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C D Evans

Publications and source records attributed to C D Evans.

At least 19 recordsLinked to original sources
PubMed1992

The local lymph node assay: results of a final inter-laboratory validation under field conditions.

The local lymph node assay (LLNA) assesses the sensitizing activity of chemicals by measurement of primary lymphocyte proliferation in lymph nodes draining the site of application. In this final inter-laboratory study the consistency of LLNA results between laboratories and with guinea pig maximization test (GPMT) data was examined under 'field' conditions. Nine chemicals were evaluated independently by each laboratory according to guidelines for test concentration and vehicle selection developed during previous validation studies to ensure assay optimization. Equivalent predictions of sensitization potential were obtained by all laboratories for eight chemicals. Five of seven chemicals identified as sensitizers in the GPMT were correctly identified in the LLNA--four by all laboratories and 1 (4-chloroaniline) by one laboratory only--although in this latter case, two other laboratories obtained clear dose responses, suggestive of sensitization. The LLNA identified correctly those chemicals predicted to be extreme or strong sensitizers in the GPMT. The remaining two chemicals were non-sensitizers in the guinea pig and failed to elicit positive proliferative responses in the LLNA. These data demonstrate that sensitivity and reliability of the LLNA is retained when chemicals are evaluated independently, and that it provides a reliable pre-screen for the identification of chemicals with significant sensitization potential.

Animals↗
PubMed1992

Sulphanilic acid: divergent results in the guinea pig maximization test and the local lymph node assay.

The guinea pig maximization test (GPMT) has proven to be a valuable tool for the identification of the skin sensitization potential of chemicals. The method identifies a hazard which can lead in the EC to compulsory labelling of that chemical. In the present study, data on sulphanilic acid derived from the GPMT has been compared with results from a second guinea pig assay (the cumulative contact enhancement test) and the murine local lymph node assay, both of which require only topical application of chemical. Except for the GPMT, no test identified any sensitizing activity associated with exposure to sulphanilic acid. These latter results are consistent with the experience gained from substantial human exposure in an occupational setting and from which no cases of allergic contact dermatitis to sulphanilic acid have arisen over a 20-year period. In consequence, it is questioned which test protocol in practice has given the more accurate identification of sensitization hazard relevant to man.

Administration, Topical↗
PubMed1992

Thyroid hormone differentially augments biliary sterol secretion in the rat. I. The isolated-perfused liver model.

Thyroid hormone lowers serum cholesterol and alters sterol metabolic processes. This laboratory has previously reported increased biliary lipid secretion as an early effect of triiodothyronine (T3) in the rat. To evaluate whether the bile lipid action of T3 is a primary or secondary effect, the isolated-perfused rat liver model was used. Red blood cells in lipid-free buffer were used to perfuse livers of euthyroid and methimazole-hypothyroid rats, as well as hypothyroid rats given T3 at intervals before perfusion. Bile flow was maintained by taurocholate perfusion. Hypothyroid rats had elevated pre-perfusion serum cholesterol compared to euthyroid (107 +/- 4 vs. 65 +/- 2 mg/dl) and decreased biliary cholesterol (0.016 +/- 0.001 vs. 0.031 +/- 0.004 mumol/g liver/h) secretion. Serum cholesterol decreased to euthyroid levels by 18 h after T3, an effect that was prevented by bile duct ligation. Bile cholesterol secretion doubled by 18 h, and reached levels twice euthyroid by 42 h, while phospholipid secretion doubled to levels just above euthyroid. The fourfold increase in biliary cholesterol secretion occurred with lipid-free perfusion and unchanging bile acid uptake or output. It occurred without a fall in hepatic lipoprotein cholesterol secretion. Blockade of cholesterol synthesis with lovastatin failed to alter T3-augmented bile cholesterol secretion. We conclude that T3 induces biliary cholesterol secretion concomitantly with the fall in serum cholesterol. This augmented biliary secretion did not appear to depend upon lipoprotein uptake, increased bile acid transport, or cholesterol synthesis. It did not occur at the expense of hepatic lipoprotein secretion. Facilitated biliary lipid secretion may be a primary effect of T3.

Animals↗
PubMed1992

Evidence for a common biliary cholesterol and VLDL cholesterol precursor pool in rat liver.

