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Search Results: 1 - 10 of 298242 matches for " Henk J. Blom "
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Neural Tube Defects, Folic Acid and Methylation
Apolline Imbard,Jean-Fran?ois Benoist,Henk J. Blom
International Journal of Environmental Research and Public Health , 2013, DOI: 10.3390/ijerph10094352
Abstract: Neural tube defects (NTDs) are common complex congenital malformations resulting from failure of the neural tube closure during embryogenesis. It is established that folic acid supplementation decreases the prevalence of NTDs, which has led to national public health policies regarding folic acid. To date, animal studies have not provided sufficient information to establish the metabolic and/or genomic mechanism(s) underlying human folic acid responsiveness in NTDs. However, several lines of evidence suggest that not only folates but also choline, B12 and methylation metabolisms are involved in NTDs. Decreased B12 vitamin and increased total choline or homocysteine in maternal blood have been shown to be associated with increased NTDs risk. Several polymorphisms of genes involved in these pathways have also been implicated in risk of development of NTDs. This raises the question whether supplementation with B12 vitamin, betaine or other methylation donors in addition to folic acid periconceptional supplementation will further reduce NTD risk. The objective of this article is to review the role of methylation metabolism in the onset of neural tube defects.
Ovarian Cyst Fluid of Serous Ovarian Tumors Contains Large Quantities of the Brain Amino Acid N-acetylaspartate
Eva Kolwijck,Ron A. Wevers,Udo F. Engelke,Jannes Woudenberg,Johan Bulten,Henk J. Blom,Leon F. A. G. Massuger
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0010293
Abstract: In humans, N-acetyl L-aspartate (NAA) has not been detected in other tissues than the brain. The physiological function of NAA is yet undefined. Recently, it has been suggested that NAA may function as a molecular water pump, responsible for the removal of large amounts of water from the human brain. Ovarian tumors typically present as large cystic masses with considerable fluid accumulation.
No Effect of Folic Acid Supplementation on Global DNA Methylation in Men and Women with Moderately Elevated Homocysteine
Audrey Y. Jung, Yvo Smulders, Petra Verhoef, Frans J. Kok, Henk Blom, Robert M. Kok, Ellen Kampman, Jane Durga
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0024976
Abstract: A global loss of cytosine methylation in DNA has been implicated in a wide range of diseases. There is growing evidence that modifications in DNA methylation can be brought about by altering the intake of methyl donors such as folate. We examined whether long-term daily supplementation with 0.8 mg of folic acid would increase global DNA methylation compared with placebo in individuals with elevated plasma homocysteine. We also investigated if these effects were modified by MTHFR C677T genotype. Two hundred sixteen participants out of 818 subjects who had participated in a randomized double-blind placebo-controlled trial were selected, pre-stratified on MTHFR C677T genotype and matched on age and smoking status. They were allocated to receive either folic acid (0.8 mg/d; n = 105) or placebo treatment (n = 111) for three years. Peripheral blood leukocyte DNA methylation and serum and erythrocyte folate were assessed. Global DNA methylation was measured using liquid chromatography-tandem mass spectrometry and expressed as a percentage of 5-methylcytosines versus the total number of cytosine. There was no difference in global DNA methylation between those randomized to folic acid and those in the placebo group (difference = 0.008, 95%CI = ?0.05,0.07, P = 0.79). There was also no difference between treatment groups when we stratified for MTHFR C677T genotype (CC, n = 76; CT, n = 70; TT, n = 70), baseline erythrocyte folate status or baseline DNA methylation levels. In moderately hyperhomocysteinemic men and women, long-term folic acid supplementation does not increase global DNA methylation in peripheral blood leukocytes. ClinicalTrials.gov NCT00110604
The Effect of Nitrogen and Phosphorus Ratios and Electrical Conductivity on Plant Growth  [PDF]
Laura Wiser, Theo J. Blom
American Journal of Plant Sciences (AJPS) , 2016, DOI: 10.4236/ajps.2016.712150
Abstract: Environmental concerns surround the use of plant growth retardants (PGRs) for plant height control, and non-chemical alternatives to PGRs can be labor intensive and expensive. Macronutrient modification is a little-studied, yet potentially effective method of controlling plant height. A number of studies have suggested that phosphorus (P) limitation may restrict plant height. Anecdotal evidence also suggests that using nitrate (NO3-), rather than ammonium (NH4+), as the principal nitrogen (N) source may help control plant height. The primary objective of this study was to evaluate different ratios of NO3-/ NH4+, NO3-/P and NH4+/P as well as electrical conductivity (EC) on plant height and growth. This was tested in a hydroponic system using marigolds, sunflowers and tomatoes. Initially, different ratios were tested at an EC of 1.2 dS·m-1, followed by using the same ratios at four ECs (0.6, 1.2, 2.2 and 4.0 dS·m-1) as a second objective. Although ratios did, at times, limit plant height, responses were season and species dependent, suggesting that modifications in plant nutrition, at the ratios used in this study, may not effectively control plant height in hydroponic systems. More consistent, yet species specific, height control was achieved by increasing EC level.
