Biomedical subjects

D T Downing

Publications and source records attributed to D T Downing.

At least 127 records · Page 7Linked to original sources

PubMed1983

Variation in skin surface lipid composition among the Equidae.

Skin surface lipids from Equus caballus, E. przewalskii, E. asinus, E. grevyi, E. hemionus onager and a mule (E. asinus/E. caballus) were analyzed in detail. In all species the surface lipid mixtures consisted of giant-ring lactones, cholesterol, cholesteryl esters and minor amounts of wax diesters. In E. caballus, the lactone hydroxyacids were entirely branched chained, while in E. asinus and E. grevyi they were almost exclusively straight chained. In E. przewalskii, the onager and the mule there were both straight and branched chain hydroxyacid lactones. These results are in harmony with published interpretations of the evolutionary relationships among Equus species.

Animals↗

PubMed1983

Skin lipids.

Explore the source record for details and available documents.

Aging↗

PubMed1983

Sustainable rates of sebum secretion in acne patients and matched normal control subjects.

Sustainable rates of sebum secretion were measured in twelve subjects with inflammatory acne and in twelve control subjects, matched in age and gender, who had no significant signs of acne. The measurements were made after first depleting the skin of an accumulation of previously secreted sebum by absorption into adherent layers of bentonite clay applied to the center of the forehead for 14 hours. Disks of fine Dacron mesh, embedded in fresh clay, were then applied to the forehead for 3 hours. The disks and adhering clay were then removed and extracted with ether to recover the collected lipids. The sebum recovered during the 3-hour period was measured by quantitative thin layer chromatography. The subjects with acne were found to have an average sustainable sebum secretion rate of 2.51 mg/10 cm2/3 hr, while the control group had an average of 0.81 mg/10 cm2/3 hr. Furthermore, all subjects with acne had secretion rates larger than those of their matched control subjects. The results indicate that a high sebum secretion rate is the decisive factor in inflammatory acne.

Acne Vulgaris↗

PubMed1983

Effect of oral 13-cis-retinoic acid at three dose levels on sustainable rates of sebum secretion and on acne.

Changes in sustainable rates of sebum secretion were followed in twenty patients with severe acne who were receiving oral treatment with 13-cis-retinoic acid in dosages of 0.1, 0.5, or 1.0 mg/kg/day. Sebum secretion was measured by absorption of skin surface lipid into bentonite clay and estimation of the amount of absorbed sebum by measurement of its wax ester component. Pretreatment rates of sebum secretion in the patients were greatly elevated in comparison with previously measured values in young adult subjects without acne. After 4 weeks of treatment, mean rates of sebum secretion on all three dose levels fell to or below the range for normal subjects. On-treatment rates of sebum secretion were significantly lower in patients on the highest dose compared to patients on the lowest dose. When the drug was discontinued, rates of sebum secretion recovered slowly. Clinical response was excellent in most of the subjects. The five subjects with least favorable response clinically all had better than average suppression of sebum production.

Acne Vulgaris↗

PubMed1983

Sclerosing lipogranuloma of the male genitalia containing vitamin E: a comparison with classical "paraffinoma".

Sclerosing lipogranuloma of the male genitalia is a rare but distinctive abnormality of the dermis and subcutaneous tissue generally attributed to paraffin injection. We present the results of lipid analysis of lesional tissue from two patients showing the classical clinicopathologic features of this process. No history of local injections could be obtained from either patient. In one case, the patient had applied a vitamin E preparation to the affected area, and tissue lipid analysis demonstrated large quantities of tocopherol and tocopheryl acetate. Analysis of the second case demonstrated a large quantity of tissue paraffin. While this latter patient had applied a topical petrolatum-containing antibiotic preparation to his genital skin, gas-liquid chromatography demonstrated that the paraffins in this preparation differed markedly from the tissue paraffins. No source for this patient's abnormal tissue lipid could be identified.

Aged↗

PubMed1983

Glucosylceramides of pig epidermis: structure determination.

