Coffee oil consumption increases plasma levels of 7alpha-hydroxy-4-cholesten-3-one in humans.
Unfiltered coffee brews such as French press and espresso contain a lipid from coffee beans named cafestol that raises serum cholesterol in humans. Cafestol decreases the expression and activity of cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in the classical pathway of bile acid synthesis, in cultured rat hepatocytes and livers of APOE3Leiden mice. Inhibition of bile acid synthesis has been suggested to be responsible for the cholesterol-raising effect of cafestol. Therefore, we assessed whether cafestol decreases the activity of cholesterol 7alpha-hydroxylase in humans. Because liver biopsies were not feasible, we measured plasma levels of 7alpha-hydroxy-4-cholesten-3-one, a marker for the activity of cholesterol 7alpha-hydroxylase in the liver. Plasma 7alpha-hydroxy-4-cholesten-3-one was measured in 2 separate periods in which healthy volunteers consumed coffee oil containing cafestol (69 mg/d) for 5 wk. Plasma levels of 7alpha-hydroxy-4-cholesten-3-one increased by 47 +/- 13% (mean +/- SEM, n = 38, P = 0.001) in the first period and by 23 +/- 10% (n = 31, P = 0.03) in the second treatment period. Serum cholesterol was raised by 23 +/- 2% (P < 0.001) in the first period and by 18 +/- 2% (P < 0.001) in the second period. We corrected individual 7alpha-hydroxy-4-cholesten-3-one levels for serum cholesterol levels, because coffee oil increases serum cholesterol and 7alpha-hydroxy-4-cholesten-3-one is probably present in the lipoprotein fraction of serum. After correction, the increase in 7alpha-hydroxy-4-cholesten-3-one was 24 +/- 11% (P = 0.04) in the first period and there was no effect in period 2. Our study showed that coffee oil did not decrease, and actually increased, plasma levels of 7alpha-hydroxy-4-cholesten-3-one in humans in 2 separate treatment periods. Therefore, this study does not support the hypothesis that cafestol decreases bile acid synthesis in humans. (+info)
Sterol structure determines miscibility versus melting transitions in lipid vesicles.
Lipid bilayer membranes composed of DOPC, DPPC, and a series of sterols demix into coexisting liquid phases below a miscibility transition temperature. We use fluorescence microscopy to directly observe phase transitions in vesicles of 1:1:1 DOPC/DPPC/sterol within giant unilamellar vesicles. We show that vesicles containing the "promoter" sterols cholesterol, ergosterol, 25-hydroxycholesterol, epicholesterol, or dihydrocholesterol demix into coexisting liquid phases as temperature is lowered through the miscibility transition. In contrast, vesicles containing the "inhibitor" sterols androstenolone, coprostanol, cholestenone, or cholestane form coexisting gel (solid) and liquid phases. Vesicles containing lanosterol, a sterol found in the cholesterol and ergosterol synthesis pathways, do not exhibit coexisting phases over a wide range of temperatures and compositions. Although more detailed phase diagrams and precise distinctions between gel and liquid phases are required to fully define the phase behavior of these sterols in vesicles, we find that our classifications of promoter and inhibitor sterols are consistent with previous designations based on fluorescence quenching and detergent resistance. We find no trend in the liquid-liquid or gel-liquid transition temperatures of membranes with promoter or inhibitor sterols and measure the surface fraction of coexisting phases. We find that the vesicle phase behavior is related to the structure of the sterols. Promoter sterols have flat, fused rings, a hydroxyl headgroup, an alkyl tail, and a small molecular area, which are all attributes of "membrane active" sterols. (+info)
The abnormal accumulation of amyloid beta-peptide (Abeta) in the form of senile (or amyloid) plaques is one of the main characteristics of Alzheimer disease (AD). Both cholesterol and Cu2+ have been implicated in AD pathogenesis and plaque formation. Abeta binds Cu2+ with very high affinity, forming a redox-active complex that catalyzes H2O2 production from O2 and cholesterol. Here we show that Abeta:Cu2+ complexes oxidize cholesterol selectively at the C-3 hydroxyl group, catalytically producing 4-cholesten-3-one and therefore mimicking the activity of cholesterol oxidase, which is implicated in cardiovascular disease. Abeta toxicity in neuronal cultures correlated with this activity, which was inhibited by Cu2+ chelators including clioquinol. Cell death induced by staurosporine or H2O2 did not elevate 4-cholesten-3-one levels. Brain tissue from AD subjects had 98% more 4-cholesten-3-one than tissue from age-matched control subjects. We observed a similar increase in the brains of Tg2576 transgenic mice compared with nontransgenic littermates; the increase was inhibited by in vivo treatment with clioquinol, which suggests that brain Abeta accumulation elevates 4-cholesten-3-one levels in AD. Cu2+-mediated oxidation of cholesterol may be a pathogenic mechanism common to atherosclerosis and AD. (+info)
Apoptosis induced by a new member of saponin family is mediated through caspase-8-dependent cleavage of Bcl-2.
