Effect of thienorphine on intestinal transit and isolated guinea-pig ileum contraction

AIM: To evaluate the effect of thienorphine on small intestinal transit in vivo and on guinea-pig ileum (GPI) contraction in vitro . METHODS: The effects of thienorphine on intestinal transit were examined in mice and in isolated GPI. Buprenorphine and morphine served as controls. The distance traveled by the head of the charchol and the total length of the intestine were measured in vivo . Gastrointestinal transit was expressed as a percentage of the distance traveled by the head of the marker relative to the total length of the small intestine. The isolated GPI preparations were connected to an isotonic force transducer and equilibrated for at least 1 h before exposure to drugs. Acetylcholine was used for muscle stimulation. RESULTS: Thienorphine (0.005-1.0 mg/kg, ig ) or bu-prenorphine (0.005-1.0 mg/kg, sc ) dose-dependently significantly inhibited gut transit compared with saline. Thienorphine inhibited gut transit less than buprenorphine. The maximum inhibition by thienorphine on the intestinal transit was 50%-60%, whereas the maximum inhibition by morphine on gut transit was about 100%. Thienorphine also exhibited less inhibition on acetylcholine-induced contraction of GPI, with a maximum inhibition of 65%, compared with 93% inhibition by buprenorphine and 100% inhibition by morphine. Thienorphine induced a concentration-dependent decrease in the basal tonus of spontaneous movement of the GPI, the effect of which was weaker than that with buprenorphine. The duration of the effect of thienorphine on the GPI was longer than that with buprenorphine. CONCLUSION: Thienorphine had less influence, but a longer duration of action on GPI contraction and moderately inhibited intestinal transit.

Thienorphine induces analgesia by binding κ -and δ-, or by partially binding μ-opioid receptor,thus further regulating cAMP-PKA activity

OBJECTIVE Thienorphine,a new oripavine derivative,has shown to possess stronger antinociceptive effects and better oral bioavailability compared to buprenorphine.The present study examines the effect of thienorphine on c AMP-dependent protein kinase A(PKA) activity in CHO cells expressing μ-,κ-,δ-and ORL1 receptors.In addition,we further examined its analgesic effect in vivo.METHODS The effect of thienorphine on cA MP-dependent PKA redistribution and cA MP inhibition were analyzed in CHO-PKAcatEGFP cells.PKA redistribution assays in CHO-PKAcatEGFP cells stably expressing μ-,κ-,δ-and ORL1 receptors were analyzed by high-throughput screening system to elucidate the efficacy of agonists or antagonists on opioid receptors.Moroever,the antinociceptive effects of thienorphine in vivo were examined using hot plate test.RESULTS Briefly,the maximum inhibition of thienorphine on PKA activity was about 36%,100%,100%and 12% in CHO-μ/κ/δ/ORL1-PKAcatE GFP cel s,respectively.In addition,thienorphine concentrationdependently inhibited the PKA activity with EC50 value of(22.7±18.1) nmol·L^(-1) in CHO-κ-PKAcatE GFP cels and(12.4±7.7) nmol·L^(-1) in CHO-δ-PKAcatE GFP cells.Thienorphine induced approximately 50%antinociceptive effect in mice lacking μ receptors compared to their wild-type controls(P<0.05).Also,the κ and δ selective antagonist nor-binaltorphimine,naltrindole decreased approximately 50%-60% in % MPE of theinorphine in μ-KO mice,respectively.The ORL1 receptor selective antagonist J113397 had no effect in %MPE of theinorphine in μ-KO mice.CONCLUSION Thienorphine induces analgesia through bindingκ-and δ-,or by partially binding μ-opioid receptor,thus further regulating the cAMP-PKA activity.Therefore,thienorphine may be used in acute or chronic pain with minimal addictive potential.

Biliary excretion and enterohepatic circulation of thienorphine and its glucuronide conjugate in rats

Thienorphine(TNP)is a new partial opioid agonist currently developed as a promising drug candidate with the intended clinical indication for the treatment of opioid dependence.The pharmacokinetic profile and biliary excretion of TNP and its glucuronide conjugate(TNP-Glu)were investigated after oral administration of TNP in rats.The concentrations of TNP and TNP-Glu were simultaneously quantified using a LC-MS/MS method.A double peak phenomenon was observed in TNP plasma concentration–time curves with the secondary peak appeared at 6–8 h.A slower decline of plasma concentrations in the terminal phase was observed for TNP with T1/2 of 7.01 h.TNP-Glu was the predominant component in rat plasma and bile.Its plasma level was about 10 times higher than TNP and the 24 h accumulative bile excretion rate was 23%.Enterohepatic circulation of TNP and TNP-Glu was evaluated using a paired rat model.In bile-donor rats,no double-peak was detected and the elimination half life of TNP was significantly shortened(3.71 h)when compared to intact rats(7.01 h,P<0.05).Both TNP and TNP-Glu were detected in bile-recipient rats.Their exposures in recipient rats due to enterohepatic circulation were 15.6%and 42.6%for the parent drug and the metabolite,respectively.The deconjugation of the glucuronide conjugate and the reabsorption of free TNP were further confirmed in in situ perfused rat intestinal preparations.These results indicate that the enterohepatic circulation has a significant influence on the systemic exposure of the parent drug and its glucuronide conjugate,particularly on the terminal elimination of TNP,which may result in the prolonged retention of the drug in body.