Increased platelet sensitivity and thromboxane B2 formation in type-II hyperlipoproteinaemic patients

Platelet Function in Aging

Aging is associated with an increased incidence of cardiovascular disease and thrombosis. Platelets play a major role in maintaining hemostasis and in thrombus formation, making them a key player in thrombotic disorders. Whereas it is well-known that platelet aggregability is increased in vascular diseases, the contribution of age-related changes in platelet biology to cardiovascular risk is not well-understood. Several lines of evidence support that platelets from older subjects differ in their function and structure, making platelets more prone to activation and less sensitive to inhibition. These age-related changes could lead to platelet hyperactivity and to the development of a prothrombotic state in advanced age. This review will focus on platelet biochemical modifications during aging and on the mechanisms by which these alterations could lead to thrombotic disease.

Increased Mean Platelet Volume in Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is a genetic disorder of lipoprotein metabolism and increases the risk of premature cardiovascular diseases. In patients with FH, platelet function may be activated; however, the extent of this activation and its etiology are unclear. We aimed to evaluate the mean platelet volume (MPV), a marker of platelet activation, in patients with FH. The study group consisted of 164 patients with FH and 160 control patients. Controls were matched for age, gender, hypertension, and smoking. The MPV was significantly higher in patients with FH than in controls (9.2 ± 0.4 vs 7.9 ± 0.6 fL, respectively; P < .001). Platelet count was significantly lower among patients with FH when compared to control patients (259 ± 51 vs 272 ± 56 × 103/L, respectively; P = .03). In linear regression analysis, MPV was independently associated only with total cholesterol (β = .6, 95% confidence interval: 0.004-0.008, P < .001). We have shown that MPV was increased in patients with FH and that it was independently associated with total cholesterol level.

Differential effects of native and oxidatively modified low-density lipoproteins on platelet function

Low-density lipoproteins (LDL) have been various reported to induce platelet aggregation independently and/or sensitise platelets to other agonists. In these earlier studies the extent of oxidation of LDL was not always reported or addressed. We have now investigated the effects of native, minimally modified and fully oxidised LDL (0-1gapolipoproteinB(100)/l on platelet function using platelet aggregometry and fluorescence activated flow cytometry. Native LDL did not activate isolated platelets but inhibited ADP- and thrombin-induced aggregation of isolated platelets by 51 % in the presence or absence of added fibrinogen. Longer pre-incubations were required to produce a comparable inhibition by native LDL on platelets in plasma. Flow cytometric analysis showed that native LDL inhibited ADP-induced fibrinogen binding by up to 38%. In contrast, minimally modified LDL induced primary platelet aggregation and fibrinogen binding in the absence of other agonists, enhanced both submaximal (1-2mumol/l) ADP-induced aggregation, fibrinogen binding and degranulation (CD63 and P-selectin expression). Fully oxidised LDL, however, inhibited ADP-induced platelet aggregation and fibrinogen binding. The effects of minimally modified LDL on platelet aggregation could be reproduced partially by adding 15-hydroperoxy-eicosatetraenoic acid to native LDL. These data indicate that the extent of oxidation of LDL is critical in determining their effects on platelet function. Native LDL did not activate platelets, whilst minimally modified LDL exerted a pro-aggregatory effect, possibly due to the presence of lipid hydroperoxides near to the concentration range found in pathological states.

L-4F alters hyperlipidemic (but not healthy) mouse plasma to reduce platelet aggregation

Background and Purpose- Hyperlipidemia is associated with platelet hyperreactivity. We hypothesized that L-4F, an apolipoprotein A-I mimetic peptide, would inhibit platelet aggregation in hyperlipidemic mice.

METHODS AND RESULTS

Injecting L-4F into apolipoprotein E (apoE)-null and low-density lipoprotein receptor-null mice resulted in a significant reduction in platelet aggregation in response to agonists; however, there was no reduction in platelet aggregation after injection of L-4F into wild-type (WT) mice. Consistent with these results, injection of L-4F into apoE-null mice prolonged bleeding time; the same result was not found in WT mice. Incubating L-4F in vitro with apoE-null platelet-rich plasma also resulted in decreased platelet aggregation. However, incubating washed platelets from either apoE-null or WT mice with L-4F did not alter aggregation. Compared with WT mice, unstimulated platelets from apoE-null mice contained significantly more 12-hydroxy 5,8,10,14-eicosatetraenoic acid, thromboxane A(2), and prostaglandins D(2) and E(2). In response to agonists, platelets from L-4F-treated apoE-null mice formed significantly less thromboxane A(2), prostaglandins D(2) and E(2), and 12-hydroxy 5,8,10,14-eicosatetraenoic acid.

CONCLUSIONS

By binding plasma-oxidized lipids that cause platelet hyperreactivity in hyperlipidemic mice, L-4F decreases platelet aggregation.

Blood platelet release correlates with serum lipids in 50 year old men with essential hypertension

50 year old men with moderate, essential hypertension (n = 39) were compared to normotensive males of similar age (n = 31). The hypertensive men were heavier (10 kg in average, p less than 0.01), and had a higher pulse rate (5 beats per minute (p less than 0.05). Plasma beta-thromboglobulin, a marker of platelet release reaction, was 49% higher in the hypertensive group (p less than 0.01). Total cholesterol, LDL + VLDL cholesterol and serum triglycerides were not significantly different between the groups. In the hypertensive group, plasma beta-thromboglobulin concentration correlated significantly with total cholesterol (r = 0.47, p less than 0.01) as well as with LDL + VLDL cholesterol (r = 0.50, p less than 0.01). In the normotensive group no such correlation was found. The results suggest activation of platelets in hypertension, and suggest that in hypertension, even a normal cholesterol concentration may influence platelet function.

