Lucy B. Esberg

High-fat diet-induced juvenile obesity leads to cardiomyocyte dysfunction and upregulation of Foxo3a transcription factor independent of lipotoxicity and apoptosis.

Background Obesity is associated with dyslipidemia, which leads to elevated triglyceride and ceramide levels, apoptosis and compromised cardiac function. Methods To determine the role of high-fat diet-induced obesity on cardiomyocyte function, weanling male Sprague–Dawley rats were fed diets incorporating 10% of kcal or 45% of kcal from fat. Mechanical function of ventricular myocytes was evaluated including peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90) and maximal velocity of shortening and relengthening (± dl/dt). Intracellular Ca2+ properties were assessed using fluorescent microscopy. Results High-fat diet induced hyperinsulinemic insulin-resistant obesity with depressed PS, ± dl/dt, prolonged TPS/TR90 reduced intracellular Ca2+ release and Ca2+ clearing rate in the absence of hypertension, diabetes, lipotoxicity and apoptosis. Myocyte responsiveness to increased stimulus frequency and extracellular Ca2+ was compromised. SERCA2a and phospholamban levels were increased, whereas phosphorylated phospholamban and potassium channel (Kv1,2) were reduced in high-fat diet group. High-fat diet upregulated the forkhead transcription factor Foxo3a, and suppressed mitochondrial aconitase activity without affecting expression of the caloric sensitive gene silent information regulator 2 (Sir2), protein nitrotyrosine formation, lipid peroxidation and apoptosis. Levels of endothelial nitric oxide synthase (NOS), inducible NOS, triglycerides and ceramide were similar between the two groups. Conclusions Collectively, our data show that high-fat diet-induced obesity resulted in impaired cardiomyocyte function, upregulated Foxo3a transcription factor and mitochondrial damage without overt lipotoxicity or apoptosis.

High-fat Diet-induced Obesity Leads to Resistance to Leptin-induced Cardiomyocyte Contractile Response

Levels of the obese gene product leptin are often elevated in obesity and may contribute to obesity‐induced cardiovascular complications. However, the role of leptin in obesity‐associated cardiac abnormalities has not been clearly defined. This study was designed to determine the influence of high‐fat diet‐induced obesity on cardiac contractile response of leptin. Mechanical and intracellular Ca2+ properties were evaluated using an IonOptix system in cardiomyocytes from adult rats fed low‐ and high‐fat diets for 12 weeks. Cardiomyocyte contractile and intracellular Ca2+ properties were examined including peak shortening, duration and maximal velocity of shortening/relengthening (TPS/TR90, ±dl/dt), Fura‐2‐fluorescence intensity change (ΔFFI), and intracellular Ca2+ decay rate (τ). Expression of the leptin receptor (Ob‐R) was evaluated by western blot analysis. High‐fat diet increased systolic blood pressure and plasma leptin levels. PS and ±dl/dt were depressed whereas TPS and TR90 were prolonged after high‐fat diet feeding. Leptin elicited a concentration‐dependent (0–1,000 nmol/l) inhibition of PS, ±dl/dt, and ΔFFI in low‐fat but not high‐fat diet‐fed rat cardiomyocytes without affecting TPS and TR90. The Janus kinase 2 (JAK2) inhibitor AG490, the mitogen‐activated protein kinase (MAPK) inhibitor SB203580, and the nitric oxide synthase (NOS) inhibitor L‐NAME abrogated leptin‐induced cardiomyocyte contractile response in low‐fat diet group without affecting the high‐fat diet group. High‐fat diet significantly downregulated cardiac expression of Ob‐R. Elevation of extracellular Ca2+ concentration nullified obesity‐induced cardiomyocyte mechanical dysfunction and leptin‐induced depression in PS. These data indicate presence of cardiac leptin resistance in diet‐induced obesity possibly associated with impaired leptin receptor signaling.

