A global view on the role of monocytes and platelets in atherogenesis

PPARγ and the Innate Immune System Mediate the Resolution of Inflammation

The resolution of inflammation is an active and dynamic process, mediated in large part by the innate immune system. Resolution represents not only an increase in anti-inflammatory actions, but also a paradigm shift in immune cell function to restore homeostasis. PPARγ, a ligand activated transcription factor, has long been studied for its anti-inflammatory actions, but an emerging body of literature is investigating the role of PPARγ and its ligands (including thiazolidinediones, prostaglandins, and oleanolic acids) in all phases of resolution. PPARγ can shift production from pro- to anti-inflammatory mediators by neutrophils, platelets, and macrophages. PPARγ and its ligands further modulate platelet and neutrophil function, decreasing trafficking, promoting neutrophil apoptosis, and preventing platelet-leukocyte interactions. PPARγ alters macrophage trafficking, increases efferocytosis and phagocytosis, and promotes alternative M2 macrophage activation. There are also roles for this receptor in the adaptive immune response, particularly regarding B cells. These effects contribute towards the attenuation of multiple disease states, including COPD, colitis, Alzheimer's disease, and obesity in animal models. Finally, novel specialized proresolving mediators-eicosanoids with critical roles in resolution-may act through PPARγ modulation to promote resolution, providing another exciting area of therapeutic potential for this receptor.

Chemical Composition and Nutraceutical Potential of Indian Borage (Plectranthus amboinicus) Stem Extract

The stem of Indian borage (Plectranthus amboinicus) was found to be an antioxidant rich fraction as evaluated byin vitromodels such as DPPH free radical scavenging, reducing power assay, superoxide anion radical scavenging, and total antioxidant capacity. The extract also exhibited antiplatelet aggregation ability, antibacterial activity, and antiproliferative effect against cancer cell lines: Caco-2, HCT-15, and MCF-7. Phytochemical evaluation of the extract revealed the occurrence of total phenolics (49.91 mg GAE/g extract), total flavonoids (26.6 mg RE/g extract), and condensed tannins (0.7 mg TAE/g extract). Among the major phenolics, rosmarinic acid (6.160 mg/g extract) was predominant, followed by caffeic acid (0.770 mg/g extract), rutin (0.324 mg/g extract), gallic acid (0.260 mg/g extract), quercetin (0.15 mg/g extract), andp-coumaric acid (0.104 mg/g extract). The appreciable biological activity and presence of biomolecules in the methanolic extract of stem indicate its potential application as functional food ingredients and nutraceuticals.

Computer simulation and experimental analysis of LDL transport in the arteries

Atherosclerosis develops from oxidized low-density lipoprotein molecules (LDL). When oxidized LDL evolves in plaque formations within an artery wall, a series of reactions occur to repair the damage to the artery wall caused by oxidized LDL. Macrophages accumulate inside arterial intima, they started to collect oxidized LDL and form foam cells. Smooth muscle cells accumulate in the atherosclerotic arterial intima, where they proliferate and secrete extracellular matrix to form a fibrous cap. In this study, experimental model of LDL transport on the isolated blood vessel from rabbit on high fat diet after 8 weeks is simulated numerically by using a specific model and histological data. The 3D blood flow is governed by the Navier-Stokes equations, together with the continuity equation. Mass transfer within the blood lumen and through the arterial wall is coupled with the blood flow by the convection-diffusion equation. LDL transport in lumen of the vessel is described by Kedem-Katchalsky equations. The inflammatory process is solved using three additional reaction-diffusion partial differential equations. Matching of histological rabbit data is performed using 3D histological image reconstruction and 3D deformation of elastic body. Computed concentrations of labeled LDL of 5.2 % and macrophages distribution of 4.2% inside the media are found to be in good agreement with experimental results. This simulation study provides a useful tool for understanding and prediction of LDL transport through the arterial wall and evolution of atherosclerotic plaques.

Upregulation of Inflammatory Mediators in End-Stage Renal Disease as Measured Using Biochip Array Technology

Systemic vascular changes contribute to both the pathogenesis and thrombotic comorbidities of end-stage renal disease (ESRD). This study aims to profile various biomarkers and better understand their role in the pathogenesis of ESRD. Plasma samples from 49 patients with ESRD and 56 control individuals were analyzed for markers for inflammation, specifically C-reactive protein (CRP), tumor necrosis factor receptor 1 (TNFR1), neutrophil gelatinase-associated lipocalin (NGAL); thrombomodulin (TM); neuron-specific enolase (NSE), and thrombosis-D-dimer (DD). Compared to controls, all markers studied showed a statistically significant upregulation in patients with ESRD. These results indicate a polypathologic process in patients with ESRD, leading to cardiovascular and cerebrovascular events. However, the clinical significance of previously untested markers, such as TNFR1, NGAL, and NSE, still needs to be further explored. This study further validates the role of endothelial damage and endogenous thrombotic processes in ESRD as evidenced by the increased levels of TM and DD.

Cocoa, chocolate, and cardiovascular disease

A significant body of evidence demonstrates that diets rich in fruits and vegetables promote health and attenuate, or delay, the onset of various diseases, including cardiovascular disease, diabetes, certain cancers, and several other age-related degenerative disorders. The concept that moderate chocolate consumption could be part of a healthy diet has gained acceptance in past years based on the health benefits ascribed to selected cocoa components. Specifically, cocoa as a plant and chocolate as food contain a series of chemicals that can interact with cell and tissue components, providing protection against the development and amelioration of pathological conditions. The most relevant effects of cocoa and chocolate have been related to cardiovascular disease. The mechanisms behind these effects are still under investigation. However, the maintenance or restoration of vascular NO production and bioavailability and the antioxidant effects are the mechanisms most consistently supported by experimental data. This review will summarize the most recent research on the cardiovascular effects of cocoa flavanols and related compounds.

