Biomedical subjects

J Hendriks

Publications and source records attributed to J Hendriks.

At least 37 records · Page 2Linked to original sources

PubMed2000

Water structural changes involved in the activation process of photoactive yellow protein.

Fourier transform infrared (FTIR) spectroscopy was applied to the blue-light photoreceptor photoactive yellow protein (PYP) to investigate water structural changes possibly involved in the photocycle of PYP. Photointermediates were stabilized at low temperature, and difference IR spectra were obtained between intermediate states and the original state of PYP (pG). Water structural changes were never observed in the >3570 cm(-)(1) region for the intermediates stabilized at 77-250 K, such as the red-shifted pR and blue-shifted pB intermediates. In contrast, a negative band was observed at 3658 cm(-)(1) in the pB minus pG spectrum at 295 K, which shifts to 3648 cm(-)(1) upon hydration with H(2)(18)O. The high frequency of the O-H stretch of water indicates that the water O-H group does not form hydrogen bonds in pG, and newly forms these upon pB formation at 295 K, but not at 250 K. Among 92 water molecules in the crystal structure of PYP, only 1 water molecule, water-200, is present in a hydrophobic core inside the protein. The amide N-H of Gly-7 and the imidazole nitrogen atom of His-108 are its possible hydrogen-bonding partners, indicating that one O-H group of water-200 is free to form an additional hydrogen bond. The water band at 3658 cm(-)(1) was indeed diminished in the H108F protein, which strongly suggests that the water band originates from water-200. Structural changes of amide bands in pB were much greater in the wild-type protein at 295 K than at 250 K or in the H108F protein at 295 K. The position of water-200 is >15 A remote from the chromophore. Virtually no structural changes were reported for regions larger than a few angstroms away from the chromophore, in the time-resolved X-ray crystallography experiments on pB. On the basis of the present results, as well as other spectroscopic observations, we conclude that water-200 (buried in a hydrophobic core in pG) is exposed to the aqueous phase upon formation of pB in solution. In neither crystalline PYP nor at low temperature is this structural transition observed, presumably because of the restrictions on global structural changes in the protein under these conditions.

Bacterial Proteins↗

PubMed2000

A new concept of carbon dioxide accelerated ammonia release from liquid manure in pig house.

Indoor air quality in animal buildings is very important to the health of agricultural workers and animals. Carbon dioxide (CO2) and ammonia (NH3) are two of the most important pollutants in pig houses. Four tests were conduced in a mechanically ventilated pig house to study release behaviors of CO2 and NH3 from liquid manure using impulse, pulse and step ventilation inputs. The CO2 and NH3 concentrations were sampled in the exhaust chimney and measured with a CO2 monitor and a NOx analyzer, respectively. The ventilation rate was measured with a ventilation rate sensor in the chimney. A new phenomenon, characterized by a delayed dynamic response of NH3 release to the high ventilation inputs as compared with the response of CO2 release, was encountered. A new CO2 factor was identified as the cause of the delayed NH3 response. An original concept of Carbon-dioxide Accelerated Ammonia Release (CAAR) was developed. It explained that, at the initial stage of gas release induced by the high ventilation, the high release of CO2 gradually raised the pH in the surface manure. The increased pH accelerated the release of NH3. The higher release of NH3 had a negative feedback to the pH. The effects of CO2 and NH3 releases on the pH finally reached a dynamic equilibrium. The NH3 release under the dynamic equilibrium was greatly accelerated compared to that under initial conditions.

Air Pollutants, Occupational↗

PubMed2000

Development and validation of a dynamic mathematical model of ammonia release in pig house.

A dynamic mathematical model of Carbon-dioxide Accelerated Ammonia Release (CAAR) was developed based on the known knowledge of the chemistry of ammonia (NH3) in liquid solution, mass transfer inside liquid and across liquid-gaseous interface, and a new concept of CAAR. It calculated the NH3 concentration, release and emission at transient and steady state conditions related to a mechanically ventilated pig house. One field experimental data set was used for estimating the proportionality coefficient in the model. Another field data set was used for model validation. The ammonia concentration and emission rate calculated in the model validation were compared with the field measurement values. R2 of 0.861 and 0.947 were obtained for NH3 concentration and emission rate, respectively. In the model validation, the pH in manure surface was found to increase from 8 at initial condition to 8.85 at dynamic equilibrium due to the co-release of CO2 from the manure. This pH change accelerated the NH3 release by 6.1-fold. The model provided a quantitative description of some new understanding of the mechanism of NH3 release in the pig house and entailed suggestions of two new techniques of NH3 emission abatement: the reduction of CO2 release and the new ventilation control strategy.

