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Biomedical subjects

B E Brown

Publications and source records attributed to B E Brown.

At least 19 recordsLinked to original sources
PubMed1998

The secretory granular cell: the outermost granular cell as a specialized secretory cell.

The contents of epidermal lamellar bodies (LB) are delivered selectively to the intercellular spaces at the stratum granulosum (SG)-stratum corneum (SC) interface. We assessed the subcellular basis for LB secretion first by confocal microscopy, following labeling with Nile red or NBD-ceramide, which reveals a tubulo-reticular membrane system within the apical cytosol of the outermost SG cell layer under basal conditions, changing to a more peripheral staining pattern when secretion is stimulated. Ultrastructural study demonstrates that this network is composed of a widely disbursed trans-Golgi-like network (TGN), associated with arrays of contiguous LB, and deep invaginations of the SG-SC interface. Under basal conditions, limited fusion of apically directed LB leads to deep, interconnected invaginations of the apical plasma membrane, resulting in the formation of an extensive, honeycomb extension of the SG-SC interface. Still deeper invaginations and more extensive organelle fusion develop after the epidermis is acutely permeabilized by either acetone treatment, sonophoresis, or iontophoresis. Finally, nascent LB appear to bud off cisternae of the TGN, a process that appears to accelerate after barrier disruption. The deep invaginations of the SG-SC interface; the wide distribution of the TGN within the apical cytosol; the association of nascent LB with the TGN; and the rapid fusion of LB with these invaginations, deep within the cytosol, account for (i) the polarized secretion of LB from the apex of the outermost SG cell, and (ii) the rapid LB-secretory response to barrier perturbations. Finally, our results point to the outermost SG cell as a uniquely specialized secretory cell. We propose the term "secretory granulocyte" to encompass the specialized features of these cells.

4-Chloro-7-nitrobenzofurazan↗
PubMed1998

Glucosylceramides stimulate mitogenesis in aged murine epidermis.

Glucosylceramides (GlcCer) and ceramides (Cer) appear to have opposite effects on epidermal growth and differentiation. Whereas Cer inhibit mitosis and induce terminal differentiation and apoptosis in cultured keratinocytes, GlcCer is mitogenic in young murine epidermis. Using a recently described murine model of chronologic senescence we explored whether GlcCer is mitogenic in aged epidermis. Epidermal GlcCer content increases following topical applications of either conduritol-B epoxide (CBE), an inhibitor of GlcCer hydrolysis, or exogenous GlcCer in a penetration-enhancing vehicle. During chronologic aging in the hairless mouse, baseline epidermal DNA synthesis rates remain normal until 18 mo, but decline significantly at 24 mo. Topical CBE stimulates a 1.5- to 1.9-fold increase in epidermal DNA synthesis in all age groups (i.e., 1-2, 18, and 24 mo). Although the CBE induced increase in [3H]thymidine incorporation in 24 mo old animals is significant (p < 0.01), it is not sufficient to reach the absolute levels reached in similarly treated, younger mouse epidermis. Moreover, topical GlcCer induced mitogenesis is both dose dependent and hexose specific in young (1-2 mo old) animals, and remains effective in aged (< or = 24 mo old) animals. Furthermore, the CBE induced increase in DNA synthesis in aged epidermis is sufficient to produce epidermal hyperplasia. Finally, although an increased GlcCer:Cer ratio can alter stratum corneum barrier function and membrane structure, neither stratum corneum function nor extracellular membrane structure change under these experimental conditions, and therefore the mitogenic effects of increased epidermal GlcCer cannot be attributed to effects on the stratum corneum. These results show that: (i) elevations in endogenous GlcCer are mitogenic for aged as well as young murine epidermis; (ii) topical GlcCer is also mitogenic when delivered in an enhancing vehicle; and (iii) despite the putative importance of epidermal DNA synthesis for barrier homeostasis, these mitogenic alterations do not alter stratum corneum function.

Administration, Topical↗
PubMed1997

Epidermal injury stimulates prenylation in the epidermis of hairless mice.