OSW-1 is a new member of cholestane saponin family, which is cytotoxic against several types of malignant cells. We reported herein that OSW-1 induced apoptosis of mammalian cells in a concentration- and time-dependent manner. The drug-induced apoptosis was mediated through the mitochondrial pathway, involving the cleavage of Bcl-2. This drug-induced Bcl-2 cleavage in Chinese hamster ovary (CHO) cells could be suppressed either by dominant-negative caspase-8 or by a caspase-8 inhibitor, suggesting that the Bcl-2 cleavage is dependent on caspase-8. In contrast, the Bcl-2 cleavage was independent of caspase-3 activity. The inhibition of caspase-8 activity also resulted in the reduction of apoptotic cells, indicating that Bcl-2 cleavage induced by caspase-8 promotes the progression of apoptosis. The involvement of the caspase-8 activity in the processes of the OSW-1-induced apoptosis was further examined by using caspase-8-deficient Jurkat T cells. It was found that the caspase-8-deficient cells were resistant to OSW-1-induced Bcl-2 cleavage or apoptosis. Furthermore, the small subunit of caspase-8 was found to interact with Bcl-2 as determined by yeast two-hybrid and coimmunoprecipitation assays. Overexpression of caspase-8 small subunit reduced the cleavage of Bcl-2 and inhibited the apoptosis induced by OSW-1. Taken together, these results demonstrate that OSW-1 is capable of inducing apoptosis in mammalian cells, in which the caspase-8-dependent cleavage of Bcl-2 plays an important role. (+info)
Pituitary control of cholesterol metabolism in normal and LDL receptor knock-out mice: effects of hypophysectomy and growth hormone treatment.
The pituitary is important in the control of lipid metabolism and studies of hypophysectomized (Hx) rats have shown strong effects of growth hormone (GH) on bile acid synthesis, hepatic LDL receptor (LDLR) expression and on the sensitivity to dietary cholesterol. It is unclear if mice may be used in such studies. The aim of the current study was to evaluate if Hx mice may be used to further explore how GH modulates cholesterol and bile acid metabolism, and to define the importance of the LDLR in this regulation by studying LDLR-deficient mice (LDLRko). Experiments on three mouse strains showed that, following Hx, HDL were reduced and LDL increased. Cholesterol/fat feeding of Hx mice increased serum cholesterol levels 2- to 3-fold. Serum triglycerides were reduced 50% in Hx mice; a further 30% reduction was seen after dietary cholesterol/fat. A serum marker for CYP7A1-mediated bile acid synthesis (C4) increased 2-fold in intact mice on cholesterol/fat diet. In Hx mice C4 levels were reduced by 50% as compared to intact controls, but were unexpectedly increased to levels seen in normal mice upon cholesterol/fat feeding. Hx of LDLRko mice moderately increased LDL-cholesterol and reduced triglycerides and GH treatment attenuated these effects; serum C4 levels were increased by GH treatment in all groups. In conclusion, mice can be used to explore the role of the pituitary in lipid metabolism. CYP7A1 is generally reduced in Hx mice but has a normal stimulatory response following dietary cholesterol suggesting that faulty regulation of CYP7A1 is not important for the reduced resistance to dietary cholesterol in Hx mice. Further, the LDLR is only to a minor part involved in the pituitary regulation of serum cholesterol in mice. (+info)
OSW-1: a natural compound with potent anticancer activity and a novel mechanism of action.
