Transepidermal water loss in developing rats: role of aquaporins in the immature skin

Mechanistic of Vesicular Ethosomes and Elastic Liposomes on Permeation Profiles of Acyclovir across Artificial Membrane, Human Cultured EpiDerm, and Rat Skin: In Vitro-Ex Vivo Study

Acyclovir (ACV) controls cutaneous herpes, genital herpes, herpes keratitis, varicella zoster, and chickenpox. From previously reported ACV formulations, we continued to explore the permeation behavior of the optimized ACV loaded optimized ethosome (ETHO2R) and elastic liposome (ELP3R) and their respective carbopol gels across artificial membrane, cultured human EpiDerm, and rat skin. Transepidermal water loss (TEWL), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and atomic force microscopy (AFM) were used to investigate the mechanistic perspective of permeation behavior. The size values of reformulated ELP3-R and ETHO2-R were observed as 217 and 128 nm, respectively (close to previous report), whereas their respective gels showed as 231 and 252 nm, respectively. ETHO2R showed high elasticity, %EE, and low vesicle size. These were investigated for the diffusion rate of the drug permeation (3 h) across the artificial membrane, cultured human EpiDerm, and rat skin. ETHO2GR showed the highest permeation flux (78.42 µg/cm2/h), diffusion coefficient (8.24 × 10-5 cm2/h), and permeation coefficient (0.67 × 10-3 cm/h) of ACV across synthetic membrane, whereas diffusion coefficient (2.4 × 10-4 cm2/h) and permeation coefficient (0.8 × 10-3 cm/h) were maximum across EpiDerm for ETHO2GR. ETHO2R suspension showed maximized permeation flux (169.58 µg/cm2/h) and diffusion rate (0.293 mg/cm2/h1/2), suggesting the rapid internalization of vesicles with cultured skin cells at low viscosity. A similar observation was revealed using rat skin, wherein the permeation flux (182.42 µg/cm2/h), permeation coefficient (0.3 × 10-2 cm/h), and diffusion rate (0.315 mg/cm2/h1/2) of ETHO2R were relatively higher than ELP3R and ELP3GR. Relative small size (128 nm), low viscosity, ethanol-mediated ultra-deformability, high drug entrapment (98%), and elasticity (63.2) are associated with ETHO2R to provide remarkable permeation behavior across the three barriers. The value of TEWL for ETHO2R (21.9 g/m2h) was 3.71 times higher than untreated control (5.9 g/m2h), indicating ethanol-mediated maximized surficial skin lipid perturbation at 3 h of application, whereas the respective ETHO2GR-treated rat skin had TEWL value (18.6 g/m2h) slightly lower than ETHO2R due to gel-based hydration into the skin. SEL, CLSM, and AFM provided a mechanistic perspective of ETHO2R and ELP3R-mediated permeation across rat skin and carrier-mediated visualization (skin-vesicle interaction). AFM provided detailed nanoscale surface roughness topographical parameters of treated and untreated rat skin as supportive data to SEM and CLSM. Thus, ethosomes ETHO2R and respective gel assisted maximum permeation of ACV across rat skin and cultured human EpiDerm to control cutaneous herpes infection and herpes keratitis.

E-cadherin and aquaporin-3 are downregulated in wound edges of human chronic wounds

Chronic wounds are defined as wounds that fail to proceed through the normal phases of wound healing; a complex process involving different dynamic events including migration of keratinocytes in the epidermis. Chronic wounds are estimated to affect 1-2% of the human population worldwide and are a major socioeconomic burden. The prevalence of chronic wounds is expected to increase with the rising number of elderly and patients with diabetes and obesity, who are at high risk of developing chronic wounds. Since E-cadherin and the water channel aquaporin-3 are important for both skin function and cell migration, and aquaporin-3 is furthermore involved in wound healing of the skin demonstrated by impaired wound healing in aquaporin-3-null mice, we hypothesized that E-cadherin and aquaporin-3 expression may be dysregulated in chronic wounds. Therefore, we investigated the expression of E-cadherin and aquaporin-3 in biopsies from the edges of chronic wounds from human patients. This was accomplished by immunohistochemical stainings of E-cadherin and aquaporin-3 on serial sections followed by qualitative evaluation of staining patterns, which revealed low expression of both E-cadherin and aquaporin-3 at the wound edge. Future studies are needed to reveal if this downregulation is associated with the pathophysiology of chronic wounds.

