Secretion of adiponectin from mouse aorta and its role in cold storage-induced vascular dysfunction

Availability of adiponectin plays a crucial role in cardiovascular function. The present study was conducted to evaluate the presence, alterations and impact of the various adiponectin isoforms in vascular tissue under clinically relevant in vitro conditions (cold storage). Presence of various adiponectin isoforms in vascular smooth muscle cells and their regulation during cold storage was evaluated by PCR, western blot, ELISA and immunohistochemistry. The impact of the various isoforms for vessel preservation was assessed using isometric force measurement as an in vitro assay for vascular function. Adiponectin is expressed in smooth muscle cells from murine aortae and human saphenous veins. Following 2 days of cold storage adiponectin mRNA expression in mouse aorta is reduced, which appears to be regulated indirectly by miR-292-3p. Despite the reduced mRNA expression, adiponectin accumulated in cold storage supernatant over 2 days indicating a net release of adiponectin. Two days of cold storage resulted in an impairment of endothelium-dependent relaxation which was prevented by addition of full-length adiponectin in concentrations similar to normal plasma levels during storage. In contrast, addition of recombinant adiponectin which is unable to form high order multimers failed to improve vessel function. High concentrations (20 μg/mL) of this trimeric isoform even reduced the vasorelaxation response and facilitated uncoupling of endothelial nitric oxide synthase. Endothelial injury by cold storage may partly be prevented by addition of high-molecular-weight adiponectin. This effect may support graft patency to avoid coagulation- and atherosclerosis-associated impairment of perfusion.

Regulation of ecto-5´-nucleotidase by docosahexaenoic acid in human endothelial cells

BACKGROUND/AIMS

Modulation of extracellular adenine nucleotide and adenosine concentrations is one potential mechanism by which docosahexaenoic acid (DHA) may exert beneficial effects in critically ill patients. This study assessed DHA effects on extracellular adenine purines.

METHODS

Experiments used human pulmonary endothelial cells (HPMEC) and umbilical vein endothelial cells (HUVEC) treated with DHA (48 h). mRNA level (real-time PCR), expression (western blot, flow cytometry) and activities (hydrolysis of etheno(ε)-purines and fluorescence HPLC) of CD73 (ecto-5´-nucleotidase) and CD39 (ecto-NTPDase-1) were quantified.

RESULTS

DHA elevated total CD73 membrane protein expression concentration-dependently but CD73 mRNA level did not change. Increased expression was paralleled by increased enzyme activity. Effects observed on membrane level were reversed in intact cells, in which ε-AMP hydrolysis decreased after DHA. In intact endothelial cells ATP release was enhanced and CD39 activity blunted following DHA treatment. Hence, extracellular ATP and ADP concentrations increased and this inhibited ε-AMP hydrolysis.

CONCLUSION

In human endothelial cells DHA caused 1) up-regulation of CD73 protein content and increased AMP hydrolysis at the cell membrane level, 2) increased cellular ATP release, and 3) decreased extracellular ATP/ADP hydrolysis. Thus, reorganization of the extracellular adenine-nucleotide-adenosine axis in response to DHA resulted in an increased extracellular ATP/adenosine ratio.

Myocardial accumulation of bupivacaine and ropivacaine is associated with reversible effects on mitochondria and reduced myocardial function

BACKGROUND

Mechanisms of local anesthetic cardiac toxicity are still not completely understood. In this study, we analyzed whether concentrations of local anesthetics found in clinical toxicity affect myocardial mitochondrial structure and oxygen consumption.

METHODS

Guinea pig isolated heart Langendorff preparations were exposed to bupivacaine (3.0 and 7.5 μg/mL) and ropivacaine (3.6 and 9.0 μg/mL) for 10 minutes. Heart rate, systolic blood pressure, the first derivative of left ventricular pressure (+dP/dt), electrocardiogram, and coronary flow were recorded. The local anesthetic tissue concentration was measured either immediately after local anesthetic exposure, or after 20- and 60-minute washout periods. In addition, electron microscopy of myocardial mitochondria was performed using a scoring system for structural damage of mitochondria. Cardiomyocyte cell culture was incubated with bupivacaine, and oxygen consumption ratio, extracellular acidification, and relative amounts of PGC-1α mRNA, a regulator of cellular energy metabolism, were determined.

