Chronic testosterone deficiency increases late inward sodium current and promotes triggered activity in ventricular myocytes from aging male mice.

Clinical studies suggest low testosterone levels are associated with cardiac arrhythmias, especially in later life. We investigated whether chronic exposure to low circulating testosterone promoted maladaptive electrical remodeling in ventricular myocytes from aging male mice and determined the role of late inward sodium current (INa,L) in this remodeling. C57BL/6 mice had a gonadectomy (GDX) or sham surgery (1 mo) and were aged to 22-28 mo. Ventricular myocytes were isolated; transmembrane voltage and currents were recorded (37°C). Action potential duration at 70 and 90% repolarization (APD70 and APD90) was prolonged in GDX compared with sham myocytes (APD90, 96.9 ± 3.2 vs. 55.4 ± 2.0 ms; P < 0.001). INa,L was also larger in GDX than sham (-2.4 ± 0.4 vs. -1.2 ± 0.2 pA/pF; P = 0.002). When cells were exposed to the INa,L antagonist ranolazine (10 µM), INa,L declined in GDX cells (-1.9 ± 0.5 vs. -0.4 ± 0.2 pA/pF; P < 0.001) and APD90 was reduced (96.3 ± 14.8 vs. 49.2 ± 9.4 ms; P = 0.001). GDX cells had more triggered activity (early/delayed afterdepolarizations, EADs/DADs) and spontaneous activity than sham. EADs were inhibited by ranolazine in GDX cells. The selective NaV1.8 blocker A-803467 (30 nM) also reduced INa,L, decreased APD and abolished triggered activity in GDX cells. Scn5a (NaV1.5) and Scn10a (NaV1.8) mRNA was increased in GDX ventricles, but only NaV1.8 protein abundance was increased in GDX compared with sham. In vivo studies showed QT prolongation and more arrhythmias in GDX mice. Thus, triggered activity in ventricular myocytes from aging male mice with long-term testosterone deficiency arises from APD prolongation mediated by larger NaV1.8- and NaV1.5-associated currents, which may explain the increase in arrhythmias.NEW & NOTEWORTHY Older men with low testosterone levels are at increased risk of developing cardiac arrhythmias. We found aged mice chronically exposed to low testosterone had more arrhythmias and ventricular myocytes had prolonged repolarization, abnormal electrical activity, larger late sodium currents, and increased expression of NaV1.8 sodium channels. Drugs that inhibit late sodium current or NaV1.8 channels abolished abnormal electrical activity and shortened repolarization. This suggests the late sodium current may be a novel target to treat arrhythmias in older testosterone-deficient men.

The Impact of Exercise on Cardiotoxicity in Pediatric and Adolescent Cancer Survivors: A Scoping Review.

Childhood and adolescent cancer survivors are disproportionately more likely to develop cardiovascular diseases from the late effects of cardiotoxic therapies (e.g., anthracycline-based chemotherapy and chest-directed radiotherapy). Currently, dexrazoxane is the only approved drug for preventing cancer treatment-related cardiac damage. While animal models highlight the beneficial effects of exercise cancer treatment-related cardiac dysfunction, few clinical studies have been conducted. Thus, the objective of this scoping review was to explore the designs and impact of exercise-based interventions for managing cancer treatment-related cardiac dysfunction in childhood and adolescent cancer survivors. Reviewers used Joanna Briggs Institute's methodology to identify relevant literature. Then, 4616 studies were screened, and three reviewers extracted relevant data from six reports. Reviewers found that exercise interventions to prevent cancer treatment-related cardiac dysfunction in childhood and adolescent cancer survivors vary regarding frequency, intensity, time, and type of exercise intervention. Further, the review suggests that exercise promotes positive effects on managing cancer treatment-related cardiac dysfunction across numerous indices of heart health. However, the few clinical studies employing exercise interventions for childhood and adolescent cancer survivors highlight the necessity for more research in this area.

Frailty and cytokines in preclinical models: Comparisons with humans.

