Biomedical subjects

D T Downing

Publications and source records attributed to D T Downing.

At least 109 records · Page 6Linked to original sources

PubMed1985

The effect of lipids on transepidermal water permeation in snakes.

Transepidermal water permeation was measured for the shed skin of 8 species of snakes under conditions where the skin formed an interface between liquid water and dry air. Extraction with chloroform: methanol removed lipids amounting to 4.9-8.7% of the dry weight of skin and increased transepidermal water permeation 35- to 175-fold. Initial extraction of snake skin with hexane removed only 25-35% of the total extractable lipid but increased water permeation 3- to 10-fold. For totally delipidized skin, water-to-air permeation was much faster than air-to-air permeation, and was also faster than evaporation from a free water surface.

Animals↗

PubMed1985

A survey of polar and non-polar lipids of mouse organs.

Total lipid was extracted from mouse (Mus musculus) heart, kidney, lung, liver, intestine, brain, stomach, dermis and epidermis and analyzed by quantitative thin-layer chromatography. All of the tissues contained phospholipids, triglycerides, sterols and free fatty acids. All tissues except brain contained small amounts of steryl esters, and all except stomach contained some glycosylceramides. Wax diesters were found in both the dermis and epidermis. Only epidermis contained a high proportion of ceramides. Acylglucosylceramides were uniquely present in epidermis.

Animals↗

PubMed1985

The time course of sebum secretion in the guinea-pig.

The time course of sebum secretion in the guinea-pig (Cavia porcellus) was determined by intradermal injection of [1-14C]acetate followed by daily collection of the skin surface lipids at the injection site. The skin surface lipids reached a peak of radioactivity at 5-6 days, indicating that this is the time which elapses between the synthesis of sebum and the surface excretion of the sebaceous lipids. Of the three major skin surface lipid components, the sterol esters (25%) and the wax diesters (25%) showed similar peaks of radioactivity after labelling, but the glycerol ether diesters (30%) showed no radioactivity at any time, suggesting that this lipid is not produced in the skin.

Acetates↗

PubMed1985

A survey of polar and nonpolar lipids extracted from snake skin.

The cast skins of 24 species of snake (four families) were extracted with chloroform:methanol and the lipids recovered (4.2-14.0% of dry weight of shed epidermis) were analyzed by thin layer chromatography (TLC). Skins from all species had large amounts of cholesterol and free fatty acids and most had one or more lipids with TLC mobility similar to triglycerides. Many had a lipid with mobility similar to cholesterol esters. Polar lipids showed much less variation in composition. All species showed large amounts of phospholipids (sphingomyelin, phosphatidylcholine, and phosphatidylethanolamine). All skins contained glycolipids with mobilities similar to monohexosylceramides as well as a number of lipids with mobilities similar to those of ceramides but giving glycolipid-like color reactions when heated with sulfuric acid.

Animals↗

PubMed1985

The composition of the ceramides from human stratum corneum and from comedones.

Human epidermal surface lipids were collected by an ethanol wash and the ceramides were quantified by thin-layer chromatography-photodensitometry. Six ceramide fractions were isolated and the structural components of each were analyzed in detail. The most unusual of the epidermal ceramides contained a sphingosine base with amide-linked 30- and 32-carbon omega-hydroxyacids and an ester-linked nonhydroxyacid, 41% of which was linoleic acid. The proportion of linoleic acid in the analogous ceramide from comedones was 6%. This supports the hypothesis that a localized insufficiency of linoleic acid in the follicular epithelium is an etiologic factor in comedogenesis.

Acne Vulgaris↗

PubMed1985

Proportions of various straight and branched fatty acid chain types in the sebaceous wax esters of young children.

The fatty acid composition of sebaceous wax esters was examined in 20 children, ages 6-8, using quartz capillary gas chromatography. The results were compared with a previously reported study of wax ester composition in 10 adults, in which the same analytical techniques were used. The children's wax esters showed more variability in the proportions of all fatty acid chain types than was found in adults. The most striking difference between the 2 age groups was in the proportions of iso-branched fatty acids with odd numbers of carbon atoms. These ranged from 1-26% of fatty acids in the children's wax esters but were not more than 3% of fatty acids in the adults' wax esters. Some of the variability in wax ester fatty acid composition in children seemed to be related to variation in rates of sebum production. The highest percentages of terminally branched (iso-even, iso-odd, and anteiso) and the lowest percentages of internally branched fatty acids were found in the children with the lowest rates of sebum secretion. However, even in children with similar rates of sebum secretion there were considerable differences in wax ester fatty acid composition, especially with respect to iso-even fatty acids. The results suggest that sebum fatty acid composition is influenced both by genetic factors and by limitations on the supply of precursors for terminally branched, but not internally branched, fatty acids.

