Isosteviol Sodium Protects Neural Cells Against Hypoxia-Induced Apoptosis Through Inhibiting MAPK and NF-κB Pathways.

BACKGROUND: Stevioside, isolated from the herb Stevia rebaudiana, has been widely used as a food sweetener all over the world. Isosteviol Sodium (STV-Na), an injectable formulation of isosteviol sodium salt, has been proved to possess much greater solubility and bioavailability and exhibit protective effects against cerebral ischemia injury in vivo by inhibiting neuron apoptosis. However, the underlying mechanisms of the neuroprotective effects STV-Na are still not completely known. In the present study, we investigated the effects of STV-Na on neuronal cell death caused by hypoxia in vitro and its underlying mechanisms. METHODS: We used cobalt chloride (CoCl2) to expose mouse neuroblastoma N2a cells to hypoxic conditions in vitro. RESULTS: Our results showed that pretreatment with STV-Na (20 µM) significantly attenuated the decrease of cell viability, lactate dehydrogenase release and cell apoptosis under conditions of CoCl2-induced hypoxia. Meanwhile, STV-Na pretreatment significantly attenuated the upregulation of intracellular Ca2+ concentration and reactive oxygen species production, and inhibited mitochondrial depolarization in N2a cells under conditions of CoCl2-induced hypoxia. Furthermore, STV-Na pretreatment significantly downregulated expressions of nitric oxide synthase, interleukin-1ß, tumor necrosis factor-α, interleukin-6, nuclear factor kappa B (NF-κB), and mitogen-activated protein kinase (MAPK) signalings in N2a cells under conditions of CoCl2-induced hypoxia. CONCLUSIONS: Taken together, STV-Na protects neural cells against hypoxia-induced apoptosis through inhibiting MAPK and NF-κB pathways.

Isosteviol sodium injection improves outcomes by modulating TLRs/NF-κB-dependent inflammatory responses following experimental traumatic brain injury in rats.

Previous studies have shown that isosteviol sodium (STVNa) protects against permanent cerebral ischemia injury by inhibition of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-mediated inflammatory responses. Overwhelming evidence shows that toll-like receptors (TLRs) are the upstream regulators of NF-κB. On the basis of the similarity of the pathology caused by traumatic brain injury (TBI) and stroke, we speculated that STVNa may have a therapeutic effect against TBI through regulation of the TLRs/NF-κB signaling-mediated inflammatory response. Thus, we studied the potential therapeutic effects of STVNa and the underlying mechanisms. Male rats, subjected to controlled cortical impact (CCI) injury, were injected intraperitoneally with STVNa (5, 10, 20, 40, and 80 mg/kg, daily for 3 or 7 days) after trauma. Neurobehavioral scores, relative numbers of cortical lesions, and histology were examined. We also measured the mRNA and protein expression levels of TLRs/NF-κB signaling pathway-related genes including TLR2, TLR4, and NF-κB by quantitative real-time-PCR and western blotting, respectively, and concentrations of tumor necrosis factor-α and interleukin-1ß by an enzyme-linked immunosorbent assay. The results indicated that STVNa (20 mg/kg) showed significant neuroprotective effects 3 and 7 days after TBI, including the reduction of cortical lesions, improvement of the neurological severity score, significantly increased number of restored neurons, decreased number of astrocytes, and lower concentrations of tumor necrosis factor-α and interleukin-1ß. Results from quantitative real-time-PCR and western blotting also show that the mRNA and protein expression levels of TLR2, TLR4, and NF-κB were significantly lower in STVNa-treated rats compared with the vehicle-treated rats. The administration of STVNa attenuates the TLR/NF-κB signaling pathway-mediated inflammatory responses in the injured rat brain, and this may be the mechanism by which STVNa improves the outcome following TBI.

Yin Yang 1 Dynamically Regulates Antiviral Innate Immune Responses During Viral Infection.

BACKGROUND/AIMS: Type I interferon (IFN-1) production and IFN-1 signaling play critical roles in the host antiviral innate immune responses. Although transcription factor Yin Yang 1 (YY1) has been reported to have a dual activator/repressor role during the regulation of interferon beta (IFN-ß) promoter activity, the roles of YY1 in the regulation of upstream signaling pathways leading to IFN-1 induction and IFN-1 signaling during viral infection remain to be elucidated. METHODS: The roles of YY1 in IFN-1 production and IFN-1 signaling were investigated using immunoblotting, real-time PCR, small interfering RNA (siRNA)-mediated YY1 knockdown, YY1 overexpression by transient transfection, and co-immunoprecipitation, using mouse cells. RESULTS: YY1 was shown to interact with STAT1 in the absence of viral infection. Following viral infection, YY1 protein expression levels were decreased. YY1 knockdown led to a considerable downregulation of phosphorylated (p) TBK1 and pIRF3 expressions, while YY1 overexpression significantly upregulated pTBK1 and pIRF3 expression levels and promoted virus-induced IFN-ß production. Additionally, YY1 knockdown led to a significant upregulation of pSTAT1, pSTAT2 and antiviral interferon-stimulated genes, and inhibited viral replication. CONCLUSION: We demonstrated here that YY1 interacts with STAT1 and dynamically regulates the induction of IFN-1 production and activation of IFN-1 signaling in different stages during viral infection.