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S Chen

Publications and source records attributed to S Chen.

At least 253 records · Page 14Linked to original sources
PubMed2001

A neural circuit for circadian regulation of arousal.

An unknown aspect of behavioral state regulation is how the circadian oscillator of the suprachiasmatic nucleus (SCN) regulates sleep and waking. In this report, we describe the necessary elements for a circuit that provides circadian regulation of arousal. Trans-synaptic retrograde tracing revealed a prominent indirect projection from the SCN to the noradrenergic nucleus locus coeruleus (LC), a brain arousal system. Double-labeling experiments revealed several possible links between the SCN and the LC, including the dorsomedial (DMH) and paraventricular hypothalamic nuclei (PVN), as well as medial and ventrolateral pre-optic areas. Lesion studies confirmed that the DMH is a substantial relay in this circuit. Next, neurophysiology experiments revealed circadian variations in LC impulse activity. Lesions of the DMH eliminated these circadian changes in LC activity, confirming the functionality of the SCN-DMH-LC circuit. These results reveal mechanisms for regulation of circadian and sleep-waking functions.

Animals↗
PubMed2001

Genetic approaches for controlling ratios of related polyketide products in fermentation processes.

Simple acyl thioesters are used as precursors for both the initiation and elongation steps in polyketide biosynthetic processes. Several structurally related polyketide products are sometimes made in these processes. These analogs are typically generated by a combination of two factors: availability of structurally similar biosynthetic precursors, and biosynthetic enzymes unable to effectively discriminate between them. Often, only one polyketide product is desired from a fermentation process, requiring a method to control the ratio of these different analogs. Preferential production of one desired analog is accomplished using random mutagenesis and manipulation of fermentation conditions. A genetic enzymatic understanding of polyketide biosynthesis, as well as the pathways that provide the relevant precursors, allows for a rational and more contemporary approach for control of analogs produced in fermentation processes. This approach involves genetic manipulation of either the pathways that provide pools of the acyl CoA thioester precursors, or the function/specificity of the appropriate biosynthetic enzymes. Reviewed herein are three such examples where these approaches have been carried out successfully with polyketide biosynthetic processes.

Acyl Coenzyme A↗
PubMed2001

Effects of the flavonoid baicalin and its metabolite baicalein on androgen receptor expression, cell cycle progression and apoptosis of prostate cancer cell lines.

Recent studies on the Chinese herbal medicine PC SPES showed biological activities against prostate cancer in vitro, in vivo and in patients with advanced stages of the disease. In investigating its mode of action, we have isolated a few of the active compounds. Among them, baicalin was the most abundant (about 6%) in the ethanol extract of PC SPES, as determined by HPLC. Baicalin is known to be converted in vivo to baicalein by the cleavage of the glycoside moiety. Therefore, it is useful to compare their activities in vitro. The effects of baicalin and baicalein were studied in androgen-positive and -negative human prostate cancer lines LNCaP and JCA-1, respectively. Inhibition of cell growth by 50% (ED(50)) in LNCaP cells was seen at concentrations of 60.8 +/- 3.2 and 29.8 +/- 2.2 microM baicalin and baicalein, respectively. More potent growth inhibitory effects were observed in androgen-negative JCA-1 cells, for which the ED(50) values for baicalin and baicalein were 46.8 +/- 0.7 and 17.7 +/- 3.4, respectively. Thus, it appears that cell growth inhibition by these flavonoids is independent of androgen receptor status. Both agents (1) caused an apparent accumulation of cells in G(1) at the ED(50) concentration, (2) induced apoptosis at higher concentrations, and (3) decreased expression of the androgen receptor in LNCaP cells.

Antineoplastic Agents, Phytogenic↗
PubMed2001

Evaluation of the mechanism of aromatase cytochrome P450. A site-directed mutagenesis study.

