Biomedical subjects

A O'Dowd

Publications and source records attributed to A O'Dowd.

At least 19 recordsLinked to original sources

PubMed2000

Vascular smooth muscle actions of carnosine as its zinc complex are mediated by histamine H(1) and H(2) receptors.

The endogenous dipeptide carnosine (beta-alanyl-L-histidine), at 0.1-10 mM, can provoke sustained contractures n rabbit saphenous vein rings with greater efficacy than noradrenaline. The effects are specific; anserine and homocarnosine are ineffective, as are carnosine's constituent amino acids histidine and beta-alanine. Zinc ions enhance the maximum carnosine-induced tension (to 127 +/- 13% of control at 10 microM Zn(total)) and muscle sensitivity is potentiated (mean K(0.5) reduced from 1.23 mM to 17 microM carnosine with 15 microM Zn(total)). The dipeptide acts as a Zn-carnosine complex (Zn. Carn). The effects of carnosine at 1 microM-10 mM (total) in the presence of 1-100 microM Zn(2+) (total) can be described as a unique function of [Zn. Carn] with an apparent K(0.5) for the complex of [7.4)(10(-8)] M. Contractures are reduced at low [Ca(2+)], unaffected by adrenoceptor antagonists, but can be blocked by antagonists to several receptor types. The most specific effect is by mepyramine, the H(1) receptor antagonist. With Zn present, carnosine can inhibit the H(1)-specific binding of [(3)H]mepyramine to isolated Guinea pig cerebella membranes. This effect of carnosine can be described as a function of the concentration of Zn. Carn with an apparent IC(50) of 2.45 microM. Like histamine, carnosine evoked an H2-mediated (cimetidine-sensitive) relaxation in the presence of mepyramine, but was less potent (10.8 +/- 3.1% of initial tension remaining at 10 mM carnosine compared with 13.4 +/- 7.5% remaining at 0.1 mM histamine). Preliminary studies with a Zn-selective fluorescent probe indicate that functionally significant levels of Zn can be released from adventitial mast cells that could modulate actions of carnosine in the extravascular space as well as those of histamine itself. We conclude that carnosine can act at the smooth muscle H(1)-receptor to provoke vasoconstriction and that it also has the potential to act at H(1)-receptors in the central nervous system. Carnosine's mode of action is virtually unique: a vascular muscle receptor apparently transduces the action of a dipeptide in the form of a metal chelate. The functional relationship of carnosine with histamine and the possible physiological relevance of Zn ions for the activity of both agents have not previously been reported.

Animals↗

PubMed1999

Fine mapping of the binding sites of monoclonal antibodies raised against the Pk tag.

The monoclonal antibody (mAb) SV5-Pk is used widely in a variety of procedures to detect recombinant proteins tagged with the Pk tag, a 14 amino acid sequence derived from the P and V proteins of the paramyxovirus Simian Virus 5. Here we report on the isolation and characterisation of four additional SV5-Pk mAbs (termed SV5-Pk2 to 5) that bind the Pk tag. All the SV5-Pk mAbs can detect Pk tagged recombinant proteins in a variety of immunological procedures, including ELISA and immunofluorescence. Using SPOT technology, the minimal binding epitope of each SV5-Pk mAb was defined by one-sided terminal truncation analysis from either the amino- or carboxy-ends of the Pk peptide. Each mAb recognises slightly different epitopes within the Pk tag, ranging from 5 to 9 amino acids in length. The equilibrium dissociation constants (Kd) of the mAbs, as measured by surface plasmon resonance, ranged from approximately 20 to 60 pmol. Cysteine scanner mutations throughout the Pk tag revealed that some amino acids within the minimal binding epitopes were critical for mAb binding, while others could readily be substituted with little or no effect on antibody binding. The development of the Pk tag as a spacer arm for site-directed chemical coupling, and the use of the mAbs to monitor purification and coupling procedures, is discussed.

Amino Acid Sequence↗

PubMed1998

Analysis of an H1 receptor-mediated, zinc-potentiated vasoconstrictor action of the histidyl dipeptide carnosine in rabbit saphenous vein.

