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Biomedical subjects

M Singer

Publications and source records attributed to M Singer.

At least 19 recordsLinked to original sources
PubMed2000

Inhibition by extracellular cAMP of phorbol 12-myristate 13-acetate-induced prostaglandin H synthase-2 expression in human pulmonary microvascular endothelial cells. Involvement of an ecto-protein kinase A activity.

Exposure of human pulmonary microvascular endothelial cells (HPMECs) to phorbol 12-myristate 13-acetate (PMA) leads to the increase of prostaglandin H synthase (PGHS)-2 protein levels. Under same conditions and according to its constitutive nature, no significant variation of PGHS-1 protein was noted. The elevation of the intracellular cAMP rate is known to enhance PGHS-2 levels through a protein kinase A pathway in various cells. To determine whether the extracellular cAMP also regulates the inducible expression of PGHS, cultured HPMECs were exposed to cAMP alone or in combination with PMA. The PMA-induced PGHS-2 protein was attenuated by the extracellular cAMP. In addition, PGHS-2 activity evaluated through 6-keto-PGF1alpha generation, which was enhanced by PMA was inhibited by extracellular cAMP. Furthermore, in HPMEC medium, PMA-induced PGHS-2 expression was accompanied by the generation of a transferable activity (TA) able to abolish platelet aggregation. This resulting TA was dependent from PGHS-2 pathway, because NS-398, a selective inhibitor of PGHS-2, suppressed its production. The inhibitory TA released by treated HPMECs was also prevented by extracellular cAMP. The specific protein kinase A (PKA) inhibitor blocked the extracellular cAMP effect on both PMA-induced 6-keto-PGF1alpha synthesis and inhibitory TA generation, suggesting the involvement of PKA signaling at the outer surface of HPMECs. Accordingly, we established, in phosphorylation experiments, the presence of an endothelial ecto-protein kinase activity, able to phosphorylate the synthetic substrate kemptide in a cAMP-dependent mode. Reverse transcription-polymerase chain reaction analysis showed that PMA-induced PGHS-2 mRNA was markedly reduced by extracellular cAMP. Together, these findings provide the first experimental evidence that extracellular cAMP is able to reduce HPMEC PGHS-2 expression in terms of mRNA, protein, and enzyme activity through an ecto-PKA pathway. In addition, they outline the potential role of endothelial PGHS-2 in the limitation of platelet activation during inflammatory processes.

Carcinogens↗
PubMed2000

1,3-Diarylcycloalkanopyrazoles and diphenyl hydrazides as selective inhibitors of cyclooxygenase-2.

Novel 1,3-diarylcycloalkanopyrazoles 1, and diphenyl hydrazides 2 were identified as selective inhibitors of cyclooxygenase-2. The 1,3-diaryl substitution pattern of the pyrazole ring in 1 differentiates these compounds from most of the known selective COX-2 inhibitors that contain two aryl rings at the adjacent positions on a heterocyclic or a phenyl ring. Similarly, the two phenyl rings in 2 are also separated by three atoms. SAR of both phenyl rings in 1 and 2, and the aliphatic ring in 1 will be discussed.

Azides↗
PubMed2000

Lack of IL-10 synthesis by murine alveolar macrophages upon lipopolysaccharide exposure. Comparison with peritoneal macrophages.

The central role of alveolar macrophages in the establishment of lipopolysaccharide (LPS)-induced lung inflammation is well demonstrated. They produce and release numerous proinflammatory molecules, among which is tumor necrosis factor alpha (TNF-alpha), a cytokine responsible in part for the neutrophilic alveolitis. Interleukin-10 (IL-10) produced by LPS-activated mononuclear phagocytes is a major anti-inflammatory cytokine that down-regulates TNF-alpha synthesis. We studied the ability of murine alveolar macrophages to produce IL-10 in vivo and in vitro, in response to LPS. Unexpectedly, the IL-10 protein was not detected in the whole lung and airspaces after LPS intranasal instillation. In addition, no IL-10 protein was found in supernatants of isolated and LPS-stimulated alveolar macrophages. The lack of IL-10 synthesis was confirmed by the absence of specific RNA transcripts. By contrast and as expected, autologous peritoneal macrophages produced IL-10 upon LPS challenge. Drugs that usually modify the TNF-alpha/IL-10 balance in favor of IL-10 were used without success. Thus, maneuvers allowing an increase in intracellular cAMP concentrations did not reverse this unexpected phenotype. Moreover, direct activation of protein kinase C with PMA was unable to trigger IL-10 formation by alveolar, by contrast to peritoneal, macrophages. The current findings describe a specific phenotype for murine alveolar macrophages during LPS-induced inflammation.

