Comparison of triphenyltetrazolium chloride (TTC) staining versus detection of fibronectin in experimental myocardial infarction

What can we do to optimize mitochondrial transplantation therapy for myocardial ischemia-reperfusion injury?

Mitochondrial transplantation is a promising solution for the heart following ischemia-reperfusion injury due to its capacity to replace damaged mitochondria and restore cardiac function. However, many barriers (such as inadequate mitochondrial internalization, poor survival of transplanted mitochondria, few mitochondria colocalized with cardiac cells) compromise the replacement of injured mitochondria with transplanted mitochondria. Therefore, it is necessary to optimize mitochondrial transplantation therapy to improve clinical effectiveness. By analogy, myocardial ischemia-reperfusion injury is like a withered flower, it needs to absorb enough nutrients to recover and bloom. In this review, we present a comprehensive overview of "nutrients" (source of exogenous mitochondria and different techniques for mitochondrial isolation), "absorption" (mitochondrial transplantation approaches, mitochondrial transplantation dose and internalization mechanism), and "flowering" (the mechanism of mitochondrial transplantation in cardioprotection) for myocardial ischemia-reperfusion injury.

Targeting DNA methylation can reduce cardiac injury associated with ischemia reperfusion: One step closer to clinical translation with blood-borne assessment

Ischemia reperfusion (I/R) injury is one of the main clinical challenges for cardiac surgeons. No effective strategies or therapy targeting the molecular and cellular mechanisms to reduce I/R exists to date, despite altered gene expression and cellular metabolism/physiology. We aimed to identify whether DNA methylation, an unexplored target, can be a potential site to curb I/R-associated cell death by using the left anterior descending artery occlusion model in male Wistar rats. I/R rat heart exhibited global DNA hypermethylation with a corresponding decline in the mitochondrial genes (PGC-1α, TFAM, POLG, ND1, ND3, ND4, Cyt B, COX1, and COX2), antioxidant genes (SOD2, catalase, and Gpx2) and elevation in apoptotic genes (Casp3, Casp7, and Casp9) expression with corresponding changes in their activity, resulting in injury. Targeting global DNA methylation in I/R hearts by using its inhibitor significantly reduced the I/R-associated infarct size by 45% and improved dysferlin levels via modulating the genes involved in cell death apoptotic pathway (Casp3, Casp7, and PARP), inflammation (IL-1β, TLR4, ICAM1, and MyD88), oxidative stress (SOD1, catalase, Gpx2, and NFkB) and mitochondrial function and its regulation (MT-ND1, ND3, COX1, ATP6, PGC1α, and TFAM) in the cardiac tissue. The corresponding improvement in the genes' function was reflected in the respective hearts via the reduction in apoptotic TUNEL positive cells and ROS levels, thereby improving myocardial architecture (H&E staining), antioxidant enzymes (SOD, catalase activity) and mitochondrial electron transport chain activities and ATP levels. The analysis of blood from the I/R animals in the presence and absence of methylation inhibition exhibited a similar pattern of changes as that observed in the cardiac tissue with respect to global DNA methylation level and its enzymes (DNMT and TET) gene expression, where the blood cardiac injury markers enzymes like LDH and CK-MB were elevated along with declined tissue levels. Based on these observations, we concluded that targeting DNA methylation to reduce the level of DNA hypermethylation can be a promising approach in ameliorating I/R injury. Additionally, the blood-borne changes reflected I/R-associated myocardial tissue alteration, making it suitable to predict I/R-linked pathology.

Monitoring of irrigated lesion formation with single fiber based multispectral system using machine learning

In radiofrequency ablation (RFA) treatment of cardiac arrhythmias, intraprocedural assessment of treatment efficacy relies on indirect measures of adequate tissue destruction. Direct sensing of diffuse reflectance spectral changes at the ablation site using optically integrated RFA catheters has been shown to enable accurate prediction of lesion dimensions, ex vivo. Challenges of optical guidance can be due to obtaining reliable measurements under various catheter-tissue contact orientations. In this work, addressed this limitation by assessing the feasibility of monitoring lesion progression using single-fiber reflectance spectroscopy (SFRS). A total of 110 endocardial lesions of various sizes were generated in freshly excised swine right ventricular tissue using a custom-built, irrigated SFRS-RFA catheter. Models were developed for assessing catheter-tissue contact, the presence of nontransmural or transmural lesions and lesion depth percentage. These results support the use of SFRS-based catheters for irrigated lesion assessment and motivate further exploration of using multi-SFRS catheters for omnidirectionality.