Pharmacological characterization of 2NTX-99 [4-methoxy-N1-(4-trans-nitrooxycyclohexyl)-N3-(3-pyridinylmethyl)-1,3-benzenedicarboxamide], a potential antiatherothrombotic agent with antithromboxane and nitric oxide donor activity in platelet and vascular preparations

Thromboxane (TX) A(2), prostacyclin (PGI(2)), and nitric oxide (NO) regulate platelet function and interaction with the vessel wall. Inhibition of TXA(2), implemented synthesis of PGI(2), and supply of exogenous NO may afford therapeutic benefit. 2NTX-99 [4-methoxy-N(1)-(4-trans-nitrooxycyclohexyl)-N(3)-(3-pyridinylmethyl)-1,3-benzenedicarboxamide], a new chemical entity related to picotamide, showed antithromboxane activity and NO donor properties. 2NTX-99 relaxed rabbit aortic rings precontracted with norepinephrine or U46619 (9,11-dideoxy-9alpha,11alpha-methanoepoxy-prosta-5Z,13E-dien-1-oic acid; EC(50), 7.9 and 17.1 microM, respectively), an effect abolished by 10 microM 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ). 2NTX-99 inhibited arachidonic acid (AA)-induced washed platelet aggregation (EC(50), 9.8 microM) and TXB(2) formation (-71% at 10 microM), and its potency increased in the presence of aortic rings (EC(50), 1.4 microM). In whole rabbit aorta incubated with homologous platelets, AA caused contraction and TXA(2) formation, reduced by 2NTX-99 (10-40 microM): contraction, -28 and -47%, TXA(2) formation, -37 and -75.4%, respectively, with concomitant increase in PGI(2). 2NTX-99 (20-40 microM) inhibited U46619-induced aggregation in rabbit platelet-rich plasma (PRP) (-74 +/- 6.7 and -96 +/- 2.4%, respectively) and inhibited collagen-induced aggregation in human PRP (-48.2 +/- 10 and -79.2 +/- 6%), whereas ozagrel was ineffective. In human embryonic kidney 293 cells transfected with the TXA(2) receptor isophorm alpha receptor, 2NTX-99 did not compete with the ligand, [(3)H]SQ29,548 ([(3)H][1S-[1alpha,2beta(5Z),3beta,4alpha]]-7-[3-[[2-(phenylamino)-carbonyl]hydrazino]methyl]-7-oxabicyclo[2,2,1]-hept-2-yl]-5-heptanoic acid), or prevent inositol phosphate accumulation. After oral administration (50-250 mg/kg), 2NTX-99 inhibited TXA(2) production in rat clotting blood (-71 and -91%); at 250 mg/kg, an area under the curve, 0 to 16 h, of 149.5 h/microg/ml and a t(1/2) of 6 h were calculated, with a C(max) value of 31.8 +/- 8.2 microg/ml. An excellent correlation between plasma concentrations and TXA(2) inhibition occurs. 2NTX-99 controls platelet function and vessel wall interaction by multifactorial mechanisms and possesses therapeutic potential.

Effect of n-3 fatty acids on carotid atherosclerosis and haemostasis in patients with combined hyperlipoproteinemia: a double-blind pilot study in primary prevention

BACKGROUND

Intake of n-3 polyunsaturated fatty acids (n-3 PUFA) either from natural sources or dietary supplementation is inversely associated with atherothrombosis.

AIM

A double-blind pilot study was designed to address the impact of n-3 PUFA on atherosclerosis, haemostasis and vascular status in patients with combined hyperlipoproteinemia.

METHODS

Carotid intima-media thickness (C-IMT), texture of intima-media complex (T-IMC), lipids and platelet function were evaluated in 64 patients with combined hyperlipoproteinemia who received placebo or n-3 PUFA (6 g/day) for 2 years. C-IMT and T-IMC were assessed by B-mode ultrasound. Lipids and platelet function were determined by validated methods.

RESULTS

C-IMT increased in placebo, but not in n-3 PUFA group with respect to baseline. In contrast T-IMC decreased in n-3 PUFA, but not in placebo; in both cases, however, treatment effect did not reach statistical significance. A fall of triglycerides, concomitant to a rise of high- and low-density lipoprotein cholesterol (HDL and LDL), was observed in the active treated group. Platelet function was significantly reduced by n-3 PUFA.

CONCLUSIONS

Results show a favourable effectiveness of n-3 PUFA on IMT progression and T-IMC that deserves to be confirmed in larger studies. Despite the small sample size, the beneficial effect of n-3 PUFA on platelet function, triglycerides and HDL-C is clearly highlighted.

Fluvastatin: effects beyond cholesterol lowering

Coronary heart disease (CHD) remains a major therapeutic challenge in the Western world, and strategies aimed at cholesterol lowering form the mainstay of treatment. Fluvastatin is an established 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor ("statin") for the treatment of hypercholesterolemia. Its efficacy and safety have been established in numerous clinical trials. Emerging evidence now indicates that treatment with fluvastatin slows the progression of atherosclerotic CHD and reduces the incidence of cardiovascular morbimortality in the secondary prevention setting. This effect of fluvastatin cannot be explained by cholesterol lowering alone; nonlipid-related mechanisms (so-called "pleiotropic effects") undoubtedly contribute to a certain extent, and are probably linked to modulation of the mevalonate pathway. This review discusses the experimental evidence regarding the antiatherosclerotic and antithrombotic effects of fluvastatin that may contribute to its beneficial action on disease progression and clinical events. Such effects include decreased expression of adhesion molecules in monocytes and leucocyte-endothelium adherence responses, immunomodulation, prevention of low-density lipoprotein oxidation, inhibition of cholesterol esterification and accumulation, along with effects on smooth muscle cell proliferation and migration. Pleiotropic actions aimed at plaque stabilization (eg, decreased secretion of matrix metalloproteinases by macrophages), together with effects on platelet activity, tissue factor expression, and endothelial function, may contribute to an antithrombotic effect of fluvastatin. Taken together, the results of these studies indicate that the effects of fluvastatin, at therapeutic doses, may extend beyond cholesterol lowering.

Effects of fish oil supplementation on platelet survival and ex vivo platelet function in hypercholesterolemic patients

Little is known about the effects of dietary supplementation on platelet survival with low doses of n-3 and n-6 fatty acids in patients with hypercholesterolemia. The effects of a 6-week intervention with fish oil capsules (daily intake: 216 mg eicosapentaenoic acid, 140 mg docosahexaenoic acid, 390 mg gamma-linolenic acid, and 3480 mg linoleic acid) on in vivo platelet survival (111 In-oxine labeled platelets) and on ex vivo markers of platelet activation were investigated in a placebo-controlled, double-blind study with 26 hypercholesterolemic patients. In vivo platelet survival increased in the fish oil group (T) from a mean of 159+/-14 hours to a mean of 164+/-12 hours (p=0.025), whereas it remained unchanged in the placebo (P) group (T vs. P; p=0.055). Ex vivo, thromboxane B2 decreased from a mean of 225+/-16 to 212+/-21 ng/mL (p=0.003) in T but did not change in P (T vs. P: p=0.002). Malondialdehyde formation was lowered significantly by fish oil supplementation from a mean of 5.49+/-1.3 to 5.12+/-1.05 nM/10(9) platelets, p=0.005, as compared with P (T vs. P; p=0.018). The trendwise decrease in 11-DH-thromboxane B2 plasma levels was not significant nor was the increase in platelet sensitivity to prostaglandin I2 by fish oil. Baseline platelet survival in patients with hyperlipoproteinemia type IIa was not different from those with hyperlipoproteinemia IIb and response to treatment in terms of platelet activation markers was not either. The changes in platelet activation parameters in T were associated with significant reductions in cholesterol (-2.9%), low density lipoprotein cholesterol (-3.5%), and triglycerides (-12.4%). Both ex vivo and in vivo platelet activation parameters exhibited signs of decreased activation by a 6-week diet supplemented with n-3 and n-6 fatty acids, which might be beneficial in reducing atherothrombotic risk, in patients with hyperlipoproteinemia type IIa and IIb.

