Dunli Wu

Mitochondria-Targeted Peptide Accelerates ATP Recovery and Reduces Ischemic Kidney Injury

The burst of reactive oxygen species (ROS) during reperfusion of ischemic tissues can trigger the opening of the mitochondrial permeability transition (MPT) pore, resulting in mitochondrial depolarization, decreased ATP synthesis, and increased ROS production. Rapid recovery of ATP upon reperfusion is essential for survival of tubular cells, and inhibition of oxidative damage can limit inflammation. SS-31 is a mitochondria-targeted tetrapeptide that can scavenge mitochondrial ROS and inhibit MPT, suggesting that it may protect against ischemic renal injury. Here, in a rat model of ischemia-reperfusion (IR) injury, treatment with SS-31 protected mitochondrial structure and respiration during early reperfusion, accelerated recovery of ATP, reduced apoptosis and necrosis of tubular cells, and abrogated tubular dysfunction. In addition, SS-31 reduced medullary vascular congestion, decreased IR-mediated oxidative stress and the inflammatory response, and accelerated the proliferation of surviving tubular cells as early as 1 day after reperfusion. In summary, these results support MPT as an upstream target for pharmacologic intervention in IR injury and support early protection of mitochondrial function as a therapeutic maneuver to prevent tubular apoptosis and necrosis, reduce oxidative stress, and reduce inflammation. SS-31 holds promise for the prevention and treatment of acute kidney injury.

Potent mitochondria-targeted peptides reduce myocardial infarction in rats.

ObjectivePreviously, we demonstrated that a novel opiate peptide, 2′,6′-dimethyl-tyrosine-D-Arg-Phe-Lys-NH2, provided cardioprotection against myocardial stunning in vivo. We subsequently showed that this peptide targeted mitochondria and can scavenge reactive oxygen species. The objective of this study was to determine the role of opioid versus antioxidant activity in cardioprotection. MethodsWe compared two mitochondria-targeted peptide analogs that lacked opioid activity: SS-31 (D-Arg-2′,6′-dimethyl-tyrosine-Lys-Phe-NH2) and SS-20 (Phe-D-Arg-Phe-Lys-NH2). They differ in that only SS-31 has scavenging ability. Rats (n=8/group) were randomized to SS-31, SS-20 or placebo. The drugs (3 mg/kg) or saline was administered intraperitoneally 30 min before ligation of the left anterior descending artery for 60 min, and another dose given intraperitoneally 5 min before reperfusion for 60 min. Study endpoints included myocardial infarct size, cardiac arrhythmia and myocardial lipid peroxidation. ResultsThe area at risk was similar among the groups. The infarct area/area at risk, however, was significantly smaller in the treatment groups (53.9±1.1% in SS-31 group, 47.1±1.4% in SS-20 group, versus 59.9±1% in the controls, P<0.01). Lipid peroxidation was significantly reduced by both SS-31 and SS-20 treatment. Arrhythmia occurred only during the early period of coronary occlusion and was less frequent and less severe in the peptide treatment groups than in the controls (Lambeth score 5 points, 3 points, versus 13 points in the controls, P<0.05). ConclusionsThis study shows that pretreatment with both SS-31 and SS-20 significantly reduced myocardial lipid peroxidation and infarct size in ischemia–reperfusion injury, and suggests that the cardioprotective properties of 2′,6′-dimethyl-tyrosine-D-Arg-Phe-Lys-NH2 was primarily mediated by its antioxidant properties. As SS-20 does not scavenge reactive oxygen species, it most likely reduces reactive oxygen species production during ischemia–reperfusion.

Opioid-induced stimulation of fetal respiratory activity by [D-Ala2]deltorphin I.

[D-Ala2]deltorphin I effects on fetal respiratory activity was characterized to determine the role delta-opioid receptors play in modulating fetal respiratory activity. [D-Ala2]deltorphin I, infused at 0.3 or 100 micrograms/h, intracerebroventricularly (i.c.v.), stimulated fetal respiratory activity without changing blood pH, PCO2 or PO2. Stimulation by 0.3 micrograms/h, but not 100 micrograms/h, was blocked by i.c.v. infusion of the delta-opioid receptor antagonist, naltrindole. Stimulation by 100 micrograms/h was blocked by the mu 1-opioid receptor antagonist naloxonazine. These data suggest stimulation of fetal respiratory activity by 0.3 micrograms/h [D-Ala2]deltorphin I are mediated specifically through delta-opioid receptors; while [D-Ala2]deltorphin I at 100 micrograms/h is no longer selective for the delta-opioid receptor, and the stimulation may be mediated through the mu 1-opioid receptor.

