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Biomedical subjects

K Arnold

Publications and source records attributed to K Arnold.

At least 19 recordsLinked to original sources
PubMed2001

Haplotype variation and linkage disequilibrium in 313 human genes.

Variation within genes has important implications for all biological traits. We identified 3899 single nucleotide polymorphisms (SNPs) that were present within 313 genes from 82 unrelated individuals of diverse ancestry, and we organized the SNPs into 4304 different haplotypes. Each gene had several variable SNPs and haplotypes that were present in all populations, as well as a number that were population-specific. Pairs of SNPs exhibited variability in the degree of linkage disequilibrium that was a function of their location within a gene, distance from each other, population distribution, and population frequency. Haplotypes generally had more information content (heterozygosity) than did individual SNPs. Our analysis of the pattern of variation strongly supports the recent expansion of the human population.

Alleles↗
PubMed2001

Counterion condensation as saturation effect under the influence of ion hydration.

Polyelectrolyte solutions are often described by structural theories. These theories in some cases yield values for the counterion concentration at the charged monomer surface that exceed the saturation concentration. This means a change of the ion properties due to ion immobilization or ion condensation in close vicinity to the polymer chain. The extent of this counterion condensation (CIC) and the respective surface potential are calculated from the saturation concentrations of the electrolyte involved including the influence of ion hydration on the effective dielectric number. In this paper, we shall consider all these influences by a fundamental differential equation and a set of explicit formulae yielding quantitative expressions without linearization. All calculations are based on the abstraction of an idealized elementary cell.

Electrolytes↗
PubMed2001

Interaction of Zn2+ with phospholipid membranes.

To characterize the specificity of zinc binding to phospholipid membranes in terms of headgroup structure, hydration and phase behavior we studied the zwitterionic lipid 1-palmitoyl-2-oleoyl-phosphatidylcholine as a function of hydration at 30 degreesC in the presence and absence of ZnCl2. Zinc forms a 2:1-1:1 complex with the lipid, and in particular with the negatively charged phosphate groups. Zn2(+)-bridges between neighboring lipid molecules stabilize the gel phase of the lipid relative to the liquid-crystalline state. Upon Zn2+ binding the C-O-P-O-C- backbone of the lipid headgroup changes from a gauche/gauche into the trans/trans conformation and it loses roughly 50% of the hydration shell. The ability of the Zn2(+)-bound phosphate groups to take up water is distinctly reduced, meaning that the headgroups have become less hydrophilic. The energetic cost (on the scale of Gibbs free energy) for completely dehydrating the lipid headgroups is decreased by approximately 10 kJ/mole in the presence of Zn2+. The interaction of phospholipid headgroups with Zn2+ is conveniently described by a hydrated zinc-phosphate complex the key energy contribution of which is more covalent than electrostatic in nature. Dehydration of phospholipid headgroups due to complexation with zinc cations is suggested to increase fusogenic potency of lipid membranes. Zinc appears to be one of the most potent divalent cation in inducing membrane fusion.

Adsorption↗
PubMed2001

Detection of individual phospholipids in lipid mixtures by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: phosphatidylcholine prevents the detection of further species.

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry is an established tool for the analysis of proteins, whereas it gained by far less interest in the field of lipid analysis. This method works well with phospholipids as well as organic cell extracts and provides high sensitivity and reproducibility. The aim of the present paper is to extend our previous studies to the analysis of lysophospholipids and phospholipid mixtures. To study the suitability of MALDI-TOF mass spectrometry for the analysis of lysophospholipids, different phospholipids like phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidic acid, and phosphatidylinositol as well as their mixtures were digested with phospholipase A(2). Positive and negative ion mass spectra of all phospholipids before and after digestion were recorded. In all these cases, the molecular ions of the expected digestion products could be detected and only a very small extent of further fragmentation was observed. On the other hand, spectra of phospholipid mixtures containing phosphatidylcholine were strongly dominated by phosphatidylcholine and lysophosphatidylcholine signals, which prevented the detection of further phospholipids even if those lipids were present in comparable amounts. This is of paramount interest for the analysis of tissue and cell extracts.

Animals↗
PubMed2001

Hydration of polymeric components of cartilage--an infrared spectroscopic study on hyaluronic acid and chondroitin sulfate.

