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Biomedical subjects

B E Brown

Publications and source records attributed to B E Brown.

At least 55 records · Page 3Linked to original sources
PubMed1984

Stratum corneum lipid abnormalities in ichthyosis. Detection by a new lipid microanalytical method.

Although the biochemical diagnosis of the ichthyoses is still in its infancy, the two recessively inherited types, recessive X-linked ichthyosis (RXLI) and nonbullous congenital ichthyosiform erythroderma (CIE), are accompanied by stratum corneum lipid abnormalities. However, in RXLI, cholesterol sulfate accumulates; in CIE, massive quantities of n-alkanes accumulate. The diagnosis of these disorders has required large quantities of scale for sequential, quantitative thin-layer chromatography (TLC). In this study, we sought to confirm the previously described lipid abnormalities with the use of a rapid, recently developed microchromatographic technique that employs silica gel-coated quartz rods and flame ionization detection (Iatroscan). The cholesterol sulfate content of RXLI (n = 5) scale and the n-alkane content of CIE (n = 8) scale were determined by both TLC and the microchromatographic technique. Less than 10 mg of scale and even single punch biopsy specimens sufficed for the microchromatographic technique, whereas more than 50 mg of scale were required for TLC. Since the microchromatographic technique can rapidly detect diagnostic biochemical abnormalities from readily obtainable, small tissue samples, this method could eventually supplant or supplement standard lipid biochemical techniques for the diagnosis of cutaneous lipidoses.

Alkanes↗
PubMed1983

Localization of de novo sterologenesis in mammalian skin.

Previous studies have demonstrated that the skin is an important site of de novo sterol synthesis and that there is a sex difference in cutaneous sterologenesis with male animals synthesizing more sterols than females. The aim of the present study was to localize the major sites of sterol synthesis within the skin and to determine which of these sites accounted for the sex differences in sterologenesis. In male and female rats whose dermal and epidermal layers are separated by dithiothreitol treatment, the dermis is the major site of skin sterologenesis (males 86% of total, females 82% of total). Moreover, the sex difference in skin sterol synthesis is quantitatively localized primarily within the dermal layer (approximately 2.5-fold greater in the dermis of males). Sterol synthesis is also increased in the epidermis of males. To rule out the possibility that sebaceous gland production accounted for our observations, we treated animals with isotretinoin (13-cis-retinoic acid), a drug that suppresses sebaceous gland sebum production. Sterol synthesis in the skin of both male and female rats is not significantly altered by isotretinoin administration and the sex difference in skin sterologenesis is unaffected. To further localize the sites of sterol synthesis within the skin, studies of hairless mice whose skin was split by DTT were initiated. In hairless mice, DTT separates the epidermis into upper (stratum corneum and granulosum) and lower (basal and spinous cells) strata. The basal layer was separated from the dermis by gentle scraping. As in rats, the dermis is the chief site of sterol synthesis in the skin. In addition, the lower layer of the epidermis (basal and spinous cells) is also a very active site of sterologenesis, accounting for 20% of total skin nonsaponifiable lipid synthesis. The upper epidermis accounted for only a small portion of total skin synthesis. It is highly likely that the bulk of cutaneous sterol synthesis occurs in the pilosebaceous epithelium.

Animals↗
PubMed1983

Glucose absorption from starch hydrolysates in the human jejunum.

The intestinal absorption and mucosal hydrolysis of a partial and a complete alpha-amylase hydrolysate of corn starch, simulating the normal intermediary and end products of luminal starch digestion, was studied using an in vivo steady state jejunal perfusion technique in normal human subjects. Alpha-amylase was excluded from the test segment by proximal balloon occlusion. Products of hydrolysis during intestinal perfusion were identified using gel permeation chromatography. Three isocaloric, isotonic sugar saline solutions containing 140 mM glucose, 70 mM maltose and the partial amylase hydrolysate of starch (51.5 +/- 1.4% of glucose content comprising glucose polymers of more than 10 glucose units) were perfused in the first study. Net glucose absorption during perfusion of the partial hydrolysate and free glucose was similar, but significantly faster from maltose (p less than 0.05). Hydrolysis of the polymer fraction containing more than 10 glucose units was significantly slower (29.5 +/- 2.0% of infused load) than the lower molecular weight fraction (56.4 +/- 3.8%, p less than 0.001). As net glucose absorption from the partial hydrolysate was similar to that from glucose, despite the slow hydrolysis of the higher molecular weight fraction, it seemed likely that oligosaccharides in the more rapidly hydrolysed lower molecular weight fractions were exerting a kinetic advantage on glucose absorption. This was confirmed in a second study, where glucose absorption from a complete amylase hydrolysate consisting predominantly of maltose, maltotriose and alpha-limit dextrins, occurred significantly faster (81.8 +/- 4.8 mmol/h/25 cm) than from isocaloric free glucose (55.8 +/- 4.9 mmol/h/25 cm, p less than 0.001). Chromatograms of intestinal aspirates suggested that (1->4), but not 1->6) linked oligosaccharides liberated during luminal and brush-border hydrolysis of dietary starch conferred a kinetic advantage on glucose absorption.

