Nathan E.K. Procter

Thioredoxin-interacting protein: pathophysiology and emerging pharmacotherapeutics in cardiovascular disease and diabetes.

The thioredoxin system, which consists of thioredoxin (Trx), nicotinamide adenine dinucleotide phosphate (NADPH) and thioredoxin reductase (TrxR), has emerged as a major anti-oxidant involved in the maintenance of cellular physiology and survival. Dysregulation in this system has been associated with metabolic, cardiovascular, and malignant disorders. Thioredoxin-interacting protein (TXNIP), also known as vitamin D-upregulated protein or thioredoxin-binding-protein-2, functions as a physiological inhibitor of Trx, and pathological suppression of Trx by TXNIP has been demonstrated in diabetes and cardiovascular diseases. Furthermore, TXNIP effects are partially Trx-independent; these include direct activation of inflammation and inhibition of glucose uptake. Many of the effects of TXNIP are initiated by its dissociation from intra-nuclear binding with Trx or other SH-containing proteins: these effects include its migration to cytoplasm, modulating stress responses in mitochondria and endoplasmic reticulum, and also potentially activating apoptotic pathways. TXNIP also interacts with the nitric oxide (NO) signaling system, with apparent suppression of NO effect. TXNIP production is modulated by redox stress, glucose levels, hypoxia and several inflammatory activators. In recent studies, it has been shown that therapeutic agents including insulin, metformin, angiotensin converting enzyme inhibitors and calcium channel blockers reduce TXNIP expression, although it is uncertain to what extent TXNIP suppression contributes to their clinical efficacy. This review addresses the role of TXNIP in health and in cardiovascular and metabolic disorders. Finally, the potential advantages (and disadvantages) of pharmacological suppression of TXNIP in cardiovascular disease and diabetes are summarized

Ramipril sensitizes platelets to nitric oxide: implications for therapy in high-risk patients.

OBJECTIVES Using 2 sequential studies in HOPE (Heart Outcomes Prevention Evaluation) study-type patients, the aims of this study were: 1) to test the hypothesis that ramipril improves platelet nitric oxide (NO) responsiveness: and 2) to explore biochemical and physiological effects of ramipril in a cohort selected on the basis of platelet NO resistance. BACKGROUND Ramipril prevents cardiovascular events, but the bases for these effects remain uncertain. NO resistance at both the platelet and vascular levels is present in a substantial proportion of patients with diabetes or ischemic heart disease and is an independent risk factor for cardiovascular events. METHODS Study 1 was a double-blind, randomized comparison of ramipril (10 mg) with placebo in a cohort of patients (n = 119) with ischemic heart disease or diabetes plus additional coronary risk factor(s), in which effects on platelet responsiveness to NO were compared. Study 2 was a subsequent short-term evaluation of the effects of ramipril in a cohort of subjects (n = 19) with impaired platelet NO responsiveness in whom additional mechanistic data were sought. RESULTS In study 1, ramipril therapy increased platelet responsiveness to NO relative to the extent of aggregation (p < 0.001), but this effect occurred primarily in patients with severely impaired baseline NO responsiveness (n = 41). In study 2, ramipril also improved platelet NO responsiveness (p < 0.01), and this improvement was correlated directly with increased NO-stimulated platelet generation of cyclic guanosine monophosphate (p < 0.02) but not with changes in plasma thrombospondin-1 levels. CONCLUSIONS Ramipril ameliorates platelet NO resistance in HOPE study-type patients, with associated increases in soluble guanylate cyclase responsiveness to NO. This effect is likely to contribute to treatment benefit and define patients in whom ramipril therapy is particularly effective.

