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 ω-hydroxy acids, each including a methyl group in the n−1 position. Most of the lactones were mono-unsaturated (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.     

Skin lipids of the Florida indigo snake

Cast skins of the Florida indigo snake (Drymarchon corais) yielded up to 8% chloroform: methanol-extractable lipid, which was found to contain methyl ketones (20%), free secondary alcohols (15%), free primary alcohols (30%), free cholesterol (15%), free fatty acids (5%), and hydrocarbons (5%). The hydrocarbons appeared to be contaminants, because gas chromatography revealed a distribution characteristic of petroleum hydrocarbons. The methyl ketones were predominantly monounsaturated, with double bonds almost exclusively in the ω7 position. The structures of the secondary alcohols corresponded with the methyl ketones in regard to chain length distribution, location of the oxygen function in the 2 position, and the proportion and position of unsaturation. The primary alcohols were also predominantly straight, odd-carbon, unsaturated compounds, with ω7 double bonds, but with chain lengths principally of 29 and 31 carbon atoms. The free fatty acids were mainly even-carbon monounsaturated compounds of 16–20 carbon atoms with double bonds mainly in the Δ9-position. Inspection of the lipid structures obtained from the Indigo snake suggest a biogenetic relationship whereby palmitic and palmitoleic acids are extended in chain length mainly to 32 and 34 carbonatom fatty acids. Retention or introduction of an oxygen function in the 3 position, followed by decarboxylation, could then yield structures corresponding with the methyl ketones and the related secondary alcohols. Insertion of an oxygen atom between carbons 2 and 3 of the methyl ketones, followed by loss of the two carbon atoms thereby isolated from the chain, would produce the series of odd-carbon primary alcohols that were observed.     

Skin lipids in health and disease

Lipids are important for normal skin function. They are generated from two main sources – the epithelial cells and the sebum which is secreted onto the surface. Important functions of the lipids are to contribute to an effective barrier towards water loss, to protect from radiation and to prevent entry of harmful chemicals and microbes. There is also an increasing interest in the inflammatory characteristics of lipid signalling molecules which have important consequences for many common skin complaints. In many cases, these bioactive lipids can be regulated through dietary intervention or by topical and other therapies.     

Skin lipids. IV. Biochemistry and function

Metabolic processes and other types of alterations of the lipids of human skin are summarized and discussed. Known functions of skin lipids are discussed, and in the light of new data presented in the papers of this series, new functions are speculated upon.     

Skin lipids. III. Fatty chains in skin lipids. The use ofvernix caseosa to differentiate between endogenous and exogenous components in human skin surface lipid

The literature on the types of fatty chains that occur in skin lipids is reviewed and new data are presented. To ascertain whether certain unusual fatty acids found in human skin surface lipids are truly products of the human skin or are due to some type of external contamination (possibly bacterial), the fatty acids ofvernix caseosa, (the lipoidal material covering the human fetus) were analyzed and compared to those found in human skin surface lipid. The same unusual fatty acids were found invernix caseosa. This indicates that these acids are products of human skin. These acids consist of five classes of saturated branched chain acids and of three classes of monoenes: straight chain,iso andanteiso. All the monoenes are Δ⁶ or derivable from this position by addition of an integral number of 2 carbon units to the carboxyl group. On the polar phase diethylene glycol succinate polyester, the saturated branched chain methyl esters have fractional carbon numbers (by gas chromatography) of 0.15, 0.23, 0.45, 0.63 and 0.75. The series at 0.63 and 0.75 areiso andanteiso, respectively. The series at 0.15 and 0.23 appear to be two newly identified classes of branched chain fatty acids.     

Skin lipids. I. Sampling problems of the skin and its appendages

A review of the problems of sampling various skin tissues for study of lipids is presented following a survey of the anatomy and physiology of skin and its appendages.     

Monounsaturated fatty acids of mouse skin surface lipids

The occurrence of the various positional isomers of monounsaturated fatty acids of mouse skin surface lipids was studied by conventional oxidative cleavage-gas liquid chromatography techniques. The pattern observed could be accommodated by the biosynthetic scheme proposed elsewhere for rat skin fatty acids, except that 18∶Δ9 replaced 16∶Δ9 as the main precursor.     