Aromatase (CYP19) catalyzes three consecutive hydroxylation reactions converting C19 androgens to aromatic C18 estrogenic steroids. In this study, five human aromatase mutants (E302D, S478A, S478T, H480K, and H480Q) were prepared using a mammalian cell expression system. These mutants were evaluated by enzyme kinetic analysis, inhibitory profile studies, and reaction intermediate measurements. Three steroidal inhibitors [4-hydroxyandrostenedione (4-OHA), 7alpha-(4'-amino)phenylthio-1,4-androstandiene-3,17-dione (7alpha-APTADD), and bridge (2,19-methyleneoxy) androstene-3,17-dione (MDL 101003)], and four nonsteroidal inhibitors [aminoglutethimide (AG), CGS 20267, ICI D1033, and vorozole (R83842)] were used in the inhibitory profile studies. Our computer model of aromatase suggests that Glu302 is situated in the conserved I-helix region and located near the C-19 position of the steroid substrate. The model was supported by significant changes in kinetic parameters and a sevenfold increase in the Ki value of MDL 101,003 for the mutant E302D. As S478A was found to have kinetic properties similar to the wild-type enzyme and a much higher activity than S478T, Ser478 is thought to be situated in a rather restricted environment. There was a 10-fold increase in the Ki value of 7alpha-APTADD for S478T over that for the wild-type enzyme, suggesting that Ser478 might be near the C-7 position of the substrate. The reaction intermediate analysis revealed that significantly more 19-ol intermediate was generated by both S478A and S478T than the wild-type enzyme. These results would support a hypothesis that Ser478 plays a role in the first and second hydroxylation reactions. A positive charged amino acid is preferred at position 480 as shown by the fact that H480K has a significantly higher activity than H480Q. The Ki value of 4-OHA for H480Q was found to be three times that of the wild-type enzyme. In addition, significantly more 19-ol and 19-al intermediates were detected for both mutants H480K and H480Q than for the wild-type enzyme. Evaluation of the two mutations at His480 allows us to propose that this residue may participate in the aromatization reaction (the third step) by acting as a hydrogen bond donor for the C-3 keto group of the substrate. Furthermore, new products were generated when the enzyme was mutated at Ser478 and His480. Thus, these two residues must play an important role in the catalysis and are likely closer to the substrate binding site than previously predicted.

Androgens↗
PubMed2001

Hydrogen peroxide increases extracellular matrix mRNA through TGF-beta in human mesangial cells.

BACKGROUND: Reactive oxygen species (ROS) are excessively produced in pathologic states, including many renal diseases. Transforming growth factor-beta (TGF-beta) may mediate renal fibrotic injury, and ROS may act through the TGF-beta pathway to exert a profibrotic effect. METHODS: The expression of TGF-beta1 and extracellular matrix (ECM) components were assessed in cultured human mesangial cells (HMCs) incubated with glucose oxidase (GO), an enzyme that continuously generates hydrogen peroxide from glucose. A neutralizing anti-TGF-beta antibody was added to test the hypothesis that hydrogen peroxide acts through activation of the TGF-beta pathway to stimulate ECM expression. RESULTS: Northern blot analysis revealed significantly increased steady-state levels of TGF-beta1 and ECM proteins (collagen types I, III, and IV, and fibronectin) by approximately twofold. While no significant effect on mRNA stability after treatment with GO was observed, other studies employing promoter-reporter assays, competitive-quantitative reverse transcription-polymerase chain reaction, mink lung epithelial cell proliferation assay, and TGF-beta1 enzyme-linked immunosorbent assay all demonstrated significant stimulation by GO (>1.5-fold) of TGF-beta1 promoter activity, mRNA level, bioactivity, and protein production, respectively. Catalase pretreatment prevented the GO-induced stimulation of TGF-beta1 mRNA. When incubations were performed with a panselective neutralizing anti-TGF-beta antibody, the GO-stimulated expression of ECM molecules was prevented. CONCLUSIONS: GO-induced hydrogen peroxide production induces TGF-beta1 synthesis and thereby increases ECM gene expression in cultured HMCs. These cellular responses may underlie the development and progression of renal diseases characterized by oxidative stress.