Early use of N-acetylcysteine with nitrate therapy in patients undergoing primary percutaneous coronary intervention for ST-segment-elevation myocardial infarction reduces myocardial infarct size (the NACIAM trial [N-acetylcysteine in acute myocardial infarction])

Background: Contemporary ST-segment–elevation myocardial infarction management involves primary percutaneous coronary intervention, with ongoing studies focusing on infarct size reduction using ancillary therapies. N-acetylcysteine (NAC) is an antioxidant with reactive oxygen species scavenging properties that also potentiates the effects of nitroglycerin and thus represents a potentially beneficial ancillary therapy in primary percutaneous coronary intervention. The NACIAM trial (N-acetylcysteine in Acute Myocardial Infarction) examined the effects of NAC on infarct size in patients with ST-segment–elevation myocardial infarction undergoing percutaneous coronary intervention. Methods: This randomized, double-blind, placebo-controlled, multicenter study evaluated the effects of intravenous high-dose NAC (29 g over 2 days) with background low-dose nitroglycerin (7.2 mg over 2 days) on early cardiac magnetic resonance imaging–assessed infarct size. Secondary end points included cardiac magnetic resonance–determined myocardial salvage and creatine kinase kinetics. Results: Of 112 randomized patients with ST-segment–elevation myocardial infarction, 75 (37 in NAC group, 38 in placebo group) underwent early cardiac magnetic resonance imaging. Median duration of ischemia pretreatment was 2.4 hours. With background nitroglycerin infusion administered to all patients, those randomized to NAC exhibited an absolute 5.5% reduction in cardiac magnetic resonance–assessed infarct size relative to placebo (median, 11.0%; [interquartile range 4.1, 16.3] versus 16.5%; [interquartile range 10.7, 24.2]; P=0.02). Myocardial salvage was approximately doubled in the NAC group (60%; interquartile range, 37–79) compared with placebo (27%; interquartile range, 14–42; P<0.01) and median creatine kinase areas under the curve were 22 000 and 38 000 IU·h in the NAC and placebo groups, respectively (P=0.08). Conclusions: High-dose intravenous NAC administered with low-dose intravenous nitroglycerin is associated with reduced infarct size in patients with ST-segment–elevation myocardial infarction undergoing percutaneous coronary intervention. A larger study is required to assess the impact of this therapy on clinical cardiac outcomes. Clinical Trial Registration: Australian New Zealand Clinical Trials Registry. URL: http://www.anzctr.org.au/. Unique identifier: 12610000280000.

Suppression of neutrophil superoxide generation by BNP is attenuated in acute heart failure : A case for 'BNP resistance'

The release of the B‐type natriuretic peptide (BNP) is increased in heart failure (HF), a condition associated with oxidative stress. BNP is known to exert anti‐inflammatory effects including suppression of neutrophil superoxide (O2−) release. However, BNP‐based restoration of homeostasis in HF is inadequate, and the equivocal clinical benefit of a recombinant BNP, nesiritide, raises the possibility of attenuated response to BNP. We therefore tested the hypothesis that BNP‐induced suppression of neutrophil O2− generation is impaired in patients with acute HF.

Platelet hyperaggregability in patients with atrial fibrillation: evidence of a background proinflammatory milieu

