Examination of the skin barrier repair/wound healing process using a living skin equivalent model and matrix-assisted laser desorption-ionization-mass spectrometry imaging

Glycolipid Biosurfactants in Skincare Applications: Challenges and Recommendations for Future Exploitation

The 21st century has seen a substantial increase in the industrial applications of glycolipid biosurfactant technology. The market value of the glycolipid class of molecules, sophorolipids, was estimated to be USD 409.84 million in 2021, with that of rhamnolipid molecules projected to reach USD 2.7 billion by 2026. In the skincare industry, sophorolipid and rhamnolipid biosurfactants have demonstrated the potential to offer a natural, sustainable, and skin-compatible alternative to synthetically derived surfactant compounds. However, there are still many barriers to the wide-scale market adoption of glycolipid technology. These barriers include low product yield (particularly for rhamnolipids) and potential pathogenicity of some native glycolipid-producing microorganisms. Additionally, the use of impure preparations and/or poorly characterised congeners as well as low-throughput methodologies in the safety and bioactivity assessment of sophorolipids and rhamnolipids challenges their increased utilisation in both academic research and skincare applications. This review considers the current trend towards the utilisation of sophorolipid and rhamnolipid biosurfactants as substitutes to synthetically derived surfactant molecules in skincare applications, the challenges associated with their application, and relevant solutions proposed by the biotechnology industry. In addition, we recommend experimental techniques/methodologies, which, if employed, could contribute significantly to increasing the acceptance of glycolipid biosurfactants for use in skincare applications while maintaining consistency in biosurfactant research outputs.

Examination of lipid profiles in abdominal fascial healing using MALDI-TOF to identify potential therapeutic targets

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Lipids change overtime in normal fascial healing in the early post-surgery period.

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Specific lipid species are correlated with the changes of inflammation cells and fibroblasts.

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Lipid species in the present study are considered as predictive markers for the formation of incisional hernia.

Background

Failure of fascial healing in the abdominal wall can result in incisional hernia, which is one of the most common complications after laparotomy. Understanding the molecular healing process of abdominal fascia may provide lipid markers of incisional hernia or therapeutic targets that allow prevention or treatment of incisional hernias.

Purpose

This study aims to investigate temporal and in situ changes of lipids during the normal healing process of abdominal fascia in the first postoperative week.

Methods

Open hemicolectomy was performed in a total of 35 Wistar rats. The midline fascia was closed identically for all rats using a single continuous suturing technique. These animals were sacrificed with equal numbers (n = 5) at each of 7-time points (6, 12, 24, 48, 72, 120, and 168 h. The local and temporal changes of lipids were examined with mass spectrometry imaging and correlated to histologically scored changes during healing using hematoxylin and eosin staining.

Results

Two phosphatidylcholine lipid species (PC O-38:5 and PC 38:4) and one phosphatidylethanolamine lipid (PE O-16:1_20:4) were found to significantly correlate with temporal changes of inflammation. A phosphatidylcholine (PC 32:0) and a monosialodihexosylganglioside (GM3 34:1;2) were found to correlate with fibroblast cell growth.

Conclusion

Glycerophospholipids and gangliosides are strongly involved in the normal healing process of abdominal fascia and their locally fluctuating concentrations are considered as potential lipid markers and therapeutic targets of fascial healing.

A review of diabetic wound models-Novel insights into diabetic foot ulcer

Diabetic foot ulcer (DFU) is a major debilitating complication of diabetes. Many research investigations have been conducted with the aims to uncover the diabetic wound healing mechanisms, develop novel therapeutics, and screen bioactive wound dressings in order to improve the current management of DFU. These would have not been possible without the utilization of an appropriate wound model, especially in a diabetic wound context. This review focuses on the different in vitro research models used in DFU investigations such as the 2D scratch wound assay, 3D skin model, and 3D angiogenesis model as well as their limitations. The current efforts and challenges to apply the 2D and 3D in vitro models in a hyperglycemic context to provide insights into DFU modeling will be reviewed. Perspectives of utilizing 3D bioprinting and skin-on-the-chip model as a diabetic wound model in the future will also be highlighted. By leveraging knowledge from past experiences and current research, an improved experimental model for DFU is anticipated to be established in near future.

