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Biomedical subjects

J A Hamilton

Publications and source records attributed to J A Hamilton.

At least 109 records · Page 6Linked to original sources
PubMed1996

Binding of ethyl oleate to low density lipoprotein, phospholipid vesicles, and albumin: a 13C NMR study.

Fatty acid ethyl esters (FAEE), esterification products of ethanol and fatty acids, have been implicated as mediators of ethanol-induced organ damage. After ethanol ingestion in humans, FAEE circulate in blood, bound to lipoproteins and albumin. We have analyzed the binding of ethyl (1-13C, 99%) oleate (EO) to small unilamellar phospholipid vesicles (SUV), human low density lipoprotein (LDL), and bovine serum albumin (BSA) by 13C-NMR spectroscopy. Binding of < or = 25 mol% EO to SUV yielded a single EO carbonyl peak (172.6-172.9 ppm) downfield from that of EO oil (171.9 ppm). Thus, the carbonyl forms hydrogen bonds with water in the SUV aqueous interface. At 30 mol% EO in SUV, a second EO carbonyl peak appeared, indicating a limit in FAEE solubility in SUV. Addition of EO to isolated human LDL yielded a peak at 171.9 ppm, suggesting that the EO exists in an unhydrated environment, most likely the core of the lipoprotein. This binding was also observed using high levels of EO added to human serum. The addition of EO dissolved in ethanol or as an oil to a solution of BSA yielded no visible EO peak, whereas addition of (1-13C, 99%) oleic acid resulted in several narrow peaks, demonstrating a much greater affinity of BSA for oleic acid than for EO. Bidirectional transfer of EO between LDL and SUV was observed and was 85% complete within 30 min. There was no measurable transfer of EO from LDL or SUV to albumin. The weak binding of EO to albumin will result in increased transport of EO by lipoproteins as plasma levels of EO increase.

Carbon Isotopes↗
PubMed1995

Magic-angle spinning and solution 13C nuclear magnetic resonance studies of medium- and long-chain cholesteryl esters in model bilayers.

The incorporation of cholesteryl esters (CE) with saturated acyl chains into the lamellar structure of phospholipids was studied by 13C nuclear magnetic resonance (NMR) spectroscopy. The CE (octanoate, palmitate, and stearate) were 13C-enriched in the carboxyl carbon to enhance the signals of the small amounts of bilayer-incorporated CE. Magic-angle spinning (MAS) NMR was used to detect signals in unsonicated multilamellar phosphatidylcholine (PC), and solution NMR was used to detect signals in PC small unilamellar vesicles (SUV). All CE showed a carbonyl peak reflecting localization of the carbonyl at the aqueous interface (Hamilton & Small, 1982). The maximal incorporation decreased with chain length, from 5 mol % for octanoate to 1.4 mol % for stearate in multilayers; the stearate ester had a solubility slightly lower than that of cholesteryl oleate (2 mol %). The maximal incorporation of a specific CE was 1.2-2.0 times higher in SUV than in multilayers. Cholesteryl oleate did not prevent solubilization of cholesteryl stearate in the PC interface. CE in excess of the solubility maximum in multilayer samples was shown to be crystalline at 35 degrees C by MAS NMR; thus, in the bilayer the CE gained considerable mobility compared to its mobility in its pure bulk phase at body temperature. Furthermore, CE with two saturated chains were not distinguishable from esters with an unsaturated chain with respect to mobility and position in the interface. These fundamental interfacial properties assure utilization of CE with common dietary fatty acyl chains.

Carbon Isotopes↗
PubMed1995

A null mutation in the gene encoding a type I interferon receptor component eliminates antiproliferative and antiviral responses to interferons alpha and beta and alters macrophage responses.