Chronic low-grade elevations of blood-borne cytokines/chemokines in older age tend to associate with frailty in humans. This persistent inflammation is often called "inflammageing" and likely contributes to frailty progression. Preclinical models such as ageing and/or genetically modified mice offer a unique opportunity to mechanistically study how these inflammatory mediators affect frailty. In this review, we summarize and contrast evidence relating cytokines/chemokines to frailty in humans and in mouse models of frailty. In humans and mice, higher levels of the pro-inflammatory cytokine interleukin-6 regularly increased in proportion to the degree of frailty. Evidence linking other cytokines/chemokines to frailty in humans and mice is less certain. The chemokines CXCL-10 and monocyte chemoattractant protein-1 related to frailty across both species, but evidence is limited and inconsistent. Several other cytokines/chemokines, including tumour necrosis factor-α relate to frailty in humans or in mice, but evidence to date is species- and tissue-dependent. It is important for future studies to validate common mechanistic inflammatory biomarkers of frailty between humans and mice. Achieving this goal will accelerate the search for drugs to treat frailty.

Serum testosterone concentrations are not associated with frailty in naturally ageing and testosterone-deficient older C57Bl/6 mice.

This study investigated how serum testosterone related to frailty in ageing male C57Bl/6 mice with or without lifelong testosterone deficiency. Mice underwent a sham surgery (n = 10) or gonadectomy (n = 11, GDX) at 4-weeks and then aged. Frailty scores (31-item frailty index) and testosterone were measured between 18- to 24-months of age. Age predicted frailty (p < 0.0001), but serum testosterone did not (p = 0.357). Life expectancy (AFRAID clock) and biologic age (FRIGHT clock) were not significantly different between groups (p = 0.485 and 0.142). The fact that lifelong testosterone deficiency did not exacerbate frailty suggests that low testosterone alone does not potently drive frailty in males.

Aerobic Exercise Attenuates Frailty in Aging Male and Female C57Bl/6 Mice and Effects Systemic Cytokines Differentially by Sex.

Aerobic exercise is a promising intervention to attenuate frailty, but preclinical studies have used only male animals. We investigated the impact of voluntary aerobic exercise on frailty, biological age (FRailty Inferred Geriatric Health Timeline [FRIGHT] clock), predicted life expectancy (Analysis of FRAIlty and Death [AFRAID] clock), and mortality in both sexes and determined whether exercise was associated with changes in inflammation. Older (21-23 months) male (n = 12) and female (n = 22) C57Bl/6 mice matched for baseline frailty scores were randomized into exercise (running wheel) and sedentary (no wheel) groups. Frailty index scores were measured biweekly (13 weeks), and 23 serum cytokines were measured at midpoint and end point. Exercise levels varied between mice but not between the sexes. Exercise had no effect on mortality, but it attenuated the development of frailty in both sexes (female = 0.32 ± 0.04 vs 0.21 ± 0.01; p = .005; male = 0.30 ± 0.02 vs 0.22 ± 0.02; p = .042) and reduced frailty in older females after 10 weeks. FRIGHT scores were unaffected by exercise but increased with time in sedentary males indicating increased biological age. Exercise prevented the age-associated decline in AFRAID scores in older females such that exercised females had a longer life expectancy. We investigated whether aerobic exercise was associated with changes in systemic inflammation. Cytokine levels were not affected by exercise in males, but levels of pro-inflammatory cytokines were positively correlated with the frequency of exercise in females. Despite increases in systemic inflammation, exercise reduced frailty and increased life span in older females. Thus, voluntary aerobic exercise, even late in life, has beneficial effects on health in both sexes but may be especially helpful in older females.

Signs of diastolic dysfunction are graded by serum testosterone levels in aging C57BL/6 male mice.

We investigated whether maladaptive, age-associated changes in heart structure and function were linked to circulating testosterone levels. Male C57BL/6 mice had a gonadectomy (GDX) or sham surgery at 4 weeks and effects of GDX on the heart were examined with echocardiography. Serum testosterone was measured with ELISA. Left ventricular (LV) mass increased with age but was smaller in GDX mice than sham at 18 months (144.0 ± 8.7 vs 118.2 ± 11.9 mg; p = 0.009). The isovolumic relaxation time (IVRT) declined with age but was prolonged in GDX mice at 18 months (10.5 ± 0.8 vs 12.5 ± 0.5 msec, p = 0.008). Ejection fraction did not change with age or GDX, but E/A ratios were lower in GDX mice than controls at 18 months (1.6 ± 0.2 vs 1.3 ± 0.1, p = 0.021). When links between serum testosterone and cardiac parameters were examined longitudinally in 18-24-month-old mice, LV mass declined with decreasing testosterone (ß = 37.70, p = 0.016), however IVRT increased as testosterone decreased (ß=-2.69, p = 0.036). Since longer IVRT and lower E/A ratios are signs of diastolic dysfunction, low circulating testosterone may promote or exacerbate diastolic dysfunction in older males. These findings suggest that lower testosterone directly modifies heart structure and function to promote maladaptive remodeling and diastolic dysfunction in the aging heart.

