The prevalence of infertility has exhibited an upward trajectory in the current era, with approximately 15% of couples experiencing infertility. The prevalence of male factors contributing to infertility is estimated to be between 40% and 50%. On a global scale, there is a consistent downward trend observed in the sperm count and semen quality of males. The etiology of approximately 50% of male infertility is currently unknown, indicating the complex nature of the underlying causes. While genetic factors can account for a portion of male infertility, it is worth considering that the ongoing rise in male infertility rates may also be influenced by the escalating levels of environmental pollution. Throughout their life cycle, males are subject to exposure to environmental pollutants, including during the embryonic period [1-4]. 

Skakkebaek et al. [2] have observed that environmental pollutants have a direct impact on the testes of adult mammals, leading to the inhibition of spermatogenesis [2]. However, it is important to note that male infertility can also arise from prenatal intake of toxic substances. The fetal interaction with environmental compounds has been found to result in the development of reproductive tract anomalies, including testicular cancer and male infertility. Environmental pollutants encompass a group of heavy metals. Cadmium ion (Cd2+) is classified as one of the heavy metals. A substantial body of research conducted on animal models, primarily rodents, as well as new data from people epidemiological investigations, consistently indicate the detrimental impact of Cadmium (Cd) on male reproductive health [5-8].

Cd is a prevalent environmental contaminant found in various industrial operations as well as tobacco smoke. Cd is a secondary product derived from the manufacturing processes of various metals, including zinc, lead, and copper. It finds predominant utilization in diverse industries such as battery production, pigment manufacturing, coating applications, electroplating processes, plastic stabilization, and other related fields. According to Chirinos-Peinado and Castro-Bedrinana [9], the presence of Cd in the food supply network occurs after contamination. Cd exposure occurs in humans and animals through the presence of pollutants in the air, consumed water, and food sources. According to Siu et al. smoking is an additional contributor to the presence of Cd. According to Takiguchi and Yoshihara [10], individuals who smoke exhibit a Cd content that is 4-5 times greater than that of individuals who do not smoke [9-17].

Milk thistle, a plant belonging to the Asteraceae family and Carduoideae subfamily, is a well-established botanical remedy with numerous medicinal uses. In terms of its location, this species is indigenous to Europe, Asia, Africa, and Russia. It has also been established to other regions such as North America and China. The primary bioactive polyphenolic constituents encompass flavonolignans, specifically silychristin, silydianin, silybin, and isosilybin, collectively referred to as silymarin (SMN). SMN has been extensively utilized in a diverse range of medical conditions including Alzheimer's disease, sepsis, cholestasis, various cancers, heart disease, and liver disease. This broad application is attributed to its favorable pharmacokinetics characteristics, safety, and preventative properties. To date, the clinical evidence has demonstrated the hepatoprotective efficacy of SMN [18-24].

The presented study, herein, was developed to identify critical prophylactic effects of SE against the NCd-induced intoxication of the reproductive system in male rats, manifested by sex hormonal and antioxidant features.

Experimental design

The presented study, herein, was developed to identify critical prophylactic effects of silymarin extract (SE) against the NCd-induced intoxication of the reproductive system in male rats, manifested by sex hormonal and antioxidant features. The experiment was conducted by using 60 male rats (190 ±10gm and 90 days of age). These rats were separated into six groups (10 rats/group). These groups were a control (CL) group that received distilled water only, a group that received 10mg/kg NCd (10NCd group), a group that received 200mg/kg SE (200SE group) for 28days. In addition, a group that received 10mg/kg NCd for 14 days then 200mg/kg SE for 14 days (NCdSE group). Moreover, a group that received 200mg/kg SE for 14 days then 10mg/kg NCd for 14 days (SENCd group). The last group received both substances in a combination (CBT group) for 28 days. All groups received the treatment compounds using oral gavage. After the end of the experiment, blood samples were collected from all groups to measure hormonal changes (FSH, LH, and testosterone) and antioxidant enzymes and oxidative stress marker, which included SOD, GSH, and MDA.

Extraction of Milk thistle

The extraction of milk thistle seeds (MTSs) was done using seeds purchased from Natures manufacturers (USA). The seeds were ground into a powder using a coffee mill. In order to prepare the suspension for the administration of a dose of 200 mg per kilogram of body weight, the subsequent procedures have been undertaken: A total of 40gm of seeds were immersed in one liter of water, resulting in a concentration of 20mg per 0.5ml. It is recommended to administer a dosage of 0.5ml of SE per 100gm of body weight. The NCd was ordered from Nanoshel nanotechnology (USA).

The results demonstrated that the groups exposed to NCd revealed significant (p<0.05) decreases in the levels of the hormones. However, these levels were significantly (p<0.05) repaired when SE was used, especially in the SENCd group, in which SE was used first for 14 days (Figure 1).