Catalase↗
PubMed2001

Glycated albumin stimulates TGF-beta 1 production and protein kinase C activity in glomerular endothelial cells.

BACKGROUND: The activation of protein kinase C (PKC) and transforming growth factor-beta (TGF-beta) in glomerular mesangial cells has been linked to mesangial matrix expansion in diabetic nephropathy. The role of these mediators in affecting the changes associated with diabetes in the biology of glomerular endothelial cells (GEnCs), which synthesize components of the glomerular basement membrane, is not known. We postulated that the PKC and TGF-beta systems promote the increased endothelial cell synthesis of glomerular basement membrane that is evoked by Amadori-modified glycated albumin, which is present in elevated concentrations in diabetes. METHODS: We examined the effects of PKC inhibition on collagen IV and TGF-beta1 production by mouse GEnCs incubated with glycated albumin and the influence of glycated albumin on PKC activity, TGF-beta 1 production, and proliferation by these cells. RESULTS: In physiologic (5.5 mmol/L) glucose concentrations, glycated albumin caused an increase in type IV collagen production that was totally prevented by a general PKC inhibitor GF 109203X (GFX), but only partly prevented by a neutralizing anti-TGF-beta antibody. Glycated albumin increased the steady-state level of TGF-beta 1 mRNA and stimulated the production of TGF-beta 1 protein, which was also prevented by the PKC inhibitor GFX. Of note, glycated albumin significantly stimulated PKC activity, as measured by the phosphorylation of a PKC-specific substrate. Cell proliferation, measured by [(3)H]-thymidine incorporation and cell counting, was decreased in the presence of glycated albumin. This effect was completely prevented by GFX and partially reversed by anti-TGF-beta antibody. Exogenous TGF-beta 1 inhibited cell proliferation to a degree similar to that of glycated albumin. CONCLUSIONS: PKC signaling and consequent TGF-beta 1 activation participate in the glycated albumin-induced stimulation of basement membrane collagen production by GEnC. By reducing the proliferative capacity, which is likely mediated by PKC and partly by TGF-beta, glycated albumin impedes the ability of the glomerular capillary endothelium to act as a first line of defense against deleterious circulating factors in the diabetic state.

Animals↗
PubMed2001

Leptin stimulates type I collagen production in db/db mesangial cells: glucose uptake and TGF-beta type II receptor expression.

BACKGROUND: Serum leptin levels correlate with fat cell mass and are elevated in patients with massive obesity and type 2 diabetes mellitus, which are strong risk factors for the development of glomerulosclerosis. We have previously shown in cultured glomerular endothelial cells that leptin stimulates cellular proliferation and expression of the prosclerotic cytokine transforming growth factor-beta1 (TGF-beta1). Although the effect of leptin on the hypothalamus to regulate energy homeostasis is well known, the effect of leptin on the kidney, and specifically on the glomerular mesangial cell, is unclear. METHODS: The obese, diabetic db/db mouse, which lacks the functional full-length Ob-Rb leptin receptor, is a suitable model to assess the effects of hyperleptinemia on peripheral tissues that express other receptor isoforms. The effects of leptin on glucose uptake, the TGF-beta system, and type I collagen production were evaluated in db/db mouse mesangial cells in culture. A phosphatidylinositol-3 kinase (PI-3K) inhibitor was used to assess the role of PI-3K in mediating the effects of leptin. RESULTS: A short form of the leptin receptor (Ob-Ra), but not Ob-Rb, was present by reverse transcription-polymerase chain reaction in the kidney and mesangial cells of both nondiabetic db/m and diabetic db/db mice. In db/db mesangial cells, leptin increased 2-deoxy-D-glucose (2DOG) uptake dose dependently and stimulated gene expression of TGF-beta type II receptor (TbetaRII) and alpha1(I) collagen, but not TGF-beta1. Protein production of type I collagen (enzyme-linked immunosorbent assay) was also increased by leptin. Both leptin-stimulated 2DOG uptake and type I collagen production were suppressed by a PI-3K inhibitor, LY294002. Mesangial cells pretreated with leptin exhibited increased responsiveness to exogenous TGF-beta1, as evidenced by a greater production of type I collagen protein in leptin-pretreated cells exposed to low-dose TGF-beta1 (0.5 ng/mL). The addition of both TGF-beta1 (2 ng/mL) and leptin (100 ng/mL) increased type I collagen production more than addition of either TGF-beta1 or leptin alone. CONCLUSIONS: Leptin increases glucose uptake and type I collagen in db/db mesangial cells through a PI-3K-dependent pathway. We postulate that increased leptin levels may transmit a signal through the short-form leptin receptor to up-regulate TbetaRII and activate the intraglomerular TGF-beta system, which may contribute to the glomerulosclerosis of obesity or type 2 diabetes.