Hepatic free cholesterol levels are influenced by cholesterol synthesis and ester formation, which, in turn, might regulate cholesterol secretion into bile and plasma. We manipulated the rates of hepatic cholesterol synthesis and esterification and measured biliary and very low density lipoprotein (VLDL) cholesterol secretion, and bile acid synthesis. Mevalonate decreased HMG CoA reductase by 80%, increased acyl coenzyme A: cholesterol acyltransferase (ACAT) by 60% and increased [3H]oleate incorporation into microsomal and VLDL cholesteryl esters by 174% and 122%, respectively. Microsomal and biliary free cholesterol remained constant at the expense of increased microsomal and VLDL cholesteryl ester content. Mevalonate did not change bile acid synthesis. 25-OH cholesterol decreased HMG-CoA reductase by 39%, increased ACAT by 24%, but did not effect 7 alpha-hydroxylase. 25-OH cholesterol increased [3H]oleate in microsomal and VLDL cholesterol esters by 71% and 120%. Biliary cholesterol decreased by 40% and VLDL cholesteryl esters increased by 83%. A small and unsustained decrease in bile acid synthesis (14CO2 release) occurred after 25-OH cholesterol. After orotic acid feeding, HMG-CoA reductase increased 352%, and [3H]oleate in microsomal and VLDL cholesteryl esters decreased by 43% and 89%. Orotic acid decreased all VLDL components including free cholesterol (68%) and cholesteryl esters (55%), and increased biliary cholesterol by 160%. No change in bile acid synthesis occurred. Hepatic cholesterol synthesis and esterification appear to regulate a cholesterol pool available for both biliary and VLDL secretion. Changing cholesterol synthesis and esterification did not alter bile acid synthesis, suggesting that either this common bile/VLDL secretory pool is functionally distinct from the cholesterol pool used for bile salt synthesis, or that free cholesterol availability in this precursor pool is not a major determinant of bile acid synthesis.

Animals↗
PubMed1991

Assessment of the relative skin sensitizing potency of 3 biocides using the murine local lymph node assay.

The relative skin-sensitizing potency of 3 biocides, 5-chloro-2-methyl-4-isothiazolin-3-one (the major active ingredient in Kathon CG), 1,2-benzisothiazolin-3-one and 2-methyl-4,5-trimethylene-4-isothiazolin-3-one, was assessed using the murine local lymph node assay. Potency was ranked according to the lowest dose of material which, following epicutaneous exposure, induced a significant proliferation of T lymphocytes in the draining lymph nodes. The results showed that 5-chloro-2-methyl-4-isothiazolin-3-one was able to induce proliferative activity at significantly lower dose levels than the other 2 biocides and that it may therefore be a more potent skin sensitizer.

Animals↗
PubMed1991

Some meanings of body and self in eating-disordered and comparison subjects.

A new repertory grid was used to compare a group of 27 eating-disordered women (EDS) with a group of 20 women of normal weight without eating disorders (NWC) on contrasts from theories which link abnormalities in the perception of body and self to the eating disorders. No evidence was found for greater polarization of either self or body images in the EDS. A negative connotation of the body at normal weight and overweight was specific to EDS, but the underweight body did not have a more positive connotation. Negative connotation of normal weight is shown to be more specific for EDS than is negative connotation of the overweight body. There was no evidence for specific implications of weight for sexuality nor for family pressures against sexuality or femininity in EDS although they did construe themselves as less sexual than the NWC.

Adult↗
PubMed1990

The lamin B receptor of the nuclear envelope inner membrane: a polytopic protein with eight potential transmembrane domains.

The lamin B receptor is a previously identified integral membrane protein in the nuclear envelope of turkey erythrocytes that associates with the nuclear intermediate filament protein lamin B (Worman, H. J., J. Yuan, G. Blobel, and S. D. Georgatos. 1988. Proc. Natl. Acad. Sci. USA. 85:8531-8534). In the present report, we use cell fractionation and antibodies against the lamin B receptor to localize it to an 8-M urea-extracted membrane fraction of chicken liver nuclei, supporting an inner nuclear membrane localization. We deduced the amino acid sequence of the chicken lamin B receptor from overlapping clones obtained by screening cDNA libraries with a probe generated by the polymerase chain reaction with primers based on the partial protein sequence of the isolated protein. The mature lamin B receptor has a calculated molecular mass of 73,375 D and eight segments of hydrophobic amino acids that could function as transmembrane domains as determined by hydropathy analysis. Preceding the first putative transmembrane segment is a highly charged 204-residue-long amino terminal region that contains two consensus sites for phosphorylation by protein kinase A. Since the lamin B receptor has been shown to be phosphorylated by protein kinase A in vitro and in vivo and this phosphorylation affects lamin B binding (Applebaum, J., G. Blobel, and S. D. Georgatos. 1990. J. Biol. Chem. 265:4181-4185), it is likely that this amino terminal region faces the nucleoplasm. The amino terminal region also contains three DNA-binding motifs that are found in gene regulatory proteins and histones, suggesting that the lamin B receptor may additionally play a role in gene regulation and/or chromatin organization.

Amino Acid Sequence↗
PubMed1989

Determination of 2-n-octadecylindole-5-carboxylic acid in human plasma by high-performance liquid chromatography.

