Topical Morus alba Extract Cream Reduces UVB-Induced Melanogenesis Without Affecting Melanocyte Viability in Wistar Rats

Abstract

Hyperpigmentation disorders such as melasma and post-inflammatory hyperpigmentation arise from excessive melanin synthesis following chronic ultraviolet (UV) exposure. Melanin production is primarily driven by tyrosinase activation through inflammatory and oxidative stress pathways. Hydroquinone remains the standard depigmenting agent but is limited by cytotoxicity and adverse effects. Morus alba (mulberry) contains bioactive polyphenols, including oxyresveratrol and mulberroside A, known for antioxidant and tyrosinase-inhibitory activities, which may provide a safer natural alternative. To evaluate the effect of topical Morus alba extract cream on melanin density and melanocyte count in UVB-exposed Wistar rats compared with hydroquinone 4% cream. This experimental study used fifteen male Wistar rats divided into three groups: a normal UVB-exposed control, a Morus alba extract treatment group, and a hydroquinone 4% group. UVB irradiation was administered for two weeks and 30 minutes irradiation each days to induce hyperpigmentation, daily topical application of treatments for three weeks. Skin samples were analyzed histologically for melanin density using Masson–Fontana staining and immunohistochemically for melanocyte count using Melan-A markers. Data were analyzed with one-way ANOVA and Tukey’s post-hoc test, with p < 0.05 considered significant. The Morus alba extract cream produced a non-significant reduction in mean melanin density and melanocyte count compared with the UVB-exposed control. In contrast, hydroquinone 4% significantly reduced melanin density and showed a decreasing trend in melanocyte count. Although Morus alba demonstrated limited depigmenting efficacy within four weeks, its antioxidant and anti-inflammatory constituents likely attenuated melanogenesis through modulation of tyrosinase and oxidative stress pathways. Morus alba extract cream exhibits weak antimelanogenic activity without melanocytotoxicity, suggesting potential as a natural depigmenting and photoprotective agent.

Keywords:    Morus alba; melanogenesis; melanin density; melanocyte; hydroquinone; UVB irradiation; antioxidant; tyrosinase inhibition