No skin off your back: the sampling and extraction of sebum for metabolomics

Discovery of small molecule ACC inhibitors: Potential treatment for excessive sebum secretion

Overproduction of sebum can lead to various skin disorders, including acne and seborrheic dermatitis. Acetyl-CoA carboxylase is a key enzyme in the de novo synthesis of sebum. Consequently, inhibiting acetyl-CoA carboxylase is a feasible strategy to reduce sebum production, thereby providing therapeutic benefits for associated skin conditions. This review described the de novo synthesis of sebum and discusseed the various isoforms, functions and catalytic mechanisms of acetyl-CoA carboxylase. Additionally, it offered a comprehensive overview of the research advancements and structural-activity relationships of small molecule inhibitors of acetyl-CoA carboxylase over the past 15 years.

Cutaneous Hormone Sampling and Analysis for Dermatologic Research

The skin can generate hormones through de novo steroid hormone synthesis. These hormones have been shown to play a significant role in inflammatory skin conditions through the regulation of skin immunity, sebum production, and skin barrier function. Although there is growing interest in understanding the composition and function of skin hormones throughout the human lifespan and in various pathologies, there remains a need to standardize sampling and quantification methods. In this article, we discuss an emerging noninvasive approach in skin hormone quantification through adhesive sebum collection tape followed by analysis through mass spectrometry or hormone-specific immunoassays. This approach is highly adaptable, allowing for repetitive sampling over time and across diverse study populations.

Monitoring Skin Volatile Emissions Using Wearable Sensors

Human skin emits a continuous flux of volatile compounds reflecting various metabolic processes in the body, microbial activity, and environmental factors. Harnessing this emission for diagnostics is of great interest given the noninvasive, passive, and accessible nature of the emission, and there is much research underway to understand the value of this skin-emitted volatile organic compound (VOC) matrix. In parallel to this, wearable skin VOC sensors are emerging and garnering attention due to their potential to provide noninvasive, real-time information for monitoring human health, overcoming many of the design challenges related to biofluid monitoring via wearables. The projected opportunities for skin VOCs are fueling innovations in wearable VOC monitoring. This review discusses the most recent developments, from fully integrated wearable skin VOC sensors that exploit existing semiconductor technology to the design and preparation of advanced new sensing materials and devices to deliver new modalities for wearable skin VOC sensors. We articulate the challenges, limitations, and opportunities for technological advances to provide a perspective on promising directions for future developments.

Optimizing Skin Surface Metabolomics: A Comprehensive Evaluation of Sampling Methods, Extraction Solvents, and Analytical Techniques

Characterizing the metabolite fingerprint from the skin surface provides invaluable insights into skin biology and microbe-host interactions. To ensure data accuracy and reproducibility, it is essential to develop standard operating procedures for skin surface metabolomics. However, there is a notable lack of studies in this area. In this study, we thoroughly evaluated different sampling materials, extraction solvents, taping methods (frequency and number of tapes), and analytical techniques to optimize skin surface metabolomics. Our results showed that the combination of D-Squame D100 tape with a methyl tert-butyl ether/methanol extractant is optimal for skin surface lipidomics. Performing the skin-taping procedure 5 times with 1 tape yields sufficient biomass for lipid analysis, whereas the optimal taping procedure varies for water-soluble compounds. In addition, our study identified associations among the skin surface metabolites, some of which potentially underlie the formation of microbial cutotypes and offer insights into host-microbe interactions.

Sebum analysis as an advantageous source of biomolecular information

Sebum, a valuable yet underexplored source of biomolecular information, offers non-invasive collection, but its analysis presents challenges due to its hydrophobic and viscous nature. This forum article highlights the challenges but immense potential of sebum analysis in shaping the next generation of diagnostics and other biotechnological applications.

Sebaceous origins of human odor

The compounds that make up human body odor have been catalogued by researchers in many fields. Yet few are aware of exactly where these molecules come from. Volatile body-odor compounds are often cited as being produced primarily via microbial activity from precursors in sweat. While this is a source of many human volatiles, here we synthesize data showing that some of the most distinctive and abundant components of human odor instead originate from precursors in sebum, via reactions that do not involve the skin microbiome. We also review the unique biochemistry of human sebaceous glands and discuss evolutionary hypotheses that may partly explain why human sebum is so unique. Finally, we discuss how sebum-derived volatiles intersect with human health and disease, for example, via attraction of disease-vector mosquitoes or use in medical diagnostics. Our review draws insights from multiple fields, which together provide surprising clarity on some of the proximate and ultimate mechanisms underlying the distinctive composition of human odor.

