Effects of EGCG on Amyloid β-Protein Fibrillogenesis and Cytotoxicity at Different pH Values†

doi:10.7503/cjcu20180260

Abstract

Abstract:

The inhibitory effects of (-)-epigallocatechin-3-gallate(EGCG) on amyloid β-protein(Aβ₄₂) aggregation were investigated under different conditions of pH=5.0, 6.0 and 7.4. The results showed that EGCG could significantly inhibit Aβ₄₂ aggregation and cytotoxicity at different pH values, but the interactions between EGCG and Aβ₄₂ were remarkably affected by the pH values. When incubating at pH=5.0, EGCG could not effectively inhibit Aβ₄₂ fibrillization at the early stage, as evidenced by the fact that 35.1% β-sheet structure and 50% thioflavin T(ThT) fluorescence remained after 24 h incubation. The reason was attributed to the rapid accumulation of Aβ₄₂ and the weakened interactions between EGCG and Aβ₄₂. At the specific condition(pH=5.0), EGCG prevented Aβ₄₂ fibrillization by reducing the hydrophobicity of Aβ₄₂, thereby remodeling amyloid aggregates. At pH=6.0, the interactions between EGCG and Aβ₄₂ increased. Therefore, EGCG displayed an enhanced inhibitory activity on Aβ₄₂ fibrillization, leading to the decrease of Aβ₄₂ aggregation rate and almost complete suppression of the conversion of Aβ₄₂ into β-sheet conformation and ThT fluorescence. By contrast, under the physiological condition(pH=7.4), slower Aβ₄₂ aggregation was observed than the aggregations at acidic conditions. The decrease in Aβ₄₂ self-assembly propensity made more stable binding of EGCG to Aβ₄₂, leading to stabilization of Aβ₄₂ structure and increased lag phase of Aβ₄₂ aggregation. As a result, EGCG significantly inhibited Aβ₄₂ aggregation and the corresponding cytotoxicity at the physiological condition.

Key words: Amyloid β-protein;, Aggregation, pH, (-)-Epigallocatechin-3-gallate, Inhibition

CLC Number:

O641

TrendMD:

ZHANG Huan, DONG Xiaoyan. Effects of EGCG on Amyloid β-Protein Fibrillogenesis and Cytotoxicity at Different pH Values^†[J]. Chem. J. Chinese Universities, 2018, 39(11): 2534.

Figures/Tables 9

Fig.1 Chemical structure of EGCG

Fig.2 Aggregation kinetics of Aβ42 incubated in the absence and presence of equimolar EGCG under different pH valuesa―c. Aβ42 under pH=5.0(a), 6.0(b), 7.4(c), respectively; d―f. Aβ42 with equimolar EGCG under pH=5.0(d), 6.0(e), 7.4(f). The incubations were done at 37 ℃, 150 r/min. Concentrations of Aβ42 and EGCG were 25 μmol/L.

Table 1 β-Sheet content(%) of Aβ42 in absence and presence of EGCG under different pH values

t/h	pH=5.0		pH=6.0		pH=7.4
t/h	—	EGCG	—	EGCG	—	EGCG
0	29.5±5.2	27.0±4.4	24.7±1.8	22.8±1.5	23.0±2.2	18.4±2.6
6	41.5±3.7	38.4±2.8	33.5±3.4	23.4±2.3	27.9±1.7	25.3±2.7
12	44.9±7.3	35.6±3.2	42.0±3.9	23.7±5.6	38.5±1.6	30.9±2.6
24	39.7±1.8	35.1±2.2	45.9±5.7	23.8±2.4	49.2±4.2	33.9±2.2
48	41.8±4.9	30.5±5.4	40.9±2.0	19.1±0.6	70.9±5.8	39.3±2.8

Fig.3 EGCG-induced remodeling of Aβ42 mature fibrils under different pH values(A) Loss of ThT fluorescence of Aβ42 fibrils measured in the absence and presence of EGCG at different conditions. a―c. Aβ42 aggregates under pH=5.0, 6.0, 7.4; d―f. Aβ42 aggregates with equimolar EGCG under pH=5.0, 6.0, 7.4. (B1—B6): AFM images of Aβ42 aggregates in the absence and presence of EGCG under different pH. (B1―B3) Aβ42 aggregates under pH=5.0, 6.0, 7.4, (B4―B6) Aβ42 aggregates with equimolar EGCG under pH=5.0, 6.0, 7.4. The samples were incubated at 37 ℃ for 4 d. Concentrations of Aβ42 aggregates and EGCG were 25 μmol/L.