Positron Emission Tomography (PET) with 18F-FGA for Diagnosis of Myocardial Infarction in a Coronary Artery Ligation Model

Location and extent of necrosis are valuable information in the management of myocardial infarction (MI). Methods. We investigated 2-deoxy-2-18F-fluoro glucaric acid (FGA), a novel infarct-avid agent, for positron emission tomography (PET) of MI. We synthesized FGA from commercially available 18F-fluoro-2-deoxy-2-D-glucose (FDG). MI was induced in mice by permanently occluding the left anterior descending coronary artery. Biodistribution of FGA was assessed 1 h after FGA injection (11 MBq). PET/CT was conducted 1 h, 6 h, 1 d, 3 d, and 4 d after MI. Subcellular compartment of FGA accumulation in necrosis was studied by tracing the uptake of biotin-labeled glucaric acid with streptavidin-HRP in H2O2-treated H9c2 cardiomyoblasts. Streptavidin-reactive protein bands were identified by LC-MS/MS. Results. We obtained a quantitative yield of FGA from FDG within 7 min ( $\text{radiochemical}\text{purity}>99\%$ ). Cardiac uptake of FGA was significantly higher in MI mice than that in control mice. Imaging after 1 h of FGA injection delineated MI for 3 days after MI induction, with negligible background signal from surrounding tissues. Myocardial injury was verified by tetrazolium staining and plasma troponin (47.63 pg/mL control versus 311.77 pg/mL MI). In necrotic H9c2 myoblasts, biotinylated glucaric acid accumulated in nuclear fraction. LC-MS/MS primarily identified fibronectin in necrotic cells as a putative high fidelity target of glucaric acid. Conclusion. FGA/PET detects infarct early after onset of MI and FGA accumulation in infarct persists for 3 days. Its retention in necrotic cells appears to be a result of interaction with fibronectin that is known to accumulate in injured cardiac tissue.

Evaluating the effects of carbon monoxide releasing molecule-2 against myocardial ischemia-reperfusion injury in ovariectomized female rats

PURPOSE

Cardioprotective effect of carbon monoxide, a gasotransmitter against myocardial ischemia-reperfusion injury (I/R), is well established in preclinical studies with male rats. However, its ischemic tolerance in post-menopausal animals has not been examined due to functional perturbations at the cellular level.

METHODS

The protective role of carbon monoxide releasing molecule-2 (CORM-2) on myocardial I/R was studied in female Wistar rats using the Langendorff apparatus. The animals were randomly divided into normal and ovariectomized (Ovx) female rats and were maintained 2 months post-surgery. Each group was further divided into 4 subgroups (n = 6/subgroup): normal, I/R, CORM-2-control (20 μmol/L), and CORM-2-I/R. The cardiac injury was estimated via myocardial infarct size, lactate dehydrogenase, and creatine kinase levels in coronary effluent and cardiac hemodynamic indices. Mitochondrial functional activity was assessed by measuring mitochondrial electron transport chain enzyme activities, swelling behavior, mitochondrial membrane potential, and oxidative stress.

RESULTS

Hemodynamic indices were significantly lower in ovariectomized rat hearts than in normal rat hearts. Sixty minutes of reperfusion of ischemic heart exhibited deteriorated cardiac physiological recovery in both ovariectomized and normal groups, where prominent decline was observed in ovariectomized rat. However, preconditioning the isolated heart with CORM-2 improved hemodynamics parameters significantly in both ovariectomized and normal rat hearts challenged with I/R, but with a limited degree of protection in ovariectomized rat hearts. The protective effect of CORM-2 was further confirmed via a reduction in cardiac injury, preservation of mitochondrial enzymes, and reduction in oxidative stress in all groups.

CONCLUSION

CORM-2 administration significantly attenuated myocardial I/R injury in ovariectomized rat hearts by attenuating I/R-associated mitochondrial perturbations and reducing oxidative stress.

S-oxiracetam Facilitates Cognitive Restoration after Ischemic Stroke by Activating α7nAChR and the PI3K-Mediated Pathway

S-oxiracetam (S-ORC), a nootropic drug, was used to protect against ischemic stroke by lessening the blood brain barrier dysfunction and inhibiting neuronal apoptosis. However, the potential effects of S-ORC in the recovery of cognitive functions after ischemic stroke and the underlying mechanisms remains unclear. In this study, middle cerebral artery occlusion/reperfusion (MCAO/R) in rats was used as the animal model. By using Y-maze test, Morris water maze, triphenyl tetrazolium chloride (TTC) staining, terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate (dUTp) nick end labeling (TUNEL) assay, hematoxylin and eosin, immunohistochemical staining and western blot to evaluate the protective effect of S-ORC on cognitive recovery, we were able to confirm that S-ORC ameliorated spatial learning impairment, tissue loss, and hippocampal neuronal apoptosis and injury induced by MCAO/R in rats. These cognitive effects were achieved by restoring the normal function of synaptophysin and increasing PSD95 expression in the hippocampus. Furthermore, we found that methyllycaconitine, the antagonist of α7 nicotinic acetylcholine receptor (α7nAChR), and LY294002, the inhibitor of phosphoinositide 3-kinase (PI3K), were able to block the cognitive effects of S-ORC after MCAO/R in rats. In conclusion, α7nAChR and PI3K are key molecules that mediated the signaling pathway leading to S-ORC-induced cognitive restoration after MCAO/R.