Isoprenylation is the covalent attachment of isoprenyl groups, intermediates of the cholesterol biosynthesis pathway, to carboxyl terminal cysteine residues of proteins. Numerous proteins are isoprenylated including small GTP binding proteins, trimeric G proteins, and nuclear lamins, and these prenylated proteins regulate a variety of cell functions, including cell growth, cytokinesis, and differentiation. Here, we quantitated protein prenylation and determined which proteins are prenylated in the epidermis of hairless mice by radiolabeling with 3H-mevalonolactone following acute or chronic epidermal injury. In normal epidermis, four major radiolabeled bands, with molecular weights of 17-26, 48, 54, and 68 kDa, were observed. The levels of each of these bands increased by 24-63% 16 h following acute epidermal injury induced by topical acetone treatment or tape stripping, returning to normal by 24 h. On 2D gel electrophoresis, there were no major differences between the patterns of labeling following barrier disruption. Subacute epidermal injury induced by either acetone or tape stripping twice a day for 7 days and chronic injury induced by feeding an essential fatty acid-deficient (EFAD) diet, also resulted in a significant increase in protein prenylation. As with an acute injury, SDS-PAGE and 2D gel electrophoresis did not reveal marked differences in the pattern of protein prenylation. These results demonstrate that the prenylation of proteins in the epidermis is stimulated by injury, suggesting that one or more of these prenylated species may be important in epidermal proliferation or differentiation.

Alkyl and Aryl Transferases↗
PubMed1996

Decreased epidermal lipid synthesis accounts for altered barrier function in aged mice.

The epidermis of aged mice displays decreased stratum corneum (SC) lipid content and decreased extracellular bilayers, which result in impaired barrier recovery following the solvent treatment or tape stripping. We assessed the role of altered lipid synthesis as the cause of the abnormal barrier and lipid content in aged epidermis, both under basal conditions and in response to acute barrier perturbations. In aged epidermis ( > or = 18 months), synthesis of one of the three key lipid classes (cholesterol) is decreased under basal conditions, and sterologenesis fails to attain the levels reached in young epidermis following comparable acute perturbations. In contrast, fatty acid and sphingolipid synthesis in aged epidermis increase sufficiently to approach the levels attained in stimulated young epidermis. The abnormalities in sterologenesis in aged epidermis are paralleled by a decrease in activity of its rate-limiting enzyme, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, under basal conditions, and enzyme activity also fails to increase as much as in young epidermis after barrier disruption. That defective lipid generation contributes to the barrier defect is shown directly by the ability of either a cholesterol-containing mixture of SC lipids or cholesterol alone to enhance barrier recovery. Finally, lipid-induced acceleration of barrier recovery in aged epidermis correlates with repletion of the extracellular spaces with normal lamellar structures. Thus, a deficiency in lipid synthesis, particularly in cholesterologenesis, accounts for the barrier abnormality in aged epidermis.

Aging↗
PubMed1995

Exogenous nonphysiologic vs physiologic lipids. Divergent mechanisms for correction of permeability barrier dysfunction.

BACKGROUND AND DESIGN: Although barrier function requires cholesterol, free fatty acids, and ceramides, applications of one or two of these lipids to damaged skin impedes barrier recovery, while equimolar mixtures allow normal recovery. Both incomplete and complete mixtures appear to be internalized within the epidermal nucleated layers, followed by the secretion of abnormal vs normal lamellar body contents, respectively. We compared the ability of complete physiologic lipid mixtures vs a nonmetabolized hydrophobic lipid, petrolatum, to repair the barrier and the requirement for intracellular processing of these lipids within the epidermis. RESULTS: Neat petrolatum, which remains restricted to the stratum corneum, produces more rapid improvement in barrier function than the solvent-dispersed physiologic lipids, and its effects are not altered by coapplication of either monensin or brefeldin A (both from Sigma Chemical Co, St Louis, Mo), known inhibitors of exocytosis and organellogenesis, respectively. In contrast, the physiologic lipids enter the nucleated layers in substantial amounts and require longer to produce barrier recovery. Whereas monensin blocks their ability to facilitate barrier recovery, the physiologic lipids overcome brefeldin A-induced delays in barrier recovery, bypassing the subcellular site of brefeldin A blockade, normalizing both lamellar body contents and intercellular bilayers. CONCLUSIONS: While petrolatum remains restricted to the stratum corneum, physiologic lipid mixtures influence barrier recovery after transport to subjacent, nucleated layers, followed by internalization, apparent transport to the distal Golgi apparatus, and incorporation into nascent lamellar bodies.