Fig.4 Effect of EGCG on Aβ42 rapid aggregation kinetics under different pH values(A) Rayleigh light scatting; (B) ANS fluorescence. a.―c. Aβ42 under pH=5.0, 6.0, 7.4; d.―f. Aβ42 with equimolar EGCG under pH=5.0, 6.0, 7.4. The detections were performed at 37 ℃. Final concentrations of Aβ42 and EGCG were 10 μmol/L.

Fig.5 ANS fluorescence spectra of Aβ42 species in the absence and presence of equimolar EGCG under different pHa—c. Aβ42 under pH=5.0, 6.0, 7.4; d—f. Aβ42 with equimolar EGCG under pH=5.0, 6.0, 7.4; g. ANS control. The samples were incubated at 37 ℃, 150 r/min for 48 h. Concentrations of Aβ42 and EGCG were 25 μmol/L.

Fig.6 DLS analysis of the Aβ42 species in the absence and presence of equimolar EGCG under different pH values(A), (C), (E): Aβ42 under pH=5.0, 6.0, 7.4; (B), (D), (F): Aβ42 with equimolar EGCG under pH=5.0, 6.0, 7.4. The samples were incubated at 37 ℃, 150 r/min for 48 h. Aβ42 concentration was 25 μmol/L.

Fig.7 TEM images of Aβ42 species in the absence and presence of EGCG under different pH values(A), (C), (E) Aβ42 under pH=5.0, 6.0, 7.4; (B), (D), (F) Aβ42 with equimolar EGCG under pH=5.0, 6.0, 7.4.The samples were incubated at 37 ℃, 150 r/min for 48 h. Aβ42 concentration was 25 μmol/L.

Fig.8 Viability of SH-SY5Y cells incubated with Aβ42 species in the absence and presence of equimolar EGCG under different pH valuesBuffer-treated group in the absence() and presence() of EGCG; Aβ42 under pH=5.0(), 6.0(), 7.4(); Aβ42 with equimolar EGCG under pH 5.0(), 6.0(), 7.4(). The incubations were performed at 37 ℃, 150 r/min. The aged-concentration of Aβ42 was 25 μmol/L, and the final concentration of Aβ42 was 5 μmol/L in cells. *** P<0.001 as compared to buffer-treated group.