Dantrolene Induces Mitigation of Myocardial Ischemia-Reperfusion Injury by Ryanodine Receptor Inhibition

The impairment of intracellular calcium homeostasis plays an essential role during ischemia-reperfusion injury. Calcium release from sarcoplasmic reticulum which is triggered by myocardial ischemia is mainly mediated by ryanodine receptors. Dantrolene sodium is a ryanodine receptor antagonist. The objective of the present study was to evaluate the in-vivo impact of dantrolene sodium on myocardial ischemia-reperfusion injury in swine models. An in vivo, experimental trial comparing 10 experimental animals which received dantrolene sodium with 9 control swine models was conducted. Their left anterior descending coronary artery was temporarily occluded for 75 minutes via a vessel tourniquet, which was then released. Myocardial reperfusion was allowed for 24 hours. Dantrolene was administered at the onset of the reperfusion period and levels of troponin, creatine phosphokinase and creatine kinase myocardial band between the two groups were compared. Additionally, various other hemodynamic parameters and left ventricular morphology and function were examined. There were significantly lower values of troponin, creatine phosphokinase and creatine kinase myocardial band in the dantrolene group indicating less ischemia-reperfusion injury. Moreover, the postischemic cardiac index was also greater in the dantrolene group, whereas viable myocardium was also better preserved. In conclusion, the in vivo cardioprotective role of dantrolene sodium against ischemia-reperfusion injury in swine models was indicated in this study. Therefore, dantrolene sodium administration could be a promising treatment against ischemia-reperfusion injury in humans. However, large randomized clinical studies should be firstly carried out to prove this hypothesis.

β-Caryophyllene as a Potential Protective Agent Against Myocardial Injury: The Role of Toll-Like Receptors

Myocardial infarction (MI) remains one of the major causes of mortality around the world. A possible mechanism involved in myocardial infarction is the engagement of Toll-like receptors (TLRs). This study was intended to discover the prospective cardioprotective actions of β-caryophyllene, a natural sesquiterpene, to ameliorate isoproterenol (ISO)-induced myocardial infarction through HSP-60/TLR/MyD88/NFκB pathway. β-Caryophyllene (100 or 200 mg/kg/day orally) was administered for 21 days then MI was induced via ISO (85 mg/kg, subcutaneous) on 20th and 21st days. The results indicated that ISO induced a significant infarcted area associated with several alterations in the electrocardiogram (ECG) and blood pressure (BP) indices and caused an increase in numerous cardiac indicators such as creatine phosphokinase (CPK), creatine kinase-myocardial bound (CK-MB), lactate dehydrogenase (LDH), and cardiac tropinine T (cTnT). In addition, ISO significantly amplified heat shock protein 60 (HSP-60) and other inflammatory markers, such as TNF-α, IL-Iβ, and NFκB, and affected TLR2 and TLR4 expression and their adaptor proteins; Myeloid differentiation primary response 88 (MYD88), and TIR-domain-containing adapter-inducing interferon-β (TRIF). On the other hand, consumption of β-caryophyllene significantly reversed the infarcted size, ECG and BP alterations, ameliorated the ISO elevation in cardiac indicators; it also notably diminished HSP-60, and subsequently TLR2, TLR4, MYD88, and TRIF expression, with a substantial reduction in inflammatory mediator levels. This study revealed the cardioprotective effect of β-caryophyllene against MI through inhibiting HSP-60/TLR/MyD88/NFκB signaling pathways.

Sequence and time course of depletion of cardiac cellular proteins and accumulation of plasma proteins in rat early ischemic myocardium

In order to investigate the sequence and time course of fibronectin (Fn), fibrinogen (Fg), complement (C5), myoglobin (Mb), actin (HHF35), and desmin (Dm) for the diagnosis of early myocardial ischemia, the myocardial ischemia model was established in rats, the positive reaction areas of Fn, Fg and C5 and the depletion areas of Mb, HHF35 and Dm in the ischemic cardiomyocytes were studied with immunohistochemistry, image analysis technique and statistical system. The results showed that the depletion of Dm, HHF35 and Mb, and the positive staining of Fg and C5 in ischemic cardiomyocytes were found as early as 15 min after the myocardial ischemia, but the positive staining of Fn occurred till 3 h after myocardial ischemia. With the prolongation of ischemia, the areas of the depletion of Dm, HHF35, Mb and the positive staining of Fg, C5 and Fn gradually enlarged. It is suggested that all the six immunohistochemical markers are more sensitive than routine H&E staining, and that Dm, HHF35, Mb, Fg, C5 are more sensitive markers than Fn for detection of early myocardial ischemia.

