Inhibitory Mechanism and Kinetics Study of Apple Polyphenols on the Activity of Tyrosinase

Employing fruit juices to hydrolyze edible bird's nest and enhance the antioxidant, anti-tyrosinase, and wound-healing activities of the hydrolysates

Enzymatic hydrolysis of edible bird's nest (EBN) has attracted great interest in both scientific and commercial fields due to the enhancement of solubility and nutraceutical values. The present study attempted to investigate the hydrolysis of EBN with papaya (Carica papaya L.), pineapple (Ananas comosus (L.) Merr.), and cantaloupe (Cucumis melo L.) juices as well as two commercial enzymes papain and bromelain. Our analysis revealed that EBN hydrolysis with pineapple juice and bromelain produced a degree of hydrolysis (DH) value of approximately 27 % while it was about 25 % for the hydrolysis with cantaloupe juice and 22 % for the hydrolysis with papaya juice and papain after 4 h of treatment. When EBN was digested by fruit juices and enzymes, the protein solubility and free sialic acid content were increased and the highest values were achieved for EBN hydrolysis with pineapple juice and bromelain (estimately 11 mg/mL of soluble protein and 18 g/kg of free sialic acid). The ABTS•+-scavenging, •OH-scavenging, and anti-tyrosinase capacities were higher in the EBN hydrolysates by papaya juice (IC50 of 0.034, 0.108, and 0.419 mg/mL, respectively), pineapple juice (IC50 of 0.025, 0.045, and 0.190 mg/mL, respectively), and cantaloupe juice (IC50 of 0.031 mg/mL, 0.056, and 0.339 mg/mL, respectively) than in the hydrolysates by unhydrolyzed EBN (IC50 of 0.094, 0.366, and 1.611 mg/mL, respectively). An improvement in ABTS•+-scavenging, •OH-scavenging, and anti-tyrosinase abilities was also observed for the hydrolysates by papain (IC50 of 0.041, 0.129, and 0.417 mg/mL, respectively) and bromelain (IC50 of 0.025, 0.069, and 0.336 mg/mL, respectively) but in a lesser extent as compared to the hydrolysates by respective papaya and pineapple juices. Noticeably, the EBN hydrolysates by fruit juices remarkably enhanced the wound closure in human fibroblasts by about 1.4-1.8 times after 24 h of treatment whereas this property was insignificant in the hydrolysates by enzymes. As papaya, pineapple, and cantaloupe juices are easily obtainable and have pleasant flavors, our results provide a possible method to hydrolyze EBN and apply the resultant hydrolysates in functional food products.

Essential Oils of the Leaves of Epaltes australis Less. and Lindera myrrha (Lour.) Merr.: Chemical Composition, Antimicrobial, Anti-inflammatory, Tyrosinase Inhibitory, and Molecular Docking Studies

Epaltes australis Less. has been traditionally used to treat fever and snake bites, whereas Lindera myrrha (Lour.) Merr. is well-known for addressing colds, chest pain, indigestion, and worm infestations. This study marks the first report on the chemical compositions and biological potentials of essential oils extracted from the leaves of Epaltes australis and Lindera myrrha. Essential oils obtained by hydro-distillation were analysed using the GC/MS (gas chromatography-mass spectrometry). E. australis exhibited a predominant presence of non-terpenic compounds (46.3 %), with thymohydroquinone dimethyl ether as the major compound, constituting 44.2 % of the oil. L. myrrha leaf oil contained a good proportion of sesquiterpene hydrocarbons (56.8 %), with principal compounds including (E)-caryophyllene (22.2 %), ledene (9.7 %), selina-1,3,7(11)-trien-8-one (9.6 %), and α-pinene (7.0 %). Both essential oils exhibited antimicrobial activity against the bacteria Bacillus subtilis and Clostridium sporogenes, and Escherichia coli, and the fungus Aspergillus brasiliensis. L. myrrha leaf essential oil exhibited potent control over the yeast Saccharomyces cerevisiae with a MIC of 32 μg/mL. Additionally, L. myrrha leaf oil showed strong anti-inflammatory activity with an IC50 value of 15.20 μg/mL by inhibiting NO (nitric oxide) production in LPS (lipopolysaccharide)-stimulated RAW2647 murine macrophage cells. Regarding anti-tyrosinase activity, E. australis leaf oil showed the best monophenolase inhibition with the IC50 of 245.59 μg/mL, while L. myrrha leaf oil successfully inhibited diphenolase with the IC50 of 152.88 μg/mL. From molecular docking study, selina-1,3,7(11)-trien-8-one showed the highest affinity for both COX-2 (cyclooxygenase-2) and TNF-α (tumor necrosis factor-α) receptors. Hydrophobic interactions play a great role in the bindings of ligand-receptor complexes.

