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Biomedical subjects

David Phillips

Publications and source records attributed to David Phillips.

At least 19 recordsLinked to original sources
PubMed2006

Microclusters of inhibitory killer immunoglobulin-like receptor signaling at natural killer cell immunological synapses.

We report the supramolecular organization of killer Ig-like receptor (KIR) phosphorylation using a technique applicable to imaging phosphorylation of any green fluorescent protein-tagged receptor at an intercellular contact or immune synapse. Specifically, we use fluorescence lifetime imaging (FLIM) to report Förster resonance energy transfer (FRET) between GFP-tagged KIR2DL1 and a Cy3-tagged generic anti-phosphotyrosine monoclonal antibody. Visualization of KIR phosphorylation in natural killer (NK) cells contacting target cells expressing cognate major histocompatibility complex class I proteins revealed that inhibitory signaling is spatially restricted to the immune synapse. This explains how NK cells respond appropriately when simultaneously surveying susceptible and resistant target cells. More surprising, phosphorylated KIR was confined to microclusters within the aggregate of KIR, contrary to an expected homogeneous distribution of KIR signaling across the immune synapse. Also, yellow fluorescent protein-tagged Lck, a kinase important for KIR phosphorylation, accumulated in a multifocal distribution at inhibitory synapses. Spatial confinement of receptor phosphorylation within the immune synapse may be critical to how activating and inhibitory signals are integrated in NK cells.

Cell Line↗
PubMed2006

Solution conformation of longifolene and its precursor by NMR and ab initio calculations.

We describe the conformation and stereospecific 1H and 13C chemical shift assignments of longifolene 1 and its penultimate precursor 2 through the combined use of ab initio calculations and experimental NMR techniques. The predicted stable conformation for both compounds was similar and adopts a twisted chair conformation at the seven-membered ring where C4 lies on top of the exocyclic double bond. The calculated chemical shifts for the stable conformation agree well with the experimental values.

Carbon Isotopes↗
PubMed2006

A national survey of the microbiological quality of beef carcasses and frozen boneless beef in Australia.

The third national baseline microbiological survey of Australian beef carcasses and frozen boneless beef was conducted in 2004. Carcasses (n=1155) sampled at 27 slaughter establishments had a mean aerobic plate count (at 25 degrees C) of 1.3 log CFU/cm2. Escherichia coli was isolated from 8.0% of the cacasses, with a mean count of -0.8 log CFU/cm2 for positive samples. On samples from 24 boning (fabrication) plants (n=1082), the mean aerobic plate count for frozen boneless beef was 1.3 log CFU/g, and the mean count for the 1.8% of samples with detectable E. coli was 1.5 log CFU/g. E. coli O157: H7 was isolated from 1 of 1,143 carcasses and from 0 of 1082 boneless samples. Salmonella was isolated from 0 of 1155 carcasses and from 1 of 1082 samples of boneless product. No Campylobacter spp. were isolated from carcasses or boneless beef. Coagulase-positive staphylococci were isolated from 28.7% of beef carcasses and 20.3% of boneless beef samples, and positive samples had a mean count of 0.3 log CFU/cm2 and 0.8 log CFU/g, respectively.

Animals↗
PubMed2006

Aortic stenosis: A review.

The prevalence of aortic stenosis has been increasing in recent decades, and nurse anesthetists are more likely to encounter this problem as the population ages. Fortunately, the widespread use of echocardiography has expanded our understanding of valvular heart disease. The purpose of this course is to evaluate the current literature regarding aortic stenosis with a focus on anesthetic management. The 2 most common causes of aortic stenosis are calcific tricuspid disease and congenital bicuspid valves. An inflammatory, atherosclerotic disease process also has been identified in aortic stenosis. Patients with aortic stenosis are at high risk for perioperative cardiac complications. Anesthetic management often includes invasive hemodynamic monitoring and carefully tailored anesthetic techniques.

Anesthesia↗
PubMed2005

Ethnic differences in nicotine metabolic rate among New Zealanders.

