Platelets and aging. I--Aggregation, arachidonate metabolism and antioxidant status

Crosstalk between adenosine receptors and CYP450-derived oxylipins in the modulation of cardiovascular, including coronary reactive hyperemic response

Adenosine is a ubiquitous endogenous nucleoside or autacoid that affects the cardiovascular system through the activation of four G-protein coupled receptors: adenosine A₁ receptor (A₁AR), adenosine A_2A receptor (A_2AAR), adenosine A_2B receptor (A_2BAR), and adenosine A₃ receptor (A₃AR). With the rapid generation of this nucleoside from cellular metabolism and the widespread distribution of its four G-protein coupled receptors in almost all organs and tissues of the body, this autacoid induces multiple physiological as well as pathological effects, not only regulating the cardiovascular system but also the central nervous system, peripheral vascular system, and immune system. Mounting evidence shows the role of CYP450-enzymes in cardiovascular physiology and pathology, and the genetic polymorphisms in CYP450s can increase susceptibility to cardiovascular diseases (CVDs). One of the most important physiological roles of CYP450-epoxygenases (CYP450-2C & CYP2J2) is the metabolism of arachidonic acid (AA) and linoleic acid (LA) into epoxyeicosatrienoic acids (EETs) and epoxyoctadecaenoic acid (EpOMEs) which generally involve in vasodilation. Like an increase in coronary reactive hyperemia (CRH), an increase in anti-inflammation, and cardioprotective effects. Moreover, the genetic polymorphisms in CYP450-epoxygenases will change the beneficial cardiovascular effects of metabolites or oxylipins into detrimental effects. The soluble epoxide hydrolase (sEH) is another crucial enzyme ubiquitously expressed in all living organisms and almost all organs and tissues. However, in contrast to CYP450-epoxygenases, sEH converts EETs into dihydroxyeicosatrienoic acid (DHETs), EpOMEs into dihydroxyoctadecaenoic acid (DiHOMEs), and others and reverses the beneficial effects of epoxy-fatty acids leading to vasoconstriction, reducing CRH, increase in pro-inflammation, increase in pro-thrombotic and become less cardioprotective. Therefore, polymorphisms in the sEH gene (Ephx2) cause the enzyme to become overactive, making it more vulnerable to CVDs, including hypertension. Besides the sEH, ω-hydroxylases (CYP450-4A11 & CYP450-4F2) derived metabolites from AA, ω terminal-hydroxyeicosatetraenoic acids (19-, 20-HETE), lipoxygenase-derived mid-chain hydroxyeicosatetraenoic acids (5-, 11-, 12-, 15-HETEs), and the cyclooxygenase-derived prostanoids (prostaglandins: PGD₂, PGF_2α; thromboxane: Txs, oxylipins) are involved in vasoconstriction, hypertension, reduction in CRH, pro-inflammation and cardiac toxicity. Interestingly, the interactions of adenosine receptors (A_2AAR, A₁AR) with CYP450-epoxygenases, ω-hydroxylases, sEH, and their derived metabolites or oxygenated polyunsaturated fatty acids (PUFAs or oxylipins) is shown in the regulation of the cardiovascular functions. In addition, much evidence demonstrates polymorphisms in CYP450-epoxygenases, ω-hydroxylases, and sEH genes (Ephx2) and adenosine receptor genes (ADORA1 & ADORA2) in the human population with the susceptibility to CVDs, including hypertension. CVDs are the number one cause of death globally, coronary artery disease (CAD) was the leading cause of death in the US in 2019, and hypertension is one of the most potent causes of CVDs. This review summarizes the articles related to the crosstalk between adenosine receptors and CYP450-derived oxylipins in vascular, including the CRH response in regular salt-diet fed and high salt-diet fed mice with the correlation of heart perfusate/plasma oxylipins. By using A_2AAR^-/-, A₁AR^-/-, eNOS^-/-, sEH^-/- or Ephx2^-/-, vascular sEH-overexpressed (Tie2-sEH Tr), vascular CYP2J2-overexpressed (Tie2-CYP2J2 Tr), and wild-type (WT) mice. This review article also summarizes the role of pro-and anti-inflammatory oxylipins in cardiovascular function/dysfunction in mice and humans. Therefore, more studies are needed better to understand the crosstalk between the adenosine receptors and eicosanoids to develop diagnostic and therapeutic tools by using plasma oxylipins profiles in CVDs, including hypertensive cases in the future.

The Association of Oxidative and Antioxidant Potential with Cardiometabolic Risk Profile in the Group of 60- to 65-Year-Old Seniors from Central Poland

Pathogenesis of cardiovascular diseases is caused by, inter alia, oxidative stress. On the other hand, cardiovascular risk factors may cause redox imbalance. The pathological pathways between those components are to be determined. In the group comprised of 300 sex-matched subjects, we evaluated a number of cardiovascular risk factors: blood pressure, body mass, lipids, glucose, homocysteine, uric acid, von Willebrand factor (vWF), VCAM-1 and ICAM-1. The presence of cardiovascular diseases and drugs for their treatment were examined. Secondly, we assessed total antioxidative status (TAS), total oxidative status (TOS) and other markers of oxidative stress. TAS was inversely related to LDL cholesterol. TOS was positively associated with BMI and female sex, but negatively associated with the use of angiotensin II receptor antagonists. Plasma lipid peroxides concentration was positively related to ICAM-1 and presence of stroke, whereas platelet lipid peroxides were positively associated with vWF. Platelets proteins thiol groups were in a positive relationship with vWF, but in a negative relationship with uric acid and diagnosed lipid disorders. Both free thiol and amino groups were positively associated with plasma glucose. Platelets free amino groups were related to platelets count. Superoxide generation by blood platelets (both with and without homocysteine) was positively connected to glucose level. Among women, oxidative markers appear to be more related to glucose level, whereas among men they are related to body mass indices. TAS, TOS and oxidative markers are largely related to modifiable cardiovascular risk factors such as body mass, and intake of drugs such as angiotensin II receptor blockers. Plasma and platelet oxidation markers appear to be especially associated with glucose concentration. The presented analyses unanimously indicate strong connections between cardiovascular risk factors and redox potential and specify how cardiometabolic interventions may counter-balance oxidative stress.

Molecular and functional characteristics of megakaryocytes and platelets in aging

PURPOSE OF REVIEW

Advances in medical care and preventive measures have contributed to increasing life expectancy. Therefore, it is critical to expand our understanding of the physiological and pathophysiological adaptations of the hematological system in aging. We highlight and review the findings from recent investigations aimed at understanding the effects of aging on megakaryocytes and platelets.

RECENT FINDINGS

Biochemical and transcriptomic studies of megakaryocytes and platelets from older humans and mice have advanced our understanding of the molecular and functional characteristics of megakaryocytes and platelets during aging. These studies have led to the identification of metabolic and inflammatory pathways associated with the generation of hyperreactive platelets that may significantly contribute to the high incidence of thrombosis in aging.

SUMMARY

By increasing our research efforts to understand and identify the characteristics of megakaryocytes and platelets in aging, we will increase our potential to develop novel therapies aimed at decreasing the incidence of aging-associated thrombosis. These efforts will also serve as a foundation to better understand the role of megakaryocytes and platelets in other age-related hematological conditions with high thrombotic risk such as clonal hematopoiesis of indeterminate potential and myeloproliferative neoplasms.