Pericytes in the macrovascular intima: possible physiological and pathogenetic impact

The frequently observed de-endothelialization of venous coronary bypass grafts prepared using standard methods exposes subendothelial prothrombotic cells to blood components, thus endangering patients by inducing acute thromboembolic infarction or long-term proliferative stenosis. Our aim was to gain deeper histological and physiological insight into these relations. An intricate network of subendothelial cells, characterized by histological features specific for true pericytes, was detected even in healthy vessels and forms, coupled to the luminal endothelium, a second leaflet of the macrovascular intima. These cells, and particularly those in the venous intima, express enormous concentrations of tissue factor and can recruit additional amounts of up to the 25-fold concentration within 1 h during preincubation with serum (intimal pericytes of venous origin activate 30.71 +/- 4.07 pmol coagulation factor x.min(-1).10(-6) cells; n = 15). Moreover, decoupled from the endothelium, they proliferate rapidly (generation time, 15 +/- 2.1 h, n = 8). Central regions of atherosclerotic plaques, as well as of those of restenosed areas of coronary vein grafts, consist almost completely of these cells. In stark contrast with the prothrombogenicity of the intimal pericytes, intact luminal endothelium recruits high concentrations of thrombomodulin (CD 141) specifically within its intercellular junctions, activates Protein C rapidly (42 +/- 5.1 pmol/min.10(6) venous endothelial cells at thrombin saturation; n = 15), can thus actively prevent coagulatory processes, and never expresses histologically detectable and functionally active tissue factor. Given this strongly prothrombotic potential of the intimal pericytes and their overshooting growth behavior in endothelium-denuded vascular regions, they may play important roles in the development of atherosclerosis, thrombosis, and saphenous vein graft disease.

Inflammation and infection do not promote arterial aging and cardiovascular disease risk factors among lean horticulturalists

Background

Arterial aging is well characterized in industrial populations, but scantly described in populations with little access to modern medicine. Here we characterize health and aging among the Tsimane, Amazonian forager-horticulturalists with short life expectancy, high infectious loads and inflammation, but low adiposity and robust physical fitness. Inflammation has been implicated in all stages of arterial aging, atherogenesis and hypertension, and so we test whether greater inflammation associates with atherosclerosis and CVD risk. In contrast, moderate to vigorous daily activity, minimal obesity, and low fat intake predict minimal CVD risk among older Tsimane.

Methods and Findings

Peripheral arterial disease (PAD), based on the Ankle-Brachial Index (ABI), and hypertension were measured in Tsimane adults, and compared with rates from industrialized populations. No cases of PAD were found among Tsimane and hypertension was comparatively low (prevalence: 3.5%, 40+; 23%, 70+). Markers of infection and inflammation were much higher among Tsimane than among U.S. adults, whereas HDL was substantially lower. Regression models examine associations of ABI and BP with biomarkers of energy balance and metabolism and of inflammation and infection. Among Tsimane, obesity, blood lipids, and disease history were not significantly associated with ABI. Unlike the Tsimane case, higher cholesterol, C-reactive protein, leukocytes, cigarette smoking and systolic pressure among North Americans are all significantly associated with lower ABI.

Conclusions

Inflammation may not always be a risk factor for arterial degeneration and CVD, but instead may be offset by other factors: healthy metabolism, active lifestyle, favorable body mass, lean diet, low blood lipids and cardiorespiratory health. Other possibilities, including genetic susceptibility and the role of helminth infections, are discussed. The absence of PAD and CVD among Tsimane parallels anecdotal reports from other small-scale subsistence populations and suggests that chronic vascular disease had little impact on adult mortality throughout most of human evolutionary history.

Studies of biological functions in blood cells from individuals with large platelets

The present study was performed to explore differences in the expression of P-selectin and IL-8 production of blood cells in healthy individuals with large size platelets (MI-families) as compared to people having normal size platelets. A positive correlation between LPS-induced IL-8 production per platelet in whole blood and mean platelet volume (MPV) was found in the large platelet group (R=0.74, P<0.05). When the large and normal groups were combined the correlation was nearly, but not quite significant (R=0.46, P<0.06). There was also a positive correlation between sP-selectin and MPV (R=0.42, P<0.05). Furthermore, IL-8 in serum was positively correlated to sP-selectin in serum (R=0.68, P<0.005). sP-selectin baseline values in citrated plasma correlated significantly with values found in serum (R=0.72, P<0.0005), indicating that sP-selectin in blood originates from the platelets rather than from endothelial cells. Significant correlations were also found in both groups between P-selectin and CD40L (R=0.44, P<0.05) and P-selectin and RANTES (R=0.44, P<0.05). A significant correlation was also found between PDGF and RANTES (R=0.44, P<0.05). Our results suggest that larger platelets enhance the production of IL-8 more than normally sized platelets. This phenomenon is probably mediated through P-selectin exposed on platelets.

Platelet-lymphocyte cross-talk

Platelets and lymphocytes reciprocally regulate mutual functions, i.e., platelet-lymphocyte cross-talk. The heterotypic interactions have emerged as important regulatory mechanisms in the pathophysiological processes of thrombosis, inflammation, immunity, and atherosclerosis. Platelets influence lymphocyte function via direct cell-cell contact and/or soluble mediators. Hence, platelets enhance adhesion and cell migration of T(H), T cytolytic (T(C)), NK, and B cells. Platelets affect other functional aspects of lymphocyte subpopulations in a complex manner. They may attenuate cytokine secretion and immunosuppressive responses of T(H) cells and enhance T(C) cell proliferation and cytotoxicity. Platelets promote isotype shifting and antibody production of B cells but ameliorate cytolytic activity of NK cells. On the other hand, lymphocytes can also regulate platelet aggregation and secretion, as well as the effector cell function of platelets in immune defense. The two cell types collaborate in transcellular phospholipid metabolism, CD40-CD40 ligand-mediated intercellular signaling, and their involvements in atherogenesis. The research perspectives of platelet-lymphocyte cross-talk have also been addressed.