Air Pollutants, Occupational↗

PubMed2000

CD27 is required for generation and long-term maintenance of T cell immunity.

The Traf-linked tumor necrosis factor receptor family member CD27 is known as a T cell costimulatory molecule. We generated CD27-/- mice and found that CD27 makes essential contributions to mature CD4+ and CD8+ T cell function: CD27 supported antigen-specific expansion (but not effector cell maturation) of naïve T cells, independent of the cell cycle-promoting activities of CD28 and interleukin 2. Primary CD4+ and CD8+ T cell responses to influenza virus were impaired in CD27-/- mice. Effects of deleting the gene encoding CD27 were most profound on T cell memory, reflected by delayed response kinetics and reduction of CD8+ virus-specific T cell numbers to the level seen in the primary response. This demonstrates the requirement for a costimulatory receptor in the generation of T cell memory.

Animals↗

PubMed2000

Predictive value of parent-reported symptoms in the assessment of otitis media with effusion during infancy.

OBJECTIVE: To determine the predictive value of parent-reported symptoms in the assessment of otitis media with effusion (OME) during infancy. DESIGN: Prospective longitudinal study that compared the results of questionnaire-based parental reports with the state of the middle ear assessed by otoscopy and tympanometry at 3-month intervals from birth to the age of 2 years. SETTING: Outpatient Department, University Hospital Maastricht, The Netherlands. SUBJECTS: One hundred and fifth healthy-born infants. MAIN OUTCOME MEASURES: Sensitivity, specificity, positive and negative predictive values of parent-reported ear infection, hearing loss, mouth breathing, snoring and common cold. RESULTS: Prevalence rates showed the following ranges: OME, 39%-53%, parent-reported ear infection, 2%-20%, hearing loss 2%-7%, mouth breathing, 30%-41%, snoring, 31%-41% and common cold, 65%-81%. Common cold demonstrated the highest sensitivity (83%) with a low specificity of 36%. Hearing loss gave the highest positive predictive value (PPV) (70%) with a moderate negative predictive value (NPV) (54%). PPV increased with the number of anamnese questions answered positively. CONCLUSIONS: The diagnostic value of parent-reported ear infection, hearing loss and common cold was found to be limited. Combinations of positively-reported symptoms gives increased diagnostic validity while the absence of parent-reported symptoms does not necessarily indicate the absence of OME.

Ambulatory Care↗

PubMed2000

Lamellar bone formation in an atherosclerotic plaque of the carotid artery, with a review of histogenesis--a case report.

Longer existing atherosclerotic lesions may contain calcifications; lamellar bone rarely develops within them. A 59-year-old man was referred with a progressive stroke. A high-grade stenosis of the left common carotid artery, formed by an ulcerating atherosclerotic plaque with a free-floating thrombus, was detected on angiography. An urgent endarterectomy was performed. Surprisingly this plaque contained pieces of lamellar bone, proved by histologic examination.

Angiography↗

PubMed1999

Kinetics of and intermediates in a photocycle branching reaction of the photoactive yellow protein from Ectothiorhodospira halophila.

We have studied the kinetics of the blue light-induced branching reaction in the photocycle of photoactive yellow protein (PYP) from Ectothiorhodospira halophila, by nanosecond time-resolved UV/Vis spectroscopy. As compared to the parallel dark recovery reaction of the presumed blue-shifted signaling state pB, the light-induced branching reaction showed a 1000-fold higher rate. In addition, a new intermediate was detected in this branching pathway, which, compared to pB, showed a larger extinction coefficient and a blue-shifted absorption maximum. This substantiates the conclusion that isomerization of the chromophore is the rate-controlling step in the thermal photocycle reactions of PYP and implies that absorption of a blue photon leads to cis-->trans isomerization of the 4-hydroxy-cinnamyl chromophore of PYP in its pB state.

Bacterial Proteins↗

PubMed1999

Protonation/deprotonation reactions triggered by photoactivation of photoactive yellow protein from Ectothiorhodospira halophila.

Light-dependent pH changes were measured in unbuffered solutions of wild type photoactive yellow protein (PYP) and its H108F and E46Q variants, using two independent techniques: transient absorption changes of added pH indicator dyes and direct readings with a combination pH electrode. Depending on the absolute pH of the sample, a reversible protonation as well as a deprotonation can be observed upon formation of the transient, blue-shifted photocycle intermediate (pB) of this photoreceptor protein. The latter is observed at very alkaline pH, the former at acidic pH values. At neutral pH, however, the formation of the pB state is not paralleled by significant protonation/deprotonation of PYP, as expected for concomitant protonation of the chromophore and deprotonation of Glu-46 during pB formation. We interpret these results as further evidence that a proton is transferred from Glu-46 to the coumaric acid chromophore of PYP, during pB formation. One cannot exclude the possibility, however, that this transfer proceeds through the bulk aqueous phase. Simultaneously, an amino acid side chain(s) (e.g. His-108) changes from a buried to an exposed position. These results, therefore, further support the idea that PYP significantly unfolds in the pB state and resolve the controversy regarding proton transfer during the PYP photocycle.

