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Biomedical subjects

J Meijer

Publications and source records attributed to J Meijer.

At least 19 recordsLinked to original sources
PubMed2001

Purification and characterization of myrosinase from the cabbage aphid (Brevicoryne brassicae), a brassica herbivore.

Aphids are among the most serious insect pests of agricultural crops in the world. They often have specific hosts, and the cabbage aphid (Brevicoryne brassicae) is a specialist on Cruciferae. It has previously been described that certain insects contain the enzyme myrosinase (EC 3.2.3.1), which is considered an important defence enzyme of crucifers. Myrosinase was purified to homogeneity from cabbage aphid soluble extracts using anion-exchange and phenyl-Sepharose chromatography. The protein has an apparent subunit molecular mass of 57-58 kDa and is a dimer. The isoelectric point is 4.9 and the enzyme has a temperature optimum around 40 degrees C. The enzyme was active towards the glucosinolates tested, sinigrin and glucotropaeolin, but was inhibited by ascorbate at concentrations that normally activate plant myrosinases. Using sinigrin as the substrate Km was determined as 0.41 mM, and the kcat as 36 s(-1). With glucotropaeolin the Km and kcat values were determined as 0.52 mM and 22.8 s(-1), respectively. The enzyme was stable upon storage at 4 degrees C for many months, but lost some activity upon freezing. The insect myrosinase did not cross-react with antibodies raised to plant myrosinase. Peptide sequencing of a tryptic digest of the protein showed homology to beta-glucosidases. The presence of myrosinase in an insect pest specialist may be an example of a coevolution process that facilitates host specialization.

Amino Acid Sequence↗
PubMed2001

Markers of inflammation and cellular adhesion molecules in relation to insulin resistance in nondiabetic elderly: the Rotterdam study.

Insulin resistance, which is highly prevalent in the elderly, is suggested to be accompanied by an increased acute phase response. Until now, it is unclear whether cellular adhesion molecules are involved in the clustering of insulin resistance. In the present study, we examined the relationship of insulin resistance (measured by postload insulin) with levels of markers of inflammation and cellular adhesion molecules in a random sample of 574 nondiabetic elderly men and women participating in the Rotterdam Study. Associations were assessed by regression analysis, with ln-insulin as the dependent variable [regression coefficient (95% confidence interval)]. In our population, insulin was strongly and significantly (P < 0.001) associated with the markers of inflammation C-reactive protein [1.52 (0.96-2.08)], alpha-1-antichymotrypsin [1.25 (0.82-1.69)], and IL-6 [2.60 (1.69-3.52)], adjusted for age and gender. Associations weakened, to some extent, after additional adjustment for measures of obesity, smoking, and cardiovascular disease. Insulin was associated with the soluble intercellular adhesion molecule 1 [2.22 (1.29-3.16; P < 0.001)], whereas no association with the soluble vascular cell adhesion molecule 1 was found. The strength of the associations of insulin with C-reactive protein, alpha-1-antichymotrypsin, IL-6, and soluble intercellular adhesion molecule 1, as assessed by standardized regression coefficients, was comparable with the strength of the associations of insulin with high-density lipoprotein cholesterol, body mass index, and waist-to-hip ratio. The results of this population-based study indicate that low-grade inflammation and the cellular adhesion molecule soluble intercellular adhesion molecule 1 are an integral part of insulin resistance in nondiabetic elderly. These factors may contribute to the well-known relationship between insulin resistance and cardiovascular disease risk and might potentially become therapeutic targets in insulin resistant subjects.

Aged↗
PubMed2001

The predictive and discriminant validity of the zone of proximal development.

BACKGROUND: Dynamic measurement procedures are supposed to uncover the zone of proximal development and to increase predictive validity in comparison to conventional, static measurement procedures. AIMS: Two alternative explanations for the discrepancies between static and dynamic measurements were investigated. The first focuses on Vygotsky's learning potential theory, the second considers the role of anxiety tendency during test taking. If test anxious tendencies are mitigated by dynamic testing procedures, in particular the availability of assistance, the concept of the zone of proximal development may be superfluous in explaining the differences between the outcomes of static and dynamic measurement. SAMPLE: Participants were students from secondary education in the Netherlands. They were tested repeatedly in grade three as well as in grade four. Participants were between 14 and 17 years old; their average age was 15.4 years with a standard deviation of .52. METHOD: Two types of mathematics tests were used in a longitudinal experiment. The first type of test consisted of open-ended items, which participants had to solve completely on their own. With the second type of test, assistance was available to participants during the test. The latter so-called learning test was conceived of as a dynamic testing procedure. Furthermore, a test anxiety questionnaire was administered repeatedly. Structural equation modelling was used to analyse the data. RESULTS: Apart from emotionality and worry, lack of self-confidence appears to be an important constituent of test anxiety. The learning test appears to contribute to the predictive validity of conventional tests and thus a part of Vygotsky's claims were substantiated. Moreover, the mere inclusion of a test anxiety factor into an explanatory model for the gathered data is not sufficient. Apart from test anxiety and mathematical ability it is necessary to assume a factor which may be construed as mathematics learning potential. CONCLUSION: The results indicate that the observed differences between a conventional, static testing procedure and an experimental, dynamic testing procedure for mathematics cannot be explained sufficiently by a differential bias towards test anxiety. The dynamic testing approach renders scores which add to the predictive validity of conventional testing procedures. Since this gain in predictive validity is not a result of the removal of bias towards test anxiety, this result should be understood as supportive for the validity of the concept of the zone of proximal development.

