Oxidative stress induced by reactive oxygen species (ROS) is believed to be a primary factor in various diseases as well as in the normal process of aging. The elimination or inactivation of reactive oxygen species, or the prevention of their cellular formation by antioxidants and free radical scavengers, is considered to be a practical approach in mitigating these conditions. The importance of antioxidants in human health has become increasingly clear due to spectacular advances in understanding the mechanisms of their reaction with oxidants. Traditional medicine has been a fertile source of novel lead molecules for modern drug discovery. In our laboratory, we focused for the last decade on the isolation, purification and identification of several natural antioxidants from traditional medicinal plants, mainly from spinach, Inula viscosa, wild watermelon (Citrullus colocynthis), and the fruit of figs. The isolated compounds are composed mainly of polyphenol and flavonoid derivatives, antocyanins, sesquiterpene lactones, and cucurbitacin (highly oxygenated tetracyclic triterpenes) derivatives. In addition to their capacity for scavenging free radicals, we demonstrated that the various natural compounds isolated exhibit anti-inflammatory and anti-cancer activities in both in vitro and in vivo models. Moreover, we have shown the involvement of these natural antioxidants in cell signaling pathways, affecting key biochemical pathways, including those leading to apoptosis or affecting the morphological structure of the cells. The effect of these antioxidants was studied in prostate cancer, breast cancer, malignant melanoma, and in in vivo inflammatory processes, especially in the eyes of rats and mice. In this review, we will present both published and unpublished data obtained using these unique natural compounds isolated and characterized in our laboratory. The results will be discussed in the context of other data presented in the literature. The main goal of this review is to focus on the involvement of these compounds in cell signaling, and deciphering their mechanism of action beyond their function as free radical scavengers.
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