Six series of glucosylceramides from pig epidermis have been identified, and their structures have been determined. The structural types identified are: 1, N-acylglucosylsphingosines (33%); 2, N-acylglucosylphytosphingosines (13%); 3, N-(omega-hydroxyacyl)-glucosylsphingosines (3%); 4, N-(alpha-hydroxyacyl)-glucosylphingosines (15%); 5, N-(alpha-hydroxyacyl)-glucosylsphingosines (16%); 6, N-(alpha-hydroxyacyl)-glucosylphytosphingosines (20%). The 4th and 5th classes of glucosylceramides differ in that the former contains mostly 24- to 28-carbon alpha-hydroxyacids, while the latter contains mostly alpha-hydroxypalmitic acid.

Animals↗

PubMed1983

Acylglucosylceramides of pig epidermis: structure determination.

The acylglucosylceramides of pig epidermis comprise 56% of the total glucosylceramides and 3.3% of the total epidermal lipid by weight. Contrary to an earlier report on this lipid, the amide-linked fatty acid is not a dihydroxypentatriacontadienoic acid; rather, the fatty acids are a series of long chain omega-hydroxy acids consisting of 58% saturates, 35% monoenes, and 7% dienes, with predominant chain lengths of 30, 32, and 34 carbons, respectively. The structure of the acylglucosylceramides may therefore be formulated as 1-(3'-O-acyl)-beta-D-glucosyl-N-(omega-hydroxy)acylsphingosines. In accord with the previous report, 74% of the total esterified fatty acids is linoleic acid and the long-chain bases consist of homologous series of sphinganines and sphingenines ranging from 16-22 carbons in length. This unique glycolipid may play a role in epidermal barrier function.

Amides↗

PubMed1983

Ceramides of pig epidermis: structure determination.

Seven distinguishable groups of ceramides have been isolated from pig epidermis and identified. In order of increasing polarity there are: 1, N-(omega-acyloxy)acylsphingosines (7.7%); 2, N-acylsphingosines (42.4%); 3, N-acylphytosphingosines (10.2%); 4, N-(alpha-hydroxy)acylsphingosines (12,1%); 5, N-(alpha-hydroxy)acylsphingosines (10.5%); 6a, N-[omega-(alpha-hydroxy)acyloxy]acylsphingosines (1.7%); 6b, N-(alpha-hydroxy)-acylphytosphingosines (15.5%). In ceramide 5, the alpha-hydroxyacid moieties are predominantly C16, whereas in ceramides 4, 6a, and 6b, the alpha-hydroxyacids are mainly C24-C28. The omega-hydroxyacids in ceramides 1 and 6a are mainly C30-C32. In ceramide 1, the fatty acids esterified to the omega-hydroxyl group contain a high proportion of linoleic acid (74.5%). These ceramides apparently form a large proportion of the intercellular lipid lamellae in the epidermal stratum corneum, which are thought to constitute the barrier to water loss.

Animals↗

PubMed1982

Glycolipids in mammalian epidermis: structure and function in the water barrier.

In the epidermis of terrestrial vertebrates, lipid lamellae between the horny cells are thought to form a barrier to water loss. The lipids are extruded from living cells after assembly in lamellar granules. This assembly might be promoted by recently identified 1-(3'-O-acyl)-beta-D-glucosyl-N-(omega-hydroxyacyl)sphingosines, which have 30- and 32-carbon hydroxy acids as amides and linoleic acid esterified to glucose. Such a role for these molecules could explain the effects of essential fatty acid deficiency, in which the lamellar granules fail to assemble and the barrier to water diffusion is lost.

Animals↗

PubMed1982

On the mechanism of sebaceous secretion.

