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Biomedical subjects

J van Leeuwen

Publications and source records attributed to J van Leeuwen.

At least 19 recordsLinked to original sources
PubMed2006

Ozonation of seawater from different locations: formation and decay of total residual oxidant--implications for ballast water treatment.

Ballast water is a likely cause for worldwide transfer of non-indigenous aquatic species because of the large volumes and frequency of possible inoculations. Ozone is one treatment option being considered for eliminating non-indigenous species in ballast water. When ozone is applied to seawater, secondary disinfectants are formed, commonly measured and expressed as total residual oxidant (TRO). The goal of this study was to determine those variables most likely to affect the rate of TRO increase during ozonation and the subsequent TRO decline that occurs over time. These parameters strongly influence the efficacy of ozone treatments aimed to eliminate organisms present in ballast water. Seawater was obtained from Puget Sound, Washington; Cape Fear, North Carolina; and San Francisco Bay. Results indicated that seawater characteristics, including the organic content and ammonia, affect the amount of ozone required to achieve a desired TRO level and rate of TRO decay, and therefore need to be considered in determining ozone requirements for ballast water treatment.

Ammonia↗
PubMed2005

Using gypsum to reduce phosphorus in runoff from subcatchments in South Australia.

Concentrations of phosphorus (P) in runoff from agricultural catchments in southern Australia are high and well above national and international limits. Phosphorus was found to exit two subcatchments of 3.6 and 4.2 ha in the Adelaide hills via both overland flow and interflow. The subcatchments had texture-contrast soils with high inputs of superphosphate and were openly grazed by cattle all year. Interflow at the boundary of the B and C soil horizons accounted for as much as half the total water flow that was measured (overland flow, A-B interflow, and B-C interflow). The average flow-weighted concentration of total P within overland flow was as high as 0.25 mg L(-1), and 0.05 mg L(-1) in B-C interflow. In most years P loss was in the dissolved (<0.45 microm) form. In some years, interflow was the major pathway for P loss off these catchments. The B-C interflow cannot be discounted when searching for management options to reduce P loss from texture-contrast soils to waterways. Preliminary laboratory experiments showed promise that gypsum could modify agricultural soils and reduce the concentrations of P (and dissolved organic C) in runoff before it enters public water supply reservoirs. In this study, gypsum, applied at a rate of 15 Mg ha(-1) to the 4.2-ha subcatchment, substantially modified the soil chemistry, and thereby soil structure. The size and stability of structural aggregates increased markedly and this change affected not only the A but also the upper B horizons, to a profile depth of approximately 50 cm. However, the impact of these physicochemical changes on P concentrations in runoff was not marked. Average profile P concentrations were only slightly lower in the runoff from the subcatchment following treatment. The high subsoil macroporosity of the gypsum-treated subcatchment caused an increase in the proportion of runoff by interflow.

Agriculture↗
PubMed2003

Simple and fast lateral flow test for classification of leprosy patients and identification of contacts with high risk of developing leprosy.

The interruption of leprosy transmission is one of the main challenges for leprosy control programs since no consistent evidence exists that transmission has been reduced after the introduction of multidrug therapy. Sources of infection are primarily people with high loads of bacteria with or without clinical signs of leprosy. The availability of a simple test system for the detection of antibodies to phenolic glycolipid-I (PGL-I) of Mycobacterium leprae to identify these individuals may be important in the prevention of transmission. We have developed a lateral flow assay, the ML Flow test, for the detection of antibodies to PGL-I which takes only 10 min to perform. An agreement of 91% was observed between enzyme-linked immunosorbent assay and our test; the agreement beyond chance (kappa value) was 0.77. We evaluated the use of whole blood by comparing 539 blood and serum samples from an area of high endemicity. The observed agreement was 85.9% (kappa = 0.70). Storage of the lateral flow test and the running buffer at 28 degrees C for up to 1 year did not influence the results of the assay. The sensitivity of the ML Flow test in correctly classifying MB patients was 97.4%. The specificity of the ML Flow test, based on the results of the control group, was 90.2%. The ML Flow test is a fast and easy-to-perform method for the detection of immunoglobulin M antibodies to PGL-I of M. leprae. It does not require any special equipment, and the highly stable reagents make the test robust and suitable for use in tropical countries.

