Biomedical subjects

M Mao-Qiang

Publications and source records attributed to M Mao-Qiang.

12 recordsLinked to original sources

PubMed2002

Impact of topical oils on the skin barrier: possible implications for neonatal health in developing countries.

UNLABELLED: Topical therapy to enhance skin barrier function may be a simple, low-cost, effective strategy to improve outcome of preterm infants with a developmentally compromised epidermal barrier, as lipid constituents of topical products may act as a mechanical barrier and augment synthesis of barrier lipids. Natural oils are applied topically as part of a traditional oil massage to neonates in many developing countries. We sought to identify inexpensive, safe, vegetable oils available in developing countries that improved epidermal barrier function. The impact of oils on mouse epidermal barrier function (rate of transepidermal water loss over time following acute barrier disruption by tape-stripping) and ultrastructure was determined. A single application of sunflower seed oil significantly accelerated skin barrier recovery within 1 h; the effect was sustained 5 h after application. In contrast, the other vegetable oils tested (mustard, olive and soybean oils) all significantly delayed recovery of barrier function compared with control- or Aquaphor-treated skin. Twice-daily applications of mustard oil for 7 d resulted in sustained delay of barrier recovery. Moreover, adverse ultrastructural changes were seen under transmission electron microscopy in keratin intermediate filament, mitochondrial, nuclear, and nuclear envelope structure following a single application of mustard oil. CONCLUSION: Our data suggest that topical application of linoleate-enriched oil such as sunflower seed oil might enhance skin barrier function and improve outcome in neonates with compromised barrier function. Mustard oil, used routinely in newborn care throughout South Asia, has toxic effects on the epidermal barrier that warrant further investigation.

Administration, Topical↗

PubMed2001

Testosterone perturbs epidermal permeability barrier homeostasis.

Although there are no known gender-related differences in permeability barrier function in adults, estrogens accelerate whereas testosterone retards barrier development in fetal skin, and male fetuses demonstrate slower barrier development than female littermates. Moreover, prenatal administration of the androgen receptor antagonist, flutamide, equalizes developmental rates in male and female fetuses. Therefore, we evaluated the effects of changes in testosterone on barrier homeostasis in adult murine and human skin. Hypogonadal mice (whether by castration or by treatment with systemic flutamide) displayed significantly faster barrier recovery at 3, 6, and 12 h than did controls, and testosterone replacement slowed barrier recovery in castrated mice. Moreover, testosterone directly effects the skin, as topical flutamide also accelerated barrier recovery in normal male mice. These findings appear to be of physiologic significance, since prepubertal male mice (age 5 wk) displayed accelerated barrier recovery in comparison with adult postpubertal (11 wk) males. These studies also appear to be relevant for humans, as a hypopituitary human subject demonstrated repeated changes in barrier recovery in parallel with peaks and nadirs in serum testosterone levels during intermittent testosterone replacement. Mechanistic studies showed that differences in epidermal lipid synthesis do not account for the testosterone-induced functional alterations. Instead, epidermal lamellar body (LB) formation and secretion both decrease, resulting in decreased extracellular lamellar bilayers in testosterone-replete animals. These studies demonstrate that fluctuations in testosterone modulate barrier function, and that testosterone repletion can have negative consequences for permeability barrier homeostasis.

Animals↗

PubMed1997

Calcium and potassium inhibit barrier recovery after disruption, independent of the type of insult in hairless mice.

Disruption of the cutaneous permeability barrier induces metabolic responses in the epidermis which result in barrier recovery. Barrier disruption by either solvent treatment or tape stripping results in the loss of the epidermal calcium gradient. Previous studies in acetone treated hairless mice have shown that maintaining this calcium gradient inhibits barrier repair, suggesting that alterations in the epidermal calcium concentration may be an important signal for barrier homeostasis. In the present study, we show that in hairless mice disruption of the barrier by treatment with the detergent, SDS, also results in the loss of the calcium gradient, as demonstrated both semi-quantitatively with ultrastructural cytochemical localization and quantitatively using proton induced X-ray emission (PIXE). Additionally, immersion in calcium containing solutions delays barrier repair after either detergent (SDS treatment) or mechanical (tape stripping) disruption of the barrier, as reported previously for acetone treated skin. These results indicate that barrier disruption, regardless of the insult, induces changes in the epidermal calcium gradient which may play an important role in signaling the metabolic changes required for barrier homeostasis.

Animals↗

PubMed1996

Secretory phospholipase A2 activity is required for permeability barrier homeostasis.

