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S Grayson

Publications and source records attributed to S Grayson.

At least 19 recordsLinked to original sources
PubMed1998

Barrier recovery is impeded at neutral pH, independent of ionic effects: implications for extracellular lipid processing.

Epidermal permeability barrier homeostasis requires the postsecretory processing of polar lipid precursors into nonpolar lipid products within the stratum corneum (SC) interstices by a family of lipid hydrolases. A specific requirement for beta-glucocerebrosidase (beta-GlcCer'ase), which exhibits a distinct acidic pH optimum, is particularly well documented. Therefore, we sought to determine whether the recovery of the barrier after acute insults requires acidification of the SC. We examined permeability barrier recovery by assessing changes in transepidermal water loss (TEWL), SC membrane ultrastructure utilizing ruthenium tetroxide (RuO4) postfixation, and beta-GlcCer'ase activity by in situ zymography at an acidic vs neutral pH. Barrier recovery proceeded normally when acetone-treated skin was exposed to solutions buffered to an acidic pH. In contrast, the initiation of barrier recovery was slowed when treated skin was exposed to neutral or alkaline pH, regardless of buffer composition. In addition, enhancement of the alkaline buffer-induced delay in barrier recovery occurred with Ca2+ and K+ inclusion in the buffer. Moreover, the pH-dependent alteration in barrier recovery appeared to occur through a mechanism that was independent of Ca(2+)- or K(+)-controlled lamellar body secretion, since both the formation and secretion of lamellar bodies proceeded comparably at pH 5.5 and pH 7.4. In contrast, exposure to pH 7.4 (but not pH 5.5) resulted in both the persistence of immature, extracellular lamellar membrane structures, and a marked decrease in the in situ activity of beta-GlcCer'ase. These results suggest first that an acidic extracellular pH is necessary for the initiation of barrier recovery, and second that the delay in barrier recovery is a consequence of inhibition of postsecretory lipid processing.

Animals↗
PubMed1990

Dispersal of proteolipid macroaggregates with trifluoroacetic acid and analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis.

The propensity of highly purified proteolipids to form macroaggregates in aqueous solutions, especially when heated with sodium dodecyl sulfate (SDS), with or without thiol reagents, has made qualitative and quantitative analyses of individual species by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) difficult and unreliable. Comparisons of proteolipid profiles from liver, brain, and cultured human keratinocytes demonstrate that 40-72% of the total proteolipid in SDS-PAGE sample buffer is in the form of macroaggregates. Treatment of proteolipids with neat trifluoroacetic acid (TFA) followed by removal of the TFA and incubation in cold SDS-PAGE sample buffer causes complete dispersal of the macroaggregates and allows recovery of virtually all of the proteolipid applied to gels (increasing yields by as much as 3.6 times, depending on tissue type). Gels of TFA-treated samples display differences not only in the relative amounts of individual species but also in novel species not found in untreated samples. Eluted macroaggregates treated with TFA display the same SDS-PAGE banding profiles as TFA-treated whole proteolipids. Hence, routine TFA treatment of proteolipids prior to SDS-PAGE increases total proteolipid yields, allows reliable quantitation of individual apoprotein species, and reveals species previously obscured by the formation of macroaggregates.

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

Human epidermal proteolipids: isolation, partial characterization, and subcellular localization.

Since the first description of organic-soluble proteins (i.e., proteolipids), much attention has focused on the isolation, purification, characterization, localization, and function of these intrinsic membrane proteins in a variety of different tissues. Using a rapid purification scheme, which allowed the transfer of organic-soluble proteolipids to aqueous phases, we have isolated proteolipids from cultured human keratinocytes and human epidermis for the first time. A partial characterization of these proteolipids, including molecular-weight determination by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), amino acid composition, and an N-terminal sequencing revealed a preponderance of hydrophobic amino acids (greater than 60% overall and greater than 78% in N-terminal sequence), typical of other proteolipids. The composition of fatty acids, covalently bound to whole purified apoprotein fractions, displayed a predominance of palmitic greater than oleic greater than stearic acids. Comparison of the molecular species of proteolipids isolated from whole epidermis with those obtained from keratinocyte cultures by SDS-PAGE revealed a comparable spectrum of apoprotein species. Finally, subcellular fractionation of cultured keratinocytes, used to localize proteolipids to specific cellular compartments, suggested that one of the major apoprotein species (30 kD) is present in mitochondria, whereas the lower molecular weight species are localized in plasma membrane-enriched fractions. Although evidence is lacking for a specific function(s) of this class of molecules in the epidermis, the hypothesis that it plays a role in epidermal differentiation, for example, as constituents of calcium and/or proton pumps, is discussed.

