Sterols and keratinization

Effects of prednisolone on the cutaneous reaction and skin barrier function in mice treated with a hapten

Glucocorticoids are effective drugs for the treatment of allergic skin diseases. In the present study, we observed the effects of prednisolone on the cutaneous reaction and skin barrier function in mice treated with a hapten, 2,4-dinitrofluorobenzene. Repeated hapten application onto the mouse ear resulted in a potent ear swelling with an elevation of specific serum IgE. The ear swelling appeared following the second application of the hapten and peaked at 24 h after each application. Specific serum IgE was detected first after the fourth hapten application. Topical treatment with prednisolone apparently suppressed the swelling, whereas it failed to affect the serum specific IgE level. The hapten application caused an increase in transepidermal water loss, which was potently inhibited by prednisolone, although the water content was not affected. Amounts of triglyceride and cholesterol in the ear skin increased after repeated hapten applications, whereas the relative amount of free fatty acid and ceramide diminished. Prednisolone exhibited an inhibitory effect on the changes in lipid content. Thus prednisolone apparently inhibits the alteration of skin barrier function caused by hapten application as well as the cutaneous reaction.

X-linked ichthyosis: an update

X-linked ichthyosis is a genetic disorder of keratinization characterized by a generalized desquamation of large, adherent, dark brown scales. Extracutaneous manifestations include corneal opacity and cryptorchidism. Since 1978 it has been known that a deficit in steroid sulphatase enzyme (STS) is responsible for the abnormal cutaneous scaling, although the exact physiological mechanism remains uncertain. The STS gene has been mapped to the distal part of the short arm of the X chromosome. Interestingly, this region escapes X chromosome inactivation and has the highest ratio of chromosomal deletions among all genetic disorders, complete deletions having been found in up to 90% of patients. Diagnosis of patients with X-linked ichthyosis and female carriers is based on biochemical and genetic analysis. The latter currently seems to be the most accurate method in the majority of cases.

Pharmacology and significance of nonsteroidal anti-inflammatory drugs in the treatment of skin diseases

Intensive studies of the molecular pathways involved in common inflammatory skin disorders, coupled with detailed pharmacologic evaluation of the responses of skin to the end products of these pathways, have resulted in a much clearer understanding of the mode of action of nonsteroidal anti-inflammatory drugs. In particular the development of lipoxygenase inhibitors is prompting intense interest in their possible role as anti-inflammatory agents in psoriasis and other dermatoses. Because of the potency of these and other classes of new anti-inflammatory drugs, careful monitoring of their pharmacokinetics in individual patients, especially those at risk for adverse reactions, will prove necessary, especially in the early stages of treatment. Meanwhile, currently available nonsteroidal anti-inflammatory drugs have a limited but significant place in the treatment of certain dermatoses. Current experience of the high incidence of adverse reactions to existing nonsteroidal anti-inflammatory drugs suggests that this will be no less a problem with new agents under development. The skin is frequently involved in adverse reactions to this class of drug, and past experience suggests that cutaneous reactions are among the earliest unwanted side effects reported in a new drug of this type. The dermatologist, therefore, has an important responsibility to observe, document, and report such "early warning signs" to the appropriate licensing authority and the manufacturer.

Effect of essential fatty acid deficiency on cutaneous sterol synthesis

The fact that the skin is a major site of total body sterologenesis, coupled both with the apparent absence of low density lipoprotein receptors on keratinocytes and with the lack of influence of serum cholesterol on epidermal sterologenesis, has created the impression that epidermal lipid synthesis might be autonomous, i.e., nonregulatable. Recent studies have shown, however, that disruption of cutaneous barrier function with acetone or detergents stimulates epidermal sterologenesis (J Lipid Res 26:418-427, 1985). To correlate further sterologenesis with barrier function, we measured de novo synthesis of cholesterol and total nonsaponifiable lipids in essential fatty acid-deficient (EFAD) hairless mice. Animals with defective barrier function, manifested by abnormal transepidermal water loss, demonstrated a 2-fold increase in epidermal cholesterol and total nonsaponifiable lipid synthesis over controls while synthesis in the dermis was unchanged. Epidermal sterologenesis in EFAD animals, repleted with linoleic acid either systematically or topically, returned toward normal as barrier function improved. Moreover, plastic occlusion of EFAD mouse skin normalized epidermal sterologenesis at 1 and 3 days. These results provide further evidence that epidermal sterologenesis is not entirely autonomous, and can be regulated by water barrier requirements.

