Extracellular flux analysis in intact cardiac tissue slices-A novel tool to investigate cardiac substrate metabolism in mouse myocardium

AIM

Cardiac pathologies are accompanied by alterations in substrate metabolism, and extracellular flux analysis is a standard tool to investigate metabolic disturbances, especially in immortalized cell lines. However, preparations of primary cells, such as adult cardiomyocytes require enzymatic dissociation and cultivation affecting metabolism. Therefore, we developed a flux analyzer-based method for the assessment of substrate metabolism in intact vibratome-sliced mouse heart tissue.

METHODS

Oxygen consumption rates were determined using a Seahorse XFe24-analyzer and "islet capture plates." We demonstrate that tissue slices are suitable for extracellular flux analysis and metabolize both free fatty acids (FFA) and glucose/glutamine. Functional integrity of tissue slices was proven by optical mapping-based assessment of action potentials. In a proof-of-principle approach, the sensitivity of the method was tested by analyzing substrate metabolism in the remote myocardium after myocardial infarction (I/R).

RESULTS

Here, I/R increased uncoupled OCR compared with sham animals indicating a stimulated metabolic capacity. This increase was caused by a higher glucose/glutamine metabolism, whereas FFA oxidation was unchanged.

CONCLUSION

In conclusion, we describe a novel method to analyze cardiac substrate metabolism in intact cardiac tissue slices by extracellular flux analysis. The proof-of-principle experiment demonstrated that this approach has a sensitivity allowing the investigation of pathophysiologically relevant disturbances in cardiac substrate metabolism.

Cardioprotective efficacy of limb remote ischemic preconditioning in rats: discrepancy between meta-analysis and a three-centre in vivo study

AIMS

Remote ischemic preconditioning (RIPC) is a robust cardioprotective intervention in preclinical studies. To establish a working and efficacious RIPC protocol in our laboratories, we performed randomized, blinded in vivo studies in three study centres in rats, with various RIPC protocols. To verify that our experimental settings are in good alignment with in vivo rat studies showing cardioprotection by limb RIPC, we performed a systematic review and meta-analysis. In addition, we investigated the importance of different study parameters.

METHODS AND RESULTS

Male Wistar rats were subjected to 20 to 45 min cardiac ischemia followed by 120 min reperfusion with or without preceding RIPC by 3 or 4×5-5 min occlusion/reperfusion of one or two femoral vessels by clamping, tourniquet, or pressure cuff. RIPC did not reduce IS, microvascular obstruction, or arrhythmias at any study centres. Systematic review and meta-analysis focusing on in vivo rat models of myocardial ischemia/reperfusion injury with limb RIPC showed that RIPC reduces IS by 21.28% on average. In addition, the systematic review showed methodological heterogeneity and insufficient reporting of study parameters in a high proportion of studies.

CONCLUSION

We report for the first time the lack of cardioprotection by RIPC in rats, assessed in individually randomized, blinded in vivo studies, involving three study centres, using different RIPC protocols. These results are in discrepancy with the meta-analysis of similar in vivo rat studies, however, no specific methodological reason could be identified by systematic review, probably due to the overall insufficient reporting of several study parameters that did not improve over the past two decades. These results urge for publication of more well-designed and well-reported studies, irrespective of the outcome, which are required for preclinical reproducibility, and the development of clinically translatable cardioprotective interventions.

Mitochondrial Telomerase Reverse Transcriptase Protects from Myocardial Ischemia/reperfusion Injury by Improving Complex I Composition and Function

Background: The catalytic subunit of telomerase, Telomerase Reverse Transcriptase (TERT) has protective functions in the cardiovascular system. TERT is not only present in the nucleus, but also in mitochondria. However, it is unclear whether nuclear or mitochondrial TERT is responsible for the observed protection and appropriate tools are missing to dissect this. Methods: We generated new mouse models containing TERT exclusively in the mitochondria (mitoTERT mice) or the nucleus (nucTERT mice) to finally distinguish between the functions of nuclear and mitochondrial TERT. Outcome after ischemia/reperfusion, mitochondrial respiration in the heart as well as cellular functions of cardiomyocytes, fibroblasts, and endothelial cells were determined. Results: All mice were phenotypically normal. While respiration was reduced in cardiac mitochondria from TERT-deficient and nucTERT mice, it was increased in mitoTERT animals. The latter also had smaller infarcts than wildtype mice, whereas nucTERT animals had larger infarcts. The decrease in ejection fraction after one, two and four weeks of reperfusion was attenuated in mitoTERT mice. Scar size was also reduced and vascularization increased. Mitochondrial TERT protected a cardiomyocyte cell line from apoptosis. Myofibroblast differentiation, which depends on complex I activity, was abrogated in TERT-deficient and nucTERT cardiac fibroblasts and completely restored in mitoTERT cells. In endothelial cells, mitochondrial TERT enhanced migratory capacity and activation of endothelial NO synthase. Mechanistically, mitochondrial TERT improved the ratio between complex I matrix arm and membrane subunits explaining the enhanced complex I activity. In human right atrial appendages, TERT was localized in mitochondria and there increased by remote ischemic preconditioning. The Telomerase activator, TA-65 evoked a similar effect in endothelial cells, thereby increasing their migratory capacity, and enhanced myofibroblast differentiation. Conclusions: Mitochondrial, but not nuclear TERT, is critical for mitochondrial respiration and during ischemia/reperfusion injury. Mitochondrial TERT improves complex I subunit composition. TERT is present in human heart mitochondria, and remote ischemic preconditioning increases its level in those organelles. TA-65 has comparable effects ex vivo and improves migratory capacity of endothelial cells and myofibroblast differentiation. We conclude that mitochondrial TERT is responsible for cardioprotection and its increase could serve as a therapeutic strategy.

