Novel Photoinduced Squalene Cyclic Peroxide Identified, Detected, and Quantified in Human Skin Surface Lipids

Skin surface lipids (SSLs) form the first barrier that protects the human organism from external stressors, disruption of the homeostasis of SSLs can result in severe skin abnormalities. One of the main causes of this disruption is oxidative stress that is primarily due to SSLs oxidation. Squalene (SQ), the most abundant lipid among SSLs, was shown to first undergo singlet molecular oxygen (1O2) oxidation to yield 6 SQ-monohydroperoxide (SQ-OOH) isomers as the primary oxidation products. However, due to the instability and lability of hydroperoxides, we found that when total SQ-OOH isomers are further photooxidized, they form a unique higher molecular weight secondary oxidation product. To generate the compound, we photooxidized total SQ-OOH isomers in the presence of ground state molecular oxygen (3O2), after its isolation and purification, we studied its structure using MS/MS, NMR, derivatization reactions, and chemical calculations. The compound was identified as 2-OOH-3-(1,2-dioxane)-SQ. Photooxidation of individual SQ-OOH isomers revealed that 6-OOH-SQ is the precursor of 2-OOH-3-(1,2-dioxane)-SQ and indicated the possibility of the formation of similar cyclic peroxides from each isomer following the same photoinduced chain reaction mechanism. An HPLC-MS/MS method was developed for the analysis of 2-OOH-3-(1,2-dioxane)-SQ and its presence on the skin was confirmed in SSLs of six healthy individuals. Its quantity on the skin correlated directly to that of SQ and was not inversely proportional to its precursor, indicating the possibility of its accumulation on the skin surface and the constant regeneration of 6-OOH-SQ from SQ’s oxidation. In general, research on lipid cyclic peroxides in the human organism is very limited, and especially on the skin. This study shows for the first time the identification and presence of a novel SQ cyclic peroxide “2-OOH-3-(1,2-dioxane)-SQ” in SSLs, shedding light on the importance of further studying its effect and role on the skin.

Non-invasive human skin transcriptome analysis using mRNA in skin surface lipids

Non-invasive acquisition of mRNA data from the skin would be extremely useful for understanding skin physiology and diseases. Inspired by the holocrine process, in which the sebaceous glands secrete cell contents into the sebum, we focused on the possible presence of mRNAs in skin surface lipids (SSLs). We found that measurable human mRNAs exist in SSLs, where sebum protects them from degradation by RNases. The AmpliSeq transcriptome analysis was modified to measure SSL-RNAs, and our results revealed that SSL-RNAs predominantly contained mRNAs derived from sebaceous glands, epidermis, and hair follicles. Analysis of SSL-RNAs non-invasively collected from patients with atopic dermatitis revealed significantly increased expression of inflammation-related genes and decreased expression of terminal differentiation-related genes, consistent with the results of previous reports. Further, we found that lipid synthesis-related genes were downregulated in the sebaceous glands of patients with atopic dermatitis. These results indicate that the analysis of SSL-RNAs is promising to understand the pathophysiology of skin diseases.

Lipidomics Profiling of Skin Surface Lipids in Senile Pruritus

Background: Senile pruritus is common, yet its etiology remains unknown. Aging-associated skin barrier defects and skin surface lipid (SSL) alterations have been postulated to play important roles in its occurrence. In the present study, the lipidomic profiles of SSLs in elderly patients were examined to better understand the potential causes of senile pruritus. Methods: Transepidermal water loss (TEWL) was evaluated to assess the skin barrier function. The Ameliorated Kawashima Itch Scale score was used to measure the pruritus severity. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and multivariate data analysis were employed to investigate SSL alterations. Results: The results showed that senile pruritus patients had higher TEWL values than control subjects (13.13±4.28 versus 6.71±2.45, p<0.01). LC-MS/MS revealed significant differences in the lipidomic profiles and identified 81 species of SSLs that differed between the two groups. Compared with control subjects, senile pruritus patients had increased levels of ceramides (Cers), diacylglycerols, fatty acids, phosphatidylcholines, phosphatidylethanolamines, phytosphingosines, sphingosines, diacylceryl-3-O-carboxyhydroxymethylcholine, diacylglyceryl trimethylhomoserine, and unsaturated free fatty acids, but decreased levels of triacylglycerol. Cer-EOS, Cer-NDS, and Cer-NS were positively correlated with TEWL value (p<0.05). Pruritus severity score was positively correlated with sphingomyelin, Cer-NP, Cer-AS, Cer-NDS, and Cer-NS, but negatively correlated with Cer-BS, Cer-EODS, Cer-EOS, and Cer-AP. Conclusions: The present study indicated that patients with senile pruritus have impaired skin barrier function and altered SSL composition. Certain SSL species identified in this study may be potential targets for future studies on the pathogenesis of senile pruritus.Trial registration: Peking University International Hospital (Number: YN2018QN04; date: January 2019).

