Neonatal skin maturation--vernix caseosa and free amino acids.

Neonatal skin hydration decreases rapidly postnatally and then increases, indicating adaptive changes in stratum corneum water handling properties. Transition from high to low humidity at birth may initiate filaggrin proteolysis to free amino acids. Neonatal skin with vernix caseosa retained is more hydrated than skin with vernix removed. This study examines the potential roles of free amino acids and vernix in postnatal adaptation of infant stratum corneum in vivo. Specifically, the ontogeny of free amino acid generation in neonatal stratum corneum and the role of vernix caseosa in postnatal adaptation were examined using high performance liquid chromatography. Free amino acids were quantified for infant skin samples collected at (i) birth and 1 month and (ii) birth and 24 hours after vernix caseosa retention or removal and compared to neonatal foreskin, vernix caseosa, and adult stratum corneum using t-tests, analysis of variance, or univariate procedures. Free amino acids were extremely low at birth, significantly higher 1 month later but lower than in adults. Vernix caseosa retention led to significantly higher free amino acids 24 hours after birth compared to infants with vernix caseosa removed, and it paralleled the higher stratum corneum hydration of vernix caseosa-retained skin. Vernix caseosa contained free amino acids, with glutamic acid and histidine levels higher than in infants. Free amino acids in vernix caseosa-retained skin appear to originate from vernix caseosa. Free amino acids were lower in neonatal foreskin than adult forearm stratum corneum. Arginine was higher than citrulline at birth, but levels were comparable in older infants. The free amino acid increase at 1 month may be initiated by the humidity transition at birth and supports results in animals. The findings have implications for infant skin care practices.

Amputee skin condition: occlusion, stratum corneum hydration and free amino acid levels.

Patients with a prosthetic limb report negative skin effects, including irritation, rash and chafing, which can lead to infection, discomfort and reduced wear time to significantly impact normal activities. The aims were to examine the epidermal integrity (transepidermal water loss, TEWL), stratum corneum (SC) hydration [moisture accumulation rate (MAT)], friction and biomechanical properties in active below the knee amputees and to determine the effects of an inert sock liner on skin condition. The liner reduced hydration, TEWL and friction and increased elasticity versus the amputee's conventional skin care methods. Residual limb TEWL was increased and MAT was reduced versus the contralateral normal skin. In a second study, we hypothesized that complete occlusion would decrease free amino acids (FAA) and quantified them by high performance liquid chromatography in an adult volar forearm model. Occlusion with a water vapor impermeable wet dressing led to increased TEWL, erythema and dryness and reduced MAT versus normal skin, comparable to the results in the amputees. The FAA levels were significantly reduced for the occluded sites. The results suggest that residual limb occlusion in amputees may block the formation of FAA in the upper SC. Therapies based on replacement of water binding FAAs, may alleviate the consequences of long-term occlusion.

Regional variation in the free amino acids in the stratum corneum.

Regional differences in water-binding free amino acids (FAAs) in the stratum corneum (SC) may be expected, since differences in skin biophysical properties are well known. The objective was to determine whether differences in skin hydration as a function of body site may arise from differences in the chemical makeup of the skin, specifically the FAAs. Levels were quantified from serial SC samples collected from the forearm, calf, back, torso, and jaw in two studies using HPLC methods. FAA levels were higher from the calf versus the forearm and lower from the jaw compared to torso and back skin. Body site variations in skin hydration could not be attributed to differences in FAA levels.

Natural moisturizing factors (NMF) in the stratum corneum (SC). I. Effects of lipid extraction and soaking.

Natural moisturizing factor (NMF) is essential for appropriate stratum corneum hydration, barrier homeostasis, desquamation, and plasticity. It is formed from filaggrin proteolysis to small, hygroscopic molecules including amino acids. We hypothesized that common lipid extraction and soaking in water would alter the level of NMF in the upper SC and its biophysical properties. A novel method of measuring and quantifying the amino acid components of NMF is presented. Adhesive tapes were used to collect samples of the stratum corneum (SC) and were extracted with 6mM perchloric acid for analysis by reverse-phase HPLC. HPLC results were standardized to the amount of protein removed by the tapes. An increase in NMF was found with increased SC depth. Also, the combination of extraction and soaking was found to increase NMF loss relative to control or to extraction or soaking alone. Our results indicate that common skin care practices significantly influence the water binding materials in the upper SC. The findings have implications for the evaluation and formulation of skin care products.

Natural moisturizing factors (NMF) in the stratum corneum (SC). II. Regeneration of NMF over time after soaking.

The detrimental effects of prolonged water exposure on skin are well known. Information on the effects of short-term exposure, e.g., during bathing, showering, and hand washing, on NMF levels is limited. In an attempt to isolate the effects of soaking on the NMF, a time course for skin sample collection was devised in which adhesive tapes were applied 0.5 and four hours after soaking of the treated arm. Significant decreases in NMF levels, quantified by HPLC analysis of serial tape strips, were observed 0.5 hours after soaking, with a replacement of NMF occurring by the four-hour mark. This replacement corresponds to a parallel rebound in skin pH also observed at these times. Stratum corneum hydration values, measured instrumentally as the rate of moisture accumulation (MAT), however, were depressed 0.5 hours post-soaking and remained low four hours later. In addition, significant increases in skin pH were observed during the immediate post-soak period. These findings suggest that short-term exposure to water alone produces significant changes in the stratum corneum.