Profile of cholesterol-related sterols in aged amyloid precursor protein transgenic mouse brain.
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Cholesterol is implicated to play a role in Alzheimer disease pathology. Therefore, the concentrations of cholesterol, its precursors, and its degradation products in brain homogenates of aging wild-type and beta-amyloid precursor protein transgenic mice carrying the Swedish mutation (APP23) were analyzed. Among the sterols measured, lanosterol is the first common intermediate of two different pathways, which use either desmosterol or lathosterol as the predominant precursors for de novo synthesis of brain cholesterol. In young mice, cholesterol is mainly synthesized via the desmosterol pathway, while in aged mice, lathosterol is the major precursor. 24S-hydroxycholesterol (cerebrosterol), which plays a key role in the removal of cholesterol from the brain, modestly increased during aging. No differences in the levels of cholesterol, its precursors, or its metabolites were found between wild-type and APP23 transgenic mice. Moreover, the levels of the exogenous plant sterols campesterol and sitosterol were significantly elevated in the brains of APP23 animals at age 12 and 18 months. This time point coincides with abundant plaque formation. (+info)
Free phytosterols effectively reduce plasma and liver cholesterol in gerbils fed cholesterol.
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The potential of free phytosterols (including 20% stanols) to lower plasma and liver lipids was assessed in three experiments with gerbils fed diets containing cholesterol. The first explored the ability of phytosterols (0.5%) to block absorption of 0.05, 0.10, and 0.5% cholesterol. The second assessed the importance of consuming phytosterols (0.75%) simultaneously with cholesterol (0.15%). The third compared free phytosterols (0.75%) with similar levels of esterified sterols or stanols using diets containing 0.15% cholesterol. A 5:1 ratio of phytosterols:cholesterol effectively blocked cholesterol absorption when the dietary cholesterol load was moderate. Consuming a 5:1 ratio with every meal was more effective than receiving equal phytosterols in a 10:1 ratio every other day. Finally, free phytosterols dissolved in fat were as effective as esterified sterols and stanols in lowering plasma and liver cholesterol, and all were equally effective at blocking cholesterol absorption as shown by increased fecal cholesterol output. Plant sterol accumulation in the liver was minimal for all test groups. (+info)
The GSK3-like kinase BIN2 phosphorylates and destabilizes BZR1, a positive regulator of the brassinosteroid signaling pathway in Arabidopsis.
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Brassinosteroids (BRs) are a class of steroid hormones essential for normal growth and development in plants. BR signaling involves the cell-surface receptor BRI1, the glycogen synthase kinase-3-like kinase BIN2 as a negative regulator, and nuclear proteins BZR1 and BZR2/BES1 as positive regulators. The interactions among these components remain unclear. Here we report that BRs induce dephosphorylation and accumulation of BZR1 protein. Experiments using a proteasome inhibitor, MG132, suggest that phosphorylation of BZR1 increases its degradation by the proteasome machinery. BIN2 directly interacts with BZR1 in yeast two-hybrid assays, phosphorylates BZR1 in vitro, and negatively regulates BZR1 protein accumulation in vivo. These results strongly suggest that BIN2 phosphorylates BZR1 and targets it for degradation and that BR signaling causes BZR1 dephosphorylation and accumulation by inhibiting BIN2 activity. (+info)
A crucial role for the putative Arabidopsis topoisomerase VI in plant growth and development.
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Plant steroid hormones, brassinosteroids (BRs), play important roles throughout plant growth and development. Plants defective in BR biosynthesis or perception display cell elongation defects and severe dwarfism. Two dwarf mutants named bin3 and bin5 with identical phenotypes to each other display some characteristics of BR mutants and are partially insensitive to exogenously applied BRs. In the dark, bin3 or bin5 seedlings are de-etiolated with short hypocotyls and open cotyledons. Light-grown mutant plants are dwarfs with short petioles, epinastic leaves, short inflorescence stems, and reduced apical dominance. We cloned BIN3 and BIN5 and show that BIN5 is one of three putative Arabidopsis SPO11 homologs (AtSPO11-3) that also shares significant homology to archaebacterial topoisomerase VI (TOP6) subunit A, whereas BIN3 represents a putative eukaryotic homolog of TOP6B. The pleiotropic dwarf phenotypes of bin5 establish that, unlike all of the other SPO11 homologs that are involved in meiosis, BIN5/AtSPO11-3 plays a major role during somatic development. Furthermore, microarray analysis of the expression of about 5500 genes in bin3 or bin5 mutants indicates that about 321 genes are down-regulated in both of the mutants, including 18 of 30 BR-induced genes. These results suggest that BIN3 and BIN5 may constitute an Arabidopsis topoisomerase VI that modulates expression of many genes, including those regulated by BRs. (+info)
2,3-Oxidosqualene cyclase and cycloartenol-s-adenosylmethionine methyltransferase activities in vivo in the cotyledon and axis tissues of germinating pea seeds.
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Axis tissues, root and shoot, of germinating pea seedlings actively synthesize sterol from [2-14C]mevalonate during the first 3 days of germination. In addition to the intermediates of sterol synthesis, cycloartenol and 24-methylenecycloartanol, these tissues also form the triterpene beta-amyrin. The cyclase catalysing the formation of cycloartenol from oxidosqualene is about four times as active as that for beta-amyrin synthesis. 2. Sterol synthesis in the cotyledon is negligible, but cycloartenol and 24-methylenecycloartanol, as well as beta-amyrin, are synthesized there. Oxidosqualene cyclase activity in this tissue is 2.6 times as active for beta-amyrin synthesis as for cycloartenol synthesis. 3. Comparison of the relative amounts of 14C in cycloartenol and 24-methylenecycloartanol in the axis tissues and cotyledons of 3-day-old seedlings point to relatively active cycloartenol-S-adenosylmethionine methyltransferase systems in both axis tissues and a poorly active system in the cotyledon. 4. The role of beta-amyrin synthesis in the germinating pea seedling is discussed. (+info)
Plant sterol ester-enriched spread lowers plasma total and LDL cholesterol in children with familial hypercholesterolemia.