To examine the in vivo role(s) of type I interferons (IFNs) and to determine the role of a component of the type I IFN receptor (IFNAR1) in mediating responses to these IFNs, we generated mice with a null mutation (-/-) in the IFNAR1 gene. Despite compelling evidence for modulation of cell proliferation and differentiation by type I IFNs, there were no gross signs of abnormal fetal development or morphological changes in adult IFNAR1-/- mice. However, abnormalities of hemopoietic cells were detected in IFNAR1 -/- mice. Elevated levels of myeloid lineage cells were detected in peripheral blood and bone marrow by staining with Mac-1 and Gr-1 antibodies. Furthermore, bone marrow macrophages from IFNAR1 -/- mice showed abnormal responses to colony-stimulating factor 1 and lipopolysaccharide. IFNAR1 -/- mice were highly susceptible to viral infection: viral titers were undetected 24 hr after infection of IFNAR1 +/+ mice but were extremely high in organs of IFNAR1 -/- mice, demonstrating that the type I IFN system is a major acute antiviral defence. In cell lines derived from IFNAR1 -/- mice, there was no signaling in response to IFN-alpha or -beta as measured by induction of 2'-5' oligoadenylate synthetase, antiviral, or antiproliferative responses. Importantly, these studies demonstrate that type I IFNs function in the development and responses of myeloid lineage cells, particularly macrophages, and that the IFNAR1 receptor component is essential for antiproliferative and antiviral responses to IFN-alpha and -beta.

Animals↗
PubMed1995

A multinuclear solid-state NMR study of phospholipid-cholesterol interactions. Dipalmitoylphosphatidylcholine-cholesterol binary system.

Multinuclear (1H, 13C, 31P) MASNMR and static solid-state 31P NMR were used to study the molecular interactions between dipalmitoylphosphatidylcholine (DPPC) and free cholesterol (CHOL) in multilayers of DPPC containing 0-65 mol % CHOL with respect to total lipid at temperatures between 25 and 55 degrees C. 13C chemical shifts and line shapes for DPPC and CHOL resonances were measured in 13C MASNMR spectra. The apparent chemical shift anisotropy (CSA) of the DPPC acyl methylene resonances [(CH2)n] was calculated from the 1H MASNMR spectra. CSA and line shape changes were recorded as a function of CHOL content by 31P static solids and MASNMR. The presence of CHOL significantly changed the 13C chemical shifts and line shapes of DPPC carbonyl carbons below or above the main transition temperature of pure DPPC. Chemical shift changes were also observed for CHOL carbons as a function of the mixing ratio, signifying a changing local environment of CHOL. For mixtures with CHOL > 50 mol %, 13C MASNMR detected crystalline CHOL in the monohydrate form. When the excess CHOL was in a submicroscopic crystalline form that was not readily detected by differential scanning calorimetry, or optical microscopy (but readily observed by 13C MASNMR), the 31P powder pattern was affected, suggesting interaction of the excess CHOL with the aqueous interface of the bilayer. These results suggest the potential of 13C MASNMR for detection of crystalline CHOL in biological samples.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

Colony-stimulating factor 1-induced STAT1 and STAT3 activation is accompanied by phosphorylation of Tyk2 in macrophages and Tyk2 and JAK1 in fibroblasts.

Colony-stimulating factor 1 (CSF-1) causes the activation of STAT1 and STAT3 transcription factors in bone marrow macrophages (BMM), in the macrophage cell line BAC1.2F5, and in fibroblasts that express the wild-type receptor for CSF-1. Fibroblasts expressing a mutant receptor in which the tyrosine 809 is replaced with phenylalanine do not activate STAT proteins in response to CSF-1. The activation of the STAT proteins in BMM is accompanied by tyrosine phosphorylation of Tyk2. In fibroblasts, the activation of the STAT proteins is accompanied by tyrosine phosphorylation of Tyk2 and JAK1. We propose that these JAK kinases are subjected to very rapid phosphorylation in response to CSF-1, followed by rapid dephosphorylation. Furthermore, we propose that kinases other than JAK kinase may be involved in the phosphorylation of the STAT proteins in response to CSF-1.

3T3 Cells↗
PubMed1995

Fatty acid flip-flop in phospholipid bilayers is extremely fast.

