Assessment of essential fatty acid and omega3-fatty acid status by measurement of erythrocyte 20:3omega9 (Mead acid), 22:5omega6/20:4omega6 and 22:5omega6/22:6omega3

BACKGROUND: Early suspicion of essential fatty acid deficiency (EFAD) or omega3-deficiency may rather focus on polyunsaturated fatty acid (PUFA) or long-chain PUFA (LCP) analyses than clinical symptoms. We determined cut-off values for biochemical EFAD, omega3-and omega3/22:6omega3 [docosahexaenoic acid (DHA)]-deficiency by measurement of erythrocyte 20:3omega9 (Mead acid), 22:5omega6/20:4omega6 and 22:5omega6/22:6omega3, respectively. METHODS: Cut-off values, based on 97.5 percentiles, derived from an apparently healthy omnivorous group (six Dominica breast-fed newborns, 32 breast-fed and 27 formula+LCP-fed Dutch low-birth-weight infants, 31 Jerusalem infants, 33 Dutch 3.5-year-old infants, 69 omnivorous Dutch adults and seven Dominica mothers) and an apparently healthy group with low dietary LCP intake (81 formula-fed Dutch low-birth-weight infants, 12 Dutch vegans). Cut-off values were evaluated by their application in an EFAD suspected group of 108, mostly malnourished, Pakistani children, three pediatric patients with chronic fat-malabsorption (abetal-ipoproteinemia, congenital jejunal and biliary atresia) and one patient with a peroxisomal beta-oxidation disorder. RESULTS: Erythrocyte 20:3omega9, 22:5omega6/20:4omega6 and 22:5omega6/22:6omega3 proved age-dependent up to 0.2 years. Cut-off values for ages above 0.2 years were: 0.46mol% 20:3omega9 for EFAD, 0.068mol/mol 22:5omega6/20:4omega6 for omega3-deficiency, 0.22mol/mol 22:5omega6/22:6omega3 for omega3/DHA-marginality and 0.48mol/mol 22:5omega6/22:6omega3 for omega3/DHA-deficiency. Use of RBC 20:3omega9 and 22:5omega6/20:4omega6 cut-off values identified 20.4% of the Pakistani subjects as EFAD+omega3-deficient, 12.9% as EFAD+omega3-sufficient, 38.9% as EFA-sufficient+omega3-deficient and 27.8% as EFA-sufficient+omega3-sufficient. The patient with the peroxisomal disorder was classified as EFA-sufficient, omega3-sufficient (based on RBC 22:5omega6/20:4omega6) and omega3/DHA-deficient (based on RBC 22:5omega6/22:6omega3). The three other pediatric patients were classified as EFAD, omega3-deficient and omega3/DHA-deficient. CONCLUSION: Use of the combination of the present cut-off values for EFA, omega3 and omega3/DHA status assessment, as based on 97.5 percentiles, may serve for PUFA supplement intervention until better concepts have emerged.     

Molecular mobility of elastin: effect of molecular architecture

The thermal and dielectric properties of elastin and two soluble derivatives (kappa-elastin and derived elastin peptides from enzymatic elastolysis) were investigated in the freeze-dried state in a wide temperature range (from -180 to +220 degrees C). The glass transition of these amorphous proteins was studied by differential scanning calorimetry (DSC). The dielectric relaxations of both proteins were followed by thermally stimulated currents (TSC), an isochronal dielectric spectrometry running at variable temperature, analogous to a low-frequency spectroscopy (10(-3)-10(-2) Hz) and by dynamic dielectric spectroscopy (DDS), performed isothermally with the frequency varying from 10(-2) to 3 x 10(6) Hz. The combination of TSC and DDS experiments and the determination of the activation parameters of the relaxation times inform about the molecular mobility of the proteins, both in the glassy state and in the liquid state. Major differences between the relaxation behavior of elastin and its soluble derivatives have been discussed and correlated with the molecular architecture of the proteins.     

Analysis of mouse Rad54 expression and its implications for homologous recombination

Homologous recombination is one of the major pathways for repair of DNA double-strand breaks (DSBs). Important proteins in this pathway are Rad51 and Rad54. Rad51 forms a nucleoprotein filament on single-stranded DNA (ssDNA) that mediates pairing with and strand invasion of homologous duplex DNA with the assist of Rad54. We estimated that the nucleus of a mouse embryonic stem (ES) cells contains on average 4.7x10(5) Rad51 and 2.4x10(5) Rad54 molecules. Furthermore, we showed that the amount of Rad54 was subject to cell cycle regulation. We discuss our results with respect to two models that describe how Rad54 stimulates Rad51-mediated DNA strand invasion. The models differ in whether Rad54 functions locally or globally. In the first model, Rad54 acts in cis relative to the site of strand invasion. Rad54 coats the Rad51 nucleoprotein filament in stoichiometric amounts and binds to the target duplex DNA at the site that is homologous to the ssDNA in the Rad51 nucleoprotein filament. Subsequently, it promotes duplex DNA unwinding. In the second model, Rad54 acts in trans relative to the site of strand invasion. Rad54 binds duplex DNA distant from the site that will be unwound. Translocation of Rad54 along the duplex DNA increases superhelical stress thereby promoting duplex DNA unwinding.     

