**3.3 Antioxidants**

*Antioxidants*

to steal an electron from another molecule.

cGMP-dependent functions [23].

and clarify free radicals.

−

Second, it can be formed from singlet oxygen (<sup>1</sup>

−

**3.2 Human body defense mechanisms**

−

) O2 + e<sup>−</sup>➔ O2

2O2 −

−

**Reactive oxygen species (ROS)**

2nd O2

Superoxide radical (O2

Hydroxyl radical (⋅OH)

1st

*Reactive oxygen species.*

Superoxide radical (O2

be formed from O2

such as lipids, proteins, and DNA for releasing the energy causes damage. So, free radicals are the products of normal cellular metabolism. In order to reach stability, an electron has to be stolen. The attacked molecule engages itself in a chain reaction

In aerobic organisms, oxygen free radicals launch autocatalytic reactions that finally damage the living cell. The unsaturated carbon-carbon double bonds in the exposed end groups are particularly sensitive to free radicals forming a covalent single bond at a carbon atom to form a free radical at the opposite carbon atom [22]. Free radicals interact with molecular cross-linking for increased structural organization by reducing the transport of oxygen. ROS can be produced from endogenous or exogenous sources. Endogenous ROS is produced in different cellular organs where oxygen consumption is high such as mitochondria, peroxisomes, and endoplasmic reticulum. Most of the intracellular ROS are derived from mitochondria. The amount of free radicals is determined by many factors. In periods of irregular hypoxia in mitochondrial energy synthesis, excess electron production can develop free radicals that can damage lipids, proteins, and greatly increase molecular size in increasing vicious cycles to further reduce oxygen availability for mitochondria during energy synthesis. Another major type of free radical in a living cell is reactive nitrogen species (RNS). Nitric oxide (NO) radical is formed by the enzyme nitric oxide synthase and involves in smooth muscle relaxation and various other

Free radicals are prominent in many pathological conditions such as cancer, diabetes, cardiovascular diseases, neurodegenerative diseases, cataracts, asthma, rheumatoid arthritis, inflammation, burns, intestinal tract diseases, progerias, and ischemic and postischemic pathologies. In particular, ROS is substantial for the pathogenesis of atherosclerosis. Low density lipoprotein (LDL) accumulates within plaques and contributes to the inflammatory state when ROS concentration is high and ROS oxidizes neighbor LDLs [24]. Also, it is believed that aging is a process mediated by free radicals [25]. At the present time, each chemical step has been investigated meticulously in order to prevent cell damage

Different reactive oxygen species are formed in biological tissue (**Table 2**).

molecule. Hydroxyl radical (⋅OH) can be formed in two different ways. First, it can

radicals may also be formed by polymorphonuclear leukocytes in ischemic tissue.

Although accumulation of this substances are harmful to cell viability, it is important to know that human body is equipped with a defense system consisting of several antioxidative enzymes, to fight with these ROS. Superoxide dismutase

−

+ H2O2 ➔ OH<sup>−</sup> + ⋅OH + <sup>1</sup>

) can be formed by adding an extra electron to the oxygen

and H2O2 with a reaction catalyzed by a metal such as iron (Fe).

+ 2H ➔ O2 + H2O2/Fe2+ + H2O2 ➔ Fe3+ + OH<sup>−</sup> + ⋅OH

O2

O2) reaction. Moreover, oxygen free

**390**

**Table 2.**

Antioxidants are molecules against free radicals and are capable of securing or deactivating free radicals before damaging the cells. There are many antioxidant systems that work synergistically with each other to protect the body's organs and organ systems against free radical damage. There are highly complex enzymatic and non-enzymatic antioxidants: the enzymes such as SOD, glutathione peroxidase, and catalase, as well as non-enzymatic compounds such as α-tocopherol (vitamin E), β-carotene, ascorbic acid (vitamin C), and glutathione. Referred enzymes aim free radicals to delocalize their proteins into side chains and peptide bonds. Also, antioxidants may be endogenous or exogenous, such as part of a diet or dietary supplement. As we know aging is related to free radicals, nutrients rich with antioxidants contend with aging. Under oxidative stress, endogenous antioxidants may not be sufficient and dietary antioxidants may be required to maintain optimal cellular functions. According to literature, exogenous antioxidants comprise the secondary defense system against oxygen free radicals. Moreover, it is believed that ischemia-reperfusion is associated with generation of excess amounts of reactive oxygen species, the removal of which is beyond the capacity of the existing antioxidant defense system [19]. So, contribution of secondary defense system is crucial for the injury associated with ischemia-reperfusion.

