenosine had a quantitatively identical effect on adhesion of human neutrophils. Total ischaemia of 15 min duration raised adhesion of subsequently applied neutrophils to 35%. This effect was completely blocked by DPCPX, as well as by ischaemic preconditioning (3 x 3 min). Preconditioning raised initial postischaemic coronary effluent adenosine from about 0.8 microM to 1.5 microM.

CONCLUSIONS

The findings suggest a bimodal participation of adenosine in the development of postischaemic dysfunction by an endothelium dependent modulation of neutrophil adhesion. Stimulation occurs via endothelial A1 receptors at submicromolar adenosine levels, whereas cardioprotection by adenosine may in part relate to the use of pharmacologically high concentrations of adenosine or enhanced endogenous production after preconditioning.

Bradykinin accounts for improved postischemic function and decreased glutathione release of guinea pig heart treated with the angiotensin-converting enzyme inhibitor ramiprilat

We investigated the role of bradykinin (BK) in cardioprotection elicited by angiotensin-converting enzyme (ACE) inhibition is isolated guinea pig heart performing pressure-volume work. Cardiac output (CO), coronary blood flow (CBF), and external heart work (EHW) were determined before and after ischemia and reperfusion (15 min each). Furthermore, the glutathione (GSH) content of hearts and the release of glutathione in coronary venous effluent were measured, as was lactate production. Addition of the ACE-inhibitor ramiprilat (RT) to the perfusate throughout the experiment improved postischemic function significantly (55% recovery of EHW for 25 microM RT vs. 30% for controls). RT was cardioprotective even if only given at onset of reperfusion (50% recovery). BK (0.1 and 1 nM) was similarly beneficial (55 and 76% recovery of EHW, respectively). The BK2-receptor antagonist HOE 140 (10 nM) inhibited the RT effect and attenuated the effect of 1 nM BK. Total CBF during reperfusion, lactate production, intracellular levels of GSH, and release of oxidized GSH (GSSG) did not differ among the groups. In contrast, release of reduced GSH during the first 5 min of reperfusion was considerably influenced by pharmacologic intervention, correlating inversely with postischemic heart function. Coapplication of Hoe 140 prevented the changes in GSH release. Our results demonstrate that BK, formed endogenously in the heart, is responsible for cardioprotection by the ACE inhibitor RT in isolated guinea pig heart and decreases GSH release during reperfusion. The exact mechanisms leading to hemodynamic improvement and metabolic changes by BK remain unclear.

Expression of complete human IFN-gamma receptor and its extracellular domain in insect cells: purification and characterization of the recombinant proteins

We here describe an efficient procedure for overexpression and purification of recombinant complete human interferon-gamma (IFN-gamma) receptor (IFN-gamma-R) and its extracellular fragment employing a baculovirus (BV) expression system. Infection of Sf 158 cells with recombinant BV results in membrane expression of high affinity IFN-gamma-R (Kd 1.6 x 10(-10) M), with approximately 10(6) molecules/cell 40 h postinfection. Solubilized, affinity-purified IFN-gamma-R and a secreted extracellular domain of IFN-gamma-R were compared for ligand-binding capacity and antagonistic activity in an IFN-gamma bioassay. Our results show that the complete receptor has a 2.5-fold higher ligand affinity and a 15-fold higher IFN-gamma in vitro-neutralizing capacity in an in vitro virus protection assay as compared to the extracellular fragment. This suggests that the transmembrane and cytoplasmic domains of IFN-gamma-R contribute to stability and/or enhance formation of biologically active receptor complexes in solution.

Adenosine contributes to neutrophil-mediated loss of myocardial function in post-ischemic guinea-pig hearts

Tissue injury associated with myocardial ischemia is assumed to largely result from the toxic effects of active oxygen species generated by accumulated polymorphonuclear leukocytes (PMNs). Recent reports have indicated that adenosine can interfere with the PMN function in vitro. The potential of adenosine to influence PMN-mediated myocardial tissue injury was assessed using a model of ischemia-reperfusion injury developed in the isolated working guinea-pig heart perfused with homologous PMNs. After an initial work phase, hearts were subjected to 30 min low-flow ischemia (1 ml/min) in the absence and presence of PMNs. Work was resumed after 15 min reperfusion in a non-working mode (Langendorff). Adenosine in the coronary effluent reached a maximum of 0.2 microM during low-flow ischemia. Recoveries of external heart work and cardiac output were reduced from about 80% to about 40% by PMNs. Infusion of adenosine deaminase (ADA, 5 U/ml), theophylline (50 microM) or the selective A1-antagonist dipropyl-8-cyclopentylxanthine (0.1 microM) prevented this effect. Furthermore, application of adenosine (0.1 microM) in combination with PMNs also resulted in a loss of pump function, even in the absence of a direct ischemic stimulus. The data indicate that adenosine contributes to post-ischemic, PMN-mediated damage in the isolated working guinea-pig heart model by a receptor-mediated action.