Aquaporins in Fetal Development

Water homeostasis is essential for fetal growth, and it depends on the successful development of the placenta. Many aquaporins (AQPs) were identified from blastocyst stages to term placenta. In the last years, cytokines, hormones, second messengers, intracellular pH, and membrane proteins were found to regulate their expression and function in the human placenta and fetal membranes. Accumulated data suggest that these proteins may be involved not only in the maintenance of the amniotic fluid volume homeostasis but also in the development of the placenta and fetal organs. In this sense, dysregulation of placental AQPs is associated with gestational disorders. Thus, current evidence shows that AQPs may collaborate in cellular events including trophoblast migration and apoptosis. In addition, aquaglyceroporins are involved in energy metabolism as well as urea elimination across the placenta. In the last year, the presence of AQP9 in trophoblast mitochondria opened new hypotheses about its role in pregnancy. However, much further work is needed to understand the importance of these proteins in human pregnancies.

Nutritional and Physiological Regulation of Water Transport in the Conceptus

Water transport during pregnancy is essential for maintaining normal growth and development of conceptuses (embryo/fetus and associated membranes). Aquaporins (AQPs) are a family of small integral plasma membrane proteins that primarily transport water across the plasma membrane. At least 11 isoforms of AQPs (AQPs 1-9, 11, and 12) are differentially expressed in the mammalian placenta (amnion, allantois, and chorion), and organs (kidney, lung, brain, heart, and skin) of embryos/fetuses during prenatal development. Available evidence suggests that the presence of AQPs in the conceptus mediates water movement across the placenta to support the placentation, the homeostasis of amniotic and allantoic fluid volumes, as well as embryonic and fetal survival, growth and development. Abundances of AQPs in the conceptus can be modulated by nutritional status and physiological factors affecting the pregnant female. Here, we summarize the effects of maternal dietary factors (such as intakes of protein, arginine, lipids, all-trans retinoic acid, copper, zinc, and mercury) on the expression of AQPs in the conceptus. We also discuss the physiological changes in hormones (e.g., progesterone and estrogen), oxygen supply, nitric oxide, pH, and osmotic pressure associated with the regulation of fluid exchange between mother and fetus. These findings may help to improve the survival, growth, and development of embryo/fetus in livestock species and other mammals (including humans).

Partially Hydrolysed Whey-Based Infant Formula Improves Skin Barrier Function

Specific partially hydrolysed whey-based infant formulas (pHF-W) have been shown to decrease the risk of atopic dermatitis (AD) in infants. Historically, AD has been associated primarily with milk allergy; however, defective skin barrier function can be a primary cause of AD. We aimed to ascertain whether oral supplementation with pHF-W can improve skin barrier function. The effect of pHF-W was assessed on transepidermal water loss (TEWL) and antibody productions in mice epicutaneously exposed to Aspergillus fumigatus. Human primary keratinocytes were stimulated in vitro, and the expression of genes related to skin barrier function was measured. Supplementation with pHF-W in neonatal mice led to a significant decrease in TEWL and total IgE, but not in allergen-specific antibody levels. The whey hydrolysate was sufficient to decrease both TEWL and total IgE. Aquaporin-3 gene expression, linked with skin hydration, was modulated in the skin of mice and human primary keratinocytes following protein hydrolysate exposure. Skin barrier improvement may be an additional mechanism by which pHF-W may potentially reduce the risk of AD development in infants. Further human studies are warranted to confirm the clinical efficacy of these observations.

Intrathrombotic appearances of AQP-1 and AQP-3 in relation to thrombus age in murine deep vein thrombosis model

Aquaporins (AQPs) are membrane-bound proteins for water transportation and are useful for diagnosing drowning and wound vitality in forensic pathology. Here, we examined intrathrombotic expression of AQP-1 and AQP-3 using deep vein thrombosis models in mice. To perform immunohistochemical analyses, we used anti-AQP-1 and anti-AQP-3 antibodies. In thrombus samples with the post-ligation intervals of 1 to 5 days, AQP-1⁺ areas were over 70%. At 7 days after the IVC ligation, AQP-1⁺ areas became less than 50%, eventually decreasing to 11% at 21 days. At 3 days after the IVC ligation, AQP-3⁺ cells started to appear from the peripheral area. Thereafter, the positive cell number progressively increased and reached to a peak at 10 days after the IVC ligation. When the intrathrombotic AQP-1⁺ area was as large as the intrathrombotic collagen area or smaller, it would indicate a thrombus age of ≥ 10 days. AQP-3⁺ cell number of > 30 would indicate a thrombus age of 10–14 days. Collectively, our study implied that the detection of AQP-1 and AQP-3 would be useful for the determination of thrombus age.

Impact of cigarette smoke on physical-chemical and molecular proprieties of human skin in an ex vivo model

BACKGROUND

This is a study about the skin ageing exposome, focusing on the effect of cigarette smoke. Human living skin explants (HSE) were exposed to cigarette smoke (CS) of two cigarettes for 2 hours using a custom-made exposure chamber, the Pollubox^® . Effects on the surface physico-chemistry and molecular properties of the skin were analyzed and reported for the first time.