The rate of movement of fatty acids (FA) across phospholipid bilayers is an important consideration for their mechanism of transport across cell membranes but has not yet been measured. When FA move undirectionally across phospholipid bilayers, the rapid movement of un-ionized FA compared to ionized FA results in transport of protons. We have previously used this property to show that FA move spontaneously ("flip-flop") across the bilayer of small unilamellar vesicles within approximately 1 s (Kamp & Hamilton, 1992, 1993). This work extends the time resolution of this assay into the millisecond time range by use of stopped flow fluorometry. In small unilamellar vesicles (diameter, approximately 25 nm) at neutral pH, flip-flop of all fatty acids studied (lauric, myristic, palmitic, oleic, and stearic) was > or = 80% complete within 5-10 ms. In large unilamellar vesicles (diameter, approximately 100 nm), the same fatty acids exhibited fast flip-flop but with a measureable rate (t 1/2 = 23 +/- 12 ms). The calculated pseudounimolecular rate constant of the un-ionized FA (kFAH) approximately 15 s-1. There was no dependence of the flip-flop rate on the fatty acid chain length or structure. We also monitored the rate of desorption and transbilayer movement of (anthroyloxy)stearic acid in small unilamellar vesicles. Whereas previous studies suggested slow flip-flop of this FA analogue, the present studies suggest that (anthroyloxy)stearic acid flip-flops rapidly and that earlier studies did not truly measure the transbilayer movement step. These findings further support the view that proteins are not required for translocation of FA across cell membranes.

Arylsulfonates↗
PubMed1995

Deregulated c-myc expression overrides IFN gamma-induced macrophage growth arrest.

Induction of c-myc gene expression is an essential response to growth promoting agents, including colony-stimulating factor 1 (CSF-1). Down regulation of c-myc expression occurs in response to a variety of negative growth regulators in many cell types. However, for many of these systems the causal link between c-myc down regulation and growth arrest remains to be established. Here we show for CSF-1-dependent BAC1.2F5 mouse macrophages that interferon-gamma (IFN gamma) results in a midlate G1 phase decrease of CSF-1-dependent c-myc mRNA and subsequent cell cycle arrest. Introduction of a deregulated c-myc gene into these cells, which prevents the IFN gamma-mediated decrease in c-myc expression, overrides the cell cycle arrest and restores CSF-1-dependent growth in the presence of the cytokine. This result contrasts with the macrophage growth arrest induced by cAMP elevation, which also suppresses c-myc expression, but is not overcome by a deregulated c-myc gene. These results show that inhibition of c-myc expression is an essential component in IFN gamma-mediated cell cycle arrest and demonstrates that distinct mechanisms contribute to IFN gamma- and cAMP-mediated growth arrest in macrophages.

Animals↗
PubMed1995

Interactions of lyso 1-palmitoylphosphatidylcholine with phospholipids: a 13C and 31P NMR study.

13C and 31P NMR spectroscopy were used to monitor interactions of lyso 1-palmitoylphosphatidylcholine (LPPC) in the interfacial region of egg phosphatidylcholine (PC) bilayers and determine the effect of LPPC on the phospholipid bilayer structure. 13C NMR spectroscopy of small amounts (0.5-10 mol%) of 13C carbonyl-enriched LPPC cosonicated with egg PC to form small unilamellar vesicles (SUVs) revealed separate carbonyl signals for LPPC in the inner and outer leaflets of the vesicles. The ratio of LPPC in the outer leaflet to that in the inner leaflet was > or = 3/1. Exchange of LPPC between bilayer leaflets ("flip-flop") was too slow to be measured (t1/2 > 12 h). Albumin added to the external buffer of LPPC/PC vesicles was shown by 13C NMR to extract LPPC only from the outer leaflet. LPPC was a poor detergent in egg PC multilayers and SUVs. Stable SUVs were prepared by cosonicating egg PC with up to 30 mol% LPPC, and preformed SUVs incorporated up to 40 mol % of LPPC (added as an aqueous solution) without undergoing any morphological changes as evidenced by 31P NMR spectroscopy. The presence of oleic or palmitic acid did not have observable effects on properties of LPPC in SUVs, such as the localization of the LPPC carbonyl in the interface, and the transbilayer distribution and movement of LPPC. The apparent pKa of the fatty acid (FA) carboxyl at the membrane interface (7.7) measured by 13C NMR was not affected by LPPC, but the FA carboxyl carbon resonance showed linewidth changes near the apparent pKa that were dependent on the FA/LPPC ratio. These data suggest weak interactions in the interfacial region between FA and LPPC when both lipids are present at low levels in PC vesicles.

