Gliopreventive effects of guanosine against glucose deprivation in vitro

Abstract

Guanosine, a guanine-based purine, is recognized as an extracellular signaling molecule that is released from astrocytes and confers neuroprotective effects in several in vivo and in vitro studies. Astrocytes regulate glucose metabolism, glutamate transport, and defense mechanism against oxidative stress. C6 astroglial cells are widely used as an astrocyte-like cell line to study the astrocytic function and signaling pathways. Our previous studies showed that guanosine modulates the glutamate uptake activity, thus avoiding glutamatergic excitotoxicity and protecting neural cells. The goal of this study was to determine the gliopreventive effects of guanosine against glucose deprivation in vitro in cultured C6 cells. Glucose deprivation induced cytotoxicity, an increase in reactive oxygen and nitrogen species (ROS/RNS) levels and lipid peroxidation as well as affected the metabolism of glutamate, which may impair important astrocytic functions. Guanosine prevented glucose deprivation-induced toxicity in C6 cells by modulating oxidative and nitrosative stress and glial responses, such as the glutamate uptake, the glutamine synthetase activity, and the glutathione levels. Glucose deprivation decreased the level of EAAC1, the main glutamate transporter present in C6 cells. Guanosine also prevented this effect, most likely through PKC, PI3K, p38 MAPK, and ERK signaling pathways. Taken together, these results show that guanosine may represent an important mechanism for protection of glial cells against glucose deprivation. Additionally, this study contributes to a more thorough understanding of the glial-and redox-related protective properties of guanosine in astroglial cells.

Guanosine inhibits LPS-induced pro-inflammatory response and oxidative stress in hippocampal astrocytes through the heme oxygenase-1 pathway

“…Guanosine has been studied in a variety of experimental neuropathological contexts, including brain trauma [49], glucose deprivation, [29] pathological events involved in spinal cord injury [50], and seizures [14,27]; however, the precise mechanism of guanosine's neuroprotective effects is not completely understood. Some data support the existence of specific receptor-like binding sites for guanosine [17,51,52], and data also indicate that the extracellular effects of guanosine may involve the activation of intracellular signaling pathways, including the involvement of G proteins, MAPK, PI3K, and HO-1 [17,30,51,53,54].…”

“…The Griess reagent was prepared by mixing equal volumes of 1 % sulfanilamide in 0.5 M HCl and 0.1 % N-(1-naphthyl) ethylenediamine in deionized water. Briefly, the Griess reagent was added directly to the cell culture, which was incubated in the dark for 15 min, at 22°C [29,30]. Samples were analyzed at 550 nm on a microplate spectrophotometer.…”

“…Previous studies from our group have shown that guanosine possesses important antioxidant properties that may be derived from both its ability to directly scavenge oxidative species and the activation of pathways involved in antioxidant defenses. Additionally, these studies point to the heme oxygenase-1 (HO-1) pathway as a fundamental defense mechanism for cells exposed to oxidant challenges [29,30].…”

Guanosine and its role in neuropathologies

“…Several lines of evidence have suggested that the activation of the phosphatidylinositol-3 kinase (PI3K)/Akt and the mitogen-activated protein kinases (MAPKs) signaling pathways mediates the biological properties elicited by guanosine, including its ability to modulate glutamatergic transmission [82,90], as well as its antiapoptotic [86,91], antioxidant [92], and antiinflammatory effects [83]. These intracellular signaling cascades may be directly or indirectly triggered by guanosine, as part of its response against neuroinflammation and oxidative stress.…”

“…In vivo ↑ Neuronal and glial viability [136] ↑ Guanosine (up to 7 days following ischemia) [ [100] ↓ ROS production; ↓ inflammatory parameters [82] ↑ Cell viability; ↑ extension of neurites [52] Alzheimer's disease-in vitro ↓ Apoptosis; ↑ pro-survival signaling [88] ↓ Neuroinflammatory parameters [90] ↓ Oxidative stress ↓ apoptosis [101] Parkinson's disease In vitro…”