PubMed Health⌕ Search

Biomedical subjects

A Graham

Publications and source records attributed to A Graham.

At least 73 records · Page 4Linked to original sources
PubMed1998

Effects of peroxynitrite on plasma components of the reverse cholesterol transport pathway.

Elimination of cholesterol from arterial tissue, crucial in limiting atherogenesis, may be achieved via high-density lipoprotein (HDL)-mediated reverse cholesterol transport (RCT); components of this pathway can be modulated by oxidative stress. Here we have examined the relations between cholesterol efflux, esterification and transfer in human plasma treated with the powerfully reactive nitrogen species, peroxynitrite. Cellular cholesterol efflux to whole plasma, or to peroxynitrite-modified HDL3, was relatively insensitive to peroxynitrite, as was the transfer of esterified cholesterol. However, plasma cholesterol esterification, via lecithin:cholesterol acyltransferase (LCAT), was markedly inhibited, both directly and indirectly, by peroxynitrite treatment, implying inefficient RCT follows HDL sequestration of cellular cholesterol.

Biological Transport↗
PubMed1998

Cloning, sequencing and functional expression of a guinea pig lung bradykinin B2 receptor.

Kinin receptors are classified as B1 and B2 based upon agonist and antagonist potencies and cloning and expression studies. Using sequences from human and rat bradykinin B2 receptors, polymerase chain reaction (PCR) was utilized to isolate cDNA from guinea pig lung. The receptor obtained is predicted to have 372 amino acids and shares > 80% sequence homology with human, rat, rabbit and mouse B2 receptors. In competition binding experiments in Chinese hamster ovary (CHO-K1) cells in which the guinea pig cDNA was expressed, [3H]bradykinin was displaced by kinin receptor ligands with an order of potency consistent with a B2 subtype. In CHO cells expressing the guinea pig receptor, bradykinin caused a concentration 45Ca2+ efflux. A B1 receptor agonist, desArg9-bradykinin, also caused 45Ca2+ efflux but with a potency several orders of magnitude lower than bradykinin. Curiously, several B1 and B2 receptor antagonists induced 45Ca2+ efflux, indicating that this receptor may be coupled differently in CHO cells than in native tissues.

Amino Acid Sequence↗
PubMed1998

Synthesis and antibacterial activity of O-methyl derivatives of azalide antibiotics: I. 4", 11 and 12-OMe derivatives via direct methylation.

A series of O-Me derivatives of 9-deoxo-8a-aza-8a-homoerythromycin has been prepared and evaluated for antibacterial activity. The relative rates of methylation of the four available hydroxyls (4", 6, 11 and 12) in 2',3'-bis-Cbz protected 9-deoxo-8a-aza-8a-homoerythromycin were compared to those given in a published report for the similarly protected 9a-azalide. An incongruity in the results prompted reinvestigation of the O-methylation of the 9a-azalide, and an error in structure assignment in the published report was discovered: the compound reported as the 6-OMe-9a-azalide has been determined to be the 12-OMe derivative.

Anti-Bacterial Agents↗
PubMed1998

Migration of hypoglossal myoblast precursors.

The intrinsic hypoglossal musculature develops from precursor myoblasts which undergo long-range migration from the occipital somites to the tongue. Little detail is known about the precise spatiotemporal pathway taken by these cells or the factors controlling migration. In this study, chick/quail chimeras in which the occipital paraxial mesoderm is quail derived, reveal that the pathway taken by the tongue muscle progenitors is both complex and highly specific. Precursor myoblasts are Pax-3 positive cells which descend from the somite and migrate around the pharyngeal endoderm. They then course rostrally, following the base of the pharynx, remaining in a tight strand. We have examined a number of factors implicated in the control of migration of the hypoglossal precursors. Replacement of the occipital somites with those originating in the flank reveals that intrinsic differences do not exist between these somites with respect to their capacity to respond to migratory cues. The lack of high level HGF/SF expression along the pathway of the migrating hypoglossal precursors suggests that this factor is not involved in the actual process of migration of the hypoglossal precursors to the tongue. The pathway followed by the migrating precursors is identical to that of both the developing hypoglossal nerve and the circumpharyngeal crest--a subpopulation of the cranial neural crest, and importantly these populations utilize this pathway before the myoblast precursors. However, ablation neither of the hypoglossal nerve nor of the neural crest results in a perturbation in the ability of this Pax-3 positive population to migrate. This demonstrates that migration of the precursors is independent of both of these cell populations, and that it is controlled by the peripheral tissues.

Animals↗
PubMed1998

An animal model for hemolytic disease of the fetus or newborn in New Zealand white and New Zealand red rabbits: newborn effects.

