Study on Lutein and Eye Health

Lutein is a type of carotenoid lutein, also known as phyto-lutein. It is a terpene compound that is widely found in nature and is the main component of plant pigments such as corn, vegetables, fruits, and flowers. Humans first discovered lutein in carrots at the beginning of the 19th century. It has since been found in many plants, with marigolds being particularly rich in it. Lutein cannot be synthesized in humans and animals and can only be obtained from food. The lutein molecule has 10 conjugated double bonds, which gives it strong free radical scavenging ability [1]. In recent years, with the deepening of research, lutein has been found to have a variety of biological functions, such as enhancing the body's antioxidant capacity, enhancing immune function, protecting vision, reducing the occurrence and development of cancer, and reducing the incidence of cardiovascular disease [2]. Because lutein is safe and non-toxic, and has strong biological functions such as anti-oxidation and improving eyesight, it has been allowed to be added to a wide range of foods and is used more and more widely.

1 Lutein's anti-oxidation function

Excessive free radicals have a damaging effect on molecules in the body. Eliminating excessive free radicals in the body can slow down aging and prevent related diseases caused by these excessive free radicals, such as cancer, cardiovascular disease, Alzheimer's disease, atherosclerosis, cataracts, etc. Because the lutein molecule has 10 conjugated double bonds (most carotenoid molecules only have 9), and the terminal group has a hydroxyl group, it can exert its antioxidant function by scavenging free radicals, quenching singlet oxygen and reducing photosensitizers, etc., to exert its antioxidant function. W. S. Michael et al. [3] fed lutein to guinea pigs to detect the distribution of lutein in guinea pig tissues. The results showed that the lutein content in each tissue, from high to low, was liver, spleen, lung, kidney, plasma, and eye, and lutein was almost undetectable in white adipose tissue.

In vitro experiments conducted by S. Bhattacharyya et al. [4] showed that lutein can inhibit the DNA oxidative damage caused by metal iron ions and H2 O2 to liver cells, and its antioxidant effect is better than that of natural carotene. The results of in vivo experiments on animals showed that after 6 weeks of feeding liver cancer model mice with 70 mg/kg of lutein per body weight, oxidative DNA damage to liver cells and the development of liver cancer could be effectively suppressed, and the amount of lutein deposited in the liver was inversely proportional to the degree of oxidative damage. One of the mechanisms by which cisplatin causes kidney toxicity is the production of free radicals and oxidative stress. The cytotoxic effect on cells is mainly through the formation of DNA adducts, which causes cells to remain in the G2 phase of the cell cycle and trigger apoptosis. The antioxidant function of lutein can provide some protection against cell damage caused by cisplatin. In vitro cell test results show that lutein has a significant preventive effect on DNA damage caused by cisplatin in the human liver cell line (HepG2).

2. The effect of lutein on the body's immune function

The immunomodulatory activity of carotenoids has been widely recognized, and lutein also has a certain regulatory effect on both cellular and humoral immunity. Since the discovery of lutein's role in regulating the body's immune response, research on its immune function has been carried out. It was found that supplementing mice with lutein can promote antigen-induced lymphocyte proliferation, and can also enhance the antibody response of mouse splenocytes to T lymphocyte antigens. The results showed that supplementing cats and dogs with lutein can promote the proliferation of cat peripheral blood lymphocytes stimulated by ConA and PWM, and the proliferation of dog peripheral blood lymphocytes stimulated by ConA, PHA and PWM stimulated canine peripheral blood lymphocytes. The effect of lutein supplementation was dose-dependent, and lutein significantly enhanced delayed-type hypersensitivity. The proportion of CD4+ T lymphocytes and CD21+ B lymphocytes in cat peripheral blood increased, while the proportions of CD4+, CD5+, CD8+ T lymphocytes and MHC II+ cells in canine peripheral blood increased.

The increase in the proportion of CD5+ T lymphocytes and CD4+ Th cells promotes the proliferative capacity of lymphocytes. In addition, the expression of cell surface molecules such as IL-2 and MHC II also affects antigen-stimulated lymphocyte proliferation. After 12 weeks of lutein supplementation, there was no significant change in the blood levels of IgM and IgG. However, after two immunizations with a polyvalent vaccine, the blood concentration of IgG increased significantly, indicating that lutein can enhance the body's antibody production capacity after stimulation by routine vaccines. The results of lutein's effect on poultry show that lutein can effectively prevent peroxidation damage to embryos by free radicals, increase the serum antioxidant level of young chicks, enhance humoral immunity by increasing Th2 cells, and significantly increase the serum IBV antibody titer of laying hens. Eggs have a high lutein content, and after incubation, the offspring have good lymphocyte synthesis ability and cellular immune levels.