Diester waxes in surface lipids of animal skin

The literature is surveyed on two types of diester lipid that occur on the skin surfaces of animals: Type 1, a hydroxy fatty acid of which the hydroxyl group and the carboxyl group are esterified respectively with another fatty acid and a fatty alcohol, and Type 2, and alkane α,β-diol of which each OH group is esterified with a fatty acid. New data presented here show that the cow, rabbit and cat produce Type 1, whereas the dog, mouse, guinea pig and baboon produce Type 2 diesters. Each occurs as a major component of the surface lipid. The homologue distribution is given for Type 1 diesters of cow, rabbit and cat as well as the Type 2 diesters of dog and mouse. Distribution of long chain fatty acids of Type 1 diesters parallels that of the fatty alcohols suggesting a biogenetic relation between the two types of compounds. GLC of total diesters for the cow suggests that the components are assembled randomly during biosynthesis. Molecular weight of these diesters are in the range of those of natural triglycerides composed mainly of C₁₆ and C₁₈ fatty acids. Presented at the 60th AOCS Annual Meeting, San Francisco, April 1969, as part of a Symposium on Natural Waxes.     

Skin surface microflora of the saddle-back tamarin monkey,Saguinus fuscicollis

The resident skin surface microflora of 12 male and three femaleSaguinus fuscicollis was studied. The suprapubic-circumgenital gland surface and the perirectal area were most heavily colonized (10⁶–10⁸ colony forming units/cm²), but high numbers of organisms were also present on the abdomen, the sternal gland surface, and palms and plantar surfaces. Bacteria were also recovered from hair clippings as well as from shaven skin surface, although at much lower densities (10²–10⁴ colony forming units/cm²). Coagulase negative staphylococci, gram-negative bacteria,Streptococcus species and coryneform bacteria were most dominant.Staphylococcus aureus and species ofBacillus were also present. Fungi, yeast, and dermatophytes were infrequently recovered or completely absent. The microbial flora of these tamarins appears to be closely associated with the secretions of the circumgenital scent gland and would therefore be ideally situated to participate in the generation or modification of chemical signals.     

Composition of the surface lipids of pea leaves (Pisum sativum)

Surface lipid of pea leaves (Pisum sativum var. Frosty) was analyzed with column, thin layer and gas liquid chromatography in conjunction with mass spectrometry and infrared spectroscopy. It contained 42%n-hentriacontane and 7.3%n-hentriacontan-16-ol. About 5% was wax esters, C₄₀–C₅₀ consisting of primarily C₂₆ and C₂₈ alcohols and C₁₆–C₂₂ acids. Almost 5% was aldehydes, mainly C₂₆ and C₂₈. Primary alcohols, chiefly C₂₆ and C₂₈, made up 20% of the surface lipid.     

1-O-alkyl-2,3-diacylglycerols in the skin surface lipids of the hairless mouse

A neutral lipid class was isolated by thin-layer chromatography from the skin surface lipids of the hairless mouse. The fraction migrated faster than triglycerides and had a migration rate similar to that of diacyl alkanediols (diester wax). Upon deacylation, however, the long-chain diols were identified as 1-alkylglycerol ethers based on their chromatographic properties and on the mass spectra of their nicotinylidene derivatives. Thus, the skin lipid fraction was identified as 1-O-alkyl-diacylglycerol. The alkyl moieties were all saturated and even-numbered and ranged in chainlength from C₁₆ to C₂₂ with 1-O-hexadecylglycerol amounting to 34% of the total glycerol ether moieties. The fatty acids derived from this lipid fraction were mostly monoenoic with chainlengths ranging from C₁₆ to C₂₄. The major acyl component was eicosenoic acid (20∶1) representing 61% of the total fatty acids.     

