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G K Menon

Publications and source records attributed to G K Menon.

45 records · Page 3Linked to original sources
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↗
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

Avian epidermal differentiation: role of lipids in permeability barrier formation.

Though avian skin is known to possess a highly lipogenic epidermis, little is known about its permeability barrier function. We correlated epidermal barrier function, fine structure and lipid biochemistry in the pigeon, Columbia livia, and compared these features with terrestrial mammalian systems. Whereas barrier function, as assessed by transepidermal water loss was not as efficient as in mammals, both groups shared certain morphological features including substantial compartmentalization of lipids in stratum corneum intercellular domains. Avian intercellular lipids derive from extrusion of intracellular non-membrane-bound droplets from lowermost corneocytes, rather than by secretion of lamellar discs from multigranular bodies, as previously reported in some avians, and in mammals. Instead, both the internal lamellae and the limiting membranes of multigranular bodies appear to degenerate, leading to the formation of non-membrane-bound droplets. The lipid content of avian epidermis and stratum corneum demonstrates important similarities to terrestrial mammals, i.e. abundant sphingolipids, a paucity of phospholipids, and abundant neutral lipids, but also certain striking differences, i.e. persistence of glycosphingolipids and triglycerides into the stratum corneum. Thus, avian stratum corneum forms a two-compartment system of lipid-depleted cells embedded in non-polar-lipid enriched intercellular domains, analogous to mammals. But, in contrast to mammals, the highly attenuated corneocytes of avians, which results from a paucity of keratin filaments, produce a 'straws-and-mortar' tissue, rather than the 'bricks-and-mortar' tissue of mammals.

Animals↗
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

De novo sterologenesis in the skin. II. Regulation by cutaneous barrier requirements.

Recent studies suggest: that the epidermis and pilosebaceous epithelium are important sites of de novo sterol synthesis, and that the rate of cutaneous cholesterol synthesis does not change with alterations in circulating sterol levels. Since cutaneous sterols may be important for permeability barrier function, we studied the effect of experimentally altered barrier function on de novo sterologenesis in the epidermal and dermal layers of the skin. Epidermal sterologenesis appeared to be modulated by the skin's barrier requirements because topical detergent and acetone treatment stimulated de novo synthesis of nonsaponifiable lipids in the epidermis, but not in the dermis. Synthetic activity paralleled both the return of barrier function toward normal and the extent of prior damage to the barrier. Moreover, plastic-wrap occlusion of solvent-treated sites simultaneously corrected both the barrier abnormality and normalized sterol synthesis, further linking increased epidermal sterologenesis to barrier requirements. Whereas topical applications of a variety of other topical lipids did not down-regulate synthesis, epicutaneously applied 25-hydroxycholesterol appeared to diminish synthesis. These results suggest that maintenance of barrier function is one purpose of epidermal de novo nonsaponifiable lipid synthesis, and demonstrate further that, despite a lack of low density lipoprotein receptors, epidermis can regulate its lipid-synthetic apparatus in response to certain specific requirements.

Acetone↗
PubMed1977

Pattern recognition II: Investigation of structure--activity relationships.

A simple form of pattern recognition is successfully used to classify a set of structurally diverse therapeutic agents. By using only organic structural information, the major pharmacological classes present were correctly identified and the pharmacologically unrelated compounds were separated out. One technique of factor analysis--principal component analysis--is shown to be readily adaptable in preprocessing the data. Simple graphical representation of the results enables their direct interpretation.

Chemistry, Pharmaceutical↗