BASIC PROCEDURES

To this end, transcriptomic study followed by immunohistochemistry, MDA (Malondialdehyde Dosage), and surface physio-chemistry data: surface free energy determination, TEWL (Trans Epidermal Water Loss), skin pH and FT-IR (Fourier Transform-Infrared) spectroscopy of the explant were collected from untreated and treated HSE.

MAIN FINDINGS

Results showed a decrease of the total surface free energy of the treated HSE. This decrease reflected higher interactions with polar compounds from the environment and consequently a decrease of the surface hydrophobicity. Additionally, an increase of TEWL and skin pH was observed after treatment. The transcriptomic analysis showed downregulation of mitochondrial genes (PON2-NDUFA4L2-ATP1A1-ALDH2-PRODH) combined with an increase of MDA in CS-treated HSE.

CONCLUSIONS

CS-induced oxidation of lipids at HSE surface alters the skin barrier: interactions with polar products are enhanced and the lipid chain packing at the surface is modified. Consequently, skin permeability could increase which correlated with repression of CA9 and AQP1 genes. Beside activation of AHR-NRF2 pathway in CS-exposed HSE, our results suggested that mitochondrial functions were strongly impacted and oxidized lipids failed to be eliminated promoting skin barrier alteration. A mitophagy activity was suggested through the confirmation of PINK1 accumulation in the epidermis by immunostaining.

Seasonal effect in expression of AQP1, AQP3 and AQP5 in skin of Murrah buffaloes

Aquaporins are transmembrane protein channels which are known to help the passage of water and solutes across the cell membranes. AQP1, AQP3 and AQP5 are isoforms of aquaporin known to aid in transepithelial water movement. AQP3 is also known to aid in glycerol transport. The present study was conducted to investigate the role of AQP1, AQP3 and AQP5 in thermoregulation of buffaloes by probing the expression of the genes in skin of buffaloes during different season viz. winter, spring and summer. The skin tissue samples were collected from the neck region of Murrah buffaloes (n = 12) and analyzed for gene expression by RT-PCR and immunolocalization. The physiological responses including respiration rate, rectal temperature and neck skin temperature observed during summer were significantly higher than winter and spring seasons. The study revealed the expression of AQP1, AQP3 and AQP5 genes in skin samples. The relative mRNA expressions of AQP1, AQP3 and AQP5 in skin relative to spring season were 1.41 ± 0.47, 1.95 ± 0.22 and 6.77 ± 1.02 folds during summer which were significantly higher than other seasons. The up-regulation of the expression of the studied AQPs were concomitant with the increase in physiological responses including skin temperature and sweating rate during summer. During summer season, AQP1 were mostly immunolocalized in the walls of skin blood capillaries, while AQP3 were observed mostly in the epidermal layer of the skin. The immunolocalization of AQP5 were mostly observed in the secretory glands of skin. The up-regulation of AQP1, AQP3 and AQP5 in skin during summer season indicates their role in thermoregulation of buffaloes.

Immunohistochemical analysis on aquaporin-1 and aquaporin-3 in skin wounds from the aspects of wound age determination

Immunohistochemical investigation of aquaporin (AQP)1 and AQP3 was performed in human skin wounds obtained from forensic autopsy cases. A total of 55 human skin wounds of different postinfliction intervals were collected as follows: group I, 0-3 days (n = 16); II, 4-7 days (n = 11); III, 9-14 days (n = 16); and IV, 17-21 days (n = 12). In uninjured skin samples, AQP1 and AQP3 could be slightly detected in dermal vessels and keratinocytes, respectively. The percentage of AQP1⁺ vessels and the number of AQP3⁺ keratinocytes were apparently elevated in accordance with wound ages. The number of AQP3⁺ keratinocytes was distinctly evident in groups II and III. Morphometrically, both AQP1⁺ vessel area and AQP3⁺ cell number were markedly increased in group II, compared with other three groups. With regard to forensic safety, AQP1⁺ vessel area of over 5% would imply wound ages of 4-12 days. Moreover, the positive area of > 15% would suggest wound age of 7-10 days. Especially, most samples of skin wounds aged 5-10 days except for only one sample (a 10-day-old wound) showed AQP3⁺ cell number of > 300, and the remaining other samples had that of < 300. Thus, the AQP3⁺ cell number of > 300 would indicate wound ages of 5-10 days. Collectively, immunohistochemical analyses of AQP1 and AQP3 in human skin wounds would support the objective accuracy of wound age determination.

Acute kidney injury in the fetus and neonate

Acute kidney injury (AKI) is an under-recognized morbidity of neonates; the incidence remains unclear due to the absence of a unified definition of AKI in this population and because previous studies have varied greatly in screening for AKI with serum creatinine and urine output assessments. Premature infants may be born with less than half of the nephrons compared with term neonates, predisposing them to chronic kidney disease (CKD) early on in life and as they age. AKI can also lead to CKD, and premature infants with AKI may be at very high risk for long-term kidney problems. AKI in neonates is often multifactorial and may result from prenatal, perinatal, or postnatal insults as well as any combination thereof. This review focuses on the causes of AKI, the importance of early detection, the management of AKI in neonates, and long-term sequela of AKI in neonates.

