1. Toxicol Appl Pharmacol. 2018 May 18;352:59-67. doi: 10.1016/j.taap.2018.05.014.
[Epub ahead of print]

Membrane cholesterol delays cellular apoptosis induced by ginsenoside Rh2, a
steroid saponin.

Verstraeten SL(1), Albert M(2), Paquot A(3), Muccioli GG(3), Tyteca D(4),
Mingeot-Leclercq MP(5).

Author information: 
(1)Louvain Drug Research Institute (LDRI), Cellular & Molecular Pharmacology Unit
(FACM), Université catholique de Louvain (UCL), Brussels 1200, Belgium; de Duve
Institute (DDUV), Cell Biology Unit (CELL), Université catholique de Louvain
(UCL), Brussels 1200, Belgium.
(2)Louvain Drug Research Institute (LDRI), Cellular & Molecular Pharmacology Unit
(FACM), Université catholique de Louvain (UCL), Brussels 1200, Belgium.
(3)Louvain Drug Research Institute (LDRI), Bioanalysis and Pharmacology of
Bioactive Lipids Research Group (BPBL), Université catholique de Louvain (UCL),
Brussels 1200, Belgium.
(4)de Duve Institute (DDUV), Cell Biology Unit (CELL), Université catholique de
Louvain (UCL), Brussels 1200, Belgium.
(5)Louvain Drug Research Institute (LDRI), Cellular & Molecular Pharmacology Unit
(FACM), Université catholique de Louvain (UCL), Brussels 1200, Belgium.
Electronic address: marie-paule.mingeot@uclouvain.be.

Saponins exhibit several biological and pharmacological activities, such as
antibacterial, anti-inflammatory and anticancer effects. Many studies attribute
their activities to their interactions with cholesterol. In this study, we focus 
on the steroid saponin ginsenoside Rh2, one of the active principles of Panax
ginseng root. Some evidence suggests that lipid rafts, defined as nanodomains
enriched in cholesterol and sphingolipids, could be involved in the Rh2-induced
apoptosis. However, the role of membrane lipids, especially cholesterol, in this 
process is still poorly understood. Here, we demonstrate that (i) A549, THP-1 and
U937 cells are all susceptible to the Rh2-induced apoptosis but to a differential
extent and (ii) the cytotoxic effect inversely correlates with the cell membrane 
cholesterol content. Upon cholesterol depletion via methyl-β-cyclodextrin, those 
three cells lines become more sensitive to Rh2-induced apoptosis. Then, focusing 
on the cholesterol-auxotroph U937 cell line, we showed that Rh2 alters plasma
membrane fluidity by compacting the hydrophobic core of lipid bilayer (DPH
anisotropy) and relaxing the interfacial packaging of the polar head of
phospholipids (TMA-DPH anisotropy). The treatment with Rh2 conducts to the
dephosphorylation of Akt and the activation of the intrinsic pathway of apoptosis
(loss of mitochondrial membrane potential, caspase-9 and -3 activation). All
these features are induced faster in cholesterol-depleted cells, which could be
explained by faster cell accumulation of Rh2 in these conditions. This work is
the first reporting that membrane cholesterol could delay the activity of
ginsenoside Rh2, renewing the idea that saponin cytotoxicity is ascribed to an
interaction with membrane cholesterol.

Copyright © 2018 Elsevier Inc. All rights reserved.

DOI: 10.1016/j.taap.2018.05.014 
PMID: 29782965