Influence of gender on ethanol-induced ventricular myocyte contractile depression in transgenic mice with cardiac overexpression of alcohol dehydrogenase

Acute ethanol exposure depresses ventricular contractility and contributes to alcoholic cardiomyopathy in both men and women chronically consuming ethanol. However, a gender-related difference in the severity of myopathy exists with female being more sensitive to ethanol-induced tissue damage. Acetaldehyde (ACA), the major oxidized product of ethanol, has been implicated to play a role in the pathogenesis and gender-related difference of alcoholic cardiomyopathy, possibly due to its direct cardiac effect and interaction with estrogen. This study was designed to compare the effects of cardiac overexpression of alcohol dehydrogenase (ADH), which converts ethanol into ACA, on the cardiac contractile response to ethanol in ventricular myocytes isolated from age-matched adult male and female transgenic (ADH) and wild-type (FVB) mice. Mechanical properties were measured with an IonOptix SoftEdge system. ACA production was assessed by gas chromatography. The ADH myocytes from both genders exhibited similar mechanical properties but a higher efficacy to produce ACA compared to FVB myocytes. Exposure to ethanol (80-640 mg/dl) for 60 min elicited concentration-dependent decrease of cell shortening in both FVB and ADH groups. The ethanol-induced depression on cell shortening was significantly augmented in female but not male ADH group. ADH transgene did not exacerbate the ethanol-induced inhibition of maximal velocity of shortening/relengthening in either gender. In addition, neither ethanol nor ADH transgene affect the duration of shortening and relengthening in male or female mice. These data suggest that females may be more sensitive to ACA-induced cardiac contractile depression than male, which may attribute to the gender-related difference of alcoholic cardiomyopathy.

Dietary interaction of high fat and marginal copper deficiency on cardiac contractile function

Objective: High‐fat and marginally copper‐deficient diets impair heart function, leading to cardiac hypertrophy, increased lipid droplet volume, and compromised contractile function, resembling lipotoxic cardiac dysfunction. However, the combined effect of the two on cardiac function is unknown. This study was designed to examine the interaction between high‐fat and marginally copper‐deficient diets on cardiomyocyte contractile function.

Adenovirus gene transfer of recombinant endothelial nitric oxide synthase enhances contractile function in ventricular myocytes.

eNOS is expressed in cardiac myocytes and plays an important role in cardiac contractile function. This study was designed to determine whether ex vivo eNOS gene transfer in ventricular myocytes affects cardiac contractile function. Replication-incompetent adenoviral vectors encoding eNOS or marker gene &bgr;-galactosidase (LacZ) were transduced into adult rat ventricular myocytes at an MOI of 10, 50, or 100 for 36 hours. Mechanical and intracellular Ca2+ properties of myocytes were evaluated by video-based edge detection and fura-2 fluorescence. NOS protein expression and activity were assessed by Western blot and 3H-arginine to 3H-citrulline assay. Myocytes transduced with eNOS but not LacZ displayed enhanced eNOS but not iNOS expression associated with elevated NOS activity. Myocytes transduced with eNOS exhibited significantly elevated peak shortening and velocity of shortening/relengthening associated with enhanced basal as well as electrically stimulated rise of intracellular Ca2+ compared with control or LacZ groups. The durations of shortening and relengthening were comparable in all groups. The eNOS-induced mechanical effects were paralleled with elevated phosphorylation of Akt. Furthermore, the phosphatidylinositol-3 (PI-3) kinase inhibitors wortmannin and LY294002 prevented eNOS-induced mechanical effects. These results revealed that gene transfer of eNOS directly promotes cardiomyocyte contractile function and intracellular Ca2+ handling, suggesting therapeutic potential of eNOS gene transfer.

Moderate ethanol administration accentuates cardiomyocyte contractile dysfunction and mitochondrial injury in high fat diet-induced obesity

Light to moderate drinking confers cardioprotection although it remains unclear with regards to the role of moderate drinking on cardiac function in obesity. This study was designed to examine the impact of moderate ethanol intake on myocardial function in high fat diet intake-induced obesity and the mechanism(s) involved with a focus on mitochondrial integrity. C57BL/6 mice were fed low or high fat diet for 16 weeks prior to ethanol challenge (1g/kg/d for 3 days). Cardiac contractile function, intracellular Ca(2+) homeostasis, myocardial histology, and mitochondrial integrity [aconitase activity and the mitochondrial proteins SOD1, UCP-2 and PPARγ coactivator 1α (PGC-1α)] were assessed 24h after the final ethanol challenge. Fat diet intake compromised cardiomyocyte contractile and intracellular Ca(2+) properties (depressed peak shortening and maximal velocities of shortening/relengthening, prolonged duration of relengthening, dampened intracellular Ca(2+) rise and clearance without affecting duration of shortening). Although moderate ethanol challenge failed to alter cardiomyocyte mechanical property under low fat diet intake, it accentuated high fat diet intake-induced changes in cardiomyocyte contractile function and intracellular Ca(2+) handling. Moderate ethanol challenge failed to affect fat diet intake-induced cardiac hypertrophy as evidenced by H&E staining. High fat diet intake reduced myocardial aconitase activity, downregulated levels of mitochondrial protein UCP-2, PGC-1α, SOD1 and interrupted intracellular Ca(2+) regulatory proteins, the effect of which was augmented by moderate ethanol challenge. Neither high fat diet intake nor moderate ethanol challenge affected protein or mRNA levels as well as phosphorylation of Akt and GSK3β in mouse hearts. Taken together, our data revealed that moderate ethanol challenge accentuated high fat diet-induced cardiac contractile and intracellular Ca(2+) anomalies as well as mitochondrial injury.