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BACKGROUND: Naturally occurring plant sterol esters (SEs) favorably affect serum cholesterol concentrations in humans and could aid in the treatment of children with familial hypercholesterolemia (FH). OBJECTIVE: We studied the effect of SE-enriched spread on serum lipids, lipoproteins, carotenoids, fat-soluble vitamins, and physiologic variables in children with FH aged 7-12 y. DESIGN: In a randomized, double-blind crossover study comprising two 8-wk interventions, 38 children with FH consumed 18.2 +/- 1.5 g SE spread/d, corresponding to 1.60 +/- 0.13 g SEs, or a control spread. Blood samples were analyzed at the start and end of each diet period. RESULTS: Plasma LDL-cholesterol concentrations decreased by 10.2% (P = 0.003) during the SE period compared with the control period. Total cholesterol and apolipoprotein B concentrations were reduced by 7.4% (P = 0.007 and P = 0.020, respectively) during the SE period. No changes were observed in HDL cholesterol, triacylglycerol, or apolipoprotein A-I. Serum concentration of lipid-adjusted lycopene decreased by 8.1% (P = 0.015) in the SE period, with no changes in the other carotenoids. Lipid-adjusted retinol and alpha-tocopherol concentrations increased by 15.6% (P < 0.001) and 7.1% (P = 0.027), respectively. There was an increase (16.8%, P = 0.04) in alanine transaminase in the SE period, but this was explained by a significantly lower starting concentration in the SE period than in the control period. The children consumed a recommended American Heart Association Step I diet during both intervention periods. CONCLUSION: A daily intake of 1.6 g SEs induces an additional reduction in LDL-cholesterol concentrations in children with FH consuming a recommended diet. (+info)
Inhibition of cholesterol biosynthesis by Delta22-unsaturated phytosterols via competitive inhibition of sterol Delta24-reductase in mammalian cells.
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Dietary phytosterols are cholesterol-lowering agents that interfere with the intestinal absorption of cholesterol. In the present study, we have studied their effects on cholesterol biosynthesis in human cells, particularly in the sterol-conversion pathway. For this, both Caco-2 (intestinal mucosa) and HL-60 (promyelocytic) human cell lines were incubated with [(14)C]acetate, and the incorporation of radioactivity into sterols was determined using HPLC and radioactivity detection online. Sterols containing a double bond at C-22 in the side chain (stigmasterol, brassicasterol and ergosterol) dramatically inhibited the activity of sterol Delta(24)-reductase, as indicated by the decrease in radioactivity incorporation into cholesterol and the accumulation of its precursors (mainly desmosterol). Phytosterols with the saturated side chain (beta-sitosterol and campesterol) were inactive in this regard. The inhibition of sterol (24)-reductase was confirmed in rat liver microsomes by using (14)C-labelled desmosterol as the substrate. The (22)-unsaturated phytosterols acted as competitive inhibitors of sterol (24)-reductase, with K(i) values (41.1, 42.7 and 36.8 microM for stigmasterol, brassicasterol and ergosterol respectively) similar to the estimated K(m) for desmosterol (26.3 microM). The sterol 5,22-cholestedien-3beta-ol, an unusual desmosterol isomer that lacks the alkyl groups characteristic of phytosterols, acted as a much stronger inhibitor of (24)-reductase (K(i)=3.34 microM). The usually low intracellular concentrations of the physiological substrates of (24)-reductase explains the strong inhibition of cholesterol biosynthesis that these compounds exert in cells. Given that inhibition of sterol (24)-reductase was achieved at physiologically relevant concentrations, it may represent an additional mechanism for the cholesterol-lowering action of phytosterols, and opens up the possibility of using certain (22)-unsaturated sterols as effective hypocholesterolaemic agents. (+info)
Inhibition of the sterol pathway in leek seedlings impairs phosphatidylserine and glucosylceramide synthesis but triggers an accumulation of triacylglycerols.
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Like most higher plants, leek seedlings (Allium porrum L.) contain a mixture of Delta(5)-sterols in which sitosterol largely predominates. As previously reported (Plant Physiol., 117 (1998) 931), these compounds, which are synthesized at the endoplasmic reticulum level, were shown to be actively transported to the plasma membrane via a membrane-mediated process, together with phosphatidylserine (PS). In the present work, leek seedlings were allowed to germinate for 7 days in the presence of fenpropimorph, a sterol biosynthesis inhibitor. Such a treatment was found to trigger an almost complete replacement of the usual sterols by 9beta,19-cyclopropylsterols (mainly cycloeucalenol and 29-norcycloartenol). Extensive lipid analyses and labeling experiments with sodium [14C]acetate were performed to examine potential changes in the content and the rate of synthesis of the other lipid molecular species. The results indicate that the inhibition of the sterol pathway was accompanied by a severe decrease in PS and glucosylceramide synthesis as well as by a redirection of fatty acids toward the storage triacylglycerol pathway. Triacyglycerols are shown to accumulate concomitantly with a significant increase in intracellular lipid droplets in both aerial parts and roots of leek seedlings. Taken together, the present data emphasize that a coordinated regulation of the biosynthetic pathways of sterols and some specific lipid molecular species could take place during plant membrane biogenesis. (+info)