Female cardiovascular biology and resilience in the setting of physiological and pathological stress

For years, females were thought of as smaller men with complex hormonal cycles; as a result, females have been largely excluded from preclinical and clinical research. However, in the last ten years, with the increased focus on sex as a biological variable, it has become clear that this is not the case, and in fact, male and female cardiovascular biology and cardiac stress responses differ substantially. Premenopausal women are protected from cardiovascular diseases, such as myocardial infarction and resultant heart failure, having preserved cardiac function, reduced adverse remodeling, and increased survival. Many underlying biological processes that contribute to ventricular remodeling differ between the sexes, such as cellular metabolism; immune cell responses; cardiac fibrosis and extracellular matrix remodeling; cardiomyocyte dysfunction; and endothelial biology; however, it is unclear how these changes afford protection to the female heart. Although many of these changes are dependent on protection provided by female sex hormones, several of these changes occur independent of sex hormones, suggesting that the nature of these changes is more complex than initially thought. This may be why studies focused on the cardiovascular benefits of hormone replacement therapy in post-menopausal women have provided mixed results. Some of the complexity likely stems from the fact that the cellular composition of the heart is sexually dimorphic and that in the setting of MI, different subpopulations of these cell types are apparent. Despite the documented sex-differences in cardiovascular (patho)physiology, the underlying mechanisms that contribute are largely unknown due to inconsistent findings amongst investigators and, in some cases, lack of rigor in reporting and consideration of sex-dependent variables. Therefore, this review aims to describe current understanding of the sex-dependent differences in the myocardium in response to physiological and pathological stressors, with a focus on the sex-dependent differences that contribute to post-infarction remodeling and resultant functional decline.

Elevated N-terminal prohormone of brain natriuretic peptide among persons living with HIV in a South African peri-urban township

AIMS

Efforts to improve access to antiretroviral therapy (ART) have shifted morbidity and mortality among persons living with HIV (PLWH) from AIDS to non-communicable diseases, such as cardiovascular disease (CVD). However, contemporary data on CVD among PLWH in sub-Saharan Africa in the current ART era are lacking. The aim of this study was to assess the burden of cardiac stress among PLWH in South Africa via measurement of N-terminal prohormone of brain natriuretic peptide (NT-proBNP).

METHODS AND RESULTS

NT-proBNP was measured at baseline in 224 PLWH enrolled in a sub-study of a tuberculosis vaccine trial in Khayelitsha township near Cape Town, South Africa. Thresholds were applied at the assay's limit of detection (≥137 pg/mL) and a level indicative of symptomatic heart failure in the acute setting (>300 pg/mL). Mean (SD) age of participants was 39 (6) years, 86% were female, and 19% were hypertensive. Mean (SD) duration of HIV diagnosis was 8.3 (3.9) years and CD4 + count was 673 (267) with 79% prescribed ART for a duration of 5.6 (2.7) years. Thirty-one percent of participants had NT-proBNP > 300 pg/mL. Elevated vs. undetectable NT-proBNP level was associated with older age (P = 0.04), no ART (P = 0.03), and higher plasma tumour necrosis factor-α (P = 0.01).

CONCLUSIONS

Among South African PLWH largely free of known CVD and on ART with high CD4 + counts and few comorbidities, we observed a high proportion with elevated NT-proBNP levels, suggesting the burden of cardiac stress in this population may be high. This observation underscores the need for more in-depth research, including the current effect of HIV on heart failure risk among a growing ART-treated population in sub-Saharan Africa.

Immediate and 24-h post-marathon cardiac troponin T is associated with relative exercise intensity

PURPOSE

We aimed at exploring whether cardiopulmonary fitness, echocardiographic measures and relative exercise intensity were associated with high-sensitivity cardiac troponin T (hs-TNT) rise and normalization following a marathon.

METHODS

Nighty-eight participants (83 men, 15 women; 38.72 ± 3.63 years) were subjected to echocardiographic assessment and a cardiopulmonary exercise test (CPET) before the race. hs-TNT was measured before, immediately after and at 24, 48, 96, 144 and 192 h post-race. Speed and mean heart rate (HR) during the race were relativized to CPET values: peak speed (%V_VMAX), peak HR (HR_%MAX), speed and HR at the second ventilatory threshold (HR_%VT2 and %V_VT2).

