• **Superoxide dismutase (SOD):**

400 Endometriosis - Basic Concepts and Current Research Trends

oxygen (O2) as substrate, generate large amounts of ROS. As the mithocondrial respiratory chain is the major O2 cell intake system, the majority of ROS are produced by this system

when electrons leak from the electron transport chain (O2 + e- **→** O2-) (Agarwal et al., 2005). The dismutation of superoxide results in the formation of **hydrogen peroxide (H2O2)** (2 O2

+ 2 H+ **→**H2O2 + O2) (Agarwal et al., 2005). The same can also be generated by reduction of

acquisition of 1 electron by **H2O2** (H2O2 + e- + H+ **→**OH + H2O) (Babior, 1997). The hydroxyl ion is highly reactive and can modify purines and pyrimidines and cause strand breaks

Under normal conditions, all organisms have enzymatic and non-enzymatic mechanisms capable of neutralizing pro-oxidants species and/or repair damages caused by reactive species, converting them to H2O, to prevent overproduction. Many antioxidants of low molecular weight such as vitamins and polyphenols are usually found in nutrients, although enzymatic neutralization of reactive species is the most effective mechanism

Also known as synthetic antioxidants or dietary supplements, this group influences in an exogenous way the antioxidant defense system of the organism. The most common are: vitamins C and E, selenium, zinc, taurine, hypotaurine, glutathione, β-carotene, and

Vitamin E may block the initiation of lipid peroxidation as well as its propagation phase

Glutathione is the major non-protein sulfhydryl component of mammalian cells and has an important role in cellular protection from oxidative stress (Meister, 1983). Glutathione synthesis increases throughout oocyte development and maturation until the periovulatory follicle stage (Perreault et al., 1988). After fertilization, glutathione participates in the sperm decondensation process, while the oocyte activation process occurs, and the sperm head turns into the male pronucleus (Calvin et al., 1986; Perreault et al., 1984, 1988; Yoshida, 1992, 1993). A study performed with bovine oocytes has shown the important role of COCs during the in vitro maturation process. Through gap junctions, cumulus oophorus cells (COCs) might mediate glutathione synthesis by the oocytes, a crucial enzyme for the cytoplasmic and nuclear maturation process. This intimate relation between COCs and oocytes apparently occurs due to the presence of gap

The enzymatic defenses responsible for ROS neutralization are mainly represented by superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), depending or not on

**-)** is formed

**) ion** is formed by the


under physiological conditions (Fujii et al., 2005). The **superoxide radical (O2**

+ 2 H+ **→**H2O2) (Babior, 1997). The **hidroxyl (OH-**

O2- (O2-

+ e-

**3. Antioxidants** 

carotene.

(Bornoden, 1994).

resulting in DNA damage (Agarwal et al., 2005).

(Agarwal et al., 2005; Fujii et al., 2005).

**4. Non-enzymatic antioxidants** 

junctions (De Matos et al., 1997).

**5. Enzymatic antioxidants** 

selenium and glutathione reductase (GR) (Fujii et al., 2005):

The superoxide anion is produced by a one-electron reduction of an oxygen molecule and initiates a radical chain reaction. It is believed that SOD, which dismutates the superoxide anion to hydrogen peroxide (2 O2 - + 2 H+ **→** H2O2 + O2), plays a central role in antioxidant reactions. Three isozymes are produced by mammals (Fujii et al., 2005):


One of the striking phenotypes of SOD1-deficient mice is female infertility, suggesting a potential role of this enzyme in female fertility. SOD2 is inducible under various oxidative stress and inflammatory conditions. EC-SOD is present at high levels in the epididymis, seminiferous tubules of the testis, as well as the lungs (Fujii et al., 2005).

The presence of SOD was evidenced in human follicular fluid (FF) and the identification of high concentrations of SOD in FF was associated with oocytes that were not fertilized (Sabatini et al., 1999). Data of a recently published study showed that SOD activity decreased with age in women, but increased in women with endometriosis and ovulatory dysfunction (Matos et al., 2009). When the cause of infertility was male factor, the success of ART was associated with increased SOD activity. Variations in SOD activity emphasize the importance of oxidative stress in the oocyte maturation process, and are suggested to be a potential biomarker of ART success (Matos et al., 2009).

A recent study has established a threshold level in FF which ROS may be considered toxic for viable embryo formation and pregnancy outcome. ROS, lipid peroxidation and total antioxidant capacity were estimated. The upper cut-off ROS level beyond which viable embryo formation is not favorable was found to be approximately 107 cps/400 microl FF. This level, determined in women with tubal factor infertility, was further validated in women with endometriosis and PCOS and correlated with fertilization and pregnancy rate and embryo quality (Jana et al., 2010).

