Sensitivity to acute methadone dose changes in maintenance patients

Transgenic increase in the β-endorphin concentration in cerebrospinal fluid alleviates morphine-primed relapse behavior through the μ opioid receptor in rats

BACKGROUND

Opioid-primed relapse is a global burden. Although current strategies have improved, optimal therapy is urgently needed.

METHODS

A recombinant adenovirus (Ad-NEP) expressing β-endorphin (β-EP) was designed and injected intracerebroventricularly (icv) into the right lateral ventricle in rats. Spatial and temporal β-EP expression in the lateral ventricle wall, subventricular zone and adjacent choroid plexus and the β-EP concentration in the cerebrospinal fluid (CSF) were observed during a 21-day period. A morphine priming-induced conditioned place preference (CPP) rat model was established. The β-EP-ir neuron counts, CSF β-EP concentration, and CPP score, which were used to evaluate morphine-primed reinstatement following extinction, were recorded 7 days after the icv injection. Additionally, the rats were pretreated with the irreversible μ opioid receptor antagonist β-funaltrexamine (β-FNA) and the selective κ opioid receptor antagonist nor-binaltorphimine (nor-BNI) to identify the receptor-dependent mechanism.

RESULTS

Both peak β-EP expression in target neurons and the peak CSF β-EP concentration occurred 7 to 8 days after Ad-NEP icv injection. The sustainable increase in the CSF β-EP concentration was correlated with a decrease in the CPP score 7 days after the Ad-NEP icv injection. Furthermore, reinstatement was almost reversed by β-FNA pretreatment 24 hours before the behavioral test, but nor-BNI had little effect.

CONCLUSION

The increasing cerebrospinal fluid β-endorphin concentrations showed that the therapeutic effect on opioid relapse occurred predominantly through a μ opioid receptor-dependent mechanism. The Ad-NEP adenovirus can be considered an alternative therapy for opioid relapse.

An Engineered Endomorphin-2 Gene for Morphine Withdrawal Syndrome

An optimal therapeutics to manage opioid withdrawal syndrome is desired for opioid addiction treatment. Down-regulation of endogenous endomorphin-2 (EM2) level in the central nervous system after continuous morphine exposure was observed, which suggested that increase of EM2 could be an alternative novel method for opioid dependence. As a short peptide, the short half-life of EM2 limits its clinical usage through conventional administration. In the present study, we engineered an EM2 gene using a signal peptide of mouse growth factor for an out-secretory expression of EM2 and an adenovirus as a vector, which ultimately sustained the release of EM-2. After administration of the adenovirus in central nervous system, a sustained increase of EM2 level in the cerebral spinal fluid (CSF) was observed along with a reduction of morphine withdrawal syndrome. These findings suggest that the engineered EM2 gene delivered to the central nervous system could be a novel therapeutics for withdrawal syndrome in opioid dependent subjects.

Effects of a single 50% extra dose of methadone on heroin craving and mood in lower- versus higher-dose methadone patients

Some patients on steady-state methadone occasionally crave for extra opioids for different reasons (eg, cue-elicited craving, stress). This study examined the acute-on-chronic effects on heroin craving, mood, and opioid-like symptoms of a single, extra half-dose on top of the patient's prescribed daily methadone dosage. A randomized, double-blind, placebo-controlled, counterbalanced crossover design was used to test the safety of this practice and the hypotheses that extra methadone would reduce heroin craving and improve mood, with greater responses in lower-dose (20-60 mg/d) as compared with higher-dose patients (80-120 mg/d). Fourteen stabilized methadone-maintained volunteers of each dose group were examined predrug and postdrug on 2 separate days using a range of self-report measures (Heroin Craving Questionnaire, visual analogs, Befindlichkeits-Skala, Short Opiate Withdrawal Scale, and Opioid Agonist Scale). Additionally, patients' expectations and guesses regarding treatment were assessed predrug and postdrug, respectively. No adverse effects occurred after extra methadone. Participants could not reliably distinguish between extra methadone and placebo. Repeated-measures analyses of variance showed no effects of extra methadone on heroin craving and opioid agonist effects. However, extra methadone improved mood on the Befindlichkeits-Skala (F1/24 = 4.71, P = 0.04), with marginally greater effects in lower-dose patients ((F1/24 = 2.94, P = 0.099). A single 50% extra methadone dose is most likely safe in patients on stable methadone doses of 20 to 120 mg/d and may improve patients' mood. Extra methadone may constitute an important factor in the attractiveness of maintenance treatment and may enhance treatment outcome.