Introduction to Lutein
Lutein, chemically known as 3,3'-dihydroxy-α-carotene, belongs to the carotenoid family, which includes well-known compounds like beta-carotene and zeaxanthin. It's renowned for its vibrant yellow pigment, often found in green leafy vegetables, fruits, and egg yolks. In nature, lutein serves a dual purpose – capturing light energy for photosynthesis in plants and acting as an antioxidant to protect cells from damage caused by free radicals.
The human body, unable to produce lutein on its own, must obtain it through diet. Foods rich in lutein include spinach, kale, broccoli, peas, and corn. Additionally, egg yolks are a notable source, further highlighting the importance of a well-balanced diet in ensuring adequate lutein intake.
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Structure of Lutein
Understanding the structure of lutein provides insights into its function within the body. Lutein consists of a central portion composed of conjugated double bonds, giving it its characteristic color. Its chemical structure includes a series of alternating single and double bonds, forming a long hydrocarbon chain. This unique arrangement allows lutein to absorb specific wavelengths of light, contributing to its yellow hue.
Lutein also possesses two hydroxyl (-OH) groups, which enhance its solubility in lipids (fats). This solubility is crucial for its effective absorption in the digestive system, facilitating its transport within the body. The structural intricacies of lutein make it a versatile compound with diverse applications in human health.
Fig. 1 Structure of all-trans lutein (Becerra M. O., et al. 2020).
Location of Lutein in the Body
Once ingested, lutein is transported throughout the body via the bloodstream, eventually accumulating in various tissues. Notably, it is found in high concentrations in the eyes, specifically in the retina. The retina, a light-sensitive layer at the back of the eye, plays a crucial role in vision.
Lutein, along with its close relative zeaxanthin, accumulates in the macula – a small, highly sensitive area within the retina responsible for sharp and detailed vision. The concentration of these carotenoids in the macula forms a protective layer, shielding the delicate cells from the harmful effects of high-energy light, particularly blue light. This helps prevent oxidative damage and reduces the risk of age-related macular degeneration (AMD), a common cause of vision impairment in older adults.
Beyond the eyes, lutein is also found in significant amounts in the skin. Its antioxidant properties contribute to protecting the skin from the harmful effects of ultraviolet (UV) radiation, helping maintain skin health and reducing the risk of premature aging.
Moreover, lutein is present in the brain, albeit in lower concentrations compared to the eyes and skin. Research suggests that lutein may play a role in cognitive function and neuroprotection. Its antioxidant capabilities may help combat oxidative stress in the brain, potentially reducing the risk of cognitive decline and neurodegenerative diseases.
Roles of Lutein in Health
Lutein has garnered attention for its multifaceted health benefits, with notable roles in antioxidant, anti-inflammatory, and neuroprotective processes.
Antioxidant Activities
Lutein exhibits various antioxidant activities, including the inhibition of membrane lipid peroxidation, particularly in photoreceptors rich in polyunsaturated fatty acids. Its direct antioxidant action and immunomodulatory properties contribute to cellular protection against oxidative stress.
In a rat model of endotoxin-induced uveitis, lutein demonstrated anti-inflammatory effects by blocking the degradation of inhibitory κB-α and preventing NF-kappa-B translocation. This resulted in reduced inducible gene transcription and the synthesis of inflammatory mediators.
Neuroprotective Properties
Lutein's neuroprotective effects extend to cultured retina photoreceptors, where it neutralizes apoptosis induced by paraquat and hydrogen peroxide. Additionally, lutein prevents photooxidation of phosphatidyl-pyridinium bisretinoid, protecting retinal pigment epithelial cells from reactive species formation.
In lipopolysaccharide-stimulated macrophages, lutein reduces intracellular hydrogen peroxide accumulation, inhibits proinflammatory gene expression, and suppresses NF-κB translocation. Similar anti-inflammatory mechanisms are observed in gastric epithelial cells, microglia, and UV-irradiated keratinocytes.
Lutein also acts as a competitive inhibitor of cytosolic calcium-dependent phospholipase A2, inhibiting arachidonic acid release from macrophages. In vascular smooth muscle cells, it attenuates free radical production induced by platelet-derived growth factor and extracellular hydrogen peroxide.
In human lens epithelial cells, lutein protects against protein oxidation, lipid peroxidation, and DNA damage induced by oxidative stress, increasing reduced glutathione levels.
Neurological and Cognitive Benefits
Recent research highlights lutein's positive association with improved cognitive function in the elderly. Higher macular pigment optical density, indicative of lutein and zeaxanthin levels in the retina, correlates with better global cognition, verbal learning, fluency, and processing speed in older individuals.
Lutein supplementation demonstrates cognitive improvements in elderly women and enhances visual processing speed and visual motor behavior in young subjects. The compound's potential benefits in neurodegenerative diseases, including Parkinson's and Alzheimer's, are under exploration, with evidence suggesting mitochondrial protection, antioxidant effects, and antiapoptotic properties.
Eye Health
In the human eye, lutein contributes to macular pigment alongside zeaxanthin and meso-zeaxanthin. This pigment protects against oxidative damage in the retina, preventing conditions like age-related macular degeneration (AMD) and cataracts. Lutein's ability to absorb blue light and quench singlet molecular oxygen contributes to its photoprotective role.
Supplementation with lutein, zeaxanthin, and meso-zeaxanthin enhances macular pigment, contrast sensitivity, and visual function. Clinical trials, such as AREDS2, demonstrate the efficacy of lutein and zeaxanthin in slowing the progression of AMD.
Cardiometabolic Health
Lutein's antioxidant and anti-inflammatory properties are implicated in promoting cardiovascular health. Animal studies show its preventive role in atherosclerosis development, reducing malondialdehyde and inflammatory cytokines.
Human studies, like ARIC and CUDAS, suggest an inverse association between plasmatic lutein and atherosclerosis. Lutein supplementation has shown promise in decreasing the risk of coronary heart disease, stroke, and metabolic syndrome.
Oxidative Stress in Perinatal Period
In the perinatal period, lutein plays a crucial role in mitigating oxidative stress-related diseases in newborns. Breast milk, a primary source of lutein for infants, contributes to antioxidant defenses.
While data on lutein supplementation's direct impact on newborn diseases like retinopathy of prematurity (ROP) are inconclusive, the compound's antioxidant and anti-inflammatory roles are recognized. Ongoing research aims to elucidate the potential therapeutic effects of lutein in neonatal morbidity.
In conclusion, lutein emerges as a versatile compound with far-reaching implications for health. Its antioxidant, anti-inflammatory, and neuroprotective properties make it a promising candidate for addressing various health concerns, from eye health and cognitive function to cardiovascular well-being and perinatal health. As research continues, unlocking the full potential of lutein promises a brighter and healthier future.
References
- Becerra M. O., et al. Lutein as a functional food ingredient: Stability and bioavailability. Journal of Functional Foods. 2020, 66: 103771.
- Perrone S., et al. The multiple facets of lutein: A call for further investigation in the perinatal period. Oxidative Medicine and Cellular Longevity. 2016, 2016: 5381540.
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