Pharmacogenomics and Placebo Response in a Randomized Clinical Trial in Asthma.

Genetic variation may differentially modify drug and placebo treatment effects in randomized clinical trials. In asthma, although lung function and asthma control improvements are commonplace with placebo, pharmacogenomics of placebo vs. drug response remains unexamined. In a genomewide association study of subjective and objective outcomes with placebo treatment in Childhood Asthma Management Program of nedocromil/budesonide vs. placebo (N = 604), effect estimates for lead single nucleotide polymorphisms (SNPs) were compared across arms. The coughing/wheezing lead SNP, rs2392165 (ß = 0.94; P = 1.10E-07) mapped to BBS9, a gene implicated in lung development that contains a lung function expression quantitative trait locus. The effect was attenuated with budesonide (Pinteraction  = 1.48E-07), but not nedocromil (Pinteraction  = 0.06). The lead forced vital capacity SNP, rs12930749 (ß = -5.80; P = 1.47E-06), mapped to KIAA0556, a locus genomewide associated with respiratory diseases. The rs12930749 effect was attenuated with budesonide (Pinteraction  = 1.32E-02) and nedocromil (Pinteraction  = 1.09E-02). Pharmacogenomic analysis revealed differential effects with placebo and drug treatment that could potentially guide precision drug development in asthma.

Cellular hypomethylation is associated with impaired nitric oxide production by cultured human endothelial cells.

Hyperhomocysteinemia (HHcy) is a risk factor for vascular disease, but the underlying mechanisms remain incompletely defined. Reduced bioavailability of nitric oxide (NO) is a principal manifestation of underlying endothelial dysfunction, which is an initial event in vascular disease. Inhibition of cellular methylation reactions by S-adenosylhomocysteine (AdoHcy), which accumulates during HHcy, has been suggested to contribute to vascular dysfunction. However, thus far, the effect of intracellular AdoHcy accumulation on NO bioavailability has not yet been fully substantiated by experimental evidence. The present study was carried out to evaluate whether disturbances in cellular methylation status affect NO production by cultured human endothelial cells. Here, we show that a hypomethylating environment, induced by the accumulation of AdoHcy, impairs NO production. Consistent with this finding, we observed decreased eNOS expression and activity, but, by contrast, enhanced NOS3 transcription. Taken together, our data support the existence of regulatory post-transcriptional mechanisms modulated by cellular methylation potential leading to impaired NO production by cultured human endothelial cells. As such, our conclusions may have implications for the HHcy-mediated reductions in NO bioavailability and endothelial dysfunction.

A study of aspirin and clopidogrel in idiopathic pulmonary arterial hypertension.

Idiopathic pulmonary arterial hypertension (IPAH) is characterised by in situ thrombosis and increased thromboxane (Tx) A2 synthesis; however, there are no studies of antiplatelet therapy in IPAH. The aim of the current study was to determine the biochemical effects of aspirin (ASA) and clopidogrel on platelet function and eicosanoid metabolism in patients with IPAH. A randomised, double-blind, placebo-controlled crossover study of ASA 81 mg once daily and clopidogrel 75 mg once daily was performed. Plasma P-selectin levels and aggregometry were measured after exposure to adenosine diphosphate, arachidonic acid and collagen. Serum levels of TxB2 and urinary metabolites of TxA2 and prostaglandin I2 (Tx-M and PGI-M, respectively) were assessed. A total of 19 IPAH patients were enrolled, of whom nine were being treated with continuous intravenous epoprostenol. ASA and clopidogrel significantly reduced platelet aggregation to arachidonic acid and adenosine diphosphate, respectively. ASA significantly decreased serum TxB2, urinary Tx-M levels and the Tx-M/PGI-M ratio, whereas clopidogrel had no effect on eicosanoid levels. Neither drug significantly lowered plasma P-selectin levels. Epoprostenol use did not affect the results. In conclusion, aspirin and clopidogrel inhibited platelet aggregation, and aspirin reduced thromboxane metabolite production without affecting prostaglandin I2 metabolite synthesis. Further clinical trials of aspirin in patients with idiopathic pulmonary arterial hypertension should be performed.

Factor XIII (FXIII) and angiogenesis.

Factor XIII is a plasma transglutaminase that participates in the final stage of the coagulation cascade. Thrombin-activated FXIII (FXIIIa) catalyzes the formation of covalent cross-links between gamma-glutamyl and epsilon-lysyl residues on adjacent fibrin chains in polymerized fibrin to yield the mature clot. In addition to its role in hemostasis, FXIII is known to participate in wound healing and embryo implantation, which are processes involving angiogenesis. In this review, we discuss the role of FXIII in angiogenesis and the molecular mechanisms underlying its proangiogenic effects. The FXIII role in tissue repair and remodeling may at least in part be attributed to its pro-angiogenic activity.