Amino Acids↗
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↗
PubMed1987

Avian sebokeratocytes and marine mammal lipokeratinocytes: structural, lipid biochemical, and functional considerations.

In terrestrial mammals, stratum corneum lipids derive from two sources: deposition of lamellar body lipids in stratum corneum interstices and excretion of sebaceous lipids onto the skin surface, resulting in a two-compartment ("bricks and mortar") system of lipid-depleted cells surrounded by lipid-enriched intercellular spaces. In contrast, intracellular lipid droplets, normally not present in the epidermis of terrestrial mammals, are prominent in avian and marine mammal epidermis (cetaceans, manatees). We compared the transepidermal water loss, ultrastructure, and lipid biochemistry of the viable epidermis and stratum corneum of pigeon apterium, fledgling (featherless) zebra finches, painted storks, cetaceans, and manatees to those of humans and mice. Marine mammals possess an even more extensive lamellar-body secretory system than do terrestrial mammals; and lamellar-body contents, as in terrestrials, are secreted into the stratum corneum interstices. In cetaceans, however, glycolipids, but not ceramides, persist into the stratum corneum; whereas in manatees, glycolipids are replaced by ceramides, as in terrestrial mammals. Acylglucosylceramides, thought to be critical for lamellar-body deposition and barrier function in terrestrial mammals, are present in manatees but virtually absent in cetaceans, a finding that indicates that they are not obligate constituents of lamellar-body-derived membrane structures. Moreover, cetaceans do not elaborate the very long-chain, saturated N-acyl fatty acids that abound in terrestrial mammalian acylglucosylceramides. Furthermore, cold-water marine mammals generate large, intracellular neutral lipid droplets not found in terrestrial and warm-water marine mammals; these lipid droplets persist into the stratum corneum, suggesting thermogenesis, flotation, and/or cryoprotectant functions. Avians generate distinctive multigranular bodies that may be secreted into the intercellular spaces under xerotic conditions, as in zebra fledglings; ordinarily, however, the internal lamellae and limiting membranes deteriorate, generating intracellular neutral lipid droplets. The sphingolipid composition of avian stratum corneum is intermediate between terrestrials and cetaceans (approximately equal to 50% glycolipids), with triglycerides present in abundance. In the midstratum corneum of avians, neutral lipid droplets are released into the interstices, forming a large extracellular, lipid-enriched compartment, surrounding wafer-thin corneocytes, with a paucity of both lipid and keratin ("plates-and-mortar" rather than the "bricks-and-mortar" of mammals).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Free sterol metabolism and low density lipoprotein receptor expression as differentiation markers of cultured human keratinocytes.

In contrast to most tissues, epidermis and its derivatives appear to lack low density lipoprotein (LDL) receptors and exhibit sterologenesis rates unaffected by circulating lipoprotein (LP) cholesterol content. Since LDL receptors have been demonstrated in both cultured squamous cell carcinoma cells and human foreskin keratinocytes, when maintained in low-calcium media, LDL receptor expression may be related to keratinocyte differentiation. We compared receptor binding and internalization of LDL-gold in normal keratinocytes at different stages of growth at physiological calcium concentrations (early, 3-5 days; preconfluent, 6-10 days; postconfluent, 12-17 days), and correlated receptor expression with sterologenesis in LP-replete vs.-depleted media. Whereas in early cultures about 60% of sterologenesis was LP dependent, this fraction declined in preconfluent and confluent cultures despite continued culture growth and little decline in total sterologenesis. Accordingly, LDL receptors were most evident in early cultures, declining in preconfluent cultures in parallel with the decrease in LP-dependent sterol synthesis. In contrast, sterologenesis in human foreskin fibroblasts was profoundly influenced by exogenous LP at all stages of confluence; total and LP-dependent sterologenesis declined in parallel with growth cessation. These studies represent the first demonstration that normal keratinocytes express functional LDL receptors at physiologic calcium concentrations. Moreover, they demonstrate that LDL receptor expression in keratinocytes, in contrast to fibroblasts, can only in part be attributed to growth requirements. Instead, loss of LDL receptor expression serves as a distinctive marker of keratinocyte differentiation and may reflect the specific functional requirements of the epidermis in vivo.

