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Biomedical subjects

M Vink

Publications and source records attributed to M Vink.

At least 19 recordsLinked to original sources
PubMed2006

Optimization of the Tet-On system for regulated gene expression through viral evolution.

The ability to control (trans)gene expression is important both for basic biological research and applications such as gene therapy. In vivo use of the inducible tetracycline (Tc)-regulated gene expression system (Tet-On system) is limited by its low sensitivity for the effector doxycycline (dox). We used viral evolution to optimize this Escherichia coli-derived regulatory system for its function in mammalian cells. The components of the Tet-On system (the transcriptional activator rtTA and its tetO DNA binding site) were incorporated into the human immunodeficiency virus (HIV)-1 genome to control viral replication. Prolonged culturing of this HIV-rtTA virus resulted in virus variants that acquired mutations in the rtTA gene. Some of these mutations enhance the transcriptional activity and dox-sensitivity of the rtTA protein. This improvement was observed with different tetO-containing promoters and was independent of the episomal or chromosomal status of the target gene. Combination of these beneficial mutations resulted in greatly improved rtTA variants that are seven-fold more active and 100-fold more dox-sensitive than the original Tet-On system. Furthermore, some of the new Tet-On systems are responsive to Tc and minocycline. Importantly, these rtTA variants show no activity in the absence of dox. The optimized rtTA variants are particularly useful for in vivo applications that require a more sensitive or more active Tet-On system.

Anti-Bacterial Agents↗
PubMed2006

Effects of aging on BOLD fMRI during prosaccades and antisaccades.

Age affects the ability to inhibit saccadic eye movements. According to current theories, this may be associated with age-induced neurophysiological changes in the brain and with compensatory activation in frontal brain areas. In the present study, the effects of aging are assessed on brain systems that subserve generation and inhibition of saccadic eye movements. For this purpose, an event-related functional magnetic resonance imaging design was used in adults covering three age ranges (18-30, 30-55, and 55-72 years). Group differences were controlled for task performance. Activity associated with saccadic inhibition was represented by the contrast between prosaccade and antisaccade activation. The tasks activated well-documented networks of regions known to be involved in generation and inhibition of saccadic eye movements. There was an age-related shift in activity from posterior to frontal brain regions after young adulthood. In addition, old adults demonstrated an overall reduction in the blood oxygenation level dependent (BOLD) signal in the visual and oculomotor system. Age, however, did not affect saccade inhibition activity. Mid and old adults appear to increase frontal activation to maintain performance even during simple prosaccades. The global reduction of the BOLD response in old adults could reflect a reduction in neural activity, as well as changes in the neuronal-vascular coupling. Future research should address the impact of altered vascular dynamics on neural activation and the BOLD signal.

Adolescent↗
PubMed2005

Negative priming in schizophrenia revisited.

Reduced spatial negative priming (SNP) in schizophrenia is commonly attributed to the inability to filter out irrelevant information. However, some investigators have suggested that reduced SNP in patients is caused by either perceptual mismatching or salience of the distracter. The goal of the present study was to determine the influence of these perceptual processes. In this preliminary report, we present data of 15 schizophrenia patients on atypical medication and 15 matched healthy controls. Compared to controls, patients showed a reduced SNP effect, even when controlled for perceptual mismatching. This reduced effect was not affected by distracter salience.

Adult↗
PubMed2004

Obstacles in large-scale epidemiological assessment of sensory impairments in a Dutch population with intellectual disabilities.