Maladaptive Changes Associated With Cardiac Aging Are Sex-Specific and Graded by Frailty and Inflammation in C57BL/6 Mice.

We investigated whether late-life changes in cardiac structure and function were related to high levels of frailty and inflammation in male and female mice. Frailty (frailty index), ventricular structure/function (echocardiography), and serum cytokines (multiplex immunoassay) were measured in 16- and 23-month-old mice. Left ventricular (LV) mass and septal wall thickness increased with age in both sexes. Ejection fraction increased with age in males (60.4 ± 1.4 vs 68.9 ± 1.8%; p < .05) but not females (58.8 ± 2.5 vs 62.6 ± 2.4%). E/A ratios declined with age in males (1.6 ± 0.1 vs 1.3 ± 0.1; p < .05) but not females (1.4 ± 0.1 vs 1.3 ± 0.1) and this was accompanied by increased ventricular collagen levels in males. These changes in ejection fraction (r = 0.52; p = .01), septal wall thickness (r = 0.59; p = .002), E/A ratios (r = -0.49; p = .04), and fibrosis (r = 0.82; p = .002) were closely graded by frailty scores in males. Only septal wall thickness and LV mass increased with frailty in females. Serum cytokines changed modestly with age in both sexes. Nonetheless, in males, E/A ratios, LV mass, LV posterior wall thickness, and septal wall thickness increased as serum cytokines increased (eg, IL-6, IL-3, IL-1α, IL-1ß, tumor necrosis factor-α, eotaxin, and macrophage inflammatory protein-1α), while ejection fraction declined with increasing IL-3 and granulocyte-macrophage colony stimulating factor. Cardiac outcomes were not correlated with inflammatory cytokines in females. Thus, changes in cardiac structure and function in late life are closely graded by both frailty and markers of inflammation, but this occurs primarily in males. This suggests poor overall health and inflammation drive maladaptive changes in older male hearts, while older females may be resistant to these adverse effects of frailty.

Frailty Assessment in Animal Models.

Although frailty has been extensively investigated for the last 2 decades, preclinical models of frailty have only been developed over the past decade. Frailty is a concept that helps to explain the difference between chronologic age and biologic age and to discuss health span along with lifespan. In general, a frail individual will be more susceptible to adverse health outcomes than a healthy, nonfrail individual of the same age. However, the biology and mechanisms of frailty are still unclear. The development of preclinical models of frailty and frailty assessment tools are invaluable to geriatric research. This review briefly describes the concept of frailty and discusses the newly developed animal models of frailty, specifically the frailty phenotype- and frailty index-based models. Mouse models are the most common models for preclinical frailty research, but rat and canine models for frailty assessment have also been developed. These models can facilitate the testing of frailty-specific treatments and help to investigate the effects of various interventions on frailty. Similarities and differences between human and animal models, including sex differences in frailty, are also discussed. The availability of animal models of frailty is a valuable and welcome addition to the study of frailty, aging, or the disorders of old age and will enable a better understanding of frailty mechanisms.

Short-term supplement of virgin coconut oil improves endothelial-dependent dilation but not exercise-mediated hyperemia in young adults.

Virgin coconut oil (VCO) is high in antioxidants, which reduce reactive oxygen species-induced conversion of vascular endothelial-derived nitric oxide (NO) to toxic peroxynitrite. As such, flow-mediated dilation (FMD, a surrogate marker of NO bioavailability) and exercise-mediated hyperemia may be enhanced following VCO treatment. Animal research supports these findings, but direct assessments of FMD after short-term VCO use in humans are unknown. We tested the hypotheses that a 4-week VCO supplement (30 mL·d-1) would improve popliteal artery (PA) FMD and the hyperemic response to aerobic exercise. Thirty-four young adults were divided into VCO (n = 19, 9 women, 22 ±â€¯2 years, 24 ±â€¯3 kg·m-2) and control (CON: n = 15, 7 women, 24 ±â€¯2 years, 24 ±â€¯3 kg·m-2) groups. PA-FMD and blood flow were assessed via high-resolution duplex ultrasonography (Vivid i, GE Healthcare, Mississauga, Ontario, Canada). PA blood flow was measured at rest and for 5 minutes following a 10-minute bout of moderate-intensity (60% heart rate reserve) cycling exercise. Total PA blood volume was calculated as the integral of the 5-minute postexercise PA blood flow response. After 4 weeks, PA-FMD increased (P = .04) following VCO supplementation (4.9% ±â€¯0.9% to 5.5% ±â€¯1.2%) with no change (P > .9) in the CON group (5.7% ±â€¯2.1% to 5.8% ±â€¯1.9%). There were no differences (both P > .28) in the postexercise total PA blood volume response in either group (VCO: 495 ±â€¯355 to 598 ±â€¯384 mL; CON: 562 ±â€¯362 to 488 ±â€¯229 mL). Short-term VCO supplementation does not alter aerobic exercise-mediated blood flow responses in young adults. However, the augmented popliteal FMD response observed in the VCO supplement group indicates that short-term VCO supplementation improves vascular endothelial function in young, healthy adults.

