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Biomedical subjects

A Graham

Publications and source records attributed to A Graham.

At least 91 records · Page 5Linked to original sources
PubMed1997

Apolipoprotein E inhibits platelet aggregation through the L-arginine:nitric oxide pathway. Implications for vascular disease.

We have previously reported that plasma apolipoprotein (apo) E-containing high density lipoprotein particles have a potent anti-platelet action, apparently by occupying saturable binding sites in the cell surface. Here we show that purified apoE (10-50 microg/ml), complexed with phospholipid vesicles (dimyristoylphosphatidylcholine, DMPC), suppresses platelet aggregation induced by ADP, epinephrine, or collagen. This effect was not due to sequestration of cholesterol from platelet membranes; apoE x DMPC chemically modified with cyclohexanedione (cyclohexanedione-apoE x DMPC) did not inhibit aggregation but nevertheless removed similar amounts of cholesterol as untreated complexes, about 2% during the aggregation period. Rather we found that apoE influenced intracellular platelet signaling. Thus, apoE x DMPC markedly increased cGMP in ADP-stimulated platelets which correlated with the resulting inhibition of aggregation (r = 0.85; p < 0.01, n = 10), whereas cyclohexanedione-apoE x DMPC vesicles had no effect. One important cellular mechanism for up-regulation of cGMP is through stimulation of nitric oxide (NO) synthase, the NO generated by conversion of L-arginine to L-citrulline, binds to and activates guanylate cyclase. This signal transduction pathway was implicated by the finding that NO synthase inhibitors of distinct structural and functional types all reversed the anti-platelet action of apoE, whereas a selective inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (100 nM), had a similar reversing action. Direct confirmation that apoE stimulates NO synthase was obtained by use of L-[3H]arginine; platelets pretreated with apoE x DMPC produced markedly more L-[3H]citrulline (0.71 +/- 0.1 pmol/h/10(9) platelets) than controls (0.18 +/- 0.03; p < 0.05). In addition, hemoglobin which avidly binds NO also suppressed the anti-aggregatory effect, indicating that apoE stimulated sufficient production of NO by platelets for extracellular release to occur. We conclude that apoE inhibits platelet aggregation through the L-arginine:NO signal transduction pathway.

1-Methyl-3-isobutylxanthine↗
PubMed1997

PDGF-alpha receptor and myelin basic protein mRNAs are not coexpressed by oligodendrocytes in vivo: a double in situ hybridization study in the anterior medullary velum of the neonatal rat.

Platelet-derived growth factor (PDGF) is a growth-regulatory dimer with A and B subunits. PDGF-AA, acting via PDGF receptors of the alpha-unit subtype (PDGF-alphaR), is implicated in the differentiation of oligodendrocyte precursors and in the survival of newly formed oligodendrocytes, which gradually lose expression of PDGF-alphaR. However, it is unclear whether terminally differentiated oligodendrocytes express PDGF-alphaR in vivo. To address this question, and to help clarify the role of PDGF-AA in late oligodendrocyte differentiation, we have used double in situ hybridization with digoxigenin- and fluorescein-labeled riboprobes to relate PDGF-alphaR mRNA and myelin basic protein (MBP) mRNA expression in the isolated intact anterior medullary velum (AMV) of rats ages Postnatal Day (P) 10-12 and P30-32. In parallel experiments, AMV were immunolabeled with the oligodendrocyte-specific monoclonal antibody Rip to provide information on oligodendrocyte development and the extent of myelination. At P10, the AMV contained tracts in which axons ranged from unmyelinated to fully myelinated, whereas myelination was complete in P30-32 AMV. The first oligodendrocytes to express MBP mRNA or Rip were promyelinating oligodendrocytes, which had a "star-burst" morphology and had not yet begun to form myelin sheaths. As myelination proceeded, MBP mRNA became dispersed throughout oligodendrocyte units, comprising cell somata, processes, and internodal myelin sheaths. By P30-32, MBP mRNA had been redistributed to the myelin sheaths only, reflecting a change in the site of protein synthesis in mature myelinated axon tracts. At no stage of oligodendrocyte differentiation did we observe cellular coexpression of mRNA for PDGFalphaR and MBP. Our results indicated that oligodendrocytes lost the expression of PDGFalphaR prior to gaining that of myelin gene products, and preclude an action of PDGF-AA on Rip+/MBP+ star-burst promyelinating oligodendrocytes. The spatial and temporal expression of PDGF-alphaR mRNA in the AMV was inversely related to the pattern of maturation of both myelin and oligodendrocytes, and is consistent with PDGF-alphaR being expressed by pro-oligodendrocytes. A notable finding was the high level of expression of PDGF-alphaR mRNA in the AMV of juvenile rats, localized to cell bodies within the myelinated axon tracts, strongly suggesting that oligodendrocyte precursors persisted in the mature velum.

