**2. What is antioxidant?**

To understand the term antioxidant, we have to tell the story from the beginning. The story begins with oxygen. Oxygen is the main source of the life, but in the body oxygen sometimes acts like a foe. Oxygen has two unpaired electrons, which spin in the same direction [9]. For this reason, oxygen is a biradical, so it is a free radical. In general, free radicals are highly reactive compounds, which are called as "reactive oxygen species" (ROS). ROS are intracellular compounds, which consist of oxygen [7, 11]. The most known ROS are listed in **Table 1**.

Oxygen is less dangerous than oxygen-derived free radical species (superoxide, hydroxyl radicals, hydrogen peroxide, etc.), and they react with lipids, proteins, and nucleic acids [12, 13]. Besides ROS, nitrogen-derived molecules are present in human body. These are known as


**Table 1.** Reactive oxygen species (ROS).


**Table 2.** Endogenous and exogenous sources of ROS.

and anaplastic astrocytoma, anaplastic oligodendroglioma, anaplastic oligoastrocytoma, anaplastic ependymoma, and glioblastoma (high-grade gliomas) [1–4]. The histological type of

Antioxidants are present in plant-based foods, for instance, some types of vegetables and fruits: wine, blueberry, different types of tea, grape, and so on [5, 6]. The main role of antioxidants is prevention of oxidants' harmful effects to human body. Principle regarding oxidant-antioxidant is related to a balance [7]. This balance's side determines the human body reaction. In case of elevated oxidant levels in organism body homeostasis is lost and oxidative stress occurs. Loss of this balance and oxidative stress lead some pathological situations: cancer, neurodegenerative diseases, cardiovascular diseases, immunological diseases, and so on [8–10]. In terms of these diseases with the antioxidant supplementation, cell damage can

In this chapter, two different stories will be told and these stories will be turned one story. We will discuss some of the basic concepts of antioxidants, antioxidant systems and antioxidants supplementation and explain how antioxidant supplementation can help with the cancer therapy, especially glioma therapy. Experimental studies are summarized and present evidences are collected under three headings: in vitro studies, animal studies, and clinical trials.

To understand the term antioxidant, we have to tell the story from the beginning. The story begins with oxygen. Oxygen is the main source of the life, but in the body oxygen sometimes acts like a foe. Oxygen has two unpaired electrons, which spin in the same direction [9]. For this reason, oxygen is a biradical, so it is a free radical. In general, free radicals are highly reactive compounds, which are called as "reactive oxygen species" (ROS). ROS are intracellular compounds, which consist of oxygen [7, 11]. The most known ROS are listed in **Table 1**.

Oxygen is less dangerous than oxygen-derived free radical species (superoxide, hydroxyl radicals, hydrogen peroxide, etc.), and they react with lipids, proteins, and nucleic acids [12, 13]. Besides ROS, nitrogen-derived molecules are present in human body. These are known as

−

•

O2

**Name Molecule formula**

Superoxide O2

Hydroxyl OH• Peroxyl ROO• Alcoxyl RO• Hydroperoxyl HO2

Lipid peroxyl LOO• Hydrogen peroxide H2

**Table 1.** Reactive oxygen species (ROS).

the tumor is the most significant thing to determine the treatment option [2].

232 Glioma - Contemporary Diagnostic and Therapeutic Approaches

be fixed.

**2. What is antioxidant?**

reactive-nitrogen species [6, 14]. These molecules can get involved with oxidant molecules, but all oxidants are not free radicals. They produce endogenously or with some exogenous sources' effects [9, 10]. Some endogenous and exogenous sources are shown in **Table 2**.

In human body, antioxidant systems are present to avoid cell damage due to free radicals. These antioxidant systems include a few enzymes for this reason they are called enzymatic antioxidants [9–11, 14]. The definition of antioxidant that it is a molecule reacts with free radicals and neutralizes them [6]. Except enzymatic antioxidants, generally, they occur naturally in foods, especially plant-based foods [15]. For instance, resveratrol is a very popular antioxidant in recent years, and it is found in grape, raspberry, blueberry, wine, and so on [16]. The most known non-enzymatic antioxidants are low-molecular-weight compounds such as vitamin C, vitamin E, beta-carotene, catechins, lycopene, glutathione, and coenzyme Q [5, 12, 17].

In summary, the story starts with oxygen and develops free radicals and stable molecules (DNA, protein, lipids, carbohydrates, etc.). Antioxidants are the good cops and they get involved the free radicals. In normal conditions, this is acceptable as happy ending. In terms of biological perspective, in course of normal metabolism energy production starts with consumption of oxygen and food nutrients. Oxygen and food enter the cell and mitochondria start to produce adenosine triphosphate (ATP). Free radicals form during cell's energy production. These free radicals are neutralized by antioxidant enzyme systems (superoxide dismutase, catalase, glutathione peroxidase, etc.) and non-enzymatic antioxidants [6]. In the presence of any pathological conditions, ROS are highly produced and although antioxidant enzyme systems and antioxidants try to eliminate them to protect the cell, they remain incapable. Redox balance breaks down, oxidative stress increases, and antioxidant levels decrease [14]. In terms of cancer, ROS imbalance is one of the hallmarks of cancer [18].