Comparison of cardiac contractile and intracellular Ca2+ response between estrogen and phytoestrogen α-zearalanol in ventricular myocytes

While the benefit and risk of estrogen replacement therapy for cardiovascular disease remains controversial, women frequently choose alternatives to estrogen such as phytoestrogen for treatment of menopause even though medical indications for estrogens may exist. Phytoestrogens also possess distinct advantages over mammalian estrogens because their usage in men without feminizing side effects. Nevertheless, the cardiac contractile function of estrogen or phytoestrogen has not been clearly elucidated. The aim of the present study was to compare the effect of 17β estradiol (E2) and phytoestrogen α-zearalanol (ZAL) on cardiac mechanical function and intracellular Ca2+ transients at cellular levels. Isolated ventricular myocytes from adult female rats were stimulated to contract at 0.5 Hz. Contractile properties were evaluated using an IonOptix MyoCam® system including peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90), and maximal velocity of shortening/relengthening (± dL/dt). Intracellular Ca2+ properties were evaluated as fura-2 fluorescent intensity change (ΔFFI) and intracellular Ca2+ decay rate. Acute administration of E2 (10−9–10−5M) elicited a concentration-dependent increase in PS and ΔFFI, with maximal augmentation of approx 35% and 25%, respectively. TPS, TR90, ± dL/dt, resting intracellular Ca2+ level, and intracellular Ca2+ decay were unaffected by E2. None of the mechanical or intracellular Ca2+ indices tested was affected by phytoestrogen ZAL (10−9–10−5M). Our results revealed a direct cardiac stimulatory action from E2 but not from phytoestrogen ZAL on ventricular contraction, likely mediated through enhanced intracellular Ca2+ release.

Iso-S-petasin, a hypotensive sesquiterpene from Petasites formosanus, depresses cardiac contraction and intracellular Ca2+ transients in adult rat ventricular myocytes

Petasites formosanus is an indigenous species of the medicinal plant Petasites which has been used to treat hypertension. Both S‐petasin and its isoform iso‐S‐petasin have been shown to be the effective ingredients in P. formosanus. However, their effect on heart function has not been revealed. This study was to examine the effect of iso‐S‐petasin on cardiac contractile function at the myocyte level. Ventricular myocytes were isolated from adult rat hearts and were stimulated to contract at 0.5 Hz under 1.0 mm extracellular Ca2+. Contractile properties were evaluated using an lonOptix MyoCam system including peak shortening (PS), time to PS (TPS), time to 90% re‐lengthening (TR90) and maximal velocity of shortening/re‐lengthening (±dL/dt). Intracellular Ca2+ properties were assessed by fura‐2 and presented as Ca2+‐induced Ca2+ release (CICR) and intracellular Ca2+ decay. Acute application of iso‐S‐petasin (10−7 to 10−4 M) elicited a concentration‐dependent inhibition in PS and CICR, with maximal inhibitions of 51.0% and 31.0%, respectively. iso‐S‐petasin also induced a concentration‐dependent inhibition of ± dL/dt without affecting TPS, TR90, baseline intracellular Ca2+ level or intracellular Ca2+ decay. Elevation of extracellular Ca2+ from 1.0 mm to 2.7 mm significantly antagonized the iso‐S‐petasin‐induced depression in PS and CICR. These results demonstrated a direct depressant action of iso‐S‐petasin on ventricular contraction, which may work in concert with its antihypertensive action to reduce the cardiac load. The iso‐S‐petasin‐induced decrease in CICR may play a role in its cardiac depressant effect.