Platelet function and antiplatelet therapy

Background

Platelets have roles other than haemostasis and many are relevant to surgical practice. This review examines both the pathophysiology of platelets in haemostasis and thrombosis, and other roles of clinical importance.

Methods

A literature review of the various functional roles of platelets was performed (Medline search, English language) including their action in inflammation (in particular in atherothrombosis), antimicrobial defence and tumour growth. Current clinical evidence for antiplatelet therapy is also reviewed.

Results and conclusion

Platelet functions are multiple, complex and not limited to haemostasis. Understanding of platelet pathophysiology continues to grow and this is relevant to many aspects of surgical practice, particularly the clinical use of antiplatelet therapy.

Postprandial monocyte activation in response to meals with high and low glycemic loads in overweight women

BACKGROUND

Recent data show that atherosclerosis is initiated and perpetuated by inflammatory events. Activation of immune cells such as monocytes initiates inflammation, a key step in atherosclerosis.

OBJECTIVE

We hypothesize that a high-glycemic load meal activates inflammatory cells, and that this is mediated by elevated circulating triacylglycerol-rich lipoproteins.

DESIGN

Sixteen women [body mass index (in kg/m2): 25.7-29.6], aged 20-48 y, consumed meals with a high or a low glycemic load in a crossover fashion. Blood samples were collected before and up to 8 h after the meals. Samples were measured for glucose, insulin, triacylglycerols, and circulating cytokines, and expression of tumor necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta) was measured by flow cytometry.

RESULTS

At 3.5 h after the test meals, we observed a significant increase in monocytes expressing TNF-alpha with both high-and low-glycemic load meals. Also, expression of IL-1beta in monocytes tended to increase, but the change was not significant. The glycemic load of the meal did not influence circulating cytokines and had only a minimal effect on postprandial triacylglycerol concentrations despite marked postprandial changes in glycemia and circulating insulin concentrations.

CONCLUSIONS

In the postprandial state, monocytes can be activated by both high-and low-glycemic load meals. The glycemic load of a single meal did not have a significant effect on the degree of activation of the monocytes in women who displayed only a modest increase in circulating triacylglycerols in response to test meals. Future studies should examine the effect of glycemic load in subjects who have a hyperlipemic response to dietary carbohydrate.

Effects of tomato extract on platelet function: a double-blinded crossover study in healthy humans

BACKGROUND

Aqueous extracts from tomatoes display a range of antiplatelet activities in vitro. We previously showed that the active components also alter ex vivo platelet function in persons with a high response to ADP agonist.

OBJECTIVE

The objective was to evaluate the suitability of a tomato extract for use as a dietary supplement to prevent platelet activation.

DESIGN

A randomized, double-blinded, placebo-controlled crossover study was conducted in 90 healthy human subjects selected for normal platelet function. Changes from baseline hemostatic function were measured 3 h after consumption of extract-enriched or control supplements.

RESULTS

Significant reductions in ex vivo platelet aggregation induced by ADP and collagen were observed 3 h after supplementation with doses of tomato extract equivalent to 6 (6TE) and 2 (2TE) tomatoes [3 micromol ADP/L: 6TE (high dose), -21.3%; 2TE (low dose), -12.7%; P < 0.001; 7.5 micromol ADP/L: 6TE, -7.8%, 2TE, -7.6%; P < 0.001; 3 mg collagen/L: 6TE, -17.5%; 2TE, -14.6%; P = 0.007]. No significant effects were observed for control supplements. A dose response to tomato extract was found at low levels of platelet stimulation. Inhibition of platelet function was greatest in a subgroup with the highest plasma homocysteine (P < 0.05) and C-reactive protein concentrations (P < 0.001).

CONCLUSION

As a functional food or dietary supplement, tomato extract may have a role in primary prevention of cardiovascular disease by reducing platelet activation, which could contribute to a reduction in thrombotic events.

Effects of antiplatelet components of tomato extract on platelet function in vitro and ex vivo: a time-course cannulation study in healthy humans

BACKGROUND

Natural antithrombotic agents that influence platelet function are of potential interest for primary prevention of cardiovascular disease. Previous reports showed that tomato extracts inhibit platelet aggregation in vitro, but little is known of the active components, their mode of action, or their efficacy in vivo.

OBJECTIVE

The objectives of the study were to examine the antiplatelet activity of specific tomato components by in vitro experimentation and to establish their ex vivo efficacy in healthy humans.

DESIGN

The mechanisms of action of antiplatelet components isolated from tomato extracts were examined in vitro. A 7-h time-course study was carried out in cannulated human subjects (n = 23) to determine the ex vivo efficacy of a supplement drink containing tomato extract and the onset and duration of antiplatelet effects.

RESULTS

The inhibition of ADP-, collagen-, thrombin-, and arachidonate-mediated platelet aggregation by tomato extract components appears to be linked to the inhibition of glycoprotein IIb/IIIa and platelet secretory mechanisms. We found a significant inhibition of baseline platelet function, from 2.9 +/- 1.4% (optimal ADP concentrations; P = 0.03) to 20.0 +/- 4.9% (suboptimal ADP concentrations; P < 0.001), 3 h after supplementation with a dose of tomato extract equivalent to 6 tomatoes. The observed effects persisted for >12 h. Coagulation variables were not affected.

CONCLUSIONS

The ingestion of tomato components with in vitro antiplatelet activity significantly affects ex vivo platelet function. The reported cardioprotective effects of tomatoes are potentially linked to a modulation of platelet function.