Acetates↗
PubMed1987

Low density lipoprotein receptor expression on keratinocytes in normal and psoriatic epidermis.

Biochemical and morphologic studies on the interaction of low density lipoprotein (LDL) with cultured normal keratinocytes and squamous carcinoma cells have shown a negative correlation between LDL receptor activity and terminal differentiation of the epidermal cells [Ponec M et al, J Invest Dermatol 83:436-440, 1984 and Vermeer, BJ et al, J Invest Dermatol 86:195-200, 1986]. Whether such in vitro studies pertain to the epidermis in vivo is not known. To obtain information on the distribution of LDL receptors in the epidermis in situ, morphologic studies were performed using LDL-gold as an ultrastructural marker. When freshly isolated mouse and human epidermal cells were incubated with LDL-gold complexes, only keratinocytes with the morphologic characteristics of basal cells showed binding and uptake of LDL-gold. No LDL receptor activity was found on Langerhans cells, melanocytes or highly differentiated keratinocytes. Since cell separation techniques can destroy receptors, the staphylococcal epidermolytic toxin was utilized to produce intercellular and intra-epithelial splitting of the epidermis. In preparations of both normal mouse and human epidermis, LDL-gold binding was restricted to basal cells and a few suprabasal keratinocytes. In contrast, in psoriatic epidermis, and to a lesser extent, essential fatty acid-deficient mouse epidermis, cells in the stratum spinosum showed abundant LDL-gold binding. Thus LDL-gold may be a useful marker for epidermal differentiation.

Animals↗
PubMed1986

Lipokeratinocytes of the epidermis of a cetacean (Phocena phocena). Histochemistry, ultrastructure, and lipid composition.

Biochemical and ultrastructural analysis of epidermis from the porpoise, Phocena phocena, revealed certain similarities and differences between cetaceans and terrestrial mammals. The predominant cell of cetacean epidermis, not found in normal terrestrial mammals, is a lipokeratinocyte, which elaborates not only keratin filaments, but also two types of lipid organelles: first, lamellar bodies, morphologically identical to those of terrestrial mammals, are elaborated in great abundance in all suprabasal epidermal layers, forming intercellular lipid bilayers in the stratum corneum interstices: and second, non-membrane-bounded droplets appear and persist in all epidermal layers. Although the porpoise lipokeratinocyte morphologically resembles the sebokeratocyte of avians in certain respects, non-membrane-bounded lipid droplets are not released into the intercorneocyte space as they are in avian stratum corneum. Whereas phospholipid/neutral lipid gradients are similar in porpoise and terrestrial mammals, PAS-positive glycoconjugates, specifically glycosphingolipids, are retained in porpoise stratum corneum, but lost from these layers in terrestrials. The novel, non-polar acylglucosyl-ceramides, which also are lost during cornification in terrestrial mammals, are retained in porpoise stratum corneum. The lipid components of porpoise lipokeratinocytes appear to subserve not only barrier function in a hypertonic milieu, but also underlie the unique buoyancy, streamlining, insulatory, and caloric properties exhibited as adaptations to the cetacean habitat.

Adaptation, Physiological↗
PubMed1986

Cytochemical and biochemical localization of lipase and sphingomyelinase activity in mammalian epidermis.

Despite a wealth of new information on epidermal lipids and their role in permeability barrier function and desquamation, little is known about the location of the enzymes that regulate their catabolism. In this study we have localized lipase (triacylglycerol hydrolase) and sphingomyelinase in the outer epidermis simultaneously by cytochemical and cell fractionation techniques. Aldehyde-fixed tissues (100-microns slices) incubated in either Tween 85 or triolein plus taurocholate/calcium chloride-containing buffer, pH 7.2 or 4.5, were then exposed to lead to form insoluble soaps, and processed for electron microscopy. Simultaneously, cell homogenates and isolated lamellar body fractions were incubated with methylumbelliferyl oleate under similar conditions, with released, free methylumbelliferone serving as an index of lipase activity. On electron microscopy and cell fractionation, both lipase and sphingomyelinase were localized primarily to intercellular domains in the stratum corneum. In the stratum granulosum lipases were found, both ultrastructurally and biochemically, in lamellar bodies and ultrastructurally in both the perinuclear cistern and mitochondria. In summary, these studies: by demonstrating lipid-catabolic enzymes in the intercellular domains of the stratum corneum, lend further support to the 2-compartment model of the stratum corneum; provide new information about the location of lipid-catabolic enzymes in differentiating epidermis; and provide insights about how lipids are processed during permeability barrier formation and desquamation.