Rodent models of frailty and their application in preclinical research.

In clinical medicine, the concept of frailty is viewed as a state of high vulnerability to adverse health outcomes in people of the same age. Frailty is an important challenge because the loss of physiological reserve means that even minor stressors can lead to disability and death in those who are frail. Even so, the biology of frailty is not well understood. Rodent models of frailty are stimulating research into the biology of frailty. These pre-clinical models are based on "reverse-translation". Investigators have adapted either the "frailty phenotype" approach or the "frailty index" approach, originally developed in humans, for use in animals. This review briefly describes rodent models of frailty, discusses how these models have been used to explore mechanisms of frailty and how they have been employed to assess the impact of frailty on various experimental outcomes. The review also highlights studies that have used rodent models to investigate interventions to attenuate frailty, including drug treatment, dietary modifications and exercise. The ability to model frailty in animals is an exciting development that promises to accelerate the translation of laboratory discoveries into new clinical interventions, and situates frailty research in the larger context of geroscience.

Long-term testosterone deficiency modifies myofilament and calcium-handling proteins and promotes diastolic dysfunction in the aging mouse heart.

The impact of long-term gonadectomy (GDX) on cardiac contractile function was explored in the setting of aging. Male mice were subjected to bilateral GDX or sham operation (4 wk) and investigated at 16-18 mo of age. Ventricular myocytes were field stimulated (2 Hz, 37°C). Peak Ca2+ transients (fura 2) and contractions were similar in GDX and sham-operated mice, although Ca2+ transients (50% decay time: 45.2 ± 2.3 vs. 55.6 ± 3.1 ms, P < 0.05) and contractions (time constant of relaxation: 39.1 ± 3.2 vs. 69.5 ± 9.3 ms, P < 0.05) were prolonged in GDX mice. Action potential duration was increased in myocytes from GDX mice, but this did not account for prolonged responses, as Ca2+ transient decay was slow even when cells from GDX mice were voltage clamped with simulated "sham" action potentials. Western blots of proteins involved in Ca2+ sequestration and efflux showed that Na+/Ca2+ exchanger and sarco(endo)plasmic reticulum Ca2+-ATPase type 2 protein levels were unaffected, whereas phospholamban was dramatically higher in ventricles from aging GDX mice (0.24 ± 0.02 vs. 0.86 ± 0.13, P < 0.05). Myofilament Ca2+ sensitivity at physiological Ca2+ was similar, but phosphorylation of essential myosin light chain 1 was reduced by ≈50% in ventricles from aging GDX mice. M-mode echocardiography showed no change in systolic function (e.g., ejection fraction). Critically, pulse-wave Doppler echocardiography showed that GDX slowed isovolumic relaxation time (12.9 ± 0.9 vs. 16.9 ± 1.0 ms, P < 0.05), indicative of diastolic dysfunction. Thus, dysregulation of intracellular Ca2+ and myofilament dysfunction contribute to deficits in contraction in hearts from testosterone-deficient aging mice. This suggests that low testosterone helps promote diastolic dysfunction in the aging heart. NEW & NOTEWORTHY The influence of long-term gonadectomy on contractile function was examined in aging male hearts. Gonadectomy slowed the decay of Ca2+ transients and contractions in ventricular myocytes and slowed isovolumic relaxation time, demonstrating diastolic dysfunction. Underlying mechanisms included Ca2+ dysregulation, elevated phospholamban protein levels, and hypophosphorylation of a myofilament protein, essential myosin light chain. Testosterone deficiency led to intracellular Ca2+ dysregulation and myofilament dysfunction, which may facilitate diastolic dysfunction in the setting of aging.

A Murine Frailty Index Based on Clinical and Laboratory Measurements: Links Between Frailty and Pro-inflammatory Cytokines Differ in a Sex-Specific Manner.

