Biomedical subjects

N G Ardlie

Publications and source records attributed to N G Ardlie.

At least 19 recordsLinked to original sources

PubMed1994

Dipyridamole inhibits the oxidative modification of low density lipoprotein.

The oxidative modification of low density lipoprotein (LDL) is believed to play an important role in the initiation of the atherosclerotic lesion. Dipyridamole, which is used clinically as a coronary vasodilator and an antiplatelet agent, has antioxidant properties. Probucol is a lipid-lowering agent which inhibits the oxidative modification of LDL. We have compared the effect of pharmacological concentrations of dipyridamole and probucol on the oxidative modification of LDL by copper or endothelial cells in vitro. Dipyridamole protected LDL from oxidative modification by either copper ions or endothelial cells at concentrations as low as 2.5 microM while probucol had no effect at this concentration. LDL oxidized with copper in the presence of dipyridamole (20 microM) was less effective than LDL oxidized in the absence of dipyridamole at inhibiting [3H]acetyl-LDL binding to cultured human. THP-1 monocyte derived macrophages. The concentrations of dipyridamole found to inhibit the oxidative modification of LDL in vitro are achieved in vivo using clinically recommended doses.

Cells, Cultured↗

PubMed1994

Abnormal platelet reactivity in men with premature coronary heart disease.

BACKGROUND: Continuous platelet aggregation does not occur in patients with stable coronary heart disease (CHD). However, there may be a latent potential for increased aggregation given appropriate stimuli, since increased in-vitro platelet aggregation appears to be predictive of cardiac events. This study evaluates the relationship between in-vitro platelet aggregation and coronary artery disease (CAD) as defined by angiography. METHODS: In-vitro platelet aggregation was assessed in a case-control study of 53 men with CHD younger than 50 years, and in 48 control subjects without CHD who were matched for age, sex, and socioeconomic status. All major risk factors were evaluated. Semi-quantitative composite scores of the extent of arterial wall involvement and composite scores for the severity of discrete lesions were documented from standard coronary angiography. Measures of platelet aggregation in response to adrenaline, adenosine diphoshate (ADP), and collagen included: (1) the maximum slope of the aggregation curve (rate); (2) lag time to 50% maximum aggregation (LT50%); and (3) the threshold concentration of each agonist to cause maximal aggregation. RESULTS: The CHD patients had larger platelets than patients in the control group (mean platelet volume 9.40 +/- 0.73 versus 8.88 +/- 0.87; P < 0.01). The aggregation rate was significantly faster with adrenaline in the group with CHD than patients in the control group (rate of aggregation 13.9 +/- 8.8 versus 8.6 +/- 4.0 cm/s respectively, mean +/- SD; LT50% for adrenaline 130 +/- 70 versus 230 +/- 10 s respectively, mean +/- SD). Fewer CHD patients had no aggregation response to adrenaline than in the control group (8 versus 31%, P < 0.05). Adrenaline-induced platelet aggregation, as measured by LT50% for adrenaline, weakly but significantly correlated with the number and severity of discrete obstructive coronary lesions (r = -0.28, P < 0.05). This association remained significant after multivariate regression analysis. No association was found between any measure of platelet reactivity and the extent of disease as measured by a semi-quantitative composite score; this measured the extent of disease of the coronary artery walls visible by angiography. CONCLUSIONS: These findings indicate that platelets from men with premature CHD are larger and aggregate more rapidly in response to platelet agonists, particularly adrenaline. An increased rate of aggregability with adrenaline predicted the severity of CAD lesion but not the extent of the disease, and this suggests that platelets play a role in the formation of localized obstructive lesions in coronary arteries, and therefore acute coronary events.

Adenosine Diphosphate↗

PubMed1993

Relationship of blood cholesterol and apoprotein B levels to angiographically defined coronary artery disease in young males.