Bacterial Proteins↗

PubMed1999

Risk factors of otitis media with effusion during infancy.

UNLABELLED: Associations of possible risk factors with prevalence of otitis media with effusion (OME) were prospectively studied in a cohort of 250 infants, aged 0-2 years. In order to determine OME, otoscopy and tympanometry were performed at 3-monthly intervals beginning at term date. Eighteen epidemiologically relevant features were inventoried by means of standardized questionnaires. Multivariate analysis controlled for possible confounding factors. Prevalence of OME was most strongly associated with age (P-value < 0.001). Other factors significantly associated with the prevalence of OME (P-value < 0.05) were gestational age, birth weight, breastfeeding, day-care attendance, number of siblings, season, and parent-reported ear infection, hearing loss, mouth breathing and common cold. No significance was found for gender, date of birth, passive smoking, family history of otitis media, parental socio-economic status and histories of snoring and consultation of a physician. IN CONCLUSION: both intrinsic and extrinsic factors appear to play an important role in the prevalence of OME. Some of the risk factors appeared to be time-dependent.

Acoustic Impedance Tests↗

PubMed1999

Prevalence rates of otitis media with effusion from 0 to 2 years of age: healthy-born versus high-risk-born infants.

In a prospective-longitudinal study, prevalence rates of otitis media with effusion (OME) were analysed in 150 healthy-born and 100 high-risk-born infants, aged 0-2 years. In order to determine OME, otoscopy and tympanometry were performed at 3-monthly intervals beginning at term date. The Maastricht Otitis Media with Effusion Study (MOMES) algorithm was used to standardize the diagnosis. The distribution of relevant background characteristics was similar in both groups except for gestational age and birth weight, which were significantly lower (P < 0.001) in the high-risk-born group. The ratio of unilateral:bilateral OME was 2:3. Prevalence rates of OME were strongly associated with age (P < 0.001). During the first months of life, OME prevalence rates increased rapidly in both groups, but did not differ significantly. However, from the age of 6 months on, OME prevalence rates of the high-risk group became significantly higher compared with the normal group (P < 0.05). The peak prevalence of OME (59% in the high-risk group versus 49% in the normal group) was observed around the age of 10 months. Although gradually decreasing prevalence rates were noted in both groups with aging, the differences between high-risk and normal infants remained, at least up to 24 months. In conclusion, OME is a very prevalent, age-dependent disorder during infancy, especially in high-risk infants. Peak prevalence of OME was found in the second half of the first year of life.

Age Factors↗

PubMed1999

The effect of CO2 pneumoperitoneum on the growth of a solid colon carcinoma in rats.

BACKGROUND: In order to investigate the effect of carbon dioxide (CO(2)) pneumoperitoneum on solid colon carcinomas, we used a colon anastomosis tumor model in 30 male syngeneic WAG rats, which were divided, at random into three groups. METHODS: In all rats, 10(6) CC531 S colon carcinoma cells were injected as an enema into the colon. Subsequently, a transection and a reanastomosis of the colon descendens was performed via laparotomy. After 2 weeks, group 1 (n = 10) was anesthetized as an anesthesia control group. Group 2 (n = 10) had a laparotomy that was closed after 20 min. In group 3 (n = 10), a CO(2) pneumoperitoneum of </=6 mmHg was created and maintained during 20 min. After 2 weeks, all rats were killed, and total tumor weight and volume was measured. RESULTS: At necroscopy tumor growth was found in 16 rats (group 1: six; group 2: five; group 3: five). No difference in tumor growth (weight or volume) was found between the three groups. CONCLUSION: In our solid colon carcinoma model, CO(2) pneumoperitoneum did not enhance tumor growth.

Animals↗

PubMed1999

Inhibition of terminal chondrocyte differentiation by bone morphogenetic protein 7 (OP-1) in vitro depends on the periarticular region but is independent of parathyroid hormone-related peptide.

