Bullfrog-derived dipeptide FW and tripeptide LAW potently inhibit tyrosinase, reducing melanin 30% in zebrafish.
Background
Excessive melanin production leads to hyperpigmentation disorders like melasma and post-inflammatory hyperpigmentation, and is a cosmetic concern. Current treatments often involve harsh chemicals or have limited efficacy and side effects. Tyrosinase (TYR) is the rate-limiting enzyme in melanogenesis, making its inhibition a primary strategy for skin brightening. Natural peptides offer a promising alternative due to their specificity, lower toxicity, and biodegradability, addressing the need for safer and more effective anti-melanogenic agents.
Study Design
Researchers employed an integrated workflow, starting with acid protease hydrolysis of bullfrog muscle protein. The resulting hydrolysates were ultrafiltered and fractionated via Sephadex G-15. The most active fraction (<1 kDa) was analyzed by LC-MS/MS to identify candidate peptides. Dipeptide FW and tripeptide LAW were selected via PeptideRanker and molecular docking against mushroom TYR (PDB ID: 2Y9X). Synthetic FW and LAW were then tested for TYR inhibition kinetics and stability after simulated gastrointestinal digestion. Finally, their anti-melanogenic efficacy and safety were evaluated in zebrafish larvae at doses of 0.0125-0.05 mg/mL.
Results
Acid protease hydrolysis yielded the highest TYR-inhibitory activity. In silico analysis predicted strong binding for FW and LAW, with docking scores of -8.0 and -7.9 kcal/mol, respectively. In vitro, synthetic FW and LAW exhibited concentration-dependent TYR inhibition, with IC₅₀ values of 0.21 mg/mL (approximately 0.60 mM) for FW and 0.14 mg/mL (approximately 0.36 mM) for LAW. Kinetic studies revealed FW as a competitive inhibitor and LAW as a non-competitive inhibitor, consistent with molecular docking predictions. Post-simulated gastrointestinal digestion, both peptides retained approximately 90% of their initial inhibitory activity, indicating good stability. In zebrafish larvae, neither peptide caused significant toxicity or developmental abnormalities at concentrations up to 0.05 mg/mL. Most notably:
At 0.05 mg/mL, FW reduced whole-body melanin content by 30%, while LAW reduced it by 27%.
Key Findings
- Acid protease hydrolysis of bullfrog muscle protein yielded the highest tyrosinase-inhibitory activity.
- Dipeptide FW and tripeptide LAW were identified as potent tyrosinase inhibitors via in silico and in vitro methods.
- FW exhibited competitive inhibition with an IC₅₀ of 0.21 mg/mL (~0.60 mM).
- LAW showed non-competitive inhibition with an IC₅₀ of 0.14 mg/mL (~0.36 mM).
- Both peptides retained ~90% tyrosinase-inhibitory activity after simulated gastrointestinal digestion.
- FW and LAW reduced whole-body melanin content by 30% and 27%, respectively, in zebrafish larvae at 0.05 mg/mL.
Why It Matters
This study identifies FW and LAW as promising natural tyrosinase inhibitors with potential for cosmetic and therapeutic applications in hyperpigmentation. Their high stability to gastrointestinal digestion suggests potential for oral bioavailability, expanding their utility beyond topical formulations. For biohackers and formulators, these peptides offer a novel, potentially safer alternative to existing skin-lightening agents, possibly integrated into topical creams or even oral supplements targeting melanin synthesis. The demonstrated efficacy in an in vivo model (zebrafish) provides a strong foundation for further preclinical and clinical development, moving closer to a usable protocol for managing skin pigmentation issues.
tyrosinase-inhibitor
melanin
hyperpigmentation
skin-lightening
bullfrog-peptides
fw-peptide