Reversible desensitization of the myocardial contractile apparatus for calcium. A new concept for improving tolerance to cold ischemia in human myocardium?

Cannabinoids acting on CB1 receptors decrease contractile performance in human atrial muscle

Cannabinoids elicit hypotension mainly via activated CB(1) receptors and show complex cardiovascular actions. Effects on human heart muscle have not been studied yet. Isolated human atrial heart muscle preparations were stimulated by electrical field with 1 Hz to contract isometrically at optimal length and were challenged with the endogenous cannabinoid arachidonyl ethanolamide (anandamide), the metabolically stable analogue R-methanandamide, and the potent synthetic CB(1) receptor agonist HU-210. Anandamide dose-dependently decreased systolic force (82.2 +/- 4.8% and 60.8 +/- 6.8% of maximal systolic force for 0.1 and 1 microM, respectively, P < 0.05). The selective CB(1) receptor antagonist AM-251 (1 microM, P < 0.05), but not the CB(2) receptor antagonist, AM-630 (1 microM), the nitric oxide synthase inhibitor N omega-nitro-l-arginine methyl ester (l-NAME) (500 microM), or the cyclooxygenase inhibitor indomethacin (100 microM), prevented the effect. Contrary to indomethacin, l-NAME alone showed negative inotropic effects (72.1 +/- 3.54%, P < 0.001). The R-methanandamide (1 microM: 50.4 +/- 3.5%, P < 0.001) and HU-210 (1 microM: 60.1 +/- 3.8%, P < 0.001) had similar negative inotropic effects. The existence of CB(1) receptors on heart muscle was verified using Western blot analysis and immunofluorescence staining. The conclusion is that anandamide, R-methanandamide, and HU-210 decrease contractile performance in human atrial muscle via CB(1) receptors.

Improved right heart function after myocardial preservation with 2,3-butanedione 2-monoxime in a porcine model of allogenic heart transplantation

BACKGROUND

Right heart dysfunction is a major cause for early morbidity and mortality after heart transplantation. Experiments were designed to evaluate the influence of the calcium-desensitizing drug 2,3-butanedione 2-monoxime (BDM) on right heart function in a porcine model of heart transplantation.

METHODS

Donor hearts of domestic pigs were arrested with BDM in Krebs solution (n = 7) and with BDM in Bretschneider's histidine-tryptophan-ketoglutarate (HTK) solution (n = 6). There were 2 control groups: University of Wisconsin (UW, n = 6) and HTK (n = 6). An isovolumic model was used in which the right ventricular volume was precisely controlled in vivo with an intracavitary high-compliance balloon. After 4 hours of ischemia, hearts were transplanted into recipients. After 1 and 2 hours of reperfusion, the right ventricular balloon volume was increased in 10-mL increments until right ventricular failure occurred and the developed pressures were recorded.

RESULTS

Maximal right ventricular developed pressures were significantly different after 2 hours of reperfusion (UW: 35 +/- 13 mm Hg; HTK: 47 +/- 8 mm Hg; Krebs+BDM: 49 +/- 9 mm Hg; HTK+BDM: 50 +/- 6 mm Hg; P =.04). Hearts subjected to BDM could be loaded with a significantly increased volume after 1 hour and after 2 hours (UW: 57 +/- 10 mL vs HTK: 43 +/- 8 mL vs Krebs+BDM: 70 +/- 10 mL vs HTK+BDM: 67 +/- 15 mL; P =.002). Postischemic right ventricular enddiastolic compliance was significantly increased in groups treated with BDM after 1 hour (P =.02) and after 2 hours (P =.039).

CONCLUSIONS

The drug BDM significantly improves right ventricular function in a heart transplantation model. The increase in volume load and developed right ventricular pressure achieved by BDM application would translate into a decreased risk of right ventricular failure after clinical transplantation.

Reprogramming of gene expression in cultured cardiomyocytes and in explanted hearts by the myosin ATPase inhibitor butanedione monoxime

BACKGROUND

Butanedione monoxime (BDM) is a reversible myosin ATPase inhibitor. Its use in transplantation medicine may be of benefit in the preservation of hearts. As little is known about its ability to prevent stress and metabolic deregulation, we wanted to investigate the genomic response in cultured cardiomyocytes and explanted, preserved hearts at the transcriptional level.

METHODS

We thus investigated the gene expression of the transcription factors GATA-4, Nkx2.5, MEF-2c, and Oct-1 and of the downstream target genes atrial and brain natriuretic peptide, alpha- and beta-myosin heavy chain, alpha-cardiac actin, and alpha-skeletal actin. Additionally, lactate dehydrogenase and creatine kinase enzyme activities were measured as markers for membrane integrity and metabolic deregulation of cardiomyocytes.

RESULTS

In untreated cardiomyocyte cultures, expression of GATA-4 and Nkx2.5 was increased 7- and 4-fold, 72 hr after isolation, but the gene expression of MEF-2c and Oct-1 was reduced to 10% and 70%, at day 3 in culture. We show atrial natriuretic peptide and brain natriuretic peptide gene expression to be maximal 24 and 72 hr after isolation, the level being 3- and 2-fold, when compared with freshly isolated cells. The gene expression of alpha- and beta-myosin heavy chain was reduced to approximately 30% at day 3 in culture and similar observations were made for alpha-cardiac and alpha-skeletal actin, which declined to approximately 20% and 10% of control values, 72 hr after isolation. BDM prevented at the transcriptional level enhanced expression of markers for stress and metabolic deregulation, and the activities of lactate dehydrogenase and creatine kinase were highly significantly reduced. Similar results were obtained when explanted hearts were stored in BDM-containing organ preservation solution.