Adolescent↗
PubMed2000

Identification and functional characterization of human soluble epoxide hydrolase genetic polymorphisms.

Human soluble epoxide hydrolase (sEH), an enzyme directing the functional disposition of a variety of endogenous and xenobiotic-derived chemical epoxides, was characterized at the genomic level for interindividual variation capable of impacting function. RNA was isolated from 25 human liver samples and used to generate full-length copies of soluble epoxide hydrolase cDNA. The resulting cDNAs were polymerase chain reaction amplified, sequenced, and eight variant loci were identified. The coding region contained five silent single nucleotide polymorphisms (SNPs) and two variant loci resulting in altered protein sequence. An amino acid substitution was identified at residue 287 in exon 8, where the more common arginine was replaced by glutamine. A second variant locus was identified in exon 13 where an arginine residue was inserted following serine 402 resulting in the sequence, arginine 403-404, instead of the more common, arginine 403. This amino acid insertion was confirmed by analyzing genomic DNA from individuals harboring the polymorphic allele. Slot blot hybridization analyses of the liver samples indicated that sEH mRNA steady-state expression varied approximately 10-fold. Transient transfection experiments with CHO and COS-7 cells were used to demonstrate that the two new alleles possess catalytic activity using trans-stilbene oxide as a model substrate. Although the activity of the glutamine 287 variant was similar to the sEH wild type allele, proteins containing the arginine insertion exhibited strikingly lower activity. Allelic forms of human sEH, with markedly different enzymatic profiles, may have important physiological implications with respect to the disposition of epoxides formed from the oxidation of fatty acids, such as arachidonic acid-derived intermediates, as well in the regulation of toxicity due to xenobiotic epoxide exposures.

Alleles↗
PubMed2000

Myrosinase: gene family evolution and herbivore defense in Brassicaceae.

Glucosinolates are a category of secondary products present primarily in species of the order Capparales. When tissue is damaged, for example by herbivory, glucosinolates are degraded in a reaction catalyzed by thioglucosidases, denoted myrosinases, also present in these species. Thereby, toxic compounds such as nitriles, isothiocyanates, epithionitriles and thiocyanates are released. The glucosinolate-myrosinase system is generally believed to be part of the plant's defense against insects, and possibly also against pathogens. In this review, the evolution of the system and its impact on the interaction between plants and insects are discussed. Further, data suggesting additional functions in the defense against pathogens and in sulfur metabolism are reviewed.

Amino Acid Sequence↗
PubMed1999

E7-specific cytotoxic T cell tolerance in HPV-transgenic mice.

The "high-risk" human papillomavirus type 16 (HPV 16) is associated with the development of cervical cancer. Although the viral gene products E6 and E7 are constitutively expressed in HPV 16-associated lesions and therefore appear as candidate antigens for a specific immune response, the immune system fails to produce an efficient defence against tumor outgrowth in affected patients. Keratinocytes are the natural target cells of HPV infection. To investigate the E7-specific immune response in vivo, we used transgenic mice expressing the oncogenes E6 and E7 of HPV 16 under the control of the keratin 10 promoter in the suprabasal layers of the epidermis. This expression pattern closely reflects the viral early gene transcription that is observed in low grade cervical intraepithelial lesions (CIN). The transgene product E7 does not induce an immune response in these transgenic mice. However, upon vaccination anti-E7 antibodies were produced without causing signs of autoimmune disease. In contrast, E7-specific cytotoxic T lymphocytes (CTL) were not detected after immunization. From these results we conclude that in K10 HPV 16 E6/E7 transgenic mice the E7 transgene expression induces specific immunological tolerance on the CTL level.

Animals↗
PubMed1999

Age-dependent wound induction of a myrosinase-associated protein from oilseed rape (Brassica napus).

