Enhancement by b-carotene and suppression by flavonoids on DNA damage induced by UVA or NNK

• Main Author: 王維譽
• Other Authors: 胡淼琳
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/45128343938540584303

碩士 === 國立中興大學 === 食品科學系 === 92 === Abstract Inconsistent results have been reported regarding the effect of β-carotene on UV-induced skin damage and on the lung cancer incidence in smoker. It has been suggested that the existence of other antioxidants may affect the behavior of β-carotene under various oxidative stress. Flavonoids are another group of natural antioxidants ubiquitously found in fruits and vegetables. However, the interactions between β-carotene and flavonoids are unclear. Therefore, this thesis work was divided in to two parts. Using cell culture model, one was to investigate the individual and combined effects of β-carotene and flavonoids, naringin, quercetin and rutin, on DNA damage induced by UVA exposure; the other was to investigate the effects of these compounds on DNA damage induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone) NNK, a smoke-related carcinogen. Effects of b-carotene and flavonoids on UVA induced DNA damage The C3H 10T1/2 cells, a cell line of mouse embryo fibroblasts, were first incubated with b-carotene and/or flavonoids for 1 hr followed by irradiation with UVA (3.8 and 7.6 KJ/m2). The aims of this part were to investigate the individual and combined effects of β-carotene and flavonoids on DNA damage induced by UVA exposure and to investigate the possible mechanisms. The results showed that b-carotene significantly enhanced the DNA damage after irradiation with UVA by about 35%. The flavonoids employed in this study significantly decreased the raise of DNA damage induced by UVA combined with or without b-carotene. The effects of these flavonoids are in an order naringin, quercetin and rutin. In contrary, the absorption of UVA (320-380 nm) was in an order quercetin, rutin and naringin. However, the activity of scavenging singlet oxygen and the prevention of loss of b-carotene induced by UVA were in the same order, i.e., naringin, rutin and quercetin. These results suggest that flavonoids may through scavenge singlet oxygen or other reactive oxygen species to inhibit DNA damage and to inhibit the prooxidation of β-carotene induced by UVA irradiation. Effects of b-carotene and flavonoids on NNK induced DNA damage The aim of this part was to investigate the individual and combined effects of b-carotene and certain common flavonoids, naringin, quercetin and rutin, on DNA damage in A549 cells induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a potent tobacco-related carcinogen in humans. In addition, we investigated the possible mechanisms. A549 cells were first pre-incubated with either b-carotene, flavonoid, or both of them for 1h, followed by incubation with NNK for 4 h. The DNA damage was determined by comet assay (single-cell DNA gel electrophoresis). In addition, using some reactive oxygen species (ROS) scavengers, DCFH-DA assay and one cytochrome P450 (CYP) inhibitor, we investigated the role of ROS and CYP in NNK-induced DNA damage. NNK induced DNA damage in A549 cells in a dose dependent manner. b-carotene significantly increased DNA damage induced by NNK up to 1.8-fold. The mechanisms likely included the increase in oxidation of β-carotene and the increased activity of CYP by β-carotene. In contrast, naringin, quercetin, rutin individually enriched in cells significantly inhibited NNK-induced DNA damage. The inhibitive effects of flavonoids were in an order quercetin, naringin and rutin. The flavonoids markedly inhibited the formation of ROS (determined by DCFH assay) induced by NNK in cells in an order as mentioned above. Furthermore, the flavonoids suppressed the enhancing effect of β-carotene on NNK-induced DNA damage. The effects of flavonoids may be attributed to the antioxidant activity and possibly, the suppression of CYP.