Animals↗
PubMed2000

The asgE locus is required for cell-cell signalling during Myxococcus xanthus development.

In response to starvation, Myxococcus xanthus undergoes a multicellular developmental process that produces a dome-shaped fruiting body structure filled with differentiated cells called myxospores. Two insertion mutants that block the final stages of fruiting body morphogenesis and reduce sporulation efficiency were isolated and characterized. DNA sequence analysis revealed that the chromosomal insertions are located in open reading frames ORF2 and asgE, which are separated by 68 bp. The sporulation defect of cells carrying the asgE insertion can be rescued phenotypically when co-developed with wild-type cells, whereas the sporulation efficiency of cells carrying the ORF2 insertion was not improved when mixed with wild-type cells. Thus, the asgE insertion mutant appears to belong to a class of developmental mutants that are unable to produce cell-cell signals required for M. xanthus development, but they retain the ability to respond to them when they are provided by wild-type cells. Several lines of evidence indicate that asgE cells fail to produce normal levels of A-factor, a cell density signal. A-factor consists of a mixture of heat-stable amino acids and peptides, and at least two heat-labile extracellular proteases. The asgE mutant yielded about 10-fold less heat-labile A-factor and about twofold less heat-stable A-factor than wild-type cells, suggesting that the primary defect of asgE cells is in the production or release of heat-labile A-factor.

Bacterial Proteins↗
PubMed2000

Inhibition by unsaturated fatty acids of type II secretory phospholipase A2 synthesis in guinea-pig alveolar macrophages evidence for the eicosanoid-independent pathway.

The effect of arachidonic acid (C20:4) on the production of secretory type II phospholipase A2 (sPLA2-II) by guinea-pig alveolar macrophages was investigated. We show that incubation of these cells with 1-30 microM of arachidonic acid inhibits the synthesis of sPLA2-II in a concentration-dependent manner with an IC50 of approximately 7.5 microM. The inhibition by low concentrations (5 microM) of arachidonic acid was partially reduced by pretreatment of alveolar macrophages with cyclooxygenase or cytochrome P450 inhibitors (aspirin and 1-aminobenzotriazole, respectively), but not by lipoxygenase inhibitor, BW A4C. However, these inhibitors failed to interfere with the effect of high concentrations (30 microM) of arachidonic acid, suggesting that the latter may act on the expression of sPLA2-II, at least in part, independently of eicosanoid generation. Indeed, a similar inhibitory effect on sPLA2-II activity and mRNA expression was observed with other unsaturated fatty acids such as eicosapentaenoic (C20:5) and oleic (C18:1) acids, but not with the saturated fatty acid, palmitic acid (C16:0). In addition, arachidonic acid partially reduced the secretion of tumor necrosis factor alpha, an important intermediate in the induction of sPLA2-II synthesis by guinea-pig alveolar macrophages. However, addition of recombinant tumor necrosis factor alpha failed to reverse the inhibitory effect of arachidonic acid on sPLA2-II expression, suggesting that this process occurs downstream of tumor necrosis factor alpha secretion. We conclude that the expression of sPLA2-II in alveolar macrophages is down-regulated at the transcriptional level by arachidonic acid either directly or via its cyclooxygenase and cytochrome P450-derived metabolites.

Animals↗
PubMed2000

A comparison of hemodynamic data derived by pulmonary artery flotation catheter and the esophageal Doppler monitor in preeclampsia.

