Effect of plasma fibrinogen concentration on the inhibition of platelet aggregation after ticlopidine compared with aspirin

An ultrastructural study of Porphyromonas gingivalis-induced platelet aggregation

One of the major pathogens of periodontitis, Porphyromonas gingivalis (P. gingivalis), has the ability to aggregate human platelets. To investigate the interaction between P. gingivalis and human platelets in platelet rich plasma (PRP), platelet aggregation was measured by an aggregometer based on laser light scattering (LS) methods, and an ultrastructural study was performed using electron microscopy. A sharp and rapid increase of small-sized platelet aggregates was observed immediately after the addition of P. gingivalis to PRP, followed by the formation of medium- and large-sized aggregates in 2-3 min. In contrast, when Staphylococcus aureus (S. aureus) was used in the control experiment, only a slight increase in small-sized aggregates was detected. By electron microscopy, discoid-shaped platelets were observed prior to adding P. gingivalis. By 5 min after the addition of the bacteria, enormous platelet aggregates were observable. Most of the P. gingivalis were present between the adherent platelets, while some were internalized in platelet engulfment vacuoles. In contrast, when washed platelets were incubated with the bacteria under a non-stirring condition to prevent platelet aggregation, and stained with ruthenium red (RR) as an electron dense tracer of the cell surface including the open canalicular system (OCS), both RR-positive and -negative vacuoles containing P. gingivalis were identified in the activated platelets. Thus, this observation suggests that P. gingivalis residing in the RR-negative vacuoles is incorporated into the platelet cytoplasm by phagocytosis.

Effects of diet, drugs, and genes on plasma fibrinogen levels

Plasma levels of fibrinogen have been identified as independent risk predictors of cardiovascular disease. This has greatly increased interest in the regulation of plasma fibrinogen levels. Many demographic and environmental factors are known to affect fibrinogen levels, such as diet, use of several drugs, age, smoking, body mass, gender, physical exercise, race, and season. Additionally, it is also known that genetic factors determine the fibrinogen levels, and also that they determine the response of fibrinogen levels to environmental factors. Estimates, based on twin studies, suggest that 30-50% of the plasma fibrinogen level is genetically determined. The effect of dietary components on plasma fibrinogen levels is modest. Several components have been identified as factors that influence fibrinogen levels. Among those are fish oil, other lipids, and fibers. Dietary components that were expected to have an effect on fibrinogen, but for which no association was observed are black and green tea. Several drugs are known to influence fibrinogen levels, the most studied of which are platelet aggregation inhibiting drugs, such as ticlopidine, and the lipid lowering fibric acid derivatives (fibrates). Both types of drugs decreased the plasma fibrinogen level by about 10%, and bezafibrate lowers fibrinogen even more in patients with diabetes. No clear effect was observed for the HMG-CoA reductase inhibitors (statins). In the Bezalip study, fibrinogen levels decreased in patients treated with bezafibrate, but this had no clear effect on the risk of cardiovascular disease. This suggests that several mechanisms influence the fibrinogen level and that these mechanisms may contribute differently to cardiovascular disease. Several variations in the fibrinogen genes have been described and especially variations in the promoter region of the fibrinogen beta-gene are interesting, because the synthesis of the fibrinogen B beta chain is considered to be the rate limiting step in the fibrinogen biosynthesis. In many studies the fibrinogen beta-gene polymorphisms (-455G/A, -148C/T, and BclI) are found to be associated with the plasma levels of fibrinogen. However, they are not associated with the risk of cardiovascular events, although in several studies an association with the severity and progression of atherosclerosis has been reported. It has also been observed frequently that the fibrinogen beta-gene promoter polymorphisms are associated with the response of fibrinogen levels to environmental factors, such as exercise and trauma. In conclusion, plasma fibrinogen levels are regulated by an interesting and complex interplay between environmental and genetic factors.

Fibrinogen levels and obstructive sleep apnea in ischemic stroke

The plasma level of fibrinogen is felt to be an independent risk factor for vascular events. Obstructive sleep apnea (OSA) has a high prevalence in patients with stroke and may also be an independent risk factor. The aim of our study was to determine the association between OSA and plasma levels of fibrinogen in patients with stroke. Polysomnography was performed during neurological rehabilitation in 113 patients (82 men, 31 women, age 58 +/- 11.1 yr, mean +/- SD) with ischemic stroke. OSA was absent (RDI < 5) in 44 patients, 42 had mild OSA (5 < or = RDI < 20), and 27 had moderate to severe OSA (RDI > or = 20). Parameters of OSA (respiratory disturbance index [RDI], oxygen indices) were correlated to plasma levels of fibrinogen, measured in the morning after admission to rehabilitation. Fibrinogen was positively correlated with RDI (r = 0.24, p = 0.007), duration of the longest apnea (r = 0.18, p = 0.049), and negatively correlated with several oxygen indices including average minimal oxygen saturation (r = -0.41, p < 0.001). Correlation coefficients were slightly higher when excluding patients with stroke of presumed cardiac origin. Multiple linear regression identified minimal mean oxygen saturation and sex as independent predictors of fibrinogen level. The correlation between severity of coexisting OSA and fibrinogen level in patients with stroke suggests a possible pathophysiological mechanism for an increased risk of stroke in patients with OSA.

