Levosimendan in intensive care and emergency medicine: literature update and expert recommendations for optimal efficacy and safety

The inodilator levosimendan, in clinical use for over two decades, has been the subject of extensive clinical and experimental evaluation in various clinical settings beyond its principal indication in the management of acutely decompensated chronic heart failure. Critical care and emergency medicine applications for levosimendan have included postoperative settings, septic shock, and cardiogenic shock. As the experience in these areas continues to expand, an international task force of experts from 15 countries (Austria, Belgium, China, Croatia, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Spain, Sweden, Switzerland, and the USA) reviewed and appraised the latest additions to the database of levosimendan use in critical care, considering all the clinical studies, meta-analyses, and guidelines published from September 2019 to November 2021. Overall, the authors of this opinion paper give levosimendan a "should be considered" recommendation in critical care and emergency medicine settings, with different levels of evidence in postoperative settings, septic shock, weaning from mechanical ventilation, weaning from veno-arterial extracorporeal membrane oxygenation, cardiogenic shock, and Takotsubo syndrome, in all cases when an inodilator is needed to restore acute severely reduced left or right ventricular ejection fraction and overall haemodynamic balance, and also in the presence of renal dysfunction/failure.

Comparison of the efficiency of Na+/Ca2+ exchanger or Na+/H+ exchanger inhibition and their combination in reducing coronary reperfusion-induced arrhythmias

During ischaemia/reperfusion, the rise in [Na(+)](i), induced by simultaneous depression of the Na(+)/K(+)-ATPase and activation of the Na(+)/H(+) exchanger (NHE), shifts the Na(+)/Ca(2+) exchanger (NCX) into reverse transport mode, resulting in Ca(2+)(i)overload, which is a critical factor in enhancing the liability to cardiac arrhythmias. The inhibition of NHE, and recently NCX has been suggested to effectively protect the heart from reperfusion-induced arrhythmias. In this study, we investigated and compared the efficacy of individual or the simultaneous inhibition of the NHE and NCX against reperfusion-induced arrhythmias in Langendorff-perfused rat hearts by applying a commonly used regional ischaemia-reperfusion protocol. The NHE and NCX were inhibited by cariporide and SEA0400 or the novel, more selective ORM-10103, respectively. Arrhythmia diagrams calculated for the reperfusion period were analysed for the incidence and duration of extrasystoles (ESs), ventricular tachycardia (VT) and ventricular fibrillation (VF). NHE inhibition by cariporide was highly efficient in reducing the recorded reperfusion-induced arrhythmias. Following the application of SEA0400 or ORM-10103, the number and duration of arrhythmic periods were efficiently or moderately decreased. While both NCX inhibitors effectively reduced ESs, the most frequently triggered arrhythmias, they exerted limited or no effect on VTs and VFs. Of the NCX inhibitors, ORM-10103 was more effective. Surprisingly, the simultaneous inhibition of the NCX and NHE failed to significantly improve the antiarrhythmic efficacy reached by NCX blockade alone. In conclusion, although principal simultaneous NHE+NCX inhibition should be highly effective against all types of the recorded reperfusion-induced arrhythmias, NCX inhibitors, alone or in combination with cariporide, seem to be moderately suitable to provide satisfactory cardioprotection - at least in the present arrhythmia model. Since ORM-10103 and SEA0400 are known to effectively inhibit after-depolarisations, it is suggested that their efficacy and that of other NCX inhibitors may be higher and more pronounced in the predominantly Ca(2+)(i)-dependent triggered arrhythmias.

ORM-10103, a novel specific inhibitor of the Na+/Ca2+ exchanger, decreases early and delayed afterdepolarizations in the canine heart

BACKGROUND AND PURPOSE

At present there are no small molecule inhibitors that show strong selectivity for the Na(+) /Ca(2+) exchanger (NCX). Hence, we studied the electrophysiological effects of acute administration of ORM-10103, a new NCX inhibitor, on the NCX and L-type Ca(2+) currents and on the formation of early and delayed afterdepolarizations.

EXPERIMENTAL APPROACH

Ion currents were recorded by using a voltage clamp technique in canine single ventricular cells, and action potentials were obtained from canine and guinea pig ventricular preparations with the use of microelectrodes.

KEY RESULTS

ORM-10103 significantly reduced both the inward and outward NCX currents. Even at a high concentration (10 μM), ORM-10103 did not significantly change the L-type Ca(2+) current or the maximum rate of depolarization (dV/dtmax ), indicative of the fast inward Na(+) current. At 10 μM ORM-10103 did not affect the amplitude or the dV/dtmax of the slow response action potentials recorded from guinea pig papillary muscles, which suggests it had no effect on the L-type Ca(2+) current. ORM-10103 did not influence the Na(+) /K(+) pump or the main K(+) currents of canine ventricular myocytes, except the rapid delayed rectifier K(+) current, which was slightly diminished by the drug at 3 μM. The amplitudes of pharmacologically- induced early and delayed afterdepolarizations were significantly decreased by ORM-10103 (3 and 10 μM) in a concentration-dependent manner.

CONCLUSIONS AND IMPLICATIONS

ORM-10103 is a selective inhibitor of the NCX current and can abolish triggered arrhythmias. Hence, it has the potential to be used to prevent arrhythmogenic events.

Effects of calcium sensitizer OR-1986 on a cardiovascular mortality and myocardial remodelling in hypertensive Dahl/Rapp rats

Calcium-sensitizing agents have been shown to improve cardiac function in patients suffering from acute decompensated heart failure, however, their long-term effects on cardiac remodeling and cardiovascular mortality are still largely unknown. In the present study we tested the hypothesis whether OR-1896, an active and long-lasting metabolite of calcium sensitizer levosimendan, prevents cardiovascular mortality and hypertension-induced myocardial remodelling in salt-sensitive Dahl/Rapp rats. OR-1896 was given orally to Dahl/Rapp SS rats on high-salt diet (NaCl 7% w/w) for 7 weeks at two different doses (0.5 and 0.05 mg/kg). OR-1896 prevented salt-induced cardiovascular mortality (survival rate 75 % in OR-1896 treated groups vs 38 % in untreated controls, p<0.01), ameliorated cardiac hypertrophy and improved systolic functions of the heart without major influence on systemic blood pressure. OR-1896 also ameliorated salt-induced increase in cardiac ANP mRNA expression and plasma BNP level. Salt-induced cardiac remodelling was associated with 4-fold increase in cardiac p16(INK4a) mRNA expression, a marker of cellular senescence. OR-1896 dose-dependently ameliorated cardiomyocyte senescence. Our findings suggest a therapeutic role for OR-1896 in the prevention of cardiac remodelling in salt-sensitive forms of hypertension. The present study also underscores the importance of cellular senescence in the pathogenesis of salt-induced hypertensive heart disease.