Figure 1: Effects of Silymarin on Nanocadmium-Induced Sex Hormonal Toxicity Of

The findings recorded that the groups exposed to NCd revealed significant (p<0.05) decreases in the levels of the SOD and GSH and increases in the levels of MDA. However, these levels were significantly (p<0.05) corrected when SE was used, especially in the SENCd group, in which SE was used first for 14 days (Figure 2). 

Figure 2: Effects of Silymarin on Nanocadmium-Induced Oxidative Stress of Male Rats

Cd, being classified as a highly toxic heavy metal, lacks any identified advantageous biological role, and presents a notable risk to the health of people, particularly in terms of reproductive toxicity. Cd exhibits a relatively slow rate of excretion, with a biological half-life ranging from 20 to 40 years. It primarily accumulates in the liver, kidney, and testes [25-28].

The reproductive system has become a subject of significant concern in recent years due to the widespread presence of Cd pollution and its detrimental impacts. An epidemiological investigation conducted by researchers observed a significant negative correlation between the concentration of Cd in seminal fluid and various sperm parameters, including sperm quantity, sperm motility, and the percentage of abnormal spermatozoa. The ingestion of substantial amounts of Cd over a brief period resulted in severe damage to the testes of rodents, including necrosis, exhaustion of germ cells, destruction to interstitial tissue, and impairment of the blood-testis barrier. Previous studies have provided evidence that the administration of a low dose of Cd (50 μg/day), which is significantly lower than short-term doses by a factor of approximately 30 to 60, has a negative impact on the reproductive processes of mammals [29-31]. 

These effects encompass the disturbance of the histology of the testis and epididymis, impairment of spermatogenesis, reduction in sperm motility, alteration in sperm morphology, and reduction in the extent of the acrosome reaction in rodents. The epididymis and vas deferens are crucial accessory organs that serve essential functions in the processes of sperm maturation and preservation. Previous studies have provided evidence indicating that rats exposed to cadmium at a dosage of 2 mg Cd/kg body mass per day experienced alkalization of the lumen fluid in the epididymis and vas deferens. This alkalization was attributed to the direct inhibition of H-ATPase function. In addition, the modified microenvironment had a detrimental impact on the functionality of sperm, specifically affecting their motility and capacitation [32-40].

Numerous studies have indicated that the utilization of antioxidants may enhance the quality of oocytes and sperm, leading to an increased likelihood of achieving successful pregnancy. A specific quantity of reactive oxygen species (ROS) is necessary for the normal functioning of cells. However, an imbalance between the generation of ROS and the presence of antioxidants can result in disturbances in the cell cycle and the progression of apoptosis. The production of ROS is influenced by both endogenous variables, such as the mitochondrial respiratory chain, and exogenous elements such as proximity to environmental contaminants. ROS, including oxygen ions, free radicals, and peroxides, are produced as a result of oxidative stress within the male reproductive systems [41-42]. These ROS have the potential to harm cells and contribute to the development of infertility. Most research investigations have primarily focused on males, with a particular emphasis on elucidating the mechanisms underlying the detrimental impacts of oxidative stress, which are more readily discernible in sperm compared to oocytes. This study has identified two main mechanisms that contribute to male infertility caused by oxidative stress. The initial pathway involves degradation of the sperm membrane, a decrease in sperm motility, and subsequent disruption in the fusion process with the oocyte. The second procedure involves DNA damage and the development of embryo defects [43].

Research has demonstrated the presence of various beneficial characteristics in SMN, including antioxidant, detoxifying, and regenerative effects. In addition to its antioxidant properties, the immunomodulatory benefits of SMN have been examined in various studies, with consideration given to the dosage and duration of treatment. The anti-inflammatory impacts of the substance are elicited through the inhibition of nuclear factor kappa B (NF-κB) and the activation of tumor necrosis factor α (TNF-α). While low doses of SMN have been found to exhibit immunomodulatory activity through the inhibition of T lymphocytes, higher doses have been shown to have stimulatory impact on inflammatory reactions. Moreover, SMN exhibits dual effects on cellular growth and apoptosis, affecting cells with varying characteristics [44-47].

In a comparable investigation involving rats with varicocele-induced oxidative stress, the application of SMN resulted in an essential improvement in the development and sustainability of spermatozoa nuclei, as opposed to the control group. In addition, the administration of SMN resulted in an elevation of the serum antioxidant ability and overall thiol molecules in rats with induced varicocele. Consequently, an increase in sperm motility and a decrease in DNA destruction were noticed. The study conducted by Mazhari et al. aimed to assess the impact of SMN and celecoxib on rats with varicocele. The findings of this study indicate that the two agents, which operate through distinct processes, have a significant impact on reducing injuries caused by varicocele [42-48].

The present study results provide important prophylactic features of silymarin extract against the nanocadmium-induced intoxication of the reproductive system in male rats.

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