Platelets in aging and cancer-"double-edged sword"

Platelets control hemostasis and play a key role in inflammation and immunity. However, platelet function may change during aging, and a role for these versatile cells in many age-related pathological processes is emerging. In addition to a well-known role in cardiovascular disease, platelet activity is now thought to contribute to cancer cell metastasis and tumor-associated venous thromboembolism (VTE) development. Worldwide, the great majority of all patients with cardiovascular disease and some with cancer receive anti-platelet therapy to reduce the risk of thrombosis. However, not only do thrombotic diseases remain a leading cause of morbidity and mortality, cancer, especially metastasis, is still the second cause of death worldwide. Understanding how platelets change during aging and how they may contribute to aging-related diseases such as cancer may contribute to steps taken along the road towards a "healthy aging" strategy. Here, we review the changes that occur in platelets during aging, and investigate how these versatile blood components contribute to cancer progression.

Association between Cyclooxygenase-2 and Indoleamine 2,3-Dioxygenase Expression in Breast Cancer Patients from Pakistan

Background:

Tumors use several immunosuppressive mechanisms to evade immune destruction. Cyclooxygenase-2 (COX-2) expression may be a driver of immunosuppression in breast cancer, but the mechanisms involved remain elusive. COX-2 expression induces the expression of indoleamine 2,3 dioxygenase (IDO) in tumor cells. IDO is an immunosuppressive enzyme which is involved in tumor immune escape mechanisms in breast cancer. Our aim was to evaluate the association between COX-2 and IDO expression to find evidence of immunosuppression in Pakistani breast cancer patients.

Methods:

Immunohistochemical analysis was performed to evaluate the expression of COX-2, IDO, estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) on formalin-fixed paraffin-embedded breast cancer tissues of 100 patients. Univariable and multivariable logistic regression model was used to identify the independent risk factors of COX-2.

Results:

A total of 100 patients were included with a mean age and standard deviation of 48.28 ± 11.83. A significant association was observed among COX-2, IDO, ER, PR and tumor grade. In multivariable analysis, three variables were identified as significant independent risk factors for high COX-2: IDO expression high; [adjusted odds ratio (AOR) 6.51; 95% confidence interval (CI) (2.00-21.20), p=0.001], ER; [AOR 5.62; 95% CI (1.80-17.84), p=0.002] and age [AOR 1.04; 95% CI (1.00-1.10), p=0.05] respectively.

Conclusion:

Our data showed that high IDO expression is associated with high COX-2 expression in Pakistani breast cancer patients. The co-expression of both enzymes may suggest their role in disease pathogenesis. Hence the concurrent targeting of COX-2 and IDO may be a promising therapy for breast cancer.

Role of oxylipins in cardiovascular diseases

Globally, cardiovascular diseases (CVDs) are the number one cause of mortality. Approximately 18 million people died from CVDs in 2015, representing more than 30% of all global deaths. New diagnostic tools and therapies are eagerly required to decrease the prevalence of CVDs related to mortality and/or risk factors leading to CVDs. Oxylipins are a group of metabolites, generated via oxygenation of polyunsaturated fatty acids that are involved in inflammation, immunity, and vascular functions, etc. Thus far, over 100 oxylipins have been identified, and have overlapping and interconnected roles. Important CVD pathologies such as hyperlipidemia, hypertension, thrombosis, hemostasis and diabetes have been linked to abnormal oxylipin signaling. Oxylipins represent a new era of risk markers and/or therapeutic targets in several diseases including CVDs. The role of many oxylipins in the progression or regression in CVD, however, is still not fully understood. An increased knowledge of the role of these oxygenated polyunsaturated fatty acids in cardiovascular dysfunctions or CVDs including hypertension could possibly lead to the development of biomarkers for the detection and their treatment in the future.

Dietary modulation of oxylipins in cardiovascular disease and aging

Oxylipins are a group of fatty acid metabolites generated via oxygenation of polyunsaturated fatty acids and are involved in processes such as inflammation, immunity, pain, vascular tone, and coagulation. As a result, oxylipins have been implicated in many conditions characterized by these processes, including cardiovascular disease and aging. The best characterized oxylipins in relation to cardiovascular disease are derived from the ω-6 fatty acid arachidonic acid. These oxylipins generally increase inflammation, hypertension, and platelet aggregation, although not universally. Similarly, oxylipins derived from the ω-6 fatty acid linoleic acid generally have more adverse than beneficial cardiovascular effects. Alternatively, most oxylipins derived from 20- and 22-carbon ω-3 fatty acids have anti-inflammatory, antiaggregatory, and vasodilatory effects that help explain the cardioprotective effects of these fatty acids. Much less is known regarding the oxylipins derived from the 18-carbon ω-3 fatty acid α-linolenic acid, but clinical trials with flaxseed supplementation have indicated that these oxylipins can have positive effects on blood pressure. Normal aging also is associated with changes in oxylipin levels in the brain, vasculature, and other tissues, indicating that oxylipin changes with aging may be involved in age-related changes in these tissues. A small number of trials in humans and animals with interventions that contain either 18-carbon or 20- and 22-carbon ω-3 fatty acids have indicated that dietary-induced changes in oxylipins may be beneficial in slowing the changes associated with normal aging. In summary, oxylipins are an important group of molecules amenable to dietary manipulation to target cardiovascular disease and age-related degeneration.NEW & NOTEWORTHY Oxylipins are an important group of fatty acid metabolites amenable to dietary manipulation. Because of the role they play in cardiovascular disease and in age-related degeneration, oxylipins are gaining recognition as viable targets for specific dietary interventions focused on manipulating oxylipin composition to control these biological processes.

Differential effects of oral and transdermal menopausal hormone therapy on prostacyclin and thromboxane in platelets

Abstract Menopausal hormone therapies (MHT) may increase thrombotic risk but modulate endothelial function and reduce development of vascular lesions. This study compared effects of MHT on prostanoid-modulated adenosine triphosphate (ATP) secretion from platelets in relationship with endothelial reactive hyperemia (RH) index and carotid intima medial thickness (CIMT). Participants were healthy, recently menopausal women of the Kronos Early Estrogen Prevention Study (KEEPS) randomized to one of three treatments: oral conjugated equine estrogen (oCEE, 0.45 mg/day), transdermal 17β-estradiol (tE2, 50 μg/day) each with intermittent oral progesterone or placebo pills and patch (PL). Prostacyclin and thromboxane A2 were assessed by quantification of their stable metabolites (6-keto-prostaglandin F1α, 6-k-PGF1α; thromboxane B2, TXB2), using ELISA. Dense granule ATP secretion from activated platelets was determined by bioluminescence; RH and CIMT were determined by fingertip tonometry and ultrasound, respectively. After 48 months of treatment, platelet content of 6-k-PGF1α and TXB2 was significantly lower in oCEE compared to the PL. Inhibition of ATP secretion by exogenous activation of cAMP associated with platelet 6-k-PGF1α (r = -0.41, P = 0.04) and TXB2 (r = 0.71, P = 0.0005) only in the oCEE group. Serum and platelet content of 6-k-PGF1α and TXB2 associated positively in the PL and tE2 groups. Serum 6-k-PGF1α positively associated with RH in the oCEE group (r = 0.73, P = 0.02), while serum TXB2 positively associated with CIMT in the tE2 group (r = 0.64, P = 0.01). Thus, oCEE and tE2 differentially affect prostanoid-mediated platelet secretory pathways but alone would not account for an increased thrombotic risk for oral MHT. Furthermore, platelet-derived prostanoids may contribute to RH and vascular remodeling in healthy menopausal women.