The contractile action of the dipeptide carnosine (beta-alanyl-L-histidine), active as a Zn.carnosine complex (Zn. Carn), was investigated in isolated rings of rabbit saphenous vein (RSV) and was found to be antagonized by the H1 antagonist mepyramine. Mepyramine-sensitive, histamine-induced contractures in RSV, were smaller (73+/-0.1%) and less well sustained than carnosine-induced contractures. Schild plot values for mepyramine antagonism were, for carnosine-induced contractures; pA2 = 7.97+/-0.12, slope= 1.33+/-0.06 (r = 0.793) and for histamine-induced contractures; pA2 = 8.48+/-0.07, slope = 0.63+/-0.05, r = 0.957). Serotonergic antagonists methiothepin and ketanserin, antagonize both carnosine- and histamine-induced contractures in RSV, probably reflecting coincidental inhibition at the H1-receptor. Carnosine, with Zn present, can inhibit the H1-specific binding of [3H]-mepyramine to isolated guinea-pig cerebellar membranes (log IC50s - 2.78+/-0.02, -3.93+/-0.03 and -4.64+/-0.03 at 10, 30 and 80 microM Zn respectively; values corrected for the Zn-specific inhibition which has a logIC50 of -4.20). In the radioligand binding assay, the effect of carnosine can be described as a function of Zn. Carn concentration with an apparent logIC50 of -5.61. This value is consistent with that obtained from the functional studies on RSV. Histamine-induced contractures have an indomethacine-sensitive component (27.2+/-8.3% of control response), not apparent with carnosine-induced contractures. Like histamine, carnosine evoked an H2-mediated (cimetidine-sensitive) relaxation in the presence of mepyramine, but was less potent (10.8+/-3.1% residual tension at 10 mM carnosine compared with 13.4+7.5% at 0.1 mM histamine). Carnosine, like mepyramine, can 'reveal' the H2-mediated relaxation of histamine providing further evidence that carnosine binds at the H1 receptor. We conclude that carnosine can act at the smooth muscle H1-receptor to provoke vasoconstriction and that it also has the potential to act at H1-receptors in CNS.

Animals↗

PubMed1996

The dipeptide carnosine constricts rabbit saphenous vein as a zinc complex apparently via a serotonergic receptor.

1. The endogenous dipeptide carnosine (beta-alanyl-L-histidine), at 0.1-10 mM, provokes sustained contractures in rabbit saphenous vein rings with greater efficacy than noradrenaline (NA). 2. The effects of carnosine are specific; anserine and homocarnosine are ineffective, as are carnosine's constituent amino acids histidine and beta-alanine. 3. Maximum carnosine-induced tension is enhanced by Zn ions (e.g. to 127.5 +/- 13.1% of control at 10 microM total Zn concentration, Zntot) and the sensitivity to carnosine potentiated (mean [carnosine] required for half-maximal tension, K1/2, reduced from 1.23 mM to 17.0 microM carnosine with 15 microM Zntot). 4. The dipeptide apparently acts as a zinc-carnosine complex. The effects of carnosine at concentrations of 1 microM to 10 mM in the presence of 1-100 microM Zntot, can be described as a unique function of the concentration of Zn-carnosine, with an apparent K1/2 for the complex of 7.4 x 10(-8) M. 5. Contractures are reduced at low [Ca2+], unaffected by adrenoceptor antagonists, but can be blocked by serotonergic receptor antagonists including ketanserin and methiothepin. 6. Competition between albumin and carnosine for Zn ions, as might occur in plasma, can be demonstrated experimentally. 7. The mode of action of carnosine is virtually unique: a vascular muscle receptor apparently transduces the action of a dipeptide in the form of a metal chelate.

Adrenergic alpha-Antagonists↗

PubMed1995

The relationship between the adrenoceptor and nonadrenoceptor-mediated effects of imidazoline- and imidazole-containing compounds.

