Cher-Rin Chong

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

Dissociation between severity of takotsubo cardiomyopathy and presentation with shock or hypotension.

Takotsubo cardiomyopathy (TTC) is increasingly well‐recognized as a cause of chest‐pain syndromes, especially in aging females. The most common complications of TTC occur in the first 24 hours post onset of symptoms and include shock and/or arrhythmias.

Occurrence of Tako-Tsubo cardiomyopathy in association with ingestion of serotonin/noradrenaline reuptake inhibitors

Tako-Tsubo cardiomyopathy (TTC) occurs particularly in post-menopausal women, being precipitated in many cases by severe emotional stress. We describe six patients in whom TTC occurred in association with therapeutic ingestion or overdose of the serotonin/noradrenaline reuptake inhibitor venlafaxine, or its metabolite desvenlafaxine. Importantly, two of the six cases were not post-menopausal women. An increased risk of TTC may account for some of the reported cardiovascular adverse effects of venlafaxine and similar agents.

Metabolic Remodeling in Diabetic Cardiomyopathy.

Abstract Diabetes is a risk factor for heart failure and cardiovascular mortality with specific changes to myocardial metabolism, energetics, structure, and function. The gradual impairment of insulin production and signalling in diabetes is associated with elevated plasma fatty acids and increased myocardial free fatty acid uptake and activation of the transcription factor PPARα. The increased free fatty acid uptake results in accumulation of toxic metabolites, such as ceramide and diacylglycerol, activation of protein kinase C, and elevation of uncoupling protein-3. Insulin signalling and glucose uptake/oxidation become further impaired, and mitochondrial function and ATP production become compromised. Increased oxidative stress also impairs mitochondrial function and disrupts metabolic pathways. The diabetic heart relies on free fatty acids (FFA) as the major substrate for oxidative phosphorylation and is unable to increase glucose oxidation during ischaemia or hypoxia, thereby increasing myocardial injury, especially in ageing female diabetic animals. Pharmacological activation of PPARγ in adipose tissue may lower plasma FFA and improve recovery from myocardial ischaemic injury in diabetes. Not only is the diabetic heart energetically-impaired, it also has early diastolic dysfunction and concentric remodelling. The contractile function of the diabetic myocardium negatively correlates with epicardial adipose tissue, which secretes proinflammatory cytokines, resulting in interstitial fibrosis. Novel pharmacological strategies targeting oxidative stress seem promising in preventing progression of diabetic cardiomyopathy, although clinical evidence is lacking. Metabolic agents that lower plasma FFA or glucose, including PPARγ agonism and SGLT2 inhibition, may therefore be promising options.

Dissociation of Early Shock in Takotsubo Cardiomyopathy from either Right or Left Ventricular Systolic Dysfunction

BACKGROUND Takotsubo cardiomyopathy (TTC) is often associated with hypotension and shock. However, development of hypotension/shock in TTC is not closely related to extent of left ventricular (LV) hypokinesis. We sought to determine whether additional right ventricular (RV) involvement in TTC might contribute to hypotension and shock development and thus to prolonged hospital stay (PHS). METHODS We evaluated 102 consecutive TTC patients with acute transthoracic echocardiography (TTE) to detect RV hypokinesis. Correlates of hypotension, shock and PHS were identified by univariate and multivariate analyses. RESULTS Of the 102 patients evaluated, 33% had RV hypokinesis but only 9% had extensive RV involvement. Within the first 24 hours of admission, severe hypotension (systolic blood pressure (SBP) ≤ 90 mmHg) occurred in 21% of the patients and shock (hypotension + peripheral organ hypo-perfusion) in 16.6% of cases. RV involvement was a univariate but not a multivariate correlate of either hypotension or shock and did not result in PHS. On the other hand, RV involvement predicted more extensive LV hypokinesis and LV systolic dysfunction. CONCLUSIONS In TTC, RV hypokinesis occurs in approximately 33% of cases and correlates with more severe LV wall motion abnormality but not with development of hypotension or shock. These data therefore reinforce previous findings that hypotension/shock in TTC are not purely by impaired cardiac output.

Can we make sense of takotsubo cardiomyopathy? An update on pathogenesis, diagnosis and natural history

Takotsubo cardiomyopathy (TTC) is a form of reversible acute cardiac dysfunction of uncertain pathogenesis, which occurs predominantly in postmenopausal women, often with antecedent severe stress. Systolic dysfunction most commonly affects the apex of the left ventricle. There is considerable uncertainty regarding the pathogenesis of TTC and the optimal diagnostic methodology. Acute catecholamine release may play a component role, but the regional hypokinesis is associated with an acute inflammatory process, with resultant early release of brain natriuretic peptide (BNP) and N-terminal pro-BNP. As the diagnosis of TTC has largely been a process of exclusion, there has been considerable underdiagnosis. The combination of demographics, preceding history, ECG appearances and N-terminal pro-BNP elevation may provide the basis for improved early diagnosis. Complete recovery takes at least several months, with a risk of recurrent episodes. Efforts to delineate pathogenesis, expedite diagnosis and evaluate residual disability may assist in the development of appropriate treatment regimens.