Animals↗
PubMed1995

The aged epidermal permeability barrier. Structural, functional, and lipid biochemical abnormalities in humans and a senescent murine model.

Aged epidermis displays altered drug permeability, increased susceptibility to irritant contact dermatitis, and often severe xerosis, suggesting compromise of the aged epidermal barrier. To delineate the functional, structural, and lipid biochemical basis of epidermal aging, we compared barrier function in young (20-30 yr) vs aged (> 80 yr) human subjects, and in a murine model. Baseline transepidermal water loss in both aged humans and senescent mice was subnormal. However, the aged barrier was perturbed more readily with either acetone or tape stripping (18 +/- 2 strippings vs 31 +/- 5 strippings in aged vs young human subjects, respectively). Moreover, after either acetone treatment or tape stripping, the barrier recovered more slowly in aged than in young human subjects (50 and 80% recovery at 24 and 72 h, respectively, in young subjects vs 15% recovery at 24 h in aged subjects), followed by a further delay over the next 6 d. Similar differences in barrier recovery were seen in senescent vs young mice. Although the total lipid content was decreased in the stratum corneum of aged mice (approximately 30%), the distribution of ceramides (including ceramide 1), cholesterol, and free fatty acids was unchanged. Moreover, a normal complement of esterified, very long-chain fatty acids was present. Finally, stratum corneum lamellar bilayers displayed normal substructure and dimensions, but were focally decreased in number, with decreased secretion of lamellar body contents. Thus, assessment of barrier function in aged epidermis under basal conditions is misleading, since both barrier integrity and barrier repair are markedly abnormal. These functional changes can be attributed to a global deficiency in all key stratum corneum lipids, resulting in decreased lamellar bilayers in the stratum corneum interstices. This constellation of findings may explain the increased susceptibility of intrinsically aged skin to exogenous and environmental insults.

Acetone↗
PubMed1992

Exogenous origin of n-alkanes in pathologic scale.

BACKGROUND: Although n-alkanes accumulate in some disorders of cornification, recent studies using radioactive carbon 14 content by accelerator mass spectrometry point to an exogenous origin for alkanes in normal stratum corneum, and their derivation in congenital ichthyosiform erythroderma remains controversial. DESIGN AND RESULTS: Using 14C content to measure sample age, the n-alkane fractions from two patients with congenital ichthyosiform erythroderma contained no detectable contemporary materials. By electron microscopy, alkane-enriched emollients (petrolatum [Vaseline]) permeated to all levels of stratum corneum of hairless mice, expanding the intercellular domains and distorting membrane bilayers. Similar ultrastructural changes were also observed in the stratum corneum of patients with congenital ichthyosiform erythroderma. When alkanes were excluded, no differences in lipid content were evident between two forms of autosomal recessive ichthyosis. CONCLUSIONS: These data demonstrate that scale n-alkanes in disorders of cornification derive from environmental sources and indicate the pervasiveness of petroleum-based emollients in skin. Therefore, epidermal lipid analyses must be interpreted with caution. However, these studies do not rule out an important therapeutic and/or pathogenic role for exogenous n-alkanes in skin.

Adult↗
PubMed1991

The lovastatin-treated rodent: a new model of barrier disruption and epidermal hyperplasia.

Recent studies have linked epidermal cholesterol synthesis with maintenance of the permeability barrier. To assess directly the importance of cholesterol synthesis, we applied lovastatin, a potent inhibitor of cholesterol synthesis, to hairless mouse skin. Transepidermal water loss (TEWL) began to increase after four to six daily applications. Co-application of cholesterol blocked the expected increase in TEWL, demonstrating the importance of cholesterol for development of the lesion. The histology of lovastatin-treated skin revealed epidermal hyperplasia, accompanied by accelerated DNA synthesis. Whereas cholesterol synthesis initially was reduced in lovastatin-treated epidermis, with further treatment cholesterol synthesis normalized, while fatty acid synthesis accelerated greatly. Although the total free sterol content of lovastatin-treated epidermis remained normal, the fatty acid content increased coincident with barrier disruption. Finally, morphologic abnormalities of both lamellar body structure and their deposited, intercellular contents occurred coincident with the emerging biochemical abnormalities. Thus, the abnormal barrier function in this model can be ascribed to an initial inhibition of epidermal sterol synthesis followed by an alteration in cholesterol and fatty acid synthesis, leading to an imbalance in stratum corneum lipid composition and abnormal membrane bilayer structure.