Docosahexaenoic acid, protectin synthesis: relevance against atherothrombogenesis

DHA is an abundant nutrient from marine lipids: its specific biological effects have been investigated in human volunteers, taking into consideration the dose effects. We report herein that, at dosages below 1 g/d, DHA proved to be effective in lowering blood platelet function and exhibited an 'antioxidant' effect. However, this was no longer the case following 1.6 g/d, showing then a U-shape response. The antioxidant effect has been observed in platelets as well as LDL, of which the redox status is assumed to be crucial in their relationship with atherosclerosis. Second, the oxygenated products of DHA, especially protectins produced by lipoxygenases, have been considered for their potential to affect blood platelets and leucocytes. It is concluded that DHA is an interesting nutrient to reduce atherothrombogenesis, possibly through complementary mechanisms involving lipoxygenase products of DHA.

ASP6537, a novel highly selective cyclooxygenase-1 inhibitor, exerts potent antithrombotic effect without "aspirin dilemma"

INTRODUCTION

Aspirin inhibits both the cyclooxygenase (COX)-1-dependent production of thromboxane A2 (TXA2) in platelets and COX-2-dependent production of anti-aggregatory prostaglandin I2 (PGI2) in vessel walls, resulting in "aspirin dilemma." Our objective is to investigate whether ASP6537 can overcome aspirin dilemma and exert a potent antithrombotic effect without a concurrent ulcerogenic effect.

METHODS

We evaluated the inhibitory effects of ASP6537 on recombinant human COX-1 (rhCOX-1) and rhCOX-2 activities using a COX-1/2 selectivity test. To determine whether ASP6537 induces aspirin dilemma, we examined the effects of ASP6537 on in vitro TXA2 and PGI2 metabolite production from platelets and isolated aorta of guinea pigs, and on plasma concentrations of TXA2 and PGI2 metabolites in aged rats. Finally, we evaluated the antithrombotic effects and ulcerogenic activity of ASP6537 using an electrically induced carotid arterial thrombosis model and a gastric ulcer model in guinea pigs.

RESULTS

The IC50 ratios of rhCOX-2 to rhCOX-1 for ASP6537 and aspirin were >142,000 and 1.63 fold, respectively. ASP6537 inhibited TXA2 production more selectively than aspirin in in vitro and in vivo TXA2/PGI2 production studies. ASP6537 exerted a significant antithrombotic effect at ≥3 mg/kg, while aspirin tended to inhibit thrombosis at 300 mg/kg but it was not statistically significant. Further, ASP6537 did not induce ulcer formation at 100 mg/kg, whereas aspirin exhibited an ulcerogenic effect at doses of ≥100 mg/kg.

CONCLUSIONS

ASP6537 functions as a highly selective COX-1 inhibitor with a superior ability to aspirin for normalizing TXA2/PGI2 balance, and exerts antithrombotic effect without ulcerogenic effect.

Dose-effect and metabolism of docosahexaenoic acid: pathophysiological relevance in blood platelets

Docosahexaenoic acid (DHA) is known as a major nutrient from marine origin. Considering its beneficial effect in vascular risk prevention, the effect of DHA on blood components, especially platelets, will be reviewed here. Investigating the dose-effect of DHA in humans shows that daily intake lower than one gram/day brings several benefits, such as inhibition of platelet aggregation, resistance of monocytes against apoptosis, and reinforced antioxidant status in platelets and low-density lipoproteins. However, higher daily intake may be less efficient on those parameters, especially by losing the antioxidant effect. On the other hand, a focus on the inhibition of platelet aggregation by lipoxygenase end-products of DHA is made. The easy conversion of DHA by lipoxygenases and the formation of a double lipoxygenation product named protectin DX, reveal an original way for DHA to contribute in platelet inhibition through both the cyclooxygenase inhibition and the antagonism of thromboxane A₂ action.

Age dependent increase in prostaglandin pathway coincides with onset of ovarian cancer in laying hens

Chronic inflammation has been linked to cancer. Prostaglandin E₂ (PGE₂) is the most pro-inflammatory lipid and one of the downstream products of 2 isoforms of cyclooxygenase (COX) enzymes: COX-1 and COX-2. Ovarian cancer is the most lethal gynecological malignancy and mainly occurs in older women. The factors that contribute to the correlation of age and ovarian cancer are unknown. The purpose of this study was to examine the expression of COX enzymes and PGE₂ levels in ovaries and correlate them to ovarian cancer and aging. White Leghorn hens aged 1, 1.5, 2, 2.5, 3 and 3.5 years were used. The incidence of ovarian cancer was determined by gross pathology and histology. COX-1 and COX-2 protein and mRNA expression and PGE₂ concentrations in ovaries were measured using Western blot, quantitative real-time PCR and ELISA, respectively. Our results indicated an increase in ovarian cancer incidence and expression of both COX enzymes in ovaries of older hens. In correlation with ovarian cancer incidence and COX enzymes expression, PGE₂ concentrations were elevated with age. Ovaries with tumor had elevated COX-1 expression and PGE₂ concentration compared to normal ovaries. Our findings suggest that the up-regulation of COX enzymes with age is the main contributing factor in the age associated increase in PGE₂. Furthermore, elevated PGE₂ in ovaries of hens concomitant with age suggests its important role in early stages of ovarian carcinogenesis. These finding may provide the basis for clinical trials utilizing COX specific inhibitors or dietary intervention targeting prostaglandin biosynthesis for the prevention and treatment of ovarian cancer.

12-lipoxygenase: a potential target for novel anti-platelet therapeutics

Platelets play an essential role in the regulation of hemostasis and thrombosis and controlling their level of activation is central to prevention of occlusive clot formation and stroke. Although a number of anti-platelet targets have been identified to address this issue including COX-1, the P2Y(12) receptor, the integrin αIIbβ3, and more recently the protease-activated receptor-1, these targets often result in a significant increased risk of bleeding which may lead to pathologies as serious as the thrombosis they were meant to treat including intracranial hemorrhage and gastrointestinal bleeding. Therefore, alternative approaches to treat uncontrolled platelet activation are warranted. Platelet-type 12-lipoxygenase is an enzyme which oxidizes the free fatty acid in the platelet resulting in the production of the stable metabolite 12-hydroxyeicosatetraenoic acid (12-HETE). The role of 12-HETE in the platelet has been controversial with reports associating its function as being both anti- and pro-thrombotic. In this review, the role of 12-lipoxygenase and its bioactive metabolites in regulation of platelet reactivity, clot formation, and hemostasis is described. Understanding the mechanisms by which 12-lipoxygenase and its metabolites modulate platelet function may lead to the development of a novel class of anti-platelet therapies targeting the enzyme in order to attenuate injury-induced clot formation, vessel occlusion and pathophysiological shifts in hemostasis.

