This article is available online at http://www.jlr.org novo pathways, such as alterations of some species of the targeted lipidomes into others. Similar to common quantitative analyses using direct MS or LC-MS that need authentic standards together with internal ones, quantitative lipidomics may also require a standard set of all lipid species targeted, because each lipid species has a different molar response in MS detection except for special cases. However, it is practically impossible to obtain all authentic species, including not only different even straight carbon chains but also odd and/or branched ones. To overcome such limitations, lipidomics researchers have contrived a novel procedure to quantify lipidomes comprehensively. Han and Gross ( 3 ) proposed a quantitative method for analyzing triglyceride molecular species using direct MS, which involves a procedure to calculate response factors for species that are not available as authentic materials, based on differences of the responses in the numbers of total carbons and double bonds among the species. For quantitative determination of phospholipid molecular species, Koivusalo et al. ( 4 ) utilized the following parameAbstract One of the key challenges in lipidomics is to quantify lipidomes of interest, as it is practically impossible to collect all authentic materials covering the targeted lipidomes. For diverse ceramides (CER) in human stratum corneum (SC) that play important physicochemical roles in the skin, we developed a novel method for quantifi cation of the overall CER species by improving our previously reported profi ling technique using normal-phase liquid chromatography-electrospray ionization-mass spectrometry (NPLC-ESI-MS). The use of simultaneous selected ion monitoring measurement of as many as 182 kinds of molecular-related ions enables the highly sensitive detection of the overall CER species, as they can be analyzed in only one SC-stripped tape as small as 5 mm × 10 mm. To comprehensively quantify CERs, including those not available as authentic species, we designed a procedure to estimate their levels using relative responses of representative authentic species covering the species targeted, considering the systematic error based on intra-/inter-day analyses. The CER levels obtained by this method were comparable to those determined by conventional thin-layer chromatography (TLC), which guarantees the validity of this method. , ceramide class consisting of non-hydroxy fatty acids and 4-sphingenines; ESI, electrospray ionization; LOD, limit of detection; LOQ, limit of quantifi cation; NPLC, normal-phase liquid chromatography; RPLC, reversed-phase liquid chromatography; RSD, relative standard deviation; SC, stratum corneum; SIM, selected ion monitoring; S/N, signal to noise; TLC, thinlayer chromatography

A skin permeability barrier is essential for terrestrial animals, and its impairment causes several cutaneous disorders such as ichthyosis and atopic dermatitis. Although acylceramide is an important lipid for the skin permeability barrier, details of its production have yet to be determined, leaving the molecular mechanism of skin permeability barrier formation unclear. Here we identified the cytochrome P450 gene CYP4F22 (cytochrome P450, family 4, subfamily F, polypeptide 22) as the long-sought fatty acid ω-hydroxylase gene required for acylceramide production. CYP4F22 has been identified as one of the autosomal recessive congenital ichthyosis-causative genes. Ichthyosis-mutant proteins exhibited reduced enzyme activity, indicating correlation between activity and pathology. Furthermore, lipid analysis of a patient with ichthyosis showed a drastic decrease in acylceramide production. We determined that CYP4F22 was a type I membrane protein that locates in the endoplasmic reticulum (ER), suggesting that the ω-hydroxylation occurs on the cytoplasmic side of the ER. The preferred substrate of the CYP4F22 was fatty acids with a carbon chain length of 28 or more (≥C28). In conclusion, our findings demonstrate that CYP4F22 is an ultra-long-chain fatty acid ω-hydroxylase responsible for acylceramide production and provide important insights into the molecular mechanisms of skin permeability barrier formation. Furthermore, based on the results obtained here, we proposed a detailed reaction series for acylceramide production.acylceramide | ceramide | lipid | skin | sphingolipid

Background: Specific species of ceramides (Cer), major constituents of lipids in the stratum corneum (SC), are decreased and are correlated with SC barrier and water-holding functions in the skin of patients with atopic dermatitis (AD) or psoriasis (Pso). However, possible correlations between Cer subclass ratios and skin properties in barrier-disrupted skin and in healthy skin remain unclear. The objective of this study was to identify a new marker to evaluate skin properties and epidermal differentiation in SC not only in barrier-disrupted skin but also in healthy skin. Methods: The Cer subclass ratios in the SC of healthy control subjects and in patients with AD or Pso were evaluated. Correlations with candidate markers and facial skin features of healthy Japanese females (20-74 years old, n = 210) were investigated. Variations of markers during epidermal differentiation were studied in human epidermis and in cultured keratinocytes.

Harlequin ichthyosis (HI) is caused by loss-of-function mutations in the keratinocyte lipid transporter ABCA12. The patients often die in the first 1 or 2 weeks of life, although HI survivors' phenotypes improve within several weeks after birth. In order to clarify the mechanisms of phenotypic recovery, we studied grafted skin and keratinocytes from Abca12-disrupted (Abca12 ؊/؊ ) mice showing abnormal lipid transport. Abca12 ؊/؊ neonatal epidermis showed significantly reduced total ceramide amounts and aberrant ceramide composition. Immunofluorescence and immunoblotting of Abca12 ؊/؊ neonatal epidermis revealed defective profilaggrin/filaggrin conversion and reduced protein expression of the differentiation-specific molecules, loricrin, kallikrein 5, and transglutaminase 1, although their mRNA expression was up-regulated. In contrast, Abca12 ؊/؊ skin grafts kept in a dry environment exhibited dramatic improvements in all these abnormalities. Increased transepidermal water loss, a parameter representing barrier defect, was remarkably decreased in grafted Abca12 ؊/؊ skin. Ten-passage sub-cultured Abca12 Harlequin ichthyosis (HI) (OMIM 242500) is one of the most severe genetic skin disorders, and its clinical features at birth include severe ectropion, eclabium, flattening of the ears, and large thick plate-like scales over the entire body. 1Infants affected with HI frequently die within the early neonatal period, although an increasing survival rate for HI newborns has recently been highlighted. 2 In 2005, we and another independent research group identified mutations in the ATP-binding cassette transporter A12 (ABCA12) gene as the cause of HI. 3,4 We previously demonstrated that a severe ABCA12 deficiency causes defective lipid transport in lamellar granules in the upper spinous and granular layer keratinocytes, resulting in malformation of intercellular lipid layers at the granular/cornified layer interface and epidermal lipid barrier disruption resulting in HI phenotype. 3 We recently generated Abca12-disrupted (Abca12 Ϫ/Ϫ ) mice by targeting Abca12, which closely reproduced the human HI phenotype and died soon after birth. 5 We tried systemic retinoid administration to the pregnant female mice as a form of fetal therapy, although no therapeutic effect was

These results suggest that not only the level of CER, but also specific CER species strongly contribute to dry skin relief and products that increase those are useful to improve dry skin conditions.