Fluid deprivation increases isotonic NaCl intake, but not hypertonic salt intake, under normal and heated conditions in obese Zucker rats

In the course of exposure to fluid deprivation and heated environment, mammals regulate their hydromineral balance and body temperature by a number of mechanisms including sweating, water and salt intakes. Here we challenged obese Zucker rats, known to have a predisposition to hypertension, with 0.9%NaCl alone or with 2%NaCl solution + water to drink under fluid deprivation and heated conditions. Food and fluid intakes, body weight, diuresis and natriuresis were measured daily throughout. Serum aldosterone levels and Na(+) concentration were also analyzed. Data showed that obese and lean rats presented similar baseline measurements of food, 0.9%NaCl and fluid intakes, diuresis and fluid balance; whereas hypertonic 2%NaCl consumption was almost absent. Before and during fluid deprivation animals increased isotonic but not hypertonic NaCl intake; the obese showed significant increases in diuresis and Na(+) excretion, whereas, total fluid intake was similar between groups. Heat increased isotonic NaCl intake and doubled natriuresis in obese which were wet on their fur and displayed a paradoxical increase of fluid gain. Fluid deprivation plus heat produced similar negative fluid balance in all groups. Body weight losses, food intake and diuresis reductions were amplified under the combined conditions. Animals exposed to 2%NaCl showed higher circulating levels of aldosterone and obese were lower than leans. In animals which drank 0.9%NaCl, obese showed higher serum levels of Na(+) than leans. We conclude that in spite of their higher sensitivity to high salt and heat obese Zucker rats can control hydromineral balance in response to fluid deprivation and heat by adjusting isotonic NaCl preference with sodium balance and circulating levels of aldosterone. This suggests a key hormonal role in the mechanisms underlying thermoregulation, body fluid homeostasis and sodium intake.

Effect of intense pulsed light on the expression of aquaporin 3 in rat skin

Intense pulsed light (IPL) technology has been popularly employed in clinical treatments for dermatological and cosmetic purposes in recent years; yet, the underlying mechanisms of its functions are not fully elucidated. On the other hand, aquaporin (AQP) 3, a member of a subgroup of the aquaporin family that transports both water and small solutes, such as glycerol, has been documented to play an important role in the skin homeostasis. We thus examined the possible involvement of AQP3 in the functional mechanisms of IPL irradiation. Rat dorsal skin areas were irradiated one to three times with IPL at doses of 15, 25, and 35 J/cm2. Skin specimens were collected 7 days after the final irradiation and analyzed for changes in histology, skin hydration, mRNA, and protein expressions of AQP3. IPL induced no significant variations in the mRNA expression levels. Twice or thrice irradiation at the dose of 25 or 35 J/cm2 significantly enhanced AQP3 protein expression. Immunofluorescence study revealed that AQP3 was mainly localized to keratinocyte membranes in the basal layer of epidermis, and the localization was unaltered by IPL. In addition, the pattern of IPL-induced changes in skin hydration was generally coincided with the expression profile of AQP3. These results suggest the possibility that one of the functional mechanisms of IPL might be related to the regulation of AQP3 protein expression.

Towards a quantitative theory of epidermal calcium profile formation in unwounded skin

We propose and mathematically examine a theory of calcium profile formation in unwounded mammalian epidermis based on: changes in keratinocyte proliferation, fluid and calcium exchange with the extracellular fluid during these cells’ passage through the epidermal sublayers, and the barrier functions of both the stratum corneum and tight junctions localised in the stratum granulosum. Using this theory, we develop a mathematical model that predicts epidermal sublayer transit times, partitioning of the epidermal calcium gradient between intracellular and extracellular domains, and the permeability of the tight junction barrier to calcium ions. Comparison of our model’s predictions of epidermal transit times with experimental data indicates that keratinocytes lose at least 87% of their volume during their disintegration to become corneocytes. Intracellular calcium is suggested as the main contributor to the epidermal calcium gradient, with its distribution actively regulated by a phenotypic switch in calcium exchange between keratinocytes and extracellular fluid present at the boundary between the stratum spinosum and the stratum granulosum. Formation of the extracellular calcium distribution, which rises in concentration through the stratum granulosum towards the skin surface, is attributed to a tight junction barrier in this sublayer possessing permeability to calcium ions that is less than 15 nm s⁻¹ in human epidermis and less than 37 nm s⁻¹ in murine epidermis. Future experimental work may refine the presented theory and reduce the mathematical uncertainty present in the model predictions.