Adult↗

PubMed1985

Measurement of sebum secretion rates in young children.

Sustainable rates of lipid secretion were measured on the foreheads of 24 children, ages 6-8. The method of measurement involved absorption of skin surface lipid into bentonite clay and subsequent separation and measurement of the various lipid classes by quantitative thin-layer chromatography. In 9 of the children, sebum secretion appeared to be virtually nonexistent, judging by the low amounts of lipid recovered and the low percentages of wax esters and squalene, which are purely sebaceous lipid classes. An effect of age on sebum secretion rates was observed with median rates of wax ester secretion, being 7, 28, and 48 micrograms/10 cm2/3 h for 6-, 7-, and 8-year-olds, respectively. These values are well below those of most young adults. The relation between wax ester secretion rate and skin surface lipid composition on the forehead was investigated and found to conform to the formula: microgram wax esters/10 cm2/3 h = 28 X wax esters/(cholesterol + cholesterol esters), with a correlation coefficient (r) of 0.94.

Aging↗

PubMed1985

Age-related changes in sebaceous wax ester secretion rates in men and women.

Sustainable rates of sebaceous wax ester secretion were measured on the foreheads of 109 men and 167 women, aged 15-97. Each measurement was made after first depleting the cutaneous sebum reservoir by overnight absorption of lipid into a layer of bentonite clay. Lipid was then absorbed for 3 h into fresh clay in which two 2-cm cloth disks were embedded. The absorbed lipid was extracted from the disks with ether and analyzed for wax esters by thin-layer chromatography. For both men and women there was a wide range of wax ester secretion rates at all ages. Rates were highest in the 15- to 35-year-olds and appeared to decline continuously throughout the adult age range. Values of log(wax esters) were better correlated with age than the untransformed values of wax ester secretion. The equations of best fit of log(wax esters) vs age suggested that sebum secretion declines about 23% per decade in men and 32% per decade in women.

Adolescent↗

PubMed1985

Uropygiols: confirmation of structure by proton magnetic resonance.

Lipids were extracted from excised uropygial glands of domestic chickens and the wax diesters were isolated by preparative thin-layer chromatography (TLC). The diesters were hydrolyzed and the liberated diols were resolved by boric acid TLC into two fractions. These were investigated by proton magnetic resonance at 360 MHz of the free diols and of their acetonide derivatives. The results showed that the cis and trans acetonides, formed from the erythro and threo isomers of the diols, respectively, could be distinguished by the degree of magnetic nonequivalence of the two acetonide methyl groups in each molecule. On the presumption that the cis isomer should show the greater nonequivalence of the methyl groups, this configuration was assigned to the acetonides of these diols which had the lesser TLC mobility on boric acid/silica gel. This agrees with the assignment of configuration made by earlier workers on the basis of the relative TLC mobility of the diol isomers on boric acid/silica gel, but was contrary to a previous assignment based on gas-liquid chromatographic (GLC) retention times. We conclude that the erythro isomers of the diols are characterized by lower mobility on boric acid TLC, as well as on silica gel TLC, and form acetonides that have longer retention times on GLC, and greater nonequivalence of the acetonide methyl groups in the NMR spectrum, than do the acetonides of the threo isomers.

Animals↗

PubMed1985

Linoleate-rich acylglucosylceramides of pig epidermis: structure determination by proton magnetic resonance.

