Proteomic investigation of human burn wounds by 2D-difference gel electrophoresis and mass spectrometry

Mass spectrometry-based proteomic strategy for ecchymotic skin examination in forensic pathology

Mass spectrometry (MS)-based proteomics has recently attracted the attention from forensic pathologists. This work is the first report of the development of a shotgun bottom-up proteomic approach based on rapid protein extraction and nano-liquid chromatography/high-resolution mass spectrometry applied to full-thickness human skin for the differential analysis of normal and ecchymotic tissues to identify new biomarkers for bruise characterization and dating. We identified around 2000 proteins from each pooled extract. The method showed excellent precision on independent replicates, with Pearson correlation coefficients always higher than 95%. Glycophorin A, a known biomarker of vital wounds from immunochemical studies, was identified only in ecchymotic tissues, as confirmed by Western blotting analysis. This finding suggests that this protein can be used as a MS-detectable biomarker of wound vitality. By focusing on skin samples from individuals with known wound dating, besides Glycophorin A, other proteins differentially expressed in ecchymotic samples and dependant on wound age were identified, although further analysis on larger datasets are needed to validate these findings. This study paves the way for an in-depth investigation of the potential of MS-based techniques for wound examination in forensic pathology, overcoming the limitations of immunochemical assays.

Serum vimentin predicts mortality in pediatric severe sepsis: A prospective observational study

OBJECTIVES

Vascular hyperpermeability by loss of endothelial barrier integrity is a hallmark of sepsis. Vimentin is involved in the regulation of the endothelial function and inflammatory response. However, the serum level of vimentin and its clinical relevance in pediatric severe sepsis (PSS) remain unknown.

METHODS

We conducted a prospective study of PSS cases who were admitted to the pediatric intensive care unit (PICU) from January 2018 to December 2020.

RESULTS

A total of 108 patients with PSS with a median age of 19.5 month were enrolled. The hospital mortality rate was 19.44% (21/108). Comparing with healthy controls, serum vimentin levels on PICU admission were significantly higher in patients with PSS (P < 0.001). The area under the ROC curve for vimentin to predict the hospital mortality was 0.712 (95% CI: 0.578-846) with a sensitivity of 71.43% and a specificity of 70.11%. Moreover, hospital mortality was significantly higher in patients with vimentin level over the cutoff value of 24.53 ng/ml than in patients with vimentin level below 24.53 ng/ml (P < 0.001).

CONCLUSIONS

Serum vimentin level as an indicator of endothelial injury is associated with the prognosis of PSS, and serum vimentin level ≥24.53 ng/ml on PICU admission predicts high risk for hospital mortality in PSS.

Time-dependent expression of high-mobility group box-1 and toll-like receptors proteins as potential determinants of skin wound age in rats: Forensic implication

The skin wound age determination in living subjects is an imperative task for forensic experts. In this study, we investigated the time-dependent expression of high-mobility group box-1 (HMGB1) and toll-like receptors 2 and 4 (TLR2 and 4) in rat skin wounds using real-time PCR and seek their forensic potentials during the skin wound repair process. In addition, the levels of serum pro-inflammatory cytokines (tumor necrosis factor-alpha (TNF-α) and interleukin 6 (IL-6)), as well as nitric oxide (NO) production, were measured. The wound tissue and serum samples were collected after 30 min, 2 h, 6 h, 12 h, 1 day, 3 days, 5 days, and 7 days after incision. As a control (zero time), skin specimens and blood samples were collected without incision. The results reveal that the HMGB1, TLR2, and TLR4 expression levels were increased in a time-dependent manner until the first day where the peak level was achieved for the three tested genes compared with the zero time. On the 7^th day, the statistical significance was lost for TLR2 and TLR4 but persisted for HMGB1. The serum TNF-α, IL6, and NO levels peaked within 30 min and 1^st and 3^rd day after injury, respectively. On the 7^th day after incision, no significant differences exist in the TNF-α serum level compared to the control group, but the statistical significance persisted for IL6 and NO. It was apparent that the analyzed genes in the wound tissues showed higher R2 values rather than the serum biochemical indicators. Of note, a strong positive correlation was evident between the HMGB1 and that of TLR2 and TLR4 relative expression as well as IL-6 serum level. Conclusively, based on the observed changes in the analyzed markers in wound tissues and serum and R2 values obtained from mathematical models established to determine the wound age, the relative expression of HMGB1, TLR2, and TLR4 could be a reliable indicator for wound age determination in living subjects. Further investigation of these markers and mathematical models in human tissues is necessary.