Recurrent de novo missense variants in GNB2 can cause syndromic intellectual disability

PURPOSE

Binding proteins (G-proteins) mediate signalling pathways involved in diverse cellular functions and comprise Gα and Gβγ units. Human diseases have been reported for all five Gβ proteins. A de novo missense variant in GNB2 was recently reported in one individual with developmental delay/intellectual disability (DD/ID) and dysmorphism. We aim to confirm GNB2 as a neurodevelopmental disease gene, and elucidate the GNB2-associated neurodevelopmental phenotype in a patient cohort.

METHODS

We discovered a GNB2 variant in the index case via exome sequencing and sought individuals with GNB2 variants via international data-sharing initiatives. In silico modelling of the variants was assessed, along with multiple lines of evidence in keeping with American College of Medical Genetics and Genomics guidelines for interpretation of sequence variants.

RESULTS

We identified 12 unrelated individuals with five de novo missense variants in GNB2, four of which are recurrent: p.(Ala73Thr), p.(Gly77Arg), p.(Lys89Glu) and p.(Lys89Thr). All individuals have DD/ID with variable dysmorphism and extraneurologic features. The variants are located at the universally conserved shared interface with the Gα subunit, which modelling suggests weaken this interaction.

CONCLUSION

Missense variants in GNB2 cause a congenital neurodevelopmental disorder with variable syndromic features, broadening the spectrum of multisystem phenotypes associated with variants in genes encoding G-proteins.

4-hydroxytamoxifen does not deteriorate cardiac function in cardiomyocyte-specific MerCreMer transgenic mice

Conditional, cell-type-specific transgenic mouse lines are of high value in cardiovascular research. A standard tool for cardiomyocyte-restricted DNA editing is the αMHC-MerCreMer/loxP system. However, there is an ongoing debate on the occurrence of cardiac side effects caused by unspecific Cre activity or related to tamoxifen/oil overload. Here, we investigated potential adverse effects of DNA editing by the αMHC-MerCreMer/loxP system in combination with a low-dose treatment protocol with the tamoxifen metabolite 4-hydroxytamoxifen (OH-Txf). αMHC-MerCreMer mice received intraperitoneally OH-Txf (20 mg/kg) for 5 or 10 days. These treatment protocols were highly efficient to induce DNA editing in adult mouse hearts. Multi-parametric magnetic resonance imaging revealed neither transient nor permanent effects on cardiac function during or up to 19 days after 5 day OH-Txf treatment. Furthermore, OH-Txf did not affect cardiac phosphocreatine/ATP ratios assessed by in vivo 31P MR spectroscopy, indicating no Cre-mediated side effects on cardiac energy status. No MRI-based indication for the development of cardiac fibrosis was found as mean T1 relaxation time was unchanged. Histological analysis of myocardial collagen III content after OH-Txf confirmed this result. Last, mean T2 relaxation time was not altered after Txf treatment suggesting no pronounced cardiac lipid accumulation or tissue oedema. In additional experiments, cardiac function was assessed for up to 42 days to investigate potential delayed side effects of OH-Txf treatment. Neither 5- nor 10-day treatment resulted in a depression of cardiac function. Efficient cardiomyocyte-restricted DNA editing that is free of unwanted side effects on cardiac function, energetics or fibrosis can be achieved in adult mice when the αMHC-MerCreMer/loxP system is activated by the tamoxifen metabolite OH-Txf.

Cardiac Hyaluronan Synthesis Is Critically Involved in the Cardiac Macrophage Response and Promotes Healing After Ischemia Reperfusion Injury

RATIONALE

Immediate changes in the ECM (extracellular matrix) microenvironment occur after myocardial ischemia and reperfusion (I/R) injury.

