Regulation Of Cellular Redox System By Natural Small Molecules

Reactive oxygen species (ROS) act as important messengers in controlling cellular redox homeostasis. However, excessive accumulation of ROS leads to oxidative stress, which can cause oxidative damage to cells. This oxidative damage has been implicated in a number of diseases. Thus, supplement of exogenous or upregulation of cellular endogenous antioxidant molecules is promising in treatment of such diseases. In contrast, cancer cells, due to their unrestrained growth, sustain a much higher level of ROS production compared to normal cells. Under this circumstance, induction of ROS is preferred to selectively kill cancer cells. In this thesis, we focused on the interaction of several natural compounds with the cellular redox system, including the following studies:1) Neuroprotection of 6-dehydrogingerdione (6-DG), xanthohumol (Xn) and chbrogenic acid (CA) via activation of Nrf2 in PC12 cells; 2) Anticancer activity of costunolide (Cos) and sanguinarine (San) via target of cellular thioredoxin reductase (TrxR) in HeLa cells; and 3) Synergistic effects of auranofin and rhein to induce HeLa cell apoptosis via inhibition of both ghitathione system and thioredoxin system. The main contents and results are summarized as follows:1. A brief review of the structure and function of Nrf2 and TrxR was presented in Chapter 1. The recently reported Nrf2 activators were also summarized.2.6-DG, Xn and CA has the protective effect in preventing oxidative stress-induced neuronal cell damage. This neuroprotection may involve its capacity in directly neutralizing free radicals and indirectly activating cellular endogenous antioxidant defense. The phenoxyl group is critical for the direct antioxidant activity, whereas the α, β-unsaturated ketone structure is indispensable for activation of the Keapl-Nrf2-ARE pathway in PC12 cells. Our discovery will provide deep insights in understanding the effects of 6-DG, Xn and CA in vivo, and this protective mechanism could lead to the development of novel small molecules as potential neuroprotective agents.3. Cos and San is the main active ingredients in Saussurea Lappa and Sanguinaria canadensis, respectively. Pharmacological studies have demonstrated potent anticancer activity of both molecules in numerous types of human cancer cells, but the mechanism is vague. We found that Cos and San may interact with TrxR to elicit oxidative stress, and eventually induce apoptosis in HeLa cells. Importantly, overexpression of functional TrxR1 attenuates the cytotoxicity of Cos and San, while knockdown of TrxR1 sensitizes cells to Cos and San treatment. Targeting TrxR1 by Cos and San thus discloses a previously unrecognized mechanism underlying the biological activity of Cos and San, and provides an in-depth insight in understanding the action of Cos and San in treatment of cancer.4. Thioredoxin and glutathione systems are two major thiol-dependent antioxidant systems in mammalian cells. Both systems participate in the defense against oxidative stress via the efficient removal of various ROS. In most cases, they were believed to function in parallel with few crosstalks. Considering the important function of the thioredoxin and the glutathione systems, we reported the combination of the inhibition of the two systems as an effective anticancer strategy. Treatment of HeLa cells with auranofin or rhein alone has the weak anticancer effects. However, combination of auranofin with rhein has the synergistic effect in inducing HeLa cells apoptosis, indicating that the simultaneous modulation of both systems is a promising anticancer strategy.