Adult↗
PubMed1983

Human stratum corneum lipids: characterization and regional variations.

The lipids of mammalian stratum corneum are known to be important regulators of skin permeability. Since the human stratum corneum displays remarkable regional variations in skin permeability, we assessed the total lipid concentration, the distribution of all major lipid species, and the fatty acid composition in Bligh-Dyer extracts from four skin sites (abdomen, leg, face, and sole) that are known to display widely disparate permeability. Statistically significant differences in lipid weight were found at the four sites that were inversely proportional to their known permeability. In all four sites, among the polar lipids, the stratum corneum contained negligible phospholipids, but substantially more cholesterol sulfate (1-7%) than previously appreciated. As in the stratum corneum from other mammals, the bulk of the lipids consisted of neutral (60-80%) and sphingolipids (15-35%). Of the neutral lipids, free sterols (4- to 5-times greater than esterified sterols), free fatty acids, triglycerides, and highly nonpolar species (n-alkanes and squalene) predominated. n-Alkanes, which were present in greater quantities than previously appreciated, comprised a homologous series of odd- and even-chained compounds ranging from C19 to C34. The sphingolipids comprised over 80% ceramides vs. lesser quantities of glycosphingolipids. In all four sites, the sphingolipids were the major repository of long-chain, saturated fatty acids. The neutral lipid:sphingolipid ratio generally was proportional to the known permeability of each site: higher neutral lipids and lower sphingolipids generally were associated with superior barrier properties. These studies provide: 1) the first detailed, quantitative analysis of human stratum corneum lipids and 2) information about the variability in lipid composition at four skin sites with known differences in permeability. The latter results suggest that variations in neutral lipids, rather than sphingolipids, may underlie local variations in skin permeability.

Alkanes↗
PubMed1981

Percutaneous transport in relation to stratum corneum structure and lipid composition.

Despite the acknowledged importance of the stratum corneum in limiting water loss and in controlling skin permeability, the basis for these functions remains unknown. To pinpoint those factor(s) of importance for cutaneous barrier function, we correlated the thickness, number of cell layers, and lipid composition of leg vs. abdominal stratum corneum samples with penetration of 3H-water and 14C-salicylic acid across the same tissue sample. Viable upper epidermal sheets were obtained by incubating fresh autopsy or amputation full-thickness skin with staphylococcal exfoliatin. Each sheet was divided into 3 portions. The first piece was mounted in a diffusion cell for penetration studies. The second stratum corneum sample was frozen sectioned, stained with the fluorochrome, ANS, and measured with a micrometer eyepiece. The 3rd piece was pooled with other leg (n = 6) and abdomen (n = 15) specimens for determination of lipid weight percent. In all cases, leg stratum corneum was congruent to 2 times more permeable than abdominal stratum corneum to water and slightly more permeable to salicylic acid, as well. Penetration of both substances correlated inversely with lipid weight % of leg (mean = 3.0%) vs. abdomen (mean = 6.8%), but neither the penetration of water nor of salicylic acid was influenced by the number of cell layers or the thickness of the stratum corneum. We conclude that: differences in the thickness and the number of cell layers in the stratum corneum are insufficient to account for differences in percutaneous transport across leg and abdomen, and that total lipid concentration may be the critical factor governing skin permeability.

Abdomen↗
PubMed1981

Retinoid effects on epidermal structure, differentiation, and permeability.

Retinoids profoundly influence epidermal differentiation, but neither the nature of their antikeratinizing activity nor their mechanism of action is known. In this study, we have correlated morphologic and histochemical findings with an assessment of stratum cohesion and water barrier integrity in adult hairless mice treated with either 13-cis-retinoic acid or the aromatic retinoid, RO 10-9359. Both the synthetic retinoids produced dose-dependent alterations in transepidermal water loss, which were about 5 to 10 times greater in RO 10-9359-treated animals. In contrast to essential fatty acid deficiency, where diminished intercellular lamellar lipids may account for defective barrier function, these lipid-rich structures were intact in retinoid-treated tissues. Instead, retinoids produced both epidermal and stratum corneum loosening, manifested both by the ready production of intraepidermal friction blisters and by ease of removal of cornified cells by tape stripping. Dyshesion correlated with loss of desmosomes and intra- and intercellular accumulation of amorphous material in the upper epidermis. Since these deposits lacked the tinctorial properties of mucin, dyshesion could not be ascribed to the development of mucous metaplasia. Finally, dyshesion could not be attributed to either gain or loss of membrane sugars demonstrated with rhodamine-conjugated lectins, since these changed only late in the course of retinoid treatment. We conclude that the antikeratinizing basis for retinoid activity comprises: (1) dose-dependent alterations in transepidermal water loss and (2) epidermal and stratum corneum loosening, which may, in turn, lead to loss of epidermal cohesion and abnormal barrier function. Neither mucous metaplasia nor stratum corneum thinning appear to play a major role.