Hydrated polysaccharides are major constituents of cartilage and play an important role in its water-binding properties. Infrared (IR) spectroscopy and sorption isotherms have been used to investigate the hydration behavior of the glycosaminoglycans hyaluronic acid and chondroitin sulfate. IR-dichroism of the vibrational modes of the pyranose ring is found at relative humidities (RH) smaller than 84%. The IR-dichroism data for the vibrational modes of the pyranose ring have been analyzed with respect to the helical structure of these polysaccharides. The orientation vanishes at higher relative humidities (>84%), because a strong increase in the water uptake occurs in the observed sorption isotherms. Differences in the IR-absorbance of the O-H stretching mode of sorbed water between hyaluronic acid and chondroitin sulfate are shown to be caused by the additional hydration of the sulfate groups. The corresponding H-bonds are weaker than those of the hydration shell of the pyranose rings.

Cartilage↗
PubMed2001

1H and 13C HR-MAS NMR investigations on native and enzymatically digested bovine nasal cartilage.

Rheumatic diseases are accompanied by a progressive destruction of the cartilage layer of the joints. Despite the frequency of the disease, degradation mechanisms are not yet understood and methods for early diagnosis are not available. Although some information on pathogenesis could be obtained from the analysis of degradation products of cartilage supernatants, the most direct information on degradation processes would come from the native cartilage as such. We have used 1H as well as 13C HR-MAS (high resolution magic angle spinning) NMR spectroscopy to obtain suitable line-widths of NMR resonances of native cartilage. 1D and 2D NMR spectra of native cartilage were compared with those of enzymatically-treated (collagenase and papain) samples. In the 1H NMR spectra of native cartilage, resonances of polysaccharides, lipids and a few amino acids of collagen were detectable, whereas the 13C NMR spectra primarily indicated the presence of chondroitin sulfate. Treatment with papain resulted only in small changes in the 1H NMR spectrum, whereas a clear diminution of all resonances was detectable in the 13C NMR spectra. On the other hand, treatment with collagenase caused the formation of peptides with an amino acid composition typical for collagen (glycine, proline, hydroxyproline and lysine). It is concluded that the HR-MAS NMR spectra of cartilage may be of significance for the investigation of cartilage degradation since they allow the fast evaluation of cartilage composition and only very small amounts of sample are required.

Animals↗
PubMed2001

Dynamics of membrane penetration of the fluorescent 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) group attached to an acyl chain of phosphatidylcholine.

Location and dynamic reorientation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) covalently attached to a short (C6) or a long (C12) sn2 acyl chain of a phosphatidylcholine molecule was investigated by fluorescence and solid-state NMR spectroscopy. 2H NMR lipid chain order parameters indicate a perturbation of the phospholipid packing density in the presence of NBD. Specifically, a decrease of molecular order was found for acyl chain segments of the lower, more hydrophobic region. Molecular collision probabilities determined by 1H magic angle spinning nuclear Overhauser enhancement spectroscopy indicate a highly dynamic reorientation of the probe in the membrane due to thermal fluctuations. A broad distribution of the fluorophore in the lipid bilayer is observed with a preferential location in the upper acyl chain/glycerol region. The distribution of the NBD group in the membrane is quite similar for both the long- and the short-chain analog. However, a slight preference of the NBD group for the lipid-water interface is found for C12-NBD-PC in comparison with C6-NBD-PC. Indeed, as shown by dithionite fluorescence assay, the long-chain analog reacts more favorably with dithionite, indicating a better accessibility of the probe by dithionite present in the aqueous phase. Forces determining the location of the fluorophore in the lipid water interface are discussed.

4-Chloro-7-nitrobenzofurazan↗
PubMed2001

Limits for the detection of (poly-)phosphoinositides by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS).

Matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been recently established as a powerful tool for the analysis of biomolecules. Here, MALDI-TOF MS was used for the detection of (poly-)phosphoinositides (PPI). PPI possess higher molecular weights than other phospholipids and a high phosphorylation-dependent negative charge. Both features affect the MALDI detection limits expressed as the minimum of analyte on the sample plate resulting in a signal-to-noise-ratio of S/N = 5. Using 2,5-dihydroxybenzoic acid (DHB) as matrix the detection limit for phosphatidylinositol (PI) is seven times higher than for phosphatidylcholine (PC) and further increases with increasing phosphorylation or in mixtures with other well-detectable phospholipids. For phosphatidylinositol-tris-phosphate (PIP3) in a mixture with PC, the limit is about 20 times higher than for PI. The consequences for the experimental conditions are discussed. It is advisable to pre-separate PPI from biological lipid mixtures prior to the application of MALDI-TOF MS.

Phosphatidylinositol Phosphates↗
PubMed2001

Needle fixation, the drug user's perspective: a qualitative study.

