NMDA receptor regulation of levodopa-induced behavior and changes in striatal G protein-coupled receptor kinase 6 and β-arrestin-1 expression in parkinsonian rats

Targeting β-Arrestins in the Treatment of Psychiatric and Neurological Disorders

Therapies for psychiatric and neurological disorders have been in the development and refinement process for the past 5 decades. Yet, most of these therapies lack optimal therapeutic efficacy and have multiple debilitating side effects. Recent advances in understanding the pathophysiological processes of psychiatric and neurological disorders have revealed an important role for β-arrestins, which are important regulators of G-protein-coupled receptor (GPCR) function, including desensitization and intracellular signaling. These findings have pushed β-arrestins to the forefront as potential therapeutic targets. Here, we highlight current knowledge on β-arrestin functions in certain psychiatric and neurological disorders (schizophrenia, Parkinson's disease, and substance abuse disorders), and how this has been leveraged to develop new therapeutic strategies. Furthermore, we discuss the obstacles impacting the field of β-arrestin-based therapeutic development and future approaches that might help advance strategies to develop optimal β-arrestin-based therapies.

Effect of Tianqi antitremor granules on behavioral manifestations and expression of G protein-coupled receptor kinase 6 and β-arrestin1 in levodopa-induced dyskinesia in a rat model of Parkinson's disease

Background

Recent studies have shown that expression of G protein-coupled receptor kinase 6 (GRK6) and β-arrestin1 in the striatum is closely associated with hyperactive dopamine receptors in rats with levodopa-induced dyskinesia (LID). Our research group has shown that Tianqi antitremor granules have a significant effect on the motor complications of Parkinson’s disease (PD). However, whether Tianqi antitremor granules have an effect on the behavioral manifestations and expression of GRK6 and β-arrestin1 in rats with LID is unknown.

Methods

Rats with PD received twice daily intraperitoneal injections of levodopa for 4 weeks to induce dyskinesia. Rats with LID were randomly divided into five groups: an LID-control group, an LID group, a levodopa plus Tianqi antitremor granules as traditional Chinese medicine (TCM)-low group, a levodopa plus TCM-medium group, and levodopa plus TCM-high group. Peak intensity of rotations was measured. GRK6 and β-arrestin1 expression in the striatum of the dyskinetic rats was observed by immunohistochemistry and Western blotting.

Results

Pulsatile treatment with levodopa induced abnormal involuntary movements in rats with PD similar to LID in patients with PD. We found that repeated levodopa administration increased peak rotations in dyskinetic rats. However, peak rotations were decreased in rats given levodopa plus the different doses of Tianqi antitremor granules. In accordance with changed behavior, GRK6 and β-arrestin1 expression was decreased in rats with PD and was persistently low in rats with LID, but this decrease was prevented by coadministration of levodopa and Tianqi antitremor granules.

Conclusion

Tianqi antitremor granules ameliorated levodopa-induced dyskinetic behavior, reversed the decrease in GRK6 and β-arrestin1 expression, and acted as a useful adjunctive medicine for the treatment of LID.