Date of Degree

2-2019

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biochemistry

Advisor

Jesus A. Angulo

Committee Members

Syed F. Ali

Konstantinos Krampis

Ratna Sircar

Thomas Schmidt-Glenewinkel

Subject Categories

Life Sciences | Medicine and Health Sciences | Nervous System Diseases

Keywords

Neurodegeneration, Dopamine, Micorglia, Astrocyte, Oxidative Stress, Neuroinflammation

Abstract

Methamphetamine (METH) is a strong psychostimulant and its exposure can lead to serious neurological complications. METH-induced neuronal injury is the result of a complex interplay of different factors including dopamine (DA) overflow, oxidative stress and neuroinflammation. Although the mechanisms of METH-induced neurotoxicity have been extensively studied, there is still no effective therapeutic treatment. Therefore, it is essential to study potential drug candidates that can treat METH-induced neurotoxicity. Green tea extract, epigallocatechin gallate (EGCG), has emerged as a neuroprotective agent that can protect against several neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases. Recently, our lab has shown that EGCG prevents the METH-induced apoptosis and dopamine terminal damage, but the mechanisms involved remain unclear. In the present study, we examined the neuroprotective effects of EGCG on the METH-induced striatal neuroinflammation and oxidative stress in mice. CD-1 Mice were given a single injection of EGCG (2 mg/kg, ip) 30 minutes prior to a single injection of METH (30 mg/kg, ip) and sacrificed 8 hr, 1 day, or 3 days after the METH injection. The results show that METH induced dopaminergic axonal neurotoxicity and hyperthermia reflected as a marked decrease of striatal tyrosine hydroxylase (TH) protein level and increase of core body temperature, respectively. EGCG prevented the METH-induced reduction of TH, but failed to affect the METH-induced hyperthermic response. To examine the effect of EGCG on the METH-induced oxidative stress, we quantified the glutathione peroxidase (GPx) activity and glutathione peroxidase 4 (GPx-4), and copper-zinc superoxide dismutase (SOD-1) and catalase (CAT) protein levels. Colorimetric analysis indicates that METH decreased GPx activity 1 day after METH injection, this result is correlated to the reduction of GPx-4 protein level caused by METH as demonstrated by Western blots. In addition, Western blot analysis shows that METH increased SOD-1 and CAT proteins level 8 hr and 1 day after METH injection, respectively. Finally, immunohistochemical staining and Western blotting were used to evaluate the changes of glial activation, cycloocygenase-2 (COX-2) and blood-brain barrier (BBB) in the striatum. The results show that METH induced microglial activation and increase of COX-2 expression 1 day after METH injection as indicated by increase of Iba-1 and COX-2 immunoreactivity, respectively. These effects were followed by the increase of astrocytic activation and compromise of the blood-brain barrier (BBB) 3 days after the METH injection. Pretreatment with EGCG failed to prevent these effects, instead EGCG potentiated the METH-induced increase of glial activations and COX-2 protein level. Nevertheless, EGCG prevented the METH-induced breakdown of BBB reflected by diminished fluorescein iosothiocynate-dextran (FITC-dextran) extravasation in the striatum. Taken together, these data indicate that EGCG is effective in preventing the METH-induced oxidative stress and compromise of the BBB although it potentiates the glial response and the increase of COX-2 protein level.

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