Antibodies, Bacterial↗
PubMed2002

ERK activation and alpha v beta 3 integrin signaling through Shc recruitment in response to mechanical stimulation in human osteoblasts.

Osteoblast growth and differentiation are critical processes for bone development and maintenance, and are regulated by both humoral and mechanical factors. Humoral (hormonal) factors can affect gene transcription via MAPkinases, e.g., extracellular signal-regulated kinase (ERK). We studied whether the ERK pathway is also involved in processing mechanical inputs in human bone cells. Exposing MG63 cells to physiologically relevant levels of fluid flow resulted in ERK phosphorylation. Genistein blocked this response, indicating that it is dependent on tyrosine phosphorylation. Furthermore, alpha v beta 3 integrins were activated in response to fluid flow, as shown by recruitment of adaptor molecule Shc and clustering of alpha v beta 3 in focal adhesion-like structures. Antibodies blocking formation of beta 1 or beta 3 integrin-matrix interactions or RGD peptides could not inhibit fluid flow-induced ERK phosphorylation, suggesting that formation of new integrin-matrix interactions is not essential for this response and that other upstream mechanosensors regulate induction of ERK phosphorylation in response to fluid flow in human bone cells.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Characterization of tyrosinase from the cap flesh of portabella mushrooms.

Tyrosinase, purified from the cap flesh tissue of portabella mushrooms, was characterized with regard to its physical and biochemical properties. A native molecular size of 41 kDa for the enzyme was obtained by size exclusion chromatography, whereas SDS-PAGE indicated that the enzyme contained a single subunit with a size of approximately 48 kDa under reduced and nonreduced conditions. The purified enzyme showed a single immunological cross-reacting protein after Western blotting when probed with antibodies against Agaricus bisporus tyrosinase. Isoelectric focusing demonstrated that the enzyme preparation, apparently homogeneous by electrophoresis, still contained three isoforms of pI 5.1, 5.2, and 5.3. The purified enzyme was able to oxidize a variety of mono-, di-, and triphenolic compounds. An apparent K(m) of 5 mM was obtained using catechol as the substrate, and an apparent K(m) of 9 mM was found using L-Dopa as a substrate. Ascorbic acid, kojic acid, tropolone, mercaptobenzothiazole, and salicylhydroxamic acid inhibited the enzyme severely at 100 microM.

Agaricus↗
PubMed1999

Kinetic study of the activation process of a latent mushroom (Agaricus bisporus) tyrosinase by serine proteases.

Latent mushroom tyrosinase can be considered as a zymogen when activated by proteases because the activation process fulfilled all of the kinetic dependencies predicted by a theoretical zymogen activation model previously reported. The activation was studied under two assay conditions: high and low ratio of latent tyrosinase/serine protease (trypsin and subtilisin Carlsberg) concentrations, in the presence and in the absence of a serine protease inhibitor (aprotinin). The size of the latent enzyme was 67 kDa, determined by denaturing SDS-PAGE electrophoresis and Western blot assays. After proteolytic activation, the size was 43 kDa, with an intermediate band of 58 kDa. The values of the catalytic () and Michaelis () constants for the active forms of tyrosinase resulting from the activation by subtilisin, trypsin, or sodium dodecyl sulfate on the substrate tert-butylcatechol were slightly different, which could support the idea of "one activator-one different active tyrosinase". Vacuum infiltration experiments tried to reproduce in vivo the role of mushroom serine proteases in the activation of latent tyrosinase. The use of serine protease inhibitors is proposed as a new alternative tool to prevent melanin formation.

Agaricales↗
PubMed1999

Electronic monitoring of treatment compliance in patching for amblyopia.