Integrated RFA/PSOCT catheter for real-time guidance of cardiac radio-frequency ablation

Radiofrequency ablation (RFA) is an important standard therapy for cardiac arrhythmias, but direct monitoring of tissue treatment is currently lacking. We demonstrate an RFA catheter integrated with polarization sensitive optical coherence tomography (PSOCT) for directly monitoring the RFA process in real time. The integrated RFA/OCT catheter was modified from a standard clinical RFA catheter and includes a miniature forward-viewing cone-scanning OCT probe. The PSOCT system was validated with a quarter-wave plate while the RFA function of the integrated catheter was validated by comparing lesion sizes with those made with an unmodified RFA catheter. Additionally, the integrated catheter guided catheter-tissue apposition and monitored RFA lesion formation in cardiac tissue in real time. The results show that catheter-tissue contact can be characterized by observing the features of the blood and tissue in the acquired OCT images and that RFA lesion formation can be confirmed by monitoring the change in phase retardance in the acquired PSOCT images. This system demonstrates the feasibility of an integrated RFA/OCT catheter to deliver RF energy and image the cardiac wall simultaneously and justifies further research into use of this technology to aid RFA therapy for cardiac arrhythmias.

Effect of Sodium Thiosulfate Postconditioning on Ischemia-Reperfusion Injury Induced Mitochondrial Dysfunction in Rat Heart

The recent research on the therapeutic applications of sodium thiosulfate (STS) has gained importance in the treatment of cardiovascular diseases. Progressively through the present work, we have demonstrated that postconditioning of isolated rat heart subjected to ischemia-reperfusion injury using STS had preserved the mitochondrial structure, function, and number. Heart comprising of two mitochondrial subpopulations interfibrillar (IFM-involved in contractile function) and subsarcolemmal (SSM-involved in metabolic function), STS postconditioning imparted a state of hypometabolism to SSM, thereby reducing the metabolic demand of the reperfused heart. The IFM, on the other hand, provided the energy required to maintain contraction. Moreover, the hypometabolic state induced in SSM can lower the free radical release in addition to STS innate ability to act as an antioxidant and radical scavenger, all of which collectively provided cardioprotection. Therefore, drugs targeting IFM specifically or those reducing the energy demand for SSM can be suitable targets for myocardial ischemia-reperfusion injury.

Fibronectin accumulation within cardiac myocytes in rats with elevated plasma angiotensin II

Elevation in plasma angiotensin II (AngII) is associated with cardiac myocyte necrosis. Myocyte necrosis followed by wound healing and fibrosis represents a structural remodeling of the myocardium thought to contribute to abnormal myocardial function. Fibronectin (FN) is generally considered an early component of the healing process that precedes collagen accumulation. To better understand the time course of this remodeling process involving both cardiac myocytes and extracellular matrix, (i.e., FN and collagen), we used two animal models: (1) endogenous activation of the renin-angiotensin system by surgical induction of renovascular hypertension and (2) exogenous AngII administration (150 ng/min/kg). Animals were killed at different time points within the first two weeks. Both "cellular" (cFN) and "plasma" (pFN) FN immunolabeling were compared with collagen distribution (picrosirius red stain), together with histopathologic (hematoxylin-eosin stain) and ultrastructural examination of cardiac myocytes. In each experimental group, the pattern and time course of FN immunolabeling was coincident with histopathologic evidence of myocyte injury and/or remodeling. We found different patterns of FN labeling of cardiac myocytes: (a) homogenous intracellular distribution in necrotic myocytes, most obvious on days 1 and 2; (b) patchy intracellular distribution in nonnecrotic myocytes starting on day 4; and (c) marking internalized capillaries. Both FNs were codistributed throughout the myocardium of each ventricle; however, cFN was less pronounced and not seen in mature scars. Ultrastructural examination revealed different kinds of intramyocytic inclusions, characterized by vacuoles containing fibrillar/flocculent material, remnants of unknown origin, or internalized capillaries. We conclude that FNs are markers of cardiac myocyte necrosis and early interstitial remodeling and that renovascular hypertension and AngII administration exhibit the same time course and pattern of FN and collagen expression.

Automated quantification of myocardial salvage in a rat model of ischemia-reperfusion injury using 3D high-resolution magnetic resonance imaging (MRI)

Background

Quantification of myocardial “area at risk” (AAR) and myocardial infarction (MI) zone is critical for assessing novel therapies targeting myocardial ischemia–reperfusion (IR) injury. Current “gold‐standard” methods perfuse the heart with Evan's Blue and stain with triphenyl tetrazolium chloride (TTC), requiring manual slicing and analysis. We aimed to develop and validate a high‐resolution 3‐dimensional (3D) magnetic resonance imaging (MRI) method for quantifying MI and AAR.