DESI-MS imaging to visualize spatial distribution of xenobiotics and endogenous lipids in the skin

The cutaneous biodistribution method (CBM) yields a high-resolution quantitative profile of drug deposition as a function of skin depth. However, it provides limited details about drug spatial distribution or penetration pathways. Mass spectrometry imaging (MSI) can complement the detailed quantitative data generated by CBM studies. The objectives of this work were to use desorption electrospray ionization (DESI)-MSI to (i) investigate the spatial cutaneous distributions of a topically applied drug and excipient and relate them to skin structures and (ii) image endogenous skin components and combine these results to gain insight into drug penetration routes. Porcine skin was used to compare two bioequivalent creams of econazole nitrate (ECZ) and a micelle formulation based on D-α-tocopheryl succinate polyethylene glycol 1000 (TPGS). DESI-MSI successfully imaged the cutaneous spatial distribution of ECZ and TPGS in 40 µm-thick horizontal sections and vertical cross-sections of the skin. Interestingly, clinically bioequivalent formulations did not appear to exhibit the same molecular distribution of ECZ in XY-horizontal sections. DESI-MSI also enabled visualization of TPGS (m/z 772.4706), mainly in the upper epidermis (≤80 µm). In conclusion, through co-localization of drugs and excipients with endogenous elements of the skin, DESI-MSI could further our understanding of the cutaneous penetration pathways of xenobiotics.

Mechanical and Immunological Regulation in Wound Healing and Skin Reconstruction

In the past decade, a new frontier in scarless wound healing has arisen because of significant advances in the field of wound healing realised by incorporating emerging concepts from mechanobiology and immunology. The complete integumentary organ system (IOS) regeneration and scarless wound healing mechanism, which occurs in specific species, body sites and developmental stages, clearly shows that mechanical stress signals and immune responses play important roles in determining the wound healing mode. Advances in tissue engineering technology have led to the production of novel human skin equivalents and organoids that reproduce cell–cell interactions with tissue-scale tensional homeostasis, and enable us to evaluate skin tissue morphology, functionality, drug response and wound healing. This breakthrough in tissue engineering has the potential to accelerate the understanding of wound healing control mechanisms through complex mechanobiological and immunological interactions. In this review, we present an overview of recent studies of biomechanical and immunological wound healing and tissue remodelling mechanisms through comparisons of species- and developmental stage-dependent wound healing mechanisms. We also discuss the possibility of elucidating the control mechanism of wound healing involving mechanobiological and immunological interaction by using next-generation human skin equivalents.

A comparison of the in vitro permeation of 3-O-ethyl-l-ascorbic acid in human skin and in a living skin equivalent (LabSkin™)

OBJECTIVES

The safety assessment of personal care products often entails determining dermal absorption of their ingredients. Such experiments are typically performed in human or animal skin in vitro; however, ethical and safety considerations are associated with obtaining these tissues. Several human skin equivalent models (HSEs) have been developed as alternatives to human tissue. The barrier function of such models however, is normally less developed than human skin. Here, we examine the permeability of the HSE LabSkin^TM to a model compound, 3-O-ethyl-l-ascorbic acid (EA) compared with human skin.

METHODS

Skin uptake and permeation of EA was investigated in vitro using heat-separated human epidermis and LabSkin^TM . Finite dose (5 μL cm^-2 ) Franz-diffusion studies were conducted using 2 % (w/w) EA in a ternary solvent mixture comprising propylene glycol (PG), propylene glycol monolaurate (PGML), and isopropyl myristate (IPM). These excipients are commonly used in cosmetic products and they have been reported to promote permeation of EA in a different model, namely porcine skin.

RESULTS

Permeation of EA through LabSkin^TM was evident from 2 h; however, EA permeation in human skin was not detected until 5 h. Similar amounts of EA permeated through the two membranes at time points 8, 10, 12 and 24 h (p > 0.05). The cumulative amounts of EA delivered through LabSkin^TM at 24 h were 41.3 ± 2.0 µg cm^-2 , corresponding to 55.1 ± 1.8 % of the applied dose. Similar amounts permeated across human skin, 49.4 ± 4.1 µg cm^-2 , accounting for 58.0 ± 4.2 % of the dose applied (p > 0.05).