BACKGROUND: A population-based epidemiological study on visual and hearing impairment was planned in a random sample of 2100 clients, drawn from a base population of 9012 users of Dutch residential and day-care intellectual disability (ID) services with the whole range of IDs. Stratification was applied for age 50 years and over and Down syndrome. Visual and hearing functions were assessed according to a standardized protocol, in cooperation with regular ophthalmologists and regional audiological centres. Anticipated obstacles in sample collection, random inclusion, informed consent, expertise of investigators, time and costs were eliminated by a careful preparation. However, inclusion and participation were incomplete. METHOD: In a descriptive retrospective design, we collected data from our study files on inclusion and participation as well as reasons for non-participation, to identify unanticipated obstacles for this kind of research. RESULTS: Consent was obtained for 1660 clients, and 1598 clients participated in the data collection (76% of intended sample of 2100). Inclusion and participation rates were especially lower in community-based care organizations, resulting in unintentional skewing of the sample towards more severe levels of ID. Complete and reliable data to diagnose visual impairment were obtained for 1358/1598 (85%) and to diagnose hearing impairment for 1237/1598 participants (77%). Unanticipated obstacles had to do with the quality of coordination within care organizations, with characteristics of screening methods, and with collaboration with the regular health care system. Assessments of visual function were more easy to organize than were those of hearing. Based on our current experience, practical recommendations are given for future multicentre research, especially in community-based settings.

Adolescent↗
PubMed2001

In vitro evolution of a highly replicating, doxycycline-dependent HIV for applications in vaccine studies.

A major concern associated with the use of vaccines based on live-attenuated viruses is the possible and well documented reversion to pathogenic phenotypes. In the case of HIV, genomic deletions or mutations introduced to attenuate viral pathogenicity can be repaired by selection of compensating mutations. These events lead to increased virus replication rates and, eventually, disease progression. Because replication competence and degree of protection appear to be directly correlated, further attenuation of a vaccine virus may compromise the ability to elicit a protective immune response. Here, we describe an approach toward a safe attenuated HIV vaccine. The system is not based on permanent reduction of infectivity by alteration of important viral genomic sequences, but on strict control of replication through the insertion of the tetracycline (Tet) system in the HIV genome. Furthermore, extensive in vitro evolution was applied to the prototype Tet-controlled HIV to select for variants with optimized rather than diminished replication capacity. The final product of evolution has properties uniquely suited for use as a vaccine strain. The evolved virus is highly infectious, as opposed to a canonically attenuated virus. It replicates efficiently in T cell lines and in activated and unstimulated peripheral blood mononuclear cells. Most importantly, replication is strictly dependent on the nontoxic Tetanalogue doxycycline and can be turned on and off. These results suggest that this in vitro evolved, doxycycline-dependent HIV might represent a useful tool toward the development of a safer, live-attenuated HIV vaccine.

AIDS Vaccines↗
PubMed2000

Regulation of Photosystem II core protein phosphorylation at the substrate level: Light induces exposure of the CP43 chlorophyll a protein complex to thylakoid protein kinase(s).

Light induces conformational changes in the CP43 chl-a-protein antenna complex in isolated PS II core-complexes exposing phosphorylation site(s) to PS II core-associated protein kinase(s), to added solubilized thylakoid protein kinase(s), as well as to tryptic cleavage. The substrate-activation effect is demonstrated by exposure of the PS II cores to light during the kinase assay as well as by preillumination of the PS II cores in which the endogenous kinase(s) has been inactivated by treatment with N-ethylmaleimid. In the latter case, phosphorylation was performed in darkness following addition of the solubilized protein kinase(s). The solubilized protein kinase(s) does not require light activation. The apparent molecular masses of the main protein kinase(s) associated with the PS II cores (about 31-35 kDa and 45 kDa) differ from that of the major protein kinase present in solubilized preparations obtained from spinach thylakoids (64 kDa). The light-induced exposure of CP43 increases with the light intensity in the range of 20-100 mumol photons m(-2) s(-1) as demonstrated by preillumination of N-ethylmaleimid treated cores followed by addition of the solubilized protein kinase(s) and performing the phosphorylation assay in darkness.

Journal Article↗
PubMed1999

Regulation of thylakoid protein phosphorylation at the substrate level: reversible light-induced conformational changes expose the phosphorylation site of the light-harvesting complex II.

