Ž.
European Journal of Pharmacology 427 2001 167–174
www.elsevier.comrlocaterejphar
Assessment of the oestrogenic activity of the contraceptive progestin
levonorgestrel and its non-phenolic metabolites
Rene Santillan
a
, Gregorio Perez-Palacios
b
, Martın Reyes
c
, Pablo Damian-Matsumura
c
,
´´ ´ ´ ´
Gustavo A. Garcıa
d
, Ivonne Grillasca
d
, Ana E. Lemus
a,c,)
´
a
Department of ReproductiÕe Biology, National Institute of Medical Sciences and Nutrition S. Zubiran, Mexico City, Mexico
´
b
()
School of Medicine, National Autonomous UniÕersity of Mexico UNAM rMexico City General Hospital, Mexico City, Mexico
c
Department of ReproductiÕe Biology, UAM-Iztapalapa, Mexico City, Mexico
d
School of Chemistry, UNAM, Mexico City, Mexico
Received 25 July 2001; accepted 31 July 2001
Abstract
Ž.
Levonorgestrel 13b-ethyl-17a-ethynyl-17b-hydroxy-4-gonen-3-one , a potent contraceptive progestin stimulates growth and prolifera-
tion of cultured breast cancer cells through a receptor-mediated mechanism, even though levonorgestrel does not bind to the oestrogen
Ž.
receptor ER . To assess whether the oestrogen-like effects induced by this synthetic progestin are exerted via its metabolic conversion
products, we studied the binding affinity of three A-ring levonorgestrel derivatives to the ER and their capability to transactivate an
oestrogen-dependent yeast system co-transfected with the human ER gene and oestrogen responsive elements fused to a b-galactosidase
reporter vector. The results demonstrated that the 3b,5a reduced levonorgestrel derivative and to a lesser extent its 3a isomer interact
Ž.
with the oestrogen receptor, with a significantly lower relative binding affinity 2.4% and 0.4%, respectively than that of oestradiol
Ž.
100% , while levonorgestrel does not. Both levonorgestrel metabolites were able to activate, in a dose-dependent manner, the
b-galactosidase reporter gene in the yeast expression system, an effect that was precluded by a steroidal antioestrogen. The oestrogenic
Ž.
potency of levonorgestrel metabolites was significantly lower 750-fold than that of oestradiol. Furthermore, high doses of 3b,5a
Ž.
levonorgestrel 2.5 mgrdayr6 days induced an increase of oestrogen-dependent progestin receptor in the anterior pituitary of castrated
rats. The overall data offer a plausible explanation for the weak oestrogenic effects induced by high, non-pharmacological doses of
levonorgestrel. q 2001 Published by Elsevier Science B.V.
Keywords: Contraceptive, progestin; Levonorgestrel; Levonorgestrel metabolites; Oestrogen receptor a
1. Introduction
Ž
Levonorgestrel 13b-ethyl-17a-ethynyl-17b-hydroxy-
.
4-gonen-3-one is a potent, totally synthetic 19-nor pro-
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gestin Smith et al., 1963 used either alone or combined
with ethynyl oestradiol in a number of contraceptive for-
Ž
mulations, including pills Ball et al., 1991; Rebar and
.Ž
Zeserson, 1991 , injectables Crabbe et al., 1983; Garza-
´
.Ž
Flores et al., 1991 , medicated intrauterine devices World
Health Organization. Task Force on the Safety and Effi-
cacy of Fertility Regulating Methods, 1990; Sivin and
.Ž.
Stern, 1994 , subdermal implants Cravioto et al., 1997 ,
)
Corresponding author. Department of Reproductive Biology, Na-
tional Institute of Medical Sciences and Nutrition S. Zubiran, Vasco de
´
Quiroga 15, Mexico City, D.F., C.P. 14000, Mexico. Tel.: q52-5573-
1160; fax: q52-5655-9859.
Ž.
E-mail address: anaelenalemus@aol.com A.E. Lemus .
Ž
vaginal rings Johannisson et al., 1991; White et al., 1991;
.
Thau and Jackanicz, 1994 and more recently emergency
Ž
contraceptive pills World Health Organization. Task Force
on Post-Ovulatory Methods of Fertility Regulation, 1998;
.
Piaggio et al., 1999 .
Levonorgestrel induces hormone agonistic effects other
than that of its progestational activity. Indeed, lev-
onorgestrel specifically binds with high affinity to the
Ž.
mineralocorticoid Rebar and Zeserson, 1991; Kuhl, 1996
Ž
and androgen receptors Phillips et al., 1990; Lemus et al.,
.
1992; Cabeza et al., 1995 and exerts the corresponding
effects with a relative high potency; however, the oestro-
genic actions of levonorgestrel still remain controversial.
Levonorgestrel, at high concentrations, induces cell growth
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and proliferation in breast adenocarcinoma cells MCF-7
Ž
Van der Burg, 1991; Van der Burg et al., 1992; Catherino
.
et al., 1993; Schoonen et al., 1995a and breast ductal
Ž.Ž .
carcinoma cells T47D Schoonen et al., 1995b , an effect
0014-2999r01r$ - see front matter q2001 Published by Elsevier Science B.V.
Ž.
PII: S0014-2999 01 01263-8