Antioxidant Effects of Peptides
Rumeysa Rabia Kocaturk, Fatmanur Zebra Zelka, Oznur Ozge Ozcan, and Fadime Canbolat
There are thousands of peptides identified and synthesized so far. Peptides have been found to have a large capacity for biological activity and therapeutic potential. Therefore, many studies have been conducted with peptides and their effects are explained more and more day by day. Peptides are used as medicines for chronic diseases in many areas, especially in the pharmaceutical industry (Wetzler and Hamilton 2018). Peptides are structures that are made up of naturally occurring amino acids. Peptides are described in detail in other chapters. Bioactive peptides have different biological functions and these biological functions contribute to human health. Biologically active peptides have many uses in medicine and new ones are added to this situation daily. The therapeutic use of peptides has received great scientific and industrial interest in the past decade. There was also an increase in the use of natural products such as plants in the production of these products, counting industrial proteins, vaccines, antibodies, and different medications in the fight against diseases (Daniell et al. 2009; Marauyama et al. 2014). The therapeutic use of peptides comes with many advantages such as high specificity, high biological activity, low cost, and high membrane penetration ability, but issues such as stability, toxicity, and immu- nogenicity remain the main concerns of those who develop peptides (Baig et al. 2018). Some peptides have been found to have extensive therapeutic effects such as antioxidant, antimicrobial, antihypertensive, anticancer/antiproliferative, anti-inflammatory, and immunomodulatory and antithrombotic effects. Peptides are of great importance in vaccine production and the properties mentioned are promising for effective vaccines. Also, the antioxidant feature of the peptides is interesting. Studies show that antioxidants can assume an essential role in fighting diseases (Carvalho-Queiroz et al. 2015; Baig et al. 2018; Girija 2018; Huang 2018; Ozcan et al. 2020).
Based on this information, we will focus on the antioxidant characteristics of peptides. Topics discussed in this chapter include antioxidants, antioxidant roles, the molecular mechanism of peptides as antioxidants, other effects of peptides and therapeutic use of bioactive peptide properties, and whether bioactive peptides can be used as vaccine agents. In conclusion, we want to emphasize the importance of bioactive peptides, their antioxidant roles, and their potentially successful role in vaccine production.
Definition of Antioxidants
The first definition for antioxidants was made by Halliwell et al. They described the antioxidants as agents that fundamentally delay or hinder the oxidation of the oxidizable substrates (carbohydrates, lipids, proteins, or nucleic acids) and are at a much lower frequency compared to the substrates mentioned (Halliwell, Gutteridge and Cross 1992). In time, Halliwell and Gutteridge (1990) described antioxidants as substances that target a molecule and act by preventing, delaying, or eliminating oxidative damage. Khlebnikov et al. (2017) made another definition of antioxidants as substances that can inhibit the production of reactive oxygen species or dispose of them directly or indirectly and act as a regulator of the antioxidant defense mechanisms (Khlebnikov et al. 2017). As seen, many definitions were made and antioxidants were understood as neutralizing the free radicals and by this action, they have a high capability for protecting cells getting damaged and in the end protect the organs and prevent them from getting damaged (Nasri 2016).
Reactive Oxygen Species and Antioxidants
Under normal physiological conditions, human beings have a balance between the produced reactive oxygen species (ROS) and antioxidants. Cells and tissues in our bodies constantly create free radicals due to metabolism, as well as environmental factors, for example, radiation, pollution, microorganisms, allergens, cigarettes, smoke, and pesticides increase the number of exposed free radicals that the body encounters (Hekimi, Lapointe, and Wen 2011). With increasing ROS types, the body’s balance is disturbed, superoxide radicals begin to accumulate in the cells and an endogenous defense system is inadequate. This accumulation and increase of free radicals, for example superoxide radicals, is defined as oxidative stress and oxidative stress is not beneficial for body composition. It causes many distortions at the molecular level. The increase in ROS is toxic to the cell, damaging the proteins, lipids, and nucleic acids (DNA and RNA) inside the cell, disrupting the intracellular signaling pathways and adversely affecting health (Aslanko9 et al. 2019).