Analysis of the non-ionic detergent-soluble lipids of human stratum corneum

Mechanical stimulation of the skin surface in the presence of non-ionic detergent (Triton X-100)-containing buffers has been used to prepare isolated corneocytes and non-ionic detergent-soluble (NIDS) material from human stratum corneum. Analysis of the major lipid classes present in the corneocytes and NIDS material has been performed by thin layer chromatography with flame ionization detection and quantitation based on the introduction of an internal standard. Results indicate that the NIDS lipid represents a disproportionately large amount of the total stratum corneum lipid and that it differs in composition from the corneocyte lipid, there being a greater proportion of the cholesteryl ester fraction in the corneocytes. Both these findings support the 'brick wall' model of the stratum corneum and provide further evidence that the NIDS material is intercellular in nature.

Acquired ichthyosis and impaired dermal lipogenesis in Hodgkin's disease

Epidermal lipid biosynthesis was normal in patients with mild ichthyosis due to Hodgkin's disease, but greatly reduced in one patient with severe ichthyosis. Dermal (sebaceous) lipid synthesis was decreased in all patients with Hodgkin's disease, whether or not they had ichthyosis, and was greatly reduced in the patient with severe ichthyosis. Neither the mechanism nor the possible relationship between the dermal and epidermal changes is understood.

X-linked ichthyosis: a metabolic disease

Sex-linked ichthyosis, a rather common genodermatosis, has recently been linked with deficiency of the enzyme steroid sulfatase. Data supporting this association and suggesting that alterations in lipid metabolism may cause abnormal keratinization are herein reviewed.

Demonstration of giant and anular nexus in the psoriatic epidermis

In the psoriatic skin, nexus were most prominent in the upper layers of the viable epidermis, using the Alcian blue-Lanthanum technique. There, they reached double and manifold the length (giant nexus) of those in normal epidermis. According to the villous transformation of the epidermal cell surface in psoriasis, the nexus showed a great variation in their shape. Undulating nexus were seen beside invagination--and anular nexus. On ther other hand, nexus were lacking in the deepest layers of the psoriatic epidermis in contrast to normal epidermis. From these findings it seems that the intercellular communication by specialized low resistant junctions is reduced in the deepest layers of the psoriatic epidermis. In the upper epidermal layers, however, the extensive formation and the variable configuration of the nexus express a high synthetic activity and a well developed intercellular information in these areas of the psoriatic epidermis.

Flux of fatty acids during epidermal differentiation

Fetal rat skin prior to cornification (18 days of gestation) was prelabeled with [14C] linoleic acid in vitro and subsequently allowed to differentiate and cornify in organ culture. During 48 hr in culture total epidermal 14C fatty acids and 14C dienes decreased in phospholipids and increased in triglycerides and sterol esters as granular layers and stratum corneum formed. During the second 24-hr period, there was no net loss in 14C fatty acids from the epidermis, suggesting that the changes in phospholipid and neutral esters represented translocations of fatty acids within the cornifying cells. The findings are consistent with the hypothesis that fatty acids liberated by hydrolysis of phospholipids are salvaged by reesterfication as neutral lipid esters during epidermal cornification.

Cholestrol and cholesteryl ester content in normal and pathologic scale

Using a sensitive new assay, we have measured the cholesteryl ester and cholesterol contents of stratum corneum from callus, normal skin, psoriatic lesions (plantar and nonplantar), and lamellar ichthyotic lesions (plantar and nonplantar). Cholesteryl ester content of normal stratum corneum was significantly higher than that of callus, suggesting that callus was not a suitable control tissue for further biochemical studies involving sterol content of stratum corneum. Both psoriatic and lamellar ichthyotic scale have increased levels of free cholesterol and decreased levels of esterified cholesterol when compared to appropriate controls.

Epidermal lipid metabolism in psoriasis and lichen simplex

The rate and pattern of epidermal lipogenesis from [14C] glucose were measured in fifteen patients with psoriasis and three with lichen simplex, compared with twenty controls. In 'uninvolved' epidermis from psoriatic subjects the mean lipogenic rate was slightly raised, although the increase was not statistically significant. There was a positive correlation between overall lipogenic rate and the percentage of isotope appearing in free sterol, while the relative proportions of the other lipid classes were unchanged. By contrast, in control epidermis sterol percentage was negatively correlated with lipogenic rate. In psoriatic lesions total epidermal lipogenesis (per unit surface area) was raised compared with matched control 'uninvolved' epidermis. Also raised were percentage labelling of free sterol and of combined (free sterol and monoesters), and the free sterol: monoester ratio was increased. Similar findings were obtained with lesions of lichen simplex, suggesting that disturbed sterol metabolism may be a common feature in conditions of abnormal keratinization.