Exploring Sample Storage Conditions for the Mass Spectrometric Analysis of Extracted Lipids from Latent Fingerprints

In large-scale studies, uncontrolled systematic variability introduced during sample preparation, processing, and storage can interfere with the detection of subtle biological signals. This study evaluates storage conditions, including two sample preparation methods and storage durations, to minimize systematic variability in the analysis of extracted lipids from latent fingerprints. In the traditional approach, samples are prepared immediately, stored as lipid extracts, and processed in multiple batches. In an alternative method, samples are stored directly on the deposition foil, and preparation is delayed until all can be processed in a single batch. Storage duration is evaluated to determine if shorter storage with analysis in multiple batches is more effective than longer storage with analysis in a single batch. Our findings demonstrate that storage of latent fingerprint samples on the deposition foil is a viable option, with minimal degradation of key features even after eight months of storage. While some differences in lipid profiles were observed across storage conditions, these differences were minor and would likely have little impact in larger studies where biological variability is greater. These insights offer practical guidance for implementing latent fingerprint sampling in large-scale studies by identifying optimal conditions that preserve sample quality and streamline workflows.

Groomed Fingerprint Sebum Sampling: Reproducibility and Variability According to Anatomical Collection Region and Biological Sex

Sebum lipids, accessible via groomed latent fingerprints, may be a valuable, underappreciated sample source for future biomarker research. Sampling sebum lipids from the skin is painless for patients, efficient for researchers, and has already demonstrated the potential to contain disease biomarkers. However, before sebum sampling can be implemented in routine studies, more information is needed regarding sampling reproducibility and variability. This information will enable researchers to choose the best practices for sebum-based studies. Herein, we use our recently established workflow for the collection and analysis of groomed fingerprints to assess the reproducibility of lipid profiles obtained via mass spectrometry. Using 180 fingerprint samples collected from 30 participants, we also assess lipid changes according to biological sex and anatomical grooming region (cheek, neck, and forehead) via supervised and unsupervised classification. The results demonstrate that this sampling protocol achieves satisfactory reproducibility, and negligible differences exist between male and female groomed fingerprint lipids. Moreover, the anatomical grooming region can impact the fingerprint lipid profile: cheek- and forehead-groomed fingerprints are more similar to one another than either collection site is to neck-groomed fingerprints. This information will inform future sebum-based biomarker investigations, enabling researchers to collect meaningful lipidomic datasets from groomed fingerprint samples.

Epidermal secretion-purified biosensing patch with hydrogel sebum filtering membrane and unidirectional flow microfluidic channels

The development of biosensing electronics for real-time sweat analysis has attracted increasing research interest due to their promising applications for non-invasive health monitoring. However, one of the critical challenges lies in the sebum interference that largely limits the sensing reliability in practical scenarios. Herein, we report a flexible epidermal secretion-purified biosensing patch with a hydrogel filtering membrane that can effectively eliminate the impact of sebum and sebum-soluble substances. The as-prepared sebum filtering membranes feature a dual-layer sebum-resistant structure based on the poly(hydroxyethyl methacrylate) hydrogel functionalized with nano-brush structured poly(sulfobetaine) to eliminate interferences and provide self-cleaning capability. Furthermore, the unidirectional flow microfluidic channels design based on the Tesla valve was incorporated into the biosensing patch to prevent external sebum contamination and allow effective sweat refreshing for reliable sensing. By seamlessly combining these components, the epidermal secretion-purified biosensing patch enables continuous monitoring of sweat uric acid, pH, and sodium ions with significantly improved accuracy of up to 12 %. The proposed strategy for enhanced sweat sensing reliability without sebum interference shows desirable compatibility for different types of biosensors and would inspire the advances of flexible and wearable devices for non-invasive healthcare.

Dermatological Manifestations and Sebum Composition in Parkinson's Disease

INTRODUCTION

Parkinson disease (PD) is a multifaceted neurodegenerative disorder known for its hallmark motor symptoms. However, nonmotor manifestations, specifically dermatological changes, precede motor symptoms and may thus serve as vital early indicators of PD.

OBJECTIVES

This article explores the skin-related changes associated with PD, focusing on alterations in sebum composition, microbial dysbiosis, and the potential for leveraging dermatological assessments as early, noninvasive diagnostic markers for PD.

