sphingosine-phosphorylcholine and Dermatitis--Atopic

A deficiency of ordinary ceramides in the stratum corneum is an essential etiologic factor for the dry and barrier-disrupted skin of patients with atopic dermatitis (AD). We have proposed that the mechanism underlying that deficiency involves a novel sphingolipid metabolizing enzyme, termed sphingomyelin (SM) glucosylceramide (GCer) deacylase, which hydrolyzes SM or GCer at the acyl site to yield their lysoforms sphingosylphosphorylcholine (SPC) or glucosylsphingosine (GSP) instead of ceramide, leading to the ceramide deficiency in the AD skin. The enzymic characteristics observed showed a pH dependency of catalytic activity with a peak at pH 5.0 and a molecular weight of 40,000. Analytical isoelectric focusing (IEF) chromatography demonstrated that the pI values of SM deacylase, GlcCDase, SMase and ceramidase were 4.2, 7.4, 7.0 and 5.7, respectively. Those enzymic characteristics of SM-GCer deacylase are completely distinct from ceramidase as well as the other known deacylases. Our enzymic measurements demonstrated that SM-GCer deacylase activity is enhanced more than 5-fold in involved stratum corneum, more than 3-fold in uninvolved stratum corneum and approximately 3-fold in the involved epidermis from patients with AD compared with healthy controls. Our findings suggest that the novel enzyme, SM-GCer deacylase, is expressed in situ at significant levels in the epidermis of AD patients. This results in the production of SPC and GSP, instead of ceramides, which leads in turn to the ceramide deficiency seen in the stratum corneum of those patients. It is likely that the biogenesis of SM-GCer deacylase may be critical to the pathogenesis of AD.

Topics: Amidohydrolases; Ceramides; Dermatitis, Atopic; Epidermis; Glucosylceramides; Humans; Phosphorylcholine; Psychosine; Sphingomyelins; Sphingosine

To elucidate the mechanisms of severe itch in atopic dermatitis, we investigated the role of leukotriene B(4) , a potent itch mediator, in spontaneous itch-related behaviour in NC mice with atopic dermatitis-like skin lesions. Topical application of the BLT leukotriene B(4) receptor antagonist ONO-4057 inhibited spontaneous itch-related behaviour. The concentration of leukotriene B(4) was significantly increased in the lesional skin. The expression levels of 5-lipoxygenase were also elevated in the lesional skin, yet present throughout the epidermis of both healthy and lesional skin. These results suggest a role for leukotriene B(4) in chronic dermatitis-related itch. Sphingosylphosphorylcholine (SPC) was increased in the epidermis of the lesional skin. Moreover, intradermal injection of SPC elicited itch-related behaviours in healthy mice. Because SPC induces itch-related responses through the production of leukotriene B(4) in keratinocytes (J Invest Dermatol, 129, 2009, 2854), these results suggest that an increase in SPC induces leukotriene B(4) -mediated itching in chronic dermatitis. BLT1 receptor and 5-lipoxygenase in the skin may be effective pharmacological targets for the treatment of itch in atopic dermatitis.

Topics: Administration, Topical; Animals; Arachidonate 5-Lipoxygenase; Dermatitis, Atopic; Disease Models, Animal; Leukotriene B4; Mice; Phenylpropionates; Phosphorylcholine; Pruritus; Receptors, Leukotriene B4; Skin; Sphingosine

In atopic dermatitis, the concentration in the skin of sphingosylphosphorylcholine (SPC), which is produced from sphingomyelin by sphingomyelin deacylase, is increased. In the present study, we investigated the itch-eliciting activity of SPC and related substances and the mechanisms of SPC action in mice. An intradermal injection of SPC, but not sphingomyelin and sphingosine, induced scratching, an itch-associated response, which was not suppressed by a deficiency in mast cells or the H(1) histamine receptor antagonist terfenadine. The action of SPC was inhibited by the mu-opioid receptor antagonist naltrexone. SPC action also was inhibited by the 5-lipoxygenase inhibitor zileuton and the leukotriene B(4) antagonist ONO-4057, but not by the cyclooxygenase inhibitor indomethacin. Moreover, SPC action was inhibited by the antiallergic agent azelastine, which suppresses the action and production of leukotriene B(4). Administration of SPC to the skin and to primary cultures of keratinocytes increased leukotriene B(4) production. SPC increased intracellular Ca(2+) ion concentration in primary cultures of dorsal root ganglion neurons and keratinocytes. These results suggest that SPC induces itching through a direct action on primary afferents and leukotriene B(4) production of keratinocytes. Sphingomyelin deacylase and SPC receptors may be previously unreported targets for antipruritic drugs.

Topics: Animals; Calcium; Dermatitis, Atopic; Ganglia, Spinal; Histamine; Histamine H1 Antagonists, Non-Sedating; Injections, Intradermal; Keratinocytes; Leukotriene B4; Male; Mast Cells; Mice; Mice, Inbred ICR; Naltrexone; Narcotic Antagonists; Neurons; Phosphorylcholine; Pruritus; Skin; Sphingomyelins; Sphingosine; Terfenadine

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.

Topics: Adolescent; Adult; Ceramides; Dermatitis, Atopic; Epidermis; Humans; Phosphorylcholine; Psychosine; Sphingosine; Up-Regulation

Previously, we demonstrated that there is a marked reduction in the amount of ceramide in the stratum corneum of both lesional and nonlesional forearms in atopic dermatitis (AD), suggesting that an insufficiency of ceramides in the stratum corneum is an etiologic factor in atopic dry and barrier-disrupted skin. In this study, we investigated, as a possible mechanism involved in the ceramide deficiency, whether sphingomyelin (SM) metabolism is altered in AD as compared to normal controls. In stripped stratum corneum and biopsied whole epidermis of patients with AD, SM hydrolysis as measured at pH 4.7 using [choline-methyl-14C]sphingomyelin as a substrate were markedly increased by 27- and 7-fold, respectively. Radio-thin-layer chromatography of the reaction products revealed that, whereas the SM hydrolysis in age-matched normal controls were associated with sphingomyelinase (SMase) that degrades SM to yield ceramides and phosphorylcholine (PC), most of the SM hydrolysis detected in AD were attributable not to the SMase but to a hitherto undiscovered epidermal enzyme, SM acylase, which releases free fatty acid and sphingosyl-PC (Sph-PC) instead of ceramides. The potential of this acylase-like enzyme to generate Sph-PC through SM hydrolysis was corroborated by thin-layer chromatographic analysis of the reaction products obtained using porcine kidney acylase, followed by high-performance liquid chromatography-mass spectrometry. Furthermore, Sph-PC was also detected by high-performance liquid chromatography-mass spectrometry after incubation of SM with atopic stratum corneum samples. On the other hand, the stratum corneum of patients with contact dermatitis or chronic eczema exhibited neither increased SM hydrolysis nor the generation of Sph-PC upon radio-thin-layer chromatographic analysis. These findings suggest that SM metabolism is altered in AD, resulting in a decrease in levels of ceramides, which could be an etiologic factor in the continuous generation of atopic dry and barrier disrupted skin observed in AD.

Topics: Amidohydrolases; Ceramides; Dermatitis, Atopic; Humans; Hydrolysis; Phosphorylcholine; Sphingomyelins; Sphingosine