Reduction of platelet activity markers in type II hypercholesterolemic patients by a HMG-CoA-reductase inhibitor

We have investigated the effects of a potent lipid-lowering therapy on the activity of platelets as measured ex vivo by the surface activation markers CD62 (PADGEM, P-selectin, GMP 140) and CD63 (GP53) in a double-blind, randomized, placebo-controlled study. Treatment with the HMG-CoA-reductase inhibitor fluvastatin (40 mg) significantly reduced the serum low density lipoprotein cholesterol concentration by 30% (p<0.01) and total cholesterol by 25% (p<0.01). The platelet membrane activation markers CD62 (PADGEM, P-selectin, GMP140) and 63 (GP53) significantly decreased by 22 and 13% (in terms of the relative fluorescence intensity) under the treatment with fluvastatin (p<0.05), respectively. The cholesterol-lowering effect is accompanied by a significant reduction of the platelet membrane activation markers CD62 and CD63 reflecting a reduced platelet activity that may contribute to the vasoprotective profile of fluvasatin.

Nitric oxide and platelet aggregation

Platelets are small cells, 1/14th the volume of erythrocytes, and about 1000 billion circulate in human blood as smooth anucleate disks. Their job is to survey the lining of our blood vessels, the endothelium. In acute damage and extravasation, platelets are activated by contact with exposed collagen and aggregate together at the wound sites to initiate clotting and stop bleeding. Forming a physical plug to seal a hemorrhaging vessel is the key role of blood platelets. However, milder injury to the endothelium, perhaps a result of high blood pressure, raised plasma cholesterol, or smoking, also causes platelets to adhere to the internal walls of arteries. Such precipitate adhesion and activation of platelets initiates an inflammatory response of the vessel wall and predisposes to vascular complications, including thrombosis, premature heart disease, myocardial infarcts or strokes, and diabetes. It is essential, therefore, that during normal vascular hemostasis platelet activation is tightly controlled. Indeed, both platelets and endothelial cells produce and secrete chemicals that directly inhibit platelet aggregation. A key agent is the free radical gas nitric oxide (NO). Here, we review how this 30-Da molecular messenger is synthesized by a catalytic cassette 10,000 times larger and how it functions to suppress platelet "stickiness." We also present new evidence that directly links plasma lipoproteins with platelet activation: we describe at the molecular level how apoE, a protein with a prominent role in cholesterol transport, interacts with the platelet surface to stimulate NO production and hence attenuate platelet activation.

Altered platelet function detected by flow cytometry. Effects of coronary artery disease and age

Platelet activation state and responsiveness to physiological agonists were measured in 65 patients with documented coronary artery disease (54 male and 11 female; mean age, 58 years). Twelve patients (mean age, 52 years), selected at random from the male cohort, were compared with 12 age-matched male control subjects (mean age, 52 years) and with 10 normal, young male subjects (mean age, 25 years). Whole-blood flow cytometry was used to measure platelet activation status ex vivo and platelet responsiveness to physiological agonists in vitro. Peripheral blood samples were analyzed for bound fibrinogen and expression of P-selectin, GPIb, and GPIIb-IIIa at rest and in response to ADP (0.1 to 10 mumol/L) and thrombin (0.02 to 0.32 mu/mL). No significant differences were seen in the basal levels of fibrinogen binding between any of the groups, but P-selectin expression was significantly lower in patients compared with age-matched control subjects (P = .0005). When stimulated with agonists, patients' platelets had significantly decreased fibrinogen binding (P < .03) but no difference in P-selectin expression compared with the age-matched group. Both agonist-induced fibrinogen binding and P-selectin expression were, however, higher in the young subjects compared with either the older control group or the patients (P < .05). GPIb and GPIIb-IIIa expression were lowest in the patients with angina and highest in the young control subjects, with levels in the age-matched control subjects falling between these values. Data from the total patient cohort (n = 65) were identical to those in the smaller cohort (n = 12). In conclusion, atherosclerosis impairs platelet aggregatory responses (fibrinogen binding) over and above the decreased response seen with age. Platelet degranulation (P-selectin expression) is also impaired in patients with coronary artery disease, but only in comparison with younger subjects, not age-matched controls.

Platelet alpha 2-adrenergic receptors in hypercholesterolemia: relationship between binding studies and epinephrine-induced platelet aggregation

BACKGROUND

Platelets isolated from patients with hypercholesterolemia are more sensitive in vitro to various aggregating agents, including epinephrine, than those isolated from normocholesterolemic subjects. Increased platelet reactivity is one mechanism that may explain the enhanced risk of thromboembolism in hypercholesterolemia. This study assessed whether platelet hyperreactivity to epinephrine in hypercholesterolemia is associated with higher alpha 2-adrenergic receptor density or affinity for epinephrine.

METHODS

Platelet aggregation and binding studies, with use of [3H]yohimbine as ligand, were performed on platelets isolated from 30 patients with type IIa hypercholesterolemia and 23 control subjects.

RESULTS

Platelet aggregation in response to epinephrine was significantly higher in patients with hypercholesterolemia than in control subjects. A statistically significantly higher alpha 2-adrenergic receptor density was observed in a subgroup of 13 patients with hypercholesterolemia than in 13 sex- and age-matched control subjects (280 +/- 61 and 230 +/- 49 fmol/mg protein respectively; p < 0.03), but no difference was observed in receptor affinity for the ligand. In these subgroups plasma total and levels of low-density lipoprotein (LDL) cholesterol were inversely correlated with platelet aggregation but directly correlated with platelet receptor density.

CONCLUSION

Platelet alpha 2-adrenergic receptor density is increased in hypercholesterolemia and directly correlates with plasma total and levels of LDL cholesterol, providing at least a partial explanation for the enhanced platelet response to epinephrine that is observed in hypercholesterolemia.