The structure of the linoleate-rich acylglycosylceramides isolated from pig epidermis has been reinvestigated. Gas-liquid chromatographic analysis of the alditol acetates produced from the sugar component indicated that 90% of the hexose is glucose while the remaining 10% is galactose. The predominance of the beta-D-glucosyl group was confirmed by 360 MHz proton magnetic resonance spectroscopy. The magnetic resonance method was also used to prove that the ester-linked linoleic acid is actually attached to the omega-hydroxyl group of the long chain hydroxyacid, not to the sugar as had been reported previously. A key spectral feature supporting this new structural assignment was a triplet at 3.82 ppm, which indicates methylene protons between another methylene and an ester linkage. After saponification, this signal moved to 3.33 ppm, a chemical shift expected for a methylene bearing a free hydroxyl group. Furthermore, all of the sugar ring protons could be accounted for both before and after acetylation. No evidence was found to suggest that an ester is attached to the sugar ring in the native material. It is concluded that the principal porcine epidermal acylglycosylceramide is 1-beta-D-glucosyl-N-(omega-O-linoleoyl)-triacontanoylsphingosine.

Animals↗

PubMed1984

Acylglucosylceramide causes flattening and stacking of liposomes. An analogy for assembly of the epidermal permeability barrier.

When 5% of 1-(3'-O-acyl)-beta-D-glucosyl-N-(omega-hydroxyacyl)sphingosine, isolated from pig epidermis, was added to distearoylphosphatidylcholine and cholesterol (10:1), the lipid mixture formed liposomes in phosphate buffer which were flattened and aggregated like stacks of coins. Other glycolipids from pig epidermis did not cause this phenomenon. This supports the hypothesis that the acylglucosylceramide is responsible for assembly of the lamellar granules found in epidermal cells.

Animals↗

PubMed1984

Cholesteryl sulfate: the major polar lipid of horse hoof.

The lipids of horse hoof have been analyzed by quantitative thin-layer chromatography. The major components include cholesterol (37-40%), six groups of ceramides (10-15%), and cholesteryl sulfate (15-20%). Free fatty acids are abundant (15.8%) in the outer fully keratinized hoof, but are present at only low levels (3.1%) in the softer hyponychium. The material identified as cholesteryl sulfate was isolated by preparative thin-layer chromatography and characterized by a combination of chemical, chromatographic, and spectroscopic methods. The infrared spectrum of the isolated material had absorption bands at 800, 1063, 1200, and 1235 cm-1, indicating a sulfate ester. This sulfolipid was nonsaponifiable, but upon acid hydrolysis yielded cholesterol as the only charrable product, which was identified by its chromatographic behavior and by its electron impact mass spectrum. The isolated sulfolipid also had the same mobility on thin-layer chromatography as authentic cholesteryl sulfate in several different solvent systems. Sulfated gangliosides, which were previously reported to be major horse hoof lipids, were not found among the principal lipid components in the present study. It is concluded that cholesteryl sulfate is the major polar lipid of horse hoof. This may be a significant factor determining the high degree of cohesiveness of this fully keratinized tissue.

Animals↗

PubMed1984

Structures of the dienoic lactones of horse sebum.

The C34, C36, and C38 dienoic omega-lactones were isolated from sebum of the horse (Equus caballus) and the double bond positions were determined by stepwise chemical dissection and analysis of the fragments. The structures found could be formed by delta 9-desaturation at the C18-stage of fatty acid biosynthesis followed by a second delta 9-desaturation when the chains reached C24, C26, C28, C30, or C32 and then addition of one to seven 2-carbon units. These findings provide insight into the dimensions and organization of the endoplasmic reticulum in cells of the sebaceous glands.

Animals↗

PubMed1984

Suppression of sebum secretion with 13-cis-retinoic acid: effect on individual skin surface lipids and implications for their anatomic origin.

The contribution of the keratinizing epidermis to the human skin surface lipid film has been difficult to ascertain because, after its release from the epidermal cells, epidermally derived lipid inevitably becomes mixed with sebum. In the present study, the sustainable rates of production of the 5 neutral lipid classes found on the skin surface (triglycerides + free fatty acids, wax esters, cholesterol, cholesterol esters, and squalene) were measured on the foreheads of acne patients before, during, and following treatment with 13-cis-retinoic acid, a drug which suppresses sebum production profoundly. Since sebum production was high in the patients before treatment and was suppressed to a few percent of the pretreatment level in some of the patients during treatment, data covering a wide range of sebum production rates were obtained. By using squalene as a measure of sebum production and plotting the rates of production of the other lipid classes vs the rate of production of squalene, it was possible through extrapolation to estimate the residual (i.e., epidermal) rate of production of each lipid class at zero sebum production. The results indicated that epidermis releases triglycerides + free fatty acids and cholesterol to the skin surface. The cholesterol esters in freshly secreted skin surface lipids appeared to be almost entirely sebaceous in origin. Measurements were also made of the percentages of cholesterol esters in lipid collected from the scalp after several days' accumulation and were compared to corresponding values for the forehead lipid. The percentages of cholesterol esters in scalp lipid tended to rise when sebum production was suppressed by the drug, rather than remaining relatively constant as occurred in the freshly secreted forehead lipid. This result indicated that epidermis may contribute to skin surface cholesterol esters, probably through skin surface esterification of epidermal cholesterol.