Human model of burn injury that quantifies the benefit of cooling as a first aid measure

BACKGROUND

Burn injuries are a major cause of morbidity and mortality worldwide. Cooling is widely practised as a first aid measure, but the efficacy of cooling burns in human skin has not been demonstrated. A safe, consistent, ethically acceptable model of burning and cooling in live human skin in vivo was developed, and used to quantify the effects of cooling.

METHODS

Novel apparatus was manufactured to create and cool burns in women who were anaesthetized for breast reconstruction surgery using a deep inferior epigastric artery perforator flap. Burns were excised between 1 and 3 h after creation, and analysed using histopathological assessment.

RESULTS

All 25 women who were approached agreed to take part in the study. There were no adverse events. Increased duration of contact led to increased burn depth, with a contact time of 7·5 s at 70°C leading to a mid-dermal burn. Burn depth progressed over time following injury, but importantly this was modified by cooling the burn at 16°C for 20 min. On average, cooling salvaged 25·2 per cent of the dermal thickness.

CONCLUSION

This study demonstrated the favourable effects of cooling on human burns. Public heath messaging should emphasize cooling as first aid for burns. This model will allow analysis of the molecular effects of cooling burns, and provide a platform for testing novel therapies aimed at reducing the impact of burn injury.

A review of the evidence for threshold of burn injury

INTRODUCTION

Burn injury is common and depth is one measure of severity. Although the depth of burn injury is determined by many factors, the relationship between the temperature of the injurious agent and exposure duration, known as the time-temperature relationship, is widely accepted as one of the cornerstones of burn research. Moritz and Henriques first proposed this relationship in 1947 and their seminal work has been cited extensively. However, over the years, readers have misinterpreted their findings and incorporated misleading information about the time-temperature relationship into a wide range of industrial standards, burn prevention literature and medicolegal opinion.

AIM

The purpose of this paper is to present a critical review of the evidence that relates temperature and time to cell death and the depth of burn injury. These concepts are used by researchers, burn prevention strategists, burn care teams and child protection professionals involved in ascertaining how the mechanism of burning relates to the injury pattern and whether the injury is consistent with the history.

REVIEW METHODS

This review explores the robustness of the currently available evidence. The paper summarises the research from burn damage experimental work as well as bioheat transfer models and discusses the merits and limitations of these approaches.

REVIEW FINDINGS

There is broad agreement between in vitro and in vivo studies for superficial burns. There is clear evidence that the perception of pain in adult human skin occurs just above 43°C. When the basal layer of the epidermis reaches 44°C, burn injury occurs. For superficial dermal burns, the rate of tissue damage increases logarithmically with a linear increase in temperature. Beyond 70°C, rate of damage is so rapid that interpretation can be difficult. Depth of injury is also influenced by skin thickness, blood flow and cooling after injury. There is less clinical evidence for a time-temperature relationship for deep or subdermal burns. Bioheat transfer models are useful in research and becoming increasingly sophisticated but currently have limited practical use. Time-temperature relationships have not been established for burns in children's skin, although standards for domestic hot water suggest that the maximum temperature should be revised downward by 3-4°C to provide adequate burn protection for children.

CONCLUSION

Time-temperature relationships established for pain and superficial dermal burns in adult human skin have an extensive experimental modeling basis and reasonable clinical validation. However, time-temperature relationships for subdermal burns, full thickness burns and burn injury in children have limited clinical validation, being extrapolated from other data, and should be used with caution, particularly if presented during expert evidence.

Imaging mass spectrometry for accessing molecular changes during burn wound healing

The spatiotemporal analysis of the proteomic profile during human wound healing is a critical investigative step that can establish the complex interplay of molecular events that comprise the local response to burn injury. Partial-thickness wound samples with adjacent "normal" skin were collected from twenty-one patients with burn wounds and examined across a time spectrum ranging from the acute injury period at 3, 6, 11 days to the later hypertrophic scar period at 7 and 15 months. The techniques used for histology-directed tissue analyses highlighted inflammatory protein markers at the early time points after injury with diminished expression as burn wounds progressed into the proliferative phase. The datasets show the usefulness of MALDI MS and imaging mass spectrometry as discovery approaches to identify and map the cutaneous molecular sequence that is activated in response to the unique systemic inflammatory response following burn trauma. This information has the potential to define the unique factors that predispose human burn victims to disfiguring hypertrophic scar formation.