BACKGROUND: Coronary heart disease is mainly caused by the effects of obstruction to blood flow in the coronary arteries from discrete mural lesions that encroach into the lumen and usually occur in arteries that are involved by atherosclerosis. Even though the level of certain lipoproteins is indisputably related to the degree of this atherosclerotic involvement of the coronary arteries, the question of whether lipoproteins are also associated with the obstructive lesions remains uncertain. METHODS: This study addressed the question in 53 males (age, 44.6 +/- 4.9 y) with premature coronary heart disease and angiographically proven coronary artery disease. The cholesterol, triglyceride, high-density lipoprotein, apoprotein B, and apoprotein A-I levels were compared by linear correlation to semiquantitative angiographic measures of coronary artery disease severity (coronary stenosis score and mean coronary stenosis score), the extent of mural involvement (coronary atheromatous score and mean coronary atheromatous score), and also the number of normal coronary artery segments, an alternative severity score (Jenkins), and left ventricular function score. RESULTS: Age, past and present cholesterol, low-density lipoprotein cholesterol, and apoprotein B levels correlated directly with the extent of disease (r = 0.27, 0.46, 0.29, 0.26, 0.35, respectively, P < 0.05 with coronary atheromatous score; r = 0.29, 0.44, 0.33, 0.30, 0.35, respectively, P < 0.05 with mean coronary atheromatous score). Age and New York Heart Association angina functional class correlated directly with disease severity (r = 0.25, 0.31, respectively, P < 0.05 with coronary stenosis score; r = 0.25, 0.34, respectively, P < 0.05 with mean coronary stenosis score). There was an inverse association between age, past and present cholesterol, low-density lipoprotein cholesterol, and apoprotein B levels with the number of normal segments (r = -0.23, -0.46, -0.38, -0.35, -0.39, respectively, P < 0.05). Multiple regression analysis was undertaken with lipoproteins and age as independent variables and angiographic scores as dependent variables; the apoprotein B level was the most predictive of the extent of coronary artery disease (P < 0.02) and inversely predicted the number of normal segments (P < 0.002). Of those variables entered into the regression model, only age was independently predictive of the severity of angiographic coronary artery disease. CONCLUSION: Apoprotein B levels are not predictive of coronary artery disease severity but do predict independently the extent of involvement of coronary atherosclerosis defined angiographically.

Adult↗

PubMed1992

Occurrence of (E)-4-hydroxy-2-nonenal in plasma and synovial fluid of patients with rheumatoid arthritis and osteoarthritis.

(E)-4-Hydroxy-2-nonenal (HNE), a cytotoxic propagation product of lipid peroxidation, is present in the synovial fluid (0.54 (0.19) mumol/l; mean (SE), n = 9) and plasma (0.34 (0.09) mumol/l, n = 9) of patients with rheumatoid arthritis. This compound was also found in the synovial fluid (0.24 (0.19) mumol/l, n = 9) and plasma (0.09 (0.03) mumol/l, n = 9) of patients with osteoarthritis. The concentration of HNE in the plasma of patients with rheumatoid arthritis was significantly greater than in patients with osteoarthritis.

Aldehydes↗

PubMed1992

Effect of anethole dithiolthione on human platelet aggregation.

Anethole dithiolthione (ADT) (10 mumol/l) inhibited platelet aggregation and the formation of thromboxane (Tx)B2 in plasma in response to adenosine diphosphate (ADP), epinephrine and arachidonic acid (AA). ADT partially inhibited platelet aggregation and TxB2 formation in plasma induced by thrombin, phorbol myristate acetate and calcium ionophore A23187 and increased the lag time of collagen-induced aggregation at concentrations in the range 10-40 mumol/l. ADT (100 mumol/l) completely inhibited the aggregation of washed platelets challenged with thrombin. ADT had no additive effect on the inhibition of thrombin-induced platelet aggregation by acetylsalicylic acid. ADT was a more effective inhibitor of AA-induced platelet aggregation than butylated hydroxytoluene. ADT inhibited the release of 3H-AA from platelet phospholipids in response to ADP and collagen. It is suggested that ADT inhibits platelet aggregation by inhibiting thromboxane synthesis and preventing AA release.

Adenosine Diphosphate↗

PubMed1991

Content of significant amounts of a cytotoxic end-product of lipid peroxidation in human semen.

(E)-4-Hydroxy-2-nonenal (HNE), a cytotoxic end-product of lipid peroxidation, is present in significant amounts in human semen (0.902 +/- 0.190 microM; mean +/- s.e.; n = 18). The addition of the divalent cation ionophore A23187 to suspensions of human spermatozoa resulted in increased production of HNE. Exogenous HNE was powerfully spermicidal and as little as 50 microM caused an irreversible loss of motility of human spermatozoa within minutes. The addition of human seminal plasma protected spermatozoa from the toxic effects of HNE.

Aldehydes↗

PubMed1990

Effects of acrolein on human platelet aggregation.

