Supplementary Material for: Influence of Buffers of Different pH and Composition on the Murine Skin Barrier, Epidermal Proliferation, Differentiation, and Inflammation

The pH of the skin is tightly regulated by endogenous buffering systems. We examined the influence of buffers of different pH and composition on skin barrier repair, pH, inflammation, and epidermal thickness/proliferation/differentiation. After tape-stripping in hairless mice buffers with pH 4–7 were applied in patch test chambers. After removal of the chambers, skin pH and transepidermal water loss (TEWL) were monitored for 24 h, and biopsies were taken for histology/immunohistology. Hairless mice showed a basal skin pH of about 5.8. Following barrier disruption and application of water, the pH increased by 0.6 units; increase in pH was reduced by the pH 4 glycolate buffer, unchanged by pH 4 citrate and pH 5.5 buffers, and even increased by the pH 7 buffer. pH 5.5, pH 4 citrate, and pH 4 glycolate buffers led to a slight, while the pH 7 buffer led to a significant increase in TEWL after barrier disruption compared to water. The pH 7 buffers led to a significant increase in epidermal thickness/proliferation/differentiation and inflammation after barrier disruption, whereas buffers with pH 4 and 5.5 caused a slight increase. In conclusion, only the pH 4 glycolate buffer significantly reduced the skin barrier disruption-related increase in skin pH. This was accompanied by only slight increase in epidermal thickness and inflammation compared to water. Application of the pH 7 buffer led to a significant increase in the skin pH, TEWL, epidermal thickness, and inflammation. The results are important for the formulation of topical products for effective acidification in pathological skin conditions.

皮肤的pH值受内源性缓冲系统的严格调控。本研究探究了不同pH值与组成的缓冲液对皮肤屏障修复、皮肤pH值、炎症反应以及表皮厚度、增殖与分化的影响。对无毛小鼠实施胶带剥离以破坏皮肤屏障后，将pH 4~7的缓冲液置于斑贴试验舱中进行局部施用。移除斑贴试验舱后，连续24小时监测皮肤pH值与经皮水分流失（transepidermal water loss, TEWL），并采集皮肤活检样本用于组织学与免疫组织化学分析。无毛小鼠的基础皮肤pH值约为5.8。在屏障破坏并施用纯水后，皮肤pH值上升了0.6个单位；pH 4羟乙酸盐缓冲液可抑制该pH上升，pH 4柠檬酸盐与pH 5.5缓冲液对其无明显影响，而pH 7缓冲液甚至会进一步升高pH值。与纯水组相比，pH 5.5、pH 4柠檬酸盐及pH 4羟乙酸盐缓冲液仅会导致经皮水分流失出现小幅上升，而pH 7缓冲液则会使其显著升高。屏障破坏后，pH 7缓冲液会显著提升表皮厚度、表皮增殖与分化水平以及炎症反应程度，而pH 4与pH 5.5的缓冲液仅会引起小幅升高。综上，仅pH 4羟乙酸盐缓冲液可显著降低皮肤屏障破坏相关的皮肤pH值上升。与纯水组相比，该缓冲液仅会伴随表皮厚度与炎症反应的小幅升高。施用pH 7缓冲液则会导致皮肤pH值、经皮水分流失、表皮厚度以及炎症反应出现显著升高。本研究结果对于开发可在病理性皮肤状态下实现有效酸化的外用制剂具有重要指导意义。