Methods and Results

Forty‐eight hours after IR was induced, rats were anesthetized and gadopentetate dimeglumine was administered intravenously. After 10 minutes, the coronary artery was re‐ligated and a solution containing iron oxide microparticles and Evan's Blue was infused (for comparison). Hearts were harvested and transversally sectioned for TTC staining. Ex vivo MR images of slices were acquired on a 9.4‐T magnet. T2* data allowed visualization of AAR, with microparticle‐associated signal loss in perfused regions. T1 data demonstrated gadolinium retention in infarcted zones. Close correlation (r=0.92 to 0.94; P<0.05) of MRI and Evan's Blue/TTC measures for both AAR and MI was observed when the combined techniques were applied to the same heart slice. However, 3D MRI acquisition and analysis of whole heart reduced intra‐observer variability compared to assessment of isolated slices, and allowed automated segmentation and analysis, thus reducing interobserver variation. Anatomical resolution of 81 μm³ was achieved (versus ≈2 mm with manual slicing).

Conclusions

This novel, yet simple, MRI technique allows precise assessment of infarct and AAR zones. It removes the need for tissue slicing and provides opportunity for 3D digital analysis at high anatomical resolution in a streamlined manner accessible for all laboratories already performing IR experiments.

In vitro characterization of cardiac radiofrequency ablation lesions using optical coherence tomography

Currently, cardiac radiofrequency ablation (RFA) is guided by indirect signals. We demonstrate optical coherence tomography (OCT) characterization of RFA lesions within swine ventricular wedges. Untreated tissue exhibited a consistent birefringence artifact within OCT images due to the organized myocardium, which was not present in treated tissue. Birefringence artifacts were detected by filtering with a Laplacian of Gaussian (LoG) to quantify gradient strength. The gradient strength distinguished RFA lesions from untreated sites (p=5.93 x 10(-15)) with a sensitivity and specificity of 94.5% and 86.7% respectively. This study demonstrates the potential of OCT for monitoring cardiac RFA, confirming lesion formation and providing feedback to avoid complications.

Timing of adenosine 2A receptor stimulation relative to reperfusion has differential effects on infarct size and cardiac function as assessed in mice by MRI

The activation of adenosine 2A receptors before reperfusion following coronary artery occlusion reduces infarct size and improves ejection fraction (EF). In this study, we examined the effects of delaying treatment with the adenosine 2A receptor agonist ATL146e (ATL) until 1 h postreperfusion. The infarct size and EF were serially assessed by gadolinium-diethylenetriaminepentaacetic acid-enhanced MRI in C57BL/6 mice at 1 and 24 h postreperfusion. The infarct size was also assessed by 2,3,5-triphenyltetrazolium chloride staining at 24 h. Mice were treated with ATL (10 microg/kg ip) either 2 min before reperfusion (early ATL) or 1 h postreperfusion (late ATL) following the 45-min coronary occlusion. The two methods used to assess infarct size at 24 h postreperfusion (MRI and 2,3,5-triphenyltetrazolium chloride) showed an excellent correlation (R=0.96). The risk region, determined at 24 h postreperfusion, was comparable between the control and ATL-treated groups. The infarct size by MRI at 1 versus 24 h postreperfusion was 25+/-1 vs. 26+/-1% of left ventricular mass (means+/-SE) in control mice, 16+/-2 versus 17+/-2% in early-ATL mice, and 24+/-2 versus 25+/-2% in late-ATL mice (intragroup, P=not significant; and intergroup, early ATL vs. control or late ATL, P<0.05). EF was reduced in control mice but was largely preserved between 1 and 24 h in both early-ATL and late-ATL mice (P<0.05). In conclusion, after coronary occlusion in mice, the extent of myocellular death due to ischemia-reperfusion injury is 95% complete within 1 h of reperfusion. The infarct size was significantly reduced by ATL when given just before reperfusion, but not 1 h postreperfusion. Either treatment window helped preserve the EF between 1 and 24 h postreperfusion.

Thrombin inhibitor reduces myocardial infarction in apoE−/−× LDLR−/−mice

We have previously shown that atherosclerotic apolipoprotein E-deficient (apoE(-/-)) x LDL receptor-deficient (LDLR(-/-)) mice develop myocardial infarction when exposed to hypoxic stress. This study was performed to assess the role of thrombin and thrombosis in this process. ApoE(-/-) x LDLR(-/-) mice were fed a cholesterol-rich diet for 8 mo and were then subjected to hypoxic stress while receiving isoflurane anesthesia. One group received a bolus dose (5.6 micromol/kg) of the thrombin inhibitor melagatran, and control animals received PBS 10 min before the hypoxic stress. The mice were exposed to 10 min of hypoxia followed by normoxia. Ten minutes after the stress, Alzet pumps delivering melagatran (20 nmol x kg x (-1)min(-1)) or PBS were implanted, and the mice were allowed to recover for 48 h. The cardiac response was analyzed by histology, immunohistochemistry, and serum troponin T assay. All animals showed reversible ECG changes as a sign of ischemia during hypoxic stress, and 50% developed infarctions afterward as judged by troponin T levels. The group that received thrombin inhibitor had significantly lower troponin T and smaller myocardial infarctions than the PBS-treated group. These data show that thrombin generation is an important pathogenetic factor and suggest that coronary thrombosis is involved in myocardial infarction in atherosclerotic mice. Exposure of atherosclerotic mice to hypoxia leads to myocardial infarction through a two-phase pathway in which acute transient ischemia is followed by thrombin-dependent, irreversible, myocardial ischemia and myocardial cell death.

