Increased platelet cholesterol and decreased percentage volume of platelets as a secondary risk factor for coronary artery disease

The LIPL study: Postprandial lipid profile, inflammation, and platelet activity in patients with chronic coronary syndrome

Background and aims

It is suggested that the changes in atherosclerosis happen mainly under the influence of non-fasting lipids. To date, the studies in the postprandial state were primarily performed on healthy subjects. This exploratory, cross-sectional study investigates the change in lipid profile, inflammation, and platelet activation in patients with different cardiovascular risk profiles in the postprandial state.

Methods

The studied population consists of 66 patients with different cardiovascular risks: patients with a history of the chronic coronary syndrome (CCS) and diabetes mellitus type 2 (DM2) (n = 20), CCS without DM2 (n = 25), and a healthy control group (n = 21). Lipid variables and markers of platelet function and inflammation were assessed during the fasting state and three and 5 h after a standardized fat meal using a standardized oral fat tolerance test (OFTT), a milkshake with 90 g of fat.

Results

Patients with CCS and DM2 were significantly older and had the highest BMI. All patients with CCS were on acetylsalicylic acid, and 95% of CCS patients were on high-dose statins. The absolute leukocyte and neutrophile count increased significantly in the control group during the OFTT in comparison to CCS subjects. There was a significant decrease of HDL and increase of triglycerides during the OFTT, however with no difference between groups. There was no difference in the change of platelet activity between all groups.

Conclusion

This study showed that OFTT leads to an increased postprandial inflammation response in healthy group compared to CCS ± DM2 while there was no change in lipid profile and platelet activity.

Role of Lipoprotein Levels and Function in Atherosclerosis Associated with Autoimmune Rheumatic Diseases

Immune and inflammatory mediators in autoimmune rheumatic diseases induce modification in the activity of enzymes pivotal for lipid metabolism and promote a proatherogenic serum lipid profile. However, disturbances in low- and high-density lipoprotein composition and increased lipid oxidation also occur. Therefore, lipoprotein dysfunction causes intracellular cholesterol accumulation in macrophages, smooth muscle cells, and platelets. Overall, both plaque progression and acute cardiovascular events are promoted. Single rheumatic diseases may present a particular pattern of lipid disturbances so that standard methods to evaluate cardiovascular risk may not be accurate enough. In general, antirheumatic drugs positively affect lipid metabolism in these patients.

Serum cholesterol loading capacity on macrophages is linked to coronary atherosclerosis and cardiovascular event risk in rheumatoid arthritis

Objectives

Cholesterol loading capacity (CLC) describes the ability of serum to deliver cholesterol to cells. It is linked to foam cell formation, a pivotal step in atherosclerotic plaque development. We evaluate the associations of CLC with coronary atherosclerosis presence, burden and cardiovascular risk in patients with rheumatoid arthritis (RA).

Methods

Coronary atherosclerosis (any, high-risk low-attenuation plaque and obstructive plaque) was evaluated with CT angiography in 141 patients. Participants were prospectively followed for 6.0±2.4 years and cardiovascular events including cardiac death, myocardial infarction, unstable angina, stroke, claudication, revascularisation and hospitalised heart failure were recorded. CLC was quantified as intracellular cholesterol in human macrophages after incubation with patient serum.

Results

CLC was not linked to overall plaque presence or burden after adjustments for atherosclerotic cardiovascular disease (ASCVD) score, statin use and low-density lipoprotein cholesterol. However, CLC associated with presence and numbers of any, low-attenuation and obstructive plaques exclusively in biologic disease-modifying antirheumatic drugs (bDMARD) non-users (p for interaction ≤0.018). CLC associated with cardiovascular event risk overall after adjustments for ASCVD and number of segments with plaque (HR=1.76 (95% CI 1.16 to 2.67) per 1 SD increase in CLC, p=0.008). Additionally, bDMARD use modified the impact of CLC on event risk; CLC associated with events in bDMARD non-users (HR=2.52 (95% CI 1.36 to 4.65) per 1SD increase in CLC, p=0.003) but not users.