[Fibrinogen as a risk factor in ischemic heart disease]

<zakljucak> Mesto fibrinogena u razvoju ateroskleroze i arterijske tromboze je verovatno znacajno jer on ucestvuje i u procesu nastanka i rasta plaka modulise hemoreoloske osobine krvi, a cini i osnovu koaguluma tokom procesa tromboze. Koncentracija fibrinogena u krvi je dobar nezavisan prognosticki parametar za razvoj akutnog infarkta miokarda, kako kod zdravih odraslih osoba, tako i kod koronarnih bolesnika. Nivo fibrinogena u krvi je delimicno genetski determinisan, ali i brojni faktori spoljasnje sredine uticu na njegov nivo. Vrlo je bitan odnos izmedju fibrinogena i nekih drugih vaznih faktora rizika. Fibrinogen i holesterol imaju izgleda sinergisticki ucinak na razvoj akutnog koronarnog sindroma. Moguce je da je fibrinogen jedna od najznacajnijih spona izmedju pusenja i koronarne bolesti. Veoma je mali broj lekova koji se mogu dugorocno primenjivati i smanjiti nivo fibrinogena u krvi, tako da za sada ne postoje klinicke studije o vrednosti ovakve terapije u lecenju i prevenciji akutnih koronarnih sindroma. Shodno tome sve dok se ne dokaze da se smanjenjem nivoa fibrinogena u krvi smanjuje rizik za ispoljavanje koronarne bolesti, njegova uloga kao faktora rizika ostaje nedovoljno definisana.

Role of vascular factors in osteoporosis

Osteoporosis is a silent epidemic in the world today. With the increase in the elderly population, there will be an increase in the prevalence of osteoporosis, and so the need for focused preventive strategies should become a public health priority. Prophylactic therapy and risk-factor reduction is important, as this is likely to be cost effective. There are scientific observations that point out that vascular dysfunction seen with aging may be related to the pathogenesis of osteoporosis. Here we review this relationship from a different angle. We think aggressive control of vascular risk factors in addition to the known existing osteoporosis risk factors may help to reduce the morbidity and mortality associated with this disease.

Effects of nonspecific beta-adrenergic stimulation and blockade on blood coagulation in hypertension

A hypercoagulable state might contribute to increased atherothrombotic risk in hypertension. The sympathetic nervous system is hyperactive in hypertension, and it regulates hemostatic function. We investigated the effect of nonspecific beta-adrenergic stimulation (isoproterenol) and blockade (propranolol) on clotting diathesis in hypertension. Fifteen hypertensive and 21 normotensive subjects underwent isoproterenol infusion in two sequential, fixed-order doses of 20 and then 40 ng. kg(-1). min(-1) for 15 min/dose. Thirteen subjects were double-blind studied after receiving placebo or propranolol (100 mg/day) for 5 days each. In hypertensive subjects, isoproterenol elicited a dose-dependent increase in plasma von Willebrand factor (vWF) antigen [F(2,34) = 5.02; P = 0.032] and a decrease in D-dimer [F(2,34) = 4.57; P = 0.040], whereas soluble tissue factor remained unchanged. Propranolol completely abolished the increase in vWF elicited by isoproterenol [F(1,12) = 10.25; P = 0.008] but had no significant effect on tissue factor and D-dimer. In hypertension, vWF is readily released from endothelial cells by beta-adrenergic stimulation, which might contribute to increased cardiovascular risk. However, beta-adrenergic stimulation alone may not be sufficient to trigger fibrin formation in vivo.

Platelet factor 4 enhances the binding of oxidized low-density lipoprotein to vascular wall cells

Accumulation of low-density lipoprotein (LDL)-derived cholesterol by macrophages in vessel walls is a pathogenomic feature of atherosclerotic lesions. Platelets contribute to lipid uptake by macrophages through mechanisms that are only partially understood. We have previously shown that platelet factor 4 (PF4) inhibits the binding and degradation of LDL through its receptor, a process that could promote the formation of oxidized LDL (ox-LDL). We have now characterized the effect of PF4 on the binding of ox-LDL to vascular cells and macrophages and on the accumulation of cholesterol esters. PF4 bound to ox-LDL directly and also increased ox-LDL binding to vascular cells and macrophages. PF4 did not stimulate ox-LDL binding to cells that do not synthesize glycosaminoglycans or after enzymatic cleavage of cell surface heparan and chondroitin sulfates. The effect of PF4 on binding ox-LDL was dependent on specific lysine residues in its C terminus. Addition of PF4 also caused an approximately 10-fold increase in the amount of ox-LDL esterified by macrophages. Furthermore, PF4 and ox-LDL co-localize in atherosclerotic lesion, especially in macrophage-derived foam cells. These observations offer a potential mechanism by which platelet activation at sites of vascular injury may promote the accumulation of deleterious lipoproteins and offer a new focus for pharmacological intervention in the development of atherosclerosis.

Cellular activation responses in blood in relation to lipid pattern: healthy men and women in families with myocardial infarction or cancer

High cholesterol is a well-established risk factor of myocardial infarction (MI). Since monocytes play a pivotal role in the development of atherosclerosis, one might anticipate that their functional properties are very important in relation to MI. In the present study, we have explored how the lipopolysaccharide (LPS)-induced reactivity of monocytes in whole blood in vitro relates to the serum lipid profile of healthy subjects with a history of MI or cancer in their close family. Twenty of the 54 subjects (of the total 266 test subjects) in the MI families had moderately high cholesterol (7.1-10.2 mmol/l), whereas 34 had normal cholesterol. Nineteen of the normocholesterol individuals had hyperactive monocytes (high responders), whereas 15 had monocytes responding normally. Two of the 20 subjects in the high cholesterol group had hyperactive monocytes. LPS-induced tissue factor, tumour necrosis factor-alpha and interleukin-6 were on the average three to four times higher in the normocholesterol group compared with the moderately hypercholesterol group, and hence no positive correlation was found between hyperactive monocytes and cholesterol. The 42 subjects in the families with cancer had normal cholesterol, and two of these subjects had very high LPS-induced tissue factor, tumour necrosis factor-alpha and interleukin-6, whereas eight of the 170 subjects without MI or cancer in their family were high responders. This further substantiates the notion that moderately high cholesterol is not associated with enhanced monocyte activation in whole blood. Hyperactive peripheral blood monocytes are suggested to be associated with a significant risk factor in developing coronary heart disease.

