Using optical coherence tomography for the longitudinal non-invasive evaluation of epidermal thickness in a murine model of chronic skin inflammation

Effect of Repeated Low-Dose UVR Exposure on Skin Inflammation Threshold, Skin Biomarkers, and Vitamin D in Healthy Adults

UVR can cause photoaging, skin burns, and skin cancer. The skin counters these effects through photoadaptation, which involves melanin production, skin thickening, and immune responses. This study investigated the effects of repeated, suberythemal low-dose UVR on the skin's inflammation threshold, assessed as minimal erythema dose, across different skin phototypes. In addition, epidermal and stratum corneum thickness, melanin index, erythema index, skin and blood levels of immunological biomarkers, and blood vitamin D3 25(OH) were measured. Over 9 weeks, 31 subjects were exposed to UVR (0.8 standard erythema dose) on the lower back 3 times per week. Results showed a 50% increase in minimal erythema dose, with a stronger effect in lighter phototypes. Increase in minimal erythema dose was paralleled by an increase in erythema index. Melanin index and stratum corneum thickness increased significantly by 12 and 34%, respectively, with melanin having a stronger effect on the minimal erythema dose increase. Vitamin D levels rose by 21%, adjusting for seasonal decline. Immunological markers of T helper 1/T helper 2 response and vascular markers declined, indicating local immunosuppression, although no systemic changes in immunological markers were observed. These findings suggest that even low UVR doses are sufficient to induce photoadaptation. Further research is needed to evaluate the long-term benefits and risks of this exposure.

Testing the Reliability of Optical Coherence Tomography to Measure Epidermal Thickness and Distinguish Volar and Nonvolar Skin

In persons with limb loss, prosthetic devices cause skin breakdown, largely because residual limb skin (nonvolar) is not intended to bear weight such as palmoplantar (volar) skin. Before evaluation of treatment efficacy to improve skin resiliency, efforts are needed to establish normative data and assess outcome metric reliability. The purpose of this study was to use optical coherence tomography to (i) characterize volar and nonvolar skin epidermal thickness and (ii) examine the reliability of optical coherence tomography. Four orientations of optical coherence tomography images were collected on 33 volunteers (6 with limb loss) at 2 time points, and the epidermis was traced to quantify thickness by 3 evaluators. Epidermal thickness was greater (P < .01) for volar skin (palm) (265.1 ± 50.9 μm, n = 33) than for both nonvolar locations: posterior thigh (89.8 ± 18.1 μm, n = 27) or residual limb (93.4 ± 27.4 μm, n = 6). The inter-rater intraclass correlation coefficient was high for volar skin (0.887-0.956) but low for nonvolar skin (thigh: 0.292-0.391, residual limb: 0.211-0.580). Correlation improved when comparing only 2 evaluators who used the same display technique (palm: 0.827-0.940, thigh: 0.633-0.877, residual limb: 0.213-0.952). Despite poor inter-rater agreement for nonvolar skin, perhaps due to challenges in identifying the dermal-epidermal junction, this study helps to support the utility of optical coherence tomography to distinguish volar from nonvolar skin.

Oral prednisolone suppresses skin inflammation in a healthy volunteer imiquimod challenge model

Imiquimod (IMQ) is a topical agent that induces local inflammation via the Toll-like receptor 7 pathway. Recently, an IMQ-driven skin inflammation model was developed in healthy volunteers for proof-of-pharmacology trials. The aim of this study was to profile the cellular, biochemical, and clinical effects of the marketed anti-inflammatory compound prednisolone in an IMQ model. This randomized, double-blind, placebo-controlled study was conducted in 24 healthy volunteers. Oral prednisolone (0.25 mg/kg/dose) or placebo (1:1) was administered twice daily for 6 consecutive days. Two days after treatment initiation with prednisolone or placebo, 5 mg imiquimod (IMQ) once daily for two following days was applied under occlusion on the tape-stripped skin of the back for 48 h in healthy volunteers. Non-invasive (imaging and biophysical) and invasive (skin punch biopsies and blister induction) assessments were performed, as well as IMQ ex vivo stimulation of whole blood. Prednisolone reduced blood perfusion and skin erythema following 48 h of IMQ application (95% CI [-26.4%, -4.3%], p = 0.0111 and 95% CI [-7.96, -2.13], p = 0.0016). Oral prednisolone suppressed the IMQ-elevated total cell count (95% CI [-79.7%, -16.3%], p = 0.0165), NK and dendritic cells (95% CI [-68.7%, -5.2%], p = 0.0333, 95% CI [-76.9%, -13.9%], p = 0.0184), and classical monocytes (95% CI [-76.7%, -26.6%], p = 0.0043) in blister fluid. Notably, TNF, IL-6, IL-8, and Mx-A responses in blister exudate were also reduced by prednisolone compared to placebo. Oral prednisolone suppresses IMQ-induced skin inflammation, which underlines the value of this cutaneous challenge model in clinical pharmacology studies of novel anti-inflammatory compounds. In these studies, prednisolone can be used as a benchmark.

