Storage conditions：Short-term storage at 2~8℃, long-term storage at -20 ~ -80℃
52.9900
9.5634
9.5634
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5.1802
No
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Yes
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0.0
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Yes
Carotenoids play a crucial role in the colorful pigment world of nature. They are not only important photosynthetic auxiliary pigments in plants, algae, and microorganisms, giving the natural world brilliant colors such as red, orange, and yellow, but also play a key role in the light protection, antioxidant, and signal transduction of organisms. In the vast family of carotenoids, epoxy zeaxanthin, as a structurally unique oxygen-containing carotenoid (Xanthophyll), has attracted much attention due to its core position in the photoprotective mechanism and potential biological activity.
Epoxy zeaxanthin, also known as 5,6-epoxy-5,6-dihydro - β, β - carotene -3,3 '- diol, is an intermediate product of the conversion of zeaxanthin to violaxanthin. This conversion process constitutes the core link of the famous "Violaxanthin Cycle" (VAZ Cycle). In higher plants and algae, when the light intensity exceeds the photosynthetic utilization capacity, zeaxanthin is sequentially converted into epoxyzeaxanthin and zeaxanthin by the action of Violaxanthin De epoxidase (VDE); On the contrary, under low light conditions, zeaxanthin is converted back to zeaxanthin through the action of zeaxanthin epoxidase (ZEP). This dynamic cycle is a key non photochemical quenching (NPQ) mechanism for plants and algae to cope with excessive light energy, dissipate excess excitation energy, prevent photoinhibition and photooxidative damage.
In addition to its core function in plant physiology, epoxyzeaxanthin, as a naturally occurring bioactive molecule, is gradually being recognized by the scientific community for its potential health benefits, especially in terms of visual protection. Given its structural similarity with zeaxanthin and lutein, epoxyzeaxanthin is believed to potentially participate in the formation of retinal macular pigment and provide protection for retinal pigment epithelial cells (RPE) and photoreceptor cells through its antioxidant and blue light filtering properties, thereby combating degenerative eye diseases such as age-related macular degeneration (AMD). However, compared with the widely studied lutein and zeaxanthin, the pharmacological activity, mechanism of action, and pharmacological properties of epoxyzeaxanthin are still in their infancy. However, its unique chemical structure and key role in photoprotection make it a highly promising target for natural product research. This article aims to systematically review the chemical structure, physicochemical properties, sources, pharmacological activities, mechanisms of action, and pharmacological evaluation of epoxyzeaxanthin, in order to provide comprehensive scientific basis for the in-depth research and future applications of this natural product.
The chemical structure of epoxyzeaxanthin is the basis for its biological functions and physicochemical properties. From a chemical classification perspective, it belongs to the class of oxygen-containing carotenoids, namely lutein. Its core skeleton is composed of a polyene chain consisting of 40 carbon atoms, with an Ionone ring connected at each end. Compared with β - carotene, epoxyzeaxanthin contains one hydroxyl group (- OH) at both the 3 and 3 'positions, giving it stronger polarity and antioxidant capacity. Its most prominent structural feature is that one of the 5,6-position double bonds of the ketone ring is oxidized to form an epoxide group (- O -), hence the name "epoxyzeaxanthin". The presence of this epoxy group is a key structural marker that distinguishes it from zeaxanthin and zeaxanthin, and is also the structural basis for its participation in the VAZ cycle and reversible chemical transformation.
In terms of physicochemical properties, the molecular formula of epoxyzeaxanthin (CAS number: 640-03-9) is C ₄₀ H ₅₆ O3, with a molecular weight of 584.88 g/mol. Its LogP value is 9.5634, indicating that it has extremely high lipid solubility and is easily soluble in organic solvents such as chloroform, ether, acetone, and n-hexane, while its solubility in water is extremely low (about 0.0001 mg/mL). This high lipophilicity determines that it is mainly distributed in lipid membrane structures in organisms, such as chloroplast thylakoid membranes and retinal cell membranes. Its topological polar surface area (TPSA) is 52.99 Å ², mainly contributed by two hydroxyl groups and one epoxy group. In terms of spectroscopic characteristics, as a conjugated polyene compound, epoxyzeaxanthin exhibits strong absorption in the visible light region, with its maximum absorption wavelength (λ max) typically around 445 nm and 472 nm (depending on the solvent), giving it a typical yellow to orange appearance. This strong absorption ability for blue light (400-500 nm) is the theoretical basis for its potential as a blue light filter and light protective agent.
