Opioid receptor-independent protection of ischemic rat hepatocytes by morphine

Nicorandil/ morphine crosstalk accounts for antinociception and hepatoprotection in hepatic fibrosis in rats: Distinct roles of opioid/cGMP and NO/KATP pathways

Previous report indicated that nicorandil potentiated morphine antinociception and attenuated hepatic injury in liver fibrotic rats. Herein, the underlying mechanisms of nicorandil/morphine interaction were investigated using pharmacological, biochemical, histopathological, and molecular docking studies. Male Wistar rats were injected intraperitoneally (i.p.) with carbon tetrachloride (CCl4, 40%, 2 ml/kg) twice weekly for 5 weeks to induce hepatic fibrosis. Nicorandil (15 mg/kg/day) was administered per os (p.o.) for 14 days in presence of the blockers; glibenclamide (KATP channel blocker, 5 mg/kg, p.o.), L-NG-nitro-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor, 15 mg/kg, p.o.), methylene blue (MB, guanylyl cyclase inhibitor, 2 mg/kg, i.p.) and naltrexone (opioid antagonist, 20 mg/kg, i.p.). At the end of the 5th week, analgesia was evaluated using tail flick and formalin tests along with biochemical determinations of liver function tests, oxidative stress markers and histopathological examination of liver tissues. Naltrexone and MB inhibited the antinociceptive activity of the combination. Furthermore, combined nicorandil/morphine regimen attenuated the release of endogenous peptides. Docking studies revealed a possible interaction of nicorandil on µ, κ and δ opioid receptors. Nicorandil/morphine combination protected against liver damage as evident by decreased liver enzymes, liver index, hyaluronic acid, lipid peroxidation, fibrotic insults, and increased superoxide dismutase activity. Nicorandil/morphine hepatoprotection and antioxidant activity were inhibited by glibenclamide and L-NAME but not by naltrexone or MB. These findings implicate opioid activation/cGMP versus NO/KATP channels in the augmented antinociception, and hepatoprotection, respectively, of the combined therapy and implicate provoked cross talk by nicorandil and morphine on opioid receptors and cGMP signaling pathway. That said, nicorandil/morphine combination provides a potential multitargeted therapy to alleviate pain and preserve liver function.

Opioids: Modulators of angiogenesis in wound healing and cancer

Opioids are potent drugs that are widely used to control wound or cancer pain. Increasing evidence suggest that opioids mediate clinically relevant effects that go beyond their classical role as analgesics. Of note, opioids appear to modulate angiogenesis - a process that is critical in wound healing and cancer progression. In this review, we focus on pro- and anti-angiogenic facets of opioids that arise from the activation of individual opioid receptors and the usage of individual concentrations or application routes. We overview the still incompletely elucidated mechanisms of these angiogenic opioid actions. Moreover, we describe plausible opioids effects, which - although not primarily studied in the context of vessel formation - may be related to the opioid-driven processes of angiogenesis. Finally we discuss the use of opioids as an innovative therapeutic avenue for the treatment of chronic wounds and cancer.

Repeated exposure to codeine alters morphine glucuronidation by affecting UGT gene expression in the rat

We have previously found that phenantrenic opioids, such as heroin or naltrexone, modulate morphine glucuronidation in the rat. Here we further investigated the effects of phenantrenic opioids on morphine glucuronidation comparing the effects of codeine and heroin. In particular, we measured the synthesis of morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) from morphine: in the liver microsomal preparations obtained from rats repeatedly treated with two different doses of codeine (ex vivo study); in primary cultures of rat hepatocytes previously incubated for 72h with codeine, or heroin (in vitro study); in the latter conditions, the levels of expression of genes coding for uridine-5'-diphosphate-glucuronosyltransferases (UGTs) A1, A6, A7 and 2B1 were also determined; finally, the levels of glucuronic acid in rat hepatocytes previously incubated for 72h with codeine or heroin were assessed. The ex vivo study shows that codeine exposure in vivo stimulated liver microsomal M3G formation and de novo synthesis of M6G. Differently, in primary hepatocyte cultures both codeine and heroin inhibited M3G formation, whereas heroin only stimulated de novo synthesis of M6G; moreover, codeine significantly reduced UGT2B1 expression at 6h and caused a trend toward inhibition of UGT1A1 expression at 72h; heroin enhanced UGT2B1 expression and inhibited that of UGT1A1 at 72h; finally, both codeine and heroin depleted UDPGA content of hepatocytes. In conclusion, codeine affects liver glucuronidation of morphine enlightening the possible contribution of changes in the spectrum of UGT gene expression and co-factor synthesis in this phenomenon.

Pretreatment with intrathecal or intravenous morphine attenuates hepatic ischaemia-reperfusion injury in normal and cirrhotic rat liver

BACKGROUND

Opioids have been shown to attenuate ischaemia-reperfusion injury (IRI) in a number of organs. We evaluated the effect of morphine pretreatment on IRI in both normal and cirrhotic rat liver.

