|عنوان فارسی مقاله:||اثرات متفاوت کاروتینوئیدها بر پراکسیداسیون لیپیدها به دلیل بر هم کنش های غشایی: آنالیز پراش X-ray|
|عنوان انگلیسی مقاله:||Differential effects of carotenoids on lipid peroxidation due to membrane interactions: X-ray diffraction analysis|
|رشته های مرتبط:||فیزیک، زیست شناسی، علوم سلولی و مولکولی، علوم گیاهی، فیزیک کاربردی و بیوشیمی|
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|نشریه||الزویر – Elsevier|
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The biological benefits of certain carotenoids may be due to their potent antioxidant properties attributed to specific physico-chemical interactions with membranes. To test this hypothesis, we measured the effects of various carotenoids on rates of lipid peroxidation and correlated these findings with their membrane interactions, as determined by small angle X-ray diffraction approaches. The effects of the homochiral carotenoids (astaxanthin, zeaxanthin, lutein, β-carotene, lycopene) on lipid hydroperoxide (LOOH) generation were evaluated in membranes enriched with polyunsaturated fatty acids. Apolar carotenoids, such as lycopene and β-carotene, disordered the membrane bilayer and showed a potent pro-oxidant effect (>85% increase in LOOH levels) while astaxanthin preserved membrane structure and exhibited significant antioxidant activity (40% decrease in LOOH levels). These findings indicate distinct effects of carotenoids on lipid peroxidation due to membrane structure changes. These contrasting effects of carotenoids on lipid peroxidation may explain differences in their biological activity.
Carotenoids are a large group of naturally-occurring pigments that are found in plants, algae and various microorganisms. To date, over 750 carotenoids have been identified in nature , but only 24 have been detected in human tissues . Carotenoids are thought to have a protective effect against degenerative conditions such as cancer, cardiovascular disease and cataracts [3,4]. The majority of epidemiologic studies on the incidence of various types of cancers and cardiovascular diseases indicate an inverse relationship with dietary carotenoids [5,6] and circulating carotenoid levels . The mechanism(s) by which carotenoids exert their health benefits are not completely understood, but may be due in part to their antioxidant activities [8,9]. Although earlier research on the antioxidant activities of carotenoids was focused primarily on β-carotene, other carotenoids have been shown to have more potent antioxidant effects  which may explain contradictory clinical findings including evidence for increased cardiovascular risk with β-carotene [11–15]. The common chemical feature of carotenoids is the polyene chain, a long conjugated double bond system forming the backbone of the molecule. This chain may be terminated by cyclic end groups that contain oxygen-bearing substitutes (Fig. 1). The electron-rich conjugated system of the polyene is responsible for the antioxidant activities of the carotenoids, both by quenching singlet oxygen [16,17], and scavenging radicals to terminate chain reactions [18–21]. Woodall et al. reported that the antioxidant capacities of various carotenoids in liposomes were very different from those in free solution and proposed that the antioxidant properties of carotenoids were determined by their inherent chemical reactivity as well as how they interact with the membrane bilayer . This view has led to a number of studies designed to better understand the interactions between carotenoids and membranes using various techniques, including nuclear magnetic resonance [23–25], electron paramagnetic resonance (EPR) spin label [26–28], differential scanning calorimetry [29–31], fluorescence measurement [32–34] and X-ray diffraction approaches [35,36]. However, it should be noted that virtually all previous studies were carried out with model membranes lacking cholesterol. Cholesterol is a ubiquitous component of animal cell membranes, comprising up to 50 mol % of plasma membrane lipids . Cholesterol is known to modulate the physical properties of membrane phospholipids . Despite the evidence supporting a relationship between carotenoid membrane interactions and their antioxidant behavior, such a relationship has not been directly measured. In this study, we examined the membrane interactions of five homochiral carotenoids with various polarities (astaxanthin, zeaxanthin, lutein, β-carotene, and lycopene). Membrane interactions were directly correlated with their effects on lipid peroxidation in membranes containing cholesterol. The results of this study demonstrate remarkable differences among these various carotenoids with respect to their effects on membrane lipid structure and rates of lipid peroxidation.