Animals↗
PubMed1980

The permeability barrier in essential fatty acid deficiency: evidence for a direct role for linoleic acid in barrier function.

Essential fatty acid (EFA) deficient rodents demonstrate abnormal epidermal permeability barrier function and differentiation, defects which can be corrected by either topical or systemic administration of linoleic acid. Since linoleic acid is a precursor of prostaglandins, correction of the defect in barrier function may either reflect a prostaglandin-mediated return toward normal epidermal differentiation, or, instead, a direct effect of linoleic acid. To test these possibilities severely EFA-deficient mice were pretreated daily with indomethacin and/or 5,8,11,14-eicosatetrayeonic acid, and then placed on normal (lineolic acid-supplemented) diets. Endogenous formation of prostaglandin E2 was determined by thin-layer chromatography after transformation into prostaglandin B2 with ethanolic-hydrochloric acid. Animals treated with both indomethacin and TYA DEMONSTRATED SUBSTANTIAL REDUCTIONS IN PROSTAGLANDIN E2 levels in liver and skin. Animals replenished with linoleic acid invariably demonstrated a rapid return of barrier function toward normal whether or not they were blockaded, while nonreplenished animals, with or without inhibition of prostaglandin biosynthesis, demonstrated continued deterioration in barrier function. In other experiments, topically applied linoleic acid rapidly reversed the defect in barrier function at the sites of application prior to systemic correction of the EFA deficient state. These results suggest that: (1) defective cutaneous barrier function in EFA deficiency can be corrected locally without prior systemic reversal of the deficiency state; and (2) that linoleic acid may play a direct role in the epidermal permeability barrier independent of its role in prostaglandin metabolism.

Animals↗
PubMed1978

Freeze-fracture identification of sterol-digitonin complexes in cell and liposome membranes.

To advance our understanding of the organization of cholesterol within cell membranes, we used digitonin in freeze-fracture investigations of model lipid vesicles and tissues. Cholesterol suspensions or multilamellar liposomes composed of phosphatidylcholine with and without cholesterol were exposed to digitonin. Freeze-fracture replicas of those multilamellar liposomes containing cholesterol displayed either 50--60-nm wide intramembrane corrugations or extramembrane tubular complexes. Comparable intramembrane hemitubular scallops and extra-cellular free tubular complexes were observed in thin sections. Exposure of sperm, erythrocytes (whole and ghosts), and intact tissues (skin, liver, adrenal gland, epididymis) to digitonin produced the same types of intra- and extramembrane complexes or furrows as were formed in liposomes. The plasma membrane of guinea pig serum tail had two unfurrowed regions: the annulus and the zipper. Incubating erythrocyte membranes with digitonin resulted in rapid displacement of cholesterol, accompanied by intramembrane particle clustering and membrane faceting, a feature which we did not see in the intact epithelia studied. In freeze-fractured epithelia, we found that plasma membranes, lysosomes, and some vesicular organelles commonly furrowed, but that mitochondrial membranes and nuclear envelopes were generally spared, correlating well with their known cholesterol content. Finally, plasma membrane corrugations approached but did not impinge on either gap or tight junctions, or on coated vesicles. We conclude that freeze-fracture of membranes exposed to digitonin: (a) reveals distinctive cholesterol-digitonin structural complexes; (b) distinguishes cholesterol-rich and -poor organelle membranes; and (c) demonstrates membrane domains rich or poor in cholesterol.

Adrenal Glands↗
PubMed1967

Neuromuscular transmitter substance in insect visceral muscle.

Stimulation of the nerves innervating the proctodeum (hindgut) of the cockroach Periplaneta americana (L.) causes a slow-type, graded contraction of the longitudinal muscles. An unidentified substance, or substances, present in the foregut and hindgut, the specific activity of which is highest in the nerves innervating these organs, effects a similar contraction. This "gut-factor" is depleted from the hindgut after surgical section of the proctodeal nerves. None of Factors P(1) and P(2), 5-hydroxytryptamine, acetylcholine, adrenaline, noradrenaline, alpha-ami-nobutyric acid or glutamate duplicates the pharmacological behavior of this substance. The active factor is associated with subcellular particles that require centrifugal forces of approximately 1,000,000 g-min for sedimentation. The substance is inactivated in homogenates of gut tissue in the absence of suitable precautions. It is proposed that the "gut-factor" functions as an excitatory neuromuscular transmitter substance in insect visceral muscle.

Acetylcholine↗