Light-dependent activation of thylakoid protein phosphorylation regulates the energy distribution between photosystems I and II of oxygen-evolving photosynthetic eukaryotes as well as the turnover of photosystem II proteins. So far the only known effect of light on the phosphorylation process is the redox-dependent regulation of the membrane-bound protein kinase(s) activity via plastoquinol bound to the cytochrome bf complex and the redox state of thylakoid dithiols. By using a partially purified thylakoid protein kinase and isolated native chlorophyll (chl) a/b light-harvesting complex II (LHCII), as well as recombinant LHCII, we find that illumination of the chl-protein substrate exposes the phosphorylation site to the kinase. Light does not activate the phosphorylation of the LHCII apoprotein nor the recombinant pigment-reconstituted complex lacking the N-terminal domain that contains the phosphothreonine site. The suggested light-induced conformational change exposing the N-terminal domain of LHCII to the kinase is evidenced also by an increase in its accessibility to tryptic cleavage after light exposure. Light activates preferentially the trimeric form of LHCII, and the process is paralleled by chl fluorescence quenching. Both phenomena are slowly reversible in darkness. Light-induced exposure of the LHCII N-terminal domain to the endogenous protein kinase(s) and tryptic cleavage occurs also in thylakoid membranes. These results demonstrate that light may regulate thylakoid protein phosphorylation not only via the signal transduction chain connecting redox reactions to the protein kinase activation, but also by affecting the conformation of the chl-protein substrate.

Journal Article↗
PubMed1997

Radiographic findings in the teeth and jaws of 14- to 17-year-old Estonian schoolchildren in Tartu and Tallinn.

Panoramic radiographs were taken of 392 Estonian schoolchildren (33% boys and 67% girls) aged 14-17 years, 197 in Tartu and 195 in Tallinn. The mean number of permanent teeth was 31.5. In 14% of the children one to four teeth (excluding wisdom teeth) were missing. The frequencies of missing wisdom teeth and supernumerary teeth agreed with those in the literature, being 17% and 3%, respectively. The mean number of radiographically detected carious teeth was 1.9 in Tartu and 3.3 in Tallinn. Secondary caries was common, being found radiographically in half of the schoolchildren. Endodontic treatment had been given to 13% of the subjects in Tartu and to 46% in Tallinn, the success rates being 47% and 44%, respectively. The percentage of radiographic signs in the mandibular condyles of girls (5%) was greater than that of the boys (1%). Changes in the maxillary sinuses were found in 16% of the children. Eight odontogenic cysts, one cyst of the incisal canal, and one solitary bone cyst were found. Tumors included two odontomas, two cemento-ossifying lesions, and one osteoma in the maxillary sinus. The health status of the jaws of the Estonian schoolchildren was considered to be fairly good.

Adolescent↗
PubMed1996

Dental health in 14- to 17-year-old Estonian schoolchildren in Tartu and Tallinn.

The dental health of 392 Estonian schoolchildren aged 14-17 years (197 in Tartu and 195 in Tallinn) was studied. In Tartu only 1 child had lost teeth because of caries, as against 30 in Tallinn. Clinically caries-free dentitions were found in 15% of the children in Tartu and in 3% in Tallinn. The mean DMFT value was 3.7 in Tartu and 7.0 in Tallinn, being higher among girls in both cities. The mean DT value was 1.0 in Tartu and 2.6 in Tallinn. All subjects examined had a gingival bleeding index (GBI) higher than zero. The mean GBI was 20% in Tartu and 18% in Tallinn.

Adolescent↗
PubMed1989

Recognition memory for words and faces in the very old.