Conclusion

CLC was linked to long-term cardiovascular event risk in RA and associated with high-risk low attenuation and obstructive coronary plaque presence and burden in bDMARD non-users. Its prospective validation as a predictive biomarker may be, therefore, warranted.

Hyperlipidemia and Platelet Parameters: Two Sides of the Same Coin

Introduction: Hyperlipidemia is a disorder in which lipid and cholesterol levels in the blood are elevated. Diabetes, coronary heart disease, obesity, and hypertension are commonly linked to hyperlipidemia. Despite this, hyperlipidemia is a widely neglected illness, owing to its asymptomatic nature, ignorance of aberrant lipid profiles on screening, and economic issues in poor countries such as India. Platelets have been shown to have a role in the thrombus consequences of atheromatous damage in hyperlipidemic individuals by initiating and propagating atherosclerotic plaques. Platelets with bigger diameters are thought to be more metabolically, enzymatically, and functionally agile than platelets with lower sizes. In steady-state operation, these bigger platelets release more thromboxane B2 than regular platelets. Platelets with bigger sizes are more hemostatically active and hence have a higher chance of forming a thrombus and thromboembolism. The aim of this study was to compare the values of key platelet parameters and platelet function in hyperlipidemic patients with normal age and sex-matched controls.

Material and methods: A total of 100 individuals were included in this study, with 68 cases of hyperlipidemia and 32 controls having normal lipid profiles. Platelet volume indices (PVI) such as platelet count (PC), mean platelet volume (MPV), platelet distribution width (PDW), platelet large cell ratio (P-LCR), plateletcrit (PCT), and platelet function (platelet aggregation with adenosine diphosphate, ADP) were compared between hyperlipidemia patients and age sex-matched controls with normal lipid profiles.

Results: The cases had a statistically significant higher mean MPV (10.55 ± 1.81), PDW (14.93 ± 2.82), and P-LCR (30.97 ± 11.74) compared to mean MPV (9.35 ± 1.85), PDW (13.10 ± 2.60), and P-LCR (25.13 ± 12.23) of controls (p-value < 0.05). No significant difference was observed between the study group and control group with respect to mean PC and PCT (p-value > 0.05). In this study, there was a statistically significant increase noted in platelet aggregation percentage in hyperlipidemic patients than in the control group (42.03 ± 25.28 vs 31.25 ± 15.11) (p-value < 0.05).

Conclusion: To conclude, platelet parameters are a significant, easy, and cost-effective method for predicting future acute episodes in hyperlipidemic patients that should be utilized more widely. To avoid vascular events, these individuals may require higher antiplatelet dosages and more rigorous hyperlipidemia therapy.

Drug repurposing for hyperlipidemia associated disorders: An integrative network biology and machine learning approach

Hyperlipidemia causes diseases like cardiovascular disease, cancer, Type II Diabetes and Alzheimer's disease. Drugs that specifically target HL associated diseases are required for treatment. 34 KEGG pathways targeted by lipid lowering drugs were used to construct a directed protein-protein interaction network and driver nodes were determined using CytoCtrlAnalyser plugin of Cytoscape 3.6. The involvement of driver nodes of HL in other diseases was verified using GWAS. The central nodes of the network and 34 overrepresented pathways had a critical role in Hyperlipidemia. The PI3K-AKT signalling pathway, non-essentiality, non-centrality and approved drug target status were the predominant features of the driver nodes. Next, a Random Forest classifier was trained on 1445 molecular descriptors calculated using PaDEL for 50 approved lipid lowering and 84 lipid raising drugs as the positive and negative training set respectively. The classifier showed average accuracy of 76.8 % during 5-fold cross validation with AUC of 0.79 ± 0.06 for the ROC curve. The classifier was applied to select molecules with favourable properties for lipid lowering from the 130 approved drugs interacting with the identified driver nodes. We have integrated diverse network data and machine learning to predict repurposing of nine drugs for treatment of HL associated diseases.

