Hemodynamic and electron spin resonance (ESR) analyses were performed on isolated ischemic and reperfused rat hearts to assess the cardioprotective and antioxidant effects of therapeutically relevant concentrations of Ginkgo biloba extract (EGb 761; 5, 50 or 200 microg/ml), its terpenoid constituents (ginkgolide A; 0.05 microg/ml and ginkgolide B; 0.05, 0.25 or 0.50 microg/ml), and a terpene-free fraction of EGb 761 (CP 205; 5 or 50 microg/ml). Hearts underwent 10 min of low-flow ischemia, 30 min of no-flow global ischemia, and 60 min of reperfusion. Test substances were added to the perfusion fluid during the last 10 min of control perfusion, low-flow ischemia and the first 10 min of reperfusion. A separate group of rats was treated with CP 205 (60 mg/kg/day; p.o.) for 15 days, after which the hearts were perfused with plain buffer. In ESR experiments, the spin-trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was added to the perfusate to determine the effects of treatments on post-ischemic myocardial free radical generation. Results showed that in vitro exposure of hearts to EGb 761 (5 or 50 microg/ml) or to ginkgolides A and B (both at 0.05 microg/ml), or in vivo pretreatment of the rats with CP 205 delayed the onset of contracture during ischemia. The strong reperfusion-induced elevation of left ventricular end-diastolic pressure observed in untreated hearts was significantly reduced by in vitro exposure to the lowest concentrations of EGb 761, by ginkgolide A, and to a lesser extent by ginkgolide B, or by prior oral treatment with CP 205. Post-ischemic functional recovery.was significantly improved by in vivo administration of CP 205, by perfusion with 5 microg/ml of EGb 761 or with both terpenoids as compared to untreated group but in vitro CP 205 was not effective. ESR analyses revealed that DMPO-OH (the DMPO/hydroxyl radical spin-adduct) concentrations in coronary effluents were markedly decreased by all treatments, except for the lowest concentration of ginkgolide B. Perfusing 5 microg/ml EGb 761 resulted in a better inhibition of baseline DMPO-OH concentration than 5 microg/ml CP 205 (-70 % and -48 % vs. control, respectively), indicating that both terpenoid and flavonoid constituents of EGb 761 are required to produce this effect. CP 205 was significantly more efficient in reducing DMPO-OH concentration when administered in vivo than when applied in vitro, indicating that the antioxidant effect of flavonoid metabolites (formed in vivo) is superior to that of intact flavonol glycosides (present in vitro). Collectively, these findings provide the first evidence that part of the cardioprotection afforded by EGb 761 is due to a specific action of its terpenoid constituents and that this effect involves a mechanism independent of direct free radical-scavenging. Thus, the terpenoid constituents of EGb 761 and the flavonoid metabolites that are formed after in vivo administration of the extract act in a complementary manner to protect against myocardial ischemia-reperfusion injury.

Oxygen plays a critical role in the pathophysiology of myocardial injury during both ischemia and subsequent reperfusion (I/R). Thus, oxygen concentration is an important variable to measure during I/R. In the present work, electron paramagnetic resonance (EPR)-based oximetry was used to measure the oxygen concentration during a series of I/R episodes and oxygenation levels were correlated with the contractile and hemodynamic functions of the heart. A custom-developed electronically tunable surface coil resonator working at 1.1 GHz was used to determine tissue pO 2 in the beating heart. Microcrystalline particulate of lithium phthalocyanine was used as an EPR oximetry probe. Isolated and perfused rat hearts were subjected to 1 or 3 hr durations of preischemic perfusion, followed by 15-min I/R cycles. In hearts perfused for 3 hr prior to 15-min I/R cycles, the myocardial pO 2 decreased gradually on subsequent reperfusions of three successive I/R cycles. However, in hearts perfused for 1 hr there was almost 100% recovery of myocardial pO 2 in all three I/R cycles. The extent of oxygenation recovered in each reperfusion cycle correlated with the recovery of hemodynamic and contractile function. The results also showed that the oxygen consumption rate of the heart at the end of each I/R episode decreased in direct proportion to the functional recovery. In summary, it was observed that the amount of myocardial oxygen consumption during I/R could provide a reliable index of functional impairment in the heart. Magn Reson Med 51:835-842, 2004.

