Mechanism of glucocorticoid-induced oxidative stress in rat hippocampal slice cultures

Abstract

Prolonged stress results in elevation of glucocorticoid (GC) hormones, which can have deleterious effects in the brain. The hippocampus, which has a high concentration of glucocorticoid receptors, is especially vulnerable to increasing levels of GCs. GCs have been suggested to endanger hippocampal neurons by exacerbating the excitotoxic glutamate-calcium-reactive oxygen species (ROS) cascade. In an effort to reveal the mechanisms underlying GC-mediated hippocampal neurotoxicity, we aimed to clarify the molecular pathway of GC-induced ROS increase by using organotypic hippocampal slice cultures. Assays for ROS, using 2',7'-dichlorodihydrofluorescein diacetate fluorescence, showed that treatment of synthetic GC, dexamethasone (DEX) significantly enhanced ROS levels. Time course and dose response analyses indicated that peak amount of ROS was generated at 4 h after treatment with 50 micromol/L DEX. By contrast, other steroid hormones, progesterone and estradiol did not influence ROS production. N-acetyl-L-cysteine completely suppressed ROS produced by DEX. Propidium iodide staining exhibited prominent cell death in the hippocampal layer after 96 h of DEX treatment. RU486, a GC receptor antagonist, almost completely blocked the effect of DEX on ROS production and cell death, indicating that DEX-induced ROS overproduction and hippocampal death are mediated via GC receptors. Real-time reverse transcriptase PCR analysis demonstrated that after DEX treatment the level of glutathione peroxidase mRNA was decreased whereas that of NADPH oxidase mRNA was significantly enhanced. These findings suggest that excess GCs cause hippocampal damage by regulating genes involved in ROS generation.

Type 1 diabetes mellitus and major depressive disorder: evidence for a biological link

“…Moreover, post-mortem analyses indicate that SOD protein levels are augmented in the prefrontal cortex of patients with depression, which may suggest compensation for oxidative stress in brain tissue in this patient population [57]. Hypercortisolism, which is present in depression (and diabetes), as described below, can also contribute to increased oxidative stress [58,59]. In rodent studies, experimental models of depression (chronic mild stress model) demonstrate that glucocorticoid hypersecretion causes oxidative stress, both by increasing lipid peroxidation in the brain cortex and medulla and by decreasing glutathione levels in the medulla [60]; this finding requires confirmation in humans.…”

Severe Life Stress and Oxidative Stress in the Brain: From Animal Models to Human Pathology

“…In microglia, dexamethasone inhibits the NOX-dependent ROS production (30,76), probably via the suppression of MKP-1-dependent MAPK pathways (76). In hippocampal neurons, both inhibition and induction of glucocorticoids on NOX-dependent ROS production have been reported (84,182).…”

Neuroprotective Effects of Genistein in Mongolian Gerbils: Estrogen Receptor–β Involvement

“…The mechanism, however, by which genistein was neuroprotective against delayed neuronal death has not been fully elucidated. Delayed neuronal death in the CA 1 region of the hippocampus following transient cerebral ischemia has been widely attributed to an intracellular Ca 2+ overload (57), free radical-related damage (58), and glutamate-receptor-mediated neurotoxicity (59). Oxidative stress predominates in the pathophysiology of ischemic/reperfusion injury and exerts its deleterious effects by oxidizing various cellular components.…”