Exploring Major Flavonoid Phytochemicals from Nelumbo nucifera Gaertn. as Potential Skin Anti-Aging Agents: In Silico and In Vitro Evaluations.

Nelumbo nucifera Gaertn., an aquatic medicinal plant (Nelumbonaceae family), has a history of use in traditional medicine across various regions. Our previous study demonstrated the skin anti-aging potential of its stamen ethanolic extract by effectively inhibiting collagenase and tyrosinase enzymes. While the major constituents of this extract are well documented, there is a lack of research on the individual compounds' abilities to inhibit skin aging enzymes. Therefore, this study aimed to evaluate the anti-aging potential of the primary flavonoids found in N. nucifera using both in silico and in vitro approaches. Our initial step involved molecular docking to identify compounds with the potential to inhibit collagenase, elastase, and tyrosinase. Among the seven flavonoids studied, kaempferol-3-O-robinobioside (Kae-3-Rob) emerged as the most promising candidate, exhibiting the highest docking scores for three skin aging-related enzymes. Subsequent enzyme-based inhibition assays confirmed that Kae-3-Rob displayed robust inhibitory activity against collagenase (58.24 ± 8.27%), elastase (26.29 ± 7.16%), and tyrosinase (69.84 ± 6.07%). Furthermore, we conducted extensive 200-ns molecular dynamics (MD) simulations, revealing the stability of the complexes formed between Kae-3-Rob and each enzyme along the MD simulation time. MM/PBSA-based binding free energy calculations indicated the considerably stronger binding affinity of Kae-3-Rob for collagenase and tyrosinase compared to elastase, which was related to the greater percentage of hydrogen bond occupations. These computational findings were consistent with the relatively high inhibitory activity of Kae-3-Rob against collagenase and tyrosinase observed in our in vitro experiment. In conclusion, the results obtained from this comprehensive study suggest that Kae-3-Rob, a key flavonoid from N. nucifera, holds significant potential as a source of bioactive compounds for anti-aging cosmeceutical and other phytopharmaceutical application.

Molecular insights on the conformational dynamics of a P76C mutant of human cytochrome c and the enhancement on its peroxidase activity.

In apoptotic pathway, the interaction of Cytochrome c (Cytc) with cardiolipin in vivo is a key process to induce peroxidase activity of Cytc and trigger the release of Cytc in the inner mitochondria into cytosol. The peroxidase active form of Cytc occurs due to local conformational changes that support the opening of the heme crevice and the loss of an axial ligand between Met80 and heme Fe. Structural adjustments at the Ω-loop segments of Cytc are required for such process. To study the role of the distal Ω-loop segments comprising residues 71-85 in human Cytc (hCytc), we investigated a cysteine mutation at Pro76, one of the highly conserved residues in this loop. The effect of P76C mutant was explored by the combination of experimental characterizations and molecular dynamics (MD) simulations. The peroxidase activity of the P76C mutant was found to be significantly increased by ∼13 folds relative to the wild type. Experimental data on global denaturation, alkaline transition, heme bleaching, and spin-labeling Electron Spin Resonance were in good agreement with the enhancement of peroxidase activity. The MD results of hCytc in the hexacoordinate form suggest the important changes in P76C mutant occurred due to the unfolding at the central Ω-loop (residues 40-57), and the weakening of H-bond between Tyr67 and Met80. Whereas the experimental data implied that the P76C mutant tend to be in equilibrium between the pentacoordinate and hexacoordinate forms, the MD and experimental information are complementary and were used to support the mechanisms of peroxidase active form of hCytc.

Bibenzyl analogue DS-1 inhibits MDM2-mediated p53 degradation and sensitizes apoptosis in lung cancer cells.

BACKGROUND: Lung cancer is a leading fatal malignancy due to the high incidence of treatment failure. Dysfunction of the tumor suppressor p53 contributes to cancer initiation, progression, and therapeutic resistance. Targeting MDM2, a negative regulator of p53, has recently attracted interest in cancer drug research as it may restore tumor suppressive function. PURPOSE: The present study aimed to investigate the effect of 3,4-dihydroxy-5,4'-dimethoxybibenzyl (DS-1) on targeting MDM2 and restoring p53 function in lung cancer cells. METHODS: The efficacy of DS-1 alone or in combination with cisplatin in lung cancer cells was determined by MTT, nuclear staining, and annexin V/PI assay. The expression of apoptosis-related proteins was determined by western blot analysis. To evaluate the role of DS-1 on the stabilization and degradation of p53, cycloheximide chasing assay and immunoprecipitation were conducted, and the active form of p53 was investigated by immunofluorescent staining assay. To confirm and demonstrate the site interaction between DS-1 and the MDM2 protein, in silico computational analysis was performed. RESULTS: DS-1 exhibited a cytotoxic effect and sensitized lung cancer cells to cisplatin-induced apoptosis. DS-1 caused a significant increase in the cellular level of p53 protein, while the active form of p53 (phosphorylation at Ser15) was unaltered. DS-1 treatment in combination with cisplatin could enhance activated p-p53 (Ser15) and p53 downstream signaling (Bax, Bcl-2, and Akt), leading to a higher level of apoptosis. Immunoprecipitation analysis revealed that DS-1 decreased the p53-ubiquitin complex, a prerequisite step in p53 proteasomal degradation. Molecular docking simulation further evidenced that DS-1 interacts with MDM2 within the p53-binding domain by carbon-hydrogen bond interaction at Lys27, π-alkyl interactions at Ile37 and Leu30, and van der Waals interactions at Ile75, Val51, Val69, Phe67, Met38, Tyr43, Gly34, and Phe31. Treatment by DS-1 and cisplatin in patient-derivated primary lung cancer cells showed consistent effects by increasing cisplatin sensitivity. CONCLUSIONS: Our findings provide evidence that DS-1 is an MDM2 inhibitor and its underlying mechanism involves MDM2 binding and p53 induction, which may benefit the development of this compound for lung cancer treatment.