References 58

[1]	Chiti F., Dobson C. M., Annu. Rev. Biochem., 2017, 86(1), 27—68
[2]	Walsh D. M., Lomakin A., Benedek G. B., Condron M. M., Teplow D. B., J. Biol. Chem., 1999, 274(36), 25945—25952
[3]	Jakob-Roetne R., Jacobsen H., Angew. Chem. Int. Ed. Engl., 2009, 48(17), 3030—3059
[4]	Zheng L., Cedazo-Minguez A., Hallbeck M., Jerhammar F., Marcusson J., Terman A., Transl. Neurodegener., 2012, 1(1), 1—7
[5]	Tam J. H., Seah C., Pasternak S. H., Mol. Brain, 2014, 7(1), 54
[6]	Peralvarez-Marin A., Barth A., Graslund A., J. Mol. Biol., 2008, 379(3), 589—596
[7]	Brännström K., Öhman A., Nilsson L., Pihl M., Sandblad L., Olofsson A., J. Am. Chem. Soc., 2014, 136(31), 10956—10964
[8]	Gorman P. M., Yip C. M., Fraser P. E., Chakrabartty A. P., J. Mol. Biol., 2003, 325(4), 743—757
[9]	Khandogin J., Brooks C. L., Proc. Natl. Acad. Sci. USA, 2007, 104(43), 16880—16885
[10]	Su Y., Chang P. T., Brain Res., 2001, 893(1/2), 287—291
[11]	Du W. J., Guo J. J., Gao M. T., Hu S. Q., Dong X. Y., Han Y. F., Liu F. F., Jiang S., Sun Y., Sci. Rep., 2015, 5, 7992
[12]	Song S. M., Ma X. W., Zhou Y. H., Xu M. T., Shuang S. M., Dong C., Chem. Res. Chinese Universities, 2016, 32(2), 172—177
[13]	Xiong N., Dong X. Y., Zheng J., Liu F. F., Sun Y., ACS Appl. Mater. Interfaces, 2015, 7(10), 5650—5662
[14]	Takahashi T., Mihara H. T., Acc. Chem. Res., 2008, 41(10), 1309—1318
[15]	Xie B. L., Li X., Dong X. Y., Sun Y., Langmuir, 2014, 30(32), 9789—9796
[16]	Kerr M. L., Gasperini R., Gibbs M. E., Hou X., Shepherd C. E., Strickland D. K., Foa L., Lawen A., Small D. H., J. Neurochem., 2010, 112(5), 1199—1209
[17]	Linse S., Cabaleiro-Lago C., Xue W. F., Lynch I., Lindman S., Thulin E., Radford S. E., Dawson K. A., Proc. Natl. Acad. Sci. USA, 2007, 104(21), 8691—8696
[18]	Xie L., Luo Y., Lin D., Xi W., Yang X., Wei G., Nanoscale, 2014, 6(16), 9752—9762
[19]	Mak J. C., Clin. Exp. Pharmacol. Physiol., 2012, 39(3), 265—273
[20]	Nagle D. G., Ferreira D., Zhou Y. D., Phytochemistry, 2006, 67(17), 1849—1855
[21]	Weinreb O., Amit T., Mandel S., Youdim M. B., Genes Nutr., 2009, 4(4), 283—296
[22]	Ehrnhoefer D. E., Bieschke J., Boeddrich A., Herbst M., Masino L., Lurz R., Engemann S., Pastore A., Wanker E. E., Nat. Struct. Mol. Biol., 2008, 15(6), 558—566
[23]	Liu Y., Liu Y., Wang S. H., Dong S. Z., Chang P., Jiang Z. F., RSC Adv., 2015, 5(77), 62402—62413
[24]	Bieschke J., Russ J., Friedrich R. P., Ehrnhoefer D. E., Wobst H., Neugebauer K., Wanker E. E., Proc. Natl. Acad. Sci. USA, 2010, 107(17), 7710—7715
[25]	Palhano F. L., Lee J., Grimster N. P., Kelly J. W., J. Am. Chem. Soc., 2013, 135(20), 7503—7510
[26]	Wang S. H., Liu F. F., Dong X. Y., Sun Y., J. Phys. Chem. B, 2010, 114(35), 11576—11583
[27]	Wang Q., Shah N., Zhao J., Wang C., Zhao C., Liu L., Li L., Zhou F., Zheng J., Phys. Chem. Chem. Phys., 2011, 13(33), 15200—15210
[28]	Tomaselli S., Esposito V., Vangone P., van Nuland N. A., Bonvin A. M., Guerrini R., Tancredi T., Temussi P. A., Picone D., Chem. Bio. Chem., 2006, 7(2), 257—267
[29]	LeVine H., Amyloid, 1995, 2(1), 1—6
