Abstract

To clarify the functional relevance of sphingomyelin (SM) deacylase to the ceramide deficiency seen in atopic dermatitis (AD), we developed a new highly sensitive method and measured the metabolic intermediate sphingosylphosphorylcholine (SPC) that accumulates in the stratum corneum. SPC in intercellular lipids extracted from stratum corneum was reacted with [(14)C]acetic anhydride to yield [(14)C-C(2)]SM, which was then analyzed by TLC. In both the lesional and non-lesional stratum corneum obtained from patients with AD, there was a significant increase in the content of SPC over that of healthy control subjects. There was a reciprocal relationship between increases in SPC and decreases in ceramide levels of stratum corneum obtained from healthy controls, and from lesional and non-lesional skin from patients with AD. Comparison with other sphingolipids present in the stratum corneum demonstrated that there is a significant positive correlation between SPC and glucosylsphingosine, another lysosphingolipid derived from glucosylceramide by another novel epidermal enzyme, termed glucosylceramide deacylase. In contrast, there was no correlation between SPC and sphingosine, a degradative product generated from ceramide by ceramidase. These findings strongly suggest the physiological relevance of SM deacylase function in vivo to the ceramide deficiency found in the skin of patients with AD.

Highlights

  • To clarify the functional relevance of sphingomyelin (SM) deacylase to the ceramide deficiency seen in atopic dermatitis (AD), we developed a new highly sensitive method and measured the metabolic intermediate sphingosylphosphorylcholine (SPC) that accumulates in the stratum corneum

  • In order to clarify the physiologic and functional relevance of SM deacylase to the ceramide deficiency in the epidermis of patients with AD, we have determined whether the major metabolic intermediate, SPC, that is produced accumulates in the stratum corneum of patients with AD as a result of SM deacylase activity

  • To determine whether SPC exists in the stratum corneum of healthy subjects at substantial levels, HPLC-MS spectrometry was carried out using lipids extracted from the stratum corneum following their separation by thin-layer chromatograms (TLC) (Fig. 3A)

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Summary

Introduction

To clarify the functional relevance of sphingomyelin (SM) deacylase to the ceramide deficiency seen in atopic dermatitis (AD), we developed a new highly sensitive method and measured the metabolic intermediate sphingosylphosphorylcholine (SPC) that accumulates in the stratum corneum. We found that the causative factor behind the ceramide deficiency in the stratum corneum of patients with AD is an abnormal expression of sphingomyelin (SM) deacylase in their epidermis [6] This enzyme hydrolyzes SM at the acyl site to yield free fatty acid and sphingosylphosphorylcholine (SPC) instead of the formation of ceramide and phosphorylcholine (PC) by sphingomyelinase (SMase). Direct enzymatic analysis of the stratum corneum or of the epidermis of patients with AD revealed that there are 9-fold or 3-fold increases, respectively, in the activity of SM deacylase in patients with AD compared with healthy normal controls [7] The sum of those findings demonstrates that the novel epidermal enzyme SM deacylase is expressed at high levels in the epidermis of patients with AD. In order to clarify the physiologic and functional relevance of SM deacylase to the ceramide deficiency in the epidermis of patients with AD, we have determined whether the major metabolic intermediate, SPC, that is produced accumulates in the stratum corneum of patients with AD as a result of SM deacylase activity

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