Ginkgolides have been demonstrated to protect the myocardium in experimental ischemiareperfusion, but the extent to which this property is not related to platelet-activating factor (PAF) inhibition remains debated. This study was undertaken to determine whether a ginkgolide devoid of any anti-PAF activity could retain a cardioprotective activity. For this purpose, a new ginkgolide C (3) analogue, 7-O-(4-methylphenyl) ginkgolide C (4), was obtained from 3 with retention of configuration, using, in the key step, a copper-catalyzed arylation with tris-(4-methylphenyl) bismuth diacetate. No PAF inhibition on rabbit platelets in vitro was found for 4 up to 1.2.10 -4 M. However, 4 was found a significantly better preserving agent than 3 or ginkgolide B, a potent PAF inhibitor (all drugs at 0.35 µM), on hemodynamic and metabolic (i.e., myocardial ATP contents and enzymatic activities) indices measured in rat isolated hearts undergoing ischemia-reperfusion. The data provide additional support to a PAF-unrelated pharmacological activity for ginkgolides. Because the water solubility of 4, estimated by high-performance liquid chromatography analysis, was significantly lower than that of the parent molecule 3, a likely mechanism for the protective action of 4 involves its increased affinity for the myocardium, as compared to the relatively more hydrophilic 3. Drug Dev. Res. 54:191-201, 2001.

Proton electron double resonance imaging (PEDRI) is a double resonance technique where proton MRI is performed with irradiation of a paramagnetic solute. A low-field PEDRI system was developed at 20.1 mT suitable for imaging free radicals in biological samples. With a new small dual resonator, PEDRI was applied to image nitroxide free radicals in isolated beating rat hearts. Experiments with phantoms showed maximum image enhancement factors (IEF) of 42 or 28 with TEMPONE radical concentrations of 2-3 mM at EPR irradiation powers of 12W or 6W, respectively. In the latter case, image resolution better than 0.5 mm and radical sensitivity of 5 microM was obtained. For isolated heart studies, EPR irradiation power of 6W provided optimal compromise of modest sample heating with good SNR. Only a small increase in temperature of about 1 degrees C was observed, while cardiac function remained within 10% of control values. With infusion of 3 mM TEMPONE an IEF of 15 was observed enabling 2D or 3D images to be obtained in 27 sec or 4.5 min, respectively. These images visualized the change in radical distribution within the heart during infusion and clearance. Thus, PEDRI enables rapid and high-quality imaging of free radical uptake and clearance in perfused hearts and provides a useful technique for studying cardiac radical metabolism.

Formation of free radicals during reperfusion of the isolated ischemic heart has often been demonstrated by detecting hydroxyl radical spin adducts of the nitrone 5,5-dimethyl-1-pyrroline N-oxide (DMPO) in coronary effluents. However, questions still remain regarding (a) whether the reported cardiovascular effects of nitrone perfusion may affect the formation of spin adducts, and (b) the primary generation of superoxide (Oᠨ Ϫ 2 ), because of the short persistency of Oᠨ Ϫ 2 /DMPO spin adduct. We therefore compared the effects of perfusing 5 mM of two nitrones, DMPO and 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO) or the two structurally related pyrrolidines, diethyl (2-methyl-2-pyrrolidinyl) phosphonate (DEPMPH) and pyrrolidine (PyH), on postischemic functional recovery of rat hearts subjected to 10 min of low-flow ischemia, 30 min of global ischemia and 60 min of reperfusion. All compounds were added to the perfusate before ischemia, throughout low-flow ischemia and during the initial 10 min of reflow. In one additional group, hearts received DEPMPO only at reflow. Hemodynamic and in vitro ESR evidence is presented indicating that the phosphonate group of DEPMPO and DEPMPH confers these molecules with an enhanced cardioprotective efficacy, unrelated to radical scavenging, acting in synergy with the intrinsic radical trapping effects of the nitronyl group. Continuous-flow ESR spin trapping using 5.7 mM DEPMPO administered at reflow, but not before ischemia, demonstrated for the first time extended formation of Oᠨ Ϫ 2 in the reperfused myocardium.Keywords : ischemia/reperfusion injury; superoxide; continuous-flow ESR; spin trap ; functional recovery.The formation of oxygen-centered free radicals such as su-ing to the very short life-span of oxyradicals under physiological conditions, two main ESR strategies for their detection and peroxide (Oᠨ Ϫ 2 ) and hydroxyl radical (HOᠨ) is a well-established phenomenon occurring during myocardial ischemia/reperfusion. quantitative analysis have been developed in cardiovascular studies. These highly reactive species have been incriminated in the pathogenesis of reperfusion-induced electrophysiological and First, ESR studies at the temperature of liquid nitrogen (freeze trapping) showed that the normal free radical content of biochemical disturbances leading to ventricular fibrillation and tissue necrosis [1Ϫ3]. Over the last decade, ESR spectroscopy cardiac tissue is markedly altered after an episode of ischemia/ reperfusion [4Ϫ9]. Plausible explanations for the origin of these has been extensively used to characterize post-ischemic free radical formation in isolated heart models or in intact animals. Ow-changes have been proposed, including a modification in the redox state of some proteins involved in the mitochondrial respi- tissue samples must be stringently controlled to avoid the formaAbbreviations. DMPO, 5,5-dimethyl-1-pyrroline N-oxide; DMPOtion of artifactual signals and it is therefore admitted that freeze OOH, 2,2-dimethyl-5-hydroperoxy-1-pyrrolidin...