[30]	Ji S. R., Wu Y., Sui S. F., Gen. Physiol. Biophys., 2002, 21(4), 415—427
[31]	Roychaudhuri R., Lomakin A., Bernstein S., Zheng X., Condron M. M., Benedek G. B., Bowers M., Teplow D. B., J. Mol. Biol., 2014, 426(13), 2422—2441
[32]	Micsonai A., Wien F., Kernya L., Lee Y. H., Goto Y., Réfrégiers M., Kardos J., Proc. Natl. Acad. Sci. USA, 2015, 112(24), E3095—E3103
[33]	Noy D., Solomonov I., Sinkevich O., Arad T., Kjaer K., Sagi I., J. Am. Chem. Soc., 2008, 130(4), 1376—1383
[34]	Meng J., Zhang H., Dong X. Y., Liu F. F., Sun Y., J. Inorg. Biochem., 2018, 181, 56—64
[35]	Fotakis G., Timbrell J. A., Toxicol. Lett., 2006, 160(2), 171—177
[36]	Lin M. S., Chen L. Y., Tsai H. T., Wang S. S., Chang Y., Higuchi A., Chen W. Y., Langmuir, 2008, 24(11), 5802—5808
[37]	Khan M. V., Rabbani G., Ahmad E., Khan R. H., Int. J. Biol. Macromol., 2014, 70(8), 606—614
[38]	Hills R. D. Jr, Brooks Ⅲ C. L., J. Mol. Biol., 2007, 368(3), 894—901
[39]	Jarrett J. T., Berger E. P., Lansbury P. T. Jr., Biochemistry, 1993, 32(18), 4693—4697
[40]	Picotti P., De Franceschi G., Frare E., Spolaore B., Zambonin M., Chiti F., de Laureto P. P., Fontana A., J. Mol. Biol., 2007, 367(5), 1237—1245
[41]	Guo M., Gorman P. M., Rico M., Chakrabartty A., Laurents D. V., FEBS Lett., 2005, 579(17), 3574—3578
[42]	Ma K., Clancy E. L., Zhang Y. B., Ray D. G., Wollenberg K., Zagorski M. G., J. Am. Chem. Soc., 1999, 121(38), 8698—8706
[43]	Bujacz A., Acta Cryst., 2012, 68(10), 1278—1289
[44]	Arya P., Srivastava A., Vasaikar S. V., Mukherjee G., Mishra P., Kundu B., ACS Chem. Neurosci., 2014, 5(10), 982—992
[45]	Walsh D. M., Selkoe D. J., J. Neurochem., 2007, 101(5), 1172—1184
[46]	Wogulis M., Wright S., Cunningham D., Chilcote T., Powell K., Rydel R. E., J. Neurosci., 2005, 25(5), 1071—1080
[47]	Tabner B. J., El-Agnaf O. M., Turnbull S., German M. J., Paleologou K. E., Hayashi Y., Cooper L. J., Fullwood N. J., Allsop D., J. Biol. Chem., 2005, 280(43), 35789—35792
[48]	Christen Y., Am. J. Clin. Nutr., 2000, 71(2), 621S—629S
[49]	Miranda S., Opazo C., Larrondo L. F., Muñoz F. J., Ruiz F., Leighton F., Inestrosa N. C., Prog. Neurobiol., 2000, 62(6), 633—648
[50]	Arispe N., Pollard H. B., Rojas E., Proc. Natl. Acad. Sci. USA, 1993, 90(22), 10573—10577
[51]	Levites Y., Amit T., Mandel S., Youdim M. B., FASEB J., 2003, 17(8), 952—954
[52]	Choi Y. T., Jung C. H., Lee S. R., Bae J. H., Baek W. K., Suh M. H., Park J., Park C. W., Suh S. I., Life Sci., 2001, 70(5), 603—614
[53]	del Amo J. M. L., Fink U., Dasari M., Grelle G., Wanker E. E., Bieschke J., Reif B., J. Mol. Biol., 2012, 421(4/5), 517—524
[54]	Zhou L., Elias R. J., Food Chem., 2013, 138(2/3), 1503—1509
[55]	Li N., Taylor L. S., Ferruzzi M. G., Mauer L. J., J. Agric. Food Chem., 2012, 60(51), 12531—12539
[56]	Liu F. F., Dong X. Y., He L., Middelberg A. P., Sun Y., J. Phys. Chem. B, 2011, 115(41), 11879—11887
[57]	Bae M. J., Ishii T., Minoda K., Kawada Y., Ichikawa T., Mori T., Kamihira M., Nakayama T., Mol. Nutr. Food Res., 2009, 53(6), 709—715
[58]	An T. T., Feng S., Zeng C. M., Redox Biol., 2017, 11(C), 315—321