In order to study the expression of the induced form of myrosinase-associated protein (iMyAP), a genomic clone encoding the protein was isolated from Brassica napus. The coding portion of the gene was found to consist of five exons separated by one long intron of 938 bp and three shorter introns of ca. 100 bp. A 1.9 kb promoter fragment including the 5'-untranslated region was cloned in front of the coding portion of the Escherichia coli iudA gene and transformed into Arabidopsis thaliana. Expression was observed in hypocotyls of 4-day seedlings, but in 7-day seedlings the iMyAP promoter did not direct expression. In flowering plants, only the abscission zone of the young silique displayed promoter activity. In contrast, mechanical wounding of 7-day seedlings induced a systemic expression in all cells of the cotyledons. Wounding of 14-day seedlings gave rise to systemic induced expression mainly in the vascular tissue. However, mechanical wounding and wounding by flea beetles (Phyllotreta undulata) of 4-week old plants only gave rise to a local induction of the promoter, suggesting that the systemic signal system is age-dependent. Methyl jasmonate also induced iMyAP expression. In situ and northern analysis of iMyAP transcripts in young leaves of B. napus showed that the induction was high after 1 h and absent after 24 h. Comparison of the effect of different types of wounding on the iMyAP promoter induction in transgenic Arabidopsis showed that similar degrees of local induction were achieved regardless of the degree of macerated tissue left on the plant.

Animals↗
PubMed1996

Alprazolam premedication and 35% carbon dioxide vulnerability in panic patients.

A group of 20 patients who met the DSM-III-R criteria for panic disorder with or without agoraphobia underwent a 35% carbon dioxide (CO2) challenge after either 1 mg alprazolam or placebo in a double-blind, randomized, cross-over design. Despite the anxiolytic potential of alprazolam, it produced no significant effects on CO2-induced anxiety and panic symptomatology when compared to placebo.

Adult↗
PubMed1996

Structural characterization of the human soluble epoxide hydrolase gene (EPHX2).

The structural organization of the human gene encoding soluble epoxide hydrolase (EPHX2) was determined. Cosmid clones containing the EPHX2 gene were identified by hybridization of a human genomic library with PCR amplified cDNA to the mouse or human soluble epoxide hydrolase as probes. The gene consists of 19 exons and is approximately 45 kb of which more than 15 kb were sequenced. The coding sequence corresponds to 555 amino acid residues, i.e., one additional residue to those in the reported cDNA sequence. The sized of the introns were defined by sequencing or PCR analysis and they contained various repetitive structure elements as expected.

Amino Acid Sequence↗
PubMed1995

Respiratory disorders as a possible predisposing factor for panic disorder.

150 consecutive anxiety patients completed a specially designed questionnaire which asked for the occurrence of respiratory and other somatic disorders before the onset of their anxiety disorder. The sample was divided into 82 panic disorder patients and 68 other anxiety patients serving as controls. Panic disorder patients had a significantly higher prevalence of respiratory diseases before the onset of their anxiety disorder than controls (42.7 vs. 16.2%). This higher prevalence was mainly due to a higher prevalence of bronchitis (26.8 vs. 8.8%). Differences in numbers of respiratory disorders mentioned appeared not to result from a tendency to hypochondria.

Adult↗
PubMed1995

Localization of the human soluble epoxide hydrolase gene (EPHX2) to chromosomal region 8p21-p12.

Epoxide hydrolases have an important function in organisms in that they catalyze the transformation of potentially toxic or carcinogenic epoxides into the corresponding diols. In this study, the chromosomal localization was determined for the human gene encoding soluble epoxide hydrolase. A polymerase chain reaction fragment corresponding to the C-terminal region of the mouse protein was used to isolate a cosmid clone from a human genomic library. By fluorescence in situ hybridization to metaphase chromosomes, the soluble epoxide hydrolase gene was then localized to chromosomal region 8p21-p12.

Animals↗
PubMed1995

Tissue specific basal expression of soluble murine epoxide hydrolase and effects of clofibrate on the mRNA levels in extrahepatic tissues and liver.

The soluble epoxide hydrolase mRNA level in liver was increased eight-fold upon administration of the hypolipidemic drug and peroxisome proliferator clofibrate for 7 days to mice. The soluble epoxide hydrolase mRNA was back at control levels within 1-2 days after clofibrate withdrawal. The highest expression was in liver, intestine and kidney. Lower levels were found in heart and muscle and very low levels were found in testes, lung, brain and spleen. The mRNA levels were increased in liver, kidney and heart by clofibrate.

Animal Feed↗
PubMed1995

Discrimination between panic disorder and generalized anxiety disorder by 35% carbon dioxide challenge.