Diabetes and Thrombosis: A Central Role for Vascular Oxidative Stress

Diabetes mellitus is the fifth most common cause of death worldwide. Due to its chronic nature, diabetes is a debilitating disease for the patient and a relevant cost for the national health system. Type 2 diabetes mellitus is the most common form of diabetes mellitus (90% of cases) and is characteristically multifactorial, with both genetic and environmental causes. Diabetes patients display a significant increase in the risk of developing cardiovascular disease compared to the rest of the population. This is associated with increased blood clotting, which results in circulatory complications and vascular damage. Platelets are circulating cells within the vascular system that contribute to hemostasis. Their increased tendency to activate and form thrombi has been observed in diabetes mellitus patients (i.e., platelet hyperactivity). The oxidative damage of platelets and the function of pro-oxidant enzymes such as the NADPH oxidases appear central to diabetes-dependent platelet hyperactivity. In addition to platelet hyperactivity, endothelial cell damage and alterations of the coagulation response also participate in the vascular damage associated with diabetes. Here, we present an updated interpretation of the molecular mechanisms underlying vascular damage in diabetes, including current therapeutic options for its control.

Platelet volume indices as predictive biomarkers for diabetic complications in Type 2 diabetic patients

BACKGROUND:

Platelet volume indices (PVI) such as mean platelet volume (MPV), platelet distribution width (PDW), and platelet-large cell ratio (P-LCR) are the indicators of increased platelet activity and can be considered as potential biomarkers for diabetic complications.

PURPOSE:

To study PVI in Type 2 diabetics with and without complications in comparison to nondiabetic patients.

MATERIALS AND METHODS:

A case–control study was conducted on 300 Type 2 diabetics and 200 nondiabetics. Detailed clinical history regarding duration, hypertension, and complications was taken. PVI was obtained using automated cell counter. Fasting blood glucose, hemoglobin A1c, lipid profile, creatinine were also obtained. Diabetics were further categorized into patients with complications and without complications. Statistical analysis was performed by Statistical Package for the Social Sciences Version 17 (Chicago, IL) Student's t-test and ANOVA test.

RESULTS:

Platelet count was significantly decreased in diabetics (P = 0.005). MPV was significantly increased in diabetic patients with complications as compared to diabetics without complications and nondiabetic group (P < 0.0001). PDW showed statistically significant difference between diabetics with and without complications and nondiabetics (P < 0.0001). However, no statistically significant difference was observed in platelet-large cell ratio (P-LCR) among all the three study groups. We found statistically significant correlation of MPV with diabetic retinopathy (P = 0.000), nephropathy (P = 0.005), and diabetic foot (P = 0.048). PDW was significantly increased in diabetic retinopathy (P = 0.035) and nephropathy (P = 0.007). P-LCR had no statistically significant correlation with diabetic complications.

CONCLUSION:

MPV and PDW are predictive biomarkers of diabetic vascular complications. They are more significant in microvascular complications than macrovascular complications.

Possible Association of Smokeless Tobacco Dependent Impairment in the Erythrocytes and Platelets Membranes of Human Male Volunteers: An Observation

Background:

Smokeless tobacco (SLT) acts as a modifier of erythrocyte and platelet membranes by disrupting antioxidant system with the concomitant increase in free radical production and induction of apoptosis.

Methods:

The SLT users was that individuals used gutkha and khaini products (Khaleja/mahak chaini brand respectively) habitually, at least >20 times per week consists of 50-60 g during the last 2-4 years.