RESULTS

Bupivacaine and ropivacaine induced reversible PR interval and QRS prolongation, and left ventricular pressure and +dP/dt reduction. Myocardial tissue concentration of local anesthetics was 3-fold the arterial concentration. Mitochondria showed a significant concentration-dependent morphological swelling after local anesthetic application. These changes were reversed by a 20-minute washout period for ropivacaine and by a 60-minute washout for bupivacaine. Bupivacaine reduced mitochondrial oxygen consumption and increased PGC-1α expression in neonatal cardiomyocyte cell cultures, whereas fatty acid metabolism remained unaffected.

CONCLUSIONS

Bupivacaine and ropivacaine accumulate in the myocardium. Reversible local anesthetic-induced mitochondrial swelling occurs at concentrations that induce a negative inotropic effect. Bupivacaine reduces cellular metabolism, whereas this reduction is reversible by fatty acids. Interaction with mitochondria may contribute to the negative inotropic effect of local anesthetics.

Preservation of endothelial vascular function of saphenous vein grafts after long-time storage with a recently developed potassium-chloride and N-acetylhistidine enriched storage solution

OBJECTIVES

Saphenous vein grafts are still commonly used in cardiac, vessel and also in transplant surgery. In cardiac surgery, a desperate graft situation could force to keep nonutilized explanted vein segments after CABG in reserve for case of early graft failure. Historically there were no options for adequate long-time graft storage protecting the endothelial layer with its important antithrombotic and immunosuppressive functional aspects. Commonly isotonic saline solution (sodium chloride [NaCl]) has been used as a storing solution in this case. We investigated the impact of long-time storage in NaCl and a recently developed potassium-chloride and N-acetylhistidine enriched storage solution (TiProtec, Dr. Köhler Chemie, Germany) on endothelial function of saphenous veins.

METHODS

Saphenous vein segments (n = 19) were intraoperatively isolated and stored for 24 and 96 hours. The segments were examined in a Mulvany-myograph to assess vessel function. Following preconstriction with norepinephrine, dose-response curves were assessed for relaxation with bradykinin and sodium-nitroprusside. We compared developed maximum wall tension and endothelial cell and smooth muscle cell (SMC) dependent vasodilatory function.

RESULTS

Maximum vessel wall tension was significantly better preserved in TiProtec-stored vessels after 24 h in comparison to segments stored in NaCl (5.11 ± 4.79 mN/mm vs. 2.48 ± 2.43 mN/mm; p = 0.033) and 96 h (4.94 ± 2.82 mN/mm vs. 2.80 ± 1.76 mN/mm; p = 0.042). Likewise endothelium-derived vasodilatory function was maintained significantly after 24 hours in TiProtec-stored vessels (36.9 ± 2.6% vs. 11.8 ± 30.9%; p = 0.005). After 96 hours, endothelium-dependent vascular function was nearly abolished in NaCl-stored vessels, but largely preserved in TiProtec-stored segments (20.6 ± 2.9% vs. 1.9 ± 4.3% in NaCl; p = 0.015). Sodium nitroprusside-mediated SMC-vasodilatory function was better maintained after 24 hours of storage in TiProtec group (88.8 ± 6.4% vs. 61.3 ± 8.2%; p = 0.009). After 96 hours of storage, SMC relaxation did not significantly differ between both storage groups which might be due to a distinct reduction of contractile function in NaCl-stored vessels (98.6 ± 5.0% and 77.9 ± 10.5% for Tiprotec and NaCl, respectively).