3 Lutein's protection of vision

In the mid-20th century, it was discovered that lutein is the main pigment that constitutes the macular region of the human eye's retina. The decline in visual function in patients with age-related macular degeneration (AMD) may be related to a decrease in the pigment density of the macular region of the retina [5]. In recent years, a large number of studies have been conducted on the protective effect of lutein on vision. It is believed that the protective effect of lutein on the eyes is mainly through its filter and antioxidant effects. High-energy blue light can induce the production of free radicals and damage retinal ganglion cells. Lutein can reduce the density of blue light before it reaches the cone cells and rod cells, reduce the oxidative stress of the retina, and reduce the incidence of AMD [6].

In recent years, more research has been done on the relationship between lutein and AMD and age-related cataracts and their effects. It has been found that adding a certain amount of lutein to the human diet over a period of time the lutein content in the blood serum and the macula of the retina significantly increased, and the damage to the photoreceptor cells on the retina from blue light was significantly reduced. This indicates that increasing lutein intake can significantly reduce the risk of AMD and significantly improve the symptoms of AMD patients. The survey found that cataract patients with high lutein intake had a significantly lower risk of surgery than those with low intake, and lutein intake can significantly enhance the visual recovery function of cataract patients [7]. Studies have shown that lutein has a protective effect on the visual function of people who work and live with long-term exposure to screen light radiation. S. Y. Li et al. [8] studied the direct protective effect of lutein on retinal ganglion cells (RGCs), as well as its resistance to oxidative damage caused by hypoxia and free radicals. The results showed that lutein not only significantly increased the number of live cells, but also significantly improved the morphological changes of cells caused by hypoxia and oxidation. M. Sasaki et al. [9] showed that lutein can inhibit inflammatory response pathways and eliminate free radicals, thereby effectively reducing the damage to the retina caused by acute uveitis induced by endotoxin.

4 Lutein and tumor and cancer prevention

In 1981, the possible role of carotenoids in reducing the incidence of human cancer was first reported. Since then, a large number of studies have shown that lutein has a certain inhibitory effect on various cancers such as breast cancer, rectal cancer and skin cancer. A high intake of carotenoids in fruits and vegetables can reduce the incidence of chronic cancers such as lung cancer, breast cancer and prostate cancer. Studies have found that feeding mice a diet high in lutein slows the growth of transplantable breast cancer cells in their bodies and enhances the proliferative effect of lymphocytes. Cell culture results show that lutein is more effective than β-carotene in inhibiting the auto-oxidation of cell lipids and preventing cell damage caused by oxidation.

Animal test results show that lutein is an anti-cancer agent for breast cancer, and lutein intake is inversely related to the incidence of pre-cancerous breast lesions [10]. The mechanisms by which lutein inhibits tumors mainly include antioxidant activity; immune activity regulation; inhibition of tumor angiogenesis and cell proliferation; and the use of the low-differentiated or undifferentiated characteristics of tumor cells to induce their differentiation potential, promote tumor cell differentiation, and reduce their malignancy. Lutein may have certain organ-specific effects in reducing the occurrence of cancer, but further research is needed to determine whether it can achieve outstanding results in human cancer prevention.

5 Lutein and the prevention of cardiovascular disease

Research has shown that lutein in food prevents the development of cardiovascular disease mainly by protecting low-density lipoprotein (LDL) particles from oxidation mediated by singlet oxygen. Epidemiological studies, in vitro experiments and animal model test results all show that increasing lutein intake can prevent atherosclerosis. Dietary lutein intake and lutein levels in the blood or adipose tissue are negatively correlated with the incidence of cardiovascular disease.

R. Vishwanathan [11] gave 52 elderly people over the age of 60 who were taking cholesterol-lowering drugs two egg yolks (containing about 0.5 mg of lutein) per day. After five weeks, the serum lutein content increased by 16%, and the high-density lipoprotein (HDL) content, which is beneficial for reducing the incidence of cardiovascular disease, increased by 5% (P < 0.05). The results of in vitro experiments showed that lutein significantly inhibited the expression of adhesion molecules VCAM-1, endothelial cell selectins and ICAM-1 on the surface of human aortic endothelial cells, which are related to the occurrence of cardiovascular disease. J. H. Sung et al. [12] found that lutein can reduce the mean arterial pressure, systolic pressure and diastolic pressure of rats with hypertension induced by N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME), and can alleviate cardiac and renal hypertrophy, reduce plasma lipid peroxidation, increase plasma nitrite and reduced glutathione concentrations, When the feeding amount reaches 2 mg/kg, it can significantly prevent the decrease in heart rate induced by L-NAME, indicating that lutein has significant antihypertensive and antioxidant effects.