Animals↗
PubMed1997

Evidence for a paraoxonase-independent inhibition of low-density lipoprotein oxidation by high-density lipoprotein.

One mechanism by which plasma high-density lipoprotein (HDL) may protect against atherogenesis is by inhibiting the oxidation of low-density lipoprotein (LDL). Recent evidence suggests that paraoxonase, an HDL-associated, calcium-dependent enzyme, may be responsible for the antioxidant action of HDL (Mackness et al., Atherosclerosis 1993;104:129; Mackness et al., FEBS Lett 1991;286:152; Watson et al., J Clin Invest 1995;96:2882; Navab et al., Arterio Thromb Vasc Biol 1996;16:831); in particular, paraoxonase activity inhibits the formation of 'minimally oxidized' LDL by hydrolyzing biologically active oxidized phospholipids (Watson et al., J Clin Invest 1995;96:2882; Navab et al., Arterio Thromb Vasc Biol 1996;16:831). However, antioxidant effects of HDL have also been demonstrated under calcium-free conditions, arguing that this enzyme may not be the only mechanism by which HDL inhibits LDL oxidation (Tribble et al., J Lipid Res 1995;36:2580). Here we have evaluated the role of paraoxonase in prevention of LDL oxidation by using HDL subfractions, isolated from human serum or EDTA-plasma, which display markedly different levels of paraoxonase activity; the abilities of modified forms of HDL to prevent LDL oxidation by cultured human (THP-1) macrophages were also assessed. Paraoxonase activity was substantially lower in HDL prepared from plasma compared to serum HDL; moreover, virtually all of the lipoprotein-associated paraoxonase activity was located in the HDL3 fraction, with HDL2 retaining only 1-5% of the total activity. Despite possessing 5-fold differences in paraoxonase activity, HDL3 isolated from plasma or serum was equally effective in inhibiting LDL oxidation by THP-1 macrophages; furthermore, although plasma HDL3 was more protective than plasma HDL2, the latter did significantly inhibit LDL oxidation. Non-paraoxonase antioxidant constituents of plasma HDL3 were investigated further. ApoHDL3, the totally delipidated form of HDL3, was much less effective than native HDL3; when examined individually, purified apolipoprotein A-II gave greater protection than apo A-I, although this effect was not evident in apo A-II-enriched HDL3. Partial delipidation of HDL3, which removes both neutral lipids and alpha-tocopherol, did not significantly diminish its ability to inhibit LDL oxidation by THP-1 macrophages; phospholipid vesicles prepared from partially delipidated HDL3 also inhibited LDL oxidation effectively. We conclude that, in this model of cellular LDL oxidation, the phospholipid fraction of HDL exerts inhibitory effects which are independent of HDL paraoxonase activity.

Apolipoproteins↗
PubMed1997

Densities of nitric oxide synthesizing nerves in smooth muscles of human gut during fetal development.