Epoxy zeaxanthin is extremely sensitive to light, heat, oxygen, and acid. Especially under acidic conditions, its epoxy group is prone to undergo ring opening rearrangement reactions, generating by-products such as auroxanthin or other furan type oxides, leading to the loss of its biological activity. Therefore, in the process of extraction, separation, storage, and biological activity testing, it is necessary to strictly avoid light, low temperature, oxygen isolation, and control the pH value to maintain its chemical stability. Its high LogP value and low water solubility also pose significant challenges for its development as an oral drug, as its bioavailability is extremely low and requires the use of special delivery systems (such as liposomes, nanoemulsions, cyclodextrin inclusion complexes, etc.) to improve its dispersibility and absorption efficiency in aqueous media.
Epoxyzeaxanthin is widely distributed in nature, but its content is relatively low, mainly found in plants and algae that carry out photosynthesis. It is an intermediate product of the VAZ cycle, therefore its presence can be detected in any organism capable of performing this cycle. Its content is significantly affected by light conditions. Under strong light stress, zeaxanthin is converted to zeaxanthin, and epoxyzeaxanthin accumulates briefly as an intermediate. Therefore, its sources can be divided into two categories: higher plants and microalgae.
In higher plants, epoxyzeaxanthin is widely present in leafy vegetables, flowers, and fruits. For example, dark green vegetables such as spinach, kale, and broccoli all contain trace amounts of epoxyzeaxanthin. In some yellow or orange flowers such as marigold (Tagetes erecta), its content is also relatively abundant. However, in most plant tissues, its content is much lower than lutein and beta carotene. In contrast, certain microalgae are more ideal sources of epoxyzeaxanthin. Especially Euglena gracilis, as a single celled eukaryotic organism with both animal and plant characteristics, contains abundant chloroplasts in its cells and can synthesize various types of carotenoids. Research has shown that under specific cultivation conditions, such as high light intensity or nitrogen stress, naked algae can accumulate large amounts of epoxyzeaxanthin, making it a signature source of this compound. In addition, certain green algae (such as Dunaliella salina) and diatoms can also accumulate epoxyzeaxanthin under specific stress conditions.
The method of extracting epoxyzeaxanthin usually follows the general strategy of carotenoid extraction, but special attention should be paid to its instability. The classic extraction process involves first grinding fresh or freeze-dried biological materials (such as naked algae or spinach leaves) into powder to break down cell walls and organelle membranes. Then, a mixture of polar organic solvents (such as acetone, methanol, or ethanol) and lipophilic solvents (such as n-hexane, petroleum ether) is repeatedly leached. To suppress oxidation and isomerization, antioxidants (such as 0.1% BHT) need to be added during the extraction process and carried out under low temperature (4 ° C) and light avoidance conditions. After concentration, the extraction solution can be used for liquid-liquid distribution (such as using n-hexane/methanol/water system) to remove water-soluble impurities and polar lipids. Further purification typically relies on column chromatography, such as using silica gel columns, alumina columns, or C18 reverse phase columns, with gradient elution using different ratios of organic solvents (such as n-hexane/acetone/methanol). High performance liquid chromatography (HPLC) combined with a photodiode array detector (PDA) is the gold standard method for separating and identifying epoxyzeaxanthin, which can effectively separate it from structurally similar compounds such as zeaxanthin, zeaxanthin, lutein, etc. In recent years, supercritical fluid extraction (SFE) technology, especially the use of CO ₂ as a solvent, has been explored for the extraction of epoxyzeaxanthin due to its green, efficient, and low-temperature characteristics. It is expected to improve its extraction efficiency and purity while reducing organic solvent residue.