A role for the RISK pathway and K(ATP) channels in pre- and post-conditioning induced by levosimendan in the isolated guinea pig heart

BACKGROUND AND PURPOSE

Myocardial reperfusion injury prevents optimal salvage of the ischaemic myocardium, and adjunct therapy that would significantly reduce reperfusion injury is still lacking. We investigated whether (1) the heart could be pre- and/or post-conditioned using levosimendan (levosimendan pre-conditioning (LPC) and levosimendan post-conditioning (LPostC)) and (2) the prosurvival kinases and/or the sarcolemmal or mitochondrial K(ATP) channels are involved.

EXPERIMENTAL APPROACH

Isolated guinea pig hearts were treated with two 5 min cycles of levosimendan (0.1 microM) interspersed with vehicle perfusion, or two 5 min cycles of ischaemia/reperfusion, before coronary artery ligation (CAL) for 40 min at 36.5 degrees C. Hearts were treated with mitochondrial or sarcolemmal K(ATP) channel blockers before LPC or LPostC. For post-conditioning, hearts received three 30 s cycles of ischaemia/reperfusion or levosimendan/vehicle. Hearts were pretreated with levosimendan immediately before CAL (without washout). Cardiac function, infarct size and reperfusion injury salvage kinase activity was assessed.

KEY RESULTS

LPC and LPostC halved the infarct size compared with controls (P<0.05). Treatment with K(ATP) channel blockers before LPC or LPostC reversed this decrease. Pretreating hearts with levosimendan increased activity of extracellular signal-regulated kinase (ERK) 42/44 on reperfusion and had the most marked infarct-lowering effect (P<0.05).

CONCLUSIONS AND IMPLICATIONS

(1) Hearts could be pharmacologically pre- and post-conditioned with levosimendan; (2) levosimendan pretreatment is the most effective way to reduce infarct size, possibly by increasing ERK 42/44 activity; (3) benefits of LPC and LPostC were abolished by both K(ATP) channel blockers and (4) LPC may be useful before elective cardiac surgery, whereas LPostC may be used after acute coronary artery events.

Effects of levosimendan on cardiac remodeling and cardiomyocyte apoptosis in hypertensive Dahl/Rapp rats

BACKGROUND AND PURPOSE

Progression of heart failure in hypertensive Dahl rats is associated with cardiac remodeling and increased cardiomyocyte apoptosis. This study was conducted to study whether treatment with a novel inotropic vasodilator compound, levosimendan, could prevent hypertension-induced cardiac remodeling and cardiomyocyte apoptosis.

EXPERIMENTAL APPROACH

6-week-old salt-sensitive Dahl/Rapp rats received levosimendan (0.3 mg kg(-1) and 3 mg kg(-1) via drinking fluid) and high salt diet (NaCl 7%) for 7 weeks, Dahl/Rapp rats on low-salt diet served as controls. Blood pressure, cardiac functions by echocardiography, cardiomyocyte apoptosis by TUNEL technique, tissue morphology, myocardial expression of calcium cycling proteins, and markers of neurohumoral activation were determined.

KEY RESULTS

Untreated Dahl/Rapp rats on high salt diet developed severe hypertension, cardiac hypertrophy and moderate systolic dysfunction. 38% of Dahl/Rapp rats (9/24) survived the 7-week-follow-up period. Cardiomyocyte apoptosis was increased by 6-fold during high salt diet. Levosimendan improved survival (survival rates in low- and high-dose levosimendan groups 12/12 and 9/12, p<0.001 and p=0.05, respectively), increased cardiac function, and ameliorated cardiac hypertrophy. Levosimendan dose-dependently prevented cardiomyocyte apoptosis. Levosimendan normalized salt-induced increased expression of natriuretic peptide, and decreased urinary noradrenaline excretion. Levosimendan also corrected salt-induced decreases in myocardial SERCA2a protein expression and myocardial SERCA2a/NCX-ratio.

CONCLUSIONS AND IMPLICATIONS

Improved survival by the novel inotropic vasodilator levosimendan in hypertensive Dahl/Rapp rats is mediated, at least in part, by amelioration of hypertension-induced cardiac remodeling and cardiomyocyte apoptosis.

Interaction of levosimendan with cardiac troponin C in the presence of cardiac troponin I peptides

The interaction between troponin C (TnC) and troponin I (TnI) is essential for the regulation of muscle contraction. There are several binding sites for TnI on TnC that are differentially occupied depending on the phase of the contraction/relaxation cycle. TnI and TnC interact in an antiparallel fashion with each other. The C-domain of cTnC and the N-domain region of cTnI(residues 33-70) always interact under physiological conditions, whereas the interaction between regulatory regions of TnC and TnI (residues 128-166) is calcium dependent. Previously, it has been shown that levosimendan, a calcium sensitizer used as a treatment for acute heart failure, can interact with both domains of isolated cTnC. To understand which interaction is relevant for the mechanism of calcium sensitization, we used a more complete troponin model obtained by complexing cTnI(32-79) and cTnI(128-180) with calcium-saturated cTnC(CS). The cTnI peptides bound to cTnC(CS) to form a 1:1:1 complex. The interaction of levosimendan with this complex was followed by 1H-(15)N heteronuclear correlation spectroscopy. It was clear that based on chemical shift changes, cTnI(32-79) blocked the levosimendan interaction sites on the C-domain, whereas cTnI(128-180) did not compete with levosimendan for the binding site on the N-domain. Hence, the effective binding site of levosimendan on cTnC resulting in the calcium-sensitizing effect is located in the regulatory domain (N-domain).