OBJECTIVE

Aim of this study was to unravel the role of the early hyaluronan (HA)-rich ECM after I/R.

METHODS AND RESULTS

Genetic deletion of Has2 and Has1 was used in a murine model of cardiac I/R. Chemical exchange saturation transfer imaging was adapted to image cardiac ECM post-I/R. Of note, the cardiac chemical exchange saturation transfer signal was severely suppressed by Has2 deletion and pharmacological inhibition of HA synthesis 24 hours after I/R. Has2 KO ( Has2 deficient) mice showed impaired hemodynamic function suggesting a protective role for endogenous HA synthesis. In contrast to Has2 deficiency, Has1-deficient mice developed no specific phenotype compared with control post-I/R. Importantly, in Has2 KO mice, cardiac macrophages were diminished after I/R as detected by ¹⁹F MRI (magnetic resonance imaging) of perfluorcarbon-labeled immune cells, Mac-2/Galectin-3 immunostaining, and FACS (fluorescence-activated cell sorting) analysis (CD45⁺CD11b⁺Ly6G^-CD64⁺F4/80⁺cells). In contrast to macrophages, cardiac Ly6C^high and Ly6C^low monocytes were unaffected post-I/R compared with control mice. Mechanistically, inhibition of HA synthesis led to increased macrophage apoptosis in vivo and in vitro. In addition, α-SMA (α-smooth muscle actin)-positive cells were reduced in the infarcted myocardium and in the border zone. In vitro, the myofibroblast response as measured by Acta2 mRNA expression was reduced by inhibition of HA synthesis and of CD44 signaling. Furthermore, Has2 KO fibroblasts were less able to contract collagen gels in vitro. The effects of HA/CD44 on fibroblasts and macrophages post-I/R might also affect intercellular cross talk because cardiac fibroblasts were activated by monocyte/macrophages and, in turn, protected macrophages from apoptosis.

CONCLUSIONS

Increased HA synthesis contributes to postinfarct healing by supporting macrophage survival and by promoting the myofibroblast response. Additionally, imaging of cardiac HA by chemical exchange saturation transfer post-I/R might have translational value.

IGF1 Treatment Improves Cardiac Remodeling after Infarction by Targeting Myeloid Cells

Insulin-like growth factor 1 (IGF1) is an anabolic hormone that controls the growth and metabolism of many cell types. However, IGF1 also mediates cardio-protective effects after acute myocardial infarction (AMI), but the underlying mechanisms and cellular targets are not fully understood. Here we demonstrate that short-term IGF1 treatment for 3 days after AMI improved cardiac function after 1 and 4 weeks. Regional wall motion was improved in ischemic segments, scar size was reduced, and capillary density increased in the infarcted area and the border zone. Unexpectedly, inducible inactivation of the IGF1 receptor (IGF1R) in cardiomyocytes did not attenuate the protective effect of IGF1. Sequential cardiac transcriptomic analysis indicated an altered myeloid cell response in the acute phase after AMI, and, notably, myeloid-cell Igf1r^-/- mice lost the protective IGF1 function after I/R. In addition, IGF1 induced an M2-like anti-inflammatory phenotype in bone marrow-derived macrophages and enhanced the number of anti-inflammatory macrophages in heart tissue on day 3 after AMI in vivo. In summary, modulation of the acute inflammatory phase after AMI by IGF1 represents an effective mechanism to preserve cardiac function after I/R.

Echocardiographic Analysis of Cardiac Function after Infarction in Mice: Validation of Single-Plane Long-Axis View Measurements and the Bi-Plane Simpson Method

Although echocardiography is commonly used to analyze cardiac function in small animal models of cardiac remodeling after myocardial infarction, the different echocardiographic methods are validated poorly. End-diastolic volume, end-systolic volume and ejection fraction were analyzed using either standard single-plane analysis from parasternal long-axis B-mode views (PSLAX) or the bi-plane Simpson method (using PSLAX and three short-axis views) and validated using magnetic resonance imaging as standard. Ejection fraction measured by PSLAX was moderately correlated with a coefficient of R² = 0.49. The standard deviation of residuals was 9.91. Simpson analysis revealed an improved correlation coefficient of R² = 0.77 and a reduction in standard deviation of residuals by 45% (5.45 vs. 9.92, p = 0.014). Subgroup analysis revealed that the high variation in PSLAX is due to changes in ventricular geometry after myocardial infarction. Our results indicate that the bi-plane Simpson method is advantageous for the assessment of cardiac function after myocardial infarction.