BACKGROUND/PURPOSE: Nitric oxide (NO) plays a role in inhibitory neurotransmission in the sphincteric and nonsphincteric smooth muscles. However, the relative contribution of NO synthesizing innervation to these functionally diverse parts of the gut, particularly during development, is unknown. METHODS: Gastrointestinal sphincters and adjoining nonsphincteric bowel segments were obtained from 14 human fetuses (gestation, 12 to 23 weeks). NO synthesizing nerves were examined by nicotinamide adenine deoxinucleotide phosphate (NADPH) diaphorase histochemistry. The densities of NADPH-positive nerves in the smooth muscles were quantified using a computerized image analyzing system on random sections. RESULTS: The NO synthesizing nerve density in intestinal smooth muscles decreased during fetal development as a result of increased interspacing between myenteric ganglia and a disproportionately larger increase in smooth muscle area than neuronal area. The nerve densities were lower in sphincteric regions than the adjoining nonsphincteric regions at the same gestation. CONCLUSION: These findings may have relevance to the occurrence of congenital dysmotility disorders of the sphincteric regions.

Digestive System↗
PubMed1997

Furuncular cuterebrid myiasis.

Myiasis is the infestation of skin bythe larvae of flies. In North America cases are caused by the botfly (Cuterebra) and occur most commonly in children. The usual presentation is a subcutaneous abscess, and for this reason these patients may be referred to surgeons. Knowledge of this entity can avoid delays in diagnosis, unnecessary incision and drainage procedures, and unnecessary courses of antibiotics.

Abscess↗
PubMed1997

Preoptic area infusions of morphine disrupt--and naloxone restores--parental-like behavior in juvenile rats.

As in the adult lactating female, opioids disrupt (and naloxone restores), parental behavior in juvenile rats (approximately 25 days of age). Because the preoptic area regulates the display of parental behavior in lactating females, we examined its parental behavior role in the juvenile rat. At 21 days of age, juvenile rats were implanted with bilateral cannulae aimed at the preoptic area using a modified Kopf stereotaxic and extrapolating from a developing-rat brain atlas [58], and divided into two groups: Initiation and maintenance. On day 25, the initiation group received bilateral infusions of either morphine (0.50 microgram), saline (0.25 microliter), or morphine plus naloxone (0.25 microgram). Thirty minutes later, they were exposed to three 1-6-day-old pups; the maintenance group was exposed to pups until they displayed 2 consecutive days of parental behavior, then infused. Morphine disrupted parental behavior in both the initiation and Maintenance groups, and naloxone restored the behavior to control/ saline levels. Parental behavior in the juvenile animal of both sexes, therefore, is under opioid regulation that parallels the adult female.

Animals↗
PubMed1997

Antibiotic resistance in Escherichia coli isolated from blood and cerebrospinal fluid: a 6-year study of isolates from patients in England and Wales.

A study of the incidence of resistance to antimicrobial drugs in Escherichia coli from blood and CSF made in England and Wales in the 6-year period 1991 1996 has demonstrated a significant increase in the incidence of strains resistant to ampicillin and ciprofloxacin, two antibiotics used for first-line therapy of invasive disease. In particular, there has been a dramatic change in the occurrence of isolates with low level or high level resistance to ciprofloxacin; over 90% of isolates in the high level group were also resistant to at least four other antimicrobials. Physicians in England and Wales should be aware that there is now an increasing possibility of treatment failures when ciprofloxacin is used for the treatment of invasive E. coli infections.

Ampicillin Resistance↗
PubMed1997

Illudinic acid, a novel illudane sesquiterpene antibiotic.

A novel illudane sesquiterpene antibiotic (1) with activity against methicillin-resistant Staphylococcus aureus (MRSA), has been isolated. Its MIC against MRSA was found to be 16 micrograms/mL. It also shows L-1210 cytotoxicity with an IC50 of 10-15 micrograms/mL.

