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Beta carotene toxic to human cells / may activate immune response independently
Beta carotene and the retinoids are unsaturated molecules, which renders them susceptible to oxidation. I think this is one of the mechanisms by which beta-carotene can be dangerous, regardless of its converting into retinol etc. This is probably why brightly coloured fruits and vegetables contain more anti-oxidants.
- Toxicity of oxidised beta-carotene to cultured human cells - "We found that oxidized beta-carotene is cytotoxic and that mitochondrial function is decreased in both K562 and RPE cells.”
- Beta-carotene breakdown products may impair mitochondrial functions - Self explanatory
In this study, the authors postulated that oxidation of carotenoids may be carried out by oxidants liberated by polymorphonuclear leukocytes (PML). PML are immune cells, so if this is true, beta carotene would be triggering an immune response on its own, without needing to be converted in to vitamin A and RA.
Thanks for pointing this out, I noticed the same various authors have published other papers on the topic as well:
Cytotoxicity of β-carotene cleavage products and its prevention by antioxidants. - 2010 (Free)
Beta-carotene degradation products - formation, toxicity and prevention of toxicity. - 2009
Proteasomal degradation of beta-carotene metabolite--modified proteins. - 2009
alpha-Tocopherol increases caspase-3 up-regulation and apoptosis by beta-carotene cleavage products in human neutrophils. - 2007 (Free)
Cyto- and genotoxic potential of beta-carotene and cleavage products under oxidative stress. - 2005
Effect of carotenoid oxidation products on neutrophil viability and function. - 2005
Cytotoxic and genotoxic effects of beta-carotene breakdown products on primary rat hepatocytes. - 2004
Oxidation of carotenoids by heat and tobacco smoke. - 2004
Carotenoid cleavage products modify respiratory burst and induce apoptosis of human neutrophils. - 2003 (Free)
Carotenoid oxidative degradation products inhibit Na+-K+-ATPase. - 2000
Hi Zach,
Thanks for sharing all that info.
https://www.ncbi.nlm.nih.gov/
Overall, such findings indicate a potential ability of vitamin A and its derivatives to negatively interact with biological membranes, an event that may lead to organelle stress, as, for instance, mitochondrial dysfunction, and to cell apoptosis or necrosis.
It seems like those who have a gene for reduced beta-carotene to Vitamin A might be even worse off, as the beta carotene sits in the body longer before it is processed.
It seems like the natural content of antioxidants in fruit and veg at least seems to be protective against the oxidation part. Theoretically, since they come in that package naturally (although carotenes still being problematic).
But beta carotene on its own, based on some of the studies above, whether synthetic or natural derrivate, is not protected from oxidation by added antioxidants such as ascorbic acid.
Well, hello there multivitamins, where most (if not all?) do contain beta carotene (and/or retinol). Indeed poisoning for profit right there! (Everybody who has ever taken supplements containing BC raise one hand!) Why else is BC still in supplements when one could just eat a carrot (please dont do that though! Carrots fxxed me up quite badly)