Electrolyte disorders

Electrolyte disorders can result in life-threatening complications. The kidneys are tasked with maintaining electrolyte homoeostasis, yet the low glomerular filtration rate of neonatal kidneys, tubular immaturity, and high extrarenal fluid losses contribute to increased occurrence of electrolyte disorders in neonates. Understanding the physiologic basis of renal electrolyte handling is crucial in identifying underlying causes and initiation of proper treatment. This article reviews key aspects of renal physiology, the diagnostic workup of disorders of plasma sodium and potassium, and the appropriate treatment, in addition to inherited disorders associated with neonatal electrolyte disturbances that illuminate the physiology of renal electrolyte handling.

Newborn boys and girls differ in the lipid composition of vernix caseosa

Vernix caseosa protects the skin of a human fetus during the last trimester of pregnancy and of a newborn after the delivery. Besides its cellular and proteinaceous components, an important constituent and functional agent is a complex lipid fraction, implicated in a multitude of salubrious effects of vernix caseosa. Little is known about how the chemical composition of vernix caseosa lipids is affected by various biological characteristics of the baby, such as the gestational age, birth weight, and, last but not least, the gender of the newborn. This study reports on the chemical variability of lipids contained in the vernix caseosa of twenty newborn girls and boys and shows that the quantitative patterns of the lipids are sex-specific. The specificity of lipids was investigated at the level of fatty acids in the total lipid extracts and intact lipids of several neutral lipid classes. Hydrocarbons, wax esters, cholesteryl esters, diol diesters and triacylglycerols were isolated using optimized semipreparative thin-layer chromatography, and the molecular species within each class were characterized using matrix-assisted laser desorption/ionization mass spectrometry. Statistical evaluation revealed significant quantitative sex-related differences in the lipid composition of vernix caseosa among the newborns, pronounced in the two lipid classes associated with the activity of sebaceous glands. Higher proportions of wax esters and triacylglycerols with longer hydrocarbon chains were observed in newborn girls.

Aquaporin-3 functions as a glycerol transporter in mammalian skin

The AQPs (aquaporins) are a family of homologous water transporting proteins expressed in many mammalian epithelial, endothelial and other cell types. Phenotype analysis of mice lacking individual AQPs has been informative in elucidating their role in mammalian physiology. For example, phenotype analysis has indicated an important role of AQPs in the renal urinary concentrating mechanism (AQP1-AQP4), brain water balance and neural signal transduction (AQP4), exocrine gland secretion (AQP5) and ocular fluid balance (AQP1, AQP5). In skin, the aquaglyceroporin AQP3 is expressed in the basal layer of epidermal keratinocytes. Mice deficient in AQP3 have dry skin with reduced SC (stratum corneum) hydration, decreased elasticity and impaired biosynthesis. Mechanistic analysis of the altered skin phenotype in AQP3 deficiency suggested that the glycerol rather than the water transporting function of AQP3 is important in skin physiology. The glycerol content of SC and epidermis of AQP3 deficient mice is reduced, whereas that of dermis and serum is normal. The dry, relatively inelastic skin in AQP3 null mice is probably related to the humectant properties of glycerol, and the impaired SC repair to impaired epidermal biosynthetic function. The key role of AQP3 in epidermal physiology might be exploited in the development of improved cosmetics and new therapies for skin diseases associated with altered skin water content.

Effects of the use of semipermeable membranes on fluid loss in low-birth-weight premature newborns

Studies have shown that the application of semipermeable membranes to the skin of premature newborns (NBs) can aid in protecting the skin, reduce disturbances in fluid and electrolyte levels, and decrease neonatal mortality. The aim of this study was to verify the effect of using semipermeable membranes in low-birth-weight preterm newborns (PTNBs). A randomized controlled trial was carried out in the neonatal intensive care unit (NICU) with 42 NBs split evenly into an intervention group (IG), in which semipermeable membranes were used to cover large areas of the skin for the first 7 days of life, and a control group (CG), which received normal care. The variables investigated for the study were weight, hydration status, urinary density, glycemic control, sodium concentration, and daily hydration quota. The following variables displayed significant daily variation: weight, hydration quota, and sodium concentration. Statistically significant individual effects by day and by group were found only for sodium concentration. In the overall analysis of the intersubject effects, sodium concentration, alone, proved to be significant (p = .055). Significant effects by group in relation to the sodium concentration were found, with the IG showing a lower average sodium concentration than the CG. Thus, the use of semipermeable membranes reduced fluid loss in premature NBs in the current study, confirming the findings of previous studies. Guidelines for practice may now be warranted.