A method is described for the determination of the novel hypocholesterolaemic drug, 2-n-octadecylindole-5-carboxylic acid (I) in plasma. A homologue of I is used as the internal standard. Methanol is added to the plasma sample in order to precipitate the plasma proteins, followed by centrifugation and removal of the supernatant. This is reduced to dryness by heating under oxygen-free nitrogen, prior to reconstitution in the chromatographic mobile phase. The solution is assayed by injection on to a 5 micron particle size ODS2 analytical column, protected by a disposable RP-18 packed guard column, using an isocratic mobile phase of acetonitrile-water-isopropyl alcohol-formic acid (75:275:150:2.5, v/v). Detection is by ultraviolet absorbance at 276 nm. At a flow-rate of 1.5 ml min-1 and ambient temperature, the retention time of the drug is 16 min, whilst that for the internal standard is 21 min. This method has been validated and successfully used to assay clinical trial plasma samples. Basic pharmacokinetic parameters are presented.

Chromatography, High Pressure Liquid↗
PubMed1989

Regulation of hepatic cholesterol ester hydrolase and acyl-coenzyme A:cholesterol acyltransferase in the rat.

Cholesterol exists within the hepatocyte as free cholesterol and cholesteryl ester. The proportion of intrahepatic cholesterol in the free or ester forms is governed in part by the rate of cholesteryl ester formation by acyl-coenzyme A:cholesterol acyltransferase (ACAT) and cholesteryl ester hydrolysis by neutral cholesterol ester (CE) hydrolase. In other cell types both ACAT and CE hydrolase activities are regulated in response to changes in the need for cellular free cholesterol. In rats, we performed a variety of experimental manipulations in order to vary the need for hepatic free cholesterol and to examine what effect, if any, this had on the enzymes that govern cholesteryl ester metabolism. Administration of a 20-mg bolus of lipoprotein cholesterol or a diet supplemented with 2% cholesterol resulted in an increase in microsomal cholesteryl ester content with little change in microsomal free cholesterol. This was accomplished by an increase in cholesteryl esterification as measured by ACAT but no change in CE hydrolase activity. An increased need for hepatic free cholesterol was experimentally induced by intravenous bile salt infusion or cholestyramine (3%) added to the diet. ACAT activity was decreased with both experimental manipulations compared to controls, while CE hydrolase activity did not change. Microsomal cholesteryl ester content decreased significantly with little change in microsomal free cholesterol content. Addition of exogenous liposomal cholesterol to liver microsomes from cholestyramine-fed and control rats resulted in a 784 +/- 38% increase in ACAT activity. Nevertheless, the decrease in ACAT activity with cholestyramine feeding was maintained. These studies allowed us to conclude that changes in hepatic free cholesterol needs are met in part by regulation of the rate of cholesterol esterification by ACAT without a change in the rate of cholesteryl ester hydrolysis by CE hydrolase.

Animals↗
PubMed1989

Lovastatin treatment inhibits sterol synthesis and induces HMG-CoA reductase activity in mononuclear leukocytes of normal subjects.

The mechanism by which competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase decrease serum cholesterol is incompletely understood. The few available data in humans suggest that chronic administration of the competitive inhibitor, lovastatin, decreases serum cholesterol with little or no change in total body sterol synthesis. To further define the effect of lovastatin on cholesterol synthesis in normal subjects, we investigated the effect of a single oral dose of lovastatin and a 4-week treatment period of lovastatin on mononuclear leukocyte (ML) sterol synthesis as a reflection of total body sterol synthesis. In parallel, we measured serum lipid profiles and HMG-CoA reductase activity in ML microsomes that had been washed free of lovastatin. ML sterol synthesis did not significantly decrease (23 +/- 5%, mean +/- SEM) at 3 h after a single 40-mg dose of lovastatin. With a single oral 80-mg dose, ML sterol synthesis decreased by 57 +/- 10% (P less than 0.05) and remained low for the subsequent 6 h. With both doses, total HMG-CoA reductase enzyme activity in microsomes prepared from harvested mononuclear leukocytes was induced 4.8-fold (P less than 0.01) over baseline values. Both the 20-mg bid dose and the 40-mg bid dose of lovastatin administered for a 4-week period decreased serum cholesterol by 25-34%. Lovastatin at 20 mg bid decreased ML sterol synthesis by 23 +/- 6% (P less than 0.02) and increased ML HMG-CoA reductase 3.8 times (P less than 0.001) the baseline values. Twenty four hours after stopping lovastatin, ML sterol synthesis and HMG-CoA reductase enzyme activity had returned to the baseline values. The higher dose of lovastatin (40 mg bid) decreased ML sterol synthesis by 16 +/- 3% (P less than 0.05) and induced HMG-CoA reductase to 53.7 times (P less than 0.01) the baseline value at 4 weeks. Stopping this higher dose effected a rebound in ML sterol synthesis to 140 +/- 11% of baseline (P less than 0.01), while HMG-CoA reductase remained 12.5 times baseline (P less than 0.01) over the next 3 days. No rebound in serum cholesterol was observed. From these data we conclude that in normal subjects lovastatin lowers serum cholesterol with only a modest effect on sterol synthesis. The effect of lovastatin on sterol synthesis in mononuclear leukocytes is tempered by an induction of HMG-CoA reductase enzyme quantity, balancing the enzyme inhibition by lovastatin.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