Browsing by Subject "Limonoids"
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Item Anti-inflammatory Properties of Citrus Limonoids and Their Isolation and Characterization(2012-02-14) Kim, Jin HeeThis dissertation investigates the role of limonoids in inflammation to reduce risk of breast cancer and cardiovascular disease. Radical scavenging activity and apoptotic effects of extracts from lemon seeds were investigated in human breast adenocarcinoma (MCF-7) cells and non-malignant breast (MCF-12F) cells. The MeOH:water (80:20) extract showed the highest (29.1%, P < 0.01) inhibition of MCF-7 cells without affecting the non-malignant breast cells. Further, the purified and modified limonoids were screened for their cytotoxicity on estrogen receptor (ER)-positive (MCF-7) or ER-negative (MDA-MB-231) human breast cancer cells. The MCF-7 cell was more susceptible to tested limonoids. Although most of limonoids induced anti-aromatase activity, the inhibition of proliferation was not related to the anti-aromatase activity. On the other hand, the anti-proliferative activity was significantly correlated with the level of caspase-7 activation by limonoids. The next study investigated the mechanism of anti-breast cancer and anti-aromatase activities of obacunone through inhibition of MCF-7 cell proliferation without affecting non-malignant breast cells. Treatment with obacunone resulted in an increased G1 cell cycle arrest and induction of apoptosis. Exposure of MCF-7 breast cancer cells to obacunone down-regulated expression of inflammatory molecules including nuclear factor-kappa B (NF--2 (COX-2). Furthermore, potential of obacunone on inhibition of COX-2 and NF-the p38 mitogen-activated protein (MAP) kinase was also investigated. In the final study, nomilin was the most potent natural inhibitor for p38 MAP kinase activity in human aortic smooth muscle cells indicating that a seven-membered A ring with acetoxy group, present in nomilin, seems to be essential for its inhibitory activity on p38 MAP kinase. The possible mechanism of nomilin for prevention of cardiovascular disease was determined. Pre-treatment with nomilin resulted in significant inhibition of TNF- induced HASMCs proliferation. The anti-proliferative activity of nomilin is due to apoptosis through mitochondrial dependent pathway.Item Citrus limonoids and flavonoids: extraction, antioxidant activity and effects on hamster plasma cholesterol distribution(Texas A&M University, 2005-11-01) Yu, JunFour in vitro models were used to measure the antioxidant activity of 11 citrus phytochemicals. The citrus limonoids and bergapten showed very weak antioxidant activity. The flavonoids demonstrated mild, to moderate, to strong antioxidant activity. In addition to some other commonly accepted structural features our data indicated that the hydroxyl group in position 6 of ring A could also increase the antioxidant activity of flavonoids. Compared with the active flavonoids, limonoids are highly oxygenated triterpenoids, with fewer hydroxyl groups to stabilize unpaired electrons (or scavenge free radicals). Bergapten lacks a hydroxyl group. This is the first report on the antioxidant activity of limonoids and neoeriocitrin. A feeding study using Syrian hamsters was followed to determine the effect of citrus limonoids and flavonoids on plasma cholesterol. Hamsters fed with limonin, limonin 17-Beta-D-glucopyranoside and grapefruit pulp significantly inhibited the increase of LDL/HDL-cholesterol (36.6%, 52.9% and 57% respectively) compared with the basal control (65.8%) and the pectin control (70%). Furthermore, hamsters fed with limonin had significantly larger LDL particle size (21.21 nm) compared with the control group (19.96 nm). Further studies demonstrated that LDLs from hamsters fed with limonin and limonin 17-Beta-D-glucopyranoside were less susceptible to oxidation. These data suggest that limonin, limonin 17-Beta-D-glucopyranoside and grapefruit pulp have potential inhibitory effects against atherogenesis. Supercritical CO2 (SC-CO2) was attempted to extract limonoids from grapefruit seeds and molasses. Limonin aglycone was successfully extracted with SC-CO2 directly from grapefruit seeds with the yield of 6.3 mg/g seeds at 48.3 MPa, 50˚C and 60 min with CO2 top feeding; and the limonin glucoside was extracted using SC-CO2 and ethanol as co-solvent from the defatted seeds with the yield of 0.73 mg/g seeds at 42 MPa, 52˚C, 45% ethanol (XEth=0.45) and 40 min with CO2 top feeding; and limonin glucoside also was extracted using SC-CO2 and ethanol with the yield of 0.61mg/g grapefruit molasses at 48.3 MPa, 50˚C and 10% ethanol (XEth=0.1), 40 min with CO2 top feeding. CO2 flow rate was around~5 l/min in experiments. The results demonstrated SC-CO2 extraction of limonoids from citrus juice industry byproducts has practical significance for future commercial production.Item Isolation and effects of citrus limonoids on cytochrome p450 inhibition, apoptotic induction and cytotoxicity on human cancer cells.(Texas A&M University, 2007-04-25) Poulose, Shibu M.This dissertation illustrates an efficient purification method for citrus limonoids and flavonoids, while examining their effects on cytochrome P450 inhibition and apoptotic induction on human neuroblastoma (SH-SY5Y) and colonic adenocarcinoma (Caco-2) cells. The first study developed a bulk purification method for limonoids, from seeds and molasses of citrus fruits, using a combination of chromatographic techniques. This also resulted in an efficient purification method for naringin and hesperidin from citrus byproducts. The second study investigated the inhibitory effects of purified limonoids and flavonoids on the enzymatic activities of different isoforms of human cytochrome P450. O-Dealkylase and hydroxylase activities of CYP1A2, CYP1B1, CYP3A4 and CYP19, using specific substrates such as ethoxyresorufin (ethoxyresorufin O-dealkylase, EROD), methoxyresorufin (methoxyresorufin O-dealkylase, MROD), and dibenzylfluorescein (DBF), were found to be significantly (P < 0.001) reduced at micromolar levels. A kinetic analysis showed competitive and non-competitive modes of inhibition by limonoids, on CYP19 hydroxylase activity. The results corroborate the active role of limonoids in the redox cycling mechanisms. The third study examined the antioxidant and apoptotic inducing ability of limonoid glucosides on human neuroblastoma cells. Four limonoid glucosides, LG (17beta-D glucopyranoside limonin), OG (obacunone 17beta-D glucopyranoside), NAG (nomilinic acid 17beta-D glucopyranoside), and DNAG (deacetylnomilinic acid 17beta-D glucopyranoside), have shown superoxide scavenging at millimolar levels. Micromolar amounts of LG and OG induced rapid necrosis of SH-SY5Y cells. Cytotoxicity was correlated (P = 0.046) to a concentration and timedependent increase in caspase 3/7 activity. Analyses of DNA content during the S phase of the cell cycle indicated reductions of 86.6% for LG and 82.3% for OG as compared to untreated. The results validate the antineoplastic distinctiveness of limonoid glucosides. In the fourth study, cytotoxic effects of limonoid aglycones and glucosides were assessed on human SH-SY5Y neuroblastoma and colon carcinoma (CaCo-2) cell lines and compared with the non-cancerous Chinese hamster ovary (CHO) cells. Significant (P < 0.001) cytotoxic effects were observed only on cancerous cells, over 24 to 36 h. The study revealed a marked increase in the DNA content of aneuploidic cells, which results in cell cycle arrest. The results confirm that glycosides are the most active apoptotic inducing form.