RESULTS

Hs-TNT increased from pre- to post-race (5.74 ± 5.29 vs. 50.4 ± 57.04 ng/L; p < 0.001), seeing values above the Upper Reference Limit (URL) in 95% of the participants. At 24 h post-race, 39% of the runners still exceeded the URL (High hs-TNT group). hs-TNT rise was correlated with marathon speed %V_VT2 (r = 0.22; p = 0.042), mean HR_%VT2 (r = 0.30; p = 0.007), and mean HR_%MAX (r = 0.32; p = 0.004). Moreover, the High hs-TNT group performed the marathon at a higher Speed %V_VT2 (88.21 ± 6.53 vs. 83.49 ± 6.54%; p = 0.002) and Speed %V_VMAX (72 ± 4.25 vs. 69.40 ± 5.53%; p = 0.009). hs-TNT showed no significant associations with cardiopulmonary fitness and echocardiographic measures, except for a slight correlation with left ventricular end systolic diameter (r = 0.26; p = 0.018).

CONCLUSION

Post-race hs-TNT was above the URL in barely all runners. Magnitude of hs-TNT rise was correlated with exercise mean HR; whereas, its normalization kept relationship with marathon relative speed.

Cardiovascular magnetic resonance: Stressing the future

Non-invasive cardiac stress imaging plays a central role in the assessment of patients with known or suspected coronary artery disease. The current guidelines suggest estimation of the myocardial ischaemic burden as a criterion for revascularisation on prognostic grounds despite the lack of standardised reporting of the magnitude of ischaemia on various non-invasive imaging methods. Future studies should aim to accurately describe the relationship between myocardial ischaemic burden as assessed by cardiovascular magnetic resonance imaging and mortality.

Coping facilitated troponin T increases and hypo-responsivity in the copeptin-HPA-axis during acute mental stress in a black cohort: The SABPA study

BACKGROUND

Defensive coping (DefS) was associated with a vulnerable cardiovascular profile in blacks. The copeptin/vasopressin system is a manifestation of hypothalamic-pituitary-adrenal-axis activity and may act as an acute compensatory mechanism when there is a disruption in volume-loading homeostasis, i.e. when cardiac stress is evident. Whether DefS will influence associations between copeptin and cardiac stress markers, remains unclear. Here we aimed to determine associations between acute mental stress responses of copeptin, vascular responsiveness and biomarkers of cardiomyocyte injury [cardiac troponin T (cTnT)] and cardiac wall-stress [N-terminal pro-brain natriuretic peptide (NT-proBNP)] in DefS race groups.

METHODS

South African black and white teachers (n = 378) of both sexes, participated in this target population study. Cases with a history of myocardial infarction, stroke and atrial fibrillation were excluded. We obtained coping scores (Coping Strategy Indicator), beat-to-beat blood pressure and fasting blood samples at rest and after 1-min exposure to the Stroop-Colour-Word-Conflict-test.

RESULTS

Interaction effects (p < .05) for copeptin percentage change (%) during the Stroop-Colour-Word-Conflict-test determined stratification of participants into race and DefS (≥26, above-median score) groups. In DefS blacks, Stroop-Colour-Word-Conflict-test exposure elicited increases in cTnT%, NT-proBNP% and diastolic-blood pressure%. Again, in these individuals, multiple regression analyses showed positive associations between copeptin% and total peripheral resistance%; with inverse associations between copeptin% and cTnT% (p < .05). None of these associations were found in DefS whites.

CONCLUSIONS

Utilisation of DefS in blacks provoked vascular hyper-responsiveness and cardiac wall stress (elevated cTnT and NT-proBNP); possibly mediated via the copeptin/vasopressin system. However, a presumably hypo-responsive hypothalamic-pituitary-adrenal-axis during stress exposure could not counteract coronary perfusion deficits via additional copeptin/vasopressin release. The presence of defensiveness may have clinical implications in preventive cardiology.