Results:

The gutkha and khaini users found to be significantly increased levels of iNOS (Inducible nitric oxide synthase) enzyme in plasma, erythrocytes, and platelet membranes when compared to normal controls. The gutkha and khaini users exhibited that the significant increase in the levels of gene expression of apoptotic proteins (Bcl₂-B cell lymphoma gene 2, Bax, caspases 8, caspase 10, and caspase 12), IL-6 (Interleukin-6), and decreased levels of TNF-α (Tumor necrosis factor-alpha) and decreased expression of caspase 12 of khaini users were observed from blood samples. The significant increase in the concentrations of peroxynitrites (ONOO-), nitric oxide (NO) (Nitrates and nitrites), malondialdehyde (MDA), cholesterol, and phospholipids were reported in the smokeless tobacco users of erythrocytes and platelets. The experimental subjects showed that the increased osmotic fragility and decreased membrane fluidity of erythrocytes and platelets in comparison with non-tobacco users. The normal subjects had been exposed that the proper functioning of antioxidant enzymes and decreased enzyme activities of antioxidants were reported by SLT users.

Conclusion:

The smokeless tobacco products are exerted chronic damage to membranes of erythrocytes and platelets and elevation of apoptosis in the prolonged periods of human male volunteers.

Lipid Metabolism and Signaling in Platelet Function

Modern society has changed its diet composition, transitioning to a higher intake of saturated fat with a 50% increase of cardiovascular risk (CVD). Within the context of increased CVD, there is an induction of a prothrombotic phenotype mainly due to increased platelet reactivity as well as decreased platelet response to inhibitors. Platelets maintain haemostasis through both blood components and endothelial cells that secrete inhibitory or stimulatory molecules to regulate thrombus formation. There exist a correlation between platelets' polyunsaturated fatty acid (PUFA) and the increase in platelet reactivity. The aim of this chapter is to review the metabolism of the main PUFAs involved in platelet function associated with the role that their enzyme-derived oxidized metabolites exert in platelet function and fate. Finally, how lipid metabolism in the organism affect platelet aggregation and activation and the pharmacological modulation of these processes will also be discussed.

CDKN2BAS polymorphisms are associated with coronary heart disease risk a Han Chinese population

The goal of our study was to determine whether CDKN2BAS polymorphisms are associated with coronary heart disease (CHD) risk in a Han Chinese population. Eight SNPs were genotyped in 676 men and 465 women. We used χ² tests and genetic model analyses to evaluate associations between the SNPs and CHD risk. We found that rs10757274 was associated with an increased risk of CHD in both men (allele G: Odds ratio [OR] = 1.30, 95% confidence interval [CI]: 1.05-1.61, P = 0.018; codominant model: P = 0.042; recessive model: OR = 1.70, 95% CI: 1.10-2.62, P = 0.016; log-additive model: OR = 1.34, 95% CI: 1.05-1.71, P = 0.019) and women (dominant model: OR = 2.26, 95% CI: 1.28-3.99, P = 0.004). In addition, rs7865618 was associated with an 8.10-fold increased risk of CHD in women under a recessive model (OR = 8.10, 95% CI: 1.74-37.68, P = 0.006). Interestingly, the haplotype AA (rs10757274 and rs1333042) of CDKN2BAS was associated with decreased the risk of CHD in men (OR = 0.72, 95% CI: 0.55 - 0.95, P = 0.022).

Platelet mean volume, distribution width, and count in type 2 diabetes, impaired fasting glucose, and metabolic syndrome: a meta-analysis

BACKGROUND

Platelet activation contributes to cardiovascular disease (CVD), the main complication of type 2 diabetes mellitus (T2DM) and pre-diabetic conditions. Mean platelet volume is an easy-to-measure platelet parameter that has been associated with CVD. We sought to assess mean platelet volume, platelet distribution width, and platelet count in T2DM, impaired fasting glucose (IFG), impaired glucose tolerance (IGT), and metabolic syndrome.

METHODS

Web-based literature search (PubMed, EMBASE, and Web of Science) of studies published in English through June 2014 was performed to select case-control and cross-sectional studies that reported data on mean platelet volume, platelet distribution width, or platelet count in cases (subjects with T2DM, IFG, IGT, or metabolic syndrome) and noncases. Descriptive and quantitative information was extracted, and within-study standardized mean difference was estimated from means and standard deviations. Standardized mean differences across studies were synthesized using a random random-effects model, and subgroup analyses were performed on pre-specified study-level characteristics.