Reduced platelet serotonin content and release in familial hypercholesterolaemia

Plasma and platelet serotonin (5-HT) concentrations, and resting and collagen-induced 5-HT release in platelet-rich plasma were studied in normal and familial hypercholesterolaemic (FH) subjects. Platelet 5-HT concentrations were significantly reduced (-37%, P < 0.01) in FH patients whilst mean plasma concentrations, although increased, were not significantly different from those in normal subjects. Platelet 5-HT correlated negatively with plasma cholesterol when the data for normal subjects and FH, patients were combined (r = -0.48, P = 0.005). It also correlated negatively with low-density lipoprotein (LDL) (FH data, r = -0.59, P = 0.03; normal and FH data, r = -0.49, P = 0.004) but positively with high-density lipoprotein (HDL) (FH r = 0.79, P = 0.001; normal and FH, r = 0.37, P = 0.03). Collagen (5-160 micrograms/ml) stimulated platelet 5-HT release occurred in a concentration-dependent manner. In FH patients stimulated 5-HT release was reduced (10 micrograms/ml collagen, -40%, P < 0.05) and accompanied by increased collagen EC50 values (P < 0.02). Resting 5-HT release was increased substantially in FH patients but not significantly. Our data provide evidence for a relationship between circulating cholesterol and platelet serotonergic mechanisms. It is proposed that abnormalities relating to platelet-plasma 5-HT dynamics, perhaps due to enhanced platelet activity or decreased platelet uptake, may contribute to the cardiovascular complications in FH.

No influence of simvastatin treatment on platelet function in vivo in patients with hypercholesterolemia

Hypercholesterolemia is associated with platelet activation. Reduction of plasma cholesterol levels by the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor simvastatin has been found to improve certain aspects of platelet function in vitro and in vivo, but controlled trials are largely lacking. The present randomized, double-blind, crossover study was performed to evaluate whether 10- to 12-week treatment with simvastatin or placebo affects platelet function in vivo in 23 hypercholesterolemic men. Measurements were performed at rest and during mental stress. Simvastatin treatment reduced plasma total cholesterol levels by 18 +/- 2% and low density lipoprotein cholesterol levels by 26 +/- 2% (P < .001 for both), whereas high density lipoprotein cholesterol levels increased slightly (6 +/- 2%, P < .05). Platelet aggregability as assessed by filtragometry ex vivo was unaffected by simvastatin treatment both at rest and during mental stress. Plasma beta-thromboglobulin levels, which reflect platelet secretion, were also unaltered by simvastatin treatment both at rest (antilog of the mean: 20.2 versus 20.0 ng/mL during placebo) and during mental stress. Moreover, nocturnal excretion of 11-dehydrothromboxane B2 in urine did not differ between placebo and active treatment: 218 versus 216 ng/mmol creatinine, respectively. The corresponding values for urinary excretion of high-molecular-weight beta-thromboglobulin were 1.78 versus 1.92 ng/mmol creatinine. Thus, simvastatin treatment had no clear-cut effect on platelet function, as assessed by four different in vivo related platelet function variables, in hypercholesterolemic men.

Ex-vivo and in-vivo platelet function in patients with severe hypercholesterolemia undergoing LDL-apheresis

Patients with severe familial hypercholesterolemia (HC) show abnormal platelet function and shortened platelet survival. Atherosclerosis is associated with platelet hyperactivity. Low-density lipoporotein (LDL)-apheresis eliminates the most atherogenic lipid fraction and inhibits the progression of atherosclerosis inducing even regression. In order to assess the influence of LDL-apheresis on platelet function ex-vivo and in-vivo, 6 patients with severe heterozygous HC, all of them being pharmacologically treated with HMG-CoA reductase inhibitors and anion exchange resins were investigated. Ex-vivo platelet function was assessed by the aggregation response to ADP before starting apheresis treatment, as well as after 2 and 24 weeks, respectively. In-vivo platelet function was determined by measuring platelet survival after radiolabeling with 111In-oxine before starting LDL-apheresis and after 24 weeks of twice monthly treatment. LDL-apheresis therapy induced a significant (p < 0.01) drop in cholesterol by 64%, LDL-cholesterol by 77% and in triglycerides by 46% over a period of 24 weeks. ADP-induced platelet aggregation revealed a decreased aggregability of platelets with a decline in the maximal amplitude and the slope of the response curve. Changes in platelet sensitivity to prostaglandins (PG) were significantly for PGI2, but did not reach statistical significance for PGE1. The results revealed a significant (p < 0.001) increase in platelet survival of 111In-oxine-radiolabeled autologous platelets from a mean of 106.50 hours before to 137.50 hours (p < 0.01) after treatment, being accompanied by an increase in labeling efficiency (p < 0.001) and recovery (p < 0.001). These data provide evidence for improved hemostatic regulation in vivo as a result of maintainance of lipid-lowering achieved with LDL-apheresis.

Therapy with HMG CoA reductase inhibitors: characteristics of the long-term permanence of hypocholesterolemic activity

Treatment with hydroxymethylglutaryl coenzyme A (HMG CoA) reductase inhibitors has gained considerable success in the management of hypercholesterolemia. A large number of studies have shown the efficacy of these drugs in lowering plasma total and low density lipoprotein (LDL) cholesterol levels, but there have been less studies evaluating their effectiveness in standard clinical practice, particularly relating to the maintenance of hypocholesterolemic activity. In the present study, the long-term effectiveness of HMG CoA reductase inhibitors has been tested in 177 patients with familial hypercholesterolemia (FH) who had been on statin therapy (simvastatin or pravastatin) for at least 12 months and up to 5 years or longer. The mean 'dose normalized' LDL cholesterol reduction in the whole group was around 20%. However, in spite of a generally good efficacy of both statins in lowering total and LDL cholesterol, a wide variety of responses, either after short- or long-term treatment, was noted. Individual responses were calculated and patients classified into three different groups: (a) responders, (b) non-responders, and (c) response losers. Of the 177 patients, 4% did not respond to treatment and a further 10% showed an initial unsatisfactory response (LDL cholesterol reduction < or = 10%). Another 10% experienced a progressive loss of response over time. There appeared to be little difference between the two treatments in the long-term efficacy and no predictive index could be established. Treatment with HMG CoA reductase inhibitors is generally effective and well tolerated, but a non-negligible number of patients may show a primary non-response or a progressive loss of response.

