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David E Williams

Publications and source records attributed to David E Williams.

47 records · Page 3Linked to original sources
PubMed2003

Biochemical and clinical aspects of the human flavin-containing monooxygenase form 3 (FMO3) related to trimethylaminuria.

Trimethylaminuria is a rare metabolic disorder that is associated with abnormal amounts of the dietary-derived trimethylamine. Excess unmetabolized trimethylamine in the urine, sweat and other body secretions confers a strong, foul body odor that can affect the individual's ability to work or engage in social activities. This review summarizes the biochemical aspects of the condition and the classification of the disorder into: 1) primary genetic form, 2) acquired form, 3) childhood forms, 4) transient form associated with menstruation, 5) precursor overload and 6) disease states. The genetic variability of the flavin-containing monooxygenase (form 3) that is responsible for detoxication and deodoration of trimethylamine is discussed and put in context with other variant forms of the flavin-containing monooxygenase (forms 1-5). The temporal-selective expression of flavin-containing monooxygenase forms 1 and 3 is discussed in terms of an explanation for childhood trimethylaminuria. Information as to whether variants of the flavin-containing monooxygenase form 3 contributes to hypertension and/or other diseases are presented. Discussion is provided outlining recent bioanalytical approaches to quantify urinary trimethylamine and trimethylamine N-oxide and plasma choline as well as data on self-reporting individuals tested for trimethylaminuria. Finally, trimethylaminuria treatment strategies and nutritional support are described including dietary sources of trimethylamine, vitamin supplementation and drug treatment and issues related to trimethylaminuria in pregnancy and lactation are discussed. The remarkable progress in the biochemical, genetic, clinical basis for understanding the trimethylaminuria condition is summarized and points to needs in the treatment of individuals suffering from trimethylaminuria.

Animals↗
PubMed2002

Developmental regulation of flavin-containing monooxygenase form 1 in the liver and kidney of fetal and neonatal rabbits.

Flavin-containing monooxygenases (FMOs) comprise a multi-gene family and catalyze the oxygenation of soft nucleophilic sulfur, nitrogen, phosphorus, and selenium in xenobiotics. Previous studies have demonstrated that FMO is regulated developmentally and by the administration of certain steroid hormones. This study examined the expression of FMO form 1 in the livers and kidneys of fetal and neonatal rabbits, from day 25 of gestation through 3 weeks of age, by assaying FMO1 mRNA and protein levels, as well as catalytic activity. FMO1 mRNA and protein expression and FMO catalytic activity were present in fetal livers at the earliest time point measured (day 25 of gestation), although at levels approximately 10% of that found in adult livers. Hepatic FMO1 mRNA levels increased during and after gestation; levels were not significantly different from those measured in adult male livers. FMO1 protein content and activity rose rapidly after birth to reach 70-80% of adult levels by 3 weeks of age. The expression of FMO1 in fetal and neonatal kidneys was markedly lower than in liver. FMO1 mRNA levels never averaged more than 3.4% of adult male liver levels, but did not differ from adult kidney levels at any of the points measured. Protein levels and enzyme activity rose significantly after birth to approximately 30% of the level in adult kidneys by 3 weeks of age. The early developmental appearance of FMO1 suggests a possible role in the metabolism of xenobiotics through transplacental or lactational exposures.

Animals↗
PubMed2002

The FMO2 gene of laboratory rats, as in most humans, encodes a truncated protein.

We describe the isolation and characterization of cDNAs for FMO2 from the laboratory rat. In contrast to FMO2 in other animals, each of which contain 535 amino acid residues, analysis of the sequence of the cDNAs and of a section of the corresponding gene revealed that the ORF of the laboratory rat FMO2 encodes a polypeptide of only 432 residues. This truncated protein is due to the presence of a double deletion corresponding to 1263 and 1264 nucleotides of the orthologous FMO2 cDNAs. This double deletion provokes a frame-shift, with the appearance of a premature stop codon in position 1297-1299. By Northern blotting, the probe for FMO2 hybridized a 2.5-kb transcript in lung and kidney samples only. Heterologous expression of the cDNA revealed that the truncated protein was catalytically inactive. By Western blotting, FMO2 was faintly detected at approximately 50 kDa in laboratory rat lung.

Amino Acid Sequence↗
PubMed2002

Why stainless steel corrodes.