Lipidomics Profiling of Skin Surface Lipids in Senile Pruritus

Background: Senile pruritus is common, yet its etiology remains unknown. Aging-associated skin barrier defects and skin surface lipids (SSL) alterations have been postulated to play important roles in its occurrence. In the present study, the lipidomic profiles of SSLs in elderly patients were examined to better understand the potential causes of senile pruritus. Methods: Transepidermal water loss (TEWL) was evaluated to assess the skin barrier function. The Ameliorated Kawashima Itch Scale score was used to measure the pruritus severity. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and multivariate data analysis were employed to investigate SSL alterations. Results: The results showed that senile pruritus patients had higher TEWL values than control subjects (13.13±4.28 versus 6.71±2.45, P<0.01). LC-MS/MS revealed significant differences in the lipidomic profiles and identified 81 species of SSLs that differed between the two groups. Compared with control subjects, senile pruritus patients had increased levels of ceramides (Cers), diacylglycerols, fatty acids, phosphatidylcholines, phosphatidylethanolamines, phytosphingosines, sphingosines, diacylceryl-3-O-carboxyhydroxymethylcholine, diacylglyceryl trimethylhomoserine, and unsaturated free fatty acids, but decreased levels of triacylglycerol. Cer-EOS, Cer-NDS, and Cer-NS were positively correlated with TEWL value (P<0.05). Pruritus severity score was positively correlated with sphingomyelin, Cer-NP, Cer-AS, Cer-NDS, and Cer-NS, but negatively correlated with Cer-BS, Cer-EODS, Cer-EOS, and Cer-AP. Conclusions: The present study indicated that patients with senile pruritus have impaired skin barrier function and altered SSL composition. Certain SSL species identified in this study may be potential targets for future studies on the pathogenesis of senile pruritus.Trial registration: Peking University International Hospital (Number: YN2018QN04; date: January 2019).

Lipidomics Profiling of Skin Surface Lipids in Senile Pruritus

Background: Senile pruritus is common, yet its etiology remains unknown. We examined the lipidomics profiles of skin surface lipids (SSL) in the elderly to better understand potential causes for senile pruritus. Methods:Transepidermal water loss (TEWL) was used to assess skin barrier function. Ameliorated Kawashima itch scale were used to measure the pruritus score. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and multivariate data analysis were used to investigate SSL alternations. Results:The results showed that the senile pruritus have higher TEWL values than controls (13.13±4.28 versus 6.71±2.45, p< 0.01). LC-MS/MS showed significant differences in lipidomics and identified 81 species of SSL that differ between two groups. Compared to controls, the levels of ceramides, diacylcerols, fatty acids, phosphatidylcholines, phosphatidylethar, phytosphingsines, sphingosines, diacylceryl-3-O-carboxyhydroxymethylcholine, diacylglyceryl trimethylhomoserine, unsaturated free fatty acids increased, whereas triacylglycerol decreased. CER-EOS, CER-NDS and CER-NS were positively correlated with TEWL values (p<0.05). Sphingomyelin, Cer-NP, Cer-AS, Cer-NDS, Cer-NS were positively correlated with pruritus severity scores, while Cer-BS, Cer-EODS, Cer-EOS, Cer-AP were negatively correlated. Conclusion:Our study indicated that the senile pruritus have impaired skin barrier function and altered SSL composition. Select SSL species identified in this study may be potential target for future studies on the pathogenesis of idiopathic senile pruritus

An untargeted investigation into the skin surface lipidome in the West Highland white terrier dog, with and without atopic dermatitis

Background – The skin barrier is important in the pathogenesis of atopic dermatitis and stratum corneum lipids have a critical role. Skin surface lipids have been largely overlooked but also contribute to barrier function. An untargeted approach was used to compare the skin surface lipids from atopic and non-atopic West Highland White terrier dogs. The primary hypothesis was that a difference in the lipidome of atopic and non-atopic dogs would be found and the secondary hypothesis was that affected and unaffected skin would differ in lipid profile.Results – Thirty-nine dogs were classified into one of four disease status groups based on strict criteria. Samples for lipid analysis were collected from affected and unaffected skin, and liquid chromatography/mass spectrometry found 421 lipid soluble features. Ten lipids were positively identified. Statistical analysis could not distinguish between non-atopic and atopic dogs. Partial least squares-discriminant analysis revealed a difference in the lipid profiles from affected and non-affected skin irrespective of disease status. Conclusions – An untargeted approach found a large array of unidentified lipids from the skin surface. There was a difference in the lipidome between affected and unaffected skin that was not related to disease status. Investigation into the lipidome of the skin surface in health and disease is an emerging area of research which could have clinical and therapeutic applications.