Animals↗
PubMed2001

Sustained expression of naked plasmid DNA encoding hepatocyte growth factor in mice promotes liver and overall body growth.

To understand the physiological functions of exogenous hepatocyte growth factor (HGF) on normal adult animals, we delivered human HGF gene into mice by a hydrodynamics-based in vivo gene transfection approach using a naked plasmid vector. Systemic administration of naked plasmid containing HGF cDNA driven under cytomegalovirus promoter (pCMV-HGF) by rapid injection via the tail vein produced a remarkable level of human HGF protein in the circulation, beginning to appear at 4 hours and peaking at 12 hours following injection. Tissue distribution studies identified the liver as the organ with the highest level of transgene expression. Through weekly repeated injections of plasmid vector, we achieved sustained, long-term, high levels of exogenous HGF expression in mice for 8 weeks. Increases of more than 31% and 16% in liver and body weights were found, respectively, in the mice that received pCMV-HGF plasmid compared with that given the control vector for 8 weeks. Expression of exogenous HGF in vivo activated mitogen-activated protein kinases and induced proliferating cell nuclear antigen expression in normal adult liver and kidneys. These data suggest that systemic administration of naked plasmid vector is a convenient, safe, and highly efficient approach to introduce and maintain exogenous HGF gene expression in vivo in a controllable fashion. Our results also indicate that long-term expression of human HGF in mice markedly activates growth-related signal transduction events, promotes cell proliferation, and leads to liver and overall body growth in whole adult animals.

Animals↗
PubMed2001

EPR investigation of the free radicals generated during the photosensitization of TiO2 colloid by hypocrellin B.

The cation radical of dye produced from the interfacial electron transfer from a surface chelated dye to the conduction band of the colloidal TiO2 was studied by laser flash photolysis and electron paramagnetic resonance (EPR) techniques. The study employed hypocrellin B (HB), a natural photodynamic pigment with strong absorption over the visible light region, as a sensitizer and titanium dioxide as a colloid semiconductor. HB formed a chelate with this colloid semiconductor and exhibited a red-shifted and strongly enhanced absorption in the visible spectrum. Laser photolysis indicated that the electron excitation in the visible absorption band of the chelate resulted in extremely rapid and efficient electron injection from the excited triplet state of the dye into the conduction band of the semiconductor. A transient absorption of cation radical of HB at 570 nm was observed. The appearance of cation radical of HB was characterized by EPR spectrometry: the photoinduced EPR signal was not quenched by oxygen and its intensity decreased in the presence of NaI, a typical hole scavenger. The generation of conduction band electrons in HB-sensitized TiO2 system was also verified by the spin elimination of a stable cyclic nitroxide, 2,2, 6,6-tetramethylpiperidine-1-oxyl (TEMPO), and by the reduction of methyl viologen (MV2+) to its radical MV+.

Animals↗
PubMed2001

Chelation of hypocrellin B with zinc ions with electron paramagnetic resonance (EPR) evidence of the photodynamic activity of the resulting chelate.