This article brings together work on imidazoline or imidazole-containing compounds concerned with the pharmacology of alpha-adrenoceptors, principally on smooth muscle, to illustrate how imidazolines have contributed to the subclassification of alpha-adrenoceptors and how, against this background, attempts have been made to use this knowledge to uncover "nonadrenoceptor"-mediated biological effects of previously uncharacterized compounds, notably imidazole-containing dipeptides and "clonidine displacing substance" (CDS). Recent data are included on (1) the pharmacology of UK-14304, (2) nonadrenoceptor actions of phentolamine, (3) the pharmacology of tissue extracts containing imidazole-containing dipeptides and CDS activity, and (4) ligand binding data at I1 and I2 sites.

Animals↗

PubMed1994

A double-blind placebo controlled trial of Efamol Marine on skin and joint symptoms of psoriatic arthritis.

Fish oil may be beneficial in the treatment of psoriasis and in RA. We examined the potential benefit of Efamol Marine, a combination of evening primrose oil and fish oil in the treatment of 38 patients with PsA. Patients with PsA were entered in a double-blind placebo controlled study and received either 12 Efamol Marine capsules or 12 placebo capsules daily for 9 months. All patients received placebo capsules for a further 3 months. At month 3 of the study patients were asked to reduce their intake of NSAIDs and maintain that decrease provided there was no worsening of their joint symptoms. Clinical assessments of skin and joint disease severity and activity were performed at 0, 1, 3, 6, 9 and 12 months. All measures of skin disease activity including severity, percentage body affected and itch were unchanged by Efamol Marine. The NSAID requirement remained the same between both treatment groups. In addition, there was no change demonstrated in the activity of arthritis as measured by duration of morning stiffness. Ritchie articular index, number of active joints, ESR and CRP. However, a rise in serum TXB2 was observed in the active group during the placebo phase; in addition a fall in leukotriene B4 production occurred during the active phase period followed by a marked rise during the placebo phase suggesting some laboratory documented anti-inflammatory effect. In conclusion, this study suggests that Efamol Marine may alter prostaglandin metabolism in patients with PsA, although it did not produce a clinical improvement and did not allow reduction in NSAID requirement. A larger dose of essential fatty acid may be needed to produce a clinical benefit.

Administration, Oral↗

PubMed1992

Analysis of novel imidazoles from isolated perfused rabbit heart by two high-performance liquid chromatographic methods.

The paper reports two analytical high-performance liquid chromatographic methods to detect and quantify cardiac-derived histidyl derivatives. Method A relies on relative hydrophobicities as a basis of separation. Method B is an ion-pairing method in which the compounds are eluted in an entirely different order. Fractions collected from method A have been co-eluted in admixture in method B with authentic reference compounds. Thus the existence of the following imidazole ring-containing compounds derived from heart have been confirmed: N-acetylhistidine, N-acetyl-1-methylhistidine, N-acetylcarnosine, N-acetylhomocarnosine, homocarnosine, anserine, carnosine, balenine. Compounds were found in both tissue samples and perfusates.

Animals↗

PubMed1992

White blood cell activation in Raynaud's phenomenon of systemic sclerosis and vibration induced white finger syndrome.

Systemic sclerosis (SSc) and vibration induced white finger syndrome (VWF) are common causes of secondary Raynaud's phenomenon. Previous studies have suggested an increase in inflammation in patients with SSc. Vibration induced white finger syndrome occurs in workers exposed to vibration and is now a prescribed disease. In VWF, although it is recognised that vibration can cause direct damage to blood vessels, it does not explain why only some workers are affected. It is possible that an inflammatory process develops in these patients in the same way as is seen in SSc. Leukotriene B4, produced mainly by polymorphonuclear cells, is a potent mediator of inflammation. The plasma thiol concentration shows the degree of oxidation of plasma and a decreased concentration indicates the increased production of free radicals which are capable of oxidative damage. In this work, the white blood cell (WBC) production of leukotriene B4 and plasma thiol concentrations were measured in patients with SSc and VWF. Fifty nine patients were studied: 34 had SSc and 25 had VWF. The results were compared with 25 matched normal controls and are expressed as the median and range. After stimulation of the polymorphonuclear cells with calcium ionophore A23187 (1 microgram/ml), patients with SSc and VWF were found to have significantly increased leukotriene B4 production (23.5 (14.4-44.0) and 26 (14.4-39.4) ng/10(6) cells, respectively) compared with normal controls (17.2 (6.0-38.0) ng/10(6) cells). The plasma thiol concentration was shown to be significantly lower in patients with SSc and VWF (445 (375-475) and 450 (417-510) mumol/l, respectively) compared with normal controls (480 (418-555) mumol/l). Our results show increased leukotriene B4 production and increased free radical activity in patients with SSc and VWF. Although previous indirect evidence has suggested increased WBC activity in patients with SSc, this is reported directly here for the first time. In addition, the possibility of an inflammatory process occurring in patients with VWF, as shown here, has not previously been studied. This may be a further mechanism to explain the poor circulation in the fingers of these patients.