Animals↗
PubMed1990

Effect of prior heat shock on heat resistance of Listeria monocytogenes in meat.

The effect of prior heat shock on the thermal resistance of Listeria monocytogenes in meat was investigated. A sausage mix inoculated with approximately 10(7) L. monocytogenes per g was initially subjected to a heat shock temperature of 48 degrees C before being heated at a final test temperature of 62 or 64 degrees C. Although cells heat shocked at 48 degrees C for 30 or 60 min did not show a significant increase in thermotolerance as compared with control cells (non-heat shocked), bacteria heat shocked for 120 min did, showing an average 2.4-fold increase in the D64 degrees C value. Heat-shocked cells shifted to 4 degrees C appeared to maintain their thermotolerance for at least 24 h after heat shock.

Colony Count, Microbial↗
PubMed1990

Cholesterol synthesis is required for cutaneous barrier function in mice.

Previous studies have shown that topical acetone treatment results in the removal of stratum corneum lipids and disruption of the permeability barrier. This disruption stimulates epidermal lipid synthesis which is associated with the rapid restoration of stratum corneum lipids and barrier function. The aim of this study was to determine the role of cutaneous cholesterol synthesis in the barrier recovery. Here we show that topical lovastatin, a competitive inhibitor of HMG CoA reductase, inhibits cholesterol synthesis. After acetone disruption of the barrier, the normal rapid return of cholesterol to the stratum corneum and recovery of barrier function is impaired in animals treated topically with lovastatin. When lovastatin animals are simultaneously treated topically with either mevalonate, the immediate product of HMG CoA reductase, or cholesterol, the final end product of the pathway, the recovery of the barrier is normalized. Lovastatin resulted in the delayed secretion and abnormal appearance of lamellar bodies. These results provide the first evidence demonstrating that cholesterol synthesis is required for the maintenance of barrier structure and function and suggests a crucial role for cholesterol synthesis in allowing for terrestrial existence.

Animals↗
PubMed1989

Avian epidermal differentiation. II. Adaptive response of permeability barrier to water deprivation and replenishment.

Zebra Finches are the epitome of desert-adapted avian species; i.e. they are able to survive without drinking water for over a year. Whereas transepidermal water loss (TEWL) in naked Zebra Finch nestlings is lower than in adults, and desert adaptation is accompanied by intercellular deposition of epidermal multigranular body (MGB) contents, MGB secretion is reduced as nestlings mature into feathered adults, indicative of less stringent barrier requirements. Here, removal of drinking water resulted in increased intercellular deposition of MGB contents, and TEWL progressively decreased. In contrast, MGB intercellular deposition decreased when birds were rehydrated, with TEWL returning towards normal within 5 days of rehydration. Finally, water-deprivation caused significant changes in epidermal lipid composition that returned toward control levels with rehydration. These studies show that adult Zebra Finches adapt to xeric stress by increased secretion of multigranular bodies resulting in reduced TEWL.

Adaptation, Physiological↗
PubMed1989

Antimicrobial activity of stratum corneum lipids from normal and essential fatty acid-deficient mice.

