TY - JOUR
T1 - Antioxidant actions of β-carotene in liposomal and microsomal membranes
T2 - Role of carotenoid-membrane incorporation and α-tocopherol
AU - Liebler, Daniel C.
AU - Stratton, Steven P.
AU - Kaysen, Kathryn L.
N1 - Funding Information:
We thank Jeanne Burr for help in preparing ®gures. This work was supported in part by USPHS Grants CA56875 and ES00694.
PY - 1997/2/15
Y1 - 1997/2/15
N2 - β-Carotene and other carotenoids are widely regarded as biological antioxidants. However, recent clinical trials indicate that β-carotene supplements are not effective in disease prevention and raise questions about the biological significance of carotenoid antioxidant actions. To further explore this issue, we have reevaluated the antioxidant actions of β- carotene in liposomal and biological membrane systems. In dilinoleoylphosphatidylcholine liposomes in which 0.35 mol % β-carotene was incorporated into the bilayer during liposome preparation, the carotenoid inhibited lipid peroxidation initiated by 10 mM azobis[amidino-propane HCl] (AAPH). In carotenoid-free liposome suspensions to which the same amount of β-carotene was added, no antioxidant effect was observed. Supplementation of rat liver microsomes with β-carotene in vitro yielded microsomes containing 1.7 nmol β-carotene mg-1 and 0.16 nmol α-tocopherol mg-1 microsomal protein. In β-carotene supplemented microsomes incubated with 10 mM AAPH under an air atmosphere, lipid peroxidation did not occur until α-tocopherol was depleted by approximately 60%. β-Carotene exerted no apparent antioxidant effect and was not significantly depleted in the incubations. Similar results were obtained when the incubation was done at 3.8 torr O2. In liver microsomes from Mongolian gerbils fed β-carotene-supplemented diets, β-carotene levels were 1637% of α-tocopherol levels. The kinetics of AAPH-induced lipid peroxidation were no different in β-carotene- supplemented microsomes than in microsomes from unsupplemented animals, although the kinetics of β-carotene and α-tocopherol depletion were similar. The results indicate that β-carotene is ineffective as an antioxidant when added to preformed lipid bilayer membranes and that α- tocopherol is a much more effective membrane antioxidant than β-carotene, regardless of the method of carotenoid-membrane incorporation. These results support a reevaluation of the proposed antioxidant role for β-carotene in biological membranes.
AB - β-Carotene and other carotenoids are widely regarded as biological antioxidants. However, recent clinical trials indicate that β-carotene supplements are not effective in disease prevention and raise questions about the biological significance of carotenoid antioxidant actions. To further explore this issue, we have reevaluated the antioxidant actions of β- carotene in liposomal and biological membrane systems. In dilinoleoylphosphatidylcholine liposomes in which 0.35 mol % β-carotene was incorporated into the bilayer during liposome preparation, the carotenoid inhibited lipid peroxidation initiated by 10 mM azobis[amidino-propane HCl] (AAPH). In carotenoid-free liposome suspensions to which the same amount of β-carotene was added, no antioxidant effect was observed. Supplementation of rat liver microsomes with β-carotene in vitro yielded microsomes containing 1.7 nmol β-carotene mg-1 and 0.16 nmol α-tocopherol mg-1 microsomal protein. In β-carotene supplemented microsomes incubated with 10 mM AAPH under an air atmosphere, lipid peroxidation did not occur until α-tocopherol was depleted by approximately 60%. β-Carotene exerted no apparent antioxidant effect and was not significantly depleted in the incubations. Similar results were obtained when the incubation was done at 3.8 torr O2. In liver microsomes from Mongolian gerbils fed β-carotene-supplemented diets, β-carotene levels were 1637% of α-tocopherol levels. The kinetics of AAPH-induced lipid peroxidation were no different in β-carotene- supplemented microsomes than in microsomes from unsupplemented animals, although the kinetics of β-carotene and α-tocopherol depletion were similar. The results indicate that β-carotene is ineffective as an antioxidant when added to preformed lipid bilayer membranes and that α- tocopherol is a much more effective membrane antioxidant than β-carotene, regardless of the method of carotenoid-membrane incorporation. These results support a reevaluation of the proposed antioxidant role for β-carotene in biological membranes.
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U2 - 10.1006/abbi.1996.9822
DO - 10.1006/abbi.1996.9822
M3 - Article
C2 - 9028879
AN - SCOPUS:0031568853
SN - 0003-9861
VL - 338
SP - 244
EP - 250
JO - Archives of Biochemistry and Biophysics
JF - Archives of Biochemistry and Biophysics
IS - 2
ER -