ObjectiveAtrial fibrillation (AF) is a condition where platelet hyperaggregability is commonly present. We examined potential physiological bases for platelet hyperaggregability in a cohort of patients with acute and chronic AF. In particular, we sought to identify the impact of inflammation [myeloperoxidase (MPO) and C-reactive protein (CRP)] and impaired nitric oxide (NO) signaling.MethodsClinical and biochemical determinants of adenosine diphosphate (ADP)-induced platelet aggregation were sought in patients (n = 106) hospitalized with AF via univariate and multivariate analysis.ResultsHyper-responsiveness of platelets to ADP was directly (r = 0.254, p < 0.01) correlated with plasma concentrations of thrombospondin-1 (TSP-1), a matricellular protein that impairs NO responses and contributes to development of oxidative stress. In turn, plasma TSP-1 concentrations were directly correlated with MPO concentrations (r = 0.221, p < 0.05), while MPO concentrations correlated with those of asymmetric dimethylarginine (ADMA, r = 0.220, p < 0.05), and its structural isomer symmetric dimethylarginine (SDMA, r = 0.192, p = 0.05). Multivariate analysis identified TSP-1 (β = 0.276, p < 0.05) concentrations, as well as female sex (β = 0.199, p < 0.05), as direct correlates of platelet aggregability, and SDMA concentrations (β = − 0.292, p < 0.05) as an inverse correlate.ConclusionWe conclude that platelet hyperaggregability, where present in the context of AF, may be engendered by impaired availability of NO, as well as via MPO-related inflammatory activation.ZusammenfassungZielBei Vorhofflimmern ist oft eine Hyperaggregabilität der Thrombozyten vorhanden. Mögliche physiologische Gründe dafür wurden in einer Kohorte von Patienten mit akutem oder chronischem Vorhofflimmern untersucht. Insbesondere wurde die Rolle von Entzündungsparametern evaluiert, namentlich Myeloperoxidase, C-reaktives Protein und eventuelle Störungen im Stickstoffmonoxid(NO)-Signalweg.MethodenBei 106 wegen Vorhofflimmerns stationär aufgenommenen Patienten wurden klinische und biochemische Ursachen der adenosindiphosphatinduzierten Thrombozytenaggregation mittels univariater und multivariater statistischer Analysen untersucht.ErgebnisseDie Hyperreaktivität von Thrombozyten auf ADP war direkt (r = 0,254; p < 0,01) mit der Plasmakonzentration von Thrombospondin-1 (TSP-1) korreliert, einem Matrixprotein, das die Funktion von NO inhibiert und damit zum oxidativen Stress beiträgt. Plasmathrombospondin-1 korrelierte dagegen mit der Plasma-MPO-Konzentration (r = 0,221; p < 0,05). MPO wiederum korrelierte signifikant mit asymmetrischem Dimethylarginin (ADMA, r = 0,220; p < 0,05) und auch dessen strukturellem Isomer, dem symmetrischen Dimethylarginin (SDMA, r = 0,192; p = 0,05). Die multivariate Analyse ergab, dass eine direkte Korrelation der Thrombozytenhyperreaktivität mit dem Plasma-TSP-1 (β = 0,276; p < 0,05) und weiblichem Geschlecht bestand, während die Plasma-SDMA-Konzentration eine negative Korrelation aufwies (β = − 0,292, p < 0,05).SchlussfolgerungDie Hypothese der Autoren lautet, dass die bei Vorhofflimmern auftretende Thromozytenhyperaggregabilität durch eine geringere Verfügbarkeit von NO und auch durch einen MPO-induzierten Entzündungszustand bedingt sein könnte.

New-onset atrial fibrillation and thromboembolic risk: Cardiovascular syzygy?

Atrial fibrillation (AF) is a condition that confers increased thromboembolic risk. Oral anticoagulant (OAC) therapy can attenuate this risk. However, use of OAC therapy is determined largely by the presence of additional clinical factors (encapsulated by the CHA2DS2VASc score) that incrementally elevate stroke risk. Currently, there is no specific recommendation regarding urgency of initiation of OAC therapy in the presence of new-onset AF, except where cardioversion is being considered. Recently, it has become increasingly apparent that there is a period immediately following the onset of AF of particularly accentuated thromboembolic risk (with respect to chronic AF): the physiological bases for this risk are as yet incompletely understood. However, given that both inflammation and impaired nitric oxide signaling are pivotally involved in the pathogenesis of AF, these factors may also mediate thrombotic risk in the context of new-onset AF. Advances in OAC therapy have recently been achieved, with development of agents that are comparable or superior to warfarin for mitigation of stroke risk, but with a safety profile similar to aspirin therapy. Thus, the incremental increase in thromboembolic risk experienced by new-onset AF patients constitutes a previously widely neglected case in favor of the rapid application of OAC therapy to such individuals. This review seeks to summarize the thromboembolic risk observed in new-onset AF and the emerging understanding of the physiological bases for this risk.