Postischemic dysfunction of the heart induced by small numbers of neutrophils via formation of hypochlorous acid

The role of polymorphonuclear neutrophils (PMN) in the injury of the heart following ischemia and reperfusion is still controversial. The aim of this study was to investigate whether small numbers of PMN may cause myocardial dysfunction in an isolated system, how the resulting loss of function can be characterized and whether the formation of hypochlorous acid (HOCl) can be responsible for the PMN-mediated effect. Isolated working guinea pig hearts were subjected to a 90% reduction of coronary flow for 30 min, with or without intracoronary infusion of homologous PMN (approximately 1-2 x 10(5) cells/min, i.e. about 5-10% of normal blood count). This ischemia was followed by a 15 min reflow period in a non-working ("Langendorff") mode before work was resumed. In hearts perfused only with buffer, post-hypoxic heart function recovered to 75-80% of the initial value. Inclusion of unstimulated PMN did not further attenuate cardiac function. However, cardiac output was decreased to 42% of the initial value, provided thrombin (0.3 U/ml) and H2O2 (10(-5) M) were also present, and the retained PMN (about 10% of those infused) were additionally stimulated during reflow by application of FMLP (10(-6) M for 1 min). In these instances, coronary flow at any time of the experiment and release of lactate or purines during ischemia and reflow did not differ significantly between hearts perfused with or without PMN. There was no substantial release of myoglobin in controls and in PMN-treated hearts. Inotropic stimulation of the hearts with noradrenaline or exogenous Ca2+ caused a sustained increase in contractile force. However, the response was significantly reduced in PMN-perfused hearts in comparison to control hearts. The myocardial contents of high-energy phosphates with and without inotropic stimulation proved to be identical irrespective of whether experiments had been performed in the absence or presence of PMN. A similar loss of myocardial function as mediated by PMN could be produced by infusing chemically generated hypochlorous acid (HOCl, 5 x 10(-7) M for 10 min). Strikingly, that portion of the infused HOCl which actually reacted with cardiac tissue was comparable to the amount shown to be generated by stimulating 10(6) PMN retained in the coronary system (about 7 nmoles). Supplementing the perfusate with the scavengers L-methionine (10(-4) M) or uric acid (5 x 10(-4) M) prevented the attenuation of heart function provoked by PMN. The results indicate that small numbers of PMN, sufficiently activated, can depress cardiac function after 30 min of ischemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Ampicillin-sulbactam susceptibility testing criteria

In vitro studies in five different medical centers documented the susceptibility of 2,440 consecutive isolates of the Enterobacteriaceae against ampicillin-sulbactam disks of different potencies. For determination of MICs, both 2:1 or 1:1 ratios were used as long as the concentrations of sulbactam at the breakpoints remained the same, i.e. MIC < or = 16/8.0 micrograms/ml or < or = 8.0/8.0 micrograms/ml for the susceptible category. Disks containing 10 micrograms of ampicillin and 10 micrograms of sulbactam are still to be preferred with interpretive criteria of > or = 15 mm for susceptible and < or = 11 mm for resistant (MIC > or = 64/32 micrograms/ml or > or = 32/32 micrograms/ml). The reliability of the disk test actually diminished when the amount of sulbactam in the disk was increased.

Relative efficacy of tazobactam, sulbactam and clavulanic acid in enhancing the potency of ampicillin against clinical isolates of Enterobacteriaceae

Three beta-lactamase inhibitors were combined with ampicillin in a fixed 2:1 ratio. The activity of ampicillin was enhanced by tazobactam and by clavulanic acid, and to a lesser extent by sulbactam when tested against fresh clinical isolates of Enterobacteriaceae. At a concentration of 8 micrograms/ml, ampicillin alone inhibited 49.6% of 2,434 consecutive isolates of enteric bacilli compared to 81% inhibited by ampicillin combined with tazobactam or clavulanic acid and 69.3% inhibited by the sulbactam/ampicillin combination. A four-fold or greater reduction in ampicillin MICs was observed in comparable numbers of isolates with all three combinations, but the most marked effects were seen with strains that were highly resistant to ampicillin.