Acrolein, a component of tobacco smoke, potentiated platelet aggregation and increased thromboxane A2 (TXA2) formation caused by thrombin and arachidonic acid (AA). Acrolein produced these effects at concentrations in the range 50-5000 microM. Acrolein had no effect on platelet responses to ADP, epinephrine, collagen or the ionophore A23187. Acrolein increased the mobilization of [3H]arachidonic acid from prelabelled platelets in response to thrombin and arachidonic acid. The increased availability of substrate could partly explain the enhanced production of TXA2 and increased aggregation observed in the presence of acrolein. These findings could provide an explanation for the increased incidence of vascular disease in cigarette smokers.

Acrolein↗

PubMed1989

Determination of the lipid peroxidation product trans-4-hydroxy-2-nonenal in biological samples by high-performance liquid chromatography and combined capillary column gas chromatography-negative-ion chemical ionisation mass spectrometry.

trans-4-Hydroxy-2-nonenal (HNE) is an aldehyde end-product of lipid peroxidation in biological systems which is capable of producing a range of powerful biological effects. We wish to describe a sensitive and selective strategy for the determination of HNE in biological samples. The method is based on the formation of the O-pentafluorobenzyl (O-PFB) oxime derivatives of HNE and its deuterated internal standard which, after sample clean-up by solid-phase extraction and purification by high-performance liquid chromatography (HPLC), were derivatised further to trimethylsilyl ethers. Subsequent capillary column gas chromatography-negative-ion chemical ionisation mass spectrometry (GC-NICIMS) using selected-ion monitoring allowed quantitation in the low ng/ml range. The use of an internal standard and the O-PFB oxime derivatives circumvented the problems encountered previously by other workers because of the volatility and instability of HNE. The syn-isomer of HNE O-PFB oxime followed the anti-isomer on the HPLC and GC columns used, giving a distinctive pair of peaks of characteristic relative proportion. Moreover, the NICI mass spectra of the geometrical isomers were significantly different, providing further evidence to validate the identity of any endogenous HNE recovered. The method was used to identify and quantify HNE in platelets, monocytes, plasma and oxidised low-density lipoprotein.

Aldehydes↗

PubMed1989

Platelet activation by oxidatively modified low density lipoproteins.

Interactions between altered lipoproteins and platelets may be important in atherosclerosis lesion formation and thrombosis. The aims of this study were to compare the effects of oxidatively modified and native low density lipoproteins (LDL) and high density lipoproteins (HDL) on platelet responses in the presence and absence of other platelet agonists, and investigate the mechanism(s) by which lipoproteins influence platelet activation. We have shown that native and oxidatively modified lipoproteins differ importantly in their effects on platelets; oxidation renders lipoproteins more reactive to platelets. Native LDL promote aggregation of human platelets, enhance the mobilization of arachidonate from phospholipids, increase thromboxane B2 production, and decrease membrane fluidity. Oxidized LDL are more reactive than native LDL and alone cause aggregation. Native HDL inhibit platelet responses and increase membrane fluidity. Oxidized HDL promote aggregation and cause spontaneous aggregation. The enhanced platelet responses cannot be attributed to increased production of thromboxane A2 since cyclooxygenase inhibitors (aspirin, indomethacin) have little inhibitory effect. The data suggest that activation of platelets by lipoproteins results from changes in membrane fluidity. These observations shed new light on the potential role of altered lipoproteins in the pathogenesis of atherosclerosis and its complications.

Arachidonic Acids↗

PubMed1988

Effect of 4-hydroxy-2,3-trans-nonenal on platelet function.

4-Hydroxy-2,3-trans-nonenal (HNE), an aldehyde end-product of lipid peroxidation, potentiated aggregation and increased thromboxane A2 formation in platelets challenged with ADP, thrombin or the ionophore A23187. These effects were observed at HNE concentrations in the range 10-100 microM. Platelet responses to collagen, epinephrine and arachidonic acid were not affected by HNE. Concentrations of HNE in excess of 100 microM inhibited platelet activation. HNE increased the release of 3H-arachidonic acid from prelabelled platelet phospholipids in response to thrombin or ADP. It is proposed that HNE may play an important role in controlling platelet function by regulating the activity of phospholipase A2.

Acrolein↗

PubMed1987

Synergistic potentiation by epinephrine of collagen or thrombin-induced calcium mobilization in human platelets.