The blister fluid proteome of paediatric burns

Burn injury is highly traumatic for paediatric patients, with the severity of the burn often dictating the extent of scar formation. The diagnosis of burn wound severity is largely determined by the attending clinician's experience. Thus, a greater understanding of the biochemistry at burn wound site environment and the biology of burns of different severities at an earlier stage may reduce the reliance on subjective diagnoses. In this study, blister fluid was collected from superficial thickness, deep-partial thickness, and full-thickness paediatric burn wounds. Samples were combined together based on burn depth classification and then subjected to four different fractionation methods followed by trypsin digestion. Peptides were analysed by liquid chromatography tandem mass spectrometry in order to measure the proteome of each fraction. In total, 811 individual proteins were identified, including 107, 84, and 146 proteins unique to superficial, deep-partial thickness and full-thickness burn wounds, respectively. The differences in the protein inventory and the associated gene ontologies represented within each burn depth category demonstrated that there are subtle, yet significant, variations in the biochemistry of burn wounds according to severity. Importantly, this study has produced the most comprehensive catalogue of proteins from the paediatric burn wound microenvironment to date.

SIGNIFICANCE

To our knowledge, this study has been the first to comprehensively measure the paediatric burn blister fluid proteome and has provided insight into the proteomic response to burn injury. The study contributes to the knowledge of blister fluid biochemistry of burn injury and provides clinically relevant knowledge through the qualitative evaluation of biochemical differences between burns of different depths. A better understanding of the burn wound environment will ultimately assist with more accurate clinical decision making and improved wound healing and scar reduction procedures.

The biochemistry of blister fluid from pediatric burn injuries: proteomics and metabolomics aspects

Burn injury is a prevalent and traumatic event for pediatric patients. At present, the diagnosis of burn injury severity is subjective and lacks a clinically relevant quantitative measure. This is due in part to a lack of knowledge surrounding the biochemistry of burn injuries and that of blister fluid. A more complete understanding of the blister fluid biochemistry may open new avenues for diagnostic and prognostic development. Burn insult induces a highly complex network of signaling processes and numerous changes within various biochemical systems, which can ultimately be examined using proteome and metabolome measurements. This review reports on the current understanding of burn wound biochemistry and outlines a technical approach for 'omics' profiling of blister fluid from burn wounds of differing severity.

Histology-guided protein digestion/extraction from formalin-fixed and paraffin-embedded pressure ulcer biopsies

Herein we present a simple, reproducible and versatile approach for in situ protein digestion and identification on formalin-fixed and paraffin-embedded (FFPE) tissues. This adaptation is based on the use of an enzyme delivery platform (hydrogel discs) that can be positioned on the surface of a tissue section. By simultaneous deposition of multiple hydrogels over select regions of interest within the same tissue section, multiple peptide extracts can be obtained from discrete histological areas. After enzymatic digestion, the hydrogel extracts are submitted for LC-MS/MS analysis followed by database inquiry for protein identification. Further, imaging mass spectrometry (IMS) is used to reveal the spatial distribution of the identified peptides within a serial tissue section. Optimization was achieved using cutaneous tissue from surgically excised pressure ulcers that were subdivided into two prime regions of interest: the wound bed and the adjacent dermal area. The robust display of tryptic peptides within these spectral analyses of histologically defined tissue regions suggests that LC-MS/MS in combination with IMS can serve as useful exploratory tools.