AIMS: To estimate (a) the prevalence of gene variants associated with slow nicotine metabolism in the general Maori population and (b) nicotine intake and metabolic rate in Maori and European smokers. METHODS: The procedure involved (a) genotyping 85 Maori participants for cytochrome P-450 2A6 (CYP2A6) gene variants, which are associated with reduced nicotine metabolic rate (ie CYP2A6*9 and *4); and (b) measuring salivary cotinine (COT) and trans-3'-hydroxycotinine (3-HC) as biomarkers of nicotine intake and metabolic rate in 12 female smokers from the Hawke's Bay Region (6 Maori and 6 European). RESULTS: (a) The frequencies of the slow nicotine metabolising variants, CYP2A6*9 and *4, were significantly higher in Maori compared to European (p<0.01). Indeed, the prevalence of the CYP2A6*9 variant in these Maori was among the highest in the world (approximately 20%). (b) In smokers, the Maori group had approximately 35% lower 3-HC:COT ratios indicating a reduced metabolic rate, as well as 2-fold lower cotinine levels per cigarette smoked, indicating reduced nicotine intake (p<0.05). The CYP2A6*9 allele was significantly more frequent in Maori smokers (70%) compared to Europeans (30%), p=0.03. CONCLUSIONS: The findings of this study provide evidence that Maori are genetically slower nicotine metabolisers compared to Europeans. Although more research is required, this study may help explain ethnic differences in smoking initiation and may also have important implications for smoking cessation programs - since metabolic differences between groups with varying ancestry implies that different optimal dosages of nicotine replacement therapy may be required for successful quitting.

Aryl Hydrocarbon Hydroxylases↗
PubMed2005

Deaths from poisoning in New Zealand: 2001-2002.

AIMS: To describe the epidemiology and toxicology of poisoning deaths in New Zealand for 2001 and 2002. METHODS: Poisoning mortality data for 2001 and 2002 were collected from the Coronial Service Office (CSO) as part of the New Zealand chemical injury surveillance system. RESULTS: There was 235 and 234 poisoning deaths in 2001 and 2002 respectively, an annual rate of 6.3 [95% CI of 5.5 to 7.1] deaths per 100,000 population for both years. Two-thirds (67.0%) of the deaths were intentional. The 25-44 year age group had the largest number of cases and highest age-specific rate (123 deaths, 11.1 [95% CI: 9.3-13.2] per 100,000 in 2001 and 119 deaths, 10.7 [(95% CI: 9.0-12.8] per 100,000 in 2002). Over two-thirds (68.9%) of the deaths were male. In 2001, the European rate was slightly higher than that for Maori but rates for the two ethnicities were similar in 2002. Geographically, West Coast District Health Board (DHB) had the highest rates. Rates increased with increasing deprivation. Nearly two-thirds (64.3%) of the intentional deaths were attributed to carbon monoxide. Methadone, morphine or heroin, and ethanol were the leading causes of the unintentional deaths. CONCLUSIONS: The rate of poisoning deaths in New Zealand is comparable with other industrial countries as is the prominence of poisoning as a leading method of suicide.

Adolescent↗
PubMed2005

ROM polymerization-capture-release strategy for the chromatography-free synthesis of novel unsymmetrical porphyrazines.

[reaction: see text] Crossover-Linstead macrocyclization reactions of two norbornenyl-tagged diaminomaleonitriles with dipropylmaleonitrile gave access to crude mixtures of porphyrazines containing diamino-hexapropyl-porphyrazine magnesium complexes. The mixtures were subjected to ring-opening metathesis polymerization to yield the insoluble diaminoporphyrazine-functionalized polymers. Acid-mediated cleavage from the polymer backbone followed by acylation of the resultant sensitive macrocyclic diamines gave monoacetyl-, monotrifluoroacetyl-, and ditrifluoroacetyl-substituted porphyrazinediamines. Conversion of these amido-porphyrazines to the corresponding zinc macrocycles and studies of their electronic absorption and emission spectra, electrochemistry, and photophysics are described.