Relationship between plasma, atrial and ventricular perhexiline concentrations in humans: insights into factors affecting myocardial uptake.

AIM Little is known regarding the steady-state uptake of drugs into the human myocardium. Perhexiline is a prophylactic anti-anginal drug which is increasingly also used in the treatment of heart failure and hypertrophic cardiomyopathy. We explored the relationship between plasma perhexiline concentrations and its uptake into the myocardium. METHODS Blood, right atrium ± left ventricle biopsies were obtained from patients treated with perhexiline for a median of 8.5 days before undergoing coronary surgery in the perhexiline arm of a randomized controlled trial. Perhexiline concentrations in plasma and heart tissue were determined by HPLC. RESULTS Atrial biopsies were obtained from 94 patients and ventricular biopsies from 28 patients. The median plasma perhexiline concentration was within the therapeutic range at 0.24 mg l⁻¹ (IQR 0.12-0.44), the median atrial concentration was 6.02  mg kg⁻¹ (IQR 2.70-9.06) and median ventricular concentration was 10.0 mg kg⁻¹ (IQR 5.76-13.1). Atrial (r² = 0.76) and ventricular (r² = 0.73) perhexiline concentrations were closely and directly correlated with plasma concentrations (both P < 0.001). The median atrial : plasma ratio was 21.5 (IQR 18.1-27.1), ventricular : plasma ratio was 34.9 (IQR 24.5-55.2) and ventricular : atrial ratio was 1.67 (IQR 1.39-2.22). Using multiple regression, the best model for predicting steady-state atrial concentration included plasma perhexiline, heart rate and age (r² = 0.83). Ventricular concentrations were directly correlated with plasma perhexiline concentration and length of therapy (r² = 0.84). CONCLUSIONS This study demonstrates that plasma perhexiline concentrations are predictive of myocardial drug concentrations, a major determinant of drug effect. However, net myocardial perhexiline uptake is significantly modulated by patient age, potentially via alteration of myocardial:extracardiac drug uptake.

Can Perhexiline Be Utilized Without Long-Term Toxicity? A Clinical Practice Audit.

Background: Perhexiline, originally used as a first-line prophylactic antianginal agent, is now regarded primarily as a treatment for otherwise refractory myocardial ischemia. Recent studies have also demonstrated its short-term utility in heart failure, hypertrophic cardiomyopathy, and inoperable aortic stenosis. Its benefits on myocardial energetics state are potentially counter-balanced by risk of hepatotoxicity and peripheral neuropathy during long-term treatment if drug accumulation occurs. Since perhexiline exhibits complex pharmacokinetics with wide inter-individual variability, its long-term use requires regular plasma concentration monitoring. In this study, the risk of neuro- and hepato-toxicity during long-term perhexiline therapy in relation to the intensity of therapeutic drug monitoring was investigated. Furthermore, determinants of mortality during perhexiline treatment were evaluated. Methods: In 170 patients treated with perhexiline for a median of 50 months (interquartile range: 31–94 months), outcomes and relationship to plasma drug concentrations were documented. Results: Rationale for treatment with perhexiline included myocardial ischemia in 88% and severe systolic heart failure in 38%. Plasma concentrations were within the therapeutic range of 150–600 ng/mL on 65% of assay occasions and toxic levels accounted for 8.8% of measurements. No patient developed hepatotoxicity attributable to perhexiline while 3 developed peripheral neuropathy possibly induced by treatment. Actuarial 5-year survival rate was 83% overall, and 76.3% in patients with associated systolic heart failure. Conclusions: This first audit of a large population treated long-term perhexiline demonstrates the following: (1) Although the frequency of monitoring is less than ideal, therapeutic drug monitoring effectively limits occurrence of toxic drug concentrations and virtually eliminates long-term hepato- and neuro-toxicity and (2) Mortality rates during long-term therapy, notably for patients with concomitant heart failure, are surprisingly low.

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.

Emerging drugs for the treatment of angina pectoris

ABSTRACT Introduction: Angina pectoris, or symptomatic myocardial ischaemia, reflects an impairment of coronary blood flow, and usually a deficiency of available myocardial energetics. Treatment options vary with the precise cause, which may vary with regards to the roles of increased myocardial oxygen demand versus reduced supply. Traditionally, organic nitrates, β-adrenoceptor antagonists, and non-dihydropyridine calcium antagonists were the only commonly used prophylactic anti-anginal agents. However, many patients failed to respond adequately to such therapy, and/or were unsuitable for their use. Areas covered: A number of ‘new’ agents have been shown to represent ancillary forms of prophylactic anti-anginal therapy and are particularly useful in patients who are relatively unsuitable for either percutaneous or surgical revascularisation. These include modulators of myocardial metabolic efficiency, such as perhexiline, trimetazidine and ranolazine, as well as high dose allopurinol, nicorandil and ivabradine. The advantages and disadvantages of these various agents are summarized. Expert opinion: ‘Optimal’ medical treatment of angina pectoris now includes use of agents primarily intended to reduce risk of infarction (e.g. statins, aspirin, ACE inhibitors). In patients whose angina persists despite the use of ‘standard’ anti-anginal therapy, and who are not ideal for invasive revascularization options, a number of emerging drugs offer prospects of symptomatic relief.