Eficácia do uso de membrana semipermeável em neonatos pré-termo na redução de perdas transepidérmicas

Neste estudo, investigou-se a eficácia do uso da membrana semipermeável na pele de recém-nascido pré-termo sobre a evolução da perda ponderal e valores da glicemia, cota hídrica, densidade urinária e sódio. Estudo experimental, tipo ensaio clínico randomizado, realizado no período de março a agosto de 2008, na Unidade de Terapia Intensiva Neonatal, de uma maternidade pública, na cidade de Fortaleza-Ceará, Brasil. A amostra foi constituída de 42 recém-nascidos pré-termo. Os dados foram apresentados em tabelas e quadros. Na aplicação da membrana semipermeável, os recém-nascidos pré-termos do Grupo de Intervenção tiveram uma diminuição de níveis de sódio e de exigências fluidas diárias, como também apresentaram menores episódios de hiperglicemia e a densidade urinária foi mantida dentro dos padrões de normalidade. A membrana semipermeável é, de fato, um recurso terapêutico eficaz para minimizar as perdas de água transepidérmicas.

[Infusion therapy for neonates, infants and children]

Intravenous administration of fluids, electrolytes and glucose are the most common interventions in hospitalized pediatric patients. Parenteral fluid administration can be life-saving, however, if used incorrectly it also carries substantial risks. Perioperatively, adequate hydration, prevention of electrolyte imbalances and maintenance of normoglycemia are the main goals of parenteral fluid therapy. Conceptionally, the distinction between maintenance requirements, deficits and ongoing loss is helpful. Although the pathophysiological basis for parenteral fluid therapy was clarified in the first half of the 20th century, some aspects still remain controversial. In newborn infants, rational parenteral fluid therapy must take into account large insensible fluid losses, adaptive changes of renal function in the first days of life and the fact that neonates do not tolerate prolonged periods of fasting. In older infants the occurrence of iatrogenic hyponatremia with the use of hypotonic solutions has led to a critical reappraisal of the validity of the Holliday-Segar method for calculating maintenance fluid requirements in the postoperative period. Pragmatically, only isotonic solutions should be used in clinical situations which are known to be associated with increases in antidiuretic hormone (ADH) secretion. In this context, it is important to realize that in contrast to lactated Ringer's solution, the use of normal saline can lead to hyperchloremic acidosis in a dose-dependent fashion. Although there is no convincing evidence that colloids are better than crystalloids, there are clinical situations where the use of the more expensive colloids seems justified. It may be reasonable to choose a solution for fluid replacement which has a composition comparable to the composition of the fluid which must be replaced. Although hypertonic saline can reduce an elevated intracranial pressure, this therapy cannot be recommended as a routine procedure because there is currently no evidence that this intervention improves long-term outcome in pediatric patients with traumatic brain injury.

Antenatal Corticosteroids and Postnatal Fluid Restriction Produce Differential Effects on AQP3 Expression, Water Handling, and Barrier Function in Perinatal Rat Epidermis

Loss of water through the immature skin can lead to hypothermia and dehydration in preterm infants. The water and glycerol channel aquaglyceroporin-3 (AQP3) is abundant in fetal epidermis and might influence epidermal water handling and transepidermal water flux around birth. To investigate the role of AQP3 in immature skin, we measured in vivo transepidermal water transport and AQP3 expression in rat pups exposed to clinically relevant fluid homeostasis perturbations. Preterm (E18) rat pups were studied after antenatal corticosteroid exposure (ANS), and neonatal (P1) rat pups after an 18 h fast. Transepidermal water loss (TEWL) and skin hydration were determined, AQP3 mRNA was quantified by RT-PCR, and in-situ hybridization and immunocytochemistry were applied to map AQP3 expression. ANS resulted in an improved skin barrier (lower TEWL and skin hydration), while AQP3 mRNA and protein increased. Fasting led to loss of barrier integrity along with an increase in skin hydration. These alterations were not paralleled by any changes in AQP3. To conclude, antenatal corticosteroids and early postnatal fluid restriction produce differential effects on skin barrier function and epidermal AQP3 expression in the rat. In perinatal rats, AQP3 does not directly determine net water transport through the skin.

Skin aquaporins: function in hydration, wound healing, and skin epidermis homeostasis

Several aquaporins (AQPs) are expressed in mammalian skin. Some are directly involved in water transport, such as AQP5, which is involved in sweat secretion. In contrast, the physiological role of skin aquaglyceroporins, which permeate both water and glycerol, appears more and more complex. AQP3 is the most abundant skin aquaglyceroporin. Both water and glycerol transport by AQP3 appear to play an important role in hydration of mammalian skin epidermis. In addition, recent data suggest that glycerol transport by AQP3 is involved in the metabolism of lipids in skin as well as in the regulation of proliferation and differentiation of keratinocytes. Finally, AQP3 is also believed to be important in wound healing, as a water channel by facilitating cell migration, and as a glycerol transporter by enhancing keratinocyte proliferation and differentiation.

