# Research Progress of Polysaccharide-Gold Nanocomplexes in Drug Delivery
## 2 Biological Activity of Polysaccharides
Non-sugar modifications such as phosphorylation and sulfation also have different degrees of influence on the activity of polysaccharides. Phosphorylation of polysaccharides is a standard method to reduce natural polysaccharides' high viscosity and increase their water solubility and bioactivity. The negatively charged phosphate groups of phosphorylated polysaccharides can bind with receptors on the surface of immune cells and activate the immune response, resulting in antitumor activity. At the same time, phosphorylated polysaccharides have a higher scavenging capacity for DPPH and superoxide anion [53]. The electrostatic repulsion and spatial resistance of polysaccharides modified by sulfate changed dramatically, which increased the flexibility of polysaccharide chains and improved water solubility, and the sulfated modified yarn polysaccharide (S-CYP) could activate macrophages through  
Figure 2: Constitutive relationship of polysaccharides. The image was prepared by Figdraw 2.0.  
the MAPK signaling pathway, which showed better immunomodulatory effects than CYP [54]. Meanwhile, polysaccharides that are directly extracted or subjected to sulfation modification have the potential to exhibit improved antiviral activity [55]. Sulfated xymann, xylan, pectin, fucoidan, dexosan, glucoarabinoglycan, and arabin glycan are polysaccharides that have been shown to possess antiviral and immunomodulatory activities [56]. Polysaccharides play a crucial antiviral role through various mechanisms, such as binding to the virus' surface via charge interaction. This binding effectively blocks virus transmission. Additionally, polysaccharides exert their antiviral effect by directly inhibiting viral transcription and replication in host cells. [PERSON] et al. demonstrated that carrageenan islandated from the Japanese sea red alga Tichocarpus crimitus has a complex structure containing polysaccharides that can inhibit virus-infected cells and that a particular enzyme was used to obtain a low molecular derivative of carrageenan, oligosaccharidesider, which could be helpful in the development of new drugs against viral infections. Oligosaccharides, low molecular products of carrageenan, were obtained with the help of a particular enzyme. Carrageenan and its oligosaccharides can significantly inhibit immunodeficiency viruses and retroviruses (10-fold and 7-fold inhibition, respectively), which will be helpful for the development of new drugs against viral infections [57]. However, further ex vivo and in vivo studies are needed to evaluate the results. Furthermore, they indirectly activate innate immunity, further enhancing their antiviral properties. Coriolus versicolor's polysaccharide peptide (PSP) has been shown to have immunomodulatory properties, activating the innate immune response through toll-like receptor 4 (TLR4), confirming the potential use of PSP as an anti-HIV drug, but studies in a larger number of infected subjects are still needed [58]. Polysaccharides are antioxidant in three main ways: first, through the modulation of antioxidant enzyme activities via the Nrf/ARE pathway; second, by removing free radicals; and third, by antagonizing nitric oxide. The expression of CAT, SOD, and GSH-Px, the main antioxidant enzymes in the human body, is regulated by Nrf2. When oxidative stress occurs in the human body, Nrf2 is released from Keap1, enters the nucleus, and interacts with the antioxidant response element (ARE) [59]. Lentinan (LNT) activated the Nrf2 pathway and inhibited hepatocyte oxidative stress [60]. Polysaccharides can induce the expression of antioxidant genes or proteins and improve antioxidant effects through the Nrf2/ARE pathway. When the body's average free radical production and elimination is imbalanced due to various external factors, polysaccharides effectively scavenge free radicals and produce antioxidant effects by regulating and enhancing the activity of oxidative enzymes.