Sensitive liquid chromatography-tandem mass spectrometry method for the determination of clarithromycin in human plasma

A sensitive method for the determination of clarithromycin in plasma is described, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. Samples were prepared using liquid-liquid extraction and separated on a Supelco Discovery C18 column with a mobile phase consisting of acetonitrile, methanol and acetic acid. Detection was performed by a PE SCIEX API 2000 mass spectrometer in the multiple reaction monitoring (MRM) mode (LC-MS-MS) using TurbolonSpray ionization and monitoring the transition of the protonated molecular ion for clarithromycin at m/z 748.5 (M+1) to the predominant product ion of m/z 158.2. The mean recovery of clarithromycin was 87.3%, with a lower limit of quantification of 2.95 ng/ml when using 0.3-ml plasma. This high-throughput method was used to quantify 230 samples per day, and is sufficiently sensitive to be employed in pharmacokinetic studies.     

Inertial shear force and the impact on facilities for the International Space Station

Inertial shear force is a surface force that is generated in centrifuges especially with attached samples on flat surfaces and plays a significant role in gravitational and space research. The magnitude of this force is proportional to the radius of the centrifuge and surface area of the sample compartment. In gravitational research we want to study the impact of weight onto a system. However, the force of inertial shear is perpendicular to the gravity vector, hence, results may be obscured or even misinterpreted by this artifact.     

"Natural cause of death or not?" How do nursing home physicians act when in doubt of natural cause of death?

The objective of the study was to explore if nursing home physicians act by law, when they doubt the natural cause of death. In May 1999, a questionnaire was sent to 153 nursing home physicians in the region of Utrecht and Nijmegen. They were asked if they consult the coroner when they have doubts about the natural cause of death. Eighty-six percent (104) returned the questionnaire. Thirty-two percent of the nursing home physicians always consult the coroner and 52% does so most of the time. Only 12% does not consult the coroner most of the time and 2% never does. The main reasons for not consulting the coroner were that nursing home physicians judge a death after a fall as an incident that fits in the descending lifeline of patients and that some nursing home physicians had bad experiences consulting the coroner. We conclude that this policy may lead to underregistration of unnatural deaths. Changing the definition or changing the law may reduce this problem. Education and information can also contribute to change in physician's attitudes.     

Structural variation and functional importance of a D-loop-T-loop interaction in valine-accepting tRNA-like structures of plant viral RNAs

Valine-accepting tRNA-like structures (TLSs) are found at the 3′ ends of the genomic RNAs of most plant viruses belonging to the genera Tymovirus, Furovirus, Pomovirus and Pecluvirus, and of one Tobamovirus species. Sequence alignment of these TLSs suggests the existence of a tertiary D-loop–T-loop interaction consisting of 2 bp, analogous to those in the elbow region of canonical tRNAs. The conserved G₁₈·Ψ₅₅ pair of regular tRNAs is found to covary in these TLSs between G·U (possibly also modified to G·Ψ) and A·G. We have mutated the relevant bases in turnip yellow mosaic virus (TYMV) and examined the mutants for symptom development on Chinese cabbage plants and for accumulation of genetic reversions. Development of symptoms is shown to rely on the presence of either A·G or G·U in the original mutants or in revertants. This finding supports the existence and functional importance of this tertiary interaction. The fact that only G·U and A·G are accepted at this position appears to result from steric and energetic limitations related to the highly compact nature of the elbow region. We discuss the implications of these findings for the various possible functions of the valine-accepting TLS.     

Ligand-dependent activation of the melanocortin 5 receptor: cAMP production and ryanodine receptor-dependent elevations of [Ca(2+)](I).

The melanocortins are involved in the regulation of various cognitive and physiological processes such as learning, feeding, immune suppression, pigmentation, and sebum production. Five melanocortin receptors have been identified, of which the melanocortin 5 receptor (MC5R) has the most widespread distribution. This subtype is found in the brain, and at numerous peripheral sites including the skin where it is expressed in the sebaceous glands. The purpose of this study was to identify the peptide that functions as a natural ligand at the MC5R in the skin. alpha-MSH, ACTH1-39, ACTH1-17, ACTH1-10, and ACTH4-10 all increased the production of cAMP in HEK293 cells transfected with the mouse MC5R. alpha-MSH and ACTH1-17 were the most potent in this respect. In addition, all peptides stimulated a rapid and transient increase in [Ca(2+)](i), and, ACTH1-10 was the most potent. The increases in [Ca(2+)](i) were of intracellular origin, but not associated with inositol phosphate production. The elevations in [Ca(2+)](i) were reduced by ruthenium red and procaine and it is therefore possible that they were mediated via ryanodine receptors.     

Exploring the active site of Trypanosoma brucei phosphofructokinase by inhibition studies: specific irreversible inhibition

This work deals with the phosphofructokinase enzyme (PFK) of the parasite Trypanosoma brucei. Inhibitors which are analogues of fructose-6-phosphate (F6P) derived from 2,5-anhydromannitol and therefore blocked in a closed conformation, both nonphosphorylated and phosphorylated, were designed. They provided information on this class of ATP-dependent PFK (structurally more similar to PPi-dependent PFKs revealing (i) an ordered mechanism, ATP binding first, inducing an essential conformational change to increase the affinity for F6P, and (ii) a rather hydrophobic environment at the ATP binding site. Nonphosphorylated mannitol derivatives bind at both the ATP and F6P binding sites, whereas the phosphorylated derivatives only bind at the ATP binding site. The inhibitors bearing an aromatic ring substituted at the meta position indicate a polar interaction with lysine 227, which is specific to T. brucei PFK and is replaced by a glycine in human PFK. This lysine can be irreversibly bound, leading to inhibition when an electrophilic carbon atom is beta to the meta position on the ring. This lysine was identified by site-directed mutagenesis. This first example of a specific irreversible inactivation of T. brucei PFK offers an opportunity to develop biologically active compounds against the sleeping sickness, the causative agent of which is the trypanosome.