The effects of flavanol-rich cocoa and aspirin on ex vivo platelet function

BACKGROUND

Flavanols modulate platelet function in vitro, but less is known of their in vivo effects and how they compare to pharmacological platelet inhibitors. We investigated the effect of a flavanol-rich cocoa beverage (897 mg/ml) in combination with and in comparison to aspirin on platelet function and activation in healthy subjects.

METHODS AND RESULTS

On separate test days in a crossover design, 16 healthy adults consumed aspirin (81 mg), cocoa (as a beverage), or aspirin plus cocoa. Platelet activation was measured by surface expression of P-selectin and PAC-1 binding to the activated conformation of the GPIIb/IIIa receptor (GPIIb/IIIa-act). Platelet function was measured on an analyzer (the PFA-100) that measures shear stress-induced platelet plug formation in response to collagen-epinephrine or collagen-ADP. Plasma epicatechin concentrations peaked approximately 2 h after subjects were given either the cocoa or aspirin plus cocoa. After 6 h, cocoa inhibited epinephrine-induced platelet function. Epinephrine-induced platelet function was inhibited 2 and 6 h after aspirin, and after aspirin plus cocoa. Epinephrine-stimulated P-selectin expression was inhibited by aspirin at 6 h, and after 2 and 6 h by aspirin plus cocoa. ADP-stimulated P-selectin expression was not affected by the treatments. Cocoa and aspirin, given separately, reduced epinephrine-stimulated GPIIb/IIIa-act expression at 2 and 6 h, respectively, and at 2 and 6 h when given together, suggesting an additive effective. ASA plus cocoa inhibited ADP-stimulated GPIIb/IIIa-act expression at 6 h.

CONCLUSIONS

Flavanol-rich cocoa inhibited epinephrine-stimulated platelet activation and function. These effects were qualitatively similar to aspirin, but less profound. These results emphasize the need to further examine the effects of food flavonoids for platelet modulating effects.

Postprandial lipemia is associated with platelet and monocyte activation and increased monocyte cytokine expression in normolipemic men

The activation of platelets and monocytes has been implicated in the development of cardiovascular diseases. We asked the question if postprandial lipemia following a fat- containing meal is associated with platelet and monocyte activation and increased platelet-monocyte interaction. Thirteen healthy, normal weight, normolipemic males, 20 to 49 years, consumed a 40% fat meal of whole foods. Blood samples were obtained at fasting and 3 1/2 and 6 hours after ingestion. Triglyceride levels increased to 48% over baseline at 3 1/2 hours postconsumption and returned to fasting levels by 6 hours. Multiparameter flow cytometry using monoclonal antibodies showed that the percentage of platelets expressing surface P-selectin and the activated conformation the GPIIb-IIa receptor was significantly higher at 3 1/2 hours compared to fasting. The percentage of platelet-monocyte aggregates increased by 36% at 3 1/2 hours and 43% at 6 hours postconsumption. The percentage of monocytes expressing intracellular tumor necrosis factor-alpha (TNF-alpha) increased seven and eightfold at 3 1/2 and 6 hours, respectively. The expression of interleukin-1beta (IL-1beta increased in a similar manner. These data suggest activation of platelets and monocytes after a moderate fat meal. Repetitive activation of platelets and monocytes could be an early event in the initiation and development of atherosclerosis.

Platelet-mediated activation of endothelial cells: implications for the pathogenesis of transplant rejection

BACKGROUND

Platelets exert their normal functions at sites of endothelial disruption by plugging discontinuities in blood vessels and secreting products that promote thrombosis, inflammation, and the healing of wounds. Whether platelets might induce these changes in xenograft blood vessels, leading to development of acute vascular rejection, has been uncertain.

METHODS

To examine the role of human platelets in modulation of xenograft endothelium, pig endothelial cells were treated with human platelets.

RESULTS

Treatment of quiescent porcine endothelial cells with human platelets modulated the endothelial cells. Whereas resting human platelets caused little change in normal porcine endothelial cells, platelets activated with small amounts of thrombin induced striking changes in the endothelial cells, including the induction of tissue factor activity, the expression of E-selectin, and the secretion of endothelin-1. These changes were induced, at least in part, by interleukin-1 (IL-1) associated with the platelet surface and were modified by the secretion of transforming growth factor-beta (TGF-beta).

CONCLUSION

These findings may explain how the activation of platelets at an early point in the rejection of vascularized organ xenografts or in chronic diseases might contribute to thrombotic, ischemic, and inflammatory changes characteristic of an organ xenograft undergoing rejection.

Individual dosing of ASA prophylaxis by controlling platelet aggregation

Acetylsalicylic acid is widely used in the primary and secondary prevention of cardiovascular diseases. In the current study, we used platelet aggregation ex vivo in platelet-rich plasma induced with arachidonic acid as a routine method for the determination of the individual dose of acetylsalicylic acid necessary to inhibit platelet aggregation in 108 patients with cardiovascular diseases. In 40% of all patients studied, a dose of 30 mg/day was sufficient to block the arachidonic acid-induced platelet aggregation nearly completely. In 50% of all patients, a dose of 100 mg/day was necessary. In 10% of all patients, the dose had to be further increased to 300 mg/day or even to 500 mg/day to inhibit platelet aggregation nearly completely. These results demonstrate that platelet aggregation can be used as a simple routine laboratory method to control acetylsalicylic acid treatment in patients with cardiovascular diseases and to determine individual doses of acetylsalicylic acid for a nearly complete inhibition of platelet aggregation. With a standard dose of 100 mg/day, 10% of the patients were nonresponders.

