Glitazones Differentially Regulate Primary Astrocyte and Glioma Cell Survival

Abstract

The glitazones or thiazolidinediones are ligands of the peroxisome proliferator-activated receptor ␥ (PPAR␥). The glitazones are used in the treatment of diabetes, regulate adipogenesis, inflammation, cell proliferation, and induce apoptosis in several cancer cell types. High grade astrocytomas are rapidly growing tumors derived from astrocytes, for which new treatments are needed. We determined the effects of two glitazones, ciglitazone and the therapeutic rosiglitazone, on the survival of serum-deprived primary rat astrocytes and glioma cell lines C6 and U251, which were assessed by the methylthiazolyl tetrazolium assay and lactate dehydrogenase release. Rosiglitazone (5-20 M) decreased survival of glioma cells without affecting primary astrocytes, whereas ciglitazone at 20 M was toxic for both cell types. Ciglitazone at 10 M was cytoprotective for primary astrocytes but toxic to glioma cells. Cell death induced by ciglitazone, but not rosiglitazone, presented apoptotic features (Hoechst staining and externalization of phosphatidylserine). Two mechanisms to explain cytotoxicity were investigated: activation of PPAR␥ and production of reactive oxygen species (ROS). PPAR␥ does not seem to be the main mechanism involved, because the order of efficacy for cytotoxicity, ciglitazone > rosiglitazone, was inverse of their reported affinities for activating PPAR␥. In addition, GW9662, an inhibitor of PPAR␥, only slightly attenuated cytotoxicity. However, the rapid increase in ROS production and the marked reduction of cell death with the antioxidants ebselen and N-acetylcysteine, indicate that ROS have a key role in glitazone cytotoxicity. Ciglitazone caused a dose-dependent and rapid loss (in minutes) of mitochondrial membrane potential in glioma cells. Therefore, mitochondria are a likely source of ROS and early targets of glitazone cytotoxicity. Our results highlight the potential of rosiglitazone and related compounds for the treatment of astrogliomas.

Novel high-affinity PPARγ agonist alone and in combination with paclitaxel inhibits human anaplastic thyroid carcinoma tumor growth via p21WAF1/CIP1

“…We also used a pharmacological approach to test the role of PPARg in Tzd regulated transcription. Using similar micromolar concentrations and conditions as cited in published reports for the irreversible PPARg antagonist, GW9662 (Perez-Ortiz et al, 2004;Rumi et al, 2004;Turturro et al, 2004), a complete blockade of PPARg mediated luciferase transcription was demonstrated for all three Tzds (Figure 3c). Thus, using a siRNA and a pharmacological approach, transcription mediated by functional PPARg was completely blocked.…”

“…At nanomolar concentrations, the ability of RS5444 to antagonize cell proliferation in ATC cells was absolutely dependent upon the presence of functional PPARg as shown by the ability of PPARg siRNA and GW9662 to inhibit cell growth. Our study is one of few that clearly documents PPARg-mediated growth inhibitory effects of a Tzd (Palakurthi et al, 2001;Place et al, 2003;Perez-Ortiz et al, 2004;Rumi et al, 2004;Turturro et al, 2004). Collectively, these data demonstrate that the high-affinity PPARg agonist, RS5444, is completely dependent upon PPARg to mediate inhibition of cell proliferation while the other two Tzds activate PPARg along with other unidentified cell proliferation inhibitory pathways in ATC cells.…”

“…Indeed, PPARg independent inhibition of cell proliferation and induction of apoptosis have been attributed to Tzds such as troglitazone, rosiglitazone, and ciglitazone. Such mechanisms include inhibition of cyclin D3 and survivin in breast cancer (Lu et al, 2005) upregulation of GADD45 in breast cancer (Yin et al, 2004), enhanced reactive oxygen species in gliomas (Perez-Ortiz et al, 2004) and ablation of cyclin D1 in breast cancer . In fact, the first generation Tzd, troglitazone, is also a vitamin E (atocopherol) analog and was originally synthesized in efforts to identify novel antioxidants (Fujiwara et al, 1998;Davies et al, 2002).…”

Ebselen Alters Mitochondrial Physiology and Reduces Viability of Rat Hippocampal Astrocytes

“…In this line, the seleno-organic compound ebselen, which was originally developed as an anti-inflammatory agent, has been shown to protect against damage caused by free radicals in the CNS (Pérez-Ortiz et al, 2004;Green and Ashwood, 2005;Funchal et al, 2006;Gabryel and Ma1ecki, 2006;Ghisleni et al, 2008). However, in spite of the positive effects of ebselen, certain signs were observed in response to selenium-containing compounds that could be the basis of potential damaging actions.…”

“…Ebselen acts as an antiaging agent by attenuating oxidative stress in Caenorhabditis elegans (Avila et al, 2012), protects neurons from ischemic damage via control of the expressions of GABA shunt enzymes (Seo et al, 2009), has a marked inhibitory effect on neuronal damage during stroke (Yamagata et al, 2008), protects against excitotoxicity induced by glutamate in isolated chick retina (Centuriã o et al, 2005), and prevents ischemia-induced cytotoxicity and apoptosis (Gabryel and Ma1ecki, 2006) and reactive oxygen species (ROS) production (Pérez-Ortiz et al, 2004) in astrocytes.…”