Tempol Reverses the Negative Effects of Morphine on Arterial Blood-Gas Chemistry and Tissue Oxygen Saturation in Freely-Moving Rats

Abstract

We have reported that pretreatment with the clinically approved superoxide dismutase mimetic, Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), blunts the cardiorespiratory depressant responses elicited by a subsequent injection of fentanyl, in halothane-anesthetized rats. The objective of the present study was to determine whether Tempol is able to reverse the effects of morphine on arterial blood-gas (ABG) chemistry in freely-moving Sprague Dawley rats. The intravenous injection of morphine (10 mg/kg) elicited substantial decreases in pH, pO2 and sO2 that were accompanied by substantial increases in pCO2 and Alveolar-arterial gradient, which results in diminished gas-exchange within the lungs. Intravenous injection of a 60 mg/kg dose of Tempol 15 min after the injection of morphine caused minor improvements in pO2 and pCO2 but not in other ABG parameters. In contrast, the 100 mg/kg dose of Tempol caused an immediate and sustained reversal of the negative effects of morphine on arterial blood pH, pCO2, pO2, sO2 and Alveolar-arterial gradient. In other rats, we used pulse oximetry to determine that the 100 mg/kg dose of Tempol, but not the 60 mg/kg dose elicited a rapid and sustained reversal of the negative effects of morphine (10 mg/kg, IV) on tissue O2 saturation (SpO2). The injection of morphine caused a relatively minor fall in mean arterial blood pressure that was somewhat exacerbated by Tempol. These findings demonstrate that Tempol can reverse the negative effects of morphine on ABG chemistry in freely-moving rats paving the way of structure-activity and mechanisms of action studies with the host of Tempol analogues that are commercially available.

D-Cysteine Ethyl Ester Reverses the Deleterious Effects of Morphine on Breathing and Arterial Blood–Gas Chemistry in Freely-Moving Rats

“…As expected (May et al, 2013a,b; Young et al, 2013 ; Baby et al, 2018 , Baby et al, 2021 SM. ; Gaston et al, 2021 ), a 10-mg/kg dose of morphine elicited a relatively transient decrease in Freq, which was not truly indicative of the actual effects of morphine, since morphine elicited sustained increases in Ti (lengthened inspiration), whereas it elicited pronounced decreases in Te (shortened expiration).…”

“…The readily conversion of L-NACme to L-cysteine in cells ( Lailey and Upshall, 1994 ) argues that the effects of D-CYSee are not due to conversion to H2S via the D-amino acid oxidase–mercaptopyruvate sulfur transferase system ( Shibuya and Kimura, 2013 ; Kimura, 2014 ). Since the superoxide anion/free radical scavenger, Tempol, attenuates OIRD elicited by morphine and fentanyl ( Baby et al, 2021a , b ), it points to the importance of redox mechanisms in the actions of opioids and potentially the ability of thiol esters to reverse OIRD. Aside from direct interactions with functional proteins, potential mechanisms of action of D-CYSee may involve (1) direct binding to myristoylated alanine-rich C-kinase substrate (MARCKS), which is a D-cysteine binding protein ( Semenza et al, 2021 ); (2) modulation of OR-β-arrestin cell signaling events that spare the analgesic G-protein–mediated actions of morphine ( Schmid et al, 2017 ; Grim et al, 2020 ); and/or (3) conversion of D-CYSee to S-nitroso-D-CYSee by nitric oxide synthase-dependent processes ( Perissinotti et al, 2005 ; Hess and Stamler, 2012 ; Stomberski et al, 2019 ; Seckler et al, 2021 ), which may act similar to the intracellular S-nitrosylating agent, S-nitroso-L-CYSee ( Clancy et al, 2001 ).…”

“…Morphine also elicited a sustained increase in EIP, but a relatively transient decrease in EEP followed by a sustained decrease. The propensity of morphine to elongate Ti while not greatly affecting Te ( Fone and Wilson, 1986 ; Kasaba et al, 1997 ; Chevillard et al, 2009 ) or shortening Te (May et al, 2013a,b; Young et al, 2013 ; Baby et al, 2018 , Baby et al, 2021 SM. ; Gaston et al, 2021 ) is known, as is the ability of opioids to differentially affect EIP and EEP ( Henderson et al, 2013 , 2014 ; May et al, 2013a,b; Young et al, 2013 ; Baby et al, 2018 , Baby et al, 2021 SM.…”

“…Ventilatory parameters were recorded continuously in the unrestrained freely-moving rats using a whole body plethysmography system (PLY3223; Data Sciences International, St. Paul, MN) as detailed previously ( May et al, 2013a ; May et al, 2013b ; Young et al, 2013 ; Getsy et al, 2014 , 2020 ; Henderson et al, 2014 ; Baby et al, 2018 , 2021a , b ; Gaston et al, 2020 , 2021 ; Seckler et al, 2021 ). The directly recorded and calculated (derived) parameters are defined in Supplementary Table S1 ( Hamelmann et al, 1997 ; Lomask, 2006 ; Tsumuro et al, 2006 ; Quindry et al, 2016 ; Gaston et al, 2021 ).…”

S-Nitroso-L-Cysteine Stereoselectively Blunts the Deleterious Effects of Fentanyl on Breathing While Augmenting Antinociception in Freely-Moving Rats

“…Due to similar changes in f R and V T , each dose of fentanyl produced qualitatively similar changes in V E consisting of rapid and large decreases followed by a recovery period and then a rise to about 50% above pre-injection values. While the ability of opioids, such as morphine, to depress breathing and the mechanisms by which this occurs have been extensively studied ( Lalley, 2008 ; Pattinson, 2008 ; Dahan et al, 2010 ; Pattinson and Wise, 2016 ; Baby et al, 2018 ; Dahan et al, 2018 ; Bateman et al, 2021 ; Baby et al, 2021a ; Baby et al, 2021b ; Ramirez et al, 2021 ), the sites/mechanisms of action by which fentanyl exerts its cardiorespiratory and antinociceptive effects are less well understood ( Laubie et al, 1977 ; Fone and Wilson, 1986 ; Mayer et al, 1989 ; Yamakura et al, 1999 ; Lalley, 2003 ; Maegawa and Tonussi, 2003 ; Griffioen et al, 2004 ; Mastronicola et al, 2004 ; Nikolaishvili et al, 2004 ; Hajiha et al, 2009 ; Tschirhart et al, 2019 ; Webster and Rauck, 2021 ; Ramos-Matos et al, 2022 ). Mechanisms of action of fentanyl involve activation of μ-ORs in brainstem nuclei controlling cardiorespiratory and nociceptive functions ( Laubie et al, 1977 ; Fone and Wilson, 1986 ; Lalley, 2003 ; Griffioen et al, 2004 ; Nikolaishvili, et al, 2004 ; Hajiha, et al, 2009 ; Webster and Rauck, 2021 ; Ramos-Matos et al, 2022 ), and in peripheral structures, including the carotid body ( Mayer et al, 1989 ; Henderson et al, 2014 ; Tschirhart et al, 2019 ; Ramos-Matos et al, 2022 ).…”