Journal Article↗
PubMed2004

Time-resolved fluorescence microscopy.

In fluorescence microscopy, the fluorescence emission can be characterised not only by intensity and position, but also by lifetime, polarization and wavelength. Fluorescence lifetime imaging (FLIM) can report on photophysical events that are difficult or impossible to observe by fluorescence intensity imaging, and time-resolved fluorescence anisotropy imaging (TR-FAIM) can measure the rotational mobility of a fluorophore in its environment. We compare different FLIM methods: a chief advantage of wide-field time-gating and phase modulation methods is the speed of acquisition whereas for time-correlated single photon counting (TCSPC) based confocal scanning it is accuracy in the fluorescence decay. FLIM has been used to image interactions between proteins such as receptor oligomerisation and to reveal protein phosphorylation by detecting fluorescence resonance energy transfer (FRET). In addition, FLIM can also probe the local environment of fluorophores, reporting, for example, on the local pH, refractive index, ion or oxygen concentration without the need for ratiometric measurements.

Fluorescence Polarization↗
PubMed2004

Time-domain fluorescence lifetime imaging applied to biological tissue.

Fluorescence lifetime imaging (FLIM) is a functional imaging methodology that can provide information, not only concerning the localisation of specific fluorophores, but also about the local fluorophore environment. It may be implemented in scanning confocal or multi-photon microscopes, or in wide-field microscopes and endoscopes. When applied to tissue autofluorescence, it reveals intrinsic excellent contrast between different types and states of tissue. This article aims to review our recent progress in developing time-domain FLIM technology for microscopy and endoscopy and applying it to biological tissue.

Animals↗
PubMed2004

Time-resolved fluorescence anisotropy imaging applied to live cells.

We have developed a wide-field time-resolved imaging system to image quantitatively both the fluorescence lifetime and the rotational correlation time of a fluorophore. Using a polarization-resolved imager, we simultaneously image orthogonal polarization components of the fluorescence emission onto a time-gated intensified CCD. We demonstrate imaging of solvent viscosity variations through the rotational correlation time of fluorescein in a multiwell plate and apply this technique to probe the microviscosity in live cells.

3T3 Cells↗
PubMed2003

Platelet and osteoclast beta3 integrins are critical for bone metastasis.

Mice with a targeted deletion of beta3 integrin were used to examine the process by which tumor cells metastasize and destroy bone. Injection of B16 melanoma cells into the left cardiac ventricle resulted in osteolytic bone metastasis in 74% of beta3+/+ mice by 14 days. In contrast, only 4% of beta3-/- mice developed bone lesions. Direct intratibial inoculation of tumor resulted in marrow replacement by tumor in beta3-/- mice, but no associated trabecular bone resorption as seen inbeta3+/+ mice. Bone marrow transplantation studies showed that susceptibility to bone metastasis was conferred by a bone marrow-derived cell. To dissect the roles of osteoclast and platelet beta3 integrins in this model of bone metastasis, osteoclast-defective src-/- mice were used. Src-null mice were protected from tumor-associated bone destruction but were not protected from tumor cell metastasis to bone. In contrast, a highly specific platelet aggregation inhibitor of activated alphaIIbbeta3 prevented B16 metastases. These data demonstrate a critical role for platelet alphaIIbbeta3 in tumor entry into bone and suggest a mechanism by which antiplatelet therapy may be beneficial in preventing the metastasis of solid tumors.

Animals↗
PubMed2003

Synthesis and reactions of aminoporphyrazines with annulated five- and seven-membered rings.

The novel five- and seven-membered ring appended aminoporphyrazines 3 and 12 have been prepared via mixed Linstead macrocyclization. The structures of both have been unequivocally established by X-ray crystallographic studies. Reductive deselenation of selenadiazole 3 in the presence of 9,10-phenanthrenequinone or 2,3-butanedione results in the formation of pyrazines 6a,b, whereas oxidation of porphyrazine 12 gave the corresponding seco derivative 14. seco-Porphyrazine 14 mediates the generation of singlet oxygen with a quantum yield of 0.74.