Among the cutaneous effects of an essential fatty acid deficient (EFAD) diet are hyperdesquamation, increased transepidermal water loss (TEWL), and altered lipid profiles, characteristics also common to inflammatory dermatoses. Because fatty acids are antimicrobial, we examined the indigenous skin flora of normal and EFAD hairless mice, and compared the antimicrobial efficacy of lipids extracted from their stratum corneum. EFAD mice supported 100-fold more bacteria than normal mice, and were the only group from which Staphylococcus aureus were routinely isolated. Despite this greater carriage, in vitro experiments demonstrated that EFAD lipids are more lethal than normal lipids against Streptococcus pyogenes, S. aureus, S. epidermidis, Micrococcus sp., and a coryneform. Skin fungi were equally susceptible to both extracts. After thin layer chromatography, the most active fractions were found to be glycosphingolipids and phospholipids. EFAD extracts had 35% more free fatty acids and 75% more glycosphingolipids; normal extracts had more triglycerides and phospholipids. S. aureus strain 502A survived equally well on EFAD as on normal mice. Normal lipids applied on EFAD mice had no additional effect, but EFAD lipids on normal mice brought about a 35% reduction of the inoculated bacteria. If the mice were pretreated with alcohol, carriage of strain 502A was reduced by 71%. If instead the mice were previously washed with acetone to increase TEWL, a 97% reduction of the staphylococcus occurred. The application of normal flora to such acetone-washed mice decreased the efficacy to 76%. EFAD and normal lipids on human subjects were equally ineffective in eliminating strain 502A.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Lipid content and metabolism of human keratinocyte cultures grown at the air-medium interface.

The differentiation of human keratinocytes in most culture systems is incomplete; e.g., lamellar bodies, the characteristic lipid-delivery organelles of epidermis, are not present. Moreover, their lipid profile does not reflect the distinctive composition found in cornifying epidermis. In contrast, keratinocytes that grow at an air-medium interface exhibit more complete differentiation. In this study, we compared the elaboration of lamellar bodies, the lipid content, and the lipid metabolism of human keratinocytes, cultured both under standard immersed conditions and after lifting to an air-medium interface. Whereas submerged cultures neither elaborated lamellar bodies nor displayed a lipid distribution characteristic of cornifying epidermis, lifted cultures displayed advanced cornification, elaborated lamellar bodies which were deposited in intercellular domains, and a lipid profile more typical of cornifying epidermis. Moreover, lipid biosynthesis was 5-10-fold more active in lifted than in immersed cultures, and was not inhibited by exogenous lipoproteins. These findings are consistent with recent studies that demonstrate both high rates of lipogenesis in differentiating layers of the epidermis as well as autonomy of lipogenesis from the influence of circulating lipoproteins. Thus, the lipid content and metabolism of human keratinocyte cultures, grown at an air-medium interface, demonstrate features that simulate the epidermis.

Cell Differentiation↗
PubMed1988

Membrane structural alterations in murine stratum corneum: relationship to the localization of polar lipids and phospholipases.

During the formation of the mammalian epidermal permeability barrier, lipids are sequestered in the stratum corneum intercellular spaces, transforming from a relatively polar lipid mixture to predominantly nonpolar species. Certain lipid catabolic enzymes, which co-localize with these lipids, may regulate this process. In order to localize the sites within the outer epidermis where polar lipids are catabolized, and their relationship to the alterations in membrane structure that occur in these layers, we compared the biochemical localization of polar lipids, the ultrastructure, and freeze-fracture morphology, as well as the localization of phospholipases within the outer epidermis. Both histochemical staining of frozen sections and biochemical studies of protease- and tape-stripped whole stratum corneum demonstrated small amounts of polar lipids in the stratum compactum, while in contrast, the stratum disjunctum was devoid of both phospholipids and glycosphingolipids. Phospholipase activity was present within lamellar bodies, among secreted lamellar body disks at the granular-cornified layer interface, and within the intercellular spaces of the stratum compactum. Both the depletion of polar lipids from the stratum compactum and deletion of these substances from the stratum disjunctum correlated with sequential changes in membrane structure observed by transmission electron microscopy and freeze-fracture. Thus, a phospholipase-mediated attack on phospholipids (with a parallel assault by other lipid catabolic enzymes on other polar species), may induce both the initial fusion and elongation of lamellar body disks and the subsequent formation of the hydrophobic membrane bilayers found in the mid-to-outer stratum corneum. These studies also may require modification of traditional views of the stratum corneum as a metabolically inert tissue, revealing its intercellular lipid domains to be partially in an active state of flux.

Animals↗
PubMed1988

Family violence. Development of a master's level specialty track in family abuse.

Family violence is a societal reality. It will not disappear if society closes its eyes and fails to recognize its existence. When this is done, the abusive cycle is perpetuated. The specialty track described in this article was the nation's first graduate nursing educational program in the area of Family Violence. This program demonstrates nursing's potential contribution to the development of competent professionals with the expertise necessary to intervene in the abusive cycle.

Adult↗