Titin-Based Cardiac Myocyte Stiffening Contributes to Early Adaptive Ventricular Remodeling After Myocardial Infarction

Rationale:

Myocardial infarction (MI) increases the wall stress in the viable myocardium and initiates early adaptive remodeling in the left ventricle to maintain cardiac output. Later remodeling processes include fibrotic reorganization that eventually leads to cardiac failure. Understanding the mechanisms that support cardiac function in the early phase post MI and identifying the processes that initiate transition to maladaptive remodeling are of major clinical interest.

Objective:

To characterize MI-induced changes in titin-based cardiac myocyte stiffness and to elucidate the role of titin in ventricular remodeling of remote myocardium in the early phase after MI.

Methods and Results:

Titin properties were analyzed in Langendorff-perfused mouse hearts after 20-minute ischemia/60-minute reperfusion (I/R), and mouse hearts that underwent ligature of the left anterior descending coronary artery for 3 or 10 days. Cardiac myocyte passive tension was significantly increased 1 hour after ischemia/reperfusion and 3 and 10 days after left anterior descending coronary artery ligature. The increased passive tension was caused by hypophosphorylation of the titin N2-B unique sequence and hyperphosphorylation of the PEVK (titin domain rich in proline, glutamate, valine, and lysine) region of titin. Blocking of interleukine-6 before left anterior descending coronary artery ligature restored titin-based myocyte tension after MI, suggesting that MI-induced titin stiffening is mediated by elevated levels of the cytokine interleukine-6. We further demonstrate that the early remodeling processes 3 days after MI involve accelerated titin turnover by the ubiquitin–proteasome system.

Conclusions:

We conclude that titin-based cardiac myocyte stiffening acutely after MI is partly mediated by interleukine-6 and is an important mechanism of remote myocardium to adapt to the increased mechanical demands after myocardial injury.

Wheat germ agglutinin staining as a suitable method for detection and quantification of fibrosis in cardiac tissue after myocardial infarction

The quantification of fibrotic tissue is an important task in the analysis of cardiac remodeling. The use of established fibrosis staining techniques is limited on frozen cardiac tissue sections due to a reduced color contrast compared to paraffin embedded sections. We therefore used FITC-labeled wheat germ agglutinin (WGA), which marks fibrotic tissue in comparable quality as the established picrosirius red (SR) staining, for the staining of post myocardial infarction scar tissue. The fibrosis amount was quantified in a histogram-based approach using the non-commercial image processing program ImageJ. Our results clearly demonstrate that WGA-FITC is a suitable marker for cardiac fibrosis in frozen tissue sections. In combination with the histogram-based analysis, this new quantification approach is i) easy and fast to perform; ii) suitable for raw frozen tissue sections; and iii) allows the use of additional antibodies in co-immunostaining.

Pharmacological options to protect the aged heart from ischemia and reperfusion injury by targeting the PKA-BK(Ca) signaling pathway

The beneficial effects of many cardioprotective strategies including ischemic or pharmacological conditioning are reduced in the aged heart. The underlying reason(s) for the age-dependent loss of cardioprotection is unclear. Recently, we demonstrated that protein kinase A (PKA) dependent cardioprotection is lost in the aged heart. However, activation of large-conductance Ca(2+)-sensitive K(+) (BK(Ca)) channels, a putative PKA downstream target, initiated cardioprotection also in the aged heart. Therefore, we aimed to investigate whether 1) BK(Ca) channels are critically involved in PKA activation induced cardioprotection and 2) the age-dependent loss of cardioprotection is caused by differences in PKA regulation. Using an in vivo rat model with regional myocardial ischemia, we treated young (2-4 months) and aged (22-24 months) Wistar rats with PKA activator forskolin, BK(Ca) channel activator NS1619 and/or BK(Ca) channel blocker iberiotoxin. Forskolin induced infarct size reduction was 1) age-dependent and 2) prevented by iberiotoxin. The effect of forskolin on myocardial PKA activity was comparable in young and aged animals. In addition, NS1619 initiated cardioprotection also in the aged heart both when administered before ischemia and during early reperfusion phase. Activation of BK(Ca) channels is critically involved in forskolin induced cardioprotection. The age-dependency of forskolin induced cardioprotection is not caused by age-dependent differences in PKA activation. Pharmacological targeting of BK(Ca) channels before or after myocardial ischemia is a promising therapeutic strategy to protect the aged heart from ischemia and reperfusion injury.