We developed a coinsized occlusion dose monitor (ODM) to measure compliance with patch-wearing during the treatment of amblyopia objectively. It measures the temperature difference between the front and back of the ODM every 2-5 minutes by means of two thermistors. The data is stored in EEPROM memory and read out after recording for a week by connecting it to a PC. The ODM measures 35x23x4 mm and weighs 6 g. The back of the ODM is glued to the front of the amblyopia patch with double-sided Scotch tape. When the patch with the ODM is on the eye, the temperature at the back of the ODM is higher than at the front. Compliance is being studied in children taking part in a large amblyopia cohort study. The parents were instructed during home visits every three months to put the ODM on the patch. After a week, the ODM was collected and read out. Although the parents knew that a recording was being made, compliance was mediocre in many cases. Children were patched infrequently, for 5 minutes only, for long periods on the last days of the recording, at night, etc. Diaries detailing patch time were unreliable.

Amblyopia↗
PubMed1998

Clinical utility of the polymerase chain reaction in the diagnosis of extrapulmonary tuberculosis.

This study examines the diagnostic utility of the polymerase chain reaction (PCR) in 156 patients (five human immunodeficiency virus (HIV) seropositive) suspected of extrapulmonary tuberculosis. The results of PCR in 226 samples from 11 different sites were compared with the results of microscopy and culture. Positive culture results were predicted in 86% of samples by PCR but in only 31% by microscopy. Specificity of PCR was 92%. In cases with culture-proven tuberculosis, PCR identified all 11 microscopy positive cases and 19 of 24 (79%) of the microscopy-negative cases. In four patients, PCR excluded the diagnosis of tuberculosis in microscopy-positive samples, which were later shown to contain mycobacteria other than Mycobacterium tuberculosis or laboratory contaminants. In 20 patients (microscopy, PCR and culture negative) a trial of antituberculous drugs was given, but patients showed no improvement and treatment was stopped. In 17 patients, all culture negative (in nine PCR was positive, three of whom also had positive microscopy) the diagnosis was probable tuberculosis based on clinical findings and response to treatment. This polymerase chain reaction has a much higher sensitivity than microscopy and can facilitate therapeutic decisions for those with suspected extrapulmonary tuberculosis.

AIDS-Related Opportunistic Infections↗
PubMed1996

Use of NASBA RNA amplification for detection of Mycobacterium leprae in skin biopsies from untreated and treated leprosy patients.

This study was performed to assess the value of NASBA RNA amplification of a 16S rRNA target for the detection of presumably viable Mycobacterium leprae in sections of skin biopsies from leprosy patients. The NASBA positivity rate was 90.4% (84/93) for untreated multibacillary (MB) patients [bacterial index (BI) > or = 2] and 16.7% (8/48) for the untreated paucibacillary (PB) patients (BI < 2). NASBA positivity showed a good concordance with the presence of solidly stained M. leprae [morphological index (MI)] in skin biopsies from leprosy patients, but no relationship could be demonstrated between the strength of the NASBA signals and the BI. Furthermore, the usefulness of the detection of 16S rRNA by NASBA to monitor the efficacy of leprosy treatment was investigated using an additional 154 biopsy specimens analyzed from 80 MB patients during the course of treatment. The NASBA positivity rate declined during treatment. A significant decrease was observed after only 1-3 months. These results favor the view that detection of RNA by NASBA may reflect the viability of M. leprae.

Biopsy↗
PubMed1995

PCR assay based on DNA coding for 16S rRNA for detection and identification of mycobacteria in clinical samples.

