Chantriolides F-P, Highly Oxidized Withanolides with Hepatoprotective Activity from Tacca chantrieri

Abstract

Eleven highly oxidized withanolides, chantriolides F-P (1-11), together with six known analogues (12-17), were isolated from the rhizomes of Tacca chantrieri. Their structures were established on the basis of comprehensive spectroscopic data analysis and comparison with published NMR data, and their absolute configurations were further confirmed by experimental ECD data and single crystal X-ray diffraction analysis. The structures of compounds 5-8 contained a chlorine atom substituted at C-3. Compounds 1 and 12 are a pair of epimers isomerized at C-24 and C-25, while compounds 9 and 16 are isomerized at C-1, C-7, C-24, and C-25. Next, the hepatoprotective effect of all the isolates was evaluated on tert-butyl hydroperoxide (t-BHP)-injured AML12 hepatocytes. Compounds 5-11 and 16 significantly enhanced cell viability. Compound 8 decreased reactive oxygen species accumulation and increased glutathione level in t-BHP injured AML12 hepatocytes through promoting nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2).

Keywords: Tacca chantrieri; chantriolides F–P; hepatoprotective effect; structural elucidation; withanolides.

Figure 1

Structures of compounds 1–17 from Taccaceae chantrieri.

Figure 2

Perspective ORTEP drawings for compounds 1 and 2.

Figure 3

Experimental ECD spectra of compounds 3, 5, and 6.

Figure 4

Perspective ORTEP drawings for compounds 4 and 5.

Figure 5

Key ¹H-¹H COSY and HMBC correlations for compounds 5 and 9.

Figure 6

Key ROESY correlations for compounds 5 and 9.

Figure 7

Experimental ECD spectra of compounds 2, 7, and 8.

Figure 8

Perspective ORTEP drawings for compounds 9 and 10.

Figure 9

Perspective ORTEP drawings for compound 11.

Figure 10

Hepatoprotective effects of withanolides on t-BHP-injured AML12 hepatocytes. (A) Cell viability of t-BHP-injured AML12 hepatocytes treated with compounds 1–17 at their maximum safe concentration. Resveratrol (Res) at 10 μM was used as a positive control. (B) Cell viability of t-BHP-injured AML12 hepatocytes treated with different concentrations of compound 8. (C) ROS contents in t-BHP-injured AML12 hepatocytes treated with different concentrations of compound 8. (D) GSH levels in t-BHP-injured AML12 hepatocytes treated with different concentrations of compound 8. Data are shown as mean ± S.D., n = 3. ^## p < 0.01 vs. vehicle; * p < 0.05 and ** p < 0.01 vs. t-BHP plus DMSO.

Figure 11

Compound 8 activates Keap-1/Nrf2/HO-1 signaling pathway in t-BHP-injured AML12 hepatocytes. (A) The total protein levels of Keap-1, Nrf2, and HO-1 were analyzed by Western blots. β-actin was used as a loading control. (B) Representative immunofluorescent image of Nrf2 distribution. Nuclei were visualized using DAPI (blue), and Nrf2 was stained as red. Scale bar = 25 µm. (C) Nuclear Nrf2 expression was analyzed by Western blots. Histone H3 was used as a loading control.