Tocotrienols-induced inhibition of platelet thrombus formation and platelet aggregation in stenosed canine coronary arteries

BACKGROUND

Dietary supplementation with tocotrienols has been shown to decrease the risk of coronary artery disease. Tocotrienols are plant-derived forms of vitamin E, which have potent anti-inflammatory, antioxidant, anticancer, hypocholesterolemic, and neuroprotective properties. Our objective in this study was to determine the extent to which tocotrienols inhibit platelet aggregation and reduce coronary thrombosis, a major risk factor for stroke in humans. The present study was carried out to determine the comparative effects of α-tocopherol, α-tocotrienol, or tocotrienol rich fraction (TRF; a mixture of α-+γ-+δ-tocotrienols) on in vivo platelet thrombosis and ex vivo platelet aggregation (PA) after intravenous injection in anesthetized dogs, by using a mechanically stenosed circumflex coronary artery model (Folts' cyclic flow model).

RESULTS

Collagen-induced platelet aggregation (PA) in platelet rich plasma (PRP) was decreased markedly after treatment with α-tocotrienol (59%; P<0.001) and TRF (92%; P<0.001). α-Tocopherol treatment was less effective, producing only a 22% (P<0.05) decrease in PA. Adenosine diphosphate-induced (ADP) PA was also decreased after treatment with α-tocotrienol (34%; P<0.05) and TRF (42%; P<0.025). These results also indicate that intravenously administered tocotrienols were significantly better than tocopherols in inhibiting cyclic flow reductions (CFRs), a measure of the acute platelet-mediated thrombus formation. Tocotrienols (TRF) given intravenously (10 mg/kg), abolished CFRs after a mean of 68 min (range 22 -130 min), and this abolition of CFRs was sustained throughout the monitoring period (50-160 min).Next, pharmacokinetic studies were carried out and tocol levels in canine plasma and platelets were measured. As expected, α-Tocopherol treatment increased levels of total tocopherols in post- vs pre-treatment specimens (57 vs 18 μg/mL in plasma, and 42 vs 10 μg/mL in platelets). However, treatment with α-tocopherol resulted in slightly decreased levels of tocotrienols in post- vs pre-treatment samples (1.4 vs 2.9 μg/mL in plasma and 2.3 vs 2.8 μg/mL in platelets). α-Tocotrienol treatment increased levels of both tocopherols and tocotrienols in post- vs pre-treatment samples (tocopherols, 45 vs 10 μg/mL in plasma and 28 vs 5 μg/mL in platelets; tocotrienols, 2.8 vs 0.9 μg/mL in plasma and 1.28 vs 1.02 μg/mL in platelets). Treatment with tocotrienols (TRF) also increased levels of tocopherols and tocotrienols in post- vs pre-treatment samples (tocopherols, 68 vs 20 μg/mL in plasma and 31.4 vs 7.9 μg/mL in platelets; tocotrienols, 8.6 vs 1.7 μg/mL in plasma and 3.8 vs 3.9 μg/mL in platelets).

CONCLUSIONS

The present results indicate that intravenously administered tocotrienols inhibited acute platelet-mediated thrombus formation, and collagen and ADP-induced platelet aggregation. α-Tocotrienols treatment induced increases in α-tocopherol levels of 4-fold and 6-fold in plasma and platelets, respectively. Interestingly, tocotrienols (TRF) treatment induced a less pronounced increase in the levels of tocotrienols in plasma and platelets, suggesting that intravenously administered tocotrienols may be converted to tocopherols. Tocotrienols, given intravenously, could potentially prevent pathological platelet thrombus formation and thus provide a therapeutic benefit in conditions such as stroke and myocardial infarction.

Longitudinal platelet reactivity to acute psychological stress among older men and women

Platelet reactivity to acute stress is associated with increased cardiovascular disease risk; however, little research exists to provide systematic methodological foundations needed to generate strong longitudinal research designs. Study objectives were: 1) to evaluate whether markers of platelet function increase in response to an acute psychological stress test among older adults, 2) to establish whether reactivity remains robust upon repeated administration (i.e. three occasions approximately 1 year apart), and 3) to evaluate whether two different acute speech stress tasks elicit similar platelet responses. The 149 subjects (mean age 71 years) gave a brief impromptu speech on one of two randomly assigned topics involving interpersonal conflict. Blood samples drawn at baseline and post-speech were assayed using flow cytometry for platelet responses on three outcomes (% aggregates, % P-selectin expression, and % fibrinogen receptor expression). Three-level hierarchical linear modeling analyses revealed significant stress-induced increases in platelet activation on all outcomes (p < 0.001). No significant habituation on any measure was found. Additional reactivity differences were associated with male gender, history of myocardial infarction, and use of aspirin, statins, and antidepressants. The results demonstrate that laboratory acute stress tests continued to produce robust platelet reactivity on three activation markers among older adults over 3 years.

Nutrition and age-associated inflammation: implications for disease prevention

Accumulating evidence suggests that aging is associated with dysregulated immune and inflammatory responses. Investigation into the cellular and molecular mechanisms underlying this phenomenon suggests that an up-regulated cyclooxygenase (COX)-2 expression, and resulting increase in production of prostaglandin E(2) (PGE(2)), is a critical factor. Macrophages from old mice have significantly higher levels of PGE(2) production compared with those from young mice, a result of increased COX-2 expression and protein levels leading to increased COX enzyme activity. Furthermore, studies suggest that the age-associated increase in macrophage PGE(2) production is due to ceramide-induced up-regulation of nuclear factor-kappa B activation. Such processes may also occur in cell types other than macrophages, lending further insight into potential mechanisms of age-related diseases. Moreover, the excess PGE(2) induces harmful effects in other cell types such as T cells and adipocytes through the negative crosstalk between macrophages with other cells, resulting in further increased susceptibility to diseases. Nutrient/dietary medications, such as antioxidants and certain lipids have suggested a promising route to reduce the age-related increase in COX activity and PGE(2) production that is associated with several disease states.

Endogenous peroxynitrite modulates PGHS-1-dependent thromboxane A2 formation and aggregation in human platelets

Aggregation of activated platelets is considerably mediated by the autocrine action of thromboxane A2 (TxA2) which is formed in a prostaglandin endoperoxide H2 synthase-1 (PGHS-1 or COX-1)-dependent manner. The activity of PGHS-1 can be stimulated by peroxides, an effect termed "peroxide tone", that renders PGHS-1 the key regulatory enzyme in the formation of TxA2. Activated platelets release nitric oxide (*NO) and superoxide (O*2) but their interactions with the prostanoid pathway have been controversially discussed in platelet physiology and pathophysiology. The current study demonstrates that endogenously formed peroxynitrite at nanomolar concentrations, originating from the interaction of *NO and *O2, potently activated PGHS-1, which parallels TxA2 formation and aggregation in human platelets. Inhibition of the endogenous formation of either *NO or O*2 resulted in a concentration-dependent decline of PGHS-1 activity, TxA2 release, and aggregation. The concept of peroxynitrite as modulator of TxA2 formation and aggregation explains the interaction of *NO and O*2 with the PGHS pathway and suggests a mechanism by which antioxidants can regulate PGHS-1-dependent platelet aggregation. This may provide a molecular explanation for the clinically observed hyperreactivity of platelets in high-risk patients and serve as a basis for novel therapeutic interventions.