Dynamic palmitoylation regulates trafficking of K channel interacting protein 2 (KChIP2) across multiple subcellular compartments in cardiac myocytes

BACKGROUND

K channel interacting protein 2 (KChIP2), initially cloned as Kv4 channel modulator, is a multi-tasking protein. In addition to modulating several cardiac ion channels at the plasma membrane, it can also modulate microRNA transcription inside nuclei, and interact with presenilins to modulate Ca release through RyR2 in the cytoplasm. However, the mechanism regulating its subcellular distribution is not clear.

OBJECTIVE

We tested whether palmitoylation drives KChIP2 trafficking and distribution in cells, and whether the distribution pattern of KChIP2 in cardiac myocytes is sensitive to cellular milieu.

METHOD

We conducted imaging and biochemical experiments on palmitoylatable and unpalmitoylatable KChIP2 variants expressed in COS-7 cells and in cardiomyocytes, and on native KChIP2 in myocytes.

RESULTS

In COS-7 cells, palmitoylatable KChIP2 clustered to plasma membrane, while unpalmitoylatable KChIP2 exhibited higher cytoplasmic mobility and faster nuclear entry. The same differences in distribution and mobility were observed when these KChIP2 variants were expressed in cardiac myocytes, indicating that the palmitoylation-dependent distribution and trafficking are intrinsic properties of KChIP2. Importantly, acute stress in a rat model of cardiac arrest/resuscitation induced changes in native KChIP2 resembling those of KChIP2 depalmitoylation, promoting KChIP2 nuclear entry.

CONCLUSION

The palmitoylation status of KChIP2 determines its subcellular distribution in cardiac myocytes. Stress promotes nuclear entry of KChIP2, diverting it from ion channel modulation at the plasma membrane to other functions in the nuclear compartment.

Estrogen regulation of cardiac cAMP-L-type Ca2+ channel pathway modulates sex differences in basal contraction and responses to β2AR-mediated stress in left ventricular apical myocytes

Backgrounds/Aim

Male and female hearts have many structural and functional differences. Here, we investigated the role of estrogen (E2) in the mechanisms of sex differences in contraction through the cAMP-L-type Ca²⁺channel pathway in adult mice left ventricular (LV) apical myocytes at basal and stress state.

Methods

Isolated LV apical myocytes from male, female (Sham) and ovariectomised mice (OVX) were used to investigate contractility, Ca²⁺ transients and L-type Ca²⁺ channel (LTCC) function. The levels of β₂AR, intracellular cAMP, phosphodiesterase (PDE 3 and PDE 4), RyR2, PLB, SLN, and SERCA2a were compared among the experimental groups.

Results

We found that (1) intracellular cAMP, I_CaL density, contraction and Ca²⁺ transient amplitudes were larger in Sham and OVX + E2 myocytes compared to male and OVX. (2) The mRNA expression of PDE 3 and 4 were lower in Sham and OVX + E2 groups compared with male and OVX groups. Treatment of myocytes with IBMX (100 μM) increased contraction and Ca²⁺ transient amplitude in both sexes and canceled differences between them. (3) β₂AR-mediated stress decreased cAMP concentration and peak contraction and Ca²⁺ transient amplitude only in male and OVX groups but not in Sham or OVX + E2 groups suggesting a cardioprotective role of E2 in female mice. (4) Pretreatment of OVX myocytes with GPR30 antagonist G15 (100 nM) abolished the effects of E2, but ERα and ERβ antagonist ICI 182,780 (1 μM) did not. Moreover, activation of GPR30 with G1 (100 nM) replicated the effects of E2 on cAMP, contraction and Ca²⁺ transient amplitudes suggesting that the acute effects of E2 were mediated by GPR30 via non-genomic signaling. (5) mRNA expression of RyR2 was higher in myocytes from Sham than those of male while PLB and SLN were higher in male than Sham but no sex differences were observed in the mRNA of SERCA2a.

Conclusion

Collectively, these results demonstrate that E2 modulates the expression of genes related to the cAMP-LTCC pathway and contributes to sex differences in cardiac contraction and responses to stress. We also show that estrogen confers cardioprotection against cardiac stress by non-genomic acute signaling via GPR30.

