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M Dawson

Publications and source records attributed to M Dawson.

At least 37 records · Page 2Linked to original sources
PubMed2000

Effect of receptor-selective retinoids on growth and differentiation pathways in mouse melanoma cells.

Treatment of B16 mouse melanoma cells with all-trans-retinoic acid (ATRA) results in inhibition of cell proliferation and induction of differentiation. Accompanying these events is an induction of retinoic acid receptor beta (RARbeta) expression, an increase in protein kinase Calpha (PKCalpha) expression, and enhanced activator protein-1 (AP-1) transcriptional activity. These cells express nuclear RARalpha and RARgamma and nuclear retinoid X receptors (RXR) alpha and beta constitutively. We tested the ability of receptor-selective retinoids to induce the biochemical changes found in ATRA-treated melanoma cells and also tested their effectiveness in decreasing anchorage-dependent and -independent growth. The RXR-selective ligand (2E,4E)-6-(5,6,7,8-tetrahydro-3,5,5,8, 8-pentamethyl-2-naphthalenyl)-3,7-dimethyl-2,4,6-octatrienoic acid (SR11246) was most effective at inhibiting anchorage-dependent growth, whereas the RARgamma-selective ligand 6-[(5,6,7, 8-tetrahydro-5,5,8, 8-tetramethyl-2-naphthalenyl)(hydroxyimino)methyl]-2-naphthalen ecarbo xylic acid (SR11254) was most potent at inhibiting anchorage-independent growth. In contrast, 4-(5,6,7,8-tetrahydro-5,5, 8,8-tetramethyl-2-naphthalenecarboxamido)-benzoic acid (Am580), an RARalpha-selective ligand, was the most effective receptor-selective agonist for inducing RARbeta mRNA and increasing the amount of PKCalpha protein. All of the retinoids induced a concentration-dependent increase in AP-1 transcriptional activity, with little difference in effectiveness among the receptor-selective retinoids. A synergistic increase in the amount of PKCalpha was found when an RAR-selective agonist was combined with an RXR-selective agonist. One possible explanation for this result is that an RXR-RAR heterodimer in which both receptors are liganded is required for maximum expression of this critical component of the ATRA-induced differentiation pathway. Our data suggest that synthetic retinoids can activate different growth and differentiation pathways preferentially in B16 melanoma cells, due, most likely, to their ability to activate a different subset of receptors.

Animals↗
PubMed2000

High-resolution solid state 13C nuclear magnetic resonance spectra of 3,4-methylenedioxyamphetamine hydrochloride and related compounds and their mixtures with lactose.

Differences between solution and solid state 13C nuclear magnetic resonance spectra of some amphetamines namely, 3,4-methylenedioxyamphetamine HCI, (R.S)-MDA HCI, the methyl derivative 3,4-methylenedioxy-N-methylamphetamine x HCI, (R,S)-MDMA x HCI, the ethyl derivative, (R,S)-MDEA x HCI, and the analogues (R,S)-methamphetamine HCI, (-)-ephedrine x HCI (the 3R,2S enantiomer as numbered here), and (+)-pseudo-ephedrine x HCI (the 3S,2S enantiomer as numbered here) have been studied and related to their crystal structure. For (R,S)-MDMA x HCI, an interesting new finding is that the observed solid state chemical shifts changed when lactose monohydrate was added as a dry powder and thoroughly mixed at room temperature. This experiment mimicked the illicit production of "Ecstasy" tablets. The mixing phenomena with lactose observed for (R.S)-MDMA x HCI was not seen for the other compounds studied. The results are discussed in terms of hydrogen bonding and possible polymorphs. It appears that lactose affects crystal packing by reducing conformational rigidity so that the molecule more closely resembles that in solution.

3,4-Methylenedioxyamphetamine↗
PubMed2000

Characterization of the murine BSE infectious agent.

Bovine spongiform encephalopathy (BSE) is a prion-associated disease where the infectious agent is thought to be a host-encoded protein with a protease-resistant conformation (PrP(Sc)). Here, data are presented on the solubilization of purified murine BSE material, using guanidine-HCl as a denaturing agent. This treatment led to loss of infectivity, which was partially recovered on renaturation after dialysis to remove the chaotropic agent. The renatured product was then fractionated on an isopycnic sucrose-density gradient and the fractions were analysed for the presence of PrP(Sc), nucleic acids and infectivity. It was found that the major part of PrP(Sc) (>90%) and the endogenous nucleic acids did not contribute towards the formation of infectious particles on renaturation. Infectivity was distributed in the top three, low-density fractions. Among these, the presence of considerable infectivity in the fraction of lowest density, with barely detectable PrP(Sc), is of particular interest.

