Regulation of gene expression in brain tissues of rats repeatedly treated by the highly abused opioid agonist,
Hazem E Hassan1, Alan L Myers, Insong J Lee
1Department of Pharmaceutical Sciences, School of Pharmacy, School of Medicine, University of Maryland, Baltimore, Maryland, USA.
Abstract:
Although oxycodone is the most often used opioid agonist, it remains one of the most understudied drugs. We used microarray analysis to better understand the global changes in gene expression in brain tissues of rats repeatedly treated with oxycodone. Many genes were significantly regulated by oxycodone (e.g., Fkbp5, Per2, Rt1.Dalpha, Slc16a1, and Abcg2). Validation of the microarray data by quantitative real-time-polymerase chain reaction (Q-PCR) indicated that there was a strong significant correlation (r = 0.979, p < 0.0000001) between the Q-PCR and the microarray data. Using MetaCore (a computational platform), many biological processes were identified [e.g., organic anion transport (p = 7.251 x 10(-4)) and regulation of immune response (p = 5.090 x 10(-4))]. Among the regulated genes, Abcg2 mRNA was up-regulated by 2.1-fold, which was further confirmed by immunoblotting (1.8-fold up-regulation). Testing the Abcg2 affinity status of oxycodone using an Abcg2 ATPase assay suggests that oxycodone behaves as an Abcg2 substrate only at higher concentrations (> or = 500 microM). Furthermore, brain uptake studies demonstrated that oxycodone-induced Abcg2 up-regulation resulted in a significant (p < 0.05) decrease (approximately 2-fold) in brain/plasma ratios of mitoxantrone. These results highlight markers/mediators of neuronal responses and identify regulatory pathways involved in the pharmacological action of oxycodone. These results also identify genes that potentially modulate tolerance, dependence, immune response, and drug-drug interactions. Finally, our findings suggest that oxycodone-induced up-regulation of Abcg2 enhanced the efflux of the Abcg2 substrate, mitoxantrone, limiting its brain accumulation and resulting in an undesirable drug-drug interaction. Extrapolating these results to other Abcg2 substrates (e.g., daunorubicin and doxorubicin) indicates that the brain uptake of these agents may be affected if they are administered concomitantly with oxycodone.
Insights
Repeated oxycodone use alters brain gene expression, notably up-regulating Abcg2. This enhances drug efflux, potentially causing interactions with other medications like mitoxantrone.
Area of Science:
- Neuroscience
- Pharmacology
- Genomics
Background:
- Oxycodone is a widely used opioid agonist but remains understudied.
- Understanding its effects on gene expression is crucial for elucidating its mechanisms of action.
Purpose of the Study:
- To investigate the global changes in brain gene expression following repeated oxycodone treatment in rats.
- To identify specific genes and biological pathways modulated by oxycodone.
- To explore the functional consequences of oxycodone-induced gene expression changes, particularly concerning Abcg2.
Main Methods:
- Microarray analysis of rat brain tissues after repeated oxycodone administration.
- Quantitative real-time-polymerase chain reaction (Q-PCR) for data validation.
- Computational analysis using MetaCore to identify biological processes.
- Immunoblotting to confirm protein level changes.
- Abcg2 ATPase assay to determine oxycodone's substrate status.
- Brain uptake studies using mitoxantrone.
Main Results:
- Oxycodone significantly regulated numerous genes in the rat brain, including Fkbp5, Per2, Rt1.Dalpha, Slc16a1, and Abcg2.
- Microarray data strongly correlated with Q-PCR validation (r = 0.979, p < 0.0000001).
- Identified biological processes included organic anion transport and immune response regulation.
- Abcg2 mRNA was upregulated 2.1-fold, confirmed by 1.8-fold protein upregulation.
- Oxycodone acted as an Abcg2 substrate only at high concentrations (≥500 μM).
- Oxycodone-induced Abcg2 upregulation significantly decreased mitoxantrone's brain/plasma ratio (approx. 2-fold).
Conclusions:
- Oxycodone alters gene expression in the brain, highlighting pathways involved in its pharmacological action, tolerance, dependence, and immune response.
- Upregulation of Abcg2 by oxycodone enhances the efflux of Abcg2 substrates like mitoxantrone, reducing brain accumulation.
- This mechanism suggests a potential for drug-drug interactions when oxycodone is co-administered with other Abcg2 substrates (e.g., daunorubicin, doxorubicin).
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