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Open Access Research

Interleukin-1 beta-induced up-regulation of opioid receptors in the untreated and morphine-desensitized U87 MG human astrocytoma cells

Linda Staikos Byrne1, Jinsong Peng13, Sraboni Sarkar12 and Sulie L Chang12*

Author Affiliations

1 Institute of NeuroImmune Pharmacology, Seton Hall University, 400 South Orange Ave, South Orange, NJ, 07079, USA

2 Department of Biological Sciences, Seton Hall University, 400 South Orange Ave, South Orange, NJ, 07079, USA

3 Wuhan Centers for Disease Control and Prevention, Wuhan, People’s Republic of China

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Journal of Neuroinflammation 2012, 9:252  doi:10.1186/1742-2094-9-252

Published: 20 November 2012

Abstract

Background

Interleukin-1beta (IL-1β) is a pro-inflammatory cytokine that can be produced in the central nervous system during inflammatory conditions. We have previously shown that IL-1β expression is altered in the rat brain during a morphine tolerant state, indicating that this cytokine may serve as a convergent point between the immune challenge and opiate mediated biological pathways. We hypothesized that IL-1β up-regulates opioid receptors in human astrocytes in both untreated and morphine-desensitized states.

Methods

To test this hypothesis, we compared the basal expression of the mu (MOR), delta (DOR), and kappa (KOR) opioid receptors in the human U87 MG astrocytic cell line to SH-SY5Y neuronal and HL-60 immune cells using absolute quantitative real time RT-PCR (AQ-rt-RT-PCR). To demonstrate that IL-1β induced up-regulation of the MOR, DOR and KOR, U87 MG cells (2 x 105 cells/well) were treated with IL-1β (20 ng/mL or 40 ng/mL), followed by co-treatment with interleukin-1 receptor antagonist protein (IL-1RAP) (400 ng/mL or 400 ng/mL). The above experiment was repeated in the cells desensitized with morphine, where U87 MG cells were pre-treated with 100 nM morphine. The functionality of the MOR in U87 MG cells was then demonstrated using morphine inhibition of forksolin-induced intracellular cAMP, as determined by radioimmunoassay.

Results

U87 MG cells treated with IL-1β for 12 h showed a significant up-regulation of MOR and KOR. DOR expression was also elevated, although not significantly. Treatment with IL-1β also showed a significant up-regulation of the MOR in U87 MG cells desensitized with morphine. Co-treatment with IL-1β and interleukin-1 receptor antagonist protein (IL-1RAP) resulted in a significant decrease in IL-1β-mediated MOR up-regulation.

Conclusion

Our results indicate that the pro-inflammatory cytokine, IL-1β, affects opiate-dependent pathways by up-regulating the expression of the MOR in both untreated and morphine-desensitized U87 MG.

Keywords:
IL-1β; Morphine; Mu-opioid receptor; U87 MG astrocytoma cells