Levosimendan is a mitochondrial K(ATP) channel opener

Levosimendan, a new inodilator developed for the treatment of heart failure has been shown to have a vasodilatory effect via opening of K(ATP) channels in the plasma membrane of vascular smooth muscle cells. In this study, we investigated the effects of levosimendan on the mitochondrial K(ATP) channel. This compound did not influence mitochondrial transmembrane potential (DeltaPsi), and at up to 2.2 microM had no effect on the respiration rate of rat liver mitochondria, respiring on 5 mM succinate (+5 microM rotenone). A sensitive method was developed for assessing K(ATP) channel opening activity employing rat liver mitochondria, respiring only on endogenous substrates in the presence of 400 microM ATP and 1 microg oligomycin/mg mitochondrial protein. In this model, levosimendan (0.7-2.6 microM) decreased DeltaPsi by 6.5-40.4% (n=3, incubation time 15 min). This effect was dependent on the K+ concentration in the incubation medium and was abolished by the selective blocker of the mitochondrial K(ATP) channel-5-hydroxydecanoate (200 microM). Our results indicate that levosimendan opens mitochondrial K(ATP) channels.

Improved survival with simendan after experimental myocardial infarction in rats

This study compared the effects of simendan, a calcium sensitizer, with those of milrinone and enalapril on survival of rats with healed myocardial infarction. Seven days after ligation-induced myocardial infarction, the rats were randomized to control, milrinone, enalapril, or simendan groups. All compounds were administered via the drinking water for 312 days, at which time there was 80% mortality in the control group--the study's primary endpoint. The infarct sizes were similar across all groups. At endpoint, the mortality rates were: 63% (milrinone), 56% (enalapril) and 53% (simendan); the risk reductions were 25% (P = 0.04 vs. control) and 28% (P = 0.02 vs. control) with enalapril and simendan, respectively. Milrinone had no statistically significant effect on the survival rate. These findings suggest that, like enalapril, simendan improved survival in rats with healed myocardial infarction.

Levosimendan increases diastolic coronary flow in isolated guinea-pig heart by opening ATP-sensitive potassium channels

Levosimendan, a novel calcium sensitizer developed for the treatment of acute heart failure, is an inodilator that increases coronary flow. Because it was recently shown that levosimendan stimulates potassium current through K(ATP) channels in isolated rat arterial cells, our aim was to assess whether the levosimendan-induced increase in coronary flow is due to the opening of the K(ATP) channels in coronary smooth muscle. The effect of levosimendan on the diastolic coronary flow velocity (DCFV) was measured in the Langendorff perfused spontaneously beating guinea-pig heart in the absence and presence of glibenclamide. Pinacidil was used as a reference compound, and the protein kinase C inhibitor bisindolylmaleimide was used to study the dilatory effect of levosimendan when the K(ATP) channels in smooth muscle are not inhibited by PKC-dependent phosphorylation. Levosimendan (0.01-1 microM) increased DCFV concentration-dependently and was noncompetitively antagonized by 0.1 microM glibenclamide, whereas pinacidil was inhibited competitively by glibenclamide. In the presence of glibenclamide the positive inotropic and chronotropic effects of levosimendan were unaltered. The effect of bisindolylmaleimide and levosimendan on DCFV was additive. The results indicate that levosimendan induced coronary vasodilation through the opening of the K(ATP) channels. Levosimendan and pinacidil probably have different binding sites on the K(ATP) channels. The additive effect of bisindolylmaleimide and levosimendan on the increase of DCFV suggests that the latter binds to the unphosphorylated form of the channel.

Binding of levosimendan, a calcium sensitizer, to cardiac troponin C

Levosimendan is an inodilatory drug that mediates its cardiac effect by the calcium sensitization of contractile proteins. The target protein of levosimendan is cardiac troponin C (cTnC). In the current work, we have studied the interaction of levosimendan with Ca(2+)-saturated cTnC by heteronuclear NMR and small angle x-ray scattering. A specific interaction between levosimendan and the Ca(2+)-loaded regulatory domain of recombinant cTnC(C35S) was observed. The changes in the NMR spectra of the N-domain of full-length cTnC(C35S), due to the binding of levosimendan to the primary site, were indicative of a slow conformational exchange. In contrast, no binding of levosimendan to the regulatory domain of cTnC(A-Cys), where all the cysteine residues are mutated to serine, was detected. Moreover, it was shown that levosimendan was in fast exchange on the NMR time scale with a secondary binding site in the C-domain of both cTnC(C35S) and cTnC(A-Cys). The small angle x-ray scattering experiments confirm the binding of levosimendan to Ca(2+)-saturated cTnC but show no domain-domain closure. The experiments were run in the absence of the reducing agent dithiothreitol and the preservative sodium azide (NaN(3)), since we found that levosimendan reacts with these chemicals, commonly used for preparation of NMR protein samples.

Conformations of the regulatory domain of cardiac troponin C examined by residual dipolar couplings

Conformations of the regulatory domain of cardiac troponin C (cNTnC) were studied by means of residual dipolar couplings measured from samples dissolved in dilute liquid crystals. Changes in the main chain HN residual dipolar couplings revealed a conformational change in cNTnC due to the complexation with the second binding region (amino acids 148-163) of cardiac troponin I (cTnI). Formation of the complex is accompanied with a molecular realignment in the liquid crystal. The residual dipolar couplings measured for apo-cNTnC and the complex with TnI were in agreement with the values computed from the corresponding closed and open solution structures, whereas for the calcium-loaded conformation the correlation and quality factor were only modest. Ca2+-cNTnC may be subject to conformational exchange. The data support the model that cardiac troponin C functions as a calcium-dependent open-closed switch, such as the skeletal troponin C.

Calcium sensitivity enhancers

Patients suffering from acute decompensated heart failure, immediately after infarction, or late in the progression of heart failure, need short-term, positive inotropic support in their therapy. To date, drugs acting through cAMP are used to increase the contractile force of the heart of such patients, although it is well-known that these kind of drugs may trigger arrhythmias and as a result may worsen the long-term prognosis of the patients. Recently, levosimendan, a new drug acting through calcium sensitization of contractile proteins, has shed new light on inotropic therapy, and, importantly, has reduced mortality in acute heart failure patients. For this reason, this review focuses on calcium sensitizers and the mechanisms behind calcium sensitization. The compounds which have been selected for detailed consideration are limited only to positive inotropic compounds that produce calcium sensitization of contractile proteins. In addition, this review elucidates the differences between various calcium sensitizing mechanisms, and mainly focuses on the relaxation of cardiac muscle.