Age-associated changes in immune and inflammatory responses: impact of vitamin E intervention

Aging is associated with dysregulated immune and inflammatory responses. Declining T cell function is the most significant and best-characterized feature of immunosenescence. Intrinsic changes within T cells and extrinsic factors contribute to the age-associated decline in T cell function. T cell defect seen in aging involves multiple stages from early receptor activation events to clonal expansion. Among extrinsic factors, increased production of T cell-suppressive factor PGE(2) by macrophages (Mphi) is most recognized. Vitamin E reverses an age-associated defect in T cells, particularly naïve T cells. This effect of vitamin E is also reflected in a reduced rate of upper respiratory tract infection in the elderly and enhanced clearance of influenza infection in a rodent model. The T cell-enhancing effect of vitamin E is accomplished via its direct effect on T cells and indirectly by inhibiting PGE(2) production in Mphi. Up-regulated inflammation with aging has attracted increasing attention as a result of its implications in the pathogenesis of diseases. Increased PGE(2) production in old Mphi is a result of increased cyclooxygenase 2 (COX-2) expression, leading to higher COX enzyme activity, which in turn, is associated with the ceramide-induced up-regulation of NF-kappaB. Similar to Mphi, adipocytes from old mice have a higher expression of COX-2 as well as inflammatory cytokines IL-1beta, IL-6, and TNF-alpha, which might also be related to elevated levels of ceramide and NF-kappaB activation. This review will discuss the above age-related immune and inflammatory changes and the effect of vitamin E as nutritional intervention with a focus on the work conducted in our laboratory.

In vitro glycoxidized low-density lipoproteins and low-density lipoproteins isolated from type 2 diabetic patients activate platelets via p38 mitogen-activated protein kinase

CONTEXT

Platelet hyperactivation contributes to the increased risk for atherothrombosis in type 2 diabetes and is associated with oxidative stress. Plasma low-density lipoproteins (LDLs) are exposed to both hyperglycemia and oxidative stress, and their role in platelet activation remains to be ascertained.

OBJECTIVE

The aim of this study was to investigate the effects of LDLs modified by both glycation and oxidation in vitro or in vivo on platelet arachidonic acid signaling cascade. The activation of platelet p38 MAPK, the stress kinase responsible for the activation of cytosolic phospholipase A(2), and the concentration of thromboxane B(2), the stable catabolite of the proaggregatory arachidonic acid metabolite thromboxane A(2), were assessed.

RESULTS

First, in vitro-glycoxidized LDLs increased the phosphorylation of platelet p38 MAPK as well as the concentration of thromboxane B(2). Second, LDLs isolated from plasma of poorly controlled type 2 diabetic patients stimulated both platelet p38 MAPK phosphorylation and thromboxane B(2) production and possessed high levels of malondialdehyde but normal alpha-tocopherol concentrations. By contrast, LDLs from sex- and age-matched healthy volunteers had no activating effects on platelets.

CONCLUSIONS

Our results indicate that LDLs modified by glycoxidation may play an important contributing role in platelet hyperactivation observed in type 2 diabetes via activation of p38 MAPK.

Effects of dietaryn-3 polyunsaturated fatty acids from plant and marine origin on platelet aggregation in healthy elderly subjects

In the present intervention study we compared the effects of α-linolenic acid with those of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on platelet aggregationin vitroandex vivoin healthy non-institutionalized elderly subjects. We also compared the effects of α-linolenic acid on platelet aggregation in elderly subjects with those in younger volunteers. During a run-in period of 3 weeks all subjects (thirty-eight elderly (> 60 years) and twelve younger volunteers (< 35 years)) received a diet rich in oleic acid. For the next 6 weeks the elderly subjects received a diet rich in oleic acid (n11), α-linolenic acid (n14) (6·8 g/d) or EPA/DHA (n13) (1·05 g EPA plus 0·55 g DHA). The younger subjects were given a diet rich in α-linolenic acid. The diets did not affect ADP- or collagen-induced platelet aggregationin vitroin either platelet-rich plasma or whole blood. Theex vivoplatelet aggregation as measured with filtragometry was significantly decreased in the elderly group that received EPA/DHA compared with the α-linolenic acid (P= 0·006) and the oleic acid (P= 0·005) diet groups. Effects of α-linolenic acid were not age-dependent. Our results suggest that α-linolenic acid and EPA/DHA do not changein vitroplatelet aggregation. Compared with oleic acid, EPA/DHA, but not α-linolenic acid, favourably affectsex vivoplatelet aggregation in healthy elderly subjects.

Vitamin E and immune response in the aged: molecular mechanisms and clinical implications

Nutritional status has been indicated as a contributing factor to age-related dysregulation of the immune response. Vitamin E, a lipid-soluble antioxidant vitamin, is important for normal function of the immune cells. The elderly are at a greater risk for vitamin E intake that is lower than recommended levels. Vitamin E supplementation above currently recommended levels has been shown to improve immune functions in the aged including delayed-type hypersensitivity skin response and antibody production in response to vaccination, which was shown to be mediated through increased production of interleukin (IL)-2, leading to enhanced proliferation of T cells, and through reduced production of prostaglandin E(2), a T-cell suppressive factor, as a result of a decreased peroxynitrite formation. Vitamin E increased both cell-dividing and IL-producing capacities of naive T cells, but not memory T cells. The vitamin E-induced enhancement of immune functions in the aged was associated with significant improvement in resistance to influenza infection in aged mice and a reduced risk of acquiring upper respiratory infections in nursing home residents. Further studies are needed to determine the signaling mechanisms involved in the upregulation of naive T-cell function by vitamin E as well as the specific mechanisms involved in reduction of risk for upper respiratory infections.

Age related elevation of serum macrophage colony stimulating factor (M-CSF) level

We recently reported that the serum level of macrophage colony-stimulating factor (M-CSF) was elevated in patients with cerebral infarction. In the present study, we measured serum M-CSF level, as well as coagulo-fibrinolytic markers and general laboratory tests in adult healthy subjects of various ages, and investigated the relationship between age and M-CSF level. M-CSF in aged subjects (>or=65 years of age) was significantly higher than that in the younger subjects (<65 years of age), and a significant positive correlation between age and M-CSF was found. Significant positive correlations between M-CSF, and plasma levels of thrombomodulin (TM), von Willebrand factor antigen (vWF), thrombin-antithrombin III complex (TAT), prothrombin fragment 1+2 (F1+2), d-dimer products cross-linked fibrin degradation products (d-dimer) and plasmin-antiplasmin complex (PAP) were also found. Among the general laboratory tests, there was only a significant correlation between M-CSF and serum creatinine; however, no significant correlation was found between M-CSF and other tests including blood cell counts. From these results, age-related elevation of serum M-CSF level was confirmed, and was suggested not to indicate the alteration of hemopoietic condition in aged subjects but to be related to thrombotic state or systemic damaged blood vessel in the apparently healthy aged people.