Cooling of burns: Mechanisms and models

The role of cooling in the acute management of burns is widely accepted in clinical practice, and is a cornerstone of basic first aid in burns. This has been underlined in a number of animal models. The mechanism by which it delivers its benefit is poorly understood, but there is a reduction in burns progression over the first 48 h, reduced healing time, and some subjective improvements in scarring when cooling is administered after burning. Intradermal temperature normalises within a matter of seconds to a few minutes, yet the benefits of even delayed cooling persist, implying it is not simply the removal of thermal energy from the damaged tissues. Animal models have used oedema formation, preservation of dermal perfusion, healing time and hair retention as indicators of burns severity, and have shown cooling to improve these indices, but pharmacological or immunological blockade of humoural and cellular mediators of inflammation did not reproduce the benefit of cooling. More recently, some studies of tissue from human and animal burns have shown consistent, reproducible, temporal changes in gene expression in burned tissues. Here, we review the experimental evidence of the role and mechanism of cooling in burns management, and suggest future research directions that may eventually lead to improved treatment outcomes.

Comparative proteomic analysis of extracellular matrix proteins secreted by hypertrophic scar with normal skin fibroblasts

The formation of hypertrophic scars (HSs) is a fibroproliferative disorder of abnormal wound healing. HSs usually characterize excessive proliferation of fibroblasts, abnormal deposition of extracellular matrix (ECM) during wound healing, associated with cosmetic, functional, and psychological problems. Owing to the role of ECM proteins in scar formation, we comparatively analyzed matrix proteins secreted by normal skin fibroblasts (NSFs) and HS fibroblasts (HSFs). The acetone-extracted secreted proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and identified by mass spectrometry (MS). Based on Go annotation of MS data, the profiling of ECM proteins was established and scar-related proteins have been screened out. The functions of several ECM proteins identified by MS have been discussed, such as collagens I, VI, XII, fibronectin, decorin, lumican, and protein procollagen C endopeptidase enhancer 1 (PCPE-1). Among them, the MS result of PCPE-1 was supported by Western blotting that PCPE-1 from HSFs were significantly upregulated than that from NSFs. It is suggested that PCPE-1 could be a potential target for scar treatment. The exploration of scar related proteins may provide new perspectives on understanding the mechanism of scar formation and open a new way to scar treatment and prevention.

A quantitative proteomic workflow for characterization of frozen clinical biopsies: laser capture microdissection coupled with label-free mass spectrometry

This paper describes a simple, highly efficient and robust proteomic workflow for routine liquid-chromatography tandem mass spectrometry analysis of Laser Microdissection Pressure Catapulting (LMPC) isolates. Highly efficient protein recovery was achieved by optimization of a "one-pot" protein extraction and digestion allowing for reproducible proteomic analysis on as few as 500 LMPC isolated cells. The method was combined with label-free spectral count quantitation to characterize proteomic differences from 3000-10,000 LMPC isolated cells. Significance analysis of spectral count data was accomplished using the edgeR tag-count R package combined with hierarchical cluster analysis. To illustrate the capability of this robust workflow, two examples are presented: 1) analysis of keratinocytes from human punch biopsies of normal skin and a chronic diabetic wound and 2) comparison of glomeruli from needle biopsies of patients with kidney disease. Differentially expressed proteins were validated by use of immunohistochemistry. These examples illustrate that tissue proteomics carried out on limited clinical material can obtain informative proteomic signatures for disease pathogenesis and demonstrate the suitability of this approach for biomarker discovery.

Reduction in inflammatory gene expression in skeletal muscle from Roux-en-Y gastric bypass patients randomized to omentectomy

Objectives

To examine the effects of Roux-en-Y gastric bypass (RYGB) surgery with and without laparoscopic removal of omental fat (omentectomy) on the temporal gene expression profiles of skeletal muscle.

Design

Previously reported were the whole-body metabolic effects of a randomized, single-blinded study in patients receiving RYGB surgery stratified to receive or not receive omentectomy. In this follow up study we report on changes in skeletal muscle gene expression in a subset of 21 patients, for whom biopsies were collected preoperatively and at either 6 months or 12 months postoperatively.

