PubMed Health⌕ Search

Biomedical subjects

David E Williams

Publications and source records attributed to David E Williams.

At least 37 records · Page 2Linked to original sources
PubMed2005

Mammalian flavin-containing monooxygenases: structure/function, genetic polymorphisms and role in drug metabolism.

Flavin-containing monooxygenase (FMO) oxygenates drugs and xenobiotics containing a "soft-nucleophile", usually nitrogen or sulfur. FMO, like cytochrome P450 (CYP), is a monooxygenase, utilizing the reducing equivalents of NADPH to reduce 1 atom of molecular oxygen to water, while the other atom is used to oxidize the substrate. FMO and CYP also exhibit similar tissue and cellular location, molecular weight, substrate specificity, and exist as multiple enzymes under developmental control. The human FMO functional gene family is much smaller (5 families each with a single member) than CYP. FMO does not require a reductase to transfer electrons from NADPH and the catalytic cycle of the 2 monooxygenases is strikingly different. Another distinction is the lack of induction of FMOs by xenobiotics. In general, CYP is the major contributor to oxidative xenobiotic metabolism. However, FMO activity may be of significance in a number of cases and should not be overlooked. FMO and CYP have overlapping substrate specificities, but often yield distinct metabolites with potentially significant toxicological/pharmacological consequences. The physiological function(s) of FMO are poorly understood. Three of the 5 expressed human FMO genes, FMO1, FMO2 and FMO3, exhibit genetic polymorphisms. The most studied of these is FMO3 (adult human liver) in which mutant alleles contribute to the disease known as trimethylaminuria. The consequences of these FMO genetic polymorphisms in drug metabolism and human health are areas of research requiring further exploration.

Amino Acid Sequence↗
PubMed2005

Dominicin, a cyclic octapeptide, and laughine, a bromopyrrole alkaloid, isolated from the Caribbean marine sponge Eurypon laughlini.

Dominicin, a new cyclic peptide, and the new bromopyrrole alkaloid laughine (4) have been isolated from the marine sponge Eurypon laughlini collected in Dominica. The structures of 1 and 4 were determined by a combination of spectroscopic analysis and chemical degradation. Single-crystal X-ray diffraction analysis confirmed the structure of dominicin (1).

Alkaloids↗
PubMed2005

Beta-orcinol depsidones from the lichen Usnea sp. from Sri Lanka.

Two beta-orcinol depsidone lactones, the methyl ethers of menegazziaic acid and stictic acid were isolated along with glyceryl trilinolate and usnic acid from an Usnea sp. new to Sri Lanka growing on rotting trees of Acacia decurrans. Usnic acid exhibited potent antitermite activity against a common pest of tea, Glyptotermes dilatatus, at low elevations.

Animals↗
PubMed2005

Haplotype and functional analysis of four flavin-containing monooxygenase isoform 2 (FMO2) polymorphisms in Hispanics.

OBJECTIVES: Previous work defined two flavin-containing monooxygenase 2 (FMO2) alleles. The major allele, FMO2*2 (g.23,238C>T), encodes truncated inactive protein (p.X472) whereas the minor allele, FMO2*1, present in African- and Hispanic-American populations, encodes active protein (p.Q472). Recently, four common (27 to 51% incidence) FMO2 single nucleotide polymorphisms (SNPs) were detected in African-Americans (N=50); they encode the following protein variants: p.71Ddup, p.V113fs, p.S195L and p.N413 K. Our objectives were to: (1) determine the incidence of these SNPs in 29 Hispanic individuals previously genotyped as g.23,238C (p.Q472) and 124 previously genotyped as homozygous g.23,238 T (p.X472); (2) determine FMO2 haplotypes in this population; and (3) assess the functional impact of SNPs in expressed proteins. METHODS: SNPs were detected via allele-specific oligonucleotide amplification coupled with real-time or electrophoretic product detection, or single strand conformation polymorphism. RESULTS: The g.7,700_7,702dupGAC SNP (p.71Ddup) was absent. The remaining SNPs were present but, except for g.13,732C>T (p.S195L), were less common in the current Hispanic study population versus the previously described African-Americans. Only expressed p.N413 K was as active as p.Q472, as determined by methimazole- and ethylenethiourea-dependent oxidation. Haplotype determination demonstrated that the g.10,951delG (p.V113fs), g.13,732C>T (p.S195L) and g.22,060T>G (p.N413 K) variants segregated with g.23,238C>T (p.X472). CONCLUSIONS: SNPs would not alter FMO2 activity in individuals possessing at least one FMO2*1 allele. It is likely that these SNPs will segregate similarly in African-American populations. Therefore, estimates that 26% of African-Americans and 2-7% of Hispanic-Americans have at least one FMO2*1 allele should closely reflect the percentages producing active FMO2 protein.