CONCLUSION

Vessel functions comprising contraction, endothelium-dependent and -independent vasodilatation are significantly reduced following 24 hours of cold storage in NaCl. After 96 hours of storage in NaCl these functions are nearly totally abolished. TiProtec is able to largely reduce this loss of function during cold storage. Therefore, TiProtec is a feasible option for longer term storage of saphenous vein grafts in CABG vessel and transplant surgery.

Functional, morphologic, and molecular characterization of cold storage injury

OBJECTIVE

Cold storage is used to preserve tissue for later transplantation. There is particular interest in prolonging cold storage time for transplantation purposes. To date, the mechanisms that contribute to vascular dysfunction in response to cold storage are poorly understood. The present study aims to characterize cold storage injury of blood vessels on functional and molecular levels.

METHODS

To assess vessel function of mouse aorta, isometric force measurements were performed in a Mulvany myograph after cold storage at 4°C for various intervals. Morphologic changes were judged by histologic analysis of aortic cross-sections. To characterize cold storage-induced alterations on RNA levels, microarray analysis with subsequent polymerase chain reaction analysis was performed.

RESULTS

Cold storage for 2 days revealed significant impairment of vessel function with respect to potassium-induced vessel tone development and acetylcholine-induced vessel relaxation. Detailed analysis of acetylcholine-mediated vascular response using specific pharmacologic blockers revealed that calcium-activated potassium channels seem to be impaired after 2 days of cold storage. At this point, no severe histologic changes (eg, elastic fiber disruption) were visible. RNA expression of 24 genes was significantly changed due to cold storage even after 2 hours. These include genes associated with vessel tone development (prostaglandin E(3) receptor), cardiovascular function (adiponectin), electron transport chain (uncoupling protein 1), or calcium signaling (protein kinase A regulatory subunit 2b).

CONCLUSIONS

Long-term cold storage impairs vascular function, especially with respect to potassium signaling by calcium-dependent potassium channels. Microarray analysis confirmed impairment of pathways that are involved in calcium signaling and vascular function. Furthermore, various genes were significantly altered even after 2 hours, significantly before functional impairment was observed.

Mechanisms of metabolic coronary flow regulation

Coronary blood flow is tightly adjusted to the oxygen requirements of the myocardium. The underlying control mechanisms keep coronary venous pO(2) at a rather constant level around 20mm Hg under a variety of physiological conditions. Because coronary flow may increase more than 5-fold during exercise without any signs of under- or overperfusion, coronary flow must be controlled, at least in part, in a feed forward manner. Likely metabolic factors contributing to feed forward control are carbon dioxide and reactive oxygen species. Adaptation of coronary flow to exercise under physiological conditions involves in addition to metabolic control feed forward neuronal and endothelium-dependent control. Under pathological conditions, e.g. vessel stenosis or anemia, or specific environmental conditions, e.g. high altitude exposure, cardiac oxygenation may become critical, especially if oxygen demand is increased during physical exercise. Under such conditions the fall of coronary pO(2) may directly result in opening of oxygen sensitive potassium or closure of calcium channels. Furthermore the fall of pO(2) results in the production of vasoactive metabolites, e.g. adenosine, nitric oxide or prostaglandins, and in proton accumulation. All of these adaptations support a reduction of coronary vessel resistance. This article is part of a Special Issue entitled "Coronoray Blood Flow".

Even short-time storage in physiological saline solution impairs endothelial vascular function of saphenous vein grafts

OBJECTIVES

A faultless endothelial layer is decisive for vascular function and therewith graft's patency. Functional impairment of the endothelium increases risk of graft thrombosis, intimal hyperplasia, and consecutive accelerated graft atherosclerosis. Storage solutions for intra-operatively harvested saphenous vein segments (SVS) might have significant impact on endothelial function. We investigated the impact of short-time storage in physiological saline solution (PSS) and a potassium-chloride- and N-acetylhistidine-enriched storage solution on venous endothelial function.