Case report: Optical coherence tomography for monitoring biologic therapy in psoriasis and atopic dermatitis

Biologic therapies are increasingly used to treat chronic inflammatory skin diseases such as psoriasis and atopic dermatitis. In clinical practice, scores based on evaluation of objective and subjective symptoms are used to assess disease severity, leading to evaluation of treatment goals with clinical decisions on treatment initiation, switch to another treatment modality or to discontinue current treatment. However, this visual-based scoring is relatively subjective and inaccurate due to inter- and intraobserver reliability. Optical coherence tomography (OCT) is a fast, high-resolution, in vivo imaging modality that enables the visualization of skin structure and vasculature. We evaluated the use of OCT for quantification and monitoring of skin inflammation to improve objective assessment of disease activity in patients with psoriasis and atopic dermatitis. We assessed the following imaging parameters including epidermal thickness, vascular density, plexus depth, vessel diameter, and vessel count. A total of four patients with psoriasis or atopic dermatitis were treated with biologic agents according to current treatment guidelines. OCT was used to monitor their individual treatment response in a target lesion representing disease activity for 52 weeks. Psoriatic and eczema lesions exhibited higher epidermal thickness, increased vascular density, and higher vessel count compared to uninvolved skin. An upward shift of the superficial vascular plexus accompanied by smaller vessel diameters was seen in psoriasis in contrast to atopic dermatitis, where larger vessels were observed. A response to biologic therapy was characterized by normalization of the imaging parameters in the target lesions in comparison to uninvolved skin during the observation period of 52 weeks. Optical coherence tomography potentially serves as an instrument to monitor biologic therapy in inflammatory skin diseases. Imaging parameters may enable objective quantification of inflammation in psoriasis or atopic dermatitis in selected representative skin areas. OCT may reveal persistent subclinical inflammation in atopic dermatitis beyond clinical remission.

Semisupervised representative learning for measuring epidermal thickness in human subjects in optical coherence tomography by leveraging datasets from rodent models

SIGNIFICANCE

Morphological changes in the epidermis layer are critical for the diagnosis and assessment of various skin diseases. Due to its noninvasiveness, optical coherence tomography (OCT) is a good candidate for observing microstructural changes in skin. Convolutional neural network (CNN) has been successfully used for automated segmentation of the skin layers of OCT images to provide an objective evaluation of skin disorders. Such method is reliable, provided that a large amount of labeled data is available, which is very time-consuming and tedious. The scarcity of patient data also puts another layer of difficulty to make the model more generalizable.

AIM

We developed a semisupervised representation learning method to provide data augmentations.

APPROACH

We used rodent models to train neural networks for accurate segmentation of clinical data.

RESULT

The learning quality is maintained with only one OCT labeled image per volume that is acquired from patients. Data augmentation introduces a semantically meaningful variance, allowing for better generalization. Our experiments demonstrate the proposed method can achieve accurate segmentation and thickness measurement of the epidermis.

CONCLUSION

This is the first report of semisupervised representative learning applied to OCT images from clinical data by making full use of the data acquired from rodent models. The proposed method promises to aid in the clinical assessment and treatment planning of skin diseases.

Effect of scratching and friction on human skin in vivo

OBJECTIVE

To investigate effect of scratching and friction on human skin function and functional differences between scratching and friction.