Stainless steels are used in countless diverse applications for their corrosion resistance. Although they have extremely good general resistance, they are nevertheless susceptible to pitting corrosion. This localized dissolution of an oxide-covered metal in specific aggressive environments is one of the most common and catastrophic causes of failure of metallic structures. The pitting process has been described as random, sporadic and stochastic and the prediction of the time and location of events remains extremely difficult. Many contested models of pitting corrosion exist, but one undisputed aspect is that manganese sulphide inclusions play a critical role. Indeed, the vast majority of pitting events are found to occur at, or adjacent to, such second-phase particles. Chemical changes in and around sulphide inclusions have been postulated as a mechanism for pit initiation but such variations have never been measured. Here we use nanometre-scale secondary ion mass spectroscopy to demonstrate a significant reduction in the Cr:Fe ratio of the steel matrix around MnS particles. These chromium-depleted zones are susceptible to high-rate dissolution that 'triggers' pitting. The implications of these results are that materials processing conditions control the likelihood of corrosion failures, and these data provide a basis for optimizing such conditions.

Journal Article↗
PubMed2002

Motuporamines, anti-invasion and anti-angiogenic alkaloids from the marine sponge Xestospongia exigua (Kirkpatrick): isolation, structure elucidation, analogue synthesis, and conformational analysis.

Extracts of the sponge Xestospongia exigua collected in Papua New Guinea were positive in a new assay for anti-invasion activity. Bioassay-guided fractionation led to the identification of the three known motuporamines A (1), B (2), and C (3) along with the new motuporamines D (4), E (5), and F (6) and a mixture of G, H, and I (15). Motuporamines A (1), B (2), and C (3) and the mixture of G, H, and I (15) were responsible for the anti-invasion activity of the crude extract. Motuporamine C (3) has also been found to be anti-angiogenic. A series of analogues of the motuporamines have been synthesized and evaluated for anti-invasive activity. These SAR results revealed that a saturated 15-membered cyclic amine fused to the natural motuporamine diamine side chain (13) represented the optimal structure for anti-invasive activity in this family. Single-crystal X-ray diffraction analysis of one of the analogues 20 showed that in the solid state its 16-membered macrocyclic amine fragment adopted the [4444] quadrangular conformation predicted by calculations to be the lowest energy conformation for the corresponding cycloalkane, cyclohexadecane. These data along with literature X-ray data and conformational analysis for derivatives of azacyclotridecane have been used as precedents for predicting the lowest energy ring conformations of other motuporamines. The SAR data from the natural and synthetic motuporamines have been combined with the conformational analyses to provide an outline of the functionality and shape required for activity in this family of alkaloids and to design a new analogue 49 that showed good anti-invasion activity.

Alkaloids↗
PubMed2002

Genetic polymorphisms of flavin-containing monooxygenase (FMO).

Mammalian flavin-containing monooxygenase (FMO) exists as six gene families and metabolizes a plethora of drugs and xenobiotics. The major FMO in adult human liver, FMO3, is responsible for trimethylamine (TMA) N-oxygenation. A number of FMO3 mutant alleles have been described and associated with a disease termed trimethylaminuria (TMAU). The TMAU patient excretes large amounts of TMA in urine and sweat. A more recent ethnically related polymorphism in expression of the major FMO in lung, FMO2, has been described. All Caucasians and Asians genotyped to date are homozygous for a CAG --> TAG amber mutation resulting in a premature stop codon and a nonfunctional protein truncated at AA 472 (wildtype FMO2 is 535 AA). This allele has been designated hFMO2*2A. Twenty-six percent of individuals of African descent and 5% of Hispanics genotyped to date carry at least one allele coding for full-length FMO2 (hFMO2*1 allele). Preliminary evidence indicates that FMO2.1 is very active toward the S-oxygenation of low MW thioureas, including the lung toxicant ethylene thiourea. Polymorphic expression of functional FMO2 in the individuals of African and Hispanic descent may markedly influence drug metabolism and/or xenobiotic toxicity in the lung.

Animals↗
PubMed2002

Identification of active flavin-containing monooxygenase isoform 2 in human lung and characterization of expressed protein.

Full-length human (hFMO2.1) and monkey (mFMO2) flavin-containing monooxygenase proteins, which share 97% sequence identity, were produced by baculovirus-mediated expression in insect cells and assayed for S-oxygenation under conditions known to affect FMO activity. Both enzymes demonstrated maximal activity at pH 9.5; but hFMO2.1 retained significantly more activity than mFMO2 did at pH 9.0 and higher. hFMO2.1 also retained significantly more activity than mFMO2 did in the presence of magnesium and all detergents tested. Although hFMO2.1 had more residual activity after heating at 45 degrees C than mFMO2, under some conditions, both had less than 10% of control activity, whereas expressed rabbit FMO2 retained over 50% activity. Screening for NADPH-oxygenation by hFMO2.1, indicated that substituted thioureas with a small cross-sectional area (2.4-4.3 A) are good substrates, whereas 1,3-diphenylthiourea (11.2 A) was not oxygenated. We confirmed the presence of hFMO2.1 in lung tissue from a heterozygous individual (hFMO2*1/hFMO2*2A) by Western analysis and confirmed activity by S-oxygenation. These microsomes also demonstrated a heat-associated loss of activity similar to expressed hFMO2.1. The heat sensitivity of hFMO2.1 may partially explain why activity in post mortem human lung samples has previously been unreported. Individuals that have the FMO2*1 allele-encoding full-length hFMO2.1 may exhibit altered drug metabolism in the lung.