AIMS: Changing drug users' injecting behaviour is central to the project of drug services. Information about the idea of "needle fixation" is fragmentary and of uncertain relevance to contemporary injecting drug users. The aim of the study is to describe injecting drug users' ideas about needle fixation. PARTICIPANTS AND DESIGN: Twenty-four participants, some of whom identified themselves as needle fixated, were recruited from four drugs agencies in south Wales. Participants took part in semi-structured interviews, recorded, transcribed and qualitatively analysed using Atlas/ti software. FINDINGS: Participants describe a range of behaviours and experiences which fit with previous ideas of needle fixation, including ritualization, substitution of other drugs, injection of water and associations with deliberate-self-harm and sex. Participants describe high levels of needle aversion and add detail to previous partial descriptions of needle fixation. CONCLUSIONS: Issues conveniently considered together as needle fixation are current among injecting drug users and may be relevant to the inability of some drug users to change from injecting drug use.

Adult↗
PubMed2001

Educational program for physicians to reduce use of non-steroidal anti-inflammatory drugs among community-dwelling elderly persons: a randomized controlled trial.

CONTEXT: Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most frequently prescribed drugs for patients 65 years of age or older, primarily for musculoskeletal symptoms of osteoarthritis. Because NSAIDs frequently cause serious gastrointestinal (GI) and other complications among elderly patients, expert guidelines for osteoarthritis recommend acetaminophen-based regimens, which are safer and often as effective as NSAIDs. OBJECTIVE: Evaluate a physician education program that communicated guidelines for management of osteoarthritis in elderly patients that emphasized avoidance of NSAIDs when possible. The program reviewed NSAID risks and benefits and recommended: re-evaluating continuous NSAID users, considering substitution of up to 4 g/d of acetaminophen for the NSAID, and trying topical agents and nonpharmacologic measures. DESIGN AND SETTING: Randomized controlled trial among community-dwelling Tennessee Medicaid enrollees. SUBJECTS: Study physicians had 5 or more patients who: were community-dwelling Medicaid enrollees 65 years of age or older; had used NSAIDs regularly for at least 180 days; had had no medical care encounters during this period suggesting an indication other than osteoarthritis; and had 1 year of baseline and follow-up data. The study thus included 209 physicians (103 intervention/106 control) with 1,566 qualifying regular NSAID users (768/798). INTERVENTIONS: Face-to-face visit to study physicians by another physician, and reminder placements in the charts of patients eligible to have NSAID use reevaluated. OUTCOMES: Change between baseline and follow-up years in: days of prescribed NSAIDs, acetaminophen, other drugs for musculoskeletal disorders, and GI drugs; outpatient visits and inpatient days of stay; SF36 measures of general health, physical function, and bodily pain (from 40% random patient sample); and over-the-counter NSAIDs (from the sample). RESULTS: Intervention-attributable reduction of 7% (95% CI, 3% to 11%) in days of prescribed NSAIDs use with concomitant increase in acetaminophen use. No significant changes in other study endpoints. The intervention effect was greater among 75 physicians with a completed study visit, whose 564 patients had a 10% (95% CI, 6% to 14%) attributable reduction in NSAID use. CONCLUSIONS: The educational program modestly reduced NSAID exposure in community-dwelling elderly patients without undesirable substitution of other medications or detectable worsening of musculoskeletal symptoms.

Acetaminophen↗
PubMed2001

Experimental hypercholesterolemia induces apoptosis in the aortic valve.

BACKGROUND AND AIM OF THE STUDY: Aortic valve disease is presently the number one indication for valve replacement in the United States, yet its molecular mechanisms remain unknown. As apoptosis (programmed cell death) occurs in degenerative disease states, it was postulated that experimental hypercholesterolemia is associated with apoptosis in rabbit aortic valves. METHODS: New Zealand White rabbits (n = 8) were fed a 1% cholesterol diet for 12 weeks; control rabbits (n = 8) were fed a normal diet. After sacrifice of the animals, the aortic valves were dissected. Apoptosis was identified in the valvular lesion by TdT-mediated dUTP-biotin nick end-labeling (TUNEL) technique, and confirmed with transmission electron microscopy. The number of apoptotic cells was measured by computed morphometry. RESULTS: Valves from hypercholesterolemic rabbits showed an increase in apoptosis. TUNEL staining was identified in the atherosclerotic layer of hypercholesterolemic valves (0.1% of cells), but not in the cells of controls (p <0.0001). CONCLUSION: Apoptosis is increased in rabbit aortic valves during experimental hypercholesterolemia. If fatal cellular degeneration occurs in hypercholesterolemic valve disease, these data suggest that apoptosis may play a role in the mechanism of valvular disease.