Platelet activation and platelet lipid composition in pulmonary cancer

In order to investigate the possible mechanisms underlying platelet functional changes in patients affected by neoplasms, platelet lipid composition, plasma beta-thromboglobulin (Beta-TG) and serum thromboxane B2 (TXB2) were investigated in 16 male patients affected by pulmonary carcinoma and in 16 comparable control subjects. In patients high levels of plasma Beta-TG (67 +/- 9 versus controls 14 +/- 4 ng/ml, p < 0.001) and serum TXB2 (434 +/- 56 versus 223 +/- 48 ng/ml, p < 0.001) were observed. Also platelet lipid composition was found altered in patients with respect to controls (lower percent levels in n-3 fatty acids and in linoleic acid esterified in the main platelet phospholipid fractions: at least p < 0.05). These results indicate that in vivo platelet activation is detectable in neoplastic patients and it is associated with alterations in platelet lipid composition. In the light of the important role played by membrane lipids in platelet functions related to thrombosis and haemostasis we conclude that platelet lipid changes could cooperate in platelet activation and increased thrombotic risk so frequently observed in neoplastic disease.

Platelet cytosolic Ca2+ and membrane dynamics in patients with primary hypercholesterolemia. Effects of pravastatin

This study was designed to evaluate the relationships between platelet cytosolic Ca2+ concentration ([Ca2+]i) and plasma lipids in patients with primary hypercholesterolemia. In a double-blind, placebo-controlled trial, we determined platelet [Ca2+]i in the presence and virtual absence of extracellular Ca2+ and the effects of prolonged treatment with pravastatin, a selective inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase. Platelet [Ca2+]i and membrane microviscosity were determined in 22 normotensive hypercholesterolemic men. Platelet [Ca2+]i was observed to vary with in vivo plasma lipid characteristics: in untreated patients, [Ca2+]i determined at low extracellular Ca2+ concentration was significantly associated with plasma triacylglycerols (P = .008) and with the total cholesterol to HDL cholesterol ratio (P = .044). Triacylglycerol levels also correlated inversely with the external Ca(2+)-dependent [Ca2+]i rise. Pravastatin treatment reduced plasma total cholesterol (-20 +/- 3%), LDL cholesterol (-30 +/- 3%), triacylglycerols (-17 +/- 6%), and apoB levels (-25 +/- 4%) and simultaneously decreased platelet [Ca2+]i measured in a low-Ca2+ medium by 14 +/- 6% (P = .03). However, [Ca2+]i values remained positively correlated with the total cholesterol to HDL cholesterol ratio (P = .04). Prvastatin treatment did not induce marked changes in membrane microviscosity, although the changes in trimethylaminodiphenylhexatriene anisotropy were inversely correlated with those of HDL cholesterol. These results indicate that plasma lipids can modulate cytosolic Ca2+ in platelets by affecting Ca2+ transport pathways that are dependent and independent of Ca2+ influx.

Spontaneous platelet aggregation in whole blood is increased in non-insulin-dependent diabetes mellitus and in female but not male patients with primary dyslipidemia

Increased platelet aggregability has been shown in hypercholesterolemia, and stirring-induced spontaneous aggregation in whole blood is increased in insulin-dependent diabetes mellitus (DM). We have determined spontaneous aggregation in citrated (10 mM) whole blood, from 27 primary dyslipidemic patients (DYS; 14F, 13M), 16 male non-insulin-dependent DM (NIDDM) patients, and 17 normolipidemic controls (N; 6F, 11M), using platelet counting to quantify aggregation. Spontaneous aggregation was significantly higher, both in the female DYS group (median 30% [interquartile range 25,50], P < 0.005) and the NIDDM group (33% [25,41], P < 0.005), than in the N group (17% [12,27]), but did not differ significantly in the male DYS group (23% [10,33]). Similar results were obtained in the presence of indomethacin (25 mumol/l) to prevent artefactual thromboxane (TX) A2 formation, indicating that increased spontaneous aggregation was TXA2-independent. Interestingly, increased spontaneous aggregation appeared to be independent of serum cholesterol and triglyceride concentrations, as well as age and sex per se. We conclude that spontaneous platelet aggregation was increased both in female primary dyslipidemic patients and NIDDM patients, but not in male DYS patients. The clinical significance of increased spontaneous platelet aggregability is that it may favour shear-induced aggregation which may occur at critical arterial stenoses in vivo leading to thrombus formation.

Platelet transmembrane signalling responses to collagen in familial hypercholesterolaemia

Washed platelets from patients with familial hypercholesterolaemia (FH) were found to be more reactive towards collagen than those from control subjects. The dose required to achieve half maximum aggregation was found to be 0.6 ml-1 for FH patients whilst that for control subjects was 1.25 micrograms ml-1. In both types of platelet, intracellular Ca2+ levels, as monitored by the Ca(2+)-dependent photoprotein, aequorin, rose on stimulation with collagen and then fell to basal levels, probably due to resequestration by the reticular system. This effect was not due to exhaustion of the supply of aequorin since sustained Ca2+ influx induced by the ionophore, A23187, gave a stable signal that did not return to baseline. Similarly, inositol 1,4,5, trisphosphate levels increased in the cytosol after stimulation and then fell to unstimulated values. When stimulated with collagen, platelets from FH patients showed a greater extent of cytoplasmic calcium mobilization (P < 0.05) when compared to controls, coupled with a greater extent of inositol phospholipid hydrolysis (P < 0.05). At doses of collagen sufficient to give either 100% or 50% aggregation, platelets from patients or control subjects showed the same amplitude of ATP release at either dose suggesting that the trigger for vesicle release is more sensitive in FH.

L-arginine attenuates platelet reactivity in hypercholesterolemic rabbits

Platelets are capable of producing nitric oxide (NO) through the L-arginine-NO synthase pathway. Acute exposure to supraphysiological concentrations of L-arginine in vitro increases the production of NO by platelets and is associated with an increase in platelet cyclic GMP (cGMP) levels and a reduction in platelet aggregation. The purpose of this study was to determine if chronic oral administration of L-arginine decreases platelet aggregation in hypercholesterolemic animals and to determine if this effect is mediated by the metabolism of L-arginine to NO. Male New Zealand White rabbits were fed normal chow (Con), a 1% cholesterol diet (Chol), or a 1% cholesterol diet supplemented with a sixfold enrichment of dietary L-arginine (Arg) or L-methionine (Met). After 10 weeks, cholesterol levels were equally increased in Chol and Arg animals, whereas plasma arginine levels were doubled in the Arg group. There was no difference in maximum aggregation initiated by ADP (100 mumol/L) between washed platelets from Con, Met, and Chol animals, but aggregation of platelets from Arg animals was significantly decreased (P < .05). In aggregating platelets from Arg animals, cGMP levels were significantly higher than the other groups (P < .05). When platelets were incubated ex vivo with the NO synthase inhibitor NG-monomethyl-L-arginine, the effects of dietary L-arginine were reversed. Chronic dietary supplementation of L-arginine decreases platelet aggregation in hypercholesterolemic rabbits. This effect appears to be due to the metabolism of L-arginine to NO.