Further evidence for the cardiac troponin C mediated calcium sensitization by levosimendan: structure-response and binding analysis with analogs of levosimendan

Levosimendan, an inodilatory drug discovered using troponin C as a target protein, has a cardiac effect deriving from the calcium sensitization of contractile proteins. The aim of this study was to give further evidence that levosimendan binds to cardiac troponin C and that the binding involves amino acid residues on helixepsilon of the N-terminal domain of this calcium-binding protein. Nine organic molecules, obtained by chemical modification of levosimendan, were tested both for their calcium-dependent binding to troponin C and troponin complex affinity HPLC columns, and for their ability to increase the calcium sensitivity of myofilaments in cardiac skinned fibers. A good correlation between the calcium sensitization and the calcium-dependent binding to troponin complex (r=0.90) and to cardiac troponin C (r=0.91) for the analogs of levosimendan was shown. In addition, the effect of levosimendan on the calcium-induced conformational changes in native and point-mutated cTnC was studied. Cys84-->Ser, Asp87-->Lys and Asp88-->Ala point-mutated cTnC were shown to maintain a high affinity to calcium, but their Ca(2+)titration curves were not influenced by levosimendan as for the native protein. Finally, it was demonstrated that the NMR chemical shifts of the terminal methyl groups of Met47, Met81, and Met85 on calcium-saturated cTnC were changed after addition of levosimendan in water solution at pH 7.4. This effect was not seen when adding an analog of levosimendan, which did not bind to the troponin C affinity HPLC column and did not increase the calcium-induced tension in cardiac skinned fibers.

Regulation of total mitochondrial Ca2+ in perfused liver is independent of the permeability transition pore

Triggering of the permeability transition pore (PTP) in isolated mitochondria causes release of matrix Ca2+, ions, and metabolites, and it has been proposed that the PTP mediates mitochondrial Ca2+ release in intact cells. To study the role of the PTP in mitochondrial energy metabolism, the mitochondrial content of Ca2+, Mg2+, ATP, and ADP was determined in hormonally stimulated rat livers perfused with cyclosporin A (CsA). Stimulation of livers perfused in the absence of CsA with glucagon and phenylephrine induced an extensive uptake of Ca2+, Mg2+, and ATP plus ADP by the mitochondria, followed by a release on omission of hormones. In the presence of CsA, the PTP was fully inhibited, but neither the hormone-induced uptake of Ca2+, ATP, or ADP by mitochondria nor their release after washout of hormones was significantly changed. We conclude that the regulation of sustained changes in mitochondrial Ca2+ content induced by hormonal stimulation is independent of the PTP.

Structure of the 1-36 amino-terminal fragment of human phospholamban by nuclear magnetic resonance and modeling of the phospholamban pentamer

The structure of a 36-amino-acid-long amino-terminal fragment of phospholamban (phospholamban[1-36]) in aqueous solution containing 30% trifluoroethanol was determined by nuclear magnetic resonance. The peptide, which comprises the cytoplasmic domain and six residues of the transmembrane domain of phospholamban, assumes a conformation characterized by two alpha-helices connected by a turn. The residues of the turn are Ile18, Glu19, Met20, and Pro21, which are adjacent to the two phosphorylation sites Ser16 and Thr17. The proline is in a trans conformation. The helix comprising amino acids 22-36 is well determined (the root mean square deviation for the backbone atoms, calculated for a family of 18 nuclear magnetic resonance structures is 0.57 A). Recently, two molecular models of the transmembrane domain of phospholamban were proposed in which a symmetric homopentamer is composed of a left-handed coiled coil of alpha-helices. The two models differ by the relative orientation of the helices. The model proposed by,Simmerman et al. (H.K. Simmerman, Y.M. Kobayashi, J.M. Autry, and L.R. Jones, 1996, J. Biol. Chem. 271:5941-5946), in which the coiled coil is stabilized by a leucine-isoleucine zipper, is similar to the transmembrane pentamer structure of the cartilage oligomeric membrane protein determined recently by x-ray (V. Malashkevich, R. Kammerer, V Efimov, T. Schulthess, and J. Engel, 1996, Science 274:761-765). In the model proposed by Adams et al. (P.D. Adams, I.T. Arkin, D.M. Engelman, and A.T. Brunger, 1995, Nature Struct. Biol. 2:154-162), the helices in the coiled coil have a different relative orientation, i.e., are rotated clockwise by approximately 50 degrees. It was possible to overlap and connect the structure of phospholamban[1-36] derived in the present study to the two transmembrane pentamer models proposed. In this way two models of the whole phospholamban in its pentameric form were generated. When our structure was connected to the leucine-isoleucine zipper model, the inner side of the cytoplasmic domain of the pentamer (where the helices face one another) was lined by polar residues (Gln23, Gln26, and Asn30), whereas the five Arg25 side chains were on the outer side. On the contrary, when our structure was connected to the other transmembrane model, in the inner side of the cytoplasmic domain of the pentamer, the five Arg25 residues formed a highly charged cluster.

Structural determination of the acidic exopolysaccharide produced by a Pseudomonas sp. strain 1.15

Pseudomonas strain 1.15 was isolated from a freshwater biofilm and shown to produce considerable amounts of an acidic polysaccharide which was investigated by methylation analysis, NMR spectroscopy and ionspray mass spectrometry (ISMS). The polysaccharide was depolymerised by a bacteriophage-associated endoglucosidase and by autohydrolysis, and the resulting oligosaccharides were investigated by NMR spectroscopy and mass spectrometry. The resulting data showed that the parent repeating unit of the 1.15 exopolysaccharide (EPS) is a branched hexasaccharide. The main chain is constituted of the trisaccharide -->4)-alpha-L-Fucp-(1-->4)-alpha-L-Fucp-(1-->3)-beta-D-Glcp- (1--> and the side chain alpha-D-Galp-(1-->4)-beta-D-GlcAp-(1-->3)-alpha-D-Galp-(1-->is linked to O-3 of the first Fuc residue. The terminal non-reducing Gal carries a 1-carboxyethylidene acetal in the R configuration at the positions 4 and 6. Of the four different O-acetyl groups present in non-stoichiometric amounts, two were established to be on O-2 of the 3-linked Gal and on O-2 of the 4-linked Fuc.