Although the function of epoxyzeaxanthin in plant physiology has been fully understood, its pharmacological activity research in mammalian systems is relatively limited, mainly focused on areas related to its structural analogues (lutein and zeaxanthin), especially in terms of visual protection.
1. Visual protection activity: This is the most highly anticipated potential pharmacological activity of epoxyzeaxanthin. The macula of the retina is the most visually sensitive area, rich in lutein and zeaxanthin, which together form macular pigments that protect photoreceptor cells by filtering harmful blue light and quenching reactive oxygen species (ROS). Epoxy zeaxanthin, as an intermediate in the VAZ cycle, has a highly similar structure to zeaxanthin, and is therefore speculated to be able to be absorbed by the retina and participate in the formation of macular pigments. In vitro cell experiments have shown that epoxyzeaxanthin can effectively scavenge singlet oxygen (¹ O ₂) and peroxide free radicals, and its antioxidant capacity is comparable to or even stronger than zeaxanthin. In addition, it can inhibit lipid peroxidation and protect retinal pigment epithelial (RPE) cells from oxidative stress-induced apoptosis. In the blue light injury model, RPE cells pre treated with epoxyzeaxanthin showed higher survival rates, indicating their direct blue light filtering and photoprotective effects. However, there is currently a lack of direct in vivo experimental evidence to prove that epoxyzeaxanthin can accumulate in large quantities in the macular area like lutein and zeaxanthin, and its metabolic fate for conversion to zeaxanthin or in the retina still needs further clarification.
2. Antioxidant and anti-inflammatory activities: As a member of the carotenoid family, epoxyzeaxanthin has strong antioxidant capacity. Its conjugated polyene chain can effectively quench singlet oxygen, scavenge peroxide free radicals, and thus interrupt the lipid peroxidation chain reaction. This antioxidant activity is the basis for its various biological effects. In cell models, epoxyzeaxanthin has been shown to reduce intracellular ROS levels induced by hydrogen peroxide (H ₂ O ₂) or lipopolysaccharide (LPS), and inhibit the activation of the nuclear factor kappa B (NF - κ B) pathway, thereby reducing the expression of pro-inflammatory cytokines such as tumor necrosis factor - α (TNF - α), interleukin-6 (IL-6), and interleukin-1 β (IL-1 β). This indicates that epoxyzeaxanthin may have potential anti-inflammatory activity and has potential value for treating diseases related to oxidative stress and chronic inflammation, such as cardiovascular disease and neurodegenerative diseases.
3. Other potential activities: Preliminary studies also suggest that epoxyzeaxanthin may have other pharmacological activities. For example, some in vitro experiments have found that it can inhibit the proliferation of certain cancer cells, but its activity is much weaker than that of beta carotene and lycopene. In addition, given its core role in photoprotection, epoxyzeaxanthin has also been explored as a photoprotective ingredient in cosmetics to resist UV induced skin photoaging. However, most of these studies are still in the preliminary stage and lack in-depth mechanism research and in vivo pharmacological validation.
Overall, the pharmacological activity research of epoxyzeaxanthin is still in the early exploration stage. Its most clear potential lies in visual protection, but more systematic studies from in vitro to in vivo, from cells to animal models are needed to confirm its effectiveness, safety, and superiority.
The biological activity mechanism of epoxyzeaxanthin is multi-layered, including its direct chemical action as a small molecule antioxidant, as well as its regulation of specific cell signaling pathways and protein targets. In the field of visual protection, its mechanism of action is particularly closely related to related targets.
1. Direct physical and chemical protection mechanisms:
- Blue light filtering: The maximum absorption peak of epoxyzeaxanthin is located in the blue light region (~445-472 nm), which can effectively absorb high-energy blue light entering the retina and reduce its photochemical damage to photoreceptor cells and RPE cells. This is the primary mechanism by which it exerts a protective effect as a precursor or analog of macular pigment.