Mechanism of age-associated up-regulation in macrophage PGE2 synthesis

Many physiological functions of the body change during the aging process. Dysregulated immune and inflammatory responses have been well documented in both humans and animals. The investigation into the cellular and molecular mechanism underlying these disorders has provided compelling evidence that up-regulated cyclooxygenase (COX)-2 and its product, particularly prostaglandin (PG)E2, play a critical role in the age-associated dysregulation of the immune and inflammatory responses. In particular, several studies have shown that increased PGE2 production in old macrophages (Mphi) contributes to the suppression of T cell function with aging. Furthermore, interventions targeted at decreasing PGE2 production have been shown to enhance T cell-mediated function. COX-2 and its catalytic products are also suggested to play a key role in age-related neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Administration of anti-inflammatory drugs which inhibit COX activity has been shown, by some investigators, to be beneficial in preventing and treating these diseases. It is, thus, important to understand the underlying mechanisms of age-related COX-2 up-regulation and to delineate the factors, which contribute to this age-related change. This review focuses on the regulation of PGE2 production in murine Mphi; the age-associated changes in COX-2 expression; and its implication for certain disorders observed in the aged immune system and brain. Increased PGE2 production has been shown to be mainly due to an increase in COX activity, which is, in turn, due to an increase in COX-2 protein and mRNA expression. Elevated COX-2 mRNA represents a higher transcription rate rather than an altered stability of COX-2 mRNA. Upon stimulation, Mphi from old mice generate more ceramide, a sphingolipid, than those from young mice. Ceramide has been shown to induce, by itself, and also augment, LPS-stimulated COX-2 expression and PGE2 production. Several lines of evidence indicate that the higher ceramide levels in old Mphi are an important contributor to the age-associated up-regulation of COX-2 in Mphi. Ceramide up-regulates COX-2 transcription by increasing activation of transcription factor NF-kappaB. Further understanding of molecular mechanisms involved in COX-2 up-regulation will help in delineating fundamental age-related changes, which lead to the development of immune and neurological disorders in the aged.

Diabetic patients without vascular complications display enhanced basal platelet activation and decreased antioxidant status

Vascular complications are the leading causes of morbidity and mortality in diabetic patients. The contribution of platelets to thromboembolic complications is well documented, but their involvement in the initiation of the atherosclerotic process is of rising interest. Thus, the aim of the present study was to evaluate basal arachidonic acid metabolism in relation to the redox status of platelets in both type 1 and type 2 diabetic patients, in the absence of vascular complications, as compared with respective control subjects. For the first time, we show that basal thromboxane B(2), the stable catabolite of thromboxane A(2), significantly increased in resting platelets from both type 1 and type 2 diabetic patients (58 and 88%, respectively), whereas platelet malondialdehyde level was only higher in platelets from type 2 diabetic subjects (67%). On the other hand, both vitamin E levels and cytosolic glutathione peroxidase activities were significantly lower in platelets from diabetic patients as compared with respective control subjects. We conclude that platelet hyperactivation was detectable in well-controlled diabetic patients without complications. This abnormality was associated with increased oxidative stress and impaired antioxidant defense in particular in type 2 diabetic patients. These alterations contribute to the increased risk for occurrence of vascular diseases in such patients.

Pathophysiologic role of redox status in blood platelet activation. Influence of docosahexaenoic acid

Decrease of platelet glutathione peroxidase activity results in increased life span of lipid hydroperoxides, especially the 12-lipoxygenase product of arachidonic acid, 12-HpETE. Phospholipase A2 activity is subsequently enhanced with the release of arachidonic acid, which results in higher thromboxane formation and platelet function. Docosahexaenoic acid may either potentiate platelet lipid peroxidation or lower it when used at high or low concentrations, respectively. In the case of slowing down lipid peroxidation, docosahexaenoic acid was specifically incorporated in plasmalogen ethanolamine phospholipids. This could have a relevant pathophysiologic role in atherothrombosis.

Pro- and antioxidant activities of docosahexaenoic acid on human blood platelets

n - 3 polyunsaturated fatty acids may protect against vascular diseases, however, their high accumulation in membranes may increase lipid peroxidation and subsequently induce deleterious effects in patients suffering from oxidative stress. This led us to investigate in vitro the dose-dependent effect of docosahexaenoic acid (DHA) on the redox status of human platelets. We have compared the effect of different DHA concentrations (0.5, 5 and 50 micro mol L(-1)) corresponding to DHA/albumin ratios of 0.01, 0.1 and 1. At the highest concentration, DHA elicited a marked oxidative stress, as evidenced by high malondialdehyde and low vitamin E levels whereas the lowest DHA concentration significantly decreased the malondialdehyde formation, with no change in vitamin E. The proportion of DHA was only increased in plasmalogen phosphatidylethanolamine at low concentration to rise in all phosphatidyl-choline and -ethanolamine subclasses at high concentration. Thus, the results show a biphasic effect of DHA with antioxidant and prooxidant effects at low and high concentrations, respectively, with a possible relationship with the phospholipid subclass in which it accumulates.

Mechanism of vitamin E inhibition of cyclooxygenase activity in macrophages from old mice: role of peroxynitrite

Vitamin E inhibits cyclooxygenase activity in macrophages from old mice by reducing peroxynitrite production. PGE(2) is a proinflammatory mediator that has been linked to a variety of age-associated diseases such as cancer, arthritis, and cardiovascular disease. Furthermore in the aged, increased cyclooxygenase (COX)-2-mediated PGE(2) production contributes to decline in T-cell-mediated function. Previously we reported that increased macrophage PGE(2) production in the aged is due to higher COX-2 activity and that supplementation with vitamin E significantly reduced the age-associated increase in macrophage PGE(2) production posttranslationally without changing COX-2 expression. Peroxynitrite, a product of nitric oxide (NO) and superoxide (O(-)(2)), increases the activity of COX without affecting its expression. Thus, we investigated if vitamin E inhibits COX activity through decreasing peroxynitrite formation. Macrophages from old mice had higher PGE(2) levels, COX activity, and NO levels than those from young mice, all of which were significantly reduced by vitamin E. When added individually, inhibitors of NO and O(-)(2) did not significantly reduce COX activity; however, when the inhibitors were combined, COX activity was significantly reduced in macrophages from old mice fed 30 ppm vitamin E. Increasing NO levels alone using SNAP or O(-)(2) levels, using X/XO, had no effect; however, increasing peroxynitrite levels using Sin-1 or X/XO + SNAP significantly increased COX activity in macrophages from old mice fed 500, but not those fed 30 ppm vitamin E. These data strongly suggest that peroxynitrite plays an important role in the vitamin E-induced inhibition of COX activity. These findings have important implications for designing interventions to reverse and/or delay age-associated dysregulation of immune and inflammatory responses and diseases associated with them.

Vitamin E and macrophage cyclooxygenase regulation in the aged

Aging is associated with increased evidence of cardiovascular disease (CVD). Atherosclerosis, a major cause of CVD, is an inflammatory process whose development is influenced by several proinflammatory mediators. Products of arachidonic acid metabolism, in particular, prostaglandin (PG) E(2) and thromboxane (TX) A(2), play an important role in the development of atherosclerosis. We showed previously that the aged have higher PGE(2) production compared with their young counterparts. This age-associated increase in PGE(2) production is mainly a consequence of increased cyclooxygenase (COX) activity. We demonstrated further that increased COX activity in old mice is due to the increased expression of mRNA and protein for the inducible form of COX, COX-2. Vitamin E has been shown to reduce PGE(2) production and risk of CVD. In aged mice, we showed that a vitamin E-induced decrease in PGE(2) production is due to decreased COX activity. However, vitamin E had no effect on COX mRNA and protein levels, indicating a post-translational regulation of COX by vitamin E. Further experiments indicated that vitamin E decreases COX activity through reducing formation of peroxynitrite, a hydroperoxide shown to be involved in the activation of COX-2. Other homologues of tocopherols were also effective in inhibiting COX activity, but their degree of inhibition varied. The varied potency to inhibit COX activity was not explained totally by differences in their antioxidant capacity. Vitamin E-induced inhibition of COX activity might contribute to its effect of reducing CVD risk.