Alleles↗
PubMed2004

A low cost instrument based on a solid state sensor for balloon-borne atmospheric O(3) profile sounding.

The design of an instrument based on a solid state tungsten oxide sensor for making profile measurements of atmospheric ozone from balloon platforms is described. The sensor is operated at a constant temperature, typically 530 [degree]C. The importance of a detailed consideration of the electronic design is demonstrated, with particular reference to the circuit to control the sensor heater. Calibration methods which are straightforward to implement are illustrated, and the results of a test flight alongside an electrochemical ozonesonde are shown. Quantitative agreement within 25% for most of the profile demonstrates the potential of this type of sensor for ozone sounding. Future improvements from manufacture to analysis are expected to improve on this.

Calibration↗
PubMed2004

Differences in FMO2*1 allelic frequency between Hispanics of Puerto Rican and Mexican descent.

A polymorphism for the phase I drug-metabolizing enzyme, flavin-containing monooxygenase isoform 2 (FMO2), encoding either truncated inactive protein, FMO2X472 (FMO2.2A), or full-length active enzyme, FMO2Q472 (FMO2.1), is known and exhibits significant interethnic differences in allelic frequency. FMO2 is the major or sole FMO isoform expressed in the lung of most mammals, including nonhuman primates. To date, FMO2.1 has been found only in African-American and Hispanic populations, rendering individuals with this allele subject to drug metabolism that is potentially different from that of the general population. Approximately 26% of African-Americans (n = 180) possess the FMO2*1 allele. In preliminary studies, we initially estimated that 5% of Hispanics (n = 40) have the FMO2*1 allele, but access to large cohorts of individuals of defined national origin has allowed us to determine the occurrence among Mexican-American and Puerto Rican-American groups. We used allele-specific genotyping to detect FMO2*1 from 632 Hispanic individuals, including 280 individuals of Mexican origin and 327 individuals of Puerto Rican origin. Statistical analysis indicated that results from Mexican (five sample sources) and Puerto Rican (three sample sources) samples were consistent with the hypothesis of homogeneity within each group from different sources. Data were subsequently pooled across sources to test for evidence of a difference in occurrence of FMO2*1 between ethnic groups. There was strong evidence (p = 0.0066) that FMO2*1 is more common among Puerto Ricans (7%) than among individuals of Mexican descent (2%). The overall occurrence of FMO2*1 among Hispanics of all origins is estimated to be between 2 and 7%.

Alleles↗
PubMed2004

S-oxygenation of the thioether organophosphate insecticides phorate and disulfoton by human lung flavin-containing monooxygenase 2.

