S-Nitroso-N-acetyl-L-cysteine ethyl ester (SNACET) and N-acetyl-L-cysteine ethyl ester (NACET)–Cysteine-based drug candidates with unique pharmacological profiles for oral use as NO, H2S and GSH suppliers and as antioxidants: Results and overview

Abstract

S-Nitrosothiols or thionitrites with the general formula RSNO are formally composed of the nitrosyl cation (NO+) and a thiolate (RS−), the base of the corresponding acids RSH. The smallest S-nitrosothiol is HSNO and derives from hydrogen sulfide (HSH, H2S). The most common physiological S-nitrosothiols are derived from the amino acid L-cysteine (CysSH). Thus, the simplest S-nitrosothiol is S-nitroso-L-cysteine (CysSNO). CysSNO is a spontaneous potent donor of nitric oxide (NO) which activates soluble guanylyl cyclase to form cyclic guanosine monophosphate (cGMP). This activation is associated with multiple biological actions that include relaxation of smooth muscle cells and inhibition of platelet aggregation. Like NO, CysSNO is a short-lived species and occurs physiologically at concentrations around 1 nM in human blood. CysSNO can be formed from CysSH and higher oxides of NO including nitrous acid (HONO) and its anhydride (N2O3). The most characteristic feature of RSNO is the S-transnitrosation reaction by which the NO+ group is reversibly transferred to another thiolate. By this way numerous RSNO can be formed such as the low-molecular-mass S-nitroso-N-acetyl-L-cysteine (SNAC) and S-nitroso-glutathione (GSNO), and the high-molecular-mass S-nitrosol-L-cysteine hemoglobin (HbCysSNO) present in erythrocytes and S-nitrosol-L-cysteine albumin (AlbCysSNO) present in plasma at concentrations of the order of 200 nM. All above mentioned RSNO exert NO-related biological activity, but they must be administered intravenously. This important drawback can be overcome by lipophilic charge-free RSNO. Thus, we prepared the ethyl ester of SNAC, the S-nitroso-N-acetyl-L-cysteine ethyl ester (SNACET), from synthetic N-acetyl-L-cysteine ethyl ester (NACET). Both NACET and SNACET have improved pharmacological features over N-acetyl-L-cysteine (NAC) and S-nitroso-N-acetyl-L-cysteine (SNAC), respectively, including higher oral bioavailability. SNACET exerts NO-related activities which can be utilized in the urogenital tract and in the cardiovascular system. NACET, with high oral bioavailability, is a strong antioxidant and abundant precursor of GSH, unlike its free acid N-acetyl-L-cysteine (NAC). Here, we review the chemical and pharmacological properties of SNACET and NACET as well as their analytical chemistry. We also report new results from the ingestion of S-[15N]nitroso-N-acetyl-L-cysteine ethyl ester (S15NACET) demonstrating the favorable pharmacological profile of SNACET.

D-Cystine di(m)ethyl Ester Reverses the Deleterious Effects of Morphine on Ventilation and Arterial Blood Gas Chemistry While Promoting Analgesia

“…Transport of cystine esters into the cell would not itself correct for the loss of sulfhydryl equivalents since cystine is already in the more oxidized disul de state, and D-cystine or D-cysteine would not participate in most of the metabolic pathways of L-cysteine, but uptake of D-cystine esters could potentially drive up levels of intracellular Lcysteine. However, our nding that the highly cell-permeable thiolester reducing agent, N-acetyl-L-cysteine methyl ester, 21 had minimal effects on the ventilatory depressant effects of morphine suggests that Dcystine diEE and D-cystine diME do not act simply by increasing reducing equivalents in cells. Potential mechanisms of action of D-cystine diEE and D-cystine diME may involve (a) interference with opioid receptor-linked β-arrestin cell signaling, which would spare the Gprotein-mediated antinociceptive actions of morphine, 45,46 and/or conversion of these thiolesters to bioactive S-nitrosothiols (i.e., S-nitroso-Dcystine diEE, S-nitroso-D-cystine diME) that may act as intracellular nitrosating agents similar to Snitroso-L-cysteine ethyl ester (28,29).…”

“…2, Supplemental Table 3). In addition, the injection of N-acetyl-L-cysteine methyl ester (L-NACme, 2 x 500 µmol/kg, IV), which is a highly cell penetrable reducing agent, 21 elicited minor effects on morphine (10 mg/kg, IV)-induced changes in Freq, TV and MV (Supplemental Fig. 3, Supplemental Table 3).…”

“…The class of compounds we have focused upon are the ethyl ester and methyl ester versions of reduced and oxidized thiols (disul des), which are known to rapidly enter cells including neurons in the brain upon systemic administration. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] Our initial publication 21 reported that systemic injection of L-cysteine ethyl ester (L-CYSee) reversed the negative effects of morphine on ABG chemistry and Alveolar-arterial (A-a) gradient (index of gas exchange in the lungs) anesthetized rats only when the rats had a tracheotomy. Since L-cysteine itself was inert, we assumed that the biological activity of L-CYSee was due to its intracellular entry and initiation of redox-related processes.…”

“…It appears that the ability of L-CYSee to reverse the negative effects of morphine on breathing and gas-exchange are overridden by the negative effects on the upper airway including collapse of the tongue over the airway. 21 Accordingly, we have begun to explore whether D-isomers of cysteine and cystine esters show positive effects against OIRD without the negative effects of the L-isomers, in the hope that (i) the intracellular mechanisms of action of thiolesters are not dependent on stereoselective processes whereas the negative effects of the L-isomers are due to them entering into metabolic pathways that D-isomers cannot. We report here the effects of D-cystine ethyl ester (D-cystine diEE) and D-cystine methyl ester (Dcystine diME) on the actions of morphine in freely moving adult male Sprague-Dawley rats.…”

S-nitrosothiols and H2S donors: Potential chemo-therapeutic agents in cancer

“…Since the donors in general have the ability to cause cell death in cancer cells but not in normal cells, it has led to the possibility that the donors may be complementarily effective in cancer treatment. As with all therapeutic interventions of chemical agents, awareness is needed of pharmacokinetics, pharmacodistribution, metabolism, drug delivery, bioavailability, tissue specificity, adverse reactions, donor-drug interactions and the physical and chemical properties of the therapeutic agent which in the case of H 2 S and NO donors are at a very early stage of our knowledge [96].…”