METHODS

Morphine was administered either i.v. or intrathecally (i.t.) 10 min before initiating 1 h of ischaemia followed by 6 h reperfusion in normal rat liver. Hepatic injury was assessed histologically using Suzuki's criteria. These manoeuvres were repeated using the optimal dose of morphine after administration of naloxone methiodide and wortmannin. Serum levels of transaminases were measured, and expression of phosphorylated Akt, Jak2, and STAT3 were assessed by immunoblotting. Similar procedures were repeated on rats with carbon tetrachloride-induced liver cirrhosis, and the levels of phosphorylated protein kinase C (PKC), haem oxygenase-1 (HO-1), and inducible nitric oxide synthase (iNOS) were also evaluated, as these proteins have beneficial effects during IRI.

RESULTS

Morphine pretreatment at 100 µg kg(-1) (i.v.) or 10 µg (i.t.) reduced necrosis, apoptosis, and serum transaminase levels, and increased phosphorylated Akt and STAT3 but not JAK2 expression in normal liver. These changes were reversed by prior administration of naloxone methiodide and wortmannin. Although morphine preconditioning was also protective in cirrhotic liver, STAT3 and JAK2 phosphorylation status was unchanged. There was, however, increased expression of phosphorylated PKC and HO-1, and a reduction in iNOS.

CONCLUSIONS

Morphine preconditioning protects against IRI in both normal and cirrhotic rat liver. This involves opioid receptors, phosphatidylinositol-3-kinase, and Akt. The downstream pathways involved are different for cirrhotic liver, with preliminary evidence suggesting involvement of HO-1.

Non-opioid induction of morphine-6-glucuronide synthesis is elicited by prolonged exposure of rat hepatocytes to heroin

BACKGROUND

Liver metabolism of morphine leads to the formation of morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G), the latter possessing strong opioid activity that however differs from that of the parent compound. In previous studies conducted in rats we have shown that repeated in vivo exposure to phenanthrene class of mu opioid receptor (MOR) agonists or antagonists (heroin, morphine, and naltrexone), but not to non-phenanthrene class of MOR agonist methadone, affects morphine glucuronidation by liver microsomes.

METHODS

In the present study, we measured the in vitro formation of M3G and M6G by rat hepatocytes incubated for 120 min with morphine (0.1-1.0 mM) after 72h pre-incubation with one of the following MOR agonists: heroin (3.3 or 6.6 microM), morphine (7.8 microM), or methadone (12 microM). The MOR antagonist naltrexone (10 or 25 microM) was also tested, alone or in combination with heroin. The amount of M3G and M6G synthesized was then measured by HPLC method.

RESULTS

Heroin inhibited M3G synthesis and induced the formation of M6G, which under basal conditions is not synthesized in rats. Heroin effects were not blocked by naltrexone. Morphine, but not methadone, produced effects similar to those of heroin but more modest in intensity. Pre-incubation with naltrexone alone slightly increased M3G synthesis, but had no effect on M6G formation.

CONCLUSIONS

These results are in agreement with those of previous ex vivo studies and indicate that exposure to heroin or, to a lesser extent, morphine, can affect morphine glucuronidation via direct non-opioid actions on the hepatocytes.

Opioids modulate post-ischemic progression in a rat model of stroke

Alterations in the opioidergic system have been found in cerebral ischemia. Neuroprotection studies have demonstrated the involvement of the opioidergic system in cerebral ischemia/reperfusion (I/R). However, the neuroprotective mechanisms remain largely unclear. This study was conducted to investigate whether intracerebroventricular administration of opioidergic agonists has a neuroprotective effect against cerebral ischemia in rats and, if this proved to be the case, to determine the potential neuroprotective mechanisms. Using a focal cerebral I/R rat model, we demonstrated that the opioidergic agents, BW373U86 (delta agonist) and Dynorphin A 1-13 (kappa agonist), but not TAPP (mu agonist), attenuated cerebral ischemic injury as manifested in the reduction of cerebral infarction and preservation of neurons. The antagonism assay showed that the neuroprotective effect of Dynorphin A was attenuated by nor-Binaltorphimine (kappa antagonist). Surprisingly, BW373U86-induced neuroprotection was not changed by Naltrindole (delta antagonist). These findings indicate that BW373U86 and Dynorphin A exerted distinct neuroprotection against ischemia via opioid-independent and -dependent mechanisms, respectively. The post-ischemic protection in beneficial treatments was accompanied by alleviations in brain edema, inflammatory cell infiltration, and pro-inflammatory cytokine interleukin 6 (IL-6) expression. In vitro cell study further demonstrated that the opioidergic agonists, delta and kappa, but not mu, attenuated IL-6 production from stimulated glial cells. Our findings indicate that opioidergic agents have a role in post-ischemic progression through both opioid-dependent and -independent mechanisms. In spite of the distinct-involved action mechanism, the potential neuroprotective effect of opioidergic compounds was associated with immune suppression. Taken together, these findings suggest a potential role for opioidergic agents in the therapeutic consideration of neuroinflammatory diseases. However, a better understanding of the mechanisms involved is necessary before this therapeutic potential can be realized.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).