## 3 Results and Discussion
### Effect of Alkaloid Extracts on TDH in PC-12 Cells Induced by OS with H\({}_{2}\)O\({}_{2}\)  
TDH is crucial as it provides insights into the redox balance [72]. Thiols, with their -SH groups, play a critical role as antioxidant buffers. These -SH groups interact with and reduce oxidizing agents, protecting against oxidative stress (OS). This interaction transforms thiols into disulfides, which can revert to thiol groups, ensuring a continuous TDH cycle [73]. However, in neurodegenerative diseases (NDs), the excessive presence of reactive oxygen species (ROS) alters cysteine functions, disrupting TDH [74]. Given this, we evaluated the impact of alkaloid extracts on TDH in PC-12 cells subjected to oxidative stress using H\({}_{2}\)O\({}_{2}\), utilizing commercial test kits. Compared to the control group, the H\({}_{2}\)O\({}_{2}\) group exhibited significantly diminished total thiol, native thiol, and disulfide activities (\(p<0.05\)). In contrast, groups treated with alkaloid extracts displayed a notable increase in these activities when compared to the H\({}_{2}\)O\({}_{2}\) group, with variations depending on the concentration used (\(p<0.05\)). Among the concentrations, 500 \(\mathrm{\SIUnitSymbolMicro g}\)/mL was most effective, followed by 250 \(\mathrm{\SIUnitSymbolMicro g}\)/mL and 100 \(\mathrm{\SIUnitSymbolMicro g}\)/mL. For disulfide activity, methanol extracts were most effective, followed by chloroform and water. However, for total and native thiol activities, chloroform extracts were most effective, trailed by methanol and water (as depicted in Figure 3). Studies by [PERSON] et al. [75] found that individuals with NDs had considerably lower total and native thiol activities compared to healthy subjects. [PERSON] et al. [76] reported that oxidative stress induced by manganese led to a reduction in the total thiol levels in the mouse hippocampus. This decline was reversed to normal levels upon treatment with an aqueous extract of _Melissa officinalis_, which is abundant in isoquinoline alkaloids. Similarly, [PERSON] et al. [77] observed in their study that isoprenaline-induced oxidative damage in Wistar rat brains significantly reduced total thiol activities. This depletion was counteracted by the bark hydroethanonic extract of _Iuglans regia_ L., known for its rich alkaloid content. Our findings align with these studies. We hypothesize that our alkaloid extracts act via multiple mechanisms, such as metal ion chelation and free radical scavenging, acting as substrates in specific redox reactions such as GSH and selectively reducing certain protein disulfide bonds, such as thioredoxin. However, further investigations are needed to substantiate this hypothesis. Figure 3: Levels of total thiol, native thiol, and disulfide (H\({}_{2}\)O\({}_{2}\): Hydrogen peroxide, CAE: Chloroform alkaloid extract, MAE: Methanol alkaloid extract, WAE: Water alkaloid extract). The figures were presented as mean \(\pm\) SD. [PERSON]’s test was used in the case of \(p<0.05\). # Significantly different from the control (n: 3 for each bar). * Significantly different from the H\({}_{2}\)O\({}_{2}\) (n: 3 for each bar). Impact of Alkaloid Extracts on TOS, TAS, and OSI Levels in PC-12 Cells Induced by OS with H\({}_{2}\)O\({}_{2}\)  
Oxidative stress (OS) in neurodegenerative diseases (NDs) primarily arises from the disparity between oxidative mechanisms and antioxidant defenses, leading to fluctuations in total oxidative status (TOS) and total antioxidant status (TAS) levels [78]. TOS, TAS, and the oxidative stress index (OSI) are utilized as indicators of this oxidative equilibrium. Instead of analyzing a multitude of individual oxidant and antioxidant molecules, these metrics offer a comprehensive view of the overall oxidative balance [79]. In this context, we examined the impact of alkaloid extracts on TOS, TAS, and OSI levels in PC-12 cells subjected to OS using H\({}_{2}\)O\({}_{2}\), employing commercial assay kits.