Methodology/Principal Findings

RNA isolated from skeletal muscle biopsies of 21 subjects (8 without omentectomy and 13 with omentectomy) taken before RYGB or at 6 and 12 months postoperatively were subjected to gene expression profiling via Exon 1.0 S/T Array and Taqman Low Density Array. Robust Multichip Analysis and gene enrichment data analysis revealed 84 genes with at least a 4-fold expression difference after surgery. At 6 and 12 months the RYGB with omentectomy group displayed a greater reduction in the expression of genes associated with skeletal muscle inflammation (ANKRD1, CDR1, CH25H, CXCL2, CX3CR1, IL8, LBP, NFIL3, SELE, SOCS3, TNFAIP3, and ZFP36) relative to the RYGB non-omentectomy group. Expressions of IL6 and CCL2 were decreased at all postoperative time points. There was differential expression of genes driving protein turnover (IGFN1, FBXW10) in both groups over time and increased expression of PAAF1 in the non-omentectomy group at 12 months. Evidence for the activation of skeletal muscle satellite cells was inferred from the up-regulation of HOXC10. The elevated post-operative expression of 22 small nucleolar RNAs and the decreased expression of the transcription factors JUNB, FOS, FOSB, ATF3 MYC, EGR1 as well as the orphan nuclear receptors NR4A1, NR4A2, NR4A3 suggest dramatic reorganizations at both the cellular and genetic levels.

Conclusions/Significance

These data indicate that RYGB reduces skeletal muscle inflammation, and removal of omental fat further amplifies this response.

Trial Registration

ClinicalTrials.gov NCT00212160

Expression of Wnt9, TCTP, and Bmp1/Tll in sea cucumber visceral regeneration

We employ non-radioactive in situ hybridization techniques, which combine good tissue morphology preservation with high sensitivity of transcript detection, to map gene expression in the regenerating digestive tube of the sea cucumber Holothuriaglaberrima. We investigated localization of transcripts of Wnt9, TCTP, and Bmp1/Tll, the genes that have been previously known to be implicated in embryogenesis and cancer. The choice was determined by our long-term goal of trying to understand how the developmental regulatory pathways known to be involved in tumor development can be activated in post-traumatic regeneration without leading to malignant growth. The gene expression data combined with the available morphological information highlight the gut mesothelium (the outer layer of the digestive tube) as a highly dynamic tissue, whose cells undergo remarkable changes in their phenotype and gene expression in response to injury. This reversible transition of the gut mesothelium from a complex specialized tissue to a simple epithelium composed of rapidly proliferating multipotent cells seems to depend on the expression of genes from multiple developmental/cancer-related pathways.

Spatial mapping by imaging mass spectrometry offers advancements for rapid definition of human skin proteomic signatures

Investigations into the human skin proteome by classical analytical procedures have not addressed spatial molecular distributions in whole-skin biopsies. The aim of this study was to develop methods for the detection of protein signatures and their spatial disposition in human skin using advanced molecular imaging technology based on mass spectrometry technologies. This technology allows for the generation of protein images at specific molecular weight values without the use of antibody while maintaining tissue architecture. Two experimental approaches were employed: MALDI-MS profiling, where mass spectra were taken from discrete locations based on histology, and MALDI-IMS imaging, where complete molecular images were obtained at various MW values. In addition, proteins were identified by in situ tryptic digestion, sequence analysis of the fragment peptides and protein database searching. We have detected patterns of protein differences that exist between epidermis and dermis as well as subtle regional differences between the papillary and reticular dermis. Furthermore, we were able to detect proteins that are constitutive features of human skin as well as those associated with unique markers of individual variability.

Proteomic analysis of human mesenchymal stromal cells derived from adipose tissue undergoing osteoblast differentiation

BACKGROUND AIMS

Stem cells derived from human adipose tissue (ASC) have the capacity for renewal, are easily obtained and have plasticity properties that allow them to differentiate into several cell types, including osteoblast cells. With the aim of understanding the issue of the osteogenic process and finding reliable biomarkers in cells undergoing the osteogeneic differentiation process, this work took advantage of a proteomic approach to identify proteins involved in osteogenesis.

METHODS

For this purpose, ASC were analyzed under three conditions: S0, in the absence of stimulation; S1, with 2 weeks of osteogenic medium stimulation; and S2, with 4 weeks of osteogenic medium stimulation. The identification of ASC was carried out by flow cytometry using antibodies specific to known undifferentiated stem cell-surface markers. Cell viability, enzymatic activity, mineral deposition, collagen structure and production and gene analyzes were evaluated for each condition.

