The present study has been designed to investigate the effect of selective inhibitors of
histone deacetylase and/or N-acetyl-
Asp-Glu-Val-Asp-al (
Ac-DEVD-CHO), a selective interleukin-1β converting
enzyme inhibitor, on the development of
naloxone-induced
opioid withdrawal syndrome both in vitro and in vivo and the effect of
histone deacetylase inhibition on
histone H3 acetylation in brain. Sub-acute
morphine administration followed by a single injection of
naloxone (8 mg/kg, i.p.) was used to precipitate
opioid withdrawal syndrome in mice. Behavioral observations were made immediately after
naloxone treatment. Withdrawal syndrome was quantitatively assessed in terms of withdrawal severity score and frequency of jumping, rearing, fore paw licking and circling. Separately
naloxone-induced contraction in
morphine-dependent isolated rat ileum was employed as an in vitro model. An isobolographic study design was employed to assess potential synergistic activity between
trichostatin A and
Ac-DEVD-CHO. Brain
histone acetylation status was examined by western blotting. Injection of
naloxone precipitated a severe form of abstinence syndrome in
morphine-dependent mice along with strong
contracture in isolated rat ileum. Administration of
tributyrin (1.5, 3 and 6 g/kg, p.o.),
trichostatin A (0.3, 1.0 and 3.0 mg/kg, p.o.) and
Ac-DEVD-CHO (0.3, 1.0 and 3.0 mg/kg, p.o.) markedly and dose dependently attenuated
naloxone-induced
morphine withdrawal syndrome in vivo as well as in vitro in rat ileum.
Trichostatin A was also observed to exert a synergistic interaction with
Ac-DEVD-CHO. Western blot analysis revealed that multiple administration with the effective dose of
tributyrin or
trichostatin A in the in vivo experiments induced hyperacetylation of
histone H3 in the mouse brain. Thus, it is proposed that
histone deacetylase activation linked mechanism might be involved in the development of
opioid dependence and the precipitation of its withdrawal syndrome.