The potential protective effect of melatonin and N-acetylcysteine alone and in combination on opioid-induced testicular dysfunction and degeneration in rat.

Methadone (Met) is the most common treatment for opioid addiction. Although Met is effective for treatment of opioid dependence, sexual dysfunctions and infertility have been reported as a major problem in patients under Met treatment. The present study aimed to evaluate the effect of melatonin and N-acetylcysteine (N) on morphine and Met-induced oxidative stress, apoptosis, suppression of blood sexual hormones, impairment in sperm parameters, and sexual dysfunction. Adult male Wistar rats (n = 66) were randomly divided into 11 equal groups (n = 6) as follows: control, sham, morphine, Met, Met+N, Met+ melatonin, Met+melatonin+N, morphine+ Met, morphine+Met+ melatonin, morphine+Met+N, and morphine+Met+ melatonin+N groups. On day 56 post-treatment, the blood was collected from the tail and the serum levels of sex hormones were evaluated, then the rats were sacrificed, and their bilateral testes and epididymis were retrieved for histological, immunohistochemical, molecular, testicular tissue stress oxidative status, and sperm parameters assays. Exposure to morphine, Met, and shift of morphine to Met resulted in testicular degeneration that can be attributed to generating the stress oxidative-induced- apoptotic testicular cell death and impairing spermatogenesis. Melatonin and N alone and particularly, in combination with each other improved testicular degeneration, sex hormone suppression, and testicular function mediated by increasing the testicular antioxidant capacity and inhibition of the apoptosis pathway. It's suggested that oral administration of antioxidants may be an effective treatment for attenuating some opioid-related testicular dysfunction and degeneration.

Toxic effects of xylazine on endothelial cells in combination with cocaine and 6-monoacetylmorphine.

The use of xylazine as a drug of abuse has emerged worldwide in the last 7 years, including Puerto Rico. Clinical findings reported that xylazine users present greater physiological deterioration, than heroin users. The aim of this study was to assess the xylazine toxicity on endothelial cells, as this is one of the first tissues impact upon administration. Human umbilical vein endothelial cells in culture were treated with xylazine, cocaine, 6-monoacetylmorphine (heroin metabolite) and its combinations, at concentrations of 0.10-400 µM, for periods of 24, 48 and 72 h. IC50 were calculated and the Annexin V assay implemented to determine the cell death mechanism. Results indicated IC50 values at 24h as follow: xylazine 62 µM, cocaine 210 µM, 6-monoacetylmorphine 300 µM. When these drugs were combined the IC50 value was 57 µM. Annexin V results indicated cell death by an apoptosis mechanism in cells treated with xylazine or in combination. Results demonstrated that xylazine use inhibits the endothelial cell proliferation, at lower concentrations than cocaine and 6-monoacetylmorphine. These findings contribute to the understanding of the toxicity mechanisms induced by xylazine on endothelial cells.

Characteristics and comparative severity of respiratory response to toxic doses of fentanyl, methadone, morphine, and buprenorphine in rats.

Opioids are known to induce respiratory depression. We aimed to characterize in rats the effects of four opioids on arterial blood gases and plethysmography after intraperitoneal administration at 80% of their LD(50) in order to identify opioid molecule-specific patterns and classify response severity. Opioid-receptor (OR) antagonists, including intravenous 10 mg kg(-1)-naloxonazine at 5 min [mu-OR antagonist], subcutaneous 30 mg kg(-1)-naloxonazine at 24 h [mu1-OR antagonist], subcutaneous 3 mg kg(-1)-naltrindole at 45 min [delta-OR antagonist], and subcutaneous 5 mg kg(-1)-Nor-binaltorphimine at 6 h [kappa-OR antagonist] were pre-administered to test the role of each OR. Methadone, morphine, and fentanyl significantly decreased PaO(2) (P<0.001) and increased PaCO(2) (P<0.05), while buprenorphine only decreased PaO(2) (P<0.05). While all opioids significantly increased inspiratory time (T(I), P<0.001), methadone and fentanyl also increased expiratory time (T(E), P<0.05). Intravenous 10 mg kg(-1)-naloxonazine at 5 min completely reversed opioid-related effects on PaO(2) (P<0.05), PaCO(2) (P<0.001), T(I) (P<0.05), and T(E) (P<0.01) except in buprenorphine. Subcutaneous 30 mg kg(-1)-naloxonazine at 24 h completely reversed effects on PaCO(2) (P<0.01) and T(E) (P<0.001), partially reversed effects on T(I) (P<0.001), and did not reverse effects on PaO(2). Naltrindole reversed methadone-induced T(E) increases (P<0.01) but worsened fentanyl's effect on PaCO(2) (P<0.05) and T(I) (P<0.05). Nor-binaltorphimine reversed morphine- and buprenorphine-induced T(I) increases (P<0.001) but worsened methadone's effect on PaO(2) (P<0.05) and morphine (P<0.001) and buprenorphine's (P<0.01) effects on pH. In conclusion, opioid-related respiratory patterns are not uniform. Opioid-induced hypoxemia as well as increases in T(I) and T(E) are caused by mu-OR, while delta and kappa-OR roles appear limited, depending on the specific opioid. Regarding severity of opioid-induced respiratory effects at 80% of their LD(50), all drugs increased T(I). Methadone and fentanyl induced hypoxemia, hypercapnia, and T(E) increases, morphine caused both hypoxemia and hypercapnia while buprenorphine caused only hypoxemia.

