Saifei Liu

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

Hypoxic potentiation of nitrite effects in human vessels and platelets.

Previous studies in non-human blood vessels and in platelets have demonstrated that under hypoxic conditions release of NO from nitrite (NO2(-)) is potentiated by deoxyhaemoglobin. In the current study, we characterized hypoxic potentiation of NO2(-) effects in human vasculature and platelets in vitro, addressing underlying mechanisms. The vasodilator efficacy of NO2(-), in comparison with glyceryl trinitrate (GTN), was evaluated in vitro, using segments of human saphenous vein. Under hypoxic conditions, there was a leftward shift of the NO2(-) concentration-response curve (EC50: 22 μM in hyperoxia vs 3.5 μM in hypoxia; p<0.01), but no significant potentiation of GTN effect. In the presence of red blood cells, hypoxic potentiation of NO2(-) vasodilator effect was accentuated. In whole blood samples and platelet-rich plasma (PRP) we assessed inhibition of platelet aggregation by NO2(-) (1mM), in comparison with that of sodium nitroprusside (SNP, 10 μM). In individual subjects (n=37), there was a strong correlation (r=0.75, p<0.0001) between anti-aggregatory effects of NO2(-) and SNP in whole blood, signifying that resultant sGC activation underlies biological effect and responses to NO2(-) are diminished in the presence of NO resistance. In PRP, the effects of NO2(-) were less pronounced than in whole blood (p=0.0001), suggesting an important role of Hb (within RBCs) in the bioconversion of NO2(-) to NO. Inhibition of platelet aggregation by NO2(-) was almost 3-fold greater in venous than in arterial blood (p<0.0001), and deoxyHb concentration directly correlated (r=0.69, p=0.013) with anti-aggregatory response. Incremental hypoxia applied to venous blood samples (in hypoxic chamber) caused a progressive increase in both deoxyHb level and anti-aggregatory effect of NO2(-). When subjects inhaled a 12% O2 mixture for 20 min, there was a 3-fold rise in blood deoxyHb fraction (p<0.01). In PRP, response to NO2(-) also increased under hypoxia, and was further enhanced (p<0.01) by deoxyHb. Furthermore, deoxyHb exerted significant anti-aggregatory effects even in the absence of added NO2(-), suggesting a role for endogenous NO2(-). The results of this work provide further mechanistic insights into hypoxic potentiation of vasodilator and anti-aggregatory actions of NO2(-). In human saphenous veins and blood, the balance of evidence suggests differential rates of NO release from NO2(-) (largely modulated by deoxyHb) as the fundamental mechanism.

The nitric oxide redox sibling nitroxyl partially circumvents impairment of platelet nitric oxide responsiveness

Impaired platelet responsiveness to nitric oxide (NO resistance) is a common characteristic of many cardiovascular disease states and represents an independent risk factor for cardiac events and mortality. NO resistance reflects both scavenging of NO by superoxide (O2(-)), and impairment of the NO receptor, soluble guanylate cyclase (sGC). There is thus an urgent need for circumvention of NO resistance in order to improve clinical outcomes. Nitroxyl (HNO), like NO, produces vasodilator and anti-aggregatory effects, largely via sGC activation, but is not inactivated by O2(-). We tested the hypothesis that HNO circumvents NO resistance in human platelets. In 57 subjects with or without ischemic heart disease, platelet responses to the HNO donor isopropylamine NONOate (IPA/NO) and the NO donor sodium nitroprusside (SNP) were compared. While SNP (10μM) induced 29±3% (p<0.001) inhibition of platelet aggregation, IPA/NO (10μM) caused 75±4% inhibition (p<0.001). In NO-resistant subjects (n=28), the IPA/NO:SNP response ratio was markedly increased (p<0.01), consistent with partial circumvention of NO resistance. Similarly, cGMP accumulation in platelets was greater (p<0.001) with IPA/NO than with SNP stimulation. The NO scavenger carboxy-PTIO (CPTIO, 200μM) inhibited SNP and IPA/NO responses by 92±7% and 17±4% respectively (p<0.001 for differential inhibition), suggesting that effects of IPA/NO are only partially NO-mediated. ODQ (10μM) inhibited IPA/NO responses by 36±8% (p<0.001), consistent with a contribution of sGC/haem to IPA/NO inhibition of aggregation. There was no significant relationship between whole blood ROS content and IPA/NO responses. Thus the HNO donor IPA/NO substantially circumvents platelet NO resistance while acting, at least partially, as a haem-mediated sGC activator.

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.

B‐Type natriuretic peptide suppression of neutrophil superoxide generation: mechanistic studies in normal subjects

Many acute cardiovascular disease states are associated with neutrophil infiltration of myocardium and subsequent release of superoxide (O2−) and myeloperoxidase (MPO), which contribute to inflammatory reactions. B‐Type natriuretic peptide (BNP) is known to exert anti‐inflammatory and antifibrotic effects, but it is not known whether these may include interactions with neutrophils. In neutrophils isolated from 20 healthy subjects, we assessed the effect of BNP on the ‘neutrophil burst’ (O2− production and MPO release) stimulated by phorbol myristate acetate (PMA) and N‐formyl‐methionyl‐leucyl‐phenylalanine (fMLP), respectively. Effects of BNP on cGMP accumulation, and the effects of the cell‐permeable cGMP analogue 8‐(4‐chlorophenylthio) guanosine‐cGMP (8‐p‐CPT‐cGMP) and protein kinase G (PKG) inhibition with KT5823 on the neutrophil–BNP interaction were also evaluated. B‐Type natriuretic peptide suppressed O2− release from neutrophils by 23 ± 6% (P < 0.001) and 24 ± 8% (P < 0.05) following PMA and fMLP stimulation, respectively. Although BNP did not significantly increase cGMP formation, 8‐p‐CPT‐cGMP suppressed both PMA‐ and fMLP‐induced neutrophil O2− release by 16% and 28%, respectively (P < 0.05). The PKG inhibitor KT5823 attenuated the effects of BNP on both fMLP‐ and PMA‐associated O2− production. Neither BNP nor 8‐p‐CPT‐cGMP significantly affected MPO release from neutrophils. Suppression of O2− release from neutrophils by BNP may contribute to its anti‐inflammatory and antifibrotic actions.