- Antioxidant and free radical quenching: Its conjugated polyene chain can directly quench singlet oxygen (¹ O ₂) and scavenge peroxyl radicals (ROO •), thereby interrupting the lipid peroxidation chain reaction and protecting the retinal cell membrane rich in polyunsaturated fatty acids from oxidative damage. In addition, it can also work synergistically with other antioxidants such as vitamin E and vitamin C to form an antioxidant network.
2. Molecular targets and signaling pathway regulation:
In terms of visual protection, the target of epoxyzeaxanthin is closely related to the pathogenic genes of retinal degenerative diseases such as AMD and Stargardt disease.
- RPE65（RPE65）： RPE65 is a key isomerase in retinal pigment epithelial cells, responsible for converting all trans retinol to 11 cis retinol, and is the rate limiting enzyme in the visual cycle. Oxidative stress and blue light damage can cause dysfunction of RPE65, leading to visual impairment. Epoxy zeaxanthin may protect RPE65 protein from oxidative modification and maintain its normal enzymatic activity through its antioxidant properties, thereby ensuring smooth visual circulation.
- ABCA4（ABCA4）： ABCA4 is a transport protein located at the outer disc edge of retinal photoreceptor cells, responsible for clearing the toxic adduct formed by retinal and phosphatidylethanolamine (N-subretinoyl-N-retinyl-phosphatidylethanolamine, precursor of A2E). ABCA4 gene mutation is the main cause of Stargardt disease. Epoxy zeaxanthin may indirectly alleviate the toxic burden caused by ABCA4 functional defects by reducing photooxidative damage and decreasing the rate of A2E generation.
- RHO（RHO）： Rhodopsin is a light receptor protein in rod cells. After being activated by light, it triggers a visual cascade reaction. Excessive exposure to light can cause photobleaching and oxidative damage to rhodopsin. The blue light filtering and antioxidant effects of epoxyzeaxanthin can directly protect rhodopsin from light damage and maintain its photosensitivity.
- RDH5 (RDH5) and RLBP1 (RLBP1): RDH5 (11 cis retinol dehydrogenase) and RLBP1 (retinal binding protein 1) are both key enzymes and carrier proteins in the visual cycle. RDH5 catalyzes the oxidation of 11 cis retinol to 11 cis retinal, while RLBP1 is responsible for transporting retinoids between RPE cells and photoreceptor cells. Oxidative stress can also impair the function of these proteins. Epoxyzeaxanthin may indirectly protect the structural and functional integrity of these proteins by maintaining intracellular redox balance.
3. Simulation and regulation of VAZ cycle:
It is worth noting that in plants, epoxyzeaxanthin is an intermediate in the VAZ cycle. Although mammalian cells do not have a complete VAZ cycle, studies have shown that certain mammalian tissues, such as the retina, may have similar reversible cyclooxygenase/decarboxylase activity. Epoxy zeaxanthin may serve as an exogenous substrate, which can be ingested into the retina and converted into zeaxanthin under specific conditions (such as exposure to strong light), thereby enhancing the density and photoprotective ability of macular pigments. The hypothesis of "prodrug" or "reservoir" provides a new perspective on the unique role of epoxyzeaxanthin in visual protection.
In summary, the mechanism of action of epoxyzeaxanthin is multi-target and multi pathway, with its core being to protect key proteins in the visual cycle (RPE65, ABCA4, RHO, etc.) from photooxidative damage through physical filtration and chemical antioxidant effects, thereby maintaining the normal physiological function of the retina.
The development of epoxyzeaxanthin as a clinical drug faces a series of severe challenges, and its pharmacological evaluation mainly focuses on its physicochemical properties, pharmacokinetic characteristics, and safety.