Carbon Isotopes↗
PubMed1995

Steroidal regulation of cell cycle progression.

Sex steroid hormones and their antagonists have well-defined mitogenic and growth-inhibitory effects on target cells including cancer cells. These effects are mediated by cell cycle phase-specific actions, implying that steroids control rates of cell cycle progression by regulating the expression of key cell cycle regulatory genes. An emerging model of cell cycle control involves transcriptional induction of cyclin genes and consequent activation of cyclin-dependent kinases, which initiate cellular events necessary to complete checkpoints within the cell cycle. Our recent studies have focused on the roles of G1 cyclins, particularly cyclin D1, in the control of cell cycle progression in human breast cancer cells. These studies show that cyclin D1 induction is an early response to mitogenic stimulation by oestrogens and progestins, is rate-limiting for G1 progression and is sufficient for completion of the cell cycle in cells arrested in early G1 phase by serum deprivation. Furthermore, inhibition of cyclin D1 expression is an early response to growth-inhibitory anti-oestrogens. These results suggest that cyclin D1 is a target for regulation of cell cycle progression by sex steroids and their antagonists.

Breast Neoplasms↗
PubMed1995

Serum IL-4, IL-10 and IL-6 levels in inflammatory arthritis.

As the available in vitro and in vivo data suggest that interleukin (IL)-4 and IL-10 have immunosuppressive activity, our hypothesis was that serum IL-4 and IL-10 levels would correlate inversely with parameters of inflammation in patients with inflammatory arthritis. IL-4 was detected in the serum of 12 out of 140 patients with rheumatoid arthritis (RA), which was increased compared to the proportion found with patients with osteoarthritis (OA; P < 0.02). In addition, IL-4 was detected in the serum of 2 of 19 patients with systemic lupus erythematosus (SLE), 2 of 24 patients with psoriatic arthritis and 1 of 5 patients with Behçet's syndrome. No IL-4 was detected in patients with the following conditions: OA (58 patients), gout (17 patients), ankylosing spondylitis (6 patients), Reiter's syndrome (6 patients), polymyalgia rheumatica (6 patients), temporal arteritis (5 patients) and scleroderma (3 patients). No IL-10 was detected in any of the sera tested. We discuss the possible relevance of these results to the regulation of the immune response evident in inflammatory arthritis.

Adolescent↗
PubMed1995

Molecular organization and motions of crystalline monoacylglycerols and diacylglycerols: a C-13 MASNMR study.

Six saturated acylglycerols (1-myristoyl-sn-glycerol, 1-palmitoyl-sn-glycerol, 1,2-dimyristoyl-sn-glycerol, 1,2-dipalmitoyl-sn-glycerol, 1,2-dipalmitoyl-rac-glycerol, and 1,3-dimyristoylglycerol) were studied in their various polymorphic forms (sub-alpha, alpha, beta') by natural abundance C-13 nuclear magnetic resonance (NMR) with magic angle spinning (MASNMR). C-13 MASNMR does not require single crystals and can observe relatively disordered crystals, distinct advantages over crystallographic diffraction methods. Well resolved spectra were obtained for each acylglycerol, and the chemical shifts of corresponding carbons were different for each crystalline phase and the isotropic liquid phase; moreover, in the case of monoacylglycerols, the symmetrically nonequivalent molecules in the same crystalline structure gave distinct C-13 resonances for the same carbon. The C-13 chemical shifts corresponding to each polymorphic phase were interpreted in terms of differences in intramolecular bond distances, intermolecular interactions (such as H bonding), and molecular motions. Mobilities of the glycerol backbone and acyl chains were assessed by the C-13 linewidths and the C-H dipolar relaxation rates. The chemical shift anisotropy(ies) (delta sigma) of the carbonyl group(s) of each acylglycerol was determined from slow-spinning MAS spectra, and was discussed in terms of the conformational and/or motional changes for the carbonyl carbon(s).