Adult↗
PubMed1985

Ionic calcium reservoirs in mammalian epidermis: ultrastructural localization by ion-capture cytochemistry.

Although calcium ions have been shown to regulate the differentiation of keratinocytes in vitro, the role of divalent cations in vivo is not known. Prior attempts to localize divalent cations in epithelial tissues have been impeded by a lack of specificity of ultrastructural techniques, as well as translocation of precipitates within tissues. The availability of an improved cytochemical method (oxalate-pyroantimonate technique) has facilitated more precise, reliable localization of calcium. When this technique (+/- 10 mM EGTA) was applied to neonatal mouse epidermis, Ca++-containing precipitates localized primarily within the cytosol, mitochondria, and nuclear chromatin of some basal and spinous cells, suggesting a possible relationship of Ca++ with the cell cycle. In the lower granular layer, progressively more Ca++ precipitates appeared intercellularly, with the only intracellular Ca++ localized within mitochondria and lamellar bodies (limiting membranes and discs). The most apical granular cells always demonstrated dense extracellular deposits, and high intracellular Ca++, free in the cytosol. The extruded contents of lamellar bodies, at the granular-cornified layer interface, also demonstrated significant amounts of Ca++-containing precipitates between the lamellar discs. Although some corneocytes in the lower stratum corneum demonstrated intracellular precipitates, most were deviod of Ca++. The striking intercellular Ca++ accumulation in the mid granular layer, coupled with Ca++ influx in the upper granular layer, supports the view that changes in intracellular Ca++ may regulate epidermal differentiation. Finally, the association of Ca++ with lamellar body disc membranes and contents suggests that divalent cations may contribute to both lamellar body secretion and to the formation of intercorneocyte membrane bilayers.

Animals↗
PubMed1985

Lamellar body-enriched fractions from neonatal mice: preparative techniques and partial characterization.

Several problems have frustrated the isolation of lamellar bodies (LB) from mammalian epidermis. We obtained pellets enriched in intact LB by utilizing the staphylococcal epidermolytic toxin to provide intact, outer epidermal sheets, by controlled homogenization in a cell disrupter, and by passage of homogenates through a graded series of nuclepore filters (Science 221:962, 1983). Such preparations contained more intact LB than did fractions prepared by a variety of differential or sucrose/metrizamide discontinuous centrifugation methods. Initial characterization of the enzymatic content of this fraction revealed it to be enriched in certain hydrolytic enzymes (acid phosphatase, carboxypeptidase, cathepsin B, acid lipase, sphingomyelinase, and phospholipase A), but strikingly depleted in all sulfatases, beta-glucuronidase, and the non-lysosomal protease, plasminogen activator. Thus, LB show some properties of lysosomes, although certain characteristic lysosomal enzymes are strikingly absent. Lamellar body fractions contained 2-3 times more lipid per unit weight than did homogenates, and were enriched in phospholipids, free sterols, and glycosphingolipids, but not in other neutral lipids or ceramides. In summary, whereas some of the enzymes in LB could participate in the metabolism of LB lipid precursors to hydrophobic barrier constituents, others may attack intercellular constituents, ultimately resulting in desquamation. The lipid profile of these organelles suggests that they deliver precursors of permeability barrier lipids to intercellular domains.

Acid Phosphatase↗
PubMed1984

Stratum corneum lipids in disorders of cornification. Steroid sulfatase and cholesterol sulfate in normal desquamation and the pathogenesis of recessive X-linked ichthyosis.