Helium-induced cardioprotection of healthy and hypertensive rat myocardium in vivo

Helium protects healthy myocardium against ischemia/reperfusion injury by early and late preconditioning (EPC, LPC) and postconditioning (PostC). We investigated helium-induced PostC of the hypertensive heart and enhancement by addition of LPC and EPC. We also investigated involvement of signaling kinases glycogen synthase kinase 3 beta (GSK-3β) and protein kinase C-epsilon (PKC-ε). To assess myocardial cell damage, we performed infarct size measurements in healthy Wistar Kyoto (WKY rats, n=8-9) and Spontaneous Hypertensive rats (SHR, n=8-9) subjected to 25 min ischemia and 120 min reperfusion. Rats inhaled 70% helium for 15 min after index ischemia (PostC), combined with 15 min helium 24h prior to index ischemia (LPC+PostC), a triple intervention with additional 3 short cycles of 5 min helium inhalation shortly before ischemia (EPC+LPC+PostC), or no further treatment. In WKY rats, PostC reduced infarct size from 46 ± 2% (mean ± S.E.M) in the control group to 29 ± 2%. LPC+PostC or EPC+LPC+PostC reduced infarct sizes to a similar extent (30 ± 3% and 32 ± 2% respectively). In SHR, EPC+LPC+PostC reduced infarct size from 53 ± 3% in control to 39 ± 3%, while PostC or LPC+PostC alone were not protective; infarct size 48 ± 4% and 44 ± 4%, respectively. Neither PostC in WKY rats nor EPC+LPC+PostC in SHR was associated with an increase in phosphorylation of GSK-3β and PKC-ε after 15 min of reperfusion. Concluding, a triple intervention of helium conditioning results in cardioprotection in SHR, whereas a single intervention does not. In WKY rats, the triple intervention does not further augment protection. Helium conditioning is not associated with a mechanism involving GSK-3β and PKC-ε.

Cyclosporine A administered during reperfusion fails to restore cardioprotection in prediabetic Zucker obese rats in vivo

BACKGROUND AND AIMS

Hyperglycaemia blocks sevoflurane-induced postconditioning, and cardioprotection in hyperglycaemic myocardium can be restored by inhibition of the mitochondrial permeability transition pore (mPTP). We investigated whether sevoflurane-induced postconditioning is also blocked in the prediabetic heart and if so, whether cardioprotection could be restored by inhibiting mPTP.

METHODS AND RESULTS

Zucker lean (ZL) and Zucker obese (ZO) rats were assigned to one of seven groups. Animals underwent 25 min of ischaemia and 120 min of reperfusion. Control (ZL-/ZO Con) animals were not further treated. postconditioning groups (ZL-/ZO Sevo-post) received sevoflurane for 5 min starting 1min prior to the onset of reperfusion. The mPTP inhibitor cyclosporine A (CsA) was administered intravenously in a concentration of 5 (ZO CsA and ZO CsA+Sevo-post) or 10 mg/kg (ZO CsA10+Sevo-post) 5 min before the onset of reperfusion. At the end of reperfusion, infarct sizes were measured by TTC staining. Blood samples were collected to measure plasma levels of insulin, cholesterol and triglycerides. Sevoflurane postconditioning reduced infarct size in ZL rats to 35±12% (p<0.05 vs. ZL Con: 60±6%). In ZO rats sevoflurane postconditioning was abolished (ZO Sevo-post: 59±12%, n.s. vs. ZO Con: 58±6%). 5 mg and 10 mg CsA could not restore cardioprotection (ZO CsA+Sevo-post: 59±7%, ZO CsA10+Sevo-post: 57±14%; n.s. vs. ZO Con). In ZO rats insulin, cholesterol and triglyceride levels were significant higher than in ZL rats (all p<0.05).

CONCLUSION

Inhibition of mPTP with CsA failed to restore cardioprotection in the prediabetic but normoglycaemic heart of Zucker obese rats in vivo.

Ischaemic and morphine-induced post-conditioning: impact of mK(Ca) channels

BACKGROUND

Mitochondrial calcium-sensitive potassium (mK(Ca)) channels are involved in cardiac preconditioning. In the present study, we investigated whether also ischaemic-, morphine-induced post-conditioning, or both is mediated by the activation of mK(Ca) channels in the rat heart in vitro.

METHODS

Animals were treated in compliance with institutional and national guidelines. Male Wistar rats were randomly assigned to one of seven groups (each n = 7). Control animals were not further treated. Post-conditioning was induced either by 3 × 30 s of ischaemia/reperfusion (I-PostC) or by administration of morphine (M-PostC, 1 µM) for 15 min at the onset of reperfusion. The mK(Ca)-channel inhibitor paxilline (1 µM) was given with and without post-conditioning interventions (M-PostC+Pax, I-PostC+Pax, and Pax). As a positive control, we determined whether direct activation of mK(Ca) channels with NS1619 (10 µM) induced cardiac post-conditioning (NS1619). Isolated hearts underwent 35 min ischaemia followed by 120 min reperfusion. At the end of reperfusion, infarct sizes were measured by triphenyltetrazolium chloride staining.

