| Reactive oxidative species (ROS) are products of the normal metabolic activities of aerobic living organism. Oxidative stress is a kind of unbalance state between oxidation and antioxidation. ROS are harmful to cells when oxidative metabolism products increase or the antioxidative defenses lack in the organism. Lots of researches show that ROS are related to some physiologic and pathological processes and play an important role in many diseases. ROS-related diseases include reperfusion injury, inflammatory process, age-related diseases, neuronal apoptosis, cancer, cataract and so on.There are two kinds of the scavengers for free radicals in the organism, namely enzymes (Antioxidative enzymes) and non-enzyme compounds. The enzyme scavengers mainly include SOD, CAT and GPX, and they form the defense system in the organism against free radicals. In addition, many small molecular compounds also have strong antioxidative ability. These compounds are vitamin C, vitamin E,α-tocopherol, reduced glutathione,β-carotene, metal chelate complex, calcium ion antagonists, flavonoid, polyphenol compouns and antioxidant peptides and so on. The enzyme scavengers have a great value in pharmaceutical application. GPX are the well-known antioxidant selenoenzymes in organisms which destroy several harmful hydroperoxides and then maintain the metabolic balance of ROS in vivo, thus protecting the biomembranes and other cellular components from oxidative damage. It's very crucial for us to mimic GPX for the reason that the codon of the catalytic site is UGA which cannot be expressesd using the traditional genetic engineering.Cyclodextrins are non-reducing cyclic glucose oligosaccharides resulting from the cyclomaltodextrin glucanotransferase catalyzed degradation of starch. There are three common cyclodextrins with 6, 7 or 8 D-glucopyranonsyl residues (α-,β-, andγ-cyclodextrin respectively) linked byα-1, 4 glycosidic bonds. They present a bottomless bowl-shaped (truncated cone) molecule stiffened by hydrogen bonding between the 3-OH and 2-OH groups around the outer rim. Cyclodextrin rings are amphipathic with the wider rim displaying the 2- and 3-OH groups and the narrower rim displaying 6-OH group on its flexible arm. These hydrophilic groups are on the outside of the molecular cavity whereas the inner surface is hydrophobic lined with the ether-like anomeric oxygen atoms and the C3-H and C5-H hydrogen atoms. CD is a good model to mimic enzyme because of the hydrophobic cavity which is suitable to recognize the substrate. To obtain higher activity, we choose -Te-Te- to mimic catalytic site instead of–Se-Se- because selenium and tellurium are in the same family, and tellurium has a more active redox properties. Also we introduced imidazole group to scavenge·OH that is the most harmful ROS.In order to overcome the shortcomings of the previous GPX mimics which were lack of substrate binding sites, we prepared 6A, 6A'-imidazole-6B, 6B'-tellurium bridgedβ-cyclodextrin(6-ImTeCD) using the cavity of CD as substrate binding site and ditellurium bond as catalytic group. The GPX activity of 6-ImTeCD with H2O2 was determined to be 6.8 U/μmol, which was higher than that of Ebselen and 6-TeCD. And the GPX activities of 6-ImTeCD catalyzed reduction of CuOOH and t-BuOOH were found to be 9.7 and 15.2 U/μmol, respectively. Detailed kinetic study of 6-ImTeCD was undertaken. Saturation kinetics was observed for both H2O2 and GSH. Double reciprocal plots of the initial velocity versus the concentration of substrates were a family of parallel lines, consistent with a Ping-Pong mechanism. The optimal pH and temperature for 6-ImTeCD is 8.95 and 45℃.We also studied the scavenging·OH by 6-ImTeCD using Rhodamine B, which showed a color change when it interacted with·OH. The results showed that the mimic can scavenge·OH effectively and protect the living cells. We constructed the H2O2-induced culture hepatocyte cells damage model system and demonstrated the hepatocyte cells had great changes in the damage system. We investigated the protective effects of culture hepatocyte cells by 6-ImTeCD using the damage system. The results showed that it could inhibit the levels of lipid peroxidation, counteract the cell death, and also could prevent the leakage of LDH to sustain the integrity of cell membrane. We found that 6-ImTeCD can penetrate cells, indicating that 6-ImTeCD has great potential value in pharmaceutical application.6-ImTeCD as well as the others derived from cyclodextrin had the advantage of low molecular weight, good solubility and stability. It also had great antioxidant activity to scavenge hydroperoxides and hydroxyl radical. So it should be a promising prodrug.
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