RESULTS

Thirty-nine studies were included. Compared with controls, mean platelet volume was significantly higher in T2DM (standardized mean difference, 95% confidence interval: 0.70, 0.50-0.91; N = 24,245), IFG (0.14, 0.02-0.26; N = 17,389) but not in metabolic syndrome (0.15, -0.24 to 0.55; N = 14,990). Platelet distribution width was wider in T2DM (0.93, 0.09-1.76; N = 471). Platelet count resulted higher in IFG (0.18, 0.12-0.24; N = 3960) and metabolic syndrome (0.39, 0.01-0.78; N = 4070). Only two studies included IGT.

CONCLUSIONS

Available data suggest that T2DM subjects tend to have higher mean platelet volume and platelet distribution width values, but nondifferent platelet count as compared with subjects without T2DM. Whether and how these morphometric changes contribute to CVD of T2DM or can be used as CVD biomarker awaits further investigation.

Plateletcrit: a sensitive biomarker for evaluating disease activity in Crohn's disease with low hs-CRP

OBJECTIVE

This study aimed to investigate whether PLT indices could act as non-invasive biomarkers for active Crohn's disease (CD).

METHODS

Altogether 130 CD patients and 130 age- and gender-matched healthy volunteers were retrospectively enrolled in the study. CD patients were further divided into patients with active disease (Crohn's disease activity index [CDAI] >150) and in remission. PLT indices including PLT count, mean platelet volume (MPV), platelet distribution width (PDW), platelet large cell ratio (P-LCR) and plateletcrit (PCT) were detected. High-sensitivity C-reactive protein (hs-CRP) and erythrocyte sedimentation rate (ESR) levels were also determined.

RESULTS

In active CD, PLT and PCT levels were notably higher but P-LCR and PDW levels were lower than those in healthy controls and patients in remission. PLT, PDW, P-LCR and PCT were significantly correlated with CDAI (P < 0.05). The receiver operating characteristic (ROC) curve showed that with a cut-off value of 0.28%, PCT achieved a sensitivity of 67% and a specificity of 63% for detecting active CD, with the area under ROC curve (AUROC) of 0.67, which was inferior to hs-CRP and ESR. For patients with active disease who had hs-CRP levels lower than 10.0 mg/L, PCT turned out to be the best index for monitoring disease activity (sensitivity 71%, specificity 85%, AUROC 0.77, P = 0.02).

CONCLUSION

PCT may act as a specific and sensitive biomarker for determining active CD, especially in patients with an hs-CRP level lower than 10.0 mg/L.

Height, its components, and coagulability among older Chinese: the Guangzhou biobank cohort study

OBJECTIVES

The causal role of some cardiovascular risk factors, such as HDL cholesterol, has been increasingly challenged and attention is returning to all elements of Virchow's triad, i.e., hypercoagulability (including viscosity) as well as endothelial function and blood flow. We examined the life course origins of coagulability.

METHODS

We used multivariable linear regression to assess whether childhood influences, proxied by height and its components, were associated with hematocrit (Hct), hemoglobin (HGB), and other hematological parameters in 28,595 older Chinese adults (mean age = 61.8 years) from the Guangzhou Biobank Cohort Study.

RESULTS

Adjusted for age, sex, and recruitment phase, leg length was negatively associated with platelets (PLT) (-0.83 × 10(9) /l per centimeter (cm), 95% confidence interval (CI) -1.01 to -0.65). Sitting height and height were positively associated with Hct (0.05% per cm, 95% CI 0.04-0.07 for sitting height; 0.02% per cm, 95% CI 0.01-0.02 for height), HGB (0.21 g/l per cm, 95% CI 0.17-0.25; 0.07 g/l per cm, 95% CI 0.04-0.09) and negatively associated with PLT (-1.2 × 10(9) /l per cm, 95% CI -1.4 to -1.0; -0.83 × 10(9) /l per cm, 95% CI -0.95 to -0.70). Further adjustment for potential confounders did little to change the estimates.

