*4.3. 8-Nitroguanine (8-NO2-Gua)*

In addition to producing 8-OHdG, guanine nitration also makes 8-NO2-Gua. These DNA metabolites are used to measure OS to DNA. In fact, in inflamed epithelial cells, 8-NO2-Gua levels increase. The amino acid polypeptides are separated by the reaction of amino acid side groups with ROS, and proteins are oxidized. With the oxidation of proteins, reactive carbonyl groups (aldehydes and ketones) are formed, and their tracing is known as an indicator of oxidative damage in protein molecules. It should also be noted that carbonyl groups are formed due to ROS reactions with proteins, carbohydrates, and lipids [43].

#### *4.4. Oxidative Products of Sugars*

Among the products produced by the oxidation of carbohydrates are advanced glycation end products (AGEs), which are formed due to non-enzymatic glycosylation of proteins. The highest presence of AGEs is in plasma and tissues, leading to diabetes, kidney failure, and aging [44].
