Supeenun Unchern

Platelet Inhibition by Nitrite Is Dependent on Erythrocytes and Deoxygenation

Background Nitrite is a nitric oxide (NO) metabolite in tissues and blood, which can be converted to NO under hypoxia to facilitate tissue perfusion. Although nitrite is known to cause vasodilation following its reduction to NO, the effect of nitrite on platelet activity remains unclear. In this study, the effect of nitrite and nitrite+erythrocytes, with and without deoxygenation, on platelet activity was investigated. Methodology/Finding Platelet aggregation was studied in platelet-rich plasma (PRP) and PRP+erythrocytes by turbidimetric and impedance aggregometry, respectively. In PRP, DEANONOate inhibited platelet aggregation induced by ADP while nitrite had no effect on platelets. In PRP+erythrocytes, the inhibitory effect of DEANONOate on platelets decreased whereas nitrite at physiologic concentration (0.1 µM) inhibited platelet aggregation and ATP release. The effect of nitrite+erythrocytes on platelets was abrogated by C-PTIO (a membrane-impermeable NO scavenger), suggesting an NO-mediated action. Furthermore, deoxygenation enhanced the effect of nitrite as observed from a decrease of P-selectin expression and increase of the cGMP levels in platelets. The ADP-induced platelet aggregation in whole blood showed inverse correlations with the nitrite levels in whole blood and erythrocytes. Conclusion Nitrite alone at physiological levels has no effect on platelets in plasma. Nitrite in the presence of erythrocytes inhibits platelets through its reduction to NO, which is promoted by deoxygenation. Nitrite may have role in modulating platelet activity in the circulation, especially during hypoxia.

Hemin: A Possible Cause of Oxidative Stress in Blood Circulation of β-Thalassemia/Hemoglobin E Disease

A correlation between endogenous hemin and pro-oxidant activity was revealed in serum of g -thalassemia/hemoglobin E disease ( g -thal/Hb E), which is the most common prevalent type of thalassemia in Thailand. The technique of low temperature electron spin resonance spectroscopy was used for characterization and quantification of high spin ferric heme, which had been identified as hemin (iron (III)-protoporphyrin IX). Hemin was present at levels ranging from 50 to 280 w M in serum of g -thal/Hb E but not detectable in serum of non-thalassemia. Pro-oxidant activity in serum of g -thal/Hb E was demonstrated by luminol-mediated chemiluminescence, a sensitive method for screening of free radical generation in vitro. In the presence of H2O2, the chemiluminescence intensity (CL) was about 20 fold enhanced in serum of g -thal/Hb E, indicating its extensive pro-oxidant activity. The CL showed a good correlation with serum hemin, r =0.778 (p <0.001), while the correlations with total serum iron and serum ferritin were 0.260 (p =0.259) and 0.519 (p =0.004), respectively. Our finding suggested that serum hemin readily catalyzed free radical reactions and it may contribute a major pro-oxidant in blood circulation of g -thal/Hb E.

The effects of vitamin E on platelet activity in β‐thalassaemia patients

Summary.  A double‐blind, crossover, placebo‐controlled study of the effect of vitamin E on platelet functions was performed on nine splenectomized and 16 non‐splenectomized β‐thalassaemia/haemoglobin E (β‐thalassaemia/HbE) patients. The patients were supplemented with a daily dose of vitamin E (525 IU) for 3 months. The functions of platelets were assessed by adenosine diphosphate (ADP)‐induced platelet aggregation and adenosine triphosphate release. Plasma α‐tocopherol, plasma thiobarbituric reactive substances (TBARs) and serum ferritin levels represented patients’ antioxidant status, lipid peroxidation status and iron status respectively. Before experimentation, all patients had low plasma α‐tocopherol levels. The splenectomized patients showed severe iron overload iron, had higher plasma TBAR levels and their platelets were more reactive to ADP than those of non‐splenectomized patients. Three months of daily vitamin E supplementation resulted in a significant increase in plasma α‐tocopherol levels and reduction in plasma TBAR levels in all patients. Serum ferritin levels of the patients were not altered; however, vitamin E reduced the platelet reactivity of the splenectomized patients towards normal levels. The influence of vitamin E on platelet reactivity may result in delaying hypoxaemia and pulmonary occlusion that commonly occurs in splenectomized β‐thalassaemia/HbE patients.

Improvement of vascular function by chronic administration of a cyclo-oxygenase inhibitor in cholesterol-fed rabbits

1. Atherosclerotic cardio‐ and cerebrovascular disease is a leading cause of mortality in Western countries. Aspirin‐like drugs are widely used to prevent and treat these occlusive cardio‐ and cerebrovascular diseases. The beneficial effects of these drugs have been largely attributed to inhibition of platelet cyclo‐oxygenase activity and thromboxane (TX) A2 production. We investigated the effect of an aspirin‐like drug, namely indomethacin, on endothelial function, plaque and platelet aggregation and the formation of vasoactive substances during the development of atherosclerosis in cholesterol‐fed rabbits.

