Up‐regulation of P‐glycoprotein expression by glutathione depletion‐induced oxidative stress in rat brain microvessel endothelial cells

Abstract

Glutathione (GSH) depletion has been implicated in the pathogenesis of neurological diseases. During GSH depletion, cells of the blood-brain barrier (BBB) are subjected to chronic oxidative stress. In this study, we investigated the effect of such stress, produced with the GSH synthesis inhibitor L-buthionine-(S,R)-sulfoximine (BSO), on expression of P-glycoprotein (Pgp) in primary cultured rat brain microvessel endothelial cells that comprise the blood-brain barrier (BBB). Application of BSO to cell monolayers at concentrations up to 800 lM caused increases in expression of Pgp. Concentrations ‡ 400 lM BSO decreased cell viability. Application of 200 lM BSO caused a significant increase in Pgp function activity, as assessed by rhodamine 123 (Rh123) accumulation experiments. At this concentration, BSO produced timedependent decreases in levels of intracellular GSH and increases in levels of intracellular reactive oxygen species (iROS). The increases were also observed within 48 h following BSO treatment in mdr1a and mdr1b mRNA. Exposure of cells to BSO for 24 h produced maximal effects in the accumulation of iROS, and in expression and function of Pgp. The ROS scavenger N-acetylcysteine prevented ROS generation and attenuated the changes of both expression and activity of Pgp induced by BSO. Therefore, the transport of Pgp substrates may be affected by changing Pgp expression under conditions of chronic oxidative stress induced by GSH depletion.

Modulation of P-Glycoprotein at the Blood-Brain Barrier: Opportunities to Improve Central Nervous System Pharmacotherapy

“…All of these signals are indeed upregulated in animal models of stroke. Consistent with these results on oxidative stress, glutathione depletion causes similar up-regulation of P-glycoprotein expression in rat brain capillary endothelial cells in primary culture (Hong et al, 2006). These effects are reversed by the reactive oxygen species scavenger, N-acetylcysteine, suggesting that loss of glutathione leads to elevated reactive oxygen species, which induces P-glycoprotein expression.…”

Energy allocations to xenobiotic transport and biotransformation reactions in rainbow trout (Oncorhynchus mykiss) during energy intake restriction

“…Laboratory and field studies in aquatic organisms, including fish, observed enhanced efflux activities and P-gp expression in response to stressors such as increased contaminant exposure, reactive oxygen species, and water temperature (Bard 2000). This modulated response suggests that cellular defence mechanisms giving rise to/capable of producing "chemo-immunity" are highly regulated and adapt to provide a specific and appropriate level of defence activity (Chin et al 1990;Hong et al 2006;Sakardi et al 2006). …”

“…In oyster gills, it has been suggested that transcriptional activation plays a role in enhancing P-gp expression with increasing water temperature (Bard 2000). Further work is needed to determine if greater efflux capacities at high temperatures may be due to increased catalytic efficiencies, or indirect up regulation of P-gp expression through cellular stress responses involving heat shock proteins or oxidative stress signalling cascades (Chin et al 1990;Minier et al 2000;Hong et al 2006). Trout in half-ration and fasted treatment groups also exhibited diminished R123 accumulation rates up to week 9 although to a lesser extent than in the control group, suggesting that the P-gp responses to seasonal temperature changes may be modulated in fish under dietary restriction.…”

The Dual Cyclooxygenase/5-Lipoxygenase Inhibitor Licofelone Attenuates P-Glycoprotein-Mediated Drug Resistance in the Injured Spinal Cord

“…Based on previous reports, Pgp upregulation in the CNS appears to be a common response under neurological conditions characterized by inflammation, excitotoxicity, and oxidative stress. 111 It is, therefore, interesting to consider whether enhanced Pgp expression might serve as an endogenous protective response in the injured or diseased CNS. Perhaps this reinforcement of active transport across the barrier is spurred in part by passive deficits in barrier integrity resulting from trauma.…”