Some dietary compounds that do not neutralize free radicals but increase endogenous activity can also be classified as antioxidants. An antioxidant should eliminate free radicals and be absorbed easily, and chelate redox metals at physiologically


#### **Table 3.**

*Antioxidative enzymes and catalyzed reactions in human body.*

relevant levels. Redox-active metals are involved in the generation of free radicals by binding strongly. It should also work in both aqueous and membrane domains and affects gene expression in a positive way.

It is a fact that all of the reactive oxygen species are formed in human body constantly but destroyed by these endogenous antioxidative mechanisms with the help of these enzymes. Endogenous antioxidants are products of the human metabolism. Except the ones that we mentioned before, human body have numerous different antioxidants. Alpha-lipoic acid (ALA), coenzyme Q, and melatonin are some of them. Alpha-lipoic acid is a disulfide derivative of octanoic acid and cysteine and a type of thiol antioxidant. ALA has significant functions such as scavenging free radicals, metal ion chelation, and antioxidant recycling. Coenzyme Q is the only lipid soluble endogenous antioxidant. It transfers electrons from complexes I and II to complex III within the mitochondria. Melatonin is produced in the pineal gland that is an indoleamine neurohormone. It has many physiopathological functions. One major function of melatonin is about oxygen metabolism to scavenge free radicals.

#### *3.3.1 Redox homeostasis*

ROS production and antioxidant capacity are in balance during the stable state of a cell and it is called "redox homeostasis" [27]. This stable state has to be reestablished in temporary derangement (**Figure 2**). When ROS concentration is detected to be high, gene expression is engaged for antioxidant activity. Signal cascades increase the amount of intracellular glutathione and other potent ROS scavengers. Thus, redox homeostasis is sustained. Another regulatory mechanism is feedback inhibition. Production of NO inactivates NO-producing enzyme, NOS. There are many physiological redox-responsive signaling pathways regulated by NO or ROS. The concentration level is modified by the balance between antioxidants and free radicals. If free radical production becomes uncontrolled, aging and diseases occur eventually.

Some major exogenous antioxidants are vitamin C, vitamin E, carotenoids, and polyphenols. Diet is the main source for exogenous antioxidants, especially fruits, vegetables, and grains [28]. Endogenous and exogenous antioxidants act in coordination in order to reach homeostasis. Vitamin C (ascorbic acid) involves in the reaction where intracellular glutathione levels raise thus protects protein thiol group against oxidation. Also, it works in cooperation with vitamin E and the carotenoids. α-Tocopherol is the most active form of vitamin E and is a membranebound antioxidant. The main function of it is to protect cell membrane against lipid peroxidation. Carotenoids are pigments known as the protector of plants against photooxidative processes. They contain conjugated double bonds, and in the human organism, their antioxidant activity arises due to scavenging singlet molecular oxygen and peroxyl radicals. There are many studies exhibiting that carotenoids protect the skin against photooxidative damage. Polyphenols are found in blueberry, and they facilitate increased neuronal signal transduction [29].

As previously described, the formation of high amount of ROS is the primary supplement of ischemia-reperfusion injury. Antioxidants can neutralize the effect or prevent the mechanism to develop. Considerable clinical and experimental data support the role of oxidative stress in I/R injury and emphasize the importance of antioxidant defense mechanisms in tissue protection [30]. In previous studies, it is shown that concentration of some antioxidants such as glutathione and uric acid decrease in response to ROS burst during skin flap ischemia-reperfusion [31]. So, supplementation of the antioxidants at I/R injury may help to neutralize the oxidative stress and reinforce tissue tolerance to reactive oxygen species [32].

**393**

*The Effect of Antioxidants on Ischemia-Reperfusion Injury in Flap Surgery*

**4. Main antioxidants and effects on flap surgery**

cial effects were shown on liver I/R injury [36].

ascorbic acid helps to decrease I/R injury [39, 40].

tive results for end-organ protection.

**5.1 Ascorbic acid (vitamin C)**

**5. α-Tocopherol**

**Figure 2.** *Redox homeostasis.*

tive stress [33].

Most of the antioxidants have been proved to be beneficial versus I/R injury, with the exception of only few [19]. There are several important antioxidants that

α-Tocopherol is the most popular one among the antioxidants; so, numerous studies were written about the positive effects of α-tocopherol in I/R injury. It can be found on foods, and also used in cosmetic and pharmaceutical industries. It is the bioavailable component of vitamin E, and appropriate consumption is considered to help to diminish risk of many chronic diseases associated to oxida-

It is a lipid soluble antioxidant and stabilizer of membranes, has been found to decrease myocardial I/R injury and reverse contractile dysfunction by inhibition on cellular Ca2+ accumulation and reduce lactate dehydrogenase (LDH) release [34, 35]. Hydrophilic analog of α-tocopherol called Trolox has been studied before, and benefi-