Bone morphogenetic protein-7, or BMP-7 (OP-1), is highly expressed in the perichondrium of embryonic long bones and is thought to play a role in endochondral ossification. Previously we have shown that BMP-7 inhibits terminal chondrocyte differentiation; that is, chondrocyte hypertrophy and mineralization in cultured explants of embryonic mouse metatarsals. However, the mechanism of this inhibition and the target cells of BMP-7 are still unknown. In this study we show that BMP-7 inhibits terminal chondrocyte differentiation indirectly, via an interaction with the periarticular region of the explants. This region also expresses parathyroid hormone-related peptide (PTHrP). PTHrP regulates terminal chondrocyte differentiation by inhibiting hypertrophic differentiation of prehypertrophic chondrocytes. The differentiating center in turn regulates PTHrP expression via a feedback loop involving Indian hedgehog (Ihh), which is expressed in the prehypertrophic chondrocytes. Ihh is thought to act on perichondrial cells, which in turn start to express an as yet unknown mediator that stimulates PTHrP expression in the periarticular region. It has been suggested that this factor belongs to the BMP-family. We investigated whether the inhibition of terminal chondrocyte differentiation by BMP-7 was due to upregulation of the PTHrP-Ihh feedback loop and whether BMP-7 was the unknown factor in the loop. Here we show that exogenous BMP-7 did not upregulate the mRNA expression of PTHrP, Ihh, or the PTH/PTHrP receptor in cultured wild-type embryonic metatarsals. Furthermore, BMP-7 could still inhibit terminal chondrocyte differentiation in the metatarsals of PTHrP-deficient (PTHrP-/-) mouse embryos. These data indicate that the BMP-7-mediated inhibition of terminal chondrocyte differentiation in vitro is independent of the PTHrP-Ihh feedback loop. We concluded that BMP-7 modulates terminal chondrocyte differentiation and cartilage mineralization of fetal bone explants in vitro via as yet unknown inhibitory factor(s) produced in the periarticular region.

Animals↗

PubMed1999

The use of X-ray for lymph node determination in the axillary dissection specimen.

A new and simple method by X-ray is described for lymph node determination in the axillary specimen of breast cancer patients. X-rays were performed of the axillary specimens of 49 women with breast cancer. The number of lymph nodes visible on the X-rays were assessed by two radiologists (A and B). The number of nodes identified in the axillary specimens was reported by the pathologist independently. The method described shows a clear correlation between the mean numbers of nodes counted on the X-rays of the specimens (radiologist A 18.3, B 16.1 nodes) and the mean numbers of nodes recovered by the pathologist (18.4). No intra-observer variation was observed and only a small inter-observer variation (2.2 nodes). This method of X-ray determination of lymph nodes can be used in auditing the surgeon's accuracy in performing complete axillary dissection as well as in auditing the number of lymph nodes found by the pathologist.

Journal Article↗

PubMed1999

Effects of suramin on anastomotic colon tumors in a rat model.

BACKGROUND: The development of antiangiogenic drugs offers new promise in the treatment of malignancy. Suramin has been reported to inhibit tumor growth by blocking angiogenesis and has been used in clinical trials. The aim of the present study was to examine the effects of suramin on colonic anastomotic tumors in the rat. METHODS: (a) Colonic anastomotic tumor was induced in 120 WAG/RIJ rats. Half of the animals were given 100 mg/kg of suramin intraperitoneally at the time of tumor induction. Rats were sacrificed after 2, 4 and 8 weeks; tumor take and tumor weight were evaluated. (b) The number of red blood cell clusters per x 400 field was counted in each tumor. (c) A lymphocyte transformation test was performed in four groups of animals, 2 weeks before and 2 weeks after tumor implantation and/or suramin administration. RESULTS: (a) A significant enhancement of tumor growth was observed in the suramin-treated animals. (b) This was accompanied by a significant increase in functional blood vessels. (c) Suramin-treated rats had markedly decreased lymphocyte stimulation, pointing to a possible immunosuppressive effect. CONCLUSIONS: The growth of an anastomotic colon tumor is rather enhanced by a single intraperitoneal administration of 100 mg/kg suramin in the rat, possibly by an unexpected immunosuppressive effect.

Adenocarcinoma↗

PubMed1999

The influence of dietary sodium restriction on anxiety levels during an in vitro fertilization procedure.

In this randomized study, influences of dietary sodium restriction as an independent factor on anxiety levels of women participating in an in vitro fertilization-embryo transfer (IVF-ET) procedure were investigated. Anxiety levels of 119 women were measured using the Spielberger State and Trait Anxiety Inventory. Data of 69 women remained for analysis. Drop-outs, mainly due to cycle cancellations, tended to have higher mean state anxiety scores compared with women who continued (p = 0.11). Bias by selection affected both diet groups in similar proportions. State as well as trait anxiety scores increased significantly (p = 0.01, and p = 0.03, respectively) from baseline (before ovarian stimulation) to the point of measurement in the luteal phase. No significant differences in this mean increase were observed between the two diet groups. The significantly higher mean increase in state and trait anxiety in conceiving women was striking compared with those who did not conceive (p = 0.03 and p < 0.01, respectively). We conclude that dietary sodium restriction does not lower anxiety levels during an IVF-ET procedure. Anxiety levels increase more from baseline (before ovarian stimulation) to the luteal phase in conceiving than in nonconceiving women. The influence of conception on anxiety levels needs further investigation.

