Comprehensive plasma and tissue profiling reveals systemic metabolic alterations in cardiac hypertrophy and failure

AIMS

Heart failure is characterized by structural and metabolic cardiac remodelling. The aim of the present study is to expand our understanding of the complex metabolic alterations in the transition from pathological hypertrophy to heart failure and exploit the results from a translational perspective.

METHODS AND RESULTS

Mice were subjected to transverse aortic constriction (TAC) or sham surgery and sacrificed 2 weeks, 4 weeks, or 6 weeks after the procedure. Samples from plasma, liver, skeletal muscle, and heart were collected and analysed using metabolomics. Cardiac samples were also analysed by transcriptional profiling. Progressive alterations of key cardiac metabolic pathways and gene expression patterns indicated impaired mitochondrial function and a metabolic switch during transition to heart failure. Similar to the heart, liver, and skeletal muscle revealed significant metabolic alterations such as depletion of essential fatty acids and glycerolipids in late stages of heart failure. Circulating metabolites, particularly fatty acids, reflected cardiac metabolic defects, and deteriorating heart function. For example, inverse correlation was found between plasma and the heart levels of triacylglycerol (C18:1, C18:2, C18:3), and sphingomyelin (d18:1, C23:0) already at an early stage of heart failure. Interestingly, combining metabolic and transcriptional data from cardiac tissue revealed that decreased carnitine shuttling and transportation preceded mitochondrial dysfunction. We, thus, studied the therapeutic potential of OCTN2 (Organic Cation/Carnitine Transporter 2), an important factor for carnitine transportation. Cardiac overexpression of OCTN2 using an adeno-associated viral vector significantly improved ejection fraction and reduced interstitial fibrosis in mice subjected to TAC.

CONCLUSION

Comprehensive plasma and tissue profiling reveals systemic metabolic alterations in heart failure, which can be used for identification of novel biomarkers and potential therapeutic targets.

Relevance of pre-analytical blood management on the emerging cardiovascular protein biomarkers TWEAK and HMGB1 and on miRNA serum and plasma profiling

BACKGROUND

Disease-independent sources of biomarker variability include pre-analytical, analytical and biological variance. The aim of the present study was to evaluate whether the pre-analytical phase has any impact on the emerging heart disease TWEAK and HMGB1 protein markers and miRNA biomarkers, and whether peptidome profiling allows the identification of pre-analytical quality markers.

METHODS

An assessment was made of sample type (serum, EDTA-Plasma, Citrate-Plasma, ACD-plasma, Heparin-plasma), temperature of sample storage (room temperature or refrigerated), time of sample storage (0.5, 3, 6 and 9h) and centrifugation (one or two-step). Aliquots of all processed samples were immediately frozen (-80°C) before analysis. Proteins were assayed by ELISAs, miRNA expression profile by microarray and peptidome profiling by MALDI-TOF/MS.

RESULTS

Temperature, time and centrifugation had no impact on TWEAK and HMGB1 results, which were significantly influenced by matrix type, TWEAK levels being significantly higher (F=194.7, p<0.0001), and HMGB1 levels significantly lower (F=36.32, p<0.0001) in serum than in any other plasma type. Unsuitable miRNA results were obtained using Heparin-plasma. Serum miRNA expression profiles depended mainly on temperature, while EDTA-plasma miRNA expression profiles were strongly affected by the centrifugation method used. MALDI-TOF/MS allowed the identification of seven features as indices of pre-analytical serum (m/z at 1206, 1350, 1865 and 2021) or EDTA-plasma (m/z 1897, 2740 and 2917) degradation.

CONCLUSIONS

Serum and EDTA-plasma allow the analysis of both proteins and miRNA emerging biomarkers of heart diseases. Refrigerated storage prevents an altered miRNA expression profile also in cases of a prolonged time-interval between blood drawing and processing.

Different inhibition patterns of tedisamil for fast and slowly inactivating transient outward current in rat ventricular myocytes

Tedisamil has been described as a selective inhibitor of a fast inactivating transient outward current (i(to,f)) in rat ventricular myocytes. Because recent reports demonstrated the existence of a second slowly inactivating transient component (i(to,s)) we investigated i(to,s) and differentiated the effects of tedisamil on both transient outward current components and their influence on action potential duration. Standard electrophysiological techniques were used for whole cell recordings at 24-26 degrees C from enzymatically isolated myocytes. Inhibition of i(to,f) by tedisamil was the result of an acceleration of inactivation at positive test potentials with a concentration for half-maximal inhibition (EC50) of 4-7 micromol/l, which is confirmatory to reports from other investigators. Our new results show that i(to,s) is more sensitive to tedisamil with an EC50 of 0.5 micromol/l. Furthermore the pattern of i(to,s) inhibition is different compared with i(to,f), because inactivation of i(to,s) is not accelerated by tedisamil. Instead the amplitude of the steady state inactivation curve of i(to,s) is attenuated which indicates a reduction of maximally available current. I(to,s) was evaluated by three different methods as time-dependently inactivating current (7.5 s test pulse duration), voltage-dependently inactivated current and tedisamil-sensitive current. All approaches yield similar inactivation curves. The potential for halfmaximal inactivation of i(to,s) lies about 35 mV more negative than that for i(to,f) and the slope factor (K = -23 mV) is different to that of i(to,f) (K = -3 mV). Effectiveness of tedisamil-induced modulation of i(to,f) and i(to,s) on action potential repolarization was tested. Action potentials stimulated at 0.5 Hz were not prolonged by 1 micromol/l tedisamil (dominant i(to,s) block) at a repolarization level of 0 mV but prolonged to about 120% of control at -70 mV. This indicates that i(to,f) was sufficient to guarantee a regular early repolarization whereas decrease of i(to,s) delayed the final repolarization. In conclusion, the observation that tedisamil inhibits i(to,f) and i(to,s) differently supports the hypothesis that the two i(to)-components are related to two different channel populations expressed in rat ventricular myocytes.