Effects of chronic administration of ethanol on platelets from rabbits with diet-induced hypercholesterolemia. Unchanged characteristics and responses to ADP but reduction of enhanced thrombin-induced, TxA2-independent platelet responses

To investigate the effect on platelet function of the interaction between dietary cholesterol and moderate, chronic doses of ethanol, hypercholesterolemia was induced in rabbits by 8 weeks of administration of a chow diet with added (0.25% wt/wt) cholesterol; during the eighth week, a moderate amount of ethanol (6% in drinking water) was given. Blood alcohol levels were not detectable in ethanol-treated rabbits at the time of exsanguination. Ethanol did not affect plasma cholesterol levels or the cholesterol to phospholipid molar ratio in platelets. Platelet membrane fluidity, which decreased with cholesterol feeding, was not altered further by administration of ethanol. The overall fatty acid composition of platelet phospholipids was not affected by either cholesterol feeding or chronic ethanol intake. Responses of washed platelets stimulated with either ADP or thrombin were studied to determine whether ethanol administration modified platelet functions in hypercholesterolemia. Primary ADP-induced aggregation was not affected by cholesterol feeding or chronic ethanol intake, but thrombin-induced aggregation and secretion of [14C]serotonin from prelabeled platelets, which were enhanced by cholesterol feeding, were diminished by administration of ethanol to hypercholesterolemic rabbits. This reduction in thrombin-induced responses was also observed with aspirin-treated platelets, which cannot form thromboxane A2. Thus, chronic short-term administration of a moderate amount of ethanol inhibited the enhanced responses of platelets from rabbits with diet-induced hypercholesterolemia, via a thrombin-induced, thromboxane A2-independent pathway.

Enhanced collagen-induced responses of platelets from rabbits with diet-induced hypercholesterolemia are due to increased sensitivity to TxA2. Response inhibition by chronic ethanol administration in hypercholesterolemia is due to reduced TxA2 formation

The effects of dietary cholesterol and chronic administration of moderate amounts of ethanol on collagen-induced platelet responses were investigated. Three groups of rabbits were fed the following diets for 8 weeks: a normal chow diet, a cholesterol-enriched (0.25% wt/wt) chow diet, and a cholesterol-enriched chow diet plus 6% ethanol in the drinking water for the final week of the dietary period. Cholesterol feeding enhanced collagen-induced responses-aggregation, secretion of [14C]serotonin from prelabeled platelets, and thromboxane formation--of suspensions of washed platelets, and chronic ethanol treatment significantly reduced these enhanced responses. These effects are mediated by thromboxane A2 (TxA2) rather than ADP. Experiments with collagen-stimulated platelets in which feedback amplification of TxA2 was blocked with the prostaglandin H2/TxA2 receptor blocker BM 13.177 and experiments with aspirin-treated platelets stimulated with the stable TxA2 mimetic U46619 showed that cholesterol feeding enhanced platelet sensitivity to TxA2 rather than formation of TxA2 by platelets that had interacted with collagen. Without BM 13.177 or aspirin, TxA2 increased the amount of TxA2 formed by feedback amplification. In contrast, decreased responsiveness to collagen by platelets from cholesterol-fed rabbits given ethanol was due to inhibition of TxA2 formation rather than reduced sensitivity to TxA2. Platelets from cholesterol-fed rabbits given ethanol did not develop tolerance to the acute inhibitory effects of ethanol. Our results indicate that administration of moderate amounts of ethanol to cholesterol-fed rabbits inhibits enhanced collagen-induced responses of platelets by a TxA2-dependent pathway that involves reduction of TxA2 formation rather than reduction of platelet responses to TxA2.

Effects of selective LDL-apheresis and pravastatin therapy on platelet function in familial hypercholesterolaemia

Platelet function was studied in 10 patients with familial hypercholesterolaemia, following lipid-lowering treatment with selective LDL-apheresis and with the HMG-CoA reductase inhibitor pravastatin. Platelet function was assessed before, and 2, 5 and 14 days after LDL-apheresis, and before and after 4 weeks of pravastatin therapy. Both treatments significantly reduced total- and LDL-cholesterol, whereas LDL-apheresis also reduced VLDL-cholesterol. Lp(a)-levels were reduced by LDL-apheresis and elevated by pravastatin treatment. Pravastatin therapy significantly enhanced platelet aggregability in vivo, as measured by ex vivo filtragometry. Plasma serotonin levels also increased. Other markers of in vivo activation of platelets, i.e. beta-thromboglobulin in plasma and urine, and 11-dehydro-thromboxane B2 in urine were unaltered. Adenosine diphosphate-induced platelet aggregation in vitro remained unchanged during pravastatin therapy, and the platelet volume distribution was not affected. LDL-apheresis reduced the mean platelet volume, as well as the percentage of large platelets, whereas the percentage of small platelets increased. Other measures of platelet function in vivo or in vitro were, however, unaltered following LDL-apheresis. Thus, pravastatin therapy enhances certain aspects of platelet aggregability in vivo, whereas a single treatment with selective LDL-apheresis does not consistently affect platelet aggregability during resting conditions. These results do not support the concept that reduction of LDL-cholesterol improves platelet function in hypercholesterolaemic patients, at least not in the short-term. However, the reduction of platelet volume after LDL-apheresis may be beneficial for patients receiving this therapy regularly.

Glycosylation pattern of platelet glycoprotein IIb and IIIa in type IIa hypercholesterolemia

The microheterogeneity and polymorphism of platelet membrane glycoproteins IIb and IIIa from hypercholesterolemic type IIA patients and from normolipidemic controls were compared by isoelectric focusing followed by immunological detection. Their size and the extent of glycosylation were investigated by polyacrylamide gel electrophoresis and carbohydrate affinity stain. No qualitative or quantitative differences could be detected, either within each test group or between the two groups. This finding rules out the hypothesis that altered molecular forms of the glycoproteins forming the fibrinogen receptor might be involved in the pathogenesis of platelet hyperaggregability in hypercholesterolemic patients.

Platelet function in patients with hypercholesterolaemia

Platelets and plasma lipoproteins, particularly low density lipoprotein, have important roles in atherogenesis. Evidence from several sources suggests that important interactions occur between these individual components of the atherogeneic process. Here we review work from our own laboratory on platelet function in normal individuals and patients heterozygous for familial hypercholesterolaemia (FH). Data is presented on the role of platelet noradrenaline and also on altered cellular signalling in platelets from FH individuals who have plasma low density lipoprotein concentrations which are approximately double those seen in normal subjects.