OBJECTIVE: This study was undertaken to compare hemodynamic data derived with the esophageal Doppler monitor against those obtained with a pulmonary artery flotation catheter in women with complicated preeclampsia. STUDY DESIGN: Seventeen women with severe preeclampsia who had a pulmonary artery flotation catheter placed for clinical indications also had an esophageal Doppler monitor inserted. Hemodynamic data were recorded on 2 occasions separated by several hours with both the pulmonary artery flotation catheter and the esophageal Doppler monitor simultaneously. RESULTS: The esophageal Doppler monitor underestimated cardiac output by 36% +/- 14% (mean +/- SD). The esophageal Doppler monitor accurately estimated cardiac output in 3 women >40 years old, whereas in the remaining women (all <35 years old) the esophageal Doppler monitor underestimated cardiac output by 38% +/- 11%. The esophageal Doppler monitor accurately reflected changes in cardiac output with time when compared with the pulmonary artery flotation catheter. CONCLUSION: In women with preeclampsia the esophageal Doppler monitor consistently underestimated cardiac output by approximately 40%. It is not known whether the apparent increase in accuracy among the women >40 years old arose by chance or reflected a real improvement in performance. The esophageal Doppler monitor accurately reflected the direction and magnitude of the changes in cardiac output with time.

Adult↗
PubMed2000

Long-term results of tendon transfers for radial nerve palsy in patients with limited rehabilitation.

The authors reviewed the long-term functional results of 22 patients who underwent tendon transfer for isolated radial nerve palsy. The average number of postoperative visits was eight (range of postoperative visits, 3-16), and the mean follow-up was 6.3 years. All but 1 patient had improved function after the tendon transfers, and could cope with the activities of daily living. Radial deviation of the wrist at rest was present in 10 of the 15 patients with flexor carpi ulnaris transfer and in 2 of 7 patients with flexor carpi radialis transfer, with a mean of 14.5 deg (range of radial deviation, 5-30 deg). Although a global decrease in wrist power and power grip was noted, 13 of 17 previously employed patients were able to work after transfer; however, only 1 of 7 heavy manual laborers was able to return to his previous employment. Despite the poor clinic attendance, the overall functional results compared favorably with other published series. It appears that tendon transfer for radial nerve palsy is a viable option, even in patients with limited rehabilitation.

Adult↗
PubMed2000

Intravenous crocetinate prolongs survival in a rat model of lethal hypoxemia.

OBJECTIVE: To examine whether a carotenoid, trans-sodium crocetinate, has beneficial effects on hemodynamic status and short-term outcome in a rat model of lethal hypoxemia. DESIGN: Randomized, placebo-controlled study. SETTING: Medical school laboratory. SUBJECTS: Eighteen spontaneously breathing, anesthetized Sprague-Dawley rats (six per group). INTERVENTIONS: Rats underwent instrumentation to measure blood pressure, aortic and renal blood flow, arterial blood gases, bladder epithelial oxygen tension (by an intraluminal Clark electrode), and hepatic microvascular oxygen tension (measured by porphyrin phosphorescence). After stabilization, the rats were subjected to breathing 10% inspired oxygen concentration. After 10 mins, they were administered 1.25 mL/kg intravenous boluses of either isotonic saline (control), normal strength crocetinate (40 microg/mL), or a concentrated crocetinate solution (60 microg/mL). These boluses were repeated at 30-min intervals until either death or 3 hrs had elapsed. MEASUREMENTS AND MAIN RESULTS: With the onset of hypoxemia, we observed a rapid reduction in blood pressure and renal blood flow, maintenance of aortic blood flow, an increase in arterial base deficit, and falls in oxygen tensions in arterial blood, bladder epithelium, and hepatic microvasculature. A progressive deterioration in the control rats was noted, with only two of the six animals surviving for 3 hrs. However, all 12 rats in the two crocetinate groups survived for 3 hrs, with hemodynamic stability until 150 mins and a slow decline thereafter. CONCLUSIONS: Trans-sodium crocetinate improved hemodynamic status and prolonged survival in this model of severe acute hypoxic hypoxia. To our knowledge, this is the first demonstration of an intravenous agent having such an effect.

Animals↗
PubMed2000

The social geography of AIDS and hepatitis risk: qualitative approaches for assessing local differences in sterile-syringe access among injection drug users.