Does cardiac resynchronization therapy restore peripheral circulatory homeostasis

To evaluate whether peripheral circulatory ‘remodelling’ as measured by changes in vascular compliance and in markers of nitric oxide signalling contributes to patient response to cardiac resynchronization therapy (CRT).

ADAM-15 and glycocalyx shedding: a new perspective on sepsis-related vasomotor dysfunction

Septic shock represents an ongoing clinical conundrum, with high mortality rates despite the usual background of extensive haemodynamic support and multiple foci of therapeutic endeavour. A prominent clinical feature in such cases is the appearance of extensive fluid extravasation, contributing not only to ‘non-haemodynamic’ pulmonary oedema, but also to further impairment of haemodynamics and of respiratory gas exchange. Impairment of left ventricular systolic function and of renal function also is observed frequently, as patients enter a ‘downhill spiral’. A major contributor to this deterioration is inflammatory erosion of the endothelial glycocalyx. Depletion of any of the proteoglycan or glycoprotein components of the glycocalyx is likely to result in increased permeability of endothelial cells to both fluid and leucocytes/monocytes, as well as platelet aggregation and development of non-laminar flow and resultant accentuation of inflammatory responses. Apart from sepsis, ‘glycocalyx shedding’ (GS) has been associated with a large number of disease states, including acute myocardial infarction and diabetic nephopathy. The list of ‘sheddases’ implicated as precipitants of GS is increasingly long (see Table 1) and includes not only catecholamines, B-type natriuretic peptide and peroxynitrite, but several enzymes, especially matrix metalloproteinases (MMP). To date, no treatment has been validated clinically as a ‘broad-spectrum’ inhibitor of sheddase activation. Preliminary data suggest that lowdose doxycycline represents a non-specific MMP inhibitor, but clinical evidence of its efficacy in sepsis and other acute GS-associated disorders is minimal at this stage. Yang et al. revisit evidence that ADAM-15, a disintegrin and metalloproteinase, is involved in the pathogenesis of GS induced by sepsis. The investigators detected increased plasma CD44 ectodomain concentrations after caecal ligation and puncture-induced sepsis in a mouse model and were able to attribute the cleavage of CD44 (thus releasing its ectodomain into plasma) to ADAM-15. In turn, in a cell culture model, transendothelial electric resistance was reduced by exogenous CD44 ectodomain, resulting in cell–cell adherence junction disorganization. Thus a ‘two-step’ process of GS, initiated by ADAM-15, and exacerbated by CD44 ectodomain, was delineated. Furthermore, the presence of this cascade was confirmed both in the isolated cell model and ADAM-15 mice. Finally, in isolated intact human lung, ADAM-15 was significantly up-regulated by lipopolysaccharide perfusion and at the same time, increased CD44 was detected in the effluent, while vascular permeability to albumin was increased. These results therefore suggest that ADAM-15 contributes substantially, but not exclusively, to the pathogenesis of GS in sepsis, and therefore, to the loss of barrier function implicit in this process. This delineation of a deleterious cascade involving both ADAM-15 and the shed ectodomain of CD44 represents a totally new mechanism for selfaccelerating glycocalyx damage.

Vitamin D supplementation lowers thrombospondin-1 levels and blood pressure in healthy adults.

Introduction Vitamin D insufficiency, defined as 25-hydroxyvitamin D (25(OH)D) levels < 75nmol/L is associated with cardio-metabolic dysfunction. Vitamin D insufficiency is associated with inflammation and fibrosis, but it remains uncertain whether these anomalies are readily reversible. Therefore, we aimed to determine the effects of vitamin D supplementation on markers of: 1) nitric oxide (NO) signaling, 2) inflammation, and 3) fibrosis, in healthy volunteers with mild hypovitaminosis. Methods Healthy volunteers (n = 35) (mean age: 45 ± 11 years) with 25(OH)D levels <75nmol/L, received vitamin D supplementation (Ostelin ® capsules 2000IU) for 12 weeks. Resting systolic and diastolic blood pressures (BP) were assessed. Routine biochemistry was examined. Plasma concentrations of asymmetric dimethylarginine (ADMA), thrombospondin-1 (TSP-1), plasminogen activator inhibitor-1 (PAI-1), hs-CRP, activin-A, and follistatin-like 3 (FSTL3) were quantitated. Results Vitamin D administration for 12 weeks significantly increased 25-(OH)D levels (48.8 ± 16 nmol/L to 100.8 ± 23.7 nmol/L, p<0.001). There was significant lowering of systolic and diastolic BP, while there was no significant change in lipid profiles, or fasting insulin. Plasma concentrations of ADMA, hs-CRP, PAI-1, activin A, and FSTL-3 did not change with vitamin D supplementation. However, there was a marked reduction of TSP-1 (522.7 ± 379.8 ng/mL vs 206.7 ± 204.5 ng/mL, p<0.001). Conclusions Vitamin D supplementation in vitamin D insufficient, but otherwise healthy individuals markedly decreased TSP-1 levels and blood pressure. Since TSP-1 suppresses signaling of NO, it is possible that the fall in BP is engendered by restoration of NO effect.