Hydroxyacid derivatives in human epidermis

Epidermal expression of an Elovl4 transgene rescues neonatal lethality of homozygous Stargardt disease-3 mice

Elongase of very long chain fatty acids-4 (ELOVL4) is the only mammalian enzyme known to synthesize C28-C36 fatty acids. In humans, ELOVL4 mutations cause Stargardt disease-3 (STGD3), a juvenile dominant macular degeneration. Heterozygous Stgd3 mice that carry a pathogenic mutation in the mouse Elovl4 gene demonstrate reduced levels of retinal C28-C36 acyl phosphatidylcholines (PC) and epidermal C28-C36 acylceramides. Homozygous Stgd3 mice die shortly after birth with signs of disrupted skin barrier function. In this study, we report generation of transgenic (Tg) mice with targeted Elovl4 expression driven by an epidermal-specific involucrin promoter. In homozygous Stgd3 mice, this transgene reinstates both epidermal Elovl4 expression and synthesis of two missing epidermal lipid groups: C28-C36 acylceramides and (O-linoleoyl)-omega-hydroxy C28-C36 fatty acids. Transgene expression also restores skin barrier function and rescues the neonatal lethality of homozygous Stgd3 mice. These studies establish the critical requirement for epidermal C28-C36 fatty acid synthesis for animal viability. In addition to the skin, Elovl4 is also expressed in other tissues, including the retina, brain, and testes. Thus, these mice will facilitate future studies to define the roles of C28-C36 fatty acids in the Elovl4-expressing tissues.

Epidermal fatty acid oxygenases are activated in non-psoriatic dermatoses

The extent of epidermal fatty acid oxygenase activation in non-psoriatic dermatoses and the nature of these oxygenases are not known. The monohydroxylated fatty acid derivatives produced in vivo and trapped in skin scales or produced in vitro by oxygenases preserved in scales were analyzed by high performance liquid chromatography in 10 patients with non-psoriatic dermatoses. Evidence for 15-lipoxygenase activation included the finding of 15(S)-hydroxyeicosatetraenoic acid (HETE) in scales from seven patients and the production of 15(S)-[14C]HETE and 13(S)-[14C]hydroxyoctadecadienoic acid (HODE) during scale incubations, respectively, with [14C]arachidonic and [14C]linoleic acid. Evidence for the activation of an arachidonic acid 12(R)-oxygenase included the finding of 12(R)-HETE in scales from eight patients and the production of 12(R)-[14C]HETE during scale incubations with [14C]arachidonic acid. 13-HODE was the predominant fatty acid derivative present in scale extracts; its lack of enantiopurity (mean S/R = 3.1) and the substantial formation of 9-HODE (mean S/R = 0.6; 9/13-HODE = 0.43) suggest its derivation from 15-lipoxygenase and a second oxygenase. The levels of 15(S)-HETE and 12(R)-HETE had a 125- to 144-fold range and were highest in scales from a patient with erythroderma and in three psoriatic scale samples similarly analyzed. These findings indicate that 15-lipoxygenase, most likely of keratinocyte origin, and an arachidonic acid 12(R)oxygenase of unknown type and cell origin are activated in diverse dermatoses.

Free sphingosines in porcine epidermis

Sphingosines and phytosphingosines serve as intermediates in the synthesis of ceramides and glucosylceramides, which are prominent components of mammalian epidermis. In the present study, we have investigated the possibility that free sphingoid bases also may be present in epidermal tissue. Samples of pig epidermis were trypsinized to separate the stratum corneum from the unkeratinized portion of the epidermis. After drying, the lipids were extracted and analyzed by thin-layer chromatography using ninhydrin to detect free amino groups. Both the stratum corneum and the unkeratinized epidermal material contained a ninhydrin-positive material with the same mobility as the sphingosine standard. Quantitation of the chromatograms by photodensitometry indicated that free sphingosine bases account for 0.44% by weight of the total stratum corneum lipid and 0.09% of the lipid in the viable portion of the epidermis. To further identify this material, it was treated with 1-fluoro-2,4-dinitrobenzene, which resulted in the production of an intensely yellow N-2,4-dinitrophenyl derivative with the same mobility as N-2,4-dinitrophenylsphingosine on thin-layer chromatography. Oxidation of the isolated dinitrophenyl derivative with lead tetraacetate produced a mixture of aldehydes which were analyzed by gas-liquid chromatography. This analysis indicates that the free sphingoid bases from the stratum corneum consist of a mixture of mainly 16- through 20-carbon sphingenines and sphinganines, the most abundant components being d17:0, d17:1, d18:1 and d20:1. The production of these free sphingosine bases may be significant in regulating epidermal differentiation.

omega-Hydroxyacid derivatives in the epidermis of several mammalian species

1. omega-Hydroxyacids from the acylceramides and acylglucosylceramides of mammalian epidermis were examined by thin-layer and gas-liquid chromatography to determine their degree of unsaturation and chain-length distributions. The species examined included human (Homo sapiens), pig (Sus scrofa), mouse (Mus musculus) and rat (Rattus rattus). 2. Within a species, the omega-hydroxyacids from the acylceramide and acylglucosylceramide were essentially identical. 3. The human omega-hydroxyacids proved to be mainly saturated with C30:0 being the major entity. 4. The pig contained similar saturated, monoenoic and small amounts of dienoic omega-hydroxyacids, with C30:0, C32:1 being the major entities. 5. The mouse and rat contained C32:0 and C34:1 as the major components.