Mechanism of allodynia evoked by intrathecal morphine-3-glucuronide in mice.

Morphine-3-glucuronide (M3G), a main metabolite of morphine, has been proposed as a responsible factor when patients present with the neuroexcitatory side effects (allodynia, hyperalgesia, and myoclonus) observed following systemic administration of large doses of morphine. Indeed, both high-dose morphine (60 nmol/5 microl) and M3G (3 nmol/5 microl) elicit allodynia when administered intrathecally (i.t.) into mice. The allodynic behaviors are not opioid receptor mediated. This chapter reviews the potential mechanism of spinally mediated allodynia evoked by i.t. injection of M3G in mice. We discuss a possible presynaptic release of nociceptive neurotransmitters/neuromodulators such as substance P, glutamate, and dynorphin in the primary afferent fibers following i.t. M3G. It is possible to speculate that i.t. M3G injection could activate indirectly both NK(1) receptor and glutamate receptors that lead to the release of nitric oxide (NO) in the dorsal spinal cord. The NO plays an important role in M3G-induced allodynia. The phosphorylation of extracellular signal-regulated protein kinase (ERK) in the dorsal spinal cord evoked via NO/cGMP/PKG pathway contributes to i.t. M3G-induced allodynia. Furthermore, the increased release of NO observed after i.t. injection of M3G activates astrocytes and induces the release of the proinflammatory cytokine, interleukin-1beta. Taken together, these findings suggest that M3G may induce allodynia via activation of NO-ERK pathway, while maintenance of the allodynic response may be triggered by NO-activated astrocytes in the dorsal spinal cord. The demonstration of the cellular mechanisms of neuronal-glial interaction underlying M3G-induced allodynia provides a fruitful strategy for improved pain management with high doses of morphine.

Spinal ERK activation via NO-cGMP pathway contributes to nociceptive behavior induced by morphine-3-glucuronide.

Intrathecal (i.t.) injection of morphine-3-glucuronide (M3G), a major metabolite of morphine without analgesic actions, produces a severe hindlimb scratching followed by biting and licking in mice. The pain-related behavior evoked by M3G was inhibited dose-dependently by i.t. co-administration of tachykinin NK(1) receptor antagonists, sendide, [D-Phe(7), D-His(9)] substance P(6-11), CP-99994 or RP-67580 and i.t. pretreatment with antiserum against substance P. The competitive NMDA receptor antagonists, D-APV and CPP, the NMDA ion-channel blocker, MK-801 or the competitive antagonist of the polyamine recognition site of NMDA receptor ion-channel complex, ifenprodil, produced inhibitory effects on i.t. M3G-evoked nociceptive response. The NO-cGMP-PKG pathway, which involves the extracellular signal-regulated kinase (ERK), has been implicated as mediators of plasticity in several pain models. Here, we investigated whether M3G could influence the ERK activation in the NO-cGMP-PKG pathway. The i.t. injection of M3G evoked a definite activation of ERK in the lumbar dorsal spinal cord, which was prevented dose-dependently by U0126, a MAP kinase-ERK inhibitor. The selective nNOS inhibitor N(omega)-propyl-l-arginine, the selective iNOS inhibitor W1400, the soluble guanylate cyclase inhibitor ODQ and the PKG inhibitor KT-5823 inhibited dose-dependently the nociceptive response to i.t. M3G. In western blotting analysis, inhibiting M3G-induced nociceptive response using these inhibitors resulted in a significant blockade of ERK activation induced by M3G in the spinal cord. Taken together, these results suggest that activation of the spinal ERK signaling in the NO-cGMP-PKG pathway contributes to i.t. M3G-evoked nociceptive response.