Four-factor response surface optimization of the enzymatic modification of triolein to structured lipids

The ability of an immobilized lipase to modify the fatty acid composition of (88.8% C_18:1, 4.3% C_16:0, 3.1% C_18:0, and 3.8% C_18:2 as determined by gas chromatography, and approximately 90% triolein) in hexane by incorporation of a medium-chain fatty acid, capric acid (C₁₀), to form structured triacylglycerol was studied. Response surface methodology was used to evaluate the effect of synthesis variables, such as reaction time (12–36 h), temperature (25–65°C), molar substrate ratio of capric acid to triolein (2:1–6:1), and enzyme amount (10–30% wt% of triacylglycerol), on the yield of structured lipid. Optimization of the transesterification was attempted to obtain maximum yield of structured lipid while using the minimum molar substrate ratio and enzyme amount as much as possible. Computer-generated contour plot interpretation revealed that a relatively high molar substrate ratio (6:1) combined with low enzyme amount (10%) after 30 h of reaction at 25°C gave optimum incorporation of capric acid. A total yield for combined monoand dicaproolein of up to 100% was obtained.     

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 explained on the basis of either their evolutionary relationship or ecological niche.     

Antioxidative cosmetic additives for the protection of human skin surface lipids against environmental stress

Studies were carried out in vitro to investigate the effect of a simulated polluted atmosphere containing ozone, sulfur dioxide, and nitrogen dioxide on human skin surface lipids and to evaluate the potency of antioxidative cosmetic additives for the protection against detrimental oxidation processes caused by air polluting substances. The experiments showed that the air pollutants caused significantly increased oxidation effects on human skin surface lipids compared to non polluted atmosphere as indicated by the increase of the peroxide values. The addition of selected derivatives of ascorbic acid, tocopherol, or retinol as specific cosmetic additives with particular antioxidative activity both as pure substances and as ingredients of cosmetic skin care formulations resulted in a considerable protection against oxidative effects of the air pollutants on human skin surface lipids, in which the antioxidative complex tocopherol/hydrogenated tallow glyceride citrate is most effective. Even by additional irradiation with artificial erythemogenic sunlight during the exposure to the air polluting substances of a skin care formulation composed of tocopherol/hydrogenated tallow glycerides as antioxidative component and zinc oxide as UV-filter substance, the significant lipid-protective efficacy of the antioxidative cosmetic additive was only slightly diminished.     

Hydrolysis of acylglycerols and phospholipids of milled rice surface lipids during storage

The relative contribution of acylglycerols and phospholipids to the lipid hydrolysis in milled rice was investigated during storage at 37°C and 70% RH for 50 d. The MAG, DAG, and lysophospholipid contents of surface lipid were determined by reversed-phase HPLC. The MAG and DAG content of milled rice increased during storage from 0.06 to 0.18% (w/w milled rice), with the MAG content increasing more than that of the DAG. Lysophosphatidylcholine increased throughout the study from 0.013 to 0.034% (w/w), whereas lysophosphatidylinositol and lysophosphatidylethanolamine contents initially increased from 0.002 to 0.003% and from 0.005 to 0.009% (w/w), respectively, and then stabilized until day 50. The relative percentage of TAG and phospholipids hydrolyzed in milled rice increased rapidly during the first 3 d of storage from 12.3 to 37.6% and 25.0 to 62.5% (w/w), respectively, and steadily increased to 53.1 and 73.8% (w/w) on day 50. A higher percentage (62.5%) of phospholipids was hydrolyzed relative to TAG (37.6%) after 3 d and probably contributed significantly to milled rice lipid hydrolysis during early storage. However, TAG concentration (0.57%, w/w) was much higher relative to phospholipids (0.08%, w/w) in surface lipids, and therefore TAG hydrolysis was the major contributor to FFA development and the quality of stored milled rice.     

Skin lipids. II. Lipid class composition of samples from various species and anatomical sites

The literature is reviewed and new data are presented for the lipid class analysis of samples of lipid from the following skin tissues and appendages: Total epidermis, stratum corneum, and living epidermis from the human leg, total epidermis (human sole), total epidermis (rat body), sebaceous glands (human scalp), Meibomian glands (human eyelid), preputial glands (rat), preen gland (domestic goose), scalp skin surface (human),vernix caseosa (human fetal body), and rat skin surface from the back. Lipid yields are also given for most of these samples. The results show that the composition of the sebaceous type excretion varies not only from species to species but for different anatomical sites within a given species. Noteworthy is the striking number of unidentified components. Evidence is presented for the existence of a wax diester in the sebaceous gland excretion of the rat.     