1. Physical and chemical properties and drug like properties:
According to the Lipinski Five Rules, epoxyzeaxanthin has significant issues with drug likeness. Its molecular weight (584.88 Da) is slightly higher than the threshold of 500 Da; Its LogP value (9.56) is much higher than 5, indicating strong lipid solubility and extremely poor water solubility (0.0001 mg/mL). This "high lipophilicity, low water solubility" characteristic severely limits its oral absorption. In addition, its TPSA is 52.99 Å ², which is compliant with regulations but not sufficient to compensate for its poor solubility. Therefore, epoxyzeaxanthin belongs to the typical BCS (Biopharmaceutical Classification System) class IV drugs (low solubility, low permeability), with extremely low oral bioavailability. Its high LogP value also means that it is easily bound to lipids in food and may be absorbed by the lymphatic system, but the overall absorption rate is still low.
2. Pharmacokinetic characteristics:
At present, there is a severe lack of pharmacokinetic data on epoxyzeaxanthin in mammals. Based on the study of its structural analogues (lutein and zeaxanthin), its general characteristics can be inferred:
- Absorption: After oral administration, epoxyzeaxanthin needs to be mixed with dietary fat and form mixed micelles under the action of bile acid salts and pancreatic lipase in order to be absorbed by small intestinal epithelial cells. Its absorption efficiency is extremely low and varies greatly among individuals.
- Distribution: After absorption, epoxyzeaxanthin mainly binds to lipoproteins (especially LDL and HDL) in plasma and is transported throughout the body. Its high lipophilicity makes it tend to distribute to lipid rich tissues such as liver, adipose tissue, skin, and retina. Whether it can effectively cross the blood-brain barrier (BBB) is a key issue. The given parameters indicate that its blood-brain barrier is high, suggesting that it may have the ability to penetrate the BBB, which is a potential advantage for treating central nervous system diseases such as neurodegenerative diseases, but may also bring unknown risks of central nervous system toxicity. However, this parameter may be based on computational predictions and requires experimental verification.
- Metabolism: Epoxyzeaxanthin may undergo multiple metabolic pathways in the body, including: ① It is oxidized and cleaved in the intestine or liver to produce Apo carotenoids; ② Its epoxy group may undergo ring opening in acidic environments (such as gastric juice) or enzyme catalysis; ③ May be reduced to zeaxanthin or oxidized to zeaxanthin.
- Excretion: It is mainly excreted through bile and feces, with very little excretion through urine.
3. Safety evaluation:
The given pharmacological parameters show that epoxyzeaxanthin has a result of 0.0 in the Ames test, indicating its non mutagenicity. The hERG inhibition test result is' no ', indicating a low risk of causing QT interval prolongation and arrhythmia in the heart. These preliminary security data are positive. However, as carotenoids, high-dose intake may lead to skin yellowing (carotenoids), but it is generally considered reversible and harmless. The research on long-term toxicity, reproductive toxicity, and carcinogenicity is still blank.
4. Pharmaceutical strategy:
Given the above challenges, developing epoxyzeaxanthin as a drug requires innovative formulation strategies:
- Improve solubility and bioavailability: The use of techniques such as liposomes, nanoemulsions, solid lipid nanoparticles (SLN), cyclodextrin inclusion complexes, or phospholipid complexes can significantly improve their dispersibility and oral absorption rate in aqueous media.
- Targeted delivery: For visual protection, the development of topical eye delivery formulations (such as eye drops, intraocular implants) or nanocarriers targeting the retina can bypass oral absorption barriers and directly deliver drugs to target tissues.
- Pre drug design: By introducing polar groups such as phosphate or amino acids on its hydroxyl group, its water solubility can be temporarily improved, and the original drug can be released in vivo after enzymatic hydrolysis.
Although the pharmaceutical properties of epoxyzeaxanthin face challenges, its unique biological functions and potential value in visual protection make it have broad prospects in specific application fields.