CONCLUSIONS

Preservation of metabolic function in donor organs is of critical importance in transplantation medicine, and we show gene markers for stress and metabolic deregulation in cultures of cardiomyocytes and explanted hearts to be significantly reduced by BDM. Reprogramming of gene expression of nuclear transcription factors and downstream target genes may prolong the acceptable storage time between explantation and transplantation.

Optimizing the oxygen balance during initial reperfusion with 2,3-butanedione monoxime attenuates cardiac reperfusion injury

The effect of 20 mmol/L butanedione monoxime on myocardial ischemia/reperfusion damage was studied in isolated guinea pig hearts. Three groups of hearts (n = 8) were perfused in the Langendorff mode and cardioplegic arrest was induced with St. Thomas Hospital II solution (STS) at 37 degrees C for 50 min. Myocardial oxygen demand, recovery of myocardial function, and creatine kinase release during 30 min of reperfusion were monitored. Preservation of myocardial ultrastructure was determined by electron microscopy. Control (C) hearts underwent cardioplegic arrest and reperfusion without treatment. BDM was added during cardioplegic arrest in BDMSTS hearts, or to the initial (20 min) reperfusate in BDMREP hearts. BDM during initial reperfusion markedly reduced O2 demand and prevented creatine kinase release from cardiac myocytes, resulting in improved recovery of myocardial function and attenuation of myocardial ultrastructural damage after washout of the drug. In contrast, addition of BDM to the cardioplegic solution provided no protection from ischemic or reperfusion injury.

Myocardial length-force relationship in end stage dilated cardiomyopathy and normal human myocardium: analysis of intact and skinned left ventricular trabeculae obtained during 11 heart transplantations

The Frank-Starling-mechanism (FSM) was analyzed in isolated intact and skinned human left ventricular myocardium obtained from 11 heart transplantations (normal donor hearts (NDH), n = 8; dilated cardiomyopathy (DCM), n = 11). The new technique to utilize muscle strips from normal donor hearts which were actually implanted is described in detail.

METHODS

I) In electrically stimulated left ventricular trabeculae (37 degrees C, oxygenated Krebs-Henseleit solution, supramaximal electrical stimulation, frequency 1 Hz) force development was analyzed as a function of muscle length (NDH = 8; DCM = 11). II) In an additional series left ventricular myocardium was demembranized ("skinned") by Triton-X-100. At different sarcomere lengths and calcium concentrations corresponding to pCa values of 4.3, 5.5, and 8.0 force development was measured (DCM = 11; NDH = 9).

RESULTS

I) Developed force increased up to an optimum as a function of muscle length in intact NDH- and DCM-myocardium. However, the relative increment of developed force after any length step was smaller in DCM than in NDH. Near "Lmax" (muscle length associated with maximum developed force) passive resting tension was considerably elevated in DCM, indicating significantly increased diastolic stiffness. II) In skinned left ventricular DCM- and NDH-myocardium developed force depended on sarcomere length with an optimum near 2.2 microns. However, a reduction of activator calcium concentration from pCa 4.3 to pCa 5.5 produces a smaller percent decline in force at short sarcomere lengths in DCM than it does in NDH.

CONCLUSION

The present study shows that except for diastolic stiffness and a smaller relative force increment after any length step in DCM the Frank Starling mechanism is still present in isolated human left ventricular DCM- as in NDH-myocardium. The current study does not allow to decide whether in skinned myocardium the smaller percent decline in force after reduction of activator calcium concentrations in DCM is caused by an increased calcium sensitivity at short sarcomere lengths or decreased sensitivity at long sarcomere lengths.

Effects of butanedione monoxime and temperature on prolonged cardiac storage

BACKGROUND

The optimal temperature for cardiac allograft storage remains controversial. We conjectured that supplementation of the potent cardioprotective agent 2,3-butanedione monoxime with calcium may improve allograft storage and make the precise storage temperature less critical.

METHODS

Hearts were harvested from Sprague-Dawley rats (250 to 350 g), mounted on a Langendorff apparatus, and instrumented with an intraventricular balloon. Hearts were flushed and stored with either unmodified University of Wisconsin solution (UWS) or UWS supplemented with 10 mmol/L of 2,3-butanedione monoxime and calcium 0.1 mmol/L (BDM). Hearts were then subjected to 12 hours of storage at one of five temperatures (0 degree, 4 degrees, 8 degrees, 12 degrees, or 16 degrees C) in a complete 2 x 5 factorial design (n = 6/group). Data are reported either as a percentage of the prestorage results or as an absolute value (mean +/- standard deviation).

RESULTS

Recovery of developed pressure (p < 0.0001), coronary flow (p < 0.0001), and diastolic volume (p < 0.001) were significantly enhanced, whereas creatine kinase (p < 0.0001) and lactate dehydrogenase release (p < 0.0001) were reduced in the BDM versus the UWS groups. In both the BDM and UWS storage groups, recovery was better at temperatures of 8 degrees C or less than at 12 degrees C or more. The single preferred temperature was 4 degrees C, significantly better than 0 degree C with unmodified UWS, while similar to 0 degree and 8 degrees C with BDM. Adenine nucleotide values were decreased equally in the BDM and UWS hearts, but preservation was enhanced at 0 degree C compared with all warmer temperatures.

CONCLUSIONS

We conclude that 4 degrees C is the preferred temperature for prolonged cardiac storage with UWS and that the inclusion of 2,3-butanedione monoxime with calcium 0.1 mmol/L markedly enhances recovery for storage temperatures of 8 degrees C or less.