S-nitroso-L-cysteine stereoselectively blunts the adverse effects of morphine on breathing and arterial blood gas chemistry while promoting analgesia

L-cysteine methyl ester overcomes the deleterious effects of morphine on ventilatory parameters and arterial blood-gas chemistry in unanesthetized rats

“…Consistent with previous findings ( Baby et al, 2018 ; Baby S. M. et al, 2021 ; Gaston et al, 2021 ; Getsy et al, 2022a ; Getsy et al, 2022c ; Getsy et al, 2022d ), morphine (10 mg/kg, IV) elicited pronounced and long-lasting adverse changes in ABG chemistry in unanesthetized rats that consisted of a decrease in arterial blood pH, an increase in pCO 2 , and decreases in pO 2 and sO 2 , responses consistent with morphine hypoventilation. These changes in ABG chemistry were associated with sustained increases in A-a gradient, suggesting that morphine adversely affected alveolar gas-exchange ( Gaston et al, 2021 ; Getsy et al, 2022a ; Getsy et al, 2022c ; Getsy et al, 2022d ). The elevation in A-a gradient could signify atelectasis (i.e., alveolar collapse) due to hypoventilation, but may also involve more complicated effects on surfactant status/alveolar fluid clearance, which if adversely affected would impair alveolar gas-exchange, despite the morphine-induced decrease in TV.…”

“…The findings with L-CYSme add to evidence regarding the efficacy of reduced (monosulfide) thiolesters, such as L-GSHee ( Jenkins et al, 2021 ) and D-CYSee ( Getsy et al, 2022c ; Getsy et al, 2022d ), and oxidized (disulfide) thiolesters, such as D-CYSdiee and D-CYSdime ( Gaston et al, 2021 ) in preventing/overcoming the deleterious actions of morphine or fentanyl on ventilation. The possibility that the mechanisms of action of L-CYSme involves formation of S-nitrosyl forms of L-CYSme and/or L-cysteine is supported by our findings that the ability of morphine or fentanyl to adversely affect ventilation, ABG chemistry and A-a gradient are markedly reduced in rats receiving continuous intravenous infusions of SNO-L-cysteine ( Getsy et al, 2022a ; Getsy et al, 2022b ), whereas the adverse effects of fentanyl (morphine not studied to date) are augmented after inhibition of nitric oxide synthase ( Seckler et al, 2022 ). It is well-studied that SNO-L-cysteine regulates many intracellular signaling cascades ( Lipton et al, 1993 ; Foster et al, 2009 ; Seth and Stamler, 2011 ; Stomberski et al, 2019 ; Gaston et al, 2020 ), including cardiorespiratory control systems ( Davisson et al, 1996 ; Davisson et al, 1997 ; Ohta et al, 1997 ; Lipton et al, 2001 ; Lewis et al, 2006 ; Gaston et al, 2020 ) and those involved in attenuation of OIRD ( Getsy et al, 2022a ; Getsy et al, 2022b ).…”

“…It is well-known that S-nitrosothiols, such as S-nitroso-L-cysteine and S-nitroso-L-glutathione, play important roles in ventilatory control processes within the brainstem, circulating red blood cells, and peripheral structures, such as the carotid bodies (Gaston et al, 2001; Lipton et al, 2001 ; Palmer et al, 2013 ; Gaston et al, 2014 ; Palmer et al, 2015 ; Gaston et al, 2020 ). The ability of morphine or fentanyl to depress breathing and adversely affect ABG chemistry is substantially reduced in rats receiving intravenous infusion of S-nitroso-L-cysteine ( Getsy et al, 2022a ; Getsy et al, 2022b ). The efficacy of S-nitroso-L-cysteine adds to our knowledge regarding the ability of L-S-nitrosothiols to profoundly affect cardiorespiratory control systems ( Davisson et al, 1996 ; Lewis et al, 1996 ; Travis et al, 1996 ; Davisson et al, 1997 ; Ohta et al, 1997 ; Travis et al, 1997 ; Gaston et al, 2001; Lewis et al, 2005 ; Lewis et al, 2006 ; Gaston et al, 2020 ).…”

“…We are evaluating the abilities of monothiol and disulfide thiolesters to prevent and/or overcome OIRD in unanesthetized Sprague Dawley rats and reported that (1) pretreatment with L-glutathione ethylester (L-GSHee) diminished the adverse effects of fentanyl on ventilation and Alveolar-arterial (A-a) gradient (index gas alveolar exchange), but did not diminish fentanyl-induced antinociception/sedation ( Jenkins et al, 2021 ), and (2) D-cysteine ethylester (D-CYSee) ( Getsy et al, 2022c ; Getsy et al, 2022d ) or D-cystine diethylester (D-CYSdiee), D-cystine dimethyl ester (D-CYSdime) ( Gaston et al, 2021 ) overcome the adverse actions of morphine on breathing and arterial blood-gas (ABG) chemistry while minimally affecting morphine antinociception/sedation. It appears that unlike OR antagonists, such as naloxone, the L-, D-thiolesters may overcome the deleterious actions of opioids by mechanisms other than direct/allosteric blockade of ORs ( Gaston et al, 2021 ; Jenkins et al, 2021 ; Getsy et al, 2022a ; Getsy et al, 2022b ). Intravenous injections of L-cysteine ethylester (L-CYSee), but not L-cysteine, elicit an immediate and sustained reversal of the adverse effects of morphine on ABG chemistry and A-a gradient in isoflurane-anesthetized rats with a tracheal tube inserted to bypass the upper airway (nasopharynx, tongue, larynx, vocal folds), but not in rats without a tracheal tube ( Mendoza et al, 2013 ).…”

The ventilatory depressant actions but not the antinociceptive effects of morphine are blunted in rats receiving intravenous infusion of L-cysteine ethyl ester

“…A key finding was that the infusion of L-SERee was without effect and as such, it appears that the sulfur atom of L-CYSee is essential to its activity. There are numerous explanations for these findings including that (i) L-CYSee can bind to functional proteins important for ventilatory control processes and especially those involved in the ability of morphine to depress breathing (see [ 54 – 57 ]) whereas L-SERee cannot, (ii) the degradation of L-CYSee to L-cysteine which then enters numerous metabolic pathways that L-serine cannot [ 58 – 66 ], and (iii) the formation of S-nitroso-L-CYSee [ 22 ] and/or S-nitroso-L-cysteine, an endogenous S-nitrosothiol [ 67 – 69 ] with many substantial roles in intracellular signaling cascades (see [ 70 – 72 ]) including those controlling cardiorespiratory function (see [ 73 – 77 ]) and those involved in attenuating OIRD [ 78 , 79 ]. With respect to potential mechanisms by which the infusion of L-CYSee inhibits the adverse effects of morphine on breathing, we have a tentative proposal that (i) morphine-activated μ-ORs recruit histidine triad nucleotide-binding protein 1 (HINT1) while simultaneously activating the neuronal form of NOS (nNOS).…”