Non‐invasive assessment of tryptophan fluorescence and confocal microscopy provide information on skin barrier repair dynamics beyond TEWL

Abstract

The stratum corneum (SC) serves a primary function of skin barrier and understanding the kinetics of SC formation may provide great insight for skin diagnosis and evaluation of therapies. Besides trans-epidermal water loss (TEWL), few methods have been characterized to assess skin barrier non-invasively in vivo, particularly for dynamic measurements on the same specimen over time. The objective of this study was to characterize alternative non-invasive methods to evaluate the dynamic processes involved in the recovery of normal human SC after total removal. TEWL, tryptophan fluorescence and reflectance confocal microscopy (RCM) were used to determine skin barrier function, cell turnover and epidermal morphology over a period of 10 days after total removal of the SC by tape stripping. The results show a biphasic recovery of TEWL over time, which contrasted with a linear increase of 2.3 μm/day in SC thickness. Tryptophan assessment of cell turnover also demonstrated a biphasic pattern attaining a maximum three to four times the levels of the control site 3 days after injury that slowly returned to baseline and displayed great correlation (R(2) > 0.95) to viable epidermis thickness that also achieved a maximum about 3 days after injury with an approximate increase of 55%. When plotting the change of TEWL versus SC thickness, a single exponential function is observed [Δ-TEWL = 55 exp (-0.157×)] which contrasts with other proposed models. These methods were able to present rates for SC recovery processes beyond skin barrier (TEWL) that may provide new insights on kinetics of barrier formation for evaluation of skin conditions and treatments.

A 3D self-organizing multicellular epidermis model of barrier formation and hydration with realistic cell morphology based on EPISIM

“…S5 at the shallowest points). Accounting for this anatomical variance, the ranges obtained in silico for homeostatic viable epidermis (22–72 μm) and SC (23–28 μm) overlap well with the ranges measured experimentally in the arm region: 30–70 μm and 10–30 μm, respectively29313233. Simulations on a flat basement membrane display qualitatively similar behaviour with respect to the impact of humidity; the homeostatic thickness is comparable to tissue thickness in shallow points of tissue simulated on the undulated basement membrane (see Supplementary Fig.…”

“…3A). Interestingly, a thickness overshoot of the viable epidermis has also been observed in tape stripping experiments in vivo 2936. Summarizing, the model epidermis grows best at high H, but once it attains homeostasis it reacts robustly to changes in H, underscoring the importance of the epidermal barrier in maintaining epidermal health.…”

“…In contrast, prematurely differentiated SC cells are considered dead and merely act as a passive obstacle; they produce no lipids. We base these rules on experimental observations282930.…”

Establishing the dynamics of neutrophil accumulation in vivo by reflectance confocal microscopy

“…It can image the superficial layers of the skin with a resolution that is comparable to conventional light microscopy (22,23). Currently, this technique is mainly used to study melanocytic cells and lesions, but also to evaluate skin barrier function (23)(24)(25)(26).…”

Confocal microscopy: a new era in understanding the pathophysiologic background of inflammatory skin diseases

“…One of the emerging and intriguing applications of RCM is the evaluation of ‘dynamic’ processes in vivo that cannot be otherwise analysed using histopathology, as the latter typically offers only a ‘static’ view of the tissue at one time point. Recent studies have underlined the effectiveness of RCM in the follow‐up of treatment responses . Recently , the role of RCM in assessing the efficacy of photodynamic therapy (PDT) in the treatment of basal cell carcinoma (BCC) and in the evaluation of the related skin changes has been studied.…”