The effects of combined antioxidant (β‐carotene, α‐tocopherol and ascorbic acid) supplementation on antioxidant capacity, DNA single‐strand breaks and levels of insulin‐like growth factor‐1/IGF‐binding protein 3 in the ferret model of lung cancer

Insulin-like growth factor 1 (IGF-1) and its major binding protein, IGF binding protein 3 (IGFBP-3) are implicated in lung cancer and other malignancies. We have previously shown that the combination of three major antioxidants beta-carotene (BC), alpha-tocopherol (AT) and ascorbic acid (AA) can prevent lung carcinogenesis in a 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-treated and smoke-exposed (SM) ferret model, which is highly analogous to humans. The present study is aimed at determining the effect of the combination of BC, AT and AA on antioxidant capacity, lymphocyte DNA damage, plasma IGF-1 and IGFBP-3 concentrations, as well as on IGF-1/IGFBP-3 mRNA expression in the tissues (lung and liver) of the ferrets. Ferrets were treated with or without combined antioxidant (BC, AT and AA) supplementation (AOX) for 6 months in the following 4 groups: (i) control; (ii) SM+NNK; (iii) AOX; and (iv) SM+NNK+AOX. Combined AOX supplementation significantly attenuated SM+NNK induced lymphocyte DNA damage in the ferret, while increasing resistance to oxidative damage when challenged with H(2)O(2) in vitro. Ferrets treated with SM+NNK had significantly lower IGFBP-3 mRNA expression in lungs, whereas there was significantly higher IGFBP-3 mRNA expression in the liver, as well as higher circulating IGFBP-3 concentrations. Combined AOX supplementation did not affect the plasma or tissue (lung and liver) ratio of IGF-1/IGFBP-3. Combined antioxidant supplementation provides protection against smoke-induced oxidative DNA damage, but does not affect the IGF-1/IGFBP-3 system. Differential expression of IGFBP-3 in different tissues indicates that caution should be taken when using plasma IGFBP-3 as a biomarker of tissue status.