Redox regulation by carotenoids: Evidence and conflicts for their application in cancer

Carotenoids have been constantly investigated since the early fifty for their chemical, biochemical and biological properties being presence in foods. Among the more than 1100 carotenoids synthesized by plants and microorganisms, approximately 50 are present in the human diet, and about 20 can be detected in human blood and tissues. Review articles that discuss the anticancer and cancer preventing activity of phytochemicals have often in common the difficulty to find a coherency between the results deriving from experimental studies and the controversial or weak clinical indications arising from epidemiological and interventional studies. In this scenario, the class of carotenoids does not represent an exception. In fact, according with World Cancer Research Fund, strong evidence exists that high-dose supplementation of β-carotene increases the risk of lung cancer, while for other types of cancer, the protective or harmful effects of food-containing carotenoids or carotenoid supplements have been considered limited, suggestive or unlikely. The analysis of the mechanistic evidence is complicated by the double nature of carotenoids being molecules acting either as antioxidant or pro-oxidant compounds. The present review analyzes the ambiguity and the unexpected results deriving from the epidemiological and interventional studies and discusses how the effects of carotenoids on cancer risk can be explained by understanding their capacity to modulate the cellular antioxidant response, depending on the concentration applied and the cellular metabolism. In the final part, a new global approach is proposed to study the contribution of carotenoids, but also of other phytochemicals, to disease prevention, including cancer.

Effects of carvacrol on human fibroblast (WS-1) and gastric adenocarcinoma (AGS) cells in vitro and on Wistar rats in vivo

Carvacrol is a natural phenolic compound found in essential oils of Lamiaceae species. In the present study, an attempt has been made to elucidate the mechanism behind the anti-cancer potential of carvacrol on human gastric adenocarcinomas (AGS) by comparing its effects on cancer cells AGS to those on normal human fibroblast (WS-1) cells, in vitro. Cytotoxicity, reactive oxygen species (ROS) generation, glutathione (GSH) levels, genotoxicity, and apoptotic effects of carvacrol (0-600 µM) were studied in both cell lines. Additionally, the effect of high dose carvacrol (100 mg/kg BW) on the oxidative status was investigated in vivo. For this purpose, carvacrol was administered orally to male Wistar rats over a period of 60 days. Rats were weighed regularly. At the end of the experiment, rats were euthanized. Blood and stomach tissues were collected for biochemical and pathological examinations. The in vitro results showed significant differences in cell viability of AGS compared to WS-1 cells exposed to carvacrol. Also the extent of ROS generation, GSH reduction and DNA damage differed significantly between the cell lines studied (P ≤ 0.001). The differences observed were statistically significant at all concentrations applied (P ≤ 0.001). The results found in AGS cells were mirrored in the pathohistological findings obtained from animals of the in vivo experimental group. Changes in body weight, and oxidative stress index for plasma and stomach tissues of animals in this group were found to differ statistically significant from those found in the control group of Wistar rats (P ≤ 0.001). The data obtained from our present study uncovered that carvacrol has the potential to cause toxic effects in both, AGS and WS-1 cells but more effectively in cancer cells than in normal cells. The carvacrol-mediated responses observed in the in vitro and in vivo experiments presented suggest a double-edged pro-oxidative effect. Via this mechanism carvacrol induced cytotoxicity, apoptosis, and DNA damage in a dose-dependent manner in both cancer and normal cells and these activities were higher in cancer cells than those of normal cells.