Analysis of the Effects of Melanin Depigmentation on Immunohistochemical Staining

An Optimized Melanin Depigmentation Method for Histopathological and Immunohistochemical Staining of Formalin-Fixed Paraffin-Embedded Tissues

Introduction. The difficulty in diagnosis of severe melanocytic lesions is a problem to be overcome in pathological practice. Melanin bleaching is an effective approach to ameliorate melanin disturbances in severely pigmented lesions. Although various methods for improving melanin pigmentation in immunohistochemical staining have been reported, these depigmentation methods still need to be optimized and standardized. In this study, the coloring efficiency of 3,3'-diaminobenzidine (DAB) and alkaline phosphatase (AP) after melanin depigmentation was compared under the automatic immunohistochemical staining platform. Methods. The applicability of the optimized depigmentation method was validated in 10 formalin-fixed paraffin-embedded (FFPE) blocks of ocular melanoma tissues. Specimens were demelaninized with 10% hydrogen peroxide at 60°C for immunohistochemical staining (Melan-A and SOX10), and tissue chromogenic staining was performed with DAB and AP detection systems, respectively. Results. The optimized depigmentation method including immunohistochemistry (IHC) could be completed in 3 h, effectively preserving cell morphology and immunoreactivity. Among these, the color-rendering effect and contrast of AP are better than DAB. Conclusion. This optimized method can effectively remove melanin and improve the accuracy of IHC staining interpretation. AP staining has better visibility and readability without the interference of residual melanin. The comparison results showed that after melanin depigmentation, the immunohistochemical staining agent was replaced with red AP, which avoided the misjudgment caused by brown DAB when melanin depigmentation was incomplete. This improved method can be applied to future histopathological and immunohistochemical staining of melanin-deposited tissues.

Rete ridges are decreased in dyschromic burn hypertrophic scar: A histological study

Dyschromic hypertrophic scar (HTS) is a common sequelae of burn injury, however, its mechanism has not been elucidated. This work is a histological study of these scars with a focus on rete ridges. Rete ridges are important for normal skin physiology, and their absence or presence may hold mechanistic significance in post-burn HTS dyschromia. It was posited that hyper-, and hypo-pigmented areas of scars have different numbers of rete ridges. Subjects with dyschromic burn hypertrophic scar were prospectively enrolled (n = 44). Punch biopsies of hyper-, hypo-, and normally pigmented scar and skin were collected. Biopsies were paraffin embedded, sectioned, stained with H&E, and imaged. The number of rete ridges were investigated. Burn hypertrophic scars that healed without autografts were first investigated. The number of rete ridges was higher in normal skin compared to HTS that was either hypo- (p < 0.01) or hyper-pigmented (p < 0.001). This difference was similar despite scar pigmentation phenotype (p = 0.8687). Autografted hyper-pigmented scars had higher rete ridge ratio compared to non-autografted hyper-pigmented HTS (p < 0.0001). Burn hypertrophihc scars have fewer rete ridges than normal skin. This finding may explain the decreased epidermal adherence to underlying dermis associated with hypertrophic scars. Though, contrary to our hypothesis, no direct link between the extent of dyschromia and rete ridge quantity was observed, the differences in normal skin and hypertrophic scar may lead to further understanding of dyschromic scars.

Depigmentation of Melanin-containing Tissues Using Hypochlorous Acid to Enhance Hematoxylin-eosin and Immunohistochemical Staining

Pathologists diagnose diseases by observing the histologic and cellular morphology microscopically. However, the high pigmentation in melanin-containing tumors can hide the tumor cell structures, making diagnosing challenging. Previously, hydrogen peroxide and potassium permanganate were utilized for melanin bleaching with several limitations. For instance, hydrogen peroxide has a weak bleaching ability, and the process is time-consuming (12 h). Meanwhile, potassium permanganate affects the antigenicity of antigens and is unsuitable for immunohistochemical (IHC) staining. In this study, the hypochlorous acid (HClO) solution was applied to hematoxylin-eosin and IHC staining of melanin tissue sections. The study discovered that 1% HClO could completely bleach melanin particles in tumor tissues in a short period (19.95 ± 2.53 min) without compromising the hematoxylin-eosin staining. In addition, 2% HClO was utilized for bleaching at room temperature for 61.17 ± 4.32 minutes after the tissue was incubated with 3,3'-diaminobenzidine in IHC staining. This treatment effectively removed melanin without negatively impacting 3,3'-diaminobenzidine signal expression, thus ensuring that the sections met the necessary diagnostic requirements. Therefore, this method could facilitate pathologists in disease diagnosis of melanin-containing tissues.