Melanin is a protective pigment against cellular damage and skin cancer. Peltophorum pterocarpum has been used for centuries to treat skin diseases like eczema and psoriasis. However, whether P. pterocarpum leaf extract can affect melanin synthesis with the advantage of antioxidant defense against ultraviolet (UV) radiation remains to be investigated. We aimed to examine the melanogenesis, cytotoxicity, and antioxidant activities of P. pterocarpum leaf extracts. A two-dimensional (2D) cell culture model was employed to demonstrate the effect of P. pterocarpum extracts on melanin synthesis. The cell viability of B16-F1 melanoma cells was measured by Neutral Red Uptake (NRU) assay. Antioxidant activity was accessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2’,7’-dichlorodihydrofluorescein diacetate (DCFH-DA) assays. The ethanol extract of P. pterocarpum dose-dependently increased the melanin content and displayed cytotoxicity to B16-F1 melanoma cells at the highest concentration. In contrast, the equal amounts of the aqueous extract significantly inhibited melanin synthesis and did not show any cytotoxic effects on B16-F1 melanoma cells. The P. pterocarpum ethanol extract had a significantly higher total phenolic and flavonoid content than the aqueous extract and was more effective at scavenging DPPH free radicals and intracellular ROS induced by UVB, with IC50 of 519.24 ± 122.57 vs 1798.45 ± 143.09 µg/mL and 878.00 ± 23.50 vs 1379.00 ± 21.81 µg/mL, respectively. These findings suggest that the pro-melanogenic and anti-melanogenic activities of P. pterocarpum extract with antioxidant capacity against UVB-induced cellular damage are affected by the total phenolic and flavonoid contents.

The DNSA assay has been widely employed for the in vitro detection and quantification of alpha-amylase inhibitory activity. However, the conventional method is associated with inconsistencies between protocols and requires a large volume of samples and other assay reagents that can compromise accurate quantitation. Therefore, the study aimed to develop a reliable, simple, and rapid analytical method for determining α-amylase activity. The developed method was carried out in 96-well microplates with a total volume of 250 µL and a total assay time of 1 hr, including pre-incubation. The method was validated for linearity, the limit of detection (LOD), the limit of quantitation (LOQ), and precision. A higher coefficient of determination (R2) value was observed for the developed method as compared to the conventional method (0.9983 ± 0.0003 vs 0.9667 ± 0.0383). The coefficient of variation (CV%) of each data point was less than 15%, indicating excellent data precision. The optimum assay conditions were identified at 2 U/mL of enzyme solution and 5% (w/v) starch solution at 50 °C incubation temperature with an IC50 value of 0.026 ± 0.005 mg/mL. It is concluded that the developed method is practical, precise, and accurate for estimating α-amylase inhibitory activity and would provide reproducible results.