Potent Tyrosinase Inhibitory Activity of Curcuminoid Analogues and Inhibition Kinetics Studies

Natural tyrosinase inhibitors from herbal plants are promising therapeutic agents for skincare and cosmetic products. Natural curcuminoids exhibit weak antityrosinase properties. The structural modification of curcumin, the major curcuminoid from Curcuma longa, gave 14 analogues. The tyrosinase inhibitory activity of the natural curcuminoids and the modified analogues on both L-tyrosine and DOPA substrates were evaluated. The inhibition kinetics were also undertaken. For analogues with potent activity on the L-tyrosine substrate, the isoxazole analogue 12 and two reduced analogues, hexahydrocurcumin (16) and the α,β-unsaturated analogue 17, showed IC50 values of 8.3, 14.6 and 9.4 µM, and were 20.9-, 11.9- and 18.4-fold more active, respectively, than kojic acid, the reference compound. For the analogues with potent antityrosinase on DOPA substrate, the dimethylated analogue 5 exhibited the strongest antityrosinase activity against the DOPA substrate, with the IC50 value of 8.0 µM, which was 16.6-fold more active than kojic acid. The inhibition kinetics revealed that curcuminoid 5 could bind with both free enzyme and with the enzyme–substrate complex. It acted as a competitive–uncompetitive mixed-II type inhibitor. Curcuminoid 17 could bind with both free enzyme and the enzyme–substrate complex. The results indicated that 17 acted as a competitive–uncompetitive mixed-I type inhibitor, while curcuminoid 12 was a noncompetitive inhibitor which bound with both free enzymes and the enzyme–substrate complex. These potent analogues might serve as new potential tyrosinase inhibitors for the prevention and treatment of skin pigmentation disorders.

Evaluation of tyrosinase inhibitory activity and mechanism of Leucrocin I and its modified peptides

This research first reports the tyrosinase inhibition and mechanism of Leucrocin I and its modified peptides (TILI-1 and TILI-2). Docking simulation showed that these peptides were predicted to bind and interact to active site of tyrosinase and exhibited the possibility to promote tyrosinase inhibition. Therefore, these peptides were synthesized, and their inhibitory activity was investigated. The results showed that the highest tyrosinase inhibition was achieved by TILI-2 followed by TILI-1 and Leucrocin I. A Lineweaver-Burk plot indicated that Leucrocin I exhibited mixed type characteristics, while its modified peptides exhibited competitive inhibition. Based on the greatest tyrosinase inhibition, TILI-2 was selected for further study. TILI-2 showed irreversible inhibition with two-step inactivation. Additionally, Leucrocin I and its modified peptides showed no toxicity toward B16F1 and HaCaT cells and decreased melanin and tyrosinase content in B16F1 cells. These results suggest that these peptides are promising peptides for the treatment of hyperpigmentation.

Exploitation of apple pomace towards extraction of triterpenic acids, antioxidant potential, cytotoxic effects, and inhibition of clinically important enzymes

Apple pomace (AP) utilised for analysis of triterpenic acids (TTAs) using HPLC-MS/MS. The methanol, ethanol and ethyl acetate extracts showed high phenolic content with significant antioxidant activity compared to chloroform and n-hexane. AP TTAs; ursolic acid, betulinic acid and maslinic acid showed potent antioxidant and enzyme inhibitory effects. The IC₅₀ values were 13.2-30.8 μg/mL (tyrosinase), 19.6-42.5 μg/mL (xanthine oxidase) and 16.6-38.6 μg/mL (urease) for AP extracts and 8.4-25.8 μg/mL (tyrosinase), 12.6-30.2 μg/mL (xanthine oxidase) and 10.1-28.6 μg/mL (urease) for TTAs, compared to the positive controls; kojic acid (10.4 ± 0.06 μg/mL), allopurinol (9.6 ± 0.04 μg/mL) and thiourea (8.9 ± 0.02 μg/mL) towards respective enzymes. UA showed a competitive type of inhibition for tyrosinase, while BA showed a noncompetitive type of inhibition towards xanthine oxidase. In addition, the AP extracts and TTAs exerted significant cytotoxic effects towards the proliferation of cancer cell lines. AP methanol extract (IC₅₀ of 38.5 ± 4.1, 47.1 ± 3.5, 70.6 ± 2.3, and 50.5 ± 3.9 μg/mL) and ursolic acid (IC₅₀ of 6.5 ± 0.7, 15.5 ± 1.4, 20.8 ± 1.3, and 5.6 ± 0.8 μg/mL) showed prominent anticancer activity on Hela, Skov-3, Caski, and NCL cancer cell lines, respectively. Thus, this study shows that the AP & TTAs could be utilized for functional food development and as a potent antioxidant, anticancer, skin whitening, and anti-urolithic agents.