Sensitivity of chondrocytes of growing cartilage to reactive oxygen species

Vascular invasion of calcified cartilage, during endochondral ossification, is initiated and sustained by invasive cells (endothelial cells and macrophages) which degrade the tissue by releasing lytic enzymes. Concurrently, reactive oxygen species (ROS) are also released by these cells and we hypothesize that ROS also contribute to the degradation of the tissue. As a preliminary approach to this problem, the antioxidant activities and the effect of ROS on hypertrophic cartilage and chondrocytes (HCs) were investigated. Compared to resting or articular chondrocytes, HCs exhibited higher catalase but lower SOD specific activities and lower PHGPx concentration, thus revealing a defence activity specific against H2O2. Moreover, dose-dependent depletion of ATP occurred after few minutes of exposure to ROS, and a long-term treatment (16 h incubation with ROS) promoted the release of LDH activity and a significant variation of the poly- to mono-unsaturated fatty acid ratio. Finally, the incubation of HCs with low ROS doses induced the release of sedimentable alkaline phosphatase activity (matrix vesicles). How the obtained results fit the in vivo occurring events is discussed.

Solution structure and main chain dynamics of the regulatory domain (Residues 1-91) of human cardiac troponin C

The three-dimensional structure of calcium-loaded regulatory, i.e. N-terminal, domain (1-91) of human cardiac troponin C (cNTnC) was determined by NMR in water/trifluoroethanol (91:9 v/v) solution. The single-calcium-loaded cardiac regulatory domain is in a "closed" conformation with comparatively little exposed hydrophobic surface. Difference distance matrices computed from the families of Ca2+-cNTnC, the apo and two-calcium forms of the skeletal TnC (sNTnC) structures reveal similar relative orientations for the N, A, and D helices. The B and C helices are closer to the NAD framework in Ca2+-cNTnC and in apo-sNTnC than in 2.Ca2+-sNTnC. However, there is an indication of a conformational exchange based on broad 15N resonances for several amino acids measured at several temperatures. A majority of the amides in the alpha-helices and in the calcium binding loop exhibit very fast motions with comparatively small amplitudes according to the Lipari-Szabo model. A few residues at the N and C termini are flexible. Data were recorded from nonlabeled and 15N-labeled samples, and backbone dynamics was investigated by 15N T1, T2, and heteronuclear nuclear Overhauser effect as well as by relaxation interference measurements.

Structural investigation of the exopolysaccharide produced by Pseudomonas flavescens strain B62--degradation by a fungal cellulase and isolation of the oligosaccharide repeating unit

Pseudomonas flavescens strain B62 (NCPPB 3063) is a recently described bacterium isolated from walnut blight cankers. This strain has been designated as the type strain of a Pseudomonas rRNA group-I species. Strain B62 produced a mixture of two exopolysaccharides, differing in weight average relative molecular mass and composition. Only the most abundant exopolysaccharide (90% by mass), corresponding to the one with the lower molecular mass, was investigated by use of methylation analysis, partial acid hydrolysis, and NMR spectroscopy. The polysaccharide was depolymerised by the action of the cellulase produced by Penicillum funiculosum and the oligosaccharide obtained, corresponding to the repeating unit, was characterised by NMR spectroscopy and ion-spray mass spectrometry. The repeating unit of the B62 exopolysaccharide is [structure in text] where X is glucose (75%) or mannose (25%), and Lac is lactate. The O-acetyl groups are present only on 75% of the repeating units, and they are linked to the C6 of the hexose residues in non-stoichiometric amounts.

Cellular UDP-glucose deficiency caused by a single point mutation in the UDP-glucose pyrophosphorylase gene

We previously isolated a mutant cell that is the only mammalian cell reported to have a persistently low level of UDP-glucose. In this work we obtained a spontaneous revertant whose UDP-glucose level lies between those found in the wild type and the mutant cell. The activity of UDP-glucose pyrophosphorylase (UDPG:PP), the enzyme that catalyzes the formation of UDP-glucose, was in the mutant 4% and in the revertant 56% of the activity found in the wild type cell. Sequence analysis of UDPG: PP cDNAs from the mutant cell showed one missense mutation, which changes amino acid residue 115 from glycine to aspartic acid. The substituted glycine is located within the largest stretch of strictly conserved residues among eukaryotic UDPG:PPs. The analysis of the cDNAs from the revertant cell indicated the presence of an equimolar mixture of the wild type and the mutated mRNAs, suggesting that the mutation has reverted in only one of the alleles. In summary, we demonstrate that the G115D substitution in the Chinese hamster UDPG:PP dramatically impairs its enzymatic activity, thereby causing cellular UDP-glucose deficiency.

Noninvasive in vivo quantitative assessment of fat content in human liver

BACKGROUND/AIMS

Since the introduction of ultrasonography, liver steatosis has become an increasingly frequent diagnosis. Both ultrasonography (US) and computerized tomography (CT) provide qualitative rather than quantitative assessment of fatty infiltration. The objective of this study was to develop a noninvasive method for the quantification of the hepatic fat content in vivo. A test object containing solutions with CT scan density (CTD) similar to normal liver ("liver-equivalent") or "fat-equivalent material" in variable proportions was prepared to measure patients with variable degrees of steatosis in vivo.

RESULTS

A linear correlation (r=0.99, p<0.001) linked CTD and the increasing percentage of fat-equivalent material. A CTD calibration curve was derived as a reference for the in vivo determinations. In 29 consecutive patients with steatosis diagnosed by histology, CTD was linearly correlated (r=0.83, p<0.001) with the hepatic fat content (HFC) expressed as percent of the whole liver, obtained by a computerized histomorphometric analysis. Based on the calibration curve obtained in 29 subjects who underwent liver biopsy, 38 additional consecutive steatotic patients were examined and the degree of hepatic fat content was calculated. The HFC was linearly correlated (r=-0.86, p<0.001) with the liver-to-spleen ratio.

CONCLUSIONS

We conclude that the use of test objects allows an accurate and reproducible noninvasive quantitative assessment of hepatic fat infiltration in humans. This technique may prove useful in the evaluation of the natural course and treatment of hepatic steatosis as well as in the assessment of donor livers prior to transplantation.