METHODS

Intra-operatively isolated SVSs (n=19) were stored in different storage solutions for 90 min. They were then immediately studied in tissue bath at 36°C with continuous oxygen insufflation. Following preconstriction with norepinephrine, dose-response relaxation curves of bradykinine (Brad) and sodium nitroprusside (SNP) were determined. We compared developed maximum wall tension, vessel constriction kinetics, endothelial cell- and smooth muscle cell (SMC)-dependent vasodilatory function.

RESULTS

Maximum vessel wall tension was reduced significantly in PSS-stored vessels (10.1 ± 9.8 mN mm(-1) vs 3.5 ± 3.4 mN mm(-1); p=0.0372). Endothelium-derived vasodilatory function was likewise significantly reduced after short-time storage (20.6 ± 34.4% vs 35.0 ± 27.0%; p=0.0437). SNP-mediated SMC-vasodilatory function was maintained equally well in both groups (88.2 ± 21.8% vs 83.0 ± 30.6% in PSS; p=n.s.).

CONCLUSION

Even short-time storage in PSS significantly impairs endothelial vascular function. Concerning the essential role of a faultless endothelial layer, the quite common use of PSS as a storage solution for SVSs in CABG surgery has to be discussed critically.

Experimental hyperhomocysteinaemia: differences in tissue metabolites between homocystine and methionine feeding in a rat model

AIM

Hyperhomocysteinaemia, diagnosed by serum levels, is regarded as an independent risk indicator for cardiovascular events and is associated with various diseases. The pathomechanisms seem to be partly due to concentrations of homocysteine metabolites and their effect on the cellular transmethylation processes.

METHODS

We compared two common models for experimental hyperhomocysteinaemia - high methionine diet and homocystine-enriched diet - regarding their effects on tissue concentrations of homocysteine metabolites.

RESULTS

Both diets induced hyperhomocysteinaemia without affecting renal function or vitamine status. However, the tissue contents of homocysteine and its precursors S-adenosyl-homocysteine (SAH) and S-adenosyl-methionine exhibited major differences between both models. Transmethylation potential was elevated 1.7-fold in liver of rats fed the methionine diet, whereas it was unaltered after homocystine-enriched diet. Kidneys of rats fed the methionine diet did not show any alterations in tissue content of homocysteine and its precursors, whereas in the homocystine group homocysteine and the transmethylation inhibitor SAH were elevated from 23.1 +/- 10.4 to 78.0 +/- 26.0 nmol g(-1) and from 106 +/- 4 to 170 +/- 22 nmol g(-1) respectively. Homocysteine tissue content was elevated in the homocystine, but not in the methionine group.

CONCLUSIONS

Alterations to homocysteine metabolism are distinct in both models. These findings may explain divergent results, which have been published for these models of hyperhomocysteinaemia and which have resulted in controversial discussions in the past.

Evidence against nitric oxide-quenching effects of chemically defined Maillard reaction products

Direct interaction between Maillard reaction products (MRPs) and nitric oxide (NO) has been suggested as a pathophysiological mechanism involved in enhanced diabetic arteriosclerosis. Only MRPs without structural characterization have been studied to date. Using chemically synthesized and analytically well defined individual MRPs, we investigated whether the native nitric oxide concentration is directly affected by the Amadori compound N-epsilon-fructosyllysine or the advanced glycation end product N-epsilon-carboxymethyllysine. MRPs were incubated with nitric oxide solution or NO donors (SNAP, spermine-NONOate). Changes in the nitrite (oxidative metabolite of NO) concentration served as indicator of NO availability. MRPs, either as free amino acids or covalently bound to bovine serum albumin (BSA), had no influence on nitrite concentration when using NO solution. In contrast, incubation of the respective NO donors with several covalently protein-bound MRPs as well as native BSA significantly reduced nitrite concentration. If SNAP was co-incubated with EDTA or with Fe (2+) ions, nitrite concentration was decreased or increased, respectively, suggesting a metal ion-dependent alteration of the NO liberation rate. Native NO concentration was not affected by the MRPs tested. Substitution of native NO by NO-releasing substances may be inadequate as a model of NO-MRP interaction, as metal ions or chelators present in compound preparations may affect the NO-liberating mechanism of the donor.