Skin surface model material as a substrate for adhesion-to-skin testing

A model material simulating the mechanical and surface properties of a real human skin was developed for use as a substrate in adhesion-to-skin evaluation. It is a protein–lipid composition possessing film-forming ability. The composition is based on gelatin plasticized by glycerol, polysaccharides and a mixture of lipids that mimick the skin's lipid structure and creates a hydrophobic surface. To enhance the material hydrolytic stability, the composition was cross-linked by formaldehyde, producing a water-swellable but insoluble matrix. The surface topography of a real skin was achieved by a silicone replica technique. Thin films with thickness of 100 ± 10 μm were cast. The effect of the components ratio and preparation technique on the film mechanical, surface and hydrolytic properties was studied. Based on the results obtained, a formulation having mechanical and surface properties comparable to that of a human skin was selected. The relevance of the model material was evaluated in lap-shear and 180°-peel adhesion tests and the results were compared to a finger or a forearm skin of ten healthy volunteers (in vivo tests). For validation purposes, commercial surgical tapes Micropore^? and Transpore^? and Mylar^® polyester film were also used. The effects of substrate, adhesive, conditions of the joint preparation and the test employed on adhesion strength were studied. The results obtained show that the mechanical and surface properties of the model material are close to those of the human skin.     

Occurrence of cholesterol as a major sterol component in leaf surface lipids

Cholesterol has been detected as one of the major sterols in the surface lipids of higher plant leaves. It was widely distributed among the plant leaves of various species as a common main sterol component with a few exceptions. The content of cholesterol amounted to 71.5% of the total sterols in the surface lipids of rape leaves. However, the proportion of cholesterol in the intracellular lipids of rape leaves was lower than that in the surface lipids, and the seed lipids contained only a trace amount of cholesterol, as reported in the literature. In the leaf surface lipids examined, a minor amount of cholestanol associated with cholesterol often was detected by capillary gas chromatography and gas chromatography-mass spectrometry. The related analysis for the surface lipids of fruits showed that cholesterol was one of the major component sterols also in those lipids of several species.     

Effect of water washing on the reduction of surface total lipids and FFA on milled rice

A simple method for removing total lipids from the rice surface by water washing is described for brewing operations, where small FFA levels can have a considerable effect on end-product flavor quality. Commercially milled (first-, second-, and third-break) rice was washed with deionized water with constant stirring for 5 and 10 min. About 60 to 80% of total surface lipids were removed by water washing, with a reduction of FFA and conjugated dienes (CD) relative to unwashed control samples. The total surface FFA content of first-, second-, and third-break milled rice was reduced by more than 50% of the original value by washing. Increases in FFA and CD in washed rice after 7 d of storage at 37°C and 70% RH were much lower than those of unwashed controls, in which FFA and CD development was considerably greater and reached brewing quality. Water washing may be a practical means of reducing off-flavor development in milled rice.     

Production of specific structured lipids by enzymatic interesterification: optimization of the reaction by response surface design

Rapeseed oil and capric acid were interesterified in solvent-free media catalyzed by Lipozyme IM from Rhizomucor miehei to produce specific-structured lipids (SSLs). The process was optimized by response surface design concerning the effects of acyl migration and the byproducts of diacylglycerols (DAGs). A five-factor response surface design was used to evaluate the influences of five major factors and their relationships. The five factors were water content (W_c, wt-% based on enzyme used), reaction temperature (T_e, °C), enzyme load (E_l, wt-% based on substrates), reaction time (T_r, h) and substrate ratio (S_r, rapeseed oil/capric acid, mol/mol), varied at three levels together with two star point levels. The net incorporation [Δ(I_f–M_f), in which I_f represents incorporation (1,3-positions) and M_f acyl migration (2-position), and the contents of DAGs were analyzed and calculated. All parameters had strong influence on the net incorporation, and the experimental and predicted values were close. The best fitting quadratic model was determined by regression and backward elimination. The coefficients of determination (R²) of the models were 0.971 for net incorporation and 0.938 for DAG content. Thus, we conclude that the quadratic response models adequately expressed the reaction. Based on the models, the reaction was optimized for the maximum net incorporation and minimum DAG content. The reaction and the control of water content or water activity (Aw) was also discussed.