Ticlopidine enhances the platelet inhibitory capacity of abciximab in vitro

Ticlopidine and abciximab are two antiplatelet agents that are frequently administered during percutaneous coronary interventions. Although they have different mechanisms of action and pharmacological profiles, the two agents are often concomitantly used in complicated stent placements. The purpose of the study was to evaluate the effect of ticlopidine therapy on the capacity of abciximab to inhibit platelet aggregation, in vitro. Blood samples from 13 ticlopidine-treated stent placement patients and 8 patients undergoing PTCA who did not receive ticlopidine were obtained prior to, 12-36 hours and 7-10 days after initiating ticlopidine treatment. For each patient, the minimal ADP and the thrombin receptor activating peptide (TRAP) concentrations that elicited maximal platelet aggregation responses at baseline were used to measure the extent of platelet aggregation and the abciximab concentration that gave a 50% decrease in aggregation (IC(50)) for both agonists at the three time points. The ticlopidine group baseline and 12-36 hour mean ADP aggregation responses were equivalent, but decreased by 34% (P = 0.009) at 7-10 days. The control group ADP and TRAP, as well as the ticlopidine group TRAP aggregation responses, were equivalent at all time points. The ticlopidine group baseline and 12-36 hour abciximab IC(50) values for ADP were comparable (1.58 +/- 1.1 ng/mL vs. 1.23 +/- 0.5 ng/mL; P = 0.266), but decreased to 1.00 +/- 0.6 ng/mL (36%; P = 0.004) at 7-10 days. In contrast, the abciximab IC(50) for TRAP increased from 1.48 +/- 1.0 ng/mL to 1.85 +/- 1.1 ng/mL (25%; P = 0.033) at 12-36 hours, but returned to baseline at 7-10 days (1.40 +/- 0.8; P = 0.975). The control group IC(50) abciximab values for ADP and TRAP were comparable throughout the monitoring period. The results demonstrate that ticlopidine elicits subtle potentiation of the platelet-inhibitory capacity of abciximab to the agonist ADP, but not TRAP, at 1 week after initiation of treatment.

A prospective study of fibrinogen and risk of myocardial infarction in the Physicians' Health Study

OBJECTIVES

We examined the association of baseline plasma fibrinogen with future risk of myocardial infarction (MI) in the Physicians' Health Study.

BACKGROUND

Elevated plasma fibrinogen increases and low dose aspirin decreases risk of MI. However, prospective data are limited about their interrelationships.

METHODS

Blood samples were prospectively collected at baseline from 14,916 men in the Physicians' Health Study, aged 40 to 84 years, who were randomly assigned to take aspirin (325 mg every other day) or placebo for 5 years. We measured baseline plasma fibrinogen among 199 incident cases of MI and 199 age- and smoking-matched control subjects free of cardiovascular disease at the time of the case's diagnosis.

RESULTS

Cases had significantly higher baseline fibrinogen levels (geometric mean: 262 mg/dl) than did control subjects (245 mg/dl, p = 0.02). Those with high fibrinogen levels (> or =343 mg/dl, the 90th percentile distribution of the control subjects) had a twofold increase in MI risk (age- and smoking-adjusted relative risk = 2.09, 95% confidence interval = 1.15 to 3.78) compared with those with fibrinogen below 343 mg/dl. Adjustment for lipids and other coronary risk factors as well as randomized aspirin assignment did not materially change the result. Furthermore, we observed no interaction between fibrinogen level and aspirin treatment.

CONCLUSIONS

Among these apparently healthy U.S. male physicians, fibrinogen is associated with increased risk of future MI independent of other coronary risk factors, atherogenic factors such as lipids and antithrombotics such as aspirin.

Hemostaseologic and hematologic parameters with aspirin and ticlopidine treatment in patients with cerebrovascular disease: a cross-over study

No direct comparisons of the effects of ticlopidine and aspirin on platelet aggregability, clotting parameters, and blood count are available in a cross-over study design in humans. We investigated 45 patients with cerebrovascular disease. Twenty-one patients received 300 mg aspirin once daily for 2 weeks and then for 2 more weeks received 250 mg ticlopidine twice daily. In 24 other patients, the scheme was reversed. ADP-induced aggregability was lower during ticlopidine treatment; epinephrine- and collagen-induced aggregabilities were lower with aspirin treatment. Platelet counts were higher during ticlopidine than during aspirin treatment (199.6/ nl with aspirin, 213.0/nl with ticlop dine, p = 0.008), probably reflecting less platelet activation and degradation and a longer platelet survival time induced by ticlopidine treatment.