RESUMEN
Stevia has been shown to prevent oxidative stress and inflammation in carbon tetrachlorideinduced cirrhosis models. This study aimed to investigate the ability of an aqueous extract of stevia (AES) to prevent thioacetamide (TAA)induced cirrhosis in rats and to explore its mechanism of action. Liver cirrhosis was established by administering TAA (200 mg/kg by i.p. injections three times a week for 10 weeks); AES was administered (100 mg/kg by gavage daily) during the TAA treatment. Liver damage and fibrosis were evaluated, and the profibrotic pathways were analyzed by western blotting and immunohistochemistry. TAA increased nuclear factor kappa B (NFκB) and proinflammatory cytokine production, as well as the malondialdehyde and 4hydroxynonenal levels, whereas the glutathione/glutathione disulfide and nuclear factorE2related factor 2 (Nrf2) levels were decreased. Moreover, TAA increased collagen production, hepatic stellate cell (HSC) activation, and expression of profibrogenic mediators. TAAtreated rats that had been exposed to Mn2+ exhibited altered striatal dopamine turnover, indicating hepatic encephalopathy. AES partially or completely prevented all of these effects. AES showed antioxidant, antiinflammatory, and antifibrotic properties, probably because of its capacity to induce Nrf2 expression, reduce NFκB expression, and block several profibrogenic signaling pathways, subsequently inhibiting HSC activation and preventing fibrosis and dopamine turnover.
Asunto(s)
Células Estrelladas Hepáticas/efectos de los fármacos , Cirrosis Hepática Experimental/prevención & control , Factor 2 Relacionado con NF-E2/fisiología , FN-kappa B/fisiología , Extractos Vegetales/uso terapéutico , Proteína smad7/fisiología , Stevia , Factor de Crecimiento Transformador beta/fisiología , Animales , Células Estrelladas Hepáticas/fisiología , Cirrosis Hepática Experimental/inducido químicamente , Masculino , Ratas , Ratas Wistar , Transducción de Señal/efectos de los fármacos , TioacetamidaRESUMEN
Transforming growth factor-beta (TGF-ß) has a dual role in epithelial malignancies, including head and neck squamous cell carcinoma (HNSCC). Attenuation of canonical TGF-ß signaling enhances de novo tumor development, whereas TGF-ß overexpression and signaling paradoxically promotes malignant progression. We recently observed that TGF-ß-induced growth arrest response is attenuated, in association with aberrant activation of nuclear factor-κB (NF-κB), a transcription factor, which promotes malignant progression in HNSCC. However, what role cross-talk between components of the TGF-ß and NF-κB pathways plays in altered activation of these pathways has not been established. Here, we show TGF-ß receptor II and TGF-ß-activated kinase 1 (TAK1) are predominantly expressed in a subset of HNSCC tumors with nuclear activation of NF-κB family member RELA (p65). Further, TGF-ß1 treatment induced sequential phosphorylation of TAK1, IKK, IκBα and RELA in human HNSCC lines. TAK1 enhances TGF-ß-induced NF-κB activation, as TAK1 siRNA knockdown decreased TGF-ß1-induced phosphorylation of IKK, IκB and RELA, degradation of IκBα, RELA nuclear translocation and DNA binding, and NF-κB-induced reporter and target gene transcription. Functionally, TAK1 siRNA inhibited cell proliferation, migration and invasion. Celastrol, a TAK1 inhibitor and anti-inflammatory compound used in traditional Chinese medicine, also decreased TGF-ß1-induced phosphorylation of TAK1 and RELA, and suppressed basal, TGF-ß1- and tumor necrosis factor-alpha (TNF-α)-induced NF-κB reporter gene activity. Celastrol also inhibited cell proliferation, while increasing sub-G0 DNA fragmentation and Annexin V markers of apoptosis. Furthermore, TGF-ß and RELA activation promoted SMAD7 expression. In turn, SMAD7 preferentially suppressed TGF-ß-induced SMAD and NF-κB reporters when compared with constitutive or TNF-α-induced NF-κB reporter gene activation. Thus, cross-talk by TGF-ß via TAK1 and NF-κB promotes the malignant phenotype of HNSCC. Moreover, NF-κB may contribute to the downstream attenuation of canonical TGF-ß signaling through increased SMAD7 expression. Celastrol highlights the therapeutic potential of agents targeting TAK1 as a key node in this pro-oncogenic TGF-ß-NF-κB signal pathway.