A frailty index (FI) based on clinical deficit accumulation (FI-Clinical) quantifies frailty in aging mice. We aimed to develop a laboratory test-based murine FI tool (FI-Lab) and to investigate the effects of age and sex on FI-Lab scores, FI-Clinical scores, and the combination (FI-Combined), as well as to explore links between frailty and inflammation. Studies used older (17 and 23 months) C57BL/6 mice of both sexes. We developed an FI-Lab (blood pressure, blood chemistry, echocardiography) based on deviation from reference values in younger adults (12 months), which showed similar characteristics to a human FI-Lab tool. Interestingly, while FI-Clinical scores were higher in females, the opposite was true for FI-Lab scores and there was no sex difference in FI-Combined scores. All three FI tools revealed a positive correlation between pro-inflammatory cytokine levels and frailty in aging mice that differed between the sexes. Elevated levels of the pro-inflammatory cytokines interleukin (IL)-6, IL-9, and interferon-γ were associated with higher FI scores in aging females, while levels of IL-12p40 rose as FI scores increased in older males. Thus, an FI tool based on common laboratory tests can quantify frailty in mice; the positive correlation between inflammation and frailty scores in naturally aging mice differs between the sexes.

Chronic Treatment With the ACE Inhibitor Enalapril Attenuates the Development of Frailty and Differentially Modifies Pro- and Anti-inflammatory Cytokines in Aging Male and Female C57BL/6 Mice.

Studies on interventions that can delay or treat frailty in humans are limited. There is evidence of beneficial effects of angiotensin converting enzyme (ACE) inhibitors on aspects related to frailty, such as physical function, even in those without cardiovascular disease. This study aimed to longitudinally investigate the effect of an ACE inhibitor on frailty in aging male and female mice. Frailty was assessed with a clinical frailty index (FI) which quantifies health-related deficits in middle-aged (9-13 months) and older (16-25 months) mice. Chronic treatment with enalapril (30 mg/kg/day in feed) attenuated frailty in middle-aged and older female mice, and older male mice, without a long-term effect on blood pressure. Enalapril treatment resulted in a reduction in the proinflammatory cytokines interleukin (IL)-1α, monocyte chemoattractant protein-1 and macrophage inflammatory protein-1a in older female mice, and an increase in the anti-inflammatory cytokine IL-10 in older male mice compared with control animals. These sex-specific effects on inflammation may contribute to the protective effects of enalapril against frailty. This is the first study to examine the longitudinal effect of an intervention on the FI in mice, and provides preclinical evidence that enalapril may delay the onset of frailty, even when started later in life.

Effects of a 12-week cardiovascular rehabilitation programme on systemic inflammation and traditional coronary artery disease risk factors in patients with rheumatoid arthritis (CARDIA trial): a randomised controlled trial.

INTRODUCTION: Patients with systemic inflammatory diseases such as rheumatoid arthritis (RA) have an increased risk of cardiovascular disease (CVD) above the baseline risk attributable to traditional CVD risk factors seen in the general population. Exercise in cardiac rehabilitation (CR) is designed specifically for high-risk primary prevention and those with established CVD. Even though the European League Against Rheumatism guidelines state that exercise is safe for individuals with RA and exercise can reduce CVD risk, patients with RA rarely participate in CR. Thus, little is known about CR's impact on inflammatory and CVD risk in the RA population. The purpose of this trial is to determine the feasibility of a 12-week CR programme for patients with RA and whether it decreases CVD risk without exacerbating RA. METHODS AND ANALYSIS: This is a randomised controlled trial whereby 60 participants with RA will be recruited and randomly assigned to either standard of care (SOC) treatment or SOC plus a 12-week CR programme (60 min of education plus two 60 min aerobic exercise sessions/week). Exercise will be performed at 60%-80% of heart rate reserve. Outcome measures (Framingham Risk Score, resting heart rate, blood pressure, blood lipids, markers of systemic inflammation (ie, interleukin (IL) 6 and tumour necrosis factor-α (TNF-α), Clinical Disease Assessment Index, Disease Activity Score-28, physical activity levels and peak cardiorespiratory fitness) will be assessed preintervention (week-0), postintervention (week-13) and 6 months postintervention. ETHICS AND DISSEMINATION: Ethical approval was obtained from the Nova Scotia Health Authority Research Ethics Board. Results will be submitted for publication in an appropriate peer-reviewed journal. TRIAL REGISTRATION NUMBER: NCT01534871; Pre-results.