RESULTS

In the control group, infarct size was 53 (5)% of the area at risk. Morphine- and ischaemic post-conditioning reduced infarct size in the same range [M-PostC: 37 (4)%, I-PostC: 35 (5)%; each P<0.05 vs control]. The mK(Ca)-channel inhibitor paxilline completely blocked post-conditioning [M-PostC+Pax: 47 (7)%, I-PostC+Pax: 51 (3)%; each P<0.05 vs M-PostC and I-PostC, respectively]. Paxilline itself had no effect on infarct size (NS vs control). NS1619 reduced infarct size to 33 (4)% (P < 0.05 vs control).

CONCLUSIONS

Ischaemic- and morphine-induced post-conditioning is mediated by the activation of mK(Ca) channels.

Hyperglycaemia blocks sevoflurane-induced postconditioning in the rat heart in vivo: cardioprotection can be restored by blocking the mitochondrial permeability transition pore

BACKGROUND

Recent studies showed that hyperglycaemia (HG) blocks anaesthetic-induced preconditioning. The influence of HG on anaesthetic-induced postconditioning (post) has not yet been determined. We investigated whether sevoflurane (Sevo)-induced postconditioning is blocked by HG and whether the blockade could be reversed by inhibiting the mitochondrial permeability transition pore (mPTP) with cyclosporine A (CsA).

METHODS

Chloralose-anaesthetized rats (n=7-11 per group) were subjected to 25 min coronary artery occlusion followed by 120 min reperfusion. Postconditioning was achieved by administration of 1 or 2 MAC sevoflurane for the first 5 min of early reperfusion. HG was induced by infusion of glucose 50% (G 50) for 35 min, starting 5 min before ischaemia up to 5 min of reperfusion. CsA (5 or 10 mg kg(-1)) was administered i.v. 5 min before the onset of reperfusion. At the end of the experiments, hearts were excised for infarct size measurements.

RESULTS

Infarct size (% of area at risk) was reduced from 51.4 (5.0)% [mean (sd)] in controls to 32.7 (12.8)% after sevoflurane postconditioning (Sevo-post) (P<0.05). This infarct size reduction was completely abolished by HG [51.1 (13.2)%, P<0.05 vs Sevo-post], but was restored by administration of sevoflurane with CsA [35.2 (5.2)%, P<0.05 vs HG+Sevo-post]. Increased concentrations of sevoflurane or CsA alone could not restore cardioprotection in a state of HG [Sevo-post2, 54.1 (12.6)%, P>0.05 vs HG+Sevo-post; CsA10, 58.8 (11.3)%, P>0.05 vs HG+CsA].

CONCLUSIONS

Sevoflurane-induced postconditioning is blocked by HG. Inhibition of the mPTP with CsA is able to reverse this loss of cardioprotection.

Ischemic preconditioning modulates mitochondrial respiration, irrespective of the employed signal transduction pathway

We tested in the in vivo rat heart the hypothesis that although ischemic preconditioning can employ different signal transduction pathways, these pathways converge ultimately at the level of the mitochondrial respiratory chain. Infarct size produced by a 60-min coronary artery occlusion (69%+/-2% of the area at risk) was limited by a preceding 15-min coronary occlusion (48%+/-4%). Cardioprotection by this stimulus was triggered by adenosine receptor stimulation, which was followed by protein kinase C and tyrosine kinase activation and then mitochondrial K(+)(ATP)-channel opening. In contrast, cardioprotection by 3 cycles of 3-min coronary occlusions (infarct size 27%+/-5% of the area at risk) involved the release of reactive oxygen species, which was followed by protein kinase C and tyrosine kinase activation, but was independent of adenosine receptor stimulation and K(+)(ATP)-channel activation. However, both pathways decreased respiratory control index (RCI; state-3/state-2, using succinate as complex-II substrate) from 3.1+/-0.2 in mitochondria from sham-treated hearts to 2.4+/-0.2 and 2.5+/-0.1 in hearts subjected to a single 15-min and triple 3-min coronary occlusions, respectively (both P<0.05). The decreases in RCI were due to an increase in state-2 respiration, whereas state-3 respiration was unchanged. Abolition of cardioprotection by blockade of either signal transduction pathway was paralleled by a concomitant abolition of mitochondrial uncoupling. These observations are consistent with the concept that mild mitochondrial uncoupling contributes to infarct size limitation by various ischemic preconditioning stimuli, despite using different signal transduction pathways. In conclusion, in the in vivo rat heart, different ischemic preconditioning (IPC) stimuli can activate highly different signal transduction pathways, which seem to converge at the level of the mitochondria where they increase state-2 respiration.