Animals↗
PubMed1997

Characterisation of ACTH peptides in human skin and their activation of the melanocortin-1 receptor.

Alpha-Melanocyte-stimulating hormone (alpha-MSH) is a proopiomelanocortin (POMC)-derived peptide, which is produced in the pituitary and at other sites including the skin. It has numerous effects and in the skin has a pigmentary action through the activation of the melanocortin-1 (MC-1) receptor, which is expressed by melanocytes. Recent evidence suggests that the related POMC peptides such as adrenocorticotrophin (ACTH), which is the precursor of alpha-MSH, is also an agonist at the MC-1 receptor. By using immunocytochemistry, we confirmed the presence of alpha-MSH in human skin where staining was evident in keratinocytes and especially strong in melanocytes and possibly Langerhans cells. ACTH was also present and tended to show the strongest reaction in differentiated keratinocytes. Immunostaining was also observed for the prohormone convertases, PC1 and PC2, which are involved in the formation of ACTH and its cleavage to alpha-MSH, respectively. The amounts of immunoreactive ACTH exceeded those of alpha-MSH. Using HPLC we identified for the first time the presence of ACTH1-39, ACTH1-17, ACTH1-10, acetylated ACTH1-10, alpha-MSH, and desacetyl alpha-MSH in epidermis and in cultured keratinocytes. The ability of these peptides to activate the human MC-1 receptor was examined in HEK 293 cells that had been transfected with the receptor. All peptides increased adenylate cyclase in these cells with the following order of potency: ACTH1-17 > alpha-MSH > ACTH1-39 > desacetyl alpha-MSH > acetylated ACTH1-10 > ACTH1-10. ACTH1-17 also increased the dendricity and melanin content of cultured human melanocytes indicating that the peptide was able to activate MC-1 receptors when present in their normal location. However, as found with alpha-MSH, not all cultures were responsive and, as we have previously suggested, we suspect that this was the result of changes at the MC-1 receptor. Nevertheless, it would appear that ACTH peptides can serve as natural ligands of the MC-1 receptor on human melanocytes and their presence in the skin suggests that, together with alpha-MSH, they may have a role in the regulation of human melanocytes.

Adrenocorticotropic Hormone↗
PubMed1997

Agouti protein inhibits the production of eumelanin and phaeomelanin in the presence and absence of alpha-melanocyte stimulating hormone.

Melanocytes synthesise two types of melanin: the brown-black eumelanin and the red-yellow phaeomelanin. In mice, the relative proportions of these two melanins are regulated by alpha-MSH, which preferentially increases the synthesis of eumelanin and by the Agouti protein (AP), the expression of which correlates with the growth of yellow phaeomelanin-containing hair. It has been proposed that AP acts by antagonizing the action of alpha-MSH at the MC1 receptor, although it has been suggested that it may also act independently of alpha-MSH. In the present study we show that AP inhibits melanogenesis in B16F1 melanoma cells in the presence and absence of alpha-MSH and also causes dose-related decreases in the synthesis of both eumelanin and phaeomelanin. In the presence of alpha-MSH AP had a greater effect on eumelanin production and this is consistent with an antagonistic action at the MC1 receptor. In the absence of alpha-MSH however, AP produced similar reductions in the synthesis of both melanins. These changes were not seen in B16G4F cells which lack the MC1 receptor, suggesting that even in the absence of alpha-MSH AP acts at the MC1 receptor. How this action is mediated at the intracellular level is not yet clear, although it appears to be associated with a decrease in tyrosinase activity.

Adenylyl Cyclases↗
PubMed1997

Resistance to ciprofloxacin in pathogenic Enterobacteriaceae in England and Wales in 1996.