New Developments in Platelet Cyclic Nucleotide Signalling: Therapeutic Implications

Altered platelet physiology may contribute to the emergence of thrombosis in patients with many forms of cardiovascular disease. Excess platelet activation may reflect increased stimulation of pro-aggregatory pathways. There is, however, increasing evidence that excessive platelet response, due to impaired efficacy of anti-aggregatory autacoids such as nitric oxide (NO) and prostacyclin (PGI2), may be just as important. For example, diminished platelet response to NO has been documented in acute and chronic myocardial ischaemia, heart failure, aortic valve disease and in the presence of hyperglycaemia. This “NO resistance” has been shown to reflect both the scavenging of NO by reactive oxygen species and dysfunction of its intracellular “receptor”, soluble guanylate cyclase. Importantly, these abnormalities of NO signalling are potentially reversible through judicious application of pharmacotherapy. The analogous condition of impaired PGI2/adenylate cyclase (AC) signalling has received comparatively less attention to date. We have shown that platelet response to prostaglandin E1 (PGE1) is frequently impaired in patients with symptomatic myocardial ischaemia. Because the effects of ADP receptor antagonists such as clopidogrel and ticagrelor at the level of the P2Y12 receptor are coupled with changes in activity of AC, impaired response to PGE1 might imply both increased thrombotic risk and a reduced efficacy of anti-aggregatory drugs. Accordingly, patient response to treatment with clopidogrel is determined not only by variability of clopidogrel bio-activation, but also extensively by the integrity of platelet AC signalling. We here review these recent developments and their emerging therapeutic implications for thrombotic disorders.

Platelet hyperaggregability in patients with atrial fibrillation

ObjectiveAtrial fibrillation (AF) is a condition where platelet hyperaggregability is commonly present. We examined potential physiological bases for platelet hyperaggregability in a cohort of patients with acute and chronic AF. In particular, we sought to identify the impact of inflammation [myeloperoxidase (MPO) and C-reactive protein (CRP)] and impaired nitric oxide (NO) signaling.MethodsClinical and biochemical determinants of adenosine diphosphate (ADP)-induced platelet aggregation were sought in patients (n = 106) hospitalized with AF via univariate and multivariate analysis.ResultsHyper-responsiveness of platelets to ADP was directly (r = 0.254, p < 0.01) correlated with plasma concentrations of thrombospondin-1 (TSP-1), a matricellular protein that impairs NO responses and contributes to development of oxidative stress. In turn, plasma TSP-1 concentrations were directly correlated with MPO concentrations (r = 0.221, p < 0.05), while MPO concentrations correlated with those of asymmetric dimethylarginine (ADMA, r = 0.220, p < 0.05), and its structural isomer symmetric dimethylarginine (SDMA, r = 0.192, p = 0.05). Multivariate analysis identified TSP-1 (β = 0.276, p < 0.05) concentrations, as well as female sex (β = 0.199, p < 0.05), as direct correlates of platelet aggregability, and SDMA concentrations (β = − 0.292, p < 0.05) as an inverse correlate.ConclusionWe conclude that platelet hyperaggregability, where present in the context of AF, may be engendered by impaired availability of NO, as well as via MPO-related inflammatory activation.ZusammenfassungZielBei Vorhofflimmern ist oft eine Hyperaggregabilität der Thrombozyten vorhanden. Mögliche physiologische Gründe dafür wurden in einer Kohorte von Patienten mit akutem oder chronischem Vorhofflimmern untersucht. Insbesondere wurde die Rolle von Entzündungsparametern evaluiert, namentlich Myeloperoxidase, C-reaktives Protein und eventuelle Störungen im Stickstoffmonoxid(NO)-Signalweg.MethodenBei 106 wegen Vorhofflimmerns stationär aufgenommenen Patienten wurden klinische und biochemische Ursachen der adenosindiphosphatinduzierten Thrombozytenaggregation mittels univariater und multivariater statistischer Analysen untersucht.ErgebnisseDie Hyperreaktivität von Thrombozyten auf ADP war direkt (r = 0,254; p < 0,01) mit der Plasmakonzentration von Thrombospondin-1 (TSP-1) korreliert, einem Matrixprotein, das die Funktion von NO inhibiert und damit zum oxidativen Stress beiträgt. Plasmathrombospondin-1 korrelierte dagegen mit der Plasma-MPO-Konzentration (r = 0,221; p < 0,05). MPO wiederum korrelierte signifikant mit asymmetrischem Dimethylarginin (ADMA, r = 0,220; p < 0,05) und auch dessen strukturellem Isomer, dem symmetrischen Dimethylarginin (SDMA, r = 0,192; p = 0,05). Die multivariate Analyse ergab, dass eine direkte Korrelation der Thrombozytenhyperreaktivität mit dem Plasma-TSP-1 (β = 0,276; p < 0,05) und weiblichem Geschlecht bestand, während die Plasma-SDMA-Konzentration eine negative Korrelation aufwies (β = − 0,292, p < 0,05).SchlussfolgerungDie Hypothese der Autoren lautet, dass die bei Vorhofflimmern auftretende Thromozytenhyperaggregabilität durch eine geringere Verfügbarkeit von NO und auch durch einen MPO-induzierten Entzündungszustand bedingt sein könnte.

