Siamese crocodile serum hydrolysate peptides: Potent tyrosinase inhibitors and melanogenesis regulators for...

Melanin safeguards cells from UV radiation, while also giving them colour (pigmentation). However, excessive melanin production (hyperpigmentation) can cause unwanted side effects such as skin freckles and food browning. As a result, there is a desire to control and in particular reduce melanin production. This study aims to identify bioactive peptides derived from Crocodylus siamensis serum that inhibit tyrosinase, which is a key enzyme in melanin production. We demonstrate hydrolysis of Crocodylus siamensis serum produces peptides that are potent inhibitors of tyrosinase. We demonstrate that alkaline hydrolysis is the most effective method (IC₅₀ = 0.4323 ± 0.049 μg/μL) and use peptidomic analysis to identify two peptides, HG8 (HIVGRGAG) and RI10 (RNIKASHILI), that are as effective alone as the serum hydrolysate. Our results show that both peptides could inhibit cellular tyrosinase activity and reduce melanin accumulation by down-regulating the expression levels of MITF, TYR, TRP1 and TRP2, which are key regulators of melanogenesis. The peptides also reduce the expression levels of Rab27A, MLPH, Myosin Va, Rab17 and gp100, suggesting they suppress melanosome maturation and transport. Furthermore, both peptides show antioxidant properties in B16F10 cells. These findings hold significant promise for the development of tyrosinase inhibitory peptides as therapeutic agents for hyperpigmentation.