Following the studies of Kligman, most investigators now believe that sebaceous glands function continuously in excreting sebum to the skin surface [7, 8]. Populations of differentiating cells are maintained by mitotic activity both in the peripheral cells of the sebaceous lobules and in aggregations of undifferentiated cells which extend through the body of the lobules. Once formed, and as long as maintained by circulating hormones, each lobule continues to produce a stream of differentiating cells which accumulate sebum as they move towards the sebaceous duct and finally disrupt to release their contents into the pilosebaceous canal. After intradermal injections of 3H-thymidine to label germinative cells during DNA replication, up to 28 days elapse before all labeled cells disappear from the glands. When differentiating cells are labeled with 3H-amino acids, much of the label is lost in 7 days. Likewise, when lipids are labeled with 14C-acetate, the average excretion time for the labeled sebum is 8 days. To this time may be added the renewal time of undifferentiated cells to give an average sebaceous cell transition time of 14 days [15]. From knowledge of the time between synthesis and excretion of sebum, sebum production rates were calculated from the sebum content of punch biopsies. The transit time of sebum in the follicular canals was estimated to be 14 h. Production rates determined in this way agree with those measured by long-term absorption of sebum at the skin surface.

Cell Division↗

PubMed1982

The polar lipids from keratinized tissues of some vertebrates.

1. The lipids from a variety of keratinized tissues from terrestrial vertebrates were extracted with chloroform:methanol and the nonpolar and saponifiable lipids were removed. The composition of the remaining polar lipids was examined by thin layer chromatography and color reactions. 2. The tissues studied included: hair from a monkey (Macacca fascicularis), dog (Canis familiaris), raccoon (Procyon lotor) and cow (Bos taurus); full-thickness epidermis from a pig (Sus scrofa) and pilot whale (Globicephala melaena); epidermal scales and feathers from a fowl (Gallus gallus); scales, feathers, beaks and claws from a turkey (Meleagris gallopavo); hoof and horn from cattle (Bos taurus); and cast skins from a Columbian boa (Boa constrictor) and a Ball python (Python regius). 3. All of the tissues contained both simple ceramides and highly polar glycolipids (presumably gangliosides). 4. Glycolipids of intermediate polarity were present in all of the tissues from birds and snakes and in the mammalian tissues which contained unkeratinized epidermal cells, but were absent from fully keratinized mammalian tissues such as hair, hoof and horn. 5. The presence of the highly polar gangliosides provides for the formation of the multiple intercellular lipid lamellae which have been observed in the epidermal horny layer of mammals, birds and reptiles and which are believed to constitute the epidermal barrier to water diffusion.

Animals↗

PubMed1982

Skin surface lipids of the cow.

1. Lipids extracted from the skin surface of cows (Bos taurus) with chloroform were analyzed by quantitative thin layer chromatography and found to contain at least 12 classes of lipids. 2. The major constituents were, in order of increasing polarity: cholesteryl esters, 3%; wax diesters Type I, 37.9%, wax dieters Type II, 7.9%; wax triesters, 29.9%; and triglycerides, 3.6%. 3. Each of the remaining constituents formed less than 5% of the lipid mixture and appeared to be derived from the above materials by loss of acyl groups. 4. With the exception of the triglycerides, all of the aliphatic constituents were composed of saturated, unbranched hydrocarbon chains having an even number of carbon atoms. 5. The triglycerides contained a high proportion of mono- and di-enoic C18 acids, suggesting that they are derived from the epidermis rather than from sebaceous glands.

Animals↗

PubMed1982

The effect of accumulated lipids on measurements of sebum secretion in human skin.

When sebum is collected from the skin surface in an absorbent material, the amounts obtained in successive collections at the same site decline steadily. In the present study, sebum was absorbed into bentonite clay applied to 2.5 sq cm areas on the foreheads of 3 subjects for 3-hr intervals during 24 hr. The amounts of sebum obtained, measured by thin-layer chromatography, declined for 12 hr and then remained constant for the remaining 12 hr. It was inferred that the final, sustainable rate represents the true rate at which sebum was being secreted by the sebaceous glands, and that the additional sebum collected at earlier intervals was obtained from an accumulation in the stratum corneum or in the follicular canals. For the 3 subjects, the accumulated sebum averaged 213 micrograms/sq cm, compared with a sustainable secretion rate of 25 micrograms/sq cm/hr. The large quantity of accumulated sebum, relative to the secretion rate, could obscure differences between subjects when sebum secretion rates are measured by short-term collections of sebum in absorbent materials.