While significant gains have been achieved in understanding and reducing AIDS and hepatitis risks among injection drug users (IDUs), it is necessary to move beyond individual-level characteristics to gain a fuller understanding of the impact of social context on risk. In this study, 6 qualitative methods were used in combination with more traditional epidemiologic survey approaches and laboratory bioassay procedures to examine neighborhood differences in access to sterile syringes among IDUs in 3 northeastern cities. These methods consisted of (1) neighborhood-based IDU focus groups to construct social maps of local equipment acquisition and drug use sites; (2) ethnographic descriptions of target neighborhoods; (3) IDU diary keeping on drug use and injection equipment acquisition; (4) ethnographic day visits with IDUs in natural settings; (5) interviews with IDUs about syringe acquisition and collection of syringes for laboratory analysis; and (6) focused field observation and processual interviewing during drug injection. Preliminary findings from each of these methods are reported to illustrate the methods' value in elucidating the impact of local and regional social factors on sterile syringe access.

Anthropology, Cultural↗
PubMed1999

Mitochondrial dysfunction in sepsis.

The current mainstream view of organ failure induced by sepsis revolves around inflammation and loss of vascular control. However, there has been a resurgence in interest in bioenergetic failure due to mitochondrial dysfunction. This concept is not new--studies date back 30 years; however, the data have been highly conflicting with findings of either decreased, increased or unchanged mitochondrial activity and/or nucleotide levels. These studies are virtually all based on non-human cells, isolated perfused organs or in vivo animal models that have received a variety of insults ranging from mild to severe, and monitored for different durations ranging from minutes to weeks. As a generalization, there does appear to be depression of mitochondrial function with longer-duration models of greater severity. This is confirmed by the scanty human data currently available. This chapter provides an overview, and attempts to relate the biochemical changes to the clinical condition. The potential roles of nitric oxide, intracellular calcium and reactive oxygen species are highlighted.

Adenosine Triphosphate↗
PubMed1999

Preliminary UK experience of dexmedetomidine, a novel agent for postoperative sedation in the intensive care unit.

Dexmedetomidine, a highly selective and potent alpha2-adrenergic agonist, has a potentially useful role as a sedative agent in patients requiring intensive care. As part of a larger European multicentre trial, a total of 119 postoperative cardiac and general surgical patients requiring ventilation and sedation in an intensive care unit were enrolled in four centres in the United Kingdom. One hundred and five patients were randomly allocated to receive either dexmedetomidine or placebo with rescue sedation and analgesia provided by midazolam and morphine, respectively. Compared with the control group, intubated patients receiving dexmedetomidine required 80% less midazolam [mean 4.9 (5.8) microg.kg-1.h-1 vs. 23.7 (27.5) microg.kg-1.h-1, p < 0.0001], and 50% less morphine [11.2 (13.4) microg.kg-1.h-1 vs. 21.5 (19.4) microg.kg-1.h-1,p = 0.0006]. Cardiovascular effects and adverse events could be predicted from the known properties of alpha-2 agonists. In conclusion, dexmedetomidine is a useful agent for the provision of postoperative analgesia and sedation.

Adolescent↗
PubMed1999

Activation of the tissue factor pathway occurs during continuous venovenous hemofiltration.

BACKGROUND: Activation of the tissue factor pathway occurs during continuous venovenous hemofiltration (CVVH). Despite adequate exogenous anticoagulation, the occlusion of CVVH circuits can occur within minutes to a few hours of use and is associated with evidence of thrombin generation. Having found no evidence of activation of the contact factor (intrinsic coagulation) pathway during CVVH, we sought to examine the effect of the first episode of CVVH on the tissue factor (extrinsic) pathway of coagulation and thrombin generation. METHODS: Twelve critically ill patients were studied prior to the commencement of hemofiltration and at regular intervals thereafter until the filter clotted. RESULTS: Prior to hemofiltration, most patients had increased levels of plasma tissue factor, thrombin-antithrombin (TAT) complexes, and tissue factor pathway inhibitor (TFPI); during hemofiltration, further generation of TAT complexes occurred. Initially, levels of activated factor VII (FVIIa) fell and TFPI increased, but during the course of hemofiltration, the levels of TFPI fell and FVIIa increased. Levels of tissue factor increased during CVVH in some patients, but this was not related to the generation of FVIIa. CONCLUSIONS: These data indicate that activation of FVII occurred during CVVH, which was related to levels of TFPI, but not tissue factor, and was coincidental to thrombin generation.