CONCLUSION

The permeation of EA in LabSkin^TM compared well with results for human epidermis in terms of the permeation profiles and the cumulative amounts of EA that permeated. The data suggest that the skin barrier of the two models was similar with regard to their overall permeability to the hydrophilic active EA. The findings are promising for the use of LabSkin^TM as a surrogate for human skin in permeability testing. Future studies will focus on exploring the reproducibility and robustness of LabSkin^TM for delivery of other actives that span a range of physicochemical properties.

Comparison of Dietary Oils with Different Polyunsaturated Fatty Acid n-3 and n-6 Content in the Rat Model of Cutaneous Wound Healing

Dietary supplementation with polyunsaturated fatty acids (PUFA) n-3 can affect cutaneous wound healing; however, recent findings demonstrate the variable extent of their influence on the quality of healing. Here, we compare the effect of several dietary oils, containing different levels of PUFA n-3 and PUFA n-6, on wound healing in the rat model. Rats were fed the feed mixture with 8% palm oil (P), safflower oil (S), fish oil (F) or Schizochytrium microalga extract (Sch) and compared to the animals fed by control feed mixture (C). Dorsal full-thickness cutaneous excisions were performed after 52 days of feeding and skin was left to heal for an additional 12 days. Histopathological analysis of skin wounds was performed, including immune cells immunolabeling and the determination of hydroxyproline amount as well as gene expression analyses of molecules contributing to different steps of the healing. Matrix-assisted-laser-desorption-ionization mass-spectrometry-imaging (MALDI-MSI) was used to determine the amount of collagen α-1(III) chain fragment in healing samples. Treatment by Schizochytrium extract resulted in decrease in the total wound area, in contrast to the safflower oil group where the size of the wound was larger when comparing to control animals. Diet with Schizochytrium extract and safflower oils displayed a tendency to increase the number of new vessels. The number of MPO-positive cells was diminished following any of oil treatment in comparison to the control, but their highest amount was found in animals with a fish oil diet. On the other hand, the number of CD68-positive macrophages was increased, with the most significant enhancement in the fish oil and safflower oil group. Hydroxyproline concentration was the highest in the safflower oil group but it was also enhanced in all other analyzed treatments in comparison to the control. MALDI-MSI signal intensity of a collagen III fragment decreased in the sequence C > S > Sch > P > F treatment. In conclusion, we observed differences in tissue response during healing between dietary oils, with the activation of inflammation observed following the treatment with oil containing high eicosapentaenoic acid (EPA) level (fish oil) and enhanced healing features were induced by the diet with high content of docosahexaenoic acid (DHA, Schizochytrium extract).

Direct identification of bacterial and human proteins from infected wounds in living 3D skin models

Trauma is one of the leading causes of death in people under the age of 49 and complications due to wound infection are the primary cause of death in the first few days after injury. The ESKAPE pathogens are a group of bacteria that are a leading cause of hospital-acquired infections and a major concern in terms of antibiotic resistance. Here, we demonstrate a novel and highly accurate approach for the rapid identification of ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) directly from infected wounds in 3D in vitro skin models. Wounded skin models were inoculated with bacteria and left to incubate. Bacterial proteins were identified within minutes, directly from the wound, by liquid extraction surface analysis mass spectrometry. This approach was able to distinguish closely related strains and, unlike genomic approaches, can be modified to provide dynamic information about pathogen behaviour at the wound site. In addition, since human skin proteins were also identified, this method offers the opportunity to analyse both host and pathogen biomarkers during wound infection in near real-time.

Development of dynamic cell and organotypic skin models, for the investigation of a novel visco-elastic burns treatment using molecular and cellular approaches

BACKGROUND

Burn injuries are a major cause of morbidity and mortality worldwide. Despite advances in therapeutic strategies for the management of patients with severe burns, the sequelae are pathophysiologically profound, up to the systemic and metabolic levels. Management of patients with a severe burn injury is a long-term, complex process, with treatment dependent on the degree and location of the burn and total body surface area (TBSA) affected. In adverse conditions with limited resources, efficient triage, stabilisation, and rapid transfer to a specialised intensive care burn centre is necessary to provide optimal outcomes. This initial lag time and the form of primary treatment initiated, from injury to specialist care, is crucial for the burn patient. This study aims to investigate the efficacy of a novel visco-elastic burn dressing with a proprietary bio-stimulatory marine mineral complex (MXC) as a primary care treatment to initiate a healthy healing process prior to specialist care.