Evaluation of the P-glycoprotein (Abcb1) affinity status of a series of morphine analogs: comparative study with meperidine analogs to identify opioids with minimal P-glycoprotein interactions.

One of the major shortcomings of many commonly used opioids is the fact that they are P-gp substrates, which represents a major obstacle towards effective pain management. P-gp can affect opioids' oral absorption, CNS accumulation, systemic clearance, antinociceptive activity, and tolerance development to their analgesic effects. Moreover, P-gp can be the locus of drug-drug interactions between opioids and other concomitantly administered drugs that are P-gp substrates/inhibitors. The objective of this study was to identify opioids that are non-P-gp substrates to overcome some of the mentioned shortcomings. We evaluated the P-gp affinity status (substrate, non-substrate, or inhibitor) of a series of morphine analogs (10 opioid agonist and 2 opioid antagonists) and compared them to previously reported meperidine analogs. The fold stimulation of the morphine analogs ranged from 1.01 to 1.54 while for the meperidine analogs the fold stimulation ranged from 1.10 to 3.66. From each series (morphine and meperidine analogs) we selected potential candidate opioids that are non-P-gp substrates and conducted in vivo assessments of their antinociceptive effects using P-gp knockout and P-gp competent mice. 6-Desoxymorphine, meperidine and N-phenylbutyl normeperidine did not significantly (p>0.05) stimulate the basal P-gp ATPase activity, where, the fold stimulations of the basal P-gp ATPase activity were 1.01+/-0.11, 1.51+/-0.29 and 1.10+/-0.23, respectively. Evaluation of the influence of P-gp ablation on their antinociceptive effects indicated that P-gp did not significantly (p>0.05) affect their antinociceptive effects. Among the evaluated opioids in vivo, 6-desoxymorphine showed high potency and induced no apparent toxicity upon low- and high-dose administration. 6-Desoxymorphine is therefore an ideal lead compound to create a library of opioids that have negligible P-gp affinity for better management of pain.

Morphine-6-glucuronide, an active morphine metabolite for the potential treatment of post-operative pain.

Morphine-6-glucuronide (M6G) is an active metabolite of morphine that is being developed by CeNeS Pharmaceuticals as an alternative to morphine (the most commonly used opioid) for the management of postoperative pain. M6G is currently undergoing phase III clinical trials in patients with postoperative pain.

Conditioned place preference induced by morphine and morphine-6-glucuronide in mice.

Morphine-6-glucuronide (M6G), an active metabolite of morphine has been shown to produce analgesia and fewer side effects than morphine, and the introduction of M6G as a new drug for treatment of postoperative pain is planned in 2007. Following morphine intake in humans, the metabolites morphine-3-glucuronide (M3G) and M6G are present in substantial concentrations and for longer periods than the parent drug. The possible reward effects of the morphine glucuronides have previously not been well studied. In the present study, conditioned place preference (CPP) was recorded after conditioning with subcutaneous injections of 5, 10, 20, 30 or 50 micromol/kg morphine or M6G, or 240 or 500 micromol/kg M3G in C57BL/6J-Bom mice, using a biased two compartment ("closed" and "open") counterbalanced paradigm. CPP was induced after treatment with both morphine and M6G with dose dependent increase up to 30 micromol/kg after treatment in the "closed" compartment. No dose response was observed in the "open" compartment, with maximal CPP after 10 micromol/kg morphine or M6G. M3G caused a tendency of condition place aversion (CPA), although not statistically significant. In the present study morphine and M6G demonstrated comparable reward effects, at doses that differed depending on which compartment the mice were conditioned in. M3G showed a tendency to exhibit aversive properties.

A highly toxic morphine-3-glucuronide derivative.