A PCR and a reverse cross blot hybridization assay were developed for the detection and identification of mycobacteria in clinical samples. The PCR amplifies a part of the DNA coding for 16S rRNA with a set of primers that is specific for the genus Mycobacterium and that flanks species-specific sequences within the genes coding for 16S rRNA. The PCR product is analyzed in a reverse cross blot hybridization assay with probes specific for M. tuberculosis complex (pTub1), M. avium (pAvi3), M. intracellulare (pInt5 and pInt7), M. kansasii complex-M. scrofulaceum complex (pKan1), M. xenopi (pXen1), M. fortuitum (pFor1), M. smegmatis (pSme1), and Mycobacterium spp. (pMyc5a). The PCR assay can detect 10 fg of DNA, the equivalent of two mycobacteria. The specificities of the probes were tested with 108 mycobacterial strains (33 species) and 31 nonmycobacterial strains (of 17 genera). The probes pAvi3, pInt5, pInt7, pKan1, pXen1, and pMyc5a were specific. With probes pTub1, pFor1, and pSme1, slight cross hybridization occurred. However, the mycobacterial strains from which the cross-hybridizing PCR products were derived belonged to nonpathogenic or nonopportunistic species which do not occur in clinical samples. The test was used on 31 different clinical specimens obtained from patients suspected of having mycobacterial disease, including a patient with a double mycobacterial infection. The samples included sputum, bronchoalveolar lavage, tissue biopsy samples, cerebrospinal fluid, pus, peritoneal fluid, pleural fluid, and blood. The results of the PCR assay agreed with those of conventional identification methods or with clinical data, showing that the test can be used for the direct and rapid detection and identification of mycobacteria in clinical samples.

Bacteriological Techniques↗
PubMed1995

Food allergens in house dust.

Selected food allergens have been measured in 11 house dust samples. The amount of ovomucoid ranged from 170 to 6,300 ng/g dust. The amount of beta-lactoglobulin ranged from < 16 to 71 ng/g dust. Ovomucoid levels in some house dust samples are probably sufficiently high to cause sensitization and/or symptoms via inhalation.

Allergens↗
PubMed1995

IgE antibodies reactive with silverfish, cockroach and chironomid are frequently found in mite-positive allergic patients.

Approximately 30% of the house dust mite allergic patients in The Netherlands have IgE antibodies reactive with silverfish, cockroach and/or chironomid. In allergic patients without IgE antibodies against Dermatophagoides pteronyssinus less than 5% have IgE antibodies reactive with these insects. By means of RAST inhibition studies it is shown that cross-reactivity exists between D. pteronyssinus and silverfish, cockroach or chironomid. This means that a positive RAST for silverfish, cockroach, chironomid or D. pteronyssinus cannot be taken as evidence for exposure.

Animals↗
PubMed1994

A more reliable PCR for detection of Mycobacterium tuberculosis in clinical samples.

Diagnostic techniques based on PCR have two major problems: false-positive reactions due to contamination with DNA fragments from previous PCRs (amplicons) and false-negative reactions caused by inhibitors that interfere with the PCR. We have improved our previously reported PCR based on the amplification of a fragment of the Mycobacterium tuberculosis complex-specific insertion element IS6110 with respect to both problems. False-positive reactions caused by amplicon contamination were prevented by the use of uracil-N-glycosylase and dUTP instead of dTTP. We selected a new set of primers outside the region spanned by the formerly used primers to avoid false-positive reactions caused by dTTP-containing amplicons still present in the laboratory. With this new primer set, 16 copies of the IS6110 insertion element, the equivalent of two bacteria, could be amplified 10(10) times in 40 cycles, resulting in a mean efficiency of 77% per cycle. To detect the presence of inhibitors of the Taq polymerase, which may cause false-negative reactions, part of each sample was spiked with M. tuberculosis DNA. The DNA purification method using guanidinium thiocyanate and diatoms effectively removed most or all inhibitors of the PCR. However, this was not suitable for blood samples, for which we developed a proteinase K treatment followed by phenol-chloroform extraction. This method permitted detection of 20 M. tuberculosis bacteria per ml of whole blood. Various laboratory procedures were introduced to reduce failure or inhibition of PCR and avoid DNA cross contamination. We have tested 218 different clinical specimens obtained from patients suspected of having tuberculosis. The samples included sputum (n=145), tissue biopsy samples (n=25), cerebrospinal fluid (n=15), blood (n=14), pleural fluid (n=9), feces, (n=7), fluid from fistulae (n=2), and pus from a wound (n=1). The results obtained by PCR were consistent with those obtained with culture, which is the "gold standard." We demonstrate that PCR is a useful technique for the rapid diagnosis of tuberculosis at various sites.

Bacteriological Techniques↗
PubMed1994

Identification of a cross-reactive allergen (presumably tropomyosin) in shrimp, mite and insects.

