Upregulation of NF-E2-related factor-2-dependent glutathione by carnosol provokes a cytoprotective response and enhances cell survival.

AIM: To explore whether glutathione (GSH) increased through Nrf-2 activation is involved in the cytoprotective effects of carnosol in HepG2 cells. METHODS: Human hepatoma cell line HepG2 were exposed to rosemarry essential oil or carnosol. Cell viability was measured using an Alamar blue assay. The production of intracellular GSH was determined using monochlorobimane. The level of protein or mRNA was examined by Western blotting or RT-PCR, respectively. RESULTS: Rosemarry essential oil (0.005%-0.02%) and carnosol (5 and 10 mol/L) increased the intracellular GSH levels and GSH synthesis enzyme subunit GCLC/GCLM expression. Rosemary essential oil and carnosol increased nuclear accumulation of Nrf2 and enhanced Nrf2-antioxidant responsive element (ARE)-reporter activity. Transfection of the treated cells with an Nrf2 siRNA construct blocks GCLC/GCLM induction. Furthermore, pretreatment of the HepG2 cells with essential oil and carnosol exerted significant cytoprotective effects against H(2)O(2) or alcohol. In TNFα-treated cells, the nuclear translocation and transcriptional activity of NF-κB was abolished for 12 h following carnosol pretreatment. Cotreatment with GSH also suppressed NF-κB nuclear translocation, whereas cotreatment with BSO, a GSH synthesis blocker, blocked the inhibitory effects of carnosol. CONCLUSION: This study demonstrated that Nrf2 is involved in the cytoprotective effects by carnasol, which were at least partially mediated through increased GSH biosynthesis.

Dual mechanisms of NF-kappaB inhibition in carnosol-treated endothelial cells.

The increased adhesion of monocytes to injured endothelial layers is a critical early event in atherogenesis. Under inflammatory conditions, there is increased expression of specific cell adhesion molecules on activated vascular endothelial cells, which increases monocyte adhesion. In our current study, we demonstrate a putative mechanism for the anti-inflammatory effects of carnosol, a diterpene derived from the herb rosemary. Our results show that both carnosol and rosemary essential oils inhibit the adhesion of TNFalpha-induced monocytes to endothelial cells and suppress the expression of ICAM-1 at the transcriptional level. Moreover, carnosol was found to exert its inhibitory effects by blocking the degradation of the inhibitory protein IkappaBalpha in short term pretreatments but not in 12 h pretreatments. Our data show that carnosol reduces IKK-beta phosphorylation in pretreatments of less than 3 h. In TNFalpha-treated ECs, NF-kappaB nuclear translocation and transcriptional activity was abolished by up to 12 h of carnosol pretreatment and this was blocked by Nrf-2 siRNA. The long-term inhibitory effects of carnosol thus appear to be mediated through its induction of Nrf-2-related genes. The inhibition of ICAM-1 expression and p65 translocation is reversed by HO-1 siRNA. Carnosol also upregulates the Nrf-2-related glutathione synthase gene and thereby increases the GSH levels after 9 h of exposure. Treating ECs with a GSH synthesis inhibitor, BSO, blocks the inhibitory effects of carnosol. In addition, carnosol increases p65 glutathionylation. Hence, our present findings indicate that carnosol suppresses TNFalpha-induced singling pathways through the inhibition of IKK-beta activity or the upregulation of HO-1 expression. The resulting GSH levels are dependent, however, on the length of the carnosol pretreatment period.

Isolating a cytoprotective compound from Ganoderma tsugae: effects on induction of Nrf-2-related genes in endothelial cells.

Ganoderma tsugae is a medicinal fungus with several biological activities. It has long been used as a folk remedy for the promotion of health and longevity in China and other oriental countries. Here, a bioactive fraction of G. tsugae was progressively purified to be enriched in the activity of cytoprotective enzymes. The highest bioactivity was detected in the 20% EtOH-precipitated fraction, which was prepared from submerged fermentation filtrate of G. tsugae. Following further purification by gel filtration chromatography and acetone extraction, the most bioactive fraction, F5-2, was identified as a peptidoglycan-like compound. Extracts of G. tsugae (F5-2) induced heme oxygenase-1 (HO-1) and thioredoxin reductase-1 (TrxR1) expression in endothelial cells by increasing NF-E2-related factor-2 (Nrf2) nuclear translocation. Pretreatment with F5-2 increased intracellular glutathione (GSH) and protected against H(2)O(2), suggesting that induction of these antioxidant enzymes is important in protection against oxidative stress. Hence the bioactive peptidoglycan-like compound from G. tsugae might protect endothelial cells.