METHODS

A comprehensive literature review was conducted to investigate dermatological manifestations of PD, focusing on sebum changes in affected individuals. Research explored the clinical relevance of altered lipid profiles, volatile organic compound (VOC) contributions, and microbiome dysbiosis in those with PD.

RESULTS

Individuals with PD exhibit excess sebum production characterized by altered lipid profiles, including elevated short-chain fatty acids (SCFAs) and disruptions in sphingolipid metabolism. The lipid-rich environment also promotes overgrowth of Malessezia yeast, contributing to varied dermatological symptoms in those with PD. VOCs identified in sebum have been linked to unique odors and serve as biomarkers for diagnostic potential. These findings support the potential for early PD diagnosis through dermatologic assessment and sebum analysis.

CONCLUSION

Dermatological manifestations in PD offer promising noninvasive biomarkers for early diagnosis. Future research should aim to further elucidate the mechanisms underlying sebum dysregulation in PD and validate the clinical relevance of these biomarkers in larger populations.

Skin Surface Sebum Analysis by ESI-MS

The skin surface is an important sample source that the metabolomics community has only just begun to explore. Alterations in sebum, the lipid-rich mixture coating the skin surface, correlate with age, sex, ethnicity, diet, exercise, and disease state, making the skin surface an ideal sample source for future noninvasive biomarker exploration, disease diagnosis, and forensic investigation. The potential of sebum sampling has been realized primarily via electrospray ionization mass spectrometry (ESI-MS), an ideal approach to assess the skin surface lipidome. However, a better understanding of sebum collection and subsequent ESI-MS analysis is required before skin surface sampling can be implemented in routine analyses. Challenges include ambiguity in definitive lipid identification, inherent biological variability in sebum production, and methodological, technical variability in analyses. To overcome these obstacles, avoid common pitfalls, and achieve reproducible, robust outcomes, every portion of the workflow-from sample collection to data analysis-should be carefully considered with the specific application in mind. This review details current practices in sebum sampling, sample preparation, ESI-MS data acquisition, and data analysis, and it provides important considerations in acquiring meaningful lipidomic datasets from the skin surface. Forensic researchers investigating sebum as a means for suspect elimination in lieu of adequate fingerprint ridge detail or database matches, as well as clinical researchers interested in noninvasive biomarker exploration, disease diagnosis, and treatment monitoring, can use this review as a guide for developing methods of best-practice.

Comparing plasma and skin imprint metabolic profiles in COVID-19 diagnosis and severity assessment

As SARS-CoV-2 continues to produce new variants, the demand for diagnostics and a better understanding of COVID-19 remain key topics in healthcare. Skin manifestations have been widely reported in cases of COVID-19, but the mechanisms and markers of these symptoms are poorly described. In this cross-sectional study, 101 patients (64 COVID-19 positive patients and 37 controls) were enrolled between April and June 2020, during the first wave of COVID-19, in São Paulo, Brazil. Enrolled patients had skin imprints sampled non-invasively using silica plates; plasma samples were also collected. Samples were used for untargeted lipidomics/metabolomics through high-resolution mass spectrometry. We identified 558 molecular ions, with lipids comprising most of them. We found 245 plasma ions that were significant for COVID-19 diagnosis, compared to 61 from the skin imprints. Plasma samples outperformed skin imprints in distinguishing patients with COVID-19 from controls, with F1-scores of 91.9% and 84.3%, respectively. Skin imprints were excellent for assessing disease severity, exhibiting an F1-score of 93.5% when discriminating between patient hospitalization and home care statuses. Specifically, oleamide and linoleamide were the most discriminative biomarkers for identifying hospitalized patients through skin imprinting, and palmitic amides and N-acylethanolamine 18:0 were also identified as significant biomarkers. These observations underscore the importance of primary fatty acid amides and N-acylethanolamines in immunomodulatory processes and metabolic disorders. These findings confirm the potential utility of skin imprinting as a valuable non-invasive sampling method for COVID-19 screening; a method that may also be applied in the evaluation of other medical conditions. KEY MESSAGES: Skin imprints complement plasma in disease metabolomics. The annotated markers have a role in immunomodulation and metabolic diseases. Skin imprints outperformed plasma samples at assessing disease severity. Skin imprints have potential as non-invasive sampling strategy for COVID-19.