The extracellular bilayers which mediate the epidermal permeability barrier are enriched in ceramides, free fatty acids, and cholesterol. Yet, the epidermal lamellar body, the source of these lipids, is enriched in a more polar mixture; i.e., glucosylceramides and phospholipids, which it delivers to the stratum corneum (SC) interstices. Whereas the extracellular processing of glucosylceramides to ceramides has been shown to be required for barrier homeostasis, the requirement for phospholipid degradation to free fatty acids is not yet established. In this study, we ascertained that topical applications of two chemically unrelated inhibitors of secretory phospholipase A2 (PLA2), bromphenacyl bromide and MJ-33, produced a progressive perturbation in barrier function in intact murine skin, first appearing at 5 d, preceded by the development of epidermal hyperplasia. Moreover, the defect in barrier homeostasis could be reversed by topical co-applications of the nonessential fatty acid, and of palmitic acid, but not by linoleic acid, both products of phospholipid catabolism. Furthermore, the barrier abnormality was accompanied by a reduction in free fatty acid levels in the stratum corneum, while phospholipid levels remained unchanged. These biochemical alterations were accompanied by the appearance of immature, incompletely processed lamellar body-derived membranes in the SC interstices, and depletion of histochemically detectable neutral lipid. Both the abnormalities and the epidermal hyperplasia were reversed by co-applications of palmitic acid (but not linoleic acid) with either inhibitor. These results demonstrate that processing of phospholipids to nonessential free fatty acids, by a yet-to-be-identified extracellular phospholipase, is required for the maintenance of barrier homeostasis in intact skin. Furthermore, our studies show that the barrier abnormalities induced by the PLA2 inhibitors are due to a failure to generate free fatty acids rather than to phospholipid accumulation.

Acetophenones↗

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

Apolipoprotein E deficiency leads to cutaneous foam cell formation in mice.

Apolipoprotein E deficiency leads to familial dysbetalipoproteinemia characterized by increases in serum lipid levels, atherosclerosis, and cutaneous xanthoma. Apolipoprotein E is synthesized in many tissues in the body, including the epidermis. In the present study, we determined whether transgenic mice deficient in apolipoprotein E develop cutaneous xanthoma and the effect of dietary fat intake on these lesions. We also determined whether apolipoprotein E-deficient mice have abnormalities in cutaneous barrier function or stratum corneum structure. Homozygous apolipoprotein E-deficient mice (-/-) fed a high-fat diet displayed a diffuse inflammatory infiltrate in the dermis surrounding fat droplets in macrophages. In homozygous mice (-/-) fed a low-fat diet, similar lesions were seen but they tended to be focal and less prominent. In heterozygous mice (+/-) fed the high-fat diet, a few inflammatory cells were present in the dermis but foam cells were not seen. Control mice (+/+) fed a high-fat diet displayed scattered inflammatory cells in the dermis. Heterozygous mice (+/-) fed a low-fat diet were similar to control mice (+/+) fed a low-fat diet. The extent of foam cell formation correlated directly with the degree of atherosclerosis. There were no abnormalities in permeability-barrier function or stratum corneum structure in apolipoprotein E-deficient mice. Thus, the lack of apolipoprotein E production in the epidermis does not appear to lead to any detectable abnormality in structure or function of the stratum corneum. However, lack of apolipoprotein E leads to cutaneous foam cell formation, presumably secondary to disturbances in lipoprotein metabolism.

Animals↗

PubMed1995

Topical stratum corneum lipids accelerate barrier repair after tape stripping, solvent treatment and some but not all types of detergent treatment.

Topical acetone treatment extracts lipids from the stratum corneum, and disrupts the permeability barrier, resulting in a homeostatic response in the viable epidermis that ultimately repairs the barrier. Recently, we have developed an optimal lipid mixture (cholesterol, ceramide, palmitate and linoleate 4.3:2.3:1:1.08) that, when applied topically, accelerates barrier repair following extensive disruption of the barrier by acetone. The present study determined if topical treatment with this optimal lipid mixture would have beneficial effects following disruption of the barrier by petroleum ether, tape stripping, or by detergent treatment. Also, we determined if barrier repair was accelerated after moderate disturbances of barrier function. Following moderate or extensive disruption of the barrier by acetone or petroleum ether (solvents), or tape stripping (mechanical), application of the optimal lipid mixture accelerated barrier repair. Additionally, following barrier disruption with N-laurosarcosine free acid or dodecylbenzensulphuric acid (detergents), the optimal lipid mixture similarly accelerated barrier repair. However, following disruption of the barrier with different detergents, sodium dodecyl sulphate and ammonium lauryl sulphosuccinate, the optimal lipid mixture did not improve barrier recovery. Thus, the optimal lipid mixture is capable of accelerating barrier repair following disruption of the barrier by solvent treatment or tape stripping (mechanical), and by certain detergents such as Sarkosyl and dodecylbenzensulphuric acid. The ability of the optimal lipid mixture to accelerate barrier repair after both moderate and extensive degrees of barrier disruption suggests a potential clinical use for this approach.