Adult↗
PubMed1999

Septic arthritis of the metacarpophalangeal and interphalangeal joints of the hand.

Septic arthritis of the small joints of the hand is not reported frequently. Twenty-eight patients were treated during a 15-month period, from November 1992 to January 1994. Prompt surgical drainage, antibiotics, and early postoperative mobilization (within 24 hours) were the cornerstones of management. Nineteen patients were available for a median follow-up of 10 months. Patients who presented after 10 days all had a poor result. Patients who presented earlier achieved a good result unless they defaulted from treatment or had sustained an associated severe traumatic joint injury. Ten of the 19 patients obtained a good result. Good functional results can be obtained with early postoperative mobilization.

Adolescent↗
PubMed1999

Prediction of postoperative cardiac surgical morbidity and organ failure within 4 hours of intensive care unit admission using esophageal Doppler ultrasonography.

OBJECTIVE: To compare esophageal Doppler ultrasonography with standard hemodynamic variables used in postoperative care for the prediction of postoperative complications after cardiac surgery. DESIGN: Prospective, observational pilot study. SETTING: University hospital, multidisciplinary intensive care unit PATIENTS: Postoperative cardiac surgical patients. INTERVENTIONS: Standard postoperative management as guided by routinely measured hemodynamic variables. MEASUREMENTS: An esophageal Doppler ultrasound probe was inserted for measurement of stroke volume (SV), cardiac output (CO), and other flow-related variables. Both these and routine hemodynamic variables (mean arterial pressure, central venous pressure, heart rate, arterial base deficit, urine output, core-toe temperature difference) were recorded at half-hourly intervals for the first 4 postoperative hrs. The incidence of systemic inflammatory response syndrome at 24 hrs, Acute Physiology and Chronic Health Evaluation II, and multiple organ failure scores, postoperative complications, and length of ICU and hospital stays were recorded. MAIN RESULTS: Twenty consecutively admitted patients were studied: eight after emergency bypass grafting and 12 after elective bypass grafts and/or valve replacement. Of the nine patients who developed postoperative complications, two died. At admission, significant differences were seen between patients with a complicated and those with an uncomplicated surgical procedure for SV, heart rate, and standard base excess, but not for cardiac output. By using receiver operator characteristic curves, SV was the best marker for predicting postoperative complications during the initial postoperative period. CONCLUSIONS: A low SV and a high heart rate, both at ICU admission and during the subsequent 4 hrs, were the best prognostic factors for development of complications after cardiac surgery. Cardiac output values were not useful. This pilot study suggests that the minimally invasive technique of esophageal Doppler ultrasonography may be a useful tool to assist early prognostication.

Analysis of Variance↗
PubMed1999

Increased interleukin-1 (IL-1) and imbalance between IL-1 and IL-1 receptor antagonist during acute inflammation in experimental Shigellosis.

Infection by the enteric bacterial pathogen Shigella results in intense mucosal inflammation and destruction of the colonic and rectal epithelium in infected humans. Initial bacterial translocation occurs through the follicle-associated epithelium. Previous experiments suggest that interleukin-1 (IL-1) is crucial to trigger inflammation, particularly in the follicular zones. During the first 4 hours of infection in a rabbit ligated-loop model of intestinal invasion, there are two salient characteristics: (i) a high concentration of IL-1alpha and IL-1beta, both in infected Peyer's patch tissue and in the corresponding efferent mesenteric blood, and (ii) a very low level of expression of IL-1 receptor antagonist (IL-1ra). These may reflect a combination of regulation of expression and secretion of IL-1alpha, IL-1beta, and IL-1ra by both resident and recruited phagocytes and the induction of mononuclear phagocyte apoptosis by Shigella. This low IL-1ra/IL-1 ratio likely accounts for the rapid, uncontrolled inflammation characteristic of shigellosis.

Acute Disease↗