Roles of aquaporin-3 in the epidermis

Aquaporin-3 (AQP3) is a membrane transporter of water and glycerol expressed in plasma membranes in the basal layer keratinocytes of epidermis in normal skin. AQP3 expression in human skin is increased in response to skin stress in diseases such as atopic eczema, to various agents such as retinoic acid, and in skin carcinomas. AQP3-knockout mice have reduced stratum corneum water content and elasticity compared with wild-type mice, as well as impaired wound healing and epidermal biosynthesis. Reduced AQP3-dependent glycerol transport in AQP3-deficient epidermis appears to be responsible for these phenotype findings, as evidenced by reduced glycerol content in epidermis and stratum corneum in AQP3-knockout mice, and correction of the phenotype abnormalities by glycerol replacement. Recent data implicate AQP3 as an important determinant in epidermal proliferation and skin tumorigenesis, in which AQP3-knockout mice are resistant to tumor formation by a mechanism that may involve reduced cell glycerol content and ATP energy for biosynthesis. AQP3 is thus a key player in epidermal biology and a potential target for drug development.

Increased expression of aquaporin-3 in the epidermis of DHCR24 knockout mice

BACKGROUND

The DHCR24 (3beta-hydroxysterol-Delta24 reductase) gene encodes an enzyme catalysing conversion of desmosterol to cholesterol. Desmosterolosis is an autosomal recessive disease due to mutation in the DHCR24 gene, with low cholesterol and high desmosterol levels. To understand the pathophysiology of this disease, we utilized DHCR24 knockout mice and reported that DHCR24-/- mice die soon after birth. Their skin was less wrinkled, shiny, and revealed features of lethal restrictive dermopathy associated with severe defects in epidermal maturation and barrier function.

OBJECTIVES

Markedly increased transepidermal water loss in DHCR24-/- mice led us to examine the role of aquaporin-3 (AQP3), because this is the only water/glycerol transporting channel protein expressed in the epidermis.

METHODS

Expression of AQP3 was studied by Western blot analysis and immunohistochemistry in the epidermis of DHCR24-/- and wild-type newborn mice. Glycerol uptake was determined in the isolated keratinocytes and glycerol content in the epidermis was analysed by an enzymatic method.

RESULTS

In control mice, AQP3 was expressed only in cells of the stratum basale, indicating its expression in immature keratinocytes. In DHCR24-/- mice, AQP3 was expressed throughout the epidermis and colocalized with the immature keratinocytes (keratin 14-positive cells). The increased AQP3 expression in the epidermis of DHCR24-/- mice was mirrored by a significantly higher glycerol uptake and glycerol content. This was associated with an increase in epidermal water content of DHCR24-/- mice.

CONCLUSIONS

This is the first demonstration that elevated AQP3 results in the retention of epidermal water, causing the taut, wrinkle-free skin phenotype of the DHCR24-/- mice.

Assessment of skin absorption and irritation potential of arachidonic acid and glyceryl arachidonate using in vitro diffusion cell techniques

Arachidonic acid (AA), a precursor of pro-inflammatory mediators, and its glycerin ester, glyceryl arachidonate (GA), are reportedly used in cosmetic products. In vitro skin penetration of AA and GA and GA's ester hydrolysis was determined in flow-through diffusion cells. AA penetration with human and rat skin was 19.5% and 52.3% of the applied dose respectively, a substantial amount of which remained in the skin at 24h. Similar penetration results were obtained with GA in human skin. However, GA penetration through cultured skin (EpiDerm) was 51% of the applied dose, almost all of which appeared in the receptor fluid. At least 27.8% of GA penetrating skin was hydrolyzed to AA. In vitro methods were used to assess skin irritation in diffusion cells. Skin irritation of AA, sodium lauryl sulfate (SLS), and Tween 80 was determined by changes in transepidermal water loss (TEWL), skin viability (3-(4,5-dimethylthiaxol-2-yl)-2,5-diphenyltetrazolium bromide, MTT, formation), and cytokine release (IL-1alpha). SLS irritation was much less pronounced in an emulsion versus an aqueous vehicle. No significant irritation was observed in vitro from AA in an emulsion. This work predicts that AA would penetrate human skin in vivo and that it could be formed in skin from topically applied GA.

Increased expression of aquaporin 3 in atopic eczema

BACKGROUND

Dry skin in atopic eczema depends on increased water loss. The mechanisms behind this are poorly understood. The aim of this work was to identify genes that may contribute to water loss in eczema.

METHODS

Affymetrix DNA microarrays U133A were used to analyse gene expression in skin biopsies from 10 patients with atopic eczema and 10 healthy controls.

