Location

Philadelphia, PA

Start Date

10-5-2021 12:00 AM

End Date

13-5-2021 12:00 AM

Description

Previously, a novel three-amino acid peptide (tripeptide) that is structurally similar to other amino acid-based delta and kappa-opioid receptor agonists (the predominant opioid receptor subtypes in heart tissue) demonstrated a significant reduction in infarct size and improved cardiac function when administered during preconditioning in isolated rat hearts using the Langendorf model. The cardioprotective effects of tripeptide were blocked by naloxone (NX, broad-spectrum opioid antagonist) and nor-binaltorphine (BNI, kappa-opioid receptor antagonist), whereas naltrindole (NTI, delta-opioid receptor antagonist) seemed to augment the effects of tripeptide. To determine whether the cardioprotective effects of the combination were due to tripeptide or NTI, the effects of NTI and other opioid antagonists were evaluated individually in the same model. Therefore, the goal was to evaluate the effects of NTI, BNI, and NX independently.

Hearts isolated from male Sprague-Dawley rats (~300g) were subjected to global ischemia (I, 30min)/reperfusion (R, 50min). NX (10 μM, n=6), BNI (5 μM, n=7), NTI (5 μM, n=8), or Krebs’ buffer control (control n=10) were given to the hearts 5 min prior to ischemia and during the first 5 min of reperfusion in a Langendorf model, perfused at a constant pressure of 80mmHg. Left ventricular (LV) functional indices were measured using an indwelling pressure transducer-tipped catheter. At the end of reperfusion (50min), hearts were frozen, sectioned (2 mm), and stained with 1% triphenyltetrazolium chloride (TTC). To determine infarct size, the weight of infarcted tissue was compared to total tissue at risk. All data were evaluated using ANOVA Student-Newman-Keuls post-hoc analysis.

Control (untreated) hearts showed an elevated final LV end-diastolic pressure (LVEDP) of 60 ± 5 mmHg compared to an average initial baseline of 8 ± 1 mmHg (similar in all groups) and a mean infarct size of 36 ± 3% at 50 min post-reperfusion. NX and BNI demonstrated no significant cardioprotective effects compared to control with final LVEDP measures of 64 ± 8 mmHg and 61 ± 2 mmHg, respectively. Infarct size for NX (35 ± 5%) and BNI (36 ± 5%) treated hearts were similar to control hearts. By contrast, NTI significantly improved final LVEDP (17 ± 3mmHg) to near baseline values and reduced infarct size to 7 ± 2% compared to all groups (p< 0.01).

The results indicate that pretreatment with NTI can prevent I/R injury and restore post-reperfused heart function to near pre-ischemic levels. In future studies, we will evaluate the cardioprotective effects of NTI in an acute in vivo heart I/R model. In separate studies, we will attempt to determine the mechanism of action of NTI preconditioning, specifically whether cardioprotection is indeed mediated via delta receptor antagonism or via some other mechanism.

Embargo Period

6-14-2021

Comments

Winner of 2021 Research Week David Miller, DO ’60 Endowed Memorial Research Day Best in Show Award

COinS
 
May 10th, 12:00 AM May 13th, 12:00 AM

Pretreatment with Naltrindole exhibits robust cardioprotection in an isolated rat heart model of ischemia-reperfusion injury

Philadelphia, PA

Previously, a novel three-amino acid peptide (tripeptide) that is structurally similar to other amino acid-based delta and kappa-opioid receptor agonists (the predominant opioid receptor subtypes in heart tissue) demonstrated a significant reduction in infarct size and improved cardiac function when administered during preconditioning in isolated rat hearts using the Langendorf model. The cardioprotective effects of tripeptide were blocked by naloxone (NX, broad-spectrum opioid antagonist) and nor-binaltorphine (BNI, kappa-opioid receptor antagonist), whereas naltrindole (NTI, delta-opioid receptor antagonist) seemed to augment the effects of tripeptide. To determine whether the cardioprotective effects of the combination were due to tripeptide or NTI, the effects of NTI and other opioid antagonists were evaluated individually in the same model. Therefore, the goal was to evaluate the effects of NTI, BNI, and NX independently.

Hearts isolated from male Sprague-Dawley rats (~300g) were subjected to global ischemia (I, 30min)/reperfusion (R, 50min). NX (10 μM, n=6), BNI (5 μM, n=7), NTI (5 μM, n=8), or Krebs’ buffer control (control n=10) were given to the hearts 5 min prior to ischemia and during the first 5 min of reperfusion in a Langendorf model, perfused at a constant pressure of 80mmHg. Left ventricular (LV) functional indices were measured using an indwelling pressure transducer-tipped catheter. At the end of reperfusion (50min), hearts were frozen, sectioned (2 mm), and stained with 1% triphenyltetrazolium chloride (TTC). To determine infarct size, the weight of infarcted tissue was compared to total tissue at risk. All data were evaluated using ANOVA Student-Newman-Keuls post-hoc analysis.

Control (untreated) hearts showed an elevated final LV end-diastolic pressure (LVEDP) of 60 ± 5 mmHg compared to an average initial baseline of 8 ± 1 mmHg (similar in all groups) and a mean infarct size of 36 ± 3% at 50 min post-reperfusion. NX and BNI demonstrated no significant cardioprotective effects compared to control with final LVEDP measures of 64 ± 8 mmHg and 61 ± 2 mmHg, respectively. Infarct size for NX (35 ± 5%) and BNI (36 ± 5%) treated hearts were similar to control hearts. By contrast, NTI significantly improved final LVEDP (17 ± 3mmHg) to near baseline values and reduced infarct size to 7 ± 2% compared to all groups (p< 0.01).

The results indicate that pretreatment with NTI can prevent I/R injury and restore post-reperfused heart function to near pre-ischemic levels. In future studies, we will evaluate the cardioprotective effects of NTI in an acute in vivo heart I/R model. In separate studies, we will attempt to determine the mechanism of action of NTI preconditioning, specifically whether cardioprotection is indeed mediated via delta receptor antagonism or via some other mechanism.