Hypocrellin B (HB), a perylenequinone derivative, is an efficient phototherapeutic agent. The chelation of HB with Zinc ions (Zn2+) results in a metal chelate (Zn-HB) which exhibits considerable absorption (lambda max = 612 nm) in the phototherapeutic window. The structure of this chelate has been characterized by UV-Vis, IR and mass spectra. The redox potentials of the Zn-HB chelate were Eox = +1.1 V (vs. SCE) and Ere = -0.7 V (vs. SCE) as measured using the circle volt curve. The quantum yield of singlet oxygen generated by the Zn-HB chelate was 0.86, which both the electron spin trap (EPR) method and the chemical trap method show to be about 0.1 higher than that of its parent compound HB. In irradiated oxygen-saturated solutions of Zn-HB chelate, superoxide radical anions and hydroxyl radicals were detected by EPR spectroscopy using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trapping agent.

Chelating Agents↗
PubMed2001

Hydrologic modeling of aquatic plant treatment systems polishing dairy lagoon effluents.

In this study, a mathematical model of the hydrologic balance of an aquatic plant treatment system (APTS) has been developed. The mass balance approach has been adopted and the major components of the water balance, such as precipitation, evapotranspiration (ET) and percolation have been incorporated into the model. For estimation of ET for duckweed and water hyacinth plants, mathematical relationships were established between ET and pan evaporation using data collected at the site. The observed ET rates of water hyacinths were up to 66% higher than the pan evaporation rates. But for duckweed, the observed ET rates were 10 to 20% lower than the pan evaporation rates. Using the available historic precipitation and pan evaporation data, several computer simulations of the model were run to estimate the HLR and HRT of the ponds under different design requirements. The results indicate that aquatic ponds with water hyacinths can operate at greater HLR's than ponds supporting duckweed. For a zero discharge system, the allowable HLR for a water hyacinth pond was found to be 5 times that of a pond containing duckweed.

Agriculture↗
PubMed2001

The relationship between structures and in vitro properties of a polyanhydride implant containing gentamicin sulfate.

Laboratory scale injection-molding equipment was utilized to fabricate an implant consisting of poly(FAD:SA 1:1) and 20% (w/w) gentamicin sulfate. Characterizations were performed to determine the molecular weight and glass transition temperature of poly(FAD:SA 1:1). A study was carried out to investigate the relationships between the in vitro performance, morphology, and micro-structures of the molded implants. It was found that implants produced with different structures exhibited different physical integrities in water, i.e., cracking or non-cracking. For the non-cracking implants, a skin-core structure formed by an oriented skin layer was observed under a polarized light microscope. The same morphology was not seen in the cracking implants. The crystal orientation in the skin layer of the non-cracking implants was further identified using a wide-angle x-ray diffraction method (WAXD). No crystal orientation could be found in the cracking implants by WAXD. Furthermore, studies were carried out to evaluate the in vitro drug release for implants showing different degrees of integrity in water. The in vitro drug release of the cracking implants was markedly faster than that of the non-cracking implants due to the pronounced initial drug-burst effect as a result of crack formation in the implants.

Absorbable Implants↗
PubMed2001

Properties of hyperpolarization-activated pacemaker current defined by coassembly of HCN1 and HCN2 subunits and basal modulation by cyclic nucleotide.