Animals↗
PubMed2002

Behavioral and neurological correlates of ALS-parkinsonism dementia complex in adult mice fed washed cycad flour.

Consumption of cycad seed products (Cycas circinalis) is one of the strongest epidemiological links to the Guamian neurological disorder amyotrophic lateral sclerosis-parkinsonism-dementia complex (ALS-PDC), however, the putative toxin which causes neurodegeneration has never been identified definitively. To reexamine this issue, 6-7-mo-old, male CD-1 mice were assessed for motor and cognitive behaviours during and following feeding with pellets made from washed cycad flour. Cycad-fed animals showed early evidence of progressive motor and cognitive dysfunctions. Neurodegeneration measured using TUNEL and caspase-3 labeling was found in neocortex, various hippocampal fields, substantia nigra, olfactory bulb, and spinal cord. In vitro studies using rat neocortex have identified toxic compounds in washed cycad flour that induce depolarizing field potentials and lead to release of lactate dehydrogenase (LDH), both blocked by AP5. High-performance liquid chromatography (HPLC)/mass spectrometry of cycad flour samples failed to show appreciable amounts of other known cycad toxins, cycasin, MAM, or BMAA; only trace amounts of BOAA were present. Isolation procedures employing these techniques identified the most toxic component as beta-sitosterol beta-D-glucoside (BSSG). The present data suggest that a neurotoxin, or a toxic metabolite, not previously identified in cycad, is able to gain access to central nervous system (CNS) resulting in neurodegeneration of specific neural populations and in motor and cognitive dysfunctions. These data are consistent with a number of major features of ALS-PDC in humans.

Amyotrophic Lateral Sclerosis↗
PubMedDate not supplied

Design and synthesis of ferrocene probe molecules for detection by electrochemical methods.

A series of ferrocenyl conjugates to fatty acids have been designed and synthesized to establish the key properties required for use in biomolecular binding studies. Amperometric detection of the ferrocene conjugates was sought in the region of 0.3 V (vs Ag/AgCl) for use in protein/blood solutions. Different linkers and solubilizing moieties were incorporated to produce a conjugate with optimal electrochemical properties. In electrochemical studies, the linker directly attached to the ferrocene was found to affect significantly the E(1/2) value and the stability of the ferrocenium cation. Ester-linked ferrocene conjugates had E(1/2) ranging from +400 to +410 mV, while amide-linked compounds ranged from +350 to +370 mV and the amines +260 to +270 mV. Folding of long-chain substituents around the ferrocene, also significantly affected by the choice of linker, was inferred as a secondary effect that increased E(1/2). The stability of the ferrocenium cation decreased systematically as E(1/2) increased. Disubstituted ferrocene ester and amide conjugates, with oxidation potentials of +640 and +570 mV, respectively, showed only a barely discernible reduction wave in cyclic voltammetry at 50 mV/s. Electrochemical measurements identified two lead compounds with the common structural characteristics of an amide and carbamate linker (compounds 17 and 21) with a C(11) fatty acid chain attached. It is envisaged that such molecules can be used to mimic and study the biomolecular binding interaction between fatty acids and molecules such as human serum albumin.

Electrochemistry↗
PubMedDate not supplied

Applications of tailored ferrocenyl molecules as electrochemical probes of biochemical interactions.

The development of electrochemical probes useful for investigating the occupancy by other molecules of sites on complex proteins such as human serum albumin (HSA) is described. Ferrocenyl-(oxoethylene)-fatty acid compounds of different fatty acid chain length probed different binding sites on HSA. The interaction could be changed from one primarily with a drug binding site, when the probe was ferrocene methanol, to one predominantly with medium-chain fatty acid binding sites, by adding an (oxoethylene)-fatty acid substituents. Finally, the interaction could be changed to one interacting primarily with high-affinity long-chain fatty acid binding sites, as the fatty acid chain length in ferrocene-(oxoethylene)-fatty acid molecules increased. These results strongly implied that the binding could be further tailored by relatively simple modifications to the probe, for example, by changing the balance of hydrophobicity and hydrophilicity. The possibility of a procedure using mass-produced electrochemical cells to determine the fractional occupancy of different sites on HSA is demonstrated.

Biochemical Phenomena↗