Homocysteine and Familial Longevity: The Leiden Longevity Study
Carolien A. Wijsman,Diana van Heemst,Maarten P. Rozing,P. Eline Slagboom,Marian Beekman,Anton J. M. de Craen,Andrea B. Maier,Rudi G. J. Westendorp,Henk J. Blom,Simon P. Mooijaart
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0017543
Abstract: Homocysteine concentrations are a read-out of methionine metabolism and have been related to changes in lifespan in animal models. In humans, high homocysteine concentrations are an important predictor of age related disease. We aimed to explore the association of homocysteine with familial longevity by testing whether homocysteine is lower in individuals that are genetically enriched for longevity. We measured concentrations of total homocysteine in 1907 subjects from the Leiden Longevity Study consisting of 1309 offspring of nonagenarian siblings, who are enriched with familial factors promoting longevity, and 598 partners thereof as population controls. We found that homocysteine was related to age, creatinine, folate, vitamin B levels and medical history of hypertension and stroke in both groups (all p<0.001). However, levels of homocysteine did not differ between offspring enriched for longevity and their partners, and no differences in the age-related rise in homocysteine levels were found between groups (p for interaction 0.63). The results suggest that homocysteine metabolism is not likely to predict familial longevity.
Epilepsy Is a Risk Factor for Sudden Cardiac Arrest in the General Population
Abdennasser Bardai, Robert J. Lamberts, Marieke T. Blom, Anne M. Spanjaart, Jocelyn Berdowski, Sebastiaan R. van der Staal, Henk J. Brouwer, Rudolph W. Koster, Josemir W. Sander, Roland D. Thijs, Hanno L. Tan
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0042749
Abstract: Background People with epilepsy are at increased risk for sudden death. The most prevalent cause of sudden death in the general population is sudden cardiac arrest (SCA) due to ventricular fibrillation (VF). SCA may contribute to the increased incidence of sudden death in people with epilepsy. We assessed whether the risk for SCA is increased in epilepsy by determining the risk for SCA among people with active epilepsy in a community-based study. Methods and Results This investigation was part of the Amsterdam Resuscitation Studies (ARREST) in the Netherlands. It was designed to assess SCA risk in the general population. All SCA cases in the study area were identified and matched to controls (by age, sex, and SCA date). A diagnosis of active epilepsy was ascertained in all cases and controls. Relative risk for SCA was estimated by calculating the adjusted odds ratios using conditional logistic regression (adjustment was made for known risk factors for SCA). We identified 1019 cases of SCA with ECG-documented VF, and matched them to 2834 controls. There were 12 people with active epilepsy among cases and 12 among controls. Epilepsy was associated with a three-fold increased risk for SCA (adjusted OR 2.9 [95%CI 1.1–8.0.], p = 0.034). The risk for SCA in epilepsy was particularly increased in young and females. Conclusion Epilepsy in the general population seems to be associated with an increased risk for SCA.