Effects of 17beta-estradiol on action potentials and ionic currents in male rat ventricular myocytes

This study describes electrophysiological effects of estrogens in isolated male rat ventricular myocytes. According to the literature these cells do not express the nuclear estrogen receptor. Action potentials or membrane currents were recorded in the whole-cell configuration with standard techniques. Action potential durations (APD) measured at a level of 0 mV (APD 0) and -70 mV (APD -70) were prolonged by 17beta-estradiol (0.5 Hz stimulation frequency, 24-26 degrees C). Threshold concentration was 1 micromol/l. At the highest concentration used (30 micromol/l) no saturation of the response was reached and APD 0 was 162% and APD -70 was 230% of the respective control. The resting potential remained unaffected in most cells. The prolongation induced by 17beta-estradiol developed fast and reached a steady state 10 min after start of hormone superfusion. Effects of estrogen were completely reversible during 10-15 min wash-out with hormone-free solution. The extent of prolongation (10 micromol/l 17beta-estradiol) was frequency dependent. Expressed as percentage of the respective control APD 0 (or APD -70) was 115% (188%) at 0.05 Hz, 118% (163%) at 0.5 Hz and 99% (129%) at 5 Hz stimulation frequency. The response was stereoselective, because 30 micromol/l 17alpha-estradiol did not prolong action potentials (APD 0: 101%, APD -70: 104% of the respective control, 0.5 Hz stimulation frequency). The endogenous estrogens estrone and estriol were less effective than 17beta-estradiol. With 30 micromol/l estrone (0.5 Hz stimulation frequency) APD 0 was 103% and ADP-70 148% of control and with 30 micromol/l estriol APD 0 was 135% and APD -70 137% of control. The prolongation of action potentials can be explained by inhibition of transient outward current which, in rat ventricle, is composed of fast (i[to,f]) and slowly (i[to,s]) inactivating components. At 30 micromol/l 17beta-estradiol i(to,f) was reduced to 50% and i(to,s) to 43% of their maximal amplitudes. The voltage sensor of i(to,f) or i(to,s) was hardly affected. Additionally, 17beta-estradiol decreased the calcium current (i[Ca,L]) to 76% (10 micromol/l) and 38% at 30 micromol/l. The inwardly rectifying potassium current (i[K1]) was reduced partly with 30 micromol/l 17beta-estradiol and its amplitude was 72% of control at -90 mV (inward current flow) and 65% at -40 mV (outward current flow). These results show that 17beta-estradiol is active in cardiac cells which do not express the nuclear estrogen receptor. The hormone exerts class III activity and reduces calcium inward current. These effects, however, occur in vitro with concentrations above the physiological level and therefore may be without significance in vivo.

Inhibition of pacemaker current by the bradycardic agent ZD 7288 is lost use-dependently in sheep cardiac Purkinje fibres

The inhibition of the pacemaker current (if) in sheep cardiac Purkinje fibers by ZD 7288 [4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino)pyrimidinium++ + chloride] is lost use-dependently. This disinhibition of if was investigated by using the two-microelectrode voltage-clamp technique. The pulse protocol consisted of a rest period (holding potential of about -50 mV, 1-10 micromol/l ZD 7288) followed by a train of test pulses (potential negative to -100 mV, stimulation frequency 0.05 Hz). At the beginning of the first test pulse there was an immediate reduction of if but inhibition was lost during continued stimulation. Activation of if is sigmoidal and the early delay in current activation was prolonged from 33 ms (no ZD 7288) to 424 ms (10 micromol/l ZD 7288). Therefore hardly any disinhibition occurred during short test pulses (0.5s). During longer test pulses (5 s, -120 mV, 10 micromol/l) disinhibition developed with a time constant of about 2 s. The inhibition of if by ZD 7288 was lost voltage-dependently. With 10 micro mol/l ZD 7288 the half-maximal disinhibition occurred at -92 mV and the slope factor of the disinhibition/voltage curve (Boltzmann relation) was 4.8 mV. The voltage-dependent disinhibition could be abolished largely by extracellular application of protease (0.5 mg/ml, 7 min). After prior disinhibition, reinhibition at the holding potential (about -50 mV) followed a bi-exponential time course indicating that inhibition may be produced by a fast (tau=0.7 min) and a slow component (tau=20-30 min). Increasing ZD 7288 concentration from 1 to 10 mu mol/l accelerated reinhibition, mainly by an increase of the amplitude (A) of the fast component. The ratio Afast/Aslow was 0.399 at 1 micromol/l and 2.65 at 10 micromol/l ZD 7288. The reinhibition of if was unchanged by shifting the holding potential from -50 mV to -20 mV. Trials to wash out the effects of 10 micromol/l ZD 7288 gave two results. The inhibition of if was slightly reversed after a wash-out of 1.5 h with drug-free solution. A second effect of the drug, the fast reinhibition, could be completely removed by wash-out. In summary if is inhibited by ZD 7288 at membrane potentials at which the virtual if gate is closed. Disinhibition occurs during long-lasting hyperpolarization but will hardly be operative in unclamped fibres under physiological conditions.