By the coupling of octylamine to the uronic acid function of morphine-3-glucuronide (M3G) a new glycoconjugate (morphine-3-octylglucuronamide, M3GOAM) was prepared. When assayed in both rats and mice up to ng/kg (i.p.) doses none of the animals survived. The aliphatic octyl chain may be the lethal factor since a closely related derivative (M3GNH2), was not toxic and showed similar opioid antagonist properties than naloxone.

Pharmacodynamic effect of morphine-6-glucuronide versus morphine on hypoxic and hypercapnic breathing in healthy volunteers.

BACKGROUND: Morphine-6-glucuronide (M6G) is an active metabolite of morphine that is generally associated with less respiratory depression than morphine. Because M6G will be on the market in the near future, the authors assessed the time profile and relative potency of M6G's effect versus morphine's effect on carbon dioxide-driven and hypoxic breathing. METHODS: In nine healthy female volunteers, the effects of 0.2 mg/kg intravenous M6G, 0.13 mg/kg intravenous morphine, and intravenous placebo were tested on ventilation at a fixed end-tidal pressure of carbon dioxide (Petco2) of 45 mmHg (Vi45) and on the acute hypoxic ventilatory response (AHR). All subjects participated in all three arms of the study. Respiratory studies were performed at 1-h intervals for 7 h after drug infusion. The data were analyzed using a population dose-driven approach, which uses a dose rate in function of time as input function driving the pharmacodynamics, and a population pharmacokinetic-pharmacodynamic (PK/PD) approach in which fixed pharmacokinetic parameter values from the literature were used as input function to the respiratory model. From the latter analysis, the authors obtained the blood effect-site equilibration half-life (t1/2ke0) and the effect-site concentration producing 25% depression of Vi45 and AHR (C25). Values reported are mean +/- SE. RESULTS: Placebo had no effect on Vi45 or AHR over time. Both analysis approaches yielded good descriptions of the data with comparable model parameters. M6G PK/PD model parameters for Vi45 were t1/2ke0 2.1 +/- 0.2 h and C25 528 +/- 88 nm and for AHR were t1/2ke0 1.0 +/- 0.1 h and C25 873 +/- 81 nm. Morphine PK/PD model parameters for Vi45 were t1/2ke0 3.8 +/- 0.9 h and C25 28 +/- 6 nm and for AHR were t1/2ke0 4.3 +/- 0.6 h and C25 16 +/- 2 nm. CONCLUSIONS: Morphine is more potent in affecting hypoxic ventilatory control than M6G, with a potency ratio ranging from 1:19 for Vi45 to 1:50 for AHR. At drug concentrations causing 25% depression of Vi45, M6G caused only 15% depression of AHR, whereas morphine caused greater than 50% depression of AHR. Furthermore, the speed of onset/offset of M6G is faster than morphine by a factor of approximately 2. The authors discuss some of the possible mechanisms for the observed differences in opioid behavior.

Does the A118G polymorphism at the mu-opioid receptor gene protect against morphine-6-glucuronide toxicity?

BACKGROUND: Some, but not all, patients with renal dysfunction suffer from side effects after morphine administration because of accumulation of the active metabolite morphine-6-glucuronide (M6G). The current study aims to identify genetic causes that put patients at risk for, or protect them from, opioid side effects related to high plasma M6G. Candidate genetic causes are the single nucleotide polymorphism (SNP) A118G of the mu-opioid-receptor gene (OPRM1), which has recently been identified to result in decreased potency of M6G, and mutations in the MDR1-gene coding P-glycoprotein, of which morphine and M6G might be a substrate. METHODS: Two men, aged 87 and 65 yr, with renal failure (creatinine clearance of 6 and 9 ml/min) received 30 mg/day oral morphine for pain treatment. Both patients had sufficient analgesia from morphine. However, while one patient tolerated morphine well despite high plasma M6G of 1735 nM, in the patient with M6G plasma concentrations of 941 nM it caused severe sleepiness and drowsiness. Patients were genotyped for known SNPs of the OPRM1 and MDR1 genes. RESULTS: The patient who tolerated morphine well despite high plasma M6G was a homozygous carrier of the mutated G118 allele of the mu-opioid-receptor gene, which has been previously related to decreased M6G potency. In contrast, the patient who suffered from side effects was "wild-type" for this mutation. No other differences were found between the OPRM1 and MDR1 genes. CONCLUSIONS: The authors hypothesize that the A118G single nucleotide polymorphism of the mu-opioid-receptor is among the protective factors against M6G-related opioid toxicity. The observation encourages the search for pharmacogenetic reasons that cause interindividual variability of the clinical effects of morphine.