The calcium inhibitor SR33805 reduces intimal formation following injury of the porcine carotid artery

We studied the effect of SR33805, a calcium channel blocker, in vitro on the proliferation of vascular smooth muscle cells (SMC) stimulated by foetal calf serum, basic fibroblast growth factor and platelet derived growth factor, and in vivo with regard to SMC migration and proliferation which occurred following injury of the porcine carotid artery. The intimal lesion was induced by a silasten collar surgically positioned around the carotid artery and by a stenosis reducing blood flow by 50% for 30 days. Animals received SR33805 (5 mg/kg/day) 8 days before the induction of the lesion and up to 30 days after. In vitro, SR33805 inhibited in a dose-dependent manner growth factor-induced proliferation of SMC (0.20<IC(50)<0.46 microM). In vivo, SR33805 reduced the intima/media ratio of the cross sectional surface area (decrease of 60%, P<0.05) without affecting neointimal SMC density. The medial SMC density was 40% lower in treated than in control animals (upstream, P<0.05 and downstream to the stenosis, P<0.01). Thus, it appears that SR33805 significantly reduced intimal hyperplasia, which occurred after perivascular manipulation of the artery, an effect consistent with its in vitro proliferation inhibitory activity, suggesting that long-term treatment with SR33805 may reduce or delay SMC proliferation.

Mechanisms of venous and arterial thrombosis in heparin-induced thrombocytopenia

Since the reports by Weismann and Tobin in 1958 and Roberts et al. in 1964 called attention to paradoxical thrombosis in patients treated with heparin, the thrombotic aspect of the heparin-induced thrombocytopenia syndrome (HIT) has been emphasized. Yet to this day, the mechanism of thrombosis associated with HIT (HITT) is unclear. It is important to understand the etiology of HITT because of its devastating clinical consequences. We believe one rational approach to understand the mechanism underlying HITTS is to invoke Virchow's triad: stasis, vascular injury and a hypercoagulable state. A hypercoagulable state exists in all HIT patients due to platelet activation by heparin antibody binding. Thrombin generation from platelet microparticles and exposed platelet phospholipid, coupled with stasis (elderly bedridden or otherwise sedentary ill patients who comprise the majority of the HIT population), provide two risk factors that can lead to venous thrombosis. A hypercoagulable state coupled with endothelial cell dysfunction due to injury from heparin antibody, activated platelets, leukocytes, platelet microparticles, complement, atherosclerosis or medical intervention can lead to arterial thrombosis. Of patients with HIT, HITT occurs in about 25%, suggesting that a second set of patient specific risk factors, in addition to the generation of pathological heparin antibodies, determine whether HITT will develop. Interaction between activated platelets and other platelets, and with endothelial cells, leukocytes, neutrophils, monocytes and cytokines are areas of research that may provide more specific characterization of the hypercoagulable state and vascular damage. Nuances involving genetic variation in platelets, endothelial cells and immune function are also likely to be a major component of the observed variability of this disease spectrum. Virchow's triad may explain the different manifestations of HITTS.

Cocoa and wine polyphenols modulate platelet activation and function

There is speculation that dietary polyphenols can provide cardioprotective effects due to direct antioxidant or antithrombotic mechanisms. We report in vitro and postingestion ex vivo effects of cocoa procyanidins, a procyanidin-rich cocoa beverage and dealcoholized red wine (DRW) on human platelet activation. In a series of in vitro studies, cocoa procyanidin trimers, pentamers or DRW (3 and 10 micromol/L) were incubated with citrated peripheral whole blood in the presence and absence of platelet agonists. Platelet activation was detected using fluorescent-labeled monoclonal antibodies recognizing the fibrinogen binding conformation of GPIIb-IIIa (referred to herein as PAC-1 binding) and the activation-dependent platelet epitope CD62P (P-selectin). The percentage of CD42a-positive platelets coexpressing PAC-1 binding and/or CD62P was determined by multiparameter flow cytometry. Procyanidin trimers, pentamers and DRW added to whole blood in vitro increased PAC-1 binding and P-selectin expression. In contrast, procyanidin trimers, pentamers and DRW inhibited the platelet activation in response to epinephrine. The effects on platelet activation of cocoa beverage and DRW consumption were also studied in healthy subjects. Citrated blood was obtained before and 2 and 6 h after the ingestion of a cocoa beverage, a caffeine-containing beverage, DRW or water. Platelet activation was measured by flow cytometry. The consumption of DRW did not affect the expression of activation-dependent platelet antigens, either unstimulated or after ex vivo activation with epinephrine. However, the consumption of DRW increased PAC-1 binding in response to 100 micromol/L ADP ex vivo. Cocoa consumption reduced platelet response to agonists ex vivo. The ingestion of water had no effect on platelet activation, whereas a caffeine-containing beverage augmented the response of platelets to epinephrine. In summary, select cocoa procyanidins and DRW added to whole blood in vitro increased expression of platelet activation markers in unstimulated platelets but suppressed the platelet activation response to epinephrine. In contrast, cocoa consumption suppressed unstimulated and stimulated platelet activation in whole blood. This suppressive effect observed on platelet reactivity may explain in part the reported cardioprotective effects of dietary polyphenols.

Cocoa inhibits platelet activation and function

BACKGROUND

Epidemiologic studies have shown inverse associations between dietary polyphenols and mortality from coronary heart disease. However, the basis for this protective association is uncertain. Food polyphenols reportedly have antioxidant properties and decrease platelet function in vitro.