Adult↗

PubMed1989

Leukotriene b4 production by peripheral blood neutrophils in rheumatoid arthritis.

Leukotriene B4 (LTB4) is an activator of white blood cells (WBC) and it has been suggested that its inhibition may be useful in rheumatoid arthritis (RA). Its production by peripheral WBC has not yet been investigated. We measured LTB4 production in 105 patients with RA and compared it with 59 matched controls. C-reactive protein (CRP) and ESR were measured in 90 patients and correlated with LTB4 values. Ten millilitres of blood were drawn. Separation was undertaken to obtain polymorphonuclear leukocytes (PMN) which were stimulated with calcium ionophore, and the supernatant was frozen for radioimmunoassay of LTB4. Results show that RA patients produce significantly higher levels of LTB4. It has been suggested that blockage of the cyclo-oxygenase enzyme by non-steroid anti-inflammatory drugs (NSAID) leads to increased production of LT via the lipoxygenase enzyme. Twenty-one patients not taking NSAID were compared with 84 on therapy. There was no significant difference. A linear regression was used to obtain Pearson's correlation coefficients. With LTB4 and CRP, r = 0.3 (p less than 0.003). With LTB4 and ESR, r = 0.25 (p less than 0.02). Low but significant correlations with CRP and ESR were obtained.

Adult↗

PubMed1988

Effects of altering dietary essential fatty acids on requirements for non-steroidal anti-inflammatory drugs in patients with rheumatoid arthritis: a double blind placebo controlled study.

In rheumatoid arthritis (RA) benefit from non-steroidal anti-inflammatory drugs (NSAIDs) is mediated through inhibition of the cyclo-oxygenase enzyme, thereby decreasing production of the 2 series prostaglandins (PGs). The lipoxygenase enzyme is intact, however, allowing leucotriene (LT) production, e.g., LTB4 (an inflammatory mediator). Treatment with evening primrose oil (EPO) which contains gamma-linolenic acid (GLA) leads to production of the 1 series PGs, e.g., PGE1, which has less inflammatory effects. Also LT production is inhibited. Eicosapentaenoic acid (EPA, fish oil) treatment provides a substrate for PGs and LTs, which are also less inflammatory. In this study 16 patients with RA were given 540 mg GLA/day (EPO), 15 patients 240 mg EPA and 450 mg GLA/day (EPO/fish oil), and 18 patients an inert oil (placebo). The aim of this study was to determine if EPO or EPO/fish oil could replace NSAID treatment in RA. The initial 12 month treatment period was followed by three months of placebo for all groups. Results at 12 months showed a significant subjective improvement for EPO and EPO/fish oil compared with placebo. In addition, by 12 months the patients receiving EPO and EPO/fish oil had significantly reduced their NSAIDs. After 3 months of placebo those receiving active treatment had relapsed. Despite the decrease in NSAIDs, measures of disease activity did not worsen. It is suggested that EPO and EPO/fish oil produce a subjective improvement and allow some patients to reduce or stop treatment with NSAIDs. There is, however, no evidence that they act as disease modifying agents.

Adult↗

PubMed1987

Abnormal biochemical and cellular parameters in the blood of patients with Raynauds phenomenon.