Adenosine A(1)-receptor induced late preconditioning and myocardial infarction: reperfusion duration is critical

We investigated the influence of coronary artery reperfusion (CAR) duration on the infarct-limiting properties of adenosine A(1)-receptor stimulation-induced delayed preconditioning (A(1)-DPC) compared with ischemia-induced delayed preconditioning (I-DPC). Sixty-one chronically instrumented conscious rabbits successfully underwent the following protocol. On day 1, rabbits were randomly divided into four groups: control (saline, iv), I-DPC (six 4-min coronary artery occlusion/4-min reperfusion cycles), A(1)-DPC(100) (N(6)-cyclopentyladenosine, 100 microg/kg iv), and A(1)-DPC(400) (N(6)-cyclopentyladenosine, 400 microg/kg iv). On day 2 (i.e., 24 h later), rabbits underwent a 30-min coronary artery occlusion after which CAR was started and maintained for either 3 or 72 h. Infarct size (percentage of the area at risk) was determined by triphenyltetrazolium chloride staining. After 3 h of CAR, I-DPC, A(1)-DPC(100), and A(1)-DPC(400) significantly decreased infarct size (36 +/- 5, 41 +/- 4, 38 +/- 5%, respectively) compared with control (55 +/- 3%). After 72 h of CAR, infarct sizes were not significantly different among the four groups. This result was confirmed by histologic analysis. Thus A(1)-DPC at the two investigated doses, as well as I-DPC, decreased infarct size after 3 h but not 72 h of CAR.

Endotoxin induces a second window of protection in the rat heart as determined by using p-nitro-blue tetrazolium staining, cardiac troponin T release, and histology

Pretreatment of rats with small doses of lipopolysaccharide (LPS), eg, for 24 hours, attenuates the cardiac dysfunction caused by subsequent period of myocardial ischemia. This phenomenon of enhanced tolerance to an ischemic insult has been termed "second window of protection." Although the cardioprotective effects of LPS were first reported in 1989, it is still unclear whether the observed attenuation by LPS of the ischemia-induced cardiac dysfunction is indeed secondary to the protection of cardiac myocytes against ischemic cell injury and death. This study was designed to investigate the effects of "preconditioning" with LPS on cell injury caused by regional myocardial ischemia and reperfusion in the anesthetized rat. Thirty-five Wistar rats were subjected to 25 minutes occlusion of the left anterior descending coronary artery followed by 2 hours of reperfusion. Hemodynamic parameters were continuously recorded, and at the end of the experiments, infarct size (using p-nitro-blue tetrazolium staining), cardiac troponin T release, and histological markers of cell injury and death were determined. In rats pretreated with a bolus of saline (vehicle for LPS) 2 or 24 hours before left anterior descending coronary artery occlusion and reperfusion, the infarct size was 59+/-4% (2 hours saline-control, n=6) and 61+/-3% (24 hours saline-control, n=6), respectively. Pretreatment of animals with a bolus of LPS (1 mg/kg IP) 24 hours before the onset of myocardial ischemia and reperfusion reduced both infarct size (to 18+/-7%; P<0.05, n=6) as well as histological signs of cell injury. Pretreatment (24 hours, as above) of rats with LPS also reduced the release of cardiac troponin T from 58+/-13 ng/mL (saline-control) to 16+/-9 ng/mL. In contrast, pretreatment of rats with LPS (2 hours, as above) did not affect infarct size (56+/-8%, n=6), cardiac troponin T release, or the histological parameters of cell injury. These data provide the first conclusive evidence that pretreatment of rats with a bolus of LPS 24 hours before intervention reduces the cell injury and death caused by a subsequent period of myocardial ischemia and reperfusion.