Polycystin 2-dependent cardio-protective mechanisms revealed by cardiac stress

Although autosomal dominant polycystic kidney disease (ADPKD) is characterized by the development of multiple kidney cysts, the most frequent cause of death in ADPKD patients is cardiovascular disease. ADPKD is linked to mutations in PKD1 or pkd2, the genes that encode for the proteins polycystin 1 and polycystin 2 (PC1 and PC2, respectively). The cardiovascular complications have been assumed to be a consequence of renal hypertension and activation of renin/angiotensin/aldosterone (RAAS) pathway. However, the expression of PC1 and PC2 in cardiac tissue suggests additional direct effects of these proteins on cardiac function. We previously reported that zebrafish lacking PC2 develop heart failure, and that heterozygous Pkd2^+/- mice are hypersensitive to acute β-adrenergic receptor (βAR) stimulation. Here, we investigate the effect of cardiac stress (prolonged continuous βAR stimulus) on Pkd2^+/- mice. After βAR stimulation for 7 days, wild-type (WT) mice had increased left ventricular mass and natriuretic peptide (ANP and BNP) mRNA levels. The WT mice also had upregulated levels of PC2 and chromogranin B (CGB, an upstream regulator of BNP). Conversely, Pkd2^+/- mice had increased left ventricular mass, but natriuretic peptide and CGB expression levels remained constant. Reversal of the increased cardiac mass was observed in WT mice 3 days after cessation of the βAR stimulation, but not in Pkd2^+/- mice. We suggest that cardiac stress leads to upregulation of the PC2-CGB-BNP signaling axis, and this pathway regulates the production of cardio-protective natriuretic peptides. The lack of a PC2-dependent cardio-protective function may contribute to the severity of cardiac dysfunction in Pkd2^+/- mice and in ADPKD patients.

Cocaine use is associated with a higher prevalence of elevated ST2 concentrations

BACKGROUND

Cocaine is a well-known risk factor for acute cardiac events, but the effects in users outside of acute events are less clear. We investigated a possible association between cocaine use and the concentration of a novel biomarker for cardiac stress and heart failure, ST2.

METHODS

A case-control study was conducted to compare ST2 concentrations by the presence of cocaine in patients presenting for care, but not cardiac care, at an urban safety net hospital.

RESULTS

In samples taken from 100 cocaine-positive and 100 cocaine-negative patients, the presence of cocaine was associated with ST2 concentrations>35ng/mL. Serum concentrations of benzoylecgonine, a major cocaine metabolite, were significantly correlated with ST2 concentrations.

CONCLUSIONS

Cocaine use is associated with subclinical cardiac stress and damage outside of acute cardiac events. This information could add to better stratification of cocaine users with elevated ST2 concentrations who may be at higher risk for developing heart failure and other cardiac complications.

Elevated Levels of N-Terminal Pro-Brain Natriuretic Peptide in Patients with Chronic Dyspnea and Moderate Renal Dysfunction: Decreased Clearance or Increased Cardiac Stress

BACKGROUND/AIMS

Serum levels of N-terminal pro-brain natriuretic peptide (NT-proBNP) are often increased in patients with impaired renal function. The objective of this study was to investigate whether the increase in NT-proBNP is predominantly due to a reduced renal clearance or an increased cardiac secretion.

METHODS

A series of 697 outpatients (age: 57.5 ± 16.4 years) referred for evaluation of dyspnea were assigned to 4 groups according to their estimated glomerular filtration rate [eGFR (ml/min per 1.73 m2)]: group 1, eGFR <60 (n = 77); group 2, eGFR ≧60 to <75 (n = 139); group 3, eGFR ≧75 to <90 (n = 191), and group 4, eGFR ≧90 (n = 289). The patients were also grouped into 2 categories based on the presence (n = 176) or absence (n = 521) of heart disease.

RESULTS

In patients with heart disease, the adjusted values for NT-proBNP were higher in eGFR group 1 than in eGFR groups 2-4 (p ≤ 0.01). In patients without heart disease, eGFR group 1 membership had no effect on NT-proBNP.

CONCLUSION

A reduced renal clearance does not explain increased NT-proBNP levels in patients with moderate renal impairment and dyspnea. Our data suggest that a moderate reduction in renal function places additional stress on the heart in patients with established cardiac disease.