CONCLUSIONS

For the first time we provide anthropometric evidence for the different roles of prepubertal and pubertal influences in relation to Hct and HGB. Whether factors that promote leg growth but reduce growth of sitting height may help to prevent cardiovascular events, via effects on hypercoagulability or viscosity, overall or in specific subgroups, remains to be determined.

Relationship between serum cholesterol and indices of erythrocytes and platelets in the US population

Whereas dyslipidemia has been associated with leukocytosis, the relationship between serum cholesterol and other hematopoietic lineages is poorly defined. Erythrocytes and platelets, anucleate cells relegated to nonspecific diffusional exchange of cholesterol with serum, have been proposed to have a distinct relationship to cholesterol from leukocytes. We examined the relationship between serum cholesterol and circulating erythrocyte/platelet indices in 4,469 adult participants of the National Health and Nutrition Examination Survey (NHANES) 2005-2006. In linear regression analyses, serum non-high density lipoprotein-cholesterol (non-HDL-C) was positively associated with mean erythrocyte number, hematocrit, hemoglobin concentration, platelet count, and platelet crit independently of age, gender, race/ethnicity, smoking, body mass index, serum folate, and C-reactive protein. The magnitude of the relationship was most marked for platelets, with lowest versus highest non-HDL-C quartile subjects having geometric mean platelet counts of 258,000/μl versus 281,000/μl, respectively (adjusted model, P < 0.001 for trend). These associations persisted in a sensitivity analysis excluding several conditions that affect erythrocyte/platelet and/or serum cholesterol levels, and were also noted in an independent analysis of 5,318 participants from NHANES 2007-2008. As non-HDL-C, erythrocytes, and platelets all impact cardiovascular disease risk, there is a need for advancing understanding of the underlying interactions that govern levels of these three blood components.

Cholesterol enrichment of rabbit platelets enhances the Ca(2+) entry pathway induced by platelet-derived secondary feedback agonists

AIMS

Hypersensitivity of platelets due to increased platelet cholesterol levels has been reported in hypercholesterolemia. However, the signaling pathways linking increased platelet reactivity and cholesterol contents are not fully understood. This study aims to determine the direct effect of cholesterol enrichment of platelets on the pathways including Ca(2+) mobilization and secondary feedback agonists such as adenosine diphosphate (ADP) and thromboxane A2 (TXA2).

MAIN METHODS

In vitro cholesterol enrichment of rabbit platelets was performed by incubation with cholesterol complexed with methyl-β-cyclodextrin. Ca(2+) mobilization was monitored using platelets loaded with fura-PE3/AM, a fluorescent calcium indicator. Released ATP and TXB2 from platelets were measured by a luciferin-luciferase ATP assay system and a TXB2 ELISA Kit, respectively.

KEY FINDINGS

Cholesterol enrichment of rabbit platelets significantly enhanced Ca(2+) mobilization induced by thrombin, accompanying an augmented Ca(2+) entry. The augmentation of Ca(2+) entry by cholesterol enrichment was significantly suppressed by treatment with inhibitors for secondary feedback agonists. In cholesterol-enriched platelets, the amount of released ATP or TXB2 induced by thrombin was not significantly altered in comparison with control platelets, whereas an increase in [Ca(2+)]i induced by ADP or U46619, a TXA2 mimetic, was significantly enhanced.

SIGNIFICANCE

These results suggest that cholesterol enrichment of rabbit platelets results in enhanced Ca(2+) mobilization via ADP/TXA2-dependent augmentation of the Ca(2+) entry pathway. The results reveal a novel mechanism by which platelet hypersensitivity is regulated by cholesterol contents.