Animals↗
PubMed2000

The effect of Zn(2+) on the secondary structure of a histidine-rich fusogenic peptide and its interaction with lipid membranes.

Membrane fusion between uncharged lipid vesicles can be triggered by the peptide sequence 'B18' from the fertilization protein 'bindin', but it only proceeds efficiently in the presence of Zn(2+) ions. We studied (i) the interaction of Zn(2+) with the fusogenic peptide B18, (ii) the binding of B18 to 1-palmitoyl-2-oleoylglycero-3-phosphocholine (POPC), and (iii) the ternary system POPC/B18/Zn(2+). The complex formation of Zn(2+) with the central histidine-rich motif of B18 appears to shift the secondary structure away from a beta-sheet towards an alpha-helical conformation. Here we observe for the first time an essentially alpha-helical structure of the peptide when immersed in POPC bilayers which appears to represent its functional fusogenic state. Infrared linear dichroism suggests a peripheral, oblique insertion mode of B18, mediated by the hydrophobic patches along one side of the amphipathic peptide. Furthermore, the hydration level of the peptide is reduced, suggesting that the hydrophobic region of the bilayer is involved in the lipid/peptide interactions. The hydration capacity of the POPC/B18/Zn(2+) system is distinctly smaller than that of POPC/Zn(2+) without peptide. The accompanying decrease in the number of tightly bound water molecules per lipid can be interpreted as a reduction in the repulsive 'hydration' forces, which usually prevent the spontaneous fusion of lipid vesicles. Binding of the B18 peptide in the presence of Zn(2+) effectively renders the membrane surface more hydrophobic, thus allowing fusion to proceed.

Amino Acid Sequence↗
PubMed2000

Complex promoter and coding region beta 2-adrenergic receptor haplotypes alter receptor expression and predict in vivo responsiveness.

The human beta(2)-adrenergic receptor gene has multiple single-nucleotide polymorphisms (SNPs), but the relevance of chromosomally phased SNPs (haplotypes) is not known. The phylogeny and the in vitro and in vivo consequences of variations in the 5' upstream and ORF were delineated in a multiethnic reference population and an asthmatic cohort. Thirteen SNPs were found organized into 12 haplotypes out of the theoretically possible 8,192 combinations. Deep divergence in the distribution of some haplotypes was noted in Caucasian, African-American, Asian, and Hispanic-Latino ethnic groups with >20-fold differences among the frequencies of the four major haplotypes. The relevance of the five most common beta(2)-adrenergic receptor haplotype pairs was determined in vivo by assessing the bronchodilator response to beta agonist in asthmatics. Mean responses by haplotype pair varied by >2-fold, and response was significantly related to the haplotype pair (P = 0.007) but not to individual SNPs. Expression vectors representing two of the haplotypes differing at eight of the SNP loci and associated with divergent in vivo responsiveness to agonist were used to transfect HEK293 cells. beta(2)-adrenergic receptor mRNA levels and receptor density in cells transfected with the haplotype associated with the greater physiologic response were approximately 50% greater than those transfected with the lower response haplotype. The results indicate that the unique interactions of multiple SNPs within a haplotype ultimately can affect biologic and therapeutic phenotype and that individual SNPs may have poor predictive power as pharmacogenetic loci.

Base Sequence↗
PubMed2000

13C NMR relaxation studies on cartilage and cartilage components.

We have investigated the molecular motions of polysaccharides of bovine nasal and pig articular cartilage by measuring the 13C NMR relaxation times (T1 and T2). Both types of cartilage differ significantly towards their collagen/glycosaminoglycan ratio, leading to different NMR spectra. As chondroitin sulfate is the main constituent of cartilage, aqueous solutions of related poly- and monosaccharides (N-acetylglucosamine and glucuronic acid) were also investigated. Although there are only slight differences in T1 relaxation of the mono- and the polysaccharides, T2 decreases about one order of magnitude, when glucuronic acid or N-acetylglucosamine and chondroitin sulfate are compared. It is concluded that the ring carbons are motion-restricted primarily by the embedment in the rigid pyranose structure and, thus, additional limitations of mobility do not more show a major effect. Significant differences were observed between bovine nasal and pig articular cartilage, resulting in a considerable line-broadening and a lower signal to noise ratio in the spectra of pig articular cartilage. This is most likely caused by the higher collagen content of articular cartilage in comparison to the polysaccharide-rich bovine nasal cartilage.

Acetylglucosamine↗