The influence of low intake of n-3 fatty acids on platelets in elderly people

A total of ten healthy elderly subjects ingested one capsule of 600 mg (corresponding to 150 mg docosahexaenoic acid and 30 mg eicosapentaenoic acid) RO-PUFA triglycerides per day and ten others ingested one capsule of 600 mg sunflower oil as a placebo for 42 days. In the n-3 polyunsaturated fatty acids (PUFA) group, a significant decrease of systolic blood pressure was observed, as well as a trend towards a decrease in both platelet activation and basal formation of thromboxane B(2). Also, a slight but significant increase of docosahexaenoic acid was observed in the phosphatidylethanolamine fraction as well as a significant increase of vitamin E level after the n-3 PUFA intake. Moreover, the basal production of malondialdehyde significantly decreased. No modification was observed for all these parameters in the placebo group. We conclude that a small intake of n-3 PUFA decreased the oxidative stress in platelets of elderly people and could be beneficial in subjects with atherothrombotic tendencies by lowering the cell peroxide tone.

Dietary modulation of prostanoid synthesis in the aging process: role of cyclooxygenase-2

To investigate the role of cyclooxygenase (COX) as a mediator for prostaglandin synthesis in relation to generation of reactive oxidant species (ROS), we quantitated the COX-derived ROS generation and the gene expression of COX-2, an inducible form of COX in aged kidney. In addition, the modulation by dietary restriction was investigated. COX-derived ROS generation increased with age in ad libitum (AL) rats, but dietary restriction (DR) suppressed the level. The amounts of COX-2 protein and mRNA increased with age in AL rats but maintained at low levels in DR group. It was found that the binding characteristics of a nuclear transcription factor, NF-kappaB were altered by aging. The binding activity of NF-kappaB in aged kidney was significantly enhanced with the corresponding increase in mRNA and protein levels. These increases were closely in parallel to the increased ROS generation and gene expression of COX-2. The COX activity shown by NF-kappaB activation and the ROS generation by COX-mediated process were all modulated by DR. Our results suggest that the upregulation of COX-2 during aging may play an important role in many age-related diseases associated with aging process. And this upregulation was attenuated by DR. We propose that the modulation of the redox-sensitive transcription factor may well be a part of the mechanisms underpinning the anti-oxidative action of DR.

Reactive oxygen metabolites, antioxidants and head and neck cancer

This manuscript will review the probable role of reactive oxygen metabolites (ROM) in the etiopathogenesis of head and neck cancer (HNC). Cancer is a heterogeneous disorder with multiple etiologies including somatic and germ-line mutations, cellular homeostatic disturbances, and environmental triggers. Certain etiologies are characteristic of HNC and include infectious agents such as the Epstein-Barr virus, the use of tobacco, and consumption of alcohol. A large body of evidence implicates ROM in tumor formation and promotion. ROM species are formed in the process of cellular respiration, specifically during oxidative phosphorylation. These ubiquitous molecules are highly toxic in the cellular environment. Of the many effects of ROM, especially important are their effect on DNA. Specifically, ROM cause a variety of DNA damage, including insertions, point mutations, and deletions. Thus, it is hypothesized that ROM may be critically involved in the etiology of malignant disease through their possible impact on protooncogenes and tumor suppressor genes. Additionally, empirical evidence suggests that ROM may also affect the balance between apoptosis and cellular proliferation. If apoptotic mechanisms are overwhelmed, uncontrolled cellular proliferation may follow, potentially leading to tumor formation. Thus, this manuscript will critically review the evidence that supports the role of ROM in tumorigenesis. ROM scavengers and blockers have shown both in vivo and in vitro effects of attenuating the toxicity of ROM. Such compounds include the antioxidant vitamins (A, C, and E), nutrient trace elements (selenium), enzymes (superoxide dismutase, glutathione peroxidase, and catalase), hormones (melatonin), and a host of natural and synthetic compounds (lazaroids, allopurinol, gingko extract). Thus, this paper will also review the possible benefit derived from the use of such scavengers/blockers in the prevention of HNC.

Age-associated increase in PGE2 synthesis and COX activity in murine macrophages is reversed by vitamin E

We previously showed that increased macrophage and PGE2 production with age is due to enhanced cyclooxygenase (COX) activity and COX-2 expression. This study determined the effect of vitamin E supplementation on macrophage PGE2 synthesis in young and old mice and its underlying mechanism. Mice were fed 30 or 500 parts per million vitamin E for 30 days. Lipopolysaccharide (LPS)-stimulated macrophages from old mice produced significantly more PGE2 than those from young mice. Vitamin E supplementation reversed the increased PGE2 production in old mice but had no effect on macrophage PGE2 production in young mice. In both LPS-stimulated and unstimulated macrophages, COX activity was significantly higher in old than in young mice at all intervals. Vitamin E supplementation completely reversed the increased COX activity in old mice to levels comparable to those of young mice but had no effect on macrophage COX activity of young mice or on COX-1 and COX-2 protein or COX-2 mRNA expression in young or old mice. Thus vitamin E reverses the age-associated increase in macrophage PGE2 production and COX activity. Vitamin E exerts its effect posttranslationally, by inhibiting COX activity.

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

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

Low concentrations of lipid hydroperoxides prime human platelet aggregation specifically via cyclo-oxygenase activation

There is mounting evidence that lipid peroxides contribute to pathophysiological processes and can modulate cellular functions. The aim of the present study was to investigate the effects of lipid hydroperoxides on platelet aggregation and arachidonic acid (AA) metabolism. Human platelets, isolated from plasma, were incubated with subthreshold (i.e. non-aggregating) concentrations of AA in the absence or presence of hydroperoxyeicosatetraenoic acids (HPETEs). Although HPETEs alone had no effect on platelet function, HPETEs induced the aggregation of platelets co-incubated with non-aggregating concentrations of AA, HPETEs being more potent than non-eicosanoid peroxides. The priming effect of HPETEs on platelet aggregation was associated with an increased formation of cyclo-oxygenase metabolites, in particular thromboxane A2, and was abolished by aspirin, suggesting an activation of cyclo-oxygenase by HPETEs. It was not receptor-mediated because the 12-HPETE-induced enhancement of AA metabolism was sustained in the presence of SQ29, 548 or RGDS, which blocked the aggregation. These results indicate that physiologically relevant concentrations of HPETEs potentiate platelet aggregation, which appears to be mediated via a stimulation of cyclo-oxygenase activity.