Acetone↗

PubMed1995

Extracellular processing of phospholipids is required for permeability barrier homeostasis.

Three key lipid types, cholesterol, ceramides (CER), and free fatty acids (FA), form the stratum corneum (SC) lamellar bilayers that mediate barrier function. Prior studies have shown that barrier requirements regulate CER generation from glucosylCER, and that this catabolic step takes place within the SC interstices. Here, we addressed whether extracellular processing of phospholipids (PL), the FA precursor delivered to the SC interstices with glucosylCER and cholesterol during exocytosis of lamellar body contents, is also required for barrier homeostasis. We applied two chemically unrelated inhibitors of phospholipase A2 (PLA2-I), BPB (irreversible) and MJ33 (reversible), topically to hairless mice after barrier perturbation with acetone. Both inhibitors delayed barrier recovery at non-cytotoxic doses, while MJ45, an analogue known to inhibit PLA2-II but not PLA2-I, had no effect. Moreover, the delays in barrier recovery induced by BPB and MJ33 could be overridden by co-applications of palmitic acid, but not linoleic acid or lysolecithin. Furthermore, inhibitor-treatment resulted in accumulation of PL and depletion of FA in the SC by 4 h, as well as the persistence of "immature" lamellar body-derived membrane structures in the SC interstices. Finally, these changes in membrane structure were reversed when inhibitor-treated SC was incubated in vitro with palmitic acid. These studies show that: 1) inhibition of PLA2 results in abnormalities in lipid composition and SC structure that alter barrier homeostasis; and 2) the functional defect can be attributed to a deficiency of nonessential FA within the SC. Thus, extracellular processing of PL into FA is required for normal barrier function.

Animals↗

PubMed1994

Role of exogenous oxygen in cutaneous barrier repair.

Occlusion of the skin with a water-vapor-impermeable membrane following disruption of the permeability barrier prevents the epidermal changes which lead to the restoration of barrier function, suggesting that water transit could be an important regulatory signal for barrier repair. However, occlusion with a water-vapor-impermeable membrane also prevents the movement of gases, which could also potentially influence permeability barrier homeostasis. Since O2 is known to have an effect on epidermal cell function, we have determined the effect of gases containing different levels of O2 on barrier repair 6 h following topical treatment of hairless mice with acetone. The disrupted barrier of air-exposed animals (O2 approximately 20%) recovered by 50.8 +/- 3.4% (mean +/- SEM) after 6 h. Under flowing air (O2 approximately 20%), O2/CO2 95/5% and argon (O2 = 0%) the barrier recovered by 43.9 +/- 28, 36.2 +/- 8.5 and 39.2 +/- 4.6%, respectively. These values were not statistically different from each other. The slightly lower levels of recovery at 6 h with the flowing gases in comparison to exposure to static air probably can be attributed to a slight cooling of the skin caused by the flowing gases. These results suggest that exogenous O2 is neither required for barrier repair nor a signal for barrier repair.

Animals↗

PubMed1993

Inhibition of cholesterol and sphingolipid synthesis causes paradoxical effects on permeability barrier homeostasis.

Cholesterol, fatty acid, and sphingolipid synthesis are required for barrier homeostasis, as demonstrated by studies where synthesis of these species is stimulated in parallel with barrier repair. Moreover, blockade of synthesis of these lipids with inhibitors of two of the rate-limiting enzymes, HMGCoA reductase (lovastatin, fluvastatin) and serine palmitoyl transferase (beta-chloroalanine), alters the kinetics of barrier repair. Whereas these studies demonstrated a requirement for these lipids individually, we asked here whether these lipids are required in either an additive or cooperative fashion. We applied each class of inhibitor alone or the two classes of inhibitors together to acetone-treated skin, or each class separately to essential fatty acid deficient murine skin. When fluvastatin or beta-chloroalanine was applied individually to acetone-treated skin, each caused a delay in the early or late stages of barrier recovery, respectively (assessed as transepidermal water loss). However, when applied together they caused no further worsening at the early time point and a paradoxical improvement at the later time points. This improvement correlated with an accelerated return of sphingolipids, which was perhaps due to a global stimulation of lipid synthesis induced by HMGCoA reductase inhibitors. In essential fatty acid deficient animals, inhibition of HMGCoA reductase caused drastic worsening of both clinical appearance and barrier function, but beta-chloroalanine caused a paradoxical improvement, which correlated with a significant reduction in epidermal sphingolipids. These results are consistent with a requirement for both cholesterol and sphingolipids for barrier homeostasis, and also with the suggestion that both of these lipids must be present (with free fatty acids) for optimal barrier function.