Organic solvent systems for 31P nuclear magnetic resonance analysis of lecithin phospholipids: applications to two-dimensional gradient-enhanced 1H-detected heteronuclear multiple quantum coherence experiments

31P NMR of lipid extracts is a reproducible, rapid, and nondegradative method for qualitative and quantitative analyses of phospholipid mixtures. This analysis, however, is hampered by the instability of the solvent system commonly used for NMR spectroscopy (CHCl3/ CH3OH/H2O-EDTA). In this work we have investigated the effects of several monophasic solvent mixtures to overcome this disadvantage. Among these mixtures we have selected a solution of triethylamine, dimethylformamide, and guanidinium chloride (Et3N/DMF-GH+) as the most efficient system. In this solvent the chemical shift dispersion of the 31P signals is about four times the frequency range observed in the standard chloroform-methanol-water system. Moreover, the stability of this solvent, as a monophasic system, allows easy reproducibility of the analysis. The use of two-dimensional 1H-31P gradient-enhanced heteronuclear multiple quantum coherence experiments can further exploit the higher resolution of the signals obtained with this solvent system for the structure elucidation of known and unidentified phospholipids.

Analysis of total lipid extracts from human liver by 13C and 1H nuclear magnetic resonance spectroscopy

Lipid extracts of liver tissue from normal donors and from patients with acute liver failure were analyzed by 13C NMR and 1H NMR at 9.4 T. The spectra allowed estimation of (i) the free fatty acid to total fatty acid chains ratio, (ii) the polyunsaturated to monounsaturated lipids ratio, (iii) the glycerophospholipids to triacylglycerols ratio, (iv) the total cholesterol to total fatty acids molar ratio, (v) the acylcholesterol to cholesterol ratio, (vi) the phosphatidylcholine to phosphatidylethanolamine molar ratio, and (vii) the unsaturation ratio of the fatty acid chains. The values obtained for normal livers agree with literature data on lipid composition obtained by other techniques. The two pathologic livers differ from the normal in the composition of some lipids and show a higher free fatty acid to total fatty acid chains ratio and a lower polyunsaturated to monounsaturated lipid ratio, a lower acylcholesterol to cholesterol ratio, and a lower phosphatidylcholine to phosphatidylethanolamine ratio, whereas the ratio of total cholesterol to fatty acids and the unsaturation ratio remained unchanged. The detailed assignment of the 13C NMR spectra of lipid extracts from normal and pathologic human liver may contribute to direct future research programs on 13C NMR spatially localized spectroscopy of the liver in vivo.

Detection and quantitation of phosphorus metabolites in crude tissue extracts by 1H and 31P NMR: use of gradient assisted 1H-31P HMQC experiments, with selective pulses, for the assignment of less abundant metabolites

The analysis of crude tissue extracts by NMR has proven to be of use in the study of metabolism due to the non-destructive and non-selective character of the technique. Lists of 1H and 31P NMR assignments of phosphorus metabolites in water solution at specified pH and ionic composition are of large general value but their usefulness may be limited when analysing complex mixtures of metabolites at low concentrations. In this work we report on the use of gradient-assisted proton detected multiple quantum 1H and 31P coherence experiments with selective pulses for the rapid and unambiguous assignments of some crowded regions in 1H and 31P spectra of crude extracts from rat liver. The amplitudes of the gradient episodes were calibrated to optimize the coherence transfer pathway between proton and phosphorus, and the delay for the evolution of the long-range coupling was calculated from values of 3JPH and 4JPH ranging from 1.4 to 7.5 Hz. Moreover, a selective 90 degrees Gaussian pulse on the 31P channel was introduced to increase the resolution in the F1-domain and make the method even faster. The procedure was then applied to unambiguously assign the ID 31P and 1H spectra of perchloric acid extracts of rat livers that had been stimulated with phenylephrine, dBcAMP and glucagon and thus detect changes in the concentration of less abundant metabolites such as phosphoenolpyruvate, UDP-glucose and AMP. The fact that the quantification of these metabolites by either 31P and 1H methods lead to different results is discussed, and the use of 1H NMR spectroscopy for the quantification of phosphorus metabolites whose signal are too weak or poorly resolved in a 31P spectrum is proposed.

Oxygen-derived free radical (ODFR) action on hyaluronan (HA), on two HA ester derivatives, and on the metabolism of articular chondrocytes

Oxygen-derived free radicals (ODFR) appear to be involved in the pathogenesis of arthritic disorders. In order to gain new insight on their role in the phenomenon and as a basis for a therapeutic approach, the effect of ODFR (produced by the xanthine oxidase-hypoxantine system) on hyaluronic acid, on two HA ester derivatives, and on pig articular chondrocytes was investigated. High M(r) HA (1.1 x 10(6)) and low M(r) HA (16 x 10(4)) were depolymerized by ODFR but the methyl and hydrocortisone esters of HA (HYAFF 2P50 and HYC13) turned out to be nearly unaffected. When articular chondrocytes were treated with ODFR, a rapid nucleoside triphosphate (NTP) depletion, a transient appearance of pyrophosphate (PPi), and an increase of phosphomonoester and diphosphodiester concentrations have been observed. The NTP depletion and the DPDE increase are related to the concentration of free radicals. Glyceraldehyde-3-phosphate accumulation during ODFR treatment suggests that ATP depletion can occur as a consequence of the blockage of glycolysis at the level of glyceraldehyde-3-P dehydrogenase. The hypothesis is presented that PPi can be produced from the pathway of the FAD-NAD (DPDE) biosynthesis and then either hydrolyzed by endogenous pyrophosphatases or precipitated in the form of insoluble calcium salts. Long-term treatment (16 h) with ODFR causes a loss of chondrocyte membrane integrity which can be revealed both by an increased free LDH activity and by the characteristic signal of free phospholipids in the 31P-NMR spectra. While high M(r) HA shows a significant protective activity for chondrocytes against ODFR action, low M(r) HA and ester derivatives do not. It is suggested that the therapeutic activity of HA ester derivatives can be ascribed to their in vivo hydrolysis products.

Proton MR spectroscopy in quantitative in vivo determination of fat content in human liver steatosis

To demonstrate that the lipid volume fraction in liver steatosis can be accurately estimated with in vivo hydrogen-1 magnetic resonance (MR) spectroscopy, the authors developed a calibration procedure based on in vitro MR spectroscopy of lipid extracts from steatotic liver specimens. The lipid volume fractions determined with the calibration procedure were compared with the results of histomorphometry and with calibrated computed tomographic (CT) data. The volume fraction of fat determined with MR spectroscopy was in good agreement with the CT results, whereas histomorphometry underestimated the amount of hepatic fat. The results indicate that determination of the fat volume fraction in steatotic liver can be achieved noninvasively with MR spectroscopy.