L-arginine increases plasma homocysteine in apoE-/-/iNOS-/- double knockout mice.

Previous studies have shown that L-arginine (L-Arg) administration to apoE-/-/iNOS-/- double knockout mice (dKO) on a Western diet paradoxically results in an increase in atherosclerotic lesion size. We hypothesized that the potential beneficial effects of L-Arg could be offset, in part, by the byproducts of L-Arg catabolism, especially the atherogenic risk factor, homocysteine. In the kidney, L-Arg is converted to L-ornithine and guanidinoacetate (GAA) by L-arginine-glycine amidinotransferase. The efficient transmethylation of GAA by an S-adenosyl-methionine (SAM)-dependent methyltransferase in liver yields creatine and S-adenosylhomocysteine (SAH), which is readily hydrolyzed to homocysteine and adenosine. We, therefore, measured total plasma homocysteine in the dKO mice and control mice. We found that L-Arg supplementation caused a 37% increase in total plasma homocysteine (tHcy) levels in dKO mice compared to controls not treated with L-Arg (5.2+/-2.2 vs 3.8+/-1.5 microM Hcy, p<0.04). In a liver cell line, HepG2, addition of 10 and 50 microM GAA in the presence of 50 microM L-methionine (L-Met) increased tHcy production by approximately 1.47 (p<0.0001) and 2.3-fold (p<0.0001), respectively. In the presence of additional 100 microM L-Met, baseline homocysteine production was elevated by 20% (p<0.005), and 10 and 50 microM GAA augmented homocysteine production by an additional 1.88- (p<0.0001) and 3.4-fold (p<0.001), respectively, compared with 50 microM L-Met. These data suggest that increased concentrations of a methyl acceptor, such as L-Arg-derived GAA, drives SAM-dependent-methylation and consequent homocysteine formation. Furthermore, L-Met levels can also influence homocysteine production likely by regulating the synthesis of the methyl donor SAM. Epidemiological studies have suggested that homocysteine is a graded risk factor. In animal models, modestelevations of homocysteine can cause endothelial dysfunction and augment atherosclerosis. Our data suggest that L-arginine supplementation may contribute to vascular injury and atherogenesis under some circumstances by elevating homocysteine levels.

Nitric oxide in vascular biology.

Nitric oxide is a highly versatile heterodiatomic molecule that effects a variety of actions in the vasculture. Originally identified as a principal determination of vascular tone, nitric oxide has since been recognized to exert anti thrombotic, antiproliferative, and anti-inflammatory effects in the vasculture. At higher concentrations and in the setting of other oxidants, nitric oxide can promote vascular pathology. In this review, we summarize the molecular mechanisms of nitric oxides actions in vascular biology and pathology.

Oxidant stress: a key determinant of atherothrombosis.

ROS (reactive oxygen species) are normal products of oxidative cellular metabolism. These biochemically active free-radical derivatives of molecular oxygen serve as normal signalling molecules in the vasculature; however, an excess of vascular ROS flux occurs in the setting of risk factors for atherothrombosis or established atherothrombosis. The oxidant stress that ROS generate promotes endothelial dysfunction, causes oxidative injury to vascular cells, oxidizes lipoproteins and accelerates atherothrombogenesis. Antioxidant enzymes that are important in limiting vascular oxidant stress include the superoxide dismutases, catalase, glutathione peroxidases and glucose-6-phosphate dehydrogenase. The consequences of acquired and inherited deficiencies of these antioxidant enzymes for vascular oxidant stress, endothelial dysfunction and atherothrombosis will be reviewed.

Organic nitrate tolerance and endothelial dysfunction: role of folate therapy.

Tolerance to organic nitrates has been demonstrated in patients with acute coronary syndromes following continuous, long-term therapy, and has been shown to occur within 24 to 48 h after administration of a nitrate preparation. Dosing schedules that include a nitrate-free period often fail to ameliorate the development of nitrate tolerance, and, in fact, can result in an increase in rebound ischemia. Several mechanisms have been suggested to explain the phenomenon of nitrate tolerance, notably, nitrate-mediated depletion of intracellular thiols, and enhanced reactive oxygen species formation. Recently, increased superoxide production, owing to the un-coupling of the endothelial isoform of nitric oxide synthase (eNOS) and/or increased NAD(P)H oxidase activity, has been implicated in the development of nitrate tolerance. Based on these observations, strategies to overcome tachyphylaxis to nitrates have been designed to modulate the production of reactive oxygen species. Folic acid and its derivatives have been shown to prevent nitrate tolerance by preventing eNOS uncoupling, and, thereby, eNOS-mediated superoxide production resulting in improved endothelial function. Folic acid, which has a benign side-effect profile, may, therefore, be a simple pharmacological intervention to prevent nitrate tolerance and may have broad application in the treatment of atherothrombotic vascular disease.