Finger blood flow is decreased in Raynauds Phenomenon (RP). This may be due not only to vasospasm, but also to blood abnormalities. 40 patients with Raynauds Disease (RD), 28 with suspected RP (SS) and 42 with secondary Raynauds syndrome (RS) were enrolled and compared to 50 controls. Results from base-line samples show that those with RP have abnormal haemostasis and rheology whereas those with mild Raynauds, RD do not. Blood sampled after cold challenge in 15 RS patients and 15 controls show that both groups exhibit platelet activation after emersion. The degree of activation however was much more marked in the RS patients. We have shown that abnormalities of haemostasis and rheology are found in patients likely to have endothelial damage (RS). These changes are probably a consequence rather than a cause of the disease. After cold challenge the results become more abnormal and correlate with severity of disease.

Blood Flow Velocity↗

PubMed1985

Evening primrose oil (Efamol) in the treatment of Raynaud's phenomenon: a double blind study.

Prostaglandin E1 (PGE1) and prostacyclin have been used in Raynaud's phenomenon (RP) but are unstable and require intravenous administration. An alternative approach is to stimulate the body's own PGE1 production via administration of the precursor essential fatty acid. We studied the effect of 12 capsules/day of evening primrose oil (EPO) on the manifestations of RP. 21 patients received a two week course of placebo, thereafter 11 received EPO for 8 weeks and 10 patients received placebo. As the weather worsened the placebo group experienced significantly more attacks than the EPO group. Visual analogue scales assessing the severity of attacks and coldness of hands improved in the EPO group. No changes were seen in either group in hand temperatures and cold challenge plethysmography. Blood tests showed some antiplatelet effects of the drug. In conclusion patients receiving EPO benefited symptomatically. This was not matched however by any change in objective assessment of blood flow, although changes in platelet behaviour and blood prostanoids were observed.

Cold Temperature↗

PubMed1985

Platelet sensitivity to a prostacyclin analogue in systemic sclerosis.

Vascular prostacyclin (PGI2) regulates platelet function and blood flow. In systemic sclerosis (SS) there is increased platelet aggregation (PA) but no information is available on the platelet/PGI2 relationship. We evaluated platelet sensitivity to a PGI2 analogue ZK36374 in 17 SS patients and 18 controls. The percentage (%) inhibition of PA was measured at two doses of ZK36374 with saline giving the 100% baseline. In the SS group 2 ng ZK36374 produced a percentage inhibition of 19 + 14 compared to a control value of 60 + 21, and 3 ng a percentage inhibition of 47 + 21 in the SS group and 82 + 20 in the controls. In 11 SS patients treated with either prostaglandin E or nifedipine the sensitivity approached normal. These data suggest that SS platelets are less sensitive to the inhibitory effect of PGI2 on PA. This may contribute to the vascular lesions of SS. Other cells are resistant to the effects of PGI2 and our findings support this picture of cellular resistance.

Adult↗

PubMed1983

Regulation of protein A biosynthesis in Staphylococcus aureus by certain antibiotics: its effect on phagocytosis by leukocytes.

Protein A, a component of the outer layer of the cell wall of Staphylococcus aureus impairs opsonization by serum complement and thereby delays phagocytosis by polymorphonuclear leukocytes. Two antibiotics with modes of action on bacterial protein biosynthesis, have been used at sub-growth inhibitory concentrations to regulate the production of protein A. Both clindamycin and fusidic acid (either at 1/2 or 1/4 MIC) reduced the amount of protein A on the cell surface. Such drug-grown cells became more susceptible to phagocytic uptake and killing. Chemiluminescence (CL) of PMN when presented with preopsonized drug-grown staphylococci was potentiated and correlated with the enhanced phagocytosis seen earlier. The level of CL appeared to depend upon the amount of human serum used to opsonize the bacteria. Reduced protein A content on the cell surface probably resulted in the exposure of a greater number of receptor sites for C3b, rendering the bacterium more susceptible to attachment and ingestion by the polymorphonuclear leukocyte.

Anti-Bacterial Agents↗

PubMedDate not supplied