Different endothelial mechanisms involved in coronary responses to known vasodilators

The role of the endothelium in mediating flow responses to acetylcholine (ACh), bradykinin (BK), adenosine (Ado), and the poorly hydrolyzable ATP-derivative beta,gamma-methylene-ATP (MeATP) was evaluated in the intact coronary system of the isolated perfused guinea pig heart. In the presence of superoxide anions, known to inactivate the endothelium-derived relaxing factor nitric oxide (NO), only steady-state dilatation induced by ACh (1 microM) was fully inhibited and that of BK (0.1 nM) attenuated. Similar effects were obtained with methylene blue and N omega-nitro-L-arginine; however, the latter also reduced the actions of Ado (0.1 microM) and MeATP (0.5 microM). Conversely, perfusion with the NO precursor L-arginine (10 microM) resulted in a potentiated relaxation by ACh, whereas steady-state responses to BK and Ado remained unchanged. Pretreatment of hearts with hydroxyl radicals (.OH) elevated vascular permeability. Under this condition, flow increases induced by ACh, BK, and Ado were enhanced by 130, 89, and 47%, respectively, whereas the effect of MeATP (0.5 microM) was reduced by 45%. Preexposure of hearts to the oxidant hypochlorous acid (HOCl) prevented dilatations by ACh, BK, MeATP and Ado (0.1 microM), and the response to Ado (5 microM) was reduced by 68%; postischemic hyperemia was attenuated. Glyburide, an inhibitor of ATP-sensitive K+ channels, halved the flow response to infused Ado (0.1 and 5 microM), inhibited MeATP, and abolished reactive hyperemia. We conclude that in the guinea pig coronary system ACh, BK, MeATP, and Ado (0.1 microM) induce endothelium-dependent vasodilatation, some step(s) of the signal transmission being vulnerable to oxidative attack by HOCl.(ABSTRACT TRUNCATED AT 250 WORDS)

No evidence for the existence of preformed antibodies against hydroxyethyl starch in man

Using the highly sensitive ELISA technique for detecting anti-hydroxyethyl starch (HES) antibodies in man sera from 1,056 patients were analyzed. Patients of both sex, who had never had any prior contact with HES, were included in the study. In none of the cases could any titer of HES-reactive antibodies be detected. These data suggest that in man preformed HES-reactive antibodies do not exist or are extremely rare. In any case, unlike dextran-reactive antibodies, they should not have a high clinical importance. The mechanism behind the very rarely observed anaphylactoid reactions after HES application is still unknown.

Uric acid as radical scavenger and antioxidant in the heart

Uric acid (UA) is released from the heart of many species, including man, and its site of formation has been shown to be the microvascular endothelium. Since UA reacts with oxygen radicals in vitro, experiments were conducted on guinea pig hearts perfused with Krebs-Henseleit buffer (KHB) to evaluate whether the formation of UA could afford protection from damage by radicals and oxidants. The following results were obtained: (1) Upon addition of the hydroxyl radical scavenger DMSO to the perfusate, the coronary rate of release of endogenous uric acid was increased relative to the precursor purines. (2) UA was degraded during passage through the coronary system and also in KHB in vitro after addition of substances generating hydroxyl radicals or hypochlorite. Superoxide (O2-) radicals did not seem to react directly with UA, though UA concentration-dependently quenched the chemiluminescence generated from luminol in the presence of O2- and OH radicals. (3) Coronary dilation by acetylcholine (Ach) and sub-microM concentrations of adenosine, induced by both via endothelial mechanisms, was attenuated after prolonged inhibition of endothelial UA formation by allopurinol. Furthermore, the effect of Ach but not of adenosine proved acutely sensitive to methylene blue and O2-, substances known to inactivate EDRF. This finding suggests involvement of EDRF in Ach-mediated, but not in adenosine-induced dilatation of the intact coronary system. Exogenously applied UA prevented the impairment of vascular responses to Ach and adenosine caused by allopurinol, and to Ach upon generation of O2-. (4) Hearts performed more pressure-volume work and exhibited greater functional stability when perfused with KHB supplemented with UA in a physiological concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of platelet aggregation following chronic in vivo treatment of rats with nicotine: prevention by simultaneous application of propranolol