A monoclonal antibody to Dermatophagoides pteronyssinus is described that cross-reacts with an IgE-binding antigen present in insects, Crustacea (e.g. shrimp) and other invertebrates. By means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel filtration and immunofluorescence it was shown that this monoclonal antibody presumably recognizes tropomyosin. Tropomyosin was shown to be involved in cross-reactivity between mite, shrimp and insects in shrimp-allergic patients.

Allergens↗
PubMed1992

Detection of Mycobacterium tuberculosis in clinical samples by using polymerase chain reaction and a nonradioactive detection system.

A test based on the polymerase chain reaction (PCR) was developed for the detection of the Mycobacterium tuberculosis complex in clinical samples. In this test, a 245-bp sequence of the insertion element IS986 was amplified and detected by agarose gel electrophoresis in the presence of ethidium bromide and by Southern blot and dot blot hybridization by using a 188-bp digoxigenin-labeled probe. We tested clinical specimens from 227 patients suspected of having tuberculosis. These included 102 cerebrospinal fluid, 48 sputum, 18 pleural fluid, 5 bronchoalveolar lavage, 18 blood, 7 pus, 8 bone marrow, and 6 urine samples and 15 tissue biopsy specimens. We also tested sputum samples from 75 patients with diseases other than tuberculosis. Sputum samples were first decontaminated, and all samples were treated with proteinase K-detergent solution to extract the DNA. Part of each sample was spiked with M. tuberculosis to provide a semiquantitative assay and to control for the loss of mycobacteria or interference with the PCR which may cause false-negative results. One femtogram of M. tuberculosis DNA could be detected. PCR was positive for all 32 culture-positive (for M. tuberculosis) and Ziehl-Neelsen staining (ZN)-positive samples, 10 of 12 culture-positive and ZN-negative samples, and all 4 culture-negative and ZN-positive samples. PCR detected M. tuberculosis complex bacteria in 35 of 178 culture- and ZN-negative samples. Clinical data supported the diagnosis of tuberculosis in the majority of the 35 patients from whom those samples were obtained.

Base Sequence↗
PubMed1988

Monoclonal antibodies to the major feline allergen Fel d I. I. Serologic and biologic activity of affinity-purified Fel d I and of Fel d I-depleted extract.

Monoclonal antibodies were raised against a major feline allergen, Fel d I. The specificity of the antibodies for Fel d I was demonstrated by a modified crossed immunoelectrophoretic procedure. These antibodies were used in affinity purification and depletion. Fed d I was eluted from the affinity matrix at a low pH. It was tested in serologic and biologic assays. Results of both the RAST and the histamine release test with affinity-purified Fel d I confirmed that it is a very potent allergen for the majority of patients allergic to cats. In the extract depleted with the monoclonal antibody, the ratio Fel d I/cat albumin was reduced by a factor of 20. With this depleted extract, 18 of 25 patients showed a reduction greater than 50% of the bound anti-IgE in the RAST compared with the RAST with crude cat extract. In the histamine release test with cells from two patients, the activity of the depleted extract was reduced by factors of 30 and 40, respectively. Depletion of Fel d I by polyclonal antibodies resulted in a reduction of the ratio Fel d I/cat albumin by a factor of 330. In the RAST, a reduction of the IgE response greater than 50% was found in 23 of 25 patients; in 12 patients the reduction was greater than 90%. In the histamine release test, the polyclonally depleted extract was 200 to 300 times less potent than the crude cat-dander extract. These results indicate that a very large proportion of the allergenic activity of cat-dander extract is caused by a single molecule: Fel d I.

Allergens↗
PubMed1986

The value of target ultrasonic mammography and cytopathology in the assessment of round-shaped shadows on mammograms.

The preoperative value of target ultrasonic mammography (TUSM) and cytopathology, combined with clinical examination and mammography, was studied in 146 mammographically demonstrated round-shaped breast lesions. All lesions were biopsied and histology was performed. Advantages of combining TUSM with cytology are the possibility to have a more precise puncture aspiration with TUSM and a subsequently higher predictive value, compared to each technique alone.

Adolescent↗