## 4 Discussion  
Hyperglycemia, which occurs during diabetes (both type 1 and type 2) and, to a lesser extent, during insulin resistance, causes oxidative stress [28]. Traditional Chinese medicine is highly favored for its natural, healthy, and environmentally friendly characteristics and has always been an important research object in antioxidant research [29]. The herbal compound, DNJ, is a representative minopyranose produced by the mulberry tree [6; 7; 8]. The content of DNJ from different parts of the mulberry tree varies a lot. [PERSON] et al. reported that DNJ levels of the mulberry tree were 4-268 mg/100 g dried weight for leaves, 27-475 mg/100 g for branches, and 11-27 mg/100 g for its fruit [30]. And for mulberry fruit, the content of DNJ differs. [PERSON] et al. detected DNJ levels in mulberry fruit at different ripening stages, and found that fruit collected at the mid-ripe stage contained the highest level of DNJ, of around 2.91 mg/100 g of fruit weight [31]. Previous reports showed that DNJ also can be synthesized by microorganisms including _Streptomyces_ sp. and _Bacillus_ sp. [PERSON] et al. reported the production of 296.56 mg/L DNJ in _Streptomyces laerudulae_[32]. [PERSON] et al. achieved a 1632.50 mg/L yield of DNJ in _Bacillus amyloliquefaciens_ via modifying its metabolic paths [33]. The \(\alpha\)-glucosidase activity inhibitor property makes DNJ a potential compound for the treatment of diabetes. In addition, previous studies showed that DNJ is effective in anti-inflammatory, anti-obesity, and anti-oxidative applications [2]. The results from [PERSON] et al. showed that DNJ treatment slightly stimulates the viability of HUVEC at concentrations of up to 200 \(\upmu\)mol/L. Our cell viability test showed that in the concentration range from 5 \(\upmu\)mol/L to 200 \(\upmu\)mol/L, DNJ treatment stimulated the viability of HUVEC, consistent with the results of [PERSON] et al. [15]. When the DNJ concentration was increased to 300 \(\upmu\)mol/L, its cell viability stimulation effect was weak compared to that observed at 200 \(\upmu\)mol/L. [PERSON] et al. observed that 50 \(\upmu\)g/L (306 \(\upmu\)mol/L) and 100 \(\upmu\)g/L DNJ treatment slightly decreased the viability of B16F10 cells, and the inhibition of matrix metalloproteinases (MMPs) by using a high concentration of DNJ was one reason [34]. This indicated that DNJ affects different physiological processes, and dose-response studies are essential for the development of DNJ in various applications. It was reported that DNJ reduces high-glucose-induced ROS generation and senescence in HUVEC [15]. Similar results were observed in our study. Treatment using 5 \(\upmu\)mol/L DNJ effectively protected cells from excessive oxidative DNA damage and senescence in HUVEC cultured with high glucose, confirming the anti-oxidant role of DNJ. Previous animal studies indicated that DNJ treatment attenuates cellular oxidative stress by upregulating the expression of detoxification enzymes with the capability to scavene ROS, for example, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) [35]. [PERSON] et al. found that DNJ treatment upregulated the mRNA levels of NRF2 in chicken intestinal epithelial cells [25]. NRF2 is an important regulator of cellular oxidative status. As well as DNJ, various natural products have been found to stimulate the NRF2 antioxidative response, such as chlorogenic acid, geniposidic acid, and glucoraphanin [36; 37; 38], which were thought to be of value to health. HO-1 is a well-known downstream target of NRF2. It catalyzes the degradation of heme into carbon monoxide, ferrous iron, and biliverdin, and is used as an indicator of the stimulation of NRF2 antioxidative signaling [18]. In addition to upregulating detoxification enzymes, NRF2 was found to have other physiological functions. MDM2 is an E3 ubiquitin-protein ligase that mediates the ubiquitination of p53. NRF2 positively regulates the expression of MDM2 and influences checkpoints upon extracellular stress conditions arising [39].