Nitric oxide and its relationship to thrombotic disorders.

Nitric oxide (NO) is released by the endothelium preventing platelet adhesion to the vessel wall. When released by platelets, NO inhibits further recruitment of platelets to a growing thrombus. Modulation of endogenous NO release may be a mechanism by which the thrombotic response can be regulated as suggested by several clinical diseases associated with impaired bioactive NO. Diseases including atrial fibrillation and coronary atherothrombotic disease have been associated with impaired NO release or decrease in NO bioavailability.

Mechanisms of oxidative stress and vascular dysfunction.

The endothelium regulates vascular homoeostasis through local elaboration of mediators that modulate vascular tone, platelet adhesion, inflammation, fibrinolysis, and vascular growth. Impaired vascular function contributes to the pathogenesis of atherosclerosis and acute coronary syndromes. There is growing pathophysiological evidence that increased generation of reactive oxygen species and oxidative stress participates in proatherogenic mechanisms of vascular dysfunction and atherothrombosis. In this review, the role of oxidative stress in mechanisms of vascular dysfunction is discussed, and potential antioxidant strategies are reviewed.

Effects of race and hypertension on flow-mediated and nitroglycerin-mediated dilation of the brachial artery.

Black Americans have increased morbidity and mortality rates from cardiovascular disease, greater prevalence of hypertension, and altered responses to vasodilator medications compared with those of white Americans. Hypertension and black race have been linked to impaired vascular function in the microcirculation. To examine these effects and their interaction in the conduit vasculature, we examined vasomotor responses of the brachial artery by using high-resolution vascular ultrasound in 228 subjects (48% hypertensive, 54% black). Subjects had no history of diabetes mellitus and were matched for age and gender. Flow-mediated dilation (8.5+/-5.3% versus 11.7+/-6.3%, P<0.001) and nitroglycerin-mediated vasodilation (14.9+/-6.0 versus 18.5+/-7.8, P=0.003) were both impaired in hypertensive compared with normotensive individuals. Multivariate analysis identified higher systolic blood pressure (P=0.003) and larger baseline vessel (P<0.001) size as independent predictors of lower flow-mediated dilation. Race did not significantly influence flow-mediated dilation. In contrast, blacks had a greater vasodilator response to nitroglycerin compared with whites (17.7+/-7.5% versus 15.0+/-6.2%, respectively; P=0.02). By multivariate analysis, black race (P=0.004), smaller vessel size (P=0.001), lower serum glucose (P=0.02), lower systolic blood pressure (P=0.02), and lower serum total cholesterol (P=0.04) were independent predictors of higher nitroglycerin-mediated dilation. Thus, hypertension is associated with impaired NO-mediated vasodilation in the conduit brachial artery. Overall, race did not influence flow-mediated dilation, but black race was associated with an enhanced response to sublingual nitroglycerin. This later observation provides further evidence of racial differences in the responses to medical therapy that may be relevant to the treatment of patients with cardiovascular disease.

Induction of platelet formation from megakaryocytoid cells by nitric oxide.

Although the growth factors that regulate megakaryocytopoiesis are well known, the molecular determinants of platelet formation from mature megakaryocytes remain poorly understood. Morphological changes in megakaryocytes associated with platelet formation and removal of senescent megakaryocytes are suggestive of an apoptotic process. Previously, we have established that nitric oxide (NO) can induce apoptosis in megakaryocytoid cell lines. To determine whether there is an association between NO-induced apoptosis and platelet production, we exposed Meg-01 cells to S-nitrosoglutathione (GSNO) with or without thrombopoeitin (TPO) pretreatment and used flow cytometry and electron microscopy to assess platelet-sized particle formation. Meg-01 cells treated with TPO alone produced few platelet-sized particles (<3% of total counts), whereas treatment with GSNO alone produced a significant percentage of platelet-sized particles (22 +/- 4% of total counts); when combined with TPO pretreatment, however, GSNO led to a marked increase in platelet-sized particle production (48 +/- 3% of total counts). Electron microscopy confirmed that Meg-01 cells treated with TPO and GSNO yielded platelet-sized particles with morphological features specific for platelet forms. The platelet-sized particle population appears to be functional, because addition of calcium, fibrinogen, and thrombin receptor-activating peptide led to aggregation. These results demonstrate that NO facilitates platelet production, thereby establishing the essential role of NO in megakaryocyte development and thrombopoiesis.