In 1996, 6% of Escherichia coli from extraintestinal infections were resistant to ciprofloxacin with minimum inhibitory concentrations (MICs) > or = 2 mg/l (high level resistance). Low level resistance (MIC 0.125-1 mg/l) was also identified in 7% of Salmonella typhi, 4% of S paratyphi A, and 4% of non-typhoidal salmonellas. However, resistance to ciprofloxacin was rarely identified in shigellas. For E coli, physicians should be aware that treatment failures may occur when patients with invasive illness are treated with ciprofloxacin before the results of laboratory sensitivity tests are available. For salmonellas an increasing number of treatment failures have been recorded for patients infected with strains with low level resistance. Because of the increasing incidence of Enterobacteriaceae with low level resistance to ciprofloxacin, it is recommended that for this group of organisms a breakpoint of 0.125 mg/l should be included in laboratory sensitivity tests.

Anti-Infective Agents↗
PubMed1997

Positional apoptosis during vertebrate CNS development in the absence of endogenous retinoids.

We have previously shown that quail embryos that develop in the absence of vitamin A have severe defects in their central nervous system. One defect is a completely missing posterior hindbrain. Here we have studied how this comes about by examining cell death using a wholemount technique. In these A- embryos we observe two narrow bands of ectopic apoptosis. One is in the mesenchyme in the region of the first somite and occurs at the 4-6 somite stage, before neural tube closure. The second band follows immediately afterwards and occurs in the neuroepithelium of the presumptive posterior hindbrain at the 6-8 somite stage. Electron microscopy shows that the dying neuroepithelial cells exhibit the characteristics of apoptosis. Rescuing the embryos by injecting retinol before gastrulation completely prevents these apoptotic events. In an effort to identify some of the genes that may be involved in the apoptotic pathway we show that Msx-2 is upregulated in the apoptotic neuroepithelium and thus may be involved, whereas Bmp-4 is not altered and thus presumably not involved. Since these apoptotic event take place at the time of specification of axial identity and segmentation in the mesenchyme and neuroepithelium we conclude that these cells die because they are wrongly specified in terms of their rostrocaudal position, a novel phenomenon which we refer to as positional apoptosis.

Age Factors↗
PubMed1996

Cholesterol esterification is not essential for secretion of lipoprotein components by HepG2 cells.

Hepatic acyl CoA:cholesterol acyltransferase (ACAT) activity may determine storage of cholesterol and supply of cholesteryl esters for the neutral lipid core of very low density lipoprotein. Inhibition of cholesterol esterification in HepG2 cells, by the ACAT inhibitor 447C88, partially reduced the secretion of labelled total cholesterol, but the secretion of apoprotein B mass, and of radiolabelled triacylglycerol and phosphatidylcholine were unaffected. Furthermore, this compound was shown to substantially deplete the intracellular cholesteryl ester mass without affecting secretion of lipoprotein components. In contrast, the less potent ACAT inhibitor, CL277,082, significantly decreased secretion of labelled triacylglycerol, phosphatidylcholine and total cholesterol, in a manner which mirrored the decreases in secretion of apoB. This study clearly illustrates that ACAT inhibitors can exert differential effects on secretion of apoB-containing lipoproteins, which do not correlate with their efficacy in inhibiting ACAT, arguing that cholesterol esterification is not essential for lipoprotein secretion from these cells.

Anticholesteremic Agents↗
PubMed1996

Teenagers' knowledge of emergency contraception: questionnaire survey in south east Scotland.