Changes in cytoplasmic free calcium in response to epinephrine in combination with other agonists were studied in human platelets loaded with the fluorescent calcium indicator, quin 2. In the presence of 1mM external calcium, epinephrine augmented the increase in cytoplasmic free calcium in response to collagen or thrombin, and this was inhibited by yohimbine. In the absence of extracellular calcium, thrombin and collagen only caused a small increase in cytoplasmic free calcium, and the response was not enhanced by epinephrine. High concentrations of epinephrine alone caused a small increase in cytoplasmic free calcium in platelets when calcium was present externally. Inhibition of cyclooxygenase by aspirin markedly reduced the calcium response to collagen and almost completely inhibited potentiation by epinephrine. The calcium response to thrombin was inhibited to a lesser extent by aspirin, and aspirin did not prevent potentiation by epinephrine. These findings suggest that augmentation of the cytoplasmic free calcium level may be involved in the potentiation of platelet responses to agonists by epinephrine, and that metabolites of arachidonic acid make an important contribution to this action of epinephrine.

Aminoquinolines↗

PubMed1986

Collagen increases cytoplasmic free calcium in human platelets.

The role of changes in cytoplasmic free calcium in response to collagen was studied in human platelets loaded with the fluorescent calcium indicator, quin2. In the presence of 1mM external calcium, collagen caused a biphasic increase in cytoplasmic free calcium. In the absence of external calcium, there was a much smaller increase in cytoplasmic free calcium. These findings suggest that collagen increases cytoplasmic free calcium, partly by discharge of internal calcium, but mainly by stimulating calcium influx. Inhibition of cyclooxygenase by aspirin markedly reduced the second phase of the calcium response. Removal of ADP with apyrase resulted in complete inhibition of the second phase of the calcium response. The combination of apyrase and aspirin completely inhibited aggregation and the shape change caused by collagen. The calcium-entry blocking agent, verapamil, also inhibited the second phase of the calcium response to collagen. The increase in cytoplasmic free calcium is fast enough to be involved in the platelet response to collagen and these findings suggest that ADP and metabolites of arachidonic acid mediate the second phase of the calcium response to collagen.

Adenosine Diphosphate↗

PubMed1985

Acute postprandial lipaemia does not influence the in vivo activity of human platelets.

Platelet function and serum lipid studies were conducted on nine healthy male subjects before and two hours after three separate meals, two of which were rich in fat: saturated fat (SF) or polyunsaturated fat (PUF), and a third control meal which contained no fat. Platelet activity was assessed by determination of in vivo platelet aggregate formation, and plasma levels of the platelet specific proteins platelet factor 4 (PF4) and beta-thromboglobulin (beta-TG). Serum triglyceride levels increased significantly after both fat containing meals but were unaffected by the fat free meal. Serum cholesterol levels were not affected by any of the three meals. Platelet function tests could not detect any alteration of in vivo platelet activity in terms of platelet aggregate formation or plasma concentrations of PF4 and beta-TG. These results are at variance with previously published studies that used less specific assays of platelet activity and which suggested platelet activation shortly after meals rich in SF.

Adult↗

PubMed1985

Effects of trifluoperazine on platelet activation.

Previous reports of the inhibitory effects of trifluoperazine on platelet responses to different aggregating agents have been conflicting, and the mechanism of action remains unclear. We have found that aggregation by minimum concentrations of collagen and arachidonic acid, and second phase aggregation by minimum concentrations of ADP, thrombin, epinephrine and the calcium ionophore A23187 were inhibited by 40-60 microM trifluoperazine. The first phase of aggregation by a minimum concentration of epinephrine was completely inhibited by 100 microM trifluoperazine, and the first phase of aggregation induced by ADP, thrombin or A23187 was decreased by 300 microM trifluoperazine. The platelet shape change caused by collagen, but by no other aggregating agent examined, was inhibited by 300 microM trifluoperazine. Secretion of 3H-5 hydroxytryptamine by minimum concentrations of ADP, collagen, epinephrine and arachidonic acid was completely suppressed by 50 microM trifluoperazine. Secretion by thrombin and A23187 was incompletely inhibited by 300 microM trifluoperazine. Thromboxane B2 formation caused by all aggregating agents, except epinephrine, was incompletely suppressed by 50 microM trifluoperazine, and 300 microM trifluoperazine only caused complete inhibition of thromboxane B2 formation by ADP, collagen and epinephrine. The phorbol ester, TPA, which mimics diacylglycerol by activating protein kinase C, caused aggregation and secretion. Aggregation, but not secretion, by low concentrations of TPA was inhibited by concentrations of trifluoperazine as low as 50 microM. However, aggregation by a combination of TPA and A23187 was only inhibited by concentrations of trifluoperazine in excess of 100 microM. Secretion by TPA was inhibited by concentrations of trifluoperazine in excess of 200 microM. Our findings suggest that low concentrations of trifluoperazine inhibit platelet activation by inhibiting phospholipase A2, and that higher concentrations inhibit platelet responses by interfering with protein kinase C.