OBJECTIVE: The authors' goal was to determine whether 35% carbon dioxide (CO2) challenge would discriminate between patients with panic disorder and patients with other anxiety disorders. METHOD: Nine patients with panic disorder and nine with generalized anxiety disorder underwent the 35% CO2 challenge. RESULTS: Patients with panic disorder experienced a significantly stronger increase in subjective anxiety than patients with generalized anxiety disorder. However, increases in panic symptom scores were high in both groups. CONCLUSIONS: These results suggest that a large increase in subjective anxiety due to the CO2 challenge is specific for patients with panic disorder but that an increase in panic symptoms is not.

Adult↗
PubMed1994

Purification and characterization of multifunctional enzyme from mouse liver peroxisomes.

A simple and rapid purification procedure for hepatic peroxisomal multifunctional enzyme (delta 3, delta 2-enoyl-CoA isomerase/enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase) from clofibrate treated mice is described. The purification is achieved within two days using ion-exchange chromatography and an easily prepared affinity resin. The overall yield is 10% or more after a 100-fold enrichment from the cytosolic fraction of liver tissue. The native enzyme is a monomer with a molecular mass of 75 kDa. The protein is blocked in the N-terminus but internal amino acid sequences was obtained after proteolytic cleavage. Western blot analysis indicated proteolysis of multifunctional enzyme in different subcellular fractions derived from liver tissue. The hydratase activity of the enzyme is heat-labile and highly dependent on the concentration of Tris buffer or potassium chloride present. Optimal activity was found around 37 degrees C and pH 7. The enzyme also shows dehydrogenase and isomerase activity.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1994

Lipid composition of liver peroxisomes isolated from untreated and clofibrate-treated mice and rats.

Peroxisomes were isolated from liver tissue of control and clofibrate-treated adult male NMRI mice and Sprague-Dawley rats. Phospholipids, cholesterol, triglycerides and free fatty acids were measured in the peroxisomes. The fatty acid profiles of the phosphatidylethanolamine, the phosphatidylcholine, the triglyceride and the free fatty acid fractions were also analyzed. Phosphatidylethanolamine was the dominating phospholipid in peroxisomes from untreated animals. The fatty acid profiles of phosphatidylethanolamine, free fatty acids and triglycerides were similar for untreated mice and rats but differences between the species were observed in the pattern derived from phosphatidylcholine. Phosphatidylcholine was the most abundant phospholipid after clofibrate treatment. Clofibrate treatment caused an increase in the concentrations of phospholipids and unsaturated long-chain fatty acids and a decrease in the concentrations of triglycerides, free fatty acids, cholesterol and shorter saturated fatty acids.

Animals↗
PubMed1994

A 35% carbon dioxide challenge in simple phobias.

Twenty-eight subjects meeting the DSM-III-R criteria for simple phobia and 30 normal controls were subjected to a 35% carbon dioxide panic provocation challenge. Simple phobics were subdivided into two groups, animal phobics and situational or natural phenomena phobics. Animal phobics were not more vulnerable to carbon dioxide than normal controls. However, situational or natural phenomena phobics reacted significantly more strongly to the challenge than normal controls. The increase in anxiety in this group was comparable to the increase of anxiety of panic disorder patients from previous studies. Our results suggest the existence of a constitutional predisposition that may not only lead to panic disorder but also to the development of certain specific phobias.

Adolescent↗
PubMed1993

Effects of clofibrate withdrawal on peroxisomes in mouse hepatocytes.

Adult male mice (NMRI strain) were initially treated with 0.5% clofibrate in the diet during four days to obtain a high level of peroxisomes in the hepatocytes. Groups of animals were then given control diet for one, two, three, or four days. Liver samples were cytochemically stained for catalase prior to examination by electron microscopy and subsequent morphometric analysis. Various enzyme activities were assayed in liver homogenates. A sixfold increase in peroxisomal area was found after four days of clofibrate feeding compared with untreated animals. The peroxisomal fractional area was unchanged after one day of refeeding control diet but was reduced with over 50% after two days on control diet and was similar to that in the untreated animals after four days. The size distribution of peroxisomes shifted to smaller values during the breakdown of peroxisomes and was similar to the untreated animals after four days of clofibrate withdrawal. During this process a more heterogeneous staining of peroxisomes was observed. The mitochondrial fractional area was not affected by the treatments, but a shift in size distribution to smaller values was observed in the most induced animals. Protein content was not affected by the treatments. The activity of catalase (twofold induction) decreased progressively to control values during recovery but enoyl-CoA hydratase activity (fourty-fold induction) decreased rapidly. NADPH-cytochrome c reductase activity (twofold induction) decreased rapidly to control levels. Citrate synthase activity was not affected by clofibrate treatment but decreased during recovery. Acid phosphatase activity (repressed) increased to control levels. Cathepsin D activity increased somewhat during recovery while proteolytic activity (towards casein) decreased transiently on control diet.

Acid Phosphatase↗