Platelet aggregability is known to be enhanced and platelet-survival time shortened in smokers when compared with nonsmokers. Up to now it is unknown which of the substances in tobacco smoke are responsible for these effects. To evaluate a possible role of nicotine, rats were chronically treated with the alkaloid (10 mg/kg/day), continuously released from subcutaneously implanted osmotic minipumps. Surprisingly, after 8 weeks, platelet sensitivity toward the aggregating stimulus adenosine 5'-diphosphate (ADP) was markedly reduced. The mean ADP concentration required to induce half the maximum rate of aggregation (EC50) was 0.88 mumol/L in nicotine-treated animals, as compared with 0.67 mumol/L in controls (p less than 0.002). Platelet aggregability remained normal when the rats were treated simultaneously with nicotine and the beta blocker propranolol (3.5 mg/kg/day); for these animals, the mean EC50 for ADP was 0.73 mumol/L. These results are suggestive of a catecholamine-mediated action of nicotine. However, neither the basal levels of cAMP in platelet-rich plasma, nor the cAMP levels attained after stimulation of platelet adenylate cyclase with prostaglandin E1 (PGE1), were affected by 8 weeks of treatment with nicotine or nicotine plus propranolol. No effect on platelet aggregation was observed when the rats were treated with nicotine for only 2 weeks, or when nicotine or nicotine plus cotinine were added to platelet-rich plasma in vitro in concentrations equal to those attained in vivo after 8 weeks. Thus, prolonged application of nicotine in vivo caused an inhibition of ADP-induced rat platelet aggregation presumably mediated by beta-catecholaminergic stimulation of platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic treatment with adrenaline or propranolol on platelet function and c-AMP levels in the rat

Most of our knowledge about the modulation of platelet function by catecholamines is based on observations of acute in vitro actions. Little is known about the effects of chronically elevated or reduced adrenergic stimulation of the platelets. We therefore treated rats for 8 weeks with either adrenaline or the beta-blocker propranolol. Adrenaline (0.5 mg.kg-1.d-1) continuously administered from subcutaneously implanted osmotic mini pumps caused an increase in the sensitivity of the platelets towards ADP as stimulating agent. In contrast, chronic application of propranolol (10 mg.kg-1.d-1) via the drinking water led to a reduction in platelet aggregability. For animals treated with adrenaline, in accordance with the results of the aggregation experiments, the levels of c-AMP found in platelet rich plasma were reduced, both basally (by 33%) and after stimulation of platelet adenylate cyclase with prostaglandin E1 (by 39%). For the propranolol treated animals, the basal c-AMP concentrations remained unchanged. The levels of c-AMP attained after stimulation with prostaglandin E1 were diminished to a similar extent as for the adrenaline treated animals (by 38%). Although the in vitro addition of adrenaline to platelet rich plasma causes a beta-adrenoceptor mediated inhibition of platelet aggregation in the rat, the simulation seen after chronic adrenaline exposure in vivo, which is associated with decreases in both basal and stimulated c-AMP levels, suggests a functional preponderance of alpha-adrenoceptors over beta-adrenoceptors on the rat platelets. Although intraplatelet metabolic changes (blockade of stimulated c-AMP formation) after chronic application of propranolol should have resulted in enhancement of platelet aggregability, an inhibition of aggregation was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Purine metabolism in cultured aortic and coronary endothelial cells

Purine salvage pathways in cultured endothelial cells of macrovascular (pig aorta) and microvascular (guinea pig coronary system) origin were investigated by measuring the incorporation of radioactive purine bases (adenine or hypoxanthine) or nucleosides (adenosine or inosine) into purine nucleotides. These precursors were used at initial extracellular concentrations of 0.1, 5, and 500 microM. In both types of endothelial cells, purine nucleotide synthesis occurred with all four substrates. Aortic endothelial cells salvaged adenine best among purines and nucleosides when applied at 0.1 microM. At 5 and 500 microM, adenosine was the best precursor. In contrast, microvascular endothelial cells from the coronary system used adenosine most efficiently at all concentrations studied. The synthetic capacity of salvage pathways was greater than that of the de novo pathway. As measured using radioactive formate or glycine, de novo synthesis of purine nucleotides was barely detectable in aortic endothelial cells, whereas it readily occurred in coronary endothelial cells. Purine de novo synthesis in coronary endothelial cells was inhibited by physiological concentrations of purine bases and nucleosides, and by ribose or isoproterenol. The isoproterenol-induced inhibition was prevented by the beta-adrenergic receptor antagonist propranolol. The end product of purine catabolism in aortic endothelial cells was found to be hypoxanthine, whereas coronary endothelial cells degraded hypoxanthine further to xanthine and uric acid, a reaction catalyzed by the enzyme xanthine dehydrogenase.

