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Biomedical subjects

J de Boer

Publications and source records attributed to J de Boer.

At least 91 records · Page 5Linked to original sources
PubMed1994

Localization of functional domains in the Escherichia coli coprogen receptor FhuE and the Pseudomonas putida ferric-pseudobactin 358 receptor PupA.

Transport of ferric-siderophores across the outer membrane of gram-negative bacteria is mediated by specific outer membrane receptors. To localize the substrate-binding domain of the ferric-pseudobactin 358 receptor, PupA, of Pseudomonas putida WCS358, we constructed chimeric receptors in which different domains of PupA were replaced by the corresponding domains of the related ferric-pseudobactin receptors PupB and PupX, or the coprogen receptor FhuE of Escherichia coli. None of the chimeric proteins composed of pseudobactin receptor domains facilitated growth on any of the original substrates, or they showed only an extremely low efficiency. However, these receptors enabled cells of Pseudomonas BN8 to grow on media supplemented with uncharacterized siderophore preparations. These siderophore preparations were isolated from the culture supernatant of WCS358 cells carrying plasmids that contain genes of Pseudomonas B10 required for the biosynthesis of pseudobactin B10. Hybrid proteins that contained at least the amino-terminal 516 amino acids of mature FhuE were active as a receptor for coprogen and interacted with the E. coli TonB protein. A chimeric PupA-FhuE protein, containing the amino-terminal 94 amino acids of mature PupA, was also active as a coprogen receptor, but only in the presence of Pseudomonas TonB. It is concluded that the carboxy-terminal domain of ferric-pseudobactin receptors is important, but not sufficient, for ligand interaction, whereas binding of coprogen by the FhuE receptor is not dependent on this domain. Apparently, the ligand-binding sites of different receptors are located in different regions of the proteins. Furthermore, species-specific TonB binding by the PupA receptor is dependent on the amino-terminal domain of the receptor.

Bacterial Outer Membrane Proteins↗
PubMed1994

Supercritical fluid extraction of polychlorinated biphenyls from lyophilized fish tissue.

A method for the rapid interference free analysis of polychlorinated biphenyl congeners (chlorinated biphenyls, CBs) in lyophilized fish tissue is presented. The method was developed on a lyophilized tuna muscle tissue that contained 2.8% lipid (dry mass based), and native CB concentrations in the range of 3-84 ng/g. Sample preparation was made by supercritical fluid extraction using pure CO2 as extraction fluid. Analysis by high-resolution gas chromatography-electron-capture detection analysis was carried out with on-column injection on two parallel coupled columns, a 60 m DB-17 column and a series combination of a 25 m SIL-8 column and a 25 m HT-5 column. Supercritical fluid extraction was compared with Soxhlet extraction and found to give quantitative recoveries, detection limits of 0.5-2 ng/g and standard deviations of less than 5% on average. The developed method was confirmed on nine different lyophilized fish samples which contained 6.1-26.5% lipid (dry mass based), and native CB concentrations in the range 0.8-134 ng/g.

Animals↗
PubMed1994

Continuous monitoring of lactate during exercise in humans using subcutaneous and transcutaneous microdialysis.

We have evaluated the possibility of monitoring the plasma lactate concentration in human volunteers during cycle ergometer exercise using subcutaneous and transcutaneous microdialysis. In transcutaneous microdialysis, the relative increase in dialysate lactate concentration exceeded that of plasma lactate concentration by a factor of 6 during exercise due to exercise-induced lactate secretion in sweat. During exercise the subcutaneous microdialysis dialysate lactate concentration underestimated the plasma lactate concentration possibly due to diffusion limitation or adipose tissue lactate production. While it was demonstrated that microdialysis can be used for on-line lactate monitoring, neither subcutaneous nor transcutaneous dialysate lactate concentration were linearly related to the plasma lactate concentration during exercise, and it was found therefore that it was not possible to monitor directly plasma lactate concentration during exercise.

Adult↗
PubMed1994

A report of the eurotransplant randomized multicenter study comparing kidney graft preservation with HTK, UW and EC solutions. HTK study group.

Special attention has been focused in this randomized study on the primary function of renal allografts preserved with different solutions. Histidine-Tryptophane-Ketoglutarate (HTK) and University of Wisconsin (UW) solutions provided a significantly lower incidence of delayed graft function compared to Euro-Collins solution. Improved renal function after transplantation was observed in the HTK and UW groups compared to the EC group.