OBJECTIVE: To determine the level of knowledge of emergency contraception among 14 and 15 year olds. DESIGN: Confidential questionnaire survey. SETTING: 10 secondary schools in Lothian, south east Scotland. SUBJECTS: 1206 pupils predominantly (98.7%) aged 14 and 15 in the fourth year of secondary school. MAIN OUTCOME MEASURES: Knowledge of the existence of emergency contraception; of its safety, efficacy, and time limits; and of where to obtain it. RESULTS: 1121 (93.0%) fourth year pupils aged 14-16 had heard of emergency contraception. 194 girls (32.7%) and 168 boys (27.5%) had experienced sexual intercourse. Of girls who had experienced sexual intercourse, 61 (31.4%) had used emergency contraception. Knowledge of correct time limits was poor, sexually active girls being the most knowledgeable. Pupils attending schools ranked lower than the national average for academic attainment were less likely to have heard of emergency contraception and more likely to have been sexually active. 861 (76.8%) pupils knew they could obtain emergency contraception from their doctor. 925 (82.5%) pupils believed emergency contraception to be effective but 398 (35.5%) thought it more dangerous than the oral contraceptive pill. CONCLUSIONS: One third of sexually active girls aged under 16 in Lothian have used emergency contraception. This may help explain the fairly constant teenage pregnancy rates despite increasing sexual activity. Scottish teenagers are well informed about the existence of emergency contraception. However, many do not know when and how to access it properly. Health education initiatives should target teenagers from less academic schools as they are more likely to be sexually active at a young age and are less well informed about emergency contraception.

Adolescent↗
PubMed1996

Role of receptor desensitization, phosphatase induction and intracellular cyclic AMP in the termination of mitogen-activated protein kinase activity in UTP-stimulated EAhy 926 endothelial cells.

We have investigated the mechanisms that bring about the termination of mitogen-activated protein kinase (MAP kinase) activation in response to UTP in EAhy 926 endothelial cells. UTP-stimulated MAP kinase activity was transient, returning to basal values by 60 min. At this time MAP kinase activation was desensitized; re-application of UTP did not further activate MAP kinase, full re-activation of MAP kinase being only apparent after a 1-2 h wash period. However, activation of MAP kinase by UTP could be sustained beyond 60 min by preincubation of the cells with the protein synthesis inhibitor cycloheximide. UTP also stimulated expression of MAP kinase phosphatase-1 and this was abolished after pretreatment with cycloheximide. Pretreatment of cells with forskolin abolished the initial activation of MAP kinase kinase or c-Raf-1 by UTP, but only affected MAP kinase activity during prolonged stimulation. The effect of forskolin on prolonged MAP kinase activation was also prevented by cycloheximide. These results suggest that the termination of MAP kinase activity in response to UTP involves a number of interacting mechanisms including receptor desensitization and the induction of a phosphatase. However, several pieces of evidence do not support a major role for MAP kinase phosphatase-1 in termination of the MAP kinase signal. Raising intracellular cyclic AMP may also be involved but only after an initial protein-synthesis step and by a mechanism that does not involve the inactivation of c-Raf-1 or MAP kinase kinase.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1996

Neural crest apoptosis and the establishment of craniofacial pattern: an honorable death.

During development of the vertebrate head neural crest cells emigrate from the hindbrain and populate the branchial arches, giving rise to distinct skeletal elements and muscle connective tissues in each arch. The production of neural crest from the hindbrain is discontinuous and crest cells destined for different arches, carrying different positional cues, are separated by regions of apoptosis centered on rhombomeres (r) 3 and r5. This cell death program is under the interactive control of the neighboring hindbrain segments. Both r3 and r5 produce large numbers of crest cells when freed from their flanking rhombomere, but when conjoined with their neighbor the cell death program is restored. Two key components of this program are Bmp 4 and msx-2, both of which are expressed in the apoptotic foci of r3 and r5 and which are also regulated by neighbor interactions. Importantly, the addition of recombinant Bmp 4 to isolated cultures of r3 and r5 induces the expression of Bmp 4 and msx-2 and restores the cell death program. This early neural crest segregation is maintained during development and it has profound effects upon the final craniofacial pattern. Even though crest cells from different axial origins will contribute to compound skeletal elements, these distinct populations do not intermingle. Furthermore head muscle connective tissues are exclusively anchored to skeletal domains arising from neural crest from the same axial level. Thus the discontinuous production of neural crest sculpts the crest into nonmixing streams and consequently ensures the fidelity of patterning.

Animals↗