According to Franch et al. [37], the α-tocopherol was compared with control group on rat hepatic I/R injury model. The SOD after I/R period catalases after reperfusion period, and glutathione peroxidase in all periods showed lower activities than those of control group. Erkut et al. [38] came across similar results on their study too. In rabbit skeletal muscle I/R injury model, they found out superoxide dismutase, catalase, and glutathione peroxidase levels that show the cellular injury

Vitamin C, one of the most popular vitamins we have heard in everyday life, has powerful antioxidant effects too. Because of the potential benefits, people pay attention to consume certain amount of fruits and vegetables these days. Ascorbic acid can protect the endothelium from direct injury by oxidants (such as H2O2) and prevent microvascular dysfunction. Moreover, it is proven that administration of

Because of its beneficial effects, ascorbic acid has been used in hepatic, cerebral, and renal I/R injury models in the literature [41–43] before and demonstrated posi-

were lower in α-tocopherol group compared with control group.

are investigated in I/R injury in previous studies as mentioned below.

*DOI: http://dx.doi.org/10.5772/intechopen.85500*

*The Effect of Antioxidants on Ischemia-Reperfusion Injury in Flap Surgery DOI: http://dx.doi.org/10.5772/intechopen.85500*

**Figure 2.** *Redox homeostasis.*

*Antioxidants*

*3.3.1 Redox homeostasis*

occur eventually.

affects gene expression in a positive way.

relevant levels. Redox-active metals are involved in the generation of free radicals by binding strongly. It should also work in both aqueous and membrane domains and

It is a fact that all of the reactive oxygen species are formed in human body constantly but destroyed by these endogenous antioxidative mechanisms with the help of these enzymes. Endogenous antioxidants are products of the human metabolism. Except the ones that we mentioned before, human body have numerous different antioxidants. Alpha-lipoic acid (ALA), coenzyme Q, and melatonin are some of them. Alpha-lipoic acid is a disulfide derivative of octanoic acid and cysteine and a type of thiol antioxidant. ALA has significant functions such as scavenging free radicals, metal ion chelation, and antioxidant recycling. Coenzyme Q is the only lipid soluble endogenous antioxidant. It transfers electrons from complexes I and II to complex III within the mitochondria. Melatonin is produced in the pineal gland that is an indoleamine neurohormone. It has many physiopathological functions. One major function of melatonin is about oxygen metabolism to scavenge free radicals.

ROS production and antioxidant capacity are in balance during the stable state of a cell and it is called "redox homeostasis" [27]. This stable state has to be reestablished in temporary derangement (**Figure 2**). When ROS concentration is detected to be high, gene expression is engaged for antioxidant activity. Signal cascades increase the amount of intracellular glutathione and other potent ROS scavengers. Thus, redox homeostasis is sustained. Another regulatory mechanism is feedback inhibition. Production of NO inactivates NO-producing enzyme, NOS. There are many physiological redox-responsive signaling pathways regulated by NO or ROS. The concentration level is modified by the balance between antioxidants and free radicals. If free radical production becomes uncontrolled, aging and diseases

Some major exogenous antioxidants are vitamin C, vitamin E, carotenoids, and polyphenols. Diet is the main source for exogenous antioxidants, especially fruits, vegetables, and grains [28]. Endogenous and exogenous antioxidants act in coordination in order to reach homeostasis. Vitamin C (ascorbic acid) involves in the reaction where intracellular glutathione levels raise thus protects protein thiol group against oxidation. Also, it works in cooperation with vitamin E and the carotenoids. α-Tocopherol is the most active form of vitamin E and is a membranebound antioxidant. The main function of it is to protect cell membrane against lipid peroxidation. Carotenoids are pigments known as the protector of plants against photooxidative processes. They contain conjugated double bonds, and in the human organism, their antioxidant activity arises due to scavenging singlet molecular oxygen and peroxyl radicals. There are many studies exhibiting that carotenoids protect the skin against photooxidative damage. Polyphenols are found in blueberry, and

As previously described, the formation of high amount of ROS is the primary supplement of ischemia-reperfusion injury. Antioxidants can neutralize the effect or prevent the mechanism to develop. Considerable clinical and experimental data support the role of oxidative stress in I/R injury and emphasize the importance of antioxidant defense mechanisms in tissue protection [30]. In previous studies, it is shown that concentration of some antioxidants such as glutathione and uric acid decrease in response to ROS burst during skin flap ischemia-reperfusion [31]. So, supplementation of the antioxidants at I/R injury may help to neutralize the oxida-

tive stress and reinforce tissue tolerance to reactive oxygen species [32].

they facilitate increased neuronal signal transduction [29].

**392**