METHODS

A new versatile emergency burn dressing saturated in a >90% translucent water-based, sterile, oil-free gel and carrying a unique bio-stimulatory marine mineral complex (MXC) was developed. This dressing was tested using LabSkin as a burn model platform. LabSkin a novel cellular 3D-dermal organotypic full thickness human skin equivalent, incorporating fully-differentiated dermal and epidermal components that functionally models skin. Cell and molecular analysis was carried out by in vitro Real-Time Cellular Analysis (RTCA), thermal analysis, and focused transcriptomic array profiling for quantitative gene expression analysis, interrogating both wound healing and fibrosis/scarring molecular pathways. In vivo analysis was also performed to assess the bio-mechanical and physiological effects of this novel dressing on human skin.

RESULTS

This hybrid emergency burn dressing (EBD) with MXC was hypoallergenic, and improved the barrier function of skin resulting in increased hydration up to 24 h. It was demonstrated to effectively initiate cooling upon application, limiting the continuous burn effect and preventing local tissue from damage and necrosis. xCELLigence RTCA® on primary human dermal cells (keratinocyte, fibroblast and micro-vascular endothelial) demonstrated improved cellular function with respect to tensegrity, migration, proliferation and cell-cell contact (barrier formation) [1]. Quantitative gene profiling supported the physiological and cellular function finding. A beneficial quid pro quo regulation of genes involved in wound healing and fibrosis formation was observed at 24 and 48 h time points.

CONCLUSION

Utilisation of this EBD + MXC as a primary treatment is an effective and easily applicable treatment in cases of burn injury, proving both a cooling and hydrating environment for the wound. It regulates inflammation and promotes healing in preparation for specialised secondary burn wound management. Moreover, it promotes a healthy remodelling phenotype that may potentially mitigate scarring. Based on our findings, this EBD + MXC is ideal for use in all pre-hospital, pre-surgical and resource limited settings.

The effect of different fatty acid sources on wound healing in rats assessed by matrix-assisted-laser-desorption-ionization mass-spectroscopy-imaging

The objective of the present study was to compare the effects of dietary oils containing polyunsaturated fatty acids (PUFA) n-3 and n-6, respectively, on cutaneous wound healing in rats, and to demonstrate the usefulness of the matrix-assisted-laser-desorption-ionization mass spectroscopy-imaging (MALDI MSI) method in this type of experiment. Superiority of PUFA n-3 in this context was the tested hypothesis. Four groups of male Wistar rats by twelve animals each were fed a diet with added 5% of palm oil (P; control), fish oil (F), Schizochytrium microalga oil (Sch) and safflower oil (S), respectively, for eight weeks. Consequently, dorsal full-thickness cutaneous excisions were performed, and selected markers of wound healing were evaluated 18 days post excision. The median of signal intensity corresponding to an amount of collagen α-1 (III) fragment, quantified using MALDI MSI, decreased in a sequence P > F > Sch > S (P < 0.001). Using haematoxylin-eosin staining of the histological preparations, semi-quantitatively assessed epithelium height tended to decrease in the order of P > S > Sch > F; the wound extent in the sequence of P > Sch > S > F; and the sequence of the progress of neo-angiogenesis was assessed as S > P > F ≈ Sch. It was concluded that the tested hypothesis was confirmed only partially: PUFA n-3 showed better results regarding the wound extent, but were inferior in terms of epithelium height and progress of neo-angiogenesis. This was the first time MALDI MSI was successfully employed for evaluating skin wound healing in a rat model.

Multimodal, in Situ Imaging of Ex Vivo Human Skin Reveals Decrease of Cholesterol Sulfate in the Neoepithelium during Acute Wound Healing