Overexpression of cellular glutathione peroxidase rescues homocyst(e)ine-induced endothelial dysfunction.

Homocyst(e)ine (Hcy) inhibits the expression of the antioxidant enzyme cellular glutathione peroxidase (GPx-1) in vitro and in vivo, which can lead to an increase in reactive oxygen species that inactivate NO and promote endothelial dysfunction. In this study, we tested the hypothesis that overexpression of GPx-1 can restore the normal endothelial phenotype in hyperhomocyst(e)inemic states. Heterozygous cystathionine beta-synthase-deficient (CBS((-/+))) mice and their wild-type littermates (CBS((+/+))) were crossbred with mice that overexpress GPx-1 [GPx-1((tg+)) mice]. GPx-1 activity was 28% lower in CBS((-/+))/GPx-1((tg-)) compared with CBS((+/+))/GPx-1((tg-)) mice (P < 0.05), and CBS((-/+)) and CBS((+/+)) mice overexpressing GPx-1 had 1.5-fold higher GPx-1 activity compared with GPx-1 nontransgenic mice (P < 0.05). Mesenteric arterioles of CBS((-/+))/GPx-1((tg-)) mice showed vasoconstriction to superfusion with beta-methacholine and bradykinin (P < 0.001 vs. all other groups), whereas nonhyperhomocyst(e)inemic mice [CBS((+/+))/GPx-1((tg-)) and CBS((+/+))/GPx-1((tg+)) mice] demonstrated dose-dependent vasodilation in response to both agonists. Overexpression of GPx-1 in hyperhomocyst(e)inemic mice restored the normal endothelium-dependent vasodilator response. Bovine aortic endothelial cells (BAEC) were transiently transfected with GPx-1 and incubated with dl-homocysteine (HcyH) or l-cysteine. HcyH incubation decreased GPx-1 activity in sham-transfected BAEC (P < 0.005) but not in GPx-1-transfected cells. Nitric oxide release from BAEC was significantly decreased by HcyH but not cysteine, and GPx-1 overexpression attenuated this decrease. These findings demonstrate that overexpression of GPx-1 can compensate for the adverse effects of Hcy on endothelial function and suggest that the adverse vascular effects of Hcy are at least partly mediated by oxidative inactivation of NO.

Anemia-induced increase in the bleeding time: implications for treatment of nonsurgical blood loss.

BACKGROUND: Preoperative bleeding time (BT) does not correlate with postoperative bleeding in patients subjected to surgical procedures. A significant positive correlation has been reported between the BT 2 hours after cardiopulmonary bypass surgery and the nonsurgical blood loss during the first 4 hours after bypass surgery. This study was done to investigate the effect of Hct and platelet count on the BT measurement in normal, healthy men and women. STUDY DESIGN AND METHODS: To assess the relative effect of RBCs and platelets on the BT, 22 healthy male and 7 healthy female volunteers were subjected to the removal of 2 units of RBCs (360 mL), followed by the return of the platelet-rich plasma (PRP) from both units and the infusion of 1000 mL of 0.9-percent NaCl. Four of the men and all seven women received their RBCs 1 hour after their removal. Shed blood levels of thromboxane B(2) (TXB(2)), 6-keto prostaglandin F(1 alpha), and peripheral venous Hct were measured. BTs were measured in 15 men and 13 women before and after a plateletpheresis procedure to collect 3.6 x 10(11) platelets per unit. RESULTS: The 2-unit RBC apheresis procedure produced a 60-percent increase in the BT associated with a 15-percent reduction in the peripheral venous Hct and a 9-percent reduction in the platelet count. The plateletpheresis procedure produced a 32-percent decrease in the platelet count, no change in peripheral venous Hct, and no change in the BT. After the removal of 2 units of RBCs, the shed blood TXB(2) level decreased significantly. Reinfusion of 2 units of RBCs restored the BT and restored the TXB(2) level to the baseline levels. CONCLUSION: The acute reduction in Hct produced a reversible platelet dysfunction manifested by an increase in BT and a decrease in the shed blood TXB(2) level at the template BT site. Return of the RBCs restored both the BT and the shed blood TXB(2) level to normal. The platelet dysfunction observed with the reduction in Hct was due in part to a reduction in shed blood TXB(2) and other, unknown mechanisms.