• **Peroxidases:** 

**Catalase** exclusively detoxifies hydrogen peroxide and has no requirement for an electron donor **(2 H2O2 → 2 H2O + O2)**. It plays a role in organs such as the liver, but its specific function in the genital tract is largely unknown (Fujii et al., 2005).

Glutathione is a tripeptidyl molecule and is present in either the reduced (GSH) or the oxidized state (GSSG). It plays pleiotropic roles, which include the maintenance of cells in a reduced state and the formation of conjugates with some harmful endogenous and xenobiotic compounds. In addition, GSH serves as an electron donor for GPx that reduces peroxide **(2GSH + H2O2 → GSSG + 2 H2O)**. At least four selenium-containing GPx isozymes are produced in mammals (Fujii et al., 2005):

The cytosolic form, GPX1, is widely distributed in tissues and has been the most extensively investigated form. However, GPX1-knockout mice show no abnormality in phenotype including reproductive capability (Ho et al., 1997);

Endometriosis and Infertility: The Role of Oxidative Stress 403

occurrence of systemic oxidative stress in women with infertility associated with

The activation of polymorphonuclear leucocytes and macrophages observed in endometriosis patients might be induced by several factors, including damaged red blood cells, apoptotic endometrial cells, cellular debris and some other inflammatory cells. In endometriosis these actions of peritoneal macrophages appear to be stimulated *in vitro* by the immune response or by agents such as α and γ-interferon, increasing inducible nitric oxide synthase (NOS) expression, producing more nitric oxide and nitrite and nitrate compounds (Agarwal et al., 2005). However, we obtained no conclusive data concerning nitric oxide, peroxidized lipids and ROS levels in the peritoneal fluid of patients with and

In women with endometriosis and adenomyosis, we also observe a greater expression of Mn-SOD and CuZn-SOD in the endometrium throughout the menstrual cycle, as well as aberrant expression of GPx and xanthine peroxidase (XO), in topic and ectopic endometrium. SOD activity seems to be significantly higher in the ectopic endometrium of endometriomas than in the topic endometrium (Alpay et al., 2006). However, this increase in the expression of antioxidant enzymes in the topic and ectopic endometrium of endometriosis patients could be a primary event or secondary to an increase of ROS, which needs to be evaluated. If, on the one hand, we have no conclusive data concerning the pattern of expression of the most important oxidant and antioxidant enzymes in topic and ectopic endometrium, on the other hand, we have not found, so far, any studies that have evaluated the expression of these enzymes in granulosa cells of patients with endometriosis, whose anomalies could contribute to the impairment of folliculogenesis and of the acquisition of oocyte competence to permit fertilization and support embryo

The above data suggest a trend to a greater production of free radicals in endometriosis patients associated with a potential alteration of antioxidant capacity. This may contribute to oxidative stress which could be related to the pathogenesis and progression of

Another very interesting aspect of endometriosis is its enigmatic association with infertility, observed in 25 to 30% of women with this affection. Until now, little is known about the mechanisms involved in the pathogenesis of infertility, especially in minimal and mild

New approaches to the treatment of infertility related to this disorder have included the increasingly more common application of ART. The introduction of *in vitro* fertilization (IVF) for the treatment of infertility secondary to endometriosis has become an important tool for the study of the potential effects of endometriosis on specific stages of the reproductive process, including folliculogenesis, fertilization, embryo development and implantation. Contradictory data have been reported for IVF outcomes in patients with endometriosis (García-Velasco & Arici, 1999; Garrido et al., 2000). This discrepancy seems to be multifactorial since IVF outcomes might be affected by different variables, such as ovulation induction protocol, patient selection criteria, laboratory procedures, and embryo

endometriosis, where there is no significant alteration of pelvic anatomy.

without endometriosis (Agarwal et al., 2003; Amaral et al., 2005).

endometriosis (Andrade et al., 2010).

development.

endometriosis.

transfer technique, among other factors.


In a reaction promoted by peroxidase, GSH is oxidized to GSSG. Regeneration of GSH is, therefore, crucial for the ability of cells to fight exposure to oxidant metabolites. GSH levels are maintained by de novo synthesis that is catalyzed by two enzymes, γ- glutamylcysteine synthetase (γ-GCS) and glutathione synthetase (GS). The reduction of GSSG is catalyzed by **glutathione reductase** (GR) using NADPH as an electron donor **(2 GSSG + NADPH + H+ → 2GSH + NADP+)**. GR is also inhibited by compounds produced in response to nitrosative stress, such as nitrosoglutathione. In the female reproductive system, GSH is assumed to play a role by reducing oxidative stress either by direct interaction with ROS, by the **glutathione redox system**, or by donating an electron to GPx (Fujii et al., 2005).

High levels of SeGPx were found in follicles that held oocytes with the potential to be fertilized and lower levels were related to fertilization failure (Paszkowski et al., 1995).