The pathological scaling in recessive x-linked ichthyosis is associated with accumulation of abnormal quantities of cholesterol sulfate in stratum corneum (J. Clin. Invest. 68:1404-1410, 1981). To determine whether or not cholesterol sulfate accumulates in recessive x-linked ichthyosis as a direct result of the missing enzyme, steroid sulfatase, we quantitated both steroid sulfatase and its substrate, we quantitated both steroid sulfatase and its substrate, cholesterol sulfate, in different epidermal strata, as well as within stratum corneum subcellular fractions obtained from normal human and neonatal mouse epidermis and from patients with recessive x-linked ichthyosis. In normal human and mouse epidermis, steroid sulfatase activity peaked in the stratum granulosum and stratum corneum, and negligible activity was detectable in lower epidermal layers. In contrast, in recessive x-linked ichthyosis epidermis, enzyme levels were virtually undetectable at all levels. In normal human stratum corneum, up to 10 times more steroid sulfatase activity was present in purified peripheral membrane preparations than in the whole tissue. Whereas in normal human epidermis cholesterol sulfate levels were lowest in the basal/spinous layer, and highest in the stratum granulosum, in recessive x-linked ichthyosis the levels were only slightly higher in the lower epidermis, but continued to climb in the stratum corneum. In both normal and in recessive x-linked ichthyosis stratum corneum, cholesterol sulfate appeared primarily within membrane domains, paralleling the pattern of steroid sulfatase localization. Finally, the role of excess cholesterol sulfate in the pathogenesis of recessive x-linked ichthyosis was directly tested by topical applications of this substance, which produced visible scaling in hairless mice in parallel to an increased cholesterol sulfate content of the stratum corneum. These results demonstrate an intimate relationship between steroid sulfatase and cholesterol sulfate in normal epidermis: both are concentrated in the outer epidermis (stratum corneum and stratum granulosum), and both are localized to membrane domains. Presumably, as a result of this distribution pattern, continued enzymatic degradation of substrate occurs in normal epidermis, thereby preventing excessive accumulation of cholesterol sulfate. In contrast, in recessive x-linked ichthyosis, degradation of cholesterol sulfate does not occur and cholesterol sulfate accumulates specifically in the stratum corneum, where it produces visible scale.

Administration, Topical↗
PubMed1983

Isolation of lamellar bodies from neonatal mouse epidermis by selective sequential filtration.

Isolation of epidermal lamellar bodies has presented a challenge because pressures required to homogenize keratinocytes can destroy these organelles and because the lamellar body readily releases its contents during prolonged isolation procedures. In an attempt to isolate lamellar bodies, sheets of intact stratum corneum and stratum granulosum were obtained from neonatal mice with highly purified staphylococcal epidermolytic toxin, disrupted, and passed through a series of filters. The final filtrate was rich in intact lamellar bodies and contained variable amounts of ribosomes and other vesicular structures. Availability of a highly purified lamellar body preparation from postnatal epidermis should help to clarify the role of this organelle in epidermal function. The technique of selective, sequential filtration represents a new approach to cell fractionation that may have wide applications in cell biology and biochemistry.

Animals↗
PubMed1983

X-ray diffraction analysis of stratum corneum membrane couplets.

X-ray diffraction analysis was done on the membrane couplets isolated from newborn mouse stratum corneum. The same lipid reflections were observed for whole stratum corneum and couplets, adding further support to the thesis that stratum corneum lipid is intercellular in location rather than associated with the intracellular filamentous protein.

Animals↗
PubMed1981

Influence of topical and systemic retinoids on basal cell carcinoma cell membranes.

Although much recent work suggests that retinoids can prevent the development of epithelial cancers, their mechanism of action remains unknown. Since malignancy has been associated with alterations in gap junctions, desmosomes, microfilaments, and hemidesmosomes, the authors examined freeze-fracture replicas and thin sections of cell membranes of: (1) 11 basal cell cancers (BCC) treated twice daily for two weeks with topical 1.0% retinoid acid (RA); (2) 21 BCC treated for 2 to 17 weeks with oral 13-cis retinoic acid (CRA) (1.0-8.0 mg/kg/day); and (3) 17 BCC prior to retinoid treatment and/or after applications of vehicle alone. Both thin sections and replicas were examined and photographed in a single-blind fashion, and the density and size distribution of gap junctions and desmosomes were computed planimetrically. Topical RA treatment induced a two-fold increase in gap junction density (P less than 0.025) over controls. In contrast, RA produced a concurrent = 35% decrease in desmosome density. Systemic CRA did not significantly alter either gap junction or desmosome density or size. Finally, neither RA nor CRA treatment appeared to influence hemidesmosome or microfilament populations. Structural changes in both treatment groups did not correlate with either tumor regression or inflammation. Topical and systemic retinoids may exert their antineoplastic activity by different cellular mechanisms.

Administration, Topical↗
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↗