In this study acetonic extracts of leaves of Pistacia lentiscus L. var. chia (mastiha tree) grown in the south as well as in the north Chios Greek island were isolated and further fractionated to give three different polarity fractions: apolar, medium-polar, and polar. The isolated fractions were assessed as regards their main composition, cytotoxic, anti-inflammatory activities, and interference with the glucocorticoid receptor (GR) signaling, applying cytotoxic assay, luciferase assays, and Western blot analysis of apoptosis-, energy-, and inflammation-associated molecules. Differences in cell viability have been detected among different polarity leaf fractions as well as among fractions of different plant origin with polar fractions showing the highest cytotoxicity. Fractions-induced anti-inflammatory activities and suppressive effects on the dexamethasone (DEX)-induced GR transcriptional activation were unveiled. The partition protocol of leaves fractions applied uncovers the enhanced glucocorticoid-associated biological activities of the medium-polar fractions, which may be associated with their enrichment in the triterpenoids that showed structural similarity with the glucocorticoids. A reduction in GR protein levels is observed by the fraction which is shown to be associated with the medium polar-induced proteolytic degradation of the receptor. In addition, the enhanced cytotoxic, anti-inflammatory, and potential anti-glycemic activities of the fractions from the Southern P. lentiscus L. that exclusively produce the mastiha resin, is revealed, indicating that leaves fractions from mastiha tree, similarly to mastiha tree resin, may have the potential to be further analyzed for their potent applications in the pharmaceutical cosmetic and nutraceutical fields.

Glucocorticoids are steroid hormones that regulate inflammation, growth, metabolism, and apoptosis via their cognate receptor, the glucocorticoid receptor (GR). GR, acting mainly as a transcription factor, activates or represses the expression of a large number of target genes, among them, many genes of anti-inflammatory and pro-inflammatory molecules, respectively. Transrepression activity of glucocorticoids also accounts for their anti-inflammatory activity, rendering them the most widely prescribed drug in medicine. However, chronic and high-dose use of glucocorticoids is accompanied with many undesirable side effects, attributed predominantly to GR transactivation activity. Thus, there is a high need for selective GR agonist, capable of dissociating transrepression from transactivation activity. Protopanaxadiol and protopanaxatriol are triterpenoids that share structural and functional similarities with glucocorticoids. The molecular mechanism of their actions is unclear. In this study applying induced-fit docking analysis, luciferase assay, immunofluorescence, and Western blot analysis, we showed that protopanaxadiol and more effectively protopanaxatriol are capable of binding to GR to activate its nuclear translocation, and to suppress the nuclear factor-kappa beta activity in GR-positive HeLa and HEK293 cells, but not in GR-low level COS-7 cells. Interestingly, no transactivation activity was observed, whereas suppression of the dexamethasone-induced transactivation of GR and induction of apoptosis in HeLa and HepG2 cells were observed. Thus, our results indicate that protopanaxadiol and protopanaxatriol could be considered as potent and selective GR agonist.

No abstract

No abstract

Abstract. Uric acid is a known danger associated molecular pattern molecule able to induce inflammation following internalization of its crystals by cells of the innate immune system. By activating antigen-presenting cells, urate boosts adaptive immunity as well. Furthermore, urate crystals can induce proliferation of isolated T-cells, which are unable to phagocytose crystal particles. In light of the evidence that urate crystals can also activate dendritic cells and macrophages without prior internalization but through sequestration of lipid rafts (and consequently receptors clustering in a non specific manner), the authors evaluated whether such a mechanism is involved in the direct activation of T-cells by urate crystals. In the present study, isolated human T-cells were cultured with or without urate at a concentration above its crystallization level. The expression and phosphorylation state of the T-cell receptor (TCR) complex zeta chain and the expression of the master regulator of cell proliferation c-Myc were assessed by western blotting. T-cell proliferation was measured by bromodeoxyuridine assay. Collectively, the results indicated that urate increased zeta chain phosphorylation indicating that it induces activation of TCR complex directly, since zeta chain phosphorylation takes place at the cell membrane and is a very proximal event in TCR complex-mediated signal transduction. In parallel, urate increased the expression of the transcription factor c-Myc and induced T-cell proliferation. In conclusion, urate crystals directly activate the TCR complex and induce T-cell proliferation.