Endothelial dysfunction in subjects with chronic cadmium exposure.

Vascular endothelium is a target of cadmium (Cd) toxicity. Cd exposure has been reported to be associated with vascular disorders. In this study, we aimed to investigate the effects of Cd exposure on markers of endothelial function in human subjects chronically exposed to Cd. Based on blood Cd levels, seventy-five women were categorized into non-exposed, Cd-exposed and severely Cd-exposed groups. Nitrite, L-arginine, asymmetric dimethylarginine (ADMA), and soluble thrombomodulin levels in blood were measured. Nitrite levels were lower in Cd-exposed subjects than non-exposed subjects. Plasma L-arginine decreased while ADMA, an endogenous endothelial nitric oxide synthase (eNOS) inhibitor, increased in Cd-exposed subjects. Soluble thrombomodulin also increased in Cd-exposed subjects. In Cd-exposed subjects, plasma malondialdehyde and protein carbonyl groups increased while the erythrocytic glutathione decreased. Multiple linear regression analysis revealed a negative association between urinary Cd and nitrite levels in erythrocytes. Our research suggests that subjects with chronic Cd exposure have endothelial dysfunction.

Decreased nitrite levels in erythrocytes of children with β-thalassemia/hemoglobin E.

Nitrite anion is bioactive nitric oxide (NO) species circulating in blood, and represents the NO bioavailability and endothelial function. In this study, we aimed to investigate the nitrite levels and the correlation with hemolysis and severity in β-thalassemia/hemoglobin E (β-thal/HbE). 38 Children (12.0±1.9 years of age) with a diagnosis of mild, moderate and severe β-thalassemia were enrolled in the study. The blood nitrite levels and potential plasma NO consumption were measured by the chemiluminescence method. The nitrite levels in whole blood and erythrocytes of the severe thalassemia subjects were lower than those of the control subjects. At day 7 after transfusion of packed erythrocytes, the nitrite levels in erythrocytes increased. The plasma hemoglobin and NO consumption increased in the severe thalassemia subjects. The nitrite levels in erythrocytes inversely correlated with plasma hemoglobin, lactate dehydrogenase activity, potential NO consumption, and lipid peroxidation. Our studies demonstrate the decreased NO bioavailability in thalassemia, which could result from endothelial dysfunction, the increased potential NO consumption in plasma by cell-free hemoglobin and oxidative stress.

Increased platelet activation in subjects chronically exposed to cadmium: A pilot study

Abstract Cadmium exposure has been reported to be associated with the risk of vascular disorders. Here, we investigated platelet activity in subjects with chronic cadmium exposure. Eighteen and 15 women participated in this study as chronically cadmium-exposed and control non-exposed subjects, respectively. Plasma P-selectin and CD40 ligand (CD40L), soluble markers of platelet activation, were measured. Platelet aggregation in whole blood, P-selectin and activated glycoprotein (aGP) IIb/IIIa expression on platelets and platelet–leukocyte aggregates were determined. The levels of plasma P-selectin and CD40L increased in subjects with chronic cadmium exposure compared with control subjects. Platelet aggregation induced by adenosine diphosphate (ADP) was higher in cadmium-exposed subjects than control subjects. Cadmium-exposed subjects had higher baseline and ADP-induced aGPIIb/IIIa expression on platelets than control subjects. Platelet–neutrophil aggregates also increased in cadmium-exposed subjects. Blood cadmium correlated with ADP-induced aggregation, aGPIIb/IIIa expression and platelet–neutrophil aggregates, while urinary cadmium correlated with soluble P-selectin. However, cadmium only at high concentration (15 µM) could potentiate ADP-induced platelet activation in vitro. In conclusion, our pilot data show that cadmium-exposed subjects have increased baseline platelet activation and reactivity.

Association between butyrylcholinesterase K variant and mild cognitive impairment in the Thai community-dwelling patients

Objective To study the association of the butyrylcholinesterase K variant (BChE-K) and the plasma BChE activity with mild cognitive impairment (MCI) in Thai community-dwelling patients. Methods One hundred patients diagnosed with MCI and 100 control subjects were recruited from the community-dwelling setting in Bangkok, Thailand. The genotype and allele distributions of the BChE-K were determined by polymerase chain reaction and subsequent DNA sequencing. The BChE activity was measured in plasma according to the Ellman’s method. Results The BChE-K allele frequencies in the Thai community-dwelling patients were in accordance with other ethnics. The BChE-K allele frequency in the control subjects (12%) was higher than that of MCI patients (5.5%), suggesting a protective role of BChE-K for MCI in the Thai community-dwelling patients. The BChE-K homozygotes were significantly associated with lower BChE activity. Conclusion Our results suggested that the BChE-K may be implicated as a protective factor for MCI in the Thai community-dwelling patients, although a further study with a large sample size is warranted to confirm this.