Skin repair is a significant aspect of human health. While the makeup of healthy stratum corneum and epidermis is generally understood, the mobilization of molecular components during skin repair remains largely unknown. In the present work, we utilize multimodal, in situ, mass spectrometry, and immunofluorescence imaging for the characterization of newly formed epidermis, following an initial acute wound for the first 96 h of epithelization. In particular, TOF-SIMS and confirmatory MALDI FT-ICR MS (/MS) analysis permitted the mapping of several lipid classes, including phospholipids, neutral lipids, cholesterol, ceramides, and free fatty acids. Endogenous lipid species were localized in discrete epidermal skin layers, including the stratum corneum (SC), stratum granulosum (SG), stratum basale (SB), and dermis. Experiments revealed that healthy re-epithelializing skin is characterized by diminished cholesterol sulfate signal along the stratum corneum toward the migrating epithelial tongue. The spatial distribution and relative abundances of cholesterol sulfate are reported and correlated with the healing time. The multimodal imaging approach enabled in situ high-confidence chemical mapping based on accurate mass and fragmentation pattern of molecular components. The use of postanalysis immunofluorescence imaging from the same tissue confirmed the localization of endogenous lipid species and Filaggrin and Cav-1 proteins at high spatial resolution (approximately a few microns).

Biomarker Mapping on Skin Tape Strips Using MALDI Mass Spectrometry Imaging

Keratinocyte organization and biochemistry are important in forming the skin's protective barrier. Intrinsic and extrinsic factors can affect skin barrier function at the cellular and molecular levels. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometric imaging, a technique which combines both molecular aspects and histological details, has proven to be a valuable method in various disciplines including pharmacology, dermatology and cosmetology. It typically requires ex vivo samples, prepared following frozen tissue sectioning. This paper demonstrates the feasibility of performing MALDI analysis on tape strips collected non-invasively on skin. The aim is to obtain molecular imaging of corneocytes on tapes towards novel biological insights. Tapes were collected from two skin sites (volar forearm and cheek) of human volunteers. Ten molecules relating to skin barrier function were detected with a single mode of acquisition at high spatial resolution with a 7 T MALDI-Fourier transform ion cyclotron resonance (FTICR) instrument. The method sensitivity was adequate to create molecular maps which could be overlaid on transmission microscopy images of the same area of the tape. Analysis of the molecular distributions from tapes at the two skin sites was consistent with the known skin properties of the two sites, confirming the validity of the observations. Hierarchical clustering analysis was used to differentiate corneocyte populations based on their molecular profiles. Furthermore, morphological analysis provided a new way of considering statistical populations of corneocytes on the same tape, rather than measuring a single averaged value, providing additional useful information relating to their structure-function relationship.

Sample Treatment for Tissue Proteomics in Cancer, Toxicology, and Forensics

Since the birth of proteomics science in the 1990, the number of applications and of sample preparation methods has grown exponentially, making a huge contribution to the knowledge in life science disciplines. Continuous improvements in the sample treatment strategies unlock and reveal the fine details of disease mechanisms, drug potency, and toxicity as well as enable new disciplines to be investigated such as forensic science.This chapter will cover the most recent developments in sample preparation strategies for tissue proteomics in three areas, namely, cancer, toxicology, and forensics, thus also demonstrating breath of application within the domain of health and well-being, pharmaceuticals, and secure societies.In particular, in the area of cancer (human tumor biomarkers), the most efficient and multi-informative proteomic strategies will be covered in relation to the subsequent application of matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) and liquid extraction surface analysis (LESA), due to their ability to provide molecular localization of tumor biomarkers albeit with different spatial resolution.With respect to toxicology, methodologies applied in toxicoproteomics will be illustrated with examples from its use in two important areas: the study of drug-induced liver injury (DILI) and studies of effects of chemical and environmental insults on skin, i.e., the effects of irritants, sensitizers, and ionizing radiation. Within this chapter, mainly tissue proteomics sample preparation methods for LC-MS/MS analysis will be discussed as (i) the use of LC-MS/MS is majorly represented in the research efforts of the bioanalytical community in this area and (ii) LC-MS/MS still is the gold standard for quantification studies.Finally, the use of proteomics will also be discussed in forensic science with respect to the information that can be recovered from blood and fingerprint evidence which are commonly encountered at the scene of the crime. The application of proteomic strategies for the analysis of blood and fingerprints is novel and proteomic preparation methods will be reported in relation to the subsequent use of mass spectrometry without any hyphenation. While generally yielding more information, hyphenated methods are often more laborious and time-consuming; since forensic investigations need quick turnaround, without compromising validity of the information, the prospect to develop methods for the application of quick forensic mass spectrometry techniques such as MALDI-MS (in imaging or profiling mode) is of great interest.