OBJECTIVE: Our purpose was to study the neonatal effects of red blood cell alloimmunization in a rabbit model. STUDY DESIGN: Eighteen does were alloimmunized to incompatible red blood cells. Does were bred twice, once with a homozygous buck of incompatible blood type and once with a homozygous buck of compatible blood type. Fetal blood sampling was undertaken on day 27 of gestation (term 28 to 31 days). Does were delivered on day 30 and the neonatal pups were anesthetized. Direct cardiac samplings were performed for hemoglobin, reticulocyte count, and direct Coombs' test. Hepatic, splenic, and renal wet weights were measured. RESULTS: Twenty-two pregnancies (12 compatible and 10 incompatible) were studied. Neonatal hemoglobin was higher in the compatible litters (11.1 gm/dL [7.7 to 12.6 gm/dL] vs 4.9 gm/dL [2.1 to 9.1 gm/dL], P <.001), whereas no difference could be detected between the respective reticulocyte counts (34.0/100 red blood cells [27.3 to 36.1/100 red blood cells] vs 32.6/100 red blood cells [26.8 to 43.5/100 red blood cells], P =.55). The direct Coombs' assay was negative in 23 pups from 8 compatible litters and false positive (weakly positive result) in 2 pups of a ninth compatible litter. The Coombs' assay was positive in all 22 incompatible pups tested. Hepatosplenomegaly was noted in affected pups but not in controls. CONCLUSIONS: A disease analogous to human hemolytic disease of the newborn can be induced in the rabbit neonate.

Animals↗
PubMed1998

Apolipoprotein E and regulation of cytokine-induced cell adhesion molecule expression in endothelial cells.

Atherosclerotic plaques develop in the arterial wall from complex multicellular processes following the early recruitment of circulating monocytes. Infiltration of monocytes is mediated by cell adhesion molecules (CAMs), including vascular cell adhesion molecule-1 (VCAM-1) which is rapidly induced in endothelial cells in response to cytokines. Apolipoprotein E (apo E), a 34-kDa polypeptide, helps protect against atherosclerosis, in part, because apo E phospholipid particles secreted by macrophages may have local protective effects within lesions. Here we have investigated whether purified plasma apo E, complexed with dimyristoyl phosphatidylcholine (DMPC) vesicles, can inhibit cytokine-induced vascular cell adhesion molecule-1 (VCAM-1) expression in human umbilical vein endothelial cells (HUVECs). Expression of VCAM-1 in endothelial cells after exposure to tumour necrosis factor-alpha (TNF-alpha) or interleukin 1beta (IL-1beta) was quantified by ELISA and shown to be partially inhibited by 17beta-estradiol (40-60% inhibition) or by S-nitroso-L-glutathione, a nitric oxide donor (20-25%). However, preincubations with physiological concentrations (10-100 microg protein/ml) of apo E DMPC did not downregulate VCAM-1 expression, even with extended preincubation times. These findings were confirmed using a fluorescence-activated cell sorter (FACS) for analysis which indicated additionally that apo E-DMPC had no effect on sub-populations within the HUVEC cultures. Finally, apo E-DMPC vesicles were also unable to suppress TNF-alpha-induced upregulation of E-selectin or intercellular adhesion molecule-1 (ICAM-1). We conclude that plasma apo E is unlikely to be important in limiting endothelial activation.

Apolipoproteins E↗
PubMed1998

Tumour necrosis factor stimulates stress-activated protein kinases and the inhibition of DNA synthesis in cultures of bovine aortic endothelial cells.

In this study, we examined the ability of tumour necrosis factor-alpha (TNF) to stimulate the mitogen-activated protein (MAP) kinase homologues p42/44 MAP kinase, c-Jun NH2-terminal kinase (JNK) and p38 MAP kinase and its effect upon DNA synthesis in primary cultures of bovine aortic endothelial cells (BAECs). TNF strongly stimulated p38 MAP kinase and JNK activity in both a time- and concentration-dependent manner. By contrast, TNF was a very poor activator of p42/44 MAP kinase relative to the known activator of p42/44 MAP kinase in endothelial cells, adenosine triphosphate (ATP). TNF-stimulated activation of p38 MAP kinase, and MAPKAP kinase-2, a known downstream target of p38 MAP kinase, was strongly inhibited by pre-incubation with the p38 MAP kinase inhibitor SB203580, whereas the minor activation of p42/44 MAP kinase was abolished by pre-incubation of the cell with the novel MAP kinase kinase 1 inhibitor PD098059. Addition of TNF resulted in a 50-60% decrease in DNA synthesis in BAECs. Pre-incubation with PD098059 or co-incubation with ATP failed to modify the inhibitory effect of TNF upon DNA synthesis. SB203580 reduced basal DNA synthesis by approximately 50%; however, if failed to modify the inhibition mediated by TNF. These results indicate that TNF strongly activates both p38 MAP kinase, JNK and, to a minor extent, p42/p44 MAP kinase. It is likely that only one of these kinases, JNK, plays a role in the regulation of DNA synthesis in these cells.

Animals↗
PubMed1998

Cervical and breast cancer screening in wheelchair dependent females.

The aim of this study was to compare the attendance rates for cervical and breast cancer screening in wheelchair dependent spinal cord injured (SCI) women with those in the general female population in England. The study was conducted as a postal questionnaire survey with an effective response rate of 79%. The attendance rates of the eligible SCI groups were 84% for cervical screening and 72% for mammography, both figures being well within the national average attendance rates in the general female population. Difficulties with cervical screening were reported in 58% and with mammography in 43% of the cases, including restricted access to clinics, examining rooms and examining couches and positioning during the procedure. These were also the main reasons given for non attendance. The article points out ways to enable even more wheelchair dependent women to benefit from the preventative screening programmes.