Adult↗

PubMed1999

Isolated lung perfusion for the treatment of pulmonary metastases an experimental study in the rat.

The lung is a common site of metastatic involvement and 5-year survival rates after complete surgical resection of lung metastases vary between 16 and 42%. As isolated limb or liver perfusion, isolated lung perfusion offers a new therapeutic option to deliver high-dose chemotherapy with minimal systemic side-effects (chapter 1). In our laboratory isolated lung perfusion was studied in a model of pulmonary metastatic adenocarcinoma in the rat and compared with intravenous chemotherapy. To improve results, techniques for intubation and anesthesia were modified and a new approach of catheterization of the pulmonary artery was developed (chapter 2). In a first series of experiments isolated lung perfusion was studied in a model of bilateral pulmonary metastases. Left isolated lung perfusion with melphalan and tumor necrosis factor was evaluated with the contralateral side serving as control (chapter 3). Toxicity, pharmacokinetic and toxicity studies were performed. Left lung melphalan levels were significantly higher after isolated lung perfusion compared to intravenous injection and significantly fewer left lung nodules were found. Tumor necrosis factor didn't show any significant effect in our model. In a second series of experiments long-term survival was evaluated after isolated lung perfusion with melphalan in a model of unilateral pulmonary metastases (chapter 4). All animals treated with melphalan intravenously died of massive tumor replacement of the left lung with a median survival time of 38 days. Rats undergoing isolated lung perfusion with melphalan had a significantly longer median survival time of 84 days (p < 0.0004). The left lung of three of the rats perfused with melphalan was even tumor-free at 3 months. In conclusion, isolated lung perfusion is effective in a rat model of pulmonary metastatic adenocarcinoma. Clinical studies are necessary to determine its effect on pulmonary metastases in man, especially in case of unresectable disease or possibly as adjuvant therapy after surgical resection.

Adenocarcinoma↗

PubMed1999

The use of alternatives to animal tests in developing countries.

Consideration of alternative methods for animal tests in developing countries is important because good quality laboratory animals and proper animal facilities are not always sufficiently available to perform the currently required quality control tests. In vitro methods have been implemented at the National Institute of Vaccines and Biological Substances (IVAC) in Vietnam. These include serological tests (such as the Toxin Binding Inhibition test and the VERO Cell test) for the estimation of potency of Tetanus and Diphtheria toxoid vaccines and for the evaluation of vaccine field trials. Currently, an inhibition ELISA test to determine anti-rabies activity in equine rabies immunoglobulin preparations is being developed with the long-term goal of its introduction in Vietnam. The results from validation studies are promising and have contributed to decisions made by the National Control Authority to replace imported DPT vaccines in the EPI program with Vietnamese-produced DPT vaccines. This paper summarizes IVAC's experience in introducing alternatives in Vietnam over the last 10 years and reports on the various local validation studies which were performed during this period.

Animal Testing Alternatives↗

PubMed1999

Tetanus antibodies measured by the toxin binding inhibition test (ToBI) in mothers and children in the Neonatal Tetanus Program in Vietnam.

The immunoresponse to vaccination in the Neonatal Tetanus Program (NNT) for pregnant women was studied in Vietnam using the Toxin Binding Inhibition Test (ToBI). The vaccination schedule consisted of two primary doses of adsorbed tetanus toxoid (TT) vaccine given with a one month interval. The seroconversion rate in the women was 98%. Two and a half months after birth, 63% of the children born from these women had tetanus antibody values higher than 0.01 IU/ml. Four women who had anti-tetanus titres < 0.01 IU/ml at delivery, despite two doses of primary vaccination, received a third booster with vaccine one year after the first injection. Their antibody levels were well above 0.01 IU/ml one month after this additional booster, suggesting that (when economically feasible) a third TT injection could be considered into the NNT to confer optimal anti-tetanus antibody levels in women for subsequent pregnancies. This study confirmed the effectiveness of the TT vaccines investigated and indicates their potential to replace, in immunosurveillance studies under field conditions, the in vivo mouse neutralisation test by in vitro alternative methods such as the ToBI test.

Adult↗