The actions of lovastatin on platelet function and platelet eicosanoid receptors in type II hypercholesterolaemia. A double-blind, placebo-controlled, prospective study

We have studied the effects of 12 weeks of lovastatin (20 mg per day) on platelet function and thromboxane formation in 18 patients with type II hypercholesterolaemia in a double-blind, placebo-controlled, prospective study. Lovastatin significantly reduced total serum and LDL-cholesterol by 20% and 25% respectively. Washed platelets of lovastatin-treated patients had significantly reduced collagen-induced aggregation and thromboxane formation ex vivo. There was no change in ADP-induced platelet aggregation, but a significant increase in prostacyclin (iloprost)-stimulated platelet cyclic AMP concentrations in lovastatin-treated patients. This was associated with a significant increase in the number of prostacyclin receptors in platelet membranes prepared from lovastatin-treated patients. There was also an increase in platelet thromboxane receptors. There were no such changes in the placebo group. These data confirm our original observation of normalization of platelet function in hypercholesterolaemia by HMGCoA reductase inhibitors and suggest changes in platelet membrane composition at the megakaryocyte level as a possible site of action.

Decreased sensitivity to adenosine in platelets from patients with familial hypercholesterolaemia--a change reversed by cholestyramine treatment

Platelet-rich plasma was obtained from patients with untreated heterozygous familial hypercholesterolaemia (FH), from FH patients treated with cholestyramine and from control subjects. Responsiveness of platelets to the aggregation inhibitors adenosine, its analogue N-ethylcarboxamidoadenosine (NECA) and prostaglandin I2 was decreased in FH. Patients on cholestyramine therapy showed normal responsiveness to adenosine and NECA. There were only minor changes in the binding of [3H]NECA to high-affinity binding sites on platelet membranes from untreated FH or cholestyramine-treated FH patients. The initial rate of cyclic AMP formation in response to a high concentration of NECA was severely decreased in platelets from FH patients. By contrast, the rate of cyclic AMP formation in response to forskolin or a high concentration of prostaglandin I2 was unchanged. These data point to a defect in the coupling of the platelet A2 adenosine receptor to adenylyl cyclase in untreated FH patients.

Influences of lipid-modifying agents on hemostasis

Drugs affecting lipid metabolism may influence, to a variable extent, the hemostatic system, that is, platelet activation, fibrinogen, and fibrinolysis. These effects may or may not be linked to the activity of these compounds on the lipid/lipoprotein profile. For this reason it may be important to consider the effects of hypolipidemic drugs on the different aspects of hemostasis, because this may allow a better understanding of their clinical use, as well as, eventually, a more proper selection in individual patients. Among the major lipid-lowering agents, fibric acids belong to a multifaceted series of abnormal fatty acids known to interact with a liver nuclear receptor, in turn activating fatty acid catabolism. A similar activity may be exerted by n-3 fatty acids from fish, as well as by other chemically related or unrelated compounds. Among fibric acids all but gemfibrozil can reduce fibrinogen levels; this last drug can, however, apparently activate fibrinolysis. Among the selective cholesterol-lowering medications, both resins and HMG CoA reductase inhibitors may reduce, in some patients, over prolonged periods of treatment, platelet sensitivity to major aggregants. This effect may be seen best with non-liver-selective agents (e.g., simvastatin), although recent data cast doubt on its constancy. A direct comparative evaluation of different HMG CoA reductase inhibitors on platelet aggregability has never been carried out. These last drugs may also reduce the circulating levels of the tissue factor pathway inhibitor (TFPI), transported by LDL in plasma, which is a potentially negative effect. A lipid-lowering molecule with antioxidant activity, for example, probucol, may also possibly play a role in controlling platelet activation.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of n-3 fatty acids on plasma lipids and lipoproteins and other cardiovascular risk factors in patients with hyperlipidemia

This review discusses the effects of dietary n-3 fatty acids on the plasma concentrations and metabolism of lipoproteins with a particular focus on work in human subjects. The influence of dietary n-3 fatty acids on the concentrations of plasma lipoproteins are affected by the amount of n-3 fatty acids as well as by the lipoprotein phenotype in the patients under investigation. On the basis of the observed changes in lipoproteins, dietary n-3 fatty acids exert the greatest effects on the concentrations of triglyceride-rich lipoproteins; their therapeutic potential is greatest in patients with hypertriglyceridemia. In addition to their effects on plasma lipoproteins, dietary n-3 fatty acids have been reported to exert potentially favorable effects on blood pressure, platelet function and viscosity. These effects may justify the use of supplements of dietary n-3 fatty acids in selected patients with hypertriglyceridemia to reduce the risk of atherosclerosis; however, the benefits of such therapy remain to be demonstrated.

Antiatherosclerotic effects of oral cicaprost in experimental hypercholesterolemia in rabbits

The efficacy of the oral prostacyclin mimetic cicaprost in preventing atheromatous plaque formation was studied in an in vivo model of experimental hypercholesterolemia. New Zealand white rabbits were fed either standard chow or a cholesterol-enriched (1%) diet for 12 weeks. Cicaprost was added to the drinking water in a non-hypotensive dose (5 micrograms/kg/day) and withdrawn 3 days prior to studying platelet, leukocyte and endothelial function. In cholesterol-fed rabbits, oral cicaprost reduced the aortic intimal surface covered by atheromatous lesions from 84 to 63% (P < 0.05). There was no major difference in serum lipid composition between cicaprost- and vehicle-treated animals. In hyper-cholesterolemic rabbits there was a significant impairment of endothelium-dependent relaxations. Cicaprost treatment considerably improved this endothelial function but had no effect in rabbits receiving standard diet. In addition, platelet and leukocyte hyperreactivity, as seen in hypercholesterolemic rabbits, were largely reduced by cicaprost treatment. These data are the first to demonstrate marked antiatherosclerotic effects of long-term oral prostacyclin treatment. The mechanism may be related to improved endothelial function and subsequent prevention of secondary platelet and neutrophil hyperreactivity.