OBJECTIVE

This study sought to evaluate whether consumption of a polyphenol-rich cocoa beverage modulates human platelet activation and primary hemostasis.

DESIGN

Peripheral blood was obtained from 30 healthy subjects before and 2 and 6 h after ingestion of a cocoa beverage (n = 10), a caffeine-containing control beverage (n = 10), or water (n = 10). Platelet activation was measured in terms of expression of activation-dependent platelet antigens and platelet microparticle formation by using fluorescent-labeled monoclonal antibodies and flow cytometry. Primary platelet-related hemostasis was measured with a platelet function analyzer.

RESULTS

Ex vivo epinephrine- or ADP-stimulated expression of the fibrinogen-binding conformation of glycoprotein IIb-IIIa was lower 2 and 6 h after consumption of cocoa than before consumption. Cocoa consumption also decreased ADP-stimulated P-selectin expression. In contrast, epinephrine-induced platelet glycoprotein IIb-IIIa expression increased after consumption of the caffeine-containing beverage but not after water consumption. Platelet microparticle formation decreased 2 and 6 h after cocoa consumption but increased after caffeine and water consumption. Primary hemostasis in response to epinephrine in vitro was inhibited 6 h after cocoa consumption. The caffeine-containing beverage inhibited ADP-induced primary hemostasis 2 and 6 h after consumption.

CONCLUSIONS

Cocoa consumption suppressed ADP- or epinephrine-stimulated platelet activation and platelet microparticle formation. Cocoa consumption had an aspirin-like effect on primary hemostasis.

The effect of red wine on the fibrinolytic system and the cellular activation reactions before and after exercise

The effect of red wine drinking was tested on fibrinolytic parameters and blood cells in nine healthy students at rest and after acute exercise. The subjects were randomly assigned in a crossover design to one of three treatment regimes: control situation, low-dose wine group, and high-dose wine group. Blood samples were drawn just prior to experimental start, at 2 and 4 hours, and the next morning at 8:00 a.m., at 8:30 a.m. just after exercise, and 2 hours after exercise. The fibrinolytic potential was measured by whole blood clot lysis time (WBCLT), tissue plasminogen activator, and plasminogen activator inhibitor-1 (PAI-1) antigens in plasma. A whole blood system was used to test the reactivity of blood cells by stimulating hirudinized blood with 5 ng/mL lipopolyusaccharide (LPS) for 2 hours at 37 degrees C and measurements of tissue necrosis factor alpha and interleukin-8 (IL-8) in the plasma. Intake of red wine caused impaired fibrinolysis shown by prolonged WBCLT (3.6, 20.7, and 55.7%, respectively, for control, low- and high-dose wine groups) due to increase in PAI-1 antigen (-0.8, 4.8, and 11.0 ng/mL, respectively, in the three groups). There was no effect of the red wine the next morning on the fibrinolytic system. A strong correlation was observed between WBCLT and PAI-1 antigen (p<0.0001). Acute exercise caused an immediate rise in both tissue plasminogen activator antigen and PAI-1 antigen levels and WBCLT was significantly shortened. In contrast to that of the wine groups, 2 hours after exercise WBCLT was prolonged in the control group, but not significantly so. Thus the red wine has a negative effect on the fibrinolytic system during rest, but may have a positive effect after strenuous exercise. The red wine had no immediate effect on LPS-induced tissue necrosis factor alpha or IL-8 production, although there was a tendency for higher cytokine production in the control group compared to the wine groups during and just after intake of wine. The next morning after exercise, the LPS-induced IL-8 production increased 137, 89, and 96%, respectively, in control, low-, and high-dose wine groups, probably due to a rise in epinephrine and activation of platelets. Although not significantly so, there was a tendency for red wine intake in the evening to suppress the reactivity of the cells after physical exercise the subsequent morning. It is suggested that the negative effect of red wine ingestion may be due to the toxic effect of ethanol on hepatocytes or adipose tissue and subsequent release of PAI-1, whereas the positive effect may be due to the red wine suppression of platelet activation and release of PAI-1 from activated platelets. It is proposed that at least part of the beneficial effect of red wine ingestion may be associated with the downregulation of cytokine production.

Potential non-glycoprotein IIb/IIIa effects of abciximab

The antithrombotic effect of abciximab is believed to be primarily due to its blockade of platelet glycoprotein IIb/IIIa receptors, leading to the inhibition of platelet aggregation. Studies have, however, identified that antibody 7E3, the parent molecule of abciximab, and/or abciximab itself, binds to both "activated" alphaMbeta2 receptors and alphaVbeta3 receptors. Because alphaMbeta2 receptors are present on granulocytes and monocytes, cells that have been implicated in contributing to atherosclerosis, intimal hyperplasia after vascular injury, reperfusion injury, and thrombin generation, it is possible that some of abciximab's effects relate to this reactivity. Similarly, because alphaVbeta3 has been implicated in platelet adhesion to osteopontin, intimal hyperplasia after vascular injury, and platelet-mediated thrombin generation, it is possible that some of abciximab's beneficial effects relate to this reactivity. Blockade of alphaVbeta3 receptors may also be beneficial in other disease states because, in animal models, such blockade inhibits tumor angiogenesis and sickle cell adhesion to blood vessel endothelium. Despite these intriguing observations, there are no direct data to support any beneficial roles or any unwanted side effects related to the reactivities of abciximab with "activated" alphaMbeta2 or alphaVbeta3 receptors.