Cardiac mitochondrial preconditioning by Big Ca2+-sensitive K+ channel opening requires superoxide radical generation

ATP-sensitive K+ channel opening in inner mitochondrial membranes protects hearts from ischemia-reperfusion (I/R) injury. Opening of the Big conductance Ca2+-sensitive K+ channel (BK(Ca)) is now also known to elicit cardiac preconditioning. We investigated the role of the pharmacological opening of the BK(Ca) channel on inducing mitochondrial preconditioning during I/R and the role of O2-derived free radicals in modulating protection by putative mitochondrial (m)BK(Ca) channel opening. Left ventricular (LV) pressure (LVP) was measured with a balloon and transducer in guinea pig hearts isolated and perfused at constant pressure. NADH, reactive oxygen species (ROS), principally superoxide (O2(-*)), and m[Ca2+] were measured spectrophotofluorometrically at the LV free wall using autofluorescence and fluorescent dyes dihydroethidium and indo 1, respectively. BK(Ca) channel opener 1-(2'-hydroxy-5'-trifluoromethylphenyl)-5-trifluoromethyl-2(3H)benzimid-axolone (NS; NS-1619) was given for 15 min, ending 25 min before 30 min of global I/R. Either Mn(III)tetrakis(4-benzoic acid)porphyrin (TB; MnTBAP), a synthetic dismutator of O2(-*), or an antagonist of the BK(Ca) channel paxilline (PX) was given alone or for 5 min before, during, and 5 min after NS. NS pretreatment resulted in a 2.5-fold increase in developed LVP and a 2.5-fold decrease in infarct size. This was accompanied by less O2(-*) generation, decreased m[Ca2+], and more normalized NADH during early ischemia and throughout reperfusion. Both TB and PX antagonized each preconditioning effect. This indicates that 1) NS induces a mitochondrial-preconditioned state, evident during early ischemia, presumably on mBK(Ca) channels; 2) NS effects are blocked by BK(Ca) antagonist PX; and 3) NS-induced preconditioning is dependent on the production of ROS. Thus NS may induce mitochondrial ROS release to initiate preconditioning.

Pharmacological characteristics of the specific transporter for the endogenous cell growth inhibitor agmatine in six tumor cell lines

BACKGROUND AND AIMS

This study examined agmatine transport into six human intestinal tumor cell lines and compared the pharmacological properties of this transporter with those of the agmatine carrier previously characterized in human glioblastoma cells.

METHODS

Carrier-mediated uptake was determined as specific accumulation of [(14)C]agmatine in the cells. The changes in intracellular agmatine concentration in the tumor cells after 24 h incubation with 1 mM agmatine was analyzed by high-performance liquid chromatography.

RESULTS

Specific [(14)C]agmatine accumulation was found in the six human intestinal tumor cell lines Caco2, Cx1, Colo320, HT29, Colo205E, and SW480. Specific [(14)C]agmatine accumulation was inhibited by phentolamine, putrescine, spermine, clonidine, and decynium-22 but not by corticosterone, O-methylisoprenaline, or l-carnitine. Incubation with exogenous agmatine for 24 h increased intracellular agmatine content in all cell lines by a multiple of the basal endogenous content. Transfection of HEK293 cells with cDNA encoding either hOCT1, hOCT2, or hOCT3 did not enhance [(14)C]agmatine accumulation compared to nontransfected cells.

CONCLUSION

All intestinal tumor cell lines investigated express a functional specific agmatine transporter which exhibit pharmacological characteristics similar to those of the agmatine transporter in glioblastoma cells. This agmatine carrier is not identical with any so far known organic cation transport system.

Effect of acute hyperglycaemia and diabetes mellitus with and without short-term insulin treatment on myocardial ischaemic late preconditioning in the rabbit heart in vivo

Diabetes mellitus (DM) and the resulting hyperglycaemia may interfere with the cardioprotective effect of ischaemic late preconditioning (LPC). Therefore, we investigated the effect of acute hyperglycaemia (part 1) and the effect of alloxan-induced DM with or without short-term insulin treatment (part 2) on LPC. Rabbits, chronically instrumented with a coronary artery occluder, were subjected to 30 min coronary artery occlusion and 2 h reperfusion (I/R) and infarct size (IS) was assessed. In part 1, four groups were studied. Controls were not treated further. LPC induced by a 5-min period of myocardial ischaemia 24 h before I/R reduced IS from 42+/-14 (controls) to 22+/-8% of the area at risk. Hyperglycaemia (600 mg dl(-1) by dextrose infusion, H(600)) before and during the 30 min ischaemia tended to increase IS (57+/-16%, P=0.14 vs. controls) and blocked cardioprotection by LPC (H(600)+LPC, 59+/-19%, P=1.0 vs. H(600), P=0.0003 vs. LPC). In part 2, LPC reduced infarct size from 43+/-13% (control) to 23+/-10% ( P=0.003). In diabetic animals, IS was 39+/-11%, and cardioprotection by LPC could not be elicited (DM+LPC, 41+/-16%, P=0.02 vs. LPC). Short-term insulin treatment (I, 90 min before I/R, blood glucose <150 mg dl(-1)) did not restore the cardioprotective effects of LPC (DM+I, 42+/-15%; DM+LPC+I, 40+/-10%, P=0.03 vs. LPC). It is concluded that acute hyperglycaemia and DM block the cardioprotection induced by LPC in rabbits and that the cardioprotection is not restored by short-term insulin treatment.