RESULTS

Phenotypic modifications were observed during the in vitro osteogenic differentiation process by two-dimensional (2-D) differential image gel electrophoresis (DIGE). The proteins were identified by mass espectrometry in tandem (MS/MS) analyzes using Matrix-assisted laser desorption/ionization with TOF/TOF is a tandem mass spectrometry method where two time-of-flight mass spectrometers are used consecutively (MALDI-TOF/TOF). A total of 51 differentially expressed proteins was identified when comparing the three observed conditions. Sixteen different spots were identified in the S0 stage compared with S2, while 28 different spots were found in S2 compared with S0. S1 expressed seven different spots compared with S0 and S2.

CONCLUSIONS

These findings suggest the involvement of several proteins directly related to the osteogenic pathway, which can be used to improve understanding of the osteogenic process.

Proteomic identification of cathepsin B and nucleophosmin as novel UVA-targets in human skin fibroblasts

Solar UVA exposure plays a causative role in skin photoaging and photocarcinogenesis. Here, we describe the proteomic identification of novel UVA-targets in human dermal fibroblasts following a two-dimensional-difference-gel-electrophoresis (2D-DIGE) approach. Fibroblasts were exposed to noncytotoxic doses of UVA or left untreated, and total protein extracts underwent CyDye-labeling followed by 2D-DIGE/mass-spectrometric identification of differentially expressed proteins, confirmed independently by immunodetection. The protein displaying the most pronounced UVA-induced upregulation was identified as the nucleolar protein nucleophosmin. The protein undergoing the most pronounced UVA-induced downregulation was identified as cathepsin B, a lysosomal cysteine-protease displaying loss of enzymatic activity and altered maturation after cellular UVA exposure. Extensive lysosomal accumulation of lipofuscin-like autofluorescence and osmiophilic material occurred in UVA-exposed fibroblasts as detected by confocal fluorescence microscopy and transmission electron microscopy, respectively. Array analysis indicated UVA-induced upregulation of oxidative stress response gene expression, and UVA-induced loss of cathepsin B enzymatic activity in fibroblasts was suppressed by antioxidant intervention. Pharmacological cathepsin B inhibition using CA074Me mimicked UVA-induced accumulation of lysosomal autofluorescence and deficient cathepsin B maturation. Taken together, these data support the hypothesis that cathepsin B is a crucial target of UVA-induced photo-oxidative stress causatively involved in dermal photodamage through the impairment of lysosomal removal of lipofuscin.

Analysis of pressure ulcer wound fluid using two-dimensional electrophoresis

The incidence rate of pressure ulcers in the USA ranges from 0.4% to 38% in acute care settings and from 2.2% to 23.9% in long-term care settings, and their treatment costs are in the billions of dollars yearly. The proteome of wound fluid may contain early indicators or biomarkers associated with healing in pressure ulcers that would enable treatment regimes to be optimised for each individual. Wound fluid was collected from the interior and periphery of 19 chronic pressure ulcers at 15 time points during 42 days for an analysis of protein expression. Proteins were fractionated using two-dimensional polyacrylamide gel electrophoresis. A comparison of the spot distributions indicates a biochemical difference between the interior and the periphery of wounds. Pressure ulcers that healed show a greater number of spots for interior and peripheral locations combined over time when compared with wounds that did not heal. Using this technique, protein S100A9 was identified as a potential biomarker of wound healing. The identification of differences within the proteome of healing versus non healing pressure ulcers could have great significance in the use of current treatments, as well as the development of new therapeutic interventions.

A microarray analysis of temporal gene expression profiles in thermally injured human skin

Partial-thickness burns incite a multitude of responses which eventually culminate in cutaneous wound repair. We hypothesized that these events would evoke extensive alterations in gene expression thereby orchestrating the complexity of spatial and temporal events that characterize "normal" human wound healing. In the present study, gene expression from partial-thickness areas at defined temporal periods (1-3 days, 4-6 days, and 7-18 days) after injury were compared to normal non-wounded skin. Gene alterations proved extensive (2286 genes). Statistically significant alterations were noted among increased and decreased genes expressed in the three different temporal groupings. Our foundational data (based on samples from 45 individuals) provide a comprehensive molecular gene expression portrait of the cutaneous reparative responses that are initiated during the first 17 days after injury. Our efforts also represent an initial endeavor to move beyond the historically defined "morphological phases" of wound repair toward reporting molecular clues that define the temporal sequence of healing in human subjects. Further analysis of genes that are either affected or remain not affected following injury to normal skin is expected to identify potential targets for therapeutic augmentation or silencing.