METHOD

Forty healthy volunteers were enrolled. Scratching and friction behavior was modeled by scalpel and sandpaper simulation to forearm for 80 times, respectively. Noninvasive bioengineering devices were used to measure basic skin physiological parameters and exfoliated stratum corneum collected and protein quantified. Parameters were recorded at baseline (BL) and after every 20 times interventions (20, 40, 60, and 80 times).

RESULTS

Compared to BL, transepidermal water loss (TEWL) value increased significantly at both scratched and friction sites (P < .001) with a significant higher value for friction (P < .001). There was no significant difference in stratum corneum hydration (SCH) value postscratching (P > .05), while it decreased first and then increased significantly at friction site (P < .001). Roughness values (contract (CONT), variety (VAR), and scaliness (SEsc)) were raised significantly at both sites (P < .001). Net change in CONT and SEsc values of friction was higher than scratched sites (P > .05). There was no significant difference in blood flow after both scratching and friction (P > .05). Quantity of keratinocyte protein from friction sites was statistically higher than scratching after 80 times interventions (P < .05).

CONCLUSION

Both noninvasive detections and protein quantification indicated more damage from friction, which may have significance for behavior guidance of patients with pruritus and implication for further investigation.

Classification of burn injury using Raman spectroscopy and optical coherence tomography: An ex-vivo study on porcine skin

Accurate depth assessment of burn wounds is a critical task to provide the right treatment and care. Currently, laser Doppler imaging is able to provide better accuracy compared to the standard clinical evaluation. However, its clinical applicability is limited by factors like scanning distance, time, and cost. Precise diagnosis of burns requires adequate structural and functional details. In this work, we evaluated the combined potential of two non-invasive optical modalities, optical coherence tomography (OCT) and Raman spectroscopy (RS), to identify degrees of burn wounds (superficial partial-thickness (SPT), deep partial-thickness (DPT), and full-thickness (FT)). OCT provides morphological information, whereas, RS provides biochemical aspects. OCT images and Raman spectra were obtained from burns created on ex-vivo porcine skin. Algorithms were developed to segment skin region and extract textural features from OCT images, and derive spectral wave features from RS. These computed features were fed into machine learning classifiers for categorization of burns. Histological results obtained from trichrome staining were used as ground-truth. The combined performance of RS-OCT reported an overall average accuracy of 85% and ROC-AUC=0.94, in distinguishing the burn wounds. The significant performance on ex vivo skin motivates to assess the feasibility of combined RS-OCT in in vivo models.

Chronic skin-specific inflammation promotes vascular inflammation and thrombosis

Patients with psoriasis have systemic and vascular inflammation and are at increased risk for myocardial infarction, stroke, and cardiovascular death. However, the underlying mechanism(s) mediating the link between psoriasis and vascular disease is incompletely defined. This study sought to determine whether chronic skin-specific inflammation has the capacity to promote vascular inflammation and thrombosis. Using the KC-Tie2 doxycycline-repressible (Dox-off) murine model of psoriasiform skin disease, spontaneous aortic root inflammation was observed in 33% of KC-Tie2 compared with 0% of control mice by 12 months of age (P=0.04) and was characterized by the accumulation of macrophages, T lymphocytes, and B lymphocytes, as well as by reduced collagen content and increased elastin breaks. Importantly, aortic inflammation was preceded by increases in serum tumor necrosis factor-α, IL-17A, vascular endothelial growth factor, IL-12, monocyte chemotactic protein-1, and S100A8/A9, as well as splenic and circulating CD11b(+)Ly-6C(hi) pro-inflammatory monocytes. Doxycycline treatment of old mice with severe skin disease eliminated skin inflammation and the presence of aortic root lesion in 1-year-old KC-Tie2 animals. Given the bidirectional link between inflammation and thrombosis, arterial thrombosis was assessed in KC-Tie2 and control mice; mean time to occlusive thrombus formation was shortened by 64% (P=0.002) in KC-Tie2 animals; and doxycycline treatment returned thrombosis clotting times to that of control mice (P=0.69). These findings demonstrate that sustained skin-specific inflammation promotes aortic root inflammation and thrombosis and suggest that aggressive treatment of skin inflammation may attenuate pro-inflammatory and pro-thrombotic pathways that produce cardiovascular disease in psoriasis patients.