Phorate and disulfoton are organophosphate insecticides containing three oxidizable sulfurs, including a thioether. Previous studies have shown that only the thioether is oxygenated by flavin-containing monooxygenase (FMO) and the sole product is the sulfoxide with no oxygenation to the sulfone. The major FMO in lung of most mammals, including non-human primates, is FMO2. The FMO2*2 allele, found in all Caucasians and Asians genotyped to date, codes for a truncated, non-functional, protein (FMO2.2A). Twenty-six percent of individuals of African descent and 5% of Hispanics have the FMO2*1 allele, coding for full-length, functional protein (FMO2.1). We have here demonstrated that the thioether-containing organophosphate insecticides, phorate and disulfoton, are substrates for expressed human FMO2.1 with Km of 57 and 32 microM, respectively. LC/MS confirmed the addition of oxygen and formation of a single polar metabolite for each chemical. MS/MS analysis confirmed the metabolites to be the respective sulfoxides. Co-incubations with glutathione did not reduce yield, suggesting they are not highly electrophilic. As the sulfoxide of phorate is a markedly less effective acetylcholinesterase inhibitor than the cytochrome P450 metabolites (oxon, oxon sulfoxide or oxon sulfone), humans possessing the FMO2*1 allele may be more resistant to organophosphate-mediated toxicity when pulmonary metabolism is an important route of exposure or disposition.

Animals↗
PubMed2004

Spirastrellolide A: revised structure, progress toward the relative configuration, and inhibition of protein phosphatase 2A.

[structure: see text] The structure of spirastrellolide A, a novel macrolide isolated from the marine sponge Spirastrella coccinea, has been revised to accommodate new MS and chemical transformation data. Relative configurations of three major fragments of the molecule have been elucidated from ROESY and coupling constant data. Spirastrellolide A has been shown to be a potent and fairly selective inhibitor of protein phosphatase 2A.

Animals↗
PubMed2004

Effects of chlorophyllin on transport of dibenzo(a, l)pyrene, 2-amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine, and aflatoxin B(1) across Caco-2 cell monolayers.

Chlorophyllin (CHL) is a sodium copper derivative of chlorophyll that is capable of forming strong non-covalent complexes with several known carcinogens. Antimutagenic and anticarcinogenic effects, including reduced DNA adduct and tumor formation have been demonstrated for CHL against aflatoxin B(1) (AFB(1)), dibenzo(a,l)pyrene (DBP) and 2-amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine (PhIP). Alterations in uptake and/or metabolism of planar molecules with at least partial ring structure have been proposed as mechanisms of action for CHL chemoprevention. The Caco-2 cell model of intestinal epithelial transport was used to evaluate the absorption of 1 microM DBP, AFB(1) and PhIP across cell monolayers in the presence of 0, 1, 10, and 100 microM CHL. No significant differences were observed in the permeability (P(e)) of DBP and AFB(1) from the basolateral-to-apical (BL --> AP) compared to apical-to-basolateral (AP --> BL) compartments for DBP and AFB(1), however, the P(e) of PhIP from BL --> AP, 1.26 x 10(5) +/- 2.10 x 10(6) cm/s, was significantly higher than AP --> BL, 5.83 x 10(6) +/- 7.56 x 10(7) cm/s, (P<0.001) suggesting an active efflux pathway. Transport of DBP from AP --> BL compartments was significantly reduced at all CHL concentrations (P<0.05). AP --> BL transport of AFB(1) was significantly reduced by the addition of 100 microM CHL (P<0.05) while 1 microM or 10 microM CHL had no effect. Complexation studies revealed a higher binding affinity (K(b)) for DBP to CHL compared to AFB(1) to CHL in transport buffer. AP --> BL transport of PhIP, which has a lower binding affinity for CHL than AFB(1) or DBP, was not significantly altered by the addition of CHL. These data suggest that the transport of AFB(1) and DBP can be inhibited by CHL, which supports a model of direct binding in the intestinal tract of CHL to these carcinogens with resultant reduction of bioavailability as one mechanism of action as a cancer chemopreventive agent.

Aflatoxin B1↗
PubMed2004

The tumor invasion inhibitor dihydromotuporamine C activates RHO, remodels stress fibers and focal adhesions, and stimulates sodium-proton exchange.