Binding of a new Ca2+ sensitizer, levosimendan, to recombinant human cardiac troponin C. A molecular modelling, fluorescence probe, and proton nuclear magnetic resonance study

The binding of a new calcium sensitizer, levosimendan, to human cardiac troponin C (cTnC) is described. Fluorescence studies done on dansylated recombinant human cTnC and a site-directed mutant showed that levosimendan modulated the calcium-induced conformational change in cTnC, and revealed the role of Asp-88 in the binding of the drug to the NH2-terminal domain of cTnC. Furthermore, NMR studies performed on the NH2-terminal fragment of cTnC showed a spatial proximity between levosimendan and Met81, Met85, and Phe77 in the drug-protein complex. These data were used to build an optimized model of the drug-protein complex, in which levosimendan binds cTnC at the hydrophobic pocket of the NH2-terminal domain. The role of the binding of levosimendan to cTnC in the pharmacological action of this drug in vivo is discussed.

Changed relation between phosphorylation potential and left ventricular developed pressure in guinea pig hearts during ischemia-reperfusion

The concentrations of phosphocreatine and inorganic phosphate in the cytosol, the cytosolic pH, and the left ventricular developed pressure were measured in isolated guinea pig heart, before and during 35 min normothermic ischemia and during the reperfusion. The phosphorylation potential and its ratio to the left ventricular developed pressure were calculated. The ratio was increased after reperfusion, indicating a change in the regulation of energy supply and demand, with a relatively higher work efficiency at a lower phosphorylation potential. In fact, after 35 min ischemia, the left ventricular developed pressure recovered to 60 +/- 8%, while the phosphorylation potential recovered to 25 +/- 10% of their original values, whereas the heart rate returned to its pre-ischemic values. This apparent inconsistency is discussed in terms of an increased Ca2+ sensitivity of the contractile system after ischemia.

Effect of phenylephrine on the compartmentation of inorganic phosphate in perfused rat liver during gluconeogenesis and urea synthesis: a 31P-n.m.r.-spectroscopic study

The transport of Pi between the cytosol and the mitochondria was investigated in perfused rat liver stimulated with phenylephrine and metabolic precursors of glucose and urea: pyruvate, lactate, NH4+ and ornithine. The relative concentrations of phosphorus metabolites in the liver were measured by 31P-n.m.r. spectroscopy. When added simultaneously, phenylephrine and the precursors induced a decrease in the Pi level which in 4-5 min reached a new steady state at 73% of the control level. After 5 min or more of stimulation the ATP level had also decreased. When the stimulation ended, Pi and ATP returned to their initial levels within 15 min. In mitochondria isolated after 5 min of stimulation, Pi was increased more than 2-fold as compared with control mitochondria and, in addition, an accumulation of Pi from the perfusion buffer into the liver was observed. Phenylephrine by itself did not cause any significant changes in the ATP or Pi levels, whereas the glucose and urea precursors in the absence of phenylephrine induced a 9% decrease in Pi, while ATP remained constant. The Pi content of mitochondria isolated under these conditions was not significantly increased as compared with control mitochondria. These results showed that Pi accumulated into the mitochondria by a mechanism possibly involving exchange for malate, and that a major part of the intramitochondrial Pi was invisible by n.m.r.

Energy metabolism, replicative ability, intracellular calcium concentration, and ionic channels of horse articular chondrocytes

Some aspects of the physiology of chondrocytes from horse articular cartilage were studied, since this animal model can be helpful in understanding arthritic processes. The replicative ability of articular chondrocytes, measured by the incorporation of [3H]thymidine, and their capacity of proteoglycan production, evaluated from the incorporation of [35S] sulfate, are very low. In addition, these cells do not differentiate in vitro as shown by the constant specific activity of alkaline phosphatase measured at different times in culture. Two types of potassium channels were identified by patch clamp experiments in the cell-attached configuration, one characterized by a conductance of 40 pS and the other of 100 pS. No active K+ channels were found at Vpip = 0. It was shown by Fura-2 experiments that the low replicative ability is paralleled by a modest variation of the intracellular calcium concentration after a mitogenic stimulus. 31P NMR experiments, both on slices of whole articular cartilage and on isolated cells, demonstrate that chondrocytes derive their energy mainly from the glycolytic pathway.

Analysis of lipids in crude extracts by 13C nuclear magnetic resonance

Phospho- and glycolipids with mono- or polyunsaturated fatty acid chains, free and acylated steroids, carotenes and carotenoids, chlorophylls, and related pheophytins were detected in crude extracts by NMR spectroscopy without any need for prior separation. A broad range of molecules belonging to different lipid classes could be identified in one-dimensional 13C NMR spectra obtained by applying a polarization transfer pulse sequence (DEPT 135 degrees). Directly detected or 1H-detected two-dimensional heterocorrelated NMR experiments were performed to facilitate the assignment of peaks arising from carotenoids, unsaturated fatty acid chains, and chlorophylls. 13C NMR data of crude lipid extracts from the macroalagae Ulva rigida and Fucus virsoides are shown to yield an informative overview of their lipid content. NMR is thus proposed as a simple, nonselective, and nondestructive technique for the first screening of the main lipid classes in complex lipid mixtures.

Hyaluronan can be protected from free-radical depolymerisation by 2,6-diisopropylphenol, a novel radical scavenger

The scavenging effect of 2,6-diisopropylphenol on hydroxy radicals produced by xanthine oxidase was assessed by evaluating the in vitro depolymerisation of hyaluronan in artificial synovial fluid by size-exclusion chromatography. After 1 hour, the number-average molecular weight of hyaluronan remained unchanged (100%) with 2,6-diisopropylphenol, whereas it dropped to 90% with methylprednisolone added, to 55% with the antioxidant 2,6-tert-butyl-4-methylphenol added, and to 10% of its initial value in the absence of scavenger.

1H NMR spectroscopic studies of lipid extracts from human fatty liver

Lipid extracts of biopsy samples from normal and non-alcohol-induced fatty human liver were studied by 1H-NMR at 200 MHz. Spectra of the lipid extracts from 10 mg samples were obtained in 6 min with routine acquisition parameters and allowed the calculation of the phosphatidylcholine to total fatty acyl chain ratio, the cholesterol to total fatty acyl chain ratio, the average fatty acyl chain length, the unsaturation ratio and the acylated glycerol to total fatty acyl chain ratio. The data suggest that lipids with a higher ratio of de novo synthesized fatty acyl chains are stored in non-alcohol-induced fatty liver. NMR lipid analysis appears to be a reliable method for the rapid assessment of hepatic lipid composition on bioptic specimens.