Animals↗
PubMed1999

Glycosaminoglycan analysis in brain stems from animals infected with the bovine spongiform encephalopathy agent.

Increasing evidence suggests that the pathological alterations observed in brains affected by neurodegenerative disorders such as Creutzfeldt-Jakob disease and Alzheimer's disease also involve changes in glycosaminoglycans (GAGs). In the present study, we have isolated, purified, and characterized total GAGs from brain stems of healthy cows or those infected with the bovine spongiform encephalopathy (BSE) agent and we report on the differences between the two groups. Purification of the GAGs was achieved by gel filtration after homogenization, delipidation, and sequential treatment with pronase, DNase, and alkali borohydride. Fractionation of the total GAGs by Superose 6 gel filtration and HPLC revealed four major fractions, with average molecular masses of 360, 180, 15, and 2.3 kDa, respectively, both in controls and infected tissues. Enzymatic characterization, using GAG-degrading enzymes, showed that in both infected and normal brain stems, the 360- and 180-kDa fractions correspond to hyaluronic acid, which was also the most abundant GAG, while the 15-kDa fractions correspond to chondroitin sulfates as well as heparan sulfate and dermatan sulfate, the latter being the least prominent GAG. Electrophoresis on cellulose acetate membranes revealed that the relative ratio of GAGs was not significantly modified in infected brain stems, compared to controls. However, total GAGs in infected brain stems was significantly decreased by approximately 40%, compared to controls, and this decrease applied equally to all of the above GAG fractions. The diminution observed in total GAGs in infected brain stems is in good agreement with the recently reported neuroprotective role of certain GAG molecules and offers an additional criterion for differential diagnosis of BSE-infected animals.

Alzheimer Disease↗
PubMed1999

Cytochrome P450105D1 (CYP105D1) from Streptomyces griseus: heterologous expression, activity, and activation effects of multiple xenobiotics.

The open reading frame of CYP105D1, a soluble cytochrome P450 from Streptomyces griseus, was cloned behind the tac promoter of the bacterial expression vector pSPg1910L and expressed in Escherichia coli. The recombinant protein retained normal spectral characteristics having a Soret peak at 448 nm in the reduced carbon monoxide difference spectrum. CYP105D1 was active, obtaining reducing equivalents from endogenous E. coli ferredoxin and ferredoxin reductase redox partners present in E. coli. In vitro activity studies revealed CYP105D1 to catalyse the NADH- and NADPH-dependent oxidation of the xenobiotic substrates benzo[a]pyrene, erythromycin, warfarin, and testosterone. Furthermore, this activity could be stimulated in the presence of either alpha-benzoflavone or beta-benzoflavone in an analogous manner to that reported for mammalian P450 forms including human liver cytochrome P4503A4 (CYP3A4). The system produces an alternative to whole-cell biotransformation of xenobiotic for the production of drug metabolites and an experimental system for probing the structural features of a cytochrome P450 with a broad substrate range.

Animals↗
PubMed1999

Activation of the p38 and JNK/SAPK mitogen-activated protein kinase pathways during apoptosis is mediated by a novel retinoid.

6-[3-(1-Adamantyl)]-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) is a novel retinoid which induces apoptosis in the retinoic acid-resistant HL-60R human leukemia cell line. CD437-mediated poly(ADP-ribose) polymerase (PARP) cleavage and apoptosis of HL-60R cells does not require gene transcription or protein synthesis since it occurs in the presence or absence of either actinomycin D or cycloheximide. Marked activation of both the p38 and the JNK/SAPK serine and threonine kinases occurs at 1 h of exposure to CD437 with subsequent PARP cleavage at 2 h and apoptosis noted at 4 to 6 h. CD437 concentrations as little as 10 nM result in p38 activation and apoptosis of HL-60R cells. However, inhibition of p38 activation utilizing the specific inhibitor SB203580 does not block CD437-mediated PARP cleavage or apoptosis. In addition, p38 activation is dependent upon the activation of the caspase system since p38 activation is blocked by the pan ICE inhibitor Z-VAD fmk, which also inhibits CD437-mediated apoptosis and PARP cleavage in these cells. CD437-mediated activation of JNK/SAPK is not inhibited by Z-VAD fmk, suggesting that it lies upstream of CD437 activation of caspase activity and subsequent apoptosis. The role of JNK/SAPK activation in CD437-mediated apoptosis remains to be defined.