Adenosine Diphosphate↗

PubMed1985

Effect on human platelets of catecholamines at levels achieved in the circulation.

Epinephrine at concentrations varying between 3.3 and 12.5 nM had no effect on blood platelets when added alone, but augmented the in vitro platelet response to collagen and thrombin. Both aggregation and secretion responses were enhanced. Norepinephrine produced similar effects but was 50-60% less active than epinephrine. The minimum concentration of epinephrine or norepinephrine to achieve potentiation of platelet responses was even lower in the presence of 5-hydroxy- tryptamine. In contrast to the effects observed with higher concentrations of catecholamines, the synergistic interaction of these low concentrations of catecholamines with other agonists was not transient. The augmented response to catecholamines was mediated by platelet alpha 2-adrenoceptors. The response was inhibited by aspirin indicating that metabolism of arachidonic acid contributes to the synergy between low concentrations of catecholamines and other agonists. These studies show that the levels of the hormones epinephrine and norepinephrine obtained in circulating blood in humans, can be sufficient to enhance platelet responses. The action of catecholamines on platelets may be important in hemostasis and could provide an explanation for the association between certain risk factors and cardiovascular disease.

Adenosine Diphosphate↗

PubMed1984

Platelet activation by circulating levels of hormones: a possible link in coronary heart disease.

Blood platelets participating in the formation of haemostatic plugs or thrombi are likely to be exposed to combinations of several agonists. We have found that platelet aggregation and the release reaction are enhanced by combinations of the hormones adrenaline, noradrenaline, vasopressin and 5 hydroxytryptamine acting synergistically at levels obtained in circulating blood for three of these hormones. If surges of adrenaline and other hormones sensitize platelets this may provide a link between some of the risk factors and coronary heart disease.

Adult↗

PubMed1983

Effect of the calcium-entry blocking agent nifedipine on activation of human platelets and comparison with verapamil.

The effects of the calcium-entry blocking agent nifedipine on the activation of human platelets by various agonists has been studied and compared with verapamil. Like verapamil, nifedipine inhibited platelet aggregation and secretion caused by collagen, the second phase of ADP-induced aggregation, and aggregation caused by the ionophore A23187. Both agents inhibited the formation of TXB2 from endogenous arachidonate, whereas only nifedipine inhibited platelet aggregation and decreased TXB2 formation caused by exogenous arachidonate without inhibiting uptake. These results indicate that both calcium-blocking agents may be inhibiting the release of arachidonate in platelets by phospholipases, and that nifedipine also inhibits the formation and action of thromboxane A2 in platelets. Epinephrine-induced aggregation was inhibited by low concentrations of verapamil while nifedipine only inhibited aggregation by epinephrine at much higher concentrations. It is suggested that low concentrations of verapamil inhibit epinephrine-induced aggregation by interacting with platelet alpha-adrenergic receptors, and that higher concentrations of both calcium-blocking agents inhibit platelet responses to other aggregating agents by preventing intracellular calcium mobilization.

Arachidonic Acid↗

PubMed1983

Verapamil and collagen-induced platelet reactions--evidence for a role for intracellular calcium in platelet activation.

Calcium is considered to have an essential role in various platelet reactions. Using platelets preincubated with chlortetracycline, a fluorescent divalent cation indicator, and suspended in a calcium free medium, it was shown that collagen-induced intracellular calcium redistribution occurred before the platelet shape change, the release reaction and thromboxane B2 formation. Verapamil, at concentrations which affect intracellular calcium movements, inhibited intracellular calcium redistribution in platelets and the subsequent collagen-induced platelet reactions. Low concentrations of the ionophore A23187 overcame the inhibitory effect of verapamil. These experiments provide evidence that intracellular calcium mobilization is involved in the activation of platelets by collagen. Furthermore, calcium may be released from different cellular pools since platelet secretion, aggregation and thromboxane B2 formation were inhibited at lower concentrations of verapamil than was the platelet shape change.

Adenosine Triphosphate↗