Acne Vulgaris↗

PubMed1984

Variation in sebum fatty acid composition among adult humans.

Quartz capillary gas chromatography was used to analyze the wax ester fatty acids of 4 sebum samples collected at 2-week intervals from each of 10 adult human subjects. Marked differences in wax ester fatty acid composition between subjects were apparent. The greatest variation was present in the even-carbon-numbered iso-branched acids, which ranged from 1-22% of the monounsaturated acids and from 1-13% of the saturated acids. The anteiso chain structures formed 3-7.5% of the unsaturated acids and 3-13.5% of the saturated acids. Fatty acids bearing one or more methyl branches at other positions in the chain made up 12-22% of the saturated acids, but were not present in the unsaturated fatty acid fraction. This and other features of the composition of the unsaturated fatty acids indicate that the delta 6-desaturase that produces the monounsaturated fatty acids of human sebum requires a substrate having a straight chain of at least 12 carbon atoms extending from the carboxyl group. The differences in fatty acid composition between subjects and the constancy of composition for each of the subjects over the 2-month period indicate that the synthesis of each of the types of chain structure is under genetic control.

Adult↗

PubMed1984

Sphingolipids of the stratum corneum and lamellar granules of fetal rat epidermis.

Sphingolipid profiles have been determined for whole epidermis, a subcellular fraction enriched in lamellar granules, and a fraction enriched with stratum corneum derived from fetal rat skin. In each case, 4 groups of glucosylceramides and 6 groups of ceramides have been identified by thin-layer chromatographic comparison with structurally defined sphingolipids from pig epidermis. The relative amounts of the sphingolipids in each preparation have been quantified by photodensitometry of the charred chromatograms. Lamellar granule sphingolipids had elevated proportions, relative to whole epidermis, of acylceramides, acylglucosylceramides, and a glucosylceramide fraction which may be produced by O-deacylation of the acylglucosylceramides. The fetal stratum corneum-enriched samples contain reduced proportions of all glucosylceramides and acylceramides as compared to lamellar granule lipids. The possible functions of these sphingolipids in the assembly and structure of lamellar granules are discussed.

Animals↗

PubMed1983

Effect of essential fatty acid deficiency on the epidermal sphingolipids of the rat.

The epidermal sphingolipids from rats maintained on either a rat stock diet or a fat-free diet have been analyzed. Thin-layer chromatographic analyses have revealed glucosylceramides, acylglucosylceramides and four fractions of ceramides, one of which proved to be an acylceramide. The relative amounts of the glucosylceramides, acylglucosylceramides and acylceramides were increased in the essential fatty acid-deficient epidermis while one ceramide fraction was diminished. The other two ceramide fractions remained unchanged. The acylceramides and acylglucosylceramides from normal rat epidermis both contained long-chain omega-hydroxy acids in amide linkage to sphingosine bases and high proportions of linoleic acid in ester linkage. The linoleate, which is known to be crucial for the formation and maintenance of the epidermal water barrier, was replaced by oleate in the essential fatty acid-deficient rats.

Animals↗

PubMed1983

Comparison of the hydroxyacids from the epidermis and from the sebaceous glands of the horse.

The acylglucosylceramides were isolated from the polar lipids of horse epidermis and examined to determine whether the component omega-hydroxyacids are straight chained as in the corresponding lipids from pig epidermis or branched as in horse sebum. The hydroxyacids from horse epidermis were found to be almost entirely straight chained compounds. The results indicate that sebaceous glands, although derived from epidermal cells, have evolved independent pathways of lipid metabolism.

Animals↗