Anisotropy↗
PubMed1995

Phase behavior and crystalline structures of cholesteryl ester mixtures: a C-13 MASNMR study.

Cholesteryl esters are a transport and storage form of cholesterol in normal physiology but also a significant lipid in atherosclerotic plaques. To understand better the molecular properties of cholesteryl esters in tissues and plaques, we have studied the polymorphic and mesomorphic features of pure and mixed cholesteryl esters by solid state C-13 NMR with magic angle sample spinning (MASNMR). The temperature-dependent properties of two single components (cholesteryl linoleate (CL, C18:2) and cholesteryl linolenate (CLL, C18:3)), four binary systems (cholesteryl palmitate (CP, C16:0) with CL, CLL or cholesteryl oleate (CO, C18:1), and CO/CL), one ternary system (CO/CP/CL), and one quaternary system (CO/CP/CL/CLL) were studied. The mixing ratios were based on the composition of an atherosclerosis plaque dissected from a cholesterol-fed New Zealand white rabbit. C-13 MASNMR determined the phase transition temperatures, identified the phases present in all systems, and provided novel information about molecular structures. For example, solid CL exhibited a disordered structure with multiple molecular conformations, whereas pure CLL had a crystalline structure different from the three most commonly characterized forms (MLII, MLI, BL). In binary mixtures, the crystalline structure of each cholesteryl ester species was identified by its own characteristic resonances. It was found that CP always existed in its native BL form, but CL and CO were influenced by the composition of the mixture. CL was induced to form MLII crystals by the coexisting CP (55 wt%). When CO was cooled from the isotropic phase, it existed as a mixture of MLII and an amorphous form. The presence of CP significantly accelerated the conversion of the amorphous form to the MLII form. For the ternary mixture co-dried from chloroform, CL cocrystallized with CO in the MLII form and CP existed in BL form. Addition of a small amount of CLL slightly increased the heterogeneity of the solid mixture, but had little effect on the crystal structures or the phase transitions. C-13 MASNMR represents a powerful method for physical characterization of cholesteryl ester mixtures reflecting the composition of biological samples.

Animals↗
PubMed1995

Interactions of a very long chain fatty acid with model membranes and serum albumin. Implications for the pathogenesis of adrenoleukodystrophy.

Adrenoleukodystrophy (ALD) is an inherited disorder of fatty acid metabolism marked by accumulation of very long chain saturated fatty acids (VLCFA), especially the 26-carbon acid, hexacosanoic acid (HA), in membranes and tissues. We have studied interactions of 13C-enriched HA with model membranes (phospholipid bilayer vesicles) and bovine serum albumin (BSA) by 13C NMR spectroscopy to compare properties of HA with those of typical dietary fatty acids. In phospholipid bilayers the carboxyl group of HA is localized in the aqueous interface, with an apparent pKa (7.4) similar to other fatty acids; the acyl chain must then penetrate very deeply into the membrane. Desorption of HA from vesicles (t1+2 = 3 h) is orders of magnitude slower than shorter chain fatty acids. In mixtures of vesicles and BSA, HA partitions much more favorably to phospholipid bilayers than typical fatty acids. BSA binds a maximum of only 1 mole of HA at one binding site. Calorimetric experiments show strong perturbations of acyl chains of phospholipids by HA. We predict that disruptive effects of VLCFA on cell membrane structure and function may explain the neurological manifestations of ALD patients. These effects will be further amplified by slow desorption of VLCFA from membranes and by the ineffective binding to serum albumin.