RESULTS

DNA microarray analysis showed up-regulation of 262 genes and down-regulation of 129 genes in atopic eczema. The known functions of these genes were analysed using Gene Ontology to identify genes that could contribute to increased water loss. This led to identification of aquaporin 3 (AQP3), which has a key role in hydrating healthy epidermis. Increased expression of AQP3 was found in eczema compared with healthy skin. This was confirmed with real-time polymerase chain reaction (P<0.001). In healthy skin, epidermal AQP3 immunoreactivity was weak and mainly found in the stratum basale. A gradient was formed with decreasing AQP3 staining in the lower layers of the stratum spinosum. By contrast, in acute and chronic atopic eczema strong AQP3 staining was found in both the stratum basale and the stratum spinosum.

CONCLUSIONS

Aquaporin 3 is the predominant aquaporin in human skin. Increased expression and altered cellular distribution of AQP3 is found in eczema and this may contribute to water loss.

Expression and function of aquaporins in human skin: Is aquaporin-3 just a glycerol transporter?

The aquaporins (AQPs) are a family of transmembrane proteins forming water channels. In mammals, water transport through AQPs is important in kidney and other tissues involved in water transport. Some AQPs (aquaglyceroporins) also exhibit glycerol and urea permeability. Skin is the limiting tissue of the body and within skin, the stratum corneum (SC) of the epidermis is the limiting barrier to water loss by evaporation. The aquaglyceroporin AQP3 is abundantly expressed in keratinocytes of mammalian skin epidermis. Mice lacking AQP3 have dry skin and reduced SC hydration. Interestingly, however, results suggested that impaired glycerol, rather than water transport was responsible for this phenotype. In the present work, we examined the overall expression of AQPs in cells from human skin and we reviewed data on the functional role of AQPs in skin, particularly in the epidermis. By RT-PCR on primary cell cultures, we found that up to 6 different AQPs (AQP1, 3, 5, 7, 9 and 10) may be selectively expressed in various cells from human skin. AQP1, 5 are strictly water channels. But in keratinocytes, the major cell type of the epidermis, only the aquaglyceroporins AQP3, 10 were found. To understand the role of aquaglyceroporins in skin, we examined the relevance to human skin of the conclusion, from studies on mice, that skin AQP3 is only important for glycerol transport. In particular, we find a correlation between the absence of AQP3 and intercellular edema in the epidermis in two different experimental models: eczema and hyperplastic epidermis. In conclusion, we suggest that in addition to glycerol, AQP3 may be important for water transport and hydration in human skin epidermis.

Aquaporin-1: a novel promoter of tumor angiogenesis

Angiogenesis is critical to solid tumor growth; therefore, understanding how blood vessels form within a developing tumor has become a principal, yet challenging, objective. The recent discovery that deletion of the water channel protein, aquaporin-1, impairs tumor angiogenesis provides novel insights into the mechanisms governing the neovascularization and growth of tumors.

Water and heat--the priority for the newborn infant

Maintaining fluid and heat balance is of vital importance to the newborn infant. At birth, the infant is exposed to a cold and dry environment, and preterm neonates in particular, are then at risk of dehydration and hypothermia. These conditions may have serious consequences and significantly influence mortality and morbidity. Preterm neonates have a high rate of water and heat loss mainly as a consequence of their immature skin. The care environment influences the magnitude of water and heat exchange and needs to be individually tailored on the basis of the infant's clinical status, maturity at birth and postnatal age. This paper reviews data obtained from series of studies on neonatal water and heat exchange using non-invasive measurements of insensible water loss and calculations of different modes of heat exchange. These studies have influenced the way in which newborn infants are being nursed today.

Besonderheiten der Haut des Neugeborenen und jungen Säuglings

Detailed knowledge of the special features of neonatal and infant skin is a prerequisite for adequate skin care in this age group. Immediately postpartum, the newborn baby's skin assumes vital functions regarding water and electrolyte homeostasis and thermoregulation, as well as innate and adaptive host defense. Due to its functional and structural immaturity, premature skin requires special care. Mature neonates demonstrate benign, transient skin lesions that do not require specific therapy but have to be distinguished from serious and potentially life-threatening illnesses.

Aquaporins in development -- a review

Water homeostasis during fetal development is of crucial physiologic importance. It depends upon maternal fetal fluid exchange at the placenta and fetal membranes, and some exchange between fetus and amniotic fluid can occur across the skin before full keratinization. Lungs only grow and develop normally with fluid secretion, and there is evidence that cerebral spinal fluid formation is important in normal brain development. The aquaporins are a growing family of molecular water channels, the ontogeny of which is starting to be explored. One question that is of particular importance is how well does the rodent (mouse, rat) fetus serve as a model for long-gestation mammals such as sheep and human? This is particularly important for organs such as the lung and the kidney, whose development before birth is very much less in rodents than in the long-gestation species.

Management of fluid balance in the very immature neonate

Preterm birth requires rapid adaptation from a liquid to a gaseous, low humidity environment. There are several ways in which this can be facilitated. The management of sodium and water balance is considered here.