Apoptosis↗
PubMed1999

Toxic shock syndrome toxin-1 (TSST-1) antibody levels in burned children.

Young children with burns are at risk of developing a toxic shock-like illness during the first 2-3 days after the injury. The staphylococcal exotoxin, toxic-shock syndrome toxin-1 (TSST-1) is implicated in development of this illness. Low levels or absence of anti-TSST-1 antibodies may indicate susceptibility to this illness. Anti-TSST-1 antibody levels were measured in consecutive cases admitted to the children's burns unit. Results of antibody levels in 38 of the youngest children, aged 0.04-4.0 years are reported. At the time of admission to the unit 50% of the children had IgG antibodies to TSST-1. A higher number of young burned children had antibodies to TSST-1 than expected.

Bacterial Toxins↗
PubMed1999

RS-127445: a selective, high affinity, orally bioavailable 5-HT2B receptor antagonist.

Efforts to define precisely the role of 5-HT2B receptors in normal and disease processes have been hindered by the absence of selective antagonists. To address this deficiency, we developed a series of naphthylpyrimidines as potentially useful 5-HT2B receptor antagonists. RS-127445 (2-amino-4-(4-fluoronaphth-1-yl)-6-isopropylpyrimidine) was found to have nanomolar affinity for the 5-HT2B receptor (pKi = 9.5+/-0.1) and 1,000 fold selectivity for this receptor as compared to numerous other receptor and ion channel binding sites. In cells expressing human recombinant 5-HT2B receptors, RS-127445 potently antagonized 5-HT-evoked formation of inositol phosphates (pK(B) = 9.5+/-0.1) and 5-HT-evoked increases in intracellular calcium (pIC50 = 10.4+/-0.1). RS-127445 also blocked 5-HT-evoked contraction of rat isolated stomach fundus (pA2 = 9.5+/-1.1) and (+/-)alpha-methyl-5-HT-mediated relaxation of the rat jugular vein (pA2 = 9.9+/-0.3). RS-127445 had no detectable intrinsic activity in these assays. In rats, the fraction of RS-127445 that was bioavailable via the oral or intraperitoneal routes was 14 and 60% respectively. Intraperitoneal administration of RS-127445 (5 mg kg(-1)) produced plasma concentrations predicted to fully saturate accessible 5-HT2B receptors for at least 4 h. In conclusion, RS-127445 is a selective, high affinity 5-HT2B receptor antagonist suitable for use is vivo. The therapeutic potential of this molecule is being further evaluated.

Animals↗
PubMed1999

Use of computerized neuropsychological tests (CANTAB) to assess cognitive effects of antihypertensive drugs in the elderly. Cambridge Neuropsychological Test Automated Battery.

OBJECTIVE: To establish reliability and ease of use of the Cambridge Neuropsychological Test Automated Battery (CANTAB) in assessing changes in cognitive function induced by antihypertensive drugs. DESIGN AND METHODS: Standard neuropsychological testing was combined with CANTAB in a double-blind 18-week cross-over study in elderly hypertensives taking perindopril or hydrochlorothiazide/triamterene (HT). Cognitive effects were assessed by employing tests of attention, visuospatial and verbal memory, learning, reasoning, planning, problem solving, speed and coordination. Affect was assessed using two different depression-rating scales. RESULTS: Perindopril and the diuretic had no adverse effects on the various aspects of cognitive function. Mood, as assessed by the Hamilton Depression Rating Scale and the Beck Depression Inventory, was improved on Perindopril, and the error rate in the motor screening test was lower. Ambulatory blood pressure monitoring showed both drugs achieved effective 24-h control. CONCLUSIONS: The ease of use and the ability to adjust the level of testing to the requirements of individual patients, together with the reliability of longitudinal test/re-test results, indicates that CANTAB is an important addition to the methods available to quantitate adverse central nervous system drug effects. The other purpose of the study was to assess any adverse cognitive effects of perindopril against a drug HT believed to have no adverse central nervous system effects. In this context, perindopril was free of adverse effects in all the objective tests employed. In addition, there was a benefit seen in two independent assessments of depression (the Hamilton and the Beck rating scales).

