Crinum Latifolium Leave Extracts Suppress Immune Activation Cascades in Peripheral Blood … 325 tryptophan degradation and neopterin production develop in patients during diseases which are associated with Th1-type immune activation such as infections, autoimmune diseases, malignant disorders, and during allograft rejection episodes [11, 17, 18]. In patients, accelerated tryptophan degradation was found to parallel, and even to predict, the future course of several clinical conditions, including HIV infection, malignancy and autoimmune syndromes such as rheumatoid arthritis [18–20]. In this study, we evaluated the effects of powdered Crinum latifolium leaves extracted in water on the T-cell/macrophage interplay by its influence on PBMC stimulated with phytohaemagglutinin (PHA), which activates formation of IFN-γ in T-cells and subsequently tryptophan degradation and neopterin production in macrophages [21]. In an approach to measure the antioxidant capacity of this Crinum latifolium extract, we applied the oxygen radical absorption capacity (ORAC) assay. In addition, antiproliferative effects of this Crinum latifolium extract were analyzed in human benign prostate hyperplasia BPH-1 cells, highly metastatic prostate carcinoma PC3 cells, and androgen-sensitive prostate adenocarcinoma LNCaP cells. Results and Discussion Antioxidant activity in vitro The antioxidant capacity of Crinum latifolium extracted in water was evaluated using the ORAC assay, which measures the direct capacity of chain-breaking antioxidants based on the hydrogen atom transfer mechanism. Crinum latifolium showed potent peroxyl-radical scavenging capacity in vitro, with an ORAC value of 1610 ± 150 µmol TE/g. This ORAC value appears to be remarkably high in comparison to the ORAC values of other herbs. In a study of Liao et al. e.g., analysis of water extracts of 45 herbs traditionally used in chinese medicine revealed a very broad range of activity in the ORAC assay (40–1990 µmol TE/g herbs), of which only two herbal extracts (Spatholobus suberectus: 1990 µmol TE/g; Sanguisorba officinalis: 1940 mmol TE/g) showed a higher ORAC value than the Crinum latifolium extract analyzed in this study [22]. Anti-inflammatory activity The aqueous extract of Crinum latifolium produced a strong anti-inflammatory effect on mitogen stimulated PBMC by counteracting both, mitogen-induced activation of IDO enzyme activity and secretion of neopterin, which directs to a down-regulatory effect of Crinum latifolium constituents on activated T-cells and production of IFN-γ In resting PBMC, the Crinum latifolium extract also suppressed tryptophan degradation mediated by spontaneous IDO activity and slightly diminished neopterin production. Suppression of IFN-γ formation and associated down-stream pathways agrees well with earlier findings by us and others, that compounds and extracts with antioxidant capacities (such as vitamin C and E, resveratrol, wine or extracts of cacao, green or black tea) exhibit strong suppressive effects on stimulated PBMC, similarly as the Crinum latifolium extract used in this study [9, 23–27]. Sci Pharm. 2011; 79: 323–335