Visualization of mitochondrial oxygen fixation in brain slices by gas-tissue autoradiography

We have developed a novel autoradiographic method of visualizing oxygen fixation with sufficient delivery of [(15)O]O(2)/O(2). Brain slices (400 microm) were preincubated in Krebs-Ringer phosphate buffer and exposed to [(15)O]O(2) in a chamber. Fixation of [(15)O]O(2) correlated with the polarographically measured oxygen consumption among tissue slices from various organs (r=0.84). The fixation of [(15)O]O(2) by brain slices was significantly reduced (7. 2% of the control) by heat-treatment or dose dependently by NaCN (18. 2% of the control on 50 mM NaCN pretreatment). The (15)O radioactivity in the brain slices prepared from rotenone injected rats was also reduced compared to the control (56.8% of the control side). In an autoradiographic study, (15)O radioactivity showed a heterogeneous distribution both in coronal and sagittal sections. Autoradiography of young and senescent rat brain sections showed reduction of oxygen uptake with aging in the cerebrum, the senescent being 77.4% of the young. This method provides information regarding basic oxygen consumption of tissue slices under condition of sufficient O(2) delivery, which reflects mitochondrial electron transport.

Myocardial infarction mediated by endothelin receptor signaling in hypercholesterolemic mice

Myocardial infarction is linked to atherosclerosis, yet the sequence leading from silent coronary atherosclerosis to acute myocardial infarction has remained unclear. Here we show that hypercholesterolemic apolipoprotein E-/- low density lipoprotein receptor-/- mice develop not only coronary atherosclerosis but also myocardial infarction. Exposure of mice to mental stress or hypoxia led to acute ischemia, which, in a large proportion of the mice, was followed by electrocardiographic changes, leakage of troponin T, and loss of dehydrogenase from the myocardium, all indicative of acute myocardial infarction. Apoptotic death of cardiomyocytes was followed by inflammation and fibrosis in the heart. All these pathological changes could be prevented by a blocker of the endothelin type A receptor. Thus, stress elicits myocardial infarction through endothelin receptor signaling in coronary atherosclerosis caused by hypercholesterolemia.

Analysis of the new indirect revascularization method by determining objective parameters of clinical chemistry, histo-chemistry and histology

OBJECTIVE

This experimental study was initiated to determine whether transmyocardial laser revascularization (TMLR) after acute myocardial ischemia may improve clinical chemistry and diminish the amount of necrosis. In addition, the influence of TMLR on healthy myocardium was analyzed.

METHODS

The prolonged short-term effectiveness of TMLR was evaluated in 44 open-chest anesthetized pigs with (n = 21) or without (n = 23) the setting of acute myocardial ischemia (observation period 6 h): seven pigs served as controls (thoracotomy only). An additional seven pigs had left anterior descending artery (LAD) occlusion only (ischemia group). A subsequent 14 pigs were treated by TMLR (CO2) prior to LAD occlusion: Seven pigs received one laser channel/cm2 (group 1) and in seven pigs two channels/cm2 in the LAD territory (group 2) were performed. In addition, 16 pigs underwent TMLR without ischemia: Eight pigs received one channel/cm2 (group 3) and eight pigs two channels/cm2 (group 4). Clinical chemistry, histo-chemical assessment and histology were performed.

RESULTS

TMLR limits the expansion of the myocardial infarction zone: laser group 2 indicated a significant smaller area of necrosis in the area at risk (ischemic group (31%) vs. laser group 1 (19%), P = ns; laser group 2 (7%) vs. ischemic group, P < 0.01; laser group 1 vs. 2, P < 0.01). The amount of the area of necrosis and ischemia of laser groups 3 and 4 compared with control did not differ significantly (P = ns). Preventive creation of microchannels before ischemia did not diminish ischemic parameters (P = ns). The myocardial water content-measurements (MWC) in the ischemia, laser 1 and 2 groups did not show any difference at the end of the experiment, except higher values of laser group 2 (P < 0.05). Laser groups 3 and 4 revealed significantly higher MWC values compared with control (P < 0.001).

CONCLUSIONS

This prolonged acute study demonstrates that CO2-TMLR significantly reduces the amount of necrosis in the area at risk, but does not reduce cardiac ischemic markers. In healthy myocardium, TMLR significantly increases myocardial water content and ischemic parameters and induces small ischemic and very small necrotic areas surrounding open laser channels. Generally, the elevated cardiac enzymes and proteins are mainly attributed to the expected rise caused by vaporization of myocardial tissue in all laser groups.

Reliability of technetium-99m Q12 and thallium-201 myocardial activity measurements after triphenyl tetrazolium chloride myocardial staining by perfusion

RATIONALE AND OBJECTIVES

Investigations in animal models of severe myocardial ischemia or infarction use triphenyl tetrazolium chloride (TTC) staining to document infarction size histologically and to correlate these data with uptake measurements of radiolabeled tracers. Previously published data suggest that TTC staining itself has an important impact on myocardial tracer activity measurements. The authors hypothesized that TTC staining by perfusion has no significant effect on relative regional myocardial activity measurements of technetium-99m Q12 and thallium-201 in an open-chest canine model.