Food Insecurity and Pediatric Nonalcoholic Fatty Liver Disease Severity

OBJECTIVE

To determine the association between food insecurity and pediatric nonalcoholic fatty liver disease (NAFLD).

METHODS

Cross-sectional study of patients < 21 years of age with histologically confirmed NAFLD. The Household Food Security Survey Module was administered to determine food insecurity status. Skin lipidomics were performed to explore pathophysiologic mechanisms.

RESULTS

Seventy-three patients with histologically confirmed NAFLD completed the Household Food Security Survey Module. Of these, the majority were male (81%) and non-Hispanic (53%), with a mean age at biopsy of 13 ± 3 years. Food insecurity was seen in 42% (n = 31). Comparison of features between food insecure and food secure subgroups revealed no differences in sex, ethnicity, BMI z-score, aminotransferases, or histologic severity. However, children experiencing food insecurity presented on average 2 years before their food secure counterparts (12.3 ± 3.0 vs 14.4 ± 3.6 years, P = .015). A subset of 31 patients provided skin samples. Skin lipidomics revealed that food insecurity was associated with down-regulated features from the lipoamino acid class of lipids, previously linked to inflammation and adipocyte differentiation.

CONCLUSIONS

Food insecurity is highly prevalent in children with NAFLD and is associated with earlier presentation. Lipidomic analyses suggest a possible pathophysiologic link that warrants further exploration.

Critical Factors in Sample Collection and Preparation for Clinical Metabolomics of Underexplored Biological Specimens

This review article compiles critical pre-analytical factors for sample collection and extraction of eight uncommon or underexplored biological specimens (human breast milk, ocular fluids, sebum, seminal plasma, sweat, hair, saliva, and cerebrospinal fluid) under the perspective of clinical metabolomics. These samples are interesting for metabolomics studies as they reflect the status of living organisms and can be applied for diagnostic purposes and biomarker discovery. Pre-collection and collection procedures are critical, requiring protocols to be standardized to avoid contamination and bias. Such procedures must consider cleaning the collection area, sample stimulation, diet, and food and drug intake, among other factors that impact the lack of homogeneity of the sample group. Precipitation of proteins and removal of salts and cell debris are the most used sample preparation procedures. This review intends to provide a global view of the practical aspects that most impact results, serving as a starting point for the designing of metabolomic experiments.

Transforming Parkinson's Care in Africa (TraPCAf): protocol for a multimethodology National Institute for Health and Care Research Global Health Research Group project

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disorder and, according to the Global Burden of Disease estimates in 2015, was the fastest growing neurological disorder globally with respect to associated prevalence, disability, and deaths. Information regarding the awareness, diagnosis, phenotypic characteristics, epidemiology, prevalence, risk factors, treatment, economic impact and lived experiences of people with PD from the African perspective is relatively sparse in contrast to the developed world, and much remains to be learned from, and about, the continent.

METHODS

Transforming Parkinson's Care in Africa (TraPCAf) is a multi-faceted, mixed-methods, multi-national research grant. The study design includes multiple sub-studies, combining observational (qualitative and quantitative) approaches for the epidemiological, clinical, risk factor and lived experience components, as appropriate, and interventional methods (clinical trial component). The aim of TraPCAf is to describe and gain a better understanding of the current situation of PD in Africa. The countries included in this National Institute for Health and Care Research (NIHR) Global Health Research Group (Egypt, Ethiopia, Ghana, Kenya, Nigeria, South Africa and Tanzania) represent diverse African geographies and genetic profiles, with differing resources, healthcare systems, health and social protection schemes, and policies. The research team is composed of experts in the field with vast experience in PD, jointly led by a UK-based and Africa-based investigator.

DISCUSSION

Despite the increasing prevalence of PD globally, robust data on the disease from Africa are lacking. Existing data point towards the poor awareness of PD and other neurological disorders on the continent and subsequent challenges with stigma, and limited access to affordable services and medication. This multi-site study will be the first of its kind in Africa. The data collected across the proposed sub-studies will provide novel and conclusive insights into the situation of PD. The selected country sites will allow for useful comparisons and make results relevant to other low- and middle-income countries. This grant is timely, as global recognition of PD and the public health challenge it poses builds. The work will contribute to broader initiatives, including the World Health Organization's Intersectoral global action plan on epilepsy and other neurological disorders.

TRIAL REGISTRATION

https://doi.org/10.1186/ISRCTN77014546 .