**3. ROS Manufacturer Resources**

Multiple factors are responsible for the production of ROS, both endogenous and exogenous. Endogenous sources are: mitochondria, cellular oxidases (xanthine oxidase (XO), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX)), nitric oxide synthase (NOS), myeloperoxidase (MPO), processes related to peroxisomes, cellular respiration, cytochrome P450 oxidases, microsomal cyclooxygenase (COX), and catalyzed metal reactions. ROS is also produced exogenously through sources such as chemical drugs, pollutants, nutrient overdose, mutagens, xenobiotics, and ionizing radiation (Figure 1) [24]. Several studies have shown that ROS-derived mitochondria and NOX are critical sources of ROS production in adipocytes [30].

**Figure 1.** Reactive oxygen species (ROS) resources [24].

#### *3.1. ROS-Derived from Mitochondria*

The main energy production source in the body is the mitochondria, which do this by oxidative phosphorylation. Interestingly, the O2 •− radical is mainly produced by oxidative phosphorylation. O2 •− is made in the mitochondrial ETC complex due to not being metabolized by about 0.15% and 2% of oxygen consumption in complexes I and III. Hence, mitochondria are one of the main sources of ROS and oxidative stress. After producing O2 •− mitochondrial manganese SOD (MnSOD) converts it to H2O2 [16,21]. On the other hand, ROS is mainly produced by the respiratory chain and during the formation of adenosine triphosphate (ATP). O2 is created by activating the oxygen molecule's base state by transferring electrons or energy in the form of a single O2 [11].