METHODS

Eight dogs underwent left anterior descending artery occlusion for 2 hours with 30 minutes of reperfusion, followed immediately by injection of technetium-99m Q12 (n = 4) or thallium-201. Total myocardial activity was recorded in a dose calibrator, and regional myocardial samples were obtained by Cope needle biopsies from the ischemic and normal zones, both before and after TTC staining.

RESULTS

The mean percent activity retention for the whole heart after perfusion staining with TTC was significantly reduced when compared to the preperfusion value for both technetium-99m Q12 and thallium-201. Regional measurements revealed no significant difference between the mean percent retention of technetium-99m Q12 in the ischemic and normal zones. After TTC perfusion, regional mean percent retention of thallium-201 was similar in the ischemic and normal zones.

CONCLUSIONS

In a canine model of myocardial ischemia and infarction with reperfusion, TTC staining can be performed by coronary artery perfusion without significantly affecting comparative regional measurements of either technetium-99m Q12 or thallium-201. Whole heart tracer retention is significantly reduced by TTC perfusion staining, but thallium-201 is more affected than technetium-99m Q12.

Myocardial viability

This article reviews various means to assess myocardial viability by imaging, and provides recommendations for current clinical practice. This article also discusses future directions in assessing myocardial viability.

Whole-body hyperthermia provides biphasic cardioprotection against ischemia/reperfusion injury in the rat

BACKGROUND

Hyperthermia increases cardiac tolerance to ischemia/reperfusion injury 24 hours after the heat stress. Free radicals and redox mechanisms have been implicated in such tolerance. However, the time course and its relation to the induction of antioxidative enzymes in the protection induced by whole-body hyperthermia against ischemia/reperfusion injury are unknown.

METHODS AND RESULTS

Hyperthermia was induced in anesthetized rats by placement in a temperature-controlled water bath. After the defined recovery interval(s) at room temperature, ischemia was induced by occlusion of the left coronary artery for 20 minutes, followed by reperfusion for 48 hours. The exposure to hyperthermia led to a recovery interval- dependent, biphasic reduction in the incidence of ventricular fibrillation during ischemia and in the size of the myocardial infarct as determined after 48 hours of reperfusion. The time course of the late-phase (24- to 96-hour recovery interval) but not the early-phase (0.5 hour) cardioprotection depended on the degree of hyperthermia. The time course of the increase in myocardial manganese superoxide dismutase (Mn-SOD) activity corresponded to that of the cardioprotective effects, although an increase in the content of Mn-SOD and of heat shock protein 72 corresponded only to the late-phase effects. Administration of an antioxidant before hyperthermia abolished the early- and late-phase cardioprotection and the increase in Mn-SOD activity.

CONCLUSIONS

THe activation of Mn-SOD mediated by free radical production during hyperthermia is important in the acquisition of early-phase and late-phase cardioprotection against ischemia/reperfusion injury in rats.

Methods for studying experimental myocardial ischemic and reperfusion injury

This review describes methodologies used to study experimental myocardial ischemic and reperfusion injury. Myocardial reperfusion injury may be manifest as myocardial stunning, ventricular arrhythmias, coronary vascular dysfunction, or the extension of the area of myocyte necrosis beyond that due to the ischemic insult alone. This review discusses methodology pertaining to the latter form of reperfusion injury. The pathophysiology of the reperfusion injury process is complex, including primarily cellular and humoral components of inflammation, as well as myocellular ionic and metabolic disturbances. Since the extent of injury may be influenced by methodological considerations this review aims to discuss the principle means of characterizing reperfusion injury in the experimental setting. The methods discussed are principally those related to in vivo research. Where appropriate, advantages, disadvantages, or alternate methods will be presented. Lastly, as understanding of the pathophysiology of reperfusion injury increases, newer techniques utilizing murine models, the study of apoptotic cell death, and the role of gender may be used more frequently and are thus briefly reviewed.

Tenascin and fibronectin expression in healing human myocardial scars

Fibronectin and tenascin are matrix proteins known to be present in early experimental wound healing. As only limited data are available regarding early matrix changes in human myocardial infarction, the presence of tenascin and fibronectin was studied in human myocardial infarctions of different post-infarction times (6 h to 17 years), using immunohistochemistry. In normal myocardium, fibronectin immunostaining was found in the subendothelial space in vessels. Tenascin was not present in normal myocardium. While fibronectin was demonstrated in the ischaemic cardiomyocytes within 1 day, tenascin was found 4-6 days post-infarction and was located at the margin of the area of infarction. Tenascin expression then shifted from the margin to the centre of the area of infarction, where it could be found 2-3 weeks post-infarction. More than 4 weeks post-infarction, the scar tissue consisted of collagen fibres, with sparse (myo)fibroblasts. By that time, both tenascin and fibronectin expression had disappeared. Another interesting observation in this study was the presence of tenascin, but not fibronectin, surrounding vacuolated glycogen-rich cells, or so-called hibernating cardiomyocytes.