Indolylmaleimide Derivative IM-17 Shows Cardioprotective Effects in Ischemia-Reperfusion Injury.

We previously developed IM-54 as a novel type of inhibitor of hydrogen-peroxide-induced necrotic cell death. Here, we examined its cell death inhibition profile. IM-54 was found to selectively inhibit oxidative stress-induced necrosis, but it did not inhibit apoptosis induced by various anticancer drugs or Fas ligand, or necroptosis. IM-17, an IM derivative having improved water-solubility and metabolic stability, was developed and confirmed to retain necrosis-inhibitory activity. IM-17 showed cardioprotective effects in an isolated rat heart model and an in vivo arrhythmia model, suggesting that IM derivatives may have therapeutic potential.

Effects of 2-Octynyladenosine (YT-146) on Mitochondrial Function in Ischemic/Reperfused Rat Hearts.

This study investigated the effects of an adenosine receptor agonist, 2-octynyladenosine (YT-146), on mitochondrial function in ischemic and ischemic/reperfused hearts. Isolated rat hearts were perfused in the Langendorff manner with a constant flow rate, and exposed to 30 min of ischemia followed by 60 min of reperfusion. Preischemic treatment with YT-146 significantly improved postischemic recovery of left ventricular developed pressure. The high-energy phosphate content in reperfused hearts treated with YT-146 was also more greatly restored than in untreated hearts. YT-146 treatment attenuated the Na(+) content of a mitochondria-enriched fraction, but not the myocardial Na(+) content, at the end of ischemia. These results suggest that preischemic YT-146 treatment preserves the energy-producing ability of mitochondria during ischemia in the Na(+)-accumulated myocardium. YT-146 also attenuated both the sodium lactate-induced decrease in mitochondrial energy-producing ability and the increase in mitochondrial Na(+) concentration in the myocardial skinned fibers. YT-146 may attenuate Na(+) influx to myocardial mitochondria in ischemic cardiac cells, resulting in both preservation of the ability of mitochondria to produce energy and enhancement of the contractile recovery in reperfused hearts. Our findings suggest that the cardioprotective effects of YT-146 against ischemia/reperfusion injury are at least partially due to the preservation of mitochondrial function in the ischemic myocardium.

The cardioprotective effects of novel Na+/H+ exchanger inhibitor TY-51924 on ischemia/reperfusion injury.

The inhibitory effects of sodium 3-guanidinocarbonyl-2-methyl-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridine-9-ylmethyl sulfate monoethanolate (TY-51924) are selective for Na(+)/H(+) exchanger (NHE)-1 in PS120 cells expressing human NHE isoforms assayed by NH(4)Cl prepulse technique. The median inhibitory concentrations (micromolar) of TY-51924 were 0.095 ± 0.008 (NHE-1), 0.621 ± 0.093 (NHE-2), and >100 (NHE-3). In anesthetized dogs subjected to 90 minutes ischemia/300 minutes reperfusion, intravenous bolus TY-51924 at 5 and 10 mg/kg administered 5 minutes before reperfusion reduced infarct size. The infarct size reduction ratios of TY-51924 at 5 and 10 mg/kg versus vehicle were 32.8% and 52.4%, respectively. But TY-51924 at 10 mg/kg administered 10 minutes after reperfusion did not reduce infarct size. In 2-step intravenous infusion initiated 15 minutes before reperfusion, TY-51924 at low dose (3.8 mg/kg per 5 minutes, then 6.2 mg/kg per 20 minutes) and at high dose (7.6 mg/kg per 5 minutes, then 12.4 mg/kg per 20 minutes) reduced infarct size. The infarct size reduction ratios of TY-51924 at 10 and 20 mg/kg versus vehicle were 39.2% and 51.7%, respectively; plasma drug concentrations at reperfusion were 16.8 and 38.8 µg/mL, respectively. This indicates that maintaining a plasma drug concentration of >20 µg/mL at reperfusion enables TY-51924 to reduce infarct size by inhibiting the NHE, which is activated during the early period of reperfusion.

Cardioprotective effects of 2-octynyladenosine (YT-146) in ischemic/reperfused rat hearts.