The naturally occurring compound 3beta,16beta,17alpha-trihydroxycholest-5-en-22-one 16-O-(2-O-4-methoxybenzoyl-beta-D-xylopyranosyl)-(1-->3)-(2-O-acetyl-alpha-L-arab inopyranoside) (OSW-1) is found in the bulbs of Ornithogalum saudersiae and is highly cytotoxic against tumor cell lines. Using various human cancer and nonmalignant cell lines, we investigated the anticancer activity and selectivity of OSW-1 and its underlying mechanisms of action. OSW-1 exhibited extremely potent cytotoxic activity against cancer cells in vitro. Nonmalignant cells were statistically significantly less sensitive to OSW-1 than cancer cells, with concentrations that cause a 50% loss of cell viability 40-150-fold greater than those observed in malignant cells. Electron microscopy and biochemical analyses revealed that OSW-1 damaged the mitochondrial membrane and cristae in both human leukemia and pancreatic cancer cells, leading to the loss of transmembrane potential, increase of cytosolic calcium, and activation of calcium-dependent apoptosis. Clones of leukemia cells with mitochondrial DNA defects and respiration deficiency that had adapted the ability to survive in culture without mitochondrial respiration also were resistant to OSW-1. In vitro analysis revealed that OSW-1 effectively killed primary leukemia cells from chronic lymphocytic leukemia patients with disease refractory to fludarabine. The promising anticancer activity of OSW-1 and its unique mechanism of action make this compound worthy of further investigation for its potential to overcome drug resistance. (+info)
A 15-ketosterol is a liver X receptor ligand that suppresses sterol-responsive element binding protein-2 activity.
Hypercholesterolemia is a major risk factor for coronary artery disease. Oxysterols are known to inhibit cholesterol biosynthesis and have been explored as potential antihypercholesterolemic agents. The ability of 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one (15-ketosterol) to lower non-HDL cholesterol has been demonstrated in rodent and primate models, but the mechanisms of action remain poorly understood. Here we show in a coactivator recruitment assay and cotransfection assays that the 15-ketosterol is a partial agonist for liver X receptor-alpha and -beta (LXRalpha and LXRbeta). The binding affinity for the LXRs was comparable to those of native oxysterols. In a macrophage cell line of human origin, the 15-ketosterol elevated ATP binding cassette transporter ABCA1 mRNA in a concentration-dependent fashion with a potency similar to those of other oxysterols. We further found that in human embryonic kidney HEK 293 cells, the 15-ketosterol suppressed sterol-responsive element binding protein processing activity and thus inhibited mRNA expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, LDL receptor, and PCSK9. Our data thus provide a molecular basis for the hypocholesterolemic activity of the 15-ketosterol and further suggest its potential antiatherosclerotic benefit as an LXR agonist. (+info)
Identification of ligands for DAF-12 that govern dauer formation and reproduction in C. elegans.
In response to environmental and dietary cues, the C. elegans orphan nuclear receptor, DAF-12, regulates dauer diapause, reproductive development, fat metabolism, and life span. Despite strong evidence for hormonal control, the identification of the DAF-12 ligand has remained elusive. In this work, we identified two distinct 3-keto-cholestenoic acid metabolites of DAF-9, a cytochrome P450 involved in hormone production, that function as ligands for DAF-12. At nanomolar concentrations, these steroidal ligands (called dafachronic acids) bind and transactivate DAF-12 and rescue the hormone deficiency of daf-9 mutants. Interestingly, DAF-9 has a biochemical activity similar to mammalian CYP27A1 catalyzing addition of a terminal acid to the side chain of sterol metabolites. Together, these results define the first steroid hormones in nematodes as ligands for an invertebrate orphan nuclear receptor and demonstrate that steroidal regulation of reproduction, from biology to molecular mechanism, is conserved from worms to humans. (+info)