The motuporamines are macrocyclic alkaloids that inhibit tumor cell invasion by an, as yet, unknown mechanism. A structure-activity study recently identified dihydromotuporamine C (dhMotC) as a highly active and readily synthesized analogue. Here, we show that dhMotC causes subtle cytoskeletal alterations in highly invasive MDA231 breast tumor cells that include an increase in the thickness and number of cytoplasmic actin stress fibers. Experiments with serum-starved Swiss 3T3 fibroblasts showed that micromolar concentrations of dhMotC that inhibit tumor cell invasion induce the formation of new stress fibers and large focal adhesion complexes that are dispersed around the entire cell periphery. dhMotC treatment of Swiss 3T3 cells also initiates a strong, long-lived activation of the small GTP-binding protein Rho, and it stimulates Rho kinase-dependent sodium-proton exchanger activity. Liposome-mediated cell loading of C3 exoenzyme prevents dhMotC-mediated Rho activation and stress fiber formation in 3T3 cells. C3 exoenzyme loading also reestablishes elongated MDA231 breast tumor cell invasion in the presence of dhMotC. Taken together, these results indicate that the ability to activate Rho is one important determinant of the anti-invasive activity of dhMotC.

Alkaloids↗
PubMed2004

Human flavin-containing monooxygenase form 2 S-oxygenation: sulfenic acid formation from thioureas and oxidation of glutathione.

Thioureas are oxygenated by flavin-containing monooxygenases (FMOs), forming reactive sulfenic and/or sulfinic acids. Sulfenic acids can reversibly react with GSH and drive oxidative stress through a redox cycle. For this reason, thiourea S-oxygenation is an example of FMO-dependent bioactivation of a xenobiotic. Functional FMO2 is expressed in the lung of 26% of individuals of African descent and 5% of Hispanics but not in Caucasians or Asians. We have previously demonstrated that human FMO2.1 protein expressed in Sf9 microsomes has high activity toward a series of thioureas that are known or suspected lung toxicants including thiourea, 1-phenylthiourea, and ethylenethiourea. We now show by HPLC and LC-MS that 1-phenylthiourea and alpha-naphthylthiourea are converted to their sulfenic acids. GSH in the incubations at concentrations of 0.5-1.0 mM completely eliminated the sulfenic acid with resultant production of GSSG. These results indicate that individuals with the FMO21 allele may be at enhanced risk of pulmonary damage upon exposure to thioureas.

Chromatography, High Pressure Liquid↗
PubMed2003

Latonduines A and B, new alkaloids isolated from the marine sponge Stylissa carteri: structure elucidation, synthesis, and biogenetic implications.

[structure: see text] Latonduines A (6) and B (7), two new alkaloids with unprecedented heterocyclic skeletons, have been isolated from the Indonesian marine sponge Stylissa carteri. The structures of the latonduines were elucidated by analysis of spectroscopic data and confirmed by the total synthesis of latonduine A (6). It is proposed that ornithine is the biogenetic precursor to the aminopyrimidine fragment of the latonduines.

Alkaloids↗
PubMed2003

Spirastrellolide A, an antimitotic macrolide isolated from the Caribbean marine sponge Spirastrella coccinea.

Sprirastrellolide A, a novel antimitotic macrolide, has been isolated from the Caribbean marine sponge Spirastrella coccinea. It has a 47-carbon linear polyketide backbone incorporated into a highly functionalized 38-membered lactone containing a tetrahydropyran and two spiro bispyran substructures embedded in the macrocycle and a side chain terminating in a carboxylic acid. Sprirastrellolide A's structure was elucidated by detailed spectroscopic analysis of its methyl ester 2. Spirastrellolide A methyl ester 2 shows potent activity in a cell-based assay that detects mitotic arrest, but it does not affect tubulin polymerization in vitro. It has the unusual biological property of being able to accelerate the entry of cells into mitosis from other cell-cycle stages, before it arrests them in mitosis.