Platelet and neutrophil function and eicosanoid release in a subject with abetalipoproteinaemia

It has been suggested that plasma low density lipoprotein (LDL) may affect platelet and leukocyte activity and the release of biologically active eicosanoids which may contribute to the pathogenesis of coronary heart disease. To evaluate the possible biological effects of LDL further we have studied platelet aggregation, leukocyte function and eicosanoid release in a young woman with abetalipoproteinaemia (ABL) who totally lacks LDL. The subject showed decreased platelet response to threshold doses of ADP, collagen and arachidonic acid compared to a matched control measured in parallel or to a larger control group of 22 normal subjects. Aggregation was normal to higher doses of the same agonists. Thromboxane formation in clotted whole blood and in PRP stimulated with collagen was lower for the ABL subject than the control group. Neutrophil function assessed by chemiluminescence following stimulation with PMA, zymosan and FMLP was normal for the ABL subject, although the release of leukotriene B4 from calcium ionophore stimulated cells less than controls. Neutrophil platelet activating factor (PAF) formation and half life in plasma was not altered in ABL. The fatty acid composition of plasma, platelet and erythrocyte membrane phospholipids showed particularly low levels of linoleic acid in ABL compared to controls. Platelet phospholipids from the ABL subject also showed low levels of arachidonic acid. The decrease in eicosanoid formation seen in ABL may be the result of altered fatty acid composition of cell membrane phospholipids, or perhaps a defect in arachidonate mobilization. These results indicate that in a subject who lacks circulating LDL the behaviour of platelets and neutrophils in some in vitro tests is altered, although the extent to which these effects are reflected in vivo with regard to inflammatory and thrombotic mechanisms is not known.

Platelet hyperreactivity in hyperlipidaemia with specific reference to platelet lipids and fatty acid composition

Platelet function after thrombin stimulation, the fatty acid composition of individual phospholipids, and levels of lipid components (cholesterol, cholesterol ester, phospholipids and triglycerides) were determined in total membranes of platelets from hyperlipidaemic (HL) and control subjects. Platelet aggregation, thromboxane (TX) B2 production and serotonin release was significantly greater in HL patients than in controls. Levels of platelet cholesterol, total phospholipids, cholesterol ester and triglycerides, were significantly higher in the HL patients. Small differences between the two groups were observed for the phospholipid fatty acid patterns. However, levels of arachidonic acid (AA) were significantly higher in phosphatidylinositol (PI) of HL patients (40.01 +/- 6.59 mol%) as compared to the controls (31.52 +/- 9.91 mol%) (P = 0.002). The higher levels of AA in PI, which is considered a donor pool for eicosanoid synthesis, may be an additional mechanism for the well documented platelet hyperfunction and greater TXB2 production in hyperlipidaemic subjects.

Possible relevance of lipid peroxidation and thromboxane production to the initiation and/or evolution of microangiopathy in non-hyperlipidemic type 2 diabetes mellitus

To investigate the possible relevance of free radicals and prostanoids to the mode of initiation and/or evolution of microangiopathy in diabetes mellitus, we measured serum lipid peroxides (LPO), an accepted index of intravascular free radicals, and plasma 11-dehydrothromboxane B2 (11-dehydro-TXB2), a stable metabolite of vasoactive thromboxane A2 released from platelets, in 95 patients with normolipidemic type 2 (non-insulin-dependent) diabetes mellitus at different stages of the disease. In general, either LPO or 11-dehydro-TXB2 was significantly greater in the patients, as a group, than in the matched controls (3.82 vs. 2.65 nmol/ml, P < 0.01 for LPO; and 17.3 vs. 5.8 pg/ml, P < 0.01 for 11-dehydro-TXB2). In patients, both LPO and 11-dehydro-TXB2 increased according to the severity of their diabetic retinopathy. A highly significant positive correlation existed between the LPO values and 11-dehydro-TXB2 in the patients (r = 0.64, P < 0.0001), while there was no such relationship in the controls (r = 0.18, P = NS). No difference in serum levels of apolipoproteins A-I, A-II, B, C-II, C-III, or E was observed between the patients and controls. Short-term glycemic control (25 cal/kg of standardized body weight/day, for 8 weeks) resulted in a small but significant reduction in LPO (4.2 vs. 4.6 nmol/ml, control; P < 0.05) without alteration in 11-dehydro-TXB2. There was a tendency towards deterioration in LPO according to the improvement in glycemic control. These results appear consistent with the view that, in addition to LPO, the release of TXA2 from activated platelet in the human circulation could be an important factor for the initiation and/or evolution of microangiopathy in diabetic patients even when they are not apparently hyperlipidemic. Further, the results of the present study emphasize the notion that more tight control of serum lipids is worthy of serious consideration in preventing the advance of diabetic microangiopathy.

Bezafibrate lowers plasma lipids, fibrinogen and platelet aggregability in hypertriglyceridaemia

The effects of bezafibrate 400 mg/day (slow release formulation) on plasma lipids/lipoproteins and on selected haemostatic parameters were evaluated in a double blind cross-over study in patients with Type IIb and IV hyperlipoproteinaemia. Placebo treatment did not influence any of those parameters, but the drug significantly reduced plasma triglycerides (-45%) and VLDL cholesterol, as well as causing a 12% fall in total cholesterol and a 20% increase in HDL cholesterol. Apo AI levels were significantly increased following bezafibrate and Apo B was reduced by about 20%. In addition to changes in the plasma lipid profile, bezafibrate reduced the sensitivity of platelets to the aggregatory effect of collagen, with no effect on TXB2 production. Fibrinogen levels after bezafibrate treatment were significantly lowered, the effect being more marked in patients with hyperfibrinogenaemia. Bezafibrate did not influence the plasma fibrinolytic profile. It is concluded that bezafibrate, besides its beneficial effects on the plasma lipoprotein profile, can exert beneficial changes on specific haemostatic parameters.

Big platelets in hyperlipidemic patients

Both "big" platelets and hyperlipidemia are associated with increased coronary risk. This study was undertaken to search for a possible effect of various hypolipidemic drugs on big platelets. The percentage of big platelets, assessed microscopically, was measured in 66 patients who had hyperlipidemia of various types. Twenty-seven patients with hypertriglyceridemia were randomly selected to receive either fish oil or placebo in a crossover study. Another group of 39 patients with hypercholesterolemia, among them 13 with heterozygous familial hypercholesterolemia (FH), received lovastatin. The pretreatment level of big platelets was elevated, and similar in all groups: 23.3 +/- 12% versus 22 +/- 9%, in the fish oil versus placebo group, 19.1 +/- 6.3% versus 24 +/- 11% in the FH versus non-FH primary hypercholesterolemia group (reference value, 6.8 +/- 3.5%). After treatment, despite the improvement in lipoprotein profile, the percentage of big platelets did not change. The relationship between lipid reduction and big platelets is thus questionable, and necessitates further study.