Scavenger receptor BI modulates platelet reactivity and thrombosis in dyslipidemia

Hypercholesterolemia is associated with increased platelet sensitivity to agonists and a prothrombotic phenotype. Mechanisms of platelet hypersensitivity are poorly understood; however, increased platelet cholesterol levels associated with hypercholesterolemia were proposed as leading to hypersensitivity. Scavenger receptor class B type I (SR-BI) in the liver controls plasma high-density lipoprotein (HDL) levels, and SR-BI-deficient mice display a profound dyslipoproteinemia. SR-BI is also expressed on platelets, and recent studies have suggested a role for SR-BI in platelet function; however, its role in hemostasis is unknown. Our present studies demonstrated that non-bone marrow-derived SR-BI deficiency and the dyslipidemia associated with it lead to platelet hyperreactivity that was mechanistically linked to increased platelet cholesterol content. Platelet-specific deficiency of SR-BI, on the other hand, was associated with resistance to hyperreactivity induced by increased platelet cholesterol content. Intravital thrombosis studies demonstrated that platelet SR-BI deficiency protected mice from prothrombotic phenotype in 2 types of dyslipidemia associated with increased platelet cholesterol content. These novel findings demonstrate that SR-BI plays dual roles in thrombosis and may contribute to acute cardiovascular events in vivo in hypercholesterolemia.

Automated assay for determining cellular cholesterol using a random access chemistry analyser

BACKGROUND

We have previously reported an ultrasensitive fluorometric assay for measuring cellular cholesterol. Although this technique is reliable, the use of the assay has limitations due to the requirement for special equipment. It is therefore difficult to apply this assay for the routine determination of cellular cholesterol.

METHODS

A colorimetric assay to measure cellular cholesterol was established that utilizes reagents widely used for the measurement of cholesterol in blood samples in conjunction with a random access chemistry analyser ARCHITECT c8000 that is also common in clinical laboratories.

RESULTS

This colorimetric assay showed excellent linearity and recovery. The within-run coefficients of variation were less than 2.5%. The sensitivity of this method, with its detection limit of 1.29 mumol/L, was found to be superior to that of the fluorometric assay we have developed previously. In platelets obtained from patients with diabetes, both the free cholesterol and cholesterol ester content were significantly increased.

CONCLUSIONS

Using this technique, measurement of cellular cholesterol could be performed routinely without the requirement for special reagents and equipment.

Modulation of rabbit platelet aggregation and calcium mobilization by platelet cholesterol content

Hypercholesterolemia is one of the major contributing factors in atherosclerosis and the development of cardiovascular disease. Platelets from hypercholesterolemic rabbit have an increased cholesterol content and a hypersensitivity to endogenous aggregating agonists. Although rabbit has been widely used in studies of hypercholesterolemia, the precise role of platelet cholesterol in rabbit platelet activation has not been studied. In the present study, to determine the direct role of cholesterol on rabbit platelet activation, we examined the effect of in vitro modulation of cholesterol content on platelet activation. Cholesterol-depleted rabbit platelets by the treatment with methyl-beta-cyclodextrin showed decreased platelet aggregation by physiological agonists such as thrombin, adenosine diphosphate, and collagen. The inhibition of thrombin-induced aggregation in cholesterol-depleted platelets was restored by cholesterol repletion in platelets. The cholesterol depletion also inhibited Ca(2+) mobilization, which plays a pivotal role in the platelet activation induced by physiological agonists. We showed that the Ca(2+) influx pathway is strongly suppressed by cholesterol depletion more than Ca(2+) release from intracellular Ca(2+) stores in platelets stimulated with thrombin. Furthermore, platelet aggregation induced by PMA, a potent protein kinase C activator, was also depressed by cholesterol depletion. On the other hand, cholesterol enrichment in platelets augmented thrombin-induced aggregation and Ca(2+) mobilization. These findings suggest that cholesterol plays a critical role in regulating rabbit platelet activation, and provides fundamental information regarding hypercholesterolemia-mediated effects on cells in the rabbit model.