Adenosine↗
PubMed1994

Lactate monitoring with subcutaneous microdialysis in patients with shock: a pilot study.

We describe the use of subcutaneous microdialysis for continuous sampling of lactate to monitor the plasma lactate concentration in eight patients with shock. The dialysate lactate concentrations were significantly correlated with the plasma lactate concentrations (r = 0.8229), but the linear regression lines varied between patients. Therefore, we used the individual regression line of each patient for calibration to calculate estimated plasma values from the dialysate concentrations. While the estimated values were linearly correlated to the plasma lactate values (r = 0.912), the 95% confidence interval of the estimated values was +/- 2.8 mmol/L. Thus, subcutaneous microdialysis does not allow accurate estimation of the plasma lactate concentration. In 3 of the 8 patients, there was a significant negative correlation between the dialysate/plasma lactate ratio and the plasma lactate concentration. This suggests that besides plasma lactate, other factors such as subcutaneous adipose tissue metabolism and blood flow, may influence subcutaneous sampling and dialysate lactate concentration as well. While microdialysis can be used for on-line sampling and continuous monitoring of the concentration of extracellular substances, for the purpose of plasma lactate monitoring, sampling probes should be designed that permit intravascular placement.

Adult↗
PubMed1993

Coamplification of hprt cDNA and gamma T-cell receptor sequences from 6-thioguanine resistant human T-lymphocytes.

The nature of mutation at the HPRT locus in human T-lymphocytes in vivo is currently a subject of considerable interest. Determination of clonality in individual mutant T-lymphocytes is essential for the proper interpretation. This requires the molecular analysis of their respective T-cell receptors (TCR). We have developed a polymerase chain reaction (PCR)-based method for coamplification of hprt cDNA and the rearranged gamma T-cell receptor genes from crude cell lysates of individual 6-thioguanine resistant human T-lymphocytes. Following reverse transcription to produce hprt cDNA, the crude cell lysate is treated with proteinase K and subjected to a primary PCR with two sets of amplification primers, one specific for the hprt cDNA and the other for the rearranged gamma TCR gene. A secondary round of PCR, employing appropriate sets of nested amplification primers, are then used to produce sufficient quantities of DNA for both the sequencing and restriction fragment length analysis, of the hprt cDNA and gamma TCR gene respectively.

Adult↗
PubMed1993

Monitoring of glucose and lactate using microdialysis: applications in neonates and rat brain.

Methods for the continuous in vivo monitoring of glucose and lactate were applied in man for studies of peripheral metabolism and, in rats, for cerebral examinations. Lactate ('lactography') and glucose were continuously measured by the enzyme formation of NADH or NADPH using appropriate dehydrogenases. Glucose was monitored with a transcutaneous probe in neonates or with probes placed directly in the brain of conscious rats. In neonates a high correlation was seen between the dialysate and blood levels. A correlation between the age of the neonates and glucose levels in the dialysate was found, suggesting that the thickness of the skin determined to a large extent the diffusion of glucose into the probe. In the rat brain transient changes in the extracellular glucose levels were seen during electroconvulsive shock and immobilization stress. Lactography was applied to striatum or hippocampus during stress, electroconvulsive shock or systemic and intracerebral drug applications. Extracellular lactate decreased during intracerebral deoxyglucose infusion and was increased by excitatory neuronal activity and the presence of glucose in the perfusion medium. The present studies show that microdialysis in combination with continuous flow analysis can be used to study metabolic trafficking in vivo and in clinical studies. In the brain both neurons and glia may contribute to extracellular lactate levels.

Animals↗
PubMed1992

Results of acute heart retransplantation in Eurotransplant.

In 1988 a special programme for acute retransplantation was introduced in Eurotransplant, giving patients awaiting acute retransplantation priority in the selection procedure. Due to scarcity of donor hearts the question arose whether graft survival after acute retransplantation justified the use of these hearts for this category of patient. A retrospective analysis on the results of transplantations performed in patients who were awaiting acute retransplantation within Eurotransplant was done. In 18 out of 46 cases the patient was treated prior to retransplantation with some kind of mechanical support device. Of the 46 grafts, 28 failed. The actuarial 1-year graft survival in this study group was 36%. In comparison, graft survival for primary cardiac transplantation is approximately 81%. Graft survival after acute heart retransplantation is very poor, especially when the patient has been pretreated with a severe mechanical support system.