Inhibition of lipid peroxidation in isolated rat liver mitochondria by the general anaesthetic propofol

The effect of the general anaesthetic propofol (2,6-diisopropylphenol) on lipid peroxidation in rat liver mitochondria was assessed with the thiobarbituric acid (TBA) assay. Propofol was shown to inhibit the accumulation of TBA-reactive compounds after initiation of radical production by the addition of the ADP-Fe2+ complex. Analysis of kinetics showed that propofol caused a concentration-dependent delay as well as a decrease in the rate of the peroxidation process. 1H-NMR spectra of mitochondrial lipid extracts indicated that 95% of the added propofol remained intact after 30 min incubation under conditions of low oxidative stress. The ESR spectrum of propofol incubated in the presence of EDTA-Fe2+ and H2O2 as initiators of radical production showed a radical that was most likely a decomposition product of the primary phenoxy radical of propofol. It is concluded that (a) propofol acts as a chain reaction-breaking antioxidant by forming a stable radical and (b) propofol does not seem to be metabolized in mitochondria in vitro.

31P NMR studies of resting zone cartilage from growth plate

31P NMR of superfused resting cartilage demonstrated the presence of phosphocreatine in chondrocytes. Changes in pH and in the NTP level were followed during carbon source starvation. From 31P spectra of perchloric acid extracts, phosphoethanolamine, phosphocholine, and the corresponding glycerol diesters were identified as the major phosphomonoester and phosphodiester components.

Energy state of chondrocytes assessed by 31P-NMR studies of preosseous cartilage

The energy state of resting and hypertrophic chondrocytes from growth plate was studied by 31P-NMR spectroscopy of superfused cartilage slices. The presence of phosphocreatine was demonstrated in both cell types, using a repetition time of 3 s. By comparing the decline in the nucleoside triphosphate level after adding blockers of the glycolysis or of the mitochondrial respiration, it was deduced that resting and hypertrophic chondrocytes use both metabolic pathways for energy production, but the glycolysis dominates. Hypertrophic cells rely more on the mitochondrial respiration than the resting cells.

1H-NMR studies of lipid extracts of rat liver mitochondria

Lipid extracts of rat liver mitochondria were studied by 1H-NMR at 200 MHz. Each spectrum, obtained in 6 min with routine acquisition parameters, allowed the estimation of the phosphatidylcholine/phosphatidylethanolamine ratio, the cholesterol/total lipid molar ratio, the average fatty acid length, the unsaturation ratio and the oxidation state of the ubiquinone/ubiquinol couple. 1H-NMR spectroscopy was also used to analyze structural changes of the lipids following peroxidation. In model liposomes subjected to enzymatic peroxidation the appearance of hydroperoxides and conjugated double bonds were detected, whereas in mitochondria no such changes were seen even after a period of relatively high oxidative stress. This suggests that the systems for protection against oxidative damage in mitochondria are able to keep the amount of peroxidation products below the detection limit of the technique.

Modification of plasma membrane of differentiating preosseous chondrocytes: evidence for a degradative process in the mechanism of matrix vesicle formation

Chondrocytes of the growth plate are differentiating cells. Their evolution leads to matrix vesicle formation and to cartilage mineralization. This is an in vitro study of the plasma membrane of chondrocytes at two differentiation stages. Differences in protein and glycoprotein components, increased membrane fluidity, and responsiveness to PTH indicate that hypertrophic ("ossifying") chondrocytes possess a plasma membrane widely different from that of resting chondrocytes. Their plasma membrane is particularly enriched in alkaline phosphatase (Mr 70K). Purified matrix vesicles contain the 70K form of alkaline phosphatase, but a 50K species is also detectable, a signal of degradative process. In fact, proteins and glycoproteins of matrix vesicles are less numerous than those of cell plasma membranes. It is suggested that, in vivo, matrix vesicle formation may be mediated by Ca2(+)-activated neutral proteases.

Possible mechanism of inhibition of cartilage alkaline phosphatase by insulin

The inhibition of alkaline phosphatase by insulin is a finding reported by many researchers but the mechanism of this inhibition has not been studied. Since alkaline phosphatase is an important factor in the mechanism of calcification and an impairment of mineralisation has been observed in diabetes mellitus, a study was carried out to assess the effect of the hormone on alkaline phosphatase measured in chondrocytes, in matrix vesicles and in a purified enzyme preparation. Enzyme activity was inhibited by insulin. The lowest active concentration was 10(-6) M and maximal inhibition was obtained at about 10(-4) M. The inhibition is of the uncompetitive type. Full recovery of the hormone-inhibited enzyme was obtained with 10(-4) M 2-mercaptoethanol. Data suggest direct interaction between the alkaline phosphatase and insulin molecules, involving either disulfide cross linkages or the metal chelating activity of insulin.

Biochemical and immunohistochemical evidence that in cartilage an alkaline phosphatase is a Ca2+-binding glycoprotein

A glycoprotein that exhibits alkaline phosphatase activity and binds Ca2+ with high affinity has been extracted and purified from cartilage matrix vesicles by fast protein liquid chromatography. Antibodies against this glycoprotein were used to analyze its distribution in chondrocytes and in the matrix of calcifying cartilage. Under the light microscope, using immunoperoxidase or immunofluorescence techniques, the glycoprotein is localized in chondrocytes of the resting zone. At this level, the extracellular matrix does not show any reaction. In the cartilage plate, between the proliferating and the hypertrophic region, a weak immune reactivity is seen in the cytoplasm, whereas in the intercolumnar matrix the collagen fibers appear clearly stained. Stained granular structures, distributed with a pattern similar to that of matrix vesicles, are also visible. Calcified matrix is the most stained area. These results were confirmed under the electron microscope using both immunoperoxidase and protein A-gold techniques. In parallel studies, enzyme activity was also analyzed by histochemical methods. Whereas resting cartilage, the intercellular matrix of the resting zone, and calcified matrix do not exhibit any enzyme activity, the zones of maturing and hypertrophic chondrocytes are highly reactive. Some weak reactivity is also shown by chondrocytes of the resting zone. The observation that this glycoprotein (which binds Ca2+ and has alkaline phosphatase activity) is synthesized in chondrocytes and is exported to the extracellular matrix at the time when calcification begins, suggests that it plays a specific role in the process of calcification.