Protein Arginine Methylation Is More Prone to Inhibition by S-Adenosylhomocysteine than DNA Methylation in Vascular Endothelial Cells
Ruben Esse, Monica S. Rocha, Madalena Barroso, Cristina Florindo, Tom Teerlink, Robert M. Kok, Yvo M. Smulders, Isabel Rivera, Paula Leandro, Pieter Koolwijk, Rita Castro, Henk J. Blom, Isabel Tavares de Almeida
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0055483
Abstract: Methyltransferases use S-adenosylmethionine (AdoMet) as methyl group donor, forming S-adenosylhomocysteine (AdoHcy) and methylated substrates, including DNA and proteins. AdoHcy inhibits most methyltransferases. Accumulation of intracellular AdoHcy secondary to Hcy elevation elicits global DNA hypomethylation. We aimed at determining the extent at which protein arginine methylation status is affected by accumulation of intracellular AdoHcy. AdoHcy accumulation in human umbilical vein endothelial cells was induced by inhibition of AdoHcy hydrolase by adenosine-2,3-dialdehyde (AdOx). As a measure of protein arginine methylation status, the levels of monomethylarginine (MMA) and asymmetric and symmetric dimethylated arginine residues (ADMA and SDMA, respectively) in cell protein hydrolysates were measured by HPLC. A 10% decrease was observed at a 2.5-fold increase of intracellular AdoHcy. Western blotting revealed that the translational levels of the main enzymes catalyzing protein arginine methylation, protein arginine methyl transferases (PRMTs) 1 and 5, were not affected by AdoHcy accumulation. Global DNA methylation status was evaluated by measuring 5-methylcytosine and total cytosine concentrations in DNA hydrolysates by LC-MS/MS. DNA methylation decreased by 10% only when intracellular AdoHcy concentration accumulated to 6-fold of its basal value. In conclusion, our results indicate that protein arginine methylation is more sensitive to AdoHcy accumulation than DNA methylation, pinpointing a possible new player in methylation-related pathology.
Hypertriglyceridaemia: Aetiology, Complications and Management
D.J Blom
Journal of Endocrinology, Metabolism and Diabetes of South Africa , 2010,
Abstract: The bulk of plasma triglycerides are carried by chylomicrons in the fed and very low-density lipoproteins in the fasted state. These triglyceriderich lipoproteins are metabolised to remnant lipoproteins by lipoprotein lipase (LPL). Hypertriglyceridaemia results if triglyceride-rich lipoproteins accumulate either due to defective clearance, overproduction or a combination of both mechanisms. Genetic and environmental factors interact in the genesis of hypertriglyceridaemia but occasionally a single factor may be dominant. At a molecular level the most common cause of severe primary hypertriglyceridaemia is loss of function mutations in both alleles of LPL. The most common environmental contributors include diabetes, diet, alcohol and medications (including oestrogen, steroids, retinoids and protease inhibitors). Severe hypertriglyceridaemia can trigger acute pancreatitis while mild to moderate hypertriglyceridaemia is an independent cardiovascular risk factor. Treatment strategies are determined by the severity and aetiology of hypertriglyceridaemia as well as the patient’s cardiovascular risk profile. General strategies include lifestyle modifications with restriction of dietary fat intake, cessation of alcohol intake and increased exercise. Contributing metabolic disorders should be controlled and aggravating medications withdrawn or reduced where possible. Moderate hypertriglyceridaemia may be treated with high doses of omega-3 fatty acids (4 g/day), fibrates, niacin or statins. Fibrates are the agents of choice in severe hypertriglyceridaemia.
Bisimulation Relations Between Automata, Stochastic Differential Equations and Petri Nets
Mariken H.C. Everdij,Henk A.P. Blom
Electronic Proceedings in Theoretical Computer Science , 2010, DOI: 10.4204/eptcs.20.1
Abstract: Two formal stochastic models are said to be bisimilar if their solutions as a stochastic process are probabilistically equivalent. Bisimilarity between two stochastic model formalisms means that the strengths of one stochastic model formalism can be used by the other stochastic model formalism. The aim of this paper is to explain bisimilarity relations between stochastic hybrid automata, stochastic differential equations on hybrid space and stochastic hybrid Petri nets. These bisimilarity relations make it possible to combine the formal verification power of automata with the analysis power of stochastic differential equations and the compositional specification power of Petri nets. The relations and their combined strengths are illustrated for an air traffic example.
Interacting Multiple Model-Feedback Particle Filter for Stochastic Hybrid Systems
Tao Yang,Henk A. P. Blom,Prashant G. Mehta
Mathematics , 2013,
Abstract: In this paper, a novel feedback control-based particle filter algorithm for the continuous-time stochastic hybrid system estimation problem is presented. This particle filter is referred to as the interacting multiple model-feedback particle filter (IMM-FPF), and is based on the recently developed feedback particle filter. The IMM-FPF is comprised of a series of parallel FPFs, one for each discrete mode, and an exact filter recursion for the mode association probability. The proposed IMM-FPF represents a generalization of the Kalmanfilter based IMM algorithm to the general nonlinear filtering problem. The remarkable conclusion of this paper is that the IMM-FPF algorithm retains the innovation error-based feedback structure even for the nonlinear problem. The interaction/merging process is also handled via a control-based approach. The theoretical results are illustrated with the aid of a numerical example problem for a maneuvering target tracking application.
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