Coronary flow regulation in mouse heart during hypercapnic acidosis: role of NO and its compensation during eNOS impairment

AIMS

This study addressed the hypotheses that the hypercapnic flow response in wild-type (WT) mouse heart is mainly mediated by nitric oxide (NO) and, thus, severely blunted in endothelial nitric oxide synthase knockout (eNOS-KO) mice and in WT mice after continuous pharmacological block (2 weeks) of NOS enzymes (WT-LN).

METHODS AND RESULTS

Step changes of arterial pCO(2) were performed in isolated perfused hearts (n = 105). Contributions of NOS (L-NAME, TRIM), cyclooxygenase (indomethacin), epoxyeicosanotrienes (miconazole), adenosine A2A-receptors (SCH 58261), KV-channels (4-AP), KCa-channels (TEA), and K ATP-channels (glibenclamide) were studied in WT and eNOS-KO mouse hearts. Change of arterial pCO(2) increased coronary flow by 31.3 +/- 4% in WT, a response that was significantly decreased to 9.2 +/- 6% after L-NAME. Additional glibenclamide infusion (n = 5) completely abolished the steady-state flow increase during hypercapnic acidosis (-4.2 +/- 2.3%, P = 0.004 vs. control). Hearts from eNOS-KO mice as well as WT-LN showed a fully preserved flow response insensitive towards NOS-blockade. Whereas indomethacin, miconazole, TEA, and SCH 58261 were ineffective to reduce the flow response, glibenclamide blunted it in eNOS-KO hearts.

CONCLUSION

NO-production and K ATP-channel activation together may fully account for the steady-state hypercapnic flow response in mouse heart. However, chronic deletion of eNOS does not result in a reduced hypercapnic flow response. Enhanced activation of K ATP-channels and potentially Kv-channels contributes to the compensatory mechanisms involved in the hypercapnic flow response when eNOS activity is absent.

The Effects of Levosimendan on Myocardial Function in Ropivacaine Toxicity in Isolated Guinea Pig Heart Preparations

BACKGROUND

Levosimendan is a novel drug used for inotropic support in heart failure, but its efficacy in local anesthetic-induced myocardial depression is not known. Therefore, we investigated the effects of levosimendan on the negative inotropic response to ropivacaine in isolated heart preparations of guinea pigs.

METHODS

Action potentials and force of contraction were studied with conventional techniques in guinea-pig papillary muscles. Heart rate, systolic pressure, the first derivative of left ventricular pressure (+dP/dt(max)), coronary flow, and PR and QRS intervals were measured in isolated constant-pressure perfused, nonrecirculating Langendorff heart preparations. Single or cumulatively increasing concentrations of levosimendan and ropivacaine were used either alone or in combination.

RESULTS

In isolated papillary muscle, ropivacaine reduced force of contraction in a concentration-dependent manner. Exposure to 10 microM levosimendan in the presence of 10 muM ropivacaine almost completely reversed the negative inotropic response. Sensitivity to the positive inotropic effect of levosimendan was not altered by 10 muM ropivacaine (-logEC50 [M] = 7.03 without versus 6.9 with ropivacaine, respectively). Action potential parameters were influenced only at the highest concentration. In the Langendorff heart, levosimendan significantly reversed the ropivacaine-induced reduction in heart rate, systolic pressure, coronary flow, and +dP/dt(max) to baseline values.

CONCLUSION

Levosimendan is an effective inotropic drug in ropivacaine-induced myocardial depression and levosimendan myocardial sensitivity, and efficacy was not affected by the local anesthetic. Our results suggest that the calcium-sensitizing action of levosimendan is effective in local anesthetic-induced cardiac depression.