β-Carotene: a cancer chemopreventive agent or a co-carcinogen?

Serum Lycopene, Other Carotenoids, and Prostate Cancer Risk: a Nested Case-Control Study in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial

“…For men in the Physicians' Health Study with low baseline serum hcarotene concentrations (lowest quartile), h-carotene supplementation (50 mg every other day for an average of 12 years) reduced prostate cancer risk (48), whereas in the Beta-Carotene and Retinol Efficacy Trial, daily supplementation with 30 mg of h-carotene and 25,000 IU vitamin A for up to 5 years was not related to risk (49), and supplementation in the AlphaTocopherol Beta-Carotene trial (20 mg h-carotene/d for 5-8 years) resulted in nonsignificant increases in prostate cancer incidence and mortality (50). Because the AlphaTocopherol Beta-Carotene trial was conducted in smokers, and animal studies showed that the combined exposure to tobacco smoke and high-dose h-carotene raises oxidative metabolites, induces P450 enzymes, diminishes retinol signaling, and enhances cell proliferation (51,52), we explored h-carotene and smoking as codeterminants of prostate cancer, but found no evidence for such an interaction.…”

“…These inconsistent findings are unlikely explained by the different blood concentrations between studies as most observational studies (25,26,28,29,32), including ours, had similar h-carotene concentrations, which were 8-to 20-fold lower (66) than observed after h-carotene supplementation in the three clinical trials, which also provided mixed results. Animal and in vitro studies further add to the complexity of h-carotene's effect on cancer: whereas antioxidative properties of h-carotene potentially reduce cancer risk, h-carotene also induces phase I carcinogen-activating enzymes associated with the generation of oxidative stress (52,67). The inconsistent results for h-carotene in prostate cancer prevention and the potentially harmful effects of high-dose supplementation on lung cancer, heart disease, and death from all causes in smokers (68-71) should lead to caution in using h-carotene supplementation, at least at high doses.…”

β-Carotene Inhibits Tumor-Specific Angiogenesis by Altering the Cytokine Profile and Inhibits the Nuclear Translocation of Transcription Factors in B16F-10 Melanoma Cells

“…Epidemiologic studies, clinical intervention trials, and laboratory experiments have suggested the protective effect of carotenoids in the incidence of various cancers, [20][21][22] but contradictory results have also been published. 23 The roles of β-carotene in the pathogenesis of cancer have been contradictory and certainly intriguing.…”

“…5 Among them, β-carotene is particularly attractive as it is known to exhibit various beneficial properties. Epidemiological studies have shown an inverse relationship between the intake of fruits and vegetables and the risk of several types of cancer 6 , and such effects of fruits and vegetables have been attributed to β-carotene. Most notably, β-carotene is shown to be an effective antioxidant by scavenging certain reactive oxygen species, especially peroxyl radical and singlet oxygen, and this antioxidant activity appears to be greatest at low oxygen tension.…”

Avaliação de mutagenicidade e antimutagenicidade de diferentes frações de Pterogyne nitens (Leguminosae), utilizando ensaio de micronúcleo em Tradescantia pallida

“…Compostos que apresentam tanto características mutagênicas como antimutagênicas são conhecidos como compostos de Janus (Zeiger, 2003). Prévios estudos descrevem compostos com a mesma característica, como é o caso dos β-carotenos e ácido ascórbico (Kaya et al, 2002;Paolini et al, 2003). Ainda na Figura 2 é possível observar a atividade antimutagênica da AcOEt somente nas maiores concentrações.…”