Additive protective effects of late and early ischaemic preconditioning are mediated by the opening of KATP channels in vivo

We investigated whether a combination of ischaemic late preconditioning (LPC) and ischaemic early preconditioning (EPC) induces additive myocardial protection in vivo, and the role of ATP-sensitive K (KATP) channels in ischaemic LPC and in LPC + EPC. Sixty rabbits were divided into seven groups. Anaesthetized animals were subjected to 30 min of coronary artery occlusion and 120 min of reperfusion (I/R). Controls (CON, n = 9) were not preconditioned. LPC (n = 10) was induced in conscious rabbits by a 5-min period of myocardial ischaemia 24 h before I/R. The KATP channel blocker 5-hydroxydecanoate (5-HD, 5 mg/kg) was given 10 min before I/R with (LPC + 5-HD, n = 9) or without LPC (5-HD, n = 8). EPC (n = 8) was induced by a 5-min period of myocardial ischaemia 10 min before I/R. Animals received LPC and EPC without (LPC + EPC, n = 8) or with 5-HD (LPC + EPC + 5-HD, n = 8). LPC reduced infarct size (IS, triphenyltetrazolium staining) from 57 +/- 11% (MW +/- SD, CON) of the area at risk to 31 +/- 19% (LPC, P = 0.004). 5-HD did not affect IS (5-HD: 60 +/- 12%, P = 0.002 versus LPC), but abolished the cardioprotective effects of LPC (LPC + 5-HD: 62 +/- 18%, P = 0.001 versus LPC). EPC reduced IS to 18 +/- 8%. Additional LPC led to a further reduction to 8 +/- 4% (LPC + EPC, n = 8; P = 0.005 versus EPC; P = 0.004 versus LPC). 5-HD abolished this additional cardioprotective effect of LPC + EPC (LPC + EPC + 5-HD, n = 8; 46 +/- 11%, P < or = 0.001 versus LPC + EPC). We conclude that the combination of ischaemic LPC and EPC induces additive cardioprotection. KATP channel opening mediates the cardioprotective effects of ischaemic LPC and LPC + EPC.

[Semi-automatic TNM classification of malignant tumors with the ESTER system exemplified by the larynx]

Classification of tumours according to the TNM scheme has been accepted worldwide. However, vague baseline assessments and borderline cases render a comparison of the outcome on the basis of TNM classification impossible. Therefore we integrated the TNM rules as a new algorithm into an existing expert system for determining therapy. Thus, every tumour documented with the ESTHER system is automatically classified according to current TNM rules. The program is designed to cope with future changes of the TNM system: raw data are used for classification so that only the algorithms need to be modified.

Haemodynamic and antiarrhythmic protective effects of intracoronary perfusion during percutaneous transluminal coronary angioplasty

In 17 anaesthetized open-chest pigs, experiments were performed to determine if a myocardial protective effect can be obtained by intracoronary perfusion through the dilatation catheter during balloon inflation for percutaneous transluminal coronary angioplasty. Placement of the catheter such that the balloon lay in the middle third of the left anterior descending coronary artery caused a significant deterioration in haemodynamic status prior to balloon inflation, and on 5 occasions led to the development of ventricular fibrillation (VF). Balloon inflation without perfusion for periods of up to 5 min produced further haemodynamic deterioration, and culminated in VF in 4/14 cases. Simultaneous perfusion during balloon inflation (proximal perfusion pressure 900-1200 mmHg), with flow rates of 14.5 ml min-1 for arterial whole blood and 21 +/- 7 ml min-1 for blood diluted with 0.90% NaCl (haematocrit approx. 25%), not only prevented the haemodynamic deterioration but resulted in an improvement compared with values obtained with the catheter in position prior to balloon inflation. In no case did VF occur during 5 min of balloon inflation plus perfusion. The use of diluted blood as the perfusate was not associated with intracatheter thrombus formation, which was sometimes seen as a complication of whole blood perfusion.