6 Other functions of lutein

Lutein can reduce the erythema, aging, and even skin cancer caused by ultraviolet radiation on the skin. Studies have shown that taking a certain amount of lutein (3 mg/d) has a protective effect against ultraviolet rays, and that compared with the control group, the amount of ROS in the body is significantly lower (P<0.05). In addition, lutein can reduce the acute inflammatory response in mice and the increase in blood lysine levels induced by ultraviolet light, preventing the negative effects of ultraviolet light on the skin. Lutein also has a certain preventive and therapeutic effect on diabetes [13].

7 Prospects

With the deepening of research on the physical and chemical properties and biological activity of lutein powder, and the development of engineering technologies such as bioengineering, fermentation engineering, enzyme engineering and genetic engineering, lutein is bound to attract the attention of the pharmaceutical industry, food and feed industry, animal production and cosmetics industry. As a natural plant pigment, lutein has a variety of biological functions and will be widely used in food, medicine and animal production. In particular, in-depth research on anti-tumor and immune regulation will open up broad prospects for the application of lutein.

References:

[1] Zhang Wei, Tong Nian-ting, Yin Li-li, et al. Experimental research progress on the role and mechanism of lutein in ophthalmic diseases [J]. Journal of Shanghai Jiaotong University: Medicine Edition, 2012, 32 (2): 231-234.

［2］  SCHWEIGERT J，REIMANN J．Micronutrients  and their relevance for the eye－function of lutein，zeaxanthin and omega－3 fatty acids ［J］．Klin Monbl Augenheilkd，2011，228 (6) : 537－543 .

［3］  Schaffer M W，Sinha  Roy S，Mukherjee S，et al．Identification of lutein，a dietary  antioxidant  carotenoid  in  guinea  pig  tissues［J］. Biochem Biophys Res Commun，2008，374(2) : 378－381 .

［4］  BHATTACHARYYA  S ，DATTA  S ，MALLICK  B ，et  al． Lutein  content and in vitro antioxidant activity of different cultivars of Indi- an marigold flower( Tagetes Patula  L．)  extracts［J］．J  Agric  Food  Chem，2010，58 ( 14) : 8259－8264 .

［5］  MA L，LIN X M．Effects of lutein and zeaxanthinon aspects of eye health［J］．J Sci Food Agric，2010，90( 1) : 2 －12 .

［6］  BONE R A，LANDRUM J T．Dose －dependent response of serum lutein and macular pigment optical density to supplementation with lutein esters［J］．Arch Biochem Biophys，2010，504( 1) : 50－55 .

［7］  STRINGHAM J M，BOVIER E R , WONG J C，et al．The influence of dietary lutein  and  zeaxanthin  on  visual  performance［J］．J  Food Sci，2010，75 ( 1) : R24 - R29 .

［8］  LI S Y，LO A C．Lutein protects RGC－5 cells against hypoxia and oxidative stress［J］．Int J Mol Sci，2010，11  (5) : 2109－2117 .

［9］  SASAKI  M ，OZAWA  Y ，KURIHARA  T ，et al． Neuroprotective  effect of an antioxidant，lutein，during  retinal  inflammation［J］．In- vest Ophthalmol Vis Sci，2009，50(3) : 1433 －1439 .

［10］ SHIM E，YEUM K J，TANG G，et al.  Retinoids，carotenoids，and  tocopherols in breast adipose tissue and serum of benign breast dis- ease and breast cancer patients［J］．Nutr Cancer，2012 ，64(7) : 956- 963.

［11］ VISHWANATHAN R , GOODRO－KOTYLA E F，WOOTEN B R ,  et al．Consumption of 2 and 4 egg yolks / d for 5 wk increases macu- lar pigment concentrations in older adults with low macular pigment  taking cholesterol －lowering  statins［J］．Am  J  Clir  Nutr，2009，90  (5) : 1272 －1279 .

［12］ SUNG J H，JO Y S，KIM S J，et al．Effect of lutein on L－NAME-  induced  hypertensive  rats［J］． Korean  J   Physiol  Pharmacol， 2013，17 (4) : 339－345 .

［13］ SUGIURA M，NAKAMURA M，OGAWA K，et al．Associations of serum carotenoid concentrations with the metabolic syndrome : inter- action with smoking［J］．Br J Nutr，2008，100(6) : 1297 －1306 .