Bentonite↗

PubMed1982

Variability in the fatty acid composition of wax esters from vernix caseosa and its possible relation to sebaceous gland activity.

Wax ester/sterol ester (WE/SE) ratios were measured in samples of vernix caseosa lipid obtained from 21 full-term infants. The mean WE/SE ratio was twice as high in males as in females, suggesting higher average fetal sebum production rates in males, but individual values varied widely and there was considerable overlap between the sexes. Wax esters (a class of lipid produced only by the sebaceous glands) were isolated from 6 of the 21 samples of vernix caseosa lipid and analyzed for fatty acid composition. The percentages of iso and anteiso branched saturated fatty acids and of delta 9-type monounsaturated fatty acids were found to be correlated negatively with the WE/SE ratios of the original lipid samples. Values for the percentages of the major delta 9-type monounsaturates, plotted as a function of WE/SE ratios, fell near a curve of the shape which would be expected if a limited quantity of delta 9-type monounsaturates were available for sebum synthesis, and were diluted with varying amounts of delta 6-type monounsaturates, the amount of the delta 6-type monounsaturates being proportional to the amount of wax esters synthesized by the sebaceous glands. The results suggested that the rate of sebum production may be the sole determinant of the percentage of delta 9-type monounsaturates in sebaceous wax esters and a partial determinant of the percentage of iso and anteiso branched saturates.

Esters↗

PubMed1981

Separation of wax esters from steryl esters by chromatography on magnesium hydroxide.

Chromatography of stearyl oleate and cholesteryl oleate on thin layer plates coated with magnesium hydroxide-celite, 1:1, or magnesia-celite, 1:1, showed that magnesium hydroxide had better resolving power for the separation of these wax ester and steryl ester model compounds than did magnesia, an adsorbent which has been used previously for this separation. By means of high pressure liquid chromatography on magnesium hydroxide, wax esters and steryl esters from the skin surface lipids of human, rat and monkey were separated completely and without hydrolysis.

Animals↗

PubMed1981

Estimation of sebum production rates in man by measurement of the squalene content of skin biopsies.

Previous studies have shown that lipids are synthesized at a constant rate in sebaceous glands and secreted onto the skin surface an average of 8 days after synthesis. As a result, measurement of the sebum content of a skin specimen of known surface area should allow calculation of the sebum production rate which had been occurring in vivo. In the present study, such measurements have been made on scalp skin specimens from 14 men. The amount of sebum in 4-mm punch biopsies was calculated from the squalene content of the specimens, as measured by quantitative thin-layer chromatography of lipid extracts. The average sebum production rate for the group was found to be 1.45 mg/10 sq cm/3 hr.

Humans↗

PubMed1980

Skin surface lipids of the horse.

Skin surface lipids from the sides of male and female horses (Equus caballus) were collected in acetone and analyzed by thin layer chromatography and gas liquid chromatography. The sole components in both sexes were cholesterol, cholesteryl esters and the lactones of 32-, 32- and 36-carbon omega-hydroxy acids, each including a methyl group in the n-1 position. Most of the lactones were monounsaturated (either n-8 or n-10), but small amounts of saturated and dienoic species were present. A pooled sample of the skin surface lipids contained 14% cholesterol, 38% cholesteryl esters and 48% lactones.

Animals↗

PubMed1980

Occurrence of squalene in skin surface lipids of the otter, the beaver and the kinkajou.

In a previous survey of the skin surface lipids of 46 mammalian species, it was found that only 3, the otter, the beaver and the kinkajou, contained components with chromatographic mobility similar to squalene, and in each case, this material was the predominant constituent. The materials in question have now been isolated from each of these species and identified as squalene by thin layer chromatography, gas chromatography and infrared spectroscopy. The occurrence of squalene in the surface lipids of these particular species cannot be examined on the basis of either their evolutionary relationship or ecological niche.

Animals↗