The present study was aimed at investigating the cardiac receptor subtypes involved in the cardioprotective effects of 2-octynyladenosine (YT-146), a novel adenosine receptor (AR) agonist. Isolated rat hearts were perfused in the Langendorff manner, and the hearts were exposed to 30 minute of ischemia followed by 60 minutes of reperfusion. YT-146 was infused for 10 minutes just before ischemia, and selective antagonists for AR subtypes were coadministered with YT-146. YT-146 (0.03­0.3 µM) dose dependently improved postischemic recovery of the left ventricular developed pressure (LVDP) of the ischemic/reperfused rat heart (maximum 59.7% ± 2.3% of the preischemic value). Coadministration of 8-(3-chlorostyryl) caffeine (A(2A) AR antagonist), alloxazine (A(2B)AR antagonist), or MRS-1191 (A(3) AR antagonist) with YT-146 failed to alter the cardioprotective effects of YT-146, and their LVDP recoveries were 55.9% ± 5.1%, 52.1% ± 1.9%, and 47.5% ± 1.7%, respectively, at the end of the reperfusion. On the other hand, coadministration of 8-cyclopentyl-1,3-dipropylxanthine (A(1) AR antagonist) abolished the YT-146­induced enhancement of postischemic LVDP recovery (31.7% ± 4.6%). The protein kinase C inhibitor chelerythrine also abolished the YT-146­induced enhancement of postischemic LVDP recovery (22.2% ± 4.5%). YT-146 has been known as an A(2) AR agonist, but our findings suggest that the cardioprotective effects of YT-146 are exerted via cardiac A(1) AR, not A(2) AR, stimulation and the activation of protein kinase C by preischemic treatment in isolated and crystalloid-perfused rat hearts.

Sphingosine 1-phosphate (S1P) regulates vascular contraction via S1P3 receptor: investigation based on a new S1P3 receptor antagonist.

Sphingosine 1-phosphate (S1P) induces diverse biological responses in various tissues by activating specific G protein-coupled receptors (S1P(1)-S1P(5) receptors). The biological signaling regulated by S1P(3) receptor has not been fully elucidated because of the lack of an S1P(3) receptor-specific antagonist or agonist. We developed a novel S1P(3) receptor antagonist, 1-(4-chlorophenylhydrazono)-1-(4-chlorophenylamino)-3,3-dimethyl- 2-butanone (TY-52156), and show here that the S1P-induced decrease in coronary flow (CF) is mediated by the S1P(3) receptor. In functional studies, TY-52156 showed submicromolar potency and a high degree of selectivity for S1P(3) receptor. TY-52156, but not an S1P(1) receptor antagonist [(R)-phosphoric acid mono-[2-amino-2-(3-octyl-phenylcarbamoyl)-ethyl] ester; VPC23019] or S1P(2) receptor antagonist [1-[1,3-dimethyl-4-(2-methylethyl)-1H-pyrazolo[3,4-b]pyridin-6-yl]-4-(3,5-dichloro-4-pyridinyl)-semicarbazide; JTE013], inhibited the decrease in CF induced by S1P in isolated perfused rat hearts. We further investigated the effect of TY-52156 on both the S1P-induced increase in intracellular calcium ([Ca(2+)](i)) and Rho activation that are responsible for the contraction of human coronary artery smooth muscle cells. TY-52156 inhibited both the S1P-induced increase in [Ca(2+)](i) and Rho activation. In contrast, VPC23019 and JTE013 inhibited only the increase in [Ca(2+)](i) and Rho activation, respectively. We further confirmed that TY-52156 inhibited FTY-720-induced S1P(3) receptor-mediated bradycardia in vivo. These results clearly show that TY-52156 is both sensitive and useful as an S1P(3) receptor-specific antagonist and reveal that S1P induces vasoconstriction by directly activating S1P(3) receptor and through a subsequent increase in [Ca(2+)](i) and Rho activation in vascular smooth muscle cells.

Amelioration of ischemia/reperfusion-induced myocardial infarction by the 2-alkynyladenosine derivative 2-octynyladenosine (YT-146).

The present study was aimed at determining whether the novel adenosine A2-agonist YT-146 may have cardioprotective effects against ischemia-reperfusion injury. Anesthetized open-chest dogs underwent 90-min occlusion of the left anterior descending artery and subsequent 300-min reperfusion. The animals were randomly assigned to receive vehicle, 3, or 10 microg/kg YT-146 or ischemic preconditioning (4 episodes of 5 min occlusion followed by 5 min of reperfusion). Blood pressure, heart rate, and regional myocardial blood flow throughout the experiment were measured, as was the myocardial infarct size after reperfusion. The infarct size of the vehicle-treated dog was 56.2% +/- 2.7% (n = 5), whereas that of 3 or 10 microg/kg YT-146-treated dog was smaller (ie, 29.5% +/- 8.7% or 20.2% +/- 7.0%, respectively; n = 5). The infarct size of the dog treated with 10 microg/kg YT-146 was reduced to a degree similar to that of the ischemic preconditioning (19.2% +/- 6.3%, n = 5). YT-146 at both doses elicited a dose-dependent increase in acute hyperemic coronary flow immediately after reperfusion. The cardioprotective effect may be attributed to the limitation of the infarct size, probably via A2-receptor-mediated coronary artery dilatation during the early period of reperfusion.