Enhanced upregulation of the Fc gamma receptor IIIa (CD16a) during in vitro differentiation of ApoE4/4 monocytes

We recently reported a positive correlation of the pool size of lipopolysaccharide receptor (CD14)dim and Fc gamma receptor IIIa (CD16a)+ monocytes in peripheral blood to the apolipoprotein E4 (apoE4) phenotype and a negative correlation to high density lipoprotein (HDL) cholesterol levels (Arterioscler Thromb Vasc Biol. 1996;16:1437-1447). In this study, the in vitro differentiation of mononuclear phagocytes derived from healthy blood donors homozygous for the E3/3 or the E4/4 phenotype was analyzed during 7 days of culture in serum-free medium supplemented with macrophage colony-stimulating factor (M-CSF). The CD16a expression, which indicates Fc receptor-dependent phagocytic activity, increased to a significantly higher level in apoE4/4 monocytes than in apoE3/3 cells. The costimulatory molecule CD40, which indicates antigen-presenting capacity, was upregulated more strongly in apoE3/3 monocytes compared with E4/4 cells, but the difference did not reach a significant level. The expression of differentiation-associated surface proteins (CD14, CD33, CD45) and adhesion molecules (CD11a, CD11b, CD11c, CD49d) was not significantly different between apoE3/3 and apoE4/4 monocytes. However, a significantly decreased intracellular apoE concentration and a reduced amount of secreted apoE were found in apoE4/4 monocytes during in vitro differentiation. No differences were found in the surface expression of the low density lipoprotein receptor-related protein (CD91) and the uptake of fluorescence labeled low density lipoprotein between apoE3/3 and apoE4/4 monocytes. These data indicate that the apoE4/4 phenotype significantly influences the M-CSF-dependent differentiation of monocytes toward a more CD16a-positive phagocytic phenotype.

IL-10 inhibits LPS-induced human monocyte tissue factor expression in whole blood

Interleukin 4 (IL-4), IL-10 and IL-13 are all known to modulate several proinflammatory functions in human monocytes. They have also previously been shown to down-regulate lipopolysaccharide (LPS)-induced tissue factor (TF) expression in isolated cultured monocytes. In this study we investigated the effect of these three cytokines on the induction of monocytic TF in a whole blood environment at three levels: mRNA quantitation, surface antigen expression and procoagulant activity. We showed that IL-10 attenuated LPS-induced monocyte TF expression and activity in whole blood in a concentration-dependent manner, both when added to the blood prior to LPS and, although to a lesser extent, when added up to 1 h subsequent to LPS challenge. Maximum inhibition occurred at 5 ng/ml of IL-10 when the cytokine was added before LPS. IL-4 and IL-13, however, did not exhibit any inhibitory effect in the whole blood environment, contrary to the reported findings in cell culture experiments. Our results confirm the potential of IL-10 as an anti-inflammatory, TF-preventing drug, whereas the effects of IL-4 and IL-13 on monocytes in whole blood seem more complex, and require further investigation.

Anticoagulant Effects of 1α,25-Dihydroxyvitamin D3 on Human Myelogenous Leukemia Cells and Monocytes

The hormonally active form of vitamin D is 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3], which is a principal regulator of calcium homeostasis. It also affects hormone secretion, cell differentiation, and proliferation by a mode of action that involves stereospecific interaction with an intracellular vitamin D receptor (VDR). We recently found that retinoids, which are vitamin A derivatives, exert anticoagulant effects by upregulating thrombomodulin (TM) and downregulating tissue factor (TF) expression in acute promyelocytic leukemia cells and monoblastic leukemia cells. Both the VDR and retinoid receptors belong to the same family of receptors. A heterodimer consisting of the retinoid X receptor and the VDR binds to vitamin D responsive elements on genes regulated by vitamin D. To determine whether 1,25(OH)2D3 would exhibit anticoagulant effects similar to retinoids, we measured the antigen level, activity, and mRNA level of TM and TF in human leukemic cells, vascular endothelial cells, and monocytes treated with 1,25(OH)2D3. We found that 1,25(OH)2D3 upregulates antigen expression, activity, and mRNA levels of TM and downregulates antigen expression, activity, and mRNA levels of TF in human monocytic leukemia cells, some acute myelogenous leukemia cells, and monocytes, but not in umbilical vein endothelial cells. Transient transfection studies with reporter plasmids in monocytic leukemia cells and mobility gel-shift assay showed interaction with 1,25(OH)2D3 and functional retinoic acid responsive elements present in the 5′-flanking region of the TM gene. However, auxiliary factors or other elements in the TM gene may contribute to VDR specificity and transactivation of the gene in specific target cells. These findings indicate that 1,25(OH)2D3 resembles the retinoids in its control of the transcription of the TM and TF genes in human monocytic cells. Analogs of 1,25(OH)2D3with anticoagulant activity may serve as adjunctive antithrombotic agents in monocytic leukemia and atherosclerotic disease.

Reactivation of the coagulation system: rationale for long-term antithrombotic treatment

Coronary artery thrombosis superimposed on a disrupted atherosclerotic plaque has emerged as the pivotal pathophysiologic event in acute coronary syndromes (i.e., unstable angina, myocardial infarction, and sudden death). The various clinical manifestations depend on the extent and duration of thrombus deposition, which are determined by several local and systemic thrombogenic risk factors. The thrombotic response to plaque disruption involves both platelet activation and thrombin generation. Accordingly, combined treatment with aspirin and heparin has proved more efficacious than either treatment alone in the risk reduction of serious cardiac events in patients with unstable angina or non-Q-wave infarction. However, withdrawal of heparin is, even after prolonged treatment, associated with an increased short-term risk of serious cardiac events relative to the risk in patients given only aspirin. Furthermore, the long-term relative event rate seems not to be influenced by administration of heparin or direct antithrombins in the acute phase. Both transient hypercoagulability associated with heparin withdrawal and continuous thrombin generation over a longer term related to the underlying disease may explain the rebound in clinical events. Longer duration of combined antiplatelet and anticoagulant treatments, e.g., until healing of the culprit lesion or even until stabilization of vulnerable, yet nondisrupted plaques, may improve long-term clinical outcome.