Adult↗
PubMed1998

Concerns and cautions about prescribing and deregulating emergency contraception: a qualitative study of GPs using telephone interviews.

OBJECTIVES: We aimed to describe GPs' responses to a clinical scenario of a request for a repeat prescription for hormonal emergency contraception (EC), their views about over-the-counter availability and beliefs about absolute contraindications. DESIGN: We conducted semi-structured tape-recorded telephone interviews with 76 GPs randomly selected from the medical registers of three health authorities which were chosen for high, medium and low prescribing rates for EC. RESULTS: There was a wide variation in the number of times that GPs would be happy to prescribe EC to the same woman in a year. The content of the consultations appeared patchy. While 59 (77.6%) of the GPs said that they would discuss future contraception with the woman, only 16 (21.1%) said they would talk about possible side effects and 28 (36.3%) would discuss the timing of the next menstrual period and the possibility of method failure. Fifty-two of the practices had a family-planning-trained practice nurse, yet only four (7.7%) had arrangements whereby the nurse could provide EC. Unqualified enthusiasm for deregulation was rare. Concerns included that women would lose out on the benefits of the consultation; worries about the safety of the method; that some women might 'abuse' it by using it frequently; and that certain characteristics of the pharmacy might make it an unsuitable setting for provision of EC. CONCLUSIONS: This qualitative telephone survey revealed concerns about repeated use of EC and caution about the prospects of deregulation. Respondents were worried that pharmacists might not be able to address all of the features of the consultation that may be valued, yet in this sample nor do most GPs. Family-planning-trained practice nurses are an under-utilized resource and could act as a halfway house between provision by GPs and deregulation.

Adult↗
PubMed1998

Does alpha-MSH have a role in regulating skin pigmentation in humans?

Over the years there has been much debate as to whether alpha-MSH has a role as a pigmentary hormone in humans. There are two main reasons for this. First, despite the observations in the 1960s that alpha-MSH increased skin darkening in humans, there are reports that the peptide has no effect on melanogenesis in cultured human melanocytes. Second, the human pituitary, unlike that of most mammals, secretes very little alpha-MSH and circulatory levels of the peptide in humans are extremely low. However, there is now evidence from several groups that alpha-MSH is capable of stimulating melanogenesis in cultured human melanocytes. Rather than producing an overall increase in melanin production, it appears that the peptide acts specifically to increase the synthesis of eumelanin. Such an action could well explain the previously observed skin darkening effects of alpha-MSH. It is also now known that alpha-MSH is not produced exclusively in the pituitary but has been found at numerous sites, including the skin where it is produced by several cell types. Related Proopiomelanocortin (POMC) peptides such as ACTH are also produced in human skin. The ACTH peptides act at the same receptor (MC-1) as alpha-MSH and certain of these would appear to be more potent than alpha-MSH in stimulating melanogenesis. The ACTH peptides are also present in greater amounts than alpha-MSH in human epidermis and it is likely that they play an important role in regulating pigmentary responses. These POMC peptides are released from keratinocytes in response to ultraviolet radiation (UVR) and it has been proposed that they serve as paracrine factors in mediating UV induced pigmentation. Their production by keratinocytes could therefore be critical in determining pigmentary responses and any changes in the availability of these POMC peptides might explain the variations in tanning ability seen in different individuals. However, the possibility that tanning ability is also dependent upon differences at the level of the MC-1 receptor cannot be ruled out and it has been suggested that an inability to tan may depend upon the presence of non-functional changes at the MC-1 receptor. alpha-MSH does, of course, affect human melanocytes in several ways and its stimulation of melanogenesis could be the consequence of some other fundamental action in the melanocyte. The peptide also has many other target sites in the skin and while it may have a role in regulating skin pigmentation in humans, it should not be viewed solely as a pigmentary peptide. alpha-MSH clearly has many different actions and its primary role in the skin may be to maintain homeostasis.

Adrenocorticotropic Hormone↗
PubMed1998

Cellular thiol production and oxidation of low-density lipoprotein.

Compelling evidence suggests that low-density lipoprotein (LDL) is oxidized by cells within the arterial intima and that, once oxidized, it is profoundly atherogenic. The precise mechanism(s) by which cells promote the oxidation of LDL in vivo are not known; in vitro, however, oxidation of LDL can be enhanced by a number of differing mechanisms, including reaction with free and protein-bound metal ions, thiols, reactive oxygen species, lipoxygenase, myeloperoxidase and peroxynitrite. This review is concerned with the mechanisms by which cells enhance the oxidation of LDL in the presence of transition metals; in particular, the regulation, pro- and anti-oxidant consequences, and mechanism of action of cellular thiol production are examined, and contrasted with thiol-independent oxidation of LDL in the presence of transition metals.

Animals↗
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↗