Aged↗
PubMed1999

The antibody response of cattle infected with bovine immunodeficiency virus to peptides of the viral transmembrane protein.

The development of the antibody response to peptides of the transmembrane glycoprotein of bovine immunodeficiency virus (BIV) was followed over a period of 50 weeks in six cattle experimentally infected with the BIV(FL112) isolate. Antibody was detected by an enzyme immunoassay using either a linear or a cyclized peptide with structural features common to an immunodominant region of other lentiviruses. The assay was specific for BIV, detecting antibody in bovine sera to BIV(FL112) or BIV(R29) but not to six other common viruses of cattle. Antibody was present in the sera of all cattle inoculated with BIV(FL112) within 4 weeks of infection, peaked between 10 and 30 weeks and persisted in most cattle during the 50 weeks of observation. These features indicate that this assay may be useful in identifying cattle infected with other strains of BIV in the field.

Amino Acid Sequence↗
PubMed1999

Outcome after severe head injury treated by an integrated trauma system.

OBJECTIVES: To describe outcome after treatment of severe head injury within an integrated trauma system. METHODS: A retrospective analysis of all patients with severe head injury admitted to the Royal London Hospital by the Helicopter Emergency Medical Service (HEMS) between 1991 and 1994. Type of injury was defined on initial computed tomography of the head and outcomes assessed 12 months after injury using the Glasgow outcome score. RESULTS: 6.5% of HEMS patients had long term severe disability (severe disability or persistent vegetative state on the outcome score); 34.5% made a good recovery. CONCLUSIONS: The concern that a large number of severely disabled long term survivors might result as a consequence of this system of trauma management is not confirmed. The case mix of severity of extracranial injuries in these patients makes comparison with other published series difficult, but these data fit the hypothesis that pre-hospital correction of hypoxia and hypotension after head injury improves outcome.

Abbreviated Injury Scale↗
PubMed1999

Enzymic acylation of 506U78 (2-amino-9-beta-D-arabinofuranosyl-6- methoxy-9H-purine), a powerful new anti-leukaemic agent.

A practical enzymic approach for acylation of 506U78 (2-amino-9-beta-D-arabinofuranosyl-6-methoxy -9H-purine), a powerful anti-leukaemic agent, is described. Novozyme-435, an immobilized preparation of Candida antarctica lipase, was used to acylate 506U78 regioselectively at the 5'-position. This rendered the compound more soluble and bioavailable. Vinyl acetate was used as the acyl donor and reactions were carried out in anhydrous 1,4-dioxane with up to 100 g/l of substrate input. Bioconversions were optimised to achieve impurity (3'-mono- and di-acetates) levels of less than 0.5%.

Acylation↗
PubMed1998

Molecular screening of sheep for bovine spongiform encephalopathy.

Bovine spongiform encephalopathy (BSE) may have transmitted to sheep through feed and pose a risk to human health. Sheep BSE cannot be clinically distinguished from scrapie, and conventional strain typing would be impractical on a significant scale. As human prion strains can be distinguished by differences in prion protein (PrPsc) conformation and glycosylation we have applied PrP(Sc) typing to sheep. We found multiple Western blot patterns of PrP(Sc) in scrapie, consistent with the known scrapie strain diversity in sheep. Sheep passaged BSE showed a PrP(Sc) banding pattern similar to BSE passaged in other species [Collinge, J., Sidle, K.C.L., Meads, J., Ironside, J. and Hill, A.F., Nature, 383 (1996) 685-690], both in terms of fragment size following proteinase K cleavage and abundance of diglycosylated PrP. However, none of the historical or contemporary scrapie cases studied had a PrP(Sc) type identical to sheep BSE. While more extensive studies, including sheep of all PrP genotypes, will be required to fully evaluate these findings, these results suggest that large scale screening of sheep for BSE may be possible.

Animals↗
PubMed1998

Prevention of transmission of sheep pulmonary adenomatosis by embryo transfer.

