후코스테롤과 후코잔틴의 항당뇨 효과

Abstract

Fucosterol, the predominant sterol in brown seaweeds, constitutes 83-97% of the content. There have been many studies on the biological activities including antioxidant, hepatoprotective, anti-inflammatory, anticancer, anti-fungal, antihistaminic, anti-diabetic and anticholinergic. Fucoxanthin is a marine carotenoid that is characteristically present in edible brown seaweeds such as Eisenia bicyclis (Arame), Undaria pinnatifida (Wakame) and Hijikia fusiformis (Hijiki). Fucoxanthin, one of the most abundant carotenoids, accounts for more than 10% of the estimated total natural production of carotenoids and has a unique structure with an unusual allenic bond and a 5,6-monoepoxide. Fucoxanthin has received considerable attention because of its wide array of beneficial functions in human health, including anti-inflammatory, antioxidant, antimutagenecity, and anticancer activities. In this study, the anti-diabetic activities of fucosterol and fucoxanthin were investigated by evaluating the ability of these compounds to inhibit α-glucosidase, PTP1B, rat lens AR (RLAR), human recombinant AR (HRAR), AGE formation. Since there is no detailed information on the mode of inhibition, or the molecular interactions of fucosterol and fucoxanthin with the corresponding enzymes, this study was also designed to identify an approach to develop potent anti-diabetic or anti diabetic complications drugs using molecular docking predictions and enzyme kinetics of these compounds. Fucosterol exhibited moderate RLAR and HRAR inhibitory activity with IC50 values of 18.94 ± 1.90 μM and 143.88 ± 3.76 μM, respectively, as compared with the positive control, quercetin with respective IC50 values of 1.34 ± 0.05 μM and 7.63 ± 0.05 μM. On the other hand, fucosterol exhibited marginal inhibitory activity on PTP1B and α-glucosidase, and AGE formation. By means of Lineweaver-Burk double reciprocal plots, the various concentration lines of fucosterol intersected in the left side, indicating mixed type inhibitors on RLAR and HRAR with respection IC50 values of 7.0 and 99.50 μM, while the lines show the same point on the x-intercept representing noncompetitive inhibitors against PTP1B with a Ki value of 77.13 μM in Dixon plots. Due to the presence of hydrophobic ring nucleus and hydrophobic hydrocarbon side chain of fucosterol, it was observed that this compound interacted with human AR and RLAR through well-known active sites, such as hydrophobic specificity residues. In particular, the hydrophobic ring system of fucosterol is bound tightly in a specificity pocket through apolar amino acid residues, including Trp80, His111, Phe122/Phe123, and Trp112. In addition, the interaction of AR and the aliphatic side chain in fucosterol with Val48, Trp80, Trp122, Phe122/Phe123, Cys299, and Leu301 residues while a polar site with Trp21 and Tyr49 residues on AR interacts with 3-hydroxyl group and double bond in side chain of fucosterol. Results of the docking simulation of fucosterol demonstrated negative binding energies (–8.2 kcal/mol for RLAR and –8.5 kcal/mol for HRAR), indicating higher affinity and tighter binding capacity of fucosterol for the active site of the enzyme. Fucoxanthin exhibited potent AGE inhibitory activity with an IC50 value of 86.48 ± 2.16 μM as compared with the positive control, aminoguanidine, with an IC50 value of 530.37 ± 6.52 μM. Notably, fucoxanthin showed six times stronger inhibition of AGE formation than aminoguanidine, a well-known inhibitor of AGE formation. On the other hand, fucoxanthin exhibited marginal AR inhibitory activities with IC50 values of 108.31 ± 3.99 μM for HRAR and 264.67 ± 13.76 μM for RLAR. Also, fucoxanthin exerted significant PTP1B inhibitory activity with an IC50 value of 4.80 ± 0.49 μM, where the positive control ursolic acid had an IC50 value of 2.56 ± 0.07 μM. On the other hand, fucoxanthin did not exhibit α-glucosidase inhibitory activity up to a concentration of 200 μM. Using Lineweaver-Burk plots, the various concentration lines of fucoxanthin had the same y-intercept, representing its ability to act as a competitive RLAR inhibitor, while the lines of fucoxanthin intersected the axis on the left side of the zero point, indicating its ability to act as a mixed-type PTP1B inhibitor. The Ki values obtained from the Dixon plotting were 67.67 μM for RLAR inhibition and 1.53 μM for PTP1B inhibition. The corresponding ligand-interactions of fucoxanthin in the active site of PTP1B are the three hydrogen bonding interactions between Phe30, Phe52 and Gly183 residues of the enzyme and the two hydroxyl groups of fucoxanthin, while the five residues, Tyr20, Lys116, Arg24, Arg254, and Gln262, of the enzyme participated in hydrogen bonding interactions with the carboxylate anions of compound 23. In addition, there were additional hydrophobic interactions between long hydrocarbon chains harboring a conjugated double bond of fucoxanthin and Ile219, Tyr46, Val49, and Ala217 residues on PTP1B. Moreover, the binding energies of both compounds were negative values of -7.66 kcal/mol for fucoxanthin and -10.18 kcal/mol for compound 23. In the present study, fucosterol and fucoxanthin showed inhibitory potential against AR, PTP1B, and AGE formation thus holds promise for its use as a therapeutic agent for the treatment of diabetes as well as related complications.