Animals↗
PubMed2003

Evaluation of chronic dietary exposure to indole-3-carbinol and absorption-enhanced 3,3'-diindolylmethane in sprague-dawley rats.

Indole-3-carbinol (I3C) and 3,3'-diindolylmethane (DIM) are naturally occurring dietary components found in cruciferous vegetables. In the stomach, I3C forms condensation products including DIM. I3C and DIM are marketed as dietary supplements, but little is known about the safety of long-term exposure. Rats were fed either control diet, 1 or 10x the current human dose of absorption-enhanced DIM or 5-7x the maximal recommended dose of I3C. Experimental diets were fed continuously for 3 or 12 months or 2 months followed by control diet for 1 month. Results at 3 or 12 months were similar in most respects. No significant differences between groups were found in blood chemistry. A general decrease in serum enzyme levels in male rats was observed, perhaps indicative of a protective effect. Males fed I3C exhibited higher serum levels of 25-hydroxy-vitamin D3 (25OH-D3). There were no observable differences grossly or histologically between groups, although a high number of hyaline casts were found throughout the kidneys of all animals. In both sexes total hepatic CYP levels were significantly induced by I3C, but not by either dose of DIM. Induction of CYP1A1 and CYP1A2 in liver and CYP1A1 in colon was detected for both sexes fed I3C and the high dose of DIM. CYP3A2 was induced in females fed I3C or the high dose of DIM; males were induced with I3C, but not DIM. No induction of CYP1B1 in the colon was observed in either sex. Long-term exposure to DIM produced no observable toxicity, and comparison to I3C indicates that DIM is a markedly less efficacious inducer of CYP in the rat at doses relevant to human supplementation.

Animals↗
PubMed2003

Electronically addressable SnO2 inverted opal gas sensors fabricated on interdigitated gold microelectrodes.

Electronically addressable thin films of tin oxide gas sensors with well-defined opaline microstructures and reproducible sensor-to-sensor responses have been fabricated on interdigitated gold microelectrodes through self-assembly growth of a monodisperse polystyrene latex film onto the electrodes followed by infiltration of tin tert-butoxide and calcination of the film.

Journal Article↗
PubMed2003

Indole-3-carbinol is a negative regulator of estrogen.

Studies increasingly indicate that dietary indole-3-carbinol (I3C) prevents the development of estrogen-enhanced cancers including breast, endometrial and cervical cancers. Epidemiological, laboratory, animal and translational studies support the efficacy of I3C. Whereas estrogen increases the growth and survival of tumors, I3C causes growth arrest and increased apoptosis and ameliorates the effects of estrogen. Our long-range goal is to best use I3C together with other nutrients to achieve maximum benefits for cancer prevention. This study examines the possibility that induction of growth arrest in response to DNA damage (GADD) in genes by diindolylmethane (DIM), which is the acid-catalyzed condensation product of I3C, promotes metabolically stressed cancer cells to undergo apoptosis. We evaluated whether genistein, which is the major isoflavonoid in soy, would alter the ability of I3C/DIM to cause apoptosis and decrease expression driven by the estrogen receptor (ER)-alpha. Expression of GADD was evaluated by real-time reverse transcription-polymerase chain reaction. Proliferation and apoptosis were measured by a mitochondrial function assay and by fluorescence-activated cell sorting analysis. The luciferase reporter assay was used to specifically evaluate expression driven by ER-alpha. The estrogen-sensitive MCF-7 breast cancer cell line was used for these studies. We show a synergistic effect of I3C and genistein for induction of GADD expression, thus increasing apoptosis, and for decrease of expression driven by ER-alpha. Because of the synergistic effect of I3C and genistein, the potential exists for prophylactic or therapeutic efficacy of lower concentrations of each phytochemical when used in combination.

Antineoplastic Agents↗