NO-induced activation of cyclic GMP-dependent pathway down regulates ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) protein in rat C6 glioma

How do phosphodiesterase-5 inhibitors affect cancer? A focus on glioblastoma multiforme

Since the discovery of phosphodiesterase-5 (PDE5) enzyme overexpression in the central nervous system (CNS) malignancies, investigations have explored the potential capacity of current PDE5 inhibitor drugs for repositioning in the treatment of brain tumors, notably glioblastoma multiforme (GBM). It has now been recognized that these drugs increase brain tumors permeability and enhance standard chemotherapeutics effectiveness. More importantly, studies have highlighted the promising antitumor functions of PDE5 inhibitors, e.g., triggering apoptosis, suppressing tumor cell growth and invasion, and reversing tumor microenvironment (TME) immunosuppression in the brain. However, contradictory reports have suggested a pro-oncogenic role for neuronal cyclic guanosine monophosphate (cGMP), indicating the beneficial function of PDE5 in the brain of GBM patients. Unfortunately, due to the inconsistent preclinical findings, only a few clinical trials are evaluating the therapeutic value of PDE5 inhibitors in GBM treatment. Accordingly, additional studies should be conducted to shed light on the precise effect of PDE5 inhibitors in GBM biology regarding the existing molecular heterogeneities among individuals. Here, we highlighted and discussed the previously investigated mechanisms underlying the impacts of PDE5 inhibitors in cancers, focusing on GBM to provide an overview of current knowledge necessary for future studies.

Protective effects of fusidic acid against sodium nitroprusside-induced apoptosis in C6 glial cells

Fusidic acid, a steroidal antibiotic, possesses antimicrobial, antioxidant, and anti-inflammatory properties, but the effect of fusidic acid against neurodegenerative disease-related cell death has not been studied. Here, we investigated the protective effects of fusidic acid on sodium nitroprusside (SNP)-induced toxicity in C6 glial cells. Fusidic acid (5-20 μM) prevented SNP (100 μM)-induced cell death dose dependently, and effectively attenuated SNP-induced generation of nitric oxide (NO), total reactive oxygen species (ROS), and peroxynitrite (ONOO). Fusidic acid (20 μM) pretreatment significantly suppressed SNP (100 μM)-induced apoptotic events, such as nuclear condensation and caspase-3 activation. In addition, fusidic acid effectively attenuated SNP-induced endoplasmic reticulum (ER) stress markers, such as GRP78, IRE1, ATF6, PERK, XBP1s, eIF2α, CHOP, and caspase-12. A specific adenosine monophosphate-activated protein kinase (AMPK) inhibitor, compound C (10 μM), reversed the preventive effects of fusidic acid against SNP-induced cytotoxicity, CHOP elevation, and caspase-3 activation. These results suggest that fusidic acid can protect C6 glial cells against cytotoxicity, through the regulation of AMPK pathway and apoptotic events.