Acetone↗

PubMed1993

Fatty acids are required for epidermal permeability barrier function.

The permeability barrier is mediated by a mixture of ceramides, sterols, and free fatty acids arranged as extracellular lamellar bilayers in the stratum corneum. Whereas prior studies have shown that cholesterol and ceramides are required for normal barrier function, definitive evidence for the importance of nonessential fatty acids is not available. To determine whether epidermal fatty acid synthesis also is required for barrier homeostasis, we applied 5-(tetradecyloxy)-2-furancarboxylic acid (TOFA), an inhibitor of acetyl CoA carboxylase, after disruption of the barrier by acetone or tape stripping. TOFA inhibits epidermal fatty acid by approximately 50% and significantly delays barrier recovery. Moreover, coadministration of palmitate with TOFA normalizes barrier recovery, indicating that the delay is due to a deficiency in bulk fatty acids. Furthermore, TOFA treatment also delays the return of lipids to the stratum corneum and results in abnormalities in the structure of lamellar bodies, the organelle which delivers lipid to the stratum corneum. In addition, the organization of secreted lamellar body material into lamellar bilayers within the stratum corneum interstices is disrupted by TOFA treatment. Finally, these abnormalities in lamellar body and stratum corneum membrane structure are corrected by coapplication of palmitate with TOFA. These results demonstrate a requirement for bulk fatty acids in barrier homeostasis. Thus, inhibiting the epidermal synthesis of any of the three key lipids that form the extracellular, lipid-enriched membranes of the stratum corneum results in an impairment in barrier homeostasis.

Acetone↗

PubMed1992

Structural basis for the barrier abnormality following inhibition of HMG CoA reductase in murine epidermis.

Recent studies have shown that increased epidermal 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG CoA) reductase activity is crucial for the barrier recovery response that follows solvent-induced barrier perturbation. Upregulation of this enzyme leads to increased cholesterologenesis, formation and secretion of cholesterol-enriched lamellar bodies, and barrier repair. Topical lovastatin-induced inhibition of HMG CoA reductase activity both delays the acute barrier-repair response, as well as leading to a chronic barrier abnormality when applied repeatedly to intact skin. Presently, we assessed the effects of repeated topical applications of two different specific inhibitors of HMG CoA reductase on barrier function, the lamellar body-secretory system, and stratum corneum intercellular domains, with functional and morphologic parameters. Once-daily applications of lovastatin or fluindostatin (XU62-320; Sandoz) for 4-8 d to intact hairless mouse epidermis produced a progressive abnormality in barrier function (transepidermal water loss greater than 2.0-5.0 in treated versus less than 0.25 mg/cm2/h for weakly active analogues or vehicle controls). The barrier defect was preceded by alterations in lamellar body internal structure and a partial failure of lamellar body secretion into the stratum corneum interstices, further confirmed by enzyme cytochemistry. Moreover, the deposition of abnormal lamellar body contents resulted in the formation of clefts in the intercellular spaces at the stratum granulosum-stratum corneum interface, resulting in increased permeability through these domains shown by lanthanum perfusion. Applications of irritants, even when producing a barrier abnormality, did not alter the lamellar body secretory system. Co-applications of cholesterol with the inhibitors reversed both the barrier abnormality and the abnormalities in the lamellar body secretory system that occur with the inhibitor alone. Finally, membrane bilayer structures in the mid-to-outer stratum corneum of inhibitor-treated specimens appeared normal, but the intercellular domains displayed enormously expanded lacunae. However, because similar dilatations also occurred in vehicle-treated samples, they can be attributed to the vehicle alone. These studies provide further evidence that the inhibitor-induced defect in barrier function a) is initiated by inhibition of HMG CoA reductase; b) can be attributed to defects in both lamellar body structure and deposition with resultant abnormalities in intercellular membrane domains in the lower stratum corneum; and c) is further enhanced by permissive effects of the vehicle on the permeability of the outer stratum corneum.

Alkanes↗