Europe↗
PubMed1992

Human bronchial cyclic nucleotide phosphodiesterase isoenzymes: biochemical and pharmacological analysis using selective inhibitors.

1 The aims of the present study were to characterize the cyclic nucleotide phosphodiesterase (PDE) isoenzyme activities present in human bronchi and to examine the ability of selective isoenzyme inhibitors to relax histamine and methacholine precontracted preparations of human bronchi. 2 Three separations of pooled human bronchial tissue samples were performed. Ion-exchange chromatography showed that the soluble fraction of human bronchial preparations contains PDE I, II, III, IV and V isoenzyme activities. Multiple forms of PDE I and PDE IV were observed and PDE IV was the main cyclic AMP hydrolytic activity. 3 3-Isobutyl-l-methylxanthine (IBMX) non-selectively inhibited all separated isoenzyme activities. Zaprinast selectively inhibited PDE V, but also effectively inhibited one of the two PDE I isoforms identified. The PDE IV selective inhibitors rolipram and RO-201724, inhibited the PDE IV activities as did the dual PDE III/IV inhibitor, Org 30029. Org 9935, a PDE III selective inhibitor, potently attenuated part of the PDE IV activity peak in one of three separations performed, indicating that some PDE III activity may co-elute with PDE IV under the experimental conditions employed. 4 PDE IV-selective (rolipram), PDE III-selective (Org 9935) and dual PDE III/IV (Org 30029) inhibitors were effective relaxants of human bronchial smooth muscle. The PDE V/PDE I inhibitor, zaprinast was relatively ineffective. 5 The present study demonstrates in human bronchi, as in animal airways smooth muscle, that inhibitors of PDE III, PDEIV and dual PDE III/IV have potentially useful bronchodilator activity and are worthy of further consideration as anti-asthma drugs.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1991

Continuous monitoring of extracellular lactate concentration by microdialysis lactography for the study of rat muscle metabolism in vivo.

A method is described for the measurement and on-line monitoring of muscular extracellular lactate concentration in both anaesthetized and freely moving rats. This method is based on microdialysis sampling and lactic dehydrogenase-catalysed nicotinamide adenine dinucleotide, reduced (NADH)-fluorescence detection techniques. In vivo calibration revealed a resting extracellular lactate concentration of 1.92 +/- 0.13 mmol/l (+/- SEM) in the gastrocnemius muscle of adult male Wistar rats (n = 6), while the average whole-blood lactate level was 0.76 +/- 0.12 mmol/l (+/- SEM). This measured extracellular lactate concentration was 1.73-times higher than that deduced from the arterial lactate concentration. Blocking glycolysis with iodoacetate reduced the extracellular lactate concentration to 52 +/- 6% (+/- SEM, n = 4) of the resting level. The extracellular lactate concentration in rat gastrocnemius muscle had increased to significantly (P less than or equal to 0.05) different levels, 2.4 +/- 0.03 (+/- SEM) or 4.0 +/- 0.55 (+/- SEM) times the control value, 1 h after aortic clamping (n = 3) or cardiac arrest (n = 3), respectively. Stimulation of the sciatic nerve induced elevations of the extracellular lactate concentration in the tibialis anterior muscle which were linearly related to the recorded isometric force-time integral. We also monitored on-line the changes in extracellular lactate concentration in the tibialis anterior muscle of a swimming rat. Our results indicate that microdialysis lactate reflects also intracellular metabolism. Lactography may be a useful alternative to biopsies and nuclear magnetic resonance spectroscopy in clinical medicine and physiology for the monitoring of metabolism in vivo.

Animals↗
PubMed1991

The presence of five cyclic nucleotide phosphodiesterase isoenzyme activities in bovine tracheal smooth muscle and the functional effects of selective inhibitors.