Effects of fatty acids on human platelet glutathione peroxidase: possible role of oxidative stress

Highly polyunsaturated fatty acids of the n-3 family are known to be inhibitors of platelet functions, but these fatty acids (FA) may alter the platelet antioxidant status, depending on their concentrations. The present study was aimed to investigate the effect of various FA on glutathione-dependent peroxidase (GPx), the required antioxidant enzyme for degrading FA hydroperoxides. Human platelets were enriched in vitro with either n-3 (18:3, 20.5, or 22.6), n-6 (18:2 or 18:3) FA, 18:1 n-9 or 16:0, and the GPx activity was then measured. It was found that n-3 FA enhanced the GPx activity whereas the others did not affect the enzyme activity. The increased GPx activity was associated with an increased amount of the enzyme measured by Western blotting. The enhanced activity and amount of GPx induced by 22:6n-3, the most potent activator among the n-3 FA, was completely abolished in the presence of cycloheximide at a concentration known to inhibit platelet protein synthesis. Because platelets are devoid of nucleus, which rules out the involvement of transcriptional factors, this suggests that 22:6n-3 might act at a translational level. On the other hand, 22:6n-3 treatment increased the malondialdehyde formation and decreased the vitamin E level in platelets, both events that could be prevented by the antioxidant epicatechin. Because epicatechin also suppressed the enhancement of both the activity and amount of GPx induced by 22:6n-3, we conclude that the increased GPx activity (possibly via protein synthesis) might be associated with an oxidative stress induced by 22:6n-3 and/or 20:4n-6 released from the platelet endogenous pool in the course of the 22:6n-3 enrichment.

The influence of antioxidant nutrients on platelet function in healthy volunteers

There is mounting evidence that antioxidants may help to prevent coronary heart disease and modulate some thrombotic events such a platelet adhesion. However, the effects of antioxidant supplementation on platelet function in vivo are controversial. A double-blind, randomised, placebo-controlled study was performed on 40 healthy volunteers (20-50 years) supplemented daily with vitamin E (300 mg), vitamin C (250 mg) or beta-carotene (15 mg) for 8 weeks. Platelet function was assessed by platelet aggregation induced by ADP, arachidonic acid or collagen, platelet responsiveness to the inhibitor PGE1, beta-thromboglobulin release and ATP secretion. Supplementation with vitamin E resulted in a significant increase in platelet alpha-tocopherol level (+68%) reflecting closely the increase in plasma alpha-tocopherol level (+69%). Platelet function was significantly decreased by vitamin E as revealed by the decreased platelet aggregation in response to ADP and arachidonic acid, the increased sensitivity to inhibition by PGE1, the decreased plasma beta-thromboglobulin concentration and the decreased ATP secretion. Supplementation with vitamin C did not affect platelet function significantly although a trend towards a decreased platelet aggregability and an increased sensitivity to the inhibitor PGE1 were observed. No significant changes in platelet function occurred after supplementation with beta-carotene. In conclusion, supplementation of healthy volunteers with vitamin E decreased platelet function whereas supplementation with vitamin C or beta-carotene had no significant effects.

Evaluation of platelet hyperfunction in aged subjects using spontaneous platelet aggregation in whole blood

To evaluate the changes in platelet function in connection with aging, spontaneous platelet aggregation in whole blood (SPAWB) from healthy aged people was measured and compared to that in the whole blood of young subjects as well as patients with old cerebral infarction. SPAWB was determined by the fall in non-aggregated single platelet count by stirring without adding platelet aggregating agents to whole blood. SPAWB in the aged subjects was significantly higher than that in the young volunteers. In patients with old cerebral infarction taking no platelet suppressive agents, SPAWB was also high but was suppressed to the level of that in young subjects by prescription of ticlopidine. Although when aspirin or a mixture of phosphocreatine and creatine phosphokinase (CP/CPK) was added in vitro to whole blood obtained from the aged subjects, SPAWB was inhibited to 50%, addition of the specific PAF (platelet activating factor) inhibitor TCV-309 induced only partial inhibition of SPAWB. Only CP/CPK showed more than 50% inhibition of SPAWB in the young volunteers. These findings suggest that platelet function in aged subjects is in a hyperaggregable state in vivo due to increased thromboxane A(2).

Habitual diet, platelet function, fibrinogen and factor VII coagulant activity in young Finns

OBJECTIVES

The objective of the study was to determine whether an association between diet and platelet function, plasma fibrinogen level and factor VII coagulant activity (VII:C) could be established in young subjects.

DESIGN

Data on the habitual diet of the subjects were collected either by a questionnaire on food habits (n = 204) or by a 48-h dietary recall interview (n = 53).

SUBJECTS

The subjects were participants in the project 'Cardiovascular Risk in Young Finns' (age range 15-30 years). A total of 204 subjects having a questionnaire on food habits participated in the platelet function tests and 53 also participated in a 48-h dietary recall interview. Plasma fibrinogen concentration and factor VII: C were measured from 79 subjects.

MAIN OUTCOME MEASURES

Platelet function was tested by turbidometric measurement of platelet aggregation using ADP and collagen as aggregation agents.

RESULTS

Platelet aggregation with ADP (at up to 4.0 mumol L-1) and collagen (at up to 5.0 micrograms mL-1 platelet-rich plasma PRP) showed that the diet characterized as 'saturated', i.e. containing high-fat milk and saturated fat, was associated with platelets less sensitive to aggregating agents in vitro when compared to the unsaturated type of diet. Collagen- but not ADP-induced aggregation decreased with age of the subjects (P = 0.026-0.057, regression coefficient). An inverse regression coefficient between plasma factor VII:C (101%; range 64-145%) and serum triglycerides (P = 0.006) and the intake of rye (g 1000 kcal-1; P = 0.03) were found.

CONCLUSIONS

In this study we showed that platelet reactivity and factor VII:C already differ considerably between subjects at a young age, and diet may explain some of this variation.

Whole-blood platelet aggregation predicts in vitro and in vivo primary hemostatic function in the elderly

Increased platelet aggregation is associated with higher coronary artery disease mortality. Enhanced platelet aggregation in platelet-rich plasma has also been described in the elderly. To define age-related changes in primary hemostasis, we studied 37 elderly and 31 young blood donors. There were no significant age-related differences in whole-blood platelet aggregation, platelet adherence and thrombus formation on human umbilical artery segments, or bleeding time. Plasma fibrinogen was significantly higher in elderly men and women, whereas activated factor VII was elevated only in elderly women. Collagen-induced platelet aggregation was significantly correlated with platelet adherence to the subendothelium in elderly (r = .488, P = .002) but not in young donors. Accordingly, collagen-induced platelet aggregation showed a significant inverse correlation with bleeding time only in the elderly (r = -.401, P = .014). Arachidonic acid-induced platelet aggregation was significantly associated with platelet adherence to the subendothelium (r = .658, P = .003) and bleeding time (r = -.540, P = .021) only in elderly men. In young donors, ADP-induced platelet aggregation was significantly correlated with platelet adherence to the thrombogenic adventitial surface (r = .395, P = .031); in the elderly this association only approached significance (r = .315, P = .058). Whole-blood platelet aggregation in response to collagen and arachidonic acid may be more useful in predicting primary hemostatic function in the elderly than in the young. Furthermore, in the elderly, the correlation between platelet aggregation in whole blood and platelet-arterial wall interactions in vitro and in vivo may contribute to the ability of this test to predict coronary risk.