Two-hundred-and-fifteen embryos recovered from 76 donor ewes from flocks endemically infected with sheep pulmonary adenomatosis (SPA) and mated with uninfected rams were transferred to 131 uninfected recipients under strict sanitary conditions using International Embryo Transfer Society protocols. The recipients and their progeny were kept in a closed, isolated SPA-free flock. Thirty-eight of 51 progeny from SPA-positive donors and 55 of 74 progeny from donors in which no lesions of SPA were detected survived for at least five years after birth. In a similar study 11 embryos from four uninfected donors mated to an SPA-infected ram were transferred to seven recipients, and four of five progeny born to four recipients survived for at least five years. No evidence of SPA was found in the recipients or their progeny by embryo transfer in either study. On the basis of clinical and pathological criteria, it is concluded that embryo transfer can be used to provide an effective barrier against the transmission of SPA from donors from infected flocks, whether or not the parents show clinical signs of the disease.

Animal Husbandry↗
PubMed1998

Suppression of relaxin gene expression by retinoids in squamous differentiated rabbit tracheal epithelial cells.

Northern blot analysis of total RNA from a variety of rabbit tissues indicated that placenta is the primary site of expression of the protein hormone relaxin (previously called SQ10) in rabbits. Relaxin was not detected by this method in other rabbit tissues, including normal trachea and several squamous tissues. However, relaxin is highly induced during squamous cell differentiation in cultured rabbit tracheal epithelial (RbTE) cells. Retinoic acid and retinoids that selectively bind to the nuclear retinoid receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs), and induce RARE- or RXRE-dependent transactivation as well as repression of AP-1-dependent transactivation, were all effective in suppressing relaxin expression. In addition, the retinoid SR11302, which exhibits only anti-AP-1 activity but does not induce RARE- or RXRE-dependent transactivation, was also able to inhibit relaxin expression. These results suggest that the suppression of relaxin expression is related to the anti-AP-1 activity of retinoids. To determine whether the relaxin gene is regulated by retinoids at the level of transcription, a 4.3 kb fragment of the 5' flanking region of the rabbit relaxin gene was cloned and analyzed. This regulatory region included a classic TATA-box as well as consensus sequences for several transcription factors, including CREB, NF-kappaB and AP-1. The ability of the 4.3 kb regulatory region to control the transcription of a luciferase reporter gene was analyzed in transiently transfected, squamous-differentiated RbTE cells. The results demonstrated that this regulatory region caused strong transactivation of the reporter gene. This transactivation was inhibited by retinoic acid, suggesting retinoid control at the transcriptional level. Deletion analysis indicated that multiple regulatory elements are involved in the regulation of relaxin gene expression during squamous differentiation as well as in the suppression by retinoids.

Animals↗
PubMed1998

Preliminary observations on the pathogenesis of experimental bovine spongiform encephalopathy (BSE): an update.

Further preliminary observations are reported of an experiment to examine the spread of infectivity and the occurrence of pathological changes in cattle exposed orally to infection with bovine spongiform encephalopathy. Calves were dosed at four months of age and clinically monitored groups were killed sequentially from two to 40 months after inoculation. Tissues were collected for bioassay, for histopathological examinations and for the detection of PrP. Previous reported observations have included the presence of infectivity in the distal ileum of cattle killed after six to 18 months, the earliest onset of clinical signs in an exposed animal after 35 months, and diagnostic histopathological changes in the brain, in association with clinical disease, after 36, 38 and 40 months. In spite of the relative inefficiency of the bioassay of scrapie-like agents across a species barrier the new observations confirm that the onset of clinical signs and pathological changes in the central nervous system (CNS) occur at approximately the same time. The earliest pathological change, the presence of abnormal PrP 32 months after inoculation, coincided with the earliest detected infectivity in the CNS and occurred shortly before there was evidence of typical spongiform changes in the brain 36 months after inoculation. Infectivity has now been demonstrated in the peripheral nervous system, in the cervical and thoracic dorsal root ganglia 32 to 40 months after inoculation and in the trigeminal ganglion 36 and 38 months after inoculation. At the time of writing evidence of infectivity in other tissues is confined to the distal ileum, not only after six to 18 months but also after 38 and 40 months, but these findings may be supplemented by the results of further mouse assays. Nevertheless, they are in general agreement with current knowledge of the pathogenesis of scrapie.

Animals↗