Respiratory depression after intravenous administration of δ-selective opioid peptide analogs

Abstract We compared the effects of three μ- (DAMGO, DALDA, TNPO) and three δ- (DPDPE, DELT, SNC-80) opioid agonists on arterial blood gas after IV administration in awake sheep. None of the μ agonists altered pO 2 , pCO 2 or pH. All three δ agonists decreased pO 2 , increased pCO 2 and decreased pH, and this effect was not sensitive to naloxone or TIPP ψ, a δ-antagonist, suggesting that it is not mediated by δ-opioid receptors. When administered to pregnant animals, there were significant changes in fetal pCO 2 and pH. It may be possible to develop δ-selective opioid agonists which do not produce respiratory depression.

Nociceptin/orphanin FQ increases blood pressure and heart rate via sympathetic activation in sheep

This study was undertaken to examine the cardiovascular effects of nociceptin/Orphanin FQ (OFQ). Nociceptin/OFQ (10-300 nmol/kg, IV) stimulates an increase in mean blood pressure (MBP) and heart rate (HR) in chronically catheterized sheep. Pretreatment with phenoxybenzamine (5 mg/kg) attenuated the pressor response, consistent with sympathetically mediated vasoconstriction. Furthermore, the lack of a reflex bradycardia suggests either blunting of the baroreflex by nociceptin/OFQ or direct beta-adrenergic activation. The bradycardic response to norepinephrine (0.6 microg/kg, IV) remained intact after nociceptin/OFQ administration, demonstrating that nociceptin/OFQ does not blunt the baroreflex. Additionally, the increase in HR was completely reversed by pretreatment with propranolol. These data suggest that nociceptin/OFQ plays a role in cardiovascular regulation via sympathetic activation.

Cardiovascular and metabolic responses to two receptor-selective opioid agonists in pregnant sheep.

OBJECTIVE Our purpose was to assess the effects of an intravenous dose of a highly selective mu-(DALDA) and delta-(DPDPE) opioid peptide to determine which class of peptide has the best clinical potential. STUDY DESIGN Chronically instrumented pregnant ewes received a 0.3 mg/kg intravenous bolus of each peptide with and without opioid receptor blockade by means of a randomized prospective design. RESULTS Intravenous DALDA produced only mild hypertension and a loss of heart rate variability, whereas DPDPE produced respiratory depression, maternal hypertension, and a fall in heart rate in both mother and fetus. Uterine blood flow, oxygen uptake, and glucose uptake were unchanged with both drugs. The effects of DALDA but not DPDPE were reversed by opioid receptor blockade. CONCLUSION The delta-selective agonist had multiple nonopioid adverse effects, whereas the mu-selective agonist was well tolerated by the pregnant ewe, suggesting that mu-selective agonists have better potential for clinical use as an analgesic in pregnancy.

Baroreflex-mediated bradycardia but not tachycardia is blunted peripherally by intravenous μ-opioid agonists

OBJECTIVE We sought to test the hypothesis that an intravenous dose of H-Tyr-D-Arg-Phe-Lys-NH2, a highly mu-receptor selective opioid peptide, suppresses baroreflex sensitivity through a peripheral mechanism. STUDY DESIGN A transient change in mean arterial pressure was produced in chronically instrumented pregnant ewes by norepinephrine or sodium nitroprusside in the absence or in the presence of H-Tyr-D-Arg-Phe-Lys-NH2, a highly mu-selective opioid peptide. In some studies naloxone methiodide, a peripheral opioid antagonist, was infused starting 60 minutes before the administration of H-Tyr-D-Arg-Phe-Lys-NH2 and maintained for a total of 90 minutes. Linear plots were obtained when the changes in mean arterial pressure during the pressure rise were plotted against the changes in heart rate and the sensitivity of the baroreflex was derived as the slope of the linear regression line. RESULTS We observed (1) lower baroreflex sensitivity after H-Tyr-D-Arg-Phe-Lys-NH2 administration with a hypertensive stimulus; (2) unchanged baroreflex sensitivity after H-Tyr-D-Arg-Phe-Lys-NH2 administration with a hypotensive stimulus; and (3) unchanged baroreflex sensitivity after H-Tyr-D-Arg-Phe-Lys-NH2 administration with a hypertensive stimulus in the presence of naloxone methiodide. CONCLUSION H-Tyr-D-Arg-Phe-Lys-NH2 suppresses the hypertensive but not the hypotensive arm of the baroreflex through peripheral opioid receptors. These results suggest that mu-opioid receptors are present in the vagus nerves and that the activation of these opioid receptors inhibits reflex bradycardia in pregnant sheep.