Adrenoleukodystrophy↗
PubMed1995

Expression and regulation of cyclin genes in breast cancer.

Cyclins, the regulatory subunits of cyclin-dependent kinases, control passage through key check-points within the cell cycle. Since dysregulated expression and function of cyclins can lead to loss of normal growth control some of these genes are oncogenes. We have studied cyclin gene expression, regulation and function in breast cancers. Induction of cyclin D1 is an early event in mitogenic stimulation of breast cancer cells by growth factors and steroids. Furthermore, inhibition of cyclin D1 expression is an early response to growth inhibition by antioestrogens. Ectopic expression of cyclin D1 in T-47D breast cancer cells demonstrated that cyclin D1 is rate-limiting for progression through G1 phase and is sufficient for growth arrested cells to complete the cell cycle. Since this gene is frequently overexpressed in human breast cancers it may contribute to the development and progression of some breast carcinomas.

Breast Neoplasms↗
PubMed1994

Changes in internal pH caused by movement of fatty acids into and out of clonal pancreatic beta-cells (HIT).

Cells require a constant influx of free fatty acids for lipid resynthesis and metabolic energy. Fatty acids also act as second messengers and modulate channel activities. In the pancreatic beta-cell, fatty acids have both acute and chronic effects on insulin secretion. We show that the addition of fatty acid to pancreatic beta-cells in vitro produces a persistent decrease in intracellular pH, which begins immediately after the addition of fatty acid and has an exponential time course with t1/2 approximately 60 s. The pH drop can be largely reversed by the addition of albumin. The observed pH effect can be explained by passive diffusion ("flip-flop") of un-ionized fatty acid across the plasma membrane. Acidification by a fatty acid dimer and alkalinization by an alkylamine also favor the flip-flop mechanism of transport rather than a protein-mediated mechanism. Our method provides for the first time a real-time measurement of fatty acid import into cells. The significant pH change may be important in mediating some of the regulatory effects of fatty acid, such as inhibition of glycolysis.

Biological Transport↗
PubMed1994

Cytokine modulation of plasminogen activator inhibitor-1 (PAI-1) production by human articular cartilage and chondrocytes. Down-regulation by tumor necrosis factor alpha and up-regulation by transforming growth factor-B basic fibroblast growth factor.

Recombinant human cytokines were examined for their effects on plasminogen activator inhibitor-1 (PAI-1) production by human articular cartilage and chondrocyte monolayer cultures. Cartilage and chondrocytes were cultured with and without added cytokines and the conditioned media assayed for PAI-1 by a specific enzyme-linked immunosorbent assay, and mRNA levels determined by Northern blot analysis. Tumor necrosis factor alpha (TNF alpha) reduced, and transforming growth factor-beta (TGF-beta) and basic fibroblast growth factor (bFGF) increased, the levels of PAI-1 antigen and mRNA in the culture fluids and cell extracts, respectively. The effects of TNF alpha and TGF-beta on PAI-1 antigen levels were both time- and concentration-dependent; optimum doses being 10-100 pM TNF alpha and 0.4-0.8 nM TGF-beta, with each cytokine exerting its effect on PAI-1 antigen levels within 8 h of addition to culture. TNF alpha (and interleukin-1 alpha) also countered the effects of TGF-beta and bFGF. The anti-inflammatory drugs, indomethacin and dexamethasone, did not appear to modulate PAI-1 levels in cultures of cartilage tissue. The inhibition of PAI-1 levels by cytokines and reagents which stimulate cartilage resorption (i.e., TNF alpha, interleukin-1 alpha, retinoic acid) and enhancement by cytokines which counter it (i.e., TGF-beta, bFGF) further implicate plasminogen activator in the mechanism(s) of cartilage degradation in diseases such as arthritis.

Aged↗