Clomiphene Citrate and Oocyte Quality

Ovary is a dynamic organ and generates excess amount of reactive oxygen species (ROS) during follicular growth, development, maturation and ovulation [1]. The increased level of ROS is scavenged by antioxidant systems [2]. A moderate increase of ROS could be beneficial for oocyte meiotic maturation and reproductive outcome [3-5]. Overproduction of ROS or depletion of enzymatic antioxidant systems causes oxidative stress [2].


Introduction
Ovary is a dynamic organ and generates excess amount of reactive oxygen species (ROS) during follicular growth, development, maturation and ovulation [1]. The increased level of ROS is scavenged by antioxidant systems [2]. A moderate increase of ROS could be beneficial for oocyte meiotic maturation and reproductive outcome [3][4][5]. Overproduction of ROS or depletion of enzymatic antioxidant systems causes oxidative stress [2].
Anovulation is one of the major causes of reproductive failure in sub-fertile and infertile women [6,7]. In the absence of other reproductive problems, successful ovulation induction and good quality oocyte often restores normal fertility in human [8]. In a common clinical practice, gonadotropins are used to stimulate ovary in infertile or subfertile women [9,10]. However, antiestrogens are widely used to induce ovulation in these patients. Clomiphene citrate (CC) is a non-steroidal ovulation-inducing drug that has been used in humans for more than 40 years [11,12]. Ovarian stimulation by gonadotropins is an expensive treatment. CC is an inexpensive, safe and effective alternative to gonadotropins [11].

Global Journal of Reproductive Medicine
releasing hormone (GnRH) secretion that stimulates release of pituitary gonadotropins [14]. Pituitary gonadotropins surge trigger growth and development of ovarian follicles [13,15]. CC treatment generates dominant follicle and results in the ovulation of metaphase-II (M-II) arrested oocytes required for successful fertilization in various assisted reproductive technology (ART) programs ( Figure 1). Although CC has been used for ovulation induction widely, the possible mechanism of its action at the level of ovary still remains ill understood.
In spite of having good ovulation induction ability of CC (60% -85%), the pregnancy rate is much lower (10% -20%) [10,16]. The higher incidence of miscarriage has been reported in the conception cycle after CC treatment [17]. Such a discrepancy could be due to anti-estrogenic effect of CC, particularly at the level of ovary, cervical mucus and endometrium [17,18]. The anti-estrogenic effects of CC may result apoptosis in granulosa cells and oocyte in ovary [6]. Studies suggest that CC induces apoptosis in human granulosa cells cultured in vitro [19]. CC induces granulosa cell apoptosis that reduces estradiol 17β level in the ovary of rat [20, 21] as well as in monkey [22].
The CC induced hypoestrogenic conditions may induce generation of ROS [6]. Animal studies suggest that CC treatment increases hydrogen peroxide (H 2 O 2 ) level and reduces catalase activity in rat The anti-estrogenic condition due to CC treatment is one of the major side effects that affects the development and maturation of oocytes in the ovary and reduces oocyte quality after ovulation. To overcome the anti-estrogenic effect of CC, supplementation of exogenous estradiol 17β has been recommended [20,23, 33]. This is further supported by the observations that the exogenous estradiol 17β prevents apoptosis and thereby deterioration of oocyte quality [20,23].
The antiestrogenic effect of CC can also be prevented by the supplementation of a naturally occurring antioxidant such as melatonin [

Conclusion
Based on existing clinical as well as animal studies, we conclude that use of either estradiol 17β or melatonin along with CC would be beneficial to overcome the anti-estrogenic effects of CC at the level of ovary during infertility management in human.