Endothelium-mediated coronary dilatation by adenosine does not depend on endothelial adenylate cyclase activation: studies in isolated guinea pig hearts

Adenosine, applied to the coronary system of guinea pigs at up to 10(-6) M, elicits dilatation solely via an endothelium-mediated process. We investigated the role of coronary A2 receptors in this dilation, since the coronary endothelium possesses adenosine A2-receptors with a stimulatory action on the adenylate cyclase. In situ, A2 receptor stimulation can be assessed by prelabeling the coronary endothelial adenine nucleotide pool with 3H-adenosine and subsequently determining the rate of release of radiolabeled cAMP induced by A2 agonists. Thus, perfusion of isolated hearts with 5'-N-ethylcarboxamidoadenosine (NECA) dose-dependently increased coronary flow and the release of 3H-cAMP from the endothelium. In the presence of 50 microM 2',5'-dideoxyadenosine (ddA), a P-site agonist which inhibits the catalytic activity of adenylate cyclase, coronary flow increases induced by both adenosine and NECA were unaffected. In contrast, ddA reduced the release of labeled cAMP in response to NECA by about 60%. In cultured endothelial cells, ddA likewise inhibited cAMP accumulation due to NECA by about 70%. Moreover, ddA antagonized the adenylate cyclase mediated flow response due to the PGI2 analogue, iloprost, as well as the positive chronotropic and inotropic actions of isoproterenol. The dissociation elicited by ddA between the coronary flow response and the release of cAMP strongly indicates that the endothelial A2 receptors which are linked to adenylate cyclase are not causally involved in endothelium-dependent coronary dilatation induced by adenosine.

Increasing platelet aggregability after venepuncture is platelet, not plasma derived

The time course of ADP induced aggregation of human platelets was determined in aliquots of stored platelet rich plasma 3.5, 10, 30 and 100 minutes after venepuncture. The maximal rate of aggregation was found to increase throughout this entire period, even though pH (7.4), CO2 (7 volume per cent) and temperature (35 degrees C) of the samples were kept constant. The mean acceleration (+/- SEM) between 3.5 and 100 minutes was 41.7 +/- 6.9 per cent (n = 67) at an ADP-concentration of 1 mumol/l and 18.3 +/- 6.2 per cent (n = 23) at 2 mumol/l ADP. The effect did not result from changes of any platelet regulatory factors putatively present alone in the plasma. Acceleration of aggregability was only found when the platelets themselves underwent storage, but not when freshly prepared plasma was given to prestored platelets. The change in aggregability was not diminished after inhibition of platelet cyclooxygenase by oral administration of acetylsalicylic acid.

The coronary endothelium: a highly active metabolic barrier for adenosine

Cultured coronary endothelial cells and the coronary endothelium of isolated perfused guinea-pig hearts are characterized by a very active adenosine and adenine nucleotide metabolism. Adenosine applied to the endothelium at low concentrations is avidly metabolized and preferentially incorporated into different nucleotide pools--only a minor amount is degraded to uric acid. Physiologically, the coronary endothelium therefore functions as an impermeable metabolic barrier for interstitially or intravascularly accumulating adenosine. Only at concentrations greater than or equal to 10(-6) M adenosine can pass the endothelial barrier. As a consequence, the vasodilatory action of adenosine formed in or administered into the coronary system cannot be induced by a direct association of the nucleoside with the putative adenosine receptor of the arteriolar smooth muscle cells, but must be mediated by the endothelium. High molecular weight derivatives of adenosine, clearly confined to the coronary system, can also induce a coronary dilation. The endothelium-mediated smooth muscle relaxation is therefore obviously due to triggering of an extracellular adenosine receptor at the luminal surface of the endothelium. Since this process is accompanied by a rapid and pronounced activation of the adenylate cyclase system, the endothelial receptor conforms to an A2-type. According to our results it is necessary to reconsider qualitative and quantitative facets of the adenosine hypothesis of metabolic regulation of coronary blood flow, which--in its original formulation--exclusively centers on the cardiomyocyte metabolism. With respect to the vasoactivity of adenosine one obviously has to distinguish between its action from the interstitial space directly via the myocyte receptors of the vessel wall, and/or its action from the intracoronary space via the newly detected endothelial A2-receptor. More information is needed to determine the extent to which both receptor populations actually participate in the metabolic regulation of coronary flow under physiological and pathophysiological conditions.