Astrocytes have a pivotal role in brain as partners of neurons in homeostatic and metabolic processes. Astrocytes also protect other types of brain cells against the toxicity of reactive oxygen species and are considered as first line of defence against the toxic potential of xenobiotics. A key component in many of the astrocytic detoxification processes is the tripeptide glutathione (GSH) which serves as electron donor in the GSH peroxidase-catalyzed reduction of peroxides. In addition, GSH is substrate in the detoxification of xenobiotics and endogenous compounds by GSH-S-transferases which generate GSH conjugates that are efficiently exported from the cells by multidrug resistance proteins. Moreover, GSH reacts with the reactive endogenous carbonyls methylglyoxal and formaldehyde to intermediates which are substrates of detoxifying enzymes. In this article we will review the current knowledge on the GSH metabolism of astrocytes with a special emphasis on GSH-dependent detoxification processes.

In active antiretroviral therapy antiretroviral drugs are employed for the restoration of a functional immune system in patients suffering from the acquired immunodeficiency syndrome. However, potential adverse effects of such compounds to brain cells are discussed in connection with the development of neurocognitive impairments in patients. To investigate potential effects of antiretroviral drugs on cell viability and the glycolytic flux of brain cells, astrocyte-rich primary cultures were exposed to various antiretroviral compounds, including the non-nucleoside reverse transcriptase inhibitor efavirenz. In a concentration of 10 μM, neither efavirenz nor any of the other investigated antiretroviral compounds acutely compromised the cell viability nor altered glucose consumption or lactate production. In contrast, the primary metabolite of efavirenz, 8-hydroxy-efavirenz, stimulated the glycolytic flux in viable astrocytes in a time- and concentration-dependent manner with half-maximal and maximal effects at concentrations of 5 and 10 μM, respectively. The stimulation of glycolytic flux by 8-hydroxy-efavirenz was not additive to that obtained for astrocytes that were treated with the respiratory chain inhibitor rotenone and was abolished by removal of extracellular 8-hydroxy-efavirenz. In a concentration of 10 μM, 8-hydroxy-efavirenz and efavirenz did not affect mitochondrial respiration, while both compounds lowered in a concentration of 60 μM significantly the oxygen consumption by mitochondria that had been isolated form cultured astrocytes, suggesting that the stimulation of glycolytic flux by 8-hydroxy-efavrienz is not caused by direct inhibition of respiration. The observed alteration of astrocytic glucose metabolism by 8-hydroxy-efavirenz could contribute to the adverse neurological side effects reported for patients that are chronically treated with efavirenz-containing medications.

J. Neurochem. (2012) 120, 78–92. Abstract Combinations of antiretroviral drugs are successfully used for the treatment of acquired immune deficiency syndrome and reduce the incidence of severe human immunodeficiency virus (HIV)‐associated dementia. To test whether such drugs affect the GSH metabolism of brain cells, we have exposed astrocyte‐rich primary cultures to various antiretroviral compounds. Treatment of the cultures with the protease inhibitors indinavir or nelfinavir in low micromolar concentrations resulted in a time‐ and concentration‐dependent depletion of cellular GSH from viable cells which was accompanied by a matching increase in the extracellular GSH content. In contrast, the reverse transcriptase inhibitors zidovudine, lamivudine, efavirenz or nevirapine did not alter cellular or extracellular GSH levels. Removal of indinavir from the medium by washing the cells terminated the stimulated GSH export immediately, while the nelfinavir‐induced accelerated GSH export was maintained even after removal of nelfinavir. The stimulation of the GSH export from viable astrocytes by indinavir or nelfinavir was completely prevented by the application of MK571, an inhibitor of the multidrug resistance protein 1. These data demonstrate that indinavir and nelfinavir stimulate multidrug resistance protein 1‐mediated GSH export from viable astrocytes and suggest that treatment of patients with such inhibitors may affect the GSH homeostasis in brain.

Antiretroviral protease inhibitors are a class of important drugs that are used for the treatment of human immunodeficiency virus infections. Among those compounds, ritonavir is applied frequently in combination with other antiretroviral protease inhibitors, as it has been reported to boost their therapeutic efficiency. To test whether ritonavir affects the viability and the glutathione (GSH) metabolism of brain cells, we have exposed primary astrocyte cultures to this protease inhibitor. Application of ritonavir in low micromolar concentrations did not compromise cell viability, but caused a time- and concentration-dependent loss of GSH from the cells which was accompanied by a matching increase in the extracellular GSH content. Half-maximal effects were observed for ritonavir in a concentration of 3 μM. The ritonavir-induced stimulated GSH export from astrocytes was completely prevented by MK571, an inhibitor of the multidrug resistance protein 1. In addition, continuous presence of ritonavir was essential to maintain the stimulated GSH export, since removal of ritonavir terminated the stimulated GSH export. Ritonavir was more potent to stimulate GSH export from astrocytes than the antiretroviral protease inhibitors indinavir and nelfinavir, but combinations of ritonavir with indinavir or nelfinavir did not further stimulate astrocytic GSH export compared to a treatment with ritonavir alone. The strong effects of ritonavir and other antiretroviral protease inhibitors on the GSH metabolism of astrocytes suggest that a chronic treatment of patients with such compounds may affect their brain GSH metabolism.

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