Cell death-inducing activity of opiates in human oral tumor cell lines.

In screening cytotoxic agents in morphine alkaloids [TE1-10], codeinone [TE8] was cytotoxic against two human oral tumor cells lines (HSC-2 and HSG). The cytotoxic activity of codeinone (CC50=1.0-1.2 microg/mL) against HSC-2 or HSG cells was higher than that of doxorubicin (CC50=1.9-2.0 microg/mL). Human oral gingival fibroblasts (HGF) were relatively resistant to codeinone, as judged by higher SI ratio (3.7) suggesting the tumor-selective cytotoxicity of codeinone. The cytotoxic activity of morphine (CC50=221 microg/mL) against HSC-2 was slightly lower than that of codeine (CC50=186 microg/mL), thebaine (CC50=125 microg/mL), etorphine (CC50=94 microg/mL) or dihydroetorphine (CC50=60 microg/mL). A study of structurally-related compounds suggested that the alpha,beta-unsaturated ketone group of codeinone was responsible for its antitumor cytotoxicity. The cytotoxic activity of codeinone was significantly reduced by N-acetylcysteine, but not affected by FeCl3, CuCl2, CoCl2, sodium ascorbate or catalase. Neither codeinone nor morphine inhibited P-glycoprotein-mediated rhodamine-123 efflux in multidrug resistant mouse T lymphoma L5178 transfected with human MDR 1 gene. These data suggest that codeinone induces cytotoxicity in oral tumor cell lines, possibly by a Michael-like addition of a protein SH or of an amino group to the bouble bond of codeinone.

Limited phase I study of morphine-3-glucuronide.

The toxicity of morphine-3-glucuronide (M3G) has been investigated in an open, uncontrolled, single-blinded, single dose study over a limited range of doses. Three cohorts each of three healthy volunteers received 7.5, 15, and 30 mg/70 kg intravenous (IV) M3G. Blood sampling was undertaken for the following 24 h. Subjective toxicity was recorded on visual analogue scales and plasma M3G concentrations measured by a specific HPLC assay. Virtually no effects and no change in cardiovascular or respiratory parameters were seen. The pharmacokinetics fitted a two-compartment model. The mean elimination half-life (+/- S.D.) of M3G was 1.66 (+/- 0.47) h. Mean AUC standardized to a dose of 1 mg/70 kg was 228 (+/- 62) etamolL(-1) x h. Mean M3G clearance was 169 (+/- 48) mLmin(-1) and the mean volume of distribution was 23.1 (+/- 4.8) liters. At the doses investigated there were no clear neuroexcitatory effects, no opioid effects, and the pharmacokinetics were very similar to those of morphine-6-glucuronide (M6G).

Is development of hyperalgesia, allodynia and myoclonus related to morphine metabolism during long-term administration? Six case histories.

BACKGROUND: Recently, clinical reports have suggested a relationship between the occurrence of hyperalgesia, allodynia and/or myoclonus and treatment with high doses of morphine in humans. Although few clinical descriptions of these phenomena are available, experimental work supports the notion that high doses of morphine may play a pathogenetic role in the observed behavioural syndrome. METHODS: Six patients, four with malignant and two with chronic, non-malignant pain conditions, treated with moderate to high doses of oral, continuous intravenous infusion or intrathecal morphine developed hyperalgesia, allodynia and/or myoclonus. When the side-effects occurred, blood or CSF samples were taken and analyzed for contents of morphine, morphine-6-glucuronide (M-6-G) and morphine-3-glucuronide (M-3-G). RESULTS: When comparing the plasma and CSF concentrations from these patients with data from available literature obtained from patients not suffering from these side-effects, it was demonstrated that the values deviated in five patients. In all six patients, the side-effects disappeared after substituting morphine with other opioid agonists or after lowering the daily dose of morphine. CONCLUSION: These results may indicate that elevated concentrations of M-3-G in plasma as well as the plasma and CSF M-3-G/M-6-G ratios may play a pathogenetic role in the development of hyperalgesia, allodynia and myoclonus.

mu Opioid receptor knockout in mice: effects on ligand-induced analgesia and morphine lethality.