1. The profile of cyclic nucleotide phosphodiesterase (PDE) isoenzymes and the relaxant effects of isoenzyme selective inhibitors were examined in bovine tracheal smooth muscle. The compounds examined were the non-selective inhibitor 3-isobutyl-1-methylxanthine (IBMX), zaprinast (PDE V selective), milrinone and Org 9935 (4,5-dihydro-6-(5,6-dimethoxy-benzo[b]thien-2-yl)-5-methyl-1 (2H)-pyridazinone; both PDE III selective), rolipram (PDE IV selective) and Org 30029 (N-hydroxy-5,6-dimethoxy-benzo[b]-thiophene-2-carboximidamide HCl a dual PDE III/IV inhibitor). 2. Ion exchange chromatography showed three main peaks of PDE activity. The first peak was stimulated by Ca2+/calmodulin (PDE I), the adenosine 3':5'-cyclic monophosphate (cyclic AMP) hydrolytic activity of the second peak was stimulated by guanosine 3':5'-cyclic monophosphate (cyclic GMP) (PDE II) whilst that of the third peak was not significantly modified by any regulator (PDE IV). Calmodulin affinity chromatography revealed the additional presence of cyclic GMP-specific PDE (PDE V) in the first peak. A clearly distinct peak of cyclic GMP-inhibited PDE (PDE III) was not observed. However, Org 9935 inhibited the third activity peak more effectively in the presence, than in the absence, of rolipram (3 mumol l-1), indicating the presence of PDE III activity. 3. Rolipram was the most potent inhibitor of PDE IV. The mean -log50 IC50 values for rolipram, IBMX, milrinone, Org 30029, Org 9935 and zaprinast were 5.9 +/- 0.1, 4.9 +/- 0.1, 4.7 +/- 0.1, 4.6 +/- 0.1 and 4.6 +/- 0.1, respectively. 4. Rolipram was a potent relaxant of both histamine (1 pumol -') and methacholine (0.03 pmol -') precontracted preparations; (pD2 values; histamine 7.1 +/- 0.1, methacholine 6.8 /-+ 0.2 and 4.5 +/- 0.1, biphasic relaxation). IBMX also relaxed all preparations (pD2 values; histamine 5.6 +/- 0.1, methacholine 5.6 +/- 0.1) whilst zaprinast (pD2 values; histamine 5.2 +/- 0.1, methacholine 4.4 +/- 0.3), milrinone (pD2 values; histamine 5.2 + 0.1, methacholine 4.3 + 0.3) and Org 9935 (pD2 values; histamine 4.1 + 0.1, methacholine 4.1 +/- 0.2) did not completely relax preparations at concentrations up to 100 pImol I-. Org 30029 (pD2 values; histamine 6.2 +/- 0.1, methacholine 5.4 +/- 0.1) was a more effective relaxant than can be explained on the basis of PDE IV inhibition alone.5. We conclude that bovine tracheal smooth muscle contains five distinct PDE isoenzymes. PDE IV appears to be more important in the modulation of tissue function than PDE III and PDE V.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1990

Lactography as an approach to monitor glucose metabolism on-line in brain and muscle.

1. Thus far metabolic processes in the intact animal (or man) have been studied either by the analysis of body fluids, of biopsies, of tissue obtained post mortem or by techniques, requiring dedicated and expensive equipment (such as positron emission tomography or magnetic resonance spectroscopy). 2. Here we describe a relatively simple and inexpensive technique, that can be applied in vivo to study metabolism in brain regions and muscle in the freely moving rat and in human peripheral tissue. 3. The method is based on microdialysis allowing continuous sampling from the extracellular space, the enzymatic conversion of lactate and the on-line detection of fluorescent NADH. 4. Examples of the application of our technique include the monitoring of lactate efflux from various brain regions of behaving animals under a variety of stress exposures, during ischemia or hypoxia and drug treatments. 5. The results indicate that in brain lactate is not exclusively formed under hypoxia and that neuronal activation leads also to lactate formation, possibly due to the compartmentation of both the involved enzymes and the energy metabolism. 6. The increase of lactate formation in contracting or ischemic muscle or during exercise could also be followed on-line in the rat, suggesting that our approach allows the continuous monitoring of anaerobic metabolism in man e.g. during traumatic or arteriosclerotic limb ischemia or lactic acidosis in shock states. 7. The principle of our approach can easily be adapted to other metabolites, thus enabling to monitor other metabolic pathways in vivo as well.

Animals↗