Members of the HCN channel family generate hyperpolarization-activated cation currents (Ih) that are directly regulated by cAMP and contribute to pacemaker activity in heart and brain. The four HCN isoforms show distinct but overlapping patterns of expression in different tissues. Here, we report that HCN1 and HCN2, isoforms coexpressed in neocortex and hippocampus that differ markedly in their biophysical properties, coassemble to generate heteromultimeric channels with novel properties. When expressed in Xenopus oocytes, HCN1 channels activate 5-10-fold more rapidly than HCN2 channels. HCN1 channels also activate at voltages that are 10-20 mV more positive than those required to activate HCN2. In cell-free patches, the steady-state activation curve of HCN1 channels shows a minimal shift in response to cAMP (+4 mV), whereas that of HCN2 channels shows a pronounced shift (+17 mV). Coexpression of HCN1 and HCN2 yields Ih currents that activate with kinetics and a voltage dependence that tend to be intermediate between those of HCN1 and HCN2 homomers, although the coexpressed channels do show a relatively large shift by cAMP (+14 mV). Neither the kinetics, steady-state voltage dependence, nor cAMP dose-response curve for the coexpressed Ih can be reproduced by the linear sum of independent populations of HCN1 and HCN2 homomers. These results are most simply explained by the formation of heteromeric channels with novel properties. The properties of these heteromeric channels closely resemble the properties of I(h) in hippocampal CA1 pyramidal neurons, cells that coexpress HCN1 and HCN2. Finally, differences in Ih channel properties recorded in cell-free patches versus intact oocytes are shown to be due, in part, to modulation of Ih by basal levels of cAMP in intact cells.

Animals↗
PubMed2001

Regulation of hyperpolarization-activated HCN channel gating and cAMP modulation due to interactions of COOH terminus and core transmembrane regions.

Members of the hyperpolarization-activated cation (HCN) channel family generate HCN currents (I(h)) that are directly regulated by cAMP and contribute to pacemaking activity in heart and brain. The four different HCN isoforms show distinct biophysical properties. In cell-free patches from Xenopus oocytes, the steady-state activation curve of HCN2 channels is 20 mV more hyperpolarized compared with HCN1. Whereas the binding of cAMP to a COOH-terminal cyclic nucleotide binding domain (CNBD) markedly shifts the activation curve of HCN2 by 17 mV to more positive potentials, the response of HCN1 is much less pronounced (4 mV shift). A previous deletion mutant study suggested that the CNBD inhibits hyperpolarization-gating in the absence of cAMP; the binding of cAMP shifts gating to more positive voltages by relieving this inhibition. The differences in basal gating and cAMP responsiveness between HCN1 and HCN2 were proposed to result from a greater inhibitory effect of the CNBD in HCN2 compared with HCN1. Here, we use a series of chimeras between HCN1 and HCN2, in which we exchange the NH(2) terminus, the transmembrane domain, or distinct domains of the COOH terminus, to investigate further the molecular bases for the modulatory action of cAMP and for the differences in the functional properties of the two channels. Differences in cAMP regulation between HCN1 and HCN2 are localized to sequence differences within the COOH terminus of the two channels. Surprisingly, exchange of the CNBDs between HCN1 and HCN2 has little effect on basal gating and has only a modest one on cAMP modulation. Rather, differences in cAMP modulation depend on the interaction between the CNBD and the C-linker, a conserved 80-amino acid region that connects the last (S6) transmembrane segment to the CNBD. Differences in basal gating depend on both the core transmembrane domain and the COOH terminus. These data, taken in the context of the previous data on deletion mutants, suggest that the inhibitory effect of the CNBD on basal gating depends on its interactions with both the C-linker and core transmembrane domain of the channel. The extent to which cAMP binding is able to relieve this inhibition is dependent on the interaction between the C-linker and the CNBD.

Animals↗
PubMed2001

iNOS and nitrotyrosine expression after spinal cord injury.

Secondary tissue damage after spinal cord injury (SCI) may be due to inflammatory mediators. After SCI, the nuclear factor-kappaB (NF-kappaB) transcription factor can activate many pro-inflammatory genes, one of which is inducible nitric oxide synthase (iNOS). iNOS catalyzes the synthesis of nitric oxide (NO), a key inflammatory mediator, which in turn reacts with superoxide to generate peroxynitrite. Peroxynitrite is a strong oxidant that can damage cellular enzymes, membranes, and subcellular organelles through the nitration of tyrosine residues on proteins. The presence of nitrotyrosine (NT) is an indirect chemical indicator of toxic NO and peroxynitrite-induced cellular damage. Using a New York University (NYU) impactor to induce SCI in adult rats, we examined the temporal and cellular expression of iNOS and NT. We observed a progressive increase in iNOS expression in the injured cord starting at day 1 with maximal expression occurring at day 7, as determined by Western blot analysis. iNOS expression corresponded temporally to an increase in iNOS enzyme activity after SCI. In parallel with the progressive increase in iNOS activity, NT expression also increased with time after SCI. The iNOS and NT immunoreactivity was localized in neurons, astrocytes, endothelial cells and ependymal cells at the epicenter and adjacent to the region of spinal cord impact and injury. Results from the present study suggest that increased iNOS and peroxynitrite anion, as reflected by the progressive accumulation of NT in the injured impacted spinal cord, may contribute to the secondary injury process after SCI.