The mu opioid receptor gene (MOR) was mutated in mice by a gene targeting procedure. In these MOR-knockout mice, the analgesic effects of morphine, its major metabolites, morphine-6-glucuronide (M-6-G) and morphine-6-ethereal sulfate (M-6-S), and endomorphin-2, as well as morphine-induced lethality, were drastically reduced, whereas the effects of DPDPE and U50488 remained unchanged. It is concluded that analgesic effects of mu-specific opioid ligands and acute morphine lethality are mediated by the mu receptor.

Differential effects of morphine-6-glucuronide, an active metabolite of morphine, and morphine on locomotor activity in mice: involvement of the opioid receptor.

Subcutaneous administration of morphine (2.5 to 20 mg/kg) or an active metabolite of morphine, morphine-6-glucuronide (2.5 to 20 mg/kg), increased the locomotor activity of mice in a dose-dependent manner. Fifteen mg/kg of morphine and 20 mg/kg of morphine-6-glucuronide were almost equipotent. Subcutaneous administration of the universal opioid antagonist, naloxone, but not the delta-selective antagonist, naltrindole, significantly suppressed the hyperlocomotion induced by morphine (15 mg kg). On the other hand the subcutaneous administration of relatively higher doses of naloxone or naltrindole significantly reduced the hyperlocomotion induced by morphine-6-glucuronide (20 mg/kg). These findings suggest that agonistic actions at the opioid receptors, especially at the delta- and mu-receptors, contribute to the morphine-6-glucuronide-induced hyperlocomotion.

Explanation at the opioid receptor level for differing toxicity of morphine and morphine 6-glucuronide.

The radiolabelled opioid receptor binding affinities of morphine and its active metabolite morphine 6-glucuronide at the total mu, mu 1, mu 2 and delta receptors were determined. Morphine 6-glucuronide was found to have a 4-fold lower affinity for the mu 2 receptor (IC50 17 nM and 82 nM for morphine and morphine 6-glucuronide respectively, P = 0.01), the receptor postulated to be responsible for mediating the respiratory depression and gastrointestinal effects after morphine. This provides a possible explanation for the reduced respiratory depression and vomiting seen following morphine 6-glucuronide in man. A similar reduction in affinity of morphine 6-glucuronide was seen at the total mu receptor whilst there was no significant difference seen at the mu 1 or delta receptor. Hence the increased analgesic potency of morphine 6-glucuronide over morphine remains unexplained.

Characterization and identification of 6 mutagens in opium pyrolysates implicated in oesophageal cancer in Iran.

Previous epidemiological studies have indicated an association between the ingestion of opium pyrolysates, dietary deficiencies, and a high incidence of oesophageal cancer in subjects in north-east Iran. Laboratory studies have shown that pyrolysates of opium and particularly of morphine, a major opium alkaloid, are highly mutagenic in bacteria and induce sister-chromatid exchanges in mammalian cells after metabolic activation. We now report the ability of these pyrolysates to transform Syrian hamster embryo cells in culture and present some evidence for their carcinogenicity in mice and hamsters following topical, subcutaneous, intratracheal and intragastric administration. 6 of the most abundant mutagenic compounds present in morphine pyrolysate were isolated and purified by high-performance liquid chromatography and characterized by gas chromatography/mass spectrometry and 1H-Fourier transform nuclear magnetic resonance spectroscopy. These hitherto unknown compounds, all containing a hydroxy-phenanthrene moiety, were identified as: 3-methyl-3H-naphth[1,2-e]indol-10-ol; 1,2-dihydro-3-methyl-3H-naphth[1,2-e]indol-10-ol; 6-methylaminophenanthren-3-ol; 2-methylphenanthro[3,4-d] [1,3]oxazol-10-ol; 2,3-dimethyl-3H-phenanthro[3,4-d]imidazol-10-ol and 2-methyl-3H-phenanthro[3,4-d]imidazol-10-ol. Mutagenicity in Salmonella typhimurium TA98 of these compounds increased in the order listed, the last compound being 35 times more active than benzo[a]pyrene. The mechanisms, by which these mutagens are formed and metabolically activated are discussed.