A Peripheral Site of Action for the Attenuation of Baroreflex-Mediated Bradycardia by Intravenous μ-Opioid Agonists

We previously reported that i.v. DAMGO (Tyr-D-Ala-Gly-NMePhe-Gly-ol), a selective mu-opioid agonist, causes an increase in blood pressure with no change in heart rate in unanesthetized sheep and subsequently demonstrated that DAMGO attenuates baroreflex-mediated bradycardia. To determine the site and mechanism by which mu-agonists inhibit baroreflex sensitivity, we have carried out further investigations by using DAMGO and another mu-agonist, DALDA (Tyr-D-Arg-Phe-Lys-NH2). The bradycardic response to norepinephrine (NE) was significantly blunted after i.v. DAMGO or DALDA in both nonpregnant and pregnant sheep. In contrast, the tachycardic response to sodium nitroprusside (SNP) remained unchanged in the presence of DAMGO or DALDA. In view of the highly restricted distribution of DALDA across the blood-brain barrier (BBB), we hypothesized that the blunting of reflex-mediated bradycardia by mu-opioid agonists can occur peripherally. Pretreatment with the quaternary opioid antagonist, naloxone methiodide (NM), completely blocked the attenuation of baroreflex sensitivity by DAMGO and DALDA in both nonpregnant and pregnant animals. These data suggest that in addition to central mechanisms, mu-opioid agonists can inhibit baroreflex sensitivity at a peripheral site, most likely by inhibiting vagal influence on heart-rate control rather than by acting directly at baroreceptors.

Cardiovascular effects of a μ-selective opioid agonist (tyrosine-D-arginine-phenylalanine-lysine-NH2) in fetal sheep: Sites and mechanisms of action

Abstract Objective: We investigated the effects of DALDA (tyrosine- D -arginine-phenylalanine-lysine-NH 2 ), a μ-selective opioid peptide, on heart rate and blood pressure in fetal sheep with long-term instrument implantation. Study design: DALDA was given as an intravenous bolus in doses ranging from 0.15 to 0.5 mg/kg. A 0.5 mg/kg dose of DALDA was given in the presence of the opioid antagonist naloxone and its quaternary analog naloxone methiodide (6 mg/h); it was also given in conjunction with the β-adrenergic antagonist propranolol (2 mg/h). Statistical analyses were performed by 1-way and 2-way analysis of variance. Results: The fetus responded to DALDA with an increase in heart rate with all doses ( P P P = .003), and propranolol ( P Conclusions: In the fetus intravenous DALDA increases heart rate without any change in blood pressure by way of the μ receptor and through central sympathetic activation. These effects of DALDA are different from those seen in the adult, suggesting different sites and mechanisms of action. (Am J Obstet Gynecol 1999;180:1127-30.)

The Role of N-Methyl-D-Aspartate Receptors in the Release of Adrenocorticotropin by Dynorphin A1–13

We previously reported that dynorphin A1–13 evokes a significant increase in plasma adrenocorticotropin (ACTH) after intravenous administration in the ovine fetus. This response was not sensitive to naloxone and was regulated differently from the response to U50,488H, a selective ĸ-opioid agonist. NMDA appears to play a role in many of the nonopioid actions of dynorphin. We therefore hypothesized that dynorphin A1–13 may release ACTH via N-methyl-D-aspartate (NMDA) receptors. To test this hypothesis, we have compared the ACTH response to dynorphin A1–13 and NMDA in the chronically-instrumented ovine fetus. Our data show that both dynorphin A1–13 (0.5 mg/kg) and NMDA (4 mg/kg) induced a significant release of immunoreactive ACTH in the late-term ovine fetus. The ACTH response to NMDA was of a smaller magnitude, but of longer duration, when compared to dynorphin A1–13. The response to both dynorphin A1–13 and NMDA was significantly attenuated by pretreatment with the noncompetitive NMDA antagonist, MK-801, but was not affected by antagonists of corticotropin-releasing hormone and arginine vasopressin. Finally, the ACTH response to both dynorphin A1–13 and NMDA were inhibited by dexamethasone. The results of this study indicate a role for NMDA receptors in the action of dynorphin A1–13, and suggest that NMDA may act directly at the level of the pituitary to release ACTH without the involvement of hypothalamic secretagogues.