*3.1. Antioxidants*

Reactive oxygen species (ROS), such as singlet oxygen (O2), hydrogen peroxide (H2O2), the superoxide anion (O2•−), and the hydroxyl radical (•OH), are often generated as byproducts of cellular metabolic reactions and exogenous induction. These ROS create homeostatic imbalances, which lead to the generation of oxidative stress, which in turn, induces cell death and tissue injury [60]. ROS in elevated levels can damage biomolecules such as nucleic acids, proteins, and lipids [61]. Even though the antioxidant defense systems like enzymatic antioxidants and non-enzymatic antioxidants are functioning, uncontrolled ROS accumulation during the life cycle promotes the development of age-dependent diseases, like cancer, atherosclerosis, arthritis etc. [62]. Natural antioxidants from plant sources have been considered a promising therapy for the prevention and treatment of these diseases, especially neurodegenerative disorders, cardiovascular diseases, cancer, and other conditions. Various natural bioactive compounds, such as mahanine, mahanimbine, isolongifolene, koenimbine, girinimbine, isomahanine, koenoline, and O-methylmurrayamine, are present in *M. koenigii* and exhibit remarkable antioxidant properties [63,64].

The leaf extracts of *M. koenigii* have high antioxidant activities [65]. Rao et al. evaluated the antioxidant activities of water and an ethanol extract of *M. koenigii* assessed by the, α-diphenyl-βpicrylhydrazyl (DPPH) free radical scavenging assay, with quercetin as a positive control. The ethanolic extract of *M. koenigii* showed an 80% scavenging activity, which was similar to the activities exhibited by the control antioxidant compound quercetin [66]. Gupta et al. evaluated the antioxidant activities of acetone, alcohol, and aqueous extracts of *M. koenigii* by the DPPH free radical scavenging assay, with ascorbic acid as a positive control. The extracts of *M. koenigii* exhibited activities with an half-maximum effective concentration (EC50) value of acetone of 81.81 ± 19.92 at 4.7 μg/mL, alcohol of 79.80 ± 18.68 at 4.1 μg/mL, and aqueous extract of 62.82 ± 13.62 at 4.4 μg/mL, which was comparable to the EC50 value exhibited by ascorbic acid (the positive control), which was 97.13 ± 12.64 at 2.69 μg/mL [67]. Zahin et al. also evaluated the antioxidant activities of both ethyl acetate and petroleum ether fractions of *M. koenigii* through DPPH radical scavenging assay, cupric reducing antioxidant capacity (CUPRAC), and ferric reducing antioxidant power (FRAP) assays, with ascorbic acid as a positive control. The benzene fraction of *M. koenigii* was found to be the most active free radical scavenger, exhibiting an 88.3% decrease at a concentration of 100 μg/mL, followed by ethyl acetate at 79.5% and petroleum ether at 78.7%, while positive controls of ascorbic acid and butylated hydroxytoluene (BHT) at a concentration of 100 μg/mL inhibited 93.1% and 86.5% DPPH absorption, respectively. Similarly, the antioxidant activity created by reducing activity and CUPRAC assays indicated the highest reducing potential in the benzene fraction, followed by petroleum ether and ethyl acetate. The activity was greater than that of ascorbic acid and on par with that of BHT [68].

Yogesh et al. evaluated the antioxidant activity of berry extracts of *M. koenigii* by DPPH free radical scavenging activity and reducing power assays. The results indicated that an *M. koenigii* berry extract is a powerful free radical scavenger compared to known antioxidants, such as butylated hydroxytoluene, ascorbic acid, and tannic acid [69]. Tomar et al. evaluated the total antioxidant activity of acetone and petroleum ether extracts of younger and older *M. koenigii* leaves by estimating the H2O2 scavenging activity. The acetone extract of old leaves was found to have a maximum activity at 151.58%, and for young leaves in petroleum ether, the value was 72.23% [70]. Waghmare et al. evaluated the antioxidant property of fruit extracts of *M. koenigii* with DPPH free radical scavenging activity, inhibition of nitric oxide radical (NO) and thiobarbituric acid reactive substances (TBARS) activity, and reducing power assays, and •OH was also estimated, with vitamin C as a positive control. The fruit extract of *M. koenigii* exhibited antioxidant activities, and the EC50 value of the extracts for the DPPH assay was 2.6 mg/mL; for the NO radical, was 2.9 mg/mL; for TBARS, was 3.1 mg/mL; for the reducing power assay, was 2.7 mg/mL; and for H2O2, was 3.3 mg/mL, which were comparable to the EC50 value of 5 mg/mL exhibited by the vitamin C positive control [71]. The antioxidant activities exhibited by the crude extracts of *M. koenigii* were probably due to the presence of flavonoids and phenolic derivatives. The above studies revealed that various extracts of *M. koenigii* display high antioxidant activity. The studies also indicated the potential for this plant to be a natural source of strong antioxidant substances that can be used in therapy for human diseases induced by ROS.