The assessment of very elderly people is hindered by a scarcity of normative and reliability data for non-verbal memory tests. We tested the suitability of Warrington's Recognition Memory Test (RMT) for use with the elderly. The RMT consists of verbal (Recognition Memory for Words, RMW) and non-verbal (Recognition Memory for Faces, RMF) subtests. The facial recognition test was used in the standard format and a Dutch-language version of the word recognition test was developed using low frequency (10 or less/million) monosyllabic words. Eighty-nine subjects, varying in age from 69 to 93, were tested with the RMF. Means and SD are provided for three age groups (69-79, 80-84 and 85-93). Forty-five consecutive subjects were tested both with the RMW and the RMF. Recognition memory for words was better than recognition memory for faces in this sample. Moderate correlations (0.30-0.48) were found between RMT and WAIS Vocabulary and Raven's Coloured Progressive Matrices scores. Warrington's RMT was well tolerated, even by very elderly adults. The standardization data for the elderly over 70 add to the usefulness of this test of verbal and non-verbal episodic memory.

Aged↗
PubMed1986

Influence of tryptophan loading on urinary excretion of anthranilic acid and 3-hydroxyanthranilic acid by men and women as determined by alkali flame ionization gas chromatography.

A gas chromatographic method with alkali flame ionization detection is described for the determination of urinary total (free and conjugated) anthranilic acid (AA) and 3-hydroxyanthranilic acid (HAA) as their pentafluorobenzyl esters. Prior to analysis, urine was hydrolysed using hydrochloric acid in a boiling water bath. The highest AA and HAA yields were obtained with 4 M hydrochloric acid and a hydrolysis time of 4 h. The coefficients of variation of the between-run analyses of AA and HAA at the endogenous level were 7.2 and 5.8%, respectively. The average recovery for both substances was 84%. The method described has been used to study the excretion of AA and HAA in the urine of healthy males and females before and after an oral load of tryptophan. Furthermore, the influence of oral contraceptives has been investigated. Results indicate that for both sexes the excretion of AA in the urine was higher than that of HAA, except after tryptophan loading. The excretion of AA by women was higher than by men. For HAA, the results of both sexes were comparable. Furthermore, for neither of the sexes was a diurnal variation of AA or HAA observed. After tryptophan loading, the formation of HAA was increased by more than that of AA. Results obtained for women on oral contraceptives indicate a hormonal-induced inhibition of AA formation.

3-Hydroxyanthranilic Acid↗
PubMed1983

Radiation-induced head and neck tumours: is the skin as sensitive as the thyroid gland?

Six hundred and five persons, randomly selected from a cohort of 2400 patients who had been irradiated 16-46 yr previously for benign diseases in the head and neck region, were traced, recalled and examined for radiation-associated tumours. Three hundred and sixty-seven patients were alive, 179 had died and 66 had emigrated. Two hundred and fifty-seven patients were clinically examined, 87 refused or were not able to participate and 16 could not be contacted. Eighteen of the clinically examined patients had been or were being treated for 20 skin carcinomas with a mean latency of 37 yr. In this group only 7 carcinomas of the thyroid gland were observed, with a mean latency of 38 yr. Eleven carcinomas of the skin and 3 of the thyroid gland were reported in the group which was examined by means of questionnaires. The observed number of carcinomas of the skin is higher than expected according to the dose-effect relationship of UNSCEAR, whereas the number of carcinomas of the thyroid gland is lower. It is concluded that there might be less difference in susceptibility for the induction of tumours by ionizing radiation between the skin and the thyroid gland than is commonly assumed.

Dose-Response Relationship, Radiation↗
PubMed1981

Diagnosis, treatment and operative complications of carotid body tumours.

A series of 42 patients who were treated in the Surgical Clinic of the University of Leyden on suspicion of a carotid body tumour between 1958 and 1979 is reported. Thirty-four patients in this series were operated upon in the University Hospital Leyden. Only 6 per cent of the tumours were malignant according to the criteria of nuclear polymorphia and metastases. Local infiltration, either histological or clinical, has no correlation with later outcome. In 11 per cent of the patients, vascular complications occurred. The necessity of operative damage to the surrounding cranial nerves increased with the size of the tumour. In one case the cranial nerve lesion was accidental. No per- or postoperative mortality was seen in this series.

Adolescent↗