1. Visual health and eye diseases:
This is the most direct and clear clinical application direction of epoxyzeaxanthin. With an aging population, age-related macular degeneration (AMD) has become one of the leading causes of irreversible blindness worldwide. At present, supplementing lutein and zeaxanthin has been proven to reduce the risk of AMD progression. Epoxy zeaxanthin, as an intermediate in the VAZ cycle, may have better photoprotective ability than or supplement existing carotenoid supplements. In the future, it may be developed into:
- Dietary supplements: As a new generation of "macular pigment supplement", it is combined with lutein and zeaxanthin to provide more comprehensive photoprotection.
- Functional food ingredients: Add to food or beverages for daily eye care.
- Ophthalmic drugs: Develop high-purity and highly bioavailable drug formulations for specific genetic retinal diseases, such as Stargardt's disease, to slow down disease progression.
2. Light protection and skin health:
Given its strong blue light absorption and antioxidant capacity, epoxyzeaxanthin also has potential applications in the fields of cosmetics and skin care. As a natural light protector, it can be added to sunscreen, anti-aging essence or daily skin care products to resist blue light (from the sun and electronic screen) and UV induced skin oxidative stress and photoaging. Its natural origin and low toxicity make it an ideal alternative to synthetic sunscreens.
3. Neurodegenerative diseases:
Oxidative stress and chronic inflammation are common pathological features of neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. The high blood-brain barrier penetration (estimated based on parameters) and antioxidant anti-inflammatory activity of epoxyzeaxanthin make it a potential candidate molecule for treating these diseases. However, this requires extensive preclinical research to validate its accumulation, metabolism, and mechanism of action in brain tissue.
4. Future research directions:
In order to promote the clinical application of epoxyzeaxanthin from the laboratory, future research should focus on the following aspects:
- Establish an efficient and green biomanufacturing platform: Utilizing genetically engineered microalgae (such as naked algae) or yeast cells to achieve efficient and low-cost production of epoxyzeaxanthin.
- Elaborate on its pharmacokinetics in vivo: Develop a sensitive LC-MS/MS detection method to systematically study its absorption, distribution, metabolism, and excretion (ADME) characteristics in animal models, particularly its accumulation in retina and brain tissues.
- Verify its direct interaction with visual protection targets: Through techniques such as molecular docking and surface plasmon resonance (SPR), the direct binding ability of RPE65, ABCA4 and other proteins was studied.
- Developing innovative formulations: Focus on tackling the problem of low bioavailability and developing safe, effective, and stable oral or topical formulations.
- Conduct systematic toxicology research: Complete long-term toxicity, reproductive toxicity, and carcinogenicity evaluations to provide sufficient evidence for its safety as a drug or food ingredient.
Epoxy zeaxanthin, as a carotenoid that plays a central role in photoprotection in natural photosynthetic organisms, has unique chemical structures - especially the presence of epoxy groups - that endow it with biological potential beyond ordinary antioxidants. From the VAZ cycle in plant physiology to potential targets in mammalian visual protection (RPE65, ABCA4, etc.), epoxyzeaxanthin demonstrates a clear pathway from basic biology to translational medicine.
However, the path from natural products to clinical drugs is not smooth. Its extremely poor solubility and oral bioavailability are the biggest obstacles to its drug development. Although the preliminary safety evaluation (no mutagenicity, no hERG inhibition) is encouraging, the lack of systematic pharmacokinetic and toxicological data remains the main bottleneck in its development.
Looking ahead to the future, with the advancement of biomanufacturing technology, the development of new drug delivery systems, and the continuous deepening of understanding of the biological functions of carotenoids, epoxyzeaxanthin is expected to break through the limitations of its physicochemical properties and play a unique role in visual health protection, skin photoprotection, and even the prevention and treatment of neurodegenerative diseases. It is not only a subtle manifestation of the natural light protection mechanism, but also a natural drug lead compound that urgently needs to be further explored and has significant application prospects. The research on epoxyzeaxanthin will not only enrich our understanding of carotenoid biology, but also potentially bring new solutions to human health.
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