Animals↗
PubMed2001

Lipid responses to plant-sterol-enriched reduced-fat spreads incorporated into a National Cholesterol Education Program Step I diet.

BACKGROUND: Plant sterol esters reduce cholesterol absorption and lower circulating blood cholesterol concentrations when incorporated into the habitual diet. OBJECTIVE: This randomized, double-blind, 3-group parallel, controlled study evaluated the influence of esterified plant sterols on serum lipid concentrations in adults with mild-to-moderate primary hypercholesterolemia. DESIGN: Subjects incorporated a conventional 50%-fat spread into a National Cholesterol Education Program Step I diet for a 4-wk lead-in period, followed by a 5-wk intervention period of the diet plus either a control reduced-fat spread (40% fat; n = 92) or a reduced-fat spread enriched with plant sterol esters to achieve intakes of 1.1 g/d (n = 92; low-sterol group) or 2.2 g/d (n = 40; high-sterol group). RESULTS: Subjects in the low- and high-sterol groups who consumed > or = 80% of the scheduled servings (per-protocol analyses) had total cholesterol values that were 5.2% and 6.6% lower, LDL-cholesterol values that were 7.6% and 8.1% lower, apolipoprotein B values that were 6.2% and 8.4% lower, and ratios of total to HDL cholesterol that were 5.9% and 8.1% lower, respectively, than values for the control group (P < 0.001 for all). Additionally, triacylglycerol concentrations decreased by 10.4% in the high-sterol group. Serum concentrations of fat-soluble vitamins and carotenoids were generally within reference ranges at baseline and postintervention. Serum plant sterol concentrations increased from baseline (0.48% of total sterol by wt) to 0.64% and 0.71% by wt for the low- and high-sterol groups, respectively (P < 0.05 compared with control). CONCLUSION: A reduced-fat spread containing plant sterol esters incorporated into a low-fat diet is a beneficial adjunct in the dietary management of hypercholesterolemia.

Adult↗
PubMed2001

The gypsy insulator of Drosophila affects chromatin structure in a directional manner.

Chromatin insulators are thought to regulate gene expression by establishing higher-order domains of chromatin organization, although the specific mechanisms by which these sequences affect enhancer-promoter interactions are not well understood. Here we show that the gypsy insulator of Drosophila can affect chromatin structure. The insulator itself contains several DNase I hypersensitive sites whose occurrence is dependent on the binding of the Suppressor of Hairy-wing [Su(Hw)] protein. The presence of the insulator in the 5' region of the yellow gene increases the accessibility of the DNA to nucleases in the promoter-proximal, but not the promoter-distal, region. This increase in accessibility is not due to alterations in the primary chromatin fiber, because the number and position of the nucleosomes appears to be the same in the presence or absence of the insulator. Binding of the Su(Hw) protein to insulator DNA is not sufficient to induce changes in chromatin accessibility, and two domains of this protein, presumed to be involved in interactions with other insulator components, are essential for this effect. The presence of Modifier of mdg4 [Mod(mdg4)] protein, a second component of the gypsy insulator, is required to induce these alterations in chromatin accessibility. The results suggest that the gypsy insulator affects chromatin structure and offer insights into the mechanisms by which insulators affect enhancer-promoter interactions.

Animals↗