Platelet Reactivity Is Independent of Left Atrial Wall Deformation in Patients with Atrial Fibrillation

It has been documented recently that left atrial (LA) deformation in AF patients (while in AF) is predictive of subsequent stroke risk. Additionally, diminished LA deformation during AF correlates with the presence of LA blood stasis. Given that endothelial function is dependent on laminar blood flow, the present study sought to investigate the effect of diminished LA deformation (during AF) on platelet reactivity and inflammation in AF patients. Patients (n = 17) hospitalised with AF underwent echocardiography (while in AF) for determination of peak positive LA strain (LASp). Whole blood impedance aggregometry was used to measure extent of ADP-induced aggregation and subsequent inhibitory response to the nitric oxide (NO) donor, sodium nitroprusside. Platelet thioredoxin-interacting protein (Txnip) content was determined by immunohistochemistry. LASp tended (p = 0.078) to vary inversely with CHA2DS2VASc scores. However, mediators of inflammation (C-reactive protein, Txnip) did not correlate significantly with LASp nor did extent of ADP-induced platelet aggregation or platelet NO response. These results suggest that the thrombogenic risk associated with LA stasis is independent of secondary effects on platelet aggregability or inflammation.

Gender and tachycardia: independent modulation of platelet reactivity in patients with atrial fibrillation

Background Female patients with atrial fibrillation (AF) experience increased risk of thromboembolism compared to males, an observation that is reflected by its inclusion in the CHA2DS2VASc score. New onset AF (often associated with tachycardia) also confers upon patients increased thromboembolic risk. The mechanisms underlying this risk are uncertain, but new onset AF is associated with profound impairment of platelet nitric oxide (NO) signalling. Given that cardiovascular responses to catecholamines are gender-dependent, and that the presence of tachycardia in new onset AF may represent a response to catecholaminergic stimulation, we explored the potential impact of gender and tachycardia on platelet aggregation and NO signalling. Methods Interactions were sought in 87 AF patients between the extent of adenosine diphosphate (ADP)-induced platelet aggregation, the anti-aggregatory effects of the NO donor, sodium nitroprusside, gender, and admission heart rate. The potential impact of platelet expression of thioredoxin-interacting protein (Txnip) was also evaluated. Results Analysis of covariance confirmed the presence of physiological antagonism between platelet ADP and NO responses [F (1, 74) = 12.212, P < 0.01], while female sex correlated with impaired NO responses independent of platelet aggregability [F (2, 74) = 8.313, P < 0.01]. Admission heart rate correlated directly with platelet aggregation (r = 0.235, P < 0.05), and inversely with NO response (r = −0.331, P < 0.01). Txnip expression varied neither with gender nor with heart rate. Conclusions These results indicate that gender and heart rate are independent determinants of platelet function. Prospective studies of the putative benefit of reversal of tachycardia on restoration of normal platelet function are therefore a priority.