Journal Article↗
PubMed2003

Relationship between polycystic ovaries, body mass index and insulin resistance.

BACKGROUND: To investigate insulin levels in lean and overweight women with and without polycystic ovaries. An observational, cross-sectional study at The Northem General Hospital, Sheffield, UK. METHODS: Sixty-eight women born at Jessop Hospital, Sheffield, between 1952 and 1953 were divided into four groups according to the status of their polycystic ovaries and body mass index: either > or approximately 25. Therefore, this was an unselected sample, unlike previous studies that have recruited from endocrine clinics or similar. Subjects underwent pelvic ultrasonography to visualize their ovaries in order to diagnose or exclude polycystic ovaries. They all underwent a short insulin tolerance test. RESULTS: Women with a body mass index > 25 and with polycystic ovaries were the most insulin resistant. Women with a body mass index of < or = ?25 and with normal ovaries were the most insulin sensitive. Women with a body mass index < or = ?25 and polycystic ovaries were the more resistant than those with a body mass index > 25 and with normal ovaries. CONCLUSION: Obesity increases insulin resistance, and the presence of polycystic ovaries increases insulin resistance. The presence of polycystic ovaries appears to have a stronger influence than obesity on insulin resistance. This is the first study to demonstrate these relationships using unselected volunteers.

Analysis of Variance↗
PubMed2003

A time-resolved study of concentration quenching of disulfonated aluminium phthalocyanine fluorescence.

The effects of concentration on the fluorescence decay kinetics of disulfonated aluminium phthalocyanine (AlPcS2) were studied in several solvents. The degree of aggregation, which increased with total dye concentration, was estimated from the absorption spectra. The measured fluorescence decays were shorter and increasingly non-monoexponential with increasing dye concentration. However, stronger quenching was not correlated with higher aggregation. The fluorescence decays were analyzed using a model that assumes excitation energy migration between diffusing monomeric AlPcS2 and quenching by diffusing dimers, both governed by the Förster energy transfer mechanism. The model can explain the observations in three of the four solvents used (phosphate-buffered saline (PBS) pH = 11.5, ethanol, and 67% glycerol-33% water mixture) on the assumption that different dimer configurations are present and not all of them act as quenchers. In PBS at pH = 7.4 the theory predicts much stronger quenching than observed. Excitation energy migration between monomeric species at high dye concentration was confirmed by the observed decrease of the decay time of fluorescence anisotropy in viscous solutions of 67% glycerol, and appears to be a major factor in fluorescence quenching of AlPcS2 at high concentration.

Dimerization↗
PubMed2003

Spectroscopy of photoinduced charge-transfer reactions between tetrasulfonated aluminium phthalocyanine and methyl viologen.

Interactions between tetrasulfonated aluminium phthalocyanine (AlPcTS4-) and methyl viologen (Mv2+) have been studied in water and ethanol solutions using several experimental techniques. UV-visible absorption and fluorescence spectroscopies show that ion-pair complexes occur in ethanol, disappearing in more polar environments such as water. Time-resolved fluorescence spectroscopy (picosecond timescale) reveals the existence of several emissive species in ethanol solutions, of which one of the components is attributed to the charge-transfer complex (AlPcTS4-)(Mv2+)2, another to higher-order aggregates and yet another to the isolated AlPcTS4- molecule. The AlPcTS4- emission is quenched by Mv2+, leading to transient diffusion in the fluorescence decay kinetics. On the other hand, the emissive complex has an exponential decay with a relatively long lifetime (above 1 ns). Time-resolved absorption measurements did not reveal the existence of radicals in aqueous solution, even on the picosecond timescale. The spectra reveal the presence of excited singlet state AlPcTS4-, which decays via the triplet excited state back to the ground state.

Journal Article↗